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[posted on behalf of MR; 2003-10-26]

A long-standing point of contention between myself and the font of
shockingly original biogerontological insight, Dr. Aubrey de Grey, is
the likely value of CR for humans. Most recently, he has advanced the
following argument to suggest that CR will lead to nearly negligible
effects in a longevos spp such as we:

http://tinyurl.com/b6n6h

Clarification here:

http://tinyurl.com/bsjbq

ISTM that several folks -- both here and on sci.l-e -- fundamentally
misunderstand the nature of the argument being made (either that, or *I*
do !). Now, I actually think that Aubrey is showing his usual creative
insight here, but I actually don't want to argue about the merits of teh
THEORETICAL case (an attempt at clarification IS appended below, after
the references -- tho' I fear I've likely failed to actually provide any
clarification for many > ).

Rather, I'm going to spend some time attacking the conclusion on
empirical grounds. However good the logic of the argument may be from a
theoretical POV (starting with the disposable soma theory, which is IMO
pretty darned airtight a priori & now well-supported empirically), I
think that there is good evidence that the metabolic effects of CR --
including, apparently, the key ANTI-AGING effects (whatever their nature
& actual evolutionary purpose) take longer to come fully into play than
the duration of the kind of famine a rodent is
realistically likely to survive. What remains of de Grey's a priori case
is some tension in the DST -- but a failed argument against CR's human relevance.

It seems difficult, moreover, to accept the notion that these ongoing
metabolic adjustments are irrelevant to the CR effect. We cannot accept
that they are of no significance whatsoever -- things exist in the
organism for evolutionary reasons -- & clearly they aren't effects that
PREVENT the life-extending effect of CR. When combined with the evidence
that it takes some time for CR to actually impact lifespan (and, by
implication, aging), it seems that these metabolic shifts are causal in
the CR effect. So even if de Grey's analysis holds with respect to
those aspects of the CR state which are needed to survive famine, it's
not the whole story on the CR state associated with retarded aging in rodents.

End preamble; the evidence:

1. TIME-DEPENDENT EFFECTS OF CR ON MITOCHONDRIAL FUNCTION. As pretty
much everyone who follows my post knows, I'm pretty darned convinced of
the critical role played by mtROS in aging -- & only a tiny bit less
convinced of de Grey's specific proposal for how mtROS actually drives
the process. Consistent with this, CR reduces mtROS generation -- the
only intervention yet known to do this (tho' I have presented arguments
that R(+)-lipoic acid &/or metformin accomplish the same thing, albeit
via different mechanisms). Consistent with this, CR -- the only
non-genetic intervention yet known to retard aging per se in mammals --
is also the only the only non-genetic intervention yet known to reduce
mtROS generation in mammals (1-8 ). (The Ames mouse genetic intervention
also has lower mtROS (9)).

The most studies on this (1,7,8) have compared older animals which have
been on very long-term CR to old AL animals. Barja's group, however, has
done several experiments measuring mtROS at different time points after
initiating CR; these studies find that 6 weeks of CR is enough to reduce
mtROS in the liver (5) but neither 6 weeks (2) nor 4 months (3) on CR
lowers mtROS in the (probably more aging-relevant) heart and skeletal
muscle in rats -- but that 1 year does (2). (Actually, (1) isn't
totally clear on this point: some animals may've been CRed for just 6
mo, which would narrow the range down even further).

If we buy into the idea that CR slows aging PRIMARILY by reducing mtROS
-- & I think the evidence favoring this is pretty darned strong -- then
this is not just *a* metabolic effect of CR (tho' that might be enough
to refute de Grey's objection), but THE metabolic effect of CR that's of
(greatest) relevance to its anti-aging effect.

2. METABOLIC RATE: One of the most persistent pseudo-myths about CR is
that it slows metabolism. Until very recently, this has been a view held
in the face of the evidence, which shows that while there is an INITIAL,
TRANSIENT depression of metabolic rate induced by CR (& also, trivially,
a permanent one, in the sense that if you measure WHOLE-BODY metabolism,
obviously a smaller body with smaller cells consumes less oxygen), in
fact this corrects itself in a matter of some weeks but not more than
4.5 mo (10,11).

I find this time-course to be an interesting coincidence with the mtROS
data, op cit: as the body adjusts its metabolism to the CR state,
producing fewer ROS, its metabolic rate returns. It's clear, from the
data, that CR induces unusual mitochondrial metabolism; de Grey's theory
of how CR reduces mtROS (12) is an hypothetical sketch of of this might
happen. A key feature of this hypothesis -- later confirmed by Barja --
is that CR reduces mtROS specifically at Complex I. de Grey argues that
this is most likely to happen via a reduction in the actual PROTEIN;
Barja states (but doesn't really prove) that it happens due to a lower
degree of reduction (e- traffic) thru' Complex I. THEN, the mt has to
'learn' to export extra One expects that What we appear to be observing
is this very shift unfolding over time.

