The ultrastructure and metal-containing inclusions of mature cell types in the hepatopancreas of a crayfish

Bioaccumulation of lead and non-specific immune responses in white shrimp (Litopenaeus vannamei) to Pb exposure

In this study, we investigated organ accumulation and nonspecific immune response in white shrimp (Litopenaeus vannamei) that were exposed to various concentrations of lead (Pb) solution. The concentrations of Pb in the hepatopancreas, haemolymph, and muscle were measured moreover the total heamocyte count, phenoloxidase activity, O₂^- and physiological factors such as glutamic oxaloacetate transaminase (GOT), glutamic pyruvic transaminase (GPT), and haemolymph glucose were detected. The results showed that the hepatopancreas was the main organ of accumulation of Pb in white shrimp and the cumulative concentration of each organ was positively correlated with the experimental Pb concentration and immersion time. By observing GOT and GPT, Pb was found to inhibit phenoloxidase and O₂^- activity and to induce organ injury. Thus, the heavy metal Pb accumulates in the hepatopancreas and haemolymph and affects the crustacean metabolic organ injury (rising of GOT and GPT) further to inhibit nonspecific immune responses.

Cytochemical characterization of gill and hepatopancreatic cells of the crab Ucides cordatus (Crustacea, Brachyura) validated by cell metal transport

Ucides cordatus (Linnaeus, 1763) is a hypo-hyper-regulating mangrove crab possessing gills for respiratory and osmoregulatory processes, separated in anterior and posterior sections. They also have hepatopancreas, which is responsible for digestion and absorption of nutrients and detoxification of toxic metals. Each of these organs has specific cells that are important for in vitro studies in cell biology, ion and toxic metals transport. In order to study and characterize cells from gills and hepatopancreas, both were separated using a Sucrose Gradient (SG) from 10 to 40% and cells in each gradient were characterized using the vital mitochondrial dye DASPEI (2-(4-dimethylaminostyryl)-N- ethylpyridinium iodide) and Trichrome Mallory's stain. Both in 20 and 40% SG for gill cells and 30% SG for hepatopancreatic cells, a greater number of cells were colored with DASPEI, indicating a larger number of mitochondria in these cells. It is concluded that the gill cells present in 20% and 40% SG are Thin cells, responsible for respiratory processes and Ionocytes responsible for ion transport, respectively. For hepatopancreatic cells, the 30% SG is composed of Fibrillar cells that possess larger number of membrane ion and nutrient transporters. Moreover, the transport of toxic metal cadmium (Cd) by isolated hepatopancreatic cells was performed as a way of following cell physiological integrity after cell separation and to study differences in transport among the cells. All hepatopancreatic cells were able to transport Cd. These findings are the first step for further work on isolated cells of these important exchange epithelia of crabs, using a simple separation method and to further develop successful in vitro cell culture in crabs.

Mitochondrial gene expression, antioxidant responses, and histopathology after cadmium exposure

The present study investigates cadmium effects on the transcription of mitochondrial genes of Procambarus clarkii after acute (0.05, 0.5, and 5 mg Cd/L; 4-10 days) and chronic exposures (10 μg Cd/L; 30-60 days). Transcriptional responses of cox1, atp6, and 12S using quantitative real-time RT-PCR were assessed in gills and hepatopancreas. Additionally, the expression levels of genes involved in detoxification and/or oxidative stress responses [mt, sod(Mn)] and enzymatic activities of antioxidants (SOD, CAT, GPX, and GST) were analyzed. The histopathological effects in hepatopancreas of crayfish were evaluated by light microscopy. Relationships between endpoints at different levels of biological organization and Cd bioaccumulation were also examined. Cd induced high levels of bioaccumulation, which was followed by mitochondrial dysfunction and histological alterations in both experiments. Moreover, perturbations in the defence mechanisms against oxidative stress tended to increase with time. Results also showed that molecular responses can vary depending on the intensity and duration of the chemical stress applied to the organisms and that the study of mt gene expression levels seemed to be the best tool to assess Cd intoxication.

Effects of uranium uptake on transcriptional responses, histological structures and survival rate of the crayfish Procambarus clarkii

This work aims to investigate the accumulation levels and effects (transcriptional responses, histopathology and survival rate) associated with a wide range of dissolved uranium (U) concentrations (0, 0.03, 0.6, 4 and 8 mg/L of U) on adult male crayfish Procambarus clarkii during 4 (T4) and 10 (T10) days of exposure. The follow-up of the crayfish mortality showed that P. clarkii was highly resistant to U. Increasing waterborne U concentrations led to increasing bioaccumulation in key crayfish organs and increasing histological damages. U distribution in tissues was also evaluated using transmission electron microscopy and showed the presence of a detoxified form of U in the gill's epithelium in the shape of flakes. Expression levels of mitochondrial genes (cox1, atp6 and 12S gene) and genes involved in oxidative stress (sod(Mn) and mt) were examined together with the housekeeping gene 18S. atp6 and mt genes of P. clarkii were cloned and sequenced before analysis. Significant correlations were observed between U bioaccumulation and the down-regulation of both cox1 and sod(Mn) genes. This work provides a first U toxicogenomic and histopathological pattern of P. clarkii, identify U biomarkers and associate gene expression endpoints to accumulation levels. It also provides new insights into the mechanisms involved in U stress.

