Understanding Free Radicals, Reactive Oxygen Species (ROS), Antioxidants, and Oxidative Stress

1. What are free radicals, their sources, and how do they affect our body?

Free radicals are unstable molecules with unpaired electrons, making them highly reactive. A common category of free radicals includes Reactive Oxygen Species (ROS), which are oxygen-containing molecules that form during normal metabolic activities.

Sources of Free Radicals and ROS:

• Internal sources:
  • Cellular respiration in mitochondria, where oxygen is used to produce energy.
  • Immune responses, such as the production of ROS to fight pathogens.
• External sources:
  • Environmental pollutants.
  • Cigarette smoke.
  • UV radiation and ionizing radiation.
  • Industrial chemicals and pesticides.

Effects on the Body:

• Excessive free radicals, including ROS, can damage cellular components like DNA, proteins, and lipids through oxidative reactions.
• This damage contributes to:
  • Premature aging and tissue degeneration.
  • Chronic diseases such as cancer, cardiovascular disease, diabetes, and neurodegenerative disorders (e.g., Alzheimer’s and Parkinson’s).
  • Inflammation and weakened immune response.

2. What are antioxidants, and how do they neutralize free radicals, including ROS?

Antioxidants are molecules capable of neutralizing free radicals and ROS by donating an electron without becoming unstable themselves. This halts the chain reaction of oxidative damage in the body.

Types of Antioxidants:

• Endogenous (produced by the body):
  • Enzymatic antioxidants: Glutathione peroxidase, superoxide dismutase (SOD), and catalase.
  • Non-enzymatic antioxidants: Glutathione and coenzyme Q10.
• Exogenous (obtained from diet):
  • Vitamins: Vitamin C, Vitamin E.
  • Minerals: Selenium, zinc.
  • Phytochemicals: Flavonoids, carotenoids, and polyphenols.

Mechanism:

Antioxidants neutralize free radicals and ROS by:

• Donating electrons, which stabilizes the reactive molecules.
• Reducing oxidative stress and preventing cellular damage.

3. Why is this process called oxidative stress?

Oxidative stress arises when there is an imbalance between free radicals/ROS and the body’s antioxidant defenses.

Why the term "oxidative"?

• Oxidation: Refers to chemical reactions where molecules lose electrons, often involving oxygen.
• ROS are a primary driver of these oxidative processes.

Why "stress"?

• The physiological strain caused by excessive ROS/free radicals damages vital biomolecules and disrupts normal cellular functions.
• Prolonged oxidative stress leads to inflammation, tissue damage, and the progression of various diseases.

4. Do antioxidants become free radicals after donating electrons?

In most cases, antioxidants do not become free radicals after donating electrons because they are inherently stable.

Details:

• Stability: Antioxidants like Vitamin C and Vitamin E are structured to remain stable after electron donation.
• Regeneration: Some antioxidants work synergistically to regenerate one another. For instance, Vitamin C can regenerate Vitamin E after it neutralizes a free radical.

Exception:

Under extreme oxidative stress, if antioxidant levels are depleted or overwhelmed, they might fail to regenerate and could, in rare cases, become reactive themselves. This scenario highlights the importance of a balanced diet and lifestyle to maintain antioxidant levels.

By maintaining adequate levels of antioxidants, the body effectively combats the damaging effects of free radicals and ROS, thereby reducing oxidative stress and its associated risks.