Modifications of erythrocyte membrane hydration induced by organic tin compounds

A study on the effects of selected organic chlorides of tin on the extent of hydration of the lipid bilayer of erythrocyte ghosts from pig blood is presented. The following compounds were used, dibutyltin dichloride (DBT), tributyltin chloride (TBT), diphenyltin dichloride (DPhT) and triphenyltin chloride (TPhT). The degree of membrane hydration was measured by the ATR FTIR technique, which makes it possible to estimate the level of carbonyl and phosphate group hydration in lipids of membranes. Other measurements were made with a fluorescence technique involving a laurdan probe. Tin organic compounds caused dehydration of the lipid bilayer of ghosts in the region of the carbonyl groups. DBT and TBT produced weak dehydration in the region of the phosphate group, whereas DPhT and TPhT increased hydration. The results allow one to determine the location of organotin compounds within a membrane, and show that TBT penetrates the membrane the deepest and DBT the shallowest. Phenyl tin compounds penetrate membranes to an intermediate depth. The results obtained indicate that the destructive properties of the organometallic compounds depend mostly on their effect on hydration of the membrane.     

Organotin-induced hemolysis,shape transformation and intramembranous aggregates in human erythrocytes

Organotin compounds examined in this study exhibited a relative order of potency for induction of in vitro hemolysis in human erythrocytes as follows: tri-n-butyltin > tri-n propyltin > tetra-n-butyltin > triphenyltin chloride > tri-n-ethyltin bromide > dibutyltin dichloride > stannous chloride > tri-n-methyltin chloride = butyltin chloride dihydroxide. All of the organotin compounds induced erythrocyte shape transformation from the normal discocyte to an echinocyte and, in addition, triphenyltin chloride, tetra-n-butyltin and tri-n-ethyltin bromide also elicited stomatocyte formation at higher concentrations. Select organotin compounds also formed tin-containing aggregates within the plasma membrane. The relative order of effectiveness for organotin induction of intramembranous aggregates was tri-n-butyltin > tri-npropyltin > tetra-n-butyltin > tri-n-ethyltin bromide, which was based upon the lowest concentration at which they were observed. These results support the previously suggested theory that organotins are membrane effectors because of their comparatively high hydrophobic, lipid partitioning properties. The relatively lipophilic compound, triphenyltin chloride, appeared to be anomalous because it did not readily promote hemolysis or induce the formation of intramembranous aggregates in human erythrocytes. A log-linear statistical model demonstrated an association of hemolysis with both tri-n-butyltin aggregate formation and shape transformation. Select organotin compounds should be useful probes in membrane studies because of their numerous effects.Abbreviations DBT dibutylin dichloride - MBT butyltinchloride dihydroxide - SnCl₂ stannous chloride - TBT tri-n-butyltin - TET tri-n-ethyltin bromide - TMT tri-n-methyltin chloride - TPhT triphenyltin chloride - TPT tri-n-propyltin - TTBT tetra-n-butyltin     

Toxicity of organotin compounds in primary cultures of rat cortical astrocytes

The neurotoxic organotin compounds trimethyl (TMT) and triethyltin (TET) are known to induce astrogliosis in vivo, which is indicated by an increased synthesis of glial fibrillary acidic protein (GFAP) in astrocytes. In contrast, tributyltin (TBT) does not induce astrogliosis. The aim of this study was to investigate whether trialkyltin derivatives can induce an increased GFAP synthesis in astrocyte cultures in the absence of neurons and whether differences between the action of TMT, TET, and TBT can be detected. Primary cultures of rat cortical astrocytes from 2-day-old rats were grown in 96-well plates until confluency and then exposed to various concentrations of TMT, TET, and TBT for 40 h. Effects on basal cell functions were measured by colorimetric determination of cell protein contents and by assessment of viability by means of the MTT assay. An indirect sandwich ELISA for 96-well plates was used for quantitative measurements of the GFAP content of the cells. All three compounds induced a concentration-dependent cytotoxicity indicated by parallel decreases of protein contents and MTT reduction. Half-maximum cytotoxic concentrations were 3 μmol/L (TBT), 30 μmol/L (TET), and 800 μmol/L (TMT). Cellular GFAP contents were reduced in parallel to cytotoxic action but no increase in GFAP expression at subcytotoxic concentrations could be observed. Thus, the astrocytes were not able to respond to TMT or TET exposure by an increased synthesis of GFAP in the absence of neuronal signals. This revised version was published online in July 2006 with corrections to the Cover Date.     

