The presence in plasma of an electronegative LDL subfraction [LDL(-)] cytotoxic for endothelial cells (ECs) has been reported. We studied the effect of LDL(-) on the release by ECs of molecules implicated in leukocyte recruitment [interleukin-8 (IL-8) and monocyte chemotactic protein-1 (MCP-1)] and in the plasminogen activator inhibitor-1 (PAI-1). LDL(-), isolated by anion-exchange chromatography, differed from nonelectronegative LDL [LDL(+)] in its higher triglyceride, nonesterified fatty acid, apoprotein E and apoprotein C-III, and sialic acid contents. No evidence of extensive oxidation was found in LDL(-); its antioxidant and thiobarbituric acid-reactive substances contents were similar to those of LDL(+). However, conjugated dienes were increased in LDL(-), which suggests that mild oxidation might affect these particles. LDL(-) increased, in a concentration-dependent manner, the release of IL-8 and MCP-1 by ECs and was a stronger inductor of both chemokines than oxidized LDL (oxLDL) or LDL(+). PAI-1 release increased slightly in ECs incubated with both LDL(-) and oxLDL but not with LDL(+). However, no cytotoxic effects of LDL(-) were observed on ECs. Actinomycin D inhibited the release of IL-8 and MCP-1 induced by LDL(-) and oxLDL by up to 80%, indicating that their production is mediated by protein synthesis. Incubation of ECs with N:-acetyl cysteine inhibited production of IL-8 and MCP-1 induced by LDL(-) and oxLDL by >50%. The free radical scavenger butylated hydroxytoluene slightly inhibited the effect of oxLDL but did not modify the effect of LDL(-). An antagonist (BN-50730) of the platelet-activating factor receptor inhibited production of both chemokines by LDL(-) and oxLDL in a concentration-dependent manner. Our results indicate that LDL(-) shows proinflammatory activity on ECs and may contribute to early atherosclerotic events.

SummaryWe studied the effect of purified immunoglobulins (Ig) from 21 patients with antiphospholipid antibodies (aPL) on factor Va degradation by activated protein C (aPC) on cultured human umbilical vein endothelial cells (HUVEC). Sera from patients were tested on an ELISA aPL assay to determine the isotype with aPL activity. HUVEC were incubated with purified IgG or IgM fraction from controls or patients. Activated PC and factor Va were then added and factor Va degradation was measured after several reaction times. 13 of 14 IgM and 8 of 10 IgG from patients showed an inhibitory effect on factor Va degradation by aPC when compared with control Ig. We also observed the same inhibitory effect with patients’ Ig on studying the degradation of factor Va by aPC in a purified system containing aPC, protein S and phospholipids. These results suggest that aPL antibodies disturb the anticoagulant activity of aPC, which may contribute to the thrombotic tendency of these patients.

Washed human platelets bound radioiodinated low density lipoprotein ( 125 I-LDL) to a class of saturable binding sites; they numbered 1,348±126 per platelet, and the dissociation constant (K D ) was 50.7±9 nM. I25I-LDL binding to platelets was reversible, and apparent equilibrium was attained within 25 minutes at 22°C and was characterized by forward and reverse rate constants of 1.47xlO4 Xsec"'xM" 1 and 8xlO~4xsec~' xM" 1 , respectively. Such binding was largely unaltered by temperature, divalent ions, and chelating agents. In addition, neither did receptor regulation (up or down) occur when platelets were loaded with cholesterol, nor did prostaglandin E, (PGE,) increase the binding of 12S I-LDL to platelets. On the other hand, the specificity of LDL binding was not typical of the LDL receptor of nucleated cells. Lipoproteins competed for the occupancy of LDL binding sites in platelets with the following order of potency: very low density >> intermediate density > high density subfraction 2. High density lipoprotein subfraction 3, heparin, and PGE, had no effect on this binding.

Haemangiomas are vascular tumours characterized by rapid growth and increased endothelial turnover. VE-cadherin is a recently discovered endothelial cell-specific cadherin located at intercellular junctions. In different types of epithelial tumours, cadherin expression is inversely correlated with invasiveness and metastatic dissemination. In this immunohistochemical study, VE-cadherin expression has been analysed in different types of haemangioma. VE-cadherin is highly expressed in endothelial cells of haemangiomas and is decreased, but still detectable, in some cases of haemangionendothelioma and angiosarcoma. The antigenic profile of most haemangioma cells was similar to that of normal endothelium. CD31, CD34, ICAM-1, von Willebrand factor, and VLA integrins were expressed in haemangioma endothelium; in addition, the major components of vascular basement membrane, namely fibronectin, collagen type IV, and laminin, were correctly expressed and organized. Surprisingly, a marked reactivity for the M form of laminin (merosin) was detected in the basement membranes of two juvenile capillary haemangiomas. Overall, this study shows that, with the exception of angiosarcoma and haemangionendothelioma, vascular tumours maintain most of the differentiation characteristics of normal endothelium. This encourages speculation that in these pathologies, abnormal endothelial proliferation is more related to the release of local factors than to an altered endothelial phenotype.

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We have recently demonstrated that the platelet low-density lipoprotein (LDL) receptor is immunologically different from the "classic" receptor of nucleated cells. We undertook the current studies to investigate the interaction of this receptor with oxidized LDL and to determine whether an endocytosis-mediated response is involved in the binding of LDL to platelets. The platelet LDL receptor recognized with the same affinity both native and oxidized LDL particles (IQo, 0.045 and 0.054 g/L; K a , 45.8 and 65.9 nmol/L, respectively). The Hill coefficients of the displacement of t is widely accepted that platelets are implicated in the initiation of atherosclerotic lesions and that they play a major role in the later thrombotic complications that are expressed as clinical evidence of the disease process.12 Moreover, the evidence, both clinical and experimental, leaves no doubt that lipoproteins are important in the development of atherosclerotic lesions. oxidized LDL at a protein concentration of 0.5 g/L enhanced ADP-and collagen-induced platelet aggregation in a manner similar to native LDL. We present ample evidence to show that LDL binding to platelets is not mediated by an endocytotic process. First, dissociation studies showed that at 4°C, 22°C, and 37°C approximately 93% of the surface-bound LDL was dissociated and that in the absence and presence of an ATPase inhibitor such as sodium azide, similar values for the reverse rate constant (K_ u 6±2 and 8.9±3xlO~4-s~' • mol/L" 1 ) and half-time (25±5 and 30±4 minutes) were found. Second, the lack of a blocking effect on LDL binding to platelets of microtubule inhibitors (colchicine), acidotropic agents (ammonium chloride and chloroquine), and Golgi apparatus disrupters (monensin) was found. Third, the inability of platelets to degrade IM I-LDL was shown; finally, imipramine and dopamine, which fully prevented platelet [

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