Structural changes in the digestive lysosomal system of sentinel mussels as biomarkers of environmental stress in mussel-watch programmes

A field study has been carried out to validate the measure of structural changes in the digestive lysosomal system of sentinel mussels as biomarkers of environmental stress. Previous laboratory studies demonstrated that the digestive lysosomal system of molluscs reponds to a variety of pollutants and to different stress situations by exhibiting significant changes in its structure. Mussels were collected monthly over 1 year at the Abra estuary (Bizkaia, Biscay Bay) from six sites with different degrees of pollution. The changes in the structure of the digestive lysosomes were quantified on cryostat sections of the digestive gland by means of automated image analysis. Four stereological parameters were recorded: lysosomal volume density, surface density, surface-to-volume ratio and numerical density. A seasonal pattern in the structure of the digestive lysosomes was evidenced with reduced volume, surface, size and numbers of lysosomes in winter-spring; increased volume, surface, size and numbers in summer and an intermediate situation in autumn. The structure of digestive lysosomes was also dissimilar among sites, the most significant differences being found between Plentzia (nonpolluted site) and Galea (polluted site). The digestive lysosomes of mussels collected from Galea were smaller and more abundant than in Plentzia's mussels in most sampling times. The basis of these differences are discussed to conclude that organic chemical pollution might be the cause for these specific changes which are different from the enlargement of digestive lysosomes described as a result of various sources of environmental stress. It is concluded that structural changes in the digestive lysosomes of sentinel mussels are sensitive to pollution-induced environmental stress even in the complex situation of the field where many factors may interact to affect the structure of the digestive lysosomal system.     

Detection of bacteria originally isolated from Alexandrium spp. in the midgut diverticula of Mytilus edulis after water-borne exposure

Bacteria associated with toxic dinoflagellates have been implicated in the production of paralytic shellfish poisoning (PSP) toxins, but it has not been substantiated that bacteria are truly capable of autonomous PSP toxin synthesis or what role bacteria may play in shellfish toxification. In this study, different putatively PSP toxin producing bacteria originally isolated from toxic Alexandrium spp. were exposed to the blue mussel Mytilus edulis. To document that these bacteria accumulated in the digestive tract of the mussels, hybridization techniques that use rRNA targeted oligonuceotides for in situ identification of these bacteria were applied. The mussel hepatopancreas was dissected and paraffin and frozen sections were made. The dissected glands were hybridized with digoxigenin-labelled 16S rRNA oligonucleotide probes. Results demonstrate that mussels will readily uptake and accumulate these bacteria in the hepatopancreas. However, the mussels were not rendered toxic by the ingestion of the bacteria as determined by HPLC with UV detection for PSP toxins and determination of sodium channel blocking activity using the mouse neuroblastoma assay. Thus, although the role that bacteria play in mussel toxification remains unclear, methods are now available which will aid in further investigation of this relatively unexplored area.     

HISTOCHEMISTRY OF OXIDASES IN SEVERAL TISSUES OF BIVALVE MOLLUSCS

Various tissues of the marine bivalveMytilus galloprovincialiswere analysed histochemically for oxidases capable of generating reactive oxygen species (ROS) using the cerium-DAB technique. Incubations were performed on unfixed cryostat sections using polyvinyl alcohol and semipermeable membranes. High xanthine oxidoreductase andd -amino acid oxidase (DAOX) activities were observed in kidney epithelial cells of mussels. DAOX also presented a strong activity in all the digestive epithelia. No xanthine oxidase activity was observed in any of the mussel tissues tested suggesting the presence of an enzyme only showing dehydrogenase activity. Mannitol oxidase, associated with special organelles called ‘mannosomes’ of terrestrial gastropods, presented a weak activity in the stomach epithelium and a strong specific activity in the haemocytes. Only DAOX presented a discrete granular distribution compatible with a peroxisomal compartmentalization. No urate oxidase activity could be demonstrated in tissues of mussels. These observations suggest a role for peroxisomes in ROS generation and determine the tissues capable of producing oxygen radicals in the digestive gland. This study raises the question of the behaviour of these enzymes in conditions in which ROS-generating organic xenobiotics are accumulated in the digestive gland of molluscs.     

