Increased Neutrophil Adenosine A3 Receptor Expression Is Associated With Hemorrhagic Shock and Injury Severity in Trauma Patients

Abstract

Hypertonic saline (HS) has been investigated as an immune modulator following hemorrhagic shock and sepsis. The neutrophil (PMN) response to HS is regulated by the release of ATP, which is converted to adenosine and activates adenosine receptors. Binding to A3 adenosine receptors promotes PMN activation and inhibition of A3 receptors improves the efficacy of HS resuscitation. A3 receptor expression of PMN has not been previously evaluated in injured patients. Methods Whole blood was obtained from 10 healthy volunteers and 60 injured patients within 2 hrs of injury. Inclusion criteria were blunt or penetrating injury with evidence of hypovolemic shock (SBP ≤ 90 mmHg and base deficit ≥6 mEq/L or need for blood transfusion); or evidence of severe traumatic brain injury (TBI) including initial Glasgow coma score (GCS) ≤ 8 or evidence of TBI on Head CT scan (Head AIS≥ 3) or intubation in the field or ED. A3 receptor expression was assessed by flow cytometry. PMN were also exposed to fMLP or HS (20-40 mM) in vitro. Clinical data was collected including admission physiology, injury severity (ISS scores), development of multiple organ failure, and survival. Results In normal volunteers, < 1% of PMN expressed A3 receptors on the cell surface. A3 receptor expression was significantly higher in injured patients and the level of expression correlated with the severity of injury (ISS ≥ 25: A3 positive PMN 36.6% vs. ISS <25: 16.2%; p=0.019) and degree of hypovolemic shock (SBP≤ 90: A3 positive PMN 43.8% vs. SBP>90: 20.6%; p=0.008). Stimulation with fMLP or HS increased A3 expression in normal volunteers, but only in patients with ISS< 25 or without hypovolemic shock. Conclusion A3 receptor expression on the surface of PMN is up-regulated by injury and increased expression levels are associated with greater injury severity and hypovolemic shock. Hypertonic saline increases A3 expression of PMN from healthy volunteers and less severely injured patients.

Prehospital Hypertonic Saline Resuscitation Attenuates the Activation and Promotes Apoptosis of Neutrophils in Patients With Severe Traumatic Brain Injury

“…HS triggers cAMP/PKA signaling via autocrine purinergic signaling processes that involve the release of cellular ATP, hydrolysis of ATP to adenosine, and the activation of adenosine receptors that modulate PMN responses [35-38]. These autocrine feedback mechanisms involve several different subtypes of the nucleotide and adenosine receptor families, collectively termed purinergic receptors, that may influence apoptosis and other PMN responses [39-44]. …”

Resuscitation of Traumatic Hemorrhagic Shock Patients With Hypertonic Saline—Without Dextran—Inhibits Neutrophil and Endothelial Cell Activation

“…Thus, it is possible that still unknown purinergic signaling events triggered by trauma and HS could be reasons for the lack of clinical efficacy of HS resuscitation. As an example, we recently found that trauma causes a dramatic increase in A3 adenosine receptor expression by neutrophils [35]. A3 receptors have a co-stimulatory role in neutrophil activation by counteracting the anti-inflammatory effect of A2a receptors [18].…”

The impact of trauma on neutrophil function

“…This was demonstrated by the fact that in formyl-peptide receptor 1 knockout mice (Fpr1 À/À ), neutrophils migrated to within 150 mm of the necrotic site (via CXCR2 mediated signalling) but failed to migrate to the area of injury [86]. Interestingly, it has recently been shown that blunt/penetrating injury and severe TBI leads to the up-regulation of the A3 adenosine receptor on the surface of circulating human neutrophils, and that the level of expression of this receptor correlated positively with patient injury severity score [87]. Since ATP is released upon tissue damage, the up-regulation of A3 receptor expression may be one mechanism underlying the heightened activation status of circulating neutrophils from trauma patients.…”