Sarcolemmal cholesterol and caveolin-3 dependence of cardiac function, ischemic tolerance, and opioidergic cardioprotection

Ischemic preconditioning/ischemic postconditioning alleviates anoxia/reoxygenation injury via the Notch1/Hes1/VDAC1 axis

Ischemic preconditioning (IPC), and ischemic postconditioning (IPost) have a significant protective effect on myocardial ischemia/reperfusion (MI/R) injury by alleviating oxidative stress and mitochondrial disturbances, although the underlying molecular mechanisms are unclear. The study was to demonstrate that cardioprotection against anoxia/reoxygenation (A/R) injury is transduced via the Notch1/Hes1/VDAC1 signaling pathway. Using mass spectrometry and tandem affinity purification (TAP), to screen for differentially expressed proteins associated with Hes1, followed by standard bioinformatics analysis. The co-immunoprecipitation (Co-IP) assay confirmed an interaction between Hes1 and VDAC1 proteins. H9c2 cells were transfected with Hes1 adenoviral N-terminal TAP vector (AD-NTAP/Hes1) and Hes1-short hairpin RNA adenoviral vector (AD-Hes1-shRNA) to establish A/R injury, IPC, and IPost models, respectively. The expression of Hes1 and VDAC1 proteins were measured by western blot analysis, while the levels of reactive oxygen species (ROS), mitochondrial membrane potential (ΔΨm), and apoptosis were evaluated by flow cytometry. AD-NTAP/Hes1 can activate the exogenous protein expression of Hes1, thus decreasing creatine phosphokinase (CPK) and lactate dehydrogenase (LDH) activity and promoting cell viability. The study found that VDAC1 was a potential target protein for Hes1 and the overexpression of Hes1 protein expression downregulated protein expression levels of VDAC1, reduced ROS production, stabilized ΔΨm, and inhibited apoptosis in H9c2 cells. Additionally, downregulation of Hes1 protein expression also upregulated VDAC1 protein expression, increased ROS production, imbalanced ΔΨm, promoted cell apoptosis, and attenuated the cardioprotection afforded by IPC and IPost. The Notch1/Hes1 signaling pathway activated by IPC/IPost can directly downregulate the protein expression of VDAC1 and consequently relieve A/R injury.

Central and cardiac stress resiliences consistently linked to integrated immuno-neuroendocrine responses across stress models in male mice

Stress resilience, and behavioural and cardiovascular impacts of chronic stress, are theorised to involve integrated neuro-endocrine/inflammatory/transmitter/trophin signalling. We tested for this integration, and whether behaviour/emotionality, together with myocardial ischaemic tolerance, are consistently linked to these pathways across diverse conditions in male C57Bl/6 mice. This included: Restraint Stress (RS), 1 hr restraint/day for 14 days; Chronic Unpredictable Mild Stress (CUMS), 7 stressors randomised over 21 days; Social Stress (SS), 35 days social isolation with brief social encounters in final 13 days; and Control conditions (CTRL; un-stressed mice). Behaviour was assessed via open field (OFT) and sucrose preference (SPT) tests, and neurobiology from frontal cortex (FC) and hippocampal transcripts. Endocrine factors, and function and ischaemic tolerance in isolated hearts, were also measured. Model characteristics ranged from no behavioural or myocardial changes with homotypic RS, to increased emotionality and cardiac ischaemic injury (with apparently distinct endocrine/neurobiological profiles) in CUMS and SS models. Highly integrated expression of HPA axis, neuro-inflammatory, BDNF, monoamine, GABA, cannabinoid and opioid signalling genes was confirmed across conditions, and consistent/potentially causal correlations identified for: i) Locomotor activity (noradrenaline, ghrelin; FC Crhr1, Tnfrsf1b, Il33, Nfkb1, Maoa, Gabra1; hippocampal Il33); ii) Thigmotaxis (adrenaline, leptin); iii) Anxiety-like behaviour (adrenaline, leptin; FC Tnfrsf1a; hippocampal Il33); iv) Depressive-like behaviour (ghrelin; FC/hippocampal s100a8); and v) Cardiac stress-resistance (noradrenaline, leptin; FC Il33, Tnfrsf1b, Htr1a, Gabra1, Gabrg2; hippocampal Il33, Tnfrsf1a, Maoa, Drd2). Data support highly integrated pathway responses to stress, and consistent adipokine, sympatho-adrenergic, inflammatory and monoamine involvement in mood and myocardial disturbances across diverse conditions.

Pathophysiology and molecular mechanism of caveolin involved in myocardial protection strategies in ischemic conditioning

Multiple pathophysiological pathways are activated during the process of myocardial injury. Various cardioprotective strategies protect the myocardium from ischemia, infarction, and ischemia/reperfusion (I/R) injury through different targets, yet the clinical translation remains limited. Caveolae and its structure protein, caveolins, have been suggested as a bridge to transmit damage-preventing signals and mediate the protection of ultrastructure in cardiomyocytes under pathological conditions. In this review, we first briefly introduce caveolae and caveolins. Then we review the cardioprotective strategies mediated by caveolins through various pathophysiological pathways. Finally, some possible research directions are proposed to provide future experiments and clinical translation perspectives targeting caveolin based on the investigative evidence.

Caveolin-3 prevents swelling-induced membrane damage via regulation of ICl,swell activity

Caveola membrane structures harbor mechanosensitive chloride channels (MCCs; including chloride channel 2, chloride channel 3, and SWELL1, also known as LRRC8A) that form a swelling-activated chloride current (ICl,swell) and play an important role in cell volume regulation and mechanoelectrical signal transduction. However, the role of the muscle-specific caveolar scaffolding protein caveolin-3 (Cav3) in regulation of MCC expression, activity, and contribution to membrane integrity in response to mechanical stress remains unclear. Here we showed that Cav3-transfected (Cav3-positive) HEK293 cells were significantly resistant to extreme (<20 milliosmole) hypotonic swelling compared with native (Cav3-negative) HEK293 cells; the percentage of cells with membrane damage decreased from 45% in Cav3-negative cells to 17% in Cav3-positive cells (p < 0.05). This mechanoprotection was significantly reduced (p < 0.05) when cells were exposed to the ICl,swell-selective inhibitor 4-[(2-butyl-6,7-dichloro-2-cyclopentyl-2,3-dihydro-1-oxo-1H-inden-5-yl)oxy]butanoic acid (10 μM). These results were recapitulated in isolated mouse ventricular myocytes, where the percentage of cardiomyocytes with membrane damage increased from 47% in control cells to 78% in 4-[(2-butyl-6,7-dichloro-2-cyclopentyl-2,3-dihydro-1-oxo-1H-inden-5-yl)oxy]butanoic acid-treated cells (p < 0.05). A higher resistance to hypotonic swelling in Cav3-positive HEK293 cells was accompanied by a significant twofold increase of ICl,swell current density and SWELL1 protein expression, whereas ClC-2/3 protein levels remained unchanged. Förster resonance energy transfer analysis showed a less than 10-nm membrane and intracellular association between Cav3 and SWELL1. Cav3/SWELL1 membrane Förster resonance energy transfer efficiency was halved in mild (220 milliosmole) hypotonic solution as well as after disruption of caveola structures via cholesterol depletion by 1-h treatment with 10 mM methyl-β-cyclodextrin. A close association between Cav3 and SWELL1 was confirmed by co-immunoprecipitation analysis. Our findings indicate that, in the MCCs tested, SWELL1 abundance and activity are regulated by Cav3 and that their association relies on membrane tension and caveola integrity. This study highlights the mechanoprotective role of Cav3, which is facilitated by complimentary SWELL1 expression and activity.

