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

Successful treatment of a severe 5-hydroxytrytophan intoxication using carbon hemoperfusion, hemodiafiltration, and mechanical ventilation in a dog

OBJECTIVE

To describe the successful use of carbon hemoperfusion and hemodiafiltration in combination with mechanical ventilation (MV) to treat a severe intoxication of 5-hydroxytryptophan (5-HTP) in a dog.

CASE SUMMARY

A dog ingested a minimum of 550 mg/kg of extended-release 5-HTP, resulting in serotonin syndrome that progressed to a comatose state and severe hypoventilation requiring MV. Extracorporeal carbon hemoperfusion coupled with hemodiafiltration was performed to remove 5-HTP from this patient. A carbon hemoperfusion cartridge was placed in series upstream in the extracorporeal circuit from the hemodialyzer. A total of 46.5 L of blood (4.89 L/kg) was processed during a 4.85-hour treatment. Serial plasma samples were obtained at 0, 60, 90, and 150 minutes during the session and 14 hours after the session. These samples were later analyzed for 5-HTP and serotonin concentrations. The extraction ratio of 5-HTP was 93.6%-98.9% through the carbon filter. The dog was weaned from MV within 8 hours after extracorporeal therapy and, after a full recovery, was successfully discharged.

NEW OR UNIQUE INFORMATION PROVIDED

Despite an extensive review of the available literature, this appears to be the first reported case of using a carbon hemoperfusion, hemodiafiltration, and MV to treat severe serotonin syndrome secondary to 5-HTP intoxication in a dog. The combination of carbon hemoperfusion and hemodiafiltration can significantly reduce plasma 5-HTP concentrations after acute intoxication and may serve to decrease morbidity and mortality in patients with severe intoxication.

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.

Assessment of Platelet and Plasma Serotonin in Canine Pulmonary Hypertension Secondary to Degenerative Mitral Valve Disease

Background: Pulmonary hypertension (PH) is a common complication of degenerative mitral valve disease (DMVD), the most common cardiovascular disease in dogs. Serotonin has been suspected to play a role in the pathogenesis of PH, so this study aimed to investigate the differences in platelet and plasma serotonin between normal, DMVD and DMVD with PH (DMVD+PH) dogs. Materials and Methods: Sixty-two small-breed dogs were enrolled to the study and divided into the normal (n = 22), DMVD (n = 20), and DMVD+PH (n = 20) groups. The platelet and plasma serotonin concentrations were measured by the competitive ELISA. Results: The Kruskal-Wallis revealed the difference among the four groups of normal (179.73 [102.37-352.24] ng/10⁹ platelets), DMVD (325.99 [96.84-407.66] ng/10⁹ platelets), DMVD with intermediate probability of PH (291.11 [106.69-400.84] ng/10⁹ platelets) and DMVD with high probability of PH (35.82 [2.69-126.35] ng/10⁹ platelets) (p = 0.014). The Dunn's post-hoc test showed a decrease in the platelet serotonin concentration of the DMVD dogs with high probability of PH compared to the DMVD group (p = 0.008). The plasma serotonin concentration was not different between normal, DMVD, and DMVD+PH dogs. Conclusion: In conclusion, a decrease in platelet serotonin concentration, which is associated with a degree of PH probability was found in DMVD dogs with PH. Further studies investigating roles of platelet serotonin in PH secondary to DMVD should be performed.

