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The extension of life span by caloric restriction has been studied across species from yeast and Caenorhabditis elegans to primates. No generally accepted theory has been proposed to explain these observations. Here, we propose that the life span extension produced by caloric restriction can be duplicated by the metabolic changes induced by ketosis. From nematodes to mice, extension of life span results from decreased signaling through the insulin/insulin-like growth factor receptor signaling (IIS) pathway. Decreased IIS diminishes phosphatidylinositol (3,4,5) triphosphate (PIP3 ) production, leading to reduced PI3K and AKT kinase activity and decreased forkhead box O transcription factor (FOXO) phosphorylation, allowing FOXO proteins to remain in the nucleus. In the nucleus, FOXO proteins increase the transcription of genes encoding antioxidant enzymes, including superoxide dismutase 2, catalase, glutathione peroxidase, and hundreds of other genes. An effective method for combating free radical damage occurs through the metabolism of ketone bodies, ketosis being the characteristic physiological change brought about by caloric restriction from fruit flies to primates. A dietary ketone ester also decreases circulating glucose and insulin leading to decreased IIS. The ketone body, d-?-hydroxybutyrate (d-?HB), is a natural inhibitor of class I and IIa histone deacetylases that repress transcription of the FOXO3a gene. Therefore, ketosis results in transcription of the enzymes of the antioxidant pathways. In addition, the metabolism of ketone bodies results in a more negative redox potential of the NADP antioxidant system, which is a terminal destructor of oxygen free radicals. Addition of d-?HB to cultures of C. elegans extends life span. We hypothesize that increasing the levels of ketone bodies will also extend the life span of humans and that calorie restriction extends life span at least in part through increasing the levels of ketone bodies. An exogenous ketone ester provides a new tool for mimicking the effects of caloric restriction that can be used in future research. The ability to power mitochondria in aged individuals that have limited ability to oxidize glucose metabolites due to pyruvate dehydrogenase inhibition suggests new lines of research for preventative measures and treatments for aging and aging-related disorders. ? 2017 The Authors IUBMB Life published by Wiley Periodicals, Inc. on behalf of International Union of Biochemistry and Molecular Biology, 2017.
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Critical Review
Ketone Bodies Mimic the Life Span Extending
Properties of Caloric Restriction
Richard L. Veech
Patrick C. Bradshaw
Kieran Clarke
William Curtis
Robert Pawlosky
M. Todd King
Lab of Metabolic Control, NIH/NIAAA, Rockville, MD, USA
East Tennessee State University College of Medicine, Johnson City, TN,
Dept. of Physiology, Anatomy & Genetics, Oxford, UK
The extension of life span by caloric restriction has been stud-
ied across species from yeast and Caenorhabditis elegans to
primates. No generally accepted theory has been proposed to
explain these observations. Here, we propose that the life
span extension produced by caloric restriction can be duplicat-
ed by the metabolic changes induced by ketosis. From nemat-
odes to mice, extension of life span results from decreased
signaling through the insulin/insulin-like growth factor receptor
signaling (IIS) pathway. Decreased IIS diminishes phosphatidy-
linositol (3,4,5) triphosphate (PIP
) production, leading to
reduced PI3K and AKT kinase activity and decreased forkhead
box O transcription factor (FOXO) phosphorylation, allowing
FOXO proteins to remain in the nucleus. In the nucleus, FOXO
proteins increase the transcription of genes encoding antioxi-
dant enzymes, including superoxide dismutase 2, catalase,
glutathione peroxidase, and hundreds of other genes. An
effective method for combating free radical damage occurs
through the metabolism of ketone bodies, ketosis being the
characteristic physiological change brought about by caloric
restriction from fruit flies to primates. A dietary ketone ester
also decreases circulating glucose and insulin leading to
decreased IIS. The ketone body, D-b-hydroxybutyrate (D-bHB),
is a natural inhibitor of class I and IIa histone deacetylases
that repress transcription of the FOXO3a gene. Therefore,
ketosis results in transcription of the enzymes of the antioxi-
dant pathways. In addition, the metabolism of ketone bodies
results in a more negative redox potential of the NADP antiox-
idant system, which is a terminal destructor of oxygen free
radicals. Addition of D-bHB to cultures of C. elegans extends
life span. We hypothesize that increasing the levels of ketone
bodies will also extend the life span of humans and that calo-
rie restriction extends life span at least in part through increas-
ing the levels of ketone bodies. An exogenous ketone ester
provides a new tool for mimicking the effects of caloric restric-
tion that can be used in future research. The ability to power
mitochondria in aged individuals that have limited ability to
oxidize glucose metabolites due to pyruvate dehydrogenase
inhibition suggests new lines of research for preventative
measures and treatments for aging and aging-related disor-
ders. V
C2017 The Authors IUBMB Life published by Wiley Peri-
odicals, Inc. on behalf of International Union of Biochemistry
and Molecular Biology, 00(0):000–000, 2017
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any
medium, provided the original work is properly cited.
Abbreviations: D-bHB, D-b-hydroxybutyrate; HIF-1a, hypoxia-inducible factor 1-alpha; IGF, insulin/insulin-like growth factor; FOXO, forkhead box transcrip-
tion factor; HDAC, histone deacetylase; IIS, insulin/insulin-like growth factor receptor signaling pathway; ILP, insulin like protein; IST-1, insulin receptor
substrate-1; Nrf2, Nuclear factor (erythroid-derived 2)-like 2; PGC1a, peroxisome proliferator-activated receptor gamma coactivator 1-alpha; PDH, pyruvate
dehydrogenase; PDK1,4, pyruvate dehydrogenase kinase isozyme 1 or 4; PDPK1, phosphoinositide-dependent kinase-1; PI3K, phosphoinositide 3 kinase;
PIP2, phosphatidylinositol (4,5)-bisphosphate; PIP3, phosphatidylinositol (3,4,5) triphosphate; PTEN, phosphatase and tensin homolog; RNS, reactive nitro-
gen species; ROS, reactive oxygen species; SASP, senescence-associated secretory phenotype; SIRT1, sirtuin 1; SOD, superoxide dismutase
C2017 The Authors IUBMB Life published by Wiley Periodicals, Inc. on behalf of International Union of Biochemistry and Molecular Biology
Volume 00, Number 00, Month 2017, Pages 00–00
*Address correspondence to: Richard L. Veech, Laboratory of Metabolic Control, NIH/NIAAA, 5625 Fishers Lane, Rockville, MD 20852, USA. Tel: 1301-
443-4620. Fax: 1301-443-0939.
Received 8 February 2017; Revised 10 March 2017;
DOI 10.1002/iub.1627
Published online 00 Month 2017 in Wiley Online Library
IUBMB Life 1
Keywords: ketone bodies; aging; lifespan; Caenorhabditis elegans;
NADPH; FOXO3a; reactive oxygen species
Ketone Bodies and Extension
of Life Span
In 1935, McCay et al. showed that caloric restriction of 30% to
50% increased the average life span of rats from 500 to 820
days (1). Since that time, caloric or dietary restriction has
been shown to increase life span in a wide variety of species,
from yeast (2) to nematodes (3) to fruit flies (4) to mice (5) and
primates. In studies of primates, calorie restriction was shown
to extend lifespan by one group (6), but an earlier study using
a slightly different calorie restriction protocol did not find an
effect on lifespan (7). A number of proposed mechanisms for
the phenomena have been suggested including: retardation of
growth, decreased fat content, reduced inflammation, reduced
oxidative damage, body temperature, and insulin signaling,
and increase in physical activity and autophagy (8). However,
no coherent mechanistic explanation has been generally
accepted for this widely observed phenomenon that caloric
restriction extends life span across the species. Yet, an obvious
metabolic change associated with caloric restriction is ketosis.
