Abstract
Pyrrolizidine alkaloids (PAs) are extensively synthesized by plants and are commonly present in herbs and foodstuffs, which exhibit hepatotoxicity requiring metabolic activation by cytochrome P450 (CYP) 3A to form the electrophilic metabolites-pyrrolic ester. PAs also cause embryo toxicity, but the metabolic profiles of PAs in fetus and placenta have been far from clear. In this study, we determined the basal metabolic activation of retrorsine (RTS) in rat maternal liver, placenta and fetal liver in vitro, and examined the fetal toxicity and bioactivation of RTS in vivo. Detection of microsomal RTS metabolites in vitro showed that the basal metabolic activity of fetal liver and placenta to RTS was much weaker than that of maternal liver. In addition, higher formation rate of pyrrolic ester was found in normal male fetal liver, compared with female pups. In vivo exposure to RTS caused fetal growth retardation as well as placenta and fetal liver injury. Little difference in serum RTS was observed in dams and fetuses, but the content of pyrrole-protein adduction in fetal liver was much lower than that in mother liver, which was consistent with basal metabolic activity. Unexpectedly, compared with basal metabolism in fetal liver, exposure to RTS during middle and late pregnancy caused an opposite gender difference in RTS metabolism and CYP3A expression in fetal liver. For the first time, our study proved that RTS was capable of permeating placenta barrier and entering fetal circulation, while intrauterine pyrrolic metabolite was mainly generated by fetal liver, but not transported from mother circulation. Induction of CYP3A by RTS was gender-dependent in fetal liver, which was probably responsible for RTS-induced fetal hepatic injury, especially for female pups.
- The American Society for Pharmacology and Experimental Therapeutics