Protective Role of Glutathione against Peroxynitrite-Mediated DNA Damage During Acute Inflammation.

Inflammation is an immune response to protect against various types of infections. When unchecked, acute inflammation can be life-threatening, as seen with the current coronavirus pandemic. Strong oxidants, such as peroxynitrite produced by immune cells, are major mediators of the inflammation-associated pathogenesis. Cellular thiols play important roles in mitigating inflammation-associated macromolecular damage including DNA. Herein, we have demonstrated a role of glutathione (GSH) and other thiols in neutralizing the effect of peroxynitrite-mediated DNA damage through stable GSH-DNA adduct formation. Our observation supports the use of thiol supplements as a potential therapeutic strategy against severe COVID-19 cases and a Phase II (NCT04374461) open-label clinical trial launched in early May 2020 by the Memorial Sloan Kettering Cancer Center.

Facile Construction of i-Motif DNA-Conjugated Gold Nanostars as Near-Infrared and pH Dual-Responsive Targeted Drug Delivery Systems for Combined Cancer Therapy.

Stimuli-responsive DNA-based nanostructures have emerged as promising vehicles for intelligent drug delivery. In this study, i-motif DNA-conjugated gold nanostars (GNSs) were fabricated in a facile manner as stimuli-responsive drug delivery systems (denoted as A-GNS/DNA/DOX) for the treatment of cancer via combined chemo-photothermal therapy. The i-motif DNA is sensitive to the environmental pH and can switch from a single-stranded structure to a C-tetrad (i-motif) structure as the environmental pH decreases from neutral (∼7.4) to acidic (<6.0). The loaded drug can then be released along with the conformational changes. To enhance cellular uptake and improve cancer cell selectivity, the aptamer AS1411, which recognizes nucleolins, was employed as a targeting moiety. The A-GNS/DNA/DOX nanocomposites were found to be highly capable of photothermal conversion and exhibited photostability under near-infrared (NIR) irradiation, and the pH and NIR irradiation effectively triggered the drug-release behaviors. In addition, the A-GNS/DNA/DOX nanocomposites exhibited good biocompatibility. The targeting recognition enabled the A-GNS/DNA/DOX to exhibit higher cellular uptake and therapeutic efficiency than the GNS/DNA/DOX. Notably, under NIR irradiation, a synergistic effect between chemotherapy and photothermal therapy can be achieved with the proposed delivery system, which exhibits much higher therapeutic efficiency both in monolayer cancer cells and tumor spheroids as compared with a single therapeutic method. This study highlights the potential of GNS/DNA nanoassemblies for intelligent anticancer drug delivery and combined cancer therapy.

DFT and MD Studies of Formaldehyde-Derived DNA Adducts: Molecular-Level Insights into the Differential Mispairing Potentials of the Adenine, Cytosine, and Guanine Lesions.

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone is a potent nicotine-based carcinogen that generates many DNA lesions, including the HOCH2-C, HOCH2-G, and HOCH2-A hydroxymethyl adducts. Despite all lesions containing an altered exocyclic amino group, which allows the hydroxymethyl group to be directed away from the Watson-Crick binding face, only the most persistent adenine adduct is mutagenic. As a first step toward understanding this differential mutagenicity, density functional theory (DFT) and molecular dynamics (MD) simulations were used to gain atomic-level structural details of these DNA damage products. DFT calculations reveal that all three lesions exhibit conformational diversity. However, regardless of the hydroxymethyl-nucleobase orientation, both DFT and MD simulations highlight that HOCH2-C and HOCH2-G form pairs with the canonical complementary base (G and C, respectively) that are structural and energetically preferred over mispairs. In contrast, depending on the hydroxymethyl-nucleobase orientation, the Watson-Crick HOCH2-A:T pair can become significantly destabilized relative to undamaged A:T. As a result, HOCH2-A mispairs with G, C, and A are energetically accessible and maintain key geometrical features of canonical DNA. Overall, our data directly correlate with the reported differential mutagenicity of the hydroxylmethyl lesions and will encourage future studies to further uncover the cellular impact of the most persistent adenine lesion.

