Structure of peroxisomes and activity of the marker enzyme catalase in digestive epithelial cells in relation to PAH content of mussels from two Basque estuaries (Bay of Biscay): seasonal and site-specific variations

Environmental assessment of the central Atlantic coast of Morocco using a multibiomarker approach in Mytilus galloprovincialis

A multibiomarker approach helps assess environmental health as it provides a complete tool to understand the effects of environmental stressors on ecosystems and human health. We applied this approach in the central Atlantic Ocean of Morocco, an area subjected to the impact of many types of pollutants, threatening the durability of its resources. In this study, four biomarkers acetylcholinesterase (AChE), glutathione-s-transferase (GST), metallothioneins (MTs), and catalase (CAT) were measured in the digestive gland of the mussel Mytilus galloprovincialis collected from four sites: Imsouane (S1), Cap Ghir (S2), Imi Ouaddar (S3), and Douira (S4). These sites were chosen due to the diversity of impacts ranging from industrial to agricultural and touristic. We also assembled all the enzymatic responses (AChE, GST, CAT, and MTs), using the integrated biomarker response (IBR), to estimate the degree of impact of pollutants at the prospected sites to reveal all the complex interactions between biomarkers and to classify sites via the integrated approach. Results show a seasonal change in biomarker responses with variability between sites. We also recorded the highest levels of AChE inhibition and GST induction in S1, higher levels of catalase activity in S4, and a significant impact on metallothionein concentration in S1 and S3. This project highlights the interest in using a multibiomarker approach to ensure accurate interpretation of biomarker variation to protect the Moroccan coast and its resources.

Integrated Biomarker responses in the mollusk, Patella vulgata: Assessing Aquatic pollution in Agadir Bay, South Morocco

In Agadir Bay, a study evaluated pollution biomarkers in the mollusk species Patella vulgata. Samples were collected seasonally from September 2021 to September 2022 at two distinct coastal sites within Agadir Bay: Cap Ghir and Anza Beach. Notable variations were observed in biomarkers like malondialdehyde, with a peak at 10.62 nmol/mg P in spring 2022 at Anza Beach. Catalase activity spiked in spring at 69.56 µmol/min/mg P for Cap Ghir and 72.73 µmol/min/mg P for Anza Beach. Acetylcholinesterase showed a decrease at 9.84 nmol/min/mg P in autumn at Anza Beach. Meanwhile, glutathione-S-transferase recorded an increase to 317.96 nmol/min/mg P at Cap Ghir in spring 2022. Using the Integrated Biomarker Response (IBR), these results were visualized, highlighting more stress in mollusks from Anza Beach compared to Cap Ghir. This research provides critical insights into the environmental effects on P. vulgata and potential conservation strategies.

Assessment of seasonal and spatial variation responses of integrated biomarkers in two marine sentinel bivalve species: Agadir Bay (Southern of Morocco)

The present study aims to assess the effects of contamination of the Agadir bay coasts using bivalves as a biomonitoring sentinel species. Seasonal variations of biochemical composition in terms of total protein content and oxidative stress biomarkers including glutathione-S-transferase, malondialdehyde, catalase and acetylcholinesterase were evaluated in the soft tissues of Scrobicularia plana and Donax trunculus specimens. The latter were collected from two sites in Agadir bay during two-year span (2018-2020). The Integrated Biomarker Response Index (IBR) was performed to classify the stress response in both species and to assess the level of exposure to xenobiotics. The data showed maximum annual values of acetylcholinesterase and malondialdehyde for Donax trunculus in Agadir beach (AG) with 6.25 nmol/mn/mg and 3 nmol/mg of protein, respectively. Those of catalase and glutathione-S-transferase for Scrobicularia plana in Oued Souss estuary (OS) were of 4.41 μmol/mn/mg and 14.43 nmol/mn/mg of protein, respectively. The studied species are considered good indicators in aquatic ecosystems.

Catalase is required for peroxisome maintenance during adipogenesis

Although obesity contributes to the onset and pathogenesis of metabolic diseases, it has been repeatedly demonstrated that being overweight or mildly obese carries a survival advantage compared with being thin or normal-weight. This relationship is called the obesity paradox. Hence, it is necessary to clarify the underlying mechanism of obesity onset for the prevention and treatment of these diseases. Catalase is distributed in peroxisomes under normal redox conditions and catalase activity is increased during the differentiation of 3T3-L1 preadipocytes to adipocytes. Although peroxisomes are responsible for lipid metabolism, the role of peroxisomal catalase in the process of lipid accumulation remains unclear. The present study aimed to investigate the relationships among catalase activity, peroxisome content, and lipid accumulation during the differentiation of 3T3-L1 preadipocytes to adipocytes. Increased catalase activity and lipid accumulation were observed during the differentiation of preadipocytes. Silencing of catalase by small interfering RNA or treatment with 3-amino-1,2,4-triazole (3-AT), a catalase inhibitor, resulted in reduced lipid accumulation. Inhibition of catalase activity in peroxisomes increases hydrogen peroxide (H₂O₂) levels, which results in a reduction of peroxisome content. Extracellular H₂O₂ had no influence on lipid accumulation during differentiation. The occurrence of autophagy was clearly enhanced in cells treated with 3-AT. Spautin-1, an inhibitor of autophagy flux, protected against a reduction in lipid accumulation by treatment with 3-AT. Our data provide evidence that catalase protects against the degradation of peroxisomes via the occurrence of autophagy triggered by the generation of H₂O₂ in peroxisomes. These results suggest that catalase in peroxisomes is crucial to adipogenesis.

