Kinetic and toxicological characteristics of acetylcholinesterase from the gills of oysters (Crassostrea rhizophorae) and other aquatic species

The use of integrative tools and multiple models for aquatic environmental quality assessment: a case study of the Mirim Lagoon, Southern Brazil

This study performed toxicity assays with microalgae, microcrustaceans, and fish as well as evaluated biochemical and behavioral biomarkers in fish and microcrustaceans to assess the quality of the surface water of Mirim Lagoon, which belongs to one of the largest hydrographic basins in the world, located in southern Brazil. Three distinct sampling periods were chosen (January, March, and June 2022) based on the rice plantation dynamics which is the main activity surrounding the lagoon. In January, the plantation is irrigated; in March, the water is drained into the Mirim Lagoon, and July is the off-season. Concerning toxicity tests, there was significant inhibition in microalgae growth when exposed to water collected in March, but no mortality was observed for Ceriodaphia dubia, Daphnia magna, and Danio rerio. Regarding biomarkers, behavioral variables contributed more to the higher values of the Integrated Biomarker Response (IBR) index for both D. magna and D. rerio, in March. The Redundancy Analysis (RDA) indicated a correlation between the biomarkers for both organisms and abiotic parameters, mainly nutrients (total phosphorus and total nitrogen), thermotolerant coliforms, total solids, and turbidity. Spatially, there was no difference during monitoring, but the most significant ecotoxicological effects were observed in March. Multivariate analysis and the IBR index proved to be useful tools for monitoring of water bodies such as Mirim Lagoon.

Glyphosate is Harmful to Early Life Stages of the Viviparous Fish Jenynsia Multidentata: Biochemical and Locomotor Effects

Glyphosate is the most widely used herbicide worldwide due to its efficacy in weed control in agriculture. This herbicide has been consistently detected in the aquatic environment, causing harmful consequences to nontarget organisms residing in agricultural regions. In this study, we assessed the effects of environmentally relevant concentrations of glyphosate (30-100 µg/L) on the early life stages of the viviparous fish Jenynsia multidentata through biochemical and locomotor endpoints. At 96 h of exposure, 30 and 65 µg/L glyphosate caused an increase in acetylcholinesterase (AChE) activity, and 65 µg/L glyphosate also augmented the levels of lipid peroxidation. Glyphosate at 100 µg/L did not alter the activity of acetylcholinesterase or the levels of lipid peroxidation, but it stimulated the activity of the cellular detoxification enzyme glutathione S-transferase. In addition, all concentrations affected the swimming of the fish. Under light conditions, glyphosate caused hypolocomotion at all concentrations tested, whereas under dark conditions, this was observed at 30 and 100 µg/L. Hyperlocomotion was observed at 65 µg/L glyphosate. These findings are alarming for the health of fish, such as J. multidentata that inhabit streams that pass through agricultural areas, especially for the early life stages of these fish. Research studying the effects of pollutants on native species is relevant to improve regulation that protects aquatic ecosystems.

Influence of temperature on biomarker responses of bullfrog tadpoles (Lithobates catesbeianus) exposed to the herbicide ametryn

The S-triazine herbicide ametryn (AMT) is relatively low adsorbed in soils and has high solubility in water, thus believed to affect non-target aquatic organisms such as amphibians. Temperature increases can intensify the effects of herbicides, possibly increasing the susceptibility of amphibians to these compounds. The aim of this study was to evaluate the influence of temperature (25 and 32 °C) on the responses of biochemical biomarkers in bullfrog tadpoles (Lithobates catesbeianus) exposed to different concentrations of AMT (0, 10, 50 and 200 ng.L^-1) for a period of 16 days. The antioxidant enzymes catalase (CAT) and superoxide dismutase (SOD) and the biotransformation enzyme glutathione S-transferase (GST) had their activity decreased at the highest temperature (32 °C). SOD activity was reduced at 200 ng.L^-1 and 32 °C compared to the control at the same temperature. AMT exposure also decreased the activities of alanine aminotransferase and gamma glutamyl transferase. On the other hand, the activities of acetylcholinesterase, carboxylesterase, alkaline phosphatase, levels of lipid peroxidation and protein carbonyl, as well genotoxic markers (micronucleus and nuclear abnormalities frequencies) were unchanged. The evaluation of integrated biomarker response index (IBR) indicated highest variations at the concentration of 200 ng.L^-1 at 32 °C, suggesting that the combination of high AMT concentrations and temperatures generate more pronounced negative effects to tadpoles.

Assessment of Pharmacological Potential of Novel Exopolysaccharide Isolated from Marine Kocuria sp. Strain AG5: Broad-Spectrum Biological Investigations

With more than 17 clinically approved Drugs and over 20 prodrugs under clinical investigations, marine bacteria are believed to have a potential supply of innovative therapeutic bioactive compounds. In the current study, Kocuria sp. strain AG5 isolated from the Red Sea was identified and characterized by biochemical and physiological analysis, and examination of a phylogenetic 16S rRNA sequences. Innovative exopolysaccharide (EPS) was separated from the AG5 isolate as a major fraction of EPS (EPSR5, 6.84 g/L⁻¹). The analysis of EPSR5 revealed that EPSR5 has a molecular weight (Mw) of 4.9 × 10⁴ g/mol and number average molecular weight (Mn) of 5.4 × 10⁴ g/mol and contains sulfate (25.6%) and uronic acid (21.77%). Analysis of the monosaccharide composition indicated that the EPSR5 fraction composes of glucose, galacturonic acid, arabinose, and xylose in a molar ratio of 2.0:0.5:0.25:1.0, respectively. Assessment of the pharmacological potency of EPSR5 was explored by examining its cytotoxicity, anti-inflammatory, antioxidant, and anti-acetylcholine esterase influences. The antioxidant effect of EPSR5 was dose- and time-dependently increased and the maximum antioxidant activity (98%) was observed at 2000 µg/mL after 120 min. Further, EPSR5 displayed a significant repressive effect regarding the proliferation of HepG-2, A-549, HCT-116, MCF7, HEP2, and PC3 cells with IC₅₀ 453.46 ± 21.8 µg/mL, 873.74 ± 15.4 µg/mL, 788.2 ± 32.6 µg/mL, 1691 ± 44.2 µg/mL, 913.1 ± 38.8 µg/mL, and 876.4 ± 39.8 µg/mL, respectively. Evaluation of the inhibitory activity of the anti-inflammatory activity of EPSR5 indicated that EPSR5 has a significant inhibitory activity toward lipoxygenase (5-LOX) and cyclooxygenase (COX-2) activities (IC₅₀ 15.39 ± 0.82 µg/mL and 28.06 ± 1.1 µg/mL, respectively). Finally, ESPR5 presented a substantial hemolysis suppressive action with an IC₅₀ of 65.13 ± 0.89 µg /mL, and a considerable inhibitory activity toward acetylcholine esterase activity (IC₅₀ 797.02 μg/mL). Together, this study reveals that secondary metabolites produced by Kocuria sp. strain AG5 marine bacteria serve as an important source of pharmacologically active compounds, and their impact on human health is expected to grow with additional global work and research.

