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Carnosine
-
life
extension agent
by
Karin Granstrom Jordan, M.D.
A
substance that protects and extends the functional life of the body's key
building blocks—cells, proteins, DNA, lipids—can be fairly called an agent
of longevity. When that agent is safe, naturally present in the body and in
food, and has demonstrated prolongation of life span in animals and cultured
human cells, it is fundamental to any life extension program. Mounting research
suggests that carnosine has just such anti-aging potential.
Carnosine
is a multifunctional dipeptide made up of a chemical combination of the amino
acids beta-alanine and l-histidine. Long-lived cells such as nerve cells
(neurons) and muscle cells (myocytes) contain high levels of carnosine. Muscle
levels of carnosine correlate with the maximum life spans of animal species
(Hipkiss AR et al., 1995).
Laboratory
research on cellular senescence (the end of the life cycle of dividing cells)
suggests that these facts may not be coincidences. Carnosine has the remarkable
ability to rejuvenate cells approaching senescence, restoring normal appearance
and extending cellular life span.
How
does carnosine rejuvenate cells? We do not yet know the full answer, but
carnosine's properties may point up key mechanisms of tissue and cell aging, as
well as the anti-aging measures that counteract them.
Carnosine
addresses the biochemical paradox of life: the elements that make and give
life—oxygen, glucose, lipids, protein, trace metals—also destroy life in
ways that are inhibited by carnosine. Carnosine protects against their
destructive sides through potent antioxidant, anti-glycating, aldehyde quenching
and metal chelating actions (Quinn PJ et al., 1992; Hipkiss AR, Preston JE et
al., 1998). A prime beneficiary is
the body's biggest target—its proteins.
These
interrelated protein modifications include oxidation, carbonylation,
cross-linking, glycation and advanced glycation endproduct (AGE) formation. They
figure prominently not only in the processes of aging but also in its familiar
signs such as skin aging, cataracts and neurodegeneration. Studies show that
carnosine is effective against all these forms of protein modification.
As
an antioxidant, carnosine potently quenches that most destructive of free
radicals, the hydroxyl radical, as well as superoxide, singlet oxygen and the
peroxyl radical. Surprisingly, carnosine was the only antioxidant to
significantly protect chromosomes from oxidative damage due to 90% oxygen
exposure.
Carnosine's
ability to rejuvenate connective tissue cells may explain its beneficial effects
on wound healing. In addition, skin aging is bound up with protein modification.
Damaged proteins accumulate and cross-link in the skin, causing wrinkles and
loss of elasticity. In the lens of the eye, protein cross-linking is part of
cataract formation. Carnosine eye drops have been shown to delay vision
senescence in humans, being effective in 100% of cases of primary senile
cataract and 80% of cases of mature senile cataract (Wang AM et al., 2000).
Carnosine
levels decline with age. Muscle levels decline 63% from age 10 to age 70, which
may account for the normal age-related decline in muscle mass and function
(Stuerenberg HJ et al., 1999). Since carnosine acts as a pH buffer, it can keep
on protecting muscle cell membranes from oxidation under the acidic conditions
of muscular exertion. Carnosine enables the heart muscle to contract more
efficiently through enhancement of calcium response in heart myocytes (Zaloga GP
et al., 1997).
The
body is made up largely of proteins. Unfortunately, proteins tend to undergo
destructive changes as we age, due largely to oxidation and interactions with
sugars or aldehydes.
The
high levels of carnosine in the brain may serve as natural protection against
excitotoxicity, copper and zinc toxicity, protein cross-linking and glycation,
and especially oxidation of cell membranes. Animal studies show broad protective
effects in simulated stroke.
New
research shows that copper and zinc dramatically stimulate senile plaque
formation in Alzheimer's disease. Chelators of these metals dissolve plaques in
the laboratory. Carnosine can also inhibit the cross-linking of amyloid-beta
that leads to plaque formation. A signature of Alzheimer's disease is impairment
of brain microvasculature. Carnosine protected the cells that line brain blood
vessels (endothelial cells) from damage by amyloid-beta (senile plaque material)
as well as by products of lipid oxidation and alcohol metabolism in laboratory
experiments.
Now
that many are cutting down on meat—the main dietary source of
carnosine—supplementation becomes especially important. Carnosine is safe,
with no toxicity even at dosages above 500 mg per kilogram of body weight in
animal studies (Quinn PJ et al., 1992).
There
are thought to be many mechanisms responsible for aging. Consequently, an agent
must work along many basic pathways of the aging process in order to control it.
Scientists have described carnosine as “pluripotent”—active in a multitude
of ways, in many tissues and organs (Hipkiss AR, Preston JE et al., 1998).
Carnosine's pluripotent life extension potential places it on a par with CoQ10
as a cornerstone of longevity nutrition.
Biological
rejuvenation
It
is well known that cells have only a limited capacity to continue to divide
through the course of life. For example, human fetal fibroblasts (connective
tissue cells) divide no more than about 60 to 80 times in laboratory cultures.
