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Low levels of vitamin D in maternal and cord blood have been associated with neonatal sepsis. This study assessed the association of vitamin D metabolites (25(OH)D, 3-epi-25(OH)D3, and 24,25(OH)2D3) levels in maternal and cord blood with newborn sepsis evaluation in Nigerian mother–infant dyads. Maternal and cord blood from 534 mothers and 536 newborns were processed using liquid chromatography-tandem mass spectrometry. Spearman correlation was used to compare continuous variables, Mann–Whitney for dichotomous variables, and Kruskal–Wallis for two or more groups. High cord percent 3-epi-25(OH)D3 levels were positively associated with newborn evaluation for sepsis (p = 0.036), while maternal and cord 25(OH)D and 24,25(OH)2D3 levels were not. Being employed was positively associated with maternal and newborn 3-epi-25(OH)D3 concentrations (p = 0.007 and p = 0.005, respectively). The maternal 3-epi-25(OH)D3 and percent 3-epi-25(OH)D3 were positively associated with vaginal delivery (p = 0.013 and p = 0.012, respectively). Having a weight-for-age Z-score ≤ −2 was positively associated with newborn percent 3-epi-25(OH)D3 levels (p = 0.004), while a weight-for-length Z-score ≤ −3 was positively associated with maternal and newborn percent 3-epi-25(OH)D3 levels (p = 0.044 and p = 0.022, respectively). Our study highlights the need to further investigate the biological role of 3-epi-25(OH)D3 and its clinical significance in fetal growth and newborn outcome. [ABSTRACT FROM AUTHOR]

Abstract Vitamin D deficiency and obesity are a worldwide health issue. Obesity refers to the accumulation of excessive fats in the body which could lead to the development of diseases. Obese people have low vitamin D levels for several reasons including larger volume of distribution, vitamin D tightly bound in fatty tissues, reduced absorption, and diets with low vitamin D. Accurately measuring vitamin D metabolites is challenging. The Ultra-High-Performance Liquid Chromatography-Tandem Mass Spectrometry (UHPLC-MS/MS) method was developed and validated for the analysis of vitamin D metabolites in the serum. Blood samples were collected from 452 subjects which consisted of baseline (vitamin D deficient obese subjects), follow-up (supplemented obese subjects), and healthy volunteers. The vitamin D metabolites were separated adequately by the developed UHPLC-MS/MS method. Moreover, the validation criteria for the method were within an acceptable range. The baseline, follow-up and even healthy volunteers were deficient in 25OHD3 and 25OHD2. The baseline and healthy subjects had comparable concentration of vitamin D2 and D3. However, healthy subjects had a higher concentration of 25OHD and its epimer compared to the baseline subjects. The vitamin D3 was increased significantly in the follow- up subjects; therefore, the 25OHD3 was increased significantly compared to the baseline as well; however, the increase was insufficient to achieve the optimal range. The UHPLC-MS/MS method test was applied successfully on estimation of vitamin D metabolites in subjects. This study indicates the significance of taking into account the metabolic and storage effects when evaluating the vitamin D status in obese subjects.

Clinical and preclinical studies have provided conflicting data on the postulated beneficial effects of vitamin D in patients with prostate cancer. In this opinion piece, we discuss reasons for discrepancies between preclinical and clinical vitamin D studies. Different criteria have been used as evidence for the key roles of vitamin D. Clinical studies report integrative cancer outcome criteria such as incidence and mortality in relation to vitamin D status over time. In contrast, preclinical vitamin D studies report molecular and cellular changes resulting from treatment with the biologically active vitamin D metabolite, 1,25-dihydroxyvitamin D3 (calcitriol) in tissues. However, these reported changes in preclinical in vitro studies are often the result of treatment with biologically irrelevant high calcitriol concentrations. In typical experiments, the used calcitriol concentrations exceed the calcitriol concentrations in normal and malignant prostate tissue by 100 to 1000 times. This raises reasonable concerns regarding the postulated biological effects and mechanisms of these preclinical vitamin D approaches in relation to clinical relevance. This is not restricted to prostate cancer, as detailed data regarding the tissue-specific concentrations of vitamin D metabolites are currently lacking. The application of unnaturally high concentrations of calcitriol in preclinical studies appears to be a major reason why the results of preclinical in vitro studies hardly match up with outcomes of vitamin D-related clinical studies. Regarding future studies addressing these concerns, we suggest establishing reference ranges of tissue-specific vitamin D metabolites within various cancer entities, carrying out model studies on human cancer cells and patient-derived organoids with biologically relevant calcitriol concentrations, and lastly improving the design of vitamin D clinical trials where results from preclinical studies guide the protocols and endpoints within these trials. [ABSTRACT FROM AUTHOR]

The active vitamin D metabolites, 25-hydroxyvitamin D3 (25D3) and 1,25-dihydroxyvitamin D3 (1,25D3), are produced by successive hydroxylation steps and play key roles in several cellular processes. However, alternative metabolic pathways exist, and among them, the 4-hydroxylation of 25D3 is a major one. This study aims to investigate the structure–activity relationships of 4-hydroxy derivatives of 1,25D3. Structural analysis indicates that 1,4α,25(OH)3D3 and 1,4β,25(OH)3D3 maintain the anchoring hydrogen bonds of 1,25D3 and form additional interactions, stabilizing the active conformation of VDR. In addition, 1,4α,25D3 and 1,4β,25D3 are as potent as 1,25D3 in regulating the expression of VDR target genes in rat intestinal epithelial cells and in the mouse kidney. Moreover, these two 4-hydroxy derivatives promote hypercalcemia in mice at a dose similar to that of the parent compound. [ABSTRACT FROM AUTHOR]

(1) Background: Vitamin D supplementation after type 1 diabetes mellitus (T1DM) onset has led to conflicting results on beta-cell preservation. Aim: This paper presents a systematic review to verify whether randomized prospective controlled trials (RCTs) demonstrate that improved vitamin D status confers protection on T1DM. (2) Methods: A systematic review was conducted up until 18 January 2024 according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, searching MEDLINE, MEDLINE In-Process, Embase, Cochrane Database of Systematic Reviews, and Cochrane Central Register of Controlled Trials, using keywords "vitamin D", "type 1 diabetes", and "children". (3) Results: Following the above-mentioned search process, 408 articles in PubMed and 791 in Embase met inclusion criteria. After removing duplicates, 471 articles remained. After exclusion criteria, 11 RCTs remained. Because of major heterogeneity in design and outcomes, no meta-analyses were conducted, allowing only for qualitative analyses. There was no strong evidence that vitamin D supplementation has lasting effects on beta-cell preservation or glycemic control in new-onset T1DM. (4) Conclusions: More rigorous, larger studies are needed to demonstrate whether vitamin D improves beta-cell preservation or glycemic control in new-onset T1DM. Because T1DM may cause osteopenia, it is advisable that patients with new onset T1DM have adequate vitamin D stores. [ABSTRACT FROM AUTHOR]

