Insulin is important for brain function and neuronal survival. Insulin signaling is initiated by the phosphorylation of insulin receptor substrate‐1 (IRS‐1) at tyrosine (pTyr) residue. However, IRS‐1 is inhibited by phosphorylation at serine (pSer). In Alzheimer's disease (AD), oxidative stress and accumulation of amyloid beta (Aβ) induce neuroinflammation, which augments pSer‐IRS‐1 and reduces pTyr‐IRS‐1 disturbing insulin signaling pathway. Coenzyme Q10 (CoQ10) and biotin possess antioxidant and anti‐inflammatory properties, and, in this study, their impact on insulin signaling is investigated in an aluminium chloride (AlCl3) model of AD. AD was induced by oral administration of AlCl3 (75 mg/kg) for 60 days. Biotin (2 mg/kg), CoQ10 (10 mg/kg), and their combination were supplemented concomitantly with AlCl3 for 60 days. Memory test and histological examination were performed. Brain levels of lipid peroxides, antioxidants (reduced glutathione and superoxide dismutase), inflammatory markers (tumor necrosis factor‐α, interleukin‐6 [IL‐6], IL‐1, and nuclear factor κB), and phosphorylated Akt (survival kinase) as well as protein levels of Aβ, IRS‐1 (pTyr and pSer), and caspase‐3 (apoptotic marker) were determined. AlCl3 resulted in impaired memory, significant increase in Aβ, lipid peroxides, inflammatory markers, caspase‐3, and pSer‐IRS‐1, with significant reduction of the antioxidants, pTyr‐IRS‐1, and p‐Akt reflecting Aβ‐induced inflammation and defective insulin signaling. Histological examination revealed focal aggregations of inflammatory cells and neuronal degeneration. The biochemical deviations and histological changes were attenuated by the concomitant treatment with biotin and, to greater extent, with CoQ10 and the combination. In conclusion, biotin and CoQ10 could protect against AD via attenuating inflammatory response and enhancing insulin signaling.

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CAR and CyA exerted a synergistic neuroprotective effect against CHI through blocking the induction of lipid peroxidation, reducing inflammatory, and oxidative stress biomarkers, preserving brain GSH content, and reducing the alterations in brain apoptotic biomarkers in traumatized animals.

Transforming growth factor-β (TGF-β1) enhances the expression of apoptosis induced by certain cytokines and oncogenes. Activation of small mother against decapentaplegic (Smads) by TGF-β results in fibrotic, apoptotic processes. PI-3/AKT focal adhesion kinase-phosphatidylinositol3-kinase (AKT), the mitogen-activated protein kinase (MAPK) and signal transducer and activator of transcription-3 (STAT3) pathways are influence in COX-2 and VEGF-stimulating pathways. NF-E2-related factor-2 (Nrf2) is an essential transcription factor that regulates an array of detoxifying and antioxidant defense genes expression in the liver. The objective of this study is to examine whether silymarin alone or in combination with vitamin E and/or curcumin plays a modulatory role against MAPK, STAT3, AKT, Smad-2 and TGF-β protein expressions that produced apoptotic damage in rat's liver by the administration of carbon tetrachloride (CCl4). The results of the present work revealed that CCl4-induced an elevation of serum alanine aminotransferase (ALT) with concomitant increase in MAPK, STAT3, AKT, Smad-2 and TGF-β hepatic protein expression, administration of silymarin alone down regulates these expressions. Treatment with vitamin E and/or curcumin along with silymarin produced best results in this concern. On the other hand, Nrf2 protein expression was down regulated by CCl4 whereas concurrent treatment with vitamin E and/or curcumin along with silymarin increased this expression. It was concluded that CCl4-induced protein expression of apoptotic and fibenorgenic factors. Whereas administration of silymarin alone or in combination with vitamin E and/or curcumin plays a modulatory role against the previous aforementioned apoptotic factors expressions. The use of vitamin E and/or curcumin potentiates the anti-apoptotic action of silymarin. So this combination can be used as hepatoprotective agent against other hepatotoxic substances.

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