Hydrogen sulfide potentiates the protective effects of nitrite against myocardial ischemia-reperfusion injury in type 2 diabetic rats.

Decreased heart levels of nitric oxide (NO) and hydrogen sulfide (H2S) in type 2 diabetes (T2D) are associated with a higher risk of mortality following ischemia-reperfusion (IR) injury. This study aimed to determine the effects of co-administration of sodium nitrite and sodium hydrosulfide (NaSH) on IR injury in the isolated heart from rats with T2D. Two-month-old male rats were divided into 5 groups (n = 7/group): Control, T2D, T2D + nitrite, T2D + NaSH, and T2D + nitrite + NaSH. T2D was induced using a high-fat diet and a single low dose streptozotocin (30 mg/kg) in intraperitoneal injection. Nitrite (50 mg/L in drinking water) and NaSH (0.28 mg/kg, daily intraperitoneal injection) were administrated for 9 weeks. At the end of the study, hemodynamic parameters were recorded, and infarct size and mRNA expression of H2S- and NO-producing enzymes were measured in the isolated hearts. Nitrite administration to rats with T2D improved recovery of left ventricular developed pressure (LVDP) and the peak rates of positive and negative changes in LV pressure (±dp/dt) by 30%, 17%, and 7.9%, respectively, and decreased infarct size by 18.4%. Co-administration of nitrite and NaSH resulted in further improve in recovery of LVDP, +dp/dt, and -dp/dt by 8.3% (P = 0.0478), 8.4% (P = 0.0085), and 9.0% (P = 0.0004), respectively, and also further decrease in infarct size by 24% (P = 0.0473). Nitrite treatment decreased inducible and neuronal NO synthases (iNOS, 0.4-fold; nNOS, 0.4-fold) and cystathionine ß-synthase (CBS, 0.1-fold) expression in the isolated heart from rats with T2D. Co-administration of nitrite and NaSH further increased cystathionine γ-lyase (CSE, 2.8-fold) and endothelial NOS (eNOS, 2.0-fold) expression and further decreased iNOS (0.4-fold) expression. In conclusion, NaSH at a low dose potentiates the favorable effects of inorganic nitrite against myocardial IR injury in a rat model of T2D. These anti-ischemic effects, following co-administration of nitrite and NaSH, were associated with higher CSE-derived H2S and eNOS-derived NO as well as lower iNOS-derived NO in the diabetic hearts.

Hepatic Remote Ischemic Preconditioning (RIPC) Protects Heart Damages Induced by Ischemia Reperfusion Injury in Mice.

It has been convincingly demonstrated that remote ischemic preconditioning (RIPC) can make the myocardium resistant to the subsequent ischemia reperfusion injury (IRI), which causes severe damages by mainly generating cell death. However, the cardioprotective effects of the hepatic RIPC, which is the largest metabolic organ against I/R, have not been fully studied. The aim of our research is whether remote liver RIPC may provide cardioprotective effects against the I/R-induced injury. Here, we generated an I/R mice model in four groups to analyze the effect. The control group is the isolated hearts with 140-min perfusion. I/R group added ischemia in 30 min following 90-min reperfusion. The third group (sham) was subjected to the same procedure as the latter group. The animals in the fourth group selected as the treatment group, underwent a hepatic RIPC by three cycles of 5-min occlusion of the portal triad and then followed by induction of I/R in the isolated heart. The level of myocardial infarction and the preventive effects of RIPC were assessed by pathological characteristics, namely, infarct, enzyme releases, pressure, and cardiac mechanical activity. Subjected to I/R, the hepatic RIPC minimized the infarct size (17.7 ± 4.96 vs. 50.06 ± 5, p < 0.001) and improved the left ventricular-developed pressure (from 47.42 ± 6.27 to 91.62 ± 5.22 mmHg) and the mechanical activity. Release of phosphocreatine kinase-myocardial band (73.86 ± 1.95 vs. 25.93 ± 0.66 IUL-1) and lactate dehydrogenase (299.01 ± 10.7 vs. 152.3 ± 16.7 IUL-1) was also decreased in the RIPC-treated group. These results demonstrate the cardioprotective effects of the hepatic remote preconditioning against the injury caused by I/R in the isolated perfused hearts.

Cardioprotective mechanisms of mitochondria-targeted S-nitrosating agent and adenosine triphosphate-sensitive potassium channel opener are mutually exclusive.