Characterization of intracytoplasmic prokaryote infections in Dreissena sp. (Bivalvia: Dreissenidae)

This study characterizes intracytoplasmic infections with prokaryote microorganisms in Dreissena sp. (near Dreissena polymorpha) from northeastern Greece and represents the first report of such infections in freshwater bivalves. Light microscope observations of stained tissues revealed basophilic, cytoplasmic inclusion bodies in 87.5% (28/32) of the mussels sectioned. Inclusions in epithelial cells and connective tissues were noted, respectively, in 34.4 and 71.9% of the sample, with 5 mussels (15.6%) having both tissue types infected. Epithelial cell infections were observed in histological sections only in digestive gland tubules and ducts; within tubules, inclusions were present more often in secretory than digestive cells. Connective tissue infections, however, were systemic; among the 32 mussels sectioned, inclusions were found in the gills (65.6%), foot (12.5%), mantle (9.4%), labial palps (6.3%), digestive gland (6.3%), stomach (6.3%), and gonads (3.1%). Cytoplasmic inclusions (maximum dimension, 138 microm) were prominent enough in the gills to be visible in 17.0% of the 247 mussels dissected. Ultrastructurally, prokaryote cells in gill connective tissues were clearly characteristic of Chlamydiales-like organisms, with each intracytoplasmic inclusion containing a loosely packed mixture of elementary, reticulate, intermediate bodies, and blebs. Prokaryote colonies in digestive gland epithelial cells exclusively contained 1 of 4 morphological cell types and were considered Rickettsiales-like. Hexagonal, virus-like particles were present in the cytoplasm of the largest of these Rickettsiales-like prokaryotes. Although host stress was evident from localized cell necrosis and dense hemocyte infiltration, overall infection was fairly benign, with no major, adverse impact on body condition evident among sectioned or dissected mussels. A possible negative effect was partial constriction of gill water tubes, but at the infection intensity observed (typical range 1 to 7 inclusion bodies per section), significant interference with respiration and other metabolic functions of the gills was highly unlikely.     

Mussel glyoxalase I as a possible marker for ecotoxicological studies: Purification and preliminary characterization

Alpha-ketoaldehydes may be formed in cells during oxidative processes and glyoxalase I is the main enzyme involved in the detoxification pathway for these highly toxic compounds. Increased glyoxalase I activity has been observed in mussels exposed to high environmental levels of pollutants and a role for this enzyme as a protection mechanism against peroxidation damage has been hypothesized. In this paper, glyoxalase I from mussel tissue has been purified and a preliminary investigation of its molecular properties carried out. A two step purification procedure for glyoxalase I from digestive gland of Mytilus galloprovincialis is described. The pure enzyme is a 48 kDa protein with an heterodimeric quaternary structure composed of 24 and 25 kDa subunits. The isoelectric point of the native enzyme is at pH 5.0 and there is a divalent cation (probably Zn⁺⁺) requirement for activity. The series of alkyl-S-glutathiones, from methyl- to decyl-, are competitive inhibitors of glyoxalase I. Ki values exponentially decrease from 1.15 mM to 2.65 μM with increasing chain length. Mussel glyoxalase I exhibits molecular properties similar to those of the mammalian enzyme. The possible role of glyoxalase I in the detoxification of α-ketoaldehydes formed during oxidative stress is discussed.     

