B6-deficient Rats Research Articles

Maternal-Periconceptional Vitamin B12 Deficiency in Wistar Rats Leads to Sex-Specific Programming for Cardiometabolic Disease Risk in the Next Generation

BackgroundMaternal vitamin B12 deficiency plays a vital role in fetal programming, as corroborated by previous studies on murine models and longitudinal human cohorts. ObjectivesThis study assessed the effects of diet-induced maternal vitamin B12 deficiency on F1 offspring in terms of cardiometabolic health and normalization of these effects by maternal-periconceptional vitamin B12 supplementation. MethodsA diet-induced maternal vitamin B12 deficient Wistar rat model was generated in which female rats were either fed a control AIN-76A diet (with 0.01 g/kg vitamin B12) or the same diet with vitamin B12 removed. Females from the vitamin B12-deficient group were mated with males on the control diet. A subset of vitamin B12-deficient females was repleted with vitamin B12 on day 1 of conception. The offspring in the F1 generation were assessed for changes in body composition, plasma biochemistry, and molecular changes in the liver. A multiomics approach was used to obtain a mechanistic insight into the changes in the offspring liver. ResultsWe showed that a 36% reduction in plasma vitamin B12 levels during pregnancy in F0 females can lead to continued vitamin B12 deficiency (60%–70% compared with control) in the F1 offspring and program them for cardiometabolic adversities. These adversities, such as high triglycerides and low high-density lipoprotein cholesterol, were seen only among F1 males but not females. DNA methylome analysis of the liver of F1 3-mo-old offspring highlights sexual dimorphism in the alteration of methylation status of genes critical to signaling processes. Proteomics and targeted metabolomics analysis confirm that sex-specific alterations occur through modulations in PPAR signaling and steroid hormone biosynthesis pathway. Repletion of deficient mothers with vitamin B12 at conception normalizes most of the molecular and biochemical changes. ConclusionsMaternal vitamin B12 deficiency has a programming effect on the next generation and increases the risk for cardiometabolic syndrome in a sex-specific manner. Normalization of the molecular risk markers on vitamin B12 supplementation indicates a causal role.

Improvement of vitamin B12 status with Spirulina supplementation in Wistar rats validated through functional and circulatory markers.

Spirulina evaluated as a source of vitamin B12 through the modulation of vitamin B12 deficiency mediated physiological and biochemical changes in experimental animals. The B12 deficient male weanling Wistar rats were fed with Spirulina-supplemented diet for 10weeks. An increase in urinary methylmalonic acid (22.70±4.08µmol/moles of creatinine) and plasma homocysteine (16.55±0.48µmol/L) levels in the B12 deficient group was observed, while these were equal to control in the Spirulina fed group (8.71±0.48µmol/mol of creatinine and 6.88±1.18µmol/L, respectively). The vitamin B12 levels in serum (874.27±89.69), plasma (615.53±26.5pg/ml), kidney (10.19±1.066ng/g), and liver tissues (6.37±0.62ng/g) in the Spirulina fed group were similar to control. Severe atrophic changes in the testes and altered tissue architecture in lung and spleen as seen in the B12 deficient group were normalized in the Spirulina fed group. The study validates that Spirulina can improve the vitamin B12 status. PRACTICAL APPLICATIONS: The present study showed that the supplementation of Spirulina in the diet of vitamin B12 deficient rats leads to the normalization of vitamin B12 deficiency-induced circulatory and functional biomarkers along with biochemical and histological changes. Vegetarian sources for vitamin B12 are limited and the results presented here provide scientific validation for the use of Spirulina as a potential vegetarian source of bioavailable vitamin B12 .

Accumulation of Liver Lipids Induced by Vitamin B6 Deficiency Was Effectively Ameliorated by Choline and, to a Lesser Extent, Betaine.

