Oxidative stress
Living organisms are constantly subjected to agressions. It could be as molecular attacks, damaging cells or biological macromolecules.
Reactive oxygen species (ROS)
When molecules (or atoms) are missing electrons, they become unstable and very reactive. In response, these reactive oxygen species adapt by reacting to their environment. To do so, they bind to proteins which causes changes in their structure and/or function. They also react with cell membranes, causing damage. In some cases, DNA may also be affected, causing mutations to the genome. Excessive oxidative stress damage could result in death to the cell.
ROS Sources
There are several types of ROS, but all these molecules contain oxygen and are highly reactive. They can interact with each other, creating more of these damaging molecules. ROS are naturally produced by endogenous mechanisms in a living organism. Cellular respiration, energy generator of the cell, requires oxygen to function. During this process, oxygen is transformed into ROS. Moreover, the immune system uses ROS to defend against microbes. The ROS can also come from outside, through food or other inputs (smoking, pollution, etc.).
Antioxidants
To protect the cells, ROS are eliminated by antioxidant molecules in which some are capable of transforming ROS into a single water molecule. The contribution of exogenous molecules such as vitamins C and E, polyphenols (red wine), carotenes (fruit and vegetables), flavones (soybeans) and several others can help neutralize ROS.
Oxidative stress
Oxidative stress is define as a imbalance between antioxidant and oxidant molecules. This may arise due to an increased production or a decreased removal of ROS. For example, an infection or illness may lead to excessive oxygen consumption and result in overproduction of ROS. Furthermore, declining or dysfunctional antioxidant molecules may also result in an increase of ROS.
In hepatic encephalopathy
It is believed that oxidative stress plays an important role in pathogenesis of hepatic encephalopathy. Studies investigating the role of ammonia in association with oxidative stress are underway.
Clinical overview
Ammonia