Anthocyanin Interactions with DNA: Intercalation, Topoisomerase I Inhibition and Oxidative Reactions

Flavylium Dye as pH-Tunable Fluorescent and CD Probe for Double-Stranded DNA and RNA

The interaction of 4′-(N,N-dimethylamino)-6-hydroxyflavylium cation with double stranded (ds-) DNA/RNA was studied by UV/Vis spectrophotometry, circular dichroism (CD), and also steady-state and time-resolved emission spectroscopies at neutral and weakly acidic conditions. At pH 5, the studied molecule, in its flavylium cationic form, showed considerable binding affinities (5 < logKs < 6) for all ds-DNA/RNA, contrary to chalcones forms (dominant at pH 7), which did not show binding to polynucleotides. Flavylium cation intercalated into ds-DNAs at variance to dominant groove aggregation within ds-RNA, which was reported by RNA-specific bisignate induced CD spectrum (ICD) bands. The intrinsically negligible fluorescence of flavylium was strongly increased upon the addition of DNA or RNA, whereby both the fluorescence intensity and emission lifetimes of complexes differed considerably: the strongest emission increase was observed for AU-RNA (detection limit estimated to 10 nM) followed by AT-DNAs and the much weaker effect of GC-DNAs. Both fluorescence sensitivity on the ds-DNA/RNA secondary structure and sequence-selective ICD bands make the flavylium–chalcones system an intriguing pH-switchable new probe for distinguishing between various polynucleotide sequences.

Chemopreventive Effect of Dietary Anthocyanins against Gastrointestinal Cancers: A Review of Recent Advances and Perspectives

Anthocyanins are a group of dietary polyphenols, abundant mainly in fruits and their products. Dietary interventions of anthocyanins are being studied extensively related to the prevention of gastrointestinal (GI) cancer, among many other chronic disorders. This review summarizes the hereditary and non-hereditary characteristics of GI cancers, chemistry, and bioavailability of anthocyanins, and the most recent findings of anthocyanin in GI cancer prevention through modulating cellular signaling pathways. GI cancer-preventive attributes of anthocyanins are primarily due to their antioxidative, anti-inflammatory, and anti-proliferative properties, and their ability to regulate gene expression and metabolic pathways, as well as induce the apoptosis of cancer cells.

State of the Art of Anthocyanins: Antioxidant Activity, Sources, Bioavailability, and Therapeutic Effect in Human Health

The antioxidant activity of anthocyanins in food is well known. Numerous antioxidant assays have been proposed to measure the capacity of anthocyanins to prevent the oxidation process that naturally occurs. Different solvents, temperatures, and pH levels are applied in each assay, and these factors should be taken into account in order to obtain useful and reproducible results. The concentration and the structure of these compounds are directly related to their antioxidant capacity and their environment. However, the effectiveness of the anthocyanin ingestion against diseases is also influenced by its bioavailability. Novel methodologies that simulate the digestion process have been developed in order to facilitate the current knowledge of anthocyanins bioavailability. Studies highlight the potential synergy effect between parent compounds and their derivatives (metabolites, conjugated products, and microbe-generated metabolites). The aim of this review is to provide an overview of advantages and disadvantages of the most common methods to determine the antioxidant activity of anthocyanins, chemical structure, and concentration of these compounds in different edible fruits, vegetables, and plants; their bioavailability after intake; as well as the main therapeutic effect described in the scientific literature.

DNA agarose gel electrophoresis for antioxidant analysis: Development of a quantitative approach for phenolic extracts

Most of the fast in vitro assays proposed to determine the antioxidant capacity of a compound/extract lack either biological context or employ complex protocols. Therefore, the present work proposes the improvement of an agarose gel DNA electrophoresis in order to allow for a quantitative estimation of the antioxidant capacity of pure phenolic compounds as well as of a phenolic rich extract, while also considering their possible pro-oxidant effects. The result obtained demonstrated that the proposed method allowed for the evaluation of the protection of DNA oxidation [in the presence of hydrogen peroxide (H₂O₂) and an H₂O₂/iron (III) chloride (FeCl₃) systems] as well as for the observation of pro-oxidant activities, with the measurements registering interclass correlation coefficients above 0.9. Moreover, this method allowed for the characterization of the antioxidant capacity of a blueberry extract while demonstrating that it had no perceived pro-oxidant effect.

Genistein and delphinidin antagonize the genotoxic effects of the mycotoxin alternariol in human colon carcinoma cells

SCOPE

Although associated with anti-oxidative properties, genistein has been reported to induce DNA strand breaks, whereby oxidative stress and topoisomerase poisoning are considered as potential mechanisms. In contrast, delphinidin, a catalytic topoisomerase inhibitor, is known to suppress the DNA-damaging properties of several topoisomerase poisons. Recently, alternariol, a mycotoxin produced by Alternaria spp., was found not only to induce oxidative stress but also to act as a topoisomerase poison. As both, polyphenols and mycotoxins, might occur in our nutrition simultaneously, the question was addressed whether potential combinatory effects on DNA integrity have to be considered.

METHODS AND RESULTS

We determined combinatory effects of either genistein or delphinidin with alternariol in HT-29 cells. Cytotoxicity was assessed by WST-1 and SRB assays, whereby only weak interactions were observed. The comet assay revealed significant antagonistic interactions of both polyphenols with the genotoxicity of AOH. The underlying mechanism comprises the suppression of alternariol-mediated stabilization of DNA/topoisomerase-II-intermediates, as observed in the ICE assay. Furthermore, DEL but not GEN was found to suppress AOH-mediated oxidative stress.

CONCLUSION

Our data indicate that a respective polyphenol-rich diet might aid to protect against genotoxic damages caused by AOH, whereby bioactive concentrations of DEL are predominantly expected locally in the intestines.

