Lysis-sensitive targets stimulate an elevation of cAMP in human natural killer cells

Immune-regulatory transcriptional responses in multiple organs of Atlantic salmon after tributyltin exposure, alone or in combination with forskolin

Tributyltin (TBT) is a widespread marine pollutant that influences physiological conditions of fish and other aquatic organisms. In addition to effects on reproduction, the immune system has been proposed as a possible target for TBT effects. In the present study, the effects of TBT exposure were examined on the expression of genes involved in immune system compentence in liver and head kidney of Atlantic salmon, in the presence and absence of a second-messenger activator (forskolin). Juvenile salmon were force-fed a diet containing TBT (0-solvent control, 0.1, 1, or 10 mg/kg fish) for 72 h. Consequently, fish from the control group and 10-mg/kg TBT group were exposed to the adenylate cyclase (AC) activator forskolin (200 μg/L) for 2 or 4 h. Forskolin was selected for this study because it is known to exhibit potent immune system enhancement by activating macrophages and lymphocytes. After sacrifice, liver and head kidney were sampled and transcript changes for interleukin (IL)-1β, IL-10, transforming growth factor (TGF) β, interferon (INF) α, INFγ, tumor necrosis factor (TNF) α, Mx3, and insulin-like growth factor (IGF)-1 were determined in both tissues by quantitative polymerase chain reaction (qPCR) using gene-specific primers. TBT, when given alone and also in combination with forskolin, decreased IL-1β, TNFα, IFNγ, IFNα, Mx3, and IGF-1 gene expression. In contrast, IL-10 and TGFβ transcripts were increased after TBT exposure alone and also in combination with forskolin. Generally, these effects were largely dependent on TBT dose and time of exposure when given in combination with forskolin. Overall, our findings suggest a possible immunomodulatory effect of TBT, possibly involving cAMP activation.

Preventive role of phyllosilicate clay on the Immunological and Biochemical toxicity of zearalenone in Balb/c mice

Zearalenone (ZEN), a mycotoxin produced by several Fusarium spp., is most commonly found as a contaminant in stored grain and has chronic estrogenic effects on mammals. ZEN and its metabolites have anabolic activities and induced severe stress on liver, kidney and immune system. The aims of the current study were twofold: (1) to investigate the changes in serum biochemical, immunological parameters and histological picture of spleen in ZEN-treated Balb/c mice and (2) to evaluate the safety and efficacy of HSCAS to ameliorate the deleterious effects of ZEN. The results indicated that a single dose of ZEN (40 mg/kg bw) significantly reduced total cholesterol, HDL, LDL, triglycerides, total protein, albumin, total count of WBCs, immunoglobulin profile (Ig A and Ig G) and T-cells subtypes (CD3+, CD4+, CD8+ and CD56+). Whereas, it significantly increased uric acid and urea and induced degenerative changes in the spleen tissues. Mice treated with HSCAS alone (400 mg/kg bw) were comparable to the control regarding all the tested parameters. While HSCAS at levels 600 and 800 mg/kg bw caused changes in some tested biochemical parameters. The combined treatment of ZEN and the lowest tested dose of HSCAS (400 mg/kg bw) showed a significant improvement of the immunological, biochemical and histological parameters. It could be concluded that HSCAS was effective in the protection against the hazards of ZEN at a dose as low as 400 mg/kg bw. These results supported our hypothesis that HSCAS tightly-bind and immobilized ZEN resulted in reduction of toxin bioavailability in animal's gastrointestinal tract.

