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Context: Type 2 diabetes (T2D) patients have reduced bone turnover and increased fractures. Advanced glycation endproducts (AGEs) impair osteoblasts and are implicated in diabetic fractures. Pyridoxamine (PM) is a vitamin B6 metabolite which inhibits formation of AGEs., Objective: We hypothesized that PM treatment in older T2D patients, by inhibiting AGEs, would increase bone formation., Design: Double-blind RCT., Setting: Academic center., Participants: Older T2D women (n=55)., Intervention: Oral PM 200 mg twice daily for one year., Main Outcomes: The primary outcome was the change in the bone formation marker P1NP. Other outcomes were changes in bone resorption, bone mineral density (BMD), HbA1c and skin autofluorescence (SAF), and in a bone biopsy sub-group, the correlation between bone fluorescent AGEs (fAGEs) and SAF., Results: P1NP increased 23.0% with PM (95% CI: 9, 37; within-group p=0.028) vs. 4.1% with placebo (-9, 17; within-group p=0.576; between-groups p=0.056). BMD increased at the femoral neck (PM: 2.6±5% vs. placebo: -0.9±4%; between-groups p=0.007). Bone resorption markers and SAF did not change. HbA1c decreased (PM: -0.38 ± 0.7% vs. placebo: 0.05 ± 1.7%; between-groups p =0.04). Within the PM group, the HbA1c change correlated inversely with the % P1NP change (r =-0.50, p=0.034). Cortical bone biopsy fAGEs correlated with SAF (r=0.86, p=0.001). Adverse events were similar between groups., Conclusion: PM tended to increase P1NP in older T2D women, as well as increasing bone density and reducing HbA1c. Further studies are needed to investigate the potential of PM as a disease mechanism-directed approach to reduce fractures in T2D., (© The Author(s) 2024. Published by Oxford University Press on behalf of the Endocrine Society. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com. See the journal About page for additional terms.)

Individuals with type 2 diabetes mellitus (T2DM) are at an increased risk for heart failure, yet preventive cardiac care is suboptimal in this population. Pyridoxamine (PM), a vitamin B 6 analog, has been shown to exert protective effects in metabolic and cardiovascular diseases. In this study, we aimed to investigate whether PM limits adverse cardiac remodeling and dysfunction in rats who develop T2DM. Male rats received a standard chow diet or Western diet (WD) for 18 weeks to induce prediabetes. One WD group received additional PM (1 g/L) via drinking water. Glucose tolerance was assessed with a 1 h oral glucose tolerance test. Cardiac function was evaluated using echocardiography and hemodynamic measurements. Histology on left ventricular (LV) tissue was performed. Treatment with PM prevented the increase in fasting plasma glucose levels compared to WD-fed rats ( p < 0.05). LV cardiac dilation tended to be prevented using PM supplementation. In LV tissue, PM limited an increase in interstitial collagen deposition ( p < 0.05) seen in WD-fed rats. PM tended to decrease 3-nitrotyrosine and significantly lowered 4-hydroxynonenal content compared to WD-fed rats. We conclude that PM alleviates interstitial fibrosis and oxidative stress in the hearts of WD-induced prediabetic rats.

Diabetes mellitus is recognized as a major predisposing factor for Moraxella keratitis. However, how diabetes mellitus contributes to Moraxella keratitis remains unclear. In this study, we examined Moraxella keratitis; based on the findings, we investigated the impact of advanced glycation end products (AGEs) deposition in the cornea of individuals with diabetic mellitus on the adhesion of Moraxella isolates to the cornea. A retrospective analysis of 27 culture-proven cases of Moraxella keratitis at Ehime University Hospital (March 2006 to February 2022) was performed. Moraxella isolates were identified using matrix-assisted laser desorption ionization time-of-flight mass spectrometry. Among the patients, 30.4% had diabetes mellitus and 22.2% had the predominant ocular condition of using steroid eye drops. The species identified were Moraxella nonliquefaciens in 59.3% and Moraxella lacunata in 40.7% of patients. To investigate the underlying mechanisms, we assessed the effects of M. nonliquefaciens adherence to simian virus 40-immortalized human corneal epithelial cells (HCECs) with or without AGEs. The results demonstrated the number of M. nonliquefaciens adhering to HCECs was significantly increased by adding AGEs compared with that in controls (p < 0.01). Furthermore, in the corneas of streptozotocin-induced diabetic C57BL/6 mice treated with or without pyridoxamine, an AGE inhibitor, the number of M. nonliquefaciens adhering to the corneas of diabetic mice was significantly reduced by pyridoxamine treatment (p < 0.05). In conclusion, the development of Moraxella keratitis may be significantly influenced by the deposition of AGEs on the corneal epithelium of patients with diabetes mellitus., (© 2024. The Author(s).)

The use of doxorubicin (DOX) chemotherapy is restricted due to dose-dependent cardiotoxicity. Pyridoxamine (PM) is a vitamin B6 derivative with favorable effects on diverse cardiovascular diseases, suggesting a cardioprotective effect on DOX-induced cardiotoxicity. The cardioprotective nature of PM was investigated in a rat model of DOX-induced cardiotoxicity. Six-week-old female Sprague Dawley rats were treated intravenously with 2 mg/kg DOX or saline (CTRL) weekly for eight weeks. Two other groups received PM via the drinking water next to DOX (DOX+PM) or saline (CTRL+PM). Echocardiography, strain analysis, and hemodynamic measurements were performed to evaluate cardiac function. Fibrotic remodeling, myocardial inflammation, oxidative stress, apoptosis, and ferroptosis were evaluated by various in vitro techniques. PM significantly attenuated DOX-induced left ventricular (LV) dilated cardiomyopathy and limited TGF-β1-related LV fibrotic remodeling and macrophage-driven myocardial inflammation. PM protected against DOX-induced ferroptosis, as evidenced by restored DOX-induced disturbance of redox balance, improved cytosolic and mitochondrial iron regulation, and reduced mitochondrial damage at the gene level. In conclusion, PM attenuated the development of cardiac damage after DOX treatment by reducing myocardial fibrosis, inflammation, and mitochondrial damage and by restoring redox and iron regulation at the gene level, suggesting that PM may be a novel cardioprotective strategy for DOX-induced cardiomyopathy.

Doxorubicin (DOX) is commonly used in cancer treatment but associated with cardiotoxicity. Pyridoxamine (PM), a vitamin B6 derivative, could be a cardioprotectant. This study investigated the effect of PM on DOX cardiotoxicity and DOX antitumor effectiveness. Sprague Dawley rats were treated intravenously with DOX (2 mg/kg/week) or saline over eight weeks. Two other groups received PM via oral intake (1 g/L in water bottles) next to DOX or saline. Echocardiography was performed after eight weeks. PM treatment significantly attenuated the DOX-induced reduction in left ventricular ejection fraction (72 ± 2% vs. 58 ± 3% in DOX; p < 0.001) and increase in left ventricular end-systolic volume (0.24 ± 0.02 µL/cm 2 vs. 0.38 ± 0.03 µL/cm 2 in DOX; p < 0.0001). Additionally, LA7 tumor cells were exposed to DOX, PM, or DOX and PM for 24 h, 48 h, and 72 h. Cell viability, proliferation, cytotoxicity, and apoptosis were assessed. DOX significantly reduced LA7 cell viability and proliferation ( p < 0.0001) and increased cytotoxicity ( p < 0.05) and cleaved caspase-3 ( p < 0.001). Concomitant PM treatment did not alter the DOX effect on LA7 cells. In conclusion, PM attenuated DOX-induced cardiomyopathy in vivo without affecting the antitumor effect of DOX in vitro, highlighting PM as a promising cardioprotectant for DOX-induced cardiotoxicity.

Pyridoxamine (PM) is one of the natural vitamins B6 (VB6) and functions as an endogenous inhibitor for the formation of AGEs (advanced glycation end products). The AGEs are implicated in aging, diabetes, and various neuropsychiatric disease, including schizophrenia, Alzheimer's disease, and Parkinson's disease. However, it is unclear whether the absence of PM per se accumulates AGEs in vivo and causes behavioral dysfunctions. To address these points, we raised PM-deficient fruit flies, Drosophila melanogaster, with the sterilized defined medium. Flies reared in a PM-deficient medium accumulated AGEs and reduced lifespan, impaired gustatory response, sleep, courtship behavior, and olfactory learning. These results suggest that PM suppresses AGE accumulation in vivo and is required for regulating innate and empirical behaviors.

Naturally occurring forms of vitamin B6 include six interconvertible water-soluble compounds: pyridoxine (PN), pyridoxal (PL), pyridoxamine (PM), and their respective monophosphorylated derivatives (PNP, PLP, and PMP). PLP is the catalytically active form which works as a cofactor in approximately 200 reactions that regulate the metabolism of glucose, lipids, amino acids, DNA, and neurotransmitters. Most of vitamers can counteract the formation of reactive oxygen species and the advanced glycation end-products (AGEs) which are toxic compounds that accumulate in diabetic patients due to prolonged hyperglycemia. Vitamin B6 levels have been inversely associate with diabetes, while vitamin B6 supplementation reduces diabetes onset and its vascular complications. The mechanisms at the basis of the relation between vitamin B6 and diabetes onset are still not completely clarified. In contrast more evidence indicates that vitamin B6 can protect from diabetes complications through its role as scavenger of AGEs. It has been demonstrated that in diabetes AGEs can destroy the functionality of macromolecules such as protein, lipids, and DNA, thus producing tissue damage that result in vascular diseases. AGEs can be in part also responsible for the increased cancer risk associated with diabetes. In this chapter the relationship between vitamin B6, diabetes and AGEs will be discussed by showing the acquired knowledge and questions that are still open., (Copyright © 2024. Published by Elsevier Inc.)

