I'm assuming that you probably know what oxygen is. Or at least have heard of it in passing, whether in a high school science course or day-to-day living.
Image source: tenor.com
You also probably know how essential it is for life, plants and humans alike. Quick biology refresher: plants use carbon dioxide to create oxygen and “breathe” it out for us. Likewise, we breathe in oxygen (created by plants) and breathe out carbon dioxide (through a series of intense and complex chemical processes) for our plant buddies. It’s an endless cycle. We need plants, and plants need us.
What does it all have to do with ROS, you ask?
I'll explain.
ROS is the medical abbreviation for Reactive Oxygen Species. And, as you might have guessed, they contains oxygen. Whether you’ve heard of the ROS acronym in passing or this is the first time you’ve ever heard of it, this article will explain what ROS are and why you should know about them.
So let’s dive in!
What Are ROS?
Before we discuss reactive oxygen species' effects, we need to understand first what they are. And to do that, we need to revisit Chemistry 101.
Class is in session!
Simply put:
Reactive oxygen species are molecules (groups of atoms linked together) that contain an oxygen atom. Think of hydrogen peroxide. If you look up the chemical structure for hydrogen peroxide, you’ll see that it is made up of 2 hydrogen atoms and 2 oxygen atoms linked together.
Here’s a picture so you can see what I’m talking about. (H = hydrogen; O = oxygen)
The lines represent the chemical bonds that link the atoms together to form a cohesive group known as a molecule. Each molecule has unique properties based on the atomic structure and the order of atoms.
Back to ROS...
So, a reactive oxygen species is any reactive molecule that contains oxygen.
So far so good?
Common reactive oxygen species include:
○ Peroxide (like hydrogen peroxide)
○ Superoxide
○ Hydroxyl radicals
○ Single oxygen atoms
○ Alpha-oxygen
What makes a molecule reactive is that it interacts with other molecules, often in a way that our bodies don't like. These molecules are also often called free radicals.
We won’t go into the individual structures and functions of each of these, but just know that they are ROS.
Internal Sources of ROS
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Biologically, ROS can be normal byproducts in several chemical processes.
For example, consider the process of oxidative phosphorylation. When the body needs to create usable ATP for energy and movement, it initiates a process called oxidative phosphorylation in mitochondria (the energy warehouse of the cell). During this process, hydrogen atoms travel through the cell membrane via a series of proteins.
Their final destination? An oxygen molecule.
Once the hydrogen atoms reach the oxygen molecule, they typically join together to form water (H2O) as a byproduct. Leftover material, if you will. Occasionally though, the oxygen molecule reacts prematurely and forms a purely oxygen compound, aka a ROS (specifically a superoxide). Fortunately, this ROS formation occurs rarely.
Another source of reactive oxygen species creation occurs in the mitochondria. In tissues where steroids are produced, ROS production occurs when steroid-based hormones, like estrogen and testosterone, are formed from cholesterol.
Additionally, reactive oxygen species aren’t always a byproduct; they’re also essential for maintaining homeostasis in the body. Several studies suggest that ROS are necessary for normal brain function and memory. Specifically, ROS may be instrumental in the plasticity of the brain; that is, the brain’s ability to change over time. For example, the amount of grey matter in the brain, synapse strength / weakness, transferring functions of the brain to new physical locations, etc.
External ROS Stimulants
As with most things in life, there must be balance. It’s possible to have too much of a good thing. And that is especially true with reactive oxygen species.
Taking a little break from reactive oxygen species, let’s discuss oxidative stress / cellular stress for a second.
For those who aren’t familiar with oxidative stress, it essentially compares the number of free radicals to the number of antioxidants in a given area.
If there are more antioxidants, then the area remains in homeostasis.
But if there are more free radicals, then your cells are said to be in a state of cellular or oxidative stress.
Chronic levels of oxidative stress are thought to be connected to tissue decay and cellular death.
Image source: slideshare.net
Now, going back to reactive oxygen species.
Remember how I said one study has evidence suggesting ROS may be important for neural function? Well, according to that same study, having excessive amounts of reactive oxygen species can be detrimental to neurological tissue too. Their evidence suggests that while some ROS are important for neural plasticity, too many ROS could be the cause for age-related memory dysfunction.
AND, excess ROS could potentially increase the chance for diseases like schizophrenia, Parkison’s disease, Alzheimer’s disease, and depression.
Oof.
Remember how I said that some ROS are a natural byproduct of chemical reactions? During these reactions, the ROS concentration in the body is low. But did you know that reactive oxygen species can also form in response to other factors?