Investigation of thermostable metalloproteins in Perna perna mussels from differentially contaminated areas in Southeastern Brazil by bioanalytical techniques

Metallomic studies regarding environmental contamination by metals are of value in elucidating metal uptake, trafficking, accumulation and metabolism in biological systems. Many proven bioindicator species, such as bivalves, have not yet, however, been well-characterized regarding their metalloprotein expression in response to environmental contaminants. In this context, the aim of the present study was to investigate metalloprotein expressions in the thermostable protein fraction of muscle tissue and digestive glands from mussels (Perna perna) from three differentially metal-contaminated sites in Southeastern Brazil in comparison with a reference site. The thermostable protein fractions were analyzed by SDS-PAGE and SEC-HPLC-ICP-MS. Metal content was also determined in both the crude and the purified extracts. Several inter-organ differences were observed, which is to be expected, while inter-site differences regarding thermostable protein content were also verified, indicating accumulation of these elements in muscle tissue and digestive glands and disruption of homeostasis of essential elements, with detoxification attempts by metal-bound proteins, since all metalloproteins present in both matrices eluted bound to at least one non-essential metal. These results are also noteworthy with regard to the adopted reference site, that also seems to be contaminated by toxic metals.     

Intertidal assemblages associated with natural<Emphasis Type="Italic">corallina</Emphasis> turf and invasive mussel beds

There is considerable concern about conservation of biodiversity in highly disturbed and urbanized environments, although a very large proportion of biodiversity (i.e. the small and cryptic invertebrates) have been little studied in this regard. Many biogenic structures (e.g. coral reefs, mussel beds, foliose algae) provide habitat for a large number of small invertebrates. The features of these habitats to which these animals respond are complex and poorly documented. Invasive species are increasing in abundance and diversity in many disturbed estuaries, but most previous studies have concentrated on effects of invasive species on surrounding macroscopic assemblages. This study examines the assemblages of small invertebrates and algae living in natural patches of coralline turf and in patches of the invasive mussel, Mytilus galloprovincialis, on seawalls in Sydney Harbour. Although most taxa identified were common to both habitats, they were generally more abundant in turf than in the mussels, especially the more widespread and numerous taxa. Few taxa were unique to either habitat and those were generally sparse and patchy. In addition, there were relatively more smaller animals in the algal turf than in the mussels, although it is not known whether these were juveniles of adults present in both habitats, or different species. These data show that coralline turf and mussel beds do not provide similar intertidal habitat for associated assemblages and that overgrowth of natural biota by mussels may have strong indirect effects on associated assemblages. These warrant further experimental investigation, so that the effects of invasive species on local biodiversity can be better understood and managed.     

Grazing on colonial and filamentous, toxic and non-toxic cyanobacteria by the zebra mussel Dreissena polymorpha

Colony forming and toxic cyanobacteria form a problem in surfacewaters of shallow lakes, both for recreation and wildlife. Zebramussels, Dreissena polymorpha, have been employed to help torestore shallow lakes in the Netherlands, dominated by cyanobacteria,to their former clear state. Zebra mussels have been presentin these lakes since they were created in the 19th century bythe excavation of peat and are usually not considered to bean invasive species. Most grazing experiments using Dreissenahave been performed with uni-cellular phytoplankton laboratorystrains and information on grazing of larger phytoplankton taxahardly exists. To gain more insight in to whether D. polymorphais indeed able to decrease cyanobacteria in the phytoplankton,we therefore performed grazing experiments with zebra musselsand two species of cyanobacteria, that greatly differ in shape:colony forming strains of Microcystis aeruginosa and the filamentousspecies Planktothrix agardhii. For both species a toxic anda non-toxic strain was selected. We found that zebra musselscleared toxic Planktothrix at a higher rate than non-toxic Planktothrix,toxic or non-toxic Microcystis. Clearance rates between theother strains were not significantly different. Both phytoplanktonspecies, regardless of toxicity, size and shape, were foundin equal amounts (based on chlorophyll concentrations) in theexcreted products of the mussels (pseudofaeces). The resultsshow that zebra mussels are capable of removing colonial andfilamentous cyanobacteria from the water, regardless of whetherthe cyanobacteria are toxic or not. This implies that the musselsmay be used as a biofilter for the removal of harmful cyanobacterialblooms in shallow (Dutch) lakes where the mussels are alreadypresent and not a nuisance. Providing more suitable substratefor zebra mussel attachment may lead to appropriate mussel densitiescapable of filtering large quantities of cyanobacteria.     

