The biochemical substrate of nitric oxide signaling is present in primitive non-cognitive organisms

Role of the Neuroendocrine System of Marine Bivalves in Their Response to Hypoxia

Mollusks comprise one of the largest phylum of marine invertebrates. With their great diversity of species, various degrees of mobility, and specific behavioral strategies, they haveoccupied marine, freshwater, and terrestrial habitats and play key roles in many ecosystems. This success is explained by their exceptional ability to tolerate a wide range of environmental stresses, such as hypoxia. Most marine bivalvemollusksare exposed to frequent short-term variations in oxygen levels in their marine or estuarine habitats. This stressfactor has caused them to develop a wide variety of adaptive strategies during their evolution, enabling to mobilize rapidly a set of behavioral, physiological, biochemical, and molecular defenses that re-establishing oxygen homeostasis. The neuroendocrine system and its related signaling systems play crucial roles in the regulation of various physiological and behavioral processes in mollusks and, hence, can affect hypoxiatolerance. Little effort has been made to identify the neurotransmitters and genes involved in oxygen homeostasis regulation, and the molecular basis of the differences in the regulatory mechanisms of hypoxia resistance in hypoxia-tolerant and hypoxia-sensitive bivalve species. Here, we summarize current knowledge about the involvement of the neuroendocrine system in the hypoxia stress response, and the possible contributions of various signaling molecules to this process. We thusprovide a basis for understanding the molecular mechanisms underlying hypoxic stress in bivalves, also making comparisons with data from related studies on other species.

Novel Insights on Nitric Oxide Synthase and NO Signaling in Ascidian Metamorphosis

Nitric oxide (NO) is a pivotal signaling molecule involved in a wide range of physiological and pathological processes. We investigated NOS/NO localization patterns during the different stages of larval development in the ascidia Ciona robusta and evidenced a specific and temporally controlled pattern. NOS/NO expression starts in the most anterior sensory structures of the early larva and progressively moves towards the caudal portion as larval development and metamorphosis proceeds. We here highlight the pattern of NOS/NO expression in the central and peripheral nervous system of Ciona larvae which precisely follows the progression of neural signals of the central pattern generator necessary for the control of the movements of the larva towards the substrate. This highly dynamic localization profile perfectly matches with the central role played by NO from the first phase of settlement induction to the next control of swimming behavior, adhesion to substrate and progressive tissue resorption and reorganization of metamorphosis itself.

Jaburetox, a urease-derived peptide: Effects on enzymatic pathways of the cockroach Nauphoeta cinerea

Jaburetox is a recombinant peptide derived from one of the Canavalia ensiformis urease isoforms. This peptide induces several toxic effects on insects of different orders, including interference on muscle contractility in cockroaches, modulation of UDP-N-acetylglucosamine pyrophosphorylase (UAP) and nitric oxide synthase (NOS) activities in the central nervous system of triatomines, as well as activation of the immune system in Rhodnius prolixus. When injected, the peptide is lethal for R. prolixus and Triatoma infestans. Here, we evaluated Jaburetox toxicity to Nauphoeta cinerea cockroaches, exploring the effects on the central nervous system through the activities of UAP, NOS, acid phosphatases (ACP), and acetylcholinesterase (AChE). The results indicated that N. cinerea is not susceptible to the lethal effect of the peptide. Moreover, both in vivo and in vitro treatments with Jaburetox inhibited NOS activity, without modifying the protein levels. No alterations on ACP activity were observed. In addition, the enzyme activity of UAP only had its activity affected at 18 hr after injection. The peptide increased the AChE activity, suggesting a mechanism involved in overcoming the toxic effects. In conclusion, our findings indicate that Jaburetox affects the nitrinergic signaling as well as the AChE and UAP activities and establishes N. cinerea as a Jaburetox-resistant model for future comparative studies.

