This covers some of the research on the most common longevity supplements and drugs. I’ve excerpted a section that I think likely is of most interest to people here - I’ve moved the “rapamycin” and “resveratrol” sections to the top for easier access:
Author: Diogo Goncalves Barardo
Advisors: Gruber, Jan
Associate Professor Jan Gruber, Main Supervisor
Associate Professor Thilo Hagen, Co-Supervisor
Examiners: Professor Brian Kennedy
Publisher: National University of Singapore (Singapore)
2.2 - Drugs Literature Review
In the following subsections, I will analyze the available literature for each drug that is part of my library plus all 5 drugs that were used in our previous work 70a The methodology for identifying the relevant literature for each compound was the following: I started by extracting the literature referred in DrugAge* 71*; I then checked the abstracts of literature that cite the previously selected DrugAge references; additionally, I included new literature that is yet to be included in DrugAge but that I was aware of.
2.2.15 - Rapamycin
Rapamycin is arguably the most famous anti-aging drug; therefore, this FDAapproved
immunosuppressant drug is vastly studied, with one of the major
aging pathways being named after it - mammalian target of rapamycin (mTOR).
A systematic review of rapamycin potential in biogerontology is outside the
scope of this dissertation, and this section provides only the upmost relevant
information. The curious reader is advised to read the cited body of work.
In fruit flies, rapamycin slightly extends mean lifespan in a gender-independent
manner, although at a significant fecundity cost148. Both these effects have been
reproduced and shown to be modulated specifically through the complex 1
branch of the TOR pathway (TORC1), including the downstream upregulation
of autophagy149. Furthermore, it is accompanied by increase stress resistance
and it is efficacious even on long/lived IIS mutant and DR flies.
The literature in C. elegans shows that the lifespan extension from rapamycin
treatment150–154 is dependent on SKN-1, but not on DAF-16155,156 or DAF-2157.
Additionally it induces mitochondrial unfolded protein response and increases
respiration158, and ameliorates the age-related decline of pharyngeal pumping
rate156. The fact that rapamycin treatment does not extend lifespan of eat-2
mutants and that it elicits a gene expression profile resembling that of a DR
state, might suggest that it could be considered a calorie restriction
mimetic156[6], although evidence in mice disputes this line of reasoning159[13].
Surprisingly, the majority of studies with rapamycin as an anti-aging
intervention have been done on Mus musculus (e.g.159,160).
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On the ITP, whether fed at 270 or 600 days of age, rapamycin extends median
and maximal lifespan in both genders of genetically heterogenous mice161. In
old mice, rapamycin restores the self-renewal and hematopoiesis of
hematopoietic stem cells and boosts immune function162.
Considering that mTOR is an evolutionary conserved aging pathway, in mice
too, rapamycin administration reduces its activity, albeit not in all tissues163.
Nonetheless, it is important to mention that muscle mass was maintained163.
Interestingly, since rapamycin improves age-related phenotypes even in young
mice, its lifespan-extension might be dissociated from the aging process
itself164.
Due to the side effects of inducing insulin resistance and immune suppression,
several intermittent schemes of rapamycin have been attempted. A 2 weeks per
month intermittent administration, is sufficient to increase lifespan, inhibit agerelated
weight gain, and delay spontaneous cancer incidence in inbred female
mice165. Moreover, a once every 5 days rapamycin treatment regimen was
shown to have no impact on blood glucose, while it still resulted on lifespan
extension in 20-months old female mice166. Although, such regiment was
elsewhere shown to not completely negate neither the immunosuppressive
effects of rapamycin, nor the associated decrease in testis weight167. Hopefully
complementary to the intermittent regimens, a 3-months transient rapamycin
treatment extends the median lifespan of middle-age mice by up to 60%168.
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2.2.16 - Resveratrol
Resveratrol is a natural polyphenol found in grapes and red wine, and it is the
compound for which there are the most lifespan assays169.
Resveratrol activates sirtuin genes and extends lifespan in yeast170–175,
worm38,154,182,183,158,170,176–181, flies170,184, fish185–188 and bees189. When nutrients
are restricted, this effect is abrogated which suggests that it is related with
caloric restriction170,171.
