Long-term restoration of cardiac dystrophin expression in golden retriever muscular dystrophy following rAAV6-mediated exon skipping

Although restoration of dystrophin expression via exon skipping in both cardiac and skeletal muscle has been successfully demonstrated in the mdx mouse, restoration of cardiac dystrophin expression in large animal models of Duchenne muscular dystrophy (DMD) has proven to be a challenge. In large animals, investigators have focused on using intravenous injection of antisense oligonucleotides (AO) to mediate exon skipping. In this study, we sought to optimize restoration of cardiac dystrophin expression in the golden retriever muscular dystrophy (GRMD) model using percutaneous transendocardial delivery of recombinant AAV6 (rAAV6) to deliver a modified U7 small nuclear RNA (snRNA) carrying antisense sequence to target the exon splicing enhancers of exons 6 and 8 and correct the disrupted reading frame. We demonstrate restoration of cardiac dystrophin expression at 13 months confirmed by reverse transcription-PCR (RT-PCR) and immunoblot as well as membrane localization by immunohistochemistry. This was accompanied by improved cardiac function as assessed by cardiac magnetic resonance imaging (MRI). Percutaneous transendocardial delivery of rAAV6 expressing a modified U7 exon skipping construct is a safe, effective method for restoration of dystrophin expression and improvement of cardiac function in the GRMD canine and may be easily translatable to human DMD patients.

Long-term systemic myostatin inhibition via liver-targeted gene transfer in golden retriever muscular dystrophy

Duchenne muscular dystrophy (DMD) is a lethal, X-linked recessive disease affecting 1 in 3,500 newborn boys for which there is no effective treatment or cure. One novel strategy that has therapeutic potential for DMD is inhibition of myostatin, a negative regulator of skeletal muscle mass that may also promote fibrosis. Therefore, our goal in this study was to evaluate systemic myostatin inhibition in the golden retriever model of DMD (GRMD). GRMD canines underwent liver-directed gene transfer of a self-complementary adeno-associated virus type 8 vector designed to express a secreted dominant-negative myostatin peptide (n = 4) and were compared with age-matched, untreated GRMD controls (n = 3). Dogs were followed with serial magnetic resonance imaging (MRI) for 13 months to assess cross-sectional area and volume of skeletal muscle, then euthanized so that tissue could be harvested for morphological and histological analysis. We found that systemic myostatin inhibition resulted in increased muscle mass in GRMD dogs as assessed by MRI and confirmed at tissue harvest. We also found that hypertrophy of type IIA fibers was largely responsible for the increased muscle mass and that reductions in serum creatine kinase and muscle fibrosis were associated with long-term myostatin inhibition in GRMD. This is the first report describing the effects of long-term, systemic myostatin inhibition in a large-animal model of DMD, and we believe that the simple and effective nature of our liver-directed gene-transfer strategy makes it an ideal candidate for evaluation as a novel therapeutic approach for DMD patients.

Cardiac gene transfer of short hairpin RNA directed against phospholamban effectively knocks down gene expression but causes cellular toxicity in canines

Derangements in calcium cycling have been described in failing hearts, and preclinical studies have suggested that therapies aimed at correcting this defect can lead to improvements in cardiac function and survival. One strategy to improve calcium cycling would be to inhibit phospholamban (PLB), the negative regulator of SERCA2a that is upregulated in failing hearts. The goal of this study was to evaluate the safety and efficacy of using adeno-associated virus (AAV)-mediated cardiac gene transfer of short hairpin RNA (shRNA) to knock down expression of PLB. Six dogs were treated with self-complementary AAV serotype 6 (scAAV6) expressing shRNA against PLB. Three control dogs were treated with empty AAV6 capsid, and two control dogs were treated with scAAV6 expressing dominant negative PLB. Vector was delivered via a percutaneously inserted cardiac injection catheter. PLB mRNA and protein expression were analyzed in three of six shRNA dogs between days 16 and 26. The other three shRNA dogs and five control dogs were monitored long-term to assess cardiac safety. PLB mRNA was reduced 16-fold, and PLB protein was reduced 5-fold, with treatment. Serum troponin elevation and depressed cardiac function were observed in the shRNA group only at 4 weeks. An enzyme-linked immunospot assay failed to detect any T cells reactive to AAV6 capsid in peripheral blood mononuclear cells, heart, or spleen. Microarray analysis revealed alterations in cardiac expression of several microRNAs with shRNA treatment. AAV6-mediated cardiac gene transfer of shRNA effectively knocks down PLB expression but is associated with severe cardiac toxicity. Toxicity may result from dysregulation of endogenous microRNA pathways.

