The Incriminating Role of Reactive Oxygen Species in Idiopathic Male Infertility: An Evidence Based Evaluation
The male factor is considered a major contributory factor to infertility. Apart from the conventional causes for male infertility such as varicocoele, cryptorchidism, infections, obstructive lesions, cystic fibrosis, trauma and tumours, a new and important cause has been identified as being responsible for the so-called idiopathic male infertility: oxidative stress. Oxidative Stress (OS) is a condition that occurs when the production of Reactive Oxygen Species (ROS) overwhelms the antioxidant defense produced against them. In male reproductive pathological conditions, the OS significantly impairs spermatogenesis and sperm function, which may lead to male infertility. Reactive Oxygen Species (ROS) known as free radicals are oxidizing agents generated as a result of metabolism of oxygen and have at least one unpaired electron that make them very reactive species. Spermatozoa generate Reactive Oxygen Species (ROS) in physiological amounts, which play a role in sperm functions during sperm capacitation, Acrosome Reaction (AR) and oocyte fusion, but they need to be controlled and their concentrations maintained at a level that is not deleterious to the cells. Administration of antioxidants in patients with male factor infertility has begun to attract considerable interest. The main difficulty of such an approach is our incomplete understanding of the role of free radicals in normal and abnormal sperm function leading to male infertility. The purpose of the present review is to address the relationship between ROS and idiopathic male factor infertility.
Received: January 28, 2010;
Accepted: March 07, 2010;
Published: June 14, 2010
Since the first appearance of humans on earth, infertility has been one of
the most controversial medical and social issues. Infertility is the inability
of a sexually active, non-contracepting couple to achieve pregnancy in one year
(World Health Organization, 2000). Infertility is a major
clinical problem, affecting people medically and psychosocially. Infertility
affects approximately 15% of all couples trying to conceive. Male causes for
infertility are found in 50% of involuntarily childless couples (Rowe,
2006). Reduced male fertility can be the result of congenital and acquired
urogenital abnormalities, infections of the genital tract, increased scrotal
temperature (varicocele), endocrine disturbances, genetic abnormalities and
immunological factors (World Health Organization, 2000).
No causal factor is found in 60-75% of cases (idiopathic male infertility).
Infertility is the main complication arising in male patients with high levels
of OS, apoptosis or sperm DNA damage. Although techniques like Intracytoplasmic
Sperm Injection (ICSI) offer considerable promise to such male factor patients,
the indiscriminate use of such assisted fertility treatments, especially when
the etiology of sperm dysfunction is poorly understood is not warranted. Idiopathic
male factor infertility has been linked with oxidative stress by several research
groups (Said et al., 2004; Kao
et al., 2007; Joffe, 2010). Oxidative stress
originates from the excessive generation of Reactive Oxygen Species (ROS) by
the spermatozoa and results in the peroxidation of unsaturated fatty acids in
the sperm plasma membrane. Oxidative stress is thought to contribute to the
development of a wide range of diseases including Alzheimers disease (Christen,
2000; Nunomura et al., 2006), Parkinsons
disease (Wood-Kaczmar et al., 2006), the pathologies
caused by diabetes (Davi et al., 2005), rheumatoid
arthritis (Hitchon, 2004), neurodegeneration in motor
neurone disease (Cookson and Shaw, 1999; Rao
and Balachandran, 2002), cancer (Valko et al.,
2004, 2007; Nakabeppu et
al., 2006), obesity (Vincent, 2007; Gomez-Cabera,
2008) and cataract (Berthood and Beyer, 2009).
Several forms of sperm DNA damage are caused by ROS, e.g., chromatin cross-linking,
chromosome deletion, DNA strand breaks and base oxidation. Moreover, ROS are
important in mediating apoptosis by inducing cytochrome c and caspases 9 and
3, which in turn result in a high frequency of single- and doublestranded DNA
strand breaks (Said et al., 2004). Human spermatozoa
exhibit a capacity to generate ROS and initiate peroxidation of the unsaturated
fatty acids in the sperm plasma membrane, which plays a key role in the etiology
of male infertility. The short half-life and limited diffusion of these molecules
is consistent with their physiologic role in key biological events such as acrosome
reaction and hyperactivation. The intrinsic reactivity of these metabolites
in peroxidative damage induced by ROS, particularly H2O2
and the superoxide anion, has been proposed as a major cause of defective sperm
function in cases of male infertility. Understanding of how such conditions
affect sperm function will help in designing new and effective treatment strategies.
Men with idiopathic infertility generally present with significantly higher
seminal ROS levels and lower antioxidant properties than healthy controls (Pasqualotto
et al., 2001). Therefore, it appears that the presence of OS in infertile
normozoospermic men may be the cause behind previously unexplained cases of
infertility. Similarly, sperm DNA damage analysis may reveal hidden sperm DNA
abnormalities in infertile men with normal standard sperm values who were diagnosed
with idiopathic infertility. The increase in sperm DNA damage in these patients
may be partly related to high levels of seminal OS. Finally and importantly,
some conditions may pass unnoticed but still affect the sperm genomic integrity.
Free radicals: origin and oxidative stress:
By definition, a free radical is any chemical compound with one or more
unpaired electrons. The assumption that free radicals can influence male fertility
has received substantial scientific support (Saalu et
al., 2009a, b, 2010).
The free radicals that have been associated with infertility are oxygen and
oxygen-derived oxidants, namely, the superoxide anion (O2¯),
hydrogen peroxide (H2O2), peroxyl radicals (ROO-) and
hydroxyl radicals (OH¯) (Agarwal et al., 2005).
These oxidants are widely known as Reactive Oxygen Species (ROS) and, due to
unpaired electron(s) tend to strongly react with other chemical compounds (Attaran
et al., 2000). The nitrogen derived free radical Nitric Oxide (NO.)
and peroxynitrite anion (ONOO-) also appear to play a significant role in the
reproduction and fertilization. The ultimate effects of (NO.) depend upon its
concentration and interactions with hydrogen peroxide. Peroxynitrite (oxoperoxonitrate)
anion may be formed in vivo from superoxide and nitric oxide and actively
reacts with glutathione, cysteine, deoxyribose and other thiols/thioethers (Koppenol
et al., 1992). This can form a strongly nitrating species in the
presence of metal ions or complexes.