Novel Exopolysaccharide from Marine Bacillus subtilis with Broad Potential Biological Activities: Insights into Antioxidant, Anti-Inflammatory, Cytotoxicity, and Anti-Alzheimer Activity

In the presented study, Bacillus subtilis strain AG4 isolated from marine was identified based on morphological, physiological, phylogenetic characteristics and an examination of 16S rRNA sequences. Novel exopolysaccharide (EPSR4) was extracted and isolated from the Bacillus subtilis strain as a major fraction of exopolysaccharide (EPS). The analysis of structural characterization indicated that EPSR4 is a β-glycosidic sulphated heteropolysaccharide (48.2%) with a molecular weight (Mw) of 1.48 × 104 g/mole and has no uronic acid. Analysis of monosaccharide content revealed that EPSR4 consists of glucose, rhamnose and arabinose monosaccharide in a molar ratio of 5:1:3, respectively. Morphological analysis revealed that EPSR4 possess a high crystallinity degree with a significant degree of porosity, and its aggregation and conformation in the lipid phase might have a significant impact on the bioactivity of EPSR4. The biological activity of EPSR4 was screened and evaluated by investigating its antioxidant, cytotoxicity, anti-inflammatory, and anti-Alzheimer activities. The antioxidant activity results showed that EPSR4 has 97.6% scavenging activity toward DPPH free radicals at 1500 µg/mL, with an IC50 value of 300 µg/mL, and 64.8% at 1500 µg/mL toward hydrogen peroxide free radicals (IC50 = 1500 µg/mL, 30 min). Furthermore, EPSR4 exhibited considerable inhibitory activity towards the proliferation of T-24 (bladder carcinoma), A-549 (lung cancer) and HepG-2 (hepatocellular carcinoma) cancer cell lines with IC50 of 244 µg/mL, 148 µg/mL and 123 µg/mL, respectively. An evaluation of anti-inflammatory activity revealed that EPSR4 has potent lipoxygenase (LOX) inhibitory activity (IC50 of 54.3 µg/mL) and a considerable effect on membrane stabilization (IC50 = 112.2 ± 1.2 µg/mL), while it showed cyclooxygenase (COX2) inhibitory activity up to 125 µg/mL. Finally, EPSR4 showed considerable inhibitory activity towards acetylcholine esterase activity. Taken together, this study reveals that Bacillus subtilis strain AG4 could be considered as a potential natural source of novel EPS with potent biological activities that would be useful for the healthcare system.

Monitoring metallothionein-like protein concentrations and cholinesterase activity in tropical cup oysters as biomarkers of exposure to metals and pesticides in the southern Caribbean, Colombia

Metallothionein-like protein concentrations (MT) and three functionally defined fractions of cholinesterase activity (ChE) were quantified in gill and digestive gland homogenates of tropical cup oysters from 5 nearshore locations in the Colombian Caribbean and correlated with sediment and tissue metal (9 metals) and pesticide (22 organophosphates, OPs, and 20 organochlorines-OCPs), as well as water physical-chemical parameters (salinity, pH, temperature, and dissolved oxygen). Tissue and sediment pesticide concentrations were below detection limits in all samples, whereas sediment and tissue metal concentrations exceeded environmental thresholds at several locations. Tissue MT and ChE biomarkers varied by a factor of 5-6 between locations. Inhibition of cholinesterase activity was negligible for all 5 sites, despite spatial-temporal variation in ChE activity, consistent with below-detection OP concentrations. Tissue MT and ChE biomarkers correlated with tissue and metal sediment concentrations, yet, statistically significant covariance between biomarkers and water chemistry parameters was also observed, indicating that both, metal concentrations and physical-chemical variables, are likely to be responsible for generating the observed spatial-temporal variations in biomarker patterns.

Acetylcholinesterase from the charru mussel Mytella charruana: kinetic characterization, physicochemical properties and potential as in vitro biomarker in environmental monitoring of mollusk extraction areas

Acetylcholinesterase (AChE; EC 3.1.1.7) from aquatic organisms have been used to evaluate the exposure of specimens to pesticides and heavy metals at sublethal levels in environmental samples. AChE of Mytella charruana was extracted to characterize its physicochemical and kinetic properties as well as the effect of organophosphate (dichlorvos, diazinon, chlorpyrifos, methyl-parathion and temephos), carbamates (carbaryl, carbofuran and aldicarb), benzoylureas (diflubenzuron and novaluron), pyrethroid (cypermethrin) and juvenile hormone analog - JHA (pyriproxyfen) and the effect of metal ions: Hg²⁺, Cd²⁺, Pb²⁺, As³⁺, Cu²⁺ and Zn²⁺, in order to evaluate the potential of the enzyme as biomarker. The optimum pH of M. charruana AChE was 8.5 and the maximum activity peak occurred at 48 °C, being highly thermostable maintaining 97.8% of its activity after incubation at 60 °C. The Michaelis-Menten constants (k_m) for the substrates acetylthiocholine and propionylthiocholine were 2.8 ± 1.26 and 4.94 ± 6.9 mmol·L^-1, respectively. The V_max values for the same substrates were 22.6 ± 0.90 and 10.2 ± 4.94 mU·mg^-1, respectively. Specific inhibition results suggest an AChE presenting active site with dimensions between those of AChE and butyrylcholinesterase (BChE). The IC₂₀ values related to the effect of the pesticides on the enzyme showed higher inhibitory power of temephos (0.17 μmol·L^-1), followed by aldicarb (0.19 μmol·L^-1) and diflubenzuron (0.23 μmol·L^-1). Metal ions inhibited M. charruana enzyme in the following order: Hg²⁺ > Pb²⁺ > Cd²⁺ > As³⁺ > Cu²⁺ > Zn²⁺. These data suggest that the enzyme showed potential as in vitro biomarker of the exposure to temephos, mercury, zinc and copper.

