Free Radicals : Role In Common Human Diseases.

Introduction 

Free radicals, as the name suggests are molecules which contain one on more unpaired electrons. And because they contain unpaired electrons, they possess the property to affect our cellular processes which in turn affects our overall health. And these free radicals are natural products of many of our metabolic (think of it as your cellular stomach) processes.

So to sum it up, a free radical is simply defined as any chemical species capable of independent existence that contains one or more unpaired electron which is easily accessible for interacting with another chemical species. Free radicals that are present in our body are reactive oxygen species(ROS) and reactive nitrogen species(RNS).

Free radicals are present in different forms in our body; one in a regulated (controlled) from where they perform essential roles and the others exist in a free form where they can interact with various processes of our body. And these interactions based on its nature and degree can have beneficial and detrimental effects on our health.

The effect and nature  of naturally produced free radicals(by our cellular components such as mitochondria, peroxisomes, endoplasmic reticulum, and in cells of our immune system, etc.)  and the external ones (alcohol, tobacco, pollution, smoke, heavy metals, industrial solvents, pesticides, drugs such as halothane, paracetamol and radiation) has been researched to understand that free radicals too, have various effects on our health and play a role in many diseases in humans. This article makes an attempt to understand the role of free radicals in some of the most important human diseases.

Free radicals and diseases

Reactive oxygen species (ROS), and reactive nitrogen species ( RNS) collectively constitute the free radicals and other reactive chemical species in our body. Free radicals can have harmful effects on important biological molecules such as nucleic acids (RNA, DNA), lipids, and proteins and hence can have adverse effects on our health. The oxidative (reactive) stress induced by free radicals is involved in several human diseases such as neurodegenerative disorders  (Parkinson’s disease-PD, Multiple sclerosis- MS, and Alzheimer’s disease-AD), diabetes mellitus, cardiovascular diseases (hypertension and atherosclerosis (narrowing of arteries because of building up of plaque).

The ROS and the RNS perform the dual role as both beneficial and detrimental compounds to the processes of life inside of us. At low and moderate levels, they are involved in significant functions such as immune function ( the defense mechanism of our body against harmful microorganisms), in cellular signaling (which helps in coordination of our cellular processes) and in regulating the conditions of the cell. But, at high concentrations, both ROS/RON exert reactive stress (oxidative and nitrosative stress respectively) on our cells which can lead to the damage of cellular components. Hence, ROS and RNS levels in the cells must be healthy and any shift in their concentrations can alter the balance and have consequences for our health.

Now let us try to understand the role of free radicals in some of the most common diseases affecting humans.

  1. Diabetes mellitus:  Diabetes mellitus is a diverse group of long-standing disorder where the patients exhibit characteristic enhanced blood glucose levels resulting from defective insulin secretion (in type I diabetes), resistance to insulin action (in type II diabetes), or both. The enhanced blood levels (known as hyperglycemia) in diabetes is associated with increased production of free radicals or decreased activity of the antioxidant system present in our body. And this induces increased free radicals in our cellular system which can have adverse effects on our body and health.
  2. Neurodegenerative Diseases : The central nervous system (consisting of brain and the spinal cord) has been reported to be more vulnerable to free radicals due to the high consumption of oxygen, lower levels of antioxidant enzymes and its natural high lipid content The regions of brain such as hippocampus, substantia nigra, and the striatum has been particularly observed to be more susceptible to stress by free radicals. The oxidative stress brought about by free radicals has been implicated in many neurodegenerative diseases including Alzheimer’s, Parkinson’s, Huntington’s, and multiple sclerosis(MS).
  3. Cancer: Cancer is one of the leading causes of death in humans. Cancer cells when compared to normal cells, show elevated levels of oxidative stress partly due to the activation of oncogenes (cancer-promoting genes) and loss of tumor suppressor (anti-tumor) genes. ROS (Reactive Oxygen Species) can alter growth signals and the expression of genes to help the continuous growth of cancer cells. ROS has the ability to damage DNA by inducing a change in the DNA chemistry of the cell and can lead to the proliferation of cancer cells.  The role of free radicals in colorectal cancer, breast cancer, bladder cancer, prostate cancer, and lung cancer has been well studied and documented.
  4. Cardiovascular diseases:     This is a class of diseases involving the blood vessels (arteries, capillaries, and veins) and the heart. They include cardiac diseases and the diseases pertaining to the circulatory system in the brain, kidney, etc. For example, in atherosclerosis which refers to a condition leading to the hardening of the arteries, there is a significant imbalance between oxidants and antioxidants resulting in oxidative stress that has been reported. Hypertension affects about 40% of total adult population and people affected by hypertension are more prone to stroke, heart disease, and kidney failure. And free radicals have been implicated in contributing the change in the physiology of the vascular cells and also leading to hypertension. So there is consistent evidence of free radicals and their involvement in cardiovascular diseases.
  5. Cataract: Cataract is one of the most common causes of visual impairment, affecting almost 25 million people globally. Cataract is characterized by the opacity of the eye lens which results in visual impairment. Even though multiple factors such as smoking, drugs, genetic factors, diabetes, radiation, and malnutrition has been implicated in its incidence, free radical-induced oxidative stress has been considered one of the major cause for cataract disorder. Oxidation of DNA, lipids, and proteins has been observed in cataract lenses and this has been shown to induce the opacity of the eye lens seen in cataract patients.
  6. Asthma: Asthma is one of the most common diseases affecting the airways of the lungs and is one of the major global health problems. Many studies have suggested that oxidative stress brought about by the build-up of free radicals contributes to tissue damage in Asthma patients. Free radicals have been implicated in various respiratory diseases such as respiratory distress syndrome, chronic bronchitis, asthma, and chronic obstructive pulmonary disease.

To conclude, free radicals are a result of normal metabolic processes in our body which are involved in many bodily processes and disorders. When there is an imbalance between the antioxidants and the oxidants, free radicals accumulate inside of our cells leading to the damage of proteins, lipids and nucleic acids in our body. This can lead to tissue degeneration and other cellular abnormalities resulting in the many human disorders. We need to strive to keep the balance of free radicals in our body so as to attain an ability to promote good health.

Disclaimer: The above article is sponsored by Thyrve, the world’s first Gut Health Program that incorporates microbiome testing and personalized probiotics to ensure a healthier gut, happier life, and a brighter future.