SHEDS-HT: an integrated probabilistic exposure model for prioritizing exposures to chemicals with near-field and dietary sources

United States Environmental Protection Agency (USEPA) researchers are developing a strategy for high-throughput (HT) exposure-based prioritization of chemicals under the ExpoCast program. These novel modeling approaches for evaluating chemicals based on their potential for biologically relevant human exposures will inform toxicity testing and prioritization for chemical risk assessment. Based on probabilistic methods and algorithms developed for The Stochastic Human Exposure and Dose Simulation Model for Multimedia, Multipathway Chemicals (SHEDS-MM), a new mechanistic modeling approach has been developed to accommodate high-throughput (HT) assessment of exposure potential. In this SHEDS-HT model, the residential and dietary modules of SHEDS-MM have been operationally modified to reduce the user burden, input data demands, and run times of the higher-tier model, while maintaining critical features and inputs that influence exposure. The model has been implemented in R; the modeling framework links chemicals to consumer product categories or food groups (and thus exposure scenarios) to predict HT exposures and intake doses. Initially, SHEDS-HT has been applied to 2507 organic chemicals associated with consumer products and agricultural pesticides. These evaluations employ data from recent USEPA efforts to characterize usage (prevalence, frequency, and magnitude), chemical composition, and exposure scenarios for a wide range of consumer products. In modeling indirect exposures from near-field sources, SHEDS-HT employs a fugacity-based module to estimate concentrations in indoor environmental media. The concentration estimates, along with relevant exposure factors and human activity data, are then used by the model to rapidly generate probabilistic population distributions of near-field indirect exposures via dermal, nondietary ingestion, and inhalation pathways. Pathway-specific estimates of near-field direct exposures from consumer products are also modeled. Population dietary exposures for a variety of chemicals found in foods are combined with the corresponding chemical-specific near-field exposure predictions to produce aggregate population exposure estimates. The estimated intake dose rates (mg/kg/day) for the 2507 chemical case-study spanned 13 orders of magnitude. SHEDS-HT successfully reproduced the pathway-specific exposure results of the higher-tier SHEDS-MM for a case-study pesticide and produced median intake doses significantly correlated (p<0.0001, R2=0.39) with medians inferred using biomonitoring data for 39 chemicals from the National Health and Nutrition Examination Survey (NHANES). Based on the favorable performance of SHEDS-HT with respect to these initial evaluations, we believe this new tool will be useful for HT prediction of chemical exposure potential.

Mechanical properties of morcellised bone graft with the addition of hydroxyapatite

Mixtures of morcellised bone graft (MBG) and hydroxyapatite (HA) are frequently used in revision arthroplasty surgery. However, the changes in the mechanical properties from adding HA to MBG are unknown. This study used a uniaxial compression test to replicate impaction bone grafting and subsequent early postoperative weightbearing to investigate the effect of adding different proportion of HA to MBG. To achieve this aim, human MBG was subjected to increasing impaction forces and the apparent stiffness and creep for each stress level determined. Subsequently, increasing proportions porous and non porous HA were added to the MBG. The major findings were that the apparent stiffness for MBG increased and the associated creep decreased both with the application of increasing stress and with the addition of increasing proportions of HA. In conclusion, greater proportions of HA in the graft mixture improved the mechanical response compared with MBG impacted under the same force. This improvement replicated the properties of pure MBG under high axial stress. This study indicates that graft mixtures of MBG and HA can be tailormade for patients. The need for less impaction force in MBG:HA mixtures to obtain the same properties as pure MBG may decrease the risk of intraoperative fracture.

