Category: Neurodegenerative Diseases

MRI and Ultrasound Combo Opens Blood-brain Barrier

In a mouse model study of MRI-guided focused ultrasound-induced blood-brain barrier (BBB) opening at MRI field strengths ranging from ­approximately 0 T (outside the magnetic field) to 4.7 T, the static magnetic field dampened the detected microbubble cavitation signal and decreased the BBB opening volume. Credit: Washington University School of Medicine in St. Louis

Using a combination of ultrasound, MRI field strength and microbubbles can open the blood-brain barrier (BBB) and allow therapeutic drugs to reach the diseased brain location with MRI guidance. 

Using the physical phenomenon of cavitation, it is a promising technique that has been shown safe in patients with various brain diseases, such as Alzheimer’s diseases, Parkinson’s disease, ALS, and glioblastoma.
While MRI has been commonly used for treatment guidance and assessment in preclinical research and clinical studies, until now, researchers did not know the impact that MRI scanner’s magnetic field had on the BBB opening size and drug delivery efficiency.

Hong Chen, associate professor of biomedical engineering at Washington University in St. Louis, and her lab have found for the first time that the magnetic field of the MRI scanner decreased the BBB opening volume by 3.3-fold to 11.7-fold, depending on the strength of the magnetic field, in a mouse model. The findings were in Radiology.

Prof Chen conducted the study on four groups of mice. After they were injected microbubbles, three groups received focused-ultrasound sonication at different strengths of the magnetic field: 1.5 T (teslas), 3 T and 4.7 T, and one group was never exposed to the field. 

The researchers found that the microbubble cavitation activity, or the growing, shrinking and collapse of the microbubbles, decreased by 2.1 decibels at 1.5 T; 2.9 decibels at 3 T; and 3 decibels at 4.7 T, compared with those that had received the dose outside of the magnetic field. Additionally, the magnetic field decreased the BBB opening volume by 3.3-fold at 1.5 T; 4.4-fold at 3 T; and 11.7-fold at 4.7 T. No tissue damage from the procedure was seen.

Following focused-ultrasound sonication, the team injected a model drug, Evans blue dye, to investigate whether the magnetic field affected drug delivery across the BBB. The images showed that the fluorescence intensity of the Evans blue was lower in mice that received the treatment in one of the three strengths of magnetic fields compared with mice treated outside the magnetic field. The Evans blue trans-BBB delivery was decreased by 1.4-fold at1.5 T, 1.6-fold at 3.0 T and 1.9-fold at 4.7 T when compared with those treated outside of the magnetic field.

“The dampening effect of the magnetic field on the microbubble is likely caused by the loss of bubble kinetic energy due to the Lorentz force acting on the moving charged lipid molecules on the microbubble shell and dipolar water molecules surrounding the microbubbles,” said Yaoheng (Mack) Yang, a doctoral student in Prof Chen’s lab and the lead author of the study.

“Findings from this study suggest that the impact of the magnetic field needs to be considered in the clinical applications of focused ultrasound in brain drug delivery,” Prof Chen said.

In addition to brain drug delivery, cavitation is also used in several other therapeutic techniques, such as histotripsy, the use of cavitation to mechanically destroy regions of tissue, and sonothrombolysis, a therapy used after acute ischaemic stroke. The magnetic field’s damping effect on cavitation is expected to affect the treatment outcomes of other cavitation-mediated techniques when MRI-guided focused-ultrasound systems are used.

Source: Washington University in St. Louis

Journal information: Yang, Y., et al. (2021) Static Magnetic Fields Dampen Focused Ultrasound–mediated Blood-Brain Barrier Opening. Radiology.

Probe over Controversial Alzheimer’s Drug’s Approval

Amyloid plaques and neurons. Source: NIAH

The interim commissioner of the US Food and Drug Administration, Janet Woodcock, MD, last week requested the country’s Office of Inspector General to perform an independent investigation into the regulator’s decision to approve Biogen’s controversial Alzheimer’s drug Aduhelm.

Dr Woodcock noted in her letter that there “continues to be concerns raised” regarding the contact between FDA officials and Biogen ahead of the agency’s decision, “including some that may have occurred outside of the formal correspondence process.”

