A new QIMR Berghofer study has added weight to the potential benefits of using ultrasound treatment to deliver disease-targeting drugs to Alzheimer’s patients.
The study is the first to examine the technique on brain cells derived from human patients with Alzheimer’s disease, building on previous research on mice and other animal models.
The findings have been published today in the journal Stem Cell Reports.
Lead Australian researcher and head of QIMR Berghofer’s Cellular and Molecular Neurodegeneration group, Associate Professor Anthony White, said the researchers found using focused ultrasound coupled with microbubble treatment, could create openings in the blood-brain barrier formed by human endothelial cells.
“The blood-brain barrier is a semipermeable barrier that lines blood vessels in the brain and importantly protects brain tissue, but that protective function also prevents the uptake of drugs and therapies targeting brain diseases,” Associate Professor White said.
“We found by using focused ultrasound and microbubble treatment we could weaken the connection between blood-brain barrier cells, which would potentially allow the brain tissue to absorb a drug treatment.
“An abnormal blood-brain barrier has been associated with several neurodegenerative diseases, including Alzheimer’s disease, so it’s very important that we better understand how the barrier works and how we can safely penetrate it to combat disease.
“Our study is the first to look at how the blood-brain barrier cells from human patients can be disrupted to improve the uptake of Alzheimer’s therapies, building on previous studies that have explored if ultrasound could be used to reduce amyloid build up in the brains of mice and other animal models.”
The researchers used brain endothelial cells derived from human stem cells of people with a family history of Alzheimer’s disease to understand how those cells of the blood-brain barrier could be weakened.
They injected lipid microbubbles into the cells and then targeted the area with ultrasound which caused the cells to expand and contract, disrupting the connections between the cells, opening the blood-brain barrier.
The ultrasound and microbubble treatment technique was developed by researchers at the Queensland Brain Institute.
First author and QIMR Berghofer researcher, Dr. Lotta Oikari, said the study also showed the ultrasound and microbubble treatment had a longer lasting effect on the brain cells of Alzheimer’s patients than on healthy controls.
“The treatment generated openings in the monolayer of the blood-brain barrier of all patients, but the brain endothelial cells of healthy controls repaired themselves quicker than the Alzheimer’s patient cells,” Dr. Oikari said.
“The blood-brain barrier in Alzheimer’s patients was slower to repair, indicating they would be more receptive to drugs and treatments for longer and that brain ultrasound treatment may have to be adjusted differently depending on the type of disease the patient has.
“It also raises questions whether reduced integrity in the blood-brain barrier, following ultrasound treatment, could lead to lower amyloid levels in the brains of Alzheimer’s patients because the brain tissue could potentially expel the build-up.”
Funding: The research was funded by QIMR Berghofer.
The study involved researchers from QIMR Berghofer, the Queensland Brain Institute at The University of Queensland, Monash University, University of Helsinki and University of Eastern Finland, in Finland.
Adult neurogenesis appears to be restricted to two regions, i.e., the subventricular zone (SVZ) of the lateral ventricles and the subgranular zone (SGZ) of the hippocampal dentate gyrus (DG).
Importantly, adult hippocampal neurogenesis (AHN) was first reported over 50 years ago by Altman and Das , and newborn neurons are generated continuously throughout life in the mammalian brain, including the human brain [2, 3].
Since then, numerous studies have reported that AHN is implicated in cognition and endogenous repair mechanisms in normal physiological conditions such as learning and memory .
Interestingly, according to the recent research, the persistence of AHN appears to be decreased in aged adults and Alzheimer’s disease (AD) [5, 6].
AD is one of the major causes of age-related dementia and is characterized by cognitive impairment, amyloid-β deposition in plaques, tau hyperphosphorylation in neurofibrillary tangles, loss of synapses, loss of neuronal cells, and cholinergic dysfunction .
Dysfunction of the basal forebrain cholinergic (BFC) system, a significant characteristic of AD, induces neuropathological changes before clinical symptoms manifest [8,9,10]. The hippocampus and cortex receive gamma-aminobutyric acidergic, glutamatergic, and cholinergic input from the basal forebrain of the medial septum-diagonal band complex (MS/DB) [11, 12].
Thus, lesions in, or the inactivation of, cholinergic neurons in MS/DB result in a decrease of acetylcholinesterase (AChE) and choline acetyltransferase (ChAT), consequently diminishing AHN [13,14,15,16].
Despite intensive research efforts, none of the currently available treatments for AD can completely cure or prevent the course of age-related cognitive impairment, and the pathological mechanism is not clearly understood.
Numerous pharmacological therapies have been developed to treat AD . However, 98% of small-molecule drugs (< 400 Da) and 100% of large-molecule drugs (> 500 Da) cannot cross the blood-brain barrier (BBB) , making the prevention and treatment of brain disorders difficult.
Focused ultrasound (FUS) combined with contrast agent microbubbles is a noninvasive technique that transiently opens BBB in targeted regions, thereby enabling localized therapeutic drug, gene, or nanoparticle delivery into the brain for treating central nervous system (CNS) disorders [19,20,21].
Considering that drugs that have been, or are currently being, developed for AD are mostly large molecules, FUS may enhance the effects of these drugs especially in patients with early-stage AD who have an intact BBB .
Moreover, several reports suggest that FUS stimulates neuronal activity and modulates proteomes and transcriptomes, independent of any therapeutic agent [23,24,25].
Previous studies indicate that FUS-mediated BBB opening can modulate the accumulation of amyloid-β and tau hyperphosphorylation in AD transgenic mice and increase AHN in wild-type mice [26,27,28,29,30]. Recently, Moreno-Jiménez et al. reported the persistence of AHN in human DG of subjects aged over 90 years; however, the number and maturation of immature neurons in DG sharply decreased in patients with AD.
This finding has gained attention for potential therapeutic strategies as an underlying memory impairment in AD . However, it remains unclear whether FUS can modulate AHN in a cholinergic-deficient condition.
In this study, we investigated the effect of FUS on AHN and the cholinergic system in a cholinergic degeneration dementia rat model, which is a key pathogenic feature of dementia. Furthermore, if FUS was effective in increasing AHN, the synergistic effects of AHN modulation and drug delivery could improve treatment outcomes of AD.
In the present study, we demonstrated that animals with BFC hypofunction causing spatial memory impairment exhibit a reduction in cholinergic activity, neurogenesis, and BDNF and ERG1 expression levels (Fig. 7a).
In contrast, FUS treatment increased AHN and improved spatial memory in cholinergic degeneration conditions. This improvement may be mediated by the upregulation of BDNF, EGR1, and AChE levels in the hippocampus, which is a critical factor for regulating AHN, synaptic plasticity, and neuroprotection (Fig. 7b).
Because patients with AD have impaired cholinergic neurons and AHN starting at the early stages, FUS treatment may restore AHN and have a protective effect against neurodegeneration.
Moreover, as FUS has been shown to be effective in increasing AHN, it could also contribute to increased permeability of BBB for drug delivery, and both these effects could be potential therapeutic strategies for AD.
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