Dibutyltin exposure decreases granzyme B and perforin in human natural killer cells

Dibutyltin alters immune cell production of the pro-inflammatory cytokines interleukin (IL) 1β and IL-6: role of mitogen-activated protein kinases and changes in mRNA

Dibutyltin (DBT) is used to stabilize plastics and as a deworming agent in some poultry. It is found in human blood (levels as high as 0.3 μM). Interleukin (IL) 1β (IL-1β) and IL-6 are pro-inflammatory cytokines produced by lymphocytes, monocytes, and other cells. Elevated levels of IL-1β and IL-6 have been associated with pathologies including rheumatoid arthritis and cancers. DBT was shown to decrease IL-1β and IL-6 secretion from immune cells at higher concentrations while causing increases at lower concentrations. However, it was not clear if these changes were due to DBT's alteration of the secretory process or due its ability to change cellular synthesis/production of these proteins. This study addresses this question, as well as mechanisms for any observed changes in synthesis/production. Monocyte-depleted peripheral blood mononuclear cells (MD-PBMCs) were exposed to DBT at concentrations of 5, 2.5, 1, 0.5, 0.25, 0.1, and 0.05 μM for 1, 6, and 24 h and the production (combination of secreted and intracellular levels from the same cells) of both IL-1β and IL-6 were measured. Effects of selected DBT exposures on cytokine production were also examined in PBMCs and DBT's effects were similar when monocytes were present. The 24-h exposures to DBT decreased production of both IL-1β and IL-6 at the two highest concentrations but increased production at lower concentrations. Both decreases and increases in cytokine production appear to be explained by DBT-induced changes in mRNA levels. DBT-induced increases in cellular production of the cytokines appear to require p38 and ERK1/2 MAPK pathways.

Dibutyltin depressed immune functions via NF-κB, and JAK/STAT signaling pathways in zebrafish (Danio rerio)

Dibutyltin (DBT) is the degradation products of TBT, which is generally considered higher toxicity than TBT in the immune system. In order to learn more about the mechanisms of immune-toxic of DBT, we exposed zebrafish (Danio rerio) to 0, 1, 10 and 100 ng/L DBT for 8 weeks. At the end of the experiment, we determined the immune parameters and immune-related genes. The results showed that with an increase in TBT dose, lysozyme activities and IgM, C3, C4 content in intestine, skin and spleen were all significantly inhibited by the DBT exposure. Fish exposed to 10 ng/L and 100 ng/L showed significantly lower lysozyme activities and IgM, C3, C4 content than those of the control group. Zebrafish exposed to 10 ng/L and 100 ng/L DBT, the mRNA transcript levels of interleukin-1β (IL-1β), interleukin-6 (IL-6), interleukin-8 (IL-8), tumor necrosis factor-α (TNF-α), interferon γ2 (INFγ2), nuclear factor-κB p65 (NF-kB p65), inhibitor protein-κBα (IκBα), IκB kinases β (IKKβ), Janus family of protein tyrosine kinases (JAKs) and the signal transducers and activators of transcription proteins (STATs) all increased with the DBT levels in the intestine and spleen. Those parameters showed significantly higher values in 10 ng/L and 100 ng/L than those of fish in the control group. However, no significant difference was found in IκB kinases α (IKKα) and IκB kinase γ (IKKγ) mRNA levels in the intestine and spleen. These data imply that DBT might be via suppression on IKKβ/IkBa/NF-kBp65 and JAK/STAT signaling pathways to regulate the immunity of zebrafish.

Dibutyltin-induced alterations of interleukin 1beta secretion from human immune cells

Dibutyltin (DBT) is used to stabilize polyvinyl chloride plastics (including pipes that distribute drinking water) and as a de-worming agent in poultry. DBT is found in human blood, and DBT exposures alter the secretion of tumor necrosis factor alpha and interferon gamma from lymphocytes. Interleukin (IL)-1β is a proinflammatory cytokine that regulates cellular growth, tissue restoration and immune response regulation. IL-1β plays a role in increasing invasiveness of certain tumors. This study reveals that exposures to DBT (24 h, 48 h and 6 days) modify the secretion of IL-1β from increasingly reconstituted preparations of human immune cells (highly enriched human natural killer cells, monocyte-depleted [MD] peripheral blood mononuclear cells [PBMCs], PBMCs, granulocytes and a preparation combining both PBMCs and granulocytes). DBT altered IL-1β secretion from all cell preparations. Higher concentrations of DBT (5 and 2.5 μm) decreased the secretion of IL-1β, while lower concentrations of DBT (0.1 and 0.05 μm) increased the secretion of IL-1β. Selected signaling pathways were examined in MD-PBMCs to determine if they play a role in DBT-induced elevations of IL-1β secretion. Pathways examined were IL-1β converting enzyme (caspase 1), mitogen-activated protein kinases and nuclear factor kappa B. Caspase 1 and mitogen-activated protein kinase pathways appear to be utilized by DBT in increasing IL-1β secretion. These results indicate that DBT alters IL-1β secretion from human immune cells in an ex. vivo system utilizing several IL-1β regulating signaling pathways. Thus, DBT may have the potential to alter IL-1β secretion in an in vivo system. Copyright © 2016 John Wiley & Sons, Ltd.

