Vitamin B6 Deficiency Induces Autism-Like Behaviors in Rats by Regulating mTOR-Mediated Autophagy in the Hippocampus.

Vitamin B6 (VB6) exhibits therapeutic effects towards autism spectrum disorder (ASD), but its specific mechanism is poorly understood. Rat dams were treated with VB6 standard, VB6 deficiency, or VB6 supplementary diet, and the same treatment was provided to their offspring, with their body weights monitored. Three-chambered social test and open field test were employed to evaluate the effect of VB6 on autism-like behaviors. Gamma-aminobutyric acid (GABA) generation and synaptic inhibition of neurons in the hippocampus of rat were detected via immunofluorescence staining, followed by the measurement of GABA concentration through high-performance liquid chromatography (HPLC). The role of VB6 in the autophagy and apoptosis of cells was determined via Western blot and terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL). In order to conduct rescue experiments, the inhibition of mammalian target of rapamycin (mTOR) or the activation of GABA was achieved by drug administration to the offspring rats with VB6 deficiency. As a result, no evident difference in weight was observed in the offspring with varied VB6 treatments. VB6 deficiency impaired social interaction; aggravated self-grooming and bowel frequency; decreased GABA concentration, VIAAT, GAD67, vGAT expressions, and LC3 II/LC3 I ratio; increased p62 level and p-mTOR/mTOR ratio; and promoted cell apoptosis. Inhibition of mTOR reversed the effect of VB6 deficiency on cell autophagy. GABA activation or mTOR inhibition offset the role of VB6 deficiency in autism-like behaviors and hippocampal GABA expression. Collectively, VB6 deficiency induces autism-like behaviors in rats by regulating mTOR-mediated autophagy in the hippocampus.

Satellite Cells Exhibit Decreased Numbers and Impaired Functions on Single Myofibers Isolated from Vitamin B6-Deficient Mice.

Emerging research in human studies suggests an association among vitamin B6, sarcopenia, and muscle strength. However, very little is known regarding its potential role at the cellular level, especially in muscle satellite cells. Therefore, to determine whether vitamin B6 affects the satellite cells, we isolated single myofibers from muscles of vitamin B6-deficient and vitamin B6-supplemented mice. Subsequently, we subjected them to single myofiber culture and observed the number and function of the satellite cells, which remained in their niche on the myofibers. Prior to culture, the vitamin B6-deficient myofibers exhibited a significantly lower number of quiescent satellite cells, as compared to that in the vitamin B6-supplemented myofibers, thereby suggesting that vitamin B6 deficiency induces a decline in the quiescent satellite cell pool in mouse muscles. After 48 and 72 h of culture, the number of proliferating satellite cells per cluster was similar between the vitamin B6-deficient and -supplemented myofibers, but their numbers decreased significantly after culturing the myofibers in vitamin B6-free medium. After 72 h of culture, the number of self-renewing satellite cells per cluster was significantly lower in the vitamin B6-deficient myofibers, and the vitamin B6-free medium further decreased this number. In conclusion, vitamin B6 deficiency appears to reduce the number of quiescent satellite cells and suppress the proliferation and self-renewal of satellite cells during myogenesis.

Novel metabolic disturbances in marginal vitamin B6-deficient rat heart.

Vitamin B6 deficiency is associated with cardiovascular disease (CVD). Although plasma biomarkers have been proposed, no studies have yet directly profiled heart tissue, and the mechanisms have to be fully defined. Thus, in order to provide better insight into vitamin B6-deficient effects on cardiac functions, we sought to identify the metabolic profile in heart tissue consequent to change in dietary vitamin B6 levels by applying metabolomics. Heart tissues of rats fed a basal diet containing a marginal vitamin B6-deficient, vitamin B6-recommended or vitamin B6-supplemented level were analyzed by metabolomics analysis. Among over 500 detected metabolites, imidazole metabolites including carnosine, anserine, homocarnosine and histamine exhibited the highest decrease upon vitamin B6 deficiency (>-45%, P<.01), along with their precursors ß-alanine, γ-aminobutyric acid (GABA) and 1-methylhistidine. Ornithine was the only metabolite exhibiting an increased level in the vitamin B6-deficient group. Vitamin B6 deficiency significantly attenuated the activity of heart tissue glutamate decarboxylase (GAD), although there was undetectable activity of aspartate decarboxylase (ADC), suggesting that the involvement of vitamin B6 in imidazole metabolite synthesis occurs partly through GABA production by regulating GAD rather than through a straightforward ß-alanine production pathway via ADC in the heart. Notably, vitamin B6 deficiency significantly attenuated citric acid cycle metabolite levels, suggesting cardiac energy metabolism impairment. This study provides a new link between vitamin B6 and cardiac functions, in which marginal vitamin B6 deficiency impairs imidazole and energy metabolism in heart. This newly revealed cardiac metabolic profile may reveal novel molecular targets or foodstuffs for CVD prevention.

