Attentuation of cardiac stunning by losartan in a cellular model of ischemia and reperfusion is accompanied by increased sarcoplasmic reticulum Ca2+ stores and prevention of cytosolic Ca2+ elevation

The Role of SIRT3 in Mediating Cardioprotective Effects of RAS Inhibition on Cardiac Ischemia-Reperfusion

Cardiac ischemia-reperfusion stimulates the renin-angiotensin system (RAS) associated with elevated levels of circulating angiotensin II. Numerous studies demonstrate that the antagonist for the angiotensin II type 1 receptor, losartan improves cardiac function in animal models of ischemia-reperfusion. Molecular mechanisms of the cardioprotective effects of RAS inhibitors on cardiac ischemia-reperfusion remain poorly understood, and are not associated with the anti-hypertensive action of these drugs. This Commentary focuses on the study published in the Journal of Pharmacy and Pharmaceutical Sciences, 2015, 18:112-123, that elucidates the role of SIRT3 in the cardioprotective action of losartan against ischemic-reperfusion injury. We provide comprehensive discussion of the role of mitochondria in the cardioprotective effects of losartan through SIRT3. This article is open to POST-PUBLICATION REVIEW. Registered readers (see "For Readers") may comment by clicking on ABSTRACT on the issue's contents page.

Acute hemodynamic effects of angiotensin- converting enzyme inhibition after prolonged cardiac arrest with Bretschneider's solution

Evidence as to how ACE inhibitors attenuate ischemia-reperfusion injury (IR) after cardioplegic arrest remains scarce. Twenty-four rabbit hearts were perfused on a Langendorff apparatus. Control hearts (n = 6) were arrested with pure histidine-tryptophan-ketoglutarate (HTK)-Bretschneider. Treatment groups received added to the cardioplegic solution (n = 6) captopril (100 μmol/l) and losartan (100 μmol/l) for selective AT1-receptor antagonism or BQ123 (100 nmol/l) for selective ETA-receptor antagonism. Pre-ischemic equilibration of 45 min was followed by 90 min of cardioplegic arrest and 30 min of reperfusion. Indices of myocardial contractility (LVP, dp/dt max, dp/dt min), coronary flow, heart rate, and O2 consumption were recorded before and after ischemic arrest. Tissue adenosine triphosphate (ATP) and malondialdehyde (MDA) contents were measured to evaluate energy content and oxidative stress, respectively. After selective cardiac arrest with Bretschneider, captopril-treated hearts showed improved hemodynamics compared to control and the other treatment groups. Oxygen consumption was significantly decreased during early reperfusion in captopril-treated hearts (34 ± 3 μmol/min/g/mmHg) compared to controls and losartan- and BQ123-treated hearts (controls: 77 ± 9 μmol/min/g/mmHg, p = 0.003; losartan: 54 ± 9 μmol/min/g/mmHg, p = 0.015; BQ123: 64 ± 13 μmol/min/g/mmHg, p = 0.046). The ATP content of the reperfused tissue was significantly elevated after captopril treatment compared to control group (24 ± 2 vs. 16 ± 2 μmol/g, p = 0.033), whereas the level of MDA was substantially decreased (0.58 ± 0.163 vs. 1.5 ± 0.28 μmol/g, p = 0.009). ACE inhibition leads to a significantly greater and faster recovery of myocardial contractility after prolonged cardiac arrest with Bretschneider solution. Due to decreased oxygen consumption, myocardial protection is enhanced. The association between ACE and ischemia cannot be clarified by selective blockade of angiotensin-II receptor type 1 (AT1-R) or ETa receptor (ETa-R).

Eprosartan improves cardiac function in swine working heart model of ischemia-reperfusion injury

BACKGROUND

Eprosartan is an angiotensin II receptor antagonist used as an antihypertensive. We sought to evaluate the regional effect of Eprosartan on postinfarct ventricular remodeling and myocardial function in an isolated swine working heart model of ischemia-reperfusion injury.

MATERIAL AND METHODS

22 swine hearts were perfused with the Langendorff perfusion apparatus under standard experimental conditions. Myocardial ischemia was induced by a 10-min left anterior descending artery ligation. Hearts were reperfused with either saline (control group, n=11), or Eprosartan (treatment group, n=11). Left ventricular pressure (LVP) and regional heart parameters such as intramyocardial pressure (IMP), wall thickening rate (WTh), and pressure-length-loops (PLL) were measured at baseline and after 30 min of reperfusion.

RESULTS

Measured parameters were statistically similar between the 2 groups at baseline. The administration of Eprosartan led to a significantly better recovery of IMP and WTh: 44.4±2.5 mmHg vs. 51.2±3.3 mmHg, p<0.001 and 3.8±0.4 µm vs. 4.4±0.3 µm, p=0.001, respectively. PLL were also significantly higher in the treatment group following reperfusion (21694±3259 units vs. 31267±3429 units, p<0.01). There was no difference in the LVP response to Eprosartan versus controls (63.6±3.0 mmHg vs. 62.5±3.1 mmHg, p=0.400).

