Acadesine during fluid resuscitation from shock and abdominal sepsis

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.

AICAR suppresses IL-2 expression through inhibition of GSK-3 phosphorylation and NF-AT activation in Jurkat T cells

We examined the effect of 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR), the dephosphorylated form of AICA ribotide (also termed "ZMP"), an intermediate of purine biosynthesis, on interleukin (IL)-2 production in T cells. AICAR inhibited IL-2 production in Jurkat T cells and peripheral blood lymphocytes activated with PMA plus ionomycin (PMA/Io) or with monoclonal anti-CD3 plus anti-CD28. Pretreatment with 5'-iodotubercidin, an adenosine kinase inhibitor, enhanced AICAR suppression of IL-2 production, suggesting that AICAR, not ZMP, is responsible for IL-2 suppression. We then showed that AICAR inhibited PMA/Io-induced IL-2 mRNA expression and IL-2 promoter activation. AICAR inhibited DNA binding and transcriptional activation of NF-AT and to a lesser extent AP-1, but not NF-kappaB, in PMA/Io-activated Jurkat cells. Finally, we found that AICAR inhibited PMA/Io-induced phosphorylation of GSK-3 but not phosphorylation of ERK1/2, p38, and JNK. These results suggest that AICAR exerts its immunosuppressive effect in activated Jurkat cells by inhibiting GSK-3 phosphorylation and NF-AT activation.

5-Aminoimidazole-4-carboxamide riboside suppresses lipopolysaccharide-induced TNF-alpha production through inhibition of phosphatidylinositol 3-kinase/Akt activation in RAW 264.7 murine macrophages

5-Aminoimidazole-4-carboxamide riboside (AICAR) is an adenosine analog and a widely used activator of AMP-activated protein kinase (AMPK). We examined the effect of AICAR on LPS-induced TNF-alpha production in RAW 264.7 and peritoneal macrophages and its molecular mechanism in RAW 264.7 macrophages. Treatment with AICAR inhibited LPS-induced increases in TNF-alpha mRNA and protein levels in these cells. AICAR or LPS did not alter the AMPK activity as well as the phosphorylations of AMPK alpha (Thr172) and ACC (Ser79). Moreover, an adenosine kinase inhibitor 5'-iodotubercidin enhanced the suppressive effect of AICAR on TNF-alpha levels. These results suggest that the effect of AICAR on TNF-alpha suppression in RAW 264.7 cells is independent of AMPK activation. In addition, an adenosine receptor antagonist 8-SPT had no effect on AICAR-induced suppression of TNF-alpha levels. Finally, we observed that AICAR inhibited LPS-induced activation of PI 3-kinase and Akt, whereas it had no effect on the activation of p38 and ERK1/2. Taken together, these results suggest that the anti-inflammatory action of AICAR in RAW 264.7 macrophages is independent of AMPK activation and is associated with inhibition of LPS-induced activation of PI 3-kinase/Akt pathway.

AICA riboside both activates AMP-activated protein kinase and competes with adenosine for the nucleoside transporter in the CA1 region of the rat hippocampus

5-Aminoimidazole-4-carboxamide riboside (AICA riboside; Acadesine) activates AMP-activated protein kinase (AMPK) in intact cells, and is reported to exert protective effects in the mammalian CNS. In rat cerebrocortical brain slices, AMPK was activated by metabolic stress (ischaemia > hypoxia > aglycaemia) and AICA riboside (0.1-10 mm). Activation of AMPK by AICA riboside was greatly attenuated by inhibitors of equilibrative nucleoside transport. AICA riboside also depressed excitatory synaptic transmission in area CA1 of the rat hippocampus, which was prevented by an adenosine A1 receptor antagonist and reversed by application of adenosine deaminase. However, AICA riboside was neither a substrate for adenosine deaminase nor an agonist at adenosine receptors. We conclude that metabolic stress and AICA riboside both stimulate AMPK activity in mammalian brain, but that AICA riboside has an additional effect, i.e. competition with adenosine for uptake by the nucleoside transporter. This results in an increase in extracellular adenosine and subsequent activation of adenosine receptors. Neuroprotection by AICA riboside could be mediated by this mechanism as well as, or instead of, by AMPK activation. Caution should therefore be exercised in ascribing an effect of AICA riboside to AMPK activation, especially in systems where inhibition of adenosine re-uptake has physiological consequences.

Role of adenosine in immunomodulation: Review of the literature

OBJECTIVE

Advances in the understanding of sepsis have failed to deliver satisfactory new treatments aimed at attenuating inflammatory-mediated organ dysfunction. Phagocytic cells play a pivotal role in driving the inflammatory response and causing direct tissue injury. Adenoreceptor stimulation may attenuate such inflammatory-mediated damage by down-regulating phagocytic activity and preventing excessive respiratory burst activation.

DATA

A Medline database was used to perform a literature search for all articles relating to the use of adenosine as an immunomodulatory agent.

CONCLUSION

There is convincing evidence to suggest that adenoreceptor modulation can prevent tissue injury through a variety of pathways. The use of adenosine modulation in ischemia/reperfusion injury has been the subject of considerable investigation, although experience with its use in sepsis is limited.

Novel resuscitation strategy for pulmonary contusion after severe chest trauma

BACKGROUND

Adenosine A2a receptor stimulation can increase coronary perfusion and also reduce leukocyte-mediated inflammatory responses in some conditions. Hextend is a novel colloid solution that may have antioxidant properties. All these actions might be beneficial after severe chest trauma, but have never been investigated. To fill these gaps, this study evaluated the therapeutic potential of a novel adenosine A2a agonist during fluid resuscitation from severe chest trauma with either standard-of-care crystalloid or Hextend.