Free radicals seek to participate in chemical reactions that relieve them of
their unpaired electron, resulting in the oxidation of lipids in membranes,
amino acids in proteins and carbohydrates within nucleic acids (Ochsendorf,
1999). The terms free radical and ROS are commonly used in an interchangeable
manner, despite the fact that not all ROS are free radicals (Cheeseman
and Slater, 1993). An expanding body of evidence now supports a role for
oxidative stress as a significant cause of male infertility. However, despite
being a common pathology in infertile men, oxidative stress is ignored by many
infertility practitioners. The currently popular response of resorting to mechanical
techniques such as IVF-ICSI in all cases of male factor infertility is unlikely
to be best practice since ROS damaged paternal DNA will result in
poor quality blastocysts, less than optimal pregnancy rates and an increase
in miscarriage. At present there are over 30 assays of oxidative stress (Ochsendorf,
1999), broadly divided into three different types (Direct methods, Indirect
methods and routine semen analysis). In many complex biological systems including
semen, the true ROS status leading to oxidative stress reflects a relative balance
between the ROS-generated and ROS-scavenged. The measurement of the rate of
ROS generation by luminal induced chemiluminescence has been the most common
method for quantitating ROS. Although this rate measurement is dynamic, it may
not accurately reflect the status of potential sperm damaging ROS. For such
evaluations, the amount of ROS-detected, rather than the ROS-generated will
represent a more physiological assessment of oxidative stress (Iwasaki
and Gagnon, 1992).
Sources of ROS:
There are several sources of reactive oxygen species in the human body.
Production of superoxide in mitochondria is a by-product of the function of
the respiratory chain (Balaban et al., 2005).
The first known example of regulated generation of Reactive Oxygen Species (ROS)
in mammalian cells was through the respiratory burst of phagocytic cells by
Nicotinamide Adenine Dinucleotide Phosphate (NADPH) oxidase. This enzyme complex
uses electrons derived from intracellular NADPH to generate superoxide anion,
which is further processed to form hydrogen peroxide and other ROS-providing
host defense against bacterial and fungal pathogens (Quinn
and Gauss, 2004). The essential role of the phagocytic oxidase in host defense
is well illustrated by the serious phenotype of Chronic Granulomatous Disease
(CGD), in which susceptibility to infections develops in the absence of a functional
phagocytic oxidase (Geiszt et al., 2001). Virtually
every human ejaculate is considered to be contaminated with potential sources
of ROS as human semen is known to contain different types of cells, such as
mature and immature spermatozoa, round cells from different stages of spermatogenesis,
leukocytes and epithelial cells. Of these different cell types, leukocytes and
spermatozoa have been shown to be the two main sources of ROS (Garrido
et al., 2004).
Physiological role of ROS:
Low levels of ROS have been shown to be essential for fertilization, acrosome
reaction, hyperactivation, motility and capacitation (Griveau
and Le Lannou, 1997; Agarwal et al., 2004).
Capacitation has been shown to occur in the female genital tract, a process
carried out to prepare the spermatozoa for interaction with the oocyte. During
this process, the levels of intracellular calcium, ROS and tyrosine kinase all
increase, leading to an increase in cyclic adenosine monophosphate (cAMP). This
increase in cAMP facilitates hyperactivation of spermatozoa, a condition in
which they are highly motile (Aitken, 1995). However,
only capacitated spermatozoa exhibit hyperactivated motility and undergo a physiological
acrosome reaction, thereby acquiring the ability to fertilize (De
Lamirande et al., 1997).
Consequences of excessive generation of ROS:
Excessive ROS production by immature, morphologically abnormal spermatozoa
with cytoplasmicresidues such as those confronted in teratozoospermic semen
specimens may induce oxidative damage of mature spermatozoa during sperm migration
from the seminiferous tubules to the epididymis and may be an important cause
of male infertility (Sikka, 2004). ROS is involved in
many physiological functions of human spermatozoa, their excess production in
semen especially during leukocytospermia can overwhelm the antioxidant defense
mechanisms of spermatozoa and seminal plasma resulting in oxidative stress.
Spermatozoa are also particularly susceptible to the damage induced by excessive
ROS because their plasma membranes contain large quantities of polyunsaturated
fatty acids (PUFA), which readily experience lipid peroxidation by ROS, resulting
in a loss of membrane integrity (Halliwell, 1990; Buettner,
Oxidative stress and apoptosis:
Apoptosis is a non-inflammatory response to tissue damage characterized
by a series of morphological and biochemical changes (Wyllie
et al., 1980; Sinha-Hikim and Swerdloff, 1999;
Sakkas et al., 1999a, b,
2002; Shen et al., 2002;
Said et al., 2004; Grunewald
et al., 2005). Apoptosis during spermatogenesis has been assessed,
discussed and supported in several studies (Hikim et
al., 1998; Print and Loveland, 2000) and has
been associated with male infertility (Lin et al.,
1997; Hikim et al., 1998; Jurisicova
et al., 1999).
Apoptosis appears to be strictly regulated by extrinsic and intrinsic factors
and can be triggered by a wide variety of stimuli. Apoptosis in sperm may also
be initiated by ROS-independent pathways involving the cell surface receptor
called as Fas or CD 95. Fas is a type I membrane protein that mediates apoptosis.
When Fas ligand or anti-Fas antibody binds to Fas, apoptosis occurs (Lee
et al., 1999). Moustafa et al. (2004)
determined that infertile patients had high ROS levels in their seminal plasma
and higher percentage of apoptosis than normal healthy donors. When the molecular
framework of apoptosis is identified, specific apoptotic inhibitors may have
a role in promoting germ-cell survival.
Lipid peroxidation (LPO) is the most extensively studied manifestation of
oxygen activation in biology. LPO is broadly defined as oxidative deterioration
of PUFA which are fatty acids that contain more than two carbon double bonds
(Halliwell, 1990). Most membrane PUFA contain unconjugated
double bonds that are separated by methylene groups. The presence of a double
bond adjacent to a methylene group makes the methylene carbon-hydrogen bond
weaker and as a result, the hydrogen is more susceptible to abstraction. Once
this abstraction has occurred, the radical produced is stabilized by the rearrangement
of double bonds. The PUFA rearranges to form a conjugated diene radical that
subsequently can be oxidized (Aitken et al., 1989,
1993; Aitken and Fisher, 1994;
Aitken, 1995; Alvarez and Storey,
1995; Griveau et al., 1995; Kodama
et al., 1996; Ochsendorf, 1999). The most
common types of LPO are: (1) nonenzymatic membrane LPO and (2) enzymatic (NADPH
and ADP dependent) LPO. The enzymatic reaction involves NADPH cytochrome P-450
reductase and proceeds via an ADP-Fe3+O2¯ (perferryl)
complex (Ernster, 1993; Oborna et
al., 2010). Mammalian spermatozoa membranes are very sensitive to free
radical induced damage mediated by lipid peroxidation, as they are rich in polyunsaturated
fatty acids. In spermatozoa, production of malondialdehyde (MDA), an end product
of LPO induced by ferrous ion promoters, has been reported by Darley-Usmar
et al. (1995). Formation of MDA can be assayed by the thiobarbituric
acid (TBA) reaction which is a simple and useful diagnostic tool for the measurement
of LPO for in vitro and in vivo systems (Taourel
et al., 1992). Lipid peroxidation caused by low levels of ROS leads
to modification of the plasma membrane, thus facilitating sperm-oocyte adhesion
(Kodama et al., 1996).
