Vibrational characteristics of bone fracture and fracture repair: application to excised rat femur

BACKGROUND: The vibrational characteristics of any object are directly dependent on the physical properties of that object. Therefore, changing the physical properties of an object will cause the object to adopt changed natural frequencies. A fracture in a bone results in the loss of mechanical stability of the bone. This change in mechanical properties of a bone should result in a change of the resonant frequencies of that bone. A vibrational method for bone evaluation has been introduced. METHOD OF APPROACH: This method uses the radiation force of focused amplitude-modulated ultrasound to exert a vibrating force directly, and remotely, on a bone. The vibration frequency is varied in the range of interest to induce resonances in the bone. The resulting bone motion is recorded and the resonance frequencies are determined. Experiments are conducted on excised rat femurs and resonance frequencies of intact, fractured, and bonded (simulating healed) bones are measured. RESULTS: The experiments demonstrate that changes in the resonance frequency are indicative of bone fracture and healing, i.e., the fractured bone exhibits a lower resonance frequency than the intact bone, and the resonance frequency of the bonded bone approaches that of the intact bone. CONCLUSION: It is concluded that the proposed radiation force method may be used as a remote and noninvasive tool for monitoring bone fracture and healing process, and the use of focused ultrasound enables one to selectively evaluate individual bones.     

Efforts to develop a cultured sponge cell line: revisiting an intractable problem

Residents of the marine environment, sponges (Porifera) have the ability to produce organic compounds known as secondary metabolites, which are not directly involved in the normal growth, development, or reproduction of an organism. Because of their sessile nature, the production of these bioactive compounds has been interpreted as a functional adaptation to serve in an important survival role as a means to counter various environmental stress factors such as predation, overgrowth by fouling organisms, or competition for limited space. Regardless of the reasons for this adaptation, a variety of isolated compounds have already proven to demonstrate remarkable anticancer, fungicidal, and antibiotic properties. A major obstacle to the isolation and production of novel compounds from sponges is the lack of a large, reliable source of sponge material. Sponge collection from the sea would be environmentally detrimental to the already stressed and sparse sponge populations. Sponge production in an aquaculture setting might appear to be an ideal alternative but would also be cost-ineffective and sponge growth is extremely slow. A third approach involves the development of a sponge cell culture system capable of producing the necessary cell numbers to harvest for research purposes as well as for the eventual commercial-scale production of promising bioactive compounds. Unfortunately, little progress has been made in this direction other than the establishment of temporary cultures containing aggregates and fragments of cells. One impediment toward successful sponge cell culture might be ascribed to a lack of published knowledge of failed methodologies, and thus, time and effort is wasted on continued reinvention of the same methods and procedures. Consequently, we have undertaken here to chart some of our unsuccessful research efforts, our methodology, and results to provide the sponge research community with knowledge to assist them to better avoid taking the same failed pathways.     

Recommended protocols based on a survey of current practice in genotoxicity testing laboratories: study design

The most commonly used genotoxicity assays for cultured mammalian cells are mammalian cell mutagenesis, chromosome aberrations/SCE, hepatocyte UDS, and cell transformation. Since their inception, protocols for these assays have been modified in various laboratories. It has been observed that minor but potentially significant method modifications frequently remain unpublished (Swierenga et al., 1983) but should be considered in the development of recommended protocols. The present study was undertaken to determine the current 'state of the art' for these tests. Detailed questionnaires on culture conditions and testing protocols for both stock and test cell populations were designed with the assistance of an international advisory committee and sent to all research and contract laboratories that could be readily identified in Canada, U.S.A. and Europe. Responses from 425 completed questionnaires were analyzed to determine the most commonly used approach and modifications for each procedural step. As expected, the results show a large degree of interlaboratory variation. Detailed protocols for conducting each assay have been prepared and include: stepwise instructions, precautionary measures and practical solutions to common problems associated with each assay; recipes for media and solutions; formulas for quantifying genotoxic responses; reference lists of related assays; guidelines for interpretation; and discussions of the applications, advantages and disadvantages of each test.     

Cardiopulmonary exercise testing in congenital heart disease: equipment and test protocols

Cardiopulmonary exercise testing (CPET) in paediatric cardiology differs in many aspects from the tests as performed in adult cardiology. Children's cardiovascular responses during exercise testing present different characteristics, particularly oxygen uptake, heart rate and blood pressure response, which are essential in interpreting haemodynamic data. Diseases that are associated with myocardial ischaemia are very rare in children. The main indications for CPET in children are evaluation of exercise capacity and the identification of exercise-induced arrhythmias. In this article we will review exercise equipment and test protocols for CPET in children with congenital heart disease. (Neth Heart J 2009;17:339–44.)     

