Cigarette smokers develop structurally modified hemoglobin: a possible way of increasing oxidative stress

Abstract

Context: Increased levels of free radicals and various reactive species along with reduced antioxidant defence system are the major threat to erythrocyte in tobacco smokers. Thus, the hemoglobin (Hb) within the erythrocyte is very prone to oxidative damage. Earlier reports suggest that cigarette smoking is related with the glutathionylation and formation of adducts of Hb.

Objective: We have highlighted the possible changes in secondary and tertiary structures of Hb in cigarette smokers and its physiological consequences.

Material and method: Twenty smokers and 18 non-smokers, aged 25-35 years were volunteered in this study. We used flow cytometry for measuring intracellular reactive oxygen species (IcROS). The purified Hb was subjected to different spectrophotometric, fluoremetric and circular dichroic (CD) analysis. The hydrophobicity, thermal stability, heme release and oxidation of purified Hb were also studied.

Result: We observed that the IcROS was also higher in cigarette smokers than non-smokers. The data of intrinsic fluorescence, synchronous fluorescence and tryptophan quenching studies showed that the microenvironments of β37 tryptophan and tyrosine residues of Hb were moved toward more hydrophobic region in cigarette smokers. Increased hydrophobicity and thermal stability furthermore indicated more compactness of smokers' hemoglobin. From CD spectra, we confirmed an overall modification of the secondary and tertiary structures of hemoglobin in smokers. Both auto- and co-oxidation rates of purified Hb were found to be higher in cigarette smokers.

Discussion and conclusion: We conclude that the modified Hb in cigarette smokers may further enhance the oxidative insult within the cell.

Keywords: Cigarette smoking; circular dichroic spectroscopy; fluorescence spectroscopy; hemoglobin; hemoglobin oxidation; thermal stability.