A-769662 potentiates the effect of other AMP-activated protein kinase activators on cardiac glucose uptake

AMP-activated protein kinase (AMPK), a key cellular sensor of energy, regulates metabolic homeostasis and plays a protective role in the ischemic or diabetic heart. Stimulation of cardiac glucose uptake contributes to this AMPK-mediated protection. The small-molecule AMPK activator A-769662, which binds and directly activates AMPK, has recently been characterized. A-769662-dependent AMPK activation protects the heart against an ischemia-reperfusion episode but is unable to stimulate skeletal muscle glucose uptake. Here, we tried to reconcile these conflicting findings by investigating the impact of A-769662 on cardiac AMPK signaling and glucose uptake. We showed that A-769662 promoted AMPK activation, resulting in the phosphorylation of several downstream targets, but was incapable of stimulating glucose uptake in cultured cardiomyocytes and the perfused heart. The lack of glucose uptake stimulation can be explained by A-769662's narrow specificity, since it selectively activates cardiac AMPK heterotrimeric complexes containing α2/β1-subunits, the others being presumably required for this metabolic outcome. However, when combined with classical AMPK activators, such as metformin, phenformin, oligomycin, or hypoxia, which impact AMPK heterotrimers more broadly via elevation of cellular AMP levels, A-769662 induced more profound AMPK phosphorylation and subsequent glucose uptake stimulation. The synergistic effect of A-769662 under such ischemia-mimetic conditions protected cardiomyocytes against ROS production and cell death. In conclusion, despite the fact that A-769662 activates AMPK, it alone does not significantly stimulate glucose uptake. However, strikingly, its ability of potentiating the action on other AMPK activators makes it a potentially useful participant in the protective role of AMPK in the heart.

Transcatheter Sapien valve implantation in a native tricuspid valve after failed surgical repair

OBJECTIVES

We describe the first report of a transcatheter Sapien implantation in a native tricuspid valve after multiple failed surgical repairs with a lack of prosthetic material and radiographic landmarks.

METHODS AND RESULTS

A 47-year old female underwent multiple valve repairs and replacements including three tricuspid valve repairs without surgical ring or bioprosthesis implantation. She developed signs of right heart failure associated with a mixed tricuspid disease combining a severe stenosis and regurgitation. After surgical turn down, a revalvulation using a transcatheter approach was attempted. The challenges in this case were the absence of a stiff region to anchor the percutaneous valve, the lack of radiographic landmarks and the difficulties of precise annulus measurements. The applied strategy was -under general anesthesia and extracorporeal membrane oxygenation-: balloon sizing, prestenting of the tricuspid annulus using covered stents followed by Sapien valve implantation through the femoral vein under fluoroscopy and transoesophageal echocardiography (TEE). The procedure was successfull, solving the tricuspid leak and stenosis (peak gradient from 22 to 3 mm Hg) using two Sapien for a perfect positioning. It was complicated by pulmonary bleeding due to a distal wire exit, treated successfully by coil embolization. The clinical and echocardiographic outcome was good up to 5 months.

CONCLUSIONS

Transcatheter Sapien valve implantation in a native tricuspid valve after failed multiple surgical repairs is feasible by the femoral vein. Technical challenges due to the lack of rigid landing zone and fluoroscopic markers were solved by prestenting and valve implantation under bi-plane fluoroscopic and TEE guidance.

Role of AMP-activated protein kinase in regulating hypoxic survival and proliferation of mesenchymal stem cells

AIMS

Mesenchymal stem cells (MSCs) are widely used for cell therapy, particularly for the treatment of ischaemic heart disease. Mechanisms underlying control of their metabolism and proliferation capacity, critical elements for their survival and differentiation, have not been fully characterized. AMP-activated protein kinase (AMPK) is a key regulator known to metabolically protect cardiomyocytes against ischaemic injuries and, more generally, to inhibit cell proliferation. We hypothesized that AMPK plays a role in control of MSC metabolism and proliferation.

METHODS AND RESULTS

MSCs isolated from murine bone marrow exclusively expressed the AMPKα1 catalytic subunit. In contrast to cardiomyocytes, a chronic exposure of MSCs to hypoxia failed to induce cell death despite the absence of AMPK activation. This hypoxic tolerance was the consequence of a preference of MSC towards glycolytic metabolism independently of oxygen availability and AMPK signalling. On the other hand, A-769662, a well-characterized AMPK activator, was able to induce a robust and sustained AMPK activation. We showed that A-769662-induced AMPK activation inhibited MSC proliferation. Proliferation was not arrested in MSCs derived from AMPKα1-knockout mice, providing genetic evidence that AMPK is essential for this process. Among AMPK downstream targets proposed to regulate cell proliferation, we showed that neither the p70 ribosomal S6 protein kinase/eukaryotic elongation factor 2-dependent protein synthesis pathway nor p21 was involved, whereas p27 expression was increased by A-769662. Silencing p27 expression partially prevented the A-769662-dependent inhibition of MSC proliferation.

