Renal Tubule Adenomas Research Articles

Cumene Documentation of proposed values of occupational exposure limits (OELs)

Cumene is a clear, colourless liquid with a strong aromatic gasoline-like odour. Cumene is used for the synthesis of phenol and acetone and as a solvent in paints, varnishes and res-ins. It is also used in the printing and rubber industries. According to data from Polish Chief Sanitary Inspectorate, in 2010, no workers were occupa-tionally exposed to cumene in concentrations exceeding Polish OEL values (100 mg/m3). In 2014, 51 workers were exposed to cumene in concentrations from 0.1 to 0.5 MAC value (from 10 mg/m3 to 50 mg/m3). Cumene vapours are irritating to the respira-tory tract. In humans, high concentrations of cumene cause painful irritation to the eyes and the respiratory tract. In animals, cumene caus-es mainly CNS depression. Chronic exposure to cumene can cause hepatotoxicity. In vitro tests indicated no mutagenic and no genotoxic potential of cumene. Intraperitoneal injection of cumene induced micronuclei in bone marrow of rats. Dose-related increases in DNA damage were observed in liver cells of male rat and lung cells of female mouse. A metabolite of cumene, α-methylstyrene, was not mutagenic in bacterial tests but induced chromosomal damage in cell cultures and ro-dent cells. IARC experts classified cumene in group 2.B – chemicals possibly carcinogenic to humans based on sufficient evidence in experimental animals for the carcinogenicity of cumene. Exposure of mice to cumene by inhalation in-creased the incidence of alveolar/bronchiolar adenoma and carcinoma in males and females mice, haemangiosarcoma of the spleen in male mice and hepatocellular adenoma in female mice. Exposure of rats to cumene by inhalation increased the incidence of nasal adenoma in males and females and renal tubule adenoma and carcinoma in male rats. Cumene is well absorbed. It is a lipophilic substance which is well distributed in the whole body. Cytochrome P-450 is involved in cumene me-tabolism. Main metabolite identified in urine was 2-phenyl-2-propanol and in exhaled air α-methylstyrene. In 2014, Scientific Committee for Occupational Exposure Limits to Chemical Agents (SCOEL) prepared change of indicative OEL for cumene – reduction of concentration from 100 mg/m3 (directive 2000/39/WE) to 50 mg/m³, STEL value 250 mg/m3 remain unchanged. The compound was included in SCOEL carcino-genicity group D (not genotoxic and not affect-ing DNA chemicals), for which a health-based OEL may be derived on the basis of NOAEL value. Poland did not submit any comments on SCOEL proposal during public consultations in 2014. A new indicative OEL was derived on the basis of 3-month NTP inhalation studies in rats and mice. SCOEL established 310 mg/m³ (62.5 ppm) level as a NOAEC for hepatotoxici-ty. A STEL of 250 mg/m3 (50 ppm) have been recommended to protect against respiratory tract irritation and behavioural effects. More-over, a “skin notation” was recommended because of its probable skin penetration. BLV recom-mended by SCOEL is 7 mg 2-phenyl-2-propanol per gramme of creatinine in urine (after hydrolysis). To determine MAC value for cumene hepato-toxicity and nephrotoxicity were adopted as a critical effect. The Expert Group for Chemi-cals Agents established 310 mg/m³ as NOAEC based on 3-month NTP inhalation studies in rats and proposed reduction of the current MAC value from 100 to 50 mg/m3. It was agreed that the previous STEL value of 250 mg/m3 should remain unchanged, which is also in accordance with the value recom-mended by SCOEL. Recommended BEI value is 7 mg 2-phenyl-2-propanol per gramme of creatinine in urine (after hydrolysis), sampled immediately after work shift. It was recom-mended to remain “I” (irritant) and “Sk” (sub-stance can penetrate skin) labelling of cumene.

Risk assessment of skin lightening cosmetics containing hydroquinone

Following reports on potential risks of hydroquinone (HQ), HQ for skin lightening has been banned or restricted in Europe and the US. In contrast, HQ is not listed as a prohibited or limited ingredient for cosmetic use in Japan, and many HQ cosmetics are sold without restriction. To assess the risk of systemic effects of HQ, we examined the rat skin permeation rates of four HQ (0.3%, 1.0%, 2.6%, and 3.3%) cosmetics. The permeation coefficients ranged from 1.2 × 10−9 to 3.1 × 10−7 cm/s, with the highest value superior than the HQ aqueous solution (1.6 × 10−7 cm/s). After dermal application of the HQ cosmetics to rats, HQ in plasma was detected only in the treatment by highest coefficient cosmetic. Absorbed HQ levels treated with this highest coefficient cosmetic in humans were estimated by numerical methods, and we calculated the margin of exposure (MOE) for the estimated dose (0.017 mg/kg-bw/day in proper use) to a benchmark dose for rat renal tubule adenomas. The MOE of 559 is judged to be in a range safe for the consumer. However, further consideration may be required for regulation of cosmetic ingredients.