Increased ketone body concentrations occur during caloric
restriction in widely different species ranging from Caenorhab-
ditis elegans (9) to Drosophila (4) to man where ketone bodies
are produced in liver from free fatty acids released from adi-
pose tissue (10).
Ketone bodies were first found in the urine of subjects with
diabetes (11) creating in physicians the thought that their pres-
ence was pathological. However, Cahill showed that ketone
bodies were the normal result from fasting in man (12), where
they could be used in man in most extrahepatic tissue including
brain (13). The ketone bodies, D-b-hydroxybutyrate (D-bHB) and
its redox partner acetoacetate are increased during fasting
(14), exercise (15), or by a low carbohydrate diet (16). Original-
ly ketone bodies were thought to be produced by a reversal of
the b-oxidation pathway of fatty acids. However, it was defini-
tively and elegantly shown by Lehninger and Greville that the
b-hydroxybutyrate of the boxidation pathway was of the Lform
while that produced during ketogenesis was the Dform (17).
This fundamental difference in the metabolism of the Dand
Lform of ketone bodies has profound metabolic effects.
The metabolism of the D-form results in oxidation of the
mitochondrial co-enzyme Q couple (18) and an increase in the
redox span between the mitochondrial NAD and Q couples
with a resultant increase in the DG0of adenosine triphosphate
(ATP). The L-form of b-hydroxybutyrate is activated by conver-
sion of ATP to adenosine monophosphate (AMP), a more ener-
getically costly process than the activation by succinyl-CoA. In
contrast to the metabolism of D-bHB, which produces only
NADH, the further metabolism of the L-form is metabolized by
the fatty acid b-oxidation system, which results in the reduc-
tion of one mitochondrial NAD and one co-enzyme Q with no
increase in redox span between the two couples and therefore
no increase in the DG0of ATP hydrolysis. When catabolized for
the synthesis of ATP in mitochondria, D-bHB produces more
ATP per oxygen molecule consumed than many other respira-
tory substrates due to this unique nature of D-bHB metabolism
Blood ketone bodies can also be elevated, without eleva-
tion of blood free fatty acids by ingestion of ketone body esters
such as D-bHB-R1,3 butanediol monoester (20). This ketone
ester has been evaluated for toxicity (21) and is recognized as
generally recognized as safe (GRAS) by the Food and Drug
Recently, it was shown that administration of D-bHB to C.
elegans caused an extension of life span resulting in that
ketone body to be presciently labeled as “an anti-aging ketone
body” (9). In the same experiment, L-b-hydroxybutyrate failed
to extend life span. If it is accepted that the ketone body, D-
bHB is an “anti-aging” compound, this could account for the
widespread observation that caloric restriction, and its resul-
tant ketosis, leads to life span extension. Many of the signaling
pathways mediating extension of life span have been deter-
mined by geneticists largely by work using the short-lived
nematode C. elegans.
Genetic Mechanisms of Life Span
There are marked heritable differences in median life span
between species: from less than 3 weeks in C. elegans,
between 2 and 3 years for the mouse or rat, 10 to 15 years for
the dog, around 70 years for humans, and up to over 400
years in a bivalve mollusk Artica islandica. This observation
makes it clear that life span has a heritable component.
The first genetically induced increase in life span in C. ele-
gans was reported for a mutation in age-1, encoding a catalyt-
ic subunit of the of phosphatidylinositol 3-OH kinase of the
insulin/insulin-like growth factor (IGF) receptor signaling (IIS)
pathway (22) (23). The Kenyon laboratory insightfully took
experimental advantage of the short life span of C. elegans to
identify mutations in the abnormal dauer formation-2 (daf-2)
insulin/IGF-1 receptor gene of the IIS pathway that led to a
twofold increase in C. elegans life span (24). This life span
extension was found to be predominately caused by the
decreased phosphorylation and nuclear translocation of the
DAF-16/FOXO transcriptional regulator leading to expression
of over 200 genes including those involved in metabolism, pro-
teostasis, and antioxidant defenses (25,26) (Fig. 1). Activation
of other factors such as the SKN-1/Nrf2 transcriptional regula-
tor also contributes to the longevity effects of reduced IIS
under certain experimental conditions (27). The increased life
span of the daf-2 mutant could be further increased by dietary
restriction indicating at least partially distinct mechanisms of
action (28).
It was at first puzzling why a mutation or decreased
expression of the daf-2 insulin/IGF-1 receptor gene in C. ele-
gans was associated with extension of life span. After all, IGF
causes proliferation in cells that are not postmitotic and
hypertrophy in myocytes. It is ironic, given the attraction to
sweettaste,thatconsumptionofglucose with resultant stim-
ulation of the insulin receptor should be a signal for shorten-
ing life span. Decreased signaling through this pathway likely
evolved as a mechanism to delay reproduction until food was
more abundant and the delay in reproduction carried with it
an increase in survival. More understandable is the finding
that an increase in the activity of the DAF-16/FOXO protein,
controlling expression of several antioxidant enzymes and
heat shock proteins should play a key role in life span exten-
sion. However, as animals have evolved longer life spans,
FOXO proteins have evolved additional more complex roles
in regulating cellular function and aging including stimulat-
ing apoptosis (29) that likely helps prevent tumorigenicity
(30). FOXO proteins are modified post-translationally by acet-
ylation and phosphorylation, which are regulated by many
factors including metabolism, inflammation, and oxidative
stress (29). The complex roles and signaling mechanisms
thought to control the expression and activity of various
FOXO proteins have recently been reviewed (31). An allele of
FOXO3a, one of four human FOXO genes, is associated with
extreme longevity in humans (32).Longevitymayberegulat-
ed through other specific signaling pathways and transcrip-
tional regulators such as mechanistic target of rapamycin
(mTOR), 50AMP-activated protein kinase (AMPK), sirtuin 1
(SIRT1), sirtuin 3 (SIRT3), nuclear factor (erythroid-derived
2)-like 2 (Nrf2), and peroxisome proliferator-activated
receptor gamma coactivator 1-a(PGC-1a) (33), although
nematode orthologs of PGC-1aand SIRT3 appear to be
The longevity effect from mutation of genes in the IIS pathway was discovered in C. elegans. This longevity effect was also lat-
er found in fruit flies and mice. In C. elegans, the normal signaling pathway results in phosphorylation and sequestration in the
cytosol of the forkhead box transcription factor DAF-16. IGF-1 receptor, IGF-1R, is a tyrosine kinase receptor. Insulin-like pepti-
des or IGFs are ligands for IGF-1R (DAF-2 in C. elegans and dInR in Drosophila) stimulating its autophosphorylation and recruit-
ment of adaptor proteins (insulin receptor substrate-1 (IST-1), AGE-1, CHICO, Shc (Src homology and collagen protein), Insulin
receptor substrate-1 (IRS-1), and Insulin receptor substrate- 2 (IRS-2)), which activate a class I phosphoinositide 3-kinase. This
leads to an increased concentration of PIP3 in the plasm membrane. PTEN and the orthologue dPTEN and DAF-18 are antago-
nists reducing the concentration of PIP3. High membrane concentrations of PIP3 stimulate the signaling cascade by inducing
PDPK1 phosphorylation of AKT-1, which in turn phosphorylates the various FOXO transcription factors. Abbreviations: AGE-1
is a phosphoinositide 3-kinase (PI3K), PIP3 stands for phosphatidylinositol (3,4,5)- triphosphate, PIP2 is the abbreviation for
phosphatidylinositol (4,5)-bisphosphate, PTEN is phosphatase and TENsin homolog, PDPK1 is phosphoinositide-dependent
kinase-1, AKT is named for the Ak mouse strain, and the t stands for thymoma. Dauer is German meaning endurance or dura-
tion, indicating a suspended developmental stage. DAF is the family of proteins that were investigated as dauer factors that
regulate entrance into the dauer state, CHICO means small boy in Spanish referring to the small body size of the mutant flies.
