Insulin-like effect of zinc in mytilus digestive gland cells: modulation of tyrosine kinase-mediated cell signaling

Waterborne zinc bioaccumulation influences glucose metabolism in orange-spotted grouper embryos

Fish embryos, as an endogenous system, strictly regulate an energy metabolism that is particularly sensitive to environmental pressure. This study used orange-spotted grouper embryos and stable isotope ⁶⁷Zn to test the hypothesis that waterborne Zn exposure had a significant effect on energy metabolism in embryos. The fish embryos were exposed to a gradient level of waterborne ⁶⁷Zn, and then sampled to quantify ⁶⁷Zn bioaccumulation and mRNA expressions of key genes involved glucose metabolism. The results indicated that the bioaccumulated ⁶⁷Zn generally increased with increasing waterborne ⁶⁷Zn concentrations, while it tended to be saturated at waterborne ⁶⁷Zn > 0.7 mg L^-1. As we hypothesized, the expression of PK and PFK gene involved glycolysis pathway was significantly up-regulated under waterborne ⁶⁷Zn exposure >4 mg L^-1. Waterborne ⁶⁷Zn exposure >2 mg L^-1 significantly suppressed PCK and G6PC gene expression involved gluconeogenesis pathway, and also inhibited the AKT2, GSK-3beta and GLUT4 genes involved Akt signaling pathway. Our findings first characterized developmental stage-dependent Zn uptake and genotoxicity in fish embryos. We suggest fish embryos, as a small-scale modeling biosystem, have a large potential and wide applicability for determining cytotoxicity/genotoxicity of waterborne metal in aquatic ecosystem.

Signaling pathways involved in metal-based nanomaterial toxicity towards aquatic organisms

Environmental risk assessment of engineered nanomaterials (ENMs) is an emergent field since nanotechnology industry is rapidly growing due to the interesting physicochemical properties of nanomaterials. Metal-based nanomaterials are among the most rapidly commercialized materials and their toxicity towards aquatic animals has been investigated at different levels of the biological organization. The objective of this synthesis review is to give an overview of the signaling molecules that have a key role in metal-based NM mediated cytotoxicity in both marine and freshwater organisms. Since toxicity of metal-based NMs could be (partly) due to metal dissolution, this review only highlights studies that showed a specific nano-effect. From this bibliographic study, three mechanisms (detoxification, immunomodulation and genotoxicity) have been selected as they represent the major cell defense mechanisms and the most studied ones following ENM exposure. This better understanding of NM-mediated cytotoxicity may provide a sound basis for designing environmentally safer nanomaterials.

Utilization of Mytilus digestive gland cells for the in vitro screening of potential metabolic disruptors in aquatic invertebrates

In vertebrate systems, many endocrine disruptors (EDs) can also interfere with energy and lipid metabolism, thus acting as metabolic disruptors. At the cellular level, these effects are mainly mediated by interactions with nuclear receptors/transcription factors, leading to the modulation of genes involved in lipid homeostasis, as well as by rapid, receptor-independent pathways. Several potential metabolic disruptors are found in aquatic environments. In fish, different EDs have been shown to affect hepatic lipid homeostasis both in vivo and in vitro. However, little information is available in aquatic invertebrates due to our poor knowledge of the regulatory pathways of lipid metabolism. In this work, primary cell cultures from the digestive gland of the bivalve Mytilus galloprovincialis were utilized to investigate the effects of model EDs (bisphenol A (BPA) and perfluorooctane sulphonate (PFOS)) on lipid homeostasis. Both compounds (at 24 and 3h of exposure) increased intracellular lipid and tryglyceride-TAG content, with strongest effects of PFOS at 10^-7M. Acyl-CoA oxidase activity was unaffected, whereas some changes in the activity of glycolytic, antioxidant/biotransformation enzymes were observed; however, no clear relationship was found with lipid accumulation. Evaluation of mitochondrial membrane potential Δψm and determination of extracellular TAG content indicate that PFOS interferes with mitochondrial function and lipid secretion, whereas BPA mainly affects lipid secretion. Experiments with specific inhibitors showed that activation of PI-3 kinase and extracellularly regulated mitogen-activated protein kinase (ERK MAPK) plays a key role in mediating lipid accumulation. Mussel digestive gland cells represent a simple in vitro model for screening the metabolic effects of EDs in marine invertebrates.

Zinc and diabetes mellitus: understanding molecular mechanisms and clinical implications

Background

Diabetes mellitus is a leading cause of morbidity and mortality worldwide. Studies have shown that Zinc has numerous beneficial effects in both type-1 and type-2 diabetes. We aim to evaluate the literature on the mechanisms and molecular level effects of Zinc on glycaemic control, β-cell function, pathogenesis of diabetes and its complications.

