Effects of Non-invasive, Targeted, Neuronal Lesions on Seizures in a Mouse Model of Temporal Lobe Epilepsy

Ultrasonic therapies for seizures and drug-resistant epilepsy

Ultrasonic therapy is an increasingly promising approach for the treatment of seizures and drug-resistant epilepsy (DRE). Therapeutic focused ultrasound (FUS) uses thermal or nonthermal energy to either ablate neural tissue or modulate neural activity through high- or low-intensity FUS (HIFU, LIFU), respectively. Both HIFU and LIFU approaches have been investigated for reducing seizure activity in DRE, and additional FUS applications include disrupting the blood-brain barrier in the presence of microbubbles for targeted-drug delivery to the seizure foci. Here, we review the preclinical and clinical studies that have used FUS to treat seizures. Additionally, we review effective FUS parameters and consider limitations and future directions of FUS with respect to the treatment of DRE. While detailed studies to optimize FUS applications are ongoing, FUS has established itself as a potential noninvasive alternative for the treatment of DRE and other neurological disorders.

Molecular Identity Changes of Tumor-Associated Macrophages and Microglia After Magnetic Resonance Imaging-Guided Focused Ultrasound-Induced Blood-Brain Barrier Opening in a Mouse Glioblastoma Model

An orthotopically allografted mouse GL26 glioma model (Ccr2RFP/wt-Cx3cr1GFP/wt) was used to evaluate the effect of transient, focal opening of the blood-brain barrier (BBB) on the composition of tumor-associated macrophages and microglia (TAMs). BBB opening was induced by magnetic resonance imaging (MRI)-guided focused ultrasound (MRgFUS) combined with microbubbles. CX3CR1-GFP cells and CCR2-RFP cells in brain tumors were quantified in microscopic images. Tumors in animals treated with a single session of MRgFUS did not exhibit significant changes in cell numbers when compared with tumors in animals not receiving FUS. However, tumors that received two or three sessions of MRgFUS had significantly increased amounts of both CX3CR1-GFP and CCR2-RFP cells. The effect of MRgFUS on immune cell composition was also characterized and quantified using flow cytometry. Glioma implantation resulted in increased amounts of lymphocytes, monocytes and neutrophils in the brain parenchyma. Tumors administered MRgFUS exhibited increased numbers of monocytes and monocyte-derived TAMs. In addition, MRgFUS-treated tumors exhibited more CD80+ cells in monocytes and microglia. In summary, transient, focal opening of the BBB using MRgFUS combined with microbubbles can activate the homing and differentiation of monocytes and induce a shift toward a more pro-inflammatory status of the immune environment in glioblastoma.

Noninvasive disconnection of targeted neuronal circuitry sparing axons of passage and nonneuronal cells

OBJECTIVE

Surgery can be highly effective for the treatment of medically intractable, neurological disorders, such as drug-resistant focal epilepsy. However, despite its benefits, surgery remains substantially underutilized due to both surgical concerns and nonsurgical impediments. In this work, the authors characterized a noninvasive, nonablative strategy to focally destroy neurons in the brain parenchyma with the goal of limiting collateral damage to nontarget structures, such as axons of passage.

METHODS

Low-intensity MR-guided focused ultrasound (MRgFUS), together with intravenous microbubbles, was used to open the blood-brain barrier (BBB) in a transient and focal manner in rats. The period of BBB opening was exploited to focally deliver to the brain parenchyma a systemically administered neurotoxin (quinolinic acid) that is well tolerated peripherally and otherwise impermeable to the BBB.

RESULTS

Focal neuronal loss was observed in targeted areas of BBB opening, including brain regions that are prime objectives for epilepsy surgery. Notably, other structures in the area of neuronal loss, including axons of passage, glial cells, vasculature, and the ventricular wall, were spared with this procedure.

CONCLUSIONS

These findings identify a noninvasive, nonablative approach capable of disconnecting neural circuitry while limiting the neuropathological consequences that attend other surgical procedures. Moreover, this strategy allows conformal targeting, which could enhance the precision and expand the treatment envelope for treating irregularly shaped surgical objectives located in difficult-to-reach sites. Finally, if this strategy translates to the clinic, the noninvasive nature and specificity of the procedure could positively influence both physician referrals for and patient confidence in surgery for medically intractable neurological disorders.