Dr Woodcock’s request comes after a bombshell report from Stat, which found that Biogen executives met with FDA officials, specifically Billy Dunn, MD, director of the FDA’s neuroscience unit, as early as 2019 to discuss a regulatory pathway for Aduhelm. The meetings took place even when it seemed there was no progress for the drug.

Earlier this week, a US House Representative, charged Biogen with “undue influence” over the FDA’s review process. Less than two weeks earlier, the House Committee on Oversight and Reform said it would conduct its own probe into the approval along with Biogen’s pricing strategies.

In the letter from Friday, Dr Woodcock said the agency would fully cooperate with the potential investigation to determine whether any of its interactions with Biogen were inconsistent with FDA policies and procedures.

“Given the ongoing interest and questions, today I requested that @OIGatHHS conduct an independent review and assessment of interactions between representatives of Biogen and FDA during the process that led to the approval of Aduhelm,” tweeted Dr Woodcock.

However, she maintained that she has “tremendous confidence” in the leadership at the FDA’s Center for Drug Evaluation and Research, which was involved in the review of Aduhelm.

“We believe this review and assessment will help ensure continued confidence in the integrity of FDA’s regulatory processes and decision-making,” Woodcock said in a tweet.

A spokesperson from Biogen told Fierce Pharma that the company would “of course” cooperate with “any inquiry in connection with a possible review of the regulatory process.”

The commissioner’s request is only the latest event in a bizarre and twisted story since the FDA’s Aduhelm approval just one month prior.

Facing fierce criticism of its wide-labelled approval, the FDA made the surprising move to narrow Aduhelm’s label last week Thursday, restricting the recommendation to just those with milder Alzheimer’s.

This comes after Biogen’s drug was essentially allowed access to the nation’s some 6 million Alzheimer’s patients. That decision was met with almost immediate pushback, as it was pointed out that the drug could overwhelm the payer budgets of most Alzheimer’s patients.

Source: Fierce Pharma

New Treatment Candidate May Reverse Neurodegenerative Decline

In the Alzheimer’s affected brain, abnormal levels of the beta-amyloid protein clump together to form plaques (seen in brown) that collect between neurons and disrupt cell function. Abnormal collections of the tau protein accumulate and form tangles (seen in blue) within neurons, harming synaptic communication between nerve cells.
Credit: National Institute on Aging, NIH

Researchers  at Tohoku University in Japan have identified a new treatment candidate that seems to not only halt but partially reverse neurodegenerative symptoms in mouse models of dementia and Alzheimer’s disease.

Kohji Fukunaga, professor emeritus in Tohoku University’s Graduate School of Pharmaceutical Sciences and paper author, said: “There are currently no disease-modifying therapeutics for neurodegenerative disorders such as Alzheimer’s disease, Lewy body dementia, Huntington disease and frontotemporal dementia in the world. We discovered the novel, disease-modifying therapeutic candidate SAK3, which, in our studies, rescued neurons in most protein-misfolding, neurodegenerative diseases.”

In previous work, the team found that the SAK3 molecule – the base structure of which is found in the enhancement of T-type Ca2+ channel activity – apparently improved memory and learning in a mouse model of Alzheimer’s disease.

SAK3 enhances the function of a cell membrane channel thereby promoting neuronal activity in the brain. Typically, SAK3 promotes neurotransmitter releases of acetylcholine and dopamine — neurotransmitters which are lowered in Alzheimer’s disease and Lewy body dementia. The Ca2+ channel enhancement is thought to trigger a change from resting to active in neuronal activity. When the Ca2+ channel is dysregulated in the brain, less acetylcholine and dopamine is released. Cognitive confusion and uncoordinated motor function arises from this dysregulated system.

SAK3 binds directly  to the subunit of this channel, enhancing neurotransmission and so improving cognitive deficits. The researchers found that the same process also seemed to work in a mouse model of Lewy body dementia, which is characterised by a buildup of proteins known as Lewy bodies.

“Even after the onset of cognitive impairment, SAK3 administration significantly prevented the progression of neurodegenerative behaviors in both motor dysfunction and cognition,” Prof Fukunaga said.

