These microscopic compounds help abolish damaging free radicals within horses
Oxygen, while necessary for fueling life, possesses damaging doppelgängers called reactive oxygen species. These highly charged, reactive forms of oxygen, known as free radicals, contribute to mass destruction at a microscopic level. Luckily, the body comes equipped to handle free radicals using vitamins, proteins, enzymes, and minerals that exert antioxidant activities. These antioxidants help cells, tissues, and organs weather harmful free radical damage.
To better understand the antioxidant and free radical “dance,” picture a team roping event at a rodeo. The steers are the free radicals while the horse and rider pairs are the antioxidants. The steers wait in a holding pen, “metabolizing,” when suddenly one is released, highly reactive and careening across the ring. The header, hot on the steer’s trail, easily subdues it with the help of the heeler and minimizes collateral damage and bystander injury inflicted by the errant free radical.
Where do free radicals come from, and how do antioxidants regain control of these wayward molecules? We’ll answer those questions and more, focusing on your horse’s main antioxidant systems.
Why Horses Need Antioxidants
All metabolic processes, even the normal, everyday chemical reactions that take place in the body to sustain life, generate free radicals. Take, for example, the breakdown of sugar molecules (glucose) in muscle cells to drive muscle contraction.
“Sugar molecules from the horse’s feed are absorbed from the small intestine and circulate throughout the body in the bloodstream,” says Carey Williams, PhD, an equine extension specialist at Rutgers University, in New Brunswick, New Jersey, who has studied exercising horses and the effects of oxidation and antioxidant supplementation for 20 years. “Muscle cells take up and metabolize those sugar molecules to produce energy, water, and carbon dioxide. Oxygen plays a key role in breaking down or ‘oxidizing’ sugar into these base components.
In this representation of how sugar is oxidized, the reaction looks perfect: Six oxygen molecules react with one sugar molecule to produce six carbon dioxide and water molecules. But oxygenation is far from perfect.
“In real life, oxidation is an imperfect process that often results in certain oxygen molecules escaping from this chain of events,” says Williams.
A more realistic image of glucose metabolism looks like this:
Here, O2-, HO•, and H2O2 are types of free radicals or reactive oxygen species— superoxide, hydroxyl , and hydrogen peroxide, respectively.
“These free radicals are reactive because they each have unpaired electrons,” says Williams. “These lonely electrons give the molecule a negative electric charge that makes them seek out positively charged molecules to become neutral. In fact, the negatively charged free radicals are so driven to become neutral that they blindly blunder around the muscle cell, smashing into other molecules, enzymes, cell membranes, and even DNA. When these reactive oxygen species overwhelm the system, we term that ‘oxidative stress.’ ”
Free Radicals Everywhere
A common source of free radical generation is muscle metabolism that’s producing energy for exercise.
“All cells need to produce energy, so all cells in the body produce free radicals,” says Williams.
Inflammation, immune cell activation, infection, intense or endurance exercise, UV radiation exposure, cancer, and aging can generate free radicals, as well. Exposure to certain compounds in the environment can also produce free radicals. Examples include chemicals ingested or inhaled; think water and air pollution, some drugs (e.g., antibiotics such as cyclosporine and gentamicin), secondhand cigarette smoke, and heavy metals (lead, cadmium, mercury).
The Effects of Free Radical Damage
As Williams described, oxidative damage occurs when excessive amounts of free radicals get produced. Those free radicals bounce around the cells, causing= damage to everything in their wake—cell membranes, structural proteins, and enzymes (proteins that act as biological catalysts), as well as DNA. This article continues in the December 2020 issue of The Horse: Your Guide to Equine Health Care. Subscribe now and get an immediate download of the issue to continue reading. Current magazine subscribers can access the digital edition here.
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