Tetsuya Shiomi

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.

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.

Overexpression of Glutathione Peroxidase Prevents Left Ventricular Remodeling and Failure After Myocardial Infarction in Mice

Background—Oxidative stress plays an important role in the pathophysiology of heart failure. We determined whether the overexpression of glutathione peroxidase (GSHPx) could attenuate left ventricular (LV) remodeling and failure after myocardial infarction (MI). Methods and Results—We created MI in 12- to 16-week-old, male GSHPx transgenic mice (TG+MI) and nontransgenic wild-type littermates (WT+MI) by ligating the left coronary artery. GSHPx activity was increased in the hearts of TG mice, with no significant changes in other antioxidant enzymes. LV concentrations of thiobarbituric acid–reactive substances measured in TG+MI at 4 weeks were significantly lower than those in WT+MI. The survival rate during 4 weeks of MI was significantly higher in TG+MI than in WT+MI, although the infarct size was comparable. LV cavity dilatation and dysfunction were significantly attenuated in TG+MI. LV end-diastolic pressure was increased in WT+MI and reduced in TG+MI. Improvement of LV function in TG+MI was accompanied by a decrease in myocyte hypertrophy, apoptosis, and interstitial fibrosis in the noninfarcted LV. Myocardial matrix metalloproteinase-9 zymographic and protein levels were increased in WT+MI after 3 days but were attenuated in TG+MI. Conclusions—Overexpression of GSHPx inhibited LV remodeling and failure after MI. Therapies designed to interfere with oxidative stress might be beneficial to prevent cardiac 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.

Angiotensin II Type 1 Receptor Blocker Attenuates Exacerbated Left Ventricular Remodeling and Failure in Diabetes-Associated Myocardial Infarction

Diabetes mellitus adversely affects the outcomes in patients with myocardial infarction (MI), due in part to the exacerbation of left ventricular (LV) remodeling. Although angiotensin II type 1 receptor blocker (ARB) has been demonstrated to be effective in the treatment of heart failure, information about the potential benefits of ARB on advanced LV failure associated with diabetes is lacking. To induce diabetes, male mice were injected intraperitoneally with streptozotocin (200 mg/kg). At 2 weeks, anterior MI was created by ligating the left coronary artery. These animals received treatment with olmesartan (0.1 mg/kg/day; n = 50) or vehicle (n = 51) for 4 weeks. Diabetes worsened the survival and exaggerated echocardiographic LV dilatation and dysfunction in MI. Treatment of diabetic MI mice with olmesartan significantly improved the survival rate (42% versus 27%, P < 0.05) without affecting blood glucose, arterial blood pressure, or infarct size. It also attenuated LV dysfunction in diabetic MI. Likewise, olmesartan attenuated myocyte hypertrophy, interstitial fibrosis, and the number of apoptotic cells in the noninfarcted LV from diabetic MI. Post-MI LV remodeling and failure in diabetes were ameliorated by ARB, providing further evidence that angiotensin II plays a pivotal role in the exacerbated heart failure after diabetic MI.