Inhibitory effect of bilirubin on complement-mediated hemolysis.
We investigated the in vitro action of the bile pigments, unconjugated bilirubin (UB) and bilirubin monoglucuronide (BMG) on complement (C) cascade reaction. Both UB and BMG inhibited hemolysis in the classical pathway (CP) in a dose-dependent manner at low micromolar concentrations, UB showing a stronger effect than BMG. The analysis of the action of UB on the hemolytic activity of the C1, C4, C2 and C-EDTA components of the C cascade revealed that the C1 step was the most inhibited. An enzyme immunoassay was developed to evaluate the effect of UB on the binding of C1q, one of the subcomponents of C1, to human IgM and IgG. The study demonstrated that the unconjugated pigment interferes both the C1q-IgM and -IgG interactions, thus tentatively explaining the inhibitory action of UB on hemolytic activity of C1. We conclude that the anti-complement effect of UB is mainly exerted on the C1 component, the recognition unit of CP. The potential clinical implication of the reported effects in hyperbilirubinemia is discussed.
Arriaga
S M
SM
Departamento de Bioquímica Clínica and Instituto de Fisiología Experimental, Facultad de Ciencias Bioquímicas y Farmacéuticas (CIUNR-CONICET), Universidad Nacional de Rosario, Suipacha 570, 2000 Rosario, Argentina.
Mottino
A D
AD
Almará
A M
AM
D000818:Animals; D001663:Bilirubin / Q000031:analogs & derivatives / Q000494:pharmacology*; D002478:Cells, Cultured; D003172:Complement C1 / Q000276:immunology; D015922:Complement C1q / Q000276:immunology; D003169:Complement Inactivator Proteins / Q000494:pharmacology*; D003165:Complement System Proteins / Q000276:immunology*; D004912:Erythrocytes / Q000187:drug effects; D006461:Hemolysis / Q000187:drug effects*; D006801:Humans; D007124:Immunoenzyme Techniques; D007074:Immunoglobulin G / Q000276:immunology; D007075:Immunoglobulin M / Q000276:immunology; D012756:Sheep
D003172:Complement C1; D003169:Complement Inactivator Proteins; D007074:Immunoglobulin G; D007075:Immunoglobulin M; C016266:bilirubin glucuronate; D015922:Complement C1q; D003165:Complement System Proteins; D001663:Bilirubin