Modelling the effect of repositioning on the evolution of skeletal muscle damage in deep tissue injury

Deep tissue injury (DTI) is a localized area of tissue necrosis that originates in the subcutaneous layers under an intact skin and tends to develop when soft tissue is compressed for a prolonged period of time. In clinical practice, DTI is particularly common in bedridden patients and remains a serious issue in todays health care. Repositioning is generally considered to be an effective preventive measure of pressure ulcers. However, limited experimental research and no computational studies have been undertaken on this method. In this study, a methodology was developed to evaluate the influence of different repositioning intervals on the location, size and severity of DTI in bedridden patients. The spatiotemporal evolution of compressive stresses and skeletal muscle viability during the first 48 h of DTI onset was simulated for repositioning schemes in which a patient is turned every 2, 3, 4 or 6 h. The model was able to reproduce important experimental findings, including the morphology and location of DTI in human patients as well as the discrepancy between the internal tissue loads and the contact pressure at the interface with the environment. In addition, the model indicated that the severity and size of DTI were reduced by shortening the repositioning intervals. In conclusion, the computational framework presented in this study provides a promising modelling approach that can help to objectively select the appropriate repositioning scheme that is effective and efficient in the prevention of DTI.     

Control of glycolysis by glyceraldehyde-3-phosphate dehydrogenase in Streptococcus cremoris and Streptococcus lactis.

The decreased response of the energy metabolism of lactose-starved Streptococcus cremoris upon readdition of lactose is caused by a decrease of the glycolytic activity (B. Poolman, E. J. Smid, and W. N. Konings, J. Bacteriol. 169:1460-1468, 1987). The decrease in glycolysis is accompanied by a decrease in the activities of glyceraldehyde-3-phosphate dehydrogenase and phosphoglycerate mutase. The steady-state levels of pathway intermediates upon refeeding with lactose after various periods of starvation indicate that the decreased glycolysis is primarily due to diminished glyceraldehyde-3-phosphate dehydrogenase activity. Furthermore, quantification of the control strength exerted by glyceraldehyde-3-phosphate dehydrogenase on the overall activity of the glycolytic pathway shows that this enzyme can be significantly rate limiting in nongrowing cells.     

Analysis of interactions of signaling proteins with phage-displayed ligands by fluorescence correlation spectroscopy

Fluorescent correlation spectroscopy (FCS) was used to measure binding affinities of ligands to ligates that are expressed by phage-display technology. Using this method we have quantified the binding of the 14-3-3 signaling protein to artificial peptide ligand. As a ligand we used the R18 artificial peptide expressed as a fusion in the cpIII coat protein that is present in 3 to 5 copies in an M13 phage. Comparisons of binding affinities were made with free R18 ligands using FCS. The result showed a relatively high binding affinity for the phage-displayed R18 peptide compared with binding to free fluorescently labeled R18. Quantification was supported by titration of the phage numbers using atomic force microscopy (AFM). AFM was shown to accurately determine phage numbers in solution as a good alternative for electron microscopy. It was shown to give reliable data that correlated perfectly with those of the viable phage numbers determined by classical bacterial infection studies. In conclusion, a very fast and sensitive method for the selection of new peptide ligands or ligates based on a quantitative assay in solution has been developed.     

Sanctions and mutualism stability: when should less beneficial mutualists be tolerated?

Why do mutualists perform costly behaviours that benefit individuals of a different species? One of the factors that may stabilize mutualistic interactions is when individuals preferentially reward more mutualistic (beneficial) behaviour and/or punish less mutualistic (more parasitic) behaviour. We develop a model that shows how such sanctions provide a fitness benefit to the individuals that carry them out. Although this approach could be applied to a number of symbioses, we focus on how it could be applied to the legume‐rhizobia interaction. Specifically, we demonstrate how plants can be selected to supply preferentially more resources to (or be less likely to senesce) nodules that are fixing more N₂ (termed plant sanctions). We have previously argued that appreciable levels of N₂ fixation by rhizobia are only likely to be selected for in response to plant sanctions. Therefore, by showing that plant sanctions can also be favoured by natural selection, we are able to provide an explanation for the stability of the plant‐legume mutualism.     

Darwinian agriculture: when can humans find solutions beyond the reach of natural selection?

Progress in genetic improvement of crop yield potential has slowed since 1985. Simultaneously, more sustainable management of agricultural ecosystems is needed. A better understanding of natural selection can help solve both problems. We illustrate this point with two specific examples. First, the genetic legacy of crop plants has been refined by millions of years of natural selection, often driven by competition among plants. We therefore suggest that most simple, tradeoff-free options to increase competitiveness (e.g., increased gene expression, or minor modifications of existing plant genes) have already been tested by natural selection. Further genetic improvement of crop yield potential over the next decade will mainly involve tradeoffs, either between fitness in past versus present environments, or between individual competitiveness and the collective performance of plant communities. Eventually, we may develop the ability to predict the consequences of genetic alterations so radical that they have not yet been tested by natural selection. Second, natural selection acts mainly at the level of genes, individuals, and family groups, rather than ecosystems as a whole. Consequently, there is no reason to expect the structure of natural ecosystems (diversity, spatial, or temporal patterns) to be a reliable blueprint for agricultural ecosystems. Natural ecosystems are nonetheless an important source of information that could be used to improve agriculture.     

Discovery and in vivo evaluation of new melanocortin-4 receptor-selective peptides

The melanocortin-4 receptor (MC4R) is involved in several physiological processes, including body weight regulation and grooming behaviour in rats. It has also been suggested that the MC4R mediates the effects of melanocortin ligands on neuropathic pain. Selective compounds are needed to study the exact role of the MC4R in these different processes. We describe here the development and evaluation of new melanocortin compounds that are selective for the MC4R as compared with the other centrally expressed receptors, MC3R and MC5R. First, a library of 18 peptides, in which a melanocortin-based sequence was systematically point-mutated, was screened for binding to and activity on the MC3R, MC4R and MC5R. Compound Ac-Nle-Gly-Lys-D-Phe-Arg-Trp-Gly-NH(2) (JK1) appeared to be the most selective MC4R compound, based on affinity. This compound is 90- and 110-fold selective for the MC4R as compared to the MC3R and MC5R, respectively. Subsequent modification of JK1 yielded compound Ac-Nle-Gly-Lys-D-Nal(2)-Arg-Trp-Gly-NH(2) (JK7)(,) a selective MC4R antagonist with 34-fold MC4R/MC3R and 109-fold MC4R/MC5R selectivity. The compounds were active in vivo as determined in a grooming assay and a model for neuropathic pain in rats. Intravenous (i.v.) injections suggested that they were able to pass the blood-brain barrier.The compounds identified here will be useful in further research on the physiological roles of the MC4R.