Immunotoxicity Evaluation of Resorcinol Bis-Diphenylphosphate (Fyrolflex RDP) in B6C3F1 Mice

RDP was administered daily to groups of female B6C3F1 mice by oral gavage for 28 days at dose levels of 500, 1500, or 5000 mg/kg/day body weight (BW). Control animals were sham dosed. Animals were euthanized 1 day following final exposure or following a 60-day recovery period. End point observations included necropsy and histopathology, spleen and thymus weights and cellularity, peritoneal cell numbers and differential cell analysis, splenic natural killer (NK) cell activity, lymphocyte blastogenesis, antibody-forming cell (AFC) response, peritoneal macrophage phagocytic activity, and host susceptibility to Listeria monocytogenes infection. In-life observations included weekly clinical examinations and body weights. No adverse clinical signs were noted and the only significant finding was an increase in body weight in high dose mice on week 4 as compared to sham controls. Small changes in body weight gain were seen in all dose groups as compared to sham controls after completion of dosing on weeks 5 and 6 and in mid-dose mice on weeks 7 and 12. No significant differences were found in spleen and thymus weights or in cellularity. No changes were found in peritoneal cell numbers or cell types, peritoneal macrophage phagocytic activity, or host susceptibility to infection. Likewise, splenic NK cell activity, lymphocyte blastogenesis, and AFC function were also unaffected. No histopathologic changes were observed. All animals that received positive-control substances demonstrated a significant effect in the respective tests. In conclusion, a standardized and validated battery of immune function tests demonstrated no immunotoxicity following daily oral exposure to up to 5000 mg/kg BW of RDP for 28 days.

Twenty-Eight Day Nose-Only Inhalation Toxicity Study of Resorcinol Bis-Diphenylphosphate (Fyrolflex RDP) in Rats

To evaluate the effects of repeated inhalation exposure to resorcinol bis-diphenylphosphate (Fyrolflex RDP), male and female Sprague-Dawley rats received nose-only inhalation exposure to Fyrolflex RDP for 6 h/day, 5 days/week for 4 weeks. Concentrations of Fyrolflex RDP tested were 0 (filtered air control), 0.1, 0.5, and 2.0 mg/l air. Ten rats/sex/group were euthanized on day 29; 10 additional rats/sex in the control and high-dose groups were euthanized after a 60-day recovery period. RDP induced no mortality or overt toxicity during the exposure or recovery periods. Body weight and body weight gain were reduced in high-dose male rats during exposure, but returned to control levels after 5 weeks of recovery. Absolute and relativelung weights were increased in mid-and high-dose groups after exposure, and in the high-dose group at the end of the recovery period. Relative fiver weights were increased after exposure in mid-and high-dose females and in high-dose males. Gross pathology was limited to confluent white foci in the lungs of all high-dose animals after exposure, and in 80 % of high-dose animals after the recovery period. Underlying lung histopathology after exposure consisted of alveolar histiocytosis in mid-and high-dose groups; this progressed to chronic foreign body inflammation in high-dose rats after recovery. This response is characteristic of a noncytotoxic, water-insoluble foreign material that reaches the alveolar region of the lung. On this basis, although the observed lung lesions were exposure-related, they were not considered to reflect a specific toxic response to Fyrolflex RDP. No exposure-relatedgross or microscopic pathology was identified in any other organ in any experimental group. The no-observed-effectlevel (NOEL) for RDP in this study was 0.1 mg/l.