Effects of interleukins 2 and 12 on the levels of granzyme B and perforin and their mRNAs in tributyltin-exposed human natural killer cells

Natural killer (NK) cells are a subset of lymphocytes that are capable of killing tumor cells, virally infected cells and antibody coated cells. Tributyltin (TBT) is a toxic chemical used for various industrial purposes such as: slime control in paper mills, disinfection of circulating industrial cooling waters, anti-fouling agents, and the preservation of wood. TBT can be found in edible items such as fish. A previous study showed that a 1 h exposure of NK cells to TBT caused persistent inhibition of NK-cell ability to destroy tumor cells in the 24 and 48 h periods following exposure and that this loss of function could be significantly prevented and/or reversed if the NK-stimulatory interleukins (IL) 2 or 12 were present during the 24 and 48 h periods. We had also shown that TBT exposure was able to significantly decrease the protein and mRNA levels of the cytotoxic proteins, granzyme B and perforin, and the phosphorylation of cAMP-response-element-binding protein (CREB) under these conditions. In this study we address the effects of IL-2 and IL-12 on the TBT-induced decreases in NK-cell levels of the cytotoxic proteins, their mRNAs, and CREB phosphorylation. IL-2 appeared to prevent/reverse TBT-induced declines in perforin protein levels and the mRNA for perforin seen in the 24 h period following a 1 h exposure to 300 nM TBT. However, the TBT-induced decreases in the levels of perforin and perforin mRNA seen in the 48 h period following a 1 h exposure to TBT were not statistically significantly prevented/reversed by IL-2. Additionally, the TBT-induced decreases in granzyme B, granzyme B mRNA, and CREB phosphorylation were not statistically significantly reversed by either IL-2 or IL-12 after 24 or 48 h.

Tributyltin exposure causes decreased granzyme B and perforin levels in human natural killer cells

Natural Killer (NK) cells are a subset of lymphocytes that are capable of killing tumor cells, virally infected cells and antibody coated cells. Tributyltin (TBT) is a toxic chemical used for various industrial purposes such as: slime control in paper mills, disinfection of circulating industrial cooling waters, anti-fouling agents in shower curtains and the preservation of wood. TBT can be found in edible items such as dairy products and fish. This study investigates the mechanism by which TBT exposure decreases the immune function of human NK cells, in vitro. Cytotoxic function, the expression of the cytotoxic proteins (granzyme B and perforin), and cAMP response element binding protein (CREB) phosphorylation were examined. NK cells exposed to 300 nM TBT for 1 h showed no significant decrease in cytotoxic function, levels of granzyme B and perforin, or phosphorylation of CREB. However, mRNA levels for the cytotoxic proteins were significantly decreased. A 24 h exposure to 200 nM TBT caused significant decreases in cytotoxic function, levels of granzyme B and perforin, and levels of granzyme B and perforin mRNA. When NK cells were exposed to 300 nM TBT for 1h followed by a 24 h period in TBT-free media, again there were significant decreases in NK cell cytotoxic function, levels of granzyme B and perforin and their mRNA. A 1h exposure to 300 nM TBT followed by a 48 h period in TBT-free media showed similar changes in cytotoxic function and levels of granzyme B and perforin as seen after 24 h in TBT-free media. Additionally, both of these exposures showed significant decreases in phosphorylation of CREB. These results indicate that TBT exposures can disrupt the transcription of granzyme B and perforin and that this disruption cannot be entirely accounted for by a decrease in phosphorylated CREB (phosphoCREB) levels.

Decreased adenylyl cyclase and cAMP-dependent protein kinase activities inhibit the cytotoxic function of human natural killer cells

