Use of the local lymph node assay in assessment of immune function

The murine local lymph node assay (LLNA) was originally developed as a predictive test method for the identification of chemicals with sensitizing potential. In this study we demonstrated that an adapted LLNA can also be used as an immune function assay by studying the effects of orally administered immunomodulating compounds on the T-cell-dependent immune response induced by the contact sensitizer 2,4-dinitrochlorobenzene (DNCB). C57Bl/6 mice were treated with the immunotoxic compounds cyclosporin A (CsA), bis(tri-n-butyltin)oxide (TBTO) or benzo[a]pyrene, (B[a]P). Subsequently, cell proliferation and interferon-gamma (IFN-gamma) and interleukin (IL)-4 release were determined in the auricular lymph nodes (LNs) after DNCB application on both ears. Immunosuppression induced by CsA, TBTO and B[a]P was clearly detectable in this application of the LLNA. Cytokine release measurements proved valuable to confirm the results of the cell proliferation assay and to obtain an indication of the effect on Th1/Th2 balance. We believe to have demonstrated the applicability of an adapted LLNA as an immune function assay in the mouse.

New insights into the mechanism of imposex induction in the dogwhelk Nucella lapillus

In an attempt to clarify the mechanism(s) of tributyltin-mediated imposex induction in females of the neogastropod Nucella lapillus, dogwhelks collected in an almost imposex free population were exposed to several treatments for a 3 month-period, and the effects on imposex induction and testosterone/estradiol levels were evaluated. As a positive control, tributyltin (50 ng TBT Sn/L) clearly induced imposex and led to a significant increase in the severity of the phenomenon. In contrast, although a selective P450 aromatase inhibitor (formestane at 0.3 mg/L) was capable of imposex induction, it failed to increase its severity. A vertebrate androgen receptor (AR) antagonist (cyproterone acetate at 1.25 mg/L) in combination with TBT completely blocked the imposex induction capacity of TBT. On the other hand, an estrogen receptor antagonist (tamoxifen at 0.3 mg/L) rendered no effect. The determination of steroid levels in female specimens revealed that TBT induces an elevation of free testosterone (but not the total amount, free+esterified), while the co-administration of the anti-androgen and TBT was able to rescue the increase of free testosterone levels. Despite a minor decrease in the amount of testosterone-fatty acid esters in the TBT group, significant differences in esterified testosterone were not found among treatments. On the contrary, free estradiol levels were elevated in the TBT, anti-androgens and TBT plus anti-androgens groups. These results indicate that free estradiol biosynthesis in TBT-exposed females does not seem to be affected. Overall, our results demonstrate that a selective aromatase inhibitor can induce imposex in N. lapillus but not to a similar extent of TBT, which may suggest the involvement of other mechanism in imposex induction, besides aromatase inhibition. Additionally, the study points to the involvement of AR receptors in imposex induction.

On membrane motor activity and chloride flux in the outer hair cell: lessons learned from the environmental toxin tributyltin

The outer hair cell (OHC) underlies mammalian cochlea amplification, and its lateral membrane motor, prestin, which drives the cell's mechanical activity, is modulated by intracellular chloride ions. We have previously described a native nonselective conductance (G(metL)) that influences OHC motor activity via Cl flux across the lateral membrane. Here we further investigate this conductance and use the environmental toxin tributyltin (TBT) to better understand Cl-prestin interactions. Capitalizing on measures of prestin-derived nonlinear capacitance to gauge Cl flux across the lateral membrane, we show that the Cl ionophore TBT, which affects neither the motor nor G(metL) directly, is capable of augmenting the native flux of Cl in OHCs. These observations were confirmed using the chloride-sensitive dye MQAE. Furthermore, the compound's potent ability, at nanomolar concentrations, to equilibrate intra- and extracellular Cl concentrations is shown to surpass the effectiveness of G(metL) in promoting Cl flux, and secure a quantitative analysis of Cl-prestin interactions in intact OHCs. Using malate as an anion replacement, we quantify chloride effects on the nonlinear charge density and operating voltage range of prestin. Our data additionally suggest that ototoxic effects of organotins can derive from their disruption of OHC Cl homeostasis, ultimately interfering with anionic modulation of the mammalian cochlear amplifier. Notably, this observation identifies a new environmental threat for marine mammals by TBT, which is known to accumulate in the food chain.

