Disposition of [14C]hydroquinone in Harlan Sprague-Dawley rats and B6C3F1/N mice: species and route comparison

1. Hydroquinone (HQ) is present in some foods and has varied industrial, medical and consumer uses. These studies were undertaken to investigate the disposition of HQ in rats and mice following gavage, intravenous (IV) and dermal exposure.

2. [^14?C]HQ administered (0.5, 5 or 50?mg/kg) by gavage or IV routes to male and female Harlan Sprague-Dawley (HSD) rats and B6C3F1/N mice was well absorbed and rapidly excreted primarily in urine. Radioactivity remaining in tissues at 72?h was?<1% for both species at all dose levels and routes. No sex, species or route related differences in disposition were found.

3. With dermal application of 2, 10 or 20% [^14?C]HQ, mice absorbed higher percentages of the dose than rats (37, 12, 12% versus 18.6, 4.43 and 1.79%, respectively). The HQ mass absorbed by mice increased with dose, while in rats it was more constant over the dose range. Absorbed HQ was rapidly excreted in urine of both species and urinary excretion indicated continued absorption over the exposure period. No sex differences in disposition were found.

4. The oral bioavailability of HQ at 5?mg/kg was low in both rats (1.6%) and mice (3.9%) demonstrating significant first pass metabolism. Dermal bioavailability in mice was 9.4% following application of 2% formulation.

5. Urinary metabolites for both species and all routes included the glucuronide and sulfate conjugates; no parent was found in urine.     

Metabolism and disposition of 2-ethylhexyl-p-methoxycinnamate following oral gavage and dermal exposure in Harlan Sprague Dawley rats and B6C3F1/N mice and in hepatocytes in vitro

1. 2-Ethylhexyl-p-methoxycinnamate (EHMC) is commonly used as an ingredient in sunscreens, resulting in potential oral and dermal exposure in humans.

2. Clearance and metabolism of EHMC in hepatocytes and disposition and metabolism of EHMC in rodents following oral (8–800?mg/kg) intravenous (IV) (8?mg/kg) or dermal (0.8–80?mg/kg representing 0.1–10% formulation concentration) exposure to [¹⁴C]EHMC were investigated in rats and mice.

3. EHMC was rapidly cleared from rat and mouse hepatocytes (half-life ≤3.16?min) and less rapidly (half-life ≤48?min) from human hepatocytes.

4. [¹⁴C]EHMC was extensively absorbed and excreted primarily in urine by 72?h after oral administration to rats (65–80%) and mice (63–72%). Oral doses to rats were excreted to a lesser extent (3–8%) in feces and as CO₂ (1–4%). Radioactive residues in tissues were <1% of the dose. There were no sex or species differences in disposition in rats.

5. Following dermal application, 34–42% of an 8–mg/kg dose was absorbed in rats, and 54–62% in mice in 72–h.

6. Among numerous urinary metabolites associated with hydrolysis of the ester, two potential reproductive and developmental toxicants, 2-ethylhexanol and 2-ethylhexanoic acid were produced by metabolism of EHMC.     

Metabolism and disposition of [14C]dimethylamine borane in male Harlan Sprague Dawley rats following gavage administration,intravenous administration and dermal application

Abstract

1. Dimethylamine borane (DMAB) is used as a reducing agent in the manufacturing of a variety of products and in chemical synthesis. National Toxicology Program is evaluating the toxicity of DMAB in rodents following dermal application. The objective of this study was to evaluate the metabolism and disposition of DMAB in male Harlan Sprague Dawley (HSD) rats.

2. Disposition of radioactivity was similar between gavage and intravenous administration of 1.5?mg/kg [¹⁴C] DMAB, with nearly 84%–89% of the administered radioactivity recovered in urine 24?h post dosing. At 72?h, only 1% or less was recovered in feces, 0.3% as CO₂, and 0.5%–1.4% as volatiles and 0.3%–0.4 % in tissues.

3. The absorption of [¹⁴C]DMAB following dermal application was moderate; percent dose absorbed increased with the dose, with 23%, 32% and 46% of dose absorbed at 0.15, 1.5 and 15?mg/kg, respectively. Urinary and fecal excretion ranged from 18%–37% and 2%–4% of dose, respectively, and 0.1%–0.2% as CO₂, and 1%–3% as volatiles. Tissue retention of the radiolabel was low ～1%, but was higher than following the gavage or intravenous administration.

4. Following co-adminsitration of DMAB and sodium nitrite by gavage, N-nitrosodimethylamine was not detected in blood or urine above the limit of quantitation of the analytical method of 10?ng/mL.

5. Absorption of DMAB in fresh human skin in vitro was ～41% of the applied dose: the analysis of the receptor fluid shows that the intact DMAB complex can be absorbed through the skin.     

