Effects of tri-n-butyltin chloride on energy metabolism, macromolecular synthesis, precursor uptake and cyclic AMP production in isolated rat thymocytes

In vitro approaches to evaluate toxicity induced by organotin compounds tributyltin (TBT), dibutyltin (DBT), and monobutyltin (MBT) in neuroblastoma cells

The toxic effects of the organotin compounds (OTCs) monobutyltin (MBT), dibutyltin (DBT), and tributyltin (TBT) were evaluated in vitro in a neuroblastoma human cell line. Mechanisms of cell death, apoptosis versus necrosis, were studied by using several markers: inhibition of cell viability and proliferation, F-actin, and mitochondrial membrane potential changes as well as reactive oxygen species (ROS) production and DNA fragmentation. The most toxic effects were detected with DBT and TBT even at very low concentrations (0.1-1 μM). In contrast, MBT induced lighter cytotoxic changes at the higher doses tested. None of the studied compounds stimulated propidium iodide uptake, although the most toxic chemical, TBT, caused lactate dehydrogenase release at the higher concentrations tested. These findings suggest that in neuroblastoma, OTC-induced cytotoxicity involves different pathways depending on the compound, concentration, and incubation time. A screening method for DBT and TBT quantification based on cell viability loss was developed, allowing a fast detection alternative to complex methodology.

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.

Selective inhibition of B lymphocytes in TBTC-treated human bone marrow long-term culture

Tributyltin chloride (TBTC) is well known for its immunotoxic effect, in particular towards immature thymocytes. TBTC is also known to induce adipocyte differentiation in primary human bone marrow cultures, which is reflected in the decrease in a number of adipocyte-derived cytokines, chemokines and the adipocyte-linked hormone leptin. Since adipocytes influence haematopoiesis and lymphopoiesis for instance by these cytokines and hormones, we here investigated whether TBTC has an effect on specific lymphocyte subsets in human bone marrow primary cultures. FACS analysis showed a reduction of CD19/CD22-positive B cells by TBTC, both in the presence or absence of cytokines. The treatment did not cause a toxic effect on mature CD3+CD4+ and CD3+CD8+ T cells, suggesting selective TBTC toxicity on B lymphocytes in the presently used in vitro system.

Gene expression profiling of Bis(tri-n-butyltin)oxide (TBTO)-induced immunotoxicity in mice and rats

Bis(tri-n-butyltin)oxide (TBTO) is one of the organotin compounds that have been used as biocides and occur as persistent environmental pollutants. Human exposure to these compounds occurs through consumption of meat and fish products in which they accumulate. The most sensitive endpoint of TBTO exposure is immunotoxicity. TBTO causes thymus atrophy and thereby interferes with T-lymphocyte-mediated immune responses. Tributyltin compounds have been found to adversely affect a wide range of cellular components and processes in many species, organ systems, and cell types. Both inhibition of proliferation and induction of apoptosis have been observed in thymocytes. We conducted microarray experiments in mice and rats in order to investigate if the immunosuppressive actions of TBTO could be detected by gene expression profiling, and if so, to elucidate the mechanisms of action. Gene expression changes that were detected in mouse thymuses after exposure to a maximum tolerable dose of TBTO correlated to previously observed effects. Most notably, reduction of expression of cell surface determinants and T-cell receptor chains, suppression of cell proliferation, and a possible involvement of nuclear receptors in interference with lipid metabolism by TBTO were observed. The TBTO-induced thymus involution may therefore primarily be caused by inhibition of thymocyte proliferation. In contrast, in rats only limited effects of a lower dose of TBTO were found at the gene expression level in the thymus, even though thymus involution was observed. Here, most gene expression regulation by TBTO was detected in the liver. These preliminary results indicate that gene expression analysis is able to reveal effects of TBTO and to gain insight into its molecular mechanism of action. It may even be a suitable tool to investigate immunotoxicology in general. However, dose and inter-species differences are apparently clearly reflected in the gene expression profiles.

TBTC induces adipocyte differentiation in human bone marrow long term culture

Organotins are widely used in agriculture and the chemical industry, causing persistent and widespread pollution. Organotins may affect the brain, liver and immune system and eventually human health. Recently, it has been shown that tri-butyltin (TBT) interacts with nuclear receptors PPAR gamma (peroxisome proliferator-activated receptor gamma) and RXR (retinoid x receptor) leading to adipocyte differentiation in the 3T3 cell line. Since adipocytes are known to influence haematopoiesis, for instance through the expression of cytokines and adhesion molecules, it was considered of interest to further study the adipocyte-stimulating effect of TBTC in human bone marrow cultures. Nile Red spectrofluorimetric analysis showed a significant increase of adipocytes in TBTC-treated cultures after 14 days of long term culture. Real-time PCR and Western blot analysis confirmed the high expression of the specific adipocyte differentiation marker aP2 (adipocyte-specific fatty acid binding protein). PPAR gamma, but not RXR, mRNA was increased after 24 h and 48 h exposure. TBTC also induced a decrease in a number of chemokines, interleukins, and growth factors. Also the expression of leptin, a hormone involved in haematopoiesis, was down regulated by TBTC treatment. It therefore appears that TBTC induced adipocyte differentiation, whilst reducing a number of haematopoietic factors. This study indicates that TBTC may interfere in the haematopoietic process through an alteration of the stromal layer and cytokine homeostasis.

