Toxicity of triorganotin compounds: comparative in vivo studies with a series of trialkyltin compounds and triphenyltin chloride in male rats

Activation of mitogen-activated protein kinases by tributyltin in CCRF-CEM cells: role of intracellular Ca(2+)

Effects of tributyltin chloride (TBT) and other organotin compounds on mitogen-activated protein kinases (MAPKs) were examined in CCRF-CEM human T lymphoblastoid cells. In response to the incubation with 0.25-2 microM TBT for 1 h, the levels of the phosphorylated form of extracellular signal-regulated protein kinase (ERK), c-Jun NH(2)-terminal kinase (JNK), and p38 MAPK increased in a dose-dependent manner. The phosphorylation was observed after 15 min and lasted for 4 h following exposure to 1 microM TBT, while the cell viability was not lowered significantly within 6 h. On the other hand, no clear changes were found in the total protein levels of ERK, JNK, and p38 MAPK. The in vitro activities of MAPKs also increased in response to TBT exposure. The potentials of MAPKs phosphorylation and of cellular damage were TBT > dibutyltin dichloride (DBT) > monobutyltin trichloride (MBT). When compared to other triorganotin compounds such as trimethyltin chloride (TMT), triphenyltin chloride (TPT), and triethyltin bromide (TET), TBT exposure induced the most marked phosphorylation of MAPKs. Chelation of intracellular Ca(2+) suppressed TBT-induced MAPKs phosphorylation almost completely, but removal of external Ca(2+) did not. The present results showed that tributyltin is a potent activator of ERK, JNK, and p38 MAPK pathways, and Ca(2+) mobilized from intracellular stores plays an important role for the phosphorylation of MAPKs in this human T cell line.

Effects of triphenyltin acetate on survival, hatching success, and liver ultrastructure of early life stages of zebrafish (Danio rerio)

In order to evaluate the toxicity of the fungicide triphenyltin acetate (TPTA) on hatching, survival, morphology, and histology of early life stages of zebrafish (Danio rerio), newly fertilized eggs were exposed to concentrations of 0.5, 5, 25, 75, and 100 microg/liter TPTA for 96 h at 28+/-0.5 degrees C. Embryos and larvae were kept under constant observation for up to 7 days and studied with respect to mortality and teratogenic effects as well as histological and cytological alterations in the liver as endpoints of sublethal toxicity of TPTA. Exposure to TPTA caused dose- and time-related effects with respect to all parameters investigated: (1) Hatching was delayed at concentrations >/=0.5 microg/liter TPTA; (2) mortality increased at >/=25 microg/liter TA after 96 h exposure, with TPTA toxicity being higher in larval than in embryonic stages; (3) from >/=25 microg/liter, larvae exhibited skeletal malformation, retarded yolk sac resorption, and edema in the heart and yolk sac regions; and (4) histo- and cytopathological alterations of larval liver included changes in nuclei and mitochondria as well as glycogen depletion from >/=0.5 microg/liter TPTA. The study thus demonstrates not only an elevated sensitivity of zebrafish embryos to TPTA in stages prior to hatching, but also the importance of continuous observation over extended periods after termination of the actual exposure for a comprehensive evaluation of the toxicity of chemical compounds.

Immunotoxic effects of organotin compounds in Tapes philippinarum

One of the most harmful groups of coastal pollutants is the organotin compounds (OTCs) which have severe effects on both aquatic organisms and mammals including humans. The immunotoxic effects of OTCs were studied in the cultivated clam Tapes philippinarum by determining the immunosuppressant role on in vitro yeast phagocytosis at low doses (0.01, 0.05, 0.1 microM). The phagocytic index was significantly reduced in an irreversible non-lethal manner depending on concentration and lipophilic affinity. The order of inhibition was TBT > or = DBT > MBT for butyltins and TPTC > TPTA > or = TPTH for triphenyltins.

