Reoxygenation attenuates the adhesion of neutrophils to microvascular endothelial cells

Reperfusion Microvascular Ischemia After Prolonged Coronary Occlusion: Implications And Treatment With Local Supersaturated Oxygen Delivery

Following a prolonged coronary arterial occlusion, heterogeneously scattered, focal regions of low erythrocyte flow are commonly found throughout the reperfused myocardium. Experimental studies have also demonstrated the presence of widespread, focally patchy regions of microvascular ischemia during reperfusion (RMI). However, the potential contribution of RMI to tissue viability and function has received little attention in the absence of practical clinical methods for its detection. In this review, the anatomic/functional basis of RMI is summarized, along with the evidence for its presence in reperfused myocardium. Advances in microcirculation research related to obstructive responses of vascular endothelial cells and blood elements to the effects of hypoxia and low shear stress are discussed, and a potential cycle of intensification of RMI from such responses and progressive loss of functional capillary density is presented. In capillaries with impaired erythrocyte flow, compensatory increases in the delivery of oxygen, because of its low solubility in plasma, are effective only at high partial pressures. As discussed herein, attenuation of the cycle with oxygen at hyperbaric levels in plasma is, very likely, responsible for improved tissue level perfusion noted experimentally. Observed clinical benefits from intracoronary SuperSaturated oxygen (SSO₂) delivery, including infarct size reduction, can be attributed to attenuation of RMI with improvement in microvascular blood flow.

The inflammatory response of neutrophils in an in vitro model that approximates the postcardiac arrest state

Purpose

Postcardiac arrest syndrome (PCAS) shares many features with sepsis including plasma cytokine elevation with dysregulation of cytokine production, and the presence of endotoxin in plasma. PCAS is closely related to ischemia-reperfusion injury. During ischemia-reperfusion injury, neutrophil, which is the first line of innate immunity, plays a major role. In this study, we investigated the inflammatory response of human neutrophils in an in vitro model which we simulated with hypoxia-normoxia and hypoxia-hyperoxia environments.

Methods

After separation of neutrophils from the whole blood, they were divided into 3 experimental groups: normoxia-normoxia, hypoxia-normoxia, and hypoxia-hyperoxia groups. The production of H₂O₂, the expression of Toll-like receptor 4 (TLR₄) receptor, and the extent of apoptosis of the neutrophils were checked.

Results

The in vitro hypoxia-normoxia and -hyperoxia models, which simulated the PCAS, showed initiation of the neutrophils' inflammatory reaction by hypoxia insult. Lipopolysaccharide amplifies such inflammation; therefore, prevention of secondary infection may be critical in postresuscitation patients. Temporary hyperoxia following hypoxic insult showed no difference in inflammatory reaction compared with hypoxia-normoxia. Rather, temporary hyperoxia may suppress or minimize inflammation by attenuation of TLR₄ receptor.

Conclusion

It is well known that continuous hyperoxygenation after successful cardiac arrest harms patients, but temporary hyperoxygenation with 100% O₂ in a clinical situation may be helpful.