Nobuhiro Suematsu

Mitochondrial DNA Damage and Dysfunction Associated With Oxidative Stress in Failing Hearts After Myocardial Infarction

Mitochondria are one of the enzymatic sources of reactive oxygen species (ROS) and could also be a major target for ROS-mediated damage. We hypothesized that ROS may induce mitochondrial DNA (mtDNA) damage, which leads to defects of mtDNA-encoded gene expression and respiratory chain complex enzymes and thus may contribute to the progression of left ventricular (LV) remodeling and failure after myocardial infarction (MI). In a murine model of MI and remodeling created by the left anterior descending coronary artery ligation for 4 weeks, the LV was dilated and contractility was diminished. Hydroxyl radicals, which originated from the superoxide anion, and lipid peroxide formation in the mitochondria were both increased in the noninfarcted LV from MI mice. The mtDNA copy number relative to the nuclear gene (18S rRNA) preferentially decreased by 44% in MI by a Southern blot analysis, associated with a parallel decrease (30% to 50% of sham) in the mtDNA-encoded gene transcripts, including the subunits of complex I (ND1, 2, 3, 4, 4L, and 5), complex III (cytochrome b), complex IV (cytochrome c oxidase), and rRNA (12S and 16S). Consistent with these molecular changes, the enzymatic activity of complexes I, III, and IV decreased in MI, whereas, in contrast, complex II and citrate synthase, encoded only by nuclear DNA, both remained at normal levels. An intimate link among ROS, mtDNA damage, and defects in the electron transport function, which may lead to an additional generation of ROS, might play an important role in the development and progression of LV remodeling and failure.

Direct Evidence for Increased Hydroxyl Radicals Originating From Superoxide in the Failing Myocardium

Experimental and clinical studies have suggested an increased production of reactive oxygen species (ROS) in the failing myocardium. The present study aimed to obtain direct evidence for increased ROS and to determine the contribution of superoxide anion (*O(2)(-)), H(2)O(2), and hydroxy radical (*OH) in failing myocardial tissue. Heart failure was produced in adult mongrel dogs by rapid ventricular pacing at 240 bpm for 4 weeks. To assess the production of ROS directly, freeze-clamped myocardial tissue homogenates were reacted with the nitroxide radical, 4-hydroxy-2,2,6, 6,-tetramethyl-piperidine-N-oxyl, and its spin signals were detected by electron spin resonance spectroscopy. The rate of electron spin resonance signal decay, proportional to *OH level, was significantly increased in heart failure, which was inhibited by the addition of dimethylthiourea (*OH scavenger) into the reaction mixture. Increased *OH in the failing heart was abolished to the same extent in the presence of desferrioxamine (iron chelator), catalase (H(2)O(2) scavenger), and 4,5-dihydroxy-1,3-benzene disulfonic acid (Tiron; LaMotte) (*O(2)(-) scavenger), indicating that *OH originated from H(2)O(2) and *O(2)(-). Further, *O(2)(-) produced in normal myocardium in the presence of antimycin A (mitochondrial complex III inhibitor) could reproduce the increase of H(2)O(2) and *OH seen in the failing tissue. There was a significant positive relation between myocardial ROS level and left ventricular contractile dysfunction. In conclusion, in the failing myocardium, *OH was produced as a reactive product of *O(2)(-) and H(2)O(2), which might play an important role in left ventricular failure.

Oxidative Stress Mediates Tumor Necrosis Factor-α–Induced Mitochondrial DNA Damage and Dysfunction in Cardiac Myocytes

Background—Tumor necrosis factor-&agr; (TNF-&agr;) and angiotensin II (Ang II) are implicated in the development and further progression of heart failure, which might be, at least in part, mediated by the production of reactive oxygen species (ROS). However, the cause and consequences of this agonist-mediated ROS production in cardiac myocytes have not been well defined. Recently, we demonstrated that increased ROS production was associated with mitochondrial DNA (mtDNA) damage and dysfunction in failing hearts. We thus investigated whether the direct exposure of cardiac myocytes to TNF-&agr; and Ang II in vitro could induce mtDNA damage via production of ROS. Methods and Results—TNF-&agr; increased ROS production within cultured neonatal rat ventricular myocytes after 1 hour, as assessed by 2′,7′-dichlorofluorescin diacetate fluorescence microscopy. TNF-&agr; also decreased mtDNA copy number by Southern blot analysis in association with complex III activity, which was prevented in the presence of the antioxidant &agr;-tocopherol. A direct exposure of myocytes to H2O2 caused a similar decrease in mtDNA copy number. In contrast, Ang II did not affect mtDNA copy number, despite the similar increase in ROS production. TNF-&agr;–mediated ROS production and a decrease in mtDNA copy number were inhibited by the sphingomyelinase inhibitor D609. Furthermore, N-acetylsphingosine (C2-ceramide), a synthetic cell-permeable ceramide analogue, increased myocyte ROS production, suggesting that TNF-&agr;–mediated ROS production and subsequent mtDNA damage were mediated by the sphingomyelin-ceramide signaling pathway. Conclusions—The intimate link between TNF-&agr;, ROS, and mtDNA damage might play an important role in myocardial remodeling and failure.

