| Hexabromocyclododecane (HBCD) belongs to add brominated flame retardants, has become ubiquitous pollutants in the environmental media and biota. HBCD has the persistence and accumulation, HBCD and its alternative material polybrominated diphenyl ethers (PBDEs) can form a complex pollution system in the environment, both bring potential harm to human health. The development children are the high-risk population exposure to HBCD and HBCD/PBDEs. It has been suggusted that HBCD and PBDEs coulld have endocrine disruptive effects. Such as: thyroid hormones disturbance and the potential impact of thyroid hormone metabolism process. To study the disrupting effects of Hexabromocyclododecane (HBCD) and its complex compounds on rat thyroid hormone metabolism after developmental exposure. According to the characteristics of the high risk population of the development children to HBCD and its complex compounds, Sprague-Dawley rats of3-days old were exposed to different doses of HBCD (10,50,100,300μg·kg-1body weight) and HBCD/DE-71(10,50,100,300μg·kg-1body weight). Respectively, with the control group, the control group does not add any pollutants. According to the characteristics of the rat brain development, the exposed time is divided to21days,42days,90days. By testing the thyroid hormone levels in serum of rats, thyroid hormone metabolism enzyme (deiodinase) activity and deiodinase gene expressing levels and so on, try to reveal the mechanism of HBCD and HBCD/PBDEs complex compounds on thyroid hormone interference. The experimental results are as follows below:1、Using radioimmunoassay with125I-anti-serun thyroid hormones to test related parameters on serun thyroid hormones, indexes include:TT3、TT4、FT3、FT4、TSH. The experimental results show that:21days of HBCD short-term exposure, all exposed groups serum TT3, TT4, FT3, FT4concentrations were significantly increased (P<0.05). HBCD exposed to42d, FT3, FT4concentration was significantly increased in10μg/kg exposed group (P<0.05); while the other exposure groups TT3, TT4, FT3, FT4concentration showed a downward trend; decline in serum TSH concentration exposure group. Exposure after HBCD to90d, Serum TT3, TT4, FT3, FT4concentration showed upward trend in treated group. HBCD/DE-71complex compounds exposed to21days, serum TT4, FT3, FT4concentration showed a upward trend in all xposed group, TT3, TSH concentration decreased, serum TT4, FT4concentration was significantly increased in50ug/kg and300ug/kg groups (P<0.05), TSH concentration decreased significantly in100ug/kg group (P<0.05). HBCD/DE-71complex compounds exposed to42d and90d, serum TT4, TT3, FT4, FT3, TSH concentrations showed a rising tendency.2^Using Chopra’s method determine thyroid hormone metabolism enzyme (deiodinase) activity, including:type Ⅰ deiodinase (D1) and type Ⅱ deiodinase (D2). The experimental results are as follows:21days by HBCD single exposure.10,100,300ug/kg dose groups Dl activity increased significantly (P<0.05). HBCD exposed for42days, all of the exposure groups rat liver type I deiodinase (D1) activity showed the reduced phenomenon, but not statistically significant (P>0.05).90days, the phenomenon of rat liver D1activity was consistent with the exposure for42days, after HBCD/DE-71exposed for21days, type I deiodinase (D1) activity increased in300ug/kg dose group D1activity appears to increased significantly (P<0.05). Exposed for42days, all of the exposure dose group rat liver D1activity is consistent with the21-day phenomenon, the activity increased, but D1activity of42days was not statistically significant (P>0.05). long-term exposure by HBCD/DE-71.10,100,300ug/kg treated groups D1activity were significantly decreased (P<0.05).After HBCD exposed for21days, D2activity of10,50,100ug/kg treated groups was significantly decreased (P<0.05),300ug/kg exposed group was not statistically significant (P>0.05).42days after exposure, the D2activity of the rat brain in exposure dose groups showed a downward trend, a significant downward trend (P<0.05) in which50ug/kg and100ug/kg exposed groups. After Ion-term exposure, exposure dose groups rat brain D2activity was significantly elevated trend, but not statistically significant (P>0.05). HBCD/DE-71exposed for21days, rat brain tissue D2activity were significantly higher trend. Especially, D2activity of lOug/kg dose group was significantly increased (P<0.05). After exposure to42days, D2activity in rat brain tissue as a whole showed increasing trend phenomenon, only300ug/kg dose group significantly increased (P<0.05), the other groups had no significant difference(P>0.05).90-day long-term exposure, rat brain tissue exhibits a distinct change in D2activity, all exposure groups D2activity all showed a tendency to increase significantly (P<0.05).3、Using real-time fluorescence quantitative PCR (Real-time PCR) and quantitative determination of changes in gene expression levels of thyroid hormone metabolism, including:type I deiodinase (D1) and type II deiodinase (D2) gene expression levels. The experimental results are as follows:HBCD