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.     

Clinical Outcome of 14 Obese,Laminitic Horses Managed with the Same Rehabilitation Protocol

A specific method of rehabilitation was used to manage obese horses with laminitis, and clinical outcome was evaluated after 5 to 20 months. Clinical data from 14 similar laminitis cases were statistically analyzed to evaluate response to rehabilitation. Data were analyzed using repeated measures or logistic regression methodologies. Each horse presented as obese and laminitic with no history of a systemic inflammatory disease. The rehabilitation method emphasized a mineral-balanced, low nonstructural carbohydrate diet; daily exercise; hoof trimming that minimized hoof wall loading; and sole protection in the form of rubber hoof boots and/or hoof casts. Distal phalanx alignment within the hoof capsule was significantly improved, and hoof wall thickness was significantly decreased (P < .0001) following treatment. Solar depth was significantly increased (P < .0015). Reduction of palmar angle measurements was detected in acutely and chronically affected horses. This treatment effect was statistically greater for horses with chronic laminitis than for horses with acute laminitis (P interaction < .0001). Horses were 5.5 times more likely to be sound post-treatment than before treatment. Daily exercise, dietary modification, and removal of ground reaction force from the hoof wall were foci of the rehabilitation program. Hoof care and husbandry as applied to these horses may be an effective method of rehabilitation of horses from obesity-associated laminitis.     

Expression of endothelin in equine laminitis.

Biosynthesis of endothelin-1 (ET-1), the most potent endogenous vasoconstrictor yet identified, is increased following myocardial infarction (MI) in man. Pathological events which occur in the connective tissues of the equine hoof during laminitis are similar in some respects, to changes occurring in the myocardial connective tissues following MI in man. The objective of this study was to determine whether ET-1 expression in connective tissues obtained from the hoof of laminitic horses is increased compared with tissues obtained from healthy horses. Expression of ET-1 in connective tissues of the equine hoof was measured following tissue extraction from 3 groups of horses: horses in which acute laminitis had been induced by the administration of starch; chronically foundered horses; nonlaminitic horses. The concentration of ET-1 in laminar connective tissues obtained from all laminitic horses (1573.0 +/- 392.8 pg/g of tissue; n = 10) was increased when compared with tissues obtained from nonlaminitic horses (392.5 +/- 117.4 pg/g of tissue; n = 5) (P<0.05). The concentration of ET-1 in laminar connective tissues obtained from the experimentally induced, acute laminitic horses (1043.6 +/- 254.4 pg/g of tissue; n = 7) and from the spontaneously affected, chronic laminitic horses (2808.3 +/- 878.6 pg/g of tissue; n = 3) was increased compared with the control group (P<0.05, P<0.01, respectively). The concentration of ET-1 in laminar connective tissues obtained from the chronic laminitic horses was greater than that of the experimentally induced, acute laminitic group (P<0.05). It is suggested that the data provide a strong argument that increased ET-1 expression in the connective tissues of the equine hoof represent a potentially important and hitherto unrecognised component of the pathophysiology of equine laminitis. Further studies are needed to determine whether inhibitors of ET-1 converting enzyme or antagonists of ET-1 receptors might be useful in the treatment and prevention of laminitis in horses.     

Equine laminitis induced with oligofructose

REASONS FOR PERFORMING STUDY: Experimental induction of equine laminitis with a reliable and clinically relevant model should facilitate understanding of the disease. Successful induction with oligofructose (OF) could link pasture consumption to laminitis. OBJECTIVES: To determine whether alimentary administration of OF induces laminitis. METHODS: Twelve horses were dosed with OF and 6 received a sham (placebo) treatment. Clinical observations were made and blood collected at 4 h intervals over a 48 h study period. Stained sections of the hoof wall lamellae, examined by light microscopy, were graded for laminitis severity. RESULTS: All horses administered OF, but no sham-treated controls, developed clinical and histological laminitis. CONCLUSIONS AND POTENTIAL RELEVANCE: Alimentary overload with OF is a valid induction model for studying the pathogenesis of laminitis. A link is therefore established between field cases of laminitis and pasture fructan content.     

