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How antioxidants can accelerate cancers, and why they don't protect against them

nutrition bioscience

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#1 johnross47

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Posted 11 July 2014 - 07:44 PM


http://www.scienceda...40710094434.htm

 

Cold Spring Harbor Laboratory
 
Summary:
Two cancer researchers have proposed why antioxidant supplements might not be working to reduce cancer development, and why they may actually do more harm than good. Their insights are based on recent advances in the understanding of the system in our cells that establishes a natural balance between oxidizing and anti-oxidizing compounds. These compounds are involved in so-called redox (reduction and oxidation) reactions essential to cellular chemistry.
 
 
140710094434-large.jpg
Drs. Tuveson and Chandel explain why eating foods rich in antioxidants, as well as taking antioxidant supplements, can actually promote cancer, rather than fight or prevent it, as conventional wisdom suggests.
Credit: CSHL
 

For decades, health-conscious people around the globe have taken antioxidant supplements and eaten foods rich in antioxidants, figuring this was one of the paths to good health and a long life.

 

Yet clinical trials of antioxidant supplements have repeatedly dashed the hopes of consumers who take them hoping to reduce their cancer risk. Virtually all such trials have failed to show any protective effect against cancer. In fact, in several trials antioxidant supplementation has been linked with increased rates of certain cancers. In one trial, smokers taking extra beta carotene had higher, not lower, rates of lung cancer.

In a brief paper appearing in The New England Journal of Medicine, David Tuveson, M.D. Ph.D., Cold Spring Harbor Laboratory Professor and Director of Research for the Lustgarten Foundation, and Navdeep S. Chandel, Ph.D., of the Feinberg School of Medicine at Northwestern University, propose why antioxidant supplements might not be working to reduce cancer development, and why they may actually do more harm than good.

Their insights are based on recent advances in the understanding of the system in our cells that establishes a natural balance between oxidizing and anti-oxidizing compounds. These compounds are involved in so-called redox (reduction and oxidation) reactions essential to cellular chemistry.

Oxidants like hydrogen peroxide are essential in small quantities and are manufactured within cells. There is no dispute that oxidants are toxic in large amounts, and cells naturally generate their own anti-oxidants to neutralize them. It has seemed logical to many, therefore, to boost intake of antioxidants to counter the effects of hydrogen peroxide and other similarly toxic "reactive oxygen species," or ROS, as they are called by scientists. All the more because it is known that cancer cells generate higher levels of ROS to help feed their abnormal growth.

Drs. Tuveson and Chandel propose that taking antioxidant pills or eating vast quantities of foods rich in antioxidants may be failing to show a beneficial effect against cancer because they do not act at the critical site in cells where tumor-promoting ROS are produced -- at cellular energy factories called mitochondria. Rather, supplements and dietary antioxidants tend to accumulate at scattered distant sites in the cell, "leaving tumor-promoting ROS relatively unperturbed," the researchers say.

Quantities of both ROS and natural antioxidants are higher in cancer cells -- the paradoxically higher levels of antioxidants being a natural defense by cancer cells to keep their higher levels of oxidants in check, so growth can continue. In fact, say Tuveson and Chandel, therapies that raise the levels of oxidants in cells may be beneficial, whereas those that act as antioxidants may further stimulate the cancer cells. Interestingly, radiation therapy kills cancer cells by dramatically raising levels of oxidants. The same is true of chemotherapeutic drugs -- they kill tumor cells via oxidation.

Paradoxically, then, the authors suggest that "genetic or pharmacologic inhibition of antioxidant proteins" -- a concept tested successfully in rodent models of lung and pancreatic cancers -- may be a useful therapeutic approach in humans. The key challenge, they say, is to identify antioxidant proteins and pathways in cells that are used only by cancer cells and not by healthy cells. Impeding antioxidant production in healthy cells will upset the delicate redox balance upon which normal cellular function depends.

