Development and validation of a porcine artificial colonic mucus model reflecting the properties of native colonic mucus in pigs

Colonic mucus plays a key role in colonic drug absorption. Mucus permeation assays could therefore provide useful insights and support rational formulation development in the early stages of drug development. However, the collection of native colonic mucus from animal sources is labor-intensive, does not yield amounts that allow for routine experimentation, and raises ethical concerns. In the present study, we developed an in vitro porcine artificial colonic mucus model based on the characterization of native colonic mucus. The structural properties of the artificial colonic mucus were validated against the native secretion for their ability to capture key diffusion patterns of macromolecules in native mucus. Moreover, the artificial colonic mucus could be stored under common laboratory conditions, without compromising its barrier properties. In conclusion, the porcine artificial colonic mucus model can be considered a biorelevant way to study the diffusion behavior of drug candidates in colonic mucus. It is a cost-efficient screening tool easily incorporated into the early stages of drug development and it contributes to the implementation of the 3Rs (refinement, reduction, and replacement of animals) in the drug development process

Understanding the gastrointestinal mucus and its impact on drug absorption

The gastrointestinal mucus is a hydrogel lining the luminal side of the gastrointestinal epithelium. Mucus is vital for gut homeostasis because it protects the epithelium from the noxious external environment. However, from a drug delivery perspective, drugs have to permeate through the mucus to reach the epithelium; therefore, mucus might pose a barrier to drug absorption. Most of the information about mucus derives from fundamental studies performed on rodents. However, information from larger preclinical animal species is highly warranted for improving study designs and guiding better interpretation of data from preclinical assessments. Furthermore, improved understanding of the nature of the gastrointestinal mucus would enable the development of in vitro mucus models with increased biorelevance. These could then be implemented in drug absorption assays to improve the (bio)predictability. Well-informed in vitro mucus models would enable quick and less variable screening of drug candidates in the early drug development stages. Finally, these models would contribute to reduction, refinement, and replacement (the 3Rs) of animal usage in the drug development process.  This thesis aims to improve our understanding of the nature of gastrointestinal mucus and its impact on drug absorption. For this purpose, mucus from the complete gastrointestinal tract of pigs and dogs was characterized and the diffusion of physicochemically diverse FITC-dextrans through colonic mucus was studied, both ex vivo and in vitro. The characterization of the gastrointestinal mucus focused on properties relevant for drug absorption and revealed the physiological characteristics, composition, and structural profiles from the various gastrointestinal regions. The findings pointed towards substantial differences between small intestinal and colonic mucus in both species and served as the basis for developing artificial colonic mucus models for drug permeation assessments. Porcine and canine artificial mucus models were developed and validated against the respective native secretions in terms of structural properties and demonstrated their potential to capture the key diffusion patterns of FITC-dextrans observed in native colonic mucus. Overall, this work provided insights into key properties of mucus from large preclinical species and validated tools for the assessment of the impact of mucus on drug absorption

Physiological properties, composition and structural profiling of porcine gastrointestinal mucus

The gastrointestinal mucus is a hydrogel that lines the luminal side of the gastrointestinal epithelium, offering barrier protection from pathogens and lubrication of the intraluminal contents. These barrier properties likewise affect nutrients and drugs that need to penetrate the mucus to reach the epithelium prior to absorption. In order to assess the potential impact of the mucus on drug absorption, we need information about the nature of the gastrointestinal mucus. Today, most of the relevant available literature is mainly derived from rodent studies. In this work, we used a larger animal species, the pig model, to characterize the mucus throughout the length of the gastrointestinal tract. This is the first report of the physiological properties (physical appearance, pH and water content), composition (protein, lipid and metabolite content) and structural profiling (rheology and gel network) of the porcine gastrointestinal mucus. These findings allow for direct comparisons between the characteristics of mucus from various segments and can be further utilized to improve our understanding of the role of the mucus on region dependent drug absorption. Additionally, the present work is expected to contribute to the assessment of the porcine model as a preclinical species in the drug development process

The use of BioGIT system to assess the impact of dose and formulation on early exposure to low solubility drugs after oral administration

Purpose: To evaluate the usefulness of the Biorelevant Gastrointestinal Transfer (BioGIT) system in assessing the impact of dose and formulation on early exposure of five lipophilic active pharmaceutical ingredients (APIs) by comparing in vitro data with previously collected plasma data in healthy adults. Methods: Lu 35-138 (HCl salt of weak base) was studied at three dose levels in a-hydroxypropyl-beta-cyclodextrin solution. Fenofibrate was studied at two dose levels in the form of a solid dispersion formulation. AZD2207 (hemi-1,5-naphthalenedisulfonate salt of weak base) was studied at three dose levels in the form of immediate release capsules. SB705498 (weak base) was studied in the form of immediate release tablets and capsules. Cyclosporine A was studied in the form of self-emulsifying drug delivery systems, Sandimmun® and Sandimmun® Neoral. Duodenal concentrations were estimated using the BioGIT system. AUC0-0.75h values were calculated from the apparent concentration versus time data in the duodenal compartment of the BioGIT system and were used for estimating early exposure. Differences in AUC0-0.75h values were evaluated versus differences in AUC0-1h and in AUC0-2h values calculated from previously collected individual plasma data in healthy adults. Results: The BioGIT system qualitatively identified the impact of dose and of formulation on early exposure in all cases. Quantitative prediction of the impact of dose was possible for the fenofibrate solid dispersion tablets. Although trends matched, slight underestimation of differences in early exposure was observed for the three weak bases. Overestimation of the impact of formulation in early exposure to cyclosporine was observed. Conclusions: The BioGIT system was useful for detecting the impact of dose and of formulation on early exposure to five model lipophilic APIs