In vitro-in vivo correlation of the chiral pesticide prothioconazole after interaction with human CYP450 enzymes.

Growing human demand for food has culminated in increased use of pesticides worldwide. Prothioconazole (PTC), a profungicide, is bioactivated by metabolic PTC oxidation to prothioconazole-desthio (D-PTC). Here, the in vitro phase I metabolism of PTC to D-PTC in human liver microsomes and human CYP450 forms was studied. The kinetic parameters for the formation of (+)-D-PTC (KM = 1.2 µmol L-1, VMAX = 1.7 pmol min-1 mg-1), (-)-D-PTC (KM = 7 µmol L-1, VMAX = 5.1 pmol min-1 mg-1), and both D-PTC enantiomers (KM = 9 µmol L-1, VMAX = 7 pmol min-1 mg-1) from rac-PTC indicated an enantioselective behavior. Formation of the enantiomer (+)-D-PTC was twice more extensive than the formation of the enantiomer (-)-D-PTC. Furthermore, CLH prediction revealed the same enantioselective behavior. The phenotyping study indicated that CYP2C19 was the sole CYP450 form accounting for the metabolism of PTC. The estimated apparent distribution volume of PTC was predicted as 2 L kg-1. This study showed that D-PTC may be formed in the human organism due to hepatic metabolism of PTC, mediated by CYP2C19 and that the enantiomer (+)-D-PTC is preferentially formed. However, it was not extensively formed (~1%). Considering a risk assessment point of view, this study provided positive evidence of PTC safety.

In vitro enantioselective inhibition of the main human CYP450 enzymes involved in drug metabolism by the chiral pesticide tebuconazole.

Tebuconazole (TEB) is a chiral triazole fungicide worldwide employed to control plant pathogens and preserve wood. People can be exposed to TEB either through diet and occupational contamination. This work investigates the in vitro inhibitory potential of rac-TEB, S-(+)-TEB, and R-(-)-TEB over the main cytochrome P450 enzymes (CYP450) using human liver microsomes to predict TEB in vivo inhibition potential. The IC50 values showed that in vitro inhibition was enantioselective for CYP2C9, CYP2C19, and CYP2D6, but not for CYP3A4/5. Despite enantioselectivity, rac-TEB and its single enantiomers were always classified in the same category. The inhibition mechanisms and constants were determined for rac-TEB and it has shown to be a mixed inhibitor of CYP3A4/5 (Ki = 1.3 ± 0.3 µM, αKi = 3.2 ± 0.5 µM; Ki = 0.6 ± 0.3 µM, αKi = 1.3 ± 0.3 µM) and CYP2C9 (Ki = 0.7 ± 0.1 µM, αKi = 2.7 ± 0.5 µM), and a competitive inhibitor of CYP2D6 (Ki = 11.9 ± 0.7 µM) and CYP2C19 (Ki = 0.23 ± 0.02 µM), respectively, suggesting that in some cases, rac-TEB has a higher or comparable inhibitory potential than well-known strong inhibitors of CYP450 enzymes, especially for CYP2C9 and CYP2C19. In vitro-in vivo extrapolations (IVIVE) were conducted based on the results and data available in the literature about TEB absorption and metabolism. R1 values were estimated based on the Food and Drug Administration guideline and suggested that in a chronic oral exposure scenario considering the acceptable daily intake dose proposed by the European Food and Safety Authority, the hypothesis of rac-TEB to inhibit the activities of CYP3A4/5, CYP2C9, and CYP2C19 in vivo and cause pesticide-drug interactions cannot be disregarded.

Enantioselective inhibition of human CYP2C19 by the chiral pesticide ethofumesate: Prediction of pesticide-drug interactions in humans.