METHODS

Anesthetized, ventilated swine received unilateral, blunt trauma to the right chest via captive bolt gun, followed by a 10- to 12-mL/kg arterial hemorrhage. After 25 minutes of shock, ATL-146e was started (10 ng/kg/min intravenously for 180 minutes). After an additional 5 minutes, the minimum amount of either colloid (Hextend, 5% hetastarch in lactate-buffered, balanced electrolyte solution) or crystalloid (lactated Ringer's [LR] solution) was administered to maintain mean arterial pressure > 70 mm Hg and heart rate < 100 beats/min and to correct lactate for 180 minutes postinjury. Cardiopulmonary function was monitored and serial bronchoalveolar lavage samples were analyzed for protein, leukocyte infiltration, and expression of cyclooxygenase (COX)-1 and COX-2 isozymes as markers of the inflammatory cascade.

RESULTS

Fluid requirements were reduced by half with Hextend compared with LR (p < 0.05). ATL-146e in either Hextend or LR transiently increased cardiac output, cardiac contractility, and systemic oxygen delivery (all p < 0.05). Pao(2)/Fio(2) ratio was 50 to 100 higher and bronchoalveolar lavage leukocytes were reduced by half with Hextend versus LR (both p < 0.05), but there was no added effect of ATL-146e. COX-1 expression was induced in macrophages (Mphis), whereas COX-2 was induced in neutrophils. Neither Hextend nor ATL-146e reduced COX expression.

CONCLUSION

Hextend reduced the volume for initial resuscitation, which may offer logistical advantages in prehospital field conditions or whenever there is limited medical resources or prolonged transport times; ATL-146e improved early cardiac performance without causing hypotension or bradycardia; when administered 25 to 30 minutes after injury, neither Hextend nor ATL-146e altered inflammatory changes in pulmonary Mphis or infiltrating PMNs; and further studies are needed to determine whether these short-term benefits correlate with long-term outcome.

Acadesine and intestinal barrier function after hemorrhagic shock and resuscitation

OBJECTIVE

To determine actions of the prototype adenosine-regulating agent, acadesine (5-amino-1-[beta-D-ribofuranosyl]imidazole-4-carboxamideriboside; AICAR), on intestinal barrier function after hemorrhagic shock and fluid resuscitation, three series of experiments were performed to measure functional (series 1: intestinal permeability and intramural blood flow), structural (series 2: histology), and biochemical (series 3: tissue concentrations of adenine nucleotides and metabolites) changes.

DESIGN

Prospective, controlled animal study.

SETTING/SUBJECTS

University laboratory; juvenile crossbred pigs of either gender.

INTERVENTIONS

Either AICAR or its saline vehicle were intravenously administered 30 mins before 40% hemorrhage. After 1 hr shock, shed blood plus crystalloid was administered for resuscitation. Data were collected for 1 hr thereafter.

MEASUREMENTS AND MAIN RESULTS

In series 1, permeability of the ileum was measured by assaying the portal venous concentration of fluorescein-labeled dextran after placement of this tracer in the lumen. In addition, serosal and mucosal blood flow were monitored with laser-Doppler probes. With vehicle, hemorrhage and resuscitation increased the dextran concentration three-fold and decreased blood flow 50% of the baseline values (both p < .05). AICAR attenuated the permeability increase (p < .05) and attenuated mucosa, but not serosal, ischemia (p < .05). Similar effects were observed with a structurally dissimilar compound-- 4-amino-1-(5-amino-5-deoxy-1-beta-D-ribofuranosyl)-3-bromo-pyrazolo [3,4-d] pyrimidine, a specific adenosine kinase inhibitor-as well as continuous intra-arterial infusion of adenosine. In series 2, AICAR ameliorated the mucosal damage caused by shock/resuscitation (p < .05). In series 3, AICAR increased ileal tissue adenine nucleotides and metabolites during the shock period (p < .05).

CONCLUSIONS

AICAR attenuated gut permeability changes, increased mucosal perfusion, and increased tissue adenine nucleotides, which is consistent with preserved intestinal barrier function after hemorrhage and fluid resuscitation. In context with previous studies from this laboratory, these results provide further evidence for a role for adenosine as an endogenous anti-inflammatory autacoid after shock and trauma. Further study is needed to determine the therapeutic potential of adenosine-regulating agents in resuscitation fluids.

Animal models for studies on cold-induced platelet activation in human beings

When human platelets are chilled below about 20 degrees C, they spontaneously activate, a phenomenon that limits their storage lifetime. We have previously shown that this activation in chilled human platelets is associated with passage through a lipid phase transition. Because animal models are necessary for Investigating methods for cold storage of platelets, it is essential to determine whether such phase transitions and chilling-induced activation are found in these models. In this study we examined platelets from some commonly used animal models-pigs, rhesus monkeys, mice, dogs, and rabbits. Using Fourier transform infrared spectroscopy (FTIR), we detected the thermotropic membrane phase transition in Intact platelets and assessed the morphologic response of the platelets to chilling. Statistical analysis of both FTIR and shape change show that of the animal models tested, pig platelets are most similar to human platelets. These studies suggest that pigs and pig platelets are the models of choice for the study of cold-induced platelet activation in human beings.