Cystathionine beta-synthase polymorphisms and hyperhomocysteinaemia: an association study

Cystathionine β-synthase and methylenetetrahydrofolate reductase mutations in Mexican individuals with hyperhomocysteinemia

Background:

Hyperhomocysteinemia, a thrombotic risk factor, may have several causes. Among the genetic causes of hyperhomocysteinemia, there are polymorphisms in the enzymes methylenetetrahydrofolate reductase (C677T) and cystathionine β-synthase (C699T, C1080T, and 844ins68). Although the frequency of hyperhomocysteinemia in our country is high, there is no evidence about the frequencies of these polymorphisms.

Methods:

We analyzed 80 healthy individuals from several regions in our country. We evaluated the fasting and post-oral methionine load plasma Hcy and the genotypes in order to obtain the allele frequencies of the polymorphisms C677T of methylenetetrahydrofolate reductase and C699T, C1080T, and 844ins68 of the cystathionine β-synthase.

Results:

No individual had deficiency of folic acid, vitamins B12, or B6, but 80% had post-oral methionine load hyperhomocysteinemia. We found a significant increase in the Hcy plasma concentration associated with age and gender. Only the polymorphism C1080T was significantly associated with hyperhomocysteinemia.

Conclusion:

There is an association between fasting and post-oral methionine load plasma Hcy concentrations with the allelic frequencies of the polymorphisms C669T, 844ins68, and C1080T of the cystathionine β-synthase and C667T of the methylenetetrahydrofolate reductase in healthy Mexican individuals. As compared with individuals with normal fasting or post-oral methionine load Hcy plasma levels, only C1080T was significantly associated with hyperhomocysteinemia.

Association of Cystathionine β-Synthase Gene Polymorphisms With Preeclampsia

Preeclampsia (PE) is a pregnancy disorder that increases maternal and fetal morbidity and mortality worldwide. High plasma levels of homocysteine (Hcy) are a risk factor for several cardiovascular diseases. Cystathionine β-synthase (CBS) plays an important role in Hcy homeostasis catalyzing the irreversible degradation of Hcy to cystathionine, protecting the endothelium from injury caused by hypoxia. Several mutations and polymorphisms may alter the expression of the CBS gene, resulting in variable levels of Hcy. The purpose of this study was to investigate the association of CBS gene polymorphisms with PE in Mexican women. A case–control study consisting of 129 pregnant women with PE (37 severe and 92 mild) and 173 women with uncomplicated pregnancies was performed. Polymorphisms, such as G797A, C785T, T833C, G919A, T959C, C1105T, and 844ins68 base pair, in the CBS gene were genotyped. The polymorphism G797A was monomorphic in cases with the presence of only G797A-G allele. Allele C785T-T and genotype C785T-C/T were associated with susceptibility in severe and mild PE. Alleles G797A-G and T959C-T were associated with susceptibility only in severe PE. Haplotype TGTWGTC was of susceptibility for severe PE and of protection for mild PE. Haplotypes CGTWGCC and CATWGTC seem to be protective for severe PE, but the latter is related to susceptibility in mild PE. The results suggest that C785T, G797A, and T959C mutations are contributing in different ways in severe and mild PE in our population and could be count as another related factor for this disease.

A liquid chromatography mass spectrometry method for the measurement of cystathionine β-synthase activity in cell extracts

BACKGROUND

In order to correctly assess the efficacy of therapy or diet in intervention studies on the activity of cystathionine β-synthase (CBS) a sensitive analytical method is necessary.

METHODS

An electrospray LC-MS/MS method preceded by a solid phase extraction step was developed for the measurement of CBS activity in cell extracts. Nonafluoropentanoic acid was used as an ionpair to provide the underivatized cystathionine the desired retention on a C18 column.