Low levels of vitamin D in maternal and cord blood have been associated with neonatal sepsis. This study assessed the association of vitamin D metabolites (25(OH)D, 3-epi-25(OH)D3, and 24,25(OH)2D3) levels in maternal and cord blood with newborn sepsis evaluation in Nigerian mother–infant dyads. Maternal and cord blood from 534 mothers and 536 newborns were processed using liquid chromatography-tandem mass spectrometry. Spearman correlation was used to compare continuous variables, Mann–Whitney for dichotomous variables, and Kruskal–Wallis for two or more groups. High cord percent 3-epi-25(OH)D3 levels were positively associated with newborn evaluation for sepsis (p = 0.036), while maternal and cord 25(OH)D and 24,25(OH)2D3 levels were not. Being employed was positively associated with maternal and newborn 3-epi-25(OH)D3 concentrations (p = 0.007 and p = 0.005, respectively). The maternal 3-epi-25(OH)D3 and percent 3-epi-25(OH)D3 were positively associated with vaginal delivery (p = 0.013 and p = 0.012, respectively). Having a weight-for-age Z-score ≤ −2 was positively associated with newborn percent 3-epi-25(OH)D3 levels (p = 0.004), while a weight-for-length Z-score ≤ −3 was positively associated with maternal and newborn percent 3-epi-25(OH)D3 levels (p = 0.044 and p = 0.022, respectively). Our study highlights the need to further investigate the biological role of 3-epi-25(OH)D3 and its clinical significance in fetal growth and newborn outcome.

Clinical and preclinical studies have provided conflicting data on the postulated beneficial effects of vitamin D in patients with prostate cancer. In this opinion piece, we discuss reasons for discrepancies between preclinical and clinical vitamin D studies. Different criteria have been used as evidence for the key roles of vitamin D. Clinical studies report integrative cancer outcome criteria such as incidence and mortality in relation to vitamin D status over time. In contrast, preclinical vitamin D studies report molecular and cellular changes resulting from treatment with the biologically active vitamin D metabolite, 1,25-dihydroxyvitamin D3 (calcitriol) in tissues. However, these reported changes in preclinical in vitro studies are often the result of treatment with biologically irrelevant high calcitriol concentrations. In typical experiments, the used calcitriol concentrations exceed the calcitriol concentrations in normal and malignant prostate tissue by 100 to 1000 times. This raises reasonable concerns regarding the postulated biological effects and mechanisms of these preclinical vitamin D approaches in relation to clinical relevance. This is not restricted to prostate cancer, as detailed data regarding the tissue-specific concentrations of vitamin D metabolites are currently lacking. The application of unnaturally high concentrations of calcitriol in preclinical studies appears to be a major reason why the results of preclinical in vitro studies hardly match up with outcomes of vitamin D-related clinical studies. Regarding future studies addressing these concerns, we suggest establishing reference ranges of tissue-specific vitamin D metabolites within various cancer entities, carrying out model studies on human cancer cells and patient-derived organoids with biologically relevant calcitriol concentrations, and lastly improving the design of vitamin D clinical trials where results from preclinical studies guide the protocols and endpoints within these trials.

The active vitamin D metabolites, 25-hydroxyvitamin D3 (25D3) and 1,25-dihydroxyvitamin D3 (1,25D3), are produced by successive hydroxylation steps and play key roles in several cellular processes. However, alternative metabolic pathways exist, and among them, the 4-hydroxylation of 25D3 is a major one. This study aims to investigate the structure–activity relationships of 4-hydroxy derivatives of 1,25D3. Structural analysis indicates that 1,4α,25(OH)3D3 and 1,4β,25(OH)3D3 maintain the anchoring hydrogen bonds of 1,25D3 and form additional interactions, stabilizing the active conformation of VDR. In addition, 1,4α,25D3 and 1,4β,25D3 are as potent as 1,25D3 in regulating the expression of VDR target genes in rat intestinal epithelial cells and in the mouse kidney. Moreover, these two 4-hydroxy derivatives promote hypercalcemia in mice at a dose similar to that of the parent compound.

(1) Background: Vitamin D supplementation after type 1 diabetes mellitus (T1DM) onset has led to conflicting results on beta-cell preservation. Aim: This paper presents a systematic review to verify whether randomized prospective controlled trials (RCTs) demonstrate that improved vitamin D status confers protection on T1DM. (2) Methods: A systematic review was conducted up until 18 January 2024 according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, searching MEDLINE, MEDLINE In-Process, Embase, Cochrane Database of Systematic Reviews, and Cochrane Central Register of Controlled Trials, using keywords “vitamin D”, “type 1 diabetes”, and “children”. (3) Results: Following the above-mentioned search process, 408 articles in PubMed and 791 in Embase met inclusion criteria. After removing duplicates, 471 articles remained. After exclusion criteria, 11 RCTs remained. Because of major heterogeneity in design and outcomes, no meta-analyses were conducted, allowing only for qualitative analyses. There was no strong evidence that vitamin D supplementation has lasting effects on beta-cell preservation or glycemic control in new-onset T1DM. (4) Conclusions: More rigorous, larger studies are needed to demonstrate whether vitamin D improves beta-cell preservation or glycemic control in new-onset T1DM. Because T1DM may cause osteopenia, it is advisable that patients with new onset T1DM have adequate vitamin D stores.

In current clinical practice, a thorough understanding of vitamin D metabolism is in high demand both for patients with various diseases and for healthy individuals. Analytical techniques that provide simultaneous measurement of multiple metabolites are preferred. Herein, the development of an HPLC-DMS-MS/MS method for the quantitation of vitamin D compounds (25(OH)D3, 25(OH)D2, 1,25(OH)2D3, 3-epi-25(OH)D3, 24,25(OH)2D3, and D3) in serum is described. The selected sample preparation procedure based on the combination of liquid–liquid and solid-phase extraction, which excluded a lengthy derivatization step, was compared with other common approaches. Sensitivity was increased through the implementation of differential ion mobility separation. The proposed assay allowed us to determine the low abundant 1,25(OH)2D3 with the detection limit of 10 pg/mL. The validation study showed good linearity (r2 > 0.99), a wide analytical range (2.5–75 ng/mL for 25(OH)D3), and acceptable precision (<7%) for all metabolites. The recovery ranged from 71% to 93% and the matrix effect from 0.80 to 0.95 depending on the metabolite; accuracy determination was performed using DEQAS controls. [ABSTRACT FROM AUTHOR]

In recent years, the physiological and molecular functions of vitamin D (Vit-D) have been deeply investigated. At first, Vit-D was considered a regulator of mineral and skeletal homeostasis. However, due to the extensive-expression pattern of Vit-D receptor (VDR) in almost every non-skeletal cell, Vit-D is considered mainly a multifunctional agent with broad effects on various tissues, notably the immune system. The expression of VDR in immune cells such as dendritic cells, monocyte/macrophage, neutrophils, B cells and T cells has been well demonstrated. Besides, such immune cells are capable of metabolizing the active form of Vit-D which means that it can module the immune system in both paracrine and autocrine manners. Vit-D binding protein (DBP), that regulates the levels and homeostasis of Vit-D, is another key molecule capable of modulating the immune system. Recent studies indicate that dysregulation of Vit-D axis, variations in the DBP and VDR genes, and Vit-D levels might be risk factors for the development of autoimmune disease. Here, the current evidence regarding the role of Vit-D axis on the immune system, as well as its role in the development of autoimmune disease will be clarified. Further insight will be given to those studies that investigated the association between single nucleotide polymorphisms of DBP and VDR genes with autoimmune disease susceptibility.

