Bioanalysis of ursodeoxycholic acid and its metabolites and improved oral bioavailability using mixed micelles with poloxamer 407 and polysorbate 80

The development of analytical methods for endogenous therapeutic substances is a critical but challenging issue as obtaining a blank matrix without endogenous substance is impossible. To address this issue, we prepared a surrogate biological matrix by removing endogenous bile acids from rat plasma using a charcoal-stripped method and developed an analytical method for ursodeoxycholic acid (UDCA) and its conjugated metabolites, tauroursodeoxycholic (TUDCA) and glycoursodeoxycholic acid (GUDCA), including the use of surrogate matrices and protein precipitation method. In addition, we applied the bioanalytical method to investigate the bioavailability of UDCA-mixed micelle powder formulation (UDCA-MM). The oral bioavailability of UDCA in rats was calculated as 15.2% and increased 3.32-fold following the oral administration of UDCA-MM with the increased production of TUDCA without significant change in GUDCA. The UDCA-MM powder was prepared by thin-layer hydration and subsequent freeze-drying method in a ratio of UDCA/polysorbate 80/poloxamer 407 = 1:1:10 (w/w/w). The UDCA-MM was easily dispersed with a particle size of 16.5 ± 2.2 nm and solubility of 1120 ± 38 μg/mL, which represented a 175.3-fold increase in its solubility of UDCA. In conclusion, we developed and validated a simple and reliable bioanalytical method for UDCA, TUDCA, and GUDCA using the charcoal-stripped plasma as surrogate matrices. Our bioanalytical method successfully supported the assessment of the pharmacokinetics or bioavailability of UDCA, TUDCA, and GUDCA after the intravenous or oral dosing of UDCA and UDCA-MM. The UDCA-MM using poloxamer 407 and polysorbate 80 is a promising technique for increasing the solubility and oral absorption of UDCA.