Subchronic oral toxicity of di-n-octyl phthalate and di(2-Ethylhexyl) phthalate in the rat

The subchronic oral toxicity of di(2-ethylhexyl) phthalate (DEHP) and di-n-octyl phthalate (DNOP) was studied. Groups of 10 male and 10 female Sprague-Dawley rats were administered DEHP in the diet at 0, 5, 50, 500 or 5000 ppm for 13 wk. In a separate study, groups of 10 male and 10 female Sprague-Dawley rats were given DNOP (5, 50, 500 and 5000 ppm) in the diet while control groups received basal diet containing 4% corn oil and positive control groups were fed a diet containing 5000 ppm DEHP. Growth rate and food consumption were not affected by treatment with either compound. Hepatomegaly was observed in the highest dose groups of both sexes administered DEHP but not in the DNOP-treated animals. At the highest dose, DNOP caused threefold (females) and 12-fold (males) increases in liver ethoxyresorufin-O-deethylase activity while DEHP did not. Mild changes in serum biochemistries were mostly confined to rats in the highest dose group of DEHP, and included increased serum albumin and albumin/globulin ratio in both sexes and decreased cholesterol in female rats. Mild vacuolations in the Sertoli cells were observed in male rats exposed to 500 ppm DEHP. At 5000 ppm DEHP, there was mild to moderate seminiferous tubule atrophy and Sertoli cell vacuolation in males, and rats of both sexes showed hepatic peroxisome proliferation. Both DEHP and DNOP at 5000 ppm caused mild histological changes in the thyroid consisting of reduced follicle size and colloid density, and the liver consisting of endothelial nuclear prominence, nuclear hyperchromicity and anisokaryosis. There was accentuation of zonation of the hepatic lobules and increased perivenous cytoplasmic vacuolation in DNOP-treated rats. Trace quantities (3-5 ppm) of DEHP and DNOP were detected in the liver, and 15-31 ppm were found in adipose tissue of the highest dose groups. The no observed-effect-level was judged to be 50 ppm in the diet or 3.7 mg/kg body weight/day for DEHP, and 500 ppm or 36.8 mg/kg body weight/day for DNOP.

Comparison of the up-and-down, conventional LD50, and fixed-dose acute toxicity procedures

The up-and-down procedure (UDP), fixed-dose procedure (FDP) and conventional LD50 tests were compared to determine their consistency in chemical hazard classification for acute oral toxicity according to the European Economic Community (EEC) system. There was consistent classification for 23 out of 25 cases between the UDP and the conventional LD50 results, in 16 out of 20 cases between the FDP and the conventional LD50, and in seven out of 10 cases between the UDP and the FDP. The UDP needed only between six and 10 animals of one sex (fewer than either the LD50 or the FDP). Available literature indicates that the sexes are usually similar in their acute toxicity responses and that of females are often more sensitive than males when acute toxicity differences do exist, thus obviating the need for both sexes to be tested in most cases. Unlike the FDP, the UDP also estimates an LD50, thus providing data directly applicable to all current hazard classification systems based on acute oral toxicity.

Effects of antimony on rats following 90-day exposure via drinking water

The subchronic toxicity of antimony in drinking water was studied in the rat. Male and female Sprague-Dawley rats (127-135 g body weight, 15 animals per group) were exposed to a soluble trivalent antimony salt, potassium antimony tartrate, in drinking water at concentrations of 0.5, 5, 50 and 500 ppm for 13 wk. Control rats received tap water as drinking water. An additional 10 male and 10 female rats were included in each of the control and 500 ppm groups and were given tap water for a further 4-wk recovery period after the 13-week treatment period. During treatment, the highest dose animals of both sexes consumed significantly less water and showed suppressed body weight gain. During recovery, water intake was quickly restored to that of the control groups and body weight gain was accelerated. At termination, one highest dose male had a cirrhotic liver, and three highest dose males exhibited gross haematuria. Female rats showed a dose-related decrease in serum glucose starting at 5 ppm, and rats of both sexes in the highest dose group had slightly decreased alkaline phosphatase activity and creatinine. The highest dose males had decreased red blood cell and platelet counts and increased mean corpuscular volume. Hepatic glutathione S-transferase activity was increased in the highest dose males and females and ethoxyresorufin-O-deethylase activity was increased in the highest dose males. In the highest dose groups, mild adaptive histological changes were observed in the thyroid, liver and pituitary gland of both sexes, and in the spleen of male rats and thymus of female rats. After a 4-wk recovery period, the pituitary gland of both sexes appeared normal and the changes in the liver and thyroid of both sexes became less severe. On the other hand, minimal changes persisted in the spleen of both sexes and in the thymus of males. Tissue antimony levels were dose-related and follow the order: red blood cells > > spleen, liver > kidney > brain, fat > serum. After the recovery period, antimony level in the highest dose animals decreased for all tissues except the spleen, which remained the same as before recovery. A NOAEL of 0.5 ppm antimony in drinking water, equivalent to an average intake of 0.06 mg/kg body weight/day, was established on the basis of the histological and biochemical changes observed at 5.0 ppm.

