Acetylated-low density lipoprotein (Ac-LDL) is taken up by macrophages and endothelial cells via the "scavenger cell pathway" of LDL metabolism. In this report, aortic and microvascular endothelial cells internalized and degraded 7-15 times more [1251]-Ac-LDL than did smooth muscle cells or pericytes. Bound [12Sl]-Ac-LDL was displaced by unlabeled Ac-LDL, but not unmodified LDL. The ability to identify endothelial cells based on their increased metabolism of Ac-LDL was examined using Ac-LDL labeled with the fluorescent probe 1,1 '-dioctadecyl-3,3,3',3'-tetramethyl-indocarbocyanine perchlorate (DiI-Ac-LDL). When cells were incubated with 10 pg/ml DiI-Ac-LDL for 4 h at 37°C and subsequently examined by fluorescence microscopy, capillary and aortic endothelial cells were brilliantly fluorescent whereas the fluorescent intensity of retinal pericytes and smooth muscle cells was only slightly above background levels. DiI-Ac-LDL at the concentration used for labeling cells had no effect on endothelial cell growth rate. When primary cultures of bovine adrenal capillary cells were labeled with 10 pg/ml of DiI-Ac-LDL for 4 h at 37°C, then trypsinized and subjected to fluorescence-activated cell sorting, pure cultures of capillary endothelial cells could be obtained. Utilizing this method, large numbers of early passage microvascular endothelial cells can be obtained in significantly less time than with conventional methods.A major problem in the study of microvascular endothelial cells is the identification of the desired cell population and the subsequent isolation of pure cultures. Our currently used method of establishing pure cultures of capillary endothelial cells involves many weeks of "weeding out" nonendothelial cells (l). The weeding technique involves the assumption that the morphology of capillary endothelial cells is similar to other endothelial cells and is thus directed at isolating colonies with those characteristics. Several markers for endothelial cells are routinely used for confirmation that established cell lines are of endothelial origin. These include the presence of factor VIII related antigen (2, 3) and angiotensin converting enzyme (4, 5). Microvascular endothelial cells differ from large vessel endothelial cells in their requirement for additional growth factors and modified surfaces for optimal growth (l), and their response to tumor factors (l, 6).The receptor-mediated uptake of low density lipoprotein (LDL ~) by cells has been studied in detail (for a review see reference 7). An alternative pathway for the metabolism of chemically modified lipoproteins has also been described (8) and has been termed the "scavenger cell pathway" of LDL metabolism, due to its occurrence in rodent and canine macrophages (9-11) and human monocytes (12). Various chemical methods for modification of LDL have been used to modify the charge of amino groups on LDL including acetylation (8), acetoacetylation (9), and malondialdehyde treatment (12). These modified lipoproteins are taken up by ~Abbreviations us...

Angiogenesis, the recruitment of new blood vessels, is an essential component of the metastatic pathway. These vessels provide the principal route by which tumor cells exit the primary tumor site and enter the circulation. For many tumors, the vascular density can provide a prognostic indicator of metastatic potential, with the highly vascular primary tumors having a higher incidence of metastasis than poorly vascular tumors. Tumor angiogenesis is regulated by the production of angiogenic stimulators including members of the fibroblast growth factor and vascular endothelial growth factor families. In addition, tumors may activate angiogenic inhibitors such as angiostatin and endostatin that can modulate angiogenesis both at the primary site and at downstream sites of metastasis. The potential use of these and other natural and synthetic angiogenic inhibitors as anticancer drugs is currently under intense investigation. Such agents may have reduced toxicity and be less likely to generate drug resistance than conventional cytotoxic drugs. Clinical trials are now underway to develop optimum treatment strategies for antiangiogenic agents.

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