Immunohistochemical localization of p53, PCNA, and TGF-alpha proteins in formaldehyde-induced rat nasal squamous cell carcinomas

Preorbital carcinoma in two Kirk's dik-diks (Madoqua kirkii)

Two Kirk's dik-diks suffered from chronic, unilateral, therapy-resistant enlargement of the preorbital gland. Computed tomographic imaging revealed a homogenous preorbital mass destroying the adjacent maxillary bone in one animal. Squamous cell carcinoma was diagnosed microscopically in both cases. Immunohistochemically, the neoplastic cells uniformly expressed cytokeratin (CK) 5/6 and CK14. Additionally, tumour cells were strongly labelled for p53 suggesting a possible role of this tumour suppressor gene in tumorigenesis. Chronic obstruction of the preorbital gland due to excessive accumulation of secretory products is considered as a likely cause of glandular and periglandular inflammation with subsequent malignant transformation.

Measurement of tumor-associated mutations in the nasal mucosa of rats exposed to varying doses of formaldehyde

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.

Uncertainties in biologically-based modeling of formaldehyde-induced respiratory cancer risk: identification of key issues

In a series of articles and a health-risk assessment report, scientists at the CIIT Hamner Institutes developed a model (CIIT model) for estimating respiratory cancer risk due to inhaled formaldehyde within a conceptual framework incorporating extensive mechanistic information and advanced computational methods at the toxicokinetic and toxicodynamic levels. Several regulatory bodies have utilized predictions from this model; on the other hand, upon detailed evaluation the California EPA has decided against doing so. In this article, we study the CIIT model to identify key biological and statistical uncertainties that need careful evaluation if such two-stage clonal expansion models are to be used for extrapolation of cancer risk from animal bioassays to human exposure. Broadly, these issues pertain to the use and interpretation of experimental labeling index and tumor data, the evaluation and biological interpretation of estimated parameters, and uncertainties in model specification, in particular that of initiated cells. We also identify key uncertainties in the scale-up of the CIIT model to humans, focusing on assumptions underlying model parameters for cell replication rates and formaldehyde-induced mutation. We discuss uncertainties in identifying parameter values in the model used to estimate and extrapolate DNA protein cross-link levels. The authors of the CIIT modeling endeavor characterized their human risk estimates as "conservative in the face of modeling uncertainties." The uncertainties discussed in this article indicate that such a claim is premature.

Formaldehyde and glutaraldehyde and nasal cytotoxicity: case study within the context of the 2006 IPCS Human Framework for the Analysis of a cancer mode of action for humans

Formaldehyde and glutaraldehyde cause toxicity to the nasal epithelium of rats and mice upon inhalation. In addition, formaldehyde above certain concentrations induces dose-related increases in nasal tumors in rats and mice, but glutaraldehyde does not. Using the 2006 IPCS human framework for the analysis of cancer mode of action (MOA), an MOA for formaldehyde was formulated and its relevance was tested against the properties of the noncarcinogenic glutaraldehyde. These compounds produce similar patterns of response in histopathology and in genotoxicity tests (although formaldehyde has been much more extensively tested studied). The MOA is based on the induction of sustained cytotoxicity and reparative cell proliferation induced by formaldehyde at concentrations that also induce nasal tumors upon long-term exposure. Data on dose dependency and temporal relationships of key events are consistent with this MOA. While a genotoxic MOA can never be ruled out for a compound that is clearly genotoxic, at least in vitro, the nongenotoxic properties fundamental to the proposed MOA can explain the neoplastic response in the nose and may be more informative than genotoxicity in risk assessment. It is not yet fully explained why glutaraldehyde remains noncarcinogenic upon inhalation, but its greater inherent toxicity may be a key factor. The dual aldehyde functions in glutaraldehyde are likely to produce damage resulting in fewer kinetic possibilities (particularly for proteins involved in differentiation control) and lower potential for repair (nucleic acids) than would be the case for formaldehyde. While there have been few studies of possible glutaraldehyde-associated cancer, the evidence that formaldehyde is a human carcinogen is strong for nasopharyngeal cancers, although less so for sinonasal cancers. This apparent discrepancy could be due in part to the classification of human nasal tumors with tumors of the sinuses, which would receive much less exposure to inhaled formaldehyde. Evaluation of the human relevance of the proposed MOA of formaldehyde in rodents is restricted by human data limitations, although the key events are plausible. It is clear that the human relevance of the formaldehyde MOA in rodents cannot be excluded on either kinetic or dynamic grounds.