Methods

A review of published studies reporting mechanisms of action of Zinc in diabetes was undertaken in PubMed and SciVerse Scopus medical databases using the following search terms in article title, abstract or keywords; (“Zinc” or “Zn”) and (“mechanism” or “mechanism of action” or “action” or “effect” or “pathogenesis” or “pathology” or “physiology” or “metabolism”) and (“diabetes” or “prediabetes” or “sugar” or “glucose” or “insulin”).

Results

The literature search identified the following number of articles in the two databases; PubMed (n = 1799) and SciVerse Scopus (n = 1879). After removing duplicates the total number of articles included in the present review is 111. Our results show that Zinc plays an important role in β-cell function, insulin action, glucose homeostasis and the pathogenesis of diabetes and its complications.

Conclusion

Numerous in-vitro and in-vivo studies have shown that Zinc has beneficial effects in both type-1 and type-2 diabetes. However further randomized double-blinded placebo-controlled clinical trials conducted for an adequate duration, are required to establish therapeutic safety in humans.

Electronic supplementary material

The online version of this article (doi:10.1186/s40199-015-0127-4) contains supplementary material, which is available to authorized users.

A multi-platform metabolomics approach demonstrates changes in energy metabolism and the transsulfuration pathway in Chironomus tepperi following exposure to zinc

Measuring biological responses in resident biota is a commonly used approach to monitoring polluted habitats. The challenge is to choose sensitive and, ideally, stressor-specific endpoints that reflect the responses of the ecosystem. Metabolomics is a potentially useful approach for identifying sensitive and consistent responses since it provides a holistic view to understanding the effects of exposure to chemicals upon the physiological functioning of organisms. In this study, we exposed the aquatic non-biting midge, Chironomus tepperi, to two concentrations of zinc chloride and measured global changes in polar metabolite levels using an untargeted gas chromatography-mass spectrometry (GC-MS) analysis and a targeted liquid chromatography-mass spectrometry (LC-MS) analysis of amine-containing metabolites. These data were correlated with changes in the expression of a number of target genes. Zinc exposure resulted in a reduction in levels of intermediates in carbohydrate metabolism (i.e., glucose 6-phosphate, fructose 6-phosphate and disaccharides) and an increase in a number of TCA cycle intermediates. Zinc exposure also resulted in decreases in concentrations of the amine containing metabolites, lanthionine, methionine and cystathionine, and an increase in metallothionein gene expression. Methionine and cystathionine are intermediates in the transsulfuration pathway which is involved in the conversion of methionine to cysteine. These responses provide an understanding of the pathways affected by zinc toxicity, and how these effects are different to other heavy metals such as cadmium and copper. The use of complementary metabolomics analytical approaches was particularly useful for understanding the effects of zinc exposure and importantly, identified a suite of candidate biomarkers of zinc exposure useful for the development of biomonitoring programs.

Biological consequences of zinc deficiency in the pathomechanisms of selected diseases

From many points of view, zinc is one of the most important trace elements in biological systems. Many articles describe the well-known role of this metal in human physiology and pathophysiology, but in the related literature, there is a lack of current and reliable reviews of the role of zinc deficiency in many diseases. In this article, we describe the role of zinc deficiency in the oxidative stress control, immune response, proliferation, and pathogenesis and pathophysiology of selected diseases such as depression, cardiovascular diseases, diabetes mellitus, Alzheimer's disease, and Wilson's disease.

Zinc homeostasis in the metabolic syndrome and diabetes

Zinc (Zn) is an essential mineral that is required for various cellular functions. Zn dyshomeostasis always is related to certain disorders such as metabolic syndrome, diabetes and diabetic complications. The associations of Zn with metabolic syndrome, diabetes and diabetic complications, thus, stem from the multiple roles of Zn: (1) a constructive component of many important enzymes or proteins, (2) a requirement for insulin storage and secretion, (3) a direct or indirect antioxidant action, and (4) an insulin-like action. However, whether there is a clear cause-and-effect relationship of Zn with metabolic syndrome, diabetes, or diabetic complications remains unclear. In fact, it is known that Zn deficiency is a common phenomenon in diabetic patients. Chronic low intake of Zn was associated with the increased risk of diabetes and diabetes also impairs Zn metabolism. Theoretically Zn supplementation should prevent the metabolic syndrome, diabetes, and diabetic complications; however, limited available data are not always supportive of the above notion. Therefore, this review has tried to summarize these pieces of available information, possible mechanisms by which Zn prevents the metabolic syndrome, diabetes, and diabetic complications. In the final part, what are the current issues for Zn supplementation were also discussed.