Background: Myocytes exposed to stress exhibit significant swelling and reduced contractility. These consequences are ameliorated by adenosine triphosphate-sensitive potassium (KATP) channel opener diazoxide (DZX) via an unknown mechanism. KATP channel openers also provide cardioprotection in multiple animal models. Nitric oxide donors are similarly cardioprotective, and their combination with KATP activation may provide synergistic benefit. We hypothesized that mitochondria-targeted S-nitrosating agent (MitoSNO) would provide synergistic cardioprotection with DZX. Methods: Myocyte volume and contractility were compared following Tyrode's physiologic solution (20 minutes) and stress (hyperkalemic cardioplegia [CPG] ± DZX; n = 5-20 each; 20 minutes) with or without MitoSNO (n = 5-11 each) at the end of stress, followed by Tyrode's solution (20 minutes). Isolated mouse hearts received CPG ± DZX (n = 8-10 each) before global ischemia (90 minutes) with or without MitoSNO (n = 8 each) at the end of ischemia, followed by reperfusion (30 minutes). Left ventricular (LV) pressures were compared using a linear mixed model to assess the impact of treatment on the outcome, adjusting for baseline and balloon volume. Results: Stress (CPG) was associated with reduced myocyte contractility that was prevented by DZX and MitoSNO individually; however, their combination was associated with loss of cardioprotection. Similarly, DZX and MitoSNO improved LV function after prolonged ischemia compared with CPG alone, and cardioprotection was lost with their combination. Conclusions: MitoSNO and DZX provide cardioprotection that is lost with their combination, suggesting mutually exclusive mechanisms of action. The lack of a synergistic beneficial effect informs the current knowledge of the cardioprotective mechanisms of DZX and will aid planning of future clinical trials.

Deletion of Sulfonylurea Receptor 2 in the Adult Myocardium Enhances Cardiac Glucose Uptake and Is Cardioprotective.

The adult myocardium relies on oxidative metabolism. In ischemic myocardium, such as the embryonic heart, glycolysis contributes more prominently as a fuel source. The sulfonylurea receptor 2 (SUR2) was previously implicated in the normal myocardial transition from glycolytic to oxidative metabolism that occurs during adaptation to postnatal life. This receptor was now selectively deleted in adult mouse myocardium resulting in protection from ischemia reperfusion injury. SUR2-deleted cardiomyocytes had enhanced glucose uptake, and SUR2 forms a complex with the major glucose transporter. These data identify the SUR2 receptor as a target to shift cardiac metabolism to protect against myocardial injury.

Red Blood Cells in Type 2 Diabetes Impair Cardiac Post-Ischemic Recovery Through an Arginase-Dependent Modulation of Nitric Oxide Synthase and Reactive Oxygen Species.

This study tested the hypothesis that red blood cell (RBC) arginase represents a potential therapeutic target in ischemia-reperfusion in type 2 diabetes. Post-ischemic cardiac recovery was impaired in hearts from db/db mice compared with wild-type hearts. RBCs from mice and patients with type 2 diabetes attenuated post-ischemic cardiac recovery of nondiabetic hearts. This impaired cardiac recovery was reversed by inhibition of RBCs arginase or nitric oxide synthase. The results suggest that RBCs from type 2 diabetics impair cardiac tolerance to ischemia-reperfusion via a pathway involving arginase activity and nitric oxide synthase-dependent oxidative stress.

Kinetics and Signal Activation Properties of Circulating Factor(s) From Healthy Volunteers Undergoing Remote Ischemic Pre-Conditioning.

Although remote ischemic pre-conditioning (RIPC) reduced infarct size in animal experiments and proof-of-concept clinical trials, recent phase III trials failed to confirm cardioprotection during cardiac surgery. Here, we characterized the kinetic properties of humoral factors that are released after RIPC, as well as the signal transduction pathways that were responsible for cardioprotection in an ex vivo model of global ischemia reperfusion injury. Venous blood from 20 healthy volunteers was collected at baseline and 5 min, 30 min, 1 h, 6 h, and daily from 1 to 7 days after RIPC (3 × 5/5 min upper-limb ischemia/reperfusion). Plasma-dialysates (cut-off: 12 to 14 kDa; dilution: 1:20) were infused into Langendorff-perfused mouse hearts subjected to 20/120 min global ischemia/reperfusion. Infarct size and phosphorylation of signal transducer and activator of transcription (STAT)3, STAT5, extracellular-regulated kinase 1/2 and protein kinase B were determined. In a subgroup of plasma-dialysates, an inhibitor of STAT3 (Stattic) was used in mouse hearts. Perfusion with baseline-dialysate resulted in an infarct size of 39% of ventricular mass (interquartile range: 36% to 42%). Perfusion with dialysates obtained 5 min to 6 days after RIPC significantly reduced infarct size by ∼50% and increased STAT3 phosphorylation beyond that with baseline-dialysate. Inhibition of STAT3 abrogated these effects. These results suggest that RIPC induces the release of cardioprotective, dialyzable factor(s) within 5 min, and that circulate for up to 6 days. STAT3 is activated in murine myocardium by RIPC-induced human humoral factors and is causally involved in cardioprotection.

