Vitamin C in cultured human (HeLa) cells: lack of effect on DNA protection and repair

Peroxiredoxin-1 Tyr194 phosphorylation regulates LOX-dependent extracellular matrix remodelling in breast cancer

BACKGROUND

Peroxiredoxin 1 (PRDX1) belongs to an abundant family of peroxidases whose role in cancer is still unresolved. While mouse knockout studies demonstrate a tumour suppressive role for PRDX1, in cancer cell xenografts, results denote PRDX1 as a drug target. Probably, this phenotypic discrepancy stems from distinct roles of PRDX1 in certain cell types or stages of tumour progression.

METHODS

We demonstrate an important cell-autonomous function for PRDX1 utilising a syngeneic mouse model (BALB/c) and mammary fibroblasts (MFs) obtained from it.

RESULTS

Loss of PRDX1 in vivo promotes collagen remodelling known to promote breast cancer progression. PRDX1 inactivation in MFs occurs via SRC-induced phosphorylation of PRDX1 TYR194 and not through the expected direct oxidation of CYS52 in PRDX1 by ROS. TYR194-phosphorylated PRDX1 fails to bind to lysyl oxidases (LOX) and leads to the accumulation of extracellular LOX proteins which supports enhanced collagen remodelling associated with breast cancer progression.

CONCLUSIONS

This study reveals a cell type-specific tumour suppressive role for PRDX1 that is supported by survival analyses, depending on PRDX1 protein levels in breast cancer cohorts.

Treatment with ascorbic acid normalizes the aerobic capacity, antioxidant defence, and cell death pathways in thermally stressed Mytilus galloprovincialis

Considering temperature's upcoming increase due to climate change, combined with the fact that Mediterranean mussels Mytilus galloprovincialis (Lamarck, 1819) live at their upper limits [critical temperatures (Tc) beyond 25 °C], we cannot be sure of this species' sustainable future in the Mediterranean Sea. Deviation from optimum temperatures leads to cellular damage due to oxidative stress. Although ascorbic acid (AA) is a major scavenger of reactive oxygen species (ROS), its capacity to minimize oxidative stress effects is scarcely studied in aquatic organisms. Thus, treatment with 5 mM and 10 mM AA of thermally stressed molluscs had been employed in order to examine its antioxidant capacity. While 5 mM had no effect, 10 mM normalized COX1 and ND2 relative mRNA levels, and superoxide dismutase (SOD), catalase, and glutathione reductase (GR) enzymatic activity levels in both examined tissues: posterior adductor muscle (PAM) and mantle. ATP levels, probably providing the adequate energy for antioxidant defence in thermally stressed mussels, is also normalized under 10 mM AA treatment. Moreover, autophagic indicators such as LC3 II/I and SQSTM1/p62 levels are normalized, indicating autophagy amelioration. Apoptosis also seems to be inhibited since both Bax/Bcl-2 and cleaved caspase substrate levels decrease with 10 mM AA treatment. Therefore, treatment of mussels with AA seems to produce threshold effects, although the precise underlying mechanisms must be elucidated in future studies. These findings show that treatment of mussels with effective antioxidants can be useful as a strategic approach for the reduction of the deleterious effects on mussels' summer mortality in aquaculture zones.

2-O-Octadecylascorbic acid represses RhoGDIβ expression and ameliorates DNA damage-induced abnormal spindle orientations

