This study aimed to evaluate the effects of green tea on the pharmacokinetics and pharmacodynamics of the β-blocker nadolol. Ten healthy volunteers received a single oral dose of 30 mg nadolol with green tea or water after repeated consumption of green tea (700 ml/day) or water for 14 days. Catechin concentrations in green tea and plasma were determined. Green tea markedly decreased the maximum plasma concentration (C(max)) and area under the plasma concentration-time curve (AUC(0-48)) of nadolol by 85.3% and 85.0%, respectively (P < 0.01), without altering renal clearance of nadolol. The effects of nadolol on systolic blood pressure were significantly reduced by green tea. [(3)H]-Nadolol uptake assays in human embryonic kidney 293 cells stably expressing the organic anion-transporting polypeptides OATP1A2 and OATP2B1 revealed that nadolol is a substrate of OATP1A2 (Michaelis constant (K(m)) = 84.3 μmol/l) but not of OATP2B1. Moreover, green tea significantly inhibited OATP1A2-mediated nadolol uptake (half-maximal inhibitory concentration, IC(50) = 1.36%). These results suggest that green tea reduces plasma concentrations of nadolol possibly in part by inhibition of OATP1A2-mediated uptake of nadolol in the intestine.

Cytochrome P450 (CYP) enzymes, which metabolize numerous drugs, are expressed both in liver and in extrahepatic tissues. CYP3A4 for example is present and inducible by rifampin in epithelial cells of the gastrointestinal tract. It has been shown that such prehepatic metabolism contributes substantially to total clearance of CYP3A4 substrates (e.g., cyclosporine) before and even more pronounced during enzyme induction. We examined the effect of enzyme induction on prehepatic and hepatic metabolism of the model compound R/S-verapamil after simultaneous oral and intravenous administration using a stable isotope technology. This approach allows us to exclude intraindividual day-to-day variability and is therefore suitable to quantitatively assess prehepatic extraction of high-clearance drugs. Moreover, because verapamil is administered as a race-mate with the S-enantiomer being preferentially metabolized, we investigated the influence of induction on stereoselectivity of prehepatic and hepatic metabolism. Eight male volunteers received 120 mg of racemic verapamil bid for 24 days. Rifampin (600 mg daily) was given from day 5 to day 16. Systemic clearance and bioavailability of the verapamil enantiomers were determined by coadministering deuterated verapamil intravenously on day 4, on day 16, and on day 24. Effects of verapamil on atrioventricular conduction after oral and intravenous (iv) administration were assessed by measuring the maximum PR-interval prolongation Rifampin increased the systemic clearance of the active S-verapamil 1.3-fold (P < .001). In contrast, rifampin increased the apparent oral clearance of S-verapamil 32-fold (P < .001) and decreased its bioavailability 25-fold (P < .001), with partial recovery after rifampin withdrawal (P < .01). With rifampin, the effect of oral verapamil on atrioventricular conduction was nearly abolished (P < .01), whereas no significant changes were observed after intravenous administration. Induction caused a considerable reduction of stereoselectivity after both intravenous and oral administration (P < .001). Rifampin altered the pharmacokinetics and the pharmacological effects of verapamil to a much greater extent after oral administration compared with intravenous administration. These data clearly indicate that prehepatic metabolism of verapamil (presumably in the gut wall) is preferentially induced compared with hepatic metabolism and that stereoselectivity of verapamil metabolism is affected by induction.

After administration of metoprolol, plasma concentrations of the drug are markedly higher in CYP2D6 poor metabolizers (PMs) than in non-PMs. In a prospective double-blind 3-month study, we investigated whether this translates into differences in metoprolol's effects after initiation of therapy. Despite administering equal doses to PMs and non-PMs, metoprolol plasma concentrations were 4.9-fold higher in the PM group. Metoprolol evoked significantly and persistently greater reductions in heart rate, diastolic blood pressure, and mean arterial pressure in PMs than in non-PMs. It appears, therefore, that the CYP2D6 genotype contributes to interindividual differences in metoprolol response.

The organic cation transporters 1 (OCT1) and 2 (OCT2) mediate drug uptake into hepatocytes and renal proximal tubular cells, respectively. Multidrug and toxin extrusion protein 1 (MATE1) is a major component of subsequent export into bile and urine. However, the functional interaction of OCTs and MATE1 for uptake and transcellular transport of the oral antidiabetic drug metformin or of the cation 1-methyl-4-phenylpyridinium (MPP + ) has not fully been characterized. EXPERIMENTAL APPROACHSingle-transfected Madin-Darby canine kidney (MDCK) cells as well as double-transfected MDCK-OCT1-MATE1 and -OCT2-MATE1 cells were used to study metformin and MPP + uptake into and transcellular transport across cell monolayers, along with their concentration and pH dependence. KEY RESULTS Cellular accumulation of MPP+ and metformin was significantly reduced by 31% and 46% in MDCK-MATE1 single-transfected cells compared with MDCK control cells (10 mM; P < 0.01). Over a wide concentration range (10-2500 mM) metformin transcellular transport from the basal into the apical compartment was significantly higher in the double-transfected cells compared with the MDCK control and MDCK-MATE1 monolayers. This process was not saturated up to metformin concentrations of 2500 mM. In MDCK-OCT2-MATE1 cells basal to apical MPP + and metformin transcellular translocation decreased with increasing pH from 6.0 to 7.5. CONCLUSIONS AND IMPLICATIONSOur data demonstrate functional interplay between OCT1/OCT2-mediated uptake and efflux by MATE1. Moreover, MATE1 function in human kidney might be modified by changes in luminal pH values. Abbreviations

Background and purpose: Organic anion transporting polypeptide 1B3 (OATP1B3) (SLCO1B3) mediates the uptake of endogenous substrates (e.g. estrone-3-sulphate) and drugs (e.g. pravastatin) from blood into hepatocytes. Structure-based modelling of OATP1B3 suggested that a pore with a positive electrostatic potential contributes to the transport mechanism. Therefore, we investigated the role of conserved positively charged amino acids for OATP1B3-mediated uptake of sulphobromophthalein (BSP) and pravastatin. Experimental approach: Residues Lys28, Lys41 and Arg580 in OATP1B3 were substituted by alanine, arginine, glutamine, glycine or lysine. Using immunofluorescence, immunoblot analysis and cellular uptake assays, the effect of these mutations on protein expression and transport activity was investigated. Key results: Immunofluorescence revealed that all mutants were localized in the plasma membrane with partial intracellular retention of the Arg580>Ala and Arg580>Lys mutants. Lys41>Ala, Lys41>Gln, Lys41>Gly, Arg580>Gly and Arg580>Lys showed significantly reduced transport for BSP and pravastatin. Kinetic analyses of BSP transport revealed a significant reduction of Vmax normalized to cell surface protein expression for Lys41>Ala (wild type: 190 Ϯ 8, Lys41>Ala:16 Ϯ 4 pmol (mg protein) -1 min -1 , P < 0.001), whereas Vmax of Lys41>Arg and Arg580>Lys (103 Ϯ 8 and 123 Ϯ 14 pmol (mg protein) -1 min -1, P > 0.05) did not change significantly. This suggests that the positive charges at positions 41 and 580 are important for transport activity of BSP. Structural modelling indicated that the positively charged side chain of Lys41 is flexible within the pore. The orientation of Arg580 is defined by adjacent residues Glu74 and Asn77, which was confirmed by kinetic analysis of Glu74>Ala. Conclusions and implications:We demonstrated that the conserved positively charged amino acids Lys41 and Arg580 are pivotal to the transport activity of OATP1B3.