Hypoxia-inducible factor-1α and vascular endothelial growth factor in the cardioprotective effects of intermittent hypoxia in rats

Intermittent Hypoxic Preconditioning Plays a Cardioprotective Role in Doxorubicin-Induced Cardiomyopathy

Intermittent hypoxic preconditioning (IHP) is a well-established cardioprotective intervention in models of ischemia/reperfusion injury. Nevertheless, the significance of IHP in different cardiac pathologies remains elusive. In order to investigate the role of IHP and its effects on calcium-dependent signalization in HF, we employed a model of cardiomyopathy induced by doxorubicin (Dox), a widely used drug from the class of cardiotoxic antineoplastics, which was i.p. injected to Wistar rats (4 applications of 4 mg/kg/week). IHP-treated group was exposed to IHP for 2 weeks prior to Dox administration. IHP ameliorated Dox-induced reduction in cardiac output. Western blot analysis revealed increased expression of sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA2a) while the expression of hypoxia inducible factor (HIF)-1-α, which is a crucial regulator of hypoxia-inducible genes, was not changed. Animals administered with Dox had further decreased expression of TRPV1 and TRPV4 (transient receptor potential, vanilloid subtype) ion channels along with suppressed Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) activation. In summary, IHP-mediated improvement in cardiac output in the model of Dox-induced cardiomyopathy is likely a result of increased SERCA2a expression which could implicate IHP as a potential protective intervention in Dox cardiomyopathy, however, further analysis of observed effects is still required.

The effect of adaptation to hypoxia on cardiac tolerance to ischemia/reperfusion

The acute myocardial infarction (AMI) and sudden cardiac death (SCD), both associated with acute cardiac ischemia, are one of the leading causes of adult death in economically developed countries. The development of new approaches for the treatment and prevention of AMI and SCD remains the highest priority for medicine. A study on the cardiovascular effects of chronic hypoxia (CH) may contribute to the development of these methods. Chronic hypoxia exerts both positive and adverse effects. The positive effects are the infarct-reducing, vasoprotective, and antiarrhythmic effects, which can lead to the improvement of cardiac contractility in reperfusion. The adverse effects are pulmonary hypertension and right ventricular hypertrophy. This review presents a comprehensive overview of how CH enhances cardiac tolerance to ischemia/reperfusion. It is an in-depth analysis of the published data on the underlying mechanisms, which can lead to future development of the cardioprotective effect of CH. A better understanding of the CH-activated protective signaling pathways may contribute to new therapeutic approaches in an increase of cardiac tolerance to ischemia/reperfusion.

Intermittent hypoxia changes the interaction of the kinin-VEGF system and impairs myocardial angiogenesis in the hypertrophic heart

Intermittent hypoxia (IH) is a feature of obstructive sleep apnea (OSA), a condition highly associated with hypertension-related cardiovascular diseases. Repeated episodes of IH contribute to imbalance of angiogenic growth factors in the hypertrophic heart, which is key in the progression of cardiovascular complications. In particular, the interaction between vascular endothelial growth factor (VEGF) and the kallikrein-kinin system (KKS) is essential for promoting angiogenesis. However, researchers have yet to investigate experimental models of IH that reproduce OSA, myocardial angiogenesis, and expression of KKS components. We examined temporal changes in cardiac angiogenesis in a mouse IH model. Adult male C57BI/6 J mice were implanted with Matrigel plugs and subjected to IH for 1-5 weeks with subsequent weekly histological evaluation of vascularization. Expression of VEGF and KKS components was also evaluated. After 3 weeks, in vivo myocardial angiogenesis and capillary density were decreased, accompanied by a late increase of VEGF and its type 2 receptor. Furthermore, IH increased left ventricular myocardium expression of the B2 bradykinin receptor, while reducing mRNA levels of B1 receptor. These results suggest that in IH, an unexpected response of the VEGF and KKS systems could explain the reduced capillary density and impaired angiogenesis in the hypoxic heart, with potential implications in hypertrophic heart malfunction.