In particular, ROS have been linked to UV damage in the skin, a leading cause of skin cancer. There are three types of UV rays:
○ UV-A
○ UV-B
○ UV-C
UV-B bands of light cause direct damage to the skin; whereas UV-A rays are a little more sneaky. They initiate indirect damage by activating ...you guessed it, reactive oxygen species! This activation of ROS then leads to oxidative stress, which is what causes some types of skin cancer AND may be responsible for premature signs of aging, like premature wrinkles & lines and loss of skin tone & texture.
Another environmental source for ROS production is heat stress. Like “hellish, blazing hot summer” type of heat stress. For those who live near the equator or work in high-temperature working conditions, you know what I mean.
Image source: gifimage.net
But did you know that ROS and heat exhaustion & heat stroke are related?
During intense heat spikes, the number of superoxides (a type of ROS) in mitochondria significantly jumps, and the hyperthermic conditions causes the concentration of superoxide dismutase (a scavenger that combats superoxides) to decrease.
Furthermore, excess heat stress can cause an overproduction of transitional ion metals, which can create even more reactive oxygen species.
Starting to see the pattern?
Heat Shock Proteins
Now, the human body does have a defense mechanism in place to fight extreme conditions: heat shock proteins. Most organisms produce these proteins in response to elevated environmental temperatures to prevent raised body temperatures. Additionally, these proteins have another cool feature. Most protein synthesis stops during high temps.
However, heat shock protein synthesis actually starts in response to raised temperatures. Thank goodness since they fight extreme heat.
But how exactly do they do that?
Glad you asked.
When the body temperature increases, other proteins can lose their structure and thereby their function. Just like boiling an egg changes its internal structure and function irreversibly, heating proteins can change a protein’s shape and properties. Permanently. This process is known as denaturation.
Well, heat shock proteins prevent that from happening. They facilitate the refolding and folding of proteins that have started to degrade.
Pretty neat, eh?
However, they can only prevent so much damage. After a certain point, they too will degrade.
ROS Scavengers
I briefly mentioned superoxide dismutase earlier, but now I want to cover that more in-depth. As I stated above, superoxide dismutase breaks down superoxide. Superoxide dismutase is known as a scavenger. Scavengers are similar to antioxidants in that they prevent unwanted chemical reactions and/or remove unwanted particles and chemical compounds.
In this case, superoxide dismutase is a ROS scavenger because it breaks down superoxide (a ROS) before it can cause tissue damage.
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There are several other types of ROS scavengers, like:
○ Sodium pyruvate
○ Mannitol
○ Carboxy-PTIO
○ Trolox (α-tocopherol)
○ Ebselen / uric acid
○ Sodium azide
○ MnTBAP / Tiron
Each of these ROS scavengers target a specific ROS, like superoxide dismutase breaks down superoxide.
Besides ROS scavengers and heat shock proteins, the human body has other ways to break down excess ROS molecules. But these are two of the primary sources.
Summary (and a Quick Recap)
I know that was a lot of technical terms and scientific concepts, so let’s have a quick recap.
ROS stands for Reactive Oxygen Species; they are molecules containing reactive oxygen atoms. In low concentrations, ROS can be helpful for memory and other neural functions, as well as various other functions throughout our bodies. But in high concentrations, ROS can damage tissue and cause premature aging and cellular death.
ROS can be produced by internal and external factors.
Common ROS External Factors
○ UV-A rays - responsible for some types of skin cancer
○ Heat exposure - responsible for breaking down internal proteins, leading to symptoms of heat stroke & heat exhaustion (heat shock proteins prevent this from happening to an extent)
Primary ROS Internal Factors
○ Oxidative phosphorylation - premature reaction with oxygen molecule in mitochondria creates superoxide
○ Steroid hormone production - formation of steroid hormones leads to the creation of superoxides and hydrogen peroxide
ROS scavengers prevent ROS concentrations from rising too high. However, chronically high levels of ROS can still be harmful to the body.
References
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5709332/
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5126069/
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6463655/
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3963566/
- https://www.liebertpub.com/doi/10.1089/ars.2010.3208
- https://journals.sagepub.com/doi/10.4137/JEN.S39887
- https://www.ncbi.nlm.nih.gov/pubmed/26589391
- https://cshperspectives.cshlp.org/content/5/2/a012559.short
- https://www.ncbi.nlm.nih.gov/pubmed/10693912
- https://www.tandfonline.com/doi/full/10.3109/02656736.2014.971446
- https://www.britannica.com/science/denaturation
- https://pdfs.semanticscholar.org/b998/9fba5d66a9470d82fbfcb660d6a94e0c98f1.pdf
- https://www.ncbi.nlm.nih.gov/pubmed/25354680
- https://www.thermofisher.com/us/en/home/references/molecular-probes-the-handbook/tables/scavengers-of-reactive-oxygen-species.html
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5731988/
- https://www.sciencedirect.com/science/article/pii/S0163725814000941
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