Jonas Agerlund Povlsen

Amino acid transamination is crucial for ischaemic cardioprotection in normal and preconditioned isolated rat hearts – focus on l‐glutamate

We have found that cardioprotection by l‐glutamate mimics protection by classical ischaemic preconditioning (IPC). We investigated whether the effect of IPC involves amino acid transamination and whether IPC modulates myocardial glutamate metabolism. In a glucose‐perfused, isolated rat heart model subjected to 40 min global no‐flow ischaemia and 120 min reperfusion, the effects of IPC (2 cycles of 5 min ischaemia and 5 min reperfusion) and continuous glutamate (20 mm) administration during reperfusion on infarct size and haemodynamic recovery were studied. The effect of inhibiting amino acid transamination was evaluated by adding the amino acid transaminase inhibitor amino‐oxyacetate (AOA; 0.025 mm) during reperfusion. Changes in coronary effluent, interstitial (microdialysis) and intracellular glutamate ([GLUT]i) concentrations were measured. Ischaemic preconditioning and postischaemic glutamate administration reduced infarct size to the same extent (41 and 40%, respectively; P < 0.05 for both), without showing an additive effect. Amino‐oxyacetate abolished infarct reduction by IPC and glutamate, and increased infarct size in both control and IPC hearts in a dose‐dependent manner. Ischaemic preconditioning increased [GLUT]i before ischaemia (P < 0.01) and decreased the release of glutamate during the first 10 min of reperfusion (P= 0.03). A twofold reduction in [GLUT]i from the preischaemic state to 45 min of reperfusion (P= 0.0001) suggested increased postischaemic glutamate utilization in IPC hearts. While IPC and AOA changed haemodynamics in accordance with infarct size, glutamate decreased haemodynamic recovery despite reduced infarct size. In conclusion, ischaemic cardioprotection of the normal and IPC‐protected heart depends on amino acid transamination and activity of the malate–aspartate shuttle during reperfusion. Underlying mechanisms of IPC include myocardial glutamate metabolism.

Protection against Myocardial Ischemia-Reperfusion Injury at Onset of Type 2 Diabetes in Zucker Diabetic Fatty Rats Is Associated with Altered Glucose Oxidation

Background Inhibition of glucose oxidation during initial reperfusion confers protection against ischemia-reperfusion (IR) injury in the heart. Mitochondrial metabolism is altered with progression of type 2 diabetes (T2DM). We hypothesized that the metabolic alterations present at onset of T2DM induce cardioprotection by metabolic shutdown during IR, and that chronic alterations seen in late T2DM cause increased IR injury. Methods Isolated perfused hearts from 6 (prediabetic), 12 (onset of T2DM) and 24 (late T2DM) weeks old male Zucker diabetic fatty rats (ZDF) and their age-matched heterozygote controls were subjected to 40 min ischemia/120 min reperfusion. IR injury was assessed by TTC-staining. Myocardial glucose metabolism was evaluated by glucose tracer kinetics (glucose uptake-, glycolysis- and glucose oxidation rates), myocardial microdialysis (metabolomics) and tissue glycogen measurements. Results T2DM altered the development in sensitivity towards IR injury compared to controls. At late diabetes ZDF hearts suffered increased damage, while injury was decreased at onset of T2DM. Coincident with cardioprotection, oxidation of exogenous glucose was decreased during the initial and normalized after 5 minutes of reperfusion. Metabolomic analysis of citric acid cycle intermediates demonstrated that cardioprotection was associated with a reversible shutdown of mitochondrial glucose metabolism during ischemia and early reperfusion at onset of but not at late type 2 diabetes. Conclusions The metabolic alterations of type 2 diabetes are associated with protection against IR injury at onset but detrimental effects in late diabetes mellitus consistent with progressive dysfunction of glucose oxidation. These findings may explain the variable efficacy of cardioprotective interventions in individuals with type 2 diabetes.

