Relationship between total plasma homocysteine, polymorphisms of homocysteine metabolism related enzymes, risk factors and coronary artery disease in the Australian hospital-based population

Modest elevations of circulating homocysteine are common in patients with vascular disease. We explored interrelations between total plasma homocysteine levels and mutations in genes for three key enzymes in methionine-homocysteine metabolism. Methyltetrahydrofolate reductase (MTHFR) 677C→T, cystathionine beta synthase (CBS) 68-bp insertion at exon 8, and methionine synthase (MS) 2756A→G were typed in 685 Australian caucasian patients aged ⩽65 years with and without angiographically documented coronary artery disease (CAD). We also assessed associations between homocysteine levels and extracellular superoxide dismutase (EC-SOD) and other CAD risk factors. There were significant correlations between plasma total homocysteine, and EC-SOD (r=0.170, p=0.001 for men; r=0.241, p=0.003 for women) and LDL (r=0.153, p=0.001 for men; r=0.132, p=0.081 for women). Levels were also significantly higher among patients with unstable angina (15.30±0.44 μmol/l for men, 14.44±0.74 μmol/l for women) than those without angina (13.98±0.38 μmol/l for men, 13.41±0.98 μmol/l for women) or with stable angina (14.00±0.37 μmol/l for men, 12.88±0.71 μmol/l for women). There were no significant associations between the levels and the presence or severity of CAD. The mutant MTHFR homozygotes tended to have higher levels and those with the MS and CBS mutations tended to have lower levels. We conclude that there is a significant correlation between plasma homocysteine levels and EC-SOD suggesting that elevated homocysteine may exert oxidative stress and that levels are associated with unstable angina, but not the occurrence or extent of coronary stenosis. The contributions to total plasma homocysteine levels of the common mutations of genes coding for the enzymes controlling homocysteine metabolism are modest.