Resveratrol (3,5,4'-trihydroxystilbene) has been subject to a lot of reasearch lately and a wide
range of positive effects have been attributed to this plant phytoalexin. Effects like increased
lifespan, cancer prevention, athletic performance enhancement, anti-oxidative, anti-viral, anti-
bacterial, anti-inflammatory, cardio protective and neuronal protective effects has been
proposed positive effects of resveratrol. The structure of resveratrol enables it to interact with
many receptors and enzymes throughout the organism. It has been shown to activate sirtuins,
inhibit lipid peroxidation, induce apoptosis in tumours, repress oxidative stress, act as an
estrogen-receptor antagonist (and agonist in some tissues), increase testosterone levels
without any adverse effects, promote vasorelaxation, inhibit platelet aggregation, protect
against neuronal cell death, inhibit pro-inflammatory cytokines and suppress inflammation
responses. However positive the outlooks seem there are still many issues to be raised
regarding the effect in humans. Bioavailability and plasma concentrations required for
desirable effect needs to be examined (re-examined). The research has not been equivocal on
these issues and there must also be a thorough toxicity evaluation of resveratrol before any
therapeutical treatments on humans can be executed. The lack of studies on human will force
the researchers to extrapolate data from in-vitro
or animal experiments to human systems.
Resveratrol is a substance produced by certain plants in response to stress conditions, such as
fungi or bacteria infection (1). The plants have also several other molecules that protect them
from toxins during such attacks resveratrol one among many. Resveratrol is a phytoalexin
which are natural plant antibiotics. The current research is pointing towards many health
benefits for this substance in humans. These benefits include: Increased lifespan, cancer
prevention, athletic performance enhancement, anti-oxidative, anti-viral, anti-bacterial, anti-
inflammatory, cardio protective and neuronal protective effects (1-20). However, there are
still many questions to be answered regarding the relevance of the effects in humans. This
report will try to elucidate some of the effects and controversies regarding this substance and
explain the possible mechanisms that resveratrol acts through.
The resveratrol molecule has a stilbene skeleton with 3 hydroxyl-groups attached on it (see
Fig 1.). Resveratrol or 3,5,4'-trihydroxystilbene (C14H12O3) exicts in two geometric isomeres cis-
. The trans
form can undergo transformation to cis
form if exposed to UV light
and the cis
form is the least common type (more unstable and stearically hindered)(2).
Stilbenoids (stilbene derivate) like resveratrol is produced through the enzyme stilbene
synthase in plants. It is lipophilic and is able to cross the blood-brain-barrier in humans (1).
Resveratrol is found only a few of our dietary scourses: in white hellebore (julrosor), Japanese
knotweed, grapes (in the skin and seeds), cranberries, peanuts, blueberries (Vaccinium
amerikanskt blåbär), bilberries (Vaccinium myrtillus,
blåbär) and mulberries (3).
The highest concentrations are observed in matured red wine berries and red wine has
therefore been of great interest in research lately. However, some in-vivo
most studies on resveratrol are in-vitro
, in yeast, worms, fruit flies, fish, mice, and rats. It’s
currently also sold as nutritional supplement, however there are no research on long-term
effect on humans.
With the simple structure it can interact with many enzymes and receptors and thus inactivate
or activate a number of pathways (1).
Fig 1.Chemical structure of Trans-resveratrol. A stilbene is just the ethene with the two phenyl groups attached to it.
There are several other stilbenes produced by these plants which are involved in protecting the plant from toxins originating from fungi and bacteria. Resveratrol is related to Pterostilbene, a substacne in blueberries and grapes which is also believed to be a potent theraputic target (See Fig 2.).
Fig 2. Pterostilbene is very similar to resveratrol
2.1 Can resveratrol increase lifespan?
The main argument for life extending properties of resveratrol is based on the hypothesis that
the stilbenes can activate sirtuins. SIRT1 activation by resveratrol
: Sirtuins are closely related enzymes that aredependent
ound inaome researchers believe
that sitruins are an important factor in the organisms respons to stress situations including heat
and starvation (4,5). The hypothesis is that the life extending effect of calorie restriction (such
as lower blood cholesterol, nlevels) is due to the activity of
The deacetylation process involves removal of acetyl groups from histone tails, which causes
DNA to bind more tightly to the histones. This leads to an interferance with transcription of
genes by blocking transcription factors. This results in a non specific reducti(4).
