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FORUM REVIEW ARTICLE
Phytochemical Antioxidants Modulate Mammalian Cellular
Epigenome: Implications in Health and Disease
Smitha Malireddy,
1
Sainath R. Kotha,
1
Jordan D. Secor,
1
Travis O. Gurney,
1
Jamie L. Abbott,
1
Gautam Maulik,
2
Krishna R. Maddipati,
3
and Narasimham L. Parinandi
1
Abstract
In living systems, the mechanisms of inheritance involving gene expression are operated by (i) the traditional
model of genetics where the deoxyribonucleic acid (DNA) transcription and messenger ribonucleic acid stability
are influenced by the DNA sequences and any aberrations in the primary DNA sequences and (ii) the epigenetic
(above genetics) model in which the gene expression is regulated by mechanisms other than the changes in DNA
sequences. The widely studied epigenetic alterations include DNA methylation, covalent modification of
chromatin structure, state of histone acetylation, and involvement of microribonucleic acids. Significance:
Currently, the role of cellular epigenome in health and disease is rapidly emerging. Several factors are known to
modulate the epigenome-regulated gene expression that is crucial in several pathophysiological states and
diseases in animals and humans. Phytochemicals have occupied prominent roles in human diet and nutrition as
protective antioxidants in prevention/protection against several disorders and diseases in humans. Recent
Advances: However, it is beginning to surface that the phytochemical phenolic antioxidants such as polyphenols,
flavonoids, and nonflavonoid phenols function as potent modulators of the mammalian epigenome-regulated
gene expression through regulation of DNA methylation, histone acetylation, and histone deacetylation in
experimental models. Critical Issues and Future Directions: The antioxidant or pro-oxidant actions and their
involvement in the epigenome regulation by the phytochemical phenolic antioxidants should be at least es-
tablished in the cellular models under normal and pathophysiological states. The current review discusses the
mechanisms of modulation of the mammalian cellular epigenome by the phytochemical phenolic antioxidants
with implications in human diseases. Antioxid. Redox Signal. 17, 327–339.
Introduction: Epigenetic Regulation of Gene Expression
Recent studies with the aid of novel and more advanced
molecular tools have provided deeper insights into the
nuclear architecture, including critical information on the
mechanisms of normal and pathophysiological states of gene
expression. Furthermore, these studies have revealed that the
mechanisms of inheritance involving gene expression are
operated through genetic alterations influencing deoxyr-
ibonucleic acid (DNA) transcription and messenger ribonu-
cleic acid (mRNA) stability through modifications of the
primary DNA sequences and epigenetic alterations involving
the covalent modification of chromatin architecture and post-
translational modifications (77). DNA in its native form is
inaccessible for transcription (46). Nucleosomes, the building
blocks of higher order chromatin structure, consist of 147 base
pairs of DNA wrapped around an octamer of histones (H2A,
H2B, H3, and H4) (46). Short stretches of linker DNA join
nucleosomes to form polymers that are further organized into
tightly compacted native chromatin configuration as seen in
the nucleus and have an appearance of beads on a string.
Chromatin has regions of transcriptionally active euchroma-
tin and inactive heterochromatin. The interconversion of these
two regions for DNA accessibility to transcription factors is
determined by the epigenome components, including his-
tone chaperones, chromatin-remodeling complexes, histone-
and histone variant-modifying enzymes, DNA methylating
agents, noncoding RNAs like the microribonucleic acids
(miRNAs), and other epigenome constituents. Thus, the term
‘‘epigenetics’’ is defined as the stable and perpetual but re-
versible and altered active states of gene expression without
modifying the primary DNA sequences (77).
1
Division of Pulmonary, Allergy, Critical Care, and Sleep Medicine, Lipid Signaling, Lipidomics, and Vasculotoxicity Laboratory, Dorothy
M. Davis Heart and Lung Research Institute, Colleges of Medicine and Pharmacy, The Ohio State University, Columbus, Ohio.
2
Department of Radiology, Harvard Medical School, Boston, Massachusetts.
3
Department of Pathology, Wayne State University School of Medicine, Detroit, Michigan.
ANTIOXIDANTS & REDOX SIGNALING
Volume 17, Number 2, 2012
ªMary Ann Liebert, Inc.
DOI: 10.1089/ars.2012.4600
327
Epigenetic regulation is furthermore involved in tissue-
specific gene expression and silencing. There are different
mechanisms that mediate and regulate the duplication of
chromatin state, which depends on the chromatin domain,
organism, and function. The key components involved in-
clude histone chaperones, chromatin-remodeling factors,
histone-modifying enzymes, RNA components, and the DNA
replication machinery itself. Mechanisms that regulate chro-
matin remodeling, a crucial step in epigenetic alterations, in-
clude DNA methylation, post-translational modifications of
histones, including acetylation, deacetylation, phosphoryla-
tion, poly-adenosine-3¢,5¢-diphosphate (ADP)-ribosylation,
ubiquitination, histone variants, and miRNAs. DNA methyl-
ation is brought about by enzymes called DNA methyl-
transferases (DNMTs), which catalyze the addition of a
methyl group to cytosine (C) located 5¢to guanines (G) on the
phosphodiester bond between cytosine and guanine (CpG)
islands. DNA methylation, an epigenetic mechanism, is
known to attenuate gene expression and has been shown to
play crucial roles in cellular functions. Histones represent a
class of proteins that are extremely arginine rich. Almost
14% of the histone H4 amino acids are arginine residues.
Histone modification involves covalent modification of the
N-terminus tail of histone in determination of the level of gene
expression. Histone acetylation of conserved lysine residues
in histone tails, the signature of transcriptionally active re-
gions, is brought about by the histone acetyltransferase (HATs)
and hypoacetylation by histone deacetylases (HDACs) as seen
in transcriptionally inactive heterochromatin regions (67).
The roles of sirtuins (SIRTs; class III HDACs) are implicated
in physiological and pathophysiological phenomena, includ-
ing inflammation, cellular aging and senescence, cell prolif-
eration, apoptosis, cell differentiation, metabolism, stem cell
pluripotency, and cell cycle regulation (18). Seven different
types of SIRTs have been identified such as SIRT 1–7 in
mammals (7, 18). SIRT1-3 has been well characterized,
whereas SIRT4 and SIRT6 have been reported to have ADP-
ribosylation activity, which may be due to their deacetylation
activity (7). However, SIRT 1, 2, 3, and 5 catalyze deacetyla-
tion. A tight and well-regulated balance between the activities
of HATs and HDACs will maintain a controlled balance be-
tween acetylation and deacetylation of histones, and the epi-
genome actions under normal physiological states in the cells
and any alterations in this balance would lead to patho-
physiological conditions.
Oxidative Stress in Epigenetic Regulation
of Gene Expression and Disease
Oxidative stress has been established as an important
mechanism of either onset or progression of several disease
states or disorders, including myocardial ischemia, cardio-
vascular diseases (CVDs), cerebrovascular diseases, neuro-
logical diseases and disorders, diabetes, renal diseases,
infection and sepsis, pulmonary diseases and disorders, and
obesity (3, 6, 14, 16, 28, 30, 34, 43, 59). Environmental, toxic,
and dietary factors are known to cause oxidative stress by
different mechanisms (40). Oxidative stress is mediated by the
oxygen-derived reactive oxygen species (ROS), reactive ni-
trogen species (RNS), and other oxidants (40). Oxidative stress
is caused by either external oxidants/pro-oxidants or intra-
cellular oxidants. The intracellular oxidants are generated by
either nonenzymatic mechanisms (often involving transition
metals such as iron) or enzymatic catalysis operated by a
variety of oxidases that activate oxygen and convert them into
the ROS or RNS. Cellular membrane lipids containing the
polyunsaturated fatty acids, proteins, and nucleic acids are
vulnerable to the attack by oxidative stress leading to the
pathophysiological alterations (15). It has long been estab-
lished that 4-hydroxy-2-nonenal (4-HNE) is a major lipid
hydroperoxide-derived aldehydic bifunctional electrophile
that reacts with DNA and proteins (53, 74). The lipid
peroxidation-derived electrophilic carbonyl, 4-HNE, has been
shown to inhibit the class II HDAC (mitochondrial SIRT3)
through a thiol mechanism, and this has implications in lipid
peroxidation-mediated alterations of epigenetic regulation
(25). Overall, convincing experimental evidence has shown
that lipid peroxidation is also an important player in the ox-
idative stress-mediated epigenetic regulation of gene expres-
sion. Oxidative stress also brings alterations in the redox
status of the cell, wherein the thiol-redox (glutathione [GSH]
and protein thiols) system crucial for the cellular thiol-anti-
oxidant defense system and cellular metabolic machinery is
jeopardized (61), leading to the oxidative deterioration of the
cell. Cellular systems have evolved several enzymatic and
nonenzymatic antioxidant systems to cope with the surge of
constant oxidative stress. However, the overwhelming pro-
duction of ROS and RNS with their empowering oxidative
stress and the endogenous antioxidant defenses are compro-
mised and lead to the cellular demise. This is one of the often-
recognized mechanisms of either disease onset or progression.