Chronic environmental stress enhances tolerance to seasonal gradual warming in marine mussels

In global climate change scenarios, seawater warming acts in concert with multiple stress sources, which may enhance the susceptibility of marine biota to thermal stress. Here, the responsiveness to seasonal gradual warming was investigated in temperate mussels from a chronically stressed population in comparison with a healthy one. Stressed and healthy mussels were subjected to gradual temperature elevation for 8 days (1°C per day; fall: 16–24°C, winter: 12–20°C, summer: 20–28°C) and kept at elevated temperature for 3 weeks. Healthy mussels experienced thermal stress and entered the time-limited survival period in the fall, became acclimated in winter and exhibited sublethal damage in summer. In stressed mussels, thermal stress and subsequent health deterioration were elicited in the fall but no transition into the critical period of time-limited survival was observed. Stressed mussels did not become acclimated to 20°C in winter, when they experienced low-to-moderate thermal stress, and did not experience sublethal damage at 28°C in summer, showing instead signs of metabolic rate depression. Overall, although the thermal threshold was lowered in chronically stressed mussels, they exhibited enhanced tolerance to seasonal gradual warming, especially in summer. These results challenge current assumptions on the susceptibility of marine biota to the interactive effects of seawater warming and pollution.

Invertebrate community responses to emerging water pollutants in Iberian river basins

Chemical pollution is one of the greatest threats to freshwater ecosystems, especially in Mediterranean watersheds, characterized by periodical low flows that may exacerbate chemical exposure. Different groups of emerging pollutants have been detected in these basins during the last decade. This study aims to identify the relationships between the presence and levels of prioritary and emerging pollutants (pesticides, pharmaceutical active compounds--PhACs, Endocrine Disrupting Compounds EDCs and Perfluorinated Compounds--PFCs) and the invertebrate community in four Mediterranean basins: the Ebro, the Llobregat, the Júcar and the Guadalquivir. Structural (species composition and density) and functional (catalase activity of the tricopteran Hydropsyche exocellata and the feeding activity of the cladoceran Daphnia magna) variables were analyzed to determine which of the pollutants would greatly influence invertebrate responses. EDCs and conductivity, followed by PhACs, were the most important variables explaining the invertebrate density changes in the studied basins, showing a gradient of urban and industrial pollutions. Despite this general pattern observed in the four studied basins - impoverishment of species diversity and abundance change with pollution - some basins maintained certain differences. In the case of the Llobregat River, analgesics and anti-inflammatories were the significant pollutants explaining the invertebrate community distribution. In the Júcar River, fungicides were the main group of pollutants that were determining the structure of the invertebrate community. Functional biomarkers tended to decrease downstream in the four basins. Two groups of pollutants appeared to be significant predictors of the catalase activity in the model: EDCs and PhACs. This study provides evidence that the information given by functional biomarkers may complement the results found for the structural community descriptors, and allowed us to detect two emerging contaminant groups that are mainly affecting the invertebrate community in these basins.

Short- and long-term responses and recovery of mussels Mytilus edulis exposed to heavy fuel oil no. 6 and styrene

Biomarkers have the potential to be used to assess the impact of anthropogenic discharges in marine waters. We have used a suite of biomarkers spanning from enzymatic to histopathological alterations and general stress responses to assess the short- and long-term impact on mussels Mytilus edulis of heavy fuel oil no. 6 and styrene. Mussels were exposed for 5 months, with a refilling of the exposure system, to a water soluble fraction of heavy fuel and, then, kept for a month in clean water for recovery. In a second experiment, mussels were exposed to styrene for 19 days and maintained in clean water for up to 4 months. Chemical body tissue levels reflected the weathering processes of these compounds. Acyl-CoA oxidase activity was induced in oil-exposed mussels after refilling, whereas styrene inhibited it after 19 days of exposure and after 2 weeks in clean water. Gamete development and alkali-labile phosphate levels suggest that neither oil nor styrene behaved as endocrine disruptors. Neutral red retention time was lower in treated groups than in controls. Lysosomal membrane stability was significantly reduced in exposed groups and recovered after withdrawal of oil but not after removal of styrene. Neither oil nor styrene exposure affected the condition index except for the reduction seen in mussels exposed to oil for 1 month. Biomarker response index discriminated exposed mussels, which showed higher values, and returned to control levels after recovery. Results obtained from these pilot experiments can help to identify relevant monitoring tools to assess the impact of oil and chemicals in marine spill scenarios.

Lysosomal and tissue-level biomarkers in mussels cross-transplanted among four estuaries with different pollution levels

A 3-4 wk cross-transplantation experiment was carried out in order to investigate the sensitivity, rapidity, durability and reversibility of lysosomal and tissue-level biomarkers in the digestive gland of mussels. Four localities in the Basque coast with different levels of chemical pollution and environmental stress were selected. Lysosomal membrane stability (LP) and lysosomal structural changes (VvL; S/VL; NvL) and changes in cell-type composition in digestive gland epithelium (VvBAS) were investigated to determine short (2d) and mid-term (3-4 wk) responses after cross-transplantation. Mussels from Txatxarramendi presented VvBAS<0.1 μm(3)/μm(3) (unstressed) whilst VvBAS>0.12 μm(3)/μm(3) was recorded in mussels from Plentzia (moderate stress) and VvBAS>0.2 μm(3)/μm(3) in Arriluze and Muskiz (high stress). Accordingly, LP<10 min (high stress) was recorded in mussels from Muskiz and Arriluze and LP~15 min (low-to-moderate stress) in those from Plentzia and Txatxarramendi. According to the VvL, S/VL and NvL data, a certain lysosomal enlargement was envisaged in mussels from Arriluze in comparison with those from Txatxarramendi and Plentzia. Mussels from Muskiz exhibited a peculiar endo-lysosomal system made of abundant tiny lysosomes (low VvL and high S/VL and NvL values). Lysosomal and tissue-level biomarkers were responsive after 2d cross-transplantation between the reference and the polluted localities, which indicated that these biomarkers were quickly induced and, to a large extent, reversible. Moreover, the tissue-level biomarker values were maintained during the entire period (3-4 wk) of cross-transplantation, which evidenced the durability of the responsiveness. In contrast, comparisons in the mid-term were unfeasible for lysosomal biomarkers as these exhibited a seasonal winter attenuation resulting from low food availability and low temperatures. In conclusion, lysosomal enlargement and membrane stability and changes in cell-type composition were sensitive, rapid and reversible responses to changes in environmental stress whilst durability of the response could not be demonstrated for lysosomal responses by interferences with the seasonal variability.