Diabetic complications present a serious health problem. Functional damage to proteins due to post-translational modifications by glycoxidation reactions is a known factor contributing to pathology. Extracellular proteins are especially vulnerable to diabetic damage because robust antioxidant defenses are lacking outside the cell. We investigated glucose-induced inactivation of peroxidasin (PXDN), a heme protein catalyzing sulfilimine crosslinking of collagen IV that reinforce the basement membranes (BM). Experiments using physiological diabetic glucose levels were carried out to exclude several potential mechanisms of PXDN inactivation i.e., direct adduction of glucose, reactive carbonyl damage, steric hindrance, and osmotic stress. Further experiments established that PXDN activity was inhibited via heme degradation by reactive oxygen species. Activity of another extracellular heme protein, myeloperoxidase, was unaffected by glucose because its heme was resistant to glucose-induced oxidative degradation. Our findings point to specific mechanisms which may compromise BM structure and stability in diabetes and suggest potential modes of protection., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Paul Voziyan reports financial support was provided by National Institute of Diabetes and Digestive and Kidney Diseases. Billy G. Hudson reports financial support was provided by National Institute of Diabetes and Digestive and Kidney Diseases. Gautam Bhave reports financial support was provided by National Institute of Diabetes and Digestive and Kidney Diseases. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Vitamins are a vast group of fundamental organic compounds, which are not produced by the human body but are essential for the living organisms' good health. Vitamins B6 and B12 belong to the same group of hydrophilic vitamins. Structurally unrelated, they share the same purpose as essential components for normal cellular operation, growth and development. Vitamin B6 is an enzymatic co-factor that is vital for countless biochemical reactions, and is also important in sugar and fatty acid metabolization. It encompasses three natural and inter-convertible pyridine-derivatives: pyridoxine, pyridoxal and pyridoxamine. Vitamin B12 is a cobalt organometallic complex also indispensable in numerous human physiological functions. It has four bioactive forms: cyanocobalamin, methylcobalamin, hydroxocobalamin and 5'-deoxyadenosylcobalamin, and only a few prokaryotes have the ability to biosynthesize cobalamin. This work reviews the significant aspects of vitamins B6 and B12: their vital roles, consequences of deficit; food sources; and methods of determination and respective matrices, with heavy emphasis on chromatographic techniques developed within the last two decades., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier Ltd.)

Aim: To determine whether the microRNA-27b-3p (miR-27b-3p)/NF-E2-related factor 2 (Nrf2) pathway plays a role in human retinal pigment epithelial (hRPE) cell response to high glucose, how miR-27b-3p and Nrf2 expression are regulated, and whether this pathway could be specifically targeted., Methods: hRPE cells were cultured in normal glucose or high glucose for 1, 3, or 6d before measuring cellular proliferation rates using cell counting kit-8 and reactive oxygen species (ROS) levels using a dihydroethidium kit. miR-27b-3p, Nrf2, NAD(P)H quinone oxidoreductase 1 (NQO1) and heme oxygenase-1 (HO-1) mRNA and protein levels were analyzed using reverse transcription quantitative polymerase chain reaction (RT-qPCR) and immunocytofluorescence (ICF), respectively. Western blot analyses were performed to determine nuclear and total Nrf2 protein levels. Nrf2, NQO1, and HO-1 expression levels by RT-qPCR, ICF, or Western blot were further tested after miR-27b-3p overexpression or inhibitor lentiviral transfection. Finally, the expression level of those target genes was analyzed after treating hRPE cells with pyridoxamine., Results: Persistent exposure to high glucose gradually suppressed hRPE Nrf2, NQO1, and HO-1 mRNA and protein levels and increased miR-27b-3p mRNA levels. High glucose also promoted ROS release and inhibited cellular proliferation. Nrf2, NQO1, and HO-1 mRNA levels decreased after miR-27b-3p overexpression and, conversely, both mRNA and protein levels increased after expressing a miR-27b-3p inhibitor. After treating hRPE cells exposed to high glucose with pyridoxamine, ROS levels tended to decreased, proliferation rate increased, Nrf2, NQO1, and HO-1 mRNA and protein levels were upregulated, and miR-27b-3p mRNA levels were suppressed., Conclusion: Nrf2 is a downstream target of miR-27b-3p. Furthermore, the miR-27b-3p inhibitor pyridoxamine can alleviate high glucose injury by regulating the miR-27b-3p/Nrf2 axis., (International Journal of Ophthalmology Press.)

Background: Ovarian advanced glycation end-products (AGEs) accumulation is associated with ovarian granulosa cells (GCs) dysfunction. Vitamin B6 derivatives positively affected reproduction. The current study was conducted to elucidate the AGEs effects on human luteinized mural GCs steroidogenesis in the presence or absence of pyridoxamine (PM)., Methods and Results: Isolated GCs of 50 healthy women were divided into four parts and treated with media alone (Control), PM alone, or human glycated albumin (HGA) with/without PM. Main steroidogenic enzymes and hormones were assessed by qRT-PCR and ELISA. The AGE receptor (RAGE) protein was also determined using Western blotting. The non-toxic concentration of HGA increased the expression of RAGE, StAR, 3β-HSD, and 17β-HSD (P < 0.0001 for all) but decreased the expression of CYP19A1 at mRNA levels. The increased RAGE protein expression was also confirmed by western blot analysis. These effects resulted in declined estradiol (E2), slightly, and a sharp rise in progesterone (P4) and testosterone (T) levels, respectively. PM, on its own, ameliorated the HGA-altered enzyme expression and, thereby, corrected the aberrant levels of E2, P4, and T. These effects are likely mediated by regulating the RAGE gene and protein expression., Conclusion: This study indicates that hormonal dysfunctions induced by the AGEs-RAGE axis in luteinized GCs are likely rectified by PM treatment. This effect is likely acquired by reduced expression of RAGE. A better understanding of how AGEs and PM interact in ovarian physiology and pathology may lead to more targeted therapy for treating ovarian dysfunction., (© 2023. The Author(s), under exclusive licence to Springer Nature B.V.)

Introduction: Vitamin B6 is a water-soluble vitamin that is naturally present in many foods and is accessible in many dietary supplements. The three natural forms are pyridoxine, pyridoxal, and pyridoxamine. Both vitamin B6 deficiency and high B6 intake have been described as risk factors for developing peripheral neuropathy (PN). The aim of this systematic review is to characterize and comprehensively describe B6-related PN., Method: A systematic, computer-based search was conducted using the PubMed database. Twenty articles were included in this review., Results: Higher vitamin B6 levels, which usually occur following the taking of nutritional supplements, may lead to the development of a predominantly, if not exclusively, sensory neuropathy of the axonal type. After pyridoxine discontinuation, such patients subjectively report improved symptoms. However, although low vitamin B6 levels can be seen in patients suffering from peripheral neuropathy of various etiologies, there is no firm evidence that low B6 levels have a direct causal relationship with PN. Many studies suggest subjective improvement of neuropathy symptoms in patients suffering from PN of various etiologies after receiving B6 supplementation; however, no data about B6 administration as a monotherapy exist, only as part of a combination treatment, usually with other vitamins. Therefore, the potential therapeutic role of B6 cannot be confirmed to date. Supplementation with vitamin B6, even as part of a nutritional multivitamin supplement, has not been proven harmful at permitted daily doses in patients who already suffer from PN., Conclusion: Current scientific evidence supports a neurotoxic role of B6 at high levels. Although some studies suggest that low B6 is also a potential risk factor, further studies in this area are needed.

Following a request from the European Commission, the EFSA Panel on Nutrition, Novel Foods and Food Allergens (NDA) was asked to deliver a scientific opinion on the tolerable upper intake level (UL) for vitamin B6. Systematic reviews of the literature were conducted by a contractor. The relationship between excess vitamin B6 intakes and the development of peripheral neuropathy is well established and is the critical effect on which the UL is based. A lowest-observed-effect-level (LOAEL) could not be established based on human data. A reference point (RP) of 50 mg/day is identified by the Panel from a case-control study, supported by data from case reports and vigilance data. An uncertainty factor (UF) of 4 is applied to the RP to account for the inverse relationship between dose and time to onset of symptoms and the limited data available. The latter covers uncertainties as to the level of intake that would represent a LOAEL. This leads to a UL of 12.5 mg/day. From a subchronic study in Beagle dogs, a LOAEL of 50 mg/kg body weight (bw) per day can be identified. Using an UF of 300, and a default bw of 70 kg, a UL of 11.7 mg/day can be calculated. From the midpoint of the range of these two ULs and rounding down, a UL of 12 mg/day is established by the Panel for vitamin B6 for adults (including pregnant and lactating women). ULs for infants and children are derived from the UL for adults using allometric scaling: 2.2-2.5 mg/day (4-11 months), 3.2-4.5 mg/day (1-6 years), 6.1-10.7 mg/day (7-17 years). Based on available intake data, EU populations are unlikely to exceed ULs, except for regular users of food supplements containing high doses of vitamin B6., (© 2023 European Food Safety Authority. EFSA Journal published by Wiley‐VCH GmbH on behalf of European Food Safety Authority.)

