Four di-O-caffeoyl quinic acid derivatives from propolis. Potent hepatoprotective activity in experimental liver injury models

The water extract of propolis (PWE) showed a strong hepatoprotective activity against CCl₄-toxicity in rats and D-galactosamine (GaIN)/lipopolysaccharide (LPS)-induced liver injury in mice. The PWE also showed a significant hepatoprotective activity against CCl₄-induced liver cell injury in cultured rat hepatocytes. The in vitro hepatoprotective activity guided fractionation and chemical analysis led to the isolation of four dicaffeoyl quinic acid derivatives from the PWE. The structure of these isolates was determined to be methyl 3,4-di-O-caffeoyl quinate (1), 3,4-di- O-caffeoyl quinic acid (2), methyl 4,5-di-O-caffeoyl quinate (3), and 3,5- di-O-caffeoyl quinic acid (4) by spectroscopic methods. These compounds were more potent hepatoprotective agents than glycyrrhizin at a concentration of 10 μg/ml and 1 was the most potent among the four compounds in the cultured hepatocytes. Quinic acid (5) alone did not show hepatoprotective effects in cultured rat hepatocytes against CCl'₄-toxicity. On the other hand, chlorogenic acid (6) or caffeic acid alone was found to be less potent than the dicaffeoyl quinic acid derivatives.