Glucocorticoid therapy and the risk of equine laminitis

Systemic absorption of triamcinolone acetonide is increased from intrasynovial versus extrasynovial sites and induces hyperglycemia, hyperinsulinemia, and suppression of the hypothalamic-pituitary-adrenal axis

Steroid-associated laminitis remains a major concern with use of corticosteroids in horses. Individual case factors such as joint pathology, pre-existing endocrinopathies, or corticosteroid type, dose, and timing influencing steroid-induced laminitis risk have not been investigated. This study aimed to determine if systemic absorption of triamcinolone acetonide (TA) varies between intrasynovial (antebrachiocarpal) and extrasynovial (sacroiliac) injection sites, and to determine the effects of TA absorption on glucose, insulin, cortisol, and adrenocorticotropic hormone (ACTH). Twenty adult horses were randomized into antebrachiocarpal or sacroiliac joint injection groups, and each horse received bilateral injections with a total dose of 18 mg triamcinolone. Blood was collected prior to injection and at 1, 2, 4, 6, 8, 10, 12, 16, 20, 24, 36, 48, 60, and 72 h post-injection. Peak TA absorption occurred at 8 h in both groups, and was significantly higher in the intrasynovial group compared to the extrasynovial group (1.397 ng/mL, 0.672 ng/mL, p < 0.05). Plasma TA levels were significantly higher in the intrasynovial group from 8 to 36 h post-injection (p < 0.05). There was no difference in glucose, insulin, cortisol, or ACTH between groups at any time point. Insulin and glucose were significantly increased from baseline at all timepoints from 10-72 h and 1-72 h post-injection, respectively. Horses with elevated baseline insulin values (>20 μU/mL) from both groups experienced a more marked hyperinsulinemia, reaching a mean peak insulin of 197.5 μU/mL as compared to 90.06 μU/mL in those with normal baseline insulin. Cortisol and ACTH were significantly decreased from baseline at timepoints from 4-72 h post-injection in both groups. This study is the first to evaluate drug absorption from the sacroiliac site and demonstrates that drug absorption varies between intrasynovial and extrasynovial injection sites. TA absorption causes metabolic derangements, most notably a marked hyperinsulinemia that is more severe in horses with elevated baseline insulin values. The influence of baseline endocrinopathies on response to corticosteroid administration as well as the effect of corticosteroid-induced metabolic derangements warrant further investigation as risk factors for corticosteroid-associated laminitis.

Equine tendon mechanical behaviour: Prospects for repair and regeneration applications

Tendons are dense connective tissues that play an important role in the biomechanical function of the musculoskeletal system. The mechanical forces have been implicated in every aspect of tendon biology. Tendon injuries are frequently occurring and their response to treatments is often unsatisfactory. A better understanding of tendon biomechanics and mechanobiology can help develop treatment options to improve clinical outcomes. Recently, tendon tissue engineering has gained more attention as an alternative treatment due to its potential to overcome the limitations of current treatments. This review first provides a summary of tendon mechanical properties, focusing on recent findings of tendon mechanobiological responses. In the next step, we highlight the biomechanical parameters of equine energy-storing and positional tendons. The final section is devoted to how mechanical loading contributes to tenogenic differentiation using bioreactor systems. This study may help develop novel strategies for tendon injury prevention or accelerate and improve tendon healing.

Endocrinopathic Laminitis

Endocrinopathic laminitis (EL) primarily occurs because of insulin dysregulation (ID) mediated through downstream effects of insulin on IGF-1R in lamellar tissues. There is likely contributing vascular and metabolic dysfunction within the lamellae, but EL is relatively non-inflammatory. EL is associated with lamellar stretching, proliferation, and failure, ultimately causing failure of the suspensory apparatus of the distal phalanx. Proper education regarding mitigating risk factors makes this a largely preventable cause of laminitis. Annual hoof evaluation plus screening geriatric horses for pituitary pars intermedia dysfunction and ID, and younger horses for ID, can significantly decrease the incidence of this devastating condition.

Glucocorticoid treatment in horses with asthma: A narrative review

Despite substantial research efforts to improve the treatment and outcome of horses with asthma, glucocorticoids (GC) remain the cornerstone of drug treatment of this prevalent disease. The high efficacy of GC to relieve airway obstruction explains their extensive use despite potential deleterious effects. However, much is yet to be uncovered concerning GC use in horses with asthma, including the comparative efficacy of the different drugs, the determination of minimal effective doses and the mechanisms underlying their variable modulation of airway inflammation. The objectives of this structured review were to report and compare the plethora of effects of the various GC used in asthmatic horses with a focus on impact on lung function, airway inflammation, and bronchial remodeling. Adverse effects are also briefly described, with an emphasis on those that have been specifically reported in horses with asthma. Ultimately, we aimed to highlight gaps in the literature and to identify future research areas.