SIRT1 have also been shown to repress PPARγ in yeast and mice (5), which results in a
number of positive effects including attenuated adipogenesis. The same study demonstrated
an upregulation of lipolysis and loss of fat.
The sirtuin SIRT1 in humans are important in many biological processes including: gene
silencing (transcription regulation i.e marker genes near telomeres are silenced), cell cykle
regulation (i.e p53 dependent processes), adipogenesis, muscle differentiation, protection
from axonal degeneration and life span extension (4). Reasearchers have demonstrated that
resveratrol can activate the sirtuins; Sir2/SIRT1 (SIRT1 is thaught to be the human
homologue of Sir2) in yeast, worms, fruit flies and mice by up to 8-fold increase in activity.
The most apperant effects were extended lifespan despite the fact that they were put on a high
calorie diet (6).
However, the question whether this is a consequense of resveratrol alone have been
studies have shown that human SIRT1 requires a fluorophore (naturally
occuring compound that are also flourecent) to be covalently bound in order to be activated
(4,7). Moreover, the fluorophore-SIRT1 complex displays higher affinity when resveratrol is
present. Of note is that one study showed no effect on lifespan in yeast experiments (7).
2.2 Resveratrol affects tumour initiation, promotion and progression
There are a numerous ways of which resveratrol is proposed to act as a chemopreventive
agent. Some of which are explained below. Most studies reviewed in this report show effects
on breast cancer or prostate cancer, although intestinal and melanoma cancers have been
reported to be affected by resveratrol (1, 16-21).
Resveratrol has been shown to prevent metabolic activation of procarcinogens (such as
polycyclic aromatic hydrocarbons (PAH’s)) by inhibition of phase I enzymes and competitive
inhibition of the aryl hydrocarbon receptor; AhR. The AhR is believed to be involved in cell
proliferation, differentiation, induction of P450 1A1 after xenobiotic exposure and is a major
contributor to tumour initiation (17). Resveratrol has an antagonising effect on this receptor.
However, this findings have been questioned by other reports showing an AhR independent
inhibition of P450 1A1 by resveratrol (17).
ROS from lipid peroxidation is believed to initiate tumour development through cell
membrane damage. Resveratrol have been shown to protect cell membranes from lipid
peroxidation, damage to our DNA caused by ROS and induction of phase II enzymes (12, 17).
Resveratrol in capable of increasing the activity of the cell-cycle regulator, p53 (17). This
highly important process can cause an arrest in the cell-cycle and make room form DNA
repair systems or activate apoptotic signals to prevent the cell from becoming a tumour cell.
However, studies on human breast cancer cell lines shows that the changes in p53
concentration are relatively small (and was not dose dependant). This lead to the conclusion
that modulation of p53 gene expression by resveratrol (and other wine polyphenols) could not
account for the anti-carcinogenic effects (19).
Furthermore, resveratrol can affect the MAPK pathways by a number of mechanisms. It can
inhibit the protein kinase C (and many of its isoenzymes) phosphorylation of arginin-rich
substrates (proteins). This, by way of a non-competitive action (17). MAPK pathways are
involved in many cellular processes such as gene expression, differentiation,
survival/apoptosis and mitosis. This MAPK cascade inhibition by resveratrol hinders tumour
formation (17). Although, as will be described below, resveratrol can also induce
phosphorylation of MAPK family members ERK-1 and -2 (1).
Moreover, prostaglandins (PG’s) are thought to play an important role in promoting cell
proliferation, suppress immune responses and stimulate tumour formation (17). To synthesise
PG’s, prostaglandin H synthase (PHS), cyclooxygenase (COX) and lipoxygenase pathways
can convert for example arachidonic acid into PG’s. Indeed, resveratrol is a competitive
inhibitor of COX and peroxidase activity of PHS in human erythroleukemia cells (17). The
mechanism of this inhibition is yet to be elucidated.
Yet another cancer preventive effect exhibited by resveratrol is the prevention of cells (in-
from entering the S/G2/M phase during the cell cycle. This is accomplished by blocking
cyklins, cdk’s pRB and other substances affecting the progression of the cell cycle (17).
Finally, resveratrol can induce cell death by up-regulation, conformational changes and
mitochondrial redistribution of Bax and Bak (both of which are pro apoptotic proteins from
the Bcl-2 gene family) along with activation of caspase-3 and -9 (proteases in the apoptotic
cascade) (17, 20).