ROS and motility:
Sperm count and sperm motility are the first and most important predictors
of fertility potential.
The underlying pathology behind free radicals ability to reduce sperm motility
was first reported by Jones et al.(1979).
They reported that ROS-induced peroxidation of the sperm membrane decreasing
its flexibility and therefore tail motion. Sperm membranes are vulnerable to
this type of damage as they contain large amounts of unsaturated fatty acids.
Direct ROS damage to mitochondria, decreasing energy availability, may also
impede sperm motility (Lamirande and Gagnon, 1992; De
Lamirande et al., 1997, 1998). The link between
ROS and reduced motility may be due to a cascade of events that results in a
decrease in axonemal protein phosphorylation and sperm immobilization, both
of which are associated with a reduction in membrane fluidity that is necessary
for sperm oocyte fusion (De Lamirande and Gagnon, 1995).
The mechanism behind this effect is ROS induced lipid peroxidation of sperm
plasma membrane (Aitken and Baker, 2006), which affects
membrane fluidity and mobility. In addition ROS may also affect the sperm axoneme,
inhibit mitochondrial function and affect the synthesis of DNA, RNA and proteins
(Lamirande and Gagnon, 1992). Sperm cell dysfunction,
a result of ROS damage, is dependent on the nature, amount and duration of exposure
to ROS. The extent of ROS damage is also dependent upon surrounding environmental
factors such as oxygen tension and temperature as well as the concentrations
of molecular components such as ions, proteins and ROS scavengers (Agarwal
and Saleh, 2002).
OS and DNA damage:
Sperm genetic material is structured in a special manner that keeps the
nuclear chromatin highly stable and compact. The normal DNA structure is capable
of decondensation at appropriate time transferring the packaged genetic information
to the egg without defects in the fertilization process. The cause of DNA damage
in sperm can be attributed to various pathological conditions including cancer
(ODonovan, 2005), varicocele (Saleh
et al., 2003), high prolonged fever (Evenson
et al., 2000), advanced age (Singh et al.,
2003) or leukocytospermia (Erenpreiss et al.,
2002). Also a variety of environmental conditions can be involved as radiation
(Aitken et al., 2005), air pollution, smoking
(Said et al., 2005), pesticides, chemicals, heat
and ART prep protocols (Potts et al., 1999; Aitken
et al., 2005; Bennetts and Aitken, 2005;
Aitken and De Iuliis, 2010). Abnormal sperm morphology
has been reported to be associated with high sperm DNA fragmentation in infertile
men (Nicopoullos et al., 2008). The oxidative
damage to mitochondrial DNA is well known to occur in all aerobic cells, which
are rich in mitochondria and this, may include spermatozoa. Two factors protect
the sperm deoxyribonucleic acid (DNA) from oxidative insult: the characteristic
tight packing of the DNA and the antioxidants present in the seminal plasma
(Twigg et al., 1998). ROS attacks the fluidity
of the sperm plasma membrane and the integrity of DNA in the sperm nucleus.
ROS induced DNA damage accelerate the germ cell apoptosis. Unfortunately spermatozoa
are unable to repair the damage induced by excessive ROS as they lack the cytoplasmic
enzymes required to accomplish the repair. Free radicals have the ability to
directly damage sperm DNA by attacking the purine and pyrimidine bases and the
deoxyribose backbone. Normally, sperm DNA is tightly packaged by protamines
protecting it from free radical attack. Oxidative stress also is associated
with high frequencies of single- and double-strand DNA breaks (Duru
et al., 2000; Aitken and Krause, 2001). ROS
also can cause various types of gene mutations such as point mutations and polymorphism,
resulting in decreased semen quality (Spiropoulos et
al., 2002; Sharma et al., 2004; Thomson
et al., 2009). However, infertile men often exhibit deficient protamination,
leaving the sperm DNA particularly vulnerable to ROS attack (Oliva,
2006). Early detection and prompt antioxidant therapy can prevent ROS induced
DNA damage. This has far reaching impact if such men opt for assisted reproductive
technology (ART)/in vitro fertilization. The assessment of sperm DNA
damage appears to be a potential tool for evaluating semen samples prior to
their use in ART as besides impairment of fertility DNA damage is likely to
increase the transmission of genetic diseases during the assisted reproductive
procedures. In addition, the redox status of human spermatozoa is likely to
affect phosphorylation and ATP generation with a profound influence on its fertilizing
potential (Aitken and Baker, 2003).
Smoking, oxidative stress and infertility:
Tobacco smoke consists of approximately 4,000 compounds such as alkaloids, nitrosamines
and inorganic molecules and many of these substances are reactive oxygen or
nitrogen species. Significant positive association has been reported between
active smoking and sperm DNA fragmentation (Sun et al.,
1997), as well as axonemal damage (Zoas et al.,
1998) and decreased sperm count (Vine et al.,
In a prospective study, Saleh et al. (2002)
compared infertile men who smoked cigarettes with nonsmoker infertile men. Smoking
was associated with a significant increase (approximately 48%) in seminal leukocyte
concentrations, a 107% ROS level increase and a 10 point decrease in ROS-TAC
score. The authors concluded that infertile men who smoke cigarettes present
higher seminal OS levels than infertile nonsmokers, possibly due to significant
increase in leukocyte concentration in their semen. The link between cigarette
smoking and high seminal ROS can be attributed in part to the associated increase
in seminal leukocytes. Indeed, smoking can increase leukocyte concentrations
by as much as 48% (Saleh et al., 2002). Smokers
have decreased levels of seminal plasma antioxidants such as Vitamin E (Fraga
et al., 1996) and Vitamin C (Mostafa et al.,
2006), placing their sperm at additional risk of oxidative damage. This
has been confirmed by the finding of a significant increase in levels of 8-OHdG
within smoker's seminal plasma (Fraga et al., 1996).
In a study carried out on 655 smokers and 1131 non smokers, cigarette smoking
was associated with a significant decrease in sperm density (-15.3%), total
sperm count (-17.5%) and total number of motile sperm (-16.6%) (Kunzle
et al., 2003). Thus, smoking does, in fact, affect the quality and
quantity of sperm present within a male.
Varicocele and ROS:
Varicocele has long been implicated as a major cause of male infertility
(Schlesinger et al., 1994; Benoff
and Gilbert, 2001; Hauser et al., 2001),
but the pathophysiology remains unclear. Clinical varicocele is found in about
15% of the general population including adolescents and adults: in 35% of men
with primary infertility and in up to 80% of men with secondary infertility
(World Health Organization, 1992; Belloli
et al., 1993; Pfeiffer et al., 2006).
