A novel pathway for the conversion of homocysteine to methionine in eukaryotes

Increased plasma protein homocysteinylation in hemodialysis patients

Hyperhomocysteinemia, an independent cardiovascular risk factor, is present in the majority of hemodialysis patients. Among the postulated mechanisms of toxicity, protein homocysteinylation is potentially able to cause significant alterations in protein function. Protein homocysteinylation occurs through various mechanisms, among which is the post-translational acylation of free amino groups (protein-N-homocysteinylation, mediated by homocysteine (Hcy) thiolactone). Another type of protein homocysteinylation occurs through the formation of a covalent -S-S- bond, found primarily with cysteine residues (protein-S-homocysteinylation). Scant data are available in the literature regarding the extent to which alterations in protein homocysteinylation are present in uremic patients on hemodialysis, and the effects of folate treatment are not known. Protein homocysteinylation was measured in a group of hemodialysis patients (n=28) compared to controls (n=14), with a new method combining protein reduction, gel filtration and Hcy derivatization. Chemical hydrolysis was performed, followed by high-pressure liquid chromatography separation. The effects of folate treatment on protein homocysteinylation, as well as in vitro binding characteristics were evaluated. Plasma Hcy, protein-N-homocysteinylation and protein-S-homocysteinylation were significantly higher in patients vs controls. Plasma Hcy and protein-S-homocysteinylation were significantly correlated. After 2 months of oral folate treatment, protein-N-homocysteinylation was normalized, and protein-S-homocysteinylation was significantly reduced. Studies on albumin-binding capacity after in vitro homocysteinylation show that homocysteinylated albumin is significantly altered at the diazepam-binding site. In conclusion, increased protein homocysteinylation is present in hemodialysis patients, with possible consequences in terms of protein function. This alteration can be partially reversed after folate treatment.

Predictors of coronary artery disease in the Lebanese population

BACKGROUND

Coronary artery disease (CAD) is one of the major causes of morbidity and mortality in the world. The disease is determined by many risk factors such as age, gender, diabetes, dyslipidemia, smoking, as well as elevated serum levels of lipoprotein (a) (Lp(a)), homocysteine, C-reactive protein (CRP) and uric acid. In this study, we evaluated the association of biologic and metabolic parameters with CAD in a group of Lebanese patients.

METHODS

Three hundred patients were recruited for the study. Biologic and blood metabolic parameters were measured. Patients were then divided into 3 groups according to their catheterization result: 0% stenosis (controls), <50% stenosis and >or=50% stenosis.

RESULTS

Hyperlipidemias, CRP, homocysteine and uric acid levels in CAD patients were not different from those of the controls. However, age, elevated fasting blood glucose (FBG) and elevated serum Lp(a) levels were found to be strong independent predictors of CAD in our study population. Association with CAD was also shown for gender, hypertension, diabetes and family history of CAD.

CONCLUSION

We report the importance of serum Lp(a) levels and FBG in the prediction and prevention of CAD in our population.

Ratios of homocysteine and nitrite to high-density lipoprotein in coronary artery patients with the different degree of stenosis

Although the interaction between Hcy, NO(2)(-) and vascular disease has been extensively studied, there are no data verifying their ratios to HDL-C in coronary artery disease (CAD). We examined whether Hcy/HDL-C and NO(2)(-)/HDL-C ratios correlated with the degree of stenosis in CAD. Also, TC/HDL-C and LDL-C/HDL-C ratios were evaluated in the same individuals. Seventy subjects were divided into three groups according to coronary angiography findings: >50% stenosis (n=35, years: 50.9+/-3.4; Group 1), 5-50% stenosis (n=20, years: 50.6+/-3.8; Group 2), <5% narrowing (n=15, years: 49.0+/-3.2; control group). Hcy/HDL-C, NO(2)(-)/HDL-C, TC/HDL-C and LDL-C/HDL-C were statistically higher in both Group 1 patients (p=0.001, for all ratios) and Group 2 patients (p=0.001, p=0.001, p=0.03, 0.041, respectively) with respect to controls. The values were correlated with the degree of stenosis in the different significance levels (r=0.496, p=0.001; r=0.384, p=0.004; r=0.334, p=0.012; r=0.321, p=0.016, respectively). In patients with >50% stenosis, NO(2)(-)/HDL-C was only shown to change significantly in relation to obstructive artery number (p=0.026) and also showed a positive correlation (r=0.379, p=0.032). In conclusion, Hcy/HDL-C and NO(2)(-)/HDL-C appear to be more indicative than TC/HDL-C and LDL-C/HDL-C in the evaluation of CAD patients regarding the degree of stenosis. However, only NO(2)(-)/HDL evaluation seems to be a reliable indicator in the patients with heavy stenosis of CAD. Further studies are needed to confirm the results of present study.

Roles of homocysteine in cell metabolism: old and new functions

Mild hyperhomocysteinemia has been suggested as a new, independent risk factor for cardiovascular disease. This fact has produced a new, increased interest in the study of homocysteine metabolism and its relation to pathogenesis. This emergent area of biomedical research is reviewed here, stressing the biochemical and metabolic basis of the pathogenicity of increased levels of homocysteine.

Homocysteine: an emergent cardiovascular risk factor?

Cardiovascular disease is the leading cause of mortality and disability in the western world. In the last years, the accumulation of evidence coming from both retrospective and prospective clinical studies has led to an increased interest in the potential role of mild hyperhomocysteinemia as a major, independent risk factor for cardiovascular disease. The present paper reviews the position of homocysteine in metabolism to understand the pathogenesis of hyperhomocysteinemia, as well as the clinical data pointing to its proposed role as an independent cardiovascular disease risk factor.