DNA fragmentation and DNA repair synthesis induced in rat and human thyroid cells by four rat thyroid carcinogens

Environmental and Safety Issues With Nanoparticles

Because nanoparticles have superior surface activity and can be applied to the production of particles with various functions, they are extremely important for the future development of sophisticated material technologies. On the other hand, this superior activity of nanoparticles is a cause of trouble from the perspective of safety and does not always have a positive influence on the environment. Attention must also be paid to impact on health. Nevertheless, all technologies have negative aspects, and overcoming these kinds of problems, we will be able to utilize the superior characteristics of nanoparticles for practical purposes. To achieve this goal, it is necessary to fully understand the influence of nanoparticles on the environment and the relevant safety issues.

ENVIRONMENTAL AND SAFETY ISSUES WITH NANOPARTICLES

This chapter evaluates the relationship between nanoparticles and the environment, and describes the trouble caused by nanoparticles as well as the safety issues. The relationship between nanoparticles and the environment is clarified from the viewpoint of the kind of influence nanoparticles generated either artificially or naturally have on the environment, such as in atmosphere, groundwater, wastewaters, and exhaust gases. Indoor nanoparticles originate from the several sources such as products of chemical reactions, nonvolatile residues (NVRs) of liquid droplets, printers/photocopiers, combustion, bioaerosols, and infiltration of outdoor air. The influence of nanoparticles on the indoor environment is discussed in the chapter. It describes the sources of nanoparticle generation in general industrial processes such as grinding processes, and in cleanroom or controlled environment industrial processes, such as exhaled air, ionizers, and haze by chemical reaction on solid surfaces. The chapter discusses safety issues related to nanoparticles such as possibility of dust explosion, health risks and biological effects of nanoparticle materials such as carbon nanotubes, fullerenes, nanosized metal oxides, and carbon black. The chapter also discusses methods for removing nanoparticles from gas and liquid as technology to control the influence of nanoparticles on the environment.

DNA damage in peripheral blood lymphocytes of patients with cirrhosis related to alcohol abuse or to hepatitis B and C viruses

BACKGROUND

Both alcohol abuse and hepatitis B or C virus infections are implicated in the development of hepatocellular carcinoma, but it is still controversial whether the pathogenetic mechanism is epigenetic or genotoxic.

AIM

Considering that alcohol promotes the generation of reactive oxygen species and both viruses infect peripheral lymphocytes, in this study we investigated the occurrence of DNA fragmentation in peripheral blood lymphocytes from patients with alcoholic cirrhosis and from patients with cirrhosis related to B and C viruses, and analyzed the correlation between the degree of DNA fragmentation and the Child-Pugh score used to assess the degree of hepatic insufficiency.

METHODS

The study population consisted of two groups: group I involved 12 patients with alcoholic cirrhosis; group II involved 25 patients with hepatic B virus or hepatic C virus cirrhosis. The control group involved 20 healthy individuals. The degree of DNA fragmentation in peripheral blood lymphocytes was determined with the alkaline Comet assay that provides two indexes of the frequency of DNA single-strand breaks and alkali-labile sites, the tail length and the tail moment.

RESULTS

Mean values of both tail length and tail moment were significantly increased (P<0.001) in lymphocytes from 12 patients with alcoholic cirrhosis and in lymphocytes from 25 patients with HBV or HCV cirrhosis, as compared with average tail length and tail moment values of lymphocytes from 20 healthy individuals. A significant positive correlation was found to exist between the degree of DNA fragmentation present in lymphocytes of each of the 37 patients with alcoholic or viral cirrhosis and the corresponding value of the Child-Pugh score.

CONCLUSION

The occurrence of DNA fragmentation in peripheral blood lymphocytes reflects a direct genotoxic effect of either alcohol or HBV and HCV and suggests that the same genotoxic effect may operate in the liver and contribute to hepatocarcinogenesis.

