Interaction of Paraquat with Calf Thymus DNA: A Terbium(III) Luminescent Probe and Multispectral Study

Abstract

Terbium(III), as a good luminescent probe, was developed for the study of the interaction between paraquat and calf thymus DNA (ctDNA) when the binding mode of small molecules to DNA was electrostatic binding. This interaction was further investigated using an ethidium bromide (EB) probe, UV absorption spectra, and circular dichroism spectra. On the basis of Scatchard plots constructed from fluorescence titration data of the ctDNA-Tb(3+) system in the presence of paraquat, the binding constants between paraquat and ctDNA were obtained. The results showed that the electrostatic attraction between positively charged sodium ion and negatively charged phosphate groups could inhibit the binding of paraquat to ctDNA, and competitive inhibition between Tb(3+) and paraquat also existed when they were bound to ctDNA. The effects of paraquat on the fluorescence intensity of the EB-ctDNA system indicated that the intercalation binding of paraquat to ctDNA could be excluded. This conclusion could be further supported by both the absorption spectra of paraquat in the presence of ctDNA and the CD spectra of the paraquat-ctDNA system.

Cytotoxic Activities and DNA Binding Properties of 1-Methyl-7H-indeno[1,2-b]Quinolinium-7-(4-dimethylamino) Benzylidene Triflate

“…Some investigators believed that these type of changes in the CD spectra may be reflected due to the base stacking interactions through intercalation and band-II exemplifying stabilization of the right-handed B form (Maheswari and Palaniandavar, 2004;Katsarou et al, 2008). Tong et al (2010) believed that this phenomenon could be due to electrostatic attraction that stabilizes the right-handed B form of DNA. It could be also suggested that the possible binding mode of MIDBT to ct-DNA was a combinational effect of the p-p stacking intercalation and electrostatic attraction, because MIDBT as a cation might bind to the phosphate group of the DNA helix by electrostatic attraction, which could stabilize the structure of DNA and make the CD intensity of ct-DNA increase.…”

Evidence for DNA-diquat interaction and cytotoxicity in in vitro rat cells

“…Recently, the effect of paraquat on the fluorescence intensity of the ethidium bromide-ctDNA system has been investigated (Tong et al 2010). Similar to diquat, the paraquat caused a decreased fluorescence intensity of the ethidium bromide-ctDNA system, showing the interactions between paraquat and ethidium bromide-ctDNA.…”

“…Although several pesticides, which have the potential of cytotoxicity, have been studied concerning on the direct interaction with several macromolecules, the relationship between interaction and toxicity needs to be further explored. (Teng et al 2010, Tong et al 2010, Xiang et al 2007) As a result, we attempted to explore the interaction of diquat with model DNA ctDNA in the next section.…”

“…Among them, fluorescence quenching is an effective method. However, to date, few reports have linked the toxicological effect of agriculture chemicals with an interaction with biomacromolecules (Tong et al 2010;Xiang et al 2007;Teng et al 2010;Athina et al 2005).…”

“…It is well known that the cytotoxicity of pesticides proceeds through the destruction of nuclear and chromatin materials (Cohen et al 1992). Paraquat, another bipyridilium herbicide, has demonstrated to interact with calf thymus DNA (Tong et al 2010), which explains its cytotoxicity in neural cells (Peng et al 2004). Considering the highly similar structure for diquat and paraquat, the toxicity of diquat might also be due to the interaction between macromolecules and diquat.…”