Granulocyte oxygen radicals as potential suppressors of hemopoiesis: potentiating roles of lactoferrin and elastase; inhibitory role of oxygen radical scavengers

In vitro studies suggest intact endothelial cells and their released growth factors are required for optimal growth and differentiation of hematopoietic cells in culture. Conversely, processes that damage endothelium might, therefore, suppress hematopoiesis. We have studied mechanisms by which stimulated inflammatory cells, particularly granulocytes, damage endothelium and suggest these studies may provide new insights into the hematopoietic suppression of inflammatory diseases. We demonstrate that the granulocyte lysosomal constituent, lactoferrin, which has independently been shown to inhibit in-vitro hematopoiesis, may act by amplifying granulocyte-mediated toxic oxidant damage to endothelium. Its deleterious effects are twofold: 1) it releases iron that catalyses the Haber-Weiss reaction, thereby producing highly toxic hydroxyl radicals; and 2) its highly positive charge facilitates its absorption to target membranes that traffics oxygen-radical damage directly to endothelium. In addition, we demonstrate that another granulocyte lysosomal component, elastase, also perturbs endothelium--not so much by direct lytic effect, but by proteolysing matrix proteins that serve to attach endothelium to its substratum. Thus, elastase promotes endothelial lift-off. Plasma alpha-1-antiproteinase, a potent antielastase, should be protective, but is inactivated by the same granulocyte oxidants that directly lyse endothelial cells. However, antielastase activity can be preserved by antioxidants and a novel, innocuous one--methionine--is described. It is oxidized as a surrogate for the critical-site methionine of alpha-1-proteinase inhibitor, preserving in the process antielastase activity. Our results suggest that strategies to reduce production of inflammatory cell toxic oxygen radicals with reagents such as antilactoferrin antibody or iron chelators might be useful adjuncts in maintaining in vitro hematopoiesis.(ABSTRACT TRUNCATED AT 250 WORDS)     

Fatty acid as markers to demonstrating trophic relationships among diatoms, rotifers and green-lipped mussels

Green-lipped mussels Perna viridis, collected from Peng Chau, Hong Kong were allotted into two treatment groups, each containing three experimental tanks. The first treatment group comprised of mussels fed with the diatom Thalassiosira pseudonana only, whereas the second treatment group contained mussels fed with the marine rotifer Brachionus plicatilis, which was in turn fed with diatom T. pseudonana. The mussels were fed two times each day over the experimental period of 14 days. On Days 4, 7 and 14, three mussels were collected from each tank of each treatment group and treated as a single replicate. Fatty acid profiles of diatoms, marine rotifers and the three organs (digestive gland, mantle margin and adductor muscle) of the two mussel groups were analyzed. Results showed that monosaturated fatty acid (MUFA) 16:1n7 was conserved along the food chain among diatoms, marine rotifers and green-lipped mussels. This suggested that 16:1n7 or the ratio of 16:1n7 to saturated fatty acid (SFA) 16:0 can be a trophic marker for diatom T. pseudonana and elevated amounts of 16:1n7 in mussels can reflect the dominance of diatoms in its diet. The present results also showed that rotifers could accumulate MUFA 18:1n7 and PUFA 20:4n6 which were transferred up to mussels, especially 18:1n7, as zooplankton have the ability to synthesize or actively accumulate certain fatty acids that they need for growth or reproduction. There was an increase in the amount of 18:1n7 in the digestive gland of mussels fed with rotifers but the level of this fatty acid remained unchanged in those fed with diatoms, further confirming that 18:1n7 can be used as a marker for the presence of rotifers in trophic relationship studies. The relatively faster responses in the digestive gland of mussels to acquire the fatty acid signatures from their food suggested that the fatty acid profiles in the digestive gland can be a good marker to show a short-term fluctuation of food conditions in the marine environment.     

