Vascular in vivo Imaging After Intra-Striatal Injection of DB53 Reveals Two Distinct Kinetics of Glymphatic Efflux

Glymphatic fluid transport eliminates metabolic waste from the brain including amyloid-s and Tau, yet the pathways and mechanisms of clearance remain unclear. Here we develop a new method to evaluate glymphatic clearance in real-time. Direct Blue 53 (DB53), a stable fluorescent compound with low toxicity, is delivered in striatum and imaged in the vascular compartment where it is retained due to its high affinity for albumin. DB53 signal was detectable in femoral veins as early as 20 min post-injection in young mice while aged mice exhibited a sharp reduction in the kinetics of DB53 clearance. Pharmacokinetic modeling revealed that DB53 efflux is consistent with the existence of two efflux paths, with fast (T1/2=32 min) kinetics and slow kinetics (T1/2=170 min), demonstrating that this real-time, in vivo methodology can provide novel insights into the kinetics of brain fluid clearance.