Orris

Antioxidants

Reading File
Asking for Preferences
Finding Sources
Searching PubMed

antioxidants oxidative stress disease

Searching Images

antioxidant defense mechanisms free radicals ROS diagram

This pathophysiology diagram illustrates the comparative antioxidant mechanisms of free phenolics (FPs) and bound phenolics (BPs) derived from olive leaves. The top panel depicts chemical structures: FPs include oleuropein, luteolin-7-O-glucoside, quercetin, and maslinic acid; BPs include ferulic, chlorogenic, and caffeic acids. The lower panel divides evaluation into two systems. On the left, the chemical antioxidant evaluation system shows direct scavenging of free radicals (DPPH, ABTS, FRAP) leading to the inhibition of oxidative stress, noting BPs are weaker than FPs in this modality. On the right, the biological antioxidant evaluation system demonstrates two pathways: 1) Antioxidant gene expression via Nrf2 signaling, upregulating HO-1, NQO1, GCLC, and GSTA2 (primarily driven by FPs); and 2) Activation of antioxidant enzymes including CAT, SOD, GSH-PX, and non-enzymatic GSH, leading to the reduction of RNS, ROS, and MDA. Red and blue arrows indicate the specific contributions of FPs and BPs respectively, highlighting that while both mitigate oxidative stress, FPs uniquely activate the Nrf2-mediated genomic response.

This pathophysiology diagram illustrates the comparative antioxidant mechanisms of free phenolics (FPs) and bound phenolics (BPs) derived from olive leaves. The top panel depicts chemical structures: FPs include oleuropein, luteolin-7-O-glucoside, quercetin, and maslinic acid; BPs include ferulic, chlorogenic, and caffeic acids. The lower panel divides evaluation into two systems. On the left, the chemical antioxidant evaluation system shows direct scavenging of free radicals (DPPH, ABTS, FRAP) leading to the inhibition of oxidative stress, noting BPs are weaker than FPs in this modality. On the right, the biological antioxidant evaluation system demonstrates two pathways: 1) Antioxidant gene expression via Nrf2 signaling, upregulating HO-1, NQO1, GCLC, and GSTA2 (primarily driven by FPs); and 2) Activation of antioxidant enzymes including CAT, SOD, GSH-PX, and non-enzymatic GSH, leading to the reduction of RNS, ROS, and MDA. Red and blue arrows indicate the specific contributions of FPs and BPs respectively, highlighting that while both mitigate oxidative stress, FPs uniquely activate the Nrf2-mediated genomic response.

This pathophysiology diagram illustrates the antioxidant mechanisms of various essential oils (EOs) in the context of dermatological health, specifically for managing acne vulgaris. The central visual depicts a cellular structure under oxidative stress, indicated by reactive oxygen species (ROS) such as superoxide (O2-) and hydroxyl radicals (OH). Surrounding this central figure are nine detailed panels for different EOs: Oregano, Rosemary, Tea Tree, Thyme, Eucalyptus, Lemon, Myrtle, Lavender, and Cymbopogon martini. Each panel categorizes the primary chemical 'Compounds' (e.g., carvacrol, thymol, 1,8-cineole, linalool) and their specific 'Mechanisms and data.' Key biological pathways highlighted include the regulation of the Keap1/Nrf2 pathway, scavenging of free radicals, and the upregulation of endogenous antioxidant enzymes such as superoxide dismutase (SOD), glutathione peroxidase (GPx), and catalase (CAT). The diagram also notes reductions in malondialdehyde (MDA) levels and lipid peroxidation, emphasizing the oils' clinical relevance in mitigating oxidative damage and inflammation associated with skin disorders.

