Oxidative stress describes an imbalance between cell production and elimination of by-products of oxygen degradation. These byproducts, known as reactive oxygen species (ROS), are important for cell function but cause damage in large amounts. ROS belong to a larger category of highly reactive chemicals called free radicals. Because cells need ROS to function, some researchers have described oxidative stress as a good thing in certain settings. Others say that oxidative stress, by definition, is bad.
Oxidative damage is implicated in aging and in several diseases. Chemicals that inhibit oxidation and the production of ROS are called antioxidants. Some research suggests that antioxidants may help limit oxidative damage. However, it is not known how many or to what effect.
What causes oxidative stress?
ROS are produced naturally when the body breaks down diatomic oxygen (O2) as part of cellular respiration, the process of extracting energy from glucose (sugar). In organisms that have one, it happens in the mitochondria, the so-called powerhouse of the cell. As part of the last step of cellular respiration, the cell separates electrons, or negative subatomic particles, from glucose byproducts. This allows the cell to make a molecule called adenosine triphosphate (ATP), its main source of energy. The cell needs oxygen to accept electrons at the end of this process, and most of the oxygen molecules are eventually turned into water.
However, some oxygen molecules receive fewer electrons and instead are turned into free radicals, especially ROS. The missing electrons of these substances are what make them extremely reactive, and they will react with many substances in the cell to gain electrons and become more chemically stable. Some common ROS are peroxides (such as hydrogen peroxide), superoxide, and hydroxyl radical.
“We’re constantly making these reactive oxygen species, as we call them, in every cell in the body,” Ursula Jakob, a professor of molecular, cellular and developmental biology at the University of Michigan, told CNET. Besides being a byproduct of respiration, ROS are used in cell signaling or sending messages within or between cells.
Ursula Jakob studies the role of oxidative stress on host defense and aging. His NIH-funded research has provided insight into exactly how physiological oxidative bleach kills bacteria and how bacteria’s own defenses can protect against cellular stress caused by bleach. She obtained her doctorate in 1995 at the University of Regensburg.
Immune responses, radiation exposure, and other cellular responses to pollutants or toxic substances can also generate ROS.
However, the production of ROS does not cause harm on its own, since cells need ROS to function. Cells use antioxidants to get rid of excess ROS, limiting potential damage. When the amount of ROS overwhelms the cell’s antioxidant system, ROS builds up, creating oxidative stress, Jakob said. This could be due to increased production of ROS or decreased elimination from the cell.
What are the effects of oxidative stress?
Normally, cells use ROS as part of their signaling processes – sending messages to other parts of a cell or to other cells. However, an excess of ROS causes oxidative damage, that is, the oxidation of certain parts of the cell. Just as the oxidation of iron forms rust, this process can transform and damage the molecules that make up cells, which includes DNA and RNA mutations, misfolded proteins, and other types of damage. to sugars and lipids.
Cells can repair a certain amount of damage, but if it’s too much, it can trigger apoptosis (programmed cell death), a kind of self-destruction mechanism. In severe cases, it can also cause necrosis, which is when cells are so damaged that they are destroyed prematurely, leading to tissue death.
Research suggests that oxidative stress plays a role in many conditions. Some of the most well-established of these are type 2 diabetes, cancer (opens in a new tab)and hardening of the arteries, or atherosclerosis (opens in a new tab).
Oxidative stress has also been linked to several different neurodegenerative diseases, including Alzheimer’s disease, Parkinson’s disease, amyotrophic lateral sclerosis (ALS), and multiple sclerosis (MS). This relationship was first observed in the late 1980s, according to a 2004 article published in Nature Reviews Drug Discovery. (opens in a new tab), with growing evidence that oxidative stress plays a role in neurodegenerative diseases since then. A 2016 article published in Experimental Neurology (opens in a new tab) reviewed the evidence for the role of oxidative stress in MS as early as 1987.
“Neurons that are at risk during [Alzheimer’s Disease]they are profoundly affected by all known types of oxidative damage,” said George Perry (opens in a new tab), professor of neurobiology at the University of Texas. In Alzheimer’s disease patients and some Parkinson’s disease patients, Perry told CNET, signs of oxidative damage appear in the cytoplasm, or main body, of certain neurons, which are full of ” mitochondrial waste” – enzymes, as well as copper and iron molecules, which are usually found only in mitochondria.
Oxidative damage is clearly part of Alzheimer’s disease. However, researchers have not been able to determine exactly how and to what extent oxidative stress throughout a person’s life contributes to disease. It’s also hard to say whether it causes aging — an idea that has long been proposed by researchers, Jakobs said.
“The jury is still out on whether that’s actually the case” for aging, she said.
What are the risk factors for oxidative stress?
Smoking “can generate some of these reactive species,” said Marino Resendiz (opens in a new tab), professor of chemistry at the University of Colorado at Denver. “So that can lead to damage,” he told GameSpot. “UV radiation, which can cause oxidative damage, is also linked to skin and other types of cancer, according to the American Cancer Society. (opens in a new tab).
Some weak evidence suggests that eating foods containing antioxidants may reduce oxidative stress and therefore a diet deficient in antioxidants may be a risk factor. Some common foods high in antioxidants include broccoli, carrots, potatoes, spinach, and many berries, among others.
However, the link between antioxidants and oxidative stress is unclear. For example, the consumption of supplements containing antioxidants did not decrease signs of oxidative stress in the brains of people with Alzheimer’s disease in a 2012 clinical trial published in JAMA, and was even associated with a decline. cognitive faster. However, a 2019 review article (opens in a new tab) found evidence that taking a supplement containing vitamin E, which is an antioxidant, may be helpful for people with Alzheimer’s disease, including evidence from clinical trials.
Obesity can increase oxidative stress because free radicals can bind to fats and damage them. Therefore, lifestyle changes such as exercise and a balanced diet could help limit oxidative stress, Jakob said.
“Obesity is a huge risk factor,” she said. In a wide variety of model organisms, from yeast to primates, Jakob said, exercise and calorie restriction are associated with less oxidative damage to cells. But this is not a simple effect. Although she said exercise and calorie restriction may actually increase oxidative stress, in a 2019 study published in Nature (opens in a new tab)she and other researchers found that in a species of roundworm, increased oxidative stress early in life may help protect against later oxidative damage.
Although she emphasized that this research was not in humans, Jakob said it does emphasize the importance of ROS, at least in controlled amounts.
“It’s not like, oh, we’re removing all reactive oxygen species and that’s healthy,” she said. “In this case, it’s actually healthy to have higher levels of reactive oxygen species.”