Microautophagy in mammalian cells: revisiting a 40-year-old conundrum

The term microautophagy was first used in 1966 by de Duve and Wattiaux and subsequently applied, over the following two decades, to processes described in mammalian cells and involving the presence of lysosome-like organelles having multiple vesicles trapped in their lumen ("multivesicular lysosomes"). Concurrently, many studies suggested a view of microautophagy where the lysosomal membrane was either invaginated or projected arm-like protrusions to sequester cytosolic constituents into intralysosomal vesicles. Although microautophagy in mammalian cells has been traditionally considered as a form of autophagy constitutively active in the turnover of long-lived proteins, little is known about the mechanism and regulation of cargo selection. The lack of specific approaches to directly detect microautophagy in mammalian systems, aside from electron microscopy, is the major current limitation to addressing its physiological role(s) and possible contribution to particular disease states. In this review we consider the current state of knowledge about microautophagic processes. We examine some of the main characteristics of microautophagy in yeast with a view to assessing their relevance for our understanding of microautophagy in mammalian cells.     

Model testing, prediction and experimental protocols in neuroscience: A case study

In their theoretical and experimental reflections on the capacities and behaviours of living systems, neuroscientists often formulate generalizations about the behaviour of neural circuits. These generalizations are highly idealized, as they omit reference to the myriads of conditions that could perturb the behaviour of the modelled system in real-world settings. This article analyses an experimental investigation of the behaviour of place cells in the rat hippocampus, in which highly idealized generalizations were tested by comparing predictions flowing from them with real-world experimental results. The aim of the article is to identify (1) under what conditions even single prediction failures regarding the behaviour of single cells sufficed to reject highly idealized generalizations, and (2) under what conditions prima facie counter-examples were deemed to be irrelevant to the testing of highly idealized generalizations. The results of this analysis may contribute to understanding how idealized models are tested experimentally in neuroscience and used to make reliable predictions concerning living systems in real-world settings.     

Pulsed electromagnetic field treatment failure in radius non-united fracture healing

Pulsed electromagnetic field (PEMF) treatment is a non-invasive technique which has wide use in promoting healing of delayed union and non-union of bone. According to reports in the literature, PEMF has a ‘success’ of about 70%, but with no clear-cut reason to explain the failures. Our tests were carred out on 11 patients with radius non-unions and delayed unions; the results suggest that PEMF failure is associated with implanted metallic plates. In our view, this can be explained because the conducting plates create a uniform bone biopotential around the fracture and thus prevent the negative polarization which stimulates callus formation. Although further controlled and randomized clinical tests are needed, our results indicate that it may be necessary to remove the plates before PEMF application.     

Validation of an HR-pQCT-based homogenized finite element approach using mechanical testing of ultra-distal radius sections

Osteoporotic (Colles’ type) fractures of the distal radius occur relatively early in lifetime and could estimate risk of fracture of other, more endangered anatomical sites. High-resolution peripheral quantitative computed tomography (HR-pQCT) based micro finite element (μFE) analysis was shown to better predict fracture load of the distal radius than densitometry or histomorphometric measures. As an alternative to μFE, homogenization-based FE (hFE) approach may provide at least equivalent predictive power with reduced computational needs. The aim of this study was to validate the hFE approach with compression tests of 25 distal radius sections extracted at the location which is relevant in Colles’ fractures. HR-pQCT-based input parameters of the hFE models were calibrated with respect to μCT. HR-pQCT-based hFE models were then built and their ability to predict experimental stiffness and ultimate load was compared to those of the density-based parameters, histomorphometric indices and μFE models assessed from the same input images. Bone mineral content was the best non-FE-based predictor (R ² = 0.86) of ultimate force. Both FE methods were not only the strongest predictors, but provided quantitatively correct fracture loads. The calibrated hFE approach provided closely as strong prediction (R ² = 0.94) as μFE (R ² = 0.95), but the former was computationally cheaper. The results of this validation study suggest that FE simulation could be used as an efficient and precise tool to predict Colles’ fracture load.     

