Endothelin-1 production is enhanced by rotenone, a mitochondrial complex I inhibitor, in cultured rat cardiomyocytes

Activated FMS-like tyrosine kinase 3 ameliorates angiotensin II-induced cardiac remodelling

AIM

FMS-like receptor tyrosine kinase 3 (Flt3) has been reported to be increased in cardiomyocytes responding to ischaemic stress. This study was to determine whether Flt3 activation could ameliorate pressure overload-induced heart hypertrophy and fibrosis, and to elucidate the mechanisms of action.

METHODS

In vivo cardiac hypertrophy and remodelling experiments were conducted by infusing angiotensin II (Ang II) chronically in male C57BL/6 mice. Flt3-specific ligand (FL) was administered intraperitoneally every two days (5 µg/mouse). In vitro experiments on hypertrophy, apoptosis and autophagy mechanism were performed in neonatal rat cardiomyocytes (NRCMs) and H9c2 cells with adenovirus vector-mediated overexpression of Flt3.

RESULTS

Our results demonstrated that following chronic Ang II infusion for 4 weeks, the mice exhibited heart hypertrophy, fibrosis, apoptosis and contractile dysfunction. Meanwhile, Ang II induced autophagic responses in mouse hearts, as evidenced by increased LC3 II and decreased P62 expression. These pathological alterations in Ang II-treated mice were significantly ameliorated by Flt3 activation with FL administration. In NRCMs and Flt3-overexpressed H9c2 cells, FL attenuated Ang II-induced pathological autophagy and inactivated AMPK/mTORC1/FoxO3a signalling, thereby efficiently mitigating cell hypertrophy and apoptosis. Conversely, the AMPK activator metformin or the mTORC1 inhibitor rapamycin reversed the effects of FL on the alterations of autophagy, hypertrophy and apoptosis in cardiomyocytes induced by Ang II.

CONCLUSION

Flt3 activation ameliorates cardiac hypertrophy, fibrosis and contractile dysfunction in the mouse model of chronic pressure overload, most likely via suppressing AMPK/mTORC1/FoxO3a-mediated autophagy. These results provide new evidence supporting Flt3 as a novel therapeutic target in maladaptive cardiac remodelling.

Arginine promotes porcine type I muscle fibres formation through improvement of mitochondrial biogenesis

The present study aimed to investigate whether arginine (Arg) promotes porcine type I muscle fibres formation via improving mitochondrial biogenesis. In the in vivo study, a total of sixty Duroc × Landrace × Yorkshire weaning piglets with an average body weight of 6·55 (sd 0·36) kg were randomly divided into four treatments and fed with a basal diet or a basal diet supplemented with 0·5, 1·0 and 1·5 % l-Arg, respectively, in a 4-week trial. Results showed that dietary supplementation of 1·0 % Arg significantly enhanced the activity of succinate dehydrogenase, up-regulated the protein expression of myosin heavy chain I (MyHC I) and increased the mRNA levels of MyHC I, troponin I1, C1 and T1 (Tnni1, Tnnc1 and Tnnt1) in longissimus dorsi muscle compared with the control group. In addition, ATPase staining analysis indicated that 1·0 % Arg supplementation significantly increased the number of type I muscle fibres and significantly decreased the number of type II muscle fibres. Furthermore, 1·0 % Arg supplementation significantly up-regulated PPAR-γ coactivator-1α (PGC-1α), sirtuin 1 and cytochrome c (Cytc) protein expressions, increased PGC-1α, nuclear respiratory factor 1 (NRF1), mitochondria transcription factor B1 (TFB1M), Cytc and ATP synthase subunit C1 (ATP5G) mRNA levels and increased mitochondrial DNA content. In the in vitro study, mitochondrial complex I inhibitor rotenone (Rot) was used. We found that Rot annulled Arg-induced type I muscle fibres formation. Together, our results provide for the first time the evidence that Arg promotes porcine type I muscle fibres formation through improvement of mitochondrial biogenesis.