In Vitro DNA Adduction Resulting from Metabolic Activation of Diosbulbin B and 8-Epidiosbulbin E Acetate.

Diosbulbin B (DBB) and 8-epidiosbulbin E acetate (EEA), belonging to furan-containing diterpenoid lactones, are the primary components of Dioscorea bulbifera L. (DB), a traditional Chinese medicine herb. Our earlier studies indicated that consumption of DBB or EEA induced acute hepatotoxicities. Both DBB and EEA were bioactivated by P450 3A4 to generate the corresponding cis-enedial reactive metabolites which are associated with the hepatotoxicities. It has been proposed that the electrophilic intermediates attack cellular nucleophiles such as protein or DNA, thought to be a mechanism of triggering toxicities. The purposes of our present study were to define the interaction of the electrophilic reactive metabolites originating from DBB and EEA with 2'-deoxyguanosine (dGuo), 2'-deoxycytidine (dCyd), and 2'-deoxyadenosine (dAdo) and to characterize DNA adducts arising from the reactive metabolites of DBB and EEA. The reactive metabolites of DBB and EEA were found to covalently bind to the exocyclic and endocyclic nitrogens of dCyd, dGuo, and dAdo to generate oxadiazabicyclo[3.3.0]octaimine adducts. The reactive metabolites of DBB and EEA also attacked dGuo, dAdo, and dCyd of calf thymus DNA. The DNA adducts possibly contribute to the toxicologies of DBB and EEA.

Dietary furocoumarins and skin cancer: A review of current biological evidence.

Furocoumarins are a class of compounds produced by several plant species, including some popularly consumed by humans. Furocoumarins are known to be well absorbed from food sources, and can be rapidly distributed into several tissues including the skin. In human skin, when exposed to UV radiation, furocoumarins may become photoactivated and form interstrand crosslinks with DNA, thereby disrupting DNA transcription. Because of this property, furocoumarins have been combined as topical or oral agents with UV irradiation as a phototherapy to treat multiple skin conditions, yet these treatments have been shown to increase risk of both melanoma and non-melanoma skin cancer. Whether or not dietary furocoumarin exposure may confer the same risk is not yet known. This review summarizes the current evidence regarding the activities of ingested furocoumarins, with particular focus on how dietary furocoumarins are absorbed, metabolized, and distributed throughout the body, and their interactions with various cellular components that may underlie a potential relationship with skin cancer.

RETRACTED: Low density lipoprotein receptor targeted doxorubicin/DNA-Gold Nanorods as a chemo- and thermo-dual therapy for prostate cancer.

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). This article has been retracted at the request of the authors and sanctioned by the Editor-in-Chief. The authors found errors in the data presentation - apoptotic statistics and in vivo distribution - which makes the conclusion not representative. The authors express sincere apologies for the error and inconvenience to readers.

Immuno-spin trapping detection of antioxidant/pro-oxidant properties of zinc or selenium on DNA and protein radical formation via hydrogen peroxide.

Trace elements can participate in the catalysis of group-transfer reactions and can serve as their structural components. However, most of them including zinc and selenium have multifunctional roles in biological environments such as antioxidant and/or pro-oxidant effects, as concentration-dependent manner. Although it has been demonstrated the antioxidant actions of either selenium or zinc compounds, there are several documents pointing out their pro-oxidant/oxidant roles in biological systems. Here we have used ELISA-based immuno-spin trapping, a method for detection of free radical formation, to detect whether or not a zinc compound, Zn3(PO4)2, or a selenium compound, Na2SeO3, has antioxidant and/or pro-oxidant effect on 5,5-Dimethyl-1-Pyrroline-N-Oxide (DMPO)-DNA nitrone adducts induced with Cu(II)-H2O2-oxidizing system in in vitro preparations. Second, we examined whether this technique is capable to demonstrate the different DMPO-protein nitrone adduct productions in isolated protein crude of hearts from normal rats (CON) or rats with metabolic syndrome (MetS). Our data demonstrated that either Zn(2+) (100 µM) or SeO3(-2) (50 nM) has very strong antioxidant action against 200 µM H2O2-induced DMPO-DNA nitrone adduct production, whereas their higher concentrations have apparent pro-oxidant actions. We also used verification by Western blotting analysis whether immuno-spin trapping can be used to assess H2O2-induced DMPO-protein nitrone adducts in heart protein crudes. Our Western blot data further confirmed the ELISA-data from proteins and demonstrated how Zn(2+) or SeO3(-2) are dual-functioning ions such as antioxidant at lower concentrations while pro-oxidant at higher concentrations. Particularly, our present data with SeO3(-2) in DMPO-protein nitrone adducts, being in line with our previous observation on its dual-actions in ischemia/reperfusion-induced damaged heart, have shown that this ion has higher pro-oxidant actions over 50 nM in MetS-group compared to that of CON group.

