Giant platelet disorder in the Cavalier King Charles Spaniel

A circle of life: platelet and megakaryocyte cytoskeleton dynamics in health and disease

Platelets are blood cells derived from megakaryocytes that play a central role in regulating haemostasis and vascular integrity. The microtubule cytoskeleton of megakaryocytes undergoes a critical dynamic reorganization during cycles of endomitosis and platelet biogenesis. Quiescent platelets have a discoid shape maintained by a marginal band composed of microtubule bundles, which undergoes remarkable remodelling during platelet activation, driving shape change and platelet function. Disrupting or enhancing this process can cause platelet dysfunction such as bleeding disorders or thrombosis. However, little is known about the molecular mechanisms underlying the reorganization of the cytoskeleton in the platelet lineage. Recent studies indicate that the emergence of a unique platelet tubulin code and specific pathogenic tubulin mutations cause platelet defects and bleeding disorders. Frequently, these mutations exhibit dominant negative effects, offering valuable insights into both platelet disease mechanisms and the functioning of tubulins. This review will highlight our current understanding of the role of the microtubule cytoskeleton in the life and death of platelets, along with its relevance to platelet disorders.

The use of a "horizontal centrifugation protocol" to prepare autologous platelet-rich fibrin membranes for corneal reconstruction surgery in dogs with complicated corneal ulcerations: A case series

OBJECTIVE

The purpose of this case series was to describe the effect of autologous PRF membrane for corneal reconstruction surgery in dogs. PRF membranes made from two healthy dogs unrelated to the current case series were used for PRF histologic analyses.

ANIMALS

Seven dogs with complicated corneal ulcerations.

PROCEDURE

A complete ophthalmic examination, hematology, and fibrinogen analysis were performed pre-surgery. A PRF clot was made from autologous blood in a serum tube after centrifugation in a horizontal Bio-PRF® Centrifuge at 700 × g for 8 min. The PRF clot was processed in a PRF-Box® into a PRF membrane. The PRF membrane was sutured to the corneal ulcer bed. Each dog had a follow-up at days 5-7, 12-14, and 30-40 post-surgery. A final long-term follow-up was performed as well.

RESULTS

A positive outcome with healing and a "good" quality PRF membrane was seen in six out of seven dogs. One dog had a fibrinogen level below normal range and the PRF membrane was of "poor" quality. This dog developed a descemetocele 13 days post-surgery and needed rescue surgery. Mean healing time for all dogs was 9 ± 5.5 days. Minimal scarring, corneal pigmentation, and vascularization were observed at the final long-term follow-up 288 ± 44 days post-surgery.

CONCLUSION

PRF membrane was successful as graft material for corneal ulceration reconstruction surgery. Low fibrinogen appeared to have negative effect on the quality of the PRF membrane, showing the importance for the surgeon to evaluate the quality of the PRF membrane prior to surgery.

Whole blood platelet impedance aggregometry with the ROTEM platelet device: comparison of 2 anticoagulants and storage times for the establishment of canine reference intervals

The ROTEM platelet device, a point-of-care whole blood platelet impedance aggregometer, is an add-on to the rotational thromboelastometry ROTEM delta device. The latter has been validated in dogs. We examined whether canine whole blood is suited for analysis with the ROTEM platelet device using adenosine-5'-diphosphate (ADP) and arachidonic acid (ARA) as agonists for platelet activation, and if there are significant differences between sample storage times and anticoagulants used. Subsequently, we determined canine reference intervals (RIs) for the ROTEM platelet device for ADP and ARA. In a pilot study, we examined whole blood from 7 dogs after 15-min and 60-min storage of lithium-heparinized samples and 40-min and 80-min storage of hirudinized samples. Statistical analysis showed no significant differences between ROTEM platelet device results for both ADP and ARA in lithium-heparin and hirudin anticoagulated canine whole blood. Lithium-heparinized blood samples analyzed after 15-min storage had the lowest coefficient of variation. RIs were determined for heparinized whole blood samples from 49 dogs after 15 min of storage.

