Mixtures of substances sharing the same molecular initiating event (MIE) are supposed to induce additive effects. The proposed MIE for azole fungicides is CYP26 inhibition with retinoic acid (RA) local increase, triggering key events leading to craniofacial defects. Valproic acid (VPA) is supposed to imbalance RA-regulated gene expression trough histone deacetylases (HDACs) inhibition. The aim was to evaluate effects of molecules sharing the same MIE (azoles) and of such having (hypothetically) different MIEs but which are eventually involved in the same adverse outcome pathway (AOP). An in silico approach (molecular docking) investigated the suggested MIEs. Teratogenicity was evaluated in vitro (WEC). Abnormalities were modelled by PROAST software. The common target was the branchial apparatus. In silico results confirmed azole-related CYP26 inhibition and a weak general VPA inhibition on the tested HDACs. Unexpectedly, VPA showed also a weak, but not marginal, capability to enter the CYP 26A1 and CYP 26C1 catalytic sites, suggesting a possible role of VPA in decreasing RA catabolism, acting as an additional MIE. Our findings suggest a new more complex picture. Consequently two different AOPs, leading to the same AO, can be described. VPA MIEs (HDAC and CYP26 inhibition) impinge on the two converging AOPs.

中文翻译：

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颅面部畸形的不良结局途径的发展：计算机模拟和体外数据的贡献。

共享相同分子引发事件（MIE）的物质混合物应诱发加性效应。拟议的唑类杀菌剂的MIE是通过维甲酸（RA）局部增加来抑制CYP26，从而触发导致颅面缺陷的关键事件。丙戊酸（VPA）可能通过组蛋白脱乙酰基酶（HDACs）抑制失衡RA调控的基因表达。目的是评估共享相同MIE（唑）和具有（假设）不同MIE但最终参与相同不良结局途径（AOP）的分子的作用。计算机方法（分子对接）研究了建议的MIE。致畸性进行了体外评估（WEC）。异常通过PROAST软件建模。共同的目标是分支机构。在计算机分析中，结果证实了与唑相关的CYP26抑制作用和对受测HDAC的一般VPA抑制作用较弱。出乎意料的是，VPA还显示出进入CYP 26A1和CYP 26C1催化位点的能力较弱，但并非微不足道，这提示VPA在降低RA分解代谢中可能起了额外的MIE作用。我们的发现提出了新的更复杂的图景。因此，可以描述导致相同AO的两个不同的AOP。VPA MIE（HDAC和CYP26抑制）撞击两个会聚的AOP。因此，可以描述导致相同AO的两个不同的AOP。VPA MIE（HDAC和CYP26抑制）撞击两个会聚的AOP。因此，可以描述导致相同AO的两个不同的AOP。VPA MIE（HDAC和CYP26抑制）撞击两个会聚的AOP。