In vitro modulation of fish phagocytic cells by beta-endorphin

Dietary plant pigment on blood-digestive physiology, antioxidant-immune response, and inflammatory gene transcriptional regulation in spotted snakehead (Channa punctata) infected with Pseudomonas aeruginosa

The current study addressed to investigate the effect of lycopene (LYC) on blood physiology, digestive-antioxidant enzyme activity, specific-nonspecific immune response, and inflammatory gene transcriptional regulation (cytokines, heat shock proteins, vitellogenins) in spotted snakehead (Channa punctata) against Pseudomonas aeruginosa. In unchallenged and challenged fish treated with 200 mg LYC enriched diet the growth performance and digestive-antioxidant enzymes increased after 30 days, whereas with inclusion of 100 or 400 mg LYC in the diets, the increase manifested on or after 45 days. No mortality in fish treated with any LYC diet against P. aeruginosa was revealed. In the unchallenged and challenged fish the phagocytic (PC) activity in head kidney (HK) and spleen were significantly enhanced when fed the control diet or other LYC diets, whereas the respiratory burst (RB) activity and nitric oxide (NO) production significantly increased when fed the 200 mg diet for 45 and 60 days. Similarly, the lysozyme (Lyz) activity in the HK and spleen, and total Ig content in serum were significantly higher in both groups fed the 200 mg LYC diet for 15, 45, and 60 days. Heat shock protein (Hsp 70) was significantly improved in the uninfected group fed the 200 mg LYC diet for 45 and 60 days, but Hsp27 did not significantly change among the experimental groups at any time points. TNF-α and IL-6 mRNA pro-inflammatory cytokine expression significantly increased in both groups fed the 200 mg LYC diet after 45 and 60 days, while the IL-12 mRNA expression was moderate in both groups fed the same diet for 60 days. The IL-10 did not significant mRNA expression between groups at any sampling. The iNOS and NF-κB mRNA expression was pointedly high in both groups fed the 200 mg LYC diet on day 45 and 60. Vitellogenin A (VgA) mRNA was significantly higher in the uninfected fish fed the 100 and 200 mg LYC diets for 45 and 60 days, but VgB did not reveal significant difference between the treatment groups at any time points. The present results suggest that supplementation of LYC at 200 mg significantly modulate the blood physiology, digestive-antioxidant enzymes, specific-nonspecific immune parameters, and cytokines, Hsp, and vitellogenins in spotted snakehead against P. aeruginosa.

20 Years of fish immunotoxicology - what we know and where we are

Despite frequent field observations of impaired immune response and increased disease incidence in contaminant-exposed wildlife populations, immunotoxic effects are rarely considered in ecotoxicological risk assessment. The aim of this study was to review the literature on immunotoxic effects of chemicals in fish to quantitatively evaluate (i) which experimental approaches were used to assess immunotoxic effects, (ii) whether immune markers exist to screen for potential immunotoxic activities of chemicals, and (iii) how predictive those parameters are for adverse alterations of fish immunocompetence and disease resistance. A total of 241 publications on fish immunotoxicity were quantitatively analyzed. The main conclusions included: (i) To date, fish immunotoxicology focused mainly on innate immune responses and immunosuppressive effects. (ii) In numerous studies, the experimental conditions are poorly documented, as for instance age or sex of the fish or the rationale for the selected exposure conditions is often missing. (iii) Although a broad variety of parameters were used to assess immunotoxicity, the rationale for the choice of measured parameters was often not given, remaining unclear how they link to the suspected immunotoxic mode of action of the chemicals. (iv) At the current state of knowledge, it is impossible to identify a set of immune parameters that could reliably screen for immunotoxic potentials of chemicals. (v) Similarly, in fish immunotoxicology there is insufficient understanding of how and when chemical-induced modulations of molecular/cellular immune changes relate to adverse alterations of fish immunocompetence, although this would be crucial to include immunotoxicity in ecotoxicological risk assessment.

