Atherosclerosis is a chronic inflammatory disease, and is the primary cause of heart disease and stroke in Western countries. Derivatives of cannabinoids such as delta-9-tetrahydrocannabinol (THC) modulate immune functions and therefore have potential for the treatment of inflammatory diseases. We investigated the effects of THC in a murine model of established atherosclerosis. Oral administration of THC (1 mg kg(-1) per day) resulted in significant inhibition of disease progression. This effective dose is lower than the dose usually associated with psychotropic effects of THC. Furthermore, we detected the CB2 receptor (the main cannabinoid receptor expressed on immune cells) in both human and mouse atherosclerotic plaques. Lymphoid cells isolated from THC-treated mice showed diminished proliferation capacity and decreased interferon-gamma secretion. Macrophage chemotaxis, which is a crucial step for the development of atherosclerosis, was also inhibited in vitro by THC. All these effects were completely blocked by a specific CB2 receptor antagonist. Our data demonstrate that oral treatment with a low dose of THC inhibits atherosclerosis progression in the apolipoprotein E knockout mouse model, through pleiotropic immunomodulatory effects on lymphoid and myeloid cells. Thus, THC or cannabinoids with activity at the CB2 receptor may be valuable targets for treating atherosclerosis.

Abstract-Increasing evidence supports the involvement of inflammation in the early phases of atherogenesis. Recruitment of leukocytes within the vascular wall, controlled by chemokines, is an essential process in the development of this common disease. In this study, we report that blocking a chemokine pathway in vivo with the CC chemokine antagonist Met-RANTES reduces the progression of atherosclerosis in a hypercholesterolemic mouse model. The reduction of lesions was correlated with a diminution of expression of several major chemokines and chemokine receptors, a decrease in leukocyte infiltration, and an increase of collagen-rich atheroma, features associated with stable atheroma. Treatment was well tolerated and serum lipid profiles were not affected. Whereas genetically engineered mice with deletion of either a CC chemokine or its receptor have demonstrated resistance to disease, to our knowledge, this is the first demonstration that treatment with a chemokine receptor antagonist limits the progression of atherosclerosis in vivo. Thus, our findings indicate that blockade of chemokine receptor/ligand interactions might become a novel therapeutic strategy to reduce the evolution of this common disease. A therosclerosis is an inflammatory disease characterized by arterial lesions containing cholesterol, immune infiltrates, and fibrosis, 1-3 resulting essentially from hyperlipidemia, hypertension, smoking, and diabetes. 4 These cardiovascular risk factors cause endothelial dysfunction, which triggers the migration of leukocytes, mainly of monocyte/ macrophage and T lymphocyte type, within the vessel wall intima area. Proinflammatory factors, such as cytokines and chemokines, released from endothelial cells (ECs), macrophages, or T cells, cause proliferation and migration of smooth muscle cells (SMCs) from the media to the intima, as well as recruitment of new immunoinflammatory cells. Within the intima, SMCs secrete extracellular matrix components, leading to the accumulation of collagen and proteoglycans, key factors implicated in plaque stability. Conversely, the secretion of matrix metalloproteinases by vascular and inflammatory cells degrades matrix components, such as collagen, gelatin, or elastin within atherosclerotic lesions.Chemokines (chemotactic cytokines) belong to a large superfamily of low molecular weight proteins with a highly homologous 3-dimensional structure, which are divided into four groups based on the configuration of the first two cysteines. 5,6 Chemokines are known to induce leukocyte migration, growth, and activation through 7 transmembrane heptahelical, G protein-coupled cell-surface receptors on target cells and regulate leukocyte trafficking during inflammation. The chemokine CCL5/RANTES (Regulated on Activated Normal T-Cell Expressed and Secreted) is a soluble chemokine of 7.8 kDa secreted by many different cell types, such as ECs, SMCs, activated T cells, macrophages, and platelets. 7,8 RANTES interacts with the chemokine receptors CCR1, CCR3, and CCR5, and has been implicated i...

Paracrine cell-to-cell interactions are crucial events during atherogenesis. However, little is known about the role of direct intercellular communication via gap junctions during this process. We have investigated the expression pattern of 3 vascular gap junction proteins (connexins) in mouse and human atherosclerotic plaques. Low density lipoprotein receptor-deficient mice were fed a high-fat diet for 0, 6, 10, or 14 weeks to induce different stages of atherosclerosis. Connexin37 (Cx37) and Cx40 were detected in the endothelium, and Cx43 was detected in the media of nondiseased aortas. In early atheromas, endothelial and medial connexin expression remained unchanged, and "islets" of Cx43 in smooth muscle cells and Cx37 in macrophages were observed in the neointima. In advanced atheromas, Cx37 was detected in medial smooth muscle cells and in macrophages in the lipid core but not in the endothelium covering the plaques. Cx40 could also no longer be detected in the endothelium covering the plaques. Cx43, on the other hand, was detected in the endothelium covering the shoulder of the plaques and also sparsely in neointimal smooth muscle cells. Similar results were obtained for human carotid arteries. In conclusion, vascular connexins are differentially expressed by atheroma-associated cells within lesions. These observations suggest a role for gap junctional intercellular communication during atherogenesis.

