Combining Low-Dose Radiation Therapy and Magnetic Resonance Guided Focused Ultrasound to Reduce Amyloid-ß Deposition in Alzheimer's Disease.

Amyloid-ß deposition is one of the neuropathological hallmarks of Alzheimer's disease (AD), but pharmacological strategies toward its reduction are poorly effective.Preclinical studies indicate that low-dose radiation therapy (LD-RT) may reduce brain amyloid-ß. Animal models and proof-of-concept preliminary data in humans have shown that magnetic resonance guided focused ultrasound (MRgFUS) can reversibly open the blood-brain-barrier and facilitate the delivery of targeted therapeutics to the hippocampus, to reduce amyloid-ß and promote neurogenesis in AD. Ongoing clinical trials on AD are exploring whole-brain LD-RT, which may damage radio-sensitive structures, i.e., hippocampus and white matter, thus contributing to reduced neurogenesis and radiation-induced cognitive decline. However, selective irradiation of cortical amyloid-ß plaques through advanced LD-RT techniques might spare the hippocampus and white matter. We propose combined use of advanced LD-RT and targeted drug delivery through MRgFUS for future clinical trials to reduce amyloid-ß deposition in AD since its preclinical stages.

Cranial irradiation significantly reduces beta amyloid plaques in the brain and improves cognition in a murine model of Alzheimer's Disease (AD).

BACKGROUND AND PURPOSE: To investigate if cranial X-irradiation reduces amyloid-ß (Aß) plaques and influences cognitive function in a transgenic mouse model of AD. METHODS AND MATERIALS: B6.Cg-Tg (APPswePSEN1dE9)85Dbo/J AD-prone mice were given cranial X-irradiation. The number of Aß plaques, along with expression of AD specific genes (84 genes: Mouse Alzheimer's Disease RT(2) Profiler), radiation-associated cytokines (Milliplex MAP Mouse Cytokine Chemokine Immunoassay) and immunohistochemistry (IL10, IL-1ß, Iba1 CD45) was assessed. Behavioral testing was performed to relate changes in Aß burden to cognitive function using a Morris water-maze task. RESULTS: Single X-ray doses reduced the number (p=0.002) and size (p=0.01) of Aß plaques. Low-dose fractionation produced greater 50.6% (1 Gy × 10), 72% (2 Gy × 5) and 78% (2 Gy × 10) reductions. Irradiation was associated with gene (Pkp4, 1.5-fold, p=0.004) and proteomic (MIP-2, 8-fold, p=0.0024) changes at 24-48 h. Microglia increased at 4 weeks post-irradiation (p=0.001). The reduction in Aß burden (2 Gy × 5) was associated with cognitive improvement (p=0.012). CONCLUSION: This is the first report that a clinically relevant course of external beam irradiation (2 Gy × 5) produces a significant reduction in AD-associated amyloid-ß plaques with a subsequent improvement in cognitive function. However, longer-term studies are needed to define the precise underlying mechanism and longevity of this response.