Carbon nanotubes (CNTs) are widely used in industry and biomedicine. While several studies have focused on biological matters, attempts to systematically elucidate the toxicity mechanisms of CNTs are limited. The aim of the present study was to evaluate and compare the cytotoxicity of raw multi-walled carbon nanotubes (MWCNTs) and MWCNTs functionalized with carboxylation (MWCNTs-COOH) or polyethylene glycol (MWCNTs-PEG) in murine macrophages. Our results show that only MWCNTs-COOH and raw MWCNTs alter the oxidative potential of macrophages by increasing reactive oxygen species and the expression of pro-inflammatory factors in both a concentration- and surface coating-dependent manner. The data suggest that compare with raw MWCNTs and MWCNTs-PEG, the MWCNTs-COOH produces a significant increase in ROS generation, interruption of ATP synthesis, and activation of the MAPK and NF-kappa B signaling pathways, which in turn upregulates IL-1 beta, IL-6, TNE-alpha, and iNOS to trigger cell death. These findings suggest that contributory cellar uptake caused by physicochemical factors rather than residual metal catalysts plays a role in ROS-mediated pro-inflammatory responses in vitro. (C) 2014 Elsevier B.V. All rights reserved.