Developmental Toxicity Study of Orally Administered Resorcinol Bis-Diphenylphosphate (RDP) in Rabbits

Fyrolflex resorcinolbis-diphenylphosphate (RDP) is a nonhalogenphosphate ester product that is widely used as a flame retardant for petrochemicalplastics and high-temperature lubricant additive applications. The potential developmental toxicity of RDP was evaluated in rabbits. Groups of 27 sperm-positive New Zealand white rabbits (Hazelton Research Products Inc., Denver, PA) were administered graded concentrations of 50, 200, or 1000 mg/kg/day of RDP in corn oil. A vehicle control group of equal size was administered corn oil alone. Rabbits were dosed daily (1.5 ml/kg) on gestationdays 6 to 28 and sacrificed on gestationday 29. The fetuses were removed by cesarean section and examined for gross external, visceral, cephalic, and skeletal anomalies. No treatment-related clinical signs of toxicity were observed. No treatment-related effects in maternal food consumption, body weight, body weight gain, or on uterus, liver, kidney, and spleen weights were detected. Fetal viability and body weight, as well as developmental end points were also unaffected by treatment. Accordingly, exposure of pregnant rabbits to doses ranging from 50 to 1000 mg/kg/day of RDP during the periods of major organogenesis and histogenesis did not result in any biologically significant toxic or teratogenic/developmental effect in the dams or fetuses.

Two-Generation Oral (Diet) Reproductive Toxicity Study of Resorcinol Bis-Diphenylphosphate (Fyrolflex RDP) in Rats

Fyrolflex resorcinol bis-diphenylphosphate (RDP) was evaluated in a two-generation reproductive study as part of a program to assess the overall toxicology of this flame retardant. RDP was administered to male and female Sprague-Dawley rats in the diet at concentrations of 1000, 10,000 or 20,000 ppm. The control group was given diet alone. Parental (P1) animals were treated for 10 weeks prior to mating, during the 2-week mating period, throughout gestation, and through lactation until sacrifice. The F1 generation (P1 offspring) was treated following a regimen similar to P1. The F2 generation was not treated. No significant difference in Utter survival was observed between the control and treated groups. Body weights were significantly decreased in P1 rats during the 1st week due to an initial flavor aversion of the test substance in the diet. Body weight, weight gains, and food consumption were decreased in the test substance-treated pups (F1) during lactationand after weaning. These changes were also attributed to a flavor aversion. Anogenital distance was similar in the control and high-dose groups, whereas vaginal opening and preputial separation were delayed in the 10,000 and 20,000 ppm groups, and were considered to be secondary to the reduction in F1 body weight. Neither parents nor offspring exhibited any test substance-related clinical signs of toxicity. Vaginal cytology and cyclicity and male reproductive functions (sperm count, motility, and morphology) were unaffected by treatment. Mating performance was similar in the treated groups relative to the control. No treatment-related lesions were noted in the reproductive organs. Increased liver weight and associated hepatic periportal hypertrophy were observed in the RDP-treated animals (P1 and F1). In conclusion, there were no adverse effects on reproductive performance or fertility parameters associated with RDP administration in the diet. Fyrolflex RDP administered for greater than 13 weeks and up to the entire life span (i.e., F1, from conception to euthanasia) resulted in increased liver weights with associated periportal hypertrophy. This change was considered an adaptive process associated with RDP metabolism in the liver.

A subchronic toxicity study of Phosflex 51B in Sprague-Dawley rats

Phosflex 51B is a flame retardant plasticizer that is blended with polyvinyl chloride films to effectively control product flammability. Its composition places it in the butylated triphenyl phosphate category. Previous studies have shown Phosflex 51B to have low acute toxicity, to lack teratogenic and mutagenic activity, and to not induce delayed peripheral neuropathy. The present study was conducted to determine the toxicity of Phosflex 51B after repeated dietary exposure. Four groups, each consisting of 20 male and 20 female Sprague-Dawley rats, received rodent diet containing either 0, 100, 400, or 1600 ppm for 90 days. Parameters measured include body weight, food consumption, clinical observations, hematology, clinical chemistry, and cholinesterase activity. Tissues were examined at necropsy for gross changes and were processed for microscopic pathology. There were no significant treatment-related effects on body weights, food consumption, hematology and clinical chemistry, or cholinesterase values. A significant increase was observed in the absolute and relative mean weights of livers in high-dose male rats, the mean relative liver weights of the high-dose female animals, the mean relative kidney weights of the high-dose male rats, and the mean absolute weights of the adrenal glands from high-dose female rats. Neither gross nor microscopic pathology examinations revealed tissue changes in these organs or in any other organs. Although increases in liver, kidney, and adrenal weights were observed in certain animals in the 1600-ppm high-dose group, the administration of Phosflex 51B did not result in significant treatment-related adverse effects at dietary dose levels of 100 and 400 ppm. The no-observable-effect level (NOEL) in this study is 400 ppm.

