Mar. 27, 1998 New York, April 1, 1998 -- Ever since vitamin C was found to prevent scurvy -- a disease that has killed millions of people throughout history -- scientists have known that the vitamin plays an essential role in the body's defense against disease. Immune cells, for example, are known to accumulate and retain high levels of vitamin C, but just how this process occurs, has largely remained a mystery. Now, researchers at Memorial Sloan-Kettering Cancer Center have found that the same class of proteins -- called growth factors -- which are known to control growth and production of immune cells also increase their ability to take up vitamin C. The findings, which are reported in the April issue of the journal Blood, shed new light on the connection between vitamin C and the immune system, showing how growth factors can increase the amount of vitamin C in immune cells.
"We now know that the growth factors that boost immunity also increase the amount of vitamin C in the immune cells," said Dr. David Golde, Physician-in-Chief of Memorial Sloan-Kettering Cancer Center and senior author of the study.
The researchers studied vitamin C in immune cells to determine whether growth factors played a role in regulating this process. Previous research had shown that growth factors caused immune cells to take up more glucose -- a process that increases the metabolic fuel available for cellular function. One of those growth factors, called granulocyte-macrophage colony-stimulating factor, or GM-CSF was purified in Dr. Golde's laboratory in 1984 and is being used in the treatment of cancer patients to help boost their immune systems following bone marrow transplantation.
Building on this discovery, Dr. Golde identified a portion of the GM-CSF receptor on the cell's surface that stimulates the immune cell to take in glucose. This discovery just happened to coincide with earlier research in his laboratory led by Dr. Juan Carlos Vera establishing that specific glucose transporter molecules were responsible for transporting vitamin C into cells.
Coupling the findings from these two lines of research, Drs. Vera, Golde and their colleagues showed that GM-CSF increased vitamin C in target immune cells by two distinct mechanisms. The first effect was to increase the function of the specialized transporters on the cell surface for glucose and vitamin C. The second mechanism involved stimulation of the oxidation of ascorbic acid to dehydroascorbic acid, the transportable form of the vitamin. Thus, the researchers found that GM-CSF increased the amount of vitamin C that was taken up by the immune cells.
"Our results establish a role for the growth factors in stimulating the uptake of vitamin C in host defense cells, connecting increased vitamin C uptake with activation of immune function," said Dr. Golde.
Although many claims have been made for the positive effects of vitamin C, Dr. Golde explains that more research is needed to determine the exact role that vitamin C plays in boosting immune defense. "It's important to understand that our laboratory research relates to the oxidized form of vitamin C, dehydroascorbic acid, which is the form that is transported into cells. This is not the same as oral vitamin C supplements that come in the reduced form of ascorbic acid, most of which is excreted through urine," added Dr. Golde.
Memorial Sloan-Kettering Cancer Center is the world's oldest and largest private institution devoted to prevention, patient care, research, and education in cancer. Throughout its long, distinguished history, the Center has played a leadership role in defining the standard of care for patients with cancer. In 1997, Memorial Sloan-Kettering was named the nation's best cancer center for the fifth consecutive year by U.S. News and World Report.
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