Pharmacokinetics in Vitro and in Vivo of Two Novel Prodrugs of Oleanolic Acid in Rats and Its Hepatoprotective Effects against Liver Injury Induced by CCl4

Oleanolic acid (OA) is a well-known pentacyclic triterpenoid compound, which has been used as a dietary supplement and is supplied as an over-the-counter drug for the treatment of human liver diseases. These are reasons for the low bioavailability of OA which have restricted its wider application. In this study, two OA prodrugs (1,3-cyclic propanyl phosphate esters of OA) were designed and synthesized. The hepatoprotective effects of these prodrugs were evaluated against carbon tetrachloride (CCl4) induced liver injury in mice; the levels of alanine aminotransferase (ALT), lactic dehydrogenase (LDH), and aspartate aminotransferase (AST) were significantly increased, and the level of the hepatic malondialdehyde (MDA) was increased. The metabolism, in vitro, of the prodrugs was studied by incubation in rat liver microsome; the plasma pharmacokinetics and the biodistribution in vivo after intravenous (iv) injection to six rats were investigated, respectively. The prodrugs diminished gradually with time; most of the parent drugs were released within 30 min in vitro, and the presumed mechanism of the in vitro metabolism was confirmed. The plasmaconcentration data in vivo was analyzed by a compartmental method: both the prodrugs and the corresponding released parent drugs existed at up to 48 h in rats. The t1/2 improved after intravenous administration in rats compared with direct injection of the parent drugs. All analyte concentrations were highest in the liver, and most of the prodrugs were excreted in feces (>47.11%). Therefore, 1,3-cyclic propanyl phosphate esters of OA can serve as a promising lead candidate for drugs.