Inhibition effects of Chinese cabbage powder on aflatoxin B1-induced liver cancer.

In this study, 0.25 µg/ml aflatoxin B1 was used to establish a liver cancer model for assessing the potential anticancer ability of Chinese cabbage powder, which is a complex water-soluble extract from Chinese cabbage by spray-drying at an outlet temperature of 130 °C. We found at least 11 potential anticancer substances in Chinese cabbage powder. A 90-d animal experiment demonstrated that 10% of Chinese cabbage powder in drinking water could improve the plasma micronutrient status, inhibit the formation of aflatoxin B1-DNA adducts in liver cells, and effectively reduce the incidence of liver tumor induced by aflatoxin B1 from 6.67% to 0%. The dose effect experiment revealed that 10% may be the minimal effective dose to prevent the occurrence of early liver tumors. This study will help elucidate the basis of epidemiological observations of dietary cancer prevention in humans, as well as explore related mechanisms.

Kava blocks 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone-induced lung tumorigenesis in association with reducing O6-methylguanine DNA adduct in A/J mice.

We previously reported the chemopreventive potential of kava against 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)- and benzo(a)pyrene (BaP)-induced lung tumorigenesis in A/J mice during the initiation and postinitiation stages. In this study, we investigated the tumorigenesis-stage specificity of kava, the potential active compounds, and the underlying mechanisms in NNK-induced lung tumorigenesis in A/J mice. In the first experiment, NNK-treated mice were given diets containing kava at a dose of 5 mg/g of diet during different periods. Kava treatments covering the initiation stage reduced the multiplicity of lung adenomas by approximately 99%. A minimum effective dose is yet to be defined because kava at two lower dosages (2.5 and 1.25 mg/g of diet) were equally effective as 5 mg/g of diet in completely inhibiting lung adenoma formation. Daily gavage of kava (one before, during, and after NNK treatment) completely blocked lung adenoma formation as well. Kavalactone-enriched fraction B fully recapitulated kava's chemopreventive efficacy, whereas kavalactone-free fractions A and C were much less effective. Mechanistically, kava and fraction B reduced NNK-induced DNA damage in lung tissues with a unique and preferential reduction in O(6)-methylguanine (O(6)-mG), the highly tumorigenic DNA damage by NNK, correlating and predictive of efficacy on blocking lung adenoma formation. Taken together, these results demonstrate the outstanding efficacy of kava in preventing NNK-induced lung tumorigenesis in A/J mice with high selectivity for the initiation stage in association with the reduction of O(6)-mG adduct in DNA. They also establish the knowledge basis for the identification of the active compound(s) in kava.

Cisplatin induces a mitochondrial-ROS response that contributes to cytotoxicity depending on mitochondrial redox status and bioenergetic functions.