Treatment With Dimethylthiourea Prevents Left Ventricular Remodeling and Failure After Experimental Myocardial Infarction in Mice Role of Oxidative Stress

Oxidative stress might play an important role in the progression of left ventricular (LV) remodeling and failure that occur after myocardial infarction (MI). We determined whether reactive oxygen species (ROS) are increased in the LV remodeling and failure in experimental MI with the use of electron spin resonance spectroscopy and whether the long-term administration of dimethylthiourea (DMTU), hydroxyl radical (·OH) scavenger, could attenuate these changes. We studied 3 groups of mice: sham-operated (sham), MI, and MI animals that received DMTU (MI+DMTU). Drugs were administered to the animals daily via intraperitoneal injection for 4 weeks. ·OH was increased in the noninfarcted myocardium from MI animals, which was abolished in MI+DMTU. Fractional shortening was depressed by 65%, LV chamber diameter was increased by 53%, and the thickness of noninfarcted myocardium was increased by 37% in MI. MI+DMTU animals had significantly better LV contractile function and smaller increases in LV chamber size and hypertrophy than MI animals. Changes in myocyte cross-sectional area determined with LV mid–free wall specimens were concordant with the wall thickness data. Collagen volume fraction of the noninfarcted myocardium showed significant increases in the MI, which were also attenuated with DMTU. Myocardial matrix metalloproteinase-2 activity, measured with gelatin zymography, was increased with MI after 7 and 28 days, which was attenuated in MI+DMTU. Thus, the attenuation of increased myocardial ROS and metalloproteinase activity with DMTU may contribute, at least in part, to its beneficial effects on LV remodeling and failure. Therapies designed to interfere with oxidative stress might be beneficial to prevent myocardial failure.

Pioglitazone, a Peroxisome Proliferator-Activated Receptor-γ Agonist, Attenuates Left Ventricular Remodeling and Failure After Experimental Myocardial Infarction

Background—Peroxisome proliferator–activated receptor-&ggr; activators have recently been implicated as regulators of cellular proliferation and inflammatory response such as cytokine expression. Because proinflammatory cytokines play a critical role in left ventricular (LV) remodeling after myocardial infarction (MI), we examined the effects of pioglitazone treatment in an experimental model of chronic heart failure. Methods and Results—Mice with extensive anterior MI were treated with placebo or pioglitazone (3 mg · kg−1 · d−1) as a dietary supplement for 4 weeks starting 6 hours after surgery. Infarct size and glucose levels were similar among all groups. LV cavity dilatation and dysfunction by echocardiography were significantly attenuated in MI mice given pioglitazone. LV end-diastolic pressure was increased in MI mice and was significantly reduced by pioglitazone treatment. Pioglitazone partially normalized LV dP/dtmax and dP/dtmin, indices of LV contractile function, which were significantly reduced in MI mice. Improvement of LV function by pioglitazone was accompanied by a decrease in myocyte hypertrophy and interstitial fibrosis and a reduced expression of tumor necrosis factor-&agr;, transforming growth factor-&bgr;, and monocyte chemoattractant protein-1 genes in the noninfarcted LV from MI mice. LV inducible nitric oxide synthase and gelatinase B protein levels were increased in MI and were not altered by pioglitazone treatment. Conclusions—Pioglitazone improved LV remodeling and function in mice with post-MI heart failure. This effect was associated with an attenuated LV expression of inflammatory cytokines and chemokines. Peroxisome proliferator–activated receptor-&ggr; ligands have promise as preventive and therapeutic agents against heart failure.

