Leukocyte emigration in the early stages of laminitis

Magnetic nanoparticle swarm with upstream motility and peritumor blood vessel crossing ability

Micro-nano-robots show great potential and value for applications in targeted drug delivery; however, very few current studies have enabled micro-nano-robots to move against blood flow, and in addition, how micro-nano-robots can penetrate endothelial cells and enter tissues via vascular permeation remains unclear. Inspired by the bionics of dynamic aggregation in wild herring schools and transvascular permeation of leukocytes, we propose a novel drug delivery strategy where thousands of magnetic nanoparticles (MNPs) can be assembled into swarms under the guidance of a specially designed electromagnetic field. The vortex-like swarms of magnetic nanoparticles exhibit excellent stability, allowing them to withstand the impact of high-speed flow and move upstream along the vessel wall, stopping at the target location. When the vortex-like swarms encounter a tumor periphery without a continuous vessel wall, their rheological properties actively adhere them to the edges of the vascular endothelial gap, using their deformability to crawl through narrow intercellular gaps, enabling large-scale targeted drug delivery. This cluster of miniature nanorobots can be reshaped and reconfigured to perform a variety of tasks according to the environmental demands of the circulatory system, providing new solutions for a variety of biomedical field applications.

A review of cellular and molecular mechanisms in endocrinopathic, sepsis-related and supporting limb equine laminitis

Equine laminitis has both fascinated and frustrated veterinary researchers and clinicians for many years. The recognition that many ponies suffering from pasture-associated laminitis have an insulin-dysregulated phenotype (endocrinopathic laminitis, EL) and that prolonged insulin and glucose infusions can experimentally induce laminar pathology and functional failure are seminal discoveries in this field. Researchers have studied the molecular basis for disease pathogenesis in models of EL, sepsis-related laminitis and supporting limb laminitis and generated much data over the last 15 years. This review attempts to synthesise those data, drawing comparisons between models and naturally occurring laminitis. A hypothesis is proposed that the basal epithelial cell stress is a central event in each category of laminitis. Furthermore, in naturally occurring pasture-associated laminitis, pathways that predominate in each type of laminitis contribute to laminar lamellar pathology to varying extents. Based on the molecular mechanisms determined in experimental models, interactions between these pathways are identified.

Plasma syndecan‐1 concentration as a biomarker for endothelial glycocalyx degradation in septic adult horses

BACKGROUND

Limited information is available regarding endothelial glycocalyx degradation during sepsis in horses. Plasma syndecan-1 concentrations are increased in consequence of sepsis in other species and have been useful for prognostication.

OBJECTIVES

To determine whether plasma syndecan-1 levels are increased in adult horses affected with sepsis.

STUDY DESIGN

Retrospective cohort study.

METHODS

Adult horses were assigned to one of three groups based on results of physical and laboratory examinations, clinical diagnosis, and results of previously described SIRS classification: Group 1 horses included healthy, nonseptic horses; Group 2 included horses in which clinical illness was identified but that were not considered to be septic; Group 3 included horses with a clinical diagnosis of sepsis. Plasma syndecan-1 concentration was determined in blood obtained at admission into the hospital for each horse, using an equine specific ELISA. Data were analysed using ANOVA and linear regression (p ≤ 0.05).

RESULTS

One hundred and ninety-one horses were included and divided into three groups. Scores for SIRS were highest for Group 3 horses and lowest in Groups 1 and 2. Plasma syndecan-1 concentrations in Group 3 horses (50.73 ± 84.24 μg/ml; n = 42) were greater than those for Group 1 (15.69 ± 11.28 μg/ml; n = 66) and Group 2 (16.88 ± 15.30 μg/ml; n = 83). There was no difference regarding syndecan concentrations between Groups 1 and 2.

MAIN LIMITATIONS

Retrospective study design, solitary time point of measurement for each patient, and lack of a widely accepted consensus regarding definitive diagnosis of sepsis in adult horses.

CONCLUSIONS

Circulating plasma levels of syndecan-1, a biochemical marker of endothelial glycocalyx damage, are increased in septic adult horses.

Presence of Myeloperoxidase in Lamellar Tissue of Horses Induced by an Euglycemic Hyperinsulinemic Clamp

Laminitis is a pathology of the equine digit leading to a failure of the dermo-epidermal interface. Neutrophil activation is recognized as a major factor in SIRS-associated laminitis. Less is known about the role of neutrophil activation in laminitis associated with metabolic disorders. The aim of this descriptive study was to observe whether myeloperoxidase is increased in the laminae during early stage laminitis in three horses subjected to a prolonged euglycemic hyperinsulinemic clamp (pEHC). After 48 h of pEHC-treatment, horses were subjected to euthanasia. Two healthy horses are used as control. Histological sections of lamellar tissue from all horses were immunohistochemically stained for myeloperoxidase and counterstained with hematoxylin-eosin. Histopathological changes that characterize insulin-induced laminitis and increased presence of myeloperoxidase, especially in the dermal lamellae, were increased in histologic sections of pEHC-treated horses. Neutrophil myeloperoxidase release may contribute to the pathophysiology of endocrinopathic laminitis.

Laminar Inflammation Responses in the Oligofructose Overload Induced Model of Bovine Laminitis

Bovine laminitis causes substantial economic losses and animal welfare problems in dairy farms worldwide. Previously published studies have reported that the inflammatory response plays a central role in the pathogenesis of the disease. To our knowledge, inflammation associated with bovine laminitis induced by high levels of exposure to oligofructose (OF) has not been reported and characterized. In fact, the disease manifestations in this model closely approximate those of clinical laminitis. The objective of this study was to characterize the inflammatory response in OF-induced bovine laminitis. A total of 12 Chinese Holstein dairy heifers were utilized in this study. The heifers were randomly divided into two groups, treatment (n = 6) and control (n = 6). The treatment group heifers were administered OF solutions via a stomach tube (dose: 17 g/kg of body weight). Upon development of a lameness score of 2 with consecutive positive reactions in the same claw, they would be humanely euthanized. Control heifers were administered deionized water (dose: 2 L/100 kg of body weight) and humanely euthanized at 72 h. Real-time quantitative PCR (qPCR) assays were performed to determine the messenger RNA (mRNA) concentrations of inflammatory mediators in the lamellae. Concentrations of interleukin (IL)-1β, IL-6, IL-8, C-X-C motif chemokine ligand-1 (CXCL-1), macrophage cationic peptide-2 (MCP-2), E-selectin, intercellular adhesion molecule-1 (ICAM-1), cyclooxygenase-2 (COX-2), inducible nitric oxide synthase-1 (iNOS-1), and plasminogen activator inhibitor-1 (PAI-1) were significantly increased (P < 0.05) in the treatment group. No significant difference was found for tumor necrosis factor alpha (TNF-α), IL-10, CXCL-6, and MCP-1. These results demonstrated and characterized the laminar inflammatory response leading to the pathogenesis of bovine laminitis at the early stages.

