Neuroinflammatory profiles and cellular localization of TNF-α associated with chronic vanadium neurotoxicity.

Vanadium, an environmental pollutant, is closely associated with neurodegeneration, primarily through oxidative damage and chronic neuroinflammation. While chronic inflammation, including tumour necrosis factor-alpha (TNF-α) upregulation has been implicated in stimulating or exacerbating neuronal damage in vanadium-induced neurotoxicity, the relative cellular specificity and pathogenic mechanisms underlying cellular cytotoxicity leading to their dysfunction and death remains poorly understood. In this study, we investigated chronic inflammatory profiles in vanadium-induced neuropathology, focusing on TNF-α expression and its cellular localization in neurons and glia cells. Four weeks old male BALB/c mice randomly divided into 3 groups were used in 18 months of experiments. Vanadium treated (sodium metavanadate 3mg/kg, intraperitoneally, i.p., 0-18 months), matched controls (sterile water volume matched with vanadium treated i.p., 0-18 months), and withdrawal group (sodium metavanadate 3mg/kg, i.p., 0-3 months, and were withdrawn from treatment). Treatments were done at 72-hour intervals in all groups. Mice were sacrificed and brain tissues collected. Sagittal sections of paraffin-embedded brain tissues were prepared and analyzed using immunofluorescence to probe for microglia (Iba1), astrocytes (GFAP) and neurons (NeuN) expression. Double immunofluorescence labelling was employed to study the immunoreactivity and cellular localization of TNF-α. Mean densitometric scores and stereological data were analyzed using descriptive statistics and ANOVA at α = 0.05. Our data revealed prolonged vanadium exposure for 6 to 18 months induced chronic inflammation, evidenced by functional astrocytic and microglial activation, and progressive increase in TNF-α expression in the frontoparietal cortices, and the dorsal CA1 and CA3 regions. TNF-α immunoreactivities were predominantly seen in astrocytes and neurons, but less in microglia. Double immunolabeling with glial cells (Iba1, GFAP) and neuronal markers (NeuN) showed neuronal degeneration with marked cell loss and functional gliosis at the sites of TNF-α immunoreactivity. The severity of glial activation, TNF-α expression and neuronal loss progressively increased with the duration of vanadium exposure. Notably, these pathologies were significantly attenuated after vanadium withdrawal. Our findings indicate that chronic vanadium neurotoxicity causes neuronal loss through oxidative damage, abnormal glial activation and TNF-mediated cell death.