Modelling shellfish growth with dynamic energy budget models: an application for cockles and mussels in the Oosterschelde (southwest Netherlands)

Dynamic energy budget models for growth of individual cockles (Cerastoderma edule) and mussels (Mytilus edulis) are adjusted and calibrated to the Oosterschelde by formulating and parametrizing their functional responses using an extensive set of field observations. The resulting model predictions fit the observations satisfactorily. Results indicate that food quality and the importance of detritus as a food source are site-specific as well as species-specific. Despite these differences in their calibrated parameter values, both species show a very similar functional response. Compared with other systems, however, the functional responses of mussels in the present study are clearly higher than those of mussels in other systems. This may be explained by the absence of intra-specific competition in the measurement set-up that was used, and therefore supports the idea that the generally small functional response of M. edulis is caused by intra-specific competition.     

A dual symbiosis shared by two mussel species, Bathymodiolus azoricus and Bathymodiolus puteoserpentis (Bivalvia: Mytilidae), from hydrothermal vents along the northern Mid-Atlantic Ridge

Bathymodiolus azoricus and Bathymodiolus puteoserpentis are symbiont-bearing mussels that dominate hydrothermal vent sites along the northern Mid-Atlantic Ridge (MAR). Both species live in symbiosis with two physiologically and phylogenetically distinct Gammaproteobacteria: a sulfur-oxidizing chemoautotroph and a methane-oxidizer. A detailed analysis of mussels collected from four MAR vent sites (Menez Gwen, Lucky Strike, Rainbow, and Logatchev) using comparative 16S rRNA sequence analysis and fluorescence in situ hybridization (FISH) showed that the two mussel species share highly similar to identical symbiont phylotypes. FISH observations of symbiont distribution and relative abundances showed no obvious differences between the two host species. In contrast, distinct differences in relative symbiont abundances were observed between mussels from different sites, indicating that vent chemistry may influence the relative abundance of thiotrophs and methanotrophs in these dual symbioses.     

Lysosomal enlargement in digestive cells of mussels exposed to cadmium, benzo[a]pyrene and their combination

Digestive cell lysosomes in mussels are known to respond to individual organic chemicals and metals after experimental exposure under laboratory conditions but reports dealing with the response to mixtures of pollutants are scarce. The aim of the present investigation was to compare the lysosomal responses elicited by exposure to a model organic chemical compound (benzo(a)pyrene, B[a]P), a model toxic metal (Cd) and their combination (B[a]P+Cd) under controlled laboratory conditions. Dimethylsulfoxide (DMSO) was used as vehicle to dissolve organic chemicals into seawater. Control mussels were either kept untreated in clean seawater or treated with DMSO. Digestive glands were excised on Day 21. beta-Glucuronidase activity was demonstrated in 8 mum cryotome sections. Lysosomal volume, surface and numerical densities (Vv, Sv and Nv), and surface-to-volume ratio (S/V) were quantified by image analysis. Lysosomal enlargement was evident in digestive cells of mussels exposed to either Cd, B[a]P or B[a]P+Cd. Such enlargement was more marked after exposure to B[a]P+Cd than to B[a]P, but did not reach the levels recorded after Cd exposure. It seems therefore that the presence of B[a]P reduced to some extent the effects of Cd on digestive cell lysosomes in mussels.     

DNA adducts as indicators of genotoxic exposure in indigenous and transplanted mussels, Mytilus edulis L. from Icelandic coastal sites

Indigenous mussels, Mytilus edulis, were collected at sites with supposed different amounts of pollution; Reykjavík harbour, Keflavík harbour, Grafarvogur and Hvalfj?rdur (reference), along the south-western coast of Iceland in March 2000. Mussels from Hvalfj?rdur and Reykjavík harbour were also collected in August the same year. Additionally, mussels were transplanted from the reference site to Reykjavík harbour for 6 weeks during both winter and summer for comparison. DNA adducts were analysed by 32P-post-labelling in gills and digestive gland. Highest adduct levels were found in gill tissue from indigenous mussels collected in Reykjavík harbour. Adduct levels in both tissues from mussels collected at the reference site were below or very close to the detection limit during winter, but seemed to increase a little during summer. Mussels from sites with supposed intermediate pollution had intermediate levels of DNA adducts in gills but did not differ from Reykjavík harbour in digestive gland. No increase in adduct levels was observed in mussels transplanted from the reference site to Reykjavík harbour, except for a slight increase in digestive gland during winter. This study shows that 32P-post-labelling analysis of DNA adducts is sensitive enough to be used on indigenous mussels from relatively pristine areas and that adduct levels are increased in harbours/urban sites. However, transplantation of mussels from a clean site to the harbour for 6 weeks did not result in increased adduct levels in gills, the tissue with the highest adduct levels. The results also indicate that seasonal variation in adduct levels may occur.     