The role of epigenome and epigenetic regulation of gene
expression in several human diseases, including cancer and
CVDs, are becoming compellingly evident (21). At present,
evidence is mounting in favor of oxidative stress modulating
the epigenome, leading toward the regulation of gene ex-
pression (81). Also, recent studies have highlighted the im-
portance of epigenetic alterations in cardiovascular,
neurological, immunological, and other more complex ge-
netic disorders and diseases (21). Taken together, it is
emerging that oxidative stress-modulated regulation of the
epigenetic mechanism of gene expression plays an important
role in certain diseases. Understanding the mechanisms of
epigenetic regulation will lead to the development of novel
therapies for treatment of diseases and the development of
regenerative medicine, and identification of strategies for
preventive intervention. In this regard, antioxidants are seri-
ously sought after to strengthen the cellular antioxidant de-
fense system to combat and counteract the overwhelming
oxidant generation and oxidative stress, thus attenuating or
normalizing the adverse oxidant-mediated epigenetic regu-
lation of gene expression that is responsible for either the
onset or progression of the disease.
Phytochemical Antioxidants: Oxidative Stress,
Disease, and Epigenome
Cellular antioxidant defense machinery has been un-
equivocally established as an oxidative stress-counteracting
entity. Cellular antioxidants comprise both the (i) nonenzy-
matic molecules and (ii) enzymes. The nonenzymatic antiox-
idants consist of the thiol antioxidants such as GSH and other
thiols and small-molecule antioxidants (vitamins C, A, D, and
E). Apart from GSH, most of the antioxidants make their entry
328 MALIREDDY ET AL.
into the cells through nutrition and diet. Also, the function of
these nonenzymatic antioxidants is regulated by the redox
state of the cell and vice versa. Antioxidant supplementation/
treatment has been adopted for either prevention of or pro-
tection against several disorders and pathophysiological
states wherein oxidative stress has been established as a
causative mechanism (5). The immunomodulatory and anti-
inflammatory effects of polyphenols have been documented
(26, 39). The beneficial effects of moderate consumption of red
wine on lessening the coronary heart disease are accredited to
the wine polyphenols such as anthocyanosides, catechins,
proanthocyanidins, stilbenes, and phenolic compounds (19).
Naturally occurring phytochemical antioxidants have occu-
pied a prominent position as effective antioxidants for the
prevention and/or treatment of several disorders and dis-
eases among humans (32, 70, 71). The premise for this has
been the antioxidant actions of the phytochemicals as free-
radical scavengers, oxidative stress relievers, and lipoperox-
idation inhibitors (68). Phytochemical antioxidants include
simple molecule antioxidants such as vitamins C, E, and K;
plant pigments such as carotenoids (b-carotene), xantho-
phylls, lycopene, anthocyanins, and phaeophytins; and sec-
ondary plant metabolites, including simple phenolics to more
complex polyphenols (13). Some of these phytochemical
polyphenols, in addition to acting as antioxidants, will also
function as pro-oxidants that cause oxidative stress (42, 62).
The pro-oxidant action of tea polyphenols has been linked to
their anticancer actions (23, 42). Polyphenols are known for
their complexing abilities (chelation) with trace metals. Poly-
phenols have been shown to attenuate the iron-induced DNA
damage by complexation with iron and keeping the Fe in the
+3 state after oxidation of Fe in the +2 state in presence of
molecular oxygen (63). Two major pathways of biosynthesis
of the phytochemical polyphenols in plants have been iden-
tified: (i) the shikimate pathway and (ii) the polyketide or
acetate pathway (57). Structurally, the plant polyphenol has a
phenolic or a benzene ring with a hydroxyl group attached,
and also certain substituents such as ester and glycosides
present as functional groups (73). The majority of the plant
polyphenols have two or three hydroxyl groups, and hence
FIG. 1. Classification of plant phenols. Here, phenols of plant origin are broadly divided into three major groups such as (i)
phenolic acids, (ii) flavonoids, and (iii) nonflavonoid polyphenols. Flavonoids are further divided into several classes.
Flavonoids such as kaempferol, quercetin, and myricetin fall under the class of flavonols. Genistein and daidzein are
classified under the class of isoflavones and thereby are called the soy isoflavones. (-)-epigallocatechin-3-gallate (EGCG) falls
under the class of flavanols. These phytochemical phenols as secondary metabolites in plants have definitive roles in plants as
the ultraviolet (UV) protectants, wound-healing action, and disease and pest resistance. Primarily, these compounds have
established protective actions against oxidative stress as potent, naturally occurring antioxidants.
EPIGENETIC REGULATION BY PLANT SECONDARY METABOLITES 329
they are called dihydric or trihydric polyphenols, respec-
tively. The classification of plant polyphenols is based on (i)
the number of phenolic or benzene rings present and (ii) the
number and type of substituents present on the phenolic
rings. Phytochemical polyphenols are broadly classified into
(i) simple phenols (ferulic and gallic acids), (ii) stilbenes (di-
hydrophenols such as resveratrol), (iii) chalcones, and (iv)
flavonoids (Fig. 1) (57). Flavonoids, a family of the most bio-
active complex phytochemical polyphenols, are further di-
vided into seven classes such as (i) flavonols, (ii) flavanols, (iii)
flavones, (iv) flavanones, (v) flavanonols, (vi) isoflavones, and
(vii) anthocyanins (73). Simple phenolic and polyphenolic
secondary plant metabolites are known to play crucial roles in
plants as protectants against oxidative stress and ultraviolet
(UV) radiation, wound healing, defense against microbes,
fungi, herbivores, plant competitors, and disease resistance in
plants (2, 20). However, the mechanism of such protection
and their physiological roles in plants are not completely
understood. Nevertheless, flavonoids have been shown to
exhibit a plethora of biological effects, including antibacterial,
antiviral, analgesic, antiallergic, hepatoprotective, cytostatic,
apoptotic, estrogenic, and antiestrogenic functions (31).
Animals and humans obtain these phytochemical poly-
phenols from diet or nutritional supplementation. The ma-
jority of the phytochemical polyphenols are present in their
native state in plants as polymers or as glycosylated molecules
(conjugated to sugars), wherein the sugar moiety is termed as
the ‘‘glycone’’ and the polyphenol is called the ‘‘aglycone’’
(76). Most of the polyphenols in the dietary plant sources
occur as complex molecules linked to the sugar residues
(O-glycosides), but some occur as C-glycosides. Polyphenol
O-glycosides undergo hydrolysis in the lumen of the intes-
tine, and the sugar residue is released upon the action of b-
glucosidase, setting the aglycone free. On the other hand, the
C-glycosides are resistant to the intestinal enzymatic hydro-
lysis (9). It is interesting to note that the polyphenols, after the
uptake by the intestinal cells, undergo metabolic biotrans-
formation similar to the xenobiotics by the involvement of
phase-I and phase-II enzymes (9). Bacteria in the large intes-
tine catalyze the conversion of aglycones of polyphenols
causing the heterocyclic B-ring opening and cleavage after
which the metabolites are absorbed and reach circulation (9).
