Differential role of hydrogen peroxide and organic peroxides in augmenting asbestos-mediated DNA damage: implications for asbestos induced carcinogenesis

Comparison of the cytotoxic responses of Escherichia coli (E. coli) AMC 198 to different fullerene suspensions (nC60)

Fullerenes are set to be produced on an industrial scale in anticipation of their wide applications. This calls for research on their environmental and health impacts. This study investigates and compares the cell toxicity of different aqueous fullerene aggregates. Popular C(60) dispersal methods were used to prepare four types of nC(60) aggregates. These aggregates were tested against the indicator species Escherichia coli (E. coli) AMC 198. With aggregates of around 150 nm in diameter, the THF/nC(60) suspension was very toxic and gave rise to a half maximal effective concentration (EC(50)) of 0.54 mg L(-1) in E. coli. By contrast, the Tol/nC(60) suspension exhibited a cytoprotective role while the Aqu-N(2)/nC(60) and Aqu-O(2)/nC(60) suspensions enhanced the metabolism of E. coli. Although some toxicants, such as THF and THF-peroxide, were introduced into the THF/nC(60) suspension during the dispersion, the toxicity of nC(60) itself cannot be neglected.

Role of mutagenicity in asbestos fiber-induced carcinogenicity and other diseases

The cellular and molecular mechanisms of how asbestos fibers induce cancers and other diseases are not well understood. Both serpentine and amphibole asbestos fibers have been shown to induce oxidative stress, inflammatory responses, cellular toxicity and tissue injuries, genetic changes, and epigenetic alterations in target cells in vitro and tissues in vivo. Most of these mechanisms are believe to be shared by both fiber-induced cancers and noncancerous diseases. This article summarizes the findings from existing literature with a focus on genetic changes, specifically, mutagenicity of asbestos fibers. Thus far, experimental evidence suggesting the involvement of mutagenesis in asbestos carcinogenicity is more convincing than asbestos-induced fibrotic diseases. The potential contributions of mutagenicity to asbestos-induced diseases, with an emphasis on carcinogenicity, are reviewed from five aspects: (1) whether there is a mutagenic mode of action (MOA) in fiber-induced carcinogenesis; (2) mutagenicity/carcinogenicity at low dose; (3) biological activities that contribute to mutagenicity and impact of target tissue/cell type; (4) health endpoints with or without mutagenicity as a key event; and finally, (5) determinant factors of toxicity in mutagenicity. At the end of this review, a consensus statement of what is known, what is believed to be factual but requires confirmation, and existing data gaps, as well as future research needs and directions, is provided.

Delineating oxidative processes of aqueous C60 preparations: role of THF peroxide

The oxidative reactivity of THF derivatives formed during THF/nC60 synthesis was evaluated with indigo dye as a model compound. The results showed that the formation of previously undetected oxidizing agents during THF/nC60 synthesis accounted for the degradation of indigo dye by THF/nC60 (THF/nC60/unwashed), while THF/nC60 after vigorous washing (THF/nC60/washed) and nC60 prepared without the use of THF were not reactive. gamma-Butyrolactone (GBL) was detected by GC-MS in the THF/nC60/unwashed as one of THF derivatives, but showed no reactivity with indigo dye. An organic peroxide was detected in the THF/nC60/unwashed by HPLC, and was reactive with indigo dye. This compound was found to also account for the elevated antibacterial and bactericidal activities of THF/nC60/unwashed on E. coli. Analysis by LC/(+ESI)MS and 1H NMR showed that the detected THF peroxide was tetrahydro-2-(tetrahydrofuran-2-ylperoxy)furan. The formation of THF peroxide during the preparation of aqueous stable C60 aggregates provides another potential explanation for the reactivity and oxidative stress mechanisms of THF/nC60 system reported in the literature, although it does not exclude the potential reactivity and toxicity of nC60 itself.

Modulation of genotoxic effects in asbestos-exposed primary human mesothelial cells by radical scavengers, metal chelators and a glutathione precursor

The genotoxicity of asbestos fibers is generally mediated by reactive oxygen species (ROS) and by insufficient antioxidant protection. To further elucidate which radicals are involved in asbestos-mediated genotoxicity and to which extent, we have carried out experiments with the metal chelators deferoxamine (DEF) and phytic acid (PA), and with the radical scavengers superoxide dismutase (SOD), dimethylthiourea (DMTU) and the glutathione precursor Nacystelyn trade mark (NAL). We investigated the influence of these compounds on the potency of crocidolite, an amphibole asbestos fiber with a high iron content (27%), and chrysotile, a serpentine asbestos fiber with a low iron content (2%), to induce micronuclei (MN) in human mesothelial cells (HMC) after an exposure time of 24-72 h. Our results show that the number of crocidolite-induced MN is significantly reduced after pretreatment of fibers with PA and DEF. This effect was not observed with chrysotile. In contrast, simultaneous treatment of cells with asbestos and the OH*scavenging DMTU or the O2- -scavenging SOD significantly decreased the number of MN induced by chrysotile and crocidolite. In particular, DMTU almost completely suppressed micronucleus induction by both fiber types. A similar effect was observed in the presence of the H(2)O(2)-scavenging NAL after chrysotile treatment of HMC. By means of kinetochore analysis, it could be shown that the number of clastogenic events is decreased after PA and DEF pretreatment of fibers as well as after application of the above-mentioned scavengers. Our results show that chrysotile asbestos induces an increased release of H(2)O(2) in contrast to crocidolite. Also, the iron content of the fiber plays an important role in radical formation, but nevertheless, chrysotile produces oxy radicals to a similar extent as crocidolite, probably by phagocytosis-mediated oxidative bursting.