Vitamin B6 is essential for serine de novo biosynthesis.

Pyridoxal 5'-phosphate (PLP), the metabolically active form of vitamin B6, plays an essential role in brain metabolism as a cofactor in numerous enzyme reactions. PLP deficiency in brain, either genetic or acquired, results in severe drug-resistant seizures that respond to vitamin B6 supplementation. The pathogenesis of vitamin B6 deficiency is largely unknown. To shed more light on the metabolic consequences of vitamin B6 deficiency in brain, we performed untargeted metabolomics in vitamin B6-deprived Neuro-2a cells. Significant alterations were observed in a range of metabolites. The most surprising observation was a decrease of serine and glycine, two amino acids that are known to be elevated in the plasma of vitamin B6 deficient patients. To investigate the cause of the low concentrations of serine and glycine, a metabolic flux analysis on serine biosynthesis was performed. The metabolic flux results showed that the de novo synthesis of serine was significantly reduced in vitamin B6-deprived cells. In addition, formation of glycine and 5-methyltetrahydrofolate was decreased. Thus, vitamin B6 is essential for serine de novo biosynthesis in neuronal cells, and serine de novo synthesis is critical to maintain intracellular serine and glycine. These findings suggest that serine and glycine concentrations in brain may be deficient in patients with vitamin B6 responsive epilepsy. The low intracellular 5-mTHF concentrations observed in vitro may explain the favourable but so far unexplained response of some patients with pyridoxine-dependent epilepsy to folinic acid supplementation.

Effects of Vitamin B6 Deficiency on the Composition and Functional Potential of T Cell Populations.

The immune system is critical in preventing infection and cancer, and malnutrition can weaken different aspects of the immune system to undermine immunity. Previous studies suggested that vitamin B6 deficiency could decrease serum antibody production with concomitant increase in IL4 expression. However, evidence on whether vitamin B6 deficiency would impair immune cell differentiation, cytokines secretion, and signal molecule expression involved in JAK/STAT signaling pathway to regulate immune response remains largely unknown. The aim of this study is to investigate the effects of vitamin B6 deficiency on the immune system through analysis of T lymphocyte differentiation, IL-2, IL-4, and INF-γ secretion, and SOCS-1 and T-bet gene transcription. We generated a vitamin B6-deficient mouse model via vitamin B6-depletion diet. The results showed that vitamin B6 deficiency retards growth, inhibits lymphocyte proliferation, and interferes with its differentiation. After ConA stimulation, vitamin B6 deficiency led to decrease in IL-2 and increase in IL-4 but had no influence on IFN-γ. Real-time PCR analysis showed that vitamin B6 deficiency downregulated T-bet and upregulated SOCS-1 transcription. This study suggested that vitamin B6 deficiency influenced the immunity in organisms. Meanwhile, the appropriate supplement of vitamin B6 could benefit immunity of the organism.

Choline and betaine ameliorate liver lipid accumulation induced by vitamin B6 deficiency in rats.

