Mapping oxidative DNA damage at nucleotide level

In vitro fermentation of glycosaminoglycans from mackerel fish waste and its role in modulating the antioxidant status and gut microbiota of high fat diet-fed C57BL/6 mice

Bioactive polysaccharides such as glycosaminoglycans (GAGs) exhibit potential health benefits for several health complications including obesity. The gut microbiota plays a key role in regulating host metabolism, nutrition and immunity. The present work assessed the potential of extracted GAGs (e-GAGs) in maintaining the gut microbiota and ameliorating the effects of high fat diet in in vitro and in vivo models. The in vitro fermentability of e-GAGs extracted from mackerel fish waste was analyzed with Lactobacillus plantarum (LP) and Bifidobacterium bifidum (BB); e-GAGs at 0.5 and 1% proved their prebiotic nature up to 48 h. The pH value decreased from 6.23 to 3.32, the cell density increased from 1.70 to 2.32, the viable cell count increased from 8 to 12 log CFU mL^-1, and short chain fatty acid (SCFA) production was ≈33, 31 and 36% for LP and ≈37, 29 and 34% for BB in terms of acetic acid, propionic acid and butyric acid, respectively. In vivo studies on high fat diet (HFD)-fed C57BL/6 mice with e-GAGs (380 and 760 mg kg^-1 diet) showed ameliorated gut microbiome and tissue/plasma antioxidant enzyme activities, and also the e-GAG-fed group showed significantly (P < 0.05) decreased lipid peroxidation. Cecal microbial analysis showed the health-promoting effects of e-GAGs in reducing (P < 0.05) the obesity ratio of Firmicutes to Bacteroidetes (F/B) within the range (5.32 and 5.26) compared with HFD (6.23). Hence, e-GAGs can be a potential molecule for the treatment of obesity by restoring the redox status under oxidative stress and ameliorating the gut microbes that produce SCFAs which are known to have health beneficial effects.

A potential screening method for epigenetic drugs: uncovering stress-induced gene silencing in Chlamydomonas

Histone modifications and DNA methylation together govern promoter availability, thereby influencing gene expression. This study queries the unicellular chlorophyte, Chlamydomonas reinhardtii using a three step "epigenetic assay" design to phenotypically track the variegation of a randomly integrated Paromomycin resistance transgene(s) (Pm^R). Based on its position of integration, the Pm^R gene expression hinged on two epigenetic hallmarks: the spreading of heterochromatin, and the transmissible memory of epigenetic states across generations. Using a spot-dilution analysis, the loss of antibiotic resistance phenotype was scored from 0 to 4, four being maximally silenced. Appropriate construct designs were used to demonstrate that the cis-spread of heterochromatin could be interfered with a stronger euchromatic barrier (TUB2 promoter). When assayed for metal ion stress, a combination of Mn deficiency with excess Cu or Zn stress was shown to induce gene silencing in Chlamydomonas. Cu stress resulted in the accumulation of intracellular ROS, while Zn stress elevated the sensitivity to ROS. As proof of functional conservation, mammalian epigenetic drugs demonstrably interfered with stress-induced gene silencing. Finally, a selected group of transgenic clones responsive to HDACi sodium butyrate, when tested in a gradient plate format showed similarity in phenotype to the plant-derived compound cinnamic acid. This indicated a possible commonality in their mode of action, unlike curcumin which might have a different mechanism. Thus, using binned libraries, based on a common set of responses to known drugs, a cost-effective high-throughput screening strategy for epigenetically active compounds from plants or other sources is described.

Development of Wheat Bran Oil Concentrates Rich in Bioactives with Antioxidant and Hypolipidemic Properties

Wheat bran, an abundant byproduct of the milling industry, comprises fat-soluble bioactives and fibers. In the present study, two concentrates were prepared from wheat bran oil (WBO) using silicic acid coupled with acetone (WBA) and hexane (WBH). WBA extract had enhanced color and viscosity and was enriched with fat-soluble bioactives (sterols, oryzanol-like compounds, tocopherols, and carotenoids) as evidenced from NMR and other techniques. In in vitro studies, WBA exhibited significant free radical scavenging activity, limited DNA and LDL oxidation, and inhibiting HMG-CoA reductase and lipase activity better than WBH and WBO. Further, an in vivo study with WBA 2 or 3.5% containing high fat diet ameliorated malonaldehyde (MDA) level, lipid profile, and antioxidant enzyme (SOD, catalase, GPx, and GR) activities in liver. A possible reason for this effect is downregulation of HMG-CoA reductase expression with WBA. Thus, WBA has significant potential as an ingredient in health food formulations.