Serum serotonin concentrations in dogs with degenerative mitral valve disease

BACKGROUND

Increased serotonin (5HT) signaling has been implicated in valvular disease of humans and animals, including canine degenerative mitral valve disease (DMVD). High circulating 5HT concentration is a potential source of increased signaling, and serum 5HT concentrations have not been previously reported in dogs with DMVD.

HYPOTHESIS

Dogs with DMVD and small breed dogs predisposed to DMVD have higher serum 5HT concentrations than large breed controls.

ANIMALS

Fifty dogs affected with DMVD, 34 dogs predisposed to DMVD but without cardiac murmur or echocardiographic evidence of DMVD, and 36 healthy large breed control dogs.

METHODS

Prospective analysis. Serum 5HT concentration was measured by an ELISA test.

RESULTS

Median serum 5HT concentration was significantly higher in dogs with DMVD and in dogs predisposed to DMVD as compared with controls (DMVD, 765.5 ng/mL [interquartile range, 561.3-944.4]; predisposed, 774.9 ng/mL [528.3-1,026]; control, 509.8 ng/mL [320.8-708.8]; P= .0001). Subgroup analysis of predisposed dogs indicated significantly higher serum 5HT concentrations in Cavalier King Charles Spaniel (CKCS) dogs than in other breeds (CKCS, 855.0 ng/mL [635.8-1,088]; non-CKCS, 554.2 ng/mL [380.6-648.4]; P= .0023). Age, platelet count, and platelet morphology were not correlated with 5HT concentration in any group.

CONCLUSIONS AND CLINICAL IMPORTANCE

Dogs with DMVD had significantly higher serum 5HT concentrations when compared with large breed control dogs. Healthy CKCS dogs had significantly higher serum 5HT concentrations than other healthy dogs predisposed to DMVD. Additional investigation into a possible role of 5HT in the pathogenesis of DMVD is warranted.

Prospective evaluation of NT-proBNP assay to detect occult dilated cardiomyopathy and predict survival in Doberman Pinschers

BACKGROUND

Occult (asymptomatic) dilated cardiomyopathy (ODCM) is highly prevalent in Doberman Pinschers.

HYPOTHESIS/OBJECTIVES

Assess ability of NT-proBNP assay to detect ODCM and predict death.

ANIMALS

155 asymptomatic Dobermans presenting for ODCM screening.

METHODS

Echocardiography, 24-hour Holter, and NT-proBNP assay were performed prospectively. Diagnosis was based on increased left ventricular end-systolic dimension, >50 ventricular premature complexes (VPCs), or both on Holter. Utility was evaluated using receiver-operating characteristic curves. Effect of age, weight, sex, disease status, VPCs, and NT-proBNP on survival was analyzed using Kaplan-Meier and Cox-proportional hazard analysis.

RESULTS

Seventy-three (47.1%) Dobermans were diagnosed with ODCM, including 31, 17, and 25 that met Holter, echocardiographic, or both criteria, respectively. Sensitivity of NT-proBNP > 457 pmol/L to detect these groups was 45.2, 76.5, and 96.0%, respectively. Combination of NT-proBNP and Holter to detect ODCM yielded sensitivity of 94.5%, specificity of 87.8%, and accuracy of 91.0%. Follow-up data were available for 78 Dobermans. The median survival time of Dobermans with > 50 VPCs (469 days), NT-proBNP > 900 pmol/L (284 days), or ODCM (474 days) was significantly (P < .0001) shorter than those with < 50 VPCs (1743 days), NT-proBNP < 900 pmol/L (1743 days), or without disease (1743 days). NT-proBNP concentration and disease status were independently predictive of all-cause mortality.

CONCLUSIONS AND CLINICAL IMPORTANCE

The combination of NT-proBNP assay and Holter detected ODCM with high accuracy. NT-proBNP and disease status were independently associated with survival. NT-proBNP assay identified Dobermans with high probability of increased LVIDs consistent with ODCM, and can facilitate pursuit of confirmatory diagnostic testing, such as echocardiography, in suspected Dobermans.