Oxidative stress is now widely believed to be the principal underlying pathology
linking varicocele with male infertility (Barbieri et
al., 1999; Hendin et al., 1999; Saleh
et al., 2003; Nallella et al., 2004;Smith
et al., 2006; Ishikawa et al., 2007;
Smith et al., 2007; Saalu
et al., 2008). It appears that infertile men with varicocele have
significantly greater spermatozoal DNA damage, which can be related to high
levels of OS in semen (Saleh et al., 2003). Levels
of ROS positively correlate with the degree of varicocele and are expected to
decrease after varicocelectomy (Barbieri et al.,
1999). According to one metaanalysis, varicocele patients as compared with
normal sperm donors have significantly increased oxidative stress parameters
such as ROS and lipid peroxidation as well as significantly decreased antioxidant
concentrations. The exact pathways by which a varicocele damages spermatogenesis
and sperm quality remain poorly understood.
Role of ROS in assisted reproductive technique:
By means of in vitro fertilization (IVF), men with very low sperm
counts can be given a reasonable chance of paternity. However, this also increases
the possibility of passing genetic abnormalities on to the next generation because
the sperm of infertile men shows an increase in aneuploidy, other genetic abnormalities
and DNA damage. Although there are prospects for screening of sperm (Griffin
and Finch, 2005), current routine clinical practice is based on the screening
of peripheral blood samples. The use of Assisted Reproductive Technologies (ART)
has the potential to exacerbate sperm oxidative stress. During IVF and intrauterine
insemination (IUI) treatment semen is centrifuged to separate sperm from seminal
plasma. This exacerbates oxidative stress as centrifugation increases sperm
ROS production many fold (Iwasaki and Gagnon, 1992;
Shekarriz et al., 1995a, b)
Spermatozoa selected for ART usually originate from an environment experiencing
oxidative stress and a high percentage of these sperm may have damaged DNA (Kodama
et al., 1997). When IUI or IVF is used; such damage may not be a
cause of concern because the collateral peroxidative damage to the sperm plasma
membrane ensures that fertilization cannot occur with a DNA-damaged sperm.
When Intracytoplasmic Sperm Injection (ICSI) is used, this natural selection
barrier is bypassed and a spermatozoon with damaged DNA is directly injected
into the oocyte (Lamirande and Gagnon, 1992; Aitken,
1999). Sperm DNA damage is critical in the context of success of assisted
reproductive techniques (Sakkas et al., 2003;
Sharma et al., 2004). Advances in ART have helped
in improving treatment of male factor infertility (Alvarez,
2003). Currently, ICSI is the most common ART method, although it is associated
with the highest number of miscarriages. One of the explanations can be the
poor selection of sperm that are possibly damaged by free radicals during ART
procedures. Thus evaluation of seminal ROS levels and extent of sperm DNA damage
especially in an infertile male may help develop new therapeutic strategies
and improve success of ART.
ROS and antioxidants:
Antioxidants, in general, are compounds and reactions which dispose, scavenge
and suppress the formation of ROS, or oppose their actions. A variety of biological
and chemical antioxidants that attack ROS and LPO are presently under investigation.
Among the well known biological antioxidants, superoxide dismutase (SOD) and
its two isozymes and catalase have a significant role. SOD spontaneously dismutates
(O2¯). anion to form O2 and H2O2,
while catalase converts H2O2 to H2O and O2:
H2O2 to O2 and H2O2
(O2¯). + 2H+ SOD H2O2 + O2
H2O2 Catalase H2O + 1/2 O2
The most common antioxidants, that protect spermatozoa from excess concentrations
of ROS and OS-induced damage and altogether represent the Total Antioxidant
Capacity (TAC) of seminal plasma are SOD (Nissen and Kreysel,
1983; Aitken and Krause, 2001), catalase (CAT) (Jeulin
et al., 1989), the glutathione (GSH) peroxidase system selenium and
selenoproteins such as the phospholipids hydroperoxide glutathione peroxidase
(PHGPx) and the glutathione reductase system (Li, 1975;
Alvarez and Storey, 1989), vitamins A, C (Niki,
1991) and E (Chow, 1991), glutathione (Kidd,
1997), spermin, thiols, urate (Ronquist and Niklasson,
1984; Gavella et al., 1997), albumin, taurine
and hypotaurine (Alvarez and Storey, 1983), L-carnitine
and zinc. Antioxidants contained within seminal plasma are obviously helpful
for preventing sperm oxidative attack following ejaculation. However, during
spermatogenesis and epididymal storage, the sperm are not in contact with seminal
plasma antioxidants and must rely on epididymal/testicular antioxidants and
their own intrinsic antioxidant capacity for protection. Sperm are therefore
vulnerable to oxidative damage during epididymal transit, especially when there
is epididymal inflammation such as male genital tract infection. A study of
46 alcoholic men of reproductive age has suggested the presence of oxidative
stress within the testicle by reporting a significant reduction in plasma testosterone,
increase in serum lipid peroxidation byproducts and a drop in antioxidants (Maneesh
et al., 2006). However, no study to date has directly examined the
link between alcohol intake and sperm oxidative damage.
The role of physiological and pathological levels of ROS in male fertility is yet to be clearly established. While ROS have been associated with the pathology of numerous diseases including male infertility, Small controlled amounts of ROS are vital for spermatozoa to develop into normal spermatozoa capable of fertilization structures. Since spermatogenesis is a complex process involving various stages and different type of cells, mutations in mitochondrial genome, as a result of excessive ROS could disturb the formation of morphologically and functionally mature spermatozoa thus leading to infertility. Recently, a phenomenal growth has occurred in our knowledge of male reproduction, sperm function and development of diagnostic tools and treatment modalities for male infertility. In addition, knowledge regarding oxidative stress has given rise to several new treatment modalities that are now being tried to improve male infertility. However a wide gap still remains in our knowledge and future multicentric studies with larger samples are needed to help gain a better insight into this essential problem.
Aitken, R.J., J.S. Clarkson and S. Fishel, 1989.
Generation of reactive oxygen species, lipid peroxidation and human sperm function. Biol. Reprod., 41: 183-187.Direct Link |
Aitken, R.J., D. Harkiss and D.W. Buckingham, 1993.
Analysis of lipid peroxidation mechanisms in human spermatozoa. Mol. Reproduct. Dev., 35: 302-315.CrossRef | PubMed | Direct Link |
Aitken, J. and H. Fisher, 1994.
Reactive oxygen species generation and human spermatozoa: The balance of benefit and risk. Bioessays, 16: 259-267.PubMed |
Aitken, R.J., 1995.
Free radicals, lipid peroxidation and sperm function. Reprod. Fertil. Dev., 7: 659-668.CrossRef | Direct Link |
Aitken, R.J., 1999.
