Cancer risk models and preselection for screening

Objective: The invitation to population screening is based on age criteria in many countries. Screening is not offered to younger or older participants, because the benefits in these age groups do not outweigh the harms. One could argue that it is not so much age that determines the benefits but the risk of developing preclinical and treatable cancer. Cancer risk varies with age but is also affected by other factors. Methods: We performed a systematic review for risk models for the three types of cancer for which population screening programs exist: breast, cervical and colon cancer. We used an evaluation scheme that distinguishes three phases of model development: model derivation, validation and impact analysis. Data were collected in August 2010. Results: We identified two colorectal, four breast and three cervix cancer risk models. One colorectal, four breast and none of the cervix cancer models have been externally validated. We could not identify evaluations of the impact on population screening effectiveness. Conclusion: We conclude that risk models for the pre-selection of screening have been developed. These models could improve the pre-selection for screening, help in making personal decisions about participation, and reduce adverse effects of population screening. The validity of this hypothesis, as well as practicalities and issues of equity and reliability, have to be tested in further studies.     

Inhibition of firefly luciferase by general anesthetics: effect on in vitro and in vivo bioluminescence imaging

Bioluminescence imaging is routinely performed in anesthetized mice. Often isoflurane anesthesia is used because of its ease of use and fast induction/recovery. However, general anesthetics have been described as important inhibitors of the luciferase enzyme reaction.

Aim

To investigate frequently used mouse anesthetics for their direct effect on the luciferase reaction, both in vitro and in vivo.

Materials and Methods

isoflurane, sevoflurane, desflurane, ketamine, xylazine, medetomidine, pentobarbital and avertin were tested in vitro on luciferase-expressing intact cells, and for non-volatile anesthetics on intact cells and cell lysates. In vivo, isoflurane was compared to unanesthetized animals and different anesthetics. Differences in maximal photon emission and time-to-peak photon emission were analyzed.

Results

All volatile anesthetics showed a clear inhibitory effect on the luciferase activity of 50% at physiological concentrations. Avertin had a stronger inhibitory effect of 80%. For ketamine and xylazine, increased photon emission was observed in intact cells, but this was not present in cell lysate assays, and was most likely due to cell toxicity and increased cell membrane permeability. In vivo, the highest signal intensities were measured in unanesthetized mice and pentobarbital anesthetized mice, followed by avertin. Isoflurane and ketamine/medetomidine anesthetized mice showed the lowest photon emission (40% of unanesthetized), with significantly longer time-to-peak than unanesthetized, pentobarbital or avertin-anesthetized mice. We conclude that, although strong inhibitory effects of anesthetics are present in vitro, their effect on in vivo BLI quantification is mainly due to their hemodynamic effects on mice and only to a lesser extent due to the direct inhibitory effect.     

Increased risk of respiratory tract infections in children with Down syndrome: the consequence of an altered immune system

Down syndrome (DS) is the most common chromosomal abnormality among live-born infants. Respiratory tract infections are the most important cause of mortality in individuals with DS at all ages. In recent decades several studies have been performed to elucidate abnormalities of the immune system in DS. However, the influence of the immune system on the occurrence of respiratory tract infections in these children has never been reviewed.     

Prolonged clonal growth: escape route or route to extinction?

Many plant species have the capability to reproduce sexually as well as clonally. The balance between clonal reproduction and sexual reproduction varies between different species. It was estimated that 66.5% of all central European flora may form independent but genetically identical daughter plants. Also within species there is great variation in the ratio clonal/sexual reproduction. Clonal reproduction can be considered as an alternative life cycle loop that allows persistence of a species in the absence of the ability to complete the normal life cycle (i.e. seed production, germination and recruitment). Plant populations exhibiting prolonged clonal growth have been referred to as 'remnant populations'. A remnant population in general is defined as "a population capable of persistence during extended time periods despite a negative population growth rate (λ<1) due to longlived life stages and life cycles, including loops, that allow population persistence without completion of the whole life cycle". Here we argue that prolonged and nearly exclusive clonal growth through environmental suppression of sexual reproduction can ultimately lead to local sexual extinction and to monoclonal populations of a species, and that this may imply significant consequences for population viability. Especially obligate or mainly outcrossing clonal plant species may be vulnerable for sexual extinction. We argue that the consequences of reduced sexual recruitment in clonally propagating plants may be understudied and underestimated and that a re-evaluation of current ideas on clonality may be necessary.     

May seed banks contribute to vegetation restoration on paths in temperate deciduous forest?