Despite previous studies suggesting that choline and betaine ameliorate lipid accumulation in rat livers, the relative effectiveness of the two nutrients is unclear. We examined the efficacy of dietary supplementation with choline or betaine in ameliorating lipid accumulation induced by vitamin B6 (B6) deficiency in the rat liver. Male Wistar rats were fed control, B6-deficient, choline-supplemented B6-deficient, betaine-supplemented B6-deficient, or both choline and betaine-supplemented B6-deficient diets (all containing 9 g of l-methionine (Met)/kg) for 35 d. Two experiments were performed, i.e., one using 17 mmol/kg diet choline bitartrate, betaine anhydrous, and the combination and another using 8.5 mmol/kg diet. Rats fed a B6-deficient diet developed lipid accumulation in the liver with a reduction of plasma lipids induced by the disruption of Met metabolism. However, the addition of 17 mmol/kg diet choline or betaine was sufficient to ameliorate the disruptions of lipid and Met metabolism. Additionally, 8.5 mmol/kg diet choline ameliorated liver lipid deposition, while the same amount of betaine had no significant effects on liver or plasma lipid profiles. Supplementation with choline resulted in a higher liver betaine than that found using the same amount of betaine alone, although the overall liver betaine content was reduced in B6-deficient rats. Our findings indicate that choline is more effective than betaine in ameliorating B6 deficiency-related disruptions in Met metabolism and liver lipid accumulation by increasing liver betaine levels.

Elevation of urinary methylmolonic acid induces the suppression of megalin-mediated endocytotic cycles during vitamin B12 deficiency

Megalin is a scavenger receptor that serves in the endocytosis of a highly diverse group of ligands that includes Vitamin B12. We found an accumulation of megalin closed to apical region in renal proximal tubule cells of Vitamin B12-deficient rats. Interestingly, Vitamin B12 levels also controlled resorption of renal retinol binding protein. Using L2 yolk sac cells, megalin localized to the submembrane compartment by methylmalonic acid (MMA), which accumulates during vitamin B12 deficiency. In addition, MMA inhibited megalin-mediated endocytosis via YWTD repeats motif in an ectodomain of megalin. Therefore, megalin endocytosis may be regulated by MMA.

Investigation of vitamin B₆ inadequacy, induced by exposure to the anti-B₆ factor 1-amino D-proline, on plasma lipophilic metabolites of rats: a metabolomics approach.

Vitamin B6 status in the body is affected by several factors including dietary supply of the antivitamin B6 factor, 1-amino D-proline (1ADP), which is present in flaxseed. Owing to the prevalence of moderate B6 deficiency in the general population, a co-occurrence of 1ADP may lead to a further deterioration of B6 status. To this end, we applied a nontargeted metabolomics approach to identify potential plasma lipophilic biomarkers of deleterious effect of 1ADP on moderately vitamin B6-deficient rats using a high-performance liquid chromatography/quadrupole time-of-flight mass spectrometry. Twenty-four rats were fed with a semi-purified diet containing pyridoxine·HCl (PN·HCl) either 7 mg/kg diet (optimal B6) or 0.7 mg/kg diet (moderate B6). The rats were divided into four treatments (n = 6), and one treatment in each B6 diet group was also fed ad libitum with 10 mg/kg diet of synthetic 1ADP. After 5 weeks of study, plasma was collected from the rats and lipophilic metabolites were extracted using acetonitrile as a solvent for analysis. Ten potential plasma lipophilic biomarkers were identified out of >2500 detected entities, which showed significant differences between the treatments. Plasma glycocholic acid, glycoursodeoxycholic acid, murocholic acid, N-docosahexaenoyl GABA, N-arachidonoyl GABA, lumula, nandrolone and orthothymotinic acid concentrations were significantly elevated, while plasma cystamine and 3-methyleneoxindole concentrations were significantly reduced as a result of either low B6 status or 1ADP or their interaction. Changes in these metabolites revealed a potential defect in pathways linked with the biosynthesis and metabolism of bile acid components, N-acyl amino acids, analgesic androgens, anti-inflammatory and neuroprotective molecules. We also noted that the changes in these biomarkers can be alleviated by the application of adequate vitamin B6.

