- Background: Antiretroviral therapy is frequently associated with adverse metabolic effects and lipodystrophy, but the role of HIV protease inhibitors and the mechanisms involved are poorly understood. The HIV protease inhibitor nelfinavir (NFV) impairs insulin signal propagation by inducing similar signalling defects to those induced by exposure to oxidative stress. Aim: We set out to determine if oxidative stress is involved in NFV-induced insulin resistance in 3T3-L1 adipocytes, and whether antioxidant agents with unique modes of action can prevent this effect. Results: Cells exposed to NFV exhibited the following markers of increased oxidative stress: a decrease in both total and low molecular weight reduced thiols, a 20-fold increase in haem oxygenase 1 (HO-1) mRNA, an increase in intracellular reactive oxygen species production (determined by 2',7'-dichlorofluorescein fluorescence), and increased markers of apoptosis. Enhancing cellular thiols with N-acetylcystein prevented the NFV-induced drop in reduced thiols and partially protected against the induction in HO-1, but failed to prevent insulin resistance or cleavage of poly ADP ribose polymerase (PARP), a process indicative of activation of pro-apoptotic caspases. Conversely, the superoxide dismutase-mimetic antioxidant MnTBAP had no effect on cellular thiols in response to NFV, but protected against HO-1 induction and against the impairment in insulin-stimulated Akt/protein kinase B activation and PARP cleavage. Conclusions: Induction of oxidative stress plays a role in adipocyte insulin resistance and apoptosis induced by NFV through a radical-dependent but thiol-independent mechanism(s). The results may suggest a new mechanism for the adverse effects of NFV on fat cells, and offer potential new intervention approaches.