A fabric-dependent fracture criterion for bone.

A fracture criterion for bone tissue is proposed. Bone material is considered to be anisotropic and its properties are described by invoking the concept of directional variation of porosity. The fracture criterion is expressed as a scalar-valued function of the stress tensor and it incorporates an orientation-dependent distribution of compressive/tensile strength. The proposed mathematical framework is applied to a numerical analysis of fracture in the proximal femur due to a fall from standing height. The risk of fracture is assessed in the context of two different porosity distributions, simulating a healthy and an osteoporotic bone.     

Arthritis susceptibility and the gut microbiome

Rheumatoid arthritis (RA) is an autoimmune disease with unknown etiology though both genetic and environmental factors have been suggested to be involved in its pathogenesis. While infections and other environmental factors (e.g. smoking) have been studied extensively and show some association, a direct link between all the factors has been difficult to prove. With the recent advances in technology, it has become possible to sequence the commensals that are residing in our gut. The gut microbiome may provide the missing link to this puzzle and help solve the mystery of many leaky gut syndromes. The gut commensals are involved in maintaining host immune homeostasis and function suggesting that they might be critical in altering the immune system, which leads to autoimmune diseases like RA. Mouse models support the role of the gut microbiota in predisposition to RA. If that is true, the power of gut-derived commensal can be harnessed to our benefit by generating a biomarker profile along with genetic factors to define individuals at risk and by altering the gut microbial composition using various means.     

Using map algebra to determine the mesoscale distribution of invasive plants: the case of <Emphasis Type="Italic">Celastrus orbiculatus</Emphasis> in Southern Illinois,USA

Since its introduction into North America in the late 19th century, Celastrus orbiculatus (Thumb.) has become a serious ecological threat to native ecosystems. Development of a method to accurately map the occurrence of invasive plants, including C. orbiculatus, would greatly assist in their assessment and control. Using an innovative map regression model, we predicted 85% of presence and absence of C. orbiculatus within our study area. We identify environmental characteristics associated with C. orbiculatus and demonstrate the use of this information to predict occurrence of C. orbiculatus across a broad area in Southern Illinois, USA. Presence and absence information were obtained at sample points within discrete areas of C. orbiculatus occurrence. Forest cover, elevation, slope gradient and aspect, soil pH and texture, distance to nearest road, and potential annual direct incident radiation were recorded for invaded and adjacent non-invaded areas. Presence of oak, elevation, slope gradient, soil pH, soil texture, and distance to road were significant factors associated with the presence or absence of C. orbiculatus. Probability of occurrence of C. orbiculatus was highest on gently sloping interfluves with successional forest canopy not dominated by oak, and less acidic, mesic soil. A logistic regression model was developed and extrapolated over a raster GIS data layer using map algebra to predict current invasion throughout the study area. The model correctly predicted at least 85% occurrence of C. orbiculatus. When combined with logistic regression, map algebra is a potentially powerful tool for evaluating the spatial distribution of invasive plants provided sound statistical principles are applied in extrapolating validated regression models.     

Effect of pituitary tumor MtT-F4 on carnitine levels in the serum,liver and heart of rats

Implantation of MtT-F4 tumor, a pituitary tumor that secretes large quantities of proclactin, growth hormone and ACTH, enhanced total liver carnitine 9-fold without alteration of the esterified to free carnitine ratio. This ratio increased and the concentration of free and total carnitine decreased in the serum of tumor bearing rats. Cardiac carnitine decreased (23%) when expressed on per unit organ weight but showed an increase on per 100 g body weight basis because of marked cardiac hypertrophy. Besides indicating that lipolytic products of pituitary affect liver carnitine, these results show that hyperlipidemia and fatty livers can exist at times despite elevation of liver carnitine content.     

Frequency,composition and mobility of Escherichia coli-derived transposable elements in holdings of plasmid repositories

By providing the scientific community with uniform and standardized resources of consistent quality, plasmid repositories play an important role in enabling scientific reproducibility. Plasmids containing insertion sequence elements (IS elements) represent a challenge from this perspective, as they can change the plasmid structure and function. In this study, we conducted a systematic analysis of a subset of plasmid stocks distributed by plasmid repositories (The Arabidopsis Biological Resource Center and Addgene) which carry unintended integrations of bacterial mobile genetic elements. The integration of insertion sequences was most often found in, but not limited to, pBR322-derived vectors, and did not affect the function of the specific plasmids. In certain cases, the entire stock was affected, but the majority of the stocks tested contained a mixture of the wild-type and the mutated plasmids, suggesting that the acquisition of IS elements likely occurred after the plasmids were acquired by the repositories. However, comparison of the sequencing results of the original samples revealed that some plasmids already carried insertion mutations at the time of donation. While an extensive BLAST analysis of 47 877 plasmids sequenced from the Addgene repository uncovered IS elements in only 1.12%, suggesting that IS contamination is not widespread, further tests showed that plasmid integration of IS elements can propagate in conventional Escherichia coli hosts over a few tens of generations. Use of IS-free E. coli hosts prevented the emergence of IS insertions as well as that of small indels, suggesting that the use of IS-free hosts by donors and repositories could help limit unexpected and unwanted IS integrations into plasmids.     

Physicochemical properties of bacterial pro-inflammatory lipids influence their interaction with apolipoprotein-derived peptides

Apolipoprotein-derived peptides have emerged as a promising candidate for the treatment of various inflammatory disease conditions. Multiple mechanisms have been proposed to explain the beneficiary effects of these peptides and prominent among them being high-affinity binding of peptides to pro-inflammatory lipids and facilitating their sequestration/metabolism/clearance in the body. Pro-inflammatory lipids differ considerably in their molecular structures, chemical compositions and physicochemical properties. Importance of the properties of the pro-inflammatory lipids in their ability to bind to apolipoprotein-derived peptides is not studied in details. In this study, we have characterized the interaction of synthetic peptides derived from human apolipoprotein E with lipopolysaccharide (LPS) and lipoteichoic acid (LTA), two potent bacterial pro-inflammatory lipids that differ considerably in their molecular structures and chemical compositions. Binding of the peptides to LPS and LTA was monitored by CD spectroscopy. Effect of the peptides on the biological activity of lipids was studied by monitoring the inhibition of LPS- or LTA-induced up-regulation of the inflammatory markers in the human blood cells. Physicochemical properties of lipid aggregates were determined by fluorescence spectroscopy and native PAGE. Our results show that physicochemical properties of LPS and LTA differ considerably and influence their interaction with apolipoprotein-derived peptides.