We investigated the efficacy of supplementing the diet with choline or betaine in ameliorating lipid accumulation induced by vitamin B6 (B6) deficiency in rat liver. Male Wistar rats were fed a control, B6-deficient, choline-supplemented (2, 4, or 6 g choline bitartrate/kg diet) B6-deficient diet or betaine-supplemented (1, 2, or 4 g betaine anhydrous/kg diet) B6-deficient diet for 35 d; all diets contained 9 g L-methionine (Met)/kg diet. Choline or betaine supplementation attenuated liver lipid deposition and restored plasma lipid profiles to control levels. These treatments restored the disruptions in Met metabolism and the phosphatidylcholine (PC)/phosphatidylethanolamine (PE) ratio induced by B6 deficiency in liver microsomes. These results suggest that choline and betaine ameliorated liver lipid accumulation induced by B6 deficiency via recovery of Met metabolism and very low-density lipoprotein secretion by restoring the supply of PC derived from PE.

Plasma homocysteine and liver tissue S-adenosylmethionine, S-adenosylhomocysteine status in vitamin B6-deficient rats.

OBJECTIVE: The aim of this study was to evaluate plasma homocysteine (Hcy), malondialdehyde (MDA), glutathione (GSH) levels, glutathione peroxidase (GSH-Px) and glutathione-S-transferase (GST) activities and liver tissue S-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH) levels in control and vitamin B6-deficient rats. MATERIALS AND METHODS: Thirty-two male rats with a weight of 65-75 g were used for the experiment. The rats were divided into control (n=16) and vitamin B6-deficient groups. At the end of the experiment, the animals were anesthetized with ketamine-HCl (Ketalar, 20 mg/kg, i.p.), and the blood was collected by cardiac puncture after thoracotomy. Plasma Hcy, pyridoxal phosphate (PLP), liver SAM, SAH levels measured by an isocratic system with high performance liquid chromatography. Plasma GSH-Px, GSH activities and GSH, MDA levels were carried out using a spectrophotometer. RESULTS: Plasma Hcy, MDA, liver tissue SAH levels were significantly increased, whereas plasma GSH, PLP, liver tissue SAM levels, plasma GST, GSH-Px activities and SAM/SAH ratio were decreased compared to those of control group. CONCLUSIONS: Vitamin B6 deficiency causes an increase in plasma homocysteine levels. Thus, we think that vitamin B6 supplementation could be used for therapeutic purposes in hyperhomocysteinemia condition.

High incidence of lipid deposition in the liver of rats fed a diet supplemented with branched-chain amino acids under vitamin B6 deficiency.

Male Wistar rats were fed four diets composed of purified 20% vitamin-free casein diet with (+) or without (-) vitamin B(6) (7.0 mg of pyridoxine HCl/kg of diet) and with (+) or without (-) branched-chain amino acids (BCAAs) of valine, leucine, and isoleucine (4.75%): B(6)(+)BCAA(-); B(6)(+)BCAA(+); B(6)(-)BCAA(-); and B(6)(-)BCAA(+) for 21 d. Among rats fed the B(6)(-)BCAA(+) diet, about a half showed lipid deposition in the liver. On the other hand, serum triacylglycerol levels in the B(6)(-)BCAA(+) group tended to be decreased. Hepatic triacylglycerol and cholesterol levels tended to increase in the B(6)(-)BCAA(+) group compared with the other three groups. Serum apolipoprotein B and apolipoprotein E (apo E) levels in the B(6)(-)BCAA(+) group were the lowest among the three groups. In contrast, hepatic apo E levels in the B(6)(-)BCAA(+) group were the highest among the three groups. High-performance liquid chromatography of pooled serum of rats with lipid deposits revealed that triacylglycerol and cholesterol levels in very low-density lipoprotein (VLDL) were decreased compared with other diet groups. These results strongly suggest that one of the mechanisms of lipid deposition in rats fed a B(6)(-)BCAA(+) diet is due to impaired secretion of VLDL.

Involvement of 5-methyltetrahydrofolate in the amelioration of hyperhomocysteinemia caused by vitamin B(6) deficiency and L-methionine supplementation.

We attempted to clarify the reason why folate fortification ameliorates hyperhomocysteinemia induced by vitamin B(6) deficiency. Hyperhomocysteinemia caused by vitamin B(6) deficiency significantly decreased the rat liver 5-methyltetrahydrofolate level which was significantly improved by folate fortification. This result suggests that the amelioration of hyperhomocysteinemia in response to folate supplementation had enhanced the removal of homocysteine via methionine synthase.

