Sara Buratti

Effects of environmental concentrations of the antiepilectic drug carbamazepine on biomarkers and cAMP-mediated cell signaling in the mussel Mytilus galloprovincialis

Pharmaceuticals represent a diverse collection of thousands of bioactive chemicals used in human and veterinary medicine. The increased consumption, together with the recent development of more sensitive analytical techniques, has identified these as emerging contaminants in the aquatic environment. According to many investigations pharmaceuticals do not cause acute toxic effects in organisms when released in the environment. However, many independent studies agree that chronic exposure and more specific endpoints should be used in risk assessment of these compounds. We thus investigated the effects of exposure to environmentally relevant concentrations of the antiepileptic drug carbamazepine (CBZ) on Mediterranean mussels (Mytilus galloprovincialis) by considering the existing knowledge about the therapeutic and side effects of this drug on humans. To do so we analysed: (a) six consolidated biomarkers related primarily to oxidative stress; (b) cAMP levels and protein kinase A (PKA) activities; (c) mRNA expression of MXR-related genes. MXR proteins are involved both in the cAMP pathway and in the protective response of organisms towards xenobiotics. Mussels exposed to 0.1 or 10microg CBZ per liter water for 7 days showed a 60% and 80% reduction in haemocyte lysosome membrane stability, respectively. Moreover, increased neutral lipid and lipofuscin accumulation in the digestive gland, and lipid peroxidation in gills and mantle/gonads were observed. Also glutathione S-tranferase and catalase activities were increased in digestive gland and mantle, while no increase in primary DNA damage was observed. In agreement with the mode of action of CBZ in humans, exposure resulted in a significant reduction in cAMP levels and PKA activities in digestive gland, gills and mantle/gonads of mussels, and lowered the mRNA expression of genes encoding three different MXR-related transporters in the same tissues. Our data indicate that CBZ, at concentrations found in the environment, affects the Mediterranean mussel by acting on specific biochemical pathways that are evolutionarily conserved.

The β-blocker propranolol affects cAMP-dependent signaling and induces the stress response in Mediterranean mussels, Mytilus galloprovincialis.

Widespread occurrence of pharmaceuticals is reported in aquatic systems, posing concerns for the health of aquatic wildlife and a theoretical risk to humans. A recent concept was developed for the identification of highly active compounds amongst the environmental pharmaceuticals, based on their mode of action, the homology between human targets and possible targets in the environment, and the importance of the affected pathway for the target species. In line with this approach, this study investigated whether propranolol (PROP) affects the cAMP-dependent pathway in Mediterranean mussels, Mytilus galloprovincialis. PROP is a prototypical β-adrenoceptor antagonist, and these receptors exist in bivalves and show gross pharmacological properties similar to their mammalian counterparts. PROP also acts as a 5-HT1 receptor antagonist, which is the sole 5-HT receptor reported in bivalves to date. Importantly, β-adrenoceptor and 5HT-1 receptor subtypes are positively and negatively coupled to cAMP-mediated signaling, respectively. PROP was administered as either l-PROP or dl-PROP. A wide range of concentrations was tested including low (0.3, 3 and 30ng/L) and high (300ng/L) environmental ranges, and a concentration 5-fold above the maximum reported environmental level (30,000ng/L). After a 7-day exposure, mussel cAMP levels and PKA activities were significantly reduced in digestive gland, increased in mantle/gonads and unaffected in gills. Similar patterns were observed for the mRNA expression of the ABCB1 gene encoding the membrane transporter P-glycoprotein, hypothesised to be under PKA modulation. The effects on the digestive gland are consistent with PROP blocking β-adrenoceptors. The observed increased cAMP levels in the mantle/gonad tissue support PROP blocking 5-HT1 receptors. Catalase and glutathione-S tranferase were differently affected by PROP in the two tissues. Mussel haemocyte lysosome membrane stability, a sensitive biomarker of animal health status, was concentration-dependently reduced following PROP exposure. Our observations provide evidence for PROP affecting cell signaling in M. galloprovincialis. Moreover, the chemical interacts with specific and evolutionally conserved biochemical pathways for which it was designed. The mode of action of PROP in mussels is related with its therapeutic properties in humans, based upon these conserved human targets. It also induced a stress response, and all these effects were displayed at the lowest concentrations tested.

An exploratory investigation of various modes of action and potential adverse outcomes of fluoxetine in marine mussels.

