Unfavourable consequences of chronic cardiac HIF-1α stabilization

Targets for therapy in sarcomeric cardiomyopathies

To date, no compounds or interventions exist that treat or prevent sarcomeric cardiomyopathies. Established therapies currently improve the outcome, but novel therapies may be able to more fundamentally affect the disease process and course. Investigations of the pathomechanisms are generating molecular insights that can be useful for the design of novel specific drugs suitable for clinical use. As perturbations in the heart are stage-specific, proper timing of drug treatment is essential to prevent initiation and progression of cardiac disease in mutation carrier individuals. In this review, we emphasize potential novel therapies which may prevent, delay, or even reverse hypertrophic cardiomyopathy caused by sarcomeric gene mutations. These include corrections of genetic defects, altered sarcomere function, perturbations in intracellular ion homeostasis, and impaired myocardial energetics.

Pre- and post-conditional inhibition of prolyl-4-hydroxylase domain enzymes protects the heart from an ischemic insult

Several genetically modified mouse models implicated that prolyl-4-hydroxylase domain (PHD) enzymes are critical mediators for protecting tissues from an ischemic insult including myocardial infarction by affecting the stability and activation of hypoxia-inducible factor (HIF)-1 and HIF-2. Thus, the current efforts to develop small-molecule PHD inhibitors open a new therapeutic option for myocardial tissue protection during ischemia. Therefore, we aimed to investigate the applicability and efficacy of pharmacological HIFα stabilization by a small-molecule PHD inhibitor in the heart. We tested for protective effects in the acute phase of myocardial infarction after pre- or post-conditional application of the inhibitor. Application of the specific PHD inhibitor 2-(1-chloro-4-hydroxyisoquinoline-3-carboxamido) acetate (ICA) resulted in HIF-1α and HIF-2α accumulation in heart muscle cells in vitro and in vivo. The rapid and robust responsiveness of cardiac tissue towards ICA was further confirmed by induction of the known HIF target genes heme oxygenase-1 and PHD3. Pre- and post-conditional treatment of mice undergoing myocardial infarction resulted in a significantly smaller infarct size. Tissue protection from ischemia after pre- or post-conditional ICA treatment demonstrates that there is a therapeutic time window for the application of the PHD inhibitor (PHI) post-myocardial infarction, which might be exploited for acute medical interventions.

Poly (ADP-ribose) polymerase-1: an emerging target in right ventricle dysfunction associated with pulmonary hypertension

Recently, inhibition of poly (ADP-ribose) polymerase-1 (PARP1) was shown to be protective in experimental pulmonary hypertension (PH) and prevented right ventricular hypertrophy (RVH) associated with it. However, molecular mechanism behind cardioprotection by PARP1 inhibition in PH still needs detailed exploration. Therefore, effect of inhibition of PARP1 on the right ventricle (RV) dysfunction was studied in monocrotaline (MCT) induced PH model. Following a single dose administration of MCT (60 mg/kg, s.c.), male Sprague-Dawley rats were treated with PARP1 inhibitor 1,5-Isoquinolinediol (ISO, 3 mg/kg, i.p.) for 35 days for preventive study and from day 21-35 for curative study. RV pressure (RVP) and RVH were measured after 35 days. Histophathological studies, PARP1 activity, mRNA and protein expression were studied in isolated RV. Oxidative and nitosative stress, inflammation and Matrix metalloproteinases (MMPs)/Tissue inhibitor of metalloproteinase 2 (TIMP2) were also assessed. Mitochondrial dysfunction was studied by mitochondrial membrane permeability and estimation of Nicotinamide adenine dinucleotide (NAD) and Adenosine triphosphate (ATP). Apoptosis in RV was assessed by Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL), caspase 3 activity and cleaved PARP1 expression. PARP1 inhibition significantly reversed the increase in RVP and RVH in both preventive and curative treatment in the MCT-injected rats. ISO lowered oxidative and nitrosative stress and inflammation and restored the balance of MMPs/TIMP2 expression. PARP1 inhibition prevented mitochondrial dysfunction and the release of cell death factors from mitochondria. ISO also decreased apoptosis by decreasing number of TUNEL positive cells, caspase 3 activity and PARP1 cleavage in RV. Thus, PARP1 inhibition ameliorated PH induced RV hypertrophy and may emerge as a new therapeutic target for PH.

