Oxygen: Origins and Biology – Part 2

When considering the role of oxygen on a cellular level, incorporating a basic understanding of free radical compounds can be helpful.

Free radicals are chemical species possessing an unpaired electron that can be considered as fragments of molecules, and which are generally very reactive (7). They are produced continuously in cells either as accidental by-products of metabolism or deliberately during, for example, phagocytosis (8). The most important reactants in free radical biochemistry in aerobic cells are oxygen and its radical derivatives (superoxide and hydroxyl radical), hydrogen peroxide and transition metals (9) . Cells have developed a comprehensive array of antioxidant defenses to prevent free radical formation or limit their damaging effects (10) . These include enzymes to decompose peroxides, proteins to sequester transition metals and a range of compounds to ‘scavenge’ free radicals. Reactive free radicals formed within cells can oxidize biomolecules and lead to cell death and tissue injury (11).

As noted in a 2008 review (12) :

When cells use oxygen to generate energy, free radicals are created as a consequence of ATP production by the mitochondria. These by-products are generally reactive oxygen species (ROS) as well as reactive nitrogen species (RNS) that result from the cellular redox process. These species play a dual role as both toxic and beneficial compounds. The delicate balance between their two antagonistic effects is clearly an important aspect of life. At low or moderate levels, ROS and RNS exert beneficial effects on cellular responses and immune function. At high concentrations, they generate oxidative stress, a deleterious process that can damage all cell structures (13-14). Oxidative stress plays a major part in the development of chronic and degenerative ailments such as cancer, arthritis, aging, autoimmune disorders, cardiovascular and neurodegenerative diseases. The human body has several mechanisms to counteract oxidative stress by producing antioxidants, which are either naturally produced in situ, or externally supplied through foods and/or supplements. Endogenous and exogenous antioxidants act as “free radical scavengers” by preventing and repairing damages caused by ROS and RNS, and therefore can enhance the immune defense and lower the risk of cancer and degenerative diseases (15-16).

The above insight into free radical impacts and potential solutions provides a context for the application of hypoxic hormesis as, in a sense, it could be considered by an exogenous (from the outside) and endogenous (from the inside) approach to effective management of free radical balance. There are various hypoxic protocols that can be mechanically applied externally to reduce oxygen intake and there are also purely biological methods to limit cellular oxidative processes. These techniques will be reviewed in future articles in this series.