Oorsig/Review
their function which can lead to sperm damage
and male infertility.
Reactive oxygen species are produced by living
organisms as a result of:
•
•
Normal cellular processes (sperm
production), inflammatory events (disease
conditions), stressful events (weaning,
mating).
Environmental factors (heat stress,
drought).
Controlled quantities (low to moderate
concentrations) of ROS have been shown to
be essential for sperm physiological processes
that are necessary to ensure fertilization. The
maintenance of suitable ROS levels is therefore
essential for adequate sperm functionality to
ensure fertilization. Regulating and reducing
ROS to physiological levels, is thus critical for
cell viability, organ function and early embryo
development.
Oxidative stress in the reproductive system is
thought to have an effect on the fertilizing ability
of sperm. Poor sperm motility, rather than low
sperm concentration, is most often the cause of
male infertility. Therefore, an antioxidant that
reduces oxidative stress and improves sperm
motility could be useful in the management of
male infertility.
Trace minerals play an important role as co-
enzymes in various metabolic processes,
antioxidants, immune responses and minimizing
the effect of stress in ruminants by supporting
the antioxidant defence mechanisms designed
to keep the reactive oxygen species (ROS) in
balance.
Oxidants can either be from endogenous sources
of ROS or from exogenous sources of oxidants.
Endogenous sources of ROS
Two of the main factors contributing to ROS
accumulation, are the absence of endogenous
defence
mechanism
and
environmental
conditions that can lead to generation of OS. The
fluctuations in ROS might be due to transient
subclinical infection, transient abnormalities
in spermatogenesis or periodic presence of
abnormal spermatozoa in semen.
Reactive oxygen species are produced from
molecular oxygen as a result of normal cellular
metabolism or during phagocytosis and
destruction of microorganisms by neutrophils
and can be divided into 2 groups:
8
1. Free radical:
Molecules containing one or more unpaired
electrons (and thus giving reactivity to the
molecule) are called free radicals and they
are able to cause DNA mutations, as seen
with hypochlorous acid (HOCI) generated by
phagocytes.
2. Non-radicals:
When 2 free radicals share their unpaired
electrons, non-radicals forms are created.
ROS is produced by both sperm and leukocytes
contaminating seminal fluid. There are four major
ROS that are of physiological significance by
adversely affecting sperm motility and impairing
fertilization ability, namely:
•
•
•
•
Superoxide anion (O 2 ),
Hydroxyl radical (OH),
Hydrogen peroxide (H 2 O 2 )
Hypochlorite radical (OHCl).
Previous research has demonstrated that high
hydrogen peroxide concentrations reduces
bull sperm motility in vitro and may impair
fertilization and embryo development.
In bovine semen ROS are generated primarily by
dead spermatozoa while leukocytes, particularly
neutrophils and macrophages, as well as
immature spermatozoa are the two main sources
of ROS that causes sperm dysfunction.
Exogenous sources of oxidants
Exogenous sources like smoke, dust, heavy
metals and heat stress lead to the release of
inflammatory mediators as well as accumulation
of neutrophils and macrophages which increase
the oxidative injury.
Chauhan et al indicated that heat stress impairs
animal performance and it has been implicated
in promoting OS. Therefore a robust antioxidant
network capable of preventing oxidative damage
of biological molecules holds promise for
improving the health and performance of animals
during heat stress.
Antioxidant enzymes, such as glutathione
peroxidase (GSH-Px) can be inhibited by various
exogenous sources. Low levels of Zinc (Zn), which
serves as a cofactor for many of these enzymes,
can lead to inactivation of such enzymes.
Antioxidants
The role of chemical elements in natural
antioxidant structures has recently attracted
much scientific interest. The body is equipped