Intermittent Hypoxic Conditioning Alleviates Post-Traumatic Stress Disorder-Induced Damage and Dysfunction of Rat Visceral Organs and Brain

Posttraumatic stress disorder (PTSD) causes mental and somatic diseases. Intermittent hypoxic conditioning (IHC) has cardio-, vaso-, and neuroprotective effects and alleviates experimental PTSD. IHC’s ability to alleviate harmful PTSD effects on rat heart, liver, and brain was examined. PTSD was induced by 10-day exposure to cat urine scent (PTSD rats). Some rats were then adapted to 14-day IHC (PTSD+IHC rats), while PTSD and untreated control rats were cage rested. PTSD rats had a higher anxiety index (AI, X-maze test), than control or PTSD+IHC rats. This higher AI was associated with reduced glycogen content and histological signs of metabolic and hypoxic damage and of impaired contractility. The livers of PTSD rats had reduced glycogen content. Liver and blood alanine and aspartate aminotransferase activities of PTSD rats were significantly increased. PTSD rats had increased norepinephrine concentration and decreased monoamine oxidase A activity in cerebral cortex. The PTSD-induced elevation of carbonylated proteins and lipid peroxidation products in these organs reflects oxidative stress, a known cause of organ pathology. IHC alleviated PTSD-induced metabolic and structural injury and reduced oxidative stress. Therefore, IHC is a promising preventive treatment for PTSD-related morphological and functional damage to organs, due, in part, to IHC’s reduction of oxidative stress.

PI3K/Akt and HIF‑1 signaling pathway in hypoxia‑ischemia (Review)

Hypoxia-ischemia (H-I) is frequently observed in perinatal asphyxia and other diseases. It can lead to serious cardiac injury, cerebral damage, neurological disability and mortality. Previous studies have demonstrated that the phosphatidylinositol-3 kinase (PI3K)/protein kinase B (Akt) signaling pathway, which regulates a wide range of cellular functions, is involved in the resistance response to H-I through the activation of proteins associated with survival and inactivation of apoptosis-associated proteins. It can also regulate the expression of hypoxia-induced factor-1α (HIF-1α). HIF-1α can further regulate the expression of downstream proteins involved in glucose metabolism and angiogenesis, such as vascular endothelial growth factor and erythropoietin, to facilitate ischemic adaptation. Notably, HIF-1α may also induce detrimental effects. The effects of HIF-1 on ischemic outcomes may be dependent on the H-I duration, animal age and species. Thus, further investigation of the PI3K/Akt signaling pathway may provide further insights of the potential targets for treating diseases accompanied by H-I.

Cardioprotection by intermittent hypoxia conditioning: evidence, mechanisms, and therapeutic potential

The calibrated application of limited-duration, cyclic, moderately intense hypoxia-reoxygenation increases cardiac resistance to ischemia-reperfusion stress. These intermittent hypoxic conditioning (IHC) programs consistently produce striking reductions in myocardial infarction and ventricular tachyarrhythmias after coronary artery occlusion and reperfusion and, in many cases, improve contractile function and coronary blood flow. These IHC protocols are fundamentally different from those used to simulate sleep apnea, a recognized cardiovascular risk factor. In clinical studies, IHC improved exercise capacity and decreased arrhythmias in patients with coronary artery or pulmonary disease and produced robust, persistent, antihypertensive effects in patients with essential hypertension. The protection afforded by IHC develops gradually and depends on β-adrenergic, δ-opioidergic, and reactive oxygen-nitrogen signaling pathways that use protein kinases and adaptive transcription factors. In summary, adaptation to intermittent hypoxia offers a practical, largely unrecognized means of protecting myocardium from impending ischemia. The myocardial and perhaps broader systemic protection provided by IHC clearly merits further evaluation as a discrete intervention and as a potential complement to conventional pharmaceutical and surgical interventions.

