Metal ions alter lipopolysaccharide-induced NFκB binding in monocytes

Metals are components of a variety of biomaterials used in orthopedic and dental appliances; however, their biocompatibility with the surrounding tissues is not completely understood. Monocytes are important immune cells that respond to inflammatory stimuli by rapidly producing a variety of inflammatory proteins. Regulation of this response often involves activation of the transcription factor NFκB. The current study was designed to determine whether monocyte activation of NFκB in response to bacterial lipopolysaccharide (LPS) is affected by pretreatment with metal ions. Concentrations of metal ions that affected cell number after 24 h of exposure were first determined. Then THP‐1 human monocytes were cultured for 2 h in media containing metal ions at concentrations below levels that altered cell growth. Parallel cultures were treated with 10 μg/mL Escherichia coli LPS, and all samples were cultured an additional 2 h. Nuclear proteins were extracted and normalized amounts were incubated with [32P]‐end‐labeled NFκB consensus oligonucleotide. NFκB–DNA complexes were identified and quantified by electrophoretic mobility shift analysis. The extent of NFκB–DNA complex formation after metal ion pretreatment with or without LPS induction was compared to no treatment or LPS‐only treated controls. Finally, LPS‐induced IL1β secretion was measured from palladium‐treated and control cells. Concentrations were identified for each metal ion (Ag+, Co2+, Cu2+, Hg2+, Ni2+, and Pd2+) that did not reduce cell number after 24 h of exposure (ranging from 5 μM for Ag+ and Hg2+ to 200 μM for Ni2+). Exposures of 2 h at these concentrations did not alter cell morphology, staining with trypan blue, or cell number. LPS exposure had no effect on cell number with or without metal ions after 2 h. When metal treatment alone was assessed, none of the metal ions had a significant effect on NFκB–DNA binding. However, pretreatment with Co2+, Ni2+, Ag1+, Hg2+, and Pd2+ significantly decreased NFκB–DNA binding by 40–70% versus LPS alone. Only Cu2+ had no effect on LPS‐induced NFκB–DNA complex formation. Pd2+ lowered, but did not abolish, IL1β secretion at concentrations comparable to those that altered NFκB–DNA binding. These results suggest that many commonly used metals alter monocyte function at concentrations that are not overtly toxic, and that protein levels controlled in part by NFκB also may be altered. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res 67A: 868–875, 2003