Comparative transcriptomic profiling of myxomatous mitral valve disease in the cavalier King Charles spaniel

BACKGROUND

Almost all elderly dogs develop myxomatous mitral valve disease by the end of their life, but the cavalier King Charles spaniel (CKCS) has a heightened susceptibility, frequently resulting in death at a young age and suggesting that there is a genetic component to the condition in this breed. Transcriptional profiling can reveal the impact of genetic variation through differences in gene expression levels. The aim of this study was to determine whether expression patterns were different in mitral valves showing myxomatous degeneration from CKCS dogs compared to valves from non-CKCS dogs.

RESULTS

Gene expression patterns in three groups of canine valves resulted in distinct separation of normal valves, diseased valves from CKCS and diseased valves from other breeds; the latter were more similar to the normal valves than were the valves from CKCS. Gene expression patterns in diseased valves from CKCS dogs were quite different from those in the valves from other dogs, both affected and normal. Patterns in all diseased valves (from CKCS and other breeds) were also somewhat different from normal non-diseased samples. Analysis of differentially expressed genes showed enrichment in GO terms relating to cardiac development and function and to calcium signalling canonical pathway in the genes down-regulated in the diseased valves from CKCS, compared to normal valves and to diseased valves from other breeds. F2 (prothrombin) (CKCS diseased valves compared to normal) and MEF2C pathway activation (CKCS diseased valves compared to non-CKCS diseased valves) had the strongest association with the gene changes. A large number of genes that were differentially expressed in the CKCS diseased valves compared with normal valves and diseased valves from other breeds were associated with cardiomyocytes including CASQ2, TNNI3 and RYR2.

CONCLUSION

Transcriptomic profiling identified gene expression changes in CKCS diseased valves that were not present in age and disease severity-matched non-CKCS valves. These genes are associated with cardiomyocytes, coagulation and extra-cellular matrix remodelling. Identification of genes that vary in the CKCS will allow exploration of genetic variation to understand the aetiology of the disease in this breed, and ultimately development of breeding strategies to eliminate this disease from the breed.

Platelet Function and Therapeutic Applications in Dogs: Current Status and Future Prospects

Significant progress has been made in the functional characterization of canine platelets in the last two decades. The role of canine platelets in hemostasis includes their adhesion to the subendothelium, activation, and aggregation, leading to primary clot formation at the site of injury. Studies on canine platelet function and advancements in laboratory testing have improved the diagnosis and understanding of platelet-related disorders as well as the knowledge of the mechanisms behind these diseases. This review focuses on the most recent discoveries in canine platelet structure, function, and disorders; and discusses the efficacy of various tests in the diagnosis of platelet-related disorders. With the relatively recent discovery of angiogenetic and reparative effects of growth factors found in platelets, this review also summarizes the use of canine platelet-rich plasma (PRP) alone or in association with stem cells in regenerative therapy. The characterization of proteomic and lipidomic profiles and development of platelet gene therapy in veterinary species are areas of future study with potential for major therapeutic benefits.

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.

Hemostatic function in Cavalier King Charles Spaniels assessed using thromboelastography

BACKGROUND

Macrothrombocytopenia is a well-known anomaly in Cavalier King Charles Spaniels (CKCSs), a breed also highly predisposed to develop myxomatous mitral valve disease (MMVD). Thromboelastography (TEG) has been shown to be a valuable instrument for whole blood hemostatic evaluation in dogs and correlates well with different physiologic and pathologic situations.

OBJECTIVES

We aimed to assess the influence of macrothrombocytopenia and the severity of MMVD on hemostatic function as measured by TEG.

METHODS

Associations between TEG variables (R, K, α, MA, and G) and dog characteristics, heart rates, systolic blood pressures, MMVD severities (healthy, mild or moderate, and severe), echocardiographic variables, platelet variables (platelet count, mean platelet volume [MPV], and plateletcrit), and hematocrits were evaluated in 47 prospectively recruited privately owned CKCSs. Blood samples were analyzed using a computerized thromboelastograph and an Advia 2120 hematology analyzer.

RESULTS

Univariable and multiple regression analyses showed an effect of left ventricular (LV) fractional shortening (FS%) on all TEG variables, an effect of LV FS% and age on TEG α, and an effect of LV FS% and MPV on TEG MA and TEG G. TEG MA and G increased with increasing MPV, but the associations were generally weak. No significant differences were detected in the TEG variables between the MMVD severity groups.