Effect of NT-pro-BNP assay on accuracy and confidence of general practitioners in diagnosing heart failure or respiratory disease in cats with respiratory signs

BACKGROUND

N-terminal pro-B-type natriuretic peptide (NT-proBNP) can distinguish congestive heart failure (CHF) from primary respiratory disease in cats with respiratory signs with approximately 90% diagnostic accuracy, but the additive benefit of NT-proBNP to improve the diagnosis obtained from conventional testing in individual cases remains unknown.

HYPOTHESIS

NT-proBNP will improve the diagnostic accuracy and confidence of general practice veterinarians in assessing cats with respiratory signs.

ANIMALS

Ten cats with respiratory signs.

METHODS

History, physical examination, thoracic radiographs, electrocardiogram (ECG), and biochemical analysis of 10 cats presented to the University of Pennsylvania or Tufts University with a history of respiratory signs were evaluated by 50 general practice veterinarians using an online survey tool. Participants were asked to provide (1) diagnosis of CHF or primary respiratory disease, and (2) level of confidence in their diagnosis (1, lowest to 10, highest) before and after disclosure of NT-proBNP results. Diagnoses (CHF, n = 5; primary respiratory, n = 5) were compared to the gold standard defined as consensus opinion of 3 board-certified cardiologists blinded to the NT-proBNP results.

RESULTS

Overall correctness of the practitioners was 69.2%, and significantly increased after practitioners were provided NT-proBNP results (87.0%, P = .0039). Median practitioner confidence before NT-proBNP disclosure was 6 (IQR, 5-8) and significantly increased after disclosure (8; IQR, 6-10; P = .0039).

CONCLUSIONS

These data indicate a relatively low accuracy and level of confidence in the diagnosis of feline respiratory signs. Use of NT-proBNP assay in conjunction with conventional evaluation by general practitioners significantly improved their diagnostic accuracy and confidence.

Serotonin concentrations in platelets, plasma, mitral valve leaflet, and left ventricular myocardial tissue in dogs with myxomatous mitral valve disease

HYPOTHESIS/OBJECTIVES

Altered serotonin (5-hydroxytryptamine, 5HT) signaling is postulated in development and progression of canine myxomatous mitral valve disease (MMVD). Little is known regarding platelet, plasma, valvular, or myocardial 5HT concentration ([5HT]) in affected dogs. We quantified [5HT] in platelet-rich plasma (PRP), platelet-poor plasma (PPP), mitral valve leaflets (MV), and left ventricular myocardium (LV).

ANIMALS

Forty-five dogs comprised 4 plasma groups of Cavalier King Charles Spaniels (CKCS) or non-CKCS, either healthy (CON) or MMVD affected: CKCS CON (n = 12); non-CKCS CON (n = 8); CKCS MMVD (n = 14); non-CKCS MMVD (n = 11). Twenty-four dogs comprised 3 tissue groups: MMVD (n = 8); other-HD (heart disease) (n = 7); non-HD, extracardiac disease (n = 9).

METHODS

High-performance liquid chromatography measured PRP, PPP, MV, and LV [5HT].

RESULTS

Platelet-rich plasma platelet [5HT] was greater in CKCS CON (1.83 femtograms/platelet [fg/plt]; range, 0.20-4.76; P = .002), CKCS MMVD (1.58 fg/plt; range, 0.70-4.03; P = .005), and non-CKCS MMVD (1.72 fg/plt; range, 0.85-4.44; P = .003) versus non-CKCS CON (0.92 fg/plt; range, 0.63-1.30). There was no group difference in PPP [5HT]. MV [5HT] was significantly higher in MMVD (32.4 ng/mg; range, 8.4-106.7) versus non-HD (3.6 ng/mg; range, 0-28.3; P = .01) and LV [5HT] was significantly higher in MMVD (11.9 ng/mg; range, 4.0-104.8) versus other-HD (0.9 ng/mg; range, 0-10.1; P = .011) and non-HD (2.5 ng/mg; range, 0-6.9; P = .001).

CONCLUSIONS AND CLINICAL IMPORTANCE

Platelet [5HT] was highest in healthy CKCS and both MMVD groups, but plasma [5HT] showed no group differences. Tissue [5HT] was highest in MV and LV of MMVD-affected dogs, suggesting altered 5HT signaling as a potential feature of MMVD. Interactions of platelet, valvular, and myocardial 5HT signaling warrant further investigation.