Accumulation and toxicity of aluminium-contaminated food in the freshwater crayfish, Pacifastacus leniusculus

The accumulation and toxicity of aluminium in freshwater organisms have primarily been examined following aqueous exposure. This study investigated the uptake, excretion and toxicity of aluminium when presented as aluminium-contaminated food. Adult Pacifastacus leniusculus were fed control (3 μg aluminium/g) or aluminium-spiked pellets (420 μg aluminium/g) over 28 days. Half the crayfish in each group were then killed and the remainder fed control pellets for a further 10 days (clearance period). Concentrations of aluminium plus the essential metals calcium, copper, potassium and sodium were measured in the gill, hepatopancreas, flexor muscle, antennal gland (kidney) and haemolymph. Histopathological analysis of tissue damage and sub-cellular distribution of aluminium were examined in the hepatopancreas. Haemocyte number and protein concentration in the haemolymph were analysed as indicators of toxicity. The hepatopancreas of aluminium-fed crayfish contained significantly more aluminium than controls on days 28 and 38, and this amount was positively correlated with the amount ingested. More than 50% of the aluminium in the hepatopancreas of aluminium-fed crayfish was located in sub-cellular fractions thought to be involved in metal detoxification. Aluminium concentrations were also high in the antennal glands of aluminium-fed crayfish suggesting that some of the aluminium lost from the hepatopancreas is excreted. Aluminium exposure via contaminated food caused inflammation in the hepatopancreas but did not affect the number of circulating haemocytes, haemolymph ion concentrations or protein levels. In conclusion, crayfish accumulate, store and excrete aluminium from contaminated food with only localised toxicity.

Trophic transfer of aluminium through an aquatic grazer-omnivore food chain

The potential for trophic transfer of aluminium (Al) was investigated using a grazing detritivore, the freshwater snail Lymnaea stagnalis, and a predator, the signal crayfish Pacifastacus leniusculus. Snails were exposed to either aqueous Al (500 microg l(-1)) in the presence or absence of an inorganic ligand (phosphate (+P); 500 microg l(-1)) for 30 days, or kept as unexposed controls. Subcellular partitioning of Al in the snail tissues was characterised using ultracentrifugation. Al content in the soft tissues and the subcellular fractions was measured using inductively coupled plasma atomic emission spectroscopy. Exposed and control snails were fed to individually housed crayfish (n=6 per group) over 40 days. Water samples, uneaten snail tissue and faeces were collected throughout the experiment in order to assess the fate of Al. Behavioural toxicity to the crayfish was assessed at four time points, and tissue accumulation of Al in soft tissues was measured following a 2-day depuration period. Snails exposed to Al+P accumulated more Al per snail than those exposed to Al only (291 microg vs 206 microg), and also contained a higher proportion of detoxified Al (in inorganic granules and associated with heat stable proteins) (39% vs 26%). There were no significant differences in behavioural activity between the different groups of crayfish at any time point. Crayfish fed snails exposed to only Al accumulated significant levels of Al in their total soft tissues, compared to controls; crayfish fed Al+P-exposed snails did not, even though concentrations of Al in these snails were higher. The highest concentrations of Al were found in the green gland in both crayfish feeding groups, and the gut and hepatopancreas in crayfish fed Al only exposed snails; all of these were significantly higher than in crayfish fed control snails. There was no significant accumulation of Al in the gills or flexor muscle in any group. At least 17% of trophically available Al in the snail tissues was accumulated by the crayfish. This proportion was similar in both feeding groups but, as the proportion of trophically available Al in the snails exposed to Al+P was lower, this led to lower accumulation in the Al+P crayfish feeding group. This study indicates that in comparison to vertebrates, aquatic invertebrates accumulate a higher proportion of Al via oral ingestion but it does not accumulate in tissues that may pose a threat to human consumers.

