IMAGING HYDROGEN PEROXIDE IN ALZHEIMER’S DISEASE VIA CASCADE SIGNAL AMPLIFICATION

Abstract

It has long been believed that Alzheimer’s disease (AD) is closely associated with oxidative stress. In AD brains, the reactive oxygen species (ROS) level is significantly higher than that of healthy control brains. Evidence suggests that under Alzheimer’s disease conditions, a vicious cycle revolves around amyloid beta (Aβ) production, Aβ aggregation, plaque formation, microglia/immunological responses, inflammation, and ROS production. In this cycle, ROS species play a central role, and H2O2is one of the most important ROS species. In this report, we have designed a fluorescent imaging probe CRANAD-88, which is capable of cascade amplifying near infrared fluorescence (NIRF) signals at three levels upon interacting with H2O2in AD brains. The first level of amplification is from the probe’s reaction with H2O2, and the second level is originated from the interaction of Abs with an intermediate produced by the H2O2 reaction. The third level of amplification is an “indirect” increase. CRANAD-88 itself is not an NIRF probe due to its short excitation (Ex=580nm), Thus, it is “invisible” under NIRF imaging parameters; however, it becomes “visible” once it reacts with H2O2 to produce a red-shift NIRF intermediate. The transformation of CRANAD-88 from “invisible” to “visible” can significantly reduce background signal, and thus lead to an increase of signal/noise ratio, which can be considered to be the third level of signal amplification. We demonstrated that the three levels of amplification were feasible in vitro and in vivo. Remarkably, we showed that, for the first time, it was feasible to monitor the changes of H2O2 concentrations from AD brains before and after treatment with pyruvate, an H2O2 scavenger. Our method opens new revenues to investigate H2O2 in AD brain and can be very instructive for drug development and treatment regime design.