CONCLUSION

Macrothrombocytopenia and increased LV FS%, of which the latter commonly increases in various positive inotropic states, were both associated with a more hypercoagulable hemostatic system, according to the TEG results, in the present study.

Serum proteomic profiles in CKCS with Mitral valve disease

Background

Myxomatous mitral valve disease (MVD) is the most common acquired heart disease in dogs, and the Cavalier King Charles Spaniel (CKCS) is the most studied breed because of the high prevalence, early onset and hereditary component evidenced in the breed. MVD has different severity levels, and there are many practical limitations in identifying its asymptomatic stages. Proteomic techniques are valuable for studying the proteins and peptides involved in cardiovascular diseases, including the period prior to the clinical onset of the disease. The aim of this study was to identify the serum proteins that were differentially expressed in healthy CKCS and those affected by MVD in mild to severe stages. Proteomics analysis was performed using two-dimensional gel electrophoresis separation and a bioinformatics analysis for the detection of differentially expressed spots. In a comparative analysis, protein spots with a p < 0.05 (ANOVA) were considered statistically significant and were excised from the gels for analysis by MALDI–TOF–MS for protein identification.

Results

Eight proteins resulted differentially expressed among the groups and significantly related to the progression of the disease.

In mild affected group versus healthy dogs complement factor H isoform 2, inhibitor of carbonic anhydrase, hemopexin, dystrobrevin beta isoform X7 and CD5 molecule-like resulted to be down-regulated, whereas fibronectin type-III domain-containing protein 3A isoform X4 was up-regulated.

In severe affected dogs versus healthy group complement factor H isoform 2, calpain-3 isoform X2, dystrobrevin beta isoform X7, CD5 molecule-like and l-2-hydroxyglutarate dehydrogenase resulted to be down-regulated.

Complement factor H isoform 2, calpain-3 isoform X2, dystrobrevin beta isoform X7, CD5 molecule-like and hydroxyglutarate dehydrogenase were found to be down-regulated in mild affected group versus healthy dogs. All of these proteins except complement factor H followed a decreasing trend according to the progression of the pathology.

Conclusion

The differential expression of serum proteins demonstrates the possibility these might be valuable for the detection and monitoring of the disease. Further longitudinal studies are required to determine whether differential protein expression occurs sufficiently early in the progression of the disease and with sufficient predictive value to allow proteomics analysis to be used as an early detection and on-line diagnostic tool.

Platelet function and activation in Cavalier King Charles Spaniels with subclinical chronic valvular heart disease

OBJECTIVE To assess platelet closure time (CT), mean platelet component (MPC) concentration, and platelet component distribution width (PCDW) in dogs with subclinical chronic valvular heart disease. ANIMALS 89 Cavalier King Charles Spaniels (CKCSs) and 39 control dogs (not CKCSs). PROCEDURES Platelet count, MPC concentration, PCDW, and Hct were measured by use of a hematology analyzer, and CT was measured by use of a platelet function analyzer. Murmur grade and echocardiographic variables (mitral valve regurgitant jet size relative to left atrial area, left atrial-to-aortic diameter ratio, and left ventricular internal dimensions) were recorded. Associations between explanatory variables (sex, age, murmur grade, echocardiographic variables, platelet count, and Hct) and outcomes (CT, MPC concentration, and PCDW) were examined by use of multivariate regression models. RESULTS A model with 5 variables best explained variation in CT (R(2), 0.74), with > 60% of the variance of CT explained by mitral valve regurgitant jet size. The model of best fit to explain variation in MPC concentration included only platelet count (R(2), 0.24). The model of best fit to explain variation in PCDW included platelet count and sex (R(2), 0.25). CONCLUSIONS AND CLINICAL RELEVANCE In this study, a significant effect of mitral valve regurgitant jet size on CT was consistent with platelet dysfunction. However, platelet activation, as assessed on the basis of the MPC concentration and PCDW, was not a feature of subclinical chronic valvular heart disease in CKCSs.