1-(8-Methoxy-4,8-dimethylnonyl)-4-(1-methyl-ethyl)benzene (MV-678): a reversible inducer of rat hepatic microsomal drug metabolism

MV-678 [1-(8-methoxy-4,8-dimethynonyl)-4-(1-methylethyl)benzene], a recently developed insect growth regulator, increased the hepatic cytochrome P-450-dependent monooxygenase enzymes that metabolize endogenous and exogenous chemicals. In an initial set of experiments, male and female rats received 0, 50, or 800 mg/kg X d of MV-678 by gavage for 3 d, and in a second set of experiments, male rats received 0, 50, or 800 mg/kg X d of MV-678 by gavage for 30 d. A significant increase in both absolute and relative liver weight, microsomal protein content, cytochrome P-450 content, NADPH-cytochrome P-450 reductase activity, and ethylmorphine N-demethylase activity was observed in male and female rats at the high dose level at 3 d. Similar increases were observed in the 800-mg/kg X d males at 30 d. Hepatocellular hypertrophy and proliferation of endoplasmic reticulum observed at both 3 and 30 d correspond to and was consistent with microsomal enzyme induction. Reversibility of both induction and changes in morphology was determined by measuring the same parameters in animals treated for 30 d after a 15- or 30-d recovery period. At 15 d recovery, all biochemical parameters at the high dose level, except relative liver weight and microsomal ethylmorphine N-demethylase activity, had returned to control levels. No significant differences between the control and high dose group animals were noted at 30 d recovery. The hepatocellular changes observed in the high-dose group at 30 d were less apparent at 15 d recovery, and absent at 30 d recovery.

Comparative sensitivity of bovine and rodent acetylcholinesterase to in vitro inhibition by organophosphate insecticides

Biochemical studies were conducted to compare the in vitro sensitivities of bovine and rodent brain and erythrocyte cholinesterases to inhibition by Dyfonate-oxon, paraoxon, and malaoxon. This comparison was done to determine if the reported greater sensitivity of cattle to Dyfonate might be explained by a greater sensitivity of the target enzyme, acetylcholinesterase, in cattle to inhibition by Dyfonate's toxic metabolite, Dyfonate-oxon. Studies were conducted with brain homogenates and lysed erythrocytes obtained from cows and from male and female rats. Additional studies were conducted with a commercially available sample of purified bovine erythrocyte acetylcholinesterase (ACHE). In all cases, the concentrations of organophosphates required to produce 50% inhibition (IC50) of enzyme activity were determined. Cow brain ACHE was 1.7 to 3.8 times more resistant to inhibition by Dyfonate-oxon, paraoxon, and malaoxon than was brain ACHE from male or female rats. For both species, paraoxon was 1.2 to 1.6 times more potent than Dyfonate-oxon and 3.8 to 6.9 times more potent than malaoxon. The bimolecular reaction rate constants (ki) were also determined for inhibition of brain ACHE of cows and male rats by the three organophosphates. In general, the ki data were in agreement with the IC50 data indicating that cow brain ACHE was less sensitive than rat brain ACHE to inhibition. Additional IC50 studies were conducted with lysed erythrocytes from cows and from male and female rats. Both quantitative and qualitative differences between species and among the organophosphates were in excellent agreement with the results of the brain ACHE studies. Also, in related studies with purified bovine erythrocyte ACHE, there was excellent agreement with the results of tests involving ACHE inhibition in erythrocyte lysates. This study demonstrated that, as an inhibitor of ACHE in vitro, Dyfonate-oxon was equal to or slightly lower in potency than paraoxon and more potent than malaoxon. In addition, the study demonstrated that, in general, ACHE from brain or erythrocytes of cows was less sensitive to in vitro inhibition by organophosphates than was that from male or female rats. Thus, the apparent greater susceptibility of cows to Dyfonate, in vivo, cannot be explained on the basis of an unusual target enzyme (ACHE) sensitivity to inhibition by Dyfonate-oxon.