Acute benzo[a]pyrene exposure induced oxidative stress, neurotoxicity and epigenetic change in blood clam Tegillarca granosa

The blood clam (Tegillarca granosa) is being developed into a model bivalve mollusc for assessing and monitoring marine pollution on the offshore seabed. However, the information on the response of blood clam to PAHs, an organic pollutant usually deposited in submarine sediment, remains limited. Herein, we employed multiple biomarkers, including histological changes, oxidative stress, neurotoxicity and global DNA methylation, to investigate the effects of 10 and 100 μg/L Bap exposure on the blood clams under laboratory conditions, as well as the potential mechanisms. Acute Bap exposure can induce significant morphological abnormalities in gills as shown through hematoxylin–eosin (H.E) staining, providing an intuitive understanding on the effects of Bap on the structural organization of the blood clams. Meanwhile, the oxidative stress was significantly elevated as manifested by the increase of antioxidants activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) and glutathione-s-transferase (GST), lipid peroxidation (LPO) level and 8-hydroxy-2′-deoxyguanosine (8-OHdG) content. The neurotoxicity was also strengthened by Bap toxicity manifested as inhibited acetylcholinesterase (AChE) and choline acetyltransferase (ChAT) activities. In addition, the global DNA methylation level was investigated, and a significant DNA hypomethylation was observed in Bap exposed the blood clam. The correlation analysis showed that the global DNA methylation was negatively correlated with antioxidants (SOD, CAT and POD) activities, but positively correlated choline enzymes (AChE and ChAT) activities. These results collectively suggested that acute Bap exposure can cause damage in gills structures in the blood clam possibly by generating oxidative stress and neurotoxicity, and the global DNA methylation was inhibited to increase the transcriptional expression level of antioxidants genes and consequently elevate antioxidants activities against Bap toxicity. These results are hoped to shed some new light on the study of ecotoxicology effect of PAHs on marine bivalves.

Multibiomarker responses and bioaccumulation of fipronil in Prochilodus lineatus exposed to spiked sediments: Oxidative stress and antioxidant defenses

Fipronil is a current use pesticide, widely used in many crops, commonly adsorbed to sediments of aquatic environments. The purpose of this study was to evaluate the biomarker responses and fipronil distribution pattern in different matrixes (fish, sediment and water) after juveniles P. lineatus exposure at two environmental concentrations (5.5 and 82 μg kg^--1) of fipronil-spiked sediments. The levels of oxidized proteins (PO), lipid peroxidation (LPO), and enzymatic activity of superoxide dismutase (SOD), reduced glutathione content (GSH), antioxidant capacity against peroxyls (ACAP) and acetylcholinesterase (AChE) were evaluated in liver, gills and brain. Concentrations of fipronil and its metabolites (f. desulfinyl, f sulphpHide and f. sulfone) were quantified by GC-ECD. F. desulfinyl was the major metabolite found in all matrixes, followed by f. sulphide in sediments, while f. sulfone was mainly accumulated in fish. Fipronil promoted oxidative stress in P. lineatus, as evidenced by the increases in LPO and PO levels and the decrease brain AChE activity. Fish exposed at both concentrations showed significant decrease in antioxidant capacity. Alterations in the antioxidant defenses system was evidenced in all organs. These results suggest that the occurrence of fipronil in aquatic environments can generate oxidative stress at different levels in P. lineatus, showing that this species is highly sensitive to the deleterious effects of fipronil and metabolites.

Biological responses of mangrove oysters (Crassostrea rhizophorae) and mercury contamination in an urban tropical estuary

This study aimed to assess the biological responses of oysters from an urban estuary in Northeast Brazil, through the evaluation of biochemical and physiological biomarkers, and integrate these responses with the investigation of mercury seasonal contamination. Oysters and sediment were collected from three sites in the estuary of the Ceará River during dry and rainy seasons. Biomarkers (AchE, CaE, GST, CAT, and Condition Index) were analyzed in different tissues. Hg bioaccumulation was higher in animals sampled in the rainy season, with increases varying from 5% to 136%, compared to the dry season. The changes in biomarkers highlight already elevated stresses for the organisms at the inner portion of the estuary, near the confluence with the Maranguapinho River, mainly during the rainy season, corroborating other studies that showed ecotoxicological effects with water and sediment samples. Finally, no correlation between Hg in sediment/oyster and biomarker results was observed.

Assessment of the oxidative and genotoxic effects of the glyphosate-based herbicide roundup on the freshwater shrimp, Macrobrachium nipponensis

In the present study, an acute toxic test was performed to assess the oxidative stress and genotoxic effects of the herbicide on the freshwater shrimp Macrobrachium nipponensis. The results showed that the 48-h and 96-h LC50 values of Roundup to M. nipponensis were 57.684 mg/L and 11.237 mg/L, respectively. For further investigation, the shrimps were exposed to sublethal concentrations of 0.35, 0.70, 1.40, 2.80 and 5.60 mg/L for 96 h. A significant decrease in total haemocytes count (THC) was observed at concentration of 5.60 mg/L throughout the experiment. The level of superoxide dismutase (SOD), catalase (CAT) and total antioxidant capacity (T-AOC) in all the treatments decreased in a dose- and time-dependent manner except for the concentration group of 0.35 mg/L. The malondialdehyde (MDA), hydrogen peroxide (H2O2) and protein carbonyl in serum increased significantly at concentrations of 2.80 mg/L and 5.60 mg/L. A significant decrease in acetylcholinesterase (AChE) activity was observed at each concentration (P＜0.05). In addition, the micronucleus (MN) frequency of haemocytes significantly increased (P＜0.05) at concentrations of 1.40, 2.80 and 5.60 mg/L, whereas the comet ratio and %DNA in the tails exhibited a clear time- and dose-dependent response during the exposure. The analysis of the integrated biomarker response (IBR) showed the induction of oxidative stress biomarkers and the inhibition of antioxidants, and this dose-dependent relation suggests the sensitivity and availability of all the biomarkers. These results revealed that Roundup had a prominent toxic effect on M. nipponensis based on the antioxidative response inhibition and genotoxicity.

Acetylcholinesterase of mangrove oyster Crassostrea rhizophorae: A highly thermostable enzyme with promising features for estuarine biomonitoring

