Complement Activation-Related Pathophysiological Changes in Anesthetized Rats: Activator-Dependent Variations of Symptoms and Mediators of Pseudoallergy.

Complement (C) activation can underlie the infusion reactions to liposomes and other nanoparticle-based medicines, a hypersensitivity syndrome that can be partially reproduced in animal models. However, the sensitivities and manifestations substantially differ in different species, and C activation may not be the only cause of pathophysiological changes. In order to map the species variation of C-dependent and -independent pseudoallergy (CARPA/CIPA), here we used known C activators and C activator liposomes to compare their acute hemodynamic, hematological, and biochemical effects in rats. These C activators were cobra venom factor (CVF), zymosan, AmBisome (at 2 doses), its amphotericin B-free vehicle (AmBisombo), and a PEGylated cholesterol-containing liposome (PEG-2000-chol), all having different powers to activate C in rat blood. The pathophysiological endpoints measured were blood pressure, leukocyte and platelet counts, and plasma thromboxane B2, while C activation was assessed by C3 consumption using the Pan-Specific C3 assay. The results showed strong linear correlation between C activation and systemic hypotension, pointing to a causal role of C activation in the hemodynamic changes. The observed thrombocytopenia and leukopenia followed by leukocytosis also correlated with C3 conversion in case of C activators, but not necessarily with C activation by liposomes. These findings are consistent with the double hit hypothesis of hypersensitivity reactions (HSRs), inasmuch as strong C activation can fully account for all symptoms of HSRs, but in case of no-, or weak C activators, the pathophysiological response, if any, is likely to involve other activation pathways.

Factor H inhibits complement activation induced by liposomal and micellar drugs and the therapeutic antibody rituximab in vitro.

Hypersensitivity reactions to particulate drugs can partly be caused by complement activation and represent a major complication during intravenous application of nanomedicines. Several liposomal and micellar drugs and carriers, and therapeutic antibodies, were shown to activate complement and induce complement activation-related pseudoallergy (CARPA) in model animals. To explore the possible use of the natural complement inhibitor factor H (FH) against CARPA, we examined the effect of FH on complement activation induced by CARPAgenic drugs. Exogenous FH inhibited complement activation induced by the antifungal liposomal Amphotericin-B (AmBisome), the widely used solvent of anticancer drugs Cremophor EL, and the anticancer monoclonal antibody rituximab in vitro. An engineered form of FH (mini-FH) was more potent inhibitor of Ambisome-, Cremophor EL- and rituximab-induced complement activation than FH. The FH-related protein CFHR1 had no inhibitory effect. Our data suggest that FH or its derivatives may be considered in the pharmacological prevention of CARPA. FROM THE CLINICAL EDITOR: Although liposomes and micelles are already in use in the clinical setting as drug carriers, there remains the potential problem of hypersensitivity due to complement activation. In this article, the authors investigated the use of complement inhibitor factor H (FH) on complement activation and showed good efficacy. The results would therefore suggest the potential application of complement inhibitor in the future.