Differential effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin, bis(tri-n-butyltin) oxide and cyclosporine on thymus histophysiology

Recent advances in the histophysiology of the normal thymus have revealed its complex architecture, showing distinct microenvironments at the light and electron microscopic level. The epithelium comprising the major component of the thymic stroma is not only involved in the positive selection of thymocytes, but also in their negative selection. Dendritic cells, however, are more efficient than epithelial cells in mediating negative selection. Thymocytes are dependent on the epithelium for normal development. Conversely, epithelial cells need the presence of thymocytes to maintain their integrity. The thymus rapidly responds to immunotoxic injury. Both the thymocytes and the nonlymphoid compartment of the organ can be targets of exposure. Disturbance of positive and negative thymocyte selection may have a major impact on the immunological function of the thymus. Suppression of peripheral T-cell-dependent immunity as a consequence of thymus toxicity is primarily seen after perinatal exposure when the thymus is most active. Autoimmunity may be another manifestation of chemically mediated thymus toxicity. Although the regenerative capacity of thymus structure is remarkable, it remains to be clarified whether this also applies to thymus function. In-depth mechanistic studies on chemical-induced dysfunction of the thymus have been conducted with the environmental contaminants 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and bis(tri-n-butyltin)oxide (TBTO) as well as the pharmaceutical immunosuppressant cyclosporine (CsA). Each of these compounds exerts a differential effect on the morphology of the thymus, depending on the cellular targets for toxicity. TCDD and TBTO exposure results in cortical lymphodepletion, albeit by different mechanisms. An important feature of TCDD-mediated thymus toxicity is the disruption of epithelial cells in the cortex. TBTO primarily induces cortical thymocyte cell death. In contrast CsA administration results in major alterations in the medulla, the cortex remaining largely intact. Medullary epithelial cells and dendritic cells are particularly sensitive to CsA. The differential effects of these three immunotoxicants suggest unique susceptibilities of the various cell types and regions that make up the thymus.

F-actin levels but not actin polymerization are affected by triphenyltin in HL-60 cells

The toxin triphenyl tin (TPT), Sn(C(6)H(5))(+)(3) caused a rapid decrease in the F-actin content of promyelocytic human leukemia cells (HL-60) chemically differentiated to neutrophils. Prior incubation (2 min) of the cells with 10 μM TPT did not modify the extent of actin polymerization inducible either by a receptor-mediated stimulus (chemotactic peptide fMLP) or by a direct activator of G proteins (AlF(-)(4)). The inorganic tin salts SnCl(2) and SnCl(4) did not affect F-actin content or production of HL-60 cells. Microfilament thiol groups were not reduced by exposure of cells to TPT, but even increased. When F-actin was exposed to 10 |GmM triphenyltin in a cell-free system, the depolymerizing effect was not detectable. Thus, TPT does not affect cytoskeletal protein directly but depends for its toxicity on some other induced change, probably ionic/osmotic in the intact cell.

Oral bis(tri-n-butyltin) oxide in pregnant mice. I. Potential influence of maternal behavior on postnatal mortality

Pregnant Swiss mice were treated with 0, 5, 10, 20, and 30 mg/kg body weight of bis(tri-n-butyltin) oxide (TBTO) on d 6-15 of gestation. At birth litters were normalized to eight pups, and postnatal evaluation of pup growth rate and behavioral observations of dams were carried out. Litters were sacrificed on postnatal days (pnd) 7, 14, and 21, to perform hematological analysis, in connection with another study. Dam weight gain was impaired in all the treated groups (except at the lowest dose level) in the late phase of gestation. A high incidence of anticipated or delayed parturitions, without any correlation with fetal mass, was observed in the treated groups. All the treated dams showed a significant increase in resorptions, and a decrease in body weight gain between gestational day (gd) 6 and pnd 1. At birth, only the 20 and 30 mg/kg dose groups showed reduced litter size and reduced pup weight. Body weight gain reduction of pups persisted in wk 1 of life only in the 10 and 20 mg/kg dose groups. In addition, the maternal weight trend was affected during the lactation period in the higher dose groups. Postnatal death rate and growth rate of treated pups were affected by an altered maternal behavior; pups, apparently viable and with normal weight, were found often scattered throughout the cage with signs of wounds, and the percentage of dams that had not built a nest increased in the 10, 20, and 30 mg/kg dose groups. Total absence of parental care was noted in many litters, and many infanticidal events were reported. Our results seem to confirm low TBTO embryofetotoxicity, and strongly support the assumption that TBTO's toxicity to the mother is much stronger than its embryo-fetotoxic potential. Most of the reproductive parameters examined in this study were unaffected in the low-dose group, while some indices, such as gestation length and maternal weight gain between gd 6 and pnd 1, were markedly altered also at the 5 mg/kg dose level and appear to be sensitive parameters in assessing maternal toxicity.

