Tissue-specific dysregulation of cortisol metabolism in equine laminitis

REASONS FOR PERFORMING STUDY: The role of glucocorticoids (GCs) in the pathogenesis of laminitis is incompletely understood. Local tissue activity of GC is regulated by the steroid converting enzyme, 11beta-hydroxysteroid dehydrogenase-1 (11beta-HSD-1). Changes in integumentary (skin and hoof lamellar) 11beta-HSD activity occurring during laminitis could affect the extent to which GCs are involved in its development. HYPOTHESIS: That changes in integumentary 11beta-HSD-1 activity associated with the laminitic condition would lead to elevated local tissue levels of GCs, which could subsequently contribute, through paracrine and autocrine mechanisms, to the further development of laminitis; and that similar changes in 11beta-HSD-1 activity would be evident in both skin and hoof lamellar tissue. METHODS: Activity of 11beta-HSD-1 was determined in skin and hoof lamellar tissue specimens obtained from normal and laminitic horses using a radiometric assay. Skin samples were obtained from 10 normal horses and from 10 horses before and after induction of acute laminitis following administration of starch via nasogastric tube. Hoof lamellar samples were obtained from 10 normal horses, 10 horses following induction of acute laminitis and 4 chronically-foundered horses. Bidirectional 11beta-HSD-1 activity was measured in both skin and lamellar tissues. RESULTS: 11-ketoreductase activity exceeded 11beta-dehydrogenase activity in both skin and lamellar tissues. Cutaneous activity was higher than lamellar 11beta-HSD-1 activity in all groups. Both ketoreductase and dehydrogenase activity increased in skin and lamellae following experimental induction of acute laminitis, but the increase in ketoreductase activity was substantially greater than that for dehydrogenase in the lamellae. Induction of acute laminitis was attended by increases of 227 and 220% in cutaneous dehydrogenase and ketoreductase activity, respectively, and 173 and 398% in lamellar dehydrogenase and ketoreductase activity, respectively (P<0.05). CONCLUSIONS: The 11-ketoreductase moiety of 11beta-HSD-1 plays a role in equine skin and hoof lamellae regarding the regulation of local glucocorticoid activity. Increased 11-ketoreductase activity will lead to increased local tissue GC activity by virtue of conversion of cortisone to cortisol. POTENTIAL RELEVANCE: The laminitic condition is attended by integumentary biochemical changes that enhance the local concentration of cortisol, especially in the hoof lamellar interface. Through multiple and diverse actions, increased local GC activity contributes to the pathogenesis and morbidity associated with laminitis. Pharmacological manipulation of 11beta-HSD-1 deserves further investigation regarding the prevention and treatment of laminitis.     

Factors involved in the prognosis of equine laminitis in the UK.

The significance of clinical and radiological parameters as prognostic indicators for laminitis, 'founder' and 'sinking syndrome' was studied using case records of 216 horses and ponies. Five animals were destroyed without treatment and were not included in the results of the study. One hundred and sixty-two (77%) animals returned to athletic soundness; 7 animals (3%) did not regain full athletic function, 42 animals (20%) died or were destroyed. Cases were assigned to 4 groups on the basis of initial clinical examination alone. These groups were laminitis, acute founder, 'sinker' and chronic founder. This grouping was found in itself to be the most important prognostic parameter which was studied. Stepwise regression analysis of the data from animals by group indicated that the radiological measurement of founder distance, was the most significant radiological prognostic measurement for acute founder cases. Less significant prognostic parameters were the severity of lameness, rotation angles, the presence of solar prolapse, and the number of feet affected. The height of the animal at the withers was not significantly related to outcome. The prognosis for horses was not significantly different from that for ponies.     

Glucocorticoid therapy and the risk of equine laminitis

Although glucocorticoids have been used successfully for the treatment of noninfectious inflammatory diseases of horses for more than 35 years, their use has been attended by a fear of the induction of laminitis. This paper reviews the evidence for this fear and the possible mechanisms whereby glucocorticoids could participate in laminitis induction. Although the association of laminitis with elevated serum cortisol in pituitary pars intermedia dysfunction suggests that chronic exposure to glucocorticoids may be part of laminitis pathogenesis, review of published reports and databases suggests that glucocorticoid‐induced laminitis is a relatively rare occurrence. However, several of the actions of glucocorticoids are similar to those known to be involved in laminitis pathogenesis. Glucocorticoid administration can induce insulin resistance, lead to vascular dysfunction that potentiates vasoconstriction, and interfere with keratinocyte proliferation and differentiation as well as matrix integrity, all mechanisms that could possibly induce laminitis. Drug formulation, dose and route of administration, and the systemic and hoof disease history of the horse must all be considered when assessing laminitis risk during glucocorticoid treatment. Generally, local glucocorticoid administration presents little risk as does systemic treatment of recurrent airway obstruction without concurrent disease. Caution should be used however in horses that are overweight and/or insulin resistant, or have had a recent bout of acute laminitis of alimentary or endotoxic origin. Overall, however, the risk of laminitis after glucocorticoid treatment, especially local use, is acceptable compared to the many benefits of these drugs.     