Seasonal and pollution-induced variations in biomarkers of transplanted mussels within the Beagle Channel

The occurrence of biomarker variations linked to environmental factors makes it difficult to distinguish the effect of pollution. In an attempt to evaluate spatial and seasonal effects of environmental parameters on biomarker responses, mussels Mytilus edulis chilensis coming from an aquaculture farm were transplanted to several points within Ushuaia Bay (Beagle Channel) for 6 weeks in summer and winter. Activities of superoxide dismutase, catalase, glutathione-S-transferase and levels of lipid peroxidation were measured in gills and digestive gland. Cu, Zn, Fe, Cd and Pb concentrations were also assessed. Results indicated a significant effect of seasons on biological responses as well as in metal bioaccumulation showing the influence of natural factors such as dissolved oxygen, temperature and food availability. The interdependence of those environmental factors is important for the homeostasis of thermoconformers, especially regarding their oxidative metabolism and should also be taken into consideration to distinguish natural from pollution-induced variations.

Peroxisomal proteomic approach for protein profiling in blue mussels (Mytilus edulis) exposed to crude oil

Peroxisomal proteomic protein profiles of exposure to marine pollution have been recently introduced in biomonitoring experiments. However, laboratory experiments to study the independent effect of common pollutants are needed to define a minimal protein expression signature (PES) of exposure to a specific pollutant. The aim of this study was to obtain PESs in blue mussels (Mytilus edulis) exposed to two different crude oil mixtures for future application in biomonitoring areas affected by oil spills. In the study, peroxisome-enriched fractions from digestive gland of M. edulis (L., 1758) were analysed by two-dimensional fluorescence difference electrophoresis (DIGE) and mass spectrometry (MS) after 3 weeks of exposure to crude oil mixtures: crude oil or crude oil spiked with alkylated phenols (AP) and extra polycyclic aromatic hydrocarbons (PAH) in a laboratory flow-through system. A minimal PES composed by 13 protein spots and unique PESs of exposure to the two different mixtures were identified. A total of 22 spots from the two-dimensional maps that had shown a significant increase or decrease in abundance in each of the exposed groups exposed were analysed. The hierarchical clustering analysis succeeded in discriminating the exposed groups from the control groups based on the unique PES. The PESs obtained were consistent with protein patterns obtained in previous field experiments. The results suggest that the protein profiles obtained by peroxisomal proteomics could be used to assess oil exposure in marine pollution assessments.

Comparative petroleum hydrocarbons levels and biochemical responses in mussels from hydrothermal vents (Bathymodiolus azoricus) and coastal environments (Mytilus galloprovincialis)

Aliphatic hydrocarbons and PAHs in the whole soft tissues of Bathymodiolus azoricus from three Mid-Atlantic Ridge hydrothermal vents (Menez-Gwen, Lucky Strike and Rainbow), and Mytilus galloprovincialis from three contaminated coastal sites in South Portugal were analysed, and its effects on the digestive gland microsomes mixed-function oxygenase system (MFO) were assessed. Aliphatic hydrocarbons levels were present in the same magnitude in both coastal and hydrothermal environments, while the UCM (unresolved complex mixture) for coastal mussels were higher than in vent mussels. In general, significantly higher PAHs concentrations were found in coastal mussels, compared to B. azoricus where low molecular weight PAHs (2-3 rings) represented the majority of PAHs contrarily to what was observed in M. galloprovincialis. The MFO components were present in both mussel species, and were detected in vent mussels for the first time. However this system seems to have different roles in species from these contrasting environments. In coastal mussels MFO responded to hydrocarbon contamination while response in hydrothermal organisms appeared to be related mainly to endogenous factors.

Antioxidant responses to variations in dissolved oxygen of Scapharca inaequivalvis and Tapes philippinarum, two bivalve species from the lagoon of Venice

The aim of the present work was to determine the activities of selected antioxidant enzymes (SOD, Se-GPX, CAT) in two species of bivalves, Scapharca inaequivalvis and Tapes philippinarum, from two sites of the lagoon of Venice that are characterized by different pO(2) (Marghera and Chioggia). The specimens were collected at four times during a 1-year period. In the two species studied, enzyme activities were found to be present in both digestive glands and gills, but with some species-specific differences that may also represent a different adaptation to seasonal variations. The presence of high SOD activities in the gills of both species may be related to their physiological role in respiration. Scapharca inaequivalvis is less sensitive than T. philippinarum to environmental changes, perhaps due to the presence of hemoglobins in this species. Moreover, in the digestive gland of T. philippinarum we found a significant negative correlation between the activities of SOD and GPX that may indicate the presence of oxidative stress. Some correlations between temperature/dissolved oxygen and antioxidant enzyme activity were present in specimens sampled in Marghera. Only GPX adequately responded to changes in dissolved oxygen and temperature, while the decrease in the activity of SOD and CAT in winter may be directly responsible for an enhanced susceptibility of mussels to oxidative stress during this period. We can conclude that the observed differences between Chioggia and Marghera are due to different concentrations of dissolved oxygen. Marghera is an appropriate location to study seasonal variations in water temperature. In fact, in this site, the differences between hot and cold months are quite evident.

