Vitamin C Shown To Cross The Blood Brain Barrier

New York, November 30, 1997 -- The blood brain barrier has long been regarded as the body's most formidable gatekeeper. It is a virtual fortress of blood vessels that forms a protective barrier between the blood and brain, screening any chemical that attempts to access the brain's inner sanctum. But the blood brain barrier's protective role can be a drawback, as it also blocks access to substances that would be good for the brain. One such substance is vitamin C, an antioxidant that is essential to keep the central nervous system functioning properly.

Now, researchers at Memorial Sloan-Kettering Cancer Center have discovered how to get large amounts of vitamin C past the blood brain barrier so that it is transported and retained in the brains of laboratory mice. This finding may prove useful in efforts to slow the progression of certain neurodegenerative diseases, such as Alzheimer's. The investigators report their findings in the December 1st issue of the Journal of Clinical Investigation.

"We now know how to get large amounts of an antioxidant into the brain," said Dr. David Agus, an oncologist at Memorial Sloan-Kettering Cancer Center and lead author of the study.

The researchers studied vitamin C absorption in the brain to determine why it was present in this organ's tissue at higher concentrations than any other area of the body. Earlier research by Dr. David Golde, Physician-in-Chief of Memorial Hospital, and his colleagues had established that specific glucose transporter molecules were responsible for transporting vitamin C into cells. This process occurs when vitamin C, which is used by cells in the form of ascorbic acid, is converted into the form of dehydroascorbic acid and transported into the cell. Once inside, the vitamin is converted back to ascorbic acid.

Building on this research, Drs. Agus, Golde and their colleagues reasoned that vitamin C would cross the blood brain barrier as dehydroascorbic acid via the same glucose transport mechanism and be retained as ascorbic acid in the brain. To find out, mice were injected with either ascorbic acid, dehydroascorbic acid, or sucrose (as a measure of blood volume) and their brains were subsequently analyzed at varying time intervals for vitamin C content. The researchers found that ascorbic acid was not able to cross the blood brain barrier, while dehydroascorbic acid readily entered the brain and was retained in the tissue as ascorbic acid.

Although scientists do not know the exact role that vitamin C plays in the brain, recent studies have shown that various vitamin compounds with antioxidant-like properties can slow the progression of moderately severe Alzheimer's disease. In addition, vitamin C is also known to act as a scavenger of free radicals - substances that play a role in causing diseases.

"Our findings from this study have therapeutic implications because we can potentially increase vitamin C concentrations in the brain by increasing the blood level of dehydroascorbic acid," said Dr. Golde. He added that this was not possible by taking vitamin C as an oral supplement because most of it would be excreted in the urine.

Now, the researchers are conducting on-going laboratory experiments in mice to test the clinical effectiveness of large amounts of dehydroascorbic acid. They hope to increase the antioxidant potential in the brain.

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 & World Report.