Topical application of a mucoadhesive freeze-dried black raspberry gel induces clinical and histologic regression and reduces loss of heterozygosity events in premalignant oral intraepithelial lesions: results from a multicentered, placebo-controlled clinical trial

PURPOSE

Approximately 30% higher grade premalignant oral intraepithelial neoplasia (OIN) lesions will progress to oral cancer. Although surgery is the OIN treatment mainstay, many OIN lesions recur, which is highly problematic for both surgeons and patients. This clinical trial assessed the chemopreventive efficacy of a natural product-based bioadhesive gel on OIN lesions.

EXPERIMENTAL DESIGN

This placebo-controlled multicenter study investigated the effects of topical application of bioadhesive gels that contained either 10% w/w freeze-dried black raspberries (BRB) or an identical formulation devoid of BRB placebo to biopsy-confirmed OIN lesions (0.5 g × q.i.d., 12 weeks). Baseline evaluative parameters (size, histologic grade, LOH events) were comparable in the randomly assigned BRB (n = 22) and placebo (n = 18) gel cohorts. Evaluative parameters were: histologic grade, clinical size, and LOH.

RESULTS

Topical application of the BRB gel to OIN lesions resulted in statistically significant reductions in lesional sizes, histologic grades, and LOH events. In contrast, placebo gel lesions demonstrated a significant increase in lesional size and no significant effects on histologic grade or LOH events. Collectively, these data strongly support BRB's chemopreventive impact. A cohort of very BRB-responsive patients, as demonstrated by high therapeutic efficacy, was identified. Corresponding protein profiling studies, which demonstrated higher pretreatment levels of BRB metabolic and keratinocyte differentiation enzymes in BRB-responsive lesions, reinforce the importance of local metabolism and differentiation competency.

CONCLUSIONS

Results from this trial substantiate the LOH reductions identified in the pilot BRB gel study and extend therapeutic effects to significant improvements in histologic grade and lesional size.

Optimization of ultrasound-assisted extraction of anthocyanins from mulberry, using response surface methodology

Mulberry is one of the most widely used traditional Chinese medicines. Anthocyanins are the main bioactive components of mulberry, and possess important biological activities, such as antimicrobial, anti-inflammatory and antioxidant activities. This study investigated the ultrasound-assisted extraction (UAE) of anthocyanins from mulberry by using response surface methodology (RSM). The extraction conditions associated with anthocyanin yield, including extraction solvent, liquid-to-solid rate, temperature and extraction time, are discussed. The optimal conditions obtained by RSM for UAE from mulberry include 63.8% methanol contains 1% (v/v) trifluoroacetic acid (TFA), 43.2 °C temperature, 23.8 (v/w) liquid-to-solid ratio, and 40 min time for the maximum yield (64.70 ± 0.45 mg/g). The results indicated that the UAE can be an effective method for the extraction of some active components from plant materials.

Measuring DNA repair incision activity of mouse tissue extracts towards singlet oxygen-induced DNA damage: a comet-based in vitro repair assay

During the past two decades, the comet-based in vitro DNA repair assay has been used regularly to measure base excision repair (BER)-related DNA incision activity. Most studies focus on the assessment of BER in human lymphocytes or cultured cells by estimating the activity of a cell extract on substrate DNA containing specific lesions such as 8-oxoguanine. However, for many 'real-life' studies, it would be preferable to measure BER in the tissues of interest instead of using in vitro models or surrogate 'tissues' such as lymphocytes. Various attempts have been made to use the comet-based repair assay for BER with extracts from rodent tissues, but high non-specific nuclease activity in such tissues were a significant impediment to robust estimates of BER. Our aim in this study was to optimise the in vitro repair assay for BER for use with rodent tissues using extracts from liver and brain from C57/BL mice. Because the DNA incision activity of an extract is dependent on its protein concentration, the first optimisation step in preventing interference by non-specific nuclease activity was to determine the protein concentration at which there is a maximal difference between the total and non-specific damage recognition. This protein concentration was 5 mg/ml for mouse liver extracts and 1 mg/ml for brain extracts. Next, we tested addition of proteinase inhibitors during the preparation of the tissue extracts, but this did not improve the sensitivity of the assay. However, addition of 1.5 μM aphidicolin to the tissue extracts improved the detection of DNA repair incision activity by reducing non-specific nuclease activity and possibly by blocking residual DNA polymerase activity. Finally, the assay was tested on tissue samples from an ageing mouse colony and in mice undergoing dietary restriction and proved capable of detecting significant inter-animal differences and nutritional effects on BER-related DNA incision activity.

Quercetin inhibits hydrogen peroxide-induced DNA damage and enhances DNA repair in Caco-2 cells

Flavonoids are known to have antioxidant activity that may limit DNA damage and help prevent degenerative diseases, including cancer. However, our knowledge of flavonoids' role in DNA protection/repair mechanism(s) is limited. This study investigated the effects of quercetin on DNA oxidation and DNA repair in Caco-2 cells with or without oxidant (H2O2) challenge. Quercetin (1, 100 microM) significantly reduced oxidative DNA damage, as measured by the number of single-strand breaks identified by single cell gel electrophoresis. Quercetin treatment also caused a measurable increase in the mRNA expression of human 8-oxoguanine DNA glycosylase (hOGG1) at 0 and 4h after H2O2 treatment (measured using RT-PCR). In addition, the highest level of quercetin tested (100 microM) maintained hOGG1 expression at basal levels or higher for up to 12h after H2O2 treatment, while oxidant treatment alone resulted in significant reduction of hOGG1 at 8h. Our study indicates that quercetin could protect DNA both by reducing oxidative DNA damage and by enhancing DNA repair through modulation of DNA repair enzyme expression.