Enzyme biomarkers from several aquatic organisms have been used for assessing the exposure to contaminants at sublethal levels. Amongst them, the cholinesterases are commonly extracted from several organisms to evaluate/measure organophosphate and carbamate neurotoxic effects. Acetylcholinesterase (AChE; EC 3.1.1.7) is an enzyme of the group of serine esterases that acts on the hydrolysis of the neurotransmitter acetylcholine allowing the intermittence of the nerve impulses responsible for the neuronal communication. This enzyme is the main target for the action of some pesticides and the inhibition of its activity in bivalve mollusks may be used as biomarker due to their filter-feeding habit. In this context, the present study aimed to characterize physicochemical and kinetic parameters of the AChE extracted from gills and viscera of the oyster Crassostrea rhizophorae and investigate the in vitro effect of pesticides (dichlorvos, diazinon, chlorpyrifos, methyl-parathion, temephos, carbaryl, carbofuran, aldicarb, diflubenzuron and novaluron) in search for assessing its potential as biomarker. Specific substrates and inhibitors evidenced the predominance of AChE in both tissues. The optimum pH found for gills and viscera AChE were 8.0 and 8.5, respectively. The maximum peak of activity occurred at 70 °C for gill AChE and 75 °C for viscera AChE. The enzymes of both tissues presented remarkable thermostability. The Michaelis-Menten constant for both enzymes were 1.32 ± 0.20 mM for gills and 0.43 ± 0.12 mM for viscera. The V_max values for gills and viscera were 53.57 ± 1.72 and 27.71 ± 1.15 mU/mg, respectively. The enzymes were able to reduce the activation energy to 9.75 kcal mol^-1 (gills) and 11.87 kcal mol^-1 (viscera) obtaining rate enhancements of 3.57 × 10⁵ and 1.01 × 10⁴, respectively, in relation to non-catalyzed reactions. Among the pesticides under study, the carbamates carbaryl and carbofuran exerted the strongest inhibitory effects on the enzyme activity achieving important degrees of inhibition at concentrations below national and international current regulations. The first observation of the effects of benzoylurea pesticides (diflubenzuron and novaluron) on AChE from mollusks is reported here. The gills AChE of C. rhizophorae showed potential to be specific biomarker for the carbamate carbaryl while the viscera AChE showed it for carbofuran. According to their features, these enzymes may be proposed as promising tools for estuarine monitoring as well as biocomponent of biosensor devices.

Assessment and monitoring of water quality of the gulf of Morbihan, a littoral ecosystem under high anthropic pressure

This field study is intended to propose a global methodology to assess and monitor the water quality of the gulf of Morbihan, a littoral ecosystem under increasing anthropic pressure. To this end, the Locmariaquer site, where Crassostrea gigas is extensively cultivated, was selected to perform a one-year follow-up of tissular glutathione S-transferase and acetylcholinesterase specific activities in this filter feeder organism. Calculation of an integrated index, corresponding to the ratio of the two enzymes activities, allowed to discriminate from the environmental noise, several clusters which could be representative environmental stress, potentially latent pollution. Moreover, the estrogenic activity was assessed in water samples collected at Locmariaquer and other strategic sites of the gulf. The results evidenced a low estrogenic-disrupting compound contamination of waters. Overall, this methodology produced an accurate outlook of a basal state for the gulf and could be developed in the context of a chronic monitoring of this site.

Antioxidant defense responses in Mytella guyanensis (Lamarck, 1819) exposed to an experimental diesel oil spill in Paranaguá Bay (Paraná, Brazil)

We evaluated the effects of diesel oil on the bivalve Mytella guyanensis using biomarkers of oxidative stress (glutathione S-transferase, glutathione peroxidase, and reduced glutathione) after an experimental in situ spill in a mangrove area in southern Brazil. A linear model was developed for the Multiple Before-After Control-Impact (MBACI) experimental design to assess the significance of biological responses. Control and impacted sites were sampled seven and two days before as well as two and seven days after the spill. With the exception of a late response of reduced glutathione (GSH) levels on day seven, none of the biomarkers were significantly altered by the impact. This result was attributed to the high environmental variability of the experimental sites combined with a low sensitivity of Mytella guyanensis to diesel oil at short time-scales. The high resistance of M. guyanensis suggests that its antioxidant response is triggered only after a medium- to long-term exposure to contaminants.

The use of cholinesterase as potential biomarker: In vitro characterization in the polychaete Capitella teleta

The ecological relevance of polychaetes coupled with their easy culture and maintenance in the laboratory, has led them to become increasingly used in marine ecotoxicological studies, raising the need to validate frequently applied monitoring tools at various biological levels. The present study was aimed to characterize the cholinesterases (ChE) activity in the polychaete Capitella teleta, using three substrates (acetylthiocholine iodide, propionylthiocholine iodide, and S-butyrylthiocholine iodide) and four known inhibitors (eserine hemisulfate, BW284c51, iso-OMPA and chlorpyrifos-oxon). Results showed that most of the measured cholinesterase activity was acetylcholinesterase (AChE). Inhibition of enzyme kinetic experiments denoted that sensitivity of C. teleta's ChE to the organophosphorous metabolite chlorpyrifos-oxon (IC₅₀=60.72 nM) was analogous to some fish species. This study highlights the relevance of ChE characterization before its use as a biomarker in ecotoxicology and biomonitoring studies.

Optimization of recovery patterns in common carp exposed to roundup using response surface methodology: evaluation of neurotoxicity and genotoxicity effects and biochemical parameters

The present study is the first report on optimization of recovery conditions of fishes exposed to pesticides using response surface methodology-central composite rotatable design (RSM-CCRD). The sub-lethal toxicity bioassay of Roundup® (2 ppm ~10 percent LC₅₀, 96 h) in common carp (1, 4, 9, 16, 25, 35 and 40 day) was investigated. After exposure for 16 days to Roundup®, some the fishes were introduced to herbicide-free water. The effects of four recovery parameters including time (5-25 d), temperature (18-26 °C), water exchange rate (WER, 10-30), and salinity (0-8 ppt) on the levels of biomarkers of genotoxicity (DNA damage), neurotoxicity (acetylcholinesterase activity (AChE)), and the serum alanine (ALT) and aspartate (AST) aminotransferase in plasma were studied. The polynomial equations were significantly fitted for all response variables with high R² values (>0.95), which revealed no indication of lack of fit. The optimum conditions for the maximum AChE activity (37.14 nmol/min/mg protein) and the minimum levels of DNA damage (8.00 percent tail DNA), ALT (27.0 IU/L) and AST (91.0 IU/L) were time of 20 d, temperature of 20 °C, WER of 25 and water salinity of 6 ppt. Thus, a promising improvement for the recovery trend of fishes exposed to Roundup® stress was obtained under the optimized conditions using RSM-CCRD.

Confinement during field studies may jeopardize antioxidant and physiological responses of Nile tilapia to contaminants

This work evaluates the effects of caging, a known confinement stress, in Nile tilapia (Oreochromis niloticus) during an environmental study in Cubatão river, southern Brazil. Caging animals for 7 days, regardless of being at the reference or at a contaminated site, resulted in lower levels of antioxidant-related defenses (glutathione, glutathione S-transferase, glucose-6-phosphate dehydrogenase) in liver and physiological parameters (blood glucose and lactate) as compared with free-swimming animals. Higher hepatic glutathione reductase activity and elevated Hb content could be associated to contaminant exposure. In conclusion, the confinement stress in caged Nile tilapia biochemical and physiological disturbances, acting as a confounding factor in field studies.

