Inhalation of organic dusts and lipopolysaccharide increases gelatinolytic matrix metalloproteinases (MMPs) in the lungs of heaves horses.

This research assessed how the inhalation of organic dusts and certain bacteria products affects lung enzyme levels in horses with a chronic lung condition. It found that exposure to moldy hay/straw and hay dust suspension increased a type of enzyme called gelatinolytic matrix metalloproteinases, which is known to cause inflammation and potentially lung damage.

Study Overview

• The study focused on the impact of three substances – mouldy hay/straw, hay dust suspension (HDS), and lipopolysaccharide (LPS) – on the levels of certain enzymes in the lung fluid (bronchoalveolar lavage fluid or BALF) in both healthy horses and those suffering from “heaves,” a chronic lung disease similar to human asthma.
• The enzymes being examined were Matrix Metalloproteinases (MMPs), which can degrade components of the connective tissue matrix. The specific MMPs under consideration were MMP-2 and MMP-9.

Methodology and Findings

• The enzyme levels in the BALF were measured using a method known as zymography. Furthermore, they used a Western immunoblotting technique to identify the gelatinases as MMP-2 and MMP-9.
• The study found that exposure to moldy hay/straw and HDS led to an increase in enzyme activity only in horses with heaves. The majority of this activity was composed of the pro- and active form of MMP-9.
• When exposed to a hay/straw challenge for 5 hours, the enzyme activity in the BALF of horses with heaves increased, but returned to normal by the fourth day.
• In contrast, inhaling LPS increased enzyme activity in both healthy horses and those with heaves.
• The study also found a significant correlation between the number of neutrophils (white blood cells) in the BALF and the levels of proMMP-9 and active MMP-9, but not with MMP-2.

Implications

• Gelatinolytic MMPs are agents that can cause inflammation, which implies that they could contribute to lung dysfunction and tissue damage in horses with heaves that are exposed to airborne organic stable dusts.
• This study provides important insights into the potential mechanisms underlying the inflammatory responses in heaves-affected horses, which could inform and guide treatment strategies for this condition.