Multimodal analysis of aged wild-type mice exposed to repeated scanning ultrasound treatments demonstrates long-term safety

Abstract

The blood-brain barrier presents a major challenge for the delivery of therapeutic agents to the brain; however, it can be transiently opened by combining low intensity ultrasound with microbubble infusion. Studies evaluating this technology have largely been performed in rodents, including models of neurological conditions. However, despite promising outcomes in terms of drug delivery and the amelioration of neurological impairments, the potential for long-term adverse effects presents a major concern in the context of clinical applications.Methods: To fill this gap, we repeatedly treated 12-month-old wild-type mice with ultrasound, followed by a multimodal analysis for up to 18 months of age.Results: We found that spatial memory in these aged mice was not adversely affected as assessed in the active place avoidance test. Sholl analysis of Golgi impregnations in the dentate gyrus of the hippocampus did not reveal any changes to the neuronal cytoarchitecture. Long-term potentiation, a cellular correlate of memory, was still achievable, magnetic resonance spectroscopy revealed no major changes in metabolites, and diffusion tensor imaging revealed normal microstructure and tissue integrity in the hippocampus. More specifically, all measures of diffusion appeared to support a neuroprotective effect of ultrasound treatment on the brain.Conclusion: This multimodal analysis indicates that therapeutic ultrasound for blood-brain barrier opening is safe and potentially protective in the long-term, underscoring its validity as a potential treatment modality for diseases of the brain.

Understanding ultrasound-mediated blood-brain barrier opening as a potential non-invasive therapeutic approach for Alzheimer’s disease

“…Olumolade and colleagues conducted biweekly or monthly sonications over 5 months, safely targeting the striatum without observing any adverse effects on the behavior of wild-type mice [203]. Another study from the lab also analyzed the long-term effects of SUS in aged wild-type mice, using various imaging tools, showing that ultrasound treatment is potentially safe in older animals [171]. Our current study complements these findings regarding the safety of multiple ultrasound treatments, suggesting that by choosing appropriate ultrasound parameters, longer durations of ultrasound treatments for the entire brain are potentially safe.…”

“…FUS has shown promising effects in tau-specific antibody delivery into the brain as well as in reducing Aβ plaque and tau load in mouse models of AD [19,20,168]. In addition, ultrasound treatment was safe in a number of animal models [17,171,251]. As such, FUS combined with microbubbles is a promising method for more efficient drug delivery across the BBB.…”

“…Safety studies have also been performed in wild-type mice following multiple ultrasound treatments, revealing no impairment in neuronal excitability or changes in dendritic morphology [170]. A multimodal analysis of long-term functional cognitive read-outs, neuronal morphology and memory in aged mice reported similar positive outcomes [171]. Importantly, these studies have also been extended to larger animals, such as sheep, macaques and aged beagles demonstrating opening of the BBB without histological evidence of microhemorrhages or cell damage [172][173][174][175].…”

“…FUS was targeted at the left hippocampus for 1 min. Previous studies have shown that these parameters successfully open the BBB when targeted to this brain region [171].…”

“…diluted with an equal volume of saline and individual vials were agitated in a dental amalgamator at 4,000 rpm for 45 s to generate the microbubbles. The microbubbles were characterized for their size and concentration using a Multisizer 4e coulter counter (Beckman Coulter) as previously described [171].…”