Objectives-Besides its predictive role in determining cardiovascular risk, C-reactive protein (CRP) may exert direct proatherogenic effects through proinflammatory properties. CRP is mainly produced by hepatocytes in response to interleukin-6 (IL-6) and is then released into the systemic circulation. 3-hydroxy-3-methylglutaryl (HMG)-coenzyme A (CoA) reductase inhibitors, or statins, significantly reduce cardiovascular events and mortality in patients with or without coronary artery disease and reduce plasma CRP levels in humans. However, the mechanism by which statins reduce plasma CRP levels remains unknown. Methods and Results-In this study, we report that statins limit both protein and RNA levels of IL-6-induced CRP in human hepatocytes. These effects are reversed by L-mevalonate and mimicked by an inhibitor of the geranylgeranyltransferase. IL-6 -induced CRP production requires the binding of IL-6 to its cognate receptors, which results in activation and phosphorylation of the transcription factor STAT3. We provide evidence that statins reduce this IL-6 -induced phosphorylation of STAT3 in hepatocytes. Recent clinical trials showed that C-reactive protein (CRP) is a powerful independent predictor of future cardiovascular events. 2,5 CRP, the major acute-phase reactant in humans, derives mainly from hepatocytes in response to interleukin-6 (IL-6) 6 and is then secreted into the systemic circulation. Recent studies reported that besides its predictive role in determining cardiovascular risk, CRP can exert a direct proatherogenic role. CRP can accelerate the progression of atherosclerosis in apolipoprotein E (apoE)-deficient mice. 7 In vitro studies reporting that CRP modulates the activity and expression of multiple factors implicated in atherogenesis provided further evidence for the proatherogenic role of CRP. CRP downregulates endothelial nitric oxide synthase, 8 resulting in decreased release of NO, and thus facilitates endothelial cell apoptosis and inhibition of angiogenesis. 9 In addition, CRP stimulates the production of the vasoconstrictor endothelin-1 and the inflammatory marker IL-6 by endothelial cells. 10 Furthermore, CRP increases the expression of vascular cell adhesion molecule-1, intercellular adhesion molecule-1, E-selectin, 11 and monocyte chemoattractant protein-1 (MCP-1), resulting in enhanced leukocyte transmigration. 12 Recent data suggest that CRP itself potently chemoattracts monocytes 13 and facilitates the uptake of low-density lipoprotein (LDL) by macrophages. 14 In smooth muscle cells, CRP upregulates angiotensin type 1 receptor and stimulates smooth muscle cells migration and proliferation and reactive oxygen species production. 15 3-hydroxy-3-methylglutaryl-coenzymeA (HMG-CoA) reductase inhibitors, or statins, effectively lower serum cholesterol levels and significantly reduce cardiovascular events and mortality in patients with or without coronary artery disease. 16 Recently, statins have also been characterized by their immunomodulatory effects, [17][18][19] as well as antiinfl...

Background— Gap junctions allow the direct exchange of ions and small molecules between cells in contact, thus coordinating physiological processes such as cell growth and differentiation. We have recently demonstrated increased expression of the gap junction protein connexin43 (Cx43) in specific subsets of cells in atherosclerotic lesions. Because the development of atherosclerosis depends critically on paracrine cell-to-cell interactions, we hypothesized that direct intercellular communication via gap junctions may be another factor controlling atherogenesis. Methods and Results— The role of Cx43 in atherogenesis was examined by use of both a genetic and a pharmacological approach. First, atherosclerosis-susceptible LDL receptor–deficient (LDLR −/− ) mice with normal (Cx43 +/+ ) or reduced (Cx43 +/− ) levels of Cx43 were fed a cholesterol-rich diet for 14 weeks. The progression of atherosclerosis was reduced by 50% ( P <0.01) in the thoracoabdominal aorta and in the aortic roots of Cx43 +/− LDLR −/− mice compared with Cx43 +/+ LDLR −/− controls. Atheroma in Cx43 +/− LDLR −/− mice contained fewer inflammatory cells and exhibited thicker fibrous caps with more collagen and smooth muscle cells. Next, we observed that HMG-CoA reductase inhibitors, or “statins,” lipid-lowering drugs well known for their pleiotropic antiatherogenic effects, reduced Cx43 expression in primary human vascular cells in vitro. Atheroma of LDLR −/− mice treated orally with pravastatin contained fewer inflammatory cells and exhibited thicker fibrous caps than controls. This was associated with reduced Cx43 expression in lesions of statin-treated mice. Conclusions— These data indicate a critical role for Cx43-mediated gap junctional communication in atherosclerotic plaque formation.