Secretion of interferon gamma from human immune cells is altered by exposure to tributyltin and dibutyltin

Tributyltin (TBT) and dibutyltin (DBT) are widespread environmental contaminants found in food, beverages, and human blood samples. Both of these butyltins (BTs) interfere with the ability of human natural killer (NK) cells to lyse target cells and alter secretion of the pro-inflammatory cytokine tumor necrosis factor alpha (TNFα) from human immune cells in vitro. The capacity of BTs to interfere with secretion of other pro-inflammatory cytokines has not been examined. Interferon gamma (IFNγ) is a modulator of adaptive and innate immune responses, playing an important role in overall immune competence. This study shows that both TBT and DBT alter secretion of IFNγ from human immune cells. Peripheral blood cell preparations that were increasingly reconstituted were used to determine if exposures to either TBT or DBT affected IFNγ secretion and how the makeup of the cell preparation influenced that effect. IFNγ secretion was examined after 24 h, 48 h, and 6 day exposures to TBT (200 - 2.5 nM) and DBT (5 - 0.05 µM) in highly enriched human NK cells, a monocyte-depleted preparation of PBMCs, and monocyte-containing PBMCs. Both BTs altered IFNγ secretion from immune cells at most of the conditions tested (either increasing or decreasing secretion). However, there was significant variability among donors as to the concentrations and time points that showed changes as well as the baseline secretion of IFNγ. The majority of donors showed an increase in IFNγ secretion in response to at least one concentration of TBT or DBT at a minimum of one length of exposure.

Effects of butyltins on mitogen-activated-protein kinase kinase kinase and Ras activity in human natural killer cells

Butyltins (BTs) contaminate the environment and are found in human blood. BTs, tributyltin (TBT) and dibutyltin (DBT) diminish the cytotoxic function and levels of key proteins of human natural killer (NK) cells. NK cells are an initial immune defense against tumors, virally infected cells and antibody-coated cells and thus critical to human health. The signaling pathways that regulate NK cell functions include mitogen-activated protein kinases (MAPKs). Studies have shown that exposure to BTs leads to activation of specific MAPKs and MAPK kinases (MAP2Ks) in human NK cells. MAP2K kinases (MAP3Ks) are upstream activators of MAP2Ks, which then activate MAPKs. The current study examined if BT-induced activation of MAP3Ks was responsible for MAP2K and thus, MAPK activation. This study examines the effects of TBT and DBT on the total levels of two MAP3Ks, c-Raf and ASK1, as well as activating and inhibitory phosphorylation sites on these MAP3Ks. In addition, the immediate upstream activator of c-Raf, Ras, was examined for BT-induced alterations. Our results show significant activation of the MAP3K, c-Raf, in human NK cells within 10 min of TBT exposure and the MAP3K, ASK1, after 1 h exposures to TBT. In addition, our results suggest that both TBT and DBT affect the regulation of c-Raf.

Risk assessment of butyltins based on a fugacity-based food web bioaccumulation model in the Jincheng Bay mariculture area: I. Model development

A fugacity-based model was developed to simulate the bioaccumulation of butyltins in the food web of the Jincheng Bay mariculture area. The predicted biological tissue residues of tributyltin (TBT), dibutyltin (DBT), and monobutyltin (MBT) were 0.04-17.09, 0.14-53.54, and 0.27-108.77 ng-Sn g(-1), respectively, and the predicted values in six mollusca agreed well with the measured ones. The lipid-normalized concentrations did not significantly increase across trophic levels, indicating no biomagnification across aquatic food webs. These results were highly consistent with those observed both in the laboratory and field, which had been reported in numerous references. The explanation, from calculating their flux equilibrium in the food web, was that butyltins were primarily taken in via respiration from the water column by marine organisms. The sensitivities of the model parameters were analyzed, revealing that the hydrophobicity of butyltins played the dominant role in their bioaccumulation phenomena. The verified model predictions of the biotic tissue concentrations of the butyltins could be readily applied to perform internal ecological risk and human health risk assessments in this area.

