"Heavy hormones
Lower weight and more physical activity can affect the production of insulin, the hormone that allows the body to soak up fuel. After a meal, food is broken down into glucose, which is the body's main source of energy. Insulin triggers cells to take up and use glucose. As a person gains excess weight, the cells can become resistant to insulin's actions. To compensate, the pancreas begins to produce more insulin, but it can't stay in overdrive indefinitely. Eventually, insulin production will fall and blood glucose levels rise in some people.
The potent hormone IGF-1 and the related IGF-2 are very similar to insulin, helping support rapidly dividing cells, especially during childhood and adolescence. IGF-1 is a powerful driver of cell growth and body size: A toy poodle is a standard poodle with a faulty IGF-1 system.
The link between these insulinlike hormones and obesity is less clear than the connection between insulin and obesity. Although insulin and IGF-1 have individual parking places, or receptors, on a cell, some experiments suggest that at high enough levels, insulin starts to trespass on the IGF-1 receptor, LeRoith says.
In the late 1980s, laboratory researchers demonstrated that IGF-1 might have a role in cancer. Tumor cells were found to contain the IGF-1 receptor. In 1989, experiments with mice showed that blocking the receptor with an antibody could stop tumor growth. Researchers also found that mice bred to lack IGF-1 receptors in all their tissues were born tiny, thereby establishing the hormone's significance in growth. More important for cancer research, cells taken from the miniature mice lacking IGF-1 receptors could not be transformed into tumor cells.
"A cancer cell has to have the IGF-1 receptor," says Renato Baserga of the Kimmel Cancer Center at Thomas Jefferson University in Philadelphia, one of the field's pioneers. "If not, it cannot grow."
At first, results like these were puzzling. Unlike cancer genes that encode other proteins and start down the path to cancer after mutating, the IGF-1 receptor gene wasn't altered in tumors. Also, IGF-1 receptors show up in normal tissues throughout the body. The hormone itself is such a basic substance for animal life that even flies produce it. It was hard to imagine that a normal receptor found in normal cells could have anything to do with cancer.
Then scientists had an idea. Malignant cells may be overly dependent on IGF-1 receptors, on a scale far surpassing the dependence of normal cells. A tumor is like a car—a gas-guzzling Hummer—with a stuck accelerator and no brakes. Even if IGF-1 doesn't spark the ignition, the hormone keeps the gas tank full. Block IGF-1, according to this line of thinking, and the tumor suddenly finds itself running on empty. "
More on this interesting and thought provoking topic tomorrow.Labels: anti-aging, cancer, health, obesity |
