Glycyrrhizic acid and silymarin alleviate the neurotoxic effects of aluminum in rats challenged with fructose-induced insulin resistance: possible role of toll-like receptor 4 pathway.

Aluminum is implicated in the etiology of different neurodegenerative diseases, diabetes and cancer. The current study was conducted to evaluate the protective effects of glycyrrhizic acid (GAM) and silymarin (SLY) on AlCl-induced neurotoxicity in insulin resistant rats. Insulin resistance (IR) was induced by fructose (10%) in drinking water for 18 weeks. Rats received AlCl (34 mg/kg/day) with or without fructose, GAM (40 mg/kg/day), or SLY (100 mg/kg/day). The administration of GAM or SLY suppressed AlCl-induced memory deficit, oxidative stress, and neuroinflammation in brain tissue of IR rats. Both agents inhibited AlCl-induced activation of TLR4 signaling pathway including the downstream activation of NF-κB. The results show that IR can partly exacerbate AlCl-induced neurotoxicity, particularly memory deficit and neuroinflammation. In addition, GAM and SLY showed promising neuroprotective effect against AlCl-induced brain damage in IR rats. The neuroprotection induced by these natural products might be mediated through their antioxidant and anti-inflammatory effects. The latter effect seems to be mediated via inhibition of TLR4 signaling pathway providing new insights on the mechanisms implicated in AlCl-induced neurotoxicity and the neuroprotection afforded by GAM and SLY.