Summary: Researchers have found that nitrous oxide can safely enhance gene therapy delivery to the brain by increasing blood-brain barrier (BBB) permeability when combined with focused ultrasound (FUS). Using nitrous oxide allowed opening the BBB with far lower microbubble concentrations and reduced ultrasound pressure compared with conventional methods, lowering the risk of tissue injury.
In mouse experiments, this strategy produced more efficient gene transfer, demonstrated by stronger expression of a fluorescent protein in the targeted brain regions. These promising preclinical results support further development and potential clinical testing aimed at safer, more effective treatments for neurological disorders.
Key Facts:
- Nitrous Oxide Role: Nitrous oxide enlarges gas microbubbles, which reduces the FUS pressure required to open the BBB.
- Improved Safety: The technique enabled up to 1,000-fold reductions in microbubble dose and lower ultrasound pressures, minimizing tissue risk.
- Enhanced Gene Delivery: Viral gene uptake in targeted brain regions was substantially greater in mice when nitrous oxide was used.
Source: UT Southwestern
Nitrous oxide, a commonly used anesthetic gas, temporarily improved opening of the blood-brain barrier (BBB) to facilitate gene therapy delivery in mice when combined with MR-guided focused ultrasound (FUS), researchers at UT Southwestern Medical Center report.
Published in Gene Therapy, the study introduces a modification to an existing BBB-opening technique that may enable safer, more efficient delivery of therapies for a range of brain disorders.
“The approach we explored in this study has the potential to advance care for brain diseases that can be treated by targeted therapeutic delivery,” said Bhavya R. Shah, M.D., Associate Professor of Radiology and Neurological Surgery and an investigator at UT Southwestern’s Advanced Imaging Research Center. Dr. Shah is also affiliated with the Peter O’Donnell Jr. Brain Institute and the Center for Alzheimer’s and Neurodegenerative Diseases. Deepshikha Bhardwaj, Ph.D., Senior Research Associate at UT Southwestern, is the study’s first author.
The blood-brain barrier is a highly selective layer of cells that lines the brain’s small blood vessels. While it protects the brain from toxins and infection, the BBB also blocks many therapeutic molecules, making treatment of conditions such as Alzheimer’s disease, multiple sclerosis, and brain tumors especially challenging.
For decades, researchers have investigated ways to open the BBB temporarily and selectively to allow drugs or genetic therapies to reach specific brain regions. One promising approach uses intravenously injected microbubbles combined with targeted FUS. Ultrasound causes the microbubbles to oscillate, transiently increasing BBB permeability. But achieving reliable opening has typically required microbubble doses and ultrasound pressures that can increase the risk of tissue damage.
In the new study, the UT Southwestern team tested whether replacing medical air with nitrous oxide during the procedure could amplify microbubble oscillation and reduce the doses and pressures needed. Nitrous oxide is known to diffuse into and expand gas-filled microbubbles, and the investigators hypothesized this effect could lower the mechanical energy required for BBB disruption.
Using Swiss Webster mice, the researchers compared BBB opening and gene delivery outcomes when animals breathed nitrous oxide versus medical air. They measured acoustic emissions and contrast-enhancement on T1-weighted MRI to quantify BBB opening, and then delivered a viral vector encoding green fluorescent protein (GFP) to assess transfection efficiency. Immunohistochemical analyses evaluated viral transduction and screened for acute cellular injury.
The experiments showed that nitrous oxide significantly potentiated acoustic emissions and MRI enhancement at all tested ultrasound pressures, compared with medical air. Critically, nitrous oxide permitted BBB opening using microbubble doses as low as 0.02 μL/kg and reduced FUS pressures to 0.28–0.39 MPa for effective viral delivery and disruption. Under these conditions, gene transfer into the targeted hippocampal tissue was markedly higher than with air, producing a brighter GFP signal in the treated regions, while posing reduced risk to brain tissue.
As a next step, the authors plan carefully controlled clinical studies to evaluate safety and efficacy in humans. If translatable, this approach could improve delivery of biologics and gene-based therapies for neurological diseases by increasing precision and lowering procedural risk.
Additional contributors to the study at UT Southwestern included Marc Diamond, M.D.; Rachel Bailey, Ph.D.; Sandi Jo Estill-Terpack, B.S.; Darren Imphean, M.D.; and Venugopal Krishnan, Ph.D. The research was supported by a UT Southwestern High Impact Grant.
About this neuroscience research news
Author: Bhavya R. Shah
Source: UT Southwestern
Contact: Bhavya R. Shah – UT Southwestern
Image: The image is credited to Neuroscience News
Original Research: Closed access.
“Nitrous oxide enhances MR-guided focused ultrasound delivery of gene therapy to the murine hippocampus” by Bhavya R. Shah et al. Gene Therapy
Abstract
Nitrous oxide enhances MR-guided focused ultrasound delivery of gene therapy to the murine hippocampus
Magnetic resonance-guided focused ultrasound can cause intravenously administered microbubbles to oscillate, transiently opening the blood-brain barrier in targeted brain regions. However, high microbubble doses or elevated focused ultrasound (FUS) pressures increase the risk of tissue injury. This study evaluated whether administering nitrous oxide (N2O) could reduce the required microbubble dose and FUS pressure for safe BBB opening.
Swiss Webster mice received either N2O or medical air while researchers varied FUS pressure and microbubble dose in controlled experiments. BBB opening was quantified by measuring acoustic emissions and contrast enhancement on T1-weighted MRI. To assess gene delivery, a viral vector expressing GFP was administered after BBB opening with either gas, and immunohistochemistry measured transfection efficiency and signs of acute cellular injury.
The results demonstrate that N2O significantly enhanced acoustic emissions and MRI contrast compared with medical air across tested pressures (0.39, 0.45, 0.67 MPa). Nitrous oxide reduced the effective microbubble dose to 0.02 μL/kg and allowed BBB disruption and improved viral gene delivery at lower FUS pressures (0.28–0.39 MPa). These findings indicate that N2O potentiates microbubble oscillation, enabling reduced microbubble doses and ultrasound pressures while improving viral gene transfer into the murine hippocampus.