Oxidants are highly reactive molecules that naturally occur in the body and the environment, but excessive levels compromise cellular function. The damage caused by these molecules is linked to the aging process and the development of numerous chronic health conditions. These reactive species are constantly generated, demonstrating the delicate balance required for maintaining the integrity of biological systems.
What are Oxidants
An oxidant is defined as a substance that accepts electrons from another molecule during a chemical reaction, a process known as oxidation. This reaction destabilizes the molecule that loses the electron.
A specific and damaging type of oxidant is the free radical, a molecule that possesses one or more unpaired electrons in its outer shell. This electronic imbalance makes the free radical unstable and extremely reactive. To regain stability, the free radical aggressively seeks to steal an electron from any stable molecule nearby.
The most common oxidants in biological systems are Reactive Oxygen Species (ROS), which are derived from oxygen. Examples include the superoxide anion radical and the hydroxyl radical, the latter being one of the most destructive free radicals in the body.
Sources of Oxidants
Oxidants are generated from two primary origins: internal (endogenous) processes within the body and external (exogenous) environmental exposures. Endogenous sources are oxidants produced naturally as unavoidable byproducts of normal cellular metabolism.
The body’s energy production system, located within the mitochondria, is the major site of internal oxidant generation. During the conversion of food into energy, the mitochondrial electron transport chain leaks electrons, which react with oxygen to form Reactive Oxygen Species.
Other endogenous sources include the inflammatory response, where immune cells intentionally produce oxidants to destroy invading pathogens. Exogenous sources are introduced from outside the body through lifestyle and environment.
These external exposures include air and water pollution, tobacco smoke, certain heavy metals, and UV radiation. Poor dietary choices, such as high sugar intake or highly processed oils, also increase the body’s oxidant load.
The Mechanism of Cellular Damage
Cellular damage begins when an unstable oxidant encounters a stable biomolecule, such as a lipid, protein, or DNA. The oxidant abstracts an electron from the stable molecule, instantly converting the previously stable molecule into a new, unstable free radical. The newly formed radical attempts to stabilize itself by stealing an electron from an adjacent molecule, initiating a destructive chain reaction that spreads damage throughout the cell.
When oxidation occurs in the cell membrane, free radicals attack polyunsaturated fatty acids, causing lipid peroxidation. This process alters the structure and fluidity of the cell membrane, compromising the cell’s ability to regulate its internal environment.
Oxidants also target proteins, modifying their amino acid side chains and causing them to lose their structure and function. This damage can inactivate enzymes and alter cellular signaling pathways.
When oxidants reach the cell nucleus, they can cause significant damage to DNA by inducing single-strand breaks, double-strand breaks, and base modifications. This molecular damage leads to errors in genetic replication and is linked to aging and chronic diseases.
When the rate of oxidant production exceeds the cell’s ability to neutralize them, the resulting imbalance is scientifically defined as oxidative stress. This condition is central to understanding the progression of oxidant-related diseases.
The Body’s Natural Defense System
The body maintains a comprehensive defense system against oxidants, primarily utilizing molecules known as antioxidants. Antioxidants function by safely donating an electron to the highly reactive oxidant, neutralizing it and stopping the damaging chain reaction. This electron donation stabilizes the free radical without becoming unstable itself.
The body’s defenses are categorized into two main groups: enzymatic and non-enzymatic antioxidants. Enzymatic antioxidants are large protein molecules produced internally that catalyze reactions to break down free radicals.
Examples include superoxide dismutase (SOD), which converts the superoxide radical into hydrogen peroxide, and catalase, which subsequently breaks down hydrogen peroxide into harmless water and oxygen.
Non-enzymatic antioxidants are smaller molecules obtained primarily through diet, offering an immediate line of defense against oxidative challenges. This group includes fat-soluble vitamins, such as Vitamin E (tocopherol), which protects cell membranes from lipid peroxidation, and water-soluble compounds like Vitamin C (ascorbic acid). Other non-enzymatic antioxidants are carotenoids and polyphenols, which are commonly found in fruits and vegetables and directly scavenge free radicals.