Fundamental and Applied Toxicology最新文献

The database of Continuous Breeding mouse studies was evaluated to determine the relationships between the functional indicators of reproduction (pup measures) and the various necropsy endpoints collected for males and females. Of 72 chemicals studied, both males and females were affected in 33 studies, while females and/or conceptuses were affected in 7. Two compounds affected only males, 17 studies were negative, and in 13 studies with effects it was not possible to clearly determine the affected gender(s). Greater F₀dam weight was correlated with increased pup mass per litter; this relationship was strongest for the first litter, and weakest for the fifth litter. For both generations of treated females (F₀and F₁), longer estrous cycles correlated with reduced numbers of pups; the relationship was stronger in F₀than in F₁females and was not seen in controls. Sperm parameters had different distributions in treated mice than in control mice. Fertility (total live pups/number of pairs cohabited) was reduced if there were > ∼15% sperm abnormalities or if sperm motility (moving/not moving) was < ≈37%. Both of these relationships appeared to have thresholds. Epididymal sperm count in treated animals, however, was linearly related to fertility, even within the control range, suggesting strongly that other factors are important. Using both treated and control data together, combining sperm count with motility could explain much (r= 0.77) of the variation in fertility; adding morphology did not significantly improve the correlation. The model was almost as strong using count and morphology, in which case adding motility did not strengthen the model. This analysis of these studies shows that while some endpoints (e.g., random-estrous-cycle-point ovary weight) correlate poorly with fertility, other necropsy endpoints (epididymal sperm count and motility, estrous cycle length, and testis and epididymal weights) can be useful (though not complete) surrogates of overall reproductive function. Indeed, over many studies, epididymal sperm count in treated animals correlates with fertility so well that even small reductions (≈20%) in count result in reduced fertility, suggesting that mice may be better models of human fertility than was previously believed.

Organophosphate (OP) pesticides can bind to carboxylesterase (CaE), which may lower the concentration of OPs at the target site enzyme, acetylcholinesterase (ChE). It is unclear from the literature whether it is the CaE's affinity for the OP and/or the number of CaE molecules which is the dominant factor in determining the protective potential of CaE. We undertook a detailed,in vitroandin vivosurvey of both CaE and ChE to ascertain ifin vitrosensitivity of CaE and ChE predicted the pattern of inhibition seen afterin vivodosing with chlorpyrifos (CPF; 80 mg/kg, p.o.) in male or female adult Long–Evans rats. For the brain, thein vitrosensitivity to CPF-oxondidpredict thein vivopatterns of inhibition:In vitro,brain ChE was approximately 25 times more sensitive to the active metabolite, CPF-oxon, than brain CaE, andin vivobrain ChE was more inhibited than brain CaE. In contrast, thein vitrosensitivity of plasma ChE and CaEdid notcorrelate well with thein vivopattern of inhibition:In vitro,plasma ChE was approximately 6.5 times less sensitive to CPF-oxon than plasma CaE, butin vivo,plasma ChE was more inhibited than CaE. In order to understand the role of CaE in protecting the brain ChE from inhibition by CPF-oxonin vitro,adult rat striatal tissue was incubated in the presence and absence of adult rat liver tissue and IC₅₀s of CPF-oxon were determined. The increase in the striatal CPF-oxon IC₅₀value noted for ChE in the presence of liver suggested that CaE was binding the CPF-oxon and limiting its access to ChE. Male liver CaE, which has the same affinity for binding CPF-oxon as female liver CaE but has twice as many binding sites, caused a greater increase in the striatal CPF-oxon IC₅₀than female liver, suggesting that the number of binding sites does play a role in the detoxification potential of a tissue. In summary, we found that (1) there are tissue and gender-related differences for basal ChE and CaE activity; (2) thein vitrosensitivity of CaE or ChE to CPF-oxon is highly tissue-specific; (3) the pattern of ChE and CaE inhibition afterin vivodosing with CPF is not necessarily predictable from thein vitroIC₅₀for these same enzymes, and (4) the number of CaE molecules may play a role in modifying the toxicity of CPF.

Ethylene glycol monomethyl ether (EGME) and its proximate metabolite, 2-methoxyacetic acid (MAA), increase ovarian luteal cell progesterone production in the female ratin vivoand in cultured rat luteal cellsin vitro,respectively. In order to better assess the potential hazard of EGME and MAA to women, these studies were conducted to determine whether the same concentrations of MAA increase progesterone in human luteinized granulosa cells as in rat luteal cells. Human cells were collected from healthy anonymous oocyte donors, washed, plated 25,000 viable cells per well, and treated with 10 IU hCG and 0–5 mmMAA for 6–48 hr. Progesterone in media was significantly elevated after 24 hr incubation at ≥1 mmMAA. MAA had no effect on ATP levels at 6 or 24 hr. Thus, MAA increased progesterone production in cultured human luteal cells at the same concentration as MAA increased progesterone in rat luteal cells. The implication is that EGME has the potential to alter ovarian luteal function in women. These data should be useful for determining the real health hazards and potential risks of EGME exposure.

