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Abstract Overconsumption of food, especially dietary fat, leads to metabolic disorders such as obesity and type 2 diabetes. Long‐chain fatty acids, such as palmitoleate are recognized as the risk factors for these disorders owing to their high‐energy content and lipotoxicity. In contrast, medium‐chain fatty acids (MCFAs) metabolic benefits; however, their underlying molecular mechanisms remain unclear. GPR84 is an MCFA receptor, particularly for C10:0. Although evidence from in vitro experiments and oral administration of C10:0 in mice suggests that GPR84 is related to the metabolic benefits of MCFAs via glucose metabolism, its precise roles in vivo remain unclear. Therefore, the present study investigated whether GPR84 affects glucose metabolism and metabolic function using Gpr84‐deficient mice. Although Gpr84‐deficient mice were lean and had increased endogenous MCFAs under high‐fat diet feeding conditions, they exhibited hyperglycemia and hyperlipidemia along with lower plasma insulin and glucagon‐like peptide‐1 (GLP‐1) levels compared with wild‐type mice. Medium‐chain triglyceride (C10:0) intake suppressed obesity, and improved plasma glucose and lipid levels, and increased plasma GLP‐1 levels in wild‐type mice; however, these effects were partially attenuated in Gpr84‐deficient mice. Our results indicate that long‐term MCFA‐mediated GPR84 activation improves the dysfunction of glucose and lipid homeostasis. Our findings may be instrumental for future studies on drug development with GPR84 as a potential target, thereby offering new avenues for the treatment of metabolic disorders like obesity and type 2 diabetes.

Abstract The increased incidence of obesity in the global population has increased the risk of several chronic inflammation-related diseases, including non-alcoholic steatohepatitis (NASH)-hepatocellular carcinoma (HCC). The progression from NASH to HCC involves a virus-independent liver carcinogenic mechanism; however, we currently lack effective treatment and prevention strategies. Several reports have suggested that fecal volatile organic compounds (VOCs) are strongly associated with NASH-HCC; therefore, we explored the biomarkers involved in its pathogenesis and progression. Fecal samples collected from control and NASH-HCC model STAM mice were subjected to headspace autosampler gas chromatography-electron ionization-mass spectrometry. Non-target profiling analysis identified diacetyl (2,3-butandione) as a fecal VOC that characterizes STAM mice. Although fecal diacetyl levels were correlated with the HCC in STAM mice, diacetyl is known as a cytotoxic/tissue-damaging compound rather than genotoxic or mutagenic; therefore, we examined the effect of bioactivity associated with NASH progression. We observed that diacetyl induced several pro-inflammatory molecules, including tumor necrosis factor-α, cyclooxygenase-2, monocyte chemoattractant protein-1, and transforming growth factor-β, in mouse macrophage RAW264.7 and Kupffer KPU5 cells. Additionally, we observed that diacetyl induced α-smooth muscle actin, one of the hallmarks of fibrosis, in an ex vivo cultured hepatic section, but not in in vitro hepatic stellate TWNT-1 cells. These results suggest that diacetyl would be a potential biomarker of fecal VOC in STAM mice, and its ability to trigger the macrophage-derived inflammation and fibrosis may partly contribute to NASH-HCC carcinogenesis.