Clinical and echocardiographic correlates of serum copper and zinc in acute and chronic heart failure

AIM

Emerging evidence suggests a pathophysiological role of micronutrient dyshomeostasis in heart failure, including promotion of adverse remodeling and clinical deterioration. We sought to evaluate serum copper (Cu) and zinc (Zn) levels in acute (AHF) and chronic (CHF) heart failure.

METHODS

We studied 125 patients, 71 % male, aged 69 ± 11 years, 37 % with preserved left ventricular ejection fraction (LVEF ≥40 %) (HFPEF), including 81 with AHF and 44 with CHF; 21 healthy volunteers served as controls. Serum Cu and Zn levels were determined using air-acetylene flame atomic absorption spectrophotometry.

RESULTS

Serum Cu levels were significantly higher in AHF (p = 0.006) and CHF (p = 0.002) patients compared to controls after adjusting for age, gender and comorbidities, whereas they did not differ between AHF and CHF (p = 0.840). Additionally, serum Cu in patients with LVEF <40 % was significantly higher compared to both controls (p < 0.001) and HFPEF patients (p = 0.003). Serum Zn was significantly lower in AHF (p < 0.001) and CHF (p = 0.039) compared to control after adjusting for the above-mentioned variables. Moreover, serum Zn was significantly lower in AHF than in CHF (p = 0.015). In multiple linear regression, LVEF (p = 0.033) and E/e ratio (p = 0.006) were independent predictors of serum Cu in total heart failure population, while NYHA class (p < 0.001) and E/e ratio (p = 0.007) were independent predictors of serum Zn.

CONCLUSION

Serum Cu was increased both in AHF and CHF and correlated with LV systolic and diastolic function. Serum Zn, in contrast, was decreased both in AHF and CHF and independently predicted by clinical status and LV diastolic function.

Agonist antibodies activating the Met receptor protect cardiomyoblasts from cobalt chloride-induced apoptosis and autophagy

Met, the tyrosine kinase receptor for hepatocyte growth factor (HGF), mainly activates prosurvival pathways, including protection from apoptosis. In this work, we investigated the cardioprotective mechanisms of Met activation by agonist monoclonal antibodies (mAbs). Cobalt chloride (CoCl₂), a chemical mimetic of hypoxia, was used to induce cardiac damage in H9c2 cardiomyoblasts, which resulted in reduction of cell viability by (i) caspase-dependent apoptosis and (ii) – surprisingly – autophagy. Blocking either apoptosis with the caspase inhibitor benzyloxycarbonyl-VAD-fluoromethylketone or autophagosome formation with 3-methyladenine prevented loss of cell viability, which suggests that both processes contribute to cardiomyoblast injury. Concomitant treatment with Met-activating antibodies or HGF prevented apoptosis and autophagy. Pro-autophagic Redd1, Bnip3 and phospho-AMPK proteins, which are known to promote autophagy through inactivation of the mTOR pathway, were induced by CoCl₂. Mechanistically, Met agonist antibodies or HGF prevented the inhibition of mTOR and reduced the flux of autophagosome formation. Accordingly, their anti-autophagic function was completely blunted by Temsirolimus, a specific mTOR inhibitor. Targeted Met activation was successful also in the setting of low oxygen conditions, in which Met agonist antibodies or HGF demonstrated anti-apoptotic and anti-autophagic effects. Activation of the Met pathway is thus a promising novel therapeutic tool for ischaemic injury.

Induction of the calcineurin variant CnAβ1 after myocardial infarction reduces post-infarction ventricular remodelling by promoting infarct vascularization

AIMS

Ventricular remodelling following myocardial infarction progressively leads to loss of contractile capacity and heart failure. Although calcineurin promotes maladaptive cardiac hypertrophy, we recently showed that the calcineurin splicing variant, CnAβ1, has beneficial effects on the infarcted heart. However, whether this variant limits necrosis or improves remodelling is still unknown, precluding translation to the clinical arena. Here, we explored the effects and therapeutic potential of CnAβ1 overexpression post-infarction.

METHODS AND RESULTS

Double transgenic mice with inducible cardiomyocyte-specific overexpression of CnAβ1 underwent left coronary artery ligation followed by reperfusion. Echocardiographic analysis showed depressed cardiac function in all infarcted mice 3 days post-infarction. Induction of CnAβ1 overexpression 1 week after infarction improved function and reduced ventricular dilatation. CnAβ1-overexpressing mice showed shorter, thicker scars, and reduced infarct expansion, accompanied by reduced myocardial remodelling. CnAβ1 induced vascular endothelial growth factor (VEGF) expression in cardiomyocytes, which resulted in increased infarct vascularization. This paracrine angiogenic effect of CnAβ1 was mediated by activation of the Akt/mammalian target of rapamycin pathway and VEGF.