Maternal micronutrient deficiency leads to alteration in the kidney proteome in rat pups

Maternal nutritional deficiency significantly perturbs the offspring's physiology predisposing them to metabolic diseases during adulthood. Vitamin B12 and folate are two such micronutrients, whose deficiency leads to elevated homocysteine levels. We earlier generated B12 and/or folate deficient rat models and using high-throughput proteomic approach, showed that maternal vitamin B12 deficiency modulates carbohydrate and lipid metabolism in the liver of pups through regulation of PPAR signaling pathway. In this study, using similar approach, we identified 26 differentially expressed proteins in the kidney of pups born to mothers fed with vitamin B12 deficient diet while only four proteins were identified in the folate deficient group. Importantly, proteins like calreticulin, cofilin 1 and nucleoside diphosphate kinase B that are involved in the functioning of the kidney were upregulated in B12 deficient group. Our results hint towards a larger effect of vitamin B12 deficiency compared to that of folate presumably due to greater elevation of homocysteine in vitamin B12 deficient group. In view of widespread vitamin B12 and folate deficiency and its association with several diseases like anemia, cardiovascular and renal diseases, our results may have large implications for kidney diseases in populations deficient in vitamin B12 especially in vegetarians and the elderly people.This article is part of a Special Issue entitled: Proteomics in India.

Effect of Vitamin B6‐antagonist from Flaxseed on Amino Acid Metabolism in Moderately Vitamin B6‐deficient Rats

Pyridoxal 5‐phosphate (PLP) plays a crucial role as a cofactor in amino acid metabolism. There is a prevalence of moderate vitamin B6 deficiency in the population that may be exacerbated through the ingestion of 1‐amino D‐proline (1ADP), a B6‐antagonist found in flaxseed. We investigated the nutritional co‐insult induced by 1ADP intake (flax‐derived vs. synthetic) and moderate B6 deficiency in a rodent model. Male weanling rats (n=8/treatment) consumed a semi‐purified diet containing either 7 (adequate) or 0.7 mg/kg diet (moderately deficient) pyridoxine(PN)•HCl, each with 0 or 10mg/kg diet of 1ADP from synthetic or flaxseed‐derived sources, for 5 weeks. Plasma B6 vitamers were significantly decreased (P蠄0.001) due to 1ADP ingestion, irrespective of source, in moderately B6‐deficient rats. Moderate B6‐deficient rats consuming 1ADP as a flaxseed extract exhibited, relative to controls, a significant increase in plasma cystathionine (P=0.007), and decreases in plasma α‐aminobutyric acid (P=0.002) and glutamic acid (P=0.01) concentrations. However, the synthetic 1ADP elicited greater perturbations in plasma amino acids, compared to the 1ADP extracted from flaxseed. Both 1ADP sources inhibited the activities of the PLP‐dependent cystathionine β‐synthase and cystathionine γ‐lyase (P<0.001). The metabolic perturbations of 1ADP exposure were not evident in rats consuming adequate B6. The current data provide evidence that an anti‐pyridoxine agent now prevalent in the human food supply may pose challenges to those individuals presenting with marginal B6 status. Supported by the Natural Sciences and Engineering Research Council of Canada (NSERC).

Oral exposure to the anti-pyridoxine compound 1-amino d-proline further perturbs homocysteine metabolism through the transsulfuration pathway in moderately vitamin B6 deficient rats

Pyridoxal 5′-phosphate (PLP; a B6 vitamer) serves as an important cofactor in a myriad of metabolic reactions, including the transsulfuration (TS) pathway, which converts homocysteine (Hcy) to cysteine. While overt vitamin B6 deficiency is rare, moderate deficiency is common and may be exacerbated by anti-pyridoxine factors in the food supply. To this end, we developed a model of moderate B6 deficiency and a study was conducted to examine the in vivo effect of 1-amino d-proline (1ADP), an anti-pyridoxine factor found in flaxseed, on indices of Hcy metabolism through the TS pathway in moderately B6 deficient rats. Male weaning rats received a semi-purified diet containing either 7mg/kg (control; CD) or 0.7mg/kg (moderately deficient; MD) diet of pyridoxine·hydrochloride (PN∙HCl), each with 1 of 4 levels of 1ADP, viz. 0, 0.1, 1 and 10mg/kg diet for 5weeks. Perturbations in vitamin B6 biomarkers were more pronounced in the MD group. Plasma PLP was significantly reduced, while plasma Hcy (8-fold) and cystathionine (11-fold) were increased in rats consuming the highest amount of 1ADP in the MD group. The activities of hepatic cystathionine β-synthase and cystathionine γ-lyase enzymes were significantly reduced in rats consuming the highest 1ADP compared to the lowest, for both levels of PN∙HCl. Dilation of hepatic central veins and sinusoids, mild steatosis and increased liver triglycerides were present in MD rats consuming the highest 1ADP level. The current data provide evidence that the consumption of an anti-pyridoxine factor linked to flaxseed may pose a risk for subjects who are moderate/severe vitamin B6 deficient.

