IN-VITRO PLASMA AND EUGLOBULIN CLOT LYSIS IN SUBJECTS WITH ELEVATED LIPOPROTEIN(A)

Lipoprotein(a) [Lp(a)] is assumed to have a prothrombotic role by interfering with the physiological functions of plasminogen due to their structural similarities. In order to establish if elevated plasma Lp(a) levels affect in vitro clot lysis, 12 subjects with elevated Lp(a) (320-1650 mg/L) and 12 subjects with normal Lp(a) (<100-141 mg/L) were studied. Groups were similar regarding age, gender, levels of other lipids and fibrinolytic variables. Spontaneous lysis and lysis induced by recombinant tissue-type plasminogen activator (rt-PA) of preformed I-125-fibrin labelled, mechanically non-compressed ('non-retracted') plasma clots, mechanically compressed ('retracted') plasma clots and euglobulin clots was measured. 'Non-retracted' and 'retracted' plasma clots lysed spontaneously in 48 h on average by 15 to 16% and by 3% respectively in both groups. In subjects with elevated Lp(a) 'non-retracted' plasma clots lysed with rt-PA (final cone. 50 and 100 ng/mL) in 4 h on average by 34+/-4% and 58+/-6%, which was not significantly different from 38+/-7% and 55+/-8% clot lysis in subjects with normal Lp(a). 'Retracted' plasma clot lysed with 200 ng/mL rt-PA in 4 h on average by 32+/-5% in subjects with elevated Lp(a) and by 35+/-6% in subjects with normal Lp(a) (not significant, all values mean+/-SD). In subjects with elevated Lp(a), Lp(a) had no effect on rt-PA induced lysis of 'retracted' plasma clots incubated in the subject's own plasma. Spontaneous and rt-PA induced euglobulin clot lysis was not significantly different between the two groups studied. The result suggested no significant effect of plasma Lp(a) on in vitro lysis of plasma and euglobulin clots.