Protective effects of grape seed proanthocyanidins on cardiovascular remodeling in DOCA-salt hypertension rats

Cardiovascular remodeling, as a hallmark of hypertension-induced pathophysiology, causes substantial cardiovascular morbidity and mortality. There is increasing evidence that has demonstrated a broad spectrum of pharmacological and therapeutic benefits of grape seed proanthocyanidins (GSP) against oxidative stress and cardiovascular diseases. In this study, 180- to 200-g SD rats treated with DOCA (120 mg/week sc with 1% NaCl and 0.2% KCl in drinking water) and GSP (150, 240, 384 mg/kg) or amlodipine (ALM) (5 mg/kg) for 4 weeks were recruited. The protective effects of GSP on blood pressure and cardiovascular remodeling in rats with DOCA-salt-induced hypertension were investigated. Our results indicated that DOCA-salt could induce hypertension, cardiovascular remodeling and dysfunction, oxidative stress and the release of endothelin-1 (ET-1) and could increase JNK1/2 and p38MAPK phosphorylation. GSP or ALM treatments significantly improved hypertension, cardiovascular remodeling and dysfunction and oxidative stress, restrained the release of ET-1 and down-regulated the JNK1/2 and p38MAPK phosphorylation. These findings demonstrate that GSP has protective effects against increase of blood pressure induced by DOCA-salt hypertension and cardiovascular remodeling by inhibiting the reactive oxygen species/mitogen-activated protein kinase pathway via restraining the release of ET-1.

Endothelin-1 induces a glycolytic switch in pulmonary arterial endothelial cells via the mitochondrial translocation of endothelial nitric oxide synthase

Recent studies have indicated that, during the development of pulmonary hypertension (PH), there is a switch from oxidative phosphorylation to glycolysis in the pulmonary endothelium. However, the mechanisms underlying this phenomenon have not been elucidated. Endothelin (ET)-1, an endothelial-derived vasoconstrictor peptide, is increased in PH, and has been shown to play an important role in the oxidative stress associated with PH. Thus, in this study, we investigated whether there was a potential link between increases in ET-1 and mitochondrial remodeling. Our data indicate that ET-1 induces the redistribution of endothelial nitric oxide synthase (eNOS) from the plasma membrane to the mitochondria in pulmonary arterial endothelial cells, and that this was dependent on eNOS uncoupling. We also found that ET-1 disturbed carnitine metabolism, resulting in the attenuation of mitochondrial bioenergetics. However, ATP levels were unchanged due to a compensatory increase in glycolysis. Further mechanistic investigations demonstrated that ET-1 mediated the redistribution of eNOS via the phosphorylation of eNOS at Thr495 by protein kinase C δ. In addition, the glycolytic switch appeared to be dependent on mitochondrial-derived reactive oxygen species that led to the activation of hypoxia-inducible factor signaling. Finally, the cell culture data were confirmed in vivo using the monocrotaline rat model of PH. Thus, we conclude that ET-1 induces a glycolytic switch in pulmonary arterial endothelial cells via the redistribution of uncoupled eNOS to the mitochondria, and that preventing this event may be an approach for the treatment of PH.

Nucleoside reverse transcriptase inhibitors induce a mitophagy-associated endothelial cytotoxicity that is reversed by coenzyme Q10 cotreatment

Cardiovascular complications have been documented in HIV-1 infected populations, and antiretroviral therapy may play a role. Nucleoside reverse transcriptase inhibitors (NRTIs) are antiretrovirals known to induce mitochondrial damage in endothelial cells, culminating in endothelial dysfunction, an initiating event in atherogenesis. Though the mechanism for NRTI-induced endothelial toxicity is not yet clear, our prior work suggested that a mitochondrial oxidative stress may be involved. To further delineate the mechanism of toxicity, endothelial cells were treated with NRTIs of varying subclasses, and the level of reactive oxygen species (ROS) and mitochondrial function were assessed. To test whether rescue of mitochondrial electron transport attenuated NRTI-induced endothelial cytotoxicity, in some cases, cells were cotreated with the electron transport cofactor coenzyme Q10 (Q10). At 4-6h, NRTIs increased levels of ROS but decreased the activities of electron transport chain complexes I-IV, levels of ATP and the NAD/NADH ratio. Moreover, nitric oxide levels were decreased, whereas endothelin-1 release was increased. Q10 abolished NRTI-induced mitochondria injury and effects on endothelial agonist production. Interestingly, in cells treated with NRTIs only, markers for mitochondrial toxicity returned to baseline levels by 18-24h, suggesting a compensatory mechanism for clearing damaged mitochondria. Using confocal microscopy, with confirmation utilizing the autophagy and mitophagy markers LC-3 and Nix, respectively, we observed autophagy of mitochondria at 8-10h after treatment. Q10 prevented NRTI-mediated increase in LC-3. These findings suggest that NRTI-induced mitophagy may be involved in NRTI-induced endothelial dysfunction and that this damage likely results from oxidant injury. Further, Q10 supplementation could potentially prevent NRTI-induced endothelial dysfunction.

