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We conducted a two-year inhalation study of butyraldehyde using F344/DuCrlCrlj rats. The rats were exposed to 0, 300, 1,000 and 3,000 ppm (v/v) for 6 hr/day, 5 days/ week for 104 weeks using whole-body inhalation chambers. The incidence of squamous cell carcinoma of the nasal cavity was increased in the 3,000 ppm groups of both male and female rats, with Fisher's exact test and the Peto test indicating that the incidence was significant. In addition to squamous cell carcinoma in the nasal cavity, in the 3,000 ppm groups one male had an adenosquamous carcinoma, one male had a carcinosarcoma, one male had a sarcoma NOS (Not Otherwise Specified), and one female had a squamous cell papilloma in the nasal cavity. The combined incidence of squamous cell carcinoma, adenosquamous carcinoma and carcinosarcoma was significantly increased in male rats and the combined incidence of squamous cell papilloma and carcinoma was significantly increased in female. Based on these results, we conclude that there is clear evidence of butyraldehyde carcinogenicity in male and female rats.

MA is a chemical intermediate, manufactured and processed within closed systems. While so far available subacute to chronic inhalation toxicity studies performed in compliance with OECD TG principles gave no indication of any carcinogenic potential for MA, a recent 2-year inhalation study with F344/DuCrlCrlj rats published in 2017 by the JBRC showed a statistically significant increase of squamous cell carcinoma in the nasal cavity of male rats at the highest tested concentration of 160 ppm. However, the results of the different studies in total indicate that this high concentration exceeded the MTC. As MA has a low potential for genotoxic and mutagenic activity, the increased tumour incidence can be attributed to a non-genotoxic mechanism, namely to a strong inflammatory response observed in this study. Together with mechanistic and epidemiologic data for other compounds related to nasal carcinogenesis via this mode of action, it can be concluded that the relevance of this increased tumour incidence in male rats for humans is questionable. Also, a long-term exposure to higher concentrations of MA is highly unlikely to be reached in the environment or at workplaces. Therefore, a risk for humans including cancer hazard is considered implausible., (Copyright © 2021 The Author(s). Published by Elsevier Inc. All rights reserved.)

The carcinogenicity and chronic toxicity of acrolein was examined by whole body inhalation to groups of 50 F344/DuCrlCrlj rats and 50 B6D2F1/Crlj mice of both sexes for two years. The concentration of acrolein was 0, 0.1, 0.5 or 2 ppm (v/v) for male and female rats; and 0, 0.1, 0.4 or 1.6 ppm for male and female mice. Two-year administration of acrolein induced the squamous cell carcinomas in nasal cavity which is rare tumor in one male and two female rats. In females, rhabdomyoma in nasal cavity was observed in four rats exposed to 2 ppm. In mice, since the survival rate of male and female of mice control group were lowered than 25% in late of the administration periods due to renal lesion and/or amyloid deposition, the mice study was terminated at 93rd week in males, and was terminated at 99th week in females. The incidences of adenomas in nasal cavity were observed in 16 females and significantly increased only in female mice. Thus, acrolein is carcinogenic in two species, i.e. rats and mice. Additionally, non-neoplastic nasal cavity lesions in rats and mice were observed., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Formaldehyde is a reactive aldehyde naturally present in all plant and animal tissues and a critical component of the one-carbon metabolism pathway. It is also a high production volume chemical used in the manufacture of numerous products. Formaldehyde is also one of the most well-studied chemicals with respect to environmental fate, biology, and toxicology-including carcinogenic potential, and mode of action (MOA). In 2006, a published MOA for formaldehyde-induced nasal tumors in rats concluded that nasal tumors were most likely driven by cytotoxicity and regenerative cell proliferation, with possible contributions from direct genotoxicity. In the past 15 years, new research has better informed the MOA with the publication of in vivo genotoxicity assays, toxicogenomic analyses, and development of ultra-sensitive methods to measure endogenous and exogenous formaldehyde-induced DNA adducts. Herein, we review and update the MOA for nasal tumors, with particular emphasis on the numerous studies published since 2006. These new studies further underscore the involvement of cytotoxicity and regenerative cell proliferation, and further inform the genotoxic potential of inhaled formaldehyde. The data lend additional support for the use of mechanistic data for the derivation of toxicity criteria and/or scientifically supported approaches for low-dose extrapolation for the risk assessment of formaldehyde.

Butyl 2,3-epoxypropyl ether (CAS No. 2426-08-6, synonym: n-butylglycidyl ether, BGE) was exposed by whole body inhalation to F344 rats and BDF1 mice of both sexes (50 animals per group) 6 hours per day, 5 days per week for 104 weeks at targeted concentrations of 0, 10, 30 or 90 ppm (v/v) for rats and 0, 5, 15 or 45 ppm for mice. In rats, 90 ppm of BGE increased the incidences of nasal squamous cell carcinomas in both sexes. Nasal adenomas and splenic mononuclear cell leukemia were increased in male rats exposed to 30 ppm. Splenic mononuclear cell leukemia was increased in female rats by trend test. Non-neoplastic nasal lesions, such as squamous cell hyperplasia with atypia, squamous cell metaplasia and the inflammation of the respiratory region and atrophy of the olfactory epithelium were increased in both sexes in a dose-dependent manner. In mice, the incidences of histiocytic sarcomas of the uterus in female mice were increased in a dose-dependent manner and the incidences of nasal hemangiomas in both sexes were increased in a dose-dependent manner. Nasal squamous cell carcinoma, a rare tumor, was observed, although not statistically significant, in both sexes. Non-neoplastic lesions such as nodular hyperplasia of the transitional epithelium and cuboidal changes of the respiratory epithelium in the nasal cavity, were increased both in males and females in a dose-dependent manner. The present study demonstrated clear evidence of carcinogenicity of BGE in both rats and mice by the 2-year whole body inhalation exposure.

Hexavalent chromium (Cr(VI)) compounds are recognized as carcinogens in the respiratory tract, giving rise to cancers of the lung, nose and nasal sinuses, especially in certain occupational environments. Inhalation exposure of Cr(VI)-containing particles, dusts and fumes commonly occurs in chromium-related occupational environments, such as chromium production, plating, welding of chromium-containing metals and alloys, electroplating, chromium-containing pigments and paints. Epidemiological surveys of chromium compounds have shown strong associations between exposure to Cr(VI) and mortality due to lung cancer, as well as positive associations with cancers of the nose and nasal cavity. Nasal symptoms, such as nasal irritation, ulceration and perforation of the nasal septum, nasal turbinate engorgement and hypertrophy, are important signs for the early diagnosis of lung cancer and cancers of the nose and nasal cavity in those with an occupational history of Cr(VI) exposure. Cr(VI) exposure in the workplace remains a serious problem as a cause of lung cancer and cancers of nose and nasal cavity, especially in relatively small enterprises that use chromium compounds. Appropriate protection for workers should be considered in occupations that involve exposure to chromium compounds.

The current study aims to provide stronger evidence to aid in our understanding of the role of cumulative occupational exposure to (softwood-dominated) mixed wood dust in aetiology of nasal cancer. We included broad exposure occurred in a range of wood-processing occupation across varied industries in four Nordic countries. A population-based case-control study was conducted on all male cases with nasal adenocarcinoma (393 cases), other types of nasal cancer (2,446) and nasopharyngeal cancer (1,747) diagnosed in Finland, Sweden, Norway and Iceland between 1961 and 2005. For each case, five male controls, who were alive at the time of diagnosis of the case (index date), were randomly selected, matched by birth-year and country. Cumulative exposures (CE)s to wood dust and formaldehyde before the index date were quantified based on a job-exposure matrix linked to occupational titles derived from population censuses. Hazard ratios (HRs) for the CE of wood dust were estimated by conditional logistic regression, adjusted for CE to formaldehyde and 95% confidence intervals (CIs) were calculated. There was an increasing risk of nasal adenocarcinoma related to wood dust exposure. The HR in the highest CE category of wood dust (≥ 28.82 mg/m 3 -years) was 16.5 (95% CI 5.05-54.1). Neither nonadenocarcinoma of the nose nor nasopharyngeal cancer could be linked to wood dust exposure. CE to softwood-dominated mixed wood dusts is strongly linked with elevated risk in nasal adenocarcinoma but not with other types of nasal or nasopharyngeal cancer., (© 2017 UICC.)