Risk assessment of butyltins based on a fugacity-based food web bioaccumulation model in the Jincheng Bay mariculture area: II. Risk assessment

A fugacity-based food web bioaccumulation model was constructed, and the biotic concentrations of butyltins in the food web of the Jincheng Bay mariculture area were estimated accordingly, using the water and sediment concentrations described in the accompanying paper (Part I). This paper presents an ecological risk assessment (ERA) and a human health risk assessment (HHRA) of the butyltins, based on the estimated tissue residues in the marine life in this area. The results showed that the ecological risk probability was greater than 0.05. At this level, management control is critical since sensitive marine species would be profoundly endangered by butyltin contamination. Few if any detrimental effects, however, would be generated for humans from exposure to butyltins through seafood consumption. The fugacity-based model can refine the ERA and HHRA of pollutants in marine areas, provide a basis for protecting marine ecology and the security of fishery products, and thus help determine the feasibility of a proposed aquaculture project.

Tributyltin and dibutyltin alter secretion of tumor necrosis factor alpha from human natural killer cells and a mixture of T cells and natural killer cells

Butyltins (BTs) have been in widespread use. Tributyltin (TBT) has been used as a biocide in a variety of applications and is found in human blood samples. Dibutyltin (DBT) has been used as a stabilizer in polyvinyl chloride plastics and as a de-worming agent in poultry. DBT, like TBT, is found in human blood. Human natural killer (NK) cells are the earliest defense against tumors and viral infections and secrete the cytokine tumor necrosis factor-alpha (TNF-α). TNF-α is an important regulator of adaptive and innate immune responses. TNF-α promotes inflammation and an association between malignant transformation and inflammation has been established. Previously, we have shown that TBT and DBT were able to interfere with the ability of NK cells to lyse tumor target cells. Here we show that BTs alter cytokine secretion by NK cells as well as a mixture of T and NK lymphocytes (T/NK cells). We examined 24-, 48-h and 6-day exposures to TBT (200-2.5 nM) and DBT (5-0.05 μM) on TNF-α secretion by highly enriched human NK cells and T/NK cells. The results indicate that TBT (200-2.5 nM) decreased TNF-α secretion from NK cells. In the T/NK cells, 200 nM TBT decreased secretion whereas 100-5 nM TBT increased secretion of TNF-α. NK cells or T/NK cells exposed to higher concentrations of DBT showed decreased TNF-α secretion whereas lower concentrations showed increased secretion. The effects of BTs on TNF-α secretion are seen at concentrations present in human blood.

Ziram activates mitogen-activated protein kinases and decreases cytolytic protein levels in human natural killer cells

Human natural killer (NK) cells are central in immune defense with their ability to lyse tumor cells and virally infected cells. Tumor formation and viral infection may increase if NK cytotoxic function is disrupted. Ziram (zinc dithiocarbamate) is used as an accelerating agent in the production of latex and to protect various fruits and vegetables from fungal infection. Previously, we have shown that exposure to ziram inhibits NK lytic function. Butyltin environmental contaminants, which also inhibit NK lytic function, cause rapid activations of mitogen-activated protein kinases (MAPKs) and decreases in expression of the cytolytic proteins granzyme B and perforin (after 24 h) in exposed NK cells. MAPKs are important regulators of the lytic response of NK cells, and spurious activation of these enzymes by contaminants would leave the NK cells unable to respond to appropriate targets. This study examined the effects of ziram exposures on MAPKs (p44/42, p38, and c-jun-N-terminal kinase) and on levels of cytolytic proteins. Ten-minute to 6-h exposures of NK cells to ziram caused activation of MAPKs, p44/42, and p38. Exposure to ziram for 24 h caused a decrease in granzyme B and perforin levels. MAPK inhibitors were able to prevent these ziram-induced decreases in granzyme B and perforin. These results suggest that ziram-induced MAPK activation is at least in part responsible for decreased cytolytic function in ziram-exposed NK cells. Furthermore, the results indicate that these changes are in common with other environmental contaminants that have been shown to decrease NK lytic function.

