Design and Evaluation of Colon-Specific Epinastine Prodrugs as Potent Anti-Colitis Agents Acting via the Activation of the Nrf2−HO-1 Pathway

The antihistamine epinastine (EPNT) is used to treat allergic and atopic diseases. To reposition EPNT as a therapeutic agent for inflammatory bowel disease (IBD), EPNT was conjugated with colon-specific promoieties: 5-aminosalicylic acid (5-ASA), aspartic acid (Asp)-conjugated 5-ASA, and glutamic acid (Glu)-conjugated 5-ASA via azo bonds to yield EPNT-azo-salicylic acid (EAS), Asp-conjugated EAS (EAS-Asp), and Glu-conjugated EAS (EAS-Glu), respectively. These EPNT derivatives exhibited lower distribution coefficients and reduced transport across Caco-2 cell monolayers. While remaining stable in the upper intestinal environment, the EPNT derivatives were converted to EPNT in the cecal contents with an efficiency comparable to that of the current anti-IBD azo prodrug, sulfasalazine (SSZ). Moreover, orally administered EPNT derivatives resulted in a higher delivery of EPNT to the cecum than oral EPNT alone. The colon-specific performance of the EPNT derivatives followed the order EAS-Asp ≈ EAS-Glu > EAS. In a dinitrobenzenesulfonic acid-induced rat colitis model, the EPNT derivatives were more effective in mitigating colonic damage and inflammation than EPNT and SSZ, with anti-colitis efficacy corresponding to their colon-targeting performance. Oral EPNT derivatives increased the levels of nuclear factor erythroid 2−related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) proteins, likely via the activation of adenosine monophosphate-activated protein kinase (AMPK) in inflamed colonic tissues. Furthermore, co-treatment with zinc protoporphyrin, an HO-1 inhibitor, markedly reduced the anti-colitis effect of EAS-Glu. Finally, oral administration of EPNT derivatives significantly reduced the systemic absorption of EPNT. In conclusion, colon-targeted EPNT may enhance the therapeutic efficacy and safety of EPNT when repositioned as an anti-IBD drug, with the AMPK−Nrf2−HO-1 pathway contributing to its anti-colitis mechanism.