Effects of sublethal, environmentally relevant concentrations of hexavalent chromium in the gills of Mytilus galloprovincialis

Hexavalent chromium Cr(VI) is an important contaminant released from both domestic and industrial effluents, and represents the predominant chemical form of the metal in aquatic ecosystems. In the marine bivalve Mytilus galloprovincialis exposure to non-toxic, environmentally relevant concentrations of Cr(VI) was shown to modulate functional parameters and gene expression in both the digestive gland and hemocytes. In this work, the effects of exposure to Cr(VI) (0.1-1-10 μg L(-1) animal(-1) for 96 h) in mussel gills were investigated. Gill morphology and immunolocalization of GSH-transferase (GST), of components involved in cholinergic (AChE and ChAT), adrenergic (TH) and serotoninergic (5-HT(3) receptor) systems, regulating gill motility, were evaluated. Total glutathione content, activities of GSH-related enzymes (glutathione reductase - GSR, GST), of catalase, and of key glycolytic enzymes (phosphofructokinase - PFK and pyruvate kinase - PK) were determined. Moreover, mRNA expression of selected Mytilus genes (GST-π, metallothionein isoforms MT10 and MT20, HSP70 and 5-HT receptor) was assessed by RT-q-PCR. Cr(VI) exposure induced progressive changes in gill morphology and in immunoreactivity to components involved in neurotransmission that were particularly evident at the highest concentration tested, and associated with large metal accumulation. Cr(VI) increased the activities of GST and GSR, and total glutathione content to a different extent at different metal concentrations, this suggesting Cr(VI) detoxication/reduction at the site of metal entry. Cr(VI) exposure also increased the activity of glycolytic enzymes, indicating modulation of carbohydrate metabolism. Significant changes in transcription of different genes were observed. In particular, the mRNA level for the 5-HTR was increased, whereas both decreases and increases were observed for GST-π, MT10, MT20 and HSP70 mRNAs, showing sex- and concentration-related differences. The results demonstrate that Cr(VI) significantly affected functional and molecular parameters in mussel gills, and indicate that this tissue represents the major target of exposure to environmentally relevant concentrations of the metal.

Effects of tumour necrosis factor α (TNFα) on Mytilus haemocytes: role of stress-activated mitogen-activated protein kinases (MAPKs)

BACKGROUND INFORMATION

Many studies indicate that innate immunity in invertebrates can be modulated by a cytokine network like in vertebrates. In molluscs, the immune response is carried out by circulating haemocytes and soluble haemolymph factors. In the present study, the effects of heterologous TNFalpha (tumour necrosis factor alpha) on cell signalling and function in the haemocytes of the bivalve Mytilus galloprovincialis Lam. were investigated.

RESULTS AND CONCLUSIONS

Addition of TNFalpha in the absence of haemolymph serum [in ASW (artificial sea water)] induced cellular stress, as indicated by lysosomal destabilization, and decreased phagocytosis; on the other hand, in the presence of serum, TNFalpha did not affect lysosomal stability and even stimulated phagocytosis. TNFalpha induced rapid phosphorylation of the stress-activated p38 and JNK (c-Jun N-terminal kinase) MAPKs (mitogen-activated protein kinases); both effects were persistent in ASW but transient in serum. Activation of p38 and JNKs in mediating the effects of TNFalpha was confirmed by the use of specific MAPK inhibitors. Moreover, flow cytometric analysis indicated that TNFalpha in the presence of serum induced transient phosphatidylserine exposure on the haemocyte surface, evaluated as annexin V binding; in ASW, the cytokine resulted in a stable increase in the percentage of both annexin- and propidium iodide-positive cells, indicating possible apoptotic/necrotic processes. The results indicate that TNFalpha can affect the function of bivalve haemocytes through conserved transduction pathways involving stress-activated MAPKs and suggest that the haemocyte response to the cytokine is influenced by soluble haemolymph components.

Pleiotropic effects of hexavalent chromium (CrVI) in Mytilus galloprovincialis digestive gland

Hexavalent Chromium Cr(VI) is an important contaminant considered as a model oxidative toxicant released from both domestic and industrial effluents, and represents the predominant chemical form of the metal in aquatic ecosystems. On the other hand, in mammals the reduced form Cr(III) is considered an essential microelement, involved in regulation of lipid and carbohydrate metabolism; moreover, recent evidence suggests that Cr may have endocrine effects. In this work, the effects of Cr(VI) were investigated in the digestive gland of the marine bivalve Mytilus galloprovincialis. Mussels were exposed to 0.1-1-10-100 μg Cr(VI) L(-1) animal(-1) for 96 h. At 100 μg L(-1), a large increase in total Cr tissue content was observed; in these conditions, the lysosomal membranes were completely destabilized, whereas other lysosomal biomarkers (neutral lipids-NL and lipofuscin-LF), as well as different enzyme activities and gene expression were unaffected, this indicating severe stress conditions in the tissue. On the other hand, at lower concentrations, changes in other histochemical, biochemical and molecular endpoints were observed. In particular, at both 1 and 10 μg L(-1), lysosomal destabilization was associated with significant NL and LF accumulation; however, no changes in catalase and GSH transferase (GST) activities were observed. At the same concentrations, GSSG reductase (GSR) activity was significantly increased, this probably reflecting the recycling of GSSG produced in the GSH-mediated intracellular reduction of Cr(VI). Increased activities of the key glycolytic enzymes PFK (phosphofructokinase) and PK (pyruvate kinase) were also observed, indicating that Cr(VI) could affect carbohydrate metabolism. Cr(VI) induced downregulation or no effects on the expression of metallothioneins MT10 and MT20, except for an increase in MT20 transcription in males. Moreover, significant up-regulation of the Mytilus estrogen receptor MeER2 and serotonin receptor (5-HTR) were observed in both sexes. The results demonstrate that exposure to Cr(VI) in the low ppb range did not result in strong toxicity or oxidative stress conditions in mussel digestive gland. On the other hand, our data support the hypothesis that low concentrations of the metal can exert pleiotropic effects on mussel physiology, from modulation of lipid and carbohydrate metabolism, to effects on the expression of estrogen-responsive genes.