Changes in primary and secondary lymphoid organ T-cell subpopulations resulting from acute in vivo exposure to propanil

Acute exposure to the herbicide propanil is immunotoxic for selected immune functions, as well as causing changes in the weights of the thymus and spleen. Although spleen cellularity and weight increase with propanil exposure, the thymus: body weight ratio decreases with increasing doses of propanil. The present study analyzes the thymocyte subpopulations in the thymus, spleen, and mesenteric lymph nodes. C57Bl/6 mice were treated with either 0, 100, 150, or 200 mg/kg propanil, and 7 d later thymocyte populations were analyzed by flow cytometry. In the thymus, propanil exposure resulted in a dose-dependent decrease in total numbers of T cells, as would be expected with its reduced weight. Determination of the thymocyte subpopulation distribution in the thymus showed a significant reduction in the number of CD3+CD4+CD8- (CD3+4+8-), CD3+CD4-CD8+ (CD3+4-8+), and CD3+CD4+CD8+ (CD3+4+8+) cells. Percent distribution of these thymic cell subpopulations showed similar decreases only with the highest dose. Apparent dose-related decreases in the numbers of CD3-CD4+CD8+ (CD3-4+8+) cells were also noted and were attributed to the general decrease in total thymus cells. The percentage of CD3- subpopulations showed an increasing trend with dose, which suggests that at 7 d postpropanil exposure there may be a specific effect on this most immature population. Although the size and cellularity of the spleen were increased, no change in CD4+ or CD8+ cell distribution was observed. Similarly, mesenteric lymph nodes showed no changes in the cell subpopulation distribution between propanil-treated and control animals.

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

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

Triphenyltin acetate (TPTA)-induced cytotoxicity to mouse thymocytes

To perform a better investigation of the toxic activity of triphenyltin acetate (TPTA) already described in vivo, primary cultures of murine thymocytes were incubated for 2 to 32 h with graded amounts (0.5-8 microM) of the triorganotin compound. The cytotoxic activity has been evaluated with the Trypan blue dye exclusion test, the 3-(4,5-dimethyl-thiazol-2-yl)-2,5 diphenyl-tetrazolium bromide (MTT) assay for cell survival and the cellular release of lactate dehydrogenase. Following 2 h of incubation with TPTA, a dose-dependent reduction (P < 0.05) of cellular viability occurred and marked increases (P < 0.05) of the MTT cytotoxic index and of lactate dehydrogenase leakage were also observed. These findings indicate that TPTA is as cytotoxic to mice thymocytes, as other triphenyltin derivatives are to other species.

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

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

Thymocyte apoptosis as a mechanism for tributyltin-induced thymic atrophy in vivo

Tributyltin (TBT) immunotoxicity in rodent species is primarily characterised by T-lymphocyte deficiency resulting from a depletion of cortical thymocytes. In this study, bis(tri-n-butyltin) oxide (TBTO) was administered to male rats as a single oral dose of 30 or 60 mg/kg, and assessments were made of thymic cytopathology and the integrity of cellular DNA. TBTO treatment did not cause severe toxicity or overt clinical signs; however, by 48 h post-dosing relative thymus weights at 30 and 60 mg/kg were reduced to 66 and 43%, respectively, of control values. Increased DNA fragmentation was evident in thymic cell isolates (principally thymocytes) obtained from treated animals during the period of thymic involution. When DNA purified from these cells was visualised by agarose gel electrophoresis a multimeric internucleosomal fragmentation pattern, indicative of supra-physiological levels of apoptosis, was detected. Although unassociated apoptotic or necrotic thymocytes were essentially absent in cell preparations from TBTO-treated rats, significantly increased numbers of mononuclear phagocytic cells were observed. Many of these cells contained either apoptotic thymocytes, with nuclear morphologies exhibiting chromatin condensation, or cell remnants which were characterised as apoptotic bodies. Dibutyltin, which is a major metabolic dealkylation product of tributyltin, failed to significantly stimulate apoptosis when added to isolated thymocytes in vitro. Collectively, these findings suggest that activation of apoptosis contributes to TBT-induced thymocyte depletion in vivo, and indicate that it is unlikely that the metabolite dibutyltin is responsible for this effect.

