Abstract
Different studies reported the presence of oxidized (carbonylated) albumin in the extravascular pool, but not in the intravascular one of cigarette smokers. In this study we attempted to explain this apparent discrepancy exposing human serum albumin (HSA) to aqueous cigarette smoke extract (CSE). CSE induces HSA carbonylation and oxidation of the HSA Cys34 sulfhydryl group. An antioxidant action of glutathione, cysteine, and its synthetic derivative N-acetylcysteine was observed only at supra-physiological concentrations, suggesting that physiological (plasma) concentrations of glutathione and cysteine in the low micromolar range are ineffective in preventing cigarette smoke–induced oxidation of HSA. Differently, human erythrocytes resulted to be protective towards CSE-induced oxidation (carbonylation and thiol oxidation) of both HSA and total human plasma proteins.
Highlights
Cigarette smoke (CS), an etiological factor for the development of many tobacco-related diseases [1,2,3], is a complex mixture containing more than 7000 different constituents, including reactive oxygen and nitrogen species (ROS and RNS) [4]
When human serum albumin (HSA)-SH solutions were incubated with increasing concentrations (0–16%, v/v) of cigarette smoke extract (CSE), the number of sulfhydryl groups, as determined by reaction with dithiobis(2-nitrobenzoic acid) (DTNB), progressively decreased from 0.9060.04 mol -SH/mol albumin to 0 mol -SH/ mol albumin (Fig. 1)
Cys34 forms a mixed disulfide with low molecular mass aminothiols, generating S-thiolated albumin; a small fraction (2– 5%) of albumin Cys34 is more highly oxidized to the sulfinic (HSA-SO2H) or sulfonic acid (HSA-SO3H) form, which cannot usually be reversed with DTT and can cause loss of protein function [13,41,42]
Summary
Cigarette smoke (CS), an etiological factor for the development of many tobacco-related diseases [1,2,3], is a complex mixture containing more than 7000 different constituents, including reactive oxygen and nitrogen species (ROS and RNS) [4]. Further ROS/RNS production mediated through inflammatory processes may exacerbate those produced through direct exposure [5]. Human plasma antioxidants include the low molecular mass aminothiols glutathione (GSH) and cysteine (Cys-SH), which occur in the micromolar range [8]. Their concentrations in plasma are decreased in association with cigarette smoking [9,10]
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