Study explains how brain cells die in patients with Alzheimer's Disease

Mar 15 2006

Researchers at Children's Hospital & Research Center at Oakland (CHRCO) have published a new study that is the first to explain how brain cells die in patients with Alzheimer's Disease.

This discovery is an important first step to helping researchers devise ways to slow, prevent and eventually cure a disease that affects an estimated 4.5 million Americans.

In a study published in the February 28th issue of the Proceedings of the National Academy of Sciences, lead scientist Hani Atamna, Ph.D., found that alterations in the production of heme (a molecule that contains iron) may be the key to understanding why excessive amyloid-beta is toxic to brain cells. Dr. Atamna had previously discovered that Alzheimer's patients have abnormal amounts of heme in their brains. In new research results, Atamna's team showed that amyloid-beta readily binds with heme to form a compound that can be flushed from cells. When there is insufficient heme or too much amyloid-beta, however, the amyloid-beta forms large toxic "clumps" that the cell cannot dissolve and eliminate.

Though heme binding with amyloid-beta can be beneficial, if too much heme is bound up with amyloid-beta, there may be insufficient heme available for the cell to properly function. When this happens, the cell's mitochondria, which are the tiny structures inside brain cells that produce the energy the cells need to function, begin to decay. Dr. Atamna refers to this phenomenon as a "functional heme deficiency" because the cells are still forming heme, but it is trapped within an amyloid-beta/heme compound.

When they examined the heme/ amyloid-beta compound researchers in the Atamna laboratory were surprised to discover it was a peroxidase--a type of enzyme that reacts harmfully with biological materials essential for proper brain function such as serotonin and L-DOPA. Dr. Atamna believes that the combination of functional heme deficiency, which harms mitochondria needed to produce energy, together with the increase in oxidative damage caused by the peroxidase, is what eventually kills the cell.

"Until now, we didn't understand all the factors that trigger Alzheimer's disease. The discovery of the formation of amyloid-beta peroxidase provides a clear picture of why cells die in the brain of Alzheimer's patients. Our next challenge is to develop drugs that directly and selectively target the excessive peroxidase of amyloid-beta, which could lead to the first significant therapy for Alzheimer's disease."