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

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

Inhibition of mouse spleen cell activity by organotin compounds: effect of attachment of a maltose residue to the organotin group

Studies are reported on the inhibition of DNA synthesis and the lowering of cell viability caused by bis(tributyltin) oxide in mouse spleen cells cultured in the presence and absence of the B-lymphocyte mitogen, bacterial lipopolysaccharide. When a maltose residue is introduced into the organotin compound these toxic effects are increased. It is suggested that the maltose residue facilitates entry of the organotin compound into the cells.

Assessment of the immunotoxic potential of the fungicide dinocap in mice

The immunotoxic potential of dinocap was evaluated in female C57BL/6J mice following in vivo and in vitro exposure to this fungicide. In in vivo studies, groups of mice were dosed by gavage with technical grade dinocap at dosages ranging from 12.5 to 50 mg/kg per day for 7 or 12 days and selected immune functions examined. Mice dosed at 50 mg/kg per day dinocap died after 4 days of dosing. Twelve days of dosing with dinocap at 25 mg/kg per day resulted in decreased thymus weights and cellularity, and increased spleen weights. No changes were observed in body weight, absolute differential peripheral leukocyte counts, the lymphoproliferative responses to B- or T-cell mitogens, the mixed lymphocyte reaction, or natural killer (NK) cell activity of spleen cells from mice exposed to dinocap. Lymphoproliferative responses to concanavalin A (Con A) and phytohemagglutinin (PHA), however, were reduced in thymocytes from mice dosed at 25 mg/kg per day dinocap. The cytotoxic T lymphocyte (CTL) response to P815 mastocytoma cells was enhanced in mice exposed for 7 days to 25 mg/kg per day dinocap. Exposure of mice for 7 days to 25 mg/kg per day dinocap also caused a significant reduction in the IgM and IgG plaque-forming cell (PFC) response to sheep red blood cells (SRBC). A time-course study indicated that dinocap-induced suppression of the IgM PFC response was due to a delay in the peak PFC response to SRBC. In vitro studies using murine thymocytes cultured with dinocap (10 micrograms/ml for 72 h) resulted in suppression of the proliferative response to Con A and PHA. Exposure of thymocytes to dinocap in vitro for as little as 30 min resulted in suppression of the mitogen-stimulated response in the absence of any apparent direct cytotoxic effect. These results suggest that dinocap alters the immune system of the mouse, however, these effects are relatively modest in terms of adverse immune function and are only seen at relatively high exposure levels.

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

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

Tri-n-butyltin increases intracellular Ca2+ in mouse thymocytes: a flow-cytometric study using fluorescent dyes for membrane potential and intracellular Ca2+

Effects of tri-n-butyltin (TBT) on mouse thymocytes were examined using a flow-cytometer and fluorescent dyes for membrane potential and intracellular Ca2+ ([Ca2+]i). TBT at concentrations from 1 x 10(-7) M to 3 x 10(-7) M caused hyperpolarization in thymocytes during 30 min. after drug application in a time- and dose-dependent manner. Further increase in TBT concentration (to 1 x 10(-6) M) made hyperpolarization of thymocytes more profound within 5 min. after application, thereafter gradually depolarized them during the next 25 min. TBT at 3 x 10(-8) M or more (up to 1 x 10(-6) M) increased the [Ca2+]i of thymocytes. After reaching maximum [Ca2+]i at the various TBT concentrations used within 5 min. after drug application, the [Ca2+]i slightly decreased in a time-dependent manner. Effects of TBT on membrane potential and the [Ca2+]i were greatly reduced under nominal external Ca(2+)-free condition. Results suggest that TBT can promote Ca(2+)-influx to thymocytes, resulting in hyperpolarization by activation of Ca(2+)-dependent K+ current. The increase in [Ca2+]i by TBT may be related to its cytotoxic action on thymocytes.

Immunotoxicity of tri-n-butyltin oxide (TBTO) and tri-n-butyltin chloride (TBTC) in the rat

In a 1-month feeding trial, pure and commercial tri-n-butyltin oxide (TBTO) and tri-n-butyltin chloride (TBTC) were fed to rats at concentrations of 5 ppm and 25 ppm. At all times, the mean body weight gain and the food consumption was significantly less in rats treated with 25 ppm pure TBTO or pure TBTC as compared to control rats or rats receiving commercial TBTO. Histological examination of the thymus of rats treated for 7 days with TBTO showed atrophy with severe lymphocytic depletion in the cortex. After 28 days of exposure, most of the lesions reversed and the thymus became markedly smaller than in control rats, both in absolute terms and in relation to body weight. Seven days of exposure to TBTO increased liver weight but this change was reversed during a further 3-week exposure. Tin concentrations were the highest in livers and kidneys. Concentrations in the thymus were less than one-fifth of hepatic values. Changes in the rats treated with the commercial TBTO were very similar. Rats treated with TBTC showed lower tin levels and less immunotoxicity as compared to those treated with TBTO.

