Alzheimer's Disease : Oxidative Damage, Inflammation, Brain Infarction

by National Institute on Aging

(Page 8 of 16)

Oxidative Damage from Free Radicals

Another promising area of investigation relates to a longstanding theory of aging. This theory suggests that over time, damage from a kind of molecule called a free radical can build up in neurons, causing a loss in function. Free radicals can help cells in certain ways, such as fighting infection. However, too many can injure cells because they are very active and can readily change other nearby molecules, such as those in the neuron's cell membrane or in DNA. The resulting molecules can set off a chain reaction, releasing even more free radicals that can further damage neurons. This kind of damage is called oxidative damage. It may contribute to AD by upsetting the delicate machinery that controls the flow of substances in and out of the cell. The brain's unique characteristics, including its high rate of metabolism and its long-lived cells, may make it especially vulnerable to oxidative damage over the lifespan. Some epidemiological and laboratory studies suggest that anti-oxidants from dietary supplements or food may provide some protection against developing AD. Other studies suggest that low calorie diets may protect against the development of Alzheimer's Disease by slowing down metabolic rates.

Inflammation

Another set of hints about the causes of AD points to inflammation in the brain. This process is part of the immune system and helps the body react to injury or disease. Fever, swelling, pain, or redness in other parts of the body are often signs of inflammation. Because cells and compounds that are known to be involved in inflammation are found in AD plaques, some researchers think it may play a role in Alzheimer's Disease.

They disagree, though, on whether inflammation is a good or a bad thing. Some think it is harmful - that it sets off a vicious cycle of events that ultimately causes neurons to die. Evidence from many studies supports this idea.

Other scientists believe that some aspects of the inflammatory process may be helpful - that they are part of a healing process in the brain. For example, certain inflammatory processes may play a role in combating the accumulation of plaques. Many studies are now underway to examine the different parts of the inflammatory process more fully and their effects on AD.

Brain Infarction

We've all heard the sensible advice about ways to live a long and healthy life: eat right, exercise, don't smoke, wear a seat belt. All of these habits can help prevent heart attacks, stroke, and injuries. This advice may even have some relevance for AD as well. Results from one long-term study of aging and Alzheimer's Disease show that participants who had evidence of stroke in certain brain regions had more symptoms of dementia than could be explained by the number of plaques and tangles in their brain tissue. These findings suggest that damage to blood vessels in the brain may not be enough to cause AD, but that it could make AD clinical symptoms worse.

New Techniques Help in Diagnosing Alzheimer's Disease

A healthy man in his early 60s begins to notice that his memory isn't as good as it used to be. More and more often, a word will be on the tip of his tongue but he just can't remember it. He forgets appointments, makes mistakes when paying his bills, and finds that he's often confused or anxious about the normal hustle and bustle of life around him. One evening, he suddenly finds himself walking in a neighborhood a couple of miles from his house. He has no idea how he got there.

Not so long ago, this man's condition would have been swept into a broad catch-all category called "senile dementia" or "senility." Today, the picture is very different. We now know that Alzheimer's and other illnesses with dementia are distinct diseases. Armed with this knowledge, we have rapidly improved our ability to accurately diagnose AD. We are still some distance from the ultimate goal - a reliable, valid, inexpensive, and early diagnostic marker - but experienced physicians now can diagnose AD with up to 90 percent accuracy.

Early diagnosis has several advantages. For example, many conditions cause symptoms that mimic those of Alzheimer's disease. Finding out early that the problem isn't Alzheimer's Disease but is something else can spur people into getting treatment for the real condition. For the small percentage of dementias that are treatable or even reversible, early diagnosis increases the chances of successful treatment.

Even when the cause of the dementia turns out to be Alzheimer's disease, it's good to find out sooner rather than later. One benefit is medical. The drugs now available to treat AD can help some people maintain their mental abilities for months to years, though they do not change the underlying course of the disease.

Other benefits are practical. The sooner the person with AD and family know, the more time they have to make future living arrangements, handle financial matters, establish a durable power of attorney, deal with other legal issues, create a support network, or even make plans to join a research study. Being able to participate for as long as possible in making decisions about the present and future is important to many people with Alzheimer's Disease.

Finally, scientists also see advantages to early diagnosis. Developing tests that can reveal what is happening in the brain in the early stages of Alzheimer's disease will help them understand more about the cause and development of the disease. It will also help scientists learn when and how to start drugs and other treatments so that they can be most effective.

About the Author

www.nia.nih.gov
NIA, one of the 27 Institutes and Centers of NIH, leads a broad scientific effort to understand the nature of aging and to extend the healthy, active years of life. In 1974, Congress granted authority to form NIA to provide leadership in aging research, training, health information dissemination, and other programs relevant to aging and older people.