Identification of carcinogenic agents and primary prevention of cancer

Association of bone mineral density with trichlorophenol: a population-based study

BACKGROUND

Trichlorophenols (TCPs) are metabolites of several organochlorine chemicals, including chlorobenzene, hexachlorocyclohexane, and chlorophenoxy acid, present in air, surface water, soil, and sediment. Many studies have shown that endocrine disruptors (EDs)may contribute to decreased bone mass and the increased risk of osteoporosis. However, the relationship between TCP and bone mineral density (BMD) has not been studied yet.

METHODS

We conducted a cross-sectional study by using data from the 2005-2010 National Health and Nutrition Examination Survey (NHANES). TCP levels were measured in urine samples from 3385 participants and bone mineral density was obtained by dual X-ray absorptiometry (DXA) lumbar spine and femur scanning. Multiple regression analysis, stratified analysis, curve fitting analysis, and trend tests were used to assess the relationship between TCP and BMD.

RESULT

After adjusting for confounding factors, the results of multiple regression analysis only showed that ln-2,4,5-TCP was negatively associated with BMD of lumbar spine. In stratified analyses, Male, Menstruating Female and Menopausal Female were divided into three groups for analysis. The results showed that ln-2,4,5-TCP and ln-2,4,6-TCP were not statistically associated with BMD in total femur, femoral neck, femoral tuberosity, intertrochanteric femur and lumbar spine, which was also confirmed by curve fitting analyses and trend tests.

CONCLUSION

This study demonstrated that 2,4,5-TCP and 2,4,6-TCP in urine samples were not significantly associated with BMD in the US population. Therefore, 2,4,5-TCP and 2,4,6-TCP may not be detrimental to BMD.

Prevention of Asbestos-Related Disease in Countries Currently Using Asbestos

More than 40 years of evaluation have consistently confirmed the carcinogenicity of asbestos in all of its forms. This notwithstanding, according to recent figures, the annual world production of asbestos is approximatively 2,000,000 tons. Currently, about 90% of world asbestos comes from four countries: Russia, China, Brazil and Kazakhstan; and the wide use of asbestos worldwide represents a global threat. The purpose of this paper is to present a review of the asbestos health impact and to discuss the role of epidemiological investigations in countries where asbestos is still used. In these contexts, new, "local" studies can stimulate awareness of the size of the problem by public opinion and other stakeholders and provide important information on the circumstances of exposure, as well as local asbestos-related health impacts. This paper suggests an agenda for an international cooperation framework dedicated to foster a public health response to asbestos, including: new epidemiological studies for assessing the health impact of asbestos in specific contexts; socio-cultural and economic analyses for contributing to identifying stakeholders and to address both the local and global implications of asbestos diffusion; public awareness on the health and socio-economic impact of asbestos use and banning.

New clues on carcinogenicity-related substructures derived from mining two large datasets of chemical compounds

In this study, new molecular fragments associated with genotoxic and nongenotoxic carcinogens are introduced to estimate the carcinogenic potential of compounds. Two rule-based carcinogenesis models were developed with the aid of SARpy: model R (from rodents' experimental data) and model E (from human carcinogenicity data). Structural alert extraction method of SARpy uses a completely automated and unbiased manner with statistical significance. The carcinogenicity models developed in this study are collections of carcinogenic potential fragments that were extracted from two carcinogenicity databases: the ANTARES carcinogenicity dataset with information from bioassay on rats and the combination of ISSCAN and CGX datasets, which take into accounts human-based assessment. The performance of these two models was evaluated in terms of cross-validation and external validation using a 258 compound case study dataset. Combining R and H predictions and scoring a positive or negative result when both models are concordant on a prediction, increased accuracy to 72% and specificity to 79% on the external test set. The carcinogenic fragments present in the two models were compared and analyzed from the point of view of chemical class. The results of this study show that the developed rule sets will be a useful tool to identify some new structural alerts of carcinogenicity and provide effective information on the molecular structures of carcinogenic chemicals.

Long-term toxicology and carcinogenicity of 2,4,6-trichlorophenol

Carcinogenesis bioassays were conducted by giving 2,4,6-trichlorophenol [2,4,6-TCP] in feed to groups of 50 male and female Fischer rats and male B6C3F1 mice for two years. Dietary concentrations were 0 [20/group], 5000 [0.5%], or 10,000 [1%] ppm. Female mice began with 10,000 and 20,000 ppm but after 38 weeks were lowered due to reduced body weights to 2500 and 5000 ppm for 67 weeks; exposures averaged 5200 and 10,400 ppm. Adverse effects at two years were leukocytosis and monocytosis of peripheral blood and hyperplasia of bone marrow in both sexes of rats. In mice, liver toxicity, including individual liver cell abnormalities, focal areas of cellular alteration, and focal and nodular areas of hyperplasia were commonly present. Regarding carcinogenic activity, TCP caused leukemias/lymphomas in male rats, and possibly in female rats and female mice as well, and induced liver tumors in male and female mice. Using NTP categories of evidence indicates 'clear evidence of carcinogenicity' for male rats [hematopoietic system tumors]; 'equivocal evidence of carcinogenicity' for female rats [hematopoietic system tumors]; 'clear evidence of carcinogenicity' for male and female mice [liver tumors].