Cisplatin is one of the most effective and widely used anticancer agents for the treatment of several types of tumors. The cytotoxic effect of cisplatin is thought to be mediated primarily by the generation of nuclear DNA adducts, which, if not repaired, cause cell death as a consequence of DNA replication and transcription blockage. However, the ability of cisplatin to induce nuclear DNA (nDNA) damage per se is not sufficient to explain its high degree of effectiveness nor the toxic effects exerted on normal, post-mitotic tissues. Oxidative damage has been observed in vivo following exposure to cisplatin in several tissues, suggesting a role for oxidative stress in the pathogenesis of cisplatin-induced dose-limiting toxicities. However, the mechanism of cisplatin-induced generation of ROS and their contribution to cisplatin cytotoxicity in normal and cancer cells is still poorly understood. By employing a panel of normal and cancer cell lines and the budding yeast Saccharomyces cerevisiae as model system, we show that exposure to cisplatin induces a mitochondrial-dependent ROS response that significantly enhances the cytotoxic effect caused by nDNA damage. ROS generation is independent of the amount of cisplatin-induced nDNA damage and occurs in mitochondria as a consequence of protein synthesis impairment. The contribution of cisplatin-induced mitochondrial dysfunction in determining its cytotoxic effect varies among cells and depends on mitochondrial redox status, mitochondrial DNA integrity and bioenergetic function. Thus, by manipulating these cellular parameters, we were able to enhance cisplatin cytotoxicity in cancer cells. This study provides a new mechanistic insight into cisplatin-induced cell killing and may lead to the design of novel therapeutic strategies to improve anticancer drug efficacy.

Conformation-dependent DNA damage induced by gold nanoparticles.

The sensitivity of two conformations of plasmid DNA, the A and B forms, to strand break formation induced by gold nanoparticles (GNPs) is investigated by varying the GNP to DNA ratio in solution and the degree of DNA hydration. Decreasing DNA hydration via lyophilisation or by replacement of water with ethanol in solution modifies its conformation from the B to the A form. The yields of single strand breaks (SSB) are found to be highly dependent on the amount of DNA in the A configuration. The damage also increases with the amount of GNPs bound to DNA. At a ratio of two GNPs for one plasmid in an 80%-ethanol, 20%-water solution, 50% of the initial supercoiled population is converted to SSB. Thus, close contact with GNPs causes extensive damage to DNA in the A form. Since during transcription the DNA-RNA duplexes adopt an A form, GNPs could be genotoxic. Our results suggest that GNPs may have potential as chemotherapeutic agents if conjugated to nuclear targeting ligands. Considering their additional radiotherapeutic properties, targeted GNPs could also become highly effective in the treatment of cancer with concomitant chemoradiation therapy.

Abundance of DNA adducts of methyleugenol, a rodent hepatocarcinogen, in human liver samples.

Methyleugenol is a genotoxic carcinogen in mice and rats, the liver being the primary target tissue. Methyleugenol occurs in fennel and many herbs and spices. Furthermore, methyleugenol-containing plant extracts and chemically prepared methyleugenol are used as flavoring agents. We analyzed surgical human liver samples from 30 subjects for the presence of DNA adducts originating from methyleugenol using isotope-dilution ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Twenty-nine samples unambiguously contained the N (2)-(trans-methylisoeugenol-3'-yl)-2'-deoxyguanosine adduct. A second adduct, N (6)-(trans-methylisoeugenol-3'-yl)-2'-deoxyadenosine, was also found in most samples, but at much lower levels, in agreement with the results from experimental models. The maximal and median levels of both adducts combined were 37 and 13 per 10(8) nucleosides (corresponding to 4700 and 1700, respectively, adducts per diploid genome). This is the first demonstration of DNA adducts formed by a xenobiotic in human liver using UPLC-MS/MS, the most reliable method available. It has been estimated for diverse rat and mouse hepatocarcinogens that 50-5500 adducts per 10(8) nucleosides are present after repeated treatment at the TD50 (daily dose that halves the probability to stay tumor-free in long-term studies). We conclude that the exposure to methyleugenol leads to substantial levels of hepatic DNA adducts and, therefore, may pose a significant carcinogenic risk.

A fluorescence-based analysis of aristolochic acid-derived DNA adducts.

Aristolochic acids (AAs), major components of plant extracts from Aristolochia species, form (after metabolic activation) pro-mutagenic DNA adducts in renal tissue. The DNA adducts can be used as biomarkers for studies of AA toxicity. Identification of these adducts is a complicated and time-consuming procedure. We present here a fast, nonisotopic, fluorescence-based assay for the detection of AA-DNA adducts in multiple samples. This approach allows analysis of AA adducts in synthetic DNA with known nucleotide composition and analysis of DNA adducts formed from chemically diverse AAs in vitro. The method can be applied to compare AA-DNA adduct formation in cells and tissues.