In worms the lifespan extension is fully dependent on SIR-2.1176,179,190 (at least
sometimes177), AAK-2190 and autophagy178, but it is independent from DAF-
16176,190. In this model organism, resveratrol treatment also induces mitonuclear
protein imbalance and activates the mitochondrial unfolded protein response158.
In Nothobranchius furzeri, a short-lived fish, it causes a 56% and 59% increase
in median and maximum lifespan, respectively. Additionally, the treated group
exhibits ameliorated decay of locomotor and cognitive function. The initial
lower survival of the treated group for the first few weeks, led the authors to
propose that resveratrol might be an hormetic compound185. In another
vertebrate model, the fish Nothobranchius guentheri, the lifespan-extending
effects and increased cognitive and locomotor function caused by resveratrol
administration were conserved. Additionally, it was shown that there was less
accumulation of lipofuscin and senescence (as measured by beta-galactosidase
activity)186. In this species too, resveratrol decreases oxidative stress188.
An additional mode of action to the hypothesis that resveratrol is a CR mimetic
acting through activating sirtuins, namely because it was contested that
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resveratrol can increase sirtuins in vivo in either worms or flies191a, is as an
antioxidant188. For example, in worms resveratrol increased mean and
maximum lifespan and also oxidative stress resistance183 (these effects have
been reproduced elsewhere179), but also there is work showing that resveratrol
does not have free-radical scavenging activity in vivo180 (albeit in this particular
work it also did not extended lifespan).
This antioxidant role it is not how resveratrol acts in bees, as the mean and
maximum lifespan extension are abolished in hyperoxic stress and the honey
bees ingest fewer quantities of food189.
After the previous brief description of the lifespan-extending effects of
resveratrol, it is also now crucial to underline the plethora of negative results.
In the ITP and in the only lifespan assay in a mammal, resveratrol did not
extended lifespan100. Also, in the model crustacean Daphnia, resveratrol has no
effect or even significantly decreases lifespan192. Furthermore, even though
resveratrol was tested in both genders of a tephritid fruit fly species and under
24 different diets it still did not elicit any lifespan extension193. In D.
melanogaster, using different strains, gender and diets, the pro-longevity effects
of resveratrol were very variable, and eventually consider dubious177. Wang et
al., reported that resveratrol has effect only on female D. melanogaster and
depending on the diet in question184. Staas et al. that dietary resveratrol had
absolutely no effect on male and female w1118 D. melanogaster in terms of
a In yeast that is clearly not the case as resveratrol does increase SIRT1 12-fold172, and
certainly there is evidence that allows a counter-argument to be made170,190.
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lifespan, locomotor activity, body composition, stress response and longevityassociated
gene expression194.
In sum, I consider that resveratrol achieves its pro-longevity effects through
caloric restriction mimicry or antioxidant capacity, in a species-specific manner.
Moreover, I consider it perhaps the most unclear anti-aging compound: the
mode of action and efficacy are highly debated, but either way it is extremely
sensitive to experiment conditions. The incredibly unreliability of resveratrol
treatment can be predicted if its main mode of action is as an antioxidant or
mitohormetic compound, as both of these are known to has an inverted Ushaped
dose-response on longevity38.
2.2.4 - Captopril
Captopril is an FDA-approved treatment for high blood pressure. It is an
angiotensin-converting enzyme (ACE) inhibitor, which is of importance as the
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ACE gene has been conserved from bacteria to mammals97 and it is one of the
few genes with genetic polymorphisms robustly associated with longevity in
humans98.
It has only been explored once under the biogerontology paradigm and was
shown to extend the mean and maximum lifespan of C. elegans97. Moreover, its
pro-longevity effect was robust in 3 distinct culture temperatures and to live and
heat-killed bacteria feeding conditions; but with no effect on brood size,
reproductive span, and pharyngeal pumping rate. The same authors replicated
these effects using acn-1a RNAi-treated worms, with the exception that the
RNAi treatment was able to increase the pharyngeal pumping rate from days
12th to 20th of adulthood.