Characteristics of 3,5,3'-triiodothyronine (T3)-uptake system of tadpole red blood cells: effect of endocrine-disrupting chemicals on cellular T3 response

We characterized the 3,5,3'-L-triiodothyronine (T3)- uptake system on the plasma membrane of Rana catesbeiana tadpole red blood cells (RBCs) in the presence of a variety of inhibitors and potentially competing amino acids. Saturable [125I]T3 uptake was inhibited by phloretin, monodansylcadaverine, bromosulfophthalein, sodium taurocholate and tryptophan. Saturable uptake obeyed simple Michaelis-Menten kinetics with an apparent Km of 110 nM and a Vmax of 2.5 pmol/min per 10(6) cells at 23 degrees C. These results suggested that a large proportion of T3 transported into RBCs was mediated by the aromatic amino acid transporter (System T)-linked transporter. To investigate the effect of endocrine-disrupting chemicals (EDCs) on [125I]T3 uptake, RBCs were incubated with [125I]T3 in the presence of each chemical. Among the test chemicals, di-n-butyl phthalate, n-butylbenzyl phthalate and the miticide, dicofol, were the most powerful inhibitors of [125I]T3 uptake, with an IC50 of 2.2 microM, which was one order of magnitude greater than that for T3 (IC50, 0.14 microM), and diethylstilbestrol and ethinylestradiol were modest inhibitors. Tributyltin accelerated saturable initial [125I]T3 uptake by 2-fold at 3.2 microM. When RBCs were cultured with 10 nM T3 at 25 degrees C for 2 days in the presence of monodansylcadaverine, ethinylestradiol, ioxynil or dicofol at the defined concentrations, these compounds inhibited significantly the induction of the thyroid hormone receptor alpha gene by T3. However, not all chemicals competed with T3 binding to the receptor at the same concentrations. Our results raise the possibility that the T3-uptake system on the plasma membrane of the tadpole RBCs could be a candidate target site for some EDCs and can modulate cellular T3 response.

Xenobiotic substances such as PCB mixtures (Aroclor 1254) and TBT can influence swimming behavior and biotransformation activity (GST) of carp (Cyprinus carpio)

Different groups of carp were treated with polychlorinated biphenyl (PCB) or tributyltin (TBT), and possible effects of the chemicals on the swimming behavior of the carp were examined using the BehavioQuant system. By evaluating quantitative behavioral parameters of the animals, it became evident that exposure to high concentrations of chemicals (organotin, 7 microg L(-1), or polychlorinated biphenyl, 22 microg L(-1)) severely affected the carp, causing a significant change in their swimming speed. TBT stress led to a rapid decrease in mean swimming activity. A decrease in the preferred swimming depth was observed in TBT- and PCB-exposed fish. Animals exposed to PCB reduced their mean daily activity and increased their mean swimming speed in the nighttime during the second week of exposure. Therefore, our findings imply that the fish were adapted to cope with the chemicals after the second week of exposure. Furthermore, our results showed that low concentrations (TBT, 0.3 and 2 microg L(-1), or PCB, 14 microg L(-1)) did not significantly alter any quantified parameters of swimming behavior. In addition, the direct effects of chemicals on enzyme activity (GST) were determined. Measurement of soluble glutathione-S-transferase activity of fish liver or gills showed a significant elevation after exposure to PCB (0.1 or 22 microg L(-1)) or TBT (0.8 or 7 microg L(-1)). We had to conclude that the two different end points tested generally are useful as biomarkers of exposure and for investigations of energy resources in organisms under the influence of toxic stress.

Inhibition of ossification in vivo and differentiation of osteoblasts in vitro by tributyltin

