Bioeffects of ultrasound-stimulated microbubbles on endothelial cells: gene expression changes associated with radiation enhancement in vitro.

Ultrasound can be used to target endothelial cells in cancer therapy where the destruction of vasculature leads to tumor cell death. Here, we demonstrate ultrasound bioeffects in which the levels of genes in endothelial cells can be significantly altered by ultrasound-stimulated microbubble exposure. These were compared with established effects of radiation on endothelial cells at a gene level. Human-endothelial cells were exposed to ultrasound and microbubbles, radiation or combinations of ultrasound, microbubbles and radiation. Gene expression analyses revealed an up-regulation of genes known to be involved in apoptosis and ceramide-induced apoptotic pathways, including SMPD2, UGT8, COX6B1, Caspase 9 and MAP2K1 with ultrasound-stimulated microbubble exposure but not SMPD1. This was supported by immunohistochemistry and morphologic changes examined with cell microscopy, which showed changes in SMPD1 gene product in cells with microbubble exposure. This supports the hypothesis that ultrasound-stimulated microbubbles can induce significant bioeffect-related changes in gene expression and can affect ceramide signaling pathways in endothelial cells, leading to apoptosis.