Biochemical properties of vascular endothelial cells.

Present knowledge in the field of vascular endothelial cells is reviewed. The role of endothelial cells in the synthesis of matrix proteins and glycosaminoglycans is described. Endothelial cells play a considerable role in the processes of coagulation and fibrinolysis. They also interact with neurotransmitters and vasomotoric substances, and participate in inflammation and immunological responses. They produce several different growth factors. Their role in lipoprotein metabolism is of special importance to research into atherosclerosis.

Immunoelectrophoretic analysis of membrane glycoproteins in cultured human endothelial cells.

Human endothelial cells isolated from umbilical cords were solubilized in Triton X-100 and examined by crossed immunoelectrophoresis using rabbit antiserum against endothelial cells. Endogenous labelling of the endothelial cell proteins with 14C-mannose followed by crossed immunoelectrophoresis and autoradiography revealed about 10 immunoprecipitates. Four of these endothelial cell glycoproteins were labelled by lactoperoxidase catalyzed iodination and thus were surface located. Three of the surface located glycoproteins showed reduced electrophoretic mobility after incubation of the endothelial cells with neuraminidase and were therefore sialoglycoproteins. Amphiphilicity of endothelial cell glycoproteins was studied by crossed hydrophobic interaction immunoelectrophoresis with phenyl-Sepharose in the intermediate gel. Amphiphilic proteins also show increasing electrophoretic migration velocity with decreasing concentration of Triton X-100 in the first dimension gels. Five of the endothelial cell glycoproteins were shown to be amphiphilic using these two techniques. Two monoclonal antibodies against the platelet glycoprotein complex IIb-IIIa and glycoprotein IIIa, respectively, reacted with the same precipitate of endothelial cells. When a polyclonal antibody against the platelet glycoprotein complex IIb-IIIa was incorporated into the intermediate gel the position of two endothelial cell precipitates were lowered. One of these was a sialoglycoprotein.

Chlamydia trachomatis: in vitro susceptibility of genital and ocular isolates to some quinolones, amoxicillin and azithromycin.

The minimum inhibitory concentration (MIC) of ofloxacin, ciprofloxacin, norfloxacin, amoxicillin and a new erythromycin analogue (azithromycin or CP 62993) against Chlamydia trachomatis was determined. There was a large difference between the MICs (microgram/ml) of different quinolones (median of 3 independent measurements; range): ofloxacin (0.5; 0.5-1) less than ciprofloxacin (1; 1-2) less than norfloxacin (16; 16-32). The MIC of amoxicillin varied from 0.25 to 1 (median 0.5) in different experiments. The MIC of azithromycin (0.125; 0.063-0.25) was lower than that of erythromycin (0.25; 0.125-0.5). The minimum lethal concentration (MLC) of ofloxacin and azithromycin was determined with and without passage of the McCoy cells. Both methods gave the same results. Ofloxacin seemed to have a lethal effect on C. trachomatis, as the MIC and MLC were equal. In contrast, the effect of the MIC of azithromycin on C. trachomatis was bacteriostatic. The MLC of azithromycin was 2-4 times higher than the MIC (p less than 0.001).

Electroimmunochemical characterization of endothelial cell proteins: antigenic relationship with platelet and erythrocyte membrane proteins.

Human endothelial cells isolated from umbilical cords and cultured in primary cultures were solubilized in Triton X-100 and examined by crossed immunoelectrophoresis using rabbit antiserum against endothelial cells. Endogeneous labelling of the endothelial cell proteins with 35S-methionine or 14C-mannose followed by crossed immunoelectrophoresis and autoradiography revealed about 30 or 8 immunoprecipitates, respectively. Antigenic relationship between endothelial cell proteins and proteins in human platelets or erythrocyte membranes was demonstrated by use of the corresponding antisera and by antigen addition experiments. One of the endothelial cell proteins cross-reacted with antiserum against erythrocyte membranes and showed a partial antigenic identity reaction with the band 3 protein complex of erythrocyte membranes. The same protein showed antigenic relationship also with a platelet protein. In addition, endothelial cells contain at least 7 proteins antigenically related to platelet proteins, of which at least 5 were labelled with 14C-mannose and thus were glycoproteins. Three of these glycoproteins were antigenically related to proteins from isolated platelet membranes and three were related to the release products obtained after thrombin treatment of platelets. The present study demonstrated numerous platelet and endothelial cell proteins that were antigenically related, more than previously anticipated.

Oxidized low density lipoprotein can reduce the pinocytic activity in cultured human endothelial cells as measured by cellular uptake of [14C]sucrose.

The effect of low density lipoprotein (LDL) on the pinocytic activity in human endothelial cells in culture, as measured by the uptake of [14C]sucrose, was studied. The cells were preincubated for 48 h with a low concentration of LDL (25 micrograms protein/ml) or a high concentration of LDL (150 micrograms protein/ml) in the presence of lipoprotein deficient serum. Then the pinocytic activity of the cells was measured in a subsequent incubation by measuring the uptake of [14C]sucrose. The higher LDL concentration resulted in a reduced cellular uptake of [14C]sucrose compared to the lower concentration of LDL. When the additional LDL (the lower concentration subtracted from the higher) was replaced by high density lipoprotein, albumin or gamma globulin, no reduction of the uptake of [14C]sucrose was observed. The inhibitory effect of LDL on the uptake of [14C]sucrose was seen in endothelial cell cultures of different age and cell density. When the endothelial cell proliferation was arrested by gamma irradiation, the reducing effect of LDL on the pinocytic activity was unchanged as compared to nonirradiated controls. LDL prepared in the presence of EDTA and glutathione did not have the same reducing effect on the uptake of [14C]sucrose as control LDL prepared in the absence of antioxidants. Thus, oxidized LDL reduced the pinocytic activity in cultured endothelial cells. The inhibitory effect of LDL on the rate of pinocytosis was present before endothelial cell injury could be observed.

Human endothelial cell culture as an evaluation system for the toxicity of intravascular contrast media.

Endothelial cells in primary cultures from human umbilical cord veins were incubated with various radiographic contrast media in increasing concentrations up to approximately 60 mgI/ml for 24 hours in order to study their toxicity. Cell death was recorded with the chromium-51 (51Cr)-release method and controlled by dye exclusion tests, Coulter counting, and protein determination. The hyperosmolar, ionic contrast medium, meglumine metrizoate, was far more toxic to the endothelium than the nonionic media, metrizamide and iohexol, which are far less hyperosmolar. The 51Cr-release test on endothelial cultures provides a simple and useful technique in the evaluation of various intravascular contrast media and their components.

Injury to human cells in culture induced by low density lipoprotein: an effect independent of receptor binding and endocytotic uptake of low density lipoprotein.

Cultured human endothelial cells isolated from umbilical cord veins and erythrocytes obtained from healthy donors were injured when exposed to low density lipoprotein (LDL). A close relationship between the amount of 125I-LDL associated with the cell surface and the degree of cell injury was demonstrated. This association occurred before any morphological signs of cell injury were observed and before any substantial release of 51Cr into the medium could be measured. Subsequent endocytotic uptake and lysosomal degradation of LDL did not seem to be a prerequisite for the LDL-induced cell injury to occur. Human serum albumin had an inhibitory effect on the association of 125I-LDL with the cell surface and in parallel a lowering effect on the 51Cr release.