Vitamin B-6 restriction impairs fatty acid synthesis in cultured human hepatoma (HepG2) cells.

Vitamin B-6 deficiency has been reported to alter n-6 and n-3 fatty acid profiles in plasma and tissue lipids; however, the mechanisms underlying such metabolic changes remain unclear. The objective of this study was to determine the effects of vitamin B-6 restriction on fatty acid profiles and fatty acid synthesis in HepG2 cells. Cells were cultured for 6 wk in media with four different vitamin B-6 concentrations (10, 20, 50, and 2,000 nM added pyridoxal, representing deficient, marginal, adequate, and supraphysiological conditions) that induced a range of steady-state cellular concentrations of pyridoxal phosphate. Total cellular lipid content was greatest in the deficient (10 nM pyridoxal) medium. The percentage of arachidonic acid and the ratio of arachidonic acid to linoleic acid in the total lipid fraction were ~15% lower in vitamin B-6-restricted cells, which suggests that vitamin B-6 restriction affects n-6 fatty acid interconversions. Metabolic flux studies indicated significantly lower fractional synthesis rate of oleic acid and arachidonic acid at 10, 20, and 50 nM pyridoxal, whereas that of eicosapentaenoic acid was lower in the cells cultured in 10 nM pyridoxal. Additionally, relative mRNA expressions of Δ5 and Δ6 desaturases were 40-50% lower in vitamin B-6-restricted cells. Overall, these findings suggest that vitamin B-6 restriction alters unsaturated fatty acid synthesis, particularly n-6 and n-3 polyunsaturated fatty acid synthesis. These results and observations of changes in human plasma fatty acid profiles caused by vitamin B-6 restriction suggest a mechanism by which vitamin B-6 inadequacy influences the cardiovascular risk.

Supplementing vitamin B6 to a low vitamin B6 diet exaggerates UVB-induced skin tumorigenesis in DMBA-treated hairless mice.

7,12-Dimethylbenz[a]anthracene (DMBA)-treated hairless mice exposed to UVB radiation were used to examine the effect of graded levels of vitamin B(6) [1, 7 or 35 mg pyridoxine (PN) HCl/kg] on skin tumorigenesis for 18 wk. Compared to the 1 mg PN HCl/kg diet, the 35 mg PN HCl/kg diet significantly elevated the incidence and multiplicity of skin tumors, while there was no difference in skin tumorigenesis between the 7 and 35 mg PN HCl/kg diets. Skin levels of oxidative stress markers (lipid peroxides and protein carbonyls) were unaffected by dietary treatment. Compared to the 1 mg PN HCl/kg diet, the 7 and 35 mg PN HCl/kg diets significantly elevated serum pyridoxal 5'-phosphate (PLP) without affecting the skin level of PLP. The results suggest that dietary supplemental vitamin B(6) exaggerates UVB-induced skin tumorigenesis in hairless mice without affecting oxidative stress in the skin.

Vitamin B-6 deficiency suppresses the hepatic transsulfuration pathway but increases glutathione concentration in rats fed AIN-76A or AIN-93G diets.

The transsulfuration pathway, which aids in regulating homocysteine concentration and mediates cysteine synthesis, may be sensitive to vitamin B-6 status because cystathionine beta-synthase (CBS) and cystathionine gamma-lyase (CGL) require pyridoxal 5'-phosphate (PLP). To assess relations between vitamin B-6 and transsulfuration, we evaluated the effects of dietary pyridoxine (PN) on the hepatic concentration of relevant metabolites and in vitro activity of CBS and CGL. Growing rats were fed AIN-93G- or AIN-76A-based diets that ranged from adequate to deficient in vitamin B-6 (2, 1, 0.5, 0.1, or 0 mg of PN/kg diet, n = 5). This design allowed assessment of the effects of supplemental methionine (AIN-76A) vs. cysteine (AIN-93G) in common research diets over a range of vitamin B-6 levels. CBS activity, assayed in the presence or absence of added S-adenosylmethionine, was independent of diet type and PN level. CGL activity was independent of diet type but proportional to dietary PN. Rats fed deficient (0 and 0.1 mg PN/kg) diets exhibited only approximately 30% of the CGL activity of those fed the 2 mg PN/kg diets. Hepatic cystathionine increased from 20 to 30 nmol/g for the 1-2 mg PN/kg diets to approximately 85 nmol/g for the 0 mg PN/kg diet; however, cysteine was reduced only in B-6-deficient rats consuming the AIN-93G diet (means of 30-40 nmol/g for adequate to 11.6 nmol/g for 0 mg PN/kg AIN-76A diet). In spite of these effects, hepatic glutathione concentration increased in vitamin B-6 deficiency. These results suggest that vitamin B-6-dependent changes in transsulfuration do not limit hepatic glutathione production.