CONCLUSION

MSCs resist hypoxia independently of AMPK whereas chronic AMPK activation inhibits MSC proliferation, p27 being involved in this regulation.

Association between early surgical intervention vs watchful waiting and outcomes for mitral regurgitation due to flail mitral valve leaflets

IMPORTANCE

The optimal management of severe mitral valve regurgitation in patients without class I triggers (heart failure symptoms or left ventricular dysfunction) remains controversial in part due to the poorly defined long-term consequences of current management strategies. In the absence of clinical trial data, analysis of large multicenter registries is critical.

OBJECTIVE

To ascertain the comparative effectiveness of initial medical management (nonsurgical observation) vs early mitral valve surgery following the diagnosis of mitral regurgitation due to flail leaflets.

DESIGN, SETTING, AND PARTICIPANTS

The Mitral Regurgitation International Database (MIDA) registry includes 2097 consecutive patients with flail mitral valve regurgitation (1980-2004) receiving routine cardiac care from 6 tertiary centers (France, Italy, Belgium, and the United States). Mean follow-up was 10.3 years and was 98% complete. Of 1021 patients with mitral regurgitation without the American College of Cardiology (ACC) and the American Heart Association (AHA) guideline class I triggers, 575 patients were initially medically managed and 446 underwent mitral valve surgery within 3 months following detection.

MAIN OUTCOMES AND MEASURES

Association between treatment strategy and survival, heart failure, and new-onset atrial fibrillation.

RESULTS

There was no significant difference in early mortality (1.1% for early surgery vs 0.5% for medical management, P=.28) and new-onset heart failure rates (0.9% for early surgery vs 0.9% for medical management, P=.96) between treatment strategies at 3 months. In contrast, long-term survival rates were higher for patients with early surgery (86% vs 69% at 10 years, P < .001), which was confirmed in adjusted models (hazard ratio [HR], 0.55 [95% CI, 0.41-0.72], P < .001), a propensity-matched cohort (32 variables; HR, 0.52 [95% CI, 0.35-0.79], P = .002), and an inverse probability-weighted analysis (HR, 0.66 [95% CI, 0.52-0.83], P < .001), associated with a 5-year reduction in mortality of 52.6% (P < .001). Similar results were observed in relative reduction in mortality following early surgery in the subset with class II triggers (59.3 after 5 years, P = .002). Long-term heart failure risk was also lower with early surgery (7% vs 23% at 10 years, P < .001), which was confirmed in risk-adjusted models (HR, 0.29 [95% CI, 0.19-0.43], P < .001), a propensity-matched cohort (HR, 0.44 [95% CI, 0.26-0.76], P = .003), and in the inverse probability-weighted analysis (HR, 0.51 [95% CI, 0.36-0.72], P < .001). Reduction in late-onset atrial fibrillation was not observed (HR, 0.85 [95% CI, 0.64-1.13], P = .26).

CONCLUSION AND RELEVANCE

Among registry patients with mitral valve regurgitation due to flail mitral leaflets, performance of early mitral surgery compared with initial medical management was associated with greater long-term survival and a lower risk of heart failure, with no difference in new-onset atrial fibrillation.

Value of adding natriuretic peptides and electrocardiographic findings to assess the presence of cardiac dysfunction in patients ≥80 years of age

Studies estimating the added value of natriuretic peptide levels and electrocardiographic findings beyond all relevant clinical information to identify cardiac dysfunction remain scarce. The aim of this study was to assess the presence of clinically relevant cardiac dysfunction in an unselected population of subjects aged ≥80 years. A cross-sectional analysis using an "intention-to-diagnose" strategy was performed within the BELFRAIL study (n = 567). Baseline B-type natriuretic peptide and N-terminal pro-B-type natriuretic peptide levels were determined and echocardiography was performed at subjects' homes. Logistic regression analysis and classification and regression tree analysis were used as complementary analytic tools. Cardiac dysfunction was present in 17% of subjects without and 31% of subjects with chronic atrial fibrillation (AF) or pacemaker. In subjects without chronic AF or pacemaker, the clinical model showed a C-statistic of 0.79 (95% confidence interval 0.74 to 0.85). The combination of natriuretic peptides with normal results on electrocardiography increased, only marginally, the C-statistic. In subjects with chronic AF or pacemaker, the clinical model showed a very high C-statistic of 0.90 (95% confidence interval 0.82 to 0.98). Classification and regression tree analysis showed that an additional 58 subjects (13%) were correctly classified using natriuretic peptides and electrocardiographic findings among those without chronic AF or pacemaker. Of participants with chronic AF or pacemaker, >90% were correctly classified. In conclusion, in a large population-based sample of patients aged ≥80 years, the clinical model possessed high accuracy to identify cardiac dysfunction in daily practice. Among subjects without chronic AF or pacemaker, a larger number were correctly classified by integrating natriuretic peptides and electrocardiographic findings in the strategy.