Nasal biopsies of children exposed to air pollutants

Southwest Metropolitan Mexico City (SWMMC) atmosphere is a complex mixture of air pollutants, including ozone, particulate matter, and aldehydes. Children in SWMMC are exposed chronically and sequentially to numerous toxicants, and they exhibit significant nasal damage. The objective of this study was to assess p53 accumulation by immunohistochemistry in nasal biopsies of SWMMC children. We evaluated 111 biopsies from 107 children (83 exposed SWMMC children and 24 control children residents in a pollutant-compliant Caribbean island). Complete clinical histories and physical examinations, including an ear-nose-throat (ENT) exam were done. There was a significant statistical difference in the upper and lower respiratory symptomatology and ENT findings between control and exposed children (p < 0.001). Control children gave no respiratory symptomatology in the 3 months prior to the study; their biopsies exhibited normal ciliated respiratory epithelium and were p53-negative. SWMMC children complained of epistaxis, nasal obstruction. and crusting. Irregular areas of whitish-gray recessed mucosa over the inferior and middle turbinates were seen in 25% of SWMMC children, and their nasal biopsies displayed basal cell hyperplasia, decreased numbers of ciliated and goblet cells, neutrophilic epithelial infiltrates, squamous metaplasia. and mild dysplasia. Four of 21 SWMMC children with grossly abnormal mucosal changes exhibited strong transmural nuclear p53 staining in their nasal biopsies (p 0.005, odds ratio 26). In the context of lifetime exposures to toxic and potentially carcinogenic air pollutants, p53 nasal induction in children could potentially represent. a) a checkpoint response to toxic exposures, setting up a selective condition for p53 mutation, or b) a p53 mutation has already occurred as a result of such selection. Because the biological significance of p53 nuclear accumulation in the nasal biopsies of these children is not clear at this point, we strongly suggest that children with macroscopic nasal mucosal abnormalities should be closely monitored by the ENT physician. Parents should be advised to decrease the children's number of outdoor exposure hours and encourage a balanced diet with an important component of fresh fruits and vegetables.

Aberrant expression of cyclin D1 in pulmonary proliferative lesions induced by high doses of urethane in transgenic mice carrying the human prototype c-H-ras gene

In our previous study, when rasH2 mice and non-transgenic (non-Tg) littermates were injected intraperitoneally with 1,000 mg/kg of urethane once or three times at two-day intervals, the incidence of lung proliferative lesions in rasH2 mice given triple doses of urethane was significantly increased, compared to that in rasH2 mice given a single dose of urethane, and the mutation frequency of the transgene in lung tumors in rasH2 mice given triple doses was lower than that in rasH2 mice given a single dose of urethane. In the present study, differential immunohistochemical expressions of Cyclin D1 and PCNA, that lead to abnormal cell proliferation and tumor development due to uncontrolled G1-S transition in the cell cycle, as well as p53 tumor suppressor gene in pulmonary proliferative lesions obtained from our previous study were investigated. Over-expression of Cyclin D1 in hyperplasias in rasH2 mice given triple doses was significantly increased, compared to that in the single-injection group, but no significant differences in Cyclin D1 between the single and triple injection groups were observed in hyperplasias in non-Tg mice or lung tumors in either rasH2 or non-Tg mice. There were no differences in the PCNA labeling index of hyperplasias in rasH2 or non-Tg mice between the triple-injection and single-injection groups, while the PCNA labeling index tended to be increased in the tumor, compared with that in hyperplasias. There was neither mutation of p53 nor an increase in immunoreactivity of wild type p53 in these proliferative lesions. These results suggest that cyclin D1 over-expression in alveolar/bronchiolar hyperplasias in rasH2 mice in the triple-injection group is not only indicative of a high cell proliferation rate but also of an important role in the process of malignant transformation.

Evolution of alachlor-induced nasal neoplasms in the Long-Evans rat

The chloracetanilide herbicide alachlor (2-chloro-2',6-diethyl-N-(methoxymethyl)-acetanilide) induces nasal neoplasms in rats following chronic dietary exposure. The present study sought to identify the cellular origin and mechanisms of tumor induction and progression. Male Long-Evans rats were fed alachlor (0 or 126 mg/kg/day) beginning at 6 weeks of age. Following 1 month of alachlor ingestion, neither histological abnormalities nor enhanced cell division (assessed by BrdU incorporation) occurred in any region of the nasal cavity. Six months of alachlor exposure resulted in proliferation of basal and nonbasal cells in the olfactory mucosa while inducing nasal masses in 7 of 15 animals. Tumors ranged from dysplastic plaques to polypoid adenomas and originated in the olfactory regions of the nasal cavity. Neoplasms were associated with regions of respiratory metaplasia and were often covered with a low cuboidal, poorly ciliated epithelium. Tumor cells did not express characteristics of the olfactory mucosa, including olfactory marker protein (OMP, for neurons) and NMa (antibody recognizing cytochrome P450 [CYP] 2A3, found in Bowman's glands). Sites of plaque and tumor development coincided with regions of NMa immunoreactivity. These data suggest that local metabolism is important in alachlor-induced olfactory tumors and support the concept that metaplastic respiratory epithelial cells give rise to the observed neoplasms.

