Person:

Libby, Peter

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 (Mφs), and endothelial cells (ECs). Methods and results. Metformin dose-dependently inhibited IL-1β–induced release of the pro-inflammatory cytokines IL-6 and IL-8 in ECs, SMCs, and Mφs. Investigation of potential signaling pathways demonstrated that metformin diminished IL-1β–induced activation and nuclear translocation of nuclear factor-kappa B (NF-κB) in SMCs. Furthermore, metformin suppressed IL-1β–induced activation of the pro-inflammatory phosphokinases Akt, p38, and Erk, but did not affect PI3 kinase (PI3K) activity. To address the significance of the anti-inflammatory effects of a therapeutically relevant plasma concentration of metformin (20 μmol/L), we conducted experiments in ECs treated with high glucose. Pretreatment with metformin also decreased phosphorylation of Akt and protein kinase C (PKC) in ECs under these conditions. Conclusions. These data suggest that metformin can exert a direct vascular anti-inflammatory effect by inhibiting NF-κB through blockade of the PI3K–Akt pathway. The novel anti-inflammatory actions of metformin may explain in part the apparent clinical reduction by metformin of cardiovascular events not fully attributable to its hypoglycemic action.

To determine whether nuclear factor (NF)-(\kappa) B is necessary to confer endothelial cell responsiveness to interferon (INF)-(\gamma) in terms of vascular cell adhesion molecule (VCAM)-1 expression and leukocyte adhesion, human endothelial cells were treated with IFN-(\gamma) in the presence of low concentrations (LCs) of interleukin (IL)-1(\alpha) (≤100 pg/mL), which activates (NF-\kappa B) but does not induce VCAM-1 expression. Although IFN-(\gamma) induced major histocompatibility complex class II antigen expression and although a high concentration of IL-1(\alpha) (10 ng/mL) induced leukocyte adhesion and VCAM-1 expression, neither IFN-(\gamma) nor LC IL-1(\alpha) was able to induce VCAM-1 expression or leukocyte adhesion. However, the combination of IFN-(\gamma) and LC IL-1(\alpha) induced VCAM-1 expression and increased leukocyte adhesion (67% and 49% of high-concentration IL-1(\alpha), respectively). Electrophoretic mobility shift assays and immunoblotting of nuclear extracts showed that IFN-(\gamma) activated signal transducers and activators of transcription (STAT)-1(\alpha) and interferon regulatory factor (IRF)-1 but not (NF-\kappa B), whereas LC IL-1(\alpha) activated (NF-\kappa B) but not STAT-1(\alpha) or IRF-1. Nuclear run-on studies showed that LC IL-1(\alpha) is necessary but not sufficient for inducing VCAM-1 gene transcription and that the combination of IFN-(\gamma) and LC IL-1(\alpha) is required for full VCAM-1 gene transcription. These findings suggest that factors that activate (NF-\kappa B) can synergize with IFN-(\gamma) in promoting endothelial-leukocyte interaction.

Summary. The study evaluated the role of thrombin in activation of vascular smooth muscle cells early after vascular injury. The direct thrombin inhibitor Hirulog (10 mg/kg SQ tid) or vehicle was administered to rabbits over 3 days following balloon injury to the abdominal aorta and the right iliac artery. Hirulog treatment yielded marked systemic anticoagulation as evidenced by an about 3.5-fold prolongation of quantitative thrombin time one hour after an injection, but with a reduction to almost baseline levels at the end of the dosing interval. After 3 days, proliferating cells in the right iliac artery were enumerated. The expression of intercellular adhesion molecule 1, macrophage-colony stimulating factor, tumor necrosis factor α, and interleukin-1β as markers for inflammatory activation of the vessel wall was examined by immunohistochemistry and graded semiquantitatively. Mitotic indices did not differ between control and Hirulog-treated animals. There was also no difference in the expression of markers of inflammatory activation between both groups. In conclusion, thrombin inhibition by Hirulog administration does not reduce acutely (within 3 days) vascular smooth muscle cell proliferation or inflammatory activation after angioplasty. Thrombin inhibitors may therefore limit restenosis in the rabbit by acting later or via other, unknown pathways. The lack of effect of the thrombin inhibitor on the cellular events during the early phase of the response to balloon injury may explain the failure of such strategies to reduce restenosis in recent clinical trials despite effects towards acute thrombotic complications. Together, these results suggest that acute thrombin generation is not a crucial stimulus for early smooth muscle cell proliferation and inflammatory activation after vascular injury.

