Cobalt Protoporphyrin IX Attenuates Antibody-Mediated, Complement-Dependent Podocyte Injury: Role of Cobalt and Porphyrin Moieties

Abstract

Metalloporphyrins (MPs) that induce heme oxygenase (HO)-1 were shown to attenuate complement-mediated glomerular injury, with cobalt protoporphyrin IX (CoPPIX) being the most effective. To decipher the efficacy between CoPPIX and its constituents (Co, PPIX), we compared the outcomes of treatment with each in a rat model of complement-dependent immune injury of glomerular epithelial cells (podocytes). Outcomes were correlated with HO-1 induction and expression levels of complement C3 and of the complement activation regulators (CARs) cluster of differentiation (CD)55, CD59, and CR1-related gene y protein product (Crry). Podocyte injury was induced in rats following a single injection of the complement-fixing antibody against the podocyte antigen, Fx1A. CoPPIX or its constituents, cobaltous chloride (CoCl₂) and protoporphyrin IX (PPIX), were injected prior to and on alternate days thereafter. Urine was assessed for protein excretion and kidney cortex samples were processed for histopathology and assessment of target gene mRNA and protein levels using digital polymerase Chain Reaction (dPCR) and capillary-based Western blot analysis. The anti-Fx1A antibody caused proteinuria and podocyte injury. Treatment with the full CoPPIX chelate reduced proteinuria but treatment with either CoCl₂ or PPIX did not. CoPPIX treatment potently induced HO-1 and reduced tissue C3 mRNA and protein levels. It also increased CD55, CD59, and Crry mRNA, with an inconsistent effect on protein levels. The Co moiety was required for HO-1 induction but not for the decrease in C3. This decrease did not significantly correlate with the effects of CoPPIX treatment on CD55 protein levels. Chelation of cobalt to PPIX enhanced its potency to induce HO-1 but reduced that on CD55 induction. These observations distinguish between the effects of CoPPIX and its constituents on proteinuria consequent to complement-mediated podocyte injury and underlying mediators and identify this MP as a potential disease-modifying agent.