By young adulthood, fibroblasts have 30 to 40 divisions left, while in old age
no more than 10 to 20 remain.
The
limited capacity of the cell to perpetuate itself through division is called the
Hayflick Limit, after the scientist who discovered it nearly four decades ago
(Hayflick L et al., 1961; Hayflick L, 1965). In concert with telomeres, which
count off the rounds of cell division, the Hayflick Limit caps life span at the
cellular level. With each division a cell becomes less likely to divide again,
until finally it stops dividing altogether and becomes senescent.
As
cultured cells approach the Hayflick Limit they divide less frequently and take
on strikingly irregular forms. They no longer line up in parallel arrays, assume
a granular appearance, and deviate from their normal size and shape (McFarland
GA et al., 1994). This distorted appearance, called the senescent phenotype,
normally ushers in a twilight state called cellular senescence that until
recently was thought to be irreversible (see the article “Carnosine and
Cellular Senescence” in this issue).
Extending
cell life span
In
a remarkable series of experiments, scientists at an Australian research
institute have shown that carnosine rejuvenates cells as they approach
senescence (McFarland GA, 1999; McFarland GA, 1994). The scientists cultured
human fibroblasts (connective tissue cells) from the lung and the foreskin.
Fibroblasts that went through many rounds of division, known as late-passage
cells, displayed a disorganized, irregular appearance before ceasing to divide.
Fibroblasts cultured with carnosine lived longer, retaining youthful appearance
and growth patterns.
What
is most exciting is the ability of carnosine to reverse the signs of aging in
cells approaching senescence. They
again grew in the characteristic whorled growth patterns of young fibroblasts,
and resumed a uniform appearance. But when they transferred the fibroblasts back
to a medium lacking carnosine, the signs of senescence quickly reappeared.
The
scientists switched late-passage fibroblasts back and forth several times
between the culture media. They consistently observed that the carnosine culture
medium restored the juvenile cell phenotype within days, whereas the standard
culture medium brought back the senescent cell phenotype.
The
carnosine medium also increased life span, even for old cells. The number of
PDs, or population doublings, provides a convenient measure of cell division.
When late-passage lung fibroblasts at 55 PDs (population doublings) were
transferred to the carnosine medium, they lived to 69 to 70 PDs, compared to 57
to 61 PDs for the fibroblasts that were not transferred. Moreover, the
fibroblasts transferred to the carnosine medium attained a life span of 413
days, compared to 126 to 139 days for the control fibroblasts. Carnosine
increased chronological life span more dramatically than PDs in the Australian
series of experiments.
When
cells in the carnosine medium eventually enter into cellular senescence, they
nevertheless retain a normal or less senescent morphology. Carnosine's ability
to retain or restore the juvenile phenotype suggests that it may help maintain
cellular homeostasis.
Two
Japanese studies demonstrate carnosine's ability to stabilize and protect
cultured fibroblasts. The first study shows that carnosine stimulates a factor
called vimentin that promotes robustness in cultured fibroblasts (Ikeda D et
al., 1999). Vimentin is a structural protein that imparts strength and stability
to fibroblasts and endothelial cells.
The
second Japanese study showed that carnosine preserves the integrity of rat
fibroblasts in a nutritionally deficient culture medium (Kantha SS et al.,
1996). Fibroblasts grown in this culture medium lost their characteristic form
after one week, while those grown in the carnosine supplemented culture retained
their healthy appearance. After four weeks those fibroblasts grown in the
carnosine medium retained cellular integrity, while the others were no longer
viable.
When
the scientists transferred late-passage fibroblasts to a culture medium
containing carnosine, they exhibited a rejuvenated appearance and often an
enhanced capacity to divide.
The
study also examined levels of 8-hydroxydeoxyguanosine (8-OH dG), a marker of
oxidative damage to DNA, in fibroblast cultures with and without carnosine. They
found that carnosine significantly reduced 8-hydroxydeoxyguanosine levels in
fibroblasts after four weeks of continuous culture. DNA oxidation is thought to
contribute importantly not only to cellular senescence, but also to
carcinogenesis, and indeed 8-hydroxydeoxyguanosine has been proposed as a marker
for cancer risk (Kasai H, 1997).
Carnosine's
revitalizing effects on cultured fibroblasts may explain why it improves
post-surgical wound healing. Another Japanese study showed that carnosine
enhances granulation, a healing process in which proliferating fibroblasts and
blood vessels temporarily fill a tissue defect (Nagai K et al., 1986). A
Brazilian study showed that granulation tissue developed and matured faster,
with a higher level of collagen biosynthesis, in carnosine treated rats (Vizioli
MR et al., 1983). The Japanese study also presented evidence that carnosine
restores the body's regenerative potential suppressed by common drugs.
Extending
organism life span
Do
carnosine's rejuvenating effects on cells extend to the entire organism? Similar
anti-senescence effects have now been demonstrated in mice. A new Russian study
tested the effect of carnosine on life span and indicators of senescence in
senescence-accelerated mice (Yuneva MO et al., 1999; Boldyrev AA et al., 1999).
