TNF-α increases endothelial progenitor cell adhesion to the endothelium by increasing bond expression and affinity.

Endothelial progenitor cells (EPCs) are a rare population of cells that participate in angiogenesis. To effectively use EPCs for regenerative therapy, the mechanisms by which they participate in tissue repair must be elucidated. This study focused on the process by which activated EPCs bind to a target tissue. It has been demonstrated that EPCs can bind to endothelial cells (ECs) through the tumore necrosis factor-α (TNF-α)-regulated vascular cell adhesion molecule 1/very-late antigen 4 (VLA4) interaction. VLA4 can bind in a high or low affinity state, a process that is difficult to experimentally isolate from bond expression upregulation. To separate these processes, a new parallel plate flow chamber was built, a detachment assay was developed, and a mathematical model was created that was designed to analyze the detachment assay results. The mathematical model was developed to predict the relative expression of EPC/EC bonds made for a given bond affinity distribution. EPCs treated with TNF-α/vehicle were allowed to bind to TNF-α/vehicle-treated ECs in vitro. Bound cells were subjected to laminar flow, and the cellular adherence was quantified as a function of shear stress. Experimental data were fit to the mathematical model using changes in bond expression or affinity as the only free parameter. It was found that TNF-α treatment of ECs increased adhesion through bond upregulation, whereas TNF-α treatment of EPCs increased adhesion by increasing bond affinity. These data suggest that injured tissue could potentially increase recruitment of EPCs for tissue regeneration via the secretion of TNF-α.

Predictions of vacuum loss of evacuated vials from initial air leak rates.

Container closure integrity is a critical factor for maintaining product sterility and stability. Therefore, closure systems (found in vials, syringes, and cartridges) are designed to provide a seal between rubber stoppers and glass containers. To ensure that the contained product has maintained its sterility and stability at the time of deployment, the seal must remain intact within acceptable limits. To this end, a mathematical model has been developed to describe vacuum loss in evacuated drug vials. The model computes equivalent leak diameter corresponding to initial air leak rate as well as vacuum loss as a function of time and vial size. The theory accounts for three flow regimes that may be encountered. Initial leak rates from 10(-8) to 10(3) sccm (standard cubic centimeters per minute) were investigated for vials ranging from 1 to 100 mL. Corresponding leak diameters of 0.25-173 µm were predicted. The time for a vial to lose half of its vacuum, the T50 value, ranged from many years at the lowest leak rates and largest vials, to fractions of a second at the highest leak rates and smallest vials. These results may be used to determine what level of initial vacuum leak is acceptable for a given product.