Abstract Background The public health measures enacted in order to control the coronavirus disease (COVID-19) pandemic have caused considerable changes to daily life. For autistic children and adolescents, adapting to the “new normal,” including mask-wearing, may be difficult because of their restricted interest and repetitive behavior (RRB) characteristics. We aimed to examine the relationships between RRB characteristics and the impact of mask-wearing on their social communications during the pandemic. Methods We recruited participants with a clinical diagnosis of autism spectrum disorder based on DSM-5 diagnostic criteria from two outpatient clinics in Tokyo, Japan, between November 2020 and April 2021 using a convenience sampling methodology. As a result, the participants consisted of 102 children and adolescents (mean (SD) age = 11.6 (5.3)). We collected data on RRB characteristics frequency before and during the pandemic using the CoRonavIruS Health Impact Survey (CRISIS) – Adapted for Autism and Related Neurodevelopmental conditions (AFAR). We then conducted factor analyses to compute the RRB severity composite scores, which are divided into lower- (e.g., sensory seeking), and higher-order (e.g., restricted interest). We also investigated mask-wearing culture using a bespoke questionnaire, and using Spearman’s rank correlation analyses, we examined the relationships between before pandemic RRB characteristics, and the impact of mask-wearing on social communications during the pandemic. Results We found that children and adolescents who exhibited lower-order RRB before the pandemic had difficulties in going-out with mask-wearing (rho = -0.25, q = .031), more challenges with mask-wearing (rho = − 0.34, q = .0018), and difficulty in referring to others’ emotions while wearing masks (rho = − 0.36, q = .0016). We also found an association between higher-order RRB before the pandemic and an uncomfortable sensation (rho = − 0.42, q = .0002) and difficulties in referring to other’s emotions while wearing masks (rho = − 0.25, q = .031). Conclusions We revealed that various behaviors, such as sensory seeking, repetitive motor mannerisms and movements, and rituals and routines, undertaken before the pandemic could be important predictors of difficulties with mask-wearing and social communication for autistic children and adolescents during the pandemic. Caregivers and teachers wearing masks may need to provide extra support for social communication to autistic children and adolescents showing RRB characteristics frequently.

IntroductionHikikomori, a form of pathological social withdrawal, has been suggested to have comorbidity with autism spectrum disorder (ASD). This study aimed to clarify how characteristics of ASD are associated with hikikomori.MethodsThirty-nine adult male patients with a diagnosis of ASD attending our outpatient clinic for neurodevelopmental disabilities were subjected to a structured interview regarding social withdrawal, various self-administered questionnaires, and blood tests. Through structured interviews, the subjects were divided into two groups: (Group 1) ASD with hikikomori condition and (Group 2) ASD without hikikomori condition. Sixteen subjects qualified as hikikomori and 23 subjects qualified as subjects without hikikomori. Age, sex, autism spectrum quotient (AQ), Autism Diagnostic Observation Schedule (ADOS), and FIQ were matched.ResultsCompared to non-hikikomori controls, hikikomori cases were likely to have stronger sensory symptoms, lower uric acid (UA) (p = 0.038), and higher rates of atopic dermatitis (p = 0.01). Cases showed more severe depressive and social anxiety symptoms based on self-rated scales: Patient Heath Questionnaire 9 (PHQ-9) (p < 0.001) and Liebowitz Social Anxiety Scale Japanese Version (LSAS-J) (p = 0.04). Tarumi's Modern-Type Depression Trait Scale (TACS-22), which measure traits of Modern-Type Depression (MTD), were significantly higher in cases (p = 0.003).ConclusionThe present study has suggested that ASD patients with hikikomori were more likely to have higher sensory abnormalities, comorbid atopic dermatitis, lower UA, stronger depressive, and anxiety tendency. Evaluating and approaching these aspects are important for appropriate interventions in ASD with hikikomori. Further investigations should be conducted to validate our pilot findings.

Objective: The gastrointestinal tract affects physiological activities and behavior by secreting hormones and generating signals through the activation of nutrient sensors. GPR119, a lipid sensor, is indirectly involved in the secretion of incretins, such as glucagon-like peptide-1 and glucose-dependent insulinotropic peptide, by enteroendocrine cells, while it directly stimulates insulin secretion by pancreatic beta cells. Since GPR119 has the potential to modulate metabolic homeostasis in obesity and diabetes, it has attracted interest as a therapeutic target. However, previous studies have shown that the deletion of Gpr119 in mice does not affect glucose homeostasis and appetite in either basal or high-fat diet-fed conditions. Therefore, the present study aimed to explore the role of GPR119 signaling system in energy metabolism and feeding behavior in mice. Methods: Gpr119 knockout (KO) mice were generated using CRISPR-Cas9 gene-editing technology, and their feeding behavior and energy metabolism were evaluated and compared with those of wild type (WT) mice. Results: Upon inducing metabolic stress via food deprivation, Gpr119 KO mice exhibited lower blood glucose levels and a higher body weight reduction compared to WT mice. Although food intake in WT and KO mice were similar under free-feeding conditions, Gpr119 KO mice exhibited increased food intake when they were refed after 24 h of food deprivation. Further, food-deprived Gpr119 KO mice presented shorter post-meal intervals and lower satiety for second and later meals during refeeding, resulting in increased food intake. Associated with this meal pattern, levels of oleoylethanolamide (OEA), an endogenous agonist of GPR119, in the luminal contents of the distal gastrointestinal tract were elevated within 2 h after refeeding. The large-intestinal infusion of OEA prolonged post-meal intervals and increased satiety in the first meal, but not the second meal. On the other hand, infusion of oleic acid increased cecal OEA levels at 2 h from the beginning of infusion, while prolonging post-meal intervals and increasing satiety on the meals that occurred approximately 2 h after the infusion. Cecal OEA levels were low in antibiotic-treated mice, suggesting that the gut microbiota partially synthesizes OEA from oleic acid. Conclusions: Collectively, our results indicate that the activation of gastrointestinal GPR119 by microbiota-produced OEA derived from oleic acid is associated with satiety control and energy homeostasis under energy shortage conditions.

