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Review Article
Oxidative Stress, Prooxidants, and Antioxidants: The Interplay
Anu Rahal,
1
Amit Kumar,
2
Vivek Singh,
3
Brijesh Yadav,
4
Ruchi Tiwari,
2
Sandip Chakraborty,
5
and Kuldeep Dhama
6
1
Department of Veterinary Pharmacology and Toxicology, Uttar Pradesh Pandit, Deen Dayal Upadhayay Pashu
Chikitsa Vigyan Vishwa Vidyalaya Evam Go-Anusandhan Sansthan (DUVASU), Mathura 281001, India
2
Department of Veterinary Microbiology and Immunology, Uttar Pradesh Pandit, Deen Dayal Upadhayay Pashu
Chikitsa Vigyan Vishwa Vidyalaya Evam Go-Anusandhan Sansthan (DUVASU), Mathura 281001, India
3
Department of Animal Husbandry, Kuchaman, Rajasthan 341508, India
4
Department of Veterinary Physiology, Uttar Pradesh Pandit, Deen Dayal Upadhayay Pashu Chikitsa Vigyan Vishwa
Vidyalaya Evam Go-Anusandhan Sansthan (DUVASU), Mathura 281001, India
5
Animal Resources Development Department, Pt. Nehru Complex, Agartala 799006, India
6
Division of Pathology, Indian Veterinary Research Institute, Izatnagar, Bareilly 243122, India
Correspondence should be addressed to Amit Kumar; balyan@gmail.com
Received May ; Revised November ; Accepted November ; Published January
AcademicEditor:AfafK.El-Ansary
Copyright © Anu Rahal et al. is is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Oxidative stress is a normal phenomenon in the body. Under normal conditions, the physiologically important intracellular levels of
reactive oxygen species (ROS) are maintained at low levels by various enzyme systems participating in the in vivo redox homeostasis.
erefore, oxidative stress can also be viewed as an imbalance between the prooxidants and antioxidants in the body. For the last two
decades, oxidative stress has been one of the most burning topics among the biological researchers all over the world. Several reasons
can be assigned to justify its importance: knowledge about reactive oxygen and nitrogen species production and metabolism;
identication of biomarkers for oxidative damage; evidence relating manifestation of chronic and some acute health problems to
oxidative stress; identication of various dietary antioxidants present in plant foods as bioactive molecules; and so on. is review
discusses the importance of oxidative stress in the body growth and development as well as proteomic and genomic evidences of its
relationship with disease development, incidence of malignancies and autoimmune disorders, increased susceptibility to bacterial,
viral, and parasitic diseases, and an interplay with prooxidants and antioxidants for maintaining a sound health, which would be
helpful in enhancing the knowledge of any biochemist, pathophysiologist, or medical personnel regarding this important issue.
1. Introduction
Man and animals are exposed to a large number of biological
and environmental factors like alterations in feed and hus-
bandry practices, climatic variables, transportation, regroup-
ing, the therapeutic and prophylactic activities, various stres-
sors, and so forth. e ability of the man and animal to ght
against these factors is important for maintenance of their
health and productivity. Today, the entire world is witnessing
an upsurge in chronic health complications like cardiovascu-
lar disease, hypertension, diabetes mellitus, dierent forms
of cancer, and other maladies. Medical surveys suggest that
diet may serve as a potential tool for the control of these
chronic diseases [, ]. Regular chewing of tobacco along with
inadequate diet is the most prominent nding to mortality
due to lung cancer in USA []. Diets rich in fruit and veg-
etables have been reported to exert a protective eect against
a variety of diseases, particularly the cardiovascular disease
and cancer [–]. e primary nutrients thought to provide
protection aorded by fruit and vegetables are the antioxi-
dants [, ]. In an analysis, Potter [] reviewed epidemi-
ological studies, the majority of which showed a protective
eect of increased fruit and vegetable intake and concluded
that the high content of polyphenolic antioxidants in fruits
and vegetables is probably the main factor responsible for
the benecial eects. is awareness has led to a tremendous
increase in the proportion of fruits and vegetables rich in
antioxidant molecules on the dining table in the last two
Hindawi Publishing Corporation
BioMed Research International
Volume 2014, Article ID 761264, 19 pages
http://dx.doi.org/10.1155/2014/761264
BioMed Research International
decades, but still the risk of chronic health problems refuses
to decline, rather it upsurged with an enhanced vigour, giving
rise to a very important question—why? If the health associ-
ated problems are due to oxidative stress and the dietary con-
stituents are potent antioxidants, then the question of prob-
lem arrival should not be there. What happens when these
antioxidants reach the body tissues of interest or are there
other factors still to be unrevealed?
2. Stress
e term “stress” has been used in physics since unknown
time as it appears in the denition of Hooke’s law of , but
its rst use in the biological science dates back to Sir Hans
Selye’slettertotheEditorofNaturein.Atthattime,itwas
not accepted, but later on, aer the famous address of Hans
Selye at the prestigious College of France, it received approval
among scientic community, but dening stress again trou-
bled Selye over several years. Today, stress can be dened
as a process of altered biochemical homeostasis produced
by psychological, physiological, or environmental stressors
[]. Any stimulus, no matter whether social, physiological,
orphysical,thatisperceivedbythebodyaschallenging,
threatening, or demanding can be labeled as a stressor. e
presence of a stressor leads to the activation of neurohor-
monal regulatory mechanisms of the body, through which
it maintains the homeostasis []. e overall physiological
impact of these factors and the adaptation ability of the body
determine the variations in growth, development, productiv-
ity, and health status of the animals [–]. ese alterations
canbeviewedasaconsequenceofgeneraladaptationsyn-
dromeaspostulatedbyHansSelye[]andusuallyreturnto
their normal status once the stimulus has disappeared from
the scene. Strong and sustained exposure to stress [, ,
] may result in higher energy negative balance and may
ultimately result in reduction in adaptation mechanisms,
increase in the susceptibility to infection by pathogens,
declineinproductivity,andnallyahugeeconomicalloss
[, , ].
Many of us puzzle between distress, stress, and oxidative
stress. Distress diers from stress, which is a physiological
reactionthatcanleadtoanadaptiveresponse[]. Distress
is comparatively dicult to dene and generally refers to a
state in which an animal cannot escape from or adapt to
the external or internal stressors or conditions it experiences
resultinginnegativeeectsuponitswell-being[]. Stress
leads to adaptation but distress does not. Stress is a commonly
used term for oxidative stress. Any alteration in homeostasis
leadstoanincreasedproductionofthesefreeradicals,much
above the detoxifying capability of the local tissues []. ese
excessive free radicals then interact with other molecules
within cells and cause oxidative damage to proteins, mem-
branes, and genes. In this process they oen create more
free radicals, sparking o a chain of destruction. Oxidative
damagehasbeenimplicatedinthecauseofmanydiseases
such as cardiovascular diseases, neuronal degeneration, and
cancer and has an impact on the body’s aging process too.
An altered response to the therapeutic agents has also been
observed []. External factors such as pollution, sunlight,
and smoking also trigger the production of free radicals.
Most importantly, stress is one of the basic etiologies of
disease []. It can have several origins like environmental
extremes for example, cold, heat, hypoxia, physical exercise
or malnutrition (Figure ).
On the basis of duration and onset, stress might be acute
and chronic stress. e stress due to exposure of cold or heat
is generally of acute type and is released with the removal of
cause. Similarly, stress due to physical exercises or complete
immobilization []isalsoacuteinnature.enutritional
and environmental stresses, where the causes persist for a
longer period of time, are chronic stress.