[Significance of exosomes in cardiology: heralds of cardioprotection]

Los exosomas tienen un papel clave en la comunicación intercelular. Debido a sus múltiples interacciones, estas estructuras cumplen con el papel de «mensajeros» de forma dinámica, transportando su contenido a células blanco específicas y generando nuevas señales celulares. En este artículo se describen algunas de las proteínas, lípidos y ácidos nucleicos que son transportados por estas vesículas y que se han relacionado con cardioprotección, con la finalidad de proporcionar información y generar interés sobre la relevancia de los exosomas como posibles blancos diagnósticos y terapéuticos.

Morphine induces physiological, structural, and molecular benefits in the diabetic myocardium

The obesity epidemic has increased type II diabetes mellitus (T2DM) across developed countries. Cardiac T2DM risks include ischemic heart disease, heart failure with preserved ejection fraction, intolerance to ischemia-reperfusion (I-R) injury, and refractoriness to cardioprotection. While opioids are cardioprotective, T2DM causes opioid receptor signaling dysfunction. We tested the hypothesis that sustained opioid receptor stimulus may overcome diabetes mellitus-induced cardiac dysfunction via membrane/mitochondrial-dependent protection. In a murine T2DM model, we investigated effects of morphine on cardiac function, I-R tolerance, ultrastructure, subcellular cholesterol expression, mitochondrial protein abundance, and mitochondrial function. T2DM induced 25% weight gain, hyperglycemia, glucose intolerance, cardiac hypertrophy, moderate cardiac depression, exaggerated postischemic myocardial dysfunction, abnormalities in mitochondrial respiration, ultrastructure and Ca2+ -induced swelling, and cell death were all evident. Morphine administration for 5 days: (1) improved glucose homeostasis; (2) reversed cardiac depression; (3) enhanced I-R tolerance; (4) restored mitochondrial ultrastructure; (5) improved mitochondrial function; (6) upregulated Stat3 protein; and (7) preserved membrane cholesterol homeostasis. These data show that morphine treatment restores contractile function, ischemic tolerance, mitochondrial structure and function, and membrane dynamics in type II diabetic hearts. These findings suggest potential translational value for short-term, but high-dose morphine administration in diabetic patients undergoing or recovering from acute ischemic cardiovascular events.

Effects of voluntary exercise duration on myocardial ischaemic tolerance, kinase signaling and gene expression

AIM

Exercise is cardioprotective, though optimal interventions are unclear. We assessed duration dependent effects of exercise on myocardial ischemia-reperfusion (I-R) injury, kinase signaling and gene expression.

METHODS

Responses to brief (2 day; 2EX), intermediate (7 and 14 day; 7EX and 14EX) and extended (28 day; 28EX) voluntary wheel running (VWR) were studied in male C57Bl/6 mice. Cardiac function, I-R tolerance and survival kinase signaling were assessed in perfused hearts.

KEY FINDINGS

Mice progressively increased running distances and intensity, from 2.4 ± 0.2 km/day (0.55 ± 0.04 m/s) at 2-days to 10.6 ± 0.4 km/day (0.72 ± 0.06 m/s) after 28-days. Myocardial mass and contractility were modified at 14-28 days VWR. Cardioprotection was not 'dose-dependent', with I-R tolerance enhanced within 7 days and not further improved with greater VWR duration, volume or intensity. Protection was associated with AKT, ERK1/2 and GSK3β phosphorylation, with phospho-AMPK selectively enhanced with brief VWR. Gene expression was duration-dependent: 7 day VWR up-regulated glycolytic (Pfkm) and down-regulated maladaptive remodeling (Mmp2) genes; 28 day VWR up-regulated caveolar (Cav3), mitochondrial biogenesis (Ppargc1a, Sirt3) and titin (Ttn) genes. Interestingly, I-R tolerance in 2EX/2SED groups improved vs. groups subjected to longer sedentariness, suggesting transient protection on transition to housing with running wheels.

SIGNIFICANCE

Cardioprotection is induced with as little as 7 days VWR, yet not enhanced with further or faster running. This protection is linked to survival kinase phospho-regulation (particularly AKT and ERK1/2), with glycolytic, mitochondrial, caveolar and myofibrillar gene changes potentially contributing. Intriguingly, environmental enrichment may also protect via similar kinase regulation.

Dietary α-Linolenic Acid Counters Cardioprotective Dysfunction in Diabetic Mice: Unconventional PUFA Protection

Whether dietary omega-3 (n-3) polyunsaturated fatty acid (PUFA) confers cardiac benefit in cardiometabolic disorders is unclear. We test whether dietary -linolenic acid (ALA) enhances myocardial resistance to ischemia-reperfusion (I-R) and responses to ischemic preconditioning (IPC) in type 2 diabetes (T2D); and involvement of conventional PUFA-dependent mechanisms (caveolins/cavins, kinase signaling, mitochondrial function, and inflammation). Eight-week male C57Bl/6 mice received streptozotocin (75 mg/kg) and 21 weeks high-fat/high-carbohydrate feeding. Half received ALA over six weeks. Responses to I-R/IPC were assessed in perfused hearts. Localization and expression of caveolins/cavins, protein kinase B (AKT), and glycogen synthase kinase-3 β (GSK3β); mitochondrial function; and inflammatory mediators were assessed. ALA reduced circulating leptin, without affecting body weight, glycemic dysfunction, or cholesterol. While I-R tolerance was unaltered, paradoxical injury with IPC was reversed to cardioprotection with ALA. However, post-ischemic apoptosis (nucleosome content) appeared unchanged. Benefit was not associated with shifts in localization or expression of caveolins/cavins, p-AKT, p-GSK3β, or mitochondrial function. Despite mixed inflammatory mediator changes, tumor necrosis factor-a (TNF-a) was markedly reduced. Data collectively reveal a novel impact of ALA on cardioprotective dysfunction in T2D mice, unrelated to caveolins/cavins, mitochondrial, or stress kinase modulation. Although evidence suggests inflammatory involvement, the basis of this "un-conventional" protection remains to be identified.

