Low-intensity pulsed ultrasound increases neurotrophic factors secretion and suppresses inflammation in in vitro models of peripheral neuropathies

Abstract

Objective. 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. Approach. 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 (β-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-α (TNF-α) 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-α, interleukin (IL)-1β, IL-6, IL-8) and anti-inflammatory ones (IL-10 and CD206). Main results. 5 MHz and 500 mW cm−2 were found as the optimal stimulation parameters on RSC96 cells. Such parameters were also found to suppress ROS and TNF-α 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-α and IL-8 gene expression, reduced IL-8 cytokine release and increased IL-10 cytokine release in M1-polarized THP-1 cells. Significance. This study represents the first step towards the use of precisely controlled LIPUS for the treatment of peripheral neuropathies.