Rose bengal conjugated gadolinium complex as a new multimodal imaging agent targeting presynaptic vesicular glutamate transporters

Glutamate is an important excitatory neurotransmitter, and vesicular glutamate transporters (VGLUTs) are critical in regulating the extent of glutamate release. Because initial increase and late stage decrease in VGLUT expression were implicated in progressive Alzheimer's disease (AD), VGLUTs can be a new imaging target for diagnosing AD. In this study, we have designed and synthesized a new multimodal gadolinium contrast agent conjugated with rose bengal to target VGLUTs (Gd-DO3A-RB). In addition to high kinetic and pH stability, magnetic resonance and fluorescence imaging using Gd-DO3A-RB showed high affinity to VGLUT1. Using the AD animal model (5XFAD), in vivo MRI with a Gd-DO3A-RB showed less MR signal enhancement in 5XFAD mouse brain than that of age-matched normal C57BL/6 mouse, suggesting a late stage decrease in VGLUT expression in AD animal model. Therefore, this new VGLUT targeting gadolinium contrast agent demonstrated a strong potential as a new diagnostic tool for AD with multimodal imaging capability.