mTORC2 is a complex containing mechanistic target of rapamycin (mTOR). It is made up of mTOR, Rictor, mLST8, Protor1/2,
Sin1, and Deptor. FOXO indicates a forkhead box transcription factor. ILP is the abbreviation for insulin-like peptides. IGF-1
stands for insulin-like growth factor-1.
Aging, Oxidative Stress, and the
NADPH-Linked Antioxidant System
In the 1950s, Harman postulated that the toxicity of reactive
oxygen species (ROS) was central to the mechanism of aging
(34) as it was to radiation toxicity (35). There has been accu-
mulating evidence since then that the mechanism limiting the
life span results from ROS damage (36,37). Later, data (37)
greatly support the mitochondrial free radical theory of aging.
The first is the strong inverse correlation between
mitochondrial ROS production and longevity, and the second is
the strong inverse correlation between the degree of fatty acid
unsaturation in tissue membranes and longevity among relat-
ed species. No other parameters measured corresponded with
life span as well as these indicators, which likely evolved to
minimize ROS-mediated damage.
While ROS and reactive nitrogen species (RNS) are neces-
sary for certain signaling pathways, their unregulated produc-
tion is destructive leading to pathology. However, in the last
10 years evidence from C. elegans and other model organisms
The NADPH system of antioxidant enzymes and NADPH-dependent molecular antioxidants. The two primary pathways provid-
ing sufficient electron donors for the reduction of oxidized species in the cytosol, organelles, and membranes are shown. This
is accomplished, in part, through NADPH-dependent reduction of glutathione (GSH), vitamin C (Vit C), and vitamin E (Vit E).
The redox potential of these secondary systems are all set by the redox potential of the free cytosolic [NADP
]/[NADPH] sys-
tem to which they are linked enzymatically.
has demonstrated that ROS-mediated signaling is required for
some mechanisms of life span extension.
The toxicity of ROS/RNS is ameliorated by the NADPH sys-
tem (Fig. 2), the redox potential of which is made more negative
by the metabolism of ketone bodies (19,38,39). The redox poten-
tial of the free cytosolic [NADP
[NADPH] system is about 20.42
V, about the same redox potential as hydrogen and is the most
negative redox potential in the body (38). Other reducing agents,
such as the ascorbic acid couple, are linked enzymatically to the
]/[NADPH] couple (19). In peripheral tissues in the fed
state, NADPH is primarily produced from glucose metabolism
by the hexose monophosphate pathway (40). During fasting
when glucose is limiting, NADPH is produced from the metabo-
lism of ketone bodies in the Krebs cycle (18,39) mainly through
the action of NADP-dependent isocitrate dehydrogenase. During
calorie restriction, mitochondrial SIRT3 deacetylates and acti-
vates the NADP-dependent isocitrate dehydrogenase IDH2 lead-
ing to increased NADPH production and an increased ratio of
reduced-to-oxidized glutathione in mitochondria (41). Both
FOXO1 and FOXO3a induce expression of IDH1 (42), a cytoplas-
mic form of NADP-dependent isocitrate dehydrogenase. Citrate
or isocitrate formed from ketone body catabolism in mitochon-
dria can be exported by the citrate–isocitrate carrier to the cyto-
plasm for the production of NADPH by IDH1 (Fig. 2).
Addition of reducing agents such as ascorbic acid did not
uniformly increase the life span of model organisms, perhaps
because these treatments had both pro and antioxidant effects
or that reducing agents block ROS signals required for life
span extension. Extravagant claims for the beneficial effects of
high doses of ascorbic acid made by Linus Pauling were large-
ly unsubstantiated. It was through the work of Krebs and
Veech that the control of redox states in the cell and the domi-
nant role of the free [NADP
]/[NADPH] was appreciated (38).
The detoxification of free radicals is dependent upon the multi-
ple redox couples which are linked to and whose redox poten-
tial is set by the most negative NADP system (19). In the
absence of malnutrition, there is little or no reason to take
antioxidant supplements because the ability of these com-
pounds to function as antioxidants is largely determined by the
]/[NADPH]. As aluded to above, this ratio is regulated
by the flux of substrates through enzymes that generate or
consume NADP
and NADPH, the reduction of which is
brought about by the metabolism of ketone bodies. Therefore,
consuming increased amounts of antioxidants has little effect
on the [NADP
Data in apparent conflict with the free radical theory of
aging has led to its increased scrutiny. In C. elegans, one study
showed that increasing free radicals by knocking out the
superoxide dismutase (SOD) genes one at a time did not short-
en life. Knockout of sod-4, an extracellular protein, even had
the counter-intuitive effect of extending life span (43). Another
group showed that mice engineered to overexpress SOD and
catalase did not live longer than normal (44). However, over-
expressing mitochondrial-targeted catalase in mice did lead to
life span extension (45). SOD and catalase are both dismutases
that are not linked to the NADPH system of clearing ROS/RNS
that we hypothesize to be the most important driving force for
life span extension.
There is substantial data supporting the ability of
decreased [NADP
]/[NADPH] to extend life span. Glucose-6-
phosphate dehydrogenase overexpression increased median
life span in Drosophila (46) and female mice (47). Longer-lived
strains of Drosophila were shown to possess higher glucose-6-
phosphate dehydrogenase activity than shorter lived strains
(48). By increasing flux through NADP-dependent forms of the
enzyme, knocking out or knocking down NAD-dependent isoci-
trate dehydrogenase increased life span in yeast (49) and C.
elegans (50). Finally, overexpression of NADP-dependent malic
enzyme extended life span in Drosophila (51). Studies should
now be performed to more directly test the hypothesis that
increased NADPH levels extend lifespan through bolstering the
NADPH antioxidant system.
