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)

P3108Microcirculation injury is involved in anthracycline-induced cardiac toxicity

Background/Introduction

Cardiotoxicity (CT) is a major concern for cancer patients receiving anthracyclines. While the effect of anthracyclines on cardiomyocytes is well established, its impact on myocardial microcirculation has not been characterized.

Purpose

To evaluate the effect of low and high cumulative doses of doxorubicin (doxo) on anatomical and functional vasculature status evaluated by serial invasive Coronary Flow Reserve (CFR) and Cardiac Magnetic Resonance (CMR)-based quantitative perfusion in a large animal model.

Methods

Large-white male pigs (n=15, 30 kg) were distributed in 2 doxo regimes: Group 1) high cumulative dose (5 biweekly intracoronary (i.c) injections of 0.45 mg/kg of doxo) followed-up until week 16 (a time when severe left ventricular systolic dysfunction is present) and then sacrificed (N=5); Group 2) low cumulative dose of doxo (3 biweekly i.c. doses) followed-up until week 16 and then sacrificed (N=5)). Group 3) pigs sacrificed at 6 weeks (2 weeks after third doxo dose), N=5. Invasive catheter-based CFR was evaluated after i.c papaverine (0.5 mg/kg) while CMR quantitative rest perfusion maps were obtained after intravenous injection of gadolinium. CFR and CMR were performed before doxo, and at 0, 2, 4, 6 and 16 weeks thereafter. Cardiac vessels were evaluated ex vivo with trichrome staining. Statistical analysis was performed using one-way ANOVA with multiple pairwise comparisons (vs. baseline) and Bonferroni corrected p-value.

Results

CFR and CMR-quantitative myocardial perfusion were non-significantly reduced after 3 doxo doses despite myocardial vasculature was overtly injured on histology at this timepoint. Animals receiving 5 doxo doses suffered a progressive deterioration of CFR and CMR-perfusion until week 16 (1.41±0.23 vs 3.71±0.94 at baseline [p=0.014] and 65.4±18.2 ml/100g/min vs 154.9±56.3 ml/100g/min at baseline [p=0.046], respectively). At 16 weeks histology revealed extensive microvascular damage with media layer involvement and perivascular fibrosis. Pigs receiving 3 doxo doses showed less pronounced CFR reduction on long-term follow-up (3.13±0.82 vs 3.69±1.57 at baseline [p>0.05] but overt CMR-perfusion reduction (138.3±11.9 vs 197.8±37.1 at baseline [p=0.045]). On histology, damage of vasculature including arterioles was evidenced to a lesser extent than in the high cumulative doxo dose group with mild microvascular disruption and smooth muscle vacuolization.

Conclusions

Doxorubicin results in a progressive damage of the myocardial microcirculation. Even low cumulative doxo doses (resulting in no overt left ventricular dysfunction) results in vascular damage. The microcirculation status may serve as an early marker of doxorubicin cardiotoxicity.