A synergistic bactericidal effect of low-frequency and low-intensity ultrasound combined with levofloxacin-loaded PLGA nanoparticles on M. smegmatis in macrophages

Abstract

<jats:title>Abstract</jats:title> <jats:p><jats:bold>Purpose:</jats:bold> Tuberculosis (TB) is a highly infectious disease caused by <jats:italic>Mycobacterium tuberculosis </jats:italic>(<jats:italic>Mtb</jats:italic>), which often parasites in macrophages. This study is performed to investigate the bactericidal effect and underlying mechanisms of low-frequency and low-intensity ultrasound (LFLIU) combined with levofloxacin-loaded PLGA nanoparticles (LEV-NPs) on <jats:italic>M. smegmatis</jats:italic> (a surrogate of <jats:italic>Mtb</jats:italic>) in macrophages.<jats:bold>Methods and results: </jats:bold>The<jats:bold> </jats:bold>LEV-NPs were prepared using a double emulsification method. The average diameter, zeta potential, polydispersity index, morphology, and drug release efficiency <jats:italic>in vitro</jats:italic> of the LEV-NPs were investigated. <jats:italic>M. smegmatis </jats:italic>in macrophages was treated using the LEV-NPs combined with 42 kHz ultrasound irradiation at an intensity of 0.13 W/cm<jats:sup>2</jats:sup> for 10 min. The results showed that ultrasound significantly promoted the phagocytosis of nanoparticles<jats:bold> </jats:bold>by macrophages (<jats:italic>p </jats:italic>&lt; 0.05). In addition, further ultrasound combined with the LEV-NPs promoted the production of reactive oxygen species (ROS) in macrophage, and the apoptosis rate of the macrophages was significantly higher than that of the control (<jats:italic>p </jats:italic>&lt; 0.05). The transmission electronic microscope showed that the cell wall of <jats:italic>M. smegmatis</jats:italic> was ruptured, the cell structure was incomplete, and the bacteria received severe damage in the ultrasound combined with the LEV-NPs group. Activity assays showed that ultrasound combined with the LEV-NPs exhibited a 10-fold higher antibacterial activity against <jats:italic>M. smegmatis</jats:italic> residing inside macrophages compared with the free drug.<jats:bold>Conclusion: </jats:bold>These data demonstrated that ultrasound combined with LEV-NPs has great potential as a therapeutic agent for TB.</jats:p>