Ultrasound stimulation improves inflammatory resolution, neuroprotection, and functional recovery after spinal cord injury

LncRNA TSIX knockdown restores spinal cord injury repair through miR-30a/SOCS3 axis

Spinal cord injury (SCI) is a serious injury to the central nervous system. Previous studies have discovered that the development of SCI is associated with gene expression. The purpose of this study was to explore the significance of lncRNA TSIX in SCI and its underlying mechanism involved. An in vivo SCI mice model and an in vitro hypoxia-treated HT22 cells model were applied in this study. TSIX and SOCS3 expression in SCI tissues was measured by qRT-PCR, western blot and FISH assay. LV-sh-TSIX was injected into SCI mice intrathecally or subjected to HT22 cells to access the consequent alteration in inflammation response, cell apoptosis and functional recovery through ELISA, immunohistochemistry, TUNEL, flow cytometry assays and BMS scores. Then, the underlying mechanism of TSIX was analyzed by bioinformatics analysis and then confirmed by RIP, RNA pull-down and dual-luciferase reporter assay. It was identified that TSIX was up-regulated in HT22 cells under hypoxia operation and spinal cord tissues of SCI mice. TSIX knockdown improved the lesion size and BMS score and inhibited inflammation and cell apoptosis. MiR-30a was identified as a target for TSIX and SOCS3, and TSIX binds to miR-30a by competing with SOCS3, thereby counteracting miR-30a-mediated SOCS3 inhibition. In addition, LV-sh-TSIX effects were significantly overturned by miR-30a inhibition or SOCS3 over-expression. Knockdown of TSIX improved functional recovery and attenuated the inflammation response and cell apoptosis via miR-30a/SOCS3 axis. These results may provide a potential novel insight for SCI treatment.

Safety Review of Therapeutic Ultrasound for Spinal Cord Neuromodulation and Blood-Spinal Cord Barrier Opening

New focused ultrasound spinal cord applications have emerged, particularly those improving therapeutic agent delivery to the spinal cord via blood-spinal cord barrier opening and the neuromodulation of spinal cord tracts. One hurdle in the development of these applications is safety. It may be possible to use safety trends from seminal and subsequent works in focused ultrasound to guide the development of safety guidelines for spinal cord applications. We collated data from decades of pre-clinical studies and illustrate a clear relationship between damage, time-averaged spatial peak intensity and exposure duration. This relationship suggests a thermal mechanism underlies ultrasound-induced spinal cord damage. We developed minimum and mean thresholds for damage from these pre-clinical studies. When these thresholds were plotted against the parameters used in recent pre-clinical ultrasonic spinal cord neuromodulation studies, the majority of the neuromodulation studies were near or above the minimum threshold. This suggests that a thermal neuromodulatory effect may exist for ultrasonic spinal cord neuromodulation, and that the thermal dose must be carefully controlled to avoid damage to the spinal cord. By contrast, the intensity-exposure duration threshold had no predictive value when applied to blood-spinal cord barrier opening studies that employed injected contrast agents. Most blood-spinal cord barrier opening studies observed slight to severe damage, except for small animal studies that employed an active feedback control method to limit pressures based on measured bubble oscillation behavior. The development of new focused ultrasound spinal cord applications perhaps reflects the recent success in the development of focused ultrasound brain applications, and recent work has begun on the translation of these technologies from brain to spinal cord. However, a great deal of work remains to be done, particularly with respect to developing and accepting safety standards for these applications.

Exploring BODIPY derivatives as sonosensitizers for anticancer sonodynamic therapy

Sonodynamic therapy (SDT) is an emerging non-invasive and effective therapeutic modality for cancer treatment bearing benefit of deep tissue-penetration in comparison to photo-inspired therapy. However, exploring novel sonosensitizers with high sonosensitivity and desirable biosafety remains a significant challenge. Although boron dipyrromethene (BODIPY) dyes have been widely used in biomedical filed, no BODIPY-based sonosensitizers have been reported yet. Herein, we synthesized four BODIPY dyes (BDP1-BDP4) and investigated their potential applications in SDT. BDP4 exhibited superb sonosensitivity and high SDT efficiency against cancer cells and tumors in tumor-bearing mice. The types of the generated reactive oxygen species, cavitation effect, and cell apoptosis were investigated to figure out the sonodynamic therapeutic mechanisms of BDP4. This work for the first time demonstrates the potential of BODIPY dyes as novel sonosensitizers for SDT, which may pave an avenue for developing more efficient and safer sonosensitizers in future.