IntroductionAmong the fatty acid ethanolamides (FAEs), oleoylethanolamide (OEA), linoleoylethanolamide (LEA), and palmitoylethanolamide (PEA) are reported to be involved in feeding regulation. In particular, OEA is well characterized as a satiety signal. Following food consumption, OEA is synthesized from oleic acid (OA) via an N-acyl phosphatidylethanolamine-specific phospholipase D-dependent pathway in the gastroenterocytes, and OEA induces satiety by recruiting sensory fibers. Thus, we hypothesized that dietary OA is an important satiety-inducing molecule. However, there has been no direct demonstration of the effect of dietary OA on satiety induction without the influence of the endogenous biosynthesis of OA from stearic acid (SA) or other FAEs.MethodsIn this study, we used two experimental diets to test our hypothesis: (i) an OA diet (OAD; 38.4 mg of OA/g and 7.2 mg of SA/g) and (ii) a low OA diet (LOAD; 3.1 mg of OA/g and 42.4 mg of SA/g).ResultsRelative to mice fed the OAD, mice fed the LOAD for two weeks exhibited reduced levels of jejunal OEA but not jejunal LEA and PEA. The LOAD-fed mice showed an increase in food intake and body weight gain. Moreover, LOAD-induced increase in food intake was immediately observed after the switch from the OAD, whereas these effects were diminished by the switch back to the OAD. Furthermore, treatment with OA and OEA diminished the effects of LOAD on food intake.ConclusionCollectively, these results show that dietary OA is a key factor in the reduction of food intake and increase in satiety mediated by OEA signaling.

Medium-chain triglycerides (MCTs), which consist of medium-chain fatty acids (MCFAs), are unique forms of dietary fat with various health benefits. G protein–coupled 84 (GPR84) acts as a receptor for MCFAs (especially C10:0 and C12:0); however, GPR84 is still considered an orphan receptor, and the nutritional signaling of endogenous and dietary MCFAs via GPR84 remains unclear. Here, we showed that endogenous MCFA-mediated GPR84 signaling protected hepatic functions from diet-induced lipotoxicity. Under high-fat diet (HFD) conditions, GPR84-deficient mice exhibited nonalcoholic steatohepatitis (NASH) and the progression of hepatic fibrosis but not steatosis. With markedly increased hepatic MCFA levels under HFD, GPR84 suppressed lipotoxicity-induced macrophage overactivation. Thus, GPR84 is an immunomodulating receptor that suppresses excessive dietary fat intake–induced toxicity by sensing increases in MCFAs. Additionally, administering MCTs, MCFAs (C10:0 or C12:0, but not C8:0), or GPR84 agonists effectively improved NASH in mouse models. Therefore, exogenous GPR84 stimulation is a potential strategy for treating NASH.

The pathological consequences leading to primary storage, autophagy impairment, impaired mitochondrial dynamics, and endoplasmic reticulum (ER) stress on neural cell dysfunction and apoptosis in metachromatic leukodystrophy (MLD) have been poorly elucidated. In the present study, we generated 2 cell lines of patient-specific-induced pluripotent stem cells (iPSCs) and modeled the progression of pathological events during the differentiation of iPSCs to motor neuron progenitors (MNPs) and mature motor neurons (MNs). The iPS cells were generated from two late-infantile MLD patient-derived skin fibroblasts using electroporation or the Sendai virus. Olig2+ MNPs were generated from both iPSC lines using a combination of small molecules in a chemically defined neural medium. Furthermore, the MNPs could be differentiated into mature MNs, which was confirmed by RT–PCR and MN markers, including SMI32 and ChAT. The population of MNs was approximately 50% under the culture conditions. Pathological observation of MLD patient-derived iPSCs revealed lysosomal accumulation and impaired autophagy. In addition, both MNPs and MNs derived from MLD-iPSCs showed increased lysosomal accumulation, dysfunctional autophagy, impaired mitophagy, endoplasmic reticulum (ER) stress or unfolded protein response (UPR) activation, and premature cellular death.

