Macrophages (MOs) play a critical role in the pathogenesis of HIV infection, both as targets for viral replication and as sources of multifunctional cytokines. We have previously reported that 1) the HIV-1 envelope glycoprotein, gp120, stimulates secretion of the potent vasoconstrictive peptide, endothelin-1 (ET-1), from human macrophages in a concentration-dependent manner, 2) that circulating monocytes in HIV-infected individuals express the ET-1 gene, while cells from healthy controls do not, 3) and that cerebral macrophages in patients with HIV-encephalopathy are positive for ET-1. Thus, monocyte-derived ET-1 appears to be stimulated during HIV infection and the potent vasoactive properties could potentially mediate alterations in the cerebral perfusion pattern associated with AIDS dementia complex. Our studies looking at the effect of HIV infection on both constitutive and stimulated production of ET-1 by human MOs suggest that infection with macrophage tropic HIV-1 isolates neither induces secretion of ET-1 nor potentiates its production by a known inducer, LPS. This analysis is being expanded to include neurotropic HIV isolates that are also macrophage tropic. In addition, mRNA prepared from HIV-infected and uninfected MOs at various times following infection are being examined using RT-PCR techniques to determine whether the genes for ET-1 and/or nitric oxide synthase (NOS), an enzyme responsible for production of the potent vasodilator, NO, are expressed. To further clarify the pathogenesis of HIV-associated cognitive/motor complex, we examined the neurotoxicity of supernatants from HIV-infected MOs and the relationship between HIV-infected MOs and astrocytes. Our preliminary data using human neuronal (NT2) and neuroblastoma (SK-M-NC) cells suggest that supernatants from HIV-infected MOs are not directly toxic to differentiated neurons. In contrast, HIV-infected MOs co-cultured in vitro with U373 human astrocytoma cells caused multiple acellular areas to appear in the cell monolayers, while uninfected MOs had no detrimental effects. These latter findings are consistent with the pathologic changes observed in vivo, in which HIV-infected MOs are surrounded by focal rarefaction in the brain. Intriguingly, the presence of U373 astrocytic cells suppressed HIV replication in MOs, suggesting that astrocytes could potentially inhibit the spread if HIV in the brain in vivo. Studies are ongoing to ascertain whether the effects observed in the astrocyte studies are mediated by cellular- or viral-derived soluble factors and, if so, to determine both the source and identity.
