Energetic study of cardioplegic hearts under ischaemia/reperfusion and [Ca(2+)] changes in cardiomyocytes of guinea-pig: mitochondrial role

Myocardial oxygen consumption during histidine-tryptophan-ketoglutarate cardioplegia in young human hearts

OBJECTIVES

Energy demand and supply need to be balanced to preserve myocardial function during paediatric cardiac surgery. After a latent aerobic period, cardiac cells try to maintain energy production by anaerobic metabolism and by extracting oxygen from the given cardioplegic solution. Myocardial oxygen consumption (MVO2) changes gradually during the administration of cardioplegia.

METHODS

MVO2 was measured during cardioplegic perfusion in patients younger than 6 months of age (group N: neonates; group I: infants), with a body weight less than 10 kg. Histidine-tryptophan-ketoglutarate crystalloid solution was used for myocardial protection and was administered during a 5-min interval. To measure pO2 values during cardioplegic arrest, a sample of the cardioplegic fluid was taken from the inflow line before infusion. Three fluid samples were taken from the coronary venous effluent 1, 3 and 5 min after the onset of cardioplegia administration. MVO2 was calculated using the Fick principle.

RESULTS

The mean age of group N was 0.2 ± 0.09 versus 4.5 ± 1.1 months in group I. The mean weight was 3.1 ± 0.2 versus 5.7 ± 1.6 kg, respectively. MVO2 decreased similarly in both groups (min 1: 0.16 ± 0.07 vs 0.36 ± 0.1 ml/min; min 3: 0.08 ± 0.04 vs 0.17 ± 0.09 ml/min; min 5: 0.05 ± 0.04 vs 0.07 ± 0.05 ml/min).

CONCLUSIONS

We studied MVO2 alterations after aortic cross-clamping and during delivery of cardioplegia in neonates and infants undergoing cardiac surgery. Extended cardioplegic perfusion significantly reduces energy turnover in hearts because the balance procedures are both volume- and above all time-dependent. A reduction in MVO2 indicates the necessity of a prolonged cardioplegic perfusion time to achieve optimized myocardial protection.

Low-flow ischaemia and reperfusion in rat hearts: energetic of stunning and cardioprotection of genistein

Objectives

Low-flow ischemia (LFI) is consequent to coronary disease and produces cardiac stunning during reperfusion (R). Energetic performance and mechanisms of Ca2+ handling during LFI/R are not known. Moreover, cardioprotection of the phytoestrogen genistein (Gen) remains to be demonstrated in LFI/R. The aim was to study the mechanisms of the stunning consequent to LFI/R and the effects of Gen on both sexes.

Methods

Rat ventricles were perfused inside a calorimeter to measure maximal pressure development (P) and total heat rate (Ht) before and during exposition to LFI/R. The mechanisms of stunning were evaluated with selective drugs.

Key findings

Female hearts (FH) developed higher postischemic contractile recovery (PICR) and muscle economy (P/Ht) than males (MH). Cardioprotection was sensitive to blockade of mKATP channels, UCam and NOS. Perfusion of 20 μmol/l Gen reduced PICR and P/Ht during LFI/R in FH, and dysfunction was increased by mNCX blockade with mPTP opening. However, intraperitoneal 5 mg/kg Gen (Gen-ip) was cardioprotective in both sexes, and the beneficial effect of Gen-ip was blocked by 100 μmol/l 5-HD.

Conclusions

FH are more protected than MH against the LFI/R dysfunction, which involves mitochondrial Ca2+ loss; Gen-ip was more cardioprotective in MH than in FH, mainly by activation of the mKATP channels.