Arsine, the hydride of arsenic (AsH₃), is the most acutely toxic form of arsenic, causing rapid and severe hemolysis upon exposure. The mechanism of action is not known, and there are few detailed investigations of the toxicity in a controlled system. To examine arsine hemolysis and understand the importance of various toxic responses, human erythrocytes were incubated with arsinein vitro,and markers of toxicity were determined as a function of time. The earliest indicators of damage were changes in sodium and potassium levels. Within 5 min incubation with 1 mmarsine, the cells lost volume control, manifested by leakage of potassium, influx of sodium, and increases in hematocrit. Arsine did not, however, significantly alter ATP levels nor inhibit ATPases. These changes were followed by profound disturbances in membrane ultrastructure (examined by light and electron microscopy). By 10 min, significant numbers of damaged cells formed, and their numbers increased over time. These events preceded hemolysis, which was not significant until 30 min. It has been proposed that arsine interacts with hemoglobin to form toxic hemoglobin oxidation products, and this was also investigated as a potential cause of hemolysis. Essentially on contact with arsine, methemoglobin was formed but only reached 2–3% of the total cellular hemoglobin and remained unchanged for up to 90 min. There was no evidence that further oxidation products (hemin and Heinz bodies) were formed in this system. Based on these observations, hemolysis appears to be dependent on membrane disruption by a mechanism other than hemoglobin oxidation.

This study was carried out to provide information on the effects of inhalation of diethylene glycol monoethyl ether, a substance used in industry which may be accidentally inhaled by man. Sprague–Dawley CD rats were exposed by inhalation to a test atmosphere containing diethylene glycol monoethyl ether in a nose-only exposure system for 6 hr a day, 5 days a week for 28 days. Mean exposure levels were 0.09, 0.27, and 1.1 mg/liter. At the two lowest exposure levels the test substance was present entirely as vapor, but at the highest exposure level the test atmosphere was approximately equally divided by mass into respirable droplets (aerosol) and vapor. A comprehensive battery of toxicological evaluations including food consumption, body weight, clinical signs, hematology, and biochemistry revealed no evidence of a systemic effect of exposure. Histopathological examination showed changes indicative of mild nonspecific irritation in the upper respiratory tract of rats exposed at the two highest exposure levels. These changes consisted of foci of necrosis in the ventral cartilage of the larynx of rats exposed at 0.27 or 1.1 mg/liter and an increase in eosinophilic inclusions in the olfactory epithelium of the nasal mucosa of rats exposed at 1.1 mg/liter. The no observed adverse effect level for systemic effects was 1.1 mg/liter and the no observed adverse effect level for signs indicative of mild nonspecific irritation of the upper respiratory tract was 0.09 mg/liter.

The increasing prevalence of allergic rhinitis in many countries is becoming a social problem. It is important to determine whether air pollutants are related to the increase in the prevalence rate of allergic rhinitis or not. In this respect, it is necessary to elucidate whether exposure to air pollutants affects the nasal mucosa and causes nasal mucosal hyperresponsiveness to chemical mediators released by antigen–antibody reactions. A previous study revealed that diesel exhaust particulates are potent in augmenting increases in nasal congestion and nasal secretion induced by histamine (T. Kobayashi and T. Ito, 1995,Fundam. Appl. Toxicol.27,195–202). In the present study, using a rhinitis model of guinea pigs, we investigated whether short-term (3-hr) exposure to diesel exhaust induces nasal mucosal hyperresponsiveness to histamine. Guinea pigs of each group were exposed to filtered air or to a low or high concentration of diesel exhaust (1 and 3.2 mg/m³particulates in diluted diesel exhaust, respectively) for 3 hr. After diesel exhaust exposure, sneezing frequency, nasal secretion from the nostril, and intranasal airway resistance induced by histamine were measured as indices of sneezing response, rhinorrhea, and nasal congestion, respectively. Short-term exposure to a low or high concentration of diesel exhaust itself did not induce sneezing, nasal secretion, or nasal congestion. However, short-term exposure to a high concentration of diesel exhaust augmented sneezing and nasal secretion, but not nasal congestion, induced by histamine. In conclusion, short-term exposure to diesel exhaust potently induces nasal mucosal hyperresponsiveness.