PPAR signaling pathway is a key modulator of liver proteome in pups born to vitamin B12 deficient rats

Maternal nutritional deficiency in-utero is known to predict risk of complex disorders like cardiovascular disease, diabetes and many neurological disorders in the offspring and vitamin B12 is one such critical micronutrient. Here we performed 2D-DIGE followed by MALDI TOF/TOF analysis to identify proteins that are differentially expressed in liver of pups born to mothers fed vitamin B12 deficient diet vis-à-vis control diet. To further establish causality, we analyzed the effect of B12 rehabilitation at parturition on the protein levels and the phenotype in pups. We identified 38 differentially expressed proteins that were enriched in pathways involved in the regulation of amino acid, lipid and carbohydrate metabolism. Further, three enzymes in the β-oxidation pathway (hydroxyacyl-coenzyme A dehydrogenase, medium-chain specific acyl-CoA dehydrogenase, 3-ketoacyl-CoA thiolase) were down-regulated in pups born to mothers fed vitamin B12 deficient diet. We observed age-dependent differential expression of peroxisome proliferator activated-receptor (PPAR) α and γ in the deficient pups. Interestingly, expression of 27 proteins that were differentially expressed was restored to the control levels after rehabilitation of female rats with vitamin B12 from parturition. Our study thus provides the first evidence that maternal vitamin B12 deficiency influences lipid and other micronutrient metabolism in pups through regulation of PPAR signaling pathway. Maternal vitamin B12 deficiency has been shown to predict the onset of complex disorders like atherosclerosis, type II diabetes etc. in the next generation during their adulthood. We have shown earlier that pups born to female rats fed with vitamin B12 deficient diet were obese and developed high levels of other intermediate traits such as triglycerides, cholesterol etc. that are related to the risk of diabetes and cardiovascular disorders. In this piece of work using differential proteomic approach we have identified the altered metabolic processes in the liver of vitamin B12 deficient pups. We have also documented that the proteins involved in β-oxidation pathway are down-regulated. Further, differential expression of PPARα and PPARγ was evidently documented as the master regulator for the alteration of lipid, amino acid and carbohydrate metabolism during maternal vitamin B12 deficiency.

In vivo Effect of 1‐Amino D‐Proline, an Anti‐pyridoxine Factor, on the Metabolism of Vitamin B6‐dependent Enzymes in Moderately Vitamin B6 Deficient Rats

Pyridoxal 5′‐phosphate (PLP) serves as an important cofactor in numerous metabolic pathways, including the transsulfuration pathway which converts homocysteine (Hcy) to cysteine (Cys). While overt deficiency is rare, marginal deficiency is common, and may be exacerbated by anti‐pyridoxine factors in the food supply. To this end, a study was conducted to examine the in vivo effect of 1‐amino D‐proline (1ADP), an anti‐pyridoxine factor found in flaxseed, on indices of sulphur amino acid metabolism in moderately B6‐deficient rats. Male weaning rats (n=6/treatment) received a semi‐purified diet (AIN‐93G) containing either 7 (control; C) or 0.7 mg/Kg diet PN·HCl (moderately deficient; MD), each with one of 4 levels of 1ADP, viz. 0, 0.1,1 and 10 mg/Kg, diet for 5 weeks. For rats receiving the C diet, final body weight was not affected by 1ADP, however rats consuming the highest 1ADP levels in the MD group were significantly lighter (p<0.001). Plasma biomarkers are given in Table 1. The data provide evidence that the consumption of an anti‐pyridoxine factor linked to flaxseed does not pose challenges for subjects who are vitamin B6‐replete. However, this may not be the case for subjects with marginal B6 status, as supported by dose‐dependent reductions in plasma PLP and increases in plasma Hcy.Grant Funding Source: Natural Sciences and Engineering Research Council of Canada (NSERC).