Chronic laminitis is associated with potential bacterial pathogens in the laminae

A common sequella of chronic laminitis in horses is repeated abscesses with variable lameness and drainage. It is unclear whether the exudate represents the debridement phase of a non-septic inflammatory process involving clearance of laminar tissue damaged during the acute episode of laminitis, or a response to a microbial infection developed by ascent of microbes from the environment to the tissue via the white line. The objective of this study was to evaluate the possibility that an undiagnosed microbial infection in laminar tissue is present in laminar tissue collected from chronically laminitic horses without an active hoof abscess. Methods to collect laminar tissue, aseptically, from control (non-laminitic) horses and those with chronic/recurrent laminitis are described. Laminae homogenates were evaluated for the presence of bacteria. Bacteria were identified using biochemical tests and sequencing of 16S rRNA and virulence genes. Laminae from chronically laminitic horses revealed 100-fold higher levels (P=0.002) of bacteria compared to control, non-laminitic horses. Although environmental organisms were identified, potential pathogens were identified. Included were Gram positive bacteria, Brevibacterium luteolum, coagulase-negative Staphylococcus spp. as well as Gram negative bacteria, enterohemorrhagic Escherichia coli and Alcaligenes faecalis. Further research is warranted to evaluate the role of bacteria in equine chronic laminitis.     

Cytokeratins of the matrices of the chestnut (torus carpeus) and periople in horses with acute laminitis

OBJECTIVES: To determine whether there is a change in the expression of cytokeratins in the epidermal cells of the non-weight-bearing parts of the limb in horses with acute laminitis and thus determine whether the morphologic changes that develop in the periople and chestnut (torus carpeus) of horses early in acute laminitis are caused by inhibition of keratinocyte differentiation. ANIMALS: 8 horses with acute laminitis. PROCEDURE: Tissue specimens were obtained from the chestnuts of all 8 horses and from the stratum externum of the hoof wall of 3 horses. Tissue specimens were obtained within 48 hours of the first clinical signs of laminitis. The cytokeratins were characterized by 1- and 2-dimensional gel electrophoresis, and the tissue distribution of the cytokeratins was studied by immunohistochemical staining. RESULTS: The biochemical findings indicated that the epidermal cells of tissues from horses affected by laminitis contained the same set of cytokeratins as corresponding tissues from clinically normal horses. Immunohistochemistry on sections from specimens of horses with laminitis versus clinically normal horses indicated a difference in the expression of cytokeratin in the basal cells in the matrix of the stratum externum of the hoof wall and in the matrix of the chestnut of horses with laminitis in which the most severe morphologic changes were observed. CONCLUSIONS: Inhibition of keratinocyte differentiation, as observed by immunohistochemical changes, in cells in parts of the chestnut and periople may indirectly indicate that the observed epidermal changes in horses with laminitis are primary and are unaffected by weight-bearing.     

Equine laminitis: Induced by 48 h hyperinsulinaemia in Standardbred horses

Reasons for performing study: Hyperinsulinaemia is known to induce laminitis experimentally in healthy ponies with no history of the condition. Horses are more insulin sensitive than ponies and whether prolonged hyperinsulinaemia and euglycaemia would have a similar laminitogenic effect requires study. Objectives: To determine if laminitis results when the prolonged euglycaemic hyperinsulinaemic clamp technique (p‐EHC) is applied to clinically normal Standardbred horses, and to monitor hoof wall temperature seeking an association between vascular activity and laminitis development. Methods: Eight young, clinically normal Standardbred horses were assigned into 4 pairs and within each pair, one was assigned randomly to either treatment (n = 4) or control (n = 4) groups. Treated horses received continuous infusions of insulin and glucose until clinical signs of laminitis developed, at which point the horses were subjected to euthanasia. Control horses received an equivalent volume of a balanced electrolyte infusion for the same period. Hoof wall surface temperature (HWST) was monitored continuously throughout the experimental period. Results: All horses in the treatment group were calculated to have normal insulin sensitivity. All treated horses, and none in the control group, developed laminitis (P = 0.01). Pronounced digital pulses were a feature of the treatment group, while insignificant digital pulses occurred in control horses. HWST was higher and less variable in treated horses once hyperinsulinaemia was established. Conclusions: Healthy Standardbred horses subjected to prolonged hyperinsulinaemia develop laminitis within 48 h, demonstrating that laminitis in horses can be triggered by insulin. Potential relevance: Insulin resistance and the associated hyperinsulinaemia place horses and ponies at risk of developing laminitis. This study demonstrates a need for prompt management of the persistent hyperinsulinaemia seen in some endocrinopathies.     