Subchronic toxicity of 3,3',4,4',5-pentachlorobiphenyl in the rat. I. Clinical, biochemical, hematological, and histopathological changes

The systemic toxicity of 3,3',4,4',5-pentachlorobiphenyl (PCB 126) following subchronic dietary exposure was investigated in Sprague-Dawley rats. PCB 126 was administered to rats of both sexes at concentrations of 0.1, 1.0, 10, or 100 ppb in their diet for 13 weeks. Another group of rats received a loading dose of 5 micrograms PCB/kg body wt at the start of the feeding period followed by exposure to 10 ppb PCB diet for the same period of time as the other groups. Growth suppression and decreased food consumption were observed in the highest dose groups of both sexes. Increased organ/body weight ratios for the liver occurred in the 10 and 100 ppb groups of both sexes. Rats of both sexes exposed to the highest dose of the PCB also exhibited increased relative kidney, spleen, and brain weights. Hematological and most serum biochemical changes were confined to the 100 ppb groups. These included elevated alkaline phosphatase, bilirubin, cholesterol, and aspartate aminotransferase, and decreased serum glucose, hemoglobin, erythrocytes, hematocrit, and platelets. A dose-dependent increase in liver ethoxyresorufin-O-deethylase activity was observed in rats of both sexes starting at 0.1 ppb. A dose-dependent increase in liver uroporphyrin levels was observed in both sexes and significant changes occurred in the female rats at 1.0 ppb and higher dose groups. Decreased liver vitamin A was observed in the 10 ppb group and higher in both sexes. Kidney vitamin A was elevated in the 100 ppb group. No statistically significant changes were noted in concentrations of brain biogenic amines. PCB 126 residues were 10-fold higher in liver than in fat. Treatment-related histopathological changes were observed in the thymus, thyroid, bone marrow, and liver of rats exposed to the 10 ppb diet, but increased frequency of mild changes was observed in most of these tissues at the 1.0 ppb level. Based on the above data, the no adverse effect level was judged to be 0.1 ppb in the diet or 0.01 micrograms/kg body wt/day.

The accumulation of mono-2-ethylhexylphthalate (MEHP) during storage of whole blood and plasma

The accumulation of the plasticizer di-2-ethylhexylphthalate (DEHP) in blood and blood components has been of considerable concern for some time. We have followed the accumulation of DEHP and one of its major metabolities, mono-2-ethylhexylphthalate (MEHP) during storage of whole blood, platelet-rich plasma, platelet concentrates, and platelet-poor plasma for periods ranging from 72 hours to four weeks. Both phthalates showed a progressive increase in concentration with time. While the levels of DEHP were much greater than those of MEHP, there was nonetheless a significant and continual increase in MEHP in all preparations. The highest concentrations of both DEHP and MEHP were found in the platelet-poor plasma, indicating that platelets do not have a major role in the accumulation of the phthalates in blood. The accumulation of MEHP was shown to be a direct result of the metabolism of DEHP by plasma protein(s) rather than leaching from the blood bag.