Imposex in Hexaplex trunculus at Some Sites on the North Mediterranean Coast as a Base-Line for Future Evaluation of the Effectiveness of the Total Ban on Organotin based Antifouling Paints

Imposex – the superimposition of male sexual organs (penis and vas deferens) onto female Neogastropods such as Hexaplex trunculus (Linné, 1758) – is used world-wide as a biomarker of ecological impact of organotin based antifouling biocides (TBT and TPhT). To limit the impact of organotin pollution, since January 1, 2003, the International Maritime Organization (IMO) has enacted a global ban on the use of organotin compounds in antifouling systems. It is important to record imposex levels and organotin contamination before the implementation of the ban, in order to assess the current situation and be able, in the future, to verify the effects of the International Protocol. In this paper, recent imposex data measured in populations of Hexaplex trunculus from three different Mediterranean regions are compared: the Ligurian Sea (Italy), the Lagoon of Venice (Italy) and the western coast of Istria (Croatia). In the two former locations, a partial ban on TBT has been in force for vessels less than 25 m since 1982, while in the latter region no restrictions on organotin antifouling paints have been applied yet. Gastropod samples collected from the Venice lagoon were analysed with an acid extraction followed by Grignard derivatisation, clean up and GC-MS determination, in order to relate the levels of TBT, TPhT and their metabolites with the imposex degree detected. Biological data show that the levels of imposex were very high (VDS from 4.3 to 5) in all the sampling sites considered, particularly in the Croatian coast stations. The concentrations of organotin compounds – butyltins and phenyltins – measured in the samples from the lagoon of Venice were found to partition differently in the visceral coil and in the rest of the soft body of the analysed organisms.     

Speciation of organotin compounds in urine by GC–MIP-AED and GC–MS after ethylation and liquid–liquid extraction

A method for the determination of organotin compounds in urine samples based on liquid–liquid extraction (LLE) in hexane and gas chromatographic separation was developed and optimized. Seven organotin species, namely monobutyltin (MBT), dibutyltin (DBT), tributyltin (TBT), tetrabutyltin (TeBT), monophenyltin (MPhT), diphenyltin (DPhT) and triphenyltin (TPhT), were in situ derivatized by sodium tetraethylborate (NaBEt₄) to form ethylated less polar derivatives directly in the urine matrix. The critical parameters which have a significant effect on the yield of the successive liquid–liquid extraction procedure were examined, by using standard solutions of tetrabutyltin in hexane. The method was optimized for use in direct analysis of undiluted human urine samples and ways to overcome practical problems such as foam formation during extraction, due to various constituents of urine are discussed. After thorough optimization of the extraction procedure, all examined species could be determined after 3 min of simultaneous derivatization and extraction at room temperature and 5 min phase separation by centrifugation. Gas chromatography with a microwave-induced plasma atomic emission detector (MIP-AED) as element specific detector was employed for quantitative measurements, while a quadrupole mass spectrometric detector (MS) was used as molecular specific detector. The detection limits were between 0.42 and 0.67 μg L^?1 (as Sn) for the quantitative LLE–GC–MIP-AED method and the precision between 4.2% and 11.7%, respectively.     

Differential gliotoxicity of organotins

On the basis of reports that astrocytes play an important role in the neurotoxicity of trimethyltin (TMT), we investigated the sensitivity of astrocytes to TMT and compared it to triethyltin (TET), a neurotoxic analog with a different in vivo specificity. The gliotoxicity of these two compounds was further compared to that of tributyltin (TBT) and triphenyltin (TPT), two purportedly nonneurotoxic organotin compounds. The time and concentration components of organotin toxicity were determined by measuring lactate dehydrogenase (LDH) release and formazan production from dimethylthiazolyldiphenyltetrazolium bromide (MTT).A TMT concentration of 100 mol/L did not elevate extracellular LDH until 48 h after exposure, while signs of toxicity were not seen at 72 h for concentrations less than 10 mol/L. Extracellular LDH activity increased 24 h after exposure to concentrations of TET, TBT, and TPT as low as 2.5 mol/L.TMT was the only organotin to produce a delayed cytotoxicity, requiring both higher concentrations and more time to produce discernible toxicity. In contrast with TBT and TPT, the toxicity of the two neurotoxic organotins (TMT and TET) produced an early increase in MTT reduction. The distinct pattern of toxicity for TMT does not explain its selective in vivo toxicity, but the lack of sensitivity of astrocytes to this organotin also does not rule out more subtle changes in these cells that could disrupt normal glial/neuronal interactions.     

