Cardiac repolarization is prolonged in CD4C/HIV transgenic mice

A new perspective on HIV: effects of HIV on brain-heart axis

The human immunodeficiency virus (HIV) infection can cause damage to multiple systems within the body, and the interaction among these various organ systems means that pathological changes in one system can have repercussions on the functions of other systems. However, the current focus of treatment and research on HIV predominantly centers around individual systems without considering the comprehensive relationship among them. The central nervous system (CNS) and cardiovascular system play crucial roles in supporting human life, and their functions are closely intertwined. In this review, we examine the effects of HIV on the CNS, the resulting impact on the cardiovascular system, and the direct damage caused by HIV to the cardiovascular system to provide new perspectives on HIV treatment.

Outcomes of implantable cardioverter-defibrillator implantation in HIV-infected patients: A single-center retrospective cohort study

BACKGROUND

HIV-infected individuals have a known increased risk of sudden cardiac death (SCD) compared to uninfected individuals. Implantable cardioverter-defibrillators (ICDs) are standard therapy for preventing SCD; however, there is limited data on the outcomes of ICDs in HIV-infected individuals.

HYPOTHESIS

HIV-infected subjects receive a higher number of appropriate ICD therapies than uninfected controls.

METHODS

This is a retrospective cohort study of 35 consecutive HIV-Infected patients and 36 uninfected controls matched by age, race, and gender who were treated at the University of North Carolina Medical Center in the outpatient or inpatient setting from 2014 to the present and had undergone ICD implantation. For HIV-infected subjects, a multivariate Poisson regression analysis was performed to evaluate the association between covariates and ICD therapies.

RESULTS

Among HIV-infected subjects, the mean CD4 count was 582.5 cells/mm³ and 69% had an undetectable viral load. The median follow-up was 6.4 years. HIV-infected subjects had both a higher number of appropriate ICD shocks or antitachycardia pacing (ATP) therapy per person-year as well as a higher number of inappropriate ICD shocks per person-year than uninfected controls (1.512 vs. 0.590 and 0.122 vs. 0.0166, respectively, p < .001 for both comparisons). After multivariate adjustment, the presence of detectable/unsuppressed viral load at the time of ICD implantation was an independent predictor of both of the following in HIV-infected subjects: (1) appropriate ICD discharge (p = .004), and (2) appropriate ICD discharge or appropriate ATP therapy (p < .001).

CONCLUSION

HIV-infected subjects had a higher number of appropriate ICD discharge or ATP therapy per person-year than matched uninfected controls.

Sudden cardiac death in HIV-infected patients: A contemporary review

HIV‐infected individuals have an increased risk of sudden cardiac death compared to the general population; yet the mechanisms underlying this increased risk remain unclear. The mechanisms underlying the heightened sudden cardiac death risk in HIV‐infected individuals is likely multifactorial. We reviewed the literature to elucidate and summarize the potential mechanisms contributing to sudden cardiac death in the HIV patient population. There is biologic plausibility that the following mechanisms may be contributing to the significantly heightened risk of sudden cardiac death in HIV to varying degrees: ventricular arrhythmias, myocardial fibrosis and scar, prolonged QTc interval (both as a direct effect of HIV on repolarization as well as a result of concurrent medications/antiretroviral therapies), substance abuse, structural heart disease, and premature atherosclerosis. Further understanding of the mechanisms underlying the increased sudden cardiac death risk in HIV can lead to identification of modifiable risk factors, implementation of public health programs, and potential revision of ICD implantation guidelines to ultimately reduce the incidence of sudden cardiac death in HIV‐infected patients. Further studies are needed to assess the relative contribution of each of these mechanisms and risk factors.

MK2-Deficient Mice Are Bradycardic and Display Delayed Hypertrophic Remodeling in Response to a Chronic Increase in Afterload

Background

Mitogen‐activated protein kinase–activated protein kinase‐2 (MK2) is a protein serine/threonine kinase activated by p38α/β. Herein, we examine the cardiac phenotype of pan MK2‐null (MK2^−/−) mice.

