Duchenne Cardiomyopathy Research Articles

Comprehensive cardiac magnetic resonance T1, T2, and extracellular volume mapping to define Duchenne cardiomyopathy

BackgroundCardiomyopathy is the leading cause of death in Duchenne muscular dystrophy (DMD). Cardiac magnetic resonance (CMR) parametric mapping sequences offer insights into disease pathophysiology. We propose a novel approach by leveraging T2 mapping in conjunction with T1 and extracellular volume (ECV) mapping to perform a virtual myocardial biopsy. While previous work has attempted to describe myocardial changes in DMD, our inclusion of T2 mapping enables comprehensive categorization of myocardial tissue characteristics of fibrosis, edema, and fat to better understand the pathological composition of the myocardium with disease progression. MethodsDMD patients (n = 49; median: 12 years-old) underwent CMR, including T1, T2, and ECV. Categories were defined as normal, isolated high T1 (normal ECV, high T1, normal T2), fibrosis (high ECV, normal or high T1, normal T2), edema (normal or high ECV, normal or high T1, high T2), fat (normal ECV, low T1, high T2) or fibrofatty (high ECV, low T1, high T2). ResultsMedian left ventricular ejection fraction (LVEF) was 59% with 27% having LVEF < 55%. Those with normal LVEF and no late gadolinium enhancement (37%) were younger in age (10.5 ± 2.6 vs. 15.0 ± 4.3 years-old, p < 0.001). Native T1 was elevated in at least one slice in 82% of patients. Those with high T2 at any slice (27%) were older (p = 0.005) and had lower LVEF (p = 0.005) compared with subjects with normal T2 (73%). The most common myocardial characterization was fibrosis (43%) followed by isolated high T1 (24%). Of the 13 with high T2, ten were categorized as edema, two as fibrofatty, and one as fat. ConclusionCMR parametric mapping sequences offer insights into Duchenne cardiomyopathy pathophysiology, which should drive development of therapeutic interventions aimed at these targets. Myocardial fibrosis is common in DMD. Patients with elevated T2 were older and had lower LVEF. Though fat infiltration was present, the majority of subjects with elevated T2 met criteria for myocardial edema.

Early-Onset Late Gadolinium Enhancement is a Prognostic Factor for Duchenne Cardiomyopathy.

Dilated cardiomyopathy (DCM) is an inevitable complication of Duchenne muscular dystrophy (DMD). Late gadolinium enhancement (LGE) demonstrated by cardiac MRI occurs in DMD-related DCM, indicating myocyte death and remodeling. We conducted a retrospective chart review identifying DMD patients in our center between January 2009 and July 2013. Subjects were cohorted by presence of LGE before age 14. We excluded patients in whom we could not determine LGE status prior to age 14. We reviewed comprehensive clinical data. Of the 41 subjects with complete data, 15 demonstrated LGE before age 14 ("early LGE") and 26 had no LGE by age 14 ("controls"). Those with early LGE exhibited a more rapid decline in LV fractional shortening (p = 0.028). Patients with early LGE were younger at age of initiation of ACE inhibition (p = 0.025), mineralocorticoid receptor antagonism (p = 0.0024), and beta-blockade (p = 0.0017), suggesting aggressive clinical management in response to abnormal MRI findings. There were no significant differences in LV dilation between the two groups (p = 0.1547). Early LGE was not associated with obesity (p = 0.32), age at loss of ambulation (p = 0.31), or heart rate (p-value > 0.8). Early onset of myocardial fibrosis as indicated by LGE on cardiac MRI is associated with earlier progression of cardiomyopathic changes despite earlier medication therapy. Identifying this risk factor, observed in 34% of our cohort during preadolescence, may guide medical therapy and early counseling about cardiomyopathy progression. We advocate for obtaining at least one MRI in patients withDMD prior to age 14 to risk stratify patients.

Cardiac Atrophy and ACE Inhibitors in Duchenne Cardiomyopathy: 10 Years is the Right Age to Start Therapy?