This pathophysiology diagram illustrates the antioxidant mechanisms of various essential oils (EOs) in the context of dermatological health, specifically for managing acne vulgaris. The central visual depicts a cellular structure under oxidative stress, indicated by reactive oxygen species (ROS) such as superoxide (O2-) and hydroxyl radicals (OH). Surrounding this central figure are nine detailed panels for different EOs: Oregano, Rosemary, Tea Tree, Thyme, Eucalyptus, Lemon, Myrtle, Lavender, and Cymbopogon martini. Each panel categorizes the primary chemical 'Compounds' (e.g., carvacrol, thymol, 1,8-cineole, linalool) and their specific 'Mechanisms and data.' Key biological pathways highlighted include the regulation of the Keap1/Nrf2 pathway, scavenging of free radicals, and the upregulation of endogenous antioxidant enzymes such as superoxide dismutase (SOD), glutathione peroxidase (GPx), and catalase (CAT). The diagram also notes reductions in malondialdehyde (MDA) levels and lipid peroxidation, emphasizing the oils' clinical relevance in mitigating oxidative damage and inflammation associated with skin disorders.

This pathophysiology diagram illustrates the cellular antioxidant defense systems and the biochemical pathways for Reactive Oxygen Species (ROS) detoxification. At the top, a mitochondrion is shown utilizing nutrients and O2 through the electron transport chain (complexes I-V) to generate ATP, with ROS produced as a metabolic byproduct. The central flowchart details the enzymatic neutralization of ROS: Superoxide Dismutase (SOD) converts superoxide radicals (O2-) into oxygen (O2) and hydrogen peroxide (H2O2). Subsequently, H2O2 is neutralized by Glutathione Peroxidase (GPx), utilizing NADH2 as a cofactor to produce water, and by Catalase (CAT) to produce water and oxygen. The bottom sections categorize protective antioxidants into Endogenous and Dietary groups. Endogenous systems are split into enzymatic (e.g., SOD, Catalase, GPx, DNA repair enzymes) and non-enzymatic (e.g., glutathione, uric acid, melatonin). Dietary antioxidants are classified by solubility: water-soluble (Betalains, Flavonoids, Vitamin C) and lipid-soluble (Carotenoids, Vitamins A and E). The diagram emphasizes the multi-layered approach to maintaining cellular redox homeostasis.

This pathophysiology diagram illustrates the cellular antioxidant defense systems and the biochemical pathways for Reactive Oxygen Species (ROS) detoxification. At the top, a mitochondrion is shown utilizing nutrients and O2 through the electron transport chain (complexes I-V) to generate ATP, with ROS produced as a metabolic byproduct. The central flowchart details the enzymatic neutralization of ROS: Superoxide Dismutase (SOD) converts superoxide radicals (O2-) into oxygen (O2) and hydrogen peroxide (H2O2). Subsequently, H2O2 is neutralized by Glutathione Peroxidase (GPx), utilizing NADH2 as a cofactor to produce water, and by Catalase (CAT) to produce water and oxygen. The bottom sections categorize protective antioxidants into Endogenous and Dietary groups. Endogenous systems are split into enzymatic (e.g., SOD, Catalase, GPx, DNA repair enzymes) and non-enzymatic (e.g., glutathione, uric acid, melatonin). Dietary antioxidants are classified by solubility: water-soluble (Betalains, Flavonoids, Vitamin C) and lipid-soluble (Carotenoids, Vitamins A and E). The diagram emphasizes the multi-layered approach to maintaining cellular redox homeostasis.

Reading File
Reading File
Finding Sources
Finding Sources
Finding Sources
Reading File
Reading File
Reading File
Now I have rich textbook content. Let me compile a thorough answer.

Antioxidants

Antioxidants are molecules that prevent or slow the oxidative damage caused by reactive oxygen species (ROS) and other free radicals. They operate through enzymatic and non-enzymatic mechanisms to maintain redox homeostasis in cells and tissues.

1. Free Radicals and Oxidative Stress

Free radicals are molecules with an unpaired electron, making them highly reactive. The major species include:
ROSSource
Superoxide anion (O₂•⁻)Mitochondrial electron transport chain (complexes I-III), NADPH oxidase
Hydrogen peroxide (H₂O₂)Dismutation of superoxide; peroxisomal oxidation
Hydroxyl radical (•OH)Fenton reaction (Fe²⁺ + H₂O₂ → Fe³⁺ + OH⁻ + •OH); Haber-Weiss reaction
Lipid peroxyl radicalsPeroxidation of polyunsaturated fatty acids (PUFAs)
When ROS production overwhelms antioxidant capacity, oxidative stress ensues, causing damage to lipids, proteins, and DNA.