Disposition and metabolism of N,N-dimethylacetoacetamide in male F344 and Wistar-Han rats and female B6C3F1 mice

1. N,N-dimethylacetoacetamide (DMAAm) is a β-dicarbonyl compound used as an industrial intermediate. This study investigated the disposition and metabolism of [¹⁴C]DMAAm in male rats and female mice.

2. A single oral dose of [¹⁴C]DMAAm (target dose of 10 or 130?mg/kg) was administered to male F344 and Wistar-Han rats. [¹⁴C]DMAAm was almost completely absorbed and excreted in urine, with ca. 80?90% of the dose recovered within 24?h for both rat strains. Fecal excretion and CO₂ exhalation were minimal (1 and 2%, respectively). Less than 3% of the dose remained in tissues at 24?h. There was no apparent dose- or strain-related difference in the disposition of [¹⁴C]DMAAm in rats.

3. In female B6C3F1 mice administered 8?mg/kg [¹⁴C]DMAAm, 80% of the administered radioactivity was recovered in urine and cage rinse in 24?h.

4. Urinary metabolites were isolated and characterized by liquid chromatography /mass spectrometry following oral administration of 435?mg/kg [¹⁴C]DMAAm in male F344 rats. Metabolism occurred via reduction of the 3-keto group and oxidation of the N-methyl groups, to give N,N-dimethyl-3-hydroxybutanamide, N-methyl-N-hydroxymethyl-3-hydroxybutanamide, and N-hydroxymethyl-3-hydroxybutanamide, and N-demethylation to give N-monomethylacetoacetamide (MMAAm).

     

Toxicokinetics of bis(2-chloroethoxy)methane following intravenous administration and dermal application in male and female F344/N rats and B6C3F1 mice

In the National Toxicology Program's toxicity studies, rats were more sensitive than mice to Bis(2-chloroethoxy)methane (CEM) - induced cardiac toxicity following dermal application to male and female F344/N rats and B6C3F1 mice. Thiodiglycolic acid (TDGA) is a major metabolite of CEM in rats. It has been implicated that chemicals metabolized to TDGA cause cardiac toxicity in humans. Therefore, the toxicokinetics of CEM and TDGA were investigated in male and female F344/N rats and B6C3F1 mice following a single intravenous administration or dermal application of CEM to aid in the interpretation of the toxicity data. Absorption of CEM following dermal application was rapid in both species and genders. Bioavailability following dermal application was low but was higher in rats than in mice with females of both species showing higher bioavailability than males. CEM was rapidly distributed to the heart, thymus, and liver following both routes of administration. Plasma CEM C_max and AUC_∞ increased proportionally with dose, although at the dermal dose of 400 mg/kg in rats and 600 mg/kg in mice non-linear kinetics were apparent. Following dermal application, dose-normalized plasma CEM C_max and AUC_∞ was significantly higher in rats than in mice (p-value < 0.0001 for all comparisons except for C_max in the highest dose groups where p-value = 0.053). In rats, dose-normalized plasma CEM C_max and AUC_∞ was higher in females than in males: however, the difference was significant only at the lowest dose (p-value = 0.009 for C_max and 0.056 for AUC_∞). Similar to rats, female mice also showed higher C_max and AUC_∞ in females than in male: the difference was significant only for C_max at the lowest dose (p-value = 0.002). Dose-normalized heart CEM C_max was higher in rats than in mice and in females than their male counterparts. The liver CEM C_max was lower compared to that of heart and thymus in both rats and mice following intravenous administration and in rats following dermal application. This is likely due to the rapid metabolism of CEM in the liver as evidenced by the high concentration of TDGA measured in the liver. Dose-normalized plasma and heart TDGA C_max values were higher in rats compared to mice. In rats, females had higher plasma and heart TDGA C_max than males; however, there was no gender difference in plasma or heart TDGA C_max in mice. These findings support the increased sensitivity of rats compared to mice to CEM-induced cardiac toxicity. Data also suggest that, either CEM C_max or AUC can be used to predict the CEM-induced cardiac toxicity. Although, both plasma and heart TDGA C_max was consistent with the observed species difference and the gender difference in rats, the gender difference in mice to cardiac toxicity could not be explained based on the TDGA data. This animal study suggests that toxicologically significant concentrations of CEM and TDGA could possibly be achieved in the systemic circulation and/or target tissues in humans as a result of dermal exposure to CEM.     

