Abstract

Background:

Markers of exposure to environmental toxicants are urgently needed. Tooth enamel, with its unique properties, is able to record certain environmental conditions during its formation. Enamel formation and quality are dependent on hormonal regulation and environmental conditions, including exposure to endocrine disrupting chemicals (EDCs). Among EDCs, phthalates such as di-(2-ethylhexyl) phthalate (DEHP) raise concerns about their contribution to various pathologies, including those of mineralized tissues.

Objectives:

The effects of exposure to low-doses of DEHP on the continually growing incisors were analyzed in mouse males and females.

Methods:

Adult male and female C57BL/6J mice were exposed daily to 0.5, 5, and $50\mathrm{\mu }\mathrm{g}/\mathrm{kg}\text{\hspace{0.17em}per\hspace{0.17em}day}$ DEHP for 12 wk and their incisors clinically examined. Incisors of males were further analyzed by scanning electron microscopy (SEM), micro X-ray computed tomography (micro-computed tomography; $\mathrm{\mu }\text{CT}$), and nanoindentation for the enamel, histology and real-time quantitative polymerase chain reaction (RT-qPCR) for the dental epithelium.

Results:

Clinical macroscopic observations of incisors showed various dose-dependent dental lesions such as opacities, scratches, and enamel breakdown in 30.5% of males (10 of 34 total incisors across three independent experiments), and 15.6% of females (7 of 46 incisors) at the highest dose, among which 18.1% (6 of 34 total incisors across three independent experiments) and 8.9% (4 of 46 incisors), respectively, had broken incisors. SEM showed an altered enamel surface and ultrastructure in DEHP-exposed male mice. Further characterization of the enamel defects in males by $\mathrm{\mu }\text{CT}$ showed a lower mineral density than controls, and nanoindentation showed a lower enamel hardness during all stages of enamel mineralization, with more pronounced alterations in the external part of the enamel. A delay in enamel mineralization was shown by several approaches ($\mathrm{\mu }\text{CT}$, histology, and RT-qPCR).

Discussion:

We conclude that DEHP disrupted enamel development in mice by directly acting on dental cells with higher prevalence and severity in males than in females. The time window of DEHP effects on mouse tooth development led to typical alterations of structural, biochemical, and mechanical properties of enamel comparable to other EDCs, such as bisphenol A. The future characterization of dental defects in humans and animals due to environmental toxicants might be helpful in proposing them as early markers of exposure to such molecules. https://doi.org/10.1289/EHP10208

中文翻译：

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使用与低剂量邻苯二甲酸二（2-乙基己基）酯相关的牙齿缺陷作为暴露于环境毒物的早期标志物

摘要

背景：

迫切需要暴露于环境毒物的标志物。牙釉质以其独特的特性，能够在其形成过程中记录某些环境条件。牙釉质的形成和质量取决于激素调节和环境条件，包括接触内分泌干扰化学品 (EDC)。在 EDC 中，邻苯二甲酸酯（如邻苯二甲酸二（2-乙基己基）酯 (DEHP)）引起了人们对它们对各种病理（包括矿化组织的病理）的影响的担忧。

目标：

在雄性和雌性小鼠中分析了暴露于低剂量 DEHP 对不断生长的门牙的影响。

方法：

成年雄性和雌性 C57BL/6J 小鼠每天暴露于 0.5、5 和$50\mathrm{\mu }\mathrm{G}/\mathrm{公斤}\text{\hspace{0.17em}每天}$DEHP 12 周和他们的门牙临床检查。通过扫描电子显微镜 (SEM)、显微 X 射线计算机断层扫描 (micro-computed tomography;$\mathrm{\mu }\text{电脑断层扫描}$)，以及牙釉质的纳米压痕、组织学和牙上皮的实时定量聚合酶链反应 (RT-qPCR)。

结果：

门牙的临床宏观观察显示，30.5% 的男性（三个独立实验中 34 颗门牙中的 10 颗）和 15.6% 的女性（46 颗门牙中的 7 颗）在最高剂量，其中分别有 18.1%（三个独立实验中 34 颗门牙中的 6 颗）和 8.9%（46 颗门牙中的 4 颗）门牙断裂。SEM 显示暴露于 DEHP 的雄性小鼠的牙釉质表面和超微结构发生了改变。通过以下方法进一步表征男性牙釉质缺陷$\mathrm{\mu }\text{电脑断层扫描}$显示出比对照更低的矿物质密度，并且纳米压痕在牙釉质矿化的所有阶段显示出较低的牙釉质硬度，牙釉质的外部变化更明显。几种方法显示了牙釉质矿化的延迟（$\mathrm{\mu }\text{电脑断层扫描}$、组织学和 RT-qPCR)。

讨论：

我们得出结论，DEHP 通过直接作用于雄性牙齿细胞的患病率和严重程度高于雌性小鼠，从而破坏了小鼠的牙釉质发育。DEHP 对小鼠牙齿发育的影响的时间窗导致牙釉质的结构、生化和机械性能发生了典型的变化，与其他 EDC（如双酚 A）相当。未来对环境毒物引起的人类和动物牙齿缺陷的表征可能是有助于将它们作为暴露于此类分子的早期标志物。https://doi.org/10.1289/EHP10208