COX-2 expression is induced by NiNPs in an ERK1,2-dependent manner in RAW264.7 cells, yet the Ni present in MWCNTs only partially mediates COX-2 induction. A) Western blot showing COX-2 expression induced by NiNPs, MWCNTs, LPS, or V2O5 was significantly inhibited by U0126. Quiescent cultures of RAW264.7 cells were exposed to MWCNTs (50 μg/ml), NiNPs (10 μg/ml), LPS (0.1 μg/ml), or V2O5 (1 μg/ml) in the absence or presence of U0126 (20 μM) for 24 hr. B) Western blot showing induction of COX-2 by 50 μg/ml “as-prepared” (AP)-MWCNTs that contain 4.49% Ni and the same MWCNTs that have been purified (PD-MWCNTs) by acid washing to reduce Ni content to 1.8%. COX-2 induction was not significantly reduced by depletion of Ni catalyst. The MEK inhibitor U0126 blocked induction of COX-2 by either AP-MWCNTs or PD-MWCNTs. Numeric values above each Western blot represent the fold-increase in relative densitometric intensity of each COX-2 band relative to control (zero) nanoparticle treatment which was normalized to 1.0. Data are typical of at least two independent experiments.