In comparison, Aduhelm, the Alzheimer’s drug recently approved by the US Food and Drug Administration, reduces the number of amyloid plaques in the brain, but whether the amyloid reduction actually prevents further cognitive or motor decline in patients is not yet known. According to Prof Fukunaga, SAK3 helps destroy amyloid plaque – at least in mice.

SAK3 also helps destroy misfolded alpha-synuclein, which normally helps regulate neurotransmitter transmission in the brain. The misfolded protein can aggregate, contributing to what researchers suspect may be an underlying cause of neurodegenerative symptoms. This aggregation can also cause loss of dopamine neurons, which are associated with learning and memory.

“We found that chronic administration of SAK3 significantly inhibited the accumulation of alpha-synuclein in the mice,” Prof Fukunaga said, noting that the mice received a daily oral dose of SAK3.

According to Prof Fukunaga, SAK3 enhances the activity of the system that identifies and destroys misfolded proteins. In neurodegenerative diseases, this system is often dysfunctional, leaving misfolded proteins to wreak havoc in the cell’s machinery.

“SAK3 is the first compound targeting this regulatory activity in neurodegenerative disorders,” Fukunaga said. “SAK3 administration promotes the destruction of misfolded proteins, meaning the therapeutic has the potential to solve the problems of diverse protein misfolding diseases such as Parkinson’s disease, Lewy body dementia and Huntington disease, in addition to Alzheimer’s disease.”

The team published their results in the International Journal of Molecular Sciences. This treatment candidate has been declared safe by Japan’s governing board, and the researchers are planning to start human clinical trials in the next year.

Source: Tohoku University

Journal information: Xu, J., et al. (2021) T-Type Ca2+ Enhancer SAK3 Activates CaMKII and Proteasome Activities in Lewy Body Dementia Mice Model. International Journal of Molecular

Are We Wrong About Amyloid Plaques in Alzheimer’s?

A recent study sheds new light on the disease and the highly debated aducanumab, a new drug recently approved by the FDA that treats the amyloid plaques.

Led by the University of Cincinnati and conducted in collaboration with the Karolinska Institute in Sweden, the study claims that the treatment of Alzheimer’s disease might lie in normalising levels of a brain protein called amyloid-beta peptide. This protein is needed in its original, soluble form to keep the brain healthy, but it sometimes hardens into ‘brain stones’ or clumps, called amyloid plaques.

“It’s not the plaques that are causing impaired cognition,” said senior author Alberto Espay, professor of neurology at UC. “Amyloid plaques are a consequence, not a cause,” of Alzheimer’s disease, stated Prof Espay, who is also a member of the UC Gardner Neuroscience Institute.

Since its discovery, scientists have focused on treatments to eliminate the plaques. But the UC team, he said, viewed it differently: Cognitive impairment could be due to a decline in soluble amyloid-beta peptide instead of the corresponding accumulation of amyloid plaques. 
To test their hypothesis, they analyzed the brain scans and spinal fluid from 600 individuals enrolled in the Alzheimer’s Disease Neuroimaging Initiative study, who all had amyloid plaques. From there, they compared the amount of plaques and levels of the peptide in the individuals with normal cognition to those with cognitive impairment. They found that individuals with high levels of the peptide were cognitively normal, despite the numbers of plaques in their brains.

They also found that higher levels of soluble amyloid-beta peptide were associated with a larger hippocampus, the area of the brain most important for memory.

According to the authors, as we age most people develop amyloid plaques, but few people develop dementia. In fact, by the age of 85, 60% of people will have these plaques, but only 10% develop dementia.

“The key discovery from our analysis is that Alzheimer’s disease symptoms seem dependent on the depletion of the normal protein, which is in a soluble state, instead of when it aggregates into plaques,” said co-author Kariem Ezzat from the Karolinska Institute.

The most relevant future therapeutic approach for the Alzheimer’s program would then be to restore these brain soluble proteins to their normal levels, said Prof Espay.

