Tinwell Helen, Ashby John
Syngenta Central Toxicology Laboratory, Alderley Park, Macclesfield, Cheshire SK10 4TJ, United Kingdom.
Environ Health Perspect. 2004 Apr;112(5):575-82. doi: 10.1289/ehp.6831.
We have evaluated whether mixtures of estrogens, present in the mix at doses that are individually inactive in the immature rat uterotrophic assay, can give a uterotrophic response. Seven chemicals were evaluated: nonylphenol, bisphenol A (BPA), methoxychlor, genistein (GEN), estradiol, diethylstilbestrol, and ethinyl estradiol. Dose responses in the uterotrophic assay were constructed for each chemical. The first series of experiments involved evaluating binary mixtures of BPA and GEN at dose levels that gave moderate uterotrophic responses when tested individually. The mixtures generally showed an intermediate or reduced uterotrophic effect compared with when the components of the mixture were tested alone at the dose used in the mixture. The next series of experiments used a multicomponent (complex) mixture of all seven chemicals evaluated at doses that gave either weakly positive or inactive uterotrophic responses when tested individually in the assay. Doses that were nominally equi-uterotrophic ranged over approximately six orders of magnitude for the seven chemicals. Doses of agents that gave a weak uterotrophic response when tested individually gave a marginally enhanced positive response in the assay when tested combined as a mixture. Doses of agents that gave a negative uterotrophic response when tested individually gave a positive response when tested as a mixture. These data indicate that a variety of different estrogen receptor (ER) agonists, present individually at subeffective doses, can act simultaneously to evoke an ER-regulated response. However, translating these findings into the process of environmental hazard assessment will be difficult. The simple addition of the observed, or predicted, activities for the components of a mixture is confirmed here to be inappropriate and to overestimate the actual effect induced by the mixture. Equally, isobole analysis is only suitable for two- or three-component mixtures, and concentration addition requires access to dose-response data and EC50 values (concentration giving 50% of the maximum response) for the individual components of the mixture--requirements that will rarely be fulfilled for complex environmental samples. Given these uncertainties, we conclude that it may be most expedient to select and bioassay whole environmental mixtures of potential concern.
我们评估了在未成熟大鼠子宫增重试验中单独无活性剂量的雌激素混合物是否能产生子宫增重反应。评估了七种化学物质：壬基酚、双酚A（BPA）、甲氧滴滴涕、染料木黄酮（GEN）、雌二醇、己烯雌酚和炔雌醇。针对每种化学物质构建了子宫增重试验中的剂量反应曲线。第一系列实验涉及评估BPA和GEN的二元混合物，其剂量水平在单独测试时能产生中等程度的子宫增重反应。与混合物各成分以混合物中使用的剂量单独测试时相比，这些混合物通常表现出中等或降低的子宫增重效应。接下来的一系列实验使用了所有七种化学物质的多组分（复合）混合物，其剂量在试验中单独测试时产生弱阳性或无活性的子宫增重反应。对于这七种化学物质，名义上等效子宫增重的剂量范围约为六个数量级。单独测试时产生弱阳性子宫增重反应的试剂剂量，在作为混合物组合测试时，在试验中产生的阳性反应略有增强。单独测试时产生阴性子宫增重反应的试剂剂量，作为混合物测试时产生阳性反应。这些数据表明，多种不同的雌激素受体（ER）激动剂，单独以亚有效剂量存在时，可同时起作用以引发ER调节的反应。然而，将这些发现转化为环境危害评估过程将很困难。这里证实，简单相加混合物各成分观察到的或预测的活性是不合适的，并且会高估混合物诱导的实际效应。同样，等效线分析仅适用于二元或三元混合物，而浓度相加需要获得混合物各成分的剂量反应数据和EC50值（产生最大反应50%的浓度）——对于复杂的环境样品，这些要求很少能满足。鉴于这些不确定性，我们得出结论，选择潜在关注的整个环境混合物并进行生物测定可能是最便捷的。
