Transepithelial Permeation of Tolbutamide across the Human Intestinal Cell Line, Caco-2

Differential Effects of 1α,25-Dihydroxyvitamin D3 on the Expressions and Functions of Hepatic CYP and UGT Enzymes and Its Pharmacokinetic Consequences In Vivo

The compound 1α,25-Dihydroxyvitamin D₃ (1,25(OH)₂D₃) is the active form of vitamin D₃ and a representative ligand of the vitamin D receptor (VDR). Previous studies have described the impacts of 1,25(OH)₂D₃ on a small number of cytochrome P450 (CYP) and uridine diphosphate-glucuronyltransferase (UGT) enzymes, but comparatively little is known about interactions between several important CYP and UGT isoforms and 1,25(OH)₂D₃ in vitro and/or in vivo. Thus, we investigated the effects of 1,25(OH)₂D₃ on the gene and protein expressions and functional activities of selected CYPs and UGTs and their impacts on drug pharmacokinetics in rats. The mRNA/protein expressions of Cyp2b1 and Cyp2c11 were downregulated in rat liver by 1,25(OH)₂D₃. Consistently, the in vitro metabolic kinetics (V_max and CL_int) of BUP (bupropion; a Cyp2b1 substrate) and TOL (tolbutamide; a Cyp2c11 substrate) were significantly changed by 1,25(OH)₂D₃ treatment in liver microsomes, but the kinetics of acetaminophen (an Ugt1a6/1a7/1a8 substrate) remained unaffected, consistent with Western blotting data for Ugt1a6. In rat pharmacokinetic studies, the total body clearance (CL) and nonrenal clearance (CL_NR) of BUP were significantly reduced by 1,25(OH)₂D₃, but unexpectedly, the total area under the plasma concentration versus time curve from time zero to infinity (AUC) of hydroxybupropion (HBUP) was increased probably due to a marked reduction in the renal clearance (CL_R) of HBUP. Additionally, the AUC, CL, and CL_NR for TOL and the AUC for 4-hydroxytolbutamide (HTOL) were unaffected by 1,25(OH)₂D₃ in vivo. Discrepancies between observed in vitro metabolic activity and in vivo pharmacokinetics of TOL were possibly due to a greater apparent distribution volume at the steady-state (V_ss) and lower plasma protein binding in 1,25(OH)₂D₃-treated rats. Our results suggest possible drug-drug and drug-nutrient interactions and provide additional information concerning safe drug combinations and dosing regimens for patients taking VDR ligand drugs including 1,25(OH)₂D₃.

Determination of the active transport of fucoidan derived from Okinawa Mozuku across the human intestinal Caco-2 cells as assessed by size-exclusion chromatography

INTRODUCTION

In order to clarify the mechanism of fucoidan transport, we developed the chromatographic determination method.

METHOD

A size-exclusion chromatography (SEC) method for the determination of Okinawa-fucoidan using Develosil 300 Diol-5 (60×8.0mm I.D., 30nm pore-diameter) with the eluent containing 1% non-ionic detergent is developed. Determination range (UV at 210nm) is from 0 to 100ng of fucoidan with the linear calibration line inserting to zero.

RESULTS

A transport activity of fucoidan is demonstrated by using Caco-2 cells (model of gut transport system); i.e., the initial transport velocity 12nmol/h/mg of protein (25-fold slower rate as compared to a bacterial l-alanine active-transport activity 300nmol/h/mg of protein) is found to occur. Since this fucoidan transport is inhibited by 10mM sodium azide (respiration inhibitor) and 0.05mM FCCP (uncoupler), this transport by Caco-2 cells is found to be an active one requiring energy-source. On the other hand, colchicine (inhibitor of phagocytosis/pinocytosis) and mannitol (putative competitive-inhibitor of tight-junction transport) cannot inhibit the fucoidan transport at all.

CONCLUSION

We firstly report that the active transport occurs for such a high molecular-weight sulphated-polyfucose of fucoidan in vitro using Caco-2 cells.

