Intracellular "In Silico Microscopes"-Comprehensive 3D Spatio-Temporal Virus Replication Model Simulations.

Despite their small and simple structure compared with their hosts, virus particles can cause severe harm and even mortality in highly evolved species such as humans. A comprehensive quantitative biophysical understanding of intracellular virus replication mechanisms could aid in preparing for future virus pandemics. By elucidating the relationship between the form and function of intracellular structures from the host cell and viral components, it is possible to identify possible targets for direct antiviral agents and potent vaccines. Biophysical investigations into the spatio-temporal dynamics of intracellular virus replication have thus far been limited. This study introduces a framework to enable simulations of these dynamics using partial differential equation (PDE) models, which are evaluated using advanced numerical mathematical methods on leading supercomputers. In particular, this study presents a model of the replication cycle of a specific RNA virus, the hepatitis C virus. The diffusion-reaction model mimics the interplay of the major components of the viral replication cycle, including non structural viral proteins, viral genomic RNA, and a generic host factor. Technically, surface partial differential equations (sufPDEs) are coupled on the 3D embedded 2D endoplasmic reticulum manifold with partial differential equations (PDEs) in the 3D membranous web and cytosol volume. The membranous web serves as a viral replication factory and is formed on the endoplasmic reticulum after infection and in the presence of nonstructural proteins. The coupled sufPDE/PDE model was evaluated using realistic cell geometries based on experimental data. The simulations incorporate the effects of non structural viral proteins, which are restricted to the endoplasmic reticulum surface, with effects appearing in the volume, such as host factor supply from the cytosol and membranous web dynamics. Because the spatial diffusion properties of genomic viral RNA are not yet fully understood, the model allows for viral RNA movement on the endoplasmic reticulum as well as within the cytosol. Visualizing the simulated intracellular viral replication dynamics provides insights similar to those obtained by microscopy, complementing data from in vitro/in vivo viral replication experiments. The output data demonstrate quantitative consistence with the experimental findings, prompting further advanced experimental studies to validate the model and refine our quantitative biophysical understanding.

Transdermal and lateral effective diffusivities for drug transport in stratum corneum from a microscopic anisotropic diffusion model.

This paper presents a computational model of molecular diffusion through the interfollicular stratum corneum. Specifically, it extends an earlier two-dimensional microscopic model for the permeability in two ways: (1) a microporous leakage pathway through the intercellular lipid lamellae allows slow permeation of highly hydrophilic permeants through the tissue; and (2) the model yields explicit predictions of both lateral (D‾‖sc) and transdermal (D‾⊥sc) effective (average, homogenized) diffusivities of solutes within the tissue. We present here the mathematical framework for the analysis and a comparison of the predictions with experimental data on desorption of both hydrophilic and lipophilic solutes from human stratum corneum in vitro. Diffusion in the lipid lamellae is found to make the effective diffusivity highly anisotropic, with the predicted ratio D‾‖sc/D‾⊥sc ranging from 34 to 39 for fully hydrated skin and 150 to more than 1000 for partially hydrated skin. The diffusivities and their ratio are in accord with both experimental data and the results of mathematical analyses performed by others.

Long distance running increases plantar pressures beneath the metatarsal heads: a barefoot walking investigation of 200 marathon runners.

BACKGROUND: The growing popularity of endurance sports activities is associated with a growing number of metatarsal stress fractures in recreational runners. Excessive foot loading has been suggested as a potential cause for these problems [Bennell, K, Matheson G, Meeuwisse W, Brukner P. Risk factors for stress fractures. Sports Med 1999;28(2):91-122]. Therefore, the question arises whether long distance running affects foot loading characteristics like ground reaction forces and peak pressure in specific areas of the foot. PURPOSE: To investigate the effects of long distance running on plantar pressure patterns before and after a marathon race. STUDY DESIGN: Repeated measurements of recreational runners before and after a marathon race. METHODS: Two hundred participants of the third Muenster marathon, 2004, were measured before and after the race with plantar pressure measurements during barefoot walking on a capacitive platform. The ratio between forefoot and toe loading was calculated to assess a suggested loading shift between these areas. RESULTS: The results of the whole group of participants revealed a significant difference in foot loading characteristics before and after the race. Post-race peak pressure and impulse values were higher in the forefoot regions and reduced under the toes. CONCLUSIONS: The increased peak pressure under the metatarsal heads after the race indicates a load shift from the toes to the metatarsal heads. This suggests an increased loading of the metatarsal bones and could explain the increased incidence of metatarsal stress fractures in long distance runners.

Quantitative Analysis of Hepatitis C NS5A Viral Protein Dynamics on the ER Surface.