Similar to the intestine, the liver also metabolizes poly-
phenols, and circulating polyphenols are in the form of
b-glucuronides and esters of sulfate with trace levels of
aglycones. Polyphenols that are hydrophobic can easily be
transported into the intestinal cells through the plasma
membrane. Nevertheless, the phytochemical polyphenol
metabolism is complex, and it is challenging to identify
whether the parent molecule or its metabolite is biologically
active. In recent times, plant polyphenols have been the at-
traction as effective antioxidants (from diet or supplementa-
tion) in prevention and treatment of several diseases,
including CVDs, cerebrovascular diseases, Alzheimer’s dis-
ease, airway disease, and cancer, with a focus to alleviate the
oxidative stress as the causative mechanism in those diseases
(17, 24, 38, 51, 70, 71, 80). In spite of the beneficial effects of the
phytochemical polyphenolic antioxidants in humans, their
mechanisms of action (physiology and pharmacology) in the
mammalian systems (including humans) are just emerging.
The regulation of gene expression by dietary polyphenols in
cellular models such as the vascular endothelial cells is evi-
dent (56, 57). One of the noteworthy current discoveries that
have emerged from the phytochemical–antioxidant inter-
actions in mammalian model systems is their nature of
modulating the mammalian epigenome (21). Totally, novel
disciplines such as nutrigenetics and nutrigenomics have
emerged with a focus on the phytochemical nutrient–gene in-
teractions toward cancer prevention in which signaling path-
ways, networks, and epigenetic phenomena are investigated
(22). Hence, this review focuses on the relevant studies on cer-
tain selected phytochemical phenolic antioxidants that have
been shown to mediate the modulation of the mammalian
epigenome and its relevance in the prevention of and protec-
tion against diseases.
Mechanisms of Epigenetic Regulation of Diseases:
Role of Phytochemical Antioxidants
As overviewed earlier, epigenetic alterations in DNA are
inheritable, which lead to the modulation of gene expression
without involving any changes in the primary sequences of
DNA. However, chemical alterations in the histone proteins
and/or DNA by covalent modifications brought by certain
enzymes are the causative mechanisms for the epigenetic al-
terations and subsequent modulation of gene expression. It is
progressively more evident that DNA methylation, an epi-
genetic phenomenon catalyzed by DNMTs using the methyl
donor, S-adenosylmethionine (SAM), leads to anomalous
DNA methylation (hypermethylation), and this is associated
with certain diseases, including cancer and CVDs (21). Me-
thylation of CpG islands is a common occurrence in the
pathological tissues such as cancer (29). Transcription of
methylated genes is either arrested or suppressed. Global
hypomethylation of DNA and hypermethylation at specific
sites of DNA are generally encountered in the tumors (21).
DNA hypomethylation is known to enhance the expression of
proto-oncogenes leading to an elevated cancer risk. DNA
hypermethylation is also associated with certain cancers. Diet
has been known to affect the DNA methylation status, espe-
cially folate, which is the precursor for SAM, the substrate for
DNMT that catalyzes DNA methylation. Dietary phyto-
chemical polyphenols have been identified to modulate DNA
methylation and subsequent epigenetic regulation of gene
expression with a change in the outcome of cancer and CVDs.
Wherever DNA hypermethylation catalyzed by DNMTs is
encountered as a key mechanism in a disease such as cancer,
DNMT inhibitors can be promising drugs in the chemother-
apy of cancer (29). However, certain phytochemicals, espe-
cially the polyphenols, are emerging as modulators of DNA
methylation and appear as promising drugs in the treatment
of cancer and myocardial pathologies (9, 36).
Post-translation modifications of nuclear proteins, the his-
tones, play a crucial role in the epigenetic regulation of gene
expression. Two important modifications of histones are (i)
acetylation and (ii) deacetylation. Histone acetylation is cat-
alyzed by the histone acetyltransferases (HATs). Histone
deacetylation is catalyzed by 11 different HDACs, which are
divided into 4 classes based on their homologies (37). These
HDACs are distributed in the cytoplasm, mitochondria, and
nucleus. There are seven members of HDACs called SIRTs
(SIRT1–SIRT7) present in the cytoplasm, mitochondria, and
nucleus, which catalyze the deacetylation of histones (37). A
tight balance between the acetylation and deacetylation of
330 MALIREDDY ET AL.
histones is maintained under normal states, but if that balance
is altered due to the abnormal activities of either HATs or
HDACs, then that will result in pathological situations as seen
in cancer (37, 41). HDAC inhibitors have been focused as
therapeutic molecules in cancer chemotherapy. Once again,
phytochemical polyphenols have been shown to act as HDAC
inhibitors with potential in prevention and therapy of certain
diseases, including cancer and CVDs (10, 36).
Phytochemical Polyphenols As Modulators
of Epigenome: Disease Prevention and Therapy
Polyphenols are a major group of phytochemicals with an-
tioxidant actions, disease prevention properties, and thera-
peutic actions. However, polyphenols have recently captured
attention as the modulators of epigenome. Although humans
consume most of the polyphenols through diet, they also can
be ingested or administered as isolated compounds from
plant sources for prevention or treatment of certain diseases
(50). Green tea contains several polyphenols, including (-)-
epicatechin, ( -)-epicatechin-3-gallate (ECG), ( -)-epigallocatechin,
and ( -)-epigallocatechin-3-gallate (EGCG) (48). Green tea as a
beverage is also seriously consumed worldwide as a health-
promoting drink due to the presence of phytochemicals, which
are considered to act as anticancer agents, retain healthy heart,
and prevent cataract. EGCG is a predominant polyphenol
present in green tea that has been shown to possess anticancer,
antitumor, and anti-inflammatory actions (Fig. 2) (52). In a
study on the human breast cancer cells (MCF-7 and MDA-MB-
231 cells), EGCG and the novel prodrug of EGCG (pro-EGCG)
have been shown to inhibit cell proliferation and transcription
of the human telomerase reverse transcriptase (hTERT), the
catalytic subunit of telomerase that is crucial in sustaining the
telomere chain length and tumor formation, the latter being
through the epigenetic regulation of the estrogen receptor (11,
52). In this study, hypomethylation of the hTERT promoter re-
gion and histone deacetylation through the inhibition of DNMT
and HAT, respectively, have contributed to the inhibition
FIG. 2. Chemical structures of different phytochemical polyphenol antioxidants (A–G). Phytochemical polyphenols have
their structural origin from the simple phenolic (benzene) ring and having two or more hydroxyl (OH) groups offer their
polyphenolic nature and name of their class of compounds. These are compounds that are bioactive natural products and act
as free-radical quenchers, potent antioxidants, trace metal-complexing molecules, pro-oxidants, and regulators of cell pro-
liferation. More strikingly, they are emerging as the modulators of epigenetic regulation of gene expression.
EPIGENETIC REGULATION BY PLANT SECONDARY METABOLITES 331
of hTERT transcription in the breast cancer cells under the
treatment of EGCG and pro-EGCG. Moreover, EGCG and pro-
EGCG also have caused the chromatin remodeling (alterations)
leading to hTERT-repressor binding in the regulatory sites. This
study reveals that the green tea polyphenol EGCG and its novel
prodrug cause inhibition of proliferation of breast cancer cells
through epigenetic mechanisms involving inhibition of DNMT
and HAT and resulting in DNA hypomethylation and histone
deacetylation (Fig. 3). The importance of estrogen receptor-a
(Era) in clinical prognosis and in the therapy of breast cancer has
been emphasized, because ERa-deficient breast cancers do not
respond to the therapies aimed at the hormone targets (49).
Having this as the premise, it has been revealed that in the
breast cancer cells (MDA-MB-231 cells), the green tea poly-
phenol (EGCG) alone or in combination with the HDAC in-
hibitor (trichostatin A) offered reactivation of the ERa
expression in the ERa-deficient breast cancer cells (49). This has
also led to the estradiol action in the ERa-deficient breast cancer
cells through the action of the ERareceptors in response to
estradiol treatment. In this context, EGCG has been found to
cause chromatin remodeling through modulation of histone
acetylation and DNA methylation, leading to the reactivation of
ERa(49). This study indicates that the green tea polyphenol,
EGCG, can reactivate ERatoward effective treatment of hor-
mone-resistant breast cancer. To establish the anticancer actions
of EGCG against skin cancer through epigenetic regulation, a
study has been conducted on the reactivation of the tumor
suppressor genes (Cip1/p21 and p16
INK4a
)inhumanskincancer
cells (55). This study reveals that EGCG suppresses global DNA
methylation, DNMT activity, and HDAC activity; lowers
DNMT protein and mRNA; and increases histone acetylation in
histones H-3 and H-4 in the skin cancer cells. Along these lines,
ECGC has been observed to cause activation of expression of
the tumor suppressor genes. This study presents convincing
results that the green tea polyphenol, EGCG, is an epigenetic
modulator that may be useful as an epigenetic drug in skin
cancer therapy.
