Since its discovery in 1917, heparin has been a fascinating, and in a way elusive, molecule. Heparin is a glycosoaminoglycan (GAG) formed by repeated sulphated oligosaccharide units. Natural preparations of heparin (usually obtained from bovine lung or porcine intestinal mucosa) can vary in the length of the polymeric unit and therefore have different molecular weights. As such, the biological actions of this GAG can vary quantitatively between different batches of the molecule. The initial activity ascribed to heparin was its capacity to prolong the process of blood clotting, an effect due to its potentiating interaction with the natural inhibitor of thrombin, antithrombin III. These properties have led to widespread use of heparin as an anticoagulant although scant attention has been paid to other biological activities of this GAG.

This situation has changed in recent years. In fact is has long been recognised that heparin has a wide range of biological effects in addition to its well characterised anticoagulant property, including the ability to display anti-inflammatory efficacy (reviewed by Jacques1 and Tyrrel and colleagues2). The anti-inflammatory activity of heparin has been reinforced by positive, although small, clinical trials in patients suffering from a range of inflammatory diseases, including rheumatoid arthritis3 and bronchial asthma.4 In addition, a number of clinical studies have recently …