Exposure to hexavalent chromium resulted in significantly higher tissue chromium burden compared with trivalent chromium following similar oral doses to male F344/N rats and female B6C3F1 mice.

In National Toxicology Program 2-year studies, hexavalent chromium [Cr(VI)] administered in drinking water was clearly carcinogenic in male and female rats and mice, resulting in small intestine epithelial neoplasms in mice at a dose equivalent to or within an order of magnitude of human doses that could result from consumption of chromium-contaminated drinking water, assuming that dose scales by body weight(3/4) (body weight raised to the 3/4 power). In contrast, exposure to trivalent chromium [Cr(III)] at much higher concentrations may have been carcinogenic in male rats but was not carcinogenic in mice or female rats. As part of these studies, total chromium was measured in tissues and excreta of additional groups of male rats and female mice. These data were used to infer the uptake and distribution of Cr(VI) because Cr(VI) is reduced to Cr(III) in vivo, and no methods are available to speciate tissue chromium. Comparable external doses resulted in much higher tissue chromium concentrations following exposure to Cr(VI) compared with Cr(III), indicating that a portion of the Cr(VI) escaped gastric reduction and was distributed systemically. Linear or supralinear dose responses of total chromium in tissues were observed following exposure to Cr(VI), indicating that these exposures did not saturate gastric reduction capacity. When Cr(VI) exposure was normalized to ingested dose, chromium concentrations in the liver and glandular stomach were higher in mice, whereas kidney concentrations were higher in rats. In vitro studies demonstrated that Cr(VI), but not Cr(III), is a substrate of the sodium/sulfate cotransporter, providing a partial explanation for the greater absorption of Cr(VI).

Effect of dose volume on the toxicokinetics of acrylamide and its metabolites and 2-deoxy-D-glucose.

Acrylamide (AA) is a known mutagen and animal carcinogen. Comparison of recent studies revealed significant quantitative differences in AA-induced germ cell mutagenicity. It was hypothesized that despite the administration of AA at similar doses, the discrepancy in the observed effects was most likely due to varying AA concentrations in the administered dosing solution. To test this hypothesis, AA was administered i.p. to mice at 50 mg/kg in a dose volume of 5 or 50 ml/kg, blood was collected at various time points, and AA and its metabolites were quantitated. Changes in dose volume resulted in significant differences in the toxicokinetics of AA and its metabolites and suggested that increased C(max) of AA led to increased metabolism. This theory, in conjunction with the fact that higher levels of AA-derived radioactivity were detected in the testes, may explain the greater toxicity of a 50 mg/kg dose when administered in 5 versus 50 ml/kg. The impact of dose volume on the toxicokinetics of 2-deoxy-d-glucose (DG), a nonreactive, nonmetabolizable substance, was also investigated. The areas under the curve for DG were not different for the two dose volumes; however, C(max) for the more concentrated dose was significantly higher. In conclusion, current studies show that the toxicokinetics of an administered xenobiotic and its metabolites is influenced by the concentration of the parent chemical in the dosing solution. Therefore, it is important to consider the concentration of an administered xenobiotic in the dosing solution because it may affect its toxicokinetics and metabolism and subsequently affect the biological effects of the administered chemical.

Neuronal effects of 4-t-Butylcatechol: a model for catechol-containing antioxidants.

Many herbal medicines and dietary supplements sold as aids to improve memory or treat neurodegenerative diseases or have other favorable effects on the CNS contain a catechol or similar 1,2-dihydroxy aromatic moiety in their structure. As an approach to isolate and examine the neuroprotective properties of catechols, a simple catechol 4-t-Butylcatechol (TBC) has been used as a model. In this study, we investigated the effects of TBC on lipopolysaccharide (LPS)-activated microglial-induced neurotoxicity by using the in vitro model of coculture murine microglial-like cell line HAPI with the neuronal-like human neuroblastoma cell line SH-SY5Y. We also examined the effects of TBC on 6-hydroxydopamine (6-OHDA)-induced neurotoxicity in human dopaminergic neuroblastoma SH-SY5Y cells. TBC at concentrations from 0.1-10 microM had no toxic effect on HAPI cells and SH-SY5Y cells, and it inhibited LPS (100 ng/ml)-induced increases of superoxide, intracellular ROS, gp91(Phox), iNOS and a decrease of HO-1 in HAPI cells. Under coculture condition, TBC significantly reduced LPS-activated microglia-induced dopaminergic SH-SY5Y cells death. Moreover, TBC (0.1-10 microM) inhibited 6-OHDA-induced increases of intracellular ROS, iNOS, nNOS, and a decrease of mitochondria membrane potential, and cell death in SH-SY5Y cells. However, the neurotoxic effects of TBC (100 microM) on SH-SY5Y cells were also observed including the decrease in mitochondria membrane potential and the increase in COX-2 expression and cell death. TBC-induced SH-SY5Y cell death was attenuated by pretreatment with NS-398, a selective COX-2 inhibitor. In conclusion, this study suggests that TBC might possess protective effects on inflammation- and oxidative stress-related neurodegenerative disorders. However, the high concentration of TBC might be toxic, at least in part, for increasing COX-2 expression.

