Effect of Lactational Exposure to Tributyltin Chloride on Innate Immunodefenses in the F1 Generation in Mice

Maternal exposure to tributyltin alters the breast milk, hormonal profile, and thyroid morphology of dams and induces sex-specific changes in neonate rat offspring

Tributyltin (TBT) is the chemical substance commonly used worldwide to prevent biofouling of vessels. Due to its ability to bioaccumulate and biomagnify, even after being banned, significant concentrations of TBT can be detected in sediment, affecting marine and human life. Although studies have shown that direct exposure to TBT alters physiological parameters in mammals, the relationship between exposure to TBT during pregnancy and lactation, considered critical windows for metabolic programming, has not been fully elucidated. Our hypothesis is that offspring whose mothers were exposed to TBT during critical stages of development may exhibit dysfunctions in endocrine-metabolic parameters. We used pregnant Wistar rats that were divided into groups and received the following treatments from gestational day 7 until the end of lactation by intragastric gavage: vehicle (ethanol 0.01%; Control), low TBT dose (100 ng/kg of body weight (bw)/day; TBT100ng) and high TBT dose (1000 ng/kg bw/day; TBT1000ng). Dams and offspring at birth and weaning (21 days old) were studied. Maternal exposure to TBT promoted dose-dependent changes in dams. The findings for adiposity, milk composition and lipid profile were more pronounced in TBT100 ng dam; however, thyroid morphology was altered in TBT1000 ng dam. Female offspring were differentially affected by the dose of exposure. At birth, females in the TBT100ng group had low body weight, lower naso-anal length (NAL), and higher plasma T4, and at weaning, females in the TBT100ng group had lower insulin and leptin levels. Females in the TBT1000ng group had lower NAL at birth and lower leptinemia and weight of white adipose tissue at weaning. Male offspring from TBT groups showed high T3 at birth, without biometric alterations at birth or weaning. Despite these findings, both sexes exhibited dose-dependent morphological changes in the thyroid gland. Thus, maternal exposure to TBT constitutes an important route of contamination for both dams and offspring.

Adult exposure to tributyltin affects hypothalamic neuropeptide Y, Y1 receptor distribution, and circulating leptin in mice

Tributyltin (TBT), a pesticide used in antifouling paints, is toxic for aquatic invertebrates. In vertebrates, TBT may act in obesogen- inducing adipogenetic gene transcription for adipocyte differentiation. In a previous study, we demonstrated that acute administration of TBT induces c-fos expression in the arcuate nucleus. Therefore, in this study, we tested the hypothesis that adult exposure to TBT may alter a part of the nervous pathways controlling animal food intake. In particular, we investigated the expression of neuropeptide Y (NPY) immunoreactivity. This neuropeptide forms neural circuits dedicated to food assumption and its action is mediated by Y1 receptors that are widely expressed in the hypothalamic nuclei responsible for the regulation of food intake and energy homeostasis. To this purpose, TBT was orally administered at a dose of 0.025 mg/kg/day/body weight to adult animals [male and female C57BL/6 (Y1-LacZ transgenic mice] for 4 weeks. No differences were found in body weight and fat deposition, but we observed a significant increase in feed efficiency in TBT-treated male mice and a significant decrease in circulating leptin in both sexes. Computerized quantitative analysis of NPY immunoreactivity and Y1-related β-galactosidase activity demonstrated a statistically significant reduction in NPY and Y1 transgene expression in the hypothalamic circuit controlling food intake of treated male mice in comparison with controls. In conclusion, the present results indicate that adult exposure to TBT is profoundly interfering with the nervous circuits involved in the stimulation of food intake.

Acute exposure to tributyltin induces c-fos activation in the hypothalamic arcuate nucleus of adult male mice