The ability of mineral dusts and fibres to initiate lipid peroxidation. Part II: relationship to different particle-induced pathological effects

Exposure to pathogenic mineral dusts and fibres is associated with pulmonary changes including fibrosis and cancer. Investigations into aetiological mechanisms of these diseases have identified modifications in specific macromolecules as well as changes in certain early processes, which have preceded fibrosis and cancer. Peroxidation of lipids is one such modification, which is observed following exposure to mineral dusts and fibres. Their ability to initiate lipid peroxidation and the parameters that determine this ability have recently been reviewed. Part II of this review examines the relationship between the capacity of mineral dusts and fibres to initiate lipid peroxidation and a number of pathological changes they produce. The oxidative modification of polyunsaturated fatty acids is a major contributor to membrane damage in cells and has been implicated in a great variety of pathological processes. In most pathological conditions where an induction of lipid peroxidation is observed it is assumed to be the consequence of disease, without further establishing if the induction of lipid peroxidation may have preceded or accompanied the disease. In the great majority of instances, however, despite the difficulty in proving this association, a causal relationship between lipid peroxidation and disease cannot be ruled out.

N-acetyl L-cysteine attenuates oxidant-mediated toxicity induced by chrysotile fibers

Chrysotile, an important commercial variety of asbestos, is known to cause oxidative stress by enhancing production of hydrogen peroxide (H(2)O(2)) and thiobarbituric acid reactive substances (TBARS), depleting glutathione (GSH) and altering levels of GSH redox system enzymes. N-acetyl L-cysteine (NAC), a compound that increases GSH levels, protects cells against chrysotile toxicity. In the present study, rats were exposed intratracheally to a single dose (5 mg/rat) of chrysotile. This was followed by a daily dose of NAC 50 mg/kg. b. wt., i.p. At 1, 4, 8 and 16 days post chrysotile exposure lung lavage fluid was collected to determine H(2)O(2) generation, TBARS production, GSH level and its redox system enzymes activities. A significant decrease in H(2)O(2) and TBARS, an increase in GSH content and its redox system enzymes was observed in chrysotile+NAC animals in comparison to chrysotile-exposed animals. In this preliminary study it appears that NAC may be protecting cells against oxidative damage. This protection may be due to its ability to maintain intracellular GSH/oxidative scavenging capability.

Age-dependent renal accumulation of 4-hydroxy-2-nonenal (HNE)-modified proteins following parenteral administration of ferric nitrilotriacetate commensurate with its differential toxicity: implications for the involvement of HNE-protein adducts in oxidative stress and carcinogenesis

In this study, we show that the toxicity of ferric nitrilotriacetate (Fe-NTA) can be correlated with the tissue accumulation of 4-hydroxy-2-nonenal (HNE)-modified protein adducts. It is observed that the toxic manifestations of Fe-NTA gradually increase with the increasing age of animals. A dose of Fe-NTA which produces almost 100% mortality in aged rats causes 70% mortality in adults, 30% in pups, 20% in litters, and less than 10% in neonates. The age-dependent increase in its toxicity is also evident from the data of renal microsomal lipid peroxidation and hydrogen peroxide generation. No significant difference in the generation of H2O2 and induction of renal microsomal lipid peroxidation between saline- and Fe-NTA-treated neonates, litters, and pups could be observed. However, in adult rats, a significant increase in both of the parameters was observed which was even greater in aged rats. On the contrary, renal glutathione levels in these animals show an inverse relationship with the oxidant generation. In neonates, litters, and pups the maximum decrease of glutathione was up to 22%, whereas in adult and aged rats, the depletion was more than 60% of their respective saline-treated controls. Parallel to this data, blood urea nitrogen and creatinine, the indicators of renal damage, show a significant increase in Fe-NTA-treated adult and aged rats only, whereas no significant alterations were observed in other groups. Similarly, the magnitude of ODC induction and [3H]thymidine incorporation was much higher in aged and adult rats in comparison to other groups of animals after Fe-NTA treatment. Additionally, the immunohistochemical localization studies show a significant increase in HNE-modified protein adducts in kidney of adult and aged rats, whereas no significant staining was observed in other groups. A similar increase in the level of protein carbonyls has also been observed with the increasing age of rats. These data suggest that the toxicity of Fe-NTA increases with the increasing age of rats and correlates with the accumulation of HNE-modified protein adducts. It may also be speculated that Fe-NTA-mediated renal toxicity leading to carcinogenesis may be related to the tissue accumulation of HNE-modified protein adducts. However, further studies are needed to establish a definite role of HNE-modified proteins in Fe-NTA-mediated carcinogenesis.