Protective effect of green tea polyphenols on tributyltin-induced oxidative damage detected by in vivo and in vitro models

The current study investigated the protective effects of green tea polyphenols (GTPP) on TBT-induced oxidative damage. The results showed that reactive oxygen species (ROS) production and malondialdehyde content of the liver in mice exposed to TBT were reduced in the GTPP-treated group compared to the untreated group. The intracellular ROS level was elevated in TBT-treated human FL cells in a time-dependent manner. Comet assay data demonstrated that the number of cells with damaged DNA in untreated mice was found to be significantly higher compared to GTPP-treated mice. Damage to the nuclei and mitochondria observed in TBT-treated mice were alleviated in mice treated with both TBT and GTPP. The results represent the first observation that GTPP were effective in reducing TBT-induced oxidative damage both in vivo and in vitro. The possible protective mechanism may be due to the powerful ability of GTPP to scavenge ROS and prevent DNA breaks. We conclude that GTPP could be an effective agent or food supplement to reduce the cytotoxicity of TBT.

Apoptotic related biochemical changes in human amnion cells induced by tributyltin

Tributyltin (TBT) is one of the environmental pollutants, which is mostly accumulated in marine animals. The toxic effects of TBT have been extensively documented in several types of cells, but the molecular mechanisms responsible for TBT-induced cell damage are still not fully elucidated. The present study was undertaken to evaluate the apoptotic related biochemical changes in human amnion cells induced by TBT. After cells were exposed to TBT at the concentrations of 1-4 microM for 2h, the results suggested that TBT could induce an early and typical apoptosis, moreover caspase-3, the modifications of cytoskeletal structure and the Bcl-2 family were involved in this process. The results will deepen our understanding about the toxic mechanism of TBT on human amnion cells.

Tri-n-butyltin-induced blockade of store-operated calcium influx in rat thymocytes

Tri-n-butyltin (TBT), one of environmental pollutants, disturbs intracellular Ca(2+) homeostasis by increasing intracellular Ca(2+) concentration ([Ca(2+)]i). Effect of TBT on oscillatory change in [Ca(2+)]i (Ca(2+) oscillation) of rat thymocytes was examined using a laser microscope with fluo-3-AM in order to further elucidate the TBT toxicity related to intracellular Ca(2+). The Ca(2+) oscillation was completely attenuated by 300nM TBT. Since store-operated Ca(2+) channels are involved in the generation of Ca(2+) oscillation, the action of TBT on an increase in [Ca(2+)]i by Ca(2+) influx through store-operated Ca(2+) channels was examined. The increase in [Ca(2+)]i by the store-operated Ca(2+) influx was not affected by 3nM TBT. However, TBT at 10nM or more significantly reduced the increase in [Ca(2+)]i. It is likely that TBT attenuates the Ca(2+) oscillation by reducing the Ca(2+) influx through store-operated Ca(2+) channels.

Tributyltin induces DNA damage as well as oxidative damage in rats

In this study, oxidative and DNA damage were measured synchronously after Sprague-Dawley rats were exposed to different dosages of tributyltin (TBT) for 3 and 7 consecutive days. Oxidative damage was measured by analyzing the production of hepatic reactive oxygen species (ROS), the activity of superoxide dismutase (SOD), and the content of malondialdehyde (MDA). DNA damage was measured by single-cell gel electrophoresis (comet assay). After 3 days of exposure, significant differences in ROS production could only be seen between the control and the highest dosage group (10 mg/kg BW d), although after 7 days of treatment, ROS production increased in a dose-dependent manner. SOD activity increased with dosage after 3 days of exposure and decreased with dosage after 7 days of exposure. TBT also induced significant production of MDA after 7 days of exposure. The changes in ROS, SOD, and MDA found in this study suggest that the antioxidative systems of rats were activated by TBT in the first 3 days of exposure but had become exhausted by 7 days of exposure. In the comet assay, the number of cells with damaged DNA in rats treated with TBT increased with dosage of TBT. The most likely mechanism of the DNA breakage induced by TBT is oxidative damage. It can be concluded that exposure of TBT can promote both oxidative and DNA damage in mammals in vivo.

Involvement of mitochondrial and death receptor pathways in tributyltin-induced apoptosis in rat hepatocytes

Tri-n-butyltin (TBT), a biocide, is known for its immunotoxicity and hepatotoxicity and is a well-characterised mitochondrial toxin. This report investigates the mechanisms involved in induction of apoptosis by TBT in primary cultures of rat hepatocytes. Release of cytochrome c from mitochondria into the cytosol was apparent after 15 min of exposure to 2.5 microM TBT. In addition, activity of initiator caspase-9 increased after 30 min, representing activation of the mitochondrial pathway in hepatocytes. The death receptor pathway was also activated by TBT, as indicated by recruitment of the adaptor protein FADD from the cytosol to the membrane as soon as 15 min after treatment. In addition, levels of the pro-apoptotic protein Bid decreased in the cytosol, while there was an increase in levels of the cleaved form tBid, in TBT-treated hepatocytes. Activity of initiator caspase-8 increased after 30 min. The principal effector caspase-3 was activated following 30 min of treatment with TBT. Activation was confirmed by immunodetection of a 17-kDa cleaved fragment. Apoptotic substrates such as Poly(ADP-ribose) polymerase and DNA fragmentation factor-45 are cleaved by caspase-3 to ensure the dismantlement of the cell. Cleavage of Poly(ADP-ribose) polymerase into a 85-kDa fragment appeared after 30 min of TBT treatment. DNA fragmentation factor-45 disappeared in TBT-exposed rat hepatocytes. This is the first detailed study reporting the involvement of initiator and effector caspases, cleavage of their intracellular substrates and activation of both death receptor and mitochondrial pathways in TBT-induced apoptosis in rat hepatocytes. The comprehension of molecular events of apoptosis is important for the evaluation of the risk to humans and animals.