RESULTS

A detection limit of 50pmol cystathionine/h/mg protein was achieved. In fibroblasts, intra- and inter-assay CVs for the CBS activity were 5.2% and 14.7%, respectively. A K(m) value of 8μmol/L for homocysteine, and 2.5μmol/L for serine was calculated. In fibroblasts wildtype, heterozygous, and homozygous CBS activity ranges measured were 8.5-27.0, 4.2-13.4, 0.0-0.7nmol/h×mg protein, respectively. The method was applied to a study where rats were fed 2 diets. Increase of dietary methionine (7.7 versus 3.8mg/kg methionine) significantly increased the CBS activity in rat liver lysates from a median of 58.0 to a median of 71.5 (P=0.037)nmol/h×mg protein. In a lymphoblasts cell culture experiment, the addition of Hcy to the culture media increased the activity of CBS 3 fold.

CONCLUSION

This LC-MS/MS is able to diagnose CBS deficiency at the enzyme level, and can accurately measure the effect diets or therapy might have on the CBS activity in a variety of cell types.

Association of polymorphisms in one-carbon metabolism genes and postmenopausal breast cancer incidence

The interconversion of folates by the one-carbon metabolism pathway is essential for the synthesis of precursors used in DNA synthesis, repair, and methylation. Perturbations in this pathway can disrupt these processes and are hypothesized to facilitate carcinogenesis. We investigated associations of 25 candidate polymorphisms in nine one-carbon metabolism genes with risk of postmenopausal breast cancer using 502 cases and 505 controls from the Cancer Prevention II Nutrition Cohort. Four single nucleotide polymorphisms (SNP) in three different genes were significantly associated with breast cancer. The nonsynonymous R134K SNP in methylenetetrahydrofolate dehydrogenase/methenyltetrahydrofolate cyclohydrolase/formyltetrahydrofolate synthase [MTHFD1; odds ratio (OR), 1.40; 95% confidence interval (95% CI), 1.06-1.85 for CT + TT] and an intronic SNP in formyltetrahydrofolate dehydrogenase (FTHFD; OR, 2.23; 95% CI, 1.09-4.54 for CC) were associated with a significant increase in risk. Significantly decreased risk was associated with an intronic SNP in FTHFD (OR, 0.75; 95% CI, 0.58-0.98 for CT + CC) and the A360A SNP in cystathionine beta-synthase (CBS; OR, 0.63; 95% CI, 0.41-0.96 for TT). The presence of at least one variant from both the methylenetetrahydrofolate reductase (MTHFR) C677T and A1298C SNPs was also associated with increased risk (OR, 2.16; 95% CI, 1.34-3.48 for 677 CT + TT/1,298 AC + CC). Investigations into interactions of the associated SNPs with each other and with dietary factors yielded inconclusive results. Our findings indicate that genetic variation in multiple one-carbon metabolism genes may influence risk of postmenopausal breast cancer and may involve changes in methyl donor synthesis. However, larger studies are needed to further examine gene/gene and gene/diet interactions in this pathway.

A CBS haplotype and a polymorphism at the MSR gene are associated with cardiovascular disease in a Spanish case–control study

OBJECTIVES

The aim of this study was to evaluate the association of polymorphisms present in genes related to homocysteine (Hcy) metabolism with coronary artery disease (CAD).

DESIGN AND METHODS

We examined 8 polymorphisms in the cystathionine beta-synthase (CBS), glutamate carboxypeptidase II (GCPII), methionine synthase (MS), methionine synthase reductase (MSR) and methylenetetrahydrofolate reductase (MTHFR) genes in 140 CAD patients and 113 controls, by means of Chi-square, logistic regression, ANOVA and the Mann-Whitney U test.

RESULTS

The c.66 G allele of MSR conferred an odds-ratio for CAD of 1.76 (95% CI 1.12-2.77), while a CBS haplotype [c.699C-c.844wt-c.1080C] was found over-represented in CAD [OR of 2.16 (1.29-3.63)].

CONCLUSIONS

Our results not only highlight the involvement of the MSR and CBS genes in the etiology of cardiovascular disease, but also emphasize the strength of haplotype analyses in association studies.