Nitric oxide mediates metabolic functions in the bivalve Arctica islandica under hypoxia

The free radical nitric oxide (NO) is a powerful metabolic regulator in vertebrates and invertebrates. At cellular concentrations in the nanomolar range, and simultaneously reduced internal oxygen partial pressures (pO₂), NO completely inhibits cytochrome-c-oxidase (CytOx) activity and hence mitochondrial- and whole-tissue respiration. The infaunal clam Arctica islandica regulates pO₂ of hemolymph and mantle cavity water to mean values of <5 kPa, even in a completely oxygen-saturated environment of 21 kPa. These low internal pO₂ values support a longer NO lifespan and NO accumulation in the body fluids and can thus trigger a depression of metabolic rate in the clams. Measurable amounts of NO formation were detected in hemocyte cells (~110 pmol NO 100⁻¹ hemocytes h^-1 at 6 kPa), which was not prevented in the presence of the NO synthase inhibitor L-NAME, and in the gill filaments of A. islandica. Adding a NO donor to intact gills and tissue homogenate significantly inhibited gill respiration and CytOx activity below 10 kPa. Meanwhile, the addition of the NO-oxidation product nitrite did not affect metabolic rates. The high nitrite levels found in the hemolymph of experimental mussels under anoxia do not indicate cellular NO production, but could be an indication of nitrate reduction by facultative anaerobic bacteria associated with tissue and/or hemolymph biofilms. Our results suggest that NO plays an important role in the initiation of metabolic depression during self-induced burrowing and shell closure of A. islandica. Furthermore, NO appears to reduce mitochondrial oxygen radical formation during surfacing and cellular reoxygenation after prolonged periods of hypoxia and anoxia.

Spatial compartmentalization of free radical formation and mitochondrial heterogeneity in bivalve gills revealed by live-imaging techniques

BACKGROUND

Reactive oxygen (ROS) and nitrogen (RNS) species are produced during normal unstressed metabolic activity in aerobic tissues. Most analytical work uses tissue homogenates, and lacks spatial information on the tissue specific sites of actual ROS formation. Live-imaging techniques (LIT) utilize target-specific fluorescent dyes to visualize biochemical processes at cellular level.

RESULTS

Together with oxidative stress measurements, here we report application of LIT to bivalve gills for ex-vivo analysis of gill physiology and mapping of ROS and RNS formation in the living tissue. Our results indicate that a) mitochondria located in the basal parts of the epithelial cells close to the blood vessels are hyperpolarized with high Δψm, whereas b) the peripheral mitochondria close to the cilia have low (depolarized) Δψm. These mitochondria are densely packed (mitotracker Deep Red 633 staining), have acidic pH (Ageladine-A) and collocate with high formation of nitric oxide (DAF-2DA staining). NO formation is also observed in the endothelial cells surrounding the filament blood sinus. ROS (namely H2O2, HOO(•) and ONOO(-) radicals, assessed through C-H2DFFDA staining) are mainly formed within the blood sinus of the filaments and are likely to be produced by hemocytes as defense against invading pathogens. On the ventral bend of the gills, subepithelial mucus glands contain large mucous vacuoles showing higher fluorescence intensities for O2 (•-) than the rest of the tissue. Whether this O2 (•-) production is instrumental to mucus formation or serves antimicrobial protection of the gill surface is unknown. Cells of the ventral bends contain the superoxide forming mucocytes and show significantly higher protein carbonyl formation than the rest of the gill tissue.

CONCLUSIONS

In summary, ROS and RNS formation is highly compartmentalized in bivalve gills under unstressed conditions. The main mechanisms are the differentiation of mitochondria membrane potential and basal ROS formation in inner and outer filament layers, as well as potentially antimicrobial ROS formation in the central blood vessel. Our results provide new insight into this subject and highlight the fact that studying ROS formation in tissue homogenates may not be adequate to understand the underlying mechanism in complex tissues.

Glycoinositolphospholipids from Trypanosomatids subvert nitric oxide production in Rhodnius prolixus salivary glands

Background

Rhodnius prolixus is a blood-sucking bug vector of Trypanosoma cruzi and T. rangeli. T. cruzi is transmitted by vector feces deposited close to the wound produced by insect mouthparts, whereas T. rangeli invades salivary glands and is inoculated into the host skin. Bug saliva contains a set of nitric oxide-binding proteins, called nitrophorins, which deliver NO to host vessels and ensure vasodilation and blood feeding. NO is generated by nitric oxide synthases (NOS) present in the epithelium of bug salivary glands. Thus, T. rangeli is in close contact with NO while in the salivary glands.