3. GENE EXPRESSION PROFILES. Many folks will, by now, be at least loosely
famiiliar with some new work that Steven Spindler et al have done on the
*time-course* of gene expression changes under CR; see, for SOME info:

http://www.biomarkerinc.com/assets/pdfs/BioMarker_Article2.pdf

Wht most of the coverage thus far hasn't highlighted (tho' Dr. S has
presented more details at some scientific conferences, incl. the
mind-blowing IABG 10 organized by the equally mind-blowing Dr. de Grey)
is the fact that this research is showing that it takes some time -- at
least 2 months & conceivably up to HOW LONG FOR WHOLE COURSE -- for the
gene expression profile of CR to set in. Over this time, many genes'
expression slowly moves in some direction; some don't budge until toward
the end, & hten suddenly jump; others move in one direction early on &
then return to baseline or even REVERSE direction.

Now, folks who've followed my posts willl know that I'm skeptical about
how much we're going to learn from these studies (tho' Spindler's method
is more likely to lead to meaningful NEW info than Weindruch & Prolla's:

[see various CR Society List Archives] and...
http://tinyurl.com/bc5ob

... but again, the point is that CR-associated metabolic changes are
still going on thru'out the plurality -- & perhaps the MAJORITY -- of a
mouse-survivable famine to complete the organism's metabolic adjustment
to low food intake. & NB, that these are effects in the LIVER, a
relatively simple, mitotic tissue; a more complex tissue like brain or
skeletal muscle -- organs more likely to be involved in aging -- were
reported, over the LONG term, to show different kinds of changes rom
those seen in the liver (compare (15) to (16-18 )).

4. LIFESPAN. Eliminating the 'coincidence' option above, there does seem
to be some evidence that it takes some time on CR before the organism
undergone sufficient changes (or, more weakly, had those changes for
long enough) to have an impact on LS. This is supported by a study
reported in 2 reviews by BJ Merry (13,14), but never published in full:
rodents put on CR from weaning for 7, 39, 159, or 236 days & then
returned to AL did not demonstrate increases in LS -- but those allowed
nearly a year on CR (334 days) DID show such increases.

If one buys into MiFRA, this dovetails nicely with the op cit findings
that the period required to reduce mtROS is > 4 mo but <= 1 yr.

Now, I've already presented mch of this to Aubrey directly. He has two
(tho' he actually presented them as one -- I'm AFAICS being both
logically exact & more fair to the strength of his arguments by
splitting them up) counter-arguments to the whole mess:

1. Perhaps it doesn't REALLY take this long to induce these effects in
CR, but rather they happen, but it takes a certain amount of time for
the effect to reach statistically significant levels. ISTM that this
just won't wash for the gene induction effects, esp the ones that
actually REVERSE themselves over the course of 2 mo & the LS data: it
can't be a progression from a small effect to a greater effect, because
it actualy changes direction over time.

2. Perhaps the reason why it takes so long to induce these changes is
that the degree of CR is not sufficiently severe. Perhaps the mild level
of CR involved allows the organism to be lackadaisical (sp?) about
making the necessary shifts, and that a more sudden, drastic induction
might bring on the full metabolic effects more rapidly.

I have 3 counterarguments to this, which I think are in sum very strong
(& indeed, the first 2 to be almost irrefutable):

a. Aubrey actually presents such a dietary situation as being more
representive of the conditions likely to hold under famine. (Indeed, it
HAS to be, in order for the evolutionary argument he's advanced to hold:
if not, we're back with it taking longer than a survivable famine for CR
to take hold, which would undermine it). I don't buy this. There isn't
that much room between the %CR involved in these studies (40%) and the
amount which is typically lethal (60-70%), even under the very sheltered
conditions of the laboratory; ISTM that in the wild -- with greater
energy expenditure necessary for activity, & more potentially lethal
threatts (infection, wounds, predators, etc) -- it's extremely unlikely
that much more CR will be survivable, even with the upregulated survival
mechanisms induced by CR. Under such conditions, CR will not be selected
for, because the rodents carrying the metabolic flexibility to make the
shift will simply die. Indeed, evolution will select AGAINST these
animals for carrying the wasteful energetic & developmental burden of
these genes.