Effect of torsemide and furosemide on clinical, laboratory, radiographic and quality of life variables in dogs with heart failure secondary to mitral valve disease

OBJECTIVES

Diuretic therapy reduces preload and relieves congestion secondary to cardiac dysfunction. Torsemide (torasemide) is a loop diuretic with longer duration of action, decreased susceptibility to diuretic resistance, and adjunctive aldosterone antagonist properties compared with furosemide. We hypothesized that torsemide would be well tolerated and no less effective than furosemide at diuresis, control of clinical signs, and maintenance of quality of life (QOL) in dogs with congestive heart failure (CHF).

ANIMALS, MATERIALS AND METHODS

Seven client-owned dogs with stable CHF receiving twice daily oral furosemide and adjunctive medications. Utilizing a double-blinded, randomized, crossover design, dogs were administered either oral furosemide at their current dose or an equivalent oral dose of torsemide (1/10 of the daily furosemide dose divided into twice daily dosing) on day 0. Crossover occurred at day 7 and the study ended on day 14. Clinical, laboratory, radiographic, and QOL variables were evaluated on days 0, 7 and 14.

RESULTS

No dogs developed recurrent CHF during the study. Mean furosemide dose on day 0 was 5.13 mg/kg/day (range 2.8-9.6). Following torsemide treatment, creatinine (P = 0.020), urea nitrogen (P = 0.013), phosphorus (P = 0.032), albumin (P = 0.019), carbon dioxide (P = 0.015) and anion gap (P = 0.005) were significantly increased, and urine specific gravity (P = 0.004) and chloride (P = 0.021) were significantly decreased compared with furosemide dosing. No differences in QOL were found.

CONCLUSIONS

Results indicate that torsemide is equivalent to furosemide at controlling clinical signs of CHF in dogs and is likely to achieve greater diuresis vs. furosemide. Larger clinical trials evaluating torsemide as a first or second-line loop diuretic for congestive heart failure in dogs are warranted.

The use of NT-proBNP assay in the management of canine patients with heart disease

The diagnosis and management of canine heart disease could be facilitated by a highly sensitive and specific laboratory test that predicts risk of morbidity and mortality, is helpful in directing therapy, easy to perform, inexpensive, and widely available. This article details if, how, and when the cardiac biomarker, N-terminal fragment of the prohormone B-type natriuretic peptide (NT-proBNP), helps in the diagnosis and management of canine heart disease. Veterinary cardiac biomarkers, specifically NT-proBNP, hold great promise. The incorporation of NT-proBNP assay into successful clinical practice requires an understanding of the science behind the technology, as well as the clinical data available to date.

Cardiac troponin-I concentrations in dogs with bradyarrhythmias before and after artificial pacing

OBJECTIVES

To quantify cardiac troponin-I (cTnI) concentration in dogs with symptomatic bradyarrhythmias before and after artificial pacing and to correlate cTnI concentration with diagnosis, echocardiographic parameters, serology, and outcome.

ANIMALS, MATERIALS AND METHODS

Medical records from the University of Pennsylvania from 2006 to 2009 were reviewed, and 14 dogs with cTnI assay results before and after pacemaker were identified. The ECG diagnosis included complete atrioventricular block (AVB), sick sinus syndrome, 2nd degree AVB, and atrial standstill. Serology, presence of premature beats, echocardiographic measurements, and pacing modality were recorded.

RESULTS

Mean cTnI concentration was elevated both pre- and post-pacing, and was significantly higher pre-pacing vs. post-pacing. Post-pacing cTnI concentration in 9 of 14 dogs (64%) remained above the reference range. Four dogs yielded high serum titers for Bartonella spp. Four dogs with markedly increased cTnI concentration had progressive left ventricular enlargement and myocardial failure as compared to pre-pacing examination.

CONCLUSIONS

Elevated cTnI concentration suggests that cardiac injury persists after artificial pacing in dogs with bradyarrhythmias. Myocarditis secondary to Bartonella spp. or other causes may be an important cause of AVB in dogs. Prospective studies investigating the correlation of cTnI to potential etiology and development of post-pacing LV dysfunction and outcome are needed.