Bimodal effect of glycyrrhizin on macrophage nitric oxide and prostaglandin E2 production

Glycyrrhizin is a major constituent of Kanzo, a popular herbal medicine used in food and cosmetics. Glycyrrhizin alone did not stimulate nitric oxide (NO) or prostaglandin E-2 (PGE(2)) production by RAW 264.7 cells, but modified lipopolysaccharide (LPS)-stimulated NO and PGE(2) production in a bimodal fashion: it was stimulatory at lower concentrations, whereas it was inhibitory at higher concentrations. Electron-spin resonance spectroscopy showed that glycyrrhizin slightly scavenged the superoxide anion generated by hypoxanthine-xanthine oxidase reaction, but did not scavenge the DPPH and NO radicals. The present study demonstrates the concentration-dependent action of glycyrrhizin on both PGE(2) and NO production by activated macrophages.