Jiliang Zhang

Tributyltin causes obesity and hepatic steatosis in male mice.

Organotin compounds such as tributyltin (TBT) have been used worldwide in agriculture and industry as biocides, heat stabilizers, and chemical catalysts. However, few studies addressing the effects of TBT on growth and metabolism have been reported. This study was conducted to investigate the effects of TBT at low doses (0.5, 5, and 50 μg/kg) on body weight gain in male mice exposed as from puberty and to determine the alterations in related hormones. The results showed that exposure to TBT for 45 days resulted in an increase in body weight gain and hepatic steatosis accompanied with hyperinsulinemia and hyperleptinemia. Reduction of hepatic adiponectin levels in a dose‐dependent manner was related to the lipid increase in the liver. These results suggest that chronic and repeat exposure to low doses of TBT can result in obesity and hepatic steatosis and induce the occurrence of insulin and leptin resistance.

EFFECT OF TRIBUTYLTIN ON TESTICULAR DEVELOPMENT IN SEBASTISCUS MARMORATUS AND THE MECHANISM INVOLVED

Organotin compounds, such as tributyltin (TBT), that have been used as antifouling biocides can induce masculinization in female mollusks. However, few studies addressing the effects of TBT on fishes have been reported. The present study was conducted to investigate the effects of TBT at environmentally relevant concentrations (1, 10, and 100 ng/L) on testicular development in Sebastiscus marmoratus and to gain insight into its mechanism of action. After exposure for 48 d, the gonadosomatic index had decreased in a dose-dependent manner. Although the testosterone levels in the testes were elevated and the 17beta-estradiol levels were decreased, spermatogenesis was suppressed. Moreover, gamma-glutamyl transpeptidase activity (which is used as a Sertoli cell marker) was decreased in a dose-dependent manner after TBT exposure, and serious interstitial fibrosis was observed in the interlobular septa of the testes in the 100 ng/L TBT test group. Increases in the retinoid X receptors and peroxisome proliferator activated receptor gamma expression and the progressive enlargement of lipid droplets in the testes were observed after TBT exposure. Estrogen receptor alpha levels in the testes of the fish exposed to TBT decreased in a dose-dependent manner. The reduction of estrogen receptor alpha mRNA resulted from the decrease of 17beta-estradiol levels, and the progressive enlargement of lipid droplets may have contributed to the dysfunction of the Sertoli cells, which then disrupted spermatogenesis.

Fluoride-induced oxidative stress is involved in the morphological damage and dysfunction of liver in female mice.

Fluoride (F), one of the most toxic environmental and industrial pollutants, is known to exert hepatotoxicity. The contribution of oxidative stress to the F tolerance of liver remains largely unknown. In this study, the morphological and ultrastructural characteristics of liver were observed using hematoxylin and eosin staining and transmission electron microscopy (TEM), respectively. Oxidative-stress participations was analysed and the mRNA expression levels of catalase (Cat), glutathione peroxidase 1 (GSH-Px1), nitric oxide synthase 2 (NOS2), and superoxide dismutase 1 (SOD1) were investigated by real-time PCR. Changes in liver-function parameters were also detected. Results showed that the reactive content of reactive oxygen species increased significantly, whereas SOD and GSH-Px activities, as well as total anti-oxidising capability (T-AOC), decreased significantly, with increased nitric oxide (NO) and malondialdehyde (MDA) contents in liver and serum after 70days of F treatment. The mRNA expression levels of Cat, GSH-Px1, and SOD were significantly downregulated, whereas NOS2 mRNA expression level was up upregulated, after F treatment for 70days. Light microscopy also revealed that hepatocytes were fused into pieces; cell boundaries were unclear, and nuclei were lightly stained. TEM further showed that hepatocytes were characterised by vague nuclear and mitochondrial membranes, dilated endoplasmic reticulum, and aggravated vacuolar degeneration. Activities of alanine transaminase, aspartate aminotransferase, alkaline phosphatase and lactate dehydrogenase, as well as the level of total bilirubin in serum increased. Overall, these results indicated that F interfered with the balance of antioxidase activity and morphological changes in liver, which were involved in mouse liver dysfunction.