<h3>Purpose</h3> <b>Background</b> Dilated cardiomyopathy (DCM) is a leading cause of morbidity and mortality in patients affected by Duchenne muscular dystrophy (DMD). DCM is commonly characterized by a hypokinetic and dilated phenotype, typically involving left ventricle (LV). Nowadays, angiotensin converting enzyme inhibitors (ACEi) are indicated in all patients older than 10 years but the mechanism of action is still unknown. Characteristics of left ventricular (LV) remodelling are unclear, and no data are currently available on the time of onset. <b>Aim:</b> characterize left ventricular remodelling before 10 years of age and the effects of ACEi on it. <h3>Methods</h3> We conducted a retrospective single center analysis on all consecutive patients affected by DMD-DCM before 10 years of age, without LV dilation. We reanalysed all echocardiographic data about LV dimension and function, at the first cardiovascular assessment (before ACEi), at one year after treatment, and at the last follow up. To evaluate LV remodelling, we derived the relative wall thickness (RWT). RWT< 0.32 was the cut off to define the cardiac atrophy. <h3>Results</h3> 45 patients have been enrolled. Median age at first CV assessment was 10.3 y (±2.9). 72% of patients presented a reduced RWT (< 0.32) at first CV evaluation (average value 0.29 ± 0.05). After 1 year of treatment the percentage of patient with cardiac atrophy was unchanged (p = 0.52): 6 patients progressed and 6 regressed. At last follow up (35.5 months, ±7.7) the prevalence of cardiac atrophy was slightly increased (78% - p = 0.15): 9 patients (28%) developed cardiac atrophy during follow-up, despite ACEi therapy, while 6 (19%) regressed. Notably, neither progression nor regression were statistically significant (p= 0.15, p = 0.4 respectively). All patients were treated with ACEi: 48% was treated with Enalapril, 26% with Ramipril, 17% with perindopril, and the remaining with Fosinopril or Lisinopril. Median age at ACEi start was 11.2 (± 2.9). <h3>Conclusion</h3> Our data suggest that cardiac atrophy is already present, before 10 years of age. ACEi seems to slow progression but not invert the process.

Human iPSC model reveals a central role for NOX4 and oxidative stress in Duchenne cardiomyopathy.

SummaryDuchenne muscular dystrophy (DMD) is a progressive muscle disorder caused by mutations in the Dystrophin gene. Cardiomyopathy is a major cause of early death. We used DMD-patient-specific human induced pluripotent stem cells (hiPSCs) to model cardiomyopathic features and unravel novel pathologic insights. Cardiomyocytes (CMs) differentiated from DMD hiPSCs showed enhanced premature cell death due to significantly elevated intracellular reactive oxygen species (ROS) resulting from depolarized mitochondria and increased NADPH oxidase 4 (NOX4). CRISPR-Cas9 correction of Dystrophin restored normal ROS levels. ROS reduction by N-acetyl-L-cysteine (NAC), ataluren (PTC124), and idebenone improved hiPSC-CM survival. We show that oxidative stress in DMD hiPSC-CMs was counteracted by stimulating adenosine triphosphate (ATP) production. ATP can bind to NOX4 and partially inhibit the ROS production. Considering the complexity and the early cellular stress responses in DMD cardiomyopathy, we propose targeting ROS production and preventing detrimental effects of NOX4 on DMD CMs as promising therapeutic strategy.

