For organisms like ours or those of our pets, oxygen is essential for energy production. The energy directly usable by our cells is generated through a reaction called "oxidative phosphorylation," which takes place in the inner membrane of mitochondria, the body’s powerhouses.
During normal metabolism, the state of oxygen evolves through successive stages. At each stage, potentially unstable intermediates appear—these are "reactive oxygen species" (ROS), far more reactive than the oxygen from which they originate. To stabilize, these ROS seek to bind, and this binding occurs at the expense of another molecule, which then becomes unstable, transforms into a free radical, and attempts to capture an electron from its surroundings. This can happen to lipids in cell membranes, proteins (such as a receptor or enzyme), or even DNA. A chain reaction then sets in.
Are Free Radicals Always Harmful?
Contrary to popular belief… No, free radicals aren’t always harmful! Many physiological functions actually depend on these ROS, thanks to their activating and/or regulatory effects in signaling pathways. They regularly act as messengers. The body may even deliberately increase radical production—such as during antimicrobial defense. When a pathogen is phagocytosed (engulfed by phagocytes, the "cleanup" cells that rid the body of "dangerous" agents or dead cells), phagocytes significantly boost their oxygen consumption and, ultimately, their radical production, which itself has antibacterial properties.
When Does Oxidative Stress Occur?
Under normal conditions, ROS are present in reasonable amounts, and balance is maintained by the body's own antioxidant systems: this is known as the antioxidant/pro-oxidant balance, or redox balance, being in equilibrium. This balance can easily be disrupted:
- Either through an overproduction of ROS (as seen in cases of stress, illness, or aging),
- or due to a decline in antioxidant defenses (such as in obese individuals).
This is when we refer to oxidative stress. When this imbalance is triggered by the body through the activation of ROS-producing systems (as in the previously mentioned antimicrobial defense), the antioxidant response is effective and sufficient, allowing a quick and smooth return to equilibrium. However, when production is high and prolonged—as in the case of chronic stress, for example—the antioxidant response proves inadequate, and the imbalance persists. This is when the body’s own components (amino acids, DNA, etc.) may be attacked or altered by ROS. This process contributes to the development of numerous diseases, including diabetes, heart and neurodegenerative diseases, joint conditions like osteoarthritis, and cancers.
How to Combat Oxidative Stress?
Combating Oxidative Stress: Key Approaches
- Reduce ROS formation,
- eliminate existing ROS,
- and boost endogenous antioxidants.
There are two sources of antioxidants: one is provided by diet through fruits and vegetables rich in vitamins C, E, carotenoids, flavonoids, and more. The other is endogenous—these include certain enzymes (such as superoxide dismutase, catalase, and ubiquinone), specific proteins (like ferritin, transferrin, ceruloplasmin, and albumin), as well as repair systems (endonuclease enzymes). Lastly, a few trace elements (notably selenium, copper, and zinc) act as cofactors for antioxidant enzymes.
Sources:
Oxidative Stress, Antioxidants, and Assessment of Oxidative Stress in Dogs and Cats: This literature review, published in the renowned *Journal of the American Veterinary Medical Association*, provides an overview of current knowledge on oxidative stress, defense mechanisms, and methods for evaluating this stress.
Reactive Oxygen Species and Oxidative Stress: This review examines the key properties of ROS and their paradoxical effects.
Oxidative Stress: This review examines the mechanisms behind oxidative stress, its key targets, and existing methods for detecting it (in human medicine).