The research team is now working to test their findings in animal models. If successful, future treatments may be very different from those tried over the last two decades. Treatment, says Espay, may consist of increasing the soluble version of the protein in a manner that keeps the brain healthy while preventing the protein from hardening into plaques.  

Source: University of Cincinnati 

Journal information: Andrea Sturchio et al, High cerebrospinal amyloid-β 42 is associated with normal cognition in individuals with brain amyloidosis, EClinicalMedicine (2021). DOI: 10.1016/j.eclinm.2021.100988

New Imaging Technique Picks up Earliest Stages of Neurological Disorders

A new imaging technique has the potential to detect neurological disorders such as Alzheimer’s disease at their earliest stages. 

The imaging methodology, called super-resolution, combines position emission tomography (PET) with an external motion tracking device to create highly detailed images of the brain. PET scanning, which is mostly used for oncology, where the activity of radioactive tracers introduced into the body is measured. Higher activity corresponds to greater uptake of that particular tracer.

In normal brain PET imaging, image quality is often limited by unwanted movements of the patient during scanning. In this study, researchers utilised super-resolution to make use of the normally unwanted head motion of subjects to enhance the resolution in brain PET.

Moving phantom and non-human primate experiments were performed on a PET scanner in conjunction with an external motion tracking device that continuously measured head movement with extremely high precision. Static reference PET acquisitions with no induced movement were also performed. After combining data from the imaging devices, researchers obtained PET images with higher resolution than the standard static reference scans.

Yanis Chemli, MSc, PhD candidate, Gordon Center for Medical Imaging, said: “This work shows that one can obtain PET images with a resolution that outperforms the scanner’s resolution by making use, counterintuitively perhaps, of usually undesired patient motion. Our technique not only compensates for the negative effects of head motion on PET image quality, but it also leverages the increased sampling information associated with imaging of moving targets to enhance the effective PET resolution.”

Though this super-resolution technique has only been tested in preclinical studies, researchers are preparing to try it with human subjects. Looking to the future, Chemli noted the important impact that super-resolution may have on brain disorders, specifically Alzheimer’s disease. “Alzheimer’s disease is characterized by the presence of tangles composed of tau protein. These tangles start accumulating very early on in Alzheimer’s disease–sometimes decades before symptoms–in very small regions of the brain. The better we can image these small structures in the brain, the earlier we may be able to diagnose and, perhaps in the future, treat Alzheimer’s disease,” he noted.

Source: Society of Nuclear Medicine and Molecular Imaging

Lifestyle Changes Shown to Reduce Risk of Dementia

Photo by Ketut Subiyanto from Pexels

After almost two decades, a new drug for Alzheimer’s disease has been approved in the US. However, some experts say it doesn’t really work — only treating amyloid plaques which are thought to cause the disease — and worry that it may cost a lot.

The amount of attention around this news reflects the importance of preventing dementia, with its devastating toll on families and patients. But millions of adults could lower their chances of needing such a drug by taking preventative measures.

That’s why a national panel of experts including the University of Michigan’s Deborah Levine, MD, MPH, recently published a guide for primary care providers on this topic as an official Scientific Statement from the American Heart Association.

People dread Alzheimer’s disease, she said. Helping people understand that they can prevent or slow future dementia by taking specific steps now could motivate them to increase their healthy behaviours for a positive effect.

The first step is to recognise that dementia risk is higher among people with seven major modifiable risk factors.

These are: depression, hypertension, physical inactivity, diabetes, obesity, hyperlipidaemia, poor diet, smoking, social isolation, excessive alcohol use, sleep disorders and hearing loss. Addressing each of these factors can, to varying extents, help reduce the risk of developing dementia, a fact backed by decades of research.

The second step is using medication, lifestyle change and other interventions to help patients reduce their dementia risk.

“Dementia is not inevitable,” said Dr Levine, a primary care provider at the University of Michigan Health, part of Michigan Medicine. “Evidence is growing that people can better maintain brain health and prevent dementia by following healthy behaviours and controlling vascular risk factors.”

These strategies can help preserve cognitive function and lower risk for heart attacks and strokes, said Dr Levine, who heads the Cognitive Health Services Research Program and sees patients at the Frankel Cardiovascular Center.

