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From: ironjustice on 10 Aug 2008 20:20
Radical-free biology of oxidative stress
Dean P. Jones1*
1 Emory University

* To whom correspondence should be addressed. E-mail:
dpjones(a)emory.edu.

Free radical-induced macromolecular damage has been studied
extensively as a mechanism of oxidative stress, but large-scale
intervention trials with free radical scavenging antioxidant
supplements show little benefit in humans.
The present review summarizes data supporting a complementary
hypothesis for oxidative stress in disease which can occur without
free radicals.
This hypothesis, which is termed the "redox hypothesis", is that
oxidative stress occurs as a consequence of disruption of thiol redox
circuits which normally function in cell signaling and physiologic
regulation.
The redox states of thiol systems are sensitive to 2-electron oxidants
and controlled by the thioredoxins (Trx), glutathione (GSH) and
cysteine (Cys).
Trx and GSH systems are maintained under stable but non-equilibrium
conditions due to a continuous oxidation of cell thiols at a rate of
about 0.5% of the total thiol pool per minute.
Redox-sensitive thiols are critical for signal transduction (e.g., H-
Ras, PTP-1B), transcription factor binding to DNA (e.g., Nrf-2, NF-B),
receptor activation (e.g., IIb3 integrin in platelet activation) and
other processes.
Non-radical oxidants, including peroxides, aldehydes, quinones and
epoxides, are generated enzymatically from both endogenous and
exogenous precursors and do not require free radicals as intermediates
to oxidize or modify these thiols. Because of the non-equilibrium
conditions in the thiol pathways, aberrant generation of non-radical
oxidants at rates comparable to normal oxidation may be sufficient to
disrupt function.
Considerable opportunity exists to elucidate specific thiol control
pathways and develop interventional strategies to restore normal redox
control and protect against oxidative stress in aging and age-related
disease.

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