Ochratoxin A (OTA, 1: X = Cl) is a fungal carcinogen that facilitates single-strand DNA cleavage and DNA adduction when metabolically activated. To determine if redox-active transition metals induce OTA-mediated DNA damage, we have examined the toxin's ability to bind Cu(II) and Fe(III) in aqueous media and facilitate DNA cleavage in their presence using agarose gel electrophoresis and supercoiled plasmid DNA. Using fluorescence spectroscopy, 1 was found to bind Cu(II) readily at physiological pH, while acidic conditions (pH 2.6) were employed to study Fe(III) binding due to the formation of Fe-oxide precipitates at higher pH values. Structure-activity relationships employing synthetic derivatives of 1 implied that 1 binds both Cu(II) and Fe(III) by its phenolic oxygen, while the carboxylic acid of its phenylalanine moiety binds Cu(II), but does not appear to play a role in Fe(III) coordination at pH 2.6. In terms of metal-mediated DNA cleavage, no role for 1 could be detected in Fe-induced DNA strand scission. With Cu(II), DNA cleavage by the 1:1 copper-bound complex of 1 could only be initiated by addition of a suitable reducing agent (sodium ascorbate). However, 1 was found to facilitate DNA cleavage by the Cu(II) complex of 1,10-phenanthroline (Cu(OP)2); a prototypical Cu-mediated nuclease system that cleaves DNA upon activation by an external reducing agent. Structure-activity relationships employing analogs lacking the chlorine atom, ochratoxin B (2: X = H), and the lactone (12), indicated that the chlorine atom is essential for activity of the OTA in potentiating DNA cleavage by Cu(OP)2. The implications of our findings to the genotoxic properties of 1 are discussed.Key words: ochratoxin, DNA cleavage, copper, iron, 1,10-phenanthroline.
奥克拉毒素A(OTA,1:X = Cl)是一种真菌致癌物质,当在代谢活化时,它促进单链DNA断裂和DNA加合物的形成。为了确定氧化还原活性过渡金属是否诱导OTA介导的DNA损伤,我们研究了毒素在水介质中结合Cu(II)和Fe(III)的能力,并在它们的存在下利用琼脂糖凝胶电泳和超螺旋质粒DNA促进DNA断裂。利用荧光光谱,发现1在生理pH下能够很容易地结合Cu(II),而在酸性条件(pH 2.6)下用于研究Fe(III)结合,因为在较高pH值下会形成Fe-氧化物沉淀。利用1的合成衍生物进行结构活性关系研究表明,1通过其酚氧结合Cu(II)和Fe(III),而其苯丙氨酸部分的羧酸结合Cu(II),但在pH 2.6下似乎不参与Fe(III)的配位。在金属介导的DNA断裂方面,未发现1在Fe诱导的DNA链切断中起作用。对于Cu(II),只有通过添加适当的还原剂(抗坏血酸钠)才能启动1的1:1铜结合复合物引发的DNA断裂。然而,发现1能够通过1,10-邻菲啰啉(Cu(OP)2)的Cu(II)复合物促进DNA断裂;这是一种原型的Cu介导核酸酶系统,只有在外部还原剂的激活下才能切割DNA。通过缺乏氯原子的类似物进行结构活性关系研究,如奥克拉毒素B(2:X = H)和内酯(12),表明氯原子对于OTA在促进Cu(OP)2介导的DNA断裂中的活性是必不可少的。我们的研究结果对于1的遗传毒性特性的影响进行了讨论。关键词:奥克拉毒素,DNA断裂,铜,铁,1,10-邻菲啰啉。