Glycyrrhizin Attenuates MPTP Neurotoxicity in Mouse and MPP-Induced Cell Death in PC12 Cells

Abstract

The present study examined the inhibitory effect of licorice compounds glycyrrhizin and a metabolite 18beta-glycyrrhetinic acid on the neurotoxicity of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in the mouse and on the 1-methyl-4-phenylpyridinium (MPP(+))-induced cell death in differentiated PC12 cells. MPTP treatment increased the activities of total superoxide dismutase, catalase and glutathione peroxidase and the levels of malondialdehyde and carbonyls in the brain compared to control mouse brain. Co-administration of glycyrrhizin (16.8 mg/kg) attenuated the MPTP effect on the enzyme activities and formation of tissue peroxidation products. In vitro assay, licorice compounds attenuated the MPP(+)-induced cell death and caspase-3 activation in PC12 cells. Glycyrrhizin up to 100microM significantly attenuated the toxicity of MPP(+). Meanwhile, 18beta-glycyrrhetinic acid showed a maximum inhibitory effect at 10microM; beyond this concentration the inhibitory effect declined. Glycyrrhizin and 18beta-glycyrrhetinic acid attenuated the hydrogen peroxide- or nitrogen species-induced cell death. Results from this study indicate that glycyrrhizin may attenuate brain tissue damage in mice treated with MPTP through inhibitory effect on oxidative tissue damage. Glycyrrhizin and 18beta-glycyrrhetinic acid may reduce the MPP(+) toxicity in PC12 cells by suppressing caspase-3 activation. The effect seems to be ascribed to the antioxidant effect.

Keywords: Brain tissue damage; Cell death; Glycyrrhizin; Inhibitory effect; MPP+; MPTP.

Fig. 1

Effect of licorice compounds on MPP⁺-induced cell death. PC12 cells were pre-treated with licorice compounds (1~100µM GL in A or 1~25µM GA in B) for 20 min, exposed to 500µM MPP⁺ for 24 h and cell viability was determined. Data represent means ± SEM (n=6). ⁺p<0.05 compared to control (percentage of control); and ^*p<0.05 compared to MPP⁺ alone.

Fig. 2

Effect of licorice compounds on MPP⁺-induced activation of caspase-3. PC12 cells were treated with 500µM MPP⁺ in the presence of licorice compounds (10~50µM) or scavengers [1 mM N-acetylcysteine (NAC), 30µM trolox or 30 µM carboxy-PTIO (PTIO)] for 24 h. Data are expressed as units for caspase-3 activity and represent means ± SEM (n=6). ⁺p<0.05 compared to control; and ^*p<0.05 compared to MPP⁺ alone.

Fig. 3

Effect of licorice compounds on cell death due to hydrogen peroxide or 3-morpholinosydnonime. PC12 cells were pre-treated with licorice compounds [1~50µM GL (A) or 1~10µM GA (B)] for 15 min, exposed to 200µM hydrogen peroxide for 4 h or 750µM 3-morpholinosydnonime for 24 h, and cell viability was determined. Data represent means ± SEM (n=6). ⁺p<0.05 compared to control; and ^*p<0.05 compared to hydrogen peroxide (HP) or 3-morpholinosydnonime (SIN).