Effects of glyphosate on cholinesterase activity of the mussel Perna perna and the fish Danio rerio and Jenynsia multidentata: in vitro studies

Although the herbicide glyphosate [N-(phosphonomethyl)glycine] is not classified as an acethylcholinesterase inhibitor, some studies have reported reduction in the acethylcolinesterase activity after in vivo exposure to both its pure form and its commercial formulations. Considering this controversy, the objective of the present study was to investigate, in vitro, the effects of glyphosate exposure on cholinesterase activity of the brown mussel Perna perna and of two fish species: zebrafish Danio rerio and onesided livebearer Jenynsia multidentata. For this purpose, samples of different tissues (brain and muscle for fish; gills and muscle for mussel) were homogenized and pre-incubated with different glyphosate concentrations before cholinesterase activity determination. Results demonstrated that cholinesterase from different fractions of all species tested was inhibited by glyphosate. The concentrations of glyphosate that inhibits 50% of cholinesterase activity (IC50) ranged from 0.62 mM for P. perna muscle to 8.43 mM for J. multidentata brain. According to this, cholinesterase from mussel seems to be more sensitive to glyphosate exposure than those from the fish D. rerio and J. multidentata.

An integrated environmental approach to investigate biomarker fluctuations in the blue mussel Mytilus edulis L. in the Vilaine estuary, France

Estuarine areas represent complex and highly changing environments at the interface between freshwater and marine aquatic ecosystems. Therefore, the aquatic organisms living in estuaries have to face highly variable environmental conditions. The aim of this work was to study the influence of environmental changes from either natural or anthropogenic origins on the physiological responses of Mytilus edulis. Mussels were collected in the Vilaine estuary during early summer because this season represents a critical period of active reproduction in mussels and of increased anthropogenic inputs from agricultural and boating activities into the estuary. The physiological status of the mussel M. edulis was evaluated through measurements of a suite of biomarkers related to: oxidative stress (catalase, malondialdehyde), detoxication (benzopyrene hydroxylase, carboxylesterase), neurotoxicity (acetylcholinesterase), reproductive cycle (vitelline, condition index, maturation stages), immunotoxicity (hemocyte concentration, granulocyte percentage, phagocytosis, reactive oxygen species production, oxidative burst), and general physiological stress (lysosomal stability). A selection of relevant organic contaminant (pesticides, (polycyclic aromatic hydrocarbons, polychlorobiphenyls) was measured as well as environmental parameters (water temperature, salinity, total suspended solids, turbidity, chlorophyll a, pheopigments) and mussel phycotoxin contamination. Two locations differently exposed to the plume of the Vilaine River were compared. Both temporal and inter-site variations of these biomarkers were studied. Our results show that reproduction cycle and environmental parameters such as temperature, organic ontaminants, and algal blooms could strongly influence the biomarker responses. These observations highlight the necessity to conduct integrated environmental approaches in order to better understand the causes of biomarker variations.

Responses of B-esterase enzymes in oysters (Crassostrea gigas) transplanted to pesticide contaminated bays form the Ebro Delta (NE, Spain)

Marine bivalves such as oysters are widely used as bioindicators to monitor marine coastal pollution. This study aimed to use B-esterase activity responses in oysters (Crassostrea gigas) cultured in Ebro Delta bays to monitor environmental effects of pesticides. The B esterases investigated were acetylcholinesterase, propionylcholinesterase, and carboxylesterase and their activities were measured in adductor muscle and gills from oysters transplanted in Ebro Delta bays where the are traditionally grown. Enzyme activities were related with physico-chemical parameters and pesticide levels measured in water. Cholinesterase activities measured in gills were unaffected across sites and periods. Conversely, carboxylesterase activities in oyster gills varied across periods and sites and were negatively correlated with residue levels of organophoshporous and carbamate pesticides in water. Therefore, inhibition of carboxylesterase activities can be considered a good indicator of exposure to anti-cholinergic pesticides in oysters.

Bivalve esterases as biomarker: identification and characterization in European cockles (Cerastoderma edule)

This study characterized esterase activity in Cerastoderma edule tissues using different substrates and specific inhibitors and identified the tissue distribution of esterases in this species. Synthetic thiocholines and thioacetate esters and specific inhibitors (eserine, BW284C51 and iso-OMPA) were used to identify and quantify cholines and carboxyl esterases. The results demonstrated the presence of a non-specific propionyl thiocholine (PrSCh)-cleaving cholinesterase (ChE) and a large amount of carboxylesterases (CaE). For further studies using C. edule esterases as biomarkers, our results suggest that the adductor muscle, with PrSCh (5 mM) as substrate should be used to analyze ChE, and for CaE analyses, phenyl thioacetate should be used in digestive gland extracts (PSA, 5 mM).

Effects of Roundup Transorb on fish: hematology, antioxidant defenses and acetylcholinesterase activity

Roundup Transorb(RDT) is a glyphosate-based herbicide containing a mixture of surfactants. The objective of this work was to evaluate the effects of this herbicide on the Neotropical fish Prochilodus lineatus. Juvenile fish were acutely exposed (6, 24 and 96 h) to 1 mg L(-1) of RDT (RDT 1), 5 mg L(-1) of RDT (RDT 5) or only water (control) and blood samples for hematological analysis, liver for antioxidants analysis, and brain and muscle for acetylcholinesterase (AChE) determination, were collected. RDT effects were more evident in fish exposed to the higher concentration of the herbicide. Hematologic alterations appeared only after 96 h exposure, when fish showed an increase in the hematocrit and in the number of both red and white blood cells. After 6h exposure fish showed a transient reduction in superoxide dismutase and catalase activity. RDT also inhibited glutathione-S-transferase, after 6 and 24h of exposure. The reduction in these enzymes is probably related to the occurrence of lipid peroxidation (LPO) in fish exposed to the herbicide for 6h. LPO returned to control levels after 24 and 96 h exposure to RDT, when fish showed an increased activity of glutathione peroxidase. The content of reduced glutathione also increased after 96 h exposure. Thus, after 24 and 96 h the antioxidant defenses were apparently enough to combat ROS, preventing the occurrence of oxidative damage. The exposure to RDT for 96 h led to an inhibition of AChE in brain and muscle at rates which may not be considered a life-threatening situation.