Antitussive, antispasmodic, bronchodilating and cardiac inotropic effects of the essential oil from Blepharocalyx salicifolius leaves

ETHNOPHARMACOLOGY RELEVANCE

Blepharocalyx salicifolius (Kunth) O. Berg (Myrtaceae) is a tree native to Argentina and Uruguay that grows and is cultivated along the riverside of the Rio de la Plata. The leaves of this plant species, locally known as "anacahuita" are used in South America to prepare infusions for the empiric treatment of cough and bronchospasm, as well as diarrhoea and other intestinal disorders. Although previous phytochemical studies have been performed with the essential oil extracted from Blepharocalyx salicifolius, pharmacological evidence supporting its traditional use is still lacking.

AIM OF THE STUDY

To experimentally evaluate the pharmacological properties of Blepharocalyx salicifolius based on its traditional use. The studies were performed with tincture (T-Bs) and essential oil (EO-Bs) prepared from its leaves, in isolated rat trachea, intestine and heart preparations.

METHODS

The ex-vivo effects of T-Bs and EO-Bs were evaluated with the agonists carbachol (CCh) and calcium chloride (Ca²⁺) in the contractile concentration-response curves (CRC) of the isolated intestine. The muscle relaxant effect of EO-Bs was evaluated in the isolated trachea and compared with the effect achieved with papaverine as a positive control. The T-Bs and EO-Bs cardiac effects were analysed by perfusion of an isolated rat heart before a period of ischemia/reperfusion (stunning model). The antitussive effect of both T-Bs and EO-Bs was evaluated in mice exposed to ammonia using codeine as a positive control.

RESULTS

Both T-Bs and EO-Bs induced a non-competitive inhibition of the CCh-CRC in the rat intestine, with IC₅₀ values of 170.3 ± 48.5µg T-Bs/mL (n = 6) and 5.9 ± 1.6µg EO-Bs/mL (n = 6), respectively. EO-Bs also inhibited non-competitively the Ca²⁺-CRC, with IC₅₀ value of 1.8 ± 0.3µg EO-Bs/mL (n = 8). A similar effect was obtained with the main active component of the EO-Bs 1,8-cineole. In isolated trachea, EO-Bs induced the relaxation of the CCh-contracted tissue (1.7 ± 0.2µg EO-Bs/mL, n = 11) up to a maximal relaxation that was 1.9 times higher than that of papaverine. In the isolated heart, EO-Bs induced a poor negative inotropic response, and did not improve the contractile and energetic recovery after ischemia and reperfusion. In the mouse cough model, EO-Bs (90mg/Kg) was as effective as codeine (30mg/Kg) in reducing cough frequency.

CONCLUSIONS

The results indicate that the preparations from Blepharocalyx salicifolius leaves were effective as central antitussive, bronchodilating and antispasmodic agents, suggestive of a mechanism associated with the inhibition of Ca²⁺ influx into smooth muscle. The EO-Bs displayed only a poor ability to reduce cardiac inotropism, and was devoid of any cardioprotective properties. Thus, the present study validates the traditional use of this South American plant for asthma, cough and bronchospasm, shedding new light into its potency and putative mechanism of action.

Cardioprotection of stevioside on stunned rat hearts: A mechano-energetical study

BACKGROUND

The sweetener and hypoglycemic properties of stevioside (STV) are well known, as the main component of the plant Stevia rebaudiana. Given its extensive use in diabetic patients, it was of interest to evaluate its effects on the most frequent cardiovascular disease, the coronary insufficiency.

PURPOSE

To study whether STV could be cardioprotective against ischemia-reperfusion (I/R) in a model of "stunning" in rat hearts.

STUDY DESIGN

A preclinical study was performed in isolated hearts from rats in the following groups: non-treated rats whose hearts were perfused with STV 0.3 mg/ml and their controls (C) exposed to either moderate stunning (20 min I/45 min R) or severe stunning (30 min I/45 min R), and a group of rats orally treated with STV 25 mg/kg/day in the drink water during 1 week before the experiment of severe stunning in the isolated hearts were done.

