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Clark et al. (accepted for publication) reported that a sample of field-matched fume condensate from a Type III built-up roofing asphalt (BURA) resulted in a carcinogenic response in a mouse skin bioassay, with relatively few tumor-bearing animals, long tumor latency and chronic skin irritation. This mouse skin initiation/promotion study was conducted to assess possible mechanisms, i.e., genotoxic initiation vs. tumor promotion subsequent to repeated skin injury and repair. The same Type III BURA fume condensate sample was evaluated in groups of 30 male Crl:CD1® mice by skin application twice per week (total dose of 50 mg/week) for 2 weeks during the initiation phase and for 26 weeks during the promotion phase. Positive control substances were 7,12-dimethylbenz(a)anthracene (DMBA, 50 μg applied once) as an initiator and 12-O-tetradecanoyl-13-acetate (TPA, 5 μg, applied twice weekly) during the promotion phase. During the 6 months of study with the asphalt fume condensate, eight skin masses were observed when tested for initiation, five of which were confirmed microscopically to be benign squamous cell papillomas. Only two papillomas were observed when tested for promotion. There was no apparent relationship between skin irritation and tumor development in this study. These results are more indicative of genotoxicity rather than a non-genotoxic mode of action.

The potential reproductive toxicity of di-isononyl phthalate (DINP: CAS RN 68515-48-0) was assessed in one- and two-generation reproductive toxicity studies. Groups of 30 male and female CRL : CD(SD)BR rats were given DINP via dietary administration at levels of either 0.0, 0.5, 1, or 1.5% (one-generation study) or 0.0, 0.2, 0. 4, or 0.8% (two-generation study). There were no changes in any of the classic reproductive parameters, i.e. mating, male or female fertility, fecundity, gestational index, or length of gestation in either study. The overall NOAELs for these effects were the highest Dietary Level (%)s tested, approximately 500 mg/kg/day in the two-generation study and 1000 mg/kg/day in the one-generation study. There were no testicular effects in parental animals exposed as juveniles and young adults at 960 mg/kg/day in the one-generation study. In the two-generation study, there were no testicular effects in either the P(1) males, exposed as juveniles and young adults or the P(2) (F(1)) offspring exposed in utero, through lactation, and continuously to terminal sacrifice. The NOAEL was 470 mg/kg/day. Offspring survival was reduced at the 1.5% level ( approximately 1100 mg/kg/day) but unaffected at the 1% level ( approximately 760 mg/kg/day). There were decreased offspring body weights both at postnatal day (PND) 0 and during lactation; however, the PND 0 effects were only clearly related to treatment at the 1.5% level. Weights of offspring during lactation were significantly reduced but within the historical control range at Dietary Level (%)s below 1%. As there was rapid recovery at the lower levels, even though treatment continued, the toxicologic significance is unclear. Adult survival was unaffected at any level in either study, but weight gain was significantly reduced at the 1% level ( approximately 600 mg/kg/day). Liver and kidney weights were elevated at Dietary Level (%)s above approximately 110 mg/kg/day, consistent with evidence from other studies of peroxisomal proliferation at these levels. This study showed that DINP treatment does not affect fertility or male reproductive development at doses of up to approximately 1000 mg/kg/day.

Certain cells present in mouse skin are resistant to calcium-induced terminal differentiation. It is believed that these calcium-resistant cells (CRCs) represent an early stage in the carcinogenic process, in part, because frequency increases after treatment with mutagens. The frequency of CRCs in C3H mouse skin was measured before and after treatment with certain petroleum-derived materials. One objective was to determine whether this assay could differentiate between genotoxic and nongenotoxic mouse skin carcinogens. An additional objective was to determine whether CRCs are an important factor in the tumorigenicity of petroleum middle distillates (PMDs), a class of apparently nongenotoxic mateials. Three petroleum-derived materials were tested: mineral oil (MO), a noncarcinogenic product used as the negative control; catalytically cracked clarified oil (CCCO), a highly carcinogenic and mutagenic material; and a lightly paraffinic (LRPO), a PMD which has produced tumors when repeatedly applied, but is not mutagenic and does not initiate most skin tumors. The CRC frequency was not increased by LRPO treatment; however, a statistically significant and dose-related increase was produced by CCCO. These results are consistent with observations that genotoxic, petroleum-derived liquids are capable of tumor initiation in mouse skin, whereas PMDs which are not genotoxic do not initiate skin tumors. The number of CRCs in untreated and MO-treated mice was approximately twice the tumor frequency measured in bioassays of PMDs. Thus, tumor production associated with these products could be due to promotion of preexisting, spontaneously initiated cells.

