The silymarin and quercetin-loaded pH-sensitive chitosan-tripolyphosphate/Eudragit® S100 nanoparticles improve acetic acid-induced colonic inflammation in rats by modulating Th1 cells, inflammatory cytokines, and oxidative stress.

Silymarin (SM) and quercetin (Que) are flavonoids with antioxidant and anti-inflammatory effects. Ulcerative colitis (UC) is a chronic inflammatory bowel disease characterized by mucosal inflammation. This study aimed to develop pH-sensitive cross-linked chitosan-tripolyphosphate/Eudragit® S100 nanoparticles (EU S100/CS-TPP NPs) as delivery systems for SM and Que, and to evaluate their anti-inflammatory and antioxidant effects in an acetic acid-induced rat model of colonic inflammation. A total of 80 rats were randomly divided into ten groups. Colonic inflammation was induced with 4% acetic acid and followed by oral treatment with SM, Que, or EU S100/CS-TPP NPs. Colon tissues were collected for macroscopic and histopathological evaluation. Th1 (CD4+ IFN-γ+) cell frequency and inflammatory cytokine expression were assessed using immunofluorescence and real-time PCR. Antioxidant parameters, catalase (CAT), malondialdehyde (MDA), nitric oxide (NO), and superoxide dismutase (SOD), were measured spectrophotometrically. Treatment with mesalazine, SM, SM/CS-TPP/EU S100 NPs, Que, Que/CS-TPP/EU S100 NPs, SM/Que, and SM/Que/CS-TPP/EU S100 NPs significantly increased colon length and reduced macroscopic damage, DAI score, colon weight, and histological damage score. Th1 cell frequency, expression of inflammatory cytokines and apoptotic genes, and oxidative stress were significantly downregulated by treatment with mesalazine, SM, SM/CS-TPP/EU S100 NPs, Que, Que/CS-TPP/EU S100 NPs, SM/Que, and SM/Que/CS-TPP/EU S100 NPs compared with the colonic inflammation group. SM/Que/EU S100/CS-TPP NPs showed the strongest therapeutic effects against UC, with potent anti-inflammatory and antioxidant activities and a reduced frequency of CD4+IFN-γ+ cells, suggesting possible involvement of Th1-related pathways. These findings support the potential of this nanoformulation for future UC therapy.