599. Neuron Loss Mediated by HIV-1 gp120 In Vivo: Neuroprotection Using SV40 Gene Transfer of Antioxidant Enzymes

Top of pageAbstract Neuronal loss in the brain of patients with HIV-associated dementia has been partly linked to neurotoxic effects of HIV-1 envelope glycoprotein, gp120. However, conflicting results are reported as to the role of this protein in vivo. The goal of this study was to devise an animal model to study gp120-induced CNS lesions and apply this model to developing new approaches to therapy. To test gp120-induced neuronal damage, different doses of g120 (100 ng/microl, 250 ng/microl, 500 ng/microl) were injected unilaterally into the caudate-putamen (CP) of the rat brain stereotaxically. Saline was used as the negative control, as was the contralateral side of the unilaterally injected brains. Brains were harvested 1, 2, 4, 7 and 14 days after the injection and were processed for histologic staining (Neutral red-NR, Neurotrace-NT, a marker of neurons) and immunochemistry (markers of neurons: neuN, DAT; astrocytes: GFAP; microglial cells: C3bi, CD68). Examination of NR-stained cryostat sections of the brain 2 days after injection of 250 ng/microl and 500 ng/microl gp120 into the CP showed an area of tissue loss centered on the injection site and extending several micrometers rostrally and caudally. Injection of 100 ng/microl gp120 induced minimal lesion. Morphometric analysis measured the extent of tissue damage/loss on NR-stained sections (about 25% 14 days after injection of 500 ng/microl gp120 into the CP) and of neuronal loss on sections stained with NT and immunostained for neuN (about 30% after injection of 500 ng/microl gp120 in the CP, 7 and 14 days after injection). A 50% reduction in DAT-positive cells was also observed. Neuron loss was minimal after injection of 100 ng/microl, and intermediate with 250 ng/microl gp120. Seven and 14 days after injection of 500 ng/microl gp120, GFAP-positive cells were far more numerous on the injected side, than on the contralateral side, suggesting proliferation of astrocytes at the edge on the injured area. C3bi/CD11b-positive microglial cells were more numerous between d1 and d7, while ED1/CD68-positive microglial cells were more frequently seen 7 and 14 days after the injection. We tested whether gene transfer of the anti-oxidant enzymes Cu/Zn superoxidase dismutase (SOD1) and glutathione peroxidase (GPx1) into the CP could protect against injury induced by gp120. SV40-derived vectors were used for this purpose because of their high transduction efficiency for neurons and the durability of transgene expression conferred by these vectors. Administration of SV(SOD1) or SV(GPx1) into the CP 2 or 4 weeks before injection of 500 ng/microl gp120 in the same structure significantly reduced the extent of the injury. Thus HIV-1 gp120 can induce extensive neuronal loss and some associated events, which damage can be limited by SV40 vector- mediated gene transfer of antioxidant enzymes. Therapy of HIV-1 encephalopathy is one area of antiretroviral treatment that is not well understood. Our data suggest that there may be a role for gene delivery in the prophylaxis of HIV-1-induced CNS disease.