Background:  HIV-associated sensory neuropathy is the most common neurological complication of HIV infection. The pathogenesis, however, remains unknown. The primary site is most likely at the level of the sensory neurons in the dorsal root ganglia leading secondarily to a dying back process with axonal degeneration. A consistent pathological observation in the dorsal root ganglia is the presence of activated macrophages, which express MHC antigens and cytokines. The chronic presence of these products may lead to dorsal root ganglia damage and axonal injury. We determined the effect of HIV-infected macrophages on dorsal root ganglia in vitro with focus on neurotoxic effects.

Methods:  Human dorsal root ganglia cultures were prepared from fetuses of 6 to 16 weeks gestational ages and cultured for 10 to 14 days. THP-1, a human monocytic leukemia cell line was infected with HIV-1_IIIB/LAV. The maximum p24 level was observed 13 days post-infection (p24 = 1.9 μg/mL). The culture supernatant was used for further experiments. Dorsal root ganglia cultures were exposed to varying dilutions of the HIV-1_IIIB/LAV-infected or -uninfected THP-1 supernatant for 24 hours in Locke`s buffer. Neurotoxicity was assessed by evidence of neuritic retraction (βIII-tubulin immunostaining), neuronal production of reactive oxygen species (dihydrorhodamine confocal microscopy) and neuronal DNA fragmentation (Hoechst 33342).

Results:  Exposure of dorsal root ganglia neurons to the supernatant from HIV-1_IIIB/LAV-THP-1-infected cells resulted in a significant dose-dependent neuritic degeneration (mean total neuritic length ± SEM THP-1 vs HIV THP-1 supernatant 717.8 μm ± 13.4 vs 518.4 μm ± 10.3 at 1:10 dilution and 725.9 μm ± 12.6 vs 677.8 μm ± 13.8 at 1:100 dilution, p < 0.05 t-test). An increased level of oxidative stress in the dorsal root ganglia neurons accompanied these changes as demonstrated by the finding that the supernatant from infected cells caused significantly higher dihydrorhodamine intensity at dilutions of 1:10 (mean ± SEM 84U ± 2.9 vs 109.4U ± 2.9), 1:100 (80.7U ± 3.1 vs 106.2U ± 2.5), and 1:1000 (77.3U ± 3 vs 106.9U ± 3). There was no significant increase in the number of apoptotic neuronal cells.

Conclusions: We describe an in vitro model for HIV-peripheral neuropathy in which supernatant from HIV-1-infected macrophages caused toxicity to human dorsal root ganglia neurons resulting in mitochondrial toxicity and neurite retraction without significant cell death. Thus antioxidants may have a therapeutic potential in patients with HIV-associated peripheral neuropathy.

Keywords: HIV-neuropathy; in vitro; macrophages