Effect of Experience on Prey Species Selection by the Bivalve Feeder Halla Okudai (Polychaeta: Lysaretidae)

We report on the effects of previous foraging experience on prey-selection by the bivalve feeding polychaete Halla okudai, including whether there was evidence of frequency-dependent predation. Three separate batches of H. okudai were maintained for 30 days on clams, mussels, or oysters, before being offered a choice among these three prey. Initially individuals from all three treatments consumed more clams than mussels, and no oysters. As the number of clams was depleted the polychaetes shifted their diet to include a greater proportion of mussels, but even after 20 days oysters were only eaten by polychaetes that had been previously acclimated to them. Nevertheless, polychaetes from each treatment inspected significantly more of the prey species to which they had initially been acclimated, suggesting that previous experience may increase the likelihood of certain prey being detected. When individuals of H. okudai were repeatedly offered the same prey species, handling time did not decrease (and therefore prey profitability did not increase) with experience, which may be because H. okudai paralyses its prey with toxic mucus. Since repeated experience of the same prey species gives no advantage in terms of reduced handling time, we suggest this may be why this species does not show frequency-dependent prey-selection.     

Enzymatic digestive activity in Mytilus chilensis (Hupé 1854) in response to food regimes and past feeding history

Digestive enzyme activities (amylase, cellulase, laminarinase and protease) were analysed in mussels (Mytilus chilensis) from intertidal and subtidal habitats in Yaldad Bay, Chiloé, Chile. In order to analyse the effects of the past-feeding history (origin) and new nutritional conditions (habitat) on these enzymatic activities, a cross-over transplant was carried out and the analysis performed after a 7-day acclimation period. Crystalline styles showed higher carbohydrase and lower protease activities than digestive glands, with the highest differences recorded for subtidal mussels. Cellulase is the enzyme with the highest activity in both the digestive gland and crystalline style in all the experimental conditions. Intertidal mussels transplanted to a subtidal habitat showed enzyme resources significantly higher than in their original habitat. In the inverse case, mussels transferred from an original subtidal habitat to an intertidal one, a significant decrease in carbohydrase and protease activities was observed. The "past feeding history' is involved in the specific and total carbohydrase and protease activities, with a highly significant effect on amylase and cellulase activities in both the crystalline style and the digestive gland. Laminarinase activity can be interpreted considering the habitat (trophic regime), either individually or interacting with mussels' origin, in relation with the feeding periods. The results establish that in M. chilensis, an investment in enzyme resources is one of the mechanisms employed to optimise the acclimated response in terms of energy gains when variations in the food regime occur.     

The effect of size and age on depuration rates of diarrhetic shellfish toxins (DST) in mussels (Mytilus edulis L.)