Inhibition of microRNA-218 reduces HIF-1α by targeting on Robo1 in mice aortic endothelial cells under intermittent hypoxia

OBJECTIVE

To investigate the effects of miR-218 on expression of hypoxia-inducible factors 1α (HIF-1α), vascular endothelial growth factor (VEGF) and cell apoptosis in normal mice aortic endothelial cells under intermittent hypoxia (IH) condition.

METHODS

Anti-miR-218 inhibitor, miR-negative control and miR-218 mimic were used to tranfect the cells in different groups under IH condition. Both RT-PCR and Western blot were used to determine the expressions of HIF-1α and VEGF. Akt, p-Akt and cell apoptosis related proteins bcl-2, bax and caspase-3 and roundabout 1 (Robo1) were measured using Western blot. Cell apoptosis was evaluated by flow cytometry. Statistical analysis was performed using SPSS 18.0.

RESULTS

Expression of miR-218 was significantly up-regulated in the IH group and was significantly inhibited when cells were transfected with miR-218 inhibitor. Down regulation of miR-218 could reduce the expression of HIF-1α and VEGF under intermittent hypoxia condition. In cells transfected with miR-218 mimic, expression of HIF-1α and VEGF significantly increased compared with the control. However, when treated with LY294002, the expression of HIF-1α and VEGF both decreased. Apoptosis assay showed that down regulation of miR-218 could inhibit intermittent hypoxia induced cell apoptosis, decrease expression of caspase-3 and bax and increase expression of bcl-2 under intermittent hypoxia condition. At last, silencing Robo1 could significantly enhance the expression of HIF-1α under IH condition.

CONCLUSION

Inhibition of miR-218 could reduce the expression of HIF-1α and protect against IH-induced apoptosis in mice aortic endothelial cells. The effects were associated with PI3K/AKT pathway and might through targeting of Robo1.

Short-term hypoxia upregulated Mas receptor expression to repress the AT1 R signaling pathway and attenuate Ang II-induced cardiomyocyte apoptosis

Hypertension-stimulated cardiac hypertrophy and apoptosis play critical roles in the progression of heart failure. Our previous study suggested that hypertensive angiotensin II (Ang II) enhanced insulin-like growth factor receptor II (IGF-IIR) expression and cardiomyocyte apoptosis, which are involved JNK activation, sirtuin1 (SIRT1) degradation, and heat-shock transcription factor 1 (HSF1) acetylation. Moreover, previous studies have implied that short-term hypoxia (STH) might exert cardioprotective effects. However, the effects of STH on Ang II-induced cardiomyocyte apoptosis remain unknown. In this study, we found that STH reduced myocardial apoptosis caused by Ang II via upregulation of the Mas receptor (MasR) to inhibit the AT₁ R signaling pathway. STH activates MasR to counteract the Ang II pro-apoptotic signaling cascade by inhibiting IGF-IIR expression via downregulation of JNK activation and reduction of SIRT1 degradation. Hence, HSF could remain deacetylated, and repress IGF-IIR expression. These effects decrease the activation of downstream pro-apoptotic and hypertrophic cascades and protect cardiomyocytes from Ang II-induced injury. In addition, we also found that silencing MasR expression enhanced Ang II-induced cardiac hypertrophy and the apoptosis signaling pathway. These findings suggest a critical role for MasR in cardiomyocyte survival. Altogether, our findings indicate that STH protects cardiomyocytes from Ang II-stimulated apoptosis. The protective effects of STH are associated with the upregulation of MasR to inhibit AT₁ R signaling. STH could be a potential therapeutic strategy for cardiac diseases in hypertensive patients.

