Anillin forms linear structures and facilitates furrow ingression after septin and formin depletion

During cytokinesis, a contractile ring consisting of unbranched filamentous actin (F-actin) and myosin II constricts at the cell equator. Unbranched F-actin is generated by formin, and without formin no cleavage furrow forms. In Caenorhabditis elegans, depletion of septin restores furrow ingression in formin mutants. How the cleavage furrow ingresses without a detectable unbranched F-actin ring is unknown. We report that, in this setting, anillin (ANI-1) forms a meshwork of circumferentially aligned linear structures decorated by non-muscle myosin II (NMY-2). Analysis of ANI-1 deletion mutants reveals that its disordered N-terminal half is required for linear structure formation and sufficient for furrow ingression. NMY-2 promotes the circumferential alignment of the linear ANI-1 structures and interacts with various lipids, suggesting that NMY-2 links the ANI-1 network with the plasma membrane. Collectively, our data reveal a compensatory mechanism, mediated by ANI-1 linear structures and membrane-bound NMY-2, that promotes furrowing when unbranched F-actin polymerization is compromised.

Melatonin has profound effects on mitochondrial dynamics in myocardial ischaemia/reperfusion

Research focus recently shifted to mitochondrial dynamics and the role of fusion and fission in cardioprotection. The aim of this study was to evaluate (i) the function and dynamics of mitochondria isolated from hearts exposed to ischaemia/reperfusion (I/R) (ii) the effects of melatonin, a powerful cardioprotectant, on mitochondrial dynamics in I/R. Isolated perfused rat hearts were stabilized for 30 min, subjected to 20 min global ischaemia, followed by 30 min reperfusion. Tissue was collected, mitochondria isolated for measurement of mitochondrial oxidative function and lysates from mitochondrial and cytosolic fractions prepared for western blotting. Melatonin (0.3 or 50 μM) was administered for 10 min immediately before the onset of ischaemia and for 10 min at the onset of reperfusion. Infarct size was assessed after 35 min regional ischaemia/60 min reperfusion using triphenyltetrazolium staining. The results show that reperfusion significantly reduced mitochondrial QO2 (states 3 and 4), with minor effects by melatonin. Cytosolic Beclin 1 and the LC3 II/I ratio were reduced by ischaemia and increased by reperfusion. Both ischaemia and reperfusion reduced mitochondrial PINK1 and Parkin levels, while reperfusion increased p62. An alternative mitophagy pathway mediated by Rab9 is activated during myocardial ischaemia/reperfusion. Ischaemia reduced and reperfusion increased cytosolic ULK1 expression, associated with redistribution of Rab9 and Drp1 between the cytosol and mitochondria. Melatonin significantly reduced mitochondrial p62 expression upon reperfusion. Throughout the protocol, melatonin significantly (i) increased cytosolic total (t) and phospho (p) ULK1, and Rab9 levels (ii) increased the cytosolic and reduced the mitochondrial pDrp1 levels and p/t Drp1 ratio, suggesting inhibition of mitochondrial fission. Fusion was affected to a lesser extent. Cardioprotection by melatonin is associated with substantial effects on mitophagy, the significance thereof remains to be established.

The Impact of Chronic Glycogen Synthase Kinase-3 Inhibition on Remodeling of Normal and Pre-Diabetic Rat Hearts

PURPOSE

There is an ongoing search for new drugs and drug targets to treat diseases like Alzheimer's disease, cancer and type 2 diabetes (T2D). Both obesity and T2D are characterized by the development of a cardiomyopathy associated with increased hypertension and compensatory left ventricular hypertrophy. Small, specific glycogen synthase kinase-3 (GSK-3) inhibitors were developed to replace lithium chloride for use in psychiatric disorders. In addition, they were advocated as treatment for T2D since GSK-3 inhibition improves blood glucose handling. However, GSK-3 is a regulator of hypertrophic signalling in the heart via phosphorylation of NFATc3 and β-catenin respectively. In view of this, we hypothesized that chronic inhibition of GSK-3 will induce myocardial hypertrophy or exacerbate existing hypertrophy.

METHODS

Rats with obesity-induced prediabetes were treated orally with GSK-3 inhibitor (CHIR118637 (CT20026)), 30 mg/kg/day for the last 8 weeks of a 20-week diet high in sugar content vs a control diet. Biometric and biochemical parameters were measured, echocardiography performed and localization and co-localization of NFATc3 and GATA4 determined in cardiomyocytes.

RESULTS

Obesity initiated myocardial hypertrophy, evidenced by increased ventricular mass (1.158 ± 0.029 vs 0.983 ± 0.03 g) and enlarged cardiomyocytes (18.86 ± 2.25 vs 14.92 ± 0.50um(2)) in association with increased end-diastolic diameter (EDD = 8.48 ± 0.11 vs 8.15 ± 0.10 mm). GSK-3 inhibition (i) increased ventricular mass only in controls (1.075 ± 0.022 g) and (ii) EDD in both groups (controls: 8.63 ± 0.07; obese: 8.72 ± 0.15 mm) (iii) localized NFATc3 and GATA4 peri-nuclearly.

CONCLUSION

Indications of onset of myocardial hypertrophy in both control and obese rats treated with a GSK-3 inhibitor were found. It remains speculation whether these changes were adaptive or maladaptive.

Myocardial susceptibility to ischaemia/reperfusion in obesity: a re-evaluation of the effects of age

Background

Reports on the effect of age and obesity on myocardial ischaemia/reperfusion (I/R) injury and ischaemic preconditioning are contradictory. The aim of this study was to re-evaluate the effects of age and diet-induced obesity (DIO) on myocardial I/R injury and preconditioning potential.

Methods

Four groups of Wistar male rats were used: age-matched controls (AMC) receiving standard rat chow for (i) 16 weeks and (ii) 16 months respectively; DIO rats receiving a sucrose-supplemented diet for (iii) 16 weeks and (iv) 16 months respectively. The ages of groups (i) and (iii) were 22 weeks (“young”) and groups (ii) and (iv) 17 months (“middle-aged”) at time of experimentation. Isolated perfused working hearts were subjected to 35 min regional ischaemia/1 h reperfusion. Endpoints were infarct size (tetrazolium staining) and functional recovery. Hearts were preconditioned by 3 × 5 min ischaemia/5 min reperfusion. Results were processed using GraphPad Prism statistical software.

Results

Age did not affect baseline heart function before induction of ischaemia and I/R damage as indicated by infarct size and similar values were obtained in hearts from both age groups. Age also had no effect on functional recovery of hearts during reperfusion after regional ischaemia in AMC rats, but cardiac output during reperfusion was better in hearts from middle-aged than young DIO rats.

The diet reduced infarct size in hearts from young rats (% of area at risk: AMC: 32.4 ± 3.6; DIO: 20.7 ± 2.9, p < 0.05), with no differences in hearts from middle-aged rats (AMC: 24.6 ± 4.6; DIO: 28.3 ± 13.5, p = NS). Compared to their respective AMC, diet-induced obesity had no significant effect on functional recovery of hearts from both age groups after exposure to regional ischaemia.

When exposed to the more severe stress of global ischaemia, the functional recovery potential of middle-aged DIO rats appeared to be impeded compared to hearts of young DIO rats, while age had no effect on the functional recovery of AMC hearts.

Preconditioning reduced infarct size in hearts from young control rats and both middle-aged groups, but not from young DIO rats. Age had a significant effect on functional recovery in preconditioning: it was improved in hearts from young control and DIO rats, but depressed in both middle-aged groups.

Conclusions

The data showed that middle-age and obesity had no effect on baseline myocardial function and did not increase susceptibility to I/R damage upon exposure to regional ischaemia. On the contrary, obesity reduced I/R damage in young rats. Preconditioned aging hearts showed a decreased infarct size, but a reduction in functional recovery.

