Biomedical subjects

M E DiLorenzo

Publications and source records attributed to M E DiLorenzo.

3 recordsLinked to original sources

PubMed2001

Antiplatelet agents in tissue factor-induced blood coagulation.

Several platelet inhibitors were examined in a tissue factor (TF)-initiated model of whole blood coagulation. In vitro coagulation of human blood from normal donors was initiated by 25 pM TF while contact pathway coagulation was suppressed using corn trypsin inhibitor. Products of the reaction were analyzed by immunoassay. Preactivation of platelets with the thrombin receptor activation peptide did not influence significantly the clotting time or thrombin-antithrombin III complex (TAT) formation. Addition of prostaglandin E(1) (5 microM) caused a significant delay in clotting (10.0 minutes) versus control (4.3 minutes). The prolonged clotting time is correlated with delays in platelet activation, formation of TAT, and fibrinopeptide A (FPA) release. In blood from subjects receiving acetylsalicylic acid (ASA or aspirin), none of the measured products of coagulation were significantly affected. Similarly, no significant effect was observed when 5 microM dipyridamole (Persantine) was added to the blood. Antagonists of the platelet integrin receptor glycoprotein (gp) IIb/IIIa had intermediate effects on the reaction. A 1- to 2-minute delay in clot time and FPA formation was observed with addition of the antibodies 7E3 and Reopro (abciximab) (10 microg/mL), accompanied by a 40% to 70% reduction in the maximal rate of TAT formation and delay in platelet activation. The cyclic heptapetide, Integrilin (eptifibatide), at 5 microM concentration slightly prolonged clot time and significantly attenuated the maximum rate of TAT formation. The disruption of the gpIIb/IIIa-ligand interaction not only affects platelet aggregation, but also decreases the rate of TF-initiated thrombin generation in whole blood, demonstrating a potent antithrombotic effect superimposed on the antiaggregation characteristics.

Abciximab↗

PubMed1998

Blood coagulation in hemophilia A and hemophilia C.

Tissue factor (TF)-induced coagulation was compared in contact pathway suppressed human blood from normal, factor VIII-deficient, and factor XI-deficient donors. The progress of the reaction was analyzed in quenched samples by immunoassay and immunoblotting for fibrinopeptide A (FPA), thrombin-antithrombin (TAT), factor V activation, and osteonectin. In hemophilia A blood (factor VIII:C <1%) treated with 25 pmol/L TF, clotting was significantly delayed versus normal, whereas replacement with recombinant factor VIII (1 U/mL) restored the clot time near normal values. Fibrinopeptide A release was slower over the course of the experiment than in normal blood or hemophilic blood with factor VIII replaced, but significant release was observed by the end of the experiment. Factor V activation was significantly impaired, with both the heavy and light chains presenting more slowly than in the normal or replacement cases. Differences in platelet activation (osteonectin release) between normal and factor VIII-deficient blood were small, with the midpoint of the profiles observed within 1 minute of each other. Thrombin generation during the propagation phase (subsequent to clotting) was greatly impaired in factor VIII deficiency, being depressed to less than 1/29 (<1.9 nmol TAT/L/min) the rate in normal blood (55 nmol TAT/L/min). Replacement with recombinant factor VIII normalized the rate of TAT generation. Thus, coagulation in hemophilia A blood at 25 pmol/L TF is impaired, with significantly slower thrombin generation than normal during the propagation phase; this reduced thrombin appears to affect FPA production and factor V activation more profoundly than platelet activation. At the same level of TF in factor XI-deficient blood (XI:C <2%), only minor differences in clotting or product formation (FPA, osteonectin, and factor Va) were observed. Using reduced levels of initiator (5 pmol/L TF), the reaction was more strongly influenced by factor XI deficiency. Clot formation was delayed from 11.1 to 15.7 minutes, which shortened to 9.7 minutes with factor XI replacement. The maximum thrombin generation rate observed ( approximately 37 nmol TAT/L/min) was approximately one third that for normal (110 nmol/L TAT/min) or with factor XI replacement (119 nmol TAT/L/min). FPA release, factor V activation, and release of platelet osteonectin were slower in factor XI-deficient blood than in normal blood. The data demonstrate that factor XI deficiency results in significantly delayed clot formation only at sufficiently low TF concentrations. However, even at these low TF concentrations, significant thrombin is generated in the propagation phase after formation of the initial clot in hemophilia C blood.

Adolescent↗

PubMed1997

Ultrasensitive fluorogenic substrates for serine proteases.

Selective, sensitive assays for the quantitation of serine proteases involved in coagulation and fibrinolysis have been developed employing fluorogenic substrates containing a 6-amino-1-naphthalenesulfonamide leaving group (PNS-substrates). Over one hundred substrates were evaluated for hydrolysis by the serine proteases of blood coagulation and fibrinolysis, and substrate structure-efficiency correlations were examined. PNS-substrates which contain Lys in the P1 position are specific for Lys-plasmin and are either not hydrolyzed or hydrolyzed at a relatively low rate by factor Xa, thrombin, or urokinase-type plasminogen activator (uPA). These substrates allow quantitation of Lys-plasmin at concentrations as low as 1 pM. Eighteen of over 90 substrates tested for factor XIa are hydrolyzed by this enzyme at a relatively high rate reaching a k(cat), value of 170 s(-1) and allowing quantitation of factor XIa at 10 fM. Eighteen of almost 90 PNS-substrates tested display high specificity for thrombin, some exceeding that for factor Xa by >10,000-fold and >100-fold for activated protein C (APC). Seven of these substrates have a k(cat) over 100 s(-1) and three of them have a K(M) below 1 microM. They allow the quantitation of thrombin at concentrations as low as 20 fM. For APC, uPA and the factor VIIa/tissue factor complex, quantitation is feasible at 1 pM concentration. For factor Xa and factor VIIa the limits are 0.4 pM and 40 pM respectively. The PNS-substrates presented in this study may be employed for the development of direct and sensitive serine protease assays.

Anilino Naphthalenesulfonates↗