Antioxidant activity of vitamin B6 delays homocysteine-induced atherosclerosis in rats.

Elevated plasma homocysteine is a risk factor for atherosclerotic disease. In the present study, we have examined whether the oxidative stress due to a low level of vitamin B6 accelerates the development of homocysteine-induced atherosclerosis in rats. First, the effect of homocysteine thiolactone intake (50 mg/kg per d) on vascular integrity, lipid peroxide concentration, endothelial NO synthase (eNOS) expression and biochemical profiles was examined at day 1, day 21 and day 42 (five rats per group). The histochemical staining of the rat aorta showed no change at day 1 and day 21, but the subendothelial space was observed to be enlarged in rat aorta at day 42 with exposure to homocysteine thiolactone. Expression of eNOS was observed in rat aorta at day 42, but not at day 1 and day 21. Serum lipid peroxide concentration and biochemical profiles including glucose cholesterol and triacylglycerol showed no change at any day. Second, the effect of homocysteine thiolactone intake in the presence and absence of vitamin B6 on vascular integrity was examined at day 1 and day 14 (five rats per group). Aortic lesions were observed in vitamin B6-deficient rat aorta at day 14 but not in vitamin B6-supplemented rats. The expression of eNOS was also observed in vitamin B6-deficient rat aorta at day 14. Serum lipid concentrations of the vitamin B6-deficient group significantly increased compared with concentrations of the vitamin B6-supplemented group, though serum concentration of homocysteine did not change between both groups. These results suggest that the oxidative stress caused by a low level of vitamin B6 accelerates the development of homocysteine-induced atherosclerosis in rats.

B6-responsive disorders: a model of vitamin dependency.

Pyridoxal phosphate is the cofactor for over 100 enzyme-catalysed reactions in the body, including many involved in the synthesis or catabolism of neurotransmitters. Inadequate levels of pyridoxal phosphate in the brain cause neurological dysfunction, particularly epilepsy. There are several different mechanisms that lead to an increased requirement for pyridoxine and/or pyridoxal phosphate. These include: (i) inborn errors affecting the pathways of B(6) vitamer metabolism; (ii) inborn errors that lead to accumulation of small molecules that react with pyridoxal phosphate and inactivate it; (iii) drugs that react with pyridoxal phosphate; (iv) coeliac disease, which is thought to lead to malabsorption of B(6) vitamers; (v) renal dialysis, which leads to increased losses of B(6) vitamers from the circulation; (vi) drugs that affect the metabolism of B(6) vitamers; and (vii) inborn errors affecting specific pyridoxal phosphate-dependent enzymes. The last show a very variable degree of pyridoxine responsiveness, from 90% in X-linked sideroblastic anaemia (delta-aminolevulinate synthase deficiency) through 50% in homocystinuria (cystathionine beta-synthase deficiency) to 5% in ornithinaemia with gyrate atrophy (ornithine delta-aminotransferase deficiency). The possible role of pyridoxal phosphate as a chaperone during folding of nascent enzymes is discussed. High-dose pyridoxine or pyridoxal phosphate may have deleterious side-effects (particularly peripheral neuropathy with pyridoxine) and this must be considered in treatment regimes. None the less, in some patients, particularly infants with intractable epilepsy, treatment with pyridoxine or pyridoxal phosphate can be life-saving, and in other infants with inborn errors of metabolism B(6) treatment can be extremely beneficial.

Vitamin B6 deficiency and dietary fats: effects on lipid composition and glutathione peroxidase activity in rat liver.

