Effect of exogenous adenosine triphosphate on the metabolic state of the excised hypothermic dog heart

High-Energy Phosphates and Ischemic Heart Disease: From Bench to Bedside

The purpose of this review is to bridge the gap between clinical and basic research through providing a comprehensive and concise description of the cellular and molecular aspects of cardioprotective mechanisms and a critical evaluation of the clinical evidence of high-energy phosphates (HEPs) in ischemic heart disease (IHD). According to the well-documented physiological, pathophysiological and pharmacological properties of HEPs, exogenous creatine phosphate (CrP) may be considered as an ideal metabolic regulator. It plays cardioprotection roles from upstream to downstream of myocardial ischemia through multiple complex mechanisms, including but not limited to replenishment of cellular energy. Although exogenous CrP administration has not been shown to improve long-term survival, the beneficial effects on multiple secondary but important outcomes and short-term survival are concordant with its pathophysiological and pharmacological effects. There is urgent need for high-quality multicentre RCTs to confirm long-term survival improvement in the future.

The effect of adenosine triphosphate on propofol-induced myopathy in rats: a biochemical and histopathological evaluation

Propofol infusion syndrome characterized by rhabdomyolysis, metabolic acidosis, kidney, and heart failure has been reported in long-term propofol use for sedation. It has been reported that intracellular adenosine triphosphate (ATP) is reduced in rhabdomyolysis. The study aims to investigate the protective effect of ATP against possible skeletal muscle damage of propofol in albino Wistar male rats biochemically and histopathologically. PA-50 (n = 6) and PA-100 (n = 6) groups of animals was injected intraperitoneally to 4 mg/kg ATP. An equal volume (0.5 ml) of distilled water was administered intraperitoneally to the P-50, P-100, and HG groups. One hour after the administration of ATP and distilled water, 50 mg/kg propofol was injected intraperitoneally to the P-50 and PA-50 groups. This procedure was repeated once a day for 30 days. The dose of 100 mg/kg propofol was injected intraperitoneally to the P-100 and PA-100 groups. This procedure was performed three times with an interval of 1 days. Our experimental results showed that propofol increased serum CK, CK-MB, creatinine, BUN, TP I, ALT, AST levels, and muscle tissue MDA levels at 100 mg/kg compared to 50 mg/kg and decreased tGSH levels. At a dose of 100 mg/kg, propofol caused more severe histopathological damage compared to 50 mg/kg. It was found that ATP prevented propofol-induced muscle damage and organ dysfunction at a dose of 50 mg/kg at a higher level compared to 100 mg/kg. ATP may be useful in the treatment of propofol-induced rhabdomyolysis and multiple organ damage.

Intracellular ATP delivery using highly fusogenic liposomes

Healthy cells must maintain a high content of adenosine triphosphate (ATP) because almost all energy-requiring processes in cells are driven, either directly or indirectly, by hydrolysis of ATP. During ischemia or hypoxia, reduced blood flow or disturbed oxygen supply results in the disrupted balance of energy production and utilization, and depletion of high-energy phosphates is the fundamental cause of cell damage. Direct intravenous infusion of high-energy phosphates, such as adenosine triphosphate (ATP), has not produced a consistent result because strongly charged molecules like ATP normally cannot pass the cell membrane in sufficient quantities to satisfy tissue metabolic requirements. Furthermore, the half-life of free ATP in blood circulation is very short, limiting its efficacy as a bioenergetic substrate. We have developed a new technique for intracellular delivery of high-energy phosphate into normal or ischemic cells by using specially formulated, highly fusogenic, unilamellar lipid vesicles that contain magnesium-ATP. In vitro studies indicated a rapid fusion with the endothelial cells, protection of endothelial cells, and cardiomyocytes during ischemia. In vivo studies have shown enhanced full-thickness skin wound healing in various animal models. This technique has the potential to reduce or eliminate many detrimental effects caused by ischemia or hypoxia.