Genetics of canine myxomatous mitral valve disease

Myxomatous mitral valve disease (MMVD) is the most common heart disease and cause of cardiac death in domestic dogs. MMVD is characterised by slow progressive myxomatous degeneration from the tips of the mitral valves onwards with subsequent mitral valve regurgitation, and left atrial and ventricular dilatation. Although the disease usually has a long asymptomatic period, in dogs with severe disease, mortality is typically secondary to left-sided congestive heart failure. Although it is not uncommon for dogs to survive long enough in the asymptomatic period to die from unrelated causes; a proportion of dogs rapidly advance into congestive heart failure. Heightened prevalence in certain breeds, such as the Cavalier King Charles Spaniel, has indicated that MMVD is under a genetic influence. The genetic characterisation of the factors that underlie the difference in progression of disease is of strong interest to those concerned with dog longevity and welfare. Advanced genomic technologies have the potential to provide information that may impact treatment, prevalence, or severity of MMVD through the elucidation of pathogenic mechanisms and the detection of predisposing genetic loci of major effect. Here we describe briefly the clinical nature of the disorder and consider the physiological mechanisms that might impact its occurrence in the domestic dog. Using results from comparative genomics we suggest possible genetic approaches for identifying genetic risk factors within breeds. The Cavalier King Charles Spaniel breed represents a robust resource for uncovering the genetic basis of MMVD.

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.

Serotonin and Tryptophan Serum Concentrations in Shelter Dogs Showing Different Behavioural Responses to a Potentially Stressful Procedure

In mammals, serotonin (5-HT) levels depend on the availability of tryptophan (TRP). Low 5-HT concentrations have been linked to behavioural disorders in dogs. This study aimed at investigating possible differences in dogs’ serum TRP and 5-HT concentrations according to their behavioural response to a potentially stressful procedure. Thirty-nine physically healthy shelter dogs, 15 females and 24 males, mean age = 5.6 years, were categorized by a certified veterinary behaviourist according to their behavioural response to medical examination and blood collection, in: relaxation, stress signals, tension without growling, tension with growling, escape attempts, and aggression attempts. Extraction and quantification of 5-HT and TRP were performed using a HLPC method. Data were statistically analysed, applying Chi-square and Spearman tests. Results showed no significant difference in TRP (χ² = 2.084, p = 0.555) nor 5-HT (χ² = 0.972, p = 0.808) serum concentrations among different categories of dogs; however, some categories were underrepresented (relaxation = 20.5%, stress signals = 30.8%, tension without growling = 43.6%, tension with growling = 5.1%, escape attempts = 0%, aggression attempts = 0%). No correlation between serum TRP and 5-HT concentrations was found (ρ = 0.086, p = 0.602). Serum 5-HT levels do not seem to be associated with dogs’ behavioural response to a stressful situation nor with serum TRP concentrations. The relationship between serum TRP and 5-HT concentrations and behaviour needs further research.

Intermittent mitral regurgitation in Cavalier King Charles spaniels: Short-term progression and influence of stress tests

In young Cavalier King Charles spaniels (CKCS), intermittent mitral regurgitation (iMR; defined as moderate to severe mitral regurgitation [MR] in a small proportion of heartbeats), has been associated with an increased risk of cardiac death due to myxomatous mitral valve disease (MMVD). It is associated with increased R-R interval variability. Little is known about response to physiological factors and whether iMR is a precursor for developing significant MR. The aim of this study was to determine the effect of stress testing on the presence of iMR and heart rate, and short-term (1-2 year) progression of MR in CKCS with and without iMR. In total, 52 CKCS were included. Substudy 1 enrolled six dogs with iMR and 11 dogs without iMR. Substudy 2 enrolled 14 dogs with iMR and 28 dogs without iMR. Substudy 1 prospectively assessed the influence of stress testing on the presence of iMR and heart rate. Substudy 2 retrospectively evaluated short-term progression of iMR. During stress testing, iMR disappeared in 50% of CKCS and no iMR was recorded at mean heart rates >150 beats/min. Heart rate response did not differ between CKCS with or without iMR. CKCS with iMR did not have a higher odds (odds ratio = 5.2; 95% confidence interval, 0.7-38.2) of MR progression compared to controls (P = 0.1). In conclusion, physical stress influenced the occurrence of iMR in CKCS, but heart rate response was not different from CKCS without iMR. Intermittent mitral regurgitation did not significantly predict short-term MR progression. In stressed CKCS with early disease, iMR may be overlooked.

