Biomedical subjects

H Certa

Publications and source records attributed to H Certa.

6 recordsLinked to original sources

PubMed1998

Modelling of residual variability in toxicokinetic studies with sparse sampling: the case of tetrahydronaphthalene.

The present study describes the kinetics of tetrahydronaphthalene in male and female rats (five animals per dose per sex) at three dose levels (15, 50, and 150 mg/kg daily). Plasma concentration measurements were performed in the course of a subacute toxicity study of 28 days duration in an enriched study design. Two blood samples per animal were taken at different time points after application at day 1 and 16 (150 mg/kg daily) and at day 3 and 18 (15 and 50 mg/kg daily), respectively. Tetrahydronaphthalene was assayed by gas chromatography-mass spectrometry (GC-MS) after extraction. The data of plasma concentration time were analysed using non-linear mixed effects modelling as implemented in NONMEM. The structural model with the best fit employed one compartment kinetics with instantaneous drug input. Interindividual variability in both k and V was found to be very small [k, 0.201 h(-1), 0.013; V, 16.19 (kg), 1.77; population mean and SE]. No unequivocal evidence of dose dependence could be found. The kinetic parameter with the highest extent of variability was the extent of bioavailability which showed an coefficient of variation (CV) of 96%. Both gender and dose had no influence on the variability. The present approach is concluded to offer more insight into the relationship between dose, concentration and effect and into factors which explain variability in kinetics without additional testing or additional animals. Proposals for a refined sampling schedule are made.

Animals↗

PubMed1996

Toxicokinetics of p-tert-octylphenol in male Wistar rats.

Only weak oestrogenic activity has been reported for p-alkylphenols compared with the physiological hormone 17 beta-estradiol. Despite the low potency, there is concern that due to bioaccumulation oestrogenically efficient blood levels could be reached in humans exposed to trace levels of p-alkylphenols. To address these concerns, toxicokinetic studies with p-tert-octylphenol [OP; p-(1,1,3,3-tetramethylbutyl)-phenol] as a model compound have been conducted in male Wistar rats. OP blood concentrations were determined by GC-MS in rats receiving either single oral (gavage) applications of 50 or 200 mg OP/kg body wt or a single intravenous injection of 5 mg/kg body wt. The OP blood concentration was approximately 1970 ng/ml immediately after a single intravenous application, decreased rapidly within 30 min, and was no longer detectable 6-8 h after application. The curve of blood concentration vs time was used to calculate an elimination half-life of 310 min. OP was detected in blood as early as 10 min after gavage administration, indicating rapid initial uptake from the gastrointestinal tract; maximal blood levels reached 40 and 130 ng/ml after applications of 50 and 200 mg/kg, respectively. Using the area under the curve (AUC) of blood concentration vs time, low oral bioavailabilities of 2 and 10% were calculated for the 50 and 200 mg/kg groups, respectively. OP toxicokinetics after repeated administration was investigated in male Wistar rats receiving daily gavage administrations of 50 or 200 mg OP/kg body wt for 14 consecutive days. Profiles of OP blood concentration vs time determined on day 1 and day 14 were similar, indicating that repeated oral gavage administration did not lead to increased blood concentrations. Another group of rats received OP via drinking water saturated with OP (approximately 8 mg/l, corresponding to a mean daily dose of approximately 800 micrograms/kg) over a period of up to 28 days. OP was not detected in any blood sample from animals treated via drinking water (detection limit was 1-5 ng/ml blood). OP concentrations were also analysed in tissues obtained from the repeated gavage (14 days) and drinking water groups (14 and 28 days). In the 50 mg/kg group, low OP concentrations were detected in fat and liver from some animals at average concentrations of 10 and 7 ng/g tissue, respectively. OP was not detected in the other tissues analysed from this group. In the 200 mg/kg group, OP was found in all tissues analysed except testes (fat, liver, kidney, muscle, brain and lung had average concentrations of 1285, 87, 71, 43, 9 and 7 ng/g tissue, respectively). OP was not detected in tissues of animals receiving OP via drinking water for 14 or 28 days, except in muscle and kidney tissue of one single animal receiving OP for 14 days. Using rat liver fractions it was demonstrated that OP was conjugated via glucuronidation and sulphation in vitro. A Vmax of 11.24 nmol/(min * mg microsomal protein) and a Km of 8.77 mumol/l were calculated for enzyme-catalysed OP glucuronidation. For enzyme-catalysed sulphation, a Vmax of 2.85 nmol/(min * mg protein) and a Km of 11.35 mumol/l were calculated. The results indicate that OP does not bioaccumulate in rats receiving low oral doses, in agreement with the hypothesis of a rapid first-pass elimination of OP by the liver after oral ingestion, via glucuronidation and sulphation. Only if these detoxification pathways are saturated may excessive doses lead to bioaccumulation.

Administration, Oral↗

PubMed1994

Species differences in the biotransformation of ethyl chloride. I. Cytochrome P450-dependent metabolism.