Decreased Pyruvate Dehydrogenase
Activity in Aged Tissues is Bypassed by
Ketone Body Metabolism
Aging has been shown to lead to decreased mitochondrial pyru-
vate dehydrogenase (PDH) complex activity. In heart, this
decreased activity was not due to lower PDH complex levels, but
due to increased phosphorylation that inhibits complex activity
(52). PDH phosphatases, which are able to increase PDH activity,
have been shown to be stimulated by insulin (53), and in skeletal
muscle, this stimulation was shown to decline with age, but be
restored by exercise (54). Decreased PDH activity has been found
in specific regions of aged brain such as in the striatum and
brain stem as a result of increased PDH kinase activity (55). This
finding could result from increased ROS production from mito-
chondria during aging that increases hypoxia-inducible factor
1-alpha (HIF-1a) activity (56) and the expression of the pyruvate
dehydrogenase kinase isoform 4 (PDK4) (57). Consistent with it
playing a role in the aging process, the PDH complex has also
been shown to regulate cellular senescence (58). However, too
much PDH activity may have pro-aging effects through a hyper-
stimulation of mitochondrial metabolism resulting in increased
ROS production. Therefore, FOXO proteins have evolved to
induce expression of PDH kinases such as PDK4 to negatively
regulate PDH activity and ROS production (59). During fasting
and caloric restriction, the FOXO-mediated expression of PDK
enzymes may also serve an important role in the shunting of
pyruvate and/or lactate to cell types or tissues with the highest
energy needs, such as neurons that cannot oxidize fatty acids.
Studies in C. elegans also support a role for PDH activity
in the regulation of longevity. Inhibiting PDH kinase activity
with dichloroacetate extended life span (60), while overex-
pression of the PDH phosphatase, PDP-1, also increased lon-
gevity through increased DAF-16/FOXO nuclear translocation
(61). It is important to determine whether PDH activity regu-
lates the activity of FOXO proteins in humans. This could
potentially occur through nuclear localized PDH providing
acetyl-CoA for histone acetylation (62) of FOXO promoters. If
PDH activity stimulates FOXO expression, declining PDH activ-
ity during aging may lead to a downstream loss of FOXO-
mediated transcriptional events and increased oxidative
stress. As metabolism of ketone bodies bypasses PDH activity
as shown in Fig. 3, ketone or ketone ester supplementation
may be able to mitigate metabolic and transcriptional altera-
tions resulting from decreased PDH activity to promote lon-
gevity. Calorie restriction was shown to stimulate skeletal
muscle mitochondrial pyruvate metabolism by increasing
expression of the mitochondrial pyruvate carrier and decreas-
ing expression of the lactate dehydrogenase A gene (63). The
longevity effects of caloric restriction in mammals require the
FOXO3a gene (64).
Telomere Shortening is Linked to
Cellular Redox Status and Metabolism
The work of Hayflick and Moorhead (65) pointed out that
shortening of the telomeres set a limit to the number of divi-
sions cells in culture could undergo before senescence occurs.
Expression of the telomerase enzyme in certain germ and pro-
genitor cells provides a solution to replicate the ends of linear
chromosomes, so that the chromosomes do not become
shorter with each new round of DNA replication. Telomeres
are lengthened by starvation (66) and shortened by ROS dam-
age (59). These observations are consistent with aging being a
function of reactive oxygen and its reversal a function of the
increasing redox potential of the NADPH system brought about
by caloric restriction. The FOXO protein FOXO1 was shown to
be essential for the calorie restriction-mediated increase in tel-
omerase subunit expression (67). As cells approach their Hay-
flick limit, the expression of the FOXO genes FOXO1 and
FOXO4 have also been shown to decline (68), which would
lead to decreased SOD2 and catalase expression. Senescent
cells and tissues not only show decreased function but also
acquire a senescence-associated secretory phenotype (SASP), a
pro-inflammatory, pro-aging state. Mitochondrial dysfunction
that increases ROS/RNS production also induces a cellular
senescence program with a modified SASP (67).
Other Potential Anti-Aging Mechanisms
of Ketone Bodies
Decreased insulin signaling activates mammalian FOXO pro-
teins such as FOXO1 and FOXO3, which stimulates expression
of many genes involved in autophagy (69). In addition,
decreased insulin signaling or nutrient deprivation inactivates
mTOR kinase to stimulate autophagy, which is required for
dietary restriction-mediated life span extension in C. elegans
(70). Consistent with these effects, D-bHB treatment has been
shown to stimulate autophagy in cultured cortical neurons (71)
and increased rates of autophagy are likely one of the several
molecular mechanisms that contribute to the life span extend-
ing effects exerted by ketone bodies. One mechanism through
which D-bHB may decrease IIS to activate FOXO proteins and
autophagy is through a direct inhibition of AKT (72). This inhi-
bition may also be responsible for the fasting-induced insulin
resistance observed in muscle, heart, and other peripheral tis-
sues that preserves glucose use for the brain (73,74).
D-bHB may also exert protective metabolic effects by bind-
ing at least two different G protein-coupled receptors, HCAR2/
Gpr109/PUMA-G (first discovered to be a nicotinic acid recep-
tor) and free fatty acid receptor 3 on the plasma membrane
(75). As these genes evolved in chordates and are not present
in invertebrates, they could not function in the evolutionarily
conserved role of ketone bodies in life span extension. But
activation of these receptors likely plays important metabolic
signaling roles mediated by D-bHB. Finally, the gut microbiome
plays an important role in providing substrates for ketone
body synthesis (76) and could therefore effect the extent of
ketone body synthesis during caloric restriction to influence
the magnitude of life span extension, but a further discussion
of this research topic is beyond the scope of this review.
Feeding Ketone Esters
One effect of feeding rats with the ketone ester, D-bHB-R1,3
butanediol monoester, was a 1.7-fold decrease in blood glu-
cose and over a twofold decrease in blood insulin (77). The
same decreases in glucose and insulin are seen after feeding
ketone esters to mice (78). These metabolic changes induced
by feeding ketone esters mimic the decreased IIS induced by a
longevity-inducing mutation in daf-2 in the nematode (23,26).
Ketone body metabolism bypasses decreased PDH
activity in aged tissues.
In addition to mutations in daf-2 that increase nuclear translo-
cation and activity of DAF-16/FOXO, there are ways to
increase the transcription of FOXO genes metabolically. For
example, in mammals, the transcription of FOXO3a can be
induced by inhibition of class I and IIa histone deacetylases
(HDACs) by D-bHB (79) or possibly by b-hydroxybutyrylation
(80) (Fig. 4). Inhibition of these HDACs by D-bHB induces the
expression of other antioxidant and detoxification genes such
as the metallothionein-1 (MTL1) that can lead to reduced ROS
toxicity. In liver, fasting also increases FOXO1 activity through
a mechanism where glucagon stimulates class IIa HDAC trans-
location to the nucleus to recruit the class I HDAC HDAC3 to
deacetylate FOXO1 (81) These pathways also affect metabo-
lism, phosphorylation potential, redox states, and the ability to
clear ROS. In C. elegans, the life span extension induced by
administration of the ketone body D-bHB required nematode
homologs of AMPK, SIRT1, FOXO, and Nrf2. No additional
increase in life span was observed for D-bHB treatment to a
long-lived S6 kinase mutant of the target of rapamycin (TOR)
signaling pathway suggesting that TOR inhibition also plays a
role in the ketone body-mediated longevity effects (33).