The effect of creatine supplementation on myocardial function, mitochondrial respiration and susceptibility to ischaemia/reperfusion injury in sedentary and exercised rats

AIM

To investigate the effects of dietary creatine supplementation alone and in combination with exercise on basal cardiac function, susceptibility to ischaemia/reperfusion injury and mitochondrial oxidative function. There has been an increase in the use of creatine supplementation among sports enthusiasts, and by clinicians as a therapeutic agent in muscular and neurological diseases. The effects of creatine have been studied extensively in skeletal muscle, but not in the myocardium.

METHODS

Male Wistar rats were swim-trained for 8 weeks, 5 days per week. Hearts were excised and either freeze-clamped for biochemical analysis or perfused on the isolated heart perfusion system to assess function and ischaemia/reperfusion tolerance. Mechanical function was documented in working heart and retrograde mode. The left coronary artery was ligated and infarct size determined. Mitochondrial oxidative capacity was quantified.

RESULTS

Aortic output recovery of hearts from the sedentary controls (CSed) was significantly higher than those from creatine-supplemented sedentary (CrSed), creatine-supplemented exercised (CrEx) as well as control exercised (CEx) groups. Ischaemic contracture of hearts from CrEx was significantly higher than that of CSed. There were no differences in infarct size and mitochondrial oxygen consumption.

CONCLUSION

This study suggests that creatine supplementation has no effects on basal cardiac function but reduces myocardial tolerance to ischaemia in hearts from exercise-trained animals, by increasing the ischaemic contracture and decreasing reperfusion aortic output. Exercise training alone also significantly decreased aortic output recovery. However, the exact mechanisms for these adverse myocardial effects are unknown and need further investigation.

Melatonin and the metabolic syndrome: a tool for effective therapy in obesity-associated abnormalities?

The metabolic syndrome (MetS) is a cluster of metabolic abnormalities associated with increased risk for cardiovascular diseases. Apart from its powerful antioxidant properties, the pineal gland hormone melatonin has recently attracted the interest of various investigators as a multifunctional molecule. Melatonin has been shown to have beneficial effects in cardiovascular disorders including ischaemic heart disease and hypertension. However, its role in cardiovascular risk factors including obesity and other related metabolic abnormalities is not yet established, particularly in humans. New emerging data show that melatonin may play an important role in body weight regulation and energy metabolism. This review will address the role of melatonin in the MetS focusing on its effects in obesity, insulin resistance and leptin resistance. The overall findings suggest that melatonin should be exploited as a therapeutic tool to prevent or reverse the harmful effects of obesity and its related metabolic disorders.

The efficacy of Prosopis glandulosa as antidiabetic treatment in rat models of diabetes and insulin resistance

ETHNOPHARMACOLOGICAL RELEVANCE

Diabetes mellitus is rampantly increasing and the need for therapeutics is crucial. In recognition of this, untested antidiabetic agents are flooding the market. Diavite™ which is a product consisting solely of the dried and ground pods of Prosopis glandulosa (Torr.) [Fabaceae] is currently marketed as a food supplement with glucose stabilizing properties. However, these are anecdotal claims lacking scientific evidence. The aim of this study was to determine the efficacy of Prosopis glandulosa as an antidiabetic agent.

MATERIALS AND METHODS

Male Wistar rats were rendered (a) type 1 diabetic after an intraperitoneal injection of STZ (40 mg/kg) and (b) insulin resistant after a 16-week high caloric diet (DIO). Zucker fa/fa ZDF rats were used in a pilot study. Half of each group of animals was placed on Prosopis glandulosa treatment (100mg/kg/day) for 8 weeks and the remaining animals served as age-matched controls. At the time of sacrifice, blood was collected for glucose and insulin level determination, the pancreata of the STZ rats were harvested for histological analysis and cardiomyocytes prepared from the DIO and Zucker fa/fa hearts for determination of insulin sensitivity.

RESULTS

Type 1 diabetic model: Prosopis glandulosa treatment resulted in significant increased insulin levels (p<0.001), which was accompanied by a significant decrease in blood glucose levels (p<0.05). Additionally, Prosopis glandulosa treatment resulted in increased small β-cells (p<0.001) in the pancreata. The body weight of the STZ animals decreased significantly after STZ injection, with Prosopis glandulosa treatment partially preventing this. Zucker fa/fa rats: Prosopis glandulosa treatment significantly reduced fasting glucose levels (p<0.01) and improved IPGTT, when comparing treated to untreated animals. DIO insulin resistant model: Prosopis glandulosa treatment resulted in an increased basal (p<0.01) and insulin-stimulated (p<0.05) glucose uptake by cardiomyocytes prepared from this group.

CONCLUSIONS

The present study showed that Prosopis glandulosa treatment moderately lowers glucose levels in different animal models of diabetes, stimulates insulin secretion, leads to the formation of small β-cells and improves insulin sensitivity of isolated cardiomyocytes.

Autophagy in heart disease: a strong hypothesis for an untouched metabolic reserve

Autophagy is a conserved catabolic process for long-lived proteins and organelles and is primarily responsible for nonspecific degradation of redundant or faulty cell components. Although autophagy has been described as the cell's major adaptive strategy in response to metabolic challenges, its influence on the cell's energy profile is poorly understood. In the myocardium, autophagy is active at basal levels and is crucial for maintaining its contractile function. Defects in the autophagic machinery cause cardiac dysfunction and heart failure. In this paper we propose that (1) autophagy contributes significantly to the metabolic balance sheet of the heart. (2) Increased autophagy contributes to an improved myocardial energy profile through changing the cardiac substrate preference. (3) Substrates generated through autophagy give rise to an alternative for ATP production with an oxygen-sparing effect. These elements identify autophagy in a new context of myocardial metabolic interregulation, which we discuss in the settings of myocardial infarction, heart failure and the diabetic heart. It is hoped that the hypothesis presented can lead to new insights aimed at exploiting autophagy to improve existing metabolic-based therapy in heart disease.

At the core of survival: autophagy delays the onset of both apoptotic and necrotic cell death in a model of ischemic cell injury

Ischemic cell injury leads to cell death. Three main morphologies have been described: apoptosis, cell death with autophagy and necrosis. Their inherent dynamic nature, a point of no return (PONR) and molecular overlap have been stressed. The relationship between a defined cell death type and the severity of injury remains unclear. The functional role of autophagy and its effects on cell death onset is largely unknown. In this study we report a differential induction of cell death, which is dependent on the severity and duration of an ischemic insult. We show that mild ischemia leads to the induction of autophagy and apoptosis, while moderate or severe ischemia induces both apoptotic and necrotic cell death without increased autophagy. The autophagic response during mild injury was associated with an ATP surge. Real-time imaging and Fluorescence Resonance Energy Transfer (FRET) revealed that increased autophagy delays the PONR of both apoptosis and necrosis significantly. Blocking autophagy shifted PONR to an earlier point in time. Our results suggest that autophagic activity directly alters intracellular metabolic parameters, responsible for maintaining mitochondrial membrane potential and cellular membrane integrity. A similar treatment also improved functional recovery in the perfused rat heart. Taken together, we demonstrate a novel finding: autophagy is implicated only in mild injury and positions the PONR in cell death.

Sustained anti-β-adrenergic effect of melatonin in guinea pig heart papillary muscle

OBJECTIVE

Anti-ss-adrenergic actions of several substances influence heart function significantly. The anti-ss-adrenergic effect of melatonin was investigated, with special attention to protein kinase C (PKC) and nitric oxide (NO).