Tributyltin is ubiquitous in the environment and an endocrine disruptor for many wildlife species. However, minimal information is available regarding the effect of this chemical on bone formation. When tributyltin chloride (TBT) (1mg/kg body weight) was administered subcutaneously to pregnant mice at 10, 12, and 14 days post coitus (dpc), fetuses at 17.5 days post coitus revealed the inhibition of calcification of supraoccipital bone. In contrast, 1mg/kg body weight monobutyltin trichloride (MBT) did not affect the fetal skeleton. Therefore, we examined the effects of TBT and its metabolites (dibutyltin dichloride, DBT, and MBT) on bone metabolism using rat calvarial osteoblast-like cells (ROB cells). The viability of ROB cells was not affected by the exposure of the cells to 10(-10) to 10(-7)M TBT. However, TBT reduced the activity of alkaline phosphatase (ALPase) and the rate of deposition of calcium of ROB cells. In addition, the expression levels of mRNA for ALPase and osteocalcin, which are markers of osteoblastic differentiation, were depressed by the treatment with TBT. TBT inhibited ALPase activity and the deposition of calcium to a greater extent than did DBT. MBT had no effect on the osteoblast differentiation of ROB cells. Tributyltin is known to inhibit the activity of aromatase. However, the aromatase inhibitor aminoglutethimide did not reproduce the inhibitory effects of TBT on osteoblast differentiation. Our findings indicate that TBT might have critical effects on the formation of bone both in vivo and in vitro although its action mechanism is not clarified.

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.

Environmental pollutant tributyltin promotes Th2 polarization and exacerbates airway inflammation

It has been shown that a relatively high dose of tributyltin (TBT), which is recognized as a particularly notable environmental pollutant, exerts immunotoxic effects such as thymic atrophy via induction of T cell apoptosis. However, the effect of low doses of TBT on the immune responses remains unknown. Here we show that environmentally relevant doses of TBT promoted strong Th2 polarization via suppression and augmentation of Th1 and Th2 development, respectively, from naive CD4(+) T cells primed with anti-CD3 and splenic antigen-presenting cells (APC). TBT-induced Th2 polarization was indirect, working through APC via suppression of IL-12 production by macrophages/DC and the augmentation of IL-10 production by B cells. Th2 polarization was also induced in mice treated with TBT and immunized with OVA or infected with Nippostrongylus brasiliensis. Furthermore, airway inflammation in mice sensitized and challenged with OVA was exacerbated by the administration of TBT with concomitant augmentation of Th2-type immunity. Our results highlight the fact that an important environmental pollutant TBT may present significant risk for the induction of allergic diseases via promotion of Th2 polarization.

Inhibition by tributyltin of herring skeletal muscle lactate dehydrogenase activity

The activity of herring (Clupea harengus) skeletal muscle lactate dehydrogenase (EC 1.1.1.27) LDH-A4 isoenzyme was examined in the presence of tributyltin chloride (TBT). This paper reports the in vitro inhibition of LDH activity with increasing concentration of TBT. Bovine serum albumin (BSA) added to the LDH-A4 isoenzyme prior to the addition of TBT was able to protect enzyme activity against inhibition by this toxicant. The observed protection of LDH-A4 activity increased with increasing BSA concentration in the incubation medium. The results suggest that the presence of BSA could protect LDH activity from direct binding of TBT to LDH.

Effects of perinatal simultaneous exposure to tributyltin (TBT) and p,p'-DDE [1,1-dichloro-2,2-bis(p-chlorophenyl) ethylene) on male offspring of Wistar rats

p,p'-DDE [1,1-dichloro-2,2-bis(p-chlorophenyl) ethylene; DDE] and tributyltin (TBT) are ubiquitous in the environment and in Japan were shown to bioaccumulate in marine products. Thus these chemicals serve as a source of contaminant in the mammalian food chain. Fetuses and neonates through maternal ingestion may be exposed to DDE and TBT. Therefore, the effects of concurrent exposure to DDE and TBT were investigated in male Wistar rat offspring of dams ingesting these two contaminants. In this study, TBT suppressed the growth and delayed eye opening. However, both growth retardation and delayed eye opening produced by TBT failed to occur in the presence of DDE. Unexpectedly, the prostate weight of male rat offspring was significantly reduced with the administration of TBT but restored in the presence of DDE. These results indicate that TBT and DDE affected the development of male rat offspring following maternal exposure, and simultaneous administration of DDE prevented some of the observed effects of TBT, especially of an antagonistic nature, through a mechanism, still to be determined.

