Elevated HPRT mutation frequencies in aflatoxin-exposed residents of daxin, Qidong county, People's Republic of China

Targeting purine metabolism in ovarian cancer

Purine, an abundant substrate in organisms, is a critical raw material for cell proliferation and an important factor for immune regulation. The purine de novo pathway and salvage pathway are tightly regulated by multiple enzymes, and dysfunction in these enzymes leads to excessive cell proliferation and immune imbalance that result in tumor progression. Maintaining the homeostasis of purine pools is an effective way to control cell growth and tumor evolution, and exploiting purine metabolism to suppress tumors suggests interesting directions for future research. In this review, we describe the process of purine metabolism and summarize the role and potential therapeutic effects of the major purine-metabolizing enzymes in ovarian cancer, including CD39, CD73, adenosine deaminase, adenylate kinase, hypoxanthine guanine phosphoribosyltransferase, inosine monophosphate dehydrogenase, purine nucleoside phosphorylase, dihydrofolate reductase and 5,10-methylenetetrahydrofolate reductase. Purinergic signaling is also described. We then provide an overview of the application of purine antimetabolites, comprising 6-thioguanine, 6-mercaptopurine, methotrexate, fludarabine and clopidogrel. Finally, we discuss the current challenges and future opportunities for targeting purine metabolism in the treatment-relevant cellular mechanisms of ovarian cancer.

Molecular Analysis of Mutations in the Human HPRT Gene

The HPRT assay uses incorporation of toxic nucleotide analogues to select for cells lacking the purine scavenger enzyme hypoxanthine-guanine phosphoribosyl transferase. A major advantage of this assay is the ability to isolate mutant cells and determine the molecular basis for their functional deficiency. Many types of analyses have been performed at this locus: the current protocol involves generation of a cDNA and multiplex PCR of each exon, including the intron/exon junctions, followed by direct sequencing of the products. This analysis detects point mutations, small deletions and insertions within the gene, mutations affecting RNA splicing, and the products of illegitimate V(D)J recombination within the gene. Establishment of and comparisons with mutational spectra hold the promise of identifying exposures to mutation-inducing genotoxicants from their distinctive pattern of gene-specific DNA damage at this easily analyzed reporter gene.

Retrospective and Prospective Look at Aflatoxin Research and Development from a Practical Standpoint

Among the array of structurally and toxicologically diverse mycotoxins, aflatoxins have attracted the most interest of scientific research due to their high toxicity and incidence in foods and feeds. Despite the undeniable progress made in various aspects related to aflatoxins, the ultimate goal consisting of reducing the associated public health risks worldwide is far from being reached due to multiplicity of social, political, economic, geographic, climatic, and development factors. However, a reasonable degree of health protection is attained in industrialized countries owing to their scientific, administrative, and financial capacities allowing them to use high-tech agricultural management systems. Less fortunate situations exist in equatorial and sub-equatorial developing countries mainly practicing traditional agriculture managed by smallholders for subsistence, and where the climate is suitable for mould growth and aflatoxin production. This situation worsens due to climatic change producing conditions increasingly suitable for aflatoxigenic mould growth and toxin production. Accordingly, it is difficult to harmonize the regulatory standards of aflatoxins worldwide, which prevents agri-foods of developing countries from accessing the markets of industrialized countries. To tackle the multi-faceted aflatoxin problem, actions should be taken collectively by the international community involving scientific research, technological and social development, environment protection, awareness promotion, etc. International cooperation should foster technology transfer and exchange of pertinent technical information. This review presents the main historical discoveries leading to our present knowledge on aflatoxins and the challenges that should be addressed presently and in the future at various levels to ensure higher health protection for everybody. In short, it aims to elucidate where we come from and where we should go in terms of aflatoxin research/development.

