Cytochrome P450 (CYP) 2B6 belongs to the set of important hepatic drug-metabolizing CYPs. It makes up roughly 3%-6% of total hepatic CYP content and metabolizes several pharmaceuticals including bupropion, efavirenz, cyclophosphamide, pethidine, ketamine and propofol. The enzyme is susceptible to drug-drug interactions by enzyme induction and inhibition. In addition to drugs, CYP2B6 is able to both detoxify and bioactivate a number of procarcinogens and environmental agents including pesticides and herbicides. There is an extensive interindividual variability in the expression of CYP2B6, which is in part explained by extensive genetic polymorphism. CYP2B6 is one of the most polymorphic CYP genes in humans with over 100 described SNPs, numerous complex haplotypes and distinct ethnic and racial frequencies. This review summarizes the basic properties of CYP2B6 and the main characteristics of clinical relevance.
Background: Aripiprazole (ARI) is an antipsychotic drug that is metabolized to dehydroaripiprazole (DARI) by CYP2D6. Because of the large interindividual variability in ARI and DARI plasma concentrations, therapeutic drug monitoring may be of use in psychiatric patients during treatment with ARI. The aim of the present study was to develop a simple and reliable method for the quantitative determination of ARI and DARI in plasma using liquid-liquid extraction and reverse-phase high-performance liquid chromatography (HPLC) with ultraviolet (UV) detection. The method was tested in psychiatric patients during regular treatment with ARI.
Methods: Separation was by the liquid-liquid method, and UV detection at 254 nm. Linear responses for ARI and DARI were obtained between 2 and 1000 ng/mL, and precision assays were lower than 10.4 for both analytes.
Results: Lower limit of quantification and detection were 1 and 0.38 ng/mL for ARI and 0.78 and 0.44 ng/mL for DARI, respectively. The method was successfully applied to plasma samples drawn from 22 patients with concentrations ranging between 2 and 189 ng/mL for ARI and between 11 and 359 ng/mL for DARI.
Conclusions: The chromatographic method developed has been demonstrated to be sensitive and reliable for the measurement of ARI and DARI simultaneously in human plasma, and the present method represents an alternative procedure to evaluate plasma concentration in patients during treatment with ARI.
Background: Losartan is metabolized to losartan carboxylic acid (E-3174) by the polymorphic cytochrome CYP2C9. The aim of the study was to develop a high-performance liquid chromatographic (HPLC) method with fluorescence detection for simultaneously measuring losartan and its metabolite E-3174 in urine to evaluate the losartan urinary metabolic ratio (MR: losartan/E-3174) for CYP2C9 phenotyping in humans.
Methods: The compounds were separated in a reversed-phase chromatographic column and detected by fluorescence at a wavelength of 250 nm for excitation and of 370 nm for emission.
Results: No analytical interferences with endogenous compounds were found, and the extraction recoveries were over 88%. Limits of quantification of 2 ng mL-1 for losartan and 5 ng mL-1 for E-3174 were achieved, as well as good reproducibility with coefficients of variation of <9% in all cases. Analyses with the present HPLC method show significant differences (p<0.05) in losartan MRs between the four CYP2C9 genotype groups in 13 Spanish healthy volunteers.
Conclusions: The method developed is simple and affordable, as well as sensitive and reliable to calculate the MR. Therefore, it appears to be useful for CYP2C9 phenotyping using losartan as a drug test in populations, such as Hispanics with different allele combinations.
Background: Pharmacokinetic parameters, drug bioavailability, and biological activities depend on the mechanisms of interaction with serum albumin. In this study, the binding properties as well as mechanisms of interaction of chloroquine with bovine serum albumin (BSA) were investigated.
Methods: The binding of chloroquine with BSA was carried out using a microcalorimetric approach. The mechanism of binding, the number of binding molecules as well as changes of BSA upon complexation with chloroquine were investigated.
Results: The binding isotherms indicated a variable number of binding sites of chloroquine on one molecule of BSA. At lower temperatures, larger numbers of binding sites were available for chloroquine, these decrease by increasing the temperature. The binding constant of chloroquine with BSA varied from 9.4×10³ M⁻¹ at 25°C to 5.7×10³ M⁻¹ at 40°C. Chloroquine showed temperature-dependent binding affinity, with stronger affinity at lower temperature. By increasing the temperature, from 25°C to 40°C, the binding affinity was decreased by approximately 60% of its value.
Conclusions: Chloroquine showed weak binding affinity with BSA. The weak binding affinity of chloroquine with BSA is important in determining the drug-drug interactions at the binding sites of BSA. The presence of stronger binding ligands, e.g., chloramphenicol, tetracyclines or diclofenac, can compete with chloroquine for its binding sites, and therefore lowers its serum albumin binding. This study will be helpful in understanding the binding properties of mechanisms of interaction of chloroquine with BSA.
Background: The transport of endogenous and exogenous organic cations across the plasma membrane of cells is mediated by multispecific organic cation transporters (OCTs), and the multidrug and toxin extrusion (MATE) transporters. MATE belongs to the SLC47 transporter family consisting of only two members, MATE1 and MATE2-K. MATE2-K is exclusively expressed in the kidney at the apical membrane of proximal tubular epithelial cells. MATE1 is highly expressed in the kidney, liver, skeletal muscle and also in adrenal glands, testes and heart. MATE1 exchanges organic cations against protons both in influx as well as in efflux modes.
Methods: Here, we examined the interaction of 25 antineoplastic agents with human MATE1. We generated stably transfected MATE1-HEK293 cells and determined the inhibition of MATE1-mediated [(3)H]1-methyl-4-phenylpyridinium (MPP) uptake by the antineoplastic agents.
Results: We found a significant inhibition of MATE1-mediated MPP uptake by several antineoplastic agents and pH dependent IC(50)values for mitoxantrone (7.8 μM at pH 7.4 and 0.6 μM at pH 8.5) as well as for irinotecan (4.4 μM at pH 7.4 and 1.1 μM at pH 8.5), respectively.
Conclusions: We suggest that hMATE1 could play a role in chemosensitivity of tumor cells. In addition, hepatic and renal MATE1 could potentially be involved in drug-drug-interactions as well as in drug metabolism and excretion during chemotherapy.