Organotin-induced apoptosis occurs in small CD4(+)CD8(+) thymocytes and is accompanied by an increase in RNA synthesis

The organotin compounds di-n-butyltin dichloride (DBTC) and tri-n-butyltin chloride (TBTC) induce thymus atrophy in rats. At low doses they inhibit immature thymocyte proliferation, whereas at higher doses in particular TBTC induces apoptotic cell death. In vitro, a similar concentration-effect relationship was observed, i.e. low concentrations inhibit DNA and protein synthesis and higher concentrations induce apoptosis. The mechanism of apoptosis by organotins has been partly investigated, but their capacity to inhibit protein synthesis seems to contradict with the idea that macromolecular synthesis is required for organotin-induced apoptosis. Therefore, we aimed to evaluate the relation between apoptosis and the synthesis of RNA and proteins, with a focus on the apoptosis-sensitive thymocyte subset. Results showed that DBTC increases RNA synthesis in particular in the subset of small CD4(+)CD8(+) thymocytes, which normally shows a high incidence of DNA fragmentation. Moreover, the RNA synthesis inhibitor actinomycin D or the protein synthesis inhibitor cycloheximide protected cells from apoptosis by DBTC or TBTC. Although organotin compounds increase synthesis of the heat shock protein HSC73/HSP72, heat shock treatment did not initiate apoptosis in thymocytes, neither antagonized organotin-induced apoptosis. This indicates that synthesis of heat shock proteins is not related to organotin-induced increase of RNA synthesis, and that other RNA-molecules are probably involved.

Identification by DNA macroarray of nur77 as a gene induced by di-n-butyltin dichloride: its role in organotin-induced apoptosis

The thymotoxic organotin compounds di-n-butyltin dichloride (DBTC) and tri-n-butyltin chloride (TBTC) are known to induce apoptosis in vitro in rat thymocytes. They also affect macromolecular synthesis, inhibiting DNA synthesis and increasing RNA synthesis. Since these RNA molecules, likely to be involved in the initiation of the apoptotic process, have not been identified yet, the purpose of this research was to characterize by a cDNA macroarray the expression of genes involved in DBTC-induced apoptosis. We found that nur77 was rapidly transcripted in vitro following exposure of freshly isolated rat thymocytes to 3 microM DBTC. nur77 induction has also been observed in vivo after treatment of rats with apoptotic doses (60 mg/kg body wt) of DBTC. The products of nur77 are known to be involved in the apoptotic process, as nur77 is a transcription factor expressed in response to T-cell receptor-mediated apoptosis in immature T cells. Antisense oligonucleotide inhibition of nur77 expression prevented apoptosis induced by DBTC, supporting a role for nur77 in organotin-induced apoptotic cell death.

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.

Effect of tributyltin chloride on the release of calcium ion from intracellular calcium stores in rat hepatocytes

The effects of tri-n-butyltin chloride (TBT), an environmental pollutant, on the release of Ca(2+) from intracellular stores were investigated in isolated rat hepatocytes. Isolated hepatocytes permeabilized with digitonin were suspended in solution, and the concentration of extracellular Ca(2+) was measured, using a fluorescent Ca(2+) dye, fura-2. In the solution containing permeabilized hepatocytes that had been preincubated with 4.0 microM TBT for 30 min, the extracellular Ca(2+) concentration was high, but the inositol 1,4,5-trisphosphate (InsP(3))-induced increase in Ca(2+) concentration was suppressed, suggesting that the extracellular release of Ca(2+) in response to TBT treatment was from intracellular stores. Images of the Ca(2+) concentration in the intracellular stores of primary cultured hepatocytes loaded with fura-2 were obtained after digitonin-permeabilization, using digitalized fluorescence microscopy. The permeabilized hepatocytes that had been preincubated with 4.0 microM TBT for 30 min had a very low fura-2 fluorescence ratio (340/380 nm), suggesting that stored Ca(2+) was released. When the hepatocytes were treated with 4.0 microM TBT after digitonin-permeabilization, the decrease in the fura-2 fluorescence ratio was very small. However, when the permeabilized hepatocytes were incubated with 4.0 microM TBT and 2.0 microM NADPH, the decrease was enhanced, raising the possibility that TBT might be metabolized to the active form(s), thus releasing Ca(2+) from intracellular stores. When the hepatocytes were preincubated with 0.1 microM TBT for 30 min and then were permeabilized, the fura-2 fluorescence ratio was almost the same as that in the control permeabilized hepatocytes. However, the InsP(3)-induced decrease in the fluorescence ratio was suppressed significantly in the permeabilized hepatocytes. These results suggest that TBT released Ca(2+) from the intracellular stores at high concentrations, and suppressed the InsP(3)-induced Ca(2+) release at non-toxic low concentrations. It is probable that the latter effect was responsible for the previously reported suppression of Ca(2+) response induced by hormonal stimulations (Kawanish et al., Toxicol Appl Pharmacol 1999;155:54-61).

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.

Organotin compounds decrease in vitro survival, proliferation and differentiation of normal human B lymphocytes

Organotin compounds (OTC) are organometallic compounds with vast industrial and agriculture applications that give rise to ubiquitous environmental contamination. OTC are immunotoxic, but most studies have been performed in rodents and almost exclusively focused on T cell immunity. Humans can be exposed to OTC by inhalation, absorption, and consumption of contaminated food and water. To analyse the effects of OTC in human immune tissue, we isolated B cells from tonsils and exposed them to five OTC at various concentrations, during in vitro culture. Non-stimulated B cells were killed by 100 nM of all tested OTC after 8 h in vitro culture, under sub-optimal conditions, except TET. OTC also decreased the proliferation of tonsillar B lymphocytes stimulated with Staphylococcus aureus Cowan 1 (SAC) and IL-2, when present at 100 nM and higher concentrations. IgM secretion was reduced in stimulated cell cultures exposed to 100 nM dibutyltin chloride (DBT). Accordingly, increased phosphatidylserine exposure demonstrated that 100 nM TPT and DBT induced B cells to die by apoptosis. These data indicate that human B cells are diminished in their capacity to survive, proliferate and differentiate in the presence of OTC in vitro.