Endothelial cells and angiogenesis in the horse in health and disease-A review

The cardiovascular system is the first functional organ in the embryo, and its blood vessels form a widespread conductive network within the organism. Blood vessels develop de novo, by the differentiation of endothelial progenitor cells (vasculogenesis) or by angiogenesis, which is the formation of new blood vessels from existing ones. This review presents an overview of the current knowledge on physiological and pathological angiogenesis in the horse including studies on equine endothelial cells. Principal study fields in equine angiogenesis research were identified: equine endothelial progenitor cells; equine endothelial cells and angiogenesis (heterogeneity, markers and assessment); endothelial regulatory molecules in equine angiogenesis; angiogenesis research in equine reproduction (ovary, uterus, placenta and conceptus, testis); angiogenesis research in pathological conditions (tumours, ocular pathologies, equine wound healing, musculoskeletal system and laminitis). The review also includes a table that summarizes in vitro studies on equine endothelial cells, either describing the isolation procedure or using previously isolated endothelial cells. A particular challenge of the review was that results published are fragmentary and sometimes even contradictory, raising more questions than they answer. In conclusion, angiogenesis is a major factor in several diseases frequently occurring in horses, but relatively few studies focus on angiogenesis in the horse. The challenge for the future is therefore to continue exploring new therapeutic angiogenesis strategies for horses to fill in the missing pieces of the puzzle.

The Equine Hoof: Laminitis, Progenitor (Stem) Cells, and Therapy Development

The equine hoof capsule, composed of modified epidermis and dermis, is vital for protecting the third phalanx from forces of locomotion. There are descriptions of laminitis, defined as inflammation of sensitive hoof tissues but recognized as pathologic changes with or without inflammatory mediators, in the earliest records of domesticated horses. Laminitis can range from mild to serious, and signs can be acute, chronic, or transition from acute, severe inflammation to permanently abnormal tissue. Damage within the intricate dermal and epidermal connections of the primary and secondary lamellae is often associated with lifelong changes in hoof growth, repair, and conformation. Decades of research contribute to contemporary standards of care that include systemic and local therapies as well as mechanical hoof support. Despite this, consistent mechanisms to restore healthy tissue formation following a laminitic insult are lacking. Endogenous and exogenous progenitor cell contributions to healthy tissue formation is established for most tissues. There is comparably little information about equine hoof progenitor cells. Equine hoof anatomy, laminitis, and progenitor cells are covered in this review. The potential of progenitor cells to advance in vitro equine hoof tissue models and translate to clinical therapies may significantly improve prevention and treatment of a devastating condition that has afflicted equine companions throughout history.

Are There Shared Mechanisms in the Pathophysiology of Different Clinical Forms of Laminitis and What Are the Implications for Prevention and Treatment?

Laminitis is a consequence of primary disease processes elsewhere in the body. The key pathophysiologic events are insulin dysregulation in endocrinopathic laminitis, ischemia in supporting limb laminitis, and inflammation in sepsis-related laminitis. These apparently disparate mechanisms converge to cause lamellar attachment failure through epithelial cell adhesion loss and stretch, possibly mediated by common growth factor signaling pathways. Tissue damage through mechanical distraction, inflammation, pain, and a proliferative epithelial healing response are features of acute laminitis regardless of the cause. Preventive and treatment strategies based on knowledge of these unique and common mechanistic events are likely to improve clinical outcomes.

Equine neutrophils and their role in ischemia reperfusion injury and lung inflammation

Horses are susceptible to a multitude of inflammatory conditions that are characterized by a strong neutrophilic response. Here, we review basic equine neutrophil biology and explore the role of neutrophils in inflammatory conditions with emphasis on intestinal ischemia and reperfusion injury and lung inflammation. In addition, unique aspects of equine neutrophil biology have been highlighted. Neutrophils comprise the highest proportion of circulating white blood cells in equine blood. The concentration of circulating equine neutrophils is a primary indicator of systemic inflammation. Additionally, equine neutrophils exposed to various stimulants develop "toxic" changes characterized as cytoplasmic basophilia, presence of Döhle bodies, cytoplasmic vacuolation and toxic granulation. In contrast to human neutrophils, equine neutrophils fail to undergo chemotaxis in response to the peptide N-formyl-methionyl-leucyl-phenylalanine and are dependent on the addition of arachidonic acid due to reduced activity of phospholipase A₂ to synthesize leukotrienes as part of the arachidonic acid pathway. Understanding the biologic function of neutrophils in horses is integral to developing methods to modulate inflammation associated with ischemia reperfusion injury and lung disease.

Effect of Continuous Digital Hypothermia on Lamellar Inflammatory Signaling When Applied at a Clinically-Relevant Timepoint in the Oligofructose Laminitis Model

BACKGROUND

Although continuous digital hypothermia (CDH) protects lamellae from injury in the oligofructose (OF) model of sepsis-related laminitis (SRL), conflicting results exist from these studies regarding effects of CDH on lamellar inflammatory events.

HYPOTHESIS/OBJECTIVES

To determine the effect of CDH on lamellar inflammatory events in normal and OF-treated horses when instituted at a clinically relevant time point (onset of clinical signs of sepsis in this model).

ANIMALS

Standardbred geldings (n = 15) aged 3-11 years were used.

METHODS

In a randomized, controlled discovery study, animals were administered either OF (OF group, n = 8) or water (CON group, n = 8) by nasogastric tube and CDH was initiated in one forelimb (ICE) 12 hours later. Lamellar tissue samples were collected 24 hours after initiation of CDH (ICE and ambient [AMB] forelimbs). Lamellar mRNA concentrations of inflammatory mediators and lamellar leukocyte numbers were assessed using qPCR and immunohistochemistry, respectively; values from four sample groups (CON AMB, OF AMB, CON ICE, and OF ICE) were analyzed using mixed model linear regression.

RESULTS

Although lamellar mRNA concentrations of multiple inflammatory mediators (IL-1β, IL-6, CXCL1, MCP2, COX-2) were increased after OF administration (OF AMB group versus CON AMB; P < 0.05), only 2 inflammatory mediators (IL-6 and COX-2) and lamellar leukocyte numbers were decreased with CDH (OF ICE versus OF AMB; P < 0.05).