b. ISTM that most famine conditions take a while to take hold. The
evolutionary pressure to develop & maintain the CR response comes from
repeated exposure to famines, which only very rarely will occur 'all at
once:' rather, energy availability will slowly decrease, as an unusually
severe winter or a drought sets in & it becomes progressively more
difficult to find food. This would allow a gradual induction of the
metabolic effects of CR as observed, at the Calorie levels observed --
ie, CR as observed -- incl the time scale of induction -- is a good
mimic for the field conditions under which the effect evolved.

c. Many studies have observed hormonal & other metabolic effects on
short-term starvation or near-starvation which are different from -- &
even opposite to -- those observed in long-term, life-extending CR.
This would seem to directly refute the idea that very extreme CR would
more rapidly induce the metabolic effets thereof; indeed, evidently the
reverse is so. (I state this, frankly, from memory; I can't, lfor the
life of me, think of any concrete examples at the moment, but darn it,
I'm sure that they exist ).

d. More weakly: when one initiates CR in adult animals (10+ mo old mice;
~30 human years), it apparently doesn't work unless CR is instituted
gradually (over the course of at least a month). This is presumably in
part due to the lower metabolic flexibility of older organisms. But it
does suggest that there is a certain level of metabolic inertia in the
organism, & that it may take some time to adapt to it; perhaps merely
less, in younger animals -- & that, again, sufficiently severe CR
(perhaps just less severe in younger animals), if rapidly induced, fails
to activate the response, or induces the response but fails to confer a
survival advantage -- in which case, its evolutionary advantage is lost
in any case.

-MR

1: Lambert AJ, Merry BJ.
Effect of Caloric Restriction on Mitochondrial Reactive Oxygen Species
Production and Bioenergetics - REVERSAL BY INSULIN.
Am J Physiol Regul Integr Comp Physiol. 2003 Sep 11 [Epub ahead of
print]
PMID: 12969875 [PubMed - as supplied by publisher]

2: Gredilla R, Sanz A, Lopez-Torres M, Barja G.
Caloric restriction decreases mitochondrial free radical generation at
complex I and lowers oxidative damage to mitochondrial DNA in the rat heart.
FASEB J. 2001 Jul;15(9):1589-91. No abstract available.
PMID: 11427495 [PubMed - indexed for MEDLINE]
http://www.fasebj.org/cgi/reprint/15/9/1589.pdf

3: Drew B, Phaneuf S, Dirks A, Selman C, Gredilla R, Lezza A, Barja G,
Leeuwenburgh C.
Effects of aging and caloric restriction on mitochondrial energy
production in gastrocnemius muscle and heart.
Am J Physiol Regul Integr Comp Physiol. 2003 Feb;284(2):R474-80. Epub
2002 Oct03.
PMID: 12388443 [PubMed - indexed for MEDLINE]

4: Lopez-Torres M, Gredilla R, Sanz A, Barja G.
Influence of aging and long-term caloric restriction on oxygen radical
generation and oxidative DNA damage in rat liver mitochondria.
Free Radic Biol Med. 2002 May 1;32(9):882-9.
PMID: 11978489 [PubMed - indexed for MEDLINE]

5: Gredilla R, Barja G, Lopez-Torres M.
Effect of short-term caloric restriction on H2O2 production and
oxidative DNA
damage in rat liver mitochondria and location of the free radical source.
J Bioenerg Biomembr. 2001 Aug;33(4):279-87.
PMID: 11710804 [PubMed - indexed for MEDLINE]

7. Lass A, Sohal BH, Weindruch R, Forster MJ, Sohal RS.
Caloric restriction prevents age-associated accrual of oxidative damage to
mouse skeletal muscle mitochondria.
Free Radic Biol Med. 1998 Dec;25(9):1089-97.
PMID: 9870563 [PubMed - indexed for MEDLINE]

8: Sohal RS, Ku HH, Agarwal S, Forster MJ, Lal H.
Oxidative damage, mitochondrial oxidant generation and antioxidant defenses
during aging and in response to food restriction in the mouse.
Mech Ageing Dev. 1994 May;74(1-2):121-33.
PMID: 7934203 [PubMed - indexed for MEDLINE]

9. Brown-Borg HM, Johnson WT, Rakoczy SG, Romanick MA.
Mitochondrial oxidant production and oxidative damage in Ames dwarf mice.
J Am Aging Assoc. 2002 Jul; 24(3):85-96.