Comparative pathology of human and canine myxomatous mitral valve degeneration: 5HT and TGF-β mechanisms

Myxomatous mitral valve degeneration (MMVD) is a leading cause of valve repair or replacement secondary to the production of mitral regurgitation, cardiac enlargement, systolic dysfunction, and heart failure. The pathophysiology of myxomatous mitral valve degeneration is complex and incompletely understood, but key features include activation and transformation of mitral valve (MV) valvular interstitial cells (VICs) into an active phenotype leading to remodeling of the extracellular matrix and compromise of the structural components of the mitral valve leaflets. Uncovering the mechanisms behind these events offers the potential for therapies to prevent, delay, or reverse myxomatous mitral valve degeneration. One such mechanism involves the neurotransmitter serotonin (5HT), which has been linked to development of valvulopathy in a variety of settings, including valvulopathy induced by serotonergic drugs, Serotonin-producing carcinoid tumors, and development of valvulopathy in laboratory animals exposed to high levels of serotonin. Similar to humans, the domestic dog also experiences naturally occurring myxomatous mitral valve degeneration, and in some breeds of dogs, the lifetime prevalence of myxomatous mitral valve degeneration reaches 100%. In dogs, myxomatous mitral valve degeneration has been associated with high serum serotonin, increased expression of serotonin-receptors, autocrine production of serotonin within the mitral valve leaflets, and downregulation of serotonin clearance mechanisms. One pathway closely associated with serotonin involves transforming growth factor beta (TGF-β) and the two pathways share a common ability to activate mitral valve valvular interstitial cells in both humans and dogs. Understanding the role of serotonin and transforming growth factor beta in myxomatous mitral valve degeneration gives rise to potential therapies, such as 5HT receptor (5HT-R) antagonists. The main purposes of this review are to highlight the commonalities between myxomatous mitral valve degeneration in humans and dogs, with specific regards to serotonin and transforming growth factor beta, and to champion the dog as a relevant and particularly valuable model of human disease that can accelerate development of novel therapies.

Urine 5-hydroxyindoleacetic acid in Cavalier King Charles spaniels with preclinical myxomatous mitral valve disease

Higher concentrations of circulating serotonin have been reported in Cavalier King Charles spaniels (CKCS) compared to other dog breeds. The CKCS is also a breed highly predisposed to myxomatous mitral valve disease (MMVD). The aim of this study was to determine urine concentrations of 5-hydroxyindoleacetic acid (5-HIAA), the major metabolite and excretion product of serotonin, in a population of CKCS with preclinical MMVD, and to evaluate whether urine 5-HIAA concentrations were associated with MMVD severity, dog characteristics, setting for urine sampling, platelet count, and serotonin concentration in serum and platelet-poor plasma (PPP). The study population consisted of 40 privately-owned CKCS (23 females; 17 males) with and without preclinical MMVD as follows: American College of Veterinary Internal Medicine (ACVIM) group A (n = 11), ACVIM group B1 (n = 21) and ACVIM group B2 (n = 8). Urine 5-HIAA concentrations were not significantly associated with preclinical MMVD disease, platelet count or circulating concentrations of serotonin (in serum and PPP; P > 0.05). Females had higher 5-HIAA concentrations than males in morning urine collected at home (females, 3.1 [2.9-3.7] μmol/mmol creatinine [median and quartiles]; males, 1.7 [1.2-2.2] μmol/mmol creatinine; P = 0.0002) and urine collected at the clinic (females, 3.5 [3.1-3.9] μmol/mmol creatinine; males, 1.6 [1.3-2.1] μmol/mmol creatinine; P < 0.0001). Five-HIAA concentrations in urine collected at home and at the clinic were significantly associated (P = 0.0004; r = 0.73), and higher concentrations were found in urine collected at the clinic (P = 0.013). Urine 5-HIAA concentration was influenced by sex and setting of urine sampling. Urine 5-HIAA concentration was not associated with MMVD severity or circulating concentrations of serotonin in CKCS with preclinical disease.

