Endogenous adenosine and hemorrhagic shock: effects of caffeine administration or caffeine withdrawal

A 2A ADENOSINE RECEPTORS REGULATE MULTIPLE ORGAN FAILURE AFTER HEMORRHAGIC SHOCK IN MICE

ABSTRACT

Trauma hemorrhagic shock (T/HS) is a clinical condition that causes multiple organ failure that needs rapid intervention. Restricted oxygen at the cellular level causes inflammation and subsequent cell death. Adenosine triphosphate is the universal intracellular energy currency and an important extracellular inflammatory signaling molecule. Adenosine, an endogenous nucleotide formed as a result of the breakdown of adenosine triphosphate, is also released during T/HS. Adenosine binds to four G protein-coupled receptors (A 1R , A 2a , A 2b , A 3R ) called adenosine receptors or P1 receptors. In the present study, we evaluated the effect of activation, inactivation, and genetic absence of A2aR (A2aR -/- mice) on T/HS-induced multiple organ failure. Wild-type mice were pretreated (30 min before shock induction) with an agonist or antagonist and then subjected to T/HS by withdrawing arterial blood and maintaining the blood pressure between 28 and 32 mm Hg. A2aR -/- mice were subjected to T/HS in the absence of pharmacologic treatment. Neutrophil sequestration was assessed by detecting myeloperoxidase, and Evans blue dye (EBD) method was used to analyze lung permeability. Blood and lung inflammatory cytokine levels were determined by sandwich enzyme-linked immunosorbent assay. The liver enzymes aspartate aminotransferase and alanine aminotransferase were determined spectrophotometrically from plasma. Activation of the apoptotic cascade was evaluated using a mouse apoptosis array. Our results demonstrate that the selective A2aR agonist CGS21680 decreases lung neutrophil sequestration, lung proinflammatory cytokines IL-6 and TNF-α, and bronchoalveolar lavage EBD. Pretreatment with the selective antagonist ZM241385 and genetic blockade in A2aR -/- mice increased neutrophil sequestration, proinflammatory cytokine levels, and bronchoalveolar lavage fluid EBD. The myeloperoxidase level in the lung was also increased in A2aR -/- mice. We observed that antiapoptotic markers decreased significantly with the absence of A2aR in the lung and spleen after T/HS. In conclusion, our data demonstrate that activation of A2aR regulates organ injury and apoptosis in the setting of T/HS.

Effects of Preinjury and Postinjury Exposure to Caffeine in a Rat Model of Traumatic Brain Injury

Background: Lethal apnea is a significant cause of acute mortality following a severe traumatic brain injury (TBI). TBI is associated with a surge of adenosine, which also suppresses respiratory function in the brainstem. Methods and Materials: This study examined the acute and chronic effects of caffeine, an adenosine receptor antagonist, on acute mortality and morbidity after fluid percussion injury. Results: We demonstrate that, regardless of preinjury caffeine exposure, an acute bolus of caffeine given immediately following the injury dosedependently prevented lethal apnea and has no detrimental effects on motor performance following sublethal injuries. Finally, we demonstrate that chronic caffeine treatment after injury, but not caffeine withdrawal, impairs recovery of motor function. Conclusions: Preexposure of the injured brain to caffeine does not have a major impact on acute and delayed outcome parameters; more importantly, a single acute dose of caffeine after the injury can prevent lethal apnea regardless of chronic caffeine preexposure.

Selective organ ischaemia/reperfusion identifies liver as the key driver of the post-injury plasma metabolome derangements

BACKGROUND

Understanding the molecular mechanisms in perturbation of the metabolome following ischaemia and reperfusion is critical in developing novel therapeutic strategies to prevent the sequelae of post-injury shock. While the metabolic substrates fueling these alterations have been defined, the relative contribution of specific organs to the systemic metabolic reprogramming secondary to ischaemic or haemorrhagic hypoxia remains unclear.

MATERIALS AND METHODS

A porcine model of selected organ ischaemia was employed to investigate the relative contribution of liver, kidney, spleen and small bowel ischaemia/reperfusion to the plasma metabolic phenotype, as gleaned through ultra-high performance liquid chromatography-mass spectrometry-based metabolomics.

RESULTS

Liver ischaemia/reperfusion promotes glycaemia, with increases in circulating carboxylic acid anions and purine oxidation metabolites, suggesting that this organ is the dominant contributor to the accumulation of these metabolites in response to ischaemic hypoxia. Succinate, in particular, accumulates selectively in response to the hepatic ischemia, with levels 6.5 times spleen, 8.2 times small bowel, and 6 times renal levels. Similar trends, but lower fold-change increase in comparison to baseline values, were observed upon ischaemia/reperfusion of kidney, spleen and small bowel.

DISCUSSION

These observations suggest that the liver may play a critical role in mediating the accumulation of the same metabolites in response to haemorrhagic hypoxia, especially with respect to succinate, a metabolite that has been increasingly implicated in the coagulopathy and pro-inflammatory sequelae of ischaemic and haemorrhagic shock.

Hemorrhagic shock and tissue injury drive distinct plasma metabolome derangements in swine

BACKGROUND

Tissue injury and hemorrhagic shock induce significant systemic metabolic reprogramming in animal models and critically injured patients. Recent expansions of the classic concepts of metabolomic aberrations in tissue injury and hemorrhage opened the way for novel resuscitative interventions based on the observed abnormal metabolic demands. We hypothesize that metabolic demands and resulting metabolic signatures in pig plasma will vary in response to isolated or combined tissue injury and hemorrhagic shock.

METHODS

A total of 20 pigs underwent either isolated tissue injury, hemorrhagic shock, or combined tissue injury and hemorrhagic shock referenced to a sham protocol (n = 5/group). Plasma samples were analyzed by UHPLC-MS.