Ethofumesate is a chiral herbicide that may display enantioselective behavior in humans. For this reason, the enantioselective potential of ethofumesate and its main metabolite ethofumesate-2-hydroxy to cause pesticide-drug interactions on cytochrome P450 forms (CYPs) has been evaluated by using human liver microsomes. Among the evaluated CYPs, CYP2C19 had its activity decreased by the ethofumesate racemic mixture (rac-ETO), (+)-ethofumesate ((+)-ETO), and (-)-ethofumesate ((-)-ETO). CYP2C19 inhibition was not time-dependent, but a strong inhibition potential was observed for rac-ETO (IC50 = 5 ± 1 µmol L-1), (+)-ETO (IC50 = 1.6 ± 0.4 µmol L-1), and (-)-ETO (IC50 = 1.8 ± 0.4 µmol L-1). The reversible inhibition mechanism was competitive, and the inhibition constant (Ki) values for rac-ETO (2.6 ± 0.4 µmol L-1), (+)-ETO (1.5 ± 0.2 µmol L-1), and (-)-ETO (0.7 ± 0.1 µmol L-1) were comparable to the Ki values of strong CYP2C19 inhibitors. Inhibition of CYP2C19 by ethofumesate was enantioselective, being almost twice higher for (-)-ETO than for (+)-ETO, which indicates that this enantiomer may be a more potent inhibitor of this CYP form. For an in vitro-in vivo correlation, the Food and Drug Administration's (FDA) guideline on the assessment of drug-drug interactions used in the early stages of drug development was used. The FDA's R1 values were estimated on the basis of the obtained ethofumesate Ki and distribution volume, metabolism, unbound plasma fraction, gastrointestinal and dermal absorption data available in the literature. The correlation revealed that ethofumesate probably inhibits CYP2C19 in vivo for both chronic (oral) and occupational (dermal) exposure scenarios.

Evaluation of the Intestinal Absorption Mechanism of Casearin X in Caco-2 Cells with Modified Carboxylesterase Activity.

The clerodane diterpene casearin X (1), isolated from the leaves of Casearia sylvestris, is a potential new drug candidate due to its potent in vitro cytotoxic activity. In this work, the intestinal absorption mechanism of 1 was evaluated using Caco-2 cells with and without active carboxylesterases (CES). An LC-MS method was developed and validated for the quantification of 1. The estimation of permeability coefficients was possible only under CES-inhibited conditions in which 1 is able to cross the Caco-2 cell monolayer. The mechanism is probably by active transport, with no significant efflux, but with a high retention of the compound inside the cells. The enzymatic hydrolysis assay demonstrates the susceptibility of 1 to first-pass metabolism as substrate for specific CES expressed in human intestine.

In vitro metabolism of the lignan (-)-grandisin, an anticancer drug candidate, by human liver microsomes.

(-)-grandisin is a tetrahydrofuran lignan that displays important biological properties, such as trypanocidal, anti-inflammatory, cytotoxic, and antitumor activities, suggesting its utility as a potential drug candidate. One important step in drug development is metabolic characterization and metabolite identification. To perform a biotransformation study of (-)-grandisin and to determine its kinetic properties in humans, a high performance liquid chromatography (HPLC) method was developed and validated. After HPLC method validation, the kinetic properties of (-)-grandisin were determined. (-)-grandisin metabolism obeyed Michaelis-Menten kinetics. The maximal reaction rate (Vmax ) was 3.96 ± 0.18 µmol/mg protein/h, and the Michaelis-Menten constant (Km ) was 8.23 ± 0.99 µM. In addition, the structures of the metabolites derived from (-)-grandisin were characterized via gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS) analysis. Four metabolites, 4-O-demethylgrandisin, 3-O-demethylgrandisin, 4,4'-di-O-demethylgrandisin, and a metabolite that may correspond to either 3,4-di-O-demethylgrandisin or 3,5-di-O-demethylgrandisin, were detected. CYP2C9 isoform was the main responsible for the formation of the metabolites. These metabolites have not been previously described, demonstrating the necessity of assessing (-)-grandisin metabolism using human-derived materials.

Stereoselective determination of hydroxychloro-quine and its major metabolites in human urine by solid-phase microextraction and HPLC.

The enantioselective analysis of hydroxychloroquine (HCQ) and its major metabolites was achieved by HPLC and solid-phase microextraction. The chromatographic separation was performed on a Chiralcel OD-H column using hexane/methanol/ethanol (96:2:2, v/v/v) plus 0.2% diethylamine as the mobile phase, at the flow rate of 1.3 mL/min. The main extraction parameters were optimized. The best condition was achieved by the addition of 10% NaCl and 1 mL phosphate buffer 1 mol/L pH 11 to 3 mL human urine. The extraction was conducted for 40 min at 25 degrees C and the desorption time was 3 min using methanol (100%). PDMS-DVB 60 microm fiber was used in this study. The mean recoveries were 9.3, 9.2, and 14.4% for HCQ, desethylhydroxychloroquine (DHCQ), and desethylchloroquine (DCQ), respectively. The method was linear over the range of 50-1000 ng/mL for HCQ enantiomers and over the range of 42-416 ng/mL for DCQ and DHCQ enantiomers. Within-day and between-day precision and accuracy assays for HCQ and its metabolites were lower than 15%. The preliminary 48 h urinary excretion study performed in human urine showed to be stereoselective. The amount of (+)-(S)-enantiomer excreted was higher than its antipode.