With intent to show the anticancer actions of EGCG, a study
has been conducted on the epigenetic anticancer effects of
EGCG on the UV-B radiation-induced skin cancer in vivo in a
hairless mouse model (54). In this study, the green tea poly-
phenol, EGCG, has been applied on the affected skin as a
topical cream. The results reveal that the EGCG as topical
cream inhibits the UV-B-induced skin papillomas and carci-
nomas and also inhibits global DNA methylation. Further-
more, this study demonstrates that the EGCG topical
application as a cream on the skin appears as a promising
epigenetic therapeutic strategy for the treatment of skin pho-
tocarcinogenesis. The antimelanoma action of EGCG has been
investigated in the human melanoma cell line (A-375 cells)
with a focus on the epigenetic action of EGCG (58). In this
study, the HDAC inhibitor drug, Vorinostat, has also been
used in conjunction with EGCG. The results reveal that the
antimelanoma effects of Vorinostat are more pronounced than
those of EGCG, but the combined treatment of EGCG and
Vorinostat has been more dramatic in causing the anti-
melanoma effects. Thus, it is clear from this study that EGCG
can be used as a combination drug along with a known HDAC
inhibitor for use in the epigenetic therapy of melanoma.
Dietary phytochemical antioxidants are also known to ex-
ert immunomodulatory effects, including upkeep of im-
munotolerance and autoimmunity suppression. Along those
lines, a study has been launched to investigate modulation of
the regulatory T cells by EGCG through epigenetic regulation
(78). Regulatory T cells are crucial for the immunotolerance
and autoimmunity suppression. The results of this study re-
veal that EGCG decreases DNMT expression and global DNA
methylation through induction of forkhead box p3 (Foxp3)
gene expression substantiating the epigenetic actions EGCG
and modulation of immunity by EGCG. Thus, it appears that
the green tea polyphenol, EGCG, also acts as an epigenetic
immunomodulator. Overall, consumption of green tea has
been attributed to the lower incidences of various cancers
such as gastric, esophageal, ovarian, pancreatic, skin, and
colorectal cancers (48). The cancer-preventive actions of green
tea are linked to the presence of the bioactive natural product
in the tea such as EGCG. Many studies have shown that
EGCG directly inhibits the DNMT activity by directly inter-
acting with the enzyme, causes demethylation of DNA, and
reactivates methylation-silenced genes (48). This mechanism
of action of EGCG in causing modulation of DNA methyla-
tion through the regulation of DNMTs and leading to epige-
netic regulation of gene expression has been demonstrated in
several cancer models, substantiating the epigenetic antican-
cer action of EGCG (48, 49).
Curcumin As a Modulator of Epigenome:
Disease Prevention and Therapy
Curcumin (diferuloylmethane) is a polyphenolic ingredient
of turmeric (the most popular and common Asian Indian
FIG. 3. Mechanism of EGCG-induced apoptosis in cancer
cells through epigenetic regulation of telomerase. Accord-
ing to Berletch et al. (11) and Meeran et al. (52), EGCG inhibits
both deoxyribonucleic acid (DNA) methyltransferase
(DNMT) and histone acetyltransferase (HAT), leading to the
DNA demethylation and histones H3 and H4 deacetylation
of the human telomerase– reverse transcriptase (hTERT)
promoter, respectively. These events result in the epigenome
regulation and chromatin restructuring involving hTERT
messenger ribonucleic acid (mRNA) downregulation and
inhibition of telomerase and ultimately cancer cell death
(apoptosis). However, these studies have not provided any
links between the antioxidant actions of EGCG and its epi-
genetic regulation of apoptosis of the cancer cells.
332 MALIREDDY ET AL.
curry spice; golden spice) obtained from the rhizomes of the
plant, Curucuma longa (Fig. 2). Recently, curcumin has gained
tremendous attention of the nutritionists, biomedical scien-
tists, pharmacologists, drug discovery scientists, clinicians,
and, above all, the common man worldwide as a preventive
molecule or therapeutic agent for several disorders and dis-
eases, which is substantiated by anecdotal accounts and sci-
entific investigations. However, curcumin has long been
known for its anticancer actions causing necrosis and apo-
ptosis and arrest of division in cancer cells (33, 35). Curcumin
has been identified as a pro-oxidant in generating ROS
(causing oxidative stress) and as an antioxidant (protecting
against oxidative stress) in cellular systems. The oxidative
stress induced by curcumin has been considered as the
probable mechanism of action of the compound to act as an
anticancer agent. The biphasic action of curcumin depends
upon its concentration that is used in experiments, for ex-
ample, at higher concentrations (*50 lM) curcumin acts as a
pro-oxidant and at lower doses (*10 lM), the same acts as an
antioxidant (35). Although several studies have revealed
multiple mechanisms/targets for the anticancer action of
curcumin, the epigenetic regulation by curcumin in different
disease states (models), including cancer, is sprouting (33). A
study on the human hepatoma cells reveals that curcumin
treatment lowers histone acetylation (hypoacetylation) by
inhibiting the HAT activity and without an effect on the
HDAC activity, which is linked with the enhancement of ROS
production in cells (35). This study suggests that HAT is the
target for curcumin, and its anticancer action could be at-
tributed to its epigenome regulatory actions wherein ROS are
apparently involved. On the other hand, curcumin has been
shown to inhibit the HDAC activity in medulloblastoma (brain
tumor) cells and to decrease medulloblastoma growth (tumor
xenografts) in vitro and in vivo (44). In this study, curcumin has
been observed to cause apoptosis and cell cycle arrest (G2/M
phase) followed by the inhibition of HDAC activity in me-
dulloblastoma cells. Also, the study reveals that curcumin
enhances the survival of the mice that received the medullo-
blastoma tumor xenograft (44). Overall, this study features the
importance of curcumin as an antimedulloblastoma agent
with an epigenetic target in its path of action. Upon screening
33 carboxylate derivatives to identify potent HDAC inhibitors
in HeLa cell nuclear extract an in vitro assay system, it has been
identified that curcumin has the highest potency along with
chlorogenic acid as compared to the established HDAC in-
hibitor, sodium butyrate (12). This study reveals that curcumin
is a potent natural phytochemical polyphenol HDAC inhibitor
with an ability to modulate the epigenome through regulation
of histone acetylation.
Phosphodiesterases (PDEs) catalyze the hydrolysis of cyclic
nucleotides such as cyclic adenosine-3¢,5¢-monophosphate
and cyclic guanosine-3¢,5¢-monophosphate in cells and thus
take crucial part in cell-signaling events responsible for cell
division (1). Using the B16F10 melanoma cells, it has been
shown that curcumin inhibits cell proliferation through PDE1-
5 involvement. In this study, curcumin has also exerted epi-
genetic modulatory effectors such as inhibiting the expression
of the epigenetic integrator ubiquitin-like containing PHD
and ring finger domains 1 (UHRF1), and DNMT1 with up-
stream targeting of PDE1 and resulting in the antiproliferative
effects in the melanoma cells (1). Thus, this study also dem-
onstrates that curcumin exerts its epigenome-modulating ef-
fects in its action as an anticancer agent. The epigenetic
regulation of HATs, HDACs, DNMTs, and miRNAs and as-
sociated modulation of gene expression by curcumin in con-
junction with its anticancer actions and clinical utilization
have been highlighted (66).
In addition to its anticancer actions, curcumin has been also
shown to offer protection against inflammation, neurode-
generative diseases, autoimmune pathologies, and cardio-
vascular and lung disorders, while the epigenetic mechanisms
of cardioprotective and lung-protective actions of curcumin
are just budding (4, 8, 65, 79). Curcumin, as an antioxidant,
has been reported to offer protection against several patho-
physiological states (79). Especially, it has been demonstrated
in studies with animal models that curcumin protects against
cardiac hypertrophy and heart failure involving epigenetic
regulation by HAT (79). One of the established mechanisms of
epigenetic regulations of gene expression is maintaining a
tight balance between the acetylation and deacetylation by a
controlled regulation of the activities of HATs and HDACs.