Tributyltin chloride results in dorsal curvature in embryo development of Sebastiscus marmoratus via apoptosis pathway

Tributyltin (TBT) is a ubiquitous marine environmental contaminant characterized primarily by its reproductive toxicity. However, the embryotoxicity of TBT has not been extensively described, especially in fishes. The aim of this study was to investigate the developmental toxicity of waterborne TBT at environmental levels (0, 0.1, 1, and 10 ng L(-1) as Sn) on Sebastiscus marmoratus embryos. Our study showed that TBT reduced the hatchability and caused apparent morphological abnormalities including dorsal curvature, severely twisted tails and pericardial edema. In addition, localized apoptosis was found in the tail regions of embryos after TBT exposure. The study provided a possible mechanistic link between apoptosis and TBT-induced twisted tails abnormality. TBT exposure induced retinoid X receptor α expression in S. marmoratus embryos at the 0.1 and 1 ng L(-1) group, which would be responsible for the increasing apoptotic cells induced by TBT. The results of the present study have widespread implications for environmental ecological assessment, management and the etiology of developmental defects.

Tributyltin exposure causes lipotoxicity responses in the ovaries of rockfish, Sebastiscus marmoratus

Tributyltin (TBT) is a well-studied endocrine disruptor in mollusks and fishes. Recently, TBT is also recognized as a metabolic disruptor. Since abnormal lipids metabolism can induce negative effects on reproduction, the present study was designed to investigate the effects of TBT on ovarian lipid accumulation and testosterone esterification in rockfish (Sebastiscus marmoratus). After exposure for 48 d, there was a decrease of neutral lipid droplets in the ooplasm of ovaries. Exposure has also induced lipotoxicity responses in the ovaries, which shown as an increase of interstitial ectopic lipid accumulation and total lipids. The decrease of serum triiodothyronine and thyroxine concentrations might be responsible for the lipotoxicity responses. In addition, the percentage of testosterone in an esterified form was significantly decreased in the ovaries by TBT exposure, which might be a mechanism by which free testosterone levels increased. The accumulation of ectopic lipids and increase of free testosterone levels in the ovaries might impact ovarian functions and oocyte development in fish. These results strongly indicate that TBT exposure can influence reproductive functions of rockfish through lipotoxic mechanism.

Inhibition of thyroidal status related to depression of testicular development in Sebastiscus marmoratus exposed to tributyltin.

Organotin compounds, such as tributyltin (TBT), which have been used as antifouling biocides, are still of concern with regard to their effects on marine organisms, and especially their reproductive systems. We investigated the toxicity of TBT at environmentally relevant concentrations (1, 10, and 100 ng/L) on testicular development in a marine fish, Sebastiscus marmoratus. After exposure for 50 days, the gonadosomatic index had decreased in a dose-dependent manner, and there was a reduced number of mature sperm and an abundance of the late stages of spermatocysts in the testes of S. marmoratus. Exposure has also caused serious histological damage to the testes including interstitial fibrosis and pyknotic nuclei. Analysis of the thyroid status revealed severe damage to the thyroid gland, decreased triiodothyronine and thyroxine in the serum and low expression of thyroid hormone receptor alpha in the testes at this time. Pearson correlation analysis indicated that the levels of thyroxine in the serum were significantly correlated with the gonadosomatic index. These results suggest that inhibition of thyroidal status induced by TBT might be one of the mechanisms affecting testicular development.

Influence of triphenyltin exposure on the hypothalamus-pituitary-gonad axis in male Sebastiscus marmoratus.

