Antioxidants & Free radicals

What are Reactive Oxygen Species?

ROS also known as Free oxygen radicals Any molecule with an unpaired electron Extremely chemically reactive Damage cell membranes Responsible for more than 100 human diseases Aging, cancer, heart attacks, stroke and arthritis Some beneficial effects

How are ROS Formed? Primary source is our body during energy

production Environmental contaminants Ionizing and ultraviolet radiation Prolonged low blood flow states

(atherosclerosis, heart attacks and stroke) Diet (fatty and processed foods) Low levels of antioxidants

Protection from ROS Damage

Superoxide dismutase Catalase Glutathion Antioxidants in diet Supplementation

Aging and Effect on Antioxidant Enzymes

Significant decline in SOD Significant decline in catalase and glutathione Significant decline in energy production Cellular, tissue and system aging and failure

Scientific Support for Antioxidants

Animals with longer life spans have higher antioxidant levels

Dietary increase in antioxidants increase life span

Caloric restriction (reduces ROS formation) leads to significantly increased life span

Questions asked

What are free radicals? Types of free radicals Sources of free radicals Oxygen metabolism

Discussion on oxidative damage and oxidative stress

What is antioxidant? Natural free radical defense systems What are Phytochemicals?

NutrientsNutrients Non-nutrientsNon-nutrients

Energy, buildingEnergy, buildingmaterialsmaterials

Factors regulatingFactors regulating metabolismmetabolism

LipidLipid ProteinProtein Carbo-Carbo-hydratehydrate

VitaminsVitamins MineralsMinerals

EFA & EFA & non-EFAnon-EFA GlucoseGlucose

WaterWater

Phyto-Phyto- chemicalschemicals•pigmentspigments•AntioxidantsAntioxidants

FibersFibers

Other food Other food componentscomponents

FoodFood

GSHGSHCysCys

Functional food Functional food or Neutraceuticalsor Neutraceuticals

C, E, C, E, -Car-CarZn, SeZn, Se

EAA & EAA & non-EAAnon-EAA

Free radical-Mediated Diseases

Diseases of the old - Chronic and degenerative diseases

(diabetes, cataracts, Alzheimer’s disease, cancers,

cardiovascular disease, and aging)

Diseases of the young and innocent -Acute and immature diseases

(Eyes: retinopathy of prematurity, Lung: bronchopulmonary displasia, Brain: cerebral pulsy, Pancreas: Type 1 diabetes)

What are free radicals?

Any molecule containing one or more unpaired electrons

Types of Free Radicals Reactive Oxygen Species (ROS) -

Reactive Nitrogen Species (RNS) -

NO. Reactive Metabolites or Intermediates

- metabolic activation of drugs, toxins, pollutants, cigarette smokes, etc.

Reactive Oxygen Species (ROS)

Superoxide (O2.-)

Hydrogen Peroxide (H2O2)

Hydroxyl Radical (OH.) - product of Fenton reaction catalyzed by free Fe and Cu

Singlet Oxygen (1gO2) - oxygen at an excited

state, requiring photosensitizers and photons

Sources of oxygen free radicals In mitochondria:

- generation of energy - ATP

- glucose, fatty acids, amino acids

- O2 2H2O

4e-

- leakage of O2-. (superoxide)

H2O2 (hydrogen peroxide)

In Smooth Endoplasmic Reticulum (microsome)

- detoxification (cytochrome P-450s)

- toxins, drugs and xenobiotics

- O2 + RH R-OH and H2O

- leakage of O2-.

- metabolic activation - X.

In Peroxisomes

- containing oxidases for degradation of various substrates

- glucose, amino acids, xanthine, etc.

- requires O2

- byproduct is H2O2

In Cytoplasm

- nitric oxide (NO.) production from Arginine

- functions as a biological messenger

- in brain, vascular endothelial cells, and macrophages

- NO. + O2-. ONOO. (peroxynitrite)

NO: a Biological Messenger

NO is a neurotransmitter (brain- bNOS) NO regulates blood pressure (vascular

endothelial cells- eNOS) NO is a cytotoxic agent (macrophages-

iNOS)

Production of Singlet Oxygen

- photosensitizers in the biological system

(bilirubin, riboflavin, retinal, porphyrin)

- requires light , O2 and photosensitizers

- chlorophyll in photosynthesis

- photodynamic therapy

Antioxidants

Prevents the transfer of electron from O2 to organic molecules

Stabilizes free radicals Terminates free radical reactions

Free Radical Defense System

Antioxidant Enzymes Antioxidant Quenchers Antioxidant from Foods

– nutrients/non-nutrients

Antioxidant Enzymes

Superoxide Dismutase (SOD) – to get rid of superoxide produced from electron transport chain, the product is hydrogen peroxide. MnSOD (mitochondria). CuZn SOD (cytosol).

Oxygen Radical Defense Enzymes

Oxygen Radical Defense Enzymes

O2•¯ H2O2 H2O + O2

Mn SOD Catalase

GSH Peroxidase

CuZnSOD

OH•

Fe2+

Antioxidant Enzymes - 2

Glutathione Peroxidase (GSH PX) – to get rid of hydrogen peroxide (H2O2) and some lipid peroxide. It requires reduced glutathione (GSH) as substrate and produces oxidized glutathione (GSSG) as product. A cytosolic enzyme.

Functions of GSH-dependent Enzymes

L-OHL-OHHH22OO

GSSGGSSG NADPHNADPH

L-OOHL-OOHHH22OO22

GSHGSH NADP+NADP+

XX..

GSXGSX

XX-Mercapturic Acid-Mercapturic Acid

GSH PxGSH Px

GSH-TRGSH-TR

GSH--RxGSH--Rx

Glutathione GSH is a tripeptide, -glutamyl-

cysteinyl-glycine The sulfur atom of the cysteine

moiety is the reactive site which provides electrons

GSH is stable because the bond in glutamyl-cysteine (not the peptide bond) is resistant to cellular peptidases

Glutathione GSH is the most abundant non-protein thiol in

mammalian cells GSH is a substrate for two enzymes that are

responsible for detoxification and antioxidation.

Other physiological roles including cysteine storage and transport, prostaglandin metabolism, immune function, cell proliferation and redox balance

Glutathione Synthesis

ProteinProtein

MethionineMethionine

CysteineCysteineGlutamateGlutamate

-Glutamylcysteine-Glutamylcysteine

GlycineGlycine

Antioxidant Enzymes - 3

Catalase –to get rid of hydrogen peroxide produced in peroxisome.

Antioxidant Quenchers

Cellular proteins which chelate pro-oxidant minerals (iron and copper or others)

Transferrin – iron transport protein Ferritin – iron storage protein Metallothionein – minerals and heavy

metals (Zn/Cu/Cd/Hg) Ceruloplasmin – copper transport and

storage

Antioxidants From Food

Antioxidant nutrients – vitamin E, vitamin C, (vitamin A?), beta-carotene

Phytochemicals – antioxidants from plants

Discovery of Other Functions of Phytochemicals

Anti-oxidant Anti-

inflammatory Anti-estrogenic Anti-allergic

Anti-cholesterolemic

Anti-hemorrhagic Anti-mutagenic Anti-neoplastic