Inhibitory effects of β-endorphin on cortisol release from goldfish (Carassius auratus) head kidney: an in vitro study

β-Endorphin (β-END) is an endogenous opioid peptide derived from the common precursor proopiomelanocortin, together with adrenocorticotropic hormone (ACTH) and melanocyte-stimulating hormone (MSH). Although the roles of ACTH and MSH in fish are well known, the roles of circulating β-END have not been elucidated. In the present study, we evaluated the biological roles of β-END in the goldfish. First, we cloned the cDNAs of the delta opioid receptor (DOR), kappa opioid receptor (KOR), and mu opioid receptor (MOR) from the brain of the goldfish. Second, we analyzed the tissues that expressed these genes by using reverse transcription polymerase chain reaction. Among the several tissues that contained the opioid gene transcripts, the mRNAs of DOR, KOR, and MOR were detected in interrenal cells of the head kidney, which produce cortisol. On the basis of these results, the effects of β-END on cortisol release were examined in vitro. β-END alone suppressed the basal release of cortisol in a dose-dependent manner. Moreover, β-END inhibited the cortisol-releasing activity of ACTH1-24. Therefore, it is probable that the role of β-END in the interrenal cells is the suppression of cortisol release. Interestingly, the suppression of cortisol release was not observed with N-acetyl-β-END, indicating that acetylation decreases the activity of β-END in interrenal cells.

In vitro effect of peas, Pisum pisum, and chickpeas, Cicer arietinum, on the immune system of gilthead seabream, Sparus aurata

The future for a sustainable aquaculture relies on the formulation of feed including alternatives to fish meal and fish oil that do not impair fish growth and that improve fish health status. Grain legumes such as field peas and chickpeas offer good sources of proteins, carbohydrates, fibers, vitamins, and minerals. The effect of peas and chickpeas on the immune system of seabream was assessed in vitro in order to detect any potential immunosuppressing problem. Peas was determined to be a better fishmeal alternative than chickpeas as they induced higher respiratory burst measured by the nitro blue tetrazolium assay and primed the Phorbol 12-myristate 13-acetate (PMA)-stimulated intracellular respiratory burst whereas chickpeas neither directly stimulated respiratory burst nor primed it. However, when the intra- and extracellular respiratory burst activities were taken into account, high concentrations of peas inhibited the zymosan- and PMA-triggered chemiluminescence. This apparent reduction of the production of reactive oxygen species may reflect in fact the antioxidant activity of legumes. This, together with the absence of effect on the phagocytosis activity, suggested that peas are not immunosuppressing gilthead seabream. Further in vivo studies preferably comporting a bacterial challenge will have to ascertain the absence of immunosuppressing effect of these legumes.

β-Endorphin inhibits phagocytic activity of lizard splenic phagocytes through μ receptor-coupled adenylate cyclase-protein kinase A signaling pathway

The receptor-coupled intracellular signaling mechanism of endogenous opioid peptide β-endorphin (β-end) is explored for the first time in ectothermic vertebrates using wall lizard as a model. β-End inhibited the percentage phagocytosis and phagocytic index of lizard splenic phagocytes in a dose-dependent manner. The inhibitory effect of β-end on phagocytosis was completely antagonized by non-selective opioid receptor antagonist naltrexone and also by selective μ-receptor antagonist CTAP. However, selective antagonists for other opioid receptors like NTI for δ-receptor and NorBNI for κ-receptor did not alter the effect of β-end on phagocytosis. This suggests that β-end mediated its inhibitory effect on phagocytic activity of splenic phagocytes exclusively through μ opioid receptors. The μ opioid receptor-coupled downstream signaling cascade was subsequently explored using inhibitors of adenylate cyclase (SQ 22536) and protein kinase A (H-89). Both SQ 22536 and H-89 abolished the inhibitory effect of β-end on phagocytosis in a concentration-related manner. Implication of cAMP as second messenger was corroborated by cAMP assay where an increase in intracellular cAMP level was observed in response to β-end treatment. It can be concluded that β-end downregulated the phagocytic activity of lizard splenic phagocytes through μ opioid receptor-coupled adenylate cyclase-cAMP-protein kinase A pathway.

Immunological control of fish diseases

All metazoans possess innate immune defence system whereas parameters of the adaptive immune system make their first appearance in the gnathostomata, the jawed vertebrates. Fish are therefore the first animal phyla to possess both an innate and adaptive immune system making them very interesting as regards developmental studies of the immune system. The massive increase in aquaculture in recent decades has also put greater emphasis on studies of the fish immune system and defence against diseases commonly associated with intensive fish rearing. Some of the main components of the innate and adaptive immune system of fish are described. The innate parameters are at the forefront of immune defence in fish and are a crucial factor in disease resistance. The adaptive response of fish is commonly delayed but is essential for lasting immunity and a key factor in successful vaccination. Some of the inherent and external factors that can manipulate the immune system of fish are discussed, the main fish diseases are listed and the pathogenicity and host defence discussed. The main prophylactic measures are covered, including vaccination, probiotics and immunostimulation. A key element in the immunological control of fish diseases is the great variation in disease susceptibility and immune defence of different fish species, a reflection of the extended time the present day teleosts have been separated in evolution. Future research will probably make use of molecular and proteomic tools both to study important elements in immune defence and prophylactic measures and to assist with breeding programmes for disease resistance.