CONCLUSIONS AND CLINICAL IMPORTANCE

Continuous digital hypothermia initiated at a time point similar to that commonly used clinically (clinical onset of sepsis) resulted in a more focused inhibition of inflammatory signaling.

Paradigm shifts in understanding equine laminitis

Laminitis, one of the most debilitating conditions of all equids, is now known to be the result of several systemic disease entities. This finding, together with other recent developments in the field of laminitis research, have provoked a rethink of our clinical and research strategies for this condition. First, laminitis is now considered to be a clinical syndrome associated with systemic disease (endocrine disease, sepsis or systemic inflammatory response syndrome, SIRS) or altered weight bearing rather than being a discrete disease entity. Next, laminitis associated with endocrine disease (endocrinopathic laminitis) is now believed to be the predominant form in animals presenting (primarily) for lameness. Third, the designation of laminitis as a primary and severe basement membrane pathology now requires revision. Instead, current data now proposes a variable subclinical phase associated with gross changes in the hoof capsule, with stretching and elongation of the lamellar cells an early and key event in the pathophysiology. These findings have fuelled new mechanistic hypotheses and research directions that will be discussed, together with their implications for future clinical management.

Effect of Delayed Digital Hypothermia on Lamellar Inflammatory Signaling in the Oligofructose Laminitis Model

Background

In the oligofructose (OF) model of sepsis‐related laminitis (SRL), digital hypothermia (“cryotherapy”) initiated before the onset of clinical signs is reported not only to limit lamellar injury, but also to cause marked inhibition of lamellar inflammatory signaling.

Hypothesis/Objectives

Because hypothermia also has been reported to be protective when not initiated until the onset of lameness in the OF model of SRL, we hypothesized that the lamellar protection conferred by hypothermia is caused by local lamellar inhibition of inflammatory signaling as described when hypothermia was initiated earlier in the disease process.

Animals

Eight Standardbred geldings aged 3–11 years with no lameness and no abnormalities of the feet detectable by gross or radiographic examination.

Methods

Using the OF model of SRL, lamellar mRNA concentrations of proinflammatory cytokines, chemokines, and endothelial adhesion proteins were compared between samples from treated limbs (CRYO, submerged in ice water for 36 hour starting at the onset of lameness), untreated limbs (NON‐CRYO, opposite limb from CRYO limbs maintained at ambient temperature), and untreated limbs from normal horses in which laminitis was not induced (CON).

Results

Although OF administration resulted in increases in lamellar mRNA concentrations of several inflammatory mediators in NON‐CRYO limbs (vs CON), digital hypothermia had no significant effect on these increases.

Conclusions and Clinical Importance

The lack of inflammatory inhibition in lamellar tissue samples in our study indicates that the protective effects of digital hypothermia instituted at the onset of clinical signs of laminitis do not arise from inhibition of inflammatory pathways.

The effect of hypothermia on influx of leukocytes in the digital lamellae of horses with oligofructose-induced laminitis

Sepsis-related laminitis (SRL) is a common complication in the septic/endotoxemic critically-ill equine patient, in which lamellar injury and failure commonly lead to crippling distal displacement of the distal phalanx. Similar to organ injury in human sepsis, lamellar injury in SRL has been associated with inflammatory events, including the influx of leukocytes into the lamellar tissue and markedly increased expression of a wide array of inflammatory mediators at the onset of Obel grade 1 (OG1) laminitis. The only treatment reported both clinically and experimentally to protect the lamellae in SRL, local hypothermia ("cryotherapy"), has been demonstrated to effectively inhibit lamellar expression of multiple inflammatory mediators when initiated at the time of administration of a carbohydrate overload in experimental models of SRL. However, the effect of hypothermia on leukocyte influx into affected tissue has not been assessed. We hypothesized that cryotherapy inhibits leukocyte emigration into the digital lamellae in SRL. Immunohistochemical staining using leukocyte markers MAC387 (marker of neutrophils, activated monocytes) and CD163 (monocyte/macrophage-specific marker) was performed on archived lamellar tissue samples from an experimental model of SRL in which one forelimb was maintained at ambient temperature (AMB) and one forelimb was immersed in ice water (ICE) immediately following enteral oligofructose administration (10g/kg, n=14 horses). Lamellae were harvested at 24h post-oligofructose administration (DEV, n=7) or at the onset of OG1 laminitis (OG1, n=7). Both MAC387-positive and CD163-positive cells were counted by a single blinded investigator on images [n=10 (40× fields/digit for MAC387 and 20x fields/digit for CD163)] obtained using Aperio microscopy imaging analysis software. Data were assessed for normality and analyzed with a paired t-test and one-way ANOVA with significance set at p<0.05. MAC387-positive cells were present in low numbers in the lamellar tissue and were decreased in the hypothermic limbs (vs. AMB limbs, p<0.05) in the OG1 group; no change in CD163-positive cell numbers was noted across the conditions of the model. This study demonstrated that hypothermia of the distal limbs instituted early in the disease process in the horse at risk of SRL significantly attenuates the increase of MAC387-positive leukocytes in the digital lamellae, but has minimal effect on increases in lamellar concentrations of the major leukocyte cell type present in that tissue, CD163-positive mononuclear cells.

Distribution of technetium-99m PEG-liposomes during oligofructose-induced laminitis development in horses

Liposomes are phospholipid nanoparticles used for targeted drug delivery. This study aimed to determine whether intravenous liposomes accumulate in lamellar tissue during laminitis development in horses so as to assess their potential for targeted lamellar drug delivery. Polyethylene-glycol (PEG) coated liposomes were prepared according to the film hydration method and labelled using (99m)Tc-hexamethyl-propylene-amine-oxime. Six horses received 10 g/kg oligofructose via nasogastric tube to induce laminitis, and four control horses received water via nasogastric tube. All horses received 300 µmol (99m)Tc-PEG-liposomes (5.5 GBq) plus 5.5 µmol/kg PEG-liposomes by slow intravenous infusion. Scintigraphic imaging was performed at 0, 6 and 12 h post-infusion. Technetium-99m liposome uptake was measured in regions of interest over the hoof, fetlock and metacarpus. At the study end-point horses were euthanased, tissue samples collected and tissue liposome levels were calculated as the percentage of the injected dose of (99m)Tc-liposomes per kilogram of tissue. Data were analysed non-parametrically. All horses receiving oligofructose developed clinical and histological signs of laminitis. Technetium-99m liposome uptake in the hoof increased with time in laminitis horses (P = 0.04), but decreased with time in control horses (P = 0.01). Technetium-99m liposome levels in lamellar tissue from laminitis horses were 3.2-fold higher than controls (P = 0.02) and were also higher in laminitis vs. control skin, muscle, jejunum, colon, and kidney (P < 0.05). Liposomes accumulated in lamellar tissue during oligofructose-induced laminitis development and demonstrated potential for targeted lamellar drug delivery in acute laminitis. This study provides further evidence that lamellar inflammation occurs during laminitis development. Liposome accumulation also occurred in the skin, muscle, jejunum, colon and kidneys, suggesting systemic inflammation in this model.

