Novel anti-inflammatory and pro-resolving mechanisms of antibiotics: leukocyte apoptosis, inhibition of nf-kb, and modulation of lipid signaling by tulathromycin

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The accumulation of neutrophils and inflammatory mediators, such as interleukin- 8 (CXCL-8) and leukotriene B4 (LTB4), are classic markers of inflammatory disease. Clearance of apoptotic neutrophil, inhibition of pro-inflammatory signaling, and production of pro-resolving mediators, including lipoxins (LXA4), are imperative for resolving inflammation. Findings indicate that immunomodulation by macrolide antibiotics generate anti-inflammatory benefits via mechanisms that remain obscure. Tulathromycin, a new antimicrobial macrolide for bovine respiratory disease (BRD), offers superior clinical efficacy for reasons not fully understood. The pathogenesis of BRD is due, at least in part, to the severe host inflammatory response to invading pathogens, such as Mannheirnia haernolytica. The aim of this study was to identify immunomodulating actions of tulathromycin and, in the process, establish tulathromycin as a new model for characterizing novel anti-inflammatory properties of antibiotics. To investigate the effects of tulathromycin in vivo, calves were challenged intra­tracheally with live M. haemolytica or zymosan, and treated with vehicle or tulathromycin. Bronchoalveolar lavage samples collected 3 and 24 h post-challenge indicated that tulathromycin promoted neutrophil apoptosis and clearance of these cells by alveolar macrophages. In addition, tulathromycin reduced pulmonary levels of LTB4 and prostaglandin E2 (PGE2); however, there was no effect of tulathromycin on neutrophil trafficking to the lungs. In vitro, tulathromycin cell-selectively and dose­dependently induced apoptosis in bovine neutrophils and macrophages. The pro-apoptotic effects of tulathromycin were caspase-dependent, and occurred in the presence and absence of live M. haemolytica. Tulathromycin increased surface expression of phosphatidylserine on neutrophils, which were readily phagocytosed by bovine macrophages. There was no apparent effect of tulathromycin on oxidative burst in neutrophils. Furthermore, tulathromycin blocked NF-KB signaling and production of CXCL-8 in LPS-stimulated neutrophils and macrophages. Tulathromycin inhibited activity of anti-apoptotic and pro-inflammatory phospholipase D (PLD) and cytosolic PLA2, the latter blocking, at least in part, the production of LTB4 in neutrophils. In contrast, tulathrornycin promoted the secretion of the pro-resolving lipid mediator, lipoxin A4, in neutrophils. Lastly, tulathromycin promoted the intracellular accumulation of phospholipids in neutrophils. Collectively, the findings illustrate novel mechanisms through which tulathromycin confers anti-inflammatory benefits, and in turn, shed light on promising avenues for the development of novel, improved, therapeutics.
Bibliography: p. 196-231
Many pages are in colour.
Fischer, C. D. (2012). Novel anti-inflammatory and pro-resolving mechanisms of antibiotics: leukocyte apoptosis, inhibition of nf-kb, and modulation of lipid signaling by tulathromycin (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from doi:10.11575/PRISM/4712