Tungsten increases plasma levels of Pro-MMP-9. A, Image of zymography gel for Pro-MMP-9 in plasma samples from tumor-bearing (control and tungsten-exposed) animals. B, Band densitometry of zymography gel shown in A. Graph shows mean Pro-MMP-9 densitometry per group. ***P < 0.001 unpaired Student’s t test. C, Spearman correlation analysis of plasma Pro-MMP-9 densitometry verses average metastatic lesion area per animal. D, Image of zymography gel for MMP-9 and MMP-2 in conditioned media from cultured 66Cl4 cells exposed to control, 4 or 15 ppb (4-week exposure) tungsten in vitro. Both the Pro- and Active forms of MMP-9 and MMP-2 were detected. E, Image of zymography gel for MMP-9 and MMP-2 in primary tumors. Both the Pro- and Active forms of MMP-9 and Pro-MMP-2 were detected. F, Band densitometry of zymography gel shown in E. Graphs show mean Pro-MMP-9 and Active MMP-9 densitometry per group.