Qidong: a crucible for studies on liver cancer etiology and prevention

Qidong (Jiangsu, China) has been of interest to cancer epidemiologists and biologists because, until recently, it was an endemic area for liver cancer, having amongst the highest incidence rates in the world. The establishment of the Qidong Cancer Registry together with the Qidong Liver Cancer Institute in 1972 has charted the patterns of liver cancer incidence and mortality in a stable population throughout a period of enormous economic, social, and environmental changes as well as of improvements in health care delivery. Updated incidence trends in Qidong are described. Notably, the China age-standardized incidence rate for liver cancer has dropped by over 50% in the past several decades. Molecular epidemiologic and genomic deep sequencing studies have affirmed that infection with hepatitis B virus as well as dietary exposure to aflatoxins through contamination of dietary staples such as corn, and to microcystins – blue-green algal toxins found in ditch and pond water – were likely important etiologic factors that account for the high incidence of liver cancer in this region. Public health initiatives to facilitate universal vaccination of newborns against HBV and to improve drinking water sources in this rural area, as well as economic and social mandates serendipitously facilitating dietary diversity, have led to precipitous declines in exposures to these etiologic factors, concomitantly driving substantive declines in the liver cancer incidence seen now in Qidong. In this regard, Qidong serves as a template for the global impact that a package of intervention strategies may exert on cancer burden.

Aflatoxins and Saccharomyces cerevisiae: yeast modulates the intestinal effect of aflatoxins, while aflatoxin B1 influences yeast ultrastructure

The gastrointestinal tract (GIT) is the main site where absorption of food components takes place and the first system coming into contact with mycotoxins of dietary origin. The aim of this work was to study the effect of probiotic Saccharomyces cerevisiae RC016 on intestinal villi of rats exposed to aflatoxins for 60 days. Moreover, the effect of in vitro aflatoxin B1 (AFB1) exposure on yeast cell ultrastructure was evaluated. Six treatments were applied (n=6) to inbred male Wistar rats: (1) uncontaminated feed control (F); (2) yeast control; (3) F + 40 μg/kg AFB1 + 20 μg/kg aflatoxin G1 (AFG1); (4) F + 100 μg/kg AFB1 + 50 μg/kg AFG1; (5) F + 40 μg/kg AFB1 + 20 μg/kg AFG1 + daily oral dose 108 viable S. cerevisiae cells; and (6) F + 100 μg/kg AFB1 + 50 μg/kg AFG1 + daily oral dose 108 viable S. cerevisiae cells. Morphometric measurements (villus length and width, crypt depth, quantification of goblet cells) were assessed using image analysis. S. cerevisiae RC016 cells were exposed to 20 μg/ml of AFB1 in intestinal solutions or in phosphate buffered saline and cells processed for transmission electron microscopy and high resolution light microscopy studies. Dietary exposure to the yeast did not induce significant differences in villus width but increased villus length and crypt depth. Aflatoxin-contaminated diets induced an increase in villus length, width and crypt depth and a significant decrease in the number of goblet cells which were improved by the addition of S. cerevisiae RC016. A significant increase in the yeast cell diameter was observed when RC016 was exposed to aflatoxins, suggesting this as an advantage since a larger cell would be able to adsorb mycotoxins more efficiently. The ability of this strain to act as probiotic and aflatoxin binder makes it a candidate for the formulation of new additives to improve animal performance.

Molecular Epidemiology of Physical Activity and Cancer

As in other areas of epidemiology, researchers studying physical activity and cancer have begun to include laboratory analyses of biological specimens in their studies. The incorporation of these “biomarkers” into epidemiology has been termed molecular epidemiology and is an approach primarily developed to study chemical carcinogens. Thus far, there has been no discussion in the field on how the established molecular epidemiologic framework might be adapted for research into physical activity, what methodologic needs exist, what the goals of such an approach might be, and what limitations exist. This article relates the literature on molecular epidemiology to the needs of physical activity research and tries to set research priorities for the field as it moves in this new direction. Although this approach will be very useful for investigating the mechanisms through which physical activity exerts effects, there are several challenges for physical activity epidemiologists in adapting molecular epidemiologic approaches. Primarily, there are currently no available biomarkers that might be considered measures of exposure or biologically effective dose. In addition, most available biomarkers of intermediate effects have been tested in training studies at activity levels much higher than those seen in population-based epidemiologic studies. Thus, it is not clear whether these biomarkers are valid at lower activity levels. Furthermore, the nature of the relationship between activity and many available biomarkers depends very much on the context of the activity. Addressing these issues should be a priority if we are to develop a molecular epidemiologic paradigm for studying physical activity.