Tributyltin (TBT) is a largely diffused environmental pollutant, banned from paints in the European Union from 2003. However, the level of TBT (and other organotins) in food, particularly fish and shellfish, remains still high. Several studies demonstrated that TBT is involved in the development of obesity, via peripheral action, but currently, there are only a few data illustrating effects of TBT on the nervous system. In the present study, we tested the hypothesis that acute exposure to TBT may directly activate brain cells in particular, in those hypothalamic nuclei regulating the food intake. To this purpose, TBT was orally administered at a single dose (10 mg/kg/body weight) to two groups of adult male mice: regularly fed or fasted for 24 h. Mice were sacrificed 90 min after the TBT administration and perfused by 4% paraformaldehyde. Brains were quickly dissected, frozen and sectioned for immunocytochemical detection of c-fos, a common marker of cell activation. In both, fed or fasted mice, exposure to TBT induced a significant increase of c-fos expression in the arcuate nucleus in comparison to control mice. The other nuclei involved in the control of feeding behavior did not show any significant increase. These data are the first in vivo demonstration that TBT has not only peripheral effects, but also may activate elements in the brain, in particular in a crucial region for the regulation of food intake like the arcuate nucleus.

Enhanced inhibitory effects of TBT chloride on the development of F1 rats

Neurotoxicity is one of the major effects of tributyltin (TBT). The effects on the next generation of F(1) rats exposed to TBT via the placenta and their dams' milk may be stronger than those on adults. Pregnant Wister rats were exposed to TBT at 0 and 125 ppm in their food. Half of the female F(1) rats in both groups were exposed to TBT at 125 ppm in their food from 9 to 15 weeks of age. Female F(1) rats were divided into the following groups: the control-control (CC) group, with no exposure; the TBT-control (TC) group, exposed to TBT via the placenta and their dams' milk; the control-TBT (CT) group, exposed to TBT via their food from 9 to 15 weeks of age; and the TBT-TBT (TT) group, exposed to TBT via the placenta, their dams' milk, and their food (n = 10/group). After administration, an open-field test and prepulse inhibition (PPI) test were performed at 15 weeks of age. The mean body weights of the TC and TT groups were significantly lower than that of the CC group from 9 to 15 weeks of age. The mean relative thymus weight of the TC and TT groups was significantly lower than that of the CC group. In the open-field test, a marked decrease in the total locomotion distance was observed in the TT group. The mean values in the TT and TC groups were significantly lower than that in the CC group. For the locomotion distance between 15 and 20 min, the mean values in the CT, TC, and TT groups were significantly lower than that in the CC group. The mean locomotor distance between 25 and 30 min in the TT group was significantly lower than that in the CC and TC groups. The mean values of instances of wall rearing in the TC, CT, and TT groups were significantly lower than that in the CC group. The mean value of face washing or body washing in the TT group was significantly lower than that in the CT group. There were no significant differences in indexes of the PPI test. Exposure to TBT via the placenta and their dams' milk inhibited the development of F(1) rats, which continued after weaning. Inhibition of the rats' activity induced by exposure to TBT via the placenta and their dams' milk and/or via their food was suggested. The effects were most evident in the TT group.

Toxic effects of tributyltin and its metabolites on harbour seal (Phoca vitulina) immune cells in vitro

The widespread environmental contamination, bioaccumulation and endocrine disruptor effects of butyltins (BTs) to wildlife are well documented. Although suspected, potential effects of BTs exposure on the immune system of marine mammals have been little investigated. In this study, we assessed the effects of tributyltin (TBT) and its dealkylated metabolites dibutyltin (DBT) and monobutyltin (MBT) on the immune responses of harbour seals. Peripheral blood mononuclear cells isolated from pup and adult harbour seals were exposed in vitro to varying concentrations of BTs. DBT resulted in a significant decrease at 100 and 200 nM of phagocytotic activity and reduced significantly phagocytic efficiency at 200 nM in adult seals. There was no effect in phagocytosis with TBT and MBT. In pups, the highest concentration (200 nM) of DBT inhibited phagocytic efficiency. A reduction of tumor-killing capacity of adult natural killer (NK) cells occurred when leukocytes were incubated in vitro with 50 nM DBT and 200 nM TBT for 24h. In adult seals, T-lymphocyte proliferation was significantly suppressed when the cells were exposed to 200 nM TBT and 100 nM DBT. In pups, the proliferative response increased after an exposure to 100 nM TBT and 50 nM DBT, but decreased with 200 nM TBT and 100 nM DBT. The immune functions were more affected by BTs exposure in adults than in pups, suggesting that other unsuspected mechanisms could trigger immune parameters in pups. The toxic potential of BTs followed the order of DBT>TBT>MBT. BT concentrations of harbour seal pups from the St. Lawrence Estuary (Bic National Park) ranged between 0.1-0.4 ng Sn/g wet weight (ww) and 1.2-13.4 ng Sn/g ww in blood and blubber, respectively. For these animals, DBT concentrations were consistently below the quantification limit of 0.04 ng Sn/g ww in blood and 0.2 ng Sn/g ww in blubber. Results suggest that concentrations measured in pups are considered too low to induce toxic effects to their immune system during first days of life. However, based on our in vitro results, we hypothesize that BTs, and DBT in particular, could pose a serious threat to the immune functions in free-ranging harbour seal adults.

