BackgroundNano- or microscale copper oxide particles (CuO NP, CuO MP) are increasingly applied as catalysts or antimicrobial additives. This increases the risk of adverse health effects, since copper ions are cytotoxic under overload conditions.MethodsThe extra- and intracellular bioavailability of CuO NP and CuO MP were explored. In addition, different endpoints related to cytotoxicity as well as direct and indirect genotoxicity of the copper oxides and copper chloride (CuCl2) were compared.ResultsComprehensively characterized CuO NP and CuO MP were analysed regarding their copper ion release in model fluids. In all media investigated, CuO NP released far more copper ions than CuO MP, with most pronounced dissolution in artificial lysosomal fluid. CuO NP and CuCl2 caused a pronounced and dose dependent decrease of colony forming ability (CFA) in A549 and HeLa S3 cells, whereas CuO MP exerted no cytotoxicity at concentrations up to 50 μg/mL. Cell death induced by CuO NP was at least in part due to apoptosis, as determined by subdiploid DNA as well as via translocation of the apoptosis inducing factor (AIF) into the cell nucleus. Similarly, only CuO NP induced significant amounts of DNA strand breaks in HeLa S3 cells, whereas all three compounds elevated the level of H2O2-induced DNA strand breaks. Finally, all copper compounds diminished the H2O2-induced poly(ADP-ribosyl)ation, catalysed predominantly by poly(ADP-ribose)polymerase-1 (PARP-1); here, again, CuO NP exerted the strongest effect. Copper derived from CuO NP, CuO MP and CuCl2 accumulated in the soluble cytoplasmic and nuclear fractions of A549 cells, yielding similar concentrations in the cytoplasm but highest concentrations in the nucleus in case of CuO NP.ConclusionsThe results support the high cytotoxicity of CuO NP and CuCl2 and the missing cytotoxicity of CuO MP under the conditions applied. For these differences in cytotoxicity, extracellular copper ion levels due to dissolution of particles as well as differences in physicochemical properties of the particles like surface area may be of major relevance. Regarding direct and indirect genotoxicity, especially the high copper content in the cell nucleus derived after cell treatment with CuO NP appears to be decisive.

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Metabolic activity as a measure of cell viability is frequently determined using the water-soluble tetrazolium salt 2-(2-methoxy-4-nitrophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium monosodium salt (WST-8), commercially available as CCK-8 reagent. In this study, CCK-8 was investigated with respect to its suitability for investigating nano- and microscale copper oxide (CuO NP and CuO MP) as well as water-soluble copper chloride (CuCl2). The results were compared to cell number and colony forming ability. Our data demonstrate that the CCK-8 assay overestimates the loss of metabolic activity by CuCl2 and CuO NP, because of interference by copper ions with the reduction of the dye.

series of enantiomerically pure bis(myrtanyl)tin compounds, cis-Myr 2 SnX 2 (1, X ) Ph; 3, X ) Cl; 5, X ) H) and trans-Myr 2 SnX 2 (2, X ) Ph; 4, X ) Cl; 6, X ) H) were prepared starting from (-)-1S-βpinene and characterized by multinuclear NMR spectroscopy and in case of 3 and 4 also by X-ray crystallography. The reduction of 3 and 4 with Mg selectively produced pentastannane rings, cyclo-(cis-Myr 2 Sn) 5 ( 7) and cyclo-(trans-Myr 2 Sn) 5 ( 8), while the dehydropolymerization of 5 and 6 produced a mixture of polystannanes, poly(cis-Myr 2 Sn) n (9) or poly(trans-Myr 2 Sn) n (10), and oligomers that could not be separated. The pentastannane rings gave rise to UV absorptions at λ max 219 and 217 nm, which were assigned to σ f σ* transitions of the Sn-Sn bonds. Due to the increased σ-electron delocalization, the polystannanes 9 and 10 show red-shifted UV absorptions at λ max 416 and 417 nm. The CD spectra of the polystannanes 9 and 10 reveal a positive cotton effect at λ max 422 and 425 nm, consistent with the idea that the chiral information is transferred from the UV-inactive myrtanyl groups to the polymer backbone, which most likely adopts a helical conformation with the right-handed screw sense being in excess.