Inflammation is pivotal in atherogenesis. Numerous prospective studies have shown that levels of high sensitive C-reactive protein (CRP) predict cardiovascular events. Recently, data suggests that CRP could be a mediator in atherothrombosis. Loss of pentameric symmetry in CRP has been shown to result in the formation of modified CRP (mCRP). The main aim of this study was to examine the biological effects of the native, pentameric form of CRP compared to a modified form in human aortic endothelial cells. Human pentameric native CRP (n-CRP) from two different sources (recombinant and serum) was purified and used. It was then subjected to EDTA chelation and urea treatment to prepare modified CRP (m-CRP). Purity of both n-CRP and m-CRP preparations was checked by gel electrophoresis. Both n-CRP and m-CRP were incubated with human aortic endothelial cells (HAEC) and biological activities was tested by assaying for interleukin-8 (IL-8), plasminogen activator inhibitor-1(PAI-1), cyclic GMP and prostaglandin F1-alpha. n-CRP significantly upregulated IL-8 at concentrations > or = 10 microg/mL while m-CRP upregulated IL-8 only at concentrations of 50 microg/mL (p < 0.05). PAI-1 levels were significantly increased to a greater extent with native compared to m-CRP (p < 0.05). While both decreased PGF1-alpha at concentrations of 50 microg/mL, the effect of native CRP was more pronounced and was evident at 10 microg/mL (p < 0.05). The most pronounced difference was observed with regard to inhibition of eNOS activity as assessed by cGMP which was observed at 10 microg/ml of native CRP but only at 50 microg/mL for m-CRP (native CRP versus mCRP: p < 0.001). Thus, native pentameric CRP compared to modified CRP exerts more potent atherogenic effects in human aortic endothelial cells.