Unfractionated heparin modifies clot structure and increases clot sensitivity to t-PA-induced lysis

Vol.70, Suppl. 1

ABSTRACTS OF 12TH NATIONAL CONGRESS

s15

c 013 EFFECT OF STANDARD HEPARIN AND LOW M.W. HEPARINCCY 216) ON PLASMA LEVELS OF TISSUE FACTOR PATHWAY INHIBITOR. M.Berrettini,P.Parise,M.Malaspina,G.Lucarelli,*V.Gallo e G.G.Nenci. Institute of Internal and Vascular Medicine,Universityof Perugia,06100 and *Medical Department,SanofiWinthrop,Milan, Italy. Single-dose intravenous or subcutaneous

administration of standard heparin

(SH) or low M.W. heparin(LMWHH) causes an increase in tissue factor pathway inhibitor(TFP1). In a randomized study of 18 patients with vascular disease we compared the effect of two 7-day treatments on TFPI:l)sc SH,twice a day,adjusted dose(aPPT ratio=1.5;mean dose=9150 IU every 12 hours);Z)LElWH(CY2161, 4200 anti-Xa IU,once a day, SC. TFPI was measured 3 hours after the morning dose by a chromogenic assay using a commercial thromboplastin(OrthoBrain,Ortho Diagnostics,Milan) and a prothrombin complex concentrate(Protromplex,Immuno,Pisa). Both treatments induced a significant increase in plasma levels of TFPI on day 2. There were no significant differences between the 2 treatments(Table).The results indicate that both hepabasal day 2 day 7 SH (N=9) LKWH (CY 216;N=9)

141+44% 144+83%

188+63%(p<.O5)

191291%

208+114%(p<.O251 -

132+39% -

rins, at the administered doses, induce a similar increase in TFPI and suggest that this effect may decrease over time.

c 014 UNFRACTIONATED CLOT SENSITIVITY

HEPARIN MODIFIES CLOT STRUCTURE AND JNCREASES M.Morini. G.Agnelli, A. TO t-PA-INDUCED LYSIS. P.Parise,

Ascani, *M. E.Rossodivita. G.G.Nenci. Institute of Internal and Vascular Medicine and ‘CME, University of Perugia. We have evaluated the sensitivity to tPA-induced lysis of clots prepared from plasma preincubated in vitro with therapeutic concentrations of unfractionated heparin (UH). Human titrated plasma was supplemented with 1251-labelled fibrinogen and then incubated for I hour at 37 “C with l/10 volume of UH at a final concentration of 0.5 and 1.O U/ml, or saline. Clots were prepared by adding 25 fl CaCl2 (25 mmolA final) and 25 PI thrombin (10 NIH U/ml. final) to 450 PI of plasma. Washed 1251-labelled fibrin clots were incubated for 2 hours at 37 “C in PBS containing t-PA (from 0.05 to 0.5 @ml) and plasminogen (20 pglml). Clot lysis was quantified by counting the residual radioactivity of the clots and by measuring the D-Dimer released. The extent of t-PA-induced lysis was significantly increased by preincubation of plasma with 0.5 and 1 .O U/ml UH. The concentrations of t-PA required to give equivalent lysis rates were reduced by about 5 times by addition of 1 .O U/ml UH to plasma. UH added to t-PA after clot formation did not exert any significant effect. The effect of UH was not mediated by the inhibition of thrombin as preincubation of plasma with hirudin did not modify clot sensitivity to t-PA-induced lysis. We also found that UH modifies fibrin assembly and clot structure as evaluated by a turbidimetric assay and by electron microscopic scanning leading to the formation of thicker fibrin fibres and clots with large pores. Thus, the UH effect on clot sensitivity to lysis is due to an increased permeability of these clots to fibrinolytic components. An increase of clot sensitivity to lysis can contribute to the antithrombotic activity as well as to the bleeding complications of heparins. Furthermore, our data suggest that the early administration of UH together with thrombofytic agents could enhance the lysability of the new fibrin possibly accreted on the lysing thrombus.