Long-Term Outcome of LVAD in Duchenne Population with End Stage Cardiomyopathy

Purpose The aim of this study was to report the effect of long-term use of VAD in patients affected by Duchenne Muscular Distrophy and end stage cardiomyopathy (DMD-DCM). Methods We collected data of end stage DMD-DCM patients who were implanted with LVAD in our center (group 1) and the ones in regular follow-up because not eligible for LVAD implantation (group 2). Each patient of group 1 underwent extensive pre-operative assessment, in-hospital treatment and was enrolled in a dedicated DMD heart failure (HF) clinic during the post-discharge period. Patients of group 2 were followed in a dedicated DMD HF clinic or as inpatient in case of need of inotropic support. All data during long-term follow-up were recorded including echocardiography, ECG examination, laboratory blood tests, BNP dosing and assessment of nutritional status and respiratory function. Survival of the groups was represented by Kaplan Meier analysis and compared by log rank. Results A total of eight DMD-DCM patients (group 1) were implanted with LVAD and treated at our center during the period from 2011 until 2018 (mean age at implantation was 16.9 ± 2.9 years)¸whilst 4 patients (group 2) were not eligible for LVAD implantation. At the time of the last follow-up, 4 out of 8 patients were alive and 2 out of 8 patients did not have post-operative complications. The most prominent complications were bleeding and infections with one episode of acute heart failure that was successfully treated. The principal causes of 3 deaths at the median follow-up of 22 months were sepsis, tracheal bleeding, and cerebral hemorrhage. After one year from implantation we noticed a significant decrease in heart rate (p=0.002), in LV volumes and diameters (LVEDD p=0.03, LVESD p=0.02, EDV p=0.01 and ESV p=0.02) together with a significant increase in ejection fraction (p=0.0036). However, relative wall thickness did not change over time, showing an eccentric remodeling pattern before and after LVADs. Analysis on short and long-term follow-up showed significant improvement of survival in DMD patients treated with LVAD compared to the group that was not implanted (log rank Conclusion Our data showed that cardiac atrophy is persistent in Duchenne cardiomyopathy despite the improvement of LV function. LVAD improved outcomes in patients with LVAD when compared to those without.

Management of rhythm disorders in Duchenne muscular dystrophy: Is sudden death a cardiac or pulmonary problem?

Dystrophin deficiency results in the cardiomyopathy of variable onset and deficiency. Myocardial scarring commonly results in cardiac dysfunction, with both atrial and ventricular dysrhythmias. Heart failure, rather than arrhythmia burden, remains the strongest cardiac predictor of mortality in this patient population. Current data suggest the overall rate of sudden cardiac death in pediatric dilated cardiomyopathy is significantly lower than in adults. Specifically, in the Duchenne cardiomyopathy population, sudden death from an arrhythmic cause appears to be rare, even in patients with previously diagnosed arrhythmias. Despite this, recommendations for implantable cardioverter-defibrillator (ICD) placement in patients with Duchenne cardiomyopathy has traditionally been extrapolated from adult heart failure recommendations based on decreased left ventricular ejection fraction <35%. Early involvement of the cardiologist in the care for patients with dystrophin-deficient cardiomyopathy is recommended for this reason. The indications for ICD placement to prevent sudden death in patients with Duchenne cardiomyopathy are not well defined. There is little evidence to suggest that placement meaningfully prolongs life in this population, and should be carefully considered in accordance with the care goals of the patient and his family.