Oxidative stress in the clam Ruditapes decussatus (Linnaeus, 1758) in relation to polycyclic aromatic hydrocarbon body burden

Seasonal variation of antioxidant enzymes activities (superoxide dismutase, catalase, and glutathione peroxidases) and lipid peroxidation (LPO) were studied in the clam Ruditapes decussatus in relation to body burdens of polycyclic aromatic hydrocarbons (PAHs). Clams were sampled in eight sites from the Ria Formosa lagoon. PAH concentrations were seasonally rather than spatially dependent, being higher in summer (August). Antioxidant enzymes activities and LPO levels in the clam digestive gland were also seasonally dependent. Antioxidant enzymes presented distinct seasonal variations: Mit SOD (superoxide dismutase activity measured in the mitochondrial fraction) was induced in the summer and down-regulated in winter and spring, while Cyt SOD activity (measured in the cytosolic fraction) was highest in autumn and lower in the summer. Neither Mit nor Cyt SOD were related to the clam PAH body burden, suggesting that cells are using other antioxidant systems to eliminate oxyradicals. Catalase (CAT), however, was induced in spring and down-regulated in summer, the inverse of the PAH concentrations in clam tissues. CAT induction in spring appears to be related to the excess of oxyradicals arising from the metabolic activity associated with the reproductive cycle. Conversely, the decrease in CAT activity in the summer may be related to the high water temperatures reached in the Ria Formosa (up to 30 degrees C). Glutathione peroxidases (total fraction - T-GPx and dependent on selenium - Se-GPx) presented a similar seasonal pattern, and were negatively related to PAH concentrations, which may indicate a precarious state of the clams, associated with PAH toxicity. Similarly, LPO was also inversely correlated to the PAH concentrations indicating that increases in PAH concentrations were not causing membrane oxidative damage in R. decussatus digestive gland. The results suggest that antioxidant enzymes in R. decussatus digestive gland are strongly affected by seasonal factors stressing the need of other experiments to clarify the PAHs effect on this clam species.

Identification of Proteomic Signatures of Exposure to Marine Pollutants in Mussels (Mytilus edulis)

Bivalves and especially mussels are very good indicators of marine and estuarine pollution, and so they have been widely used in biomonitoring programs all around the world. However, traditional single parameter biomarkers face the problem of high sensitivity to biotic and abiotic factors. In our study, digestive gland peroxisome-enriched fractions of Mytilus edulis (L., 1758) were analyzed by DIGE and MS. We identified several proteomic signatures associated with the exposure to several marine pollutants (diallyl phthalate, PBDE-47, and bisphenol-A). Animals collected from North Atlantic Sea were exposed to the contaminants independently under controlled laboratory conditions. One hundred and eleven spots showed a significant increase or decrease in protein abundance in the two-dimensional electrophoresis maps from the groups exposed to pollutants. We obtained a unique protein expression signature of exposure to each of those chemical compounds. Moreover a set of proteins composed a proteomic signature in common to the three independent exposures. It is remarkable that the principal component analysis of these spots showed a discernible separation between groups, and so did the hierarchical clustering into four classes. The 14 proteins identified by MS participate in alpha- and beta-oxidation pathways, xenobiotic and amino acid metabolism, cell signaling, oxyradical metabolism, peroxisomal assembly, respiration, and the cytoskeleton. Our results suggest that proteomic signatures could become a valuable tool to monitor the presence of pollutants in field experiments where a mixture of pollutants is often present. Further studies on the identified proteins could provide crucial information to understand possible mechanisms of toxicity of single xenobiotics or mixtures of them in marine ecosystems.

Specificity of the peroxisome proliferation response in mussels exposed to environmental pollutants

Peroxisome proliferation has been proposed as novel biomarker of exposure to organic pollutants in aquatic organisms. Peroxisome proliferator compounds comprise a heterogeneous group of substances known for their ability to cause massive proliferation of peroxisomes and liver carcinogenesis in sensitive species such as rodents. Recently, several marine organisms (mussels and fish) have been shown as target species of peroxisome proliferators. In the present work, we aimed to investigate the specificity of the peroxisome proliferation response in mussels. For this purpose, mussels (Mytilus edulis) were exposed for three weeks to North Sea crude oil (NSO), a mixture of NSO, alkylphenols and extra PAHs (MIX), diallylphthalate (DAP), bisphenol-A (BPA) and tetrabromodiphenylether (TBDE), or transplanted for three weeks to four stations showing different copper concentrations in a copper mine. Peroxisome proliferation was assessed by measuring the activity of the peroxisomal beta-oxidation enzyme acyl-CoA oxidase (AOX) and the volume density occupied by peroxisomes (V(VP)) in the digestive gland. Mussels exposed to NSO and MIX showed significantly increased AOX activities and V(VP) compared to control animals. Significantly higher V(VP) was also found in DAP and TBDE exposed mussels. V(VP) did not vary in mussels transplanted into a copper concentration gradient. Our results confirm the usefulness and specificity of peroxisome proliferation as a suitable biomarker of exposure to organic contaminants such as oil derived hydrocarbons, phthalate plasticizers and polybrominated flame retardants in mussels.

Field application of a set of cellular biomarkers in the digestive gland of the freshwater snail Radix peregra (Gastropoda, Pulmonata)

An active biomonitoring study was performed in the vicinity of two pulp and paper mill effluents (PPMEs) released in two different streams in northeastern France. Freshwater gastropods, Radix peregra (=Lymnaea peregra or Lymnaea pereger), were transplanted for 0, 3, 14 and 21 days at two to three sites located upstream and downstream from the mill discharge points in both rivers. Lysosomal and peroxisomal systems, as well as lipofuscin and neutral lipids, were tested using histochemical methods on cryostat sections of digestive gland tissues, and stereological data were obtained by image analysis. Evidence of structural changes in the lysosomal system was found in animals exposed to both effluents, comprising general stress responses such as enlarged and more numerous lysosomes; and also possible specific pluri-phasic effects. Modifications of the lysosomal and cytoplasmic contents of lipid-related materials were also described, namely enhanced lipofuscin deposit and neutral lipid depletion. The peroxisomal proliferation in exposed snails seems to show its implication in oxidative stress detoxication, without preventing higher lipoperoxidation, as indicated by the increased amounts of digestive lipofuscin. Structural changes of the lysosomal and peroxisomal systems, digestive lipofuscin and neutral lipid contents have potential for use as early cellular biomarkers in Radix peregra exposed to environmental stressors, which deserve further investigations.