exposed for21days, rat liver type I deiodinase (D1) mRNA expression levels of exposed groups first decreased and then increased trend, but the overall level of mRNA expression was no significant difference (P>0.05). Exposed to42days,300ug/kg exposure group D1mRNA expression levels was significantly decreased (P<0.05). After the HBCD long-term exposure, Rat liver type I deiodinase (D1) mRNA expression levels with increasing doses of an increasing trend, which10,50,100ug/kg dose groups type I deiodinase (D1) mRNA expression levels were significantly increased (P<0.05). HBCD/DE-71exposed for21days, D1mRNA expression levels of10-100ug/kg dose groups were significantly increased (P<0.05). After42days, type I deiodinase (D1) mRNA expression were elevated in100ug/kg dose group D1mRNA expression levels was significantly elevated (P<0.05).90days after exposure, D1mRNA expression levels in50,100,300ug/kg exposure doses were significantly decreased (P<0.05).HBCD exposed for21days, type Ⅱ deiodinase enzyme (D2) mRNA expression of rat brain tissue in all exposed group were significantly decreased (P<0.05). HBCD exposed for42days,50ug/kg treated rats brain tissue D2mRNA expression levels was significantly decreased (P<0.05). After the HBCD long-term exposure, type Ⅱ deiodinase (D2) mRNA expression in10-300ug/kg exposure dose groups are beginning to show trend significantly higher, but not statistically significant (P>0.05). After21days exposure,100ug/kg and300ug/kg exposed rats D2mRNA expression level were significantly increased (P<0.05). HBCD/DE-71exposed for42days, compared with the control group,10～300ug/kg exposure dose groups type II deiodinase (D2) gene expression levels increased trend, but no significant differences (P>0.05). After90days, lOug/kg and300ug/kg groups D2mRNA expression levels were significantly increased (P<0.05). According to the experimental results, the following conclusions:1、The experimental study found that HBCD has the effect of promoting or agonists on thyroid hormone, resulting in elevated thyroid hormone levels, and thus interferes with thyroid hormone relative equilibrium. For polybrominated diphenyl ethers, previous studies usually show their thyroid hormone suppression role, often leading to a decline in the level of thyroid hormone. HBCD and DE-71as a complex pollution system in this study, thyroid hormone levels did not decline, but increased, and the interference effects of thyroid hormone levels significantly higher than the result of a pollutant alone, which display more toxic effects in rats. In addition, the experiments also show that HBCD and HBCD/DE-71easier through the impact on free thyroid hormone (FT3, FT4) which have an impact on the body’s physiological processes.2、HBCD alone exposed in this study, short-term exposure, the type Ⅰ deiodinase activity increased; After long-term exposure, as time goes on type Ⅰ deiodinase activity had no significant effect. The ratswere treated by HBCD/DE-71short-term and long-term exposure, the study found that short-term exposure to high exposure dose combined effects of the two pollutants cause rat type Ⅰ off iodine enzyme activity was significantly higher, long-term exposure to low exposure dose and high dose group were significantly inhibited the type Ⅰ deiodinase activity, there is a great difference with the toxic effects of HBCD alone. Short-term and low-dose exposureof HBCD exerts an inhibitory potential impact on tissue type Ⅱ deiodinase activity of rat brain. After long-term exposure, the activity of type Ⅱ deiodinase had no effect on this inhibition is reversible, and gradually disappear over time. When after HBCD/DE-71compounds exposure, whether short-term exposure or long-term exposure, the combined pollution of the system make D2activity become significantly higher, long-term exposure time is90days, D2activity has become more evident. The above results show that the HBCD and HBCD/DE-71be able to affect thyroid hormone metabolism process by changing the activity of deiodinase thus further affecting the thyroid hormone levels in the body homeostasis.3, This study found that after HBCD short-term exposure, the type Ⅰ deiodinase (D1) gene transcription level did not affect. After long-term exposure, low concentrations of HBCD promot the level of gene transcription of type Ⅰ deiodinase (D1). But the mid-exposure we found high concentrations of HBCD inhibit type Ⅰ deiodinase (D1) gene transcription level. Exposed by HBCD/DE-71compounds study found that short-term exposure, HBCD/DE-71play a facilitating role; after long-term exposure, it play an inhibitory role in D2gene transcription level. This indicates that the difference between HBCD and HBCD/DE-71impact type Ⅰ deiodinase gene transcription process as different manifestations of the toxic effects of exposure time. For type Ⅱ deiodinase, HBCD have an inhibitory performance on the D2gene transcription level, but HBCD/DE-71play an important role in promoting the D2gene transcription level. |
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