One of the fundamental goals of chemists is to develop highly efficient methods for producing optically active compounds, given their wide range of applications in chemistry, pharmaceutical industry, chemical biology, and material science. Biomimetic asymmetric catalysis, which imitates the structures and functions of enzymes, has emerged as an extremely attractive strategy for producing chiral compounds. This field has drawn tremendous research interest and has led to various protocols for constructing complex molecular scaffolds. The Vitamin B 6 family, including pyridoxal, pyridoxamine, pyridoxine, and the corresponding phosphorylated derivatives, serves as the cofactors to catalyze more than 200 enzymatic functions, accounting for ∼4% of all enzyme activities. Although significant progress has been made in simulating the biological roles of vitamin B 6 during the past several decades, its extraordinary catalytic power has not yet been successfully applied into asymmetric synthesis. In recent years, our group has been devoted to developing vitamin B 6 -based biomimetic asymmetric catalysis using chiral pyridoxals/pyridoxamines as catalysts. We are particularly interested in mimicking the processes of enzymatic transamination and biological aldol reaction of glycine, respectively, developing asymmetric biomimetic transamination and carbonyl catalysis enabled α-C-H transformation of primary amines. Using a chiral α,α-diarylprolinol-derived pyridoxal as the catalyst, we reported the first chiral pyridoxal catalyzed asymmetric transamination of α-keto acids in 2015. A significant breakthrough in biomimetic transamination was achieved by using an axially chiral biaryl pyridoxamine catalyst that bears a lateral amine side arm. The amine side arm acts as an intramolecular base, accelerating the transamination and proving highly effective for transamination of α-keto acids and α-keto amides. In addition, we discovered the catalytic power of chiral pyridoxals as carbonyl catalysts for asymmetric biomimetic Mannich/aldol reactions of glycinates. These chiral pyridoxals also enabled more α-C-H conversions of glycinates, such as asymmetric 1,4-addition toward α,β-unsaturated esters and asymmetric α-allylation with Morita-Baylis-Hillman acetates. Moreover, carbonyl catalysis can be further applied to highly challenging primary amines with inert α-C-H bonds, such as propargylamines and benzylamines, which represents a powerful strategy for direct asymmetric α-C-H functionalization of various primary amines without protection of the NH 2 group. These biomimetic/bioinspired transformations provide efficient new protocols for the synthesis of chiral amines. Herein, we summarize our recent efforts on the development of the vitamin B 6 -based biomimetic asymmetric catalysis.

Aim: To investigate the effects of pyridoxamine (PM), a B6 vitamer and dicarbonyl scavenger, on glycation and a large panel of metabolic and vascular measurements in a randomized double-blind placebo-controlled trial in abdominally obese individuals., Materials and Methods: Individuals (54% female; mean age 50 years; mean body mass index 32 kg/m 2 ) were randomized to an 8-week intervention with either placebo (n = 36), 25 mg PM (n = 36) or 200 mg PM (n = 36). We assessed insulin sensitivity, β-cell function, insulin-mediated microvascular recruitment, skin microvascular function, flow-mediated dilation, and plasma inflammation and endothelial function markers. PM metabolites, dicarbonyls and advanced glycation endproducts (AGEs) were measured using ultra-performance liquid chromatography tandem mass spectrometry. Treatment effects were evaluated by one-way ANCOVA., Results: In the high PM dose group, we found a reduction of plasma methylglyoxal (MGO) and protein-bound Nδ-(5-hydro-5-methyl-4-imidazolon-2-yl)-ornithine (MG-H1), as compared to placebo. We found a reduction of the endothelial dysfunction marker soluble vascular cell adhesion molecule-1 (sVCAM-1) in the low and high PM dose group and of soluble intercellular adhesion molecule-1 (sICAM-1) in the high PM dose, as compared to placebo. We found no treatment effects on insulin sensitivity, vascular function or other functional outcome measurements., Conclusions: This study shows that PM is metabolically active and reduces MGO, AGEs, sVCAM-1 and sICAM-1, but does not affect insulin sensitivity and vascular function in abdominally obese individuals. The reduction in adhesion markers is promising because these are important in the pathogenesis of endothelial damage and atherosclerosis., (© 2023 The Authors. Diabetes, Obesity and Metabolism published by John Wiley & Sons Ltd.)

Methylglyoxal (MGO) is a reactive glucose metabolite linked to diabetic cardiovascular disease (CVD). MGO levels surge during intermittent hyperglycemia. We hypothesize that these MGO spikes contribute to atherosclerosis, and that pyridoxamine as a MGO quencher prevents this injury. To study this, we intravenously injected normoglycemic 8-week old male C57Bl6 ApoE -/- mice with normal saline (NS, n = 10) or 25 µg MGO for 10 consecutive weeks (MGO iv , n = 11) with or without 1 g/L pyridoxamine (MGO iv +PD, n = 11) in the drinking water. We measured circulating immune cells by flow cytometry. We quantified aortic arch lesion area in aortic roots after Sudan-black staining. We quantified the expression of inflammatory genes in the aorta by qPCR. Intermittent MGO spikes weekly increased atherosclerotic burden in the arch 1.8-fold (NS: 0.9 ± 0.1 vs 1.6 ± 0.2 %), and this was prevented by pyridoxamine (0.8 ± 0.1 %). MGO iv spikes increased circulating neutrophils and monocytes (2-fold relative to NS) and the expression of ICAM (3-fold), RAGE (5-fold), S100A9 (2-fold) and MCP1 (2-fold). All these changes were attenuated by pyridoxamine. This study suggests that MGO spikes damages the vasculature independently of plasma glucose levels. Pyridoxamine and potentially other approaches to reduce MGO may prevent excess cardiovascular risk in diabetes., (Copyright © 2023 The Authors. Published by Elsevier Masson SAS.. All rights reserved.)

Age-related increases in large artery stiffness are associated with cerebrovascular dysfunction and cognitive impairment. Pyridoxamine treatment prevents large artery stiffening with advancing age, but the effects of pyridoxamine treatment on the cerebral vasculature or cognition is unknown. The purpose of this study was to investigate the effects of pyridoxamine on blood pressure, large artery stiffness, cerebral artery function, and cognitive function in old mice. Old male C57BL/6 mice consumed either pyridoxamine (2 g/L) or vehicle control in drinking water for ∼7.5 months and were compared with young male C57BL/6 mice. From pre- to post-treatment, systolic blood pressure increased in old control mice, but was maintained in pyridoxamine treated mice. Large artery stiffness decreased in pyridoxamine-treated mice but was unaffected in control mice. Pyridoxamine-treated mice had greater cerebral artery endothelium-dependent dilation compared with old control mice, and not different from young mice. Old control mice had impaired cognitive function; however, pyridoxamine only partially preserved cognitive function in old mice. In summary, pyridoxamine treatment in old mice prevented age-related increases in blood pressure, reduced large artery stiffness, preserved cerebral artery endothelial function, and partially preserved cognitive function. Taken together, these results suggest that pyridoxamine treatment may limit vascular aging.

Pyridoxine and its derivatives, pyridoxamine, and pyridoxal have been recognized for more than 70 years and are known for regulating cellular biology and metabolism. During the past few decades, the anti-oxidant and anti-inflammatory properties of pyridoxine and its vitamers were explored. However, an interesting turnabout was observed in pyridoxine chemical modification in the last two decades. The various important pathophysiological aspects of pyridoxine and its derivatives on several cellular systems have been discovered by researchers. Recent findings have shown that many diseases, like cancer, diabetes, hypertension, tuberculosis, epilepsy, and neurodegenerative diseases are linked to the alteration of pyridoxine. Herein, our main focus is to review the importance of pyridoxine and its derivatives obtained by various chemical modifications, in various disease areas and to recognize important directions for future research., (Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.net.)