There is substantial evidence that the pro-longevity MoA of captopril is the
inhibition of the ACN-1 gene: combined treatment of acn-1 RNAi with
captopril, did not have and addictive effect on lifespan and both interventions
have the same results in distinct genetic backgrounds. Going into more detail
on the later point, reducing the activity of ACN-1: has additive pro-longevity
benefits with caloric restriction (eat-2), mitochondrial insufficiency (isp-1) and
with long-lived IIS pathway mutants (daf-2 and age-1); it is a lifespan-extension
pathway independent of TOR (rict-1), proteotoxic stress (hsf-1)b and of sir-2.1
activity; and it is toxic to daf-16 worms, reducing their lifespan.
a the C. elegans homologue of the ACE gene.
b although it is also revealed that acn-1 RNAi increases resistance to heat-stress.
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Even though captopril has not been assayed for longevity in mammals, its prolongevity
MoA is tractable and evolutionary conserved in humans98 and fliesa,
robust to different conditions and additive to the main pro-longevity genetic
interventions (which indicates its potential to be combined with other drugs).
2.2.5 - Curcumin
Curcumin is a component of turmeric in Indian curry. The metabolite of
curcumin, tetrahydrocurcumin, extends the mean and maximum lifespan of
male C57BL/6 mice when treatment is initiated at 13-months of age, but is of
no effect when started at the 19th month of age99. However, in under the ITP
these benefits were not reproduced100. Despite failing in the gold standard
testing program, curcumin is still consideration from a biogerontology
perspective due to its very robust results in all the other model organisms tested,
e.g. in worms, curcumin does promote lifespan101b. The rest of supporting
literature was conducted in flies.
Curcumin robustly extends lifespan of male and female D. melanogaster from
two distinct wild-type strain, confers additional protection against oxidative
stress and improves climbing ability102. In yet another fly strain, a female and a
male group of flies exhibited increased mean lifespan and activity of the
superoxide dismutase103. Moreover, several works reproduced the gender and
strain-independent pro-longevity effect of curcumin in flies104–106. Other
beneficial effects include enhanced progeny viability and parental reproductive
a another FDA-approved ACE inhibitor, lisinopril, extends the lifespan of 3 D.
melanogaster strains through the same MoA307.
b I am disregarding results in which the control group had a mean lifespan of less than
9 days. Albeit there is still lifespan-extension in this work308.
fitness107. Larval feeding of curcumin in flies did not yield any additional benefit
on CR flies, which indicates potential overlapping modes of action between
these two pro-longevity interventions. Furthermore, age-specific lifespan assays
reveal that curcumin treatment effects are incredibly age-dependent, going from
benefic to harmful; accordingly to if the treatment is stated at the healthspan to
the senescent span, respectively104,106. An additional factor influencing the
magnitude of lifespan-extension caused by curcumin treatment is temperature.
Through regulation of heat shock proteins, the higher the environmental
temperature, in other words, heat stress, the larger the effect size relative to
untreated flies, independently of gender108.
2.2.6 - Epigallocathecin gallate
The first trial of the popular green tea polyphenol epigallocatechin gallate
(EGCG), resulted in no effects on the survival of worms, but improvement in
healthspan-associated traits including augmented resistance to oxidative stress,
attenuated decline of pharyngeal pumping rate and enhance chemotaxis index
in old age109. Three years after, the potent oxidative stress resistance induced by
EGCG was replicated, but this time it was accompanied the a reported mean
lifespan-extending effect of 10%110.
The unclear role of EGCG as a lifespan-extending compound in worms was
resolved by Liu Gui Xiong et al.111 which showed that this effect is robust to
different temperatures and genetic backgrounda, but highly sensitive to
a two distinct wild-type strains were used.
concentrationa. EGCG induces longevity by causing a transient increase in
reactive oxygen species, that stimulates the endogenous detoxification defense
system. More importantly for my approach, co-administration of n-acetyl-lcysteine
abolished EGCG-mediated lifespan and oxidative stress resistance
benefits and further supports that EGCG is a case of mitohormesis112. Due to
the transient induction of reactive oxygen species, and consequent defense
response, declining with age, EGCG treatment is progressively blunted with
age. This work also reiterated the requirement of the DAF-16 pathway for the
EGCG-induced longevity that was reported in a previous manuscript113.
The proposed mode of action of EGCG seems to be conserved in mammals, as
male weaning Wistar rats fed EGCG display increased median lifespan,
improved age-associated oxidative stress and superior activation of the FoxO3a
longevity factor114.
For the sake of completeness I must mention that there is an alternative mode
of action for EGCG based on results obtained in flies that proposes that
reduction in glucose metabolism is the key contributor for the superior fitness
and lifespan observed in EGCG-treated D. melanogaster115.
