Glycine modulates the toxicity of benzyl acetate in F344 rats.

The influence of supplemental glycine on benzyl acetate (BA; a compound metabolized via the hippurate pathway)-induced toxicity was investigated. Groups of male F344 rats were fed NIH-07 diet containing 0, 20,000, 35,000, or 50,000 ppm BA for up to 28 days. Two additional groups were fed NIH-07 diet with 50,000 ppm BA and 27,000 ppm glycine or 50,000 ppm BA 32,000 ppm L-alanine; supplemental glycine and L-alanine were equimolar. The L-alanine group served as an amino nitrogen control. A third group was fed NIH-07 diet with 32,000 ppm L-alanine and served as an untreated isonitrogenous control BA caused increase in mortality, body weight loss, the incidence of abnormal neurobehavioral signs such as ataxia and convulsions, along with astrocyte hypertrophy and neuronal necrosis in the cerebellum, hippocampus, and pyriform cortex of the brain. These effects were reduced significantly by supplementation with glycine but not with L-alanine. These results suggest that the neurodegeneration induced by BA is mediated by a depletion of the glycine pool and the subsequent excitotoxicity.

Toxicokinetics in the National Toxicology Program.

Toxic responses to test chemicals are known to be dependent on the exposure route, the kinetic behavior of the chemical, and the dose used in the toxicology study. Therefore, knowledge of internal dose is indispensable for the interpretation of toxicology study results, for the facilitation of interspecies scaling, and for risk assessment. By monitoring the blood and/or tissue concentrations of test chemical and/or metabolites versus time after administration of study chemicals by different routes, the bioavailability and kinetic characteristic of test chemicals can be readily obtained. This data can define the so-called linear dose range using area under the plasma concentration versus time curve, clearance, or other related toxicokinetic parameters, and can also be used to predict the possible bioaccumulation under multiple dose regimes. Changes in kinetic parameters after multiple exposures indicate alteration in how the animal handles the chemical (e.g., that there was enzyme induction or inhibition). A recommended approach for conducting toxicokinetic studies generally involves three steps. Step 1 is a preliminary study, which uses a minimum number of animals to estimate the range of blood/tissue concentrations, the required quantitation limit for the analytical method, and the optimal sampling times for the definitive toxicokinetic studies. Step 2 is the definitive study and generates blood and/or tissue concentration data for calculating the toxicokinetic parameters. Step 3 is the toxicokinetic study conducted in conjunction with the toxicology study to determine the internal dose and the effects of age and continuous exposure on kinetic parameters. Examples of the application of NTP toxicokinetic evaluations were also presented in this chapter, demonstrating their use in the design and interpretation of toxicology studies.

Effects of gavage versus dosed feed administration on the toxicokinetics of benzyl acetate in rats and mice.

Effects of gavage versus dosed feed administration on the toxicokinetics of benzyl acetate were studied in male F344 rats and B6C3F1 mice. Benzyl acetate was rapidly hydrolysed to benzyl alcohol and then oxidized to benzoic acid. After gavage administration of benzyl acetate in corn oil at 500 mg/kg (rats) and 1000 mg/kg (mice), high benzoic acid plasma concentrations were observed. In contrast, much lower benzoic acid plasma concentrations were found after dosed feed administration at about 615 mg/kg/day for rats and about 850 mg/kg/day for mice. Results show that although the daily doses of benzyl acetate are comparable, bolus gavage administration effectively saturated the benzoic acid elimination pathway whereas dosed feed administration did not. In contrast, hippuric acid plasma concentrations were similar after both gavage and dosed feed administration due to the depletion of the glycine supply pool. Study results could explain the different toxicity and carcinogenicity responses of benzyl acetate observed in 2-yr chronic gavage and dosed feed studies.

Toxicokinetics of oxazepam in rats and mice.

The comparative toxicokinetics of oxazepam were studied in F344 rats, B6C3F1 mice, and Swiss-Webster mice of both sexes after an i.v. dose of 20 mg/kg and oral gavage doses of 50, 200, and 400 mg/kg. In addition, the toxicokinetics of oxazepam in a 3-week dosed-feed study of male B6C3F1 mice at 125 and 2500 ppm were also investigated. Results indicated that the elimination of oxazepam from plasma after i.v. injection in both rats and mice were first-order and could be best described by a two-compartment model with a terminal elimination half-life of 4-5 h for rats and 5-7 h for mice. After oral gavage dosing the peak oxazepam plasma concentrations in most rodents were reached within 2-3.5 h. At all doses studied, female rodents had significantly higher plasma concentrations than males. Absorption of oxazepam was significantly extended at higher oral doses of 200 and 400 mg/kg. At 50 mg/kg, the bioavailability of oxazepam in rats (< 50%) was lower than in Swiss-Webster mice (> 80%). The bioavailability of oxazepam in both B6C3F1 and Swiss-Webster mice decreased with increasing dose. A dose proportionality of Cmax was not observed in rats and mice after gavage doses of 50, 200, and 400 mg/kg. Plasma concentrations of oxazepam in the dosed-feed study increased with the concentration of oxazepam in the feed, a quasi-steady-state of plasma concentrations of oxazepam was reached after approximately 4 days ad libitum exposure. In B6C3F1 mice, the estimated relative bioavailability of oxazepam from dosed feed (relative to gavage study at 50 mg/kg) was about 43%.