Different redox response elicited by naturally occurring antioxidants in human endothelial cells

Evidences that higher natural antioxidant (NA) intake provides protection against cardiovascular disease (CVD) are contradictory. Oxidative-induced endothelial cells (ECs) injury is the key step in the onset and progression of CVD and for this reason the cellular responses resulting from NA interaction with ECs are actively investigated. This study was designed to investigate the direct impact of different naturally occurring antioxidants on the intracellular ROS levels in cultured human ECs. NA-induced redox changes, in terms of modulation of the intracellular ROS levels, were assessed by using the ROS fluorescent probe 2',7'-dichlorodihydrofluorescein diacetate (H2DCF-DA). While caffeic and caftaric acid exerted an anti-oxidant effect, both coumaric acid and resveratrol were pro-oxidant. Anti- and pro-oxidant effects of the tested compounds were concentration dependent, showing the induction or the tendency to promote a pro-oxidant outcome with increasing concentrations. Interestingly, the anti- and pro-oxidant behavior of chlorogenic and ferulic acid was dependent on the basal intracellular redox state. Our data indicate that naturally occurring antioxidants are able to induce a rapid modification of the intracellular ROS levels in human ECs, which is dependent on both the applied concentration and the intracellular redox state.

Attenuation of Doxorubicin-induced cardiomyopathy by endothelin-converting enzyme-1 ablation through prevention of mitochondrial biogenesis impairment

Doxorubicin is an effective antineoplastic drug; however, its clinical benefit is limited by its cardiotoxicity. The inhibition of mitochondrial biogenesis is responsible for the pathogenesis of doxorubicin-induced cardiomyopathy. Endothelin-1 is a vasoconstrictive peptide produced from big endothelin-1 by endothelin-converting enzyme-1 (ECE-1) and a multifunctional peptide. Although plasma endothelin-1 levels are elevated in patients treated with doxorubicin, the effect of ECE-1 inhibition on doxorubicin-induced cardiomyopathy is not understood. Cardiomyopathy was induced by a single IP injection of doxorubicin (15 mg/kg). Five days after treatment, cardiac function, histological change, and mitochondrial biogenesis were assessed. Echocardiography revealed that cardiac systolic function was significantly deteriorated in doxorubicin-treated wild-type (ECE-1(+/+)) mice compared with ECE-1 heterozygous knockout (ECE-1(+/-)) mice. In histological analysis, cardiomyocyte size in ECE-1(+/-) mice was larger, and cardiomyocyte damage was less. In ECE-1(+/+) mice, tissue adenosine triphosphate content and mitochondrial superoxide dismutase were decreased, and reactive oxygen species generation was increased compared with ECE-1(+/-) mice. Cardiac mitochondrial deoxyribonucleic acid copy number and expressions of key regulators for mitochondrial biogenesis were decreased in ECE-1(+/+) mice. Cardiac cGMP content and serum atrial natriuretic peptide concentration were increased in ECE-1(+/-) mice. In conclusion, the inhibition of ECE-1 attenuated doxorubicin-induced cardiomyopathy by inhibiting the impairment of cardiac mitochondrial biogenesis. This was mainly induced by decreased endothelin-1 levels and an enhanced atrial natriuretic peptide-cGMP pathway. Thus, the inhibition of ECE-1 may be a new therapeutic strategy for doxorubicin-induced cardiomyopathy.

Mechanism of uptake and retention of F-18 BMS-747158-02 in cardiomyocytes: a novel PET myocardial imaging agent

BACKGROUND

BMS-747158-02 is a novel fluorine 18-labeled pyridazinone derivative designed for cardiac imaging. The uptake and retention mechanisms of F-18 BMS-747158-02 in cardiac myocytes were studied in vitro, and the biodistribution of F-18 BMS-747158-02 was studied in vivo in mice.