An apparent vitamin D paradox, characterized by lower serum 25-hydroxyvitamin D (25(OH)D) levels and higher bone mineral density, is present in black population. In contrast, blacks have higher serum 1,25-dihydroxyvitamin D (1,25(OH)2D) levels. The effect of 1,25(OH)2D on the skeleton is not fully understood. We examined serum 25(OH)D, 1,25(OH)2D and bone histomorphometry in 50 black and white women (25 each) matched for age, menstrual status, and BMI. Histomorphometric indices related to bone structure, remodeling and mineralization were measured in cancellous bone in iliac bone biopsies. Data analyses led to the following results: 1) serum 25(OH)D was significantly lower and 1,25(OH)2D was significantly higher in black than in white women, but neither blacks nor whites revealed significant correlation between these two vitamin D metabolites. 2) there was no significant difference in PTH levels between blacks and whites. 3) except for greater trabecular thickness (Tb.Th) in blacks, there were no significant differences in other histomorphometric variables between the two ethnic groups. 4) osteoid surface (OS/BS), unlabeled osteoid surface (ulOS/BS), and osteoblast surface (ObS/BS) significantly correlated with serum 1,25(OH)2D levels. We conclude that lower serum 25(OH)D levels in blacks do not impair bone structure and remodeling, nor decrease bone mineralization. Higher serum 1,25(OH)2D levels in blacks may help preserve bone mass by stimulating bone formation via increasing osteoblast number and function, but moderately inhibit terminal bone mineralization as shown by higher ulOS/BS.

The determination of vitamin D metabolites as status marker or for diagnostic purposes is almost entirely conducted from blood serum or plasma. Other biological matrices, however, have also interested researchers, for two main reasons: (1) alternative matrices may allow non-invasive sampling, permit easier sample transfer and require less demanding storage conditions; and (2) the levels of vitamin D metabolites in other body compartments may further aid the understanding of vitamin D metabolism and function. Thus, the development of reliable and efficient sample preparation protocols for sample matrices other than serum/plasma, which will remove potential interferences and selectively extract the targeted metabolites, is of great importance. This review summarizes sample preparation methods for measurement of vitamin D metabolites using liquid chromatography-(tandem)mass spectrometry in more than ten different human tissues, including hair, saliva, adipose tissue, brain and others. [ABSTRACT FROM AUTHOR]

In current clinical practice, a thorough understanding of vitamin D metabolism is in high demand both for patients with various diseases and for healthy individuals. Analytical techniques that provide simultaneous measurement of multiple metabolites are preferred. Herein, the development of an HPLC-DMS-MS/MS method for the quantitation of vitamin D compounds (25(OH)D3, 25(OH)D2, 1,25(OH)2D3, 3-epi-25(OH)D3, 24,25(OH)2D3, and D3) in serum is described. The selected sample preparation procedure based on the combination of liquid–liquid and solid-phase extraction, which excluded a lengthy derivatization step, was compared with other common approaches. Sensitivity was increased through the implementation of differential ion mobility separation. The proposed assay allowed us to determine the low abundant 1,25(OH)2D3 with the detection limit of 10 pg/mL. The validation study showed good linearity (r2 > 0.99), a wide analytical range (2.5–75 ng/mL for 25(OH)D3), and acceptable precision (

During the past 40 years, the National Institute of Standards and Technology (NIST) has developed over 180 natural matrix Standard Reference Materials® (SRMs) for the determination of trace organic constituents in environmental, clinical, food, and dietary supplement matrices. A list of the Top Ten SRMs intended for organic analysis was identified based on selection criteria including analytical challenge to assign certified values, challenges in material preparation, novel matrices, longevity, widespread use, and unique design concept or intended use. The environmental matrix SRMs include air particulate matter, marine sediment, mussel tissue, and human serum with the focus on contaminants such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), chlorinated pesticides, and polybrominated diphenyl ethers (PBDEs). Human serum and plasma SRMs for clinical diagnostic markers including vitamin D metabolites represent clinical analysis, whereas infant formula, multivitamin/multielement tablets, and Ginkgo biloba constitute the food and dietary supplement matrices on the list. Each of the SRMs on the Top Ten list is discussed relative to the selection criteria and significance of the material, and several overall lessons learned are summarized. [ABSTRACT FROM AUTHOR]

Abstract Background Vitamin D deficiency is diagnosed by total serum 25-hydroxyvitamin D (25(OH)D) concentration and is associated with poor health and increased mortality; however, some populations have low 25(OH) D concentrations without manifestations of vitamin D deficiency. The Vitamin D Metabolite Ratio (VMR) has been suggested as a superior indicator of vitamin D status. Therefore, VMR was determined in a population with type 2 diabetes at high risk for vitamin D deficiency and correlated with diabetic complications. Research design and methods Four hundred sisty patients with type 2 diabetes (T2D) were recruited, all were vitamin D3 supplement naive. Plasma concentration of 25-hydroxyvitamin D3 (25(OH)D3) and its metabolites 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) and 24,25-dihydroxyvitamin D3 (24,25(OH)2D3) and its epimer, 3-epi-25-hydroxyvitamin D3 (3-epi-25(OH)D3), were measured by LC-MS/MS analysis. VMR-1 was calculated as a ratio of 24,25(OH)2D3:25(OH)D3; VMR-2 as a ratio of 1,25(OH)2D3:25(OH)D3; VMR-3 was calculated as a ratio of 3-epi-25(OH)D3: 25(OH)D3. Results An association means that there were significant differences between the ratios found for those with versus those without the various diabetic complications studied. VMR-1 was associated with diabetic retinopathy (p = 0.001) and peripheral artery disease (p = 0.012); VMR-2 associated with hypertension (p

Abstract Aims Vitamin D measurement is a composite of vitamin D2 (25(OH)D2) and D3 (25(OH)D3) levels, and its deficiency is associated with the development of type 2 diabetes (T2DM) and diabetic complications; vitamin D deficiency may be treated with vitamin D2 supplements. This study was undertaken to determine if vitamin D2 and D3 levels differed between those with and without T2DM in this Middle Eastern population, and the relationship between diabetic microvascular complications and vitamin D2 and vitamin D3 levels in subjects with T2DM. Methods Four hundred ninety-six Qatari subjects, 274 with and 222 without T2DM participated in the study. Plasma levels of total vitamin D2 and D3 were measured by LC-MS/MS analysis. Results All subjects were taking vitamin D2 and none were taking D3 supplements. Vitamin D2 levels were higher in diabetics, particularly in females, and higher levels were associated with hypertension and dyslipidemia in the diabetic subjects (p

