Rhein: an anthraquinone that modulates superoxide anion production from human neutrophils

Rhein (4,5‐dihydroxyanthraquinone‐2‐carboxylic acid), the active metabolite of diacetylrhein, which has been reported as an effective antirheumatic drug in man, inhibited superoxide anion production from human neutrophils challenged with N‐formylmethionyl‐leucyl‐phenylalanine (FMLP: IC50, 2 times 10⁻⁵_M) and A23186 (IC50, 10⁻⁵_M), but not with phorbol myristate acetate. In the same concentration range (10⁻⁶‐10⁻³_M), the drug did not affect oxy‐radical production by a cell‐free hypoxanthine‐xanthine oxidase system and exerted weak inhibitory effects on FMLP‐evoked lysosomal enzyme release. Rhein inhibitory effects on neutrophil functioning may contribute to the overall therapeutic activity of the parent drug, diacetylrhein. 1987 Royal Pharmaceutical Society of Great Britain