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Commentary

Oxygen treatment attenuates systemic inflammation viacholinergic pathways

Rupesh Kotecha, BS, and Luis H. Toledo-Pereyra, MD, PhD*

Departments of Research and Surgery, Michigan State University/Kalamazoo Center for Medical Studies, Kalamazoo, Michigan

a r t i c l e i n f o

Article history:

Received 18 January 2012

Received in revised form

18 January 2012

Accepted 20 January 2012

Available online 28 March 2012

* Corresponding author. Departments of ResTel.: 1 269 226 6896; fax: 1 616 226 6735.

E-mail address: toledo@kcms.msu.edu (L0022-4804/$ e see front matter ª 2013 Elsevdoi:10.1016/j.jss.2012.01.034

Despite the many advances in critical care medicine, sepsis

continues to be a major health problem, with a high mor-

bidity and mortality [1]. Sepsis is best characterized as

a systemic inflammatory response with ongoing multiple

organ failures. The inciting pathogens, signs, and symptoms

vary significantly between patients. Yet one of the central

themes in the pathophysiology of sepsis is the understanding

that the host immune system is responsible for much of the

toxic clinical nature of this disease [2]. Therefore, it is clini-

cally relevant and important to determine protective mech-

anisms to modulate this injury and improve treatment

outcomes.

To determine the underlying mechanisms in systemic

inflammatory response syndrome, sepsis, and shock, many

transitional animal models have been developed. In partic-

ular, the injection of zymosan in rats results in acute func-

tional and chronic structural changes in the liver, intestine,

lungs, and kidneys, leading to multiple organ failure [3,4].

Using this model, a few studies have investigated the

protective anti-inflammatory role of oxygen treatment in

earch and Research Surge

.H. Toledo-Pereyra).ier Inc. All rights reserved

attenuating inflammation. For example, Luongo et al. evalu-

ated the effects of hyperbaric oxygen therapy in zymosan-

injected rats [5]. They showed that hyperbaric oxygen

treatment resulted in a significant reduction in peritoneal

leukocytes and exudates and TNF-a levels, and an improve-

ment in morbidity and mortality. Additional research using

thismodel has also shown the therapeutic effect of hyperbaric

oxygen treatment on vascular reactivity and its role in pre-

venting cardiovascular failure [6]. Although it was determined

that oxygen treatment was clearly beneficial in attenuating

the inflammatory response in sepsis, the mechanism by

which this effect was produced remained largely unrecog-

nized. In a paper recently published in the Journal of Surgical

Research, Zhang et al. advance our understanding of the

underlying mechanisms by which oxygen treatment protects

against generalized inflammation using three different anti-

cholinergic blockade models [7].

Building on their previously performed research, Zhang

et al. first designed an experimental protocol to analyze the

effect of 100% oxygen inhalation on a zymosan-induced

ry, Kalamazoo Center for Medical Studies, Kalamazoo, Michigan.

.

j o u r n a l o f s u r g i c a l r e s e a r c h 1 8 1 ( 2 0 1 3 ) 7 1e7 372

generalized inflammation mouse model. The primary

endpoints evaluated in this study included overall survival,

organ histopathologic changes, measurements of liver and

kidney function, and serum inflammatory cytokine concen-

trations. In the first part of the study, experimental (zymosan)

and control (normal saline) injected mice were divided into

two groups, one exposed to 100% oxygen and the other to

room air. In the zymosan-injected model, there was a 70%

reduction in the 7-day survival rate; however, those mice

maintained at 100% oxygen levels experienced an 80% overall

survival rate. Similarly, zymosan-challenged mice treated

with 100% oxygen also showed significant reductions in the

infiltration of inflammatory cytokines, and on histologic

analysis showed little distortion in overall tissue architecture

compared to the animals maintained in room air. In addition

to changes in organ structure, Zhang et al. also reported

significant deteriorations in organ function resulting from

zymosan injection. However, the 100% oxygen exposed mice

showed significant improvements in serum ALT, AST, BUN,

and creatinine compared to control mice. To further examine

this protective effect, they demonstrated that oxygen treat-

ment reduced levels of TNF-a and increased levels of serum

cytokine IL-10. Taken together, these results clearly illustrate

that 100% oxygen treatment improves organ structure and

function as well as suppresses the inflammatory cascade

response.