METHODS AND RESULTS

Fluorine 19 BMS-747158-01 inhibited mitochondrial complex I (MC-I) in bovine heart submitochondrial particles with an IC(50) of 16.6 +/- 3 nmol/L that was comparable to the reference inhibitors of MC-1, rotenone, pyridaben, and deguelin (IC(50) of 18.2 +/- 6.7 nmol/L, 19.8 +/- 2.6 nmol/L, and 23.1 +/- 1.5 nmol/L, respectively). F-18 BMS-747158-02 had high uptake in monolayers of neonatal rat cardiomyocytes (10.3% +/- 0.7% of incubated drug at 60 minutes) that was inhibited by 200 nmol/L of rotenone (91% +/- 2%) and deguelin (89% +/- 3%). In contrast, an inactive pyridaben analog, P-070 (IC(50) value >4 micromol/L in MC-1 assay), did not inhibit the binding of F-18 BMS-747158-02 in cardiomyocytes. Uptake and washout kinetics for F-18 BMS-747158-02 in rat cardiomyocytes indicated that the time to half-maximal (t((1/2))) uptake was very rapid (approximately 35 seconds), and washout t((1/2)) for efflux of F-18 BMS-747158-02 was greater than 120 minutes. In vivo biodistribution studies in mice showed that F-18 BMS-747158-02 had substantial myocardial uptake (9.5% +/- 0.5% of injected dose per gram) at 60 minutes and heart-to-lung and heart-to-liver ratios of 14.1 +/- 2.5 and 8.3 +/- 0.5, respectively. Positron emission tomography imaging in the mouse allowed clear cardiac visualization and demonstrated sustained myocardial uptake through 55 minutes.

CONCLUSIONS

F-18 BMS-747158-02 is a novel positron emission tomography cardiac tracer targeting MC-I in cardiomyocytes with rapid uptake and slow washout. These characteristics allow fast and sustained accumulation in the heart.

Vascular endothelin in hypertension

Endothelins are powerful vasoconstrictor peptides that also play numerous other functions in many different organs. Endothelin-1 (ET-1) is the most abundant and important of this family of peptides in blood vessels. Production of ET-1 is increased in the endothelium and the kidney in salt-dependent models of hypertension (e.g.: DOCA-salt rats and Dahl salt-sensitive rats, in salt-loaded SHR-SP, in angiotensin II-infused and in diabetic rats). ET-1 elicits an inflammatory response by increasing oxidant stress in the vascular wall, which induces vascular remodeling and endothelial dysfunction found in the hypertensive models that exhibit an endothelin-mediated component. Endothelin receptor antagonism reduces blood pressure and vascular hypertrophic remodeling present in these hypertensive models. Patients with stage 2 hypertension have enhanced vascular expression of ET-1. Endothelin receptor antagonists lower blood pressure in hypertensive patients. They could become therapeutic agents for prevention of target organ damage in hypertension and in type 2 diabetes, chronic renal failure and congestive heart failure. Side effects of endothelin receptor blockers have prevented up to the present their development for these indications. New endothelin antagonists devoid of these side effects, or alternatively inhibitors of the endothelin converting enzymes that generate ET-1 may in the future become available to block the endothelin system. However, to date endothelin antagonists have been approved only for the treatment of primary pulmonary hypertension, a rapidly fatal condition in which the endothelin system plays an important role and endothelin antagonists exert favorable effects.

Angiotensin II and endothelin-1 regulate MAP kinases through different redox-dependent mechanisms in human vascular smooth muscle cells

OBJECTIVE

The role of reactive oxygen species (ROS) in mitogen-activated protein kinase (MAPK) signaling by angiotensin (Ang) II and endothelin-1 (ET-1) in human vascular smooth muscle cells (VSMC) was investigated.

DESIGN

VSMCs were derived from resistance arteries from healthy subjects. MAPK activity was assessed using phospho-specific antibodies. ROS generation was measured by CMH2DCFDA fluorescence and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity by lucigenin chemiluminescence.