Controlled Degradation of Polycaprolactone Polymers through Ultrasound Stimulation

This study describes the development of an ultrasound-responsive polymer system that provides on-demand degradation when exposed to high-intensity focused ultrasound (HIFU). Diels-Alder cycloadducts were used to crosslink polycaprolactone (PCL) polymers and underwent a retro Diels-Alder reaction when stimulated with HIFU. Two Diels-Alder polymer compositions were explored to evaluate the link between reverse reaction energy barriers and polymer degradation rates. PCL crosslinked with isosorbide was also used as a non-Diels-Alder-based control polymer. An increase of HIFU exposure time and amplitude correlated with an increase of PCL degradation for Diels-Alder-based polymers. Ultrasound imaging during HIFU allowed for real-time visualization of the on-demand degradation through cavitation-based mechanisms. The temperature surrounding the sample was monitored with a thermocouple during HIFU stimulation; a minimal increase in temperature was observed. PCL polymers were characterized using Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), optical profilometry, and mechanical testing. PCL degradation byproducts were identified by mass spectrometry, and their cytocompatibility was evaluated in vitro. Overall, this study demonstrated that HIFU is an effective image-guided, external stimulus to control the degradation of Diels-Alder-based PCL polymers on-demand.

Ultrasound therapy for a week promotes regeneration and reduces pro-inflammatory macrophages in a rat sciatic nerve autograft model

Peripheral nerve injury causes long-term motor dysfunction. Ultrasound (US) therapy is expected to accelerate peripheral nerve regeneration. However, its optimal usage and effects on macrophage phenotypes during peripheral nerve regeneration remain unknown. In this study, we investigated the optimal duration of US therapy and its effects on macrophage phenotype. Twenty-seven rats with autologous sciatic nerve grafting were divided into three groups: two received US therapy (1 MHz frequency, intensity of 140 mW/cm², 20% duty cycle, 5 min/day) for one (US1) or 4 weeks (US4), and one group received sham stimulation. Immunohistochemistry was performed 3 and 7 days after injury in another set of 12 rats. Eight weeks after the injury, the compound muscle action potential amplitude of the gastrocnemius in the US1 and US4 groups was significantly higher than that in the sham group. The toe-spreading test showed functional recovery, whereas the gait pattern during treadmill walking did not recover. There were no significant differences in motor function, histomorphometry, or muscle weight between groups. Immunohistochemistry showed that US therapy decreased the number of pro-inflammatory macrophages seven days after injury. Therefore, US therapy for both one or 4 weeks can similarly promote reinnervation and reduce proinflammatory macrophages in autograft model rats.

Disruption of the Blood-Spinal Cord Barrier using Low-Intensity Focused Ultrasound in a Rat Model

Low-intensity focused ultrasound (LIFU) uses ultrasonic pulsations at lower intensities than ultrasound and is being tested as a reversible and precise neuromodulatory technology. Although LIFU-mediated blood-brain barrier (BBB) opening has been explored in detail, no standardized technique for blood-spinal cord barrier (BSCB) opening has been established to date. Therefore, this protocol presents a method for successful BSCB disruption using LIFU sonication in a rat model, including descriptions of animal preparation, microbubble administration, target selection and localization, as well as BSCB disruption visualization and confirmation. The approach reported here is particularly useful for researchers who need a fast and cost-effective method to test and confirm target localization and precise BSCB disruption in a small animal model with a focused ultrasound transducer, evaluate the BSCB efficacy of sonication parameters, or explore applications for LIFU at the spinal cord, such as drug delivery, immunomodulation, and neuromodulation. Optimizing this protocol for individual use is recommended, especially for advancing future preclinical, clinical, and translational work.