Potential Value of N-Desulfated Heparin without Anticoagulant Activity in Treatment of Complement-Mediated Lysis of Paroxysmal Nocturnal Hemoglobinuria Erythrocytes.

Abstract

Paroxysmal nocturnal hemoglobinuria (PNH) is clinically characterized by the complement (C')-mediated intravascular lysis of PNH-affected erythrocytes and thrombotic diathesis. Treatment methods of intravascular hemolysis, especially on the hemolytic crisis, have not been established yet. Although several reagents have been used for the treatment of PNH hemolysis, the value of prednisone/prednisolone in treating the hemolysis of PNH is controversial; anti-C5 antibody is under clinical study. We previously demonstrated that heparin and low-molecular weight heparin (LMWH) inhibit C'-mediated hemolysis of PNH erythrocytes in vitro, by inhibiting insertion of C5b-7 into the erythrocyte membranes (Ninomiya et al: Inhibition of complement-mediated haemolysis in paroxysmal nocturnal haemoglobinuria by heparin or low-molecular weight heparon. Brit J Haematol 109,875–881, 2000). However, that the concentration of heparin (or even that of LMWH) required to inhibit C'-mediated lysis of PNH erythrocytes efficiently induces a profound prolongation of APTT (activated partial thromboplastin time) of plasma unables their clinical application. In the current study, we examined the inhibitory effects of heparin, LMWH (dalteparin), and N-desulfated heparin on C'-mediated lysis of PNH erythrocytes (sucrose hemolytic assay) and their anticoagulant effects on normal plasma coagulation system (APTT, TT (thrombin time), and AT-III (antithrombin)-enhancing activity). N-desulfated heparin inhibited C'-mediated lysis of PNH erythrocytes, equivalently to heparin or LMWH, on the basis of their uronic acid (UA) contents; IC50 values of heparin, LMWH, and N-desulfated heparin, was 0.8 U/ml (UA 2.9 μg/ml), 0.5 IU/ml (UA 2.3μg/ml), and 3.0μg/ml (UA 0.9μg/ml), respectively. Whereas the concentrations of heparin and LMWH, that exerted their anti-C' activity efficiently, induced prolongations of APTT profoundly to clinically unapplicable extents, N-desulfated heparin (up to 50 μg/ml) did not show any anticoagulant activity. These data show a potential value of N-desulfated heparin for the treatment of C'-mediated intravascular lysis of PNH erythrocytes without bleeding complications due to its administration. Because anticoagulant therapy may be beneficial and indicated for the treatment of hemolysis in PNH, especially in hemolytic crisis increasing the risk of thrombotic complications, cocktail therapy of heparin (or LMWH) with N-desulfated heparin may be proposed.