In vivo effects of triorganotins on calmodulin activity in rat brain

We have recently reported that the triorganotins are effective inhibitors of calmodulin (CaM) activity in vitro. The present experiments were designed to investigate the in vivo effects of triorganotins, that is, tributyltin (TBT), triethyltin (TET), and trimethyltin (TMT) on rat brain CaM activity. Male Sprague-Dawley rats were treated orally with TET (0.5, 1.0, and 1.5 mg/kg/d), TMT (0.75, 1.50, and 2.50 mg/kg/d), and TBT (0.75, 1.50, and 2.50 mg/kg/d) for 6 d and they were sacrificed 24 h after the last dose. There was significant loss of body weight in the high-dose group of the organotin treated rats. Ca(2+)-ATPase activity was determined in rat brain synaptic membranes. TET and TMT inhibited Ca(2+)-ATPase in a dose-dependent manner but TBT exhibited its inhibitory effect only at the highest dose (2.5 mg/kg/d). The inhibition of Ca(2+)-ATPase by these triorganotin compounds was reversed to control levels by the addition of CaM (5-10 micrograms) exogenously. The CaM levels of the synaptic membranes of the organotin-treated rats were not significantly changed. The data presented in this paper demonstrate that triorganotins impair the Ca(2+)-pump activity by interacting with CaM, which is a regulatory protein of Ca(2+)-ATPase. The present in vivo data and our previously reported in vitro data together indicate that triorganotins associated neurotoxicity may be due to an altered CaM activity in brain.

Effects of triphenyltin acetate on pregnancy in rats by oral administration

A teratological test was carried out on triphenyltin acetate (TPTA) used as a fungicide and antifouling agent. Pregnant Wistar rats were treated orally with TPTA at dose levels of 0, 1.5, 3.0, 6.0, 9.0 and 12.0 mg/kg/d during days 7-17 of gestation. Cesarean sections were performed on day 20 of gestation. In the pregnant rats, 2 of 13 and 2 of 12 dams died at 9.0 and 12.0 mg/kg, respectively. Vaginal bleeding, bloody mouth and nose, somnolence and depression of body weight gain and food intake were observed at 9.0 and 12.0 mg/kg at late stages of pregnancy. No statistically significant reductions in maternal thymus and spleen weights were observed on day 20 of gestation. Increase in embryonic and fetal deaths and in dams with total resorption of fetuses were observed at doses of more than 6.0 mg/kg. The doses of TPTA in this experiment, however, induced no teratogenic effects in rats.

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

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

Occupational triphenyltin acetate poisoning: a case report

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

Teratogenicity study of tri-n-butyltin acetate in rats by oral administration

A teratological test was carried out on tri-n-butyltin acetate (TBTA) used as a biocide and anti-fouling agent. Pregnant Wistar rats were treated orally with TBTA at dose levels of 0, 1, 2, 4, 8, and 16 mg/kg from days 7-17 of gestation. Cesarean sections were performed on day 20 of gestation. In pregnant rats, salivation and depression of body weight gain and food intake were observed at a late stage of pregnancy at the highest dose level of TBTA. Atrophy of the thymus was also observed in a dose-dependent manner on day 20 of gestation. In the fetuses, treatment with the highest dose level increased embryonic and fetal deaths, increased the incidence of fetuses with cleft palate, cervical rib and/or rudimentary lumbar rib, and decreased the body weights of fetuses.