Detection and imaging of the free radical DNA in cells--site-specific radical formation induced by Fenton chemistry and its repair in cellular DNA as seen by electron spin resonance, immuno-spin trapping and confocal microscopy.

Oxidative stress-related damage to the DNA macromolecule produces lesions that are implicated in various diseases. To understand damage to DNA, it is important to study the free radical reactions causing the damage. Measurement of DNA damage has been a matter of debate as most of the available methods measure the end product of a sequence of events and provide limited information on the initial free radical formation. We report a measurement of free radical damage in DNA induced by a Cu(II)-H(2)O(2) oxidizing system using immuno-spin trapping supplemented with electron paramagnetic resonance. In this investigation, the short-lived radical generated is trapped by the spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO) immediately upon formation. The DMPO adduct formed is initially electron paramagnetic resonance active, but is subsequently oxidized to the stable nitrone adduct, which can be detected and visualized by immuno-spin trapping and has the potential to be further characterized by other analytical techniques. The radical was found to be located on the 2'-deoxyadenosine (dAdo) moiety of DNA. The nitrone adduct was repaired on a time scale consistent with DNA repair. In vivo experiments for the purpose of detecting DMPO-DNA nitrone adducts should be conducted over a range of time in order to avoid missing adducts due to the repair processes.

Theoretical investigation of differences in nitroreduction of aristolochic acid I by cytochromes P450 1A1, 1A2 and 1B1.

OBJECTIVES: The herbal drug aristolochic acid (AA) derived from Aristolochia species has been shown to be the cause of aristolochic acid nephropathy (AAN), Balkan endemic nephropathy (BEN) and their urothelial malignancies. One of the common features of AAN and BEN is that not all individuals exposed to AA suffer from nephropathy and tumor development. One cause for these different responses may be individual differences in the activities of the enzymes catalyzing the biotransformation of AA. Thus, the identification of enzymes principally involved in the metabolism of AAI, the major toxic component of AA, and detailed knowledge of their catalytic specificities is of major importance. Human cytochrome P450 (CYP) 1A1 and 1A2 enzymes were found to be responsible for the AAI reductive activation to form AAI-DNA adducts, while its structurally related analogue, CYP1B1 is almost without such activity. However, knowledge of the differences in mechanistic details of CYP1A1-, 1A2-, and 1B1- mediated reduction is still lacking. Therefore, this feature is the aim of the present study. METHODS: Molecular modeling capable of evaluating interactions of AAI with the active site of human CYP1A1, 1A2 and 1B1 under the reductive conditions was used. In silico docking, employing soft-soft (flexible) docking procedure was used to study the interactions of AAI with the active sites of these human enzymes. RESULTS: The predicted binding free energies and distances between an AAI ligand and a heme cofactor are similar for all CYPs evaluated. AAI also binds to the active sites of CYP1A1, 1A2 and 1B1 in similar orientations. The carboxylic group of AAI is in the binding position situated directly above heme iron. This ligand orientation is in CYP1A1/1A2 further stabilized by two hydrogen bonds; one between an oxygen atom of the AAI nitro-group and the hydroxyl group of Ser122/Thr124; and the second bond between an oxygen atom of dioxolane ring of AAI and the hydroxyl group of Thr497/Thr498. For the CYP1B1:AAI complex, however, any hydrogen bonding of the nitro-group of AAI is prevented as Ser122/Thr124 residues are in CYP1B1 protein replaced by hydrophobic residue Ala133. CONCLUSION: The experimental observations indicate that CYP1B1 is more than 10× less efficient in reductive activation of AAI than CYP1A2. The docking simulation however predicts the binding pose and binding energy of AAI in the CYP1B1 pocket to be analogous to that found in CYP1A1/2. We believe that the hydroxyl group of S122/T124 residue, with its polar hydrogen placed close to the nitro group of the substrate (AAI), is mechanistically important, for example it could provide a proton required for the stepwise reduction process. The absence of a suitable proton donor in the AAI-CYP1B1 binary complex could be the key difference, as the nitro group is in this complex surrounded only by the hydrophobic residues with potential hydrogen donors not closer than 5 Å.

