Open- vs. closed-chest pig models of donation after circulatory death.

Background: During donation after circulatory death (DCD), cardiac grafts are exposed to potentially damaging conditions that can impact their quality and post-transplantation outcomes. In a clinical DCD setting, patients have closed chests in most cases, while many experimental models have used open-chest conditions. We therefore aimed to investigate and characterize differences in open- vs. closed-chest porcine models. Methods: Withdrawal of life-sustaining therapy (WLST) was simulated in anesthetized juvenile male pigs by stopping mechanical ventilation following the administration of a neuromuscular block. Functional warm ischemic time (fWIT) was defined to start when systolic arterial pressure was <50 mmHg. Hemodynamic changes and blood chemistry were analyzed. Two experimental groups were compared: (i) an open-chest group with sternotomy prior to WLST and (ii) a closed-chest group with sternotomy after fWIT. Results: Hemodynamic changes during the progression from WLST to fWIT were initiated by a rapid decline in blood oxygen saturation and a subsequent cardiovascular hyperdynamic (HD) period characterized by temporary elevations in heart rates and arterial pressures in both groups. Subsequently, heart rate and systolic arterial pressure decreased until fWIT was reached. Pigs in the open-chest group displayed a more rapid transition to the HD phase after WLST, with peak heart rate and peak rate-pressure product occurring significantly earlier. Furthermore, the HD phase duration tended to be shorter and less intense (lower peak rate-pressure product) in the open-chest group than in the closed-chest group. Discussion: Progression from WLST to fWIT was more rapid, and the hemodynamic changes tended to be less pronounced in the open-chest group than in the closed-chest group. Our findings support clear differences between open- and closed-chest models of DCD. Therefore, recommendations for clinical DCD protocols based on findings in open-chest models must be interpreted with care.

Spatiotemporal AMPKα2 deletion in mice induces cardiac dysfunction, fibrosis and cardiolipin remodeling associated with mitochondrial dysfunction in males only.

BACKGROUND: The AMP-activated protein kinase (AMPK) is a major regulator of cellular energetics which plays key role in acute metabolic response and in long-term adaptation to stress. Recent works have also suggested non-metabolic effects. METHODS: To decipher AMPK roles in the heart, we generated a cardio-specific inducible model of gene deletion of the main cardiac catalytic subunit of AMPK (Ampkα2) in mice. This allowed us to avoid the eventual impact of AMPK-KO in peripheral organs. RESULTS: Cardio-specific Ampkα2 deficiency led to a progressive left ventricular systolic dysfunction and the development of cardiac fibrosis in males. We observed a reduction in complex I-driven respiration without change in mitochondrial mass or in vitro complex I activity, associated with a rearrangement of the cardiolipins and reduced integration of complex I into the electron transport chain supercomplexes. Strikingly, none of these defects were present in females. Interestingly, suppression of estradiol signaling by ovariectomy partially mimicked the male sensitivity to AMPK loss, notably the cardiac fibrosis and the rearrangement of cardiolipins, but not the cardiac function that remained protected. CONCLUSION: Our results confirm the close link between AMPK and cardiac mitochondrial function, but also highlight links with cardiac fibrosis. Importantly, we show that AMPK is differently involved in these processes in males and females, which may have clinical implications for the use of AMPK activators in the treatment of heart failure.

Inducible Cardiac-Specific Deletion of Sirt1 in Male Mice Reveals Progressive Cardiac Dysfunction and Sensitization of the Heart to Pressure Overload.

Heart failure is associated with profound alterations of energy metabolism thought to play a major role in the progression of this syndrome. SIRT1 is a metabolic sensor of cellular energy and exerts essential functions on energy metabolism, oxidative stress response, apoptosis, or aging. Importantly, SIRT1 deacetylates the peroxisome proliferator-activated receptor gamma co-activator 1α (PGC-1α), the master regulator of energy metabolism involved in mitochondrial biogenesis and fatty acid utilization. However, the exact role of SIRT1 in controlling cardiac energy metabolism is still incompletely understood and conflicting results have been obtained. We generated a cardio-specific inducible model of Sirt1 gene deletion in mice (Sirt1ciKO) to decipher the role of SIRT1 in control conditions and following cardiac stress induced by pressure overload. SIRT1 deficiency induced a progressive cardiac dysfunction, without overt alteration in mitochondrial content or properties. Sixteen weeks after Sirt1 deletion an increase in mitochondrial reactive oxygen species (ROS) production and a higher rate of oxidative damage were observed, suggesting disruption of the ROS production/detoxification balance. Following pressure overload, cardiac dysfunction and alteration in mitochondrial properties were exacerbated in Sirt1ciKO mice. Overall the results demonstrate that SIRT1 plays a cardioprotective role on cardiac energy metabolism and thereby on cardiac function.

Mitochondrial integrity during early reperfusion in an isolated rat heart model of donation after circulatory death-consequences of ischemic duration.