Vitamin D deficiency significantly correlates with the severity of SARS-CoV-2 infection. Molecular docking-based virtual screening studies predict that novel vitamin D and related lumisterol hydroxymetabolites are able to bind to the active sites of two SARSCoV-2 transcription machinery enzymes with high affinity. These enzymes are the main protease (Mpro) and RNA-dependent RNA polymerase (RdRP), which play important roles in viral replication and establishing infection. Based on predicted binding affinities and specific interactions, we identified 10 vitamin D3 (D3) and lumisterol (L3) analogs as likely binding partners of SARSCoV-2 Mpro and RdRP and, therefore, tested their ability to inhibit these enzymes. Activity measurements demonstrated that 25 (OH)L3, 24(OH)L3, and 20(OH)7DHC are the most effective of the hydroxymetabolites tested at inhibiting the activity of SARSCoV-2 Mpro causing 10%-19% inhibition. These same derivatives as well as other hydroxylumisterols and hydroxyvitamin D3 metabolites inhibited RdRP by 50%-60%. Thus, inhibition of these enzymes by vitamin D and lumisterol metabolites may provide a novel approach to hindering the SARS-CoV-2 infection. [ABSTRACT FROM AUTHOR]

Vitamin D Binding Protein (VDBP), also well-known as Gc-globulin, is a plasma protein which acts as a carrier molecule for vitamin D and its metabolites. This multifunctional glycoprotein is a member of the albumin superfamily of binding proteins. It is predominantly synthesized as a single long chain glycoprotein in the liver. VDBP helps in vitamin D metabolites transport, control bone development, binds actin monomers and fatty acids and prevents their polymerization; which might be harmful in circulatory system. A less defined role in modulating immune and inflammatory response is also known. VDBP plays an important role in protection of microcirculation, inflammation, infection and also known to have antiviral and antitumoral activity. Recent studies documented its use as a early marker for diagnosis of chronic kidney disease. This review discusses the multifunctional characters of VDBP in spectra of diseases with emphasis on its use as marker for diabetic nephropathy. [ABSTRACT FROM AUTHOR]

Neonatal dried blood spots (DBS) provide a remarkable resource for biobanks. These microsamples can provide information related to the genetic correlates of disease and can be used to quantify a range of analytes, such as proteins and small molecules. However, after routine neonatal screening, the amount of DBS sample available is limited. To optimize the use of these samples, there is a need for sensitive assays which are integrated across different analytic platforms. For example, after DNA extraction, protein extracts are available for additional analyses. We describe a sensitive and robust LC-MS/MS method for 25-hydroxyvitamin D2 and 25-hydroxyvitamin D3 optimized for leftover protein extracts from DBS, which has excellent recovery, precision, and accuracy.

Background: Vitamin D deficiency is diagnosed by total serum 25-hydroxyvitamin D (25(OH)D) concentration and is associated with poor health and increased mortality; however, some populations have low 25(OH) D concentrations without manifestations of vitamin D deficiency. The Vitamin D Metabolite Ratio (VMR) has been suggested as a superior indicator of vitamin D status. Therefore, VMR was determined in a population with type 2 diabetes at high risk for vitamin D deficiency and correlated with diabetic complications. Research design and methods: Four hundred sisty patients with type 2 diabetes (T2D) were recruited, all were vitamin D3 supplement naive. Plasma concentration of 25-hydroxyvitamin D3 (25(OH)D3) and its metabolites 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) and 24,25-dihydroxyvitamin D3 (24,25(OH)2D3) and its epimer, 3-epi-25-hydroxyvitamin D3 (3-epi-25(OH)D3), were measured by LC-MS/MS analysis. VMR-1 was calculated as a ratio of 24,25(OH)2D3:25(OH)D3; VMR-2 as a ratio of 1,25(OH)2D3:25(OH)D3; VMR-3 was calculated as a ratio of 3-epi-25(OH)D3: 25(OH)D3. Results: An association means that there were significant differences between the ratios found for those with versus those without the various diabetic complications studied. VMR-1 was associated with diabetic retinopathy (p = 0.001) and peripheral artery disease (p = 0.012); VMR-2 associated with hypertension (p < 0.001), dyslipidemia (p < 0.001), diabetic retinopathy (p < 0.001), diabetic neuropathy (p < 0.001), coronary artery disease (p = 0.001) and stroke (p < 0.05). VMR-3 associated with hypertension (p < 0.05), dyslipidemia (p < 0.001) and coronary artery disease (p < 0.05). Conclusions: In this cross sectional study, whilst not causal, VMR-2 was shown to be the superior predictor of diabetic and cardiovascular complications though not demonstrative of causality in this cross-sectional study population over VMR-1, VMR-3 and the individual vitamin D concentration measurements; VMR-2 associated with both microvascular and cardiovascular indices and therefore may have utility in predicting the development of diabetic complications. [ABSTRACT FROM AUTHOR]

Aims: Vitamin D measurement is a composite of vitamin D2 (25(OH)D2) and D3 (25(OH)D3) levels, and its deficiency is associated with the development of type 2 diabetes (T2DM) and diabetic complications; vitamin D deficiency may be treated with vitamin D2 supplements. This study was undertaken to determine if vitamin D2 and D3 levels differed between those with and without T2DM in this Middle Eastern population, and the relationship between diabetic microvascular complications and vitamin D2 and vitamin D3 levels in subjects with T2DM. Methods: Four hundred ninety-six Qatari subjects, 274 with and 222 without T2DM participated in the study. Plasma levels of total vitamin D2 and D3 were measured by LC-MS/MS analysis. Results: All subjects were taking vitamin D2 and none were taking D3 supplements. Vitamin D2 levels were higher in diabetics, particularly in females, and higher levels were associated with hypertension and dyslipidemia in the diabetic subjects (p < 0.001), but were not related to diabetic retinopathy or nephropathy. Vitamin D3 levels measured in the same subjects were lower in diabetics, particularly in females (p < 0.001), were unrelated to dyslipidemia or hypertension, but were associated with retinopathy (p < 0.014). Neither vitamin D2 nor vitamin D3 were associated with neuropathy. For those subjects with hypertension, dyslipidemia, retinopathy or neuropathy, comparison of highest with lowest tertiles for vitamin D2 and vitamin D3 showed no difference. Conclusions: In this Qatari cohort, vitamin D2 was associated with hypertension and dyslipidemia, whilst vitamin D3 levels were associated with diabetic retinopathy. Vitamin D2 levels were higher, whilst vitamin D3 were lower in diabetics and females, likely due to ingestion of vitamin D2 supplements. [ABSTRACT FROM AUTHOR]

The active metabolites of vitamin D3 (D3) and lumisterol (L3) exert a variety of antiaging and photoprotective effects on the skin. These are achieved through immunomodulation and include anti-inflammatory actions, regulation of keratinocytes proliferation, and differentiation programs to build the epidermal barrier necessary for maintaining skin homeostasis. In addition, they induce antioxidative responses, inhibit DNA damage and induce DNA repair mechanisms to attenuate premature skin aging and cancerogenesis. The mechanism of action would involve interaction with multiple nuclear receptors including VDR, AhR, LXR, reverse agonism on RORα and -γ, and nongenomic actions through 1,25D3-MARRS receptor and interaction with the nongenomic binding site of the VDR. Therefore, active forms of vitamin D3 including its canonical (1,25(OH)2D3) and noncanonical (CYP11A1-intitated) D3 derivatives as well as L3 derivatives are promising agents for the prevention, attenuation, or treatment of premature skin aging. They could be administrated orally and/or topically. Other forms of parenteral application of vitamin D3 precursor should be considered to avoid its predominant metabolism to 25(OH)D3 that is not recognized by CYP11A1 enzyme. The efficacy of topically applied vitamin D3 and L3 derivatives needs further clinical evaluation in future trials.

