Effect of composition and different fractions of hay dust suspension on inflammation in lungs of heaves-affected horses: MMP-9 and MMP-2 as indicators of tissue destruction.
Authors: Simonen-Jokinen T, Pirie R S, McGorum B C, Maisi P
Journal: Equine veterinary journal
Summary
# Editorial Summary Recurrent airway obstruction (heaves) in horses involves pathological airway remodelling driven by matrix metalloproteinase (MMP) activation following organic dust inhalation, yet the specific dust components responsible for this inflammatory cascade remained poorly characterised. Simonen-Jokinen and colleagues challenged seven heaves-susceptible horses with saline control, two different hay dust suspensions, and separated soluble and particulate fractions thereof, measuring bronchoalveolar lavage fluid MMP-2 and MMP-9 activity using gelatin zymography at 6 hours post-exposure. Whole hay dust suspension induced significant elevations in proMMP-9 and total MMP-9, but individual soluble or particulate fractions alone produced minimal response; notably, the two hay dust suspensions differed markedly in mould (glucan) content and triggered distinct MMP profiles, with higher-glucan dust elevating active MMP-9, total MMP-2, and complex forms. These findings indicate synergistic activation of MMPs requires combined exposure to multiple dust components—primarily endotoxin-bearing particulates and soluble factors—but implicate fungal content as the dominant driver of the pathological MMP response in heaves-susceptible horses. For practitioners, this work suggests that dust mitigation strategies must address both particulate load and mould contamination rather than targeting either component alone, and supports future investigation of MMP inhibitors as disease-modifying therapeutics, whilst highlighting that hay quality assessment should incorporate mycological analysis as a critical parameter.
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Practical Takeaways
- •Hay dust quality matters significantly—moulds and endotoxin levels in hay are key drivers of airway inflammation in heaves-prone horses; prioritize clean, dust-free forage management
- •MMP inhibition may offer future therapeutic options for treating and preventing heaves, providing a rationale for pursuing anti-inflammatory strategies beyond dust avoidance
- •Dust exposure recommendations should focus on mould contamination thresholds rather than total dust burden alone, since mould content is the primary driver of pathological MMP response
Key Findings
- •Hay dust suspension (HDS-1) increased bronchoalveolar lavage proMMP-9 and total MMP-9 following inhalation challenge
- •Soluble and particulate fractions of dust showed synergistic effects on MMP-9 elevation when combined, but not when inhaled separately
- •HDS-2 with higher glucan concentration elevated complex MMP forms, proMMP-9, active MMP-9, total MMP-9, and total MMP-2
- •Mould content and endotoxin act synergistically to drive MMP activation in heaves-susceptible horses, with moulds playing the predominant role