A specific transcription factor such as the hypertrophy-
responsive transcription factor requires p300 (adenovirus
E1A-associated protein), which also acts as a HAT bringing
out the chromatin remodeling (79). p300-HAT has also been
shown to be responsible for the cardiomyocyte growth and
differentiation in the course of development (79). However,
the activity of p300-HAT has been elevated during cardiac
hypertrophy, and by inhibiting the p300-HAT activity, it has
been possible to protect against the cardiac hypertrophy.
Curcumin has been established as an inhibitor of p300-HAT
(79). Thus, it is conclusive that curcumin protects against
cardiac hypertrophy through modulation of epigenetic regu-
lation that is mediated by p300-HAT. As histone acetylation
mediated by HAT has been established as a critical player in
the development of the heart, its inhibition or attenuation by
curcumin has been studied in the cardiomyocytes (72). Cur-
cumin has been revealed to inhibit p300-HAT in cardiomyo-
cytes causing decreased acetylation of histone H3 in the
promoter regions of certain cardiac-specific genes responsible
for the cardiogenesis (72). This observation has been associ-
ated with curcumin-induced cell morphological alterations,
inhibition of the HAT (p300-HAT) activity, decreased acety-
lation of histone H3, and suppression of cardiac-specific gene
expression confirming curcumin-mediated modulation of
epigenetic regulation of cardiomyocyte gene expression dur-
ing cardiogenesis. This study also underscores the importance
of curcumin as a therapeutic compound in alleviating con-
genital myocardial diseases and cardiac hypertrophy through
epigenetic regulation.
Mechanisms behind several debilitating lung diseases in
humans are complex, and specific targets in the onset and
progression of those lung diseases such as chronic obstructive
pulmonary diseases (COPDs) for pharmacological (drug) in-
tervention are being constantly hunted. In this regard, specific
and effective drugs are also highly warranted. Multiple
mechanisms operating behind COPD have been documented,
including the role of ROS, oxidative stress, membrane lipid
deterioration by lipid peroxidation, loss of cellular thiol (GSH)
redox, weakened antioxidant defense system, and other
complex signaling mechanisms (65). Several therapeutic in-
terventions, such as antioxidant therapy, thiol-redox and GSH
boosting, enhancement of antioxidant defenses, enzyme ac-
tivators, spin traps for reactive radicals have been sought after
EPIGENETIC REGULATION BY PLANT SECONDARY METABOLITES 333
for the COPD therapy (65). Among those, polyphenols and
curcumin have been described as therapeutic agents for
COPD. More strikingly, the role of epigenome in the curcumin
therapy of COPD has been brought to the lime light (8).
HDAC, especially HDAC2, has been recognized to play an
important role in the inflammatory gene expression and in-
flammatory lung pathologies, including COPD, asthma, and
airway diseases, since histone acetylation upregulates the
lung inflammatory genes and causes lung inflammation (8).
Therefore, any pharmacological activation of HDAC appears
to offer therapeutic intervention for lung inflammatory dis-
eases. Curcumin has been suggested as a possible HDAC2
activator in protecting against the inflammatory lung dis-
eases, but the challenge lies in its inhibitory action on HAT (8).
However, the epigenetic mechanisms of protective action of
curcumin on inflammatory lung diseases have to be thor-
oughly investigated prior to its clinical use.
Flavonoids As Modulators of Epigenome:
Disease Prevention and Therapy
Flavonoids comprise a major group of phytochemicals, and
they fall under polyphenol category with diverse chemical
structures. Although their source of entry into humans is diet,
there is a growing interest in flavonoids for their disease-
preventive and therapeutic actions. Flavonoids have been es-
tablished as potent and naturally available antioxidants with
properties to relieve oxidative stress, disease prevention, and
protection (60). However, the epigenome-regulating actions of
flavonoids are just surfacing (27). Flavonoids—in particular,
isoflavones, flavonols, and catechins—have been emphasized
as the phytochemical polyphenol regulators of the epigenome
with a focus on DNA methylation, histone acetylation, and
chromatin alterations (27). Here, the findings of some selected
studies dealing with the flavonoid-modulated epigenetic reg-
ulation with a relevance to diseases are discussed.
In the human leukemia-60 cells (HL-60 cells), quercetin
(Fig. 2) has been shown to exert epigenetic modulations in-
volving activation of HAT and inhibition of HDAC, leading to
histone acetylation (45). This study revealed that quercetin
induces Fas ligand-mediated apoptosis in HL-60 cells that is
associated with the epigenetic regulation through HAT and
HDAC (Fig. 4). Soybean isoflavones have been identified as
phytochemical therapeutic flavonoids for the treatment of
colorectal cancer wherein the isoflavones suppress metastasis
of the tissue through epigenetic modulation of DNA meth-
ylation and histone modifications (47). In particular, this
study highlights genistein, one of the soybean isoflavones, as
an effective epigenetic modulator of the colorectal cancer
metastasis, and dietary genistein may be beneficial for colo-
rectal cancer (Fig. 2) (47). Genistein, through epigenetic
modulations, including chromatin remodeling and DNA
methylation, leads to the activation of tumor suppressor
genes and suppression of the survival of cancer cells (82).
Genistein has also been shown to inhibit the DNMT activity,
which causes inhibition of DNA methylation and thus may be
acting as an anticancer agent (48). Genistein has been ob-
served to enhance the acetylation of histones H3 and H4 in the
transcription sites of p21 and p16 with which the upregulation
of the tumor suppressor genes in prostate cancer cells (82).
The cell-cycle arrest results from the genistein-induced
downregulation of cyclins from the upregulation of p21 and
p16 in prostate cancer cells. From this study, genistein appears
as a promising anticancer flavonoid that operates through
epigenetic regulation of gene expression. An association be-
tween genistein consumption and the low mortality rate
among Asian women with breast cancer has been docu-
mented (48). In various experimental cellular models of cancer
such as the prostate, esophagus, and colon cancer cells, gen-
istein has been shown to act as an anticancer flavonoid (48).
Although multiple mechanisms of the anticancer actions of
genistein, such as inhibition of DNA mutation, suppression of
FIG. 4. Mechanism of quercetin-
induced apoptosis of cancer cells
through epigenetic regulation of
Fas ligand (Fas L) expression. As
investigated by Lee et al. (45),
quercetin inhibits the histone dea-
cetylase (HDAC) activity and acti-
vates HAT through the upstream
activation of the extracellular-
regulated kinase (ERK) and Jun
N-terminus kinase ( JNK). Here, the
transactivation of c-jun/AP-1 is in-
volved. Thus, the epigenome is
regulated by quercetin, leading to
apoptosis of the cancer cells (me-
dulloblastoma) through elevation
of histone H3 acetylation, which
causes downstream upregulation of
Fas L. In this study, no attempt has
been made to establish the connec-
tion between the antioxidant ac-
tions of quercetin and its epigenetic
regulation of apoptosis of the me-
dulloblastoma.
334 MALIREDDY ET AL.
cancer cell division, antiangiogenic effect, and stimulation of
cell differentiation have been reported, the mechanism of
epigenetic regulation of gene expression by genistein while
exerting its anticancer actions is becoming more evident. An
important discovery that has led to the understanding of the
estrogenic activity of genistein in which prenatal exposure to
genistein permanently affects the erythropoiesis in fetus and
alters the gene expression and DNA methylation in hemato-
poietic cells (75). Also, ligands for isoflavones in the ERa-
mediated HAT activity have been identified, and genistein
has been observed to cause modulation of the HAT activity
and extent of histone acetylation (64). These studies under-
score the estrogenic nature of the phytoestrogen and genistein
and their effects on ERa, which may be seriously considered
for use as an anticancer agent.
Isoflavones of dietary origin have been documented to
offer vascular protection in different experimental models
and humans through protection against oxidative stress
and upregulation of the antioxidant-signaling mechanisms
(69). Dietary isoflavones have been shown to elevate the
production of nitric oxide and ROS in the vessel wall and
enhance the activities of antioxidant enzymes in the vas-
cular endothelial and smooth muscle cells, which are at-
tributed to the estrogenic activities of isoflavones that
upregulate the genes for antioxidant enzymes in those
vascular cells. Although the isoflavones offer vasculopro-
tection and, in particular, are capable of inhibiting HAT
andDNMT(69),theexactepigenetic mechanism of pro-
tection of vascular endothelial and smooth muscle cells
needs to be established.