In oral carcinogenicity bioassays, zidovudine (ZDV) induced vaginal epithelial cell tumors in mice given 30 or 40 mg/kg/day and rats given 300 mg/kg/day. To determine if lifetime exposure to ZDV, beginning perinatally, would alter this pattern of carcinogenicity, two groups of 60 pregnant CD-1 mice were given 20 or 40 mg/kg/day of ZDV in 0.5% methyl cellulose from Gestation Day 10 through Lactation Day 21. At weaning, 2 pups per sex from each of 35 litters in each group were assigned to the study and given 20 or 40 mg/kg/day of ZDV in the drinking water until 17–35 days of age, followed by daily gavage for 24 months. Two additional groups of 60 pregnant CD-1 mice each were given 40 mg/kg/day of ZDV daily from Gestation Day 10 through Lactation Day 21; in one, ZDV treatment was halted at weaning and in the other, treatment was stopped 90 days after weaning. Two other groups of 60 pregnant CD-1 mice were left untreated (environmental control) or were given 0.5% methyl cellulose beginning on Gestation Day 10 (vehicle control). Vehicle control progeny received plain drinking water for 17–35 days postweaning and then 0.5% methyl cellulose daily by gavage for 24 months. ZDV treatment did not affect survival or body weight in either sex. In females given 20 or 40 mg/kg/day of ZDV for 24 months there was mild macrocytic anemia. Similar, non-dose-related changes were seen in males in these groups. ZDV-related tumor findings were limited to the vagina, where there were 2 and 11 vaginal squamous cell carcinomas in mice given 20 or 40 mg/kg/day of ZDV daily, respectively. This incidence was not remarkably different from that seen in previously reported bioassays. It was concluded that lifetime oral treatment of mice with ZDV, beginning perinatally, did not alter the previously reported pattern of carcinogenicity and that under the conditions tested ZDV was not a transplacental carcinogen.

Previous work has shown a reduction in cephaloridine nephrotoxicity in a diabetic rat model. The following studies examinedin vitrocephaloridine toxicity in renal slices from normoglycemic and diabetic Fischer 344 rats. Diabetes was induced by acute intraperitoneal injection of 35 mg/kg streptozotocin. Renal cortical slices were isolated from normoglycemic and diabetic animals. Tissues were exposed to 0–5 mmcephaloridine for 15–120 min. Pyruvate-directed gluconeogenesis was diminished in all groups exposed to 2–5 mmcephaloridine for 60–120 min. Leakage of lactate dehydrogenase (LDH) was apparent only in the normoglycemic group in the presence of 4–5 mmcephaloridine for 120 min. LDH leakagewas notincreased at any cephaloridine concentration in the diabetic tissue. Total glutathione levels were compared in renal cortical slices exposed to cephaloridine for 30–120 min. Baseline values for glutathione were comparable between normoglycemic and diabetic tissue suggesting that the mechanism for reduced toxicity was not due to higher glutathione levels in diabetic tissue. Total glutathione levels were diminished more rapidly in normoglycemic than diabetic tissue by incubation with 5 mmcephaloridine. Comparison of cephaloridine accumulation indicated that diabetic tissue accumulated less cephaloridine than the normoglycemic group when tissues were incubated with 0–2 mmcephaloridine. However, renal slice accumulation was similar between normoglycemic and diabetic groups followingin vitroincubation with 4–5 mmcephaloridine. These results suggest that the mechanism for reducedin vitrocephaloridine toxicity in diabetic tissue cannot be limited to differences in accumulation and must include an unidentified cellular component.

The mesothelial lining is a target for the fibrotic and carcinogenic effects of mineral fibers. Fiber geometry, dimensions, chemical composition, surface reactivity, and biopersistence at the target tissue have been proposed to contribute to these toxic endpoints. We established a dose–response relationship between the number of fibers delivered to the parietal peritoneal lining, inflammation, and mesothelial cell proliferation induced by intraperitoneal injection of crocidolite asbestos fibers in mice. Persistence of these inflammatory and proliferative responses depended on persistence of fibers at the target tissue. Intraperitoneal injection of wollastonite fibers induced an early inflammatory and proliferative response that subsided after 21 days. Approximately 50% of wollastonite fibers were recovered by bleach digestion after 21 days and only 2% were recovered after 6 months. In contrast, the number of fibers recovered from tissue digests had not declined 6 months after injection of crocidolite asbestos. These results support the hypothesis that biopersistent fibers cause persistent inflammation and chronic mesothelial cell proliferation.