Risk factors for development of acute laminitis in horses during hospitalization: 73 cases (1997-2004)

OBJECTIVE: To identify risk factors for development of acute laminitis in horses during hospitalization for illness or injury. DESIGN: Retrospective case-control study. ANIMALS: 73 horses that developed laminitis (case horses) and 146 horses that did not develop laminitis (control horses) during hospitalization. PROCEDURES: Case and control horses were matched in a 2:1 ratio by the date on which each horse was evaluated. Potential risk factors investigated included age, breed, and sex; highest and lowest values recorded during hospitalization for fibrinogen concentration, WBC count, PCV, and total solids concentration; and comorbid disease states, including pneumonia, endotoxemia, diarrhea, medically treated colic, surgically treated colic, pituitary adenoma, retained placenta or metritis, forelimb lameness, hind limb lameness, acute renal failure, and vascular abnormalities. A univariate screening of all potential risk factors was performed to determine which variables should be selected for further analysis. All factors found to be associated with development of laminitis were included in a multivariate conditional logistic regression model. RESULTS: Development of laminitis was marginally associated with lowest and highest fibrinogen concentrations, highest PCV, and lowest total solids concentration and significantly associated with pneumonia, endotoxemia, diarrhea, abdominal surgery for colic, and vascular abnormalities. In the multivariate analysis, only endotoxemia was significantly associated with laminitis. CONCLUSIONS AND CLINICAL RELEVANCE: Endotoxemia is an important risk factor for development of acute laminitis in horses during hospitalization for medical or surgical conditions. Early recognition of endotoxemia, or the potential for it to develop in certain disease states, and initiation of treatment directed at endotoxemia or its consequences may help prevent laminitis in horses during hospitalization.     

Equine laminitis model: Cryotherapy reduces the severity of lesions evaluated seven days after induction with oligofructose

Reasons for performing study: A previous preliminary study demonstrated the potential of distal limb cryotherapy (DLC) for preventing laminitis. Clinically, DLC must be effective for periods longer than 48 h and the preventive effect must extend beyond its discontinuation. Objectives: To evaluate the effect of DLC, applied during the developmental phase of induced laminitis, on the severity of clinical laminitis and lamellar histopathology 7 days after dosing. Methods: Eighteen normal Standardbred horses were divided into 3 groups of 6. Continuous cryotherapy was applied for 72 h to the distal limbs of the first group. The second and third groups were administered laminitis inducing doses of oligofructose and 72 h of cryotherapy applied (immediately after dosing) to the second group. After clinical assessment all horses were subjected to euthanasia 7 days after dosing and hoof lamellar tissues were harvested and analysed. Results: In the laminitis induced horses clinical lameness and laminitis histopathology was significantly reduced in horses that underwent 72 h of DLC compared with untreated controls. Cryotherapy alone produced no significant lameness or other ill effect. Conclusions: Continuous, medium‐ to long‐term (72 h) cryotherapy applied to the distal limbs of horses safely and effectively ameliorates the clinical signs and pathology of acute laminitis. Potential relevance: Pre‐emptive distal limb cryotherapy is a practical method of ameliorating laminitis in ill horses at risk of developing the disease.     

Hindlimb laminar inflammatory response is similar to that present in forelimbs after carbohydrate overload in horses

Reasons for performing study: A significant proinflammatory response is known to occur in the forelimb lamina after carbohydrate administration. As the hindlimbs are often less affected by laminitis compared with the forelimbs, we assessed hindlimb inflammatory response in the early stages of carbohydrate‐induced laminitis to determine whether differences in the response existed. Objective: To determine whether a similar proinflammatory response occurs in the hindlimb laminae to that previously reported for the forelimb. Methods: Archived laminar samples from 12 horses administered 17.6 g of starch (85% corn starch, 15% wood flour)/kg bwt via nasogastric tube that were anaesthetised either after developing a temperature >38.9°C (DEV; n = 6) or at the onset of Obel grade 1 lameness (OG1; n = 6) were used in addition to 6 control horses (CON) that were anaesthetised 24 h after administration of water. Real‐time quantitative polymerase chain reaction for selected proinflammatory mediators and MAC387 immunohistochemistry were performed. The data were analysed nonparametrically to compare groups. Results: Increases in laminar MAC387‐positive leucocytes and laminar messenger ribonucleic acid (mRNA) concentrations (P<0.05) for interleukin‐1β, interleukin‐6, cyclo‐oxygenase‐2, chemokine (C‐X‐C motif)ligand (CXCL)1 and CXCL8 were present in both fore‐ and hindlimb laminae from horses with OG1 lameness. Both CXCL1 and CXCL8 were also increased in forelimb and hindlimb laminae in the DEV horses. Conclusions: Administration of carbohydrate resulted in a similar inflammatory response in the hindlimb laminae to that previously reported for the forelimb laminae. These findings suggest that other factors, such as weightbearing, may play an important role in the development of laminitis after a systemic inflammatory condition develops. Potential relevance: Evidence of inflammation in the hindlimb laminae suggests that the hindfeet should be addressed in the septic horse at risk for laminitis; however, laminitis is often less severe in the hindlimbs due to other factors, such as weightbearing and hoof angle.     

