Re: If free radicals promote aging, then why is nitric oxide involved in...

Okay.

I didn't have time to read the paper you mentioned, but I can tell that you're
trying to oversimplify the situation. First of all, free radicals are not all
bad; in fact, they are necessary for life. Reactive oxygen species have been
associated with the promotion of aging (visit http://
en.wikipedia.org/wiki/Free-radical_theory for a quick primer), 
but there are numerous endogenously synthesized antioxidants that keep free
radicals in at healthy levels and we don't know how all of these important
molecular players may be involved. Nitric oxide is a reactive 
oxygen species, as well as being a reactive nitrogen species; it is ubiquitous
in the human body and plays important roles in the maintenance of health (visit
http://en.wikipedia.org/wiki/
Nitric_oxide for a quick primer). Diseases probably arise at the extremely high
or extremely low physiological concentrations of NO. The role of free radicals
in aging is somewhat controversial(and it depends greatly on what free radicals
are in question), but scientists are building our understanding.

Thanks for your question.

You can find numerous research articles on free radicals, such as nitric oxide,
and aging at PubMed.

Hope this helps,
Chris Reigstad