Efflux transport of N-monodesethylamiodarone by the human intestinal cell-line Caco-2 cells

Cardiovascular Ion Channel Inhibitor Drug-Drug Interactions with P-glycoprotein

P-glycoprotein (Pgp) is an ATP-binding cassette (ABC) transporter that plays a major role in cardiovascular drug disposition by effluxing a chemically and structurally diverse range of cardiovascular therapeutics. Unfortunately, drug-drug interactions (DDIs) with the transporter have become a major roadblock to effective cardiovascular drug administration because they can cause adverse drug reactions (ADRs) or reduce the efficacy of drugs. Cardiovascular ion channel inhibitors are particularly susceptible to DDIs and ADRs with Pgp because they often have low therapeutic indexes and are commonly coadministered with other drugs that are also Pgp substrates. DDIs from cardiovascular ion channel inhibitors with the transporter occur because of inhibition or induction of the transporter and the transporter's tissue and cellular localization. Inhibiting Pgp can increase absorption and reduce excretion of drugs, leading to elevated drug plasma concentrations and drug toxicity. In contrast, inducing Pgp can have the opposite effect by reducing the drug plasma concentration and its efficacy. A number of in vitro and in vivo studies have already demonstrated DDIs from several cardiovascular ion channel inhibitors with human Pgp and its animal analogs, including verapamil, digoxin, and amiodarone. In this review, Pgp-mediated DDIs and their effects on pharmacokinetics for different categories of cardiovascular ion channel inhibitors are discussed. This information is essential for improving pharmacokinetic predictions of cardiovascular therapeutics, for safer cardiovascular drug administration and for mitigating ADRs emanating from Pgp.

In vitro kinetics of amiodarone and its major metabolite in two human liver cell models after acute and repeated treatments

The limited value of in vitro toxicity data for the in vivo extrapolation has been often attributed to the lack of kinetic data. Here the in vitro kinetics of amiodarone (AMI) and its mono-N-desethyl (MDEA) metabolite was determined and modelled in primary human hepatocytes (PHH) and HepaRG cells, after single and repeated administration of clinically relevant concentrations. AMI bioavailability was influenced by adsorption to the plastic and the presence of protein in the medium (e.g. 10% serum protein reduced the uptake by half in HepaRG cells). The cell uptake was quick (within 3h), AMI metabolism was efficient and a dynamic equilibrium was reached in about a week after multiple dosing. In HepaRG cells the metabolic clearance was higher than in PHH and increased over time, as well as CYP3A4. The interindividual variability in MDEA production in PHHs was not proportional to the differences in CYP3A4 activities, suggesting the involvement of other CYPs and/or AMI-related CYP inhibition. After repeated treatment AMI showed a slight potential for bioaccumulation, whereas much higher intracellular MDEA levels accumulated over time, especially in the HepaRG cells, associated with occurrence of phospholipidosis. The knowledge of in vitro biokinetics is important to transform an actual in vitro concentration-effect into an in vivo dose-effect relationship by using appropriate modelling, thus improving the in vitro-to-in vivo extrapolation.

Oseltamivir (tamiflu) is a substrate of peptide transporter 1

Oseltamivir, an ester-type prodrug of the neuraminidase inhibitor [3R,4R,5S]-4-acetamido-5-amino-3-(1-ethylpropoxy)-1-cyclohexene-1-carboxylate phosphate (Ro 64-0802), has been developed for the treatment of A and B strains of the influenza virus but has neuropsychiatric and other side effects. In this study, we characterized the transport across intestinal epithelial cells and the absorption of oseltamivir in rats. Uptake by Caco-2 cells (human carcinoma cell line) and HeLa cells transfected with peptide transporter 1 (HeLa/PEPT1) was time- and temperature-dependent and was inhibited by typical PEPT1 inhibitors such as glycyl-sarcosine (Gly-Sar). The uptake by Caco-2 cells and HeLa/PEPT1 was saturable, with similar K(m) values. Oseltamivir absorption in adult rats was greatly reduced by simultaneous administration of milk, casein, or Gly-Sar. Furthermore, the plasma and brain concentrations of oseltamivir were higher in fasting than in nonfasting rats after oral administration. These results suggest that oseltamivir is a substrate of PEPT1 and that PEPT1 is involved in its intestinal absorption.