“We need to address the significant disparities that lead women, Black, Hispanic and less-educated Americans to have a much higher risk of dementia,” said Levine, a member of the U-M Institute for Healthcare Policy and Innovation.

She added that it’s never too late in life to start working on cognitive risk factor control.

“We have no treatments that will halt dementia – so it’s important to protect your brain health.”

Source: University of Michigan

Molecule Found to Play a Key Role in Brain Rejuvenation

Image source: Pixabay

A new study shows that a molecule could play a key role in support cells in the brain, allowing them to repair and properly communicate.

Studies have shown that new brain cells continually formed in response to injury, physical exercise, and mental stimulation. Glial cells, and in particular oligodendrocyte progenitors, are highly responsive to external signals and injuries. They can detect changes in the nervous system and form new myelin, which forms a sheath around nerves, providing metabolic support and accurate transmission of electrical signals. However, less myelin is formed with age, and this progressive decline has been linked to the age-related cognitive and motor deficits observed in older people. Impaired myelin formation also has been reported in older individuals with neurodegenerative diseases such as Multiple Sclerosis or Alzheimer’s and identified as one of the causes of their progressive clinical deterioration.

A new study from the Neuroscience Initiative team at the Advanced Science Research Center at The Graduate Center, CUNY (CUNY ASRC) has identified a molecule called ten-eleven-translocation 1 (TET1) as a necessary component of myelin repair. shows that TET1 modifies the DNA in specific glial cells in adult brains so they can form new myelin in response to injury. The study was published in Nature Communications.

“We designed experiments to identify molecules that could affect brain rejuvenation,” said lead author Sarah Moyon, PhD, a research assistant professor with the CUNY ASRC Neuroscience Initiative. “We found that TET1 levels progressively decline in older mice, and with that, DNA can no longer be properly modified to guarantee the formation of functional myelin.”

The authors are currently exploring whether raising levels of TET1 in older mice could rejuvenate the oligodendroglial cells, restoring their regenerative functions.

Combining whole-genome sequencing bioinformatics, the authors showed that the DNA modifications induced by TET1 in young adult mice were essential to promote healthy communication among central nervous system cells and for ensuring proper function. The authors also showed that young adult mice with a genetic modification of TET1 in the myelin-forming glial cells could not produce functional myelin, and so behaved like older mice.

“This newly identified age-related decline in TET1 may account for the inability of older individuals to form new myelin,” said Patrizia Casaccia, founding director of the CUNY ASRC Neuroscience Initiative, a professor of Biology and Biochemistry at The Graduate Center, CUNY, and the study’s primary investigator. “I believe that studying the effect of aging in glial cells in normal conditions and in individuals with neurodegenerative diseases will ultimately help us design better therapeutic strategies to slow the progression of devastating diseases like multiple sclerosis and Alzheimer’s.”

The findings could also hold important implications for molecular rejuvenation of ageing brains in healthy individuals, the researchers noted. Future studies aimed at increasing TET1 levels in older mice are underway to define whether the molecule could restore new myelin formation and favour proper neuro-glial communication. The long-term goal of the team is to promote recovery of cognitive and motor functions in older people and in patients with neurodegenerative diseases.

Source: Advanced Science Research Center

A Neurologist Confronts His Alzheimer’s Disease

Image by valelopardo from Pixabay

Neurologist Daniel Gibbs, MD, PhD, related his experiences of having been diagnosed with Alzheimer’s disease and taking part in clinical trials of possible treatments for it.

“I’m fascinated by this disease that, for my entire career as a scientist and a neurologist, I could only observe from the outside,” Dr Gibbs wrote in his new book, A Tattoo on my Brain: A Neurologist’s Personal Battle against Alzheimer’s Disease. “Now I’ve got a front-row seat — or rather, I’m in the ring with the tiger.”

Dr Gibbs stumbled upon his diagnosis accidentally, when he and his wife tested their DNA to learn about their ancestry that he discovered he had two copies of the APOE4 allele, the most common genetic risk factor for Alzheimer’s disease.