The brain’s supply with vitamin D is poorly understood. Therefore, the present study aimed to determine 25-hydroxy vitamin D3 (25(OH)D) and 24,25-dihydroxy vitamin D (24,25(OH)2D3) in serum and cerebrospinal fluid (CSF) from individuals with intact and disturbed brain-CSF-barrier (BCB) function. In 292 pairs of serum and CSF samples the vitamin D metabolites were measured with liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). CSF/serum ratios (QALB, Q25(OH)D, Q24,25(OH)2D3) were calculated. Median (IQR) serum concentrations of 25(OH)D and 24,25(OH)2D3 were 63.8 (43.4–83.9) nmol/L and 4.2 (2.2–6.2) nmol/L. The CSF concentrations of both metabolites accounted for 3.7 and 3.3% of the respective serum concentrations. Serum 25(OH)D correlated inversely with Q25(OH)D and Q24,25(OH)2D3 implying a more efficient transport of both metabolites across the BCB when the serum concentration of 25(OH)D is low. In patients with BCB dysfunction, the CSF concentrations and the CSF/serum ratios of both vitamin D metabolites were higher than in individuals with intact BCB. The CSF concentrations of 25(OH)D and 24,25(OH)2D3 depend on BCB function and the respective serum concentrations of both metabolites. Higher vitamin D metabolite concentrations in CSF of patients with impaired BCB function may be due to passive diffusion across the BCB.

(1) Background: Vitamin D, a well-established regulator of calcium and phosphate metabolism, also has immune-modulatory functions. An uncontrolled immune response and cytokine storm are tightly linked to fatal courses of COVID-19. The present retrospective study aimed to inves-tigate vitamin D status markers and vitamin D degradation products in a mixed cohort of 148 hospitalized COVID-19 patients with various clinical courses of COVID-19. (2) Methods: The serum concentrations of 25(OH)D3, 25(OH)D2, 24,25(OH)2D3, and 25,26(OH)2D3 were determined by a validated liquid-chromatography tandem mass-spectrometry method in leftover serum samples from 148 COVID-19 patients that were admitted to the University Hospital of the Medical Uni-versity of Graz between April and November 2020. Anthropometric and clinical data, as well as outcomes were obtained from the laboratory and hospital information systems. (3) Results: From the 148 patients, 34 (23%) died within 30 days after admission. The frequency of fatal outcomes did not differ between males and females. Non-survivors were significantly older than survivors, had higher peak concentrations of IL-6 and CRP, and required mechanical ventilation more frequently. The serum concentrations of all vitamin D metabolites and the vitamin D metabolite ratio (VMR) did not differ significantly between survivors and non-survivors. Additionally, the need for res-piratory support was unrelated to the serum concentrations of 25(OH)D vitamin D and the two vitamin D catabolites, as well as the VMR. (4) Conclusion: The present results do not support a relevant role of vitamin D for the course and outcome of COVID-19.

Objective: The relationship between fertilization rates and 1,25-dihydroxyvitamin D (1,25(OH)2D3), 25-hydroxyvitamin D2 (25(OH)D2), 25-hydroxyvitamin D3 (25(OH)D3), 24,25-dihydroxyvitamin D (24,25(OH)2D3), and 25-hydroxy-3epi-Vitamin D3 (3epi25(OH)D3) concentrations in age and weight matched women with and without PCOS was studied.Methods: Fifty nine non-obese women, 29 with PCOS, and 30 non-PCOS undergoing IVF, matched for age and weight were included. Serum vitamin D metabolites were taken the menstrual cycle prior to commencing controlled ovarian hyperstimulation.Results: Vitamin D metabolites did not differ between PCOS and controls; however, 25(OH)D3 correlated with embryo fertilization rates in PCOS patients alone (p = 0.03). For all subjects, 3epi25(OH)D3 correlated with fertilization rate (p < 0.04) and negatively with HOMA-IR (p < 0.02); 25(OH)D2 correlated with cleavage rate, G3D3 and blastocyst (p < 0.05; p < 0.009; p < 0.002, respectively). 24,25(OH)2D3 correlated with AMH, antral follicle count, eggs retrieved and top quality embryos (G3D3) (p < 0.03; p < 0.003; p < 0.009; p < 0.002, respectively), and negatively with HOMA-IR (p < 0.01). 1,25(OH)2D3 did not correlate with any of the metabolic or embryo parameters. In slim PCOS, 25(OH)D3 correlated with increased fertilization rates in PCOS, but other vitamin D parameters did not differ to matched controls.Conclusion: 3epi25(OH)D3, 25(OH)D2, and 24,25(OH)2D3, but not 1,25(OH)2D3, were associated with embryo parameters suggesting that vitamin D metabolites other than 1,25(OH)2D3 are important in fertility.

Objective: The relationship between fertilization rates and 1,25-dihydroxyvitamin D (1,25(OH)2D3), 25-hydroxyvitamin D2 (25(OH)D2), 25-hydroxyvitamin D3 (25(OH)D3), 24,25-dihydroxyvitamin D (24,25(OH)2D3), and 25-hydroxy-3epi-Vitamin D3 (3epi25(OH)D3) concentrations in age and weight matched women with and without PCOS was studied. Methods: Fifty nine non-obese women, 29 with PCOS, and 30 non-PCOS undergoing IVF, matched for age and weight were included. Serum vitamin D metabolites were taken the menstrual cycle prior to commencing controlled ovarian hyperstimulation. Results: Vitamin D metabolites did not differ between PCOS and controls; however, 25(OH)D3 correlated with embryo fertilization rates in PCOS patients alone (p = 0.03). For all subjects, 3epi25(OH)D3 correlated with fertilization rate (p < 0.04) and negatively with HOMA-IR (p < 0.02); 25(OH)D2 correlated with cleavage rate, G3D3 and blastocyst (p < 0.05; p < 0.009; p < 0.002, respectively). 24,25(OH)2D3 correlated with AMH, antral follicle count, eggs retrieved and top quality embryos (G3D3) (p < 0.03; p < 0.003; p < 0.009; p < 0.002, respectively), and negatively with HOMA-IR (p < 0.01). 1,25(OH)2D3 did not correlate with any of the metabolic or embryo parameters. In slim PCOS, 25(OH)D3 correlated with increased fertilization rates in PCOS, but other vitamin D parameters did not differ to matched controls. Conclusion: 3epi25(OH)D3, 25(OH)D2, and 24,25(OH)2D3, but not 1,25(OH)2D3, were associated with embryo parameters suggesting that vitamin D metabolites other than 1,25(OH)2D3 are important in fertility. [ABSTRACT FROM AUTHOR]

