Microbial enzyme-responsive inulin nanoparticles for colon-targeted oral delivery of 5-ASA toward improved therapy of inflammatory bowel disease

Abstract

Colon-targeted delivery of 5-aminosalicylic acid (5-ASA) offers an effective strategy for treating inflammatory bowel disease (IBD) while minimizing systemic side effects. However, conventional oral 5-ASA formulations suffer from premature drug release and poor colon specificity. To overcome these limitations, we developed a biodegradable, prebiotic, and immunomodulatory inulin nanoparticle (INP) platform enabling microbial enzyme-responsive and site-specific release of 5-ASA in the colon. Methods INP was fabricated via a mild nanoprecipitation method and loaded with 5-ASA (5-ASA@INP). Physicochemical characteristics, drug-loading performance, and enzyme-responsive sequential release profiles under simulated gastrointestinal fluids were evaluated. Antioxidant and anti-inflammatory effects were assessed in vitro. Biodistribution of DiR-labeled INPs was analyzed to demonstrate colon-targeting efficacy. Therapeutic efficacy, inflammatory cytokine expression, Treg responses in the colon and gut-associated lymphoid tissues, and microbiota-related effects, including short-chain fatty acid (SCFA) production, were evaluated in a colitis mouse model. Results 5-ASA@INP showed 97.02% drug-loading efficiency. The cumulative release of 5-ASA was 7.6% in simulated gastric fluid, 18.7% in simulated intestinal fluid, and 99.2% in simulated colonic fluid. In contrast, only 35.6% of 5-ASA was released under enzyme-free simulated colonic conditions. Compared with free 5-ASA, 5-ASA@INP showed enhanced antioxidant and anti-inflammatory effects in vitro. In vivo, INPs preferentially accumulated in the colon with minimal off-target distribution. In colitic mice, 5-ASA@INP significantly attenuated body weight loss (p = 0.0067) and colon shortening (p = 0.0002). Histological analysis showed that the colonic tissue damage was minimized and the inflammation scores were reduced (p < 0.001). Treatment increased the number of FOXP3+ cells in the colonic tissue and suppressed the expression of IL-17A, TNF-α, and IL-1β. The gut microbial profile was restored toward that of the normal group and fecal SCFA levels were increased. Conclusions This study demonstrates that the INP platform enables microbial enzyme-responsive, colon-targeted delivery of 5-ASA while complementarily harnessing the intrinsic prebiotic and immunomodulatory properties of inulin. This dual-function nanoplatform provides a promising strategy for efficient oral treatment of IBD.