Clinical usefulness of a HPLC method for simultaneous quantitation of plasma homocysteine and cysteine

Abstract

Objective: Homocysteine (Hcy) is a risk for vascular occlusion. It is metabolized via remethylation to methionine and transsulfuration to cysteine which has also been related to vascular occlusion. Simultaneous determination of Hcy and cysteine has additional clinical usefulness in providing a presumptive clue to the nature of hyperhomocysteinemia. Material and Method: A manual HPLC method has been worked out for simultaneous determination of plasma Hcy and cysteine. Concentrations of Hcy were validated with the widely used automated Abbott AxSYM assay. Its usefulness was tested in 87 omnivores and 111 vegans. Results: Excellent correlation between the values of Hcy was found between the manual HPLC method and the automated Abbott assay. The vegans had significantly higher levels of Hcy but lower levels of cysteine than the omnivores (mean ± SD, μmol/L 23.6 ± 18.0 vs. 8.8 ± 2.1 p < 0.001, 225 ± 30 vs. 245 ± 34 p < 0.001, respectively). In contrast, the vegans had significantly lower levels of serum vitamin B12 and plasma vitamin B6 than the omnivores (median values 186 vs 565 pg/ml, p < 0.001; 37.4 vs. 47.4 nmol/L, p < 0.001 respectively). These findings indicate that the hyperhomocysteinemia in the vegans results from impairment of both remethylation and transsulfuration pathways of Hcy secondary to inadequacy of vitamins B12 and B6 respectively. Thus simultaneous determination of Hcy and cysteine is more useful than determination of only Hcy in that it provides a clue to the nature of hyperhomocysteinemia. Conclusion: The manual HPLC method and the Abbott assay gave comparable Hcy values, and thus can be used interchangeably. The HPLC method is economical, useful for hospitals with less demand for determination of Hcy, and capable of simultaneously determining cysteine which has implication in clinical practice.