The Effects of Treatment with N-Acetyl Cysteine on Clinical Signs in Persistent Breeding-Induced Endometritis Susceptible Mares

Persistent breeding-induced endometritis (PBIE) is a major cause of infertility in mares. Endometrial inflammation that persists until embryonic descent ultimately results in early embryonic death. A poor endometrial biopsy grade (IIb or III) has been identified as a risk factor for PBIE. Intrauterine fluid accumulation (>2 cm in depth), pathologic endometrial edema, and elevated intrauterine neutrophil levels are all clinical features of PBIE. Commonly applied treatment options include uterine lavage and oxytocin therapy. N-acetyl cysteine (NAC), a mucolytic used to treat bacterial endometritis in mares, has anti-inflammatory properties and was investigated as a potential treatment for PBIE. A randomized, blinded, cross-over design clinical trial used NAC before breeding in PBIE-susceptible mares (n = 9). Intrauterine infusion of 3.3% NAC was performed 12 hours before insemination, and endometrial cytology and endometrial biopsy samples were obtained at 12 and 60 hours after insemination. Endometrial biopsies were evaluated for the degree of inflammation present. Clinical signs of endometrial edema and intrauterine fluid volumes were assessed by transrectal ultrasound at 12 and then every 24 hours after breeding. Data were analyzed using repeated measures analysis of variance and a Mann Whitney Wilcoxon Test. Treatment with NAC did not improve clinical signs in PBIE-affected mares. However, endometrial biopsies from mares treated with NAC displayed more diffuse and severe neutrophil infiltration than control cycles. Further research using a larger population of mares is required to evaluate the effects of NAC treatment on the endometrium of PBIE-susceptible mares.

Development of a comprehensive protein microarray for immunoglobulin E profiling in horses with severe asthma

BACKGROUND

Severe asthma in horses, known as severe equine asthma (SEA), is a prevalent, performance-limiting disease associated with increased allergen-specific immunoglobulin E (IgE) against a range of environmental aeroallergens.

OBJECTIVE

To develop a protein microarray platform to profile IgE against a range of proven and novel environmental proteins in SEA-affected horses.

ANIMALS

Six SEA-affected and 6 clinically healthy Warmblood performance horses.

METHODS

Developed a protein microarray (n = 384) using protein extracts and purified proteins from a large number of families including pollen, bacteria, fungi, and arthropods associated with the horses, environment. Conditions were optimized and assessed for printing, incubation, immunolabeling, biological fluid source, concentration techniques, reproducibility, and specificity.

RESULTS

This method identified a number of novel allergens, while also identifying an association between SEA and pollen sensitization. Immunolabeling methods confirmed the accuracy of a commercially available mouse anti-horse IgE 3H10 source (R2 = 0.91). Biological fluid source evaluation indicated that sera and bronchoalveolar lavage fluid (BALF) yielded the same specific IgE profile (average R2 = 0.75). Amicon centrifugal filters were found to be the most efficient technique for concentrating BALF for IgE analysis at 40-fold. Overnight incubation maintained the same sensitization profile while increasing sensitivity. Reproducibility was demonstrated (R2 = 0.97), as was specificity using protein inhibition assays. Arthropods, fungi, and pollens showed the greatest discrimination for SEA.

CONCLUSIONS AND CLINICAL IMPORTANCE

We have established that protein microarrays can be used for large-scale IgE mapping of allergens associated with the environment of horses. This technology provides a sound platform for specific diagnosis, management, and treatment of SEA.

Effect of dietary carbohydrates and time of year on ACTH and cortisol concentrations in adult and aged horses