Immunotoxicity of environmentally relevant concentrations of butyltins on human natural killer cells in vitro

The widespread environmental contamination, bio-accumulation, and toxic effects of butyltins (BTs) in wildlife is well documented, but the role of BTs in debilitating human immune function mediated through natural killer (NK) lymphocytes (a primary immune defense against tumor and virally infected cells) has not been described. In this study, we assessed the effects of in vitro exposure to a range of concentrations (encompassing environmentally relevant concentrations) of MBT, DBT, and TBT on human natural killer lymphocytes obtained from adult male and female donors. TBT inhibited the tumor-killing capacity of NK cells when the NK cells were pretreated in vitro at 200 nM for as little as 1 h. Inhibition of NK cytotoxic function ranged from 40 to greater than 90%. The toxic potential of butyltins followed the order of TBT > DBT > MBT. Conjugation assays revealed that after a 24-h exposure to TBT, there was about a 50% decrease in NK cell binding to tumor cells, indicating alteration of the NK cell receptors for tumor cells. Analysis of whole-blood samples for BTs revealed the presence of detectable concentrations of MBT, DBT, and TBT in all of the donors, indicating possible exposure of NK cells to BTs in the blood. The results of this study provide evidence that butyltin compounds significantly inhibit NK cell function and possible NK cell-mediated immunotoxic potential in humans.

In vitro exposure effects of cyclosporin A and bis(tri-n-butyltin)oxide on lymphocyte proliferation, cytokine (receptor) mRNA expression, and cell surface marker expression in rat thymocytes and splenocytes

Rat thymocytes and splenocytes were exposed in vitro to the model compounds Cyclosporin A (CsA), an immunosuppressive drug, and bis(tri-n-butyltin)oxide (TBTO), an immunotoxic environmental contaminant. The lymphocyte transformation test (LTT), cytokine (receptor) mRNA expression (RT-PCR and dot blot hybridisation), and flow cytometry were evaluated as assays for in vitro immunotoxicity, at dose levels that did not show effects on viability, this being the aim of the study. LTT and RT-PCR proved useful assays. Lymphocyte transformation was suppressed by both compounds, while IL-2 mRNA expression was suppressed by CsA but not by TBTO, and both compounds suppressed IL-2R mRNA expression in splenocytes but not in thymocytes. Furthermore, the data obtained suggest that antiproliferative effects may be more relevant than apoptosis induction for TBTO induced thymus atrophy.

In vitro inhibition of hepatic cytochrome P450 and enzyme activity by butyltin compounds in marine mammals

The present study attempted to examine the in-vitro inhibition of hepatic microsomal P450 content and activity by butyltins in marine mammals and discussed on their possible effects in animals in the wild. Decreases in P450 content and the activities of ethoxyresorufin O-deethylase (EROD, catalyzed by CYPIA subfamily) and penthoxyresorufin O-depentylase (PROD, catalyzed by CYP2B subfamily) by tributyltin (TBT) were observed in in-vitro experiments using hepatic microsomes of a pinniped and a cetacean. Among P450 family, EROD activity is more sensitive to TBT than P450 content and PROD activity, indicating a specific mode of action of TBT on different P450 forms. On the other hand, dibutyltin and monobutyltin have no inhibitory effect on EROD activity at concentrations less than 0.5 mM, indicating that the inhibition of enzyme activity in hepatic microsome of marine mammal is mainly by TBT. TBT concentrations that affect P450 contents and activities are above 10 times higher than the values found in the liver of various marine mammals.

Triphenyltin acetate toxicity: a biochemical and ultrastructural study on mouse thymocytes

1. Triphenyltin acetate (TPTA) has been shown to exert in vivo a selective toxic effect on the immune system. To assess in vitro possible alterations induced by TPTA exposure, primary cultures of mouse thymocytes were incubated up to 24 h with graded amounts (1-12 microM) of the organotin. 2. The cytotoxic activity has been evaluated with the MTT colorimetric assay, the neutral red (NR) assay and the lactic dehydrogenase (LDH) cellular release. Cell pellets were fixed with 2.5% glutaraldehyde, resin-embedded and ultrathin sections were observed through transmission electron microscopy. 3. After 2 h of incubation, dose-dependent increases of cytotoxicity were observed in thymocytes submitted to MTT and NR tests (up to 41.43% and 18.9%, respectively), while 22 h later this overt effect on cell viability was noticed merely in cells exposed to 12 microM TPTA. Dose-dependent increases of LDH leakage in the culture medium were observed all throughout the study. 4. Morphological investigations revealed features (chromatin condensation, cell membranes fragmentation and formation of membrane bound apoptotic bodies) suggestive of apoptosis. 5. This study indicates that TPTA is cytotoxic to mouse thymocytes: morphologically, the rising of apoptosis is likely to be recognized, as previously reported in different in vitro studies with other immunosuppressive agents as dioxin and corticosteroids.

Immunotoxic organotins as possible model compounds in studying apoptosis and thymocyte differentiation

In the mid-seventies it appeared that some organotin compounds selectively caused thymus atrophy. From that time onward efforts were made to reveal molecular and cellular mechanisms involved. In this review recent studies into organotin-sensitive stages and processes of thymocyte maturation are discussed. Together these studies resulted in the recognition of organotin compounds as possible model compounds in studying immature thymocyte differentiation and protein synthesis-independent apoptotic cell death of thymocytes.