Metabolism and disposition of [14C]5-amino-o-cresol in female F344 rats and B6C3F1 mice

The metabolism and disposition of [¹⁴C]5-amino-o-cresol (AOC) in female F344 rats following oral, intravenous, and dermal administration and in female B6C3F1 mice following oral administration were studied. Greater than 80% of a single oral dose (4.0–357 mg kg^?1) or intravenous dose (2.7 mg kg^?1) was excreted in urine within 24 h. When the dosing site was protected from grooming, less than 10% of the dermal dose (2.5 and 26 mg kg^?1, rinsed off after 6 h) was absorbed within 24 h, and most of the absorbed radioactivity was excreted in urine. For the unprotected dermal dose, grooming played a major role in the absorption of AOC. Very little AOC-derived radioactivity was present in the surveyed tissues after 24 or 72 h regardless of route, dose level, or species. Five urinary metabolites were identified: 5-acetamido-1,4-dihydroxy-2-methylbenzene glucuronide, AOC O-glucuronide, AOC O-sulfate, N-acetyl-AOC O-glucuronide, and N-acetyl-AOC O-sulfate.     

Disposition of fragrance ingredient [14C]1-(1,2,3,4,5,6,7,8-octahydro-2,3,8,8-tetramethyl-2-naphthalenyl)ethanone in male Fisher rats following oral administration and dermal application

Abstract

1. Disposition of 1-(1,2,3,4,5,6,7,8-octahydro-2,3,8,8-tetramethyl-2-naphthalenyl)ethanone (β-OTNE), a fragrance ingredient in variety of consumer products, was investigated following a single oral (20?mg/kg) or a dermal (55 or 550?mg/kg) dose of [¹⁴C]β-OTNE to male Fisher rats.

2. Following oral administration, 28% and 39% of the dose was recovered in urine and feces, respectively, 48?h following administration. About 73% of a 20?mg/kg dose was excreted in bile within 48?h post-administration supporting significant oral absorption of [¹⁴C]β-OTNE.

3. Following dermal application to a covered site, absorption of [¹⁴C]β-OTNE 96?h following application was low (ca. 14%) and dose-independent. When the dose site was uncovered, the absorption increased to ca. 33% (55?mg/kg) and ca. 72% (550?mg/kg).

4. [¹⁴C]β-OTNE was distributed to tissues following both routes of exposure with the highest radioactive equivalents found in bladder, liver, kidney, adipose and pancreas.

5. Elimination of [¹⁴C]β-OTNE equivalents in blood and tissues was slow following both oral and dermal application suggesting potential for accumulation following multiple exposure.     

The pharmacokinetics of dichloromethane. I. Disposition in B6C3F1 mice following intravenous and oral administration

The tissue distribution and metabolism of dichloromethane (DCM; CH2Cl2) was investigated in B6C3F1 mice following iv or oral administration. The route of exposure and the composition of the dosing solution were found to have a significant effect on the pharmacokinetics. Following single iv doses of 10 or 50 mg [14C]DCM/kg dose-dependent metabolism to 14CO2 and 14CO and rapid pulmonary clearance of unchanged 14CH2Cl2 characterized the elimination of DCM from the body. The highest concentrations of 14CH2Cl2 were found in the liver, lung and kidney, with more than 50% of the total radioactivity in these tissues represented by the parent compound. When DCM was administered orally in single gavage doses for 14 consecutive days at treatment levels of 50 mg/kg in water or 500 and 1000 mg/kg in corn oil, rapid absorption and elimination of DCM characterized the treatment in water while distinctly slower trends were found for the doses in corn oil. No observable pharmacokinetic or metabolic effect resulted from repeated oral dosing over the 2-wk treatment period.     

Disposition and metabolism of N,N-dimethylacetoacetamide in male F344 and Wistar-Han rats and female B6C3F1 mice

N,N-dimethylacetoacetamide (DMAAm) is a β-dicarbonyl compound used as an industrial intermediate. This study investigated the disposition and metabolism of [1?C]DMAAm in male rats and female mice. A single oral dose of [1?C]DMAAm (target dose of 10 or 130?mg/kg) was administered to male F344 and Wistar-Han rats. [1?C]DMAAm was almost completely absorbed and excreted in urine, with ca. 80-90% of the dose recovered within 24?h for both rat strains. Fecal excretion and CO? exhalation were minimal (1 and 2%, respectively). Less than 3% of the dose remained in tissues at 24?h. There was no apparent dose- or strain-related difference in the disposition of [1?C]DMAAm in rats. In female B6C3F1 mice administered 8?mg/kg [1?C]DMAAm, 80% of the administered radioactivity was recovered in urine and cage rinse in 24?h. Urinary metabolites were isolated and characterized by liquid chromatography /mass spectrometry following oral administration of 435?mg/kg [(1?C]DMAAm in male F344 rats. Metabolism occurred via reduction of the 3-keto group and oxidation of the N-methyl groups, to give N,N-dimethyl-3-hydroxybutanamide, N-methyl-N-hydroxymethyl-3-hydroxybutanamide, and N-hydroxymethyl-3-hydroxybutanamide, and N-demethylation to give N-monomethylacetoacetamide (MMAAm).     