Toxicokinetics of pentachlorophenol in the F344 rat. Gavage and dosed feed studies.

1. The toxicokinetics of pentachlorophenol (PCP) were studied in the Fischer 344 rat using i.v. and oral (gavage, dosed feed) routes of exposure. 2. Only minor sex differences were observed in the elimination kinetics of PCP after i.v. administration at 5 mg/kg. 3. Absorption of PCP from the gastrointestinal tract after gavage doses of 9.5 and 38 mg/kg in aqueous methylcellulose vehicles was first order with an absorption half-life of about 1.3 h. 4. The absorption rate constant of PCP from doses feed was comparable with that obtained from aqueous methylcellulose gavage formulations. 5. Bioavailability of PCP administered in dosed feed was significantly lower than the bioavailability of PCP administered by gavage. 6. Dose proportionality was established to a dosage of at least 38 mg/kg. 7. Daily fluctuation of PCP plasma concentrations was observed during the dosed feed study with peak and trough concentrations occurring in early morning and late afternoon, respectively. 8. The time course of PCP plasma concentrations during the dosed feed study were simulated using a computer model based on linear theory. The simulations were comparable with the experimentally determined concentrations.

Comparison of the toxicity of citral in F344 rats and B6C3F1 mice when administrated by microencapsulation in feed or by corn-oil gavage.

A study of the potential effects of microencapsulation on the toxicity of citral was conducted in 14-day continuous feeding studies with both sexes of F344 rats and B6C3F1 mice. Toxicity by the feeding route was compared with that from bolus doses of the neat chemical in corn oil administrated by gavage. Both sexes of rats and mice were given diet containing 0, 0.63, 1.25, 2.5, 5 and 10% citral microcapsules. These feed formulations were equivalent to daily doses of 0, 142, 285, 570, 1140 and 2280 mg citral/kg body weight for rats and 0, 534, 1068, 2137, 4275 and 8550 mg citral/kg body weight for mice. The daily gavage doses were 0, 570, 1140 and 2280 mg citral/kg body weight for both sexes of rats, and 0, 534, 1068 and 2137 mg citral/kg body weight for both sexes of mice. Citral microcapsules administered in the diet did not cause mortality in mice or rats. Toxicity was confined to decreases in body weight at the 10% concentration in mice, at the 5 and 10% concentrations in rats, and decreases in absolute weights of the liver, kidney and spleen at the 10% concentration in rats. The only histopathological change observed was minimal to mild hyperplasia and/or squamous metaplasia of the respiratory epithelium in the anterior portion of the nasal passages of rats fed 5 or 10% citral microcapsules. By contrast, citral gavage caused mortality in five out of five male and female mice at 2137 mg/kg body weight, and in two out of five male mice at 1068 mg/kg body weight. There were dose-related increases in absolute liver weights of male and female mice. Cytoplasmic vacuolization of hepatocytes occurred in all female mice gavaged with 1068 and 2137 mg citral/kg body weight, and in male mice from the 2137 mg/kg dose group. Necrosis, ulceration and/or acute inflammation of the forestomach occurred in the high-dose mice of both sexes. Inflammation and/or hyperplasia of the forestomach occurred in about half of the male and female mice dosed with 1068 mg citral/kg. Citral gavage at doses that were equivalent to up to 10% in the diet (2280 mg/kg body weight) did not cause toxicity in rats, except for minimal hyperplasia of the squamous epithelium of the forestomach in high-dose males.(ABSTRACT TRUNCATED AT 400 WORDS)

Toxicokinetics of pentachloroanisole in F344 rats and B6C3F1 mice.

1. Toxicokinetics of pentachloroanisole (PCA) were studied in F344 rat and B6C3F1 mouse of both sexes by gavage at doses of 10, 20 and 40 mg/kg and by i.v. at 10 mg/kg. 2. PCA was rapidly demethylated to pentachlorophenol (PCP) in both rat and mouse and the resulting PCP plasma concentrations were much higher than that of parent PCA due to the much smaller apparent volume of distribution of PCP. 3. Peak plasma concentrations of PCA and PCP increased with dose in both rat and mouse. 4. Bioavailability of PCA was low in both rat and mouse and was sex independent. 5. The high plasma concentrations and relatively long biological half-life of PCP in both species after both i.v. and oral dosing with PCA indicate possible bioaccumulation of PCP upon multiple oral administrations of PCA.

Zidovudine bioavailability and linear pharmacokinetics in female B6C3F1 mice.