Diagnosis of equine pituitary pars intermedia dysfunction (PPID) remains a challenge as multiple factors (stress, exercise, and time of year) influence ACTH and cortisol concentrations. To assess endocrine status in a study designed to evaluate the effects of age and diet on glucose and insulin dynamics, we performed thyrotropin-releasing hormone (TRH) stimulation tests and overnight dexamethasone suppression tests in March, May, August, and October on 16 healthy Thoroughbred and Standardbred mares and geldings. Horses were grouped by age: adult (mean ± SD; 8.8 ± 2.9 yr; n = 8) and aged (20.6 ± 2.1 yr; n = 8). None of the horses showed clinical signs (hypertrichosis, regional adiposity, skeletal muscle atrophy, lethargy) of pituitary pars intermedia dysfunction. Horses were randomly assigned to groups of 4, blocked for age, and fed grass hay plus 4 isocaloric concentrate diets (control, starch-rich, fiber-rich, and sugar-rich) using a balanced Latin square design. Data were analyzed using a multivariable linear mixed regression model. Baseline ACTH was significantly higher in aged horses (mean ± standard error of the mean; 60.0 ± 10.7 pg/mL) adapted to the starch-rich diet compared to adult horses (15.7 ± 12.0 pg/mL) on the same diet (P = 0.017). After controlling for age and diet, baseline ACTH concentrations were significantly increased in October (57.7 ± 7.1 pg/mL) compared to March (13.2 ± 7.1 pg/mL; P < 0.001), May (12.4 ± 7.1 pg/mL; P < 0.001), and August (24.2 ± 7.1 pg/mL; P < 0.001), whereas post-TRH ACTH was higher in August (376.6 ± 57.6 pg/mL) and October (370.9 ± 57.5 pg/mL) compared to March (101.9 ± 57.3 pg/mL; P < 0.001) and May (74.5 ± 57.1 pg/mL; P < 0.001). Aged horses had significantly higher post-dexamethasone cortisol on the starch-rich diet (0.6 ± 0.1 μg/dL) compared to the sugar-rich diet (0.2 ± 0.1 μg/dL; P = 0.021). Post-dexamethasone cortisol was significantly higher in October (0.6 ± 0.1 μg/dL) compared to March (0.3 ± 0.1 μg/dL; P = 0.005), May (0.2 ± 0.1 μg/dL; P < 0.001), and August (0.3 ± 0.1 μg/dL; P = 0.004). Breed did not influence ACTH or cortisol measurements. In conclusion, in addition to age and time of year, diet is a potential confounder as animals on a starch-rich diet may be incorrectly diagnosed with pituitary pars intermedia dysfunction.

Revealing the influence of glucocorticoid treatment on the excretion of anabolic-androgenic steroids in horses through in vitro digestive simulations and an in vivo case study

Anabolic-androgenic steroids (AAS) are strictly forbidden in equine sports because of their stimulating effect on muscle growth and performance. Nevertheless, low levels of AAS have been found in some horses, untreated with AAS. Glucocorticoids (GC), used as an anti-inflammatory therapy and structurally related to AAS, might play a role in this phenomenon. In order to unravel this possible correlation the influence of glucocorticoid treatment on the excretion of AAS was studied both in vivo and in vitro. In vivo effects were investigated by analysing urine samples collected from a gelding treated with betamethasone. Additionally, multiple in vitro digestion simulations were set up, according to a previously validated protocol, to study the possibility of a direct biotransformation of glucocorticoids to AAS, by the microbiota of the equine hindgut. Urine and in vitro digestion samples were extracted and analysed with UHPLC-MS/MS and UHPLC-Orbitrap-HRMS analytical methods. A significant influence on the urinary excretion of α-testosterone (αT), β-testosterone (βT) and androsta-1,4-diene-3,17-dione (ADD) was seen. αT-concentrations up to 20ng/mL were detected. ADD was not found before treatment but could be detected post-treatment. Cortisone and cortisol also peaked (>30ng/mL) between day 37 and 48 post-treatment. The in vitro digestion results however revealed no direct biotransformation of glucocorticoids to AAS by the microbiota of the equine hindgut. This study shows that a glucocorticoid treatment can disrupt the synthesis and excretion of AAS, not by direct biotransformation upon gastrointestinal digestion, but more likely by influencing the hypothalamic-pituitary-adrenal axis.

Disease and pharmacologic risk factors for first and subsequent episodes of equine laminitis: A cohort study of free-text electronic medical records

Electronic medical records from first opinion equine veterinary practice may represent a unique resource for epidemiologic research. The appropriateness of this resource for risk factor analyses was explored as part of an investigation into clinical and pharmacologic risk factors for laminitis. Amalgamated medical records from seven UK practices were subjected to text mining to identify laminitis episodes, systemic or intra-synovial corticosteroid prescription, diseases known to affect laminitis risk and clinical signs or syndromes likely to lead to corticosteroid use. Cox proportional hazard models and Prentice, Williams, Peterson models for repeated events were used to estimate associations with time to first, or subsequent laminitis episodes, respectively. Over seventy percent of horses that were diagnosed with laminitis suffered at least one recurrence. Risk factors for first and subsequent laminitis episodes were found to vary. Corticosteroid use (prednisolone only) was only significantly associated with subsequent, and not initial laminitis episodes. Electronic medical record use for such analyses is plausible and offers important advantages over more traditional data sources. It does, however, pose challenges and limitations that must be taken into account, and requires a conceptual change to disease diagnosis which should be considered carefully.

