Involvement of the extrinsic pathway in the activities of low molecular weight heparins

Tinzaparin: considerations for use in clinical practice

OBJECTIVE

To evaluate the safety and effectiveness of tinzaparin for the prevention and treatment of venous thromboembolism (VTE).

DATA SOURCES

A MEDLINE and PubMed database search (1980-December 2002) was conducted. Only articles written in English were reviewed.

STUDY SELECTION AND DATA EXTRACTION

Articles reporting the safety, efficacy, and cost-effectiveness of tinzaparin in humans were evaluated. Emphasis was placed on randomized, controlled trials.

DATA SYNTHESIS

Tinzaparin sodium is a low-molecular-weight heparin (LMWH) that exerts its anticoagulant effect through inhibition of factors Xa and IIa and release of tissue factor pathway inhibitor from the vascular epithelium. Tinzaparin is indicated for treatment of acute symptomatic deep-vein thrombosis (DVT), with or without pulmonary embolism. Clinical studies suggest that tinzaparin is also effective for VTE prophylaxis, as well as other indications. Once-daily subcutaneous tinzaparin is equally or more effective than intravenous unfractionated heparin (UFH) for prevention and treatment of VTE, at least as safe as UFH for bleeding complications, and requires little or no monitoring. No dose "cap" is required for obese patients, and no initial dosing adjustments are necessary in elderly and/or renally impaired patients, although some monitoring is recommended. The few comparative data available suggest that tinzaparin efficacy may be comparable to that of other LMWHs; more comparative studies are needed. Pharmacoeconomic studies indicate a favorable cost-benefit ratio.

CONCLUSIONS

Tinzaparin is safe and effective for prevention and treatment of DVT. Consistent once-daily dosing may facilitate self-administration of tinzaparin in the outpatient setting.

Tissue factor pathway inhibitor production by human proximal tubular epithelial cells in culture

Fibrin deposition in the peritubular capillaries and along the tubular basement membrane is commonly observed in several renal diseases and suggests the involvement of blood coagulation in tubulointerstitial damage. It has been demonstrated that tissue factor (TF) is present in tubular epithelial cells of animal models of nephritis. Tissue factor pathway inhibitor (TFPI) regulates the extrinsic pathway of blood coagulation through its ability to inhibit TF activity and it is now thought to be produced mainly by the vascular endothelial cells. We examined whether human proximal tubular epithelial cells (PTEC) could produce TFPI and attempted to clarify the regulatory factors affecting TFPI production. Cultured human PTEC were used. The procoagulant activity (PCA) in PTEC lysate was quantified by measurement of the one-stage recalcification time. TFPI in the cell supernatants was measured by ELISA. The mRNA of TF and TFPI in PTEC was analyzed by reverse transcriptase polymerase chain reaction (RT-PCR). PCA which is compatible with TF activity was present in the PTEC lysate. TF mRNA and TFPI mRNA were detected in PTEC. The amount of TFPI increased over time in the cell supernatants. Immnoblot analysis revealed 40 kD protein of TFPI, and TFPI antigen was demonstrated in PTEC by immunofluorescence. The concentration of TFPI was significantly increased following incubation with thrombin and heparin in a dose- and time-dependent manner, although the amount of TFPI mRNA was not changed. Our study showed that TFPI is produced in cultured PTEC and added one more cell type that produced TFPI other than endothelial cells. Thrombin and heparin stimulated TFPI secretion from PTEC. TFPI of PTEC may act against generation of thrombin and tubular fibrin formation induced by tissue factor activation. The augmentation of TFPI secretion by heparin may play an important role in the modulation of anticoagulant properties of PTEC.

The lack of effect of a prophylactic dose of enoxaparin on thrombin generation in patients subjected to nephrectomy because of kidney cancer

It is assumed that major surgery, connected with extensive tissue dissection, brings about the release of tissue factor into circulation and subsequent activation of coagulation system. This activation results in the thrombin generation, which is supposed to be suppressed by the low-molecular-mass heparins (LMMH), administered to the surgical patients as the prophylaxis against postoperative venous thromboembolism. We have estimated the concentration of circulating thrombin-antithrombin (TAT) complex in patients subjected to transperitoneal nephrectomy and randomized into controls and who received 40-mg enoxaparin 12 h before and 12 h after the operation and then once daily for 7 days. We have observed a sharp rise of TAT concentration at the end of surgery and it corresponded to the simultaneous drop of antithrombin (AT) activity. TAT concentration gradually decreased and AT activity increased up to the end of observations on the seventh postoperative day, but there were no differences observed between the groups of patients. We have also observed a biphasic increase of plasmin-plasmin inhibitor (PPI) complex concentration in our patients. Again, there were no differences in PPI between the groups of patients. It is our conclusion that under the conditions of this study, the well-known prophylactic effect of enoxaparin against the venous thromboembolic complications was not mediated by the inhibition of intraoperative thrombin generation. The anti-inflammatory or biophysical influence of LMMH may be rather taken into account in surgical patients receiving prophylactic doses of these heparins.