Chemical and enzymatic oxidation of furosemide: formation of pyridinium salts.

Furosemide (Lasix) is frequently used in the treatment of cardiovascular and renal disease. Only one metabolite, furosemide glucuronide, has ever been identified. Oxidation of furosemide by cytochrome P450 has been demonstrated, but the metabolite(s) has never been identified. The oxidation of furosemide by dimethyldioxirane in acetone and by liver microsomal incubations was explored in this study. The first observable product from dimethyldioxirane oxidation was a ring-expanded enone resulting from an intramolecular condensation of the aldehyde group of the enonal, the secondary amine, and the carboxylic acid in a Mannich-like reaction. Keto-enol tautomerization and opening of the lactone gave a stable pyridinium salt. The pyridinium salt was also observed in the microsomal incubations of furosemide. The presence of an internal nucleophile in furosemide may have a significant effect on the toxicology and possibly the pharmacology of this furan.

14C-labeled pulegone and metabolites binding to alpha2u-globulin in kidneys of male F-344 rats.

Pulegone is a major constituent of pennyroyal oil and a minor component of peppermint oil. Pulegone is biotransformed to menthofuran and menthones (diastereomeric menthone and isomenthone) in pennyroyal and peppermint as well as in rodents. Pulegone and menthofuran are hepatotoxic to rodents, and menthones are less toxic. The metabolism and disposition of pulegone and menthofuran were previously studied in rodents, and higher concentrations of pulegone- and menthofuran-derived radioactivity were observed in male than female rat kidney. One explanation is the association of pulegone and metabolites with a male rat-specific protein, alpha2u-globulin. To test this hypothesis, male and female rats were dosed orally with 14C-labeled pulegone (80 mg/kg, 120 microCi/kg) or menthofuran (60 mg/kg, 120 microCi/kg) or menthones (80 mg/kg, 120 microCi/kg) in corn oil, and the kidney cytosol was prepared 24 h after dosing. An equilibrium dialysis experiment showed that in all three studies the radioactivity was associated with kidney cytosol proteins of male but not female rats. The chemicals present in the male rat kidney cytosol after dialysis were extracted with dichloromethane and characterized by high-performance liquid chromatography (HPLC) and gas chromatography/mass spectrometry (GC-MS). All parent compounds were detected, and the metabolites characterized included piperitone from pulegone or menthones treatment, menthones and possibly 8-hydroxymenthones from pulegone treatment, and mintlactones (diastereomeric mintlactone and isomintlactone) and 7a-hydroxymintlactone from menthofuran treatment. Analysis of the male rat kidney cytosol by a gel filtration column demonstrated that the retention was due to reversible binding of these chemicals with the male rat-specific protein alpha2u-globulin. However, binding of pulegone and/or metabolites to alpha2u-globulin did not produce accumulation of this protein in the kidney.

Immunohistochemical analysis of expressions of hepatic cytochrome P450 in F344 rats following oral treatment with kava extract.