2.2.7 - Icariin
At the optimal dosage of 45μM when under 25ºC, icariin extends the mean
lifespan of worms by 25%116. Icariin is not the active biological form, and this
flavonoid is eventually hydrolyzed to icariside II. The direct administration of
a the reader might notice that this is common for compounds that act mainly by
antioxidant mechanisms. For the relevant literature please read the subsection about nacetyl-
l-cysteine.
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icariside II resulted in increased tolerance to thermo and oxidative stress and
slowed the locomotion (as measured by swimming bends) decline in late
adulthood. In terms of the genetic pathways involved, both icariin and icariside
II fail to extend the mean lifespan of daf-16(mu86) and daf-2(e1370) mutants,
but they did prolong the lifespan of eat-2(ad1116) and rsks-1(ok1255) strains;
suggesting that icariin depends on the IIS pathway and it is not a caloric
restriction mimetic116. Furthermore, the expression of SOD-3 increased as
confirmed by PCR and fluorescent marking.
The results from mice are in agreement with the ones obtained in worms: there
is a mean lifespan extended by 8% but no maximal lifespan; and the SOD gene
expression is increased, moreover it is indistinguishable from youth levels117.
Treated mice were lighter than the control individuals, even though they
consumed more calories. Healthspan improved as measured by the Morris water
maze, rotarod and bone mineral density (worth notice that bone mineral density
is conserved at youth levels). The icariin-treated mice also display less DNA
damage as indicated by the decreased expression of gamma-H2AX.
2.2.8 - Lipoic Acid
Lipoic acid was first shown to extend the lifespan of female and male D.
melanogaster, by 12% and 4%, respectively118. Very recently, this effect on
female flies was replicated even when started only at day 26 (mid-aged)119. The
pro-longevity effect of lipoic acid are associated with the prevention of ageassociated
functional decline and hyperproliferation of intestinal stem cells,
through the activation of the endocytosis-autophagy network119.
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The literature in C. elegans reveals that lipoic acid administration results in an
increase in the mean and maximum lifespan, with no effect on pharyngeal
pumping rate, but with the enhancement of the chemotaxis indexa in aged
worms. The lifespan-extending effect of lipoic acid on this model organism has
been confirmed only in regard to mean lifespan, but not maximum120.
Male rats fed an ad libitum diet supplemented with lipoic acid display similar
survival profiles as the control animals121.
2.2.9 - Lithium
The first initial report of lithium as a lifespan-extending drug showed that this
effect was independent of DR, FOXO/IIS or germline signaling pathways122.
Additionally, it was observed a trade-off between longevity and fertility, as
lithium treated animals produced less eggs, and most eggs that were laid
subsequently failed to hatch. Due to the lithium status as an FDA-approved drug
for the treatment of psychiatric disorders123 as a classic glycogen synthase
kinase-3 (GSK-3) inhibitor, the authors conducted lifespan assays of lithium
under different genetic interventions in the worm orthologue of this gene.
Inhibition of GSK-3β is not sufficient for lifespan extension (mutants live
shorter), and lifespan extension by lithium actually requires GSK-3β (because
it further decreases the short lifespan of gsk3 mutants).
The beneficial effects of lithium on the mean lifespan of worms were
reproduced, and there were no changes seen in maximum lifespan. Although,
a it measures the fraction of worms able to display goal-oriented motor responses from
the transformation of specific sensory stimuli.
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lithium treatment did not significantly slow the rate of aging as measured by
mortality rate doubling time. The slower decline in locomotor phenotype at all
ages, together with the previous mention studies, shows that lithium treatment
in worms as a mixed effect on healthspan assays. Moreover, the authors create
a dynamical model and supporting it by several lines of evidence conclude that
lithium elicits a greater increase in autophagy than in mitochondrial biogenesis,
and that this dictates the cellular respiratory capacity by influencing the ratio of
functional and dysfunctional mitochondria. In sum, the increase in the ATP
levels by lithium is due to a higher ratio of functional to dysfunctional
mitochondria124.
