Bittner M, Hilscherová K, Giesy J P
RECETOX, Masaryk University, Kamenice 126/3, 62500 Brno, Czech Republic.
Environ Int. 2007 Aug;33(6):812-6. doi: 10.1016/j.envint.2007.03.011. Epub 2007 Apr 30.
Humic substances (HS) and natural organic matter (NOM) are natural organic compounds ubiquitous in the environment. However, some studies indicate that both HS and NOM can act as xenobiotics, e.g. induce hormone-like effects in fish, amphibians and invertebrates. Molecules of these substances contain a number of aromatic rings and conjugated double bonds--the so called chromophores. Irradiation of dissolved HS and NOM can lead to a series of photochemical reactions which can act on these substances itself, or on other substances present in aquatic environment along with HS and NOM such as e.g. xenobiotics. In our previous study, we have found significant interactions of five humic acids (HA) with cytosolic aryl hydrocarbon receptor (AhR) in an in vitro bioassay based on H4IIE-luc cells. In the present study, we have studied the changes in AhR-mediated activities both of HS and NOM after irradiation that simulated natural solar light. Nine different HS and two NOM samples were irradiated in Pyrex tubes with a medium-pressure mercury lamp for a duration of 0 to 52 h (which corresponds to 0-52 d natural solar radiation). Original concentrations of the samples were 50 mg L(-1), and the greatest concentration of HS and NOM photoproducts subsequently tested in the bioassay was 17 mg L(-1), which is an environmentally relevant concentration. After irradiation the absorbances of all the samples were less than the original materials. The AhR-mediated activity of the HA-Fluka and HA Sodium Salt were partially decreased by irradiation. The activities of other HS and NOM, that were either AhR-active or -inactive were not changed by irradiation. The results of the study demonstrate that AhR-mediated activities of two active HA is caused by both photo-stable and photo-labile AhR activators, while the other three active HA contain only photo-stable AhR activators. Potential mechanisms of the observed irradiation-induced changes in AhR-mediated activities are discussed.
腐殖质（HS）和天然有机物（NOM）是环境中普遍存在的天然有机化合物。然而，一些研究表明，HS和NOM都可以作为外源性物质，例如在鱼类、两栖动物和无脊椎动物中诱导类似激素的效应。这些物质的分子含有许多芳香环和共轭双键——即所谓的发色团。溶解的HS和NOM的辐照会导致一系列光化学反应，这些反应可以作用于这些物质本身，或者作用于与HS和NOM一起存在于水生环境中的其他物质，如外源性物质。在我们之前的研究中，我们在基于H4IIE-luc细胞的体外生物测定中发现了五种腐殖酸（HA）与胞质芳烃受体（AhR）之间的显著相互作用。在本研究中，我们研究了模拟自然太阳光辐照后HS和NOM的AhR介导活性的变化。九个不同的HS和两个NOM样品在派热克斯玻璃管中用中压汞灯辐照0至52小时（相当于0 - 52天的自然太阳辐射）。样品的原始浓度为50 mg L(-1)，随后在生物测定中测试的HS和NOM光产物的最大浓度为17 mg L(-1)，这是一个与环境相关的浓度。辐照后所有样品的吸光度均低于原始材料。HA-弗卢卡和HA钠盐的AhR介导活性因辐照而部分降低。其他HS和NOM的活性，无论其对AhR是激活还是失活，均未因辐照而改变。研究结果表明，两种活性HA的AhR介导活性是由光稳定和光不稳定的AhR激活剂共同引起的，而其他三种活性HA仅含有光稳定的AhR激活剂。本文讨论了观察到的辐照诱导的AhR介导活性变化的潜在机制。