Characterization of calcitonin gene-related peptide(CGRP) receptors in intramural coronary arteries from male and female Sprague Dawley rats

1. In this study we characterized the CGRP-receptor subtype by Schild-plot analysis using the C-terminal fragment, human-αCGRP(8–37), a putative competitive CGRP₁-receptor selective antagonist. In addition, the effect of rat-αCGRP was compared with that of homologous peptides rat-βCGRP, rat-amylin, rat-adrenomedullin and [Cys(Acm)^2,7]-human-αCGRP, a putative selective CGRP₂-receptor agonist, in the left coronary arteries of 3 months old male and female Sprague Dawley rats.
2. Isolated rings from the distal, intramural part of the left anterior descending (LAD) coronary artery in both groups of rats were mounted on a double wire-myograph. The arteries were then stretched to their optimal lumen diameter for active tension development and precontracted with 10⁻⁵ M prostaglandin F_2α (PGF_2α), after which agonists were added to the organ bath in a cumulative manner.
3. Rat-αCGRP induced endothelium-independent relaxations in male and female Sprague-Dawley rats. Rat-βCGRP concentration-response relations (10⁻¹¹–10⁻⁷ M) were similar to those of rat-αCGRP in either sex. The maximal relaxations induced by rat-amylin and rat-adrenomedullin, both at 10⁻⁶ M, were significantly (P<0.05) lower than those induced by rat-α- and rat-βCGRP. In contrast, the selective CGRP₂-receptor agonist [Cys(Acm)^2,7]-human-αCGRP failed to induce significant relaxations at the highest concentration used (10⁻⁷ M) in the coronary arteries of male and female rats.
4. The C-terminal fragment, human-αCGRP(8–37) blocked concentration-dependently (10⁻⁷–10⁻⁶ M) the rat-αCGRP-induced relaxation in 10⁻⁵ M PGF_2α-precontracted coronary arteries. The slopes of the regression lines of the Schild-plots for both male and female rats were not significantly (P>0.05) different from unity and the pA₂ values for human-αCGRP(8–37) were 6.93 and 6.98 in arteries from male and female rats, respectively. There was no significant (P>0.05) difference in estimated pK_B values for human-αCGRP(8–37) between male (6.99±0.10, n=13) and female (6.95±0.08, n=13) rats.
5. The concentration-response relationships for rat-α- and rat-βCGRP were similar in male and female Sprague Dawley rats. The predominant CGRP receptor subtype in small intramural coronary arteries appeared to belong to the CGRP₁-receptor subtype in both sexes.

     

Distribution and metabolism of (5-hydroxymethyl)furfural in male F344 rats and B6C3F1 mice after oral administration.

(5-Hydroxymethyl)furfural (HMF), a heat-induced decomposition product of hexoses, is present in food and drink. Recent reports have shown HMF to be an in vitro mutagen after sulfate conjugation and to be a promoter as well as a weak initiator of colonic aberrant foci in rats. In order to investigate the metabolic activation further and to provide information for HMF toxicology studies, the disposition of [14C]-HMF has been investigated in male F344 rats and B6C3F1 mice following po administration of either 5, 10, 100, or 500 mg/kg. Tissue distribution results indicated that absorption of HMF was rapid in male rats and mice and that tissue concentrations in male mice at the earliest time point are not linearly proportional to dose. Excretion was primarily via the urine in both, with 60-80% of the administered dose excreted by this route in 48 h. Tissue/blood ratios of HMF-derived radioactivity were greater than 1 for liver and kidney. Three metabolites were identified and quantitated in urine. Formation of one of the metabolites, N-(5-hydroxymethyl-2-furoyl)glycine, was inversely proportional to dose in rats but not mice. None of the metabolites were sulfate conjugates nor likely to be formed from sulfate conjugates. There were relatively low levels of nonextractable radioactivity in liver, kidney, and intestines, indicating that some reactive intermediate(s) may be formed.     

Toxicity and carcinogenicity studies of 4-methylimidazole in F344/N rats and B6C3F1 mice