Diethylnitrosamine (DEN) is a chemical broadly used in animal models as a hepatocarcinogen, reported to also cause pulmonary neoplasms in mice. The original objective was to evaluate the impact of a Western diet with or without 10% broccoli on DEN-induced on liver cancer. We administered DEN (45 mg/kg) intraperitoneally to young adult male B6C3F1 mice by 6 weekly injections and evaluated liver cancer 6 months after the DEN treatments. Here, we report unexpected primary tumorigenesis in nasal epithelium, independent of dietary treatment. More than 50% of DEN-treated B6C3F1 mice developed nasal neoplasm-related lesions, not reported previously in the literature. Only one of these neoplasms was visible externally prior to postmortem examination. Intraperitoneal DEN treatment used as a model for liver cancer can have a carcinogenic effect on the nasal epithelium in B6C3F1 mice, which should be carefully monitored in future liver cancer studies., (© 2016 by The Author(s) 2016.)

Objectives: to extend up to year 2013 the follow-up for mortality of a cohort of workers in a chromium and nickel plating plant, where an excess of lung cancers was already identified., Design: 10 years after the first study about cancer mortality in a cohort of workers involved in the chromium thin-layer plating, published in 2006, we updated the evaluation of themortality of a cohort ofworkers employed in the same chromiumthin-layer plating factory with at least 6 months of work between 1968 and 1994.The mortality rates are compared with those of the Italian and Veneto Region (Northern Italy) populations.The dose-response relationship between work duration and lung cancer is assessed by adjusted Poisson regression., Setting and Participants: 127 unskilled or skilled workers involved in the production process., Results: in the updated follow-up, 35 deaths occurred among the subjects under study: 19 for cancer (of which 11 for lung cancer and 3 for pancreatic cancer). A marked excess ofmortality due to lung cancer is observed. In addition, the newfollowup shows a significant excess of pancreatic cancer mortality. Lung cancer mortality is positively associated with work duration and the risk increases by 13%(95%CI 1-26) for each additional year of work., Conclusions: the extension of followup confirms that this cohort expresses an increased mortality from cancer deaths, due to a marked excess of lung and pancreatic cancers. The effect of smoking has only a secondary effect in the cancer onset expressed by this cohort. The risk of lung cancer increased with work duration and thus with occupational exposure to chromium and nickel.

Rheumatoid arthritis (RA) patients have increased risk of lymphoma which seems associated mainly with high inflammatory state and disease activity, but also with immunosuppressive agents or Epstein-Barr virus (EBV) infection. Many case reports describe lymphoproliferative lesions arising during methotrexate therapy, often EBV positive with possible regression after methotrexate withdrawal. The authors report the case of an 85-year-old patient with erosive and seronegative RA, in remission under methotrexate who developed a midfacial destructive lesion with epistaxis and local inflammatory signs. The magnetic resonance imaging showed a large nasal septum defect. Anti-neutrophil cytoplasmic antibodies titres and angiotensin converting enzyme were normal. Biopsies of the lesion identified a NK/ T nasal type lymphoma. EBV latent membrane protein research on the lesion was negative. Polymerase chain reaction analysis of the bone marrow aspirate showed EBV DNA positivity. Withdrawal of methotrexate was performed without tumour regression. The authors described the single case of a patient with RA in stable remission under methotrexate who presented a rare type of lymphoma, a nasal type NK/T. EBV active replication was found in the bone marrow.

Nose and paranasal sinus cancers are among the diseases related to exposure to wood dusts. The aim of this study was to evaluate exposure to hardwood dust by workers in small carpentry industries in central Italy (Tuscany, Italy) employing from one to ten workers each, and to investigate pathogenetic mechanisms. The efficacy of ventilation systems was assessed and exposure levels determined. Exposure conditions of hardwood workers were then reproduced in the laboratory and a physical/kinetic model prepared to simulate patterns of air uptake by workers. Various parameters were then measured to investigate possible risk factors that may be related to the onset of the disease. In addition to particle size of wood dust, a factor that requires further investigation is the temperatures reached by wood dust during processing, which may lead to the formation of new harmful molecules.

Background: Occupational exposure to carcinogens contributes greatly to the etiology of sinonasal cancer (SNC), but the role of different risk factors in determining different histological subtypes is disputed., Methodology: All consecutive surgical epithelial SNC cases (case-series study) underwent a systematic occupational medicine examination to determine previous exposure to a wide range of work-related chemical hazards., Results: We investigated 65 SNC cases including intestinal-type adenocarcinoma [ITAC] squamous-cell carcinoma [SCC], and others. Occupational exposure was recognized for 39 cases. Occupational exposures were sensibly more frequent among ITAC than among SCC or other histotypes. Occupational exposure in ITAC cases was to leather or wood dust only, while among non-ITAC cases, we recognised exposure to formaldehyde, solvents and metal fumes. A high proportion of SNC with occupational exposure originated in the ethmoidal epithelium., Conclusion: In our case-series of SNC, a very high frequency of previous occupational exposure to carcinogens was detected, suggesting that occupational hazards may be associated to the aetiopathogenesis, primarily for ITAC, but also for other histotypes. Besides leather or wood, other chemical agents must be recognized as occupational risk factors.

Bioassays in mice and rats exposed via inhalation to naphthalene show incidences of lung and nasal cancer, respectively. To address the question of human relevancy, a literature search for cancer case reports in workers exposed to naphthalene was performed, along with an evaluation of major studies from industries with naphthalene-containing streams having the highest naphthalene exposures and/or most extensive epidemiology data. Although no epidemiologic studies of workers exposed solely to naphthalene were found, a population-based case-control study of oral and oropharynx cancer found no relation with naphthalene exposure. Limited case reports of laryngeal and colorectal cancer and naphthalene exposure exist, but these data are inadequate for evaluating human cancer risk. No case reports of nasal tumors were found, which is informative because case reports have historically identified several occupational carcinogens. Combined with anatomic and metabolic differences between rodent and human upper airways and data suggesting that cancer potency based on the rat bioassay is overestimated, relevancy of rat nasal tumors to humans is questionable. For lung cancer, existing human studies are insufficient to make firm conclusions about the presence or absence of a potential naphthalene-related risk, although no occupationally-related lung cancer risks were identified in the industries evaluated., (Copyright © 2011. Published by Elsevier Inc.)

The sinonasal cancer (SNC) are a rare tumors characterized by high occupational etiologic fraction. For this reason their incidence and etiology can be actively monitored by a dedicated cancer registry. The National Registry of these tumours is situated at the Italian Institute for Occupational Safety and Prevention (ISPESL) and is based on Regional Operating Centres (ROCs). In Lombardy Region the ROC has been established at the end of 2007 with the purpose to make a systematic surveillance and therefore to support in the most suitable way the scientific research and the prevention actions in the high risk working sectors. The aims of this surveillance are: to estimate the regional incidence of SNC, to define different sources of occupational and environmental exposure both known (wood, leather, nickel, chromium) and unknown. The registry collects all the new incident cases of epithelial SNC occurring in residents in Lombardy Region since 01.01.2008. The regional Registry is managed according to National Guidelines. Until January 2010 we received 596 cases of suspected SNC; only 91 (15%) of these were actually incident cases according to the inclusion criteria of the Registry, and they were preferentially adenocarcinoma and squamous carcinoma. In 2008 the regional age-standardized incidence rate of SNC for males and females, respectively, is 0.8 and 0.5 per 100,000. Occupational or environmental exposure to wood or leather dust is ascertained in over the 50% of cases. The occupational exposure to leather dust was duo to work in shoe factories. Our preliminary findings confirm that occupational exposure to wood and leather dusts are the more relevant risk factors for SNC. The study of occupational sectors and job activity in cases without such exposure could suggest new etiologic hypothesis.

