The contribution of the contact system in ulcerative colitis

Background. Ulcerative colitis (UC) is a life-long disease often diagnosed in younger individuals. The relapsing nature of UC represents a challenge as disease activity causes poor quality of life and absenteeism from work. Complications related to disease activity are hospitalisation, colectomy and thromboembolic events. Detection of disease activity is important to maintain quality of life and reduce the risk of complications. However, none of the existing modalities for monitoring UC are ideal. Those with high sensitivity are invasive or troublesome i.e, lower endoscopy and faecal calprotectin, respectively. While patient-friendly methods i.e. c-reactive protein has lower sensitivity. Thus, a more ideal patient-friendly marker is of interest.
The contact system (CAS) may offer such a marker. Animal studies demonstrated CAS activation and inhibition, respectively, induced and alleviated different types of experimental colitis. Research including patients is limited to one study, where patients with active UC had increased CAS activation compared to controls and inactive UC. Potential activators of CAS are polymerised proteins, whether the occurs in UC is unknown. However, studies link UC to polmerised α-1 antitrypsin.
We hypothesised that CAS contributes to the inflammation of UC and that AAT polymers might activate CAS.
Study I was designed as a cross sectional study comparing CAS in patients with active UC to non-IBD controls. We included adults with symptomatic and endoscopically active UC. Comorbidity and use of medication affecting inflammation or CAS was prohibited. Gender-matched blood donors served as control. 96 patients and 100 controls were included for analysis. Patients had significantly higher plasma levels of cleaved H-kininogen (cHK) compared to controls. The cHK distinguished patients from controls regardless of disease activity in our subanalyses. Patients and controls did not differ in their analyses on coagulation factor XII, prekallikrein, H-kininogen, C1 inhibitor and kallikrein generation. Conclusively, despite having a similar CAS response patients presented higher cHK levels than controls. This may be due to CAS-independent activation of plasma kallikrein. Further, cHK was identified as a potential biomarker in UC.
Study II was designed as a prospective cohort study comparing CAS during exacerbation to remission. 55 patients from Study I were endoscopically evaluated 26 weeks after inclusion and stratified to Group 1 (endoscopic remission), n=28 and Group 2 (active disease), n=27. We observed no significant changes during treatment in either group. Interestingly, cHK levels during remission was significantly higher compared to controls of Study I. Conclusively, the CAS response did not reflect change in disease activity. Because the study was statistically underpowered, our results needs confirmation.
Study III was designed as a laboratory study aiming to clarify whether polymerised α-1 antitrypsin is present in patients with active UC and activates CAS. Human α-1 antitrypsin was polymerised by heating. Native polyacrylamide gel electrophoresis and silver staining verified successful polymerisation and a functional elastase assay confirmed polymers lost their function to inhibit elastase. A functional assay designed for studying the activation of CAS by polymerised C1 inhibitor was modified for our study. The generated α-1 antitrypsin polymers did not activate CAS. Plasma samples from patients with extensive UC (n=7) and unmatched healthy controls (n=7) were subjected to western blotting using a pool of in-house generated monoclonal antibodies recognising native and polymerised α-1 antitrypsin. We detected no polymers in patients or controls, only native α-1 antitrypsin. Conclusively, polymerised α-1 antitrypsin do not induce CAS activation in extensive UC.