Histone peptide AKRHRK enhances H2O2-induced DNA damage and alters its site specificity

Relevance of arginine residues in Cu(II)-induced DNA breakage and Proteinase K resistance of H1 histones

This work analyzes the involvement of arginines in copper/H₂O₂-induced DNA breakage. Copper is a highly redox active metal which has been demonstrated to form compounds with arginines. For this aim we used mixtures of pGEM3 DNA plasmid and two types of H1 histones which differ only in their arginine content. The sperm H1 histone from the annelid worm Chaetopterus variopedatus (arginine content 12.6 mol% K/R ratio 2) and the somatic H1 histone from calf thymus (arginine content 1.8 mol% and K/R ratio 15). Copper/H₂O₂-induced DNA breakage was observed only in presence of sperm H1 histones, but it was more relevant for the native molecule than for the deguanidinated derivative (K/R ratio 14), in which 80% of arginine residues were converted to ornithine. Further, copper induced proteinase K resistance and increase of DNA binding affinity on native sperm H1 histones. These observations are consistent with a copper induced reorganization of the side-chains of arginine residues. Copper, instead, did not affect DNA binding affinity of somatic and deguanidinated H1 histones, which show similar K/R ratio and DNA binding mode. These results indicate that arginine residues could affect these H1 histones properties and provide new insights into copper toxicity mechanisms.

New iminodibenzyl derivatives with anti-leishmanial activity

Leishmaniasis is an infection caused by protozoa of the genus Leishmania and transmitted by sandflies. Current treatments are expensive and time-consuming, involving Sb(V)-based compounds, lipossomal amphotericin B and miltefosine. Recent studies suggest that inhibition of trypanothione reductase (TR) could be a specific target in the development of new drugs because it is essential and exclusive to trypanosomatids. This work presents the synthesis and characterization of new iminodibenzyl derivatives (dado) with ethylenediamine (ea), ethanolamine (en) and diethylenetriamine (dien) and their copper(II) complexes. Computational methods indicated that the complexes were highly lipophilic. Pro-oxidant activity assays by oxidation of the dihydrorhodamine (DHR) fluorimetric probe showed that [Cu(dado-ea)]²⁺ has the highest rate of oxidation, independent of H₂O₂ concentration. The toxicity to L. amazonensis promastigotes and RAW 264,7 macrophages was assessed, showing that dado-en was the most active new compound. Complexation to copper did not have an appreciable effect on the toxicity of the compounds.

Cellular oxido-reductive proteins of Chlamydomonas reinhardtii control the biosynthesis of silver nanoparticles

Background

Elucidation of molecular mechanism of silver nanoparticles (SNPs) biosynthesis is important to control its size, shape and monodispersity. The evaluation of molecular mechanism of biosynthesis of SNPs is of prime importance for the commercialization and methodology development for controlling the shape and size (uniform distribution) of SNPs. The unicellular algae Chlamydomonas reinhardtii was exploited as a model system to elucidate the role of cellular proteins in SNPs biosynthesis.

Results

The C. reinhardtii cell free extract (in vitro) and in vivo cells mediated synthesis of silver nanoparticles reveals SNPs of size range 5 ± 1 to 15 ± 2 nm and 5 ± 1 to 35 ± 5 nm respectively. In vivo biosynthesized SNPs were localized in the peripheral cytoplasm and at one side of flagella root, the site of pathway of ATP transport and its synthesis related enzymes. This provides an evidence for the involvement of oxidoreductive proteins in biosynthesis and stabilization of SNPs. Alteration in size distribution and decrease of synthesis rate of SNPs in protein-depleted fractions confirmed the involvement of cellular proteins in SNPs biosynthesis. Spectroscopic and SDS-PAGE analysis indicate the association of various proteins on C. reinhardtii mediated in vivo and in vitro biosynthesized SNPs. We have identified various cellular proteins associated with biosynthesized (in vivo and in vitro) SNPs by using MALDI-MS-MS, like ATP synthase, superoxide dismutase, carbonic anhydrase, ferredoxin-NADP⁺ reductase, histone etc. However, these proteins were not associated on the incubation of pre-synthesized silver nanoparticles in vitro.

Conclusion

Present study provides the indication of involvement of molecular machinery and various cellular proteins in the biosynthesis of silver nanoparticles. In this report, the study is mainly focused towards understanding the role of diverse cellular protein in the synthesis and capping of silver nanoparticles using C. reinhardtii as a model system.

Antioxidant and prooxidant effects of polyphenol compounds on copper-mediated DNA damage

Inhibition of copper-mediated DNA damage has been determined for several polyphenol compounds. The 50% inhibition concentration values (IC(50)) for most of the tested polyphenols are between 8 and 480 μM for copper-mediated DNA damage prevention. Although most tested polyphenols were antioxidants under these conditions, they generally inhibited Cu(I)-mediated DNA damage less effectively than Fe(II)-mediated damage, and some polyphenols also displayed prooxidant activity. Because semiquinone radicals and hydroxyl radical adducts were detected by EPR spectroscopy in solutions of polyphenols, Cu(I), and H(2)O(2), it is likely that weak polyphenol-Cu(I) interactions permit a redox-cycling mechanism, whereby the necessary reactants to cause DNA damage (Cu(I), H(2)O(2), and reducing agents) are regenerated. The polyphenol compounds that prevent copper-mediated DNA damage likely follow a radical scavenging pathway as determined by EPR spectroscopy.