Laminar inflammatory events in lean and obese ponies subjected to high carbohydrate feeding: Implications for pasture-associated laminitis

REASONS FOR PERFORMING STUDY

Acute, massive enteral carbohydrate overload is associated with laminar inflammation in equids; it is unclear if the same is true for a more prolonged period of moderate dietary carbohydrate intake.

OBJECTIVES

To characterise laminar inflammation in ponies exposed to a dietary carbohydrate challenge meant to mimic acute pasture exposure.

STUDY DESIGN

In vivo experiment.

METHODS

Mixed-breed ponies (n = 22) received a diet of hay chop (nonstructural carbohydrate [NSC] ∼7% on a dry matter [DM] basis) for 4 weeks prior to initiation of the experimental feeding protocol. Following dietary acclimation, ponies were stratified into either Lean (n = 11, body condition score [BCS] ≤4) or Obese (n = 11, BCS ≥7) groups and each group further stratified to either remain on the control, low NSC diet (n = 5 each for Obese and Lean) or receive a high NSC diet (hay chop supplemented with sweet feed and oligofructose, total diet ∼42% NSC; n = 6 each for Obese and Lean) for a period of 7 days. Laminar samples were collected following euthanasia and sections stained immunohistochemically for CD163, MAC387/calprotectin and cyclo-oxygenase-2 (COX-2) using commercially available antibodies. The number of CD163 (+) and MAC387(+) cells was quantified for each section; the distribution of COX-2 expression was qualitatively assessed. Laminar mRNA concentrations of several proinflammatory molecules (interleukin-1β [IL-1β], IL-6, tumour necrosis factor-α [TNFα], IL-8, IL-10, monocyte chemoattractant protein-1 [MCP-1], MCP-2), inducible nitric oxide synthase (iNOS), intercellular adhesion molecule-1 (ICAM-1), E-selectin, plasminogen activator inhibitor-1 (PAI-1) and COX-2 were evaluated using real-time quantitative polymerase chain reaction (qPCR).

RESULTS

High carbohydrate feeding resulted in no increase in laminar proinflammatory cytokine expression; laminar COX-2 expression was increased by high carbohydrate feeding. No laminar leucocyte infiltration was observed in response to high carbohydrate feeding.

CONCLUSIONS

These results suggest that the marked laminar inflammation observed in models of sepsis-associated laminitis may not play a central role in the pathophysiology of pasture-associated laminitis.

The effect of tumour necrosis factor-α and insulin on equine digital blood vessel function in vitro

OBJECTIVE AND DESIGN

Insulin and inflammatory cytokines may be involved in equine laminitis, which might be associated with digital vascular dysfunction. This study determined the effects of TNF-α and insulin on the endothelial-dependent relaxant responses of equine digital blood vessels and on equine digital vein endothelial cell (EDVEC) cGMP production.

MATERIAL

Isolated rings of equine digital arteries (EDAs) and veins (EDVs) were obtained and EDVECs were cultured from horses euthanized at an abattoir.

METHODS

The effect of incubation with TNF-α (10 ng/ml) and/or insulin (1,000 μIU/ml) for 1.5 h or overnight under hyperoxic and hypoxic conditions on carbachol (endothelium-dependent) induced relaxation was assessed. The time course and concentration dependency of the effect of TNF-α and the effect of insulin (1,000 μIU/ml) on EDVEC cGMP production was determined.

RESULTS

Incubation of EDAs overnight with TNF-α under hypoxic conditions resulted in endothelial-dependent vascular dysfunction. EDVs produced a more variable response. TNF-α increased EDVEC cGMP formation in a time- and concentration-dependent manner. Insulin had no significant effects.

CONCLUSIONS

There is a mismatch between the results obtained from isolated vessel rings and cultured endothelial cells suggesting TNF-α may reduce the biological effect of NO by reducing its bioavailability rather than its formation, leading to endothelial cell dysregulation.

Relação entre obesidade, insulina plasmática e posicionamento da falange distal em equinos da raça Crioula

Verificaram-se características radiográficas do posicionamento da falange distal em relação ao estojo córneo em equinos da raça Crioula e correlacionaram-se tais achados com sinais de obesidade e concentrações plasmáticas de insulina. Consideraram-se dois grupos com base no escore da condição corporal (ECC). A média de idade entre os grupos foi de 9,2±5,8 anos em indivíduos normais (ECC 5-7) e de 10,3±3,7 anos em obesos (ECC 8-9). Diferenças estatísticas entre grupos ocorreram para valores de peso, perímetro torácico, escore da condição corporal, escore da crista do pescoço, comprimento do pescoço, circunferência do pescoço em três regiões referentes a 25%, 50% e 75% do comprimento do pescoço e entre o posicionamento da falange distal em relação ao estojo córneo. O ângulo formado entre as superfícies dorsais de falange distal e casco (ângulo de rotação) correlacionou-se estatisticamente com ECC (r = 0,30; P=0,02) e com peso e perímetro torácico (r = 0,50; P<0,01). Quanto à concentração de insulina plasmática, foram encontradas correlações positivas com ECP (r = 0,40; P<0,01) e com ângulo de rotação (r = 0,23; P = 0,08), e correlação negativa com idade (r = -0,42; P<0,01). Em oito animais (27%) o ângulo de rotação foi maior que 2 graus; destes, 25% eram normais e 75%, obesos (P<0,05). Aparentemente, em equinos da raça Crioula, características morfométricas no casco diferiram dos padrões internacionais obtidos de outras raças. A obesidade interferiu na relação espacial da falange distal com o estojo córneo, indicando que os animais obesos dessa raça são mais propensos a desenvolver laminite.