Kappa-opioid receptor-mediated modulation of innate immune response by dynorphin in teleost Channa punctatus

The immunomodulatory role of endogenous opioid peptides released during stress has been extensively studied in mammals, but least explored in lower vertebrates. The present in vitro study for the first time reports the specific opioid receptor-mediated immunomodulatory role of dynorphin-A((1-17)) in ectotherms. Dynorphin-A((1-17)) had pleiotropic effects on phagocyte functions, stimulatory on phagocytosis and superoxide production while inhibitory on the nitrite release. However, the effect of dynorphin-A((1-17)), whether stimulatory or inhibitory, markedly declined at high (10(-5)M) concentration. Dynorphin-A((1-17)) seems to mediate its action through opioid receptors since non-selective opioid receptor antagonist, naltrexone, completely blocked the effect of dynorphin-A((1-17)) on phagocytosis, superoxide production and nitrite release. Moreover, among specific opioid receptors antagonists, only selective kappa (kappa)-opioid receptor antagonist norbinaltorphimine was capable to antagonize the pleiotropic effects on phagocyte functions. The present study provides the direct evidence of immunomodulatory role of dynorphin-A((1-17)) via kappa-opioid receptor in freshwater teleost Channa punctatus.

A Comparative Analysis of Immunorestoration and Recovery with Conventional and Immunotherapeutic Protocols in Canine Generalized Demodicosis: A Newer Insight of Immunotherapeutic Efficacy of T11TS

Demodex canis is a natural inhabiting mite of canine skin. Immunological disorder or genetic disorder induces the Demodex population to proliferate vigorously resulting in generalized demodicosis with consequent chronic immunosuppression. Signs of generalized demodicosis include alopecia, crysting, erythema, secondary pyoderma etc. Amitraz, an acaricide, is used conventionally for the treatment of generalized demodicosis. In many instances, the disease relapses due to the residual immunosuppression. The need of an immunorestorative therapy has been urged in generalized demodicosis. Two immunorestorative drugs, namely, Immuplus, a herbal drug, and T11TS, a sheep erythrocyte surface glycoprotein, has been used in two separate groups of dogs having generalized demodicosis and receiving Amitraz treatment. It was observed that though Amitraz treated group responded to the therapy showing increased E-rosettes and nonspecific cytotoxic efficacy of T-lymphocytes and decrease in phagocytic potential of macrophages, the groups treated with the immunotherapeutics like Immuplus and T11TS, responded better. However, the group treated with T11TS showed best recovery. These results emphasize the need for an immunorestorative therapy in generalized demodicosis and provide data in favor of T11TS as a better immunomodulator in comparison to Immuplus.

Structural and functional diversity of proopiomelanocortin in fish with special reference to barfin flounder

Proopiomelanocortin (POMC) is a precursor of adrenocorticotropic hormone (ACTH), melanocyte-stimulating hormone (MSH), and endorphin (END). We have characterized POMC systems in barfin flounder. The results revealed unique aspects of POMC systems. Notable features in terms of pituitary functions are the occurrence of three functional POMC genes, the mutation of an essential sequence in the beta-END in one of the genes, occurrence of alpha-MSH in addition to ACTH in the pars distalis of the pituitary, and expression of the three genes in a single cell. While MSHs stimulate pigment dispersion, expression of the POMC gene and plasma levels of MSH do not always respond to background color changes between black and white. The functions of MSHs in skin pigmentation are very unique, because acetylation at the N-terminal of alpha-MSH inhibits its pigment dispersing activity. This is in contrast to results from other teleosts and amphibians, in which acetylation increases the activity. In the skin, the POMC gene is expressed in the non-chromatophoric dermal cells, indicating that MSH produced in the skin de novo has a paracrine function. The detection of MSH peptides in skin extracts seems to show that the control of skin pigmentation by MSHs is twofold-endocrine control by the pituitary, and paracrine control by the skin itself. Thus, fish provide an interesting model to help understand the structural and functional diversity of POMC systems. In this review, we provide an overview of our recent studies on the characterization of molecules and biological significance of POMC systems in barfin flounder.