Limited plasticity in the phenotypic variance-covariance matrix for male advertisement calls in the black field cricket, Teleogryllus commodus

Phenotypic integration and plasticity are central to our understanding of how complex phenotypic traits evolve. Evolutionary change in complex quantitative traits can be predicted using the multivariate breeders' equation, but such predictions are only accurate if the matrices involved are stable over evolutionary time. Recent study, however, suggests that these matrices are temporally plastic, spatially variable and themselves evolvable. The data available on phenotypic variance-covariance matrix (P) stability are sparse, and largely focused on morphological traits. Here, we compared P for the structure of the complex sexual advertisement call of six divergent allopatric populations of the Australian black field cricket, Teleogryllus commodus. We measured a subset of calls from wild-caught crickets from each of the populations and then a second subset after rearing crickets under common-garden conditions for three generations. In a second experiment, crickets from each population were reared in the laboratory on high- and low-nutrient diets and their calls recorded. In both experiments, we estimated P for call traits and used multiple methods to compare them statistically (Flury hierarchy, geometric subspace comparisons and random skewers). Despite considerable variation in means and variances of individual call traits, the structure of P was largely conserved among populations, across generations and between our rearing diets. Our finding that P remains largely stable, among populations and between environmental conditions, suggests that selection has preserved the structure of call traits in order that they can function as an integrated unit.

Whole Genome Methylation Scanning Based on phi29 Polymerase Amplification

Identifying differences in DNA methylation is critical to understanding how epigenetics influences gene expression during processes such as development. Here, we propose a method that employs a single, methylation-sensitive restriction endonuclease of choice, to produce discrete pools of methylated and unmethylated DNA from the same sample. A pool of restriction fragments representing unmethylated regions of the genome is first obtained by digestion with a methylation-sensitive endonuclease. The restriction-digested DNA is then concatamerized in the presence of stuffer-adaptor DNA, which prevents interference from originally unmethylated DNA by blocking the ends of the restriction fragments. The concatamerized DNA is amplified by phi29 polymerase to remove methylation marks, and again digested with the same endonuclease to produce a pool of DNA fragments representing methylated portions of the genome. The two pools of DNA fragments thus obtained can be analyzed by end-sequencing or hybridization to a genomic array. In this report we detail a proof of concept experiment that demonstrates the feasibility of our method.

The effect of the addition of hydroxyapatite graft substitutes upon the hoop strain and subsequent subsidence of a femoral model during impaction bone grafting

Impaction bone grafting using morcellised allograft can successfully restore bone stock in revision surgery. However, concerns exist regarding supply of bone and transmission of infection. Bone-graft extenders, such as tricalcium phosphate (TCP) and hydroxyapatite (HA), are used to minimise the use of donor bone. However, concerns exist around a reported increased risk of femoral fracture during impaction bone grafting with a 1:1 mixture of TCP/HA and morcellised bone graft (MBG) during impaction grafting in human cadaveric femora. Using a sawbones model, it was evaluated whether there was increased femoral cortical strain with a HA:MBG mixture during impaction grafting compared to MBG impacted at the same and a greater force. Subsequently the subsidence behaviour of the different graft mixes was compared by using a loaded femoral stem in an endurance test. It was demonstrated that the femora with the MBG:HA graft had greater cortical hoop stresses but improved subsidence behaviour compared to a graft composed of pure MBG impacted at the same force.

Much more than a ratio: multivariate selection on female bodies

Studies of the attractiveness of female bodies have focussed strongly on the waist, hips and bust, but sexual selection operates on whole phenotypes rather than the relative proportions of just two or three body parts. Here, we use body scanners to extract computer-generated images of 96 Chinese women's bodies with all traits unrelated to body shape removed. We first show that Chinese and Australian men and women rate the attractiveness of these bodies the same. We then statistically explore the roles of age, body weight and a range of length and girth measures on ratings of attractiveness. Last, we use nonlinear selection analysis, a statistical approach developed by evolutionary biologists to explore the interacting effects of suites of traits on fitness, to study how body traits interact to determine attractiveness. Established proxies of adiposity and reproductive value, including age, body mass index and waist-to-hip ratio, were all correlated with attractiveness. Nonlinear response surface methods using the original traits consistently outperform all of these indices and ratios, suggesting that indices of youth and abdominal adiposity tell only part of the story of body attractiveness. In particular, our findings draw attention to the importance of integration between abdominal measures, including the bust, and the length and girth of limbs. Our results provide the most comprehensive analysis to date of the effect of body shape and fat deposition on female attractiveness.