Despite their histological resemblance to colorectal adenocarcinoma, there is little information on the molecular events involved in the pathogenesis of intestinal-type sinonasal adenocarcinoma (ITACs). The aim of this paper is to evaluate the possible role of TP53 and Bcl-2 gene defects in ITAC by investigating the immunohistochemical expression of TP53 and Bcl-2 gene products in a group of ethmoidal ITACs associated with occupational exposure. A retrospective study on 15 patients with pathological diagnosis of primary ethmoidal ITAC was conducted. Representative formalin-fixed, paraffin wax-embedded block from each case was selected for immunohistochemical studies using the antibodies against p53 and Bcl-2. Clinical-pathological data were also correlated with the staining results. The results of immunohistochemical examination demonstrated that poorly differentiated cases showed a higher percentage of p53 and Bcl-2 expressing cells in comparison to well-differentiated cases. No correlation was found with other clinico-pathological parameters, including T, stage and relapses. The relationship between up-regulation of p53 and Bcl-2 and poorly differentiated ethmoidal adenocarcinoma suggests a role of these genes, in combination with additional genetic events, in the pathogenesis of ITAC.

The toxicity and carcinogenicity of 1,2-dichloropropane (DCP) were examined by inhalation exposure of male and female F344 rats to DCP for either 13 wk or 2 years. In the 13-wk study, the DCP concentrations used were 125, 250, 500, 1000, or 2000 ppm (v/v), and in the 2-year study the DCP concentrations were 80, 200, or 500 ppm (v/v). Thirteen-week exposure to DCP induced hyperplasia in the respiratory epithelium and atrophy of the olfactory epithelium at 125 ppm and above. At the higher levels of exposure, hemolytic anemia and lesions of liver and adrenal gland were observed. Two-year exposure to DCP significantly increased incidences of papilloma in the nasal cavity of male and female rats exposed to 500 ppm DCP. In addition, three cases of esthesioneuroepithelioma were observed in the DCP-exposed male rats. Total nasal tumors increased in a concentration-dependent manner. Hyperplasia of the transitional epithelium and squamous cell hyperplasia, both of which were morphologically different from the hyperplasia of the respiratory epithelium observed in the 13-wk exposure study, occurred in a concentration-dependent manner; these lesions are considered to be preneoplastic lesions. Atrophy of the olfactory epithelium, inflammation of the respiratory epithelium, and squamous cell metaplasia were also seen in the 2-year study. These results demonstrate that DCP is a nasal carcinogen in rats. Lifetime cancer risks for humans exposed to DCP in the ambient air and work environment were quantitatively estimated, using both nonthreshold and threshold approaches, with the data obtained from the 2-year study.

Inhaled formaldehyde is classified as a known human and animal carcinogen, causing nasopharyngeal cancer. Additionally, limited epidemiological evidence for leukemia in humans is available; however, this is inconsistent across studies. Both genotoxicity and cytotoxicity are key events in formaldehyde nasal carcinogenicity in rats, but mechanistic data for leukemia are not well established. Formation of DNA adducts is a key event in initiating carcinogenesis. Formaldehyde can induce DNA monoadducts, DNA-DNA cross-links, and DNA protein cross-links. In this study, highly sensitive liquid chromatography-tandem mass spectrometry-selected reaction monitoringmethods were developed and [(13)CD(2)]-formaldehyde exposures utilized, allowing differentiation of DNA adducts and DNA-DNA cross-links originating from endogenous and inhalation-derived formaldehyde exposure. The results show that exogenous formaldehyde induced N(2)-hydroxymethyl-dG monoadducts and dG-dG cross-links in DNA from rat respiratory nasal mucosa but did not form [(13)CD(2)]-adducts in sites remote to the portal of entry, even when five times more DNA was analyzed. Furthermore, no N(6)-HO(13)CD(2)-dA adducts were detected in nasal DNA. In contrast, high amounts of endogenous formaldehyde dG and dA monoadducts were present in all tissues examined. The number of exogenous N(2)-HO(13)CD(2)-dG in 1- and 5-day nasal DNA samples from rats exposed to 10-ppm [(13)CD(2)]-formaldehyde was 1.28 +/- 0.49 and 2.43 +/- 0.78 adducts/10(7) dG, respectively, while 2.63 +/- 0.73 and 2.84 +/- 1.13 N(2)-HOCH(2)-dG adducts/10(7) dG and 3.95 +/- 0.26 and 3.61 +/- 0.95 N(6)-HOCH(2)-dA endogenous adducts/10(7) dA were present. This study provides strong evidence supporting a genotoxic and cytotoxic mode of action for the carcinogenesis of inhaled formaldehyde in respiratory nasal epithelium but does not support the biological plausibility that inhaled formaldehyde also causes leukemia.

Several naphthalene Unit Risk Factors (URFs) were proposed by the US Environmental Protection Agency in 2004 using data on the development of olfactory epithelial neuroblastomas and nasal respiratory epithelial adenomas in rats, but these URFs may be inappropriate and unnecessarily conservative for estimating human cancer risks. The purpose of the present exercise was to perform a screening-level population risk assessment of the US population to compare the observed number of naphthalene-induced nasal tumors in the US to the number that would be predicted if the URFs for naphthalene were as proposed. Nine scenarios were evaluated to represent the range of exposures individuals have typically experienced. Results indicate that the total predicted burden of naphthalene-induced nasal tumors per year in the US (65,905 rare nasal tumors, of which 29,121 are olfactory epithelial neuroblastomas) is much greater than the number of these tumors actually observed per year (910 total nasal tumors, of which 66 are olfactory neuroblastomas) over the period 1973-2006. This suggests that using rat nasal tumor data to derive a naphthalene URF for humans should be re-evaluated., (Copyright 2010 Elsevier Inc. All rights reserved.)

This study examined the potential induction of tumor-associated mutations in formaldehyde-exposed rat nasal mucosa using a sensitive method, allele-specific competitive blocker-PCR (ACB-PCR). Levels of p53 codon 271 CGT to CAT and K-Ras codon 12 GGT to GAT mutations were quantified in nasal mucosa of rats exposed to formaldehyde. In addition, nasal mucosa cell proliferation was monitored because regenerative cell proliferation is considered a key event in formaldehyde-induced carcinogenesis. Male F344 rats (6-7 weeks old, 5 rats/group) were exposed to 0, 0.7, 2, 6, 10, and 15 ppm formaldehyde for 13 weeks (6 h/day, 5 days/week). ACB-PCR was used to determine levels of p53 and K-Ras mutations. Although two of five untreated rats had measureable spontaneous p53 mutant fractions (MFs), most nasal mucosa samples had p53 MFs below 10(-5). All K-Ras MF measurements were below 10(-5). No dose-related increases in p53 or K-Ras MF were observed, even though significant increases in bromodeoxyuridine incorporation demonstrated induced cell proliferation in the 10 and 15 ppm formaldehyde-treatment groups. Therefore, induction of tumor-associated p53 mutation likely occurs after several other key events in formaldehyde-induced carcinogenesis., (Published by Elsevier Inc.)