Methods and Results

Survival curves for male MK2^+/+ and MK2^−/− mice did not differ (Mantel‐Cox test, P=0.580). At 12 weeks of age, MK2^−/− mice exhibited normal systolic function along with signs of possible early diastolic dysfunction; however, aging was not associated with an abnormal reduction in diastolic function. Both R‐R interval and P‐R segment durations were prolonged in MK2‐deficient mice. However, heart rates normalized when isolated hearts were perfused ex vivo in working mode. Ca²⁺ transients evoked by field stimulation or caffeine were similar in ventricular myocytes from MK2^+/+ and MK2^−/− mice. MK2^−/− mice had lower body temperature and an age‐dependent reduction in body weight. mRNA levels of key metabolic genes, including Ppargc1a, Acadm, Lipe, and Ucp3, were increased in hearts from MK2^−/− mice. For equivalent respiration rates, mitochondria from MK2^−/− hearts showed a significant decrease in Ca²⁺ sensitivity to mitochondrial permeability transition pore opening. Eight weeks of pressure overload increased left ventricular mass in MK2^+/+ and MK2^−/− mice; however, after 2 weeks the increase was significant in MK2^+/+ but not MK2^−/− mice. Finally, the pressure overload–induced decrease in systolic function was attenuated in MK2^−/− mice 2 weeks, but not 8 weeks, after constriction of the transverse aorta.

Conclusions

Collectively, these results implicate MK2 in (1) autonomic regulation of heart rate, (2) cardiac mitochondrial function, and (3) the early stages of myocardial remodeling in response to chronic pressure overload.

Assessment of Tp-e interval and Tp-e/QT ratio in patients with human immunodeficiency virus

OBJECTIVE

Sudden cardiac death (SCD) plays an important part in all-cause mortality in patients infected with human immunodeficiency virus (HIV). The T-peak to T-end (Tp-e) interval, corrected Tp-e (Tp-ec) interval, and Tp-e/QT ratio on the ECG are parameters used to stratify risk for SCD. The objective of this study was to investigate the differences between HIV-infected patients and healthy individuals in terms of Tp-e interval, Tp-ec interval, and Tp-e/QT ratio, as well as other influencing factors.

METHODS

Ninety-eight HIV-infected patients and 62 healthy controls were included in this prospective case-control study. Tp-e interval, Tp-ec interval, and Tp-e/QT ratio were measured in all participants. Echocardiographic examination and routine laboratory analysis were performed. In addition, CD4 T-cell count and HIV RNA levels were assessed in HIV-infected patients.

RESULTS

All baseline characteristics were comparable in both groups. The median survival of those living with HIV was 20.63 months; 53% of them had controlled viral load, and 74% were receiving antiretroviral therapy. Mean baseline CD4 T-cell count was 409. In HIV-infected patients, the Tp-e interval and Tp-ec interval were prolonged, and the Tp-e/QT ratio was higher (p<0.001, p<0.001 and p=0.021, respectively). In bivariate and partial correlation analyses, there was a negative correlation between CD4 T-cell level and Tp-e interval, Tp-ec interval, and Tp-e/QT ratio.

CONCLUSION

Tp-e interval, Tp-ec interval, and Tp-e/QT ratio were greater in HIV-infected patients compared with healthy individuals. HIV-infected patients, particularly those with low baseline CD4 T-cell counts, should be closely monitored due to risk of SCD.

Abnormal Dispersion of Ventricular Repolarization as a Risk Factor in Patients with Human Immunodeficiency Virus: Tp-e Interval, Tp-e/QTc Ratio

OBJECTIVE

In recent years, there has been worldwide recognition of the problems associated with Human Immunodeficiency Virus (HIV) infection and Acquired Immune Deficiency Syndrome (AIDS). The prevalence of cardiovascular disease in the HIV-infected population is increasing. Repolarization abnormalities, the significant contributor to life-threatening arrhythmias and mortality, are the most frequent electrocardiographic changes in this population. This study aimed to evaluate the changes in Tp-e interval, Tp-e/QT and Tp-e/corrected QT (QTc) ratios, and traditional electrocardiographic features of electrical dispersion in adults infected with HIV.

SUBJECTS AND METHODS

A total of 235 participants were selected in the current study. The HIV group consisted of 85 subjects (median age 36 years [25-48], and the control group included 150 individuals (median age 39 years [27-51]). Tp-e interval, Tp-e/QT and Tp-e/QTc ratios were measured by the 12-lead electrocardiogram.

RESULTS

Tp-e interval, cTp-e interval, and Tp-e/QT and Tp-e/QTc ratios were significantly higher in HIV patients compared to the control group (p = 0.006, p = 0.004, p = 0.003, and p = 0.002, respectively). In correlation analysis, there was inverse correlation between the mean cTp-e interval and CD4 count and Tp-e/QTc ratios and CD4 count (r = - 0.407, p < 0.001, r = - 0.416, p < 0.001, respectively). Besides, there was correlation between the mean cTp-e interval and high-sensitivity C-reactive protein (hsCRP) and Tp-e/QTc ratios and hsCRP (r = 0.403, p = 0.001, r = 0.406, p = 0.001, respectively).