DESIGN

Guinea pig papillary muscles were exposed to melatonin (500 pM) for 15 min and 20 min washout. Contractile force was measured during a bolus of isoproterenol (300 nM) given before melatonin, at the end of melatonin-exposure and after washout. In separate experiments blockers of PKC, NO-synthase (NOS) and melatonin receptors were added, or forskolin (10 microM) substituted for isoproterenol.

RESULTS

Melatonin significantly reduced the increase in contractile force in response to isoproterenol, both when present and after melatonin-washout. The reduction was unaffected by inhibition of PKC, while inhibition of melatonin receptors or NOS seemed to abolish the effect. Melatonin induced a sustained but not acute reduction of contractile force response with forskolin stimulation. This was abolished by NOS-inhibition.

CONCLUSION

Receptor-mediated immediate and sustained anti-ss-adrenergic effects of melatonin were demonstrated in contractile function. A role for NO in the response was indicated, while a role for PKC was not verified.

Dexamethasone-induced cardioprotection: a role for the phosphatase MKP-1?

AIMS

Previous studies suggested that p38 MAPK activation during sustained myocardial ischaemia and reperfusion was harmful. We hypothesize that attenuation of p38MAPK activity via dephosphorylation by the dual-specificity phosphatase MKP-1 should be protective against ischaemia/reperfusion injury. Since the glucocorticoid, dexamethasone, induces the expression of MKP-1, the aim of this study was to determine whether upregulation of this phosphatase by dexamethasone protects the heart against ischaemia/reperfusion injury.

MAIN METHODS

Male Wistar rats were treated with dexamethasone (3 mg/kg/day ip) for 10 days, before removal of the hearts for Western blot (ip Dex-P) or perfusion in the working mode (ip Dex+P). Hearts were subjected to 20 min global or 35 min regional ischaemia (36.5 degrees C) and 30 or 120 min reperfusion. In a separate series, dexamethasone (1 microM) was added to the perfusate for 10 min (Pre+Dex) before or after (Rep+Dex) ischaemia.

KEY FINDINGS

Dexamethasone, administered intraperitoneally or added directly to the perfusate, significantly improved post-ischaemic functional recovery and reduced infarct size compared to untreated controls (p<0.05). These were associated with enhanced up-regulation of MKP-1 protein expression (arbitrary units (mean+/-SD): Untreated: 1; ip Dex-P: 2.59+/-0.22; ip Dex+P: 1.51+/-0.22; Pre+Dex: 4.11+/-0.73, Rep+15'Dex: 1.51+/-0.14; untreated vs. all groups, p<0.05) and attenuation of p38 MAPK activation (p<0.05) in all dexamethasone-treated groups, except for Rep+10'Dex. ERK and PKB/Akt activation were unchanged.

SIGNIFICANCE

Dexamethasone-induced cardioprotection was associated with upregulation of the phosphatase MKP-1 and inactivation of pro-apoptotic p38 MAPK.

Protection of the ischaemic heart: investigations into the phenomenon of ischaemic preconditioning

Exposure of the heart to one or more short episodes of ischaemia/reperfusion protects the heart against a subsequent prolonged period of ischaemia, as evidenced by a reduction in infarct size and an improvement in functional recovery during reperfusion. Elucidation of the mechanism of this endogenous protection could lead to the development of pharmacological mimetics to be used in the clinical setting. The aim of our studies was therefore to gain more information regarding the mechanism of ischaemic preconditioning, using the isolated perfused working rat heart as model. A preconditioning protocol of 1 x 5 or 3 x 5 min of ischaemia, interspersed with 5 min of reperfusion was found to protect hearts exposed to 25 min of global ischaemia or 35-45 min of regional ischaemia. These models were used throughout our studies. In view of the release of catecholamines by ischaemic tissue, our first aim was to evaluate the role of the alphaadrenergic receptor in ischaemic preconditioning. However, using a multi-cycle ischaemic preconditioning protocol, we could not find any evidence for alpha-1 adrenergic or PKC activation in the mechanism of preconditioning. Cyclic increases in the tissue cyclic nucleotides, cAMP and cGMP were found, however, to occur during a multi-cycle preconditioning protocol, suggesting roles for the beta-adrenergic signalling pathway and nitric oxide (NO) as triggers of cardioprotection. This was substantiated by the findings that (1) administration of the beta-adrenergic agonist, isoproterenol, or the NO donors SNAP or SNP before sustained ischaemia also elicited cardioprotection similar to ischaemic preconditioning; (2) beta-adrenergic blockade or nitric oxide synthase inhibition during an ischaemic preconditioning protocol abolished protection. Effectors downstream of cAMP, such as p38MAPK and CREB, were also demonstrated to be involved in the triggering process. Our next step was to evaluate intracellular signalling during sustained ischaemia and reperfusion. Our results showed that ischaemic preconditioned-induced cardioprotection was associated with a significant reduction in tissue cAMP, attenuation of p38MAPK activation and increased tissue cGMP levels and HSP27 activation, compared to non-preconditioned hearts. The role of the stress kinase p38MAPK was further investigated by using the inhibitor SB203580. Our results suggested that injury by necrosis and apoptosis share activation of p38MAPK as a common signal transduction pathway and that pharmacological targeting of this kinase offers a tenable option to manipulate both these processes during ischaemia/reperfusion injury.

A role for the RISK pathway and K(ATP) channels in pre- and post-conditioning induced by levosimendan in the isolated guinea pig heart

BACKGROUND AND PURPOSE

Myocardial reperfusion injury prevents optimal salvage of the ischaemic myocardium, and adjunct therapy that would significantly reduce reperfusion injury is still lacking. We investigated whether (1) the heart could be pre- and/or post-conditioned using levosimendan (levosimendan pre-conditioning (LPC) and levosimendan post-conditioning (LPostC)) and (2) the prosurvival kinases and/or the sarcolemmal or mitochondrial K(ATP) channels are involved.

EXPERIMENTAL APPROACH

Isolated guinea pig hearts were treated with two 5 min cycles of levosimendan (0.1 microM) interspersed with vehicle perfusion, or two 5 min cycles of ischaemia/reperfusion, before coronary artery ligation (CAL) for 40 min at 36.5 degrees C. Hearts were treated with mitochondrial or sarcolemmal K(ATP) channel blockers before LPC or LPostC. For post-conditioning, hearts received three 30 s cycles of ischaemia/reperfusion or levosimendan/vehicle. Hearts were pretreated with levosimendan immediately before CAL (without washout). Cardiac function, infarct size and reperfusion injury salvage kinase activity was assessed.

KEY RESULTS

LPC and LPostC halved the infarct size compared with controls (P<0.05). Treatment with K(ATP) channel blockers before LPC or LPostC reversed this decrease. Pretreating hearts with levosimendan increased activity of extracellular signal-regulated kinase (ERK) 42/44 on reperfusion and had the most marked infarct-lowering effect (P<0.05).

CONCLUSIONS AND IMPLICATIONS

(1) Hearts could be pharmacologically pre- and post-conditioned with levosimendan; (2) levosimendan pretreatment is the most effective way to reduce infarct size, possibly by increasing ERK 42/44 activity; (3) benefits of LPC and LPostC were abolished by both K(ATP) channel blockers and (4) LPC may be useful before elective cardiac surgery, whereas LPostC may be used after acute coronary artery events.

The many faces of H89: a review

H89 is marketed as a selective and potent inhibitor of protein kinase A (PKA). Since its discovery, it has been used extensively for evaluation of the role of PKA in the heart, osteoblasts, hepatocytes, smooth muscle cells, neuronal tissue, epithelial cells, etc. Despite the frequent use of H89, its mode of specific inhibition of PKA is still not completely understood. It has also been shown that H89 inhibits at least 8 other kinases, while having a relatively large number of PKA-independent effects which may seriously compromise interpretation of data. Thus, while recognizing its kinase inhibiting properties, it is advised that H89 should not be used as the single source of evidence of PKA involvement. H-89 should be used in conjunction with other PKA inhibitors, such as Rp-cAMPS or PKA analogs.

