Low-intensity pulsed ultrasound increases neurotrophic factors secretion and suppresses inflammation in<i>in vitro</i>models of peripheral neuropathies.

Abstract

<i>Objective</i>. In this study, we aimed to verify the beneficial effects of low-intensity pulsed ultrasound (LIPUS) stimulation on two cell types: H₂O₂-treated RSC96 Schwann cells and THP-1 macrophages, used to model neuropathic inflammation.<i>Approach</i>. Using a set-up guaranteeing a fine control of the ultrasound dose at the target, different frequencies (38 kHz, 1 MHz, 5 MHz) and different intensities (20, 100, 500 mW cm^-2) were screened to find the most effective experimental conditions for triggering beneficial effects on metabolic activity and release of neurotrophic cytokines (<i>β</i>-nerve growth factor, brain-derived neurotrophic factor, glial cell-derived neurotrophic factor) of RSC96 cells. The combination of parameters resulting the optimal one was applied to evaluate anti-inflammatory effects in terms of reactive oxygen species (ROS) and tumor necrosis factor-<i>α</i>(TNF-<i>α</i>) production, also investigating a possible anti-oxidant activity and mechanotransduction pathway for the anti-inflammatory process. The same optimal combination of parameters was then applied to THP-1 cells, differentiated into M1 and M2 phenotypes, to assess the effect on the expression and release of pro-inflammatory markers (TNF-<i>α</i>, interleukin (IL)-1<i>β</i>, IL-6, IL-8) and anti-inflammatory ones (IL-10 and CD206).<i>Main results.</i>5 MHz and 500 mW cm^-2were found as the optimal stimulation parameters on RSC96 cells. Such parameters were also found to suppress ROS and TNF-<i>α</i>in the same cell line, thus highlighting a possible anti-inflammatory effect, involving the NF-kB pathway. An anti-oxidant effect induced by LIPUS was also observed. Finally, the same LIPUS parameters did not induce any differentiation towards the M1 phenotype of THP-1 cells, whereas they decreased TNF-<i>α</i>and IL-8 gene expression, reduced IL-8 cytokine release and increased IL-10 cytokine release in M1-polarized THP-1 cells.<i>Significance.</i>This study represents the first step towards the use of precisely controlled LIPUS for the treatment of peripheral neuropathies.