Half the mice were given carnosine in their drinking water starting at two
months of age. Carnosine extended the life span of the treated mice by 20% on
average, compared to the mice not fed carnosine.
Carnosine
did not alter the 15 month maximum life span of the senescence-accelerated mice
strain, but it did significantly raise the number of mice surviving to old age.
The mice given carnosine were about twice as likely to reach the “ripe old
age” of 12 months as untreated mice. It also improved indicators of senescence
measured at the “old age” of ten months.
Carnosine
distinctly improved the appearance of the aged mice, whose coat fullness and
color remained much closer to that of young animals. Significantly more
carnosine-treated mice had glossy coats (44% vs. 5%), while significantly fewer
had skin ulcers (14% vs. 36%). However, carnosine did not affect the loss or
texture of hair. Carnosine significantly reduced the rates of spinal
lordokyphosis (spinal curvature) and periopthalmic lesions, but did not affect
corneal opacities.
The
sharpest contrast between the treated and untreated mice was seen in their
behavior. Only 9% of the untreated mice displayed normal behavioral reactivity,
compared to 58% of the carnosine treated mice.
The
researchers also measured biochemical indicators associated with brain aging.
Brain membranes of the carnosine treated mice had significantly lower levels of
MDA (malondialdehyde), a highly toxic product of membrane lipid oxidation. MAO-B
(monoamine oxidase B) activity was 44% lower in the carnosine-treated mice,
indicating maintenance of dopamine metabolism. Glutamate binding to its cellular
receptors nearly doubled in the carnosine treated group. Since glutamate is the
main excitatory neurotransmitter, this may explain the more normal behavioral
reactivity of the carnosine-fed mice.
This
study showed that carnosine significantly improved most measures of appearance,
physiological health, behavior, and brain biochemistry—as well as extended
life span—in senescence-accelerated mice. The researchers therefore conclude
that “carnosine-treated animals can be characterized as more resistant to the
development of features of aging” (Boldyrev AA et al., 1999).
Protein
carbonylation
The
reason why older people—and animals—look different than younger ones has to
do with changes in the proteins of the body. Proteins are the substances most
responsible for the daily functioning of living organisms, which gives protein
deterioration its dramatic impact on the body's function and appearance. Many
lines of research over the last decade converge on protein modification as a
major pathway for aging and degenerative disease. These modifications result
from oxidation (as by free radicals) and interrelated processes such as
protein-sugar reactions (glycation).
Modified
proteins accumulate as we age, while carnosine levels are declining. Once a
protein is modified it has lost its ability to function normally, and when a
significant portion of the body's protein has reached this point, the body
becomes more prone to degenerative diseases.
The
telltale sign of destructive protein modification is the protein carbonyl group.
Accumulation of proteins with carbonyl groups is a molecular indicator of cell
aging. Protein carbonyl levels increase markedly in the last third of the life
span, rising almost exponentially with age in a wide variety of animal species
and tissues. In humans, about a third of proteins become carbonylated later in
life. At that level, these aberrant proteins are considered likely to have
deleterious effects on most aspects of cellular function (Stadtman ER et al.,
2000).
Many
pathways of protein modification produce carbonyl groups, including oxidation of
amino acid side chains, glycation and reactions with aldehydes and lipid
peroxidation products (Berlett BS et al., 1997; Stadtman ER et al., 2000, 1992).
The multiplicity of mechanisms behind protein modification places this problem
beyond the scope of simple antioxidants. A pluripotent agent is needed whose
biochemical profile matches this array of mechanisms. Carnosine emerges as the
most promising broad spectrum shield against protein modification.
Carnosine
addresses the major pathways through which proteins become carbonylated through
its antioxidant and anti-glycation actions, its ability to quench reactive
aldehydes and chelate metals, and its effectiveness against lipid peroxidation.
Carnosine's properties fit the mechanisms of protein carbonylation so well as to
invite the speculation that evolution “designed” carnosine to protect
proteins from carbonylation and other deleterious modifications.
An
excellent example of carnosine's broad-spectrum defense against protein
modification is provided by MDA (malondialdehyde). This noxious product of lipid
peroxidation causes protein carbonylation, cross-linking, glycation and AGE
formation (Burcham PC et al., 1997).
Carnosine
inhibits MDA from carbonylating albumin (the main serum protein) and crystallin
(eye lens protein) in a concentration-dependent manner. MDA glycates albumin
leading to cross-linking and production of advanced glycation end products
(AGEs), however these changes too were prevented by carnosine.
One
of the processes that carbonylates proteins, glycation, is itself recognized as
a major cause of aging and degenerative disease. Glycation occurs when proteins
react with sugars. Then, through a series of reactions including oxidation,
advanced glycation end products (aptly called AGEs) form.