Melatonin prevents cardioprotection induced by a multi-cycle ischaemic preconditioning protocol in the isolated perfused rat heart

The powerful cardioprotective actions of melatonin, the chief secretory product of the pineal gland, have been attributed largely to its free radical-scavenging properties. Free radicals play an important role in the triggering action of ischaemic preconditioning, the phenomenon whereby exposure of the heart to one or more short episodes of ischaemia leads to protection against a subsequent long period of ischaemia. The aim of this study was, therefore, to establish whether melatonin, in view of its free radical-scavenging ability, would affect the beneficial actions of preconditioning. Isolated, perfused, working hearts were subjected to 1 x 5 minute or 3 x 5 min ischaemic preconditioning protocols, in the presence or absence of melatonin (50 microM), followed by 20 minutes global ischaemia and 30 minutes reperfusion. Use was also made of sodium nitroprusside (100 microM), a nitric oxide (NO) donor and preconditioning mimetic. Using functional recovery as the endpoint, melatonin abolished the cardioprotective effects of a multi-cycle (3 x 5 min) preconditioning protocol, while having no effect on a one-cycle (1 x 5 min) protocol or SNP (1 x 5 or 3 x 5 min) preconditioning. The results suggest that free radicals play an important role in the cardioprotection induced by a multi-cycle ischaemic preconditioning protocol and that this process could be attenuated by a potent scavenger such as melatonin.

Long-chain polyunsaturated fatty acids protect the heart against ischemia/reperfusion-induced injury via a MAPK dependent pathway

The mechanisms by which long-chain dietary polyunsaturated fatty acids (PUFAs) protect against cardiovascular disease are largely unknown. The present study determines the effects of eicosapentaenoic acid (EPA) and arachidonic acid (ARA) on the response of neonatal rat cardiomyocytes to simulated ischaemia (SI) and reperfusion (R). Myocytes isolated from 1-2 day old Wistar rat hearts were cultured with or without EPA or ARA and exposed to 1 h SI followed by 30 minutes reperfusion. Apoptosis was evaluated by caspase-3 activation, poly-(ADP-ribose) polymerase (PARP) cleavage and nuclear condensation. EPA (20microM) and ARA (20microM) significantly inhibited caspase-3 activation and PARP-cleavage and reduced the apoptotic index during reperfusion. Both fatty acids significantly increased ERK phosphorylation and decreased p38 phosphorylation during reperfusion. The mechanism of action of ARA on the MAPKs was further investigated with okadaic acid (to inhibit serine-threonine phosphatases) and orthovanadate (to inhibit tyrosine phosphatases). Vanadate, but not okadaic acid, significantly reduced ARA-induced inhibition of p38 phosphorylation, suggesting the involvement a tyrosine phosphatase during SI/R. Mitogen-activated protein kinase phosphatase-1 (MKP-1), a dual-specificity phosphatase, was targeted and a significant induction of MKP-1 by ARA and EPA was observed. It was demonstrated for the first time that EPA and ARA protect neonatal cardiac myocytes from ischaemia/reperfusion-induced apoptosis through activation of ERK as well as induction of a dual-specific phosphatase, causing dephosphorylation of the pro-apoptotic kinase, p38. The cardioprotective effects of EPA and ARA could also be demonstrated on the functional recovery of isolated perfused hearts subjected to global ischemia.

A potential role for angiotensin II in obesity induced cardiac hypertrophy and ischaemic/reperfusion injury

BACKGROUND

The mechanisms for obesity induced myocardial remodelling and subsequent mechanical dysfunction are poorly understood. There is good evidence that angiotensin II and TNFalpha have strong growth promoting properties and are elevated with obesity. In addition, these two peptides may interact to exacerbate myocardial ischaemic/reperfusion injury.

HYPOTHESIS

Obesity increases systemic and myocardial renin-angiotensin system (RAS) activity and TNFalpha levels and contributes to obesity induced cardiac remodelling and ischaemic/reperfusion injury.

METHODS

Male Wistar rats were placed on a standard rat chow diet or cafeteria diet for 16 weeks. Two additional groups of rats received the respective diets and losartan (30 mg/ kg/d) in their drinking water. Hearts were perfused on the isolated working rat heart perfusion system and mechanical function was documented before and after 15 min normothermic total global ischaemia. Blood and myocardial samples were collected for angiotensin II, TNFalpha and NADPH oxidase activity determinations.

RESULTS

The rats on the cafeteria diet became obese compared to rats on the standard rat chow (438 +/- 5.9 g vs 393 +/- 7.3 g for control, p < 0.05). Obesity was associated with elevated serum angiotensin II (0.050 +/- 0.015 pmol/ml vs. 0.035 +/- 0.003 pmol/ml, p < 0.05) and TNFalpha levels (42.8 +/- 5.93 pg/ml vs. 13.18 +/- 2.50 pg/ml, p < 0.05), and increased heart to body weight ratios (3.1 +/- 0.04 mg/g vs. 2.8 +/- 0.03 mg/g, p < 0.05). Losartan had no effect on body weight but decreased basal myocardial angiotensin II and TNFAlpha levels as well as heart to body weight ratio in the obese and lean controls (2.5 +/- 0.05 mg/g and 2.6 +/- 0.04 mg/g relative to their controls, p < 0.05). Hearts from obese rats had lower reperfusion aortic outputs (AO) than their concurrent controls (18.42 +/- 1.17 ml/min vs. 27.8 +/- 0.83 ml/min, p < 0.05). Losartan improved aortic output recoveries in obese rats (23.0 +/- 1.71 ml/min, p < 0.05).

CONCLUSIONS

Obesity increased serum angiotensin II and TNFalpha levels, blood pressure, and heart weight to body weight ratios. These changes were associated with decreased basal and post-ischaemic myocardial mechanical function. Chronic AT(1) receptor antagonism prevented the adverse changes in heart weight, mechanical function and susceptibility to ischaemic/reperfusion injury. Although current data do not exclude additional mechanisms for obesity induced cardiac remodelling, they suggest that angiotensin II may contribute to obesity induced cardiac remodelling and ischaemic/reperfusion injury.

Proposed mechanisms for the anabolic steroid-induced increase in myocardial susceptibility to ischaemia/reperfusion injury

Androgenic anabolic steroids (AAS) are often used by athletes to enhance athletic performance but are strongly associated with detrimental cardiovascular effects including sudden cardiac death.

HYPOTHESIS

AAS use increases myocardial susceptibility to ischaemia/reperfusion injury.

METHODS

Rats were trained (swimming) with or without intramuscular injection of nandrolone laurate (0.375 mg/kg). Untrained rats with or without nandrolone served as controls. Hearts were mounted on the Langendorff perfusion apparatus and mechanical function was measured before and after 20-min normothermic global ischaemia. Myocardial tissue samples were collected for determination of tissue cyclic nucleotide and TNFalpha concentrations.

RESULTS

Anabolic steroids decreased the rate pressure product (RPP) of the exercise-trained rat heart [34 582 +/- 1 778 mmHg/min vs 28 868 +/- 2 446 mmHg/min for exercise-trained steroid-treated hearts (p < 0.05)]. Reperfusion RPP was lower in both the sedentary, and the exercise-trained, steroid-treated hearts than in their concurrent vehicle-treated controls (18 276 +/- 2 026 mmHg/min vs 12 018 +/- 1 725 mmHg/min for sedentary steroid-treated hearts and, 21 892 +/- 2 912 mmHg vs 12 838 +/- 1 536 mmHg/min for exercise-trained steroid-treated hearts). Myocardial TNFalpha [267.75 +/- 44.25 pg/g vs 190.00 +/- 15.75 pg/g (p < 0.05)] and cAMP concentrations [406.04 +/- 18.41 pmol/g vs 235.6 +/- 43.26 pmol/g (p < 0.05)] were elevated in the steroid-treated hearts when compared with their untreated counterparts.

