PD worsens mainly due to increased cell death—the process is explained in this section. There are 100 billion neurons in the brain. For each nerve cell there are, perhaps, 10 times as many support cells, called glial cells, which bring oxygen and needed chemicals to the nerve cells. All cells in the body, including the brain, have parts called organelles. The cell’s organelles include the nucleus, the “brain” of the cell, which contains the cell’s DNA (genes).
Neurons are designed to perform specific tasks by their genes, but are vulnerable to dying. There are a few ways in which neurons die: they can be killed by infectious agents such as viruses; they can be killed by toxins such as iron, calcium, manganese, and nitrous oxide; or they can be killed by a lack of oxygen (or too much oxygen).
Nerve cells can also “commit suicide:” they can initiate suicide programs that are built into all cells. These programs, called apoptosis, are partly con-trolled by genes and partly by outside agents. This has been one of the popular theories as to why neurons die, but recent studies have moved away from apoptosis as a cause of cell death in PD.
Whether cells are killed by an infection or a toxin, are genetically vulnerable, or commit suicide, much research focuses on the mitochondria—the “power plants” of the cells. Mitochondria vary in number from a few dozen to several thousand, depending on the cell and its requirement for energy. Mitochondria mainly die from either a lack of nutrients or a lack of replacement parts.
As they extract energy from food molecules, such as fats and sugars, they use oxygen to produce a basic chemical fuel called ATP, the “gasoline,” so to speak, that powers most of the cell’s activity. There are carriers called complexes in the mitochondria that use oxygen dis-solved in the cell to extract energy from fats and sugars. Different carriers are derived from some of the B vitamins.
In humans, 100% of your mitochondria come from your mother, as only mitochondria and their genes are passed along to the fertilized egg. The mitochondrial genes are more stable and less susceptible to variation than the genes in the nucleus of the cell.
The process of generating energy in the cell, like the process of generating energy for industry, results in the production of toxic products, or pollutants. Like industry, the cell must remove the pollutants so that its environment, especially the environment inside and outside the mitochondria, isn’t poisoned. The toxic products produced inside the mitochondria are reactive chemical species called free radicals, and have the ability to attack the normal components of the cell.
Antioxidants are chemicals that “neutralize” free radicals and play a major role in protecting the mitochondria and the rest of the cell. The antioxidants consist of a series of enzymes, each specific for a specific free radical. The work of the enzyme is helped by additional scavengers of free radicals such as Vitamins C and E, glutathione, and Coenzyme Q10.
If the free radical scavengers fail and free radicals increase inside the cell, changes in proteins such as alpha synuclein may occur, causing it to aggregate and clump, altering its function and resulting in death. The death of the cell by apoptosis is required to destroy cells that represent a threat to the integrity of the body, such as cells infected with viruses. It is unclear whether this process is relevant to the cell death associated with progression of PD.