Background: Tissue Factor Pathway Inhibitor (TFPI) is synthesized and constitutively secreted by endothelial cells. A major portion of intravascular TFPI is stored associated with endothelial cells. TFPI has valuable effects on various cellular and vascular events that might broaden the efficacy and utility of Heparin and Low Molecular Weight Heparins (LMWH). Hence, the present study was undertaken to examine the effect of heparin molecular weigh fractions ranging from 3,000 -12,000 Dalton and different LMWH on the release of TFPI from human umbilical vein endothelial cells (HUVEC). 

Methods: Confluent HUVEC (200 ul of 1x10 6 cells /ml) cells were resuspended and plated in 48 well plate (95% O2/5% CO2, at 37 oC). Cells were allowed to attach to fibronectin polymer for 3 hours, washed and fresh media with and without the different LMWH or heparin molecular weight fractions were added at different concentrations. At different intervals ranging from 15-300 minutes, TFPI released in the media was measured using IMUBIND total TFPI ELISA Kit. 

Results: Both unfractionated heparin and LMWH (Tinzaparin) time and concentration-dependently induced a significant enhancement of TFPI release. Heparin molecular weight fractions 8,000-12,000 Dalton demonstrated optimal potency in releasing TFPI from HUVEC as compared the lower molecular weight fractions (3,000 - 7,000 Dalton). The degree of TFPI release was shown to be dependent on the heparin molecular weight, with minimal to no effect at 3,000 Dalton and maximal at 8,000 Dalton. Furthermore, LMWH containing relatively higher molecular weight fractions such as Tinzaparin demonstrated greater potency in releasing TFPI from HUVEC as compared to LMWH with relatively lower molecular weight fractions. This data indicated a different profile among the different LMWH based on the molecular weight distribution within each LMWH in releasing TFPI from endothelial cells. This data also suggest a differential efficacy among different LMWH based on their potency in releasing TFPI from endothelium.