Mechanism Of Melanin Nanozymes On DSS-induced Colitis Mice

BackgroundInflammatory bowel disease（IBD）is a chronic and non-specific gastrointestinal inflammatory disorder mainly characterized by disturbed mucosal homeostasis and mucosal ulcerations of the gut.,including ulcerative colitis（UC）and Crohn’s disease（CD）.Due to the long course and repeated episodes of IBD,not only should the clinical symptoms be managed,but also"mucosal healing"or"sustained and deep mucosal remission"must be achieved.Therefore,more effective treatment strategies that target the pathogenesis of IBD are needed.Excessive reactive oxygen and nitrogen species（RONS）can break the balance between oxidative and antioxidant systems and induce oxidative stress,which lead to apoptosis of intestinal epithelial cells（IECs）,disruption of intestinal mucosal barrier,and increased intestinal permeability,bacterial translocation,and inflammation.Therefore,scavenging excessive RONS to maintain the balance of redox balance is an effective strategy to alleviate intestinal mucosal injury and colitis.Melanin is a powerful cationic chelator containing a population of functional groups such as catechol,amine,and imine,which confer the ability to scavenge a wide range of RONS.Synthetic Melanin nanozymes（MeNPs）have better biocompatibility and stability.The strong RONS scavenging ability of MeNPs have been indicated by previous studies,but its role and mechanism in IBD are still unclear.The present study aims to investigate the therapeutic efficacy and mechanism of MeNPs by constructing a mice model of ulcerative colitis,and provide the experimental basis for more effective treatment strategies for IBD.Methods（1）MeNPs were synthesized by a st（?）rber-like method and characterized by TEM,XRD,Zeta potential,XPS,and UV-Visible spectrophotometer.（2）The stability of MeNPs in the simulated digestive tract（SDF）was detected by TEM,XRD,Zeta potential,XPS,and UV-Visible spectrophotometer.（3）The effects of MeNPs on the cell viability,ROS level,and mitochondrial function of HT-29 were indicated by CCK8,DCFH-DA,Mito SOX（?）Red mitochondrial superoxide indicator,and JC-1 kit were used to detect（4）Dextran sulfate sodium was used to establish models of ulcerative colitis in mice.A variety of biological methods such as H&E staining,TEM,ELISA,and western blot,were performed to explore the effects and underlying mechanism of MeNPs on ulcerative colitis in vivo.Results（1）MeNPs were negatively charged,possessed the uniform and monodisperse spherical structures with an average diameter of¹20 nm and effectively eliminated O₂^·-,H₂O₂and ONOO^-.（2）There were no significant differences in the shape,particle size,structure,potential,elemental composition and RONS scavenging ability of MeNPs after exposing to SDF.（3）MeNPs have no obvious cytotoxicity,could significantly reduce the level of ROS and improve mitochondrial function and cell apoptosis in H₂O₂-induced HT-29 cell models.（4）MeNPs ameliorated body weight loss,DAI score,and blood in the stool in mice with ulcerative colitis.In the MeNPs-treated mice group,the colonic intestinal mucosa was intact,with neat villi,healthy crypt structure,intestinal glands arranged in order,abundant goblet cells,and few inflammatory cell infiltration.MeNPs downregulated the levels of MDA,MPO,IL-6,TNF-α,and the expression of Bax in the colon tissues,while upregulated the levels of SOD,IL-10,and the expression of NRF2,Bcl-2,ZO-1,Occludin,relieved symptoms of ulcerative colitis mice.Conclusions（1）MeNPs effectively scavenged a variety of RONS in vitro and maintain structural and functional stability in the digestive tract.（2）MeNPs had the potential to alleviate ulcerative colitis by suppressing colonic oxidative stress,reducing inflammation,restoring intestinal barrier function and ameliorating symptoms of ulcerative colitis.