Biomarkers of exposure and reproduction-related effects in mussels exposed to endocrine disruptors

Biomarkers are useful tools to study the health of estuarine and marine ecosystems. Biomarkers can be measured in different organisms, but mussels have acquired a global importance as sentinels in marine pollution-monitoring programs. In the present work, we aimed to determine the effects of different endocrine disruptors in mussels by using peroxisome proliferation as a biomarker of exposure to organic pollutants and the levels of vitellogenin (Vtg)-like proteins as biomarker of endocrine disruption. In experiment 1, mussels Mytilus edulis were exposed for 3 weeks to North Sea crude oil (NSO 0.5 ppm) and a mixture of 0.5 ppm NSO, 0.1 ppm alkylphenol mix, and 0.1 ppm extra polycyclic aromatic hydrocarbons (PAHs) (MIX). In experiment 2, mussels were exposed for 3 weeks to diallylphthalate (DAP 50 ppb), bisphenol-A (BPA 50 ppb), and tetrabromodiphenylether (TBDE 5 ppb). Peroxisome proliferation was assessed by measuring acyl-CoA oxidase (AOX) activity and peroxisomal volume density (VVp) in digestive gland. Vtg-like protein levels were measured in gonads by the alkali-labile phosphate (ALP) method. Gonad was also analyzed histologically, and the gonad index (GI) calculated. Mussels exposed to NSO and MIX showed significantly increased AOX activities and VVP compared with control animals. Significantly higher VVP was also found in DAP- and TBDE-exposed mussels. Effects on ALP and GI depended significantly on sex and time of year. In female mussels, ALP levels and GI were lower in the NSO group. In male mussels, ALP levels were significantly increased in the MIX group. The volume density of athretic oocytes was higher in the NSO and MIX exposure groups than in controls, and gonad resorption was observed in the BPA exposure group. Our results confirm the usefulness of peroxisome proliferation as a biomarker of exposure to organic contaminants in mussels and indicate that changes in Vtg-like proteins could be used as potential indicator of pollutant effects on mussel reproduction.

Cell and tissue biomarkers in mussel, and histopathology in hake and anchovy from Bay of Biscay after the Prestige oil spill (Monitoring Campaign 2003)

In order to assess the biological effects of the Prestige oil spill (POS), mussels (Mytilus galloprovincialis), European hake (Merluccius merluccius) and European anchovy (Engraulis encrasicolus) were sampled between April and September 2003 in various geographical areas of Bay of Biscay: Galicia, Central Cantabrian and East Cantabrian. In mussels, several cell and tissue biomarkers were measured: peroxisome proliferation as induction of acyl-CoA oxidase (AOX) activity, lysosomal responses as changes in the structure (lysosomal volume density, V(V(L)), surface-to-volume ratio, S/V(L), and numerical density, N(V(L))) and in membrane stability (labilization period, LP), cell type replacement as relative proportion of basophilic cells (volume density of basophilic cells, V(V(BAS))) in digestive gland epithelium, and changes in the morphology of digestive alveoli as mean luminal radius to mean epithelial thickness (MLR/MET). Additionally, flesh condition index (FCI) and gonad index (GI) were measured as supporting parameters. In hake and anchovy, liver histopathology was examined to determine the prevalence of parasites, melanomacrophage centers, non-specific lesions (inflammatory changes, atrophy, necrosis, apoptosis), early non-neoplastic toxicopathic lesions (i.e., hepatocellular nuclear polymorphism), foci of cellular alteration, benign and malignant neoplasms. In mussels, AOX induction was noticeable in April except in Galicia. LP values were low in all the geographical areas studied, indicating disturbed health, especially in Galicia. Alike, lysosomal enlargement was observed in most stations as shown by the extremely low S/V(L) values. V(V(BAS)) and MLR/MET values were markedly high. Overall, employed biomarkers detected exposure to toxic chemicals and disturbed health in mussels from Bay of Biscay, with impact decreasing from April to September. Although hepatocellular nuclear polymorphism and nematode parasitization in fish liver were remarkably prominent in some areas, they cannot be hitherto related to POS, since we lack historical data to determine whether the prevalences found were normal or significantly raised after POS.

The activity of antioxidant defence enzymes in the mussel Mytilus galloprovincialis from the Adriatic Sea

The activity of the antioxidant defence enzymes superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), glutathione peroxidase (GSH-Px, EC 1.11.1.9), glutathione reductase (GR, EC 1.6.4.2) and the phase II biotransformation enzyme glutathione-S-transferase (GST, EC 2.5.1.18) in whole mussels (Mytilus galloprovincialis) were studied. The mussels were collected in winter and in spring at two localities in the Adriatic Sea: Bar Port and Tivat Bay. Our results show that the activities of SOD, GSH-Px and GST were seasonally dependent with higher activities in winter. GR activity was also higher in winter, but only in mussels from Bar Port. In mussels from Tivat Bay, GR activity was lower in winter compared to spring. In addition, a decrease in CAT activity in mussels from Bar Port compared to those from Tivat Bay was found. It can be concluded that seasonal variations should be incorporated into interpretation of biomonitoring studies in mussels.

