The atrial natriuretic peptide (ANP) is a cardiovascular hormone possessing antiinflammatory potential due to its inhibitory action on the production of inflammatory mediators, such as tumor necrosis factor-␣ (TNF-␣). The aim of this study was to determine whether ANP is able to attenuate inflammatory effects of TNF-␣ on target cells. Human umbilical vein endothelial cells (HUVECs) were treated with TNF-␣ in the presence or absence of ANP. Changes in permeability, cytoskeletal alterations,

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... horylation of p38 MAPK and HSP27, and expression of MKP-1 were determined by macromolecule permeability assay, fluorescence labeling, RT-PCR, and immunoblotting. Antisense studies were done by transfecting cells with MKP-1 antisense oligonucleotides. Activation of HUVECs with TNF-␣ lead to a significant increase of macromolecule permeability and formation of stress fibers. Treatment of cells with ANP (10 Ϫ8 to 10 Ϫ6 mol/L) significantly reduced the formation of stress fibers and elevated permeability. Both TNF-␣-induced effects were shown to be mediated via the activation of p38 using SB203580, a specific inhibitor of p38. ANP significantly reduced the TNF-␣-induced activation of p38 and attenuated the phosphorylation of HSP27, a central target downstream of p38. ANP showed no effect on p38 upstream kinases MKK3/6. However, a significant induction of the MAPK phosphatase MKP-1 mRNA and protein could be observed in ANP-treated cells. Antisense experiments proved a causal role for MKP-1 induction in the ANP-mediated inhibition of p38. These data show the inhibitory action of ANP on TNF-␣-induced changes in endothelial cytoskeleton and macromolecule permeability involving an MKP-1-induced inactivation of p38 MAPK. These effects point to an antiinflammatory and antiatherogenic potential of this cardiovascular hormone. (Circ Res. 2002;90:874-881.) HUVECs were transiently transfected with antisense (5Ј-cc-CACTTCCATGACCA-tgg-3Ј) or sense (5Ј-ccATGGTCATGGAAGTggg-3Ј) phosphorothioate-modified oligonucleotides as described under Mosmann 33 (phosphorothioate modifications are shown by small letters). Oligonucleotides were used in a final concentration of 0.03 g/well (12-well plates). The cells were transfected using an Effectene