The oxidation of p-phenylenediamine, an ingredient used for permanent hair dyeing purposes, leads to the formation of hydroxyl radicals: Oxidative stress and DNA damage in human immortalized keratinocytes

The hair-dyeing ingredient, p-phenylenediamine (PPD), was previously reported to be mutagenic, possibly by inducing oxidative stress. However, the exact mechanism of PPD in inducing oxidative stress upon skin exposure during hair-dyeing in human keratinocytes remains unknown. The aim of our studies was therefore to investigate the toxicity of PPD and its by-products in human immortalized keratinocytes (HaCaT) after auto-oxidation and after reaction with hydrogen peroxide (H2O2). We found that the PPD half maximal effective cytotoxic concentration (EC50) to HaCaT is 39.37 and 35.63 μg/mL after 24 and 48 h, respectively, without addition of H2O2 to induce oxidation. When PPD (10 or 100 μg/mL) is combined with 10.5 μg/mL of H2O2, intracellular ROS production by HaCaT after 1 h was significantly increased and enhanced levels of DNA damage were observed after 4 h of exposure. After 24 h incubations, 20 μg/mL of PPD increased the level of DNA oxidation in HaCaT. Also, we found that the in vitro reaction between PPD and H2O2, even below the maximum allowance by cosmetic industries, released hydroxyl radicals which can damage DNA. Taken together, we conclude that PPD alone and when combined with H2O2 increases the formation of reactive oxygen species in human keratinocytes, leading to oxidative stress and subsequent DNA damage. These alterations suggest that the mechanism by which PPD exposure, alone or combined with H2O2, damages keratinocytes by the formation of the high reactive HO∙ radicals.

Cytosine containing dipyrimidine sites can be hotspots of cyclobutane pyrimidine dimer formation after UVB exposure

Exposure to the UV component of sunlight is the principal factor leading to skin cancer development. Cyclobutane pyrimidine dimers (CPD) are considered to be the most important pre-mutagenic type of DNA damage involved in skin carcinogenesis. To better understand the biological mechanisms of UV carcinogenesis, it is critical to understand the CPD distribution between the four types of dipyrimidine sites. Most of our knowledge regarding CPD distribution comes from in vitro studies or from investigations using UVC, even though we are not naturally exposed to these UV wavelengths. We exposed normal human fibroblasts and purified DNA to UVB. Using ligation-mediated PCR, we quantified the CPD formation at 952 dipyrimidine sites among the PGK1 (phosphoglycerate kinase 1), JUN, HRAS, KRAS, NRAS and TP53 genes. In cellulo, we found a CPD distribution of 27 : 27 : 25 : 21 for TT : CC : TC : CT. This distribution is similar to that observed in vitro. In the analysed genes, we observed some extremely frequently damaged dipyrimidine sites and many of these occurred at potentially frequently mutated sites, i.e. at dipyrimidine sites containing cytosine. Also, most of the frequently damaged dipyrimidine sites in cellulo that are not frequently damaged in vitro are found on TP53 and NRAS. This indicates that many of the frequently damaged dipyrimidine sites in cellulo are on genes frequently mutated in skin cancer. All these results support the view that CPD are the main UVB-induced mutagenic photoproducts and provide evidence of the importance of CPD formation at sites containing cytosine.

Targeted detection of in vivo endogenous DNA base damage reveals preferential base excision repair in the transcribed strand

Endogenous DNA damage is removed mainly via base excision repair (BER), however, whether there is preferential strand repair of endogenous DNA damage is still under intense debate. We developed a highly sensitive primer-anchored DNA damage detection assay (PADDA) to map and quantify in vivo endogenous DNA damage. Using PADDA, we documented significantly higher levels of endogenous damage in Saccharomyces cerevisiae cells in stationary phase than in exponential phase. We also documented that yeast BER-defective cells have significantly higher levels of endogenous DNA damage than isogenic wild-type cells at any phase of growth. PADDA provided detailed fingerprint analysis at the single-nucleotide level, documenting for the first time that persistent endogenous nucleotide damage in CAN1 co-localizes with previously reported spontaneous CAN1 mutations. To quickly and reliably quantify endogenous strand-specific DNA damage in the constitutively expressed CAN1 gene, we used PADDA on a real-time PCR setting. We demonstrate that wild-type cells repair endogenous damage preferentially on the CAN1 transcribed strand. In contrast, yeast BER-defective cells accumulate endogenous damage preferentially on the CAN1 transcribed strand. These data provide the first direct evidence for preferential strand repair of endogenous DNA damage and documents the major role of BER in this process.