Methyl isobutyl ketone exposure-related increases in specific measures of α2u-globulin (α2u) nephropathy in male rats along with in vitro evidence of reversible protein binding.

Chronic exposure to methyl isobutyl ketone (MIBK) resulted in an increase in the incidence of renal tubule adenomas and occurrence of renal tubule carcinomas in male, but not female Fischer 344 rats. Since a number of chemicals have been shown to cause male rat renal tumors through the α2u nephropathy-mediated mode of action, the objective of this study is to evaluate the ability of MIBK to induce measures of α2u nephropathy including renal cell proliferation in male and female F344 rats following exposure to the same inhalation concentrations used in the National Toxicology Program (NTP) cancer bioassay (0, 450, 900, or 1800ppm). Rats were exposed 6h/day for 1 or 4 weeks and kidneys excised approximately 18h post exposure to evaluate hyaline droplet accumulation (HDA), α2u staining of hyaline droplets, renal cell proliferation, and to quantitate renal α2u concentration. There was an exposure-related increase in all measures of α2u nephropathy in male, but not female rat kidneys. The hyaline droplets present in male rat kidney stained positively for α2u. The changes in HDA and α2u concentration were comparable to d-limonene, an acknowledged inducer of α2u nephropathy. In a separate in vitro study using a two-compartment vial equilibration model to assess the interaction between MIBK and α2u, the dissociation constant (Kd) was estimated to be 1.27×10(-5)M. This Kd is within the range of other chemicals known to bind to α2u and cause nephropathy. Together, the exposure-related increase in measures of α2u nephropathy, sustained increase in renal cell proliferation along with an indication of reversible binding of MIBK to α2u, support the inclusion of MIBK in the category of chemicals exerting renal effects through a protein droplet α2u nephropathy-mediated mode of action (MoA).

Chronic Carcinogenicity Study of Gasoline Vapor Condensate (GVC) and GVC Containing Methyl Tertiary-Butyl Ether in F344 Rats

Chronic inhalation studies were conducted to compare the toxicity and potential carcinogenicity of evaporative emissions from unleaded gasoline (GVC) and gasoline containing the oxygenate methyl tertiary-butyl ether (MTBE; GMVC). The test materials were manufactured to mimic vapors people would be exposed to during refueling at gas stations. Fifty F344 rats per gender per exposure level per test article were exposed 6 h/d, 5 d/wk for 104 wk in whole body chambers. Target total vapor concentrations were 0, 2, 10, or 20 g/m3 for the control, low-, mid-, and high-level exposures, respectively. Endpoints included survival, body weights, clinical observations, organs weights, and histopathology. GVC and GMVC exerted no marked effects on survival or clinical observations and few effects on organ weights. Terminal body weights were reduced in all mid- and high-level GVC groups and high-level GMVC groups. The major proliferative lesions attributable to gasoline exposure with or without MTBE were renal tubule adenomas and carcinomas in male rats. GMV exposure led to elevated testicular mesothelioma incidence and an increased trend for thyroid carcinomas in males. GVMC inhalation caused an increased trend for testicular tumors with exposure concentration. Mid- and high-level exposures of GVC and GMVC led to elevated incidences of nasal respiratory epithelial degeneration. Overall, in these chronic studies conducted under identical conditions, the health effects in F344 rats following 2 yr of GVC or GMVC exposure were comparable in the production of renal adenomas and carcinomas in male rats and similar in other endpoints.

P05: Carcinogenicity study of 3-Monochloropropane-1,2-diol in Sprague-Dawley rats

3-Monochloropropane-1,2-diol (α-chlorohydrin, 3-MCPD) is a well-known contaminant which has been detected in a wide range of foods and ingredients and is a suspected cause of cancer. In this study, we investigated the carcinogenicity of 3-MCPD in SD rats. Groups of 50 male and 50 female rats were exposed to drinking water containing 0, 25, 100, 400 ppm 3-MCPD for 2 years. Body weights and water consumption of male and female rats given 400 ppm were significantly lower than those of the controls. The incidences of renal tubule adenoma or carcinoma and Leydig cell tumor occurred with dose-related positive trends in male rats. The incidences of renal tubule carcinoma and Leydig cell tumor were significantly increased in 400 ppm males. Incidence of renal tubule adenoma had a positive trend in female rats, with the incidence being significant in 400 ppm group. In conclusion, there was clear evidence of carcinogenic activity of 3-MCPD in male SD rats based on increased incidences of renal tubule carcinoma and Leydig cell tumor. There was some evidence of carcinogenic activity of 3-MCPD in female SD rats based on increased incidences of renal tubule adenoma.

