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Objective: To investigate the effects of activation of the AMP-activated protein kinase (AMPK) on muscle perfusion and to elucidate the mechanisms involved., Methods and Results: In a combined approach, we studied the vasoactive actions of AMPK activator by 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR) on rat cremaster muscle resistance arteries ( approximately 100 mum) ex vivo and on microvascular perfusion in the rat hindlimb in vivo. In isolated resistance arteries, AICAR increased Thr172 phosphorylation of AMPK in arteriolar endothelium, which was predominantly located in microvascular endothelium. AICAR induced vasodilation (19+/-4% at 2 mmol/L, P<0.01), which was abolished by endothelium removal, inhibition of NO synthase (with N-nitro-L-arginine), or AMPK (with compound C). Smooth muscle sensitivity to NO, determined by studying the effects of the NO donor S-nitroso-N-acetylpenicillamine (SNAP), was not affected by AICAR except at the highest dose. AICAR increased endothelial nitric oxide synthase activity, as indicated by Ser1177 phosphorylation. In vivo, infusion of AICAR markedly increased muscle microvascular blood volume (approximately 60%, P<0.05), as was evidenced by contrast-enhanced ultrasound, without effects on blood pressure, femoral blood flow, or hind leg glucose uptake., Conclusions: Activation of AMPK by AICAR activates endothelial nitric oxide synthase in arteriolar endothelium by increasing its Ser1177 phosphorylation, which leads to vasodilation of resistance arteries and recruitment of microvascular perfusion in muscle.

Acadesine (5-amino-4-imidazole carboxamide riboside) is a purine nucleoside analog that has been shown in animals to reduce myocardial ischemic injury by selectively increasing the availability of adenosine in ischemic tissues. Because patients undergoing coronary artery bypass graft (CABG) surgery are especially vulnerable to developing myocardial ischemia, we investigated whether perioperative use of this adenosine-regulating drug with potential anti-ischemic properties could modify the incidence and severity of perioperative myocardial ischemia. The goals of this study were to evaluate safety and the effects of acadesine on myocardial ischemia, left ventricular function, and, secondarily, on adverse clinical outcomes (myocardial infarction, heart failure, life-threatening dysrhythmias, and death) in patients undergoing CABG surgery. One hundred sixteen patients were randomized to receive one of three continuous intravenous dosing regimens (placebo [control] or one of two doses of acadesine [high- and low-dose infusion]) in double-blind fashion intraoperatively and in the early postoperative period (total infusion time was 7 h). Multidose cold crystalloid cardioplegia (each containing either acadesine or placebo) was used for myocardial protection. All were monitored for potentially drug-related adverse events and the presence of myocardial ischemia was assessed by continuous Holter electrocardiography (ECG) and transesophageal echocardiography (TEE). All patients received standardized anesthetic, surgical, and hemodynamic management during the intraoperative period. All research data (ECG, TEE, outcome data) were evaluated at the coordinating center (San Francisco) in blinded fashion to ensure that uniform data analysis criteria were employed. The administration of acadesine was safe: mild increases in plasma uric acid (a metabolite of acadesine) occurred only in patients receiving high doses (mean increase 1.6 +/- 0.2 mg/dL) and were without clinical sequelae. Before drug administration in the preoperative period (baseline), the incidence and severity of ECG ischemia did not differ among the three groups (placebo = 18%; low-dose = 14%; high-dose = 14%). During prebypass, the incidence of ECG ischemia was similar in all three groups (0%, 3%, 3%, respectively). The incidence of TEE ischemia was numerically lower in the two acadesine groups (high-dose = 6%, low-dose = 15%) than in the control group (19%), but this was not statistically significant (P = 0.22). During postbypass, the incidence of ECG ischemia was 11% in the high-dose group, 22% in the low-dose group, and 18% in the control group (P = 0.42), and TEE ischemia was similar in incidence in all groups (placebo = 29%; low dose = 27%; high-dose = 24%) (P = 0.86).(ABSTRACT TRUNCATED AT 400 WORDS)

Background: Adenosine is a cardioprotective autacoid that exerts receptor-mediated protection from ischemia/reperfusion injury. In ischemically injured hearts, avoidance of ischemia/reperfusion injury with hypothermic chemical cardioplegia may be incomplete, and consequently, postischemic left ventricular (LV) function may be severely depressed and chamber stiffness increased. This study tested the hypothesis that the adenosine-regulating agent acadesine improves myocardial protection with hypothermic blood cardioplegia (BCP), resulting in better postischemic LV function and diastolic characteristics in hearts injured by 45 minutes of normothermic global ischemia., Methods and Results: Eighteen anesthetized (350 micrograms fentanyl citrate, 5 mg diazepam) dogs on total vented bypass were randomized to receive vehicle (n = 5), low-dose acadesine (LDA, 0.125 mg.kg-1.min-1, n = 6) or high-dose acadesine (HDA, 0.5 mg.kg-1.min-1, n = 7) continuously infused 30 minutes before global ischemia and discontinued 10 minutes after aortic cross-clamp removal. Hearts were protected with cold (4 degrees C) multidose (every 20 minutes) potassium BCP, which contained saline vehicle, 1 mg/L acadesine (LDA), or 4 mg/L acadesine (HDA) for a total of 1 hour of cardioplegic arrest. Postischemic LV function, assessed by the slope of the end-systolic pressure-volume (impedance catheter) relation, was depressed by 34 +/- 7% of baseline (5.6 +/- 1.0 versus 2.7 +/- 0.7 mm Hg/mL, P < .05) in vehicle. With LDA, there was variable improvement in postischemic function (5.1 +/- 1.3 versus 3.6 +/- 0.6 mm Hg/mL, P = .26 versus baseline). In contrast, there was complete postischemic functional recovery with HDA (5.9 +/- 0.6 versus 5.2 +/- 0.8 mm Hg/mL, P = .54). Postischemic chamber stiffness was preserved in both LDA and HDA., Conclusions: We conclude that the higher dose of acadesine improves myocardial protection when used as a pretreatment and BCP adjuvant, resulting in better postischemic LV systolic function and diastolic characteristics.