4-Methylimidazole (4MI) is used in the manufacture of pharmaceuticals, photographic chemicals, dyes and pigments, cleaning and agricultural chemicals, and rubber. It has been identified as a by-product of fermentation in foods and has been detected in mainstream and side stream tobacco smoke. 4MI was studied because of its high potential for human exposure. Groups of 50 male and 50 female F344/N rats were fed diets containing 0-, 625-, 1,250-, or 2,500 ppm 4MI (males) or 0-, 1,250-, 2,500-, or 5,000 ppm 4MI (females) for 106 weeks. Based on the food consumption the calculated average daily doses were approximately 30, 55, or 115 mg 4MI/kg body weight to males and 60, 120, or 250 mg 4MI/kg to females. Survival of all exposed groups of males and females was similar to that of the control groups. The mean body weights of males in the 1,250- and 2,500 ppm groups and females in the 2,500- and 5,000 ppm groups were less than those of the control groups throughout the study. Feed consumption by 5,000 ppm females was less than that by the controls. Clonic seizures, excitability, hyperactivity, and impaired gait were observed primarily in 2,500- and 5,000 ppm females. The incidence of mononuclear cell leukemia in the 5,000 ppm females was significantly greater than that in the controls. The incidences of hepatic histiocytosis, chronic inflammation, and focal fatty change were significantly increased in all exposed groups of male and female rats. The incidences of hepatocellular eosinophilic and mixed cell foci were significantly increased in 2,500 ppm males and 5,000 ppm females. Groups of 50 male and 50 female B6C3F1 mice were fed diets containing 0-, 312-, 625-, or 1,250 ppm 4MI for 106 weeks. Based on the food consumption the calculated average daily doses were approximately 40, 80, or 170 mg 4MI/kg body weight to males and females. Survival of all exposed groups of males and females was similar to that of the control groups. Mean body weights of males and females in the 1,250 ppm groups and that in the 312- and 625 ppm females were less than those of the control groups. Feed consumption by exposed groups of male and female mice was similar to that by the controls. The incidences of alveolar/bronchiolar adenoma in all exposed groups of females, alveolar/bronchiolar carcinoma in 1,250 ppm males, and alveolar/bronchiolar adenoma or carcinoma (combined) in 1,250 ppm males and 625- and 1,250 ppm females were significantly greater than those in the control groups. The incidence of alveolar epithelial hyperplasia was significantly increased in the 1,250 ppm females. 4MI is carcinogenic inducing alveolar/bronchiolar adenoma and carcinoma in male and female mice. 4MI may also induce mononuclear cell leukemia in female rats. An erratum to this article can be found at     

A double-tracer technique to characterize absorption,distribution, metabolism and excretion (ADME) of [14C]-basimglurant and absolute bioavailability after oral administration and concomitant intravenous microdose administration of [13C6]-labeled basimglurant in humans

1.?The emerging technique of employing intravenous microdose administration of an isotope tracer concomitantly with an [¹⁴C]-labeled oral dose was used to characterize the disposition and absolute bioavailability of a novel metabotropic glutamate 5 (mGlu5) receptor antagonist under clinical development for major depressive disorder (MDD).

2. Six healthy volunteers received a single 1?mg [¹²C/¹⁴C]-basimglurant (2.22 MBq) oral dose and a concomitant i.v. tracer dose of 100?μg of [¹³C₆]-basimglurant. Concentrations of [¹²C]-basimglurant and the stable isotope [¹³C₆]-basimglurant were determined in plasma by a specific LC/MS-MS method. Total [¹⁴C] radioactivity was determined in whole blood, plasma, urine and feces by liquid scintillation counting. Metabolic profiling was conducted in plasma, urine, blood cell pellet and feces samples.

3. The mean absolute bioavailability after oral administration (F) of basimglurant was ～67% (range 45.7–77.7%). The major route of [¹⁴C]-radioactivity excretion, primarily in form of metabolites, was in urine (mean recovery 73.4%), with the remainder excreted in feces (mean recovery 26.5%). The median t_max for [¹²C]-basimglurant after the oral administration was 0.71?h (range 0.58–1.00) and the mean terminal half-life was 77.2?±?38.5?h. Terminal half-life for the [¹⁴C]-basimglurant was 178?h indicating presence of metabolites with a longer terminal half-life. Five metabolites were identified with M1-Glucuronide as major and the others in trace amounts. There was minimal binding of drug to RBCs. IV pharmacokinetics was characterized with a mean?±?SD CL of 11.8?±?7.4?mL/h and a Vss of 677?±?229?L.

4. The double-tracer technique used in this study allowed to simultaneously characterize the absolute bioavailability and disposition characteristics of the new oral molecular entity in a single study.     

NTP Toxicology and carcinogenesis studies of bromodichloromethane (CAS No. 75-27-4) in male F344/N rats and female B6C3F1 mice (Drinking Water Studies)