Low-dose radiation and genotoxic chemicals can protect against stochastic biological effects

A protective apoptosis-mediated (PAM) process that is turned on in mammalian cells by low-dose photon (X and gamma) radiation and appears to also be turned on by the genotoxic chemical ethylene oxide is discussed. Because of the PAM process, exposure to low-dose photon radiation (and possibly also some genotoxic chemicals) can lead to a reduction in the risk of stochastic effects such as problematic mutations, neoplastic transformation (an early step in cancer occurrence), and cancer. These findings indicate a need to revise the current low-dose risk assessment paradigm for which risk of cancer is presumed to increase linearly with dose (without a threshold) after exposure to any amount of a genotoxic agent such as ionizing radiation. These findings support a view seldom mentioned in the past, that cancer risk can actually decrease, rather than increase, after exposure to low doses of photon radiation and possibly some other genotoxic agents. The PAM process (a form of natural protection) may contribute substantially to cancer prevention in humans and other mammals. However, new research is needed to improve our understanding of the process. The new research could unlock novel strategies for optimizing cancer prevention and novel protocols for low-dose therapy for cancer. With low-dose cancer therapy, normal tissue could be spared from severe damage while possibly eliminating the cancer.

Hprt mutant frequencies in splenic T-cells of male F344 rats exposed by inhalation to propylene

Propylene is a major industrial intermediate and atmospheric pollutant to which humans are exposed by inhalation. In this study, 6-week-old male F344 rates were exposed to 0, 200, 2000, or 10,000 ppm propylene by inhalation for 4 weeks (6 h/day, 5 days/week), and mutant frequencies were determined in the Hprt gene of splenic T-lymphocytes. Twenty milligrams of cyclophosphamide monohydrate (CPP)/kg bw, given on the penultimate day of propylene exposure, was used as a positive control mutagen. Rats (n = 8/group) were necropsied for isolation of T-cells 8 weeks after the last dose, a sampling time that produced peak spleen Hprt mutant frequencies (Mfs) in a preliminary mutant manifestation study using CCP treatment. Hprt Mfs were measured via the T-cell cloning assay, which was performed without knowledge of the animal treatment groups. Mean Hprt Mfs were significantly increased over control values (mean Mf = 5.24 +/- 1.55 (SD) x 10(-6)) in CPP-treated rats (10.37 +/- 4.30 x 10(-6), P = 0.007). However, Hprt Mfs in propylene-exposed rats were not significantly increased over background, with mean Mfs of 4.90 +/- 1.84 x 10(-6) (P = 0.152), 5.05 +/- 3.70 x 10(-6) (P = 0.895), and 5.95 +/- 2.49 x10(-6) (P = 0.500) for animals exposed to 200, 2000, or 10,000 ppm propylene, respectively. No significant increase in F344 rat or B6C3F1 mouse cancer incidence was reported in the National Toxicology Program carcinogenicity studies of propylene across this same exposure range. Taken together, these findings support the conclusion that inhalation exposure of rats to propylene does not cause mutations or cancer.

Susceptibility and biomarker knowledge for improvement of environmental health

At the international level, environmental health problems are usually most serious in countries that have the least resources to deal with the problems. Therefore, international efforts have been initiated to achieve equitable environmental health globally. One approach is to conduct international collaborative studies. This approach has been successful in the building of scientific infrastructure in these countries so that they can address their own environmental health concerns and to sustain the environmental health programs. Using liver and oral cancers as models for discussion, examples of success in the identification of etiology and the mechanisms for the diseases are provided. For example, biomarkers are used to provide early warning signals for the disease. In addition, the application of the collected information for developing disease prevention and intervention programs is presented. Expertise in genetic susceptibility is used to provide a more precise understanding of the cancer process. With the precise knowledge, the information can potentially be used to screen for high-risk individuals and to develop "designer" intervention procedures against specific biochemical defects. Success in disease prevention is dependent upon multidisciplinary collaborations at the local and international levels.