Toxicokinetic and bioavailability studies on retrorsine in mice, and ketoconazole-induced alteration in toxicokinetic properties.

Retrorsine (RTS) is a toxic retronecine-type pyrrolizidine alkaloid, which is widely distributed. The purpose of this study was to develop a high-performance liquid chromatography-tandem mass spectrometric (LC-MS/MS) method for serum RTS determination in mice. Serum samples were deproteinated by acetonitrile, separated on a C18 -PFP column and delivered at 0.8 ml/min with an eluting system composed of water containing 0.1% (v/v) formic acid and acetonitrile containing 0.1% (v/v) formic acid as mobile phases. RTS and the internal standard S-hexylglutathione (H-GSH) were quantitatively monitored with precursor-to-product transitions of m/z 352.1 → 120.1 and m/z 392.2 → 246.3, respectively. The method showed excellent linearity over the concentration range 0.05-50 μg/ml, with correlation coefficient r2  = 0.9992. The extraction recovery was >86.34%, and the matrix effect was not significant. Inter- and intra-day precisions (RSD) were <4.99%. The validated LC-MS/MS method was successfully applied to study the toxicokinetic profiles of serum RTS in mice after intravenous, oral administration and co-treated with ketoconazole, which showed that RTS displayed a long half-life (~11.05 h) and good bioavailability (81.80%). Co-administration of ketoconazole (KTZ) increased the peak serum concentration and area under the concentration-time curve and decreased the clearance and mean residence time. Summing up, a new standardized method was established for quantitative determination of RTS in sera.