As somewhat distinct from genetic manipulation of the IIS
pathway, feeding ketone bodies results in the reduction of the
free cytosolic [NADP
]/[NADPH] ratio (39), which provides the
thermodynamic force required to reduce glutathione and other
antioxidant couples that destroy oxygen free radicals (19). The
metabolism of ketone bodies, which lower both blood glucose
and insulin, decrease the activity of the IIS pathway that in
turn leads to an increase in the level and activity of the
unphosphorylated FOXO transcription factors central for life
span extension (26). Ketosis, which is a common consequence
of caloric restriction, may provide an explanation for why calo-
ric restriction leads to life span extension in most species.
Here, we propose that the life span extension produced by
caloric restriction can be duplicated by the metabolic changes
induced by ketosis.
Aging in man is accompanied by deterioration of a number of
systems. Most notable are a gradual increase in blood sugar
and blood lipids, increased narrowing of blood vessels, an
increase in the incidence of malignancies, the deterioration
and loss of elasticity in skin, loss of muscular strength and
physiological exercise performance, deterioration of memory
and cognitive performance, and in males decreases in erectile
function. Many aging-induced changes, such as the incidence
of malignancies in mice (82), the increases in blood glucose
and insulin caused by insulin resistance (39,78), and the mus-
cular weakness have been shown to be decreased by the
In the well-fed state, the FOXO3a transcription factor is prevented from entering the nucleus by phosphorylation. FOXO3A is
marked for degradation by ubiquitin (Ub). DNA with FOXO3a promoter remains out of reach due to lysine (K1) interacting with
negative charges in DNAs phosphodiester backbone keeping histones in the condensed state. In a state of ketosis, HDAC is
inhibited by D-b-hydroxybutyrate. The acetyl (Ac-) group neutralizes the charge on lysine opening the histone complex expos-
ing the FOXO3a promoter and upregulating superoxide dismutase (MnSOD), catalase, and metallothionein MT. An alternative
mechanism proposed by Xie et al. is shown in the third panel.
metabolism of ketone bodies (18,83), a normal metabolite pro-
duced from fatty acids by liver during periods of prolonged
fasting or caloric restriction (12).
The unique ability of ketone bodies to supply energy to
brain during periods of impairment of glucose metabolism
make ketosis an effective treatment for a number of neurologi-
cal conditions which are currently without effective therapies.
Impairment of cognitive function has also been shown to be
improved by the metabolism of ketone bodies (84). Additional-
ly, Alzheimer’s disease, the major cause of which is aging (20)
can be improved clinically by the induction of mild ketosis in a
mouse model of the disease (85) and in humans (86). Ketosis
also improves function in Parkinson’s disease (87) which is
thought to be largely caused by mitochondrial free radical
damage (19,88). Ketone bodies are also useful in ameliorating
the symptoms of amyotrophic lateral sclerosis (89). It is also
recognized that ketosis could have important therapeutic
applications in a wide variety of other diseases (90) including
Glut 1 deficiency, type I diabetes (91), obesity (78,92), and
insulin resistance (20,39,93), and diseases of diverse etiology
In addition to ameliorating a number of diseases associat-
ed with aging, the general deterioration of cellular systems
independent of specific disease seems related to ROS toxicity
and the inability to combat it. In contrast increases in life span
occur across a number of species with a reduction in function
of the IIS pathway and/or an activation of the FOXO transcrip-
tion factors, inducing expression of the enzymes required for
free radical detoxification (Figs. 1 and 2). In C. elegans, these
results have been accomplished using RNA interference or
mutant animals. Similar changes should be able to be achieved
in higher animals, including humans, by the administration of
D-bHB itself or its esters.
In summary, decreased signaling through the insulin/IGF-1
receptor pathway increases life span. Decreased insulin/IGF-1
receptor activation leads to a decrease in PIP
, a decrease in
the phosphorylation and activity of phosphoinositide-
dependent protein kinase (PDPK1), a decrease in the phos-
phorylation and activity of AKT, and a subsequent decrease in
the phosphorylation of FOXO transcription factors, allowing
them to continue to reside in the nucleus and to increase the
transcription of the enzymes of the antioxidant pathway.
In mammals, many of these changes can be brought about
by the metabolism of ketone bodies. The metabolism of
ketones lowers the blood glucose and insulin thus decreasing
the activity of the IIS and its attendant changes in the pathway
described above. However, in addition ketone bodies act as a
natural inhibitor of class I HDACs, inducing FOXO gene
expression stimulating the synthesis of antioxidant and meta-
bolic enzymes. An added important factor is that the metabo-
lism of ketone bodies in mammals increases the reducing pow-
er of the NADP system providing the thermodynamic drive to
destroy oxygen free radicals which are a major cause of the
aging process.
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... In addition to the extension of the absolute lifespan, the prevention of heart and circulatory diseases, type II diabetes and cancer are prominent [7,12,13]. The restriction of glucose in the form of a reduced increase (low carb) or as absolute an avoidance as possible (ketogenic) results in similar mechanisms to calorie restriction [14]. ...
... It is possible that the system must be incubated for a longer period than 7 days so that the specific restriction profiles can be more extreme. On the other hand, the different forms of restriction also have many common molecular mechanisms, as already described [14]. Thus, the results can also be interpreted as a slow but sure alignment of the metabolites over time, while in the short term, the differences are much larger. ...
Full-text available
All forms of restriction, from caloric to amino acid to glucose restriction, have been established in recent years as therapeutic options for various diseases, including cancer. However, usually there is no direct comparison between the different restriction forms. Additionally, many cell culture experiments take place under static conditions. In this work, we used a closed perfusion culture in murine L929 cells over a period of 7 days to compare methionine restriction (MetR) and glucose restriction (LowCarb) in the same system and analysed the metabolome by liquid chromatography mass spectrometry (LC-MS). In addition, we analysed the inhibition of glycolysis by 2-deoxy-D-glucose (2-DG) over a period of 72 h. 2-DG induced very fast a low-energy situation by a reduced glycolysis metabolite flow rate resulting in pyruvate, lactate, and ATP depletion. Under perfusion culture, both MetR and LowCarb were established on the metabolic level. Interestingly, over the period of 7 days, the metabolome of MetR and LowCarb showed more similarities than differences. This leads to the conclusion that the conditioned medium, in addition to the different restriction forms, substantially reprogramm the cells on the metabolic level.
... Complex changes in DNA methylation patterns have also been found during aging [56,57] and have been associated with various age-related diseases [39]. It has been suggested that KD or exogenous ketogenic supplements [58] may promote anti-aging effects [58][59][60][61]. It is likely that these effects occur via the modulation of the DNA methylation of the same genes that respond to changes in brain adenosine levels [50,57], including KLF14, ELOVL2, FHL2, OTUD7A, SLC12A5, ZYG11A, and CCDC102B genes [57]. ...
Ketogenic diets (KD) are dietary strategies low in carbohydrates, normal in protein, and high, normal, or reduced in fat with or without (Very Low-Calories Ketogenic Diet, VLCKD) a reduced caloric intake. KDs have been shown to be useful in the treatment of obesity, metabolic diseases and related disorders, neurological diseases, and various pathological conditions such as cancer, nonalcoholic liver disease, and chronic pain. Several studies have investigated the intracellular metabolic pathways that contribute to the beneficial effects of these diets. Although epigenetic changes are among the most important determinants of an organism's ability to adapt to environmental changes, data on the epigenetic changes associated with these dietary pathways are still limited. This review provides an overview of the major epigenetic changes associated with KDs.
