Introduction: Acute alcohol consumption leads to induction of lipid peroxidation in renal tissues, but its chronic consumption has moderate effects on biochemical and histological characteristics of this organ. Antioxidants have protective effects against ethanol-induced oxidative stress and tissue injury. The aim of this study was to assess antioxidant activity of Glycyrrhiza glabra leaf and stem extracts and the protective effect of its leaf extract on ethanol-induced nephrotoxicity.
 
Materials & methods: Total phenol and flavonoid contents of leaf and stem extracts of G. glabra were measured by Folin Ciocalteu and AlCl₃ assays, respectively. Antioxidant activity of both extracts was assessed using 2, 2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging. In addition, protective effect of the leaf extract was assessed using biochemical and histological analyses of renal tissues of male Wistar rats, which were divided into four groups including group 1 or control (received 1 ml distilled water daily), group 2 or ethanol group (received 1 ml of 50% ethanol daily), group 3 or ethanol + leaf extract group (received 1 ml of 50% ethanol + 500 mg/kg leaf extract daily), and group 4 (received 500 mg/kg of leaf extract daily). All treatments are performed through intragastric administration. Biochemical and histological analyses were used for the evaluation of nephrotoxicity. For histological study, the samples were stained with Hematoxylin-Eosin and examined by light microscopy. Finally, all the data were analyzed by SPSS (Ver. 20) and grouped by Duncan's Multiple Range Test at P <0.05 level.
 
Findings: There was no significant difference between total phenol contents of the stem and leaf extracts. However, the stem extract showed a higher total flavonoid content than the leaf extract. Also, both the extracts showed higher antioxidant activities (86-93%) than that of ascorbic acid (71%). Results from biochemical analysis indicated a significant increase in superoxide dismutase (SOD) activity and H₂O₂ content in the renal tissues of ethanol-treated rats in comparison with other groups; however, there were no significant changes in total protein and malondialdehyde (MDA) contents. Results from histological examination showed that alcohol consumption intensity injured kidney tissues, which was effectively moderated by the studied extract.
 
Discussion & Conclusions: Results from the present study showed that G. glabra extract has biological activity and can be used in future as a new natural antioxidant in food and drug industries.