Dietary Antioxidants

Intro to Antioxidants - Radicals Rumble

• Antioxidants: Molecules that inhibit oxidation, neutralizing harmful free radicals and protecting cells.
• Free Radicals: Unstable, highly reactive species with unpaired electrons.
  • Reactive Oxygen Species (ROS): e.g., Superoxide ($O_2^{\cdot-}$), Hydrogen peroxide ($H_2O_2$), Hydroxyl radical ($OH^{\cdot}$).
  • Reactive Nitrogen Species (RNS): e.g., Nitric oxide ($NO^{\cdot}$), Peroxynitrite ($ONOO^-$).
• Oxidative Stress: Imbalance: ↑Free radicals / ↓Antioxidant defenses → cellular injury (lipids, proteins, DNA).

  ⭐ Key endogenous antioxidant enzymes include Superoxide Dismutase (SOD), Catalase, and Glutathione Peroxidase.

• Types of Antioxidants:
  • Endogenous: Body-synthesized (e.g., SOD, Catalase, Glutathione).
  • Exogenous (Dietary): From diet (e.g., Vitamin C, Vitamin E, Carotenoids, Flavonoids).

Vitamin Antioxidants - Shield Squad

• Vitamin E (Tocopherols, Tocotrienols):
  • Primary lipid-soluble, chain-breaking antioxidant.
  • Protects cell membranes from lipid peroxidation.
  • Sources: Vegetable oils, nuts (almonds), seeds.
  • Deficiency: Hemolytic anemia, ataxia.

  ⭐ Vitamin E (alpha-tocopherol) is the primary lipid-soluble antioxidant protecting cell membranes against lipid peroxidation.

• Vitamin C (Ascorbic Acid):
  • Water-soluble; regenerates Vitamin E.
  • Scavenges superoxide, hydroxyl radicals.
  • Sources: Citrus fruits (amla, lemon), guava, peppers, broccoli.
  • Deficiency: Scurvy (impaired collagen synthesis).
  • 📌 Mnemonic: "Citrus Cures Scurvy."
• Vitamin A (Carotenoids - e.g., β-carotene):
  • Lipid-soluble; provitamin A activity.
  • Quenches singlet oxygen ($^{ ext{1}}O_2$) and other ROS.
  • Sources: Carrots, sweet potatoes, spinach, mangoes.

Minerals & Phytochemicals - Nature's Ninjas

• Essential Mineral Cofactors:
  • Selenium (Se): Integral to Glutathione Peroxidase (GPx); synergizes with Vit E.

    ⭐ Selenium is an essential trace element and a crucial component of the antioxidant enzyme Glutathione Peroxidase (GPx).

  • Zinc (Zn): For Cu/Zn-Superoxide Dismutase (SOD); membrane stabilization.
  • Copper (Cu): For Cu/Zn-SOD & ceruloplasmin (ferroxidase activity).
  • Manganese (Mn): For mitochondrial Mn-SOD.
• Phytochemicals: Plant Defenders:
  • Polyphenols: Broad-spectrum radical scavengers.
    • Flavonoids: Quercetin (apples), Catechins (green tea), Resveratrol (grapes).
    • Phenolic acids (e.g., Caffeic acid).
  • Carotenoids (non-Vit A): Potent singlet oxygen ($^1O_2$) quenchers.
    • Lycopene (tomatoes), Lutein & Zeaxanthin (leafy greens).
  • Organosulfur Compounds: Nrf2 pathway activators.
    • Allicin (garlic), Isothiocyanates (cruciferous veggies). 📌 Mnemonic: "SeCuMZn" (Selenium, Copper, Manganese, Zinc) for key antioxidant minerals.

Clinical Relevance - Health Guardians

• Chronic Disease Shield:
  • Cardiovascular: ↓ LDL oxidation, improves endothelial function, ↓ atherosclerotic plaque formation.
  • Cancer: Protect DNA from oxidative damage, modulate cell signaling pathways.
  • Neuroprotection: Combat oxidative stress in Alzheimer's, Parkinson's; may slow progression.
  • Anti-ageing: Reduce cumulative oxidative damage, support cellular health.
• Pro-oxidant Risks: ⚠️
  • High, isolated doses may act as pro-oxidants (e.g., β-carotene in smokers ↑ lung cancer risk).
  • "Antioxidant paradox": Balance is key.
• Status Assessment:
  • Direct: Plasma levels (Vit C, E, uric acid, carotenoids).
  • Indirect: Enzyme activity (SOD, GPx, catalase); oxidative damage markers (MDA, 8-OHdG, F2-isoprostanes).

⭐ Oxidative damage to LDL cholesterol is a key event in the pathogenesis of atherosclerosis; antioxidants can potentially mitigate this.

High‑Yield Points - ⚡ Biggest Takeaways

• Vitamin E (Tocopherol): Key lipid-soluble antioxidant; protects cell membranes from lipid peroxidation.
• Vitamin C (Ascorbic Acid): Main water-soluble antioxidant; regenerates Vitamin E, enhances iron absorption.
• Beta-carotene: Provitamin A; quenches singlet oxygen, synergistic with Vitamin E.
• Selenium: Essential cofactor for glutathione peroxidase (neutralizes H2O2).
• Glutathione (GSH): Major intracellular antioxidant; vital for detoxification, regenerates Vitamins C & E.
• Uric acid: Significant plasma antioxidant in humans; scavenges various free radicals.
• Flavonoids: Plant polyphenols (e.g., quercetin); potent antioxidants, inhibit LDL oxidation.