Carcinogenesis studies of cresols in rats and mice

Cresols, monomethyl derivatives of phenol, are high production chemicals with potential for human exposure. The three isomeric forms of cresol are used individually or in mixtures as disinfectants, preservatives, and solvents or as intermediates in the production of antioxidants, fragrances, herbicides, insecticides, dyes, and explosives. Carcinogenesis studies were conducted in groups of 50 male F344/N rats and 50 female B6C3F1 mice exposed to a 60:40 mixture of m- and p-cresols ( m-/ p-cresol) in feed. Rats and mice were fed diets containing 0, 1500, 5000, or 15,000 ppm and 0, 1000, 3000, or 10,000 ppm, respectively. Survival of each exposed group was similar to that of their respective control group. Mean body weight gains were depressed in rats exposed to 15,000 ppm and in mice exposed to 3000 ppm and higher. A decrease of 25% over that of controls for the final mean body weight in mice exposed to 10,000 ppm appeared to be associated with lack of palatability of the feed. A marginally increased incidence of renal tubule adenoma was observed in the 15,000-ppm-exposed rats. The increased incidence was not statistically significant, but did exceed the range of historical controls. No increased incidence of hyperplasia of the renal tubules was observed; however, a significantly increased incidence of hyperplasia of the transitional epithelium associated with an increased incidence of nephropathy was observed at the high exposure concentration. The only significantly increased incidence of a neoplastic lesion related to cresol exposure observed in these studies was that of squamous cell papilloma in the forestomach of 10,000-ppm-exposed mice. A definitive association with irritation at the site-of-contact could not be made because of limited evidence of injury to the gastric mucosa at the time of necropsy. However, given the minimal chemical-related neoplastic response in these studies, it was concluded that there was no clear evidence of carcinogenicity in male rats or female mice exposed to the cresol mixture.

Carcinogenicity study of 3-monochloropropane-1,2-diol in Sprague–Dawley rats

3-Monochloropropane-1,2-diol (α-chlorohydrin, 3-MCPD) is a well-known contaminant, which has been detected in a wide range of foods and ingredients, and is also a suspected cause of cancer. In this study, the carcinogenicity of 3-MCPD in SD rats was investigated. Groups of 50 male and 50 female rats were exposed for two years to drinking water containing 0, 25, 100 or 400 ppm 3-MCPD. The body weights and water consumptions of the male and female rats given 400 ppm 3-MCPD were significantly lower than those of the controls. The incidences of renal tubule adenomas or carcinomas and Leydig cell tumors occurred with dose-related positive trends in male rats. The incidences of renal tubule carcinomas and Leydig cell tumors were significantly increased in male rats given 400 ppm 3-MCPD. The incidence of renal tubule adenomas showed a positive trend in female rats, which was significant in 400 ppm 3-MCPD group. In conclusion, there was clear evidence of the carcinogenic activity of 3-MCPD in male SD rats, based on the increased incidences of renal tubule carcinomas and Leydig cell tumors. There was some evidence of the carcinogenic activity of 3-MCPD in female SD rats, based on the increased incidence of renal tubule adenomas.

Hydroquinone: An Evaluation of the Human Risks from its Carcinogenic and Mutagenic Properties

