Adsorption of bile salts onto crystalline ritonavir particles under simulated gastrointestinal conditions.

The formation of a biomolecular corona on nanoparticles in blood is a well-known phenomenon influencing in vivo performance. Analogous phenomena in other biological fluids, such as the formation of a gastrointestinal (GI) corona, remain under-investigated. The ingestion of medicines leads to the generation of drug particles in the GI fluids. Consequently, an understanding of the behavior of drug particles in the gut requires determination of the adsorption of bile components onto these drug particles. This work aims to elucidate the factors affecting adsorption of bile salts onto ritonavir (RTV) particles. Crystalline RTV particles were incubated with non-micellar or micellar bile salts and bile salt depletion from solution was measured using HPLC and small angle X-ray scattering (SAXS). HPLC results show that bile salts adsorb onto RTV particles, with greater adsorption observed for more hydrophobic bile salts, following the order sodium glycodeoxycholate (SGDC)>sodium taurodeoxycholate (STDC)>sodium glycochenodeoxycholate SGCDC>sodium glycocholate (SGC)>sodium taurocholate (STC). Increasing the ionic strength of the solution led to increased adsorption of STDC, where buffer containing 300 mM NaCl resulted in greater adsorption than 150 mM NaCl. Additionally, micellar bile salts showed greater affinity for RTV particles than unimeric bile salts. In contrast, the extent of bile salt depletion was unaltered by addition of phospholipid to form mixed micelles. SAXS analysis of mixed micelles after incubation with RTV particles confirms depletion of bile salt from the supernatant, evidenced by reduced intensity of the micellar scattering feature. In conclusion, this study investigated factors influencing bile salt adsorption onto drug particles, highlighting the need to consider adsorption of bile components in forming the GI-corona.