Effect of tri-n-butyltin on intracellular Ca2+ concentration of rat cerebellar neurons

The effect of tri-n-butyltin on the intracellular Ca2+ concentration ([Ca2+]i) of cerebellar neurons dissociated from rats was examined using fluo-3 and a flow cytometer. Tri-n-butyltin at 100 nM or more (up to 1 microM) increased the [Ca2+]i in a dose-dependent manner. The effect of tri-n-butyltin on the [Ca2+]i was greatly reduced under external Ca(2+)-free ([Ca2+]o-free) conditions, suggesting its dependence on the presence of [Ca2+]o. Lower trialkyltins, such as triethyltin and trimethyltin at 1 microM, exerted little or no action on the [Ca2+]i. Therefore, the cytotoxic action of tri-n-butyltin may be different from those of lower trialkyltins.

The evaluation of data-derived safety factors for bis(tri-n-butyltin)oxide

In this report the evaluation of a safety factor is assessed, according to the decision tree suggested by Renwick (1991a,b), to determine a Tolerable Daily Intake (TDI) value for the environmental contaminant bis(tri-n-butyltin)oxide (TBTO). Based on available literature the nature of the most sensitive parameter of TBTO-toxicity was perceived to be on lymphoid organs and lymphoid function. Subsequently, safety factors were derived in relation to published data on inter-species and inter-individual differences in both kinetics and dynamics of TBTO. Lack of information on human data concerning the nature of toxicity as well as kinetics and dynamics of TBTO finally resulted in a safety factor of 100. A TDI of 5 or 0.25 mg/kg bw per day was assessed based on reductions of lymphoid organ weights (thymus) or lymphoid function (resistance to T. spiralis), respectively. In addition, based on available data in rodents on kinetics and dynamics of TBTO, it is suggested that a combined TDI value for both tri- and dibutyltin compounds might have to be considered.

Tributyltin increases cytosolic free Ca2+ concentration in thymocytes by mobilizing intracellular Ca2+, activating a Ca2+ entry pathway, and inhibiting Ca2+ efflux

The immunotoxic environmental pollutant tri-n-butyltin (TBT) kills thymocytes by apoptosis through a mechanism that requires an increase in intracellular Ca2+ concentration. The addition of TBT (EC50 = 2 microM) to fura-2-loaded rat thymocytes resulted in a rapid and sustained increase in the cytosolic free Ca2+ concentration ([Ca2+]i) to greater than 1 microM. In nominally Ca(2+)-free medium, TBT slightly but consistently increased thymocyte [Ca2+]i by about 0.11 microM. The subsequent restoration of CaCl2 to the medium resulted in a sustained overshoot in [Ca2+]i; similarly, the addition of MnCl2 produced a rapid decrease in the intracellular fura-2 fluorescence in thymocytes exposed to TBT. The rates of Ca2+ and Mn2+ entry stimulated by TBT were essentially identical to the rates stimulated by 2,5-di-(tert.-butyl)-1,4-benzohydroquinone (tBuBHQ), which has previously been shown to empty the agonist-sensitive endoplasmic reticular Ca2+ store and to stimulate subsequent Ca2+ influx by a capacitative mechanism. The addition of excess [ethylenebis(oxyethylenenitrilo)]tetraacetic acid to thymocytes produced a rapid return to basal [Ca2+]i after tBuBHQ treatment but a similar rapid return to basal [Ca2+]i was not observed after TBT treatment. In addition, TBT produced a marked inhibition of both Ca2+ efflux from the cells and the plasma membrane Ca(2+)-ATPase activity. Also, TBT treatment resulted in a rapid decrease in thymocyte ATP level. Taken together, our results show that TBT increases [Ca2+]i in thymocytes by the combination of intracellular Ca2+ mobilization, stimulation of Ca2+ entry, and inhibition of the Ca2+ efflux process. Furthermore, the ability of TBT to apparently mobilize the tBuBHQ-sensitive intracellular Ca2+ store followed by Ca2+ and Mn2+ entry suggests that the TBT-induced [Ca2+]i increase involves a capacitative type of Ca2+ entry.

Modification of voltage-dependent Na+ current by triphenyltin, an environmental pollutant, in isolated mammalian brain neurons

In order to reveal the profile of neurotoxicity of triphenyltin on the mammalian central nervous system (CNS) through the modification of a voltage-dependent Na+ channel, the effects of triphenyltin on the kinetics of voltage-dependent Na+ current (INa) were examined in acutely dissociated pyramidal neurons of rat hippocampus. Triphenyltin at the concentration of 1.10(-6) M decreased both the time to peak and the half-decay time of the INa without affecting the current-voltage relationship. Triphenyltin moved the steady-state inactivation curve to a depolarizing direction. In the presence of triphenyltin, the reactivation of Na+ channel inactivated during the depolarization occurred quicker than that of the control at the pulse intervals of less than 10 ms. It can be suggested that triphenyltin potentially increases the cell excitability in mammalian CNS through the modification of the INa.

