Hard sphere-like glass transition in eye lens α-crystallin solutions

We study the equilibrium liquid structure and dynamics of dilute and concentrated bovine eye lens α-crystallin solutions, using small-angle X-ray scattering, static and dynamic light scattering, viscometry, molecular dynamics simulations, and mode-coupling theory. We find that a polydisperse Percus–Yevick hard-sphere liquid-structure model accurately reproduces both static light scattering data and small-angle X-ray scattering liquid structure data from α-crystallin solutions over an extended range of protein concentrations up to 290 mg/mL or 49% vol fraction and up to ca. 330 mg/mL for static light scattering. The measured dynamic light scattering and viscosity properties are also consistent with those of hard-sphere colloids and show power laws characteristic of an approach toward a glass transition at α-crystallin volume fractions near 58%. Dynamic light scattering at a volume fraction beyond the glass transition indicates formation of an arrested state. We further perform event-driven molecular dynamics simulations of polydisperse hard-sphere systems and use mode-coupling theory to compare the measured dynamic power laws with those of hard-sphere models. The static and dynamic data, simulations, and analysis show that aqueous eye lens α-crystallin solutions exhibit a glass transition at high concentrations that is similar to those found in hard-sphere colloidal systems. The α-crystallin glass transition could have implications for the molecular basis of presbyopia and the kinetics of molecular change during cataractogenesis.The cytoplasm of the tightly packed fiber cells of the eye lens contains concentrated aqueous protein mixtures that have high refractive indexes, while normally remaining clear enough for vision. Lens clarity depends on short-range order between lens proteins (1, 2) and can be disrupted by both protein aggregation and liquid–liquid phase separation in cataract, a leading cause of blindness. At the high protein concentrations of lens cytoplasm, 25–60% by weight in mammals, small changes in interprotein interactions can disrupt transparency. For human lens proteins with cataractogenic point mutations, and for high-concentration lens protein mixtures, protein interaction changes as small as a fraction of thermal energy, k_BT, can induce phase separation and thus lead to opacification (3–7).In addition to equilibrium phase transitions, dynamical transitions including glass formation and gelation can also occur at high protein concentrations like those of the eye lens (8, 9). Relatively abrupt viscoelastic changes associated with glass formation or gelation could harden the lens and contribute to presbyopia and could alter cataract formation rates by affecting aggregation and phase separation kinetics.Here we study the equilibrium liquid structure and dynamics of concentrated solutions of eye-lens α-crystallin protein solutions, using small-angle X-ray scattering (SAXS), static light scattering (SLS) and dynamic light scattering (DLS), viscometry, liquid-state theory, event-driven molecular dynamics (MD) simulations, and mode-coupling theory (MCT). α-Crystallin is a polydisperse protein with about 40 subunits of two types, αA and αB, and accounts for up to 50% of lens protein mass. The forward scattering intensity from SAXS and light scattering experiments with concentrated α-crystallin solutions can be well represented by monodisperse hard-sphere liquid-structure models that have been key for understanding short-range order needed for lens transparency (1, 2). However, in physiological conditions α-crystallin ranges in molecular weight from 3 × 10⁵ to 2 × 10⁶, with an average near 8 × 10⁵ (10). There have indeed been reports that structure factors obtained from SAXS and small-angle neutron scattering data deviate from predictions for monodisperse hard spheres (11, 12).Accordingly, we first show that a polydisperse hard-sphere liquid-structure model (PHSM) based on the Percus–Yevick (PY) approximation (13) can accurately model SAXS data obtained from the present bovine α-crystallin preparations for volume fractions up to 49%, using a polydispersity of 20%. In contrast, polydispersity did not strongly influence model predictions for the observed SLS, which unlike SAXS probes length scales much larger than molecular sizes.We then test for glassy dynamics of α-crystallin solutions, using DLS and viscometry, and find glass transition features like those previously found for hard spheres. In particular, with increasing α-crystallin concentration, DLS intermediate scattering functions show expected progressively slower relaxations along with fast decays, and the viscosity diverges, both when approaching volume fractions in the vicinity of 58%. Using MCT (14), we obtain semiquantitative models of DLS data and corresponding data from MD simulations of high-concentration polydisperse sphere systems, in which MD polydispersity values were obtained from fits of the PHSM to the SAXS data. We note that for MCT we have used the theory for monodisperse systems, because the majority of the MCT work to date has focused on such systems. Recent results for polydisperse systems (15) support a similar overall picture.In brief, the data show that the present α-crystallin solutions have liquid structure and glassy dynamics similar to those of polydisperse hard-sphere solutions. Thus, eye lens protein solutions show analogs to ordinary glass in linking short-range order, transparency, and arrested dynamics.     

The Clinical Education Partnership Initiative: an innovative approach to global health education

Background

Despite evidence that international clinical electives can be educationally and professionally beneficial to both visiting and in-country trainees, these opportunities remain challenging for American residents to participate in abroad. Additionally, even when logistically possible, they are often poorly structured. The Universities of Washington (UW) and Nairobi (UoN) have enjoyed a long-standing research collaboration, which recently expanded into the UoN Medical Education Partnership Initiative (MEPI). Based on MEPI in Kenya, the Clinical Education Partnership Initiative (CEPI) is a new educational exchange program between UoN and UW. CEPI allows UW residents to partner with Kenyan trainees in clinical care and teaching activities at Naivasha District Hospital (NDH), one of UoN’s MEPI training sites in Kenya.