Yeast (ADPribosyl)ation: revisiting a controversial question

The controversy about the occurrence of an (ADPribosyl)ating activity in yeast is still standing up. Here we discuss this topic on the basis of results obtained with classic experiments proposed over years as basis to characterize an (ADPribosyl)ation system in any organism. Independent results obtained in two different laboratories were in line with each other and went towards the occurrence of an active (ADPribosyl)ating system in Saccharomyces cerevisiae. In fact data collected from nuclear preparations of cultured cells matched those from baker's yeast and lyophilized yeast cells. Yeast (ADPribosyl)ating enzyme is a protein of 80-90 kDa, as determined by electrophoresis on polyacrylamide gel in sodium dodecyl sulphate, followed by immunoblotting with antibodies against anti-poly(ADPribose) polymerase catalytic site. It synthesizes products, that, after digestion with phosphodiesterase, co-migrates mainly with phosphoribosyl adenosine monophosphate after thin layer chromatography on silica gel plate.     

Simulating distal radius fracture strength using biomechanical tests: a modeling study examining the influence of boundary conditions

Distal radius fracture strength has been quantified using in vitro biomechanical testing. These tests are frequently performed using one of two methods: (1) load is applied directly to the embedded isolated radius or (2) load is applied through the hand with the wrist joint intact. Fracture loads established using the isolated radius method are consistently 1.5 to 3 times greater than those for the intact wrist method. To address this discrepancy, a validated finite element modeling procedure was used to predict distal radius fracture strength for 22 female forearms under boundary conditions simulating the isolated radius and intact wrist method. Predicted fracture strength was highly correlated between methods (r = 0.94; p < 0.001); however, intact wrist simulations were characterized by significantly reduced cortical shell load carriage and increased stress and strain concentrations. These changes resulted in fracture strength values less than half those predicted for the isolated radius simulations (2274 ± 824 N for isolated radius, 1124 ± 375 N for intact wrist; p < 0.001). The isolated radius method underestimated the mechanical importance of the trabecular compartment compared to the more physiologically relevant intact wrist scenario. These differences should be borne in mind when interpreting the physiologic importance of mechanical testing and simulation results.     

Replicating instabilities in yeast: occurrence in different mutational systems

Summary Following mutagenesis of yeast cells with nitrosoguanidine, primary mosaic colonies exhibiting prototrophic/auxotrophic phenotypes were obtained. Upon replating of these primary mosaics, numerous secondary mosaics were present in the progeny. This study shows that replicating instabilities occur at many different loci within the Schizosaccharomyces pombe genome. In addition, the ade-1 gene of Saccharomyces cerevisiae (causing red pigmentation) was used to show that the phenomenon also occurs in this yeast.NRCC#240/8     

Wolbachia detection: an assessment of standard PCR protocols

Wolbachia is a large monophyletic genus of intracellular bacteria, traditionally detected using PCR assays. Its considerable phylogenetic diversity and impact on arthropods and nematodes make it urgent to assess the efficiency of these screening protocols. The sensitivity and range of commonly used PCR primers and of a new set of 16S primers were evaluated on a wide range of hosts and Wolbachia strains. We show that certain primer sets are significantly more efficient than others but that no single protocol can ensure the specific detection of all known Wolbachia infections.     

Kinetic Origin of Heredity in a Replicating System with a Catalytic Network

The origin of heredity is studied as a recursive state in a replicatingprotocell consisting of many molecule species in mutually catalyzingreaction networks. Protocells divide when the number of molecules, increasing due to replication, exceeds a certain threshold. We study how the chemicals in a catalytic network can form recursive production states in the presence of errors in the replication process. Depending on the balance between the total number of molecules in a cell and the number of molecule species, we have found three phases; a phase without a recursive production state, a phase with itinerancy over a few recursive states, and a phase with fixedrecursive production states. Heredity is realized in the latter two phaseswhere molecule species that are population-wise in the minority are preserved and control the phenotype of the cell. It is shown that evolvability is realized in the itinerancy phase, where a change in the number of minority molecules controls a change of the chemical state.     

Coexistence theory in the Cape Floristic Region: revisiting an example of leaf niches in the Proteaceae

Competition in plant communities is often a contentious issue because the mechanisms of competitive interactions are not obvious. We sought evidence that Proteaceae communities are competing along two leaf niche axes as observed in a previous study. Two functional characters, leaf size and leaf shape were measured on numerous individuals per species per plot of six communities from two different regions. Patterns of overdispersion along these leaf trait axes between species were observed, similar to the earlier study. The observed results were compared with the patterns expected under a null model using standard and novel indices to test the significance of trait dispersion between species within a plot. Competition and niche differentiation in the observed plots were not supported as the observed trait overlaps were not significantly different from the null expectation. Our results do not support the theory that Proteaceae communities compete along the two proposed functional leaf traits.