Heparins in ulcerative colitis: proposed mechanisms of action and potential reasons for inconsistent clinical outcomes.

Current drug therapies for ulcerative colitis (UC) are not completely effective in managing moderate-to-severe UC and approximately 20% of patients with severe UC require surgical interventions. Heparins, polydisperse mixtures of non-anticoagulant and anticoagulant oligosaccharides, are widely used as anticoagulants. However, heparins are also reported to have anti-inflammatory properties. Unfractionated heparin was initially used in patients with UC for the treatment of rectal microthrombi. Surprisingly, it was found to be effective in reducing UC-associated symptoms. Since then, several pre-clinical and clinical studies have reported promising outcomes of heparins in UC. In contrast, some controlled clinical trials demonstrated no or only limited benefits, thus the potential of heparins for the treatment of UC remains uncertain. This review discusses potential mechanisms of action of heparins, as well as proposed reasons for their contradictory clinical effectiveness in the treatment of UC.