Bromodichloromethane is a by-product of the chlorination of drinking water. It is formed by the halogen substitution and oxidation reactions of chlorine with naturally occurring organic matter (e.g., humic or fulvic acids) in water containing bromide. Bromodichloromethane has been shown to be carcinogenic at multiple sites in rats (large intestine and kidney) and in mice (liver and kidney) after administration by gavage in corn oil. To further characterize its dose-response relationships for evaluations of human risk, bromodichloromethane was nominated to the NTP by the United States Environmental Protection Agency for toxicity and carcinogenicity studies in rats and mice by drinking water exposure. Male F344/N rats and female B6C3F1 mice were exposed to bromodichloromethane (greater than 98% pure) in drinking water for 3 weeks or 2 years. Genetic toxicology studies were conducted in Salmonella typhimurium, L5178Y mouse lymphoma cells, cultured Chinese hamster ovary cells, mouse bone marrow cells, and mouse peripheral blood erythrocytes. 3-WEEK STUDY IN RATS: Groups of 10 male F344/N rats were exposed to target concentrations of 0, 43.7, 87.5, 175, 350, or 700 mg/L bromodichloromethane (equivalent to average daily doses of approximately 0, 6, 12, 20, 38, or 71 mg bromodichloromethane/kg body weight) in drinking water for 3 weeks. All rats survived to the end of the study. The mean body weight gains of 350 and 700 mg/L rats were significantly less than that of the controls. Concentration-related decreases in water consumption were evident during the first week on study. Relative kidney weights of rats in the 175, 350, and 700 mg/L groups were significantly greater than that of the controls. There were no significant chemical-related histopathological changes. 3-WEEK STUDY IN MICE: Groups of 10 female B6C3F1 mice were exposed to target concentrations of 0, 43.7, 87.5, 175, 350, or 700 mg/L bromodichloromethane (equivalent to average daily doses of approximately 0, 6, 10, 16, 29 or 51 mg/kg) in drinking water for 3 weeks. All mice survived to the end of the study. Final mean body weights of the 175, 350, and 700 mg/L mice and mean body weight gains of 350 and 700 mg/L mice were significantly less than those of the controls. These decreases were attributed to decreased water consumption. There were significant concentration-related decreases in water consumption by groups exposed to 87.5 mg/L or greater throughout the study; these decreases were attributed to poor palatability of the dosed water. Relative liver, kidney, and thymus weights of mice in the 350 and 700 mg/L groups were significantly greater than those of the controls. Absolute lung weights of mice in the 350 and 750 mg/L groups were significantly less than that of the controls. There were no significant chemical-related histopathological changes. 2-YEAR STUDY IN RATS: Groups of 50 male F344/N rats were exposed to target concentrations of 0, 175, 350, or 700 mg/L bromodichloromethane (equivalent to average daily doses of approximately 0, 6, 12, or 25 mg/kg) in drinking water for 2 years. Survival of exposed groups was similar to that of the controls. Mean body weights of all exposed groups were generally similar to those of the controls throughout the study. Water consumption by exposed rats was less than that by the controls throughout the study; the decreases were attributed to poor palatability of the dosed water. There were no increased incidences of neoplasms that were attributed to bromodichloromethane. The incidences of chronic inflammation in the liver of the 350 and 700 mg/L groups were significantly greater than that in the controls; however, the biological significance of these increases is uncertain. 2-YEAR STUDY IN MICE: Groups of 50 female B6C3F1 mice were exposed to target concentrations of 0, 175, 350, 700 mg/L bromodichloromethane (equivalent to average daily doses of approximately 9, 18, or 36 mg/kg) in drinking water for 2 years. Survival of exposed groups was similar to that of the controls. Mean body weights of all exposed groups were generally less than those of the controls from week 4 through the end of the study. Water consumption by exposed mice was less than that by the controls throughout the study; the decreases were attributed to poor palatability of the dosed water. The incidences of hepatocellular adenoma or carcinoma (combined) occurred with a negative trend, and the incidence in the 700 mg/L group was significantly decreased relative to the control group. The incidence of hemangiosarcoma in all organs was significantly decreased in the 350 mg/L group. GENETIC TOXICOLOGY: The results of in vitro mutagenicity tests with bromodichloromethane were mixed. Bromodichloromethane did not induce mutations in any of several tester strains of Salmonella typhimurium, with or without exogenous metabolic activation (S9 liver enzymes). In contrast to the negative results in Salmonella, tests for mutation induction in mouse lymphoma L5178Y/tk(+/-)cells were positive in the presence of induced rat liver S9; no mutagenic activity occurred in tests conducted without S9. In cytogenetic tests with cultured Chinese hamster ovary cells, bromodichloromethane induced a small increase in sister chromatid exchanges (SCEs) in one of four trials conducted in the presence of induced rat liver S9 enzymes; no significant increase in SCEs occurred without S9, and no induction of chromosomal aberrations occurred in bromodichloromethane-treated Chinese hamster ovary cells with or without S9. Results of in vivo tests for chromosomal damage were negative. No increases in the frequency of micronucleated erythrocytes were seen in bone marrow of male B6C3F1 mice administered bromodichloromethane by intraperitoneal injection for 3 days. In addition, no induction of micronuclei was observed in circulating erythrocytes of female B6C3F1 mice administered up to 700 mg/L bromodichloromethane in drinking water for 3 weeks. CONCLUSIONS: Under the conditions of this 2-year drinking water study, there was no evidence of carcinogenic activity of bromodichloromethane in male F344/N rats exposed to target concentrations of 175, 350, or 700 mg/L. There was no evidence of carcinogenic activity of bromodichloromethane in female B6C3F1 mice exposed to target concentrations of 175, 350, or 700 mg/L.     

