Oxygen radical formation and DNA damage due to enzymatic reduction of bleomycin-Fe(III)

Tight control of genomic phosphorothioate modification by the ATP-modulated autoregulation and reusability of DndB

DNA phosphorothioate (PT) modification was recently identified to occur naturally in diverse bacteria and to be governed by DndABCDE proteins. The nuclease resistance as well as the redox and nucleophilic properties of PT sulfur make PT modification a versatile player in restriction-modification (R-M) defense, epigenetic regulation, environmental fitness and the maintenance of cellular redox homeostasis. In this study, we discovered that tight control of PT levels is mediated by the ATPase activity of DndB. The ATP-binding activity of DndB stimulates the dissociation of the DndB-DNA complex, allowing transcriptional initiation, whereas its ATP hydrolysis activity promotes the conversion of DndB-ATP to free DndB that is capable of rebinding to promoter DNA for transcriptional inhibition. Since sulfur incorporation is an ATP-consuming process, these activities provide an economical way to fine-tune PT modification in an ATP-sensing manner. To our knowledge, this ATP-mediated regulation is a rare example among DNA epigenetic modification systems; the features of autoregulation and the repeated usage of DndB allow the dedicated regulation of PT levels in response to cellular ATP concentrations, providing insight into PT function and its role in physiology.

The peroxidase activity of bleomycin-Fe3+ is associated with damage to biological components

In this study, bleomycin-Fe(3+) steadily oxidized tetramethylbenzidine (TMB) in the presence of peroxides. However, the ability of bleomycin-Fe(3+) to function as a peroxidase was extremely low compared with that of other peroxidases. A characteristic property of bleomycin-Fe(3+) different from that observed for other peroxidases is its ability to oxidize TMB at the similar rate at both a pH 5 and 8 in the presence of lipid hydroperoxide (LOOH). In the present experiments, hydroxyl radicals (HO•) were generated only when bleomycin-Fe(3+) was incubated with H2O2 at a pH of 5. No generation of HO• was observed during the incubation of bleomycin-Fe(3+) with LOOH. Meanwhile, bleomycin-Fe(3+) induced the formation of LOOH from linoleic acid and alcohol dehydrogenase was inactivated by bleomycin-Fe(3+) with peroxides. Thiobarbituric acid reactive substances were formed from DNA by bleomycin-Fe(3+) with H2O2, and strand breaks were caused by bleomycin-Fe(3+) with LOOH. The oxidative substrates for bleomycin-Fe(3+) blocked the damage to biological components induced by bleomycin-Fe(3+). These results suggest that compound I-like species contribute to the process of damage to biological components induced by bleomycin-Fe(3+).

Physical basis and biological mechanisms of gold nanoparticle radiosensitization

The unique properties of nanomaterials, in particular gold nanoparticles (GNPs) have applications for a wide range of biomedical applications. GNPs have been proposed as novel radiosensitizing agents due to their strong photoelectric absorption coefficient. Experimental evidence supporting the application of GNPs as radiosensitizing agents has been provided from extensive in vitro investigation and a relatively limited number of in vivo studies. Whilst these studies provide experimental evidence for the use of GNPs in combination with ionising radiation, there is an apparent disparity between the observed experimental findings and the level of radiosensitization predicted by mass energy absorption and GNP concentration. This review summarises experimental findings and attempts to highlight potential underlying biological mechanisms of response in GNP radiosensitization.

Mitochondrial DNA-depleted A549 cells are resistant to bleomycin

Alveolar epithelial cells are considered to be the primary target of bleomycin-induced lung injury, leading to interstitial fibrosis. The molecular mechanisms by which bleomycin causes this damage are poorly understood but are suspected to involve generation of reactive oxygen species and DNA damage. We studied the effect of bleomycin on mitochondrial DNA (mtDNA) and nuclear DNA (nDNA) in human alveolar epithelial A549 cells. Bleomycin caused an increase in reactive oxygen species production, DNA damage, and apoptosis in A549 cells; however, bleomycin induced more mtDNA than nDNA damage. DNA damage was associated with activation of caspase-3, cleavage of poly(ADP-ribose) polymerase, and cleavage and activation of protein kinase D1 (PKD1), a newly identified mitochondrial oxidative stress sensor. These effects appear to be mtDNA-dependent, because no caspase-3 or PKD1 activation was observed in mtDNA-depleted (ρ(0)) A549 cells. Survival rate after bleomycin treatment was higher for A549 ρ(0) than A549 cells. These results suggest that A549 ρ(0) cells are more resistant to bleomycin toxicity than are parent A549 cells, likely in part due to the depletion of mtDNA and impairment of mitochondria-dependent apoptotic pathways.