Damage to cellular and isolated DNA induced by a metabolite of aspirin

Aspirin has been proposed as a possible chemopreventive agent. On the other hand, a recent cohort study showed that aspirin may increase the risk for pancreatic cancer. To clarify whether aspirin is potentially carcinogenic, we investigated the formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), which is correlated with the incidence of cancer, in cultured cells treated with 2,3-dihydroxybenzoic acid (2,3-DHBA), a metabolite of aspirin. 2,3-DHBA induced 8-oxodG formation in the PANC-1 human pancreatic cancer cell line. 2,3-DHBA-induced DNA single-strand breaks were also revealed by comet assay using PANC-1 cells. Flow cytometric analyses showed that 2,3-DHBA increased the levels of intracellular reactive oxygen species (ROS) in PANC-1 cells. The 8-oxodG formation and ROS generation were also observed in the HL-60 leukemia cell line, but not in the hydrogen peroxide (H(2)O(2))-resistant clone HP100 cells, suggesting the involvement of H(2)O(2). In addition, an hprt mutation assay supported the mutagenicity of 2,3-DHBA. We investigated the mechanism underlying the 2,3-DHBA-induced DNA damage using (32)P-labeled DNA fragments of human tumor suppressor genes. 2,3-DHBA induced DNA damage in the presence of Cu(II) and NADH. DNA damage induced by 2,3-DHBA was enhanced by the addition of histone peptide-6 [AKRHRK]. Interestingly, 2,3-DHBA and histone peptide-6 caused base damage in the 5'-ACG-3' and 5'-CCG-3' sequences, hotspots of the p53 gene. Bathocuproine, a Cu(I) chelator, and catalase inhibited the DNA damage. Typical hydroxyl radical scavengers did not inhibit the DNA damage. These results suggest that ROS derived from the reaction of H(2)O(2) with Cu(I) participate in the DNA damage. In conclusion, 2,3-DHBA induces oxidative DNA damage and mutations, which may result in carcinogenesis.

Radical production and DNA damage induced by carcinogenic 4-hydrazinobenzoic acid, an ingredient of mushroom Agaricus bisporus

4-Hydrazinobenzoic acid, an ingredient of mushroom Agaricus bisporus, is carcinogenic to rodents. To clarify the mechanism of carcinogenesis, we investigated DNA damage by 4-hydrazinobenzoic acid using (32)P-labeled DNA fragments obtained from the human p53 and p16 tumor suppressor genes. 4-Hydrazinobenzoic acid induced Cu(II)-dependent DNA damage especially piperidine-labile formation at thymine and cytosine residues. Typical hydroxyl radical scavengers showed no inhibitory effects on Cu(II)-mediated DNA damage by 4-hydrazinobenzoic acid. Bathocuproine and catalase inhibited the DNA damage, indicating the participation of Cu(I) and H(2)O(2) in the DNA damage. These findings suggest that H(2)O(2) generated by the autoxidation of 4-hydrazinobenzoic acid reacts with Cu(I) to form reactive oxygen species, capable of causing DNA damage. Interestingly, catalase did not completely inhibit DNA damage caused by a high concentration of 4-hydrazinobenzoic acid (over 50 microM) in the presence of Cu(II). 4-Hydrazinobenzoic acid induced piperidine-labile sites frequently at adenine and guanine residues in the presence of catalase. 4-Hydrazinobenzoic acid increased formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), a characteristic oxidative DNA lesion, in calf thymus DNA, whereas 4-hydrazinobenzoic acid did not increase the formation of 8-oxodG in the presence of catalase. ESR spin-trapping experiments showed that the phenyl radical was formed during the reaction of 4-hydrazinobenzoic acid in the presence of Cu(II) and catalase. Matrix-assisted laser desorption/ionization time-of-flight mass (MALDI-TOF/mass) spectrometry analysis showed that phenyl radical formed adduct with adenosine and guanosine. These results suggested that 4-hydrazinobenzoic acid induced DNA damage via not only H(2)O(2) production but also phenyl radical production. This study suggests that both oxidative DNA damage and DNA adduct formation play important roles in the expression of carcinogenesis of 4-hydrazinobenzoic acid.

Oxidative and nitrative DNA damage as biomarker for carcinogenesis with special reference to inflammation

Reactive oxygen and nitrogen species are known to participate in a wide variety of human diseases. Oxidative DNAdamage is involved in chemical carcinogenesis and aging. Monocyclic chemicals induce mainly oxidative DNAdamage, whereas polycyclic chemicals can induce oxidative DNA damage in addition to DNA adduct formation. Recently, chronic infection and inflammation have been recognized as important factors for carcinogenesis. Nitrative DNA damage as well as oxidative DNA damage is induced in relation to inflammationrelated carcinogenesis. The authors examined the formation of 8-nitroguanine, a nitrative DNA lesion, in humans and animals under inflammatory conditions. An immunofluorescence labeling study demonstrated that 8-nitroguanine was strongly formed in gastric gland epithelial cells in gastritis patients with H. pylori infection, in hepatocytes in patients with hepatitis C, and in oral epithelium of patients with oral lichen planus. 8-Nitroguanine was also formed in colonic epithelial cells of model mice of inflammatory bowel diseases and patients with ulcerative colitis. Interestingly, 8-nitroguanine was formed at the sites of carcinogenesis regardless of etiology. Therefore, 8-nitroguanine could be used as a potential biomarker to evaluate the risk of inflammation- related carcinogenesis.