... They found that the western dietary pattern, which was mainly composed of meat, fat, and butter, increased the risk of AMD, but the relationship between meat and the risk of AMD was not investigated. The ketogenic diet was reported to increase β-hydroxybutyrate (β-HB) level, which may prevent or alleviate symptoms of age-related diseases, exert antiaging effect [33], and prolong the lifespan [34,35]. In mammals, β-HB may down-regulate senescence-associated secretory phenotype (SASP) and retard the senescence of vascular cells [36]. ...
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Purpose To estimate the frequency of age-related macular degeneration (AMD) among people who underwent health examination in Hunan, China and to determine the relationship between dietary pattern and the risk of AMD. Methods The Questionnaire was used to collect dietary data from 56,775 study participants of ≥ 50 years old who underwent health examination at the Department of Health Management, the Third Xiangya Hospital of Central South University between January 2017 and December 2019. The diagnosis of AMD was based on the results of color fundus photography (CFP), spectral-domain optical coherence tomography (OCT) and multispectral imaging (MSI). After excluding participants with incomplete records or other ocular disease that may affect the results of fundus examination, a total of 43,672 study participants were included. The univariate and multivariate logistic regression analyses were used to determine the relationship between dietary pattern and the frequency of AMD. Results Among the 43,672 study participants, 1080 (2.5%) had early AMD: the frequencies were 2.6% (n = 674) in men and 2.3% (n = 406) in women; the frequencies were 1.0% (n = 289), 3.6% (n = 401), 9.1% (n = 390) in 50–59, 60–69, ≥ 70 years old, respectively. And the age-standard frequency was 6.6% over the 60 years old in Hunan China. The high-salt intake increased the risk of early AMD [odds ratio (OR) = 1.61, 95% confidence interval (CI) = 1.54–1.68], whereas the intake of meat decreased the risk (OR = 0.90, 95% CI = 0.81–0.99). Conclusion In Hunan China, there was a high frequency of early AMD detected through health examination over the 60 years old. And high-salt intake increases the risk of early AMD, whereas intake of meat decreases the risk. Modulating the dietary pattern and reducing the salt intake as an AMD prevention strategy warrant further study.
... Cunnane and colleagues also reported positive results using shorter medium chain triglycerides to treat persons with dementia. 14 In addition, Swerdlow 15 and colleagues and Veech et al. 16 have used the ketogenic diet in the treatment of persons with Alzheimer's Disease. ...
... As a metabolite, BHB has several G-protein coupled receptors, including the hydroxycarboxylic acid receptor 2 (HCAR2), which inhibits histone deacetylases (HDACs) to alter gene expression [56][57][58][59]. In this manner, BHB can enhance the production of pro-longevity sirtuin proteins and the Forkhead box O3A (FOXO3A) transcription factor, the neurotropic factor brain-derived neurotrophic factor (BDNF), the Peroxisome Proliferator-Activated Receptor Gamma (PPARG) coactivator-1 alpha (PGC1-α), and several others [60]. ...
Objective: The aim of the present systematic review was to assess the efficacy of ketogenic therapy in Parkinson's disease (PD), using all available data from randomized controlled trials (RCTs) on humans and animal studies with PD models. Design: Systematic review of in vivo studies. Methods: Studies related to the research question were identified through searches in PubMed, Cochrane Central Register of Controlled Trials (CENTRAL), Scopus, and the gray literature, from inception until November 2021. Rayyan was employed to screen and identify all studies fulfilling the inclusion criteria. Cochrane's revised Risk of Bias 2.0 and SYRCLE tools evaluated bias in RCTs and animal studies, respectively. An effect direction plot was developed to synthesize the evidence of the RCTs. Results: Twelve studies were identified and included in the qualitative synthesis (4 RCTs and 8 animal trials). Interventions included ketogenic diets (KDs), supplementation with medium-chain triglyceride (MCT) oil, caprylic acid administration and ketone ester drinks. The animal research used zebrafish and rodents, and PD was toxin-induced. Based on the available RCTs, ketogenic therapy does not improve motor coordination and functioning, cognitive impairment, anthropometrics, blood lipids and glycemic control, exercise performance or voice disorders in patients with PD. The evidence is scattered and heterogenous, with single trials assessing different outcomes; thus, a synthesis of the evidence cannot be conclusive regarding the efficacy of ketogenic therapy. On the other hand, animal studies tend to demonstrate more promising results, with marked improvements in locomotor activity, dopaminergic activity, redox status, and inflammatory markers. Conclusions: Although animal studies indicate promising results, research on the effect of ketogenic therapy in PD is still in its infancy, with RCTs conducted on humans being heterogeneous and lacking PD-specific outcomes. More studies are required to recommend or refute the use of ketogenic therapy in PD.
... Along with immune response, another aspect of homeostasis in living organisms is resistance to oxidative stress. Ketone bodies with reducing power have been reported to have various physiological functions (192), among which are physiological functions related to oxidative stress, such as anti-inflammatory and antioxidant effects. However, since a significant increase in blood ketone concentration was observed when more than 7 g of MCTs were ingested (193), it is unlikely that the antioxidant effect of MCTs can be expected without deliberate ingestion of MCTs Since MCTs do not require carnitine for transfer to the mitochondria, they are quickly beta-oxidized and become energy. ...
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In the 1950s, the production of processed fats and oils from coconut oil was popular in the United States. It became necessary to find uses for the medium-chain fatty acids (MCFAs) that were byproducts of the process, and a production method for medium-chain triglycerides (MCTs) was established. At the time of this development, its use as a non-fattening fat was being studied. In the early days MCFAs included fatty acids ranging from hexanoic acid (C6:0) to dodecanoic acid (C12:0), but today their compositions vary among manufacturers and there seems to be no clear definition. MCFAs are more polar than long-chain fatty acids (LCFAs) because of their shorter chain length, and their hydrolysis and absorption properties differ greatly. These differences in physical properties have led, since the 1960s, to the use of MCTs to improve various lipid absorption disorders and malnutrition. More than half a century has passed since MCTs were first used in the medical field. It has been reported that they not only have properties as an energy source, but also have various physiological effects, such as effects on fat and protein metabolism. The enhancement of fat oxidation through ingestion of MCTs has led to interest in the study of body fat reduction and improvement of endurance during exercise. Recently, MCTs have also been shown to promote protein anabolism and inhibit catabolism, and applied research has been conducted into the prevention of frailty in the elderly. In addition, a relatively large ingestion of MCTs can be partially converted into ketone bodies, which can be used as a component of “ketone diets” in the dietary treatment of patients with intractable epilepsy, or in the nutritional support of terminally ill cancer patients. The possibility of improving cognitive function in dementia patients and mild cognitive impairment is also being studied. Obesity due to over-nutrition and lack of exercise, and frailty due to under-nutrition and aging, are major health issues in today's society. MCTs have been studied in relation to these concerns. In this paper we will introduce the results of applied research into the use of MCTs by healthy subjects.