Hydrogen sulfide: neurochemistry and neurobiology

Current evidence suggests that hydrogen sulfide (H2S) plays an important role in brain functions, probably acting as a neuromodulator as well as an intracellular messenger. In the mammalian CNS, H2S is formed from the amino acid cysteine by the action of cystathionine beta-synthase (CBS) with serine (Ser) as the by-product. As CBS is a calcium and calmodulin dependent enzyme, the biosynthesis of H2S should be acutely controlled by the intracellular concentration of calcium. In addition, it is also regulated by S-adenosylmethionine which acts as an allosteric activator of CBS. H2S, as a sulfhydryl compound, has similar reducing properties as glutathione. In neurons, H2S stimulates the production of cAMP probably by direct activation of adenylyl cyclase and thus activate cAMP-dependent processes. In astrocytes, H2S increases intracellular calcium to an extent capable of inducing and propagating a "calcium wave", which is a form of calcium signaling among these cells. Possible physiological functions of H2S include potentiating long-term potentials through activation of the NMDA receptors, regulating the redox status, maintaining the excitatory/inhibitory balance in neurotransmission, and inhibiting oxidative damage through scavenging free radicals and reactive species. H2S is also involved in CNS pathologies such as stroke and Alzheimer's disease. In stroke, H2S appears to act as a mediator of ischemic injuries and thus inhibition of its production has been suggested to be a potential treatment approach in stroke therapy.

The use of betaine in the treatment of elevated homocysteine

Elevation of homocysteine is implicated in multiple medical conditions, including classical homocystinuria, a variety of remethylation disorders, and most recently in coronary artery disease. Betaine is a methyl donor agent that is beneficial in lowering homocysteine through the remethylation of methionine. Betaine therapy alone has been shown to prevent vascular events in homocystinuria and may have clinical benefits in other hyperhomocysteinemic disorders when used as adjunctive therapy. Betaine does raise the methionine level and cerebral edema has occurred when plasma methionine exceeds 1000 micromol/L. Thus the plasma methionine as well as homocysteine must be monitored in patients receiving betaine.

Polymorphisms in folate metabolic genes and lung cancer risk in Xuan Wei, China

The aim of this study is to investigate the role of genetic polymorphisms in twelve folate metabolism genes on the risk of lung cancer in Xuan Wei, China, where the lung cancer mortality rate is among the highest and is mainly caused by indoor smoky coal emissions. A total of 122 incident primary lung cancer cases and 122 matched controls were enrolled. Three single nucleotide polymorphisms were associated with increased risk of lung cancer including homozygotes of the C allele of CBS Ala360Ala (OR: 4.02; 95% CI: 1.64-9.87), the 222Val allele of MTHFR (OR: 2.32; 95% CI: 1.34-4.03), and the C allele of SLC19A1 Pro232Pro (OR: 1.83; 95% CI: 1.02-3.28). The distribution of CBS and MTHFR haplotypes differed between cases and controls (P=0.002 and P=0.07, respectively). In summary, three genetic variants in folate metabolism genes are associated with an increased risk of lung cancer in Xuan Wei, China.

Homocysteine metabolism, hyperhomocysteinaemia and vascular disease: an overview

Hyperhomocysteinaemia has been regarded as a new modifiable risk factor for atherosclerosis and vascular disease. Homocysteine is a branch-point intermediate of methionine metabolism, which can be further metabolised via two alternative pathways: degraded irreversibly through the transsulphuration pathway or remethylated to methionine by the remethylation pathway. Both pathways are B-vitamin-dependent. Plasma homocysteine concentrations are determined by nongenetic and genetic factors. The metabolism of homocysteine, the role of B vitamins and the contribution of nongenetic and genetic determinants of homocysteine concentrations are reviewed. The mechanisms whereby homocysteine causes endothelial damage and vascular disease are not fully understood. Recently, a link has been postulated between homocysteine, or its intermediates, and an alterated DNA methylation pattern. The involvement of epigenetic mechanisms in the context of homocysteine and atherosclerosis, due to inhibition of transmethylation reactions, is briefly overviewed.