[4-(4-氟苯基)-6-异丙基-2-(N-甲基-N-甲磺酰基氨基)嘧啶-5-基]甲醇含量测定和有关物质检查

目的:建立[4-(4-氟苯基)-6-异丙基-2-(N-甲基-N-甲磺酰基氨基)嘧啶-5-基]甲醇(瑞舒伐他汀中间体Ⅵ)含量及其有关物质的测定方法。方法:采用高效液相色谱法检测3批样品中主成分和有关物质的含量。色谱柱为Grace-Alltima C18;流动相为乙腈-0.025mo·lL-1磷酸二氢钠溶液(57∶43);检测波长235nm为主成分测定波长,220nm为有关物质测定波长;流速为1.0mL·min-1;柱温为25℃。结果:主成分与其有关物质均能完全分离;主成分检测浓度线性范围为65.20～391.18μg·mL-1(r=0.9999);低、中、高3个浓度回收率分别为99.16%、98.73%、100.59%(RSD分别为0.59%、0.67%、1.06%)。有关物质检测限为195.8ng·mL-1。3批样品中主成分含量分别为98.48%、99.32%、98.14%,有关物质含量分别为0.17%、0.13%、0.17%。结论:本方法准确、可靠、专属性强,可用于瑞舒伐他汀中间体Ⅵ的含量测定及质量控制。     

Oxidative stress in female B6C3F1 mice following acute and subchronic exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD).

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a highly persistent trace environmental contaminant and is one of the most potent toxicants known to man. Hassoun et al. (1998, Toxicol. Sci. 42, 23-27) reported an increase in the production of reactive oxygen species (ROS) in the brain of female B6C3F1 mice following subchronic exposure to TCDD at doses as low as 0.45 ng/kg/day. In the present study, oxidative stress was characterized in liver, spleen, lung, and kidney following subchronic (0.15-150 ng/kg; 5 days/week for 13 weeks, po) or acute exposure (0.001-100 microg/kg, po) to TCDD in order to investigate the interaction between tissue concentration and time for production of ROS. Seven days following acute administration of TCDD, mice were sacrificed; they demonstrated increases in liver superoxide anion production (SOAP) and thiobarbituric acid reactive substances (TBARS) at doses of 10 and 100 microg/kg, associated with hepatic TCDD concentrations of 55 and 321 ng/g, respectively. Liver obtained from mice following subchronic TCDD exposure demonstrated an increase in SOAP and TBARS above controls at doses of 150 ng/kg/day with liver TCDD concentration of only 12 ng/g. Interestingly, glutathione (GSH) levels in lung and kidney following sub-chronic TCDD exposure were decreased at the low dose of 0.15 ng/kg/day. This effect disappeared at higher TCDD doses. The data suggest that higher tissue TCDD concentrations are required to elicit oxidative stress following acute dosing than with subchronic TCDD exposure. Therefore, the mechanism of ROS production following TCDD exposure does not appear to be solely dependent upon the concentration of TCDD within the tissue. In addition, very low doses of TCDD that result in tissue concentrations similar to the background levels found in the human population produced an effect on an oxidative stress endogenous defense system. The role of this effect in TCDD-mediated toxicity is not known and warrants further investigation.     

Metabolic changes in fed rats caused by chronic administration of ethyl 2[5(4-chlorophenyl)pentyl]oxirane-2-carboxylate, a new hypoglycaemic compound

Ethyl 2[5(4-chlorophenyl)pentyl]oxirane-2-carboxylate (POCA) is strongly hypoglycaemic in fasted normal and diabetic rats [H. P. O. Wolf, K. Eistetter and G. Ludwig, Diabetologia 22, 456 (1982)]. POCA was fed for 12 weeks to rats on a standard low-fat (3%) diet at levels of 0.05% and 0.2% to give daily intakes of about 50 and 200 mg/per kg body-wt respectively. This is much more than effective hypoglycaemic doses in fasted rats (5-10 mg/kg body-wt). The animals appeared healthy but they had slightly decreased rates of weight gain compared with the controls. POCA caused a 15% increase in the weight of the myocardium and accumulation of lipid in the liver. Chronic administration of POCA did not cause any large changes in water-soluble blood metabolite concentrations, although VLDL-triacylglycerol and both VLDL and HDL cholesterol concentrations were lowered. There were only small changes in some metabolites of the glycolytic and gluconeogenic pathways and the citrate cycle in liver and skeletal muscle. ATP concentrations were maintained in all groups. There were 2- to 3-fold increases in the total content of CoA and of carnitine and their acylated forms. POCA-feeding caused small decreases in LPL activities in heart and had variable effects in adipose tissue. POCA was also fed to a few rats on a high fat (30%) diet for 4 weeks. Only small changes in blood, liver and muscle metabolite concentrations were found, except for large increases in the liver CoA and carnitine contents. It was concluded that POCA does not cause large perturbations of glucose homeostasis, or acute toxic effects, during 12 weeks administration to normal animals at high dose levels. The very-long term importance of accumulation of lipid in liver; increase in myocardial weight; and also of hepatic peroxisomal proliferation [A. J. Bone, H. S. A. Sherratt, D. M. Turnbull and H. Osmundsen, Biochem. biophys. Res. Commun. 104, 708 (1982)] cannot yet be determined. The possible use of POCA and related compounds in the chemotherapy of diabetes merits further investigation.     