The ABC transporter AtABCB14 is a malate importer and modulates stomatal response to CO2

Carbon dioxide uptake and water vapour release in plants occur through stomata, which are formed by guard cells. These cells respond to light intensity, CO2 and water availability, and plant hormones. The predicted increase in the atmospheric concentration of CO2 is expected to have a profound effect on our ecosystem. However, many aspects of CO2-dependent stomatal movements are still not understood. Here we show that the ABC transporter AtABCB14 modulates stomatal closure on transition to elevated CO2. Stomatal closure induced by high CO2 levels was accelerated in plants lacking AtABCB14. Apoplastic malate has been suggested to be one of the factors mediating the stomatal response to CO2 (Refs 4,5) and indeed, exogenously applied malate induced a similar AtABCB14-dependent response as high CO2 levels. In isolated epidermal strips that contained only guard cells, malate-dependent stomatal closure was faster in plants lacking the AtABCB14 and slower in AtABCB14-overexpressing plants, than in wild-type plants, indicating that AtABCB14 catalyses the transport of malate from the apoplast into guard cells. Indeed, when AtABCB14 was heterologously expressed in Escherichia coli and HeLa cells, increases in malate transport activity were observed. We therefore suggest that AtABCB14 modulates stomatal movement by transporting malate from the apoplast into guard cells, thereby increasing their osmotic pressure.

Amiodarone increases the accumulation of DEA in a human alveolar epithelium-derived cell line

Amiodarone (AMD)-induced pulmonary toxicity (AIPT) is the most life-threatening side-effect of AMD treatment. N-Monodesethylamiodarone (DEA), an active metabolite of AMD, also exhibits cytotoxicity and tends to accumulate in the lung more intensively than AMD. In this study, we characterized the mechanism of DEA accumulation using A549 cells as a model of the alveolar epithelium. Typical ATP-depletion compounds caused an approximately 30% increase in the accumulation of DEA in A549 cells, although these effects were less than those in Caco-2 cells. Triiodothyronine (T(3)), which exhibited an inhibitory effect on DEA efflux in Caco-2 cells, did not affect the accumulation of DEA in A549 cells. On the other hand, 100 microM AMD caused an approximately 200% increase in DEA content in A549 cells, although AMD accumulation was not affected by 100 microM DEA. Since the reducing effect of AMD on cellular ATP levels and that of FCCP were similar, the mechanism by which DEA accumulation is increased by AMD might be different from the ATP-dependent DEA efflux mechanism. The decrease in cell viability by DEA in the presence of AMD (IC(50) value of DEA for A549 cell viability: 25.4+/-2.4 microM) was more pronounced than that by DEA alone (IC(50) value: 11.5+/-3.0 microM). This further DEA accumulation by AMD might be a factor responsible for the greater accumulation of DEA than that of AMD in the lung in long-term AMD-treated patients.

Interaction of coenzyme Q10 with the intestinal drug transporter P-glycoprotein

In clinical trials, patients usually take many kinds of drugs at the same time. Thus, drug-drug interactions can often directly affect the therapeutic safety and efficacy of many drugs. Oral delivery is the most desirable means of drug administration. Changes in the activity of drug transporters may substantially influence the absorption of administered drugs from the intestine. However, there have been a few studies on food-drug interactions involving transporters. It is important to be aware of the potential of food-drug interactions and to act in order to prevent undesirable and harmful clinical consequences. Coenzyme Q10 (CoQ10) is very widely consumed by humans as a food supplement because of its recognition by the public as an important nutrient in supporting human health. Since intestinal efflux transporter P-glycoprotein (P-gp) is one of the major factors in drug-drug interactions, we focused on this transporter. We report here for the first time that CoQ10, which is widely used as a food supplement, affects the transport activity of P-gp.

Pharmacokinetics of desethylamiodarone in the rat after its administration as the preformed metabolite, and after administration of amiodarone

The pharmacokinetics of desethylamiodarone (DEA), the active metabolite of amiodarone (AM), were studied in the rat after administration of AM or preformed metabolite. Rats received 10 mg/kg of either intravenous or oral AM HCl or DEA base. Blood samples were obtained via a surgically implanted jugular vein cannula. Plasma concentrations were measured by a validated LC/MS method. In all AM treated rats, AM plasma concentrations greatly exceeded those of the formed DEA. The fraction of AM converted to DEA after i.v. administration was 14%. Amiodarone had a significantly lower (approximately 50%) clearance than DEA, although the volume of distribution and terminal phase half-life did not differ significantly. The hepatic extraction ratio of DEA was 0.48, similar to that of AM (0.51). Oral AM demonstrated higher plasma AUC (5.6 fold) and higher C(max) (6.1 fold) than oral DEA and oral bioavailability of AM (46%) was greater than DEA (17%). The estimated fraction of the oral dose of AM converted to DEA was 4.5 fold higher than after i.v. administration, suggesting first-pass formation of DEA from AM. Amiodarone and DEA differed in their pharmacokinetic characteristics mostly due to a higher CL of DEA. With oral dosing, AM appeared to undergo significant presystemic first-pass metabolism within the intestinal tract.