Effect of vitamin B6 deficiency on S-adenosylhomocysteine hydrolase activity as a target point for methionine metabolic regulation

Pyridoxine deficiency modulates benzene inhalation-induced hematotoxicity associated with hepatic CYP2E1 activity in B6C3F1 mice

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Modifying effects of pyridoxine deficiency on benzene toxicity were assessed in B6C3F1 mice.

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The mice were fed either a pyridoxine-deficient diet or control diet.

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Pyridoxine deficiency was combined with nose-only benzene inhalation exposure (100 ppm).

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Pyridoxine deficiency and benzene inhalation led to lower body, thymus and spleen weights.

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The treatment combination also led to higher hepatic CYP2E1 protein expression and activity.

Pyridoxine is a co-factor in many enzymatic reactions and impacts of deficiency have been observed in affected populations. A possible modifying effect of pyridoxine deficiency on benzene toxicity was assessed in male B₆C₃F₁ mice fed either a pyridoxine-deficient diet or a control diet. This treatment was combined with benzene inhalation exposure (100 ppm) or no benzene treatment. Pyridoxine-deficient mice exposed to 100 ppm benzene had significantly lower body, thymus and spleen weights. While total white blood cell counts, percentage of lymphocytes, hematocrit and hemoglobin levels were lower, the percentage of neutrophils was significantly higher in deficient and benzene-exposed mice compared to non-exposed controls. Hepatic CYP2E1 protein expression and activity in the deficient and exposed mice were also significantly higher compared to the non-exposed controls. A significant correlation between CYP2E1 activity and several hematological parameters was observed. These results demonstrated that pyridoxine deficiency significantly impacted benzene-induced hematotoxicity. Moreover, the observed agonistic effect of pyridoxinedeficiency and benzene inhalation exposure on CYP2E1 would seem to indicate an involvement of metabolism, but this needs to be further assessed.

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.

Identification of altered brain metabolites associated with TNAP activity in a mouse model of hypophosphatasia using untargeted NMR-based metabolomics analysis

Tissue non-specific alkaline phosphatase (TNAP) is a key player of bone mineralization and TNAP gene (ALPL) mutations in human are responsible for hypophosphatasia (HPP), a rare heritable disease affecting the mineralization of bones and teeth. Moreover, TNAP is also expressed by brain cells and the severe forms of HPP are associated with neurological disorders, including epilepsy and brain morphological anomalies. However, TNAP's role in the nervous system remains poorly understood. To investigate its neuronal functions, we aimed to identify without any a priori the metabolites regulated by TNAP in the nervous tissue. For this purpose we used ¹ H- and ³¹ P NMR to analyze the brain metabolome of Alpl (Akp2) mice null for TNAP function, a well-described model of infantile HPP. Among 39 metabolites identified in brain extracts of 1-week-old animals, eight displayed significantly different concentration in Akp2^-/- compared to Akp2^+/+ and Akp2^+/- mice: cystathionine, adenosine, GABA, methionine, histidine, 3-methylhistidine, N-acetylaspartate (NAA), and N-acetyl-aspartyl-glutamate, with cystathionine and adenosine levels displaying the strongest alteration. These metabolites identify several biochemical processes that directly or indirectly involve TNAP function, in particular through the regulation of ecto-nucleotide levels and of pyridoxal phosphate-dependent enzymes. Some of these metabolites are involved in neurotransmission (GABA, adenosine), in myelin synthesis (NAA, NAAG), and in the methionine cycle and transsulfuration pathway (cystathionine, methionine). Their disturbances may contribute to the neurodevelopmental and neurological phenotype of HPP.

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.

