Читать книгу Alzheimer's Disease - Michelle Deetken - Страница 14

A healthy immune system keeps up with normal, reactive oxygen species interactions. It also handles the variety of other reactions that generate free radicals formed normally in cells as they continuously use carbohydrates, fats, and proteins for energy and other normal metabolic functions. Oxygen is not the only molecule that causes oxidation; a number of other factors contribute to the generation of free radicals that come from external sources. The major contributors are environmental contaminants, our modern diet, and the stress of our lifestyles. These external sources may overwhelm the body's natural antioxidant defense system leading to oxidative stress. Even our healthy immune system generates free radicals to combat what it perceives as foreign invaders.

One of many tools the immune system uses is a tactic called “oxidative burst” produced by specialized cells called phagocytes. To kill a bacteria or virus, a phagocyte blasts the invader with many free radicals—called hydroxyl radicals—that are derived from hydrogen peroxide. This blast kills the invader and also sends out hydroxyl radicals that miss the invader. The hydroxyl radicals continue to actively search for an electron with which to pair. These free radicals have the potential to damage healthy cells and tissues if not stopped right away. Fortunately, a healthy immune system can handle these attacks. When we have a cold or flu virus, the symptoms we experience are the result of the immune system fighting back and repairing the damage so that the body can recover.

The brain, however, is different from the rest of the body in that it is highly vulnerable to oxidative damage. This difference is due to the brain's immense energy needs. The brain has a high oxygen consumption as well as a high lipid content and retains relatively few natural antioxidants compared to other organs in the body. Unless ample supplies of antioxidants are continually made available through our diet, the external sources of free radicals can easily overwhelm the brain's defense system, causing unwanted oxidative stress.

In the twenty-first century, we need to consume more antioxidants than we did a hundred years ago because of the many toxic free radical generators that we encounter each day. Cigarette smoke and air pollution are huge free radical generators; pesticides, additives, and preservatives in our food and water supplies also harbor many sources of free radicals. And now we are learning that hazardous chemicals used in the production of food products do not have to be recorded on the ingredient list because they are considered to be “components in a production procedure” by the US Department of Agriculture (USDA). Prime examples are the ammonia in “pink slime” beef and arsenic in fruit juices. It has also been revealed that hazardous chemicals employed in the manufacturing of products that we use are everywhere in our environment—even inside our tissues and cells. Examples are the chemicals bisphenol A (BPA) found in plastics and in the lining of food containers and fire retardants used in clothing, curtains, and upholstered furniture. Cumulative oxidative damage in the brain over a lengthy period of time might activate pathways that lead to cell death (called apoptosis). This process may cause the brain to shrink, which leads to dementia. If oxidative damage does begin in one's twenties, this factor might account for the slow progression of the disease and the later life onset of AD that is not related to genetic factors.