Because he had an early diagnosis, Dr Gibbs has volunteered to participate in several Alzheimer’s clinical trials in recent years, including one for aducanumab, the controversial Alzheimer’s treatment the FDA is expected to decide upon in June.

During a trial of aducanumab, he developed a serious amyloid-related imaging abnormality (ARIA) involving both brain oedema and intracerebral haemorrhage, which he recovered from. Dr Gibbs went on to co-author a case report about the clinical course and treatment of his complication. In the wake of much controversy, aducanumab has today received FDA approval.

MedPage Today interviewed Dr Gibbs on his experiences and perspectives since his Alzheimer’s diagnosis.

Dr Gibbs said that “as a patient and as a neurologist” it is a coping mechanism which gives hime “a huge advantage” to be able to look at the disease through his two “masks”. “Looking at it from the neurologist scientist’s point of view is a lot less threatening and is intellectually very satisfying. I enjoy reading and writing about it,” he said.

Regarding his future, he said: “One of the messages I try to get across in the book is that you need to plan for the future while you are still cognitively intact, and make very clearly known what you want done when you’re unable to give instructions about your care. I’ve done that. My family knows, my doctor knows: I don’t want anything done if I can’t participate in making decisions.” 

Dr Gibbs said he was excited to volunteer for the aducanumab study partly because of the way aducanumab was discovered; a reverse-engineered antibody found in cognitively normal aged people. Another reason was the more aggressive nature of the trial. He explained the meaning of “tattoo on my brain” alluded to in the title of his book, an adverse effect of the experimental drug.

“For me, a ‘tattoo on my brain’ has two forms. In the ARIA — the amyloid-related imaging abnormality complication I had from aducanumab — there was both leakage of fluid causing swelling in my brain and leakage of blood, microhaemorrhages. Those went away, as did the swelling in my brain, but they left behind this haemosiderin, this iron-containing pigment which is not dissimilar to tattoo ink, if you will.

“I haven’t had a recent MRI scan, but at least the last one I looked at a year or two ago still showed those little dots of hemosiderin. In a literal sense, that is the tattoo on my brain. In the figurative sense, the tattoo is a symbol of a kind of coming out of the closet and showing something that you’re not ashamed of.” 

The book, he said, is about people with early disease and the children of people with Alzheimer’s disease because they’re at risk. The aim is to “loosen up the conversation” so that interventions such as lifestyle changes can take place.

He suspects that the first disease-modifying drugs will be effective in early stages, which are going to be really hard studies to do. Recruiting participants without cognitive impairment but the pathology of  of Alzheimer’s disease is extremely difficult.
Finally, he offered some advice on dealing with Alzheimer’s.

“What I would recommend is for everybody to start doing things that are good for them. A heart-healthy diet is good for you in so many ways. It’s hard to say that’s not a good idea, although we’re a country of hamburger-loving people. And exercise — I don’t know how you overcome that bar of convincing people if you want to be a healthy 70- or 80-year-old, you have to exercise and get a good diet. And good sleep.”

Source:MedPage Today

Alzheimer’s Disease Disrupts Blood Vessels in Vicious Circle

Researchers have discovered a new mechanism of Alzheimer’s disease, one that disrupts the blood vessels around the disease’s characteristic amyloid plaques and worsens the disease progression. 

Image source: Wikimedia

Presently, Alzheimer’s disease is the leading cause of dementia worldwide. As economies develop and people live longer lives, its incidence is increasing dramatically as the population ages and yet, unfortunately, the origin of the disease is still unknown and there is no truly effective treatment.

The study was published in the international journal Nature Communications, and led by Dr Alberto Pascual’s laboratory, from the Neuronal Maintenance Mechanisms Group at the Biomedicine Institute of Seville (IBiS) and was chiefly carried out by María Isabel álvarez Vergara and Alicia E Rosales-Nieves.

Blood vessel formation disrupted

The study focuses on the dysfunction of a physiological process called angiogenesis, which is important during development to form the vessels of the brain, and in adulthood to repair any damage to pre-existing vessels. The researchers found that Alzheimer’s disease induces angiogenesis dysfunction, resulting in the loss of vessels instead of the formation of new ones and worsening the progression of the disease. Identification of the molecular pathways involved will enable new therapeutic strategies to alleviate the effects of this disease can be rationally designed. Their data also links familial (genetic) Alzheimer’s to problems in the formation of new blood vessels, which demonstrates the importance of the vascular component of the disease.

