Factors affecting the incidence of genotoxicity biomarkers in peripheral blood lymphocytes: impact on design of biomonitoring studies.

A review of risk factors affecting background rates of micronuclei and chromosomal aberration (CA) formation in peripheral blood lymphocytes (PBLs) was undertaken with a view to aiding the interpretation of genotoxicity biomonitoring studies. Both endogenous factors and those due to methodological variation were evaluated. Background variation of other indices of genotoxicity in PBLs (specifically 8-hydroxy-deoxyguanosine and comet assays) were also considered as these data likely reflect overlapping causes of DNA damage and may provide some indicators for future research areas. A number of host risk factors, namely age, gender, smoking, vitamin B(12) and folate status, were identified for which there is strong or sufficient evidence that they impact on background levels of genotoxicity biomarkers. Evaluation of these factors should be routinely included in genotoxicity biomonitoring studies. Although data on the influence of smoking is somewhat inconsistent, because of its known association with cancer and DNA damage, it is also classified as a high-risk factor. A number of other factors were identified for which there is weak or insufficient evidence including alcohol consumption, disease conditions and infections, physical exercise, body mass index and genotype. The review shows that the evaluation of biomonitoring studies of genotoxicity is complex and there is a need to improve study designs by setting an a priori hypothesis, collecting good exposure data and stratifying groups appropriately, using appropriate power calculations before initiating biomonitoring studies, and collecting information on appropriate risk factors. There is a need for further collaborative work and the establishment of centres of excellence on genotoxicity biomonitoring. If these measures are achieved, then it would be possible to use the data from biomonitoring studies in risk assessments to derive risk management measures.

Evidence for genotoxicity of pesticides in pesticide applicators: a review.

A systematic review of the literature has been conducted and studies reporting investigations of genotoxicity biomarkers in pesticide workers have been assessed with view to establishing whether there was evidence for any risk to those using pesticides approved in the United Kingdom. Each of the studies was evaluated using a set of criteria drawn up by members of the UK Committee of Mutagenicity based upon the guidelines proposed by the International Programme on Chemical Safety (IPCS) working group [R. J. Albertini, D. Anderson, G. R. Douglas, L. Hagmar, K. Hemminki, F. Merlo, A. T. Natarajan, H. Norppa, D. E. Shuker, R. Tice, M. D. Waters and A. Aitio (2000) Mutat. Res., 463, 111-172]; 24 out of 70 studies met the criteria for inclusion in the substantive evaluation. Positive findings were compared with occupational practices and evidence of exposure to specific pesticides with view to developing hypotheses for further consideration. Seventeen of the 24 studies reported positive findings, although in the majority of these the magnitude of increase was small. There was some limited evidence that the use of benzimidazoles was more consistently associated with positive findings. However, limitations in the data, particularly evidence of exposure, did not allow definitive conclusions to be drawn. Also, it was noted that the use (or not) of personal protective equipment (PPE) was not well documented and in the few studies in which its use was reported, the findings were more likely to be positive in the absence of PPE usage. An independent epidemiological review concluded that all studies were of limited design, particularly with regards to study size, the assessment of subject selection and potential recruitment bias. Variance in genotoxicity indices in the control population and a lack of understanding of the factors influencing this variability complicate attempts to characterize positive responses. More substantive data are needed in this respect so that the significance of relatively small increases in biomonitoring indices can be accurately assessed. Once these data are available, a study in workers using benzimidazoles would be appropriate.

An approach to investigating the importance of high potency polycyclic aromatic hydrocarbons (PAHs) in the induction of lung cancer by air pollution.

Evidence suggests that people living in urban areas have an increased risk of lung cancer due to higher levels of air pollution in these areas. Benzo[a]pyrene (B[a]P) is currently used as the main indicator of carcinogenic polycyclic aromatic hydrocarbons (PAHs) in air pollution, but there is concern that B[a]P may not be the ideal surrogate of choice for PAH mixtures since higher potency PAHs have recently been identified which could potentially contribute more and variably to the overall carcinogenicity. Dibenzo[a,h]anthracene (DBA) and dibenzo[a,l]pyrene (DB[a,l]P) are estimated to have carcinogenic potencies 10 or more times greater than B[a]P but data on their presence and formation in the environment are limited. Several occupational and environmental PAH biomonitoring studies are reviewed here, with particular focus on the specific exposure groups, study design, sample tissue, in particular the use of nasal tissues, and biomarkers used in each study. Consideration of these data is then used to propose a novel biomonitoring approach to evaluate exposure, uptake and the role of high potency PAHs in air pollution-related lung cancer. This is based upon an occupational study examining specific DNA adducts for DBA and DB[a,l]P in nasal cells to evaluate the extent to which these high potency PAHs might contribute to the increased risk of developing lung cancer from air pollution.

Approaches to carcinogenic risk assessment for polycyclic aromatic hydrocarbons: a UK perspective.

