The Hepatobiliary Disposition of Timosaponin B2 Is Highly Dependent on Influx/Efflux Transporters but Not Metabolism

Abstract

The purpose of this study was to characterize the hepatobiliary disposition of timosaponin B2 (TB-2), a natural saponin. Although TB-2 has multiple pharmacologic activities, the mechanism of its hepatobiliary disposition has not been explored. Because the metabolism of TB-2 is limited and the accumulation of TB-2 in primary hepatocytes is highly temperature dependent (93% of its accumulation is due to active uptake), the contribution of hepatic transporters was investigated. Organic anion-transporting polypeptide (OATP) 1B1-and OATP1B3-transfected human embryonic kidney 293 cells were employed. TB-2 serves as a substrate for OATP1B1 and OATP1B3, with the former playing a predominant role in the hepatic uptake of TB-2. An inhibition study in sandwich-cultured rat hepatocytes suggested that TB-2 is a substrate for both breast cancer resistance protein (Bcrp) and multidrug resistance-associated protein 2 (Mrp2), consistent with its high biliary excretion index (43.1-44.9%). This hypothesis was further verified in BCRP and MRP2 membrane vesicles. The cooperation of uptake and efflux transporters in TB-2 hepatic disposition could partially explain the doublepeak phenomenon observed in rat plasma and liver and biliary clearance, which accounted for 70% of the total TB-2 clearance. Moreover, TB-2 significantly increased the rosuvastatin concentration in rat plasma in a concentration-dependent manner and decreased its biliary excretion, which corresponded to reductions in rosuvastatin accumulation in hepatocytes and the biliary excretion index in sandwich-cultured rat hepatocytes, representing a perfect example of a potential saponin-statin drug-drug interaction. These studies demonstrate that transporters (Oatp, Bcrp/Mrp2), but not metabolism, contribute significantly to rat TB-2 hepatobiliary disposition.

Pharmacokinetics of mangiferin and its metabolite—norathyriol, Part 2: Influence of UGT, CYP450, P‐gp, and enterobacteria and the potential interaction in Rhizoma Anemarrhenae decoction with timosaponin B2 as the major contributor

“…Thus, the increased MGF and NTR exposure by TB‐2 was probably caused though the enlarged absorption window, which augmented the permeability because of the following reasons: on one hand, in the case of permeation enhancers‐sodium deoxycholates, share the similar steroid skeleton with TB‐2, which could substantially improve the bioavailability of MGF probably because of the enhanced transcellular and paracellular permeation . On the other hand, a limited overlap on the transporter spectra occurred because TB‐2 is the substrate of the organic anion‐transporting polypeptide (OATP) influx transporter and the breast cancer resistance protein (BCRP) and multidrug resistance‐associated protein 2 (MRP2) efflux transporters according to our previous report , whereas no related reports are available for the abovementioned transporters of MGF. Moreover, the hepatic metabolism of MGF is relatively limited in the vivo–vitro comparison (seen in part 1), and a similar trend for TB‐2 was found in our previous study , thereby indicating the impossible overlap of the metabolic enzyme or transporter spectra between them.…”

“…On the other hand, a limited overlap on the transporter spectra occurred because TB-2 is the substrate of the organic anion-transporting polypeptide (OATP) influx transporter and the breast cancer resistance protein (BCRP) and multidrug resistance-associated protein 2 (MRP2) efflux transporters according to our previous report [42], whereas no related reports are available for the abovementioned transporters of MGF. Moreover, the hepatic metabolism of MGF is relatively limited in the vivo-vitro comparison (seen in part 1), and a similar trend for TB-2 was found in our previous study [42], thereby indicating the impossible overlap of the metabolic enzyme or transporter spectra between them. Correspondingly, as the above mentioned, the inhibition of CYP450, UGT, P-gp, and enterobacteria could hardly induce the substantial improvement (less than 50%) upon MGF exposure regardless of whether in the purified form, the herb, or the compatible compounds treatment, implying that the more than tenfold improvement of the MGF bioavailability caused by TB-2 was impossible through transporter and metabolic enzyme inhibition.…”

“…Enterobacteria inhibition influence on the exposure to the NTR metabolite by P-gp and CYP450 inhibition was different between treatment with the herb and compatible compounds treatment based on the discovery that the pretreatment with P-gp inhibitors in rats decreased the exposure of NTR by 42…”

Organic anion-transporting polypeptides contribute to the hepatic uptake of berberine

“…Primary human hepatocytes were purchased from GIBCO. The study of the accumulation of berberine was performed as previously described with slight modifications (Guo et al, 2014;Sheng et al, 2015). Briefly, rat primary hepatocytes and human primary hepatocytes (1.5 Â 10 6 cells/ml) were seeded in 24-well plates coated with collagen-I.…”

Sandwich-Cultured Hepatocytes as a Tool to Study Drug Disposition and Drug-Induced Liver Injury

“…For example, disposition of a natural product timosaponin b2 (TB2) was characterized using rat SCH and involvement of specific transporters was confirmed using human OATP1B1- and OATP1B3-expressing HEK-293 cells and membrane vesicles isolated from cells expressing human MRP2 and BCRP. 34 …”