Structural Determinants of the Capacity of Heparin to Inhibit the Formation of the Human Amplification C3 Convertase

Abstract

A B S T R A C T The ability of heparin glycosaminoglycan to prevent formation ofthe properdin-stabilized amplification C3 convertase is independent of antithrombin binding activity and requires substitution of the amino sugar and a degree of oxygen (0)-sulfation which could be on the uronic acid or the amino sugar. Preparations of heparin glycosaminoglycan isolated by different techniques from different species (rat, human, and porcine) exhibited an equivalent capacity to inhibit generation ofthe amplification C3 convertase. Hyaluronic acid, which is devoid of 0-sulfation, had no inhibitory activity; chondroitin 4-sulfate of rat and whale origins, chondroitin 6-sulfate of rat and shark origins, and dermatan sulfate from porcine skin are 0-sulfated on the galactosamine and had minimal activity. Porcine heparin glycosaminoglycan, isolated on the basis of affinity for antithrombin III, had no greater anticomplementary activity than porcine glycosaminoglycan, which failed to bind antithrombin III and had essentially no anticoagulant activity. Nitrogen (N)-desulfation of porcine heparin reduced anticomplementary activity to the level of the other sulfated mucopolysaccharides, and both N-resulfation and N-acetylation restored the original activities, thereby indicating a requirement for N-substitution, but not N-sulfation. N-resulfation of N-desulfated and 0-desulfated heparin did not restore any activity, thus indicating that 0-sulfation and N-substitution represent independent, critical structural requirements for the anticomplementary activity of heparin glycosaminoglycan.

Determination of alternative pathway of complement activity in mouse serum using rabbit erythrocytes

“…With MRBC as indicator cells, however, human AP50 activity is 1.5 times higher, while mouse and guinea pig serum have no measurable activity. This discrepancy suggests that besides sialic acid (Kazatchkine et al, 1979) other membrane components govern the inhibition of alternative C pathway activation by erythrocytes. Experiments to investigate the possible use of a combination of human serum and mouse erythrocytes as a tool for quantitation of the murine Cab inactivator system are in progress.…”

“…The mechanism of alternative C pathway activation by MRBC, RRBC and sialase-treated SRBC seems to be protection of membrane-bound alternative pathway C3 convertase against decay<tissociation by the C3b inactivator system (Fearon and Austen, 1977;Kazatchkine et al, 1979).…”

Analysis of the recognition mechanism of the alternative pathway of complement by monoclonal anti‐factor H antibodies: evidence for multiple interactions between H and surface bound C3b

“…the effects of polyanions [12,35,36] or various trypsin treatments of H [17,37] on H binding to surface-associated C3b. The binding sites on C3b for H have been analyzed by synthetic peptides and mAb, and at least two segments of C3b (residues 1187 1249 and 727-768) have been found to be involved in binding of C3b to H [20,21].…”

“…PH SO0 1 4-5793(96)00905-2 factor B to C3b and by supporting dissociation of C3bBb and rapid cleavage of C3b by factor I [7,8,13,14]. High affinity of H to C3b is favored by cell surface components present on AP 'non-activators', e.g.…”

“…High affinity of H to C3b is favored by cell surface components present on AP 'non-activators', e.g. by sialic acid residues on glycophorin A and glycosaminoglycans [10][11][12]14,15], and leads to down-regulation of complement activation. C3b on 'activators', i.e.…”