Nicotine protects rat hypoglossal motoneurons from excitotoxic death via downregulation of connexin 36

Motoneuron disease including amyotrophic lateral sclerosis may be due, at an early stage, to deficit in the extracellular clearance of the excitatory transmitter glutamate. A model of glutamate-mediated excitotoxic cell death based on pharmacological inhibition of its uptake was used to investigate how activation of neuronal nicotinic receptors by nicotine may protect motoneurons. Hypoglossal motoneurons (HMs) in neonatal rat brainstem slices were exposed to the glutamate uptake blocker DL-threo-β-benzyloxyaspartate (TBOA) that evoked large Ca2+ transients time locked among nearby HMs, whose number fell by about 30% 4 h later. As nicotine or the gap junction blocker carbenoxolone suppressed bursting, we studied connexin 36 (Cx36), which constitutes gap junctions in neurons and found it largely expressed by HMs. Cx36 was downregulated when nicotine or carbenoxolone was co-applied with TBOA. Expression of Cx36 was preferentially observed in cytosolic rather than membrane fractions after nicotine and TBOA, suggesting protein redistribution with no change in synthesis. Nicotine raised the expression of heat shock protein 70 (Hsp70), a protective factor that binds the apoptotic-inducing factor (AIF) whose nuclear translocation is a cause of cell death. TBOA increased intracellular AIF, an effect blocked by nicotine. These results indicate that activation of neuronal nicotinic receptors is an early tool for protecting motoneurons from excitotoxicity and that this process is carried out via the combined decrease in Cx36 activity, overexpression of Hsp70 and fall in AIF translocation. Thus, retarding or inhibiting HM death may be experimentally achieved by targeting one of these processes leading to motoneuron death.

Correlation between vascular endothelial growth factor and long-term prognosis in patients with acute myocardial infarction

The aim of the present study was to investigate the correlation between plasma the levels of vascular endothelial growth factor (VEGF) and major adverse cardiovascular events (MACE) in patients with acute myocardial infarction (AMI). A total of 124 patients with AMI undergoing emergency percutaneous coronary intervention (PCI) were selected, and plasma VEGF levels were measured 7 days after the onset of AMI using an enzyme-linked immunosorbent assay. The patients were divided into the L (≤190 pg/ml VEGF) and H (>190 pg/ml VEGF) groups, and were followed up every 2 months for an average of 12 months. MACE were recorded during follow-up. On the basis of these results, the patients were further divided into the MACE and non-MACE (N-MACE) groups, and the serum VEGF concentration was compared between the two groups. At the 6-month follow-up, the incidence of MACE in the H group was found to be significantly reduced compared with the L group. The serum VEGF concentration in the N-MACE group was significantly higher compared with the MACE group. Multinomial logistic regression revealed that reduced VEGF levels (β=1.243; 95% CI, 1.018-1.326; P=0.026) were independent risk factors for MACE. In conclusion, high plasma VEGF levels at 7 days after AMI onset facilitate the long-term prognosis in the same infarct zone in patients with AMI, while low plasma VEGF levels are independent risk factors for MACE.

Intravenous high mobility group box 1 upregulates the expression of HIF-1α in the myocardium via a protein kinase B-dependent pathway in rats following acute myocardial ischemia

The effects of intravenous high mobility group box 1 (HMGB1) on myocardial ischemia/reperfusion (I/R) injury remains to be elucidated. The purpose of the present study was to investigate the effects of intravenous HMGB1 on the expression of hypoxia inducible factor-1α (HIF-1α) in the myocardium of rats following acute myocardial ischemia, and to examine the effects of intravenous HMGB1 on myocardial I/R injury. Male Wistar rats were divided into the following groups: Sham operation group (n=10), a group exposed to ischemia for 30 min and reperfusion for 4 h (I/R group) as a control (n=10), an HMGB group, in which 100 ng/kg HMGB was administered intravenously 30 min prior to ischemia (n=10), an LY group, in whic LY294002, an inhibitor of phosphoinositide 3-kinase (PI3K), was administered intravenously (0.3 mg/kg) 40 min prior to ischemia (n=10), and the HMGB1+LY group, in which HMGB1 (100 ng/kg) and LY294002 (0.3 mg/kg) were administered intravenously 30 min and 40 min prior to ischemia, respectively (n=10). The serum levels of cardiac troponin I (cTnI) and tumor necrosis factor-α (TNF-α), and myocardial infarct size were measured. The expression levels of phosphorylated Akt and HIF-1α were investigated using western blot analyses. The results showed that pre-treatment with HMGB1 significantly decreased serum levels of cTnI, and TNF-α, and reduced myocardial infarct size following 4 h reperfusion (all P<0.05). HMGB1 also increased the expression levels of HIF-1α and p-Akt induced by I/R (P<0.05). LY294002 was found to eliminate the effects of intravenous HMGB1 on myocardial I/R injury (P<0.05). These results suggest that intravenous pre-treatment with HMGB1 may exert its cardioprotective effects via the upregulation of the myocardial expression of HIF-1α, which may be regulated by the PI3K/Akt signaling pathway, in rats following acute myocardial I/R.