BackgroundDietary triglycerides are an important energy source; however, their excess intake causes metabolic diseases such as obesity and type 2 diabetes. Medium-chain triglycerides (MCTs) as triglyceride forms of medium-chain fatty acids (MCFAs) are applied to meet the energy demands of athletes, the elderly, and people with stunted growth, because MCFAs are efficiently converted into energy for immediate utilization by the organs and do not accumulate as fat. Although the intake of each MCT type (octanoate; C8:0, decanoate; C10:0, and dodecanoate; C12:0) exhibits beneficial metabolic effects, individual functional differences remain unclear.MethodsMCTs or MCFAs were administrated to male GPR84-deficient mice with a C57BL/6J background and mouse enteroendocrine cell line STC-1, and the effects on glucose homeostasis and gut hormone GLP-1 secretion were evaluated.ResultsC10:0 intake improves glucose metabolism through the MCFA receptor GPR84-mediated GLP-1 secretion. Each MCT intake showed resistance to obesity and improved metabolic parameters compared with lard intake. Moreover, oral administration of MCTs enhanced glucose tolerance, especially C10:0 administration, which sufficiently increased plasma GLP-1 levels. Additionally, C10:0 stimulation promoted GLP-1 secretion via GPR84 in STC-1, enhanced glucose tolerance through GPR84-mediated GLP-1 secretion, and showed resistance to high-fat diet (HFD)-induced obesity in mice.ConclusionsDietary MCT (C10:0) intake efficiently may protect against obesity and improve insulin resistance via GLP-1 secretion.

Abstract Lingual thyroglossal duct cysts can be a rare cause of feeding difficulties in infants. Here, we describe a case of an infant with vomiting and feeding difficulty diagnosed with Hirschsprung's disease. However, she developed an unexpected difficult airway during anesthesia induction due to an undiagnosed lingual thyroglossal duct cyst.

The gut microbiome is an important regulator of metabolic health. Here the authors show that intestinal bacteria metabolize dietary linoleic acid to 10-hydroxy-cis-12-octadecenoic acid (HYA) which confers host resistance to high fat diet-induced obesity in mice.

Background Dietary fiber, including inulin, promotes health via fermentation products, such as short-chain fatty acids (SCFAs), produced from the fiber by gut microbiota. SCFAs exert positive physiological effects on energy metabolism, gut immunity, and the nervous system. Most of the commercial inulin is extracted from plant sources such as chicory roots, but it can also be enzymatically synthesized from sucrose using inulin producing enzymes. Studies conducted on rodents fed with a cafeteria diet have suggested that while increasing plasma propionic acid, synthetic inulin modulates glucose and lipid metabolism in the same manner as natural inulin. Therefore, this study aimed to determine the effects of a synthetic inulin, Fuji FF, on energy metabolism, fecal SCFA production, and microbiota profiles in mice fed with a high-fat/high-sucrose diet. Methods Three-week-old male C57BL/6J mice were fed a high-fat/high-sucrose diet containing cellulose or Fuji FF for 12 weeks, and the effects on energy metabolism, SCFA production, and microbiota profiles were evaluated. Results Body weight gain was inhibited by Fuji FF supplementation in high-fat/high-sucrose diet-fed C57BL/6J mice by reducing white adipose tissue weight while increasing energy expenditure, compared with the mice supplemented with cellulose. Fuji FF also elevated levels of acetic, propionic and butyric acids in mouse feces and increased plasma propionic acid levels in mice. Moreover, 16S rRNA gene amplicon sequencing of fecal samples revealed an elevated abundance of Bacteroidetes and a reduced abundance of Firmicutes at the phylum level in mice supplemented with Fuji FF compared to those supplemented with cellulose. Fuji FF also resulted in abundance of the family Bacteroidales S24-7 and reduction of Desulfovibrionaceae in the feces. Conclusion Long term consumption of Fuji FF improved the gut environment in mice by altering the composition of the microbiota and increasing SCFA production, which might be associated with its anti-obesity effects.

