Simultaneous determination of ezetimibe and simvastatin in rat plasma by stable-isotope dilution LC-ESI-MS/MS and its application to a pharmacokinetic study.

A simple, sensitive and specific liquid chromatography-tandem mass spectrometry method was developed for simultaneous quantification of ezetimibe and simvastatin in rat plasma. The deuterium isotopes: ezetimibe d4 and simvastatin d6 were used as internal standards for ezetimibe and simvastatin, respectively. MS/MS detection involved a switch of electron spray ionization mode from negative to positive at retention time 3.01 min. Samples were extracted from plasma by liquid-liquid extraction using tertiary butyl methyl ether. Chromatographic separation was achieved with Agilent Eclipse XBD-C18 column using mobile phase that consisted of a mixture of ammonium acetate (pH4.5; 10 mM)-acetonitrile (25:75 v/v). The method was linear and validated over the concentration range of 0.2-40.0 ng/mL for simvastatin and 0.05-15.0 ng/mL for ezetimibe. The transitions selected were m/z 408.3→271.1 and m/z 412.0→275.10 for ezetimibe and ezetimibe d4, and m/z 419.30→285.20 and m/z 425.40→199.20 for simvastatin and simvastatin d6. Intra- and inter-batch precisions for ezetimibe were 1.6-14.8% and 2.1-13.4%; and for simvastatin 0.94-9.56% and 0.79-12%, respectively. The proposed method was sensitive, selective, precise and accurate for the quantification of ezetimibe and simvastatin simultaneously in rat plasma. The method was successfully applied to a pharmacokinetic study by oral co-administration of ezetimibe and simvastatin in SD rats.

Total activity of glutathione-S-transferase (GST) and polymorphisms of GSTM1 and GSTT1 genes conferring risk for the development of age related cataracts.

The pathogenesis of cataract is influenced by a number of factors including oxidative stress. Glutathione-S-transferase (GST) catalyses the nucleophilic addition of the thiol of GSH to electrophilic acceptors. It is important for detoxification of xenobiotics in order to protect tissues from oxidative damage. In humans, GSTT1 and GSTM1 deletion genotypes are associated with a variety of pathological conditions including certain ophthalmic diseases. In the present study, it is aimed to determine the risk of genetic polymorphisms of GSTM1 and GSTT1 isoforms of GST for developing of age related cataracts (ARCs). We compared the prevalence of GSTT1 and GSTM1 deletion genotypes, which were determined by multiplex polymerase chain reaction, in 455 patients with ARCs (108 with nuclear (NC), 105 with cortical (CC), 96 with posterior subcapsular, (PSC) and 146 with mixed type (MT)) and 205 age and sex matched controls. The GST activity in erythrocytes (RBC) and cataractous lenses was measured spectrophotometrically using 1-chloro-2,4-dinitrobenzene (CDNB) as substrate. The frequency of GSTM1 positive individuals was significantly higher in MT cataracts followed by NC, CC and PSC types with corresponding decrease in the GSTM1 null genotypes as compared to controls. Considering the GSTT1 locus, GSTT1 null genotypes showed high frequency in patients in general as compared to controls with corresponding reduction in the GSTT1 positive genotype. The activity of GST in RBC was higher in all the types of cataracts as compared to that in controls and in cataractous lenses the mean values were slightly higher in cases of NC cataracts as compared to CC, PSC and MT. The data suggests that GSTM1 positive, GSTT1 null and double null (GSTM1 null and GSTT1 null) genotypes may confer risk for the development of ARC. The increased activity of GST found in the present study could be due to a compensatory mechanism operating in response to increased oxidative stress.