Substance abuse is a risk factor for HIV infection and progression to AIDS. Recent evidence establishes that cocaine use promotes brain perivascular macrophage infiltration and microglia activation. The lysosomal protease cathepsin B is increased in monocytes from patients with HIV dementia and its secretion induces 10-15% of neurotoxicity. Here we asked if cocaine potentiates cathepsin B secretion from HIV-infected monocyte-derived macrophages (MDM) and its effect in neuronal apoptosis. Samples of plasma, CSF, and post-mortem brain tissue from HIV positive patients that used cocaine were tested for cathepsin B and its inhibitors to determine the in vivo relevance of these findings. MDM were inoculated with HIV-1ADA, exposed to cocaine, and the levels of secreted and bioactive cathepsin B and its inhibitors were measured at different time-points. Cathepsin B expression (p<0.001) and activity (p<0.05) increased in supernatants from HIV-infected cocaine treated MDM compared with HIV-infected cocaine negative controls. Increased levels of cystatin B expression was also found in supernatants from HIV-cocaine treated MDM (p<0.05). A significant increase in 30% of apoptotic neurons was obtained that decreased to 5% with the specific cathepsin B inhibitor (CA-074) or with cathepsin B antibody. Cathepsin B was significantly increased in the plasma and post-mortem brain tissue of HIV/cocaine users over non-drug users. Our results demonstrated that cocaine potentiates cathepsin B secretion in HIV-infected MDM and increase neuronal apoptosis. These findings provide new evidence that cocaine synergize with HIV-1 infection in increasing cathepsin B secretion and neurotoxicity.

BACKGROUND HIV-1-infected mononuclear phagocytes release soluble factors that affect the homeostasis in tissue. HIV-1 can prompt metabolic encephalopathy with the addition of neuronal dysfunction and apoptosis. Recently, we reported that HIV-1 enhances the expression and secretion of bioactive cathepsin B in monocyte-derived macrophages, ultimately contributing to neuronal apoptosis. In this research, we request if microglia respond to HIV infection similarly by modifying the expression, secretion, neurotoxic potential of cathepsin B and the in vivo relevance of these findings. METHODS HIV-ADA infected human primary microglia and CHME-5 were assessed for expression and activity of cathepsin B, its inhibitors, cystatins B and C, and neurotoxicity associated with these changes. Human primary neurons were exposed to supernatants from HIV-infected and uninfected microglia in the presence of cathepsin B inhibitors and apoptosis was assessed by TUNEL. Microglial expression of cathepsin B was validated in brain tissue from HIVE patients. RESULTS HIV-infected microglia secreted significantly greater levels of cathepsin B, cystatin B, and cystatin C compared to uninfected cells. Increased apoptosis was observed in neurons exposed to supernatants from HIV-1 infected microglia at days 12 post-infection. The cathepsin B inhibitor CA-074 and cathepsin B antibody prevented neuronal apoptosis. Increased microglia-derived cathepsin B, cystatin B, and cystatin C and caspase-3+ neurons were detected in HIVE brains compared to controls. CONCLUSIONS Our results suggest that HIV-1-induced cathepsin B production in microglia contributes to neuronal apoptosis and may be an important factor in neuronal death associated with HIVE.