Hornung Michael W, Kosian Patricia A, Haselman Jonathan T, Korte Joseph J, Challis Katie, Macherla Chitralekha, Nevalainen Erica, Degitz Sigmund J
US Environmental Protection Agency, ORD, NHEERL, Mid-Continent Ecology Division, Duluth, Minnesota
US Environmental Protection Agency, ORD, NHEERL, Mid-Continent Ecology Division, Duluth, Minnesota.
Toxicol Sci. 2015 Aug;146(2):254-64. doi: 10.1093/toxsci/kfv090. Epub 2015 May 7.
As in vitro assays are increasingly used to screen chemicals for their potential to produce endocrine disrupting adverse effects, it is important to understand their predictive capacity. The potential for a set of 6 benzothiazoles to affect endpoints related to thyroid hormone synthesis inhibition were assessed using in vitro, ex vivo, and in vivo assays. Inhibition of thyroid peroxidase (TPO) derived from pig thyroid glands was determined for benzothiazole (BTZ), 2-mercaptobenzothiazole (MBT), 5-chloro-2-mercaptobenzothiazole (CMBT), 2-aminobenzothiazole (ABT), 2-hydroxybenzothiazole (HBT), and 2-methylthiobenzothiazole (MTBT). Their rank order potency for TPO inhibition was MBT=CMBT>ABT>BTZ, whereas HBT and MTBT exhibited no inhibitory activity. The benzothiazoles were tested further in a Xenopus laevis thyroid gland explant culture assay in which inhibition of thyroxine (T4) release was the measured endpoint. In this assay all 6 benzothiazoles inhibited T4 release. The activity of the benzothiazoles for disrupting thyroid hormone activity was verified in vivo using X. laevis tadpoles in a 7-day assay. The 2 most potent chemicals for TPO inhibition, MBT and CMBT, produced responses in vivo indicative of T4 synthesis inhibition including induction of sodium iodide symporter mRNA and decreases in glandular and circulating thyroid hormones. The capability to measure thyroid hormone levels in the glands and blood by ultrahigh performance LC-MS/MS methods optimized for small tissue samples was critical for effects interpretation. These results indicate that inhibition of TPO activity in vitro was a good indicator of a chemical's potential for thyroid hormone disruption in vivo and may be useful for prioritizing chemicals for further investigation.
由于体外试验越来越多地用于筛选化学物质产生内分泌干扰不良反应的潜力，了解其预测能力很重要。使用体外、离体和体内试验评估了一组6种苯并噻唑影响与甲状腺激素合成抑制相关终点的潜力。测定了苯并噻唑（BTZ）、2-巯基苯并噻唑（MBT）、5-氯-2-巯基苯并噻唑（CMBT）、2-氨基苯并噻唑（ABT）、2-羟基苯并噻唑（HBT）和2-甲基硫代苯并噻唑（MTBT）对猪甲状腺来源的甲状腺过氧化物酶（TPO）的抑制作用。它们对TPO抑制的效力排序为MBT = CMBT>ABT>BTZ，而HBT和MTBT没有表现出抑制活性。在非洲爪蟾甲状腺外植体培养试验中对苯并噻唑进行了进一步测试，该试验以甲状腺素（T4）释放的抑制作为测量终点。在该试验中，所有6种苯并噻唑均抑制T4释放。使用非洲爪蟾蝌蚪进行7天试验在体内验证了苯并噻唑破坏甲状腺激素活性的能力。对TPO抑制作用最强的2种化学物质MBT和CMBT在体内产生了表明T4合成抑制的反应，包括诱导钠碘同向转运体mRNA以及腺体和循环甲状腺激素的降低。通过针对小组织样本优化的超高效液相色谱-串联质谱法测量腺体和血液中甲状腺激素水平的能力对于效应解释至关重要。这些结果表明，体外抑制TPO活性是化学物质在体内破坏甲状腺激素潜力的良好指标，可能有助于对化学物质进行优先排序以进行进一步研究。
