Clinical Usefulness of a HPLC Method for Simultaneous Quantitation of Plasma Homocysteine and Cysteine
Kalayanee Atamasirikul MSc*, Saowanee Kajanachumpol MSc**, Prapin Wilairat PhD***, Phienvit Tantibhedhyangkul MD, MS, PhD****
Affiliation : * Department of Pathology, Faculty of Medicine, Ramathibodi Hospital and Center for Research and Development of Immunodiagnostics, Institute of Science and Technology of Research and Development, Mahidol University, Salaya Campus, Nakorn Pathom ** Research Center, Faculty of Medicine, Ramathibodi Hospital, Mahidol University, Bangkok *** Department of Chemistry, Faculty of Science, Mahidol University, Bangkok **** Department of Pediatrics, Faculty of Medicine, Ramathibodi Hospital, Mahidol University, Bangkok
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 respec-
tively. 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.
Keywords : HPLC, Homocysteine, Cysteine, Abbott AxSYM
