Specific inhibition of C3 to facilitate general complement inhibition on endotoxin affinity sorbents for apheresis applications

Complement activation, as a result of human blood exposure to biomaterial surfaces, continues to be a concern in medical applications. The purpose of this study was to identify sorbent(s) and surface modification(s) that allow specific removal of endotoxin, while minimizing complement activation. Maleic anhydride (MA) modification of Sepharose CL-4B, cellulose, and Toyopearl HW-65F resulted in reduced generation of C3a, a marker of complement activation, by two orders of magnitude over unmodified surfaces. Surfaces modified with both MA and polymyxin B (PMB), utilized for binding endotoxin, reduced complement activation in a similar manner. Western Blot analysis of the larger C3 cleavage product C3dg showed a similar reduction, for all MA-modified sorbents, as observed for C3a by ELISA. C3α43 levels (constituent of iC3b and C3c) were also reduced, although only MA–Sepharose CL-4B levels were similar to C3a. Activation of C5, measured as the SC5b-9 complex, was also reduced by two orders of magnitude after MA modification of Sepharose CL-4B; the decrease was similar to all chemical modifications tested. PMB immobilized via CNBr on MA-modified cellulose maintained its endotoxin-binding capacity, while the latter was eliminated when PMB was immobilized via CNBr to MA-modified Sepharose CL-4B and Toyopearl HW-65F.