2.1. Cold Stress. Cold stress is evident whenever the temper-
ature falls below
∘
C and the body experiences severe cold
related illness and permanent tissue damage. An acute cold
stress (−
∘
Cforhours)inratscausesprofoundreduction
in contraction amplitude with an increase in heart rate in the
isolated heart preparations []. e decrease in amplitudes is
associated with inadequate ATP formation. While changing
perfusion of poststress isolated heart, myocardial rigidity
furtherslowsdownandthisseemedtobeassociatedwith
activated glycolysis. ere are no signs of cardiomyocytic
lesion aer cold stress. Reduced coronary ow is the only
abnormal eect of acute cold stress under these conditions.
High cardiac resistance to the damaging eect of cold is
likely to be related to increased processes of glycolysis and
glycogenolysis in the cardiomyocytes. e activity of succi-
nate dehydrogenase also gets elevated indicating the inuence
of cold stress on the Krebs cycle []. Coronary blood ow
isalsoreducedandlateronresultsinanalteredbasophils
activity in the myocardium [].
2.2. Physical Exercise and Stress. Health benets of regular
physical exercise are undebatable. Both resting and contract-
ingskeletalmusclesproducereactiveoxygenandnitrogen
species (ROS, RNS). Low physiological levels of ROS are
generated in the muscles to maintain the normal tone and
contractility, but excessive generation of ROS promotes con-
tractile dysfunction resulting in muscle weakness and fatigue
[].isisperhapsthereasonwhyintenseandprolonged
exercise results in oxidative damage to both proteins and
lipids in the contracting muscle bers [].
Regular exercise induces changes in both enzymatic and
nonenzymatic antioxidants in the skeletal muscle. Further-
more, oxidants can modulate a number of cell signaling path-
ways and regulate the expression of multiple genes in eukary-
otic cells. is oxidant-mediated change in gene expression
involves changes at transcriptional, mRNA stability, and sig-
nal transduction levels. e magnitude of exercise-mediated
changes in superoxide dismutase (SOD) activity of skeletal
muscle increases as a function of the intensity and duration
of exercise [, ]. Mild physical activity increases nuclear
factor-kappa B(NF-𝜅B) activity in the muscle of rats as well
as the gene expression for manganese superoxide dismutase
(MnSOD) and endothelial nitric oxide synthase (eNOS) [].
BioMed Research International
Prooxidant
Exogenous
Pathogens
Bacteria
Virus
Fungus
Parasite
Drugs
Toxicants
Dietary
ingredients
Lipids
Carbohydrates
Highly
processed
food
Antioxidants
Transition
metals
Pesticides
Drug residuesClimate
Endogenous
Endogenous
metabolites
Drug
metabolites
Cellular
metabolism
Ion ux
Anxiety
Ischemia
Environmental
pollution
Pathophysiology
F : General classication of prooxidants.
2.3. Chronic Stress. Chronic stress signicantly alters limbic
neuroarchitecture and function and potentiates oxidative
stress [] and emotionality in rats []. Chronic restraining
of laboratory animals has been found to increase aggres-
sion, potentiate anxiety, and enhance fear conditioning [].
Chronic immobilization induces anxiety behavior and den-
dritic hypertrophy in the basolateral amygdala, which persist
beyond a recovery period. Restraint of rats causes increased
mucin release, as measured by [H] glucosamine incorpo-
ration and goblet cell depletion, prostaglandin E (PGE)
secretion, and mast cell activation in colonic explants [].
Upregulation of the neurotensin precursor mRNA in the
paraventricular nucleus of the hypothalamus aer immobi-
lization has also been reported []. Neurotensin stimulates
mucin secretion from human colonic goblet cell line by a
receptor mediated mechanism [].
2.4. Nutritional Stress. Nutrition is one of the most signicant
external etiologies for oxidative stress including its char-
acteristics, type and quality, ratio of the various nutrients,
dietary balance with regard to protein, carbohydrates, fats,
macro- and trace elements, and so forth. Feed exercises a
considerable inuence over the physiological condition and
thus the homeostasis of the animal body [, , –].
BioMed Research International
Feeding of endogenous or exogenous antioxidants can sensi-
tively regulate glycolysis and the Warburg eect in hepatoma
cells []. Fasting induces an increase in total leukocytes
counts, eosinophils, and metamyelocytes in the blood prole,
accompanied by a decrease in the basophils and monocytes,
a typical “stress leukogram” produced in the animal body due
to the increased endogenous production of cortisol from the
adrenal glands during oxidative stress [, , –]. e
leukocytosis with neutrophilia associated with fasting may be
a consequence of an inammatory reaction, caused by the
direct action of ammonia on the rumen wall [, ]. e
monocytopenia may be a result of adaptation and defense
mechanism undergoing in the body and leads to higher
susceptibility to pathogens [, ].
Nutritional stress causes adrenal gland hyperfunction
and, thus, an increased release of catecholamines in the blood,
with a simultaneous inhibition of the production of insulin in
the pancreas [, , –]. e process of glycogenolysis is
observed in the rst hours of fasting [, , –]. ere-
aer, gluconeogenesis from amino acid precursors and lipol-
ysisfromglycerol,aswellasfromlactatethroughtheCori
cycle, maintain a regular supply of glucose. Lactate gets trans-
formed into pyruvate and participates in the gluconeogenesis
along with the deaminated amino acids. e increased
production of catecholamines (epinephrine and dopamine)
owing to fasting results in peripheral vasoconstriction and
redistribution in blood which is expressed as erythrocytosis,
leukocytosis, and neutrophilia [].
2.5. Hypoxic Stress. Hypoxia is known to stimulate mito-
chondria to release ROS (mROS). Under hypoxic conditions,
mitochondria participate in a ROS burst generated at com-
plex III of the electron transport chain []. Hypoxia and
reoxygenation result in reversible derangement of ATPase
and architecture of mitochondrial membrane. Cardiac hemo-
dynamic parameters, which decline immediately under
hypoxic conditions, recover during reoxygenation [], but
the biochemical and histopathological studies provide a com-
plicated pattern []. High CAT (carboxyatractyloside) sensi-
tivityoftheATPaseisobservedatminofhypoxia.einitial
phase in hypoxic perfusion (< min) exhibits a steep increase
of ADP contents and ATPase activities and a drastic fall of
ATP/ADP ratios in mitochondria, as well as in tissues. Fur-
thermore, the number of ATPase particles visible at the inner
aspect of mitochondrial membrane decreases. During the
second phase of hypoxic perfusion (from min onwards),
the count of ATPase particles visible at the inner mito-
chondrial membrane further decreases. ATPase activities
uctuate, retaining close contact with the membrane dur-
ing hypoxia. e mitochondrial ultrastructural damage
becomes more evident. High-energy phosphates reserves of
myocardiumcouldhelpmyocardialcellstomaintaintheir
structural integrity []. ATP/ADP ratios attain values of
almost . During reoxygenation (aer min of hypoxia),
the levels of mitochondrial adenine nucleotides, oxidative
phosphorylation rate, and respiratory control index increase
within min and then slightly decline again. e ATP/ADP
ratio is diminished in the course of reoxygenation. ATPase
activity also decreases within min of reoxygenation and
the ADP/O ratio reaches control values. e ATPase activity
gains its highest sensitivity towards catalase at min of
reoxygenationattainingavaluesimilartothatofminof
hypoxic perfusion.