The authors propose new research to profile antioxidant pathways in tumor and adjacent normal cells, to identify possible therapeutic targets.

 

Story Source:

The above story is based on materials provided by Cold Spring Harbor Laboratory. The original article was written by Peter Tarr. Note: Materials may be edited for content and length.

Journal Reference:

  1. Elizabeth G. Phimister, Navdeep S. Chandel, David A. Tuveson. The Promise and Perils of Antioxidants for Cancer PatientsNew England Journal of Medicine, 2014; 371 (2): 177 DOI: 10.1056/NEJMcibr1405701

 


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#2 niner

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Posted 12 July 2014 - 01:20 PM

 

Drs. Tuveson and Chandel propose that taking antioxidant pills or eating vast quantities of foods rich in antioxidants may be failing to show a beneficial effect against cancer because they do not act at the critical site in cells where tumor-promoting ROS are produced -- at cellular energy factories called mitochondria. Rather, supplements and dietary antioxidants tend to accumulate at scattered distant sites in the cell, "leaving tumor-promoting ROS relatively unperturbed," the researchers say.

 

 

Herein lies the key:  most antioxidants don't get into the mitochondria where the worst ROS production occurs.   Meanwhile, people are seeing profound effects from mitochondrial antioxidants:  SkQ1, MitoQ, SS-31/Bendavia, all of which are targeted to the mitochondria through the use of a positive charge that's attracted by the mitochondrial membrane potential, and c60-oo, which is probably incorporated into membranes in general, including the mitochondrial membrane, by virtue of its long chain fatty acid nature.  There have also been reports of other fullerenes being preferentially located in mitochondria.

 

The idea that eating antioxidant-rich foods isn't helpful doesn't agree with a large body of epidemiology.  Maybe they mean something special about "vast quantities"?


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#3 gt35r

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Posted 12 July 2014 - 07:03 PM

I think the antioxidants that cause deleterious activity tend to suppress endogenous production of antioxidants without adequately addressing ROS/RNS.

 



#4 Strelok

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Posted 14 July 2014 - 03:35 AM

 

  Meanwhile, people are seeing profound effects from mitochondrial antioxidants:  SkQ1, MitoQ, SS-31/Bendavia, all of which are targeted to the mitochondria through the use of a positive charge that's attracted by the mitochondrial membrane potential, and c60-oo, which is probably incorporated into membranes in general, including the mitochondrial membrane, by virtue of its long chain fatty acid nature. 

 

Does PQQ fall into the same category?



#5 niner

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Posted 14 July 2014 - 08:31 PM

 

 Meanwhile, people are seeing profound effects from mitochondrial antioxidants:  SkQ1, MitoQ, SS-31/Bendavia, all of which are targeted to the mitochondria through the use of a positive charge that's attracted by the mitochondrial membrane potential, and c60-oo, which is probably incorporated into membranes in general, including the mitochondrial membrane, by virtue of its long chain fatty acid nature. 

Does PQQ fall into the same category?

 

No, not exactly.  It's not specifically targeted to the mitochondria, although it has a lot of biological activities that are related to mitochondria, and appears to foster mitochondrial biogenesis.  It's an antioxidant by virtue of its quinone functionality, and is something like ubiquinone in this regard.   It can act similar to the mitochondrially- targeted compounds, suggesting that it's active at the mitochondria, at whatever concentration it's able to achieve.  It would be interesting to see what would happen if you attached it to a hydrophobic cation like in MitoQ or SkQ1.


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#6 goodman

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Posted 31 July 2014 - 09:03 AM

niner but there r not many in human studies about this

#7 Kalliste

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Posted 31 July 2014 - 08:47 PM

Isn't this a problem with antioxidant pills for most of the time?

Here is Phil Goetz take on it a few years ago:

http://lesswrong.com...ammers_are_the/

 

There are plenty of studies demonstrating that a higher amount of fruits, berries, nuts, vegetables etc reduce the risk of cancer and even more importantly all cause mortality.







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