With increasing reports of resistance of Leishmania to antimonials (Thakur et al., 2004) and other traditional antileishmanial drugs, the need for the discovery of new antileishmanial agents is rising. In an attempt to find new antileishmanial agents, two new benzodiazepine (BNZ) analogues (7-chloro-4-(cyclohexylmethyl)-1-methyl-3,4-dihydro-1H-1,4-benodiazepine-2,5-dione (BNZ-1) and 4-(cyclohexylmethyl)-1-methyl-3,4-dihydro-1H-1,4-benzodiazepine-2,5-dione (BNZ-2)) were synthesised, and found to be effective against leishmaniasis in mice. This study investigates the metabolism of these two drugs together with the prototype BNZ, flurazepam (FZP), using rat hepatocytes, and investigates their interaction with glutathione in macrophages. Hepatocytes (>80% viability by Trypan Blue exclusion isolated by liver perfusion with collagenase) were prepared from male Sprague-Dawley rats (200-250 g). Drugs (100 μM) were incubated with 2 × 106 viable cells/ml in Krebs-Hepes buffer, pH 7.4, in rotating round bottomed flasks under an atmosphere of 95% O2/5% CO2, at 37 °C for 3 h, and timed samples taken for metabolite measurement. Samples were extracted twice with ethyl acetate at pH 10, the combined organic phases evaporated to dryness and stored at −20 °C until analysis. Metabolites were separated by HPLC using an ACE C18 column (50 mm × 3.0 mm i.d., 5 μm packing), and a solvent gradient consisting of 0.1% formic acid: acetonitrile (starting composition 95:5%, and composition after 25 min 65:35% for FZP and 70:30% for both BNZ 1 and 2). Flow rate was 0.5 ml/min, and detection was at 230 nm. Identification of the metabolites was by mass spectrometry with both positive and negative ion electronspray ionization. The effects of 24 h exposure to the compounds (100 μM) was investigated in the macrophage cell line J774.1 in terms of reduced glutathione content (GSH) and the activity of glutathione reductase (GR). There was no evidence of significant cytotoxicity with any of the compounds at the concentration used. FZP (m/z 388) was metabolised by dealkylation of the two N-1 ethyl substituents (m/z 360 and m/z 332), followed by hydroxylation on the BNZ ring. There was no evidence for either N- or O-glucuronidation of the resulting metabolites. BNZ-1 (m/z 321) was metabolised by N-demethylation (m/z 307) followed by hydroxylation (m/z 323), mono- and di-hydroxylation of the parent (m/z 337 and m/z 353) and by glucuronidation of the mono-hydroxylated metabolite (m/z 513). BNZ-2 (m/z 287) was transformed by N-demethylation (m/z 273) and hydroxylation of the parent (m/z 303), with the latter further metabolised by O-glucuronidation (m/z 479). In addition, the hydroxylated N-demethylated product (m/z 289) was also formed. Macrophages did not produce detectable metabolism of any of the drugs. All the drugs depleted macrophage GSH significantly (p < 0.05 by ANOVA followed by Dunnett's test) with BNZ-1 and BNZ-2 causing greater depletion than FZP (40.6 ± 4.0 and 45.8 ± 8.4, respectively, compared with 55.5 ± 4.9 nmol/mg protein with FZP, n = 3). Control macrophage GSH was 74.1 ± 6.6 nmol/mg protein. The depletion in GSH was not due to inhibition of GR: only FZP caused a significant decrease in macrophage GR activity (28.0 ± 5.9 compared with 42.1 ± 8.0 nmol/ml/min in control cells, p < 0.05 by ANOVA followed by Dunnett's test, n = 3). The marked depletion of macrophage GSH indicates a potential toxic interaction in mammalian cells. The new BNZ analogues were rapidly metabolised by hepatocytes, producing N-dealkylated and multiple hydroxylated phase I metabolites, followed by glucuronidation. This rapid metabolism may limit the therapeutic effect of BNZ 1 and 2 if their metabolites are inactive against leishmaniasis and suggest the need to optimise these lead structures further to obtain compounds with reduced rates and extent of metabolism.
- glutathione reductase