The Amoroso lecture: The human spermatozoon a cell in crisis. J. Reprod. Fert., 115: 1-7.PubMed |
Aitken, R.J. and C. Krause, 2001.
Oxidative stress, DNA damage and the Y chromosome. Reproduction, 122: 497-506.PubMed | Direct Link |
Aitken, R.J. and M.A. Baker, 2003.
Oxidative stress and male reproductive biology. Reprod. Fertil Dev., 16: 581-588.CrossRef | Direct Link |
Aitken, R.J., L.E. Bennetts, D. Sawyer, A.M. Wiklendt and B.V. King, 2005.
Impact of radio frequency electromagnetic radiation on DNA integrity in the male germline. Int. J. Androl., 28: 171-179.PubMed |
Aitken, R.J. and G.N. de Iuliis, 2010.
On the possible origins of DNA damage in human spermatozoa. Mol. Human Reprod., 16: 3-13.PubMed |
Agarwal, A. and A. Saleh, 2002.
Role of oxidants in male infertility: Rationale, significance and treatment. Urol. Clin., 29: 816-827.PubMed | Direct Link |
Agarwal, A., K.P. Nallella, S.S.R. Allamaneni and T.M. Said, 2004.
Role of antioxidants in treatment of male infertility: An overview of the literature. Reprod. Biomed. Online, 8: 616-627.CrossRef | PubMed |
Agarwal, A., S. Gupta and R.K. Sharma, 2005.
Role of oxidative stress in female reproduction. Reprod. Biol. Endocrinol., 3: 28-47.CrossRef | Direct Link |
Alvarez, J.G. and B.T. Storey, 1983.
Taurine, hypotaurine, epinephrine and albumin inhibit lipid peroxidation in rabbit spermatozoa and protect against loss of motility. Biol. Reprod., 29: 548-555.PubMed |
Alvarez, J.G. and B.T. Storey, 1989.
Role of glutathione peroxidase in protecting mammalian spermatozoa from loss of motility caused by spontaneous lipid peroxidation. Gamete Res., 23: 77-90.PubMed | Direct Link |
Alvarez, J.G. and B.T. Storey, 1995.
Differential incorporation of fatty acids into and peroxidative loss of fatty acids from phospholipids of human spermatozoa. Mol. Reprod. Dev., 42: 334-346.PubMed | Direct Link |
Alvarez, J.G., 2003.
Nurture vs nature: How can we optimize sperm quality?. J. Androl., 24: 640-648.PubMed |
Attaran, M., E. Pasqualotto, T. Falcone, J.M. Goldberg, K.F. Miller and A. Agarwal, 2000.
The effect of follicular fluid reactive oxygen species on the outcome of in vitro
fertilization. Int. J. Fertil. Womens Med., 45: 314-320.PubMed |
Aitken, R.J. and M.A. Baker, 2006.
Oxidative stress, sperm survival and fertility control. Mol. Cell. Endocrinol., 250: 66-69.CrossRef | PubMed | Direct Link |
Barbieri, E.R., M.E. Hidalgo, A. Venegas, R. Smith and E.A. Lissi, 1999.
Varicocele-associated decrease in antioxidant defenses. J. Androl., 20: 713-717.PubMed |
Balaban, R.S., S. Nemoto and T. Finkel, 2005.
Mitochondria, oxidants and aging. Cell, 120: 483-495.PubMed |
Belloli, G., S. D`Agostino, C. Pesce and E. Fantuz, 1993.
Varicocele in childhood and adolescence and other testicular anomalies: An epidemiological study. Pediatr. Med. Chir., 15: 159-162.PubMed |
Bennetts, L.E. and R.J. Aitken, 2005.
A comparative study of oxidative DNA damage in mammalian spermatozoa. Mol. Reprod. Dev., 71: 77-87.PubMed |
Benoff, S. and B.R. Gilbert, 2001.
Varicocele and male infertility: Part I. Preface. Human Reprod. Update, 7: 47-54.PubMed |
Berthood, V.M. and E.C. Beyer, 2009.
Oxidative stress, lens cap junctions and cataracts. Antioxidants Redox Signaling, 11: 339-354.CrossRef |
Buettner, G.R., 1993.
The peeking order of free radicals and antioxidants: Lipid peroxidation, α-tocopherol and ascorbate. Arch. Biochem. Biophys., 300: 535-543.PubMed |
Cheeseman, K.H. and T.F. Slater, 1993.
An introduction to free radical biochemistry. Br. Med. Bull., 49: 481-493.PubMed |
Chow, C.K., 1991.
Vitamin E and oxidative stress. Free Radic. Biol. Med., 11: 215-232.CrossRef | Direct Link |
Christen, Y., 2000.
Oxidative stress and Alzheimer disease. Am. J. Clin. Nutr., 71: 621S-629S.PubMed | Direct Link |
Cookson, M. and P. Shaw, 1999.
Oxidatine stress and motor neurone disease. Brain Pathol., 9: 165-186.PubMed |
Darley-Usmar, V., H. Wiseman and B. Halliwell, 1995.
Nitric oxide and oxygen radicals: A question of balance. FEBS Lett., 369: 131-135.PubMed |
Davi, G., A. Falco and C. Patrono, 2005.
Lipid peroxidation in Diabetis mellitus. Antiotid Redox Signal, 7: 256-258.PubMed |
Erenpreiss, J., S. Hlevicka, J. Zalkalns and J. Erenpreisa, 2002.
Effect of leukocytospermia on sperm DNA integrity: A negative effect in abnormal semen samples. J. Androl., 23: 717-723.PubMed |
Ernster, L., 1993.
Lipid Peroxidation in Biological Membranes: Mechanisms and Implications. In: Active Oxygen, Lipid Peroxides and Antioxidants, Yagi, K. (Ed.). CRC Press, Boca Raton, pp: 1-38
Evenson, D., L. Jost, M. Corzett and R. Balhorn, 2000.
Characteristics of human sperm chromatin structure following an episode of influenza and high fever: A case study. J. Androl., 21: 739-765.Direct Link |
Fraga, G.G., P.A. Motchnik, A.J. Wyrobek, D.M. Rempel and B. Ames, 1996.
Smoking and low antioxidants levels increase oxidative damage to sperm DNA. Mutat. Res., 351: 199-203.PubMed | Direct Link |
Geiszt, M., A. Kapus and E. Ligeti, 2001.
Chronic granulomatous disease: More than the lack of superoxide?. J. Leukoc. Biol., 69: 191-196.PubMed |
Garrido, N., M. Meseguer, C. Simon, A. Pellicer and J. Remohi, 2004.
Pro-oxidative and anti-oxidative imbalance in human semen and its relation with male fertility. Asian J. Androl., 6: 59-65.PubMed |
Gavella, M., V. Lipovac, M. Vucic and B. Rocic, 1997.