Vaccenic acid (VA), the predominant ruminant-derived trans fat in the food chain, ameliorates hyperlipidemia, yet mechanisms remain elusive. We investigated whether VA could influence tissue endocannabinoids (ECs) by altering the availability of their biosynthetic precursor, arachidonic acid (AA), in membrane phospholipids (PLs). JCR:LA-cp rats were assigned to a control diet with or without VA (1% w/w), cis-9, trans-11 conjugated linoleic acid (CLA) (1% w/w) or VA+CLA (1% + 0.5% w/w) for 8 weeks. VA reduced the EC, 2-arachidonoylglycerol (2-AG), in the liver and visceral adipose tissue (VAT) relative to control diet (P < 0.001), but did not change AA in tissue PLs. There was no additive effect of combining VA+CLA on 2-AG relative to VA alone (P > 0.05). Interestingly, VA increased jejunal concentrations of anandamide and those of the noncannabinoid signaling molecules, oleoylethanolamide and palmitoylethanolamide, relative to control diet (P < 0.05). This was consistent with a lower jejunal protein abundance (but not activity) of their degrading enzyme, fatty acid amide hydrolase, as well as the mRNA expression of TNFα and interleukin 1β (P < 0.05). The ability of VA to reduce 2-AG in the liver and VAT provides a potential mechanistic explanation to alleviate ectopic lipid accumulation. The opposing regulation of ECs and other noncannabinoid lipid signaling molecules by VA suggests an activation of benefit via the EC system in the intestine.

The consumption of soybean protein has well-known favorable metabolic effects (e.g., reduced body weight, body fat, hyperglycemia, insulin resistance, hepatic steatosis, and lipogenesis). These effects of soy protein have been linked to modulation by the gut microbiota; however, the dynamic interplay among these factors remains unclear. Accordingly, we examined the metabolic phenotype, intestinal BA pool, and the gut microbiome of male C57BL/6 mice that were randomized to receive either a regular high-fat diet (HFD) or HFD that contained soybean protein isolate (SPI) in place of dairy protein. The intake of SPI significantly reduced the HFD-induced weight gain and adipose tissue mass accumulation and attenuated hepatic steatosis. Along with an enhancement in the secretion of intestinal Glucagon-like peptide-1 (GLP-1), an enlarged cecal BA pool with an elevated secondary/primary BA ratio was observed in the mice that consumed SPI, while fecal BA excretion remained unaltered. SPI also elicited dramatic changes in the gut microbiome, characterized by an expansion of taxa that may be involved in the biotransformation of BAs. The observed effects were abolished in germ-free (GF) mice, indicating that they were dependent on the microbiota. These findings collectively indicate that the metabolic benefits of SPI under the HFD regime may arise from a microbiota-driven increase in BA transformation and increase in GLP-1 secretion.

Isotope feeding studies report a wide range of conversion fractions of dietary shorter-chain polyunsaturated fatty acids (PUFAs) to long-chain PUFAs, which limits assessing nutritional requirements and organ effects of arachidonic (AA, 20:4n-6) and docosahexaenoic (DHA, 22:6n-3) acids. In this study, whole-body (largely liver) steady-state conversion coefficients and rates of circulating unesterified linoleic acid (LA, 18:2n-6) to esterified AA and other elongated n-6 PUFAs were quantified directly using operational equations, in unanesthetized adult rats on a high-DHA but AA-free diet, using 2 h of intravenous [U-13C]LA infusion. Unesterified LA was converted to esterified LA in plasma at a greater rate than to esterified γ-linolenic (γ-LNA, 18:3n-6), eicosatrienoic acid (ETA, 20:3n-6), or AA. The steady-state whole-body synthesis-secretion (conversion) coefficient to AA equaled 5.4 × 10−3 min−1, while the conversion rate (coefficient × concentration) equaled 16.1 μmol/day. This rate exceeds the reported brain AA consumption rate by 27-fold. As brain and heart cannot synthesize significant AA from circulating LA, liver synthesis is necessary to maintain their homeostatic AA concentrations in the absence of dietary AA. The heavy-isotope intravenous infusion method could be used to quantify steady-state liver synthesis-secretion of AA from LA under different conditions in rodents and in humans.

