SummaryThrombomodulin (TM) exists not only in endothelial cells but also in circulating plasma as soluble heterogeneous fragments. A release mechanism of soluble TM antigen from endothelial cells was investigated. Cultured human umbilical vein endothelial cells released about 0.6% of total cellular TM antigen into conditioned medium during 24 h. The release of TM antigen was not influenced by addition of various concentrations (0.01-5.0 μM) of monensin, which inhibits intracellular transport of secretory proteins, though the secretion of plasminogen activator inhibitor-1 from the cells was inhibited. The release of TM antigen was not increased when total cellular TM level increased 1.3- or 1.4-fold relative to control cells after stimulation with 0.1-1.0 U/ml thrombin or 3 mM dibutyryl cAMP, respectively. Exposure of endothelial cells for 6 h to mixture of 1 μM N-formyl-methionyl-leucyl-phenylalanine (FMLP) and 100 ng/ml lipopolysaccharide (LPS) decreased cellular TM level by 30% relative to control cells without increase in the TM release. The FMLP and LPS-stimulated leukocyte treatment of the cells increased the release of TM antigens into the medium in a time-dependent manner and the increased release of TM antigen paralleled the extent of cell damage as measured by 51Cr release. Hydrogen peroxide treatment of the cells increased the release of TM antigens into the medium in a time- and concentration-dependent manner. The increased release of TM antigen by hydrogen peroxide also paralleled the extent of cell damage. Soluble TM antigen in conditioned medium from the untreated control cells was composed of six heterogeneous fragments of 105, 56, 48, 33, 31 and 28 kDa observed on Western blots after sodium dodecyl sulfatepolyacrylamide gel electrophoresis under reducing conditions, and the soluble TM antigen from the hydrogen peroxide-treat-ment cells was composed of five heterogeneous fragments of 80, 56, 33, 31 and 28 kDa. These compositions were quite similar to that observed for soluble TM fragments in human plasma. It is suggested that soluble TM antigen is not secreted from endothelial cells, but results from cellular damage.

SummaryThrombomodulin, TM, is an endothelial cell membrane protein acting as a cofactor for the activation of plasma protein C. Soluble TM is present in plasma and urine of normal subjects. Enzyme immunoassay, EIA, for human TM was developed using mouse monoclonal antibodies against human placental TM in this paper. We obtained four types of the monoclonal antibodies against human placental TM. EIA sandwich method using three types of the monoclonal antibodies enabled us to measure almost all of 6 and 7 TM subspecies in plasma and urine, respectively, except 1 subspecies, 31 kDa TM. There was no interference from other components of plasma and urine in the assay conditions. Titration curves of purified TM in buffer or in normal plasma were linear within the range from 0.08 to 10 ng/ml. The coefficient of variation at 0.08 ng/ml TM was 4.7%. TM titer with buffer, assayed by this method, was reduced by the addition of thrombin at the final concentration of 20 U/ml, but the titer with plasma was not reduced even at 100 U/ml. These concentrations of thrombin are far larger than those which would be formed in circulation. TM levels in plasma and urine of normal subjects collected in the morning were 35.2 ± 8.32 ng/ml (n = 346) and 111 ± 31.6 ng/ml (n = 33), respectively. TM level in plasma did not differ from the level in serum. Circadian fluctuation of plasma TM was not significant in 10 normal adults, although a tendency of increase in TM excretion to urine was found rather in the day time than the other times. It was concluded that this EIA is reliable for TM assay in human plasma and urine, which will reflect activation or injury of endothelial cells.

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107 hemodialysis patients at high risk for intradialytic bleeding due to previous surgery or active bleeding from other sites were treated with nafamostat mesilate (FUT-175; FUT) as hemodialysis anticoagulant for 2 weeks. In contrast to heparin. FUT prolonged clotting times only in the extracorporeal circuit. Clotting times were not prolonged even at the conclusion of the treatment, and bleeding from the puncture site after removal of the needle was shorter than with heparin. The exacerbation of bleeding by hemodialysis was noted in only 21 out of 573 hemodialysis procedures (3.7%), and 134 of 145 hemodialysis procedures (92.4%) with active bleeding were successfully completed without increasing the bleeding. Adverse effects of FUT were noted in only 6 cases (5.6%) or 1.2% of HD procedures. These results indicate that FUT is a very useful anticoagulant for HD, especially in patients with high risk of bleeding.

Inflammatory cytokines such as tumor necrosis factor-alpha (TNF-alpha) shift the hemostatic balance of endothelial cell surfaces in favor of prothrombotic properties by downregulating thrombomodulin (TM) and inducing tissue factor (TF) expression. We investigated the effects of retinoic acid (RA) on the prothrombotic properties of cultured umbilical vein endothelial cells exposed to TNF-alpha. The approximate 50% downregulation of TM antigen and cofactor activity induced by TNF- alpha (10 U/mL for 24 hours) was completely prevented when the cells were coincubated with both TNF-alpha and 10 mumol/L RA. In accordance with changes in cell surface TM antigen levels, the 70% decrease in TM messenger RNA (mRNA) induced by TNF-alpha was also prevented by 10 mumol/L RA. TNF-alpha induced TF activity of lysed cells (100-fold greater than untreated controls), an effect prevented when the cells were coincubated with both the TNF-alpha and 10 mumol/L RA. The 34-fold increase in TF mRNA levels induced by TNF-alpha (10 U/mL for 3 hours) was only two-fold in the presence of both TNF-alpha and RA. The effects of RA on the regulation of TM and TF expression in the cells exposed to TNF-alpha was dose-dependent from 0.01 to 10 mumol/L RA. The present results suggest that RA may affect on the mRNA level to alter TM and TF expression, effectively counteracting expression of prothrombotic properties of endothelial cells induced by inflammatory cytokines such as TNF-alpha.