Efeito de anti-inflamatórios não esteroidais na apoptose de células epidermais lamelares de equinos com laminite

O objetivo deste trabalho foi avaliar a influência da administração dos anti-inflamatórios não esteroidais (AINEs) cetoprofeno, fenilbutazona e flunixin meglumine sobre o índice apoptótico de células epiteliais do tecido lamelar de cavalos com laminite induzida por administração de amido. Foram empregados 20 equinos hígidos, divididos em quatro grupos experimentais (n=5): solução salina, cetoprofeno, fenilbutazona e flunixin meglumine. O tecido lamelar foi coletado por biópsia, fixado e corado pela técnica de TUNEL. À marcação positiva por essa técnica adicionou-se a avaliação morfológica celular para identificação da apoptose. Não houve diferença significativa no índice apoptótico entre os grupos tratados com anti-inflamatórios e o controle (P>0,05). Os anti-inflamatórios não interferiram sobre o índice apoptótico possivelmente porque foram administrados após a fase prodrômica da laminite e/ou porque não são eficazes em alterar a dinâmica da apoptose. Concluiu-se que a administração de anti-inflamatórios não esteroidais após a fase prodrômica da laminite não contribui para uma intervenção no curso da apoptose no tecido lamelar de cavalos com laminite quando comparados ao grupo controle não tratado. Outros estudos, com diferentes períodos de avaliação, são necessários para esclarecer os efeitos dos anti-inflamatórios não esteroidais na fisiopatologia da laminite em equinos, especialmente no que concerne à participação da apoptose.

Avaliação clínica e hematológica de equinos submetidos ao modelo de laminite por oligofructose, tratados ou não com um agente antagonista de receptores CXCR1/2

O recrutamento de leucócitos aos tecidos é uma parte essencial da resposta imune inata e esse processo de forma desregulada pode resultar em lesões aos tecidos. Assim, a infiltração de leucócitos tem sido implicada na patogênese de laminite aguda em equinos. Os objetivos dessa pesquisa foram verificar a ação da ICXCR1/2 sobre os sinais clínicos e parâmetros hematológicos de cavalos com laminite induzida por oligofrutose. Doze equinos receberam oligofrutose (10g/kg de peso vivo PO) no tempo 0 e foram divididos em 2 grupos: tratados (30mg/kg p.v. ICXCR1/2 IV, nos tempos 6, 12, 18 e 24 h) e não tratados. As frequências cardíaca e respiratória, temperatura retal, coloração de membranas mucosas, presença e intensidade de pulso digital, sensibilidade ao exame com pinça de casco e grau de claudicação segundo Obel, bem como parâmetros hematológicos e bioquímicos (hemograma e as concentrações sanguíneas de glicose, uréia, creatinina, ALT, AST, FA, GGT, bilirrubina total e proteína total) foram aferidos nos tempos 0, 6, 12, 18, 24, 36, 48, 60 e 72 horas . O modelo usando oligofructose foi adequado para induzir sinais de laminite e de sinais de endotoxemia, como diarreia, febre e leucocitose em cavalos sem raça definida de origem nacional. Também, não foram observadas quaisquer reações adversas clínicas ou hematológicas relacionadas ao uso intravenoso do antagonista de CXCR1/2, contudo essa substância, quando administrada na dose de 30mg/kg de peso vivo, 4 vezes ao dia, por 4 aplicações, não foi capaz de prevenir os sinais clínicos e as alterações hematológicas causadas pela administração de oligofructose nos equinos deste estudo.

Regulation of hypoxia-inducible factor-1α and related genes in equine digital lamellae and in cultured keratinocytes

REASONS FOR PERFORMING STUDY

Hypoxia-inducible factor-1α (HIF-1A) is an important protein in the regulation/induction of many genes in the cellular and tissue response to hypoxia and a central mediator in inflammatory signalling. As both hypoxia and inflammatory events are purported to occur in the lamellar epidermis in sepsis-related laminitis in the equid, HIF-1A may play a central role in this disease process.

OBJECTIVESS

To assess the regulation of HIF-1A and HIF-1A-related genes in the equine keratinocyte in vitro and in the lamellar tissue of horses with sepsis-related laminitis.

STUDY DESIGN

In vivo and in vitro experiments.

METHODS

Real-time quantitative PCR (RT-qPCR) and immunoblotting were performed to assess the mRNA and protein concentrations of HIF-1A and the mRNA concentrations of HIF-1A-related genes in cultured equine keratinocytes and in lamellar samples from black walnut extract (BWE)- and carbohydrate overload (CHO)-induced laminitis. Hypoxia-inducible factor-1α was further localised via indirect immunofluorescence in frozen lamellar tissue sections.

RESULTS

Hypoxia-inducible factor-1α appears to be regulated primarily at the post transcriptional level in the cultured equine keratinocyte, resulting in increased HIF-1A in response to hypoxia but not to lipopolysaccharide exposure. Hypoxia-inducible factor-1α is present at high concentrations in the normal equine lamina, and is increased in Obel grade 1 (OG1) stage laminitis in the CHO model of laminitis. Equine lamellar mRNA concentrations of cyclo-oxygenase-2 and inducible nitric oxide synthase, but not glucose transporter 1, are increased in the BWE and CHO models of laminitis.

CONCLUSIONS AND POTENTIAL RELEVANCE

These data indicate that the normal equine lamellae are profoundly hypoxic in comparison with other tissues. The increased mRNA concentrations of cyclo-oxygenase-2 and inducible nitric oxide synthase 2 in equine keratinocytes exposed to hypoxia and lipopolysaccharide, and in lamellar tissue from BWE and CHO models of sepsis-related laminitis, suggest that the marked lamellar inflammatory gene expression in sepsis-related laminitis may be due to an interaction of constitutively high lamellar keratinocyte HIF-1A signalling with inflammatory signalling, possibly induced by circulating inflammatory mediators.

A review of recent advances and current hypotheses on the pathogenesis of acute laminitis

With the increasing number of studies being published on the different experimental models used to induce and study acute laminitis, the pathophysiological events associated with these various models (i.e. starch overload, oligofructose overload, black walnut extract and hyperinsulinaemia) can be compared more realistically. Within this review, the mechanisms for metabolic vs. inflammatory laminitis are discussed, and the question of how pasture laminitis may fit into any of the proposed mechanisms is addressed.

