A phase 1 study to evaluate the safety, tolerability, pharmacokinetics and pharmacodynamics of danuglipron (PF-06882961), an oral small-molecule glucagon-like peptide-1 receptor agonist, in Japanese adults with type 2 diabetes mellitus.

AIMS: This study investigated the safety, tolerability, pharmacokinetics and pharmacodynamics of danuglipron (PF-06882961), which is a novel, oral small-molecule glucagon-like peptide-1 receptor agonist, in Japanese participants with type 2 diabetes mellitus (T2DM). MATERIALS AND METHODS: This phase 1, randomized, double-blind, placebo-controlled, parallel-group study enrolled adult Japanese participants with T2DM inadequately controlled on diet and exercise. Participants received twice-daily oral doses of placebo or multiple ascending doses of danuglipron titrated to 40, 80 or 120 mg twice daily over 8 weeks. The primary outcome was the safety and tolerability of danuglipron. Secondary and exploratory outcomes included plasma pharmacokinetics, glycaemic parameters and body weight. RESULTS: In the 37 participants randomized, the most common treatment-emergent adverse events were nausea, vomiting, abdominal discomfort, diarrhoea and headache. Most treatment-emergent adverse events were of mild or moderate intensity. Dose-proportional increases in danuglipron exposure parameters were observed at steady state (Day 56). Significant reductions from baseline were observed with danuglipron on Day 56 for mean daily glucose [least squares mean (90% confidence interval) placebo-adjusted difference of up to -67.89 (-88.98, -46.79) mg/dl] and on Day 57 for fasting plasma glucose [up to -40.87 (-53.77, -27.98) mg/dl], glycated haemoglobin [up to -1.41% (-2.01%, -0.82%)] and body weight [up to -1.87 (-3.58, -0.17) kg]. CONCLUSIONS: In Japanese adults with T2DM, danuglipron exhibited dose-proportional increases in plasma exposure at steady state and robustly reduced glycaemic parameters and body weight after 8 weeks of dosing, with a safety profile consistent with the mechanism of action.

Double-Blind, Randomized, Placebo-Controlled Trial Evaluating the Efficacy and Safety of Eplerenone in Japanese Patients With Chronic Heart Failure (J-EMPHASIS-HF).

BACKGROUND: The mineralocorticoid receptor antagonist eplerenone improved clinical outcomes among patients with heart failure with reduced ejection faction (HFrEF) in the EMPHASIS-HF (Eplerenone in Mild Patients Hospitalization And SurvIval Study in Heart Failure) study. However, similar efficacy and safety have not been established in Japanese patients. We evaluated the efficacy and safety of eplerenone in patients with HFrEF in a multicenter, randomized, double-blind placebo-controlled outcome study (ClinicalTrials.gov Identifier: NCT01115855). The aim of the study was to evaluate efficacy predefined as consistency of the primary endpoint with that of EMPHASIS-HF at a point estimate of <1 for the hazard ratio.Methods and Results:HFrEF patients with NYHA functional class II-IV and an EF ≤35% received eplerenone (n=111) or placebo (n=110) on top of standard therapy for at least 12 months. The primary endpoint was a composite of death from cardiovascular causes or hospitalization for HF. The primary endpoint occurred in 29.7% of patients in the eplerenone group vs. 32.7% in the placebo group [hazard ratio=0.85 (95% CI: 0.53-1.36)]. Hospitalization for any cause and changes in plasma BNP and LVEF were favorable with eplerenone. A total of 17 patients (15.3%) in the eplerenone group and 10 patients (9.1%) in the placebo group died. Adverse events, including hyperkalemia, were similar between the groups. CONCLUSIONS: Eplerenone was well-tolerated in Japanese patients with HFrEF and showed results consistent with those reported in the EMPHASIS-HF study.

Cardiotoxicity of doxorubicin is mediated through mitochondrial iron accumulation.