Effects of tributyltin on barrier functions in human intestinal Caco-2 cells

The effect of tributyltin (TBT) on human intestinal epithelial cell functions was investigated by using human intestinal Caco-2 cell monolayers. We paid particular attention to the effect of TBT on two barrier functions: the tight junction as a physical barrier and MDR1/P-glycoprotein as a biological barrier. A loss of monolayer integrity was apparent from the TBT treatment and the paracellular permeability was increased by TBT. On the other hand, the activity of P-glycoprotein, which was examined by measuring the accumulation of Rhodamine-123 and daunomycin, was increased by prolonged TBT treatment in a concentration-dependent manner (1-100 nM). Furthermore, it was clarified by Western and Northern blots that this increase was accompanied by the increased expression of MDR1 mRNA and protein. The activation of a multidrug resistance transporter P-glycoprotein by TBT would cause a disorder of the human intestines by changing the drug pharmacokinetics.

TbtABM, a multidrug efflux pump associated with tributyltin resistance inPseudomonas stutzeri

Tributyltin (TBT) is a toxic agent used in marine antifouling paints. Among the bacterial flora of a polluted harbor, TBT-resistant strains of Pseudomonas stutzeri have been isolated. In the strain 5MP1 (TBT minimum inhibitory concentration (MIC) > or =1000 mg l(-1)), TBT resistance was found to be associated with the presence of the operon tbtABM, homologous to the resistance-nodulation-cell division (RND) efflux pump family, as demonstrated by cloning in Escherichia coli. TbtABM exhibited the greatest homology (60.9-84.9%) with the TtgDEF and SrpABC systems, both involved in aromatic compound tolerance in P. putida. TbtABM conferred multidrug resistance (MDR) including to n-hexane, nalidixic acid, chloramphenicol, and sulfamethoxazole (antibiotic MICsx4 for the E. coli host strain carrying the operon). By polymerase chain reaction amplification and hybridization experiments, the presence of tbtABM was detected in the TBT-sensitive P. stutzeri 3MP1 (TBT MIC 25 mg l(-1)). However, the latter strain did not seem to express TbtABM. This is the first description of a MDR efflux pump in P. stutzeri, and of a new kind of substrate, TBT, for the RND family of transporters.

Seasonal variation of antifouling activities of marine algae from the Brittany coast (France)

The antifouling activity of extracts (aqueous, ethanol, and dichloromethane) of 9 marine macroalgae against bacteria, fungi, diatoms, macroalgal spores, mussel phenoloxidase activity, and barnacle cypris larvae has been investigated in relation to season in bimonthly samples from the Bay of Concarneau (France). Of the extracts tested, 48.2% were active against at least one of the fouling organisms, and of these extracts, 31.2% were seasonally active with a peak of activity in summer corresponding to maximal values for water temperature, light intensity, and fouling pressure, and 17% were active throughout the year. This seasonal activity may be adaptive as it coincides with maximal fouling pressure in the Bay of Concarneau. Dichloromethane extracts of Rhodophyceae were the most active in the antifouling assays.

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.

Effects of 17beta-estradiol, bisphenol A and tributyltin chloride on germ cells of Caenorhabditis elegans

Effects of a one-generation exposure to a natural estrogen, 17beta-estradiol (E2), and environmental pollutants such as bisphenol A (BPA) and tributyltin chloride (TBTCL) on the number of germ cells were investigated in the hermaphrodite Caenorhabditis elegans. The eggs of gravid adult worms isolated by alkaline hypochlorite treatment were seeded on a test chemical-containing NGM (nematode growth medium) agar plate without cholesterol. After incubation for 6 days at 16 degrees C, the germ cells of adult worms were stained with 4', 6-diamino-2-phenylindole dihydrochloride (DAPI). The staining procedure was completed within one hour and the stained germ cells were counted under a fluorescence microscope without dissection. The number of germ cells in the worms treated with E2 (10(-10)-10(-6) M) and BPA (10(-9)-10 (-5) M) was significantly increased. Maximal increases were observed at 10(-8) M E2 (156 +/- 15.3% of control) and 10(-5) M BPA (168 +/- 20.0 % of control). TBTCL (10(-9)-10(-6) M) significantly decreased the number of germ cells. The minimal decrease was observed at 10(-6) M TBTCL (30.2 +/- 3.51% of control). These results indicate that changes in the number of germ cells are a sensitive indicator of the effects of chemicals on the reproductive system. Since the method described in this paper is a novel, simple, time- and money-saving bioassay, C. elegans is an excellent model with which to determine the reproductive toxicity of chemicals including environmental pollutants.

