Inhibition of tissue factor by low-density lipoproteins

Low-density lipoproteins (LDL) are circulating inhibitors of the pro-coagulant activity of tissue factor. The objective of the present work was to explore the electrophoretic mobility of the involved proteins and the kinetic of pro - coagulant activity inhibition, that allow us to propose a quantitative in vitro assay of potential clinical use. For the kinetic assay, commercial calcic thromboplastine was incubated with increasing volumes of redisolved selectively precipitated LDL at 37 degrees C. Then the prothrombine time in one step was made; the inhibitory activity and percentage of inhibition against a blank were calculated. The results show an increasing inhibition of procoagulant activity until 60 min between 0.013 - 0.026 nmol apoB. The conditions for the assay of 30 samples of normolipemic individuals (ages between 30 - 70 years old) were selected on the basis of these results. The assay of % coagulation inhibition / nmol apoB showed signficative differences for control group versus diabetic one. The protein electrophoresis showed two bands in pre-beta and beta positions corresponding to thromboplastine and LDL respectively at time zero. After 60 min of incubation one intense band corresponding to LDL - tissue factor complex can be observed. This work proposes a simple assay for the evaluation of LDL role in haemostatic control in pathological conditions, although further clinical assays are still required.