Plasma reduced homocysteine concentrations are increased in end-stage renal disease

Background. Plasma total homocysteine (tHcy) concentrations >15 mu mol/L are associated with an increased risk of cardiovascular disease. This is especially the case in end-stage renal disease (ESRD), in which tHcy concentrations commonly range between 20 and 30 mu mol/L. Adverse vascular or prothrombotic effects associated with hyperhomocysteinemia are assumed to be mediated by the free sulfhydryl (reduced) form of the molecule (rHcy), but data based on fluorescence high-pressure liquid chromatography (HPLC) indicate that rHcy concentrations are not increased in ESRD despite two- to threefold elevations in tHcy. Methods. We developed a sensitive method for measuring plasma rHcy concentrations in which freshly drawn blood is incubated with sodium iodoacetate, and the resulting S-carboxymethylhomocysteine is analyzed by gas chromatography mass spectrometry. Results. Unlike with the earlier methodology, we found plasma rHcy concentrations two to four times higher than normal in ESRD. These concentrations were lowered by hemodialysis and were proportional to plasma tHcy over the range of tHcy concentrations that has been associated with increased cardiovascular risk (r(2) = 0.39, P < 0.0001). Conclusions. These results support the hypothesis that homocysteine could directly mediate vascular disease through mechanisms related to the reactivity of its free sulfhydryl group. It remains to be determined how much of the variability between plasma tHcy and rHcy is due to analytical variation and how much is due to biologic factors that separately influence concentrations of the disease marker, tHcy, and its presumed mediator, rHcy.