Thermosensitive and pH-responsive quercus infectoria gall-containing gel with long-lasting anti-inflammatory activity for ulcerative colitis

In the study, quercus infectoria gall (QIG) was used to develop a pH/thermosensitive gel in situ delivery system for enema administration of to treat acute ulcerative colitis (UC). The QIG ethanol extract pH/temperature-sensitive gel (QIG-pH-TSG) was characterized by using DSC, SEM, rheological and drug release analyses. The therapeutic effect in UC mice of the obtained gel were studied. The gel was maintained in a flowing liquid state under nonphysiological conditions (25 °C) to facilitate drug administration, and was transformed into a pseudoplastic liquid state under physiological conditions (37 °C), which prolonged its retention time in the colon. The gel drug was completely released within 24 h, and the temperature and viscosity of the gel were within the required range. In the <i>in vitro</i> anti-inflammatory test, QIG-pH-TSG decreased the level of TNF-α and IL-6, and increased IL-10 in RAW 264.7 actived by LPS. Moreover, the administration of QIG-pH-TSG resulted in a decrease in the colon histopathological score and an increase in colonic length, and also could reduce the IL-6, TNF-α, and C-reactive protein (CRP) levels in UC mice along with significant increases in IL-10 level in the colon. The QIG-pH-TSG could increase the concentration of QIG at the local inflammatory site and lead to an effective repair of the colonic mucosa. Therefore, the pH/thermosensitive in situ gel may serve as a drug delivery system for QIG to treat UC and overcome the limitations of some existing formulations. These results indicated that this composite gel was effectively in UC mice and the study provided a practical reference for the application of QIG-pH-TSG in the treatment of UC.