Book 1 Reading and Speaking (1108795), страница 22
Текст из файла (страница 22)
The reason, say scientists who study this elite group: centenarians may possess genes that protect themfrom disease into old age. One in every 10,000 individuals in the U.S. reaches the age of 100. There are currentlyan 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 intotheir 90s, if not longer.To better understand their exceptional longevity, scientists have recruited centenarians for extensive physicaland genetic screening.
Of particular interest to researchers is that some of the oldsters have a history of obesityand heavy smoking. But despite these risk factors, most centenarians remain healthy up to the last few months oftheir 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 geneticcomponent," says Nir Barzilai, a geneticist at the Albert Einstein College of Medicine in New York City. In fact, headds, the odds of centenarians having a relative who lived into old age is 20 times that of the average person.
Thegoal now is "to find the subtle genetic differences between individuals in the genes or families of genes associatedwith 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 thatwill promote healthy aging and delay age-related diseases such as some cancers, arthritis, diabetes, high bloodpressure and heart disease.The first genetic clues for slowing aging emerged from animal models in which the effect of individual geneson average life spans could be tested. From these early studies, it became clear that insulin (a hormone secretedby the pancreas that signals cells to absorb sugar) and its receptors are critical for longevity in species from yeastor fungi to humans.
Insulin lies at the heart of the "biological pathway whose main function is to affect howefficiently we process food into energy," says Bradley Willcox, a geriatrics specialist at the University of Hawaii. Histeam recently found that a variant in the insulin-pathway gene, FOXO3A, in Japanese men over age 95 wasassociated with improved energy usage and greater sensitivity to insulin. (Type 2 diabetes, marked by resistance toinsulin, now affects 24 million people in the U.S. alone.)Examining the blood profiles of centenarians has also yielded tantalizing targets for further study.
Barzilaiobserved that centenarians had higher levels and larger particles of HDL—high-density lipoprotein, or the so-calledgood cholesterol. Genetic screening later revealed that 24 percent of centenarians from Ashkenazi Jewishpopulations carry a variant in the CETP gene—an enzyme important for cholesterol metabolism—that reduces thelevel of the protein CETP in the blood and is linked to a lower prevalence of hypertension, cardiovascular diseaseand memory loss.CETP inhibitors have been sought by the pharmaceutical industry as a method for increasing HDL levels andprotecting patients against heart disease. But clinical trials of such a drug, Pfizer's Torcetrapib, were halted in 2006when investigators discovered that it was associated with an increased risk of death from heart attack and othercomplications, including cancers and infections.Daniel Rader, a cardiologist at the University of Pennsylvania School of Medicine in Philadelphia, remainsoptimistic, 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 testinga new CETP inhibitor, Anacetrapib, but Rader cautions that any potential longevity benefits could simply stem fromthe 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 variationacross the entire genome" of centenarians, says Thomas Perls, director of the New England Centenarian Study at51Boston University.
By examining over one million gene variations, scientists hope to find additional target genes forlongevity 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 toogenetically diverse to pinpoint any common factors that promote healthy aging. But he points out thatsupercentenarians (those living past age 110) share even more genetic factors than centenarians, possiblyimproving the chances of finding protective gene variants. "We already know what it takes for the vast majority ofus to reach our late 80s in good health," Perls says. That is, stop smoking, exercise, eat a balanced diet andmanage 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 theyrepresent? What studies have they carried out?• Daniel Rader• Thomas Perls• Nir Barzilai• Bradley Willcox• Judith CampisiExercise 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 longevityof 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 anoutstanding trait: they were creative and productive in old age. They defied the popular notion that aging alwaysleads 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, andthat 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 onreasoning and other intellectual activities.It appears that the effects of age on brain function vary widely. The vast majority of people get only a bitforgetful in old age, particularly in forming memories of recent events.
For example, once you reach your 70s, youmay 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 thatinterferes with daily living. The senile dementias include Alzheimer’s and cerebrovascular diseases and affectabout one percent of people younger than age 65, with the incidence increasing to nearly 50 percent in those olderthan 85. In a small, third group, that includes the Picassos, Einsteins and others, mental functioning seemsunaffected by age. The oldest human, Jeanne Calment, was considered to have all her wits during her 122-yearlifespan. 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 severalreasons.
For one, until the 20th century, few people lived to healthy old ages. In 1900, when life expectancy wasabout 47 years, three million people, or four percent of the population, were older than age 65, and typically theywere 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 typicalamong those in their 80s.
Moreover, few people challenged the notion that aging meant inevitable brain declinebecause scientists knew little about the brain or the aging process.Aging neuronsToday’s understanding of how the normal brain ages comes from studies of the nervous system that begandecades ago and are just now bearing results. Modern technologies now make it possible to explore the structureand functions of the brain in more depth than ever before and to ask questions about what actually happens in itsaging cells. Thus, neuroscientists are increasingly able to distinguish between the processes of normal aging anddisease. 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 thecascade of one of these systems results in a disturbance of normal functions.
Such a failure may be caused by anabnormal 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 “aginggenes” are switched on at a certain time of life. Another points to genetic mutations or deletions. Other theories52implicate hormonal influences, an immune system gone awry and the accumulation of damage caused by cellbyproducts 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 alifetime.
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