Alteration of superoxide- and nitric oxide-mediated antimicrobial function of macrophages by in vivo cocaine exposure

Abstract

Cocaine is a popular drug of abuse and despite impressive advances in the understanding of its physiological, pharmacological, and toxic effects, its mechanism of immunosuppression at the cellular level is not well understood. In this paper we report the role of effector molecules like superoxide and nitric oxide in the antibacterial function of macrophages exposed to acute and chronic doses of cocaine in vivo. Bacterial killing by acute cocaine-exposed macrophages (ACE-Mφs) increased significantly, with a concomitant rise in respiratory burst and generation of superoxide and nitric oxide, compared with control macrophages. In contrast, chronic cocaine-exposed macrophages (CCE-Mφs) exhibited limited antimicrobial activity, which correlated closely with diminished respiratory burst and reduced production of superoxide and nitric oxide. Further, a killing assay was carried out in the presence of NG-methyl-l-arginine acetate, an inhibitor of iNOS, to evaluate the role of nitric oxide in the killing process. The results obtained indicate that while about 30% killing of input bacteria by control and ACE-Mφs was attributable to NO-mediated killing, only about 6% killing from NO was found with CCE-Mφs. The findings indicate that acute exposure to cocaine possibly caused upregulation of enzymes responsible for the generation of ROI (reactive oxygen intermediates) and RNI (reactive nitrogen intermediates), leading to enhanced antimicrobial function. On the other hand, chronic exposure to cocaine impaired the oxygen-dependent microbicidal capacity of macrophages, possibly through impaired expression of enzymes responsible for ROI and RNI formation. Proinflammatory cytokines may play a key role in cocaine-mediated immunosuppression, since exposure of macrophages to cocaine impairs the ability of the cells to produce these cytokines.