In vitro performance prediction of LBFs using lipolysis-permeation assay with the LiDo artificial membrane: Validation and protocol optimization

Abstract: Lipid-based formulations (LBFs) can be an effective formulation strategy to improve the bioavailability of lipophilic drugs. However, conventional single-compartment in vitro lipolysis assays often underestimate LBF performance in vivodue to the absence of absorption sink. Recently, a two-compartment setup separated by an absorptive membrane provided good in vivo in vitro relationship (IVIVR). The goal of this study was therefore to investigate the use of the artificial membrane “LiDo” in two-compartment assays with regards to digestive enzymes, donor volume and different pH-control methods. The in vivo relevance of the assay was investigated using a single LBF and carvedilol, varying drug-to-formulation ratio and physical state of carvedilol. These formulations were already examined in vivo in a previous study. Digestion was performed using three different enzymes: porcine pancreatin, porcine lipase and Novozyme 435. Due to the incompatibility of pH electrodes with LiDo membrane, high strength lipolysis buffer was tested as alternative to the normal lipolysis buffer. The latter cannot counteract pH decreases caused by lipid digestion and requires dynamic titration.  In vitro assays were conducted in full-size as well as small-size setup. The barrier integrity was evaluated using Lucifer Yellow as a membrane marker. It was found that use of porcine pancreatin best reflected in vivo drug plasma exposure. In contrast, no relationship was observed between in vitro data obtained from lipolysis assays with lipase and Novozymes 435 and in vivo data. Results from assays with lipase may not reliably compare to assays with Novozyme 435 where the latter showed tendency to aggregate in low donor volume, resulting in poor lipid digestion. The outcomes from assays performed in the small-scale setup did not produce good IVIVR either. This outcome could be caused by insufficient agitation in the donor compartment, leading to poor dispersion of LBFs. However, “LiDo'' membrane retained its integrity during lipolysis by all three enzymes. Hence, we can demonstrate further evidence on the utility of LiDo membrane for in vitro lipolysis-permeation.