Immunohistochemical and clinical evaluation of p53 in canine cutaneous mast cell tumors

One hundred twenty-six cutaneous mast cell tumors obtained by excisional biopsy from 106 dogs were evaluated using immunohistochemical staining for the presence of p53 protein. A standard avidin-biotin immunohistochemical protocol was used incorporating a polyclonal antibody of rabbit origin (CM-1) as the primary antibody. Histopathologic grading of tumors was performed on hemotoxylin and eosin-stained samples. There was a significant difference in the percentage of cells staining positive for p53 for the histopathologic grades (P = 0.0005). Grade III tumors had a significantly greater p53 content than did grade I or II tumors (P < 0.05). Clinical data obtained retrospectively was available for 54 dogs. Tumor recurred in 19 of 54 (35.2%) dogs. Twenty-nine dogs died by the end of the study; 9 of 29 (31.0%) died of mast cell tumor disease. Histopathologic grade showed a significant negative association with survival time. Both clinical stage and histopathologic grade showed a significant negative association with time to recurrence. The percentage of cells staining positive for p53 did not significantly improve the forward analysis. Immunohistochemical detection of p53 did not appear useful in characterizing the clinical association between cutaneous mast cell tumor cellular features and survival time or time to tumor recurrence in dogs.

Spontaneous proliferative lesions in the nasopharyngeal meatus of F344 rats

Spontaneous proliferative lesions in the nasopharyngeal meatus were identified as the cause of death in 12 of 1,600 male and 5 of 1,600 female Fisher 344 (F344) rats used in 2-yr carcinogenicity studies; none of the lesions were considered treatment related. All the rats showed dyspnea, abdominal distension, and clinical deterioration. Gross features were characterized by simultaneous occurrence of conspicuous gaseous distension of the intestinal tract, especially in the ileum and cecum, and focal nodular lesions in the nasopharyngeal meatus. Histopathologically, the nasopharyngeal meatus was partially obstructed by the following proliferative lesions: 3 areas of hyperplasia of the ectopic sebaceous glands in the soft and hard palate, 4 areas of squamous metaplasia (SM) with massive hyperkeratosis, 5 squamous cell papillomas (SCPs), and 5 squamous cell carcinomas (SCCs). No pathological changes were found in the distended portion of the intestinal tract. Formalin-fixed, paraffin-embedded samples of the proliferative lesions from the nasopharyngeal meatus were examined for the presence of mutations in the c-H-ras and c-K-ras genes. In vitro amplification of DNA using a polymerase chain reaction was combined with a nonisotopic method for selective oligonucleotide hybridization. Two of the 4 SM lesions, 3 of the 5 SCPs, and 5 of the 5 SCCs contained 1-3 point mutations in the c-H-ras and/or c-K-ras gene. Immunohistochemically, overexpression of p53 protein was found in 1 area of SM with a dysplastic lesion and 2 SCCs. These findings indicate that detailed examination of the upper respiratory system, including the nasopharyngeal meatus, may be particularly helpful for identifying primary occult lesions in F344 rats that show only gut distension at necropsy in long-term toxicity studies. In addition, mutations of the ras genes may be an important step in the early stages of carcinogenesis in the rat nasopharyngeal meatus, whereas p53 mutations could occur relatively late.

Oncogene and tumor suppressor gene alterations in nasal tumors

The development of nasal tumors in humans and rodents is likely mediated through the accumulation of genetic alterations in genes that regulate cell proliferation, cell death and differentiation (oncogenes and tumor suppressor genes). By examination of the relationship between genetic alterations that are known to occur in human cancers with those induced in rodent tumors with defined carcinogenic exposures, biologically relevant mechanistic linkages of molecular events leading to tumors in rodents and humans can be established. Molecular genetic studies on nasal squamous cell carcinomas (SCC) in rats thus far have indicated the presence of oncogenes unrelated to the ras oncogene family and that p53 mutation occurs at a high frequency among the nasal SCC examined. The finding of p53 mutations in rat nasal SCC and the high prevalence of p53 mutations among human SCC, indicates that a common molecular alteration is shared between rodent and human SCC.

Absence of p53 gene mutations in rat colon carcinomas induced by azoxymethane

The K-ras and p53 genes are two of the most frequently mutated genes found in the human colonic tumors. Since azoxymethane (AOM) induced rat colonic neoplasms are similar to human colonic tumors in their histological features and proliferation characteristics, the rat has been used as an experimental model to study the pathogenesis of colon cancer in humans. Although the presence of K-ras point mutations has been reported in AOM induced rat colonic tumors, there are no reports describing the frequency for mutation of the p53 gene in these tumors. In this study, colon adenocarcinomas induced in rats by AOM were examined for the presence of point mutations in exons 5-8 of the p53 gene, using a combination of single strand conformation (SSCP) analysis, immunohistochemistry and direct DNA sequencing. SSCP analysis showed no differences in banding patterns between the normal mucosa and any of the 20 adenocarcinomas analyzed. Nuclear p53 immunoreactivity was absent in all tumors examined. Since p53 point mutations predominate in malignant colonic tumors, five adenocarcinomas with the greatest local invasiveness were analyzed by direct DNA sequencing of exons 5-8 of the p53 gene. Direct DNA sequencing did not reveal mutations in any of the adenocarcinomas analyzed, within the coding region of p53 gene that were sequenced. The results from the present study indicate that point mutations in the p53 gene, at least in the coding region (exons 5-8) are not involved in the development of colon cancer induced by AOM in the rat.