3. Stress and Well-Being
Each cell in the human body maintains a condition of home-
ostasis between the oxidant and antioxidant species [].
Up to –% of the pulmonary intake of oxygen by humans
is converted into ROS []. Under conditions of normal
metabolism, the continuous formation of ROS and other free
radicals is important for normal physiological functions like
generation of ATP, various catabolic and anabolic processes
and the accompanying cellular redox cycles. However, exces-
sive generation of free radicals can occur due to endogenous
biological or exogenous environmental factors, such as chem-
ical exposure, pollution, or radiation.
ere are ROS subgroups: free radicals such as superoxide
radicals (O
2
∙−
) and nonradical ROS such as hydrogen perox-
ide (H
2
O
2
)[]. e primary free radicals generated in cells
aresuperoxide(O
2
∙
) and nitric oxide (NO). Superoxide is
generated through either incomplete reduction of oxygen in
electron transport systems or as a specic product of enzy-
matic systems, while NO is generated by a series of specic
enzymes (the nitric oxide synthases). Both superoxide and
NO are reactive and can readily react to form a series of other
ROS and RNS.
Generally, mitochondria are the most important source
of cellular ROS where continuous production of ROS takes
place []. is is the result of the electron transport chain
located in the mitochondrial membrane, which is essential for
the energy production inside the cell [, ]. Additionally,
some cytochrome enzymes are also known to produce
ROS [].
4. Biochemical Basis of Stress
Several endogenous cells and cellular components participate
in initiation and propagation of ROS (Table )[–].
All these factors play a crucial role in maintenance of cel-
lular homeostasis. A stressor works by initiating any of these
mechanisms. Oxidative stress occurs when the homeostatic
processes fail and free radical generation is much beyond
the capacity of the body’s defenses, thus promoting cellular
injury and tissue damage. is damage may involve DNA and
proteincontentofthecellswithlipidperoxidationofcellular
membranes, calcium inux, and mitochondrial swelling and
lysis [, , ]. ROS are also appreciated as signaling
molecules to regulate a wide variety of physiology. It was rst
proposed in the s when hydrogen peroxide was shown
to be required for cytokine, insulin, growth factor, activator
protein- (AP-), and NF-𝜅B signaling [, ]. e role of
hydrogen peroxide in promoting phosphatase inactivation by
cysteine oxidation provided a likely biochemical mechanism
by which ROS can impinge on signaling pathways []. e
role of ROS in signaling of cytochrome c mediated apop-
tosis is also well established []. ROS can cause reversible
BioMed Research International
T : Endogenous mediators of oxidative stress.
Leakage of free radicals
Membrane-bound enzymes NADPH oxidase
Electron transport systems Mixed function oxidases
Activation of oxygen
Soluble cell constituents
Transition metals, thiol containing proteins, quinine
derivatives, epinephrine, metalloproteins, hemeproteins,
and avoproteins
Xenobiotic metabolizing enzymes
Cyt P
-dependent monooxygenases, Cyt b
,and
NADPH-dependent cytochrome reductases
ROS generation/propagation
Soluble cytosolic enzymes Xanthine oxidase, superoxide dismutase, catalase
Phagocytic cells
Neutrophils, macrophages, and monocytes involved in
inammation, respiratory burst, and removal of toxic
molecules
Local ischemia Damaged blood supply due to injury or surgery
posttranslational protein modications to regulate signaling
pathways. A typical example of the benecial physiological
role of free radicals is a molecule of nitric oxide (NO).
NOisformedfromargininebytheactionofNO-synthase
(NOS) []. NO is produced by constitutive NOS during
vasodilating processes (eNOS) or during transmission of
nerveimpulses(nNOS).Inthepresenceofstressors,NOis
produced by catalytic action of inducible NOS (iNOS) and
is at higher concentrations [–]. NO can cause damage to
proteins, lipids, and DNA either directly or aer reaction with
superoxide, leading to the formation of the very reactive
peroxynitrite anion (nitroperoxide) ONOO– [–].
Lipid peroxidation of polyunsaturated lipids is one of
themostpreferredmarkersforoxidativestress.eproduct
of lipid peroxidation, malondialdehyde, is easily detected in
blood/plasma and has been used as a measure of oxidative
stress. In addition, the unsaturated aldehydes produced from
these reactions have been implicated in modication of cellu-
lar proteins and other constituents []. e peroxidized lipid
can produce peroxy radicals and singlet oxygen.
5. Physiological Role of Stress
Stress has a signicant ecological and evolutionary role and
may help in understanding the functional interactions among
life history traits [–]. Stress leads to a number of phys-
iological changes in the body including altered locomotor
activity and general exploratory behavior. e physiological
role of ROS is associated with almost all of the body processes,
for example, with reproductive processes []. Since under
physiological conditions a certain level of free radicals and
reactive metabolites is required, complete suppression of FR
formation would not be benecial []. One further benecial
example of ROS seen at low/moderate concentrations is the
induction of a mitogenic response.
Stress leads to activation of hypothalamic-pituitary-
adrenal axis. e increased endogenous catecholamine
release has been observed in cold environmental conditions.
e activity of succinate dehydrogenase also gets elevated
indicating the inuence of ROS as evident in cold environ-
mental conditions []. Coronary blood ow is reduced and
an altered basophils activity in the myocardium is also
observed [].
Free radicals play an irreplaceable role in phagocytosis
as one of the signicant microbicidal systems [], or in
several biochemical reactions, for example, hydroxylating,
carboxylating, or peroxidating reactions, or in the reduction
of ribonucleotides []. At present, free radicals and their
metabolites are assumed to have important biomodulating
activities and a regulatory ability in signal transduction
process during transduction of intercellular information [].
Among the reactive oxygen species, H
2
O
2
best fullls the
requirements of being a second messenger []. Its enzy-
matic production and degradation, along with its functional
requirement for thiol oxidation, facilitate the specicity for
time and place that are required in signaling. Both the ther-
modynamic and kinetic considerations support that among
dierent possible oxidation states of cysteine, formation of
sulfenic acid derivatives or disuldes can be applicable as
thiol redox switches in signaling. H
2
O
2
readily diuses across
biological membranes, and so it is well-suited as a diusible
messenger [, ].
Inthepresenceoftransitionmetalssuchasironorcopper,
H
2
O
2
cangiverisetotheindiscriminatelyreactiveand
toxic hydroxyl radical (HO
∙
)byFentonchemistry.Increasing
evidence indicates that H
2
O
2
is a particularly an intrigu-
ing candidate as an intracellular and intercellular signaling
molecule because it is neutral and membrane permeable
[, ].
Specically, H
2
O
2
can oxidize thiol (–SH) of cysteine
residues and form sulphenic acid (–SOH), which can get
glutathionylated (–SSG), form a disulde bond (–SS–) with
adjacent thiols, or form a sulfenyl amide (–SN–) with amides
[]. Each of these modications modies the activity of the
target protein and thus its function in a signaling pathway.
Phosphatases appear to be susceptible to regulation by ROS
in this manner, as they possess a reactive cysteine moiety
in their catalytic domain that can be reversibly oxidized,
which inhibits their dephosphorylation activity []. Specic
examples of phosphatases known to be regulated in this
manner are PTPb, PTEN, and MAPK phosphatases [].