CONCLUSION

Our study revealed that the cTp-e interval, Tp-e/QT and cTp-e/QT ratios were prolonged and correlated to the severity of the disease in HIV-infected patients. Our findings may shed light on the cTp-e interval and Tp-e/QTc ratio and lead to further studies showing a relationship with ventricular arrhythmias and mortality in HIV-infected individuals.

QT prolongation in HIV-positive patients: Review article

Introduction

Antiretrovirals have immensely increased the average life expectancy of HIV-positive patients. However, the incidence of QT interval prolongation and other arrhythmias has also increased.

Methods

Pubmed and Google Scholar were searched for relevant literature published between 1990 and 2019.

Results and discussion

HIV-positive patients with high viral load, low CD4 count, chronic inflammation, and autonomic neuropathy can develop QT interval prolongation. Another factor prolonging QT interval includes exposure to the HIV transactivator protein, which inhibits hERG K (+) channels controlling IKr K (+) currents in cardiomyocytes. Protease inhibitors inhibiting the CYP3A4 enzyme can also lead to QT interval prolongation. QT interval prolongation can potentially be exacerbated by opioids, antipsychotics, antibiotics, and antifungals, the adjunct medications often used in HIV-positive patients. Hepatic insufficiency in seropositive patients on antiretrovirals may also increase the risk of QT interval prolongation.

Conclusion

Baseline and follow-up EKG in the susceptible population is suggested.

ADCY9 (Adenylate Cyclase Type 9) Inactivation Protects From Atherosclerosis Only in the Absence of CETP (Cholesteryl Ester Transfer Protein)

BACKGROUND

Pharmacogenomic studies have shown that ADCY9 genotype determines the effects of the CETP (cholesteryl ester transfer protein) inhibitor dalcetrapib on cardiovascular events and atherosclerosis imaging. The underlying mechanisms responsible for the interactions between ADCY9 and CETP activity have not yet been determined.

METHODS

Adcy9-inactivated ( Adcy9^Gt/Gt) and wild-type (WT) mice, that were or not transgenic for the CETP gene (CETPtg Adcy9^Gt/Gt and CETPtg Adcy9^WT), were submitted to an atherogenic protocol (injection of an AAV8 [adeno-associated virus serotype 8] expressing a PCSK9 [proprotein convertase subtilisin/kexin type 9] gain-of-function variant and 0.75% cholesterol diet for 16 weeks). Atherosclerosis, vasorelaxation, telemetry, and adipose tissue magnetic resonance imaging were evaluated.

RESULTS

Adcy9^Gt/Gt mice had a 65% reduction in aortic atherosclerosis compared to WT ( P<0.01). CD68 (cluster of differentiation 68)-positive macrophage accumulation and proliferation in plaques were reduced in Adcy9^Gt/Gt mice compared to WT animals ( P<0.05 for both). Femoral artery endothelial-dependent vasorelaxation was improved in Adcy9^Gt/Gt mice (versus WT, P<0.01). Selective pharmacological blockade showed that the nitric oxide, cyclooxygenase, and endothelial-dependent hyperpolarization pathways were all responsible for the improvement of vasodilatation in Adcy9^Gt/Gt ( P<0.01 for all). Aortic endothelium from Adcy9^Gt/Gt mice allowed significantly less adhesion of splenocytes compared to WT ( P<0.05). Adcy9^Gt/Gt mice gained more weight than WT with the atherogenic diet; this was associated with an increase in whole body adipose tissue volume ( P<0.01 for both). Feed efficiency was increased in Adcy9^Gt/Gt compared to WT mice ( P<0.01), which was accompanied by prolonged cardiac RR interval ( P<0.05) and improved nocturnal heart rate variability ( P=0.0572). Adcy9 inactivation-induced effects on atherosclerosis, endothelial function, weight gain, adipose tissue volume, and feed efficiency were lost in CETPtg Adcy9^Gt/Gt mice ( P>0.05 versus CETPtg Adcy9^WT).

CONCLUSIONS

Adcy9 inactivation protects against atherosclerosis, but only in the absence of CETP activity. This atheroprotection may be explained by decreased macrophage accumulation and proliferation in the arterial wall, and improved endothelial function and autonomic tone.

