Abstract-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, phosphorylation 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. Key Words: signal transduction Ⅲ inflammation Ⅲ endothelium Ⅲ hormones Ⅲ natriuretic peptides T umor necrosis factor-␣ (TNF-␣) is one of the primary inflammatory cytokines associated with developing atherosclerotic lesions. It is mainly produced by activated monocytes and macrophages and influences the growth and behavior of endothelial cells, monocytes, and smooth muscle cells. 1 TNF-␣ exerts several effects that facilitate the formation of an atheromatous plaque: it increases the expression of endothelial cell adhesion molecules, induces proliferation of smooth muscle cells, and increases endothelial cell leakiness. Formation of intercellular gaps in vascular endothelium is regarded as one of the initial conditions contributing to the development of an atheromatous plaque. 2 An increased vascular permeability is commonly attributed to the reorganization of F-actin filaments followed by contraction of cells and formation of intercellular gaps. [3][4][5][6] The TNF-␣-induced reorganization of F-actin, ie, the formation of stress fibers, is associated with the polymerization of G-actin into F-actin fibers. 4 Heat shock protein HSP27 has been closely associated with the regulation of actin polymerization ...

Alpha-lipoic acid mediates its antiapoptotic action via activation of the insulin receptor/PI3-kinase/Akt pathway. We show for the first time a direct binding site for alpha-lipoic acid at the insulin receptor tyrosine kinase domain, which might make alpha-lipoic acid a model substance for the development of insulin mimetics.

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This work represents a systematic investigation of MAPK activation during liver ischemia and reperfusion. Employing ANP, for the first time a pharmacological approach to modulate these central signal transduction molecules is presented.

This study reveals that ANP-mediated p38 MAPK activation leads to changes in hepatocyte cytoskeleton involving an elevation of phosphorylated Hsp27 and thereby for the first time shows functional consequences of ANP-induced hepatic p38 MAPK activation.