Association of prothrombin and protein S with plasma triglyceride-rich lipoproteins in humans after test meals rich in milk fat or soybean oil

Human protein S inhibits the uptake of AcLDL and expression of SR-A through Mer receptor tyrosine kinase in human macrophages

Human protein S is an anticoagulation protein. However, it is unknown whether protein S could regulate the expression and function of macrophage scavenger receptor A (SR-A) in macrophages. Human THP-1 monocytes and peripheral blood monocytes were differentiated into macrophages and then treated with physiological concentrations of human protein S. We found that protein S significantly reduced acetylated low-density lipoprotein (AcLDL) uptake and binding by macrophages and decreased the intracellular cholesteryl ester content. Protein S suppressed the expression of the SR-A at both mRNA and protein levels. Protein S reduced the SR-A promoter activity primarily through inhibition in the binding of transcription factors to the AP-1 promoter element in macrophages. Furthermore, human protein S could bind and induce phosphorylation of Mer receptor tyrosine kinase (Mer RTK). Soluble Mer protein or tyrosine kinase inhibitor herbimycin A effectively blocked the effects of protein S on AcLDL uptake. Immunohistochemical analysis revealed that the level of protein S was substantially increased in human atherosclerotic arteries. Thus, human protein S can inhibit the expression and activity of SR-A through Mer RTK in macrophages, suggesting that human protein S is a modulator for macrophage functions in uptaking of modified lipoproteins.

Alimentary lipemia enhances procoagulatory effects of inflammation in patients with a history of acute myocardial infarction complicated by ventricular fibrillation

INTRODUCTION

Acute myocardial infarction, often occurring postprandially, can be complicated by ventricular fibrillation. The role of acute alimentary lipemia and inflammation in the occurrence of ventricular arrhythmias in acute myocardial infarction has not been described yet.

METHODS AND RESULTS

Before and 2 h after consumption of a defined fatty meal, blood samples of 27 patients with a history of acute myocardial infarction (AMI) were incubated with lipopolysaccharide (LPS). In 10 patients, AMI was complicated by ventricular fibrillation (VF), in 17 patients, AMI occurred without VF. CD40-ligand and CD62P expression on platelets, tissue-factor binding on monocytes and platelet-monocyte aggregates were measured with flow cytometry. Soluble CD40-ligand plasma levels were measured with an ELISA. With the meal, serum triglyceride levels increased from 211.85+/-94.60 mg/dl to 273.59+/-122.52 mg/dl (p=0.0002). LPS stimulation before the meal showed a non-significant tendency to increase platelet-monocyte aggregates and tissue factor on monocytes in both patient groups. LPS stimulation in acute alimentary lipemia significantly increased tissue-factor expression on monocytes in both patient groups and platelet-monocyte aggregates in patients with VF. Baseline plasma levels of soluble CD40L did not differ significantly between both groups. Acute alimentary lipemia significantly decreased total plasma levels of sCD40L, leading to a significantly lower level of sCD40L in patients with a history of VF.

CONCLUSIONS

Alimentary lipemia enhances procoagulatory effects of inflammatory stimulation in patients with a history of AMI complicated by ventricular fibrillation. These observations might reveal a mechanism for an increased risk of VF in acute coronary syndromes in a postprandial state.

Effects of alimentary lipemia and inflammation on platelet CD40-ligand

INTRODUCTION

In patients with chronic hypercholesterolemia, the CD40-CD40L dyad is upregulated, contributing to the initiation and progression of atherosclerosis. Our aim was to describe the role of postprandial lipemia and inflammatory stimulation on platelet and monocyte activation and CD40-ligand (CD40L) levels.

METHODS AND RESULTS

Before and 2 h after consumption of a defined fatty meal, whole blood samples of 31 healthy subjects were incubated with endotoxin (LPS). CD40-ligand and CD62P expression on platelets, tissue-factor expression on monocytes and platelet-monocyte aggregates were measured with flow cytometry. Soluble CD40-ligand plasma levels were measured with an ELISA. After the meal, serum triglyceride levels increased from 137.6+/-60.5 mg/dl to 201.5+/-75.0 mg/dl. Expression of CD40L and CD62P on platelets and plasma levels of soluble CD40L were significantly decreased. No significant changes after the meal were observed concerning tissue factor expression on monocytes and platelet-monocyte aggregates. Addition of LPS showed no significant effect concerning CD40L or CD62P expression on platelets, whereas the amount of platelet-monocyte aggregates significantly increased under LPS stimulation after the fatty meal.

CONCLUSIONS

Acute alimenatry lipemia leads to a decreased expression of CD40L on platelets and a reduced plasma level of sCD40L, suggesting an increased turnover in the CD40L system.

CONDENSED ABSTRACT

Before and after a fatty meal, blood samples of 31 healthy subjects were incubated with LPS. After the meal, expression of CD40L and CD62P on platelets and plasma levels of soluble CD40L were significantly decreased. Addition of LPS showed no effect concerning CD40L or CD62P expression, whereas the amount of platelet-monocyte aggregates significantly increased under LPS stimulation after the fatty meal.