Therapeutic inhibition of the lectin pathway in thrombotic thrombocytopenic purpura

As a result of the close interaction between the complement system and the coagulation system, complement activation participates in the pathogenesis of many disease processes that are characterised by thrombosis, and the control of complement activation may ameliorate the severity of disease processes involving thrombotic microangiopathies. This study addresses the therapeutic utility of the targeted inhibition of one of the three complement activation pathways, the lectin pathway, to treat a rare fatal microangiopathy named Thrombotic thrombocytopenic purpura (TTP). TTP occurs due to the absence of the enzyme ADAMTS-13 (for "a disintegrin and metalloproteinase with a thrombospondin type-1 motif, member 13"- von Willebrand factor cleaving protein). This defect impairs the cleavage of large vWF multimers, which in turn predisposes to thrombosis through platelet aggregation and the formation of vWF-rich micro-thrombi that occlude the lumen of small blood vessels. ADAMTS-13 deficient mice (on C57BL/6 background) were used in our study. They were injected intraperitonially (ip) with purified human plasma vWF (Haemate-p), plus Lipopolysaccharide (LPS) from E.coli O111:B4. ADAMTS-13 deficient mice were either given LPS i.p. in a dose of 0.5 mg/kg plus vWF in a dose of 2000 iu/kg body weight (n=36) or LPS 2mg/kg plus vWF 2000 iu/kg (n=18) or LPS 2mg/kg plus vWF 4000 iu/kg body weight (n=36). The experimental mice in each dose level were sorted into three treatment groups. The first group was pre-treated with an inhibitory monoclonal anti-MASP-2 antibody (OMS721-SGMI2). The second group was pre-treated with the relevant isotype control antibody IgG4 (ET-904) while the third group was given saline injections only. Treatment of mice with OMS721-SGMI2 achieved that vWF and LPS challenges of ADAMTS-13 deficient mice resulted in a significant prevention of platelets loss with lower plasma LDH levels and higher haptoglobin levels in circulation compared to the two different control groups (isotype treated mice as well as saline-treated mice) at all experimental levels. Blood Urea Nitrogen (BUN) levels (as parameters for the impairment of renal functions) were elevated in all mouse groups, but those mice treated with anti-MASP-2 Abs presented with lower BUN levels than the other two groups without statistical significance. Histologically, mice treated with anti-MASP-2 Abs showed significantly lower level of vWF/platelet aggregates and a statistically not significant trend of lower levels of macrophages infiltration than both control groups. In conclusion there may be a role for the lectin pathway of complement activation system in the pathophysiology of TTP and inhibition of the lectin pathway of complement activation system by anti-MASP-2 Abs may be helpful in treatment of TTP.