Cerebral embolization during percutaneous valve implantation does not occur during balloon inflation valvuloplasty: prospective diffusion-weighted brain MRI study

BACKGROUND AND AIM OF THE STUDY

The study aim was to define the timing of cerebral embolization events during transcatheter aortic valve implantation (TAVI), and to determine if events were more closely associated with valve implantation or with balloon inflation.

METHODS

Between January 2008 and November 2011, a total of 114 patients underwent TAVI at the author's institution. Of these patients, 44 had previously undergone imaging before and after TAVI, and were included in the study (26 transfemoral (TF); 18 transapical (TA)). Eleven patients who had only balloon valvuloplasty (BV) during the same period were included, as were 22 patients who had open aortic valve replacement (AVR), as controls. All 77 patients underwent neurological examination, and all had cerebral MRIs before and after their procedures.

RESULTS

Fifty of the 77 patients who underwent postprocedural MRI had new cerebral lesions, as follows: 24/26 (92%) in TF patients; 17/18 (94%) in TA patients; 3/11 (27%) in BV patients; and 6/22 (27%) in AVR patients (TF and TA versus BV and AVR, p < 0.0001). The mean number and volume of embolic lesions per patient were respectively 5.4/438 mm3 for TF, 11.6/3414 mm3 for TA, 0.7/46 mm3 for BV, and 0.4/48 mm3 for AVR (TF versus TA and BV versus AVR, p = NS; TF and TA versus BV and AVR, p < 0.0001). No association was found between either the EuroSCORE or patient age and the number of events.

CONCLUSION

In the present study, an incidence of silent cerebral embolic lesions after TAVI was identified which was significantly higher than that for BV or AVR. This indicated an association of embolism with valve implantation rather than with balloon inflation.

Myocardial infarct size quantification in mice by SPECT using a novel algorithm independent of a normal perfusion database

Background

There is a growing interest in developing non-invasive imaging techniques permitting infarct size (IS) measurements in mice. The aim of this study was to validate the high-resolution rodent Linoview single photon emission computed tomography (SPECT) system for non-invasive measurements of IS in mice by using a novel algorithm independent of a normal database, in comparison with histology.

Methods

Eleven mice underwent a left coronary artery ligature. Seven days later, animals were imaged on the SPECT 2h30 after injection of 173 ± 27 MBq of Tc-99m-sestamibi. Mice were subsequently killed, and their hearts were excised for IS determination with triphenyltetrazolium chloride (TTC) staining. SPECT images were reconstructed using the expectation maximization maximum likelihood algorithm, and the IS was calculated using a novel algorithm applied on the 20-segment polar map provided by the commercially available QPS software (Cedars-Sinai Medical Center, CA, USA). This original method is attractive by the fact that it does not require the implementation of a normal perfusion database.

Results

Reconstructed images allowed a clear delineation of the left ventricles borders in all mice. No significant difference was found between mean IS determined by SPECT and by TTC staining [37.9 ± 17.5% vs 35.6 ± 17.2%, respectively (P = 0.10)]. Linear regression analysis showed an excellent correlation between IS measured on the SPECT images and IS obtained with TTC staining (y = 0.95x + 0.03 (r = 0.97; P < 0.0001)), without bias, as demonstrated by the Bland-Altman plot.

Conclusion

Our results demonstrate the accuracy of the method for the measurement of myocardial IS in mice with the Linoview SPECT system.

The impact of confounders on the test performance of natriuretic peptides for cardiac dysfunction in subjects aged 80 and older

The hypothesis that natriuretic peptides could be used to identify 'pancardiac' damage has been proposed. However, multiple factors are known to influence circulating levels of natriuretic peptides, especially in the very old. Therefore, the impact of confounders on the association between natriuretic peptide levels and cardiac dysfunction was further explored in subjects aged 80 and older. A diagnostic cross-sectional study embedded within the BELFRAIL study (n=567) was performed. Baseline BNP and NT-proBNP levels were measured and echocardiograms were performed at the subject's home. Cardiac dysfunction was defined as systolic dysfunction, valvular heart disease or isolated severe diastolic dysfunction. Several functional and structural echocardiographic parameters were independently related to circulating levels of natriuretic peptides. Cystatin C, BMI, β blockers, diabetes, heart frequency, usCRP, age and sex were identified as confounders. The prevalence of cardiac dysfunction was 17.1% in the subjects without and 30.8% in the subjects with chronic atrial fibrillation (CAF) or pacemaker (PM). Only in subjects with CAF or PM the C statistic for cardiac dysfunction improved after correcting for confounders. The post-test probability for a negative test (PTP-) ranged from 3.7% to 12.2% and the PTP+ ranged from 21.9% to 62.2% in different strata of confounders. According to these data adjusting for identified confounders does not improve the diagnostic accuracy of the natriuretic peptides for cardiac dysfunction, except in subjects with CAF or PM. Stratifying for individual confounders showed that different cut-off values could be used to optimize the diagnostic characteristics of natriuretic peptides.