Kava (Piper methysticum), used for relaxation and pain relief, has been one of the leading dietary supplements and several reports linking hepatic functional disturbances and liver failure to kava have resulted in a ban on sales in Europe and Canada and the issuance of warnings by the US FDA. The National Toxicology Program conducted 14-week rat studies to characterize the toxicology of kava exposure in Fischer 344 rats [National Toxicity Program. 90 day gavage toxicity studies of KAVA KAVA EXTRACT in Fischer rats and B6C3F1 mice. Research Triangle Park, NC; 2005a; National Toxicity Program. Testing status of agents at NTP (KAVA KAVA EXTRACT M990058). Research Triangle Park, NC; 2005b. (http://ntp.niehs.nih.gov/index.cfm?objectid=071516E-C6E1-7AAA-C90C751E23D14C1B)]. Groups of 10 male and 10 female rats were administered kava extract by gavage at 0, 0.125, 0.25, 0.5, 1.0, and 2.0 g/kg/day. Increased gamma-glutamyl-transpeptidase (GGT) activities were observed in the 2.0 g/kg males and 1.0 and 2.0 g/kg females, as well as increased serum cholesterol levels in males and females at 0.5 g/kg and higher. Increases in incidence and severity of hepatocellular hypertrophy (HP) were noted in males at 1.0 g/kg and females at 0.5 g/kg and higher, as well as increased liver weights. Immunohistochemical analyses of the expression of cytochrome-P450 (CYP) enzymes in liver of the control and 1.0- and 2.0-g/kg-treated groups indicated decreased expression of CYP2D1 (human CYP2D6 homolog) in 2.0 g/kg females and increased expression of CYP1A2, 2B1, and 3A1 in 1.0 and 2.0 g/kg groups of both sexes. The no observed adverse effect levels were decided as 0.25 g/kg in both genders, based on neurotoxic effects, increases in GGT, cholesterol, liver weight, and HP and decreases in body weight. Kava-induced hepatic functional changes in the F344 rat might be relevant to human clinical cases of hepatotoxicity following exposure.

Metabolism of furans in vitro: ipomeanine and 4-ipomeanol.

Ipomeanine (IPN), 4-ipomeanol (4-IPO), 1-ipomeanol (1-IPO), and 1,4-ipomeadiol (DIOL) are toxic 3-substituted furans found in mold-damaged sweet potatoes. IPN and 4-IPO are the most toxic, but all produce pulmonary toxicity in cattle and rodents, and 4-IPO induces hepatotoxicity in humans. These furans require metabolic activation to elicit toxicity, but the limited information obtained from previous metabolism studies prompted us to initiate the investigation reported here. Our initial studies of 4-IPO metabolism by rat liver microsomes demonstrated that the oxidation of 4-IPO to IPN and reduction to DIOL occurred and that more IPN was metabolized to a reactive species than 4-IPO or DIOL. Incubation of IPN and Gly produced a 2'-pyrrolin-5'-one adduct establishing that IPN was metabolized to an enedial. N-Acetylcysteine reacted with the 5'-aldehyde of the enedial to give two 2',5'-dihydro-2'-hydroxyfurans stabilized by H bonding between the 2'-OH and 3'-keto group. Reaction of the enedial metabolite of IPN with one GSH gave several adducts including a pyrrole derived from the 1,2-addition of GSH to the 5'-aldehyde as well as two tricyclic 2'-pyrrolines derived from the 1,4-addition of GSH at the 4'-position. The identities of the pyrrole and 2'-pyrroline GSH adducts were confirmed by observation of structurally similar adducts from Cys conjugation with the enedial metabolite of IPN. Several minor adducts from the conjugation of the enedial metabolite of IPN with two GSH were also detected. Mono-GSH and bis-GSH adducts were derived from both the 1,2-and 1,4-addition of GSH to the enedial metabolite of 4-IPO in rat liver microsomal incubations of 4-IPO and GSH. Sequential oxidation of 4-IPO to IPN and then to the enedial metabolite followed by GSH conjugation also occurred in the 4-IPO incubations. The complex structures of the reaction products of the enedial with biological nucleophiles may explain why the many attempts to identify 4-IPO adducts to protein have not been successful.

Pharmacokinetics and disposition of the kavalactone kawain: interaction with kava extract and kavalactones in vivo and in vitro.

