Trees as environmental sentinels

Trees are reliable indicators of the long-term effects of atmospheric pollution. As the botanical big game of the planet they are also standing guard and may be providing a warning signal about our own future.     

Synanthropic primates in Asia: Potential sentinels for environmental toxins

Macaques are similar to humans both physiologically and behaviorally. In South and Southeast Asia they are also synanthropic, ecologically associated with humans. Synanthropy with humans raises the possibility that macaques come into contact with anthropogenic toxicants, such as lead and mercury, and might be appropriate sentinels for human exposures to certain toxic materials. We measured lead (Pb) and mercury (Hg) levels and characterized the stable isotopic compositions of δ¹⁵N and δ¹³C in hair from three groups of free‐ranging macaques at the Swoyambhu temple in Kathmandhu, Nepal, an urban population that has abundant contact with humans. Hair lead levels were significantly higher among young macaques and differed among the three groups of macaques that were sampled. Hair Hg levels were low. No statistical association was found between stable isotopic compositions (δ¹⁵N and δ¹³C) and Pb and Hg levels. Our data did not find evidence that lead levels were associated with diet. We conclude that, in this population of macaques, behavioral and/or physiologic factors may play a significant role in determining exposure to lead. Chemical analysis of hair is a promising, noninvasive technique for determining exposure to toxic elements in free‐ranging nonhuman primates. Am J Phys Anthropol, 2010. © 2009 Wiley‐Liss, Inc.     

Migrating shorebirds as integrative sentinels of global environmental change

Many shorebirds travel over large sections of the globe during the course of their annual cycle and use habitats in many different biomes and climate zones. Increasing knowledge of the factors driving variations in shorebird numbers, phenotype and behaviour may allow shorebirds to serve as 'integrative sentinels' of global environmental change. On the basis of numbers, timing of migration, plumage status and body mass, shorebirds could indicate whether ecological and climate systems are generally intact and stable at hemispheric scales, or whether parts of these systems might be changing. To develop this concept, we briefly review the worldwide shorebird migration systems before examining how local weather and global climatic features affect several performance measures of long-distance migrants. What do variations in numbers, phenotype and behaviour tell us about the dependence of shorebirds on weather and climate? How does data on migrating shorebirds integrate global environmental information? Documenting the dependencies between the population processes of shorebirds and global environmental features may be an important step towards assessing the likely effects of projected climate change. In the meantime we can develop the use of aspects of shorebird life histories on large spatial and temporal scales to assay global environmental change.     

Are food and environmental toxicants 'overdetected' by bioassay?

The definition of clean bioprocessing of foods should relate to the discharge of clean effluents that do not disturb functional ecosystems in the environment. Clean effluents should not pollute aquatic or terrestrial environments by increasing the levels or determined bioavailibility of reactive oxygen species (ROS), traces of heavy metals (e.g. arsenic, mercury, lead, cadmium) or radionuclides or other ecotoxicants such as the endocrine disrupting chemicals (e.g. xenoestrogens), herbicides and pesticides. Some saleable foodstuffs can contain very small amounts of potentially toxic components. Strategies dealing with potential toxins should be aimed at targeting remedial bioprocessing to safe limits as stipulated by regulatory agencies, rather than trying to eliminate all toxic components of food so that they can no longer be detected by bioassay or other highly sensitive techniques. The ability to detect even the tiniest amounts of toxicants may not be necessary. This 'overdetection' could lead to inappropriate courses of action in some situations.     

Wild mink (Neovison vison) as sentinels in environmental monitoring

Superficial inguinal lymph nodes from 72 wild boars examined in a previous immunohistochemical (IHC) study on porcine circovirus type 2 (PCV2) were selected for a PCV2 polymerase chain reaction (PCR) analysis. Four of these lymph nodes were PCV2-IHC strongly positive with PMWS histological lesions (outcome 1), 6 weak to mild PCV2-IHC positive without PMWS histological lesions (outcome 2) and 62 PCV2-IHC negative. Considering IHC the gold standard for diagnosis, the aims of the study were to evaluate the suitability of the PCV2-DNA extraction from formalin-fixed and paraffin-embedded (FFPE) tissue and the sensitivity and specificity of PCR under two IHC interpretations criteria: (A) the sample was considered positive if the result was outcome 1; (B) the sample was considered positive if the result was outcome 1 or 2. Under (A) criteria, sensitivity and specificity of PCR were 100% and 89.7%, respectively; the Cohen's Kappa coefficient was 0.49. Under (B) criteria, sensitivity and specificity of PCR were 80.0% and 95.2%, respectively; the Cohen's Kappa coefficient was 0.72. The high Cohen's Kappa coefficient under the (B) interpretative criteria indicates good agreement between the two methods. In conclusion, 1) DNA extracted from FFPE specimens of wild boar is suitable for PCR and further represents a screening test for PCV2/PCVD (PCV2 Diseases) investigations in wild boar as well; 2) routine histological sampling can also be useful for PCV2 virological studies in wild boar.     