Objective—Obesity associates with increased numbers of inflammatory cells in adipose tissue (AT), including T cells, but the mechanism of T-cell recruitment remains unknown. This study tested the hypothesis that the chemokine receptor CXCR3 participates in T-cell accumulation in AT of obese mice and thus in the regulation of local inflammation and systemic metabolism.

Approach and Results—Obese wild-type mice exhibited higher mRNA expression of CXCR3 in periepididymal AT-derived stromal vascular cells compared with lean mice. We evaluated the function of CXCR3 in AT inflammation in vivo using CXCR3-deficient and wild-type control mice that consumed a high-fat diet. Periepididymal AT from obese CXCR3-deficient mice contained fewer T cells than obese controls after 8 and 16 weeks on high-fat diet, as assessed by flow cytometry. Obese CXCR3-deficient mice had greater glucose tolerance than obese controls after 8 weeks, but not after 16 weeks. CXCR3-deficient mice fed high-fat diet had reduced mRNA expression of proinflammatory mediators, such as monocyte chemoattractant protein-1 and regulated on activation, normal T cell expressed and secreted, and anti-inflammatory genes, such as Foxp3, IL-10, and arginase-1 in periepididymal AT, compared with obese controls.

Conclusions—These results demonstrate that CXCR3 contributes to T-cell accumulation in periepididymal AT of obese mice. Our results also suggest that CXCR3 regulates the accumulation of distinct subsets of T cells and that the ratio between these functional subsets across time likely modulates local inflammation and systemic metabolism.

Adenovirus vectors are capable of high efficiency in vivo arterial gene transfer, and are currently in use as therapeutic agents in animal models of vascular disease. However, despite substantial data on the ability of viruses to cause vascular inflammation and proliferation, and the presence in current adenovirus vectors of viral open reading frames that are translated in vivo, no study has examined the effect of adenovirus vectors alone on the arterial phenotype. In a rabbit model of gene transfer into a normal artery, we examined potential vascular cell activation, inflammation, and neointimal proliferation resulting from exposure to replication-defective adenovirus. Exposure of normal arteries to adenovirus vectors resulted in: (a) pronounced infiltration of T cells throughout the artery wall; (b) upregulation of intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 in arterial smooth muscle cells; (c) neointimal hyperplasia. These findings were present both 10 and 30 d after gene transfer, with no evidence of a decline in severity over time. Adenovirus vectors have pleiotropic effects on the arterial wall and cause significant pathology. Interpretation of experimental protocols that use adenovirus vectors to address either biological or therapeutic issues should take these observations into account. These observations should also prompt the design of more inert gene transfer vectors.

Objective—Both asthma and abdominal aortic aneurysms (AAA) involve inflammation. It remains unknown whether these diseases interact.

Approach and Results—Databases analyzed included Danish National Registry of Patients, a population-based nationwide case–control study included all patients with ruptured AAA and age- and sex-matched AAA controls without rupture in Denmark from 1996 to 2012; Viborg vascular trial, subgroup study of participants from the population-based randomized Viborg vascular screening trial. Patients with asthma were categorized by hospital diagnosis, bronchodilator use, and the recorded use of other anti-asthma prescription medications. Logistic regression models were fitted to determine whether asthma associated with the risk of ruptured AAA in Danish National Registry of Patients and an independent risk of having an AAA at screening in the Viborg vascular trial. From the Danish National Registry of Patients study, asthma diagnosed <1 year or 6 months before the index date increased the risk of AAA rupture before (odds ratio [OR]=1.60–2.12) and after (OR=1.51–2.06) adjusting for AAA comorbidities. Use of bronchodilators elevated the risk of AAA rupture from ever use to within 90 days from the index date, before (OR=1.10–1.37) and after (OR=1.10–1.31) adjustment. Patients prescribed anti-asthma drugs also showed an increased risk of rupture before (OR=1.12–1.79) and after (OR=1.09–1.48) the same adjustment. In Viborg vascular trial, anti-asthmatic medication use associated with increased risk of AAA before (OR=1.45) or after adjustment for smoking (OR=1.45) or other risk factors (OR=1.46).

Conclusions—Recent active asthma increased risk of AAA and ruptured AAA. These findings document and furnish novel links between airway disease and AAA, 2 common diseases that share inflammatory aspects.

