Background: Dysfunction in mononuclear phagocyte (MP, macrophages and microglia) immunity is thought to play a significant role in the pathogenesis of HIV-1 associated dementia (HAD). In particular, elevated extracellular concentrations of the excitatory transmitter glutamate produced by MP, as a consequence of viral infection and immune activation, can induce neuronal injury. Methods: To determine the mechanism by which this neuronal injury occurs, the concentration and rates of production of extracellular glutamate were measured in human monocyte-derived macrophage (MDM) supernatants by reverse phase high performance liquid chromatography (RP-HPLC). Measurements were taken from supernatants from MDM infected with multiple HIV-1 strains including IIIB (lymphocyte tropic, T-tropic), ADA, JR-FL, Bal and DJV (macrophage tropic, M-tropic), and 89.6 (dual tropic).

Results: High rates of glutamate generation occurred from MDM infected with M-tropic viruses. AZT, an inhibitor of HIV-1 replication inhibited glutamate generation demonstrating a linkage between HIV-1 infection and increased production of glutamate. This glutamate generation was dependent on the presence of glutamine and inhibited by 6-diazo-5-oxo-l-norleucine, a glutaminase inhibitor, implicating the involvement of phosphorylated (activated) mitochondrial glutaminase (PMG) in this process. PMG was also detected in HIV-1 infected MDM. Further, supernatants removed from HIV-1 infected MP could generate more glutamate after glutamine addition than supernatants removed from uninfected MP strongly supporting the presence of and an HIV-1 mediated increase in a glutamate generating enzyme, such as PMG. Finally, the neuro toxicity induced by HIV-1 infected MDM was partially blocked by the glutamate receptor (NMDA) antagonists, AP5 and MK-801.

Conclusions: Taken together, these results demonstrate a potential role for glutaminase in the MP-mediated neuro toxicity observed in HAD.