Activated platelets in paroxysmal nocturnal haemoglobinuria

One of the major causes of morbidity and mortality in paroxysmal nocturnal haemoglobinuria (PNH) is venous thrombosis. We have studied fibrinolysis, coagulation and platelets in 11 patients with PNH in an attempt to identify the possible mechanism(s) of thrombosis in PNH. In this study we did not identify any fibrinolytic defects, evidence of coagulation activation, nor reduction in coagulation inhibitors. In contrast, in this cohort of 11 PNH patients we have identified varying degrees of platelet activation as defined by the surface expression of activation-dependent proteins and the binding of adhesive proteins to the platelet surface. The thrombotic events in PNH usually occur in the venous system. Our studies and previous experimental studies suggest that anti-platelet therapy may be efficacious in reducing the incidence and severity of venous thrombosis in PNH.

Toxicity of PCB 77 (3,3',4,4'-tetrachlorobiphenyl) and PCB 118 (2,3',4,4'5-pentachlorobiphenyl) in the rat following subchronic dietary exposure

The toxicity of 3,3',4,4'-tetrachlorobiphenyl (PCB 77) and 2,3',4,4',5-pentachlorobiphenyl (PCB 118) was investigated in rats following subchronic dietary exposure. Groups of 10 male and 10 female weanling Sprague-Dawley rats were administered PCB 77 in the diet at 0, 10, 100, 1000, or 10,000 ppb for 13 weeks. PCB 118 was administered to males in the diet at 0, 10, 100, 1000, and 10,000 ppb, while the female groups received 0, 2, 20, 200, or 2000 ppb of the congener for 13 weeks. Growth rate and food consumption were not affected by treatment. No clinical signs of toxicity were observed. Increased spleen weight occurred in male rats fed 1000 or 10,000 ppb PCB 77. Male rats receiving 10,000 ppb PCB 118 had increased liver weight and hepatic ethoxyresorufin O-deethylase (EROD) activity. Increased hepatic EROD activity but not liver weight was observed in female rats given the 2000-ppb PCB 118 diet. Increased EROD activity was also noted in male rats given 10,000 ppb and in female groups receiving 1000 or 10,000 ppb PCB 77. Male rats exposed to 10,000 ppb PCB 77 had decreased vitamin A in the liver and lung and elevated levels in the kidney. Liver vitamin A of both 1000- and 10,000-ppb PCB 77 female groups was decreased. PCB 118 had no effects on tissue vitamin A at the levels studied. No hematological changes or serum biochemical changes were seen in any of PCB 118- and PCB 77-treated groups, nor were liver uroporphyrin levels altered. A reduction in dopamine and homovanillinic acid in substantia nigra region of the brain was observed in female rats fed 2000 ppb PCB 118, while 10,000 ppb PCB 77 was associated with an elevation in 3,4-dihydroxyphenylacetic acid in the nucleus accumbens region of male rat brains. Mild to moderate changes were observed in the liver and thyroid of rats given PCB 77 or PCB 118. PCB 118 accumulated in a dose-dependent manner in fat and to a much lesser extent in liver. In contrast, very low levels of PCB 77 residue were found in the tissues examined. Based on the above data it was concluded that NOAEL of PCB 77 is 100 ppb in diet or 8.7 micrograms/kg and that of PCB 118 is 200 ppb in diet or 17 micrograms/kg body wt/day.

Percutaneous absorption and metabolism of pyrene, benzo[a]pyrene, and di(2-ethylhexyl) phthalate: comparison of in vitro and in vivo results in the hairless guinea pig

The in vitro and in vivo absorption and metabolism of pyrene, benzo[a]pyrene, and di(2-ethylhexyl) phthalate (DEHP) were investigated in the hairless guinea pig. The in vitro method, which involved the use of flow-through diffusion cells and Hepes-buffered Hanks' balanced salt solution containing 4% bovine serum albumin as perfusate, was demonstrated to be a suitable system for predicting in vivo absorption of the above lipophilic compounds. The successful application of the in vitro technique for these compounds is significant because no satisfactory in vitro method has hitherto been developed to predict in vivo absorption of highly lipophilic chemicals. Quantification of parent compounds and metabolites that permeated into perfusates and those that remained in skin discs provided insight into the process by which the chemicals penetrated through the skin. Pyrene was absorbed primarily by a passive diffusion process, although a small fraction of the administered dose was biotransformed into metabolites in the skin and partitioned into the receptor fluid. Absorption of benzo[a]pyrene was mediated by biotransformation processes. A metabolite derived from the ultimate carcinogen of this compound, benzo[a]pyrene r-7, t-8,9,10-tetrahydrotetrol, was identified in the receptor fluid. Most of the administered DEHP remained in the skin and only a very small fraction of the dose partitioned into the receptor fluid in either viable or nonviable skin. Data from the present study led to the conclusion that the in vitro method can be utilized to predict in vivo absorption for compounds of high lipophilicity and that dermal metabolism facilitates partitioning of metabolites into the receptor fluid and hence may affect the biological activities of dermally applied compounds.

