Remote ischemic preconditioning ameliorates anthracycline-induced cardiotoxicity and preserves mitochondrial integrity: results from a randomized preclinical trial in pigs

Introduction

Anthracycline-induced cardiotoxicity (AIC) is a serious adverse effect occurring in a significant proportion of patients. Irreversible mitochondrial damage is a central mechanism of AIC. Despite many efforts, there is a lack of therapies able to prevent AIC. Remote ischemic preconditioning (RIPC) could be a promising therapy to prevent AIC due to the scheduled application of chemotherapy in cancer patients.

Purpose

To evaluate the cardioprotective efficacy of RIPC in large animal model of AIC.

Methods

Large-White pigs (n=20) underwent a validated protocol of AIC consisting on five intracoronary doxorubicin injections (0.45 mg/kg), on weeks 0, 2, 4, 6, 8 of the study. Pigs were randomized before the initiation of the study to remote ischemic pre-conditioning (RIPC, 3 cycles of 5 min lower limb ischemia followed by 5 min reperfusion) or sham procedure immediately before doxorubicin injections. An additional group of 10 pigs without any exposure to doxorubicin was carried out as controls. Pigs underwent a comprehensive serial cardiac magnetic resonance (CMR) exam baseline, and on weeks 6, 8, 12, and 16. After 16-week CMR, pigs were sacrificed and tissue samples collected. A second group of 10 pigs (randomized 1:1 for RIPC) underwent the same protocol but were sacrificed 2 weeks after the third doxorubicin dose for early evaluation of tissue changes. Primary endpoint of the study was CMR-based left ventricular ejection fraction on week 16.

Results

Until week 6 (time of fourth doxorubicin injection), LVEF remained unchanged in both groups. From there on, a progressive decline in LVEF was observed. LVEF depression trajectory was blunted in RIPC animals. Compared to controls, pigs undergoing RIPC before each doxorubicin dose had a significantly higher LVEF at week 16: median (IQR) 45% (27–50%) vs 33% (19–47%) in RIPC and controls respectively, p=0.04. Improvement in LVEF was mainly due to a more preserved contractile function, as evidence by smaller LVESV, and better regional contractile function. After 3 doxorubicin doses, a time where global (LVEF) and regional contractile function was still unchanged, transmission electron microscopy (TEM) showed fragmented mitochondria with remodeled cristae only in control pigs. At the end of the 16 weeks, TEM evaluation in control pigs (as compared to RIPC pigs) showed overt cardiomyocyte's mitochondrial fragmentation with overt structural derangement. At this time, RIPC pigs had significantly less interstitial fibrosis on histology.

Conclusions

In a translatable large animal model of AIC, RIPC applied immediately before each doxorubicin cycle resulted in a preservation of cardiac contractility with significantly higher long-term LVEF and less cardiac fibrosis. RIPC prevented the deleterious effects of doxorubicin on mitochondria since early stages of AIC. RIPC is a promising intervention to be tested in clinical trials to prevent cardiotoxicity.

Funding Acknowledgement

Type of funding source: Public grant(s) – National budget only. Main funding source(s): The CNIC is supported by the Instituto de Salud Carlos III (ISCIII), the Ministerio de Ciencia e Innovaciόn and the Pro CNIC Foundation, and is a Severo Ochoa Center of Excellence (SEV-2015-0505)

3070Caloric restriction increases lifespan in dilated cardiomyopathy mice by enhancing mitochondrial quality control

Background/Introduction

Dilated cardiomyopathy (DCM) is a leading cause of heart failure (HF) in young and middle aged individuals worldwide. Alterations in mitochondrial dynamics (fusion/fission) and quality control (mitophagy) are critical for normal cardiac function. Imbalanced mitochondrial dynamics towards fission has been shown to contribute to DCM development in mice with ablation of the mitochondrial protease YME1L, which results in altered OPA1 processing precluding mitochondrial fusion. In these mice, the DCM phenotype includes a metabolic reprogramming of cardiomyocytes, shifting from fatty acid (FA) oxidation towards glucose. High fat diet (HFD) in these mice results in reversal of this metabolic reprogramming and rescue from DCM despite the genetic defect (lack of YME1) still present. These results opened a new venue for dietary approaches as a therapeutic strategy in HF. To understand whether the fat itself contained in the HFD was responsible of HF rescue, we studied the trajectories of cardiac function in mice with altered mitochondrial dynamics under HFD, caloric restriction and control chow.