RESULTS

Ang II and ET-1 increased MAPK phosphorylation (P < 0.01). Pre-treatment with Tiron and Tempol, *O2 scavengers, attenuated agonist-stimulated phosphorylation of p38MAPK, c-Jun N-terminal kinases (JNK) and ERK5, but not of ERK1/2 (extracellular signal-regulated kinases). Apocynin and diphenylene iodinium (DPI), NAD(P)H oxidase inhibitors, decreased Ang II-induced responses 60-70%. ET-1-mediated MAPK phosphorylation was unaffected by apocynin but was reduced (> 50%) by thenoyltrifluoroacetone (TIFT) and carboxyl cyanide-m-chlorophenylhydrazone (CCCP), mitochondrial inhibitors. Allopurinol and N-nitro-l-arginine methyl ester (l-NAME), xanthine oxidase and nitric oxide synthase (NOS) inhibitors, respectively, did not influence MAPK activation. Intracellular ROS generation, was increased by Ang II and ET-1 (P < 0.01). DPI inhibited Ang II- but not ET-1-mediated ROS production. Expression of p22phox and p47phox and activation of NAD(P)H oxidase were increased by Ang II but not by ET-1. CCCP and TIFT significantly attenuated ET-1-mediated ROS formation (P < 0.05), without influencing Ang II effects.

CONCLUSIONS

Ang II activates p38MAPK, JNK and ERK5 primarily through NAD(P)H oxidase-generated ROS. ET-1 stimulates these kinases via redox-sensitive processes that involve mitochondrial-derived ROS. These data suggest that redox-dependent activation of MAPKs by Ang II and ET-1 occur through distinct ROS-generating systems that could contribute to differential signaling by these agonists in VSMCs.

Prostaglandin E2 protects the heart from ischemia-reperfusion injury via its receptor subtype EP4

BACKGROUND

In the heart with acute myocardial infarction, production of prostaglandin (PG) E2 increases significantly. In addition, several subtypes of PGE2 receptors (EPs) have been reported to be expressed in the heart. The role of PGE2 in cardiac ischemia-reperfusion (I/R) injury, however, remains unknown. We intended to clarify the role of PGE2 via EP4, an EP subtype, in I/R injury using mice lacking EP4 (EP4-/- mice).

METHODS AND RESULTS

In murine cardiac ventricle, competitive reverse transcription-polymerase chain reaction revealed the highest expression level of EP4 mRNA among EP mRNAs. EP4-/- mice had larger infarct size than wild-type mice in a model of I/R; the left anterior descending coronary artery was occluded for 1 hour, followed by 24 hours of reperfusion. In addition, isolated EP4-/- hearts perfused according to the Langendorff technique had greater functional and biochemical derangements in response to I/R than wild-type hearts. In vitro, AE1-329, an EP4 agonist, raised cAMP concentration remarkably in noncardiomyocytes, whereas the action was weak in cardiomyocytes. When 4819-CD, another EP4 agonist, was administered 1 hour before coronary occlusion, it reduced infarct size significantly in wild-type mice. Notably, a similar cardioprotective effect was observed even when it was administered 50 minutes after coronary occlusion.

CONCLUSIONS

Both endogenous PGE2 and an exogenous EP4 agonist protect the heart from I/R injury via EP4. The potent cardioprotective effects of 4819-CD suggest that the compound would be useful for treatment of acute myocardial infarction.

Apoptotic death in Leishmania donovani promastigotes in response to respiratory chain inhibition: complex II inhibition results in increased pentamidine cytotoxicity

The biochemical changes consequent to respiratory chain inhibition and their relationship to cell death in Leishmania spp. remain elusive. Inhibitors of respiratory chain complexes I, II, and III were able to induce apoptotic death of the bloodstream form of Leishmania donovani. Complex I inhibition resulted in mitochondrial hyperpolarization that was preceded by increased superoxide production. Limitation of electron transport by thenoyltrifluoroacetone and antimycin A, inhibitors of complexes II and III, respectively, resulted in dissipation of mitochondrial membrane potential that was sensitive to cyclosporin A, a blocker of mitochondrial permeability transition pore. Further studies conducted with thenoyltrifluoroacetone showed maximal generation of hydrogen peroxide with a moderate elevation of superoxide levels. Complex III inhibition provoked superoxide generation only. Interference with complex II but not complexes I and III increased intracellular Ca(2+). A tight link between Ca(2+) and reactive oxygen species was demonstrated by antioxidant-induced diminution of the Ca(2+) increase. However, chelation of extracellular Ca(2+) could not abrogate the early increase of reactive oxygen species, providing evidence that Ca(2+) elevation was downstream to reactive oxygen species generation. Ca(2+) influx occurred through nonselective cation and L-type channels and Na(+)/Ca(2+) exchanger-like pathways. Antioxidants such as glutathione and Ca(2+) channel blockers reduced apoptotic death. This study provides a new possibility that concurrent inhibition of respiratory chain complex II with pentamidine administration increases cytotoxicity of the drug. This increased cytotoxicity was connected to a 4-fold elevation in intracellular Ca(2+) that was pooled only from intracellular sources. Therefore, inhibition of complexes I, II, and III leads to apoptosis and complex II inhibition in parallel with pentamidine administration-enhanced drug efficacy.

