Effect of unfractionated and low molecular weight heparin on microcirculatory antithrombin effects during endotoxemia

Objective

A recent prospective randomized clinical sepsis trial (Kybersept study) shows a reduction in 90-day mortality by antithrombin (ATIII) only in the prospectively defined subgroup of patients without simultaneous heparin treatment. To investigate whether this clinically observed heparin-ATIII antagonism is caused by a heparin-related reversal of ATIII effects on the microcirculation during endotoxemia, experimental ATIII administration was combined with administration of different heparins at a clinically relevant dose.

Methods

In skin fold preparations of the Syrian hamster, normotensive endotoxemia was induced by i.v. administration of 2 mg/kg endotoxin (LPS, E. coli, 2 mg/kg), whereby intravital video fluorescence microscopy allowed determination of venular adherent leukocyte count (VALC) and functional capillary density (FCD), which served as a measure of capillary perfusion. ATIII (ATIII group, n = 6, Kybernin, 250 IU/kg i.v.) was substituted 5 min before LPS administration. Another group simultaneously received intravenous unfractionated heparin (ATIII + Hep, n = 5, sodium heparin, 100 IE/24 hours, i.v.), whereas additional animals received low molecular weight heparin (ATIII + LMWH, n = 5, fraxiparin, 5 μl/kg, 2 hours before LPS, s.c.).

Controls

Saline-treated animals receiving only LPS.

Results

LPS induced a massive increase in VALC with a maximum at 8 hours and a decrease in FCD (P < 0.01 vs baseline). Both LPS effects were effectively prevented by ATIII (P < 0.01), whereas ATIII + Hep and ATIII + LMWH animals showed microcirculatory disturbances comparable to that observed in endotoxemic controls. In accordance with the clinical finding that beneficial AT III effects during sepsis are antagonized by concomitant heparin administration, our study indicates a relevant in-vivo adverse effect of heparins on microcirculatory AT III effects.