Objective: Oxidative stress contributes to the development of insulin resistance (IR) and atherosclerosis. Peroxidation of lipids produces reactive dicarbonyls such as Isolevuglandins (IsoLG) and malondialdehyde (MDA) that covalently bind plasma/cellular proteins, phospholipids, and DNA leading to altered function and toxicity. We examined whether scavenging reactive dicarbonyls with 5'-O-pentyl-pyridoxamine (PPM) protects against the development of IR and atherosclerosis in Ldlr -/- mice., Methods: Male or female Ldlr -/- mice were fed a western diet (WD) for 16 weeks and treated with PPM versus vehicle alone. Plaque extent, dicarbonyl-lysyl adducts, efferocytosis, apoptosis, macrophage inflammation, and necrotic area were measured. Plasma MDA-LDL adducts and the in vivo and in vitro effects of PPM on the ability of HDL to reduce macrophage cholesterol were measured. Blood Ly6C hi monocytes and ex vivo 5-ethynyl-2'-deoxyuridine (EdU) incorporation into bone marrow CD11b+ monocytes and CD34+ hematopoietic stem and progenitor cells (HSPC) were also examined. IR was examined by measuring fasting glucose/insulin levels and tolerance to insulin/glucose challenge., Results: PPM reduced the proximal aortic atherosclerosis by 48% and by 46% in female and male Ldlr -/- mice, respectively. PPM also decreased IR and hepatic fat and inflammation in male Ldlr -/- mice. Importantly, PPM decreased plasma MDA-LDL adducts and prevented the accumulation of plaque MDA- and IsoLG-lysyl adducts in Ldlr -/- mice. In addition, PPM increased the net cholesterol efflux capacity of HDL from Ldlr -/- mice and prevented both the in vitro impairment of HDL net cholesterol efflux capacity and apoAI crosslinking by MPO generated hypochlorous acid. Moreover, PPM decreased features of plaque instability including decreased proinflammatory M1-like macrophages, IL-1β expression, myeloperoxidase, apoptosis, and necrotic core. In contrast, PPM increased M2-like macrophages, Tregs, fibrous cap thickness, and efferocytosis. Furthermore, PPM reduced inflammatory monocytosis as evidenced by decreased blood Ly6C hi monocytes and proliferation of bone marrow monocytes and HSPC from Ldlr -/- mice., Conclusions: PPM has pleotropic atheroprotective effects in a murine model of familial hypercholesterolemia, supporting the therapeutic potential of reactive dicarbonyl scavenging in the treatment of IR and atherosclerotic cardiovascular disease., (Copyright © 2022 The Author(s). Published by Elsevier GmbH.. All rights reserved.)

Oxidative stress is strongly associated with the onset and/or progression of diabetes. Under conditions of oxidative stress, lipid hydroperoxides are decomposed to reactive aldehydes that have been reported to induce insulin resistance by modifying proteins involved in insulin signaling. Pyridoxamine (PM) can inhibit the formation of advanced glycation/lipoxidation end products by scavenging reactive carbonyl species. Thus, PM has emerged as a promising drug candidate for various chronic conditions, including diabetic complications. In this study, L6 skeletal muscle cells were treated with 4-oxo-2( E )-nonenal (ONE), one of the most abundant and reactive lipid-derived aldehydes. Cellular insulin resistance was assessed by measuring insulin-stimulated glucose uptake using 2-deoxyglucose. ONE induced a time- and dose-dependent decrease in glucose uptake. Liquid chromatography/electrospray ionization-mass spectrometry analysis of the reaction between ONE and insulin receptor substrate 1 (IRS1) lysate identified multiple modifications that could disturb the interaction between IRS1 and activated IR, leading to insulin resistance. Pretreatment of the cells with PM restored the ONE-induced decrease in glucose uptake. Concomitantly, the formation of PM-ONE adducts in cell culture medium was increased in a PM-dose dependent manner. PM can therefore prevent lipid hydroperoxide-derived insulin resistance by quenching ONE., Supplementary Information: The online version contains supplementary material available at 10.1007/s43188-022-00155-z., Competing Interests: Conflict of interestThe authors do not have any conflicts of interest to declare., (© The Author(s) under exclusive licence to Korean Society of Toxicology 2022, Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.)

Previously, we reported, based on an untargeted metabolomics, carnitine derivatives are part of a mechanism to overcome impaired mitochondrial functioning triggered by an acyl-group overflow in CHO cells. In this study, we analyzed the cell-specific rates of 24 selected metabolites using two metrics: correlation coefficients and root-mean-square deviations (RMSDs) between glucose-fed versus glucose/lactic acid-fed cultures. The time-course profiles of acetylcarnitine, adipoylcarnitine, glutarylcarnitine, glutamate, and succinate exhibited significant negative correlations between the two culture conditions. Based on RMSDs, seven carnitine derivatives, 3-hydroxy-methyl-glutarate, mevalonate, pyridoxamine-5-phosphate, succinate, and glycine were substantially different. The analyses from the two metrics reveal a distinctive rearrangement of rates from the following metabolic pathways: (i) high secretion rates of carnitines as part of the acyl-group removal, (ii) low secretion rates of succinate, related to the tricarboxylic acid cycle and the electron-transport chain, (iii) low secretion rates of pyridoxamine-5-phosphate - a co-factor for amino acid catabolism, transaminations, and transsulfuration, and (iv) increases in the consumption rates of glutamate and glycine, both used to produce glutathione. The rewiring in rates observed upon feeding lactic acid is best explained by the activation of pathways supporting homeostasis of acyl-groups and antioxidant synthesis, which are required for continuous proper functioning of oxidative phosphorylation., Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Juan Aon, Daniel Sevin, and Pramthesh Patel report a relationship with GlaxoSmithKline that includes equity or stocks., (Copyright © 2022 Elsevier B.V. All rights reserved.)

In response to the COVID-19 pandemic, and the lack of effective and safe antivirals against it, we adopted a new approach in which food supplements with vital antiviral characteristics, low toxicity, and fast excretion have been targeted. The structures and chemical properties of the food supplements were compared to the promising antivirals against SARS-COV-2. Our goal was to exploit the food supplements to mimic the topical antivirals' functions but circumventing their severe side effects, which has limited the necessary dosage needed to exhibit the desired antiviral activity. On this line, after a comparative structural analysis of the chemicals mentioned above, and investigation of their potential mechanisms of action, we selected caffeine and some compounds of the vitamin B family and further applied molecular modeling techniques to evaluate their interactions with the RDB domain of the Spike protein of SARS-CoV-2 (SC2Spike) and its corresponding binding site on human ACE-2 (HssACE2). Our results pointed to vitamins B1 and B6 in the neutral form as potential binders to the HssACE2 RDB binding pocket that might be able to impair the SARS-CoV-2 mechanism of cell invasion, qualifying as potential leads for experimental investigation against COVID-19., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Bioprosthetic heart valves (BHV) fabricated from heterograft tissue, such as glutaraldehyde pretreated bovine pericardium (BP), are the most frequently used heart valve replacements. BHV durability is limited by structural valve degeneration (SVD), mechanistically associated with calcification, advanced glycation end products (AGE), and serum protein infiltration. We investigated the hypothesis that anti-AGE agents, Aminoguanidine, Pyridoxamine [PYR], and N-Acetylcysteine could mitigate AGE-serum protein SVD mechanisms in vitro and in vivo, and that these agents could mitigate calcification or demonstrate anti-calcification interactions with BP pretreatment with ethanol. In vitro, each of these agents significantly inhibited AGE-serum protein infiltration in BP. However, in 28-day rat subdermal BP implants only orally administered PYR demonstrated significant inhibition of AGE and serum protein uptake. Furthermore, BP PYR preincubation of BP mitigated AGE-serum protein SVD mechanisms in vitro, and demonstrated mitigation of both AGE-serum protein uptake and reduced calcification in vivo in 28-day rat subdermal BP explants. Inhibition of BP calcification as well as inhibition of AGE-serum protein infiltration was observed in 28-day rat subdermal BP explants pretreated with ethanol followed by PYR preincubation. In conclusion, AGE-serum protein and calcification SVD pathophysiology are significantly mitigated by both PYR oral therapy and PYR and ethanol pretreatment of BP., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Robert J. Levy reports financial support was provided by National Institutes of Health. Robert J. Levy reports a relationship with National Institutes of Health that includes: funding grants., (Copyright © 2022 The Authors. Published by Elsevier Ltd.. All rights reserved.)

The cysteine desulfurase SufS is a pyridoxal-5'-phosphate-dependent enzyme and is essential for the SUF system, which participates in iron-sulfur cluster biosynthesis. Inhibition of SufS in the SUF system by D-cycloserine (DCS) in Plasmodium falciparum apicoplast has recently been reported, indicating that SufS could be a target for malaria therapeutics. However, the mechanistic details underlying the inhibition of SufS by DCS have not yet been clarified. Moreover, inhibition of SufS by the other enantiomer, L-cycloserine (LCS), has not been investigated. Herein, we investigated the structure-based inhibition mechanisms of SufS by DCS and LCS using Bacillus subtilis SufS, whose catalytic mechanism has been well characterized in comparison to that of the P. falciparum SufS. Surprisingly, DCS- and LCS-mediated inhibitions of SufS occur via distinct mechanisms resulting in pyridoxamine-5'-phosphate (PMP) in DCS-mediated inhibition and PMP-3-hydroxyisoxazole adduct (PMP-isoxazole) in LCS-mediated inhibition. Biochemical and structural evaluation of SufS variants identified conserved His and Arg residues at the active site as the key determinants of the distinct inhibition mechanisms. The importance of structural elements involved in DCS and LCS-mediated inhibitions of SufS provides valuable insights for the structure-based design of new drugs targeting SufS. DATABASE: Structural data are available in PDB database under the accession numbers 6KFY, 7CEO, 7CEP, 7CEQ, 7CER, 7CES, 7CET, 7CEU, 7E6A, 7E6B, 7E6C, 7E6D, 7E6E, and 7E6F., (© 2022 Federation of European Biochemical Societies.)

