Fundamental and Applied Toxicology最新文献

Tributyl phosphate (TBP) was tested for reproductive toxicity in rats. Thirty weanlings/sex (F0) were exposed to TBP in the dietad libitumat 0, 200, 700, or 3000 ppm for 10 weeks and then randomly mated within groups for 3 weeks with continued exposure. F0 parents and 10 F1 weanlings/sex/dose were necropsied, and adult reproductive organs, urinary bladders (both sexes), kidneys (males), and livers (females) were evaluated histologically. Thirty F1 weanlings/sex/dose continued exposure for 11 weeks and were bred as described above. F1 parents and F2 weanlings, 10/sex/dose, were then necropsied as described above. Adult toxicity was observed in both sexes and generations at 700 and 3000 ppm; observations included reduced body weights, weight gain and feed consumption, urinary bladder epithelial hyperplasia (both sexes), renal pelvis epithelial hyperplasia only at 3000 ppm (male kidneys), and centrilobular hypertrophy (female livers). At 200 ppm, transient reductions in body weight were observed in F0 and F1 females, with urinary bladder epithelial hyperplasia in F0 males and females and in F1 males. There was no evidence of reproductive toxicity, of reproductive organ pathology, or of effects on gestation or lactation at any dose tested. Postnatal toxicity was evidenced by consistent reductions in F1 and F2 pup body weights at 3000 ppm and by occasional weight reductions in F2 litters at 700 ppm, and was associated with maternal toxicity observed at these doses and times. Under the conditions of this study, a NOAEL was not determined for adult toxicity; the NOAEL for reproductive toxicity was at least 3000 ppm and the NOAEL for postnatal toxicity was approximately 200 ppm.

Regulatory decisions should be made in the most expert and informed way since they are precipitated by real and perceived threats to human health, under the glare of public scrutiny. In 1994, the National Research Council (NRC) reported that the U.S. Environmental Protection Agency's (USEPA's) overall approach to assessing risks is fundamentally sound, but the Agency must more clearly establish the scientific and policy basis for risk estimates and better communicate the associated uncertainties. On March 21, 1995, USEPA issued a risk characterization policy and guidance. In this policy, an effective risk characterization must fully and clearly characterize risks and disclose the scientific analysis, uncertainties, assumptions, and science policy that underlie decisions throughout the risk assessment process. A number of regulatory reform bills which required risk characterization as part of all Federal risk assessments were introduced by the 104th Congress. The purpose of this workshop was to familiarize Society of Toxicology members with: (1) key elements to be considered in risk characterization and (2) new advances in risk characterization addressed by Federal and State agencies, industry, academia, NRC, and Presidential/Congressional Commission on Risk Assessment and Risk Management. Furthermore, the main objective was to engage the audience in discussing the proper role of science in risk assessment–risk management interface to make informed decisions in the face of scientific uncertainty.

Divinylbenzene (DVB) is a crosslinking monomer used primarily for copolymerization with styrene to produce ion-exchange resins. The toxicity of inhaled DVB was investigated because of the potential for worker exposure and the structural similarity of DVB to styrene, a potential carcinogen. Male and female B6C3F1 mice were exposed to 0, 25, 50, or 75 ppm DVB for 6 hr/day, 5 days/week for up to 2 weeks. Six mice/sex/dose group were killed after 3, 5, and 10 exposures and six mice/sex in the 75 ppm group were killed 7 days after 10 exposures. The most severe effects occurred in the nasal cavity and liver, with less severe effects occurring in the kidneys. In the nasal cavity olfactory epithelium acute necrosis and inflammation were present at early time points followed by regeneration, architectural reorganization, and focal respiratory metaplasia by 7 days after the last exposure. Olfactory epithelial changes were concentration-dependent with extensive involvement at 75 ppm and peripheral sparing at 25 ppm. There was also necrosis and regeneration of olfactory-associated Bowman's glands as well as the lateral nasal (Steno's) glands. Hepatocellular centrilobular (CL) necrosis was observed only in the 75 ppm dose group and was similar to that caused by styrene. A time-dependent progression was observed, characterized by CL degeneration after 1 exposure, necrosis after 3 and 5 exposures, and chronic inflammation with CL karyomegaly after 10 exposures and 7 days after the 10th exposure. Hepatic GSH levels were decreased in a dose-dependent manner. In the kidneys, transient tubular damage was observed in some male mice exposed to 75 ppm, and appeared to be a response to DVB-induced tubular epithelial injury.

