Effects of melagatran, a novel direct thrombin inhibitor, during experimental septic shock

Early endotoxin-mediated haemostatic and inflammatory responses in the clopidogrel-treated pig

We have previously shown that the thrombin inhibiting agent melagatran markedly prolongs aPTT and counteracts creatinine increase in endotoxemic pigs. Against this background the effects of the platelet-inhibiting agent, clopidogrel on basic haemostatic, inflammatory and physiological variables were evaluated during porcine endotoxemia. Clopidogrel (10 mg/kg) or saline was randomly injected i.v. 30 min before start of a 6-h continuous infusion of endotoxin in 12 anaesthetised pigs. Another three pigs were given clopidogrel but not endotoxin. Clopidogrel did not affect physiological variables, formation of activated platelet microparticles, PK, aPTT, platelet count, plasma fibrinogen, TNF-alpha, or IL-6 during porcine endotoxemia. Although renal function, as evaluated by creatinine clearance (CLcr) deteriorated significantly (P = 0.01) in the saline-endotoxin, but not in the clopidogrel-endotoxin group, there was no significant difference between the saline-endotoxin and the clopidogrel-endotoxin groups. Renal biopsies were marked with a FITC-labelled chicken anti-fibrinogen antibody detecting fibrinogen and platelet bound fibrinogen, as a marker of porcine platelet activation, and examined by light microscopy. Evaluation of these immunohistochemical slides did not indicate that clopidogrel, significantly reduced the amount of intrarenal fibrin or fibrinogen depositions. Besides a trend to preserve renal function, clopidogrel did not affect haemodynamics or the coagulatory and inflammatory responses in porcine endotoxemia.

The effect of anticoagulants and the role of thrombin on neutrophil-endothelial cell interactions in septic shock

To examine the effects of anticoagulants and the role of thrombin on neutrophil-platelet-endothelial cell interactions in septic shock. Controlled experiments using phase-contrast microscopy to study neutrophil, platelet, and endothelial cell interactions in flowing cell suspensions under simulated physiologic conditions. University research laboratory. Adult patients with septic shock and normal volunteers. Microslides were coated with human umbilical vein endothelial cells. Neutrophils and platelets removed from control subjects were stimulated with plasma from patients in septic shock and perfused over endothelial cells. Heparin (H), argatroban (A), antithrombin III (ATIII), and recombinant human activated protein C (rhAPC) with and without thrombin were added to cells suspended in septic plasma and normal plasma. The number of neutrophils adherent to endothelial cells, neutrophil rolling velocity, and the number of neutrophils in aggregates were determined. Flow cytometric analysis of cells was used to identify cell activation and the formation of platelet-neutrophil aggregates. Heparin, A, ATIII, rhAPC all significantly decreased neutrophil adhesion and aggregation, and increased rolling velocity of neutrophils suspended in septic plasma. These results are similar to those observed with normal plasma but present greater absolute changes. Platelet-neutrophil aggregation, platelet activation, and neutrophil activation were significantly decreased by each of the anticoagulants. The addition of thrombin to cell suspensions containing anticoagulants reversed the effects of H, A, ATIII, rhAPC on neutrophil adhesion, adherence, and rolling velocity. In addition, thrombin attenuated the effects of each of these agents on platelet-neutrophil aggregation, platelet activation, and neutrophil activation. These data suggest that H, A, ATIII, and rhAPC decrease sepsis-induced neutrophil-endothelial cell interactions. The reversal of this effect by thrombin suggests that these agents alter neutrophil-endothelial interactions through their anticoagulant effects and the resulting decrease in thrombin activity.

Novel cyclooxygenase-catalyzed bioactive prostaglandin F2alpha from physiology to new principles in inflammation

Prostaglandin F2alpha (PGF2alpha), a foremost stable vasoactive cyclooxygenase (COX)-catalyzed prostaglandin, regulates a number of key physiological functions such as luteolysis, ovarian function, luteal maintenance of pregnancy, and parturition as a constitutive part of ongoing reproductive processes of the body. It has recently been implicated in the regulation of intricate pathophysiological processes, such as acute and chronic inflammation, cardiovascular and rheumatic diseases. Since the discovery of a second isoform of COXs, it has been shown that PGF2alpha can be formed in vivo from arachidonic acid through both isoforms of COXs, namely cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2). Being synthesized in various parts of the body, it metabolizes instantly to a number of rather inactive metabolites mainly in the lungs, liver, kidney, and efficiently excretes into the urine. 15-Keto-dihydro-PGF2alpha, a major stable metabolite of PGF2alpha that reflects in vivo PGF2alpha biosynthesis, is found in larger quantities than its parent compound in the circulation and urine in basal physiological conditions, with short-lived pulses during luteolysis, induced termination of pregnancy and parturition, and is increased in tissues and various body fluids during acute, sub-chronic, and severe chronic inflammation. Further, the close relationship of PGF2alpha with a number of risk factors for atherosclerosis indicates its major role in inflammation pathology. This review addresses multiple aspects of PGF2alpha in addition to its emerging role in physiology to inflammation.

