Removal of circulating mitochondrial N-formyl peptides via immobilized antibody therapy restores sepsis-induced neutrophil dysfunction

Abstract

Abstract During recovery from septic shock, circulating mitochondrial N-formyl peptides predispose to secondary infection by occupying formyl peptide receptor 1 on the neutrophil (polymorphonuclear leukocyte) membrane, suppressing cytosolic calcium ([Ca2+]i)-dependent responses to secondarily encountered bacteria. However, no study has yet investigated therapeutic clearance of circulating mitochondrial N-formyl peptides in clinical settings. Thus, we studied how to remove mitochondrial N-formyl peptides from septic-shock plasma and whether such removal could preserve cell-surface formyl peptide receptor 1 and restore sepsis-induced polymorphonuclear leukocyte dysfunction by normalizing [Ca2+]i flux. In in vitro model systems, mitochondrial N-formyl peptide removal rescued polymorphonuclear leukocyte formyl peptide receptor 1-mediated [Ca2+]i flux and chemotaxis that had been suppressed by prior mitochondrial N-formyl peptide exposure. However, polymorphonuclear leukocyte functional recovery occurred in a stepwise fashion over 30 to 90 min. Intracellular Ca2+-calmodulin appears to contribute to this delay. In ex vivo model, systems using blood samples obtained from patients with septic shock, antimitochondrial N-formyl peptide antibodies alone failed to eliminate mitochondrial N-formyl peptides from septic-shock plasma or inhibit mitochondrial N-formyl peptide activity. We therefore created a beads-based antimitochondrial N-formyl peptide antibody cocktail by combining protein A/sepharose with antibodies specific for the most potent human mitochondrial N-formyl peptide chemoattractants. The beads-based antimitochondrial N-formyl peptide antibody cocktail treatment successfully removed those active mitochondrial N-formyl peptides from septic-shock plasma. Furthermore, the beads-based antimitochondrial N-formyl peptide antibody cocktail treatment significantly restored chemotactic and bactericidal dysfunction of polymorphonuclear leukocytes obtained from patients with septic shock who developed secondary infections. By clearing circulating mitochondrial N-formyl peptides, the immobilized antimitochondrial N-formyl peptide antibody therapy prevented mitochondrial N-formyl peptide interactions with surface formyl peptide receptor 1, thereby restoring [Ca2+]i-dependent polymorphonuclear leukocyte antimicrobial function in clinical septic-shock environments. This approach may help prevent the development of secondary, nosocomial infections in patients recovering from septic shock.