The lifespan-extending of lithium in C. elegans were reproduced in yet two
other studies and with a similar dose-response curve125,126, giving rise to the
view that lithium is a robust pro-longevity treatment. Lithium therapy as a
biphasic dose-dependent effect on lifespan, seen at similar concentrations in in
vitro127, worms and flies128. After a minimum threshold to elicit a therapeutic
effect, lithium treatment eventually becomes toxic at higher concentrations122.
On top of the biphasic lifespan extension effects being reproduced in flies, in
this model organism these are independent from gender and genetic
background128. Lithium is arguably even more benefic than in worms because
it elicits a significant improvement and protection against age-related locomotor
decline, but this time without compromising feeding behavior or fecundity.
With relevancy for the translational potential of lithium as an anti-aging therapy,
this work validated that lithium extends lifespan even when administration starts
only in mid-life or just with a short-term treatment in the case of young flies.
Like in worms, lithium extends the lifespan of DR flies, but it seems that it does
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so by inhibiting the fly orthologue of GSK-3. Also, in opposition to what was
suggested based on worm experiments, lithium does not induce or require
autophagy to promote longevity in flies. These authors propose a model in
which lithium inhibits GSK-3, which indirectly leads to the activation of the
transcription factor nuclear factor erythroid 2-related factor (NRF-2)a.
Very exciting form a translational point-of-view, are two studies showing
correlation evidence that lithium concentration in drinking water is associated
with reduced all-cause mortality, in distinct human populations, and with a
similar dosage therapeutic window to the aforementioned pre-clinical
results125,129.
As discussed in the known drug synergies section (section X), lithium as a prolongevity
treatment can be paired with rapamycin or trametinib for additional
benefits, which can be even more powerful by combining all these drugs as a
triple pharmaceutical treatment37.
2.2.10 - N-acetyl-L-cysteine
N-acetyl-L-cysteine (NAC) is a natural source of cysteine which in turn is used
in the synthesis of glutathione, and as such, it is a potent antioxidant in vivo. It
was initially discovered to increase the mean and maximum lifespan of flies by
26.6%130. Albeit this effect seems to be only conserved in the male gender of
genetically heterogenous mice, and it is marked by an accentuated weight loss,
which might hint at the induction of a partially DR-like state131.
a since GSK-3 is an NRF-2 inhibitor.
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In C. elegans, it was first shown that liposomal delivery of NAC improves
survival, in opposition with the lack of effect seen from its direct
administration132. In contrast, it was later shown that direct NAC administration
extended the mean and maximum lifespan, by up to 30.5% and 8 days,
respectively. Furthermore, it was found that NAC increases the number of
progeny, and resistance to radiation and heat shock stress133. These discrepant
evidence can be conciliated by the recent results showing that NAC has a highly
sensitive dose-response curve. NAC is a canonical antioxidant and as such its
efficacy is slave to the inverted U-shaped dose-response relation between
reactive oxygen species levels and lifespan38.
2.2.11 - Metformin
Metformin is a biguanide drug commonly used to treat type-2 diabetes.
In worms it extends median lifespan134–137 and delays the age-related decay of
mobility134,138[2,11]. The lifespan extension seems to be independent of the IIS
pathway (DAF-16, DAF-2, and AGE-1). The lack of effect of metformin in eat-
2(ad1116) mutants coupled with the display of several phenotypes associated
with DR (lower lipofuscin accumulation138, slimmer bodies, extended period of
egg-laying) and the genetic requirement of SKN-1 and AAK-2 strongly
suggests that metformin is a CR mimetic. Important from a translational
perspective, metformin did not impaired feeding134. An alternative model for
the mode of action of metformin is mitohormesis. Metformin increases reactive
oxygen species production, metabolic heat production and respiration, and,
crucial to our paradigm of combinatorial drug interventions, the antioxidant
NAC abolishes its benefits135a. These are the two main ones, but not the only
models seeking to elucidate the mode of action of metformin137,138.
In an attempt to confirm that metformin promotes longevity in an evolutionary
conserved manner in flies, indeed it was observed a robust activation of AMPK
and reduced body fat, but no lifespan extension in either gender. Moreover,
metformin was toxic in some of the concentrations tested139.
Metformin has also been tested in some less common animal models. In crickets
metformin extends survivorship and maximal longevity86. Metformin
significantly reduced growth rates and delayed maturation in crickets of both
genders. The same authors also tried the aspirin plus metformin drug pair, but
the lifespan-extension was less than in any of the single drugs. Furthermore,
metformin prolongs the lifespan of in short-lived fish and delays several
markers of aging, including lipofuscin, inflammagingb, cell senescence and
cognitive decline140.
