Dose responses to inhalation of endotoxin, hay dust suspension and Aspergillus fumigatus extract in horses as measured by levels and activation of matrix metalloproteinase-9.
Authors: Simonen-Jokinen T, Pirie R S, McGorum B, Maisi P
Journal: Equine veterinary journal
Summary
# Editorial Summary: Matrix Metalloproteinase Response to Inhaled Challenges in Horses Airway inflammation in horses exposed to organic dust involves complex enzymatic cascades that remain incompletely understood; this 2005 study investigated whether matrix metalloproteinase-9 (MMP-9) and MMP-2 show dose-dependent increases in bronchoalveolar lavage fluid (BALF) following inhalation of common respiratory irritants. Seven heaves-susceptible and six control horses were challenged with three escalating doses of hay dust suspension and lipopolysaccharide (LPS), whilst heaves-susceptible animals additionally received graded doses of *Aspergillus fumigatus* extract and endotoxin-depleted fungal extract, with BALF analysed using gelatin zymography to quantify both inactive (pro-) and active enzyme forms. All challenge substances produced dose-dependent rises in gelatinolytic activity, with the most pronounced dose-response relationship observed for pro-MMP-9 and total MMP-9 in heaves-susceptible horses challenged with LPS, suggesting these animals mount a heightened protease response. The findings implicate MMP-9 as a key mediator in heaves pathogenesis and indicate that different organic dust components elicit varying inflammatory potency, opening therapeutic avenues for protease inhibitor use in managing dust-induced airway disease. For practitioners, these results support the mechanistic rationale for aggressive dust control in susceptible animals and hint at emerging pharmacological interventions targeting the enzymatic drivers of inflammatory airway disease.
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Practical Takeaways
- •Heaves-susceptible horses show exaggerated matrix metalloproteinase responses to environmental challenges, which may explain their enhanced susceptibility to airway disease and could guide identification and management of at-risk individuals
- •Protease inhibitor therapy may represent a novel treatment approach to reduce airway inflammation in heaves by targeting the underlying MMP-mediated tissue damage pathway
- •Environmental dust exposure should be minimized in heaves-susceptible horses, as dose-dependent inflammatory responses indicate that cumulative dust exposure significantly worsens airway pathology
Key Findings
- •Each challenge substance (hay dust suspension, LPS, Aspergillus fumigatus extract) induced dose-dependent elevation in gelatinolytic activity, with pro-MMP-9 and total MMP-9 showing the most evident dose-dependency in heaves-susceptible horses following LPS challenges
- •MMP-9 elevation in bronchoalveolar lavage fluid was more marked in heaves-susceptible horses compared to control horses across all organic dust challenges
- •Organic dust components vary in their pro-inflammatory potential, with endotoxin-depleted Aspergillus fumigatus extract eliciting different responses than endotoxin-containing preparations
- •Findings support matrix metalloproteinases as key mediators in heaves pathogenesis and suggest protease inhibitors as potential therapeutic targets for attenuating airway inflammation