Liver fibrosis is a common chronic hepatic disease. This study was done to examine the effect of pyridoxamine against thioacetamide-induced hepatic fibrosis. Animals were divided into four groups (1) control group; (2) Thioacetamide group (200 mg/kg, i.p.) twice a week for eight weeks; (3) Pyridoxamine-treated group treated with pyridoxamine (100 mg/kg/day, i.p.) for eight weeks; (4) Thioacetamide and pyridoxamine group, in which pyridoxamine was given (100 mg/kg/day, i.p.) during thioacetamide injections. Thioacetamide treatment resulted in hepatic dysfunction manifested by increased serum levels of bilirubin, gamma-glutamyl transferase (GGT), alanine aminotransferase (ALT), and aspartate aminotransferase (AST). Oxidative stress was noted by increased hepatic lipid peroxidation and decreased glutathione (GSH). Increased concentrations of total nitrite/nitrate, advanced glycation end products (AGEs), monocyte chemoattractant protein-1 (MCP-1), tumor necrosis factor-α (TNF-α), transforming growth factor-β (TGF-β), matrix metalloproteinases (MMP-2&9) and tissue inhibitor of metalloproteinase-1 (TIMP-1) were noticed in hepatic tissues. Immunostaining sections also revealed overexpression of MMP-2, MMP-9 and collagen IV. Liver fibrosis was confirmed by severe histopathological changes. Pyridoxamine improved the assessed parameters. Moreover, histopathological and immunohistological studies supported the ability of pyridoxamine to reduce liver fibrosis. The findings of the present study provide evidence that pyridoxamine is a novel target for the treatment of liver fibrosis., (Copyright © 2022. Published by Elsevier B.V.)

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder for which dietary interventions can be a useful treatment. In recent years, the low-FODMAP approach is gaining traction in this regard. The fermentation of these non-absorbed carbohydrates by the gut microbiota can generate toxic glycating metabolites, such as methylglyoxal. These metabolites can have harmful effects by their role in the generation of advanced glycation end products (AGEs), which activates Receptor for AGEs (AGER). Mast cells can be stimulated by AGEs and play a role in IBS. We have treated mice with lactose or fructo-oligosaccharides (FOS), with or without co-administration of pyridoxamine and investigated the colonic mucus barrier. We have found that an increased intake of lactose and fructo-oligosaccharides induces a dysregulation of the colonic mucus barrier, increasing mucus discharge in empty colon, while increasing variability and decreasing average thickness mucus layer covering the fecal pellet. Changes were correlated with increased mast cell counts, pointing to a role for the crosstalk between these and goblet cells. Additionally, AGE levels in colonic epithelium were increased by treatment with the selected fermentable carbohydrates. Observed effects were prevented by co-treatment with anti-glycation agent pyridoxamine, implicating glycation processes in the negative impact of fermentable carbohydrate ingestion. This study shows that excessive intake of fermentable carbohydrates can cause colonic mucus barrier dysregulation in mice, by a process that involves glycating agents and increased mucosal mast cell counts., (© 2022 The Authors. The FASEB Journal published by Wiley Periodicals LLC on behalf of Federation of American Societies for Experimental Biology.)

Curcumin is proven to have potent anti-inflammatory activity, but its low water solubility and rapid degradation in physiological conditions limit its clinical use, particularly in intravenous drug delivery. In this study, we fabricated rod-shaped, acid-labile nanogels, using high biosafe and biocompatible polymers, for intravenous application in systemic inflammation treatment. The constituent polymers of the nanogels were prepared via the conjugation of vitamin B 6 derivatives, including pyridoxal and pyridoxamine, onto poly(glutamate) with ester bonds. The aldehyde groups of the pyridoxal and amine groups of the pyridoxamine on the polymers enable crosslinking using a Schiff base during the solvent evaporation procedure for the preparation of the rod-shaped nanogels. Our study is the first to introduce this linkage, which is generated from two vitamin B 6 derivatives into a nanogel system. It is also the first to fabricate a rod-shaped nanogel system via simple solvent evaporation. Under acidic conditions, such as those encountered in the endosomes and lysosomes within inflammatory macrophage cells spread in the whole body, imine bonds are cleaved and release payloads. The nanogel polymers were successfully synthesized and characterized, and the formation and disappearance of the Schiff base under neutral and acidic conditions were also confirmed using Fourier transform infrared spectroscopy. Following curcumin encapsulation, the long, rod-shaped nanogels were able to rapidly internalize into macrophage cells in static or adhere to cells under the flows, release their payloads in the acid milieus, and, thus, mitigate curcumin degradation. Consequently, curcumin-loaded, rod-shaped nanogels displayed exceptional anti-inflammatory activity both in vitro and in vivo, by efficiently inhibiting pro-inflammatory mediator secretion. These results demonstrate the feasibility of our acid-labile, rod-shaped nanogels for the treatment of systemic inflammation., Competing Interests: Declaration of competing interest The authors declare no conflict of interest in known competing financial interests or personal relationships, having influences in any work in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Methylglyoxal (MGO) is a highly reactive dicarbonyl compound formed during hyperglycaemia. MGO combines with proteins to form advanced glycation end products (AGEs), leading to cellular dysfunction and organ damage. In type 2 diabetes mellitus (T2DM), the higher the plasma MGO concentration, the higher the lower extremity amputation rate. Here, we aimed to identify the mechanisms of MGO-induced dysfunction. We observed that the accumulation of MGO-derived AGEs in human diabetic wounds increased, whereas the expression of glyoxalase 1 (GLO1), a key metabolic enzyme of MGO, decreased. We show for the first time that topical application of pyridoxamine (PM), a natural vitamin B6 analogue, reduced the accumulation of MGO-derived AGEs in the wound tissue of type-2 diabetic mice, promoted the influx of macrophages in the early stage of tissue repair, improved the dysfunctional inflammatory response, and accelerated wound healing. In vitro, MGO damaged the phagocytic functions of M1-like macrophages induced by lipopolysaccharide (LPS), but not those of M0-like macrophages induced by PMA or of M2-like macrophages induced by interleukins 4 (IL-4) and 13 (IL-13); the impaired phagocytosis of M1-like macrophages was rescued by PM administration. These findings suggest that the increase in MGO metabolism in vivo might contribute to macrophage dysfunction, thereby affecting wound healing. Our results indicate that PM may be a novel therapeutic approach for treating diabetic wounds. MGO forms protein adducts that cause macrophage dysfunction. These adducts cause cell and organ dysfunction that is common in diabetes. Pyridoxamine scavenges MGO to ameliorate this dysfunction, promoting wound healing. Pyridoxamine could be used therapeutically to treat non-healing diabetic wounds., (© 2021 The Authors. International Wound Journal published by Medicalhelplines.com Inc (3M) and John Wiley & Sons Ltd.)

Hypophosphatasia (HPP) is the heritable dento-osseous disease caused by loss-of-function mutation(s) of the gene ALPL that encodes the tissue-nonspecific isoenzyme of alkaline phosphatase (TNSALP). TNSALP is a cell-surface homodimeric phosphomonoester phosphohydrolase expressed in healthy people especially in the skeleton, liver, kidneys, and developing teeth. In HPP, diminished TNSALP activity leads to extracellular accumulation of its natural substrates including inorganic pyrophosphate (PPi), an inhibitor of mineralization, and pyridoxal 5'-phosphate (PLP), the principal circulating form of vitamin B 6 (B 6 ). Autosomal dominant and autosomal recessive inheritance involving >450 usually missense defects scattered throughout ALPL largely explains the remarkably broad-ranging severity of this inborn-error-of-metabolism. In 1985 when we identified elevated plasma PLP as a biochemical hallmark of HPP, all 14 investigated affected children and adults had markedly increased PLP levels. However, pyridoxal (PL), the dephosphorylated form of PLP that enters cells to cofactor many enzymatic reactions, was not low but often inexplicably elevated. Levels of pyridoxic acid (PA), the B 6 degradation product quantified to assess B 6 sufficiency, were unremarkable. Canonical signs or symptoms of B 6 deficiency or toxicity were absent. B 6 -dependent seizures in infants with life-threatening HPP were later explained by their profound deficiency of TNSALP activity blocking PLP dephosphorylation to PL and diminishing gamma-aminobutyric acid synthesis in the brain. Now, there is speculation that altered B 6 metabolism causes further clinical complications in HPP. Herein, we assessed the plasma PL and PA levels accompanying previously reported elevated plasma PLP concentrations in 150 children and adolescents with HPP. Their mean (SD) plasma PL level was nearly double the mean for our healthy pediatric controls: 66.7 (59.0) nM versus 37.1 (22.2) nM (P < 0.0001), respectively. Their PA levels were broader than our pediatric control range, but their mean value was normal; 40.2 (25.1) nM versus 39.3 (9.9) nM (P = 0.7793), respectively. In contrast, adults with HPP often had plasma PL and PA levels suggestive of dietary B 6 insufficiency. We discuss why the B 6 levels of our pediatric patients with HPP would not cause B 6 toxicity or deficiency, whereas in affected adults dietary B 6 insufficiency can develop., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Background and Aims: Vitamin B6 is involved in a large spectrum of physiological processes and comprises of the vitamers pyridoxamine (PM), pyridoxal (PL), pyridoxine (PN), and their phosphorylated derivatives including the biological active pyridoxal 5'-phosphate (PLP). While PN toxicity is known to complicate several treatments, PM has shown promise in relation to the treatment of metabolic and age-related diseases by blocking oxidative degradation and scavenging toxic dicarbonyl compounds and reactive oxygen species. We aimed to assess the metabolization of oral PM supplements in a single and three daily dose., Materials and Methods: We optimized and validated a method for the quantification of the B6 vitamers in plasma and urine using ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS). Five healthy volunteers were recruited to study PM metabolization after a single oral dose of 200 mg PM or a three daily dose of 67 mg PM. A third protocol was implemented as control for dietary intake. Venous blood samples, 24 h urine and fasted second void urine samples were collected., Results: After a single oral dose of 200 mg PM, plasma PM increased in the first 3 h to a maximum of 2324 ± 266 nmol/L. While plasma PM levels returned to baseline after ~10 h of PM intake, PLP increased to a maximum of 2787 ± 329 nmol/L and reached a plateau. We found a small increase of PN to a maximum of 13.5 ± 2.1 nmol/L; it was nearly undetectable after ~12 h. With a three daily dose of 67 mg PM we observed an increase and decline of plasma PM, PL, and PN concentrations after each PM intake. PLP showed a similar increase as in the single dose protocol and accumulated over time., Conclusion: In this study we showed high plasma levels of PM after oral PM supplementation. We found steadily increasing levels of the biologically active PLP, with minimal formation of PN. The B6 vitamer PM is an interesting supplement as an inhibitor of harmful processes in metabolic diseases and for the treatment of vitamin B6 deficiency., Clinical Trial Registry: The study was approved by the Medical Ethics Committee of Maastricht University (NL) and was registered at ClinicalTrials.gov as NCT02954588., Competing Interests: Conflicts of interest The authors declare no conflict of interest., (Copyright © 2021 The Authors. Published by Elsevier Ltd.. All rights reserved.)