BioMed Research International
Physical
Bacteria
Viruses
Necrosis/other
disorders
Damage to
DNA
Transcription
factors
inhibited
Telomere
shortening
Ageing
Endobiotic or
xenobiotic
Peroxidases
Carcinogen/
mutation
Pituitary
Endocrine
dysfunction
Alzheimer’s
disease
Proinammatory
mediators
Change in Ca
homeostasis
Hypertension
Chronic
inammation
Cardiovascular
disease
Autoimmune
disorder
Renal
damage/
apoptosis
Hepatic
damage
Limited ATP
generation
Energy
crisis
Protein
kinase
Parkinson’s
disease
Phagocytes/
other cell organelles
Cytosolic
enzyme
ROS
PKc
NADPH
oxidase
Mitochondrial oxidative burst
Hepatocellular,
cervical, colon,
breast cancers
Immune
dysfunction
Neurological
disorders
XME
Electron
transport
Susceptible
to infection
s
a
tor
y
s
Ati
am
m
m
m
a
a
a
e
e
e
e
e
d
e
iato
r
r
r
r
r
r
h
dys
dys
dy
dy
dys
dy
dys
dy
y
y
y
y
y
y
y
y
y
y
y
y
y
y
y
y
y
y
y
y
y
y
y
y
y
y
y
y
y
y
y
fun
fun
fun
fun
ct
c
d
T
s
Tl
Smoking
UV/X rays
External stimuli (drugs/toxicants/environment/nutrition/physical)
Internal agents
(disease/ischemia/
necrosis)
Macrophage-
fatty acid-binding
protein-4 (aP2)
O
2
H
2
O
2
H
2
O
Hypothalamo-
pituitary-
adrenal axis
NF-𝜅B
Alternative in
protein/lipid
CYP
450
modulation
Antioxidants
GSH
NADPH
ioredoxin vitamins E
and C and trace metals
such as selenium
OH−
al
st
sti
ti
i
i
i
i
i
i
i
mul
mul
l
mul
mu
mul
mul
mul
mul
mul
m
mul
mul
mu
m
u
m
i
i
i
i (
i
i
i
i
i
i
i
dr
dru
ru
ru
u
u
g
gs
gs/
t
Food
V
iruses
Cardioprotective
Altered
xenobiotic bio-
transformation
ROS
ROS
O
2
∙−
F : Oxidative stress and disease development.
Any emotional stress leads to a decrease in sympathetic out-
owaswellasenergyproductionofthetissues[].
6. Oxidative Stress
e harmful eect of free ROS and RNS radicals causing
potential biological damage is termed oxidative stress and
nitrosative stress, respectively [–].isisevidentinbio-
logical systems when there is either an excessive production
of ROS/RNS and/or a deciency of enzymatic and nonenzy-
matic antioxidants. e redox stress/oxidative stress is a com-
plex process. Its impact on the organism depends on the type
of oxidant, on the site and intensity of its production, on the
composition and activities of various antioxidants, and on the
ability of repair systems [].
e term “ROS” includes all unstable metabolites of
molecular oxygen (O
2
) that have higher reactivity than O
2
like superoxide radical (O
2
∙
) and hydroxyl radical (HO
∙
)
and nonradical molecules like hydrogen peroxide (H
2
O
2
).
ese ROS are generated as byproduct of normal aerobic
metabolism, but their level increases under stress which
proves to be a basic health hazard. Mitochondrion is the
major cell organelle responsible for ROS production [, ].
It generates ATP through a series of oxidative phosphory-
lation processes. During this process, one- or two-electron
reductions instead of four electron reductions of O
2
can
occur, leading to the formation of O
2
∙
or H
2
O
2
,andthese
species can be converted to other ROS. Other sources of
ROS may be reactions involving peroxisomal oxidases [],
cytochrome P- enzymes [], NAD (P)H oxidases [],
or xanthine oxidase [].
7. Oxidative Stress and Diseases
Today the world is experiencing a rise in age related chronic
health diseases like cardiovascular disorders, cancer, and
so forth and their associated negative health impacts and
mortality/casualty [–]. Some metabolic diseases like
diabetes are also associated with an enhanced level of lipoper-
oxidation (Figure ).
e central nervous system (CNS) is extremely sensitive
to free radical damage because of a relatively small total
antioxidant capacity. e ROS produced in the tissues can
inict direct damage to macromolecules, such as lipids,
nucleic acids, and proteins []. e polyunsaturated fatty
acids are one of the favored oxidation targets for ROS.
Oxygen-free radicals, particularly superoxide anion radical
(O
2
∙−
), hydroxyl radical (OH
∙−
), and alkylperoxyl radical
(
∙
OOCR), are potent initiators of lipid peroxidation, the role
of which is well established in the pathogenesis of a wide
range of diseases. Once lipid peroxidation is initiated, a prop-
agation of chain reactions will take place until termination
BioMed Research International
products are produced. erefore, end products of lipid
peroxidation, such as malondialdehyde (MDA), -hydroxy-
-nonenol (-HNE), and F-isoprostanes, are accumulated
in biological systems. DNA bases are also very suscep-
tible to ROS oxidation, and the predominant detectable
oxidation product of DNA bases in vivo is -hydroxy--
deoxyguanosine. Oxidation of DNA bases can cause muta-
tions and deletions in both nuclear and mitochondrial DNA.
Mitochondrial DNA is especially prone to oxidative damage
due to its proximity to a primary source of ROS and its
decient repair capacity compared with nuclear DNA. ese
oxidative modications lead to functional changes in various
typesofproteins(enzymaticandstructural),whichcanhave
substantial physiological impact. Similarly, redox modulation
of transcription factors produces an increase or decrease in
their specic DNA binding activities, thus modifying the
gene expression.
Among dierent markers of oxidative stress, malondi-
aldehyde (MDA) and the natural antioxidants, metalloen-
zymes Cu, Zn-superoxide dismutase (Cu, Zn-SOD), and
selenium dependent glutathione peroxidase (GSHPx), are
currently considered to be the most important markers [–
]. Malondialdehyde (MDA) is a three-carbon compound
formed from peroxidized polyunsaturated fatty acids, mainly
arachidonic acid. It is one of the end products of membrane
lipid peroxidation. Since MDA levels are increased in various
diseases with excess of oxygen free radicals, many relation-
ships with free radical damage were observed.
Cu, Zn-SOD is an intracellular enzyme present in all
oxygen-metabolizing cells, which dismutates the extremely
toxic superoxide radical into potentially less toxic hydrogen
peroxide. Cu, Zn-SOD is widespread in nature, but being a
metalloenzyme, its activity depends upon the free copper and
zinc reserves in the tissues. GSHPx, an intracellular enzyme,
belongs to several proteins in mammalian cells that can
metabolize hydrogen peroxide and lipid hydroperoxides.
8. Oxidative Stress and Altered
Immune Function
e relationship between oxidative stress and immune func-
tion of the body is well established. e immune defense
mechanism uses the lethal eects of oxidants in a benecial
manner with ROS and RNS playing a pivotal role in the killing
of pathogens. e skilled phagocytic cells (macrophages,
eosinophils, heterophils), as well as B and T lymphocytes,
contain an enzyme, the nicotinamide adenine dinucleotide
phosphate (NADPH) oxidase [, ], which is responsible
for the production of ROS following an immune challenge. At
the onset of an immune response, phagocytes increase their
oxygen uptake as much as – folds (respiratory burst).
e O
∙−
generatedbythisenzymeservesasthestarting
material for the production of a suite of reactive species.