Methodology/Principal Findings

Here we show by immunohistochemical, biochemical and molecular techniques that inositolphosphate-containing glycolipids from trypanosomatids downregulate NO synthesis in the salivary glands of R. prolixus. Injecting insects with T. rangeli-derived glycoinositolphospholipids (Tr GIPL) or T. cruzi-derived glycoinositolphospholipids (Tc GIPL) specifically decreased NO production. Salivary gland treatment with Tc GIPL blocks NO production without greatly affecting NOS mRNA levels. NOS protein is virtually absent from either Tr GIPL- or Tc GIPL-treated salivary glands. Evaluation of NO synthesis by using a fluorescent NO probe showed that T. rangeli-infected or Tc GIPL-treated glands do not show extensive labeling. The same effect is readily obtained by treatment of salivary glands with the classical protein tyrosine phosphatase (PTP) inhibitor, sodium orthovanadate (SO). This suggests that parasite GIPLs induce the inhibition of a salivary gland PTP. GIPLs specifically suppressed NO production and did not affect other anti-hemostatic properties of saliva, such as the anti-clotting and anti-platelet activities.

Conclusions/Significance

Taken together, these data suggest that trypanosomatids have overcome NO generation using their surface GIPLs. Therefore, these molecules ensure parasite survival and may ultimately enhance parasite transmission.

Regulation of nitric oxide production in snail (Lymnaea stagnalis) defence cells: a role for PKC and ERK signalling pathways

BACKGROUND INFORMATION

Nitric oxide (NO) is an important molecule in innate immune responses. In molluscs NO is produced by mobile defence cells called haemocytes; however, the molecular mechanisms that regulate NO production in these cells is poorly understood. The present study focused on the role of cell signalling pathways in NO production by primary haemocytes from the snail Lymnaea stagnalis.

RESULTS

When haemocytes were challenged with PMA (10 microM) or the beta-1,3-glucan laminarin (10 mg/ml), an 8-fold and 4-fold increase in NO production were observed after 60 min respectively. Moreover, the NOS (NO synthase) inhibitors L-NAME (N(G)-nitro-L-arginine methyl ester) and L-NMMA (N(G)-monomethyl-L-arginine) were found to block laminarin- and PMA-induced NO synthesis. Treatment of haemocytes with PMA or laminarin also increased the phosphorylation (activation) status of PKC (protein kinase C). When haemocytes were preincubated with PKC inhibitors (calphostin C or GF109203X) or inhibitors of the ERK (extracellular-signal-regulated kinase) pathway (PD98059 or U0126) prior to challenge, significant reductions in PKC and ERK phosphorylation and NO production were observed following exposure to laminarin or PMA. The greatest effect on NO production was seen with GF109203X and U0126, with PMA-induced NO production inhibited by 94% and 87% and laminarin-induced NO production by 50% and 91% respectively.

CONCLUSIONS

These data suggest that ERK and PKC comprise part of the signalling machinery that regulates NOS activation and subsequent production of NO in molluscan haemocytes. To our knowledge, this is the first report that shows a role for these signalling proteins in the generation of NO in invertebrate defence cells.

Placental expression of endothelial and inducible nitric oxide synthase and nitric oxide levels in patients with HELLP syndrome

OBJECTIVE

To determine placental gene expression of endothelial and inducible nitric oxide synthases and measure nitric oxide levels in patients with hemolysis, elevated liver enzyme levels, and low platelet count syndrome.

STUDY DESIGN

Preterm placentas were obtained from 15 patients with hemolysis, elevated liver enzyme levels, and low platelet count syndrome and 30 controls matched for age, parity, and gestational age. mRNA levels were evaluated by real-time polymerase chain reaction, whereas nitric oxide and peroxynitrite production was measured by a commercially available kit.

RESULTS

Placental gene expression of inducible nitric oxide and endothelial nitric oxide synthases were significantly lower in the hemolysis, elevated liver enzyme levels, and low platelet count syndrome group than in controls, whereas nitric oxide and peroxynitrite production were significantly higher in hemolysis, elevated liver enzyme levels, and low platelet count syndrome compared with controls.

CONCLUSION

The reduced endothelial nitric oxide and inducible nitric oxide synthases gene expression in women with hemolysis, elevated liver enzyme levels, and low platelet count syndrome may indicate extreme placental dysfunction that is unable to compensate the endothelial derangement and the related hypertension. The higher nitric oxide formation found in hemolysis, elevated liver enzyme levels, and low platelet count syndrome placentas could be explained as a counteraction to the impaired fetoplacental perfusion, typical of the syndrome.