Vitamin D is responsible for multiple metabolic functions in humans. Rickets are the most common disease caused by vitamin D deficiency. It is caused by poor calcium intake resulting in poor serum-ionized calcium. The purpose of this study is to develop a rapid, sensitive, and feasible method to determine the 25-hydroxy-vitamin D3 (25(OH)D3) levels in blood samples for clinical assessment. In this study, gas chromatography coupled mass spectrometry with trimethylsilyl derivatization (TMS-GC-MS) is the most suitable protocol for quantitative analyses of 25(OH)D3. Performance of method was evaluated and compared with liquid chromatography and immunoassay. Method validation has been carried out with plasma specimens. The limit of quantitation of TMS-GC-MS method is 1.5 ppb with good linear correlation. Furthermore, the dietary intake and nutritional status of vegetarian and non-vegetarians in Taiwan were assessed by our validated method. As a result, this vitamin D nutrition survey demonstrates that most Taiwanese people have insufficient vitamin D. Due to dietary habits; the male vegans may have the highest risk of vitamin D deficiency. [ABSTRACT FROM AUTHOR]

While the independent roles of vitamin D and sex hormones in skeletal health are well established, the associations of vitamin D and its metabolites to sex hormones and their indices are less investigated. In this observational study, clinical information of 189 Saudi postmenopausal women aged ≥50 years old [N = 80 with normal bone mineral density (BMD), aged 53.3 ± 7.7 years with body mass index (BMI)= 34.1kg/m2 ± 5.8, and N = 109 with low BMD (T-score −1.0 to −2.5), aged 57.0 ± 8.2 years, BMI = 32.4kg/m2 ± 6.2] was extracted from an existing capital-wide osteoporosis registry in Riyadh, Saudi Arabia. Data included were BMD scores, serum total 25(OH)D, sex hormones, and bone turnover markers which were measured using commercially available assays. Age- and BMI-adjusted comparisons revealed significantly higher parathyroid hormone (PTH) levels as well as significantly lower testosterone and bioavailable testosterone in the low BMD group than the normal BMD group (p-values 0.04, 0.02, and 0.03, respectively). Stepwise linear regression showed that circulating testosterone levels accounted for 9.7% and 8.9% of the variances perceived in bioavailable 25(OH)D and free 25(OH)D, respectively (p < 0.01), independent of other sex hormones, sex hormone indices, and bone turnover markers. Our study suggests that androgens are significantly associated with non-conventional vitamin D metabolites and these associations may have clinical relevance in assessing risk for low BMD and osteoporosis in Arab postmenopausal women.

The association between low vitamin D status and the development of type 2 diabetes mellitus is well established; however, intervention trials that increased serum vitamin D (through ultraviolet B exposure or dietary supplementation) provide mixed outcomes. Recent evidence suggests that metabolites directly related to vitamin D receptor activation—1α,25-dihydroxyvitamin D3 and 24R,25-dihydroxyvitamin D3—may be better markers of vitamin D repletion status. We tested the hypothesis that a vitamin D metabolite (VDM) index, calculated as the sum of normalized fasting serum concentrations of 1α,25-dihydroxyvitamin D3 and 24R,25-dihydroxyvitamin D3, is associated with metabolic function. We measured subcutaneous and visceral adipose tissue volume, intrahepatic triglyceride content, maximum oxygen uptake, insulin sensitivity (4 h hyperinsulinemic-euglycemic clamp), and insulin secretion (3 h meal tolerance test with mathematical modeling) and calculated the VDM index in 65 healthy Asian adults. Subjects with a low VDM index had lower peripheral insulin sensitivity and beta-cell function compared to subjects with a high VDM index (both p < 0.05), matched for age, sex, BMI, and serum 25-hydroxyvitamin D3. Serum 25-hydroxyvitamin D3 was not associated with peripheral insulin sensitivity or beta-cell function. Our results suggest that, rather than enhancing vitamin D substrate availability, upregulation of vitamin D action is more likely to lead to improvements in glucose homeostasis.

To analyze if the prometastatic activity of calcitriol (active vitamin D3 metabolite), which was previously observed in a 4T1 breast cancer model, is also found in other breast cancers, and to assess the impact of various schemes of vitamin D supply, we used 4T1 and E0771 mouse metastatic and 67NR nonmetastatic cells in this study. BALB/c and C57BL/6 healthy and tumor-bearing mice were exposed to a control (1000 IU), low- (100 IU), and high- (5000 IU) vitamin D3 diets. Additionally, from day 7 of tumor transplantation, the 1000 and 100 IU groups were gavaged with calcitriol (+cal). After 8 weeks of feeding, plasma levels of 25(OH)D3, 24,25(OH)2D3, and 3-epi-25(OH)D3 were significantly lower in calcitriol-treated and vitamin D-deficient groups than in the control, whereas the levels of all metabolites were increased in the 5000 IU group. The ratio of 25(OH)D3:24,25(OH)2D3 was increased in both calcitriol-treated groups, whereas the ratio of 25(OH)D3:3-epi-25(OH)D3 was increased only in the 100 IU group but decreased in the 5000 IU group. In contrast to E0771, 4T1 lung metastasis was accelerated in all vitamin D-supplemented mice, as well as in the deficient group with an increased inflammatory response. 67NR tumor growth was transiently inhibited in the 1000 IU+cal group, but single metastases were observed in the 5000 and 100 IU groups. Based on the results, we conclude that various schemes of vitamin D supply and vitamin D deficiency led to similar metabolite profiles irrespective of the mice strain and tumor burden. However, depending on the type of breast cancer, different effects on tumor growth and metastasis were noticed.

Vitamin D deficiency in pregnant women and their offspring may result in unfavorable health outcomes for both mother and infant. A 25hydroxyvitamin D (25(OH)D) level of at least 75 nmol/L is recommended by the Endocrine Society. Validated, automated sample preparation and liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods were used to determine the vitamin D metabolites status in mother-infant pairs. Detection of 3-Epi25(OH)D3 prevented overestimation of 25(OH)D3 and misclassification of vitamin D status. Sixty-three percent of maternal 25(OH)D plasma levels were less than the recommended level of 25(OH)D at 3 months. Additionally, breastmilk levels of 25(OH)D decreased from 60.1 nmol/L to 50.0 nmol/L between six weeks and three months (p < 0.01). Furthermore, there was a positive correlation between mother and infant plasma levels (p < 0.01, r = 0.56) at 3 months. Accordingly, 31% of the infants were categorized as vitamin D deficient (25(OH)D < 50 nmol/L) compared to 25% if 3-Epi25(OH)D3 was not distinguished from 25(OH)D3. This study highlights the importance of accurate quantification of 25(OH)D. Monitoring vitamin D metabolites in infant, maternal plasma, and breastmilk may be needed to ensure adequate levels in both mother and infant in the first 6 months of infant life.