The heart is better protected against myocardial infarction in the fed state compared to the fasted state.

OBJECTIVE: A variety of calorie restriction diets and fasting regimens are popular among overweight people. However, starvation could result in unexpected cardiovascular effects. Therefore, it is necessary to evaluate the short-term effects of diets on cardiovascular function, energy metabolism and potential risk of heart damage in case of myocardial infarction. The objective of the present study was to investigate whether the increased level of glucose oxidation or reduction of fatty acid (FA) load in the fed state provides the basis for protection against myocardial infarction in an experimental rat model of ischemia-reperfusion. MATERIALS/METHODS: We tested the effects of the availability of energy substrates and their metabolites on the heart functionality and energy metabolism under normoxic and ischemia-reperfusion conditions. RESULTS: In a fasted state, the heart draws energy exclusively from FAs, whereas in a fed state, higher concentration of circulating insulin ensures a partial switch to glucose oxidation, while the load of FA on heart and mitochondria is reduced. Herein, we demonstrate that ischemic damage in hearts isolated from Wistar rats and diabetic Goto-Kakizaki rats is significantly lower in the fed state compared to the fasted state. CONCLUSIONS: Present findings indicate that postprandial or fed-state physiology, which is characterised by insulin-activated glucose and lactate utilisation, is protective against myocardial infarction. Energy metabolism pattern in the heart is determined by insulin signalling and the availability of FAs. Overall, our study suggests that even overnight fasting could provoke and aggravate cardiovascular events and high-risk cardiovascular patients should avoid prolonged fasting periods.

Pharmacological characterization of the vascular effects of aryl isothiocyanates: is hydrogen sulfide the real player?

Hydrogen sulfide (H2S) is an endogenous gasotransmitter, which mediates important physiological effects in the cardiovascular system. Accordingly, an impaired production of endogenous H2S contributes to the pathogenesis of important cardiovascular disorders, such as hypertension. Therefore, exogenous compounds, acting as H2S-releasing agents, are viewed as promising pharmacotherapeutic agents for cardiovascular diseases. Thus, this paper aimed at evaluating the H2S-releasing properties of some aryl isothiocyanate derivatives and their vascular effects. The release of H2S was determined by amperometry, spectrophotometry and gas/mass chromatography. Moreover, the vascular activity of selected isothiocyanates were tested in rat conductance (aorta) and coronary arteries. Since H2S has been recently reported to act as an activator of vascular Kv7 potassium channels, the possible membrane hyperpolarizing effects of isothiocyanates were tested on human vascular smooth muscle (VSM) cells by spectrofluorescent dyes. Among the tested compounds, phenyl isothiocyanate (PhNCS) and 4-carboxyphenyl isothiocyanate (PhNCS-COOH) exhibited slow-H2S-release, triggered by organic thiols such as L-cysteine. These compounds were endowed with vasorelaxing effects on conductance and coronary arteries. Moreover, these two isothiocyanates caused membrane hyperpolarization of VSM cells. The vascular effects of isothiocyanates were strongly abolished by the selective Kv7-blocker XE991. In conclusion, the isothiocyanate function can be viewed as a suitable slow H2S-releasing moiety, endowed with vasorelaxing and hypotensive effects, typical of this gasotransmitter. Thus, such a chemical moiety can be employed for the development of novel chemical tools for basic studies and promising cardiovascular drugs.

The novel anti-inflammatory agent VA694, endowed with both NO-releasing and COX2-selective inhibiting properties, exhibits NO-mediated positive effects on blood pressure, coronary flow and endothelium in an experimental model of hypertension and endothelial dysfunction.

Selective cyclooxygenase 2 (COX2) inhibitors (COXIBs) are effective anti-inflammatory and analgesic drugs with improved gastrointestinal (GI) safety compared to nonselective nonsteroidal anti-inflammatory drugs known as traditional (tNSAIDs). However, their use is associated with a cardiovascular (CV) hazard (i.e. increased incidence of thrombotic events and hypertension) due to the inhibition of COX2-dependent vascular prostacyclin. Aiming to design COX2-selective inhibitors with improved CV safety, new NO-releasing COXIBs (NO-COXIBs) have been developed. In these hybrid drugs, the NO-mediated CV effects are expected to compensate for the COXIB-mediated inhibition of prostacyclin. This study evaluates the potential CV beneficial effects of VA694, a promising NO-COXIB, the anti-inflammatory effects of which have been previously characterized in several in vitro and in vivo experimental models. When incubated in hepatic homogenate, VA694 acted as a slow NO-donor. Moreover, it caused NO-mediated relaxant effects in the vascular smooth muscle. The chronic oral administration of VA694 to young spontaneously hypertensive rats (SHRs) significantly slowed down the age-related development of hypertension and was associated with increased plasma levels of nitrates, stable end-metabolites of NO. Furthermore, a significant improvement of coronary flow and a significant reduction of endothelial dysfunction were observed in SHRs submitted to chronic administration of VA694. In conclusion, VA694 is a promising COX2-inhibiting hybrid drug, showing NO releasing properties which may mitigate the CV deleterious effects associated with the COX2-inhibition.