Reported adverse drug interactions with the popular herb kava have spurred investigation of the mechanisms by which kava could mediate these effects. In vivo and in vitro experiments were conducted to examine the effects of kava extract and individual kavalactones on cytochrome P450 (P450) and P-glycoprotein activity. The oral pharmacokinetics of the kavalactone, kawain (100 mg/kg), were determined in rats with and without coadministration of kava extract (256 mg/kg) to study the effect of the extract on drug disposition. Kawain was well absorbed, with >90% of the dose eliminated within 72 h, chiefly in urine. Compared with kawain alone, coadministration with kava extract caused a tripling of kawain AUC(0-8 h) and a doubling of C(max). However, a 7-day pretreatment with kava extract (256 mg /kg/day) had no effect on the pharmacokinetics of kawain administered on day 8. The 7-day pretreatment with kava extract only modestly induced hepatic P450 activities. The human hepatic microsomal P450s most strongly inhibited by kava extract (CYP2C9, CYP2C19, CYP2D6, CYP3A4) were inhibited to the same degree by a "composite" kava formulation composed of the six major kavalactones contained in the extract. K(i) values for the inhibition of CYP2C9 and CYP2C19 activities by methysticin, dihydromethysticin, and desmethoxyyangonin ranged from 5 to 10 microM. Kava extract and kavalactones (< or =9 microM) modestly stimulated P-glycoprotein ATPase activities. Taken together, the data indicate that kava can cause adverse drug reactions via inhibition of drug metabolism.

Transcriptional profiling of the left and median liver lobes of male f344/n rats following exposure to acetaminophen.

The liver is a common organ for transcriptional profiling because of its role in xenobiotic metabolism and because hepatotoxicity is a common response to chemical exposure. To explore the impact that sampling different lobes may have on transcriptional profiling experiments we have examined and compared gene expression profiles of the left and median lobes of livers from male F344 rats exposed to toxic and nontoxic doses of acetaminophen. Transcript profiling using micorarrays revealed clear differences in the response of the left and median liver lobes of F344 rats to acetaminophen exposure both at low doses as well as doses that caused hepatotoxicity. Differences were found in the total number of differentially expressed genes in the left and median lobes, the number and identity of genes that were differentially expressed uniquely only in the left or median lobe, and in the patterns of gene expression. While it is not possible to generalize these results to compounds other than acetaminophen or other strains of rat, these results highlight the potential impact of sampling differences on the interpretation of gene expression profiles in the liver.

Mercury concentrations in brain and kidney following ethylmercury, methylmercury and Thimerosal administration to neonatal mice.

The distribution of mercury to the brain following an injection of methylmercury (MeHg) or ethylmercury (EtHg) was examined in immature mice. Postnatal day (PND) 16 CD1 mice received MeHg chloride either by IM injection or by gavage. At 24 h and 7 days post-injection, total mercury concentrations were determined in blood, kidney, brain, and muscle by cold vapor atomic fluorescence spectrometry. At 24 h, an IM injection of MeHg chloride (17.4 microg) produced total mercury concentrations in the blood (6.2 +/- 0.9 microg/g), brain (5.6 +/- 1.3 microg; 0.6% delivered dose), and kidney (25.2 +/- 5.6 microg; 1.1%), approximately 30% of that obtained from oral administration (blood: 17.9 +/- 1.0 microg; brain: 16.1 +/- 1.2 microg, 1.5%; kidney: 64.9 +/- 6.3 microg, 2.7%). For comparison, PND 16 mice received an IM injection of concentrated dosing suspensions (2 microl dosing vol.) for EtHg chloride (6 microg) or Thimerosal (15.4 microg). For EtHg, approximately 0.39 +/- 0.06% of the injected mercury was detected in the brain and 3.5 +/- 0.6% in the kidney at 24 h. Thimerosal IM injection resulted in 0.22 +/- 0.04% in the brain, and 1.7 +/- 0.3% in the kidney. By 7 days, mercury levels decreased in the blood but were unchanged in the brain. An acute IM injection to adult mice of each suspension at a 10-fold higher dose resulted an average 0.1% mercury in the brain, and higher levels in the blood, kidney, and muscle as compared to the young. In immature mice, MeHg delivered via oral route of administration resulted in significantly greater tissue levels as compared to levels from IM injection. Comparisons of tissue distribution following IM administration suggest that an oral route of administration for mercury is not comparable to an IM delivery and that MeHg does not appear to be a good model for EtHg-containing compounds.

NTP technical report on the toxicity studies of Butanal oxime (CAS No. 110-69-0) administered in drinking water and by gavage to F344/N rats and B6C3F1 mice.