Forest paths are characterised by a zonation in vegetation composition as a result of gradients in abiotical conditions and continued recreational impact. Little is known about how much seed bank composition is affected by recreation and the existing path structure. As it is difficult to assess the contribution of seed banks to vegetation restoration, this study imparts relevant knowledge to restore vegetation on paths which are closed for recreational use. We surveyed seed bank and field layer vegetation composition in transects across path ecotones in deciduous forest. Analysis concentrated on seed bank characteristics and similarities of the seed bank and field layer vegetation in terms of ecological and seed size groups. A total of 74 species and 9,815 seedlings germinated out of the seed bank samples. The total seed density does not differ between path zones, but significant differences exist in the depth distribution and composition of the seed bank throughout transects. There is a large discrepancy between the composition of the seed bank and the vegetation. Small seeded species of disturbed environments dominate in each path zone. Typical forest species dominate in the vegetation while their contribution to the seed bank is low. Only with reference to the proportion of species of forest edges and clearings, the seed bank and vegetation do not differ significantly. Similarity between the seed bank on the path centre and the vegetation in the respective path zones decreases towards the undisturbed forest vegetation. Some competitive species like Urtica dioica and Lythrum salicaria are excessively represented in the seed bank and efficiently may obstruct further visitor use. However, these early successional species may not contribute to the conservation values of forests. Therefore management should carefully consider alternative amendments (e.g. soil scarification and seeding) to stimulate vegetation restoration.     

Scale‐dependent frequency distributions of plant species in dune slacks: Dispersal and niche limitation

Question: How do distribution patterns change with increasing scale level, and can this shift be attributed to dispersal and/or niche limitation? Location: Dune slacks at the Belgian and North French coast. Method: Frequency distribution patterns of species were tested over different scale levels (ranging from 0.008 to 45 km²). Analyses were executed for the total species pool and for subsets of species with high and low dispersal rates and habitat generalist and specialist species. Results: Species distributions for the total species pool on scale levels larger than 1.5 km² were unimodal, with an overrepresentation of rare species. With decreasing scale level, the proportion of common species increased, leading to weak bimodality. Distributions of subsets of slowly dispersing and habitat specialist species are on all scale levels characterised by a strongly unimodal pattern. The subset of species with high dispersal rates and habitat generalist species has a higher proportion of common species, leading to a significant core peak. Conclusions: On all scale levels both dispersal and niche limitation are hampering the wider distribution of rare species. However, since isolation and habitat heterogeneity are limited on the smaller scale levels, a larger proportion of well dispersing and habitat generalist species is able to occupy a high number of patches, resulting in a significant core peak for the total species pool.     

Seed bank assembly follows vegetation succession in dune slacks

Question: Is the seed bank in dune slacks during the whole successional range mainly composed of early successional species or does it vary according to the changing vegetation? Location: Belgium, western part of the coast. Methods: We investigated the soil seed bank composition using a seedling germination method in a chronosequence of 20 dune slacks, ranging in age from five to 55 yr. Results: Both seed density and species richness in the seed bank were very low in the first successional stages and increased with age, mainly as a result of increasing seed production. The similarity between seed bank and vegetation was higher in older slacks. A comparison of characteristics between seed bank and vegetation showed that the seed bank was, to a large extent, composed of later successional species. Occurrence patterns of individual species also showed that seeds become incorporated in the soil after the species has established in the vegetation. Conclusion: The seed bank is not likely to be the driving force for successional changes in the vegetation, and successional changes rely on dispersal. Some early successional species persist in the seed bank, but generally only in low numbers. The results also confirm that most typical dune slack species do not form persistent seeds, so that re‐establishment from the seed bank is not to be expected when the species has disappeared from the vegetation.     

Uncertainties in the Environmental Risk Assessment of Metals

As life has evolved in the presence of metals, the assessment of the potential adverse effects of metals on ecosystems requires a different approach than those presently used for man-made organic substances. This article provides a brief review of applications and limitations of current techniques and presents, based on recent research results, suggestions for improving the scientific relevance and accuracy of environmental risk assessments of metals. The importance of the following factors responsible for major uncertainties in current environmental risk assessments of metals are discussed: factors affecting metal bioavailability and toxicity, the potential importance of deficiency effects (for essential metals), and field extrapolation of laboratory toxicity data. Possible (regulatory) consequences of inaccurately assessing the natural background concentrations of metals and acclimatization/adaptation potential of laboratory organisms and resident communities are illustrated using examples of recent research, hypothesis development, and a probabilistic environmental risk assessment.