SIRT1 activation by curcumin pretreatment attenuates mitochondrial oxidative damage induced by myocardial ischemia reperfusion injury.

Ischemia reperfusion (IR) injury (IRI) is harmful to the cardiovascular system and causes mitochondrial oxidative stress. Silent information regulator 1 (SIRT1), a type of histone deacetylase, contributes to IRI. Curcumin (Cur) is a strong natural antioxidant and is the active component in Curcuma longa; Cur has protective effects against IRI and may regulate the activity of SIRT1. This study was designed to investigate the protective effect of Cur pretreatment on myocardial IRI and to elucidate this potential mechanism. Isolated and in vivo rat hearts and cultured neonatal rat cardiomyocytes were subjected to IR. Prior to this procedure, the hearts or cardiomyocytes were exposed to Cur in the absence or presence of the SIRT1 inhibitor sirtinol or SIRT1 siRNA. Cur conferred a cardioprotective effect, as shown by improved postischemic cardiac function, decreased myocardial infarct size, decreased myocardial apoptotic index, and several biochemical parameters, including the up-regulation of the antiapoptotic protein Bcl2 and the down-regulation of the proapoptotic protein Bax. Sirtinol and SIRT1 siRNA each blocked the Cur-mediated cardioprotection by inhibiting SIRT1 signaling. Cur also resulted in a well-preserved mitochondrial redox potential, significantly elevated mitochondrial superoxide dismutase activity, and decreased formation of mitochondrial hydrogen peroxide and malondialdehyde. These observations indicated that the IR-induced mitochondrial oxidative damage was remarkably attenuated. However, this Cur-elevated mitochondrial function was reversed by sirtinol or SIRT1 siRNA treatment. In summary, our results demonstrate that Cur pretreatment attenuates IRI by reducing IR-induced mitochondrial oxidative damage through the activation of SIRT1 signaling.

Effects of Vasodilators on Coronary Vasospasm Induced by Endothelin in the Isolated Perfused Rat Heart / 대한마취과학회지

BACKGROUND: An endothelium derived vasoconstrictor peptide, endothelin, has been shown to be a potent coronary vascular constrictor. In the clinical settings of angina or myocardial ischemia, the endothelial injury of coronary artery can stimulate the endothelin production. In this study, the authors assessed the response to endothelin of the coronary artery in isolated rat heart and compared the relative effects of three vasodilators (nifedipine, adenosine, nitroprusside) on coronary vasospasm which was induced by endothelin. METHODS: The isolated rat heart preparations (Langendorff model) were obtained from fourty male Sprague-Dawley rats (350-400 gm). Preparations were perfusated with Krebs-Hanseleit solution of (mM): NaCl 115, NaHCO3 25, KCl 4.7, CaCl2 2H2O 2.5, MgCl2 6H2O 1.2, KH2PO4 1.2, glucose 10. The perfusate was maintained at 37oC and aerated with carbogen (oxygen 95% and carbon dioxide 5%). The coronary perfusion was maintained at 80 cmH20 pressure and Latex balloon was positioned in left ventricle. After the preparations were stabilized, endothelin (10(-9) M) was added to perfusate for 5 minutes and followed the perfusion without vasodilators (control, n = 10) or with vasodilators (nifedipine, adenosine and nitroprusside 10(-7) M to 10(-6) M, n = 10 each) for 45 minutes. The left ventricular developed pressure (LDP) and heart rate (HR) was recorded and the coronary effluent (VOL) was collected to measure the unit volume and the CPK isoenzyme (CK-MB). Effects of the interventions were assessed using analysis of variance. All values are presented as means +/- SE. RESULTS: VOL, HR and VDP were significantly reduced after infusion of 10(-9) M endothelin in 3 and 5 minutes. VOL was recovered efficiently after infusion of three vasodilators. Adenosine and nitroprusside groups showed superior recovery in the changes of rate pressure product (RPP) than in nifedipine group, which was significant reduced in VDP. CONCLUSIONS: These results suggest that in the situation of endothelin induced severe coronary vasospasm, adenosine and nitroprusside effectively reversed the coronary vasospasm without severe myocardial depression.