Immunotoxicity of bis(tri-n-butyltin) oxide in the rat

Previous studies in the rat have shown that bis(tri-n-butyltin) oxide (TBTO), used as a biocide, was immunotoxic at dose levels that did not affect other organs. In order to determine a no-effect level, weanling rats were treated for at least 28 consecutive days with TBTO at 0, 0.5, 2, 5, or 50 mg/kg of diet. Studies on clinical chemistry, hematology, pathology, and immune function, that is, plaque-forming cell (PFC) assay, delayed-type hypersensitivity (DTH) response, and the splenic clearance of Listeria monocytogenes, were performed at the end of treatment. No treatment-related effects were noted on clinical chemistry and hematology parameters and on PFC and DTH response, whereas thymic atrophy and impaired clearance of L. monocytogenes were noted only at a dietary concentration of 50 mg/kg. These results confirm the thymus as a target organ of TBTO immunotoxicity. Under the conditions of these experiments the dietary concentration of 5 mg/kg, equivalent to a dose of 0.5 mg/kg body weight, represents a no observed effect level (NOEL) for immunotoxicity in the Sprague-Dawley rat.

Bis(tri-n-butyltin)oxide induces programmed cell death (apoptosis) in immature rat thymocytes

In order to characterise the mechanism of cytotoxicity of the immunotoxic organotin compound bis(tri-n-butyltin)oxide (TBTO) to lymphoid cells, isolated thymocytes from immature rats were exposed to TBTO (0.1-5 microM) for up to 6 h. At lower TBTO concentrations (0.1 and 1 microM) vital staining showed that only marginal loss of viability occurred, although morphological studies demonstrated increased numbers of cells with abnormal features indicative of programmed cell death (apoptosis). These changes included nuclear chromatin condensation (which was associated with increased DNA fragmentation), cytoplasmic contraction and formation of membrane bound apoptotic bodies. When visualised by agarose gel electrophoresis, genomic DNA appeared as a series of fragments with a repeat multiple of 180-200 base pairs. Comparable morphological changes and cleavage of DNA into oligonucleosomal fragments were evident in thymocytes incubated with 10 microM methyl prednisolone hemisuccinate (MPS); a glucocorticoid hormone known to induce programmed cell death in thymocytes. Marked cytotoxicity associated with degenerative changes indicative of necrosis was observed in thymocytes incubated with 5 microM TBTO. These findings indicate that, at levels which are not overtly cytotoxic, TBTO is capable of inducing programmed cell death in rat thymocytes. This suggests a possible mechanism for the T-cell immunodeficiency previously reported for TBTO in vivo.

Occupational triphenyltin acetate poisoning: a case report

A case of triphenyltin acetate (TPTA) poisoning is described. The patient, who had been exposed mainly to cutaneous absorption, showed acute stages of an urticarial eruption, signs of hepatic injury, slight glucose intolerance, and electroencephalographic abnormalities. Concomitant with the highest concentrations of tin in plasma and the peak of tin excretion in urine, neutrophils did not show the normal increase in actin polymerisation after stimulation with a chemotactic peptide (100 nM fMLP). The peak of urinary excretion of tin occurred between the fifth and the sixth day after poisoning; subsequently, the rate of excretion became slow, suggesting biphasic kinetics with the possibility of a cumulative trend.

Organotin compounds induce aneuploidy in human peripheral lymphocytes in vitro

In vitro exposure of PHA-stimulated human lymphocytes to organotin compounds resulted in statistically significant increases in the frequencies of hyperdiploid cells. When taken together with our previous study demonstrating spindle inhibiting effects of the same organotin compounds by an indirect method (Jensen et al., 1989), the present study strongly indicates that organotin compounds are able to induce aneuploidy, probably by affecting spindle function.

Tributyltin stimulates apoptosis in rat thymocytes

Treatment of rat thymocytes with micromolar concentrations of tributyltin caused a rapid increase in the cytosolic free Ca2+ concentration that was inhibited by Ni2+, which blocks Ca2+ influx through membrane channels. The elevation of cytosolic Ca2+ was associated with extensive DNA fragmentation, which was prevented by pretreatment of the cells with either of the intracellular Ca2+ chelators quin-2 or 1,2-bis(2-amino-phenoxy)ethane-N',N',N',N',-tetraacetic acid. Loss of thymocyte viability, which followed DNA fragmentation, was also prevented by the two Ca2+ chelators or by removing extracellular Ca2+ with ethylene glycol bis(beta-aminoethyl ether)N,N'-tetraacetic acid. The pattern of DNA fragmentation was characteristic of that produced by agents which activate a Ca2(+)- and Mg2(+)-dependent endogenous endonuclease during apoptosis or programmed cell death. Additional studies showed that other organotin compounds, including trimethyltin, triphenyltin, and dibutyltin had minimal effects on cytosolic Ca2+, DNA fragmentation, and cell viability. These results are consistent with a greater susceptibility of thymocytes to tributyltin and provide a basis for understanding its selective immunotoxicity in vivo.

Flow cytometric comparison of the effects of trialkyltins on the murine erythroleukemic cell

Cellular effects of exposure to tributyltin (TBT), triethyltin (TET), or trimethyltin (TMT) were investigated by flow cytometry employing the murine erythroleukemic cell (MELC) as a model cellular system. Cell viability was investigated by the carboxyfluorescein diacetate (CFDA) uptake/propidium iodide (PI) exclusion method: above a critical concentration (exposure for 4 h), which was specific for each of the trialkyltin compounds, the cell becomes permeable to PI, indicating loss of viability. Cellular CF fluorescence (derived from intracellular hydrolysis of CFDA) increased as a function of alkyltin concentration below the critical concentration and decreased as viability decreased above the critical concentration. Relative membrane potential, monitored with a cyanine dye (DiOC6), correlated with viability (PI exclusion), remaining essentially unaltered below the critical concentration and decreasing above it. At/above 1 microM TBT, 5 microM TET, or 100 microM TMT, the cell cycle was blocked in the G2/M phase. The 90 degrees light scatter (a measure of refractive index), axial light loss (a measure of volume), and fluorescein isothiocyanate (FITC) fluorescence (a measure of protein content) of nuclei isolated from trialkyltin-treated MELC by detergent treatment, increased as a function of organotin dose. Fluorescence and interference microscopy revealed increased quantities of residual cytoplasmic tags adherent to the nuclei as a function of organotin dose, apparently resulting from increased cytoplasmic resistance to detergent-mediated solubilization. The effects of the trialkyltins correlated with their lipophilicity (octanol/water coefficient). These data support the hypothesis that fixation (protein denaturation, cross-linking, etc.) is an important mode of organotin cytotoxicity.

