Methods: To clarify the intestinal absorption mechanisms of OVA and the effect of aspirin, in situ intestinal re-circulating perfusion study was performed using OVA and fluorescein isothiocyanate-labeled dextran 40 (FD-40), a marker for non-specific-absorption pathways in the presence or absence of various endocytosis inhibitors and aspirin. In addition, plasma concentrations of OVA and FD-40 were measured after oral administration by gavage in rats. To investigate the effect of aspirin on the oral sensitization to OVA, rats were orally administered with OVA by gavage at 3 times a week every other day for 8 weeks. Aspirin or absorption enhancer, spermine was administered 30 min before or simultaneously with OVA, respectively. To evaluate the sensitization to OVA, plasma levels of OVA-specific IgE and IgG1were determined by ELISA at 2, 4, 6 and 8 weeks after initiation of OVA sensitization.
Results: The absorption rate of OVA in the distal intestine was higher compared with that for a marker of FD-40. Colchicine (general endocytosis inhibitor), bafiromycin A1 (inhibitor for receptor-mediated endocytosis) and phenylarsine oxide (inhibitor for clathrin-mediated endocytosis) suppressed the OVA absorption whereas mehyl-β-cyclodextrin (inhibitor for caveolin-mediated endocytosis) exerted no significant effects at distal region, indicating that OVA is preferentially absorbed from the distal intestine via paracellular, and receptor- and clathrin-mediated endocytic pathways. Aspirin increased intestinal absorptions of OVA and FD-40 via the paracellular pathway and exhibited higher plasma levels of OVA-specific IgE and IgG1 than those in control at 6 and 8 weeks. Spermine also increased the oral absorptions of OVA almost to the same extent of aspirin whereas the plasma IgE and IgG1levels exhibited no significant differences against those in untreated control.
Conclusions: Facilitation of OVA absorption via paracellular pathway due to impairment of intestinal barrier function by aspirin is considered to be one of the reasons of enhanced oral sensitization with OVA by aspirin. However, our results have also shown that facilitated oral sensitization to OVA cannot be ascribed to increased absorption of OVA from the intestinal tract only.