A 6-month dietary toxicity study of acidic sodium aluminium phosphate in beagle dogs

Sodium aluminium phosphate [NaAl3H14(PO4)8. 4H2O], a leavening acid, was administered to groups of six male and six female beagle dogs at dietary concentrations of 0, 0.3, 1.0 or 3.0% for 6 months. No adverse treatment-related clinical signs were observed. There were no statistically significant differences in mean body weights between test and control groups at any of the weekly determinations. Weekly mean food consumption values of all male treated groups did not differ significantly from those of the control group at any stage of the study. Statistically significant reductions in food consumption occurred sporadically in all treated groups of female dogs. No significant absolute or relative organ-weight differences were found between any of the treated groups and their respective controls. Haematological, blood chemistry and urinalysis data showed no toxicologically significant trends. Histopathological examination revealed no changes considered to be related to treatment. Thus dietary administration of sodium aluminum phosphate for 6 months at concentrations of 3% or lower caused no significant toxicological effects in beagle dogs.

Dietary subacute toxicity of ethylene thiourea in the laboratory rat

Ethylene thiourea (ETU) was fed to groups of rats at 0, 1, 5, 125 or 625 ppm for up to 90 days. Other groups of rats received either propylthiouracil (PTU; 125 ppm) or amitrole (50 ppm) in their diets as positive controls. Only those rats which received ETU at 125 or 625 ppm and those ingesting PTU or amitrole demonstrated a measurable toxic response. This toxicity was reflected as an alteration in thyroid function and a significant change in thyroid morphology. Ingestion of 625 ppm ETU or 125 ppm PTU resulted in very substantial decrease in serum triiodothyronine (T-3) and thyroxine (T-4). Marked increases in serum thyroid stimulating hormone (TSH) levels were found in the 625 and 125 ppm ETU rats, the 125 PTU rats, and the rats receiving amitrole, each time this hormone was measured. Rats which ingested 625 ppm ETU also exhibited a decrease in iodide uptake by the thyroid. While a statistically significant increase in serum T-4 and degree of thyroid hyperplasia was observed for rats ingesting 25 ppm ETU for 60 days, normal thyroid hormone levels and thyroid morphology was found in rats on 25 ppm ETU for either 30 or 90 days. Based on diochemical and microscopic changes examined, the no-effect level for dietary ETU in this 90-day study is considered to be 25 ppm.

The metabolism of ftorafur in the beagle dog and rhesus monkey

1. Ftorafur, a fluorinated pyrimidine nucleoside antimetabolite, is metabolized by the beagle dog and rhesus monkey to 5-fluorouracil, which is subsequently biotransformed to the corresponding nucleosides, to alpha-fluoro-beta-ureidopropionic acid, to urea and to CO2. 2. In the dog, urea was the primary urinary metabolite while in the monkey, alpha-fluoro-beta-ureidopropionic acid predominated. 3. The dog and monkey excrete about 35 percent of the recovered dose as CO2. 4. The possibility that ftorafur is a relatively inactive transport form of 5-fluorouracil is discussed.

