Substantial efforts have been made for the standardization of nanotechnology vocabulary by the ISO Technical Committee 229, which has already produced a few standards. However, in view of growing interest in the environmental, health, and safety issues of nanomaterials, the definition of nanomaterial still remains controversial in some respects, especially for regulatory purposes. This is related with difficulties in specifying requirements for a broad range of nanomaterials with a variety of applications.

Hepatocellular carcinoma (HCC) is one of the 5th most common cancers, with 80% of the cases occurring in low resource countries. Its etiology is dominated by complex interplay between chronic infection by hepatitis virus B or C (HBV, HCV), metabolic diseases and exposure to environmental carcinogens. In areas of high incidence of HCC, the most common risk factors are chronic HB carriage and exposure to a mycotoxin, aflatoxin B1 (AFB1), which contaminates many staples and causes mutations at the third base of codon 249 in the TP53 tumor suppressor gene in hepatocytes (R249S mutation). In this review, we summarize studies using a very sensitive and quantitative detection method, short-oligonucleotide mass analysis, to measure R249S in cell-free DNA isolated from the plasma of asymptomatic subjects and patients with chronic liver disease and/or HCC. These studies have identified that high levels of R249S were strongly associated with HBV-related HCC. Low to intermediate levels of R249S, in contrast, were detectable in asymptomatic subjects exposed to AFB1, with seasonal variations informative of the complex interactions between mutagenesis by AFB1 and chronic infection by HBV. Overall, we suggest that formation of R249S occurs in response to AFB1 exposure, well ahead of cancer development, thus generating large populations of cells at high risk for neoplastic transformation. In addition, R249S mutations may inactivate pro-apoptotic activities of p53 and contribute to rendering hepatocytes resistant to liver cell destruction by chronic inflammation, thus limiting chronic liver disease symptoms.

Capsaicin from the red chili pepper is a prospective chemopreventive agent. To explore the possible antigenotoxic effects of capsaicin on N-diethylnitrosamine (DEN)-induced mutagenesis in vitro, we conducted bacterial mutation assays with Salmonella typhimurium YG7108, a sensitive strain to mutagenic alkylating agents. Capsaicin was not mutagenic either with or without S9 activation. Unexpectedly,it enhanced the mutagenicity of DEN in the presence of S9 activation significantly. Capsaicin also enhanced the mutagenicity of 2-aminoanthracene and benzo[a]pyrene in the presence of S9 activation and benzo[a]pyrene diolepoxide in the absence of S9 activation. However, it reduced the mutagenicity of ethylnitrosourea in the absence of S9 activation. To examine whether capsaicin modulates DEN-induced mutagenesis and hepatocarcinogenesis in vivo, we took advantage of gpt delta rats, transgenic rodents that carry reporter genes for mutations. Female gpt delta rats were given drinking water containing 40 ppm DEN for five weeks. They were fed diets containing capsaicin at doses of 0, 100 or 500 ppm for seven weeks, starting one week before the DEN treatment. Samples were collected at weeks 7 and 32, respectively, for mutagenicity and carcinogenicity assays. DEN enhanced gpt mutant frequency more than 200 fold in the liver. However, capsaicin displayed no modulating effects on the mutagenesis. Rather, it reduced the number of liver neoplasms, especially liver cell adenomas, in a dose-dependent manner although the reduction in hepatocellular carcinoma was statistically insignificant. These results suggest that chemopreventive effect of capsaicin against DEN-induced hepatocarcinogenesis is slight and that the effect is not due to antimutagenesis. The results also caution that chemopreventive effects of chemicals should be examined not only in vitro but also in vivo with multiple indexes, e.g., in vitro and in vivo mutations and pathological examinations.

The hepatocarcinogenicity of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), a carcinogen contained in fried meat and fish, was examined in the medium-term rat liver carcinogenicity bioassay. Induction of DNA-MeIQx adducts occurred with low doses of the chemical, followed by increasing doses by elevation of 8-hydroxy-2'-deoxyguanosine (8-OHdG) formation in DNA and lacI gene mutations, which might have been related to the initiation of carcinogenesis by MeIQx. Further elevation of the MeIQx dose was shown to cause the formation of glutathione S-transferase placental form (GST-P) positive foci in the liver, a well-known preneoplastic marker in rat hepatocarcinogenesis. In studies with N-nitrosocompounds such as N-nitrosodiethylamine and N-nitrosodimethylamine, no induction of GST-P positive foci was observed after their administration at low doses. When the carcinogenicity of a well-known colon carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) was examined, PhIP-DNA adduct formation was observed after treatment with low doses, while only high doses of the chemical were found to induce aberrant crypt foci (ACF), which are a surrogate marker of preneoplastic lesions in the colon. In experiments with potassium bromate, carcinogenicity, mutagenicity, and 8-OHdG formation in the rat kidney were observed only after administration at high dose. From these results, the genotoxic carcinogens were concluded to have a threshold, at least practical, with respect to their carcinogenicity.