Iron and nitrosative metabolism in the Antarctic mollusc Laternula elliptica

The objective of this work was to study Fe distribution, and oxidative and nitrosative metabolism in Laternula elliptica for physiological analysis and interspecific comparisons. Lipid peroxidation, superoxide dismutase and catalase activity and total Fe content were estimated in the digestive glands (DG) of L. elliptica. The labile Fe pool (LIP) represents the amount of cellular Fe responsible for catalyzing radical-dependent reactions. LIP assessed by the calcein assay, represents 3.5% of the total Fe in L. elliptica. Experimental isolation of ferritin (Ft) was performed. Subunit analyses of the protein by SDS-polyacrilamide gel electrophoresis indicated that the protein was composed of 20.6kDa protein subunits, consistent with the horse spleen Ft and the molecular weight markers, however, a higher molecular mass subunit could appear. The identity of the protein was confirmed by Western blot analysis. The nitrate+nitrite content was 73±7pmol/mg fresh mass (FW). The nitric oxide (NO) content in DG homogenates, assessed by electronic paramagnetic resonance (EPR) spin trapping measurements using the NO trap sodium-N-methyl-D-glucamine dithiocarbamate-Fe at room temperature, was 30±2pmol/mg FW. Nitric oxide synthase-like activity (1.50±0.09pmol/mg FW min) was assessed by measuring NO production by EPR in the presence of L-arginine (L-A) and NADPH. This activity was significantly inhibited by L-A analogs such as Nω-nitro-L-arginine methyl ester hydrochloride (-77%) and Nω-nitro-L-arginine (-62%), or by the lack of added L-A (-55%). The data presented here documented the physiological presence of labile Fe, Ft and highly reactive nitrogen species, and are the first evidence that support the hypothesis that NO being generated in L. elliptica might contribute to restrict oxidative damage by a close link with Fe metabolism.

Distribution of NADPH-diaphorase activity in the central nervous system of the young and adult land snail Megalobulimus abbreviatus

Nitric oxide (NO) is a gas produced through the action of nitric oxide synthase that acts as a neurotransmitter in the central nervous system (CNS) of adult gastropod mollusks. There are no known reports of the presence of NOS-containing neurons and glial cells in young and adult Megalobulimus abbreviatus. Therefore, NADPH-d histochemistry was employed to map the nitrergic distribution in the CNS of young and adult snails in an attempt to identify any transient enzymatic activity in the developing CNS. Reaction was observed in neurons and fibers in all CNS ganglia of both age groups, but in the pedal and cerebral ganglia, positive neurons were more intense than in other ganglia, forming clusters symmetrically located in both paired ganglia. However, neuronal NADPH-d activity in the mesocerebrum and pleural ganglia decreased from young to adult animals. In both age groups, positive glial cells were located beneath the ganglionic capsule, forming a network and surrounding the neuronal somata. The trophospongium of large and giant neurons was only visualized in young animals. Our results indicate the presence of a nitrergic signaling system in young and adult M. abbreviatus, and the probable involvement of glial cells in NO production.

Anorexia nervosa: a role for L-arginine supplementation in cardiovascular risk factors?

OBJECTIVE

The aim of the present study was to evaluate the effects of a short-term oral L-arginine treatment on platelet NO production, intracellular calcium concentration, iNOS and eNOS expression, in AN patients.

METHOD

Forty outpatients belonging to restricting subtype and 40 normal participants age and sex matched were enrolled in the study.

RESULTS

NO production was significantly elevated in the platelets from AN patients compared with controls while [Ca(2+)](i) was significantly decreased in patients with respect to controls. Western blot analysis demonstrated that iNOS isoform was more pronounced in the cell lysates from AN patients than controls. After supplementation with L-arginine, both NO production and [Ca(2+)](i) seem to return to control levels, suggesting a probable recovery of their metabolisms. The same was found after western blot analysis of NOS expression.

DISCUSSION

The results here proposed can be considered highly indicative of a positive effect of L-arginine supplementation on platelet NO production in AN patients.