Formation of dopamine quinone-DNA adducts and their potential role in the etiology of Parkinson's disease.

The neurotransmitter dopamine is oxidized to its quinone (DA-Q), which at neutral pH undergoes intramolecular cyclization by 1,4-Michael addition, followed by oxidation to form leukochrome, then aminochrome, and finally neuromelanin. At lower pH, the amino group of DA is partially protonated, allowing the competitive intermolecular 1,4-Michael addition with nucleophiles in DNA to form the depurinating adducts, DA-6-N3Ade and DA-6-N7Gua. Catechol estrogen-3,4-quinones react by 1,4-Michael addition to form the depurinating 4-hydroxyestrone(estradiol)-1-N3Ade [4-OHE1(E2)-1-N3Ade] and 4-OHE1(E2)-1-N7Gua adducts, which are implicated in the initiation of breast and other human cancers. The effect of pH was studied by reacting tyrosinase-activated DA with DNA and measuring the formation of depurinating adducts. The most adducts were formed at pH 4, 5, and 6, and their level was nominal at pH 7 and 8. The N3Ade adduct depurinated instantaneously, but N7Gua had a half-life of 3 H. The slow loss of the N7Gua adduct is analogous to that observed in previous studies of natural and synthetic estrogens. The antioxidants N-acetylcysteine and resveratrol efficiently blocked formation of the DA-DNA adducts. Thus, slightly acidic conditions render competitive the reaction of DA-Q with DNA to form depurinating adducts. We hypothesize that formation of these adducts could lead to mutations that initiate Parkinson's disease. If so, use of N-acetylcysteine and resveratrol as dietary supplements may prevent initiation of this disease.

Identification of a reduction product of aristolochic acid: implications for the metabolic activation of carcinogenic aristolochic acid.

Aristolochic acids are nephrotoxic and carcinogenic natural products that have been implicated both in endemic nephropathy in the Balkan region and in ailments caused by ingestion of herbal remedies. Aristolochic acids are metabolized to active intermediates that bind to DNA. In this study, reduction of aristolochic acid I with zinc in acetic acid afforded a new product that was characterized as 9-methoxy-7-methyl-2H-1,3-oxazolo[5',4'-10,9]phenanthro[3,4-d]-1,3-dioxolane-5-carboxylic acid, designated as aristoxazole, along with the expected aristolactam I. This new compound is a condensation product of aristolochic acid and acetic acid that may be related to the aristolochic acid-DNA adducts. The proposed mechanism of formation of aristoxazole involves nucleophilic attack of acetic acid on the nitrenium ion of aristolochic acid I. On the basis of these studies, a route to the metabolic activation of aristolochic acids and formation of adducts with DNA in in vitro systems is proposed and discussed.

Effect of green tea catechins and hydrolyzable tannins on benzo[a]pyrene-induced DNA adducts and structure-activity relationship.

Green tea catechins and hydrolyzable tannins are gaining increasing attention as chemopreventive agents. However, their mechanism of action is poorly understood. We investigated the effects of four green tea catechins and two hydrolyzable tannins on microsome-induced benzo[a]pyrene (BP)-DNA adducts and the possible structure-activity relationship. BP (1 microM) was incubated with rat liver microsomes and DNA in the presence of the test compound (1-200 microM) or vehicle. The purified DNA was analyzed by (32)P-postlabeling. The inhibitory activity of the catechins was in the following descending order: epigallocatechin gallate (IC(50) = 16 microM) > epicatechin gallate (24 microM) > epigallocatechin (146 microM) > epicatechin (462 microM), suggesting a correlation between the number of adjacent aromatic hydroxyl groups in the molecular structure and their potencies. Tannic acid (IC(50) = 4 microM) and pentagalloglucose (IC(50) = 26 microM) elicited as much DNA adduct inhibitory activity as the catechins or higher presumably due to the presence of more functional hydroxyl groups. To determine if the activity of these compounds was due to direct interaction of phenolic groups with electrophilic metabolite(s) of BP, DNA was incubated with anti-benzo[a]pyrene-7,8-diol-9,10-epoxide (anti-BPDE) (0.5 microM) in the presence of test compounds (200 microM) or vehicle. Significant inhibition of DNA adduct formation was found (tannic acid > pentagalloglucose > epigallocatechin gallate > epicatechin gallate). This notion was confirmed by analysis of the reaction products of anti-BPDE with the catechins and pentagalloglucose by electrospray ionization mass spectrometry and liquid chromatography-mass spectrometry. In conclusion, our data demonstrate that green tea catechins and the hydrolyzable tannins are highly effective in inhibiting BP-DNA adduct formation at least, in part, due to direct interaction of adjacent hydroxyl groups in their structures and that the activity is higher with an increasing number of functional hydroxyl groups.

