Plasma homocysteine reference values of adult Malaysians from three ethnic groups

Homocysteine and asymmetric dimethylarginine in relation to B vitamins in elderly people

OBJECTIVE

Homocysteine is a cardiovascular risk factor, its metabolism is influenced by certain B vitamins and it is associated with endothelial dysfunction probably due to impaired bioavailability of NO caused by homocysteine-induced accumulation of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of NO synthase. On this basis, we investigated the cardiovascular risk factors homocysteine and ADMA in relation to vitamins B(6), B(12) and folate in elderly people.

METHODS

A total of 102 subjects were recruited and divided into three groups according to age: A (70-74y, n = 48), B (75-79y, n = 35) and C (≥80y, n = 19). Plasma levels of vitamin B(6) were determined with HPLC, vitamin B(12) and folate by RIA. Plasma concentrations of homocysteine were analyzed with HPLC and levels of ADMA were measured by ELISA.

RESULTS

Plasma levels of vitamins B(6), B(12) and folate were found to be adequate in 93, 67 and 55% of participants, respectively. This study showed a significant age-associated decrease in vitamins B(6) (A > B, A > C: p < 0.05), B(12) and folate (A > C: p < 0.05) in parallel to a significant age-related increase in the cardiovascular risk factors homocysteine (A < C, B < C: p < 0.05) and ADMA (A < B: p < 0.05; A < C: p < 0.001). Moreover, homocysteine was significantly negatively (p < 0.01) related to vitamins B(6), B(12) and folate, and significantly positively (p < 0.01) correlated to ADMA.

CONCLUSIONS

The significant correlation between homocysteine and ADMA observed in this study may be an important mechanism decreasing NO bioavailability and so causing endothelial dysfunction. Due to the significant relation of vitamins B(6), B(12) and folate to plasma homocysteine, these vitamins may thus indirectly influence endothelial function and cardiovascular risk in elderly people.

TT Genotype of the Methylenetetrahydrofolate Reductase C677T Polymorphism is an Important Determinant for Homocysteine Levels in Multi-Ethnic Malaysian Ischaemic Stroke Patients

Introduction: The functional point mutation C677T in the methylenetetrahydrofolate reductase (MTHFR) gene, has been reported to contribute to hyperhomocysteinaemia which is a risk factor for atherothrombotic ischaemic strokes. This study evaluated the prevalence of the C677T polymorphism of the gene in Malaysian ischaemic stroke subjects of Malay, Chinese and Indian ethnicities, and its association with homocysteine levels (tHcy). Materials and Methods: A total of 292 subjects were recruited, comprising 150 ischaemic stroke patients and 142 control subjects who were age and sex matched. Plasma homocysteine, serum folate and vitamin B12 were measured in all subjects. Genotyping was carried out using PCR-RFLP. Results: The homocysteine levels were significantly higher (P = 0.001) in the stroke group (11.35 ± 2.75 μmol/L) compared to the control group (10.38 ± 2.79 μmol/L). The MTHFR C677T genotype distribution for the stroke group was 46%, 40% and 14%, respectively for CC, CT and TT genotypes and 59.9%, 33.8% and 6.3%, respectively for the control group. The genotype and allelic frequencies were significantly different between the 2 groups, with P = 0.02 and P = 0.004 respectively. No significant difference was seen in the genotype distribution inter-ethnically. An increasing tHcy was seen with every additional T allele, and the differences in the tHcy for the different genotypes were significant in both the control (P <0.001) and stroke groups (P <0.001). Conclusion: This study shows that TT genotype of the methylenetetrahydrofolate reductase C677T polymorphic gene is an important determinant for homocysteine levels in Malaysian ischaemic stroke patients. Key words: Homocysteine, Ischaemic stroke, Malaysia, MTHFR polymorphism

Differences in Mexican American and Non-Hispanic White veterans' homocysteine levels

PURPOSE

To compare homocysteine (Hcy) levels and possible modulatory factors, such as nutrient or supplement intake, between Mexican American and Non-Hispanic White (NHW) male military veterans scoring at high- versus low-risk for stroke.

DESIGN

A cross-sectional survey with a high and low stroke risk biomarkers substudy.

METHODS

Voluntary participants were Mexican American (n=109) and NHW (n=120) veteran outpatients 54 to 85 years of age at a Southwestern Veterans Administration (VA) medical center. Measures included food frequency, health history, and stroke risk scale derived from the Framingham Study. Biomarker subgroups, 30 Mexican American and 30 NHW, half of each group scoring high or low on stroke risk, who were tested for morning fasting blood levels of Hcy, B12, and folate.

FINDINGS

In the cross-sectional study (n=229), nutrient intake was comparable between ethnic groups. In the substudy, Mexican Americans (n=30) with high or low stroke risk scores and NHW (n=30) with high stroke risk scores had elevated Hcy levels (12.5; 11.9; 11.4 micromol/L respectively) compared to NHW veterans with low stroke risk scores (7.8 micromol/L) even after controlling for age, education, folate, diabetes, and smoking pack-years (p=.001). Mexican Americans compared to NHW were significantly more likely to be in the preclinical (17% versus 3% >10 micromol/L) and clinical ranges (69% versus 35% >15 micromol/L) for Hcy.

CONCLUSIONS

Mexican Americans showed higher levels of Hcy whether they scored high or low for stroke, and greater representation in clinical and preclinical Hcy ranges compared to NHW veterans. The Framingham-derived, predominantly NHW population-based stroke risk measure might require ethnically relevant stroke risk factors for Mexican Americans.