The bioavailability and pharmacokinetics of zidovudine (3'-azido-3'-deoxythymidine) (AZT) were determined in female B6C3F1 mice after administration of 15, 30, and 60 mg/kg doses via oral gavage or intravenous injection. Three animals in each administration group were sacrificed, and blood samples were collected at each of the following times: 0, 5, 10, 15, 20, 30, 45, 60, 75, 90, 105, and 120 min after drug administration. Plasma zidovudine concentrations were determined by HPLC. After oral administration, mean maximum plasma concentrations (Cmax) of 9.1, 18.9, and 40.3 mg/liter were observed at 18.3, 21.7, and 15.0 min (tmax) for the 15, 30, and 60 mg/kg doses, respectively. Following intravenous administration, mean Cmax values of 15.9, 41.8, and 76.0 mg/liter were observed for the 15, 30, and 60 mg/kg doses, respectively. Nonlinear least squares regression of all data sets, using a 1/y weight, indicated that zidovudine disposition was best described by a one-compartment open model with first-order absorption, where appropriate, and first-order elimination. The mean elimination half-life values ranged from 17.3 to 19.9 min for the three intravenous doses and from 16.5 to 21.9 min for the three oral doses. The mean values for the apparent volume of distribution (Vd) ranged from 0.8 to 1.0 liter/kg following oral and intravenous administration. There were no significant differences in Vd between the oral and intravenous groups. The mean total body clearance values ranged from 28.9 to 34.3 ml/min/kg following intravenous administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitation of cinnamaldehyde and cinnamic acid in blood by HPLC.

A rapid and sensitive high performance liquid chromatographic (HPLC) method is described for the quantitation of cinnamaldehyde (CNMA) in rat blood at concentrations of 0.1-100 micrograms/mL. One of the metabolites of CNMA, cinnamic acid, can also be quantified simultaneously. CNMA is unstable in rat blood, probably because of rapid oxidation to cinnamic acid by enzymatic catalysis and nonenzymatic Schiff base formation with free amine groups of blood proteins. The disappearance of CNMA from rat blood follows first-order reaction kinetics with a half-life of 9 min at room temperature. The current analysis method involves the addition of an agent that will prevent CNMA degradation by denaturing protein and competitively blocking nucleophilic addition reactions, resulting in the nearly complete recovery of CNMA from blood. Recovery of cinnamic acid was approximately 80% at concentrations of 1-10 micrograms/mL.

Application of molecular encapsulation for toxicology studies: comparative toxicity of p-Chloro-alpha, alpha, alpha-trifluorotoluene in alpha-cyclodextrin vehicle versus corn oil vehicle in male and female Fischer 344 rats and B6C3F1 mice.

The application of alpha-cyclodextrin (alpha-CD) as an alternative vehicle for water insoluble and volatile chemicals was investigated in toxicity studies of p-chloro-alpha, alpha, alpha-trifluorotoluene (CTFT). Groups of F344 rats and B6C3F1 mice of each sex were administered CTFT (97% pure) by gavage in either corn oil or alpha-CD aqueous formulations daily for 14 consecutive days. The dose levels used were 10 (mice only), 50, 400, and 1000 mg/kg for corn oil vehicle and 10, 50, and 400 mg/kg (maximum achievable dose at gavage volume of 5 ml/kg) for alpha-CD vehicle. With both vehicles CTFT and alpha 2u-globulin were found to accumulate in the male rat kidney after 14 days of exposure and a dose-related toxic nephropathy was observed at dose of 50 mg/kg or higher. The hepatocellular hypertrophy and cytoplasmic vacuolation of the adrenal cortex which appeared in dosed male and female rats were also found to be independent of vehicle. Clinical pathology findings suggested a mild anemia and cholestasis in rats. With both vehicles no tissue bioaccumulation of CTFT was found in male or female mice. Vehicle-independent hepatocellular hypertrophy and cholestasis were also observed in mice at doses of 400 and 1000 mg/kg. In conclusion, the alpha-CD vehicle does not affect the toxic responses of CTFT in both sexes of both species. The results of the studies suggest that alpha-CD may be an appropriate alternative vehicle for toxicity studies.

Application of molecular encapsulation for toxicology studies: toxicokinetics of p-chloro-alpha,alpha,alpha-trifluorotoluene in alpha-cyclodextrin or corn oil vehicles in male F344 rats.

Toxicokinetics of p-chloro-alpha,alpha,alpha-trifluorotoluene (CTFT) after administration as an aqueous alpha-cyclodextrin (alpha-CD) molecular encapsulation suspension (alpha-CD vehicle) or as a corn oil solution (corn oil vehicle) were compared. Male F344 rats were administered intragastrically CTFT in alpha-CD vehicle or corn oil vehicle at dose levels of 10, 50, or 400 mg/kg. Other male F344 rats were administered CTFT intravenously in a 10% Tween 80 aqueous solution. Serial blood samples were taken from a cannulated jugular vein for up to 52 hr after dosing and the CTFT concentrations in whole blood were determined by gas chromatography. The biological elimination half-life of CTFT from the center compartment was not affected by the vehicle used; however, absorption of CTFT from the alpha-CD vehicle was much faster than from the corn oil vehicle. The average absorption half-lives from the alpha-CD vehicle and corn oil vehicle were 17 and 98 min, respectively. Despite the differences in absorption, no statistical difference was observed in the calculated areas under the blood concentration versus time curves (AUC) obtained from rats dosed with either vehicle. Dose proportionality for CTFT was established up to 400 mg/kg and bioavailability was shown to be complete for both vehicles.