Human endothelial cell growth and phenotypic expression on three dimensional poly(lactide-co-glycolide) sintered microsphere scaffolds for bone tissue engineering

Bone tissue engineering offers promising alternatives to repair and restore tissues. Our laboratory has employed poly(lactide-co-glycolide) PLAGA microspheres to develop a three dimensional (3-D) porous bioresorbable scaffold with a biomimetic pore structure. Osseous healing and integration with the surrounding tissue depends in part on new blood vessel formation within the porous structure. Since endothelial cells play a key role in angiogenesis (formation of new blood vessels from pre-existing vasculature), the purpose of this study was to better understand human endothelial cell attachment, viability, growth, and phenotypic expression on sintered PLAGA microsphere scaffold. Scanning electron microscopy (SEM) examination showed cells attaching to the surface of microspheres and bridging the pores between the microspheres. Cell proliferation studies indicated that cell number increased during early stages and reached a plateau between days 10 and 14. Immunofluorescent staining for actin showed that cells were proliferating three dimensionally through the scaffolds while staining for PECAM-1 (platelet endothelial cell adhesion molecule) displayed typical localization at cell-cell contacts. Gene expression analysis showed that endothelial cells grown on PLAGA scaffolds maintained their normal characteristic phenotype. The cell proliferation and phenotypic expression were independent of scaffold pore architecture. These results demonstrate that PLAGA sintered microsphere scaffolds can support the growth and biological functions of human endothelial cells. The insights from this study should aid future studies aimed at enhancing angiogenesis in three dimensional tissue engineered scaffolds.     

Shifts in coding properties and maintenance of information transmission during adaptation in barrel cortex

Neuronal responses to ongoing stimulation in many systems change over time, or “adapt.” Despite the ubiquity of adaptation, its effects on the stimulus information carried by neurons are often unknown. Here we examine how adaptation affects sensory coding in barrel cortex. We used spike-triggered covariance analysis of single-neuron responses to continuous, rapidly varying vibrissa motion stimuli, recorded in anesthetized rats. Changes in stimulus statistics induced spike rate adaptation over hundreds of milliseconds. Vibrissa motion encoding changed with adaptation as follows. In every neuron that showed rate adaptation, the input–output tuning function scaled with the changes in stimulus distribution, allowing the neurons to maintain the quantity of information conveyed about stimulus features. A single neuron that did not show rate adaptation also lacked input–output rescaling and did not maintain information across changes in stimulus statistics. Therefore, in barrel cortex, rate adaptation occurs on a slow timescale relative to the features driving spikes and is associated with gain rescaling matched to the stimulus distribution. Our results suggest that adaptation enhances tactile representations in primary somatosensory cortex, where they could directly influence perceptual decisions.     

Binding of S-layer homology modules from Clostridium thermocellum SdbA to peptidoglycans

S-layer homology (SLH) module polypeptides were derived from Clostridium josui xylanase Xyn10A, Clostridium stercorarium xylanase Xyn10B, and Clostridium thermocellum scafoldin dockerin binding protein SdbA as rXyn10A-SLH, rXyn10B-SLH, and rSdbA-SLH, respectively. Their binding specificities were investigated using various cell wall preparations. rXyn10A-SLH and rXyn10B-SLH bound to native peptidoglycan-containing sacculi consisting of peptidoglycan and secondary cell wall polymers (SCWP) prepared from these bacteria but not to hydrofluoric acid-extracted peptidoglycan-containing sacculi (HF-EPCS) lacking SCWP, suggesting that SCWP are responsible for binding with SLH modules. In contrast, rSdbA-SLH interacted with HF-EPCS, suggesting that this polypeptide had an affinity for peptidoglycans but not for SCWP. The affinity of rSdbA-SLH for peptidoglycans was confirmed by a binding assay using a peptidoglycan fraction prepared from Escherichia coli cells. The SLH modules of SdbA must be useful for cell surface engineering in bacteria that do not contain SCWP.     

Metal ion specificities for folding and cleavage activity in the Schistosoma hammerhead ribozyme

The effects of various metal ions on cleavage activity and global folding have been studied in the extended Schistosoma hammerhead ribozyme. Fluorescence resonance energy transfer was used to probe global folding as a function of various monovalent and divalent metal ions in this ribozyme. The divalent metals ions Ca²⁺, Mg²⁺, Mn²⁺, and Sr²⁺ have a relatively small variation (less than sixfold) in their ability to globally fold the hammerhead ribozyme, which contrasts with the very large difference (>10,000-fold) in apparent rate constants for cleavage for these divalent metal ions in single-turnover kinetic experiments. There is still a very large range (>4600-fold) in the apparent rate constants for cleavage for these divalent metal ions measured in high salt (2 M NaCl) conditions where the ribozyme is globally folded. These results demonstrate that the identity of the divalent metal ion has little effect on global folding of the Schistosoma hammerhead ribozyme, whereas it has a very large effect on the cleavage kinetics. Mechanisms by which the identity of the divalent metal ion can have such a large effect on cleavage activity in the Schistosoma hammerhead ribozyme are discussed.     

Health risk assessment due to exposure of arsenic contamination in drinking water of district Shiekhupura,Punjab, Pakistan

Abstract

The present study was conducted to assess the magnitude and health impacts of As in drinking water. Drinking water samples (n?=?60) were collected from twenty different sites of Shiekhupura District (Pakistan). Health risk assessment through average daily dose (ADD), hazard indices (HI), hazard quotient (HQ), carcinogenic risk (CR), and cancer indices (CI) for dermal and oral exposure were determined. Results revealed that As concentration ranged from 2 to 900?µg?L^?1 in water samples, which was significantly greater than the safe limit of As (10?µg?L^?1) in water. Health risk assessment of As showed that ADD (1.07E?02–9.85E?04), HQ (1.06E+01–9.85E+00), and CR (1.60E?02–9.85E?04) for oral exposure and ADD (1.03E?05–9.69E?06), HQ (1.19E?02–7.96E?03), and CR (1.11E?05–8.98E?05) for dermal exposure which were exceeded the toxic risk index value. Comparison of the two exposure pathways indicated that the oral exposure is much higher risk than the dermal contact. Both values of HI and CI were greater than WHO limit. It is concluded that residents of study area are at higher risk of As induced diseases and carcinogenicity.     

Quality control of the parasitoid wasp Trichogramma brassicae(Hymenoptera:Trichogrammatidae)over 45 generations of rearing on Sitotroga cerealella

Trichogramma brassicae(Bezdenko)is an important biological control agent that has been used widely against many lepidopteran pests.Commonly,colonies of Tri-chog...     

Dosimetric effect of limited aperture multileaf collimator on VMAT plan quality: A study of prostate and head-and-neck cancers

Aim

The aim of study was to evaluate the dosimetric effect of collimator-rotation on VMAT plan quality, when using limited aperture multileaf collimator of Elekta Beam Modulator? providing a maximum aperture of 21 cm × 16 cm.