Heparin and derivatized heparin inhibit zymosan and cobra venom factor activation of complement in serum.

Heparin has been shown to inhibit activity of the alternative, classical and terminal pathways of complement by regulating C1, C1 inhibitor, C4 binding protein, C3b, factor H and S-protein. In vivo, heparin inhibits cobra venom factor activation of complement in a dose-related manner in guinea pigs. However, the ability of heparin and of modified heparin to inhibit complement activation in serum has not been examined systematically. The present study compared commercial heparin with a modified heparin that has reduced anticoagulant activity (N-desulfated, N-acetylated heparin) for ability to inhibit cobra venom factor and zymosan-induced complement activation in guinea pig and human serum. Both heparins inhibited cobra venom factor and zymosan-induced consumption of C3 activity in both human and guinea pig serum. In both serum types, commercial heparin was about twice as active as modified heparin on a weight basis for ability to inhibit cobra venom factor-induced complement activation. Both heparins also inhibited zymosan-induced complement activation in human serum. About four times more heparin was required to inhibit cobra venom factor-induced complement activation in guinea pig serum than in human serum while heparin was more than ten times more active in human serum than in guinea pig serum when zymosan was used as the activator of complement. This study suggests that heparin is considerably more effective in regulating complement activity in humans than in guinea pigs, an animal model in which heparin clearly has in vivo capacity to regulate complement activity. These observations represent an important step in the development of new clinically relevant oligosaccharide-derived pharmacologic agents to regulate complement activity.