Detailed exposure assessment of dietary furan for infants consuming commercially jarred complementary food based on data from the DONALD study

Furan is a possible human carcinogen regularly occurring in commercially jarred complementary foods. This paper will provide a detailed exposure assessment for babies consuming these foods considering different intake scenarios. The occurrence data on furan in complementary foods were based on our own headspace-gas chromatography/mass spectrometry (HS-GC/MS) analytical results (n = 286). The average furan content in meals and menus was between 20 and 30 µg kg(-1), which is in excellent agreement with results from other European countries. Using measured food consumption data from the Dortmund Nutritional and Anthropometric Longitudinally Designed (DONALD) study, the average exposures for consumers of commercially jarred foods ranged between 182 and 688 ng kg(-1) bw day(-1), with a worst case scenario for P95 consumers ranging between 351 and 1066 ng kg(-1) bw day(-1). The exposure data were then used to characterize risk using the margin of exposure method based on a benchmark dose lower confidence limit for a 10% response (BMDL10) of 1.28 mg kg(-1) bw day(-1) for hepatocellular tumours in rats. The margin of exposures (MOEs) were below the threshold of 10 000, which is often used to define public health risks, in all scenarios, ranging between 7022 and 1861 for average consumers and between 3642 and 1200 for the P95 consumers. Mitigative measures to avoid furan in complementary foods should be of high priority for risk management.

Environmental justice and primary prevention of cancer: the odyssey and legacy of lorenzo tomatis

Lorenzo Tomatis [1929-2007] devoted his private and professional life to the betterment of mankind. As a physician, scientist, and humanitarian he championed against the plight of social injustice and promoted the obvious benefits of primary prevention of diseases compared to treatments that prevent or delay disease progression, especially occupational cancers. An avowed student and scholar of literature, the arts, the history of medicine and science, and chemical carcinogenesis, he believed in and wrote about these issues throughout his storied life. Some of his achievements, with excerpts from his writings, especially on primary prevention and on social injustice, are highlighted herein.

Alternatives to the carcinogenicity bioassay for toxicity prediction: are we there yet?

INTRODUCTION

For decades, traditional toxicology has been the ultimate source of information on the carcinogenic potential of chemicals; however, with increasing demand on regulation of chemicals and decreasing resources for testing, opportunities to accept 'alternative' approaches have dramatically expanded. The need for tools able to identify carcinogens in shorter times and at a lower cost in terms of animal lives and money is still an open issue, and the present strategies and regulations for carcinogenicity prescreening do not adequately protect human health.

AREAS COVERED

This paper briefly summarizes the theories on the early steps of carcinogenesis and presents alternative detection methods for carcinogens based on genetic toxicology, structure-activity relationships and cell transformation assays.

EXPERT OPINION

There is evidence that the combination of Salmonella and structural alerts for the DNA-reactive carcinogens, and in vitro cell transformation assays for nongenotoxic carcinogens, permits the identification of a very large proportion of carcinogens. If implemented, this alternative strategy could improve considerably the protection of human health.

Styrene exposure and risk of cancer

Styrene is widely used in the manufacture of synthetic rubber, resins, polyesters and plastics. Styrene and the primary metabolite styrene-7,8-oxide are genotoxic and carcinogenic. Long-term chemical carcinogenesis bioassays showed that styrene caused lung cancers in several strains of mice and mammary cancers in rats and styrene-7,8-oxide caused tumours of the forestomach in rats and mice and of the liver in mice. Subsequent epidemiologic studies found styrene workers had increased mortality or incidences of lymphohematopoietic cancers (leukaemia or lymphoma or all), with suggestive evidence for pancreatic and esophageal tumours. No adequate human studies are available for styrene-7,8-oxide although this is the primary and active epoxide metabolite of styrene. Both are genotoxic and form DNA adducts in humans.

Lorenzo Tomatis and primary prevention of environmental cancer

The leading 20th century proponent for primary prevention of environmental cancer was Dr. Lorenzo Tomatis, the former Director of the International Agency for Research on Cancer and founder of the IARC Monographs program. This paper is dedicated to the memory of Dr. Tomatis--eminent scientist, scholar, teacher, humanitarian, and public health champion--and includes many perspectives that he promoted throughout his career, with original quotations from some of his scientific writings on primary prevention of environmental cancer. Any attempt by us to simply summarize his views would only detract from the power and logic of his language."Cancer still remains a mainly lethal disease. Primary prevention remains the most relevant approach to reduce mortality through a reduction in incidence".