Isoprostanes: novel bioactive products of lipid peroxidation

Isoprostanes, are a novel group of prostaglandin-like compounds that are biosynthesised from esterified polyunsaturated fatty acid (PUFA) through a non-enzymatic free radical-catalysed reaction. Several of these compounds possess potent biological activity, as evidenced mainly through their pulmonary and renal vasoconstrictive effects, and have short half-lives. It has been shown that isoprostanes act as full or partial agonists through thromboxane receptors. Both human and experimental studies have indicated associations of isoprostanes and severe inflammatory conditions, ischemia-reperfusion, diabetes and atherosclerosis. Reports have shown that F2-isoprostanes are authentic biomarkers of lipid peroxidation and can be used as potential in vivo indicators of oxidant stress in various clinical conditions, as well as in evaluations of antioxidants or drugs for their free radical-scavenging properties. Higher levels of F2-isoprostanes have been found in the normal human pregnancy compared to non-pregnancy, but their physiological role has not been well studied so far. Since bioactive F2-isoprostanes are continuously formed in various tissues and large amounts of these potent compounds are found unmetabolised in their free acid form in the urine in normal basal conditions with a wide inter-individual variation, their role in the regulation of normal physiological functions could be of further biological interest, but has yet to be disclosed. Their potent biological activity has attracted great attention among scientists, since these compounds are found in humans and animals in both physiological and pathological conditions and can be used as reliable biomarkers of lipid peroxidation.

Effects of endothelin-1 (ET-1) and thrombin antagonism on cardiovascular and respiratory dysfunctions during endotoxic shock in pig

We evaluated the endothelin-1 (ET-1) and thrombin involvement in cardiovascular and respiratory dysfunction during endotoxic shock in 18 anaesthetized, mechanically ventilated pigs, divided into three groups. Group 1 was pre-treated only with lipopolysaccharide (LPS), group 2 was treated with lepirudin, a thrombin inhibitor, group 3 was pre-treated with bosentan, a dual inhibitor of ET-1 receptors. Results show that LPS caused systemic hypotension, pulmonary biphasic hypertension, increase in lung resistances (R(L)) and decrease in compliance (C(L)). Lepirudin partially reduced the LPS-dependent pulmonary hypertension, without affecting the changes in C(L) and R(L). On the contrary, bosentan completely abolished the pulmonary hypertension and the changes inC(L) and R(L), and worsened the LPS-dependent systemic hypotension. Our results show that ET-1 is largely responsible for pulmonary derangement due to endotoxic shock; at bronchial level, the ET-1 release seems due only to LPS, while, at pulmonary vascular level, it results also from LPS-dependent thrombin activation.

Pharmaceutical thrombosis prevention in cardiovascular disease

Cardiovascular diseases are a leading cause of morbidity and mortality in modern society. As a result of this, great efforts have been made to establish regimens for prophylaxis and treatment of such disorders. Pharmacological intervention is also a prerequisite for the success of other therapeutic approaches, e.g. coronary angioplasty. Prevention of platelet aggregation is a goal that can be achieved by counteracting various receptors on the platelet surface. The main attentions for such interventions are focused on inhibiting the glycoprotein IIb/IIIa receptor. So far, they are limited to intravenous usage. Adenosine diphosphate receptor inhibitors are available for intravenous and oral usage. Their effect is, at least partly, also exerted via the counteraction of adenosine diphosphate-mediated activation of the glycoprotein IIb/IIIa complex. An oral direct thrombin inhibitor is under clinical evaluation. This review focuses on atherothrombotic disorders, but recent advances within new fields of anticoagulation (i.e., treatment of severe septic shock and a novel approach to prevent thromboembolic disorder during surgery) should not be overlooked.

Advances in the development of thrombin inhibitors

Thromboembolic diseases are a major cause of morbidity and mortality, particularly in the Western world, which has stimulated enormous research efforts by the pharmaceutical industry to introduce new antithrombotic therapies. One strategy is the development of direct inhibitors of the serine protease thrombin, which holds a central position in the final steps of the blood coagulation cascade and in platelet activation. At present there is only limited clinical use of some parenteral preparations of thrombin inhibitors in acute situations, especially when the common antithrombotic drugs heparin, warfarin and aspirin are ineffective or associated with side effects. However, for use in prophylaxis of thrombotic diseases such inhibitors should be orally available, must be safe to avoid bleeding complications and should have an appropriate half-life, allowing once or twice daily dosing to maintain adequate antithrombotically effective blood levels. Details of several new and potent thrombin inhibitors have been published during the last years. For some of them oral bioavailability is claimed and they are effective in in vitro coagulation assays. However, most of them showed only limited efficacy in animal studies with respect to the doses administered. For that reason, effort is concentrated on the evaluation and optimisation of the overall physicochemical characteristics of the inhibitors in order to improve the pharmacokinetics and, thus, the development of promising drug candidates. Nevertheless, only careful clinical studies can give clear answers about the true therapeutical benefit of new developments in this field. This review summarises the current status of direct thrombin inhibitors which are already in clinical use and clinical development and gives an overview on recently published and promising new compounds.