Although considerable evidence implicates the cytokine interferon (IFN)-γ in atherogenesis, the proximal inducers and the range of sources of its expression remain unknown. This study tested the hypothesis that interleukin (IL)-18 regulates IFN-γ expression during atherogenesis. Indeed, human atheroma in situ expressed IL-18 and elevated levels of its receptor subunits, IL-18Rα/β, compared with nondiseased arterial tissue. IL-18 occurred predominantly as the mature, 18-kD form and colocalized with mononuclear phagocytes (MØ), while endothelial cells (ECs), smooth muscle cells (SMCs), and MØ all expressed IL-18Rα/β. Correspondingly in vitro, only MØ expressed IL-18, while all three cell types displayed the IL-18Rα/β complex constitutively, exhibiting enhanced expression upon stimulation with LPS, IL-1β, or tumor necrosis factor (TNF)-α. IL-18 signaling evoked effectors involved in atherogenesis, e.g., cytokines (IL-6), chemokines (IL-8), intracellular adhesion molecules (ICAM)-1, and matrix metalloproteinases (MMP-1/-9/-13), demonstrating functionality of the receptor on ECs, SMCs, and MØ. Finally, IL-18, particularly in combination with IL-12, induced the expression of IFN-γ in cultured MØ and, surprisingly, in SMCs (but not in ECs). The expression of functional IL-18 and IL-18 receptor on human atheroma-associated ECs, SMCs, and MØ, and its unexpected ability to induce IFN-γ expression in SMCs, suggests a novel paracrine proinflammatory pathway operating during atherogenesis.

Objective-Metformin may benefit the macrovascular complications of diabetes independently of its conventional hypoglycemic effects. Accumulating evidence suggests that inflammatory processes participate in type 2 diabetes and its atherothrombotic manifestations. Therefore, this study examined the potential action of metformin as an inhibitor of pro-inflammatory responses in human vascular smooth muscle cells (SMCs), macrophages (Ms), and endothelial cells (ECs). Methods and Results-Metformin

SummaryResearch during the last two decades established atheromatous lesions as active sites of inflammation and immune responses, contrasting to the traditional view of atherosclerosis as an acellular lesion composed of lipid deposits. In particular, cytokines appear to orchestrate the chronic development of atherosclerosis, eventually leading to the formation of complex atherosclerotic plaques, which can trigger acute thromboembolic complications, such as myocardial infarction or stroke. Indeed the rupture-prone plaque, characterized by a thin fibrous cap overlaying a voluminous lipid core, exhibits accumulation of various pro-inflammatory cytokines. These cytokines may control the clinical consequences of plaques by mediating infiltration and accumulation of immunocompetent cells, directing the turnover of fibrillar collagens (governing the fragility of the fibrous cap), or enhancing foam cell formation and thrombogenicity of the lipid core, among other processes outlined in this review. Thus, understanding the role of cytokines in the pathophysiology of the atherosclerotic plaque might provide a promising therapeutic avenue for this prevalent human disease. This review will focus on members of the interleukin, tumor necrosis factor, and interferon families of cytokines in modulating key processes of atherogenesis.

Interleukin-1β–converting enzyme (ICE, caspase-1) regulates key steps in inflammation and immunity, by activating the proinflammatory cytokines interleukin (IL-)1β and IL-18, or mediating apoptotic processes. We recently provided evidence for the regulation of caspase-1 activity via an endogenous inhibitor expressed by human vascular smooth muscle cells (SMCs) (Schönbeck, U., M. Herzberg, A. Petersen, C. Wohlenberg, J. Gerdes, H.-D. Flad, and H. Loppnow. 1997. J. Exp. Med. 185:1287–1294). However, the molecular identity of this endogenous inhibitor remained undefined. We report here that the serine proteinase inhibitor (serpin) PI-9 accounts for the endogenous caspase-1 inhibitory activity in human SMCs and prevents processing of the enzyme's natural substrates, IL-1β and IL-18 precursor. Treatment of SMC lysates with anti–PI-9 antibody abrogated the caspase-1 inhibitory activity and coprecipitated the enzyme, demonstrating protein–protein interaction. Furthermore, PI-9 antisense oligonucleotides coordinately reduced PI-9 expression and promoted IL-1β release. Since SMCs comprise the majority of cells in the vascular wall, and because IL-1 is implicated in atherogenesis, we tested the biological validity of our in vitro findings within human atheroma in situ. The unaffected arterial wall contains abundant and homogeneously distributed PI-9. In human atherosclerotic lesions, however, PI-9 expression correlated inversely with immunoreactive IL-1β, supporting a potential role of the endogenous caspase-1 inhibitor in this chronic inflammatory disease. Thus, our results provide new insights into the regulation of this enzyme involved in immune and inflammatory processes of chronic inflammatory diseases, and point to an endogenous antiinflammatory action of PI-9, dysregulated in a prevalent human disease.