Naturally_Speaking_L_N_Shevyrdyaeva (Л.Н. Шевырдяева - Naturally Speaking & Listening), страница 16

2. Have people reached the upper limit of longevity?

3. How can average life expectancy be increased?

4. Would you like to live to be a hundred years old? Why? Why not?

Exercise 4. Read the text.

Is 100 the New 80?: Centenarians Studied to Find the Secret of Longevity

Healthy aging may be possible with some genetic help

By Barbara Juncosa

Centenarians—those who live past age 100—may help researchers find the key to living longer, healthier lives. The reason, say scientists who study this elite group: centenarians may possess genes that protect them from disease into old age. One in every 10,000 individuals in the U.S. reaches the age of 100. There are currently an estimated 60,000 centenarians in the U.S. with up to 70 beyond the age of 110. For the past decade, researchers have marveled at these folks who often live independently—and free of major disabilities—well into their 90s, if not longer.

To better understand their exceptional longevity, scientists have recruited centenarians for extensive physical and genetic screening. Of particular interest to researchers is that some of the oldsters have a history of obesity and heavy smoking. But despite these risk factors, most centenarians remain healthy up to the last few months of their lives and, in some cases, up until their dying breaths.

Although sheer luck no doubt plays a role, "there is also a striking family history that supports a genetic component," says Nir Barzilai, a geneticist at the Albert Einstein College of Medicine in New York City. In fact, he adds, the odds of centenarians having a relative who lived into old age is 20 times that of the average person. The goal now is "to find the subtle genetic differences between individuals in the genes or families of genes associated with longevity," says Judith Campisi, a senior scientist at the Lawrence Berkeley National Laboratory in California. By understanding the underlying biology of aging, she notes, it may be possible to develop drugs in the future that will promote healthy aging and delay age-related diseases such as some cancers, arthritis, diabetes, high blood pressure and heart disease.

The first genetic clues for slowing aging emerged from animal models in which the effect of individual genes on average life spans could be tested. From these early studies, it became clear that insulin (a hormone secreted by the pancreas that signals cells to absorb sugar) and its receptors are critical for longevity in species from yeast or fungi to humans. Insulin lies at the heart of the "biological pathway whose main function is to affect how efficiently we process food into energy," says Bradley Willcox, a geriatrics specialist at the University of Hawaii. His team recently found that a variant in the insulin-pathway gene, FOXO3A, in Japanese men over age 95 was associated with improved energy usage and greater sensitivity to insulin. (Type 2 diabetes, marked by resistance to insulin, now affects 24 million people in the U.S. alone.)

Examining the blood profiles of centenarians has also yielded tantalizing targets for further study. Barzilai observed that centenarians had higher levels and larger particles of HDL—high-density lipoprotein, or the so-called good cholesterol. Genetic screening later revealed that 24 percent of centenarians from Ashkenazi Jewish populations carry a variant in the CETP gene—an enzyme important for cholesterol metabolism—that reduces the level of the protein CETP in the blood and is linked to a lower prevalence of hypertension, cardiovascular disease and memory loss.

CETP inhibitors have been sought by the pharmaceutical industry as a method for increasing HDL levels and protecting patients against heart disease. But clinical trials of such a drug, Pfizer's Torcetrapib, were halted in 2006 when investigators discovered that it was associated with an increased risk of death from heart attack and other complications, including cancers and infections.

Daniel Rader, a cardiologist at the University of Pennsylvania School of Medicine in Philadelphia, remains optimistic, however, that other CETP inhibitors could work, because the failure of Torcetrapib was likely due to "effects on blood pressure that were unrelated to CETP inhibition." Pharmaceutical giant Merck is currently testing a new CETP inhibitor, Anacetrapib, but Rader cautions that any potential longevity benefits could simply stem from the drug's ability to decrease the risk of heart disease—the number one killer in the U.S.

More expansive genetic studies are now underway as researchers "look at the rate of genetic variation across the entire genome" of centenarians, says Thomas Perls, director of the New England Centenarian Study at Boston University. By examining over one million gene variations, scientists hope to find additional target genes for longevity studies that may not be obvious from blood screening and animal testing.

Perls acknowledges that the research is controversial as critics insist that centenarians may be too genetically diverse to pinpoint any common factors that promote healthy aging. But he points out that supercentenarians (those living past age 110) share even more genetic factors than centenarians, possibly improving the chances of finding protective gene variants. "We already know what it takes for the vast majority of us to reach our late 80s in good health," Perls says. That is, stop smoking, exercise, eat a balanced diet and manage stress. "The trick will be to get people from 88 to 100," Perls adds, "but there will never be a magic bullet." (From Scientific American Online, October 28, 2008)

Exercise 4. Who are the following scientists mentioned in the article? What point of view do they represent? What studies have they carried out?

• Daniel Rader • Thomas Perls

• Nir Barzilai • Bradley Willcox

• Judith Campisi

Exercise 5. Answer the questions:

1. Who are centenarians? What is so special about this group of people?

2. What gives scientists reasons to believe that there may be some genetic factors involved in the longevity of centenarians?

3. What is the role of insulin in fighting aging?

4. Why are expansive genetic studies necessary to uncover the secrets of longevity?

Exercise 6. Read the chapter from the book Brain Facts: a Primer on the Brain and Nervous System, 2002.

What changes occur to the brain as people age?

Picasso, Georgia O’Keefe and Grandma Moses, artists. Louise Nevelson, sculptor. Albert Einstein, physicist. Giuseppe Verdi, musician. Robert Frost, poet. Each of these great minds worked differently, but they all shared an outstanding trait: they were creative and productive in old age. They defied the popular notion that aging always leads to a pronounced decline and loss of cognitive ability.