Treatment of rats withpara-aminophenol (PAP) (300 mg/kg ip) produced decreases in renal nonprotein sulfhydryl (NPSH) content, oxygen consumption, and adenine nucleotide concentrations 2–4 hr following administration. In contrast, incubation of rat renal tubules with up to 1 mmPAP for 4 hr produced inconsistent changes in renal tubules. This discrepancy suggested that extrarenal metabolism of PAP may be involved in PAP bioactivation and nephrotoxicity. We designed the present studies to test the hypothesis that hepatic metabolism of PAP potentiates the effects of PAP on renal tubules. Incubation of renal tubules with 0.5 mmPAP and 10 mg protein from hepatic postmitochondrial supernatant (S9 fraction) in the absence of glutathione (GSH) for 4 hr did not alter renal oxygen consumption or adenine nucleotide metabolite concentrations. We observed no changes when we incubated tubules with 0.5 mmPAP and 1 mmGSH in the absence of hepatic S9 fraction. However, incubation of renal tubules with 0.5 mmPAP, 1 mmGSH, and 10 mg hepatic S9 protein for 4 hr significantly decreased renal oxygen consumption and adenosine triphosphate and total nucleotide concentrations. These data suggest that the effects of PAP in renal tubules may be potentiated by enzymatic metabolism of PAP, possibly involving oxidation and GSH conjugation. From experiments using hepatic microsomes or cytosol instead of S9 fraction, we found that changes were produced when we incubated tubules with PAP in the presence of hepatic microsomes, but not cytosol. These data suggest that hepatic microsomal metabolism of PAP may contribute to the production of changes in renal tubulesin vitro.PAP-induced changes in renal proximal tubules were prevented when we included a β-nicotinamide adenine dinucleotide phosphate (NADPH) generating system in the incubation medium. The protective effect of NADPH persisted when microsomes were inactivated by incubation with 1-aminobenzotriazole, a cytochrome P450 inhibitor. These data suggest that cytochrome P450-dependent oxidation is not involved in the production or prevention of PAP-induced changes in renal tubules. The enzyme(s) responsible for PAP bioactivation and the mechanism(s) by which NADPH protects renal tubules from PAP-induced decrements in oxygen consumption and adenine nucleotide concentrations are currently unclear.

It has generally been assumed that the skin contributes only minor amounts to the total uptake of solvent vapors, relative to the respiratory tract. Contrary to this assumption, the widely used glycol ether solvent, 2-butoxyethanol (BE), has been reported to be more effectively absorbed through the skin (75% of the total uptake) than through the lungs of humans (Johanson and Boman, 1991,Br. J. Ind. Med.48,788). The possibility that the finger prick blood sampling technique used in the Johanson and Boman study was confounded by locally high concentrations of BE at the site of absorption was suggested using a previously developed PBPK model (Corleyet al.,1994,Toxicol. Appl. Pharmacol.129,61). The current study was conducted to verify the PBPK analysis and to determine whether or not the skin was the major site for absorption of BE vapor by exposing one arm from each of six human volunteers to 50 ppm¹³C₂-BE vapor for 2 hr. To evaluate the potential consequences of blood sampling techniques, samples were taken from both the unexposed arm (catheter; during and after exposure) and the exposed arm (finger prick; end of the exposure only) for analysis of both BE and its major metabolite, butoxyacetic acid (BAA). Butoxyacetic acid is responsible for the hemolysis observed in toxicity studies with laboratory animals. Humans, however, are significantly less sensitive to this effect. The concentration of BE in the finger prick blood samples averaged 1500 times higher than the corresponding concentration in venous blood sampled from a catheter installed in the unexposed arm at the end of the exposure. Blood BAA levels were generally within a factor of 4 of each other for the two techniques and, therefore, was considered a better indicator of systemic absorption. Urine was collected for 24 hr and analyzed for the following metabolites found in rat metabolism studies: free and conjugated BE, BAA, ethylene glycol (EG), and glycolic acid (GA), with only BAA detected in the human urine. More importantly, urinary BAA was found to be extensively conjugated (∼67%) with glutamine, confirming recent reports. These results, coupled with PBPK modeling of worst-case exposure scenarios (no clothing, 100% of the body was exposed), demonstrated that no more than 15–27% (low-to-high relative temperatures and humidities), not 75%, of the total uptake of BE could be attributed to the skin of humans during simulated 8-hr exposures to the ACGIH TLV concentration of 25 ppm. Even less of the total uptake was attributed to the skin during simulations of exercise with whole-body exposures (5–9%) or by more realistic exposures of only the arms and head (1–8%). As a result, humans are unlikely to reach hemolytic concentrations of the metabolite BAA in blood following vapor exposures to BE.