AGEs
accelerate aging processes and promote degenerative disease. This is not
surprising when one considers that AGE formation in the body is the chemical
equivalent of the browning of food in the oven—and equally irreversible. When
proteins accumulate AGEs they do in fact turn brown. The “slow oven” of AGE
formation turns proteins fluorescent, and cross- links them to a point where the
body cannot break them down. As AGEs build up, tissues lose tone and resiliency
and organ systems degenerate. For example, AGEs are now recognized as an
important factor in atherosclerosis (Bierhaus A et al., 1998), cataracts,
Alzheimer's disease (Munch G et al., 1998), and loss of skin elasticity (see
“Skin Aging” in the article “Carnosine and Cellular Senescence” in this
issue).
AGEs
exert their harmful effects on two levels. Most obviously, they physically
impair proteins, DNA and lipids, altering their chemical properties. They also
act as cellular signals, triggering a cascade of destructive events when they
attach to their cellular binding sites (see sidebar titled “AGEs and RAGE”).
One consequence is a 50-fold increase in free radical generation. Since
oxidative stress is often described as a “fixative” of AGE formation, a
vicious cycle can ensue of oxidative stress and AGE accumulation.
Carnosine
is by far the safest and most effective natural anti-glycating agent. Studies in
a wide variety of experimental models demonstrate that carnosine inhibits
protein glycation and AGE formation.
Through
its structural resemblance to the sites that glycating agents attack in
proteins, carnosine is thought to act as a “sacrificial sink.” When
carnosine becomes glycated, it spares proteins from the same fate. Glycated
carnosine is not mutagenic, in contrast to amino acids such as lysine which
becomes mutagenic when glycated, according to the well-known Ames test (Hipkiss
AR, Michaelis J, Syrris P, et al., 1995).
Carnosine
not only inhibits the formation of AGEs, it can also protect normal proteins
from the toxic effects of AGEs that have already formed. An elegant experiment
carried out at King's College, University of London, made this point (Brownson C
et al., 2000; Hipkiss AR et al., 2000). The scientists employed a glycating
agent called methylglyoxal (MG) that reacts with lysine and arginine residues in
body proteins.
The
scientists used MG to glycate ovalbumin (egg white protein). This produced a
brown colored solution typical of the “browning” effect of glycation. They
then incubated the glycated albumin with a normal protein, a-crystallin, from
the lens of the eye. The glycated albumin formed cross-links with the
crystallin, but this was inhibited by carnosine.
The
study demonstrated that carnosine can stop protein damage from spreading to
healthy proteins. It also found evidence that carnosine reacts with and removes
the carbonyl groups in glycated proteins. This study reinforces the body of
research demonstrating carnosine's unique three-stage protection against
accumulation of aberrant proteins: carnosine protects against protein
carbonylation, inhibits damaged proteins from damaging healthy proteins, and
helps the proteolytic system dispose of damaged and unneeded proteins.
Genome
protection
DNA
is organized into chromosomes, each of which contains a double helical DNA
structure carrying the genes. Oxidative stress causes breaks and other
aberrations in the chromosome that accumulate with age. A fascinating experiment
shows the paradoxical effects of antioxidants on oxidative damage to chromosomes
(Gille JJ et al., 1991). This study used hyperoxia, exposure to nearly pure
oxygen (90%), as a physiologically natural oxidative stressor. Hyperoxia is
thought to generate free radicals at the same intracellular sites where they
normally form over time.
The
scientists tested the ability of several antioxidants—including vitamin C, N-acetyl
cysteine (NAC), vitamin E, carnosine and a form of glutathione—to protect the
chromosomes in Chinese hamster ovary cells from oxidative damage. Some of the
antioxidants tested acted instead as pro-oxidants: they increased chromosomal
damage, aggravating the effects of hyperoxia. It is a well known phenomenon that
single antioxidants can sometimes exert a pro-oxidant effect in the body, which
is the reason
people
take multiple antioxidants. In this study, only one antioxidant, carnosine,
significantly reduced chromosomal damage. Cells cultured without any antioxidant
exhibited 133 chromosomal aberrations per 100 cells. Carnosine reduced this
level of damage by two-thirds, to only 44 chromosomal aberrations per 100 cells.
Carnosine preserved 68% of cells fully intact, as compared to 46% of the control
cells.
Neurodegeneration
The
brain's rich supply of oxygen, glucose, membrane lipids and metals may explain
why it is also richly endowed with carnosine. Carnosine suppresses oxidative
stress, protein-sugar interactions leading to AGE formation (see above), lipid
peroxidation, and copper and zinc toxicity. Moreover, carnosine's ability to
forestall cellular senescence may help sustain the long lives of neurons, which
do not divide to form new cells. We will survey carnosine's neuroprotective
actions, with special attention to Alzheimer's disease.
Brain
aging and degeneration are marked by protein carbonylation. A highly sensitive
and specific assay was recently developed for protein carbonyls. Applied to
human brain tissue, this assay reveals that the carbonyl content of neurons is
several times as high in Alzheimer's disease patients as in control subjects
similar in age (Smith MA et al., 1998).