Dietary docosahexaenoic acid (DHA; 22:6n-3) and eicosapentaenoic acid (EPA; 20:5n-3) are considered important for maintaining normal heart and brain function, but little EPA is found in brain, and EPA cannot be elongated to DHA in rat heart due to the absence of elongase-2. Ingested EPA may have to be converted in the liver to DHA for it to be fully effective in brain and heart, but the rate of conversion is not agreed on. This rate was determined in male adult rats fed a standard n-3 PUFA, containing diet by infusing unesterified albumin-bound [U-13C]EPA intravenously for 2 h and measuring esterified [13C]labeled PUFAs in arterial plasma lipoproteins, as well as the specific activity of unesterified plasma EPA. Whole-body (presumably hepatic) synthesis secretion rates from circulating unesterified EPA, calculated from peak first derivatives of plasma esterified concentration × volume curves, equaled 2.61 μmol/day for docosapentaenoic acid (22:5n-3) and 5.46 μmol/day for DHA. The DHA synthesis rate was 24-fold greater than the reported brain DHA consumption rate in rats. Thus, dietary EPA could help to maintain brain and heart DHA homeostasis because it is converted at a relatively high rate in the liver to circulating DHA.

Docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), long-chain n-3 PUFAs important for brain and heart function, can be obtained from dietary fish products or by liver synthesis from α-linolenic acid (α-LNA). Their daily human dietary requirements are not clear, and their liver synthesis rates in humans and nonhumans are unknown. We estimated whole-body (presumably liver) synthesis rates in unanesthetized rats by infusing [U-13C]α-LNA intravenously for 2 h and measuring labeled and unlabeled n-3 PUFA in arterial plasma using negative chemical ionization GC-MS. Newly synthesized esterified [13C]DHA, [13C]EPA, and [13C]docosapentaenoic acid (DPA) appeared in arterial plasma after 60 min of infusion, then their concentrations rose in an S-shaped manner. Esterified concentration × plasma volume data were fit with a sigmoidal equation, whose peak first derivatives provided synthesis rates of unlabeled EPA, DPA, and DHA equal to 8.40, 6.27, and 9.84 μmol/day, respectively. The DHA synthesis rate exceeded the published daily rat brain DHA consumption rate by 30-fold, suggesting that liver synthesis from α-LNA could maintain brain DHA homeostasis were DHA absent from the diet. This stable isotope infusion method could be used to quantify whole-body DHA synthesis rates in human subjects.

The extent to which the heart can convert α-linolenic acid (α-LNA, 18:3n-3) to longer chain n-3 PUFAs is not known. Conversion rates can be measured in vivo using radiolabeled α-LNA and a kinetic fatty acid model. [1-14C]α-LNA was infused intravenously for 5 min in unanesthetized rats that had been fed an n-3 PUFA-adequate [4.6% α-LNA, no docosahexaenoic acid (DHA, 22:6n-3)] or n-3 PUFA-deficient diet (0.2% α-LNA, nor DHA) for 15 weeks after weaning. Arterial plasma was sampled, as was the heart after high-energy microwaving. Rates of conversion of α-LNA to longer chain n-3 PUFAs were low, and DHA was not synthesized at all in the heart. Most α-LNA within the heart had been β-oxidized. In deprived compared with adequate rats, DHA concentrations in plasma and heart were both reduced by >90%, whereas heart and plasma levels of docosapentaenoic acid (DPAn-6, 22:5n-6) were elevated. Dietary deprivation did not affect cardiac mRNA levels of elongase-5 or desaturases Δ6 and Δ5, but elongase-2 mRNA could not be detected. In summary, the rat heart does not synthesize DHA from α-LNA, owing to the absence of elongase-2, but must obtain its DHA entirely from plasma. Dietary n-3 PUFA deprivation markedly reduces heart DHA and increases heart DPAn-6, which may make the heart vulnerable to different insults.