10.McCarter RJ, McGee JR.
Transient reduction of metabolic rate by food restriction.
Am J Physiol. 1989 Aug;257(2 Pt 1):E175-9.
PMID: 2764100 [PubMed - indexed for MEDLINE]

11: McCarter R, Masoro EJ, Yu BP.
Does food restriction retard aging by reducing the metabolic rate?
Am J Physiol. 1985 Apr;248(4 Pt 1):E488-90.
PMID: 3157325 [PubMed - indexed for MEDLINE]

12. de Grey ADNJ.
A proposed mechanism for the lowering of mitochondrial electron leak by
caloric restriction.
Mitochondrion 2001 Aug; 1(2):129-139.
http://www.gen.cam.ac.uk/sens/manu9.pdf

13. Merry BJ. Food Restriction and the Aging Process. (Photocopy in my
posession; damned if I know what book it came from!).

14. Merry BJ. "Dietary Manipulation of Ageing: An Animal Model." In
Bittles AH & KJ Collins, The Biology of Human Ageing, Cambridge
University Press, Cambridge, 1986.

15 Cao SX, Dhahbi JM, Mote PL, Spindler SR.
Genomic profiling of short- and long-term caloric restriction effects
in the
liver of aging mice.
Proc Natl Acad Sci U S A. 2001 Sep 11;98(19):10630-5. Epub 2001 Sep 04.
PMID: 11535822 [PubMed - indexed for MEDLINE]

16: Lee CK, Weindruch R, Prolla TA.
Gene-expression profile of the ageing brain in mice.
Nat Genet. 2000 Jul;25(3):294-7.
PMID: 10888876 [PubMed - indexed for MEDLINE]

17: Lee CK, Klopp RG, Weindruch R, Prolla TA.
Gene expression profile of aging and its retardation by caloric restriction.
Science. 1999 Aug 27;285(5432):1390-3.
PMID: 10464095 [PubMed - indexed for MEDLINE]

18. Shelke RR, Leeuwenburgh C.
Lifelong caloric restriction increases expression of apoptosis
repressor with a caspase recruitment domain (ARC) in the brain.
FASEB J. 2003 Mar;17(3):494-6. Epub 2003 Jan 02.
PMID: 12514107 [PubMed - indexed for MEDLINE]

The issue is not the duration *OF CR* to which an organism
would be exposed (clearly, longer CR = greater LS extension, and this is
not under dispute), nor the NUMBER of famines (CR events) to which one
is going to be exposed. The issue is also not directly related to the
EVOLUTIONARY PURPOSE of the CR effect. The issue is the RELATIVE
survival & reproductive fitness THREAT posed by a famine of a certain
ABSOLUTE period of famine in the 2 organisms, & the degree & time-frame
of the response required to pull that off, & the implications of this
for the extrapolability of the RELATIVE magnitude of CR's anti-aging
effect per se in rodents to humans (& thence the ABSOLUTE LS to be
gained from a GIVEN ABSOLUTE period on CR).

That is: whether CR literally evolved as an anti-aging mechanism (by
which you are to age slower during famine & thus be biologically younger
& ready to go when the good times return) or more narrowly as a simpler
hormetic response designed to make the rigors of lean times THEMSELVES
more survivable (evidence I present below & have discussed previously
argue against this IMO, but that's a side point), the question is
whether we can reasonably expect the SAME ABSOLUTE exposure to CR (a few
weeks or months of famine, for (wo)man or mouse) to elicit the same
RELATIVE response (ie, X% CR ---> Y% age retardation during the famine
period, where Y is proportional to X (which latter phenomenon is the
empirical finding of the studies), irrespective of the
evolutionary-selective teleology of the anti-aging effect per se).

The essential point of A's argument is that the magnitude of the
response doesn't HAVE to be as great for an human as for a rodent,
because the nature of the threat is less. Because both animals only have
to survive the same ABSOLUTE period, there is no need for an effect
which *leads to* a PROPORTIONAL anti-aging effect in humans as we see in
rodents. To concretize: if selective pressure comes from repeated
exposure to 1 mo famines @ 40% CR (eg), the CR effect induced in rodents
has to be strong enough to remobilize its resources for what is 2.5% of
its lifespan -- LEADING TO an appropriate, proportional LS extension. By
contrast, the same 1 mo at 40% CR only requires a human to induce an
effect which facilitates survival (LEADING TO retarded aging) for ~0.06%
of its LS.

What de Grey is suggesting is that it doesn't make evolutionary sense
for the organism to increase its survival programs to equal PROPORTIONAL
degrees to cover the same ABSOLUTE time period -- not that a longer
period on CR won't lead to a greater ABSOLUTE amount of LS increase.