Advances
in cell culturing techniques permit scientists for the first time to maintain
neurons in culture for extended periods. Scientists at the University of
Kentucky used these techniques to study “aging in a dish” (Aksenova MV et
al., 1999). They found that cultured neurons from the hippocampus of the rat
fetus begin to rise in protein carbonyl content about a week before noticeable
changes in neuronal viability appear. At a point when only 10% to 20% of neurons
are no longer viable, protein carbonyl levels have already doubled. They
observed swollen, unhealthy cell bodies in many of the cells with high carbonyl
levels
The
Kentucky study also reinforced earlier findings correlating protein oxidation
with declining activity of the energy-transfer enzyme creatine kinase, which is
very sensitive to oxidation. This leads to diminished energy metabolism in the
brain, a hallmark of Alzheimer's disease.
Animal
studies demonstrate that brain protein carbonylation is associated with
cognitive and behavioral dysfunctions. A study in senescent mice found that
protein carbonyl levels in the brain cortex correlate with the degree of
cognitive impairment, while levels in the cerebellum correlate with motor
deficits (Forster MJ et al., 1996). An earlier study in aged gerbils showed
increased protein carbonyl levels are associated with spatial memory loss
(Carney JM et al., 1991, 1994).
Excitotoxicity
and stroke
A
pathology common to many neurological disorders is excitatory toxicity, or
excitotoxicity. It is caused by an excess of, or excessive sensitivity to,
glutamate—the main excitatory neurotransmitter. Excitotoxicity triggers a
cascade of events including membrane polarization, ending in cell death.
Oxidative stress and excitotoxicity are thought to reinforce each other in a
vicious cycle.
It
is probable that excitotoxic complications determine the long-term effects of
stroke. In Alzheimer's disease, laboratory experiments show that amyloid-beta
sensitizes cultured neurons to excitotoxic death (Doble A, 1999).
Carnosine
and glutamate are found together in presynaptic terminals in the brain.
Experimental evidence shows that carnosine protects cells against excitotoxic
death, supporting the notion that carnosine serves the same purpose in the
brain. An interesting Russian study showed that rat cerebellar cells incubated
in carnosine were resistant to excitotoxic cell death from the glutamate analogs
NMDA and kainite (Boldyrev A et al., 1999).
Copper
and zinc
Copper
and zinc are neurological double-edged swords. While the body cannot live
without them, new research from Florida State University confirms that they can
also be neurotoxic (Horning MS et al., 2000). Abnormal copper-zinc metabolism is
implicated in Alzheimer's disease, stroke, seizures and many other diseases with
neurological components.
Copper
and zinc are thought to modulate synaptic transmission, but are rapid
neurotoxins at the concentrations reached when they are released from synaptic
terminals. The brain must buffer these metals so that they can perform their
functions without neurotoxicity. The new research on copper and zinc toxicity
shows that carnosine provides that buffering action.
Copper
and zinc in Alzheimer's disease
Copper
and zinc contribute to amyloid-beta formation and toxicity through a host of
mechanisms. When amyloid-beta aggregates, as it does in plaque formation, it
becomes more neurotoxic. Laboratory experiments show that tiny amounts of zinc
and especially copper cause amyloid-beta to aggregate.
The
mildly acidic environment characteristic of Alzheimer's disease dramatically
increases aggregation of amyloid-beta by copper ions (Atwood CS et al., 1998).
Inflammation, thought to aggravate and possibly cause Alzheimer's disease, also
creates an acidic environment. Moreover, the acidosis, inflammation and
disturbed
energy
metabolism associated with the disease are thought to increase copper and zinc
levels, thus setting the stage for accelerated formation of amyloid-beta plaques
(Atwood CS et al., 1998).
In
the presence of copper ions amyloid-beta is thought to generate hydrogen
peroxide, which can then react with iron or copper ions to produce highly
neurotoxic hydroxyl radicals. In addition, copper forms complexes with
amyloid-beta that markedly potentiate amyloid-beta neurotoxicity (Huang X et
al., 1999).
The
brain must buffer copper and zinc so that they can perform their functions
without inducing toxicity. New research show that copper and zinc toxicity in
the brain can be buffered by carnosine. (Horning MS et al., 2000)
When
scientists exposed rat neurons to physiological concentrations of copper or
zinc, the neurons died. However carnosine, at a modest physiological
concentration, protected the neurons from the toxic effects of these metals
(Horning MS et al., 2000).
A
spate of recent research papers point up the central role of copper and zinc in
the development of Alzheimer's disease. Levels of these metals are elevated in
the Alzheimer's disease brain, even more so in the amyloid-beta plaques
(“senile plaques”) which are the central feature of the disease (see the
sidebar “Copper and Zinc in Alzheimer’s disease”).
A
groundbreaking study discovered that chelators of copper and zinc solubilize
(dissolve) aggregates of amyloid-beta in post-mortem human tissue samples from
the brains of Alzheimer's disease patients (Cherny RA et al., 1999). The
researchers conclude, “agents that specifically chelate copper and zinc ions
but preserve Mg(II) and Ca(II) may be of therapeutic value in Alzheimer's
disease.”