Inhibition of rat testis microsomal 3beta-hydroxysteroid dehydrogenase activity by tributyltin

In this study, we have examined the effects of a range of organotin compounds (mono-, di-, tributyltin, mono-, di-, trioctyltin) on the activities of rat testis microsomal 3beta-hydroxysteroid dehydrogenase (3beta-HSD), 17-hydroxylase (17-OHase) and 17beta-hydroxysteroid dehydrogenase (17beta-HSD). 17-OHase activity was inhibited by more than 50% compared with the control rate by 59 microM tributyltin (TBT) but other organotin compounds showed no inhibition. 17beta-HSD activity was unaffected by all organotins tested. 3beta-HSD was inhibited by monooctyltin (81 microM) and by TBT at all concentrations tested in a dose-dependent manner, with almost complete loss of activity at TBT concentrations of 12 microM. The mechanism of inhibition of 3beta-HSD was investigated in kinetic analysis with 0-12 microM TBT. Three rat testis microsomal preparations were incubated with dehydroepiandrosterone as the steroid substrate ranging from 1 to 10,000 nM. Tributyltin was primarily a competitive inhibitor of 3beta-HSD activity, causing an increase in the value of the K(m(app)). However, the mechanism was not entirely competitive as while there was an increase in K(m(app)), a decrease in the V(max(app)) was also observed with increasing concentrations of TBT. Slope and intercept replots demonstrated that the K(i)((app)) from slope replots was around 2.7 microM whereas the K(i)((app)) value from intercept replots was around 30 microM. When compared with the K(m(app)) for 3beta-HSD of around 0.42 microM, TBT could be an effective inhibitor of this enzyme.

Effects of tributyltin chloride on the reproductive system in pubertal male rats

Detrimental effects of tributyltin (TBT) chloride on the reproductive system were investigated in pubertal male rats. Sixty Sprague-Dawley rats aged with 35 days were assigned to six different groups; negative control receiving vehicle, positive control receiving methyltestosterone (10 mg/kg B.W.), TBT chloride (5 mg/kg B.W., 10 mg/kg B.W., and 20 mg/kg B.W.), and a combination of TBT chloride (10 mg/kg B.W.) and flutamide (10 mg/kg B.W). The animals were treated with test compounds by oral gavage daily for 10 days and sacrificed on the next day of the final treatment. The treatment with TBT chloride at the doses of 10 and 20 mg/kg B.W. significantly decreased seminal vesicle weights, compared to the negative control. The combined treatment of TBT chloride and flutamide caused a significant decrease in accessory sex organ weights, compared to the control and TBT chloride treatments. The treatment with TBT chloride or in the combination with flutamide increased detached debris and sloughed cells in the tubules of epididymis and narrowed seminal vesicles. In addition, the combined treatment with TBT chloride and flutamide caused a noticeable increase in serum androgen level, compared to the negative control. These results suggest that TBT chloride exposed during pubertal period cause partial reproductive disorders in male rats.

Tributyltin (TBT) induces ultra-rapid caspase activation independent of apoptosome formation in human platelets

Activation of caspases has been demonstrated to be involved in thrombocytopenia and prolonged storage of platelet concentrates. Platelets represent enucleate cells that comprise all elements of the mitochondrial apoptosis pathway. However, no apoptotic stimuli capable of activating the endogenous caspase cascade have been identified so far. Using tributyltin (TBT) we could identify a compound that is capable of activating caspase-9 and -3 in platelets. Recent studies implicate that TBT induces apoptosis via the mitochondrial signaling pathway that is characterized by the formation of a high-molecular-weight complex (apoptosome) containing the adapter protein Apaf-1 and active caspase-9. Interestingly, addition of TBT induced the activation of caspase-9 in an ultra-rapid kinetic within the first 2 min. In addition, size exclusion chromatography revealed that TBT-mediated processing of caspase-9 occurs in the absence of the apoptosome. Thus, these data implicate that TBT induces the activation of caspase-9 by a mechanism not involving the formation of the apoptosome.