Formaldehyde is a ubiquitous indoor air pollutant that is classified as "Carcinogenic to humans (Group 1)" (IARC, Formaldehyde, 2-butoxyethanol and 1-tert-butoxypropanol-2-ol. IARC monographs on the evaluation of carcinogenic risks to humans, vol 88. World Health Organization, Lyon, pp 39-325, 2006). For nasal cancer in rats, the exposure-response relationship is highly non-linear, supporting a no-observed-adverse-effect level (NOAEL) that allows setting a guideline value. Epidemiological studies reported no increased incidence of nasopharyngeal cancer in humans below a mean level of 1 ppm and peak levels below 4 ppm, consistent with results from rat studies. Rat studies indicate that cytotoxicity-induced cell proliferation (NOAEL at 1 ppm) is a key mechanism in development of nasal cancer. However, the linear unit risk approach that is based on conservative ("worst-case") considerations is also used for risk characterization of formaldehyde exposures. Lymphohematopoietic malignancies are not observed consistently in animal studies and if caused by formaldehyde in humans, they are high-dose phenomenons with non-linear exposure-response relationships. Apparently, these diseases are not reported in epidemiological studies at peak exposures below 2 ppm and average exposures below 0.5 ppm. At the similar airborne exposure levels in rodents, the nasal cancer effect is much more prominent than lymphohematopoietic malignancies. Thus, prevention of nasal cancer is considered to prevent lymphohematopoietic malignancies. Departing from the rat studies, the guideline value of the WHO (Air quality guidelines for Europe, 2nd edn. World Health Organization, Regional Office for Europe, Copenhagen, pp 87-91, 2000), 0.08 ppm (0.1 mg m(-3)) formaldehyde, is considered preventive of carcinogenic effects in compliance with epidemiological findings.

As the initial effort in a multi-step uncertainty analysis of a biologically based cancer model for formaldehyde, a Markov chain Monte Carlo (MCMC) analysis was performed for a compartmental model that predicts DNA-protein cross-links (DPX) produced by formaldehyde exposure. The Bayesian approach represented by the MCMC analysis integrates existing knowledge of the model parameters with observed, formaldehyde-DPX-specific data, providing a statistically sound basis for estimating model output uncertainty. Uncertainty and variability were evaluated through a hierarchical structure, where interindividual variability was considered for all model parameters and that variability was assumed to be uncertain on population levels. The uncertainty of the population mean and that of the population variance were significantly reduced through the MCMC analysis. Our investigation highlights several issues that must be dealt with in many real-world analyses (e.g., issues of parameters' nonidentifiability due to limited data) while demonstrating the feasibility of conducting a comprehensive quantitative uncertainty evaluation. The current analysis can be viewed as a case study, for a relatively simple model, illustrating some of the constraints that analysts will face when applying Bayesian approaches to biologically or physiologically based models of increasing complexity.

Alachlor and butachlor are chloracetanilide herbicides that induce olfactory tumors in rats, whereas propachlor does not. The mechanism by which alachlor induces tumors is distinct from many other nasal carcinogens, in that alachlor induces a gradual de-differentiation of the olfactory mucosa (OM) to a more respiratory-like epithelium, in contrast to other agents that induce cytotoxicity, followed by an aberrant regenerative response. We studied biochemical and genomic effects of these compounds to identify processes that occur in common between alachlor- and butachlor-treated rats. Because we have previously shown that matrix metalloproteinase-2 (MMP2) is activated in OM by alachlor, in the present studies we evaluated both MMP2 activation and changes in OM gene expression in response to carcinogenic and non-carcinogenic chloracetanilide treatments. All three chloracetanilides activated MMP2, and >300 genes were significantly up- or downregulated between control and alachlor-treated rats. The most significantly regulated gene was vomeromodulin, which was dramatically upregulated by alachlor and butachlor treatment (>60-fold), but not by propachlor treatment. Except for similar gene responses in alachlor- and butachlor-treated rats, we did not identify clear-cut differences that would predict OM carcinogenicity in this study.

Propylene oxide (PO) concentrations >or=300 ppm induced cell proliferation and tumors in rat nasal respiratory epithelium (NRE). Cell proliferation was suggested to result from depletion of glutathione (GSH) in NRE. In order to substantiate this hypothesis, cell proliferation - measured by bromodeoxyuridine incorporation into DNA of the epithelium lining middle septum, dorsal medial meatus, and medial and lateral surfaces of the nasoturbinate in transverse nasal sections taken immediately posterior to the upper incisor teeth - and water-soluble non-protein thiol (NPSH) in NRE were determined after exposing male Fischer 344 rats to 50 ppm, 100 ppm, 200 ppm, or 300 ppm PO (6 h/day, 3 days). Both parameters were also investigated after treating rats for 3 days with diethylmaleate (DEM; 2 x 250 mg/kg/day or 500 + 150 mg/kg/day) or buthionine sulfoximine (BSO; 500 mg/kg/day). Exposure to 50 ppm PO and treatment with 2 x2 50 mg/kg/day DEM resulted in NPSH levels approximating 50% and 80% of the level in untreated controls, respectively. Cell proliferation did not increase. After exposures to >or= 100 ppm PO or treatment with BSO or 500 + 150 mg/kg/day DEM, NPSH was depleted to

Objective: To investigate the enhancive effect of N,N'-dinitrosopiperazine (DNP) on induced carcinogenesis in nasal and/or nasopharyngeal epithelia among TgN(p53mt-LMP1)/HT transgenic mice to examine the underlying mechanism for the development of nasopharyngeal carcinoma (NPC)., Methods: TgN(p53mt-LMP1)/HT transgenic mice and the same strain of C(57)BL/6J wild-type mice both at the age of 5 months were randomly divided into 2 groups in parallel, respectively, i.e., TgN(p53mt-LMP1)/HT cancerous lesion-inducing group (TI), TgN(p53mt-LMP1)/HT control group (TC), C57BL/6J cancerous lesion-inducing group (CI), and C57BL/6J control group (CC). TI and CI mice were treated only with DNP for 16 weeks, twice each week, while TC and CC mice were given the same volume of saline as controls. At the end of treatment, animals were sacrificed to collect epithelial tissue samples from nasal cavity and nasopharynx for pathohistological evaluation by haematoxylin and eosin (HE) staining and for determination on the expression of TRAF2, c-Jun, and p16 by immunohistochemistry., Results: Atypical hyperplasia was more significant in the samples of TI than in those of TC, CI, and CC, with the rates of lesions being 90%, 10%, 0, and 0 (P<0.01) respectively, though DNP was used alone in a much shortened inducing period at less dosage and without the use of carcinogenic promoter 12-O-tetradecanoylphorbol-13-acetate as usual. The expressions of tumor necrosis factor (TNF) receptor-associated factor 2 (TRAF2) and c-Jun in these samples were significantly up-regulated in TI (P<0.01), while the expression of p16 was significantly lower in TI than in the other groups (P<0.01)., Conclusion: TgN(p53mt-LMP1)/HT mice hold inherited constitutional defect in immune surveillance function, which can be aggravated by environmental carcinogens, such as DNP used even though in a much less strength. The enhanced carcinogenesis-inducing effect of DNP on TgN(p53mt-LMP1)/HT mice should be closely associated with abnormal signaling of activator protein-1 (AP-1) pathway, especially up-regulated expressions of TRAF2 and c-Jun, and down-regulated expression of p16.

The U.S. Environmental Protection Agency (USEPA) guidelines for cancer risk assessment recognize that some chemical carcinogens may have a site-specific mode of action (MOA) involving mutation and cell-killing-induced hyperplasia. The guidelines recommend that for such dual MOA (DMOA) carcinogens, judgment should be used to compare and assess results using separate "linear" (genotoxic) versus "nonlinear" (nongenotoxic) approaches to low-level risk extrapolation. Because the guidelines allow this only when evidence supports reliable risk extrapolation using a validated mechanistic model, they effectively prevent addressing MOA uncertainty when data do not fully validate such a model but otherwise clearly support a DMOA. An adjustment-factor approach is proposed to address this gap, analogous to reference-dose procedures used for classic toxicity endpoints. By this method, even when a "nonlinear" toxicokinetic model cannot be fully validated, the effect of DMOA uncertainty on low-dose risk can be addressed. Application of the proposed approach was illustrated for the case of risk extrapolation from bioassay data on rat nasal tumors induced by chronic lifetime exposure to naphthalene. Bioassay data, toxicokinetic data, and pharmacokinetic analyses were determined to indicate that naphthalene is almost certainly a DMOA carcinogen. Plausibility bounds on rat-tumor-type-specific DMOA-related uncertainty were obtained using a mechanistic two-stage cancer risk model adapted to reflect the empirical link between genotoxic and cytotoxic effects of the most potent identified genotoxic naphthalene metabolites, 1,2- and 1,4-naphthoquinone. Bound-specific adjustment factors were then used to reduce naphthalene risk estimated by linear extrapolation (under the default genotoxic MOA assumption), to account for the DMOA exhibited by this compound.