Toxicity of dibutyltin, tributyltin and other organotin compounds to humans and to experimental animals

Alkyltin compounds are used as stabilizers and antifouling agents. Food chain accumulation and bioconcentration have been demonstrated in crabs, oysters and salmon exposed to tributyltin oxide. In mammalian species, tributyltin compounds may be metabolized to dibutyltin derivatives and related metabolites. Di- and tributyltins appear to be less potent neurotoxicants than trimethyltins and triethyltins. Dibutyltins and tributyltins produced bile duct damage in rats, mice and hamsters. Tributyltin oxide and dibutyltin and dioctyltin compounds are potent thymolytic and immunotoxic agents in rats. Tributyltin oxide at 5 ppm in the rat diet produced immunotoxicity in a 2-year feeding study, and at 50 ppm increased the incidence of tumors of endocrine origin. In preliminary reports, 5 ppm tributyltin produced no detectable increase in tumor incidence, and 0.5 ppm produced no detectable immunotoxicity in long-term studies. Tributyltin oxide and dibutyltin acetate did not appear to be mutagenic in a large battery of mutagenicity assays but produced base-pair substitutions in one of the bacterial strains tested. Tributyltin oxide produced mutations in Chinese hamster ovary cells, increased the incidence of micronuclei in the erythrocytes of exposed male BALB/c mice, and was highly embryotoxic in vitro. Embryotoxic and teratogenic effects in mice exposed to tributyltin oxide in vivo may have been due either to direct tributyltin oxide action or responses secondary to maternal toxicity. More information is needed to determine the applicability to human risk assessments of the immunotoxicity data derived from rat studies and to establish a definitive tolerable daily intake for tributyltin oxide.

Effects of tributyltin on biomembranes: alteration of flow cytometric parameters and inhibition of Na+, K+-ATPase two-dimensional crystallization

Carboxyfluorescein diacetate (CFDA) is a lipophilic nonfluorescent molecule that readily crosses the cell membrane. In the cytoplasm, it is hydrolyzed by nonspecific esterases to carboxyfluorescein (CF), a negatively charged fluorescent molecule, which is retained incompletely by cells with an intact plasma membrane. Exposure (4 hr) of the murine erythroleukemic cell (MELC) to micromolar quantities (0.1 to 5.0 microM) of tributyltin (TBT) results in increased cellular CF fluorescence. The increase occurs within a range below a critical value of the product (CPV) of the concentration (C) of TBT X duration (T) of exposure to TBT. Fluorescence increase is a sensitive indicator of the interaction of TBT with the cell: it is observed following exposure to 0.1 microM TBT for 4 hr at 37 degrees C. In the range above the CPV, cellular CF fluorescence is reduced apparently resulting from perturbation of membrane structure. For example, exposure of MELC to 2.5 microM TBT for 4 hr at 37 degrees C produces resistance to detergent-mediated cytolysis and inhibition of vanadate-mediated two-dimensional crystallization of Na+, K+-ATPase molecules in porcine renal microsomal membrane preparations, a process requiring molecular mobility within the membrane. Taken together, the increased cellular CF fluorescence and resistance of the MELC to cytolysis along with the inhibition of Na+, K+-ATPase crystallization in the microsomal membrane preparations suggest fixation (protein denaturation, cross-linking, etc.) at the level of the plasma membrane as a mode of toxic action of TBT.

Flow cytometric analysis of the cellular toxicity of tributyltin

Flow cytometric and light/fluorescence microscopic analyses indicate that tributyltin (TBT) alters the plasma membrane/cytoplasm complex of the murine erythroleukemic cell (MELC) in a dose-dependent and time-dependent manner. The flow cytometric parameter axial light loss, a measure of cell volume, decreases in cells exposed to 5 microM TBT relative to control cells or cells exposed to 50 microM TBT. The flow cytometric parameter 90 degrees light scatter, a function of refractive index and a measure of protein content, increases as a function of TBT concentration above 0.5 microM. Following exposure to TBT concentrations greater than 0.5 microM, but less than 50 microM, DNA distribution across the cell cycle cannot be resolved adequately by flow cytometry. Also, the cells become resistant to solubilization of the cell membrane/cytoplasm complex by nonionic detergents. Relative to logarithmically growing cells, MELC in the stationary phase of the growth cycle and butyric acid-differentiated cells exhibit decreased plasma membrane permeability resulting in increased carboxyfluorescein (CF) retention derived from the intracellular hydrolysis of carboxyfluorescein diacetate (CFDA). Similarly, cells exposed to TBT concentrations below 50 microM exhibit increased cellular CF retention. Viability in terms of CFDA hydrolysis/CF retention and propidium iodide (PI) exclusion is not decreased by exposure to TBT concentrations below 1 microM. At doses between 5 and 50 microM, however, cells exhibit both CF and PI fluorescence simultaneously and are programmed for death. At TBT concentrations greater than 1.0 microM, MELC plasma membrane potential, measured with the cyanine dye, 3,3'-dihexyloxacarbocyanine iodide (DiOC6) decreases at the same time that the uptake of PI is observed. In conjunction with other data, the concentration-dependent increase in CF fluorescence, resistance to detergent-mediated solubilization of the plasma membrane/cytoplasm complex, and increase in 90 degrees light scatter suggest fixation (protein denaturation, cross-linking, etc.) as a mechanism of the toxic action of TBT.

