Safety, tolerability, and pharmacokinetics of a novel, selective antiprogestagen (Org 31710) in healthy male volunteers.

The safety and tolerability as well as pharmacokinetics of a new selective antiprogestagen, Org 31710, were studied after oral administration of single doses of 10, 25, 50, or 75 mg to 24 healthy male volunteers. Per dose-group, five subjects received active and one subject received placebo treatment. In subjects receiving 75 mg, the effects of Org 31710 on serum levels of follicle-stimulating hormone (FSH), luteinizing hormone (LH), and testosterone were also studied. No adverse or seriously adverse events were observed. All doses of Org 31710 were well tolerated. Characterization of the Org 31710 plasma pharmacokinetics revealed a statistically significant deviation from linearity: the dose normalized Cmax (nCmax) and dose normalized area under the curve (nAUC) values were significantly lower for the higher dosages (p < 0.05). Furthermore, tmax tended to decrease (from 1.6 to 0.9 h), whereas the elimination half-life (t1/2) tended to increase (from on average 45 to 57 h) with increasing dose. Org 31710 did not have any effect on serum levels of FSH, LH, and testosterone. In conclusion, Org 31710 appears to be a safe and well-tolerated compound in the dosage range studied.

PIP: The pharmacokinetics, safety, and tolerability of a new selective antiprogestagen--Org 31710--were investigated in 24 healthy Dutch men. Single oral doses of 10, 25, 50, or 75 mg were administered. In each dose group, 5 subjects received Org 31710 and 1 was given placebo. All dosages were well tolerated and no clinically relevant adverse events were recorded. Plasma pharmacokinetic characterizations revealed a statistically significant deviation from linearity after single doses of 10-75 mg of Org 31710. The dose-normalized maximum plasma concentrations was significantly higher in the 10 mg group and significantly lower in the 75 mg group compared with the 25 mg and 50 mg groups. Mean values of the normalized area under the plasma concentration time curve at 10 and 25 mg were significantly higher than values at higher dosages. The time to reach maximum plasma concentration decreased from 1.6 to 0.9 hours with increasing Org 31710 dose, while the elimination half-life increased from 45 to 57 hours. Serum levels of follicle-stimulating hormone, luteinizing hormone, and testosterone were not affected by a single dose of 75 mg of Org 31710. These findings demonstrate the safety and tolerability of the novel antiprogestagen Org 31710. The low antiglucocorticoid activity of Org 31710 represents a potential advantage over RU 486.

Glycated proteins modulate tissue-plasminogen activator-catalyzed plasminogen activation.

Plasminogen activation by tissue-plasminogen activator (t-PA) is accelerated by the presence of a macromolecular surface, which acts as a template that brings enzyme and substrate in close proximity. Modification of lysine residues, which are important for this template function, occurs in diabetic patients as a consequence of glycation of proteins. In this study, we investigated the effects of glycation of fibrin and other proteins in t-PA-catalyzed plasmin formation. Plasminogen activation on glycated fibrin(ogen) was increased compared to non-glycated fibrin(ogen), which could fully be attributed to an increased affinity of t-PA for glycated fibrin(ogen). Binding of plasminogen to glycated fibrin was increased, but did not contribute to increased plasminogen activation. Both plasminogen activator inhibitor-1 (PAI-1) binding and activity were increased on glycated fibrin. Induction of template function in plasminogen activation was also observed on immobilized glycated bovine serum albumin (BSA) and human gamma-globulins (IgG). Increased plasmin generation at sites of deposition of glycated proteins may lead to increased extracellular matrix breakdown and thereby affect the integrity of the endothelial monolayer. Moreover, soluble glycated BSA and glycated IgG can inhibit t-PA binding to immobilized glycated fibrin and interfere with fibrinolysis in diabetic patients.

Effect of extracellular matrix glycation on endothelial cell adhesion and spreading: involvement of vitronectin.

Glycation of proteins of the vessel wall is thought to play an important role in the pathogenesis of vascular complications in diabetes by affecting structure and function of these proteins. Adhesive proteins in the extracellular matrix (ECM) of endothelial cells (ECs) are essential for attachment of ECs to the subintima. In this study, we investigated the effect of glycation of ECM and purified adhesive proteins on EC adhesion and spreading. ECM was incubated with the reactive sugar glucose-6-phosphate (0-500 mmol/l) for different time periods (0-14 days) at 37 degrees C. Degree of glycation, measured in an enzyme-linked immunosorbent assay using a monoclonal antibody specific for advanced glycation end products, increased in a time- and concentration-dependent manner. Glycation of ECM with 50 mmol/l glucose-6-phosphate resulted in increased coverage by ECs as measured in a cell adhesion assay and was the result of an increase in number of adhered cells, while cell size was unaffected. Glycation of ECM with higher concentrations of glucose-6-phosphate resulted in decreased coverage by ECs caused by both a reduction in number of adhered ECs and impaired spreading. Experiments with purified glycated matrix proteins indicate that the decrease in EC adhesion and spreading on glycated ECM may result from glycation of vitronectin. Impaired EC adhesion and spreading caused by vitronectin glycation may result in impaired endothelial function and contribute to vascular disease.

Antiphospholipid antibodies directed against a combination of phospholipids with prothrombin, protein C, or protein S: an explanation for their pathogenic mechanism?

Despite many studies on the pathophysiology of antiphospholipid antibodies (aPL), the mechanism by which aPL causes thrombosis has not been established. We have tried to elucidate the paradox between the prolongation of the clotting time of phospholipid-dependent coagulation tests in vitro and the occurrence of thrombosis in vivo. The effect on endothelial cell-mediated prothrombinase activity of 30 IgG fractions, of which 22 prolong the aPTT of normal plasma, was investigated. Only 4 of 22 fractions (18%) inhibited prothrombinase activity when tested on this more physiologic phospholipid surface, indicating that in most patients with aPL the prolongation of clotting tests is predominantly as in vitro phenomenon. It was recently reported that in detection methods for aPL, two plasma proteins, beta 2-glycoprotein I and prothrombin, enhance the binding of aPL to phospholipids. We have studied the specificity of the 4 IgG fractions that inhibit the prothrombinase activity and found that they were directed against a combination of phospholipids and prothrombin. However, the involvement of prothrombin in binding of aPL leading to impaired thrombin generation could still result in both a bleeding and a thrombotic tendency. Therefore, we proposed a new thrombogenic mechanism for aPL in which aPL bind to complexes of phospholipids and coagulation proteins, thereby interfering in different coagulation reactions. We tested this new hypothesis by investigating the effect of IgG from the same 30 patients on the activated protein C (APC)-mediated factor Va inactivation in the absence and presence of protein S. Three IgGs that inhibited APC-mediated factor Va inactivation independent of protein S and 4 additional IgGs that inhibited in the presence of protein S were found. Furthermore, we could specifically adsorb the inhibitory IgG with cardiolipin vesicles to which APC with or without protein S was bound. In conclusion, these results suggest that subpopulations of aPL exist that are directed to complexes of phospholipids and different plasma proteins. The identity of the plasma proteins involved in the binding of aPL might determine which pathogenic mechanism causes thrombosis.