CONCLUSIONS

Supraphysiological doses of anabolic steroids, whether taken during exercise training or under sedentary conditions increase myocardial susceptibility to ischaemia/reperfusion injury in our model. This increased susceptibility may be related to steroid-induced increases in the pre-ischaemic myocardial cAMP concentrations and/or increases in both pre-ischaemic and reperfusion TNFalpha concentrations.

p38 and JNK have distinct regulatory functions on the development of apoptosis during simulated ischaemia and reperfusion in neonatal cardiomyocytes

Rat neonatal ventricular myocytes exposed to simulated ischaemia and reperfusion (SI/R) were used as an in vitro model to delineate the role(s) of extracellular signal-regulated kinase (ERK), p38 and c-Jun NH(2)-terminal protein kinase (JNK), as well as PKB in apoptosis. Exposure of the myocytes to SI (simulated ischaemia - energy depletion induced by KCN and 2-deoxy- D-glucose) reduced cell viability, as measured by the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) assay, and stimulated apoptosis as evidenced by caspase-3 activation and poly(ADP-ribose) polymerase (PARP) cleavage. However, morphological evidence of increased apoptosis, detected by staining with Hoechst 33342, was only seen in response to reperfusion. This suggests that although ischaemic conditions are sufficient to induce cellular markers of apoptosis (PARP cleavage and caspase-3 activation), reperfusion is required to complete the apoptotic pathway in these cells. Furthermore, SI resulted in a rapid, strong, biphasic activation of p38 concomitant with a weak and transient activation of the two ERK isoenzymes, p42/p44-MAPK. Reperfusion for 5 minutes resulted in a strong phosphorylation of p42/p44-MAPK, while no additional p38 activation was seen at this stage. On the other hand, p46/p54-MAPK (JNK) was phosphorylated in response to 5 minutes of reperfusion only and not during SI alone. A peak of PKB/Akt (Ser(473)) activity was seen within 5 minutes of exposure to SI, whereas PKB/Akt (Thr(308)) phosphorylation remained at the baseline level. Both PKB/Akt phosphorylation sites (Ser(473) and Thr(308)) were phosphorylated after 5 minutes of reperfusion. Inhibition of PI-3-kinase activity, using wortmannin, decreased phosphorylation on both sites during SI. However, only SI/R-induced PKB/Akt phosphorylation on Thr(308) was reduced by wortmannin. Myocytes pre-treated with SB203580, a p38-inhibitor, displayed a significant increase in cell viability [63.67 +/- 1.85 to 84.33 +/- 4.8% (p < 0.05)] and attenuation of the apoptotic index during SI/R [22.6 +/- 2.94% to 9 +/- 0.43% (p < 0.001)], while SP600125, a specific JNK inhibitor, caused a significant increase in caspase-3 activation [1.66 +/- 0.03 fold to 2.56 +/- 0.27 fold (p < 0.001)] and apoptotic index [22.6 +/- 2.94% to 32.75 +/- 6.13% (p < 0.05)]. However, PD98059, an ERK inhibitor, failed to affect apoptosis during SI/R. Inhibition of PI-3-kinase prevented the increase in mitochondrial viability usually observed during reperfusion. Interestingly, wortmannin caused a significant increase in PARP cleavage during reperfusion, but had no effect on caspase-3 activation or the apoptotic index. Our results suggest that p38 has a pro-apoptotic role while JNK phosphorylation is protective in our cell model and that these kinases act via caspase-3 to prevent or promote cell survival in response to SI/R-induced injury.

Comparison between ischaemic and anisomycin-induced preconditioning: role of p38 MAPK

To further evaluate the significance of p38 MAPK as trigger or mediator in ischaemic preconditioning, anisomycin and SB 203580 were used to manipulate its activation status. Special attention was given to the concentration of the drugs and protocols used. The isolated perfused rat heart, subjected to either 25 min global ischaemia or 35 min regional ischaemia, was used as experimental model. This was preceded by anisomycin (2 or 5 muM: 3 x 5 min; 5 muM: 5 min or 10 min; 5 muM: 10 min + 10 min washout or 20 muM: 20 min) or SB 203580 (2 muM: 3 x 5 min; before and during 3 x 5 min or 1 x 5 min ischaemic preconditioning; 10 min). Endpoints were functional recovery during reperfusion and infarct size.Anisomycin, regardless of the protocol, reduced infarct size, but did not improve functional recovery. In a number of experiments activation of JNK by anisomycin was blocked by SP 600125 (10 muM). SP 600125 had no effect on the anisomycin-induced reduction in infarct size. SB 203580 when administered for 10 min before sustained ischaemia, improved functional recovery and reduced infarct size. SB 203580 could not abolish the beneficial effects of a multi-cycle preconditioning protocol, but it significantly reduced the outcome of 1 x 5 min preconditioning. In all hearts improved functional recovery and reduction in infarct size were associated with attenuation of p38 MAPK activation during sustained ischaemia-reperfusion. The results indicate that activation of p38 MAPK acts as a trigger of preconditioning, while attenuation of its activation is a prerequisite for improved recovery and a reduction in infarct size.

Ischemic preconditioning: infarct size is a more reliable endpoint than functional recovery

The search for the mechanism of preconditioning-induced cardioprotection has been hampered by controversial results obtained by workers using different animal species, experimental models, protocols and endpoints. The aim of this study was to evaluate the role of the perfusion model (retrograde vs working), the infarct size and severity of ischaemia (regional vs global) as well as the endpoint (functional recovery vs infarct size) in preconditioning. The isolated perfused rat heart was preconditioned by 3 x 5 min global ischaemia, followed by different periods of regional or global ischaemia and reperfusion. Ischaemic preconditioning of working hearts resulted in increased functional recovery after 25-35 min global ischaemia, while retrogradely perfused hearts showed no significant improvement (except after 30 min global ischaemia). In addition, the percentage reduction in functional performance during reperfusion observed in the latter group was significantly less than in working hearts. Hearts were also subjected to regional ischaemia, perfused in either retrograde or working mode and infarct size determined. Regionally ischaemic working as well as retrogradely perfused hearts when preconditioned showed a significant increase in functional recovery after 35 min ischaemia only. In contrast to global ischaemia, the percentage recovery in mechanical performance of regionally ischaemic hearts was not affected by the mode of perfusion. Preconditioning of working hearts caused a significant reduction in infarct size after both 30 and 35 min ischaemia. However, preconditioned retrogradely perfused hearts showed a significant decline in infarct size after 35 min regional ischaemia only. In conclusion, the effect of the perfusion mode on functional recovery is dependent on the size and severity of ischaemia. It also affects the ischaemic time at which infarct size reduction by prior preconditioning occurs in the retrogradely perfused heart.

