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.     

Organotin compounds and aquatic bacteria: A review

Organotins are toxic to microorganisms. Trisubstituted organotins (R₃SnX) are considered more toxic than disubstituted (R₂SnX₂) or monosubstituted (RSnX₃) compounds, and tetrasubstituted compounds (R₄Sn) are not considered toxic. In the R₃Sn series propyl-, butyl-, pentyl-, phenyl- and cyclohexyltins are the most toxic to microorganisms. Toxicity towards aerobes in the R₃Sn series is related to total molecular surface area and to the octanol: water partition coefficient,Kow, which is a measure of hydrophobicity. Care must be taken when testing the toxicity of tin compounds in the laboratory, for a number of biological, chemical and physical factors can influence the apparent toxicity. Although TBT is generally the most toxic of the butyltins, there are instances where monobutyltin (MBT) is as toxic, or more toxic, than TBT to microorganisms. Thus, debutylation in the sequence TBT→DBT→MBT→Sn does not detoxity TBT for all microorganisms. Some microorganisms can methylate inorganic or organic tins under aerobic or anaerobic conditions. Methylation can also occur by chemical means and the relative contributions of biotic and abiotic mechanisms are not clear. It is difficult to isolate a pure culture which can methylate tin compounds aerobically, and it is difficult to isolate a pure culture which degrades TBT, suggesting that microbial consortiums may be involved in transformations of organotins in the aquatic environment. Methylation and debutylation alter the adsorbtivity and solubility of tin compounds; thus microorganisms can influence the environmental mobility of tin. TBT-resistant microorganisms can be isolated, and in some of them resistance to TBT can be plasmid-mediated. The literature review for this paper was completed in July, 1992.     

Toxic effects of tin compounds on microorganisms

Summary Organotins are used for industrial and agricultural purposes and in antibiologic agents. They are significantly more toxic than inorganic tins, and eventually reach the environment where they can be toxic to a wide variety of organisms. Particular attention has been given to tributyltins which are highly toxic components of antifouling paints. Realization that the molecular species of organotin influences fate and effects of organotins led to development of sensitive methods for quantifying individual molecular species. Even though such methods are now available, little information has been obtained on the ability of microorganisms to bioaccumulate tin compounds. Trisubstituted alkyl and aryltins (R₃Sn's) are more toxic than disubstituted compounds (R₂Sn's) while monosubstituted organotins (RSn's) are still less toxic. R₄Sn's are toxic only if they are metabolized to R₃Sn's. Among trisubstituted compounds propyl-, butyl-, pentyl-, phenyl-, and cyclohexyl Sn's are generally the most toxic to microorganisms. Toxicity in the R₃Sn series is related to total molecular surface area of the tin compound and to the octanol:water partition coefficient,K _ow, which is a measure of hydrophobicity; a highK _ow indicates greater hydrophobicity and predicts greater toxicity. Care must be taken when testing the toxicity of tin compounds, for a number of biological, physical and chemical factors can influence the apparent toxicity. Although little is known of the effects of tin compounds on microbial processes, a number of bacterial processes can be inhibited by organotins and all relate to membrane functions. They include effects on energy transduction, solute transport and retention and oxidation of substrates. Very little is known of how organotins exert their toxic effects on algae and fungi; Information on effects on chloroplasts and mitochondria stems principally from animal systems and from higher plants. Triorganotins act against chloroplasts and mitochondria by causing swelling, by acting as ionophores and by acting against ATPase, while diorganotins appear to act by binding to dithiol groups on enzymes and cofactors. Nucleic acids do not seem to be affected at environmentally relevant concentrations. Virtually nothing is known of the action of tin compounds on microbial enzymes, but resistant mutants are easy to obtain and should facilitate work to understand modes of microbial interaction with tin compounds and mechanisms of resistance.     

Microbial transformations of tin and tin compounds

Summary The use of organotins for agricultural and industrial purposes and in the marine environment has been increasing steadily for more than 20 years. Recently, reliable methodologies have been developed to permit quantification of individual molecular species of organotins in cultures and in the environment. Particular attention has been given to methyltins which can be formed abiotically and by microorganisms, and to tributyltins which are toxic components of effective antifouling paints. In the aquatic environment tin, tributyltins and other organotins accumulate in the surface microlayer, in sediments, and on suspended particulates. Tin compounds are toxic to a variety of organisms and some aquatic organisms can bioaccumulate them. When tin compounds, particularly di-or tri-substituted tins, enter an ecosystem, a portion of the microbial population is killed. Among the survivors are organisms which can methylate inorganic or organic tins, but the relative contribution of biotic and abiotic mechanisms is not clear. While many details of methylations and demethylations need to be worked out, it is clear that transformations of tins can influence the toxicity, volatility and mobility of tin in natural ecosystems. Tributyltins can be debutylated by microorganisms, and hydroxybutyl tins may be intermediates, as they are in mammalian systems. Little is known of the potential and probable microbial transformations of other economically important organotins, but the transformations should be studied for they may have industrial and environmental importance.     

