In Vitro Formation of Homocysteine in Whole Blood in the Presence of Anticoagulants

Abstract

We read with great interest the letter by Hubner et al. (1) on the stability of plasma sulfur-containing metabolites in the presence of anticoagulants (EDTA and citrate) and a homocysteine stabilizer. These authors observed time-dependent increases in plasma concentrations of homocysteine (Hcy)1 and similar increases in plasma S -adenosylhomocysteine (SAH) in EDTA- and citrate-containing whole blood after 24 h at room temperature. In discussing the mechanisms of these increases, they postulated that plasma Hcy is generated from SAH in erythrocytes by the SAH-hydrolase–catalyzed reaction, and Hcy and SAH leak into plasma from erythrocytes (1). They further noted that the inhibition of SAH hydrolase by citrate results in a smaller Hcy increase compared with EDTA, which they claimed does not inhibit this enzyme. We recently reported the iron-dependent in vitro chemical formation of Hcy from methionine (Met), SAH, and cystathionine, where EDTA or …