Comparisons of brain, uterus, and liver mRNA expression for cytochrome p450s, DNA methyltransferase-1, and catechol-o-methyltransferase in prepubertal female Sprague-Dawley rats exposed to a mixture of aryl hydrocarbon receptor agonists

Non-ortho polychlorinated biphenyls (PCBs), polychlorinated dibenzodioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs) are ubiquitous environmental contaminants that exert their toxicity mostly through activation of the aryl-hydrocarbon receptor (AhR), and are referred to as AhR agonists. The objective was to study, by real time reverse-transcriptase-polymerase chain reaction (RT-PCR), the effects of postnatal exposure to a reconstituted mixture of AhR agonists present in breast milk (3 non-ortho PCBs, 6 PCDDs, and 7 PCDFs, referred to here-in-after as AhRM) on mRNA expression of estrogen receptor (ERalpha), enzymes involved with the metabolism of estrogens [catechol-o-methyltransferase (Comt), cytochrome P450 (Cyp)1A1, 1B1 and 2B1], and DNA methyltransferase-1 (Dnmt1), in brain areas, liver and uterus of immature female rats. Neonates were exposed by gavage during postnatal day (PND) 1-20 with dosages equivalent to 1, 10, 100, and 1000 times the estimated average human exposure level, and were sacrificed at PND 21. None of the end points were affected in uterine cross-sections, or in samples of uterine tissue layers collected by laser capture microdissection. At 1000x, the AhRM reduced Dnmt1 mRNA abundance to 28% and 32% of control in the liver and hypothalamus, respectively. In the brain, Cyp1A1 was increased (409%) but ERalpha was reduced (66%). Similarly, mRNA abundance for Comt isoforms was reduced in the liver (45%) and brain areas (55-70%). AhRM at 100x, the lowest effective dose, exerted a 220% increase in brain cortex Comt [membrane bound (Mb)], a 219% increase in hepatic Cyp1B1, and a 63% decrease in hepatic Comt (soluble (S)+Mb). These results support the possibility that early exposure to environmental contaminants could lead to effects mediated by changes in DNA methylation and/or estrogen metabolism and signaling.

In vivo and in vitro dermal absorption of benzo[a]pyrene in rat, guinea pig, human and tissue-cultured skin

Cross-species in vitro dermal absorption tests were conducted with 14C-labelled benzo[a]pyrene dissolved in acetone and applied to dermatomed skin (0.5 mm thickness) at comparable dose rates (8-13 micrograms/cm2). Skin absorption was determined using the Bronaugh in vitro flow-through procedure. The percentage (%) dermal absorption included the % 14C-activity detected persisting in the skin added to that detected in the receiver solution. Listed in decreasing order, total % in vitro dermal absorption obtained by 48 h postexposure was: 95 +/- 9.6% (rat), 51 +/- 3.0% (hairless guinea pig), 43 +/- 8.7% (human; 50-year-old), 34 +/- 12.4% (Testskin) and 23 +/- 5.3% (human; 32-year-old). Comparative in vivo studies demonstrated urinary recovery of 8 +/- 1.8% and 25 +/- 5.0% for rats (dose rate: 6 micrograms/cm2) and hairless guinea pigs (dose rate: 9 micrograms/cm2), respectively. Total faecal recovery was 61 +/- 6.0% and 43 +/- 6.1% for rats and guinea pigs, respectively. Necropsies conducted at 14 days postexposure demonstrated total 14C-activity tissue recoveries of 0.5 +/- 0.13% and 0.6 +/- 0.17% in rats and guinea pigs, respectively. Including the 14C-activity extracted from the skin removed from the dose site at 14 days postexposure, the total % in vivo dermal absorbtion was 70 +/- 7.6% and 68 +/- 9.3% for rats and guinea pigs, respectively. In summary, the in vitro data was consistent with the in vivo data in demonstrating that 14C-benzo[a]pyrene was well absorbed through skin.