Label-Free Optical Detection of Multiple Biomarkers in Sweat, Plasma, Urine, and Saliva

We report a novel label-free quantitative detection of human performance "stress" biomarkers in different body fluids based on optical absorbance of the biomarkers in the ultraviolet (UV) region. Stress biomarker (hormones and neurotransmitters) concentrations in bodily fluids (blood, sweat, urine, saliva) predict the physical and mental state of the individual. The stress biomarkers primarily focused on in this manuscript are cortisol, serotonin, dopamine, norepinephrine, and neuropeptide Y. UV spectroscopy of stress biomarkers performed in the 190-400 nm range has revealed primary and secondary absorption peaks at near-UV wavelengths depending on their molecular structure. UV characterization of individual and multiple biomarkers is reported in various biofluids. A microfluidic/optoelectronic platform for biomarker detection is reported, with a prime focus toward cortisol evaluation. The current limit of detection of cortisol in sweat is ∼200 ng/mL (∼0.5 μM), which is in the normal (healthy) range. Plasma samples containing both serotonin and cortisol resulted in readily detectable absorption peaks at 203 (serotonin) and 247 (cortisol) nm, confirming feasibility of simultaneous detection of multiple biomarkers in biofluid samples. UV spectroscopy performed on various stress biomarkers shows a similar increasing absorption trend with concentration. The detection mechanism is label free, applicable to a variety of biomarker types, and able to detect multiple biomarkers simultaneously in various biofluids. A microfluidic flow cell has been fabricated on a polymer substrate to enable point-of-use/care UV measurement of target biomarkers. The overall sensor combines sample dispensing and fluid transport to the detection location with optical absorption measurements with a UV light emitting diode (LED) and photodiode. The biomarker concentration is indicated as a function of photocurrent generated at the target wavelength.

A pilot study investigating circulating trimethylamine N-oxide and its precursors in dogs with degenerative mitral valve disease with or without congestive heart failure

BACKGROUND

Pathophysiologic mechanisms for the development and progression of degenerative mitral valve disease (DMVD) remain elusive. Increased concentrations of circulating trimethylamine N-oxide (TMAO) and its precursors choline and l-carnitine are associated with the presence and severity of heart disease in people.

OBJECTIVES

To determine if differences exist in plasma concentrations of TMAO, choline, or l-carnitine among dogs with DMVD and congestive heart failure (CHF), dogs with asymptomatic DMVD, and healthy control dogs.

ANIMALS

Thirty client-owned dogs: 10 dogs with CHF secondary to DMVD, 10 dogs with asymptomatic DMVD, and 10 healthy control dogs.

METHODS

A pilot cross-sectional study in which echocardiography was performed and fasting plasma concentrations of TMAO, choline, and l-carnitine (total and fractions) were measured.

RESULTS

TMAO (P = .03), total l-carnitine (P = .03), carnitine esters (P = .05), and carnitine esters to free carnitine ratio (E/F ratio; P = .05) were significantly higher in dogs with CHF compared to those with asymptomatic DMVD. TMAO (P = .02), choline (P = .01), total l-carnitine (P = .01), carnitine esters (P = .02), free carnitine (P = .02), and E/F ratio (P = .009) were significantly higher in dogs with CHF compared to healthy controls.

CONCLUSIONS AND CLINICAL IMPORTANCE

Dogs with CHF secondary to DMVD had higher concentrations of TMAO compared to both asymptomatic DMVD dogs and healthy controls. Larger prospective studies are warranted to determine if TMAO plays a role in the development or progression of DMVD or CHF.