Long-Term Outcome of LVAD in Duchenne Population with End Stage Cardiomyopathy

The aim of this study was to report the effect of long-term use of VAD in patients affected by Duchenne Muscular Distrophy and end stage cardiomyopathy. We collected data of DMD patients with end-stage cardiomyopathy implanted with LVAD in our center (group 1) and the ones in regular follow-up not eligible for LVAD implantation (group 2). Each patient of group 1 underwent extensive pre-operative assessment, in-hospital treatment and was enrolled in a dedicated DMD HF (heart failure) clinic during the post-discharge period. Patients of group 2 were followed in a dedicated DMD HF clinic or as inpatient in case of need of inotropic support. During long-term follow-up all data were recorded including echocardiography, ECG examination, laboratory blood tests, and respiratory function. Survival was represented by Kaplan Meier analysis and compared by log rank. A total of 8 DMD patients (group 1) were implanted with LVAD and treated at our center during the period from 2011 until 2018 (mean age at implantation was 16.9 ± 2.9 years)¸ whilst 4 patients (group 2) were not eligible for LVAD implantation. At the time of the last follow-up, 4 out of 8 patients were alive and 2 out of 8 patients did not have post-operative complications. The principal causes of 3 deaths at the median follow-up of 22 months were sepsis, tracheal bleeding, and cerebral hemorrhage. After 1 year from implantation we noticed a significant decrease in heart rate (p=0.002), in LV volumes and diameters (LVEDD p=0.03, LVESD p=0.02, EDV p=0.01 and ESV p=0.02) and significant increase in ejection fraction (p=0.0036). However, relative wall thickness did not change over time, showing an eccentric remodeling pattern before and after LVADs. Analysis on short and long-term follow-up showed significant improvement of survival in DMD patients treated with LVAD compared to the group that was not implanted (log rank&lt0.001), with a 5-year increase in life expectancy. Our data showed that cardiac atrophy is persistent in Duchenne cardiomyopathy despite the improvement of EF due to a significant ventricular unloading coupled with chronic therapy. LVAD improved outcomes in patients with LVAD when compared to those without. An integration of outpatient DMD HF clinic and patient-centered palliative care will most likely increase the quality of life and delivery of care for this population.

P3446Left-ventricular assist device as a destination therapy in Duchenne cardiomyopathy: are we ready to change the natural history?

Abstract Background Heart failure is becoming the most prominent cause of death among patients with Duchenne Muscular Dystrophy (DMD) and end-stage cardiomyopathy (CMP). Implantation of left ventricular assist devices (LVAD) as destination therapy (DT) in this group of patients is still matter of debate. No current data are available on long-term follow- up of young patients. Purpose The aim of this study was to evaluate the long-term outcome of LVAD in DMD end stage heart failure (HF) compared to a group treated optimal medical treatment (OMT) with inotropes Methods All patients affected by DMD patients presenting with end-stage HF receiving OMT or LVAD have been reviewed. All data about characteristics of HF at presentation including assessment of nutritional status and respiratory function, left ventricular ejection fraction, brain natriuretic peptide, serum sodium, in-hospital treatment and long term follow up have been collected. OMT group was constituted by 4 patients matching implantation VAD criteria but not eligible or refusing treatment. Survival was represented by Kaplan Meier analysis. Results A total of 12 DMD patients with end-stage CMP were considered for this analysis. 8 have been implanted with LVAD during the period from 2011 until mid-2017 and compared with 4 treated with OMT. Mean systolic pressure was 103 versus 91 mmHg in those not receiving LVAD (p=0.2), and left ventricular ejection fraction at the time of presentation was 16‰ for LVAD group and 22‰ for the second group (p=0.1). LVADs improved survival throughout follow-up for patients undergoing baseline inotropic infusions (P=0.0014); for the LVAD group versus the OMT group, 1-month survival was 100‰ and 67‰ respectively and 2-month survival was 100‰ versus 0‰. For LVAD group survival was 86‰ at one year, 71‰ at 2 years and 48‰ at 5 years from implantation. Analysis on short and long-term follow-up showed significant improvement of survival in DMD patients treated with LVAD (log rank&lt;0.001), with a 5-year increase in life expectancy. Conclusions LVAD improved outcomes in patients with LVAD when compared to those without. Long-term follow-up was similar to DT LVAD adult population. Further studies are necessary to confirm these data.

Abstract 184: Cardioprotective Effects of Brain-derived Neurotrophic Factor rs6265 Polymorphism in Duchenne Cardiomyopathy