Flow cytometric assessment of activation of peripheral blood platelets in dogs with normal platelet count and asymptomatic thrombocytopenia

Platelets play a crucial role in hemostasis. Their activation has not yet been evaluated in healthy dogs with a normal and low platelet count. The aim of this study was to determine the influence of activators on platelet activation in dogs with a normal platelet count and asymptomatic thrombocytopenia. 72 clinically healthy dogs were enrolled. Patients were allocated into three groups. Group 1 consisted of 30 dogs with a normal platelet count, group 2 included 22 dogs with a platelet count between 100 and 200×109/l and group 3 consisted of 20 dogs with a platelet count lower than 100×109/l. Platelet rich-plasma (PRP) was obtained from peripheral blood samples using tripotassium ethylenediaminetetraacetic acid (K3-EDTA) as anticoagulant. Next, platelets were stimulated using phorbol-12-myristate-13-acetate or thrombin, stabilized using procaine or left unstimulated. The expression of CD51 and CD41/CD61 was evaluated. Co-expression of CD41/CD61 and Annexin V served as a marker of platelet activation. The expression of CD41/CD61 and CD51 did not differ between the 3 groups. Thrombin-stimulated platelets had a significantly higher activity in dogs with a normal platelet count than in dogs with asymptomatic thrombocytopenia. Procaine inhibited platelet activity in all groups. In conclusion, activation of platelets of healthy dogs in vitro varied depending on the platelet count and platelet activator.

Comparison of cellular changes in Cavalier King Charles spaniel and mixed breed dogs with myxomatous mitral valve disease

INTRODUCTION

The aim of this study was to determine if there are differences in cellular changes in Cavalier King Charles spaniel (CKCS) myxomatous mitral valves compared to non-CKCS dogs.

ANIMALS

Cavalier King Charles spaniels (n = 6) and age-matched mixed breed (n = 6) with severe myxomatous mitral valve disease (MMVD), and normal mixed breed (n = 4) dogs.

MATERIALS AND METHODS

Immunohistochemistry staining and qualitative and quantitative analysis of mitral valves sections, examining for the presence of CD11c and CD45, vimentin, alpha smooth muscle actin (α-SMA) and embryonic smooth muscle myosin heavy chain (Smemb), von Willebrand factor and CD31 and Ki-67.

RESULTS

Vimentin positive cell numbers were increased in the MMVD dogs and distributed throughout the valve with greatest density close to the endothelium. There were no significant differences in cell marker expression for the two diseased groups, but cell numbers were significantly increased compared to controls for α-SMA (CKCS only) and Smemb (CKCS and mixed breed: p < 0.05). Alpha smooth muscle actin+ cells were primarily located at the valve edge, with Smemb+ cells similarly located, but also present throughout the valve stroma. A small number of cells close to the valve edge co-expressed α-SMA and Smemb. Endothelial von Willebrand factor expression was identified in all valves, with evidence of disrupted endothelium in the diseased, but was also found in diseased valve stroma. There was no staining for CD11c, CD45 or CD31 in any valve. Ki-67+ cells formed linear clusters at the leaflet tip and were sparsely distributed throughout both myxomatous valve groups.

CONCLUSIONS

The cellular changes notes with advanced stage MMVD appear similar for CKCS when compared to mixed breed dogs.

Myocardial infarct associated with a partial thickness left atrial tear in a dog with mitral insufficiency

A 10-year-old male neutered cavalier King Charles Spaniel with a 1-year history of degenerative mitral valve disease presented for dyspnea and severe weakness. He was diagnosed with congestive heart failure, systolic dysfunction, presumptive myocardial infarction and a left atrial thrombus based on thoracic radiographs, electrocardiogram and echocardiographic findings. Clinical signs also suggested right foreleg embolism. The dog was euthanized due to the grave prognosis and a postmortem evaluation was performed. The postmortem examination confirmed myocardial infarction and was thought to be due to embolic showering from the thrombus attached to a partial thickness left atrial endocardial tear.

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.

Serum serotonin concentration is associated with severity of myxomatous mitral valve disease in dogs

BACKGROUND

The neurotransmitter serotonin (5-hydroxytryptamine, 5-HT) has recently been suggested to play a role in the development of naturally acquired myxomatous mitral valve disease (MMVD) in dogs.

AIM

To investigate the association between serum 5-HT concentration and MMVD severity in dogs, and to assess potential associations between serum 5-HT concentrations and dog characteristics, echocardiographic variables, heart rate, systolic blood pressure, presence of macrothrombocytosis, and plateletcrit.