Carnosine
fits this profile, offering in addition pH buffering and hydroxyl radical
scavenging actions. Not only does carnosine chelate copper and zinc, but the
presence of copper and zinc ions enhances carnosine's potency as a scavenger of
the superoxide radical (Gulyaeva NV, 1987). This is especially significant since
amyloid-beta damages brain endothelial (blood vessel wall) cells quickly and at
low concentrations by generating oxidative stress, particularly in the form of
superoxide radicals (Thomas T et al., 1996). Microvascular damage is the
harbinger of Alzheimer's disease, precdeding its other pathological features.
One
theory of Alzheimer's disease development holds that the distorted
microvasculature seen in the disease is the primary cause of Alzheimer's,
impairing delivery of nutrients to the brain (de la Torre JC, 1997). An
experiment on rat brain endothelium shows that carnosine prevents this damage.
When endothelium was incubated with amyloid-beta and a physiological
concentration of carnosine, damage to endothelial cells was significantly
reduced or completely eliminated (Preston JE et al., 1998).
In
another experiment carried out by the same British team, carnosine protected
brain endothelial cells from damage by MDA (malondialdehyde), a toxic product of
lipid peroxidation. Carnosine inhibited protein carbonylation and cross-linking,
while protecting cellular and mitochondrial function (Hipkiss AR et al., 1997).
A third experiment showed that carnosine also protects these cells against the
toxicity of acetaldehyde, which is produced when alcohol is metabolized (Hipkiss
AR et al., 1998).
AGEs
and amyloid plaque
Carnosine
thus works along multiple pathways that prevent the formation of amyloid plaque,
inhibit amyloid-beta toxicity and promote amyloid plaque breakdown in laboratory
experiments. An examination of how the plaques form reveals an additional
pathway.
Stroke
Neuroprotection
Two
Russian studies show that carnosine protects the brain in simulated strokes
(Stvolinsky SL et al., 1999; Boldyrev AA et al., 1997). In the first experiment,
rats were exposed to low pressure hypoxia. Rats given carnosine beforehand were
able to keep standing and breathing almost twice as long as the others. After
the hypoxia, carnosine treated rats were able to stand after 4.3 minutes, as
compared to 6.3 minutes for the untreated rats.
The
second study simulated stroke through arterial occlusion. Rats treated with
carnosine displayed a more normal EEG, less lactate accumulation (a common
measure of injury severity), and better cerebral blood flow restoration. The
study also demonstrated that carnosine preserves activity of a key enzyme,
Na/K-ATPase, which extracts energy stored in ATP to drive the cellular sodium
pump. Na/K-ATPase inhibition has been found to correlate with edema in the
ischemic (blood-deprived) region.
The
first step in plaque formation is thought to be the slow and reversible
development of a nucleus, followed by a phase of rapid cross-linking and growth.
AGEs (see “Glycation and AGE formation”) accelerate both these steps by
cross-linking soluble monomers to form insoluble aggregates. In fact,
researchers hypothesize that the crucial step in the formation of a stable
amyloid nucleus is the cross-linking of amyloid-beta by AGEs (Munch G et al.,
1997).
These
researchers found that amyloid-beta cross-linking was inhibited by three AGE
inhibitors: the pharmaceuticals aminoguanadine and tenilsetam, and carnosine.
Tenilsetam has demonstrated clinical benefit in Alzheimer's disease. The
researchers incubated amyloid-beta with fructose, which is abundant in the brain
and cross-links proteins up to ten times faster than glucose. Soluble amyloid
disappeared as aggregates formed, driven by AGE cross-linking. All three AGE
inhibitors prevented cross-linking of amyloid-beta, keeping nearly 100% of it in
a soluble form.
Given
the brain's dependence upon glucose for energy metabolism and the unusually high
ratio of fructose to glucose in the brain (about 1:4, compared to 1:20 in
plasma), it seems likely that carnosine serves as a natural glycation inhibitor
in the brain.
We
have seen that carnosine extends life span at the level of the cell and of the
organism. It is equally beneficial to dividing cells and non-dividing cells such
as neurons. Moreover, like CoQ10, nature appears to have anticipated us in the
purposes carnosine naturally serves in the body.
References
Aksenova
MV, Aksenov MY, Markesbery WR, et al. Aging in a dish: age-dependent changes of
neuronal survival, protein oxidation, and creatine kinase BB expression in
long-term hippocampal cell culture. J
Neurosci Res.
1999; 58(2):308-17.
Atwood
CS, Moir RD, Huang X, et al. Dramatic aggregation of Alzheimer Ab by Cu(II) is
induced by conditions representing physiological acidosis. J
Biol Chem.
1998; 273(21):12817-26.
Berlett
BS, Stadtman ER. Protein oxidation in aging, disease, and oxidative stress. J
Biol Chem.
1997; 272(33):20313-6.
Bierhaus
A, Hofmann MA, Ziegler R, et al. AGEs and their interaction with AGE-receptors
in vascular disease and diabetes mellitus. I. The AGE concept. Cardiovascular
Research.