Vascular and hepatic impact of short-term intermittent hypoxia in a mouse model of metabolic syndrome

Background

Experimental models of intermittent hypoxia (IH) have been developed during the last decade to investigate the consequences of obstructive sleep apnea. IH is usually associated with detrimental metabolic and vascular outcomes. However, paradoxical protective effects have also been described depending of IH patterns and durations applied in studies. We evaluated the impact of short-term IH on vascular and metabolic function in a diet-induced model of metabolic syndrome (MS).

Methods

Mice were fed either a standard diet or a high fat diet (HFD) for 8 weeks. During the final 14 days of each diet, animals were exposed to either IH (1 min cycle, FiO₂ 5% for 30s, FiO₂ 21% for 30s; 8 h/day) or intermittent air (FiO₂ 21%). Ex-vivo vascular reactivity in response to acetylcholine was assessed in aorta rings by myography. Glucose, insulin and leptin levels were assessed, as well as serum lipid profile, hepatic mitochondrial activity and tissue nitric oxide (NO) release.

Results

Mice fed with HFD developed moderate markers of dysmetabolism mimicking MS, including increased epididymal fat, dyslipidemia, hepatic steatosis and endothelial dysfunction. HFD decreased mitochondrial complex I, II and IV activities and increased lactate dehydrogenase (LDH) activity in liver. IH applied to HFD mice induced a major increase in insulin and leptin levels and prevented endothelial dysfunction by restoring NO production. IH also restored mitochondrial complex I and IV activities, moderated the increase in LDH activity and liver triglyceride accumulation in HFD mice.

Conclusion

In a mouse model of MS, short-term IH increases insulin and leptin levels, restores endothelial function and mitochondrial activity and limits liver lipid accumulation.

Effect of intermittent hypoxia on the cardiac HIF-1/VEGF pathway in experimental type 1 diabetes mellitus

OBJECTIVE

High altitude and hypoxic preconditioning have cardioprotective effects by increasing coronary vascularity, reducing post-ischemic injury, and improving cardiac function. Our purpose was to examine if intermittent hypoxia treatment has any restoring effects related to the possible role of the HIF-1/VEGF pathway on diabetic cardiomyopathy.

METHODS

Wistar Albino male rats (n=34) were divided into four groups: control (C), intermittent hypoxia (IH), diabetes mellitus (DM), and diabetes mellitus plus intermittent hypoxia (DM+IH). Following a streptozotocin (STZ) injection (50 mg/kg, i.p.), blood glucose levels of 250 mg/dL and above were considered as DM. IH and DM+IH groups were exposed to hypoxia 6 h/day for 42 days at a pressure corresponding to 3000 m altitude. Twenty-four hours after the IH protocol, hearts were excised. Hematoxylin and eosin-stained apical parts of the left ventricles were evaluated. Hypoxia inducible factor-1 (HIF-1), vascular endothelial growth factor 164 (VEGF164), and VEGF188 polymerase chain reaction products were run in agarose gel electrophoresis. Band density analysis of UV camera images was performed using Image J. The data were compared by one-way ANOVA, repeated measures two-way ANOVA, and the Kruskal-Wallis test.

