Montelukast has been recommended as a selective in vitro and in vivo probe of cytochrome P450 (P450) CYP2C8 activity, but its selectivity toward this enzyme remains unclear. We performed detailed characterization of montelukast metabolism in vitro using human liver microsomes (HLMs), expressed P450s, and uridine 59-diphospho-glucuronosyltransferases (UGTs). Kinetic and inhibition experiments performed at therapeutically relevant concentrations reveal that CYP2C8 and CYP2C9 are the principal enzymes responsible for montelukast 36-hydroxylation to 1,2-diol. CYP3A4 was the main catalyst of montelukast sulfoxidation and stereoselective 21-hydroxylation, and multiple P450s participated in montelukast 25-hydroxylation. We confirmed direct glucuronidation of montelukast to an acyl-glucuronide. We also identified a novel peak that appears consistent with an etherglucuronide. Kinetic analysis in HLMs and experiments in expressed UGTs indicate that both metabolites were exclusively formed by UGT1A3. Comparison of in vitro intrinsic clearance in HLMs suggest that direct glucuronidation may play a greater role in the overall metabolism of montelukast than does P450-mediated oxidation, but the in vivo contribution of UGT1A3 needs further testing. In conclusion, our in vitro findings provide new insight toward montelukast metabolism. The utility of montelukast as a probe of CYP2C8 activity may be compromised owing to involvement of multiple P450s and UGT1A3 in its metabolism.

Abstract. The molecular structures of the halotelluroxetanes pMeOC6H4Te(X)[C(=C(H)Xꞌ)C(CH2)nO], X = Xꞌ = Cl and n = 6 (1) and X = Cl, Xꞌ = Br and n = 5 (4), show similar binuclear aggregates sustained by { … Te-O}2 cores comprising covalent Te-O and secondary Te⋯O interactions. The resulting C2ClO2(lone-pair) sets define pseudo-octahedral geometries. In each structure, C-X⋯(arene) interactions lead to supramolecular layers. Literature studies have shown these and related compounds (i.e. 2: X = Xꞌ = Cl and n = 5; 3: X = Xꞌ = Br and n = 5) to inhibit Cathepsins B, K, L and S to varying extents. Molecular docking calculations have been conducted on ligands (i.e. cations derived by removal of the telluriumbound X atoms) 1ꞌ-3ꞌ (note 3ꞌ = 4ꞌ) enabling correlations between affinity for sub-sites and inhibition. The common feature of all docked complexes was the formation of a Te-S covalent bond with cysteine residues, the relative stability of the ligands with an E-configuration and the formation of a C-O … π interaction with the phenyl ring; for 1ꞌ the Te-S covalent bond was weak, a result correlating with its low inhibition profile. At the next level differences are apparent, especially with respect to the interactions formed by the organic-ligand-bound halides.

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This work presents an in vitro investigation of the effect of protein restriction on the metabolism of albendazole (ABZ). This study was conducted using liver microsomal fractions obtained from Wistar rats. For the quantitative analysis, a multidimensional High Performance Liquid Chromatography (2D HPLC) method was fully validated for the determination of the ABZ metabolites: albendazole sulfoxide, albendazole sulfone and albendazole 2-aminesulfone. The target compounds were directly extracted using a C8-RAM-BSA column (5.0x0.46 cm i.d.) and analyzed on a chromatographic chiral column containing amylose tris(3,5-dimethylphenylcarbamate) (150x4.6 mm i.d.). The in vitro biotransformation results showed that the protein restriction influenced the oxidative metabolism of ABZ. The production of R-(+)-ABZ-SO (1309 nmol/L) and S-(-)-ABZ-SO (1456 nmol/L) was higher in the control animals than in the animals fed with a diet containing 6% protein, which produced 778.7 nmol/L and 709.5 nmol/L for R-(+) and S-(-)-ABZ-SO enantiomers, respectively. These results were statistically inspected by Student´s t test and the results showed a significant difference between the two means (p<0.05). Moreover, the production of ABZ-SO enantiomers was enantioselective where the S-(-)-ABZ-SO was formed in greater amounts than the R-(+)-ABZ-SO in control animals (p=0.0231). However, the enantioselectivity was not observed when the in vitro biotransformation of ABZ was conducted using the microsomal fractions obtained from protein restriction animals (p>0.05). Furthermore, animal nutritional condition could affect the pattern of ABZ sulphoxidation indicating that the protein nutrition affect primarily the formation of R-(+)-ABZSO and S-(-)-ABZ-SO enantiomers.