Conolly et al. (2003, 2004) developed biologically motivated models of formaldehyde carcinogenicity in F344 rats and humans based on a two-stage clonal expansion model of cancer. Based on the human model, Conolly et al. (2004) claimed that cancer risks associated with inhaled formaldehyde are deminimis at relevant human exposure levels. However, they did not conduct a sensitivity analysis to evaluate the robustness of this conclusion. Here, we present a limited sensitivity analysis of the formaldehyde human model. We show that when the control animals from the National Toxicology Program (NTP) studies are replaced with control animals only from NTP inhalation studies, estimates of human risk are increased by 50-fold. When only concurrent control rats are used, the model does not provide any upper bound (UB) to human risk. No data went into the model on the effect of formaldehyde on the division rates and death rates of initiated cells. We show that slight numerical perturbations to the Conolly et al. assumptions regarding these rates can be made that are equally consistent with the underlying data used to construct the model, but produce estimates of human risk ranging anywhere from negative up to 10,000 times higher than those deemed by Conolly et al. to be 'conservative'. Thus, we conclude that estimates of human risk by Conolly et al. (2004) are extremely sensitive to modeling assumptions. This calls into question the basis for the Conolly et al. claim of de minimis human risk and suggests caution in using the model to derive human exposure standards for formaldehyde.

This report provides a summary of deliberations conducted under the charge for members of Module A participating in the Naphthalene State-of-the-Science Symposium (NS3), Monterey, CA, October 9-12, 2006. Whole animal bioassays have been performed by the National Toxicology Program in mice and rats to ascertain the carcinogenic potential of naphthalene by inhalation exposure. A statistically significant increased incidence of pulmonary alveolar/bronchiolar adenoma (a benign lesion), was observed among female mice; an observed increase among the males did not reach statistical significance. No nasal tumors were observed in either sex. A tumorigenic response was observed in both sexes of rats, in males an increased incidence of nasal respiratory epithelium adenoma (a benign rather than malignant lesion) and in females, olfactory epithelial neuroblastoma. Interpretations of these studies vary. On the one hand, evidence of extensive non-neoplastic response in both sexes of both species indicates cytotoxicity occurred at all doses, and strongly suggests that cytotoxicity played a significant role in the tumor responses observed in the target tissues. On the other hand, olfactory epithelial neuroblastoma has rarely been observed in NTP bioassays. This review seeks to develop a consensus understanding of the scientific evidence provided by these studies, taking into account that they have been used as the basis for quantitative human cancer risk assessment, and suggests scientific studies that, if performed, could resolve scientific uncertainties.

This report provides a summary of deliberations conducted under the charge for members of Module C Panel participating in the Naphthalene State-of-the-Science Symposium (NS(3)), Monterey, CA, October 9-12, 2006. The panel was charged with reviewing the current state of knowledge and uncertainty about naphthalene metabolism in relation to anatomy, physiology and cytotoxicity in tissues observed to have elevated tumor incidence in these rodent bioassays. Major conclusions reached concerning scientific claims of high confidence were that: (1) rat nasal tumor occurrence was greatly enhanced, if not enabled, by adjacent, histologically related focal cellular proliferation; (2) elevated incidence of mouse lung tumors occurred at a concentration (30 ppm) cytotoxic to the same lung region at which tumors occurred, but not at a lower and less cytotoxic concentration (tumorigenesis NOAEL=10 ppm); (3) naphthalene cytotoxicity requires metabolic activation (unmetabolized naphthalene is not a proximate cause of observed toxicity or tumors); (4) there are clear regional and species differences in naphthalene bioactivation; and (5) target tissue anatomy and physiology is sufficiently well understood for rodents, non-human primates and humans to parameterize species-specific physiologically based pharmacokinetic (PBPK) models for nasal and lung effects. Critical areas of uncertainty requiring resolution to enable improved human cancer risk assessment were considered to be that: (1) cytotoxic naphthalene metabolites, their modes of cytotoxic action, and detailed low-dose dose-response need to be clarified, including in primate and human tissues, and neonatal tissues; (2) mouse, rat, and monkey inhalation studies are needed to better define in vivo naphthalene uptake and metabolism in the upper respiratory tract; (3) in vivo validation studies are needed for a PBPK model for monkeys exposed to naphthalene by inhalation, coupled to cytotoxicity studies referred to above; and (4) in vivo studies are needed to validate a human PBPK model for naphthalene. To address these uncertainties, the Panel proposed specific research studies that should be feasible to complete relatively promptly. Concerning residual uncertainty far less easy to resolve, the Panel concluded that environmental, non-cytotoxic exposure levels of naphthalene do not induce tumors at rates that can be predicted meaningfully by simple linear extrapolation from those observed in rodents chronically exposed to far greater, cytotoxic naphthalene concentrations.

Scientists at the CIIT Centers for Health Research (Conolly et al., 2000, 2003; Kimbell et al., 2001a, 2001b) developed a two-stage clonal expansion model of formaldehyde-induced nasal cancers in the F344 rat that made extensive use of mechanistic information. An inference of their modeling approach was that formaldehyde-induced tumorigenicity could be optimally explained without the role of formaldehyde's mutagenic action. In this article, we examine the strength of this result and modify select features to examine the sensitivity of the predicted dose response to select assumptions. We implement solutions to the two-stage cancer model that are valid for nonhomogeneous models (i.e., models with time-dependent parameters), thus accounting for time dependence in variables. In this reimplementation, we examine the sensitivity of model predictions to pooling historical and concurrent control data, and to lumping sacrificed animals in which tumors were discovered incidentally with those in which death was caused by the tumors. We found the CIIT model results were not significantly altered with the nonhomogeneous solutions. Dose-response predictions below the range of exposures where tumors occurred in the bioassays were highly sensitive to the choice of control data. In the range of exposures where tumors were observed, the model attributed up to 74% of the added tumor probability to formaldehyde's mutagenic action when our reanalysis restricted the use of the National Toxicology Program (NTP) historical control data to only those obtained from inhalation exposures. Model results were insensitive to hourly or daily temporal variations in DNA protein cross-link (DPX) concentration, a surrogate for the dose-metric linked to formaldehyde-induced mutations, prompting us to utilize weekly averages for this quantity. Various other biological and mathematical uncertainties in the model have been retained unmodified in this analysis. These include model specification of initiated cell division and death rates, and uncertainty and variability in the dose response for cell replication rates, issues that will be considered in a future paper.

The association between nasal snuff and malignancy is not well established. There is epidemiological evidence suggesting that oral tobacco when mixed with lime and betel leaves causes oral cancer in the Indian subcontinent. Similarly, snuff spiced with dried aloe has been reported to cause upper jaw malignancies in the Bantu tribes. The last reported case of nasal snuff causing cancer of the nose was described by John Hill in 1761. We describe here a case of a 69-year-old woman who developed a nasal vestibular malignancy after 30 years of snuff usage, and this, we believe, is the only reported case of nasal snuff causing cancer in the last 2 centuries.