Doxorubicin is an effective anticancer drug with known cardiotoxic side effects. It has been hypothesized that doxorubicin-dependent cardiotoxicity occurs through ROS production and possibly cellular iron accumulation. Here, we found that cardiotoxicity develops through the preferential accumulation of iron inside the mitochondria following doxorubicin treatment. In isolated cardiomyocytes, doxorubicin became concentrated in the mitochondria and increased both mitochondrial iron and cellular ROS levels. Overexpression of ABCB8, a mitochondrial protein that facilitates iron export, in vitro and in the hearts of transgenic mice decreased mitochondrial iron and cellular ROS and protected against doxorubicin-induced cardiomyopathy. Dexrazoxane, a drug that attenuates doxorubicin-induced cardiotoxicity, decreased mitochondrial iron levels and reversed doxorubicin-induced cardiac damage. Finally, hearts from patients with doxorubicin-induced cardiomyopathy had markedly higher mitochondrial iron levels than hearts from patients with other types of cardiomyopathies or normal cardiac function. These results suggest that the cardiotoxic effects of doxorubicin develop from mitochondrial iron accumulation and that reducing mitochondrial iron levels protects against doxorubicin-induced cardiomyopathy.

Disruption of ATP-binding cassette B8 in mice leads to cardiomyopathy through a decrease in mitochondrial iron export.

Mitochondrial iron levels are tightly regulated, as iron is essential for the synthesis of Fe/S clusters and heme in the mitochondria, but high levels can cause oxidative stress. The ATP-binding cassette (ABC) transporter ABCB8 is a mitochondrial inner membrane protein with an unknown function. Here, we show that ABCB8 is involved in mitochondrial iron export and is essential for baseline cardiac function. Induced genetic deletion of ABCB8 in mouse hearts resulted in mitochondrial iron accumulation and cardiomyopathy, as assessed by echocardiography and invasive hemodynamics. Mice with ABCB8 deletion in the heart also displayed mitochondrial damage, and higher levels of reactive oxygen species and cell death. Down-regulation of ABCB8 in vitro resulted in decreased iron export from isolated mitochondria, whereas its overexpression had the opposite effect. Furthermore, ABCB8 is needed for the maturation of the cytosolic Fe/S proteins, as its deletion in vitro and in vivo led to decreased activity of cytosolic, but not mitochondrial, iron-sulfur-containing enzymes. These results indicate that ABCB8 is essential for normal cardiac function, maintenance of mitochondrial iron homeostasis and maturation of cytosolic Fe/S proteins. In summary, this report provides characterization of a protein involved in mitochondrial iron export.

microRNA-210 is upregulated in hypoxic cardiomyocytes through Akt- and p53-dependent pathways and exerts cytoprotective effects.

microRNA-210 (miR-210) is upregulated in hypoxia, but its function in cardiomyocytes and its regulation in response to hypoxia are not well characterized. The purpose of this study was to identify upstream regulators of miR-210, as well as to characterize miR-210's function in cardiomyocytes. We first showed miR-210 is upregulated through both hypoxia-inducible factor (HIF)-dependent and -independent pathways, since aryl hydrocarbon nuclear translocator (ARNT) knockout mouse embryonic fibroblasts (MEF), lacking intact HIF signaling, still displayed increased miR-210 levels in hypoxia. To determine the mechanism for HIF-independent regulation of miR-210, we focused on p53 and protein kinase B (Akt). Overexpression of p53 in wild-type MEFs induced miR-210, whereas p53 overexpression in ARNT knockout MEFs did not, suggesting p53 regulates miR-210 in a HIF-dependent mechanism. Akt inhibition reduced miR-210 induction by hypoxia, whereas Akt overexpression increased miR-210 levels in both wild-type and ARNT knockout MEFs, indicating Akt regulation of miR-210 is HIF-independent. We then studied the effects of miR-210 in cardiomyocytes. Overexpression of miR-210 reduced cell death in response to oxidative stress and reduced reactive oxygen species (ROS) production both at baseline and after treatment with antimycin A. Furthermore, downregulation of miR-210 increased ROS after hypoxia-reoxygenation. To determine a mechanism for the cytoprotective effects of miR-210, we focused on the predicted target, apoptosis-inducing factor, mitochondrion-associated 3 (AIFM3), known to induce cell death. Although miR-210 reduced AIFM3 levels, overexpression of AIFM3 in the presence of miR-210 overexpression did not reduce cellular viability either at baseline or after hydrogen peroxide treatment, suggesting AIFM3 does not mediate miR-210's cytoprotective effects. Furthermore, HIF-3α, a negative regulator of HIF signaling, is targeted by miR-210, but miR-210 does not modulate HIF activity. In conclusion, we demonstrate a novel role for p53 and Akt in regulating miR-210 and demonstrate that, in cardiomyocytes, miR-210 exerts cytoprotective effects, potentially by reducing mitochondrial ROS production.