The effect of starvation on the ultrastructure of the digestive cells of Dolops ranarum (Stuhlmann, 1891) (Crustacea: Branchiura)

Transmission electron microscopy was conducted on the digestive epithelium of the crustacean ectoparasite Dolops ranarum to elucidate its ultrastructure for the first time, both in a nourished and starved condition. Specimens were collected from the Limpopo Drainage System in South Africa, and the specimens were killed and dissected in Todd's fixative. The anterior midgut is composed mostly of absorptive cells or R cells, while the diverticula are composed of R cells and of F cells, which are moderately abundant in rough endoplasmic reticulum. They are probably responsible for producing digestive enzymes. The posterior midgut is composed of papilliform B cells with large apically located vesicles and R' cells devoid of cell inclusions. Under starvation, specimens survive for a maximum of 12 days; R cells show the most conspicuous changes in ultrastructural characteristics. It is concluded that D. ranarum has adapted to short-term survival only without a host.

The ultrastructure of the digestive cells of Argulus japonicus, Thiele 1900 (Crustacea: Branchiura)

The ultrastructure of the cells of the digestive system of Argulus japonicus is described with the use of transmission electron microscopy. Specimens of Argulus japonicus were collected from the Vaal Dam in South Africa and fixed in Todd's fixative. The samples were post fixed in osmium tetroxide and embedded in resin. The anterior midgut is composed mostly of R cells while the enteral diverticula are composed mainly of R cells in the proximal diverticules and of F cells in the distal diverticula. The posterior midgut is composed of very large papilliform B cells and of R cells. The R cells in the anterior midgut probably absorb nutrients including lipids. The F cells are filled mostly with rough endoplasmic reticulum, suggesting enzyme synthesis, while the B cells portrayed endocytotic vesicles, indicating intracellular digestion of predigested food. The R cells of the posterior midgut are less active than cells present in the anterior midgut. E cells and peritrophic membrane were not observed.

The use of two species of crayfish as environmental quality sentinels: the relationship between heavy metal content, cell and tissue biomarkers and physico-chemical characteristics of the environment

In systems as heavily disturbed as rivers, the use of biological sentinels is a most interesting way of obtaining continuous assessment of environmental quality. This study seeks to establish the value of such sentinels of two species of crayfish: the native crayfish (Austropotamobius pallipes, Lereboullet 1858) and an introduced species, signal crayfish (Pacifastacus leniusculus, Dana 1852), by comparing the habitat quality (water and sediments) and heavy metal contents in crayfish with the degree of stress manifested by the animals, measured by cell and tissue biomarkers. For this purpose a histological study of the digestive gland was carried out together with measurements of heavy metal contents in samples from various points of the river network of Bizkaia (Spain), selected on the basis of their degree of disturbance. The results establish a positive correlation between these environmental conditions, the cell and tissue biomarkers of the digestive gland (thinning of the digestive epithelium, enlargement of digestive lysosomes) and the heavy metal contents of the animals (converted to an index of pollutant load).

The uptake and storage of iron and lead in cells of the crayfish (Orconectes propinquus) hepatopancreas and antennal gland

The heavy metals iron and lead are taken up and metabolized in a similar manner by the crayfish hepatopancreas, but only lead appears to enter cells of the antennal gland (green gland). Iron, on the other hand, which apparently is not taken up by the antennal gland cells following systemic injections of low doses (0.05 mg), exerts striking alterations in cell ultrastructure after pericardial injections of massive doses (0.5 mg). Electron microscopic examination and atomic absorption spectrophotometric analyses of the hepatopancreas and antennal glands of iron-injected crayfish revealed that iron was selectively stored in metal-containing vacuoles of R- and F-cells in the hepatopancreatic cells, where it accumulated in concentrations that were toxic to these cells. High doses of iron caused alterations in the ultrastructural morphology of the cells of the antennal glands, although no accumulation of iron was apparent. Lead was similarly stored in metal-containing vacuoles of the cells of the hepatopancreas of lead-injected crayfish, but also accumulated in high concentrations (prior to being excreted) in vacuoles, cytoplasmic bodies and vesicles in the cells of the antennal gland. In contrast, lead in high concentrations was relatively non-toxic to any of these cells, suggesting that crayfish were more efficient in detoxifying and eliminating lead than iron.

Metal-protein binding patterns in the hepatopancreas of the crayfish (Austropotamobius pallipes) during short term cadmium stress

Cd-binding patterns in the hepatopancreas of the crayfish (Austropotamobius pallipes) have been analysed in response to the administration of a single dose of Cd ions. Four main components, with apparent molecular weights of 3-4, 12, 20 and greater than 70 K daltons, have been isolated from soluble cell fractions. The variation in molar metal/protein ratios of these components is discussed in terms of the uptake, transfer and detoxification of Cd in the hepatopancreas. A model is proposed which describes Cd flux at the subcellular level and indicates that metallothionein-like proteins may mediate in this process.