We previously identified brain-derived neurotrophic factor (BDNF) as a putative cardiac-specific biomarker for preserved cardiac function in Duchenne Muscular Dystrophy (DMD). BDNF has cardioprotective qualities that may attenuate dilated cardiomyopathy, and a common, functional BDNF single nucleotide polymorphism rs6265 (Val66-Met) may be correlated with increased risk of cardiovascular events. We hypothesized that BDNF is protective in the setting of DMD and that BDNF’s beneficial effects are diminished in rs6265 allelic carriers. We compared circulating BDNF levels with cardiovascular and skeletal muscle functional parameters in DMD patients stratified by carrier status. Positive association of circulating BDNF with left ventricular ejection fraction in DMD patients was restricted to non-carriers of the rs6265 allele, whereas carriers exhibited worse cardiac function with increased BDNF, more fibrosis and worse skeletal muscle function. To more directly assess association of rs6265 with cardiac function, we used mice with knock-in of BDNF polymorphic Val66Met allele. RNASeq showed higher expression of extracellular matrix genes in Val66Met hearts, and there was a negative correlation of cardiac BDNF protein levels with fibrosis. Additionally, there were baseline echocardiographic and ECG differences, and isolated cardiomyocytes had decreased contractility. This overall cardiac phenotype was substantially enhanced when Val66Met mice were crossed with muscular dystrophy mice. Considered together, our results indicate that BDNF plays a protective role in the dystrophic heart and may represent a novel therapeutic candidate for DMD cardiomyopathy.

Prevention and Treatment of Duchenne Cardiomyopathy with Hydrogen Sulfide‐Donor Therapy

BackgroundDuchenne muscular dystrophy (DMD) is the most frequently inherited human myopathy and represents the most devastating type of muscular dystrophy. This progressive disease is caused by X‐linked recessive defects in the gene encoding for the structural protein, dystrophin. Young boys with DMD exhibit symptoms between 3–5 years of age, primarily involving skeletal muscles. Although the heart is also impacted, limited exercise tolerance masks early symptoms of cardiomyopathy (DMD‐CM). The defects in dystrophin in cardiac tissue lead to loss of membrane integrity, extracellular calcium influx and subsequent cardiomyocyte necrosis, inflammation and increased overall fibrosis. Respiratory failure has long been the leading cause of death in boys with DMD, however, with the advent of respiratory therapy, patients with DMD may now survive longer to unfortunately die in the 2nd or 3rd decade of life from heart failure. Based on its mito‐protective, anti‐inflammatory, anti‐apoptotic and anti‐fibrotic effects, we believe that hydrogen sulfide (H2S) is a promising candidate for therapy against the devastating consequences of DMD‐CM.Methods‘Humanized’ dystrophic G2 mice (shorter telomeres) were generated by inbreeding G1 mdx4cv/mTR mice. The effects of SG1002, an orally active slow releasing H2S prodrug, were tested in the G2 mice (40 mg/kg) either immediately after weaning (~3 weeks of age; Early Treatment) or after cardiac dysfunction (~7 months of age; Late Treatment). Cardiac function was analyzed by echocardiography. Muscle fibrosis was assessed via picrosirius red staining of diaphragm, gastrocnemius, and heart collected at 2, 4 and 9 months. Cardiac mitochondria and protein were isolated to measure oxidative phosphorylation and NLRP3 expression, respectively.ResultsEarly treatment with SG1002 preserved cardiac function (ejection fraction; EF) throughout study duration, whereas untreated mice exhibited significant decline in EF by 4 months of age and continued to worsen over time (Fig. A). Delayed treatment with SG1002 significantly improved EF within 1 month after treatment initiation. SG1002 also significantly attenuated fibrosis in the diaphragm and gastrocnemius, and had a tendency to decrease cardiac fibrosis by 9 months of age (Fig. B). A steady decline in mitochondrial function was observed over time in untreated mice compared to wild type mice (−26%), which was attenuated with SG1002 (−12%, P&lt;0.05 vs. untreated group). Although there was no difference in NLRP3 expression in the heart of G2 mice at 4 months of age compared to wild type, a significant 2‐fold increase in cardiac NLRP3 expression was observed by 9 months (Fig. C).ConclusionIn a ‘humanized’ mouse model of DMD, our results strongly support daily H2S therapy for preservation of cardiac function, attenuation of skeletal muscle fibrosis and cardiac NLRP3 expression. Accordingly, modulation of the inflammasome and scar formation with H2S may represent an important mechanism to mitigate DMD‐CM as well as skeletal muscle injury.Support or Funding InformationR01HL133167 to FNSThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Interventions for preventing and treating cardiac complications in Duchenne and Becker muscular dystrophy and X-linked dilated cardiomyopathy.