Strategy for genotoxicity testing—Metabolic considerations

The report from the 2002 International Workshop on Genotoxicity Tests (IWGT) Strategy Expert Group emphasized metabolic considerations as an important area to address in developing a common strategy for genotoxicity testing. A working group convened at the 2005 4th IWGT to discuss this area further and propose practical strategy recommendations. To propose a strategy, the working group reviewed: (1) the current status and deficiencies, including examples of carcinogens "missed" in genotoxicity testing, established shortcomings of the standard in vitro induced S9 activation system and drug metabolite case examples; (2) the current status of possible remedies, including alternative S9 sources, other external metabolism systems or genetically engineered test systems; (3) any existing positions or guidance. The working group established consensus principles to guide strategy development. Thus, a human metabolite of interest should be represented in genotoxicity and carcinogenicity testing, including evaluation of alternative genotoxicity in vitro metabolic activation or test systems, and the selection of a carcinogenicity test species showing appropriate biotransformation. Appropriate action triggers need to be defined based on the extent of human exposure, considering any structural knowledge of the metabolite, and when genotoxicity is observed upon in vitro testing in the presence of metabolic activation. These triggers also need to be considered in defining the timing of human pharmaceutical ADME assessments. The working group proposed two strategies to consider; a more proactive approach, which emphasizes early metabolism predictions to drive appropriate hazard assessment; and a retroactive approach to manage safety risks of a unique or "major" metabolite once identified and quantitated from human clinical ADME studies. In both strategies, the assessment of the genotoxic potential of a metabolite could include the use of an alternative or optimized in vitro metabolic activation system, or direct testing of an isolated or synthesized metabolite. The working group also identified specific areas where more data or experiences need to be gained to reach consensus. These included defining a discrete exposure action trigger for safety assessment and when direct testing of a metabolite of interest is warranted versus the use of an alternative in vitro activation system, a universal recommendation for the timing of human ADME studies for drug candidates and the positioning of metabolite structural knowledge (through in silico systems, literature, expert analysis) in supporting metabolite safety qualification. Lastly, the working group outlined future considerations for refining the initially proposed strategies. These included the need for further evaluation of the current in vitro genotoxicity testing protocols that can potentially perturb or reduce the level of metabolic activity (potential alterations in metabolism associated with both the use of some solvents to solubilize test chemicals and testing to the guidance limit dose), and proposing broader evaluations of alternative metabolic activation sources or engineered test systems to further challenge the suitability of (or replace) the current induced liver S9 activation source.

DNA fragmentation and DNA repair synthesis induced in rat and human thyroid cells by chemicals carcinogenic to the rat thyroid

Five chemicals that are known to induce in rats thyroid follicular-cell adenomas and carcinomas were assayed for their ability to induce DNA damage and DNA repair synthesis in primary cultures of human thyroid cells. Significant dose-dependent increases in the frequency of DNA single-strand breaks and alkali-labile sites, as measured by the same Comet assay, were obtained after a 20-h exposure to the following subtoxic concentrations of the five test compounds: methimazole from 2.5 to 10mM; nitrobenzene, potassium bromate, N,N'-diethylthiourea and ethylenethiourea from 1.25 to 5mM. Under the same experimental conditions, DNA repair synthesis, as evaluated by quantitative autoradiography, was present in potassium bromate-exposed thyroid cells from all the three donors and in those from two of three donors with either nitrobenzene or ethylenethiourea, but did not match the criteria for a positive response in thyroid cells from any of the donors with methimazole and N,N'-diethylthiourea. Consistently with their ability to induce thyroid tumors, all the five test compounds, administered p.o. in rats in a single dose corresponding to 1/2 LD50, induced a statistically significant degree of DNA fragmentation in the thyroid. These findings suggest that the five test compounds might be carcinogenic to thyroid in humans.

Correlation between induction of DNA fragmentation in lung cells from rats and humans and carcinogenic activity

Six chemicals, known to induce lung tumors in rats, were examined for their ability to induce DNA fragmentation in primary cultures of rat and human lung cells, and in the lung of intact rats. Significant dose-dependent increases in the frequency of DNA single-strand breaks and alkali-labile sites, as measured by the single-cell gel electrophoresis (Comet) assay, were obtained in primary lung cells from male rats with the following, minimally toxic, concentrations of the six test compounds: N-nitrosodimethylamine (NDMA; 2.5-10 mM), hydrazine (HZ; 0.5-4 mM), cadmium sulfate (CD; 31.2 and 62.5 μM), 4,4'-methylene bis (2-chloroaniline) (MOCA; 31.2-125 μM), isobutyl nitrite (IBN; 7.8-31.2 μM) and tetranitromethane (TNM; 1.9-15.6 μM). Similar degrees of DNA fragmentation were obtained in primary human lung cells; however, due to inter-donor differences, the minimum effective concentrations were in some donors lower and in others higher than in rats, and IBN induced DNA damage only in one of three donors. The DNA-damaging potency of HZ was higher in rats than in humans, and the opposite was true for MOCA. In agreement with these findings, statistically significant increases in the average frequency of DNA breaks were obtained in the lung of rats given a single oral dose (1/2 LD50) of the six test compounds. These findings give evidence that genotoxic lung carcinogens may be identified by use of the DNA fragmentation/Comet assay on rat lung cells as targets cells, and show that the six compounds tested produce in primary cultures of lung cells from human donors DNA-damaging effects substantially similar to those observed in rats.