The Interaction Between Anthraquinones And Renal OATs And The Interaction Between Aristolochic Acid A And Intestinal Efflux Transporters

Renal organic anion transporters (OATs) are expressed in the basolateral or apical side of renal tubular epithelial cell. They play important roles in the renal secretion or reabsorption. Many drugs and disease-related endogenous compounds could interact with OATs. Radix et Rhizoma Rhei is a traditional medicine in China. Main active compounds in Radix et Rhizoma Rhei are anthraquinones, including rhein, emodin, aloe-emodin, chrysophanol and physcion. Previous research indicated that rhein has a relatively higher concentration in kidney tissue. Rhein is a anion in physiological environment, which is in accordance with OATs substrate features. We thus speculate that rhein is a substrate of OATs. Other anthraquinones has similar structures to rhein and may interact with OATs too. The present study investigated the interaction between five anthraquinones with OATs and tried to clarify scientific questions as follows: whether anthraquinones were substrates or inhibitors of OATs, did renal OATs related to the high renal distribution of rhein, could anthraquinones interact with OATs substrates in vivo, and whether there were clinic applications based on the interaction between anthraquinones. This study intends to provide reference for the clinical rational use of Radix et Rhizoma Rhei. In our study, we also find that intestinal efflux transporters may be involved in the transport of aristolochic acid A (AAI), a renal toxic OATs substrate. The interaction between AAI and intestinal efflux transporters (P-gp, MRP2 and BCRP) was conducted, which suggested the role of intestinal efflux transporters in AAI bioavailability and toxicity.Part I The interaction between five anthraquinones and hOAT1/3We investigated the interaction between five anthraquinones (emodin, rhein, physcion, chrysophanol and aloe-emodin) and hOATl/3 in cells models highly expressing with hOATl/3. The results showed that all five anthraquinones could inhibit hOAT1 and hOAT3, and rhein was the most potent inhibitor to hOAT1 and hOAT3, followed by emodin and aloe-emodin. Chrysophanol and physcion were relatively weak hOAT1 and hOAT3 inhibitors. Further study found that preincubation with some anthraquinones could increase their inhibitory effect to hOAT1 and hOAT3. Cellular accumulation study indicated that five anthraquinones were not hOATl/3 substrates.Part Ⅱ The effect of rhein and Radix et Rhizoma Rhei extract on the pharmacokinetics of furosemide in ratsIn order to investigate the inhibitory effect of anthraquinones to OATs in vivo, we study the effect of rhein and Radix et Rhizoma Rhei extract (single dose or multiple dose) on the pharmacokinetics of furosemide (a typical OAT 1/3 substrate) in rats. Coadministration with rhein increased the AUC(0-t) value of furosemide by 65% and also increased the MRT and decreased the Vz and Clz of furosemide. Coadministration with Radix et Rhizoma Rhei extract (single dose or multiple dose) increased the AUC(o-t) value of furosemide by 32% and 52%. This study suggested that rhein and Radix et Rhizoma Rhei extract could inhibit OATs in vivo and might increase the plasma concentration of OATs substrates.Part Ⅲ The effect of rhein and Radix et Rhizoma Rhei extract on the pharmacokinetics and tissue distribution of AAI and its demethylation metabolite in ratsAAI is a renal toxic substance and also a substrate of OATs. Renal OATs could uptake AAI to kidney tissue and mediate its renal toxicity. In this study, the effect of rhein and Radix et Rhizoma Rhei extract on the pharmacokinetics and tissue distribution of AAI and its demethylation metabolite (AAIa) in rats was investigated.The experimental results indicated that coadministration with rhein increased the AUC(o-t) value of AAI and AAIa by 38%　and 31%. Coadministration with Radix et Rhizoma Rhei extract did not significantly change the plasma concentration of AAI and AAIa. Tissue distribution study showed that coasministration with rhein and Radix et Rhizoma Rhei extract could significantly decrased the renal distribution of AAI. At 5min, 10min and 20min, kidney concentrations of AAI were decreased to 50%,42% and 58%　of control by rhein and decreased to 63%,58%　and 68%　of control by Radix et Rhizoma Rhei extract.Part IV The interaction between AAI and intestinal efflux transportersOur previous research investigated the bi-directional transport of AAI in Caco2 cells and found that efflux ratio of AAI was about 5.8, higher than 2, which indicated that efflux transporters might be involved in the transport of AAI. Then in cell models highly expressing with MDR1, MRP2 and BCRP (main efflux drug transporters expressed in intestinal), we study the interaction between AAI and these transporters. Our results showed that AAI was not a substrate of P-gp or MRP2, but a substrate of BCRP.ConclusionOur study proved that five anthraquinones were inhibitors of hOAT1 and hOAT3, with rhein as the most potent inhibitor of hOATl and hOAT3. Five anthraquinones were not substrates of hOATl or hOAT3, which could hardly prove the speculation that whether renal OATs were related to the high renal distribution of rhein. Rhein and Radix et Rhizoma Rhei extract could interact with furosemide in rats and increased the plasma concentration of fusosemide, which indicated that anthraquinones could interact with OATs substrates in vivo. Renal OATs mediate the accumulation of renal toxic substances. Coadministration with rhein or Radix et Rhizoma Rhei extract significantly decreased the renal distribution of AAI, which suggested that anthraquinones could have renal protection effect by decreasing the renal distribition of toxic OATs substrates. Besides, we found that AAI was a substrate of BCRP, but not P-gp or MRP2.