Protective role of cardiac-specific overexpression of caveolin-3 in cirrhotic cardiomyopathy

Cirrhotic cardiomyopathy is a clinical syndrome in patients with liver cirrhosis characterized by blunted cardiac contractile responses to stress and/or heart rate-corrected QT (QTc) interval prolongation. Caveolin-3 (Cav-3) plays a critical role in cardiac protection and is an emerging therapeutic target for heart disease. We investigated the protective role of cardiac-specific overexpression (OE) of Cav-3 in cirrhotic cardiomyopathy. Biliary fibrosis was induced in male Cav-3 OE mice and transgene negative (TG_neg) littermates by feeding a diet containing 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC; 0.1%) for 3 wk. Liver pathology and blood chemistries were assessed, and stress echocardiography, telemetry, and isolated heart perfusion studies to assess adrenergic responsiveness were performed. Cav-3 OE mice showed a similar degree of hyperdynamic contractility, pulmonary hypertension, and QTc interval prolongation as TG_neg mice after 3 wk of DDC diet. Blunted systolic responses were shown in both DDC-fed Cav-3 OE and TG_neg hearts after in vivo isoproterenol challenge. However, QTc interval prolongation after in vivo isoproterenol challenge was significantly less in DDC-fed Cav-3 OE hearts compared with DDC-fed TG_neg hearts. In ex vivo perfused hearts, where circulatory factors are absent, isoproterenol challenge showed hearts from DDC-fed Cav-3 OE mice had better cardiac contractility and relaxation compared with DDC-fed TG_neg hearts. Although Cav-3 OE in the heart did not prevent cardiac alterations in DDC-induced biliary fibrosis, cardiac expression of Cav-3 reduced QTc interval prolongation after adrenergic stimulation in cirrhosis.NEW & NOTEWORTHY Prevalence of cirrhotic cardiomyopathy is up to 50% in cirrhotic patients, and liver transplantation is the only treatment. However, cirrhotic cardiomyopathy is associated with perioperative morbidity and mortality after liver transplantation; therefore, management of cirrhotic cardiomyopathy is crucial for successful liver transplantation. This study shows cardiac myocyte specific overexpression of caveolin-3 (Cav-3) provides better cardiac contractile responses and less corrected QT prolongation during adrenergic stress in a cirrhotic cardiomyopathy model, suggesting beneficial effects of Cav-3 expression in cirrhotic cardiomyopathy.

Cardiac ischemia-reperfusion injury induces ROS-dependent loss of PKA regulatory subunit RIα

Type I PKA regulatory α-subunit (RIα; encoded by the Prkar1a gene) serves as the predominant inhibitor protein of the catalytic subunit of cAMP-dependent protein kinase (PKAc). However, recent evidence suggests that PKA signaling can be initiated by cAMP-independent events, especially within the context of cellular oxidative stress such as ischemia-reperfusion (I/R) injury. We determined whether RIα is actively involved in the regulation of PKA activity via reactive oxygen species (ROS)-dependent mechanisms during I/R stress in the heart. Induction of ex vivo global I/R injury in mouse hearts selectively downregulated RIα protein expression, whereas RII subunit expression appears to remain unaltered. Cardiac myocyte cell culture models were used to determine that oxidant stimulus (i.e., H2O2) alone is sufficient to induce RIα protein downregulation. Transient increase of RIα expression (via adenoviral overexpression) negatively affects cell survival and function upon oxidative stress as measured by increased induction of apoptosis and decreased mitochondrial respiration. Furthermore, analysis of mitochondrial subcellular fractions in heart tissue showed that PKA-associated proteins are enriched in subsarcolemmal mitochondria (SSM) fractions and that loss of RIα is most pronounced at SSM upon I/R injury. These data were supported via electron microscopy in A-kinase anchoring protein 1 (AKAP1)-knockout mice, where loss of AKAP1 expression leads to aberrant mitochondrial morphology manifested in SSM but not interfibrillar mitochondria. Thus, we conclude that modification of RIα via ROS-dependent mechanisms induced by I/R injury has the potential to sensitize PKA signaling in the cell without the direct use of the canonical cAMP-dependent activation pathway.NEW & NOTEWORTHY We uncovered a previously undescribed phenomenon involving oxidation-induced activation of PKA signaling in the progression of cardiac ischemia-reperfusion injury. Type I PKA regulatory subunit RIα, but not type II PKA regulatory subunits, is dynamically regulated by oxidative stress to trigger the activation of the catalytic subunit of PKA in cardiac myocytes. This effect may play a critical role in the regulation of subsarcolemmal mitochondria function upon the induction of ischemic injury in the heart.

Mitochondrial connexin 43 in sex-dependent myocardial responses and estrogen-mediated cardiac protection following acute ischemia/reperfusion injury

Preserving mitochondrial activity is crucial in rescuing cardiac function following acute myocardial ischemia/reperfusion (I/R). The sex difference in myocardial functional recovery has been observed after I/R. Given the key role of mitochondrial connexin43 (Cx43) in cardiac protection initiated by ischemic preconditioning, we aimed to determine the implication of mitochondrial Cx43 in sex-related myocardial responses and to examine the effect of estrogen (17β-estradiol, E2) on Cx43, particularly mitochondrial Cx43-involved cardiac protection following I/R. Mouse primary cardiomyocytes and isolated mouse hearts (from males, females, ovariectomized females, and doxycycline-inducible Tnnt2-controlled Cx43 knockout without or with acute post-ischemic E2 treatment) were subjected to simulated I/R in culture or Langendorff I/R (25-min warm ischemia/40-min reperfusion), respectively. Mitochondrial membrane potential and mitochondrial superoxide production were measured in cardiomyocytes. Myocardial function and infarct size were determined. Cx43 and its isoform, Gja1-20k, were assessed in mitochondria. Immunoelectron microscopy and co-immunoprecipitation were also used to examine mitochondrial Cx43 and its interaction with estrogen receptor-α by E2 in mitochondria, respectively. There were sex disparities in stress-induced cardiomyocyte mitochondrial function. E2 partially restored mitochondrial activity in cardiomyocytes following acute injury. Post-ischemia infusion of E2 improved functional recovery and reduced infarct size with increased Cx43 content and phosphorylation in mitochondria. Ablation of cardiac Cx43 aggravated mitochondrial damage and abolished E2-mediated cardiac protection during I/R. Female mice were more resistant to myocardial I/R than age-matched males with greater protective role of mitochondrial Cx43 in female hearts. Post-ischemic E2 usage augmented mitochondrial Cx43 content and phosphorylation, increased mitochondrial Gja1-20k, and showed cardiac protection.