Results in middle-aged male mice of two different strains are more
encouraging141. Metformin improves general fitness and lifespan at a low
dosagec, but it is significantly nephrotoxic (renal failure) at a higher one.
Animals in the low-dose long-term metformin treatment are initially slimmer
(even though they consumed more calories than the control animals, like in
worms), but tended to preserve their bodyweight with advancing age.
Intermittent treatment regimens of every-other week or two consecutive weeks
a the requirement of AAk-2 would equally be justified under this alternative model.
b the chronic low-grade inflammation that its characteristic of advanced age.
c this dosage still corresponds to serum levels an order of magnitude higher than those
used in the treatment diabetic human patients.
43 per month were tested, with the aim of bypassing the toxicity associated with
high levels (relative to the human therapeutic dosages) of long-term metformin
treatment. Unfortunately, neither extend mean or maximum lifespan in mice142.
In rats, metformin supplementation replicates the reduced food intake and body
weight seen in the caloric restricted group but did not extended lifespan at any
quantile143.
2.2.12 - Myricetin
The two works with lifespan assays using the naturally occurring flavonol
myricetin were conducted in worms. Their findings agree: on its pro-longevity
effects (18%144 and 33%145 mean lifespan increase, 22% maximum lifespan
increase144), on its anti-oxidant capacity and that it elicits the nuclear
translocation of the daf-16 protein. They do diverge, however, in the effects of
myricetin on the daf-16(mu86) genetic background. On one there is a prolongevity
effect on this background144, while on the other this is completely
abolished145. It is suggested that the differences might be consequence of the
markedly different culturing conditions used, solid medium at 20ºC versus
liquid medium at 25ºC, respectively.
The great anti-oxidant potential of myricetin might explain its reduction on the
accumulation of lipofuscin145, a biomarker of aging, if one takes into
consideration that lipofuscin are highly oxidized crossed-linked proteins.
Additionally, myricetin does not increase tolerance to heat-stress, pharyngeal
pumping rate or body size, which are all evidence against a possible role as a
caloric restriction mimetic145.
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2.2.17 - Rifampicin
The FDA-approved antibiotic rifampicin (RIF) or rifampin extends the lifespan
of C.elegans by almost 45%, even in heat-killed bacterial lawns, which clearly
indicates that its pro-longevity effects are not due to its bactericidal
properties195. The very same work showed that rifampicin acts as a potent
glycation inhibitor in vivo, reducing the age-relate accumulation of advanced
glycation end products. It is worth mentioning that rifampicin treatment
extended lifespan even when initiated at only day 9 of adulthood.
Besides its anti-glycation effects, rifampicin pro-longevity effects depend on
the DAF-16 gene, as it was shown to activate daf-16 protein translocation into
the nucleus, had no influence on the longevity of the daf-16(mgdf50) null
mutant strain, and led to an increase in the expression of SOD-3 (which is a
direct target of DAF-16). Although the targets downstream of DAF-16
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modulated by rifampicin seem to be a separate subset from those regulated by
the IIS pathway195.
2.2.18 - Spermidine
Spermidine is a polyamine naturally present in humans, and its intracellular
levels are known to decline during the human aging process. Therapeutic
quantities are hard to be obtain through diet alone, but its supplementation is
regarded as safe196.
Research of spermidine in murine models is compelling. Four-months old
C57BL/6J wild-type female mice subjected to a lifelong supplementation of
spermidine in their drinking water, have their median lifespan extended. Even
more relevant from a translational medicine perspective, there is still a 10%
increase of the median lifespan of a group of male and female mice when
spermidine supplementation is started later in life, on the 18th month197.