Direct evidence also certies production of other powerful
prooxidants, such as hydrogen peroxide (H
2
O
2
), hypochlor-
ous acid (HOCl), peroxynitrite (ONOO–), and, possibly,
hydroxyl (OH
∙
)andozone(O
3
) by these cells. Although the
use of these highly reactive endogenous metabolites in the
cytotoxic response of phagocytes also injures the host tissues,
the nonspecicity of these oxidants is an advantage since they
take care of all the antigenic components of the pathogenic
cell [].
Several studies have demonstrated the interdependency
of oxidative stress, immune system, and inammation.
Increased expression of NO has been documented in dengue
and in monocyte cultures infected with dierent types of viral
infections. Increased production of NO has also been accom-
panied with enhancement in oxidative markers like lipid
peroxidation and an altered enzymatic and nonenzymatic
antioxidative response in dengue infected monocyte cultures
[]. More specically, the oxygen stress related to immune
system dysfunction seems to have a key role in senescence, in
agreement with the oxidation/inammation theory of aging.
Moreover, it has been revealed that reduced NADPH oxidase
is present in the pollen grains and can lead to induction of
airway associated oxidative stress. Such oxidative insult is
responsible for developing allergic inammation in sensitized
animals. ere is triggering of production of interleukin
(IL)-alongwithproinammatorycytokines,namely,tumor
necrosis factor (TNF)-alpha and IL-. ere is initiation
of dendritic cell (DC) maturation that causes signicant
upregulation of the expression of cluster of dierentiation
(CD)-, and with a slight overexpression of CD- in
the membrane. So altogether, innate immunity locally may
be alleviated due to oxidative stress induced by exposure to
pollen. is in turn helps in participation to initiate adaptive
immune response to pollen antigens [].
e immune status directly interplays with disease pro-
ductionprocess.eroleofphysicalandpsychological
stressors contributes to incidences and severity of various
viral and bacterial infections. Both innate as well as acquired
immune responses are aected by the altered IFN-𝛾secretion,
expression of CD, production of the acute-phase proteins,
and induction of TNF-𝛼. Fatal viral diseases produce severe
oxidative stress (OS) leading to rigorous cellular damage.
However, initiation, progress, and reduction of damages are
governedbytheredoxbalanceofoxidationandantioxida-
tion. e major pathway of pathogenesis for cell damage is via
lipidperoxidationparticularlyinmicrosomes,mitochondria,
and endoplasmic reticulum due to OS and free radicals
[, ]. All the factors responsible for the oxidative stress
directly or indirectly participate in immune system defense
mechanism. Any alteration leading to immunosuppression
can trigger the disease production (Table ).
9. Oxidative Stress and Incidence of
Autoimmune Diseases
Oxidative stress can induce production of free radicals
that can modify proteins. Alterations in self-antigens (i.e.,
modied proteins) can instigate the process of autoimmune
diseases [, ]. Under oxidative stress, cells may produce
an excess of ROS/RNS which react with and modify lipids
andproteinsinthecell[]. e end products of these
reactions may be stable molecules such as -chlorothyrosine
and -nitrotyrosine that may not only block natural bio-
transformations of the tyrosine like phosphorylation but also
change the antigenic prole of the protein. e oxidative
BioMed Research International
T : Deadly diseases that have got positive correlation to oxidative stress.
Sl.
number
Disease Organs involved Etiology References
() Macular degeneration Eyes Reactive oxygen intermediates (ROI) []
() Diabetes Multi-organ
Superoxide dismutase, catalase, glutathione
reductase, glutathione peroxidase
[]
() Chronic fatigue Multiorgan C-reactive protein []
() Atherosclerosis Blood vessels Reduced NADPH oxidase system []
()
Autoimmune disorders (systemic lupus
erythematosus)
Immune system R
𝑜
ribonucleoprotein []
()
Neurodegenerative diseases
(Alzheimer’s and Parkinson’s disease)
Brain Reactive oxygen species (ROS) []
() Asthma Lungs ROS particularly H
O
[]
() Rheumatoid and osteoarthritis Joints Radical oxygen species []
() Nephritis Kidney Glutathione transferase kappa (GSTK -) []
() Melanoma Skin
Pathophysiological processes including DNA
damage and lipid peroxidation (LPO)
[]
() Myocardial infarction Heart Reactive oxygen species (ROS) []
modication of the proteins not only changes the antigenic
prole of latter but also enhances the antigenicity as well [].
ere exist several examples of autoimmune diseases result-
ing from oxidative modications of self-proteins, namely,
systemic lupus erythematosus ( kD Ro ribonucleoprotein)
[], diabetes mellitus (high molecular weight complexes of
glutamic acid decarboxylase) [], and diuse scleroderma
(oxidation of beta--glycoprotein) [, ].
Moreover, oxidative stress poses an additional threat to
the target tissues as in the case of insulin-producing beta cells
in the islet of Langerhans []. To add to this, autoimmune
diseases oen occur only in a single tissue irrespective of
thefactthatothertissuesalsocontainthesameantigenbut
perhaps lack the level of oxidative stress required to initiate
the process. is pathological autoreactivity targeted towards
redox-modied self-antigens and diagnostic assays designed
to measure its cross-reactivity to normal self-antigens further
complicate the detection of autoimmune diseases []. In
the development of autoimmune disease pathogenesis, there
is possibly role of psychological stress along with major
hormones that are related to stress. It is thereby presumed
that the neuroendocrine hormones triggered by stress lead to
dysregulation of the immune system ultimately resulting in
autoimmune diseases by alteration and amplication of
production of cytokine [].
10. Oxidative Stress and Altered Susceptibility
to Bacterial, Viral, and Parasitic Infections
All pathogens, irrespective of their classication, bacterial,
viral, or parasitic, with impaired antioxidant defenses show
increased susceptibility to phagocytic killing in the host
tissues, indicating a microbicidal role of ROS []. Vice versa
to this, dierent studies have proven that individuals decient
in antioxidative mechanism are more susceptible to severe
bacterial and fungal infections as in case of HIV infections
[]. Reactive species are important in killing pathogens but
asanegativesideeectcanalsoinjurethehosttissues(immu-
nopathology). is is particularly apparent during chronic
inammation, which may cause extensive tissue damage with
a subsequent burst in oxidative stress []. e production of
free radicals involves macrophages and neutrophils to combat
the invading microbes. e whole of the process is performed
in host cells during the activation of phagocytes or the eect
of bacteria, virus, parasites, and their cell products reactivity
with specic receptors. e multicomponent avoprotein
NADPH oxidase plays vital role in inammatory processes
by catalyzing the production of superoxide anion radical O
2
−
and excessive production of reactive oxygen species (ROS)
leads to cellular damage. ese cellular damages in general
lead to altering immune response to microbes and ultimately
altered susceptibility to bacterial, viral, and parasitic infec-
tions [].
11. Oxidative Stress and Increase in
Levels of Incidence and Prevalence of
Various Malignancies
Carcinogenesis can be dened as a progressive erosion of
interactions between multiple activating and deactivating
biological activities (both immune and nonimmune) of host
tissue resulting in progressive loss of integrity of susceptible
tissues. e primitive steps in development of cancer, muta-
tion, and ageing are the result of oxidative damage to the
DNA in a cell. A list of oxidized DNA products has been
identied currently which can lead to mutation and cancer.
