Protective effects of roasted licorice on neuronal injury after transient forebrain ischemia in the gerbil hippocampus

Abstract

Licorice, the root part of species of the genus Glycyrrhiza (Leguminosae), is an extensively used herbal drug in Western and Eastern medicine. In traditional Chinese formulations, it is mainly roasted licorice that has been used rather than raw licorice. We have compared the chemical components and neuroprotective effects of licorice before and after roasting to clarify the pharmaceutical significance of the roasting. We used Glycyrrhiza inflata Bat. one of major licorice from China. Roasting licorice at 150–250 °C for 20–100 min resulted in the conversion of glycyrrhizin to glycyrrhetic acid and glycyrrhetic acid monoglucuronide. To examine whether roasted licorice ethanol extract (rLee) exhibits neuroprotective effects, transient forebrain ischemia was induced in gerbils by blocking both common carotid arteries for 5 min. The neuroprotective effect was evaluated by measuring cresyl violet positive pyramidal cells (CVPPC) in the CA1 region at 5 days after ischemia / reperfusion. The percentage of CVPPC in transient forebrain ischemia group was decreased by 89% compared to that of the sham-operated group. Neuronal cell density in rLee-treated ischemic animals was significantly increased compared to vehicle-treated ischemic animals, whereas raw licorice ethanol extract had no effect. In the rLee-treated ischemic group (50 mg / kg, po), the numbers of CVPPC were approximately 66% of those in the vehicle-treated control group. This result suggests that the rLee may be applicable to protective foods against ischemic damage.