Background: Although there are many factors that might contribute to tissue injury during ischemia and reperfusion, the loss of adenine nucleotides has long been considered to be of importance. This has led to the study of interventions designed to limit the loss of nucleotides or to enhance the rate of nucleotide resynthesis during reperfusion. Alternatively, the breakdown of adenosine triphosphate to adenosine might represent a protective response of the ischemic heart because adenosine is considered an anti-injury autocoid. Augmentation of endogenous adenosine levels might be beneficial. For these reasons, the protective properties of acadesine (AICAr: 5-amino-4-imidazole carboxamide riboside) were assessed in a rat model of myocardial ischemia and reperfusion., Methods and Results: The protective properties of acadesine were studied in the isolated, perfused rat heart subjected to global hypothermic (20 degrees C) ischemia and reperfusion. When acadesine was given as an in vivo pretreatment (100 mg/kg i.v. 15 minutes before study) followed by being administered as an additive (20 mumol/l) to the St. Thomas' Hospital cardioplegic solution (single dose) and then as an additive (20 mumol/l) to the initial reperfusion (15 minutes) solution, the recovery of aortic flow after 2.5 hours of ischemia was improved from its control value of 16.5 +/- 3.9 ml/min to 28.9 +/- 4.1 ml/min (n = 8 per group; p less than 0.05). Similar protection was seen with other indexes of cardiac function. Analysis of hearts obtained at the end of 2.5 hours of ischemia and 35 minutes of reperfusion revealed no significant differences in metabolite content between control and drug-treated hearts with the exception of inosine monophosphate, which was increased from its drug-free control value of 0.10 +/- 0.01 mumol/g dry wt to 0.86 +/- 0.06 mumol/g dry wt (p less than 0.05). In further studies (n = 8 per group), with multidose (every 30 minutes) cardioplegia and extended periods (6 hours) of hypothermic ischemia, acadesine consistently led to higher mean recoveries of function and lower levels of creatine kinase leakage. Again, the only significant metabolic effect was an increase in tissue inosine monophosphate content. In studies (n = 12 per group) to determine whether acadesine was acting before, during, or after ischemia, the drug was given 1) only as pretreatment (100 mg/kg i.v.), 2) only during single-dose cardioplegia (20 mumol/l), or 3) only during reperfusion (20 mumol/l). Significant protection was observed in the first two groups (recovery of aortic flow increased from 10.6 +/- 2.6 ml/min in the acadesine-free control to 22.6 +/- 2.8 and 23.6 +/- 3.1 ml/min, respectively; p less than 0.05). No significant protection was observed when acadesine was given only during reperfusion. In dose-response studies, acadesine (0, 5, 20, 50, 200, and 1,000 mumol/l; n = 12 per group) was given only as a cardioplegic additive; the postischemic recoveries of aortic flow were 15.4 +/- 2.8, 16.9 +/- 3.6, 29.5 +/- 3.8, 27.4 +/- 3.8, 26.7 +/- 4.2, and 27.1 +/- 2.7 ml/min, respectively., Conclusions: Acadesine improves the ability of the heart to recover from ischemia and reperfusion when administered before ischemia or with cardioplegia. The mechanism underlying the protection remains to be resolved.

Members of children's cancer study group designed Study CCG 351 to determine whether three drug chemotherapy improved the survival experience of children with localized neuroblastoma. Patients in stages I-III were treated with surgical removal of the primary tumor and those in stages II and III received radiation therapy to the tumor bed and chemotherapy. Treatment included cyclophosphamide, imidazolecarboxamide, and vincristine given in 5-day pulses each month for 12 courses. The results were compared to those from a previous study, CCG 011, for localized neuroblastoma, in which children were randomized between a treatment regimen that included cyclophosphamide and one with no chemotherapy. There were 133 evaluable patients, subdivided as follows: stages I-26, stages II-74, and stages III-33. The 3-year life-table survival rates by stage of 96, 89 and 50% were not significantly different from the patients in CCG 011 similarly staged who received either no chemotherapy or oral CPM. These data suggest that multiagent chemotherapy, as prescribed, did not improve the outlook for children with locally advanced but nonmetastatic neuroblastoma. The staging criteria employed showed a modest difference in outcome between patients in stages I and II, but a significant poorer survival for stage III as compared to either stage I or II.