Inhibition of 1, 2-dimethylhydrazine-induced mucin-depleted foci and O6-methylguanine DNA adducts in the rat colorectum by boiled garlic powder.

The scavenging capacity of reactive oxygen species, such as hydroxyl radicals, is reported not to decrease in boiled garlic (an odorless garlic preparation). We therefore examined the modifying effect of boiled garlic powder (BGP) on 1,2-dimethylhydrazine-induced mucin-depleted foci (MDF) and aberrant crypt foci (ACF), preneoplastic lesions, in the rat colorectum. Male F344 rats (5 weeks old) were fed a basal diet, or experimental diets containing 5% or 1% BGP for 5 weeks. One week later, all rats were injected s.c. with DMH (40 mg/kg, once weekly for 2 weeks). At 10 weeks of age, all the rats were sacrificed, and the colorectum was evaluated for MDF and ACF. In rats given DMH and the 5% or 1% BGP diets (Groups 2 and 3), the numbers of MDF decreased significantly in a dose-dependent manner, compared with the DMH and basal diet value (Group 1) (p<0.01). The numbers of ACF in Group 2, but not Group 3, showed a non-significant tendency to decrease. Next, the effects of BGP on the formation of DMH-induced O6-methylguanine (O6-MeG) DNA adducts in rats were studied. Male F344 rats (5 weeks old) were fed the basal diet, or 10% BGP diet for 5 weeks. All rats were injected i.p. once with 40 mg/kg DMH at the end of week 5. The animals were sacrificed 6 hours after DMH injection to analyze the O6-MeG DNA adducts in the colorectal mucosa. Dietary administration of BGP significantly inhibited the O6-MeG DNA adduct levels in the colorectal mucosa, compared with the controls (p<0.01). These results suggested that BGP may exert chemopreventive effects against colon carcinogenesis at least in the initiation stage.

An overview of structural features of DNA and RNA complexes with saffron compounds: Models and antioxidant activity.

Saffron is the red dried stigmas of Crocus sativus L. flowers and used both as a spice and as a drug in traditional medicine. Its numerous applications as an antioxidant and anticancer agent are due to its secondary metabolites and their derivatives (safranal, crocetin, dimethylcrocetin). In this work we are comparing the spectroscopic results and antioxidant activities of saffron components safranal, crocetin (CRT) and dimethylcrocetin (DMCRT) complexes with calf-thymus DNA (ctDNA) and transfer RNA (tRNA) in aqueous solution at physiological conditions Intercalative and external binding modes of saffron compounds to DNA and RNA were observed with overall binding constants of K(safranal)=1.24x10(3)M(-1), K(CRT)=6.20x10(3)M(-1) and K(DMCRT)=1.85x10(5)M(-1), for DNA adducts and K(safranal)=6.80x10(3)M(-1), K(CRT)=1.40x10(4)M(-1) and K(DMCRT)=3.40x10(4)M(-1) for RNA complexes. A partial B- to A-DNA transition occurred at high ligand concentrations, while tRNA remained in A-conformation in saffron-RNA complexes. The antioxidant activity of CRT, DMCRT and safranal was also tested by the DPPH (2,2-diphenyl-1-picrylhydrazyl) antioxidant activity assay and their IC(50) values were compared to that of well known antioxidants such as Trolox and Butylated Hydroxy Toluene (BHT). The IC(50) values were 95+/-1microg/mL for safranal and 18+/-1microg/mL for crocetin. The inhibition of DMCRT reached a point of 38.8%, which corresponds to a concentration of 40microg/mL.