No abstract

Glutathione (GSH), glutathione disulfide (GSSG), and ophthalmic acid (OA) are important biological oxidative stress biomarkers to be monitored in pathological and toxicological studies. With the advent of liquid chromatography tandem mass spectrometry (LC-MS-MS) technology, sensitive and selective analysis of these biomarkers in biological samples is now being performed routinely. Due to the hydrophilic and polar natures of GSH and its endogenous derivatives, achieving good retention, resolution, and peak shape is often a chromatographic challenge. In this study, three ultra-performance (UP) LC column chemistries (namely, BEH C18, BEH HILIC, and HSS T3 [C18]) are evaluated for the UPLC-MS-MS analysis of GSH, GSSG, and OA extracted from mouse liver and human plasma samples. The chromatographic parameters evaluated are retentivity, tailing factor, MS sensitivity, and resolution of the three analytes. Based on the optimized method for each column chemistry, our results indicate that the HSS T3 (C18) column chemistry affords the best retention and separation of these analytes when operated under the ultra high-pressure chromatographic conditions.

A rapid and sensitive ultra-performance liquid chromatography/tandem mass spectrometry (UPLC/MS/MS) method was developed and validated for the determination of troglitazone in mouse plasma. Troglitazone and its internal standard (IS), rosiglitazone, were separated on an ACQUITY UPLC BEH C(18) column (1.7 microm particle size, 50 x 2.1 mm i.d.) by gradient elution with water and methanol at a flow rate of 0.5 mL/min. The cycle time of each analysis was 2.5 min. Rosiglitazone and troglitazone eluted at 1.13 and 1.57 min, respectively, and were chromatographically resolved from the ion suppression and enhancement zones due to the biological matrix effect. Quantitation of the analytes was performed in electrospray negative ionization mode (ESI -ve) using multiple reaction monitoring (MRM) experiments. The weighted (1/x) calibration curve was quadratic over the plasma concentration range 1-2500 ng/mL with a correlation coefficient (r(2)) of 0.9966. The limit of quantitation (LOQ) of troglitazone in mouse plasma was lower than 1 ng/mL. The inter- and intra-day variations of the assay were lower than 12.1%; the overall accuracy ranged from 86.4-110.2% and recovery from spiked plasma was more than 60%. The developed method was successfully applied to determine troglitazone in mouse plasma after intraperitoneal administration.

We used immortalized human hepatocytes to study the bioactivation of leflunomide and the metabolic degradation to its major metabolite, A77 1726. Both leflunomide and A77 1726 caused a time- and concentration-dependent increase in LDH release. The cytotoxicity of leflunomide, but not that of A77 1726, was prevented by the pan-CYP inhibitor, 1-aminobenzotriazole, indicating that an oxidative metabolite(s) was responsible for the cell injury. LC/MS/MS analysis revealed that leflunomide was rapidly degraded in hepatocytes biphasically (t((1/2))(a) = 1.5 h, t((1/2)) >24 h), but much slower in cell-free medium (t((1/2)) >24 h). In contrast, the generation of A77 1726 occurred at a similar rate in cells and cell-free systems. In conclusion, leflunomide was rapidly metabolized in human hepatocytes to A77 1726, but its toxicity was dependent on other, CYP-dependent intermediates.

Leflunomide was found to be metabolized predominantly to A77-1726 and two novel hydroxylated metabolites, M1 and M2, in microsomes while A77-1726 was only biotransformed to M1. M1 and M2 were proposed to be the hydroxylated alpha-cyanoenol form of A77-1726 and the hydroxylated 5 methyl-isoxazole form of leflunomide, respectively.