Investigation of EROD, CYP1A immunopositive proteins and SOD in haemocytes of Chamelea gallina and their role in response to B[a]P

CYP1A sub-family represents the main form of cytochrome P450 involved in benzo[a]pyrene (B[a]P) detoxification, but there are no clear evidences about its presence in invertebrates. 7-Ethoxy resorufin O-deethylase (EROD) activity is strictly related to CYP1A presence, at the same time P450-dependent oxidative metabolism leads to reactive oxygen species (ROS) production, thought to be an important mechanism of pollutant-mediated toxicity in aquatic organisms. Superoxide dismutases (SODs), EROD and CYP1A activities and/or expressions were detected in haemocytes of pooled clams (Chamelea gallina) and cell-free haemolymph after 24 h, 7 and 12 days of exposure to 0.5 mg/L of B[a]P. After 24 h, B[a]P content was maximum in whole tissues. A 61 kDa band was recognized in haemocytes and cell-free haemolymph by polyclonal anti-fish CYP1A, while 53.5 and 63.8 kDa CYP1A immunopositive proteins were discriminate without differences of expression. Differently, EROD, MnSOD activity/expression and ECSOD expression decreased in haemocytes and haemolymph. C. gallina immune system presents an interesting response dose/time exposure of B[a]P and the 7 days condition highlights the major effects of xenobiotic action. The identification of basal EROD levels supports the possible presence of the CYP1A, never identified in C. gallina and more specifically never isolated in immune cells, as confirmed by CYP1A-immunopositive proteins identification.

NADPH-diaphorase activity in the central nervous system of the Gray mussel Crenomytilus grayanus (Dunker) under stress conditions: a histochemical study

NADPH-diaphorase (NADPH-d) is a histochemical marker for nitric oxide synthase (NOS) and is widely used to identify nitric oxide (NO) producing cells in the central nervous system (CNS) of both vertebrates and invertebrates. NADPH-d histochemistry was used to quantitatively characterize putative NO-producing neurons in the CNS of the Gray mussel Crenomytilus grayanus subjected to two kinds of stress, environmental pollution and hypoxia, the latter caused by the mollusk transportation in a small volume of water. Mussels were sampled from one relatively clean (reference) and four polluted sites in Amursky and Ussuriysky Bays (Peter the Great Bay, Sea of Japan) in August, 2003. The number of NADPH-d-positive neurons was estimated and enzyme activity was determined from the optical density of the formazan precipitate in the CNS ganglia at 0, 3, and 72 h after sampling. Just after sampling, NADPH-d-positive neurons were found in the cerebropleural, visceral, and pedal ganglia. The number and staining intensity of NADPH-d-positive neurons were significantly higher in the pedal ganglia than the other two ganglia. There were significant differences in the number of NADPH-d-positive neurons and enzyme activity between the mussels from the reference and heavily polluted stations. The proportion and staining intensity of NADPH-d-positive neurons were maximum in the pedal ganglia of the mussels from the heavily polluted station in Amursky Bay. Transportation of mussels in a limited volume of water for 3h resulted in a significant increase in the proportion and staining intensity of NADPH-d-positive neurons in all ganglia. In mollusks from all stations kept in aerated aquaria for 72 h, both the proportion and staining intensity of NADPH-d-positive neurons did not differ significantly from the initial level. However, the differences in the proportion and staining intensity of NADPH-d-positive neurons between the reference and heavily polluted stations were significant. The present results suggest that NO is involved in mollusk nerve cell adaptation to environmental changes.

Nitric oxide and peroxynitrite platelet levels in women with small-for-gestational-age fetuses

OBJECTIVE

The placenta produces reactive oxygen species (ROS) including nitric oxide (NO) and peroxynitrite (ONOO(-)) that have pronounced effects on placental function. Excessive ROS production may occur in pathological pregnancies, such as those complicated by small-for-gestational-age (SGA) fetuses.

DESIGN

The aim of the present work was to study NO and ONOO(-) levels in platelets of pregnant women with SGA fetuses compared with a control group.

SETTING AND POPULATION

The study was performed on 30 pregnant women with SGA fetuses (SGA group) and on 30 healthy pregnant women (appropriate-for-gestational-age [AGA] group) matched for maternal and gestational age. All women included in this study were in the third trimester of pregnancy.

METHODS

Platelets were isolated by differential centrifugation. NO metabolites, after enzymatic conversion followed by the Griess reaction, were measured as nitrite by spectrophotometric detection. Peroxynitrite (ONOO(-)) levels were evaluated using the fluorescence probe 2,7-dichlorofluorescein diacetate (DCFDA).

MAIN OUTCOME MEASURES

The following determinations were made: platelet nitric oxide and peroxynitrite levels in the SGA group and controls; inducible nitric oxide synthase (iNOS), endothelial nitric oxide synthase (eNOS) and nitrotyrosine (N-Tyr) expression in the same groups.

RESULTS

Our results show that both platelet NO and ONOO(-) levels were significantly higher in the SGA group than in the controls.