Spermidine caused no changes in food and water consumption, and on body
weight and composition, so the possibility of CR-like state being in play can be
rejected. Instead, spermidine delays the aging process (namely cardiac aging)
by eliciting autophagy. The same authors also report an inverse correlation
between dietary spermidine intake and human cardiovascular disease197. I note
that the corresponding spermidine human dosage to the one used in this mice
study would be too high to be achieved easily by diet198, which suggests that
extra spermidine supplementation might have unexplored cardioprotective
potential in humans. The pro-longevity effects of life-long intake of spermidine,
at the same dosage, were replicated on a different wild-type mouse strain with
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a median lifespan extension of up to 25%, and the autophagy-based mode of
action was further substantiated199. In middle-aged Sprague-Dawley male rats
spermidine supplementation fails to extend mean or maximum lifespan200, but
the dosage given was only 72% of the converted mice dosage198. Nonetheless,
it still extended healthspan (if only very slightly), as measured by improved
kidney tubules, liver, and heart morphology; increased exploratory behavior;
and diminished expression of neuroinflammatory markers (once again the
autophagy process was enhanced)200.
Regarding other model organisms, spermidine retards chronological aging and
rejuvenates replicative old yeast cells, and enhances the lifespan in D.
melanogaster, C. elegans and human peripheral blood mononuclear cells. In
yeast, mice and human cells, this spermidine-induced longevity is correlated
with hypoacetylation of histone H3. Furthermore, and in completely agreement
with the rest of the literature, it is shown that spermidine induces autophagy,
and that this process is required for its lifespan-extension effect in yeast, flies
and worms201.
2.2.19 - Thioflavin-T
The intuition that compounds traditionally used in histopathology to stain
amyloid in tissues might be candidate drugs for delaying the aging process
comes from evidence that such compounds do bind and slow the aggregation of
such protein aggregates in vitro202, and that loss of proteostasis is one of the
main hallmarks of aging203. Thioflavin T is an amyloid-binding dye that was
first explored under this rationale in C. elegans, with an impressive 70% median
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lifespan extension and 43%-78% maximum lifespan extension204a. These are
perhaps the largest drug-induced pro-longevity effects ever reported for an
adult-onset monotherapy at the standard culturing conditions of 20ºC in solid
medium15. The efficacy of thioflavin T requires HSF-1 and SKN-1, but it is
partly independent of caloric restriction, as it prolongs lifespan (albeit not to the
same degree) in nutrient-based models of CR and eat-2(ad1116) mutants.
With this effect size on lifespan, it is not very surprising that thioflavin T was
the most robust compound assayed in the CITP, showing significant media
lifespan-extension in 5 of the 6 strains of Caenorhabditis tested83. Not only that,
but it was also the most potent convincingly reproducing the initial result. The
robustness and potency of thioflavin T suggest that its mode of action is wellconserved
and of major importance among aging processes, respectively.
2.2.20 - Ursolic Acid
Ursolic acid is a lipophilic pentacyclic triterpenoid of botanical origins that was
first shown to increase the mean and maximum lifespan of treated worms by up
to 30%, although these effects were relative to a control group that had a mean
lifespan of less than 15 days205. Later, the same group, with equally relatively
short-lived controls, replicated their initial results and complement them with
healthspan assays206. These latter also showcase the anti-aging potential of
ursolic acid including in delaying the accumulation of lipofuscin, protecting
against heat-shock, achieving an healthier chemotaxis index, and improving
motility. Regarding the mode of action, since there is similar lifespan extension
a it also decreased age-specific mortality across all ages.
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on the daf-16(mgDf50) and daf-2(e1370) genetic backgrounds, the mode of
action is thought to be independent of the IIS pathway. Instead, the failure to be
of benefit to a JNK-1 mutant strain and its predicted binding affinity with the
jnk-1 protein supports that it is through the modulation of JNK-1 that ursolic
acid exerts its pro-longevity effect205. Another additional mode of action is the
initiation of a DR-like, supported by the observation that treated worms are
slimmer and that there are no effects on the lifespan of eat-2(ad1116) animals206.
In w1118 Drosophila melanogaster flies, ursolic acid is of benefit to males only.
In this gender it increases the mean and maximum lifespan and healthspan (as
measured by climbing ability and immune function), without any fertility tradeoff.
However, it does not increase oxidative stress resistance or affect gut health.
Interestingly, total body weight remains the same even though ursolic acid-fed
male flies ate significantly more food than controls. This makes sense in light
that removal of the microbiome negates the anti-aging effects of ursolic acid.
Which to me suggests that the treated flies could be benefiting from a
microbiome-derived metabolite that is produced from the extra calories and
activated by ursolic acid.
Full PHD Thesis: