A synchrotron light source helped provide one more piece of the puzzle that may help doctors diagnose Alzheimer’s disease early on, before it does permanent neurological damage.
A research team led by Lisa Miller, a biophysical chemist at the National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory and Stony Brook University, reports high levels of iron are associated with the formation of amyloid plaques, the misfolded protein clumps responsible for the deterioration of neurons in Alzheimer’s victims.
A protein is a string of amino acids folded into a three-dimensional shape that gives it its function. In patients with Alzheimer’s disease, Abeta proteins improperly fold, causing them to have a high affinity for each other. The resulting protein clumps, known as amyloid plaques, are associated with the progression of Alzheimer’s and have been found to contain high levels of metals.
Miller’s team performed X-ray fluorescence microscopy (XFM) experiments to study brain tissue samples in a mouse model of Alzheimer’s disease. XFM uses synchrotron X-rays to light up metals in brain tissue samples.
“We’re trying to understand the role of normal metal ions— iron, copper, zinc— in the formation of Alzheimer’s disease and its progression and pathology,” Miller said.
Previous studies have found elevated levels of metal ions are associated with the plaques in the brain tissue of patients with late-stage Alzheimer’s disease, but it remains unclear when and why this metal accumulation occurs.
Researchers in Miller’s lab studied mice that had been genetically engineered to overexpress Abeta – the protein that aggregates to form amyloid plaques. They used XFM, at both NSLS at Brookhaven National Laboratory and the Advanced Photon Source at Argonne National Laboratory, to image the Ca, Fe, Cu, and Zn in the mouse brains and looked at how the levels of each metal changed over time.
They found that late-stage mouse plaques accumulated zinc in the hippocampus, the region of the brain responsible for long-term memory storage. They also noticed a correlation between elevated iron levels in the cortex, the region responsible for higher brain functions such as thought and reasoning, and the onset of plaque formation, although iron was not found within the plaques themselves (see Figure).
The latter observation provides extremely valuable information to doctors, who may be able to look at patients’ brain iron levels using MRI to get clues about the early onset of Alzheimer’s disease, Miller said.
On a molecular scale, Miller is interested in shedding light on the complex mechanism underlying Alzheimer’s disease. Her lab’s involvement in Alzheimer’s research started eight years ago when they analyzed samples of human brain tissue from patients who had died of Alzheimer’s disease and found amyloid plaques loaded with metals.
Since that time, Miller has been designing experiments to figure out how amyloid plaques exert their toxic effects and what role metal ions play. Her lab uses XFM for these experiments since it is a unique technique for simultaneously imaging and quantifying the levels of iron, copper and zinc at microscopic resolution in biological samples.
When it comes to imaging with XFM, brighter photon sources can achieve higher spatial resolution. The researchers used NSLS to achieve a spatial resolution on the order of tens of microns for imaging the mouse and human plaques. For more precise imaging of the cortex and hippocampus, they looked to APS, a newer and brighter synchrotron, to image large areas with a spatial resolution down to a few microns.
Not only will these experiments pave the way for early diagnosis, they could help lay the groundwork for the development of therapeutic interventions.
Currently, there is no cure for Alzheimer’s disease and diagnosis depends on a series of cognitive tests performed long after the onset of the disease process.
“Symptoms for Alzheimer’s disease don’t start until well after amyloid plaques have formed and many brain cells have died,” Miller said. However, it appears as though iron levels become elevated long before symptoms develop, making Fe a potentially important biomarker for early Alzheimer’s disease diagnosis and intervention before the disease progresses.
For more information, read the paper in NeuroImage.