Both triphenyltin (TPT) and tributyltin (TBT) have been used as ingredients of antifouling biocides. However, far fewer studies addressing the reproductive toxicity of TPT on fishes are available than for TBT. The present study was conducted to investigate the effects of TPT at environmentally relevant concentrations on testicular development in male rockfish Sebastiscus marmoratus and to gain insight into its mechanism of action. After exposure for 48 days, the gonadosomatic index had decreased, and there was a reduced number of mature sperm and an abundance of the late stages of spermatocysts in the testes. Although the testosterone levels in the testes were elevated and the 17β-estradiol levels were decreased, spermatogenesis was suppressed. The activity of γ-glutamyl transpeptidase (which is used as a Sertoli cell marker) was decreased after TPT exposure, and serious interstitial fibrosis was observed in the interlobular septa of the testes exposed to TPT. The increased expression of cGnRH-II (chicken-II type gonadotropin-releasing hormone) and sGnRH (salmon-type GnRH), and the decreased expression of LHβ (luteinizing hormone) in the fish brains were detected. The expression of FSHβ (follicle-stimulating hormone) was decreased at day 21, while was increased slightly at day 48. The changes of cGnRH-II, sGnRH, FSHβ and LHβ mRNA levels might have mainly resulted from the alteration of the sex steroids via feedback mechanisms. The decrease of the FSHβ mRNA might have been one of the reasons causing the dysfunction of Sertoli cells, which play a critical role during spermatogenesis. The results suggested that TPT could perturb the function of hypothalamus-pituitary-gonad axis, and inhibiting the spermatogenesis.

Tributyltin disrupts feeding and energy metabolism in the goldfish (Carassius auratus)

Tributyltin (TBT) can induce obesogen response. However, little is known about the adverse effects of TBT on food intake and energy metabolism. The present study was designed to investigate the effects of TBT, at environmental concentrations of 2.44 and 24.4 ng/L (1 and 10 ng/L as Sn), on feeding and energy metabolism in goldfish (Carassius auratus). After exposure for 54 d, TBT increased the weight gain and food intake in fish. The patterns of brain neuropeptide genes expression were in line with potential orexigenic effects, with increased expression of neuropeptide Y and apelin, and decreased expression of pro-opiomelanocortin, ghrelin, cocaine and amphetamine-regulated transcript, and corticotropin-releasing factor. Interestingly, the energy metabolism indicators (oxygen consumption, ammonia exertion and swimming activity) and the serum thyroid hormones were all significantly increased at the 2.44 ng/L TBT group in fish. However, no changes of energy metabolism indicators or a decrease of thyroid hormones was found at the 24.4 ng/L TBT group, which indicated a complex disrupting effect on metabolism of TBT. In short, TBT can alter feeding and energy metabolism in fish, which might promote the obesogenic responses.

Tributyltin exposure results in craniofacial cartilage defects in rockfish (Sebastiscus marmoratus) embryos

Tributyltin (TBT) is a ubiquitous marine environmental contaminant, which has been known to cause axial skeletal deformities in fish embryos. However, the effects of TBT on the craniofacial cartilage development of fishes remain unclear. The present study was designed to investigate the effects of waterborne TBT at environmental levels (0, 0.1, 1, and 10 ng L(-1) as Sn) on craniofacial cartilage development in embryos of the rockfish (Sebastiscus marmoratus). Our study showed that TBT exposure induced craniofacial skeletal deformities, such as reduction of the craniofacial skeleton elements and a shorter lower jaw. The expressions of retinoic acid receptor α, sonic hedgehog, and proliferating cell nuclear antigen were depressed and the expressions of vitamin D receptor were increased in the rockfish embryos after TBT exposure. In addition, the activities of Ca(2+)-ATPase were inhibited after TBT exposure. These results suggested that TBT might perturb the proliferation and differentiation of chondrocytes, and disturb calcium homeostasis, thus disorganizing craniofacial skeletal development.

Sex-different effects of tributyltin on brain aromatase, estrogen receptor and retinoid X receptor gene expression in rockfish (Sebastiscus marmoratus).

Since the brain plays important roles in reproduction, the brain aromatase (Cyp19b), estrogen receptor (ER), retinoid X receptor (RXR) α and peroxisome proliferator-activated receptor γ were examined in rockfish after TBT exposure (1, 10, and 100 ng L(-1)). The results showed that the Cyp19b expression was elevated in the male rockfish, while no effect was produced in the females. Inconsistently, serum testosterone and 17β-estradiol showed no change in the males, while an increase of testosterone and a decrease of 17β-estradiol were observed in the females. TBT affected the ER expression in the males depending on the concentrations, however, no change was observed in the females. In addition, TBT elevated the RXRα expression in the males but produced an opposite effect in the females. In conclusion, TBT might have had sex-different effects on the brain Cyp19b, ER and RXR expression in rockfish, indicating a complex endocrine disrupting effect of TBT.