Effect of the mineral exposome on the pro-inflammatory impact of inhalable mineral dusts generated from racehorse working soils

Air quality is a main determinant of human and animal respiratory health. Among animal species, racehorses are particularly sensitive to the effects of increased respirable dust levels¹.

In equine medicine, lower airway inflammatory conditions are commonly encountered and are a significant cause of poor performance and a major concern for animal welfare².

Respiratory diseases in horses is commonly associated with exposure to organic dust derived from bedding and feed materials³. However, the potential contribution of inorganic mineral dust, such as respirable crystalline silica (RCS), to equine lung inflammation is currently unexplored.

RCS is a pro-inflammatory agent in many mammalian species, inducing macrophage activation via the inflammasome pathway, and has been implicated in the development of chronic respiratory diseases in humans, including pulmonary disease, silicosis, and lung cancer⁴.

In this study, we challenge the hypothesis that inorganic dust generated from equine working soils may adversely affect respiratory health in horses. Investigating the respiratory exposure pattern (mineral exposome) is crucial for understanding the environmental impact of inorganic dust on equine respiratory health.

To this aim, we assessed the quantitative composition of racetrack soils and assessed the potential toxicity associated with the respirable inorganic fractions of training and racing track soils.

A prospective proof-of-concept study on a limited number (n=7) of representative samples from working soils of six different racetracks was carried out.

Particle size distributions (PSD) and the quantitative composition were determined by X-Ray Powder Diffraction (XRPD) and Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM/EDS).

To evaluate the potential toxicity of the samples, in chemico approaches were employed, including a membranolytic activity assay and a cell-free radical generation assay to assess dust surface .

The particle size distribution of the soil samples revealed that over 90% of the fine fraction (<20 µm) had an equivalent circular diameter (ECD) of less than 5 µm, consistent with the size range of respirable dust.

The predominant mineral phases identified in all soil samples were silica (mainly quartz), silicates and alumino-silicates (K-feldspars and plagioclase), while minor phases included carbonates, titanium oxides, and iron oxides.

Although the main mineral classes were consistent among soils from different racetracks, the membranolytic activity, i.e., the ability of dust to induce cell membrane lysis, varies significantly among the samples.

On three representative soil samples with high, medium and low hemolytic activity ('Bologna,' 'Ferrara,' and 'Vinovo 1') were also analyzed with the cell-free radical generation assay to assess the potential of mineral soil surfaces to generate free radicals. The results indicated no correlation between the membranolytic activity of the soils and their ability to generate free radicals, as all three samples exhibited no significant radical activity.

Future studies will concentrate on investigating potential correlations between specific mineral phases in racetrack soils and their associated toxicity.

 

References:

[1] S.L. Raymond, A.F. Clarke, Australian Equine Veterinarian 1998, 16, 21-31

[2] K.J. Allen, W.H. Tremaine, S.H. Franklin, Equine Veterinarian 2006, 36, 529-34.

[3] K.M. Ivester, L. L. Couëtil, N.J Zimmerman, Journal of Veterinary Internal Medicine 2014, 28, 1653-1665.

[4] R.F. Hoy, D.C. Chambers, Allergy.2020, 75(11), 2805-2817.