N-nitrosomethylbenzylamine (NMBA) is one of the most potent organ-specific carcinogens routinely used in rat esophageal tumorigenesis. The aim of the study was to evaluate NMBA effect on nasal mucosa, one of the non-target organs. NMBA was administered subcutaneously to 20 male albino rats of Wistar strain for 5 weeks (0.5mg/kg/dose; three doses/week). The experiment was terminated on week 22. In each case, seven standard frontal sections of the nose were taken after fixation for assessment of all the parts of the nasal mucosa. Microscopic examination revealed one small squamous cell papilloma located on the ventro-lateral surface of the left superior nasal concha, one focus on simple hyperplasia and two foci of squamous epithelium dysplasia within the mucosa covering nasal vestibule near the respiratory part of the nasal cavity. Furthermore, statistically significant increase of proliferation activity in both lesional and non-lesional nasal squamous epithelium in NMBA-exposed animals was also found. These phenomena could be potentially induced by carcinogen exposure.

In 2004, the category of formaldehyde carcinogenicity was changed in Poland so that it is now coherent with the requirements of the European Union classification of carcinogenicity. Formaldehyde was categorized into group 3 as the substance not classifiable as to its carcinogenecity to humans because the collected information was not adequate for making a satisfactory assessment. There is some evidence from appropriate animal studies, but it is insufficient to categorize this substance in group 2: probably carcinogenic to humans. In 2006, the International Agency for Research on Cancer categorized formaldehyde in group 1 as the substance carcinogenic to humans. Three types of cancer were assessed: nasopharyngeal cancer, leukemia and sinonasal cancer. There was sufficient evidence that formaldehyde causes nasopharyngeal cancer, strong but not sufficient evidence that the substance induces leukemia and limited evidence for sinonasal cancer. Based on the irritation effect, the value of maximum admissible concentration of formaldehyde in the work environment has been established in Poland at 0.5 mg/m3 as average weighed concentration, and 1 mg/m3 as short-term concentration. In the European Union, the values of 0.2 ppm and 0.4 ppm, respectively are now being considered. It is assumed that the MAC value for formaldehyde in the work environment will be soon verified in Poland and adapted to European Union standards.

Propylene oxide (PO) is a DNA-reactive genotoxic agent; that is, it reacts with DNA to produce lesions in the genetic material. PO also induces tumors in rodents, although only at high concentrations and at portals of entry. This review of PO's genotoxicity profile is organized according to endpoints measured, that is, nonmutational or mutational endpoints, and as to whether the results were from in vitro or in vivo studies. In addition to results of experimental studies, PO's genotoxicity for humans is assessed by reviewing results of published biomarker studies. The weight of evidence indicates that although it is genotoxic, PO's potency as a DNA-reactive mutagen is weak. Other aspects of PO's overall tissue toxicities are also reviewed, with attention to glutathione (GSH) depletion and its consequences, that is, cell proliferation, death, and necrosis. These toxic tissue responses occur in the same anatomical regions in rodents as do the PO-induced tumors. Furthermore, some of these tissue toxicities can produce effects that may either augment PO's DNA-reactive mutagenicity or be genotoxic in themselves, not dependent on PO's DNA reactivity. Although its DNA reactivity may be a necessary component of PO's overall genotoxicity and rodent carcinogenicity, it is likely not sufficient, and the associated tissue toxicities, which are rate-limiting, also seem to be required. This complex mode of action has implications for estimations of PO's cancer potential in humans, especially at low exposure concentrations.

Chronic exposure to high concentrations of PO induced inflammation in the respiratory nasal mucosa (RNM) of rodents and, for concentrations >or= 300 ppm, caused nasal tumors. Considering the nose to be the most relevant target organ for PO-induced tumorigenicity, we developed a physiological toxicokinetic model for PO in rats and humans. It includes compartments for arterial, venous, and pulmonary blood, liver, muscle, fat, richly perfused tissues, lung, and nose. It simulates inhalation of PO, its distribution into tissues by blood flow, and its elimination by exhalation and metabolism. In nose, lung, and liver of rats, PO conjugation with glutathione (GSH), PO-induced GSH depletion, and formation of PO adducts to DNA are described. Also modeled are PO adducts to hemoglobin of rats and humans. Required partition coefficients and metabolic parameters were derived experimentally or from publications. In rats, simulated PO concentrations in blood and GSH levels in tissues agreed with measured data. If compared with reported values, levels of adducts with hemoglobin were underpredicted up to a factor of about 2. Adducts with DNA differed up to a factor of 3. Hemoglobin adducts predicted for PO-exposed workers were 1.5-1.9 times higher than the reported ones. Considering identical conditions of PO exposure, similar PO concentrations in RNM were modeled for rats and humans. Also, PO concentrations in blood, about 1/30th of those in RNM, were similar in both species. Since the model was evaluated on all available data in rats and humans, we consider it to be useful for estimating the risk from inhalation exposure to PO.

Objective: To evaluate the risk of lung cancer and nasal cancer among workers employed at the Clydach nickel refinery, South Wales since 1930 by combining data from the two most recently published papers on this cohort., Methods: Observed and expected numbers of cancer deaths were extracted for workers who had a minimum of five years service and were employed for the first time between 1902 and 1992. Standardised mortality ratios (SMR) were calculated for subgroups according to year of employment, time since first employment, and process work., Results: A persisting excess of respiratory cancer was found for workers employed in the period 1930-92, with a lung cancer SMR of 133 (95% CI 103 to 172) and a SMR for nasal cancer of 870 (95% CI 105 to 3141). The lung cancer excess was most clearly seen 20 years or more after first employment and seemed to be confined to process workers. There was no indication of a further reduction in risk since 1930., Conclusion: The extreme nickel related cancer hazard at the refinery before 1920 was greatly reduced during subsequent years. Some of the carcinogenic exposures seem to have remained after 1930, producing an elevated risk of nasal cancer and a 30% excess of lung cancer in the workforce. There was evidence of a persisting risk among process workers first employed since 1953.

Objectives: The critical health effects of formaldehyde exposure include sensory irritation and the potential to induce tumours in the upper respiratory tract. In literature, a concentration as low as 0.24 ppm has been reported to be irritating to the respiratory tract in humans. Nasal tumour-inducing levels in experimental animals seem to be 1-2 orders of magnitude larger. In this paper, the subjectively measured sensory irritation threshold levels in humans are discussed in line with findings obtained in animal experiments. In addition, a Benchmark dose (BMD) analysis of sensory irritation was used to estimate response incidences at different formaldehyde concentrations., Methods: Data on respiratory irritation and carcinogenicity of formaldehyde were retrieved from public literature and discussed. BMD analysis was carried out on human volunteer studies using the US-EPA BMD software., Results: Subjective measures of irritation were the major data found in humans to examine sensory (eye and nasal) irritation; only one study reported objectively measured eye irritation. On a normalized scale, mild/slight eye irritation was observed at levels 1 ppm, and mild/slight respiratory tract irritation at levels 2 ppm. With the BMD software, it was estimated that at a level of 1 ppm, only 9.5% of healthy volunteers experience 'moderate' (i.e., annoying) eye irritation (95% upper confidence limit). An important factor modulating the reported levels of irritation and health symptoms most probably includes the perception of odour intensity. In several studies, the 0-ppm control condition was missing. From the results of the long-term inhalation toxicity studies in experimental animals, a level of 1 ppm formaldehyde has been considered a NOAEL for nasal injury., Conclusions: Sensory irritation is first observed at levels of 1 ppm and higher. From both human and animal studies, it was concluded that at airborne levels for which the prevalence of sensory irritation is minimal both in incidence and degree (i.e., <1 ppm), risks of respiratory tract cancer are considered to be negligibly low.