Evaluation of ascorbate and urate antioxidant capacity in human semen. Andrologia, 29: 29-35.PubMed |
Gomez-Cabera, M., 2008.
Bionegative and biopositive effects of free radicals. Free Radical Biol. Med., 44: 126-131.
Griffin, D.K. and K.A. Finch, 2005.
The genetic and cytogenetic basis of male infertility. Human Fertil., 8: 19-26.PubMed |
Griveau, J.F., E. Dumont, P. Renard, J.P. Callegari and D. Le Lannou, 1995.
Reactive oxygen species, lipid peroxidation and enzymatic defence systems in human spermatozoa. J. Reprod. Fertil., 103: 17-26.PubMed |
Griveau, J. and D. Le Lannou, 1997.
Reactive oxygen species and human spermatozoa: Physiology and pathology. Int. J. Androl., 20: 61-69.PubMed |
Grunewald, S., U. Paasch, T.M. Said, R.K. Sharma, H.J. Glander and A. Agarwal, 2005.
Caspase activation in human spermatozoa in response to physiological and pathological stimuli. Fertil. Steril., 83: 1106-1112.CrossRef | PubMed | Direct Link |
Halliwell, B., 1990.
How to characterize a biological antioxidant. Free Raical Res. Commun., 9: 1-32.PubMed | Direct Link |
Hauser, R., G. Paz, A. Botchan, L. Yogev and H. Yavetz, 2001.
Varicocele: Effect on sperm functions. Human Reprod. Update, 7: 482-485.
Hendin, B.N., P.N. Kolettis, R.K. Sharma, A.J. Jr. Thomas and A. Agarwal, 1999.
Varicocele is associated with elevated spermatozoal reactive oxygen species production and diminished seminal plasma antioxidant capacity. J. Urol., 161: 1831-1834.PubMed |
Hikim, A.P., C. Wang, Y. Lue, L. Johnson, X.H. Wang and R.S. Swerdloff, 1998.
Spontaneous germ cell apoptosis in humans: Evidence for ethnic differences in the susceptibility of germ cells to programmed cell death. J. Clin. Endocrinol. Metab., 83: 152-156.PubMed | Direct Link |
Hitchon, C., 2004.
Oxidative stress in rheumathoid arthritis. Res. Therpy, 6: 265-278.
Ishikawa, T., H. Fujioka, T. Ishimura, A. Takenake and M. Fujisawa, 2007.
Increased testicular 8-hydroxy-2`-deoxyguanosine in patients with varicocele. BJU Int., 100: 863-866.PubMed |
Iwasaki, A. and C. Gagnon, 1992.
Formation of reactive oxygen species in spermatozoa of infertile patients. Fertil. Steril., 57: 409-416.PubMed | Direct Link |
Jeulin, C., J.C. Soufir, P. Weber, D. Laval-Martin and R. Calvayrac, 1989.
Catalase activity in human spermatozoa and seminal plasma. Gamete Res., 24: 185-196.PubMed |
Joffe, M., 2010.
What has happened to human fertility?. Human Reprod., 25: 295-307.PubMed |
Jones, R., T. Mann and R. Sherins, 1979.
Peroxidative breakdown of phospholipids in human spermatozoa, spermicidal properties of fatty acid peroxides and protective action of seminal plasma. Fertil. Steril., 31: 531-537.PubMed |
Jurisicova, A., S. Lopes, J. Meriano, L. Oppedisano, R.F. Casper and S. Varmuza, 1999.
DNA damage in round spermatids of mice with a targeted disruption of the Pp1cgamma gene and in testicular biopsies of patients with non-obstructive azoospermia. Mol. Human Reprod., 5: 323-330.PubMed |
Kao, S.H., H.T. Chao, H.W. Chen, T.I. Hwang, T.L. Liao and Y.H. Wei, 2007.
Increase of oxidative stress in human sperm with lower motility. Fertil. Steril., 89: 1183-1190.CrossRef |
Duru, N.K., M. Morshedi and S. Oehninger, 2000.
Effects of hydrogen peroxide on DNA and plasma membrane integrity of human spermatozoa. Fertil. Steril., 74: 1200-1207.PubMed | Direct Link |
Kidd, P.M., 1997.
Glutathione: Systemic protectant against oxidative and free radical damage. Altern. Med. Rev., 2: 155-176.Direct Link |
Kodama, H., Y. Kuribayashi and C. Gagnon, 1996.
Effect of sperm lipid peroxidation on fertilization. J. Androl., 17: 151-157.PubMed |
Kodama, H., R. Yamaguchi, J. Fukuda, H. Kasai and T. Tanaka, 1997.
Increased oxidative deoxyribonucleic acid damage in the spermatozoa of infertile male patients. Fertil. Steril., 68: 519-524.CrossRef |
Koppenol, W., J. Moreno, W. Pryor, H. Ischiropoulos and J.S. Beckman, 1992.
Peroxynitrite, a cloaked oxidant formed by nitric oxide and superoxide. Chem. Res. Toxicol., 5: 834-842.PubMed |
Kunzle, R., M.D. Mueller, W. Hanggi, M.H. Birkhauser, H. Drescher and N.A. Bersinger, 2003.
Semen quality of male smokers and nonsmokers in infertile couples. Fert. Ster., 79: 287-291.CrossRef | Direct Link |
De Lamirande, E. and C. Gagnon, 1992.
Reactive oxygen species and human spermatozoa. II. Depletion of adenosine triphosphate plays an important role in the inhibition of sperm motility. J. Androl., 13: 379-386.PubMed | Direct Link |
De Lamirande, E. and C. Gagnon, 1995.
Impact of reactive oxygen species on spermatozoa: A balancing act between beneficial and detrimental effects. Human Reprod., 10: 15-21.PubMed |
De Lamirande, E., H. Jiang, A. Zini, H. Kodama and C. Gagnon, 1997.
Reactive oxygen species and sperm physiology. Rev. Reprod., 2: 48-54.PubMed |
De Lamirande, E., C. Tsai, A. Harakat and C. Gagnon, 1998.
Involvement of reactive oxygen species in human sperm arcosome reaction induced by A23187, lysophosphatidylcholine and biological fluid ultrafiltrates. J. Androl., 19: 585-594.
Lee, J., J.H. Richburg, E.B. Shipp, M.L. Meistrich and K. Boekelheide, 1999.
The Fas system, a regulator of testicular germ cell apoptosis, is differentially up-regulated in Sertoli cell Versus
germ cell injury of the testis. Endocrinology, 140: 852-858.CrossRef | PubMed | Direct Link |
Li, T.K., 1975.
The glutathione and thiol content of mammalian spermatozoa and seminal plasma. Biol. Reprod., 12: 641-646.PubMed |
Lin, W.W., D.J. Lamb, T.M. Wheeler, L.I. Lipshultz and E.D. Kim, 1997. In situ
end-labeling of human testicular tissue demonstrates increased apoptosis in conditions of abnormal spermatogenesis. Fertil. Steril., 68: 1065-1069.PubMed |
Maneesh, M., S. Dutta, A. Chakrabarti and D.M. Vasudevan, 2006.