Antioxidant responses of the Mediterranean mussel, Mytilus galloprovincialis, to environmental variability of dissolved oxygen

Physiological responses of Mytilus galloprovincialis against environmental dissolved oxygen partial pressure (pO(2)) variation were studied in terms of the modulated induction of the main antioxidant enzymes: superoxide dismutase (SOD), catalase (CAT) and selenium-dependent glutathione peroxidase (GPX). Field in vivo studies were performed at two sites of the Lagoon of Venice, characterized by different aquatic environmental conditions implying different pO(2). SOD and GPX are more active in gills, and their complementary role is discussed. CAT is more active in the digestive gland, where the enzyme dismutates H(2)O(2) derived from divalent reduction of O(2) performed by various oxidases in peroxisomes. Antioxidant enzyme activities are correlated with water dissolved oxygen (DO), especially in the gills. This tissue, because of its anatomical localization and its physiological role, responds to DO variations modulating the induction of the antioxidant enzymes as a protection mechanism against potential toxicity due to increases in ROS formation.

Peroxidation in muscle and liver tissues from fish in a contaminated river due to a petroleum refinery industry

In this study, we aimed to investigate the possible effects of the wastewater water contamination of a petroleum industry on the oxidant/antioxidant status of muscle and liver tissues from fish in the Kizilirmak River, Kirikkale, Turkey. The antioxidant/oxidant parameters were analyzed in the muscle and liver tissues from fish in 10 km of the river above and below the industry. Malondialdehyde (MDA) and susceptibility to oxidation (SO) values were measured in the liver and muscle tissues as indexes of oxidation, and antioxidant potential (AOP), superoxide dismutase (SOD), glutathion peroxidase (GSH-Px), and catalase(CAT) activities were measured as indexes of antioxidant status. There was significant oxidation in the muscle tissue of the fish obtained in the river downstream of the industry compared to those obtained upstream of the industry. Although there were no meaningful differences between the SOD and GSH-Px activities, the AOP value and CAT activities were found to be reduced in the muscle tissues from the fish obtained downstream. In the liver tissues, the SOD and GSH-Px activities were found to be increased in the fish obtained downstream but no differences were observed in the MDA, SO, AOP, and CAT values. Our results suggest that some contaminants from the petrochemical industry cause oxidation in fish muscle tissues by impairing the antioxidant system. However, because no peroxidation was observed in the liver tissue from the downstream fish, it is possible that liver tissues have a stronger antioxidant capacity than muscle.

The application of histo-cytopathological biomarkers in marine pollution monitoring: a review

During the past two decades, a variety of histopathological alterations in fish and bivalves have been developed and used as biomarkers in pollution monitoring. Some of these have been successfully adopted in major national monitoring programmes, while others, although show promise, are still in the experimental stage. This paper critically reviews the scientific basis, cause and effect relationship, reliability, advantages and limitations of 14 histo-cytopathological biomarkers. The usefulness and practical application of each biomarker have been evaluated against a number of objective criteria including: ecological relevance, sensitivity, specificity, dose-response relationship, confounding factors, technical difficulties and cost-effectiveness.

Expression of peroxisome proliferator-activated receptors in the liver of gray mullet (Mugil cephalus)

During the last decade, peroxisome proliferation has emerged as a novel biomarker of exposure to certain organic chemical pollutants in aquatic organisms. Peroxisome proliferation is mediated by nuclear receptors, peroxisome proliferator-activated receptors (PPARs). Three PPAR subtypes have been described in mammals: PPAR alpha, PPAR beta and PPAR gamma. PPARs have also been discovered in several fish species. The aim of the present study was to investigate the expression of PPAR subtypes and their cellular distribution patterns in the liver of gray mullet Mugil cephalus, a fish species widely distributed in estuaries and coastal areas in Europe and used as sentinel of environmental pollution. For this purpose, antibodies were generated against the three subtypes of mouse PPARs and different protocols of antigen retrieval were used. In western blots, main bands were detected of approximately 44 kDa for PPAR alpha, two bands of 44 and 58 kDa for PPAR beta and a single band of 56 kDa for PPAR gamma. Similar results were obtained in mouse liver and may indicate antibody recognition of two forms of the protein in certain cases. PPAR alpha was the subtype most markedly expressed in gray mullet liver, being expressed mainly in melanomacrophages, nuclei of hepatocytes and sinusoidal cells and connective tissue surrounding bile ducts. PPAR beta was expressed in the same cell types but immunolabeling was generally weaker than for PPAR alpha. PPAR gamma showed very weak expression; positivity was mainly found in melanomacrophages and connective tissue surrounding bile ducts. Our results demonstrate that all the three PPAR subtypes are expressed in gray mullet liver but in different intensities. The cellular distribution patterns of PPAR subtypes in gray mullet liver resembled partly those found in mouse liver with PPAR alpha as the main subtype expressed in hepatocytes. The fact that melanomacrophages, cells of the immune system in fish, show strong expression of both PPAR alpha and PPAR beta whereas PPAR gamma expression is almost restricted to this cell type suggest a significant role of PPAR-mediated regulation of cell function in melanomacrophages.