RESULTS

Hemorrhagic shock promoted a hypermetabolic state. Tissue injury alone dampened metabolic responses in comparison to sham and hemorrhagic shock, and attenuated the hypermetabolic state triggered by shock with respect to energy metabolism (glycolysis, glutaminolysis, and Krebs cycle). Tissue injury and hemorrhagic shock had a more pronounced effect on nitrogen metabolism (arginine, polyamines, and purine metabolism) than hemorrhagic shock alone.

CONCLUSION

Isolated or combined tissue injury and hemorrhagic shock result in distinct plasma metabolic signatures. These findings indicate that optimized resuscitative interventions in critically ill patients are possible based on identifying the severity of tissue injury and hemorrhage.

Adenosine A2A receptor activation reduces lung injury in trauma/hemorrhagic shock*

OBJECTIVE

Hemorrhagic shock and resuscitation trigger a global ischemia/reperfusion phenomenon, in which various inflammatory processes critically contribute to the ensuing tissue damage. Adenosine is an endogenous nucleoside that is released during shock. Activation of adenosine A(2A) receptors can broadly inactivate inflammatory cascades. The current study was designed to evaluate the effect of A(2A) receptor activation on organ injury and inflammation in the setting of global ischemia/reperfusion elicited by trauma/hemorrhagic shock and resuscitation.

DESIGN

Prospective animal study with concurrent control.

SETTING

Small animal laboratory.

SUBJECTS

Adult male Sprague-Dawley rats.

INTERVENTIONS

The rats were subjected to a laparotomy (trauma) and 90 mins of hemorrhagic shock or trauma/sham shock. The selective A(2A) receptor agonist CGS-21680 (2-p-(2-carboxyethyl) phenethylamino-5'-N-ethyl-carboxamidoadenosine; 0.5 mg/kg) or its vehicle was injected 30 mins before shock or immediately after resuscitation. At 3 hrs following resuscitation, animals were killed and tissue was harvested for analysis. Lung permeability and pulmonary myeloperoxidase levels were used to quantitate lung injury. Intestinal injury was determined by histologic analysis of terminal ileum. Red blood cell deformability was measured by a laser-assisted ektacytometer. In this assay, a decrease in the elongation index is a marker of decreased red blood cell deformability.

MEASUREMENTS AND MAIN RESULTS

Pretreatment with CGS-21680 protected the lung but not the gut against shock-induced injury and prevented the shock-induced decrease in red blood cell deformability. Posttreatment with CGS-21680 ameliorated shock-induced lung injury but failed to prevent gut injury and preserve red blood cell deformability.

CONCLUSION

A(2A) receptor agonists may represent a novel therapeutic approach in preventing organ injury following trauma/hemorrhagic shock.

Antagonism of the cardiodepressant effects of adenosine during acute hypoxia

OBJECTIVE

To determine whether pharmacologic antagonism of adenosine A1-receptor-mediated cardiovascular changes can improve cardiac function and prolong survival during systemic hypoxia.

METHODS

Rats were anesthetized with ketamine, instrumented [including left ventricular (LV) pressure transducing catheters], paralyzed with vecuronium, then ventilated to pCO2 = 35-40 torr. After 10 minutes of equilibration (baseline), treatment commenced with saline (n = 7), NPC-205, an adenosine A1 receptor selective antagonist, at doses of 1 mg/kg (n = 10) or 10 mg/kg (n = 10), or drug vehicle (n = 9). Ten minutes later, inspired oxygen was reduced to 5%.

RESULTS

Survival duration (min) post-hypoxia increased in a dose-dependent fashion from 10.4 +/- 1.4 (mean +/- SEM) with vehicle control to 23.0 +/- 4.7 and 41.1 +/- 5.7 with 1 and 10 mg/kg NPC-205, respectively (p < 0.000). Five minutes post-hypoxia, dose-dependent increases were also seen in the percentage of pre-hypoxic values of LV contractility [25.9 +/- 8.1 (vehicle), 39.5 +/- 9.6 (1 mg/kg NPC-205), and 56.5 +/- 8.7 (10 mg/kg NPC-205), p = 0.01], heart rate [60.6 +/- 8.3 (vehicle), 74.7 +/- 8.2 (1 mg/kg NPC-205), and 90.4 +/- 24.1 (10 mg/kg NPC-205), p = 0.02], and blood pressure [16.1 +/- 4.8 (vehicle), 28.8 +/- 8.6 (1 mg/kg NPC-205), and 51.7 +/- 8.2 (10 mg/kg NPC-205), p = 0.004].

CONCLUSIONS

The adenosine A1 selective antagonist prolonged survival in this model. This prolongation was attributed to inhibition of adenosine A1 receptor-mediated decline in cardiac inotropy and chronotropy. Adenosine A1 receptor-selective antagonists show promise as adjunctive therapy for hypoxia-induced cardiac insufficiency by prolonging the treatment window until more definitive resuscitation measures are taken.

Arterial and venous plasma concentrations of adenosine during haemorrhage

A haemorrhage model was used to impose severe metabolic stress in anaesthetized cats by removing blood (15.3 ml min-1) to attain an arterial pressure of ca. 50 mmHg for a 2 h period. Adenosine levels in central venous blood rose by 5 min, reached a peak of about 3.5 times control levels by 15 min and then returned to the basal level (1 microM) by 60 min. However, the adenosine concentration in arterial blood remained unchanged for the entire 2 h period of hypotension. These data demonstrate that haemorrhage results in rapid adenosine release, but the released adenosine is not able to serve a role as a systemic circulating vasodilator even in this severe model.