Borghoff S J, Wikoff D, Harvey S, Haws L
ToxStrategies, Inc., Cary, NC, United States.
ToxStrategies, Inc., Austin, TX, United States.
Toxicol Rep. 2016 Jan 12;3:190-201. doi: 10.1016/j.toxrep.2016.01.007. eCollection 2016.
Tetrabromobisphenol A (TBBPA), a nongenotoxic flame retardant, causes uterine tumors in female rats. A proposed mode of action (MoA) for these tumors involves an increase in the bioavailability of estradiol as a result of TBBPA inhibiting estrogen sulfotransferases (ES), the enzymes responsible for inactivating and enhancing the elimination of estradiol. The objective of this study was to evaluate the effect of dose and repeated administration of TBBPA on the level of TBBPA, TBBPA-glucuronide (GA) and TBBPA-sulfate (S) conjugates in plasma, liver and uterus of female Wistar Han rats administered TBBPA (50, 100, 250, 500 or 1000 mg/kg) for 28 consecutive days. In accordance with this objective, TBBPA sulfation was used as a surrogate for evaluating the potential for estradiol sulfation to be limited at high dose levels of TBBPA. Blood samples were collected at 4 and 8 h post-dosing on study day 7, 14, and 28, while liver and uterus were collected at the same time points following 28 days of dosing. Tissue samples were analyzed for TBBPA, TBBPA-GA and TBBPA-S by LC-MS/MS. A dose-related increase in the concentration of all three analytes occurred in plasma (day 7, 14, and 28) as well as liver and uterus tissue (day 28) at both 4 and 8 h post dose. The plasma concentration of TBBPA-GA and TBBPA-S was higher in animals dosed for 28 days compared to those dosed for 7 or 14 days showing an increase in systemic circulation of these conjugates with repeated administration. The balance of these conjugates was also different in tissues with TBBPA-S > TBBPA-GA at high doses in the liver and TBBPA-GA > TBBPA-S in both plasma and uterus. In all three tissues the ratio of TBBPA-S/TBBPA-GA showed a decreasing trend with dose, suggesting that at high TBBPA dose levels sulfation of TBBPA becomes limited. This effect was most apparent in the liver and plasma at 28 days of administration. Together these data show that administration of high doses of TBBPA associated with the induction of uterine tumors, results in a disruption in the balance of conjugates reflected by a decrease in the TBBPA-S/TBBPA-GA ratio. A limitation in the sulfation of TBBPA supports data defining TBBPA as an inhibitor of ES activity, thus providing further support that the proposed MoA occurs under conditions of high dose, chronic TBBPA administration to Wistar Han rats. Given that the uterine tumors observed in rats (250-1000 mg/kg-day) only occur at very high doses that perturb homeostatic control, it is unlikely such effects would occur in humans given that current TBBPA exposure levels are approximately eight orders of magnitude lower than these doses that are associated with exceeding the capacity of conjugation pathways in animal studies.
四溴双酚A（TBBPA）是一种非遗传毒性阻燃剂，可导致雌性大鼠患子宫肿瘤。这些肿瘤的一种假定作用模式（MoA）涉及由于TBBPA抑制雌激素硫酸转移酶（ES），导致雌二醇的生物利用度增加，而ES是负责使雌二醇失活并促进其消除的酶。本研究的目的是评估TBBPA的剂量和重复给药对连续28天给予TBBPA（50、100、250、500或1000mg/kg）的雌性Wistar Han大鼠血浆、肝脏和子宫中TBBPA、TBBPA - 葡萄糖醛酸苷（GA）和TBBPA - 硫酸盐（S）结合物水平的影响。根据这一目的，将TBBPA硫酸化用作评估在高剂量TBBPA下雌二醇硫酸化可能受到限制的替代指标。在研究第7、14和28天给药后4小时和8小时采集血样，给药28天后在相同时间点采集肝脏和子宫样本。通过液相色谱 - 串联质谱法（LC - MS/MS）分析组织样本中的TBBPA、TBBPA - GA和TBBPA - S。给药后4小时和8小时，血浆（第7、14和28天）以及肝脏和子宫组织（第28天）中所有三种分析物的浓度均出现剂量相关增加。与给药7天或14天的动物相比，给药28天的动物血浆中TBBPA - GA和TBBPA - S的浓度更高，表明这些结合物的全身循环随着重复给药而增加。这些结合物在组织中的平衡也有所不同，在肝脏中高剂量时TBBPA - S > TBBPA - GA，在血浆和子宫中TBBPA - GA > TBBPA - S。在所有三种组织中，TBBPA - S/TBBPA - GA的比值随剂量呈下降趋势，表明在高TBBPA剂量水平下TBBPA的硫酸化受到限制。这种效应在给药28天时在肝脏和血浆中最为明显。这些数据共同表明，与子宫肿瘤诱导相关的高剂量TBBPA给药会导致结合物平衡的破坏，表现为TBBPA - S/TBBPA - GA比值降低。TBBPA硫酸化的限制支持了将TBBPA定义为ES活性抑制剂的数据，从而进一步支持了所提出的作用模式在对Wistar Han大鼠进行高剂量、慢性TBBPA给药的条件下发生。鉴于在大鼠中观察到的子宫肿瘤（250 - 1000mg/kg - 天）仅在非常高的剂量下发生，这些剂量会扰乱稳态控制，鉴于目前人类TBBPA暴露水平比动物研究中与超过结合途径能力相关的剂量低约八个数量级，因此这种效应在人类中不太可能发生。
