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.

REASONS FOR PERFORMING STUDY

Airway matrix metalloproteinases (MMPs) increase after endotoxin (LPS) exposure, but there are no reports describing dose-dependent increases or activation following exposure.

OBJECTIVES

To study matrix metalloproteinase-9 (MMP-9) and -2 (MMP-2) responses in bronchoalveolar lavage fluid (BALF) from heaves-susceptible and control horses following inhalation of hay dust suspension (HDS), LPS and Aspergillus fumigatus extract (AFE).

METHODS

Heaves-susceptible (n = 7) and control (n = 6) horses received inhalation challenges with 3 different doses of HDS and LPS. Heaves-susceptible horses (n = 6) also received 3 different doses of AFE and one dose of AFE depleted of endotoxin (AFE-LPS). BALF collected following inhalation challenges was analysed using gelatin zymography. Gelatinolytic bands were identified as complex, pro-MMP-9, active MMP-9, pro-MMP-2 and active MMP-2 based on molecular weights.

RESULTS

Each challenge substance induced a dose-dependent elevation in gelatinolytic activity. The dose-dependency was most evident for pro-MMP-9 and total MMP-9 levels in heaves-susceptible horses following LPS challenges.

CONCLUSIONS

There is a dose-dependent elevation in MMP-9 in BALF of heaves-susceptible and control horses following inhalation challenge with organic dust and some of its components, elevation being more marked in heaves-susceptible horses. Organic dust components vary in their pro-inflammatory potential.

POTENTIAL RELEVANCE

This study supports the role of MMPs in the pathogenesis of heaves and highlights the potential value of protease inhibitors in attenuating the airway inflammatory response to inhaled organic dust.