Mechanisms of Arrhythmia and Sudden Cardiac Death in Patients With HIV Infection

Long-term survival of HIV-infected patients has significantly improved with the use of antiretroviral therapy (ART). As a consequence, cardiovascular diseases are now emerging as an important clinical problem in this population. Sudden cardiac death is the third leading cause of mortality in HIV patients. Twenty percent of patients with HIV who died of sudden cardiac death had previous cardiac arrhythmias including ventricular tachycardia, atrial fibrillation, and other unspecified rhythm disorders. This review presents a summary of HIV-related arrhythmias, associated risk factors specific to the HIV population, and underlying mechanisms. Compared with the general population, patients with HIV have several cardiac conditions and electrophysiological abnormalities. As a result, they have an increased risk of developing severe arrhythmias, that can lead to sudden cardiac death. Possible explanations may be related to non-ART polypharmacy, electrolyte imbalances, and use of substances observed in HIV-infected patients; many of these conditions are associated with alterations in cardiac electrical activity, increasing the risk of arrhythmia and sudden cardiac death. However, clinical and experimental evidence has also revealed that cardiac arrhythmias occur in HIV-infected patients, even in the absence of drugs. This indicates that HIV itself can change the electrophysiological properties of the heart profoundly and cause cardiac arrhythmias and related sudden cardiac death. The current knowledge of the underlying mechanisms, as well as the emerging role of inflammation in these arrhythmias, are discussed here.

The role of HIV Tat protein in HIV-related cardiovascular diseases

The human immunodeficiency virus (HIV) is a major global public health issue. HIV-related cardiovascular disease remains a leading cause of morbidity and mortality in HIV positive patients. HIV Tat is a regulatory protein encoded by tat gene of HIV-1, which not only promotes the transcription of HIV, but it is also involved in the pathogenesis of HIV-related complications. This review is aimed at summarizing the current understanding of Tat in HIV-related cardiovascular diseases.

Prevalence and predictors of long corrected QT interval in HIV-positive patients: a multicenter study

AIMS

HIV and highly active antiretroviral therapy (HAART) may affect cardiac conduction, and a higher incidence of sudden death has been recognized in HIV-positive patients. Nevertheless, predictors of prolonged corrected QT interval (cQT) have been poorly described. The aim of the study was to investigate the prevalence and predictors of long cQT in a cohort of HIV-positive patients.

METHODS

Consecutive HIV-positive patients followed in a primary prevention clinic at two Italian institutions were retrospectively enrolled. A 12-lead ECG was recorded in all patients; main clinical features were collected. Prevalence of long cQT (defined as cQT >470 ms in women and >450 ms in men) was the primary end-point. Secondary end-points were the identification of predictors of cQT prolongation, and the association between HAART and HIV-related features with long cQT.

RESULTS

Three hundred and fifty-one HIV-positive patients were included, 26 (7.4%) with long cQT. Mean age was higher among those with long cQT (51.6 vs. 57.6 years; P = 0.007). A higher prevalence of long cQT was reported for patients with a CD4+ cell count below 200 cells/μl at the moment of ECG (60 vs. 24.2%; P = 0.002) and with a nadir of CD4+ cell count below 200 cells/μl (91.3 vs. 58.6%; P = 0.001). At multivariate analysis, only the nadir of CD4+ cell count below 200 cells/μl consistently related to the presence of long cQT (odds ratio 5.8, 95% confidence interval 1.3-26.4).

CONCLUSION

A low CD4+ cell count is associated with long cQT independently from HAART in HIV-positive patients and may be useful to correctly stratify arrhythmic risk in these patients.

Viral dependence on cellular ion channels - an emerging anti-viral target?

The broad range of cellular functions governed by ion channels represents an attractive target for viral manipulation. Indeed, modulation of host cell ion channel activity by viral proteins is being increasingly identified as an important virus-host interaction. Recent examples have demonstrated that virion entry, virus egress and the maintenance of a cellular environment conducive to virus persistence are, in part, dependent on virus manipulation of ion channel activity. Most excitingly, evidence has emerged that targeting ion channels pharmacologically can impede virus life cycles. Here, we discuss current examples of virus-ion channel interactions and the potential of targeting ion channel function as a new, pharmacologically safe and broad-ranging anti-viral therapeutic strategy.