Early long-term L-T3 replacement rescues mitochondria and prevents ischemic cardiac remodelling in rats.

3,5,3'-Levo-triiodothyronine (L-T3) is essential for DNA transcription, mitochondrial biogenesis and respiration, but its circulating levels rapidly decrease after myocardial infarction (MI). The main aim of our study was to test whether an early and sustained normalization of L-T3 serum levels after MI exerts myocardial protective effects through a mitochondrial preservation. Seventy-two hours after MI induced by anterior interventricular artery ligation, rats were infused with synthetic L-T3 (1.2 µg/kg/day) or saline over 4 weeks. Compared to saline, L-T3 infusion restored FT3 serum levels at euthyroid state (3.0 ± 0.2 versus 4.2 ± 0.3 pg/ml), improved left ventricular (LV) ejection fraction (39.5 ± 2.5 versus 65.5 ± 6.9%), preserved LV end-systolic wall thickening in the peri-infarct zone (6.34 ± 3.1 versus 33.7 ± 6.21%) and reduced LV infarct-scar size by approximately 50% (all P < 0.05). Moreover, L-T3 significantly increased angiogenesis and cell survival and enhanced the expression of nuclear-encoded transcription factors involved in these processes. Finally, L-T3 significantly increased the expression of factors involved in mitochondrial DNA transcription and biogenesis, such as hypoxic inducible factor-1α, mitochondrial transcription factor A and peroxisome proliferator activated receptor γ coactivator-1α, in the LV peri-infarct zone. To further explore mechanisms of L-T3 protective effects, we exposed isolated neonatal cardiomyocytes to H(2)O(2) and found that L-T3 rescued mitochondrial biogenesis and function and protected against cell death via a mitoKATP dependent pathway. Early and sustained physiological restoration of circulating L-T3 levels after MI halves infarct scar size and prevents the progression towards heart failure. This beneficial effect is likely due to enhanced capillary formation and mitochondrial protection.

Reduction in hexokinase II levels results in decreased cardiac function and altered remodeling after ischemia/reperfusion injury.

RATIONALE: Cardiomyocytes switch substrate utilization from fatty acid to glucose under ischemic conditions; however, it is unknown how perturbations in glycolytic enzymes affect cardiac response to ischemia/reperfusion (I/R). Hexokinase (HK)II is a HK isoform that is expressed in the heart and can bind to the mitochondrial outer membrane. OBJECTIVE: We sought to define how HKII and its binding to mitochondria play a role in cardiac response and remodeling after I/R. METHODS AND RESULTS: We first showed that HKII levels and its binding to mitochondria are reduced 2 days after I/R. We then subjected the hearts of wild-type and heterozygote HKII knockout (HKII(+/)⁻) mice to I/R by coronary ligation. At baseline, HKII(+/)⁻ mice have normal cardiac function; however, they display lower systolic function after I/R compared to wild-type animals. The mechanism appears to be through an increase in cardiomyocyte death and fibrosis and a reduction in angiogenesis; the latter is through a decrease in hypoxia-inducible factor-dependent pathway signaling in cardiomyocytes. HKII mitochondrial binding is also critical for cardiomyocyte survival, because its displacement in tissue culture with a synthetic peptide increases cell death. Our results also suggest that HKII may be important for the remodeling of the viable cardiac tissue because its modulation in vitro alters cellular energy levels, O2 consumption, and contractility. CONCLUSIONS: These results suggest that reduction in HKII levels causes altered remodeling of the heart in I/R by increasing cell death and fibrosis and reducing angiogenesis and that mitochondrial binding is needed for protection of cardiomyocytes.

Comparative effects of telmisartan and valsartan on insulin resistance in hypertensive patients with metabolic syndrome.

