Relationship between syringomyelia and myxomatous mitral valve disease in Cavalier King Charles spaniels.

BACKGROUND: Syringomyelia (SM) and myxomatous mitral valve disease (MMVD) are highly prevalent in Cavalier King Charles spaniels (CKCS). Cardiac status in CKCS with and without SM is currently unknown. OBJECTIVES: To investigate the association between SM and MMVD severity in CKCS and CKCS with SM with and without clinical signs of SM. ANIMALS: Fifty-five CKCS: 40 with SM (22 symptomatic and 18 asymptomatic) and 15 without SM. METHODS: A combined retrospective and prospective study. MRI and echocardiography were used to diagnose SM and MMVD, respectively. The association between SM and MMVD severity (left ventricle internal diameter in diastole normalized to bodyweight [LVIDDN] and left atrium to aortic ratio [LA/Ao]) were tested using multivariable linear regression analysis adjusting for sex and age. RESULTS: Overall, no significant difference in LVIDDN and LA/Ao was found between CKCS with or without SM. However, CKCS with symptomatic SM had significantly smaller LVIDDN (1.45 [1.30-1.50]) (median [IQR]) and LA/Ao (1.20 [1.10-1.28]) compared to CKCS with asymptomatic SM (1.60 [1.50-1.90] and 1.40 [1.20-1.75]) as well as CKCS without SM (0.24 [0.03-0.45] and 0.30 [0.05-0.56]) (all P values <.03). CONCLUSIONS AND CLINICAL IMPORTANCE: An association between MMVD and SM was not confirmed in this cohort of CKCS, indicating that MMVD and SM do not co-segregate. However, CKCS with symptomatic SM had smaller left ventricle and atrial size compared to CKCS with asymptomatic SM and CKCS without SM.

Mitral valve transcriptome analysis in thirty-four age-matched Cavalier King Charles Spaniels with or without congestive heart failure caused by myxomatous mitral valve disease.

We here report the results of a mitral valve transcriptome study designed to identify genes and molecular pathways involved in development of congestive heart failure (CHF) following myxomatous mitral valve disease (MMVD) in dogs. The study is focused on a cohort of elderly age-matched dogs (n = 34, age ~ 10 years) from a single breed-Cavalier King Charles Spaniels (CKCS)-with a high incidence of MMVD. The cohort comprises 19 dogs (10♀, 9♂) without MMVD-associated CHF, and 15 dogs (6♀, 9♂) with CHF caused by MMVD; i.e., we compare gene expression in breed and age-matched groups of dogs, which only differ with respect to CHF status. We identify 56 genes, which are differentially expressed between the two groups. In this list of genes, we confirm an enrichment of genes related to the TNFß-signaling pathway, extracellular matrix organization, vascular development, and endothelium damage, which also have been identified in previous studies. However, the genes with the greatest difference in expression between the two groups are CNTN3 and MYH1. Both genes encode proteins, which are predicted to have an effect on the contractile activity of myocardial cells, which in turn may have an effect on valvular performance and hemodynamics across the mitral valve. This may result in shear forces with impact on MMVD progression.

No impact of polymorphism in the phosphodiesterase 5A gene in Cavalier King Charles Spaniels on pimobendan-induced inhibition of platelet aggregation response.

BACKGROUND: A variant in the canine phosphodiesterase (PDE) 5A gene (PDE5A:E90K) is associated with decreased concentrations of circulating cyclic guanosine monophosphate (cGMP) and response to PDE5 inhibitor treatment. Pimobendan is a PDE inhibitor recommended for medical treatment of certain stages of myxomatous mitral valve disease (MMVD) in dogs. HYPOTHESIS: PDE5A:E90K polymorphism attenuates the inhibitory effect of pimobendan on in vitro platelet aggregation and increases basal platelet aggregation in Cavalier King Charles Spaniels (CKCS). Selected clinical variables (MMVD severity, sex, age, hematocrit, platelet count in platelet-rich plasma [PRP], and echocardiographic left ventricular fractional shortening [LV FS]) will not show an association with results. ANIMALS: Fifty-two privately owned CKCS with no or preclinical MMVD. METHODS: Using blood samples, we prospectively assessed PDE5A genotype using Sanger sequencing and adenosine diphosphate-induced platelet aggregation response (area under the curve [AUC], maximal aggregation [MaxA], and velocity [Vel]) with and without pimobendan using light transmission aggregometry. Dogs also underwent echocardiography. RESULTS: Pimobendan inhibited platelet function as measured by AUC, MaxA, and Vel at a concentration of 10 µM (P < .0001) and Vel at 0.03 µM (P < .001). PDE5A:E90K polymorphism did not influence the inhibitory effect of pimobendan or basal platelet aggregation response. CONCLUSIONS AND CLINICAL IMPORTANCE: The PDE5A:E90K polymorphism did not influence in vitro basal platelet aggregation response or the inhibitory effect of pimobendan on platelet aggregation in CKCS. Dogs with the PDE5A:E90K polymorphism did not appear to have altered platelet function or response to pimobendan treatment.