Effects of exposure to oxamyl, carbofuran, dichlorvos, and lindane on acetylcholinesterase activity in the gills of the Pacific oyster Crassostrea gigas

Acetylcholinesterase (AChE) activity has been used to test the exposure of mollusk bivalves to pesticides and other pollutants. The Pacific oyster Crassostrea gigas is a species with a worldwide distribution, and it has a high commercial value. The use of this species as a bioindicator in the marine environment, and the use of measurements of AChE activity in tissues of C. gigas require prior evaluation of organisms exposed to several toxic compounds in the laboratory. In our study, the effects of pesticides on AChE activity in the gills and mantle tissues of C. gigas were analyzed by exposing animals to organophosphate (dichlorvos), carbamate (carbofuran and oxamyl), and organochlorine (lindane) pesticides. Adult Pacific oysters were exposed to several concentrations (0.1-200 microM) of dichlorvos, carbofuran, and oxamyl for 96 h, and lindane (1.0 and 2.5 microM) was applied for 12 days. In gill tissues, all pesticides analyzed caused a decrease in AChE activity when compared to the control unexposed group. The mean inhibition concentration (IC(50)) values were determined for dichlorvos, carbofuran, and oxamyl pesticides. Dichlorvos had the highest toxic effect, with an IC(50) of 1.08 microM; lesser effects were caused by oxamyl and carbofuran, with IC(50)s of 1.67 and 3.03 microM, respectively. This study reports the effects of pesticides with several chemical structures and validates measurement of AChE activity in the gill tissues of C. gigas for use in environmental evaluations or food quality tests.

Roundup causes oxidative stress in liver and inhibits acetylcholinesterase in muscle and brain of the fish Prochilodus lineatus

This work aimed to evaluate Roundup effects on biochemical biomarkers of the neotropical fish Prochilodus lineatus. Fish were acutely exposed (6, 24 and 96 h) to 10 mg L(-1) of Roundup (RD) or only water (control) and samples of liver, for antioxidants analysis, and brain and muscle, for acetylcholinesterase (AChE) determination, were collected. Fish exposed to RD for 24h showed reduction on superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities, and increased glutathione (GSH) content. After 24 and 96h, fish of RD group showed increased glutathione-S-transferase (GST) activity and lipid peroxidation. AChE activity was inhibited in brain after 96h and in muscle after 24 and 96h of exposure. Thus, acute exposure to RD stimulated the biotransformation pathway, with increased GST, but interfered on the antioxidant defenses, with reduction of SOD and GPx activity, leading to the occurrence of lipid peroxidation. Inhibition of AChE showed that RD acts as a contaminant with anti-AChE action.

Cholinesterase and glutathione S-transferase activities of three mollusc species from the NW Portuguese coast in relation to the 'Prestige' oil spill

In November 2002, the tanker 'Prestige' released about 19,000 tonnes of a heavy fuel oil (no. 6) before sinking with about 58,000 tonnes of its cargo, 135 miles from Cabo Finisterra (Spain). A considerable part of the released fuel oil reached the Galician coast, causing a heavy black tide and an ecological disaster. Although the black tide did not reach the NW coast of Portugal, it is possible that some of the fuel oil or its components also arrived to this area directly through the sea water and/or indirectly through the food chain. Therefore, the aim of this study was to investigate possible changes in two widely used biomarkers, the activity of the enzymes cholinesterases (ChE) and glutathione S-transferases (GST), of three molluscs (Mytilus galloprovincialis, Nucella lapillus and Monodonta lineata) from wild populations of the NW Portuguese coast in relation to the 'Prestige' oil spill. Molluscs were collected seasonally before (autumn 2002) and after (winter 2002/2003), spring and summer 2003) the oil spill at several sites along the Portuguese NW coast. Enzymatic activities determined before the accident were compared with those determined at different times after the oil spill taking into consideration abiotic factors. Information from different parameters was integrated by Redundancy Analysis and Principal Response Curves (PRC). Results show that GST and ChE activities were influenced by abiotic factors. Despite this influence, the results of PRC analysis also suggest that some of the fuel oil reached the NW Portuguese coast changing the patterns of ChE and GST activities of local populations of rocky shore species. Furthermore, the present study highlights the need of long-term monitoring with wild populations to assess both historical and punctual effects of pollution in the marine environment.

Cholinesterases in the Antarctic scallop Adamussium colbecki: characterization and sensitivity to pollutants

Antarctica is affected by man-made contamination and development of sensitive ecotoxicological tools for impact assessment is a priority task. The aims of the present study were to characterize cholinesterase (ChE) activities in an Antarctic key species, the scallop Adamussium colbecki, and to investigate their sensitivity as biological markers (biomarkers) of exposure to pollutants and of their effects. Our results show that ChEs in gills share most characteristics with true acetylcholinesterase. The present results show that ChE activities in A. colbecki are significantly inhibited by organophosphates (OPs) and somehow affected by in vitro exposure to mixtures of marine contaminants such as polycyclic aromatic hydrocarbons (PAHs), even if no concentration-dependent pattern of response was observed and no effect was elicited by polychlorinated biphenyls (PCBs). The present results do not demonstrate ChEs in A. colbecki as sensitive tools to measure exposure to the above chemicals, but they may be worthy of further study considering the importance of the scallop in Antarctic marine ecosystems and its suitability as a sentinel species.

An assessment of acute biomarker responses in the demersal catfish Cathorops spixii after the Vicuña oil spill in a harbour estuarine area in Southern Brazil

The Vicuña oil tanker exploded in Paranaguá Bay (South of Brazil), during methanol unloading operations in front of Paranaguá Harbour, on November 15th, 2004, releasing a large amount of bunker oil and methanol. Two weeks after the accident, the acute effects of the Vicuña Oil Spill (VOS) were evaluated in the demersal catfish Cathorops spixii, comparing a contaminated (at the spill site) and a reference site inside the Bay. Data were compared to previous measurements, taken before the accident, in the same species, from the same sites. The physiological biomarkers were the ones that best reflected acute effects of the spill: plasma osmolality, chloride, calcium, magnesium, and potassium. Morphological (liver and gill histopathology) and genetic (piscine micronucleus and DNA strand breaks) biomarkers revealed that damage was already present in fishes from both reference and contaminated sites inside the Bay. Thus, the reference site is not devoid of contamination, as water circulation tends to spread the contaminants released into other areas of the Bay. Acute field surveys of oil spill effects in harbour areas with a long history of contamination should thus be viewed with caution, and whenever possible previous evaluations should be considered for proper appraisal of biomarker sensitivity, especially in mobile bioindicators such as fish.

Determination of esterase activity and characterization of cholinesterases in the reef fish Haemulon plumieri

White grunt (Haemulon plumieri) has been proposed by the Mesoamerican Barrier Reef System (MBRS) Synoptic Monitoring Program as a bioindicator species. It is in this sense that the present study has a main goal to evaluate this organism's suitability as an indicator species. Individuals were captured during three seasons at the port of Sisal, Yucatan, Mexico which is located in an area that is considered to be weakly impacted by human activities such as agriculture or industry. Both cholinesterase (ChE) and carboxylesterase (CbE) activities were measured in brain, muscle, liver and eye of sampled individuals. Results indicated that ChE and CbE activities were greatest in the brain (256.3 ± 43) and in the liver (191 ± 21), respectively. Furthermore, ChEs detected in brain, liver and muscle were characterized, and results suggested that the acetylcholinesterase (AChE) type was more abundant relative to pseudocholinesterase (BChE) which was rare. In addition, K(m) and V(max) and IC(50) values were calculated from the Michaelis-Menten equation. Finally, an additional experiment in vitro showed a significant decrease in both ChE and CbE activities when different tissues were exposed to model xenobiotics, such as benzo[a]pyrene and Chlorpyrifos. In conclusion, findings from this study confirm the potential suitability of H. plumieri as an organic pollution bioindicator species, and thus of practical use for environmental biomonitoring purposes.

