534 Meeting Summary The 14th Annual Meeting of the European Lipoprotein Club Lawrence P. Aggerbeck, Bo Angelin, David E. Bowyer, Rudolf Poledne, Maryvonne Rosseneu, and Gerd Schmitz T he European Lipoprotein Club met September 9-12, 1991, in Tiitzing, Germany. There were 92 participants from 13 European countries, Israel, Canada, and the United States. Dr. Alan Fogelman (Los Angeles) opened the meeting with a state-of-the-art lecture entitled "Lipoprotein and cell interactions in the development of early atheroscle- rotic lesions." He discussed the factors influencing the dominant stages in the formation of early fatty streak lesions of atherosclerosis, in particular 1) the trapping of low density lipoprotein (LDL); 2) modification of LDL by mild oxidation to yield a minimally modified LDL (MM-LDL); and 3) the effects of MM-LDL on the adhesion of monocytes to the endothelium, with subse- quent migration and differentiation into macrophages. Dr. Fogelman described freeze-fracture studies of the rabbit aorta that showed that after injection of a bolus of LDL, it was trapped in the interstitial matrix and then coalesced into droplets. It was pointed out that similar droplets had been isolated by Kruth and others and shown to be rich in free cholesterol. Dr. Bakti had also shown that such particles were potent stimulants of complement activation. Dr. Fogelman then described a very extensive series of experiments showing that many facets of monocyte adhesion, migration, and activation were activated not by native LDL but by MM-LDL produced by mild oxidation, e.g., by storage of LDL at 4°C in air for 3-6 months or by mild oxidation in the presence of iron. MM-LDL was taken up by cells via the native LDL receptor. The biologic activities appeared to reside in the lipid moiety and were destroyed by more extensive oxidation. MM-LDL stimulated monocyte adhesion to endothelial cells (ECs). Unlike interleukin-1 (IL-1), MM-LDL did not induce ELAM-1 or VCAM-1 expres- sion and, indeed, suppressed endogenous ICAM-1 ex- pression. Adhesion was dependent on either calcium or magnesium and showed specificity for sugar residues, being inhibited only by lactose 1-phosphate, maltose 1-phosphate, and N-acetyl glucosamine. The effect of MM-LDL on chemotaxis for monocytes was studied in a variety of ways, including a system in which the organization of arterial cells was reconsti- tuted by using human ECs and smooth muscle cells (SMCs) from aortas of human transplant tissue. MM- LDL enhanced migration, and this was inhibited by antibodies to monocyte chemotactic protein (MCP-1). MM-LDL also induced mRNA for MCP-1 in cultured ECs and SMCs. Studies in the mouse of the expression of the JE gene, the mouse homologue of MCP-1, showed that MM-LDL enhanced gene transcription but did not affect message stability. MM-LDL also influ- enced the differentiation of monocytes into macro- phages and induced the message for granulocyte-mac- rophage colony stimulating factor (GM-CSF) for cells in culture. In vivo injections of MM-LDL into mice caused an increase in serum levels of CSF. The possibility that this was due to contaminating endotoxin was excluded by studies with C3H/He J mice, which are unresponsive to endotoxin but still release CSF after injection of MM-LDL. In further studies, the conditions necessary for pro- duction of MM-LDL in the arterial wall were explored by using reconstituted human arterial tissue. Production of MM-LDL from native LDL occurred only in the presence of both ECs and SMCs. Furthermore, modifi- cation by ECs plus SMCs occurred in the presence of serum. This suggested that microdomains between ECs and SMCs and their matrix might act to exclude serum antioxidants, thus permitting production of MM-LDL. Studies were also performed to investigate the inhibi- tion of formation of MM-LDL and its effects. High density lipoprotein subtraction 2 (HDL 2 ) inhibited MM- LDL-induced monocyte migration, and the lipid fraction was responsible for this activity. The effect occurred only when LDL and HDL 2 were in intimate contact. Studies of antioxidants showed that pretreatment of cells with probucol, ^-carotene, or a-tocopherol inhibited MM- LDL production but that if the LDL was pretreated, then only probucol was effective. Oxidative modification ap- peared to be occurring at the cell membrane. Dr. Fogelman concluded by considering the potential cellular interactions in the genesis of atherosclerosis that their studies had revealed, in particular that 1) monocyte/macrophage interaction induces MCP-1 pro- duction, thus amplifying chemotaxis; 2) EC/SMC inter- action causes GM-CSF production, thus stimulating macrophage differentiation; 3) EC/SMC interaction and EC/SMC/monocyte interaction cause fibronectin production. This effect is largely due to the formation of the EC/SMC gap junction, as measured by the expres- sion of connexin 43, which is stimulated by macro- phages; and 4) studies with neutralizing antibodies to interleukins showed that the effect of macrophages is largely mediated by IL-6, the production of which is stimulated in an autocrine manner by IL-1. In the opening lecture of the first session on "Inter- action of lipoproteins with the vessel wall," Dr. Andreas Habenicht (Heidelberg) described the LDL-dependent production of eicosanoids by a variety of cells. 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