High plasma levels of the sphingolipid intermediates ceramide (Cer) and sphingosine-1-phosphate (S1P) are suggested to be involved in the development of insulin resistance (IR). Recent evidence indicates that advanced glycation endproducts (AGEs) can alter the sphingolipids metabolism equilibrium. Since enzymes responsible for sphingolipid rheostat maintenance are highly expressed in liver, we thus investigated whether AGEs accumulation can affect hepatic sphingolipids metabolism in insulin resistant mice. Two different models of IR were examined: genetically diabetic LeptrDb-/- (DbDb) and diet-induced insulin resistant C57Bl/6J mice fed a 60% trans-fat diet (HFD). In addition, a group of HFD mice was supplemented with the anti-AGEs compound pyridoxamine. AGEs were evaluated in the liver by western blotting. Cer and S1P were measured by UHPLC-MS/MS. The expression of RAGE and of enzymes involved in sphingolipid metabolism were assessed by RT-PCR and western blotting. HepG2 cells were used to study the effect of the major AGE Nε-(carboxymethyl)lysine (CML)-albumin on sphingolipid metabolism and the role of the receptor of AGEs (RAGE). High levels of AGEs and RAGE were detected in the liver of both DbDb and HFD mice in comparison to controls. The expression of enzymes of sphingolipid metabolism was altered in both models, accompanied by increased levels of Cer and S1P. Specifically, ceramide synthase 5 and sphingosine kinase 1 were increased, while neutral ceramidase was reduced. Pyridoxamine supplementation to HFD mice diminished hepatic AGEs and prevented alterations of sphingolipid metabolism and the development of IR. CML administration to HepG2 cells evoked alterations similar to those observed in vivo, that were in part mediated by the binding to RAGE. The present study shows a direct involvement of AGEs in alterations of sphingolipid metabolism associated to the development of IR. The modulation of sphingolipids metabolism through the prevention of AGEs accumulation by pyridoxamine may reduce the development of IR., (Copyright © 2021. Published by Elsevier Inc.)

Recent studies have shown that carbonyl stress is a causative factor of schizophrenia, categorized as carbonyl stress-related schizophrenia (CS-SCZ). However, the correlation between carbonyl stress and the pathogenesis of this disease is not well established. In this study, glyoxalase 1(Glo1)-knockout and vitamin B6-deficient mice (KO/VB6 (-) mice), which are susceptible to methylglyoxal (MGO)-induced oxidative damages, were used as a CS-SCZ model to analyze MGO-modified protein and the carbonyl stress status in the brain. A comparison between Wild/VB6(+) mice and KO/VB6(-) mice for accumulated carbonyl proteins levels, with several advanced glycation end products (AGEs) in the brain, revealed that carbonyl protein levels with the Nδ-(5-hydro-5-methyl-4-imidazolon-2-yl) ornithine (MG-H1) moiety were significantly increased in the hippocampus, prefrontal cortex, striatum, cerebral cortex, and brainstem regions of the brain in KO/VB6(-) mice. Moreover, two-dimensional electrophoresis and Liquid chromatography-tandem mass spectrometry analysis showed MG-H1-modified arginine residues in mitochondrial creatine kinase, beta-adrenergic receptor kinase 1, and T-complex protein in the hippocampus region of KO/VB6(-) mice, but not in Wild/VB6(+) mice. In particular, MG-H1 modification of mitochondrial creatine kinase was quite notable. These results suggest that further studies focusing on MG-H1-modified and accumulated proteins in the hippocampus may reveal the onset mechanism of CS-SCZ induced by MGO-induced oxidative damages.

Introduction: This study aims to examine the effect of a diet intervention and pyridoxamine (PM) supplementation on hepatic microcirculatory and metabolic dysfunction in nonalcoholic fatty liver disease (NAFLD)., Methods: NAFLD in Wistar rats was induced with a high-fat diet for 20 weeks (NAFLD 20 weeks), and control animals were fed with a standard diet. The NAFLD diet intervention group received the control diet between weeks 12 and 20 (NAFLD 12 weeks), while the NAFLD 12 weeks + PM group also received PM. Fasting blood glucose (FBG) levels, body weight (BW), visceral adipose tissue (VAT), and hepatic microvascular blood flow (HMBF) were evaluated at the end of the protocol., Results: The NAFLD group exhibited a significant increase in BW and VAT, which was prevented by the diet intervention, irrespective of PM treatment. The FBG was elevated in the NAFLD group, and caloric restriction improved this parameter, although additional improvement was achieved by PM. The NAFLD group displayed a 31% decrease in HMBF, which was partially prevented by caloric restriction and completely prevented when PM was added. HMBF was negatively correlated to BW, FBG, and VAT content., Conclusion: PM supplementation in association with lifestyle modifications could be an effective intervention for metabolic and hepatic vascular complications., (© 2021 S. Karger AG, Basel.)

The thermodynamic stability of 11 complexes of Cu(II) and 26 complexes of Fe(III) is studied, comprising the ligands pyridoxamine (PM), ascorbic acid (ASC), and a model Amadori compound (AMD). In addition, the secondary antioxidant activity of PM is analyzed when chelating both Cu(II) and Fe(III), relative to the rate constant of the first step of the Haber-Weiss cycle, in the presence of the superoxide radical anion (O2•-) or ascorbate (ASC - ). Calculations are performed at the M05(SMD)/6-311+G(d,p) level of theory. The aqueous environment is modeled by making use of the SMD solvation method in all calculations. This level of theory accurately reproduces the experimental data available. When put in perspective with the stability of various complexes of aminoguanidine (AG) (which we have previously studied), the following stability trends can be found for the Cu(II) and Fe(III) complexes, respectively: ASC < AG < AMD < PM and AG < ASC < AMD < PM. The most stable complex of Cu(II) with PM (with two bidentate ligands) presents a ΔGf0 value of -35.8 kcal/mol, whereas the Fe(III) complex with the highest stability (with three bidentate ligands) possesses a ΔGf0 of -58.9 kcal/mol. These complexes can significantly reduce the rate constant of the first step of the Haber-Weiss cycle with both O2•- and ASC - . In the case of the copper-containing reaction, the rates are reduced up to 9.70 × 10 3 and 4.09 × 10 13 times, respectively. With iron, the rates become 1.78 × 10 3 and 4.45 × 10 15 times smaller, respectively. Thus, PM presents significant secondary antioxidant activity since it is able to inhibit the production of ·OH radicals. This work concludes a series of studies on secondary antioxidant activity and allows potentially new glycation inhibitors to be investigated and compared relative to both PM and AG.

Adherent neutrophils on vascular endothelium positively contribute to cell-cell aggregation and vaso-occlusion in sickle cell disease. In the present study, we demonstrated that pyridoxamine, a derivative of vitamin B6, might be a therapeutic agent to alleviate intravascular cell-cell aggregation in sickle cell disease. Using real-time intravital microscopy, we found that one oral administration of pyridoxamine dose-dependently increased the rolling influx of neutrophils and reduced neutrophil adhesion to endothelial cells in cremaster microvessels of sickle cell disease mice challenged with hypoxia-reoxygenation. Short-term treatment also mitigated neutrophil-endothelial cell and neutrophil-platelet interactions in the microvessels and improved the survival of sickle cell disease mice challenged with tumor necrosis factor-α. The inhibitory effects of pyridoxamine on intravascular cell-cell interactions were potentiated by co-treatment with hydroxyurea. We observed that long-term (5.5 months) oral treatment with pyridoxamine significantly diminished the adhesive function of neutrophils and platelets and down-regulated the expression of E-selectin and intercellular adhesion molecule-1 on the vascular endothelium in tumor necrosis factor-α-challenged sickle cell disease mice. Ex vivo studies revealed that the surface amount of αMβ2 integrin was significantly decreased in stimulated neutrophils isolated from sickle cell disease mice treated with pyridoxamine-containing water. Studies using platelets and neutrophils from sickle cell disease mice and patients suggested that treatment with pyridoxamine reduced the activation state of platelets and neutrophils. These results suggest that pyridoxamine may be a novel therapeutic and a supplement to hydroxyurea to prevent and treat vaco-occlusion events in sickle cell disease.

