Eugene D. Barber

Peroxisome Induction Studies On Seven Phthalate Esters

Seven phthalate esters, representing a variety of chain lengths and degrees of branching in the alcohol moiety, were tested for their ability to produce peroxisome proliferation in the Fischer 344 rat. Di(2-ethylhexyl)adipate (DEHA) was tested using the same protocol and di(2-ethylhexyl)phthalate (DEHP) was run with each study as an internal control. Each ester was administered in the feed for a period of 21 days at levels of 2.5%, 1.2% and either 0.6% or 0.3%. DEHP and DEHA were also fed at levels of 0.1% and 0.01%. The animals were sacrificed and samples of liver were prepared for both light and electron microscopy. Serum samples were assayed for both triglyceride and cholesterol. The remaining portion of the liver was homogenized and assayed for cyanide-insensitive palmitoyl-CoA oxidation, lauric acid 11-hydroxylase and lauric acid 12-hydroxylase. The results show that there is approximately a ten-fold difference between the weakest and strongest esters in terms of their potency to induce changes in relative liver weight and in several of the biochemical parameters. In general, the longer chain esters were more potent than the shorter chain ones, and branched chain esters seemed more potent than straight. Several statistical analyses of the dataset have been performed and all render similar conehcsions. The results of one of these evaluations are presented elsewhere in this volume (Lin, 1987).

A Comparative Study of the Rates of in Vitro Percutaneous Absorption of Eight Chemicals Using Rat and Human Skin

In vitro percutaneous absorption studies were carried out for eight chemicals using full thickness rat skin and human stratum corneum. The purpose of the studies was to compare the rates of absorption for the two species. For each of the chemicals, the observed rate using full thickness rat skin was greater than that observed for human stratum corneum. The ratios of the rates (rat/human) varied from 1.7 to 5.8 with a mean value of 3.1. The chemicals tested were tritiated water, 2-ethoxyethyl acetate, diethylene glycol monobutyl ether, urea, di(2-ethylhexyl) phthalate, 2-ethylhexanol, ethyl 3-ethoxypropionate, and 2-propoxyethanol. The chemicals were chosen to represent a wide range of physical properties and permeability constant values. It was concluded that rat skin was more permeable than human skin for each of these eight chemicals. This conclusion is supported by similar findings from studies in other laboratories and suggests that results from studies in the rat overestimate skin absorption in man.

Bacterial mutagenicity testing of urine from rats dosed with 2-ethylhexanol derived plasticizers.

Di-(2-ethylhexyl)phthalate (DEHP) produced hepatocellular carcinomas in rodents at high doses in a NTP/NCI bioassay. DEHP has not shown evidence of genotoxic activity in in vitro mutagenicity tests. We extended these studies by examining the mutagenicity of urine from rats dosed with DEHP, 2-ethylhexanol (2-EH), and several other 2-EH derived plasticizers, i.e. di-(2-ethylhexyl)adipate (DEHA), di-(2-ethylhexyl)terephthalate (DEHT) and tri-(2-ethylhexyl)trimellitate (TEHT). A modified Ames Salmonella/microsome assay was used to determine mutagenicity. Urine was pooled from male Sprague--Dawley rats dosed daily for 15 days with 2000 mg/kg of each test substance with the exception of 2-EH which was given at 1000 mg/kg. Direct plating procedures were used to determine the presence of mutagens in urine. Urine from rats dosed with 8-hydroxyquinoline was used as a positive control. There was no evidence that mutagenic substances were excreted in the urine by rats dosed with either DEHP, DEHA, DEHT, TEHT or 2-EH as determined in the presence or absence of rat liver microsomes, and with or without treatment with beta-glucuronidase/aryl sulfatase. Our findings indicate that the above test compounds were not converted to urinary metabolites that were mutagenic. These observations provide no evidence for a genotoxic mechanism for DEHP carcinogenicity in rodents.