OBJECTIVE: Metabolic syndrome (MetS) is a cluster of metabolic abnormalities that includes hyperglycemia, dyslipidemia, hypertension and increased waist circumference. Individuals with this syndrome are at increased risk for development of cardiovascular disease. Since an insulin-resistance state has a critical role in the development of MetS, there is growing concern about insulin-sensitizing effects of antihypertensives, including angiotensin II receptor blockers (ARBs). Telmisartan has been reported to have an effect on the activity of peroxisome proliferator-activated receptor gamma, a well-known target for insulin-sensitizing antidiabetic drugs. The aim of this study was to determine the effects of administration of two different ARBs at low doses (telmisartan at 20 mg/day and valsartan at 40 mg/day) on insulin sensitivity. METHODS: Patients with MetS meeting the Japanese criteria were treated with telmisartan or valsartan for 4 weeks in combination with lifestyle modification. RESULTS: A significant reduction in blood pressure was found after 4 weeks of both treatments. The homeostasis model assessment of insulin resistance (HOMA-R) was significantly reduced by telmisartan compared to the baseline value (3.11+/-2.06 vs 2.56+/-1.48, p=0.031) but was not significantly changed by valsartan. A statistically significant correlation was found between HOMA-R at baseline and changes in HOMA-R after 4 weeks of treatment only in telmisartan-treated subjects. Body mass index, glycosylated hemoglobin and lipid profile were not changed by either treatment. CONCLUSION: Our data revealed that treatment with telmisartan even at a low dose improves insulin sensitivity in hypertensive patients with MetS. This ameliorating effect of telmisartan on glucose metabolism clinically deserves to be considered.

MitoKATP channel activation suppresses gap junction permeability in the ischemic myocardium by an ERK-dependent mechanism.

BACKGROUND: Ischemic preconditioning accelerates suppression of gap junction (GJ) permeability during myocardial ischemia, and GJ blockers reduce infarct size. We hypothesized that the mitochondrial ATP-sensitive K+ (mitoKATP) channel is one of the mechanisms regulating GJ permeability through the mitogen-activated protein kinase ERK, leading to cardioprotection. METHODS AND RESULTS: In isolated rabbit hearts, tissues were sampled before and after infusion of diazoxide, a selective mitoKATP channel opener, and their intercalated disc-rich fractions were obtained for immunoblotting of mitogen-activated protein kinases. GJ permeability in the myocardium was assessed by using Lucifer yellow as a tracer of GJ communication. Infarction was induced by 30-min global ischemia/2 h reperfusion, and infarct size was expressed as a percent of area-at-risk (%IS/AR). Diazoxide (100 microM) induced phosphorylation of ERK1/2 and 279Ser/282Ser of connexin-43, a GJ subunit protein, and phospho-ERK1/2 was co-immunoprecipitated with connexin-43 in the diazoxide-treated myocardium. This ERK1/2 phosphorylation by diazoxide was inhibited by N-2-mercaptopropionyl-glycine, a free radical scavenger. Diazoxide at 10 and 100 microM reduced intercellular transport of Lucifer yellow during ischemia by 44% and 69%, respectively, and this effect of diazoxide on GJ communication was abolished by PD98059, an ERK inhibitor. Pretreatment with 10 microM and 100 microM diazoxide reduced %IS/AR from 57.1+/-3.7% to 21.5+/-10.5% and 5.0+/-1.3%, respectively. PD98059 abolished cardioprotection by 10 microM diazoxide but not that by 100 microM diazoxide. CONCLUSIONS: Opening of the mitoKATP channel activates ERK1/2 via free radicals and induces ERK-mediated suppression of GJ permeability. This suppression of GJ permeability may partly contribute to cardioprotection afforded by mitoKATP channel activation.

Macrophage colony-stimulating factor treatment after myocardial infarction attenuates left ventricular dysfunction by accelerating infarct repair.