Depuration or elimination of diarrhetic shellfish toxins (DST) was followed for 73 days in 1- and 2-year-old mussels. The age groups also differed in size, providing a broad approach to studying the effect of the differences in physiology accompanying the differences in size. Content of DST was analysed both on groups and individual mussels. Environmental variables were measured to evaluate their effect on depuration.We found no significant differences in elimination rate of DST between 1- and 2-year-old mussels under natural conditions. This suggests that size and age do not affect the elimination rate of the DST. The present study is the first study on the effect of age and size on the elimination rate of algal toxins in bivalves. The natural variations in food levels and temperature were not found to affect the elimination rate of DST.The digestive gland weights in the 1-year-old mussels increased four times while the DST content per individual decreased eight times. This demonstrated that dilution of toxins due to tissue growth could have an important contribution to declines in toxin concentrations. Changes in tissue mass are affected by environmental variables via growth or starvation, and when such changes lead to concentration or dilution of toxins this does not reflect the accumulation or removal of toxins from the tissues. We hence suggest that when evaluating the actual elimination capacity of the mussels, as in the present study, the total content of toxins per individual should be used, rather than toxin concentrations.The 1-year-old mussels had faster growth compared to the 2-year-old mussels in both total soft tissue and digestive glands. The mechanism of DST elimination is still unknown. If this process involves metabolism of the toxins, one could expect the rates of elimination to follow overall metabolic rates. However, the results from the present study suggest that large differences in growth rates, which also include difference in feeding and metabolic rates, do not affect the elimination rate of DST. Our results support the assumption that the depuration rates cannot be accelerated, even in artificial systems, as a cost-effective way to solve the problem with toxic mussels for the industry.     

Heavy metal effects on lipid peroxidation in the tissues of mytilus gallopro vincialis lam.

1. The effects of heavy metals on lipid peroxidation in the gills and digestive gland of mussels exposed for six days to Cu²⁺, Cd²⁺ or Zn²⁺ (40 μg/l/animal) were investigated.2. In the tissues of Cu-exposed mussels a significant increase of the level of malondialdehyde (MDA), which is indicative of the peroxidative process, and a decrease of the concentration of glutathione were observed.3. Moreover, in the digestive gland of mussels, copper exposure results in an increase of other carbonyl compounds and in the lysosomal accumulation of lipofuscin granules.4. The exposure of mussels to Zn or to Cd did not elicit any of the above effects.5. The results are discussed in relation to the possible role that Cu-induced lysosomal lipofuscin accumulation may play in heavy metal detoxification.     

Epithelial cell renewal in the digestive gland and stomach of mussels: season, age and tidal regime related variations

The natural variability in cell proliferation activity in the epithelium of the digestive gland and stomach was investigated in mussels, Mytilus galloprovincialis (Lmk), of different age and tidal level at different seasons. After treating mussels with the thymidine analogue bromodeoxyuridine (BrdU) for 6 hours, BrdU immunohistochemistry was performed every 2 hours for the next 36. The relative proportion of BrdU positive cells was quantified as BrdU labelling (per thousand). Marked seasonal differences were recorded in BrdU labelling, with much higher proliferating activity in summer than in autumn and winter. Cell proliferation seemed not to be significantly dissimilar between mussels of different age (size). In contrast, the digestive gland epithelium of mussels from intertidal and subtidal populations differed not only in the levels but also in the pattern of variation of BrdU labelling, which in intertidal mussels appeared to be modulated by photoperiod and tide, unlike in subtidal mussels, in which variations followed a circatidal pattern.     

The nutrient-toxin dosage continuum in human evolution and modern health.

Recent findings support the long-recognized principle that nutritive and toxic effects of an ingested material depend not only on its nature but very much on its quantity. The well known observation that essential nutrients can be toxic at high dosages suggests that the same reversal of effect may be true of many substances that could be beneficial but not essential at low dosages (the phenomenon of hormesis). This has been demonstrated for many well known toxins. We suggest a mathematical model that describes these dosage effects as an expected result of the evolution of human metabolic and dietary adaptations for maximizing benefits and minimizing costs of the ingestion or other intake of any substance. Evolved mechanisms for achieving benefits may be unrelated to those for reducing costs. These evolutionary considerations suggest important consequences demonstrable by experimental or epidemiological studies. They also suggest ways in which our evolved dietary adaptations may be currently maladaptive, and individual development of taste preferences poorly calibrated by early experience in modern environments. The apparent reality of hormesis raises the possibility of counterproductive effects of current dosage recommendations and limits for nutrients and pollutants. We propose that some conceptual and factual problems are urgently in need of resolution. Fundamental to evolutionary biology is the tendency for organisms to become increasingly adapted to those environments to which they are most commonly exposed (Parsons 1990).