Steroidogenesis during in vitro maturation of bovine cumulus oocyte complexes and possible effects of tri-butyltin on granulosa cells

Steroids are known as important factors on the route of oocytes development and cumulus oocyte complexes (COC) as well as follicular granulosa cells (GC) are suggested to be themselves involved in steroidogenesis. The aim of this study was to characterize such a local sex steroidogenic system during in vitro maturation (IVM) of bovine COCs according to the production of estradiol (E), testosterone (T) and progesterone (P). The expression of two steroid-converting key-enzymes was measured in parallel by quantitative RT-PCR. Furthermore, possible effects of the environmental pollutant tri-butyltin (TBT) were elucidated for the first time on bovine COC and GC in vitro concerning that steroidogenic system. During IVM of bovine COCs concentrations of P increased continuously, corresponding with steady-state levels of 3-beta-hydroxy-steroid-dehydrogenase (HSD) transcripts. In contrast, E together with P450 aromatase mRNA (ARO) increased in the first hours of IVM but declining thereafter, whereas T reached almost balanced levels. However, TBT showed only slight effects during IVM of COC. In cultured GC, LH caused highest P- and E-production within 24h and treatment with 50pM TBT induced a significant decrease of E in contrast to 100pM TBT and the control. These results indicate, that (1) COCs were able to modulate their steroidogenic environment in vitro and that (2) TBT may possibly influence or disturb steroidogenesis in the cows reproductive tract shown here for GC.

Inhibitory effects of tributyltin on dopamine biosynthesis in rat PC12 cells

The inhibitory effects of tributyltin chloride (TBTC) on dopamine biosynthesis in PC12 cells were investigated. Twenty-four hour exposure to TBTC at 0.5 microM showed 32.9% inhibition of dopamine content: the IC(50) value of TBTC was 0.72 microM. Dopamine content decreased at 6 h and reached a minimal level at 24 h after exposure to TBTC at 0.5 microM. The decreased dopamine level was maintained for up to 48 h. Under these conditions, tyrosine hydroxylase (TH) activity was inhibited at 6 h following the treatment with TBTC and the activity was maintained at a reduced level for up to 48 h (20-35% inhibition at 0.5 microM of TBTC). TH mRNA level also started to decrease at about 6 h and reached a minimal level at 24 h after exposure of PC12 cells to TBTC. In addition, treatment with L-3,4-dihydroxyphenylalanine (L-DOPA) at 20-50 microM increased the intracellular dopamine content in PC12 cells and the increase of dopamine level by L-DOPA was significantly inhibited after exposure to TBTC at 0.5-2.0 microM for 24 h. These results indicate that TBTC decreases dopamine content by the inhibition of TH activity and TH mRNA level in PC12 cells. It is, therefore, proposed that TBTC may exacerbate the Parkinson's symptoms because of the inhibition of dopamine biosynthesis and dopamine increase induced by L-DOPA.

Effects of butyltins on human 5alpha-reductase type 1 and type 2 activity

Butyltins are widely used biocides and accumulate in the food chain. Tributyltin is an imposex-inducing endocrine disrupter in animals. Imposex is characterized by the development of additional male sex organs on females. In a previous study, we identified tributyltin as an inhibitor of human cytochrom P450 aromatase activity. The present work focuses on the impact of butyltins on human androgen metabolism. Activation of androgens is mediated by two human 5alpha-reductase isoenzymes. 5alpha-Reductase type 1 was completely inhibited by tributyltin chloride (IC50=19.9 microM) and dibutyltin dichloride (IC50=32.9 microM), whereas 5alpha-reductase type 2 was only inhibited by tributyltin chloride (IC50=10.8 microM). Both isoenzymes were not affected by tetrabutyltin or monobutyltin indicating that at least two butyl groups bound to the positively charged Sn are required for the interaction of butyltins with the enzymes. Tributyltin inhibited 5alpha-reductase type 1 competitively whereas an irreversible inhibition was evident for the type 2 isoenzyme. In contrast to the distinct effects on 5alpha-reductases, reductive brain 17beta-hydroxysteroid dehydrogenase activity was not inhibited by any butyltin. Insufficient activation of androgens is responsible for developmental disorders of the male reproductive system such as hypospadias. At pharmacologic levels butyltins might contribute to the onset of developmental disorders of the male reproductive system. At present, however, it is unknown whether these levels are reached after acute or chronic exposure to butyltins.

