The protective effect of pyrroloquinoline quinone and its derivatives against carbon tetrachloride-induced liver injury of rats.

Pyrroloquinoline quinone (PQQ) and its derivative, oxazo pyrroloquinoline (OPQ-G), protected rats from experimental liver injury induced by carbon tetrachloride (CCl4) in vivo. This effect was observed after an intraperitoneal injection of 5 mg/kg PQQ or OPQ-G, which was given twice, 10 min and 1 h before CCl4 administration. Pyrroloquinoline quinone protected primary cultured rat hepatocytes from CCl4 toxicity in vitro. This protection was most effective at a concentration of 3 mumol/L PQQ. Pyrroloquinoline quinone derivatives (oxazo pyrroloquinoline, methyl-thioethyl oxazo pyrroloquinoline and PQQ-allylester) also protected the hepatocytes from CCl4 toxicity. Pyrroloquinoline quinone and its derivatives inhibited the lucigenin-enhanced chemiluminescence from isolated hepatocytes initiated by CCl4. These results suggest that eliminating free radicals is one of the protective mechanisms of PQQ and its derivatives against CCl4-induced liver injury.