Advertisement
 

doctorslounge.com

 
Powered by
Careerbuilder

 

                    Home  |  Forums  |  Humor  |  Advertising  |  Contact
   Ask a Doctor

   News via RSS

   Newsletter

   Home

   News

   Conferences

   CME

   Forum Archives

   Diseases

   Symptoms

   Labs

   Procedures

   Drugs

   Links
   Specialties

   Cardiology

   Dermatology

   Endocrinology

   Fertility

   Gastroenterology

   Gynecology

   Hematology

   Infections

   Nephrology

   Neurology

   Oncology

   Orthopedics

   Pediatrics

   Pharmacy

   Primary Care

   Psychiatry

   Pulmonology

   Rheumatology

   Surgery

   Urology

   Other Sections

   Membership

   Research Tools

   Medical Tutorials

   Medical Software

 

 Headlines:

 
 

Back to table of contents

Antioxidants, nature and chemistry

Submitted by Dr. Tamer Fouad, M.D.

 

Antioxidants are substances that protect other chemicals of the body from damaging oxidation reactions

 
 

tellfrnd.gif (30x26 -- 1330 bytes)send to a friend
 
prntfrnd.gif (30x26 -- 1309 bytes)printer friendly version
 
 
  Related
 
  Free radicals
Oxidative mechanisms in carcinogenesis
 
   
 

Antioxidant System

The body has developed several endogenous antioxidant systems to deal with the production of ROI. These systems can be divided into enzymatic and nonenzymatic groups. Figure 4 summarizes the sites of action of the various antioxidants.

Fig. 4: Generation sequence of reactive oxygen species following univalent reduction of oxygen and the various sites of action of the different antioxidants (Nohl, 1993).

The enzymatic antioxidants include superoxide dismutase (SOD), which catalyses the conversion of O2?to H2O2 and H2O; catalase, which then converts H2O2 to H2O and O2; and glutathione peroxidase, which reduces H2O2 to H2O.

Fig. 5: Sources of intracellular oxidative stress and sites of antioxidant activity (Bulger and Helton, 1998).

The nonenzymatic antioxidants include the lipid-soluble vitamins, vitamin E and vitamin A or provitamin A (beta-carotene), and the water-soluble vitamin C and GSH. Vitamin E has been described as the major chain-breaking antioxidant in humans (Packer, 1992). Because of its lipid solubility, vitamin E is located within cell membranes, where it interrupts lipid peroxidation and may play a role in modulating intracellular signalling pathways that rely on ROI (Kagan et al. 1990; Azzi et al. 1993). Vitamin E can also directly quench ROI, including O2?, ?OH, and (Algayer et al. 1992) 1O2.

advertisement.gif (61x7 -- 0 bytes)
 

Are you a doctor or a nurse?

Do you want to join the Doctors Lounge online medical community?

Participate in editorial activities (publish, peer review, edit) and give a helping hand to the largest online community of patients.

Click on the link below to see the requirements:

Doctors Lounge Membership Application


The enzymatic and nonenzymatic antioxidant systems are intimately linked to one another and appear to interact with one another (Fig.6). Both vitamin C and GSH have been implicated in the recycling of alpha-tocopherol radicals (Reed, 1993). In addition, the trace elements selenium, manganese, copper, and zinc also play important roles as nutritional antioxidant cofactors. Selenium is a cofactor for the enzyme glutathione peroxidase, and manganese, copper, and zinc are cofactors for SOD (see earlier). Zinc also acts to stabilize the cellular metallothionein pool, which has direct free radical quenching ability (Bray and Bettger, 1990). The complex interactions of these different antioxidant systems may imply that therapeutic strategies will depend on combination therapy of various antioxidants rather than a single agent.


Fig. 6: Interactions among antioxidants. Reactive oxygen intermediates (ROI) induce membrane lipid peroxidation resulting in a chain reaction that can be interrupted by the direct scavenging of lipid peroxyl radicals by vitamin E (VE) and beta-carotene. Vitamin E can then be recycled by both vitamin C (VC) and glutathione (GSH). The reducing ability of GSH is catalyzed by the enzyme glutathione peroxidase (GSSG). Glutathione is then recycled by NADPH, which is facilitated by glutathione reductase (GSSG). LOO? = active species of the lipid peroxyradical; LOOH-reduced lipid radical; VE-O? = active radical form of VE; VE-OH = the reduced form (Bulger and Helton, 1998).

previous.gif (72x17 -- 347 bytes)

next.gif (72x17 -- 277 bytes)

 

 advertisement.gif (61x7 -- 0 bytes)

 

 



We subscribe to the HONcode principles of the HON Foundation. Click to verify.
We subscribe to the HONcode principles. Verify here

Privacy Statement | Terms & Conditions | Editorial Board | About us
Copyright 2001-2012 DoctorsLounge. All rights reserved.