FIG. 5. Proposed mechanisms
of epigenetic regulation by
phytochemical polyphenol
antioxidants and the link be-
tween reactive oxygen species
(ROS) and oxidative stress
and antioxidative and non-
antioxidative pathways in
physiological and pathophys-
iological states. Stress, diet,
chemicals, drugs, and envi-
ronmental factors cause oxi-
dative stress through ROS
and thiol-redox dysregula-
tion, which result in epigen-
ome alterations resulting in
chromatin restructuring through
modulations in DNMT,
HDACs, and HAT and sub-
sequent changes in DNA
methylation and histone acet-
ylation. Thus, the regulation
of gene expression is brought
by the alterations in the epi-
genome. Phytochemical poly-
phenol antioxidants may act
either as (i) antioxidants re-
lieving the oxidative stress
and/or (ii) direct modulators
of DNMT, HDACs, and
HATs.
EPIGENETIC REGULATION BY PLANT SECONDARY METABOLITES 335
Conclusions: Critical Issues and Future Directions
Studies conducted so far have provided convincing evi-
dence that phytochemical antioxidants (polyphenols and
flavonoids such as quercetin and curcumin) do modulate
epigenetic regulation of gene expression, which could stand
out as a plausible target for the intervention of certain dis-
eases by the phytochemicals of choice (Fig. 5). In cancer bi-
ology, the phytochemical-modulated epigenome actions
have picked up the pace, and the clinical use of phyto-
chemical polyphenols as epigenetic therapeutics is promis-
ing. However, with respect to other diseases and disorders,
studies on the epigenome actions of phytochemical antioxi-
dants are nascent. The most important aspects of phyto-
chemical antioxidants that should be understood thoroughly
are (i) the metabolism of the phytochemicals in mammalian
and human cells in vitro and in vivo to identify the active
metabolite of the phytochemical that is responsible for its
pharmacological actions and (ii) precise cellular targets (re-
ceptors or proteins) for either the parent phytochemical
molecule or its cellular metabolites under normal physio-
logical and pathological states. In this regard, specific bio-
active metabolites of a particular phytochemical antioxidant
of choice, in target cells and their normal counterparts, have
to be identified and characterized (Fig. 5). In addition, the
redox biology of these phytochemical antioxidants in the
cellular milieu has to be established as most of these natural
compounds have a dual behavior of acting either as a pro-
oxidant or as an antioxidant. The question that still remains
to be answered is whether the redox-active phytochemical
antioxidant that causes epigenetic regulation is either de-
pendent upon the oxidants generated through the pro-
oxidant actions or the antioxidant nature of the phyto-
chemical polyphenol antioxidant (Fig. 6). In spite of the
well-established fact that the phytochemical polyphenolics
are among the most effective naturally occurring antioxi-
dants, there is a void bridging their antioxidant actions and
redox-signaling mediation to their epigenetic regulatory
actions. It is high time to establish whether the epigenome
regulatory actions of the phytochemical polyphenol antiox-
idants are related or unrelated to their antioxidative actions
(Fig. 6). So far, laboratory studies conducted offer convinc-
ing evidence in favor of a connection between the chromatin
remodeling and epigenetic regulation of gene expression,
and this should be established or verified in the preclinical
and clinical studies.
Acknowledgments
Funding support from the International Academy of Oral
Medicine and Toxicology (IAOMT); Dorothy M. Davis Heart
& Lung Research Institute; the Division of Pulmonary, Al-
lergy, Critical Care, and Sleep Medicine of the Ohio State
University College of Medicine; and the National Institutes of
Health (HL 093463) is acknowledged.
References
1. Abusnina A, Keravis T, Yougbare I, Bronner C, and Lugnier
C. Anti-proliferative effect of curcumin on melanoma cells is
mediated by PDE1A inhibition that regulates the epigenetic
integrator UHRF1. Mol Nutr Food Res 55: 1677–1689, 2011.
2. Acamovic T and Brooker JD. Biochemistry of plant second-
ary metabolites and their effects in animals. Proc Nutr Soc 64:
403–412, 2005.
3. Adibhatla RM and Hatcher JF. Lipid oxidation and perox-
idation in CNS health and disease: from molecular mecha-
nisms to therapeutic opportunities. Antioxid Redox Signal 12:
125–169, 2010.
4. Aggarwal BB and Harikumar KB. Potential therapeutic effects
of curcumin, the anti-inflammatory agent, against neurode-
generative, cardiovascular, pulmonary, metabolic, autoimmune
and neoplastic diseases. Int J Biochem Cell Biol 41: 40–59, 2009.
5. Arts IC and Hollman PC. Polyphenols and disease risk in
epidemiologic studies. Am J Clin Nutr 81: 317S–325S, 2005.
FIG. 6. Proposed mechanisms of
epigenome regulatory activities of
phytochemical polyphenols through
their antioxidant actions, pro-
oxidant nature, and bioactive me-
tabolite functions. As the phyto-
chemical polyphenols are known
to act as effective antioxidants,
they may regulate the functions of
cellular epigenome by acting as
antioxidants. Phytochemical poly-
phenols also act as pro-oxidants in
presence of iron (Fe
+2
) and oxygen
or in concert with oxidases and in-
duce oxidative stress, which may
cause the modulation of the cellular
epigenome through oxidant and
thiol-redox signaling. Phytochem-
ical polyphenols are also known to
undergo biotransformation into
metabolites that is catalyzed by
the cellular phase-I and phase-II
xenobiotic-metabolizing enzymes.
It is possible that these metabo-
lites regulate the cellular epigen-
ome through signaling cascades.
336 MALIREDDY ET AL.
6. Baker JE. Oxidative stress and adaptation of the infant heart to
hypoxia and ischemia. Antioxid Redox Signal 6: 423–429, 2004.
7. Bao J and Sack MN. Protein deacetylation by sirtuins: de-
lineating a post-translational regulatory program responsive
to nutrient and redox stressors. Cell Mol Life Sci 67: 3073–
3087, 2010.
8. Barnes PJ. Histone deacetylase-2 and airway disease. Ther
Adv Respir Dis 3: 235–243, 2009.
9. Barnes S, Prasain J, D’Alessandro T, Arabshahi A, Botting N,
Lila MA, Jackson G, Janle EM, and Weaver CM. The me-
tabolism and analysis of isoflavones and other dietary
polyphenols in foods and biological systems. Food Funct 2:
235–244, 2011.
10. Barry SP and Townsend PA. What causes a broken heart—
molecular insights into heart failure. Int Rev Cell Mol Biol
284: 113–179, 2010.
11. Berletch JB, Liu C, Love WK, Andrews LG, Katiyar SK, and
Tollefsbol TO. Epigenetic and genetic mechanisms contrib-
ute to telomerase inhibition by EGCG. J Cell Biochem 103:
509–519, 2008.
12. Bora-Tatar G, Dayangac-Erden D, Demir AS, Dalkara S,
Yelekci K, and Erdem-Yurter H. Molecular modifications on
carboxylic acid derivatives as potent histone deacetylase
inhibitors: activity and docking studies. Bioorg Med Chem 17:
5219–5228, 2009.
13. Bors W and Michel C. Chemistry of the antioxidant effect of
polyphenols. Ann N Y Acad Sci 957: 57–69, 2002.
14. Cave AC, Brewer AC, Narayanapanicker A, Ray R, Grieve DJ,
Walker S, and Shah AM. NADPH oxidases in cardiovascular
health and disease. Antioxid Redox Signal 8: 691–728, 2006.
15. Cheeseman KH. Mechanisms and effects of lipid peroxida-
tion. Mol Aspects Med 14: 191–197, 1993.
16. Chen H, Yoshioka H, Kim GS, Jung JE, Okami N, Sakata H,
Maier CM, Narasimhan P, Goeders CE, and Chan PH.
Oxidative stress in ischemic brain damage: mechanisms of
cell death and potential molecular targets for neuroprotec-
tion. Antioxid Redox Signal 14: 1505–1517, 2011.
17. Choi DY, Lee YJ, Hong JT, and Lee HJ. Antioxidant prop-
erties of natural polyphenols and their therapeutic potentials
for Alzheimer’s disease. Brain Res Bull 87: 144–153, 2012.
