Role Of Plasma Kallikrein-kinin System In The Pathogenesis Of Inflammatory Bowel Disease

Background and significance:Inflammatory bowel diseases(IBD),including ulcerative colitis(UC)and Crohn's disease(CD),are associated with chronic relapsing inflammation of the intestinal tract of unknown etiology.The incidence of IBD has increased in recent years,and has become a major disease of the digestive system that endangers human health.The efficacy and safety of current treatment of inflammatory bowel disease are not satisfactory.Plasma kallikrein-kinin system(KKS)is a group of plasma proteins that are associated with tissue injury.The KKS consists of two serine proteinases including coagulation factor ?(F?)and prekallikrein(PK),and the nonenzymatic cofactor high-molecular-weight kininogen(HK).When these proteins form a complex on activation surface such as negatively charged molecules,this system turns to be activated.F? becomes autoactivated(F?a)and activates PK by cleaving it to kallikrein,Both F?a and kallikrein cleaves HK to generate HKa and release bradykinin(BK).Both HKa and BK can induce proinflammation.Although it has been known the KKS is activated in patients and animals bearing IBD,its pathogenic role in IBD is still unknown.Objective:This study is to characterize the role of plasma KKS in the pathogenesis of IBD and the underlying mechanisms.Method:(1)To determine the role of plasma KKS in IBD,we generated a mouse strain with deletion of Kng1 gene that encodes HK,and a mouse strain with deletion of Klkb1 gene that encodes PK.(2)For induction of DSS-induced colitis,mice were treated with 2.5%(wt/vol)DSS in drinking water for 8 days.The disease activity index(DAI)was the combined score of weight loss,stool consistency,and bleeding.(3)For induction of 2,4,6-Trinitrobenzene sulfonic acid(TNBS)-induced colitis,mice was treated with 3 mg TNBS intrarectally.(4)Mice were treated with kallikrein antibody in DSS-induced colitis.(5)The levels of BK and C5a in plasma,cytokines and MPO in colon tissue were measured by ELISA.(6)The mRNA levels of inflalmatory factors were quantitated by real-time PCR.(7)The percentage of neutrophile in colon Lamina propria cells were measured using flow cytometer.(8)The parafin sections of distal colon were stained using H&E standard technique.(9)The cleavage of the KKS proteins was analyzed by Western blotting.(10)Kallikrein activity was spectrophotometrically monitored via conversion of chromogenic substrate S-2302 on a Bio-Kinetics Reader.Results:(1)KKS was activated in DSS-induced colitis.(2)Compared with WT mice,the mice deficient of HK,PK,and double bradykinin receptors,but not FXll,exhibited attenuation of DSS-induced colitis.(3)Specific inhibition of kallikrein ameliorated DSS-induced colitis in wild-type mice.(4)Kallikrein increased cytokines production and C5a release.(5)DSS activated PK to induce cleavage of HK and release of bradykinin.(6)In TNBS-induced colitis,another model of IBD,the mice deficient of HK,PK,and double bradykinin receptors were also pretected against TNBS-induced colitis.Conclusion:The kallikrein-kininogen-bradykinin pathway is critical in the pathogenesis of IBD,kallikrein activation is a potential target for treatment of IBD.