Cellular and humoral immunity in chronic equine laminitis

Chronic equine laminitis causes persistent pain and lameness in affected animals and often necessitates euthanasia when pain management strategies become ineffective. Published studies as well as anecdotal reports suggest that this chronic inflammatory disease is associated with systemic alterations in immune responsiveness, perhaps involving an autoimmune component. We investigated this broad hypothesis by measuring a variety of immune indicators in healthy control horses (CON) and horses with chronic laminitis (LMN). We found that white blood cells from LMN horses produced more IFNγ than did cells from CON horses when stimulated in vitro with polyinosinic-polycytidylic acid [poly(I:C)], possibly due to an elevated number of circulating monocytes. No differences between groups were observed in plasma concentrations of IgG, IgA, IgM, IgE, or rheumatoid factor. Laminar tissue from LMN horses expressed elevated levels of keratinocyte damage-related genes as well as inflammatory cytokines and chemokines, which corresponded with a modest amount of neutrophil infiltration as shown by histological staining of fixed tissue and accumulation of neutrophil elastase protein. Taken together, our results do not support the hypothesis of an autoimmune component in chronic laminitis, although the strong induction of neutrophil chemokines and the presence of tissue neutrophils suggests that this cell type is likely involved in perpetuating the inflammation and tissue damage associated with this disease.

Extracellular ATP signaling in equine digital blood vessels

The functional distribution of ATP-activated P2 receptors is well characterized for many blood vessels, but not in the equine digital vasculature, which is a superficial vascular bed that displays thermoregulatory functions and has been implicated in ischemia-reperfusion injuries of the hoof. Isolated equine digital arteries (EDA) and veins (EDV) were submitted to isometric tension studies, whereby electric field stimulation (EFS) and concentration-response curves to exogenously applied agonists were constructed under low tone conditions. Additionally, immunofluorescent localization of P2X and P2Y receptor subtypes was performed. EFS-induced constriction was abolished by tetrodotoxin (1 μM, n=4). Endothelium denudation did not modify the EFS-induced constriction (n=3). The EFS-induced constriction in EDA was inhibited by phentolamine (67.7±1.8%, n=6; 10 μM), and by the non-selective P2 receptor antagonist suramin (46.2±1.3%, n=6; 10 μM). EFS-induced constriction in EDV was reduced by suramin (48.2±2.4%, n=6; 10 μM), the P2 receptor antagonist pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid (58.3±4.5%, n=6; 10 μM), and phentolamine (23.2±2.5%, n=6; 10 μM). Exogenous methoxamine and ATP mimicked EFS-induced constriction in EDA and EDV. Immunostaining for P2X1, P2X2 and P2X3, and, for P2X1 and P2X7 receptor subunits were observed in EDA and EDV smooth muscle and adventitia, respectively. ATP and noradrenaline are co-transmitters in sympathetic nerves supplying the equine digital vasculature, noradrenaline being the dominant agonist in EDA, and ATP in EDV. In conclusion, P2X receptors mediate vasoconstriction in EDA and EDV, although different P2X subunits are involved in these vessels. The physiological significance of this finding in relation to thermoregulatory functions and equine laminitis is discussed.

Histological and morphometric lesions in the pre-clinical, developmental phase of insulin-induced laminitis in Standardbred horses

Lamellar pathology in experimentally-induced equine laminitis associated with euglycaemic hyperinsulinaemia is substantial by the acute, clinical phase (∼48h post-induction). However, lamellar pathology of the developmental, pre-clinical phase requires evaluation. The aim of this study was to analyse lamellar lesions both qualitatively and quantitatively, 6, 12 and 24h after the commencement of hyperinsulinaemia. Histological and histomorphometrical analyses of lamellar pathology at each time-point included assessment of lamellar length and width, epidermal cell proliferation and death, basement membrane (BM) pathology and leucocyte infiltration. Archived lamellar tissue from control horses and those with acute, insulin-induced laminitis (48h) was also assessed for cellular proliferative activity by counting the number of cells showing positive nuclear immuno labelling for TPX2. Decreased secondary epidermal lamellar (SEL) width and increased histomorphological evidence of SEL epidermal basal (and supra-basal) cell death occurred early in disease progression (6h). Increased cellular proliferation in SELs, infiltration of the dermis with small numbers of leucocytes and BM damage occurred later (24 and 48h). Some lesions, such as narrowing of the SELs, were progressive over this time period (6-48h). Cellular pathology preceded leucocyte infiltration and BM pathology, indicating that the latter changes may be secondary or downstream events in hyperinsulinaemic laminitis.

Neutrophil and cytokine dysregulation in hyperinsulinemic obese horses

Equine metabolic syndrome is characterized by obesity and regional adiposity coupled with evidence of recurrent laminitis. Although inflammation has been well characterized in several experimental models of acute laminitis, the inflammatory events associated with endocrinopathic laminitis are not well documented. The aim of this study was to characterize selected markers of inflammation in horses with clinical evidence of equine metabolic syndrome (EMS). Neutrophil phagocytosis and oxidative burst, as well as endogenous and stimulated cytokine expression were evaluated. A marked increase in neutrophil reactive oxygen species production upon phagocytosis was observed in horses with EMS that was strongly correlated to the blood insulin concentration. Increased oxidative burst activity of neutrophils in hyperinsulinemic horses may predispose horses with metabolic syndrome to laminitis. In contrast, peripheral blood cells of obese hyperinsulinemic horses showed decreased endogenous proinflammatory cytokine gene expression (IL-1 and IL-6) and similar cytokine response following immune stimulation compared to that of control horses. This may suggest that, unlike in people, cytokine-mediated inflammation does not increase in direct response to obesity or insulin resistance in horses. This species-specific disparity may explain the difference in clinical outcomes observed in obese horses compared to obese people.

Immunohistochemical distribution of laminin-332 and collagen type IV in the basement membrane of normal horses and horses with induced laminitis

The basement membrane (BM) is a thin layer of extracellular matrix that regulates cell functions as well as providing support to tissues of the body. Primary components of the BM of epithelial tissues are laminin-332 (Ln-332) and collagen type IV. Equine laminitis is a disease characterized by destruction and dislocation of the hoof lamellar BM. Immunohistochemistry was used to characterize the distribution of Ln-332 and collagen type IV in the organs of normal horses and these proteins were found to be widespread. Analysis of a panel of tissue samples from horses with experimentally-induced laminitis revealed that Ln-332 and collagen type IV degradation occurs in the skin and stomach in addition to the hoof lamellae. These findings suggest that BM degradation is common to many epithelial tissues during equine laminitis and suggests a role for systemic trigger factors in this disease.

The timeline of metalloprotease events during oligofructose induced equine laminitis development

REASON FOR PERFORMING STUDY

The role of matrix metalloproteases (MMPs) and the timeline of proteolysis during laminitis development are incompletely understood.