Neuroscientists now believe that the brain can remain relatively healthy and fully functioning as it ages, and that diseases are the causes of the most severe decline in memory, intelligence, verbal fluency and other tasks. Researchers are investigating the normal changes that occur over time and the effect that these changes have on reasoning and other intellectual activities.

It appears that the effects of age on brain function vary widely. The vast majority of people get only a bit forgetful in old age, particularly in forming memories of recent events. For example, once you reach your 70s, you may start to forget names or phone numbers, or respond more slowly to conflicting information. This is not disease. However, other individuals develop senile dementia, the progressive and severe impairment in mental function that interferes with daily living. The senile dementias include Alzheimer’s and cerebrovascular diseases and affect about one percent of people younger than age 65, with the incidence increasing to nearly 50 percent in those older than 85. In a small, third group, that includes the Picassos, Einsteins and others, mental functioning seems unaffected by age. The oldest human, Jeanne Calment, was considered to have all her wits during her 122-year lifespan. The wisdom and experience of older people often make up for deficits in performance.

The belief that pronounced and progressive mental decline is inevitable was and still is popular for several reasons. For one, until the 20th century, few people lived to healthy old ages. In 1900, when life expectancy was about 47 years, three million people, or four percent of the population, were older than age 65, and typically they were ill. In 1990, when life expectancy was more than 75 years, 30 million people, or 12 percent of the population, were older than age 65. A generation ago, frailty was seen among people in their 60s; today it is more typical among those in their 80s. Moreover, few people challenged the notion that aging meant inevitable brain decline because scientists knew little about the brain or the aging process.

Aging neurons

Today’s understanding of how the normal brain ages comes from studies of the nervous system that began decades ago and are just now bearing results. Modern technologies now make it possible to explore the structure and functions of the brain in more depth than ever before and to ask questions about what actually happens in its aging cells. Thus, neuroscientists are increasingly able to distinguish between the processes of normal aging and disease. While some changes do occur in normal aging, they are not as severe as scientists once thought.

All human behavior is determined by how well the brain’s communication systems work. Often a failure in the cascade of one of these systems results in a disturbance of normal functions. Such a failure may be caused by an abnormal biochemical process or by a loss of neurons.

The cause of brain aging still remains a mystery. Dozens of theories abound. One says that specific “aging genes” are switched on at a certain time of life. Another points to genetic mutations or deletions. Other theories implicate hormonal influences, an immune system gone awry and the accumulation of damage caused by cell byproducts that destroy fats and proteins vital to normal cell function.

The brain reaches its maximum weight near age 20 and slowly loses about 10 percent of its weight over a lifetime. Subtle changes in the chemistry and structure of the brain begin at midlife in most people. During a lifetime, the brain is at risk for losing some of its neurons, but neuron loss is not a normal process of aging. Brain tissue can respond to damage or loss of neurons in Alzheimer’s disease or after stroke by expanding dendrites and refining connections between neurons. A damaged brain neuron can readjust to damage only if its cell body remains intact. If it does, regrowth can occur in dendrites and axons. When neurons are completely destroyed, nearby surviving neurons can compensate, in part, by growing new dendrites and connections.

Intellectual capacity

In the first large studies to follow the same group of normal healthy humans for many years, scientists have uncovered unexpected results. They report declines in some mental functions and improvements in others. In one study, the speed of carrying out certain tasks became slower, but vocabulary improved. Several studies found less severe declines in the type of intelligence relying on learned or stored information, compared with the type that uses the ability to deal with new information.

This research is supported by animal studies in which scientists found that changes in mental function are subtle. For example, in rodents and primates in which only minor brain abnormalities can be detected, certain spatial tasks, such as navigating to find food, tend to become more difficult with age.

The aging brain is only as resilient as its circuitry. Scientists debate whether this circuitry is changed only by neuron atrophy or whether some neuron loss over time also is inevitable. In any event, when the circuitry begins to break down, remaining neurons can respond by expanding their roles.

Learning conditions may dictate what happens to brain cells. Studies of rats shed light on some of the changes that occur in brain cells when the animals live in challenging and stimulating environments. In tests of middle-aged rats exposed to these environments, researchers found that dendrites in the cerebral cortex, which is responsible for all conscious activity, developed more and longer branches when compared with rats housed in isolated conditions. Another study showed that brain cells in rats given acrobatic training had greater numbers of synapses per cell than rats given only physical exercise or rats who were inactive. The scientists concluded that motor learning generates new synapses. Physical exercise, however, improved blood circulation in the brain.

Other scientists report that rats reared in a stimulating environment made significantly fewer errors on a maze test than did similar rats kept in an isolated environment. Moreover, the stimulated rats showed an increase in brain weight and cortical thickness when compared with the control animals.

Older rats tend to form new dendrites and synapses as do younger animals in response to enriched environments. But the response is more sluggish and not as large. Compared to younger rats, the older rats have less growth of the new blood vessels that nourish neurons.

While much has been learned about the aging brain, many questions remain to be answered. For instance, does the production of proteins decline with age in all brain neurons? In a given neuron, does atrophy cause a higher likelihood of death? How does aging affect gene expression in the brain—the organ with the greatest number of active genes? Are there gender differences in brain aging that may be due to hormonal changes at menopause?

Neuroscientists speculate that certain genes may be linked to events leading to death in the nervous system. By understanding the biology of the proteins produced by genes, scientists hope to be able to influence the survival and degeneration of neurons. (From the book Brain Facts: a Primer on the Brain and Nervous System, 2002)