Thrombin-Induced Podocyte Injury Is Protease-Activated Receptor Dependent.

Nephrotic syndrome is characterized by massive proteinuria and injury of specialized glomerular epithelial cells called podocytes. Studies have shown that, whereas low-concentration thrombin may be cytoprotective, higher thrombin concentrations may contribute to podocyte injury. We and others have demonstrated that ex vivo plasma thrombin generation is enhanced during nephrosis, suggesting that thrombin may contribute to nephrotic progression. Moreover, nonspecific thrombin inhibition has been shown to decrease proteinuria in nephrotic animal models. We thus hypothesized that thrombin contributes to podocyte injury in a protease-activated receptor-specific manner during nephrosis. Here, we show that specific inhibition of thrombin with hirudin reduced proteinuria in two rat nephrosis models, and thrombin colocalized with a podocyte-specific marker in rat glomeruli. Furthermore, flow cytometry immunophenotyping revealed that rat podocytes express the protease-activated receptor family of coagulation receptors in vivo High-concentration thrombin directly injured conditionally immortalized human and rat podocytes. Using receptor-blocking antibodies and activation peptides, we determined that thrombin-mediated injury depended upon interactions between protease-activated receptor 3 and protease-activated receptor 4 in human podocytes, and between protease-activated receptor 1 and protease-activated receptor 4 in rat podocytes. Proximity ligation and coimmunoprecipitation assays confirmed thrombin-dependent interactions between human protease-activated receptor 3 and protease-activated receptor 4, and between rat protease-activated receptor 1 and protease-activated receptor 4 in cultured podocytes. Collectively, these data implicate thrombinuria as a contributor to podocyte injury during nephrosis, and suggest that thrombin and/or podocyte-expressed thrombin receptors may be novel therapeutic targets for nephrotic syndrome.

Structure-based design, synthesis, and biological evaluation of irreversible human rhinovirus 3C protease inhibitors. 8. Pharmacological optimization of orally bioavailable 2-pyridone-containing peptidomimetics.

The optimization of the pharmacokinetic performance of various 2-pyridone-containing human rhinovirus (HRV) 3C protease (3CP) inhibitors following oral administration to either beagle dogs or CM-monkeys is described. The molecules described in this work are composed of a 2-pyridone-containing peptidomimetic binding determinant and an alpha,beta-unsaturated ester Michael acceptor moiety which forms an irreversible covalent adduct with the active site cysteine residue of the 3C enzyme. Modification of the ester contained within these compounds is detailed along with alteration of the P(2) substituent present in the peptidomimetic portion of the inhibitors. The pharmacokinetics of several inhibitors in both dogs and monkeys are described (7 h plasma concentrations after oral administration) along with their human plasma stabilities, stabilities in incubations with human, dog, and monkey microsomes and hepatocytes, Caco-2 permeabilities, and aqueous solubilities. Compounds containing an alpha,beta-unsaturated ethyl ester fragment and either an ethyl or propargyl P(2) moiety displayed the most promising combination of 3C enzyme inhibition (k(obs)/[I] 170 000-223 000 M(-1) s(-1)), antiviral activity (EC(50) = 0.047-0.058 microM, mean vs seven HRV serotypes), and pharmacokinetics following oral administration (7 h dog plasma levels = 0.248-0.682 microM; 7 h CM-monkey plasma levels = 0.057-0.896 microM).

Structure-based design of a parallel synthetic array directed toward the discovery of irreversible inhibitors of human rhinovirus 3C protease.

Utilizing the tools of parallel synthesis and structure-based design, a new class of Michael acceptor-containing, irreversible inhibitors of human rhinovirus 3C protease (HRV 3CP) was discovered. These inhibitors are shown to inhibit HRV-14 3CP with rates of inactivation ranging from 886 to 31 400 M(-1) sec(-1). These inhibitors exhibit antiviral activity when tested against HRV-14 infected H1-HeLa cells, with EC(50) values ranging from 1.94 to 0.15 microM. No cytotoxicity was observed at the limits of the assay concentration. A crystal structure of one of the more potent inhibitors covalently bound to HRV-2 3CP is detailed. These compounds were also tested against HRV serotypes other than type 14 and were found to have highly variable activities.