Toxicity and carcinogenicity in the mucosa of the nasal passages in rodents has been produced by a variety of organic chemicals which are systemically distributed. In this review, 14 such chemicals or classes were identified that produced rodent nasal cytotoxicity, but not carcinogenicity, and 11 were identified that produced nasal carcinogenicity. Most chemicals that affect the nasal mucosa were either concentrated in that tissue or readily activated there, or both. All chemicals with effects in the nasal mucosa that were DNA-reactive, were also carcinogenic, if adequately tested. None of the rodent nasal cytotoxins has been identified as a human systemic nasal toxin. This may reflect the lesser biotransformation activity of human nasal mucosa compared to rodent and the much lower levels of human exposures. None of the rodent carcinogens lacking DNA reactivity has been identified as a nasal carcinogen or other cancer hazard to humans. Some DNA-reactive rodent carcinogens that affect the nasal mucosa, as well as other tissues, have been associated with cancer at various sites in humans, but not the nasal cavity. Thus, findings in only the rodent nasal mucosa do not necessarily predict either a toxic or carcinogenic hazard to that tissue in humans.

We summarize studies herein that relate to use of molecular techniques to assess mechanism of toxicant and carcinogen action on the nasal mucosa. Specifically, we present the results of an in vivo mutagenesis assay with the herbicide alachlor, which causes olfactory mucosal tumors in rats following dietary administration. A positive response was found in olfactory mucosa after 3 mo of treatment. There was no increase in mutant frequency in the adjacent nasal respiratory mucosa or in liver, which are both non-target tissues for alachlor carcinogenesis. We also summarize previous findings of gene expression studies. One on these was a GeneChip experiment aimed at elucidating the mechanism of alachlor olfactory carcinogenesis, wherein we found that oxidative stress and gelatinase genes were upregulated early in the carcinogenic process, while genes consistent with activation of Wnt signaling were activated later in the carcinogenic process. The final example presented summarizes the results of a microarray experiment designed to identify novel olfactory genes involved in the plasticity of the olfactory mucosa. Those studies identified novel olfactory mucosal genes including Sgpl1 and Pon1. In each instance, precise sampling is emphasized and proper controls are discussed, and examples of independent means of validation of genomics experiments are presented.

High concentrations of propylene oxide (PO) induced inflammation in the respiratory nasal mucosa (RNM) of rodents. Concentrations > or =300 ppm caused nasal tumors. In order to investigate if glutathione depletion could be relevant for these effects, we determined in PO exposed male Fischer 344/N rats PO in blood and soluble nonprotein SH-groups (NPSH) in RNM and other tissues. Rats were exposed once (6 h) to PO concentrations between 0 and 750 ppm, and repeatedly for up to 20 days (6 h, 5 days/week) to concentrations between 0 and 500 ppm. At the end of the exposures, PO in blood and NPSH in tissues were determined. PO in blood was dependent on concentration and duration of exposure. After the 1-day exposures, NPSH depletion was most distinctive (RNM > liver > lung). Compared to controls, NPSH levels were 43% at 50 ppm PO in RNM and 16% at > or =300 ppm in both RNM and liver. Lung NPSH fell linearly to 20% at 750 ppm. After repeated exposures over 3 and 20 days to 5, 25, 50, 300, and 500 ppm, NPSH losses were less pronounced. At both time points, NPSH were 90%, 70%, 50%, 30%, and 30% of the control values in RNM. Liver NPSH decreased to 80% and 50% at 300 and 500 ppm, respectively. After 20 days, lung NPSH declined to 70% (300 ppm) and 50% (500 ppm). We conclude that continuous, severe perturbation of GSH in RNM following repeated high PO exposures may lead to inflammatory lesions and cell proliferation, critical steps on the path towards tumorigenicity.

Chronic exposure to the chloracetanilide herbicide alachlor has been shown to cause olfactory mucosal neoplasms. Genomic analysis of olfactory mucosa from rats given alachlor (126 mg/kg/d) for from 1 day to 18 mo suggested that matrix metalloproteinases MMP-2 and MMP-9 were upregulated in the month following initiation of treatment. The present studies were designed to confirm this latter finding and to explore the potential role of MMPs in alachlor-induced olfactory carcinogenesis. Zymographic analysis of olfactory mucosal extracts confirmed that MMP-2 activity is higher in the olfactory mucosa of alachlor-treated rats. Therefore, rats were fed alachlor (126 mg/kg/d in the diet for 1 year) either with or without the MMP-2/MMP-9 inhibitor Ro 28-2653 (100 mg/kg daily by gavage for the first 2 months of alachlor treatment). The number of olfactory mucosal neoplasms was reduced by 25% after 1 year of alachlor treatment in rats that received both alachlor and Ro 28-2653. The morphology of alachlor-induced olfactory tumors was similar whether or not Ro 28-2653 had been given; the MMP inhibitor itself had no impact on olfactory mucosal histology. These data confirm that olfactory mucosal MMP-2 activity is increased following short-term alachlor exposure and show that administration of an MMP-2/9 inhibitor reduced the incidence of olfactory neoplasms in alachlor-treated rats, thereby implicating MMP-2 activity as a mediator of alachlor-induced carcinogenicity.

Formaldehyde inhalation at 6 ppm and above causes nasal squamous cell carcinoma (SCC) in F344 rats. The quantitative implications of the rat tumors for human cancer risk are of interest, since epidemiological studies have provided only equivocal evidence that formaldehyde is a human carcinogen. Conolly et al. (Toxicol. Sci. 75, 432-447, 2003) analyzed the rat tumor dose-response assuming that both DNA-reactive and cytotoxic effects of formaldehyde contribute to SCC development. The key elements of their approach were: (1) use of a three-dimensional computer reconstruction of the rat nasal passages and computational fluid dynamics (CFD) modeling to predict regional dosimetry of formaldehyde; (2) association of the flux of formaldehyde into the nasal mucosa, as predicted by the CFD model, with formation of DNA-protein cross-links (DPX) and with cytolethality/regenerative cellular proliferation (CRCP); and (3) use of a two-stage clonal growth model to link DPX and CRCP with tumor formation. With this structure, the prediction of the tumor dose response was extremely sensitive to cell kinetics. The raw dose-response data for CRCP are J-shaped, and use of these data led to a predicted J-shaped dose response for tumors, notwithstanding a concurrent low-dose-linear, directly mutagenic effect of formaldehyde mediated by DPX. In the present work the modeling approach used by Conolly et al. (ibid.) was extended to humans. Regional dosimetry predictions for the entire respiratory tract were obtained by merging a three-dimensional CFD model for the human nose with a one-dimensional typical path model for the lower respiratory tract. In other respects, the human model was structurally identical to the rat model. The predicted human dose response for DPX was obtained by scale-up of a computational model for DPX calibrated against rat and rhesus monkey data. The rat dose response for CRCP was used "as is" for the human model, since no preferable alternative was identified. Three sets of baseline parameter values for the human clonal growth model were obtained through separate calibrations against respiratory tract cancer incidence data for nonsmokers, smokers, and a mixed population of nonsmokers and smokers, respectively. Additional risks of respiratory tract cancer were predicted to be negative up to about one ppm for all three cases when the raw CRCP data from the rat were used. When a hockey-stick-shaped model was fit to the rat CRCP data and used in place of the raw data, positive maximum likelihood estimates (MLE) of additional risk were obtained. These MLE estimates were lower, for some comparisons by as much as 1,000-fold, than MLE estimates from previous cancer dose-response assessments for formaldehyde. Breathing rate variations associated with different physical activity levels did not make large changes in predicted additional risks. In summary, this analysis of the human implications of the rat SCC data indicates that (1) cancer risks associated with inhaled formaldehyde are de minimis (10(-6) or less) at relevant human exposure levels, and (2) protection from the noncancer effects of formaldehyde should be sufficient to protect from its potential carcinogenic effects.