CONCLUSIONS

Our results indicate that CnAβ1 exerts beneficial effects on the infarcted heart by promoting infarct vascularization and preventing infarct expansion. These findings emphasize the translational potential of CnAβ1 for gene-based therapies.

Partial deficiency of HIF-1α stimulates pathological cardiac changes in streptozotocin-induced diabetic mice

BACKGROUND

Diabetic cardiomyopathy is associated with a number of functional and structural pathological changes such as left ventricular dysfunction, cardiac remodeling, and apoptosis. The primary cause of diabetic cardiomyopathy is hyperglycemia, the metabolic hallmark of diabetes. Recent studies have shown that a diabetic environment suppresses hypoxia-inducible factor (HIF)-1α protein stability and function. The aim of this study was to analyze the functional role of HIF-1α in the development of diabetic cardiomyopathy. We have hypothesized that the partial deficiency of HIF-1α may compromise cardiac responses under diabetic conditions and increase susceptibility to diabetic cardiomyopathy.

METHODS

Diabetes was induced by streptozotocin in wild type (Wt) and heterozygous Hif1a knock-out (Hif1a+/-) mice. Echocardiographic evaluations of left ventricular functional parameters, expression analyses by qPCR and Western blot, and cardiac histopathology assessments were performed in age-matched groups, diabetic, and non-diabetic Wt and Hif1a+/- mice.

RESULTS

Five weeks after diabetes was established, a significant decrease in left ventricle fractional shortening was detected in diabetic Hif1a+/- but not in diabetic Wt mice. The combination effects of the partial deficiency of Hif1a and diabetes affected the gene expression profile of the heart, including reduced vascular endothelial growth factor A (Vegfa) expression. Adverse cardiac remodeling in the diabetic Hif1a+/- heart was shown by molecular changes in the expression of structural molecules and components of the extracellular matrix.

CONCLUSIONS

We have shown a correlation between heterozygosity for Hif1α and adverse functional, molecular, and cellular changes associated with diabetic cardiomyopathy. Our results provide evidence that HIF-1α regulates early cardiac responses to diabetes, and that HIF-1α deregulation may influence the increased risk for diabetic cardiomyopathy.

Oxygen consumption and usage during physical exercise: the balance between oxidative stress and ROS-dependent adaptive signaling

The complexity of human DNA has been affected by aerobic metabolism, including endurance exercise and oxygen toxicity. Aerobic endurance exercise could play an important role in the evolution of Homo sapiens, and oxygen was not important just for survival, but it was crucial to redox-mediated adaptation. The metabolic challenge during physical exercise results in an elevated generation of reactive oxygen species (ROS) that are important modulators of muscle contraction, antioxidant protection, and oxidative damage repair, which at moderate levels generate physiological responses. Several factors of mitochondrial biogenesis, such as peroxisome proliferator-activated receptor-γ coactivator 1α (PGC-1α), mitogen-activated protein kinase, and SIRT1, are modulated by exercise-associated changes in the redox milieu. PGC-1α activation could result in decreased oxidative challenge, either by upregulation of antioxidant enzymes and/or by an increased number of mitochondria that allows lower levels of respiratory activity for the same degree of ATP generation. Endogenous thiol antioxidants glutathione and thioredoxin are modulated with high oxygen consumption and ROS generation during physical exercise, controlling cellular function through redox-sensitive signaling and protein-protein interactions. Endurance exercise-related angiogenesis, up to a significant degree, is regulated by ROS-mediated activation of hypoxia-inducible factor 1α. Moreover, the exercise-associated ROS production could be important to DNA methylation and post-translation modifications of histone residues, which create heritable adaptive conditions based on epigenetic features of chromosomes. Accumulating data indicate that exercise with moderate intensity has systemic and complex health-promoting effects, which undoubtedly involve regulation of redox homeostasis and signaling.

Preoperative HO-1 levels as prognostic factor for adverse cardiac events in elder patients undergoing non-cardiac surgery

BACKGROUND

Hypoxia-inducible factor-1α (HIF-1α) and heme oxygenase-1(HO-1) are involved in the tissue hypoxic response.

HYPOTHESIS

HIF-1α and HO-1 levels may predict cardiac ischemia and adverse cardiac events during non-cardiac surgery.

METHODS

HIF-1α and HO-1 levels were determined in elderly patients undergoing non-cardiac surgery preoperatively and at 30 minutes, 48 and 72 hours postoperatively. Results were analyzed with respect to the occurrence of adverse cardiac events.