Toxicity of 2,2',4,4',5,5'-hexachlorobiphenyl in rats: effects following 90-day oral exposure

The subchronic toxicity of 2,2',4,4',5,5'-hexachlorobiphenyl (PCB 153) was investigated in rats after 13 weeks of dietary exposure. Groups of 10 male and 10 female rats were administered PCB 153 in their diet at levels of 0.05, 0.50, 5.0 or 50 ppm for 13 weeks. The control groups received the diet containing 4% corn oil. Growth rate and dietary consumption were not affected by treatment. Clinical signs of toxicity were not observed. Enlarged, fatty liver was observed in treated animals at necropsy, but most were confined to the two highest dose groups. Increased hepatic microsomal ethoxyresorufin-O-deethylase, aminopyrine-N-demethylase and aniline hydroxylase activities occurred in high-dose groups of both sexes, with increased ethoxyresorufin-O-deethylase activity being observed starting at 0.05 ppm in females and at 0.5 ppm in males. Treatment-related reduction in hepatic and pulmonary vitamin A was seen in the highest dose group of both sexes. Changes in brain biogenic amines and intermediate products were observed mainly in females; these included decreased dopamine and 5-hydroxytryptamine concentrations in the frontal cortex region, and dihydroxyphenylacetic acid in the caudate nucleus region at 5.0 and 50 ppm. Female rats appeared to be more sensitive to the neurotoxic effects of PCB 153 than males. Dose-dependent histological changes were observed in the thyroid and liver of rats of both sexes and significant changes occurred at 5.0 and 50 ppm. Based on these data, the no-observable-adverse-effect level (NOAEL) of PCB 153 was judged to be 0.5 ppm in the diet or 34 micrograms kg-1 body wt. day-1.

Skin reservoir formation and bioavailability of dermally administered chemicals in hairless guinea pigs

There is concern as to whether dermally applied chemicals that remain in the skin after exposure are bioavailable and should be included as part of the systemic dose; this study was conducted to investigate the temporal relationship between the skin depot and absorbed dose. Single doses of 14C-labelled phenanthrene, benzo[a]pyrene or di(2-ethylhexyl) phthalate were administered dermally to groups of four female, Hartley hairless guinea pigs which were housed individually in metabolism cages to collect urine and faeces for radioassay. The animals were sacrificed at 6 hr, 24 hr, 48 hr, 7 days or 14 days after dosing to harvest skin specimens for the determination of radioactivity by autoradiographic and liquid scintillation methods, and to determine the dose that remained in the body. It was found that for all three compounds the amount of chemical left in the skin decreased over time while the cumulative percent dose excreted in urine and faeces increased. The autoradiographic results were consistent with those obtained from the liquid scintillation method showing a gradual decrease in radioactivity grain accumulation over the time periods for the three compounds, with the highest grain density observed around hair follicles of the skin. The results of this study indicate that the chemicals left in the skin after surface washing eventually enter the systemic circulation and should be considered as part of the total dose absorbed, and that the hair follicle may play an important role in percutaneous penetration.

Synthesis and biological evaluation of xanthine oxidase inhibitors. Pyrazolo(3,4-d)pyrimidines and pyrazolo(3,4-b)pyridines

1-, 3-, and 5-substituted pyrazolo[3,4-d]pyrimidines and pyrazolo[3,4-b]pyridines related to allopurinol were synthesized and evaluated as xanthine oxidase inhibitors. Among these compounds, 4-hydroxypyrazolo[3,4-b]pyridine-5-carboxylic acids 12 were found to possess potency in the same order of allopurinol. The influence of the substitutions on the enzyme inhibitory effect and the bulk tolerance of the enzyme-inhibitor complex are discussed.

Short-lived mutagen in Salmonella produced by reaction of trichloroacetic acid and dimethyl sulphoxide

A chemical reaction occurs when trichloroacetic acid (TCA) is dissolved in dimethyl sulphoxide (DMSO), with the production of a short-lived mutagenic derivative which was detected using the Salmonella/mammalian-microsome plate overlay assay. Other interactions between test chemicals and solvents are discussed. Choice of proper solvents in mutagenicity testing is emphasized.

