(584f) Impact of Food-Associated Stimuli On Barrier Properties of Gastrointestinal Mucus to Particle Transport

Hasan Yildiz, yildiz.h@husky.neu.edu

Rebecca L. Carrier, rebecca@coe.neu.edu

Introduction:

Mucus is composed of a highly complex network including glycoproteins, lipids, cellular and serum macromolecules. Orally delivered drugs and nutrients must diffuse through mucus in order to enter the circulatory system. The transport of drug vectors through the mucus barriers has shown significant effects to enhance drug delivery systems, however the transport of these vectors and the barrier properties of mucus are poorly characterized. The main objectives of this study were to analyze the barrier properties of mucus and understand the mechanisms of effects of physiologically relevant stimuli: Lipids, pH and [Ca⁺²] on particle transport through the gastrointestinal mucus barrier. All these factors are contributed with gastrointestinal changes regarding food intake and they can also be easily controlled. 

Materials and Methods:

Native porcine intestinal mucus was collected from porcine jejunum within 2 h of slaughter. 200 nm amine-, carboxylate-, and sulfate-modified microsphere solutions (2 % solids in distilled water with 2 mM azide) were diluted in media: fed state levels of maleate buffer, bile salts-maleate buffer and fed state lipids in digested states. All these media were prepared at a relevant ph (3.5, 5.5, 6.5), physiological [Ca⁺²] concentrations (5, 10, 20 mM). 10 µl of diluted particle solutions (0.0025 % wt/vol) was added to 200 µl of native mucus for a final particle concentration of 1.25 x 10 ^-4 % wt/vol. Particle diffusion was measured by tracking the positions of microspheres using an Olympus IX51 microscope at 40 X magnification and videomicroscopy. 10 μl of diluted particle solution was added to 200 μl of native mucus. Samples were covered and left at room temperature for 2 h prior to microscopy. Five videos were taken from each individual preparation for a total 100 particle trajectories. The coordinates of particle centroids were used to calculate time-averaged mean squared displacements: MSD=[x(t+r)-x(t)]²+[y(t+r)-y(t)]²,  where t is the time scale and x, y are the coordinates. Two dimensional time-independent diffusion coefficients (D₀) were determined by plotting MSD versus time scale to the anomalous subdiffusive transport relation: MSD=4D₀T^α, where α is the anomalous exponent, which is the degree of particle transport obstruction.

Results:

Lipid content associated with fed state intestinal contents significantly decreased the transport rate of microspheres through gastrointestinal mucus. The affinity of pig gastric mucus glycoprotein [Ca⁺²] was examined, and it was found that a higher concentration of [Ca⁺²] resulted in the reduction of nanoparticle transport rate. This is likely due to binding of [Ca⁺²] to mucin glycoproteins and thus enhanced cross-linking of the mucus gel network. Elevation of pH affects mucus viscoelasticity, leading to less hindered particle transport.

Conclusions:

 Gastrointestinal mucus can pose a significant barrier to drug carrier transport dependent on medium properties. Promising results provide the influence of lipids, [Ca⁺²] and pH support the significance of food contents on mucus barrier properties and also the use of naturally changing factors in the GI tract, lipids, Ca⁺² and pH, to control drug carrier or pathogen transport.