Decreased expression of p63, a regulator of epidermal stem cells, in the chronic laminitic equine hoof

Reasons for performing study: Abnormal epidermal stem cell regulation may contribute to the pathogenesis of equine chronic laminitis. Objective: To analyse the involvement of p63, a regulator of epidermal stem cell proliferative potential, in chronic laminitis. Methods: Epidermal tissues from skin, coronet and lamellae of the dorsal foot were harvested from 5 horses with chronic laminitis and 5 control horses. Tissues were analysed using histopathology, immunofluorescence microscopy and quantitative immunoblotting Results: Hoof lamellae of laminitic horses had a lower frequency of p63 positive cells than control lamellae, particularly in the distal region. Quantitative immunoblotting confirmed reduced p63 expression in the laminitic distal lamellar region. The decreased p63 expression in laminitic epidermal lamellae was most apparent in the abaxial region adjacent to the hoof wall and highly associated with the formation of terminally differentiated, dysplastic and hyperkeratotic epidermis in this region, whereas lamellae from control horses maintained high p63 expression throughout the axial‐abaxial axis. Conclusions: Expression of p63 in equine skin resembles that reported in other species, including man and rodents, suggesting that p63 can serve as a marker for the proliferative potential of equine epidermal stem cells. p63 expression was significantly lower in the chronic laminitic hoof than in that of control horses, suggesting laminitic hoof epithelium has more limited proliferative potential with a shift towards differentiation. This may reflect reduced activity of epidermal stem cells in laminitic hoof. It is proposed that p63 contributes to the maintenance of hoof lamellae and that misregulation of p63 expression may lead to epidermal dysplasia during lamellar wedge formation. Potential relevance: This study suggests that loss of epidermal stem cells contributes to the pathogenesis of equine laminitis. Autologous transplantation of p63‐positive epidermal stem cells from unaffected regions may have regenerative therapeutic potential for laminitic horses.     

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.     

Glucose transport in the equine hoof

Reasons for performing study: Several conditions associated with laminitis in horses are also associated with insulin resistance, which represents the failure of glucose uptake via the insulin‐responsive glucose transport proteins in certain tissues. Glucose starvation is a possible mechanism of laminitis, but glucose uptake mechanisms in the hoof are not well understood. Objectives: To determine whether glucose uptake in equine lamellae is dependent on insulin, to characterise the glucose transport mechanism in lamellae from healthy horses and ponies, and to compare this with ponies with laminitis. Methods: Study 1 investigated the effects of insulin (300 µU/ml; acute and 24 h) and various concentrations of glucose up to 24 mmol/l, on 2‐deoxy‐D‐[2,6‐³H]glucose uptake in hoof lamellar explants in vitro. Study 2 measured the mRNA expression of GLUT1 and GLUT4 transport proteins by PCR analysis in coronary band and lamellar tissue from healthy horses and ponies, ponies with insulin‐induced laminitis, and ponies suffering from chronic laminitis as a result of equine Cushing's syndrome. Results: Glucose uptake was not affected by insulin. Furthermore, the relationship between glucose concentration and glucose uptake was consistent with an insulin‐independent glucose transport system. GLUT1 mRNA expression was strong in brain, coronary band and lamellar tissue, but was weak in skeletal muscle. Expression of GLUT4 mRNA was strong in skeletal muscle, but was either absent or barely detectable in coronary band and lamellar tissue. Conclusions: The results do not support a glucose deprivation model for laminitis, in which glucose uptake in the hoof is impaired by reduced insulin sensitivity. Hoof lamellae rely on a GLUT1‐mediated glucose transport system, and it is unlikely that GLUT4 proteins play a substantial role in this tissue. Potential relevance: Laminitis associated with insulin resistance is unlikely to be due to impaired glucose uptake and subsequent glucose deprivation in lamellae.     