Formate can differentiate between hyperhomocysteinemia due to impaired remethylation and impaired transsulfuration

Formate can differentiate between hyperhomocysteinemia due to impaired remethylation and impaired transsulfuration. Am J Physiol Endocrinol Metab 301: E000-E000, 2011. First published September 20, 2011; 10.1152/ajpendo.00345.2011.-We carried out a (1)H-NMR metabolomic analysis of sera from vitamin B(12)-deficient rats. In addition to the expected increases in methylmalonate and homocysteine (Hcy), we observed an approximately sevenfold increase in formate levels, from 64 μM in control rats to 402 μM in vitamin B(12)-deficient rats. Urinary formate was also elevated. This elevation of formate could be attributed to impaired one-carbon metabolism since formate is assimilated into the one-carbon pool by incorporation into 10-formyl-THF via the enzyme 10-formyl-THF synthase. Both plasma and urinary formate were also increased in folate-deficient rats. Hcy was elevated in both the vitamin B(12)- and folate-deficient rats. Although plasma Hcy was also elevated, plasma formate was unaffected in vitamin B(6)-deficient rats (impaired transsulfuration pathway). These results were in accord with a mathematical model of folate metabolism, which predicted that reduction in methionine synthase activity would cause increased formate levels, whereas reduced cystathionine β-synthase activity would not. Our data indicate that formate provides a novel window into cellular folate metabolism, that elevated formate can be a useful indicator of deranged one-carbon metabolism and can be used to discriminate between the hyperhomocysteinemia caused by defects in the remethylation and transsulfuration pathways.

Vitamin B6 suppresses serine protease inhibitor 3 expression in the colon of rats and in TNF‐α‐stimulated HT‐29 cells

Previous reports in the areas of animal studies and, recently epidemiology, have linked anti-tumorigenic and anti-inflammatory effects to dietary vitamin B6. This study investigated the molecular mechanism of these effects of vitamin B6. DNA microarray analysis was used to obtain information on changes in colon gene expression from vitamin B6 (pyridoxine) repletion in vitamin B6-deficient rats. Pyridoxine supplementation down-regulated the inflammatory molecule, serine protease inhibitor clade A member 3 (SPI-3) mRNA expression in the colon. This study also showed that tumor necrosis factor α (TNF-α) induced SPI-3 mRNA expression in HT-29 human colon cancer cells, and vitamin B6 (pyridoxal hydrochloride) pretreatment of HT-29 cells inhibited TNF -induced mRNA expression of SPI-3. Vitamin B6 inhibited TNF-α-induced NF-κB activation via suppression of IκBα degradation in HT-29 cells. HT-29 cells stably expressing epitope-tagged ubiquitin were generated and vitamin B6 pretreatment was shown to inhibit ubiquitination of the IkB protein in response to TNF-α-i. Vitamin B6 suppressed SPI-3 expression in the colon of rats and in TNF-α-stimulated HT-29 cells. Further, this study showed a possible role of vitamin B6 in the regulation of protein ubiquitination.

Antioxidative status and lipid peroxidation in kidney tissue of rats fed with vitamin B6-deficient diet

Introduction: The aim of this study was to evaluate lipid peroxidation (LP) and free radical scavenging enzyme activities in kidney tissue of vitamin B6-deficient rats. Material and Methods: The rats were divided into control and vitamin B6-deficient groups. After 4 weeks of feeding, animals in all groups were anesthetized by thiopental sodium (50 mg/kg). Thoraces were opened, 2 mL blood samples were taken from aortas, then the rats were killed by cervical dislocation, and kidney tissues were removed. Biochemical measurements in kidney tissue were carried out using a spectrophotometer. Results: Total superoxide scavenger activity (TSSA), nonenzymatic superoxide scavenger activity (NSSA), superoxide dismutase (SOD) activities, and antioxidant potential (AOP) values in the vitamin B6-deficient group were significantly lower than those of the control group, whereas glutathione peroxidase (GSH-Px), glutathione reductase (GRD), glutathione-S-transferase (GST) activities, and malondialdehyde (MDA) level were significantly higher than those of the control group (p < 0.05). Discussion: The results show that vitamin B6 deficiency causes an attenuation in antioxidant defense system and an increase in oxidative stress in kidney tissue of rats.