p38 MAPK activation triggers pharmacologically-induced beta-adrenergic preconditioning, but not ischaemic preconditioning

p38 Mitogen-activated protein kinase (p38 MAPK) is activated by short episodes of ischaemia-reperfusion as well as by sustained ischemia followed by reperfusion, Whether activation of this kinase is beneficial or deleterious to the ischaemic heart is still a subject of controversy. Since transient beta-adrenergic stimulation (5 min) stimulates p38 MAPK activation and mimics the cardioprotection of ischaemic preconditioning, it was used as a tool to further evaluate the role of this kinase in cardioprotection. The isolated perfused working rat heart, subjected to 25 min ischaemia and 30 min reperfusion was used as experimental model. p38 MAPK and ATF2 activation was determined using Western blots. The results showed that isoproterenol stimulated p38 MAPK in a dose- and time-dependent manner. Ischaemia-induced activation of p38 MAPK could be partially abolished by beta- and alpha1-adrenergic receptor blockade. Isoproterenol activation of the kinase could be abolished by alprenolol and verapamil, but not by 8-cyclopentyladenosine. p38 MAPK activation induced by either a multi-episode preconditioning protocol or isoproterenol (10(-7) M for 5 min) was associated with a significant reduction in p38 MAPK activation at all time intervals studied during 25 min global ischaemia and at 20 and 30 min of reperfusion, compared with the marked activation observed in untreated non-preconditioned hearts. In each case attenuation of p38 MAPK activation during ischaemia and during reperfusion was associated with improved functional recovery during reperfusion. Cyclic elevations in tissue cAMP during an ischaemic preconditioning protocol acted as trigger of cardioprotection, since pretreatment of such hearts with alprenolol abolished cardioprotection. Mechanical failure in such hearts was characterized by a significant stimulation of p38 MAPK activity during ischaemia and reperfusion. However, p38 MAPK activation during an ischaemic preconditioning protocol did not act as trigger: inhibition of p38 MAPK activation by SB 203580 during the preconditioning phase did not abolish cardioprotection. In fact, functional recovery was significantly better than that of untreated preconditioned hearts. On the other hand, SB 203580, when administered before and during the isoproterenol-preconditioning protocol abolished cardioprotection, suggesting that p38 MAPK activation by a beta -adrenergic-induced preconditioning protocol does act as trigger of cardioprotection. In addition, attenuation of p38 MAPK activity during sustained ischaemia and reperfusion as occurs in ischaemic- or isoproterenol-preconditioned hearts, is beneficial.

Serial changes in the myocardial beta-adrenergic signalling system in two models of non-insulin dependent diabetes mellitus

Since it was reported in 1991 by Schaffer et al. that myocardial contractile responsiveness was altered in NIDDM in the absence of alterations in the beta-adrenergic receptor population, researchers have been seeking a post-receptor defect to account for this. The present study addresses this issue by comparing alterations occurring in the myocardial beta-receptor signalling pathway in two different models of rat NIDDM, as well as the response of the pathway after stimulation with isoproterenol in the presence or absence of insulin. The characteristics of the beta-receptor population, adenylyl cyclase activity and cAMP levels were determined at three different ages. The main results demonstrate that: (i) the two models of NIDDM myocardium differ biochemically; (ii) the beta-adrenergic signalling system of the insulin deficient model was altered more than the hyperinsulinemic model and (iii) the observed exaggerated cAMP response of NIDDM hearts after stimulation with a beta-adrenergic agonist is in contrast with lower responsivity.

Insulin in combination with vanadate stimulates glucose transport in isolated cardiomyocytes from obese Zucker rats

Insulin stimulates glucose uptake in muscle cells via activation of protein kinase B (PKB). The protein tyrosine phosphatase (PTP) inhibitor vanadate, is a known insulin mimetic agent but the mechanism whereby vanadate exerts its effect is not clearly understood. Vanadate also has beneficial effects in the diabetic myocardium. The aim of this study was to correlate insulin stimulation of glucose uptake and PKB activation with that induced by vanadate in adult ventricular myocytes from lean and obese Zucker fa/fa rats. In lean Zucker rats, 100 nM insulin and 5 mM vanadate stimulated myocardial 2-deoxy-D-[3]glucose (2-DG) uptake from 27.17 +/- 1.72 to 96.52 +/- 10.87 and 43.86 +/- 4.02 pmole/mg protein p/30 min respectively while a combination of insulin and vanadate could not improve the maximal response of insulin. In obese Zucker hearts, basal as well as insulin and vanadate stimulated glucose uptake were severely impaired (15.49 +/- 1.44 vs 25.51 +/- 3.11 and 20.11 +/- 1.68 pmole/mg protein/30 min respectively). A combination of insulin and vanadate, resulted in a response significantly improved from the maximal response of insulin. This stimulation of 2-DG uptake was, in all instances, blocked by the PI 3-kinase inhibitors wortmannin and LY 294002. Insulin could not activate PKB, as measured by the Ser473 phosphorylated form of the enzyme, in the obese Zucker rats to the same extent as in lean controls. Similar to glucose uptake, activation of PKB by vanadate plus insulin was significantly more than that accomplished by insulin alone in obese rats. Both insulin and vanadate activation of PKB was prevented by wortmannin and LY 294002. Thus, the present study demonstrates that: (i) in cardiomyocytes from lean and obese Zucker rats, both insulin and vanadate stimulate glucose uptake and PKB activation through a PI 3-kinase sensitive pathway. (ii) In obese Zucker rats, neither insulin nor vanadate could induce glucose uptake or activation of PKB to the same extent as in lean controls. (iii) A combination of insulin with vanadate may be beneficial to increase glucose uptake in diabetic hearts, as this gives a better response than insulin alone.

The effects of insulin and beta-adrenergic stimulation on glucose transport, glut 4 and PKB activation in the myocardium of lean and obese non-insulin dependent diabetes mellitus rats

Glucose uptake, glut 4 translocation and activation of protein kinase B were measured in Langendorff perfused hearts from (i) Wistar control, (ii) lean, neonatal Streptozotocin induced (Stz) and (iii) Zucker (fa/fa) obese diabetic rats of 10-12 weeks old. Hearts were subjected to stimulation with insulin, isoproterenol (beta-adrenergic agonist) or a combination of insulin and isoproterenol, during the perfusion protocol. Basal myocardial glucose uptake was impaired in both diabetic models, but could be stimulated significantly by insulin. In the Zucker rats, the time-course of insulin action was delayed. Insulin and beta-stimulation of glucose uptake were not additive. Evaluation of sarcolemmal membranes from these hearts showed that the affinity of glut 4 was significantly lower in the Zucker but not in the Stz hearts while a reduced affinity found with a combination of insulin and beta-stimulation in control hearts, was absent in both diabetic models. Total membrane lysates were analyzed for glut 4 expression while an intracellular component was generated to quantify translocation on stimulation as well as activity of protein kinase B (PKB). At this age, the neonatal Streptozotocin induced diabetic animals presented with more faulty regulation concerning adrenergic stimulated effects on elements of this signal transduction pathway while the Zucker fa/fa animals showed larger deviations in insulin stimulated effects. The overall response of the Zucker myocardium was poorer than that of the Stz group. No significant modulation of beta-adrenergic signaling on insulin stimulated glucose uptake was found. The PI-3-kinase inhibitor wortmannin, could abolish glucose uptake as well as PKB activation elicited by both insulin and isoproterenol.

