Myeloperoxidase and Eosinophil Peroxidase Inhibit the in vitro Endotoxin Activities of Lipopolysaccharide (LPS) and Lipid A and Increase Survival in an in vivo Mouse LPS LD90 model

Abstract

Myeloperoxidase (MPO) and eosinophil peroxidase (EPO) are cationic leukocyte 21 haloperoxidases with potent microbicidal and detoxifying activities. MPO selectively binds and 22 kills specific Gram-positive bacteria (GPB) and all Gram-negative bacteria (GNB) tested. 23 Endotoxin, i.e., lipopolysaccharide (LPS) comprising a toxic Lipid A component, is a 24 characteristic of all GNB. The possibility that haloperoxidases bind to and inhibit the endotoxin 25 of GBN was considered and tested by contacting MPO and EPO with LPS and Lipid A and 26 measuring for inhibition of endotoxin activity using either the in vitro gel or chromogenic 27 Limulus amebocyte lysate (LAL) assays. Contacting MPO and EPO with LPS purified from 28 Escherichia coli O55:B5 and with diphosphoryl Lipid A purified from E. coli F583 inhibited 29 their endotoxin activities in proportion to the natural log of the MPO or EPO concentration. 30 Although MPO is less cationic than EPO, MPO consistently demonstrated inhibition of 31 endotoxin activity that is about threefold superior to EPO. Haloperoxidase enzymatic activity 32 was not required for inhibition, and MPO haloperoxidase action did not increase endotoxin 33 inhibition. MPO and EPO inhibition of LPS endotoxin activity was also measured using a 90% 34 lethal dose (LD90) mouse model studied over a five-day period. Based on Kaplan Meier survival 35 analysis, MPO significantly increased mouse survival in a dose-dependent manner. EPO was less 36 effective. In conclusion, contacting MPO and EPO with LPS and Lipid A inhibits in vitro 37 endotoxin activities, but inhibition is independent of haloperoxidase enzymatic function. MPO 38 significantly increases mouse survival against LPS in an in vivo LD90 endotoxin model. 39 40 41 42 Introduction:

Characterization of myeloperoxidase and its contribution to antimicrobial effect on extracellular traps in flounder (Paralichthys olivaceus)

“…MPO and EPO in human are encoded by genes on chromosome 17, which share a 70% amino acid homology, suggesting that the two peroxidase genes are generated from a common ancestral gene ( 6 , 7 ). MPO and EPO can both utilize H 2 O 2 and chloride ions (Cl - ) to generate hypochlorous acid (HOCl), which contributes to microbial killing and may contribute to protein immunogenicity ( 8 – 10 ). Interestingly, Marcinkiewicz et al.…”