Collectins: sentinels of innate immunity

Collectins, present in plasma and on mucosal surfaces, are humoral molecules of the innate immune system. They were discovered a hundred years ago in 1906 as the first association of an animal lectin with the immune system. They are a family of calcium-dependent lectins that recognize pathogen-associated molecular patterns. They share a similar modular domain architecture consisting of four regions; a cysteine-rich N-terminal domain, a collagen-like region, an alpha-helical neck domain and a C-terminal carbohydrate recognition domain. There have been eight collectins members defined so far, of which, MBL, SP-A and SP-D are the most characterized. Collectins represent the first line of host defense. Upon recognition of the infectious agents, collectins put into action effector mechanisms like direct opsonization, neutralization, agglutination, complement activation and phagocytosis to curb the microbial growth. In addition, they also modulate inflammatory and allergic responses and apoptotic cell clearance. These functions limit infection and subsequently modulate the adaptive immune responses. The role of collectins, their structure, function, characteristics and clinical significance are reviewed in this article.     

Dendritic cells: sentinels against pathogens

Dendritic cells (DCs) are the most potent antigen-presenting cells, and are regarded as "natural adjuvants" for the induction of primary T or T-dependent immunity. DCs in the peripheral sites capture and process antigens. Encounter of exogenous or endogenous stimuli mature the function of DCs, and they thus acquire T-cell stimulatory capacity and distinct chemotactic behavior which enables them to migrate to lymphoid tissue. In the secondary lymphoid organs, they present antigens to T- and B-cells and stimulate their proliferation. Dendritic cells are also involved in tolerance induction, in particular, to self antigens. DCs also play a key role in the transmission of many pathogens, and therefore may become targets for designing new therapies. DCs have been manipulated in vitro and in vivo for cancer immunotherapy. In this article, we provide a concise overview of DC biology and its current and future role in clinical settings.     

Endocrine regulation of the reproduction in crustaceans: Identification of potential targets for toxicants and environmental contaminants

Progress in ecotoxicological research documents that crustaceans are highly vulnerable to diverse chemicals and toxicants in the environment. In particular, pollutants affecting endocrine homeostasis in crustaceans (i.e., endocrine disruptors) are intensively studied, and serious reproductive disorders have been documented. In this review, current knowledge about the endocrine regulation of the crustacean reproduction is put together with the published ecotoxicological data with an attempt to summarize the potential of xenobiotics to affect crustacean reproduction. Following gaps and trends were identified: (1) Studies are required in the field of neurohormone (serotonin and dopamine) regulation of the reproduction and possible modulations by environmental toxicants such as antidepressant drugs. (2) Molting-related parameters (regulated by ecdysteroid hormones) are closely coordinated with the development and reproduction cycles in crustaceans (cross-links with methyl farnesoate signalling), and their susceptibility to toxicants should be studied. (3) Other biochemical targets for xenobiotics were recently discovered in crustaceans and these should be explored by further ecotoxicological studies (e.g., new information about ecdysteroid receptor molecular biology). (4) Some sex steroid hormones known from vertebrates (testosterone, progesterone) have been reported in crustaceans but knowledge about their targets (crustacean steroid receptors) and signalling is still limited. (5) Determination of the sex in developing juveniles (affecting the sex ratio in population) is a sensitive parameter to various xenobiotics (including endocrine disruptors) but its modulation by general environmental stress and non-specific toxicity should be further studied.     

Macrophages: sentinels and regulators of the immune system

The important role of macrophages in host defense against a variety of pathogens has long been recognized and has been documented and reviewed in numerous publications. Recently, it has become clear that tissue macrophages are not entirely derived from monocytes, as has been assumed for a long time, but rather show an ontogenetic dichotomy in most tissues: while part of the tissue macrophages are derived from monocytes, a major subset is prenatally seeded from the yolk sac. The latter subset shows a remarkable longevity and is maintained by self‐renewal in the adult animal. This paradigm shift poses interesting questions: are these two macrophage subsets functionally equivalent cells that are recruited into the tissue at different development stages, or are both macrophage subsets discrete cell types with distinct functions, which have to exist side by side? Is the functional specialization that can be observed in most macrophages due to their lineage or due to their anatomical niche? This review will give an overview about what we know of macrophage ontogeny and will discuss the influence of the macrophage lineage and location on their functional specialization.     

Inter-individual differences in the metabolism of environmental toxicants: cytochrome P450 1A2 as a prototype.

