Toxicogenomic Comparison of TCDD and PCB 126 Responsiveness in Primary Human Hepatocytes. Homo sapiens

(Abstract) Toxicogenomics has great potential for enhancing our understanding of environmental chemical toxicity, hopefully leading to better-informed human health risk assessments. This study employed toxicogenomic technology to reveal species differences in response to two prototypical aryl hydrocarbon receptor (AHR) agonists, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and the polychlorinated biphenyl (PCB) congener PCB 126. Dose responses of primary cultures of rat and human hepatocytes were determined using species-specific microarrays sharing over 4,000 gene orthologs. Forty-seven human and 79 rat genes satisfied dose response criteria for both chemicals and were subjected to further analysis including the calculation of EC50 and the relative potency (REP) of PCB 126 for each gene. Only 5 responsive orthologous genes were shared between the two species, yet the geometric mean of the REPs for all rat and human modeled responsive genes were 0.06 (95% Confidence Interval (CI); 0.03-0.1) and 0.002 (95% CI; 0.001-0.005), respectively, suggesting broad species differences in the initial events that follow AHR activation but precede toxicity. This indicates that there are species differences in both the specific genes that responded and the agonist potency and relative potency for those genes. This observed insensitivity of human cells to PCB 126 is consistent with more traditional measurements of AHR activation (i.e., CYP1A1 enzyme activity) and suggests that the species difference in PCB 126 sensitivity is likely due to certain aspects of AHR function. That a species divergence also exists in this expanded AHR-regulated gene repertoire is a novel finding and should help when extrapolating animal data to humans. Overall design: Primary hepatocyte cultures derived from 3 human donors were treated with vehicle (0.5% DMSO), TCDD (-14 to -6.5 log10 M) , or PCB 126 (-12 to -5 log10 M) for 48h. Total RNA was extracted and screened with HG-U133A microarrays for dose response.

(摘要) 毒理基因组学（Toxicogenomics）在加深我们对环境化学物毒性的理解方面具备巨大潜力，有望助力更科学的人类健康风险评估。本研究运用毒理基因组学技术，探究了两种典型芳香烃受体（aryl hydrocarbon receptor, AHR）激动剂——2,3,7,8-四氯二苯并对二噁英（TCDD）与多氯联苯（PCB）同系物PCB 126暴露下的物种响应差异。
研究通过搭载超过4000个同源基因的物种特异性微阵列，测定了大鼠与人原代肝细胞培养物的剂量反应关系。最终有47个人类基因与79个大鼠基因同时满足两种受试物的剂量反应判定标准，随后对这些基因开展进一步分析，包括计算半数效应浓度（EC50）以及各基因对应的PCB 126相对效力（REP）。
两种物种间仅共享5个响应性同源基因；而所有经建模的响应基因的相对效力几何均数，大鼠组为0.06（95%置信区间（CI）：0.03~0.1），人类组为0.002（95%置信区间（CI）：0.001~0.005），这提示在AHR激活后、毒性发生前的早期信号事件中存在显著的物种差异。
该结果表明，不仅响应的特异性基因存在物种差异，对应激动剂的效力及这些基因的相对效力也存在物种差异。本次观察到的人类细胞对PCB 126的不敏感性，与此前针对AHR激活（即CYP1A1酶活性）的传统检测结果一致，提示PCB 126敏感性的物种差异可能源于AHR功能的某些特定方面。在这一扩展的AHR调控基因库中存在物种分化，是一项全新发现，可为将动物实验数据外推至人类提供重要参考。
实验整体设计：将来自3名人类供体的原代肝细胞培养物分别以溶剂对照（0.5%二甲基亚砜，DMSO）、TCDD（-14至-6.5 log₁₀ M）或PCB 126（-12至-5 log₁₀ M）处理48小时。提取总RNA后，采用HG-U133A微阵列进行剂量反应筛选。