新しいアプローチから見た食品機能性成分の動態研究

Dietary habits are related to many problems including food, energy, environment and health. Thus, the researches in dietary habits must be conducted in the paradigm of complex system. But, it is important to accumulate the experimental observations by the reductionistic approarch. In this review, I focus on the new approach to the materials and methods. First, I examined the function of oleuropein, a major polyphenol in olive leaf using the rats fed on high cholesterol diets. As the result, the values of total bile acids and total lipids in the feces decreased significantly in the rat fed on the olive leaf powder and oleuropein. The values of total cholesterol in the feces and triglyceride in the liver decreased significantly in the group fed on the olive leaf extract. These results indicate that the oleuropein facilitates the lipid absorption and the bile acid reabsorption in the ileum. Second, in order to reveal the relationship between renal reabsorptional systems of vitamin B12 (B12) and vitamin A, I analized the effect of B12 deficient status on the localization of megalin, the receptor of both vitamins, and retinol binding protein (RBP). As the result, in B12 deficient rats, megalin was accumulated on the membrane in the proximal tubules and a few tubules containing RBP were identified, which suggested inhibition of megalin-mediated endocytosis and renal vitamin A uptake. Third, I produced D-histidine specific antibody to trace biokinetics. Histochemical approach may be a useful tool to understand the nutrition and dietary habits.

Excretion of methylmalonic acid by vitamin B 12 deficient rats kept under germfree or conventional conditions.

Excretion of Methylmalonic Acid by Vitamin B12Deficient Rats Kept under Germfree Or Conventional Conditions Get access Nutrition Reviews, Volume 30, Issue 8, August 1972, Pages 186–188, https://doi.org/10.1111/j.1753-4887.1972.tb04037.x Published: 01 August 1972

Effects of dietary supplementation of high-dose folic acid on biomarkers of methylating reaction in vitamin B12-deficient rats

Folate is generally considered as a safe water-soluble vitamin for supplementation. However, we do not have enough information to confirm the potential effects and safety of folate supplementation and the interaction with vitamin B12 deficiency. It has been hypothesized that a greater methyl group supply could lead to compensation for vitamin B12 deficiency. On this basis, the present study was conducted to examine the effects of high-dose folic acid (FA) supplementation on biomarkers involved in the methionine cycle in vitamin B12-deficient rats. Sprague-Dawley rats were fed diets containing either 0 or 100 µg (daily dietary requirement) vitamin B12/kg diet with either 2 mg (daily dietary requirement) or 100 mg FA/kg diet for six weeks. Vitamin B12-deficiency resulted in increased plasma homocysteine (p<0.01), which was normalized by dietary supplementation of high-dose FA (p<0.01). However, FA supplementation and vitamin B12 deficiency did not alter hepatic and brain S-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH) concentrations and hepatic DNA methylation. These results indicated that supplementation of high-dose FA improved homocysteinemia in vitamin B12-deficiency but did not change SAM and SAH, the main biomarkers of methylating reaction.