Resveratrol treated rats demonstrated a reduction in mammary tumour incidence by
approximately 50% (low-dose <100 mg / kg) (16). The tumours on treated animals where
examined and evidence of apoptotic cells within peripheral tumour areas where observed (16).
This indicates that resveratrol could induce apoptosis in tumour cell lines and proposes a
possible treatment target for breast cancer.
2.3 Resveratrol as an anti-oxidant?
Resveratrol have been said to have various antioxidant activities, however when reviewing the
research it seems that the interaction of resveratrol with other biomolecules that do the actual
“antioxidative job” is contributing more to this observed effect. Therefore, resveratrol is
thought to be a weak ROS (radical oxygen species) scavenger (9).
But one study suggested three different mechanisms that resveratrol acts as a natural (direct)
1, Competition with CoenzymeQ (decreases the respiration chain formation of ROS).
2, Scavenge oxygen radicals formed in the mitochondria (debated in other studies).
3, Inhibition of lipidperoxidation induced by Fenton reaction products (12).
It seems that resveratrol can lower the amount of oxidative damaged DNA; however the
mechanism is currently unknown.
MnSOD (mitochondrial superoxid dismutase, a member of iron/manganese superoxid
dismutase family) converts the byproducts of oxidative phosphorylation into hydrogen
peroxide and O2. This is a major process of our defence against oxidative stress since an
overexpression of MnSOD itself can significantly reduce intracellular oxidative stress, extend
life span and inhibit cancer cell growth (9). One study resulted in a 14-fold increase in
MnSOD activity after two weeks of resveratrol (50µM) incubation in human lung fibroblasts
(MRC-5) (9). The mechanism by which resveratrol stimulates MnSOD is not known to
researchers. Interestingly, at higher concentrations than 50µM resveratrol, the effects
(including MnSOD activity) on the cells did not increase further. This is suggests that lower
concentrations will still have some effect on the cells. Since the concentrations in human
tissues after ingestion of resveratrol rich food (typically red wine) ends up at low µM
concentrations (1, 9).
The research on resveratrol effects on other antioxidant enzymes has been equivocal. For
example, several glutathione enzymes have been shown to be increased in some studies while
in others no or adverse effect have been demonstrated (9, 12). Concentration levels were
significantly higher in the study that showed an increase compared with the study that showed
no or adverse effect (9, 12).
2.4 Resveratrol is estrogenic/anti-estrogenic
Estrogen plays an important role in development of for example breast cancer. Current
research is looking for ways to inhibit estrogen synthesis as a target for breast cancer
treatment (21). The Cyt-P450 enzyme, aromatase, transforms androgens to become estrogens
(like estradiol). Resveratrol have demonstrated an inhibition of aromatase at both enzyme and
mRNA levels in-vitro
(10, 11, 21).
Resveratrol has been shown to bind to both estrogen-receptor-α and –β (ER- α / β) in-vitro
(15, 16). The binding affinity is equally low for both receptors when compared with the potent
estrogen; estradiol. It has been classified as a phytoestrogen due to its modulating effects of
estrogenic pathways (1, 8). It exhibits agonistic/antagonistic effects depending on the cell type
and gene promoter (as does the breast cancer preventive tamoxifen (TAM)) (15, 16). This
makes resveratrol especially interesting in preventing for example breast cancer. An estradiol
antagonistic effect is observed on resveratrol-liganded ER-α, but not ER-β (1, 15, 16).
Interestingly, resveratrol-liganded ER-β has higher transcriptional activity than estradiol has
on the same receptor. This means that tissues expressing more ER-β than ER-α may be more
affected by resveratrols estrogen agonistic effects (15, 16).
Resent studies also show lack of estrogenic activity in the uterus and mammary (and possibly
even anti-estrogenic activity in these tissues by resveratrol). Moreover, there have been
demonstrated estrogenic activities in bone and endothelial cells (1). All this taken into account
it would seem relevant to administer resveratrol together with a selective ER-modulator in
order to treat breast cancer.
2.5 Performance enhancement by resveratrol
Athletes are constantly looking for natural ways to boost their testosterone levels without
using illegal drugs such as androgenic-anabolic steroids.
