PM-induced MMP-3 elevation occurs independently of oxidative stress. A, PM induced a concentration-dependent increase in MMP-3 levels. Data are mean ± S.D. MMP-3 levels were assessed by electrochemiluminescence in supernatants taken from treated cells. n = 6 in each case. *p < 0.05 compared to controls. B, PM-induced MMP-3 expression was not affected by ascorbate pre-treatment. n = 6 in each case. *p < 0.05 compared to controls. #, p > 0.05 compared to TPM alone.