CONCLUSION

Increased platelets levels of nitric oxide and peroxynitrite might play a role in the pathophysiology of intrauterine growth restriction. Further investigations are in progress to clarify if these molecules are pathogenetic factors, an epiphenomenon or a pathophysiological marker.

Reactive oxygen species plasmatic levels in ischemic stroke

Oxidative stress is probably one of the mechanisms involved in neuronal damage induced by ischemia-reperfusion, and the antioxidant activity of plasma may be an important factor providing protection from neurological damage caused by stroke-associated oxidative stress. The aim of this study was to investigate the status of oxidative stress, NO and ONOO(-) levels in patients with atherothrombotic and lacunar acute ischemic stroke and iNOS, eNOS and nitrotyrosine expression in the same patients. Plasma ONOO(-) levels were significantly higher in patients than in controls while NO decreases in patients in respect to controls. Densitometric analysis of bands indicated that iNOS and N-Tyr protein levels were significantly higher in patients in respect to controls. This study has highlighted a significant NO decrease in our patients compared with controls and this is most probably due to the increased expression of inducible NO synthase by the effect of thrombotic attack. In fact, the constitutive NO isoforms, which produce small amounts of NO, are beneficial, while activation of the inducible isoform of NO, which produces much more NO, causes injury, being its toxicity greatly enhanced by generation of peroxynitrite. The significant ONOO(-) increase observed in our patients, compared to controls, is most probably due to reaction of NO with O(2)(*-) . These findings suggest that free radical production and oxidative stress in ischemic stroke might have a major role in the pathogenesis of ischemic brain injury. Peroxynitrite might be the main marker of brain damage and neurological impairment in acute ischemic stroke.

Immunomodulation by 17β-estradiol in bivalve hemocytes

In mammals, estrogens have dose- and cell-type-specific effects on immune cells and may act as pro- and anti-inflammatory stimuli, depending on the setting. In the bivalve mollusc Mytilus, the natural estrogen 17β-estradiol (E2) has been shown to affect neuroimmune functions. We have investigated the immunomodulatory role of E2 in Mytilus hemocytes, the cells responsible for the innate immune response. E2 at 5–25 nM rapidly stimulated phagocytosis and oxyradical production in vitro; higher concentrations of E2 inhibited phagocytosis. E2-induced oxidative burst was prevented by the nitric oxide (NO) synthase inhibitor NG-monomethyl-l-arginine and superoxide dismutase, indicating involvement of NO and O2−; NO production was confirmed by nitrite accumulation. The effects of E2 were prevented by the antiestrogen tamoxifen and by specific kinase inhibitors, indicating a receptor-mediated mechanism and involvement of p38 MAPK and PKC. E2 induced rapid and transient increases in the phosphorylation state of PKC, as well as of a aCREB-like (cAMP responsive element binding protein) transcription factor, as indicated by Western blot analysis with specific anti-phospho-antibodies. Localization of estrogen receptor-α- and -β-like proteins in hemocytes was investigated by immunofluorescence confocal microscopy. The effects of E2 on immune function were also investigated in vivo at 6 and 24 h in hemocytes of E2-injected mussels. E2 significantly affected hemocyte lysosomal membrane stability, phagocytosis, and extracellular release of hydrolytic enzymes: lower concentrations of E2 resulted in immunostimulation, and higher concentrations were inhibitory. Our data indicate that the physiological role of E2 in immunomodulation is conserved from invertebrates to mammals.

Association of the ERK1/2 and p38 kinase pathways with nitric oxide-induced apoptosis and cell cycle arrest in colon cancer cells

To investigate the mechanism by which nitric oxide (NO) induces cell death in colon cancer cells, we compared two types of colon cancer cells with different p53 status: HCT116 (p53 wild-type) cells and SW620 (p53-deficient) cells. We found that S-nitrosoglutathione (GSNO), the NO donor, induced apoptosis in both types of colon cancer cells. However, SW620 cells were much more susceptible than HCT116 cells to apoptotic death by NO. We investigated the role of extracellular signal-regulated kinase 1/2 (ERK1/2) and p38 kinase on NO-induced apoptosis in both types of colon cancer cells. GSNO treatment effectively stimulated activation of the ERK1/2 and p38 kinase in both types of cells. In HCT116 cells, pretreatment with PD98059, an inhibitor of ERK1/2, or SB203580, an inhibitor of p38 kinase, had no marked effect on GSNO-induced apoptosis. However, in SW620 cells, SB203580 significantly reduced the NO-induced apoptosis, whereas PD098059 increases NO-induced apoptosis. Furthermore, we found evidence of cell cycle arrest of the G0/G1 phase in SW620 cells but not in HCT116 cells. Inhibition of ERK1/2 with PD098059, or of p38 kinase with SB203580, reduced the GSNO-induced cell cycle arrest of the G0/G1 phase in SW620 cells. We therefore conclude that NO-induced apoptosis in colon cancer cells is mediated by a p53-independent mechanism and that the pathways of ERK1/2 and p38 kinase are important in NO-induced apoptosis and in the cell cycle arrest of the G0/G1 phase.