2. Enzymatic Antioxidants

These form the primary cellular defense line.

a. Superoxide Dismutase (SOD)

SOD catalyzes the dismutation of superoxide to H₂O₂ and O₂ - considered the "primary defense" because superoxide is such a potent chain reaction initiator.
Three isoforms:
  • Cu⁺-Zn²⁺ SOD (cytosol) - encoded by SOD1; mutations cause ~5-10% of familial ALS (amyotrophic lateral sclerosis)
  • Mn²⁺ SOD (mitochondria)
  • Cu⁺-Zn²⁺ SOD (extracellular)
2 O₂•⁻ + 2H⁺ → H₂O₂ + O₂
  • Basic Medical Biochemistry, p. 917

b. Catalase

Found principally in peroxisomes (highest activity in liver and kidney), catalase reduces H₂O₂ to water and O₂, preventing it from generating the toxic hydroxyl radical via the Fenton reaction. In immune cells, it protects against the oxidative burst.
2 H₂O₂ → 2 H₂O + O₂

c. Glutathione Peroxidase (GPx) and Glutathione Reductase

Glutathione (GSH) - the tripeptide γ-glutamyl-cysteinyl-glycine - is the most important antioxidant in the mammalian liver. GPx uses its reactive sulfhydryl groups to:
  • Reduce H₂O₂ to water
  • Reduce lipid peroxides to nontoxic alcohols
Two GSH molecules are oxidized to glutathione disulfide (GSSG), which is recycled back to GSH by glutathione reductase (using NADPH from the pentose phosphate pathway). Glucose-6-phosphate dehydrogenase (G6PD) is therefore critical for maintaining antioxidant capacity - explaining why G6PD-deficient individuals are vulnerable to oxidative hemolysis.
  • Fishman's Pulmonary Diseases, p. 2549; Basic Medical Biochemistry, p. 918

3. Non-Enzymatic Antioxidants

a. Vitamin E (α-Tocopherol) - Fat-Soluble

The most widely distributed antioxidant in nature. Functions as a chain-breaking, free radical-trapping antioxidant in cell membranes and plasma lipoproteins. It reacts with lipid peroxyl radicals formed during PUFA peroxidation; the resulting tocopherol radical is relatively stable and can be regenerated by vitamin C.
  • Harper's Biochemistry, p. 564
Deficiency: Fat malabsorption, cystic fibrosis, chronic liver disease, premature infants. Causes hemolytic anemia (fragile erythrocyte membranes from lipid peroxidation) and nerve/muscle damage.

b. Vitamin C (Ascorbate) - Water-Soluble

Acts in aqueous phases (plasma, cytosol). Scavenges superoxide (→ H₂O₂) and hydroxyl radicals (→ H₂O), and recycles vitamin E from the tocopherol radical.
Dual role - the antioxidant paradox: At high concentrations, ascorbate can become pro-oxidant - reacting with Cu²⁺ to generate hydroxyl radicals. The renal threshold (~30 mmol/L plasma) limits tissue accumulation. Similarly, β-carotene is antioxidant at low O₂ tension (most tissues) but becomes a pro-oxidant in the lungs at high O₂ partial pressure - explaining why β-carotene supplementation increased lung cancer mortality in two major 1990s trials.
  • Harper's Illustrated Biochemistry, p. 564

c. β-Carotene and Carotenoids

Lipid-soluble radical trappers. Epidemiology initially suggested protection against lung and other cancers, but intervention trials showed increased mortality from lung cancer in supplemented high-risk individuals (smokers) due to pro-oxidant behavior at high pulmonary O₂ tensions.

d. Other Non-Enzymatic Antioxidants

AntioxidantLocationNotes
Uric acidPlasmaMajor extracellular antioxidant
CeruloplasminPlasmaCopper-binding; scavenges free iron
MelatoninWidespreadScavenges •OH, O₂•⁻
BilirubinPlasmaAntioxidant at physiological levels
ThioredoxinIntracellularAlternative to glutathione system

