Safety and tolerability of the protein C activator AB002 in end-stage renal disease patients on hemodialysis: a randomized phase 2 trial.

Background: The protein C system regulates blood coagulation, inflammation, and vascular integrity. AB002 is an injectable protein C activating enzyme under investigation to safely prevent and treat thrombosis. In preclinical models, AB002 is antithrombotic, cytoprotective, and anti-inflammatory.

Physioxic Culture of Chondrogenic Cells.

Cartilage resides under a low oxygen tension within articulating joints. The oxygen tension within cartilage of the knee joint has been measured to be between 2% and 5% oxygen. Although the literature has historically termed this level of oxygen as hypoxia, particularly when doing experiments in vitro in this range, this is actually the physiological oxygen tension experienced in vivo and is more accurately termed physioxia.

The contact activation inhibitor AB023 in heparin-free hemodialysis: results of a randomized phase 2 clinical trial.

End-stage renal disease (ESRD) patients on chronic hemodialysis have repeated blood exposure to artificial surfaces that can trigger clot formation within the hemodialysis circuit. Dialyzer clotting can lead to anemia despite erythropoietin and iron supplementation. Unfractionated heparin prevents clotting during hemodialysis, but it is not tolerated by all patients.

The protein C activator AB002 rapidly interrupts thrombus development in baboons.

Although thrombin is a key enzyme in the coagulation cascade and is required for both normal hemostasis and pathologic thrombogenesis, it also participates in its own negative feedback via activation of protein C, which downregulates thrombin generation by enzymatically inactivating factors Va and VIIIa. Our group and others have previously shown that thrombin's procoagulant and anticoagulant activities can be effectively disassociated to varying extents through site-directed mutagenesis. The thrombin mutant W215A/E217A (WE thrombin) has been one of the best characterized constructs with selective activity toward protein C.

Physioxia Promotes the Articular Chondrocyte-Like Phenotype in Human Chondroprogenitor-Derived Self-Organized Tissue.

Introduction: Biomaterial-based tissue engineering has not successfully reproduced the structural architecture or functional mechanical properties of native articular cartilage. In scaffold-free tissue engineering systems, cells secrete and organize the entire extracellular matrix over time in response to environmental signals such as oxygen level. In this study, we investigated the effect of oxygen on the formation of neocartilage from human-derived chondrogenic cells.

Responses to altered oxygen tension are distinct between human stem cells of high and low chondrogenic capacity.

Background: Lowering oxygen from atmospheric level (hyperoxia) to the physiological level (physioxia) of articular cartilage promotes mesenchymal stem cell (MSC) chondrogenesis. However, the literature is equivocal regarding the benefits of physioxic culture on preventing hypertrophy of MSC-derived chondrocytes. Articular cartilage progenitors (ACPs) undergo chondrogenic differentiation with reduced hypertrophy marker expression in hyperoxia but have not been studied in physioxia.

Hypoxia-inducible factor 3-alpha expression is associated with the stable chondrocyte phenotype.

The hypoxia-inducible factors HIF-1α and HIF-2α are important regulators of the chondrocyte phenotype but little is known about HIF-3α in cartilage. The objective of this study was to characterize HIF-3α (HIF3A) expression during chondrocyte differentiation in vitro and in native cartilage tissues. HIF3A, COL10A1, and MMP13 were quantified in mesenchymal stem cells (MSCs) and articular chondrocytes from healthy and osteoarthritic (OA) tissue in three-dimensional cultures and in human embryonic epiphyses and adult articular cartilage.

Hypoxia promotes redifferentiation and suppresses markers of hypertrophy and degeneration in both healthy and osteoarthritic chondrocytes.

Introduction: Hypoxia is considered to be a positive influence on the healthy chondrocyte phenotype and cartilage matrix formation. However, hypoxia-inducible factors (HIFs) have been implicated in the pathogenesis of osteoarthritis (OA). Thus, we assessed whether healthy and OA chondrocytes have distinct responses to oxygen, particularly with regard to hypertrophy and degradation during redifferentiation.

Enhanced chondrogenic differentiation of human bone marrow-derived mesenchymal stem cells in low oxygen environment micropellet cultures.

Chondrogenesis of mesenchymal stem cells (MSCs) is typically induced when they are condensed into a single aggregate and exposed to transforming growth factor-beta (TGF-beta). Hypoxia, like aggregation and TGF-beta delivery, may be crucial for complete chondrogenesis. However, the pellet dimensions and associated self-induced oxygen gradients of current chondrogenic methods may limit the effectiveness of in vitro differentiation and subsequent therapeutic uses.

Controlled presentation of recombinant proteins via a zinc-binding peptide-linker in two and three dimensional formats.

The presentation of proteins on surfaces is fundamental to numerous cell culture and tissue engineering applications. While a number of physisorption and cross-linking methods exist to facilitate this process, few avoid denaturation of proteins or allow control over protein orientation, both of which are critical to the functionality of many signal proteins and ligands. Often recombinant protein sequences include a poly-histidine tag to facilitate purification.

Membrane bioreactors enhance microenvironmental conditioning and tissue development.

In membrane bioreactors the cells are isolated from the bulk medium through a semipermeable membrane. This concept, which is analogous to how the circulatory system supplies solid tissues with nutrients, allows the maintenance of cells at much higher densities than is possible in traditional cultures. The membrane-based microbioreactor described herein is easy to operate, requiring only a pipette to load and harvest cells.

Surface-bound stem cell factor and the promotion of hematopoietic cell expansion.

In vivo, stem cell factor (SCF) exists in both a bound and soluble isoform. It is believed that the bound form is more potent and fundamentally required for the maintenance of hematopoietic stem cells (HSCs). This theory is supported by the observation that steel-Dickie mice lacking the bound isoform of SCF are unable to maintain hematopoiesis and by the fact that bound SCF displayed on the surface of transgenic cells is better able to maintain c-kit activation than soluble SCF.

Capture of flowing endothelial cells using surface-immobilized anti-kinase insert domain receptor antibody.

In humans, self-endothelialization of synthetic grafts is severely limited, but a recent interesting idea is to attract endothelial progenitor cells (EPCs) from peripheral blood onto grafts via antibodies directed at proposed EPC markers. Results with anti-CD34 antibodies have shown some promise, but it is unclear whether CD34 is the best marker for cells with re-endothelializing potential. Much evidence points to kinase insert domain receptor (KDR) as an important indicator of endothelial potential if not a definitive marker.

Potential of baboon endothelial progenitor cells for tissue engineered vascular grafts.

Thrombosis and intimal hyperplasia limit the usefulness of small caliber vascular grafts. While some improvements have been reported for grafts seeded with mature endothelial cells (EC), the harvesting of ECs from autologous sources, for example, veins or adipose tissue, remains problematic. More recently, endothelial progenitor cells (EPCs) have been considered a promising source of ECs because EPCs can be readily isolated from whole blood then rapidly expanded in vitro.