Nitric oxide in marine invertebrates: a comparative perspective

Since the discovery of the biological effects of nitric oxide (NO) more than two decades ago, NO has been identified as an important physiological modulator and a messenger molecule in mammals. Parallel to these studies, evidence that has accumulated in recent years has revealed that the NO signalling pathway is spread throughout the entire phylogenetic scale, being increasingly found in lower organisms, ranging from Chordata to Mollusca. The present review attempts to provide a survey of current knowledge of the genesis and possible roles of NO and the related signalling pathway in marine invertebrates, with special emphasis on Sepia, a choice dictated by the increasing appreciation of cephalopods as most valuable model systems for studies of NO biology and the present expectation for new exciting insights into as yet little explored segments of NO biology.

Melanogenesis and associated cytotoxic reactions: applications to insect innate immunity

Insects transmit the causative agents for such debilitating diseases as malaria, lymphatic filariases, sleeping sickness, Chagas' disease, leishmaniasis, river blindness, Dengue, and yellow fever. The persistence of these diseases provides testimony to the genetic capacity of parasites to evolve strategies that ensure their successful development in two genetically diverse host species: insects and mammals. Current efforts to address the problems posed by insect-borne diseases benefit from a growing understanding of insect and mammalian immunity. Of considerable interest are recent genomic investigations that show several similarities in the innate immune effector responses and associated regulatory mechanisms manifested by insects and mammals. One notable exception, however, is the nearly universal presence of a brown-black pigment accompanying cellular innate immunity in insects. This response, which is unique to arthropods and certain other invertebrates, has focused attention on the elements involved in pigment synthesis as causing or contributing to the death of the parasite, and has even prompted speculation that the enzyme cascade mediating melanogenesis constitutes an ill-defined recognition mechanism. Experimental evidence defining the role of melanin and its precursors in insect innate immunity is severely lacking. A great deal of what is known about melanogenesis comes from studies of the process occurring in mammalian systems, where the pigment is synthesized by such diverse cells as those comprising portions of the skin, hair, inner ear, brain, and retinal epithelium. Fortunately, many of the components in the metabolic pathways leading to the formation of melanin have been found to be common to both insects and mammals. This review examines some of the factors that influence enzyme-mediated melanogenic responses, and how these responses likely contribute to blood cell-mediated, target-specific cytotoxicity in immune challenged insects.

Modulatory effects of ammonia-N on the immune system of Penaeus japonicus to virulence of white spot syndrome virus

To study response to white spot syndrome virus (WSSV) under ammonia stress, Penaeus japonicus were exposed to 5 mg l^-1 ammonia-N and challenged orally with WSSV (NW). Controls consisted of an ammonia-N-exposed control group (N), a WSSV-challenged positive control group (W), and an untreated control group (control). Immune parameters measured were total haemocyte count (THC), haemocyte phagocytosis, plasma protein content and haemolymph enzymatic activities for prophenoloxidase (proPO), alkaline phosphatase (ALP), and nitric oxide synthase (NOS). THC and plasma protein had downward trends with time in all treatment groups (NW, N, and W) in contrast to the untreated control group (control). The percentage phagocytosis, NOS activity, and ALP and proPO activity of W and NW decreased initially then increased from 6 to 78 h (except for NOS and ALP, from 6 to 54 h) before declining thereafter until the end of the experiment. Compared with untreated controls (control), there was a downward trend for all measured parameters in the treatment groups (N, NW, and W), but the degree was W>NW>N. WSSV was detected at 78 h postchallenge in both W and NW. In conclusion, 5 mg l^-1 ammonia-N reduced the immunocompetence of P. japonicus and may have decreased the virulence of WSSV.