Activation of MAP kinase signaling pathway in the mussel Mytilus galloprovincialis as biomarker of environmental pollution

Stimulation of MAP kinase signal transduction pathway by various stressful stimuli was investigated in the marine bivalve Mytilus galloprovincialis. Analyses were performed in animals exposed in laboratory to selected pollutants and in mussels collected in winter and summer along the eastern Adriatic coast (Croatia). Effects of oxidative stress, induced by tributyltin, hydrogen peroxide and water soluble fraction of diesel fuel on the activation/phosphorylation of the three Mitogen-Activated Protein Kinases (MAPKs) p38, JNK and ERK using a newly developed ELISA procedure were evaluated. MAP kinase activation was analyzed 1h after exposure of mussels to chemical agents, and after recovery periods of 6 and 24h. Our results clearly indicated that pollutants generated different patterns of induction of the MAPK phosphorylation. Indeed, only pp38 and pJNK were activated with 11, 33 and 100 microg/L TBT, reaching a maximum activation after 6h in seawater following treatment of mussels with 11 microg/L TBT. Treatment with 0.074 and 0.222 mM H2O2 enhanced activation of both p38 and ERK. These two kinases were activated after 1h exposure, followed by a diminution after 6h of recovery in seawater and a reactivation after 24h. The levels of phosphorylated P38 and JNK were increased after mussel exposure with 7.5, 15 and 30% of water soluble fraction of diesel oil. P38 was activated concentration dependently at 1h exposure. Additionally, field study pointed out seasonal differences in MAP kinases activation as mussels collected during summer had a higher enzyme activation state than in winter, as well as sampling site differences which could be correlated to the industrial/tourism activity and environmental stresses (salinity). All the results converge towards MAP kinase signaling pathway being induced by various pollutants in M. galloprovincialis. This signaling cascade should be considered as a possible biomarker of environmental stress and pollution.

Cell-type-specific roles of IGF-1R and EGFR in mediating Zn2+-induced ERK1/2 and PKB phosphorylation

Zn(2+) exerts insulin-mimetic and antidiabetic effects in rodent models of insulin resistance, and activates extracellular-signal-regulated kinases 1 and 2 (ERK1/2) and protein kinase B (PKB), key components of the insulin signaling pathway. Zn(2+)-induced signaling has been shown to be associated with an increase in the tyrosine phosphorylation of insulin receptor (IR), as well as of insulin-like growth factor 1 receptor (IGF-1R) and epidermal growth factor receptor (EGFR) in several cell types. However, the specific contribution of these receptor protein tyrosine kinases (R-PTKs) in mediating Zn(2+)-induced responses in a cell-specific fashion remains to be established. Therefore, using a series of pharmacological inhibitors and genetically engineered cells, we have investigated the roles of various R-PTKs in Zn(2+)-induced ERK1/2 and PKB phosphorylation. Pretreatment of Chinese hamster ovary (CHO) cells overexpressing a human IR (CHO-HIR cells) with AG1024, an inhibitor for IR protein tyrosine kinase (PTK) and IGF-1R-PTK, blocked Zn(2+)-induced ERK1/2 and PKB phosphorylation, but AG1478, an inhibitor for EGFR, was without effect in CHO cells. On the other hand, both of these inhibitors were able to attenuate Zn(2+)-induced phosphorylation of ERK1/2 and PKB in A10 vascular smooth muscle cells. In addition, in CHO cells overexpressing tyrosine kinase deficient IR, Zn(2+) was still able to induce the phosphorylation of these two signaling molecules, whereas the insulin effect was significantly attenuated. Furthermore, both Zn(2+) and insulin-like growth factor 1 failed to stimulate ERK1/2 and PKB phosphorylation in IGF-1R knockout cells. Also, Zn(2+)-induced responses in CHO-HIR cells were not associated with an increase in the tyrosine phosphorylation of the IR beta-subunit and insulin receptor substrate 1 in CHO-HIR cells. Taken together, these data suggest that distinct R-PTKs mediate Zn(2+)-evoked ERK1/2 and PKB phosphorylation in a cell-specific manner.