The present study investigated possible adverse outcome pathways (AOPs) of the antidepressant fluoxetine (FX) in the marine mussel Mytilus galloprovincialis. An evaluation of molecular endpoints involved in modes of action (MOAs) of FX and biomarkers for sub-lethal toxicity were explored in mussels after a 7-day administration of nominal FX concentrations encompassing a range of environmentally relevant values (0.03-300ng/L). FX bioaccumulated in mussel tissues after treatment with 30 and 300ng/L FX, resulting in bioconcentration factor (BCF) values ranging from 200 to 800, which were higher than expected based solely on hydrophobic partitioning models. Because FX acts as a selective serotonin (5-HT) re-uptake inhibitor increasing serotonergic neurotransmission at mammalian synapses, cell signaling alterations triggered by 5-HT receptor occupations were assessed. cAMP levels and PKA activities were decreased in digestive gland and mantle/gonads of FX-treated mussels, consistent with an increased occupation of 5-HT1 receptors negatively coupled to the cAMP/PKA pathway. mRNA levels of a ABCB gene encoding the P-glycoprotein were also significantly down-regulated. This membrane transporter acts in detoxification towards xenobiotics and in altering pharmacokinetics of antidepressants; moreover, it is under a cAMP/PKA transcriptional regulation in mussels. Potential stress effects of FX were investigated using a battery of biomarkers for mussel health status that included lysosomal parameters, antioxidant enzyme activities, lipid peroxidation, and acetylcholinesterase activity. FX reduced the health status of mussels and induced lysosomal alterations, as suggested by reduction of lysosomal membrane stability in haemocytes and by lysosomal accumulation of neutral lipids in digestive gland. No clear antioxidant responses to FX were detected in digestive gland, while gills displayed significant increases of catalase and glutathione-s-transferase activities and a significant decrease of acetylcholinesterase activity. Though AOPs associated with mammalian therapeutic MOAs remain important during assessments of pharmaceutical hazards in the environment, this study highlights the importance of considering additional MOAs and AOPs for FX, particularly in marine mussels.

The mode of action (MOA) approach reveals interactive effects of environmental pharmaceuticals on Mytilus galloprovincialis

Aquatic organisms are unintentionally exposed to a large number of pharmaceutical residues in their natural habitats. Ecotoxicological studies have agreed that these compounds are not harmful to aquatic organisms, as their environmental concentrations are typically too low. However, recent reports have shown biological effects at such low concentrations when biological endpoints related to the therapeutic effects are assessed. Therefore, conservation of molecular targets is now addressed as a key aspect for the development of more efficient test strategies for pharmaceutical environmental risk assessment, providing the rationale for the mode of action (MOA) approach. In the present study the MOA approach was used to investigate the interactive effects of fluoxetine (FX) and propranolol (PROP) on the Mediterranean mussels (Mytilus galloprovincialis). Indeed, organisms in the environment are exposed to pharmaceutical mixtures throughout their lifetime, and particular combinations may be of concern. The antidepressant FX increases serotonin (5-HT) levels in the synaptic cleft by inhibiting 5-HT reuptake. PROP, a prototypical β-adrenoceptor antagonist, also blocks 5-HT1 receptors, which are negatively coupled to cAMP-mediated signaling. Cell signaling alterations potentially triggered by 5-HT1 receptor occupation were therefore assessed after a 7-day mussel exposure to FX or PROP, alone or in combination, each at 0.3 ng/L concentration. FX decreased cAMP levels and PKA activities in digestive gland and mantle/gonads, in agreement with an increased occupation of 5-HT1 receptors. PROP caused a decrease in cAMP levels and PKA activities in digestive gland and an increase in cAMP levels in mantle/gonads, consistent with a differential expression of adrenergic and 5-HT receptors in the two tissues. Co-exposure to FX and PROP provides significant indications for antagonistic effects of the pharmaceuticals, consistent with a direct (PROP) and indirect (FX) action on the same molecular target. Interestingly, FX induced over-expression of a 5-HT1 gene product, and PROP counteracted such increase when the mixture was administered, while having per se no effect. Finally, mRNA expression of the ABCB gene encoding the MXR-related transporter P-glycoprotein was reduced by both pharmaceuticals in the digestive gland, while decreased by FX, increased by PROP, and not affected by the mixture in mantle/gonads. Since transcription of this gene product is under cAMP/PKA modulation, the impairment of regulatory pathways triggered by low concentrations of pharmaceuticals have the potential to affect the ability of animals to elaborate strategies of defense or adaptation toward further stress factors. In this specific case, the pharmaceutical mixture limits the detrimental effects of the single compounds.

Exposure of mussels to a polluted environment: Insights into the stress syndrome development

Coastal environments are often subjected to contamination, whose biological impact is profitably evaluated through sentinel organisms and biomarkers. mRNA profiling was also proposed as a potential biomarker, whose relevance is still under discussion. Indeed, correlation between molecular and cell-organism responses need further investigations, especially under field conditions. In this study, we followed the development of physiological alterations in Mytilus galloprovincialis transplanted into a polluted coastal lagoon for 2, 4, 7, 14 and 30 days. Three consolidated biomarkers were measured, i.e. lysosomal membrane stability, lipofuscin and metallothionein contents. In parallel, the expressions of stress-related genes encoding metallothioneins (mt10 and mt20), 70-kDa heat shock proteins (MgHSC70 and MgHSP70), and Multi Xenobiotic Resistance-related transporters (MgPgp, MgMrp2, and MgMvp) were analyzed, to have a greater insight into the time-related evolution of the response. Significant (p<0.05) biomarker responses were induced after 7 days of exposure and further increased with time, whereas gene expression profiles were dramatically altered 2 days after transplanting. Biomarkers and gene expression profiles indicated a stress syndrome development in mussels, although with different temporal patterns. Their combined application provided insights into the molecular and cellular basis of mussel responses to challenging environments, and may have far-reaching implications for monitoring environmental health.

