Vitamin C prevents cigarette smoke induced oxidative damage of proteins and increased proteolysis

Aqueous extract of cigarette smoke (CS) contains some stable oxidants, whic h oxidize human plasma proteins, bovine serum albumin, amino acid homopolym ers, and also cause extensive oxidative degradation of microsomal proteins. Similar observations are made when the aqueous extract of cigarette smoke is replaced by whole phase CS solution or whole phase cigarette smoke. CS-i nduced microsomal protein degradation is a two step process: (i) oxidation of proteins by the oxidants present in the CS and (ii) rapid proteolytic de gradation of the oxidized proteins by proteases present in the microsomes. Using aqueous extract of CS equivalent to that produced from one-twentieth of a cigarette, the observed initial and postcigarette smoke treated values of different parameters of oxidative damage per milligram of microsomal pr oteins are respectively: 0.24 and 1.74 nmoles for carbonyl formation, 125.4 and 62.8 fluorescence units for tryptophan loss, 10.2 and 33.4 fluorescenc e units for bityrosine formation, and 58.3 and 12.2 nmoles for loss of prot ein thiols. When compared with sodium dodecyl sulphate polyacrylamide gel e lectrophoresis profiles of untreated microsomal proteins, the extent of mic rosomal protein degradation after treatment with whole phase CS solution or aqueous extract of CS is above 90%. Ascorbate (100 mu M) almost completely prevents cigarette smoke-induced protein oxidation and thereby protects th e microsomes from subsequent proteolytic degradation. Glutathione is partia lly effective, but other antioxidants including superoxide dismutase, catal ase, vitamin E, probucol, beta-carotene, mannitol, thiourea, and histidine are ineffective. The gas phase cigarette smoke contains unstable reactive o xygen species such as superoxide (O-2(-.)) and hydrogen peroxide (H2O2) tha t can cause substantial oxidation of pure protein like albumin but is unabl e to produce significant oxidative damage of microsomal proteins. Gas phase cigarette smoke-induced albumin oxidation is not only inhibited by ascorba te and glutathione but also by superoxide dismutase, catalase and mannitol. The stable oxidants in the cigarette smoke are not present in the tobacco and are apparently produced by the interaction of O-2(-.)/H2O2/OH. of the g as phase with some components of the tar phase during/following the burning of tobacco. (C) 1999 Elsevier Science Inc.