Butanal oxime is used as a volatile antiskinning agent in paints, inks, and similar products. Butanal oxime was chosen for toxicology testing as a representative of the aldoxime class. Male and female F344/N rats and B6C3F1 mice received butanal oxime (99 percent pure) in drinking water for 15 days or by gavage in 0.5 percent methylcellulose for 14 weeks. Animals were evaluated for clinical pathology, reproductive system effects, and histopathology. Genetic toxicology studies were conducted in Salmonella typhimurium, cultured Chinese hamster ovary cells, and mouse peripheral blood erythrocytes. In the 15-day studies, groups of five male and five female rats and mice received 0, 312, 625, 1,250, 2,500, or 5,000 ppm butanal oxime in drinking water, resulting in average daily doses of approximately 40, 70, or 100 mg butanal oxime/kg body weight to male and female rats; 45, 90, 130, 200, or 300 mg/kg to male mice; and 45, 85, 100, 130, or 170 mg/kg to female mice. Due to body weight loss and lack of water consumption, all male and female rats receiving 2,500 or 5,000 ppm were removed from the study on day 9; average daily doses were not calculated for these groups. All other rats and mice survived until the end of the studies. Mean body weights of 1,250 ppm male and female rats and 2,500 and 5,000 ppm male and female mice were significantly less than those of the controls. Male mice receiving 5,000 ppm and females receiving 2,500 or 5,000 ppm lost weight during the study. Water consumption by rats and mice receiving 1,250 ppm or greater was less than that by the controls. Thinness in 2,500 and 5,000 ppm rats and mice was the only clinical finding of toxicity. Spleen weights were significantly decreased in 2,500 and 5,000 ppm female mice. No chemical-related lesions were observed grossly; histologic examinations were not performed. In the 14-week studies, groups of 10 male and 10 female rats and mice received butanal oxime by gavage at doses of 0, 25, 50, 100, 200, or 600 mg/kg, 5 days per week for 14 weeks. All 600 mg/kg rats died or were killed moribund during the first week of the study; in the 600 mg/kg mouse groups, seven males and nine females died, were killed moribund, or were killed accidentally before the end of the study. Mean body weights of 100 and 200 mg/kg male rats, 600 mg/kg male mice, and female mice administered 50 mg/kg or greater were less than those of the controls. Clinical findings of toxicity in 600 mg/kg rats included loss of coordination, wobbly gait, shaking, blinking, constant grooming and scratching of the face, head weaving, burying of the face in bedding, lethargy, and prostration; in 600 mg/kg mice, clinical findings included ataxia, loss of balance after rearing, squinting, and burying of the face in the bedding. Hematology results of the 14-week gavage studies indicate that butanal oxime induces a methemoglobinemia and a responsive anemia in rats and mice. Spleen weights of 100 and 200 mg/kg male rats, female rats administered 50 mg/kg or greater, and 200 and 600 mg/kg male mice were increased, as were the liver weights of 200 mg/kg female rats and mice. In animals that died early due to butanal oxime administration, hepatocellular necrosis was the primary pathologic finding. Degeneration of the nasal olfactory epithelium was observed in dosed rats and mice that died early as well as in animals that survived to the end of the studies. Additional chemical-related nasal findings were respiratory epithelial changes in male rats and suppurative exudate in male and female mice. Increased incidences and/or severities of splenic hematopoietic cell proliferation and pigmentation (hemosiderin) as well as bone marrow hyperplasia were also observed in dosed groups, particularly in the 200 and 600 mg/kg groups, and were indicative of erythrocyte damage. Butanal oxime (3 to 10,000 ug/plate) was mutagenic in S. typhimurium strain TA1535 in the presence of 5 percent or 10 percent rat liver S9; an equivocal response was seen in TA100 with 30 percent rat S9, and no mutagenic activity was seen in TA98, with or without rat or hamster liver S9. Butanal oxime induced chromosomal aberrations in cultured Chinese hamster ovary cells, with and without S9. Significant increases in the frequencies of micronucleated normochromatic erythrocytes were observed in vivo in peripheral blood of male and female mice administered 25 to 600 mg/kg butanal oxime for 14 weeks by gavage. Synonyms: Butanaloxime; butylaldoxime; butyraldehyde oxime; n-butyraldehyde oxime; butyraldoxime; n-butyraldoxime Trade names: Exkin 1, Exkin No. 1 Anti-Skinning Agent, Skino #1, Troykyd Anti-Skin BTO

Lung deposition and clearance of inhaled vanadium pentoxide in chronically exposed F344 rats and B6C3F1 mice.

