At ICAD 2010 in Hawaii Dr. Sam Gandy of Cure Alzheimer’s Research Consortium presented the results of a study showing a new class of biomarkers that can stick to protein structures in the body and emit colors reflecting the different shapes or forms of the proteins. They are called luminescent conjugated oligothiophenes (LCOs) or luminescent conjugated polymers (LCPs). Among other uses, they are currently being employed in test tubes, animal models and autopsied Alzheimer’s brains to study the structure of protein deposits caused by the disease. The new markers bind to the two well-established hallmarks of Alzheimer’s – beta amyloid plaques and tau tangles – and glow different colors depending on which forms of the deposits they “stick” to (e.g., plaques often “glow” orange, while tangles glow yellowish green).
In this study Sam Gandy, MD, PhD, of Mount Sinai School of Medicine, New York, and colleagues used LCOs/LCPs to investigate the possibility that the shape of brain protein deposits in people with Alzheimer’s who have the APOE ε4/ε4 gene type (highest risk) is different from those having APOE ε3/ε3 (neutral risk).
Frozen brain sections from people who died with Alzheimer’s were stained using two LCPs/LCOs: pentamer formyl thiophene acetic acid (pFTAA) and polythiophene acetic acid (PTAA). Using PTAA, the researchers observed that Alzheimer patients with APOE ε4/ε4 had core and cerebrovascular amyloid of different shapes, while in people with APOE ε3/ε3 the two amyloid structures had the same shape. Using pFTAA revealed that tau tangle densities in ε4/ε4 Alzheimer patients that were apparently greater than those with ε3/ε3.
“The findings support our hypothesis that APOE genotype changes amyloid structure,” Gandy said. “This is important because the different shapes might respond differently to treatments that attempt to clear amyloid deposits from the brain.”
In some recent drug trials, the experimental therapy provided benefits in people who had a certain type of the APOE gene (known as ) but were less effective or not effective in another type ().
LCOs and LCPs have been pioneered by Peter Nilsson of Linköping University in Sweden, and the study involved collaborating teams from Charité Medical University in Berlin (led by Frank Heppner), from Washington University in St Louis (led by David Holtzman), and from other labs at Mount Sinai (led by Patrick Hof and Dara Dickstein).