Unifying electrostatic mechanism for metal cations in receptors and cell signaling

Previously, an electrostatic mechanism was proposed for receptor-ligand action and for cell signaling by phosphate and sulfate. The hypothesis is further elaborated by application to metal ions, mainly calcium, magnesium, zinc, iron, and copper, in receptors and cell signaling. Evidence is provided for involvement of electrostatics in various reaction modes in biosystems. Calcium plays an important role electrochemically in neurotransmission. In some cases, electron transfer and redox processes are also involved. Electrostatics are known to participate in plant biochemistry. Mechanistically, the electrostatic field may act as a conduit for electrons and radicals and in involvement with energetics.

Effects of blood lipid lowering pharmaceuticals (bezafibrate and gemfibrozil) on immune and digestive gland functions of the bivalve mollusc, Mytilus galloprovincialis

Fibrates are hypolipidemic pharmaceuticals that have been detected as contaminants in wastewaters and surface waters. In this work, the possible effects of two fibrates, Bezafibrate (BEZA) and Gemfibrozil (GEM) in the bivalve mollusc Mytilus spp were investigated. In the immune cells, the hemocytes, addition of both compounds in vitro induced rapid lysosomal membrane destabilization, extracellular lysozyme release, NO production and decreased phagocytic activity. The effect of fibrates were partly mediated by activation of ERK and p38 MAPKs (Mitogen Activated Protein Kinases), as demonstrated by the use of specific inhibitors of different kinases. The effects of fibrates on hemocyte function were confirmed in vivo, in the hemocytes of mussels injected with 0.01, 0.1 and 1 nmol/animal (corresponding to nominal concentrations of 3.61, 36.18 and 361.8ng/g dry weight for BEZA and of 2.50, 25.03 and 250.35 ng/g dry weight for GEM, respectively) and sampled at 24h post-injection. Both compounds induced a concentration-dependent lysosomal destabilization and extracellular lysozyme release; an increase in phagocytosis was observed at the highest concentration. In vivo exposure to fibrates also induced significant effects on mussel digestive gland, the key metabolic organ in bivalves. Both BEZA and GEM increased the activity of the glycolytic enzymes phosphofructokinase (PFK) and pyruvate kinase (PK), and of Glutathione transferase (GST) glutathione reductase (GSR), and total glutathione content. A significant increase in the peroxisomal enzyme catalase was observed; however, BEZA exposure decreased Palmytoyl CoA oxidase activity, whereas GEM was ineffective. The results indicate that in mussels environmental concentrations of hypolipidemic drugs can affect the immune function, as well as glycolysis, redox balance and peroxisomal function.

Effects of 17beta-estradiol on mussel digestive gland

In bivalve molluscs the digestive gland (hepatopancreas) plays a central role in metabolism. In this work, the effects of 17beta-estradiol (E(2)) on digestive gland were evaluated in Mytilus galloprovincialis. Mussels were injected into the adductor muscle sinus with different amounts of the hormone (5, 25 and 100pmol) and tissues were sampled 24h post-injection. Functional parameters (lysosomal membrane stability-LMS, lysosomal accumulation of neutral lipids-NL and of lipofuscin-LF), as well as the activity of the key glycolytic enzymes PFK (phosphofructokinase) and PK (pyruvate kinase), and of the antioxidant enzyme catalase were evaluated. Selected genes, whose expression can be modulated by estrogens in mammalian systems and whose sequences have been identified in Mytilus, were investigated as possible targets for the action of E(2). E(2) induced a concentration-dependent decrease in LMS; such an effect was accompanied by an increase in NL accumulation, whereas the level of lipofuscin showed a slight, although not significant decrease. E(2) exposure also led to a significant increase in the activity of PFK and catalase but not of PK. Moreover, E(2) induced significant changes in the pattern of gene expression at the lower concentrations tested (5 and 25pmol) as evaluated by quantitative RT-PCR. In particular, increased transcription of catalase, as well as of the metallothionein 20 (MT20) isoform were observed; on the other hand, a decreased transcription of the p53 gene was detected. The results demonstrate that in Mytilus the digestive gland represents a target for the action of E(2), and that the hormone can modulate the lysosomal function, as well as lipid and glucose metabolism. Moreover, these data suggest that E(2) may also alter oxidative stress conditions in this tissue, as indicated by the increased transcription of genes (metallothionein and catalase) that play a role in antioxidant defences. Overall, the results indicate that E(2) can modulate both functional parameters and gene expression in mussel hepatopancreas and underline the importance of investigating also non-reproductive effects of estrogenic compounds in bivalve molluscs.