Vitamin B 6 comprises an important set of molecules tightly interwoven with the human amino acid, fatty acid, and carbohydrate metabolism. Analytical methods striving for the quantification of individual B 6 vitamers so far mostly rely on methods based on HPLC in combination with fluorescence detection, but their application encounters multiple difficulties due to the chemical divergence of the single vitamers. The present study describes the development of a method based on LC-MS/MS and stable isotope dilution assay (SIDA) for the simultaneous quantification of five vitamers (PN, PL, PM, PMP, and PNG) of the B 6 group in food samples. [ 13 C 3 ]-PN, [ 13 C 3 ]-PL, and [ 13 C 6 ]-PNG were applied as internal standards for the analysis of PN, PL, and PNG. PM and PMP were quantified via matrix-matched calibration referring to [ 13 C 3 ]-PN. The developed method was validated using starch matrix. The limits of detection and quantification ranged from 0.0028 to 0.02 mg/kg and from 0.0085 to 0.059 mg/kg, respectively, for all analytes. Calculated recoveries varied from 92 to 111%. Intra-injection precisions ranged from 0 to 9%, inter-day precisions from 4 to 10%, and intra-day precisions from 4 to 10%. A total of 14 plant-based food samples including fruits, vegetables, and cereals were examined for their content of vitamin B 6 using the validated method. Furthermore, the first quantitation of PNG without enzymatic steps or divergent internal standards was undertaken utilizing LC-MS/MS and SIDA.

Artifacts due to metabolite extraction, derivatization, and detection techniques can result in aberrant observations that are not accurate representations of actual cell metabolism. Here, we show that α-ketoglutarate (α-KG) is reductively aminated to glutamate in methanol:water metabolite extracts, which introduces an artifact into metabolomics studies. We also identify pyridoxamine and urea as amine donors for α-KG to produce glutamate in methanol:water buffer in vitro, and we demonstrate that the addition of ninhydrin to the methanol:water buffer suppresses the reductive amination of α-KG to glutamate in vitro and in metabolite extracts. Finally, we calculate that glutamate levels have been overestimated by 10-50%, depending on cell line, due to α-KG reductive amination. These findings suggest that precautions to account for α-KG reductive amination should be taken for the accurate quantification of glutamate in metabolomics studies., Competing Interests: Declaration of Competing Interest The authors declare no competing interests., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Objective: We investigated the protective effects of pyridoxamine against metabolic and microcirculatory complications in nonalcoholic fatty liver disease., Methods: Nonalcoholic fatty liver disease was established by a high-fat diet administration over 28 weeks. Pyridoxamine was administered between weeks 20 and 28. The recruitment of leukocytes and the number of vitamin A-positive hepatic stellate cells were examined by in vivo microscopy. Laser speckle contrast imaging was used to evaluate microcirculatory hepatic perfusion. Thiobarbituric acid reactive substances measurement and RT-PCR were used for oxidative stress and inflammatory parameters. advanced glycation end products were evaluated by fluorescence spectroscopy., Results: The increase in body, liver, and fat weights, together with steatosis and impairment in glucose metabolism observed in the nonalcoholic fatty liver disease group were attenuated by pyridoxamine treatment. Regarding the hepatic microcirculatory parameters, rats with high-fat diet-induced nonalcoholic fatty liver disease showed increased rolling and adhesion of leukocytes, increased hepatic stellate cells activation, and decreased tissue perfusion, which were reverted by pyridoxamine. Pyridoxamine protected against the increased hepatic lipid peroxidation observed in the nonalcoholic fatty liver disease group. Pyridoxamine treatment was associated with increased levels of tumor necrosis factor alpha (TNF-α) mRNA transcripts in the liver., Conclusion: Pyridoxamine modulates oxidative stress, advanced glycation end products, TNF-α transcripts levels, and metabolic disturbances, being a potential treatment for nonalcoholic fatty liver disease-associated microcirculatory and metabolic complications., (© 2019 John Wiley & Sons Ltd.)

Objective: The impact of diabetes mellitus on the central nervous system is less widely studied than in the peripheral nervous system, but there is increasing evidence that it elevates the risk of developing cognitive deficits. The aim of this study was to characterize the impact of experimental diabetes on the proteome and metabolome of the hippocampus. We tested the hypothesis that the vitamin B6 isoform pyridoxamine is protective against functional and molecular changes in diabetes., Methods: We tested recognition memory using the novel object recognition (NOR) test in streptozotocin (STZ)-induced diabetic, age-matched control, and pyridoxamine- or insulin-treated diabetic male Wistar rats. Comprehensive untargeted metabolomic and proteomic analyses, using gas chromatography-mass spectrometry and iTRAQ-enabled protein quantitation respectively, were utilized to characterize the molecular changes in the hippocampus in diabetes., Results: We demonstrated diabetes-specific, long-term (but not short-term) recognition memory impairment and that this deficit was prevented by insulin or pyridoxamine treatment. Metabolomic analysis showed diabetes-associated changes in 13/82 identified metabolites including polyol pathway intermediates glucose (9.2-fold), fructose (4.9-fold) and sorbitol (5.2-fold). We identified and quantified 4807 hippocampal proteins; 806 were significantly altered in diabetes. Pathway analysis revealed significant alterations in cytoskeletal components associated with synaptic plasticity, glutamatergic signaling, oxidative stress, DNA damage and FXR/RXR activation pathways in the diabetic rat hippocampus., Conclusions: Our data indicate a protective effect of pyridoxamine against diabetes-induced cognitive deficits, and our comprehensive 'omics datasets provide insight into the pathogenesis of cognitive dysfunction enabling development of further mechanistic and therapeutic studies., (Copyright © 2019 The Authors. Published by Elsevier GmbH.. All rights reserved.)

It is known that receptor for advanced glycation end products (RAGE) and its ligands accumulate in the fat tissues of obese individuals, and RAGE ligands induce M1 macrophage polarization, which in turn induces inflammation. We evaluated the effect of pyridoxamine on RAGE ligand accumulation and M1 polarization in the visceral, subcutaneous, and perivascular fat tissues of Sprague-Dawley rats fed a high fat diet (HFD). Pyridoxamine reduced HFD-induced weight gain, attenuated adipocyte size increases, RAGE ligand accumulations, RAGE-RAGE ligands binding, decreased macrophage M1 polarization and increased M2 polarization in visceral fat tissues, but not in subcutaneous tissues. Pyridoxamine induced glyoxalase 1 (Glo-1) expression in visceral fat in the HFD group, whereas pyridoxamine induced Glo-1 expression in perivascular fat tissues was no higher than that observed in the normal fat diet (NFD) controls. In vitro, pyridoxamine suppressed the release of RAGE ligands from AGE treated macrophages, but non-significantly attenuated RAGE ligands release in AGE treated adipocytes. Pyridoxamine was found to suppress weight increases and M1 polarization, and to increase Glo-1 expression through the RAGE pathway in perivascular and visceral fat tissues of HFD-induced obese rats. These findings suggest pyridoxamine is a candidate for the treatment of obesity or complications related to obesity-induced inflammation., (Copyright © 2019 The Authors. Published by Elsevier Inc. All rights reserved.)

Neonatal epileptic encephalopathy (NEE), as a result of pyridoxine 5'-phosphate oxidase (PNPO) deficiency, is a rare neural disorder characterized by intractable seizures and usually leads to early infant death. The clinical phenotypes do not respond to antiepileptic drugs but are alleviated in most cases by giving large doses of pyridoxal 5'-phosphate (PLP). PLP is the active form of vitamin B6 participating in more than 100 enzymatic pathways. One of the causes of NEE is pathogenic mutations in the gene for human PNPO (h PNPO ). PNPO is a key enzyme in converting pyridoxine (PN), the common dietary form of vitamin B6, and some other B6 vitamers to PLP. More than 25 different mutations in hPNPO, which result in reduced catalytic activity, have been described for PNPO-deficiency NEE. To date, no animal model is available to test new therapeutic strategies. In this report, we describe using zebrafish with reduced activity of Pnpo as an animal model. Knocking down zPnpo resulted in developmental anomalies including brain malformation and impaired locomotor activity, similar to the clinical features of PNPO-deficiency NEE. Other anomalies include a defective circulation system. These anomalies were significantly alleviated by co-injecting either z pnpo or h PNPO mRNAs. As expected from clinical observations in humans, supplementing with PLP improved the morphological and behavioral anomalies. PN only showed marginal positive effects, and only in a few anomalies. Remarkably, pyridoxamine (PM), another dietary form of vitamin B6, showed rescue effects even at a lower concentration than PLP, presenting a possible new therapeutic treatment for PNPO-deficiency NEE. Finally, GABA, a neurotransmitter whose biosynthesis depends on a PLP-dependent enzyme, showed some positive rescue effect. These results suggest zebrafish to be a promising PNPO-deficiency model for studying PLP homeostasis and drug therapy in vivo ., (Copyright © 2019 Chen, Tu, Schirch, Safo and Fu.)