Dysfunction of mitochondrial respiratory chain complex I in human failing myocardium is not due to disturbed mitochondrial gene expression

OBJECTIVES

Activity of mitochondrial respiratory chain complexes with and without mitochondrially encoded subunits was assessed in failing human myocardium together with parameters of mitochondrial gene expression.

BACKGROUND

Mutations and deletions in mitochondrial genome (mtDNA) sporadically accumulate in the aging myocardium. In experimental heart failure, they are discussed to be a generalized problem resulting in disturbances of mitochondrial gene expression and mitochondrial function.

METHODS

In left ventricular specimens from 43 explanted failing hearts and 10 donor hearts, enzyme activities of respiratory chain complexes, messenger ribonucleic acid (mRNA) expression of mitochondrially and nuclear encoded mitochondrial components (reverse transcriptase-polymerase chain reaction, Northern blot), undeleted wildtype mtDNA (Southern blot), and nuclear encoded mitochondrial transcription factor A (mtTFA) (Western blot) were quantified.

RESULTS

Citrate synthase normalized activity of mitochondrial respiratory chain complex I, which contains seven mitochondrially encoded subunits, was decreased by 28% in terminally failing myocardium, whereas the activity of the exclusively nuclear encoded complex II was unchanged. However, the amount of intact mtDNA, the mRNA of all mitochondrially encoded subunits of the entire respiratory chain, the amount of mtTFA, and the enzymatic activity of complex III and complex IV, which also contain mitochondrially encoded subunits, were normal compared with donor hearts, excluding generalized disturbance of mitochondrial gene expression. Retrospective analysis of drug therapy before transplantation identified beta-blockers as one putative protection against this disturbance.

CONCLUSIONS

In terminally failing human myocardium of patients receiving drug therapy, complex I depression is not caused by mtDNA damage and disturbed mitochondrial gene expression. The absence of mtDNA damage should facilitate recovery of the overloaded myocardium, if effective unloading could be achieved.

Endothelin-1 stimulates cardiomyocyte injury during mitochondrial dysfunction in culture

To understand the pathophysiological role of endothelin-1 in the failing heart, we constructed a cellular mitochondrial impairment model and demonstrated the effect of endothelin-1. Primary cultured cardiomyocytes from neonatal rats were pretreated with rotenone, a mitochondrial complex I inhibitor, and the cytotoxic effect of endothelin-1 on the cardiomyocytes was demonstrated. Rotenone gradually decreased the pH of the culture medium with incubation time and caused slight cell injury. Endothelin-1 markedly enhanced the effect of rotenone that decreased the pH of the medium and enhanced cellular injury. The enhancement of the decrease in pH and cell injury induced by endothelin-1 was counteracted by the endothelin ET(A) receptor antagonist BQ123 or by maintaining the pH of the medium by the addition of 50 mM HEPES. Endothelin-1 markedly increased the uptake of 2-deoxyglucose and lactic acid production when the cardiomyocytes were pretreated with rotenone. These findings suggest that the stimulation of glucose uptake and anaerobic glycolysis followed by the increase in lactic acid accumulation in cardiomyocytes under the condition of mitochondrial impairment may be involved, at least in part, in the cellular injury by endothelin-1. Moreover, these findings suggest the possibility that the effect of endothelin-1 on myocardium is reversed by the condition of the mitochondria, and endogenous endothelin-1 may deteriorate cardiac failure with mitochondrial dysfunction. This may contribute to clarify the beneficial effect of endothelin receptor blockade in improving heart failures.