RESULTS

The percent weight change was lower in the DM group than in the controls (p=0.004). The tissue injury was the highest in the DM group and the least in the IH group. Diabetes decreased, whereas the IH treatment increased the vascularity. A decrease was observed in the VEGF188 mRNA levels in the DM+IH group compared with the C group, but there were no difference in HIF-1α and VEGF164 mRNA levels between the groups.

CONCLUSION

The IH treatment restored the diabetic effects on the heart by reducing tissue injury and increasing the capillarity without transcriptional changes in HIF-1/VEGF correspondingly.

Protective effect of resveratrol against pressure overload-induced heart failure

Transverse aortic constriction (TAC)-induced pressure overload (PO) causes adverse cardiac remodeling and dysfunction that progresses to heart failure (HF). The purpose of this study was to determine whether the potent antioxidant, resveratrol, significantly attenuates PO-induced HF in wild-type mice. Male C57BL6 mice were subjected to either sham or TAC surgery. One group of TAC mice was given daily resveratrol treatment. Echocardiographic, biometric, and immunohistological analyses were performed on the three groups of mice. All echocardiographic parameters demonstrated significantly greater adverse cardiac remodeling and dysfunction in the TAC compared to the sham mice. Increases in the ratios of heart weight (HW)/body weight (BW) and lung weight (LW)/BW and a sharp decline in the percentage of ejection fraction and fractional shortening were found in TAC relative to sham mice. Likewise, the TAC protocol increased markers of oxidative stress, cardiac hypertrophy, inflammation, fibrosis, hypoxia, and apoptosis. These pathological changes were significantly attenuated by resveratrol treatment. Resveratrol treatment significantly attenuates the adverse cardiac remodeling and dysfunction produced by the TAC protocol in C57/BL6 mice and this activity is mediated, at least in part, by the inhibition of oxidative stress and inflammation indicating a therapeutic potential of resveratrol in HF.

Molecular biomarkers of vascular dysfunction in obstructive sleep apnea

Untreated and long-lasting obstructive sleep apnea (OSA) may lead to important vascular abnormalities, including endothelial cell (EC) dysfunction, hypertension, and atherosclerosis. We observed a correlation between microcirculatory reactivity and endothelium-dependent release of nitric oxide in OSA patients. Therefore, we hypothesized that OSA affects (micro)vasculature and we aimed to identify vascular gene targets of OSA that could possibly serve as reliable biomarkers of severity of the disease and possibly of vascular risk. Using quantitative RT-PCR, we evaluated gene expression in skin biopsies of OSA patients, mouse aortas from animals exposed to 4-week intermittent hypoxia (IH; rapid oscillations in oxygen desaturation and reoxygenation), and human dermal microvascular (HMVEC) and coronary artery endothelial cells (HCAEC) cultured under IH. We demonstrate a significant upregulation of endothelial nitric oxide synthase (eNOS), tumor necrosis factor-alpha-induced protein 3 (TNFAIP3; A20), hypoxia-inducible factor 1 alpha (HIF-1α?? and vascular endothelial growth factor (VEGF) expression in skin biopsies obtained from OSA patients with severe nocturnal hypoxemia (nadir saturated oxygen levels [SaO2]<75%) compared to mildly hypoxemic OSA patients (SaO2 75%-90%) and a significant upregulation of vascular cell adhesion molecule 1 (VCAM-1) expression compared to control subjects. Gene expression profile in aortas of mice exposed to IH demonstrated a significant upregulation of eNOS and VEGF. In an in vitro model of OSA, IH increased expression of A20 and decreased eNOS and HIF-1α expression in HMVEC, while increased A20, VCAM-1 and HIF-1αexpression in HCAEC, indicating that EC in culture originating from distinct vascular beds respond differently to IH stress. We conclude that gene expression profiles in skin of OSA patients may correlate with disease severity and, if validated by further studies, could possibly predict vascular risk in OSA patients.