Oxidative stress, mitochondria, and infertility: is the relationship fully established?
VOLUME 116, ISSUE 2, P306-308
Luciana Cacciottola, M.D., Jacques Donnez, M.D., Ph.D., Marie-Madeleine Dolmans, M.D., Ph.D.
Oxygen is thought to have been formed in the universe when stars much larger than our own sun were born, burning their stored hydrogen and creating heavier chemical elements by nuclear fusion reactions. Explosions of these giant dying stars scattered all chemical elements into space as stardust, which became the base material for the formation of our solar system. Nevertheless, diatomic oxygen, or free oxygen, which now makes up 20.9% of our atmosphere, appeared much later than the earth itself. In fact, when life was evolving 2.4 billion years ago, cyanobacteria able to use sunlight to produce energy in the form of carbohydrate and oxygen as a waste product of such chemical processes emerged. Oxygen levels increased over time, resulting in the development of new bacteria with more efficient oxygen-dependent energy-producing systems. These prokaryotic bacteria, known as mitochondria ancestors, were incorporated into larger host cells to serve as engines for energy supply. The payoff of this successful endosymbiosis approximately 1.5 billion years ago was the appearance of the aerobic eukaryotic cell, which further evolved into multicellular organisms, leading to the development of specialized organs for oxygen intake, distribution, and processing to supply the body’s constant metabolic need for energy production in all cell compartments.