Characterization of N-homocysteinylated albumin adducts

Increased plasma homocysteine levels are considered an important risk factor for vascular disease. Homocysteine, an intermediate compound in methionine metabolism, is an amino acid that includes a thiol group, and circulates as different species. One of them, Homocysteine thiolactone (HTL) forms adducts through irreversible reactions with epsilon-NH2 groups of lysine residues. These processes can alter the structure and biological function of diverse proteins that may be involved in the detrimental effects of homocysteine. Particularly, in this work we evaluated HTL-mediated molecular changes in human serum albumin (HSA) through electrophoretic techniques. Albumin and HTL were incubated (37 °C, 6 h) at HSA:HTL molar ratios of 1:25, 1:50 and 1:100. Polyacrylamid gel electrophoresis showed that electrophoretic mobility was increased in the treated HSA respect to control, in an HTL-concentration-dependent manner. That anodic shift of the treated samples was also observed in crossed immunoelectrophoresis profiles. As expected, a decrease in the isoelectric point of the homocysteinylated albumin (pI 4.7) in comparison to that of control (pI 4.8) was shown by the isoelectric focusing technique. Moreover, the electropherogram acquired by capillary zone electrophoresis indicated that migration times and full width at half height were enhanced with the rise of HTL concentration. We propose that the in vitro structural changes of albumin described in the present work would be involved in the harmful effects of the N-homocysteinylation process.