Determination of the stress biomarker corticosterone in serum of tumor-bearing mice by surrogate-based liquid chromatography-tandem mass spectrometry.

A simple, robust and specific liquid chromatography tandem mass spectrometry (LC-MS/MS) method was developed and validated to determine the concentration of corticosterone (Cort) which is usually regarded as a stress biomarker in mouse serum. Since Cort is an endogenous hormone, a 'surrogate analyte' strategy was adopted using the stable isotope-deuterated corticosterone as a surrogate of the authentic analyte to generate the calibration curve. With telmisartan as the internal standard, the analytes were extracted with methanol, ethanol and acetone (1:1:1, v/v/v) and separated on a XTerra C18 (2.1 × 50 mm, 3.5 µm) column using a mobile phase consisting of 0.2% formic acid in water-methanol (30:70, v/v). Detection was performed in multiple reaction monitoring mode with an electrospray ionization source operated in positive ion mode. The standard curves were linear (r(2) > 0.999) over the dynamic range of 8.60-430 ng/mL, with a lower limit of quantification of 8.60 ng/mL. The intra- and inter-assay precisions were less than 15.0% of the relative standard deviation. This method was further used for analysis of serum samples from C57B/L tumor-bearing mice before and after the treatment of fluoxetine. Validation of the assay and its application to the analysis demonstrated that the method was applicable to determine meaningful changes in Cort concentrations in serum samples of the tumor-bearing mice for the stress status evaluation.