Monitoring the (photo)genotoxicity of photosensitizer drugs: Direct quantitation of single-strand breaks in deoxyribonucleic acid using an oligonucleotide chip

Fast and simple method for screening of single-stranded DNA breaking photosensitizers using graphene oxide

A fast and simple method for screening of ssDNA-breaking photosensitizers was developed using graphene oxide. The ultraviolet light-induced DNA breaks are one of the most harmful DNA damages and cause skin cancer if they are left unrepaired. Since graphene oxide showed relatively strong affinity to the broken DNA than intact DNA, and it quenched fluorescence of the DNA labeling dye effectively, the degree of ultraviolet light-induced broken DNAs could be analyzed by measuring decreased fluorescence after mixing the DNA with graphene oxide. The decrease of fluorescence was highly correlated with the ultraviolet light-irradiating time and concentration of the added drugs. As a result, it was possible to evaluate the efficacy of different ssDNA-breaking photosensitizers in a high-throughput manner. However, conventional methods for the damaged-DNA analysis are time-consuming and require additional manipulations such as purification, radio-labeling, enzymatic digestion, or chemical modification of DNA. The phototoxicity of five drugs such as benzophenone, ketoprofen, indomethacin, naproxen, and norfloxacin was tested using the proposed method. The ssDNA-breaking efficiency of the drugs was well matched with reported efficiency of the tested drugs. In contrast to naked gold nanoparticles, graphene oxide is stably dispersed in the presence of salt, the phototoxicity of the drugs could be successfully tested at a physiological condition using the graphene oxide based method.

Fenton process on single and mixture components of phenothiazine pharmaceuticals: Assessment of intermediaries, fate, and preliminary ecotoxicity

Pharmaceuticals do not occur isolated in the environment but in multi-component mixtures and may exhibit antagonist, synergistic or additive behavior. Knowledge on this is still scarce. The situation is even more complicated if effluents or potable water is treated by oxidative processes or such transformations occur in the environment. Thus, determining the fate and effects of parent compounds, metabolites and transformation products (TPs) formed by transformation and degradation processes in the environment is needed. This study investigated the fate and preliminary ecotoxicity of the phenothiazine pharmaceuticals, Promazine (PRO), Promethazine (PRM), Chlorpromazine (CPR), and Thioridazine (THI) as single and as components of the resulting mixtures obtained from their treatment by Fenton process. The Fenton process was carried out at pH7 and by using 0.5-2mgL^-1 of [Fe²⁺]₀ and 1-12.5mgL^-1 of [H₂O₂]₀ at the fixed ratio [Fe²⁺]₀:[H₂O₂]₀ of 1:10 (w:w). No complete mineralization was achieved. Constitutional isomers and some metabolite-like TPs formed were suggested based on their UHPLC-HRMSⁿ data. A degradation pathway was proposed considering interconnected mechanisms such as sulfoxidation, hydroxylation, N-dealkylation, and dechlorination steps. Aerobic biodegradation tests (OECD 301 D and OECD 301 F) were applied to the parent compounds separately, to the mixture of parent compounds, and for the cocktail of TPs present after the treatment by Fenton process. The samples were not readily biodegradable. However, LC-MS analysis revealed that abiotic transformations, such hydrolysis, and autocatalytic transformations occurred. The initial ecotoxicity tested towards Vibrio fischeri as individual compounds featured a reduction in toxicity of PRM and CPR by the treatment process, whereas PRO showed an increase in acute luminescence inhibition and THI a stable luminescence inhibition. Concerning effects of the mixture components, reduction in toxicity by the Fenton process was predicted by concentration addition and independent action models.

Quantification of UV-induced cyclobutane pyrimidine dimers using an oligonucleotide chip assay

A lesion-specific enzyme-induced DNA strand break assay was developed for an oligonucleotide chip for the determination of UVB-induced cyclobutane pyrimidine dimers (CPDs). A 20-mer of fluorophore-labeled and biotinylated oligonucleotide was immobilized on the chip. CPDs in DNA on the chip were formed by UVB irradiation (312 nm). T4 endonuclease V (T4N5) was used to excise the CPD site as T4N5 sensitively and specifically detects CPDs. The fluorophore-labeled DNA fragments were detected by a laser-induced fluorescence (LIF) detection system. The number of CPDs induced by UVB was determined based on a mathematical equation obtained from a predetermined calibration curve. The yield of UVB-induced CPDs was 1.73 CPDs per megabase per (kJ/m(2)). The reliability of this value was proved by its similarity to reference values obtained from gel electrophoresis. The developed assay has strong potential to quantify most kinds of UV-induced DNA lesions.

Oligonucleotide chip assay for quantification of gamma ray-induced single strand breaks

An oligonucleotide chip assay was designed for direct quantification of single strand breaks (SSBs) induced by gamma-ray irradiation. The oligonucleotides used were 20-mers, which were short enough to produce only a single strand break within a single oligonucleotide. The two ends of the oligonucleotides were labeled with fluorescein and biotin, respectively. The biotinylated ends of the oligonucleotides were immobilized on a silicon wafer chip treated with (3-aminopropyl)triethoxysilane (APTES), glutaraldehyde, and avidin. The DNA fragments cleaved by gamma-ray irradiation were detected by a laser-induced fluorescence (LIF) detection system. The gamma-ray-induced SSBs were quantified using a calibration curve (fluorescence intensity versus gamma-ray dose) without the need for complicated mathematical calculation based on gel-based separation. The experimentally determined gamma-ray-induced SSBs yield was almost equal to the theoretical value derived from gel electrophoresis of plasmid DNAs and DNA surface coverage.