Neuroprotective effects of roasted licorice, not raw form, on neuronal injury in gerbil hippocampus after transient forebrain ischemia

Aim: To observe neuroprotective effects of raw and roasted licorice against hypoxia and ischemic damage. Methods: When elucidating the protective effects of raw and roasted licorice, we analyzed the lactate dehydrogenase (LDH) release using PC12 cells after hypoxia in an in vitro study and after transient forebrain ischemia in an in vivo study on Mongolian gerbils. Results: Raw and roasted licorice significantly reduced LDH release from PC 12 cells exposed to an hypoxic chamber for 1 h. In the roasted licorice-treated group, the decrease of LDH release was more pronounced compared to that of the raw licorice-treated group. In roasted licorice-treated animals, approximately 66%-71% of CA1 pyramidal cells in the ischemic hippocampus were stained with cresyl violet compared to the control group. However, in the raw licorice-treated animals, no significant neuroprotection against ischemic damage was shown. In addition, ischemic animals in roasted licorice-treated group maintained the Cu, Zn-superoxide dismutase (SOD1) activity and protein levels compared to the control group, while in raw licorice-treated group SOD1 activity and protein levels were reduced significantly. High pressure liquid chromatography analysis showed that non-polar compounds containing glycyrrhizin-degraded products, such as glycyrrhetinic acid (GA) and glycyrrhetinic acid monoglucuronide (GM), were increased in roasted licorice. Conclusion: Roasted licorice had neuroprotective effects against ischemic damage by maintaining the SOD1 levels. In addition, the difference in protective ability between raw and roasted licorice may be associated with non-polar compounds, such as GA and GM.