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This is SCIENCE IN THE NEWS, in VOA Special English. I'm Bob Doughty.

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And I'm Faith Lapidus. This week, we report on two medical studies, including one for an experimental drug. We also tell how officials in some American cities are fighting climate change.

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Pfizer headquarters in New York. Researchers say it is not known yet if similar drugs being developed are dangerous, or just torcetrapib.

Earlier this month, the drug company Pfizer stopped tests of an experimental medicine because of possible health dangers. The medicine is called torcetrapib. It was developed as a way to prevent heart disease by changing cholesterol levels in the blood.

Cholesterol is a fatty substance. The human body uses cholesterol to help build and operate cells. All the cholesterol a person needs is produced in one organ, the liver. This cholesterol goes into the blood so that cells can get some when they need it.

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Low density lipoproteins, also known as L.D.L., carry cholesterol into the blood. Cholesterol in the blood that cells has not been used is considered bad cholesterol. High density lipoproteins are called H.D.L. They gather up the unused cholesterol and take it back to the liver to be destroyed.

High L.D.L. levels are evidence that the H.D.L. has been unable to remove some cholesterol from the blood. The extra cholesterol sticks to artery walls. This can block blood flow and cause a heart attack or stroke. High H.D.L. levels mean that the unneeded cholesterol is being moved out of the blood and back to the liver. This prevents cholesterol from sticking to the arteries.

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Torcetrapib was designed to increase the amount of good cholesterol in the blood. Pfizer was testing the drug on fifteen thousand heart patients when the study ended. The patients were divided into two groups of seventy-five hundred each.

One group took torcetrapib and Lipitor -- a drug that reduces bad cholesterol. The other took Lipitor alone. A Pfizer official said the group taking the torcetrapib experienced too many heart problems and deaths for the study to continue. He said eighty-two people died in the group taking both drugs. Fifty-one people died in the group taking only Lipitor.

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Reports say torcetrapib was causing concerns among researchers because another study showed it could increase blood pressure in some persons. Still, it is not known why the patients taking the drug suffered unacceptable levels of health problems.

Researchers say other drugs to increase good cholesterol are also being tested. But they say it is too early to tell if all such drugs are dangerous or if it was just something about torcetrapib that caused the problem.

In fact, an already approved drug raises good cholesterol without causing serious health problems. That drug, Niaspan, is made by Kos Pharmaceuticals.

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A study done two years ago found that Niaspan taken with drugs to reduce bad cholesterol stopped blocked arteries from getting worse. The study also involved two groups of patients. One took only a drug that lowers bad cholesterol. The other took that drug and Niaspan. The study showed fewer health problems among those who took Niaspan.

Today, Kos Pharmaceuticals and America's National Institutes of Health are carrying out a similar test. It involves more than three thousand patients at about sixty medical centers.

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Another study is expected to change the way doctors treat people with severe back pain from a herniated disk. The American Academy of Orthopedic Surgeons says disks are soft substances found between the bones of the back. These bones extend from the back of the head in a line down the body. In the center of this line of bones is a space that contains the spinal cord and other nerves. Disks help the back to move. They also protect the spinal cord and the nerves.

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Disks in the lower back have a thick, outer covering and a softer, gel-like substance on the inside. A disk is said to herniate when some of the gel-like substance pushes through the outer covering. This puts pressure on the nerves. The result is pain or weakness in one or both legs.

Spinal disks reduce in size as people age. The spaces between them get smaller, and the disks are able to move less easily than before. So a fall or any sudden movement can damage them. The most common sign that this has happened is a sharp pain from the top of the back of the leg all the way down to the foot. Other signs include weakness or a lack of feeling in one or both legs.

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Normal medical treatment of a herniated disk is to operate and remove it. A study concerning this treatment was recently published in the Journal of the American Medical Association.

The study looked at patients who suffered a herniated disk in the lower back. It compared those who had the operation with those treated with a combination of rest, light exercise and pain medicine. Both groups reported improvement after three to six months. After two years, about seventy percent of the patients in both groups reported major improvement in their conditions.

The researchers say the study showed that people with this kind of disk damage often recover, even when they do not have the operation. The study did find that operating soon after the injury appeared to ease the pain more quickly than waiting. But it found that using other methods to ease the pain did not cause any real damage to the body.

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Many cities in the United States are competing against each other to be the greenest. The cities are attempting to limit the industrial gases they release into Earth's atmosphere.

Studies have shown that average temperatures are slowly rising worldwide. Many scientists believe industrial gases are to blame. But other scientists are unsure how such gases affect the climate.

Industrial gases are also known as greenhouse gases. Greenhouses are clear glass or plastic buildings used to grow plants. The glass or plastic traps the heat of the sun.

Earth's atmosphere acts like a greenhouse. Carbon dioxide, water vapor and other gases in the atmosphere trap heat from the sun. Some human activities have been shown to increase production of these gases.

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Recently, officials in cities like Seattle, Washington have been setting goals for carbon dioxide reduction. They are also urging people to use methods of transportation other than cars.

The city of Chicago, Illinois, for example, is planting trees and creating grassy areas on building tops where plants and flowers can grow. And, the mayor of New York has announced plans to make his city the leader in reducing greenhouse gases.

In all, mayors of more than three hundred American cities have said they will recognize the goals of the Kyoto Protocol. The treaty was reached nine years ago at the United Nations Conference on Climate Change in Kyoto, Japan.

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At the conference, major industrial nations agreed to reduce the amount of greenhouse gases they release into the atmosphere. The reductions are to take place between two thousand eight and two thousand twelve.

The United States Senate never approved the Kyoto Protocol. The main reason is because President Bush said the reductions would hurt the American economy. The Bush administration says it supports efforts to reduce greenhouse gases as long as they are done by choice, and not required by law.

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Yet some local governments are making changes. One of the biggest examples is in the state of California. Earlier this year, California Governor Arnold Schwarzenegger signed a law requiring reductions in the state's release of greenhouse gases. The plan limits major industries, including coal-burning producers of electric power. Others include oil and gas processing centers and producers of building materials.

Recently, the United States Conference of Mayors announced an agreement with the American Institute of Architects. They plan to cut in half the amount of oil, coal and gas used to build and operate buildings by two thousand ten. They then want to continue with reductions. By two thousand thirty, they want make buildings that will completely end their use of such fuels.

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SCIENCE IN THE NEWS was written by Nancy Steinbach and Brianna Blake, who also served as our producer. I'm Bob Doughty.

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And I'm Faith Lapidus. Join us again next week for more news about science in Special English on the Voice of America.