Female F344 rats and B6C3F1 mice were exposed to vanadium pentoxide (V2O5) at concentrations of 0, 0.5, 1, or 2 mg/m3 (rats) and 0, 1, 2, or 4 mg/m3 (mice) for 6 h/day, 5 days/week (for up to 18 months), by whole-body inhalation. Lung weights and lung burdens of vanadium were determined for exposed animals after 1, 5, and 12 days and after 1, 2, 6, 12, and 18 months of V2O5 exposure. Blood vanadium concentrations were determined at 1, 2, 6, 12, and 18 months for all animals including controls. A model that assumed a first-order deposition rate and a first-order elimination rate for vanadium was employed to fit the lung burden data. Comparisons between exposed groups indicated a progressive increase in lung weight with exposure concentration and time on exposure for both species. The vanadium lung burdens appeared to reach steady state in the lowest exposure groups (0.5 and 1 mg/m3 for rats and mice, respectively) but showed a decline in the higher exposure groups. This deposition pattern was similar between rats and mice but the maximum lung burdens were observed at different times (1 or 2 months in mice vs. 6 months in rats). The vanadium deposition rate decreased faster in mice, while the elimination half-lives of vanadium lung burdens were about six- to nine-fold shorter in mice than in rats at 1 and 2 mg/m3. Thus, the retention of vanadium in the lungs at 18 months was lower in mice (approximately 2% retained) compared with rats (13-15% retained) at the common exposure concentrations of 1 and 2 mg/m3. The lung burden data were approximately proportional to the exposure concentration in both species, likely due to concomitant decreases in deposition and elimination to a similar extent with increasing exposure. The area under the lung burden versus time curves and the area under the blood concentration (control-normalized) versus time curves were also proportional to exposure concentration. The progression of pathological changes in the lung with exposure and time is thought to affect the pattern and/or extent of vanadium deposition in the lungs following repeated exposures to V2O5.

Single administration toxicokinetic studies of decalin (decahydronaphthalene) in rats and mice.

Decalin (decahydronaphthalene) is an industrial solvent known to cause alpha2u-globulin nephropathy in male rats. Studies were conducted using decalin (mixture of cis and trans isomers) to (1) characterize systemic elimination of decalin in rats and mice and (2) evaluate disposition of decalin, its metabolites, and kidney alpha2u-globulin in young and old rats of both sexes following a single 6-h whole-body inhalation exposure at up to 400 ppm decalin. Additionally, a separate group of young male F344/N rats were administered either cis- or trans-decalin iv at doses up to 20 mg/kg to assess disposition of each isomer, its metabolites, and kidney alpha2u-globulin. Decalin was eliminated from blood in a dose-dependent manner, regardless of sex, age, or species. C0 and AUC infinity increased supra-proportionally with exposure concentration. Mice were more efficient in eliminating decalin than rats at lower exposure concentrations, but nonlinear elimination kinetics were more noticeable at 400 ppm. Sex differences in blood decalin elimination were observed in rats; females had a consistently higher AUC infinity at all exposure concentrations. There was a dose-dependent increase in kidney decalin, decalone, and alpha2u-globulin in male rats exposed to decalin. Kidney alpha2u-globulin and decalone concentrations in old male rats were substantially lower than those in young males, but were similar to those observed in all (young and old) females. Compared to old males and all females, young male rats had significantly lower urinary decalol concentrations, but higher kidney decalin, decalone, and alpha2u-globulin concentrations. Administration of decalin to male rats as either the cis or trans isomer revealed that more cis -decalone is produced per unit dose as compared to trans-decalone, and that more trans-decalin accumulated in the kidney (as alpha2u-globulin-ligand complexes) compared to cis-decalin. These patterns of isomer-specific metabolism were also reflected in the cis/trans ratios of decalin in blood, as well as urinary decalol metabolites. The ratio of alpha2u-globulin to the total amount of decalin plus decalone measured in the male rat kidney was approximately 1.0. Therefore, alpha2u-globulin was a key factor in the accumulation of decalin and decalone in kidneys of young male rats, decalin and decalone were practically absent in all females and in old males.