Activation of RXR–PPAR heterodimers by organotin environmental endocrine disruptors

The nuclear receptor retinoid X receptor‐α (RXR‐α)–peroxisome proliferator‐activated receptor‐γ (PPAR‐γ) heterodimer was recently reported to have a crucial function in mediating the deleterious effects of organotin compounds, which are ubiquitous environmental contaminants. However, because organotins are unrelated to known RXR‐α and PPAR‐γ ligands, the mechanism by which these compounds bind to and activate the RXR‐α–PPAR‐γ heterodimer at nanomolar concentrations has remained elusive. Here, we show that tributyltin (TBT) activates all three RXR–PPAR‐α, ‐γ, ‐δ heterodimers, primarily through its interaction with RXR. In addition, the 1.9 Å resolution structure of the RXR‐α ligand‐binding domain in complex with TBT shows a covalent bond between the tin atom and residue Cys 432 of helix H11. This interaction largely accounts for the high binding affinity of TBT, which only partly occupies the RXR‐α ligand‐binding pocket. Our data allow an understanding of the binding and activation properties of the various organotins and suggest a mechanism by which these tin compounds could affect other nuclear receptor signalling pathways.     

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.     

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     

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.     

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.     

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.     

Resistance to oxidative damage but not immunosuppression by organic tin compounds in natural populations of Daubenton's bats (Myotis daubentonii)

The acute toxicity of organic tin compounds (OTCs) has been studied in detail. However, due to their complex nature, very little is known about species-specific methods of accumulation and consequences for food-webs. Chironomids, on which e.g. Daubenton's bats feed, may act as vectors for the transport of organic tin compounds from aquatic to terrestrial ecosystems. Bats are prone to environmental toxins because of their longevity and their ecological role as top predators. Organic tin compounds are associated with increased formation of reactive oxygen species and associated oxidative damage as well as suppression of immune function. The present paper investigates whether the OTC, tributyltin (TBT) and its metabolite, dibutyltin (DBT), accumulate in natural populations of Daubenton's bats and whether TBT-associated effects are seen in general body condition, redox balance, redox enzyme activities, associated oxidative damage of red blood cells and complement function. We discovered the concentration of bat fur DBT correlated with local marine sediment TBT concentrations. However, we did not find a correlation between the explanatory factors, bat fur DBT and marine sediment TBT concentrations, and several physiological and physical response variables apart from complement activity. Higher DBT concentrations resulted in weaker complement activity and thus a weaker immune response. Although the observed physiological effects in the present study were not strongly correlated to butyltin concentrations in fur or sediment, the result is unique for natural populations so far and raises interesting questions for future ecotoxicological studies.     

Effect of triethyltin on enzyme activity in human adult and cord red cells

Since organotin compounds represent an environmental health hazard, we determined the effect of triethyltin bromide (TTB) on red blood cell (RBC) enzyme activity. TTB produced a concentration-dependent inhibition of hexokinase and pyrimidine 5'-nucleotidase for both adult and cord RBC. D-Glucose, but not ATP or MgCl2, prevented the hexokinase inhibition by TTB. Glucose-6-phosphate dehydrogenase, adenylate kinase, and hypoxanthine-guanine phosphoribosyltransferase were also inhibited by TTB. Cord RBC enzymes were more resistant to the effects of TTB than were adult RBC enzymes. Although TTB is a potent inhibitor of hexokinase, physiologic concentrations of glucose appear to protect the RBC during clinical tin intoxication.     

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.     

Pattern of organotin inhibition of methanogenic bacteria.

Seven organotin compounds and tin chloride were tested for their effects on the methanogenic bacteria Methanococcus thermolithotrophicus, Methanococcus deltae delta LH, and Methanosarcina barkeri 227. The methanogens were strongly inhibited by triethyltin, tripropyltin, and monophenyltin compounds, generally at concentrations below 0.05 mM. Less inhibition by tributyltin and diphenyltin was observed at levels below 0.1 mM, but complete inhibition was observed at a 1 mM concentration. Tin chloride inhibited all methanogens, with nearly complete inhibition at a 1 mM concentration. There was no inhibition by tetra-n-butyltin and triphenyltin compounds even at 2 mM, the highest concentration tested. The 50 and 100% inhibitory concentrations of all compounds were estimated; these values varied with both the compound tested and the bacterium tested. The 50% inhibitory concentration estimate generally decreased (i.e., giving a higher toxicity) as the total surface area of the alkyltin molecules decreased. These results differ considerably from those reported previously for aerobic microorganisms (G. Eng, E. J. Tierney, J. M. Bellama, and F. E. Brinckman, Appl. Organometallic Chem. 2:171-175, 1988), where a clear correlation between increasing total molecular surface area and increasing toxicity was documented with a variety of organisms. Using the same procedures as for the methanogens, we examined the effects of organotin compounds on Escherichia coli growing aerobically or anaerobically. The E. coli inhibition pattern clearly resembled that seen in the data of Eng et al., under both aerobic and anaerobic conditions.     