Introduction: This study aimed to investigate changes in renal function and the AGE-RAGE axis in the kidney of a non-genetic animal model of metabolic syndrome (MetS) induced by high-fat diet (HFD). Additionally, we evaluated the protective effect of pyridoxamine (PM), a vitamin B6 analog with anti-AGE effects, in the context of diet-related renal endothelial dysfunction., Methodology: In Wistar rats, the MetS animal model was induced by 20 or 28 weeks of HFD feeding. When indicated, a subgroup of animals was treated daily with PM (60 mg/kg) for 2 months. Tissue perfusion in renal microcirculation was examined by laser speckle contrast imaging. Oxidative stress was analyzed by thiobarbituric acid reactive species and the inflammatory markers by ELISA (TNF-α and IL-1β). Reverse transcription polymerase chain reaction was used to analyze eNOs, IL-6, vascular cell adhesion molecule (VCAM), NADPH oxidase subunit 47 (N47), catalase, and receptor for AGE (RAGE) gene expression., Results: Wistar rats fed a HFD showed negligible alteration in renal function, decrease in catalase mRNA transcripts and catalase enzyme activity compared to control (CTL) animals. Increased levels of IL-1β were observed in the kidney of MetS-induced rats. HFD-fed rats exhibited kidney endothelial dysfunction, with no significant differences in basal microvascular blood flow. PM significantly improved kidney vasorelaxation in HFD-fed rats. eNOS, VCAM, and RAGE gene expression and AGE content were not altered in kidneys of HFD-induced MetS rats in comparison to CTLs., Conclusions: Our findings suggest that HFD-induced microvascular dysfunction precedes the decline in renal function, and could be related to antioxidant machinery defects and inflammation activation in the kidney. PM showed a vasoprotective effect, and thus, could be an important contributory factor in ameliorating diet-induced renal damage., Competing Interests: The authors report no conflicts of interest in this work., (© 2019 Rangel Silvares et al.)

Pyridoxamine, one of the natural forms of vitamin B 6 , is known to be an effective inhibitor of the formation of advanced glycation end products (AGEs), which are closely related to various human diseases. Pyridoxamine forms stable complexes with metal ions that catalyze the oxidative reactions taking place in the advanced stages of the protein glycation cascade. It also reacts with reactive carbonyl compounds generated as byproducts of protein glycation, thereby preventing further protein damage. We applied Density Functional Theory to study the primary antioxidant activity of pyridoxamine towards three oxygen-centered radicals (•OOH, •OOCH 3 and •OCH 3 ) to find out whether this activity may also play a crucial role in the context of protein glycation inhibition. Our results show that, at physiological pH, pyridoxamine can trap the •OCH 3 radical, in both aqueous and lipidic media, with rate constants in the diffusion limit (>1.0 × 10 8 M - 1 s - 1 ). The quickest pathways involve the transfer of the hydrogen atoms from the protonated pyridine nitrogen, the protonated amino group or the phenolic group. Its reactivity towards •OOH and •OOCH 3 is smaller, but pyridoxamine can still scavenge them with moderate rate constants in aqueous media. Since reactive oxygen species are also involved in the formation of AGEs, these results highlight that the antioxidant capacity of pyridoxamine is also relevant to explain its inhibitory role on the glycation process.

Vitamin B 6 compounds, including pyridoxine, pyridoxal, pyridoxamine, and their phosphorylated forms, have been investigated with regard to their cancer preventive and therapeutic effects through epidemiological, in vivo, and in vitro studies. In particular, in vitro studies in cancer cells have evaluated the effects of several B 6 vitamers such as pyridoxine, pyridoxal, pyridoxamine, and pyridoxal-5'-phosphate, which is a bioactive form of vitamin B 6 However, the anticancer activity and concentration required to influence cancer cells vary among B 6 vitamers. In this review, the various in vitro effects of vitamin B 6 compounds on cancer cells are presented and discussed., (Copyright© 2019, International Institute of Anticancer Research (Dr. George J. Delinasios), All rights reserved.)

Pyridoxamine, which is a form of vitamin B 6 , is a promising candidate for a prophylactic and/or remedy for diabetic complications. Pyridoxamine is chemically synthesized by an oxidative method in manufacturing. However, pyridoxamine production by bioconversion, which is generally preferable for environmental and energetic aspects, has been little investigated. Therefore, I aimed to produce pyridoxamine from pyridoxine, which is a readily and economically available starting material, by bioconversion using a Rhodococcus expression system. I found in the bioconversion of pyridoxine to pyridoxal, approximately 450 mM pyridoxal was produced from 500 mM pyridoxine using recombinant Rhodococcus erythropolis expressing the pyridoxine 4-oxidase gene derived from Mesorhizobium loti. Next, in the bioconversion of pyridoxal to pyridoxamine using recombinant R. erythropolis expressing the pyridoxamine-pyruvate aminotransferase gene derived from M. loti, the bioconversion rate was approximately 80% under the same conditions as pyridoxal production. Finally, in the bioconversion of pyridoxine to pyridoxamine through pyridoxal using recombinant R. erythropolis coexpressing the genes for pyridoxine 4-oxidase and pyridoxamine-pyruvate aminotransferase, the bioconversion rate was approximately 75%. Based on these findings, pyridoxamine production by bioconversion using a Rhodococcus expression system may be of interest for future industrial applications., (Copyright © 2018 The Society for Biotechnology, Japan. Published by Elsevier B.V. All rights reserved.)

Hyperglycaemia is considered to be a driving factor for advanced glycated end products (AGEs). Inhibiting the process of glycation play an important role in reducing the diabetes related complications. We have explored the glucose mediated glycation and antiglycation activity of pyridoxamine using human serum albumin (HSA). Protein was incubated with glucose for 28 days at physiological temperature to achieve glycation. Antiglycation activity was assessed by the estimation of carbonyl content, free lysine and AGE specific fluorescence. Molecular docking was used to study the interaction of pyridoxamine with HSA and to get a detailed understanding of binding sites and binding energy. Glycation was reduced by pyridoxamine to commendable levels which was evident by the quantification of free lysine and carbonyl content. Pyridoxamine treatment also prevented the loss in secondary structure induced by glycation. It has also emerged as the quencher of reactive oxygen species which lead to the protection of DNA from oxidative damage. Pyridoxamine was found to be located at subdomain IIA of HSA with binding energy of -5.6 kcal/mol. These results are high points in the antiglycation activity of pyridoxamine. Its antioxidant nature and antiglycation activity are proof of its potential in preventing disease progression in diabetes., (Copyright © 2018 Elsevier B.V. All rights reserved.)

[ 13 C₃]-labelled vitamers (PN, PL and PM) of the B6 group were prepared starting from [ 13 C₃]-propionic acid. [ 13 C₃]-PN was synthesized in ten linear steps with an overall yield of 17%. Hereby, higher alkyl homologues of involved esters showed a positive impact on the reaction outcome of the intermediates in the chosen synthetic route. Oxidation of [ 13 C₃]-PN to [ 13 C₃]-PL was undertaken using potassium permanganate and methylamine followed by acid hydrolysis of the imine derivative. [ 13 C₃]-PM could be prepared from the oxime derivative of [ 13 C₃]-PN by hydrogenation with palladium.

Multiple sclerosis (MS) is a demyelinating autoimmune disease of the central nervous system (CNS). The immune response in MS patients leads to the infiltration of immune cells in the CNS and their subsequent activation. Immune cell activation induces a switch towards glycolysis. During glycolysis, the dicarbonyl product methylglyoxal (MGO) is produced. MGO is a glycating agent that can rapidly form advanced glycation endproducts (AGEs). In turn, AGEs are able to induce inflammatory responses. The glyoxalase system is the endogenous defense system of the body to reduce the burden of MGO thereby reducing AGE formation. This system consists of glyoxalase-1 and glyoxalase-2 which are able to detoxify MGO to D-lactate. We investigated whether AGE levels are induced in experimental autoimmune encephalitis (EAE), an inflammatory animal model of MS. Twenty seven days post EAE induction, MGO and AGE ( N &epsilon; -(carboxyethyl)lysine (CEL), 5-hydro-5-methylimidazolone (MG-H1)) levels were significantly increased in the spinal cord of mice subjected to EAE. Yet, pyridoxamine treatment and glyoxalase-1 overexpression were unable to counteract AGE production during EAE and did not influence the clinical course of EAE. In conclusion, AGEs levels increase during EAE in the spinal cord, but AGE-modifying treatments do not inhibit EAE-induced AGE production and do not affect disease progression.N &epsilon; -(carboxyethyl)lysine (CEL), 5-hydro-5-methylimidazolone (MG-H1)) levels were significantly increased in the spinal cord of mice subjected to EAE. Yet, pyridoxamine treatment and glyoxalase-1 overexpression were unable to counteract AGE production during EAE and did not influence the clinical course of EAE. In conclusion, AGEs levels increase during EAE in the spinal cord, but AGE-modifying treatments do not inhibit EAE-induced AGE production and do not affect disease progression.