Effects of cholesterol levels on outcomes of out-of-hospital cardiac arrest: a cross-sectional study

Objective

High cholesterol level is a risk factor for coronary artery disease, and coronary artery disease is a major risk factor for out-of-hospital cardiac arrest (OHCA). However, the effect of cholesterol level on outcomes of OHCA has been poorly studied. This study aimed to determine the effect of cholesterol level on outcomes of OHCA.

Methods

This cross-sectional study used the CAPTURES (Cardiac Arrest Pursuit Trial with Unique Registration and Epidemiologic Surveillance) project database in Korea. Multivariable conditional logistic regression analysis was performed to estimate the effect of cholesterol level on outcomes in OHCA.

Results

In all, 584 cases of OHCA were analyzed; those with cholesterol levels <120 mg/dL were classified as having low total cholesterol (TC) (n=197), those with levels ranging from 120–199 mg/dL as middle TC (n=322), and those with ≥200 mg/dL as high TC (n=65). Compared to low TC, more patients with middle TC and high TC survived to discharge (9.1% vs. 22.0% and 26.2%, respectively, P=0.001). The good cerebral performance category also increased in that order (4.1 % vs. 14.6% and 23.1%, respectively, P≤0.001). Comparing middle TC and high TC with low TC, adjusted odds ratios (95% confidence intervals) were 1.97 (1.06 to 3.64) and 2.53 (1.08 to 5.92) for survival to discharge, respectively, and 2.53 (1.07 to 5.98) and 4.73 (1.63 to 13.71) for good neurological recovery, respectively.

Conclusion

Higher cholesterol is associated with better outcomes in OHCA; cholesterol level is a good predictor of outcomes of OHCA.

Hurdles to Cardioprotection in the Critically Ill

Cardiovascular disease is the largest contributor to worldwide mortality, and the deleterious impact of heart failure (HF) is projected to grow exponentially in the future. As heart transplantation (HTx) is the only effective treatment for end-stage HF, development of mechanical circulatory support (MCS) technology has unveiled additional therapeutic options for refractory cardiac disease. Unfortunately, despite both MCS and HTx being quintessential treatments for significant cardiac impairment, associated morbidity and mortality remain high. MCS technology continues to evolve, but is associated with numerous disturbances to cardiac function (e.g., oxidative damage, arrhythmias). Following MCS intervention, HTx is frequently the destination option for survival of critically ill cardiac patients. While effective, donor hearts are scarce, thus limiting HTx to few qualifying patients, and HTx remains correlated with substantial post-HTx complications. While MCS and HTx are vital to survival of critically ill cardiac patients, cardioprotective strategies to improve outcomes from these treatments are highly desirable. Accordingly, this review summarizes the current status of MCS and HTx in the clinic, and the associated cardiac complications inherent to these treatments. Furthermore, we detail current research being undertaken to improve cardiac outcomes following MCS/HTx, and important considerations for reducing the significant morbidity and mortality associated with these necessary treatment strategies.

Caveolins as Regulators of Stress Adaptation

Caveolins have been recognized over the past few decades as key regulators of cell physiology. They are ubiquitously expressed and regulate a number of processes that ultimately impact efficiency of cellular processes. Though not critical to life, they are central to stress adaptation in a number of organs. The following review will focus specifically on the role of caveolin in stress adaptation in the heart, brain, and eye, three organs that are susceptible to acute and chronic stress and that show as well declining function with age. In addition, we consider some novel molecular mechanisms that may account for this stress adaptation and also offer potential to drive the future of caveolin research.

Delta Opioid Receptors and Cardioprotection

The opioid receptor family, with associated endogenous ligands, has numerous roles throughout the body. Moreover, the delta opioid receptor (DORs) has various integrated roles within the physiological systems, including the cardiovascular system. While DORs are important modulators of cardiovascular autonomic balance, they are well-established contributors to cardioprotective mechanisms. Both endogenous and exogenous opioids acting upon DORs have roles in myocardial hibernation and protection against ischaemia-reperfusion (I-R) injury. Downstream signalling mechanisms governing protective responses alternate, depending on the timing and duration of DOR activation. The following review describes models and mechanisms of DOR-mediated cardioprotection, the impact of co-morbidities and challenges for clinical translation.

Myocyte membrane and microdomain modifications in diabetes: determinants of ischemic tolerance and cardioprotection

Cardiovascular disease, predominantly ischemic heart disease (IHD), is the leading cause of death in diabetes mellitus (DM). In addition to eliciting cardiomyopathy, DM induces a ‘wicked triumvirate’: (i) increasing the risk and incidence of IHD and myocardial ischemia; (ii) decreasing myocardial tolerance to ischemia–reperfusion (I–R) injury; and (iii) inhibiting or eliminating responses to cardioprotective stimuli. Changes in ischemic tolerance and cardioprotective signaling may contribute to substantially higher mortality and morbidity following ischemic insult in DM patients. Among the diverse mechanisms implicated in diabetic impairment of ischemic tolerance and cardioprotection, changes in sarcolemmal makeup may play an overarching role and are considered in detail in the current review. Observations predominantly in animal models reveal DM-dependent changes in membrane lipid composition (cholesterol and triglyceride accumulation, fatty acid saturation vs. reduced desaturation, phospholipid remodeling) that contribute to modulation of caveolar domains, gap junctions and T-tubules. These modifications influence sarcolemmal biophysical properties, receptor and phospholipid signaling, ion channel and transporter functions, contributing to contractile and electrophysiological dysfunction, cardiomyopathy, ischemic intolerance and suppression of protective signaling. A better understanding of these sarcolemmal abnormalities in types I and II DM (T1DM, T2DM) can inform approaches to limiting cardiomyopathy, associated IHD and their consequences. Key knowledge gaps include details of sarcolemmal changes in models of T2DM, temporal patterns of lipid, microdomain and T-tubule changes during disease development, and the precise impacts of these diverse sarcolemmal modifications. Importantly, exercise, dietary, pharmacological and gene approaches have potential for improving sarcolemmal makeup, and thus myocyte function and stress-resistance in this ubiquitous metabolic disorder.

