(596p) Food-Associated Stimuli Impact On Particle Penetration Through Gastrointestinal Mucus Barrier

Food-associated Stimuli Impact on Particle Penetration
through Gastrointestinal Mucus Barrier

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

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

Introduction:

Mucus is a complex gel network comprised
of mucins, lipids, salts, proteins, macromolecules
and cellular debris. A heterogeneous mucus layer protects the gastrointestinal
(GI) tract and other mucosal surfaces. Orally delivered drug and gene vectors
must traverse through mucus in order to enter the circulatory system. However,
the transport of these vectors and general barrier properties of mucus are not
well characterized. The main objective of this project is to analyze the impact
of food-derived lipids and bile salts as well as physiologically relevant stimuli,
pH and [Ca⁺²], on particle transport across GI tract mucus. These
post-prandial stimuli could potentially be used to
control drug carrier transport or prevent pathogen invasion.

Materials and Methods:

Particle transport across porcine intestinal mucus
from pig jejunum was investigated. 200 nm amine-, carboxylate-,
sulfate- and 100 nm carboxylate-modified particles
were diluted in maleate buffer, bile salts (NaTDC) and simulated fed intestinal contents (?FED state?)
including maleate buffer, bile salts/phospholipids
(lecithin) and a lipid mixture containing soybean oil and monoglycerol
for a particle concentration of 0.0025 wt.-%. Calcium ion composition was
adjusted by changing CaCI₂ levels in maleate
buffer, and medium pH was controlled by adjusting NaOH
concentration. Particle diffusion was measured by tracking the positions of
diluted microspheres using real- time multiple particle tracking technique
(MPT). Olympus IX51 was used to detect particles at 40 X magnification and videomicroscopy. Positions of particle centroids
were used to calculate time-averaged mean squared displacements (MSD) and
effective diffusivities (D_eff): MSD = [x(t+τ)-x(t)]² + [y(t+τ)-y(t)]²
and D_eff = MSD/(4τ) where x and y are
positional data and τ is the time scale. Particle effective diffusion
coefficients were then used to estimate the fraction of nanoparticles
expected to penetrate an intestinal mucus layer with a given thickness using a
numerical integration of Fick's second law : dC/dt = D_eff
d²C/dx² where C is the concentration of particles, t is
time and x is position.

Results:

Lipids associated with fed state intestinal contents reduced particle
transport rate through gastrointestinal mucus. Estimated fraction of dosed particle
penetration was reduced by half for microspheres dosed with lipids.
Surprisingly, particles dosed in Bile Salts have higher transport rates (~ 1.5
times faster diffusion rate) than particles dosed in Maleate
Buffer. This could be related to BS adsorption changing the electrostatic
interactions with the mucus network. Lower diffusion rates were also observed at
higher calcium ion concentration. Acidity also plays important role on particle
diffusion rates. pH elevation induced a dramatic decrease in effective diffusivities
of microspheres.

Conclusions:

The observed impact of physicochemical stimuli: lipids,
bile salts, pH, and [Ca⁺²] on particle transport support the
significance of food contents on mucus barrier properties and the use of
naturally changing factors in the GI tract to improve the effective transport
of drug carriers for oral drug delivery. In addition, these factors could
contribute to food effect on oral drug absorption, an important factor to oral
drug delivery.