Recent clinical studies have found that HIV infection of the central nervous system results in neurologic dysfunction termed HIV-1 associated dementia. The pathogenesis of HIV-1 associated dementia from HIV-l-induced neurotoxicity is not clear, but lt is unlikely that direct infection of neurons is responsible for the neurologic deficits commonly associated with HIV-1 infection of the CNS. In fact, HIV-1 infected neurons have been demonstrated in only one postmortem case, but there is no evidence that neurons are productively infected. Rather the macrophages and microglial cells of the CNS are the predominant cell types productively infected with HIV-1. Many investigators have proposed that the effects of HIV-1 in the CNS at the clinical and histological levels are indirect through the induction of such cytokines as tumor necrosis factor alpha (TNFa) and the phospholipid mediator platelet activating factor (PAF). It has also been suggested that PAF and TNFa may lead to an autocrine feedback loop involving further HIV replication and induction of other cytokines. The neurotoxic effects of TNFa have recently been implicated in primary human neuronal cultures with this effect being mediated by activation of the glutamate AMPA receptor subtype. Our goal is to develop a model utilizing cell cultures to further study the mechanisms that mediate the effects of TNFa and other cytokines on the neurotoxicity of HI infection. The methods used were an M'TT assay to assess neurotoxicity. Briefly, this assay depends on enzymatic reduction of 3-(4,5-dimethylthiazol-2 yl)-2,5-diphenyl tetrazolium bromide (MTT1 in viable cells to yield a product that can be quantified colorimetrically. MTT assays of human neural SK-N-MC cells and primary human cortical neurons treated with varying doses of TNFa up to 25 ng/ml, demonstrate a dose dependent drop in viability of <67%. SK-N-MC cultures showed a similar response when treated with the HIV-1-induced neurotoxins TNFa and PAF. Similar studies with human neuronal cultures ad aggregates are in progress. These experiments suggest that TNFa along with other cytokines and arachidonic acid metabolites may be indirectly responsible for neurotoxic effects seen on the SK-N-MC neuroblastoma cell line and primary human cortical neurons following treatment with HIV-1-induced neurotoxins.
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