Atherosclerosis is a maladaptive, nonresolving chronic inflammatory disease that occurs at sites of blood flow disturbance. The disease usually remains silent until a breakdown of integrity at the arterial surface triggers the formation of a thrombus. By occluding the lumen, the thrombus or emboli detaching from it elicits ischaemic symptoms that may be life-threatening. Two types of surface damage can cause atherothrombosis: plaque rupture and endothelial erosion. Plaque rupture is thought to be caused by loss of mechanical stability, often due to reduced tensile strength of the collagen cap surrounding the plaque. Therefore, plaques with reduced collagen content are thought to be more vulnerable than those with a thick collagen cap. Endothelial erosion, on the other hand, may occur after injurious insults to the endothelium instigated by metabolic disturbance or immune insults. This review discusses the molecular mechanisms involved in plaque vulnerability and the development of atherothrombosis.

Background—Healing after myocardial infarction (MI) involves the biphasic accumulation of inflammatory Ly-6Chigh and reparative Ly-6Clow monocytes/macrophages. Excessive inflammation disrupts the balance between the 2 phases, impairs infarct healing, and contributes to left ventricle remodeling and heart failure. Lipoprotein-associated phospholipase A2 (Lp-PLA2), a member of the phospholipase A2 family of enzymes, produced predominantly by leukocytes, participates in host defenses and disease. Elevated Lp-PLA2 levels associate with increased risk of cardiovascular events across diverse patient populations, but the mechanisms by which the enzyme elicits its effects remain unclear. This study tested the role of Lp-PLA2 in healing after MI.

Methods and Results—In response to MI, Lp-PLA2 levels markedly increased in the circulation. To test the functional importance of Lp-PLA2, we generated chimeric mice whose bone marrow–derived leukocytes were Lp-PLA2–deficient (bmLp-PLA2−/−). Compared with wild-type controls, bmLp-PLA2−/− mice subjected to MI had lower serum levels of inflammatory cytokines tumor necrosis factor-α, interleukin (IL)-1β, and IL-6, and decreased number of circulating inflammatory myeloid cells. Accordingly, bmLp-PLA2−/− mice developed smaller and less inflamed infarcts with reduced numbers of infiltrating neutrophils and inflammatory Ly-6Chigh monocytes. During the later, reparative phase, infarcts of bmLp-PLA2−/− mice contained Ly-6Clow macrophages with a skewed M2-prone gene expression signature, increased collagen deposition, fewer inflammatory cells, and improved indices of angiogenesis. Consequently, the hearts of bmLp-PLA2−/− mice healed more efficiently, as determined by improved left ventricle remodeling and ejection fraction.

Conclusions—Lp-PLA2 augments the inflammatory response after MI and antagonizes healing by disrupting the balance between inflammation and repair, providing a rationale for focused study of ventricular function and heart failure after targeting this enzyme acutely in MI.

Background— Healing after myocardial infarction (MI) involves the biphasic accumulation of inflammatory Ly-6Chigh and reparative Ly-6Clow monocytes/macrophages. Excessive inflammation disrupts the balance between the 2 phases, impairs infarct healing, and contributes to left ventricle remodeling and heart failure. Lipoprotein-associated phospholipase A2 (Lp-PLA2), a member of the phospholipase A2 family of enzymes, produced predominantly by leukocytes, participates in host defenses and disease. Elevated Lp-PLA2 levels associate with increased risk of cardiovascular events across diverse patient populations, but the mechanisms by which the enzyme elicits its effects remain unclear. This study tested the role of Lp-PLA2 in healing after MI. Methods and Results— In response to MI, Lp-PLA2 levels markedly increased in the circulation. To test the functional importance of Lp-PLA2, we generated chimeric mice whose bone marrow–derived leukocytes were Lp-PLA2–deficient (bmLp-PLA2−/−). Compared with wild-type controls, bmLp-PLA2−/− mice subjected to MI had lower serum levels of inflammatory cytokines tumor necrosis factor-α, interleukin (IL)-1β, and IL-6, and decreased number of circulating inflammatory myeloid cells. Accordingly, bmLp-PLA2−/− mice developed smaller and less inflamed infarcts with reduced numbers of infiltrating neutrophils and inflammatory Ly-6Chigh monocytes. During the later, reparative phase, infarcts of bmLp-PLA2−/− mice contained Ly-6Clow macrophages with a skewed M2-prone gene expression signature, increased collagen deposition, fewer inflammatory cells, and improved indices of angiogenesis. Consequently, the hearts of bmLp-PLA2−/− mice healed more efficiently, as determined by improved left ventricle remodeling and ejection fraction. Conclusions— Lp-PLA2 augments the inflammatory response after MI and antagonizes healing by disrupting the balance between inflammation and repair, providing a rationale for focused study of ventricular function and heart failure after targeting this enzyme acutely in MI.