Monocytes modulate the fibrinolytic balance of endothelial cells

Arterial stiffness, endothelial dysfunction and impaired fibrinolysis are pathogenic mechanisms contributing to cardiovascular risk in ANCA-associated vasculitis

Cardiovascular disease is a complication of systemic inflammatory diseases including anti-neutrophil cytoplasm antibody-associated vasculitis (AAV). The mechanisms of cardiovascular morbidity in AAV are poorly understood, and risk-reduction strategies are lacking. Therefore, in a series of double-blind, randomized case-control forearm plethysmography and crossover systemic interventional studies, we examined arterial stiffness and endothelial function in patients with AAV in long-term disease remission and in matched healthy volunteers (32 each group). The primary outcome for the case-control study was the difference in endothelium-dependent vasodilation between health and AAV, and for the crossover study was the difference in pulse wave velocity (PWV) between treatment with placebo and selective endothelin-A receptor antagonism. Parallel in vitro studies of circulating monocytes and platelets explored mechanisms. Compared to healthy volunteers, patients with AAV had 30% reduced endothelium-dependent vasodilation and 50% reduced acute release of endothelial active tissue plasminogen activator (tPA), both significant in the case-control study. Patients with AAV had significantly increased arterial stiffness (PWV: 7.3 versus 6.4 m/s). Plasma endothelin-1 was two-fold higher in AAV and independently predicted PWV and tPA release. Compared to placebo, both selective endothelin-A and dual endothelin-A/B receptor blockade reduced PWV and increased tPA release in AAV in the crossover study. Mechanistically, patients with AAV had increased platelet activation, more platelet-monocyte aggregates, and altered monocyte endothelin receptor function, reflecting reduced endothelin-1 clearance. Patients with AAV in long-term remission have elevated cardiovascular risk and endothelin-1 contributes to this. Thus, our data support a role for endothelin-blockers to reduce cardiovascular risk by reducing arterial stiffness and increasing circulating tPA activity.

Effects of raloxifene treatment on the phenotype of blood monocytes

Raloxifene (RLX), a selective oestrogen receptor modulator, has oestrogen-agonist effects on bone, lipoproteins, and homocysteine and oestrogen-antagonist activity in the breast and uterus, positioning it as a potential drug for long-term prevention of coronary heart disease in postmenopausal women. To further evaluate its influence on cardiovascular risk factors, we studied the effects of 60 mg/day RLX on serum lipid levels, inflammatory (high-sensitivity C-reactive protein, and coagulation (fibrinogen) markers, monocytes, and fibrinolysis in 15 healthy postmenopausal women. Markers were measured at baseline, after 1 month without treatment, and after 3 months of treatment. Fibrinolysis was evaluated using the euglobulin clot lysis time (ECLT) determined with a new semiautomatic optical method. Monocyte phenotype was determined by measurement of the expression of the antigens CD14, HLA-DR, and CD62-L using flow cytometry. After 3 months of RLX treatment, we observed a decrease in total cholesterol (p = 0.002), in low-density lipoprotein cholesterol (p <0.001), and in lipoprotein A (p = 0.01). Fibrinogen (p = 0.002) decreased significantly, and high-sensitivity C-reactive protein had a tendency to decrease, but this did not reach statistical significance (p = 0.06). RLX treatment had no effect on ECLT (p = 0.223) or on white blood cell, lymphocyte, and total monocyte counts (p = 0.313). Monocyte expression of HLA-DR, CD14, and CD62-L was not modified by the treatment. In conclusion, we confirm that RLX has beneficial short-term effects on levels of lipids and inflammatory markers, with no effect on fibrinolysis or monocyte phenotype.

Monocyte-endothelial cell interaction in atherogenesis and thrombosis

Cellular interactions between leukocytes and the endothelium are critical events in vascular biology, such as atherosclerosis and acute coronary syndrome. When monocytes and endothelial cells are activated via direct cell-cell interaction, both types of cells express several biologically active molecules such as adhesion molecules, cytokines, coagulation and fibrinolytic factors, metalloproteinases, and vasoactive substances. All of these molecules could contribute to atherogenesis and thrombosis.