MajorchangenoticedduetoROScausedDNAdamageis
the break in the DNA strand, due to the alterations in the
purine or pyrimidine ring [, ]. Alongside with ROS other
redox metals also play a critical role in development of ageing,
BioMed Research International
mutation, and tumour []. In regular cellular mechanism,
free radicals scavenger vitamin E, C and glutathione along
with enzymes like catalase, peroxidases, and superoxide dis-
mutase control the mechanism of DNA repair. ese damages
are either in the form of single strand breaks (SSBs), double
strand breaks (DSBs), or oxidatively generated clustered DNA
lesions(OCDLs).Irregularrepairorabsenceofrepairofdam-
aged DNA due to OS might lead to mutagenesis and genetic
transformation along with alteration in apoptotic pathway
[].
Oxidative stress produced due to unresolved and per-
sistent inammation can be a major factor involved in the
change of the dynamics of immune responses. ese alter-
ations can create an immunological chaos that could lead to
loss of architectural integrity of cells and tissues ultimately
leading to chronic conditions or cancers []. Oxidative
stress is reported to be the cause of induction of aller-
gies, autoimmune or neurodegenerative diseases along with
altered cell growth, chronic infections leading to neoplasia,
metastatic cancer, and angiogenesis []. Damage to the
cellular components such as proteins, genes, and vasculature
is behind such alterations. Moreover, further accumulation
of conuent, useless, and complex cells causes additional
oxidative stress and maintains continuous activation of
immunesystemandunansweredinammation[]. Tissue
necrosis and cellular growth are stimulated by coexpression
of inammatory mediators due to oxidative stress-induced
alteredactivityofthecellsoftheimmunesystem.Such
changes of tissue function are mainly responsible for autoim-
mune, neurodegenerative, and cancerous conditions [,
]. Various factors produced due to oxidative stress along
with excessively produced wound healing and apoptotic
factors, namely, TNF, proteases, ROSs, and kinases, actively
participate in tumor growth and proliferation. ese factors
are also required for the membrane degradation, invasion of
neighboring tissues, and migration of tumor cells through
vasculature and lymphatic channels for metastasis [–].
e incidences of thyroid cancers have increased in the last
decades worldwide which is most likely due to exposure of
humanpopulationinmasstoradiationcausingincreasedfree
radical generation [].
12. Oxidative Stress and Aging
Aging is an inherent mechanism existing in all living cells.
ere is a decline in organ functions progressively along with
theage-relateddiseasedevelopment.etwomostimportant
theories related to ageing are free radical and mitochondrial
theories, and these have passed through the test of time.
ere is claim by such theories that a vicious cycle is gen-
erated within mitochondria wherein reactive oxygen species
(ROS) is produced in increased amount thereby augmenting
the damage potential [].Oxidativestressispresentat
genetic, molecular, cellular, tissue, and system levels of all
living beings and is usually manifested as a progressive
accumulation of diverse deleterious changes in cells and
tissues with advancing age that increase the risk of disease
and death []. Recent studies have shown that with age,
ROS levels show accumulation in major organ systems such
as liver, heart, brain, and skeletal muscle [–]eitherdue
to their increased production or reduced detoxication. us,
aging may be referred to as a progressive decline in biological
function of the tissues with respect to time as well as
a decrease in the adaptability to dierent kinds of stress or
brieyanoverallincreaseinsusceptibilitytodiseases[].
Oxidative stress theory is presently the most accepted expla-
nation for the aging which holds that increases in ROS lead
to functional alterations, pathological conditions and other
clinically observable signs of aging, and nally death [].
No matter whether mitochondrial DNA damage is involved
or electron transport chain damage is responsible for aging,
modulation of cellular signal response to stress or activa-
tion of redox-sensitive transcriptional factors by age-related
oxidative stress causes the upregulation of proinammatory
gene expression, nally leading to an increase in the ROS
levels [].
13. Genomic Evidences of the Stress-Disease
Development Interrelationship
Persistent oxidative stress due to altered inammation acts
asprecancerousstateofhostcellsleadingtotheinitiation
of genetic mutations, genetic errors, epigenetic abnormal-
ities, wrongly coded genome, and impaired regulation of
gene expression []. Events like methylation of nucleic
acid, binding of DNA proteins, formation and binding of
histone proteins, function of repair, and enzyme mediated
modications are sensitive to free radicals formed during
oxidative stress []. ese events involved in epigenetic
modication and telomere-telomerase pathways can induce
mutations of suppressor genes []. e suppression of genes
alters somatic maintenance and repair leading to altered
proliferative control of gene expression, polymorphism, and
contact inhibition regulation and telomere shortening [].
e activation or progressive transformation of cancer cells
is also augmented by inactivated or mutated suppressor gene
pathways. Moreover, abnormal DNA methylation of CpG and
various enzymatic pathways inuence inammation and car-
cinogenesis []. e theory of modus operandi for patho-
genesis of vitiligo, a multifactorial polygenic disorder, also
moves around autoimmune, cytotoxic, oxidant-antioxidant,
and neural mechanisms [].
Lipid originated atherosclerosis also involves endoplas-
mic reticulum (ER) stress in macrophages. ER stress mitiga-
tion with a chemical chaperone leads to massive protection
against macrophage associated lipotoxic death. is causes
prevention of expression of macrophage-fatty acid-binding
protein- (aP). ere is also an increase in the phospholipid
(rich in monounsaturated fatty acid as well as bioactive lipids)
productionduetoabsenceoflipidchaperones.ereis
alsofurtherimpactofaPonmetabolismoflipidinthe
macrophages. e stress response in ER is also mediated
by key lipogenic enzymes upregulation in the liver [].
Similarly, OS due to alcohol toxicity triggers the release of
certain cytokines to activate collagen gene expression in liver
stellate cells leading to progression of liver brosis [].
BioMed Research International
T : Dierent classes of prooxidants and their common mechanism for development of oxidative stress.
Sl.
number
Class Examples Mechanism
() Drugs
Common over-the-counter drug
like analgesic (paracetamol) or
anticancerous drug
(methotrexate)
ROS generation leading to alterations in macromolecules which
nally can fatally damage the tissues mainly liver and kidney
()
Transition
metals
Magnesium, iron, copper, zinc,
and so forth
ese metals induce Fenton reaction and Haber-Weiss reaction
leading to generation of excessive ROS. Chronic magnesium is a
classicprooxidantdisease.eothercanbehemochromatosis
duetohighironlevelsorWilsondiseaseduetocopper
() Pesticide BHC, DDT, and so forth
Stimulation of free radical production, induction of lipid
peroxidation, alterations in antioxidant enzymes and the
glutathione redox system
() Physical exercise Running, weight liing
Relaxationcontraction of muscle involves production of ROS.
Rigorous exercise leads to excessive ROS
() Mental anxiety Tension, apprehension
Imbalance in the redox system plays a role in
neuroinammation and neurodegeneration, mitochondrial
dysfunction, altered neuronal signaling, and inhibition of
neurogenesis
() Pathophysiology Local ischemia Gives rise to increased ROS generation
()
Environmental
factor
Extreme weather (heat, cold,
thunderstorm)
During adaptation, mitochondrial membrane uidity decreases
which may disrupt the transfer of electrons, thereby increasing
the production of ROS
() Antioxidants
Ascorbic acid, vitamin E,
polyphenols
Act as prooxidant under certain circumstances, for example,
heavy metals
14. Proteomic Evidences of
the Stress-Disease Development
Interrelationship
Oxidative damages mediated by free radicals lead to protein
modication and ultimately cellular damages and disease
pathogenesis. ere lies equilibrium between the antioxi-
dants level and cellular prooxidants under normal conditions
of physiology. But when there is occurrence of environ-
mental factors or stressors, there exists an imbalance in the
homeostasis which is in favour of prooxidants. is results
in the oxidative stress phenomenon []. An antioxidant
deciency can also result in oxidative stress leading to
generation of reactive oxygen or nitrogen species in excess
[]. e S proteosome oen removes the proteins that
are damaged oxidatively. e proteosome systemic defects
result in increased levels of proteins that are oxidatively
modied along with development of neurotoxicity [–].