Tributyltin impairs dentin mineralization and enamel formation in cultured mouse embryonic molar teeth

Tributyltin (TBT), earlier used as an antifouling agent in marine paints, causes damage to the aquatic ecosystem, for example, impaired shell calcification in oysters. TBT affects hard tissue mineralization even in mammals: delayed bone mineralization has been observed in rodents exposed to TBT in utero. To see if TBT interferes with tooth development, especially dental hard tissue formation, we exposed mouse E18 mandibular first and second molars to 0.1, 0.5, 1.0, and 2.0 microM TBT chloride in organ culture for 7-12 days. The amount of enamel was assessed and the sizes of the first molars were measured from photographs taken after the culture. TBT concentration dependently impaired enamel formation (p < 0.001) and reduced tooth size (p < 0.001). Histological analysis showed slight arrest of dentin mineralization and enamel formation in first molars exposed to 0.1 microM TBT. At the concentration of 1.0 microM the effect was overt. The differentiation of ameloblasts in the mesial cusps was retarded but TBT had no effect on odontoblast morphology. The dental epithelium showed enhanced apoptosis. The failure of ameloblasts to form enamel was likely to be secondary to the effect of TBT on dentin mineralization. In the second molars, where predentin deposition had not started, ameloblasts and odontoblasts were nonpolarized and proliferative. The results showed that TBT concentration dependently impairs dental hard tissue formation and reduces tooth size in cultured mouse embryonic molars. The effects depend on the stage of tooth development at the start of exposure and may involve epithelial-mesenchymal interactions.

Organotin speciation and tissue distribution in rat dams, fetuses, and neonates following oral administration of tributyltin chloride

Tributyltin (TBT) is a biocide that contaminates human foodstuffs, especially shellfish. TBT is an endocrine disrupter, producing imposex in several marine gastropods. Previous studies showed that oral dosing of rat dams with TBT chloride leads to abnormal fetal and postnatal development. In this study, the tissue distribution and speciation of organotins in tissues were examined in dams, fetuses, and neonates following dosing of rat dams commencing on gestational day (GD) 8 by oral gavage with TBT in olive oil at 0, 0.25, 2.5, or 10 mg/kg body weight (BW)/d. Dams' body weights were significantly reduced by the 10-mg/kg BW/d TBT treatment. At GD20, there were no significant effects of any TBT treatment on pup weights, litter size, sex ratio, or tissue weights. However, at postnatal day (PND) 6 and 12, neonatal pup weights were reduced by the 10-mg/kg BW/d TBT treatment but tissue weights were unaffected, except for the liver weight of female pups, which was reduced by the 10-mg/kg BW/d TBT treatment. Tissues harvested on GD20 and PND6 and PND12 were extracted for determination of organotins by gas chromatography-atomic emission detection (GC-AED). In most tissues, TBT and its metabolite dibutyltin (DBT) were evident but monobutyltin (MBT) was rarely measured above the detection limit. The livers and brains of fetuses contained TBT and DBT at levels that were approximately 50% of the equivalent tissues in the dams. Furthermore, these tissues appeared to preferentially absorb/retain organotins, since the concentrations were greater than were found for the total loading in whole pups. The placenta also contained relatively large quantities of TBT and DBT. Postnatally, the TBT levels in pups decreased markedly, a probable consequence of the extremely low levels of organotins in rat milk. However, DBT levels in pups livers and brains were maintained, probably due to metabolism of TBT to DBT. Similarly, while dams' spleens contained significant quantities of organotins, the pups' spleens contained smaller quantities, and these decreased rapidly between PND6 and PND12. These results show that organotins cross the placenta and accumulate in fetal tissues but that during lactation, the pups would receive minimal organotins through the milk and during this period, the levels of TBT in pups' tissues decreases rapidly. Consequently, fetuses would be at greater risk of the adverse effects of TBT, but due to the lack of transfer through milk, the risk would be reduced during the lactational period.