Delta opioid receptor-mediated immunoregulatory role of methionine-enkephalin in freshwater teleost Channa punctatus (Bloch.)

The immunoregulatory role of methionine-enkephalin (Met-enk) is well studied in mammals, but has not been explored in ectotherms despite the fact that this peptide is highly conserved in vertebrates. The present study demonstrates the diverse effects of Met-enk depending on its concentration and specific function of splenic phagocytes in the freshwater fish Channa punctatus. Although Met-enk increased both phagocytic as well as respiratory burst activity, the concentration-related response was opposite to each other. It had the maximum stimulatory effect on phagocytosis at 10(-9)M, while the same concentration was least effective in increasing superoxide production. Similarly, Met-enk at concentrations lower or higher than 10(-9)M was either ineffective or less effective in case of phagocytosis, while highly effective in stimulating superoxide production. On the other hand, concentration-independent inhibitory effect of Met-enk was observed in case of nitrite production. Nonetheless, Met-enk regulated all the functions of phagocyte through opioid receptors since non-specific opioid receptor antagonist naltrexone completely blocked the effect of Met-enk on phagocytosis, superoxide and nitrite production by splenic phagocytes of C. punctatus. Among selective opioid receptor antagonists, delta-opioid receptor antagonist naltrindole completely antagonized the effect of Met-enk on phagocytosis, superoxide and nitrite production, while mu- and kappa-opioid receptor antagonist, CTAP and norbinaltorphimine, respectively, were ineffective in influencing any of the functions. This suggests that Met-enk modulates splenic phagocyte functions in the fish C. punctatus via delta-opioid receptor. This is further substantiated by using highly selective delta-opioid receptor agonist, SNC80.

Cloning of opioid receptors in common carp (Cyprinus carpio L.) and their involvement in regulation of stress and immune response

In mammals opiate alkaloids and endogenous opioid peptides exert their physiological and pharmacological actions through opioid receptors (MOR, DOR and KOR) expressed not only on neuroendocrine cells but also on leukocytes. Therefore, opioids can modulate the immune response. We cloned and sequenced all three classical opioid receptors (MOR, DOR and KOR) in common carp, and studied changes in their expression during stress and immune responses. Messenger RNA of opioid receptors was constitutively expressed in brain areas, specially in the preoptic nucleus NPO (homologous to mammalian hypothalamus). After exposure to prolonged restraint stress, mRNA levels of MOR and DOR decreased in the NPO and in the head kidney. Increased expression of all studied opioid receptors was observed in the pituitary pars distalis (containing ACTH-producing cells). In immune organs, constitutive but lower expression of opioid receptor genes was observed. During in vivo zymosan-induced peritonitis or after in vitro LPS-induced stimulation, when pro-inflammatory functions are activated, expression of the OR genes in leukocytes was concomitantly up-regulated. Additionally, specific agonists of opioid receptors especially reduced leukocyte migratory properties, manifested by reduced chemotaxis and down-regulated expression of chemokine receptors. Our data indicate an evolutionary conserved role for the opioid system in maintaining a dynamic equilibrium while coping with stress and/or infection.

Morphine affects the inflammatory response in carp by impairment of leukocyte migration

Opioid peptides are evolutionary conserved and in teleost fish their specific receptor types have been identified not only on neuroendocrine cells but also on immunocytes. In the present work we have studied the effects of morphine, ligand for the mu3 opioid receptor, on innate immune responses of common carp. Both in vitro and in vivo, during zymosan-induced peritonitis, morphine reduced gene expression of pro-inflammatory cytokines/chemokines and chemokine receptors. Furthermore, in vitro morphine administration also affects nitric oxide production, chemotaxis and apoptosis of head kidney leukocytes. These results provide evidence for an anti-inflammatory function of morphine and suggest an evolutionary conserved cross-talk between chemokines and opioids.

beta-Endorphin regulates diverse functions of splenic phagocytes through different opioid receptors in freshwater fish Channa punctatus (Bloch): an in vitro study