1998; 37(3):586-600.
Boldyrev
A, Song R, Lawrence D, et al. Carnosine protects against excitotoxic cell death
independently of effects on reactive oxygen species. Neuroscience.
1999; 94(2):571-7.
Boldyrev
AA, Stvolinsky SL, Tyulina OV, et al. Biochemical and physiological evidence
that carnosine is an endogenous neuroprotector against free radicals. Cell
Mol Neurobiol.
1997; 17(2):259-71.
Brownson
C, Hipkiss AR. Carnosine reacts with a glycated protein. Free
Radic Biol Med.
2000; 28(10):1564-70.
Burcham
PC, Kerr PG, Fontaine F. The antihypertensive hydralazine is an efficient
scavenger of acrolein. Redox
Rep.
2000; 5(1):47-9.
Burcham
PC, Kuhan YT. Diminished susceptibility to proteolysis after protein
modification by the lipid peroxidation product malondialdehyde: inhibitory role
for crosslinked and noncrosslinked adducted proteins. Arch
Biochem Biophys.
1997; 340(2):331-7.
Butterfield
DA. Alzheimer's b-amyloid peptide and free radical oxidative stress. Gilbert DL
and Colton CA, editors. Reactive
oxygen species in biological systems: an interdisciplinary approach.
New York, 1999. Pp. 609-638.
Carney
JM, Smith CD, Carney AM, et al. Aging- and oxygen-induced modifications in brain
biochemistry and behavior. Ann
NY Acad Sci.
1994; 738:44-53.
Carney
JM, Starke-Reed PE, Oliver CN, et al. Reversal of age-related increase in brain
protein oxidation, decrease in enzyme activity, and loss in temporal and spatial
memory by chronic administration of the spin-trapping compound
N-tert-butyl-alpha phenylnitrone. Proc
Natl Acad Sci USA.
1991; 88(9):3633-6.
Cherny
RA, Legg JT, McLean CA, et al. Aqueous dissolution of Alzheimer's disease Ab
amyloid deposits by biometal depletion. J
Biol Chem.
1999; 274(33):23223-8.
Doble
A. The role of excitotoxicity in neurodegenerative disease: implications for
therapy. Pharmacol
Ther.
1999; 81(3):163-221.
Forster
MJ, Dubey A, Dawson KM, et al. Age-related losses of cognitive function and
motor skills in mice are associated with oxidative protein damage in the brain.
Proc Natl Acad Sci USA. 1996; 93(10):4765-9.
Gille
JJ, Pasman P, van Berkel CG, et al. Effect of antioxidants on hyperoxia-induced
chromosomal breakage in Chinese hamster ovary cells: protection by carnosine. Mutagenesis.
1991; 6(4):313-8.
Gulyaeva
NV. Superoxide-scavenging activity of carnosine in the presence of copper and
zinc ions. Biochemistry
(Moscow). 1987; 52(7 Part 2):1051-4.
Gulyaeva
NV, Dupin AM, Levshina IP. Carnosine prevents activation of free-radical lipid
oxidation during stress. Bull
Exp Biol Med.
1989; 107(2):148-152.
Hayflick
L. The limited in vitro lifetime of human diploid cell strains. Exp Cell Res.
1965; 37:614-36.
Hayflick
L, Moorhead PS. The serial cultivation of human diploid cell strains. Exp
Cell Res.
1961; 25:585-621.
Hipkiss
AR, Brownson C. A possible new role for the anti-ageing peptide carnosine. Cell
Mol Life Sci.
2000; 57(5):747-53.
Hipkiss
AR, Chana H. Carnosine protects proteins against methylglyoxal-mediated
modifications. Biochem
Biophys Res Commun.
1998; 248(1):28-32.
Hipkiss
AR, Michaelis J, Syrris P. Non-enzymatic glycosylation of the dipeptide
L-carnosine, a potential anti-protein-cross-linking agent. FEBS
Lett.
1995; 371(1):81-5.
Hipkiss
AR, Michaelis J, Syrris P, et al. Strategies for the extension of human life
span. Perspect
Hum Biol.
1995; 1:59-70.
Hipkiss
AR, Preston JE, Himswoth DT, et al. Protective effects of carnosine against
malondialdehyde-induced toxicity towards cultured rat brain endothelial cells. Neurosci
Lett.
1997; 238(3):135-8.
Hipkiss
AR, Preston JE, Himsworth DT, et al. Pluripotent protective effects of
carnosine, a naturally occurring dipeptide. Ann
NY Acad Sci.
1998; 854:37-53.
Horning
MS, Blakemore LJ, Trombley PQ. Endogenous mechanisms of neuroprotection: role of
zinc, copper, and carnosine. Brain
Res.
2000; 852(1):56-61.
Huang
X, Cuajungco MP, Atwood CS, et al. Cu(II) potentiation of alzheimer Ab
neurotoxicity. Correlation with cell-free hydrogen peroxide production and metal
reduction. J
Biol Chem.
