Intestinal Metabolic Pathways and Key Metabolites of Phytoestrogenic Fractions From Cuscutae Semen in Estrogen-Deficient Rats: Insights From UPLC-Q-TOF MS.

While flavonoids from Cuscutae Semen (CS) exert significant estrogen-regulating effects, their intestinal metabolism under estrogen-deficient conditions remains poorly understood. This study aimed to elucidate the metabolic fate of these active constituents. Using ovariectomized rats, we collected ileal sac fluid, colonic sac fluid, hepatic portal blood, and feces to establish metabolic profiles along the "ileum-colon-hepatic portal vein-feces" axis via UPLC-Q-TOF-MS. By employing a combined approach to evaluate both mucosa-mediated and microbiota-mediated metabolism, we identified 37 parent compounds (predominantly flavonoids) and 48 metabolites. The ileum and colon were confirmed as primary metabolic sites, predominantly involving Phase I and Phase II reactions. Metabolic pathways were detailed using quercetin as a representative phytoestrogen. Furthermore, we analyzed the intestinal metabolic patterns of nine in vivo direct-acting compounds highly correlated with CS's estrogenic effects. Collectively, this study uncovers the intestinal metabolic characteristics of CS active fractions under estrogen deficiency, providing a crucial foundation for future in vivo studies and elucidating the pharmacologically active basis of CS.