Vitamin D and its analogues are fat-soluble vitamins that carry out important functions in human and animal organisms. Many studies have pointed out the relationship between the deficiency of these substances and the development of both skeletal- and extra-skeletal diseases. Although vitamin D is fundamentally derived from the bio-transformation of its precursor, 7-dehydrocholesterol, through the action of UV-B radiation in the skin, dietary intake also plays an important role in the regulation of its status in an organism. For this reason, the application of reliable methodologies that enable monitoring the content of vitamin D and its analogues in food and supplements constitutes an aspect of special relevance to establish adequate habits, which avoid the deficiency of these substances in organisms and, consequently, the appearance of related diseases. The use of chromatographic techniques in combination with conventional and novel sample pre-treatments has become a suitable strategy to achieve this aim. This review compiles the most relevant methodologies reported in the last ten years for vitamin D analogues analysis in food matrices. Particular attention has been paid to provide a general overview of the most suitable approaches in terms of reliability, sensitivity and simplicity, used in the field of food analysis.

Vitamin D-binding protein (VDBP), the main carrier of vitamin D, has recently been implicated in reproductive health and pregnancy outcomes including endometriosis, polycystic ovary syndrome (PCOS), pre-eclampsia, and gestational diabetes mellitus (GDM). Improved methods for measuring VDBP and an increased understanding of its role in biological processes have led to a number of newly published studies exploring VDBP in the context of pregnancy. Here, we synthesize the available evidence regarding the role of VDBP in reproductive health and pregnancy, and we highlight areas requiring further study. Overall, low levels of maternal serum VDBP concentrations have been associated with infertility, endometriosis, PCOS and spontaneous miscarriage, as well as adverse pregnancy outcomes including GDM, pre-eclampsia, preterm birth and fetal growth restriction. However, increased VDBP concentration in cervicovaginal fluid has been linked to unexplained recurrent pregnancy loss and premature rupture of membranes. Some genetic variants of VDBP have also been associated with these adverse outcomes. Further studies using more accurate VDBP assays and accounting for ethnic variation and potential confounders are needed to clarify whether VDBP is associated with reproductive health and pregnancy outcomes, and the mechanisms underlying these relationships.

Serum vitamin D metabolite levels are of interest as biomarkers for vitamin D status, which has influence on numerous body functions and pathologies. The determination of vitamin D metabolite levels by liquid chromatography/mass spectrometry (LC/MS) is challenging due to their low concentrations and relatively low ionization efficiencies. Three ionization sources, dielectric barrier discharge ionization (DBDI), atmospheric pressure chemical ionization (APCI), and electrospray ionization (ESI), were compared regarding achievable limits of detection and occurring matrix effects. The latter were mainly caused by phospholipids. Therefore, in addition to a conventional solid phase extraction (SPE) stationary phase, a material for selective removal of phospholipids was examined. The selective removal of phospholipids significantly reduced observed matrix effects, especially when ESI was applied. Achievable limits of detection and observed matrix effects were lowest for APCI and with some limitations, also for DBDI.Graphical abstract [ABSTRACT FROM AUTHOR]

ABSTRACT: Most trials of vitamin D supplementation have shown no benefits on bone mineral density (BMD), although severe vitamin D deficiency causes osteomalacia, which is associated with profound BMD deficits. Recently, the ViDA‐BMD study from New Zealand demonstrated a threshold of baseline 25‐hydroxyvitamin D (25OHD; 30 nmol/L) below which vitamin D supplementation did benefit BMD. We have now reexamined data from a similar trial in Aberdeen to determine whether a baseline 25OHD threshold of 30 nmol/L is also observed in that database. The Aberdeen study recruited 305 postmenopausal women in late winter and randomized them to receive placebo, vitamin D 400 IU/d, or vitamin D 1000 IU/d over 1 year. As previously reported, BMD loss at the hip was reduced by vitamin D 1000 IU/d only, and there was no significant treatment effect of either dose at the lumbar spine. In the present analysis, when the trial participants were grouped according to whether their baseline 25OHD was ≤30 nmol/L or above this threshold, significant treatment effects were apparent at both the spine and hip in those with baseline 25OHD ≤30 nmol/L, but no significant effects were apparent in those with baseline 25OHD above this level. There was evidence of a similar threshold for effects on parathyroid hormone, but no groups showed changes in bone turnover markers during the study. It is concluded that vitamin D supplements only increase bone density in adults with nadir 25OHD ≤30 nmol/L. This moves us further toward a trial‐based definition of vitamin D deficiency in adults with adequate calcium intakes and suggests that supplement use should be targeted accordingly. Future trials of vitamin D supplementation should focus on individuals with 25OHD concentrations in this range. © 2018 American Society for Bone and Mineral Research. [ABSTRACT FROM AUTHOR]

In recent years, the physiological and molecular functions of vitamin D (Vit-D) have been deeply investigated. At first, Vit-D was considered a regulator of mineral and skeletal homeostasis. However, due to the extensive-expression pattern of Vit-D receptor (VDR) in almost every non-skeletal cell, Vit-D is considered mainly a multifunctional agent with broad effects on various tissues, notably the immune system. The expression of VDR in immune cells such as dendritic cells, monocyte/macrophage, neutrophils, B cells and T cells has been well demonstrated. Besides, such immune cells are capable of metabolizing the active form of Vit-D which means that it can module the immune system in both paracrine and autocrine manners. Vit-D binding protein (DBP), that regulates the levels and homeostasis of Vit-D, is another key molecule capable of modulating the immune system. Recent studies indicate that dysregulation of Vit-D axis, variations in the DBP and VDR genes, and Vit-D levels might be risk factors for the development of autoimmune disease. Here, the current evidence regarding the role of Vit-D axis on the immune system, as well as its role in the development of autoimmune disease will be clarified. Further insight will be given to those studies that investigated the association between single nucleotide polymorphisms of DBP and VDR genes with autoimmune disease susceptibility. • The vitamin D axis is crucial for the maintenance of immune system homeostasis. • Vitamin D status, VDR and DBP gene polymorphisms are associated with autoimmune-related disorders. • The precise mechanisms of the vitamin D/DBP/VDR axis in the pathogenesis of autoimmune disorders remain to be elucidated. [ABSTRACT FROM AUTHOR]

Vitamin D (VitD) insufficiency is common in multiple sclerosis (MS). VitD has possible anti-inflammatory effects on the immune system. The ratio between VitD metabolites in MS patients and the severity of the disease are suggested to be related. However, the exact effect of the bone-derived hormone fibroblast-growth-factor-23 (FGF23) and VitD binding protein (VDBP) on this ratio is not fully elucidated yet. Therefore, the aim is to study differences in total, free, and bioavailable VD metabolites and FGF23 between MS patients and healthy controls (HCs). FGF23, vitD (25(OH)D), active vitD (1,25(OH)2D), inactive 24,25(OH)D, and VDBP were measured in 91 MS patients and 92 HCs. Bioavailable and free concentrations were calculated. No difference in FGF23 (p = 0.65) and 25(OH)D/24.25(OH)2D ratio (p = 0.21) between MS patients and HCs was observed. Bioavailable 25(OH)D and bioavailable 1.25(OH)2D were lower (p < 0.01), while VDBP concentrations were higher in MS patients (p = 0.02) compared with HCs, specifically in male MS patients (p = 0.01). In conclusion, FGF23 and 25(OH)D/24.25(OH)2D did not differ between MS patients and HCs, yet bioavailable VitD concentrations are of potential clinical relevance in MS patients. The possible immunomodulating role of VDBP and gender-related differences in the VD-FGF23 axis in MS need further study.