Polymorphisms in the serotonin transporter gene and circulating concentrations of neurotransmitters in Cavalier King Charles Spaniels with myxomatous mitral valve disease.

BACKGROUND: The neurotransmitter serotonin (5-HT) affects valvular degeneration and dogs with myxomatous mitral valve disease (MMVD) exhibit alterations in 5-HT signaling. In Maltese dogs, 3 single nucleotide polymorphisms (SNPs) in the 5-HT transporter (SERT) gene are suggested to associate with MMVD. HYPOTHESIS/OBJECTIVES: Determine the association of SERT polymorphisms on MMVD severity and serum 5-HT concentration in Cavalier King Charles Spaniels (CKCS). Additionally, investigate the association between selected clinical and hematologic variables and serum 5-HT and assess the correlation between HPLC and ELISA measurements of serum 5-HT. ANIMALS: Seventy-one CKCS (42 females and 29 males; 7.8 [4.7;9.9] years (median [Q1;Q3])) in different MMVD stages. METHODS: This prospective study used TaqMan genotyping assays to assess SERT gene polymorphisms. Neurotransmitter concentrations were assessed by HPLC and ELISA. RESULTS: TaqMan analyses identified none of the selected SERT polymorphisms in any of the CKCS examined. Serum 5-HT was associated with platelet count (P < .001) but not MMVD severity, age or medical therapy and did not correlate with serum concentration of the 5-HT metabolite, 5-hydroxyindoleacetic acid. The ELISA serum 5-HT correlated with HPLC measurements (ρ = .87; P < .0001) but was lower (mean difference = -22 ng/mL; P = .02) independent of serum 5-HT concentration (P = .2). CONCLUSIONS AND CLINICAL IMPORTANCE: Selected SERT SNPs associated with MMVD in Maltese dogs were not found in CKCS and only platelet count influenced serum 5-HT concentration. These SNPs are unlikely to be associated with MMVD pathophysiology or serum 5-HT concentration in CKCS. HPLC and ELISA serum 5-HT demonstrated good correlation but ELISA systematically underestimated 5-HT.

Depleted Myocardial Coenzyme Q10 in Cavalier King Charles Spaniels with Congestive Heart Failure Due to Myxomatous Mitral Valve Disease.

Congestive heart failure (CHF) has been associated with depleted myocardial coenzyme Q10 (Q10) concentrations in human patients. The aim of this study was to investigate associations between myocardial Q10 concentrations and myxomatous mitral valve disease (MMVD) severity in dogs. Furthermore, citrate synthase (CS) activity was analysed to determine if a reduction in myocardial Q10 was associated with mitochondrial depletion in the myocardium. Thirty Cavalier King Charles spaniels (CKCS) in MMVD stages B1 (n = 11), B2 (n = 5) and C (n = 14) according to the American College of Veterinary Internal Medicine (ACVIM) guidelines and 10 control (CON) dogs of other breeds were included. Myocardial Q10 concentration was analysed in left ventricular tissue samples using HPLC-ECD. CKCS with congestive heart failure (CHF; group C) had significantly reduced Q10 concentrations (median, 1.54 µg/mg; IQR, 1.36-1.94), compared to B1 (2.76 µg/mg; 2.10-4.81, p < 0.0018), B2 (3.85 µg/mg; 3.13-4.46, p < 0.0054) and CON dogs (2.8 µg/mg; 1.64-4.88, p < 0.0089). CS activity was comparable between disease groups. In conclusion, dogs with CHF due to MMVD had reduced myocardial Q10 concentrations. Studies evaluating antioxidant defense mechanisms as a therapeutic target for treatment of CHF in dogs are warranted.