Interventions for preventing and treating cardiac complications in Duchenne and Becker muscular dystrophy and X-linked dilated cardiomyopathy.

Abstract 114: A Role for Brain-derived Neurotrophic Factor in Duchenne Cardiomyopathy

Brain-derived neurotrophic factor (BDNF) and its receptor, tropomyosin receptor kinase B (TrkB) harbor cardioprotective qualities that may attenuate CM. In a small cohort of DMD patients we found that BDNF blood levels positively correlated with preserved ejection fraction (EF) and less fibrosis, and carriers of the common BDNF single nucleotide polymorphism rs6265 (Val66-Met) tended to exhibit earlier age of onset of fibrosis with subsequent progression to LV dysfunction, compared to non-carriers. We thus hypothesized that BDNF/TrkB signaling delays CM progression in DMD. To test this hypothesis, we administered the TrkB agonist 7,8-dihydroxyflavone (DHF) to mdx 4cv ; mTR KO mice in their drinking water for 26 weeks, beginning at 8 weeks of age. Based on echocardiography, DHF treatment preserved cardiac output compared to vehicle-treated controls. Conversely, mdx 4cv ; mTR KO mice injected intraperitoneally with the TrkB inhibitor (K252a) displayed bradycardia and PR interval prolongation, as measured by EKG, as well as acute (10-20 min) reduction in percent EF and fractional shortening, as measured by echocardiography. K252a also significantly reduced sarcomere shortening in isolated murine cardiomyocytes. BDNF might also contribute to cardiac repair. Using humanized BDNF polymorphic mice, which have the Val66-Met mutation, we found that post-myocardial infarction cardiac dysfunction was significantly exacerbated in Met/Met mice compared to Val/Val littermate controls. Finally, we evaluated the role of BDNF/TrkB in human cardiomyocytes differentiated from induced pluripotent cells obtained from DMD patients (DMD iPSC-CMs) and found that they highly express BDNF protein in lysates and supernatants. DMD iPSC-CMs also expressed a truncated version of TrkB that lacks the tyrosine kinase domain essential for canonical BDNF/TrkB signaling. Nonetheless, DMD iPSC-CMs responded to treatment with recombinant BDNF, including increased phosphorylation of GSK-3α, mTOR, AMPK, and MSK1/2. Considered together, our results indicate that BDNF plays a protective role in the dystrophic heart and might represent a novel therapeutic candidate for DMD cardiomyopathy.

Cardiac-Specific Expression of ΔH2-R15 Mini-Dystrophin Normalized All Electrocardiogram Abnormalities and the End-Diastolic Volume in a 23-Month-Old Mouse Model of Duchenne Dilated Cardiomyopathy.

Heart disease is a major health threat for Duchenne/Becker muscular dystrophy patients and carriers. Expression of a 6-8 kb mini-dystrophin gene in the heart holds promise to change the disease course dramatically. However, the mini-dystrophin gene cannot be easily studied with adeno-associated virus (AAV) gene delivery because the size of the minigene exceeds AAV packaging capacity. Cardiac protection of the ΔH2-R19 minigene was previously studied using the cardiac-specific transgenic approach. Although this minigene fully normalized skeletal muscle force, it only partially corrected electrocardiogram and heart hemodynamics in dystrophin-null mdx mice that had moderate cardiomyopathy. This study evaluated the ΔH2-R15 minigene using the same transgenic approach in mdx mice that had more severe cardiomyopathy. In contrast to the ΔH2-R19 minigene, the ΔH2-R15 minigene carries dystrophin spectrin-like repeats 16 to 19 (R16-19), a region that has been suggested to protect the heart in clinical studies. Cardiac expression of the ΔH2-R15 minigene normalized all aberrant electrocardiogram changes and improved hemodynamics. Importantly, it corrected the end-diastolic volume, an important diastolic parameter not rescued by ΔH2-R19 mini-dystrophin. It is concluded that that ΔH2-R15 mini-dystrophin is a superior candidate gene for heart protection. This finding has important implications in the design of the mini/micro-dystrophin gene for Duchenne cardiomyopathy therapy.