METHODS

The mechano-calorimetrical performance of isolated beating hearts was recorded during stabilization period with control Krebs perfusion inside a calorimeter, with or without 0.3 mg/ml STV before the respective period of I/R. The left ventricular maximal developed pressure (P) and total heat rate (Ht) were continuously measured.

RESULTS

Both, orally administered and perfused STV improved the post-ischemic contractile recovery (PICR, as % of initial control P) and the total muscle economy (P/Ht) after the severe stunning, but only improved P/Ht in moderate stunning. However, STV increased the diastolic pressure (LVEDP) during I/R in both stunning models. For studying the mechanism of action, ischemic hearts were reperfused with 10 mM caffeine-36 mM Na⁺-Krebs to induce a contracture dependent on sarcorreticular Ca²⁺ content, whose relaxation mainly depends on mitochondrial Ca²⁺ uptake. STV at 0.3 mg/ml increased the area-under-curve of the caffeine-dependent contracture (AUC-LVP). Moreover, at room temperature STV increased the mitochondrial Ca²⁺ uptake measured by Rhod-2 fluorescence in rat cardiomyocytes, but prevented the [Ca²⁺]m overload assessed by caffeine-dependent SR release.

CONCLUSIONS

Results suggest that STV is cardioprotective against I/R under oral administration or direct perfusion in hearts. The mechanism includes the regulation of the myocardial calcium homeostasis and the energetic during I/R in several sites, mainly reducing mitochondrial Ca²⁺ overload and increasing the sarcorreticular Ca²⁺ store.

Mitochondrial Bioenergetics During Ischemia and Reperfusion

During ischemia and reperfusion (I/R) mitochondria suffer a deficiency to supply the cardiomyocyte with chemical energy, but also contribute to the cytosolic ionic alterations especially of Ca²⁺. Their free calcium concentration ([Ca²⁺]m) mainly depends on mitochondrial entrance through the uniporter (UCam) and extrusion in exchange with Na⁺ (mNCX) driven by the electrochemical gradient (ΔΨm). Cardiac energetic is frequently estimated by the oxygen consumption, which determines metabolism coupled to ATP production and to the maintaining of ΔΨm. Nevertheless, a better estimation of heart energy consumption is the total heat release associated to ATP hydrolysis, metabolism, and binding reactions, which is measurable either in the presence or the absence of oxygenation or perfusion. Consequently, a mechano-calorimetrical approach on isolated hearts gives a tool to evaluate muscle economy. The mitochondrial role during I/R depends on the injury degree. We investigated the role of the mitochondrial Ca²⁺ transporters in the energetic of hearts stunned by a model of no-flow I/R in rat hearts. This chapter explores an integrated view of previous and new results which give evidences to the mitochondrial role in cardiac stunning by ischemia o hypoxia, and the influence of thyroid alterations and cardioprotective strategies, such as cardioplegic solutions (high K-low Ca, pyruvate) and the phytoestrogen genistein in both sex. Rat ventricles were perfused in a flow-calorimeter at either 30 °C or 37 °C to continuously measure the left ventricular pressure (LVP) and total heat rate (Ht). A pharmacological treatment was done before exposing to no-flow I and R. The post-ischemic contractile (PICR as %) and energetical (Ht) recovery and muscle economy (Eco: P/Ht) were determined during stunning. The functional interaction between mitochondria (Mit) and sarcoplasmic reticulum (SR) was evaluated with selective mitochondrial inhibitors in hearts reperfused with Krebs-10 mM caffeine-36 mM Na⁺. The caffeine induced contracture (CIC) was due to SR Ca²⁺ release, while relaxation mainly depends on mitochondrial Ca²⁺ uptake since neither SL-NCX nor SERCA are functional under this media. The ratio of area-under-curves over ischemic values (AUC-ΔHt/AUC-ΔLVP) estimates the energetical consumption (EC) to maintain CIC. Relaxation of CIC was accelerated by inhibition of mNCX or by adding the aerobic substrate pyruvate, while both increased EC. Contrarily, relaxation was slowed by cardioplegia (high K-low Ca Krebs) and by inhibition of UCam. Thus, Mit regulate the cytosolic [Ca²⁺] and SR Ca²⁺ content. Both, hyperthyroidism (HpT) and hypothyroidism (HypoT) reduced the peak of CIC but increased EC, in spite of improving PICR. Both, CIC and PICR in HpT were also sensitive to inhibition of mNCX or UCam, suggesting that Mit contribute to regulate the SR store and Ca²⁺ release. The interaction between mitochondria and SR and the energetic consequences were also analyzed for the effects of genistein in hearts exposed to I/R, and for the hypoxia/reoxygenation process. Our results give evidence about the mitochondrial regulation of both PICR and energetic consumption during stunning, through the Ca²⁺ movement.