Acute diabetes modulates response to ischemia in isolated rat heart

Diabetic hearts are suggested to exhibit either increased or lower sensitivity to ischemia. Detrimental effects of prolonged ischemia can be attenuated by preconditioning, however, relatively little is known about its effects in the diseased myocardium. This study was designed to test the susceptibility to ischemia-induced arrhythmias and the effect of preconditioning in the diabetic heart. Rats were made diabetic with streptozotocin (45 mg/kg, i.v.). After 1 week, isolated Langendorff-perfused hearts were subjected to 30 min occlusion of LAD coronary artery without or with preceding preconditioning induced by one cycle of 5 min ischemia and 10 min reperfusion. Glycogen and lactate contents were estimated in the preconditioned and non-preconditioned hearts before and after ischemia. Diabetic hearts were more resistant to ischemia-induced arrhythmias: incidence of ventricular tachycardia (VT) decreased to 42% and only transient ventricular fibrillation (VF) occurred in 17% of the hearts as compared to the non-diabetic controls (VT 100% and VF 70% including sustained VF 36%; p < 0.05). Preconditioning effectively suppressed the incidence and severity of arrhythmias (VT 33%, VF 0%) in the normal hearts. However, this intervention did not confer any additional protection in the diabetic hearts. Despite higher glycogen content in the diabetic myocardium and greater glycogenolysis during ischemia, production of lactate in these hearts was significantly lower than in the controls. Preconditioning caused a substantial decrease in the accumulation of lactate in the normal hearts, whereby in the diabetic hearts, this intervention did not cause any further reduction in the level of lactate. In conclusion, diabetic rat hearts exhibit lower susceptibility to ischemic injury and show no additional response to preconditioning. Reduced production of glycolytic metabolites during ischemia can account for the enhanced resistance of diabetic hearts to ischemia as well as for the lack of further protection by preconditioning.

Effects of adenine nucleotide analogues on myocardial dysfunction during reperfusion after ischemia in dogs

We examined effects of adenine nucleotide on ischemic myocardial stunning in dogs. Pentobarbitalanesthetized open-chest dogs were subjected to 20-min ligation of the left anterior descending coronary artery (LAD), followed by reperfusion for 30 min. Either saline, 5 mM 8-bromo-5'-AMP (tributyryl-AMP), or 30 mM N6, 2', 3'-tributyryl-5'-AMP (tributyryl-AMP), 5 mM 5-amino-4-imidazole carboxamide riboside (AICAr) as a positive reference, was infused at 0.1 ml/kg/min in the left femoral vein throughout the experiment. The myocardial contractile function was measured by ultrasonometry. The tissue levels of high-energy phosphates in the reperfused heart were determined. Myocardial contractile function assessed by % segment shortening (%SS) in the saline-infused group decreased during ischemia and returned toward the preischemic level during reperfusion but incompletely. A significant improvement in the %SS during reperfusion was observed in the 8-bromo-AMP- and AICAr-infused groups but not in the tributyryl-AMP-infused group. The magnitude of the protective effect of the drugs on myocardial contractility during reperfusion was 8-bromo-AMP > AICAr > tributyryl-AMP = saline. Only in the 8-bromo-AMP-infused group were the levels of ATP, ADP, and total adenine nucleotides in the reperfused heart significantly higher than those in the saline-infused group. The present result indicates that 8-bromo-AMP improves the ability of the heart to recover from ischemia and reperfusion associated with a significant restoration of ATP.

Exogenous fructose-1,6-bisphosphate is a metabolizable substrate for the isolated normoxic rat heart

Isolated rat hearts were perfused by the recirculating Langendorff mode under normoxic conditions for 60 min. The Krebs-Ringer buffer was supplemented with 10 mM glucose + 12 IU/l insulin and either [U-14C]-fructose-1,6-bisphosphate (together with 5 mM cold fructose-1,6-bisphosphate) or [U-14C]-fructose (together with 5 mM cold fructose). At the end of perfusion, gaseous 14CO2, 14CO2 trapped in the perfusates, 14C-lactate output and tissue 14C-lactate were assayed in both groups of hearts. Analysis of high-energy compounds, glycogen, lactate, and pyruvate was also performed on the neutralized perchloric acid extracts of the freeze-clamped hearts. Data obtained from the 14C catabolites, originating from the metabolism of the radiolabeled substrates, indicated that the isolated normoxic rat heart metabolizes an 8.5 times higher amount of fructose-1,6-bisphosphate (7.07 mumoles/min/g d.w.) than of fructose (0.83 mumoles/min/g d.w.). CrP, CrP/Cr, glycogen, and total lactate in both tissue and perfusate were significantly higher in fructose-1,6-bisphosphate-perfused hearts. The overall indication is that fructose-1,6-bisphosphate can be taken up in its intact form by myocytes and successively metabolized to support their energy demand, and that its effects on myocardial performance and metabolism should be attributed to the molecule itself rather than to its eventual degradation products.