Automatic quantification of microscopic heart damage in a mouse model of Duchenne muscular dystrophy using optical polarization tractography.

Quantification of microscopic myocardium damage in a diseased heart is important in studying disease progression and evaluating treatment outcome. However, it is challenging to use traditional histology and existing medical imaging modalities to quantify all microscopic damages in a small animal heart. Here, a method was developed for fast visualization and quantification of focal tissue damage in the mouse heart based on the fiber alignment index of the local myofiber organization obtained in optical polarization tractography (OPT). This method was tested in freshly excised hearts of the mdx4cv mouse, a commonly used mouse model for studying Duchenne cardiomyopathy. The hearts of age-matched C57BL/6 mice were also imaged as the normal controls. The results revealed a significant amount of damage in the mdx4cv hearts. Histology comparisons confirmed the damage identified by OPT. This fast and automatic method may greatly enhance preclinical studies in murine models of heart diseases.

Progression of Duchenne Cardiomyopathy Presenting with Chest Pain and Troponin Elevation.

Improved neuromuscular and respiratory therapies have altered the natural history of Duchenne muscular dystrophy (DMD) such that the most common cause of mortality is progressive cardiomyopathy. Despite imaging evidence of progressive cardiomyopathy, troponin I (cTn) is not significantly elevated in asymptomatic DMD patients. We describe eight boys with DMD evaluated for acute chest pain (ACP) and found to have acute cTn elevation with depressed left ventricular ejection fraction (LVEF). Of our eight patients, five presented with a primary complaint of ACP, while three presented with secondary myocardial injury in the context of systemic illness requiring hospitalization. Electrocardiograms showed diffuse ST changes and mean peak cTn level was 44±15.4 ng/mL (reference range <0.03 ng/mL). cTn levels normalized with only supportive care. Cardiac magnetic resonance imaging (CMR) was performed during the event on all but one patient, demonstrating increased late gadolinium enhancement (LGE) from 12.4±11.4% to 36.5±10.3% with associated deterioration of LVEF from 61±4.4% to 47.6±6.6% which remained depressed on follow-up CMR study (49.1±7.8%). All viral studies were negative. Additional investigations varied among patients, but no causative findings were demonstrated. ACP with cTn elevation occurs in DMD boys and may be indicative of cardiomyopathy progression as evidenced by acute left ventricular dysfunction and development or progression of myocardial fibrosis. This clinical presentation is under recognized. These events may represent an important pathophysiological mechanism in cardiomyopathy progression.

A Five-Repeat Micro-Dystrophin Gene Ameliorated Dystrophic Phenotype in the Severe DBA/2J-mdx Model of Duchenne Muscular Dystrophy

Micro-dystrophins are highly promising candidates for treating Duchenne muscular dystrophy, a lethal muscle disease caused by dystrophin deficiency. Here, we report robust disease rescue in the severe DBA/2J-mdx model with a neuronal nitric oxide synthase (nNOS)-binding micro-dystrophin vector. 2 × 1013 vector genome particles/mouse of the vector were delivered intravenously to 10-week-old mice and were evaluated at 6 months of age. Saturated micro-dystrophin expression was detected in all skeletal muscles and the heart and restored the dystrophin-associated glycoprotein complex and nNOS. In skeletal muscle, therapy substantially reduced fibrosis and calcification and significantly attenuated inflammation. Centronucleation was significantly decreased in the tibialis anterior (TA) and extensor digitorum longus (EDL) muscles but not in the quadriceps. Muscle function was normalized in the TA and significantly improved in the EDL muscle. Heart histology and function were also evaluated. Consistent with the literature, DBA/2J-mdx mice showed myocardial calcification and fibrosis and cardiac hemodynamics was compromised. Surprisingly, similar myocardial pathology and hemodynamic defects were detected in control DBA/2J mice. As a result, interpretation of the cardiac data proved difficult due to the confounding phenotype in control DBA/2J mice. Our results support further development of this microgene vector for clinical translation. Further, DBA/2J-mdx mice are not good models for Duchenne cardiomyopathy.