Cavin-1 deficiency modifies myocardial and coronary function, stretch responses and ischaemic tolerance: roles of NOS over-activity

Caveolae and associated cavin and caveolins may govern myocardial function, together with responses to mechanical and ischaemic stresses. Abnormalities in these proteins are also implicated in different cardiovascular disorders. However, specific roles of the cavin-1 protein in cardiac and coronary responses to mechanical/metabolic perturbation remain unclear. We characterised cardiovascular impacts of cavin-1 deficiency, comparing myocardial and coronary phenotypes and responses to stretch and ischaemia-reperfusion in hearts from cavin-1 ^+/+ and cavin-1 ^-/- mice. Caveolae and caveolins 1 and 3 were depleted in cavin-1 ^-/- hearts. Cardiac ejection properties in situ were modestly reduced in cavin-1 ^-/- mice. While peak contractile performance in ex vivo myocardium from cavin-1 ^-/- and cavin-1 ^+/+ mice was comparable, intrinsic beating rate, diastolic stiffness and Frank-Starling behaviour (stretch-dependent diastolic and systolic forces) were exaggerated in cavin-1 ^-/- hearts. Increases in stretch-dependent forces were countered by NOS inhibition (100 µM L-NAME), which exposed negative inotropy in cavin-1 ^-/- hearts, and were mimicked by 100 µM nitroprusside. In contrast, chronotropic differences appeared largely NOS-independent. Cavin-1 deletion also induced NOS-dependent coronary dilatation, ≥3-fold prolongation of reactive hyperaemic responses, and exaggerated pressure-dependence of coronary flow. Stretch-dependent efflux of lactate dehydrogenase and cardiac troponin I was increased and induction of brain natriuretic peptide and c-Fos inhibited in cavin-1 ^-/- hearts, while ERK1/2 phospho-activation was preserved. Post-ischaemic dysfunction and damage was also exaggerated in cavin-1 ^-/- hearts. Diverse effects of cavin-1 deletion reveal important roles in both NOS-dependent and -independent control of cardiac and coronary functions, together with governing sarcolemmal fragility and myocardial responses to stretch and ischaemia.

TIR/BB-loop mimetic AS-1 attenuates cardiac ischemia/reperfusion injury via a caveolae and caveolin-3-dependent mechanism

AS-1, the TIR/BB loop mimetic, plays a protective role in cardiac ischemia/reperfusion (I/R) but the molecular mechanism remains unclear. The muscle specific caveolin3 (Cav-3) and the caveolae have been found to be critical for cardioprotection. This study aimed to evaluate our hypothesis that caveolae and Cav-3 are essential for AS-1-induced cardioprotection against myocardial I/R injury. To address these issues, we analyzed the involvement of Cav-3 in AS-1 mediated cardioprotection both in vivo and in vitro. We demonstrate that AS-1 administration significantly decreased infarct size, improved cardiac function after myocardial I/R and modulated membrane caveolae and Cav-3 expression in the myocardium. For in vitro studies, AS-1 treatment prevented Cav-3 re-distribution induced by H/R injury. In contrast, disruption of caveolae by MCD treatment or Cav-3 knockdown abolished the protection against H/R-induced myocytes injury by AS-1. Our findings reveal that AS-1 attenuates myocardial I/R injury through caveolae and Cav-3 dependent mechanism.

Cardioprotective kinase signaling to subsarcolemmal and interfibrillar mitochondria is mediated by caveolar structures

The demonstration that caveolin-3 overexpression reduces myocardial ischemia/reperfusion injury and our own finding that multiprotein signaling complexes increase in mitochondria in association with caveolin-3 levels, led us to investigate the contribution of caveolae-driven extracellular signal-regulated kinases 1/2 (ERK1/2) on maintaining the function of cardiac mitochondrial subpopulations from reperfused hearts subjected to postconditioning (PostC). Rat hearts were isolated and subjected to ischemia/reperfusion and to PostC. Enhanced cardiac function, reduced infarct size and preserved ultrastructure of cardiomyocytes were associated with increased formation of caveolar structures, augmented levels of caveolin-3 and mitochondrial ERK1/2 activation in PostC hearts in both subsarcolemmal (SSM) and interfibrillar (IFM) subpopulations. Disruption of caveolae with methyl-β-cyclodextrin abolished cardioprotection in PostC hearts and diminished pho-ERK1/2 gold-labeling in both mitochondrial subpopulations in correlation with suppression of resistance to permeability transition pore opening. Also, differences between the mitochondrial subpopulations in the setting of PostC were evaluated. Caveolae disruption with methyl-β-cyclodextrin abolished the cardioprotective effect of postconditioning by inhibiting the interaction of ERK1/2 with mitochondria and promoted decline in mitochondrial function. SSM, which are particularly sensitive to reperfusion damage, take advantage of their location in cardiomyocyte boundary and benefit from the cardioprotective signaling driven by caveolae, avoiding injury propagation.

The mitochondrial permeability transition pore in AD 2016: An update

Over the past 30years the mitochondrial permeability transition - the permeabilization of the inner mitochondrial membrane due to the opening of a wide pore - has progressed from being considered a curious artifact induced in isolated mitochondria by Ca(2+) and phosphate to a key cell-death-inducing process in several major pathologies. Its relevance is by now universally acknowledged and a pharmacology targeting the phenomenon is being developed. The molecular nature of the pore remains to this day uncertain, but progress has recently been made with the identification of the FOF1 ATP synthase as the probable proteic substrate. Researchers sharing this conviction are however divided into two camps: these believing that only the ATP synthase dimers or oligomers can form the pore, presumably in the contact region between monomers, and those who consider that the ring-forming c subunits in the FO sector actually constitute the walls of the pore. The latest development is the emergence of a new candidate: Spastic Paraplegia 7 (SPG7), a mitochondrial AAA-type membrane protease which forms a 6-stave barrel. This review summarizes recent developments of research on the pathophysiological relevance and on the molecular nature of the mitochondrial permeability transition pore. This article is part of a Special Issue entitled: Mitochondrial Channels edited by Pierre Sonveaux, Pierre Maechler and Jean-Claude Martinou.