S-adenosylhomocysteine induces inflammation through NFkB: A possible role for EZH2 in endothelial cell activation

S-adenosylhomocysteine (SAH) can induce endothelial dysfunction and activation, contributing to atherogenesis; however, its role in the activation of the inflammatory mediator NFkB has not been explored. Our aim was to determine the role of NFkB in SAH-induced activation of endothelial cells. Furthermore, we examined whether SAH, as a potent inhibitor of S-adenosylmethionine-dependent methyltransferases, suppresses the function of EZH2 methyltransferase to contribute to SAH-induced endothelial cell activation. We found that excess SAH increases the expression of adhesion molecules and cytokines in human coronary artery endothelial cells. Importantly, this up-regulation was suppressed in cells expressing a dominant negative form of the NFkB inhibitor, IkB. Moreover, SAH accumulation triggers the activation of both the canonical and non-canonical NFkB pathways, decreases EZH2, and reduces histone 3 lysine 27 trimethylation. EZH2 knockdown recapitulated the effects of excess SAH on endothelial activation, i.e., it induced NFkB activation and the subsequent up-regulation of adhesion molecules and cytokines. Our findings suggest that suppression of the epigenetic regulator EZH2 by excess SAH may contribute to NFkB activation and the consequent vascular inflammatory response. These studies unveil new targets of SAH regulation, demonstrating that EZH2 suppression and NFkB activation mediated by SAH accumulation may contribute to its adverse effects in the vasculature.

Accumulation of lipid in rat liver was induced by vitamin B6 deficiency and was ameliorated by supplemental phosphatidylcholine in the diet

We investigated the efficacy of supplementing the diet with pteroylmonoglutamic acid (PGA), choline, or phosphatidylcholine (PC) in ameliorating the lipid accumulation in rat liver that is induced by vitamin B6 (B6) deficiency. In Experiment 1, male Wistar rats were fed a control, B6-deficient, or PGA-, choline-, or PC-supplemented (10 mg, 4 g, and 6.3 g/kg of diet, respectively) B6-deficient diet containing l-methionine at 9 g/kg of diet for 35 days. In Experiment 2, rats were fed a control, B6-deficient, or PC-supplemented (at 3.15, 6.3, or 12.6 g PC/kg of diet) B6-deficient diet for 35 days. Choline or PC supplementation ameliorated liver lipid deposition and returned plasma lipids to normal. Judging from these results, it appeared that B6 deficiency decreased the synthesis of PC in the liver, thereby decreasing the secretion of very low-density lipoproteins, and in consequence producing lipid accumulation in the liver and reductions of plasma lipids.

Folic acid fortification ameliorates hyperhomocysteinemia caused by a vitamin B₆-deficient diet supplemented with L-methionine

Vitamin B₆ (B₆) deficiency affects homocysteine metabolism, and this leads to hyperhomocysteinemia. In this study, we examined i) the effects of B₆-deficiency and graduated levels of dietary methionine on homocysteine metabolism, and ii) the effects of fortified folate on homocysteine metabolism. In experiment 1, Wistar male rats were fed a control or a B₆-deficient diet supplemented with L-methionine at a level of 3, 6, or 9 g/kg of diet for 5 weeks. The resulting plasma homocysteine levels in the B₆-deficient groups increased in relation to the increase in dietary methionine level. Next, in experiment 2, rats were fed a control, B₆-deficient, or folate enriched (10 mg pteroylmonoglutamic acid/kg) B₆-deficient diet containing L-methionine at 9 g/kg for 5 weeks. Although the B₆-deficient diet induced hyperhomocysteinemia, folate fortification ameliorated the plasma homocysteine concentration. Overall, our results indicate that folate fortification ameliorates the hyperhomocysteinemia induced by B₆ deficiency and supplemental methionine intake.

Homocysteine as a risk factor for atherosclerosis: is its conversion to s-adenosyl-L-homocysteine the key to deregulated lipid metabolism?