OBJECTIVES: We aimed to determine the effects of macrophage colony-stimulating factor (M-CSF) and granulocyte colony-stimulating factor (G-CSF) treatment on both the repair process and ventricular function after myocardial infarction (MI). BACKGROUND: The M-CSF and G-CSF have multiple potential effects on cells involved in wound repair. METHODS: Myocardial infarction was induced by 45- or 90-min coronary occlusion and reperfusion in rats with or without subsequent injection of M-CSF (10(6) IU/kg/day) or G-CSF (50 microg/kg/day) for five days. We examined histology and messenger ribonucleic acid (mRNA), and assessed left ventricular function in situ using a conductance catheter. RESULTS: Five days after MI, M-CSF increased the number of ED-1-positive cells, mRNA levels of transforming growth factor-beta-1, collagen I and III, and collagen fibers within the infarct. Fourteen days after MI, induced by 45-min ischemia, left ventricular end-systolic elastance (Ees) was reduced (1,191 +/- 87 mm Hg/ml vs. 1,812 +/- 150 mm Hg/ml) and both isovolumic relaxation time constant (tau) (11.9 +/- 0.9 ms vs. 8.5 +/- 0.4 ms) and left ventricular end-diastolic volume (LVEDV) (0.225 +/- 0.014 ml vs. 0.172 +/- 0.011 ml) increased versus sham-operated rats. These alterations after MI were attenuated by M-CSF (Ees = 1,650 +/- 146, tau = 9.7 +/- 0.7, LVEDV = 0.199 +/- 0.012) but not by G-CSF. This beneficial effect of M-CSF on Ees was also detected in hearts with MI induced by 90-min ischemia. Furthermore, M-CSF increased collagen content within infarcts and reduced the proportion of thin collagen fibers 14 days after MI. The Ees significantly correlated with infarct collagen content. Nevertheless, neither M-CSF nor G-CSF modified infarct size. CONCLUSIONS: The M-CSF treatment attenuates deterioration of left ventricular function after MI by accelerating infarct repair.

Role of microtubules in ischemic preconditioning against myocardial infarction.

OBJECTIVE: The role of microtubules in ischemic preconditioning (PC) was investigated in isolated perfused rabbit hearts. METHODS: Myocardial infarction was induced by 30-min global ischemia and 2-h reperfusion, and infarct size was expressed as a percentage of the left ventricle (%IS/LV). Using separate groups of rabbits, ventricular biopsies were taken before and after PC for determination of protein kinase C (PKC) translocation and p38-mitogen-activated protein kinase (p38MAP kinase) activation. To depolymerize microtubules, we used two structurally different agents, colchicine (50 microM) and nocodazole (1 microM). RESULTS: PC with two cycles of 5-min ischemia/5-min reperfusion significantly reduced infarct size from 60.1+/-5.0% to 20.0+/-5.0%. Although neither colchicine nor nocodazole modified infarct size in nonpreconditioned hearts, these agents abolished the infarct size-limiting effects of PC (%IS/LV=56.1+/-6.0% and 53.5+/-2.5%, respectively). Colchicine prevented translocation of PKC-epsilon and p38MAP kinase activation by PC. PKC translocation by infusion of 1-oleyl-2-acetyl-sn-glycerol in nonischemic hearts was also prevented by colchicine. CONCLUSION: Microtubules play a crucial role in the development of anti-infarct tolerance by PC as a mechanism supporting translocation of activated PKC.

The role of ADAM protease in the tyrosine kinase-mediated trigger mechanism of ischemic preconditioning.

OBJECTIVE: The aim of this study was to determine the role of an a disintegrin and metalloprotease (ADAM) in tyrosine kinase-mediated mechanisms of ischemic preconditioning (PC). METHODS AND RESULTS: In isolated rabbit hearts, PC was performed with two cycles of 5 min ischemia/5 min reperfusion and infarction was induced by 30 min global ischemia/2 h reperfusion. Translocation of protein kinase C- (PKC-) and tyrosine phosphorylation in the tissue and TNF-alpha in coronary effluent were determined by immunoblotting. PC reduced infarct size from 55.1+/-6.8% of the left ventricle to 24.4+/-5.2%, and this protection was mimicked by pretreatment with 100 nM angiotensin II. Both the PC effect and angiotensin II-induced protection were abolished by genistein and by 10 microM KB-R7785 (KBR), an inhibitor of ADAM12/17, but not by a lower ADAM12-selective dose (1 microM) of KBR. AG1478, an inhibitor of EGF receptor tyrosine kinase, did not inhibit protection afforded by PC. PC provoked release of TNF-alpha into the coronary effluent, which was abolished by 10 microM KBR but not by 1 microM of KBR or calphostin C, a PKC inhibitor. PKC- translocation by PC was not affected by KBR. PC induced tyrosine phosphorylation of 60 and 90 kDa proteins, and this phosphorylation was abolished by 10 microM KBR but not by calphostin C. Pretreatment with TNF-alpha limited infarct size to 16.7+/-3.7% and induced tyrosine phosphorylation of a 60 kDa protein. CONCLUSIONS: The results support the hypothesis that an ADAM contributes to the triggering of a tyrosine kinase-mediated and PKC-independent pathway of PC. The ADAM responsible for this tyrosine kinase-mediated pathway is likely to be ADAM17, which sheds TNF-alpha.