A vicious circle

A characteristic feature of Alzheimer’s patients is the accumulation of highly toxic substances in their brains, known as senile plaques. Normally, the brain is capable of cleaning out these toxic substances by carrying them away in the bloodstream. Therefore, the loss of the vessels due to plaques creates a vicious circle: having fewer vessels reduces the brain’s cleaning ability and so allowing more toxic substances to accumulate, which in turn continue to destroy the vessels and worsen the situation further. Additionally, since the human brain is a major consumer of the body’s oxygen and nutrients a local reduction in the supply of these substances through the blood represents an additional strain on it.

Source: News-Medical.Net

Journal information: Alvarez-Vergara, M.I., et al. (2021) Non-productive angiogenesis disassembles Aß plaque-associated blood vessels. Nature Communications.

Precise Ultrasound Heating of Neurons Could Treat Neurological Disorders

Image source: Fakurian Design on Unsplash

A multidisciplinary team at Washington University in St. Louis has developed a new brain stimulation technique using focused ultrasound that is able to turn specific types of neurons in the brain on and off and precisely control motor activity without surgical device implantation.

Being able to turn neurons on and off can treat certain neurological disorders such as Parkinson’s disease and epilepsy. Used for over six decades, deep brain stimulation techniques have had some treatment success in neurological disorders, but those require surgical device implantation. 

The team, led by Hong Chen, assistant professor of biomedical engineering in the McKelvey School of Engineering and of radiation oncology at the School of Medicine, is the first to provide direct evidence showing noninvasive activation of specific neuron types in mammalian brains by combining an ultrasound-induced heating effect and genetics, which they have named sonothermogenetics. It is also the first work to show that the ultrasound- genetics combination can robustly control behaviour by stimulating a specific target deep in the brain.

The results of the three years of research were published online in Brain Stimulation

“Our work provided evidence that sonothermogenetics evokes behavioural responses in freely moving mice while targeting a deep brain site,” Chen said. “Sonothermogenetics has the potential to transform our approaches for neuroscience research and uncover new methods to understand and treat human brain disorders.”

Chen and colleagues delivered a viral construct containing TRPV1 ion channels to genetically-selected neurons in a mouse model. Then, they delivered small pulses of heat generated by low-intensity focused ultrasound to the selected neurons in the brain via a wearable device. The heat, only a few degrees warmer than body temperature, activated the TRPV1 ion channel, which then acted as a switch to turn the neurons on or off.

“We can move the ultrasound device worn on the head of free-moving mice around to target different locations in the whole brain,” said Yaoheng Yang, first author of the paper and a graduate student in biomedical engineering. “Because it is noninvasive, this technique has the potential to be scaled up to large animals and potentially humans in the future.”

Building on prior research from his lab, professor of biomedical engineering Jianmin Cui and his team found for the first time that ion channel activity can be influenced by ultrasound alone, possibly leading to new and noninvasive ways to control the activity of specific cells. They discovered that focused ultrasound modulated the currents flowing through the ion channels on average by up to 23%, depending on channel and stimulus intensity. Following this work, researchers found close to 10 ion channels with this capability, but all of them are mechanosensitive, not thermosensitive.

The work also builds on the concept of optogenetics, the combination of the targeted expression of light-sensitive ion channels and the precise delivery of light to stimulate neurons deep in the brain. While optogenetics has increased discovery of new neural circuits, it has limited penetration depth due to light scattering, requiring surgical implantation of optical fibres to reach deeper into the brain.

Sonothermogenetics has the promise to target any location in the mouse brain with millimetre-scale resolution without causing any damage to the brain, Chen said. She and her team are further refining the technique and validating their work.

Source: Sci Tech Daily

Journal information: Yaoheng Yang et al, Sonothermogenetics for noninvasive and cell-type specific deep brain neuromodulation, Brain Stimulation (2021). DOI: 10.1016/j.brs.2021.04.021