BACKGROUND: Cardioprotection and graft evaluation after ischemia-reperfusion (IR) are essential in facilitating heart transplantation with donation after circulatory death. Given the key role of mitochondria in IR, we aimed to investigate the tolerance of cardiac mitochondria to warm, global ischemia and to determine the predictive value of early reperfusion mitochondria-related parameters for post-ischemic cardiac recovery. METHODS: Isolated, working rat hearts underwent 0, 21, 24, 27, 30, or 33 minutes of warm, global ischemia, followed by 60 minutes of reperfusion. Functional recovery (developed pressure × heart rate) was determined at 60 minutes of reperfusion, whereas mitochondrial integrity was measured at 10 minutes of reperfusion. RESULTS: Functional recovery at 60 minutes of reperfusion decreased with ≥ 27 minutes of ischemia vs no ischemia (n = 7-8/group; p < 0.01). Cytochrome c, succinate release, and mitochondrial Ca2+ content increased with ≥ 27 minutes of ischemia vs no ischemia (p < 0.05). Ischemia at ≥ 21 minutes decreased mitochondrial coupling, adenosine 5'-triphosphate content, mitochondrial Ca2+ retention capacity, and increased oxidative damage vs no ischemia (p < 0.05). Reactive oxygen species (ROS) from reverse electron transfer increased with 21 and 27 minutes of ischemia vs no ischemia and 33 minutes of ischemia (p < 0.05), whereas ROS from forward electron transfer increased only with 33 minutes of ischemia vs no ischemia (p < 0.05). Mitochondrial coupling and adenosine 5'-triphosphate content correlated positively and cytochrome c, succinate, oxidative damage, and mitochondrial Ca2+ content correlated negatively with cardiac functional recovery (p < 0.05). CONCLUSIONS: Mitochondrial dysfunction occurs with shorter periods of ischemia than cardiac dysfunction. Mitochondrial coupling, ROS emission from reverse electron transfer, and calcium retention are particularly sensitive to early reperfusion injury, reflecting potential targets for cardioprotection. Indicators of mitochondrial integrity may be of aid in evaluating suitability of donation after circulatory death grafts for transplantation.

AMPK in skeletal muscle function and metabolism.

Skeletal muscle possesses a remarkable ability to adapt to various physiologic conditions. AMPK is a sensor of intracellular energy status that maintains energy stores by fine-tuning anabolic and catabolic pathways. AMPK's role as an energy sensor is particularly critical in tissues displaying highly changeable energy turnover. Due to the drastic changes in energy demand that occur between the resting and exercising state, skeletal muscle is one such tissue. Here, we review the complex regulation of AMPK in skeletal muscle and its consequences on metabolism ( e.g., substrate uptake, oxidation, and storage as well as mitochondrial function of skeletal muscle fibers). We focus on the role of AMPK in skeletal muscle during exercise and in exercise recovery. We also address adaptations to exercise training, including skeletal muscle plasticity, highlighting novel concepts and future perspectives that need to be investigated. Furthermore, we discuss the possible role of AMPK as a therapeutic target as well as different AMPK activators and their potential for future drug development.-Kjøbsted, R., Hingst, J. R., Fentz, J., Foretz, M., Sanz, M.-N., Pehmøller, C., Shum, M., Marette, A., Mounier, R., Treebak, J. T., Wojtaszewski, J. F. P., Viollet, B., Lantier, L. AMPK in skeletal muscle function and metabolism.

Acute mitochondrial actions of glitazones on the liver: a crucial parameter for their antidiabetic properties.

BACKGROUND/AIMS: Glitazones are synthetic insulin-sensitizing drugs which act as agonists of peroxisome proliferator-activated receptor gamma (PPARγ). However, TZDs action does not exclude independent PPARγ-activation effects. Remarkably, direct mitochondrial action of these agents has not been fully studied yet. METHODS: Oxygen consumption rates (JO(2)) were measured using a Clark-type oxygen electrode in intact hepatocytes and isolated liver mitochondria. Mitochondrial reactive oxygen species (ROS) production was quantified by fluorescence assay. Moreover, activities of mitochondrial respiratory chain complex I, II and III were spectrometrically determined. RESULTS: Pioglitazone and rosiglitazone inhibited JO(2) in liver cells and mitochondria. This inhibition affected the state 3 of respiration (in the presence of ADP) and the uncoupled state (after addition of dinitrophenol). Moreover, these agents dramatically reduced mitochondrial ROS production in all situations tested. We also demonstrated that both glitazones specifically inhibited the activities of complex I and complex III, by 50% and 35% respectively. Additionally, they do not modify neither the oxidative phosphorylation yield nor the permeability transition pore opening. CONCLUSIONS: Pioglitazone and rosiglitazone reduce both respiration intensity and ROS production, acutely and by a probable PPARγ-independent way, through inhibition of complex I and III activities. This new finding could positively contribute to their anti-diabetic properties.