Activation of p38 MAPK induced by a multi-cycle ischaemic preconditioning protocol is associated with attenuated p38 MAPK activity during sustained ischaemia and reperfusion

The role of p38 mitogen-activated protein kinase (MAPK) in ischaemic preconditioning remains controversial. Since most previous studies focussed on events only during sustained ischaemia, the aim of this study was to establish the activation pattern of p38 MAPK during a multicycle preconditioning protocol, sustained ischaemia as well as reperfusion and to correlate these events with functional recovery of the isolated perfused rat heart. Isolated perfused rat hearts were preconditioned by 3x5 min global ischaemia followed by 25 min global ischaemia and 30 min reperfusion. Non-preconditioned hearts were subjected to 25 min global ischaemia and 30 min reperfusion. Hearts were freeze-clamped and p38 MAPK activation in tissue lysates was assessed by standard Western blotting techniques, using a dual phospho-p38 MAPK antibody as well as a non-radioactive IP-kinase assay. The results showed that transient dual phosphorylation and activation of p38 MAPK occurs during a 3x5 min preconditioning protocol: the activation was maximal during the first episode, becoming progressively lower during the second and third episodes. p38 MAPK activation was significantly less during both sustained ischaemia and reperfusion in preconditioned hearts, when compared with non-preconditioned hearts. Attenuation of p38 MAPK activity during sustained ischaemia and reperfusion was associated with improved functional recovery. The effect of inhibition of p38 MAPK activation on cardioprotection was further evaluated in adult, isolated cardiomyocytes. Administration of SB 203580 (1-10 microM) before and during the preconditioning protocol, had no effect on cell morphology and viability after 2 h hypoxia, compared to untreated preconditioned cardiomyocytes. When administered to non-preconditioned cells before the onset of 2 h hypoxia, it caused a significant improvement in both morphology and viability. In summary, the results suggest that attenuation of the kinase activity during sustained ischaemia and reperfusion may be an essential element of the preconditioning process.

Melatonin protects against ischaemic-reperfusion myocardial damage

OBJECTIVES

Melatonin, a hormonal product of the pineal gland, is now known to be a multi-faceted free radical scavenger and anti-oxidant. Since little information is available regarding the action of melatonin on the heart, we studied the effects of melatonin on adult ventricular myocytes subjected to chemical hypoxia and reoxygenation.

METHODS

Adult rat ventricular myocytes were preloaded with tetramethylrhodamine (TMRM) in combination with one of the following fluorophores: dichlorodihydrofluorescein diacetate (DCDHF), dihydrorhodamine 123 (DHR) or fluo 3 (Fluo) and then investigated with confocal laser scanning microscopy. Chemical hypoxia was induced by addition of 1.5 mM KCN and 20 mM deoxyglucose to the superfusion buffer. Melatonin (50-100 microM) was added at intervals during the protocol.

RESULTS

Cells subjected to 12.5 min chemical hypoxia showed marked morphological changes, increased fluorescence intensity of DCDHF, DHR and Fluo, suggesting Ca2+ accumulation and generation of H2O2 and reactive oxygen species. The number of cells showing increased fluorescence also increased significantly. Melatonin (50 and 100 microM) caused a significant reduction in morphological changes, number of cells with increased fluorescence and fluorescence intensity of DHR and Fluo, (but not DCDHF).

CONCLUSION

Melatonin effectively reduced damage induced by chemical hypoxia in adult cardiomyocytes, probably by virtue of its effects on reactive oxygen species generation and intracellular Ca2+ accumulation.

Opioid receptor stimulation acts as mediator of protection in ischaemic preconditioning

Involvement of the opioid receptors in preconditioning-induced protection has recently been described. The aims of this study were to establish whether: (i) opioid receptor stimulation acts as a trigger ( during the preconditioning protocol) or as a mediator ( during sustained ischaemia) of cardioprotection using either morphine or [D-ala(2), D-leu(5)] enkephalin (DADLE), a synthetic delta-opioid receptor agonist; ( ii) the beneficial effects of DADLE are protein kinase C ( PKC) -mediated; and (iii) inhibitory 'cross-talk' occurs between the beta-adrenergic and phosphatidylinositol pathways activated by release of endogenous catecholamines and opioids respectively during sustained ischaemia. The isolated, perfused working rat heart, subjected to 25 minutes' global ischaemia and 30 minutes' reperfusion, was used as the experimental model. The results showed that delta-opioid receptor stimulation with DADLE (10(-8) M), when administered for 3 x 5 minutes, had no effect, while when given 10 minutes before sustained ischaemia the drug significantly improved functional recovery during reperfusion. This indicates that opioid receptor stimulation acts as a mediator rather than a trigger in the protection elicited. Morphine ( 3 x 10(-7)) when administered in the same manner was without effect. Opioid receptor stimulation caused a marked reduction in the beta -adrenergic response to isoproterenol, indicating inhibitory cross-talk between the phosphatidyl-inositol and beta-adrenergic signal transduction pathways. However, reduction of the beta-adrenergic response to ischaemia does not appear to be the mechanism of opioid-induced protection, as indicated by 3',5' -cyclic adenosine monophosphate (cAMP) levels at the end of 25 minutes' global ischaemia. Opioid receptor-mediated protection against ischaemic damage is PKC-dependent, since DADLE-induced protection could be abolished by the inhibitor chelerythrine.

Nitric oxide: a trigger for classic preconditioning?

To determine whether nitric oxide (NO) is involved in classic preconditioning (PC), the effect of NO donors as well as inhibition of the L-arginine-NO-cGMP pathway were evaluated on 1) the functional recovery during reperfusion of ischemic rat hearts and 2) cyclic nucleotides during both the PC protocol and sustained ischemia. Tissue cyclic nucleotides were manipulated with NO donors [S-nitroso-N-penicillamine (SNAP), sodium nitroprusside (SNP), or L-arginine] and inhibitors of nitric oxide synthase (N(omega)-nitro-L-arginine methyl ester or N-nitro-L-arginine) or guanylyl cyclase (1H-[1,2,4]oxadiazolol-[4,3-a]quinoxaline-1-one). Pharmacological elevation in tissue cGMP levels by SNAP or SNP before sustained ischemia elicited functional improvement during reperfusion comparable to that by PC. Administration of inhibitors before and during the PC protocol partially attenuated functional recovery, whereas they had no effect when given after the ischemic PC protocol and before sustained ischemia only, indicating a role for NO as a trigger but not as a mediator. Ischemic PC, SNAP, or SNP caused a significant increase in cGMP and a reduction in cAMP levels after 25 min of sustained ischemia that may contribute to the protection obtained. The results obtained suggest a role for NO (and cGMP) as a trigger in classic PC.

Effect of vanadate and insulin on glucose transport in isolated adult rat cardiomyocytes

It is now widely accepted that insulin stimulation of glucose uptake by muscle cells is due to the activation of protein kinase B, leading to the recruitment of glucose transporter proteins from an intracellular compartment to the plasma membrane. Vanadate is a protein tyrosine phosphatase (PTP) inhibitor and a known insulin mimetic agent. Vanadate causes an increase of glucose transport in various tissues, but the mechanism of stimulation is not clearly understood. Hence in the present study, we have compared the mechanism of 2-deoxy-D-glucose transport induced by vanadate and insulin in isolated rat cardiomyocytes. Vanadate stimulated deoxyglucose transport in a time- and concentration-dependent manner. Insulin (100 nM) and vanadate (5 mM) stimulated 2-deoxy-D-glucose transport on an average by 3- and 2-fold respectively over basal values. The stimulation of glucose transport was accompanied by an activation of protein kinase B (PKB). This study also revealed that the activation of PKB and stimulation of 2-deoxyglucose uptake by vanadate and insulin are inhibited by treatment with wortmannin, a specific inhibitor of phoshatidylinositol 3-kinase (PI 3-kinase). Hence, we conclude that both insulin and vanadate follow the same signalling pathway downstream of PI 3-kinase to stimulate 2-deoxy-D-glucose transport.