Methods

Cardiomyocyte-specific Yme1l knock-out (cYKO) male mice (N=10–15) known to develop DCM phenotype at 20–25 weeks of age were randomized to 3 different diets (1: HFD containing >30% crude fat; 2: non-fat diet containing <0.5% crude fat, and 3: control diet containing 10% crude fat) at 10 weeks of age. Every 10 weeks, cardiac function was tested by echocardiography. At 30 weeks, animals underwent a multitracer microPET/CT (glucose and FA uptake) to evaluate myocardial substrate utilization. At the end of the study, animals were sacrificed and hearts were harvested for histological and further tissue analyses.

Results

As expected, HFD was associated with a better left ventricular ejection fraction (LVEF; %) at 30 weeks: 37.97±8.59 vs. 29.16±8.9 in control diet, p=0.04. This functional improvement was associated with an increase in FA uptake on microPET/CT. Non-fat diet was associated with even higher LVEF at 30 weeks: 44.94±11 vs. 29.16±8.9 in control diet, p=0.0001, as well as smaller LV diameter (mm): 3.58±0.29 vs. 4.3±0.39 in control diet, p<0.0001 (A). Lifespan of mice on non-fat diet was significantly prolonged (70% extension compared to control) (B). Enhanced mitochondrial clearance (mitophagy) mediated by Parkin, together with an increase in autophagy related protein as LC3B was identified in the non-fat diet group (C).

Conclusion

Different dietary approaches have been shown to be beneficial in the prevention of DCM in mice with altered mitochondrial dynamics. Caloric restriction (non-fat diet) is able to prevent DCM, reverse metabolic reprogramming, increase mitochondrial quality control and ultimately prolong lifespan in mice with genetic defect associated with altered mitochondrial dynamics. Interventions aiming at enhancing cardiac mitophagy might represent a new therapeutic option in DCM.

P5999Heart failure rescue by high fat diet in a porcine model of hibernated myocardium

Background

Extensive coronary artery disease without revascularization options results in ischemic hibernated myocardium and ultimately heart failure (HF). A metabolic reprogramming of the heart characterized by a shift from fatty acids (FFA) to glucose as the preferential metabolic substrate is frequent in HF and hibernated myocardium. Previous studies in mouse models of HF have shown that high fat diet (HFD) is able to reverse the metabolic reprogramming of the heart and improve cardiac function. Here we used a translational large animal model of ischemic HF evaluated by state-of-the-art imaging modalities

Methods

IHM was generated in Yucatan minipigs (N=50) by progressive stenosis of the proximal left anterior descending (LAD) after surgical insertion of a casein ameroid around the artery. Pigs underwent a serial multimodality imaging study including magnetic resonance imaging (MRI), multi-tracer PET/CT (18FDG & 14(R,S)-[18F]Fluoro-6-thia-heptadecanoic acid (18F-FTHA) 19F-palmitate in-house synthetized), and invasive coronary angiography (ICA). Once hibernated myocardium with metabolic switch was documented (complete occlusion of LAD, LVEF<50% on MRI, viable myocardium with dobutamine/MRI- evaluated contractile reserve, and metabolic substrate utilization shift towards glucose on PET/CT), animals were randomized to HFD or regular diet for 3 months

Results

The first part of the study was dedicated to establish the model in 42 pigs. Pigs were followed-up for 170±24 days with monthly ICA, MRI and PET/CT. Severe LAD stenosis was documented in all pigs 3–4 weeks after surgery. Mortality during follow-up was 57% (n=24) (15 peri-procedure, 2 between day 1 and 7, seven between day 7 and 45). Among those surviving beyond the sixth week, 90% (16/18) developed hibernated myocardium (mean LVEF 36±10%, absence of transmural delayed enhancement, contractile reserve and metabolic switch on PET/CT).

In the second part of the study, 5 long-term survivors were allocated to receive HFD (20% extra lard), while 3 pigs served as controls. Mean LVEF before HFD initiation was 35±8%, and 36±5% in controls. Three months HFD was associated with a LVEF improvement in all treated animals (mean LVEF at the end of follow-up was 45±9%). Control animals on regular diet did not show any change in LVEF (35±5% at the end of follow-up)

Conclusions

We present a large animal model of HF due hibernated myocardium by placing an ameroid around the LAD. Mortality of this model is high (approx. 55%) but long-term survivors resemble all features seen in patients: LAD progressive stenosis with final occlusion but viable myocardium, LVEF deterioration and metabolic switch

Feeding pigs with HFD to force cardiac reutilization of FFA, results in a consistent and large LVEF improvement in all animals

Cardiac metabolic switch might be implicated in the pathogenesis of systolic dysfunction in hibernated myocardium and is a potential target for nutritional approaches