4. The Nrf2-ARE Pathway (Master Regulatory Switch)

Under oxidative stress, Nrf2 (nuclear factor-erythroid-2-related factor 2) dissociates from its inhibitor Keap1 and translocates to the nucleus, where it binds the Antioxidant Response Element (ARE) and upregulates antioxidant gene expression, including:
  • Heme oxygenase-1 (HO-1)
  • NAD(P)H quinone oxidoreductase 1 (NQO1)
  • Glutamate-cysteine ligase catalytic subunit (GCLC)
  • Glutathione S-transferase A2 (GSTA2)
Age-related deterioration of the Nrf2/ARE pathway is a key mechanism of impaired oxidative stress resilience in the elderly cardiovascular system.
  • Fuster and Hurst's The Heart, 15th Ed

5. Antioxidants in Disease

DiseaseRole of Oxidative StressAntioxidant Relevance
Atherosclerosis / CVDLDL oxidation, endothelial dysfunctionVitamin E meta-analyses show no benefit from supplements; may increase mortality at high doses
CancerDNA oxidation, mutagenesisβ-carotene supplements harmful in smokers; dietary antioxidants generally protective
Neurodegeneration (ALS, Parkinson's, Alzheimer's)Mitochondrial ROS, SOD1 mutations in familial ALSSOD/catalase dysfunction implicated
Alcoholic liver disease (ALD)Hepatic GSH depletion, ROS from CYP2E1Low mitochondrial glutathione worsens injury
Inflammatory bowel diseaseOxidative stress biomarkers correlate with disease activityGSH, SOD, catalase reduced in active disease
Pulmonary O₂ toxicityHyperoxia overwhelms cellular SOD/catalaseLung tissue has high extracellular antioxidant reserve to tolerate O₂
Recurrent pancreatitisOxidant-antioxidant imbalanceSelenium, ascorbic acid, α-tocopherol measured and supplemented in RAP/CP

6. Dietary Sources

AntioxidantRich Sources
Vitamin CCitrus, bell peppers, kiwi, broccoli
Vitamin ENuts, seeds, wheat germ, vegetable oils
β-CaroteneCarrots, sweet potato, dark leafy greens
Selenium (GPx cofactor)Brazil nuts, seafood, meat
Flavonoids/PolyphenolsBerries, tea, cocoa, red wine
CurcuminTurmeric - activates Nrf2, scavenges ROS

7. The Antioxidant Supplementation Problem

Clinical trials have consistently shown that high-dose antioxidant supplements often fail to replicate the benefits of dietary antioxidants and may cause harm:
  • High-dose vitamin E meta-analyses show increased all-cause mortality
  • β-carotene supplements increased lung cancer in smokers (ATBC and CARET trials)
  • Vitamin C at very high doses can act as a pro-oxidant
The probable explanations include:
  1. Supplements provide single molecules, while foods contain hundreds of synergistic compounds
  2. Some ROS are beneficial signaling molecules - excessive scavenging disrupts redox signaling
  3. Several antioxidants are pro-oxidant at high concentrations
  • Harper's Illustrated Biochemistry, p. 564
Key diagram showing the multi-layered cellular antioxidant defense:
Cellular antioxidant defense systems showing SOD, catalase, GPx pathways and dietary antioxidants
Endogenous enzymatic (SOD, catalase, GPx) and non-enzymatic (glutathione, uric acid, melatonin) antioxidants, plus dietary water-soluble (vitamin C, flavonoids) and lipid-soluble (vitamin E, carotenoids) antioxidants work in concert to neutralize ROS.
Recent evidence (2024-2026): A systematic review on curcumin and aging (PMID 39203857, Nutrients 2024) highlights curcumin's antioxidant and Nrf2-activating mechanisms as relevant to healthy aging. Oxidative stress biomarkers (including GSH, SOD, MDA) are now validated indicators of IBD activity in a 2024 meta-analysis (PMID 39368456, Redox Biol).
This is a shared conversation. Sign in to Orris to start your own chat.