Bioaccumulation of algal toxins and changes in physiological parameters in Mediterranean mussels from the North Adriatic Sea (Italy)

The Northwestern Adriatic Sea is a commercially important area in aquaculture, accounting for about 90% of the Italian mussel production, and it was subjected to recurring cases of mussel farm closures due to toxic algae poisoning. A spatial and temporal survey of four sites along the North Adriatic Sea coasts of Emilia Romagna (Italy) was undertaken to study the possible impairments of physiological parameters in Mytilus galloprovincialis naturally exposed to algal toxins. The sites were selected as part of the monitoring network for the assessment of algal toxins bioaccumulation by the competent Authority. Samples positive to paralytic shellfish toxins and to lipophilic toxins were detected through the mouse bioassay. Lipophilic toxins were assessed by HPLC. Decreasing yessotoxins (YTX) levels were observed in mussels from June to December, while homo‐YTX contents increased concomitantly. Lysosome membrane stability (LMS), glutathione S‐transferase and catalase activities, and multixenobiotic resistance (MXR)‐related gene expressions were assessed as parameters related to the mussel health status and widely utilized in environmental biomonitoring. Levels of cAMP were also measured, as possibly involved in the algal toxin mechanisms of action. Low LMS values were observed in hemocytes from mussels positive to the mouse bioassay. MXR‐related gene expressions were greatly inhibited in mussels positive to the mouse bioassay. Clear correlations were established between increasing homo‐YTX contents (and decreasing YTX) and increasing cAMP levels in the tissues. Similarly, significant correlations were established between the increase of homo‐YTX and cAMP levels, and the expressions of three MXR‐related genes at submaximal toxin concentrations. In conclusion, YTXs may affect mussel physiological parameters, including hemocyte functionality, gene expression and cell signaling.

Use of an integrated biomarker-based strategy to evaluate physiological stress responses induced by environmental concentrations of caffeine in the Mediterranean mussel Mytilus galloprovincialis

The occurrence of caffeine (CF), a biologically active drug, has widely been documented in coastal waters, and whether its environmental concentrations do represent a threat for marine organisms is unclear. The present study aimed at assessing sub-lethal effects induced by a 7-day exposure to environmentally relevant concentrations of CF (5, 50 and 500ng/L) in the Mediterranean mussel, Mytilus galloprovincialis. CF in water and mussel tissues, and a battery of biomarkers, including lysosomal parameters of general stress, oxidative stress responses and endpoints of neurological and genetic damages, were evaluated and tested for significance vs controls (p<0.05). CF exposure triggered a significant decrease of lysosomal membrane stability in both haemocytes and digestive gland (at 50 and 500ng/L CF) and a significant increase of lysosomal content of neutral lipids (at 500ng/L CF), indicating the onset of a stress syndrome. No effects were noted on lipid peroxidation parameters, such as malondialdehyde and lipofuscin content. The activity of the antioxidant enzymes glutathione S-transferase (GST) and catalase was unmodified in gills, while a significant increase of GST activity was observed in digestive gland (at 5 and 500ng/L CF), suggesting the occurrence of GST-mediated phase II detoxifying processes. CF did not induce geno/neurotoxicity, as shown by the lack of effects on primary DNA damages and acetylcholinesterase activity. In line with its high hydrophilicity, CF did not bioaccumulate in mussel tissues. Data were integrated using the Mussel Expert System, which assigned a low stress level to mussels exposed to 500ng/L CF, whereas no alterations of animal health status were highlighted at lower dosages. This study revealed a low profile of toxicity for environmental concentrations of CF, and confirmed the suitability of an integrated biomarker-based approach to provide a comprehensive picture of the degree of stress induced by emerging contaminants in marine invertebrates.

Characterization of a β2 adrenergic receptor protein precursor in the European eel ( Anguilla anguilla ) and its tissue distribution across silvering

This study provides the characterization and tissue distribution of a β2-AR in the female European eel during silvering, aiming to better understand the adrenergic system involvement in this critical maturation event. A putative β2-AR (ADRB2) mRNA was cloned and sequenced. Amino acid residues and motifs important for ligand binding are generally conserved across fish and between fish and mammals, although the occurrence of some sequence variabilities may explain the noted peculiarities of eel AR interaction with pharmacological ligands. The tissue distribution of the ADRB2 gene product was analyzed in five tissues of the eel at different silvering stages and compared with that of the ADRA1 mRNA encoding an α1-AR subtype. On the whole, data suggested that relative ADRA1/ADRB2 tissue expression across silvering is part of the preparatory (molecular) adjustments required to face changes in habitats and migration efforts.