A team of researchers from Université Laval, CHU de Québec, and pharmaceutical firm GlaxoSmithKline (GSK) has discovered a way to stimulate the brain’s natural defense mechanisms in people with Alzheimer’s disease. This major breakthrough, details of which are presented today in an early online edition of the Proceedings of the National Academy of Sciences (PNAS), opens the door to the development of a treatment for Alzheimer’s disease and a vaccine to prevent the illness.
One of the main characteristics of Alzheimer’s disease is the production in the brain of a toxic molecule known as amyloid beta. Microglial cells, the nervous system’s defenders, are unable to eliminate this substance, which forms deposits called senile plaques.
The team led by Dr. Serge Rivest, professor at Université Laval’s Faculty of Medicine and researcher at the CHU de Québec research center, identified a molecule that stimulates the activity of the brain’s immune cells. The molecule, known as MPL (monophosphoryl lipid A), has been used extensively as a vaccine adjuvant by GSK for many years, and its safety is well established.
In mice with Alzheimer’s symptoms, weekly injections of MPL over a twelve-week period eliminated up to 80% of senile plaques. In addition, tests measuring the mice’s ability to learn new tasks showed significant improvement in cognitive function over the same period.
The researchers see two potential uses for MPL. It could be administered by intramuscular injection to people with Alzheimer’s disease to slow the progression of the illness. It could also be incorporated into a vaccine designed to stimulate the production of antibodies against amyloid beta. “The vaccine could be given to people who already have the disease to stimulate their natural immunity,” said Serge Rivest. “It could also be administered as a preventive measure to people with risk factors for Alzheimer’s disease.”
Alzheimer’s disease (AD) is the most common cause of dementia worldwide. The pathogenesis of this neurodegenerative disease, currently without curative treatment, is associated with the accumulation of amyloid β (Aβ) in brain parenchyma and cerebral vasculature. AD patients are unable to clear this toxic peptide, leading to Aβ accumulation in their brains and, presumably, the pathology associated with this devastating disease. Compounds that stimulate the immune system to clear Aβ may therefore have great therapeutic potential in AD patients. Monophosphoryl lipid A (MPL) is an LPS-derived Toll-like receptor 4 agonist that exhibits unique immunomodulatory properties at doses that are nonpyrogenic. We show here that repeated systemic injections of MPL, but not LPS, significantly improved AD-related pathology in APPswe/PS1 mice. MPL treatment led to a significant reduction in Aβ load in the brain of these mice, as well as enhanced cognitive function. MPL induced a potent phagocytic response by microglia while triggering a moderate inflammatory reaction. Our data suggest that the Toll-like receptor 4 agonist MPL may be a treatment for AD.
SOURCES – Eurekalert, PNAS