Sarcolemmal dependence of cardiac protection and stress-resistance: roles in aged or diseased hearts

Disruption of the sarcolemmal membrane is a defining feature of oncotic death in cardiac ischaemia-reperfusion (I-R), and its molecular makeup not only fundamentally governs this process but also affects multiple determinants of both myocardial I-R injury and responsiveness to cardioprotective stimuli. Beyond the influences of membrane lipids on the cytoprotective (and death) receptors intimately embedded within this bilayer, myocardial ionic homeostasis, substrate metabolism, intercellular communication and electrical conduction are all sensitive to sarcolemmal makeup, and critical to outcomes from I-R. As will be outlined in this review, these crucial sarcolemmal dependencies may underlie not only the negative effects of age and common co-morbidities on myocardial ischaemic tolerance but also the on-going challenge of implementing efficacious cardioprotection in patients suffering accidental or surgically induced I-R. We review evidence for the involvement of sarcolemmal makeup changes in the impairment of stress-resistance and cardioprotection observed with ageing and highly prevalent co-morbid conditions including diabetes and hypercholesterolaemia. A greater understanding of membrane changes with age/disease, and the inter-dependences of ischaemic tolerance and cardioprotection on sarcolemmal makeup, can facilitate the development of strategies to preserve membrane integrity and cell viability, and advance the challenging goal of implementing efficacious 'cardioprotection' in clinically relevant patient cohorts. Linked Articles This article is part of a themed section on Molecular Pharmacology of G Protein-Coupled Receptors. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v173.20/issuetoc.

Cholesterol Depletion Alters Cardiomyocyte Subcellular Signaling and Increases Contractility

Membrane cholesterol levels play an important factor in regulating cell function. Sarcolemmal cholesterol is concentrated in lipid rafts and caveolae, which are flask-shaped invaginations of the plasma membrane. The scaffolding protein caveolin permits the enrichment of cholesterol in caveolae, and caveolin interactions with numerous proteins regulate their function. The purpose of this study was to determine whether acute reductions in cardiomyocyte cholesterol levels alter subcellular protein kinase activation, intracellular Ca²⁺ and contractility. Methods: Ventricular myocytes, isolated from adult Sprague Dawley rats, were treated with the cholesterol reducing agent methyl-β-cyclodextrin (MβCD, 5 mM, 1 hr, room temperature). Total cellular cholesterol levels, caveolin-3 localization, subcellular, ERK and p38 mitogen activated protein kinase (MAPK) signaling, contractility, and [Ca²⁺]i were assessed. Results: Treatment with MβCD reduced cholesterol levels by ~45 and shifted caveolin-3 from cytoskeleton and triton-insoluble fractions to the triton-soluble fraction, and increased ERK isoform phosphorylation in cytoskeletal, cytosolic, triton-soluble and triton-insoluble membrane fractions without altering their subcellular distributions. In contrast the primary effect of MβCD was on p38 subcellular distribution of p38α with little effect on p38 phosphorylation. Cholesterol depletion increased cardiomyocyte twitch amplitude and the rates of shortening and relaxation in conjunction with increased diastolic and systolic [Ca²⁺]i. Conclusions: These results indicate that acute reductions in membrane cholesterol levels differentially modulate basal cardiomyocyte subcellular MAPK signaling, as well as increasing [Ca²⁺]_i and contractility.

Chronic β1-adrenoceptor blockade impairs ischaemic tolerance and preconditioning in murine myocardium

β-adrenoceptor antagonists are commonly used in ischaemic heart disease (IHD) patients, yet may impair signalling and efficacy of 'cardioprotective' interventions. We assessed effects of chronic β1-adrenoceptor antagonism on myocardial resistance to ischaemia-reperfusion (IR) injury and the ability of cardioprotective interventions [classic ischaemic preconditioning (IPC); novel sustained ligand-activated preconditioning (SLP)] to reduce IR injury in murine hearts. Young male C57Bl/6 mice were untreated or received atenolol (0.5g/l in drinking water) for 4 weeks. Subsequently, two cardioprotective stimuli were evaluated: morphine pellets implanted (to induce SLP, controls received placebo) 5 days prior to Langendorff heart perfusion, and IPC in perfused hearts (3×1.5min ischaemia/2min reperfusion). Atenolol significantly reduced in vivo heart rate. Untreated control hearts exhibited substantial left ventricular dysfunction (~50% pressure development recovery, ~20mmHg diastolic pressure rise) with significant release of lactate dehydrogenase (LDH, tissue injury indicator) after 25min ischaemia/45min reperfusion. Contractile dysfunction and elevated LDH were reduced >50% with IPC and SLP. While atenolol treatment did not modify baseline contractile function, post-ischaemic function was significantly depressed compared to untreated hearts. Atenolol pre-treatment abolished beneficial effects of IPC, whereas SLP protection was preserved. These data indicate that chronic β1-adrenoceptor blockade can exert negative effects on functional IR tolerance and negate conventional IPC (implicating β1-adrenoceptors in IR injury and IPC signalling). However, novel morphine-induced SLP is resistant to inhibition by β1-adrenoceptor antagonism.

Caveolin-1/-3: therapeutic targets for myocardial ischemia/reperfusion injury

Myocardial ischemia/reperfusion (I/R) injury is a major cause of morbidity and mortality worldwide. Caveolae, caveolin-1 (Cav-1), and caveolin-3 (Cav-3) are essential for the protective effects of conditioning against myocardial I/R injury. Caveolins are membrane-bound scaffolding proteins that compartmentalize and modulate signal transduction. In this review, we introduce caveolae and caveolins and briefly describe the interactions of caveolins in the cardiovascular diseases. We also review the roles of Cav-1/-3 in protection against myocardial ischemia and I/R injury, and in conditioning. Finally, we suggest several potential research avenues that may be of interest to clinicians and basic scientists. The information included, herein, is potentially useful for the design of future studies and should advance the investigation of caveolins as therapeutic targets.