Upgrading acellular to sanguineous cardioplegic efficacy

To determine which biochemical entity of the red cell is responsible for preventing augmented postischemic myocardial oxygen consumption (MVO2), 28 canine hearts instrumented with ultrasonic dimension crystals underwent simultaneous determination of stroke work (SW) and MVO2 during incremental volume loading on right heart bypass before and 30 min after 2 hr of 10 degrees C cardioplegic arrest with unmodified oxygenated crystalloid cardioplegia (OC), OC with histidine of equal buffering capacity as 18% hematocrit blood (OC + H), or OC with 200 units/ml of superoxide dismutase and catalase (OC + SOD/C). In all groups, the slope of the linear SW vs end-diastolic volume relationship, Mw, and the slope of the linear SW vs MVO2 relationship, Me, were unchanged after cardioplegic arrest. The intercept of the SW vs MVO2 relationship, Eo, was augmented an average of 22.2% in the OC group, but both OC + H and OC + SOD/C prevented this subtle expression of ischemic injury. The characteristic of the red cell most likely responsible for the myoprotective efficacy of blood cardioplegia is buffering capacity; however, since the effects of tissue acidosis are partially mediated by free radicals, the use of free radical scavengers can also ameliorate ischemic damage incurred during cardioplegic arrest.

Reperfusion with ATP-MgCl2 following prolonged ischemia improves myocardial performance

This study was designed to test the hypothesis that infusion of ATP-MgCl2 during reperfusion following a prolonged period of hypothermic global ischemia would result in enhanced functional recovery of cardiac function. Two groups of dogs (n = 6 each) were placed on cardiopulmonary bypass (CP) with systemic hypothermia to 28 degrees C and subjected to 150 min of aortic cross-clamping. Crystalloid cardioplegia was infused every 20 min during ischemia. Reperfusion and rewarming were carried out for 20 min before discontinuation of CP bypass. During reperfusion, the experimental group received ATP-MgCl2(1.0 mg/kg/min ATP, 0.33 mg/kg/min magnesium). At 15 and 45 min following bypass, hemodynamic assessment was carried out for each animal by constructing Starling curves over a range of filling pressures at constant heart rate and comparing each animal to its own prebypass control level. The results indicated that ATP-treated animals exhibited complete functional recovery whereas control animals showed marked reduction in hemodynamic performance and myocardial compliance and had a higher myocardial water content (P less than 0.05). We conclude that infusion of ATP-MgCl2 during reperfusion following hypothermic ischemia may help ameliorate reperfusion injury.

Creatine phosphate and protection against reperfusion-induced arrhythmias in the rat heart

An isolated perfused working rat heart preparation was used to assess the effect of including creatine phosphate (10 mmol/l) in the perfusion fluid of hearts subjected to aerobic perfusion (20 min), regional ischaemia (15 min) and reperfusion (2 min). Creatine phosphate had no detectable effect upon pre-ischaemic, ischaemic or post-ischaemic contractile function, it also had no statistically significant effect upon myocardial tissue ATP content. However, creatine phosphate was found to afford striking protection against reperfusion-induced arrhythmias. The incidence of ventricular fibrillation was reduced from over 80% (13/16) in the control group to 10% in the creatine phosphate-treated group (P less than 0.001). Possible mechanisms underlying the anti-arrhythmic effects of creatine phosphate were investigated using isolated rat papillary muscles superfused with or without added creatine phosphate (10 mmol/l). During aerobic superfusion at 37 degrees C creatine phosphate did not cause any statistically significant changes in contractile (developed tension) or electrophysiological (dV/dtmax and action potential duration) indices. Creatine phosphate did however influence the extent to which hypoxia (10 min) and reoxygenation (10 min) altered tension and electrophysiological characteristics. It accelerated the hypoxia-induced decline in developed tension and also the reoxygenation-induced recovery of developed tension. Relatively small changes in dV/dtmax and action potential duration were observed during hypoxia and these rapidly normalized during reoxygenation. In general creatine phosphate acted to exacerbate any changes during hypoxia and accelerate the recovery during reoxygenation. While some of the electrophysiological changes observed would indicate an anti-arrhythmic effect, they were relatively small and perhaps insufficient to explain fully the potent anti-arrhythmic properties of creatine phosphate.