High-pressure liquid chromatography analysis of benzo(a)pyrene metabolism by microsomal enzymes from rhesus liver and lung

The metabolism of benzo(a)pyrene was determined, using rhesus monkey hepatic and pulmonary microsomal enzymes. Metabolites were separated by high-pressure liquid chromatography and identified using known reference standards. Metabolites were quantitated by scintillation spectrometry. Both liver and lung microsomes metabolized benzo(a)pyrene to the following metabolites: 9,10-, 7,8-, and 4,5-dihydrodihydroxybenzo(a)pyrene; benzo(a)pyrene-1,6-dione, -3,6-dione, and -6,12-dione; and 9- and 3-hydroxybenzo(a)pyrene. Two unidentified metabolites and one metabolite region which chromatographed prior to 9,10-dihydrodihydroxybenzo(a)pyrene were produced by both liver and lung microsomes. The two unknown peaks were located between, 9,10- and 4,5-dihydrohidroxybenzo(a)pyrene. Two additional unknown metabolites were produced only in the liver and had retention times slightly greater than the 4,5- and 7,8-dihydrodihydroxybenzo(a)pyrene metabolites, respectively. Quantitative determination of benzo(a)pyrene metabolism revealed large differences for the three monkeys and the respective tissue activities. Liver activity for each animal was substantially higher than lung activity for all benzo(a)pyrene metabolites. The ratio of the metabolites also differed between the liver and lung. 3-Hdyroxybenzo(a) pyrene represented over 60% of the total liver metabolite fraction and 30% of the total lung metabolite fraction. The total quinone fraction represented between 7 and 13% of the total metabolites in the liver and comprised over 40% of the total lung metabolites. The metabolite ratios for the dihydrodiols were very similar for both tissues.

Comparison of the drug metabolizing enzymes in the liver and kidneys from homozygous nude swiss, heterozygous normal swiss, homozygous normal Swiss and DBA/2 mice

The hepatic and renal microsomal drug metabolizing enzyme systems were isolated from homozygous nude Swiss (nu/nu), heterozygous normal Swiss (nu/+), homozygous normal Swiss (+/+) and DBA/2 mice. Microsomal protein and cytochrome P-450 concentrations were measured and the activity of ethylmorphine demethylase, aniline hydroxylase, aryl hydrocarbon hydroxylase and UDP-glucuronyl transferase were determined. Hepatic microsomes from both experimental groups carrying the nude gene were able to metabolize aniline and ethylmorphine more rapidly (20% and 36%, respectively) than the DBA/2 or Swiss homozygous normal mice. No difference between test groups was observed for hepatic aryl hydrocarbon hydroxylase or UDP-glucuronyl transferase activity. Kidney microsomes from mice carrying the nude gene had approximately twice the aryl hydrocarbon hydroxylase activity of the other two experimental groups. Renal mixed-function oxidase pathways measured for the homozygous nude mouse showed a higher overall rate of activity than the other three experimental groups. No significant difference in renal UDP-glucuronyl transferase was observed between mouse groups.

A comprehensive study of in vitro drug metabolism in several laboratory species

A shortage of rhesus monkeys for use in drug toxicity studies has made it necessary to search for a potential replacement species in the event that one should be needed in the near future. To this end, 14 parameters of drug metabolism in hepatic microsomal and soluble fractions were examined in preparations from adult male and female rhesus monkeys, squirrel monkeys, Hanford miniature pigs, common tree shrews, and Sprague-Dawley rats. Model substrates were utilized and comparisons were made on a quantitative basis. All species tested demonstrated activity in all but one test assay and all showed some similarity to the rhesus. None of the species, however, was totally comparable to the rhesus in drug-metabolizing ability. The squirrel monkey showed the least similarity to the rhesus and the miniature pig was the most similar. With the exception of the expected differences in the rat, the tree shrew demonstrated the only sex difference in drug metabolism, the enzyme activities of females being higher than the male in several pathways. The data suggest that any of the four species tested could be a suitable replacement for the rhesus in studies of drug metabolism in vitro.

Characterization of the hepatic microsomal mixed-function oxidase enzyme system in miniature pigs

Hepatic microsomal protein, cytochrome P-450, UDP-glucuronyltransferase, ethylmorphine demethylase, aniline hydroxylase, and aryl hydrocarbon hydroxylase levels were measured in the 2-, 4-, 5-, 6-, and 8-month-old Hanford miniature pig. The activities or concentrations of all of the liver parameters measured had apparently reached their adult plateau level by 2 months of age. The use of the miniature pig in toxicology research programs is discussed.

