Fluorescence labelling of DNA by carboxylic polypyridyl-Ru complexes containing bpy and DIP ligands: a study revisited.

The coordination complexes (DIP)(2)Ru(CH(3)bpyCOOH) and (DIP)(2)Ru(COOHbpyCOOH), where DIP and bpy are diphenylphenanthroline and bispyridine, have been recently proposed as fluorescent markers of nuclear DNA (Musatkina et al., J. Inorg. Biochem. 101:1086-1089, 2007), but no DNA binding investigation and no quantitative fluorescence evaluations had been done. Both complexes, as well as the smaller ones with bpy's in place of DIP's, have been investigated here by spectroscopic DNA titrations (UV-vis absorption, fluorescence, circular dichroism) and by in vitro cellular studies (flow cytometry and fluorescence imaging). Contrary to previous reports, neither the carboxylic function nor the more extended DIP ligand ensures any appreciable binding to DNA. This is clearly illustrated by the appearance of an isosbestic point of a second kind and by the proportionality of the fluorescence maximum intensity to the absorbance at the excitation wavelength. Above all, the lack of enhanced fluorescence in the presence of DNA definitively rules out the use of such complexes as DNA markers. Moreover, there is no detectable nuclear uptake. However, the fluorescent complexes with the DIP ligands, especially (DIP)(2)Ru(CH(3)bpyCOOH), are massively incorporated into the cytoplasm while preserving cell integrity, which could suggest other types of biological application.

Mono- and dicarboxylic polypyridyl-Ru complexes as potential cell DNA dyes and transfection agents.

A ruthenium coordination complex, incorporating two highly extended pi-systems DIP and two carboxylic groups: [Ru(DIP)2(L-L)]2+ where DIP=4,7-diphenyl-1,10-phenanthroline and L-L=4,4'-dicarboxy-2,2'-bipyridine, is found to be of biological interest. It constitutes an effective nuclear DNA dye for living cells: fluorescent, permeant, biocompatible, high Stokes shift. These features are commented in terms of hydrophobicity and DNA binding. In addition, this complex is shown to internalize a plasmid carrying the enhanced green fluorescent protein (EGFP) gene. Positive results are obtained for gene expression, which is related to condensation of the DNA by this ruthenium agent. This opens up an innovative transfection route based on metal complexes.

Spectroscopic and structural impact of a stem base-pair change in DNA hairpins: GTTC-ACA-GAAC versus GTAC-ACA-GTAC.

Successive investigations over the last decade have revealed and confirmed a stable loop closure in a family of d-[GTAC-5Pur6N7N-GTAC] hairpins, where 5Pur6N7N is a AAA, GAG and AXC loop (X being any nucleotide). The trinucleotide loop is characterized by a well defined 5Pur-7N mispairing mode, and by upfield chemical shifts for three sugar protons of the apical nucleotide 6N. The GTTC-ACA-GAAC DNA hairpin, of interest for its likely involvement in Vibrio cholerae genome mutations, has now been investigated. The GTAC-ACA-GTAC DNA hairpin has also been studied because it is intermediate between the other structures, as it contains the loop of the hairpin under consideration and the stem of the above family. The two hairpins with the ACA loop are stable. They show the same mispairing mode and similar upfield shifts as the previous family, but GTTC-ACA-GAAC seems to be slightly less compact than any other. GTTC-ACA-GAAC is remarkable in that it exhibits a B(II) character for the phosphate-ester conformation at 8Gp9A, together with a swing of the upper hairpin into the major groove that, in particular, brings 6CH1' roughly as close to 7AH2 as to 6CH6. These unexpected structural features are qualitatively deduced from (1)H and (31)P NMR spectra, and confirmed by Raman spectroscopy. This comparative study shows that not only the loop sequence but also the stem sequence may control hairpin structures.

Cellular inactivation and chromosomal aberrations: initial damage.

It has been proposed that unrepaired or misrepaired complex lesions of DNA are responsible for cell inactivation and chromosomal aberrations. The detailed features of the critical damage and the nature of initiating physical events are actively investigated. We studied the role of inner-shell (core) ionizations in DNA atoms is studied. Ultrasoft X-rays from LURE synchrotron radiation have been used to mimic core events induced by ionizing radiations. For biological matter, inner-shell photoionization is indeed the main interaction channel of these radiations. Moreover, by tuning the X-ray energy below and above the carbon K-threshold, it is possible to achieve a two-fold increase in the number of core-ionizations in DNA for a same dose. Cell survival and chromosome aberrations have thus been studied at three iso-attenuated energies: 250, 350, and 810 eV. Relative biological efficiencies (RBEs) for cell inactivation and chromosome aberrations were found to be strongly correlated with the yields of core events in DNA.