Tributyltin stimulates apoptosis in rat thymocytes

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

Immune alterations in rats following subacute exposure to tributyltin oxide

Adult male Fischer 344 rats were dosed by oral gavage with bis(tri-n-butyltin)oxide (TBTO) in peanut oil for 10 consecutive days, at dosages ranging from 1.25 to 15 mg/kg/day. Other groups of rats were dosed daily for 10 days by oral gavage with cyclophosphamide (CY) at dosages ranging from 0.75 to 6 mg/kg/day. These rats served as positive controls for the immune assays employed. The immune function parameters examined included the following: delayed-type hypersensitivity (DTH) and antibody responses to bovine serum albumin (BSA), primary antibody responses to sheep red blood cells (SRBC) and trinitrophenyl lipopolysaccharide (TNP-LPS) and enumeration of splenic lymphocyte populations. The DTH and antibody responses to BSA were not affected by TBTO exposure; however these responses were suppressed in rats dosed with CY at 6 mg/kg/day. The plaque forming cell (PFC) response to the T cell-dependent antigen SRBC was enhanced in rats dosed with TBTO at from 5 to 15 mg/kg/day. On the other hand, the PFC response to the T cell-independent antigen TNP-LPS was unaffected by TBTO exposure. Rats dosed with CY had suppressed PFC responses to SRBC and TNP-LPS at dosages of 3 and 6 mg/kg/day, respectively. Enumeration of splenic lymphocyte populations from TBTO-exposed rats revealed a reduction in OX8- but not W3/25- or IgG-positive cells. These results, as well as results from an earlier study from this lab, suggest that T lymphocytes are a primary target for TBTO-induced immune alterations and that the enhancement of the PFC response to SRBC in TBTO-exposed rats may be mediated by alterations in the suppressor (OX8-positive) T lymphocyte population.

Acute triphenyltin intoxication: a case report

A 23 year old male developed abdominal pain, diarrhoea, and vomiting several hours after poisoning with acute triphenyltin intoxication in a suicide attempt. Severe ataxia, dysmetria, nystagmus, and blurring of vision soon supervened. Disturbance of consciousness and confusion developed 12 days later and lasted for two months. A delayed sensorimotor polyneuropathy was shown by electrophysiological studies to be due to axonal degeneration and demyelination. The neuropathy rapidly recovered after consciousness was regained.

Embryotoxic evaluation of bis(tri-n-butyltin)oxide (TBTO) in mice

Pregnant mice were treated on days 6-15 of gestation with 5, 20 and 40 mg/kg/d bis(tri-n-butyltin)oxide (TBTO), and sacrificed on gestational day 17. At the highest dose TBTO caused a significant reduction of maternal body weight gain and also proved to be highly embryotoxic. Necropsy showed a dose-related decrease in spleen weight while a dose-dependent increase in placental weight was observed.

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

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

The disposition of 14C-trimethyltin in the pregnant rat and fetus

Trimethyltin (TMT) is a potent neurotoxicant. For unknown reasons, age at exposure to TMT may dramatically influence the severity of TMT-induced neuropathology. We have demonstrated previously that radiolabel derived from [14C]-TMT given to pregnant dams on gestational day (GD) 17 is found in fetal brain and blood. The present study was designed to determine the distribution of radiolabel derived from [14C]-TMT to brain and other tissue in fetuses from dams dosed on either GD 12 or 17 with 7.0 mg/kg TMT chloride. Radioactivity in GD 12 and GD 17 maternal whole blood peaked 1 hour after IP treatment. Whole blood elimination half-lives were 12-15 days. Peak radiolabel concentrations in GD 12 maternal and fetal brain were only 11-30% of those from GD 17 animals, however, peak fetal brain concentrations of radiolabel were not different from their respective maternal brain concentrations. Radiolabel concentrations in liver, kidney, and adrenal of GD 17 dams were higher than those in corresponding GD 12 tissues. Combined urinary and fecal elimination of radiolabel for two weeks after dosing accounted for 31 and 22% of the GD 12 and 17 doses, respectively. It appears that gestational age influences the distribution and elimination of TMT in the rat.

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

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

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

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

Biological activity of organotin compounds--an overview

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

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

The inhibitor of oxidative phosphorylation tri-n-butyltin chloride (TBTC) causes membrane damage and disintegration of isolated rat thymocytes at concentrations higher than 1 microM. From a concentration of 0.1 microM, TBTC disturbs energy metabolism as indicated by an increase in methylglucose uptake, glucose consumption and lactate production and by a decrease in cellular ATP levels. Over the same TBTC concentration range, the incorporation of DNA, RNA and protein precursors are markedly reduced. Moreover the production of cyclic AMP upon stimulation of the cells with prostaglandin E1 is effectively inhibited. These effects cannot be explained by an inhibition of nucleoside kinase activity, amino acid uptake or adenylate cyclase activity. The effects of TBTC on macromolecular synthesis and cyclic AMP production are possibly due to a disturbance of the cellular energy state.

