Multi-walled carbon nanotubes induce COX-2 and iNOS expression via MAP Kinase-dependent and -independent mechanisms in mouse RAW264.7 macrophages

Background: carbon nanotubes (cnts) are engineered graphene cylinders with numerous applications in engineering,electronics and medicine. however,cnts cause inflammation and fibrosis in the rodent lung,suggesting a potential human health risk. we hypothesized that multi-walled cnts (mwcnts) induce two key inflammatory enzymes in macrophages,cyclooxygenase-2 (cox-2) and inducible nitric oxide synthase (inos),through activation of extracellular signal-regulated kinases (erk1,2).methods: raw264.7 macrophages were exposed to mwcnts or carbon black nanoparticles (cbnps) over a range of doses and time course. uptake and subcellular localization of mwcnts was visualized by transmission electron microscopy (tem). protein levels of cox-2,inos,and erk1,2 (total erk and phosphorylated erk) were measured by western blot analysis. prostaglandin-e2 (pge2) and nitric oxide (no) levels in cell supernatants were measured by elisa and greiss assay,respectively.results: mwcnts,but not cbnps,induced cox-2 and inos in a time- and dose-dependent manner. cox-2 and inos induction by mwcnts correlated with increased pge2 and no production,respectively. mwcnts caused erk1,2 activation and inhibition of erk1,2 (u0126) blocked mwcnt induction of cox-2 and pge2 production,but did not reduce the induction of inos. inhibition of inos (l-name) did not affect erk1,2 activation,nor did l-name significantly decrease cox-2 induction by mwcnt. nickel nanoparticles (ninps),which are present in mwcnts as a residual catalyst,also induced cox-2 via erk-1,2. however,a comparison of cox-2 induction by mwcnts containing 4.5 and 1.8% ni did not show a significant difference in ability to induce cox-2,indicating that characteristics of mwcnts in addition to ni content contribute to cox-2 induction.conclusion: this study identifies cox-2 and subsequent pge2 production,along with inos induction and no production,as inflammatory mediators involved in the macrophage response to mwcnts. furthermore,our work demonstrates that cox-2 induction by mwcnts in raw264.7 macrophages is erk1,2-dependent,while inos induction by mwcnts is erk1,2-independent. our data also suggest contributory physicochemical factors other than residual ni catalyst play a role in cox-2 induction to mwcnt. © 2012 lee et al.; licensee biomed central ltd.