Two-year skin carcinogenicity studies were conducted in C3H mice to assess the effects of irritation and selected compositional parameters on the carcinogenic potential of four petroleum liquids. Three samples (lightly refined paraffinic oil, LRPO; lightly hydrodesulfurized specialty oil, LHSO; jet fuel, JF) can be generically classified as middle distillates, i.e. distillation occurs between 350 and 700 degrees F (175-370 degrees C). The fourth sample was a Steam Cracked Gas Oil (SCGO) that distilled within the same range. In studies that assess the effects of irritation on tumorigenicity, LRPO was tested undiluted or was diluted to 50% and 25% in either mineral oil (which eliminated irritation of the skin) or toluene (which did not). Undiluted LRPO elicited tumors in 8% of the mice. Both dilution procedures eliminated tumorigenic potential. Thus, it was possible to maintain a visible level of skin irritation equivalent to that elicited by undiluted LRPO without inducing tumors. SCGO elicited a chronic irritant state grossly equivalent to LRPO but was not tumorigenic. Jet Fuel A (JF) was tested undiluted using both a standard skin painting protocol and an intermittent dosing schedule in which treatment was suspended periodically to allow skin irritation to resolve. The standard treatment protocol of JF resulted in both marked skin irritation and tumors in 44% of the mice. However, using the intermittent schedule, the tumor yield was reduced to 2%. Collectively these data demonstrate that tumor formation is not a necessary sequelae to chronic skin irritation. Conversely, prevention of a marked chronic irritant state was accompanied by decreased tumor yield. These data suggest that the chronic irritant state may be a necessary but not sufficient condition for tumor formation. In studies to assess the effects of compositional parameters, a lightly hydrodesulfurized specialty oil (LHSO) similar to LRPO but refined to have negligible levels of sulfur compounds (3 ppm), elicited chronic irritant and tumor responses (10%) similar to LRPO. Thus, the level of sulfur compounds does not appear to affect the tumorigenic activity for products in this boiling range. The SCGO which did not produce tumors contained only aromatic hydrocarbons, a finding consistent with previous reports that aromatics may not be the source of tumorigenic potential in petroleum fractions boiling between 350 and 700 degrees F (175-370 degrees C).

The metabolism of saturated nitriles, including acetonitrile, has been assumed to occur by a cytochrome P-450-dependent oxidation at the alpha-carbon, yielding a cyanohydrin intermediate which may spontaneously degrade to hydrogen cyanide and an aldehyde. However, results of studies in our laboratory suggest that formaldehyde is not a metabolite of acetonitrile. Since acetonitrile is structurally similar to iodomethane, a substrate for glutathione (GSH) S-transferases, we hypothesized that the metabolism of acetonitrile to cyanide might also occur by a nucleophilic substitution reaction involving GSH. The present studies were conducted to investigate these hypotheses and to further our study of the effects of acetone on acetonitrile metabolism. Female Sprague-Dawley rats were pretreated with buthionine sulfoximine BSO (4 mmol/kg ip, at -4 and -2 hr), cobalt heme (90 mumol/kg sc, at -48 hr), acetone (1960 mg/kg po, at -24 hr), or vehicle, and hepatocytes were isolated after collagenase perfusion of the liver. BSO reduced the cellular GSH content by greater than 80%, but did not appear to affect the metabolism of acetonitrile: the liberation of cyanide correlated with cytochrome P-450, and not GSH, concentrations. Cobalt heme depleted hepatocellular cytochrome P-450 (-45%) content, decreased cell yield and viability, and resulted in a marked reduction in the metabolism of acetonitrile to cyanide. Cobalt heme did not affect the recovery of sodium cyanide from hepatocyte suspensions. Pretreatment of rats with acetone resulted in a twofold increase in the metabolism of acetonitrile to cyanide. Addition of acetone in vitro inhibited acetonitrile metabolism, with an IC50 of 319 microM.(ABSTRACT TRUNCATED AT 250 WORDS)

Oral acetone exposure delays and potentiates acetonitrile toxicity in rats. Results of previous pharmacokinetic studies suggested that acetone exerted a biphasic effect on the metabolism of acetonitrile to cyanide; the presence of acetone in vivo appeared to inhibit the metabolism of acetonitrile to cyanide, whereas the disappearance of acetone from serum was followed by stimulation of acetonitrile metabolism. The current experiments were designed to characterize further the metabolism of acetonitrile to cyanide and the effects of acetone and other compounds upon this metabolism. Liver microsomes were isolated and pooled 24 hr after oral pretreatment of female Sprague-Dawley rats (180-250 g) with acetone (1960 mg/kg) or water. Microsomal metabolism of acetonitrile to cyanide was found to be oxygen and NADPH dependent, and heat-inactivated tissue was unable to catalyze the reaction. NADH antagonized the NADPH-dependent metabolism of acetonitrile. The metabolism of acetonitrile to cyanide was linear with protein concentrations of 0-8 mg per incubation. Following a characteristic lag period of 10 min, the reaction was linear from 15 to 30 min. This metabolism was inhibited by carbon monoxide, metyrapone and SKF 525-A. Acetone pretreatment (-24 hr) in vivo increased the apparent Vmax for acetonitrile metabolism without affecting the apparent Km. When added in vitro, acetone competitively inhibited the metabolism of acetonitrile, with a KI of 0.41 mM. Dimethyl sulfoxide (KI = 0.51 mM) and ethanol (KI = 0.11 mM) were also competitive inhibitors of acetonitrile metabolism, and aniline HCl (KI = 4.77 microM) appeared to be a mixed inhibitor. These data are consistent with the hypothesis that the metabolism of acetonitrile to cyanide is mediated by a specific acetone-inducible isozyme of cytochrome P-450.