18. Chung S, Yao H, Caito S, Hwang JW, Arunachalam G, and
Rahman I. Regulation of SIRT1 in cellular functions: role of
polyphenols. Arch Biochem Biophys 501: 79–90, 2010.
19. Dell’Agli M, Busciala A, and Bosisio E. Vascular effects of
wine polyphenols. Cardiovasc Res 63: 593–602, 2004.
20. Dinkova-Kostova AT. Phytochemicals as protectors against
ultraviolet radiation: versatility of effects and mechanisms.
Planta Med 74: 1548–1559, 2008.
21. Duthie SJ. Epigenetic modifications and human pathologies:
cancer and CVD. Proc Nutr Soc 70: 47–56, 2011.
22. Ferguson LR and Schlothauer RC. The potential role of nu-
tritional genomics tools in validating high health foods for
cancer control: broccoli as example. Mol Nutr Food Res 56:
126–146, 2012.
23. Forester SC and Lambert JD. The role of antioxidant versus
pro-oxidant effects of green tea polyphenols in cancer pre-
vention. Mol Nutr Food Res 55: 844–854, 2011.
24. Fraga CG. Plant polyphenols: how to translate their in vitro
antioxidant actions to in vivo conditions. IUBMB Life 59: 308–
315, 2007.
25. Fritz KS, Galligan JJ, Smathers RL, Roede JR, Shearn CT,
Reigan P, and Petersen DR. 4-Hydroxynonenal inhibits
SIRT3 via thiol-specific modification. Chem Res Toxicol 24:
651–662, 2011.
26. Ghiringhelli F, Rebe C, Hichami A, and Delmas D. Im-
munomodulation and anti-inflammatory roles of polyphenols
as anticancer agents. Anticancer Agents Med Chem 2012 Jan 31.
[Epub ahead of print] PubMed PMID: 22292769.
27. Gilbert ER and Liu D. Flavonoids influence epigenetic-
modifying enzyme activity: structure—function relation-
ships and the therapeutic potential for cancer. Curr Med
Chem 17: 1756–1768, 2010.
28. Gill PS and Wilcox CS. NADPH oxidases in the kidney.
Antioxid Redox Signal 8: 1597–1607, 2006.
29. Gravina GL, Festuccia C, Marampon F, Popov VM, Pestell
RG, Zani BM, and Tombolini V. Biological rationale for the
use of DNA methyltransferase inhibitors as new strategy for
modulation of tumor response to chemotherapy and radia-
tion. Mol Cancer 9: 305, 2010.
30. Guo RF and Ward PA. Role of oxidants in lung injury
during sepsis. Antioxid Redox Signal 9: 1991–2002, 2007.
31. Hodek P, Trefil P, and Stiborova M. Flavonoids—potent
and versatile biologically active compounds interacting
with cytochromes P450. Chem Biol Interact 139: 1–21,
2002.
32. Hollman PC, Cassidy A, Comte B, Heinonen M, Richelle M,
Richling E, Serafini M, Scalbert A, Sies H, and Vidry S. The
biological relevance of direct antioxidant effects of poly-
phenols for cardiovascular health in humans is not estab-
lished. J Nutr 141: 989S–1009S, 2011.
33. Huang J, Plass C, and Gerhauser C. Cancer chemopreven-
tion by targeting the epigenome. Curr Drug Targets 12: 1925–
1956, 2011.
34. Janssen LJ, Catalli A, and Helli P. The pulmonary biology of
isoprostanes. Antioxid Redox Signal 7: 244–255, 2005.
35. Kang J, Chen J, Shi Y, Jia J, and Zhang Y. Curcumin-induced
histone hypoacetylation: the role of reactive oxygen species.
Biochem Pharmacol 69: 1205–1213, 2005.
36. Khan SI, Aumsuwan P, Khan IA, Walker LA, and Dasma-
hapatra AK. Epigenetic events associated with breast cancer
and their prevention by dietary components targeting the
epigenome. Chem Res Toxicol 25: 61–73, 2012.
37. Kim HJ and Bae SC. Histone deacetylase inhibitors: molec-
ular mechanisms of action and clinical trials as anti-cancer
drugs. Am J Transl Res 3: 166–179, 2011.
38. Kim J, Lee HJ, and Lee KW. Naturally occurring phyto-
chemicals for the prevention of Alzheimer’s disease. J Neu-
rochem 112: 1415–1430, 2010.
39. Korkina L, Kostyuk V, De Luca C, and Pastore S. Plant
phenylpropanoids as emerging anti-inflammatory agents.
Mini Rev Med Chem 11: 823–835, 2011.
40. Kulkarni AC, Kuppusamy P, and Parinandi N. Oxygen, the
lead actor in the pathophysiologic drama: enactment of the
trinity of normoxia, hypoxia, and hyperoxia in disease and
therapy. Antioxid Redox Signal 9: 1717–1730, 2007.
41. Kurdistani SK. Histone modifications in cancer biology and
prognosis. Prog Drug Res 67: 91–106, 2011.
42. Lambert JD and Elias RJ. The antioxidant and pro-oxidant
activities of green tea polyphenols: a role in cancer preven-
tion. Arch Biochem Biophys 501: 65–72, 2010.
43. Lappas M, Hiden U, Desoye G, Froehlich J, Hauguel-de
Mouzon S, and Jawerbaum A. The role of oxidative stress in
the pathophysiology of gestational diabetes mellitus. Anti-
oxid Redox Signal 15: 3061–3100, 2011.
44. Lee SJ, Krauthauser C, Maduskuie V, Fawcett PT, Olson JM,
and Rajasekaran SA. Curcumin-induced HDAC inhibition
and attenuation of medulloblastoma growth in vitro and
in vivo.BMC Cancer 11: 144, 2011.
EPIGENETIC REGULATION BY PLANT SECONDARY METABOLITES 337
45. Lee WJ, Chen YR, and Tseng TH. Quercetin induces FasL-
related apoptosis, in part, through promotion of histone H3
acetylation in human leukemia HL-60 cells. Oncol Rep 25:
583–591, 2011.
46. Li G and Reinberg D. Chromatin higher-order structures
and gene regulation. Curr Opin Genet Dev 21: 175–186, 2011.
47. Li Q and Chen H. Epigenetic modifications of metastasis
suppressor genes in colon cancer metastasis. Epigenetics 6:
849–852, 2011.
48. Li Y and Tollefsbol TO. Impact on DNA methylation in
cancer prevention and therapy by bioactive dietary compo-
nents. Curr Med Chem 17: 2141–2151, 2010.
49. Li Y, Yuan YY, Meeran SM, and Tollefsbol TO. Synergistic
epigenetic reactivation of estrogen receptor-alpha (ERalpha)
by combined green tea polyphenol and histone deacetylase
inhibitor in ERalpha-negative breast cancer cells. Mol Cancer
9: 274, 2010.
50. Link A, Balaguer F, and Goel A. Cancer chemoprevention by
dietary polyphenols: promising role for epigenetics. Biochem
Pharmacol 80: 1771–1792, 2010.
51. Manach C, Mazur A, and Scalbert A. Polyphenols and preven-
tion of cardiovascular diseases. Curr Opin Lipidol 16: 77–84, 2005.
52. Meeran SM, Patel SN, Chan TH, and Tollefsbol TO. A novel
prodrug of epigallocatechin-3-gallate: differential epigenetic
hTERT repression in human breast cancer cells. Cancer Prev
Res (Phila) 4: 1243–1254, 2011.
53. Minko IG, Kozekov ID, Harris TM, Rizzo CJ, Lloyd RS,
and Stone MP. Chemistry and biology of DNA containing
1,N(2)-deoxyguanosine adducts of the alpha,beta-unsaturated
aldehydes acrolein, crotonaldehyde, and 4-hydroxynonenal.
Chem Res Toxicol 22: 759–778, 2009.
54. Mittal A, Piyathilake C, Hara Y, and Katiyar SK. Ex-
ceptionally high protection of photocarcinogenesis by topical
application of (-)-epigallocatechin-3-gallate in hydrophilic
cream in SKH-1 hairless mouse model: relationship to inhi-
bition of UVB-induced global DNA hypomethylation. Neo-
plasia 5: 555–565, 2003.