Polyunsaturated fatty acyl (PUFA) chains in both the ω3 and ω6 series are essential for normal animal brain development, and cannot be interconverted to compensate for a dietary deficiency of one or the other. Paradoxically, a dietary ω3-PUFA deficiency leads to the accumulation of docosapentaenoate (DPA, 22:5ω6), an ω6-PUFA chain that is normally scarce in the brain. We applied a high-precision LC/MS method to characterize the distribution of DPA chains across phospholipid headgroup classes, the fatty acyl chains with which they were paired, and the extent to which they were oxidatively damaged in the cortical brain of rats on an ω3-deficient diet. Results indicate that dietary ω3-PUFA deficiency markedly increased the concentrations of phospholipids with DPA chains across all headgroup subclasses, including plasmalogen species. The concentrations of phospholipids containing docosahexaenoate chains (22:6ω3) decreased 20-25%, while the concentrations of phospholipids containing arachidonate chains (20:4ω6) did not change significantly. Although DPA chains are more saturated than DHA chains, a larger fraction of DPA chains were monohydroxylated, particularly among diacyl-phosphatidylethanolamines and plasmalogen phosphatidylethanolamines, suggesting that they were disproportionately subjected to oxidative stress. Differences in the pathological significance of ω3 and ω6 oxidation products suggest that greater oxidative damage among the ω6 PUFAs that increase in response to dietary ω3 deficiency may have pathological significance in Alzheimer's disease.

Fifteen weeks of dietary n-3 PUFA deprivation increases coefficients of conversion of circulating α-linolenic acid (α-LNA; 18:3n-3) to docosahexaenoic acid (DHA; 22:6n-3) in rat liver but not brain. To determine whether these increases reflect organ differences in enzymatic activities, we examined brain and liver expression of converting enzymes and of two of their transcription factors, peroxisome proliferator-activated receptor α (PPARα) and sterol-regulatory element binding protein-1 (SREBP-1), in rats fed an n-3 PUFA “adequate” (4.6% α-LNA of total fatty acid, no DHA) or “deficient” (0.2% α-LNA, no DHA) diet for 15 weeks after weaning. In rats fed the deficient compared with the adequate diet, mRNA and activity levels of Δ5 and Δ6 desaturases and elongases 2 and 5 were upregulated in liver but not brain, but liver PPARα and SREBP-1 mRNA levels were unchanged. In rats fed the adequate diet, enzyme activities generally were higher in liver than brain. Thus, differences in conversion enzyme expression explain why the liver has a greater capacity to synthesize DHA from circulating α-LNA than does the brain in animals on an adequate n-3 PUFA diet and why liver synthesis capacity is increased by dietary deprivation. These data suggest that liver n-3 PUFA metabolism determines DHA availability to the brain when DHA is absent from the diet.

We quantified incorporation rates of plasma-derived α-linolenic acid (α-LNA, 18:3n-3) into “stable” liver lipids and the conversion rate of α-LNA to docosahexaenoic acid (DHA, 22:6n-3) in male rats fed, after weaning, an n-3 PUFA-adequate diet (4.6% α-LNA, no DHA) or an n-3 PUFA-deficient diet (0.2% α-LNA, no DHA) for 15 weeks. Unanesthetized rats were infused intravenously with [1-14C]α-LNA, and arterial plasma was sampled until the liver was microwaved at 5 min. Unlabeled α-LNA and DHA concentrations in arterial plasma and liver were reduced >90% by deprivation, whereas unlabeled arachidonic acid (20:4n-6) and docosapentaenoic acid (22:5n-6) concentrations were increased. Deprivation did not change α-LNA incorporation coefficients into stable liver lipids but increased synthesis-incorporation coefficients of DHA from α-LNA by 6.6-, 8.4-, and 2.3-fold in triacylglycerol, phospholipid, and cholesteryl ester, repectively. Assuming that synthesized-incorporated DHA even tually would be secreted within lipoproteins, calculated liver DHA secretion rates equaled 2.19 and 0.82 μmol/day in the n-3 PUFA-adequate and -deprived rats, respectively. These rates exceed the published rates of brain DHA consumption by 6- and 10-fold, respectively, and should be sufficient to maintain normal and reduced brain DHA concentrations, respectively, in the two dietary conditions.