OBJECTIVES

To determine the temporal progression of selected MMPs and protease regulators during laminitis development.

METHODS

Five clinically normal Standardbred horses received, via nasogastric intubation, an oligofructose (OF) bolus (10 g/kg bwt). Laminitis induction proceeded for 48 h followed by euthanasia. Lamellar biopsies were obtained prior to dosing and at intervals during the treatment period for analysis (12, 18, 24, 30 and 36 h and at 48 h following euthanasia). Tissue samples were analysed by real-time PCR, zymography and western blotting.

RESULTS

Activation of proMMP-2 occurs either simultaneously or at least 12 h following lamellar basement membrane (BM) damage, while no activation of proMMP-9 is seen during OF laminitis induction. Aggrecanase gene expression increased initially at 12-18 h post OF dosing, similar to BM changes. Gene expression of TIMP-2, a MMP regulator, decreases during laminitis development.

CONCLUSIONS

The MMP-2/MT1-MMP complex may not play a major role in initiating lamellar BM damage. Aggrecanase and TIMP-2 gene expression appear related to BM lamellar changes.

POTENTIAL RELEVANCE

MMPs, historically thought to cause laminitis, do not appear to play an initiating role in the lamellar lesion. Other host derived proteases and degradation of alternative lamellar matrix components need to be considered.

Laminar inflammatory gene expression in the carbohydrate overload model of equine laminitis

REASONS FOR PERFORMING STUDY

There is a need to assess the laminar inflammatory response in a laminitis model that more closely resembles clinical cases of sepsis-related laminitis than the black walnut extract (BWE) model.

OBJECTIVES

To determine if a similar pattern of laminar inflammation, characterised by proinflammatory cytokine expression, occurs in the CHO model of laminitis as has been previously reported for the BWE model.

METHODS

Sixteen horses administered 17.6 g of starch (85% corn starch/15% wood flour)/kg bwt via nasogastric (NG) tube were anaesthetised either after developing a temperature>38.9°C (DEV group, n=8) or at onset of Obel grade 1 lameness (OG1 group, n=8). Control horses (CON group, n=8) were anaesthetised 24 h after NG administration of 6 l of deionised water. Laminar tissue was collected from horses while under anaesthesia, followed by humane euthanasia. Real time-quantitative PCR was used to assess laminar mRNA concentrations of genes involved in inflammatory signalling.

RESULTS

Increased mRNA concentrations (P<0.05) for IL-1β, IL-6, IL-12p35, COX-2, E-selectin and ICAM-1 were present in laminae from horses with OG1 lameness but not at the DEV time, when compared to the CON horses. No differences between the groups were found for IL-2, IL-4, IL-10, TNF-α, IFN-γ or COX-1 at either the DEV or OG1 time points.

CONCLUSIONS

There was a notable difference in the temporal pattern of inflammatory events between the BWE and CHO models, with the majority of laminar inflammatory events appearing to occur at or near the onset of lameness in the CHO model, whereas many of these events peak earlier in the developmental stages in the BWE model. This suggests that, in addition to circulating inflammatory molecules, there may be a local phenomenon in the CHO model resulting in the simultaneous onset of multiple laminar events including endothelial activation, leucocyte emigration and proinflammatory cytokine expression.

POTENTIAL RELEVANCE

The similar (although somewhat delayed) inflammatory response in the CHO model of laminitis indicates that inflammatory signalling is a consistent entity in the pathophysiology of laminitis.

Role of oxidative tissue injury in the pathophysiology of experimentally induced equine laminitis: a comparison of 2 models

BACKGROUND

Oxidative stress reportedly plays a role in sepsis-induced organ dysfunction and failure in many species. In septic horses, laminae are targeted; evidence of laminar oxidative stress has been reported experimentally in the black walnut extract (BWE) model. Carbohydrate (CHO)-induced laminitis may be more similar to clinical sepsis-related laminitis than the BWE model in that animals with CHO-induced disease commonly develop laminar failure. The role of oxidative stress in the CHO model remains unknown.

HYPOTHESIS/OBJECTIVES

Markers of oxidative stress will be increased in laminae from horses with BWE- and CHO-induced laminitis.

ANIMALS

Banked laminar tissue from various time points from animals subjected to BWE (n = 15) and CHO (n = 20) protocols.

METHODS

Laminar 4-hydroxynonenal (4-HNE) and protein carbonyl content were evaluated by slot blot analysis. Laminar 3-nitrotyrosine (3-NT) immunohistochemistry was performed.

RESULTS

The number of laminar 3-NT (+) cells was increased at developmental and Obel grade 1 (OG1) time points in the BWE model (versus control [CON]; P= .013) and lower in OG1 tissues than CON in the CHO model (P = .04). No change in 4-HNE content was observed in the CHO model, and no increase in laminar protein carbonyl content was present in either model (P > .05).

CONCLUSIONS AND CLINICAL IMPORTANCE

These results do not support a prominent role for oxidative stress at examined time points in CHO-overload laminitis and support transient oxidative stress in the BWE model. Tissue oxidation does not appear to be a central early pathophysiologic event in CHO-associated laminitis.

Insulin resistance in equine digital vessel rings: an in vitro model to study vascular dysfunction in equine laminitis

REASONS FOR PERFORMING STUDY

One of the causes of equine laminitis is hyperinsulinaemia, which may be associated with endothelial dysfunction and insulin resistance of vessels.

HYPOTHESIS AND OBJECTIVES

Insulin resistance can be induced in palmar digital vessels by continued exposure to insulin in vitro. The objective was to evaluate this in vitro model for future studies.

METHODS

Palmar digital vessel segments were collected immediately after euthanasia from horses with normal insulin/glucose blood values. Four arterial and 4 venous rings (3 mm wide) were prepared and each ring mounted in a tissue bath, containing Tyrode's solution at 37°C, 2 g tension was applied and the rings allowed to equilibrate for 45 min. Of the 4 rings of each vessel type, one was used as a control. One each of the remaining 3 rings was used for incubation with insulin (to induce resistance), wortmannin (to block PI3-kinase) and PD-098059 (to block MAP-kinase), respectively, for 30 min. After the incubation period, the rings were contracted with phenylephrine. When the response reached a plateau, a single dose of insulin was added to the baths and the response of each ring monitored for 30 min.

RESULTS

Insulin relaxed the control rings and those treated with PD 098059 but contracted those pretreated with insulin and wortmannin. Normal relaxation responses of the rings were converted to contractions by insulin resistance. Insulin resistance was confirmed by the qualitative response of insulin-incubated and wortmannin-incubated rings.