The appropriate regulation of spindle orientation maintains proper tissue homeostasis and avoids aberrant tissue repair or regeneration. Spindle misorientation due to imbalance or improper functioning leads to a loss of tissue integrity and aberrant growth, such as tissue loss or overgrowth. Pharmacological manipulation to prevent spindle misorientation will enable a better understanding of how spindle orientation is involved in physiological and pathological conditions and will provide therapeutic possibilities to treat patients associated with abnormal tissue function caused by spindle misorientation. N-terminal-deleted Rho guanine nucleotide dissociation inhibitor β (RhoGDIβ/RhoGDI2/LyGDI) produced by caspase-3 activation perturbs spindle orientation in surviving cells following exposure to either ionizing radiation or UVC. Thus, presumably, RhoGDIβ cleaved by caspase-3 activation acts as a determinant of radiation-induced spindle misorientation that promote aberrant tissue repair due to deregulation of directional organization of cell population and therefore becomes a potential target of drugs to prevent such response. The objective of this study was to screen and identify chemicals that suppress RhoGDIβ expression. We focused our attention on ascorbic acid (AA) derivatives because of their impact on the maintenance of skin tissue homeostasis. Here, we screened for AA derivatives that suppress RhoGDIβ expression in HeLa cells and identified a lipophilic derivative, 2-O-octadecylascorbic acid (2-OctadecylAA), as a novel RhoGDIβ inhibitor that ameliorated ionizing radiation-induced abnormal spindle orientations. Among all examined AA derivatives, which were also antioxidative, the inhibition activity was specific to 2-OctadecylAA. Therefore, this activity was not due to simple antioxidant properties. 2-OctadecylAA was previously shown to prevent hepatocellular carcinoma development. Our findings suggest that the anticarcinogenic effects of 2-OctadecylAA are partly due to RhoGDIβ inhibition mechanisms by which spindle orientation perturbations are attenuated. Thus, the molecular targeting features of RhoGDIβ warrant its further development for the treatment or control of spindle orientation abnormalities that affect epithelial homeostasis.

The enzyme-modified comet assay: Past, present and future

The enzyme-modified comet assay was developed in order to detect DNA lesions other than those detected by the standard version (single and double strand breaks and alkali-labile sites). Various lesion-specific enzymes, from the DNA repair machinery of bacteria and humans, have been combined with the comet assay, allowing detection of different oxidized and alkylated bases as well as cyclobutane pyrimidine dimers, mis-incorporated uracil and apurinic/apyrimidinic sites. The enzyme-modified comet assay has been applied in different fields - human biomonitoring, environmental toxicology, and genotoxicity testing (both in vitro and in vivo) - as well as in basic research. Up to now, twelve enzymes have been employed; here we describe the enzymes and give examples of studies in which they have been applied. The bacterial formamidopyrimidine DNA glycosylase (Fpg) and endonuclease III (EndoIII) have been extensively used while others have been used only rarely. Adding further enzymes to the comet assay toolbox could potentially increase the variety of DNA lesions that can be detected. The enzyme-modified comet assay can play a crucial role in the elucidation of the mechanism of action of both direct and indirect genotoxins, thus increasing the value of the assay in the regulatory context.

An optimized comet-based in vitro DNA repair assay to assess base and nucleotide excision repair activity

This optimized protocol (including links to instruction videos) describes a comet-based in vitro DNA repair assay that is relatively simple, versatile, and inexpensive, enabling the detection of base and nucleotide excision repair activity. Protein extracts from samples are incubated with agarose-embedded substrate nucleoids ('naked' supercoiled DNA) containing specifically induced DNA lesions (e.g., resulting from oxidation, UVC radiation or benzo[a]pyrene-diol epoxide treatment). DNA incisions produced during the incubation reaction are quantified as strand breaks after electrophoresis, reflecting the extract's incision activity. The method has been applied in cell culture model systems, human biomonitoring and clinical investigations, and animal studies, using isolated blood cells and various solid tissues. Once extracts and substrates are prepared, the assay can be completed within 2 d.

Differences in electrochemical response of prospective anticancer drugs IPBD and Cl-IPBD, doxorubicin and Vitamin C at plasmid modified glassy carbon

For the comparison of the DNA interactions with drugs, two newly synthesized prospective anticancer drugs, 6-(1H-imidazo[4,5-b]phenasine-2-yl)benzene-1,3-diol (IPBD) and, its -Cl derivative (Cl-IPBD) have been compared with doxorubicin, a drug widely used in medicine, and with Vitamin C. These compounds were accumulated at a supercoiled scpUC19 plasmid layer formed on a glassy carbon electrode (GCE). Stability of the drug-plasmid/GCE layer was achieved by initial plasmid accumulation using prolonged potential cycling for ca. 200 min. from highly diluted scpUC19 solutions (8 pg/mL), followed by accumulation of the drugs from 1 µM - 50 µM. Electrochemical properties in terms of the redox potentials of the compounds and capacitative/resistive characteristics of the layers have been tested using, in sequence, four voltammetric methods: Square Wave (SWV), Differential Pulse (DPV) and Alternating Current (ACV) with phase detection 0° and 90°. Importantly, with progressive drug accumulation in the plasmid, for Cl-IPBD, but not for IPBD, an increase in peak (I) at -0.42 V vs. SCE was observed, while biological tests revealed a higher cytotoxic activity for Cl-IPBD vs. IPBD. Moreover, an additional redox signal of Cl-IPBD was observed with the compound reductive accumulation at the plasmid layer in the presence of Vitamin C.

