Tributyltin induces DNA damage as well as oxidative damage in rats

The effect of in vitro exposure to tributyltin on the immune competence of Chinook salmon (Oncorhynchus tshawytscha) leukocytes

We evaluated the direct effects of in vitro exposures to tributyltin (TBT), a widely used biocide, on the cell-mediated immune system of Chinook salmon (Oncorhynchus tshawytscha). Splenic and pronephric leukocytes isolated from juvenile Chinook salmon were exposed to TBT (0, 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6 mg/l) in cell cultures for 24 h. Effects of TBT on cell viability, induction of apoptosis, and mitogenic responses were measured by flow cytometry. Splenic and pronephric leukocytes in the presence of TBT experienced a concentration-dependent decrease in viability in cell cultures. Apoptosis was detected as one of the mechanisms of cell death after TBT exposure. In addition, pronephric lymphocytes exhibited a greater sensitivity to TBT exposure than pronephric granulocytes. The functional ability of splenic B-cells to undergo blastogenesis upon lipopolysaccharide stimulation was also significantly inhibited in the presence of 0.05, 0.07, or 0.10 mg/l of TBT in the cell cultures. Flow cytometric assay using a fluorescent conjugated monoclonal antibody against salmon surface immunoglobulin was employed for the conclusive identification of B-cells in the Chinook salmon leukocytes. Our findings suggest that adverse effects of TBT on the function or development of fish immune systems could lead to an increase in disease susceptibility and its subsequent ecological implications.

Low levels of lead exposure induce oxidative damage and DNA damage in the testes of the frog Rana nigromaculata

We have investigated the chronic effects of low concentrations of lead (Pb) on oxidative damage and DNA damage in testes of the frog Rana nigromaculata. Sixty adult male frogs were randomly divided into six groups of ten. Based on the levels of the Integrated Wastewater Discharge Standard (GB 8978-1996) of China, five groups (II-VI) were treated by epidermal absorption with a PbNO(3) solution at concentrations of 0.1, 0.2, 0.4, 0.8, 1.6 mg/l, respectively. The first group (I), which served as a control, was treated with distilled water only. Thirty days after treatment, all frogs were sacrificed and the testis tissues removed for the measurement of malondialdehyde (MDA) and glutathione (GSH) levels. DNA damage, including indicators of damage rate, DNA tail length (TL), and DNA tail moment (TM), was also analyzed by comet assays. Our data suggest that MDA levels in all treatment groups and GSH levels in the 0.2-1.6 mg/l Pb groups increased significantly relative to the controls (P < 0.01). Treatment with Pb at concentrations >0.4 mg/l also increased DNA damage rate and TM, while TL increased when the Pb level was >0.2 mg/l (P < 0.01 for DNA damage rate and TM, P < 0.05 for TL). Positive correlations were also found between DNA damage levels in the testes and MDA levels (r = 0.796 for DNA damage rate, r = 0.811 for TL, r = 0.796 for TM; P < 0.01 for all) as well between MDA and GSH levels (r = 0.455, P < 0.05) in the testes. Results from MDA measurements indicated that Pb-induced DNA damage in the testes of R. nigromaculata was possibly due to oxidative damage. Taken together, we conclude that Pb can induce male reproductive toxicity in R. nigromaculata.

Protective effect of green tea polyphenols on tributyltin-induced oxidative damage detected by in vivo and in vitro models

The current study investigated the protective effects of green tea polyphenols (GTPP) on TBT-induced oxidative damage. The results showed that reactive oxygen species (ROS) production and malondialdehyde content of the liver in mice exposed to TBT were reduced in the GTPP-treated group compared to the untreated group. The intracellular ROS level was elevated in TBT-treated human FL cells in a time-dependent manner. Comet assay data demonstrated that the number of cells with damaged DNA in untreated mice was found to be significantly higher compared to GTPP-treated mice. Damage to the nuclei and mitochondria observed in TBT-treated mice were alleviated in mice treated with both TBT and GTPP. The results represent the first observation that GTPP were effective in reducing TBT-induced oxidative damage both in vivo and in vitro. The possible protective mechanism may be due to the powerful ability of GTPP to scavenge ROS and prevent DNA breaks. We conclude that GTPP could be an effective agent or food supplement to reduce the cytotoxicity of TBT.

