Abstract 121 Poster Session II, Sunday, 5/2 (poster 258)

Complement is an important part of the immune system and consists of more than twenty serum proteins and cellular receptors. Unwanted activation of the complement cascade is an important part of the pathogenesis of numerous disease processes including transplant rejection, the inflammatory response of bypass, atherogenesis, reperfusion injuries, autoimmune disorders and neurodegenerative disorders. Heparin and other glycosaminoglycans are well known to inhibit complement activity. It is also known that when heparin is N-desulfated and N-acetylated it has greatly diminished anticoagulant activity while maintaining complement inhibitory activity. However, to date, the precise structural requirements in glycosaminoglycans for complement modulatory activity have not been determined, but must be derived before glycosaminoglycan-based structures could be used clinically to regulate complement activity. We structurally modified heparin and Acharan sulfate (a glycosaminoglycan structurally similar to heparin isolated from the Giant African Snail) to produce seven structurally distinct heparins and three distinct Acharans. Specifically, the heparins were modified at the 2-O-sulfate, the 6-O-sulfate, and the N-position of the heparin sugar ring in various combinations. Similar structural variations were made in the Acharan sulfate. These glycosaminoglycans were analyzed in vitro for their ability to inhibit complement activity directly as well as to augment the inhibitory activity of C1 Inhibitor. We found that removal of the sulfate group at the 6-O-sulfate position decreased heparin's complement inhibitory activity almost threefold. However, removal of the sulfate at the 2-position resulted in only a 15-20% reduction in complement inhibitory activity compared with heparin. Substitution of the N-sulfate group with an acetyl group did not diminish the complement inhibitory activity. We also found that full sulfation of Acharan sulfate resulted in a 30-40% increase in the complement inhibitory activity. These experiments demonstrate that alterations of glycosaminoglycan structure can be made the change the degree to which the glycosaminoglycan regulates complement activity. This study has improved our understanding of the structure-activity relationships present in glycosaminoglycan interaction with the complement system, which is critical to the goal of designing a glycosaminoglycan-based complement inhibitor.

Funded by the National Heart, Lung and Blood Institute of the NIH under the Research Training Program in Pediatric Cardiology #HL 07413

Funded by NIH #HL 52622