Differential effects of tri-n-butyltin chloride on macromolecular synthesis and ATP levels of rat thymocyte subpopulations obtained by centrifugal elutriation

Using centrifugal elutration, rat thymocytes were separated into three fractions by size. Fraction 1 (F1) consisted of a large population (greater than 88% of all cells) of small, nonproliferating thymocytes. Fraction 2 (F2; 7% of all cells) was enriched in medium-sized thymocytes and showed an increased macromolecular synthesis. In the small fraction 3 (F3; less than 5% of all cells), large thymocytes, monocytes, granulocytes and cells in mitosis were concentrated. F3 demonstrated the highest proliferative activity. Fractions were characterized by size, cell morphology, DNA, RNA and protein synthesis and steady state ATP levels. The effects of the inhibitor of oxidative phosphorylation, tri-n-butyltin chloride (TBTC) on ATP levels and the incorporation of DNA, RNA and protein precursors were investigated for each thymocyte fraction. Although ATP levels increased with increasing thymocyte volume, TBTC reduced ATP levels in each subfraction proportionally. The incorporation of thymidine and leucine was markedly reduced in all fractions by TBTC, but not to the same extend. Dependent on the TBTC concentration, the rapidly proliferating cells of F2 and F3 were less affected compared to the noncycling cells of F1. The incorporation of uridine in the unfractionated cells and in F2 and F3 was also decreased by TBTC. However, at concentrations between 0.1 and 1 microM, TBTC stimulated uridine incorporation in the small thymocytes of F1. Therefore, fractionation of thymocyte suspensions was necessary to detect differential effects of TBTC on subpopulations. Centrifugal elutriation was found to be a useful tool with which to obtain subfractions of isolated rat thymocytes.

Dibutyltin and tributyltin compounds induce thymus atrophy in rats due to a selective action on thymic lymphoblasts

Di-n-butyltin dichloride (DBTC) or tri-n-butyltin chloride (TBTC) given in the diets of rats have previously been shown to cause atrophy of the thymus and subsequently suppression of the T-cell-dependent immune responses. To study the mechanism of the immunotoxic effects, the dose-effect relationships and the kinetics of the thymus atrophy caused by DBTC and TBTC were investigated in detail. A single oral dose of DBTC or TBTC to rats induced a dose-related reduction of relative thymus weight, which was maximal 4 days after intubation. The log dose-effect relationships for both compounds were linear and ran parallel over a dose range of 5-60 mg/kg. Dose levels calculated to cause 50% reduction of relative thymus weight were 18 mg DBTC and 29 mg TBTC per kg body wt. A single oral dose of mono-n-butyltin trichloride (MBTC), however, did not cause thymus atrophy at dose levels up to 180 mg/kg. The kinetics of the dibutyltin- and tributyltin-induced thymus atrophy in rats were investigated by measuring thymus weight, total thymic cell count, number of small, intermediate and large cells and the incorporation of DNA, RNA and protein precursors into isolated thymocytes during a period of 9 days after a single oral dose. DBTC and TBTC caused atrophy of the thymus due to a selective reduction in the number of rapidly proliferating lymphoblasts in the first 2 days after dosing. As a consequence the large pool of small lymphocytes declined in the following 2 days. On the fourth day, when atrophy was most pronounced, the frequency of the lymphoblasts increased above the controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Biological activity of organotin compounds--an overview

As a consequence of the rapid expansion of the uses and applications of the organotin compounds, the concern about their environmental and health effects is increasing. The main subject of this overview is the current understanding of the mammalian toxicity of the organotin compounds. Four different types of target organ toxicity, namely neurotoxicity, hepatoxicity, immunotoxicity, and cutaneous toxicity, are discussed in more detail. The effects of the organotin compounds on the mitochondrial and cellular level are summarized and discussed in relation to the mode of action of these compounds on the central nervous system, the liver and bile duct, the immune system, and the skin.

Effects of various inhibitors of oxidative phosphorylation on energy metabolism, macromolecular synthesis and cyclic AMP production in isolated rat thymocytes. A regulating role for the cellular energy state in macromolecular synthesis and cyclic AMP production

Inhibitors of oxidative phosphorylation such as several triorganotin compounds, oligomycin, 2,4-dinitrophenol and carbonylcyanide p-trifluoromethoxyphenylhydrazone suppress energy metabolism of isolated rat thymocytes as indicated by a reduction of ATP levels, an increase in glucose consumption and by a marked accumulation of lactate. Also these compounds effectively inhibit the incorporation of DNA, RNA and protein precursors into acid-precipitable material of thymocytes. Moreover, the prostaglandin E1-induced elevation of cAMP is markedly reduced by these inhibitors. A correlation is observed between the effects on energy metabolism, macromolecular synthesis and cAMP production, since from a series of trialkyltin chlorides, tri-n-propyltin, tri-n-butyltin and tri-n-hexyltin are very effective inhibitors of these functions, while trimethyltin and tri-n-octyltin affect neither of them; other inhibitors of oxidative phosphorylation, each of them with quite different mechanisms of action, also inhibit macromolecular synthesis and cAMP production. The finding that a rise in intracellular ATP concentrations leads to a reversion of the tri-n-butyltin-induced inhibition of cAMP production and uridine incorporation, indicates a regulating role for the cellular energy state in these aspects of cellular function.