ANIMALS

A total of 120 client-owned dogs.

MATERIAL AND METHODS

Dogs were prospectively recruited and were classified by standard echocardiography into healthy (dogs of breeds predisposed to MMVD, but without echocardiographic evidence of the disease), mild, moderate, or severe MMVD groups. Serum 5-HT concentrations were analyzed using an ELISA.

RESULTS

Dogs with severe MMVD had lower serum 5-HT concentrations than healthy dogs (P = .0025) and dogs with mild MMVD (P = .0011). Unilinear and multiple regression analyses showed that serum 5-HT concentrations decreased with increasing left atrial to aortic root ratio (LA/Ao), were higher in Cavalier King Charles Spaniel (CKCS) dogs compared to dogs of other breeds, and were higher in female dogs than in male dogs. The LA/Ao was the variable most strongly associated with serum 5-HT concentration.

CONCLUSIONS AND CLINICAL IMPORTANCE

The finding of higher serum 5-HT concentrations in dogs of breeds predisposed to the early onset of MMVD (CKCS) and dogs with mild MMVD suggests that alterations in 5-HT signaling might play a role in progression of early stages of MMVD.

Inherited platelet disorders

OBJECTIVE

To present the latest information on inherited platelet disorders in domestic animals.

DATA SOURCES

Research articles and reviews spanning 40 years available on PubMed.

HUMAN DATA SYNTHESIS

Information regarding inherited platelet disorders in people is plentiful and often descriptions of human conditions have led to the identification of similar disorders in veterinary species. There are exceptions, however, in which specific inherited platelet disorders were first described in animals with subsequent identification in people.

VETERINARY DATA SYNTHESIS

Many inherited platelet disorders have been documented in animals at the functional and molecular level and that information is presented in this review.

CONCLUSIONS

Much progress has been made in the past 20 years in the characterization of inherited platelet disorders in animals at the functional, biochemical, and molecular level. The study of inherited platelet disorders has greatly enhanced the understanding of platelet physiology and has led in some instances to the development of platelet inhibitory medications. Characterization of inherited disorders at the molecular level greatly facilitates diagnosis and identification of affected and heterozygous animals thus avoiding propagation of the defect by breeders. When used with available functional and biochemical diagnostic tests, it significantly enhances the quality of care and case management.

Asymptomatic Macrothrombocytopenia in a Young Pure-Bred Beagle Dog

During baseline evaluation prior to a preclinical safety study, a 10-month-old male pure-bred Beagle dog was found to have marked thrombocytopenia (6 × 103 platelets [PLT]/µL) associated with a mean platelet volume (MPV) of 17.9 fL. Tests for Rickettsia rickettsii, Ehrlichia canis, and Borrelia burgdorferi were negative. Buccal bleeding time was normal. Over 3 months, PLT were 4 to 141 × 103 PLT/µL, and MPV was 11.4 to 25.1 fL; however, PLT were <50 × 103 PLT/µL and MPV was >16 fL during most of this period. Antinuclear antibody (ANA) and anti-PLT antibody tests were negative. Genotyping for the presence of a beta 1-tubulin mutation demonstrated the normal wild-type gene. Treatment with prednisone resulted in normal values after only 3 days. Ultrastructure of enlarged PLT was consistent with that of immature PLT, characterized by reduced numbers of peripheral microtubules and the presence of rough endoplasmic reticulum, free ribosomes, Golgi apparatus, and a prominent canalicular system. PLT ultrastructure and glucocorticoid responsiveness supported a diagnosis of immune-mediated thrombocytopenia that was masked by the cyclic nature of PLT decreases and lack of clinical signs. Inclusion of such a dog in a preclinical safety study could result in misinterpretation of clinical pathology findings.

Chronic heart failure due to severe endocardiosis in a Gambian giant pouched rat (Cricetomys gambianus)

A 1.5-yr-old captive male Gambian giant pouched rat (Cricetomys gambianus) died after suffering from anorexia, weakness, and dyspnea for 3 wk. Thoracic radiographs of thorax and abdomen and computed tomography showed a severe biventricular enlargement of the heart and a moderate hepatomegaly. Necropsy revealed a severe, bilateral hypertrophic cardiomyopathy and dilation of the right ventricle due to multifocal bilateral, valvular endocardiosis of all atrioventricular valves and acute hepatic congestion. Histologically, the atrioventricular valves were multifocally thickened by a marked endocardiosis with stromal accumulation of Periodic acid-Schiff (PAS)-positive, mucinous material. Although common in dogs, endocardiosis has not been described in Nesomyidaes. As in other affected species, the pathogenesis of endocardiosis in this species remains unclear.