Interleukin-1β reduces L-type Ca2+ current through protein kinase Cϵ activation in mouse heart

Inflammation is now widely recognized as a key component of heart disease. Patients suffering from arrhythmias and heart failure have increased levels of tumor necrosis factor-α (TNFα) and interleukin-1β (IL-1β). Evidence suggests that these cytokines are important mediators of cardiac remodeling; however, their effects on ion channels and arrhythmogenesis remain incompletely understood. The L-type Ca(2+) current (ICaL) is a major determinant of the plateau phase of cardiac action potential and has a critical excitation-contraction coupling role. Thus, altering its properties could have detrimental effects on cardiac electrical and contractile functions. Accordingly, the objective of this study was to elucidate the effect of TNFα and IL-1β on ICaL, while exploring the underlying regulatory mechanisms. Neonatal mouse ventricular myocytes were treated with a pathophysiological concentration (30 pg/ml) of TNFα and IL-1β for 24 h. Voltage-clamp recordings showed that TNFα had no effect on ICaL, whereas IL-1β decreased the current density by 36%. Although both IL-1β- and TNFα-treated myocytes showed significant increase in reactive oxidative species (ROS), Western blot experiments revealed that only IL-1β increased PKCϵ membrane translocation. The antioxidant N-acetyl-L-cysteine normalized ROS levels and restored ICaL density. Furthermore, the PKCϵ translocation inhibitor ϵ-V1-2 blocked the effect of IL-1β on ICaL. The reduction of ICaL by IL-1β was also seen in cultured adult ventricular myocytes. Overall, chronic IL-1β treatment decreased ICaL density in cardiomyocytes. These effects implicated ROS signaling and PKCϵ activation. These findings could contribute to explain the role of IL-1β in the development of arrhythmia and heart failure.

Effect of left ventricular dysfunction and viral load on risk of sudden cardiac death in patients with human immunodeficiency virus

Human immunodeficiency virus (HIV)-infected patients are disproportionately affected by cardiovascular disease and sudden cardiac death (SCD). Whether left ventricular (LV) dysfunction predicts SCD in those with HIV is unknown. We sought to determine the impact of LV dysfunction on SCD in patients with HIV. We previously characterized all SCDs and acquired immunodeficiency syndrome (AIDS) deaths in 2,860 consecutive patients in a public HIV clinic from 2000 to 2009. Transthoracic echocardiograms (TTEs) performed during the study period were identified. The effect of ejection fraction (EF), diastolic dysfunction, pulmonary artery pressure, and LV mass on SCD and AIDS death were evaluated: 423 patients had at least 1 TTE; 13 SCDs and 55 AIDS deaths had at least 1 TTE. In the propensity-adjusted analysis, EF 30% to 39% and EF<30% predicted SCD (hazard ratio [HR] 9.5, 95% confidence interval [CI] 1.7 to 53.3, p=0.01 and HR 38.5, 95% CI 7.6 to 195.0, p<0.001, respectively) but not AIDS death. Diastolic dysfunction also predicted SCD (HR 14.8, 95% CI 4.0 to 55.4, p<0.001) but not AIDS death, even after adjusting for EF. The association between EF<40% and SCD was greater in subjects with detectable versus undetectable HIV RNA (adjusted HR 11.7, 95% CI 2.9 to 47.2, p=0.001 vs HR 2.7, 95% CI 0.3 to 27.6, p=0.41; p=0.07 for interaction). In conclusion, LV systolic dysfunction and diastolic dysfunction predict SCD but not AIDS death in a large HIV cohort, with greater effect in those with detectable HIV RNA. Further investigation is needed to thoroughly evaluate the effect of low EF and HIV factors on SCD incidence and the potential benefit of implantable cardioverter-defibrillator therapy in this high-risk population.

Sudden cardiac death in patients with human immunodeficiency virus infection

OBJECTIVES

The aim of this study was to determine the incidence and clinical characteristics of sudden cardiac death (SCD) in patients with human immunodeficiency virus (HIV) infection.

BACKGROUND

As the HIV-infected population ages, cardiovascular disease prevalence and mortality are increasing, but the incidence and features of SCD have not yet been described.

METHODS

The records of 2,860 consecutive patients in a public HIV clinic in San Francisco between April 2000 and August 2009 were examined. Identification of deaths, causes of death, and clinical characteristics were obtained by search of the National Death Index and/or clinic records. SCDs were determined using published retrospective criteria: 1) the International Classification of Diseases-10th Revision, code for all cardiac causes of death; and (2) circumstances of death meeting World Health Organization criteria.