Endogenous oxalogenesis after acute intravenous loading with ethylene glycol or glycine in rats receiving standard and vitamin B6‐deficient diets

The effect on endogenous oxalate synthesis of acute intravenous loading with ethylene glycol or glycine was investigated in rats on a standard or a vitamin B6-deficient diet. Twenty-four male Wistar rats weighing approximately 180 g were randomly divided into ethylene glycol and glycine groups of 12 animals each. These groups were further divided into two subgroups of six animals each that were fed either a standard or a vitamin B6-deficient diet for 3 weeks. Animals of these two subgroups received an intravenous infusion of 20 mg (322.22 micromol) of ethylene glycol or 100 mg (1332.09 micromol) of glycine, respectively. Urine samples were collected just before intravenous infusion of each substance and at hourly intervals until 5 h after receiving the infusion. Urinary oxalate, glycolate, and citrate levels were measured by capillary electrophoresis. Urinary oxalate and glycolate excretion was significantly increased after ethylene glycol administration. Significant differences between the control and vitamin B6-deficient groups were found. In contrast, there were only small changes of oxalate and glycolate excretion after glycine administration. Recovery of the given dose of ethylene glycol as oxalate in 5-h urine was 0.31% and 7.15% in the control and vitamin B6-deficient groups, respectively, whereas recovery of glycolate was 0.68% and 7.22%, respectively. Ethylene glycol loading has a significant effect on urinary oxalate excretion in both normal and vitamin B6-deficient rats, whereas glycine loading only has a small effect. Oxalate and glycolate excretion after ethylene glycol loading were respectively 23-fold and 11-fold higher in vitamin B6-deficient rats than in controls.

Vitamin B12deficiency results in the abnormal regulation of serine dehydratase and tyrosine aminotransferase activities correlated with impairment of the adenylyl cyclase system in rat liver

The aim of the present study was to elucidate the mechanism of the vitamin B(12) deficiency-induced changes of the serine dehydratase (SDH) and tyrosine aminotransferase (TAT) activities in the rat liver. When rats were maintained on a vitamin B(12)-deficient diet, the activities of these two enzymes in the liver were significantly reduced compared with those in the B12-sufficient control rats (SDH 2.8 (sd 0.56) v. 17.5 (sd 6.22) nmol/mg protein per min (n 5); P < 0.05) (TAT 25.2 (sd 5.22) v. 41.3 (sd 8.11) nmol/mg protein per min (n 5); P < 0.05). In the B(12)-deficient rats, the level of SDH induction in response to the administration of glucagon and dexamethasone was significantly lower than in the B(12)-sufficient controls. Dexamethasone induced a significant increase in TAT activity in the primary culture of the hepatocytes prepared from the deficient rats, as well as in the cells from the control rats. However, a further increase in TAT activity was not observed in the hepatocytes from the deficient rats, in contrast to the cells from the controls, when glucagon was added simultaneously with dexamethasone. The glucagon-stimulated production of cAMP was significantly reduced in the hepatocytes from the deficient rats relative to the cells from the control rats. Furthermore, the glucagon-stimulated adenylyl cyclase activity in the liver was significantly lower in the deficient rats than in the controls. These results suggest that vitamin B(12) deficiency results in decreases in SDH and TAT activities correlated with the impairment of the glucagon signal transduction through the activation of the adenylyl cyclase system in the liver.

Testicular Injury to Rats Fed on Soybean Protein-Based Vitamin B12-Deficient Diet Can Be Reduced by Methionine Supplementation

We have previously reported that rats fed on a vitamin B12 (B12)-deficient diet containing 180 g soybean protein per kg diet showed marked histologic damage in their testes. In this paper, we report the effect of B12-deficiency on B12-dependent methionine synthase in the rats' testes and the effect of methionine supplementation of the diet on testicular damage. Rats were fed the soybean protein-based B12-deficient diet for 120 d. We confirmed that those rats were in serious B12-deficiency by measuring urinary methylmalonic acid excretion and B12 content in tissues. Methionine synthase activity in the testis of the B12-deficient rats was less than 2% of that in B12-supplemented (control) rats. To complement disrupted methionine biosynthesis, methionine was supplied in the diet. A supplement of 5 g D,L-methionine per kg diet to the B12-deficient diet did not affect urinary methylmalonic acid excretion of B12-deficient rats. The testicular histology of rats fed the methionine-supplemented B12-deficient diet was almost indistinguishable from that of control rats. Thus, we conclude that the lowered testicular methionine synthase activity is the primary cause of the histologic damage due to B12-deficiency and that methionine supplementation to the diet can reduce the damage. These findings would indicate the importance of the methionine synthase activity, especially for testicular function.

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.