Changes in leucine transport activity in Chironomus riparius larvae after short-term exposure to potassium dichromate and fenitrothion

The effect of sublethal concentrations of potassium dichromate and fenitrothion on sodium-leucine cotransport in brush border membrane vesicles from Chironomus riparius larvae has been investigated. Exposure to potassium dichromate and fenitrothion caused a dose- and time-dependent inhibition of leucine uptake. Transport inhibition is easily detectable at doses 100-fold lower than LD50. Kinetic experiments showed that inhibition was mainly caused by a decrease of the Vmax (680 +/- 53 vs. 382 +/- 23 and 555 +/- 27 nmol/15s/mg protein in control and exposed larvae to K2Cr2O7 and fenitrothion, respectively). Inhibition is possibly related to a variation of sodium ions permeability as evidenced by increased membrane lipid peroxidation. Appropriate control experiments ruled out that the observed differences could be due to changes in general features of membrane preparations. Transport inhibition observed in larvae exposed to potassium dichromate was accompanied by changes in ascorbate peroxidase and dehydroascorbate reductase activities, whereas those exposed to fenitrothion displayed an increase in transaminase activity. The possible value of leucine uptake as biochemical biomarker is briefly discussed. Arch. Insect Biochem. Physiol. 55:90-101, 2004.

Inhibition of cell proliferation and fibronectin biosynthesis by Na ascorbate

BACKGROUND

The importance of ascorbate on the production of extracellular matrix proteins (as elastin and collagens) is now well documented, but no studies have been published concerning its effects on fibronectin biosynthesis. Fibronectin is important for cell attachment and for proliferation.

MATERIALS AND METHODS

The effects of Na ascorbate were investigated on cell attachment, proliferation, viability and fibronectin biosynthesis by human skin fibroblasts in vitro. Proliferation was followed by the monitoring of [(3)H]-thymidine incorporation; viability by the MTT-test, cell adherence by counting adherent and nonadherent cells and fibronectin biosynthesis by immunoprecipitation of biosynthetically labelled fibronectin.

RESULTS

In the presence of ascorbate, the fibroblasts showed a biphasic growth pattern. At 500 microM ascorbate, [(3)H]-thymidine incorporation was stimulated by 15% as compared to the controls. Higher concentrations gradually decreased proliferation up to 36% of the control value at 5 mM. These effects of ascorbate on DNA synthesis were followed to > 1.25 mM by a strong inhibition, cytotoxic effect and cell death. The non-adherent cell count increased to 10% of the total population at 2.5 mM and to 31% at 5.0 mM ascorbate.Increasing concentrations of ascorbate resulted in a dose-dependent decrease of fibronectin biosynthesis, both in the culture supernates and cell extracts. This inhibition mainly concerned cell membrane-associated fibronectin.Superoxide-dismutase or catalase could inhibit Na ascorbate-induced cytotoxicity and partially re-establish fibronectin biosynthesis. Desferrioxamine, ergothionein and vitamin E were inefficient.

CONCLUSIONS

Our results indicate that ascorbate decreases fibronectin biosynthesis of cultured human skin fibroblasts, thereby producing cell detachment and decreased proliferation. This effect is mainly mediated by the reactive oxygen species and can be inhibited by superoxide-dismutase and catalase.

Rapid up-regulation of peptide elongation factor EF-1alpha protein levels is an immediate early event during oxidative stress-induced apoptosis

Hydrogen peroxide (H(2)O(2)) induces apoptosis in cultured cells, in a dose-dependent manner. Treatment with H(2)O(2) causes decreased mitochondrial respiration, along with DNA degradation and the formation of an oligonucleosomal ladder, all hallmarks of apoptotic cell death. In this report, we investigate alterations in expression of a peptide elongation factor, EF-1alpha, during oxidative challenge. EF-1alpha protein levels undergo rapid increase upon treatment with H(2)O(2); however, whereas sublethal doses of H(2)O(2) stimulate only transient increases of EF-1alpha protein levels, lethal doses produce sustained elevation of EF-1alpha levels. Furthermore, pretreatment of H9c2(2-1) cells with transcriptional inhibitors fails to abolish the oxidant-induced increase in EF-1alpha, and Northern blotting analysis reveals that EF-1alpha mRNA levels remain steady throughout the H(2)O(2) treatment period, suggesting that the up-regulation of EF-1alpha is mediated posttranscriptionally. Transient transfection with an antisense EF-1alpha cDNA protects against hydrogen peroxide-mediated cytotoxicity in proportion to the degree of repression of EF-1alpha protein levels, suggesting that up-regulation of EF-1alpha plays a role in expediting the execution of the apoptotic program in response to oxidative stress.