Analytical validation of platelet microparticle quantification in cats

BACKGROUND

Cardiogenic embolism (CE) in cats is a devastating condition primarily associated with hypertrophic cardiomyopathy (HCM). Hypercoagulability may pose a risk for thrombus formation; however, no single test can predict CE development. Platelet microparticles (PMPs) released from platelet membranes are associated with thrombosis in humans.

OBJECTIVES

The aims were to validate flow cytometric PMP quantification in cats analytically and, in a pilot study, evaluate the procoagulant annexin V (AnV) positive PMP concentration in healthy cats and cats with asymptomatic HCM.

METHODS

With CD61 as a platelet marker, CD61⁺ AnV⁺ PMPs (0.3-1.0 μm) were quantified in citrated whole blood (WB) and platelet-poor plasma (PPP) using flow cytometry. Analyses were performed in 6 healthy cats and 5 cats with asymptomatic HCM. The coefficient of variation (CV) for duplicate (intra-assay) and parallel (inter-assay) analyses were calculated.

RESULTS

PMP concentrations were quantified with acceptable intra-assay CV for WB (CD61⁺ /AnV^- ; 2.4%, 0.2%-8.4% (median, range), CD61⁺ /AnV⁺ ; 3.8%, 0.1%-12.5%) and PPP (CD61⁺ /AnV^- ; 5.0%, 0.7%-12.8%, CD61⁺ /AnV⁺ ; 7.4%, 0.5%-15.3%), and acceptable inter-assay CV for WB in 10/11 cats (CD61⁺ /AnV^- ; 6.2%, 1.4%-13.3%, CD61⁺ /AnV⁺ ; 6.4%, 0.7%-17.2%), but unacceptable for PPP (CD61⁺ /AnV^- ; 15.6%, 5.8%-42.7%, CD61⁺ /AnV⁺ ; 27.8%, 8.4%-77.1%). For WB PMP concentrations, the pilot data demonstrated no differences between healthy cats and cats with asymptomatic HCM (4/5 with left ventricular outflow obstruction) for either the CD61⁺ /AnV^- or the CD61⁺ /AnV⁺ PMPs.

CONCLUSIONS

Only WB PMP concentrations could be quantified reliably in cats in a clinical setting. PMP concentrations did not differ between healthy and asymptomatic HCM cats in this pilot study.

Interbreed variation in serum serotonin (5-hydroxytryptamine) concentration in healthy dogs

INTRODUCTION

Serotonin (5-hydroxytryptamine [5-HT]) has several biological functions. In different species, excessive 5-HT has been linked to valvular lesions, similar to those seen in dogs with myxomatous mitral valve disease. Previous studies suggest higher 5-HT in healthy Cavalier King Charles Spaniels (CKCSs), a breed highly affected by myxomatous mitral valve disease, compared to other breeds.

OBJECTIVE

To investigate potential interbreed variation in serum 5-HT in healthy dogs.

ANIMALS

483 healthy dogs of nine breeds aged 1-7 years.

METHODS

Dogs were examined at five European centers. Absence of cardiovascular, organ-related, or systemic diseases was ensured by thorough clinical investigations including echocardiography. Serum was frozen and later analyzed by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Median 5-HT concentration was 252.5 (interquartile range = 145.5-390.6) ng/mL. Overall breed difference was found (p<0.0001), and 42% of pairwise breed comparisons were significant. Univariate regression analysis showed association between serum 5-HT concentration and breed, center of examination, storage time, and sex, with higher 5-HT in females. In multiple regression analysis, the final model had an adjusted R² of 0.27 with breed (p<0.0001), center (p<0.0001), and storage time (p=0.014) remaining significant. Within centers, overall breed differences were found at 3/5 centers (p≤0.028), and pairwise comparisons within those centers showed breed differences in 42% of comparisons. Among the included breeds, Newfoundlands, Belgian Shepherds and CKCSs had highest 5-HT concentrations.

CONCLUSIONS

Interbreed variation in serum 5-HT concentration was found in healthy dogs aged 1-7 years. These differences should be taken into account when designing clinical studies.