Alcohol abuse-duration dependent decrease in plasma testosterone and antioxidants in males. Indian J. Physiol. Pharmacol., 50: 291-296.Direct Link |
Moustafa, M.H., R.K. Sharma, J. Thornton, E. Mascha, M.A. Abdel-Hafez, A.J. Thomas and A. Agarwal, 2004.
Relationship between ROS production, apoptosis and DNA denaturation in spermatozoa from patients examined for infertility. Human Reprod., 19: 129-138.Direct Link |
Mostafa, T., G. Tawadrous, M.M. Roaia, M.K. Amer, R.A. Kader and A. Aziz, 2006.
Effect of smoking on seminal plasma ascorbic acid in infertile and fertile males. Andrologia, 38: 221-224.PubMed |
Nakabeppu, Y., K. Sakumi, K. Sakamoto, D. Tsuchimoto, T. Tsuzuki and Y. Nakatsu, 2006.
Mutagenesis and carcinogenesis caused by the oxidation of nucleic acids. Biol. Chem., 387: 373-379.PubMed |
Nallella, K.P., S.S. Allamaneni, F.F. Pasqualotto, R.K. Sharma, A.J. Jr. Thomas and A. Agarwal, 2004.
Relationship of interleukin-6 with semen characteristics and oxidative stress in patients with varicocele. Urology, 64: 1010-1013.PubMed |
Nicopoullos, J.D., C. Gilling-Smith, P.A. Almeida, S. Homa, J.Q. Norman-Taylor and J.W. Ramsay, 2008.
Sperm DNA fragmentation in subfertile men: The effect on the outcome of intracytoplasmic sperm injection and correlation with sperm variables. BJU Int., 101: 1553-1560.PubMed |
Niki, E., 1991.
Action of ascorbic acid as a scavenger of active and stable oxygen radicals. Am. J. Clin. Nutr., 54: 1119S-1124S.Direct Link |
Nissen, H.P. and H.W. Kreysel, 1983.
Superoxide dismutase in human semen. Klin Wochenschr, 61: 63-65.PubMed |
Nunomura, A., R.J. Castellani, X. Zhu, P.I. Moreira, G. Perry and M.A. Smith, 2006.
Involvement of oxidative stress in Alzheimer disease J. Neuropathol. Exp. Neurol., 65: 631-641.CrossRef | PubMed | Direct Link |
Oborna, I., G. Wojewodka, J.B. de Sanctis, H. Fingerova and M. Svobodova et al
Increased lipid peroxidation and abnormal fatty acid profiles in seminal and blood plasma of normozoospermic males from infertile couples. Human Reprod., 25: 308-316.PubMed |
Ochsendorf, F.R., 1999.
Infections in the male genital tract and reactive oxygen species. Human Reprod. Update, 5: 399-420.PubMed |
O`Donovan, M., 2005.
An evaluation of chromatin condensation and DNA integrity in the spermatozoa of men with cancer before and after therapy. Andrologia, 37: 83-90.PubMed |
Oliva, R., 2006.
Protamines and male infertility. Human Reprod. Update, 12: 417-435.PubMed |
Pasqualotto, F., R. Sharma, H. Kobayashi, D. Nelson, A. Jr. Thomas and A. Agarwal, 2001.
Oxidative stress in normospermic men undergoing infertility evaluation. J. Androl., 22: 316-322.PubMed |
Pfeiffer, D., J. Berger, C. Schoop and R. Tauber, 2006.
A doppler-based study on the prevalence of varicocele in German children and adolescents. Andrologia, 38: 13-19.PubMed |
Potts, R.J., C.J. Newbury, G. Smith, L.J. Notarianni and T.M. Jefferies, 1999.
Sperm chromatin damage associated with male smoking. Mutat. Res., 423: 103-111.PubMed |
Print, C.G. and K.L. Loveland, 2000.
Germ cell suicide: New insights into apoptosis during spermatogenesis. Bioessays, 22: 423-430.PubMed |
Quinn, M.T. and K.A. Gauss, 2004.
Structure and regulation of the neutrophil respiratory burst oxidase: Comparison with nonphagocyte oxidases. J. Leukoc. Biol., 76: 760-781.PubMed |
Rao, A.V. and B. Balachandran, 2002.
Role of oxidative stress and antioxidants in neurodegenerative diseases. Nutr. Neurosci., 5: 291-309.CrossRef | PubMed | Direct Link |
Ronquist, G. and F. Niklasson, 1984.
Uridine, xanthine and urate contents in human seminal plasma. Arch. Androl., 13: 63-70.PubMed |
Rowe, T., 2006.
Fertility and a woman`s age. J. Reprod. Med., 51: 157-163.PubMed |
Saalu, L.C., A.A. Osinubi and J.A. Olagunju, 2010.
Early and delayed effects of doxorubicin on testicular oxidative status and spermatogenesis in rats. Int. J. Cancer Res., 6: 1-9.CrossRef | Direct Link |
Saalu, L.C., L.A. Enye and A.A. Osinubi, 2009.
An assessment of the histomorphometric evidences of doxorubicin-induced testicular cytotoxicity in wistar rats. Int. J. Med. Med. Sci., 1: 370-374.Direct Link |
Saalu, L.C., G.O. Ajayi, A.A. Adeneye, I.O. Imosemi and A.A. Osinubi, 2009.
Ethanolic seed extract of grapefruit (Citrus paradisi
Macfad) as an effective attenuator of doxorubicin-induced oxidative stress in the rat heart. Int. J. Cancer Res., 5: 44-52.CrossRef | Direct Link |
Saalu, L.C., R. Udeh, P.I. Jewo, K.A. Oluyemi and I.O. Fadeyibi, 2008.
Grapefruit seed moderates the testicular toxicity associated with experimental varicocele in rats. Int. J. Morphol., 26: 1059-1064.
Said, T.M., U. Paasch, H.J. Glander and A. Agarwal, 2004.
Role of caspases in male infertility. Human Reprod. Update, 10: 39-51.Direct Link |
Said, T.M., A. Agarwal, R.K. Sharma, A.J. Jr. Thomas and S.C. Sikka, 2005.
Impact of sperm morphology on DNA damage caused by oxidative stress induced by β-nicotinamide adenine dinucleotide phosphate. Fertil. Steril., 83: 95-103.CrossRef | PubMed | Direct Link |
Sakkas, D., E. Mariethoz, G. Manicardi, D. Bizzaro, P.G. Bianchi and U. Bianchi, 1999.