Cell-specific radiosensitization by gold nanoparticles at megavoltage radiation energies

PURPOSE

Gold nanoparticles (GNPs) have been shown to cause sensitization with kilovoltage (kV) radiation. Differences in the absorption coefficient between gold and soft tissue, as a function of photon energy, predict that maximum enhancement should occur in the kilovoltage (kV) range, with almost no enhancement at megavoltage (MV) energies. Recent studies have shown that GNPs are not biologically inert, causing oxidative stress and even cell death, suggesting a possible biological mechanism for sensitization. The purpose of this study was to assess GNP radiosensitization at clinically relevant MV X-ray energies.

METHODS AND MATERIALS

Cellular uptake, intracellular localization, and cytotoxicity of GNPs were assessed in normal L132, prostate cancer DU145, and breast cancer MDA-MB-231 cells. Radiosensitization was measured by clonogenic survival at kV and MV photon energies and MV electron energies. Intracellular DNA double-strand break (DSB) induction and DNA repair were determined and GNP chemosensitization was assessed using the radiomimetic agent bleomycin.

RESULTS

GNP uptake occurred in all cell lines and was greatest in MDA-MB-231 cells with nanoparticles accumulating in cytoplasmic lysosomes. In MDA-MB-231 cells, radiation sensitizer enhancement ratios (SERs) of 1.41, 1.29, and 1.16 were achieved using 160 kVp, 6 MV, and 15 MV X-ray energies, respectively. No significant effect was observed in L132 or DU145 cells at kV or MV energies (SER 0.97-1.08). GNP exposure did not increase radiation-induced DSB formation or inhibit DNA repair; however, GNP chemosensitization was observed in MDA-MB-231 cells treated with bleomycin (SER 1.38).

CONCLUSIONS

We have demonstrated radiosensitization in MDA-MB-231 cells at MV X-ray energies. The sensitization was cell-specific with comparable effects at kV and MV energies, no increase in DSB formation, and GNP chemopotentiation with bleomycin, suggesting a possible biological mechanism of radiosensitization.

Bleomycin initiates apoptosis of lung epithelial cells by ROS but not by Fas/FasL pathway

Epithelial cells are considered to be a main target of bleomycin-induced lung injury, which leads to fibrosis in vivo. We studied the characteristics of in vitro bleomycin-induced apoptosis in a mouse lung epithelial (MLE) cell line. Bleomycin caused an increase of reactive oxygen species (ROS) resulting in oxidative stress, mitochondrial leakage, and apoptosis. These were associated with elevated caspase-8 and resultant caspase-9 activity and with upregulation of Fas expression. Glutathione and inhibitors of caspase-8 or caspase-9, but not of FasL, inhibited these effects, suggesting their dependence on ROS, caspase-8 and -9, in a Fas/FasL-independent pathway. However, postbleomycin-exposed MLE cells were more sensitive to Fas-mediated apoptosis. These results demonstrate that the initial bleomycin-induced oxidative stress causes a direct apoptotic effect in lung epithelial cells involving a regulatory role of caspase-8 on caspase-9. Fas represents an amplification mechanism, and not a direct trigger of bleomycin-induced epithelial cell apoptosis.

Levels of reactive oxygen species and primary antioxidant enzymes in WI38 versus transformed WI38 cells following bleomcyin treatment

Bleomycin (BLM) is an anticancer drug that generates reactive oxygen species (ROS) after interacting with iron and oxygen. We hypothesized that BLM could cause a different status of oxidative stress in normal versus tumor cells due to possible altered redox status and gene expression in cells following transformation. In this study, the extent of cytotoxicity, levels of ROS, and activities of antioxidant enzymes were compared between normal WI38 cells and SV40-transformed WI38 (VA13) cells following BLM treatment. Basal activities of MnSOD and catalase were lower in VA13 cells and basal ROS levels were higher in VA13 cells. Although BLM caused greater growth inhibition and apoptosis in VA13 cells, it increased ROS levels at an earlier time point in WI38 cells. Moreover, BLM treatment (100 microg/ml) had no effect on the activities of MnSOD, CuZnSOD, and catalase, but increased the activities of glutathione peroxidase (GPX) in WI38 cells after a 48-h treatment and in VA13 cells after a 24- and 48-h treatment. Northern blot analysis indicated that the increase in GPX activities was due to increased transcript levels of GPX1 but not GPX4 in both cells. Our results indicate selective induction of the GPX1 gene by BLM and different redox responses to BLM between WI38 and VA13 cells.