... Accumulating evidence suggested that the most prominent ketone metabolite, β-hydroxybutyrate (BHB), possesses a lot of beneficial effects in the field of clinical science and medicine [22][23][24]. Previous studies reported that BHB presents the anti-aging effects during caloric restriction or fasting, which was generally considered to be beneficial to stem cell maintenance and tissue regeneration [18,25,26]. Recent studies also indicated that BHB can serve as important and instructive immune cell effectors through inhibiting Nlrp3 inflammasome activation and regulating intestinal pro-inflammatory Th17 cells [27][28][29][30]. ...
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Background Ketone body β-hydroxybutyrate (BHB) has received more and more attentions, because it possesses a lot of beneficial, life-preserving effects in the fields of clinical science and medicine. However, the role of BHB in intestinal inflammation has not yet been investigated. Methods Colonic mucosa of inflammatory bowel disease (IBD) patients and healthy controls were collected for evaluation of BHB level. Besides, the therapeutic effect of exogenous BHB in a murine model of acute dextran sulfate sodium (DSS)-induced colitis were assessed by body weight change, colon length, disease activity index, and histopathological sections. The regulatory effectors of BHB were analyzed by RT-qPCR, immunofluorescence, and microbe analysis in vivo. Moreover, the molecular mechanism of BHB was further verified in bone marrow-derived macrophages (BMDMs). Results In this study, significantly reduced BHB levels were found in the colonic mucosa from IBD patients and correlated with IBD activity index. In addition, we demonstrated that the administration of exogenous BHB alleviated the severity of acute experimental colitis, which was characterized by less weight loss, disease activity index, colon shortening, and histology scores, as well as decreased crypt loss and epithelium damage. Furthermore, BHB resulted in significantly increased colonic expression of M2 macrophage-associated genes, including IL-4Ra, IL-10, arginase 1 (Arg-1), and chitinase-like protein 3, following DSS exposure, suggesting an increased M2 macrophage skewing in vivo. Moreover, an in vitro experiment revealed that the addition of BHB directly promoted STAT6 phosphorylation and M2 macrophage-specific gene expression in IL-4-stimulated macrophages. Besides, we found that BHB obviously increased M2 macrophage-induced mucosal repair through promoting intestinal epithelial proliferation. However, the enhancement effect of BHB on M2 macrophage-induced mucosal repair and anti-inflammation was completely inhibited by the STAT6 inhibitor AS1517499. Conclusions In summary, we show that BHB promotes M2 macrophage polarization through the STAT6-dependent signaling pathway, which contributes to the resolution of intestinal inflammation and the repair of damaged intestinal tissues. Our finding suggests that exogenous BHB supplement may be a useful therapeutic approach for IBD treatment.
Over the past 20+ years, the U.S. Government has made significant strides in establishing research funding and initiating a portfolio consisting of subject matter experts on radiation-induced biological effects in normal tissues. Research supported by the National Cancer Institute (NCI) provided much of the early findings on identifying cellular pathways involved in radiation injuries, due to the need to push the boundaries to kill tumor cells while minimizing damage to intervening normal tissues. By protecting normal tissue surrounding the tumors, physicians can deliver a higher radiation dose to tumors and reduce adverse effects related to the treatment. Initially relying on this critical NCI research, the National Institute of Allergy and Infectious Diseases (NIAID), first tasked with developing radiation medical countermeasures in 2004, has provided bridge funding to move basic research toward advanced development and translation. The goal of the NIAID program is to fund approaches that can one day be employed to protect civilian populations during a radiological or nuclear incident. In addition, with the reality of long-term space flights and the possibility of radiation exposures to both acute, high-intensity, and chronic lower-dose levels, the National Aeronautics and Space Administration (NASA) has identified requirements to discover and develop radioprotectors and mitigators to protect their astronauts during space missions. In sustained partnership with sister agencies, these three organizations must continue to leverage funding and findings in their overlapping research areas to accelerate biomarker identification and product development to help safeguard these different and yet undeniably similar human populations – cancer patients, public citizens, and astronauts.
Short-term fasting is beneficial for the regeneration of multiple tissue types. However, the effects of fasting on muscle regeneration are largely unknown. Here, we report that fasting slows muscle repair both immediately after the conclusion of fasting as well as after multiple days of refeeding. We show that ketosis, either endogenously produced during fasting or a ketogenic diet or exogenously administered, promotes a deep quiescent state in muscle stem cells (MuSCs). Although deep quiescent MuSCs are less poised to activate, slowing muscle regeneration, they have markedly improved survival when facing sources of cellular stress. Furthermore, we show that ketone bodies, specifically β-hydroxybutyrate, directly promote MuSC deep quiescence via a nonmetabolic mechanism. We show that β-hydroxybutyrate functions as an HDAC inhibitor within MuSCs, leading to acetylation and activation of an HDAC1 target protein p53. Finally, we demonstrate that p53 activation contributes to the deep quiescence and enhanced resilience observed during fasting.
Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited cause of renal failure and has limited pharmacological treatment options. Disease progression is relentless, and regression is not a known feature of ADPKD even with pharmacological intervention. Recent research has uncovered underlying pathogenic mechanisms that may be amenable to dietary interventions. Cyst cells in ADPKD are thought to depend on glucose for energy and are unable to metabolize fatty acids and ketones. High-carbohydrate diets and lifestyles leading to hyperglycemia appear to worsen progression of ADPKD. Additionally, renal stressors such as oxalate, phosphate and uric acid, that lead to renal tubular micro-crystal burden appear to accelerate disease progression. Based on these research findings, we have created a remote, dietitian-supervised training program to teach individuals with ADPKD the implementation of dietary and lifestyle changes to avoid factors that may worsen disease progression. Using web-based platforms, digital tools, one-on-one remote meetings, and video group meetings, participants learn to implement a plant-focused ketogenic diet that avoids renal stressors, the science behind these changes, how to self-measure health parameters, and track nutrient intake. Dietary changes are supplemented with a medical food containing the ketone beta-hydroxybutyrate and alkaline citrate, and mindfulness exercises. Here, we report the first experience with this program from a beta test with approximately 24 participants. Most participants completed the program and reported improvements in their health and well-being including pain levels, weight loss, hypertension, and eGFR. Adherence to the program was very high and the feasibility of the dietary and lifestyle changes was rated highly. The Ren.Nu program is now publicly available to individuals with ADPKD.