Peroxisome proliferation as a biomarker in environmental pollution assessment

Peroxisome proliferators comprise a heterogeneous group of compounds known for their ability to cause massive proliferation of peroxisomes and liver carcinogenesis in rodents. In recent years it has become evident that other animals may be threatened by peroxisome proliferators, in particular aquatic organisms living in coastal and estuarine areas. These animals are exposed to a variety of pollutants of industrial, agricultural and urban origin which are potential peroxisome proliferators. Both laboratory and field studies have shown that phthalate ester plasticizers, PAHs and oil derivatives, PCBs, certain pesticides, bleached kraft pulp and paper mill effluents, alkylphenols and estrogens provoke peroxisome proliferation in different fish or bivalve mollusc species. The response appears to be mediated by peroxisome-proliferator activated receptors, members of the nuclear receptor family, recently cloned in fish. Based on these results it is proposed that peroxisome proliferation could be used as a biomarker of exposure to a variety of pollutants in environmental pollution assessment. This is illustrated by a case study in which mussels, used worldwide as sentinels of environmental pollution, were transplanted from reference to contaminated areas and vice versa. In mussels native to an area polluted with PAHs and PCBs, peroxisomal acyl-CoA oxidase (AOX) activity and peroxisomal volume density were 2-3 fold and 5-fold higher, respectively, compared to the reference site. When animals were transplanted to the polluted station, with increased concentration of organic xenobiotics, a concomitant significant increase of AOX was recorded. Conversely, in animals transplanted to the cleaner station, AOX activity and peroxisomal volume density decreased significantly. These results indicate that peroxisome proliferation is a rapid (i.e., two days) and reversible response to pollution in mussels. Before peroxisome proliferation can be implemented as a biomarker in biomonitoring programs, a well-defined protocol should be established and validated in intercalibration and quality assurance programmes. Furthermore, the influence of biotic and abiotic factors, some of which are known to affect peroxisome proliferation (season, tide level, interpopulation and interindividual variability), should be taken into consideration. The possible hepatocarcinogenic effects as well as the potential adverse effects on reproduction, development, and growth of peroxisome proliferators are unknown in aquatic organisms, thus providing a challenge for future investigations.

Antioxidant enzymes and peroxisome proliferation in relation to contaminant body burdens of PAHs and PCBs in bivalve molluscs, crabs and fish from the Urdaibai and Plentzia estuaries (Bay of Biscay)

With the aim of studying levels of antioxidant and peroxisomal enzymes and the structure of peroxisomes in relation to body burdens of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs), mussels Mytilus galloprovincialis, oysters Crassostrea sp., crabs Carcinus maenas and mullets Mugil cephalus were sampled in two Basque estuaries (Bay of Biscay): Urdaibai (Laida, Txatxarramendi, Arteaga, and downstream a sewage treatment plant-STP) and Plentzia. In general, animals showed higher concentrations of contaminants in winter than in summer and no relevant differences were detected among locations. Conversely, antioxidant enzyme activities were higher in summer. Enzyme expression was studied in mullets using immunochemical methods. By immunoblotting season-dependent differences were detected for Mn-superoxide dismutase (Mn-SOD). As for the immunohistochemical staining, mullets sampled in summer in Plentzia showed significantly higher optical densities for acyl-CoA oxidase and lower for both Cu,Zn-SOD and Mn-SOD than those collected downstream a STP as well as higher catalase immunostaining than those collected in winter. Peroxisomal volume density (V(vp)) of mussels sampled in Laida and Txatxarramendi did not show seasonal variations, while for oysters collected in Laida and Arteaga V(vp) was higher in summer. Crab and mullet V(vp) were also higher in summer. In conclusion, the estuaries of Urdaibai and Plentzia can be considered as low to moderately polluted areas and levels of PAHs and PCBs do not show marked variations apart from seasonal variations. Animals can be adapted to low pollution conditions and, under these circumstances, seasonal factors might affect biomarker responses to a greater extent than pollution variations.

Interactive effects of benzo(a)pyrene and cadmium and effects of di(2-ethylhexyl) phthalate on antioxidant and peroxisomal enzymes and peroxisomal volume density in the digestive gland of mussel Mytilus galloprovincialis Lmk

Exposure of marine animals to certain organic and metal pollutants is thought to enhance reactive oxygen species (ROS) production with concomitant alterations of antioxidant defence mechanisms. Some of these organic pollutants cause peroxisome proliferation, a process resulting also in possible enhanced production of ROS. The aim of this study was to investigate the effects of two organic xenobiotics, benzo(a)pyrene (B(a)P) and di(2-ethylhexyl)phthalate (DEHP), as well as the effects of cadmium (Cd), on antioxidant and peroxisomal enzymes and on peroxisomal volume density in the digestive gland of mussel, Mytilus galloprovincialis Lmk., experimentally exposed for 21 days. Special attention was paid to the interactive effects of organic and metal compounds by exposing one group of mussels to a mixture of B(a)P and Cd. Exposure of mussels to Cd caused a decrease in superoxide dismutase (SOD) activity, in Mn-SOD protein levels and in volume density of peroxisomes. B(a)P exposure significantly increased catalase and glutathione peroxidase (GPX) and inhibited Mn-SOD after 21 days of exposure. B(a)P also caused a slight increase in acyl-CoA oxidase (AOX) activity and peroxisomal volume density after 21 days of exposure. Cd tended to inhibit changes provoked by B(a)P, indicating that responses to organic xenobiotics can be modulated by concomitant exposure to metal contaminants. Exposure to DEHP increased catalase and AOX and inhibited SOD activity and Mn-SOD protein levels. In conclusion, peroxisome proliferation, measured as an increase of the peroxisomal enzymes catalase and AOX (up to 1.53-fold for AOX), is a specific response to organic contaminants such as B(a)P and DEHP, whereas Cd does not cause peroxisome proliferation. Thus, peroxisome proliferation may be a specific biomarker of organic pollutants in mussels. Both organic and metal pollutants inhibited SOD activity and protein levels (up to 0.21-fold for Mn-SOD protein levels), the latter offering potential as general marker of pollution.

D-Aspartate oxidase and D-amino acid oxidase are localised in the peroxisomes of terrestrial gastropods

D-Aspartate oxidase and D-amino acid oxidase were found in high activity in the tissues of representative species of terrestrial gastropods. Analytical subcellular fractionation demonstrated that both of these oxidases co-localised with the peroxisome markers, acyl-CoA oxidase and catalase, in the digestive gland homogenate. Electron microscopy of peak peroxisome fractions showed particles of uniform size with generally well preserved variably electron-dense matrices bounded by an apparently single limiting membrane. Many of the particles exhibited a core region of enhanced electron density. Catalase cytochemistry of peak fractions confirmed the peroxisome identity of the organelles. Peroxisome-enriched subcellular fractions were used to investigate the properties of gastropod D-aspartate oxidase and D-amino acid oxidase activities. The substrate and inhibitor specificities of the two activities demonstrated that two distinct enzymes were present analogous to, but not identical to, the equivalent mammalian peroxisomal enzymes.