Effects of Triclosan on Mytilus galloprovincialis hemocyte function and digestive gland enzyme activities: possible modes of action on non target organisms

Pharmaceuticals and Personal Care Products (PPCPs) are a class of emerging environmental pollutants with the potential of affecting various aquatic organisms through unexpected modes of action. Triclosan (2,4,4'-trichloro-2'-hydroxydiphenyl ether) (TCS), is a common antibacterial agent that is found in significant amounts in the aquatic environment. In this work, the possible effects and modes of action of TCS were investigated in the marine bivalve Mytilus galloprovincialis Lam. In mussel immune cells, the hemocytes, in vitro short-term exposure to TCS in the low microM range reduced lysosomal membrane stability (LMS) and induced extracellular release of lysosomal hydrolytic enzymes. The effects on LMS were mediated by activation of ERK MAPKs (Extracellularly Regulated Mitogen Activated Protein Kinases) and PKC (protein kinase C) alpha and betaII isoforms, as demonstrated by both specific kinase inhibitors and Western blotting with specific anti-phospho-antibodies. The effects of TCS were confirmed in vivo, in the hemocytes of mussels injected with different concentrations of TCS (corresponding to 0.29, 2.9 and 29 ng/g dry weight) and sampled at 24 h post-injection. The possible in vivo effects of TCS were also evaluated on the activity of different enzymes in the digestive gland, the tissue mainly involved in accumulation and metabolism of organic contaminants in mussels. Significant increases were observed in the activity of the glycolytic enzymes PFK (phosphofructokinase) and PK (pyruvate kinase), as well as of GST (GSH transferase) and GSR (GSSG reductase), whereas a decrease in catalase activity was observed. The results demonstrate that in mussels TCS can act on kinase-mediated cell signalling, lysosomal membranes and redox balance in different systems/organs. Although further studies are needed in order to evaluate possible consequences of environmental exposure to TCS on mussel health, the results represent the first data on the possible modes of action of this widespread antibacterial in aquatic invertebrates.

The influence of Zn on signaling pathways and attachment of Mytilus galloprovincialis haemocytes to extracellular matrix proteins

The present study investigates the cytotoxic mechanisms induced by zinc (Zn) in haemocytes of mussel Mytilus galloprovincialis. Haemocytes play a key role in the immune defence of mussels. Micromolar concentration of Zn (50 microM) play an important role in the elevation of pHi and increase in Na+ influx in haemocytes. The observed effects were inhibited by the Na+/H+ exchanger (NHE) inhibitor, ethyl-N-isopropyl-amiloride (EIPA). Furthermore, our results showed that Zn caused an increase in O(-)(2) production that was reversed after NHE inhibition. Phorbol ester (PMA) caused a significant rise both in pHi and Na+ influx as well as in O(-)(2) production. These effects were reversed by calphostin C. Our results indicated that Zn also enhanced haemocyte attachment to both BSA and laminin which was reversed by EIPA and calphostin C. The enhancement of haemocytes attachment to both BSA and laminin after Zn suggests that it is likely to play a signal role in cytoskeleton-dependent process of cell growth and migration in mussel M. galloprovincialis haemocytes. We conclude that Zn induces a signaling pathway with the involvement of NHE, PKC, O(-)(2) and alpha1- and beta-adrenergic receptors.

Gene transcription profiling in pollutant exposed mussels (Mytilus spp.) using a new low-density oligonucleotide microarray

In this study we describe the design and implementation of a novel low-density oligonucleotide microarray (the "Mytox-chip"). It consists of 24 mussel genes involving both normalizing elements and stress response related genes, each represented on the array with one or two different 50 mer oligonucleotide-probe reporters spotted in replicated samples on glass-activated slides. Target genes were selected on the basis of their potential involvement in mechanisms of pollutant and xenobiotic response. They are implicated in both basic and stress related cellular processes such as shock response, biotransformation and excretion, cell-cycle regulation, immune defense, drug metabolism, etc. The microarray was tested on mussels exposed to sublethal concentrations of mercury or a crude North Sea oil mixture. RNA samples were extracted from digestive glands of control and treated mussels for the synthesis of fluorescence labeled cDNAs to be used in dual color hybridizations. Transcription rates of two metallothionein iso-genes (mt10 and mt20), a p53-like gene and actin were quantitatively estimated also by real-time PCR to confirm microarray data. Significant alterations in the gene transcription patterns were seen in response to both treatments.

Zinc and 17beta-estradiol induce modifications in Na+/H+ exchanger and pyruvate kinase activity through protein kinase C in isolated mantle/gonad cells of Mytilus galloprovincialis

We investigated the transduction pathway mediated by Zn and 17beta-estradiol in isolated mantle/gonad cells of the mussel Mytilus galloprovincialis. Both the essential metal Zn, and the estrogen 17beta-estradiol, caused an increase in intracellular pH (pHi) of isolated mantle/gonad cells of the mussel M. galloprovincialis, thus indicating the activation of the Na+/H+ exchanger (NHE). The observed effect was inhibited by EIPA (20 nM), a specific NHE inhibitor, thus verifying NHE activation. Protein kinase C (PKC) also seemed to play an activating role in zinc and 17beta-estradiol effects on NHE and PK activity. In addition, the glycolytic enzyme pyruvate kinase (PK) was increased after zinc, while it was decreased after 17beta-estradiol treatment. It is noteworthy that, both the latter effects were reversed in the presence of EIPA, indicating the involvement of NHE in the signaling mechanism. cAMP seems to participate in the signaling mechanism induced by Zn but not to that induced by 17beta-estradiol. The potential implication of the heavy metal and 17beta-estradiol on the reproductive activity of the marine animals is discussed.