Dibutyltin activates MAP kinases in human natural killer cells, in vitro

Previous studies have shown that dibutyltin (DBT) interferes with the function of human natural killer (NK) cells, diminishing their capacity to destroy tumor cells, in vitro. DBT is a widespread environmental contaminant and has been found in human blood. As NK cells are our primary immune defense against tumor cells, it is important to understand the mechanism by which DBT interferes with their function. The current study examines the effects of DBT exposures on key enzymes in the signaling pathway that regulates NK responsiveness to tumor cells. These include several protein tyrosine kinases (PTKs), mitogen-activated protein kinases (MAPKs), and mitogen-activated protein kinase kinases (MAP2Ks). The results showed that in vitro exposures of NK cells to DBT had no effect on PTKs. However, exposures to DBT for as little as 10 min were able to increase the phosphorylation (activation) of the MAPKs. The DBT-induced activations of these MAPKs appear to be due to DBT-induced activations of the immediate upstream activators of the MAPKs, MAP2Ks. The results suggest that DBT-interference with the MAPK signaling pathway is a consequence of DBT exposures, which could account for DBT-induced decreases in NK function.

Effects of butyltin exposures on MAP kinase-dependent transcription regulators in human natural killer cells

Natural killer (NK) cells are a major immune defense mechanism against cancer development and viral infection. The butyltins (BTs), tributyltin (TBT) and dibutyltin (DBT), have been widely used in industrial and other applications and significantly contaminate the environment. Both TBT and DBT have been detected in human blood. These compounds inhibit the lytic and binding function of human NK cells and thus could increase the incidence of cancer and viral infections. Butyltin (BT)-induced loss of NK function is accompanied by activation of mitogen activated protein kinases (MAPKs) and decreases in expression of cell-surface and cytolytic proteins. MAPKs activate components of the transcription regulator AP-1 and activate the transcription regulator Elk-1. Based on the fact that BTs activate MAPKs and alter protein expression, the current study examined the effect of BT exposures on the levels and phosphorylation states of the components of AP-1 and the phosphorylation state of Elk-1. Exposure to 300 nM TBT for 10 min increased the phosphorylation of c-Jun in NK cells. One hour exposures to 300 nM and 200 nM TBT increased the phosphorylation and overall level of c-Jun. During a 300 nM treatment with TBT for 1 h the binding activity of AP-1 was significantly decreased. There were no significant alterations of AP-1 components or of Elk-1 with DBT exposures. Thus, it appears that TBT-induced alterations on phosphorylation, total levels, and binding activity of c-Jun might contribute to, but are not fully responsible for, TBT-induced alterations of NK protein expression.

Isolation of Streptomyces sp. strain capable of butyltin compounds degradation with high efficiency

Dibutyltin (DBT), a widely used plastic stabilizer, has been detected in the environment as well as in human tissues. DBT is considered to be highly neurotoxic and immunotoxic. Hence, DBT needs to be considered as a potential toxic chemical. Degradation of butyltin compounds by Streptomyces sp. isolated from plant waste composting heaps was studied. Glucose grown cells degraded organotin from 10 to 40 mg l(-1). After 1 day of incubation 90% of DBT (added at 20 mg l(-1)) was converted to less toxic derivative--monobutyltin (MBT). DBT metabolism was inhibited by metyrapone addition, a known cytochrome P-450 inhibitor. It could provide evidence that cytochrome P-450 system is involved in DBT metabolism in Streptomyces sp. IM P102. Moreover, according to our knowledge, the degradation of DBT by actinobacterium has not been previously described.

Serum supplementation modulates the effects of dibutyltin on human natural killer cell function

Natural killer (NK) cells are a subset of lymphocytes capable of killing tumor cells, virally infected cells and antibody-coated cells. Dibutyltin (DBT) dichloride is an organotin used as a stabilizer in polyvinylchloride (PVC) plastics and as a deworming product in poultry. DBT may leach from PVC water supply pipes and therefore poses a potential risk to human health. We previously reported diminished NK cells lysis of tumor cells following exposure to DBT in serum-free cell culture medium. However, under in vivo conditions, circulating cells will be exposed to DBT in the presence of 100% plasma; thus we investigated whether serum supplementation and incubation time modulates DBT effects on NK cell killing and the accumulation of DBT in freshly isolated NK cells, to determine whether a serum-free model accurately predicts possible effects of DBT on human NK cells under in vivo conditions. Lytic function was decreased by approximately 35% at an intracellular DBT (DBTi) concentration of 200 microM and nearly complete loss of lytic function was observed at DBTi above 300 microM for one h. However, an intracellular concentration of 50 microM DBT, achieved over 24 h of exposure in 50% serum, reduced lytic function by 50%. Thus, conditions that reflect prolonged contact with circulating DBT, in the presence of serum, suggest that NK cell activity is decreased at lower DBTi. These data indicate that the model is useful in predicting potential human effects of relatively low DBTi concentrations.