Electrophysiology and metabolism of caveolin-3-overexpressing mice

Caveolin-3 (Cav-3) plays a critical role in organizing signaling molecules and ion channels involved in cardiac conduction and metabolism. Mutations in Cav-3 are implicated in cardiac conduction abnormalities and myopathies. Additionally, cardiac-specific overexpression of Cav-3 (Cav-3 OE) is protective against ischemic and hypertensive injury, suggesting a potential role for Cav-3 in basal cardiac electrophysiology and metabolism involved in stress adaptation. We hypothesized that overexpression of Cav-3 may alter baseline cardiac conduction and metabolism. We examined: (1) ECG telemetry recordings at baseline and during pharmacological interventions, (2) ion channels involved in cardiac conduction with immunoblotting and computational modeling, and (3) baseline metabolism in Cav-3 OE and transgene-negative littermate control mice. Cav-3 OE mice had decreased heart rates, prolonged PR intervals, and shortened QTc intervals with no difference in activity compared to control mice. Dobutamine or propranolol did not cause significant changes between experimental groups in maximal (dobutamine) or minimal (propranolol) heart rate. Cav-3 OE mice had an overall lower chronotropic response to atropine. The expression of Kv1.4 and Kv4.3 channels, Nav1.5 channels, and connexin 43 were increased in Cav-3 OE mice. A computational model integrating the immunoblotting results indicated shortened action potential duration in Cav-3 OE mice linking the change in channel expression to the observed electrophysiology phenotype. Metabolic profiling showed no gross differences in VO2, VCO2, respiratory exchange ratio, heat generation, and feeding or drinking. In conclusion, Cav-3 OE mice have changes in ECG intervals, heart rates, and cardiac ion channel expression. These findings give novel mechanistic insights into previously reported Cav-3 dependent cardioprotection.

δ-Opioid receptor (DOR) signaling and reactive oxygen species (ROS) mediate intermittent hypoxia induced protection of canine myocardium

Intermittent, normobaric hypoxia confers robust cardioprotection against ischemia-induced myocardial infarction and lethal ventricular arrhythmias. δ-Opioid receptor (DOR) signaling and reactive oxygen species (ROS) have been implicated in cardioprotective phenomena, but their roles in intermittent hypoxia are unknown. This study examined the contributions of DOR and ROS in mediating intermittent hypoxia-induced cardioprotection. Mongrel dogs completed a 20 day program consisting of 5-8 daily, 5-10 min cycles of moderate, normobaric hypoxia (FIO2 0.095-0.10), with intervening 4 min room air exposures. Subsets of dogs received the DOR antagonist naltrindole (200 μg/kg, sc) or antioxidant N-acetylcysteine (250 mg/kg, po) before each hypoxia session. Twenty-four hours after the last session, the left anterior descending coronary artery was occluded for 60 min and then reperfused for 5 h. Arrhythmias detected by electrocardiography were scored according to the Lambeth II conventions. Left ventricles were sectioned and stained with 2,3,5-triphenyl-tetrazolium-chloride, and infarct sizes were expressed as percentages of the area at risk (IS/AAR). Intermittent hypoxia sharply decreased IS/AAR from 41 ± 5 % (n = 12) to 1.8 ± 0.9 % (n = 9; P < 0.001) and arrhythmia score from 4.1 ± 0.3 to 0.7 ± 0.2 (P < 0.001) vs. non-hypoxic controls. Naltrindole (n = 6) abrogated the cardioprotection with IS/AAR 35 ± 5 % and arrhythmia score 3.7 ± 0.7 (P < 0.001 vs. untreated intermittent hypoxia). N-acetylcysteine (n = 6) interfered to a similar degree, with IS/AAR 42 ± 3 % and arrhythmia score 4.7 ± 0.3 (P < 0.001 vs. untreated intermittent hypoxia). Without the intervening reoxygenations, hypoxia (n = 4) was not cardioprotective (IS/AAR 50 ± 8 %; arrhythmia score 4.5 ± 0.5; P < 0.001 vs. intermittent hypoxia). Thus DOR, ROS and cyclic reoxygenation were obligatory participants in the gradually evolving cardioprotection produced by intermittent hypoxia.

Endogenous opiates and behavior: 2014

This paper is the thirty-seventh consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2014 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (endogenous opioids and receptors), and the roles of these opioid peptides and receptors in pain and analgesia (pain and analgesia); stress and social status (human studies); tolerance and dependence (opioid mediation of other analgesic responses); learning and memory (stress and social status); eating and drinking (stress-induced analgesia); alcohol and drugs of abuse (emotional responses in opioid-mediated behaviors); sexual activity and hormones, pregnancy, development and endocrinology (opioid involvement in stress response regulation); mental illness and mood (tolerance and dependence); seizures and neurologic disorders (learning and memory); electrical-related activity and neurophysiology (opiates and conditioned place preferences (CPP)); general activity and locomotion (eating and drinking); gastrointestinal, renal and hepatic functions (alcohol and drugs of abuse); cardiovascular responses (opiates and ethanol); respiration and thermoregulation (opiates and THC); and immunological responses (opiates and stimulants). This paper is the thirty-seventh consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2014 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (endogenous opioids and receptors), and the roles of these opioid peptides and receptors in pain and analgesia (pain and analgesia); stress and social status (human studies); tolerance and dependence (opioid mediation of other analgesic responses); learning and memory (stress and social status); eating and drinking (stress-induced analgesia); alcohol and drugs of abuse (emotional responses in opioid-mediated behaviors); sexual activity and hormones, pregnancy, development and endocrinology (opioid involvement in stress response regulation); mental illness and mood (tolerance and dependence); seizures and neurologic disorders (learning and memory); electrical-related activity and neurophysiology (opiates and conditioned place preferences (CPP)); general activity and locomotion (eating and drinking); gastrointestinal, renal and hepatic functions (alcohol and drugs of abuse); cardiovascular responses (opiates and ethanol); respiration and thermoregulation (opiates and THC); and immunological responses (opiates and stimulants).

Inhibition of PKCβ2 overexpression ameliorates myocardial ischaemia/reperfusion injury in diabetic rats via restoring caveolin-3/Akt signaling

