The influence of l‐asparaginase therapy on the fibrinolytic system

Fibrinolytic factors were assessed during L‐asparaginase administration, to study whether their changes may predispose to a haemorrhagic or thrombotic diathesis. The total level of α2‐antiplasmin declined, as well as the ratio of the plasminogen‐binding form of α2‐antiplasmin to the non‐plasminogen‐binding form. After cessation of L‐asparaginase administration, the ratio increased to 1.6 times that of the pretreatment value. These data indicate that the plasminogen‐binding form of α2‐antiplasmin is the form primarily synthesized in vivo. L‐Asparaginase therapy reduced plasma levels of plasminogen and histidine‐rich glycoprotein (HRG) and influenced the equilibrium between HRG, plasminogen and HRG‐plasminogen complex, with a more pronounced decrease of plasminogen (62%±8) and HRG (76%±11) in comparison to the free‐plasminogen levels (51%±6). α2‐Macroglobulin was only slightly influenced by L‐asparaginase and may consequently play a more pronounced role in inhibition. This is suggested by moderate declines in functional tests of plasmin, urokinase and tissue activator inhibition by patients plasma, and by the ratio of inhibition of these enzymes over α2‐antiplasmin. Thus the bleeding tendency described during L‐asparaginase therapy can be ascribed not only to a temporary deficiency of coagulation factors but also to temporary α2‐antiplasmin deficiency