PyrPeg, a Blood-Brain-Barrier-Penetrating Two-Photon Imaging Probe, Selectively Detects Neuritic Plaques, Not Tau Aggregates.

Amyloid-β (Aβ) tracers have made a significant contribution to the treatment of Alzheimer's disease (AD) by allowing a definitive diagnosis in living patients. Unfortunately, they also detect tau and other protein aggregates that compromise test accuracy. In AD research, there has been a growing need for in vivo Aβ imaging by two-photon microscopy, which enables deep-brain-fluorescence imaging. There is no suitable neuritic Aβ probe for two-photon microscopy. Here we report PyrPeg, a novel two-photon fluorescent probe that can selectively target insoluble Aβ rather than tau and α-synuclein aggregates in the AD model brain and postmortem brain. When injected intravenously, PyrPeg detects the neuritic plaques in the brain and olfactory bulb of the AD model. PyrPeg may serve as a useful blood-brain-barrier-penetrating diagnostic tool for optical and functional monitoring of insoluble forms of Aβ aggregates in the living AD brain.