Anti-Monocyte Chemoattractant Protein-1 Gene Therapy Attenuates Left Ventricular Remodeling and Failure After Experimental Myocardial Infarction

Background—Increased expression of monocyte chemoattractant protein-1 (MCP-1) has recently been described in clinical and experimental failing heart. However, its pathophysiological significance in heart failure remains obscure. We thus determined whether MCP-1 is increased in post-myocardial infarction (MI) hearts and its blockade can attenuate the development of left ventricular (LV) remodeling and failure. Methods and Results—Anterior MI was produced in mice by ligating the left coronary artery. After 4 weeks, MI mice exerted LV dilatation and contractile dysfunction in association with myocyte hypertrophy and interstitial fibrosis of noninfarcted LV. MCP-1 mRNA levels were increased by 40-fold in noninfarcted LV 1 day after ligation, which persisted until 28 days. To block the MCP-1 signals, an N-terminal deletion mutant of the human MCP-1 gene was transfected into the limb skeletal muscle 3 days before and 14 days after ligation. This method improved the survival rate of mice with MI at 4 weeks (61% versus 87%, P <0.05) as well as attenuated LV cavity dilatation and contractile dysfunction, interstitial fibrosis, recruitment of macrophages, and myocardial gene expression of tumor necrosis factor-&agr; and transforming growth factor-&bgr; compared with the nontreated MI mice despite the comparable infarct size calculated as percent LV circumference. Conclusions—The activation of MCP-1 expression contributes to the LV remodeling and failure after MI. An anti-MCP-1 gene therapy can be a useful novel strategy for preventing post-MI heart failure.

Enhanced Generation of Reactive Oxygen Species in the Limb Skeletal Muscles From a Murine Infarct Model of Heart Failure

Background—The generation of reactive oxygen species (ROS) is enhanced in the failing myocardium. We hypothesized that ROS were also increased in the limb skeletal muscles in heart failure. Methods and Results—Myocardial infarction (MI) was created in mice by ligating the left coronary artery. After 4 weeks, the left ventricle was dilated and contractility was diminished by echocardiography. Left ventricular end-diastolic pressure was elevated after MI in association with an increase in lung weight/body weight and the presence of pleural effusion. The generation of ROS in the limb muscles, including the soleus and gastrocnemius muscles, which were excised after MI, was measured by electron spin resonance spectroscopy with 4-hydroxy-2,2,6,6-tetramethyl-piperidine-N-oxyl (hydroxy-TEMPO). Overall, generation was increased, but it was attenuated in the presence of dimethylthiourea or 4,5-dihydroxy-1,2-benzenedisulfonic disodium salt in the reaction mixture, indicating increased generation of hydroxyl radicals originating from superoxide anion. Thiobarbituric acid-reactive substance formation was also increased in muscles after MI. Mitochondrial complex I and III activities were both decreased after MI, which may have caused the functional uncoupling of the respiratory chain and ROS production. Antioxidant enzyme activities, including superoxide dismutase, catalase, and glutathione peroxidase, were comparable between groups. Conclusions—Skeletal muscle in post-MI heart failure expressed an increased amount of ROS in association with ROS-mediated lipid peroxidation. This supports the hypothesis that oxidative stress may cause (at least in part) skeletal muscle dysfunction in heart failure.

Streptozotocin-induced hyperglycemia exacerbates left ventricular remodeling and failure after experimental myocardial infarction.

OBJECTIVES The aim of the present study was to determine whether streptozotocin (STZ)-induced hyperglycemia exacerbates progressive left ventricular (LV) dilation and dysfunction after myocardial infarction (MI). BACKGROUND Diabetes mellitus (DM) adversely affects the outcomes in patients with MI. However, it is unknown whether DM can directly affect the development of post-MI LV remodeling and failure. METHODS Male mice were injected intraperitoneally with STZ (200 mg/kg; DM group) or vehicle only. At two weeks, MI was created in the STZ-injected (DM+MI group) or vehicle-injected mice (MI group) by left coronary artery ligation, and they were followed up for another four weeks. RESULTS Survival during six weeks was significantly lower in the DM+MI versus MI group (25% vs. 71%; p < 0.01), despite a similar infarct size (60 +/- 2% vs. 61 +/- 2%; p = NS). Echocardiography after two weeks of ligation showed LV dilation and dysfunction with MI, both of which were exaggerated in the DM+MI group. Likewise, LV end-diastolic pressure and lung weight were increased in mice with MI, and this increase was enhanced in the DM+MI group. The myocyte cross-sectional area in the non-infarcted LV increased to a similar degree in the DM+MI and MI groups, whereas the collagen volume fraction was greater in the DM+MI group. Deoxyribonucleic acid laddering was greater in the DM+MI group. CONCLUSIONS Hyperglycemia decreased survival and exaggerated LV remodeling and failure after MI by increasing interstitial fibrosis and myocyte apoptosis. Diabetes mellitus could be a risk factor for heart failure, independent of coronary artery lesions.