Results of the l5178y mouse lymphoma assay and the balb/3t3 cell in vitro transformation assay for eight phthalate esters

Eight phthalate esters, with alcohol chain lengths of 1–11 carbon atoms and with various degrees of branching, were tested in vitro in the L5178Y mouse lymphoma mammalian cell mutation assay and in the Balb/3T3 cell transformation assay. The tests were performed as part of a voluntary testing agreement between the Chemical Manufacturers Association’s Phthalate Esters Panel and the United States Environmental Protection Agency (US EPA). The esters tested were: dimethyl phthalate (DMP), di‐n‐butyl phthalate (DBP), butyl benzyl phthalate (BBP), di‐{n‐hexyl, n‐octyl, n‐decyl} phthalate (610P), di‐isononyl phthalate (DINP), di‐{heptyl, nonyl, undecyl} phthalate (711P), di‐isodecyl phthalate (DIDP) and di‐undecyl phthalate (DUP). Both DMP and DBP were found to produce significant increases in the mutant frequency in the mouse lymphoma assay in the presence but not in the absence of an Aroclor‐induced rat liver activation system (S‐9). Ester 610P gave equivocal results in the mouse lymphoma assay in the presence and absence of rat liver S‐9. There was no indication of mutagenic potential for any of the other test materials in the mouse lymphoma assay, and none of the test materials increased transformation frequency in the Balb/3T3 cell transformation assay. Aldehyde metabolites of the de‐esterified alcohols are postulated to play a role in the positive results for DMP and DBP. Copyright

The lack of binding of methyl-n-amyl ketone (MAK) to rat liver DNA as demonstrated by direct binding measurements, and 32P-postlabeling techniques

It has been reported that 14C-labeled methyl-n-amyl ketone (MAK, 2-heptanone) is able to bind spontaneously, in vitro, to isolated rat liver DNA to the extent of 400 pmol/mg DNA; and that 14C-MAK, when given by gavage to female Fischer 344 rats, resulted in HPLC chromatograms of isolated, hydrolyzed liver DNA in which some radiolabel was not associated with the four normal DNA bases dA, dT, dC, and dG. The present studies were undertaken to re-examine the hypothesis that MAK is able to bind to rat liver DNA. In the in vitro study, liver nuclear DNA was incubated with [2-14C]-labeled MAK (25 mCi/mmol) in the absence, or in the presence of rat liver microsomes, precipitated, washed free of unbound MAK, and counted by scintillation spectrometry. No binding to DNA by MAK was detectable. In the in vivo study, groups of five female F344 rats were exposed by inhalation to 0, 80, 400, or 1000 ppm MAK for 6 h/day for 10 days. DNA was purified from the liver nuclei of the 0 and 1000 ppm dosed animals, and 32P-postlabeling techniques were used to assay for adducts. No DNA adducts were detected using these techniques. It was concluded that MAK lacks the ability to bind to rat liver DNA in vitro and in vivo.

An Exposure System for Quantitative Measurements of the Microbial Mutagenicity of Volatile Liquids

It has been estimated that 5 × 1010 grams per day of vapor-phase chemicals and 109 grams per day of particulate matter are released into the atmosphere in the United States (1). Since both of these fractions may contribute to the toxic potential of the atmosphere, it seems important to be able to evaluate them in a precise manner.

Methods for measuring mutagenicity in urine of rats dosed with [14C]DI(2-ethylhexyl)phthalate

Di(2-ethylhexyl)phthalate (DEHP) is extensively used as a plasticizer for vinyl plastic articles. It has been found to be positive in an NCI rodent bioassay but has generally given negative results in in vitro genotoxicity tests. We therefore decided to test the urine of rats fed [14C]DEHP for mutagenic activity in the Ames Salmonella test. The recovery of radioactivity from the urine of rats dosed with [14C]DEHP was examined by solvent extraction and XAD-2 resin absorption procedures. Both of these procedures were inadequate for quantitative recovery of urinary metabolites required for subsequent mutagenicity testing using the Ames Salmonella/microsome procedure. Recoveries of less than 5% were observed using standard solvent extraction techniques whereas the XAD-2 adsorption technique gave about 67% at high resin/urine ratios. Treatment of the urine with beta-glucuronidase/aryl sulfatase did not affect these recoveries. The direct urine plating procedure represents a viable alternative to the above concentration procedures for this phthalate ester. The effects of L-histidine and the beta-glucuronidase/aryl sulfatase preparation on the background reversion frequencies of the Ames tester strains is discussed.