Angiotensin-converting enzyme activity in Cavalier King Charles Spaniels with an ACE gene polymorphism and myxomatous mitral valve disease.

OBJECTIVES: Myxomatous mitral valve disease (MMVD) is the most common heart disease in the dog. It is particularly common in the Cavalier King Charles Spaniel (CKCS) breed and affected dogs are frequently managed with angiotensin-converting enzyme inhibitors (ACE-I). We have previously identified a canine ACE gene polymorphism associated with a decrease in angiotensin-converting enzyme (ACE) activity. The aim of this study was to evaluate for the prevalence of the ACE polymorphism in CKCS with mitral valve disease and to determine whether the presence of the polymorphism is associated with alterations in ACE activity at different stages of cardiac disease. METHODS: Seventy-three dogs with a diagnosis of mitral valve disease were evaluated and a blood sample was drawn for ACE polymorphism genotyping and ACE activity measurement. RESULTS: Forty-three dogs were homozygous for the ACE polymorphism; five were heterozygous and 25 were homozygous wild type. The mean age and the median severity of disease were not different for dogs with the polymorphism and dogs with the wild-type sequence. The median baseline ACE activity was significantly lower for the ACE polymorphism (27.0 U/l) than the wild-type sequence dogs (31.0 U/l) (P=0.02). Dogs with more severe disease and the ACE polymorphism had significantly lower levels of ACE activity than dogs with the wild-type sequence (P=0.03). CONCLUSION: The CKCS appears to have a high prevalence of the ACE variant. Dogs with the ACE variant had lower levels of ACE activity even in more advanced mitral valve disease than dogs without the variant. The clinical significance of this finding and its impact on the need for ACE-I in dogs with the polymorphism and heart disease deserves further study.

Plasma and serum serotonin concentrations and surface-bound platelet serotonin expression in Cavalier King Charles Spaniels with myxomatous mitral valve disease.

OBJECTIVE: To investigate serum and plasma serotonin concentrations, percentage of serotonin-positive platelets, level of surface-bound platelet serotonin expression (mean fluorescence intensity [MFI]), and platelet activation (CD62 expression) in platelet-rich plasma from Cavalier King Charles Spaniels with myxomatous mitral valve disease (MMVD). ANIMALS: Healthy dogs (n = 15) and dogs with mild MMVD (18), moderate-severe MMVD (19), or severe MMVD with congestive heart failure (CHF; 10). PROCEDURES: Blood samples were collected from each dog. Serum and plasma serotonin concentrations were measured with an ELISA, and surface-bound platelet serotonin expression and platelet activation were determined by flow cytometry. RESULTS: Dogs with mild MMVD had higher median serum (746 ng/mL) and plasma (33.3 ng/mL) serotonin concentrations, compared with MMVD-affected dogs with CHF (388 ng/mL and 9.9 ng/mL, respectively), but no other group differences were found. Among disease groups, no differences in surface-bound serotonin expression or platelet activation were found. Thrombocytopenic dogs had lower serum serotonin concentration (482 ng/mL) than nonthrombocytopenic dogs (731 ng/mL). In 26 dogs, a flow cytometry scatterplot subpopulation (FSSP) of platelets was identified; dogs with an FSSP had a higher percentage of serotonin-positive platelets (11.0%), higher level of surface-bound serotonin expression (MFI, 32,068), and higher platelet activation (MFI, 2,363) than did dogs without an FSSP (5.7%, 1,230, and 1,165, respectively). An FSSP was present in 93.8% of thrombocytopenic dogs and in 29.5% of nonthrombocytopenic dogs. CONCLUSIONS AND CLINICAL RELEVANCE: A substantive influence of circulating serotonin on MMVD stages prior to CHF development in Cavalier King Charles Spaniels was not supported by the study findings. An FSSP of highly activated platelets with pronounced serotonin binding was strongly associated with thrombocytopenia but not MMVD.