In vitro tests to evaluate immunotoxicity: A preliminary study

The implementation of Registration, Evaluation and Authorisation of new and existing Chemicals (REACH) will increase the number of laboratory animals used, if alternative methods will not be available. In the meantime, REACH promotes the use of in vitro tests and, therefore, a set of appropriated alternative testing methods and assessment strategies are needed. The immune system can be a target for many chemicals including environmental contaminants and drugs with potential adverse effects on human health. The aim of this study was to evaluate the predictivity of a set of in vitro assays to detect immunosuppression. The tests have been performed on human, rat and murine cells. Different endpoints have been assessed: cytotoxicity, cytokine release, myelotoxicity and mitogen responsiveness. For each of these endpoints IC50s values have been calculated. Six chemical substances, representative of the full range of in vivo responses and for which good human and/or animal data are available either from databases or literature, have been selected: two chemicals classified as not immunotoxic (Urethane and Furosemide), and four (tributyltin chloride (TBTC), Verapamil, Cyclosporin A, Benzo(a)pyrene) with different effect on immune system. All the tests confirmed the strong immunotoxic effect of TBTC as well as they confirmed the negative controls. For one chemical (Verapamil) the IC50 is similar through the different tests. The IC50s obtained with the other chemicals depend on the endpoints and on the animal species. The clonogenic test (CFU-GM) and the mitogen responsiveness showed similar IC50s between human and rodent cells except for Cyclosporin A and TBTC. All different tests classified the compounds analyzed in the same way.

Subacute administration of tributyltin chloride modulates neurotransmitters and their metabolites in discrete brain regions of maternal mice and their F1 offspring

Tributyltin (TBT) compounds have been used as anti-fouling agents and the central nervous system is one of its target organs. TBT-induced modulations of neurotransmitters in the brains of adult mice have been reported. However, little is known about the developmental neurotoxicity of TBT. In this study, we evaluated the effects of TBT on neurotransmitters and their metabolites in discrete brain regions of female ICR mice and their offspring. Pregnant ICR mice were exposed to TBT chloride at concentrations of 0, 15 or 50 ppm in water or 125 ppm in food. Male offspring were sacrificed at one, two and three weeks after birth. The concentrations of norepinephrine, dopamine (DA), dihydoxyphenylacetic acid, homovanillic acid (HVA), serotonin (5-HT), and 5-hydroxyindoleacetic acid (5-HIAA) were determined in different brain regions by HPLC. All offspring from the 125 ppm group died immediately after birth. A significant decrease in the body weight of the TBT-treated F1 groups compared to the control group was observed in the first week. Significant increases compared to the controls were observed for the DA concentration in the striatum of the 50 ppm F1 group, and for the HVA concentration in the cerebrum and the 5-HT concentration in the medulla oblongata of the 15 and 50 ppm F1 groups in the third week. At three weeks of age, the neurotransmitters and their metabolites may be useful indexes for developmental neurotoxicity. For the dams, a significant decrease in the 5-HT concentration was observed in the cerebellum, medulla, midbrain and striatum of the 125 ppm group compared to the control group. A significant decrease in the 5-HIAA concentration was also observed in the cerebellum, midbrain and striatum of the dams in the 125 ppm group compared to the control. TBT may induce a decrease in the synthesis of 5-HT in the dams. The discrepancy between dams and offspring may be due to several factors such as age, dose, route, sex and pregnancy.

Down-regulation of mdr1b mRNA expression in the kidneys of mice following maternal exposure to tributyltin chloride

We investigated the change in renal mdr1b mRNA expression in offspring exposed to tributyltin chloride (TBTC) via the placenta and lactation or via lactation, using the real-time reverse transcription-polymerase chain reaction. Pregnant ICR mice were given water containing TBTC (0, 15, and 50 microg/ml) ad libitum from the start of pregnancy to weaning or from parturition to weaning. Exposure via the placenta and lactation significantly reduced the renal mdr1b level in offspring. Exposure to TBTC through the mother might impair the exclusion system of toxic compounds in offspring.