Granulocyte colony stimulating factor/macrophage colony stimulating factor improves postinfarct ventricular function by suppression of border zone remodelling in rats.

1. The aim of the present study was to examine the effects of mobilization of bone marrow cells by granulocyte colony stimulating factor (G-CSF) and macrophage colony stimulating factor (M-CSF) on ventricular function after myocardial infarction (MI). 2. After ligation of the left coronary artery, rats were divided into a vehicle control group (MI group) and a CSF-treated group (MI-CSF group). Rats in the MI-CSF group received a combination of G-CSF (50 microg/kg per day) and M-CSF (10(6) IU/kg per day) for 5 days after MI. Two weeks after MI, hearts were isolated and perfused with a Krebs' buffer and their functional responses to step-wise elevation of left ventricular end-diastolic pressure (LVEDP) were assessed. In histological analysis, proliferating cells and bone marrow-derived cells were identified by antibodies against Ki-67 and c-kit and organization of collagen was examined by picrosirius red staining. The mRNA levels of transforming growth factor (TGF)-beta(1), collagen type I and collagen type III were measured by quantitative reverse transcription-polymerase chain reaction. 3. Numbers of Ki-67- and c-kit-positive cells in the infarct border zone after MI were increased by CSF treatment, but few of those cells were stained by anti-alpha-sarcomeric actin. The levels in mRNA of TGF-beta1 and collagen type I in the infarct border zone were higher in the CSF-treated group compared with the MI group. Although CSF treatment did not reduce ventricular hypertrophy or infarct size at 2 weeks after MI, it did significantly improved the response of left ventricular developed pressure to step-wise elevation of LVEDP. This effect was mimicked by treatment with M-CSF alone. The functional improvement by CSF treatment was correlated with suppression of enlargement of the infarct-non-infarct border associated with infarct expansion. Collagen fibres in the border zone were thicker and orientated more orderly in the CSF-treated group than in the untreated group. 4. The results suggest that G-CSF/M-CSF treatment improves contractile function of the ventricle after infarction, presumably by acceleration of infarct repair and suppression of remodelling in the border zone.

Protective role of gap junctions in preconditioning against myocardial infarction.

The aim of the present study was to examine the hypothesis that acceleration of gap junction (GJ) closure during ischemia contributes to anti-infarct tolerance afforded by preconditioning (PC). First, the effects of PC on GJ communication during ischemia were assessed. Isolated buffer-perfused rabbit hearts were subjected to 5-min global ischemia with or without PC with two cycles of 5-min ischemia/5-min reperfusion or a GJ blocker (2 mM heptanol), and then the tissue excised from the ischemic region was incubated in anoxic buffer containing lucifer yellow (LY; 2.5 mg/ml), a tracer of GJ permeability, for 20 min at 37 degrees C. PC and heptanol significantly reduced the area to which LY was transported in the ischemic myocardium by 39% and by 54%, respectively. In the second series of experiments, three GJ blockers (heptanol, 18beta-glycyrrhetinic acid, and 2,3-butanedione monoxime) infused after the onset of ischemia reduced infarct size after 30-min ischemia/2-h reperfusion to an extent equivalent to that in the case of PC. In the third series of experiments, Western blotting for connexin43 (Cx43) showed that PC shortened the time to the onset of ischemia-induced Cx43 dephosphorylation but reduced the extent of Cx43 dephosphorylation during a 30-min period of ischemia. Calphostin C, a protein kinase C (PKC) inhibitor, abolished preservation of phosphorylated Cx43 but not the early onset of Cx43 dephosphorylation after ischemia in the preconditioned myocardium. These results suggest that PC-induced reduction of GJ permeability during ischemia, presumably by PKC-mediated Cx43 phosphorylation, contributes to infarct size limitation.

Interruption of signal transduction between G protein and PKC-epsilon underlies the impaired myocardial response to ischemic preconditioning in postinfarct remodeled hearts.