The use of high pressure liquid chromatography to study chemically induced alterations in the pattern of benzo[a]pyrene metabolism

The metabolism of radiolabeled benzo[a]pyrene (BP) by control, 3-methyl-cholanthrene (3-MC) induced, and 1,1,1-trichloropropene-2,3-oxide (TCPO)-inhibited rat liver microsomes was measured using fluorescence, radiometric, and high-pressure liquid chromatographic (HPLC) assays. Significant differences in the total measurable metabolism of BP by the three microsomal enzyme incubations resulted from the use of the three assay procedures. Appreciable differences in the concentration of the metabolite fractions after 3-MC induction and TCPO inhibition are clearly demonstrated. NMR analysis revealed that while the 3-hydroxy-BP fraction is greater than 90% pure, the 9-hydroxy fraction contains a number of metabolites having essentially identical retention times.

Correlation of brain levels of barbiturate enantiomers with reported differences in duration of sleep

The concentrations of R(+)-and S(-)-pentobarbital and R(+)-and S(-)-secobarbital were determined in the brain stem, hypothalamus, cerebellum and cortex of mice after i.v. administration. No regional differences in enantiomer concentration or barbiturate/metabolite ratio were observed to account for the substantial potency differences reported for the enantiomeric forms of pentobarbital and secobarbital. Stereoselective differences in the rate of enantiomer metabolism and in stereochemical fit to the central nervous system receptor are discussed as possible reasons for the differences in duration of action.

Partial characterization of hepatic micorsomes from tupaia glis

The dithionite difference spectrum of Tupaia microsomal cytochrome P-450-CO complex has an absorbance maximum at 449 nm, rather than at 450 nm as found for rat, rabbit, mouse, guinea pig, and human microsomes. N-octylamine difference spectroscopy showed the ratio of high- and low-spin forms of cytochrome P-450 to be different from that of the rat, indicating that the 449 nm absorption maximum might be due to a high concentration of the high-spin form, cytochrome P-448. The Tupaia microsomes demonstrated greater aryl hydrocarbon activity than microsomes prepared from male rats. These preliminary results suggest that Tupaia microsomes contain a modified terminal oxygenase which is responsible for the observed rapid metabolism of benzo[alpha]pyrene.

Distribution of delta 9-tetrahydrocannabinol in the mouse

1. The distribution of Delta(9)-tetrahydrocannabinol-(14)C in the pregnant and nonpregnant mouse is very similar. High concentrations of radiolabel can be seen in the maternal liver, spleen, lungs, brown fat, adrenal glands, mammary glands, yolk sac placenta and corpora lutea. In the pregnant mouse Delta(9)-THC crosses the placenta and enters the foetuses in very low concentrations, with no apparent selective intrafoetal radiolabel accumulation sites. Autoradiograms showing the distribution of (14)C-cannabinoid 2 h after dosing are presented.2. A small amount of maternal liver and foetal tissue was removed from the mice, used for autoradiography and extracted with ethyl acetate. Most of the radiolabel in these tissues was solvent extractable and was separated by thin layer chromatography into two fractions, THC and metabolites.3. It appears that most of the cannabinoid is present in a free rather than conjugated form.

Activity of delta8- and delta9-tetrahydrocannabinol and related compounds in the mouse

The 11-hydroxy metabolites of Delta(8).- and Delta(9)-tetrahydrocannabinol are more active than the parent compounds when administered to mice by either the intravenous or intracerebral route. Both Delta(8)- and Delta(9)-tetrahydrocannabinol are rapidly and extensively metabolized by the liver and not by the brain. The hypothesis that the 11-hydroxy metabolites may be the active form of tetrahydrocannabinol is discussed