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The thiol protease, bromelain, an extract from pineapple stem, was
suggested to have antithrombotic and anticoagulant activities in
vivo. We studied the effects of bromelain on cell size distribution
of isolated human platelets in vitro by Coulter Counter measurements.
Preincubation of platelets with bromelain (10 micrograms/mL)
completely prevented the thrombin (0.2 U/mL) induced platelet
aggregation. Papain was less active in preventing platelet
aggregation. In vitro, bromelain (0.1 microgram/mL) reduced the
adhesion of bound, thrombin stimulated, fluorescent labeled platelets
to bovine aorta endothelial cells. In addition, preincubation of
platelets with bromelain, prior to thrombin, activation, reduced the
platelet adhesion to the endothelial cells to the low binding value
of unstimulated platelets. On the basis of mass concentrations, the
proteases papain and trypsin were as effective as bromelain. Using a
laser thrombosis model, the in vivo effects of orally and
intraveneously applied bromelain on thrombus formation in rat
mesenteric vessels were studied. Bromelain, orally applied at 60
mg/kg body weight, inhibited the thrombus formation in a time
dependent manner, the maximum being after 2 hours in 11% of
arterioles and 6% of venoles. Intravenous application at 30 mg/kg was
slightly more active in reducing thrombus formation in arterioles
(13%) and venoles (5%), suggesting that orally applied bromelain is
biologically active. These results may help to explain some of the
clinical effects observed after bromelain treatment in patients with
thrombosis and related diseases.
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