Stabilization of Peptide Vesicles by Introducing Inter-Peptide Disulfide Bonds

PURPOSE: Previously, we have shown that the amphiphilic oligopeptide SA2 (Ac-Ala-Ala-Val-Val-Leu-Leu-Leu-Trp-Glu-Glu-COOH) spontaneously self-assemble into nano-sized vesicles in aqueous environment. Relative weak individual intermolecular interactions dominate such oligopeptide assemblies. In this study we aimed at improving the stability of such peptide vesicles by covalently crosslinking the oligopeptide vesicles using disulfide bonds. Two and three cysteines were introduced in the SA2 peptide sequence to allow crosslinking (Ac-Ala-Cys-Val-Cys-Leu-(Leu/Cys)-Leu-Trp-Glu-Glu-COOH). RESULTS: Upon disulfide formation the crosslinked vesicles remained stable under conditions that disrupted the non-crosslinked peptide vesicles. The stabilized vesicles were more closely examined in terms of particle size (distribution) using atomic force microscopy, cryogenic electron microscopy, as well as dynamic light scattering analysis, showing an average particle radius in number between 15 and 20 nm. Using entrapment of calcein it was shown that intermolecular crosslinking of peptides within the vesicles did not affect the permeability for calcein. CONCLUSION: Introduction of cysteines into the hydrophobic domain of the SA2 amphiphilic oligopeptides is a feasible strategy for crosslinking the peptide vesicles. Such small crosslinked oligopeptide vesicles may hold promise for drug delivery applications

Membrane organization determines barrier properties of endothelial cells and short-chain sphingolipid-facilitated doxorubicin influx

International audienc

Human head-neck response during low-speed rear end impacts

Neck injuries resulting from rear-end collisions rank among the top car safety problems and have serious implications for society. Many rear impact sled experiments with volunteers and PMHSs have been performed in the past. However, in most of these studies, T1 kinematics were not obtained so that the kinematic behavior of the neck could not be separated from the motion of the rest of the spine. Also, to the best knowledge of the authors, the effect of anthropometric parameters on the head-neck kinematics was not studied before. The objective of this study is to describe the kinematic response of the head-neck system during low severity rear end impacts. In addition, the effect of anthropometric parameters such as height, weight and neck circumference was investigated. For this purpose, a total of 43 tests with 19 subjects was performed. Values for (delta)V ranged between 6,5 and 9.5 km/h. Linear accelerations of the head-CG and the first thoracic vertebra (T1) and angular accelerations of the head were obtained. Head angle and head-CG trajectories were obtained from film targets. Finally, head restraint impact forces were measured using a strain gauge attached to the support rods of the head restraint. Trajectories of the occipital condyles (OC trajectories) as well as upper neck forces and moments were calculated. All measured and calculated kinematic data were presented in response corridors representing the mean +/- one standard deviation. Although only three females participated in this study, a marked increase in head x-acceleration was observed for the females compared to the males. Also, neck circumference correlated well with peak x-accelerations: a thinner neck resulted in higher values for the x-accelerations. The results of this study can be used for evaluation of biofidelity of crash dummy necks, and for validation of mathematical head-neck models. Also, our finding that thinner necks result in higher head peak accelerations may be a partial answer to the question why women are at higher risk for whiplash injuries compared to men

The effect of implementing undergraduate competency-based medical education on students' knowledge acquisition, clinical performance and perceived preparedness for practice:a comparative study

<p>Background: Little is known about the gains and losses associated with the implementation of undergraduate competency-based medical education. Therefore, we compared knowledge acquisition, clinical performance and perceived preparedness for practice of students from a competency-based active learning (CBAL) curriculum and a prior active learning (AL) curriculum.</p><p>Methods: We included two cohorts of both the AL curriculum (n = 453) and the CBAL curriculum (n = 372). Knowledge acquisition was determined by benchmarking each cohort on 24 interuniversity progress tests against parallel cohorts of two other medical schools. Differences in knowledge acquisition were determined comparing the number of times CBAL and AL cohorts scored significantly higher or lower on progress tests. Clinical performance was operationalized as students' mean clerkship grade. Perceived preparedness for practice was assessed using a survey.</p><p>Results: The CBAL cohorts demonstrated relatively lower knowledge acquisition than the AL cohorts during the first study years, but not at the end of their studies. We found no significant differences in clinical performance. Concerning perceived preparedness for practice we found no significant differences except that students from the CBAL curriculum felt better prepared for 'putting a patient problem in a broad context of political, sociological, cultural and economic factors' than students from the AL curriculum.</p><p>Conclusions: Our data do not support the assumption that competency-based education results in graduates who are better prepared for medical practice. More research is needed before we can draw generalizable conclusions on the potential of undergraduate competency-based medical education.</p>

Live-cell imaging of receptors around postsynaptic membranes.

This protocol describes how to image the trafficking of glutamate receptors around excitatory postsynaptic membrane formed on an adhesion protein-coated glass surface. The protocol was developed to clarify how receptors move during the induction of synaptic plasticity. Dissociated neurons are cultured on a coverslip coated with neurexin, which induces the formation of postsynaptic membrane-like structures on the glass surface. A glutamate receptor tagged with a fluorescent protein is then transfected into neurons, and it is observed with total internal reflection fluorescence microscopy. The whole process takes about 3 weeks. Changes in the amount of cell-surface receptors caused by neuronal activities can be quantified, and individual exocytosis events of receptors can be clearly observed around the pseudo-postsynaptic membrane. This protocol has potential applications for studies of movements of membrane proteins around other specialized regions of the cell membrane, such as the inhibitory postsynaptic membrane, the presynaptic membrane or the immunological synapses