The toxicology of hydroquinone has been reviewed on a number of previous occasions. This review targets its potential for carcinogenicity and possible modes of carcinogenic action. The evaluation made by IARC (1999) of its carcinogenic risk to humans was that hydroquinone is not classifiable as to its carcinogenicity to humans (Group 3). This evaluation was based on inadequate evidence in humans and limited evidence in experimental animals. The epidemiological information comes from four cohort studies involving occupational exposures. A cohort of lithographers, some of whom had worked with hydroquinone, had an excess of malignant melanoma based on five cases, but only two of the cases had reported exposure to hydroquinone. In a study of photographic processors the number of exposed individuals was uncertain and the numbers of cases of individual cancer sites were small. In view of the statistical power limitations of these studies for individual diagnostic categories of cancers, they are not considered to be informative with regard to the carcinogenicity of hydroquinone. A cohort of workers with definite and lengthy exposure to hydroquinone, during either its manufacture or its use, had low cancer rates compared with two comparison populations; the reason for the lower than expected rates is unclear. In a motion picture film processing cohort there were significant excess malignancies of the respiratory system among workers engaged in developing, where there was exposure to hydroquinone as well as other chemicals. There was no information on tobacco smoking habits and no dose-response relationship. Hydroquinone has been shown reproducibly to induce benign neoplasms in the kidneys of male F344 rats dosed orally either by gavage (25 and 50 mg/kg body weight) or diet (0.8%). The gavage study has been evaluated in considerable detail. This evaluation showed that all renal tubule adenomas and all cases of renal tubule atypical hyperplasia occurred in areas of severe or end-stage chronic progressive nephropathy and that the neoplasms were not otherwise confined to any particular part of the kidney. It is likely that the mode of carcinogenic action of hydroquinone is exacerbation of this natural disease process. Hydroquinone is mutagenic in vitro and in vivo, having caused genotoxicity or chromosomal aberrations in rodent bone-marrow cells. At least a portion, if not all, of the chromosomal effects are caused by interference by hydroquinone or its metabolites with chromosomal segregation, probably due to interaction with mitotic spindle proteins. However, the dose routes used to demonstrate these effects in almost all of the studies in vivo were intraperitoneal or subcutaneous injection, which were considered inappropriate. There were five studies by the oral route. These included a mouse bone-marrow cell micronucleus test in which a weak, marginally positive response was obtained following a single oral dose of 80 mg/kg body weight. The remaining oral route studies all showed no significant effect. They included a mouse bone-marrow cell micronucleus test in which there was no genotoxic activity after exposure to a diet containing 0.8% hydroquinone for 6 days; two 32P-post-labeling assays, one with targets of Zymbal gland, liver, and spleen in Sprague-Dawley rats, the other with the kidney as target in F344 rats; and the last oral assay was for 8-hydroxydeoxyguanosine adducts in F344 rat kidney DNA. Thus, the evidence (and the database) for any genotoxic effect in vivo is sparse and none has been observed in kidney. While glutathione conjugates could be responsible for the tumor induction, careful histology seems to show that the most actively toxic of several glutathione compounds tested, 2,3,5-triglutathion-S-yl hydroquinone, targets a very specific region of the kidney, the outer stripe of the outer medulla (OSOM), whereas hydroquinone-associated adenomas are more randomly distributed and occur in the cortex as well as the medulla. A nongenotoxic mode of action that involves exacerbation of a spontaneously occurring rodent renal disease, chronic progressive nephropathy (CPN), is proposed and evaluated. This disease is particularly prominent in male rats and the evidence is consistent with an absence of any human counterpart; therefore, the increased incidence of renal tubule adenomas in hydroquinone-dosed male rats is without human consequence.

Ethyl tertiary-Butyl Ether: A Toxicological Review

A number of oxygenated compounds (oxygenates) are available for use in gasoline to reduce vehicle exhaust emissions, reduce the aromatic compound content, and avoid the use of organo-lead compounds, while maintaining high octane numbers. Ethyl tertiary-butyl ether (ETBE) is one such compound. The current use of ETBE in gasoline or petrol is modest but increasing, with consequently similar trends in the potential for human exposure. Inhalation is the most likely mode of exposure, with about 30% of inhaled ETBE being retained by the lungs and distributed around the body. Following cessation of exposure, the blood concentration of ETBE falls rapidly, largely as a result of its metabolism to tertiary-butyl alcohol (TBA) and acetaldehyde. TBA may be further metabolized, first to 2-methyl-1,2-propanediol and then to 2-hydroxyisobutyrate, the two dominant metabolites found in urine of volunteers and rats. The rapid oxidation of acetaldehyde suggests that its blood concentration is unlikely to rise above normal as a result of human exposure to sources of ETBE. Single-dose toxicity tests show that ETBE has low toxicity and is essentially nonirritant to eyes and skin; it did not cause sensitization in a maximization test in guinea pigs. Neurological effects have been observed only at very high exposure concentrations. There is evidence for an effect of ETBE on the kidney of rats. Increases in kidney weight were seen in both sexes, but protein droplet accumulation (with α2u-globulin involvement) and sustained increases in cell proliferation occurred only in males. In liver, centrilobular necrosis was induced in mice, but not rats, after exposure by inhalation, although this lesion was reported in some rats exposed to very high oral doses of ETBE. The proportion of liver cells engaged in S-phase DNA synthesis was increased in mice of both sexes exposed by inhalation. ETBE has no specific effects on reproduction, development, or genetic material. Carcinogenicity studies have been conducted with ETBE, TBA, and ethanol (included in this review as an endogenous precursor of acetaldehyde in the absence of TBA). A single experiment with ETBE in rats and several experiments with ethanol in rats and mice were not considered adequate for an evaluation of ETBE carcinogenicity. In male rats only, TBA induced α2u-globulin nephropathy-related renal tubule adenomas. These are generally considered to have no human relevance. In addition, increases in thyroid follicular cell adenoma incidence were associated with TBA treatment in female mice. This result lacks independent confirmation and is not supported by experiments in which similar or higher internal doses of TBA were delivered.