Dietary selenium, vitamin B6 and fatty acids modulate both tissue acyl composition by regulating polyunsaturated fatty acid metabolism and antioxidant defences by influencing glutathione peroxidase activity. Alteration in the intake of one of them could therefore lead to different results depending on the intake of the others. To clarify this complex relationship, in the present study we have evaluated the modifications occurring in fatty acid composition and glutathione peroxidase activity in total liver and liver microsomes of rats fed diets containing the same amount of selenium, but different vitamin B6 content and fatty acid composition. Our data indicate that both acyl composition and glutathione peroxidase activity are greatly influenced not only by vitamin B6 deficiency, but also by the diet unsaturation degree. This study underlines that not only selenium availability but also other nutrients can modulate glutathione peroxidase activity.

Inflammation causes tissue-specific depletion of vitamin B6.

Previously we observed strong and consistent associations between vitamin B6 status and several indicators of inflammation in patients with rheumatoid arthritis. Clinical indicators, including the disability score, the length of morning stiffness, and the degree of pain, and biochemical markers, including the erythrocyte sedimentation rate and C-reactive protein levels, were found to be inversely correlated with circulating vitamin B6 levels. Such strong associations imply that impaired vitamin B6 status in these patients results from inflammation. In the present study we examined whether inflammation directly alters vitamin B6 tissue contents and its excretion in vivo. A cross-sectional case-controlled human clinical trial was performed in parallel with experiments in an animal model of inflammation. Plasma and erythrocyte and pyridoxal 5'-phosphate concentrations, urinary 4-pyridoxic acid excretion, and the activity coefficient of erythrocyte aspartate aminotransferase were compared between patients and healthy subjects. Adjuvant arthritis was induced in rats for investigating hepatic and muscle contents as well as the urinary excretion of vitamin B6 during acute and chronic inflammation. Patients with rheumatoid arthritis had low plasma pyridoxal 5'-phosphate compared with healthy control subjects, but normal erythrocyte pyridoxal 5'-phosphate and urinary 4-pyridoxic acid excretion. Adjuvant arthritis in rats did not affect 4-pyridoxic acid excretion or muscle storage of pyridoxal 5'-phosphate, but it resulted in significantly lower pyridoxal 5'-phosphate levels in circulation and in liver during inflammation. Inflammation induced a tissue-specific depletion of vitamin B6. The low plasma pyridoxal 5'-phosphate levels seen in inflammation are unlikely to be due to insufficient intake or excessive vitamin B6 excretion. Possible causes of decreased levels of vitamin B6 are discussed.

[Effect of vitamin B6 status on selenium retention in the tissues in rats fed selenium from sodium selenate].

OBJECTIVE: To study the effect of vitamin B6 status on selenium retention in tissues. METHODS: Weaning male Wistar, 4-week-old, fed with vitamin B6-selenium-deficient basal diet for 3 weeks was randomly divided into 6 groups. There were six experimental diets, that is basal diet (vitamin B6-selenium-deficient), basal diet supplemented with vitamin B6, and supplemented with Se 0.25 mg/kg as Na2 SeO4 and vitamin B6 0, 1.0 2.5 and 5.0 mg/kg diet as pyridoxine HCl for 4 weeks, three-days metabolic test was carried out before finished the study. RESULTS: Compared with each group supplemented with vitamin B6, the vitamin B6 deficient groups had a significantly low body weight gain and diet availability, and lower selenium retention in heart, liver, and kidneys, however, the status of vitamin B6 had no significant effect on the weight and selenium retention in the testes. Vitamin B6 had no significant influence on the selenium apparent absorption and retention by the three days metabolic test. CONCLUSION: Providing adequate vitamin B6 could be benefit for improving rat growth and development and increasing selenium retention in the tissues.

Renal calcium phosphate and oxalate deposition in prolonged vitamin B6 deficiency: studies on a rat model of urolithiasis.