Natural killer (NK) cells are lymphocytes that are capable of destroying tumor cells and virally infected cells without prior sensitization. Elevation of cyclic 3', 5' adenosine monophosphate (cAMP) levels in NK cells is known to cause dramatic inhibition of NK cytolytic function. However, the effect of lowering cellular levels of cAMP on the cytolytic function of natural killer (NK) cells has not been studied. The current study investigated the effects of inhibiting adenylyl cyclase (AC) or cAMP-dependent protein kinase (PKA) activities on the ability of NK cells to lyse K562 tumor cells, and on the activation of NK-cell phospholipase C (PLC) by tumor targets. Exposure of NK cells to the AC inhibitors MDL-12,330A (MDL) or 2',5',-Dideoxyadenosine (DDA) completely blocked their ability to destroy K562 tumor cells. Further, target-induced stimulation of NK-cell PLC was inhibited by as much as 90% when NK cells were treated with the AC inhibitors. Treatment of NK cells with the PKA inhibitor, H-89, caused essentially complete inhibition of cytotoxic function while decreasing target-induced stimulation of PLC by about 50%. Additionally, exposure to the organotin compound, tributyltin (TBT), which decreases cAMP levels in NK cells (as much as 80%) caused a decrease in cytotoxic function by as much as 90%. These data suggest that decreased levels of cAMP may cause very significant loss of NK cytotoxic function and that this may be mediated by decreased PKA activity. These data coupled with previous work revealing that increased cAMP levels inhibit NK cytotoxic function, suggest that tight regulation of cAMP levels is critical to NK cell function.

Brief exposure to triphenyltin produces irreversible inhibition of the cytotoxic function of human natural killer cells

Phenyltin (PT) compounds (mono-, di-, and triphenyltins) are used in agricultural and consumer products. They contaminate the environment and have toxic effects on aquatic and terrestrial animals including humans. In an earlier study we demonstrated that PTs (1 micro M, for 1h in vitro exposure) could cause considerable inhibition of the tumor-killing function of human natural killer (NK) cells (as much as 85%). In this study we examined whether cytotoxic function can be recovered after a brief exposure (1h) to PTs. Freshly isolated lymphocytes were exposed to triphenyltin (TPT) or diphenyltin (DPT) for 1h. The compound was then removed and the cells were incubated in PT-free medium for as long as 6 days. The results indicated that exposure to 750nM TPT for 1h caused an approximately 63+/-10% decrease in NK-cytotoxic function. However, if the cells were exposed to 750nM TPT for 1h and then allowed to incubate in TPT-free medium for 24h, there was a 91+/-12% loss of cytotoxic function. NK-cytotoxic function remained inhibited for as long as 6 days after removal of the TPT. A 1-h exposure to as much as 5 micro M DPT caused no loss of NK-cytotoxic function when the cells were tested immediately after the exposure. However, if the cells were allowed to incubate in DPT-free medium for 24h after the 1-h exposure to 5 micro M DPT, cytotoxicity was inhibited by 68+/-29% and this inhibition persisted for at least 6 days. These results indicated that short-term exposure to PTs caused persistent negative effects on human NK-cell function. The persistent effects of PTs are compared to those of the butyltins (BTs).

Daidzein, coumestrol and zearalenone affect lipogenesis and lipolysis in rat adipocytes

Daidzein, coumestrol and zearalenone - compounds called phytoestrogens, considered as active biological factors affecting many important physiological and biochemical processes appeared to be also significant regulators of adipocyte metabolism. In our experiments the influence of daidzein (0.01, 0.1 and 1 mM), coumestrol (0.001, 0.01 and 0.1 mM), zearalenone (0.01, 0.1 and 1 mM) and estradiol (0.01, 0.1 and 1 mM) on basal and insulin-stimulated (1 nM) lipogenesis from glucose and acetate was tested in adipocytes isolated from growing (160 +/- 5 g b.w) male Wistar rats. All tested compounds significantly attenuated glucose conversion to lipids. In the case of daidzein and coumestrol, this effect was probably due to inhibition of glycolysis. Daidzein (0.01, 0.1 and 1 mM), coumestrol (0.01 and 0.1 mM) and zearalenone (0.01, 0.1 and 1 mM) affected also basal and epinephrine-stimulated (1 microM) lipolysis. Daidzein (0.01 and 1 mM) augmented basal glycerides breakdown in adipocytes. The epinephrine-induced lipolysis was dependent on daidzein concentration and its stimulatory (0.1 mM) or inhibitory (1 mM) influence was observed. Zearalenone changed lipolysis only at the concentration of 1 mM and its effect was contradictory in the absence or presence of epinephrine (the stimulatory or inhibitory effect, respectively). Results obtained in experiments with inhibitors (insulin, 1 nM and H-89, 50 microM) and activators (dibutyryl-cAMP, 1 mM and forskolin, 1 microM) of lipolysis allowed us to assume that daidzein augmented basal lipolysis acting on PKA activity. The inhibitory effect of daidzein and zearalenone on epinephrine-induced lipolysis is probably due to restriction of HSL action. The influence of coumestrol on glycerides breakdown was less marked. Estradiol augmented only epinephrine-stimulated lipolysis.

