Transient
permeability enhancers (PEs), such as caprylate, caprate,
and salcaprozate sodium (SNAC), improve the bioavailability of poorly
permeable macromolecular drugs. However, the effects are variable
across individuals and classes of macromolecular drugs and biologics.
Here, we examined the influence of bile compositions on the ability
of membrane incorporation of three transient PEs—caprylate,
caprate, and SNAC—using coarse-grained molecular dynamics (CG-MD).
The availability of free PE monomers, which are important near the
absorption site, to become incorporated into the membrane was higher
in fasted-state fluids than that in fed-state fluids. The simulations
also showed that transmembrane perturbation,
i.e
.,
insertion of PEs into the membrane, is a key mechanism by which caprylate
and caprate increase permeability. In contrast, SNAC was mainly adsorbed
onto the membrane surface, indicating a different mode of action.
Membrane incorporation of caprylate and caprate was also influenced
by bile composition, with more incorporation into fasted- than fed-state
fluids. The simulations of transient PE interaction with membranes
were further evaluated using two experimental techniques: the quartz
crystal microbalance with dissipation technique and total internal
reflection fluorescence microscopy. The experimental results were
in good agreement with the computational simulations. Finally, the
kinetics of membrane insertion was studied with CG-MD. Variation in
micelle composition affected the insertion rates of caprate monomer
insertion and expulsion from the micelle surface. In conclusion, this
study suggests that the bile composition and the luminal composition
of the intestinal fluid are important factors contributing to the
interindividual variability in the absorption of macromolecular drugs
administered with transient PEs.