Vascular Dysfunction in Horses with Endocrinopathic Laminitis

Endocrinopathic laminitis (EL) is a vascular condition of the equine hoof resulting in severe lameness with both welfare and economic implications. EL occurs in association with equine metabolic syndrome and equine Cushing’s disease. Vascular dysfunction, most commonly due to endothelial dysfunction, is associated with cardiovascular risk in people with metabolic syndrome and Cushing’s syndrome. We tested the hypothesis that horses with EL have vascular, specifically endothelial, dysfunction. Healthy horses (n = 6) and horses with EL (n = 6) destined for euthanasia were recruited. We studied vessels from the hooves (laminar artery, laminar vein) and the facial skin (facial skin arteries) by small vessel wire myography. The response to vasoconstrictors phenylephrine (10⁻⁹–10^-5M) and 5-hydroxytryptamine (5HT; 10⁻⁹–10^-5M) and the vasodilator acetylcholine (10⁻⁹–10^-5M) was determined. In comparison with healthy controls, acetylcholine-induced relaxation was dramatically reduced in all intact vessels from horses with EL (% relaxation of healthy laminar arteries 323.5 ± 94.1% v EL 90.8 ± 4.4%, P = 0.01, laminar veins 129.4 ± 14.8% v EL 71.2 ± 4.1%, P = 0.005 and facial skin arteries 182.0 ± 40.7% v EL 91.4 ± 4.5%, P = 0.01). In addition, contractile responses to phenylephrine and 5HT were increased in intact laminar veins from horses with EL compared with healthy horses; these differences were endothelium-independent. Sensitivity to phenylephrine was reduced in intact laminar arteries (P = 0.006) and veins (P = 0.009) from horses with EL. Horses with EL exhibit significant vascular dysfunction in laminar vessels and in facial skin arteries. The systemic nature of the abnormalities suggest this dysfunction is associated with the underlying endocrinopathy and not local changes to the hoof.

Does oral prednisolone treatment increase the incidence of acute laminitis?

REASONS FOR PERFORMING STUDY

It is accepted among equine practitioners that glucocorticoid treatment is a risk factor for the development of laminitis. However, there is little published evidence of a link between glucocorticoids and laminitis.

OBJECTIVES

To determine whether horses receiving oral prednisolone are at increased risk of laminitis.

STUDY DESIGN

Retrospective case-control study.

METHODS

Clinical records of horses registered with the ambulatory service at Liphook Equine Hospital between January 2001 and November 2014 were reviewed retrospectively to identify horses that had received treatment with oral prednisolone. For each treated horse, 2 time-matched controls that received veterinary attention but were not treated with prednisolone were selected. Incidence of laminitis was compared between the 2 groups and factors associated with laminitis were assessed using Cox regression analysis.

RESULTS

Of the 416 horses treated with prednisolone, 16 (3.8%) were diagnosed with laminitis subsequent to the initiation of prednisolone treatment with an overall incidence of 2.60 (95% CI 1.49-4.22) cases per 100 horse-years at risk. A total of 7 horses (1.7%) developed laminitis during the course of their treatment and 3 (0.7%) of the horses treated with prednisolone were ultimately subjected to euthanasia as a result of laminitis. A total of 46 (5.7%), of the 814 time-matched control horses were diagnosed with laminitis during the study period with an overall incidence of 3.46 (95% CI 2.54-4.62) cases per 100 horse-years at risk. Of these, 12 (1.5%) were subjected to euthanasia as a result of laminitis. There were no significant differences in the overall laminitis incidence rate (P = 0.8), incidence rate during prednisolone treatment (P = 0.09), or probability of laminitis (P = 0.3) between the 2 groups. Mean survival time was greater in the prednisolone than the control group. Equine metabolic syndrome and increasing age were associated with increased risk of laminitis.

CONCLUSIONS

Administration of oral prednisolone did not increase the risk of laminitis.

Musculoskeletal Pathology

The current understanding of pathology as it relates to common diseases of the equine musculoskeletal system is reviewed. Conditions are organized under the fundamental categories of developmental, exercise-induced, infectious, and miscellaneous pathology. The overview of developmental pathology incorporates the new classification system of juvenile osteochondral conditions. Discussion of exercise-induced pathology emphasizes increased understanding of the contribution of cumulative microdamage caused by repetitive cyclic loading. Miscellaneous musculoskeletal pathology focuses on laminitis, which current knowledge indicates should be regarded as a clinical syndrome with a variety of possible distinct mechanisms of structural failure that are outlined in this overview.

Recurrent airway obstruction: a review

Recurrent airway obstruction is a widely recognised airway disorder, characterised by hypersensitivity-mediated neutrophilic airway inflammation and lower airway obstruction in a subpopulation of horses when exposed to suboptimal environments high in airborne organic dust. Over the past decade, numerous studies have further advanced our understanding of different aspects of the disease. These include clarification of the important inhaled airborne agents responsible for disease induction, improving our understanding of the underlying genetic basis of disease susceptibility and unveiling the fundamental immunological mechanisms leading to establishment of the classic disease phenotype. This review, as well as giving a clinical overview of recurrent airway obstruction, summarises much of the work in these areas that have culminated in a more thorough understanding of this debilitating disease.