CONCLUSIONS

This study demonstrated successful induction of insulin resistance in both arterial and venous rings. It also suggested that the MAP-kinase pathway plays a minor role in controlling vasomotor tone under normal physiological conditions.

POTENTIAL RELEVANCE

The study suggests that the induction of insulin resistance in equine palmar digital vessel rings is reliable and provides a good in vitro model for studying the vascular insulin resistance which may occur in equine laminitis.

Histopathology of insulin-induced laminitis in ponies

REASONS FOR PERFORMING STUDY

Ponies with laminitis associated with insulin resistance and hyperinsulinaemia lack systemic and/or intestinal inflammatory signs, suggesting a different pathogenesis potentially reflected in differing histopathology.

OBJECTIVES

To describe the histological appearance and quantify morphological changes in primary and secondary epidermal lamellae (PEL and SEL) of laminitis lesions from ponies with insulin-induced laminitis.

METHODS

Equine hoof lamellar tissue was obtained from 4 control ponies and 5 ponies with laminitis induced following infusion of insulin (1036 ± 55 µU/ml) while maintaining euglycaemia for 55.4 ± 5.5 h. Sections from all 4 hooves were stained and examined by a veterinary pathologist. Measurements of lamellar length (PEL and SEL) were made in mid-dorsal sections of the right forefeet by 2 blinded observers. Immunolabelling for calprotectin was performed using a monoclonal antibody.

RESULTS

No lesions were detected in normal ponies. Lesions detected in ponies with laminitis were variable in severity between ponies. Within ponies, SEL lesions were more severe along the axial region of PEL. Lesions included swelling, disorganisation and abnormal keratinisation of epidermal cells, increased mitotic activity and apoptosis. Separation of basement membranes was minimal. Immunostaining revealed inflammatory cells within the lamellar dermis. SEL were significantly elongated in laminitic hooves relative to controls, with the greatest elongation in those attached to abaxial and middle regions of PEL.

CONCLUSIONS

Laminitis induced by prolonged infusion of insulin lacked widespread basement membrane disintegration, and increases in epidermal cellular proliferation at axial aspects were marked for this acute stage of disease.

POTENTIAL RELEVANCE

Defining equine laminitis entirely in terms of separation of the basement membrane may not be appropriate for laminitis associated with hyperinsulinaemia.

Laminar leukocyte accumulation in horses with carbohydrate overload-induced laminitis

BACKGROUND

While there is evidence of laminar leukocyte infiltration in black walnut extract (BWE)-induced laminitis, there is no such evidence for carbohydrate overload (CHO) laminitis.

OBJECTIVE

To assess presence of leukocytes and signs of epidermal stress/injury in the laminar tissue from horses with CHO-induced laminitis.

ANIMALS

Twenty-four adult horses.

METHODS

Immunohistochemistry for myeloid cell markers calprotectin (CP) and monocyte-specific marker (CD163) was performed on laminar sections obtained from 2 groups of horses in the CHO model: the developmental time point (DTP) group (n = 6) and the onset of lameness (LAM) group (n = 6), and a control (CON) group (n = 8).

RESULTS

DTP was characterized by an increase in CP(+) leukocytes (7.8-fold increase versus CON, P < .001), and LAM time point was characterized by a more marked increase in laminar CP(+) (108.5-fold, P < .001) and mild increase in CD163(+) (1.9-fold, P = .007) cell counts. Increased CP epidermal signal (indicating epidermal stress or injury) occurred consistently at the LAM time point, although histological evidence of basement membrane (BM) detachment was minor, only being present in 3/6 horses.

CONCLUSIONS AND CLINICAL RELEVANCE

Maximal laminar leukocyte infiltration and epithelial stress occurred at the onset of lameness in the CHO model showing a different temporal pattern from the BWE model, where maximal leukocyte infiltration clearly precedes epithelial stress. Leukocyte infiltration before major histological changes in the CHO model indicates that leukocyte infiltration can be a cause of and not a reaction to BM degradation and structural failure.

Morphological abnormalities and apoptosis in lamellar tissue of equines after intestinal obstruction and treatment with hydrocortisone

Four experimental groups of equines were used in order to study morphological abnormalities and apoptosis in lamellar tissue. Group Cg (control) was composed of animals without any surgical procedure; group Ig (instrumented), animals that underwent enterotomy; group Tg (treated), animals that were subjected to intestinal obstruction and were treated with hydrocortisone; and group Ug (untreated), animals that were subjected to intestinal obstruction without treatment. The lamellar tissue was analyzed regarding the presence of tissue abnormalities and apoptosis. No morphological abnormalities were observed in animals of surgical groups, and no difference in apoptosis was observed between groups. It was concluded that intestinal obstruction allowed laminitis to develop, probably by systemic activation, and that the maneuvers performed in the enterotomy aggravated the process. Hydrocortisone did not aggravate the lesions of the lamellar tissue

RT-qPCR comparison of mast cell populations in whole blood from healthy horses and those with laminitis

Inflammatory damage to the digital laminae, a structure responsible for suspension of the distal skeleton within the hoof capsule, results in a painful and often life-threatening disease in horses called laminitis. There can be many diverse causes of laminitis; however, previous work in the horse has suggested that in each case, the inflammation and resulting tissue damage is consistent with the action of mediators released from mast cells (MC), as well as the downstream consequences of their activation. The recent development of molecular genetics tools to characterize cells based on their transcriptional activity makes a new approach for measuring MCs possible. Healthy thoroughbred horses from a variety of age groups were used to assess the amount of variation in KIT (encoding mast cell growth factor receptor) and TPSB2 (encoding mast cell tryptase beta 2) gene expression present in the population and to establish "normal" values. Horses (n=9) with a wider range of body condition scores (3-8), because of a more lax management setting that could predispose them to laminitis, had significantly higher KIT expression in circulating peripheral blood cells than horses under individualized management conditions (n=10) that produced ideal body condition scores (4-6) (mean 2.573-fold, P<0.0005). Likewise, horses affected with acute laminitis (n=11) had elevated expression of TPSB2 (2.760-fold, P=0.0011) relative to control horses (n=15). These data suggest that investigation of MC-related genes KIT and TPSB2 may be effective to assay MC population and activity. More work is needed to refine the diagnostic criteria to better describe at what point MC activation occurs and illustrate the use of gene expression assays in clinical cases of laminitis. Additionally, MC activation is associated with inflammatory disease in several mammalian species and may prove a valuable therapeutic target in the horse.