Microbial transformation studies can be used as models to simulate mammalian drug metabolism. In the present investigation, biotransformation of celecoxib was studied in microbial cultures. Bacterial, fungal, and yeast cultures were employed in the present study to elucidate the metabolism of celecoxib. The results indicate that a number of microorganisms metabolized celecoxib to various levels to yield eight metabolites, which were identified by high-performance liquid chromatography diode array detection and liquid chromatography tandem mass spectrometry analyses. HPLC analysis of biotransformed products indicated that majority of the metabolites are more polar than the substrate celecoxib. The major metabolite was found to be hydroxymethyl metabolite of celecoxib, while the remaining metabolites were produced by carboxylation, methylation, acetylation, or combination of these reactions. The methyl hydroxylation and further conversion to carboxylic acid was known to occur in metabolism by mammals. The results further support the use of microorganisms for simulating mammalian metabolism of drugs.

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Twenty-five fungal cultures were screened for their ability to transform the anthelmintic drug albendazole. A filamentous fungi Cunninghamella blakesleeana transformed albendazole to three metabolites in significant quantities. The transformation of albendazole was identified by HPLC. Based on the LC-MS-MS data, two metabolites were predicted to be albendazole sulfoxide and albendazole sulfone, the major mammalian metabolites reported previously. A new N-methylated metabolite of albendazole sulfoxide was also produced, where the methylation took place on the N-atom of the imidazole ring system. A temperature of 30°C, pH of 8 and high substrate concentrations produced highest transformation of albendazole. Among the various concentrations studied, 2% w/v of glucose produced highest transformation. The results reveal that the microbial model can be used to produce large quantities of mammalian metabolites.

A simple stereoselective high performance liquid chromatographic method was developed for the determination of the in vitro transport of the enantiomers of nateglinide (N-(trans-4-isopropylcyclohexyl-carbonyl)-phenylalanine) in the rat intestine using a Chiralcel OJ-RH column (150 x 4.0 mm, 5 microm). The effects of the mobile phase composition, pH, the flow rate, and the temperature on the chromatographic separation were investigated. The enantioseparation was achieved at 33 degrees C using a mobile phase containing 100 mM potassium dihydrogen phosphate, pH 2.5, and ACN (32:68 v/v) delivered at a flow rate of 1 mL/min. The analytes were monitored at 210 nm and linearity (r >0.99) was obtained for a concentration range of 0.5-50 microg/mL. The LOD and LOQ were 0.2 and 0.5 microg/mL for the R-enantiomer and 0.2 and 0.8 microg/mL for the S-enantiomer, respectively. Both, the intra- and interday accuracy and precision of the calibration curves were determined. The method was successfully applied to estimate the in vitro passage of the enantiomers and the racemate of nateglinide in duodenum, jejunum, and ileum of rats. Generally, higher concentrations of nateglinide and the S-enantiomer were observed when the racemate was administered compared to administration of the individual enantiomers of nateglinide.