In this in vitro study, the role of beta-endorphin in the control of phagocytic and cytotoxic activities of fish splenic phagocytes was investigated. Further, the involvement of specific opioid receptor was explored. beta-Endorphin stimulated phagocytosis, whereas inhibited nitric oxide production as assessed by nitrite release. However, it had concentration-related biphasic effects on superoxide production, stimulatory at low and inhibitory at high concentration. Naltrexone, non-selective opioid receptor antagonist, antagonized the effect of beta-endorphin on phagocyte functions. Moreover, CTAP, selective mu-receptor antagonist, completely blocked the effect of beta-endorphin on phagocytosis and nitrite release. With regard to superoxide production, CTAP blocked the stimulatory effect of beta-endorphin at low concentration, while the inhibitory effect at high concentration was completely antagonized by selective delta-receptor antagonist, NTI. In conclusion, beta-endorphin acting via mu-receptor stimulated phagocytosis and inhibited nitric oxide production, while its biphasic effect on superoxide production seems to be mediated by mu- and delta-receptors.

Evolution of melanocortin systems in fish

Proopiomelanocortin (POMC) is a common precursor of melanocortin (MC), the collective term for adrenocorticotropic hormone (ACTH) and melanophore-stimulating hormone (MSH), and of beta-endorphin (beta-END). Over the past decade, considerable progress has been made in the analysis of the POMC gene from a board taxonomic group of vertebrates and invertebrates. The results suggest that three MSHs (alpha-, beta-, and gamma-MSH) and a single END were established in ancestral invertebrates. Thereafter, unequal crossing over may have resulted in class-specific numbers of MSH segments during the radiation of fish. Moreover, duplication of the entire POMC gene may have led to the differentiation of POMC as shown in lampreys; one of the two subtypes is a precursor for ACTH and beta-END, the other is a precursor for two forms of MSH and the other form of beta-END. On the other hand, at least five subtypes of MC receptor (MCR) have been observed in fish. These are G-protein-coupled receptors with seven transmembrane domains. The ancestral MCR is suggested to have appeared before vertebrates, and then MCRs may have diverged by genome duplication and local duplication of each receptor gene during the evolution of vertebrates. They are distributed in many tissues in rather a subtype-specific manner and are responsible for a variety of biological functions. Thus, MC systems may have diverged by producing structurally different MC peptides from POMC and expressing MCR subtypes differing in ligand selectivity in a variety of tissues.

Interaction between endocrine and immune systems in fish

Diseases in fish are serious problems for the development of aquaculture. The outbreak of fish disease is largely dependent on environmental and endogenous factors resulting in opportunistic infection. Recent studies, particularly on stress response, have revealed that bidirectional communication between the endocrine and immune systems via hormones and cytokines exists at the level of teleost fish. Recently information on such messengers and receptors has accumulated in fish research particularly at the molecular level. Furthermore, it has become apparent in fish that cells of the immune system produce or express hormones and their receptors and vice versa to exchange information between the two systems. This review summarizes and updates the knowledge on endocrine-immune interactions in fish with special emphasis on the roles of such mediators or receptors for their interactions.

Modulation of the fish immune system by hormones

Immune-neuroendocrine interactions in fish, as in mammals, have become a focus of considerable interest, with the modulation of immune responses by hormones receiving particular attention. Cortisol, growth hormone (GH), prolactin (PRL), reproductive hormones, melanin-concentrating hormone (MCH) and proopiomelanocortin (POMC)-derived peptides have all been shown to influence immune functions in a number of fish species. This review summarises the known effects of these hormones on the fish immune system, as well as the often complex interactions between different hormones. The possible implications for fish health, with respect to aquaculture and the changes in immunocompetence that take place during different stages in the fish life cycle are also discussed.

Kidney leucocytes of rainbow trout, Oncorhynchus mykiss, are activated by intraperitoneal injection of beta-endorphin

The immunomodulatory effects of beta-endorphin were studied by measurements of the production of superoxide anion, phagocytosis and chemotaxis of kidney phagocytic cells in rainbow trout, Oncorhynchus mykiss. The production of superoxide anion in phagocytic cells increased significantly in rainbow trout injected with chum salmon beta-endorphin. The responses were dose-dependent. The phagocytosis and chemotaxis also significantly increased in kidney phagocytic cells of rainbow trout injected with alpha-endorphin. These results show that beta-endorphin in rainbow trout activates the function of phagocytic cells in vivo.