Interleukins 2 and 12 produce recovery of cytotoxic function in tributyltin-exposed human natural killer cells

Cytotoxic function of human natural killer (NK) cells is modulated by a variety of cytokines. Interleukins (IL) 2 and 12 are both potent stimulators of NK cell cytotoxic function. Tributyltin (TBT) is used in a variety of consumer products and industrial applications. TBT is found in dairy products, meat, and fish. We and others have shown that there are measurable levels of TBT in human blood. Butyltins appear to increase the risk of cancer and viral infections in exposed individuals. We have demonstrated that the ability of NK cells to kill tumor cells is greatly diminished after a l-h exposure to TBT and that this inhibition persists even after removal of the compound. In the current study we examine the effects of the NK-stimulatory ILs, IL2 and IL12, on the ability of NK cells to recover from the persistent inhibitory effects of a 1-h TBT treatment. Highly purified NK cells (> 95% CD16(+)) or a lymphocyte preparation containing both T lymphocytes and NK cells were treated with 300 nM TBT and then allowed to recover for 24 h, 48 h, 4 days, and 6 days in TBT-free media containing no interleukin, 1000 U/mL IL2, 20 ng/mL IL l2, or a combination of IL2 plus IL12. Tumor killing function was then tested using a radioactive chromium release assay. As seen in our previous studies there is no recovery of NK cell cytotoxic function even after a 6-day recovery period when no interleukin is present in the medium. However, there is significant recovery of NK cytotoxic function when IL2, IL12, or the combination of IL2 plus IL12 is present in the medium during the recovery period.

Interleukins 2 and 12 produce significant recovery of cytotoxic function in dibutyltin-exposed human natural killer cells

Cytotoxic function of human natural killer (NK) cells is modulated by a variety of cytokines. Interleukins (IL) 2, 12, 15, and 18 and Interferon gamma (IFNgamma) are potent stimulators of NK cell cytotoxicity. Butyltins (BTs) are used in a variety of consumer products and industrial applications. Dibutyltin (DBT) is found in plastic products, beverages stored in PVC pipes during manufacturing, and poultry products. BTs appear to increase the risk of cancer and viral infections in exposed individuals. Recently, we have demonstrated that the ability of NK cells to kill tumor cells is greatly diminished after a 1-h exposure to dibutyltin. This inhibition of tumor killing function continues even after removal of the compound. There is no significant recovery of NK cytotoxic function even when the cells are allowed to recover for 6 days. In the current study we examine the effects of NK-stimulatory cytokines on the ability of NK cells to recover from the inhibitory effects of a 1-h DBT treatment. Highly purified NK cells (>95% CD16(+)) or a lymphocyte preparation containing both T lymphocytes and NK cells were treated with 5 microM DBT and then allowed to recover for 24 h, 48 h, 4 days, and 6 days in DBT-free medium containing either no cytokine or a maximally stimulatory dose of several NK-stimulatory cytokines. Tumor killing function was tested using a radioactive chromium release assay. As seen in our previous studies there is no recovery of NK cell cytotoxic function even after a 6-day recovery period when no cytokine is present in the medium. However, there is significant recovery of NK cytotoxic function when IL2, IL12, or the combination of IL2 plus IL12 is present in the medium during the recovery period. The other cytokines tested (IL15, IL18, and IFNgamma) were unable to increase the cytotoxicity of DBT-exposed NK cells.