Somatic mutations in cancer development

The transformation of a normal cell into a cancer cell takes place through a sequence of a small number of discrete genetic events, somatic mutations: thus, cancer can be regarded properly as a genetic disease of somatic cells. The analogy between evolution of organisms and evolution of cell populations is compelling: in both cases what drives change is mutation, but it is Darwinian selection that enables clones that have a growth advantage to expand, thus providing a larger target size for the next mutation to hit. The search for molecular lesions in tumors has taken on a new dimension thanks to two powerful technologies: the micro-arrays for quantitative analysis of global gene expresssion (the transcriptome); and 'deep' sequencing for the global analysis of the entire genome (or at least the exome). The former offers the most complete phenotypic characterization of a tumor we could ever hope for--we could call this the ultimate phenotype; the latter can identify all the somatic mutations in an individual tumor--we could call this the somatic genotype. However, there is definitely the risk that while we are 'drowned by data, we remain thirsty for knowledge'. If we want to heed the teachings of Lorenzo Tomatis, I think the message is clear: we ought to take advantage of the new powerful technologies--not by becoming their slaves, but remaining their masters. Identifying somatic mutations in a tumor is important not because it qualifies for 'oncogenomics', but because through a deeper understanding of the nature of that particular tumor it can help us to optimize therapy or to design new therapeutic approaches.

Reducing occupational exposure to chemical carcinogens

Strategies for controlling occupational exposure to chemical carcinogens are set out in the European Union Carcinogens Directive and in national legislation such as the British Control of Substances Hazardous to Health Regulations. While such legislative requirements must apply to all occupational chemical carcinogens, it is argued that priority should be given to controlling those agents that contribute most to the cancer burden. Examples of possible strategies to reduce exposure to two agents (diesel exhaust particulate and paint emissions) are discussed. It is concluded that there are no real technical difficulties in controlling exposures to chemical carcinogens; however, for many of the key agents, we need to change attitudes to the potential risks and clearly demonstrate to employers and employees how to reduce the exposures.

The limits of two-year bioassay exposure regimens for identifying chemical carcinogens

BACKGROUND

Chemical carcinogenesis bioassays in animals have long been recognized and accepted as valid predictors of potential cancer hazards to humans. Most rodent bioassays begin several weeks after birth and expose animals to chemicals or other substances, including workplace and environmental pollutants, for 2 years. New findings indicate the need to extend the timing and duration of exposures used in the rodent bioassay.

OBJECTIVES

In this Commentary, we propose that the sensitivity of chemical carcinogenesis bio-assays would be enhanced by exposing rodents beginning in utero and continuing for 30 months (130 weeks) or until their natural deaths at up to about 3 years.

DISCUSSION

Studies of three chemicals of different structures and uses-aspartame, cadmium, and toluene-suggest that exposing experimental animals in utero and continuing exposure for 30 months or until their natural deaths increase the sensitivity of bioassays, avoid false-negative results, and strengthen the value and validity of results for regulatory agencies.

CONCLUSIONS

Government agencies, drug companies, and the chemical industry should conduct and compare the results of 2-year bioassays of known carcinogens or chemicals for which there is equivocal evidence of carcinogenicity with longer-term studies, with and without in utero exposure. If studies longer than 2 years and/or with in utero exposure are found to better identify potential human carcinogens, then regulatory agencies should promptly revise their testing guidelines, which were established in the 1960s and early 1970s. Changing the timing and dosing of the animal bioassay would enhance protection of workers and consumers who are exposed to potentially dangerous workplace or home contaminants, pollutants, drugs, food additives, and other chemicals throughout their lives.

Canada's asbestos legacy at home and abroad

Despite international efforts to block Canada's export of asbestos, the Canadian federal government continues to defend the economic interests of the asbestos industry. Ironically, Canadian asbestos miners, mill workers, and those engaged in a wide range of other occupations continue to suffer asbestos-related disease and premature death. Although there is an employer-funded compensation system in each province, many workers with mesothelioma and other asbestos-related diseases remain uncompensated. The export of Canadian asbestos to developing countries sets the stage for another preventable occupational disease epidemic that will manifest over the coming decades. There is growing support from the Canadian labor movement for an end to asbestos exportation and for a just transition strategy for the asbestos workers and their communities.

Benzene-induced cancers: abridged history and occupational health impact

Benzene-induced cancer in humans was first reported in the late 1920s. Carcinogenesis findings in animals were not reported conclusively until 1979. Industry exploited this "discrepancy" to discredit the use of animal bioassays as surrogates for human exposure experience. The cardinal reason for the delay between first recognizing leukemia in humans and sought-after neoplasia in animals centers on poor design and conduct of experimental studies. The first evidence of carcinogenicity in animals manifested as malignant tumors of the zymbal glands (sebaceous glands in the ear canal) of rats, and industry attempted to discount this as being irrelevant to humans, as this organ is vestigial and not present per se in humans. Nonetheless, shortly thereafter benzene was shown to be carcinogenic to multiple organ sites in both sexes of multiple strains and multiple species of laboratory animals exposed via various routes. This paper presents a condensed history of the benzene bioassay story with mention of benzene-associated human cancers.