A self-crosslinking hydrogel made from a modified amino acid polymer was developed to stabilize and slowly release KPV tripeptide when administered rectally for ulcerative colitis. KPV alone is unstable at body temperature, but the hydrogel preserved its activity significantly longer. In rats with chemically induced colitis, the KPV-hydrogel combination was more effective than free KPV at reducing colon damage, lowering inflammatory cytokines, and restoring normal colon architecture.
Abstract
KPV (Lys-Pro-Val), which is a tripeptide derived from α-MSH (α-melanocyte-stimulating hormone), has an anti-inflammatory effect on colitis. However, KPV solution is very unstable when rectally administered, compromising its therapeutic efficacy. Herein, cysteamine-grafted γ-polyglutamic acid (SH-PGA) was synthesized by conjugating cysteamine with the carboxyl groups of γ-PGA. The synthesized SH-PGA has the thiol grafting amount of 4.5 ± 0.3 mmol/g. Without the use of the cross-linker, the SH-PGA hydrogel with 4% of the polymer was formed by self-cross-linking of thiol groups. Moreover, the formation of the SH-PGA hydrogel was not affected by KPV. The KPV/SH-PGA hydrogel presented higher elastic modulus (') than the corresponding viscous modulus (″) at 0.01-10 Hz, exhibiting good mechanical stability. The KPV/SH-PGA hydrogel presented a shear-thinning behavior, which was helpful for rectal administration. Only 30% of KPV was released from the KPV/SH-PGA hydrogel within 20 min, followed by a sustained-release behavior. Importantly, the stability of KPV in the SH-PGA hydrogel was obviously enhanced, which was presented by detecting its anti-inflammatory activity and promoting cell migration potential after 2 h of exposure to 37 °C. The enhanced therapeutic effect of the KPV/SH-PGA hydrogel on colitis was confirmed on 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced ulcerative colitis rats. The colitis symptoms including body weight loss and the disease activity index score were obviously attenuated by rectally administering the KPV/SH-PGA hydrogel. Besides, the KPV/SH-PGA hydrogel treatment prevented the colon shortening of TNBS-infused rats and decreased the colonic myeloperoxidase level. The morphology of the colon including the epithelial barrier, crypt, and intact goblet cells was recovered after KPV/SH-PGA hydrogel treatment. Besides, the KPV/SH-PGA hydrogel decreased the expression of proinflammatory cytokines such as tumor necrosis factor α and interleukin 6. Collectively, the KPV/SH-PGA hydrogel may provide a promising strategy for the treatment of ulcerative colitis.