Groups of male and female F-344 rats and B6C3F1 mice were exposed to 15,000 ppm ethyl chloride (monochloroethane, ECL) or to air for 5 days (6 h/day). In this report, features of the P450-dependent ECL metabolism in the animals are described. A concurrent report describes the in vitro and in vivo features of the GSH-dependent ECL metabolism (Fedtke et al. 1994). ECL is oxidatively dechlorinated in an NADPH- and O2-dependent reaction, resulting in the formation of acetaldehyde (AC). The oxidative ECL metabolism rates in microsomal incubations were measured. The results indicated induction of the oxidative ECL metabolism by ECL itself in mice and female rats. The hydroxylation of p-nitrophenol, which was used as an indicator of P450IIE1 activity, was also induced in microsomal incubations from ECL-exposed mice and female rats, but, corresponding to the ECL metabolism, not in male rats. In contrast, catalytic activities related to P450IA and IIB subfamilies were not induced by ECL treatment. Additional experiments with the P450IIE1-specific inhibitor 3-amino-1,2,4-triazole and induction experiments with acetone, phenobarbital and methylcholanthrene confirmed that the isoenzyme mainly involved in the dechlorination reaction is cytochrome P450IIE1. AC was not detected in serum of ECL exposed animals and only slightly enhanced amounts were detected in urine samples from ECL exposed mice, reflecting the high capacities of the AC metabolizing pathways in vivo. The data are discussed with regard to the results of a 2-year bioassay with F-344 rats and B6C3F1 mice exposed to 15,000 ppm ECL (NTP 1989a).(ABSTRACT TRUNCATED AT 250 WORDS)

Acetaldehyde↗

PubMed1994

Species differences in the biotransformation of ethyl chloride. II. GSH-dependent metabolism.

Groups of male and female F-344 rats and B6C3F1 mice were exposed to 15,000 ppm ethyl chloride (monochloroethane, ECL) or to air for 5 days (6 h/day). In this report, features of GSH-dependent ECL metabolism in the animals are described. A concurrent report describes the features of the cytochrome P450-dependent oxidative ECL metabolism (Fedtke et al. 1994). ECL conjugation to GSH in hepatic cytosolic fractions was catalyzed by GSH S-transferases. The specific activities were 0.16 +/- 0.03 and 0.17 +/- 0.01 nmol ECL conjugated/(min mg protein) in air treated male and female F-344 rats, respectively. These activities were not significantly altered by the ECL treatment. Compared with rats, the GSH-transferase activities towards ECL were generally higher in male and female B6C3F1 mice (0.71 +/- 0.19 and 1.01 +/- 0.19, respectively) and were slightly decreased by ECL treatment. The ECL conjugation to GSH resulted in a marked reduction of the GSH concentration in the lung and the uterus after 5 days of exposure. In contrast, liver and kidney GSH concentrations were affected only to a minor degree. Formed S-ethyl-glutathione was converted to the mercapturic acid S-ethyl-N-acetyl-L-cysteine (SENACys), which was detected in the urine of both species. In addition, the non-acetylated intermediate S-ethyl-L-cysteine (SECys) was excreted in mouse urine but not in rat urine. The cumulative amounts of SENACys and SECys excreted after 5 days were up to fivefold higher in mice than in rats and the excretion kinetics were species specific.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Inhalation↗

PubMed1994

Genotoxicity studies with chloroethane.

In a recent 2-year inhalation study with F344 rats and B6C3F1 mice conducted as part of the U.S. National Toxicology Program (NTP, 1989), chloroethane (ECl) at an exposure concentration of 15,000 ppm induced a high incidence of endometrial uterine carcinomas only in female mice but not in rats, leading to the conclusion of "clear evidence of carcinogenicity" for the mouse. In order to elucidate whether a genotoxic effect may be a critical factor for the carcinogenicity of ECl in the mouse, we have performed three genotoxicity tests: (1) in vitro HPRT test with CHO cells according to a specially developed gas protocol, (2) in vivo/in vitro UDS with female B6C3F1 mice at an exposure concentration of 25,000 ppm (6 h/day, 3 days), (3) in vivo micronucleus assay with male and female B6C3F1 mice exposed to 25,000 ppm ECl according to the same schedule. In the in vitro HPRT test a mutagenic potential of ECl was detected in the presence as well as in the absence of S9 mix. In contrast, both in vivo test systems failed to detect any indications of genotoxicity of chloroethane at an exposure concentration even higher than that of the NTP study. It is suggested that in vivo the genotoxic potential of ECl is so low that an assumed genotoxic damage is below the detection limit of the test systems used. This leads to the conclusion that genotoxicity may not be a key factor in the induction of the uterine carcinomas in the B6C3F1 mouse.

Animals↗

PubMedDate not supplied

Toxicokinetics of p-tert-octylphenol in female DA/Han rats after single i.v. and oral application.

Female DA/Han rats were administered p-tert-octylphenol [OP; p-(1,1,3,3-tetramethylbutyl)-phenol], either intravenously (5 mg/kg body wt.) or orally by gavage (50 or 200 mg/kg body wt.). After i.v. administration the blood concentration-time curve of OP was fitted to a tri-exponential model, resulting in a final half-life (gamma-phase) of 36.1 h. This contrasts to much more rapid eliminations previously reported in male Wistar rats. The oral bioavailability of 50 mg/kg OP was 12.3% and of 200 mg/kg 8.4%. The higher dose (200 mg kg) was absorbed slower than the smaller dose, probably due to low solubility of OP in aqueous media. Maximal OP blood levels in female DA/Han rats receiving 50 and 200 mg OP/kg body wt, were 4.5 and 3 times higher than previously reported in male Wistar rats. The blood concentration-time curves after oral administration of OP to female DA/Han rats revealed pronounced interindividual differences, indicating extensive enterohepatic circulation of OP in this rat strain. In contrast to male Wistar rats, after application of high doses of OP to female DA/Han rats the compound was not completely eliminated within 48 h: under these conditions some bioaccumulation might therefore occur. The experimental toxicokinetics of OP appears as a relevant subject to be integrated into extrapolation of toxicological data, from in vitro to in vivo, and into systems of risk assessment of endocrine modulating activity which are currently being developed.

Administration, Oral↗