Ninety-day toxicity of photomirex in the male rat

Photomirex (8-monohydromirex) is a demonstrated environmental contaminant and was observed in previous short-term studies to produce lesions in the liver, thyroid and testes of male rats. The present study was undertaken to confirm those observations and to determine the effects after a longer period of exposure. Male rats were fed photomirex for 13 weeks at levels of 0.20, 1.0, 5.0, 25 and 125 ppm in the diet. Deaths were observed in animals receiving the highest dose. Decreased body weight gain and food intake were also observed in that group. Liver weights were increased at 5.0 ppm photomirex and higher. Photomirex caused changes in several biochemical parameters including serum sorbitol dehydrogenase and hepatic aniline hydroxylase activities. Dose-related histological abnormalities were observed in the thyroid and liver starting at the lowest dose level. These results confirm earlier findings and show that photomirex is a potent hepato- and thyrotoxin.

Pharmacokinetics of benzo[a]pyrene in the rat

Groups of 4 male Wistar rats were dosed intravenously with 14C-labeled benzo[a]pyrene dissolved in an Emulphor/water vehicle at 3 different dose levels and killed at 1 of 15 specific time intervals from 5 min to 32 h after dosing. 14C-Radiolabel concentration-time data were obtained for blood, brain, adipose, heart, kidney, liver, lung, spleen, and testes. Benzo[a]pyrene concentration-time data were obtained for blood, adipose, kidney, liver, and lung. Appropriate mathematical models were fitted to these data and to the data for metabolites derived as the residuals from 14C-radiolabel minus benzo[a]pyrene difference, where applicable. Nonlinear kinetics were found for 14C-radiolabel in liver, while the data from lung for both 14C-radiolabel and for benzo[a]pyrene per se supported the binding of benzo[a]pyrene in that tissue.

Effect of environmental conditions on the penetration of benzene through human skin

The in vitro penetration of [14C]benzene through freshly prepared human skin was examined under a variety of skin conditions associated with swimming and bathing. The experimental system utilized a recirculating donor solution and a flow-through receiver solution, and was modified to accommodate the analysis of volatiles. The permeability coefficient of 0.14 cm/h under standard conditions at 26 degrees C was found to increase to 0.26 cm/h at 50 degrees C and decrease to 0.10 cm/h at 15 degrees C. Storage of the skin at- 20 degrees C did not affect the penetration of benzene. Application of baby oil, moisturizer, or insect repellant to the skin before exposure under standard conditions did not affect the flux of benzene, but a significant increase was observed when the skin was pretreated with sunscreen (permeability coefficient 0.24 cm/h). These results suggest that risk assessment or exposure modeling for benzene and other environmental contaminants should account for appropriate changes in the environmental conditions when considering the dermal route of exposure.

Percutaneous absorption/metabolism of phenanthrene in the hairless guinea pig: comparison of in vitro and in vivo results

The in vitro and in vivo percutaneous absorption/metabolism of phenanthrene was investigated in hairless guinea pigs. Flow-through diffusion cells and Hepes-buffered Hanks' balanced salt solution (HHBSS) as receptor fluid were used in the in vitro system. When phenanthrene was applied to excised guinea pig skin mounted on the cells at dose levels of 6.6 and 15.2 micrograms/cm2, 89.7 and 79.1% of the administered doses were respectively absorbed into the skin and receptor fluids during a 24-hr perfusion period. These results are consistent with the in vivo data which showed approximately 80% absorption over the same period of time. Phenanthrene was metabolized in vitro into phenanthrene 9,10-dihydrodiol, 3,4-dihydrodiol, 1,2-dihydrodiol, and traces of hydroxy phenanthrenes. Of the materials absorbed in vitro, 92% was the parent compound and 7% the dihydrodiol metabolites. When a nonviable in vitro system was used, 68% of the applied 15.2 micrograms/cm2 dose was absorbed. Data from the present study demonstrate that the in vitro system is a good model for predicting in vivo percutaneous absorption of phenanthrene, and that penetration of phenanthrene through the skin is controlled more by the passive rate of diffusion than by metabolism.