This paper reviews the approaches to carcinogenic risk assessment of polycyclic aromatic hydrocarbons (PAHs) in air pollution with emphasis on high potency PAHs such as dibenzo[a,l]pyrene (DB[a,l]P). The potency of DB[a,l]P may be 100-fold greater than benzo[a]pyrene (B[a]P); thus the B[a]P surrogate approach currently used to monitor for compliance with UK air pollution standards may not be appropriate. It is suggested that an approach based on potency equivalency factors (PEFs) could be developed to include highly potent PAHs provided an appropriate reference data set for relevant PAHs using a route acceptable for inhalation risk assessment is selected. Available data suggest that intratracheal administration of low doses of PAHs to rats is likely to simulate the kinetics of inhalation exposure to PAHs in a feasible manner. The use of a measure of total DNA adducts as an endpoint, which correlates well with lung tumourigenicity, would provide surrogate data for setting PEFs without the need for long-term bioassays in rodents. Further, dose-response studies using intratracheal administration of a range of PAHs singly and in combination to assess additivity are required to develop a PEF system for inhalation PEFs derived from DNA adduct measurements.

Mouse-specific carcinogens: an assessment of hazard and significance for validation of short-term carcinogenicity bioassays in transgenic mice.

1. The International Conference on the Harmonisation of Technical Requirements for the Registration of Pharmaceuticals for human use (ICH) has agreed that bioassay data from only one species, the rat, supported by appropriate mutagenicity and pharmacokinetic data and also information from new (unvalidated) short term in vivo screening tests for potential carcinogenicity, could be used for the licensing of human medicines. This proposal has been supported by reviews of the utility of testing pharmaceuticals in the mouse which have concluded that the mouse bioassay contributes little to regulatory decisions. The current review was undertaken to identify 'genuine' mouse-specific carcinogens using the Gold Carcinogenicity Potency Database (CPD) for the initial identification of potential mouse-specific carcinogens from published literature. Hazard assessments were completed for these chemicals with particular attention focused on the 'genuine' mouse-specific carcinogens. The significance of such chemicals has been discussed together with consideration of on-going work on the validation of short-term carcinogenicity bioassays using transgenic mice. 2. Seventy-six potential mouse specific carcinogens were identified through the Gold Carcinogenicity Potency Database. Following more detailed consideration a total of ten chemicals were excluded from further consideration (three were multispecies carcinogens, five were considered to be non-carcinogenic in the mouse, and the data for two were uninterpretable). The review focused on the remaining 66 chemicals. There was equivocal evidence of carcinogenicity to the rat for 28 chemicals and inadequate data for a further 23 chemicals. Fifteen 'genuine' mouse-specific carcinogens were identified. These 15 chemicals comprise two genotoxic mouse-specific carcinogens (N-methylolacrylamide (924-42-5), 2,6-Dichloro-p-phenylenediamine (609-20-1); five non-genotoxic mouse-specific carcinogens 2-Aminobiphenyl.HCl (2185-92-4), Captan (133-06-2), Dieldrin (60-57-7), Diethylhexyladipate (103-23-1), and Probenicid (57-66-9); five mouse-specific carcinogens with equivocal evidence of mutagenicity were identified; (2,4-diaminophenol.2HCl (137-09-7), Dipyrone (68-89-3), Ozone (10028-15-6), Vinylidene chloride (75-35-4), and Zearalenone (17924-92-4)), and three mouse-specific carcinogens with inadequate mutagenicity data (Benzaldehyde (100-52-7), Piperonyl sulphoxide (120-62-7), Ripazepam (26308-28-1)). 3. It is suggested that the two genotoxic mouse carcinogens would have been considered as potential carcinogens in the absence of a mouse bioassay. Of the five non-genotoxic mouse-specific carcinogens; three induced tumours in mouse liver only and are considered as being of low potential hazard to human health. The remaining two chemicals would have been missed in the absence of a mouse bioassay (2-aminobiphenyl (2185-92-4) and captan (133-06-2)) and thus are good candidates for evaluation in the short term bioassays in transgenic mice currently being validated. 4. The hardest group of mouse-specific carcinogens to evaluate are those for which there is equivocal or inadequate mutagenicity data. The difficulty in evaluating these particular chemicals emphasises the need for adequate mutagenicity data in addition to adequate carcinogenicity data in order to assess potential hazards to human health. Hazard assessments and a consideration of the potential role for short-term bioassays in transgenic mice for the eight chemicals in this subgroup are presented. 5. A number of general conclusions have been derived from this review. Firstly, there are insufficient published genotoxicity data to allow a full assessment fo mutagenic potential for 57/76 of the potential mouse-specific carcinogens identified from the CPD. This is surprising given the clear value of such data in interpreting bioassay results and the much greater resources required for carcinogenicity bioassays. (ABSTRACT TRUNCATED)

Review of the safety assessment of polychlorinated biphenyls (PCBs) with particular reference to reproductive toxicity.

