Effects of clofibric acid on porcine hepatocytes: a new model for the study of peroxisomal metabolism

Data on interspecies peroxisomal metabolism are limited almost entirely to rodents. Species differences are likely and the application of rodent data to man is questionable. An alternative to rodent models is desirable. Porcine tissue offers such an alternative and was explored. Porcine hepatocyte organelles were separated by isopycnic sucrose gradient centrifugation from livers of 6-month-old Yorkshire pigs. The presence of a peroxisomal palmityl-CoA oxidizing pathway, peroxisomal superoxide dismutase (SOD), and a peroxisomal NAD:aldehyde dehydrogenase (ALDH) with high K[subscript] m for acetaldehyde was demonstrated. Peroxisomal palmitate oxidizing capacity was found to be equal to that of the surviving mitochondria. The high K[subscript] misozyme of ALDH was mainly located in the mitochondria (54%), with a significant portion in the peroxisomes (32%). Remaining activity is distributed among the microsome (8.3%) and cytosol (4.6%). The low K[subscript] m isozyme was confined almost exclusively to the mitochondria. ALDH may exist in the peroxisome as a detoxification mechanism and contribute to shorter half-lives of reactive aldehydes in the cell. SOD was distributed among the peroxisomes (10%), mitochondria (20%), and cytosol (70%). SOD may scavenge reactive species of oxygen produced through peroxisomal [beta]-oxidation. A protocol for the isolation and growth of viable porcine hepatocytes is reported. The effects of clofibric acid on isolated porcine hepatocytes was investigated. Activity of selected enzymes from intact tissue were compared to isolated cells not exposed to the drug. Catalase activity was lower in isolated cells, but NAD:glutamate dehydrogenase, peroxisomal [beta]-oxidation, mitochondrial [beta]-oxidation, aldehyde dehydrogenase, and NADPH:cytochrome c reductase were similar. Isolated hepatocytes were exposed to clofibric acid concentrations ranging from 0 to 3.0 mM. Catalase, mitochondrial [beta]-oxidation, and peroxisomal [beta]-oxidation were not affected by treatments. Treatments did result in a 40% increase in protein content, a 900% increase in NADPH:cytochrome c reductase, a 400% increase in both isozymes of aldehyde dehydrogenase, and a 40% induction of superoxide dismutase activity. Responses were significantly quadratic. Porcine hepatocyte peroxisomes appear to differ significantly from those of rodents. Our data support the hypothesis that phylogenetically higher animals are different from rodents in peroxisome metabolism. Interspecies differences in metabolism is discussed

A micromechanical fracture analysis to investigate the effect of healing particles on the overall mechanical response of a self-healing particulate composite

A computational fracture analysis is conducted on a self‐healing particulate composite employing a finite element model of an actual microstructure. The key objective is to quantify the effects of the actual morphology and the fracture properties of the healing particles on the overall mechanical behaviour of the (MoSi2) particle‐dispersed Yttria Stabilised Zirconia (YSZ) composite. To simulate fracture, a cohesive zone approach is utilised whereby cohesive elements are embedded throughout the finite element mesh allowing for arbitrary crack initiation and propagation in the microstructure. The fracture behaviour in terms of the composite strength and the percentage of fractured particles is reported as a function of the mismatch in fracture properties between the healing particles and the matrix as well as a function of particle/matrix interface strength and fracture energy. The study can be used as a guiding tool for designing an extrinsic self‐healing material and understanding the effect of the healing particles on the overall mechanical properties of the material

Computational multiscale modeling of steels assisted by transformation-induced plasticity

The contribution of the martensitic transformation to the overall stress-strain response of a multiphase steel assisted by a transformation- induced plasticity effect is analyzed in detail. A recently-developed multiscale transformation model is combined with a plasticity model to simulate the response of a three-dimensional grain of retained austenite embedded in a ferrite-based matrix. Results show that the effective hardening behavior of the material depends strongly on the grain orientation and, to a lesser extent, on the grain size

A cohesive-zone crack healing model for self-healing materials

A cohesive zone-based constitutive model, originally developed to model fracture, is extended to include a healing variable to simulate crack healing processes and thus recovery of mechanical properties. The proposed cohesive relation is a composite-type material model that accounts for the properties of both the original and the healing material, which are typically different. The constitutive model is designed to capture multiple healing events, which is relevant for self-healing materials that are capable of generating repeated healing. The model can be implemented in a finite element framework through the use of cohesive elements or the extended finite element method (XFEM). The resulting numerical framework is capable of modeling both extrinsic and intrinsic self-healing materials. Salient features of the model are demonstrated through various homogeneous deformations and healing processes followed by applications of the model to a self-healing material system based on embedded healing particles under non-homogeneous deformations. It is shown that the model is suitable for analyzing and optimizing existing self-healing materials or for designing new self-healing materials with improved lifetime characteristics based on multiple healing events

Recent advances in biomedical applications of accelerator mass spectrometry

After publication of our article, it was noted that we inadvertently failed to include the complete list of authors. The full list, including co-authors, has now been added and the Authors' contributions and Competing interests sections modified accordingly

