Comparative studies of the stereoisomers of glycyrrhetinic acid on anti-inflammatory activities.

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Abstract
Anti-inflammatory activity of the stereoisomers, 18.alpha. and 18.beta.-glycyrrhetinic acid (18.alpha. and 18.beta.-GA), obtained from Glycyrrhizae Radix [the root of Glycyrrhiza glabra] was investigated using carrageenan-induced edema in mice and 18.alpha.-GA was found to be more active than 18.beta.-GA. Therefore, to clarify the difference of action of 18.alpha. and 18.beta.-GA, the inhibitory effects of both stereoisomers on the cotton pellet granuloma formation in adrenalectomized rats and on the reduction of steroidal compounds by .DELTA.4-5.beta.-reductase in the microsome fraction of rat liver were investigated. 18.alpha.-GA, 30 mg/kg (orally), showed the similar antigranulomatous action in normal and adrenalectomized rats. On the other hand, 18.beta.-GA, 30 mg/kg (orally), which exhibited the inhibitory effects in normal rats, showed no action in adrenalectomized rats. More than 50% of inhibitory effects of 18.alpha. and 18.beta.-GA on the 5.beta.-reduction of testosterone and cortisol were recognized by an equimolar ratio of steroids to 18.alpha. or 18.beta.-GA. From these results, the activity of 18.alpha.-GA is similar to that of glucocorticoid and the difference of action between 18.alpha.-GA and 28.beta.-GA could be explained by its stereochemical structure of D/E trans conformation. In addition to the glucocorticoid action, 18.alpha.-GA inhibited the inactivation of endogenous glucocorticoid in liver, which is also recognized by the application of 18.beta.-GA.