Singlet oxygen potentiates thrombolysis.

Activated polymorphonuclear neutrophils (PMN) participate in physiologic thrombolysis. PMN produce large amounts of urokinase (u-PA) and oxidants of the hypochlorite/chloramine-type that generate nonradical excited singlet oxygen ((1)O(2)). The u-PA/(1)O(2)-mediated thrombolysis was imitated in vitro. One hundred microliters microclots of normal human plasma were oxidized with 25 microL 0 to 5.0 micromoles of chloramine-T in physiol. NaCl in the absence or presence of 100 microL 6% bovine serum albumin or 100 microL normal plasma. Twenty-five microliters 0 to 167 IU/mL (related to 150 microL added supernatant) u-PA or 0 to 2.08 microg/mL t-PA were added. The absorbance at 405 nm was determined after 0 to 27 hours (37 degrees C). The specific clot turbidity was calculated, subtracting the 100% lysis absorbance from the respective measured absorbance. The chloramine-effective dose 50% (ED(50)) after 27 hours was determined in the presence of 2.6 IU/mL u-PA. The plasminogen activator-ED(25) was determined after 2 hours (37 degrees C), and the ET(25); i.e., the time needed to lyse a microclot by 25%, was determined for each respective clot-oxidation. The ED(25) of u-PA depends on the oxidation of the microclots: 1.25 micromoles chloramine/100 microL clot enhances thrombolysis approximately 20-fold; here, 25% of clot lysis is achieved within 50 minutes (using approximately 20 IU/mL u-PA), whereas approximately 5 hours are needed to lyse an unoxidized microclot by 25%. The present global assay technique imitates the u-PA/(1)O(2) aspects of physiologic thrombolysis by PMN.