Ischemic Preconditioning Reduces Right Ventricular Infarct Size through Opening of Mitochondrial Potassium Channels

Objectives: We investigated whether ischemic preconditioning (IPC) protects the right ventricular (RV) myocardium against ischemic injury in hearts treated with the specific mitochondrial ATP-sensitive potassium (KATP) channel blocker 5-hydroxydecanoate (5-HD). Methods: Hearts from male Wistar rats (300 g, n = 39) were isolated and perfused with Krebs-Henseleit buffer and randomized to no IPC (control, n = 16), IPC (n = 16) or IPC preceded by addition of 5-HD (100 µm, n = 7). IPC consisted of 2 × 5 min of global ischemia followed by 40 min of global ischemia and 120 min of reperfusion. The effect of IPC on RV myocardial infarct size was evaluated by measurement of the infarct size/area-at-risk ratio (RVIS/AAR). Postischemic RV function was evaluated by RV pressures. Results: IPC produced a marked decrease in RVIS/AAR (24.4 ± 8.1 vs. 42.6 ± 10.6%, p < 0.0001) and improved hemodynamic recovery of RV contractile function compared with the control group. We found no difference in RVIS/AAR (45.2 ± 4.4 vs. 42.6 ± 10.6, p > 0.05) or hemodynamic recovery between IPC + 5-HD and control hearts. Blockade of mitochondrial KATP channels by 5-HD abolished the cardioprotective response to IPC. Conclusion: IPC reduces RV myocardial infarct size and improves postischemic RV contractile function in the isolated rat heart, possibly through opening of the mitochondrial KATP channel.

A novel protocol for dispatcher assisted CPR improves CPR quality and motivation among rescuers—A randomized controlled simulation study

BACKGROUND Emergency dispatchers use protocols to instruct bystanders in cardiopulmonary resuscitation (CPR). Studies changing one element in the dispatchers protocol report improved CPR quality. Whether several changes interact is unknown and the effect of combining multiple changes previously reported to improve CPR quality into one protocol remains to be investigated. We hypothesize that a novel dispatch protocol, combining multiple beneficial elements improves CPR quality compared with a standard protocol. METHODS A novel dispatch protocol was designed including wording on chest compressions, using a metronome, regular encouragements and a 10-s rest each minute. In a simulated cardiac arrest scenario, laypersons were randomized to perform single-rescuer CPR guided with the novel or the standard protocol. PRIMARY OUTCOME a composite endpoint of time to first compression, hand position, compression depth and rate and hands-off time (maximum score: 22 points). Afterwards participants answered a questionnaire evaluating the dispatcher assistance. RESULTS The novel protocol (n=61) improved CPR quality score compared with the standard protocol (n=64) (mean (SD): 18.6 (1.4)) points vs. 17.5 (1.7) points, p<0.001. The novel protocol resulted in deeper chest compressions (mean (SD): 58 (12)mm vs. 52 (13)mm, p=0.02) and improved rate of correct hand position (61% vs. 36%, p=0.01) compared with the standard protocol. In both protocols hands-off time was short. The novel protocol improved motivation among rescuers compared with the standard protocol (p=0.002). CONCLUSIONS Participants guided with a standard dispatch protocol performed high quality CPR. A novel bundle of care protocol improved CPR quality score and motivation among rescuers.

Influence of diabetes mellitus duration on the efficacy of ischemic preconditioning in a Zucker diabetic fatty rat model