The Speciation of Organotin Compounds in Sediment and Water Samples from the Port of Gdynia

Organotin compounds (OTC) are toxic towards all living organisms. The application of organitin-based antifouling systems is becoming the main source of OTC in the ocean. Harbor sediments and water contain large deposits of organotin compounds due to application of antifouling systems in the shipping industry. OTC contamination presents a potential risk to the marine environment.

Sediment and water samples were collected in 2009 from Gdynia Harbor. For all the analyzed organotin compounds, the mean concentration values were determined: water samples monobutyltin (MBT): 13.2, dibutyltin (DBT): 16.7, tributyltin (TBT): 60.7 (ng cation dm^?3), and sediment samples MBT: 261.4, DBT: 751.9, TBT: 2148.2 (ng cation g^?1 d.w.). The estimated content of monophenyltin (MPhT), diphenyltin (DPhT), triphenyltin (TPhT), monooctyltin (MOT), dioctyltin (DOT), and tricyclohexyltin (TCHT) were below the detection limit of the applied method. It was found that the content of organic matter, the amount of fine fraction, and the pH all play a significant role in the distribution and sorption process of OTC between the water and the sediment on the bottom. Compared to an earlier study, the concentrations of all OTC are much lower, confirming that the applied legislation has had a positive impact.     

Comparison of different liquid chromatography conditions for the separation and analysis of organotin compounds in mussel and oyster tissue by liquid chromatography-inductively coupled plasma mass spectrometry

In this paper, a new high-performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICP-MS) methodology for the analysis of organotin compounds in complex matrices is described. Earlier studies had failed to show baseline resolution between dibutyltin (DBT) and triphenyltin (TPhT). The data presented in this paper show that, by using a different C-18 stationary phase material (Ace C-18) with decreased particle size, baseline resolution of DBT and TPhT can be achieved, with the resultant separation of a third interfering component. In addition, the Ace C-18 stationary phase yields a significant increase in the number of theoretical plates, and, combined with changes in the mobile phase composition, a reduction in run-time by approximately 25%. It is shown that the minor compounds detected are present in the sample and not artefacts of the analytical procedure. The accuracy and precision of the proposed HPLC-ICP-MS method was demonstrated for the determination of TBT in oyster tissue during the BCR "MULSPOT" international interlaboratory certification project.     

Inhibition of human cytochrome P450 aromatase activity by butyltins

Organotin compounds are widely used as antifouling agents and bioaccumulate in the food chain. Tributyltin chloride (TBT) has been shown to induce imposex in female gastropods. On the basis of this observation it has been suggested that TBT acts as an endocrine disrupter inhibiting the conversion of androgens to estrogens mediated by the aromatase cytochrome P450 enzyme. However, to date, the molecular basis of TBT-induced imposex and in particular its putative inhibitory effects on human aromatase cytochrome P450 activity have not been investigated. Therefore, we examined the effects of the organotin compounds tetrabutyltin (TTBT), TBT, dibutyltin dichloride (DBT) and monobutyltin trichloride (MBT) on human placental aromatase activity. TBT was found to be a partial competitive inhibitor of aromatase activity with an IC(50) value of 6.2 microM with 0.1 microM androstenedione as substrate. TBT impaired the affinity of the aromatase to androstenedione but did not affect electron transfer from NADPH to aromatase via inhibiting the NADPH reductase. DBT acted as a partial but less potent inhibitor of human aromatase activity (65% residual activity), whereas TTBT and MBT had no effect. The residual activity of TBT-saturated aromatase was 37%. In contrast, human 3beta-HSD type I activity was only moderately inhibited by TBT (80% residual activity). Moreover, neither TTBT or DBT nor MBT inhibited the 3beta-HSD type I activity. Together, these results suggest that the environmental pollutants TBT and DBT, both present in marine organisms, textile and plastic products, may have specific impacts on the metabolism of sex hormones in humans.     

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.     