Fibrinolysis and cardiovascular risk factors: association with fibrinogen, lipids, and monocyte count

BACKGROUND

Numerous risk factors for cardiovascular disease (CVD) have been determined by clinical epidemiological observations. The missing link could be related to endothelial dysfunction and the resulting hypofibrinolysis.

METHODS

In this cross-sectional study, we evaluated 160 subjects (134 in primary prevention) characterized by their clinical cardiovascular risk factors (CVRF), i.e., age, gender, diabetes, hypertension, smoking habit, and history of coronary event or stroke, and by their blood parameters, i.e., C-reactive protein (CRP), fibrinogen, leukocyte count (WBC), monocyte count (MC), total cholesterol, HDL cholesterol (HDL-c), LDL cholesterol (LDL-c), and triglycerides. We assessed their fibrinolytic capacity with a new method, Euglobulin Clot Lysis Time (ECLT). The effects of these clinical and biological parameters were evaluated in multivariate analysis (backward stepwise regression).

RESULTS

ECLT was correlated with the Framingham risk score and was significantly influenced by the number of clinical CVRF. MC was confirmed to be an important predictive factor influencing ECLT. In subjects without clinical CVRF (n=46), 67% of the variability of ECLT was explained by a combination of MC, LDL-c, and fibrinogen.

CONCLUSION

ECLT is related to the number of epidemiologically defined clinical CVRF and to MC. Because it integrates many risk factors, we suggest that fibrinolytic function could be a biological test useful for physicians in the cardiovascular risk assessment of their patients.

Increased levels of monocyte-related cytokines in patients with unstable angina

Inflammatory cytokines play important roles in coronary artery disease. We investigated the clinical significance of monocyte-related cytokine expression in patients with angina pectoris. We studied 26 patients with stable effort angina and 20 patients with unstable angina in whom stenotic lesions of the coronary arteries were confirmed by selective coronary angiography. Plasma levels of interleukin-6 (IL-6), macrophage colony stimulating factor (MCSF), and monocyte chemoattractant protein-1 (MCP-1) were measured. Plasma levels of IL-6, MCSF, and MCP-1 in patients with unstable angina were significantly higher than those in patients with stable angina or control subjects. Patients with unstable angina were further divided into sub-groups according to their clinical classification; Levels of IL-6, MCSF, and MCP-1 in patients, who had anginal attacks at rest within the 48 h prior to admission (Braunwald class IIIB) were significantly higher than those in patients, who did not have attacks at rest (class IB). Five unstable patients, who were refractory to medical therapy and were referred for emergency coronary revascularization showed marked elevation of plasma MCSF and MCP-1 levels. In conclusion, plasma levels of monocyte-related cytokines were elevated in unstable angina. These increases were marked in patients with unstable angina with recent ischemic attack at rest, suggesting that activation of monocytes is involved in vulnerability of underlying atheromatous plaque.

Interaction between monocytes and vascular endothelial cells induces adrenomedullin production

Adrenomedullin (AM), a potent vasodilator peptide, has natriuretic effects, and its plasma concentration is elevated in cardiovascular diseases. In the present study, we investigated the induction of AM expression due to interactions between THP-1 cells (human monocytic cell line) and human umbilical cord vein endothelial cells (HUVECs). AM levels in the culture medium were measured by radioimmunoassay. The luciferase vector containing the 5'-flanking region of the human AM gene was transfected into either HUVECs or THP-1 cells. Addition of THP-1 cells to HUVECs for 48 h induced marked increases in AM levels, which were 16-fold higher than those of HUVECs alone. Luciferase vectors containing the 5'-flanking region of human AM gene (pLCF-1534) were transferred into THP-1 cells or HUVECs. Addition of THP-1 cells to pLCF-1534-transfected HUVECs induced an increase in luciferase activity in cell lysates, which was 5-fold higher than that of the transfected HUVECs alone. In contrast, the luciferase activity of lysates from pLCF-1534-transfected THP-1 cells was not affected by coculture with HUVECs. A separate coculture experiment revealed that direct contact of THP-1 cells and HUVECs contributed to enhanced AM production in the cocoulture. Co-incubation of the cell membrane fraction from THP-1 cells augmented AM production by HUVECs. Both anti-interleukin (IL)-1alpha antibody and IL-1 receptor antagonist significantly inhibited AM production in the cocultures. The cell-to-cell interaction between monocytes and HUVECs induces AM production by HUVECs, which may play an important role in the pathogenesis of vascular disorders.