Multibiomarker assessment of three Brazilian estuaries using oysters as bioindicators

Oysters have been largely employed as bioindicators of environmental quality in biomonitoring studies. Crassostrea rhizophorae was selected to evaluate the health status of three estuarine areas impacted by anthropogenic activities along the Brazilian coast, in three estuarine complexes, ranging in latitude from 7 to 25 degrees S. In each estuary three sites were sampled in Winter and in Summer: a site considered as reference, and two sites next to contamination sources. Condition index was similar at all sites and estuaries, with the highest values found for Itamaracá oysters in Summer. Necrosis, hyperplasia, mucocyte hypertrophy and fusion of ordinary filaments were the main histopathological lesions observed. Muscle cholinesterase activity was overall similar, but with a strong seasonal effect. Inhibition or activation of branchial total ATPase and Na,K-ATPase activities at the contaminated sites was observed. The health status of these estuarine areas is quite similar, and the combined use of biomarkers is recommended.

Muscular and brain cholinesterase sensitivities to azinphos methyl and carbaryl in the juvenile rainbow trout Oncorhynchus mykiss

The organophosphate azinphos methyl (AzMe) and the carbamate carbaryl are the insecticides mostly used in the irrigated valley of Río Negro and Neuquén, Patagonia, Argentina. Juvenile rainbow trout were exposed to AzMe and carbaryl and the sensitivity of skeletal muscular cholinesterase (ChE) and the time course of inhibition and recovery were evaluated. EC50 values demonstrated that AzMe was a stronger in vivo inhibitor of muscular ChE (1.05+/-0.23 microg/L) than carbaryl (270+/-62.23 microg/L). Muscular ChE was significantly less sensitive to both insecticides than brain ChE. EC50 values obtained for muscular ChE were closer than those for brain ChE to the respective pesticide lethal concentrations, pointing out the relevance of the muscular enzyme in determining acute toxicity. The recovery process of ChE activity after carbaryl exposure (500 microg/L) was fast, whereas no significant recovery was observed with AzMe (1 microg/L) after 21 days in uncontaminated media. Brain and muscular ChE were inhibited and showed a significant but not complete recovery after three consecutive 48-h exposures to AzMe (1 microg/L) followed by a recovery period of 7 days. This scheme mimics the periodical application of the insecticides in the region and suggests a certain probability of a sustained ChE inhibition under field conditions, affecting fish development and survival.

Pollution biomarkers in estuarine animals: critical review and new perspectives

In this review, recent developments in monitoring toxicological responses in estuarine animals are analyzed, considering the biomarker responses to different classes of pollutants. The estuarine environment imposes stressful conditions to the organisms that inhabit it, and this situation can alter their sensitivity to many pollutants. The specificity of some biomarkers like metallothionein tissue concentration is discussed in virtue of its dependence on salinity, which is highly variable in estuaries. Examples of cholinesterase activity measurements are also provided and criteria to select sensitive enzymes to detect pesticides and toxins are discussed. Regarding non-specific biomarkers, toxic responses in terms of antioxidant defenses and/or oxidative damage are also considered in this review, focusing on invertebrate species. In addition, the presence of an antioxidant gradient along the body of the estuarine polychaete Laeonereis acuta (Nereididae) and its relationship to different strategies, which deal with the generation of oxidative stress, is reviewed. Also, unusual antioxidant defenses against environmental pro-oxidants are discussed, including the mucus secreted by L. acuta. Disruption of osmoregulation by pollutants is of paramount importance in several estuarine species. In some cases such as in the estuarine crab Chasmagnathus granulatus, there is a trade off between bioavailability of toxicants (e.g. metals) and their interaction with key enzymes such as Na(+)-K(+)-ATPase and carbonic anhydrase. Thus, the metal effect on osmoregulation is also discussed in the present review. Finally, field case studies with fish species like the croaker Micropogonias furnieri (Scianidae) are used to illustrate the application of DNA damage and immunosuppressive responses as potential biomarkers of complex mixture of pollutants.

Cholinesterase activity in Gammarus pulex (Crustacea Amphipoda): Characterization and effects of chlorpyrifos

The aim of this study was to characterize cholinesterase (ChE) activity in Gammarus pulex, an abundant and ecologically relevant species of the European stream environment. Biochemical and pharmacological properties were tested using different substrates (acetylthiocholine iodide, propionylthiocholine iodide and butyrylthiocholine iodide) and selective inhibitors (eserine sulfate, BW284c51 and iso-OMPA). In a second part, the in vitro and in vivo effects of a widely used organophosphorous pesticide, chlorpyrifos, on ChE activity were investigated. The results suggest that G. pulex possess only one ChE which displays the typical properties of an acetylcholinesterase, since: (1) it hydrolyses to the substrate acetylthiocholine at a higher rate than all other tested substrates and (2) it is highly sensitive to eserine sulphate and BW284c51, but not to iso-OMPA. In vitro and in vivo inhibitions were observed for highly different contamination levels, which suggests that bioaccumulation and biotransformation mechanisms are involved. In vivo AChE inhibition was observed at realistic environmental concentrations, with lethal effects appearing at inhibitions higher than 50%. The results of this study show the value of G. pulex as a sentinel organism for environmental assessment.

Brain acetylcholinesterase as a marine pesticide biomarker using Brazilian fishes

Brain acetylcholinesterase (AChE) of some fishes from the coast of Rio de Janeiro State was studied as a possible pesticide biomarker in marine environmental monitoring. AChE specific activity in brain varied from 145 to 530 U/g of proteins and the Michaelis-Menten constant (K(M)) for acetylthiocholine varied from 104 to 291 microM among the 20 species studied. The enzyme sensitivity to methyl paraoxon, evaluated by the inhibition kinetic constants, shows that some species (Paralonchurus brasiliensis and Genidens genidens) are more sensitive (IC50-30 min=455 and 468 nM, respectively). The less sensitive Merluccius hubbsi and Percophis brasiliensis (IC50-30 min=3339 and 3259 nM, respectively) belong to the super-order Paracanthopterygii, which includes the more ancient species. On the other hand, more susceptible species belong to the super-order Acanthopterygii, which includes more recent species. These results suggest a possible evolutionary linkage for AChE sensitivity to methyl paraoxon. The application of inhibition kinetic constants for fish brain AChE in phylogenetic studies is still being investigated. The results have shown that a fish sentinel species should have the highest brain AChE level among the more sensitive ones.

