SHOULD RADICALS BE FREE?

Free radicals have gained importance in the field of biology due to their central role in various physiological conditions as well as their implication in a diverse range of diseases. The free radicals or reactive oxygen species (ROS) are derived from both endogenous sources where the oxygen consumption is high (mitochondria, peroxisomes, endoplasmic reticulum, phagocytic cells etc.) and exogenous sources (mycotoxins, heavy metals, oxidized lipids).

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A free radical can be defined as a molecule containing one or more unpaired electrons. The odd number of electron(s) of a free radical makes it unstable, short lived and highly reactive, hence the name of reactive oxygen species or ROS. Because of their high reactivity, they can exchange electrons with other compounds to attain stability. Thus, the attacked molecule gets its pool of electrons disturbed and becomes a free radical itself, beginning a chain reaction cascade which finally damages the living cell.


Reactive oxygen Species (ROS) are by-products of the oxygen metabolism. Most of the intracellular ROS are derived from the normal respiration process in mitochondria which is the main site of oxygen metabolism accounting for approximately 85-90% of the oxygen consumed by the cell.


But ROS are produced as well by phagocytic cells like neutrophils to aggress bacteria. Neutrophils accumulates ROS into their phagosomes and will release it either during phagocytosis of small bacteria or by secretion onto bacteria too large to be phagocyted.


Once released, the Reactive Oxygen Species will circulate and activate other neutrophils to attract them to the inflamed location. That contributes to activate the inflammation and the defense mechanisms against aggression.

Moreover, when inflammatory cells clean up damaged tissues, the destruction of the dead cells by the macrophages will lead to the production of even more ROS which can create a negative circle bringing about inflammation overheat.


Fortunately, physiology set up a control system of ROS to maintain homeostasis. The excess of ROS will trigger the synthesis of neutralizing enzymes. The most powerful neutralizing enzyme against ROS is the Superoxide Dismutase (SOD). The presence of SOD is essential to maintain the level of ROS under control, whether it is inside the mitochondria, inside cytosol or outside the cells.

Everything would work according to plan if there were no exogenous sources of ROS that could weaken the balance. In South East Asian highly productive farms, animals are exposed to four major exogenous causes of ROS; mycotoxins, oxidized lipids, heat, and/or heavy metals.


To fight against heat, the organisms will require the mitochondria to produce more energy leading to an increase supply of ROS that could overflow the pool of superoxide dismutase. That is part of what we call heat stress.


Mycotoxins at the opposite will negatively affect the production of Superoxide Dismutase and Catalase which will result as well in an increase of ROS.