In vitro platelets/endothelial cells interactions in presence of acetylsalicylic acid at various dosages.

Venous endothelium is able to release in vitro substances which modifies platelet aggregation. A vascular fragment incubated in Michaelis buffer (pH 7.30), aliquoted and tested on platelet-rich-plasma partially inhibits the aggregometry parameters. Addition of acetylsalicylic acid (ASA) at ultra low dose (0.1 nM final solution in the incubation tube) presents a reversed effect on this inhibition. To explain this phenomenon, 6-keto-PGF1 alpha and von Willebrand factor were dosed in the incubation media. After determination of an active level of 6-keto-PGF1 alpha (200 pg/100 microliters), 2 series were made: series 1 included the values below 200 pg/100 microliters incubation media, series 2, the values above 200 pg/100 microliters incubation media. When the vascular fragment was incubated as described above, the results of aggregometry ratio for series 1 were: test A (without ASA): 0.84 +/- 0.18, test B1 (with 0.1 nM of ASA): 0.87 +/- 0.13. For series 2, they became: test A: 0.75 +/- 0.27, test B1: 0.93 +/- 0.16. Control was always: 1.00 +/- 0.00. For the same groups, 6-keto-PGF1 alpha values were: for series 1, test A: 81 +/- 57, test B1: 81 +/- 60 pg/100 microliters incubation medium, for series 2, test A: 596 +/- 495, test B1: 383 +/- 263 pg/100 microliters incubation medium. Analyses were also performed with 2 high doses of ASA (B2: 10(5) nM and B3: 10(6) nM final solution) in the same experimental conditions. In these groups, aggregation parameters were decreased (0.86 +/- 0.14 for 10(5) nM, 0.84 +/- 0.15 for 10(6) nM) as well as 6-keto-PGF1 alpha production (189 +/- 199 for 10(5) nM, 152 +/- 182 for 10(6) nM). For these two last ASA treatments, comparison of the results in groups set up according to the sensitive 6-keto-PGF1 alpha value (200 pg/100 microliters solution) showed no modification. So it seems that a certain reactive state, specific of ultra low dose treatment is necessary for the vascular endothelium to be sensitive at such treatment.

Could proteolytic enzyme modulate the interaction platelets/vessel wall in presence of ASA at ultra low doses?

Acetylsalicylic acid (ASA) is known to act on platelets and vessel walls. At ultra low doses it reverses the inhibitory effects produced by a vascular fragment. Use of papain on normal platelets in vitro led to the appearance of platelet aggregation without collagen induction with a range of 20.25 +/- 28.91%. In the presence of vascular fragments (without ASA), this "spontaneous" aggregation remained but was reduced (13.26 +/- 27.73%). This effect was reversed by ASA treatment (29.41 +/- 24.17%). Reversion of vascular inhibition by ASA was not modified by papain.

Aspirin at very ultra low dosage in healthy volunteers: effects on bleeding time, platelet aggregation and coagulation.

Aspirin at very ultra low dosage was tested in healthy volunteers (n = 20) in a randomized, double-blind and placebo-controlled trial. The results showed a bleeding time reduction (p less than 0.05) in volunteers having previously ingested aspirin. Platelet aggregation on platelet-rich plasma was not statistically modified after aspirin ingestion. Thrombin clotting time was always higher (p less than 0.05) in the treated group.

[How to standardize low molecular weight heparins]. / Quel standard utiliser pour les héparines de bas poids moléculaire?

Heparin, used in anticoagulant and antithrombotic therapeutic for over fifty years, turns out to mean important side effects and serious haemorrhagic risk. The obtaining, from 1976, of the first low molecular weight heparins (LMWH) preparations is partly allowed to overcome those problems. The LMWH present an identical or greater antithrombotic capacity than the unfractioned heparin and mean a lower haemorrhagic risk. Thus their use in antithrombotic therapy is very interesting. However, the existence of different units for the LMWH sets a standardization problem for their clinical use and for their biological follow up. The first international LMWH standard introduction by the World Health Organisation in 1986 may be useful to give a great homogeneity of the interlaboratory results, to serve as reference to the biologists, as activity standardization for the manufacturers or as security for the clinicians. However, it seems its definition mode and its validity call into question by several authors. The anti Xa activity, advocated in the biological surveillance, does not seem to perfectly fit to the LMWH therapy. The debate about the standardization of the low molecular weight heparins keeps open.

Could thrombus age be a modulator of heparin or L.M.W.H. activities?

The main thrombotic diseases are caused by old constituted thrombi. However, experiments to demonstrate the effects of heparin or heparin fragments on tPA release have been on fresh thrombi. This study on thrombi induced 6, 24, 48 or 72 hours before sampling shows variations in the main biological activities of both heparin and heparin fragment (CY222) as the thrombus ages. This effect is particularly observed on tPA release which is statistically reduced (p less than 0.001). Thrombus age seems to be a modulator of heparin and heparin fragment biological activities.

[Low molecular weight heparins]. / Les héparines de bas poids moléculaire.

The apparition in the 80's of low molecular weight heparins (LMWHs) obtained by chemical or enzymatical splitting, modified the fields of prophylactic treatment of thromboembolic diseases. These drugs present on heparin numerous advantages: equal antithrombotic activity with a smaller bleeding risk, higher bioavailability, longer pharmacokinetic, which simplify their use. The definite mode of action remains unknown, but LMWH act at different steps like coagulation (by AT III), fibrinolysis, blood cells, endothelial cells. Further, like heparin, they can be neutralized by protamine. However the right, simple, specific biological assay which presents a good correlation with the antithrombotic activity, remained to be established.

[Low-molecular weight heparins in post-surgical recovery]. / Les héparines de bas poids moléculaire en réanimation post-chirurgicale.

Low molecular weight heparins are used in human therapy for preventing venous thrombosis during the postoperative period. The monitoring of this therapy uses a measurement of the factor Xla activity. A value of this activity higher than 0.4 IU/ml, suggests a hemorrhage risk. The use of these low molecular weight heparins for the treatment of venous thrombosis is now under investigation. However, the biological monitoring of this treatment has not yet been defined. The anti IIa and anti Xa activities seem to be interesting. In fact the antithrombotic power would be due to the anti IIa and profibrinolytic activities.

Influence of heparin and a low molecular weight heparin fraction of the leukocytes in an experimental venous thrombosis model.

A randomized study was performed to observe the effects induced by heparin and a low molecular weight heparin fraction (at different dosages) on the leukocytes of rats in the presence of experimental venous thrombosis. The experimentation was carried out on two series of animals: the first with a ligature of the inferior vena cava inducing the formation of a thrombus, the second without any ligature. The results show that the induction of thrombosis involves: in the blood, an increase of the number leukocytes, principally polymorphonuclear cells; in the thrombi, a significant rise in the total count of leukocytes, here mononuclear cells; the latter number increases with the dosages of the administered drugs.