Beneficial metabolic effect of nucleoside augmentation on reperfusion injury following cardioplegic arrest

Restoration of coronary flow after hyperkalemic cardioplegic arrest (HCA) is associated with a unique metabolic reperfusion injury (RI) manifested by declining nucleotide stores despite their end-ischemic preservation. Prevention of this RI by exogenous provision of adenosine with or without inhibition of adenosine's major catabolic enzyme was assessed in 27 dogs subjected to 60 minutes of HCA. The effect of aortic root infusion of 40 mg/kg of adenosine in addition to adenosine deaminase inhibition by 10 mg/kg of EHNA (group 2) initiated during 60 minutes of reperfusion on myocardial adenosine triphosphate (ATP) and creatine phosphate (CP) stores and coronary blood flow (CBF) were compared to animals having adenosine infusion alone (group 3) or controls (group 1). Although ATP levels were preserved at the end of HCA in all groups, adenosine infusion with or without EHNA prevented the significant 23 percent decline in ATP stores incurred during unmodified reperfusion (p less than 0.01, group 1). The CP stores decreased (p less than 0.05, all groups) during arrest, but were restored to preischemic levels during reperfusion. When measured 60 minutes after aortic unclamping, CBF was 312 percent of preischemic flow in group 3 (p less than 0.01), only 170 percent in group 2 (p less than 0.05), and unchanged in controls (group 1). The data indicate that provision of adenosine as a nucleotide precursor prevents the metabolic RI following HCA. In addition, inhibition of adenosine catabolism is not necessary for this salutary effect, nor is adenosine's efficacy solely mediated by augmentation of CBF.

Appearance of adenosine triphosphate in the coronary sinus effluent from isolated working rat heart in response to hypoxia

1. A working rat heart preparation was used to study the release of adenosine-5'-triphosphate (ATP) into the coronary sinus effluent in response to hypoxia. 2. The left ventricle was set to pump against an hydrostatic pressure of 65 cm water; the left atrial filling pressure was kept constant at 10 cm water. The power output of the heart at these pressures was estimated to be approximately one half of the maximum power development. 3. Samples for ATP assay were collected (a) 30 sec before onset of hypoxia, (b) 60-90 sec after onset of hypoxia, (c) 5 min after restoration of oxygenated buffer solution. Respective concentrations of ATP were (nM +/- S.E.) 0.63 (+/- 0.18), 4.70 (+/- 0.39) and 0.63 (+/- 0.06). The total amounts of ATP detected were (p-mole/min) 5.9 (+/- 0.9), 46.1 (+/- 6.0) and 5.5 (+/- 1.2) respectively. 4. Viability of the hearts was judged to be satisfactory on the following grounds. Alterations in left atrial filling pressure produced typical Frank-Starling responses of the left ventricle. Oxygen extraction from the perfusate increased in response to increased workload. Coronary blood flow increased immediately upon introduction of hypoxic conditions and mechanical recovery from hypoxia was always complete within 5 min of restoring oxygen. 5. In view of the marked extracellular ATPase activity it is concluded that significant vasodilatory concentrations of ATP are released into the myocardial extracellular space in response to hypoxia. A scheme is proposed describing the possible role of adenine nucleotides in the local control of myocardial blood flow.

Protection of the myocardium with high-energy solutions

An approach to intraoperative protection of the myocardium is described that attempts to increase glucose utilization by infusion of high-energy solutions during aortic cross-clamping. Infusion of hypertonic glucose or glucose plus insulin prior to aortic cross-clamping has enhanced contractility and increased high-energy phosphate moieties in animals with induced ischemia. Recent pilot experiments in our laboratory suggest that infusions of creatine may result in increased production of creatine phosphate, which in turn induces phosphorylation of adenosine diphosphate to adenosine triphosphate, possibly enhancing myocardial contractility. The intraoperative clinical benefits of these infusions remain to be proved, however.

Spontaneous rhythmic contraction of separated heart muscle cells

Muscle cells that conitract spontaneously and rhythmically can be obtained from adult mouse myocardium. Contractions are observed immediately after homogenization in a solution that is ionically similar to intracellular fluid. Contraction frequency varies directly with temperature and decreases as a function of time after homogenization. At 16 degrees C rhythmic relaxation and contraction occur for about 20 minutes. Contractions are dependent on the presence of adenosine triphosphate in the homogenization medium.