Pattern of organotin inhibition of methanogenic bacteria

Seven organotin compounds and tin chloride were tested for their effects on the methanogenic bacteria Methanococcus thermolithotrophicus, Methanococcus deltae delta LH, and Methanosarcina barkeri 227. The methanogens were strongly inhibited by triethyltin, tripropyltin, and monophenyltin compounds, generally at concentrations below 0.05 mM. Less inhibition by tributyltin and diphenyltin was observed at levels below 0.1 mM, but complete inhibition was observed at a 1 mM concentration. Tin chloride inhibited all methanogens, with nearly complete inhibition at a 1 mM concentration. There was no inhibition by tetra-n-butyltin and triphenyltin compounds even at 2 mM, the highest concentration tested. The 50 and 100% inhibitory concentrations of all compounds were estimated; these values varied with both the compound tested and the bacterium tested. The 50% inhibitory concentration estimate generally decreased (i.e., giving a higher toxicity) as the total surface area of the alkyltin molecules decreased. These results differ considerably from those reported previously for aerobic microorganisms (G. Eng, E. J. Tierney, J. M. Bellama, and F. E. Brinckman, Appl. Organometallic Chem. 2:171-175, 1988), where a clear correlation between increasing total molecular surface area and increasing toxicity was documented with a variety of organisms. Using the same procedures as for the methanogens, we examined the effects of organotin compounds on Escherichia coli growing aerobically or anaerobically. The E. coli inhibition pattern clearly resembled that seen in the data of Eng et al., under both aerobic and anaerobic conditions.     

Sex alteration in soft-shell clams (Mya arenaria) in an intertidal zone of the Saint Lawrence river (Quebec,Canada)

The purpose of this study was to verify whether any changes in sex ratio might occur in soft-shell clams (Mya arenaria) located in an intertidal harbor zone located at the mouth of the Saguenay Fjord in the Saint Lawrence estuary (Baie Sainte-Catherine (BSC), Québec, Canada) likely to be contaminated by organotin compounds. Bivalves were harvested at the BSC harbor site and from two reference sites. Condition index (weight to length ratio), gonado-somatic index, sex ratio, vitellin-like proteins, organotin concentrations in gonad tissue, maturation stages of the gonads, the number of estradiol-17beta binding sites and the capacity of female gonad extracts to produce estradiol-17beta were determined in collected animals. Results showed that sex ratio in clams was significantly skewed toward males. Moreover, the condition and gonad-somatic indices, vitellin-like proteins in female gonads and the capacity of female gonads to produce estradiol-17beta were significantly reduced at the harbor site with respect to the reference sites. Maturation status of male gonads was clearly delayed at the harbor site. Additionally, gonad tissue contained tributyltin (TBT) at an average level of 109+/-18 ngSn/gdry wt. at the harbor site while organotins were not detected from the reference sites. Finally, female gonads had a higher number of unoccupied estradiol binding sites at the harbor site indicating low levels of this steroid in this tissue. Overall, this paper is first to report that clams collected in the vicinity of a TBT contaminated harbor are subject to masculinizing effects which seems to be consistent with biological effects that organotins are known to exert toward some other marine invertebrates.     

Effect of organotins on fecal pollution indicator organisms.

Pure cultures of Escherichia coli and Streptococcus faecalis and environmental water samples were examined for the possibility that pollution involving organotin compounds could decrease the values for indicator organisms when standard methods were applied to the analysis of water samples. (CH3)2SnCl2 and (CH3)3SnCl decreased viable counts at about 10 to 100 mg of Sn liter-1 (8.4 X 10(-5) to 8.4 X 10(-4) mol of Sn liter-1), and tributyltin chloride was effective at about 0.1 to 1.0 mg of Sn liter-1 (8.4 X 10(-7) to 8.4 X 10(-6) mol of Sn liter-1. These concentrations, particularly for the methyltin compounds, are greater than the concentrations reported to date for these compounds in aquatic ecosystems. Thus, organotin compounds alone would not be likely to cause reductions in counts of indicator organisms measured by standard methods. However, it is suggested that, when combined with other environmental stressors or upon long exposure, organotins such as butyltins may contribute to the injury of indicator organisms.     

Effect of organotins on fecal pollution indicator organisms

Pure cultures of Escherichia coli and Streptococcus faecalis and environmental water samples were examined for the possibility that pollution involving organotin compounds could decrease the values for indicator organisms when standard methods were applied to the analysis of water samples. (CH3)2SnCl2 and (CH3)3SnCl decreased viable counts at about 10 to 100 mg of Sn liter-1 (8.4 X 10(-5) to 8.4 X 10(-4) mol of Sn liter-1), and tributyltin chloride was effective at about 0.1 to 1.0 mg of Sn liter-1 (8.4 X 10(-7) to 8.4 X 10(-6) mol of Sn liter-1. These concentrations, particularly for the methyltin compounds, are greater than the concentrations reported to date for these compounds in aquatic ecosystems. Thus, organotin compounds alone would not be likely to cause reductions in counts of indicator organisms measured by standard methods. However, it is suggested that, when combined with other environmental stressors or upon long exposure, organotins such as butyltins may contribute to the injury of indicator organisms.     

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.