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"Antioxidants are compounds that inhibit oxidation (usually occurring as autoxidation), a chemical reaction that can produce free radicals."
For example Vitamin C (normally Antioxidant), Vitamin e, and Trolox are anti-oxidants.
Berries: Blueberries, Strawberries, Raspberries, Blackberries
Fruits: Grapes, Pomegranates, Oranges, Apples
Vegetables: Spinach and other leafy greens, Kale, Broccoli, Brussels sprouts
Nuts and Seeds: Walnuts, Almonds, Flaxseeds, Chia seeds
Beverages: Green tea, Black tea
Spices and Herbs: curcumin, Ginger, Garlic, Cinnamon
Other: Dark chocolate (with high cocoa content), Beans and legumes, Tomatoes (rich in lycopene)
Antioxidants are compounds that help neutralize free radicals—unstable molecules that can damage cells and contribute to the development of chronic diseases including cancer.
Cancer Prevention:
Mechanism: Antioxidants protect cells from oxidative damage caused by free radicals, which can lead to mutations in DNA. Over time, these mutations might initiate or promote the growth of cancer cells.
Dietary Role: Eating a diet rich in antioxidants (fruits, vegetables, and other plant-based foods) has been associated with a lower risk of some cancers. Many epidemiological studies suggest that diets high in natural antioxidants are linked to a reduced risk of cancer.
During Cancer Treatment:
Controversy: There is debate about whether taking antioxidant supplements during chemotherapy or radiation therapy is beneficial or harmful. Many therapies such as Chemotherapy raise the ROS(Reactive oxygen Species) intentionally to kill cancer cells. Some theory applies that antioxidants might prevent the ROS from being raised, and hence reduce treatment effectiveness. Some laboratory and clinical studies indicate that antioxidants might protect not only healthy cells but also cancer cells against the oxidative damage intentionally induced by these treatments. This could potentially reduce the effectiveness of cancer therapies. Another theory is there is a differential effect from taking antioxidants. Meaning the antioxidants help protect normal cells, but not the cancer cells.
Recommendation: Many oncologists recommend caution with high-dose antioxidant supplements during active cancer treatment. Instead, a balanced diet with naturally occurring antioxidants is typically advised.
thiol-containing antioxidants: -Contain a functional –SH (sulfhydryl) group
-Can undergo oxidation to form disulfide bonds. This reversible redox behavior allows these molecules to neutralize reactive oxygen species (ROS).
-Thiol antioxidants (like N‑acetylcysteine or glutathione) are potent because the –SH group can directly scavenge ROS.
-There is concern that supplementation with thiol antioxidants during chemotherapy could neutralize some of the ROS generated by the treatment, potentially reducing the intended cytotoxic effects on cancer cells.
Examples:
-NAC
-GSH
-NMPG
-dihydrolipoic acid (reduced form of ALA)
-Cysteamine
-Methionine
-Ergothioneine
-Thioredoxin
Non-thiol ROS scavengers:
-Act by donating electrons or hydrogen atoms to free radicals, thereby stabilizing them or converting them into less reactive species.
-Non‑thiol antioxidants (like vitamin C, vitamin E, flavonoids, etc.) have different mechanisms of action and may not interact as directly with ROS in the specific context of chemotherapy-induced cell death.
-That said, even non‑thiol antioxidants could potentially interfere with chemotherapy in some cases. For example, high doses of vitamin C or vitamin E might also diminish the oxidative stress essential for the efficacy of some chemotherapeutics.
Examples
-Ascorbic Acid(VitC)
-Vitamin E
-Flavoniods (Quercetin)
-Carotenoids(beta-carotene)
-Resveratrol
-Coenzyme Q10 (ubiquinone)
-Curcumin
-Selenium‑Dependent Enzymes (e.g., Glutathione Peroxidase)
-Polyphenols (ferulic acid and caffeic acid)
-manganese(III)
-tetrakis( (4-benzoic acid)
-porphyrin chloride (MnTBAP)
-SOD
*** NOTE:
Thiol AntiOxidants could block ROS generation caused by Gambogic Acid, but not NON-Thiol AntiOxidants.
Question: does this mean NON-thiol AntiOxidants, might not interfere with therapies that raise ROS?
-It is a common notion that non‑thiol antioxidants might be less likely to interfere with chemotherapy compared to thiol antioxidants, both classes have the potential to impact treatment efficacy under the right (or wrong) circumstances.
OTHER CLASSES of antioxidants
1. Enzymatics Antioxidants (SOD, Catalase, GPXs)
-proteins that catalyze reactions to detoxify reactive oxygen species (ROS).
2. Non-Enzymatic (Small-Molecule) Antioxidants.
Further divided to Thiol-Based Antioxidants, vs Non-Thiol Based Antioxidants.
3. Metal-Binding Proteins and Chelators (Ferritin, Transferrin)
These compounds limit oxidative damage indirectly by sequestering transition metals (like iron and copper) that catalyze reactive oxygen species formation via the Fenton reaction.
4. Indirect Antioxidants (Nrf2 Activators): (Sulforaphane, Curcumin)
enhance the body’s own antioxidant defenses by upregulating the expression of antioxidant enzymes.