Exploring biophysical properties of virus-encoded components and their requirement for virus replication is an exciting new area of interdisciplinary virological research. To date, spatial resolution has only rarely been analyzed in computational/biophysical descriptions of virus replication dynamics. However, it is widely acknowledged that intracellular spatial dependence is a crucial component of virus life cycles. The hepatitis C virus-encoded NS5A protein is an endoplasmatic reticulum (ER)-anchored viral protein and an essential component of the virus replication machinery. Therefore, we simulate NS5A dynamics on realistic reconstructed, curved ER surfaces by means of surface partial differential equations (sPDE) upon unstructured grids. We match the in silico NS5A diffusion constant such that the NS5A sPDE simulation data reproduce experimental NS5A fluorescence recovery after photobleaching (FRAP) time series data. This parameter estimation yields the NS5A diffusion constant. Such parameters are needed for spatial models of HCV dynamics, which we are developing in parallel but remain qualitative at this stage. Thus, our present study likely provides the first quantitative biophysical description of the movement of a viral component. Our spatio-temporal resolved ansatz paves new ways for understanding intricate spatial-defined processes central to specfic aspects of virus life cycles.

Vacuum cushioned removable cast walkers reduce foot loading in patients with diabetes mellitus.

BACKGROUND: Diabetes mellitus is one of the most common diseases worldwide and the number of patients is expected to increase dramatically in future. Plantar ulceration is partly caused by high plantar pressures and a major complication in diabetic patients. PURPOSE: The aim of this study was to investigate the pressure-relieving effects of two vacuum orthoses in patients with diabetes mellitus. METHODS: Twenty patients with diabetes mellitus were included. They presented with plantar callosities but no ulceration. Exclusion criteria included the use of walking aids and other systemic diseases. Plantar pressure distribution was measured with sensor insoles (Pedar-X, Novel GmbH) during walking in two vacuum orthoses, a post-operative shoe and an off-the-shelf shoe as reference condition. Statistical analysis was conducted using Friedman and Wilcoxon signed-rank tests. RESULTS: Significant differences in plantar pressure distribution were found between the four walking conditions. The contact area increased in the midfoot with the vacuum orthoses. Maximum force and peak pressures showed a significant decrease under the rearfoot and forefoot and increased in the midfoot area during walking with both vacuum orthoses. The high-cut vacuum orthosis revealed equal pressure relief under the forefoot and significantly lower rearfoot pressures compared to the post-operative shoe. CONCLUSIONS: The vacuum orthoses demonstrated a comparable pressure-relieving efficacy under the forefoot to post-operative shoes. Using vacuum orthosis significantly benefited re-distribution of plantar pressure and the roll-over process. Clinical significance of the pressure-relieving efficacy could not be confirmed in this investigation and has to be addressed in further studies.

From "first" to "last" steps in life--pressure patterns of three generations.

BACKGROUND: The human foot has to bear loads during all kinds of bipedal locomotion throughout the whole life. Rapid developmental changes of foot morphology and foot function occur during the first years of walking. Furthermore, disease dependent modifications can also have an influence on plantar loading. Therefore, it is reasonable to assume that foot function will undergo changes in life. However, the main differences between the pressure patterns in young and elderly have not been well described. The aim of the study was to evaluate age-dependent pressure patterns in different age-related stages. METHODS: Hundred and four healthy humans of four different age groups were retrospectively analysed by means of plantar pressure measurements (toddlers: mean age 1.0 (SD 0.2) year; 7-year olds: 7.0 (SD 0.4) years; adults: 31.9 (SD 2.1) years; seniors: 68.7 (SD 3.2) years). The emed pressure platform was used to evaluate peak pressure, maximum force, contact time, contact area and arch index. FINDINGS: Significant differences were found for each parameter between almost every age group. The highest peak pressure values were observed for the seniors' (P<0.001). Peak pressures are low in toddlers (145 kPa), high in 7-year olds and adults (400-600 kPa) and even higher in elderly (> or =800 kPa). INTERPRETATION: Elderly adults can still be functionally mobile even if pressures are high. The results for the investigated age groups can be used as normative foot loading data to compare to pathological foot function.

Cluster analysis to classify gait alterations in rheumatoid arthritis using peak pressure curves.

OBJECTIVE: To detect gait alterations in rheumatoid arthritis (RA) patients using peak pressure curves (PPC) and normalized force curves (NFC) instead of clinical classification based on the health assessment questionnaire (HAQ). METHODS: Three RA groups--30 patients each--were classified according to their HAQ score. Cluster analysis based on a k-means algorithm was applied to PPCs and NFCs in order to classify RA patients with respect to amplitude and shapes of such gait parameters. RESULTS: The best gait pattern identification was obtained by clustering PPCs into three clusters. Peak pressures of the three identified patterns were 1169.5+/-99.4 kPa for cluster 1, 885.8+/-165.2 kPa for cluster 2 and 402.0+/-128.5 kPa for cluster 3 (statistically different, Student's t-test, p<0.001). 41 patients were included in cluster 3, 31 in cluster 2 and only 18 patients in cluster 1. Most RA3 patients--17 out of 30--showed low peak pressures and almost normal PPCs (cluster 3). Cluster 2, which incorporated altered PPCs, was mainly formed by RA1 and RA2 patients. CONCLUSIONS: PPC appears as a reliable gait parameter for a shape-based clustering algorithm. The proposed cluster analysis was proved to be reliable and the delivered classifications stable. The distribution of RA patients among the three identified PPC clusters showed only a partial agreement between clinical and functional classification, thus revealing the development of specific gait strategies related to the pathology more than to its clinical level of severity. This finding may be clinically relevant and support effective treatment of RA gait related pathologies.