Electrochemical studies on the binding of a carcinogenic anthraquinone dye, Purpurin (C.I. 58 205) with DNA
Introduction
Anthraquinones enjoy widespread applications such as in food coloring, textile dyeing, paints and medical treatments [1], [2]. However, as little information on their potentially hazardous effects on humans has been published [3] it was required to determine the correlation between anthraquinones and carcinogenesis. For this, Purpurin (PP, C.I. 58 205), a naturally occurring anthraquinone colorant found in species of madder root (Rubia tinctorum), was selected for investigation. Marczylo et al. [4] found that the presence of Purpurin was responsible for a marked inhibition of mutagenicity induced by food-derived heterocyclic amines. In contrast, it has been reported that the dye has mutagenic activity [5] and can cause urinary bladder tumors (papilloma and carcinoma) in rats [6]. However, the detailed mechanism of its carcinogenesis is unclear. As DNA is often the target for many tumorigenic and mutagenic molecules [7], [8], clarification on the interactions between this typical anthraquininoid dyes with DNA might help understand the toxicity of this type of compound.
Compared with many established technologies for investigating the interaction of DNA and small molecules, such as UV–Vis, FTIR, NMR, ESR and Raman, electrochemistry offers the advantages of high efficiency, convenience, simplicity and low cost [9], [10], [11]. Additionally, in view of the similarity between electrochemical reactions that occur at the electrode/solution interface and real reactions that take place in the living cell in vivo, knowledge of the electrochemical mechanism of the interaction of a biomacromolecule with its binder could provide useful pharmacological and toxicity information [12], [13].
This paper concerns an electrochemical study of the mechanism of the interactions that occur between PP and DNA at a molecular level so as to obtain information about the toxicity of PP. The results show that PP can intercalate into the base pairs of DNA and form a new complex, thereby demonstrating that the approach adopted may offer potential for the interpretation of the toxicity of PP and its derivatives.
Section snippets
General
Voltammetry was performed using a CHI 832 electrochemical analysis system (CHI Instrument, China) equipped with a three-electrode system that comprised a bare glassy carbon electrode (GCE, Φ = 3 mm) as working electrode, a saturated calomel electrode (SCE) as reference electrode and a platinum wire as auxiliary electrode. Fluorescence was measured using an Hitachi F-4500 fluorospectrophotometer (Japan).
Native fish-sperm DNA from Beijing Baitai Biochemistry Technology Company (China) was used as
Cyclic voltammetry
Fig. 1 shows the typical CVs of PP interaction with DNA in 0.02 mol L−1 pH 7.0 B–R buffer solution. As showed in Fig. 1, PP had a pair of asymmetric redox peaks at +0.087 V and +0.175 V, respectively on GCE. The ratio of the oxidation peak current (Ipa) to the reduction peak current (Ipc) was determined to be about 40, suggesting that the electrochemical process of PP was irreversible. As the oxidation peak was more sensitive than the reduction peak, the former one was chosen as the analysis
Conclusions
As an important member of the anthraquinone dye, PP has been reported to display mutagenic action, which suggested that information relating to both the nature and strength of the interaction between DNA and the dye might be helpful in understanding the toxicity mechanism of PP. This electrochemical study shows that PP binds to DNA mainly via typical intercalation; the corresponding binding constant (K) and binding site size (s), as determined by voltammetric titration and non-linear fitting
Acknowledgments
The work was supported by the National Natural Science Foundation of China (Grant No. 20635020, 20805041), Youth Innovation Foundation of Fujian (Grant No. 2007F3106) and Key Provincial University Project of Fujian (Grant No. 2008F5064).
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