Triphenyltin and Tributyltin inhibit pig testicular 17beta-hydroxysteroid dehydrogenase activity and suppress testicular testosterone biosynthesis

We previously reported that tributyltin chloride (TBT) and triphenyltin chloride (TPT) powerfully suppressed human chorionic gonadotropin- and 8-bromo-cAMP-stimulated testosterone production in pig Leydig cells at concentrations that were not cytotoxic [Nakajima Y, Sato Q, Ohno S, Nakajin S. Organotin compounds suppress testosterone production in Leydig cells from neonatal pig testes. J Health Sci 2003;49:514-9]. This study investigated the effects of these organotin compounds on the activity of enzymes involved in testosterone biosynthesis in pig testis. At relatively low concentrations of TPT, 17beta-hydroxysteroid dehydrogenase (17beta-HSD; IC(50)=2.6microM) and cytochrome P450 17alpha-hydroxylase/C(17-20) lyase (IC(50)=117microM) activities were inhibited, whereas cholesterol side-chain cleavage cytochrome P450 and 3beta-HSD/Delta(4)-Delta(5) isomerase activities were less sensitive. Overall, TPT was more effective than TBT. TPT also inhibited both ferredoxin reductase and P450 reductase activities at concentrations over 30microM; however, TBT had no effect, even at 100microM. The IC(50) values of TPT were estimated to be 25.7 and 22.8microM for ferredoxin reductase and P450 reductase, respectively. The inhibitory effect of TPT (30microM) on microsomal 17beta-HSD activity from pig testis was eliminated by pretreatment with the reducing agents dithiothreitol (1mM) and dithioerythritol (1mM). On the other hand, TPT (0.03microM) or TBT (0.1microM) exposure suppressed the testosterone production from androstenedione in pig Leydig cells indicating that these organotins inhibit 17beta-HSD activity in vivo as well as in vitro, and the IC(50) values of TPT and TBT for 17beta-HSD activity were estimated to be 48 and 114nM, respectively. Based on these results, it appears possible that the effects of TBT and TPT are largely due to direct inhibition of 17beta-HSD activity in vivo.     

Modulation of acute steroidogenesis,peroxisome proliferator-activated receptors and CYP3A/PXR in salmon interrenal tissues by tributyltin and the second messenger activator,forskolin

There are uncertainties regarding the role of sex steroids in sexual development and reproduction of gastropods, leading to the recent doubts as to whether organotin compounds do inhibit steroidogenic enzymes in these species. These doubts have led us to suspect that organotin compounds may affect other target molecules, particularly signal transduction molecules or secondary mediators of steroid hormone and lipid synthesis/metabolism. Therefore, we have studied the effects of TBT exposure through food on acute steroidogenesis, PPARs and CYP3A responses in the presence and absence of a cyclic AMP (cAMP) activator, forskolin. Two experiments were performed. Firstly, juvenile salmon were force-fed once with diet containing TBT doses (0.1, 1 and 10 mg/kg fish) dissolved in ethanol and sampled after 72 h. Secondly, fish exposed to solvent control and 10 mg/kg TBT for 72 h were transferred to new tanks and exposed to waterborne forskolin (200 μg/L) for 2 and 4 h. Our data show that juvenile salmon force-fed TBT showed modulations of multiple biological responses in interrenal tissues that include, steroidogenesis (cAMP/PKA activities; StAR and P450scc mRNA, and plasma cortisol), and mRNA for peroxisome proliferator-activated receptor (PPAR) isoforms (α, β, γ), acyl-CoA oxidase-1 (ACOX1) and CYP3A/PXR (pregnan X receptor). In addition, forskolin produced differential effects on these responses both singly and also in combination with TBT. Overall, combined forskolin and TBT exposure produced higher effects compared with TBT exposure alone, for most of the responses (cortisol, PPARβ, ACOX1 and CYP3A). Interestingly, forskolin produced PPAR isoform-specific effects when given singly or in combination with TBT. Several TBT mediated toxicity in fish that includes thymus reduction, decrease in numbers of lymphocytes, inhibition of gonad development and masculinization, including the imposex phenomenon have been reported. When these effects are considered with the present findings, it suggests that studies on mechanisms of action or field studies may reveal endocrine, reproductive or other effects of TBT at lower concentrations than those reported to date from subchronic tests of fishes. Since the metabolic fate of organotin compounds may contribute to the toxicity of these chemicals, the present findings may represent some new aspects of TBT toxicity not previously reported.     

