Lipoprotein-associated paf (LA-paf) was found in washed human platelets and monocyte/macrophage-like U937 cells

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Antibodies to platelet-activating factor are associated with borderline hypertension, early atherosclerosis and the metabolic syndrome

OBJECTIVE

Platelet-activating factor (PAF) is a phospholipid inflammatory mediator which is synthesized by a variety of cells, including monocytes and endothelial cells, and PAF can be retained in activated endothelial cell membranes. Furthermore, PAF-like lipids are produced in other phospholipid membranes as in oxidized LDL. Atherosclerosis is a chronic inflammation in the artery wall, but little is known about the role of immune reactions in the early stages of development of cardiovascular disease. In the present study we investigated if there are antibodies to PAF (aPAF) that may play a role in borderline hypertension and early atherosclerosis.

DESIGN

Seventy-three men with borderline hypertension (BHT) and 73 age-matched normotensive (NT) men (diastolic blood pressure 85-94 and <80 mmHg, respectively) were recruited from a population screening programme. Antibody levels were determined by use of ELISA. Carotid intima-media (IM)-thickness and atherosclerosis was determined by B-mode ultrasonography.

RESULTS

BHT men had 49.3% higher aPAF levels of IgG class than NT controls (P = 0.0007). Antibodies to the biologically inactive lysoPAF did not differ between BHT and NT group. aPAF levels were associated with IM-thickness in the left (P = 0.02) and right (P = 0.009) carotid artery. Furthermore, aPAF levels were enhanced in individuals with the metabolic syndrome (n = 44) as compared to those without (n = 102; P = 0.009), and also significantly associated with insulin levels (P = 0.02) and insulin resistance (P = 0.02).

CONCLUSIONS

aPAF antibodies may reflect early vascular changes and thus serve as novel markers for disease, and they may also be pathogenic, by eliciting an inflammatory reaction in the vascular wall.

Platelet-activating factor and oxidized LDL induce immune activation by a common mechanism

Platelet activating factor (PAF) is a phospholipid with proinflammatory and thrombogenic properties, which has been implicated in inflammatory disorders including vasculitis and asthma. PAF-like compounds are present in oxidized LDL (oxLDL), which has been detected in the atherosclerotic lesion, where it may activate monocytes, macrophages, and T cells. OxLDL may therefore both initiate and perpetuate inflammatory reactions in the artery wall. Herein we demonstrate that PAF has the capacity to induce enhanced interferon gamma (IFN-gamma) secretion in peripheral blood mononuclear leukocytes (PBMCs), as does oxLDL. Both oxLDL- and PAF-induced IFN-gamma secretions were inhibited by a specific PAF-receptor antagonist, WEB 2170. PAF-like lipids in oxLDL could thus be responsible for oxLDL-induced activation of immune-competent cells. The effects of PAF and oxLDL were inhibited by antibodies to major histocompatibility complex class II and thus depend on accessory cells like monocytes. Both PAF and oxLDL induced tumor necrosis factor-alpha (TNF-alpha) synthesis in peripheral blood. PAF-mediated TNF-alpha production was inhibited by WEB 2170, whereas oxLDL-induced TNF-alpha was only partially inhibited. These findings indicate that both PAF and oxLDL have the capacity to induce TNF-alpha, which may increase atherogenesis due to its pleiotropic proinflammatory effects. Our findings suggest that the PAF receptor plays an important role in the inflammatory component of atherosclerosis.

Non-specific PAF binding to embryonal F9 cells and prostacyclin synthesis in human umbilical vein endothelial cells

Our data suggest non-specific Paf binding to intact embryonal F9 cells. Non-specific Paf binding might have some physiological relevance when Paf metabolites interfere with prostacyclin synthesis, for example, in umbilical vein endothelial cells.

Human umbilical vein endothelial cells: specific binding of platelet-activating factor and cytosolic calcium flux

An interaction of the platelet-activating factor (Paf) with endothelial cells was investigated using human umbilical vein endothelial cells. Confluent endothelial cells bound [3H]Paf in the presence of 0.25% fatty acid-free serum albumin after culture in media containing either heat-inactivated foetal calf serum or serum substitute. The Scatchard analysis of the saturated specific [3H]Paf binding showed a Bmax of 2.5 fmol indicating 2800 binding sites per endothelial cell. [3H]Paf binding was partially reversible at 20 degrees and 4 degrees and endothelial cells partially metabolized [3H]Paf at 20 degrees but not at 4 degrees. [3H]Paf binding and Paf-mediated increase of cytosolic free calcium were inhibited by specific Paf receptor antagonists which do not interfere with Paf metabolism. Immortalized umbilical vein endothelial cells bound [3H]Paf specifically after culture in the presence of insulin (20 hr, 0.4 U/mL) with non-specific binding in the absence of insulin. The results show that specific Paf binding mediated calcium flux in human endothelial cells.