The cellular stress response induced by aqueous extracts of cigarette smoke is critically dependent on the intracellular glutathione concentration

Abstract

Mainstream cigarette smoke (CS) trapped in phosphate-buffered saline solutions (smoke-bubbled PBS) has been shown to induce a strong stress response in cultured cells. This is reflected, for example, by the expression of stress genes such as c-fos and haem oxygenase, a transient decrease in the translation efficiency and the induction of cell cycle arrest. In these studies, peroxynitrite, the reaction product of nitric oxide (NO) and superoxide (O2-·), was identified as an active principle formed by CS in aqueous solutions. In the present study, we show that the CS-induced stress response is critically dependent on the intracellular glutathione (GSH) content which itself becomes diminished in cells exposed to smoke-bubbled PBS. Investigations using c-fos expression as a measure for cellular stress revealed a direct correlation between the smoke-bubbled PBS concentration necessary for stress-dependent c-fos expression and the intracellular GSH concentration observed in different cell lines. Correspondingly, 3T3 fibroblasts artificially depleted of GSH by pretreatment with buthionine-sulphoximine (BSO), an inhibitor of GSH synthesis, require significantly lower amounts of smoke-bubbled PBS to obtain a detectable c-fos expression, whereas, supplementation of the medium with N-acetyl-cysteine is an efficient treatment for the inhibition of a CS-induced c-fos response. We also show that the smoke-bubbled PBS-dependent loss of intracellular GSH is mainly attributable to the aldehyde fraction of CS, although these aldehydes by themselves cannot induce c-fos in these cells. The smoke-bubbled PBS-dependent c-fos response can, however, be mimicked when peroxynitrite and CS-related aldehydes, at the concentrations calculated to appear in smoke-bubbled PBS, are used in combination for cell exposure. Taken together, these results suggest that in cells exposed to aqueous extracts of CS, smoke-related aldehydes decrease the intracellular GSH content significantly, allowing peroxynitrite to interfere with specific target molecules resulting in the stress-specific expression of c-fos.