[escepticos] vitamina C y las tres C

[Javier Armentia]

Nota de prensa en NewsWise:
http://www.newswise.com/articles/view/533158/


  How Vitamin C Stops the Big “C”


Newswise — Nearly 30 years after Nobel laureate Linus Pauling famously 
and controversially suggested that vitamin C supplements can prevent 
cancer, a team of Johns Hopkins scientists have shown that in mice at 
least, vitamin C - and potentially other antioxidants - can indeed 
inhibit the growth of some tumors ― just not in the manner suggested by 
years of investigation.

The conventional wisdom of how antioxidants such as vitamin C help 
prevent cancer growth is that they grab up volatile oxygen free radical 
molecules and prevent the damage they are known to do to our delicate 
DNA. The Hopkins study, led by Chi Dang, M.D., Ph.D., professor of 
medicine and oncology and Johns Hopkins Family Professor in Oncology 
Research, unexpectedly found that the antioxidants’ actual role may be 
to destabilize a tumor’s ability to grow under oxygen-starved 
conditions. Their work is detailed this week in /Cancer Cell/.

“The potential anticancer benefits of antioxidants have been the driving 
force for many clinical and preclinical studies,” says Dang. “By 
uncovering the mechanism behind antioxidants, we are now better suited 
to maximize their therapeutic use.”

“Once again, this work demonstrates the irreplaceable value of letting 
researchers follow their scientific noses wherever it leads them,” Dang 
adds.

The authors do caution that while vitamin C is still essential for good 
health, this study is preliminary and people should not rush out and buy 
bulk supplies of antioxidants as a means of cancer prevention.

The Johns Hopkins investigators discovered the surprise antioxidant 
mechanism while looking at mice implanted with either human lymphoma (a 
blood cancer) or human liver cancer cells. Both of these cancers produce 
high levels of free radicals that can be suppressed by feeding the mice 
supplements of antioxidants, either vitamin C or N-acetylcysteine (NAC).

However, when the Hopkins team examined cancer cells from 
cancer-implanted mice not fed the antioxidants, they noticed the absence 
of any significant DNA damage. “Clearly, if DNA damage was not in play 
as a cause of the cancer, then whatever the antioxidants were doing to 
help was also not related to DNA damage,” says Ping Gao, Ph.D, lead 
author of the paper.

That conclusion led Gao and Dang to suspect that some other mechanism 
was involved, such as a protein known to be dependent on free radicals 
called HIF-1 (hypoxia-induced factor), which was discovered over a 
decade ago by Hopkins researcher and co-author Gregg Semenza, M.D., 
Ph.D., director of the Program in Vascular Cell Engineering. Indeed, 
they found that while this protein was abundant in untreated cancer 
cells taken from the mice, it disappeared in vitamin C-treated cells 
taken from similar animals.

“When a cell lacks oxygen, HIF-1 helps it compensate,” explains Dang. 
“HIF-1 helps an oxygen-starved cell convert sugar to energy without 
using oxygen and also initiates the construction of new blood vessels to 
bring in a fresh oxygen supply.”

Some rapidly growing tumors consume enough energy to easily suck out the 
available oxygen in their vicinity, making HIF-1 absolutely critical for 
their continued survival. But HIF-1 can only operate if it has a supply 
of free radicals. Antioxidants remove these free radicals and stop 
HIF-1, and the tumor, in its tracks.

The authors confirmed the importance of this “hypoxia protein” by 
creating cancer cells with a genetic variant of HIF-1 that did not 
require free radicals to be stable. In these cells, antioxidants no 
longer had any cancer-fighting power.

The research was funded by the National Institutes of Health.

Authors on the paper are Dean Felsher of Stanford; and Gao, Huafeng 
Zhang, Ramani Dinavahi, Feng Li, Yan Xiang, Venu Raman, Zaver Bhujwalla, 
Linzhao Cheng, Jonathan Pevsner, Linda Lee, Gregg Semenza and Dang of 
Johns Hopkins.

On the Web:
http://www.hopkinsmedicine.org/hematology/faculty_staff/dang.html
http://www.hopkins-ice.org/vascular/int/semenza.html
http://www.cancercell.org/