Equine laminitis model: Lamellar histopathology seven days after induction with oligofructose

Reasons for performing study: The histopathology of laminitis during its transition from the acute to the chronic phase has not been previously documented. Studying hoof lamellar tissues 7 days after induction of laminitis may provide insight into the intractable nature of the chronic phase of the disease. Objectives: To induce laminitis and investigate hoof wall lamellar tissues 7 days after dosing. Methods: Laminitis was induced using oligofructose in 6 normal Standardbred horses. The dorsal hoof lamellar tissues of these and 12 normal horses were processed and examined by light microscopy. Serial sections of a lamellar tip affected by laminitis were used to create a 3 dimensional reconstruction. Results: Transverse sections of dorsal hoof wall lamellae were significantly longer than normal. Many secondary epidermal lamellae were not connected to primary lamellae and existed as spherical or ovoid, discrete islands isolated in the lamellar dermis. The lamellar basement membrane was intact. Conclusions: Lamellar tissue has the ability to reorganise rapidly following an episode of acute laminitis. Although histopathological evidence of ongoing acute laminitis was absent by 7 days, there was marked disruption of lamellar architecture. Potential relevance: The architecture and subsequent strength of the resultant lamellar interface could be greatly influenced for the better by strategies that minimise mechanical displacement during the acute phase of laminitis.     

The treatment of laminitis in horses

The structural and vascular anatomy of the healthy equine foot is compared with the pathologic changes in the foot of horses with acute and chronic laminitis. The structural and vascular abnormalities present in the foot of horses with laminitis are demonstrated in order to explain the abnormal manner in which their feet grow. The medical, surgical, dietary, and endocrine management of acute and chronic laminitis is discussed. Various forms of hoof trimming beneficial to the reestablishment of normal digital perfusion, normal hoof growth, and normal spatial orientation among the distal phalanx, hoof wall, and sole are described. Guidelines for the provision of frog support provided by adjustable heart-bar shoes are presented.     

Evaluation of hoof wall surface temperature as an index of digital vascular perfusion during the prodromal and acute phases of carbohydrate-induced laminitis in horses.

OBJECTIVE: To evaluate the use of hoof wall surface temperature (HWST) as an indirect indicator of digital perfusion and to describe HWST patterns during the prodromal and acute phases of carbohydrate-induced laminitis in horses. ANIMALS: 30 adult horses without foot abnormalities. PROCEDURES: Three experiments were performed. In the first, HWST was measured in 2 groups of horses acclimatized to hot (n = 6), or cold (6) environments and exposed to cold (15 C) ambient temperature. In the second experiment, HWST were measured in both forefeet of 6 horses before and after application of a tourniquet to 1 forefoot to induce vascular occlusion. In the third experiment, HWST were recorded in 12 horses before and during the prodromal and acute phases of carbohydrate-induced laminitis. RESULTS: Mean HWST of hot-acclimatized cold-challenged horses was significantly less than that of cold-acclimatized cold-challenged horses at all times. Transient episodes of high HWST were observed during prolonged cold-induced vasoconstriction. Hoof wall surface temperature significantly decreased during arterial occlusion and increased during reperfusion. Digital hypothermia was observed during the prodromal phase of carbohydrate-induced laminitis. CONCLUSIONS AND CLINICAL RELEVANCE: Determination of HWST is a valid technique to evaluate digital perfusion under appropriate controlled conditions in horses. Digital hypothermia detected during the prodromal phase of laminitis is consistent with decreased digital vascular perfusion or metabolic activity. If administered to horses during the prodromal phase, agents that enhance digital perfusion may prevent development of laminitis.     

A gross and histopathological study of an ectopic white line development in equine laminitis

In horses with chronic laminitis, an abnormal horny structure called lamellar wedge, is generated between the hoof wall and the laminar epidermis. To be able to manage horses with chronic laminitis correctly, more information about the pathological state of this abnormal horn is required. The aim of this study was to collect and analyze objective morphological data about the abnormal horn in order to understand its morphology and development. In the study, the abnormal horn was grossly visible on the sagittal hoof section from approximately 20 days after the onset of disease. In the histological observations, the structural characteristics of this abnormal horn were similar to the white line tissue, suggesting it is an ectopic white line. Mean value of the cross-sectional area of the abnormal horn against the distal phalanx section area (A/D) was 0.29 cm(2) SD +/- 0.14 and it finally showed an eight-fold increase over the mean value of normal white line section area against the distal phalanx section area. In conclusion, a large amount of the ectopic white line is thought to be finally able to inhibit normal hoof wall growth, so that it should be resected at the optimum time when would be after one month from the onset of the disease.     