Origin of DNA damage in ejaculated human spermatozoa. Rev. Reprod., 4: 31-37.PubMed |
Sakkas, D., E. Mariethoz and J.C. St. John, 1999.
Abnormal sperm parameters in humans are indicative of an abortive apoptotic mechanism linked to the Fas-mediated pathway. Exp. Cell Res., 251: 350-355.CrossRef |
Sakkas, D., O. Moffatt, G.C. Manicardi, E. Mariethoz, N. Tarozzi and D. Bizzaro, 2002.
Nature of DNA damage in ejaculated human spermatozoa and the possible involvement of apoptosis. Biol. Reprod., 66: 1061-1067.Direct Link |
Sakkas, D., G.C. Manicardi and D. Bizzaro, 2003.
Sperm nuclear DNA damage in the human. Adv. Exp. Med. Biol., 518: 73-84.
Saleh, R.A., A. Agarwal, R.K. Sharma, D.R. Nelson and A.J. Thomas Jr., 2002.
Effect of cigarette smoking on levels of seminal oxidative stress in infertile men: A prospective study. Fertil. Steril., 78: 491-499.CrossRef | PubMed | Direct Link |
Saleh, R., A. Agarwal, R. Sharma, T. Said, S. Sikka and A. Jr. Thomas, 2003.
Evaluation of nuclear DNA damage in spermatozoa from infertile men with varicocele. Fertil. Steril., 80: 1431-1436.PubMed |
Schlesinger, M.H., I.F. Wilets and H.M. Nagler, 1994.
Treatment outcome after varicocelectomy: A critical analysis. Urol. Clin. North Am., 21: 517-529.PubMed |
Sinha-Hikim, A.P. and R.S. Swerdloff, 1999.
Hormonal and genetic control of germ cell apoptosis in the testis. Rev. Reprod., 4: 38-47.CrossRef |
Sharma, R.K., T. Said and A. Agarwal, 2004.
Sperm DNA damage and its clinical relevance in assessing reproductive outcome. Asian J. Androl., 6: 139-148.PubMed |
Shekarriz, M., A.J. Jr. Thomas and A. Agarwal, 1995.
Incidence and level of seminal reactive oxygen species in normal men. Urology, 45: 103-107.PubMed |
Shekarriz, M., D.M. DeWire, A.J. Jr. Thomas and A. Agarwal, 1995.
A method of human semen centrifugation to minimize the iatrogenic sperm injuries caused by reactive oxygen species. Eur. Urol., 28: 31-35.PubMed |
Shen, H.M., J. Dai, S.E. Chia, A. Lim and C.N. Ong, 2002.
Detection of apoptotic alterations in sperm in subfertile patients and their correlations with sperm quality. Human Reprod., 17: 1266-1273.PubMed |
Sikka, S.C., 2004.
Role of oxidative stress and antioxidants in andrology and assisted reproductive technology. J. Androl., 25: 5-18.CrossRef | PubMed | Direct Link |
Singh, N.P., C.H. Muller and R.E. Berger, 2003.
Effects of age on DNA double-strand breaks and apoptosis in human sperm. Fertil. Steril., 80: 1420-1430.CrossRef | Direct Link |
Smith, R., H. Kaune, D. Parodi, M. Madariaga, R. Rios, I. Morales and A. Castro, 2006.
Increased sperm DNA damage in patients with varicocele: Relationship with seminal oxidative stress. Human Reprod., 21: 986-993.CrossRef | Direct Link |
Smith, G.R., G.H. Kaune, C.D. Parodi, A.M. Madariaga, D.I. Morales, S.R. Rios and G.A. Castro, 2007.
Extent of sperm DNA damage in spermatozoa from men examined for infertility: Relationship with oxidative stress. Rev. Med. Chil., 135: 279-286.PubMed |
Spiropoulos, J., D.M. Turnbull and P.F. Chinnery, 2002.
Can mitochondrial DNA mutations cause sperm dysfunction?. Mol. Human Reprod., 8: 719-721.PubMed |
Sun, J.G., A. Jurisicova and R.F. Casper, 1997.
Detection of deoxyribonucleic acid fragmentation in human sperm: correlation with fertilization in vitro
. Biol. Reprod., 56: 602-607.Direct Link |
Taourel, D.B., M.C. Guerin and J. Torreilles, 1992.
Is melonaldehyde a valuable indicator of lipid peroxidation?. Biochem. Pharmacol., 44: 985-988.
Thomson, L.K., S.D. Fleming, R.J. Aitken, G.N. de Iuliis, J.A. Zieschang and A.M. Clark, 2009.
Cryopreservation-induced human sperm DNA damage is predominantly mediated by oxidative stress rather than apoptosis. Human Reprod., 24: 2061-2070.PubMed |
Twigg, J., D.S. Irvine and R.J. Aitken, 1998.
Oxidative damage to DNA in human spermatozoa does not preclude pronucleus formation at intracytoplasmic sperm injection. Human Reprod., 13: 1864-1871.CrossRef | PubMed | Direct Link |
Valko, M., M. Izakovic, M. Mazur, C.J. Rhodes and J. Telser, 2004.
Role of oxygen radicals in DNA damage and cancer incidence. Mol. Cell. Biochem., 266: 37-56.CrossRef | Direct Link |
Valko, M., D. Leibfritz, J. Moncol, M.T.D. Cronin, M. Mazur and J. Telser, 2007.
Free radicals and antioxidants in normal physiological functions and human disease. Int. J. Biochem. Cell Biol., 39: 44-84.CrossRef | PubMed | Direct Link |
Vincent, H., 2007.
Diabetes, obesity and metabolism. Clin. Chem., 9: 813-839.
Vine, M.F., C.K.J.P.C. Tse Hu and K.Y. Truong, 1996.
Cigarette smoking and semen quality. Fert. Ster., 65: 835-842.
World Health Organization, 1992.
The influence of varicocele on parameters of fertility in a large group of men presenting to infertility clinics. Fertil. Steril., 57: 1289-1293.
Wood-Kaczmar, A., S. Gandhi and W.N. Wood, 2006.
Understanding the molecular causes of Parkinson's disease. Trends Mol. Med., 12: 521-528.CrossRef | PubMed | Direct Link |
World Health Organization, 2000.
WHO Manual for the Standardised Investigation and Diagnosis of the Infertile Couple. Cambridge University Press, Cambridge
Wyllie, A.H., J.F.R. Kerr and A.R. Currie, 1980.
Cell death: The significance of apoptosis. Int. Rev. Cytol., 68: 251-306.CrossRef | PubMed | Direct Link |
Zoas, P.M., J.R. Correa, C.S. Karagounis, A. Ahparaki, C. Phorouglu and C.L. Hicks, 1998.
An electron microscope study of the axonemal ultrastructure in human spermatozoa from male smokers and nonsmokers. Fertil. Steril., 69: 430-434.Direct Link |