Enalapril protects against myocardial ischemia/reperfusion injury in a swine model of cardiac arrest and resuscitation

There is strong evidence to suggest that angiotensin-converting enzyme inhibitors (ACEIs) protect against local myocardial ischemia/reperfusion (I/R) injury. This study was designed to explore whether ACEIs exert cardioprotective effects in a swine model of cardiac arrest (CA) and resuscitation. Male pigs were randomly assigned to three groups: sham-operated group, saline treatment group and enalapril treatment group. Thirty minutes after drug infusion, the animals in the saline and enalapril groups were subjected to ventricular fibrillation (8 min) followed by cardiopulmonary resuscitation (up to 30 min). Cardiac function was monitored, and myocardial tissue and blood were collected for analysis. Enalapril pre-treatment did not improve cardiac function or the 6-h survival rate after CA and resuscitation; however, this intervention ameliorated myocardial ultrastructural damage, reduced the level of plasma cardiac troponin I and decreased myocardial apoptosis. Plasma angiotensin (Ang) II and Ang-(1–7) levels were enhanced in the model of CA and resuscitation. Enalapril reduced the plasma Ang II level at 4 and 6 h after the return of spontaneous circulation whereas enalapril did not affect the plasma Ang-(1–7) level. Enalapril pre-treatment decreased the myocardial mRNA and protein expression of angiotensin-converting enzyme (ACE). Enalapril treatment also reduced the myocardial ACE/ACE2 ratio, both at the mRNA and the protein level. Enalapril pre-treatment did not affect the upregulation of ACE2, Ang II type 1 receptor (AT1R) and MAS after CA and resuscitation. Taken together, these findings suggest that enalapril protects against ischemic injury through the attenuation of the ACE/Ang II/AT1R axis after CA and resuscitation in pigs. These results suggest the potential therapeutic value of ACEIs in patients with CA.

Benzothiazepine CGP37157 Analogues Exert Cytoprotection in Various in Vitro Models of Neurodegeneration

Mitochondria regulate cellular Ca(2+) oscillations, taking up Ca(2+) through its uniporter and releasing it through the mitochondrial sodium/calcium exchanger. The role of mitochondria in the regulation of Ca(2+) cycle has received much attention recently, as it is a central stage in neuronal survival and death processes. Over the last decades, the 4,1-benzothiazepine CGP37157 has been the only available blocker of the mitochondrial sodium/calcium exchanger, although it targets several other calcium transporters. We report the synthesis of 4,1-benzothiazepine derivatives with the goal of enhancing mitochondrial sodium/calcium exchanger blockade and selectivity, and the evaluation of their cytoprotective effect. The compound 4c presented an interesting neuroprotective profile in addition to an important blockade of the mitochondrial sodium/calcium exchanger. The use of this benzothiazepine could help to understand the physiological functions of the mitochondrial sodium/calcium exchanger. In addition, we hypothesize that a moderate blockade of the mitochondrial sodium/calcium exchanger would provide enhanced neuroprotection in neurons.

