cron-web.org

[A1CR]

[posted on behalf of MR and Dean; Oct 24, 2000]

Before I start, please don't anyone ask me to clarify MiFRA itself in
its various aspects: it's extremely complex. Everything below assumes
that readers have read de Grey's book (12) and/or core papers (9-11).

On 18 Oct 2000, Dean wrote:

>My one criticism of the book (and the MiFRA theory in general) is that there
>doesn't seem to be a very strong connection between the MiFRA and CR, the
>one intervention that has been consistently shown to extend max lifespan.

>... the early hopeful results that CR slowed metabolic rate... has
shown not to be the case...

de
>Grey falls back on what seems to me to be a rather weak explanation of CR's
>effects relative to the theory, namely that CR upregulates repair enzymes,
>and hence minimizes the damage from free radicals. I'm sure this
>upregulation of repair mechanisms is true, but somehow I would expect (or
>hope for) a more direct link between the MiFRA and CR.
>
>MR, does Aubrey really believe this upregulation of repair
>mechanisms is the primary way CR extends MLS?

I'm sure he believes it is A way. And it's entirely plausible that CR
might work entirely by such mechanisms: the germ line, after all, is
exposed to AL conditions, but manages (in vivo) to evidently preserve
itself without aging, despite the aging of the organism, apparently
entirely due to better repair mechanisms and more rigorous apoptotic mechanisms.

He has others, however. One way which
he hasn't formally invoked, but which is implicit in some discussions
between he and I on
my pet theory on DHA, is the fact that CR reduces DHA incorporation into
MIM (most explicitly in (1)). Since more desaturated MIM means (barring
some factor which manages to PERFECTLY prevent it) more ROS damage to
MIM (note that recent speculations on DHA, UCP, and ROS production are
irrelevant, here, as SMR is evidently NOT altered by CR, as would be
predicted by any such hypotheses), and MIM peroxidation oxidatively
damages the mtDNA, which per MiFRA gets the aging ball rolling.

This can, in turn, be explained as upregulating of the mechanisms used
by more longevous spp to keep DHA out of MIM -- evidently decrease in
endogenous desaturase activity (yet apparently NOT d6d (2) -- in
fascinating support of the Zone!) and the activity of MIM phospholipid
acyl side-chain remodelling enzymes.

I found in a recent Deja post
>that Aubrey seems also to believe that CR reduces free radical production.
>From:
>
>http://x69.deja.com/getdoc.xp?AN=653965959&search=thread&CONTEXT=971881186.1
>616445506&HIT_CONTEXT=971880916.1613692950&HIT_NUM=4&hitnum=9
>
>"This says (presuming ROS are indeed instrumental in causing the common
>deletion/SDH++/COX- phenomenon) that CR reduces ROS production (which
has of
>course been shown by direct measurement too) and increases the degree of
>coupling of mitochondria."
>
>By what mechanism does Aubrey believe CR reduces ROS production, if it
>doesn't reduce metabolic rate and actually increases the degree of coupling
>(which would seem to increase the proton gradient and thereby increase ROS
>production)?

First, remember that Aubrey has already beaten me over the head w/this
one, & I have gently rapped yours in turn. "Coupling" is a laboratory
artifact. We don't know a damned thing about what an isolated mt's
coupling means in real-world terms of the in vivo ETS. The fact that CR
animals' mt are more coupled and show diffferent state 3:state 4 ratios
says that CR is affecting their function and tells us something about
what they CAN do under the right conditions -- not something about what
they DO do. So the fact that CRONie mt are more coupled doesn't mean
that in vivo the p+ gradient or ROS production is any higher.

Next, remember that MiFRA does not depend on showing WHY mt ROS
production is reduced by CR. The fact that it DOES so is, again, good
support for the theory. The fact that it does so ACCOMPANIED by the
lower incidence of mt which are overactive in succinate dehydrogenase
and null for complex I ("SDH++/COX-") (3) is quite striking
support for the RHH part of his theory: these are the PRECISE conditions
predicted to
occur in the cells which drive aging. That CR reduces the incidence of
such mt, AND reduces mt ROS production, AND reduces mt peroxidizability
(which would make mtDNA less susceptible to damage from said ROS) is
striking support for the elaborate, baroque, even sci-fi visionary
aspects of his theory. (BTW, RHH now has some real-world experimental
support (5)). It was IMHO a gross oversight for de Grey not to mention
this in the book (despite the fact that he was aware of it).

All this is just pedantic elaboration of de Grey's statement above, of
course .

Before I answer this, let me point out x that the established fact that CR
reduces the incidence of
With all of that as background: Aubrey has just advanced an hypothesis
to explain the reduced GENERATION of ROS by CRONies, which is surely of
interest.

