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 (10\ua0g/kg, n\ua0=\ua014 horses). Lamellae were harvested at 24\ua0h post-oligofructose administration (DEV, n\ua0=\ua07) or at the onset of OG1 laminitis (OG1, n\ua0=\ua07). Both MAC387-positive and CD163-positive cells were counted by a single blinded investigator on images [n\ua0=\ua010 (40× fields/digit for MAC387 and 20\ua0x 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\ua

Digital lamellar inflammatory signaling in an experimental model of equine preferential weight bearing

Abstract Background Supporting limb laminitis (SLL) is a complication of severe orthopedic disease in horses and is often life‐limiting, yet the pathophysiology remains obscure. Hypothesis/Objectives To investigate the role of digital lamellar inflammatory signaling in the pathophysiology of SLL using a model of unilateral weight bearing, hypothesizing that there would be evidence of lamellar inflammation in limbs subjected to the model. Animals Thirteen healthy adult Standardbred horses were used for this study (11 geldings, 2 mares; mean age 6.5 ± 2.5 years; mean body weight 458.3 ± 32.8 kg). Methods Randomized controlled experimental study. A steel shoe with a custom insert was applied to a randomly selected front foot of 7 horses; 6 horses were unshod and served as controls. After 92 hours, all horses were humanely euthanized, and digital lamellar samples were collected. Lamellar protein and mRNA were isolated and used to perform western blot and PCR. Results Lamellar concentrations of IL‐6 mRNA were higher in SL tissue than IL HIND tissue (median [25%‐75%] normalized copy number 191 [111‐3060] and 48 [25‐74], respectively; P=.003), and lamellar concentrations of COX‐2 mRNA were higher in SL tissue than CON tissue (normalized copy number 400 [168‐634] and 125 [74‐178], respectively; P=.007). Lamellar concentrations of IL‐1B, IL‐10, and COX‐1 mRNA were not significantly different between groups. The concentrations of phosphorylated (activated) STAT1 and STAT3 proteins were higher in SL (0.5 [0.35‐0.87] and 1.35 [1.1‐1.7], respectively) compared to CON (0.24 [0.09‐0.37] and 0.31 [0.16‐037]) and UL HIND (0.27 [0.19‐0.37] and 0.38 [0.24‐0.5]); P=0.01 and P<0.001. Conclusions and Clinical Importance Lamellar inflammatory signaling was higher in tissue from horses subjected to prolonged unilateral weight‐bearing, suggesting that these pathways could be relevant to the pathophysiology of SLL

Effect of 5′‐adenosine monophosphate‐activated protein kinase agonists on insulin and glucose dynamics in experimentally induced insulin dysregulation in horses

Abstract Background 5′‐adenosine monophosphate‐activated protein kinase (AMPK) agonists, particularly resveratrol (RES), have not been extensively evaluated for their effect on insulin dysregulation (ID) in horses. Objectives Evaluate the effects of treatment with RES (10 mg/kg PO q12h), metformin (MET; 30 mg/kg PO q12h), and aspirin (ASP; 20 mg/kg PO q24h) on experimentally induced ID. Animals Thirty‐three healthy, adult, light‐breed horses. Methods Unblinded, placebo‐controlled, experimental trial evaluating effects of AMPK agonists (RES, MET, and ASP) on experimentally induced ID. Horses were randomly assigned to a treatment group (RES, MET/ASP, RES/ASP, RES/MET/ASP, or placebo [CON]) after induction of ID with dexamethasone (0.08 mg/kg PO q24h for 7 days). Frequently sampled insulin‐modified IV glucose tolerance tests (FSIGTT) and oral sugar tests (OST) were performed at baseline, 7 days after ID, and ID plus 7 days of treatment. Minimal model and OST variables were compared between (1‐way ANOVA) and within (1‐way ANOVA for repeated measures) groups over time to determine effects of treatment on ID. Results Administration of dexamethasone for 14 days resulted in significantly altered insulin and glucose dynamics (SI, DI, basal [glucose], and [insulin]) and produced clinical signs of laminitis in 5 out of 33 (15%) of horses included in the study. Combination therapy with RES, MET, and ASP did not significantly improve insulin and glucose dynamics in horses with experimentally induced ID. Conclusions and Clinical Importance Metabolic testing before glucocorticoid administration should be considered in horses with clinical signs of metabolic syndrome