Human serum albumin Cys34 oxidative modifications following infiltration in the carotid atherosclerotic plaque

Aim: Oxidative stress has been implicated in the outcome of atherosclerotic plaques. To date, only few data are available on the extent of plaque protein-SH oxidation and its relationship with plaque vulnerability. The formation of mixed disulfides between low molecular weight-thiols (LMW-thiols) and protein-SH to form thiolated proteins is known to occur after oxidative stress and has been recently suggested as a possible means of redox regulation of protein functions. Recently, by means of a proteomic approach on human carotid plaques, we evidenced that the majority of extracted proteins were of plasma origin, being albumin (HSA) the most represented. Furthermore, we developed a highly sensitive method for quantification of all LMW-thiols bound to circulating and intra-plaque HSA. The aim of this study was to evaluate if the plaque pro-oxidant environment could oxidatively modify the filtered albumin. Methods: We evaluated HSA-Cys34 total oxidation in both plasma and plaque extracts of patients undergoing carotid endarterectomy by non-reducing SDS-PAGE of fluorescein-5-maleimide (F5M) adducts. Moreover, we determined HSA-Cys34 thiolation levels and patterns by capillary zonal electrophoresis. Results: Intra-plaque HSA showed lower levels of Cys34 labeling by F5M than the corresponding circulating form and a different pattern of S-thiolation. In particular, intra-plaque HSA showed reduced amounts of homocysteine and cysteinylglycine. Conclusions: Our data indicate that the circulating HSA, upon infiltration, is subjected to Cys34 oxidative modifications and suggest that it may represent a homocysteine and cysteinylglycine vehicle inside the plaque environment. The relevance of albumin oxidative modifications in the plaque patho-physiology deserves further investigations.