Summary
Studies have shown that inhibition of TAFI by small peptides enhances pharmacological
effects of tPA in animal models of thrombosis, suggesting that TAFI modulates the
fibrinolytic system. In this study, we investigated the effect of activated human
TAFI (TAFIa) on endogenous fibrinolysis in a rat model of intravascular fibrin deposition.
125I-labeled fibrinogen was injected intravenously followed by a bolus injection of batroxo-bin,
a thrombin-like enzyme. Batroxobin cleaved fibrinogen to form insoluble fibrin that
was deposited in tissues, including the lungs. This was shown by a decrease of radioactivity
in the blood as a result of consumption of 125I-labeled fibrinogen and an elevation of radioactivity in the lungs 5 min following
batroxobin administration. Endogenous fibrinolysis was detected by a gradual increase
in radioactivity in the blood and a decrease in radioactivity in the lungs at 30 min,
an indication of radio-labeled fibrin degradation products (FDPs) being released into
the circulation from the tissues. Intravenous administration of human TAFIa dose-dependently
attenuated the later phase reduction of radioactivity in the lungs. When the dose
of TAFIa was 218 μg/kg, giving a peak plasma level of TAFIa 0.9 ± 0.05 μg/ml, the
spontaneous fibrinolysis was completely prevented. These results provide direct evidence
that an increase in circulating TAFIa impairs endogenous clot lysis in a rat model
of fibrin deposition.
Keywords
TAFI - PAI-1 - batroxobin - fibrinolysis - rat - lung fibrin deposition