OBJECTIVE: To determine the effect on kidney oxalate-salt deposition of a prolonged diet which induced vitamin B6 deficiency in adult rats, as there are reports of the pathogenic involvement of vitamin B6 deficiency in the formation of renal calcium oxalate calculi. MATERIALS AND METHODS: The study comprised 24 6-month-old male albino Wistar rats; 12 were fed with a purified vitamin B6-deficient diet and the others provided with the same diet but supplemented with 6 mg/kg of vitamin B6. After 12 weeks, all rats were killed, and their kidneys fixed in formalin and routinely processed to paraffin for morphological examination; some fragments were fixed in glutaraldehyde and prepared for ultrastructural examination. From each rat consecutive sections of both kidneys were cut and stained with haematoxylin and eosin, periodic-acid Schiff, Sirius red and the Von Kossa method for calcium. Sections were examined in polarized light and by electron microscopy. RESULTS: The histopathological and ultrastructural features of the kidney of vitamin B6-deficient rats were those of tubular-interstitial nephritis, characterized by tubular atrophy, interstitial fibrosis and chronic inflammatory infiltration. Oxalate and phosphate crystals were present in the papillary and parenchymal connective tissue. Ultrastructural features confirmed severe tubular epithelial lesions and the presence of an interstitial and intraepithelial inflammatory infiltrate; there was mild interstitial fibrosis. None of these features were apparent in the kidney of control rats. CONCLUSIONS: Histopathological and ultrastructural data indicate that a prolonged vitamin B6-deficient diet may contribute to the formation and deposition of calcium phosphate and oxalate crystals, which lead to severe damage of the renal parenchyma. This phenomenon may occur not only in growing rats, which have more active protein metabolism and consequently higher vitamin B6 requirements, but also in adult rats.

Effects of vitamin B-6 on (n-3) polyunsaturated fatty acid metabolism.

To investigate interactions between vitamin B-6 and fatty acid metabolism, male Wistar rats were fed a vitamin B-6 (B-6)-deficient diet consisting of 70% vitamin-free casein and 10% perilla oil [approximately 63% alpha-linolenic acid, (n-3)] for 5 wk. The amounts of linoleic acid (n-6) and arachidonic acid (n-6) in the B-6-deficient group changed only slightly compared with those in a pair-fed control group. The amount of linoleic acid increased and arachidonic acid decreased in the plasma total lipid fraction, and the ratios of both eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in the B-6-deficient group were significantly lower than for the controls. The ratios of alpha-linolenic acid and EPA were higher, and DHA lower, in the B-6-deficient group than in the pair-fed control group in the total lipid as well as phospholipid fractions in liver microsomes. The activity of delta6-desaturase was significantly lower in the B-6-deficient group than in the pair-fed control group (approximately 64%), and acyl-CoA oxidase activity, an initial enzyme of the peroxisomal beta-oxidation pathway, was reduced by approximately 80% in the B-6-deficient group. These data suggest that B-6 deficiencies impair the metabolism of (n-3) PUFA from alpha-linolenic acid to EPA and DHA with the most pronounced reduction in the production of DHA.

The effect of a subnormal vitamin B-6 status on homocysteine metabolism.

Homocysteine, an atherogenic amino acid, is either remethylated to methionine or metabolized to cysteine by the transsulfuration pathway. The biochemical conversion of homocysteine to cysteine is dependent upon two consecutive, vitamin B-6-dependent reactions. To study the effect of a selective vitamin B-6 deficiency on transsulfuration, we performed oral methionine load tests on 22 vitamin B-6-deficient asthma patients treated with theophylline (a vitamin B-6 antagonist) and 24 age- and sex-matched controls with a normal vitamin B-6 status. Both groups had normal circulating vitamin B-12 and folate concentrations. Methionine loading resulted in significantly higher increases in circulating total homocyst(e)ine (P < 0.01) and cystathionine (P < 0.05) concentrations in vitamin B-6-deficient patients compared with controls. 6 wk of vitamin B-6 supplementation (20 mg/d) significantly (P < 0.05) reduced post-methionine load increases in circulating total homocyst(e)ine concentrations in deficient subjects, but had no significant effect on the increase in total homocyst(e)ine concentrations in controls. The increases in post-methionine load circulating cystathionine concentrations were significantly (P < 0.01) reduced in both groups after vitamin supplementation. It is concluded that a vitamin B-6 deficiency may contribute to impaired transsulfuration and an abnormal methionine load test, which is associated with premature vascular disease.