Activation of PKCβ (protein kinase Cβ) plays a critical role in myocardial I/R (ischaemia/reperfusion) injury in non-diabetic rodents. In the myocardium of diabetes, PKCβ2 overexpression is associated with increased vulnerability to post-ischaemic I/R injury with concomitantly impaired cardiomyocyte Cav (caveolin)-3 and Akt signalling compared with non-diabetic rats. We hypothesized that myocardial PKCβ overexpression in diabetes exacerbates myocardial I/R injury through impairing Cav-3/Akt signalling. Streptozotocin-induced diabetic rats were treated with the selective PKCβ inhibitor ruboxistaurin (RBX, 1 mg/kg per day) for 4 weeks, starting from 1 week after diabetes induction, before inducing myocardial I/R achieved by occluding the left descending coronary artery followed by reperfusion. Cardiac function was measured using a pressure-volume conductance system. In an in vitro study, cardiac H9C2 cells were exposed to high glucose (30 mmol/l) and subjected to hypoxia followed by reoxygenation (H/R) in the presence or absence of the selective PKCβ2 inhibitor CGP53353 (1 μmol/l), siRNAs of PKCβ2 or Cav-3 or Akt. Cell apoptosis and mitochondrial membrane potential were assessed by TUNEL (terminal deoxynucleotidyltransferase-mediated dUTP nick-end labelling) and JC-1 staining respectively. RBX significantly decreased post-ischaemic myocardial infarct size (35±5% compared with 49±3% in control, P<0.05) and attenuated cardiac dysfunction, and prevented the reduction in cardiac Cav-3 and enhanced phosphorylated/activated Akt (p-Akt) in diabetic rats (P<0.05). H/R increased cardiomyocyte injury under high glucose conditions as was evident by increased TUNEL-positive and increased JC-1 monomeric cells (P<0.05 compared with control), accompanied with increased PKCβ2 phosphorylation/activation and decreased Cav-3 expression. Either CGP53353 or PKCβ2 siRNA significantly attenuated all of these changes and enhanced p-Akt. Cav-3 gene knockdown significantly reduced p-Akt and increased post-hypoxic cellular and mitochondrial injury despite a concomitant reduction in PKCβ2 phosphorylation. PKCβ2 inhibition with RBX protects diabetic hearts from myocardial I/R injury through Cav-3-dependent activation of Akt.

Opioid receptors and cardioprotection - 'opioidergic conditioning' of the heart

Ischaemic heart disease (IHD) remains a major cause of morbidity/mortality globally, firmly established in Westernized or 'developed' countries and rising in prevalence in developing nations. Thus, cardioprotective therapies to limit myocardial damage with associated ischaemia-reperfusion (I-R), during infarction or surgical ischaemia, is a very important, although still elusive, clinical goal. The opioid receptor system, encompassing the δ (vas deferens), κ (ketocyclazocine) and μ (morphine) opioid receptors and their endogenous opioid ligands (endorphins, dynorphins, enkephalins), appears as a logical candidate for such exploitation. This regulatory system may orchestrate organism and organ responses to stress, induces mammalian hibernation and associated metabolic protection, triggers powerful adaptive stress resistance in response to ischaemia/hypoxia (preconditioning), and mediates cardiac benefit stemming from physical activity. In addition to direct myocardial actions, central opioid receptor signalling may also enhance the ability of the heart to withstand I-R injury. The δ- and κ-opioid receptors are strongly implicated in cardioprotection across models and species (including anti-infarct and anti-arrhythmic actions), with mixed evidence for μ opioid receptor-dependent protection in animal and human tissues. A small number of clinical trials have provided evidence of cardiac benefit from morphine or remifentanil in cardiopulmonary bypass or coronary angioplasty patients, although further trials of subtype-specific opioid receptor agonists are needed. The precise roles and utility of this GPCR family in healthy and diseased human myocardium, and in mediating central and peripheral survival responses, warrant further investigation, as do the putative negative influences of ageing, IHD co-morbidities, and relevant drugs on opioid receptor signalling and protective responses.

Opioid receptors and cardioprotection - 'opioidergic conditioning' of the heart

Ischaemic heart disease (IHD) remains a major cause of morbidity/mortality globally, firmly established in Westernized or 'developed' countries and rising in prevalence in developing nations. Thus, cardioprotective therapies to limit myocardial damage with associated ischaemia-reperfusion (I-R), during infarction or surgical ischaemia, is a very important, although still elusive, clinical goal. The opioid receptor system, encompassing the δ (vas deferens), κ (ketocyclazocine) and μ (morphine) opioid receptors and their endogenous opioid ligands (endorphins, dynorphins, enkephalins), appears as a logical candidate for such exploitation. This regulatory system may orchestrate organism and organ responses to stress, induces mammalian hibernation and associated metabolic protection, triggers powerful adaptive stress resistance in response to ischaemia/hypoxia (preconditioning), and mediates cardiac benefit stemming from physical activity. In addition to direct myocardial actions, central opioid receptor signalling may also enhance the ability of the heart to withstand I-R injury. The δ- and κ-opioid receptors are strongly implicated in cardioprotection across models and species (including anti-infarct and anti-arrhythmic actions), with mixed evidence for μ opioid receptor-dependent protection in animal and human tissues. A small number of clinical trials have provided evidence of cardiac benefit from morphine or remifentanil in cardiopulmonary bypass or coronary angioplasty patients, although further trials of subtype-specific opioid receptor agonists are needed. The precise roles and utility of this GPCR family in healthy and diseased human myocardium, and in mediating central and peripheral survival responses, warrant further investigation, as do the putative negative influences of ageing, IHD co-morbidities, and relevant drugs on opioid receptor signalling and protective responses.

Investigation of therapeutic potential and molecular mechanism of vitamin P and digoxin in I/R-induced myocardial infarction in rat

Ischemic-reperfusion (I/R) is a major event in the pathogenesis of ischemic heart disease that leads to higher rate of mortality. The study has been designed to investigate the therapeutic potential and molecular mechanism of vitamin P and digoxin in I/R-induced myocardial infarction in isolated rat heart preparation by using Langendorff apparatus. The animals were treated with vitamin P (50 and 100 mg/kg; p.o.) and digoxin (500 μg/kg) for 5 consecutive days. Digoxin served as a positive control in the present study. On the sixth day, the heart was harvested and induced to 30 min of global ischemia followed by 120 min of reperfusion using Langendorff apparatus. The coronary effluent was collected at different time intervals (i.e. basal, 1, 15, 30, 45, 60 and 120 min.) for the assessment of myocardial contractility function. In addition, creatine kinase-M and B subunits (CK-MB), lactate dehydrogenase (LDH1) and Na(+)-K(+)-ATPase activity along with oxidative tissue biomarkers (i.e. thio-barbituric acid reactive substances (TBARS) and reduced glutathione (GSH)) changes were estimated. The I/R of myocardium produced decrease in coronary flow rate; increase in CK-MB, LDH1 and Na(+)-K(+)-ATPase activity along with increase in TBARS and decrease in GSH levels as compared to normal group. The treatment with vitamin P (100 mg/kg) and digoxin (500 μg/kg) have produced a significant (p < 0.05) ameliorative effect against I/R induced above functional, metabolic and tissue biomarkers changes. Vitamin P has an ameliorative potential against I/R induced myocardial functional changes. It may be due to its free radical scavenging and anti-infarct property via inhibition of Na(+)-K(+)-ATPase activity. Therefore, it can be used as a potential therapeutic medicine for the management of cardiovascular disorders.