Brief butyltin exposure induces irreversible inhibition of the cytotoxic function on human natural killer cells, in vitro

Despite mounting evidence on butyltin (BT) contamination and related immunotoxic effects on wildlife, very little is known about BT-associated immunotoxic effects on humans, particularly the effects on human natural killer (NK) lymphocyte function. Our earlier studies demonstrated that in vitro exposure to environmentally relevant concentrations of BTs negatively affect human NK cells and that there are measurable levels of BTs in human blood. In this study we examined whether the inhibition of NK cell cytotoxic function induced by a brief exposure (1 h) to BTs is reversible when the cells are allowed to recover in BT-free media for up to 6 days. Standard methods were used in chemical preparation, blood sampling, NK cell isolation, and 51-Chromium release assay. The results revealed that exposure to 300 nM TBT for 1 h caused an approximately 65- decrease in NK cytotoxic function, whether the lymphocytes were given as long as a 6-day recovery period or no recovery period. There was no recovery (nor any further loss) of NK cytotoxic function following removal of the compound. Exposure to 5 microM DBT for 1 h showed a 41% decrease in cytotoxic function with 0-h recovery and an 83% decrease after a 24-h recovery period. Thus, not only is there no significant recovery of NK cytotoxic function when the lymphocytes are allowed to incubate in BT-free medium for up to 6 days but there is additional loss of cytotoxic function. The results indicated that short-term exposure to BTs causes persistent negative effects on NK cell ability to kill cancer cells.

Butyltin exposure causes a rapid decrease in cyclic AMP levels in human lymphocytes

Natural killer (NK) cells are a subset of lymphocytes that are capable of killing tumor cells, virally infected cells, and antibody-coated cells. Butyltins (BTs) are used in a variety of consumer products and industrial applications. Tributyltin (TBT) is found in dairy products, meat, and fish. Dibutyltin (DBT) is found in plastic products, beverages stored in PVC pipes during manufacturing, and poultry products. BTs appear to increase the risk of cancer and viral infections in exposed individuals. This increased risk may be due in part to the inhibitory effect of these compounds on the cytotoxic function of NK cells. A 24-h exposure of NK cells to 200 nM TBT or 1.5 microM DBT decreased the cytotoxic function of NK cells by greater than 90%. Higher concentrations of TBT and DBT decreased the cytotoxic function of NK cells (by greater than 90%) after only a 1-h exposure. A 24-h exposure to either TBT or DBT decreased intracellular ATP levels by about 30%. However, as much as a 1-h exposure to either 300 nM TBT or 10 microM DBT caused no significant decrease in ATP levels. Thus, a decrease in ATP levels is a longer-term consequence of BT exposure. Intracellular levels of cAMP are decreased by as much as 80% within 5 min of exposure to either TBT or DBT. This rapid decline in cAMP levels in NK cells may be a consequence of BT exposure that is related to the rapid decrease in the cytotoxic function of NK cells.

Phenyltin inhibition of the cytotoxic function of human natural killer cells

Phenyltin (PT) contamination has been reported in water, sediment, and fish. However, the role of PT in weakening human immune function mediated through natural killer (NK) lymphocytes has not been elucidated. In this study, we report the effects of in vitro exposure to triphenyltin (TPT), diphenyltin (DPT), and monophenyltin (MPT) on the function of human NK cells. Exposure to TPT (1 microM, for 1 h) inhibited the tumor killing capacity of NK cells by 85%. Exposure of NK cells to DPT for 1 h (5 microM) and 24h (1.5 microM) reduced tumor lysis by greater than 90%. A 24-h exposure of NK cells to 5 microM MPT reduced tumor lysis by greater than 80%. Assays assessing the ability of NK cells to bind to tumor cells showed that a 24-h pretreatment with TPT, DPT, or MPT reduced NK cell binding to tumor cells by greater than 50%. The toxic potential of the PTs followed the order TPT > DPT > MPT. In comparison with butyltins (BTs), in vitro effects of PTs revealed that these compounds are relatively less toxic to NK cells than BTs. The results of this study provide evidence that phenyltin compounds are immunotoxic to human NK cells under in vitro experimental conditions.

