Development of Novel  Models to Study Sub and Post Cellular Uptake of Drugs Following Oral Administration
Creators: Yousef, Malaz AE
Publisher: name: University of Alberta Library
Year: 2024

<p>Given the numerous benefits of oral administration, this thesis investigates two key phenomena influencing the pharmacokinetics and pharmacodynamics of orally administered active pharmaceutical ingredients (APIs): lysosomal trapping and intestinal lymphatic uptake via chylomicrons, with a particular emphasis on the latter.</p>

<p>The absence of a standardized lysosomal fluid composition in pharmaceutical compendia represents a current gap. To address it, a simulated lysosomal fluid was developed by incorporating essential components necessary for lysosomal homeostasis. This new fluid demonstrated superiority over existing commercial fluids, and that was further evidenced by its performance in a basic model for capturing lysosomal trapping. Consequently, this simulated lysosomal fluid could fill the gap for a standardized lysosomal fluid, making it applicable to various pharmaceutical and biomedical uses.</p>

<p>Certain drugs can be packaged within enterocyte-formed lipoproteins known as chylomicrons, which naturally facilitate the absorption of dietary lipids and their transport through intestinal lymphatic uptake rather than the portal circulation. This pathway is particularly important in the context of current drug delivery efforts, which focus on lipid-based formulations for both traditional and novel applications in medication and vaccination delivery. However, it is generally overlooked and there is a need for a standardized lymphatic fluid and representative in-vitro models to investigate and quantify intestinal lymphatic uptake in-vitro. </p>

<p>This work advocates for considering the intestinal lymphatic uptake and emphasizes the need for further research to optimize lymphatic drug delivery, particularly via chylomicrons. The development of simulated lymphatic fluids, both general and intestinal, marks an advancement towards creating a standardized fluid for pharmaceutical research. Moreover, the established in-vitro model offers a promising platform for evaluating drug lymphatic uptake. This model successfully differentiated between drugs with varying lymphotropic affinities. Various enhancers and inhibitors were investigated, revealing that lymphatic uptake could be increased or decreased accordingly. Pluronic® L-81, a known inhibitor of chylomicron uptake, exhibited an inhibitory effect, likely through a novel biophysical mechanism. Furthermore, the in-vitro data suggested that zeta potential influences intestinal lymphatic uptake, leading to corresponding increases or decreases based on the agent used. These novel finding necessitates further in-vivo investigation. The model also examined the effects of food that may stimulate lymphatic uptake, distinguishing between oils containing long-chain fatty acids. However, it did not differentiate between long-chain-rich oils and medium-chain-rich oils in terms of lymphatic uptake. Additionally, in a real-world scenario assessing the impact of excipients through the developed model, the lipid-based excipient Labrafil® 2125 CS exhibited a statistically significant increase in the in-vitro uptake of cannflavin A in a novel formulation.</p>

<p>First-generation dissolution models with a focus on lymphatic uptake were also created to evaluate pharmaceutical formulations and identify factors affecting intestinal lymphatic uptake through this pathway. These new models incorporated the lymphatic absorption pathway, previously neglected in all existing dissolution tests. They showed their capacity to distinguish between different lymphotropics. In addition, they proved to be superior to the biphasic dissolution test in assessing lipid solubility related to lymphatic uptake via chylomicrons. This represented an important step towards more accurate performance testing for assessing lymph-targeted formulations and delivery systems.</p>

<p>As regulatory submissions increasingly incorporate physiologically based pharmacokinetic (PBPK) modeling, one was developed to simulate intestinal lymphatic uptake after a fatty meal. In the absence of direct simulation algorithms for lymphatic uptake, the model was built by adjusting the metabolic profile of the drug to account for its ability to circumvent first-pass liver metabolism. This occurs when the drug is incorporated into postprandially formed chylomicrons, allowing it to be absorbed through the lymphatic system rather than portal blood passing through the liver.</p>

<p>The developed in-vitro models for studying the intestinal lymphatic uptake via chylomicrons would reduce reliance on animal studies, addressing ethical concerns and save time and resources for development of lymph targeted drug delivery. Moving forward, establishing a mathematical framework to correlate these in-vitro models with in-vivo lymphatic uptake would further enhance their reliability. This could streamline regulatory submissions, potentially accelerating the approval process for new therapies and fostering innovation in drug development. Also, incorporating intestinal lymphatic uptake into existing in-silico softwares would enable more accurate predictions of drug behavior and provide a deeper mechanistic understanding of lymphotropic drugs and formulations, ultimately aiding in improved formulation development and facilitating regulatory submissions.</p>