Cobalt-mediated oxidative DNA damage and its prevention by polyphenol antioxidants.

Although cobalt is a required nutrient, it is toxic due to its ability to generate reactive oxygen species (ROS) and damage DNA. ROS generation by Co2+ often has been compared to that of Fe2+ or Cu+, disregarding the reduction potential differences among these metal ions. In plasmid DNA damage studies, a maximum of 15% DNA damage is observed with Co2+/H2O2 treatment (up to 50 µM and 400 µM, respectively) significantly lower than the 90% damage observed for Fe2+/H2O2 or Cu+/H2O2 treatment. However, when ascorbate is added to the Co2+/H2O2 system, a synergistic effect results in 90% DNA damage. DNA damage by Fe2+/H2O2 can be prevented by polyphenol antioxidants, but polyphenols both prevent and promote DNA damage by Cu+/H2O2. When tested for cobalt-mediated DNA damage affects, eight of ten polyphenols (epicatechin gallate, epigallocatechin gallate, propyl gallate, gallic acid, methyl-3,4,5-trihydroxybenzoate, methyl-4,5-dihydroxybenzoate, protocatechuic acid, and epicatechin) prevent cobalt-mediated DNA damage with IC50 values of 1.3 to 27 µM and two (epigallocatechin and vanillic acid) prevent little to no DNA damage. EPR studies demonstrate cobalt-mediated formation of •OH, O2•-, and •OOH, but not 1O2 in the presence of H2O2 and ascorbate. Epigallocatechin gallate and methyl-4,5-dihydroxybenzoate significantly reduce ROS generated by Co2+/H2O2/ascorbate, consistent with their prevention of cobalt-mediated DNA damage. Thus, while cobalt, iron, and copper are all d-block metal ions, cobalt ROS generation and its prevention is significantly different from that of iron and copper.

Stability constant determination of sulfur and selenium amino acids with Cu(II) and Fe(II).

Sulfur- and selenium-containing amino acids are of great biological importance, but their metal-binding properties with biologically-relevant metal ions are not well investigated. Stability constants of the methionine, selenomethionine, methylcysteine, and methylselenocysteine with Cu(II) and Fe(II) were determined by potentiometric titration. Stability constants of Cu(II) with these thio- and selenoether amino acids are in the range of 8.0-8.2 ([CuL]+) and 14.5-14.7 (CuL2) (L = amino acid). Fe(II) interactions with the same thio- and selenoether amino acids are much weaker, with stability constants between 3.5 and 3.8 ([FeL]+) and -4.9 and -5.7 (FeL(OH)). Stability of Fe(II) with penicillamine, a thiol-containing amino acid, is much higher (FeL = 7.48(7) and [FeL]2- = 13.74(2)). For both copper and iron complexes, thio- and selenoether amino acid coordination occurs through the carboxylate and the amine groups as confirmed by infrared spectroscopy, with no stability afforded by thio- or selenoether coordination. The first single-crystal structure of Cu(II) with a selenium-containing amino acid, Cu(SeMet)2, also confirms binding through only the amine and carboxylate groups. The measured Cu(II)-amino-acid stability constants confirm that nearly 100% of the available Cu(II) can be coordinated by these amino acids at pH 7, but very little Fe(II) is bound under these conditions. The relative instability of Fe(II) complexes with thio- and selenoether amino acids is consistent with their inability to prevent metal-mediated oxidative DNA damage. In contrast, the stability constants of these amino acids with Cu(II) weakly correlate to their ability to inhibit DNA damage inhibition.

Fluconazole induces ROS in Cryptococcus neoformans and contributes to DNA damage in vitro.

Pathogenic basidiomycetous yeast, Cryptococcus neoformans, causes fatal meningitis in immunocompromised individuals. Fluconazole (FLC) is a fungistatic drug commonly administered to treat cryptococcosis. Unfortunately, FLC-resistant strains characterized by various degree of chromosomal instability were isolated from clinical patients. Importantly, the underlying mechanisms that lead to chromosomal instability in FLC-treated C. neoformans remain elusive. Previous studies in fungal and mammalian cells link chromosomal instability to the reactive oxygen species (ROS). This study provides the evidence that exposure of C. neoformans to FLC induces accumulation of intracellular ROS, which correlates with plasma membrane damage. FLC caused transcription changes of oxidative stress related genes encoding superoxide dismutase (SOD1), catalase (CAT3), and thioredoxin reductase (TRR1). Strikingly, FLC contributed to an increase of the DNA damage in vitro, when complexed with iron or copper in the presence of hydrogen peroxide. Strains with isogenic deletion of copper response protein metallothionein were more susceptible to FLC. Addition of ascorbic acid (AA), an anti-oxidant at 10 mM, reduced the inhibitory effects of FLC. Consistent with potential effects of FLC on DNA integrity and chromosomal segregation, FLC treatment led to elevated transcription of RAD54 and repression of cohesin-encoding gene SCC1. We propose that FLC forms complexes with metals and contributes to elevated ROS, which may lead to chromosomal instability in C. neoformans.

DNA interactions of non-chelating tinidazole-based coordination compounds and their structural, redox and cytotoxic properties.

Novel tinidazole (tnz) coordination compounds of different geometries were synthesised, whose respective solid-state packing appears to be driven by inter- and intramolecular lone pairπ interactions. The copper(ii) compounds exhibit interesting redox properties originating from both the tnz and the metal ions. These complexes interact with DNA through two distinct ways, namely via electrostatic interactions or/and groove binding, and they can mediate the generation of ROS that damage the biomolecule. Cytotoxic studies revealed an interesting activity of the dinuclear compound [Cu(tnz)2(µ-Cl)Cl]27, which is further more efficient towards cancer cells, compared with normal cells.