Neuroprotective Activities of <i>Nigella sativa</i> Ethanolic Extract and Telmisartan Against Fipronil-Induced Neurotoxicity in Rats via Regulation of Apoptosis, Endosomal Micro-autophagy, and miRNA-137-5p

The purpose of our study was to investigate the neuroprotective effects of Nigella sativa (NSt) ethanolic extract (200 mg/kg) and/or Telmisartan(Tel) (10 mg/kg) against fipronil (Fip) (9.7 mg/kg)-induced neurobehavioral toxicity in rats, besides exploring the underlying mechanistic signaling pathways. Our results showed that the phytochemical analysis of NSt ethanolic extract by ultra-performance liquid chromatography-electrospray ionization-tandem mass spectrometry (UPLC-ESI-MS) revealed 43 compounds, mainly alkaloids, phenolics, terpenoids, fatty acids and flavonoids. While in our in vivo model of neurotoxicity, the combination of NSt and Tel effectively restored neurobehavioral alterations in rotarod, open field and T-maze tests. Additionally, the cotreatments of NSt and Tel significantly decreased acetylcholine, tumor necrosis factors-α, interleukin (IL)-6, IL-1β, MDA, BAX, P62, LC3B and IBA-1. Conversely, they significantly upregulated GABA, brain-derived neurotrophic factor, superoxide dismutase, catalase, glutathione peroxidase and antiapoptotic BCl2, P70S6K and miRNA137-5P without significant change in mTOR expression in hippocampus. Also, they ameliorated pathological alterations as detected by H&E staining, reduced glial fibrillary acidic protein and caspase-3 immunoreactivity. Electron microscopic examination of the combination group revealed the restoration of nuclear and mitochondrial structures with less glial activation and multivesicular bodies. In conclusion, the combination of NSt and Tel are notable agents in mitigating hippocampal neuronal necrosis and astrogliosis and reduced Fip-induced neurotoxicity.