Effect of antioxidants on the genotoxicity of phenethyl isothiocyanate

Isothiocyanates are plant-derived compounds that may be beneficial in the prevention of certain chronic diseases. Yet, by stimulating the production of reactive oxygen species (ROS), isothiocyanates can be genotoxic. Whether antioxidants influence isothiocyanate-induced genotoxicity is unclear, but this situation was clarified appreciably herein. In HCT116 cells, phenethyl isothiocyanate (PEITC) increased ROS production, which was inhibited by N-acetylcysteine (NAC) and deferoxamine (DFO) but not by ascorbic acid (ASC) and trolox (TRX) that were found to be more potent radical scavengers. Surprisingly, ASC and TRX each intensified the DNA damage that was caused by PEITC, but neither ASC nor TRX by themselves caused any DNA damage. In contrast, NAC and DFO each not only attenuated PEITC-induced DNA damage but also attenuated the antioxidant-intensified, PEITC-induced DNA damage. To determine if the DNA damage could be related to possible changes in the major antioxidant defence system, glutathione (GSH) was investigated. PEITC lowered GSH levels, which was prevented by NAC, whereas ASC, TRX and DFO neither inhibited nor enhanced the GSH-lowering effect of PEITC. The GSH synthesis inhibitor, buthionine sulphoxime, intensified PEITC-induced DNA damage, although by itself buthionine sulphoxime did not directly cause DNA damage. The principal findings suggest that ASC and TRX make PEITC more genotoxic, which might be exploited in killing cancer cells as one approach in killing cancer cells is to extensively damage their DNA so as to initiate apoptosis.

Comet assay to measure DNA repair: approach and applications

Cellular repair enzymes remove virtually all DNA damage before it is fixed; repair therefore plays a crucial role in preventing cancer. Repair studied at the level of transcription correlates poorly with enzyme activity, and so assays of phenotype are needed. In a biochemical approach, substrate nucleoids containing specific DNA lesions are incubated with cell extract; repair enzymes in the extract induce breaks at damage sites; and the breaks are measured with the comet assay. The nature of the substrate lesions defines the repair pathway to be studied. This in vitro DNA repair assay has been modified for use in animal tissues, specifically to study the effects of aging and nutritional intervention on repair. Recently, the assay was applied to different strains of Drosophila melanogaster proficient and deficient in DNA repair. Most applications of the repair assay have been in human biomonitoring. Individual DNA repair activity may be a marker of cancer susceptibility; alternatively, high repair activity may result from induction of repair enzymes by exposure to DNA-damaging agents. Studies to date have examined effects of environment, nutrition, lifestyle, and occupation, in addition to clinical investigations.

Can consumption of raw vegetables decrease the count of sister chromatid exchange? Results from a cross-sectional study in Krakow, Poland

Background

Sister chromatid exchange (SCE) is a widely used sensitive cytogenetic biomarker of exposure to genotoxic and cancerogenic agents. Results of human monitoring studies and cytogenetic damage have revealed that biological effects of genotoxic exposures are influenced by confounding factors related to life-style. Vegetable and fruit consumption may play a role, but available results are not consistent. The purpose of the study was to investigate the effect of consumption of raw and cooked vegetables and fruits on SCE frequency.

Methods

A total of 62 participants included colorectal cancer (CRC) patients, hospital-based controls and healthy laboratory workers. SCE frequency was assessed in blood lymphocytes. Frequency of vegetable and fruit consumption was gathered by structured semi-quantitative food frequency questionnaire.

Results

SCE frequency was lowest among hospital-based controls (4.4 ± 1.1), a bit higher in CRC patients (4.5 ± 1.0) and highest among laboratory workers (7.4 ± 1.2) (p < 0.05). Multivariable linear regression showed a significant inverse effect (b = −0.20) of raw vegetable consumption, but not so for intake of cooked vegetables and fruits.

Conclusions

The results of the study have shown the beneficial effect of consumption of raw vegetables on disrupted replication of DNA measured by SCE frequency, implying protection against genotoxic agents. Further effort is required to verify the role of cooked vegetables and fruits.