Fluctuations of cellular, available zinc modulate insulin signaling via inhibition of protein tyrosine phosphatases

Extracellular zinc ions are effectors of many signaling pathways in mammalian cells, including the insulin/IGF-1 pathway. Molecular targets of zinc are intracellular, however, because otherwise ineffective zinc concentrations alter the extent of protein phosphorylation only in the presence of the ionophore pyrithione. The tight inhibition of protein tyrosine phosphatases by zinc (nanomolar inhibition constants) is likely responsible for the known insulinomimetic effects of zinc ions, which increase net phosphorylation of the insulin/IGF-1-receptors and activate their signaling cascades. More importantly, not only do extracellular zinc ions affect signal transduction, but growth factors induce cellular zinc fluctuations that are of sufficient magnitude to inhibit protein tyrosine phosphatases. In conclusion, a pool of cellular, available zinc participates in phosphorylation/dephosphorylation cascades, suggesting the existence of a cellular signaling system based on zinc as a second messenger.

Cadmium induces both pyruvate kinase and Na+/H+exchanger activity through protein kinase C mediated signal transduction, in isolated digestive gland cells ofMytilus galloprovincialis(L.)

The present study investigates the transduction pathway mediated by cadmium in isolated digestive gland cells of mussel Mytilus galloprovincialis. The effects of cadmium treatment on a key glycolytic enzyme, pyruvate kinase (PK), and on Na+/H+ exchanger activity were examined. Cadmium (50 μmol l–1) caused a significant elevation of intracellular pH (pHi) and a rise (176%) of Na influx relative to control values. The amiloride analogue, EIPA (20 nmol l–1), a Na+/H+ exchanger blocker,together with cadmium, significantly reduced the effect of treatment by cadmium alone on both Na+ influx and pHi. In addition, PK activity was significantly increased after treatment with cadmium. PK activity was inhibited after treatment of cells with amiloride or EIPA together with cadmium. Moreover, phorbol-ester (PMA), a potent activator of protein kinase C(PKC), caused a significant rise in both pHi and PK activity, while staurosporine or calphostin C reversed both events. Adrenaline, isoprenaline and phenylephrine alone or together with cadmium also significantly increased the pHi and PK activity of isolated digestive gland cells. The latter effectors in combination with cadmium showed a synergistic effect on pHi and PK. These responses seem to be blocked by propranolol, metoprolol and prazosin. Our findings suggest a hormone-like effect of cadmium on digestive gland cells. The signal transduction pathway induced by cadmium involves the stimulation of PK, PKC and Na+/H+ exchanger in isolated digestive gland cells of Mytilus galloprovincialis.

Rapid effects of 17beta-estradiol on cell signaling and function of Mytilus hemocytes

Estrogens affect the functioning of several non-reproductive tissues, the immune system in particular. In mammalian immunocytes, 17beta-estradiol (E2) has both dose- and cell-type specific effects and the responses to E2 seem to be mediated by rapid, non-genomic mechanisms; these may be initiated at either membrane or cytosolic locations, and can result in both direct local effects, such as modification of ion fluxes, and regulation of gene transcription secondary to activation of different kinase cascades, including mitogen activated protein kinases (MAPKs). In this work, the short-term effects of E(2) and the possible mechanisms of estrogen-mediated cell signaling were investigated in the hemocytes, the immune cells of the bivalve mollusc, the mussel Mytilus galloprovincialis Lam. The results show that E2 (25nM) caused a rapid and significant increase in hemocyte cytosolic [Ca2+]; lower concentrations (5 nM) showed a smaller, not significant effect. Both E2 concentrations affected the phosphorylation state of the components of tyrosine kinase-mediated signal transduction MAPK- and STAT- (signal transducers and activators of transcription) like proteins within 5-15 min from E2 addition. A greater effect and clearer time course were observed with 25 nM E2: in particular, E2 induced a transient increase in p-ERK2 MAPK and a persistent increase in p-p38 MAPK. Moreover, both STAT3 and STAT5 were tyrosine phosphorylated in response to E2. E2 (5 nM) induced both morphological (as evaluated by SEM) and functional changes (such as extracellular release of hydrolytic enzymes, lysosomal membrane destabilisation, and stimulation of the bactericidal activity) within 10-30 min from addition. Lysosomal membrane destabilisation induced by both E2 concentrations was abolished by hemocyte preincubation with the p38 MAPK inhibitor SB203580, and significantly reduced by PD98059 and Wortmannin (inhibitors of ERK MAPK and PI3-K, respectively), this suggesting that rapid activation of kinase cascades is involved in mediating the effects of E2 in mussel hemocytes. The antiestrogen Tamoxifen prevented or strongly reduced most, but not all, the effects of E2. Western blotting with heterologous anti-ERalpha-anti-ERbeta-antibodies revealed the presence of immunoreactive ERalpha- and ERbeta-like proteins in hemocyte protein extracts. Overall, our data support the hypothesis that the rapid effects and mechanisms of action of 17beta-estradiol are extremely conserved and that they may play a crucial role in endocrine-immune interactions in invertebrates.

