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

Abstract

BackgroundIn 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/ObjectivesBecause 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.AnimalsEight Standardbred geldings aged 3–11 years with no lameness and no abnormalities of the feet detectable by gross or radiographic examination.MethodsUsing 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).ResultsAlthough 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 ImportanceThe 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.

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

“…Due to the findings of a previous study which demonstrated profound inhibition of a wide array of inflammatory mediators when CDH was instituted prior to either systemic sepsis or lamellar disease, CDH has been purported to limit lamellar injury due to its anti‐inflammatory effects. However, a more recent study in which CDH was initiated at the onset of clinical lameness (OG2) did not find the same degree of inhibition of lamellar inflammation with CDH despite it still conferring a dramatic protective effect upon the lamellae . Similarly, a recent study investigating the effects of CDH (instituted immediately after administration of enteral OF) on leukocyte infiltration in the OF SRL model reported only minor changes in lamellar leukocyte numbers, indicating that leukocyte infiltration may have less of a role in lamellar tissue damage than previously thought …”

“…In contrast to previous studies of CDH, a non‐septic control group was incorporated into the study in order to (1) assess the effect of CDH on lamellar signaling in the normal limb, and (2) to be able to accurately assess whether CDH effectively inhibits inflammatory signaling in SRL to a level comparable to that observed in the normal limb. Additionally, in contrast to the study in which minimal anti‐inflammatory effect was detected when CDH was initiated at the onset of OG2 laminitis (where lamellar samples were harvested late in the disease process), the objective of the current study was to harvest samples at an earlier time point (prior to the onset of severe lamellar separation/failure) to avoid the effect that extensive structural tissue injury may have on inflammatory signaling.…”

Interleukin-17 pathway activation inEquus caballussupporting limb laminitis

“…The IL-17 pathway upregulation observed here in natural cases of SLL is also likely present in laminitis associated with other risk factors. In models of SRL, one or more target genes of the IL-17 pathway have been identified as genes upregulated after experimental induction of laminitis [5; 15; 38; 39; 42-46; 52; 70]. One study in an SRL experimental model also hints that the IL-17 pathway may contribute to disease onset or progression.…”

“…In general, most of these studies used treatments that mimic SRL, although several reports also examined models of EL or SLL [15; 38-49]. Models of SRL provide the most evidence for inflammation, either through upregulation of inflammatory mediators [15; 38; 39; 42-47] or leukocyte infiltration [50-52]. Recently, a model to mimic some aspects of SLL was reported [48].…”

Evaluation of digital cryotherapy using a commercially available sleeve style ice boot in healthy horses and horses receiving i.v. endotoxin

“…Horses that have clinical signs of endotoxaemia are at high risk of developing sepsisassociated laminitis. The oligofructose overload (OF) model has been used to study the pathogenesis of sepsis-associated laminitis [2][3][4][5][6][7][8]. These studies have also shown that continuous digital cryotherapy prevents the development and reduces the severity of sepsis-associated laminitis [9][10][11][12][13].…”