Regional distributions of curcumin and tetrahydrocurcumin in the liver and small intestine of rats when orally co‐administered with quercetin and paeoniflorin

Curcumin (CUR), derived from the dietary spice turmeric, is a polyphenolic compound with various biological and pharmacological activities. Tetrahydrocurcumin (THC) is one of the major reductive metabolites of curcumin. A pharmacokinetic study using ultra‐high‐performance liquid chromatography‐tandem mass spectrometry (UHPLC‐MS/MS) for the simultaneous determination of curcumin, THC, quercetin (QR), and paeoniflorin (PF) in rat plasma had been performed. In this study, the regional distributions of curcumin and tetrahydrocurcumin in the liver and the three segments of small intestine (duodenum, jejunum, and ileum) of rats when orally co‐administered with quercetin and paeoniflorin were carried out. Drug concentrations were determined using UHPLC‐MS/MS. The results showed that curcumin was well distributed in the small intestine, while the distributions of tetrahydrocurcumin in the liver, duodenum, jejunum were similar, but much more abundant in the ileum. When orally co‐administered with quercetin and paeoniflorin, the tissue to plasma concentration ratios (Kp values) of curcumin in the three segments of the small intestine were increased, indicating that the presence of quercetin and paeoniflorin increases the distribution of curcumin in these regions. Moreover, the half‐life (t1/2) of THC in the liver was significantly prolonged, and the Kp value of THC in the liver was increased and the Kp values in the small intestine were decreased, suggesting that the combination of quercetin and paeoniflorin might suppress the metabolism of curcumin in the small intestine. In brief, the combination had an effect on the distributions of curcumin and tetrahydrocurcumin in the liver and small intestine of rats. Curcumin was well distributed in the small intestine, while tetrahydrocurcumin was in the ileum. When orally co‐administered with quercetin and paeoniflorin, curcumin concentrations were increased in the small intestine, most obviously in the duodenum. And tetrahydrocurcumin concentrations were increased in the liver and decreased in the small intestine. The metabolism of curcumin to tetrahydrocurcumin was active in the ileum.