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.

Effect of Anticoagulant and Storage Conditions on Platelet Size and Clumping in Healthy Dogs

The potential impact of preanalytical factors, such as type of anticoagulant, storage temperature, and time, on the formation of macroplatelets and platelet aggregates (platelet clumping) in dogs is largely elusive. The objective of the current study was to assess the effect of anticoagulant, temperature, and blood storage time in the light microscopy-generated macroplatelet percentages and the frequency of visually inspected platelet aggregates in clinically healthy dogs. Giemsa-stained blood smears from 70 healthy dogs were reviewed after exposure to different anticoagulants (ethylenediamine tetra-acetic acid [EDTA] vs. citrate), temperatures (25°C vs. 4°C), and storage times (up to 24 hr postsampling). The mean percentage of macroplatelets (platelets with diameter or length ≥ μm) was higher ( P = 0.0006) when EDTA was used as the anticoagulant. For either anticoagulant, the mean percentage of macroplatelets was higher ( P < 0.0001) at 25°C than at 4°C. Platelet clumping was 1.9 times ( P < 0.0001) more likely to occur when citrate- rather than EDTA-anticoagulated blood was examined; regardless of the anticoagulant used, clumping occurred 3 times ( P < 0.0001) more often when samples were preserved at 4°C than when they were preserved at 25°C. Storage time did not significantly influence the macroplatelet percentages or the frequency of platelet clumping. The results of this study indicate that macroplatelet percentages in the canine blood should be interpreted in relation to anticoagulant- and temperature-specific reference intervals and that future studies are warranted in order to investigate the clinical relevance of this calculation. In addition, the significant association of citrate with the formation of platelet aggregates may preclude its use for platelet enumeration in the dog.

Mutation of the beta1-tubulin gene associated with congenital macrothrombocytopenia affecting microtubule assembly

Congenital macrothrombocytopenia is a genetically heterogeneous group of rare disorders. We identified the first TUBB1 mutation, R318W, in a patient with congenital macrothrombocytopenia. The patient was heterozygous for Q43P, but this single-nucleotide polymorphism (SNP) did not relate to macrothrombocytopenia. Although no abnormal platelet beta1-tubulin localization/marginal band organization was observed, the level of beta1-tubulin was decreased by approximately 50% compared with healthy controls. Large and irregular bleb protrusions observed in megakaryocytes derived from the patient's peripheral blood CD34(+) cells suggested impaired megakaryocyte fragmentation and release of large platelets. In vitro transfection experiments in Chinese hamster ovary (CHO) cells demonstrated no incorporation of mutant beta1-tubulin into microtubules, but the formation of punctuated insoluble aggregates. These results suggested that mutant protein is prone to aggregation but is unstable within megakaryocytes/platelets. Alternatively, mutant beta1-tubulin may not be transported from the megakaryocytes into platelets. W318 beta1-tubulin may interfere with normal platelet production, resulting in macrothrombocytopenia.

Platelet function in dogs: breed differences and effect of acetylsalicylic acid administration

BACKGROUND

Clinical studies investigating platelet function in dogs have had conflicting results that may be caused by normal physiologic variation in platelet response to agonists.

OBJECTIVES

The objective of this study was to investigate platelet function in clinically healthy dogs of 4 different breeds by whole-blood aggregometry and with a point-of-care platelet function analyzer (PFA-100), and to evaluate the effect of acetylsalicylic acid (ASA) administration on the results from both methods.

METHODS

Forty-five clinically healthy dogs (12 Cavalier King Charles Spaniels [CKCS], 12 Cairn Terriers, 10 Boxers, and 11 Labrador Retrievers) were included in the study. Platelet function was assessed by whole-blood aggregation with ADP (1, 5, 10, and 20 microM) as agonist and by PFA-100 using collagen and epinephrine (Col + Epi) and Col + ADP as agonists. Plasma thromboxane B(2) concentration was determined by an enzyme immunoassay. To investigate the effect of ASA, 10 dogs were dosed daily (75 or 250 mg ASA orally) for 4 consecutive days.