Esterases as pesticide biomarkers in crayfish (Procambarus clarkii, Crustacea): tissue distribution, sensitivity to model compounds and recovery from inactivation

The specific activities of acetyl- and butyrylcholinesterase and carboxylesterase were assayed in the digestive gland and in nervous and muscle tissues of the crayfish Procambarus clarkii. Since acetylcholinesterase prevails in nervous tissue and carboxylesterase in digestive gland, they are proposed as biomarkers. Muscle had negligible activities of all esterases, and all tissues had a low butyrylcholinesterase activity. Esterases were mostly cytosolic in digestive gland and muscle, but membrane-bound in nervous tissue; use of Triton X-100 is not recommended due to its widely diverging effects in esterase assays. Phenylmethylsulphonylfluoride inhibited acetyl- and butyrylcholinesterase in extracts from all tissues, and in digestive gland only carboxylesterase. In digestive gland, tetra[monoisopropyl]-pyrophosphorotetramide inhibited all esterases with different sensitivities, while in muscle and nervous tissue it only partially inhibited all esterases. Carbamates inhibited 100-fold more strongly than organophosphates acetyl- and butyrylcholinesterase activities. Carboxylesterase was inhibited by carbaryl and chlorpyrifos, but not by eserine and malathion. In vitro conditions to evaluate recovery from inactivation of esterases by model pesticides were established for acetylcholinesterase and carboxylesterase. The new reactivation protocol could be useful as a biomarker of pesticide exposure to differentiate between dilution-reversible inhibitions, indicating carbamate exposure, from dilution-irreversible effect, attributed to organophosphate exposure.

Importance of cholinesterase kinetic parameters in environmental monitoring using estuarine fish

The aim of the present study was to determine the kinetic parameters and cholinesterase (ChE) activity in two teleost fish, the white mouth croaker Micropogonias furnieri (Scianidae) and the Madamango sea catfish Cathorops spixii (Ariidae), to verify their suitability as sentinel species of aquatic pollution by anticholinergic compounds. Individuals of each species were captured in one reference and one polluted site in the Southern Brazilian coast. Brain tissue was used as enzyme source. Inhibition kinetic parameters indicated that ChE from C. spixii collected at the reference site showed more affinity (Ka) for eserine that from those collected at the polluted site. The opposite was observed for the carbamylation constants (Kc). Thus, similar inhibition constants (Ki) were observed. M. furnieri brain showed an extremely low sensitivity to in vitro inhibition by eserine, indicating that it is not a suitable biomarker to be employed in environmental monitoring of anticholinergic compounds. Results from the present study also point to the need for considering kinetic analysis when cholinesterase activity is employed as a biomarker.

Effects of salinity on biomarker responses in Crassostrea rhizophorae (Mollusca, Bivalvia) exposed to diesel oil

Crassostrea rhizophorae is a euryhaline oyster that inhabits mangrove areas, which are widely distributed along the Brazilian coast. The aim of this study was to investigate the effects of salinity (9, 15, 25, and 35ppt) on the activities of glutathione S-transferase (GST), glucose 6-phosphate dehydrogenase (G6PDH), catalase (CAT), and acetylcholinesterase (AChE) in the digestive gland of this species after exposure to diesel oil for 7 days at nominal concentrations of 0.01, 0.1, and 1mlL(-1) and after depuration for 24h and 7 days. GST activity increased in a diesel oil concentration-dependent manner at salinities 25 and 15ppt and remained slightly elevated even after depuration periods of 24h and 7 days. No changes were observed in the activities of G6PDH, CAT, and AChE in the oysters exposed to diesel and depurated. Based on these results, GST activity in the digestive gland of C. rhizophorae might be used as a biomarker of exposure to diesel oil in sites where the salinity is between 15 and 25ppt, values usually observed in mangrove ecosystems.

Cardiac responses of Pacific oyster Crassostrea gigas to agents modulating cholinergic function

To examine the functional effects of cholinergic modulation compounds in oyster hearts and to explore their possible use in monitoring intoxication with acetylcholine-esterase (AChE) inhibitors such as organophosphates, tests were performed with in situ oyster heart preparations. The endogenous cholinergic agonist acetylcholine (ACh), AChE-resistant synthetic agonist carbachol, and the reversible carbamate type of AChE inhibitor physostigmine, all potently depressed spontaneous cardiac contractility. The depression was reversed by extensive washout, or prevented by muscarinic cholinergic antagonist atropine. The irreversible organophosphate type AChE inhibitor parathion or its active metabolite paraoxon at concentrations up to 100 microM failed to depress cardiac contractility. While other reversible AChE inhibitors such neostigmine and pyridostigmine also depressed the contractility, organophosphate AChE inhibitors malathion, diazinon, or phenthoate did not. Despite the differential effect in depressing cardiac function between the reversible and irreversible inhibitors, both of these inhibitors effectively inhibited cardiac AChE activity. The results suggest that the activation of muscarinic cholinergic receptors is coupled to inhibitory cardiac modulation, and organophosphate AChE inhibitors may inhibit only an AChE isozyme located at sites that are not important for control of cardiac activity in oysters.

Characterization of cholinesterase activity in three bivalves inhabiting the North Adriatic sea and their possible use as sentinel organisms for biosurveillance programmes

Anticholinesterases constitute a major portion of modern synthetic insecticides and the assessment of cholinesterase (ChE) inhibition is widely used as a specific biomarker for evaluating the exposure of non-target organisms to these pollutants. To evaluate the possible exposure of the North Adriatic sea coastal environment to residues of agriculture practices, we ascertained whether the oyster, Ostrea edulis and the clam, Tapes philippinarum, highly valuable resources commercially harvested in the area, could be selected as sentinel species. We characterized the ChE biochemical properties in their gills, and for comparison the analysis was carried out also in gills of the mussel, Mytilus galloprovincialis, extensively used as a biological indicator of water quality. In the oysters and mussels, the ChE activity was a function of increasing concentrations of substrate in the range 0.01-0.5 mM. K(m) values were 93+/-15 and 77+/-8 microM for O. edulis and M. galloprovincialis, respectively. No detectable ChE activity was found in gills of T. philippinarum, at any tested condition. Significant inhibition of ChE activity by eserine, carbaryl, and ethyl-paraoxon was observed in gills of O. edulis and M. galloprovincialis. Although field validation is needed, the present study suggests that O. edulis may be employed as a biological indicator for assessing pesticide contamination, whilst T. philippinarum does not seem useful for this purpose.