We have recently shown that the protective mechanism of ischemic preconditioning (PC) is impaired in the myocardium that survived infarction and underwent postinfarct ventricular remodeling. In this study, we examined the hypothesis that failure of PC to activate PKC-epsilon underlies the refractoriness of the remodeling heart to PC. Circumflex coronary arteries were ligated in rabbits to induce infarction and subsequent ventricular remodeling, and only sham operations were performed in controls. Hearts were isolated before (i.e. 4 days later) or after (i.e. 2 weeks later) remodeling of the left ventricle and used for isolated buffer-perfused heart experiments. Myocardial infarction was induced in isolated hearts by 30 min global ischemia/2 h reperfusion, and its size was measured by tetrazolium staining. Using separate groups of hearts, tissue biopsies were taken before and after PC, and PKC translocation was assessed by Western blotting. Areas infarcted in vivo by coronary ligation (CL) were excluded from subsequent infarct size/PKC analyses. In the hearts 4 days after CL, PC with 2 cycles of 5 min ischemia/5 min reperfusion induced PKC-epsilon translocation from cytosol to particulate fractions and limited infarct size to 40% of control value. In the hearts remodeled 2 weeks after CL, PC failed to induce PKC-epsilon translocation and infarct size limitation. In this group, PKC activity and hemodynamic responses to adenosine were similar to those in sham-operated controls. When remodeling after CL was prevented by valsartan infusion (10 mg/kg/day), an angiotensin II type 1 (AT1) receptor blocker, PC could induce both infarct limitation and PKC-epsilon translocation. The present results suggest that persistent activation of AT1 receptors during remodeling disturbed the PC signaling between G proteins and PKC-epsilon, which underlies the refractoriness of the remodeled myocardium to PC.

K(ATP) channel opening is an endogenous mechanism of protection against the no-reflow phenomenon but its function is compromised by hypercholesterolemia.

OBJECTIVE: This study aimed to clarify the role of adenosine triphosphate-sensitive K(+) (K(ATP)) channels in the no-reflow phenomenon and in its extension by hypercholesterolemia. BACKGROUND: The no-reflow phenomenon is an important target of therapy in patients with acute myocardial infarction, but its mechanism remains unclear. METHODS: The left circumflex coronary artery was occluded for 30 or 60 min and reperfused in rabbit hearts in situ. The no-reflow zone, area at risk, and infarct size were determined by thioflavin-S, Evans blue, and tetrazolium staining, respectively. No-reflow zone size was expressed as a percentage of infarct size (%NR/IS). Hypercholesterolemia was induced by two weeks of cholesterol-enriched diet. RESULTS: A K(ATP) channel blocker, glibenclamide (0.3 mg/kg), increased %NR/IS after 30-min ischemia/90-min reperfusion from 33.6 +/- 1.9% to 45.9 +/- 1.6% and %NR/IS after 60-min ischemia/90-min reperfusion from 32.8 +/- 3.4% to 46.1 +/- 1.7%. However, N(G)-monomethyl-L-arginine (L-NMMA), a nitric oxide (NO) synthase inhibitor, and nicorandil, a hybrid of K(ATP) channel opener and nitrate, failed to significantly modify %NR/IS. Hypercholesterolemia increased %NR/IS to 61.6 +/- 0.6%, which was not further enlarged by glibenclamide, and delayed infarct healing during the subsequent five days of reperfusion. These effects of hypercholesterolemia were significantly suppressed by nicorandil. Neither glibenclamide, L-NMMA, nicorandil, nor hypercholesterolemia modified infarct size. CONCLUSIONS: The K(ATP) channel activation, but not NO, is a major mechanism of protection against microvascular injury, causing the no-reflow phenomenon in the heart. Suppression of K(ATP) channel opening may underlie the hypercholesterolemia-induced extension of no-reflow, which delays infarct healing.

Infarct size limitation by nicorandil: roles of mitochondrial K(ATP) channels, sarcolemmal K(ATP) channels, and protein kinase C.