Caffeic acid (CA, 3,4-dihydroxycinnamic acid), at 2% in the diet, had been shown to be carcinogenic in forestomach and kidney of F344 rats and B6C3F1 mice. Based on its occurrence in coffee and numerous foods and using a linear interpolation for cancer incidence between dose 0 and 2%, the cancer risk in humans would be considerable. In both target organs, tumor formation was preceded by hyperplasia, which could represent the main mechanism of carcinogenic action. The dose–response relationship for this effect was investigated in male F344 rats after 4-week feeding with CA at different dietary concentrations (0, 0.05, 0.14, 0.40, and 1.64%). Cells in S-phase of DNA replication were visualized by immunohistochemical analysis of incorporated 5-bromo-2′-deoxyuridine (BrdU), 2 hr after intraperitoneal injection. In the forestomach, both the total number of epithelial cells per millimeter section length and the unit length labeling index of BrdU-positive cells (ULLI) were increased, about 2.5-fold, at 0.40 and 1.64%. The lowest concentration (0.05%) had no effect. At 0.14%, both variables were decreased by about one-third. In the kidney, the labeling index in proximal tubular cells also indicated a J-shaped (or U-shaped) dose response with a 1.8-fold increase at 1.64%. In the glandular stomach and in the liver, which are not target organs, no dose-related effect was seen. The data show a good correlation between the organ specificity for cancer induction and stimulation of cell division. With respect to the dose–response relationship and the corresponding extrapolation of the animal tumor data to a human cancer risk, a linear extrapolation appears not to be appropriate.

The effects of pregnancy on the flux of lead from maternal bone were investigated in five females from a unique colony of cynomolgus monkeys (Macaca fascicularis) which had been dosed orally with lead (approximately 1100–1300 μg Pb/kg body wt) throughout their lives (about 14 years). Through the use of stable lead isotopes²⁰⁴Pb,²⁰⁶Pb, and²⁰⁷Pb, it was possible to differentiate between the lead contributed to blood lead from the skeleton and the lead contributed from the current oral dose. Blood samples and bone biopsy samples taken before, during, and after pregnancy were analyzed for lead (total and stable isotope ratios) by thermal ionization mass spectrometry. Through the use of end-member unmixing equations, the contribution to blood of lead from maternal bone during pregnancy was estimated and compared to the contribution of lead from maternal bone before pregnancy. A 29 to 56% decrease in bone lead mobilization in the first trimester was followed by an increase in the second and third trimesters, up to 44% over baseline levels. In one monkey, the third-trimester increase did not reach baseline levels. In a single low-lead monkey, a similar decrease in the first trimester was followed by a 60% increase in the third trimester, indicating that a similar pattern of flux is seen over a wide range of lead concentrations. Analysis of maternal bone and fetal bone, brain, liver, and kidneys confirmed a substantial transplacental transfer of endogenous lead. Lead concentrations in fetal bone often exceeded maternal bone lead concentrations. From 7 to 39% of the lead in the fetal skeleton originated from the maternal skeleton.