1999; 274(52):37111-6.
Ikeda D, Wada S, Yoneda C, et al. Carnosine stimulates
vimentin expression in cultured rat fibroblasts. Cell
Struct Funct. 1999; 24(2):79-87.
Kantha SS, Wada S, Tanaka H, et al. Carnosine sustains
the retention of cell morphology in continuous fibroblast culture subjected to
nutritional insult. Biochem Biophys Res
Commun. 1996; 223(2):278-82.
Kasai H. Analysis of a form of oxidative DNA damage,
8-hydroxy-2'-deoxyguanosine, as a marker of cellular oxidative stress during
carcinogenesis. Mutat Res.
1997; 387(3):147-63.
McFarland GA, Holliday R. Retardation of the senescence
of cultured human diploid fibroblasts by carnosine. Exp
Cell Res 1994; 212(2):167-75.
McFarland GA, Holliday R. Further evidence for the
rejuvenating effects of the dipeptide L-carnosine on cultured human diploid
fibroblasts. Exp Gerontol.
1999; 34(1):35-45.
Mark RJ, Lovell MA, Markesbery WR, et al. A role for
4-hydroxynonenal, an aldehydic product of lipid peroxidation, in disruption of
ion homeostasis and neuronal death induced by amyloid beta-peptide. J
Neurochem. 1997; 68(1):255-64.
Munch G, Mayer S, Michaelis J, et al. Influence of
advanced glycation end-products and AGE-inhibitors on nucleation-dependent
polymerization of beta-amyloid peptide. Biochim
Biophys Acta. 1997; 1360(1):17-29.
Munch G, Schinzel R, Loske C, et al. Alzheimer's
disease--synergistic effects of glucose deficit, oxidative stress and advanced
glycation endproducts. Journal of Neural
Transmission. 1998; 105(4-5):439-61.
Nagai K, Suda T, Kawasaki K, et al. Action of carnosine
and beta-alanine on wound healing. Surgery.
1986; 100(5):815-21.
Preston JE, Hipkiss AR, Himsworth DT, et al. Toxic
effects of beta-amyloid(25-35) on immortalised rat brain endothelial cell:
protection by carnosine, homocarnosine and beta-alanine. Neurosci
Lett. 1998; 242(2):105-8.
Quinn PJ, Boldyrev AA, Formazuyk VE. Carnosine: its
properties, functions and potential therapeutic applications. Mol
Aspects Med. 1992; 13(5):379-444.
Schmidt AM, Yan SD, Wautier JL, et al. Activation of
receptor for advanced glycation end products: a mechanism for chronic vascular
dysfunction in diabetic vasculopathy and atherosclerosis. Circ
Res. 1999; 84(5):489-97.
Smith MA, Sayre LM, Anderson VE, et al. Cytochemical
demonstration of oxidative damage in Alzheimer disease by immunochemical
enhancement of the carbonyl reaction with 2,4-dinitrophenylhydrazine. J
Histochem Cytochem. 1998; 46(6):731-5.
Stadtman ER. Protein oxidation and aging. Science.
1992; 257(5074):1220-4.
Stadtman ER, Levine RL. Protein oxidation. Ann
NY Acad Sci. 2000; 899:191-208.
Stuerenburg HJ, Kunze K. Concentrations of free
carnosine (a putative membrane-protective antioxidant) in human muscle biopsies
and rat muscles. Arch Gerontol Geriatr.
1999. 29: 107-113.
Stvolinsky SL, Kukley ML, Dobrota D, et al. Carnosine:
an endogenous neuroprotector in the ischemic brain. Cell
Mol Neurobiol. 1999; 19(1):45-56.
Thomas T, Thomas G, McLendon C, et al.
b-Amyloid-mediated vasoactivity and vascular endothelial damage. Nature.
1996; 380(6570):168-71.
de la Torre JC. Cerebromicrovascular pathology in
Alzheimer's disease compared to normal aging. Gerontology.
1997; 43(1-2):26-43.
Vizioli MR, Blumen G, Almeida OP, et al. Effects of
carnosine on the development of rat sponge-induced granulation tissue. II.
Histoautoradiographic observations on collagen biosynthesis. Cell
Mol Biol. 1983; 29(1):1-9.
Wang AM, Ma C, Xie ZH, et al. Use of carnosine as a
natural anti-senescence drug for human beings. Biochemistry
(Moscow). 2000; 65(7):869-71.
Yan SD, Chen X, Fu J, et al. RAGE and amyloid-beta
peptide neurotoxicity in Alzheimer's disease. Nature.
1996; 382(6593):685-91.
Yuneva MO, Bulygina ER, Gallant SC, et al. Effect of
carnosine on age-induced changes in senescence-accelerated mice. J
Anti-Aging Med. 1999; 2(4):337-42.
Zaloga GP, Roberts PR, Black KW. Carnosine is a novel
peptide modulator of intracellular calcium and contractility in cardiac cells. Am
J Physiol 1997; 272(1 Pt 2):H462-8.
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