Further analysis suggested that the pro-apoptotic effect of paeoniflorin may be due to miR-16-mediated down-regulation of the expression of matrix metalloproteinase-9 (MMP-9), an indicator of malignant human brain glioma (Figure 9) (Nakano et al., 1995), as exogenous miR-16 up-regulation can reduce the expression levels of MMP-9 protein in U87 cells (Li et al., 2015). The gene discussed is MMP9; the disease is brain glioma.