Carcinogenesis studies of benzophenone in rats and mice

Benzophenone, an aryl ketone, is used primarily as a photoinitiator and fragrance enhancer. Groups of 50 male and 50 female F344 rats and B6C3 F1 mice were fed diets containing 0, 312, 625, and 1250 ppm benzophenone for 105 weeks. Survival of males exposed to 1250 ppm benzophenone was significantly less than that of controls. There was a positive trend in the incidence of renal tubule adenoma in male rats; these neoplasms were accompanied by significantly increased incidences of renal tubule hyperplasia. Increased incidences of mononuclear cell leukemia were observed in male rats exposed to 312 or 625 ppm benzophenone and in female rats exposed to 625 ppm benzophenone. Liver lesions observed included significantly increased incidences of hepatocytic centrilobular hypertrophy in all exposed groups of rats. In mice, survival of all exposed groups was generally similar to that of the control groups. In male mice, there were significantly increased incidences of hepatocellular adenoma in the 625 and 1250 ppm groups. In female mice, the incidences of hepatocellular adenoma in the 625 and 1250 ppm groups were higher than expected after adjusting for the lower body weights in these groups. The incidences of kidney nephropathy in exposed groups of female mice, as well as the severity of nephropathy in exposed groups of males, were significantly increased. The incidences of metaplasia of the olfactory epithelium were significantly increased in 1250 ppm mice. Rare histiocytic sarcomas were observed in female rats and mice in the 625 and 1250 ppm groups. Under the conditions of these 2-year studies, there was some evidence of carcinogenic activity of benzophenone in male F344/N rats based on increased incidences of renal tubule adenoma. There was equivocal evidence of carcinogenic activity of benzophenone in female F344/N rats based on the marginal increased incidences of mononuclear cell leukemia and histiocytic sarcoma. There was some evidence of carcinogenic activity of benzophenone in male B6C3F 1 mice based on increased incidences of hepatocellular neoplasms, primarily adenoma. There was some evidence of carcinogenic activity of benzophenone in female B6C3F 1 mice based on increased incidences of histiocytic sarcoma; the incidences of hepatocellular adenoma in female B6C3F 1 mice may have been related to benzophenone exposure.

Development of α2u-Globulin Nephropathy and Adrenal Medullary Pheochromocytomas in Male Rats Following Exposure to Stoddard Solvent IIC

Stoddard solvent IIC is widely used as a solvent in paints and varnishes, and for dry cleaning and other grease removal applications. Because concern exists regarding the long-term effects of occupational exposure in industrial settings, the toxicity and carcinogenicity of Stoddard solvent IIC were evaluated in male and female F344/N rats and B6C3F1 mice. Rats and mice were exposed to 0, 138, 275, 550, 1100, or 2200 mg/m3 Stoddard solvent IIC by whole-body inhalation for 3 mo, and to 0, 138 (male rats), 550, 1100, or 2200 (female rats and male and female mice) mg/m3 for 2 yr. The kidney, liver, and adrenal medulla were targets of Stoddard solvent IIC toxicity in rats. After 3 mo of exposure, male rats developed lesions characteristic of α2u-globulin nephropathy. Male and female rats displayed increased liver weights and/or clinical pathology changes suggestive of hepatic injury, although no accompanying histopathologic changes were observed. After 2 yr, increased incidences of adrenal medullary pheochromocytomas provided some evidence of carcinogenicity in male rats. Renal tubule adenomas were slightly increased in male rats after 2 yr, and may have been related to exposure. In mice, there was no chemical-related toxicity after 3 mo, with the exception of increased liver weights in male mice exposed to 2200 mg/m3. After 2 yr, the incidences of hepatocellular adenomas were increased in female mice exposed to 2200 mg/m3; however, these increases were marginal and associated with increases in body weight. There was no evidence of Stoddard solvent IIC carcinogenicity in female rats or male mice. In summary, inhalation exposures of Stoddard solvent IIC resulted in renal toxicity and adrenal medullary pheochromocytomas in male rats. The liver also appeared to be a site of toxicity in male and female rats and mice.

Fumonisin b1 carcinogenicity in a two-year feeding study using F344 rats and B6C3F1 mice.

Fumonisin B1 (FB1) is a mycotoxin isolated from Fusarium fungi that contaminate crops worldwide. A previous study demonstrated that FB1 promoted preneoplastic foci in initiated rats and induced hepatocellular carcinomas in BD IX rats at 50 parts per million (ppm), but fundamental dose-response data were not available to assist in setting regulatory guidelines for this mycotoxin. To provide this information, female and male F344/N/Nctr BR rats and B6C3F1 Nctr BR mice were fed for two years a powdered NIH-31 diet containing the following concentrations of FB1: female rats, 0, 5, 15, 50, and 100 ppm; male rats, 0, 5, 15, 50, and 150 ppm; female mice, 0, 5, 15, 50, and 80 ppm; male mice, 0, 5, 15, 80, and 150 ppm. FB1 was not tumorigenic in female F344 rats with doses as high as 100 ppm. Including FB1 in the diets of male rats induced renal tubule adenomas and carcinomas in 0/48, 0/40, 9/48, and 15/48 rats at 0, 5, 15, 50, and 150 ppm, respectively. Including up to 150 ppm FB1 in the diet of male mice did not affect tumor incidence. Hepatocellular adenomas and carcinomas were induced by FB1 in the female mice, occurring in 5/47, 3/48, 1/48, 19/47, and 39/45 female mice that consumed diets containing 0, 5, 15, 50, and 80 ppm FB1, respectively. This study demonstrates that FB1 is a rodent carcinogen that induces renal tubule tumors in male F344 rats and hepatic tumors in female B6C3F1 mice.