Methods

UW and UoN faculty collaborated to create a curriculum and structure for the program. A Chief Resident from the UW Department of Medicine coordinated the program at NDH. From August 2012 through April 2014, 32 UW participants from 5 medical specialties spent between 4 and 12 weeks working in NDH. In addition to clinical duties, all took part in formal and informal educational activities. Before and after their rotations, UW residents completed surveys evaluating clinical competencies and cross-cultural educational and research skills. Kenyan trainees also completed surveys after working with UW residents for three months.

Results

UW trainees reported a significant increase in exposure to various tropical and other diseases, an increased sense of self-reliance, particularly in a resource-limited setting, and an improved understanding of how social and cultural factors can affect health. Kenyan trainees reported both an increase in clinical skills and confidence, and an appreciation for learning a different approach to patient care and professionalism.

Conclusions

After participating in CEPI, both Kenyan and US trainees noted improvement in their clinical knowledge and skills and a broader understanding of what it means to be clinicians. Through structured partnerships between institutions, educational exchange that benefits both parties is possible.

     

Clinical presentation of young people (10–24 years old) with brain tumors: results from the international MOBI-Kids study

Journal of Neuro-Oncology - We used data from MOBI-Kids, a 14-country international collaborative case–control study of brain tumors (BTs), to study clinical characteristics of the tumors in...     

Vascular endothelial growth factor (VEGF) expression in prostatic tumours and its relationship to neuroendocrine cells.

Vascular endothelial growth factor (VEGF) expression was examined by immunohistochemistry in 45 prostatic carcinoma specimens and ten benign prostatic tumours (BPH). The majority of carcinoma specimens exhibited cytoplasmic staining for VEGF and showed a trend of increasing expression with dedifferentiation (2p = 0.003). Immunoreactive VEGF was also seen in the prostatic carcinoma cell lines, the order of staining intensity was PC3 > DU145 > LNCaP. Intense granular cytoplasmic staining for VEGF was observed in neuroendocrine-like cells which were seen focally in many of the prostatic specimens. Consecutive sections were incubated with a chromogranin A antibody to confirm the neuroendocrine phenotype of these cells. A significant correlation (P < 0.0001) between the total number of intensely stained VEGF-positive cells and chromogranin A-positive cells was found. A subpopulation of neuroendocrine-like cells also showed intense immunoreactivity for transforming growth factor alpha (TGF-alpha). A correlation was observed (2p = 0.0092) between the intensity of VEGF and TGF-alpha immunostaining in carcinoma cells which were not of neuroendocrine differentiation. The presence of these two angiogenic factors may aid the neovascularisation of carcinomas and their increased expression in tumour-associated neuroendocrine cells may contribute to a more aggressive phenotype.     

Virtual reality surgical simulation for lower urinary tract endoscopy and procedures

BACKGROUND AND PURPOSE: To provide a realistic experience of lower urinary tract endoscopic procedures, we have developed and continue to expand a computer-based surgical simulator that incorporates a surgical tool interface with anatomic detail and haptic feedback. METHODS: Surface-based geometric data for the lower urinary tract were generated from the National Library of Medicine Visible Human dataset. The three-dimensional texture map of the surface geometry was developed from recorded endoscopic video procedures. Geometry and associated texture maps were rendered in real time using the Silicon Graphics Extreme Impacts program. The surgical interface device incorporated all normal ranges of motion and resistance that occur within an actual operative environment. The hands-on endoscopic device attached to the interface device was provided by Circon-ACMI, Inc. Urologic residents evaluated the program for correlation with actual endoscopic procedures. RESULTS: Texture-mapped digitized images provided a close anatomic similarity to actual videoendoscopic images. Virtual endoscopy of the lower urinary tract was reproducible and closely simulated actual visual and tactile endoscopic experience. CONCLUSIONS: Virtual reality surgical simulation is feasible for a variety of lower urinary tract procedures. This system coordinates visual perception with appropriate haptic feedback in both longitudinal and rotational axes. These types of procedures may be incorporated into future educational experiences for urologists to introduce new techniques and to provide documentation of surgical experience.     

International expert workshop on the analysis of the economic and public health impacts of air pollution: workshop summary

Forty-nine experts from 18 industrial and developing countries met on 6 September 2001 in Garmisch-Partenkirchen, Germany, to discuss the economic and public health impacts of air pollution, particularly with respect to assessing the public health benefits from technologies and policies that reduce greenhouse gas (GHG) emissions. Such measures would provide immediate public health benefits, such as reduced premature mortality and chronic morbidity, through improved local air quality. These mitigation strategies also allow long-term goals--for example, reducing the buildup of GHG emissions--to be achieved alongside short-term aims, such as immediate improvements in air quality, and therefore benefits to public health. The workshop aimed to foster research partnerships by improving collaboration and communication among various agencies and researchers; providing a forum for presentations by sponsoring agencies and researchers regarding research efforts and agency activities; identifying key issues, knowledge gaps, methodological shortcomings, and research needs; and recommending activities and initiatives for research, collaboration, and communication. This workshop summary briefly describes presentations made by workshop participants and the conclusions of three separate working groups: economics, benefits transfer, and policy; indoor air quality issues and susceptible populations; and development and transfer of dose-response relationships and exposure models in developing countries. Several common themes emerged from the working group sessions and subsequent discussion. Key recommendations include the need for improved communication and extended collaboration, guidance and support for researchers, advances in methods, and resource support for data collection, assessment, and research.