55. Nandakumar V, Vaid M, and Katiyar SK. (-)-Epigalloca-
techin-3-gallate reactivates silenced tumor suppressor genes,
Cip1/p21 and p16INK4a, by reducing DNA methylation
and increasing histones acetylation in human skin cancer
cells. Carcinogenesis 32: 537–544, 2011.
56. Nicholson SK, Tucker GA, and Brameld JM. Physiological
concentrations of dietary polyphenols regulate vascular en-
dothelial cell expression of genes important in cardiovas-
cular health. Br J Nutr 103: 1398–1403, 2010.
57. Nicholson SK, Tucker GA, and Brameld JM. Effects of die-
tary polyphenols on gene expression in human vascular
endothelial cells. Proc Nutr Soc 67: 42–47, 2008.
58. Nihal M, Roelke CT, and Wood GS. Anti-melanoma effects
of vorinostat in combination with polyphenolic antioxidant
(-)-epigallocatechin-3-gallate (EGCG). Pharm Res 27: 1103–
1114, 2010.
59. Otani H. Oxidative stress as pathogenesis of cardiovascular
risk associated with metabolic syndrome. Antioxid Redox
Signal 15: 1911–1926, 2011.
60. Panickar KS and Anderson RA. Effect of polyphenols on
oxidative stress and mitochondrial dysfunction in neuronal
death and brain edema in cerebral ischemia. Int J Mol Sci 12:
8181–8207, 2011.
61. Pereira CV, Nadanaciva S, Oliveira PJ, and Will Y. The
contribution of oxidative stress to drug-induced organ tox-
icity and its detection in vitro and in vivo.Expert Opin Drug
Metab Toxicol 8: 219–237, 2012.
62. Perron NR and Brumaghim JL. A review of the antioxidant
mechanisms of polyphenol compounds related to iron
binding. Cell Biochem Biophys 53: 75–100, 2009.
63. Perron NR, Wang HC, Deguire SN, Jenkins M, Lawson M,
and Brumaghim JL. Kinetics of iron oxidation upon poly-
phenol binding. Dalton Trans 39: 9982–9987, 2010.
64. Piaz FD, Vassallo A, Rubio OC, Castellano S, Sbardella G,
and De Tommasi N. Chemical biology of histone acetyl-
transferase natural compounds modulators. Mol Divers 15:
401–416, 2011.
65. Rahman I. Antioxidant therapeutic advances in COPD. Ther
Adv Respir Dis 2: 351–374, 2008.
66. Reuter S, Gupta SC, Park B, Goel A, and Aggarwal BB.
Epigenetic changes induced by curcumin and other natural
compounds. Genes Nutr 6: 93–108, 2011.
67. Santos-Reboucas CB and Pimentel MM. Implication of ab-
normal epigenetic patterns for human diseases. Eur J Hum
Genet 15: 10–17, 2007.
68. Scalbert A, Johnson IT, and Saltmarsh M. Polyphenols:
antioxidants and beyond. Am J Clin Nutr 81: 215S–217S,
2005.
69. Siow RC and Mann GE. Dietary isoflavones and vascular
protection: activation of cellular antioxidant defenses by
SERMs or hormesis? Mol Aspects Med 31: 468–477, 2010.
70. Spatafora C and Tringali C. Natural-derived polyphenols as
potential anticancer agents. Anticancer Agents Med Chem
2012 Jan 31. [Epub ahead of print] PubMed PMID 22292761.
71. Stoclet JC, Chataigneau T, Ndiaye M, Oak MH, El Bedoui
J, Chataigneau M, and Schini-Kerth VB. Vascular protec-
tion by dietary polyphenols. Eur J Pharmacol 500: 299–313,
2004.
72. Sun H, Yang X, Zhu J, Lv T, Chen Y, Chen G, Zhong L, Li Y,
Huang X, Huang G, and Tian J. Inhibition of p300-HAT
results in a reduced histone acetylation and down-regulation
of gene expression in cardiac myocytes. Life Sci 87: 707–714,
2010.
73. Tsao R. Chemistry and biochemistry of dietary polyphenols.
Nutrients 2: 1231–1246, 2010.
74. Usatyuk PV and Natarajan V. Hydroxyalkenals and oxi-
dized phospholipids modulation of endothelial cytoskele-
ton, focal adhesion and adherens junction proteins in
regulating endothelial barrier function. Microvasc Res 83: 45–
55, 2012.
75. Vanhees K, Coort S, Ruijters EJ, Godschalk RW, van
Schooten FJ, and Barjesteh van Waalwijk van Doorn-Khos-
rovani S. Epigenetics: prenatal exposure to genistein leaves a
permanent signature on the hematopoietic lineage. FASEB J
25: 797–807, 2011.
76. Visioli F, De La Lastra CA, Andres-Lacueva C, Aviram M,
Calhau C, Cassano A, D’Archivio M, Faria A, Fave G, Fo-
gliano V, Llorach R, Vitaglione P, Zoratti M, and Edeas M.
Polyphenols and human health: a prospectus. Crit Rev Food
Sci Nutr 51: 524–546, 2011.
77. Waggoner D. Mechanisms of disease: epigenesis. Semin Pe-
diatr Neurol 14: 7–14, 2007.
78. Wong CP, Nguyen LP, Noh SK, Bray TM, Bruno RS, and Ho
E. Induction of regulatory T cells by green tea polyphenol
EGCG. Immunol Lett 139: 7–13, 2011.
79. Wongcharoen W and Phrommintikul A. The protective role
of curcumin in cardiovascular diseases. Int J Cardiol 133:
145–151, 2009.
80. Wood LG, Wark PA, and Garg ML. Antioxidant and anti-
inflammatory effects of resveratrol in airway disease. Anti-
oxid Redox Signal 13: 1535–1548, 2010.
338 MALIREDDY ET AL.
81. Yao H and Rahman I. Current concepts on oxidative/car-
bonyl stress, inflammation and epigenetics in pathogenesis
of chronic obstructive pulmonary disease. Toxicol Appl
Pharmacol 254: 72–85, 2011.
82. Zhang Y and Chen H. Genistein, an epigenome modifier
during cancer prevention. Epigenetics 6: 888–891, 2011.
Address for correspondence:
Dr. Narasimham L. Parinandi
Division of Pulmonary, Allergy, Critical Care, and Sleep Medicine
Dorothy M. Davis Heart and Lung Research Institute
Colleges of Medicine and Pharmacy
The Ohio State University College of Medicine
473 W. 12th Ave.
Columbus, OH 43210
E-mail: narasimham.parinandi@osumc.edu
Date of first submission to ARS Central, March 4, 2012; date of
acceptance, March 11, 2012.
Abbreviations Used
4-HNE ¼4-hydroxy-2-nonenal
ADP ¼adenosine-3¢,5¢-diphosphate
C¼cytosine
COPDs ¼chronic obstructive pulmonary diseases
CpG ¼phosphodiester bond between cytosine
and guanine
CVD ¼cardiovascular disease
DNA ¼deoxyribonucleic acid
DNMT ¼DNA methyltransferase
ECG ¼(-)-epicatechin-3-gallate
EGCG ¼(-)-epigallocatechin-3-gallate
ERK ¼extracellular-regulated kinase
Era¼estrogen receptor-a
Foxp3 ¼forkhead box p3
G¼guanine
GSH ¼glutathione
H2A ¼histone 2A
H2B ¼histone 2B
H3 ¼histone 3
H4 ¼histone 4
HAT ¼histone acetyltransferase
HDAC ¼histone deacetylase
HL-60 cells ¼human leukemia-60 cells
hTERT ¼human telomerase reverse transcriptase
JNK ¼Jun N-terminus kinase
miRNA ¼micro-ribonucleic acid
mRNA ¼messenger ribonucleic acid
PDE ¼phosphodiesterase
pro-EGCG ¼pro-drug of (-)-epigallocatechin-3-gallate
RNA ¼ribonucleic acid
RNS ¼reactive nitrogen species
ROS ¼reactive oxygen species
SAM ¼S-adenosylmethionine
SIRT ¼sirtuin
UHRF1 ¼ubiquitin-like containing PHD and ring
finger domains 1
UV ¼ultraviolet
EPIGENETIC REGULATION BY PLANT SECONDARY METABOLITES 339