Transepithelial transport of rosuvastatin and effect of ursolic acid on its transport in Caco-2 monolayers

The aim of this study was to determine transepithelial transport characteristics of rosuvastatin and effect of ursolic acid (P-gp potential inhibitor) and ko143 (ABC transporters selective inhibitor) on its transport in Caco-2 monolayers. A reliable Caco-2 cell monolayers model was established. The TEER value was used to inspect integrity of cell model. Apparent permeability coefficients (Papp(BL-AP) and Papp(AP-BL)) were used to analyze transepithelial transport of rosuvastatin. Uptake of rosuvastatin was time- and concentration-dependent in Caco-2 cell. The ko143 but not ursolic acid had effect on the uptake of rosuvastatin in Caco-2 cell monolayer model and affected apparent permeability coefficient and apparent permeability of rosuvastatin. Active transport and passive diffusion absorption existed in transepithelial transport of rosuvastatin in Caco-2 cell model. Ursolic acid had no effect on transport of rosuvastatin in Caco-2 cell monolayer. The result indicated that ursolic acid may not cause effect on intestinal absorption of rosuvastatin.

Effects of Pomegranate Juice on Human Cytochrome P450 2C9 and Tolbutamide Pharmacokinetics in Rats

In this study, we investigated whether pomegranate juice could inhibit CYP2C9 activity. The ability of pomegranate juice to inhibit the diclofenac 4'-hydroxylase activity of human CYP2C9 was examined using human liver microsomes. Pomegranate juice was shown to be a potent inhibitor of human CYP2C9. The addition of 25 microl (5% v/v) of pomegranate juice resulted in almost complete inhibition of human CYP2C9 activity. In addition, we investigated the effect of pomegranate juice on the pharmacokinetics of tolbutamide (substrate for CYP2C9) in rats. Relative to the control group, the area under the concentration-time curve was approximately 1.2-fold greater when pomegranate juice (3 ml) was injected p.o. 1 h before the p.o. administration of the tolbutamide (20 mg/kg). The elimination half-life of tolbutamide was not altered by pomegranate juice administration. These results suggest pomegranate juice ingestion inhibits the intestinal metabolism of tolbutamide without inhibiting the hepatic metabolism in rats. Thus, we discovered that pomegranate juice inhibited human CYP2C9 activity and furthermore increased tolbutamide bioavailability in rats.

Effects of Chinese Herbal Medicines on Intestinal Drug Absorption

Sho-saiko-to (Xiao-Chai-Hu-Tang), one of the major traditional Chinese medicines, has been frequently prescribed with other synthetic or biotechnological drugs for the treatment of various acute or chronic diseases in Japan, and thus it is important to understand the interactions between Sho-saiko-to and coadministered drugs. This paper reviews the effects of Sho-saiko-to on the pharmacokinetics and pharmacodynamics of concomitant drugs in the gastrointestinal tract. Sho-saiko-to slightly hastens the gastrointestinal absorption of the sulfonylurea compound tolbutamide. Furthermore, it is considered that the increase in the gastrointestinal absorption rate by Sho-saiko-to may potentiate the hypoglycemic effects of tolbutamide in the early period after oral administration. Sho-saiko-to can facilitate the epithelial membrane permeability of tolbutamide at an early phase across the rat jejunum in situ and Caco-2 cell monolayers. It is also suggested that Sho-saiko-to enhances the energy-dependent transport of tolbutamide and has an inhibitory effect on the passive paracellular transport of tolbutamide in Caco-2 cells. This result might be related to the accelerated in vivo absorption rate of tolbutamide by concomitant dosing with Sho-saiko-to in rats. In addition, Sho-saiko-to has inhibitory effects on the efflux pump mediated by MDR1, and it appears that the crude constituents in Glycyrrhizae radix, glycyrrhizic acid and liquiritin, contribute to MDR1 suppression.