1. The methods used to evaluate the toxicological effects of PCBs in animals have been reviewed. 2. The data show that Toxic Equivalency Factors (TEFs) could be developed to assess the potential toxicity of PCB mixtures for certain specific target organ effects (such as the liver and immune system) but would be inappropriate for other effects (e.g. thyroid function and neurochemical effects). More data on a wider range of individual PCB congeners and a method for systematically balancing toxicodynamic and toxicokinetic data are required before the TEF approach can be fully evaluated. 3. With the exception of the teratogenic effects seen in mice and the anti-oestrogenic effects reported in in vitro studies, there are insufficient data on individual PCB congeners to evaluate the structure-activity relationships for the effects of PCBs on reproduction. The data also show that individual PCBs may have opposing effects on a particular aspect of reproduction (for example individual PCB congeners may have either oestrogenic or anti-oestrogenic effects). Studies with individual PCB congeners have shown both enhancement and antagonism of the teratogenic effects of 2, 3, 7, 8-tetrachloro dibenzo-p-dioxin (TCDD) in the mouse. It is not possible to use TEFs to evaluate the reproductive effects of PCBs. 4. The mechanism(s) responsible for the effects of PCBs on postnatal neurobehavioural development in rodents and monkeys have not been elucidated. At least two groups of PCBs which might be responsible for the observed effects have been identified in this review, one affecting the dopaminergic system and the other group affecting thyroid hormone levels. Considerably more research would be required before the TEF approach could be applied to the effects of PCBs on postnatal neurobehavioural development. This would include research on an appropriate animal model to determine whether the critical toxicological mechanism is mediated through the Ah receptor. 5. The reproductive toxicity of complex PCB mixtures such as those found in foods will depend on the identifies and relative proportions of individual PCB congeners in the mixture. It is not possible to give an accurate estimate of a NOAEL or LOAEL from the reproduction studies using commercial PCB mixtures which could be readily applied to the safety assessment of PCBs present as contaminants in food. 6. It is concluded that the data presented in this paper support the hypothesis that there is no satisfactory method derived from the available studies in laboratory animals for evaluating the potential risk of adverse effects on reproduction posed by contamination of foods with PCBs.

Guidelines for the safety assessment of microbial enzymes used in food.

The regulatory approach in the UK to the safety assessment of microbial enzymes has been reviewed. The Committee on the Toxicity of Chemicals in Food, Consumer Products and the Environment (COT) devised, in December 1992, a strategy based on toxicological testing of a representative batch of the final purified fermentation product and achieving a high standard of quality control through the development and maintenance of quality assurance specifications.

Colonial dissociation and susceptibility to phagocytosis of Pseudomonas aeruginosa grown in a chamber implant model in mice.

Pseudomonas aeruginosa strains were grown in 1-cm plastic chambers sealed at both ends with porous Millipore filters and implanted in the peritonea of mice. Mucoid and nonmucoid strains of P. aeruginosa isolated from a patient with cystic fibrosis largely retained their phenotypes when grown for up to 1 year in this in vivo system, although colonial dissociation occurred, as observed in chronic lung infections of patients with cystic fibrosis. In the absence of added opsonins, P. aeruginosa M2 cells taken directly from the in vivo system were significantly more susceptible to phagocytosis than were the same P. aeruginosa cells after being washed in buffer. Phagocytosis of in vivo-grown P. aeruginosa cells could be further enhanced by using a porin protein F-specific monoclonal antibody.

Use of monoclonal antibodies to protein F of Pseudomonas aeruginosa as opsonins for phagocytosis by macrophages.

Five protein F-specific monoclonal antibodies were found to opsonize Pseudomonas aeruginosa for complement-independent phagocytosis by unelicited mouse peritoneal macrophages, mouse macrophage cell line P388D1, and human monocyte-derived macrophages. Immunoglobulin G1 antibodies seemed to be a preferred isotype.

Metabolic activation of paracetamol by highly purified forms of cytochrome P-450.

The metabolic activation of paracetamol (acetaminophen) to reactive intermediate(s) which bind covalently to proteins was studied in reconstituted systems, employing highly purified preparations of cytochromes P-450 and P-448 isolated from the liver of rats pretreated with phenobarbitone and beta-naphthoflavone respectively. Cytochrome P-448 readily catalysed the activation of paracetamol, but in contrast no activation was observed when cytochrome P-450 was used at the same concentration. Addition of purified epoxide hydratase to the incubation system had no effect on the extent of covalent binding to proteins, indicating that an arene oxide is unlikely to be the reactive intermediate responsible for the paracetamol-induced hepatotoxicity.

Cutaneous testing in the elderly patient with tuberculosis.

A hypothesis is presented that the fully developed cutaneous reaction to tuberculin, as exemplified by diagnostic cutaneous testing in culture-positive patients with tuberculosis, is an "all-or-nothing" phenomenon. In the elderly, this characteristic is maintained, with the value of the test being limited only by an increase in anergy.