Carcinogenicity of dermally administered 1,2-dihydro-2,2,4-trimethylquinoline monomer in F344 rats and B6C3F1 mice.

1,2-Dihydro-2,2,4-trimethylquinoline (TMQ) was evaluated in a 2-year study in which groups of 60 male or female F344 rats received 0, 36 or 60 mg kg(-1) (0, 0.022, or 0.037 mg cm(-2)) and groups of 60 male or female B6C3F1 mice received 0, 3.6 or 10 mg kg(-1) (0, 0.00136, 0.00435 mg cm(-2)) in acetone by topical administration. Survival of all treated groups was comparable to survival of controls. Mean body weights of female rats were lower than those of controls throughout the study but mean body weights of male rats and male and female mice were comparable to the mean body weights of controls. No neoplasms of the skin were observed in any group of rats or mice. Acanthosis at the site of application was increased in male and female rats that received 60 or 100 mg kg(-1) and hyperkeratosis was increased in female rats that received 60 mg kg(-1). The incidences of renal tubule adenoma and renal tubule adenoma or carcinoma were increased significantly in the 60 and 100 mg kg(-1) groups of male rats. There were no neoplastic or non-neoplastic lesions in mice associated with exposure to 1,2-dihydro-2,2,4-trimethylquinoline. In a 1-year initiation-promotion study, groups of 30 female SENCAR mice received an initiating dose of 50 mg kg(-1) 1,2-dihydro-2,2,4-trimethylquinoline followed by promotion with 12-O-tetradecanoylphorbol-13-acetate (TPA), or an initiating dose of 7,12-dimethylbenzanthracene (DMBA) followed by promotion with 5, 10 or 25 mg kg(-1) 1,2-dihydro-2,2,4-trimethylquinoline. Other groups served as initiator control, promoter control, vehicle control and positive control (DMBA initiation, TPA promotion). In this system, 1,2-dihydro-2,2,4-trimethylquinoline-initiated skin was not promoted by TPA, and DMBA-initiated skin was not promoted by 1,2-dihydro-2,2,4-trimethylquinoline.

Toxicity and Carcinogenicity Studies of Oxazepam in the Fischer 344 Rat

Oxazepam and related benzodiazepines are used in the treatment of anxiety. Carcinogenicity studies of oxazepam were performed with the F344 rat because of marked differences in tumor responses observed in NTP studies with B6C3F1 and Swiss-Webster mice compared to the results of Sprague-Dawley rat studies submitted to the FDA by a manufacturer to support registration of the drug. Groups of 50 male and 50 female F344/N rats were fed diets containing 0, 625, 2500, or 5000 ppm oxazepam for up to 105 weeks. A stop-exposure group of 50 males and 50 females received 10,000 ppm oxazepam in diet for 26 weeks, after which animals received control diet. All 5000- and 10, 000-ppm stop-exposure males died before the end of the study. Survival of 2500-ppm males and females was lower than that of controls. Body weight gains of 2500- and 5000-ppm males and females were less than those of controls. Male rats exposed to 2500 ppm had an increased incidence of renal tubule adenoma and hyperplasia. In addition, the incidences of renal tubule adenoma and hyperplasia were increased in the 10,000-ppm stop-exposure group. The incidences of nephropathy in exposed females were greater than those in controls, and the severity of nephropathy increased in exposed males. Epithelial hyperplasia and chronic inflammation of the nonglandular stomach were increased in males given 2500 and 5000 ppm and the incidence of ulcers of the nonglandular stomach in 2500-ppm males was also greater than that in controls. In males exposed to 5000 ppm, mineralization of the glandular stomach and erosion of the duodenum were observed. In females exposed to 2500 ppm, the incidences of epithelial hyperplasia, chronic inflammation, and ulcers of the nonglandular stomach and the incidence of erosion in the glandular stomach were increased. The incidences of centrilobular hepatocyte hypertrophy in males and females given 2500 and 5000 ppm were greater than those in controls. In summary, there was equivocal evidence of carcinogenicity in males based on increased renal tubule adenomas in groups which also had significantly enhanced nephropathy. There was no evidence of carcinogenicity of oxazepam in females given a diet containing 625, 2500, or 5000 ppm for 2 years or 10,000 ppm for 6 months.

Relationship of hydroquinone-associated rat renal tumors with spontaneous chronic progressive nephropathy.