Tributyltin and triphenyltin inhibit osteoclast differentiation through a retinoic acid receptor-dependent signaling pathway

Organotin compounds, such as tributyltin (TBT) and triphenyltin (TPT), have been widely used in agriculture and industry. Although these compounds are known to have many toxic effects, including endocrine-disrupting effects, their effects on bone resorption are unknown. In this study, we investigated the effects of organotin compounds, such as monobutyltin (MBT), dibutyltin (DBT), TBT, and TPT, on osteoclast differentiation using mouse monocytic RAW264.7 cells. MBT and DBT had no effects, whereas TBT and TPT dose-dependently inhibited osteoclast differentiation at concentrations of 3-30 nM. Treatment with a retinoic acid receptor (RAR)-specific antagonist, Ro41-5253, restored the inhibition of osteoclastogenesis by TBT and TPT. TBT and TPT reduced receptor activator of nuclear factor-kappaB ligand (RANKL) induced nuclear factor of activated T cells (NFAT) c1 expression, and the reduction in NFATc1 expression was recovered by Ro41-5253. Our results suggest that TBT and TPT suppress osteoclastogenesis by inhibiting RANKL-induced NFATc1 expression via an RAR-dependent signaling pathway.     

Endocrine-disrupting organotin compounds are potent inducers of adipogenesis in vertebrates

Dietary and xenobiotic compounds can disrupt endocrine signaling, particularly of steroid receptors and sexual differentiation. Evidence is also mounting that implicates environmental agents in the growing epidemic of obesity. Despite a long-standing interest in such compounds, their identity has remained elusive. Here we show that the persistent and ubiquitous environmental contaminant, tributyltin chloride (TBT), induces the differentiation of adipocytes in vitro and increases adipose mass in vivo. TBT is a dual, nanomolar affinity ligand for both the retinoid X receptor (RXR) and the peroxisome proliferator-activated receptor gamma (PPARgamma). TBT promotes adipogenesis in the murine 3T3-L1 cell model and perturbs key regulators of adipogenesis and lipogenic pathways in vivo. Moreover, in utero exposure to TBT leads to strikingly elevated lipid accumulation in adipose depots, liver, and testis of neonate mice and results in increased epididymal adipose mass in adults. In the amphibian Xenopus laevis, ectopic adipocytes form in and around gonadal tissues after organotin, RXR, or PPARgamma ligand exposure. TBT represents, to our knowledge, the first example of an environmental endocrine disrupter that promotes adipogenesis through RXR and PPARgamma activation. Developmental or chronic lifetime exposure to organotins may therefore act as a chemical stressor for obesity and related disorders.     

Influence of dodecyltrimethylammonium halides on interaction of phenyltin compounds with model membranes

The effects were studied of dodecyltrimethylammonium chloride (DTAC), dodecyltrimethylammonium bromide (DTAB) and dodecyltrimethylammonium iodide (DTAI) on thermotropic phase behaviour of phosphatidylcholine bilayers, as well as on 1H NMR and 31P NMR spectra, in the presence of diphenyltin dichloride (DPhT) and triphenyltin chloride (TPhT). The obtained results indicate that in the presence of the surfactant studied the interaction of phenyltin compounds with model membranes was changed and the changes depended on the kind of the counterion. The surfactants studied (especially DTAC) decrease the ability of phenyltin compounds to induce structural changes in the bilayer. It is suggested that DTAB, and especially DTAC, prevent DPhT induced interdigitated phase formation as well as formation of an inverted hexagonal phase (H(II)) in the case of TPhT/DPPC liposomes.     

Effect of tin and lead chlorotriphenyl analogues on fruit fly Drosophila hydei and liposomes membrane

This article presents the results of a study investigating the biological activity of triphenyltin chloride (TPhT) and two metalloorganic compounds, triphenyllead chloride (TPhL) and triphenylmethane chloride (TPhC), in their interaction with model membranes and the living organisms of fruit flies Drosophila hydei. The study of model membranes (sonicated liposomes) was conducted using the electron spin resonance (ESR) spin probe technique, whereas the experiment on fruit flies involved investigating their viability on media containing the studied compounds. The test results clearly demonstrate that TPhT affects fruit flies more actively than TPhL (complete lethality after 7 days of culture with a TPhT-containing medium). No toxic effect of TPhC on fruit flies was shown. The results of the biological experiment were reflected in the physical experiment involving an ESR study of liposomes: TPhT activity manifested itself as a considerable increase in fluidity of the central region of the liposome lipid bilayer.     