A field study on EROD activity and quantitative hepatocytological changes in an immature demersal fish

Demersal fish, Solea ovata, were sampled from a reference site and a site where highly contaminated sediment is dumped. Sexually immature fish from the contaminated site exhibited significantly higher EROD activity compared with counterparts sampled from the reference site. No significant difference in EROD activity could be found for sexually mature males and females between sites. The relationship between EROD activity and quantitative changes in hepatic lipofuscin/ceroid, as well as peroxisome, was investigated for immature S. ovata. A significant correlation was found between EROD activity and volume density of lipofuscin/ceroid in fish hepatocyte (r = 0.750; P < 0.05), but no significant correlation was discernible between EROD activity and peroxisomes. Results from this field study corroborate our earlier laboratory findings, in which induction of EROD activity by intraperitoneal injection of benzo[a]pyrene was associated with increase in absolute volume and absolute number of lipofuscin/ceroid in hepatocytes. The present study provides further evidence that induction of EROD activity is associated with an increase in hepatic lipofuscin/ceroid and possibly cytological damages in immature S. ovata. This cytological change may serve as a potential marker for exposure to PAHs and PCBs.

Cell biology of peroxisomes and their characteristics in aquatic organisms

The general characteristics of peroxisomes in different organisms, including aquatic organisms such as fish, crustaceans, and mollusks, are reviewed, with special emphasis on different aspects of the organelle biogenesis and mechanistic aspects of peroxisome proliferation. Peroxisome proliferation and peroxisomal enzyme inductions elicited by xenobiotics or physiological conditions have become useful tools to study the mechanisms of peroxisome biogenesis. During peroxisome proliferation, the induction of peroxisomal proteins is heterogeneous, enzymes that show increased activity being involved in different aspects of lipid homeostasis. The process of peroxisome biogenesis is coordinately triggered by a whole array of structurally dissimilar compounds known as peroxisome proliferators, and investigating the effect of some of these compounds that commonly appear as pollutants in the environment on the peroxisomes of aquatic animals inhabiting marine and estuarine habitats seems interesting. It is also important to determine whether peroxisome proliferation in these animals is a phenomenon that might occur under normal physiological or season-related conditions and plays a metabolic or functional role. This would help set the basis for understanding the process of peroxisome biogenesis in aquatic animals.

The use of biomarkers to assess the impact of pollution in coastal environments of the Iberian Peninsula: a practical approach

Within the frame of the 2nd Iberian Congress of Environmental Contamination and Toxicology (University of the Basque Country, Leioa, June 1998) a workshop was held about the use of biomarkers in marine pollution monitoring. Among others, the following biomarkers received special attention: metallothionein induction, acetylcholinesterase inhibition, cytochrome P450 system induction, imposex, lysosomal enlargement and lysosomal membrane destabilisation, and peroxisome proliferation. These biomarkers can be used to evaluate exposure to and effect of different contaminants (metals, organic xenobiotics and organometallic compounds) and they can be measured using different methodological approaches (biochemistry, cytochemistry, immunochemical methods based on the use of biotechnology). Before the application of a set of biomarkers in pollution monitoring programmes, well-defined protocols of Quality Assurance have to be established to allow adequate comparison of results. It is also necessary to include analysis of standard reference materials and to obtain detailed knowledge of basal values and seasonal variations of the biomarkers in various species, as well as to integrate the information obtained with the different biomarkers. Marine bivalve molluscs such as mussels are appropriate sentinel species for most of the biomarkers proposed except for the induction of the cytochrome P450 system, which should be measured in fish, and the degree of imposex, which is a biomarker of exposure to TBT specifically measured in certain gastropod molluscs. As a result of the workshop, a battery of biomarkers of contaminant exposure and effects are proposed that could be incorporated into programmes monitoring the quality of the coastal environment in the Iberian Peninsula. These measures would be undertaken in conjunction with chemical measures of contaminant burdens in selected sentinel species.

Seasonal variation of peroxisomal enzyme activities and peroxisomal structure in mussels Mytilus galloprovincialis and its relationship with the lipid content

Variations in structure and function of peroxisomes in digestive tissues of marine mussels have been proposed to be valid biomarkers of environmental contamination by organic xenobiotics. The aim of the present work was to study the seasonal variations in peroxisomal enzyme activities, catalase, palmitoyl-CoA oxidase (AOX) and D-amino acid oxidase (DAOX) and peroxisomal structure in mussels. Peroxisomal changes were related to the seasonal variation in the contents of neutral lipids in the digestive gland as the lipid metabolism in mussels is subjected to seasonal variations linked to the reproductive cycle and food intake. Significant higher catalase activities were recorded from April to June when compared to the rest of the year and AOX activity was also markedly induced during the late winter and spring (February to May) with maximal activities in April. DAOX activity did not vary seasonally, the highest activities being measured in November, February and May. Stereological studies of peroxisomes in digestive tubule cells revealed significantly higher volume, surface and numerical densities in animals collected in spring and summer. Changes in peroxisomal volume density were found to be significantly and positively correlated with changes in AOX and catalase activities. The peroxisomal structure and enzyme activities were negatively correlated with the lipid contents of digestive tubules. In April, the volume density occupied by neutral lipids was higher in duct epithelia while previously it was higher in digestive tubule epithelia. This trend was maintained during the period in which peroxisomes were more abundant until July. In the following September, digestive tubules recovered their lipid load. It is concluded that seasonal changes related to food intake and reproductive cycle induce changes in peroxisomal parameters that can be compared to typical peroxisome proliferation, with a 25-fold increase in AOX activity and an 8-fold increase in the peroxisomal numerical density in early spring.