Overview: 
A mucolytic is a substance that can break down the “stickiness” of the mucus in the lungs. This is helpful when there is a large number of small particles in the area, like you would find in wildfires.
N-Acetyl Cysteine (NAC) has been a known mucolytic for the last 60 years. NAC has also been shown to reduce the oxidative stress that the wildfire smoke creates. It does this by reversing the oxidate stress state and restoring glutathione levels within the cells. The glutathione is depleted following exposure to wildfire smoke. The increase in oxidative stress due to the reactive oxygen species results in an inflammatory response. This response is not limited to the lungs, but also is picked up in the bloodstream, with increased inflammatory markers in the blood stream, and even within the linings of the blood vessels.
How can you help your horse when there is excessive smoke from wildfires?
- N-Acetyl Cysteine is one possible choice for nutritional support.
- Spirulina’s anti-inflammatory properties can also be helpful for nutritional support.
- Shielding the horse from smoke as best as possible.
- Avoid excessive exercise, as the exercise creates ROS, as well as causing the horse to breathe deeply into their lungs.
Deep Dive:
A review study published in Particle and Fibre Toxicology discussed the effects of wildfire smoke on cardiovascular health (Chen et al., 2021). Little is discussed about the impact of wildfires. Globally, it’s estimated that there are over 300,000 deaths annually that are attributable to wildfire smoke. Critically, cardiovascular disease has been shown to be associated with increased levels of air pollutants. Wildfire smoke increases the level of these pollutants.
A part of this review study focused on a 2008 peat bog fire in North Carolina and the effects that it had on the population in the area. They found that the effects of the increase in small-diameter particulate matter resulted in an increased incidence of hypertension, as well as cardiac events. These same correlations occurred in the 2006-2007 wildfires in Victoria, as well as a large-scale study in Sydney running from 2004-2015.
When the review was conducted, we already knew that wildfire smoke caused vascular injuries in the lungs (Koivunen et al., 1996). A 2005 study measured the glutathione levels in cultured endothelial cells which were exposed to wood smoke. N-Acetyl Cysteine was shown to result in a reduction of Reactive Oxygen Species (Liu et al., 2005).
Most studies regarding cardiovascular damage occurred with regards to humans because of the impact on human mortality. However, studies have also been done in horses, with oxidative stress and lung functioning. ROS in horses leads to proteolytic activity which impairs lung functioning. In an older study, it was shown that N-Acetylcysteine inhibited the destructive proteolytic activity.
References
Chen, H., Samet, J. M., Bromberg, P. A., & Tong, H. (2021). Cardiovascular health impacts of wildfire smoke exposure. Part Fibre Toxicol, 18(1), 2. https://doi.org/10.1186/s12989-020-00394-8
Koivunen, A. L., Maisi, P., Fang, W., & Sandholm, M. (1996). Inhibition of the protease activity in tracheobronchial aspirates of horses with chronic obstructive pulmonary disease. Am J Vet Res, 57(5), 603-607.
Liu, P. L., Chen, Y. L., Chen, Y. H., Lin, S. J., & Kou, Y. R. (2005). Wood smoke extract induces oxidative stress-mediated caspase-independent apoptosis in human lung endothelial cells: role of AIF and EndoG. Am J Physiol Lung Cell Mol Physiol, 289(5), L739-749. https://doi.org/10.1152/ajplung.00099.2005