RESULTS

A total of 380 patients with a mean age of 65.3 years were included, and 54 (14.2%) who had adverse cardiac events during or after the surgery. HIF-1α and HO-1 levels in the adverse cardiac event group were significantly higher than in the group without adverse cardiac events at each time point (all, P<0.05). In multivariates regression analysis, the odds of an adverse cardiac event was increased by every 1-year increase in age (odd ratio [OR] 1.39, P<0.001), abnormal ECG at baseline (OR 2.27, P = 0.048), myocardial infarction history (OR 3.18, P = 0.015), and positive baseline cTnI level were associated with an increased likelihood of an adverse cardiac event (OR 8.78, P = 0.019), and for every 1 unit increase of HO-1, the odds of an adverse cardiac event increased by 1.30 (P = 0.002).

CONCLUSION

Determination of preoperative HO-1 levels may aid in identifying patients at risk of developing ischemic cardiac events.

Infarct-remodelled hearts with limited oxidative capacity boost fatty acid oxidation after conditioning against ischaemia/reperfusion injury

AIMS

Infarct-remodelled hearts are less amenable to protection against ischaemia/reperfusion. Understanding preservation of energy metabolism in diseased vs. healthy hearts may help to develop anti-ischaemic strategies effective also in jeopardized myocardium.

METHODS AND RESULTS

Isolated infarct-remodelled/sham Sprague-Dawley rat hearts were perfused in the working mode and subjected to 15 min of ischaemia and 30 min of reperfusion. Protection of post-ischaemic ventricular work was achieved by pharmacological conditioning with sevoflurane. Oxidative metabolism was measured by substrate flux in fatty acid and glucose oxidation using [(3)H]palmitate and [(14)C]glucose. Mitochondrial oxygen consumption was measured in saponin-permeabilized left ventricular muscle fibres. Activity assays of citric acid synthase, hydroxyacyl-CoA dehydrogenase, and pyruvate dehydrogenase and mass spectrometry for acylcarnitine profiling were also performed. Six weeks after coronary artery ligation, the hearts exhibited macroscopic and molecular signs of hypertrophy consistent with remodelling and limited respiratory chain and citric acid cycle capacity. Unprotected remodelled hearts showed a marked decline in palmitate oxidation and acetyl-CoA energy production after ischaemia/reperfusion, which normalized in sevoflurane-protected remodelled hearts. Protected remodelled hearts also showed higher β-oxidation flux as determined by increased oxygen consumption with palmitoylcarnitine/malate in isolated fibres and a lower ratio of C16:1+C16OH/C14 carnitine species, indicative of a higher long-chain hydroxyacyl-CoA dehydrogenase activity. Remodelled hearts exhibited higher PPARα-PGC-1α but defective HIF-1α signalling, and conditioning enabled them to mobilize fatty acids from endogenous triglyceride stores, which closely correlated with improved recovery.

CONCLUSIONS

Protected infarct-remodelled hearts secure post-ischaemic energy production by activation of β-oxidation and mobilization of fatty acids from endogenous triglyceride stores.

Hypoxia-inducible factor as a therapeutic target for cardioprotection

Hypoxia inducible factor (HIF) is an oxygen-sensitive transcription factor that enables aerobic organisms to adapt to hypoxia. This is achieved through the transcriptional activation of up to 200 genes, many of which are critical to cell survival. Under conditions of normoxia, the hydroxylation of HIF by prolyl hydroxylase domain-containing (PHD) enzymes targets it for polyubiquitination and proteosomal degradation by the von Hippel-Lindau protein (VHL). However, under hypoxic conditions, PHD activity is inhibited, thereby allowing HIF to accumulate and translocate to the nucleus, where it binds to the hypoxia-responsive element sequences of target gene promoters. Experimental studies suggest that HIF may act as a mediator of ischemic preconditioning, and that the genetic or pharmacological stabilization of HIF under normoxic conditions, may protect the heart against the detrimental effects of acute ischemia-reperfusion injury. The mechanisms underlying the cardioprotective effect of HIF are unclear, but it may be attributed to the transcriptional activation of genes associated with cardioprotection such as erythropoietin, heme oxygenase-1, and inducible nitric oxide synthase or it may be due to reprogramming of cell metabolism. In this review article, we highlight the role of HIF in mediating both adaptive and pathological processes in the heart, as well as focusing on the therapeutic potential of the HIF-signaling pathway as a target for cardioprotection.