Cytochrome P450 (P450) 1A2 provides an interesting paradigm for inter-individual differences in the metabolism of pro-carcinogens. The enzyme is known to vary 40-fold among individuals and may contribute to cancers caused by heterocyclic amines and other chemicals. Rat and human P450 1A2 are known to be 75% identical and were compared for several catalytic activities. The human enzyme was an order of magnitude more efficient in the N-hydroxylation of two heterocyclic amines. Further, the levels of P450 1A2 expressed in human livers show a 40-fold variation, with some as high as 0.25 nmol P450 1A2 per milligram microsomal protein. Some human liver samples are more active (than those isolated from polychlorinated biphenyl-treated rats) in the activation of heterocyclic amines. A bacterial genotoxicity assay has been developed in which human P450 1A2 and NADPH-P450 reductase are expressed within Escherichia coli and bacterial mutants can be assayed using reversion to lac prototrophy. A random mutagenesis strategy for human P450 1A2 has been developed and used to examine the changes in catalytic activity seen with many single-amino acid substitutions. These results may be of relevance in consideration of genetic polymorphisms. Further, the findings pose a challenge to molecular epidemiology effort in that results with one substrate do not necessarily predict those for others. Some dinitropyrenes are P450 1A2 substrates but others are not. 6-Nitrochrysene can be activated by human P450 1A2 but the (mono) nitropyrenes examined were not; these were oxidized by P450 3A4 instead.     

The role of caveolae in endothelial cell dysfunction with a focus on nutrition and environmental toxicants

Complications of vascular diseases, including atherosclerosis, are the number one cause of death in Western societies. Dysfunction of endothelial cells is a critical underlying cause of the pathology of atherosclerosis. Lipid rafts, and especially caveolae, are enriched in endothelial cells, and down-regulation of the caveolin-1 gene may provide protection against the development of atherosclerosis. There is substantial evidence that exposure to environmental pollution is linked to cardiovascular mortality, and that persistent organic pollutants can markedly contribute to endothelial cell dysfunction and an increase in vascular inflammation. Nutrition can modulate the toxicity of environmental pollutants, and evidence suggests that these affect health and disease outcome associated with chemical insults. Because caveolae can provide a regulatory platform for pro-inflammatory signalling associated with vascular diseases such as atherosclerosis, we suggest a link between atherogenic risk and functional changes of caveolae by environmental factors such as dietary lipids and organic pollutants. For example, we have evidence that endothelial caveolae play a role in uptake of persistent organic pollutants, an event associated with subsequent production of inflammatory mediators. Functional properties of caveolae can be modulated by nutrition, such as dietary lipids (e.g. fatty acids) and plant-derived polyphenols (e.g. flavonoids), which change activation of caveolae-associated signalling proteins. The following review will focus on caveolae providing a platform for pro-inflammatory signalling, and the role of caveolae in endothelial cell functional changes associated with environmental mediators such as nutrients and toxicants, which are known to modulate the pathology of vascular diseases.     

Transition-state regulators: sentinels of Bacillus subtilis post-exponential gene expression

When Bacillus subtilis encounters a nutrient-depleted environment, it expresses a wide variety of genes that encode functions in alternative pathways of metabolism and energy production. Expression of these genes first occurs during the transition from active growth into stationary phase and is controlled by a class of proteins termed transition-state regulators. In several instances, a given gene is redundantly controlled by two or more of these regulators and many of these regulators control genes in numerous different pathways. The AbrB, Hpr and Sin proteins are the best-studied examples of these regulatory molecules. Their role is to prevent inappropriate and possibly detrimental functions from being expressed during exponential growth when they are not needed. They serve as elements integrating sporulation with ancillary stationary-phase phenomena and appear to participate in the timing of early sporulation events and in fine-tuning the magnitude of gene expression in response to specific environmental conditions.     

State-dependent sentinels: an experimental study in the Arabian babbler

Natural patterns of cooperative sentinel behaviour in Arabian babblers, Turdoides squamiceps, have proven consistent with state-dependent models of individually selfish anti-predator strategies. Here we demonstrate experimentally that sentinel effort within groups is determined simply by individual state. The two highest-ranking males in eight groups were separately fed a supplement of mealworms, each for one day at a time. Control days before and after each treatment confirmed that no carry-over effects occurred, and that most normal sentinel activity was carried out by alpha males, then beta males and then by the rest of the group. When supplemented, both alpha and beta males exhibited similar marked increases in sentinel activity, relative to control days. Unsupplemented males and the rest of the group incompletely compensated for these increases with reductions in sentinel effort. Differences in individual body mass within groups reflected natural and experimental variation in sentinel effort. Alpha and beta males weighed more than other group members, and gained mass only when supplementally fed. There was no evidence either for competitive sentinel behaviour, nor for any increased interference between males during the supplementation treatments. These results therefore provide strong evidence in support of the state-dependent approach to cooperative sentinel behaviour.