BETHY NGUYENBETHY NGUYENCHEMISTRY 12BCHEMISTRY 12BSPRING, 2006SPRING, 2006

INTRODUCTIONINTRODUCTION Green tea is natural dried leaves of the Green tea is natural dried leaves of the

tea plant, camellia sinensis.tea plant, camellia sinensis. Most of the polyphenols in green tea areMost of the polyphenols in green tea are

flavanols, commonly known as catechins.flavanols, commonly known as catechins. The primary catechins in green tea are The primary catechins in green tea are

epicatechin, epicatechin-3-gallate (ECG), epicatechin, epicatechin-3-gallate (ECG), epigallocatechin (EGC), and epigallocatechin (EGC), and epigallocatechin-3-gallate (EGCG).epigallocatechin-3-gallate (EGCG).

INTRODUCTION (CONT.)INTRODUCTION (CONT.)

http://www.micronutrient.org/IDPAS/pdf/447GreenTea.pdf#search='mechanism%20of%20phenol%20in%20green%20tea'

What are Antioxidants?What are Antioxidants? Green tea is regarded as an antioxidant. The polyphenols, Green tea is regarded as an antioxidant. The polyphenols,

especially EGCG.especially EGCG.

The human body constantly produces unstable molecules called The human body constantly produces unstable molecules called oxidants, also commonly referred to as free radicals. oxidants, also commonly referred to as free radicals.

These free radicals readily react and damage other molecules and These free radicals readily react and damage other molecules and cell DNA.  Antioxidants "mop up" these free radicals and eliminate cell DNA.  Antioxidants "mop up" these free radicals and eliminate them before they can damage healthy tissue. them before they can damage healthy tissue.

  Furthermore, oxidative damage by free radicals on low density Furthermore, oxidative damage by free radicals on low density lipoproteins (LDL) is believed to be a precursor in the development lipoproteins (LDL) is believed to be a precursor in the development of atherosclerosis and coronary heart disease.of atherosclerosis and coronary heart disease.

Oxidation to cell membranes and other cell components is also Oxidation to cell membranes and other cell components is also theorized to be part of the aging process. theorized to be part of the aging process.

http://www.imperialteagarden.com/greenteaantioxidants.htmlhttp://www.imperialteagarden.com/greenteaantioxidants.html

MECHANISM OF ANTIOXIDANTSMECHANISM OF ANTIOXIDANTS

AntioxidantsAntioxidants are molecules that are molecules that can neutralize free radicals by can neutralize free radicals by accepting or donating an electron to accepting or donating an electron to eliminate the unpaired condition eliminate the unpaired condition

Example of Formation of a complex Example of Formation of a complex between the lipid radical and the between the lipid radical and the antioxidant radical (free radical antioxidant radical (free radical acceptor).acceptor).

http://class.fst.ohio-state.edu/fst821/Lect/AA.pdf

Mechanisms of Metals in Mechanisms of Metals in Accelerating Lipid OxidationAccelerating Lipid Oxidation

http://class.fst.ohio-state.edu/fst821/Lect/AA.pdf

MECHANISMS OF FATTY ACID OXIDATIONMECHANISMS OF FATTY ACID OXIDATION

Autoxidation by free radical reaction, In a Autoxidation by free radical reaction, In a peroxide-free lipid system.peroxide-free lipid system.1.Initiation:1.Initiation:the initiation of a peroxidation sequence refers the initiation of a peroxidation sequence refers to the attack of a ROS able to abstract a to the attack of a ROS able to abstract a hydrogen atom from a methylene group (- hydrogen atom from a methylene group (- CH2-). This attack generates easily free CH2-). This attack generates easily free radicals from polyunsaturated fatty acids. OH radicals from polyunsaturated fatty acids. OH is the most efficient ROS to do that attack, is the most efficient ROS to do that attack, whereas O2.- is insufficiently reactive.whereas O2.- is insufficiently reactive.

The carbon radical tends to be stabilized by a molecular rearrangement to form a conjugated diene.