Cell culture of bivalves: tool for the study of the effects of environmental stressors

Spontaneous beating cells can be isolated from the heart of the oyster (Crassostrea gigas) and cultured for more than two months. They form adherent contractile networks in culture conditions. They show muscarinic and beta-adrenergic reactivity thus showing that they are functional cardio-myocytes: Acetylcholine induced a dose dependent decrease in spontaneous beating rate via an increase in potassium conductance, this effect being blocked by atropine. Epinephrine induced a dramatic increase in calcium conductance which was blocked by high concentrations of propranolol but not by sotalol and reversed by verapamil. Tributyltin and cadmium induced a dose and time dependent decrease mainly in inward ionic conductances, leading to a decrease or even a total suppression of the beating rate. Present study indicates that this model could be used as a sensitive test to study the effects of some marine pollutants at the cellular level in molluscs.

Trialkyltin compounds enhance human CG secretion and aromatase activity in human placental choriocarcinoma cells

Human choriocarcinoma cell lines have been used as placental models for the study of endocrine function, including aromatase (CYP19) activity and the secretion of human CG (hCG). In the present study, we investigated the effects of trialkyltin compounds, which are suspected endocrine disrupters, on aromatase activity and hCG secretion in human choriocarcinoma JAR, JEG-3, and BeWo cells. Protein synthesis as measured by (35)S-methionine incorporation in all cell lines was markedly decreased by treatment with both tributyltin (TBT) and triphenyltin (TPT) at concentrations above 3 x 10(-7) M, due to cytotoxicity. In JAR cells, (35)S-methionine uptake was decreased by 50% at 3 x 10(-7) M of TBT. At a TPT concentration of 1 x 10(-7) M, protein synthesis in JAR cells was not affected, whereas JEG-3 and BeWo cells demonstrated slightly decreases. In all cell lines, both TBT and TPT increased levels of hCG secretion and aromatase activity in a dose- and time-dependent fashion following exposure to nontoxic concentration ranges. In addition, these trialkyltin compounds enhanced 8-bromo-cAMP-induced hCG secretion and aromatase activity in JAR cells. TBT caused dose-related increases in steady-state mRNA levels of both hCGbeta and CYP19 in JAR cells following 24- or 48-h exposure to nontoxic concentrations of TBT. However, these mRNA changes in JAR cells were not comparable to the changes in both hCG secretion and aromatase activity. These results indicate that the observed trialkyltin-induced alterations in human choriocarcinoma cells are due to other mechanism in addition to a regulation of hCG and CYP19 mRNA levels. Our studies suggest that trialkyltin compounds are potent stimulators of human placental hCG production and aromatase activity in vitro; and the placenta represents a potential target organ for trialkyltin compounds, whose endocrine-disrupting effects might be the result of local changes in hCG and estrogen concentrations in pregnant women.

Modification of NMDA responses by tri-n-butyltin in rat brain neurons

1. The effects of the organotin, tri-n-butyltin (TBT), on N-methyl-D-aspartate (NMDA) induced membrane currents were investigated in order to evaluate possible neuronal actions of this toxic environmental pollutant. Experiments were conducted on neurons acutely dissociated from the rat dorsal motor nucleus of vagus (DMV) using the nystatin-perforated patch clamp recording technique. 2. In Mg(2+)-free physiological recording solutions, the application of NMDA to single DMV neurons held at a holding potential (V(H)) of -40 mV evoked an inward current which rapidly reached a peak before declining to a steady-state inward current. This was followed, immediately after NMDA washout, by a transient outward current. TBT (100 nM) reversibly caused a slight reduction in the inward currents and greatly increased the amplitude of the outward currents. 3. The reversal potential of the NMDA-induced outward current in the presence of TBT was -86.7 mV, close to the theoretical K(+) equilibrium potential of -85.7 mV. 4. The NMDA-induced outward current was completely blocked when the K(+) in the internal solution was replaced with equimolar Cs(+). Under these conditions, the NMDA induced current was more sustained and was unaffected by TBT. 5. The NMDA-induced outward current was markedly inhibited by 5 mM tetraethylammonium chloride and 300 nM charybdotoxin, and it was abolished by removal of extracellular Ca(2+), suggesting that the outward current was due to the activation of Ca(2+)-activated K(+) channels by Ca(2+) influx through NMDA receptors. 6. In conclusion, in rat DMV neurons, TBT potentiates the Ca(2+)-activated K(+) current induced by NMDA application without having any direct effects on the NMDA-induced inward current. Given the significant role of NMDA receptor mediated excitation in various physiological and pathological processes, the modulation of this response by TBT may have an important influence on neuronal function.