Recent Advances in the Use of Focused Ultrasound as a Treatment for Epilepsy

Epilepsy affects about 1% of the population. Approximately one third of patients with epilepsy are drug-resistant (DRE). Resective surgery is an effective treatment for DRE, yet invasive, and not all DRE patients are suitable resective surgery candidates. Focused ultrasound, a novel non-invasive neurointerventional method is currently under investigation as a treatment alternative for DRE. By emitting one or more ultrasound waves, FUS can target structures in the brain at millimeter resolution. High intensity focused ultrasound (HIFU) leads to ablation of tissue and could therefore serve as a non-invasive alternative for resective surgery. It is currently under investigation in clinical trials following the approval of HIFU for essential tremor and Parkinson’s disease. Low intensity focused ultrasound (LIFU) can modulate neuronal activity and could be used to lower cortical neuronal hyper-excitability in epilepsy patients in a non-invasive manner. The seizure-suppressive effect of LIFU has been studied in several preclinical trials, showing promising results. Further investigations are required to demonstrate translation of preclinical results to human subjects.

Low Intensity Focused Ultrasound for Epilepsy- A New Approach to Neuromodulation

Patients with drug-resistant epilepsy (DRE) who are not surgical candidates have unacceptably few treatment options. Benefits of implanted electrostimulatory devices are still largely palliative, and many patients are not eligible to receive them. A new form of neuromodulation, low intensity focused ultrasound (LIFUS), is rapidly emerging, and has many potential intracranial applications. LIFUS can noninvasively target tissue with a spatial distribution of highly focused acoustic energy that ensures a therapeutic effect only at the geometric focus of the transducer. A growing literature over the past several decades supports the safety of LIFUS and its ability to noninvasively modulate neural tissue in animals and humans by positioning the beam over various brain regions to target motor, sensory, and visual cortices as well as frontal eye fields and even hippocampus. Several preclinical studies have demonstrated the ability of LIFUS to suppress seizures in epilepsy animal models without damaging tissue. Resection after sonication to the antero-mesial lobe showed no pathologic changes in epilepsy patients, and this is currently being trialed in serial treatments to the hippocampus in DRE. Low intensity focused ultrasound is a promising, novel, incisionless, and radiation-free alternative form of neuromodulation being investigated for epilepsy. If proven safe and effective, it could be used to target lateral cortex as well as deep structures without causing damage, and is being studied extensively to treat a wide variety of neurologic and psychiatric disorders including epilepsy.

Focused Ultrasound for Pediatric Diseases

Focused ultrasound (FUS) is a noninvasive therapeutic technology with multiple pediatric clinical applications. The ability of focused ultrasound to target tissues deep in the body without exposing children to the morbidities associated with conventional surgery, interventional procedures, or radiation offers significant advantages. In 2021, there are 10 clinical pediatric focused ultrasound studies evaluating various musculoskeletal, oncologic, neurologic, and vascular diseases of which 8 are actively recruiting and 2 are completed. Pediatric musculoskeletal applications of FUS include treatment of osteoid osteoma and bone metastases using thermal ablation and high-intensity FUS. Pediatric oncologic applications of FUS include treatment of soft tissue tumors including desmoid tumors, malignant sarcomas, and neuroblastoma with high-intensity FUS ablation alone, or in combination with targeted chemotherapy delivery. Pediatric neurologic applications include treatment of benign tumors such as hypothalamic hamartomas with thermal ablation and malignant diffuse intrinsic pontine glioma with low-intensity FUS for blood brain barrier opening and targeted drug delivery. Additionally, low-intensity FUS can be used to treat seizures. Pediatric vascular applications of FUS include treatment of arteriovenous malformations and twin-twin transfusion syndrome using ablation and vascular occlusion. FUS treatment appears safe and efficacious in pediatric populations across many subspecialties. Although there are 7 Food and Drug Administration-approved indications for adult applications of FUS, the first Food and Drug Administration approval for pediatric patients with osteoid osteoma was obtained in 2020. This review summarizes the preclinical and clinical research on focused ultrasound of potential benefit to pediatric populations.

Ultrasound Neuromodulation: Integrating Medicine and Engineering for Neurological Disease Treatment

Abstract Neurological diseases associated with dysfunctions of neural circuits, including Alzheimer’s disease (AD), depression and epilepsy, have been increasingly prevalent. To tackle these issues, artificial stimulation or regulation of specific neural circuits and nuclei are employed to alleviate or cure certain neurological diseases. In particular, ultrasound neuromodulation has been an emerging interdisciplinary approach, which integrates medicine and engineering methodologies in the treatment. With the development of medicine and engineering, ultrasound neuromodulation has gradually been applied in the treatment of central nervous system diseases. In this review, we aimed to summarize the mechanism of ultrasound neuromodulation and the advances of focused ultrasound (FUS) in neuromodulation in recent years, with a special emphasis on its application in central nervous system disease treatment. FUS showed great feasibility in the treatment of epilepsy, tremor, AD, depression, and brain trauma. We also suggested future directions of ultrasound neuromodulation in clinical settings, with a focus on its fusion with genetic engineering or nanotechnology.