Comparative study of the effects of vitamin C and bleomycin on smokers' and non-smokers' lymphocytes in clastogenicity assays

Free radicals are products of metabolic reactions and of external factors that can injure different biological molecules. However, different antioxidant agents can prevent the action of these reactive species and the damage they cause. Vitamin C (VC) is an important micronutrient found in the diet, which presents defense mechanisms against the free radicals that challenge the cells of the organism. The objective of the present study was to investigate the effect of VC as a modulator of the damage induced in DNA by bleomycin (BLM) in lymphocytes from smokers and non-smokers. The difference in response to the mutagenic potential of BLM between smokers and non-smokers was also investigated. Peripheral blood lymphocyte cultures were treated simultaneously with BLM (20 microg/ml) and/or VC (100, 200, and 400 microg/ml) in the G2 phase of the cell cycle. The results obtained did not demonstrate a statistically significant difference in the response to the antitumor agent BLM between smokers and non-smokers. The data also showed that VC had no significant modulating effect on the frequency of chromosome aberrations induced by BLM in the cells of smokers and non-smokers under the experimental conditions used.

Attenuation of bleomycin-induced Hprt mutant frequency in female and male rats by calorie restriction

Calorie restriction modulates spontaneous and chemically induced tumors and increases maximal life span in experimental animals; however, the mechanism by which calorie restriction exerts its ameliorating effects is not fully elucidated, although reduced levels of reactive oxygen species (ROS) by calorie restriction has generated much interest. In the present study, we have determined whether or not calorie restriction would affect the mutagenic response in rats treated with bleomycin (BLM) a radiomimetic drug that is associated with DNA damage by a free radical mechanism. Fourteen weeks after weaning, the rats were divided into two groups; ad libitum (AL)-fed and 40% calorie restriction. Both AL and calorie-restricted animals were injected with 2.5, 5.0 and 10.0 mg BLM/kg, or with phosphate-buffered saline (PBS), and they were killed 4 weeks post drug treatment. Lymphocytes from the spleens were seeded in 96-well microtiter plates to determine mutant frequency in the hypoxantine guanine phosphoribosyl transferase (Hprt) gene. The mutant frequency in the BLM-treated rats was higher in AL males (P=0.001), and AL females (P=0.0174) than in their calorie-restricted counterparts. The difference in mutagenic response relative to AL males and AL females appeared unrelated to a low percent cloning efficiency seen in the males, since the mean absolute number of Hprt mutant clones was higher in the AL males compared to the females. A reduction in animal weight by calorie restriction was significant in both sexes (P<0.001), but the dose effect appeared non-significant. The results indicate that calorie intake of 60% reduced the mutagenic response of BLM, a compound known to induce oxidative DNA damage, and suggest a possible decrease in ROS as a function of calorie restriction.

Prophylaxis of oral mucositis associated with chemoradiotherapy for oral carcinoma by Azelastine hydrochloride (Azelastine) with other antioxidants

BACKGROUND

One of the dose-limiting adverse effects of chemoradiotherapy is mucositis, especially oral mucositis. Prophylaxis of severe mucosal reaction would allow application of aggressive chemoradiotherapy to malignancies.

METHODS

Sixty-three patients who received inductive concomitant chemoradiotherapy with cobalt 60 (60Co, approximately 30 Gy), peplomycin (PLM, approximately 38 mg), and 5-fluorouracil (5-FU, approximately 3,500 mg) were included in this study. From the start of therapy to the disappearance of oral erosion, 37 patients received daily doses of Azelastine (2 mg) + vitamin C (500 mg) + vitamin E (200) + glutathione (200 mg) (azelastine group), whereas the other 26 patients received the same regimen without azelastine (control group). The severity of oral mucositis in both groups was evaluated periodically.

RESULTS

At 10 Gy with 15 mg PLM and 1,250 mg 5-FU, grade 1 mucositis (redness of the oral mucosa) was induced in 14 patients in the control group and five patients in the Azelastine group. At 20 Gy with 30 mg PLM and 2,500 mg 5-FU, grade 2 (erosion with mild irritation) and grade 3 (extensive erosion with marked irritation) stomatitis were observed in 9 and 3 of the control patients and 5 and 1 in the Azelastine group, respectively. At the completion of treatment, mucositis in 21 patients in the Azelastine group remained at grade 1 or grade 2, whereas grades 3 and 4 (ulceration with severe contact pain) mucositis were observed in 6 and 10 patients, respectively. However, in the control group, grades 1 and 2 were observed in only 2 and 3 cases, whereas grades 3 and 4 stomatitis were induced in 6 and 15, respectively. Azelastine suppressed neutrophil respiratory burst both in vivo and in vitro, and also suppressed cytokine release from lymphocytes. However, neutrophil superoxide dismutase (SOD) activity was negligibly suppressed.