Toxicology and carcinogenesis studies of 4-methylimidazole (Cas No. 822-36-6) in F344/N rats and B6C3F1 mice (feed studies)

4-Methylimidazole is used in the manufacture of pharmaceuticals, photographic chemicals, dyes and pigments, cleaning and agricultural chemicals, and rubber. It has been identified as a by-product of fermentation in foods and has been detected in mainstream and sidestream tobacco smoke. 4-Methylimidazole was nominated by the National Cancer Institute for a long-term study because of the high potential for human exposure. Male and female F344/N rats and B6C3F1 mice were exposed to 4-methylimidazole (99.5% pure) in feed for 2 years. Fifteen-day and 14-week toxicity studies of 4-methylimidazole in F344/N rats and B6C3F1 mice are reported in NTP Toxicity Report No. 67. Genetic toxicology studies were conducted in Salmonella typhimurium, rat and mouse bone marrow cells, and mouse peripheral blood. 2-YEAR STUDY IN RATS: Groups of 50 male and 50 female rats were fed diets containing 0, 625, 1,250, or 2,500 ppm 4-methylimidazole (males) or 0, 1,250, 2,500, or 5,000 ppm 4-methylimidazole (females) (equivalent to average daily doses of approximately 30, 55, or 115 mg 4-methylimidazole/kg body weight to males and 60, 120, or 260 mg/kg to females) for 106 weeks. Survival of all exposed groups of male and female rats was similar to that of the control groups. Mean body weights of males in the 1,250 and 2,500 ppm groups and females in the 2,500 and 5,000 ppm groups were less than those of the control groups throughout the study; mean body weights of 1,250 ppm females were less after week 41. Feed consumption by 5,000 ppm females was less than that by the controls. Clonic seizures, excitability, hyperactivity, and impaired gait were observed primarily in 2,500 and 5,000 ppm females. The incidence of mononuclear cell leukemia in 5,000 ppm females was significantly greater than that in the controls, and the incidence exceeded the historical range in feed study controls. The incidences of hepatic histiocytosis, chronic inflammation, and focal fatty change were generally significantly increased in all exposed groups of male and female rats. The incidences of hepatocellular eosinophilic and mixed cell focus were significantly increased in 2,500 ppm males and 5,000 ppm females. 2-YEAR STUDY IN MICE: Groups of 50 male and 50 female mice were fed diets containing 0, 312, 625, or 1,250 ppm 4-methylimidazole (equivalent to average daily doses of approximately 40, 80, and 170 mg 4-methylimidazole/kg body weight to males and females) for 106 weeks. Survival of all exposed groups of male and female mice was similar to that of the control groups. Mean body weights of males and females in the 1,250 ppm groups were less than those of the control groups after weeks 17 and 12, respectively. Mean body weights of 312 and 625 ppm females were less after weeks 85 and 65, respectively. Feed consumption by exposed groups of male and female mice was generally similar to that by the controls. The incidences of alveolar/bronchiolar adenoma in all exposed groups of females, alveolar/bronchiolar carcinoma in 1,250 ppm males, and alveolar/bronchiolar adenoma or carcinoma (combined) in 1,250 ppm males and 625 and 1,250 ppm females were significantly greater than those in the control groups. The incidence of alveolar epithelium hyperplasia was significantly increased in 1,250 ppm females. GENETIC TOXICOLOGY: 4-Methylimidazole was not mutagenic in the S. typhimurium mutation assay when tested in strains TA97, TA98, TA100, and TA1535, with and without hamster or rat liver metabolic activation enzymes. No consistent or significant increases in the frequencies of micronucleated erythrocytes were seen in the bone marrow of male rats or mice treated with 4-methylimidazole by intraperitoneal injection, or in peripheral blood samples from male and female mice administered the compound in dosed feed for 14 weeks. CONCLUSIONS: Under the conditions of these 2-year studies, there was no evidence of carcinogenic activity of 4-methylimidazole in male F344/N rats exposed to 625, 1,250, or 2,500 ppm. There was equivocal evidence of carcinogenic activity of 4-methylimidazole in female F344/N rats based on increased incidences of mononuclear cell leukemia. There was clear evidence of carcinogenic activity of 4-methylimidazole in male and female B6C3F1 mice based on increased incidences of alveolar/bronchiolar neoplasms. Exposure to 4-methylimidazole resulted in nonneoplastic lesions in the liver of male and female rats and the lung of female mice and in clinical findings of neurotoxicity in female rats.