Endovascular Treatment for Infrainguinal Vessels in Patients With Critical Limb Ischemia OLIVE Registry, a Prospective, Multicenter Study in Japan With 12-Month Follow-up

Background—Recent technical advances have made endovascular treatment (EVT) an alternative first-line treatment for critical limb ischemia. Methods and Results—A prospective multicenter study was conducted to evaluate the clinical outcomes of 314 Japanese critical limb ischemia patients (mean age, 73±10 years) with infrainguinal arterial lesions who underwent EVT. Patients were enrolled from December 2009 to July 2011 and were followed-up for 12 months. The primary end point was amputation-free survival (AFS) at 12 months. Secondary end points were anatomic, clinical, and hemodynamic measures, including 12-month freedom from major adverse limb events. The 12-month AFS rate was 74%, with body mass index <18.5 (hazard ratio [HR], 2.22; P=0.008), heart failure (HR, 1.73; P=0.04), and wound infection (HR, 1.89; P=0.03) associated with a poor prognosis for AFS. The 12-month major adverse limb event-free rate was 88%, with hemodialysis (HR, 1.98; P=0.005), heart failure (HR, 1.69; P=0.02), and Rutherford classification 6 (HR, 2.25; P=0.002) associated with a poor prognosis for major adverse limb events. The median time for wound healing was 97 days, with body mass index <18.5 (HR, 0.54; P=0.03) and wound infection (HR, 0.60; P=0.04) being significant risk factors for unhealed wounds after EVT. At 12 months, 34% had undergone reintervention (bypass surgery, 2.6%; repeat EVT, 31.7%), and 73% were major adverse event–free. Conclusions—The high reintervention rate notwithstanding, EVT was an effective treatment for Japanese critical limb ischemia patients with infrainguinal disease, with satisfactory AFS and major adverse limb event-free rates. The results of this study will be helpful for the future evaluation of critical limb ischemia therapy. Clinical Trial Registration—URL: http://www.umin.ac.jp/ctr. Unique identifier: UMIN000002830.

Hyperhomocysteinemia Alters Cardiac Substrate Metabolism by Impairing Nitric Oxide Bioavailability Through Oxidative Stress

Background— Hyperhomocysteinemia (HHcy) has been considered a vascular disease associated with increased levels of oxidative stress that results in scavenging of NO. However, little is known of the impact of HHcy on cardiac function and especially myocardial metabolism. Methods and Results— L-Homocysteine was intravenously infused into conscious dogs, and the dogs were fed methionine to increase plasma homocysteine to 10 &mgr;mol/L for acute and 24 &mgr;mol/L for chronic HHcy. There was no significant change in hemodynamics with HHcy. Veratrine-induced, NO-dependent, coronary vasodilation (Bezold-Jarisch reflex) was reduced by 32% but was restored by simultaneous intravenous infusion of ascorbic acid or apocynin. Acute and chronic HHcy significantly increased uptake of glucose and lactate and decreased uptake of free fatty acid by the heart. HHcy significantly decreased bradykinin- or carbachol-induced reduction of myocardial oxygen consumption in vitro, and this effect was completely restored by coincubation with ascorbic acid, Tempol, or apocynin. Western blot analysis indicated an increase in Nox2 (82%) and a reduction in endothelial nitric oxide synthase (39%), phospho-endothelial nitric oxide synthase (39%), and superoxide dismutase-1 (45%). Microarray analysis of gene expression in heart tissue from chronic HHcy indicated a switch in cardiac phenotype to enzymes that metabolize glucose. Conclusions— HHcy directly modulates substrate use by the heart independent of changes in hemodynamics or ventricular function by reducing NO bioavailability through the generation of superoxide. The progression of cardiac or coronary heart disease associated with HHcy should be evaluated in light of the impact of alterations in the regulation of cardiac metabolism and substrate use.