In one experiment on rats the researchers studied the serum concentration of LH (signals to
Leydig cells to produce testosterone), FSH (stimulate spermatogenesis) and testosterone to
determine weather the resveratrol treated group had any difference in these reproduction
hormones. The results after 90 days treatment with orally administered resveratrol (20 mg/kg
* d) were around 100% or more than 100% increase in concentrations of all the hormones
including sperm count in the resveratrol treated group (8). No adverse effects or side effects
(like sperm abnormalities) were seen in the treated group compared with the untreated group.
Furthermore, the body weight and food/water consumption did not differ among the groups.
Nor were there any estrogenic effects on the testes of the treated rats. These findings lead the
researchers to conclude that resveratrol acts as a week estrogen antagonist/agonist without any
estrogenic properties, which is in agreement with several other studies (8).
One proposed mechanism resveratrol uses to accomplish this is through its aromatase
inhibitory effects. This leaves the androgens to execute their masculine activity instead of
converting it to estradiol (10, 11).
2.6 Resveratrol as a cardio-vascular protective agent
A possible important cardio protective effect of resveratrol is to inhibit peroxidation of LDL
by chelating activity and oxygen radical scavenging (1). Resveratrol also seem to function as
a vasorelaxation agent by nitric-oxide (NO) mediated way (NO is known to inhibit vascular
smooth muscle contraction and growth, platelet aggregation, and leukocyte adhesion to the
endothelium). This has been demonstrated through administration of NO-synthase inhibitor to
isolated rat aorta. The result was an antagonising pattern on resveratrols vasorelaxation effect
Another mechanism proposed for the vasorelaxation effect is that resveratrol stimulates Ca2+-
activated K+-channels (BKCa) that exists in human vascular endothelial cells. This can lead to
an increase in K+ concentration in myoendothelial space which then leads to hyperpolarisation
of vascular monocytes. The result is dilated blood vessels (1). 2.7 Neuronal protective effects of resveratrol
Resveratrol, as described above can affect several MAPK pathways. One if these is induction
of phosphorylation of MAPK family members, ERK1 and 2 in human neuroblastoma cells
(konc. 1 pM). Epidemiological studies show inverse relation to dementia. It has also been
showed that resveratrol can protect against neuronal cell death that could manifest
Alzheimer’s disease, through inhibition of LDL peroxidation in treated PC-12 cells (1).
2.8 Anti-inflammatory properties of resveratrol
Resveratrol demonstrated a dose-dependant inhibition of interleukin-6 (a pro-inflammatory
cytokine released my macrophages and T-cells), by blockade of Ca2+ influx into cells.
Another anti-inflammatory action by resveratrol is suppression of activation of NF-κB (key
regulator of stress, immune, infection and inflammation responses) by LPS and inhibited
phosphorylation of inhibitory κBα (1).
Indeed, resveratrol displays a wide and complex interaction with different tissues, cells and
proteins throughout the human body. The main thing one comes across when reading the
literature on resveratrol is that it is hard to prove or illustrate if resveratrol itself is responsible
for the changes seen or if it is because of resveratrol derivates or even other compounds with
similar structure and shape (when grape extract was administered to subjects). Some studies
have demonstrated an up to 100 times greater growth inhibitory activity on cancer cells in
synthesised resveratrol derivates (18). This should be the focus of future studies, to determine
the effectiveness of resveratrol in therapeutical doses. As seen in some of the research,
concentrations of resveratrol into subjects or cells are far greater than the normal diet could
provide (5.9). However, many studies displays no toxic effects, there have been reports on
pro-oxidative effects by resveratrol under certain conditions (12). This implicates that there
should still be some cautiousness in recommending people daily use of resveratrol or
resveratrol containing foods.
Despite some problems and unanswered questions regarding mechanisms and interactions,
resveratrol seem to be a promising target for more research. Taken into account that
resveratrol-like molecules could be more effective in certain chemopreventive actions the
question still remains weather it is efficient to use resveratrol as a research tool for possible
Indeed, numerous studies displays many positive actions including affecting pathways that
control inflammation, lipidperoxidation, platelet aggregation, vasodilation, sex-hormone
responses, detoxifying enzymes and longevity.
Finally, the lack of studies on human is a problem and proves that the research have still many
steps to go through before any certainties can be issued. The researchers need to extrapolate
data from in-vitro
or animal experiments to human systems in order to advance the knowledge
of resveratrol further.
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