RESULTS

Of 230 deaths over a median of 3.7 years of follow-up, 30 (13%) met SCD criteria, 131 (57%) were due to acquired immune deficiency syndrome (AIDS), 25 (11%) were due to other (natural) diseases, and 44 (19%) were due to overdoses, suicides, or unknown causes. SCDs accounted for 86% of all cardiac deaths (30 of 35). The mean SCD rate was 2.6 per 1,000 person-years (95% confidence interval: 1.8 to 3.8), 4.5-fold higher than expected. SCDs occurred in older patients than did AIDS deaths (mean 49.0 vs. 44.9 years, p = 0.02). Compared with AIDS and natural deaths combined, SCDs had a higher prevalence of prior myocardial infarction (17% vs. 1%, p < 0.0005), cardiomyopathy (23% vs. 3%, p < 0.0005), heart failure (30% vs. 9%, p = 0.004), and arrhythmias (20% vs. 3%, p = 0.003).

CONCLUSIONS

SCDs account for most cardiac and many non-AIDS natural deaths in HIV-infected patients. Further investigation is needed to ascertain underlying mechanisms, which may include inflammation, antiretroviral therapy interruption, and concomitant medications.

Heart rate-associated mechanical stress impairs carotid but not cerebral artery compliance in dyslipidemic atherosclerotic mice

The cardiac cycle imposes a mechanical stress that dilates elastic carotid arteries, while shear stress largely contributes to the endothelium-dependent dilation of downstream cerebral arteries. In the presence of dyslipidemia, carotid arteries stiffen while the endothelial function declines. We reasoned that stiffening of carotid arteries would be prevented by reducing resting heart rate (HR), while improving the endothelial function would regulate cerebral artery compliance and function. Thus we treated or not 3-mo-old male atherosclerotic mice (ATX; LDLr(-/-):hApoB(+/+)) for 3 mo with the sinoatrial pacemaker current inhibitor ivabradine (IVA), the β-blocker metoprolol (METO), or subjected mice to voluntary physical training (PT). Arterial (carotid and cerebral artery) compliance and endothelium-dependent flow-mediated cerebral dilation were measured in isolated pressurized arteries. IVA and METO similarly reduced (P < 0.05) 24-h HR by ≈15%, while PT had no impact. As expected, carotid artery stiffness increased (P < 0.05) in ATX mice compared with wild-type mice, while cerebral artery stiffness decreased (P < 0.05); this paradoxical increase in cerebrovascular compliance was associated with endothelial dysfunction and an augmented metalloproteinase-9 (MMP-9) activity (P < 0.05), without changing the lipid composition of the wall. Reducing HR (IVA and METO) limited carotid artery stiffening, but plaque progression was prevented by IVA only. In contrast, IVA maintained and PT improved cerebral endothelial nitric oxide synthase-dependent flow-mediated dilation and wall compliance, and both interventions reduced MMP-9 activity (P < 0.05); METO worsened endothelial dysfunction and compliance and did not reduce MMP-9 activity. In conclusion, HR-dependent mechanical stress contributes to carotid artery wall stiffening in severely dyslipidemic mice while cerebrovascular compliance is mostly regulated by the endothelium.

Homocysteine enriched diet leads to prolonged QT interval and reduced left ventricular performance in telemetric monitored mice

BACKGROUND AND AIMS

Homocysteine (Hcy) is a sulfur-containing, non-protein amino acid produced in the metabolic pathway of methionine. Hyperhomocysteinemia is associated with cerebro- and cardiovascular disease in industrialized countries, mostly resulting from protein rich diet and sedentary life style. Matrix metalloproteinases are involved in cardiac remodeling, leading to degradation of intercellular junctions, cardiac connexins and basement membranes. The study was designed to investigate the relationship between Hcy, cardiac remodeling, cardiac performance, and rhythm disturbances in an animal model of hyperhomocysteinemia. We tested the hypothesis that induction of matrix metalloproteinase-2 and matrix metalloproteinase-9 leads to connexin 40, connexin 43, connexin 45 expression changes contributing to decreased cardiac performance and disturbed atrioventricular conduction.

METHODS AND RESULTS

Hcy was added to drinking water of male C57/BL6J mice to achieve moderate Hcy blood levels. ECG was monitored in conscious mice with a telemetric ECG device; echocardiography was used for assessment of left ventricular function. Immunoblotting was used to evaluate matrix metalloproteinase-2, matrix metalloproteinase-9, connexin 40, connexin 43, and connexin 45 expression in cardiac tissue. Animals fed Hcy showed significant prolongation of QRS, QTc, and PR intervals along with reduced left ventricular function. Western blotting showed increased expression of matrix metalloproteinase-2, matrix metalloproteinase-9 and decreased expression of connexin 40, 43, and 45.

