Malondialdehyde–acetaldehyde-adducted bovine serum albumin activates protein kinase C and stimulates interleukin-8 release in bovine bronchial epithelial cells

Abstract

Previous study results have demonstrated that cigarette smoke or acetaldehyde rapidly stimulates protein kinase C (PKC)–mediated release of interleukin-8 (IL-8) in bovine bronchial epithelial cells (BECs). Low concentrations of acetaldehyde combine synergistically with malondialdehyde to increase significantly maximal BEC PKC activity at 48 to 96 h stimulation. Because more than 95% of alcoholics are cigarette smokers, we hypothesized that malondialdehyde, an inflammation product of lipid peroxidation, and acetaldehyde, both a product of ethanol metabolism and a component of cigarette smoke, might stimulate PKC-mediated IL-8 release in BECs by malondialdehyde–acetaldehyde (MAA) adduct formation, rather than as free aldehydes. Protein kinase C activity is maximally elevated in BECs treated with 50 μg/ml of BSA–MAA from approximately 1 to 3 h. This activity subsequently begins to decrease by 4 to 6 h, with a return to baseline unstimulated kinase activity levels by 24 h. No activation of cyclic AMP–dependent protein kinase (PKA) or cyclic GMP–dependent protein kinase (PKG) was observed in BSA–MAA-treated BECs. The MAA adduct activation of PKC was followed by a fourfold to tenfold greater release of IL-8 over that observed for both BECs exposed to media only and BSA control–treated BECs. Protein kinase C activation and IL-8 release were blocked by pretreating BECs with 1 μM calphostin C or 100 nM of the PKC alpha–specific inhibitor, Gö 6976. Isoform-specific inhibitors to PKC beta, PKC delta, and PKC zeta failed to inhibit completely MAA adduct–stimulated PKC or IL-8 release. Results of these studies indicate that metabolites derived from ethanol and cigarette smoke, such as acetaldehyde and malondialdehyde, form adducts that stimulate airway epithelial cell PKC alpha–mediated release of promigratory cytokines.