Bovine laminitis: clinical aspects, pathology and pathogenesis with reference to acute equine laminitis

This review deals with the features of clinical and subclinical laminitis in cattle. Prominent clinical signs of acute laminitis are a tender gait and arched back. The sole horn reveals red and yellowish discolourations within five days. In subacute and chronic cases clinical signs are less severe. In chronic laminitis the shape of the claws is altered. Laminitis is frequently followed by sole ulceration and white zone lesions. Blood tests showed no significant changes for laminitic animals. Arteriographic studies of claws affected by laminitis indicated that blood vessels had narrowed lumens. Gross pathology revealed congestion of the corium and rotation of the distal phalanx. Histopathologic studies indicate that laminitis is associated with changes of the vasculature. Peripartum management and nutrition are important factors in its aetiology. It is hypothesised that laminitis is evoked by disturbed digital circulation. In the pathogenesis of acute laminitis three factors are considered important: the occurrence of thrombosis, haemodynamic aspects of the corium, and endotoxins which trigger these pathologic events.     

Ultrastructural study of the equine cecum during onset of laminitis

The morphologic and pathologic changes which occurred within the cecal mucosa of 4 horses during the onset of laminitis were determined from cecal biopsy materials obtained via a cecal fistula; the laminitis was induced with carbohydrate overload. The cecal epithelial mucosa specimens were obtained at 0 (base line), 24, 32, 48, and 72 hours after horses were given carbohydrate overload, and these were fixed and subsequently photographed. Changes in the cecal epithelium were examined by transmission electron and scanning electron microscopies. These histopathologic changes indicated that the mucosal barrier was substantially damaged by the carbohydrate overload.     

The prevalence of endocrinopathic laminitis among horses presented for laminitis at a first-opinion/referral equine hospital

Endocrinopathic causes of laminitis may be a common underlying causative pathogenesis in first-opinion or field cases presenting with laminitis, as opposed to laminitis produced in inflammatory research models. This study aimed to determine whether evidence of an underlying endocrinopathy was present in horses presented for laminitis to a first-opinion/referral veterinary teaching hospital. A second aim was to compare the signalment of horses and ponies with laminitis with the equine hospital population during the same period. All horses presenting for laminitis at Helsinki University Equine Teaching Hospital, Finland, over a 16-month period were examined for an underlying endocrinopathy. Horses presenting for laminitis were compared with the hospitalized population over the same period. There were 36 horses presented for laminitis, and evidence of endocrinopathy was present in 89%. Of the horses showing an underlying endocrinopathy, one-third had a diagnosis of pituitary pars intermedia dysfunction, and two-thirds showed basal hyperinsulinemia indicative of insulin resistance, without evidence of hirsutism. Phenotypic indicators of obesity were present in 95% of horses with basal hyperinsulinemia without hirsutism. Compared with the hospital population during the same period, horses with laminitis associated with an underlying endocrinopathy were significantly older and more likely to be pony breeds. Our data support that endocrine testing should be performed on all cases of laminitis that do not have a clear inflammatory or gastrointestinal origin.     

In vitro evidence for a bacterial pathogenesis of equine laminitis

Utilizing an in vitro laminitis explant model, we have investigated how bacterial broth cultures and purified bacterial proteases activate matrix metalloproteinases (MMPs) and alter structural integrity of cultured equine lamellar hoof explants. Four Gram-positive Streptococcus spp. and three Gram-negative bacteria all induced a dose-dependent activation of MMP-2 and MMP-9 and caused lamellar explants to separate. MMP activation was deemed to have occurred if a specific MMP inhibitor, batimastat, blocked MMP activity and prevented lamellar separation. Thermolysin and streptococcal pyrogenic exotoxin B (SpeB) both separated explants dose-dependently but only thermolysin was inhibitable by batimastat or induced MMP activation equivalent to that seen with bacterial broths. Additionally, thermolysin and broth MMP activation appeared to be cell dependent as MMP activation did not occur in isolation.These results suggest the rapid increase in streptococcal species in the caecum and colon observed in parallel with carbohydrate induced equine laminitis may directly cause laminitis via production of exotoxin(s) capable of activating resident MMPs within the lamellar structure. Once activated, these MMPs can degrade key components of the basement membrane (BM) hemidesmosome complex, ultimately separating the BM from the epidermal basal cells resulting in the characteristic laminitis histopathology of hoof lamellae. While many different causative agents have been evaluated in the past, the results of this study provide a unifying aetiological mechanism for the development of carbohydrate induced equine laminitis.     

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.