Cohesive-zone modelling of crack nucleation and propagation in particulate composites

A cohesive-zone approach is used to study the interaction between an approaching crack and a particle embedded in a matrix material as a function of the mismatch in elastic and fracture properties. Crack-particle interaction is a crucial issue governing fracture behavior of particle-dispersed materials. Special attention is given in the present work to the effect of the mismatch in fracture properties, namely fracture strength and energy, which has not been fully-explored in the literature. Based on extensive finite element simulations using cohesive elements, the basic fracture mechanisms governing the crack-particle interaction are identified, namely particle fracture, crack deflection and interface debonding. The details of the cracking sequences are elucidated and the role of secondary cracks is highlighted. The effect of pre-existing flaws on the fracture behavior is analyzed both for flaws inside the particle as well as flaws on the particle/matrix interface. Several flaw configurations in terms of size, orientation and location are considered. In addition, the effect of the mismatch between the matrix and the interface fracture properties is also considered for a wide range of adhesive characteristics. The results of the simulations are summarized in the form of several fracture maps for different configurations, whereby the main fracture mechanisms are identified in regions inside a two-dimensional space of strength and toughness mismatch between the particle and the matrix. It is observed that the mismatch in the fracture properties usually plays a more dominant role on the crack trajectory than the mismatch in elastic properties in a particle-dispersed system. Pre-existing flaws/defects in the particle and the interface are found to be one of the principal controlling factors that alter the crack propagation characteristics. These results can be used as a guideline for designing particulate composite system with a preferred fracture mechanism, namely matrix cracking, interface debonding or particle fracture

Accelerator mass spectrometry as a bioanalytical tool for nutritional research

Accelerator Mass Spectrometry is a mass spectrometric method of detecting long-lived radioisotopes without regard to their decay products or half-life. The technique is normally applied to geochronology, but recently has been developed for bioanalytical tracing. AMS detects isotope concentrations to parts per quadrillion, quantifying labeled biochemicals to attomole levels in milligram- sized samples. Its advantages over non-isotopeic and stable isotope labeling methods are reviewed and examples of analytical integrity, sensitivity, specificity, and applicability are provided

Statistical Analysis of Variation in the Human Plasma Proteome

Quantifying the variation in the human plasma proteome is an essential prerequisite for disease-specific biomarker detection. We report here on the longitudinal and individual variation in human plasma characterized by two-dimensional difference gel electrophoresis (2-D DIGE) using plasma samples from eleven healthy subjects collected three times over a two week period. Fixed-effects modeling was used to remove dye and gel variability. Mixed-effects modeling was then used to quantitate the sources of proteomic variation. The subject-to-subject variation represented the largest variance component, while the time-within-subject variation was comparable to the experimental variation found in a previous technical variability study where one human plasma sample was processed eight times in parallel and each was then analyzed by 2-D DIGE in triplicate. Here, 21 protein spots had larger than 50% CV, suggesting that these proteins may not be appropriate as biomarkers and should be carefully scrutinized in future studies. Seventy-eight protein spots showing differential protein levels between different individuals or individual collections were identified by mass spectrometry and further characterized using hierarchical clustering. The results present a first step toward understanding the complexity of longitudinal and individual variation in the human plasma proteome, and provide a baseline for improved biomarker discovery

Elucidating the effect of cohesive zone length in fracture simulations of particulate composites

The influence of the cohesive zone length on the crack driving force is quantified and analyzed in a representative system of particles dispersed in a matrix of a composite material. For heterogeneous material systems, e.g. particulate composites, it is known that as a crack approaches the particles, the crack driving force may increase (shielding) or decrease (anti-shielding) depending on the relative stiffness of the particles. These results have been established in numerous studies using the classical linear elastic fracture mechanics approach (LEFM). The cohesive zone method (CZM) introduces a length scale parameter, referred to as the cohesive zone (or fracture process zone) length scale, into the formulation of fracture mechanics. It is generally established that fracture mechanics predictions using the CZM are similar to those obtained using LEFM in the limit case where the process zone is very small relative to a suitable characteristic dimension of the problem. However, the influence of the length scale parameter has not been clearly demonstrated for crack propagation in a heterogeneous material system, especially when the cohesive zone length is not negligible. By considering a simple crack-particle-matrix system, it is shown that, in addition to the elastic properties, the process zone length scale parameter exhibits a critical influence on the crack driving force. For this study, the concept of configurational forces is utilized and the eXtended Finite Element Method (XFEM) is employed as a tool to simulate crack propagation. Through numerical simulations, it is shown that (i) the magnitude of the driving force vector directly depends on the length scale parameter and (ii) the direction of the driving force is largely influenced by the presence of a cohesive zone. This, in turn, alters the crack trajectory in the particulate system if the criterion for the direction of crack propagation depends on the orientation of the driving force vector. Towards this end, two different criteria for direction of crack propagation, namely maximum principal stress and maximum energy dissipation, are compared in the presence of a cohesive zone and the results are reported. The study reveals the crucial influence of the inherent length scale associated with the cohesive zone method when applied to crack propagation in particulate composite systems and elucidates important differences when comparing predictions from distinct theories of fracture mechanics