Studies On Metabolism Of FR429, A Bioactive Ellagitannin From Miao Herb Polgonum Capitatum

Polygonum capitatum Buch.-Ham.ex D. Don, a traditional Miao-nationality herbal medicine, is widely used in the treatment of various urologic disorders including pyelonephritis and urinary tract infection. Its preparation (namely as "Re-Lin-Qing" granule) has been widely used in clinic in China. FR429, an ellagitannin, is the major component isolated from Polygonum capitatum Buch.-Ham.ex D. Don. FR429exhibits potential antitumor activity in recent research. Although FR429possesses favorable activity, its metabolic characteristics are still unknown. This study was designed to investigate the absorption characteristics, as well as in vitro and in vivo metabolic profiles of FR429. The metabolites were identified by HPLC-electrospray ionization-ion trap-time of fight mass spectrometry (LC/MSn-IT-TOF), and the metabolic pathways were subsequently deduced.FR429was isolated and purified from Polygonum capitatum Buch.-Ham. ex D. Don with Sephadex LH-20. The purity of FR429was determined by HPLC with peak area normalization method.The absorption of FR429in the intestine was evaluated using in vitro Caco-2cell monolayer. The results showed that FR429had poor permeability, suggesting a low oral bioavailability. The in vitro metabolism of FR429was studied in rat and human liver microsomes, cytosol, as well as in primary rat hepatocytes. LC/MSn-IT-TOF was used for the identification of metabolites, providing the information of accurate molecular weights and the fragments of MSn spectra. Total eight metabolites were identified in vitro, of which ellagic acid, methyl conjugates of FR429and ellagic acid were the major metaoblites. Catechol-O-methyl transferase enzyme was involved in metabolic processes.The pharmacokinetic parameters of FR429were also determined after intravenous injection. FR429was rapidly eliminated in plasma, with2.08±0.74min and110.26±34.74min for T1/2a and T1/2β, respectively. Total twenty-one metabolites were detected in rats in vivo. Among these metabolites, eight of them were observed after intravenous injection, including ellagic acid, FR429methyl ether and glucuronide conjugates of mono/di-methylellagic acid. Other thirteen metaoblites were detected after oral administration, including seven Phase I metabolites and six Phase II metabolites. Most Phase I metabolites were urolithins, and some of them were also identified in rat intestinal bacteria in vitro. The Phase II metabolites were glucuronide conjugates. In conclusion, the results demonstrated that FR429had poor permeability on Caco-2cell monolayer and can be metabolized by liver cytosolic COMT besides intestinal microflora. The metabolic profiles varied between different routes of administration. FR429was mainly metabolized in liver after intravenous injection, and methyl and glucuronide conjugation were mainly observed. Whereas it was primarily metabolized in intestinal microflora after oral administration, and dehydroxylation and conjugation with glucuronide mainly occurred in the metabolic processes.