Under aerobic conditions conjugated dienes are able to combine with O2 to give a peroxyl (or peroxy) radical, ROO..

2. Propagation

As a peroxyl radical is able to abstract H from another lipid molecule (adjacent fatty acid), especially in the presence of metals such as copper or iron, thus causing an autocatalytic chain reaction. The peroxyl radical combines with H to give a lipid hydroperoxide (or peroxide).

http://www.cyberlipid.org/perox/oxid0006.htm#3

TERMINATIONTERMINATION

Termination (formation of a hydroperoxide) is most often achieved by reaction of a peroxyl radical with a-tocopherol which is the main lipophilic "chain-breaking molecule" in the cell membranes.

OXIDATIVE DAMAGE TO DNA: formation of   8−OHdG/8−oxoG

8−OHdG from Guanosine with Hydroxyl 8−oxoG

                                                            

       

                           

          

8−OHdG/8−oxoG is the most commonly studied biomarker of DNA oxidation [1] and is believed to constitute 5% of all oxidative DNA damage [2] 8−OHdG is mutagenic because it inhibits methylation and because it can be paired with adenosine rather than cytosine during DNA replication leading to GC-to-AT conversion

http://www.benbest.com/lifeext/aging.html#mitochondria

BENEFIT OF GREEN TEA BENEFIT OF GREEN TEA POLYPHENOLSPOLYPHENOLS

Years of research, in the United States and Years of research, in the United States and Japan support the theory that Tea (Camellia Japan support the theory that Tea (Camellia Sinensis) has the ability to ward off many Sinensis) has the ability to ward off many types of cancer types of cancer

The belief is that polyphenol (-)-The belief is that polyphenol (-)-epigallocatechin gallate (EGCG) have an epigallocatechin gallate (EGCG) have an inhibitory effect on the enzyme, urokinase, inhibitory effect on the enzyme, urokinase, which is required for tumor formation.which is required for tumor formation.

help prevent the oxidation of LDL cholesterol. help prevent the oxidation of LDL cholesterol. The phenol groups in Green Tea polyphenols The phenol groups in Green Tea polyphenols

are extremely active, easily able to capture are extremely active, easily able to capture and neutralize free radicals and other pro-and neutralize free radicals and other pro-oxidants oxidants

ConclusionConclusion

In conclusion, green tea and its polyphenols In conclusion, green tea and its polyphenols (catechins)-- gallocatechin, epigallocatechin, (catechins)-- gallocatechin, epigallocatechin, epicatechin, epigallocatechin, and epicatechin, epigallocatechin, and epicatechin gallate-- have been shown to not epicatechin gallate-- have been shown to not only inhibit carcinogenesis before it begins, only inhibit carcinogenesis before it begins, and decrease the number of tumors, but and decrease the number of tumors, but also, amazingly, induce apoptosis and cell also, amazingly, induce apoptosis and cell cycle arrest in carcinoma cells, as well. cycle arrest in carcinoma cells, as well.

Nevertheless, more work is required to Nevertheless, more work is required to elucidate the molecular and clinical elucidate the molecular and clinical chemopreventive effects of green tea on chemopreventive effects of green tea on human colorectal cancer. human colorectal cancer.

http://carbon.hampshire.edu/~cjarvis/NS120/projects/gt&cancer.htm

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447GreenTea.pdf#search='mechanism%20of%20catechins%20in447GreenTea.pdf#search='mechanism%20of%20catechins%20in%20green%20tea‘%20green%20tea‘

http://www.cyberlipid.org/perox/oxid0006.htm#3http://www.cyberlipid.org/perox/oxid0006.htm#3 http://class.fst.ohio-state.edu/fst821/Lect/AA.pdfhttp://class.fst.ohio-state.edu/fst821/Lect/AA.pdf http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/R/ROS.htmlhttp://users.rcn.com/jkimball.ma.ultranet/BiologyPages/R/ROS.html JOURNALS:

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