Benzothiazepine CGP37157 and its 2'-isopropyl analogue modulate Ca²⁺ entry through CALHM1

CALHM1 is a Ca(2+) channel discovered in 2008, which plays a key role in the neuronal electrical activity, among other functions. However, there are no known efficient blockers able to modulate its Ca(2+) handling ability. We herein describe that benzothiazepine CGP37157 and its newly synthesized analogue ITH12575 reduced Ca(2+) influx through CALHM1 at low micromolar concentrations. These results could serve as a starting point for the development of more selective CALHM1 ligands using CGP37157 as a hit compound, which would help to study the physiological role of CALHM1 in the control of [Ca(2+)]cyt in excitable cells, as well as its implication in CNS diseases.

Effects of pyruvate on the energetics of rat ventricles stunned by ischemia–reperfusion

Pyruvate (Pyr) was proposed as an additive to cold high-K+–low-Ca2+ cardioplegia (CPG) to protect the heart during surgery. We explored whether Pyr and CPG would work synergistically to protect rat hearts from stunning during ischemia–reperfusion (I/R). We measured the heat release and contractility of perfused ventricles during I/R, and the cytosolic and mitochondrial [Ca2+] in cardiomyocytes by confocal microscopy. We found that under cold-CPG (30 °C), 10 mmol·L−1 Pyr reduced the post-ischemic contractile recovery (PICR) as well as muscle economy, when added either before ischemia or during I/R, which was reversed by blockade of UCam. In noncardioplegic hearts, Pyr was cardioprotective when it was present during I/R, more so at 37 °C than at 30 °C, with improved economy. In cardiomyocytes, the addition of Pyr to CPG slightly increased the mitochondrial [Ca2+] but decreased cytosolic [Ca2+]. The results suggest that Pyr only protects hearts from stunning when present before ischemia and during reperfusion, and that it dampens the cardioprotective properties of CPG. The mechanisms underlying such different behavior depend on the dynamic balance between Pyr stimulation of the energetic state and mitochondrial Ca2+ uptake. Our results support the use of Pyr in stunned hearts, but not in cold high-K+ cardioplegia.

Eudistomin D and penaresin derivatives as modulators of ryanodine receptor channels and sarcoplasmic reticulum Ca2+ ATPase in striated muscle

Eudistomin D (EuD) and penaresin (Pen) derivatives are bioactive alkaloids from marine sponges found to induce Ca(2+) release from striated muscle sarcoplasmic reticulum (SR). Although these alkaloids are believed to affect ryanodine receptor (RyR) gating in a "caffeine-like" manner, no single-channel study confirmed this assumption. Here, EuD and MBED (9-methyl-7-bromoeudistomin D) were contrasted against caffeine on their ability to modulate the SR Ca(2+) loading/leak from cardiac and skeletal muscle SR microsomes as well as the function of RyRs in planar bilayers. The effects of these alkaloids on [(3)H]ryanodine binding and SR Ca(2+) ATPase (SERCA) activity were also tested. MBED (1-5 μM) fully mimicked maximal activating effects of caffeine (20 mM) on SR Ca(2+) leak. At the single-channel level, MBED mimicked the agonistic action of caffeine on cardiac RyR gating (i.e., stabilized long openings characteristic of "high-open-probability" mode). EuD was a partial agonist at the maximal doses tested. The tested Pen derivatives displayed mild to no agonism on RyRs, SR Ca(2+) leak, or [(3)H]ryanodine binding studies. Unlike caffeine, EuD and some Pen derivatives significantly inhibited SERCA at concentrations required to modulate RyRs. Instead, MBED's affinity for RyRs (EC50 ∼ 0.5 μM) was much larger than for SERCA (IC50 > 285 μM). In conclusion, MBED is a potent RyR agonist and, potentially, a better choice than caffeine for microsomal and cell studies due to its reported lack of effects on adenosine receptors and phosphodiesterases. As a high-affinity caffeine-like probe, MBED could also help identify the caffeine-binding site in RyRs.