Potassium bromate (KBrO3) induces renal proliferative response and damage by elaborating oxidative stress

Many chemical compounds which induce oxidative stress in the tissue produce carcinogenesis either alone or act as a tumor promoter in carcinogen-initiated animals after prolonged exposure. Here, we report that potassium bromate (KBrO3) induces renal proliferative response and damage by elaborating oxidative stress. KBrO3 administration dose dependently induced renal ornithine decarboxylase (ODC) activity several fold compared to its activity in saline-treated rats. Similarly renal DNA synthesis which has been measured as [3H]thymidine incorporation in DNA also increases. KBrO3 administration also depleted the level of renal glutathione and glutathione reductase activity in a time dependent manner. The maximum depletion in the levels of renal glutathione and glutathione reductase activity was observed 3 h after KBrO3 treatment which was 60 and 40%, respectively, of saline-treated controls. Parallel to these changes, a sharp increase in the blood urea nitrogen and serum creatinine levels was observed which is indicative of the concurrent renal damage. These results suggest that oxidant generating KBrO3 acts as a potent proliferator of kidney and acts by producing oxidative damage.

Evidence that exposure of particulate air pollutants to human and rat alveolar macrophages leads to differential oxidative response

Macrophages and inflammatory cells generate active oxygen species in the process of killing and degrading microorganisms. Air pollutant particles may be ingested by macrophages and stimulate the same mechanisms to produce a long term oxidative burden to the lung if particles are not degraded. In the present study human and rat alveolar macrophages (AM) were compared in their response to inhaled particles using luminol dependent chemiluminescence (CL) and peroxide dependent CL assays. Cytotoxicity was measured by the release of lactate dehydrogenase (LDH) activity in the supernatant. Human AM produced more oxidants than rat AM whether, unstimulated, after addition of particles or addition of particles then peroxidase. Human AM also had a different spectrum of response to the same particles. Our results suggest that human macrophages produce more reactive oxygen species in respond to particles than rat AM.

On the role of DNA double-strand breaks in toxicity and carcinogenesis

DNA double-strand breaks are associated with various endogenous processes, such as transcription, recombination, replication, and with the process of active cell death, which aims to eliminate cells. In addition, DNA double-strand breaks can be induced by irradiation, exposure to chemicals, increased formation of reactive oxygen species, and, indirectly, during repair of other types of DNA damage or as a consequence of extranuclear lesions. In addition to the neutral filter elution of DNA, the recently introduced pulsed-field gel electrophoresis is capable of determining DNA double-strand breaks with higher accuracy and sensitivity and is expected to increase our knowledge on the frequency and the role of DNA breakage. Parallel determination of parameters for cytotoxicity is necessary to elucidate the causal primary lesion. Although the repair of DNA double-strand breaks is a complex task, cells are capable of repairing--with or without errors and up to a certain extent--and surviving this DNA lesion. Gene translocations, rearrangements, amplifications, and deletions arising during repair and misrepair of double-strand breaks may contribute to cell transformation and tumor development.

Iron-induced carcinogenesis: the role of redox regulation

Redox cycling is a characteristic of transition metals such as iron. Iron is hypothesized to have been actively involved in the birth of primitive life on earth through the generation of reducing equivalents in the presence of UV light. Iron is an essential metal in mammals for oxygen transport by hemoglobin and for the function of many enzymes including catalase and cytochromes. However, the "free" or "catalytic" form of iron mediates the production of reactive oxygen species via the Fenton reaction and induces oxidative stress. Serum "free" iron is observed in rare situations such as in severe hemochromatosis in which serum transferrin is saturated. However, it is known that superoxide can release "free" iron from ferritin and hemosiderin in the cell. "Free" iron is quite cytotoxic as well as mutagenic and carcinogenic. Iron compounds were first reported to induce sarcomas in rats by Richmond in 1959. Thereafter, several iron-induced carcinogenesis models were established, including the ferric nitrilotriacetate model by Okada and colleagues. Iron may have a role in the carcinogenic process of other transition metals such as copper and nickel, or other kinds of carcinogens such as nitrosamine and even virus-induced carcinogenesis. In humans, genetic hemochromatosis and asbestosis are two major diseases associated with iron-induced carcinogenesis. There is an increasing number of reports of an association between increased body iron stores and increased risk of cancer. Iron-induced oxidative stress results in two possible consequences: (1) redox regulation failure that leads to lipid peroxidation and oxidative DNA and protein damage; (2) redox regulation that activates a variety of reducing and oxystress-protective mechanisms via signal transduction. Both consequences appear to play a role in iron-induced carcinogenesis.