Inhibition of a phosphodiesterase III in the lysis-sensitive target-induced elevation of cyclic AMP (cAMP) in human natural killer cells

Natural killer (NK) cells are lymphocytes that are capable of destroying tumor cells and virally infected cells (cytolysis) without prior sensitization. When cyclic AMP (cAMP) is elevated artificially in NK cells, it is a potent inhibitor of their cytolytic function. Recently, we have shown that when NK cells are exposed to a range of lysis-sensitive (LS) tumor target cells, there is an increase in intracellular cAMP levels in the NK cells over a 60-min period. There is no increase in NK-cell cAMP in response to lysis-resistant (LR) tumor target cells. We determined that this cAMP elevation is due, in part, to an LS target-induced activation of adenylyl cyclase (AC), and that the AC-activation component appears to require a protein tyrosine kinase (PTK) activity. In the present study, we demonstrated that an LS target-induced inhibition of phosphodiesterase (PDE) is also contributing to the overall elevation of cAMP. Direct measurement of PDE activity showed an inhibition in lymphocytes that were exposed to LS targets but not in those exposed to LR targets. The inhibition of PDE activity was maximal by 30 min. Lymphocytes were exposed to targets and then lysed, so that PDE activity could be measured. Addition of class-selective inhibitors of PDE (at levels sufficient to completely block that class of PDE) to the lysate focused the measurement of PDE activity on those classes of PDE that were unaffected by the selective inhibitor. Using the PDE IV selective inhibitor rolipram and the PDE III selective inhibitors trequinsin and milrinone, we showed that a PDE III is being inhibited in lymphocytes by exposure to LS targets. As PDE III is known to be inhibited by elevated cyclic GMP (cGMP) levels, increased cGMP in NK cells following exposure to LS targets was a possible mechanism by which a PDE III in NK cells might be inhibited. However, when we measured cGMP levels in control and LS target-stimulated lymphocytes, we saw no change.

Indomethacin inhibits circulating PGE2 and reverses postexercise suppression of natural killer cell activity

Natural killer (NK) cells are important in combating viral infections and cancer. NK cytolytic activity (NKCA) is often depressed during recovery from strenuous exercise. Lymphocyte subset redistribution and/or inhibition of NK cells via soluble mediators, such as prostaglandin (PG) E2 and cortisol, are suggested as mechanisms. Ten untrained (peak O2 consumption = 44.0 +/- 3.5 ml. kg-1. min-1) men completed at 2-wk intervals a resting control session and three randomized double-blind exercise trials after the oral administration of a placebo, the PG inhibitor indomethacin (75 mg/day for 5 days), or naltrexone (reported elsewhere). Circulating CD3(-)CD16(+)/56(+) NK cell counts, PGE2, cortisol, and NKCA were measured before, at 0.5-h intervals during, and at 2 and 24 h after a 2-h bout of cycle ergometer exercise (65% peak O2 consumption). During placebo and indomethacin conditions, exercise induced significant (P < 0.0001) elevations of NKCA (>100%) and circulating NK cell counts (>350%) compared with corresponding control values. With placebo treatment, total NKCA was suppressed (28%; P < 0.05) 2 h after exercise, and a postexercise elevation (36%; P = 0.02) of circulating PGE2 was negatively correlated (r = 0.475, P = 0.03) with K-562 tumor cell lysis. NK counts were unchanged in the postexercise period, but at this stage CD14(+) monocyte numbers were elevated (P < 0.0001). Indomethacin treatment eliminated the postexercise increase in PGE2 concentration and completely reversed the suppression of total and per CD16(+)56(+) NKCA 2 h after exercise. These data support the hypothesis that the postexercise reduction in NKCA reflects changes in circulating PGE2 rather than a differential lymphocyte redistribution.