An animal model of lung carcinogenicity induced by chronic inhalation of mainstream cigarette smoke would be useful for research on carcinogenic mechanisms, smoke composition-response relationships, co-carcinogenicity, and chemoprevention. A study was conducted to determine if chronic whole-body exposures of rats would significantly increase lung tumor incidence. Male and female F344 rats (n = 81 to 178/gender) were exposed whole-body 6 h/day, 5 days/week for up to 30 months to smoke from 1R3 research cigarettes diluted to 100 (LS) or 250 (HS) mg total particulate matter/m(3), or sham-exposed to clean air (C). Gross respiratory tract lesions and standard lung and nasal sections were evaluated by light microscopy. A slight reduction of survival suggested that the HS level was at the maximum tolerated dose as commonly defined. Cigarette smoke exposure significantly increased the incidences of non-neoplastic and neoplastic proliferative lung lesions in females, while nonsignificant increases were observed in males. The combined incidence of bronchioloalveolar adenomas and carcinomas in females were: HS = 14%; LS = 6%; and C = 0%. These incidences represented minima because only standard lung sections and gross lesions were evaluated. Mutations in codon 12 of the K-ras gene occurred in 4 of 23 (17%) tumors. Three mutations were G to A transitions and one was a G to T transversion. The incidence of neoplasia of the nasal cavity was significantly increased at the HS, but not the LS level in both males and females (HS = 6%, LS = 0.3%, C = 0.4% for combined genders). These results demonstrate that chronic whole-body exposure of rats to cigarette smoke can induce lung cancer.

Formaldehyde (FA) is a mutagen that, at high concentrations and long durations, has been reported to cause nasal cancer in rats and in some humans. The level of FA-induced modified DNA in nasal cells should serve as a biomarker of FA exposure and effect. In the present study, a high-performance liquid chromatography (HPLC)-ultraviolet (UV) method at 254 nm was developed and optimized to detect and quantify hydroxymethyldeoxynucleosides after the isolated DNA in exposed human nasal epithelial cells (HNEC) was enzymically digested. Normal and modified deoxynucleosides were successfully resolved from one another and from tissue and enzyme blank interferences. The viability of HNEC exposed to FA in solution for 24 h decreased, and there was a linear dose response between % nonviability and FA dose from 10 to 500 microg/mL. Amounts of 18.0 +/- 1.5 pmol N6-dA and 12.0 +/- 1.2 pmol N2-dG derivatives were determined in a 10 microL injection after 1.4 x 10(7) HNEC (106 microg DNA) were exposed to 500 microg/mL in solution. The respective tissue concentrations in pmol hydroxymethyldeoxynucleoside/mg DNA were 170 +/- 14 and 113 +/- 11. The lower quantifiable limits were about 97 and 88 pmol/mg DNA, respectively. Diffusive exposure of HNEC to air FA up to 100 ppm (v/v) for 24 h did not produce quantifiable hydroxymethylnucleosides. FA-modified deoxynucleosides may be useful biomarkers for FA exposure in biological monitoring samples taken by nasal lavage or brush biopsy.

Naphthalene (CAS No. 91-20-3) administered by inhalation at concentrations of 10, 30, or 60 ppm for 6 hours per day, 5 days per week for 105 weeks caused nonneoplastic and neoplastic effects in nasal respiratory and olfactory regions of male and female F344/N rats. Non-neoplastic nasal effects were characterized by an increase in the incidence and severity of a complex group of lesions, including atypical hyperplasia, atrophy, chronic inflammation, and hyaline degeneration of olfactory epithelium; hyperplasia, squamous metaplasia, hyaline degeneration, and goblet cell hyperplasia of the respiratory epithelium; and hyperplasia and squamous metaplasia of mucosal glands. Neoplastic effects were characterized by the induction of two types of rare primary nasal tumors, olfactory neuroblastomas and respiratory epithelial adenomas. The incidences of olfactory neuroblastomas in males at 0 ppm, 10 ppm, 30 ppm, and 60 ppm were, respectively, 0%, 0%, 8%, and 6%, whereas in females they were 0%, 4%, 6%, and 24%. The incidences of respiratory epithelial adenomas in males at 0 ppm, 10 ppm, 30 ppm, and 60 ppm were, respectively, 0%, 12%, 17%, and 31% and in females 0%, 0%, 8%, and 4%. The olfactory neuroblastomas and respiratory epithelial adenomas were considered carcinogenic effects related to naphthalene exposure based on their relatively high incidence in exposed rats, their absence in concurrent control rats and NTP historical controls, and their rare spontaneous occurrence in rats of any strain.

Formaldehyde inhalation at 6 ppm and above causes nasal squamous cell carcinoma (SCC) in F344 rats. The human health implications of this effect are of significant interest since human exposure to environmental formaldehyde is widespread, though at lower concentrations than those that cause cancer in rats. In this article, which is part of a larger effort to predict the human cancer risks of inhaled formaldehyde, we describe biologically motivated quantitative modeling of the exposure-tumor response continuum in the rat. An anatomically realistic, three-dimensional fluid dynamics model of the F344 rat nasal airways was used to predict site-specific flux of formaldehyde from inhaled air into tissue, since both SCC and preneoplastic lesions develop in a characteristic site-specific pattern. Flux into tissue was used as a dose metric for two modes of action, direct mutagenicity and cytolethality-regenerative cellular proliferation (CRCP), which in turn were linked to key parameters of a two-stage clonal growth model. The direct mutagenicity mode of action was represented by a low dose linear dose-response model of DNA-protein cross-link (DPX) formation. An empirical J-shaped dose-response model and a threshold model fit to the empirical data were used for CRCP. In the clonal growth model, the probability of mutation per cell generation was a function of the tissue concentration of DPX while the rate of cell division was calculated from the CRCP data. Maximum likelihood methods were used to estimate parameter values. Survivor (a nontumor outcome) and tumor data for controls from the National Toxicology Program database and from two formaldehyde inhalation bioassays were used for likelihood calculations. The J-shaped dose-response for CRCP provided a better description of the SCC data than did the threshold model. Sensitivity analyses indicated that the rodent tumor response is due to the CRCP mode of action, with the directly mutagenic pathway having little, if any, influence. When evaluated in light of modeling and database uncertainties, particularly the specification of the clonal growth model and the dose-response data for CRCP, this work provides suggestive though not definitive evidence for a J-shaped dose-response for formaldehyde-mediated nasal SCC in the F344 rat.

Formaldehyde induced squamous-cell carcinomas in the nasal passages of F344 rats in two inhalation bioassays at exposure levels of 6 ppm and above. Increases in rates of cell proliferation were measured by T. M. Monticello and colleagues at exposure levels of 0.7 ppm and above in the same tissues from which tumors arose. A risk assessment for formaldehyde was conducted at the CIIT Centers for Health Research, in collaboration with investigators from Toxicological Excellence in Risk Assessment (TERA) and the U.S. Environmental Protection Agency (U.S. EPA) in 1999. Two methods for dose-response assessment were used: a full biologically based modeling approach and a statistically oriented analysis by benchmark dose (BMD) method. This article presents the later approach, the purpose of which is to combine BMD and pharmacokinetic modeling to estimate human cancer risks from formaldehyde exposure. BMD analysis was used to identify points of departure (exposure levels) for low-dose extrapolation in rats for both tumor and the cell proliferation endpoints. The benchmark concentrations for induced cell proliferation were lower than for tumors. These concentrations were extrapolated to humans using two mechanistic models. One model used computational fluid dynamics (CFD) alone to determine rates of delivery of inhaled formaldehyde to the nasal lining. The second model combined the CFD method with a pharmacokinetic model to predict tissue dose with formaldehyde-induced DNA-protein cross-links (DPX) as a dose metric. Both extrapolation methods gave similar results, and the predicted cancer risk in humans at low exposure levels was found to be similar to that from a risk assessment conducted by the U.S. EPA in 1991. Use of the mechanistically based extrapolation models lends greater certainty to these risk estimates than previous approaches and also identifies the uncertainty in the measured dose-response relationship for cell proliferation at low exposure levels, the dose-response relationship for DPX in monkeys, and the choice between linear and nonlinear methods of extrapolation as key remaining sources of uncertainty.