Pyrogallol-associated dermal toxicity and carcinogenicity in F344/N rats and B6C3F1/N mice.

Pyrogallol (CAS No. 87-66-1), a benzenetriol used historically as a hair dye and currently in a number of industrial applications, was nominated to the National Toxicology Program (NTP) for testing based on the lack of toxicity and carcinogenicity data. Three-month and two-year toxicity studies to determine the toxicity and carcinogenicity of pyrogallol when applied to naïve skin (i.e. dermal administration) were conducted in both sexes of F344/N rats and B6C3F1/N mice. In the three-month studies, adult rodents were administered pyrogallol in 95% ethanol five days per week for 3 months at doses of up to 150 mg/kg body weight (rats) or 600 mg/kg (mice). Based on the subchronic studies, the doses for the two-year studies in rats and mice were 5, 20 and 75 mg/kg of pyrogallol. All mice and most rats survived until the end of the three-month study and body weights were comparable to controls. During the two-year study, survival of dosed rats and male mice was comparable to controls; however survival of 75 mg/kg female mice significantly decreased compared to controls. The incidences of microscopic non-neoplastic lesions at the site of application were significantly higher in all dosed groups of rats and mice and in both the 3-months and two-year studies. In the two-year study, hyperplasia, hyperkeratosis and inflammation tended to be more severe in mice than in rats, and in the mice they tended to be more severe in females than in males. The incidence of squamous cell carcinoma at the site of application (SOA) in 75 mg/kg female mice and SOA squamous cell papillomas in 75 mg/kg male mice were greater than controls. Pyrogallol was carcinogenic in female mice and may have caused tumors in male mice.

Hepatic gene expression changes throughout the day in the Fischer rat: implications for toxicogenomic experiments.

There is increasing use of transcriptional profiling in hepatotoxicity studies in the rat. Understanding hepatic gene expression changes over time is critical, since tissue collection may occur throughout the day. Furthermore, when comparing results from different data sets, times of dosing and tissue collection may vary. Circadian effects on the mouse hepatic transcriptome have been well documented. However, limited reports exist for the rat. In one study approximately 7% of the hepatic genes showed a diurnal expression pattern in a comparison of rat liver samples collected during the day versus livers collected at night. The results of a second study comparing rat liver samples collected at multiple time points over a circadian day suggest only minimal variation of the hepatic transcriptome. We studied temporal hepatic gene expression in 48 untreated F344/N rats using both approaches employed in these previous studies. Statistical analysis of microarray (SAM) identified differential expression in day/night comparisons, but was less sensitive for liver samples collected at multiple times of day. However, a Fourier analysis identified numerous periodically expressed genes in these samples including period genes, clock genes, clock-controlled genes, and genes involved in metabolic pathways. Furthermore, rhythms in gene expression were identified for several circadian genes not previously reported in the rat liver. Transcript levels for twenty genes involved in circadian and metabolic pathways were confirmed using quantitative RT-PCR. The results of this study demonstrate a prominent circadian rhythm in gene expression in the rat that is a critical factor in planning toxicogenomic experiments.

Perinatal toxicity and carcinogenicity studies of styrene-acrylonitrile trimer, a ground water contaminant.

Styrene acrylonitrile (SAN) trimer is a by-product in the production of acrylonitrile styrene plastics. Following a report of a childhood cancer cluster in the Toms River section of Dover Township, New Jersey, SAN Trimer was identified as one of the groundwater contaminants at Reich Farm Superfund site in the township. The contaminants from the Reich Farm site's ground water plume impacted two wells at the Parkway well field. The National Toxicology Program (NTP) studied the toxicity and carcinogenicity of SAN Trimer in rats exposed during their perinatal developmental period and adulthood. The chronic toxicity and carcinogenicity studies in F344/N rats were preceded by 7- and 18-week perinatal toxicity studies to determine the exposure concentrations for the 2-year studies. Subsequently, Fisher 344 pregnant dams were exposed to SAN Trimer containing diet at 400, 800, or 1600ppm concentrations during gestation, nursing and weaning periods of offspring followed by two year of adult exposures to both male and female pups. There was no statistically significant evidence of carcinogenic activity following SAN-Trimer exposure; however, rare neoplasms in the brain and spinal cord were observed in males and to lesser extent in female rats. These incidences were considered within the range of historical background in the animal model used in the current studies. Therefore, the presence of a few rarely occurring CNS tumors in the treated groups were not judged to be associated with the SAN Trimer exposure. The major finding was a dose-related peripheral neuropathy associated with the sciatic nerves in females and spinal nerve roots in males and females thereby suggesting that SAN Trimer is potentially a nervous system toxicant.

Variation in the hepatic gene expression in individual male Fischer rats.

A new tool beginning to have wider application in toxicology studies is transcript profiling using microarrays. Microarrays provide an opportunity to directly compare transcript populations in the tissues of chemical-exposed and unexposed animals. While several studies have addressed variation between microarray platforms and between different laboratories, much less effort has been directed toward individual animal differences especially among control animals where RNA samples are usually pooled. Estimation of the variation in gene expression in tissues from untreated animals is essential for the recognition and interpretation of subtle changes associated with chemical exposure. In this study hepatic gene expression as well as standard toxicological parameters were evaluated in 24 rats receiving vehicle only in 2 independent experiments. Unsupervised clustering demonstrated some individual variation but supervised clustering suggested that differentially expressed genes were generally random. The level of hepatic gene expression under carefully controlled study conditions is less than 1.5-fold for most genes. The impact of individual animal variability on microarray data can be minimized through experimental design.