Augmented mortality and morbidity following an acute myocardial infarction in patients with diabetes mellitus Type 2 (T2DM) may be caused by increased sensitivity to ischemia reperfusion (IR) injury or altered activation of endogenous cardioprotective pathways modified by T2DM per se or ischemic preconditioning (IPC). We aimed to investigate, whether the duration of T2DM influences sensitivity against IR injury and the efficacy of IPC, and how myocardial glucose oxidation rate was involved. Male Zucker diabetic fatty rats (homozygote (fa/fa)) at ages 6-(prediabetic), 12- (onset diabetes) and 24-weeks of age (late diabetes) and their age-matched non-diabetic controls (heterozygote (fa/+) were subjected to IR injury in the Langendorff model and randomised to IPC stimulus or control. T2DM rats were endogenously protected at onset of diabetes, as infarct size was lower in 12-weeks T2DM animals than in 6- (35±2% vs 53±4%; P = 0.006) and 24-weeks animals (35±2% vs 72±4%; P<0.0001). IPC reduced infarct size in all groups irrespective of the presence of T2DM and its duration (32±3%; 20±2%; 36±4% respectively; (ANOVA P<0.0001). Compared to prediabetic rats, myocardial glucose oxidation rates were reduced during stabilisation and early reperfusion at onset of T2DM, but these animals retained the ability to increase oxidation rate in late reperfusion. Late diabetic rats had low glucose oxidation rates throughout stabilisation and reperfusion. Despite inherent differences in sensitivity to IR injury, the cardioprotective effect of IPC was preserved in our animal model of pre-, early and late stage T2DM and associated with adaptations to myocardial glucose oxidation capacity.

Effects of fatty acids on cardioprotection by pre-ischaemic inhibition of the malate–aspartate shuttle

The malate–aspartate shuttle (MAS) is the main pathway for balancing extra‐ and intramitochondrial glucose metabolism. Pre‐ischaemic shutdown of the MAS by aminooxyacetate (AOA) mimics ischaemic preconditioning (IPC) in rat glucose‐perfused hearts. The aim of the present study was to determine the effects of fatty acids (FA) on cardioprotection by pre‐ischaemic inhibition of the MAS. Isolated rat hearts were divided into four groups (control; pre‐ischaemic AOA (0.2 mmol/L); IPC; and AOA + IPC) and were perfused with 11 mmol/L glucose, 3% bovine serum albumin plus 0, 0.4 or 1.2 mmol/L FA. The perfusion protocol included 30 min global no‐flow ischaemia and 120 min reperfusion. Infarct size (IS), haemodynamic recovery, glucose oxidation and lactate release were evaluated in all four groups. Pre‐ischaemic AOA reduced the IS of the left ventricle in hearts perfused with 0, 0.4 and 1.2 mmol/L FA compared with that in control hearts (26 ± 2% vs 53 ± 4%, 29 ± 3% vs 53 ± 4% and 61 ± 4% vs 81 ± 3%, respectively; P < 0.01 for all). After 2 h reperfusion, AOA improved haemodynamic recovery in the absence (52 ± 2 vs 27 ± 3 mmHg in the AOA and control groups, respectively; P < 0.001) but not in the presence, of FA. Both IPC and AOA + IPC reduced IS and improved haemodynamic recovery regardless of FA levels. Postischaemic glucose oxidation was suppressed by FA and did not differ significantly between the different groups. In conclusion, the reduction in IS induced by pre‐ischaemic MAS shutdown is not compromised by physiological FA concentrations. Transient MAS shutdown may be involved in IPC, but is not sufficient on its own as the underlying mechanism for IPC.

Skills among young and elderly laypersons during simulated dispatcher assisted CPR and after CPR training

Dispatcher assisted cardiopulmonary resuscitation (DA‐CPR) increase the rate of bystander CPR. The aim of the study was to compare the performance of DA‐CPR and attainable skills following CPR training between young and elderly laypersons.

TEMPORAL CHARACTERIZATION OF CARDIAC ISCHEMIA-REPERFUSION INJURY BY FREQUENT MEASUREMENT OF BIOMARKER RELEASE FROM THE ISOLATED RAT HEART

The aim of the present study was to characterize the dynamics of reperfusion injury by portraying the temporal release of lactate dehydrogenase (LDH) during ischemia-reperfusion (IR) injury in an isolated heart model. We studied infarct size (IS) and LDH release in three groups: I) Effect of