Equine laminitis caused by distal displacement of the distal phalanx: 12 cases (1976-1985)

Clinical data from 12 cases of equine laminitis characterized by distal displacement of the distal phalanx (P3) were reviewed. Clinical features of horses that survived the syndrome were compared with the nonsurvivors to obtain prognostic indicators. Animals affected included 8 Quarter Horses, 2 Welsh ponies, 1 Thoroughbred, and 1 Arabian. Eight of the animals were females (67%), 2 were stallions, and 2 were geldings. The mean age of affected animals was 8.6 years (2 to 14 years), and the mean body weight was 442 kg. The survivors weighed less than the nonsurvivors (384 kg vs 473 kg, respectively), suggesting that body weight may be of prognostic value for horses affected with distal displacement of P3. Ten of the 12 animals (83%) were admitted because of a disorder other than laminitis, but subsequently developed laminitis during the treatment period. All affected animals had clinical evidence of endotoxemia and/or sepsis before the onset of laminitis. Cavitation or depression of the dorsal coronary band was detected in all animals and was the most reliable clinical indicator of distal displacement of P3. Five horses had fluid (blood or serum) ooze from their coronary bands and 2 of these sloughed one or more of their hooves. Necropsy findings of the 8 horses that were euthanatized included severe hemorrhagic, congested laminae and complete detachment of P3 from the hoof wall. Histologic examination of affected laminae revealed vascular thrombosis and multifocal areas of hemorrhage and necrosis. Radiography failed to reveal distal displacement of P3 in 8 animals, but the remaining 4 animals had an accentuation of the dorsal proximal hoof wall and cavitation of the coronary band visible on lateral radiographs.     

Cytokeratins of the stratum medium and stratum internum of the equine hoof wall in acute laminitis

The cytoskeleton of living keratinocytes consists mainly of cytokeratins that have polymerised into intermediate filaments. The aim of this study was to describe the expression of cytokeratins in the living epidermal cells of the weight-bearing parts of the equine hoof wall during acute spontaneous laminitis. A total of 9 hooves from 3 horses subjected to euthanasia within 48 h of the first clinical signs of laminitis were sectioned and examined. The cytokeratins in the stratum medium and stratum internum of the hoof wall were characterized by 1- and 2-dimensional gel electrophoresis, and the tissue distribution of the cytokeratins was studied by immunohistochemical staining. The biochemical results showed the same set of cytokeratins as was seen in 8 normal horses, reported on previously, used as controls. The immunohistochemical results indicated a difference between normal horses and horses with acute laminitis in the content of cytokeratins in the basal cells of the matrix of the stratum medium of the hoof wall and in the basal and suprabasal cells in the stratum internum at the mid level of the hoof wall. However, no conclusion could be drawn as to whether this change in the cytokeratin distribution in laminitis was primary or was caused by the initiation of the local tissue-repairing process.     

Nuclear Factor-κB Inhibitor as a Preventive Factor of Digital Hypothermia Induced by Lipopolysaccharide in Horses

Although the mechanism of development of equine laminitis is unclear, involvement of endotoxemia has been proposed. Endotoxemia is one of the described pathways for laminitis but not the only one. Lipopolysaccharide (LPS) promotes the release of vasoconstrictors from platelets and endothelium through the activation of nuclear factor (NF)-κB in these cells. The vasoconstrictors induced by LPS may cause digital hypothermia with vasoconstriction and local ischemia, contributing to the development of laminitis. In the present study, we evaluated beneficial effect of NF-κB inhibition on digital hypothermia induced by LPS in adult horses. To generate a model for the local ischemia below the pastern, LPS was infused to the palmar lateral digital vein. As an index of blood circulation, hoof wall surface temperature (HWST) was measured. LPS infusion reduced HWST time dependently; however, the reduction of HWST was significantly prevented by pretreatment of a NF-κB inhibitor, IMD-0354. Our results clearly demonstrated that the inhibition of NF-κB prevented the digital hypothermia induced by LPS, suggesting that the NF-κB inhibitor might have a therapeutic effect on laminitis associated with endotoxemic conditions in horses.