Peptide drugs and biologics provide opportunities for
treatments
of many diseases. However, due to their poor stability and permeability
in the gastrointestinal tract, the oral bioavailability of peptide
drugs is negligible. Nanoparticle formulations have been proposed
to circumvent these hurdles, but systemic exposure of orally administered
peptide drugs has remained elusive. In this study, we investigated
the absorption mechanisms of four insulin-loaded arginine-rich nanoparticles
displaying differing composition and surface characteristics, developed
within the pan-European consortium TRANS-INT. The transport mechanisms
and major barriers to nanoparticle permeability were investigated
in freshly isolated human jejunal tissue. Cytokine release profiles
and standard toxicity markers indicated that the nanoparticles were
nontoxic. Three out of four nanoparticles displayed pronounced binding
to the mucus layer and did not reach the epithelium. One nanoparticle
composed of a mucus inert shell and cell-penetrating octarginine (ENCP),
showed significant uptake by the intestinal epithelium corresponding
to 28 ± 9% of the administered nanoparticle dose, as determined
by super-resolution microscopy. Only a small fraction of nanoparticles
taken up by epithelia went on to be transcytosed via a dynamin-dependent
process.
In situ
studies in intact rat jejunal loops
confirmed the results from human tissue regarding mucus binding, epithelial
uptake, and negligible insulin bioavailability. In conclusion, while
none of the four arginine-rich nanoparticles supported systemic insulin
delivery, ENCP displayed a consistently high uptake along the intestinal
villi. It is proposed that ENCP should be further investigated for
local delivery of therapeutics to the intestinal mucosa.