Effect of a calcium-sensitizing agent, levosimendan, on the postcardioplegic inotropic response of the myocardium

Myocardial contractile function after coronary artery bypass graft surgery is often depressed and may require inotropic support, particularly in patients on treatment with beta-adrenergic and Ca2+ blockers. In view of the increase in cytosolic Ca2+ during early reperfusion, use of Ca2+ sensitizing agents may be preferable to adrenergic agonists for enhancement of contractile function after cardioplegic arrest. The aim of this study was to assess the efficacy of the Ca2+ sensitizer, levosimendan, as an inotrope on the mechanical recovery of hearts after normothermic and hypothermic cardioplegic arrest in the absence and presence of Ca2+ and beta-blockers. Isolated perfused working guinea pig hearts were perfused in the absence or presence of propranolol (10(-6) M) and/or nifedipine (10(-8) M), subjected to 45 minutes of normothermic or 180 minutes of hypothermic cardioplegic arrest, reperfused, and exposed to increasing concentrations of levosimendan (10(-9) to 10(-6) M). Levosimendan (10(-7) to 10(-6) M) has positive inotropic, chronotropic, and vasodilatory effects on normoxic perfused control hearts, as well as during reperfusion after 45 minutes of normothermic cardioplegic arrest. Similar effects were elicited in the presence of the blockers. Levosimendan had no stimulatory effect during reperfusion of hearts subjected to prior hypothermic arrest. Except for the increase in heart rate, the effects of levosimendan on functional performance during reperfusion were comparable with those of adrenaline. Levosimendan elicits a positive inotropic and chronotropic response during reperfusion of hearts after normothermic cardioplegic arrest, both in the absence and presence of Ca2+ and beta-adrenergic blockers.

Reduction of postischemic contractile dysfunction of the isolated rat heart by sevoflurane: comparison with halothane

Our aims were to evaluate the effect of sevoflurane on postcardioplegic functional recovery of the isolated rat heart including the role of the adenosine triphosphate regulated potassium (K(ATP)) channels and to compare the cardioprotective effects of equipotent concentrations of halothane and sevoflurane. Isolated perfused rat hearts were subjected to 45 or 60 min normothermic cardioplegic arrest and 30 min reperfusion. Sevoflurane (0.9% and 1. 7%), halothane (0.4% and 0.8%), or sevoflurane (0.9%) plus glibenclamide (10 microM) (a K(ATP) channel blocker) were administered at different time intervals. Measurements of mechanical activity were made before and after arrest. Function during reperfusion after cardioplegic arrest was significantly depressed in both untreated and treated hearts. However, sevoflurane administered both before and after arrest, or before only, significantly improved functional recovery after 45 min of cardioplegia. This protective effect was abolished by simultaneous administration of glibenclamide, suggesting a role of the K(ATP) channel. Sevoflurane was as effective as halothane in improving postcardioplegic functional performance. After 45 min of arrest, hearts exposed to either anesthetic at both concentrations had a significantly higher work performance on discontinuation of their administration than untreated controls. After 60 min of arrest, neither anesthetic elicited protection.

Ischemic preconditioning and the beta-adrenergic signal transduction pathway

BACKGROUND

Previous studies from our laboratory showed cyclic increases in tissue cAMP during a multiple-cycle preconditioning (PC) protocol, followed by attenuated cAMP accumulation during sustained ischemia. The aim of this study was to determine whether ischemia-induced activation of the beta-adrenergic signaling pathway could act as a trigger in eliciting protection.

METHODS AND RESULTS

Isolated perfused rat hearts were preconditioned by 3x5 minutes of global ischemia, interspersed by 5 minutes of reperfusion. beta-Adrenergic responsivity was assessed by measurement of tissue cAMP generation after beta-adrenergic agonist administration at the end of the PC protocol. Tissue cAMP, adenylyl cyclase, and protein kinase A (PKA) activities and beta-adrenergic receptor characteristics were assessed at different times. The role of cAMP generation in eliciting PC was studied by investigation of functional recovery during reperfusion after 25 minutes of global ischemia after (1) cAMP increases in the trigger period were prevented with the beta-adrenergic blocker alprenolol 7.5x10(-5) mol/L and (2) increases in cAMP were elicited by administration of forskolin 10(-7) and 10(-6) mol/L or isoproterenol 10(-8), 10(-7), and 10(-6) mol/L. Intermittent ischemia resulted in reduced beta-adrenergic responsivity at the end of the protocol, although B(max) and K(d) values of the beta-adrenergic receptor population and adenylyl cyclase and PKA activities were increased. Abolishment of cyclic increases in cAMP before sustained ischemia attenuated myocardial protection against ischemia, whereas agonists elicited protection. No clear correlation between protection and beta-adrenergic desensitization was observed.

CONCLUSIONS

Ischemia-induced activation of the beta-adrenergic signaling pathway during preconditioning should also be considered a trigger in eliciting preconditioning.

Role of cyclic nucleotide phosphodiesterases in ischemic preconditioning

Several signal transduction pathways have been implicated in the mechanism of protection induced by ischemic preconditioning (PC). For example, stimulation of a variety of G-protein coupled receptors results in stimulation of protein kinase C (PKC) which has been suggested to act as common denominator in eliciting protection. PC also significantly attenuated cAMP accumulation during sustained ischemia, suggesting involvement of an anti-adrenergic mechanism. The aim of this study was to evaluate the beta-adrenergic signal transduction pathway (as evidenced by changes in tissue cAMP and cAMP- and cGMP-phosphodiesterase) during the PC protocol as well as during sustained ischemia. Isolated perfused rat hearts were preconditioned by 3 x 5 min global ischemia (PC1,2,3) interspersed by 5 min reperfusion, followed by 25 min global ischemia. Tissue cAMP- and cGMP-PDE activity as well as cAMP and cGMP levels were determined at different time intervals during the PC protocol and sustained ischemia. Tissue cAMP increased with each PC ischemic event and normalized upon reperfusion, while PDE activity showed the opposite, viz a reduction during ischemia and an increase during reperfusion. Except for PC1, tissue cGMP showed similar fluctuations. Throughout 25 min sustained ischemia, cAMP- and cGMP-PDE activities were higher in PC than in nonpreconditioned hearts, associated with a significantly lesser accumulation in cAMP and higher cGMP levels in the former. Fluctuations in cyclic nucleotides during preconditioning were associated with concomitant changes in PDE activity, while the attenuated beta-adrenergic response of preconditioned hearts during sustained ischemia may partially be due to increased PDE activity.

Postcardioplegic myocardial recovery: effects of halothane, nifedipine, HOE 694, and quinacrine

Halothane has been shown to be a powerful myocardial protectant during normothermic cardioplegic arrest and subsequent reperfusion. In view of its multiple effects on cellular Ca2+ movements and the role of this ion in ischemia-reperfusion injury, the questions of whether halothane is capable of maximally protecting the heart or whether combination therapy of halothane with other Ca2+ blocking agents may be more effective arose. Therefore, the effects of combination therapy with halothane and a calcium antagonist (nifedipine), or a Na+/H+ inhibitor (HOE 694), or a Na+/Ca2+ inhibitor (quinacrine) on postcardioplegic functional recovery were evaluated. The isolated perfused rat heart subjected to 45 minutes normothermic cardiac arrest was used as an experimental model. Dose-response curves were performed for each drug. Using the optimal dosage for each drug, the following results were obtained: (1) Nifedipine (10(-7) M; administered retrogradely 10 minutes before and after cardioplegia) and halothane (1.5% administered during cardioplegia), when administered separately, improved functional recovery. Combination therapy did not further improve protection. (2) HOE 694 (10(-7) M) or quinacrine (10(-9) M) improved post-cardioplegic functional recovery when added for 2 minutes at the onset of reperfusion. Simultaneous administration of HOE 694 and 1.5% halothane was the only combination that yielded additive protection. (3) Quinacrine, a phospholipase and Na+/Ca2+ exchanger inhibitor, appeared to be the most powerful drug used. In summary, the results obtained indicate that interventions aimed at preventing intracellular Ca2+ overload improve recovery after cardioplegic arrest. The beneficial effects of halothane could be further improved by HOE 694.