Acoustic holograms for bilateral blood-brain barrier opening in a mouse model

Transcranial focused ultrasound (FUS) in conjunction with circulating microbubbles injection is the sole non-invasive technique that temporally and locally opens the blood-brain barrier (BBB), allowing targeted drug delivery into the central nervous system (CNS). However, single-element FUS technologies do not allow the simultaneous targeting of several brain structures with high-resolution, and multi-element devices are required to compensate the aberrations introduced by the skull. In this work, we present the first preclinical application of acoustic holograms to perform a bilateral BBB opening in two mirrored regions in mice. The system consisted of a single-element focused transducer working at 1.68~MHz, coupled to a 3D-printed acoustic hologram designed to produce two symmetric foci in anesthetized mice \textit{in vivo} and, simultaneously, compensate the aberrations of the wavefront caused by the skull bones. T1-weighed MR images showed gadolinium extravasation at two symmetric quasi-spherical focal spots. By encoding time-reversed fields, holograms are capable of focusing acoustic energy with a resolution near the diffraction limit at multiple spots inside the skull of small preclinical animals. This work demonstrates the feasibility of hologram-assisted BBB opening for low-cost and highly-localized targeted drug delivery in the CNS in symmetric regions of separate hemispheres.

Non-invasive, neurotoxic surgery reduces seizures in a rat model of temporal lobe epilepsy

Surgery can be highly effective for treating certain cases of drug resistant epilepsy. The current study tested a novel, non-invasive, surgical strategy for treating seizures in a rat model of temporal lobe epilepsy. The surgical approach uses magnetic resonance-guided, low-intensity focused ultrasound (MRgFUS) in combination with intravenous microbubbles to open the blood-brain barrier (BBB) in a transient and focal manner. During the period of BBB opening, a systemically administered neurotoxin (Quinolinic Acid: QA) that is normally impermeable to the BBB gains access to a targeted area in the brain, destroying neurons where the BBB has been opened. This strategy is termed Precise Intracerebral Non-invasive Guided Surgery (PING). Spontaneous recurrent seizures induced by pilocarpine were monitored behaviorally prior to and after PING or under control conditions. Seizure frequency in untreated animals or animals treated with MRgFUS without QA exhibited expected seizure rate fluctuations frequencies between the monitoring periods. In contrast, animals treated with PING targeting the intermediate-temporal aspect of the hippocampus exhibited substantial reductions in seizure frequency, with convulsive seizures being eliminated entirely in two animals. These findings suggest that PING could provide a useful alternative to invasive surgical interventions for treating drug resistant epilepsy, and perhaps for treating other neurological disorders in which aberrant neural circuitries play a role.

Targeted Neuronal Injury for the Non-Invasive Disconnection of Brain Circuitry

Surgical intervention can be quite effective for treating certain types of medically intractable neurological diseases. This approach is particularly useful for disorders in which identifiable neuronal circuitry plays a key role, such as epilepsy and movement disorders. Currently available surgical modalities, while effective, generally involve an invasive surgical procedure, which can result in surgical injury to non-target tissues. Consequently, it would be of value to expand the range of surgical approaches to include a technique that is both non-invasive and neurotoxic. Here, a method is presented for producing focal, neuronal lesions in the brain in a non-invasive manner. This approach utilizes low-intensity focused ultrasound together with intravenous microbubbles to transiently and focally open the Blood Brain Barrier (BBB). The period of transient BBB opening is then exploited to focally deliver a systemically administered neurotoxin to a targeted brain area. The neurotoxin quinolinic acid (QA) is normally BBB-impermeable, and is well-tolerated when administered intraperitoneally or intravenously. However, when QA gains direct access to brain tissue, it is toxic to the neurons. This method has been used in rats and mice to target specific brain regions. Immediately after MRgFUS, successful opening of the BBB is confirmed using contrast enhanced T1-weighted imaging. After the procedure, T2 imaging shows injury restricted to the targeted area of the brain and the loss of neurons in the targeted area can be confirmed post-mortem utilizing histological techniques. Notably, animals injected with saline rather than QA do demonstrate opening of the BBB, but dot not exhibit injury or neuronal loss. This method, termed Precise Intracerebral Non-invasive Guided surgery (PING) could provide a non-invasive approach for treating neurological disorders associated with disturbances in neural circuitry.