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

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

Toxicity of organotin compounds for polymorphonuclear leukocytes: the effect on phagocytosis and exocytosis

Phagocytosis and concomitant release of enzymes by rabbit polymorphonuclear leukocytes (PMNs) are inhibited by micromolar concentrations of triphenyltin and tributyltin; inhibition by triethyltin occurs at higher concentrations. Chemotactic peptide-induced exocytosis is inhibited at the same concentrations as phagocytosis. Tributyltin causes cell lysis at slightly higher concentrations as required for inhibition of phagocytosis and exocytosis. The organotin compounds have little effect on ATP level in PMNs, which makes an effect on metabolic energy providing processes unlikely. The increase of Ca2+-permeability of the plasma membrane, induced by chemotactic peptide, is inhibited by the organotin compounds. Inhibition of exocytosis by triphenyltin can be counteracted by a number of sulfhydryl compounds. The results suggest that the organotin compounds interfere with PMN function in an early phase of cell activation, where all functions have a common pathway, and where vulnerable sulfhydryl groups play a pivotal role.

Diurnal patterns in homecage behavior of rats after acute exposure to triethyltin

Diurnal patterns of eating, drinking, locomotor activity, and rearing in male Fischer-344 rats were examined for 11 days after a single oral dose of triethyltin bromide (TET) at 0, 1.5, 3, or 5 mg/kg. The 5 mg/kg group exhibited a time-related drop in food consumption and body weight until 3 of 10 rats were sacrificed moribund 11 days after dosing. Doses of 1.5 and 3 mg/kg TET did not reduce body weight or consumption of food and water. In contrast, food consumption was significantly increased 7 and 11 days after 3 mg/kg TET, and diurnal patterns of eating and drinking were disrupted 7 days after 3 and 5 mg/kg TET. A phase shift in licking patterns was induced by the high dose. Unlike trimethyltin (TMT), TET did not affect efficiency of eating. Diurnal patterns of both horizontal and vertical activity were disrupted at all dose levels on Day 2 after dosing; by 16 days after dosing, recovery was evident in all rats including those surviving 5 mg/kg TET. These results show that a near-lethal dose of TET produced a reversible syndrome of hypoactivity, aphagia, and weight loss similar to that seen after acute TMT; in the absence of the above signs, diurnal patterns of behavior revealed effects of TET at doses as low as 1.5 mg/kg; the magnitude of the effect depended on the time of day at which the response was measured; and TET did not produce the same effects on ingestive behaviors (polydipsia and reduced feeding efficiency) that were previously observed after acute TMT.

Triorganotin-induced cytotoxicity to rat thymus, bone marrow and red blood cells as determined by several in vitro assays

To further investigate the immunotoxic effects of tri-n-propyltin chloride (TPTC), tri-n-butyltin chloride (TBTC) and triphenyltin chloride (TPhTC) several cytotoxicity tests with a series of trialkyltin chlorides and TPhTC were carried out, using isolated rat thymocytes as target cells. Thymocytes, cultured in a serum-supplemented medium, were exposed to organotin concentrations ranging from 0.01 to 10 microM for periods up to 30 h. Parameters such as cell count, trypan blue exclusion, chromium release, thymidine incorporation and cyclic AMP production were used to evaluate the cytotoxicity of these compounds. The more lipophilic compounds TPTC, TBTC, tri-n-hexyltin chloride (THTC) and TPhTC appeared most cytotoxic, reducing thymidine incorporation at concentrations as low as 0.05-1 microM. Membrane damage as determined by trypan blue exclusion and chromium release occurred at higher levels (1-10 microM). The water soluble homologue trimethyltin chloride (TMTC) was least effective in all test models. When phosphate-buffered saline supplemented with glucose was used as incubation medium, TBTC appeared more cytotoxic to thymocytes. Using this medium in 5-h incubations the cytotoxicity of TBTC to thymus, bone marrow and red blood cells was compared. Bone marrow cells were slightly less sensitive than thymocytes, while red cells were relatively resistant. In conclusion, of the triorganotin compounds especially the lipophilic homologues are cytotoxic in vitro.