Serial failure of the brain clearance continuum in Alzheimer's disease: mechanisms and therapeutic perspectives.

Alzheimer's disease (AD) is usually regarded as a neurodegenerative disorder defined by amyloid-β (Aβ) deposition and abnormal tau accumulation. Increasing evidence suggests that reduced clearance of metabolic waste and pathological proteins from the brain also contributes to disease onset and progression. Previous studies have often considered choroid plexus (CP) function, glymphatic exchange, and meningeal lymphatic drainage as separate clearance processes. A continuous framework linking these structures and functions is still lacking. This review integrates recent clinical and experimental evidence and proposes the brain clearance continuum as an interpretative framework. It describes three interlinked functional interfaces: the upstream choroid plexus-cerebrospinal fluid (CP-CSF) inflow interface, the midstream parenchymal perivascular exchange interface, and the downstream meningeal lymphatic outflow interface. Under physiological conditions, these interfaces support CSF movement, parenchymal solute exchange, and the outward removal of metabolic waste. In AD, disrupted CSF homeostasis, impaired perivascular exchange, and obstructed meningeal lymphatic outflow may interact, leading to serial failure of the brain clearance continuum. This process is closely associated with Aβ/tau accumulation, vascular dysfunction, neuroinflammation, and cognitive decline. We also summarise potential therapeutic strategies directed at different clearance interfaces, whilst emphasising that most evidence remains preclinical or exploratory. The brain clearance continuum provides a systematic framework for understanding clearance failure in AD. It may also offer a theoretical basis for future mechanistic studies and therapeutic development that are stratified by clearance interface and disease stage.