Validation of higher-throughput high-performance liquid chromatography/atmospheric pressure chemical ionization tandem mass spectrometry assays to conduct cytochrome P450s CYP2D6 and CYP3A4 enzyme inhibition studies in human liver microsomes

In the early stage of drug discovery, thousands of new chemical entities (NCEs) may be screened before a single drug candidate can be identified for development. In order to accelerate the drug discovery process, we have developed higher-throughput enzyme assays to evaluate the inhibition of cytochrome P450 isoforms 2D6 (CYP2D6) and 3A4 (CYP3A4) in human liver microsomes. The assays are based on high-performance liquid chromatography/tandem mass spectrometry (LC/MS/MS) techniques. The analysis time for each sample was reduced from approximately 20 minutes for the conventional HPLC assay to 30 seconds for the LC/MS/MS assay. For both LC/MS/MS assays, the linearity (r(2) > 0.99), precision (%CV < 15%) and accuracy (% bias <15%) for both inter- and intraday validations were satisfactory. Since the implementation of the LC/MS/MS assays, our sample throughput has increased by over 40-fold.

Toxicity of 2,4,4'-trichlorobiphenyl in rats following 90-day dietary exposure

The toxicity of 2,4,4'-trichlorobiphenyl (PCB 28) was investigated in rats after a 90-d dietary exposure. Groups of 10 male and 10 female weanling Sprague-Dawley rats were administered PCB 28 in the diet at 0, 0.05, 0.50, 5.0, or 50.0 ppm for 13 wk. Growth rate and food consumption were not affected by treatment, and no clinical signs of toxicity were observed. Mottled liver was noted in both control and PCB-treated males, but was found with increased incidence in the highest treatment group. Increased urinary ascorbic acid and hepatic microsomal ethoxyresorufin O-deethylase activity were observed in the 50.0 ppm group of both sexes. The vitamin A content in liver, lung, and kidney was not significantly affected by treatment. Analysis of brain biogenic amines showed a decreased dopamine concentration in the substantia nigra region of female rats receiving 0.5 ppm PCB 28 and higher doses. Female rats appeared to be more sensitive than males to the neurochemical effects of PCB 28. Dose-dependent histologic changes were observed in the thyroid and liver, with biologically significant changes occurring at 5.0 ppm and above. Based on these data, the no observable-adverse-effect level (NOAEL) for this PCB congener was considered to be 0.5 ppm in diet or 36 micrograms/kg body weight/d.

Urinary ascorbic acid--HPLC determination and application as a noninvasive biomarker of hepatic response

A high-performance liquid chromatograph (HPLC) procedure has been developed for the determination of rat urinary ascorbic acid, a major metabolite of the hepatic glucuronic acid pathway. The presence of EDTA and HCl effectively inhibited degradation of ascorbic acid during the collection of urine specimens. The reliability of the procedure was demonstrated by its high recovery (90%), specificity (characteristic absorption maximum and discrimination from isoascorbic acid), and reproducibility (2-3% coefficient of variation). The usefulness of this assay as an indicator of hepatic response was demonstrated in preliminary experiments where increases in urinary ascorbic acid excretion were detected in male rats treated with PCB 126 (3,3',4,4',5-pentachlorobiphenyl) or PCB 105 (2,3,3',4,4'-pentachlorobiphenyl). The HPLC measurement also showed that the two PCB congeners differed markedly in their potency in stimulating urinary ascorbic acid excretion. For example, 10 micrograms/kg bw/day of PCB 126 was sufficient to cause a fourfold increase in urinary ascorbic excretion while 5000 micrograms/kg bw/day of PCB 105 was required for a sevenfold increase. In response to the administration of PCB 105 or PCB 126, urinary ascorbic acid appeared to increase to the same extent as increases in hepatic ethoxyresorufin O-deethylase (EROD) and UDP-glucuronosyltransferase (UGT) activities, and to a much higher extent than changes in liver weight and hematological and serum clinical chemical parameters. The sensitivity and specificity, the ease in obtaining timed specimens, and the noninvasive nature make this assay a useful biomarker of hepatic response in dose-finding and various acute and chronic studies.