We quantified the rates of incorporation of α-linolenic acid (α-LNA; 18:3n-3) into “stable” lipids (triacylglycerol, phospholipid, cholesteryl ester) and the rate of conversion of α-LNA to docosahexaenoic acid (DHA; 22: 6n-3) in the liver of awake male rats on a high-DHA-containing diet after a 5-min intravenous infusion of [1-14C]α-LNA. At 5 min, 72.7% of liver radioactivity (excluding unesterified fatty acid radioactivity) was in stable lipids, with the remainder in the aqueous compartment. Using our measured specific activity of liver α-LNA-CoA, in the form of the dilution coefficient λα-LNA-CoA, we calculated incorporation rates of unesterified α-LNA into liver triacylglycerol,phospholipid, and cholesteryl ester as 2,401, 749, and 9.6 nmol/s/g × 10−4, respectively, corresponding to turnover rates of 3.2, 8.7, and 2.9%/min and half-lives of 8–24 min. A lower limit for the DHA synthesis rate from α-LNA equaled 15.8 nmol/s/g × 10−4 (0.5% of the net in corporation rate). Thus, in rats on a high-DHA-containing diet, rates of β-oxidation and esterification of α-LNA into stable liver lipids are high, whereas its conversion to DHA is comparatively low and insufficient to supply significant DHA to the brain. High incorporation and turnover rates likely reflect a high secretion rate by liver of stable lipids within very low density lipoproteins.

Male rat pups at weaning (21 days of age) were subjected to a diet deficient or adequate in n-3 polyunsaturated fatty acids (n-3 PUFAs) for 15 weeks. Performance on tests of locomotor activity, depression, and aggression was measured in that order during the ensuing 3 weeks, after which brain lipid composition was determined. In the n-3 PUFA-deprived rats, compared with n-3 PUFA-adequate rats, docosahexaenoic acid (22:6n-3) in brain phospholipid was reduced by 36% and docosapentaenoic acid (22:5n-6) was elevated by 90%, whereas brain phospholipid concentrations were unchanged. N-3 PUFA-deprived rats had a significantly increased (P = 0.03) score on the Porsolt forced-swim test for depression, and increased blocking time (P = 0.03) and blocking number (P = 0.04) scores (uncorrected for multiple comparisons) on the isolation-induced resident-intruder test for aggression. Large effect sizes (d > 0.8) were found on the depression score and on the blocking time score of the aggression test. Scores on the open-field test for locomotor activity did not differ significantly between groups, and had only small to medium effect sizes. This single-generational n-3 PUFA-deprived rat model, which demonstrated significant changes in brain lipid composition and in test scores for depression and aggression, may be useful for elucidating the contribution of disturbed brain PUFA metabolism to human depression, aggression, and bipolar disorder.

Dietary long-chain n-3 polyunsaturated fatty acid (PUFA) supplementation may be beneficial for chronic brain illnesses, but the issue is not agreed on. We examined effects of dietary n-3 PUFA deprivation or supplementation, compared with an n-3 PUFA adequate diet (containing alpha-linolenic acid [18:3 n-3] but not docosahexaenoic acid [DHA, 22:6n-3]), on brain markers of lipid metabolism and excitotoxicity, in rats treated chronically with NMDA or saline.Male rats after weaning were maintained on one of three diets for 15 weeks. After 12 weeks, each diet group was injected i.p. daily with saline (1 ml/kg) or a subconvulsive dose of NMDA (25 mg/kg) for 3 additional weeks. Then, brain fatty acid concentrations and various markers of excitotoxicity and fatty acid metabolism were measured.Compared to the diet-adequate group, brain DHA concentration was reduced, while n-6 docosapentaenoic acid (DPA, 22:5n-6) concentration was increased in the n-3 deficient group; arachidonic acid (AA, 20:4n-6) concentration was unchanged. These concentrations were unaffected by fish oil supplementation. Chronic NMDA increased brain cPLA2 activity in each of the three groups, but n-3 PUFA deprivation or fish oil did not change cPLA2 activity or protein compared with the adequate group. sPLA2 expression was unchanged in the three conditions, whereas iPLA2 expression was reduced by deprivation but not changed by supplementation. BDNF protein was reduced by NMDA in N-3 PUFA deficient rats, but protein levels of IL-1β, NGF, and GFAP did not differ between groups.N-3 PUFA deprivation significantly worsened several pathological NMDA-induced changes produced in diet adequate rats, whereas n-3 PUFA supplementation did not affect NMDA induced changes. Supplementation may not be critical for this measured neuropathology once the diet has an adequate n-3 PUFA content.