JNK and p38 MAPK are independently involved in tributyltin-mediated cell death in rainbow trout (Oncorhynchus mykiss) RTG-2 cells

Mitogen-activated protein kinases (MAPKs) are a family of Ser/Thr protein kinases that transmit various extracellular signals to the nucleus inducing gene expression, cell proliferation, and apoptosis. Recent studies have revealed that organotin compounds induce apoptosis and MAPK phosphorylation/activation in mammal cells. In this study, we elucidated the cytotoxic mechanism of tributyltin (TBT), a representative organotin compound, in rainbow trout (Oncorhynchus mykiss) RTG-2 cells. TBT treatment resulted in significant caspase activation, characteristic morphological changes, DNA fragmentation, and consequent apoptotic cell death in RTG-2 cells. TBT exposure induced the rapid and sustained accumulation of phosphorylated MAPKs, including extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 MAP kinase (p38 MAPK). Further analysis using pharmacological inhibitors against caspases and MAPKs showed that TBT also induced cell death in a caspase-independent manner and that p38 MAPK is involved in TBT-induced caspase-independent cell death, whereas JNK is involved in the caspase-dependent apoptotic pathway. Thus, TBT employs at least two independent signaling cascades to mediate cell death in RTG-2 cells. To our knowledge, this is the first study revealing the relationship between MAPK activation and TBT cytotoxicity in RTG-2 cells.     

Exposure to TBT increases accumulation of lipids and alters fatty acid homeostasis in the ramshorn snail Marisa cornuarietis

Recent studies have shown that organotin compounds affect lipid homeostasis in vertebrates, probably through interaction with RXR and/or PPARgamma receptors. Molluscs are sensitive species to the toxic effects of tributyltin (TBT), particularly to masculinization, and TBT has been recently shown to bind to molluscs RXR. Thus, we hypothesized that exposure to TBT could affect lipid homeostasis in the ramshorn snail Marisa cornuarietis. For comparative purposes, the synthetic androgen methyl-testosterone (MT) was included in the study due to its masculinization effects, but its lack of binding to the RXR receptor. M. cornuarietis was exposed to different concentrations of TBT (30, 125, 500 ng/L as Sn) and MT (30, 300 ng/L) for 100 days. Females exposed to 500 ng/L TBT showed increased percentage of lipids and increased levels of fatty acids in the digestive gland/gonad complex (2- to 3-fold). In addition, fatty acid profiles were altered in both males and females exposed to 125 and 500 ng/L TBT. These effects were not observed in females exposed to MT. Overall, this work suggest that TBT acts as a potent inducer of lipid and fatty acid accumulation in M. cornuarietis as shown in vertebrate studies earlier, and that sex differences in sensitivity do exist.     

Inorganic tin and organotin interactions with<Emphasis Type="Italic"> Candida maltosa</Emphasis>

As a consequence of the widespread industrial and agricultural applications of organotins, contamination of various ecosystems has occurred in recent decades. Understanding how these compounds interact with microorganisms is important in assessing the risks of organotin pollution. The organotins, tributyltin (TBT), trimethyltin (TMT) and inorganic tin, Sn(IV), were investigated for their physical interactions with non-metabolising cells and protoplasts of the yeast Candida maltosa, an organism that is often associated with contaminated environments. Uptake, toxicity and membrane-acting effects of these compounds, at concentrations approximating those found in polluted environments, were assessed. Sn(IV) and TBT uptake occurred by different mechanisms. Uptake of Sn(IV) was 2-fold greater in intact cells than protoplasts, underlining the importance of cell wall binding, whereas TBT uptake levels by both cell types were similar. TBT uptake resulted in cell death and extensive K⁺ leakage, while Sn(IV) uptake had no effect. TMT did not interact with cells. Of the three compounds, TBT alone altered membrane fluidity, as measured by the fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene incorporated into cells. Anisotropy of 1-(4-trimethylaminophenyl-6-phenyl-1,3,5-hexatriene) was not affected, implying that TBT is not confined to the surface of the cytoplasmic membrane, but acts within membrane lipids. These results indicate that the cell wall is the dominant site of Sn(IV) interactions with yeast, while lipophilic interactions play an important role in uptake and toxicity of TBT.