CONCLUSIONS

Pre-treatment with Eprosartan is associated with a significant improvement in regional cardiac function under ischemic conditions. Pharmacological treatment with eprosartan may exert a direct cardioprotective effect on ischemic myocardium.

Diastolic Ca2+ overload caused by Na+/Ca2+ exchanger during the first minutes of reperfusion results in continued myocardial stunning

The pathogenesis of myocardial stunning caused by brief ischemia and reperfusion remains unclear. The aim of the present study was to investigate the underlying mechanism of myocardial stunning. An isolated cell model of myocardial stunning was firstly established in isolated rat ventricular myocytes exposed to 8 min of simulated ischemia and 30 min of reperfusion, the cardiomyocyte contractile function was used to evaluate myocardial stunning. A diastolic Ca(2+) overload without significant changes in systolic Ca(2+) and the amplitude of Ca(2+) transient during the first 10 min of reperfusion played an important role in the occurrence of myocardial stunning. Decreasing Ca(2+) entry into myocardial cells with low Ca(2+) reperfusion was a very efficient way to prevent myocardial stunning. Diastolic Ca(2+) overload was closely related to the reverse mode of Na(+)/Ca(2+) exchanger (NCX) rather than L-type Ca(2+) channel. The activity of the reverse mode of NCX was found significantly higher at the initial time of reperfusion, and KB-R7943, a selective inhibitor of the reverse mode of NCX, administered at first 10 min of reperfusion rather than at the time of ischemia significantly attenuated myocardial stunning. In addition, NCX inhibition also attenuated the Ca(2+) oscillation and cardiac dysfunction when field stimulus was stopped at first 10 min of reperfusion. These data suggest that one of the important mechanisms of triggering myocardial stunning is diastolic Ca(2+) overload caused by activation of the reverse mode of NCX of cardiomyocytes during the initial period of reperfusion following brief ischemia.

Temporal differences in the influence of ischemic factors and deformation on the metabolism of engineered skeletal muscle

Prolonged periods of tissue compression may lead to the development of pressure ulcers, some of which may originate in, for example, skeletal muscle tissue and progress underneath intact skin, representing deep tissue injury. Their etiology is multifactorial and the interaction between individual causal factors and their relative importance remain unknown. The present study addressed the relative contributions of deformation and ischemic factors to altered metabolism and viability. Engineered muscle tissue was prepared as previously detailed ( 14 ) and subjected to a combination of factors including 0% oxygen, lactic acid concentrations resulting in pH from 5.3 to 7.4, 34% compression, and low glucose levels. Deformation had an immediate effect on tissue viability {[3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] (MTT) assay}, which increased with time. By contrast, hypoxia evoked metabolic responses (glucose and lactate levels) within 24 h, but viability was only reduced after 48 h. In addition, lactic acidification downregulated tissue metabolism up to an acid concentration (∼23 mM) where metabolism was arrested and cell death enhanced. A similar tissue response was observed during glucose deprivation, which, at negligible concentration, resulted in both a cessation of metabolic activity and a reduction in cell viability. The combination of results suggests that in a short-term (<24 h) deformation, extreme acidification and glucose deprivation increased the level of cell death. By contrast, nonextreme acidification and hypoxia influenced tissue metabolism, but not the development of cell death. These data provide more insight into how compression-induced factors can lead to the onset of deep tissue injury.

Cardiac excitation-contraction coupling is altered in myocytes from aged male mice but not in cells from aged female mice

This study characterized age-related alterations in excitation-contraction (EC)-coupling in ventricular myocytes and investigated whether these alterations are affected by the sex of the animal. Voltage-clamp experiments were conducted in myocytes from young adult (∼7 mo) and aged (∼24 mo) male and female mice. Intracellular Ca2+ concentrations and unloaded cell shortening were measured at 37°C with fura-2 and a video edge detector. Fractional shortening and Ca2+ current density were significantly reduced in aged male myocytes compared with those in young adult male cells. In addition, Ca2+ transients were significantly smaller in aged male myocytes. Sarcoplasmic reticulum (SR) content, assessed by rapid application of 10 mM caffeine, declined with age in male myocytes. However, EC coupling gain and fractional release of SR Ca2+ were similar in young adult and aged male cells. In contrast to results in male animals, fractional shortening and Ca2+ current densities were similar in young adult and aged myocytes isolated from female hearts. Furthermore, Ca2+ transient amplitudes were unaffected by age in female cells. Interestingly, SR Ca2+ content was elevated in aged female myocytes, and fractional SR Ca2+ release declined with age in females. However, the gain of EC coupling was not different in myocytes from young adult and aged female mice. These data demonstrate that age-related alterations in EC coupling are more prominent in myocytes from male hearts than in cells from female hearts and suggest that it is important to consider sex as a variable in studies of the effects of aging on cardiac EC coupling.