Alpha 2u-globulin nephropathy and carcinogenicity following exposure to decalin (decahydronaphthalene) in F344/N rats.

Decalin (decahydronaphthalene) is a widely used industrial solvent known to cause male rat-specific alpha2u-globulin nephropathy. In this project, 13-week and two-year inhalation studies of decalin were conducted consecutively in both sexes of F344/N rats. The key objectives were to (1) characterize the 13-week toxicity of decalin in rats, with an emphasis on nephropathy in males; (2) compare the kidney concentrations of decalin, 2-decalone, and alpha2u-globulin in males over 2 to 13 weeks of decalin exposure; and (3) correlate male rat nephropathy observed in the 13-week study with renal carcinogenicity in the two-year study. F344 rats (M/F) were exposed via whole-body inhalation to 0, 25, 50, 100, 200, or 400 ppm decalin for 13 weeks. Urine was collected at weeks 2 and 6 for creatinine and decalol analyses and at week 12 for clinical urinalysis. Right kidneys were collected from male rats at weeks 2 and 6 and from both sexes at week 13, homogenates were prepared using the whole kidney, and these homogenates were analyzed for alpha2u-globulin, decalin, and 2-decalone. Left kidneys were evaluated for histopathology and cell proliferation utilizing a proliferating cell nuclear antigen technique and counting proximal renal tubular epithelial cells to determine cell labeling indices. Necropsies and histopathologic evaluations were performed at week 13. Decalin exposure caused increases in kidney weight, urinalysis parameters (protein, AST, LDH), kidney alpha2u-globulin concentration, and proximal convoluted renal tubular cell proliferation in males. These changes were accompanied by microscopic lesions (accumulation of hyaline droplets in cortical tubules, regeneration of proximal tubular epithelium, and granular casts in medullary tubules) clearly linked to alpha2u-globulin nephropathy. Both decalin and 2-decalone were related to increased alpha2u-globulin in male kidneys. Kidney concentrations of decalin, 2-decalone, and alpha2u-globulin in exposed females were negligible, while females excreted greater amounts of decalol metabolites in urine than males at weeks 2 and 6. There were no exposure-related microscopic lesions in females. For chronic exposure, F344 rats were exposed via whole-body inhalation to 0, 25, 50 (males only), 100, or 400 ppm decalin for two years. Chronic exposure induced a spectrum of nonneoplastic and neoplastic lesions in the renal cortex of males, ranging from regenerative lesions of chronic nephropathy to tubular carcinomas. Incidences of renal tubular adenoma, tubular carcinoma, combined tubular adenomas and carcinomas, cortical tubular hyperplasia, hyaline droplet accumulation, hyperplasia of pelvic epithelium, and mineralization in renal papilla were increased in exposed males compared to controls. There was a clear increase in the mean severity of chronic nephropathy in decalin-exposed males. It was concluded that the carcinogenic effect on the renal cortical epithelium of male rats exposed to decalin was related to increased turnover of this epithelium, resulting from the cytotoxic effects of alpha2u-globulin accumulation in the renal cortical tubular cell cytoplasm.

Mouse bone marrow micronucleus test results do not predict the germ cell mutagenicity of N-hydroxymethylacrylamide in the mouse dominant lethal assay.

N-Hydroxymethylacrylamide (NHMA), a mouse carcinogen inactive in the Salmonella assay and mouse micronucleus (MN) assay, was tested for reproductive effects in a mouse continuous breeding study. In that study, increased embryonic deaths were observed after 13 weeks exposure of parental animals to NHMA via drinking water (highest dose, 360 ppm); the results indicated the possible induction of chromosome damage in germ cells of treated males. An additional mouse MN test was conducted using a 31-day treatment period to better match the dosing regimen used in the breeding study; the results were negative. Additional studies were conducted to explore the germ cell activity of NHMA. A male mouse dominant lethal study was conducted using a single intraperitoneal injection of 150 mg/kg NHMA; the results were negative. A follow-up study was conducted using fractionated dosing, 50 mg/kg/day for 5 days; again, no increase in dominant lethal mutations was observed. NHMA (180-720 ppm) was then administered to male mice in drinking water for 13 weeks, during which three sets of matings occurred. Two weeks after mating, females were killed and the uterine contents were analyzed. Large, dose-related increases in dominant lethal mutations were observed with increasing length of exposure. The magnitude of the increases stabilized after 8 weeks of treatment. However, the frequency of micronucleated peripheral blood erythrocytes was not elevated in mice treated for 13 weeks with NHMA in drinking water. Thus, NHMA appears to be unique in inducing genetic damage in germ cells but not somatic cells of male mice.

