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The folate and cobalamin (Cbl-) dependent enzyme methionine synthase (MS) is highly sensitive to oxidation and its activity affects all methylation reactions. Recent studies have revealed alternative splicing of MS mRNA in human brain and patient-derived fibroblasts. Here we show that MS mRNA in SH-SY5Y human neuroblastoma cells is alternatively spliced, resulting in three primary protein species, thus providing a useful model to examine cofactor dependence of these variant enzymes. MS activity was dependent upon methylcobalamin (MeCbl) or the combination of hydroxocobalamin (OHCbl) and S-adenosylmethionine (SAM). OHCbl-based activity was eliminated by depletion of the antioxidant glutathione (GSH) but could be rescued by provision of either glutathionylcobalamin (GSCbl) or MeCbl. Pretreatment of cells with lead, arsenic, aluminum, mercury, or the ethylmercury-containing preservative thimerosal lowered GSH levels and inhibited MS activity in association with decreased uptake of cysteine, which is rate-limiting for GSH synthesis. Thimerosal treatment decreased cellular levels of GSCbl and MeCbl. These findings indicate that the alternatively spliced form of MS expressed in SH-SY5Y human neuronal cells is sensitive to inhibition by thimerosal and neurotoxic metals, and lower GSH levels contribute to their inhibitory action.

Genetic, nutrition, and environmental factors have each been implicated as sources of risk for autism. Oxidative stress, including low plasma levels of the antioxidant glutathione, has been reported by numerous autism studies, which can disrupt methylation-dependent epigenetic regulation of gene expression with neurodevelopmental consequences. We investigated the status of redox and methylation metabolites, as well as the level of protein homocysteinylation and hair mercury levels, in autistic and neurotypical control Omani children, who were previously shown to exhibit significant nutritional deficiencies in serum folate and vitamin B₁₂. The serum level of glutathione in autistic subjects was significantly below control levels, while levels of homocysteine and S-adenosylhomocysteine were elevated, indicative of oxidative stress and decreased methionine synthase activity. Autistic males had lower glutathione and higher homocysteine levels than females, while homocysteinylation of serum proteins was increased in autistic males but not females. Mercury levels were markedly elevated in the hair of autistic subjects vs. control subjects, consistent with the importance of glutathione for its elimination. Thus, autism in Oman is associated with decreased antioxidant resources and decreased methylation capacity, in conjunction with elevated hair levels of mercury.

Background: Methionine synthase (MS) is a ubiquitous enzyme that requires vitamin B12 (cobalamin) and 5-methyl-tetrahydrofolate for the methylation of homocysteine to methionine. Previous studies have shown that acute or chronic ethanol (ETOH) administration results in the inhibition of MS and depletion of glutathione (GSH), and it has been proposed that GSH is required for the synthesis of methylcobalamin (MeCbl)., Methods: We measured GSH levels and investigated the ability of different cobalamin cofactors [cyano- (CNCbl), glutathionyl- (GSCbl), hydroxo- (OHCbl), and MeCbl] to support MS activity in liver and brain cortex from control and ETOH-treated rats., Results: In control animals, MS activity was higher in liver than in cortex for all cobalamins and MeCbl-based activity was higher than for other cofactors. S-adenosylmethionine (SAM) was required for OHCbl, CNCbl, and GSCbl-based activity, but not for MeCbl. Feeding an ETOH-containing diet for four weeks caused a significant decrease in liver MS activity, in a cobalamin-dependent manner (OHCbl ≥ CNCbl > GSCbl > MeCbl). In brain cortex, OHCbl, CNCbl, and GSCbl-based activity was reduced by ETOH treatment, but MeCbl-based activity was unaffected. GSH levels were reduced by ETOH treatment in both liver and cortex homogenates, and addition of GSH restored OHCbl-based MS activity to control levels. Betaine administration had no significant effect on GSH levels or MS activity in either control or ETOH-fed groups., Conclusions: The ETOH-induced decrease in OHCbl-based MS activity is secondary to decreased GSH levels and a decreased ability to synthesize MeCbl. The ability of MeCbl to completely offset ETOH inhibition in brain cortex, but not liver, suggests tissue-specific differences in the GSH-dependent regulation of MS activity., (Copyright © 2010 by the Research Society on Alcoholism.)

This study aimed to assess the status of B-vitamins (folate, vitamin B6, and B12) and homocysteine (HCY) in the sera of Omani coronary artery disease (CAD) patients. Sixteen Omani patients (10 males and 6 females) gave consent for blood sampling and were enrolled in the study on voluntary basis. All patients were evaluated for their anthropometric and biochemical measurements of B-vitamins, glutathione (reduced and oxidized), HCY, and quantification of N-homocysteinylated albumin protein. It was observed that both male and female patients had a comparable age (57.64 ±9.86, 56.5 ±10.04 years, respectively) with no significant difference, P = 0.69 and both genders were obese based on their body mass index (31.22 ± 8.17 kg/m2 for males and 30.26 ± 4.70 kg/m2for females). Serum levels of folate, vitamins B6, and B12 were lower than the normal reference values in all the study participants. There was depletion in glutathione levels (higher level of oxidized glutathione versus lower level of reduced glutathione) in the sera of all study participants. High serum HCY levels in both males and females (75.81±9.21 and 68.66±8.1 μmol/L, respectively) suggest that both males and females had hyperhomocysteinemia. Correlation coefficient analysis revealed that the serum HCY levels were negatively correlated with serum reduced glutathione, folic acid, vitamins B6, and B12 levels in both male and female study participants. The serum HCY level was positively correlated with age, body mass index, and serum oxidized glutathione. Proteomic measurements of N-homocysteinylation in serum albumin revealed that N-homocysteinylated albumin was present in all the assayed serum samples of study participants. The results suggest that low serum status of B-vitamins might act as a metabolic trigger for the observed hyperhomocysteinemia, oxidative stress, and pathological formation of N-homocysteinylated albumin protein, which collectively aggravates the CAD risk in the studied Omani patients. [ABSTRACT FROM AUTHOR]