>http://x71.deja.com/[ST_rn=ps]/threadmsg_ct.xp?AN=674685652.1&mhitnum=9&CONTEXT\
=972089630.316866575
To go thru' this in a bit more detail: the Desai paper (4) shows that CR
reduces Complex I activity. Fumbling
of e- by complex I as it hands them over to Complex III via the
two-faced CoQ is the main ROS producer in mt, so this does explain, in
one sense, how CR reduces mt ROS generation. But, as Aubrey points out,
this just becomes a third wo/man argument: if the TCA (which makes both
the NADH which is shutled thru' Compl I, and the FADH2 which goes thru'
Compl II) is running normally, it should produce a defined amount of
NADH, and a defined amount of FADH2, which should require a steady ratio
of activity of the 2 Complexes. So wussup?

"Well," says Aubrey, "maybe CRONies are shuttling extra NADH thru' the
PMOR." Unbeknownst to him, (7) (as pointed out by our own Bob Firestine)
has shown that some NADH is indeed being oxidized by a mechanism which
does is not inhibited by rotenone, as ETS activity normally would. The
abstract asserts that it is an mt oxidation, but Aubrey, who rushed out
to grab the paper as soon as Bob drew his attention to the abstract,
found that they actually provide "no analysis of what this mysterious
NADH-oxidiser might be; in particular there is no proposal for where the
electrons go." He speculates that they may have accidentally gotten some
PMOR from the CELL membrane mixed in wiht their mt fraction.

It's currently believed that mt are actually the decendants of symbiotic
bacteria, incorporated into eukaryotic cells eons ago. This allowed
cells to more effectively compartmentalize the hazardous reactions of
ETS. Before that, how did such cells make energy? Books discussing this
hypothesis tend to assume a primitive cell membrane ETS. The PMOR could
be just this beast, normally used these days just as a safety valve for
extreme excess NADH, brought into more active duty by CR. The normal
need for such a safety valve would explain why the PMOR appears to be
ubiquitous across all modern species, as other ideas (such as
stabilizing circulating ascorbate) seem inadequate, esp as it now
appears that ascorbate is NOT pro-oxidant in vivo (8 ).

"But," we say, "the PMOR is supposed [per MiFRA] to be puking forth
superoxide! That's no improvement: that's actually making things worse!"
Aubrey: "Just as more superoxide is generated as Complex I becomes
overloaded [because e- are hanging in limbo longer before being picked
up by Complex III], so more superoxide is generated when the PMOR is
overloaded with NADH under RHH. When PMOR activity is lower (as he
hypothesizes may be the
case in CR), it can work reasonably efficiently. By creating a low level
of e- flow thru' BOTH Complex I AND PMOR, CR optimizes the efficient
functioning of both."

Because the PMOR, as the putative pre-mt ETS, is no longer functional as an
ATP generator (pre-mt, it would have functioned anaerobically, per
orthodoxy), this is expected to reduce energy production. But a large
portion of cellular energy is spent pumping Na out of the cell, and by
spitting H+ out of the cell (as part of its proto-ETS activity), the
PMOR makes
this energetically cheaper, because of an extant Na/H antiport transporter.
This STILL leaves a certain energetic problem, of course -- while the
cell will have plenty of energy under non-stressed conditions, it won't
be able to really churn out ATP for peak output purposes -- and this, in
turn, helps explain why CRONies (who normally handle most stressors much
better than AL littermates) can't handle certain stressors the
resistance to which is known to be ATP-dependent (such as that to cold,
with which the organism normally deals via waste heat production in
futile cycling).

The question, then: what exactly prompts this shift in NADH targetting?

De Grey frankly admits he dunno. This is of course unfortunate, but we
don't mechanistically know what causes many major CR changes. Something
involving gene expression, of course (whic says nothing at all).

Aubrey admits that this is even more speculative than MiFRA itself, but
he'll run with it for now -- and there really aren't any alternatives,
granted that CR reduces mt O2- producton WITHOUT lowering SMR (as it's
accepted that it does not).

-MR

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7. Lemeshko VV, Belostotskaya LI.
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PMID: 1602841; UI: 92292673

8. Carr A, Frei B.
Does vitamin C act as a pro-oxidant under physiological conditions?
FASEB J. 1999 Jun;13(9):1007-24. Review.
PMID: 10336883; UI: 99270895

9. de Grey AD.
The reductive hotspot hypothesis: an update.
Arch Biochem Biophys. 2000 Jan 1;373(1):295-301. Review.
PMID: 10620352; UI: 20088624

10. de Grey AD.
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Bioessays. 1997 Feb;19(2):161-6. Review.
PMID: 9046246; UI: 97198192

11. de Grey AD.
A mechanism proposed to explain the rise in oxidative stress during aging.
J Anti-Aging Med. 1998; 1(1):53-66.

12. Title: The Mitochondrial Free Radical Theory of Aging
Author: Aubrey D.N.J. de Grey
Price: $89.00 (212pp, hardback)
Publisher: Landes Bioscience, 810 South Church Street Georgetown, TX, USA
tel: +1 512 863 7762, fax: +1 512 863 0081
ISBN: 1-57059-564-X

http://www.landesbioscience.com/degrey.html