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Ketone bodies are the most energy-efficient fuel and yield more ATP per mole of substrate than pyruvate and increase the free energy released from ATP hydrolysis. Elevation of circulating ketones via high-fat, low-carbohydrate diets has been used for the treatment of drug-refractory epilepsy and for neurodegenerative diseases, such as Parkinson's disease. Ketones may also be beneficial for muscle and brain in times of stress, such as endurance exercise. The challenge has been to raise circulating ketone levels by using a palatable diet without altering lipid levels. We found that blood ketone levels can be increased and cholesterol and triglycerides decreased by feeding rats a novel ketone ester diet: chow that is supplemented with (R)-3-hydroxybutyl (R)-3-hydroxybutyrate as 30% of calories. For 5 d, rats on the ketone diet ran 32% further on a treadmill than did control rats that ate an isocaloric diet that was supplemented with either corn starch or palm oil (P < 0.05). Ketone-fed rats completed an 8-arm radial maze test 38% faster than did those on the other diets, making more correct decisions before making a mistake (P < 0.05). Isolated, perfused hearts from rats that were fed the ketone diet had greater free energy available from ATP hydrolysis during increased work than did hearts from rats on the other diets as shown by using [(31)P]-NMR spectroscopy. The novel ketone diet, therefore, improved physical performance and cognitive function in rats, and its energy-sparing properties suggest that it may help to treat a range of human conditions with metabolic abnormalities.-Murray, A. J., Knight, N. S., Cole, M. A., Cochlin, L. E., Carter, E., Tchabanenko, K., Pichulik, T., Gulston, M. K., Atherton, H. J., Schroeder, M. A., Deacon, R. M. J., Kashiwaya, Y., King, M. T., Pawlosky, R., Rawlins, J. N. P., Tyler, D. J., Griffin, J. L., Robertson, J., Veech, R. L., Clarke, K. Novel ketone diet enhances physical and cognitive performance.
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Reactive oxygen species (ROS) are constantly generated by cells and ROS-derived damage contributes to ageing. Protection against oxidative damage largely relies on the reductive power of NAPDH, whose levels are mostly determined by the enzyme glucose-6-phosphate dehydrogenase (G6PD). Here, we report a transgenic mouse model with moderate overexpression of human G6PD under its endogenous promoter. Importantly, G6PD-Tg mice have higher levels of NADPH, lower levels of ROS-derived damage, and better protection from ageing-associated functional decline, including extended median lifespan in females. The G6PD transgene has no effect on tumour development, even after combining with various tumour-prone genetic alterations. We conclude that a modest increase in G6PD activity is beneficial for healthspan through increased NADPH levels and protection from the deleterious effects of ROS.
Ketosis, the metabolic response to energy crisis, is a mechanism to sustain life by altering oxidative fuel selection. Often overlooked for its metabolic potential, ketosis is poorly understood outside of starvation or diabetic crisis. Thus, we studied the biochemical advantages of ketosis in humans using a ketone ester-based form of nutrition without the unwanted milieu of endogenous ketone body production by caloric or carbohydrate restriction. In five separate studies of 39 high-performance athletes, we show how this unique metabolic state improves physical endurance by altering fuel competition for oxidative respiration. Ketosis decreased muscle glycolysis and plasma lactate concentrations, while providing an alternative substrate for oxidative phosphorylation. Ketosis increased intramuscular triacylglycerol oxidation during exercise, even in the presence of normal muscle glycogen, co-ingested carbohydrate and elevated insulin. These findings may hold clues to greater human potential and a better understanding of fuel metabolism in health and disease.
The purpose of this study was to determine if plasma lactate and skeletal muscle glucose regulatory pathways, specifically PDH dephosphorylation, are impaired during hyperinsulinemic conditions in middle- to older-aged individuals, and determine if exercise training could improve key variables responsible for skeletal muscle PDH regulation. Eighteen young (19-29 years, n=9/9, male/female) and twenty middle- to older-aged (57-82 years, n=10/10, male/female) underwent a 2-hr euglycemic-hyperinsulinemic clamp. Plasma samples were obtained at baseline, 30 min, 50 min, 90 min, and 120 min for analysis of lactate and skeletal muscle biopsies were performed at 60 min for analysis of protein associated with glucose metabolism. In response to insulin, plasma lactate was elevated in aged individuals when normalized to insulin action. Insulin-stimulated phosphorylation of skeletal muscle PDH on serine sites 232, 293, and 300 decreased in young individuals only. Changes in insulin-stimulated PDH phosphorylation was positively related to changes in plasma lactate. No age-related differences were observed in skeletal muscle phosphorylation of LDH, GSK3α, or GSK3β in response to insulin, or PDP1, PDP2, PDK2, PDK4 or MPC1 total protein. Twelve weeks of endurance- or strength-oriented exercise training, improved insulin-stimulated PDH dephosphorylation which was related to a reduced lactate response. These findings suggest that impairments in insulin-induced PDH regulation in a sedentary aging population contribute to impaired glucose metabolism and that exercise training is an effective intervention for treating metabolic inflexibility.
Ketone bodies β-hydroxybutyrate (BHB) and acetoacetate are important metabolic substrates for energy production during prolonged fasting. However, BHB also has signaling functions. Through several metabolic pathways or processes, BHB modulates nutrient utilization and energy expenditure. These findings suggest that BHB is not solely a metabolic intermediate, but also acts as a signal to regulate metabolism and maintain energy homeostasis during nutrient deprivation. We briefly summarize the metabolism and emerging physiological functions of ketone bodies and highlight the potential role for BHB as a signaling molecule in starvation response.
Here we report the identification and verification of a β-hydroxybutyrate-derived protein modification, lysine β-hydroxybutyrylation (Kbhb), as a new type of histone mark. Histone Kbhb marks are dramatically induced in response to elevated β-hydroxybutyrate levels in cultured cells and in livers from mice subjected to prolonged fasting or streptozotocin-induced diabetic ketoacidosis. In total, we identified 44 histone Kbhb sites, a figure comparable to the known number of histone acetylation sites. By ChIP-seq and RNA-seq analysis, we demonstrate that histone Kbhb is a mark enriched in active gene promoters and that the increased H3K9bhb levels that occur during starvation are associated with genes upregulated in starvation-responsive metabolic pathways. Histone β-hydroxybutyrylation thus represents a new epigenetic regulatory mark that couples metabolism to gene expression, offering a new avenue to study chromatin regulation and diverse functions of β-hydroxybutyrate in the context of important human pathophysiological states, including diabetes, epilepsy, and neoplasia.
Mitochondria are central regulators of energy homeostasis and play a pivotal role in mechanisms of cellular senescence. The objective of the present study was to evaluate mitochondrial bio-energetic parameters in five brain regions [brain stem (BS), frontal cortex (FC), cerebellum (CER), striatum (STR), hippocampus (HIP)] of four diverse age groups [1 Month (young), 4 Month (adult), 12 Month (middle-aged), 24 Month (old age)] to understand age-related differences in selected brain regions and their possible contribution to age-related chemical sensitivity. Mitochondrial bioenergetic parameters and enzyme activities were measured under identical conditions across multiple age groups and brain regions in Brown Norway rats (n = 5/group). The results indicate age- and brain region-specific patterns in mitochondrial functional endpoints. For example, an age-specific decline in ATP synthesis (State III respiration) was observed in BS and HIP. Similarly, the maximal respiratory capacities (State V1 and V2) showed age-specific declines in all brain regions examined (young > adult > middle-aged > old age). Amongst all regions, HIP had the greatest change in mitochondrial bioenergetics, showing declines in the 4, 12 and 24 Month age groups. Activities of mitochondrial pyruvate dehydrogenase complex (PDHC) and electron transport chain (ETC) complexes I, II, and IV enzymes were also age- and brain-region specific. In general, changes associated with age were more pronounced with enzyme activities declining as the animals aged (young > adult > middle-aged > old age). These age and brain-region specific observations may aid in evaluating brain bioenergetic impact on the age-related susceptibility to environmental chemical stressors.