For instance, oxidation of nucleic acid and protein along with
peroxidation of lipid is highest and most severe in the hip-
pocampus of the brain, which is involved in the processing of
memory along with cognitive function [, ]. Such study
is strongly suggestive of the fact that a primary event in the
Alzheimer’s disease development is an oxidative stress [].
ese alterations and modications in proteomes elicit anti-
bodies formation in diseases like rheumatoid arthritis (RA),
diabetes mellitus (DM), and systemic lupus erythematosus
[].
15. Assessment of Oxidative Stress
e concentration of dierent reductant-oxidant markers is
considered an important parameter for assessing the proox-
idant status in the body tissues []. Several indicators of in
vivo redox status are available, including the ratios of GSH to
GSSG, NADPH to NAPD
−
, and NADH to NAD
−
,aswellas
the balance between reduced and oxidized thioredoxin. Out
of these redox pairs, the GSH-to-GSSG ratio is thought to be
oneofmostabundantredoxbuersystemsinmammalian
species []. A decrease in this ratio indicates a relative shift
from a reduced to an oxidized form of GSH, suggesting the
presence of oxidative stress at the cellular or tissue level.
In aging, an age-related shi from a redox balance to an
oxidative prole is observed which results in a reduced ability
to buer ROS that are generated in both “normal” conditions
andattimesofchallenge[, , , ]. us, a progressive
shi in cellular redox status could potentially be one of the
primary molecular mechanisms contributing to the aging
process and accompanying functional declines.
16. Prooxidants
Prooxidant refers to any endobiotic or xenobiotic that induces
oxidative stress either by generation of ROS or by inhibiting
antioxidant systems. It can include all reactive, free radical
containing molecules in cells or tissues. Prooxidants may be
classied into several categories (Table ).
BioMed Research International
Some of the popular and well known antioxidant avon-
oids have been reported to act as prooxidant also when a
transition metal is available []. ese have been found to
be mutagenic in vitro [, –]. e antioxidant activ-
ities and the copper-initiated prooxidant activities of these
avonoids depend on their structures. e OH substitution
is necessary for the antioxidant activity of a avonoid [].
Flavone and avanone, which have no OH substitutions
andwhichprovidethebasicchemicalstructuresforthe
avonoids, show neither antioxidant activities nor copper-
initiated prooxidant activities. e copper initiated prooxi-
dant activity of a avonoid also depends on the number of
free OH substitutions on its structure []. e more the
OH substitutions, the stronger the prooxidant activity. O-
Methylation and probably also other O-modications of the
avonoid OH substitutions inactivate both the antioxidant
and the prooxidant activities of the avonoids.
e antioxidant activity of quercetin has been found to
be better than its monoglucosides in a test system wherein
lipid peroxidation was facilitated by aqueous oxygen radicals
[]. Luteolin has also proved to be a signicantly stronger
antioxidant than its two glycosides [].
Flavonoids generally occur in foods as O-glycosides with
sugars bound at the C position. Methylation or glycosidic
modication of the OH substitutions leads to inactivation of
transition metal-initiated prooxidant activity of a avonoid.
e protection provided by fruits and vegetables against
diseases, including cancer and cardiovascular diseases,
has been attributed to the various antioxidants, including
avonoids, contained in these foods. Flavonoids, such as
quercetin and kaempferol, induce nuclear DNA damage and
lipid peroxidation in the presence of transition metals. e
in vivo copper-initiated prooxidant actions of avonoids and
other antioxidants including ascorbic acid and 𝛼-tocopherol
are generally not considered signicant, as copper ion will
be largely sequestered in the tissues, except in case of metal
toxicity. e prevention of iron-induced lipid peroxidation in
hepatocytes by some avonoids including quercetin is well
known [, ].
17. Antioxidants
To counteract the harmful eects taking place in the cell,
system has evolved itself with some strategies like prevention
of damage, repair mechanism to alleviate the oxidative dam-
ages, physical protection mechanism against damage, and the
nal most important is the antioxidant defense mechanisms.
Basedontheoxidativestressrelatedfreeradicaltheory,the
antioxidants are the rst line of choice to take care of the
stress. Endogenous antioxidant defenses include a network
of compartmentalized antioxidant enzymic and nonenzymic
molecules that are usually distributed within the cytoplasm
and various cell organelles. In eukaryotic organisms, several
ubiquitous primary antioxidant enzymes, such as SOD, cata-
lase, and several peroxidases catalyze a complex cascade of
reactions to convert ROS to more stable molecules, such as
water and O
2
. Besides the primary antioxidant enzymes, a
largenumberofsecondaryenzymesactincloseassociation
with small molecular-weight antioxidants to form redox
cycles that provide necessary cofactors for primary antioxi-
dant enzyme functions. Small molecular-weight nonenzymic
antioxidants (e.g., GSH, NADPH, thioredoxin, vitamins E
and C, and trace metals, such as selenium) also function
as direct scavengers of ROS. ese enzymatic and nonenzy-
matic antioxidant systems are necessary for sustaining life
by maintaining a delicate intracellular redox balance and
minimizing undesirable cellular damage caused by ROS [].
Endogenous and exogenous antioxidants include some high
molecular weight (SOD, GPx, Catalse, albumin, transferring,
metallothionein) and some low molecular weight substances
(uric acid, ascorbic acid, lipoic acid, glutathione, ubiquinol,
tocopherol/vitamin E, avonoids).
Natural food-derived components have received great
attention in the last two decades, and several biological activ-
ities showing promising anti-inammatory, antioxidant, and
anti-apoptotic-modulatory potential have been identied [,
, ]. Flavonoids comprise a large heterogeneous group
of benzopyran derivatives present in fruits, vegetables, and
herbs. ey are secondary plant metabolites and more than
molecular species have been described. Flavonoids exert
a positive health eect in cancer and neurodegenerative dis-
orders, owing to their free radical-scavenging activities [].
One of the most abundant natural avonoids present in a
large number of fruits and vegetables is quercetin (,,,
,
,
pentahydroxyavone) which prevents oxidative injury and
cell death by scavenging free radicals, donating hydrogen
compound, quenching singlet oxygen, and preventing lipid
peroxidation or chelating metal ions []. Red wines also
have a high content of phenolic substances including catechin
and resveratrol [], which are responsible for the antiox-
idant action, anti-inammatory, antiatherogenic property,
oestrogenic growth-promoting eect, and immunomodula-
tion. Recently, the potential of resveratrol as an antiaging
agent in treating age-related human diseases has also been
proven.
18. Interplay of Antioxidative and
Prooxidative Role of Antioxidants
Ascorbic acid has both antioxidant and prooxidant eects,
depending upon the dose []. Low electron potential and
resonance stability of ascorbate and the ascorbyl radical
haveenabledascorbicacidtoenjoytheprivilegeasan
antioxidant [, ]. In ascorbic acid alone treated rats,
ascorbic acid has been found to act as a CYP inhibitor.