Female guinea pigs (12/group) were given a single dose of [¹⁴C]olestra by gavage after consuming either 3% poligeenan in tap water (Compromised group) or just tap water (Normal group) for 5 weeks. A Sentinel group (N= 2) was given 3% poligeenan for 5 weeks. Ten sentinel animals were killed 1 day before and 10 1 day after the other animals were dosed with [¹⁴C]olestra and their gastrointestinal tracts were examined by histology. The Compromised and Normal animals were endoscoped just before dosing with [¹⁴C]olestra. Urine and feces were collected continuously and CO₂was collected for 7 days after dosing. The samples were analyzed for¹⁴C and urine was also analyzed for [¹⁴C]sucrose. Animals (3/group) were killed 1, 3, 7, and 21 days after dosing, and tissues were collected and assayed for¹⁴C. Tissue lipids were extracted, fractionated by high-pressure liquid chromatography, and analyzed for [¹⁴C]olestra by liquid scintillation. Animals fed poligeenan showed mucosal edema, congestion, ulceration, and fibrin deposition within the distal colon and rectum. Histology revealed inflammation, epithelial degeneration, and multifocal ulceration of the cecum, distal colon, and rectum. The gastrointestinal mucosae of nonpoligeenan fed animals were normal. No [¹⁴C]olestra was detected in liver lipids and no [¹⁴C]sucrose was found in the urine for any animal in the Normal or Compromised groups, indicating that intact olestra was not absorbed. The amount, distribution, and elimination of absorbed¹⁴C did not differ between guinea pigs with normal and compromised gastrointestinal tracts. The poligeenan-treated animals displayed mucosal damage similar to that seen in human inflammatory bowel diseases; therefore, these results suggest that patients with inflammatory bowel conditions will not absorb olestra to any greater extent than normal healthy people.

This study evaluates the developmental toxicity and placental and milk transfer ofN,N-dimethylformamide (DMF) in rats. Sprague–Dawley rats were given 0, 50, 100, 200, and 300 mg DMF/kg/day, by gavage, on Gestational Days (GD) 6 through 20. Maternal toxicity was indicated by depressions in weight gain and food consumption at doses ≥100 mg/kg. Fetal toxicity was indicated by decreased fetal body weight at doses ≥100 mg/kg, and by increased incidences of two skeletal variations (absent or poorly ossified supraoccipital and sternebrae) at 200 and 300 mg/kg. Thus, the maternal and developmental no-observed-adverse-effect level was 50 mg/kg/day. The time course disposition of [¹⁴C]DMF was examined over a 48-hr period in GD12- and GD18-pregnant rats after a single oral dose of 100 mg [¹⁴C]DMF/kg. Peak concentrations of radiocarbon occurred within 1 hr after dosing. Embryonic (GD12) and fetal (GD18) tissues accounted for 0.15 and 6% of the administered dose, respectively. Levels of radiocarbon in embryonic and fetal tissues were equal or slightly less than in maternal plasma up to 8 and 24 hr, respectively, and higher thereafter. HPLC analysis performed at intervals from 1 to 8 hr on GD12 and 1–24 hr on GD18 indicated that unchanged DMF and metabolites were readily transferred to the embryonic and fetal tissues, where their levels were generally equal to those in maternal plasma. The parent compound accounted for most of the radioactivity until 4–8 hr and then decreased.N-Hydroxymethyl-N-methylformamide (HMMF) andN-methylformamide (NMF) were the predominent metabolites and increased with time. Much lower concentrations were found for formamide andN-acetyl-S-(N-methylcarbamoyl)cysteine. Transfer of radioactivity into milk was studied in dams given a single oral administration of 100 mg [¹⁴C]DMF on Lactation Day 14. DMF, HMMF, and NMF were found in the milk at concentrations equal to those in plasma.