Hydroquinone exposure has been reported by the National Toxicology Program (NTP) to produce renal tubule adenomas and to exacerbate spontaneous chronic progressive nephropathy (CPN) in male F344 rats. A mechanism for hydroquinone-related tumorigenesis has not been established, but CPN is known to involve, and hydroquinone produces, enhanced renal tubule cell proliferation. Through an independent review of the renal histopathology from the NTP study, the grade of CPN and the presence of atypical tubule hyperplasia and adenomas was evaluated. Hydroquinone exposure in males at 50 mg/kg, produced a statistically significant increase in the grade of CPN. At 0, 25, and 50 mg/kg, 0/44, 4/49, and 15/51 male rats had either atypical tubule hyperplasias or adenomas; all were within areas of severe or end-stage CPN and were statistically significantly associated with CPN grade. Additionally, there was a dose-related increase in profiles believed to represent new tubule proliferation within areas of advanced CPN, as well as an apparent expansion of these into unusual complex tubule profiles in end-stage kidneys of the high-dose male group. In summary, this histopathological review suggest a mechanism for hydroquinone-related adenoma formation that includes enhancement of the severity of CPN coupled with stimulation of tubule proliferation.

Chronic Nephropathy and Renal Carcinogenicity of o-Benzyl- p-chlorophenol in F344/N Rats and B6C3F 1 Mice

Chronic Nephropathy and Renal Carcinogenicity of o -Benzyl- pchlorophenol in F344/N Rats and B6C3F 1 Mice. Marsman, D. S., Grumbein, S. L., Haseman, J. K., and Hailey, J. R. (1995). Fundam. Appl. Toxicol. 27, 252-262. o-Benzyl- p-chlorophenol, an aryl halide biocide, was evaluated in male and female F344/N rats and B6C3F 1 mice in a series of subchronic and 2-year toxicity and carcinogenicity studies. Kidney was the primary target of toxicity in the 13-week gavage studies in rats and mice, with increased nephropathy noted as low as 240 mg/kg in male rats. Considering the nephropathy to be dose-limiting, the chronic (2-year) study was conducted at lower doses (male rats: 30, 60, or 120 mg/kg; female rats: 60, 120, or 240 mg/kg; male and female mice: 120, 240, or 480 mg/kg; in corn oil; n = 50/group). Survival and body weights of dosed rats were similar to controls in the 2-year study. Survival of high-dose male and female mice, and body weights of all dosed male and mid- and high-dose female mice, were lower than controls. The incidence and severity of nephropathy increased with dose and length of treatment in both rats and mice. There was an increased incidence of renal tubule adenomas or carcinomas in both the mid- and high-dose male mice. Despite similar evidence of nephropathy, however, there were no increased incidences of neoplasms in female mice or in male or female rats. This study suggests therefore that while nephrotoxicity may have been a necessary component, factors other than the marked nephrotoxicity of o -benzyl- p-chlorophenol were critical to the development of renal carcinogenesis induced in only male mice.

Toxicity and carcinogenicity of t-butyl alcohol in rats and mice following chronic exposure in drinking water.

t-Butyl alcohol (TBA) was administered in drinking water to F344/N rats and B6C3F1 mice for two years using 60 animals/dose/sex/species. Male rats received doses of 0, 1.25, 2.5, or 5 mg/ml and females received 0, 2.5, 5, or 10 mg/ml, resulting in average daily doses of approximately 85, 195, or 420 mg TBA/kg body weight for males and 175, 330, or 650 mg/kg for females. Ten rats per group were evaluated after 15 months. Male and female mice received doses of 0, 5, 10, or 20 mg/ml, resulting in average daily doses of approximately 535, 1,035, or 2,065 mg TBA/kg body weight for males and 510, 1,015, or 2,105 mg/kg for females. Survival was significantly reduced in male rats receiving 5 mg/ml, female rats receiving 10 mg/ml, and male mice receiving 20 mg/ml. Long-term exposure to TBA produced increased incidences of renal tubule adenoma and carcinoma in male rats; transitional epithelial hyperplasia of the kidney in male and female rats; follicular cell adenoma of the thyroid in female mice; and follicular cell hyperplasia of the thyroid and inflammation and hyperplasia of the urinary bladder in male and female mice. In addition, a slight increase in follicular cell adenoma or carcinoma of the thyroid (combined) in male mice may have been related to the administration of TBA.

Chronic Nephropathy and Renal Carcinogenicity of o-Benzyl-p-chlorophenol in F344/N Rats and B6C3F1 Mice

o-Benzyl-p-chlorophenol, an aryl halide biocide, was evaluated in male and female F344/N rats and B6C3F1 mice in a series of subchronic and 2-year toxicity and carcinogenicity studies. Kidney was the primary target of toxicity in the 13-week gavage studies in rats and mice, with increased nephropathy noted as low as 240 mg/kg in male rats. Considering the nephropathy to be dose-limiting, the chronic (2-year) study was conducted at lower doses (male rats: 30, 60, or 120 mg/kg; female rats: 60, 120, or 240 mg/kg; male and female mice: 120, 240, or 480 mg/kg; in corn oil; n=50/group). Survival and body weights of dosed rats were similar to controls in the 2-year study. Survival of high-dose male and female mice, and body weights of all dosed male and mid- and high-dose female mice, were lower than controls. The incidence and severity of nephropathy increased with dose and length of treatment in both rats and mice. There was an increased incidence of renal tubule adenomas or carcinomas in both the mid- and high-dose male mice. Despite similar evidence of nephropathy, however, there were no increased incidences of neoplasms in female mice or in male or female rats. This study suggests therefore that while nephrotoxicity may have been a necessary component, factors other than the marked nephrotoxicity of o-benzyl-p-chloro-phenol were critical to the development of renal carcinogenesis induced in only male mice.