Folate and vitamin B12 deficiency is associated with depletion of the major intracellular antioxidant glutathione, and oxidative stress is emerging as an etiological mechanism for colon cancer. Azoxymethane (AOM), a potent carcinogen, induces colon cancer in rats by causing pathophysiological changes and oxidative stress. We investigated the synergistic effect of folate and vitamin B12 supplementation against AOM-induced carcinogenesis and oxidative stress in rat colon. Adult male rats were distributed into four groups: 1) Basal diet only; 2) AOM injection (15 mg/kg once per week in weeks 5 and 6); 3) Folate and vitamin B12 supplemented diet; 4) Folate and B12 diet with AOM injection. After 16 weeks, rats were sacrificed, colon tissue dissected, indicators of oxidative stress were measured, and immunohistochemical and ultrastructural changes were evaluated. AOM-injected rats showed oxidative stress, evident by glutathione depletion, oxidation of cellular proteins, and DNA oxidative damage. AOM increased mucosal levels of antiapoptotic and proapoptotic proteins Bcl2 and Bax and caused ultrastructure changes in colonic cell organelles. Folate and vitamin B12 supplementation decreased the level of oxidative stress and ameliorated the cytotoxic effects of AOM. In this in vivo experimental model of colon cancer, folate and vitamin B12 supplementation combats carcinogen-induced oxidative stress. [ABSTRACT FROM AUTHOR]

Purpose: Literature emerging from Western countries has reported increased levels of serum oxidative stress markers among polycystic ovarian syndrome (PCOS) women. In the Arab region, there is limited research about the association between oxidative stress and PCOS. This study aimed to compare sociodemographic and clinical characteristics, sex hormones, and oxidative stress indices between PCOS women and non-PCOS women and to investigate the correlation between oxidative stress biomarkers and sex hormones.Methods: This hospital-based case-control study was conducted among reproductive-aged women. The study included 51 women diagnosed with PCOS (as per Rotterdam 2003 criteria) and 45 control women who were not diagnosed with PCOS. Serum samples were collected to measure the mean levels of the following sex hormones: total testosterone, dehydroepiandrosterone sulfate, estradiol and progesterone, as well as to measure biomarkers of oxidative stress including glutathione peroxidase (GPx), glutathione reductase (GR), glutathione (GSH), and total antioxidant capacity (TAC).Results: PCOS women exhibited clinical characteristics including irregular menses, hirsutism, and acne compared to the control group (P≤0.05). Significant differences were observed in the waist-hip ratio of PCOS women compared to controls (P=0.004). GPx and GR activity levels appeared to be higher among PCOS women compared to controls; however, no statistically significant differences were observed between the two groups (P>0.05). PCOS women had lower GSH and TAC levels compared to controls with a statistically significant difference observed for GSH levels (P=0.006). Correlation analysis showed a significant negative correlation between estradiol and TAC in the total sample (r=-0.284, P=0.005).Conclusion: This study provides supportive evidence that oxidative stress might play a role in the pathogenesis of PCOS and, hence, oxidative stress parameters could be suggested as diagnostic markers for early diagnosis of high-risk groups. Also, the study provides supportive evidence that obesity and sex hormones, particularly estradiol, in PCOS may contribute to enhanced oxidative stress. [ABSTRACT FROM AUTHOR]

Abstract: Objective: The purpose of this study was to examine the status of folate and vitamin B12 (B12) in relation to serum homocysteine (HCY) and oxidative stress indices in patients with type 2 diabetes (T2DM). Methods: This case–control study involved 100 Omani adults (50 patients newly diagnosed with T2DM and 50 age- and gender-matched healthy controls). Several parameters were investigated, including dietary intake and biochemical assessments of folate, B12, HCY, oxidative stress markers (glutathione and total antioxidant status), and antioxidant enzymes (superoxide dismutase, glutathione peroxidase, and catalase). Results: Low serum levels of folate, B12, and hyperhomocysteinemia were prevalent in patients with T2DM compared with controls. Oxidative stress was evident in patients with T2DM as indicated by low serum levels of glutathione, total antioxidant status, and impaired antioxidant enzymatic activities (superoxide dismutase, glutathione peroxidase, and catalase). Conclusion: The low intake of folate and B12 is associated with low serum levels of these two nutrients and hyperhomocysteinemia in Omani adults with T2DM. [Copyright &y& Elsevier]