In vitro effects of lead ions on peripheral benzodiazepine receptors and adenylyl cyclase activity in the mantle of Mytilus galloprovincialis

As an extension of our previous work, where the density of peripheral benzodiazepine receptors (PBR) increased in mantle mitochondria of the marine mollusk Mytilus galloprovincialis Lmk. under chronic exposure to lead, the present study investigates the in vitro effects of an exogenous source of lead ions on PBR and on adenylyl cyclase (AC) complex in mantle membranes of mussels collected from a non-polluted coastal area. PBR binding experiments used the specific isoquinoline carboxamide derivative [3H]PK 11195, and AC activity was measured using a modified procedure adapted to M. galloprovincialis. Lead ions (Pb2+) dose-dependently decreased either the [3H]PK 11195 specific binding in mitochondria or basal AC velocity in plasma membranes of mussel mantle. The IC50 values for lead ions were 10 microM with [3H]PK 11195 binding and 25 microM with AC activity, with maximal inhibition values of 60% and 70%, respectively. Moreover, lead behaved as a non-competitive inhibitor on [3H]PK 11195 binding and as a 'mixed' inhibitor on AC activity. The present results suggest that some of the early effects induced by lead in mussel cell metabolism consist in significant changes of the PBR density and cyclic AMP production in the mantle of M. galloprovincialis.

Requirement of caspase and p38MAPK activation in zinc-induced apoptosis in human leukemia HL-60 cells

Zinc (Zn), an endogenous regulator of apoptosis, and has abilities both to induce apoptosis and inhibit the induction of apoptosis via the modulation of caspase activity. Due to the multifunctions of Zn, the intracellular Zn level is strictly regulated by a complex system in physiological and pathological conditions. The commitment of Zn to the regulation of apoptosis is not fully understood. In the present study, we investigated the role of intracellular Zn level in the induction of apoptosis in human leukemia cells (HL-60 cells) using a Zn ionophore [pyrithione (Py)]. Treatment of HL-60 cells with Zn for 6 h in the presence of Py (1 micro m) exhibited cytotoxicity in a Zn dose-dependent manner (25-200 micro m). Necrotic cells, assayed by trypan blue permeability, increased in number in a Zn dose-dependent fashion (50-100 micro m), but the appearance of apoptotic cells, assayed by formation of a DNA ladder and terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end-labeling method, peaked at 25 micro m, suggesting the dependence of intracellular Zn level on the execution of apoptosis. In fact, treatment with Py resulted in increases in intracellular Zn levels, and N,N,N',N'-tetrakis (2-pyridylmethyl)ethylenediamine, a cell-permeable Zn chelator, inhibited DNA ladder formation induced by Py/Zn treatment (1 micro m Py and 25 micro m Zn). Py/Zn treatment activated the caspases, as assessed by the proteolysis of poly(ADP-ribose) polymerase (PARP), which is a substrate of caspase, and activated p38 mitogen-activated protein kinase (p38MAPK), which is a transducer of apoptotic stimuli to the apparatus of the apoptosis execution. Z-Asp-CH2-DCB, a broad-spectrum inhibitor of caspase, attenuated proteolysis of PARP and DNA ladder formation by Py/Zn, indicating that apoptosis induced by Py/Zn is mediated by caspase activation. The p38MAPK-specific inhibitor SB203580 also inhibited induction of apoptosis by Py/Zn. Although SB203580 suppressed the proteolysis of PARP, Z-Asp-CH2-DCB did not inhibit the phosphorylation of p38MAPK, raising the possibility that apoptosis triggered by Py/Zn might be mediated by the p38MAPK/caspase pathway.

Signaling pathways involved in the physiological response of mussel hemocytes to bacterial challenge: the role of stress-activated p38 MAP kinases

In this work the mechanisms of transduction triggered in Mytilus galloprovincialis hemocytes by bacterial challenge were investigated in an in vitro model of infection of hemocyte monolayers with Escherichia coli. Western blot analyses of hemocyte extracts with phospho-specific anti-MAPK (Mitogen Activated Protein Kinase) antibodies indicate that E. coli induced a time dependent activation of different classes of MAPKs, mainly of the stress-activated p38 MAPK. P38 activation was confirmed by the use of the selective kinase inhibitor SB203580. Moreover, hemocyte pretreatment with SB203580 significantly reduced bacterial killing, whereas PD98059, an inhibitor of extracellularly regulated kinase (ERK) activation, was ineffective. Interestingly, the PI3-kinase (phosphatidylinositol-3-OH-kinase) inhibitor, Wortmannin, reduced both p38 activation and bacterial killing, indicating a critical role also for this lipid kinase in the hemocyte immune response.