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Purpose

To evaluate the performance of artificial membranes in in vitro lipolysis-permeation assays useful for absorption studies of drugs loaded in lipid-based formulations (LBFs).

Methods

Polycarbonate as well as PVDF filters were treated with hexadecane, or lecithin in n-dodecane solution (LiDo) to form artificial membranes. They were thereafter used as absorption membranes separating two compartments mimicking the luminal and serosal side of the intestine in vitro. Membranes were subjected to dispersions of an LBF that had been digested by porcine pancreatin and spiked with the membrane integrity marker Lucifer Yellow (LY). Three fenofibrate-loaded LBFs were used to explore the in vivo relevance of the assay.

Results

Of the explored artificial membranes, only LiDo applied to PVDF was compatible with lipolysis by porcine pancreatin. Formulation ranking based on mass transfer in the LiDo model exposed was the same as drug release in single-compartment lipolysis. Ranking based on observed apparent permeability coefficients of fenofibrate with different LBFs were the same as those obtained in a cell-based model.

Conclusions

The LiDo membrane was able to withstand lipolysis for a sufficient assay period. However, the assay with porcine pancreatin as digestive agent did not predict the in vivo ranking of the assayed formulations better than existing methods. Comparison with a Caco-2 based assay method nonetheless indicates that the in vitro in vivo relationship of this cell-free model could be improved with alternative digestive agents.

Self-emulsifying drug-delivery systems (SEDDS) have been extensively shown to increase oral absorption of solvation-limited compounds. However, there has been little clinical and commercial use of these formulations, in large part because the demonstrated advantages of SEDDS have been outweighed by our inability to precisely predict drug absorption from SEDDS using current in vitro assays. To overcome this limitation and increase the biological relevancy of in vitro assays, an absorption function can be incorporated using biomimetic membranes. However, the effects that SEDDS have on the integrity of a biomimetic membrane are not known. In this study, a quartz crystal microbalance with dissipation monitoring and total internal reflection fluorescence microscopy were employed as complementary methods to in vitro lipolysis-permeation assays to characterize the interaction of various actively digested SEDDS with a liquescent artificial membrane comprising lecithin in dodecane (LiDo). Observations from surface analysis showed that interactions between the digesting SEDDS and LiDo membrane coincided with inflection points in the digestion profiles. Importantly, no indications of membrane damage could be observed, which was supported by flux profiles of the lipophilic model drug felodipine (FEL) and impermeable marker Lucifer yellow on the basal side of the membrane. There was a correlation between the digestion kinetics of the SEDDS and the flux of FEL, but no clear correlation between solubilization and absorption profiles. Membrane interactions were dependent on the composition of lipids within each SEDDS, with the more digestible lipids leading to more pronounced interactions, but in all cases, the integrity of the membrane was maintained. These insights demonstrate that LiDo membranes are compatible with in vitro lipolysis assays for improving predictions of drug absorption from lipid-based formulations.

Permeation across Caco-2 cells in lipolysis-permeation setups can predict the rank order of in vivo drug exposure obtained with lipid-based formulations (LBFs). However, Caco-2 cells require a long differentiation period and do not capture all characteristics of the human small intestine. We therefore evaluated two in vitro assays with artificial lecithin-in-dodecane (LiDo) membranes and MDCK cells as absorptive membranes in the lipolysis-permeation setup. Fenofibrate-loaded LBFs were used and the results from the two assays compared to literature plasma concentrations in landrace pigs administered orally with the same formulations. Aqueous drug concentrations, supersaturation, and precipitation were determined in the digestion chamber and drug permeation in the receiver chamber. Auxiliary in vitro parameters were assessed, such as permeation of the taurocholate, present in the simulated intestinal fluid used in the assay, and size of colloidal structures in the digestion medium over time. The LiDo membrane gave a similar drug distribution as the Caco-2 cells and accurately reproduced the equivalent rank-order of fenofibrate exposure in plasma. Permeation of fenofibrate across MDCK monolayers did not, however, reflect the in vivo exposure rankings. Taurocholate flux was negligible through either membrane. This process was therefore not considered to significantly affect the in vitro distribution of fenofibrate. We conclude that the artificial LiDo membrane is a promising tool for lipolysis–permeation assays to evaluate LBF performance.