Subsequently, to demonstrate the involvement of the

cholinergic pathways in attenuating the inflammatory

response, each group of animals was further divided into

three subgroups: animals that underwent a left cervical

vagotomy (compared to sham operated controls), those

exposed to the nAChRs antagonist mecamylamine, and

a subset exposed to the a7nAChRs antagonist methyl-

lycaconitine. With regard to overall survival at 7 days after

zymosan challenge, the protective effect of oxygen was

essentially negated by blocking any of the cholinergic path-

ways. Similarly, from a histopathologic standpoint, cholin-

ergic blockade was characterized by an infiltration of

neutrophils, in essence a reversal of the protective effect of

oxygen treatment on the heart, lung, liver, and kidney. Con-

cerning liver and kidney function, all three experimental

groups showed a reversal of the protective effect of oxygen

treatment on the serum AST, AST, BUN, and creatinine.

Furthermore, these anticholinergic experimental procedures

reversed the effect of oxygen treatment on the concentrations

of the inflammatory cytokines TNF-a and IL-10. This evidence

provides credence to the theory that the cholinergic anti-

inflammatory pathways are activated during oxygen treat-

ment in a sepsis model.

The results demonstrated by Zhang et al. clearly illustrate

the importance of the cholinergic pathways in curtailing the

host immune response in sepsis. Prior studies have also

demonstrated that on a cellular level, activation of the anti-

inflammatory reflex response via the vagus nerve curtails

cytokine synthesis and cytokine-mediated disease [8]. Addi-

tionally, in a lung mouse model, activation of the a7nAChR

correlated with a reduction in chemokine production and

transalveolar neutrophil migration [9]. Therefore, although

the mechanism and outcomes of oxygen treatment have been

elucidated, we must now turn our attention to determining

the optimum duration, partial pressure, and timing of treat-

ment. For example, Zhang et al. have determined that the

arterial partial pressure of oxygen is an important factor in

determining the survival advantage of oxygen treatment.

Those animals exposed to 80% oxygen did not experience the

survival benefit of those animals exposed to 100% oxygen.

Considering the concerns of oxygen toxicity due to proin-

flammatory consequences of exposure to sustained high

oxygen levels, we must now further investigate the delicate

balance between oxygen protection and toxicity [10].

Furthermore, most of the studies examining the toxic effects

of reactive oxygen radicals have used a normal, healthy

model.Moving forward,wemust now investigate this effect in

the disease model as well.

Sepsis is the leading cause of death in critically ill patients

in the United States [11] and there are fewmedical challenges

as common, expensive, and frequently fatal [2]. The

zymosan-injection mouse model represents one of the

primary translational approaches to studying systemic

illness, hypotension, and shock in sepsis [5]. The study by

Zhang et al. demonstrates the importance of oxygen treat-

ment and its action via cholinergic pathways in the attenu-

ation of the inflammatory damage in sepsis. By evaluating

changes in organ system histopathology, biochemical

parameters, and concentrations of the inflammatory

response cytokines, their study clearly shows that the effect

of oxygen can be essentially reversed by anticholinergic

blockade. Looking forward, we should continue to investigate

the role of cholinergic receptors on a cellular and molecular

level, as well as begin to characterize optimal oxygen treat-

ment strategies.

r e f e r e n c e s

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[2] Angus DC. The search for effective therapy for sepsis. JAMA2011;306:2614.

[3] Mainous MR, Tso P, Berg RD, et al. Studies of theroute, magnitude, and time course of bacterialtranslocation in a model of systemic inflammation.Arch Surg 1991;126:33.

[4] Damas J, Remacle-Volon G, Bourdon V. Platelet-activatingfactor and the vascular effects of zymosan in rats. Eur JPharmacol 1993;231:231.

[5] Luongo C, Imperatore F, Cuzzocrea S, et al. Effects ofhyperbaric oxygen exposure on a zymosan-induced shockmodel. Crit Care Med 1998;26:1972.

[6] Imperatore F, Cuzzocrea S, Luongo C, et al. Hyperbaricoxygen therapy prevents vascular derangement duringzymosan-induced multiple-organ-failure syndrome.Intensive Care Med 2004;30:1175.

[7] Zhang Z, Bai X, Du K, et al. Activation of cholinergicanti-inflammatory pathway contributes to the protective

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effects of 100% oxygen inhalation on zymosan-inducedgeneralized inflammation in mice. J Surg Res 2012;174:e75.

[8] Tracey KJ. Physiology and immunology of thecholinergic antiinflammatory pathway. J Clin Invest 2007;117:289.

[9] Su X, Matthay MA, Malik AB. Requisite role of the cholinergicalpha7 nicotinic acetylcholine receptor pathway in

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[10] Waisman D, Brod V, Rahat MA, et al. Dose-related effects ofhyperoxia on the lung inflammatory response in septic rats.Shock 2012;37:95.

[11] Hotchkiss RS, Karl IE. The pathophysiology and treatment ofsepsis. N Engl J Med 2003;348:138.