Sequence, phylogenetic and variant analyses of antithrombin III.

Antithrombin III (ATIII) performs a critical anticoagulant function by precluding the activation of blood clotting proteinases, aided by its two cofactors, heparin and heparan sulfate. Though several studies have been carried out on physiological, biochemical and structural perspectives on ATIII, so far there are limited studies on the molecular evolution of ATIII. Herein, we carried out molecular phylogenetic analyses of ATIII genes, combining gene structures, synteny and sequence-structural features for ATIII spanning 50 vertebrate genomes. ATIII is maintained over 450 MY on same genomic loci in vertebrates with few changes in ray-finned fishes and lost one intron 262c in tetrapods and coelacanth. In ray-finned fishes, ATIII gene has additional intron at the position 262c, which shared by group V1 members, corroborating that it is lost in other vertebrates and also in lobed-finned fish coelacanth (Latimeria chalumnae). We found that heparin binding basic residues, hD helix, three pairs of Cys-Cys salt bridges, N-glycosylation sites, serpin motifs and inhibitory reactive center loop (RCL) of ATIII protein are highly conserved. Using 1092 human genomes available from 1000G project, we also compiled 1997 ATIII variants, which reveals 76.2% single nucleotide polymorphisms (SNPs), 11.8% deletions and 8.1% insertions as three major classes of gene variations. These understandings may have medical importance as well.

Discovery of sulfonylalkylamides: A new class of orally active factor Xa inhibitors.

Factor Xa (FXa) is a trypsin-like serine protease involved in the coagulation cascade and has received great interest as a potential target for the development of new antithrombotic agents. Most of amidine-type FXa inhibitors reported have been found to show extremely poor oral bioavailability. Compound 1 is one of the first reported non-amidine type FXa inhibitors. To discover novel and orally active FXa inhibitors, we investigated flexible linear linkers between the 6-chloronaphthalene ring and the 1-(pyridin-4-yl)piperidine moiety of 1 and found the orally active sulfonylalkylamide 2f with an FXa IC(50) of 0.05 microM, comparable with that of 1. Further modification to reduce the CYP3A4 inhibitory activity of 2f resulted in the potent, selective, and orally active 2-methylpyridine analogue 2s (FXa IC(50) of 0.061 microM), for which the liability of CYP3A4 inhibition was significantly weakened compared to 2f. Compound 2s also showed long lasting anticoagulant activity in cynomolgus monkeys.

The race to an orally active Factor Xa inhibitor: recent advances.

Factor Xa (fXa) is a key enzyme in the coagulation cascade and an essential component of the prothrombinase complex, which activates prothrombin to thrombin, leading to fibrin clot formation. In the search for a more effective and safer orally active anticoagulant, fXa has emerged as a major target for potential therapeutic applications in the treatment and prevention of thrombosis. This review focuses on recent advances in the chemistry of drug design and lead optimization of orally bioavailable fXa inhibitors. Many of these orally active fXa inhibitors are currently in clinical trials and are anticipated to change the landscape of thrombosis therapy.

Venous thrombosis: antithrombin III deficiency.

Antithrombin (ATIII) is believed to be one of the body's most powerful natural anticoagulants, so individuals with a deficiency of this protein exhibit a marked propensity to venous thrombosis. This article will focus on the pathophysiology of this disorder, including clinical presentation, diagnosis, and treatment.

Effect of heparin on the vascular distribution of *I-antithrombin III isoforms in rabbits.

Studies of radioiodinated antithrombin III kinetic behavior in vivo have shown that a pool of this protein partitions into a vascular compartment that could be the result of antithrombin III interaction with heparin-related glycosaminoglycans present on the vessel wall (J. Clin. Invest. 74, 191-191, 1984). As this partitioning was demonstrated by the rapid initial clearance of the labeled antithrombin III, new studies were performed to determine the effect on this clearance of large doses of intravenously administered heparin. In addition, as previous studies had shown unequal clearance rates for tracer-labeled antithrombin III isoforms differing in affinity for heparin, the effect of heparin treatment was assessed for each isoform. Comparison of data from heparin-treated and control animals demonstrated that heparin markedly decreased the clearance rates for each of the *I-labeled antithrombin III isoforms. Heparin also abolished the difference in *I-antithrombin III isoform plasma-clearance rates, and this effect rapidly disappeared after treatment was discontinued. Inhibition by heparin of the initial clearance of *I-labeled ATIII isoforms is the first direct evidence from in vivo studies for the notion that the pool of antithrombin III which is in rapid equilibrium with the plasma pool is, at least in part, the result of the interaction of antithrombin III with vessel wall heparin-related glycosaminoglycans.

Hereditary antithrombin III deficiency: biochemical aspects.

Since the description of the first thrombophilic family with congenital AT-III deficiency, increasing numbers of different types of the condition have become evident. Initially the anomaly seemed to be homogeneous and simple: the three main characteristics of AT-III (thrombin inactivating and heparin cofactor activity, antigen concentration) were decreased. This type of AT-III deficiency (type 1) was later divided into type 1a and 1b on the basis of the heparin affinity of the AT-III molecule. The first family with a different qualitative AT-III disorder (type 2) was described by our group in 1974. In the members of this family the AT-III antigen concentration was normal, but the molecule had no functional activity (AT-III Budapest). In the last few years some new variants of type 2 hereditary AT-III disorders have been observed; they are characterized by a loss of one or more functional properties of the AT-III molecule.