RESULTS

A higher platelet aggregation response was found in CKCS compared to the other breeds. Longer PFA-100 closure time (Col + Epi) was found in Cairn Terriers compared to Boxers. Plasma thromboxane B(2) concentration was not statistically different between groups. Administration of ASA prolonged the PFA-100 closure times, using Col + Epi (but not Col + ADP) as agonists. Furthermore, ASA resulted in a decrease in whole-blood platelet aggregation.

CONCLUSIONS

Platelet function is influenced by breed, depending upon the methodology applied. However, the importance of these breed differences remains to be investigated. The PFA-100 method with Col + Epi as agonists, and ADP-induced platelet aggregation appear to be sensitive to ASA in dogs.

Comparison of methods for determining platelet numbers and volume in Cavalier King Charles spaniels

OBJECTIVE

The purpose of this study was to compare platelet concentration in cavalier King Charles spaniels (CKCS) measured by different methods commonly used in veterinary hospitals and commercial laboratories.

METHODS

Blood samples obtained from 41 CKCS [corrected] were analysed by impedance cell counter, laser cell counter and microscopic estimation. Quantitative buffy coat analysis was performed only on 17 samples, selected from CKCS [corrected] that had low platelet counts detected by cell counters. Platelet counts, platelet estimations and platelet parameters using these different methods were compared.

RESULTS

The median platelet number was lower when estimated using impedance cell counter (1363x10(9)/I) with respect to laser cell counter (1723x10(9)/I), microscopic estimation (238x10(9)/I) [corrected] or quantitative buffy coat analyser (292x10(9)/I) [corrected] (P<0.01). Although impedance cell counter, laser cell counter and microscopic estimation were positively correlated, there was no acceptable agreement among methods. CKCS [corrected] with macrothrombocytes in blood smears had significantly lower counts on impedance cell counter, laser cell counter and microscopic estimation. The percentages of CKCS [corrected] with platelet count < 100x10(9)/I [corrected] were 34.1 per cent (impedance cell counter), 26.8 per cent (laser cell counter), 22.0 per cent (microscopic estimation) (not statistically different) and 5.8 per cent (quantitative buffy coat analyser) (P<0.05).

CLINICAL SIGNIFICANCE

CKCS [corrected] with macrothrombocytosis have low platelet counts on impedance cell counters, laser cell counters and microscopic estimation. CKCS [corrected] with low platelet counts may have a normal platelet crit detected by a quantitative buffy coat analyser and thus a normal circulating platelet mass.

Genomic expression patterns of mitral valve tissues from dogs with degenerative mitral valve disease

OBJECTIVE

To evaluate global genome expression patterns of mitral valve tissues from dogs with degenerative mitral valve disease (DMVD).

SAMPLE POPULATION

Anterior mitral valve leaflets of 4 dogs with severe DMVD and 4 healthy control dogs.

PROCEDURES

Transcriptional activities of 23,851 canine DNA sequences were determined by use of an oligonucleotide microarray. Genome expression patterns of tissue from dogs with DMVD were evaluated by measuring the relative amount of complementary RNA hybridization to the microarray probes and by comparing it with gene expression from healthy control dogs.

RESULTS

229 transcripts were differentially expressed (>or= 2-fold change). In dogs with DMVD, expression of 159 transcripts was upregulated and expression of 70 transcripts was downregulated. Of the 229 transcripts, 152 genes could be specifically identified. These genes were grouped into 1 of 9 categories on the basis of their primary physiologic function. Grouping revealed that pathways involving cell signaling, inflammation, extracellular matrix, immune function, cell defense, and metabolism were generally upregulated. Inflammatory cytokines and the serotonin-transforming growth factor-beta pathway were identified as contributory to the pathophysiologic aspects of DMVD.

CONCLUSIONS AND CLINICAL RELEVANCE

Evaluation of global expression patterns provides a molecular portrait of mitral valve disease, yields insight into the pathophysiologic aspects of DMVD, and identifies intriguing genes and pathways for further study.