25-hydroxyvitamin D (25(OH)D) is commonly measured to assess vitamin D status. Other vitamin D metabolites such as 24,25-dihydroxyvitamin D (24,25(OH)2D) provide additional insights into vitamin D status or metabolism. Earlier studies suggested that the vitamin D metabolite ratio (VMR), calculated as 24,25(OH)2D/25(OH)D, could predict the 25(OH)D increase after vitamin D supplementation. However, the evidence for this additional value is inconclusive. Therefore, our aim was to assess whether the increase in 25(OH)D after supplementation was predicted by the VMR better than baseline 25(OH)D. Plasma samples of 106 individuals (25(OH)D < 75 nmol/L) with hypertension who completed the Styrian Vitamin D Hypertension Trial (NC.T.02136771) were analyzed. Participants received vitamin D (2800 IU daily) or placebo for 8 weeks. The treatment effect (ANCOVA) for 25(OH)D3, 24,25(OH)2D3 and the VMR was 32 nmol/L, 3.3 nmol/L and 0.015 (all p < 0.001), respectively. Baseline 25(OH)D3 and 24,25(OH)2D3 predicted the change in 25(OH)D3 with comparable strength and magnitude. Correlation and regression analysis showed that the VMR did not predict the change in 25(OH)D3. Therefore, our data do not support routine measurement of 24,25(OH)2D3 in order to individually optimize the dosage of vitamin D supplementation. Our data also suggest that activity of 24-hydroxylase increases after vitamin D supplementation.

Background: High levels of fibroblast growth factor-23 (FGF23) are associated with mortality. In chronic kidney disease (CKD), FGF23 levels rise as renal function declines. We analyzed the contribution of laboratory values to the variance of FGF23 levels in relationship to a curve of expected FGF23 levels for a given GFR.Methods: Following approval by the research ethics boards, we measured FGF23, CysC eGFR, creatinine, urea, albumin, calcium, phosphate, vitamin D metabolites, PTH, alkaline phosphatase, CRP, and venous gases in 141 pediatric CKD patients (45, 37, 32, 13 and 14 CKD stages I, II, III, IV, and V, respectively). Data were expressed as median (25th, 75th percentile).Results: FGF23 correlated significantly with CysC, CysC eGFR, PTH, 1.25 (OH)2 vitamin D, phosphate, and pH. The correlation of the latter three remained significant in the multivariate analysis. We calculated a formula for the expected FGF23 value for a given level of eGFR which reads Y = 1295 * e-0.07247*X + 38.35. Deviation by more than 20% from the curve also depended on phosphate, 1.25 (OH)2 vitamin D and pH.Conclusions: Our data emphasize the importance of phosphate and 1.25 (OH)2 vitamin D levels. The impact of acidosis on FGF23 warrants further studies. [ABSTRACT FROM AUTHOR]

Vitamin D and its metabolites are lipophilic molecules with low aqueous solubility and must be transported bound to plasma carrier proteins, primarily to vitamin D binding protein (DBP). The biological functions of vitamin D metabolites are intimately dependent on the protein, hence the importance of determining their affinity for DBP. In this study, we developed a novel procedure for measuring the kinetic and equilibrium constants of human-DBP with vitamin D and three metabolites: 1,25-dihydroxyvitamin D [1,25(OH)D], 25-hydroxyvitamin D (25OHD) and 24,25-dihydroxyvitamin D [24,25(OH)D] by surface plasmon resonance (SPR). At the same time, five different analogues, synthetized in our laboratory, were evaluated in order to compare the affinity values with the metabolites. Real-time SPR measurements showed that 25OHD and 24,25(OH)D had higher affinity (0.3 μM) than 1,25(OH)D (5 μM), with the higher affinity of 25OHD and 24,25(OH)D due to dissociation constants 1 order of magnitude slower. In the case of the analogues, the affinity values were lower, with 1-hydroxy-25-nitro-vitamin D (NO-446), structurally closer to 1,25(OH)D, showing the highest value with a K of 50 μM. (24R)-1,25-dihydroxyvitamin-24-buthyl-28-norvitamin D (Bu-471) and (24R)-1,25-dihydroxyvitamin-24-phenyl-28-norvitamin D (Ph-491), structurally similar, had affinities of 180 and 170 μM, respectively. (22R,23E)-1-hydroxy-22-ethenyl-25-methoxy-23-dehydrovitamin D (MeO-455) and 1-hydroxy-20(R)-[5(S)-(2,2-dimethyltetrahydropyran-5-yl)]-22,23-dinor vitamin D (Oxan-429) had affinities of 310 and 100 μM, respectively. The binding of the metabolites and analogues was reversible allowing the rapid capture of data for replicates. The kinetic and equilibrium data for both the metabolites and the analogues fitted to the Langmuir model describing a 1:1 interaction. [ABSTRACT FROM AUTHOR]

The aim was to determine the intestinal Ca 2 + absorption in type I diabetic rats after different times of STZ induction, as well as the gene and protein expression of molecules involved in both the transcellular and paracellular Ca 2 + pathways. The redox state and the antioxidant enzymes of the enterocytes were also evaluated in duodenum from either diabetic or insulin-treated diabetic rats as compared to control rats. Male Wistar rats (150–200 g) were divided into two groups: 1) controls and 2) STZ-induced diabetic rats (60 mg/kg b.w.). A group of diabetic rats received insulin for five days. The insulin was adjusted daily to maintain a normal blood glucose level. Five 5 d after STZ injection, there was a reduction in the intestinal Ca 2 + absorption, which was maintained for 30 d and disappeared at 60 d. Similar changes occurred in the GSH and ˙ O 2 − levels. The protein expression of molecules involved in the transcellular pathway increased at 5 and 30 d returning to control values at 60 d. Their mRNA levels declined considerably at 60 d. The gene and protein expression of claudin 2 was upregulated at 30 d. Catalase activity increased at 5 and 30 d normalizing at 60 d. To conclude, type I D.m. inhibits the intestinal Ca 2 + absorption, which is transient leading to a time dependent adaptation and returning the absorptive process to normal values. The inhibition is accompanied by oxidative stress. When insulin is administered, the duodenal redox state returns to control values and the intestinal Ca 2 + absorption normalizes. [ABSTRACT FROM AUTHOR]