Genotoxic effects of binary mixtures of xenoandrogens (tributyltin, triphenyltin) and a xenoestrogen (ethinylestradiol) in a partial life-cycle test with Zebrafish (Danio rerio)

A partial life-cycle test with the model fish Danio rerio was performed in order to evaluate the genotoxic potential of binary mixtures of xenoandrogenic (tributyltin--TBT; triphenyltin--TPT) and an estrogenic compound (ethinylestradiol--EE2). Five days post-fertilisation larvae were diet-exposed to environmental relevant concentrations of TBT and TPT (25 ng/g-100 ng/g), and water-exposed to ethinylestradiol (3.5 ng/L) for a four-month period; binary mixtures of TBT plus EE2 and TPT plus EE2 were run in parallel. The erythrocytic nuclear abnormalities (ENA) assay in circulating erythrocytes was used to evaluate genotoxicity in the end of the four-month exposure period. A significant increase (p<0.05, Kruskall-Wallis non-parametric ANOVA) in ENA frequency, in comparison with control animals, was observed in those animals exposed to TBT and TPT (the highest doses only), and to EE2 and the binary mixtures, although neither synergistic nor additive effects of the tested compounds were evident. Overall, the results clearly indicate that chronic exposure to low levels of TBT, TPT, EE2 and binary mixtures of TBT plus EE2 and TPT plus EE2 are genotoxic to zebrafish, which may suggest that wild fish populations may be under increased DNA damage in areas contaminated by these endocrine disrupting chemicals.

Tributyltin induces apoptotic signaling in hepatocytes through pathways involving the endoplasmic reticulum and mitochondria

Tri-n-butyltin is a widespread environmental toxicant, which accumulates in the liver. This study investigates whether tri-n-butyltin induces pro-apoptotic signaling in rat liver hepatocytes through pathways involving the endoplasmic reticulum and mitochondria. Tri-n-butyltin activated the endoplasmic reticulum pathway of apoptosis, which was demonstrated by the activation of the protease calpain, its translocation to the plasma membrane, followed by cleavage of the calpain substrates, cytoskeletal protein vinculin, and caspase-12. Caspase-12 is localized to the cytoplasmic side of the endoplasmic reticulum and is involved in apoptosis mediated by the endoplasmic reticulum. Tri-n-butyltin also caused translocation of the pro-apoptotic proteins Bax and Bad from the cytosol to mitochondria, as well as changes in mitochondrial membrane permeability, events which can activate the mitochondrial death pathway. Tri-n-butyltin induced downstream apoptotic events in rat hepatocytes at the nuclear level, detected by chromatin condensation and by confocal microscopy using acridine orange. We investigated whether the tri-n-butyltin-induced pro-apoptotic events in hepatocytes could be linked to perturbation of intracellular calcium homeostasis, using confocal microscopy. Tri-n-butyltin caused changes in intracellular calcium distribution, which were similar to those induced by thapsigargin. Calcium was released from a subcellular compartment, which is likely to be the endoplasmic reticulum, into the cytosol. Cytosolic acidification, which is known to trigger apoptosis, also occurred and involved the Cl(-)/HCO(3)(-) exchanger. Pro-apoptotic events in hepatocytes were inhibited by the calcium chelator, Bapta-AM, and by a calpain inhibitor, which suggests that changes in intracellular calcium homeostasis are involved in tri-n-butyltin-induced apoptotic signaling in rat hepatocytes.

Garlic oil prevents tributyltin-induced oxidative damage in vivo and in vitro

Tributyltin (TBT) can be transported to the human body by contaminated seafood. Presently, there is no known effective strategy to eliminate TBT's toxic effects from contaminated food. The present study was conducted to investigate the ability of garlic oil (GO) to prevent TBT-induced oxidative damage in vivo as well as in vitro. The results follow: both reactive oxygen species (ROS) production and malondialdehyde content decreased in mice pretreated with GO, the number of cells with damaged DNA in unprotected mice increased significantly compared with that in GO-protected mice (comet assay), and the alleviation of the depletion of cortical thymocytes and damage to nucleoli and mitochondria in GO-protected mice was observed. In human FL (human amniotic cells; American Type Culture Collection) cell studies, TBT-induced intracellular ROS generation was significantly inhibited after FL cells were pretreated with GO, and the TBT-induced cytotoxic effects were also prevented by GO. The results led to the first observation that GO was effective in reducing TBT-induced oxidative damage both in vivo and in vitro. The possible protective mechanism may stem from the considerable ability of GO to scavenge ROS. We conclude that GO could be an effective agent or food supplement in reducing the toxicity of TBT.