Heart structural remodeling in a mouse model of Duchenne cardiomyopathy revealed using optical polarization tractography [Invited

We investigated the heart structural remodeling in the mdx4cv mouse model of Duchenne cardiomyopathy using optical polarization tractography. Whole heart tractography was obtained in freshly dissected hearts from six mdx4cv mice. Six hearts from C57BL/6J mice were also imaged as the normal control. The mdx4cv hearts were significantly larger than the control hearts and had significantly higher between-subject variations in myofiber organization. While both strains showed classic cross-helical fiber organization in the left ventricle, the rate of the myocardial fiber orientation change across the heart wall was significantly altered in the right ventricle of the mdx4cv heart.

Uniform low-level dystrophin expression in the heart partially preserved cardiac function in an aged mouse model of Duchenne cardiomyopathy

Dystrophin deficiency results in Duchenne cardiomyopathy, a primary cause of death in Duchenne muscular dystrophy (DMD). Gene therapy has shown great promise in ameliorating the cardiac phenotype in mouse models of DMD. However, it is not completely clear how much dystrophin is required to treat dystrophic heart disease. We and others have shown that mosaic dystrophin expression at the wild-type level, depending on the percentage of dystrophin positive cardiomyocytes, can either delay the onset of or fully prevent cardiomyopathy in dystrophin-null mdx mice. Many gene therapy strategies will unlikely restore dystrophin to the wild-type level in a cardiomyocyte. To determine whether low-level dystrophin expression can reduce the cardiac manifestations in DMD, we examined heart histology, ECG and hemodynamics in 21-m-old normal BL6 and two strains of BL6-background dystrophin-deficient mice. Mdx3cv mice show uniform low-level expression of a near full-length dystrophin protein in every myofiber while mdx4cv mice have no dystrophin expression. Immunostaining and western blot confirmed marginal level dystrophin expression in the heart of mdx3cv mice. Although low-level expression did not reduce myocardial histopathology, it significantly ameliorated QRS prolongation and normalized diastolic hemodynamic deficiencies. Our study demonstrates for the first time that low-level dystrophin can partially preserve heart function.

Abstract 16015: Exosome-mediated Reversal of Duchenne Cardiomyopathy

Duchenne muscular dystrophy, a crippling genetic disease leading to premature death, affects the heart as well as skeletal muscle. Indeed, cardiomyopathy is the leading cause of death in Duchenne patients. There are no approved treatments for the cardiomyopathy, and novel Duchenne-specific experimental approaches such as exon skipping do not benefit the heart. Here we demonstrate that cardiosphere-derived cells (CDCs), which are in advanced clinical testing for therapeutic regeneration after myocardial infarction, reverse the key pathophysiological hallmarks of Duchenne cardiomyopathy (oxidative stress, inflammation, fibrosis and mitochondrial dysfunction) in mdx mice. Exosomes secreted by human CDCs reproduce the benefits of CDCs in mdx mice, and reverse mitochondrial dysfunction in human Duchenne cardiomyocytes. Both CDCs and their exosomes improve heart function in mdx mice (P&lt;0.05); a single injection of CDCs suffices to increase maximal exercise capacity and improve survival (P&lt;0.005). Delivery of a microRNA enriched in CDC exosomes, miR 148a, mimics key effects of CDCs and CDC exosomes. Thus, CDCs effectively treat Duchenne cardiomyopathy, via exosome-mediated transfer of signaling molecules including miR 148a. The present findings motivate clinical testing of CDCs in patients with Duchenne cardiomyopathy.

Gender: the state of being male or female.

Gender: the state of being male or female.