CONCLUSION

Hcy has been identified as a nutritional factor contributing to cardiovascular disease. Cardiac remodeling induced by matrix metalloproteinase-2 and matrix metalloproteinase-9 and decreased expression of connexin 40, 43, and 45 appears to play a role in the pathomechanism of atrioventricular conduction delay and ventricular dilatation in hyperhomocysteinemia.

Prolonged QT interval and lipid alterations beyond β-oxidation in very long-chain acyl-CoA dehydrogenase null mouse hearts

Patients with very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency frequently present cardiomyopathy and heartbeat disorders. However, the underlying factors, which may be of cardiac or extra cardiac origins, remain to be elucidated. In this study, we tested for metabolic and functional alterations in the heart from 3- and 7-mo-old VLCAD null mice and their littermate counterparts, using validated experimental paradigms, namely, 1) ex vivo perfusion in working mode, with concomitant evaluation of myocardial contractility and metabolic fluxes using (13)C-labeled substrates under various conditions; as well as 2) in vivo targeted lipidomics, gene expression analysis as well as electrocardiogram monitoring by telemetry in mice fed various diets. Unexpectedly, when perfused ex vivo, working VLCAD null mouse hearts maintained values similar to those of the controls for functional parameters and for the contribution of exogenous palmitate to β-oxidation (energy production), even at high palmitate concentration (1 mM) and increased energy demand (with 1 μM epinephrine) or after fasting. However, in vivo, these hearts displayed a prolonged rate-corrected QT (QTc) interval under all conditions examined, as well as the following lipid alterations: 1) age- and condition-dependent accumulation of triglycerides, and 2) 20% lower docosahexaenoic acid (an omega-3 polyunsaturated fatty acid) in membrane phospholipids. The latter was independent of liver but affected by feeding a diet enriched in saturated fat (exacerbated) or fish oil (attenuated). Our finding of a longer QTc interval in VLCAD null mice appears to be most relevant given that such condition increases the risk of sudden cardiac death.

Reduction of ventricular sodium current in a mouse model of HIV

INTRODUCTION

Cardiac arrhythmias have been reported in AIDS patients. Arrhythmias can arise from alterations in ventricular Na(+) channel function. However, it is unknown whether HIV affects cardiac Na(+) channel function. Therefore, the purpose of this study was to characterize the effect of HIV on ventricular Na(+) current (I(Na)) in a transgenic model of HIV (CD4C/HIV mice), which exhibit a severe AIDS-like disease.

METHODS AND RESULTS

Patch-clamp techniques were used to examine I(Na) and action potentials (AP) in ventricular myocytes isolated from HIV and wild-type (WT) mice. In HIV myocytes peak I(Na) was reduced (at -50 mV: HIV, -55.3 +/- 4.3 pA/pF, n = 15; WT, -79.4 +/- 5.2 pA/pF, n = 16, P < 0.05), whereas late I(Na) was similar in both groups (HIV, -4.3 +/- 0.4 pA/pF; WT, -4.4 +/- 0.4 pA/pF, n = 22/group). AP amplitude (HIV 91.5 +/- 4.7 mV, n = 12; WT 104.4 +/- 3.1 mV, n = 15, P < 0.05) and the maximal velocity of the AP upstroke (V(max); HIV, 57.2 +/- 9.3 mV/ms, n = 12; WT, 113.5 +/- 8 mV/ms, n = 15, P < 0.05) were decreased in HIV myocytes. ECG recordings revealed that the QRS complex was prolonged in HIV mice (HIV, 15.7 +/- 0.2 ms, n = 22; WT, 14.1 +/- 0.5 ms, n = 10, P < 0.05). The serum levels of interleukin-1beta were elevated in HIV mice (HIV, 18.1 +/- 3.1 pg/mL, n = 3; WT, 5.1 +/- 1.1 pg/mL, n = 4, P < 0.05) in line with previous evidence that suggests that elevated levels of cytokines can affect cardiac ion currents.

CONCLUSION

Overall, our observations suggest that elevated levels of proinflammatory cytokines in CD4C/HIV mice could alter Na(+) channel function, thus altering cardiac depolarization and contribute to the generation of arrhythmias.