Matrix metalloproteinase-1 expression by interaction between monocytes and vascular endothelial cells

There is accumulating evidence of complicated interactions among vascular cells, i.e. endothelial cells, smooth muscle cells and monocytes/macrophages, in the regulation of vascular function and remodeling. We have investigated the mechanisms responsible for matrix metalloproteinase (MMP)-1 expression by interactions between monocytes and vascular endothelial cells. THP-1 cells (human monocytic cell line) and human umbilical vein endothelial cells (HUVECs) were cocultured. MMP-1 levels in the culture medium were measured by enzyme-linked immunosorbent assays. Collagenolytic activity in the culture medium was measured by fluorescence labeled-collagen digestion. Immunohistochemistry using an anti-MMP antibody was carried out to determine which types of cell produce MMP-1. The addition of THP-1 cells to HUVECs for 48 h induced increases in MMP-1 levels and collagenolytic activity, which were 5- and 2-fold relative to those of HUVECs alone, respectively. A separate coculture experiment revealed that direct contact of THP-1 cells and HUVECs contributed to enhanced MMP-1 production in the cocolture. Immunohistochemical analysis revealed that both types of cell produce MMP-1 in the coculture. Neutralizing anti-interleukin-1 beta and tumor necrosis factor- alpha antibodies inhibited MMP-1 production by the coculture. The Src kinase and MEK inhibitors significantly inhibited MMP-1 production by the coculture. Coculture of THP-1 cells and HUVECs induced significant increases in Src and mitogen activated protein (MAP) kinase activities. Enhanced MMP-1 expression induced by monocyte-endothelial cell interactions may play an important role in the pathogenesis of atherosclerosis and plaque rupture.

Interaction between human monocytes and vascular smooth muscle cells induces vascular endothelial growth factor expression

The objective of this study was to investigate whether synthesis of vascular endothelial growth factor (VEGF), a major mitogen for vascular endothelial cells, was induced by a cell-to-cell interaction between monocytes and vascular smooth muscle cells (VSMCs). Human VSMCs and THP-1 cells (human monocytoid cell) were cocultured. VEGF levels in the coculture medium were determined by enzyme-linked immunosorbent assay. Northern blot analysis of VEGF mRNA was performed using a specific cDNA probe. Immunohistochemistry was performed to determine which types of cell produce VEGF. Adding THP-1 cells to VSMCs for 24 h increased VEGF levels of the culture media, 8- and 10-fold relative to those of THP-1 cells and VSMCs alone, respectively. Northern blot analysis showed that VEGF mRNA expression was induced in the cocultured cells and peaked after 12 h. Immunohistochemistry disclosed that both types of cell in the coculture produced VEGF. Separate coculture experiments revealed that both direct contact and a soluble factor(s) contributed to VEGF production. Neutralizing anti-interleukin (IL)-6 antibody inhibited VEGF production by the coculture of THP-1 cells and VSMCs. A cell-to-cell interaction between monocytes and VSMCs induced VEGF synthesis in both types of cell. An IL-6 mediated mechanism is at least partially involved in VEGF production by the cocultures. Local VEGF production induced by a monocyte-VSMC interaction may play an important role in atherosclerosis and vascular remodeling.