Carcinogenic potential of o-nitrotoluene and p-nitrotoluene.

The potential of o-nitrotoluene and p-nitrotoluene to cause cancer in mammalian species was studied in male and female F344/N rats and B6C3F1 mice. These chemicals are on the EPA list of high production chemicals and there is potential for human exposure (High Production Volume Chemical List (2000) http://oaspub.cpa.gov/opptintr/chemrtk/volchall.htm.). o-Nitrotoluene, administered in the feed for up to 2 years, caused clear evidence for cancer at multiple sites in rats and mice. Male rats, receiving o-nitrotoluene in the feed ( approximately 0, 25, 50, or 90 mg/kg per day), developed treatment-related mesotheliomas, subcutaneous skin neoplasms, mammary gland fibroadenomas, and liver neoplasms. By 2 years, mesotheliomas, skin, liver, mammary gland and liver tumors also occurred in 'stop-study' male rats that received o-nitrotoluene at 125 or 315 mg/kg per day for only the first 3 months of study. These 'stop-studies' showed that the critical events leading to tumor formation occurred after 3 months of dosing, and these events were irreversible and eventually led to cancer at multiple sites. o-Nitrotoluene given in the feed to female rats (approximately 0, 30, 60, or 100 mg/kg per day) and to male and female mice (approximately 0, 150, 320, or 700 mg/kg per day) also caused a carcinogenic response. In female rats, treatment-related subcutaneous skin neoplasms and mammary gland fibroadenomas occurred. Hemangiosarcomas and carcinomas of the large intestine (cecum) were seen in treated male and female mice. In contrast to o-nitrotoluene, p-nitrotoluene given in the feed over approximately the same exposure levels caused only equivocal evidence of carcinogenic activity in male rats (subcutaneous skin neoplasms); some evidence of carcinogenic activity in female rats (clitoral gland neoplasms); equivocal evidence of carcinogenic activity in male mice (lung neoplasms); and no evidence of carcinogenic activity in female mice. Differences in the o-nitrotoluene and p-nitrotoluene carcinogenic activity may be due to differences in the metabolism of the parent compound to carcinogenic metabolites.

Disposition of 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5h)-furanone (mx) in b6c3f1 mice and f344 rats.

3-Chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX) is a mutagenic by-product of chlorination of drinking water, particularly where the water contains humic matter. MX has been estimated to account for 50% of the mutagenic activity in some drinking water. A bioassay in rats demonstrated an increased tumor incidence, primarily in liver and thyroid glands. This study was designed to provide disposition/metabolism information in mice to evaluate the necessity of a National Toxicology Program chronic bioassay and to provide data for female rats. Radioactivity was rapidly absorbed and excreted near equally in urine (42-54%) and feces (40-51%) 72 h following oral administration of (14)C-labeled MX at single doses from 0.2 to 20 mg/kg to male and female mice and female rats. A larger percentage (71-73%) of MX-derived radioactivity was excreted in urine after an iv dose (0.2 mg/kg) in both female rats and male mice. Most MX-derived radioactivity was excreted within the first 24 h postdosing. MX was transformed to urinary and biliary metabolites. A major extremely polar urinary metabolite was tentatively identified as 1-hydroxy-1,2,2-ethanetricarboxylic acid. This metabolite is likely transformed from the MX degradation product 2-hydroxy-3-formyl-4-oxo-2-butenoic acid. Oral administration produced highest tissue/blood ratios in the following order: forestomach (>100), glandular stomach, intestine, and kidney. Intravenous administration resulted in high, prolonged levels of radioactivity in blood compared to oral dosing. Therefore, MX disposition appears to be dominated by its chemical reactivity with highest concentrations of radioactivity being found at the site of administration.