Similar activity has also been observed for other antioxidants-
quercetin [] and chitosan oligosaccahrides [], which
may act as potential CYP inhibitors. Specically, Phase
I genes of xenobiotic biotransformation, namely, CYPA,
CYPE, and CYPC, have been previously reported to be
downregulated in female rats in the presence of a well known
antioxidant, resveratrol []. e antioxidant and prooxidant
role of ascorbic acid in low ( and mg/kg body weight)
and high doses ( mg/kg body weight), respectively, has
also been reported in case of ischemia induced oxidative
stress []. e in vivo prooxidant/antioxidant activity of
betacarotene and lycopene has also been found to depend
on their interaction with biological membranes and the other
BioMed Research International
co-antioxidant molecules like vitamin C or E []. At higher
oxygen tension, carotenoids tend to lose their eectiveness as
antioxidants. In a turn around to this, the prooxidant eect
oflowlevelsoftocopherolisevidentatlowoxygentension
[].
Moreover, 𝛼-lipoic acid exerts a protective eect on the
kidney of diabetic rats but a prooxidant eect in nondiabetic
animals []. e prooxidant eects have been attributed to
dehydroxylipoic acid (DHLA), the reduced metabolite of 𝛼-
lipoic acid owing to its ability to reduce iron, initiate reactive
sulfur-containing radicals, and thus damage proteins such
as alpha -antiproteinase and creatine kinase playing a role
in renal homeostasis []. An increase in 𝛼-lipoic acid and
DHLA-induced mitochondrial and submitochondrial O
2
−
production in rat liver []andNADPH-inducedO
2
−
and
expression of pphox in the nondiabetic kidney has also
been observed [].
Withaferins, the pharmacological molecules of Withania
somnifera L. Dunal (commonly known as Ashwagandha),
have been used safely for thousands of years in Ayurvedic
medicine practice for the treatment of various disorders [–
]. In the last – years, numerous reports revealed the
proapoptotic eects of withaferins [–]. Withaferins
can also initiate apoptosis and prevent metastasis of breast
carcinomas under the inuence of interleukin--induced
activation and transcription [] and prove to be of tremen-
dous clinical benet to human patients. In accordance to
these reports, recently withaferin-induced apoptosis has been
found to be mediated by ROS production due to inhibition of
mitochondrial respiration [].
Use of ginseng and Eleutherococcus senticosus is thought
to increase the body’s capacity to tolerate external stresses,
leading to increased physical or mental performance [].
Although an extensive literature documenting adaptogenic
eects in laboratory animal systems exists, results from
human clinical studies are conicting and variable [–
]. However, there is evidence that extracts of ginseng and
Eleutherococcus sp. can have an immunostimulatory eect in
humans, and this may contribute to the adaptogen or tonic
eects of these plants [, ]. From laboratory studies,
it has been suggested that the pharmacological target sites
for these compounds involve the hypothalamus-pituitary-
adrenal axis due to the observed eects upon serum levels
of adrenocorticotropic hormone and corticosterone [].
However, it should also be noted that the overall eects of the
ginsenosides can be quite complex due to their potential for
multiple actions even within a single tissue [].
e avonoids present in ginkgo extracts exist primarily
as glycosylated derivatives of kaempferol and quercetin [–
]. ese avonoid glycosides have been shown to be
extremely eective free radical scavengers [, , ]. It is
believed that the collective action of these components leads
to a reduction in damage and improved functioning of the
blood vessels [, ].
Depending on the type and level of ROS and RNS, dura-
tion of exposure, antioxidant status of tissues, exposure to free
radicals and their metabolites leads to dierent responses—
increased proliferation, interrupted cell cycle, apoptosis, or
necrosis []. A typical example is a hydrophilic antioxidant,
ascorbic acid (vitamin C). Ascorbic acid reacts with free
radicals to produce semidehydro- or dehydroascorbic acids
(DHA). DHA is then regenerated by antioxidant enzymes
present in the organism (semidehydroascorbic acid reductase
and dehydroascorbic acid reductase) back to the functional
ascorbate. In the presence of ions of transition metals, ascor-
bic acid reduces them and it gets oxidized to DHA. Hydrogen
peroxide formed in the reaction further reacts with reduced
metal ions leading to generation of hydroxyl radical through
Fenton type reaction. Iron ions practically never occur in the
free form in the tissues; therefore, the occurrence of Fenton
type reaction in vivo is not likely.
Recently, toxicity of ascorbic acid has also been attributed
to its autooxidation. Ascorbic acid can be oxidized in the
extracellular environment in the presence of metal ions to
dehydroascorbic acid, which is transported into the cell
through the glucose transporter (GLUT). Here it is reduced
back to ascorbate. is movement of electrons changes the
redox state of the cell inuencing gene expression.
19. Conclusions
Oxidative stress is nothing but the imbalance between oxi-
dants and antioxidants in favor of the oxidants which are
formed as a normal product of aerobic metabolism but
during pathophysiological conditions can be produced at an
elevated rate. Both enzymatic and nonenzymatic strategies
are involved in antioxidant defense, and antioxidant ecacy
of any molecule depends on the cooxidant. Well proven free
radical scavengers can be prooxidant unless linked to a radical
sink.Moreover,asthefreeradicalsshareaphysiologicalas
well as pathological role in the body, the same antioxidant
molecule just due to its free radical scavenging activity may
act as disease promoter, by neutralizing the physiologically
desired ROS molecules, and as disease alleviator by removing
the excessive levels of ROS species. e importance of several
vitamins like vitamin A and tocopherols as well as carotenes,
oxycarotenoids, and ubiquinols in their lipid phase has been
understood in recent years. Low molecular mass antioxidant
molecules that include nuclear as well as mitochondrial
matrices, extracellular uids, and so forth have been studied
vividly to understand how they accelerate the body defense
signicantly. Protection from the inuence of oxidants being
an important issue has become the centre of attraction of
the scientists and various research groups in recent years to
understand the mechanism of action of various antioxidants
present in herbs as well as fruits and vegetables that can act
asantiagingagentsaswell.erehasbeeneverincreasing
knowledge in the role of oxygen derived prooxidants and
antioxidants that play crucial role in both normal metabolism
and several clinical disease states. Advances in the eld
of biochemistry including enzymology have led to the use
of various enzymes as well as endogenous and exogenous
antioxidants having low molecular weight that can inhibit
the harmful eect of oxidants. Still much research works are
needed to understand the antioxidant status of any organ that
is susceptible to oxidative stress induced damage particularly
the involvement of genetic codes and gene protein inter-
action. Understanding of genetic alterations and molecular
BioMed Research International
mechanism is certainly helping out to reveal the interaction
of free radicals and their role in proteomics, genomics and
disease development process. Moreover, the prooxidant or
antioxidant behavior of the universally accepted antioxidant
molecules is now duly expressed in term of dependence upon
the actual molecular conditions prevailing in the tissues.
Nevertheless, other environmental factors like oxygen
tension, concentration of transition metals along with their
redox status will also be a deciding factor. us, it can be con-
cluded that a thorough knowledge of biochemistry and gen-
eral chemistry will help the researchers to explore more the
interplay between oxidative stress, prooxidants, and antioxi-
dants.
Conflict of Interests
e authors declare that there is no conict of interests
regarding the publication of this paper.
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