Toxicologists are accustomed to using methods of hypothesis testing in order to recognize the existence of target toxicity, on the basis of experimental data. However, in principle, it is impossible to identify the threshold via hypothesis testing in toxicological experiments since the probability of false-negative decisions cannot be determined in the context of hypothesis testing. When a mechanism for producing a threshold is hypothesized from a toxicological (or biological) perspective, and it is mathematically formulated as a dose-response relationship, statistics may be helpful in evaluating the existence (or non-existence) of the threshold, that is, in addressing the threshold identification problem. Consequently, it is important to select a model from a particular set of mathematical dose-response functions. Although the Akaike information criterion (AIC) or its modification is often used as a criterion index in the selection of the optimum model, their effectiveness in the threshold identification problem have not been validated. In these circumstances, the determination of a practical threshold using in vitro experiments may be an alternative to the identification of a “true” threshold, provided an appropriate in vitro assay affords a large scale experiment. Although quite difficult, it is important to maintain the homogeneity of experiments throughout the entire procedure. Only after establishing the experimental skills, the statistics may provide appropriate statistical methods that satisfy the requirements of toxicologists.

Variants of the error-prone gene, mucAB, were found in Escherichia coli plasmids from 3 out of 63 healthy Japanese donors. As compared with mucAB of pKM101, one contained unaltered mucA only, while two others contained full-sized, mutated mucAB with mutation-enhancing activity in E. coli. Possible interaction between bacterial plasmid genes and host humans was discussed.

We investigated the clastogenic potential of antimycin A, which is well known as a mitochondrial inhibitor (Complex III blocker), utilizing two cultured cell lines, CHL/IU and CHO-WBL. Antimycin A induced chromosome structural aberrations in CHL cells in the presence of S9 mix. However, no chromosome structural aberrations were induced under three different treatment conditions in CHO cells with or without S9 mix. Instead, it induced polyploidy, including endoreduplicated cells, in CHO cells with or without S9 mix. By conducting the comet assay, we found that the antimycin A has no potential to induce DNA damage in these cells. Thus, the chromosome aberrations induced in these cells might be caused by non-DNA-reactive mechanism. Based on these findings, it is suggested that some of the differences between the congenital characteristics of these cells play an important role in the differences of the clastogenic response.

Dietary factors are implicated in approximately 35% of cancers attributed to environmental factors. Although an extremely wide variety of dietary factors are considered to contribute to carcinogenesis, its precise mechanism remains to be clarified. We focused on the role of oxidative DNA damage in carcinogenesis mediated by various dietary factors. We investigated the mechanism of oxidative DNA damage induced by a) amino acid metabolites, in relation to carcinogenesis caused by protein intake and amino acid imbalance, b) heterocyclic amines formed during cooking meat and fish, c) sugar and hyperglycemia-related aldehydes, d) carcinogens contained in fermented foods, such as urethane, e) phytoestrogens including soy isoflavones, f) carcinogens in edible plants, such as caffeic acid and isothiocyanate, g) food additives, such as potassium bromate and benzoyl peroxide. These dietary factors and their metabolites induced metal-mediated oxidative damage to DNA in human cultured cells and 32P-labeled DNA fragments obtained from human cancer-relevant genes. On the basis of our results, it is concluded that polycyclic compounds, such as heterocyclic amines, can cause oxidative DNA damage, although they appear to mainly form DNA adduct. On the other hand, monocyclic and aliphatic compounds, such as amino acid metabolites and urethane, may mainly cause oxidative DNA damage whereas they do not appear to form DNA adduct. Soy isoflavones may cause carcinogenesis through initiation via oxidative DNA damage caused by their metabolites and promotion via cell proliferation induced by themselves. In this review, we discuss the role of oxidative DNA damage as the common mechanism of dietary carcinogenesis.