Experimental and theoretical ventricular electrograms and their relation to electrophysiological gradients in the adult rat heart

The electrical activity of adult mouse and rat hearts has been analyzed extensively, often as a prerequisite for genetic engineering studies or for the development of rodent models of human diseases. Some aspects of the initiation and conduction of the cardiac action potential in rodents closely resemble those in large mammals. However, rodents have a much higher heart rate and their ventricular action potential is triangular and very short. As a consequence, an interpretation of the electrocardiogram in the mouse and rat remains difficult and controversial. In this study, optical mapping techniques have been applied to an in vitro left ventricular adult rat preparation to obtain patterns of conduction and action potential duration measurements from the epicardial surface. This information has been combined with previously published mathematical models of the rat ventricular myocyte to develop a bidomain model for action potential propagation and electrogram formation in the rat left ventricle. Important insights into the basis for the repolarization waveform in the ventricular electrogram of the adult rat have been obtained. Notably, our model demonstrated that the biphasic shape of the rat ventricular repolarization wave can be explained in terms of the transmural and apex-to-base gradients in action potential duration that exist in the rat left ventricle.

Ventricular K+ currents are reduced in mice with elevated levels of serum TNFalpha

In the present study mice were treated with tumor necrosis factor alpha (TNFalpha) for 6 weeks to determine if chronic TNFalpha treatment could produce serum levels of TNFalpha similar to what has been observed in disease states (heart failure, HIV) and to determine if these levels of TNFalpha alter ventricular K(+) currents. Mice chronically treated with TNFalpha and sham treated mice were utilized for experiments. Serum levels were measured with a Searchlight protein array. Patch-clamp techniques, real-time PCR and Western blot analysis were used to study K(+) current densities and K(+) channel expression. Results showed that serum concentrations of TNFalpha were significantly higher in TNFalpha treated mice compared to controls (control: 9.5+/-1.5 pg/ml, TNFalpha: 27.4+/-5.0 pg/ml; p<0.05) and comparable to serum TNFalpha levels observed in heart failure and HIV models. In ventricular myocytes from TNFalpha treated mice the outward K(+) currents I(to) and I(Kur) were significantly reduced (at +30 mV: I(to): control: 45.0+/-2.9 pA/pF, TNFalpha: 34.5+/-2.9 pA/pF; p<0.05; I(Kur): control 34.1+/-2.7 pA/pF, TNFalpha: 25.0+/-2.2 pA/pF; p<0.05). Expression studies revealed that ventricular mRNA and protein expression for the channels underlying I(to) and I(Kur) did not differ between the two groups. However, the recovery from inactivation for I(Kur) was significantly longer in TNFalpha treated mice. Overall, this study shows that pathologically relevant levels of serum TNFalpha modulate K(+) currents in mouse ventricle. These findings could help to explain the role of TNFalpha in the pathogenesis of cardiac arrhythmia.

Chronic heart rate reduction by ivabradine prevents endothelial dysfunction in dyslipidaemic mice

BACKGROUND AND PURPOSE

High resting heart rate is a predictor for total and cardiovascular mortality independent of other risk factors in patients with coronary artery disease. We tested the hypothesis that a reduction of resting heart rate with the cardiac pacemaker I(f) current inhibitor ivabradine prevents the endothelial dysfunction associated with dyslipidaemia.

EXPERIMENTAL APPROACH

Three-month-old dyslipidaemic (DL) male mice expressing the human ApoB-100 were assigned or not (DL, n=16), to treatment for 3 months with ivabradine (10 mg kg(-1) d(-1), n=17). Wild-type C57Bl/6 mice (WT, n=15) were used as controls. Heart rate was measured at 3, 4.5 and 6 months. Dilatation to acetylcholine (ACh) of isolated cerebral and renal arteries was investigated at 6 months.

KEY RESULTS

Heart rate remained stable in anaesthetized WT mice, increased (25%, P<0.05) with age in DL mice but was limited (11%, P<0.05) by ivabradine. At 6 months, left ventricular maximal pressure was similar in all groups. The minimal and end-diastolic left ventricular pressures were increased (P<0.05) in DL (10.2+/-1.0 and 18.7+/-1.4 mm Hg) compared to WT (-0.4+/-0.7 and 6.3+/-1.0 mm Hg) and reduced (P<0.05) by ivabradine (4.2+/-1.3 and 11.5+/-1.5 mm Hg). ACh-induced maximal dilatation was impaired (P<0.05) in renal and cerebral arteries isolated from DL compared to WT (56+/-7 versus 83+/-3% in renal arteries; 22+/-2 versus 42+/-2% in cerebral arteries). Ivabradine completely prevented (P<0.05) this dysfunction in renal and cerebral arteries.

CONCLUSIONS AND IMPLICATIONS

Selective heart rate reduction with ivabradine limits cardiac dysfunction and prevents the renovascular and cerebrovascular endothelial dysfunction associated with dyslipidaemia.