CONCLUSION

A regimen including Azelastine, which suppresses reactive oxygen production and stabilizes cell membranes, may be useful for the prophylaxis of mucositis due to chemoradiotherapy.

Chromosomal sensitivity of human lymphocytes to bleomycin. Influence of antioxidant enzyme activities in whole blood and different blood fractions

The activity of the antioxidant enzymes catalase (CAT), peroxidases (POD), and superoxide dismutases (SOD) in whole blood and different blood fractions was analyzed in 20 normal human beings and correlated with the chromosomal sensitivity of lymphocytes to bleomycin (BLM) (measured as frequency of dicentric chromosomes per BLM dose). Our results demonstrate that both the physiologic activities of the enzymes and the chromosomal sensitivity to BLM exhibit an ample and significant interindividual variability. An inverse and linear correlation between chromosomal sensitivity to BLM and the concentration of 1) CAT and POD in plasma and 2) SOD in whole blood, erythrocytes, and plasma was found. On the other hand, the chromosomal sensitivity to BLM showed a direct correlation with the concentration of SOD and POD in mononuclear leukocytes. It is suggested that a determination of antioxidant enzyme (AOE) activities in a given cell population may serve to predict the chromosomal sensitivity to BLM.

Bleomycin-dependent damage to the bases in DNA is a minor side reaction

The antitumor antibiotic bleomycin degrades DNA in the presence of ferric ions and H2O2 or in the presence of ferric ions, oxygen, and ascorbic acid. When DNA degradation is measured as formation of base propenals by the thiobarbituric acid assay, it is not inhibited by superoxide dismutase and scavengers of the hydroxyl radical or by catalase (except that catalase inhibits in the bleomycin/ferric ion/H2O2 system by removing H2O2). Using the technique of gas chromatography/mass spectrometry with selected-ion monitoring, we show that DNA degradation is accompanied by formation of small amounts of modified DNA bases. The products formed are identical with those generated when hydroxyl radicals react with DNA bases. Base modification is significantly inhibited by catalase and partially inhibited by scavengers of the hydroxyl radical and by superoxide dismutase. We suggest that the bleomycin-oxo-iron ion complex that cleaves the DNA to form base propenals can decompose in a minor side reaction to generate hydroxyl radical, which accounts for the base modification in DNA. However, hydroxyl radical makes no detectable contribution to the base propenal formation.

Effect of bleomycin on hematoporphyrin derivative phototherapy of solid tumors

Hematoporphyrin derivative phototherapy (HpD-PT) has been successfully used to localize and treat superficial squamous cell cancers. Bleomycin sulfate is a glycopeptide antibiotic that has antineoplastic properties against squamous cell cancers. Because both HpD-PT and bleomycin chemotherapy are accepted forms of treatment for squamous cell cancer and their cytotoxicity is mediated by singlet oxygen and oxygen radicals, we studied the possibility of enhancing the response of solid tumors to HpD-PT by combining this modality with systemic bleomycin chemotherapy in a murine tumor model. Bleomycin did not enhance HpD-PT significantly. Also, we are not confident that HpD-PT alone or in combination with other agents can eradicate solid tumors; it certainly did not in this syngeneic murine tumor model.

Oxidative stress in chemical toxicity

The toxic effects of compounds which undergo redox cycling via enzymatic one-electron reduction are reviewed. First of all, the enzymatic reduction of these compounds leads to reactive intermediates, mainly radicals which react with oxygen, whereby superoxide anion radicals are formed. Further oxygen metabolites are hydrogen peroxide, singlet oxygen and hydroxyl radicals. The role of these oxygen metabolites in toxicity is discussed. The occurrence of lipid peroxidation during redox cycling of quinonoide compounds, e.g., adriamycin, and the possible relationship to their toxicity is critically evaluated. It is shown that iron ions play a crucial role in lipid peroxidation induced by redox cycling compounds. DNA damage by metal chelates, e.g., bleomycin, is discussed on the basis of findings that enzymatic redox cycling of a bleomycin-iron complex has been observed. The involvement of hydroxyl radicals in bleomycin-induced DNA damage occurring during redox cycling in cell nuclei is claimed. Redox cycling of other substances, e.g., aromatic amines, is discussed in relation to carcinogenesis. Other chemical groups, e.g., nitroaromatic compounds, hydroxylamines and azo compounds are included. Other targets for oxygen radical attack, e.g., proteins, are also dealt with. It is concluded that oxygen radical formation by redox cycling may be a critical event in toxic effects of several compounds if the protective mechanisms of cells are overwhelmed.