[Polymorphisms in cystathionine beta-synthase and methylenetetrahydrofolate reductase genes as risk factors for cerebral vascular disease]

BACKGROUND AND OBJECTIVE

High plasma total homocysteine (tHcy), low dietary intake of folate and other B vitamins, and genetic polymorphisms related to the metabolism of homocysteine may interactively contribute to the risk of cerebral vascular disease (CVD). We explored interrelations between total homocysteine levels and mutations in genes for the two key enzymes in methionine-homocysteine metabolism.

PATIENTS AND METHOD

We analyzed two polymorphisms, C677T in the MTHFR gene and 844ins68 in the CBS gene. We assessed their association with fasting homocysteine in 64 patients with CVD, and in 159 controls.

RESULTS

No differences in CBS and MTHFR genotype frequencies between cases and controls were found (C677T p = 0.87 and 844ins68 p = 0.63), nor was a particular CBS and MTHFR genotype associated with an elevated risk of CVD. None of the genotypes defined by the CBS and MTHFR variants studied showed an association with elevated fasting homocysteine concentrations (C677T p = 0.07 and 844ins68 p = 0.47).

CONCLUSIONS

We did not find any indication that genetic variation in the CBS and MTHFR genes are associated with homocysteine-related risk of CVD, hence needing further investigation. The contributions to total plasma homocysteine levels of the common mutations of genes coding for the enzymes controlling homocysteine metabolism are modest.

Single-nucleotide polymorphisms in genes relating to homocysteine metabolism: how applicable are public SNP databases to a typical European population?

To facilitate the association studies in complex diseases characterized by hyperhomocysteinemia, we collected structural and frequency data on single-nucleotide polymorphism (SNPs) in 24 genes relating to homocysteine metabolism. Firstly, we scanned approximately 1.2 Mbp of sequence in the NCBI SNP database (dbSNP) build 110 and we detected 1353 putative SNPs with an average in silico genic density of 1:683. Out of 112 putative SNPs in coding regions (cSNPs), we selected a subset of 42 cSNPs and we assessed the applicability of the NCBI dbSNP to the Czech population - a typical representative of European Caucasians - by determining the frequency of the putative cSNPs experimentally by PCR-RFLP or ARMS-PCR in at least 110 control Czech chromosomes. As only 25 of the 42 analyzed cSNPs met the criterion of >/=1% frequency, the positive predictive value of the NCBI data set for our population reached 60%, which is similar to other studies. The correlation of SNP frequency between Czechs and other Caucasians - obtained from NCBI and/or literature - was stronger (r(2)=0.90 for 20 cSNPs) than between Czechs and general NCBI database entries (r(2)=0.73 for 27 cSNPs). Moreover, frequencies of all 20 putative cSNPs, for which data in Caucasians were available, were congruently below or above the 1% frequency criterion both in Czechs and in other Caucasians. In summary, our study shows that the NCBI dbSNP is a useful tool for selecting cSNPs for genetic studies of hyperhomocysteinemia in European populations, although experimental validation of SNPs should be performed, especially if the cSNP entry lacks any frequency data in Caucasians.

Characterization of cystathionine beta-synthase gene mutations in homocystinuric Venezuelan patients: identification of one novel mutation in exon 6

This study describes for the first time the cystathionine beta-synthase (CBS) gene mutations in Venezuelan patients. A total of five disease-causing mutations were identified in 9 out of 10 independent chromosomes. Four of the mutations have been previously described (G85R, T191M, D234N, and D444N) and a novel mutation was found (Q243X). Two common polymorphisms (699C/T and 1080C/T) were found in the CBS gene. Mutation analysis was performed using a combined screening approach for CBS mutations: restriction analysis, single-strand conformational polymorphism (SSCP) scanning, and sequencing. All the mutations were detected in homozygous state, except for Q243X, detected in three heterozygous siblings. Each one of the patients studied presented a different mutation. All mutations and polymorphisms detected involved hypermutable CpG sites, except for the novel mutation Q243X. The most common mutations I278T and G307S were not found in any of the patients. The CBS mutations present in each country differ from each other depending on the demographic profile; therefore, specific mutations scanning must be performed in each population for diagnosis and prognosis purposes.