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

Abstract

Background: Although continuous digital hypothermia (CDH) protects lamellae from injury in the oligofructose (OF) model of sepsis-related laminitis (SRL), conflicting results exist from these studies regarding effects of CDH on lamellar inflammatory events.

Hypothesis/objectives: To determine the effect of CDH on lamellar inflammatory events in normal and OF-treated horses when instituted at a clinically relevant time point (onset of clinical signs of sepsis in this model).

Animals: Standardbred geldings (n = 15) aged 3-11 years were used.

Methods: In a randomized, controlled discovery study, animals were administered either OF (OF group, n = 8) or water (CON group, n = 8) by nasogastric tube and CDH was initiated in one forelimb (ICE) 12 hours later. Lamellar tissue samples were collected 24 hours after initiation of CDH (ICE and ambient [AMB] forelimbs). Lamellar mRNA concentrations of inflammatory mediators and lamellar leukocyte numbers were assessed using qPCR and immunohistochemistry, respectively; values from four sample groups (CON AMB, OF AMB, CON ICE, and OF ICE) were analyzed using mixed model linear regression.

Results: Although lamellar mRNA concentrations of multiple inflammatory mediators (IL-1β, IL-6, CXCL1, MCP2, COX-2) were increased after OF administration (OF AMB group versus CON AMB; P < 0.05), only 2 inflammatory mediators (IL-6 and COX-2) and lamellar leukocyte numbers were decreased with CDH (OF ICE versus OF AMB; P < 0.05).

Conclusions and clinical importance: Continuous digital hypothermia initiated at a time point similar to that commonly used clinically (clinical onset of sepsis) resulted in a more focused inhibition of inflammatory signaling.

Keywords: Cryotherapy; Digital hypothermia; Equine laminitis; Inflammation; Leukocyte.

Figure 1

Note the increased number of calprotectin‐positive WBC (A) and CD163‐positive WBC (C) in the perivascular region of the primary dermal lamellae (open black arrows) in the AMB OF lamellae (A) compared to the OF ICE lamellae (B, calprotectin; D, CD163). Also note that, in the secondary epidermal lamellae (white arrows), the consistent calprotectin staining in the epithelial ells of the OF AMB lamellae (A) compared to the OF ICE lamellae (B). In the secondary dermal lamellae (solid black arrows), CD163‐positive cells are also present in both the OF AMB (C) and OF ICE (D) lamellar sections. AMB, limbs at ambient temperature; OF, oligofructose; ICE, limbs treated with continuous digital hypothermia.