Differential anti-inflammatory and anti-oxidative effects of dexamethasone and N-acetylcysteine in endotoxin-induced lung inflammation

Inhalation of bacterial endotoxin induces an acute inflammation in the lower respiratory tract. In this study, the anti-inflammatory effects of the anti-oxidant N-acetylcysteine (NAC) and the glucocorticoid dexamethasone were investigated in mice exposed to aerosolized endotoxin (lipopolysaccharide (LPS)). Powerful reduction of neutrophils in bronchoalveolar lavage fluid (BALF) was obtained by a single i.p. injection of dexamethasone (10 mg/kg), whereas treatment with NAC only resulted in reduction of neutrophils when administered at a high dose (500 mg/kg). Measurement of cytokine and chemokine expression in lung tissue revealed a significant decrease of tumour necrosis factor-alpha, IL-1 alpha, IL-1 beta, IL-6, IL-12p40, and MIP-1 alpha mRNA when mice where treated with dexamethasone but not when treated with NAC. Analysis of oxidative burst demonstrated a remarkable reduction of oxygen radicals in BALF neutrophils after treatment with dexamethasone, whereas the effect of NAC was not significantly different from that in untreated animals. In conclusion, dexamethasone exerted both anti-inflammatory and anti-oxidative effects in acute airway inflammation, probably by blocking early events in the inflammatory cascade. In contrast, treatment with NAC resulted in a weak reduction of the inflammatory response but no inhibition of proinflammatory cytokines or reduction of oxidative burst in neutrophils. These results demonstrate dramatic differences in efficiency and also indicate that the two drugs have different actions. Combined treatment with NAC and dexamethasone revealed an additive action but no synergy was observed.