Homocysteine (Hcy) has been recognized for the past five decades as a risk factor for atherosclerosis. However, the role of Hcy in the pathological changes associated with atherosclerosis as well as the pathological mechanisms triggered by Hcy accumulation is poorly understood. Due to the reversal of the physiological direction of the reaction catalyzed by S-adenosyl-L-homocysteine hydrolase Hcy accumulation leads to the synthesis of S-adenosyl-L-homocysteine (AdoHcy). AdoHcy is a strong product inhibitor of S-adenosyl-L-methionine (AdoMet)-dependent methyltransferases, and to date more than 50 AdoMet-dependent methyltransferases that methylate a broad spectrum of cellular compounds including nucleic acids, proteins and lipids have been identified. Phospholipid methylation is the major consumer of AdoMet, both in mammals and in yeast. AdoHcy accumulation induced either by Hcy supplementation or due to S-adenosyl-L-homocysteine hydrolase deficiency results in inhibition of phospholipid methylation in yeast. Moreover, yeast cells accumulating AdoHcy also massively accumulate triacylglycerols (TAG). Similarly, Hcy supplementation was shown to lead to increased TAG and sterol synthesis as well as to the induction of the unfolded protein response (UPR) in mammalian cells. In this review a model of deregulation of lipid metabolism in response to accumulation of AdoHcy in Hcy-associated pathology is proposed.

Body mass index is an important determinant of methylation biomarkers in women of reproductive ages

B vitamin deficiencies lead to moderate hyperhomocysteinemia, which has been associated with health and disease. However, concomitant derangements in cellular methylation, reflected by altered plasma S-adenosylmethionine (SAM) or S-adenosylhomocysteine (SAH) concentrations, may be the primary cause. Therefore, we identified determinants of homocysteine, SAM, and SAH concentrations in 336 women, aged 20-48 y, as part of a large study focusing on risk factors for reproductive disorders. Blood was obtained to determine plasma SAM, SAH, and total homocysteine (tHcy), serum vitamin B-12 and folate, RBC folate concentrations, and the related single nucleotide polymorphisms 5,10-methylenetetrahydrofolate reductase (MTHFR) 677C > T and 1298A > C, methionine synthase reductase (MTRR) 66A > G, and nicotinamide N-methyltransferase IVS1-151G > A. Questionnaires provided information on demographics, lifestyles, and nutrient intakes. Correlation coefficients were calculated and multivariable associations were assessed with a general linear model. Serum folate was positively correlated with SAM concentrations (r = 0.159; P = 0.004). Folate and vitamin B-12 were not correlated with SAH concentrations or the SAM:SAH ratio but were inversely correlated with tHcy concentrations (serum folate r = -0.324; RBC folate r = -0.294; vitamin B-12 r = -0.307; P < 0.01). From the multivariable analysis, BMI was the strongest determinant of SAM (standardized beta = 19.145; P < 0.001) and SAH concentrations (standardized beta = 3.241; P = 0.010). MTHFR 677TT (standardized beta = 0.195; P = 0.001), B vitamin supplement use (standardized beta = -0.156; P < 0.001) and dietary protein intake (standardized beta = -0.011; P < 0.001) were the strongest determinants of tHcy concentrations. Thus, the determinants of SAM and SAH differ from those of tHcy concentrations. Given that BMI was a strong determinant of SAM concentrations, it should be included in future studies on cellular methylation.

Increase in S-Adenosylhomocysteine Content and Its Effect on the S-Adenosylhomocysteine Hydrolase Activity under Transient High Plasma Homocysteine Levels in Rats

The objective of this study was to examine how transient high plasma homocysteine (Hcy) levels affect the metabolism of Hcy, the activity and expression of S-adenosylhomocysteine (SAH) hydrolase which catalyzes both SAH hydrolysis and SAH synthesis. Wistar ST rats (males) were cannulated in the right jugular vein for intravenous infusion of physiological saline or DL-Hcy solutions (15 and 30 mg/mL) for 1 h at 1.1 mL/h/rat. The content of S-adenosylmethionine (SAM), SAH-synthetic activity of SAH hydrolase and the expression of SAH hydrolase mRNA in liver extracts showed no significant difference in the Hcy infused groups as compared to the Control group. On the other hand, the contents of hepatic SAH in the Hcy infused groups were dose-dependent and significantly higher than that of the Control group. Thus, this study showed that hepatic SAH increased without any increase in the SAH-synthetic activity and the expression of SAH hydrolase mRNA under transient high plasma Hcy levels after intravenous infusion of Hcy.