Reproductive and thyroid hormone levels in rats following 90-day dietary exposure to PCB 28 (2,4,4'-trichlorobiphenyl) or PCB 77 (3,3'4,4'-tetrachlorobiphenyl)

Subchronic exposure to the PCB congener 77 (PCB 77) and 28 (PCB 28) was previously shown to induce histological changes in the thyroid and in the brain biogenic amines levels, suggesting possible effects on thyroid and reproductive hormone levels. Thus, the effects of a 90-day dietary exposure to PCB 28 or 77 on luteinizing hormone, follicle-stimulating hormone, and testosterone concentrations were studied in male rats, as well as the levels of thyroid-stimulating hormone, thyroxine (T4) and uridine diphosphate-glucuronyl transferase (UDP-GT) activity in both genders. Weanling Sprague Dawley rats were randomly distributed into groups of 10 rats and were fed, for the next 13 weeks, purina lab chow containing 50, 500, 5,000 or 50 000 ppb of PCB 28 or 10, 100, 1000, or 10 000 ppb of PCB 77. The serum concentrations of T4 were decreased in rats of both sexes receiving 1000 ppb or more of PCB 77, and was associated with an increased activity of UDP-GT which reached significance only in the females. There was a tendency for the highest dose of PCB 28 also to decrease serum T4 concentrations in the female rats. None of the PCB treatments significantly altered gonadotropin, TSH, or testosterone concentrations. These results suggest that thyroid functions may be more susceptible or adapt less readily than the pituitary gland and the testes to endocrine disruption caused by PCB congeners.

A teratological assessment of four trihalomethanes in the rat

Four trihalomethanes were administered by gavage to Sprague-Dawley rats from day 6 to day 15 of gestation. Chloroform (Ch) was administered at levels of 100, 200 and 400 mg/kg and bromoform (Br), bromodichloromethane (BDCM) and chlorodibromomethane (CDBM) were administered at levels of 50, 100 or 200 mg/kg/day. A separate control was used for each compound. Maternal weight gain was depressed in all groups receiving Ch and at the highest dose levels of BDCM and CDBM. Ch administration caused decreased maternal hemoglobin and hematocrit values at all dose levels and also produced increased serum inorganic phosphorus and cholesterol at the highest dose. Liver enlargement was observed at all dose levels of Ch but in no other treatment groups. Evidence of a fetotoxic response was observed with Ch, CDBM and Br but not BDCM. No dose-related histopathological changes were observed in either mothers or fetuses as a result of treatment. None of the chemicals tested produced any teratogenic effects.

Subchronic toxicity of PCB 105 (2,3,3',4,4'-pentachlorobiphenyl) in rats

The toxicity of 2,3,3',4,4'-pentachlorobiphenyl (PCB 105) was investigated in Sprague-Dawley rats following dietary exposure to this substance at levels of 0, 0.05, 0.5, 5 or 50 ppm for 13 weeks. Growth rate and food consumption were not affected and no clinical signs of toxicity were observed. Increased incidences of enlarged, fatty liver and decreased thymic weight were observed in the highest-dose groups of both genders; these groups also had elevated hepatic microsomal ethoxyresorufin deethylase activity and uroporphyrin. Significant increases in serum cholesterol and hepatic pentoxyresorufin dealkylase activity were observed in the highest-dose males and two highest-dose females. By contrast, liver UDP-glucuronosyl transferase activity was elevated in the two highest-dose males and the highest-dose females. Urinary ascorbic acid excretion was increased in the highest-dose males. While the amount of vitamin A was decreased dose-dependently, starting at 0.5 ppm in the liver of both sexes and in the lung of the females, the level in the kidney of the highest-dose group was increased. Administration of PCB 105 resulted in decreased dopamine in the caudate nucleus region of the brain in males and homovanillic acid in caudate nucleus and nucleus accumbens of females. Increased 5-hydroxytryptamine and 5-hydroxyindoleacetic acid were observed in the substantia nigra region of both sexes, with most of the increases being seen in highest-dose females. Anemia, characterized by decreased hemoglobin, hematocrit and red cell indices, occurred in the highest-dose group, as did eosinophilia. Treatment with PCB 105 caused dose-dependent histopathological changes in the liver and thyroid. Thymic changes were observed in the highest-dose males and two highest-dose females. Tissue residue data showed a dose-dependent accumulation of this congener in fat, liver and spleen, kidney and brain. Based on these data the no-observable-effect level of PCB 105 was judged to be 0.05 ppm or 3.9 microg kg(-1) body wt. day(-1) in males and 4.2 microg kg(-1) body wt. day(-1) in females.