OBJECTIVES: This study aimed to examine:1) whether nicorandil protects the ischemic myocardium by activating sarcolemmal adenosine triphosphate (ATP)-sensitive K(+) (sarcK(ATP)) channels or the mitochondrial K(ATP) (mitoK(ATP)) channels, and 2) whether protein kinase C (PKC) activity is necessary for cardioprotection afforded by nicorandil. BACKGROUND: Nicorandil is a hybrid of nitrate and a K(ATP) channel opener that activates the sarcK(ATP) and mitoK(ATP) channels. Both of these K(ATP) channels are regulated by PKC, and this kinase may be activated by nitric oxide and also by oxygen free radicals (OFR) generated after mitoK(ATP) channel opening. METHODS: In isolated rabbit hearts, infarction was induced by 30-min global ischemia/2-h reperfusion with monitoring of the activation recovery interval (ARI), an index of action potential duration. Protein kinase C translocation was assessed by Western blotting. RESULTS: Nicorandil did not change ARI before ischemia, but it accelerated ARI shortening after the onset of ischemia and reduced infarct size by 90%. A sarcK(ATP) channel selective blocker, HMR1098, abolished acceleration of ischemia-induced ARI-shortening by nicorandil and eliminated 40% of nicorandil-induced infarct size limitation. A mitoK(ATP) channel selective blocker, 5-hydroxydecanoate, abolished the protection afforded by nicorandil without affecting ARI. Cardioprotection by nicorandil was inhibited neither by an OFR scavenger, N-2-mercaptopropionylglycine nor by a PKC inhibitor, calphostin C, at a dose that was capable of inhibiting PKC- epsilon translocation after preconditioning. CONCLUSIONS: Both the sarcK(ATP) and mitoK(ATP) channels are involved in anti-infarct tolerance afforded by nicorandil, but PKC activation induced by nitric oxide or OFR generation, if any, does not play a crucial role.

Effects of neutral endopeptidase 24.11 inhibition on myocardial infarct size and ischemic preconditioning in rabbits.

This study was designed to determine whether inhibition of neutral endopeptidase 24.11 (NEP) reduces infarct size and enhances protection afforded by ischemic preconditioning (PC) by elevation of the tissue bradykinin (BK) level in the heart in situ. In experiments to determine a dose of thiorphan (Thio) that inhibits NEP activity in the rabbit, infusion of Thio at a rate of 15 micro g/kg per min was found to be NEP-selective, since it increased the extent and duration of hypotension after BK injection (50 ng/kg and 100 ng/kg, i.v.) but did not inhibit pressor response to angiotensin I (100 ng/kg and 500 ng/kg, i.v.). Infusion of Thio at a rate of 25 micro g/kg per min blunted pressor response to angiotensin I by 30%, suggesting this dose partially inhibits angiotensin-converting enzyme activity. In the second series of experiments, myocardial infarction was induced by 30-min coronary occlusion and 3-h reperfusion in rabbits. In untreated controls, infarct size as a percentage of area at risk (%IS/AR) was 50.1+/-4.1%, and infusion of Thio at 15 micro g/kg per min and 25 micro g/kg per min failed to limit infarct size (54.3+/-4.0% and 50.1+/-2.8%, respectively). However, these doses of Thio significantly reduced %IS/AR when combined with PC with 2-min ischemia to 25.7+/-3.3% and 19.7+/-3.1%, respectively, although this submaximal PC protocol alone did not achieve significant cardioprotection (%IS/AR=35.6+/-4.0%). This effect of Thio on PC was abolished by pretreatment with icatibant (2 micro g/kg), a BK B(2) receptor blocker. The results of the present study suggest that NEP inhibition does not increase anti-infarct tolerance of the myocardium but significantly enhances cardioprotection of PC via a B(2) receptor-mediated mechanism.

Long-term follow-up after coronary stent implantation in patients with coronary artery disease.

Prospective randomized trials of coronary stenting in patients with coronary artery disease have shown a reduced incidence of cardiac events. However, little is known of the late outcome of patients treated with coronary stenting. The purpose of this study was to evaluate the relatively long-term clinical outcomes (3 to 6 years) of patients treated with successful coronary stenting. The long-term clinical outcome was studied in 101 consecutive patients (78 males and 23 females) who had undergone successful coronary stent implantation for coronary artery disease in our hospital from October 1994 to September 1997. During a follow-up period of 48.9+/-9.5 months (range, 6-73 months), cardiac events were documented in 37 patients. The rate of survival free of cardiac events was 67% at 3 years. Multiple logistic regression analysis showed that ACC/AHA lesion type and residual percent diameter stenosis greater than 20% after stenting were the significant explanatory factors of adverse cardiac events. Long-term clinical outcome in patients with coronary artery disease treated with successful coronary stenting was influenced by the ACC/AHA lesion type of stented lesion and residual percent diameter stenosis after stent implantation.