Measurement of Nuclear DNA Modification by 32P-Postlabeling in the Kidneys of Male and Female Fischer 344 Rats after Multiple Gavage Doses of Hydroquinone

Measurement of Nuclear DNA Modification by 32P-Postlabeling in the Kidneys of Male and Female Fischer 344 Rats after Multiple Garage Doses of Hydroquinone. English, J. C., Hill, T., O'Donoghue, J. L., and Reddy, M. V. (1994). Fundam. Appl. Toxicol. 23, 391-396.Oral administration of hydroquinone (HQ) to male Fischer 344 (F344) rats results in dose-related kidney toxicity beginning with mild enzymuria by 1 week, significant cell proliferation by 6 weeks, and nephropathy and an increase in the incidence of renal tubule adenomas after 2 years. Female F344 rats, B6C3F1 mice, Sprague-Dawley rats, dogs, and humans are resistant to the renal toxicity of HQ associated with repeated exposure. To determine the potential of HQ to induce covalent DNA adducts in the kidney, male and female F344 rats were given 0, 2.5, 25, or 50 mg/kg HQ by gavage for 6 weeks, and nuclear DNA isolated from kidneys was analyzed by the 32 P-postlabeling assay. At 50 mg/kg, males, but not females, showed an increase in the rate of excretion of N -acetyl-β-d-glucosaminidase, indicative of proximal tubular damage. Analysis of nuclear DNA preparations by the postlabeling assay showed that HQ does not produce covalent DNA adducts in the kidneys of male and female rats. The assay's lower limit of detection is 1 adduct in 109 to 1010 DNA nucleotides. No treatment-related increases in background radioactivity levels on the chromatograms were seen at locations corresponding to the major in vitro adducts of HQ and p-benzoquinone. HQ treatment, however, resulted in the reduction of the levels of certain endogenous adducts (I-compounds), the biological significance of which is unknown. The results indicate that HQ does not produce covalent DNA adducts in the kidneys of male and female rats after repeated oral administration at nephrotoxic dose levels, and suggest a nongenotoxic etiology of benign tumors in the kidneys of male F344 rats treated with HQ.

Measurement of Cell Proliferation in the Kidneys of Fischer 344 and Sprague-Dawley Rats after Gavage Administration of Hydroquinone

Measurement of Cell Proliferation in the Kidneys of Fischer 344 and Sprague-Dawley Rats after Garage Administration of Hydroquinone. English, J. C., Perry, L. G., Vlaovic, M., Moyer, C., and O'Donoghue, J. L. (1994). Fundam. Appl. Toxicol. 23, 397-406.Oral administration of hydroquinone (HQ) over 2 years to male Fischer 344 (F344) rats results in a dose-related nephropathy and an increase in the incidence of renal tubule adenomas. Female F344 rats, B6C3F1 mice, and Sprague-Dawley (SD) rats are resistant to the chronic renal toxicity of HQ, and nephrotoxicity was not seen in dogs or humans following subchronic exposure. To better characterize the early development of renal toxicity in rats, cell proliferation was quantitated within the proximal (P1, P2, and P3) and distal tubule segments of the kidney in rats given 0, 2.5, 25, or 50 mg/kg HQ by gavage. Male and female F344 rats were treated for 1, 3, or 6 weeks, and male SD rats were treated for 6 weeks. Cell proliferation was quantitated by incorporation of bromodeoxyuridine, detected immunohistochemically, into newly synthesized DNA. At 6 weeks, renal cell proliferation was increased over vehicle-controls in male F344 rats dosed at 50 mg/kg. Significant elevations (p < 0.001) occurred in the P1 segments (87%) and in the P2 segments (50%) but the elevation in the P3 segment (34%) was not statistically significant. Urinalyses revealed increases in the rate of excretion of enzymes indicative of proximal tubular damage. Histopathologic evaluation of the kidneys was consistent with a dose-related tubular degeneration in the male F344 rat. No chemical-related effects were observed in the kidneys of female F344 and male SD rats. These data parallel the findings of sex and strain-specific kidney adenomas in the 2-year bioassays, and suggest that chemically induced cell proliferation secondary to toxicity may be important in the pathogenesis of benign renal tumors in male F344 rats treated with HQ.