Presence and role of nitric oxide in the central nervous system of the freshwater snail Planorbarius corneus: possible implication in neuron–microglia communication

The aim of the present study was to investigate the involvement of nitric oxide (NO) as a messenger molecule in neuron-microglia communication in the central nervous system (CNS) of the freshwater snail Planorbarius corneus. The presence of both neuronal (nNOS) and inducible nitric oxide synthase (iNOS) was studied using NADPH-diaphorase (NADPH-d) histochemistry and NOS immunocytochemistry. The experiments were performed on whole ganglia and cultured microglial cells after different activation modalities, such as treatment with lipopolysaccharide and adenosine triphosphate and/or maintaining ganglia in culture medium till 7 days. In sections, nNOS immunoreactivity was found only in neurons and nNOS-positive elements were less numerous than NADPH-d-positive ones, with which they partially overlapped. The iNOS immunoreactivity was observed only after activation, in both nerve and microglial cells. We also found that the number of iNOS-immunoreactive neurons and microglia varied, depending on the activation modalities. In microglial cell cultures, iNOS was expressed in the first generation of cells only after activation, whereas a second generation, proliferated after ganglia activation, expressed iNOS even in the unstimulated condition.

Colocalization of urocortin and neuronal nitric oxide synthase in the hypothalamus and Edinger-Westphal nucleus of the rat

Different lines of studies suggest that both the corticotropin-releasing hormone-related peptide Urocortin I (Ucn) and the neuromodulator nitric oxide (NO) are involved in the regulation of the complex mechanisms controlling feeding and anxiety-related behaviors. The aim of the present study was to investigate the possible interaction between Ucn and NO in the hypothalamic paraventricular nucleus (PVN), an area known to be involved in the modulation of these particular behaviors. Therefore, we mapped local mRNA and peptide/protein presence of both Ucn and the NO producing neuronal NO synthase (nNOS). This investigation was extended to include the hypothalamic supraoptic nucleus (SON) and the Edinger-Westphal nucleus area (EW), the latter being one of the major cellular Ucn-expressing sites. Furthermore, we compared the two predominantly used laboratory rat strains, Wistar and Sprague-Dawley. Ucn mRNA and immunoreactivity were detected in the SON and in the EW. A significant difference between Wistar and Sprague-Dawley rats was found in mRNA levels in the EW. nNOS was detected in all brain areas analyzed, showing a significantly lower immunoreactivity in the PVN and EW of Sprague-Dawley versus Wistar rats. Contrary to some previous reports, no Ucn mRNA and only a very low immunoreactivity were detectable in the PVN of either rat strain. Interestingly, double-labeling immunofluorescence revealed that in the SON approximately 75% of all cells immunoreactive for Ucn were colocalized with nNOS, whereas in the EW only approximately 2% of the Ucn neurons were found to contain nNOS. These findings suggest an interaction between Ucn and NO signaling within the SON, rather than the PVN, that may modulate the regulation of feeding, reproduction, and anxiety-related behaviors.

Immunocytochemical evidence for nitric oxide- and carbon monoxide-producing neurons in the stomatogastric nervous system of the crayfishCherax quadricarinatus

Nitric oxide (NO) and carbon monoxide (CO) have been shown to serve neuromodulatory roles in both vertebrates and invertebrates. Here, we use antibodies to their respective biosynthetic enzymes, nitric oxide synthase (NOS) and heme oxygenase 2 (HO-2), to map the distribution of putative gas-producing neurons in the stomatogastric nervous system (STNS) of the crayfish Cherax quadricarinatus. In this species, NOS immunolabeling is found in the neuropil of the stomatogastric ganglion (STG). This staining originates from two immunopositive axons that project to the STG through the superior oesophageal and stomatogastric nerves, presumably from cell bodies located in the commissural ganglia (CoGs). HO-2 immunoreactivity is present in small diameter fibers and varicosities in the periphery of nerves located in the anterior portion of the STNS. This labeling originates from approximately 12 somata in each CoG. Transmission electron microscopy done on the nerves of the anterior STNS shows they contain a neuroendocrine plexus. Collectively, our results indicate that NO- and CO-producing neurons are likely to exist in the crayfish STNS. Moreover, these gases appear to be produced by distinct subsets of the neurons present there. The localization of NO to the STG neuropil suggests that it serves as a locally released modulator or is involved in the local release of other substances within this ganglion. The presence of CO in the neurohemal plexus of the anterior STNS suggests that it serves as a circulating hormone or is involved in the control of neuroendocrine release from this plexus.