Biomedical subjects

B I Ghanayem

Publications and source records attributed to B I Ghanayem.

At least 37 records · Page 2Linked to original sources

PubMed1997

Disruption of the mouse cyclooxygenase 1 gene. Characteristics of the mutant and areas of future study.

Surprisingly, disruption of the COX-1 gene resulted in generally healthy mice. This is in spite of the fact that prostaglandin levels in the tissues examined were reduced by greater than 99%. The results obtained to date with the COX-1 deficient mice indicate that some of the physiological roles previously attributed to COX-1 may not be entirely correct. Ongoing studies with the COX deficient mice are aimed at better defining the physiological roles of the cyclooxygenases and concomitantly the mechanisms by which NSAIDs cause their biological effects.

Animals↗

PubMed1996

Nonoxidative metabolism of 2-butoxyethanol via fatty acid conjugation in Fischer 344 rats.

Nonoxidative metabolism of ethylene glycol monobutyl ether (2-butoxyethanol or BE) via fatty acid conjugation was studied in the liver of Fischer 344 male rats following a single oral administration of 500 mg/kg body weight [ethyl-1,2-14C]BE (70 microCi/kg). Animals were killed 2 h after the treatment, hepatic lipids extracted, and the neutral lipids were separated using solid-phase extraction. The neutral lipid fraction was subjected to preparative thin-layer chromatography, and the esters corresponding to the relative flow of authentic fatty acid 2-butoxyethyl esters were recovered and analyzed by reversed-phase high-performance liquid chromatography (HPLC) using methanol-water (37:3, v/v) as solvent. Approximately 85% of the 14C label present in the ester fraction was coeluted at retention times corresponding to the different fatty acid 2-butoxyethyl ester standards. The radioactive fractions were analyzed by electron impact mass spectrometry. Molecular ion peaks and fragmentation patterns similar to that of 16:0, 18:0, 18:1, 18:2, and 20:4 fatty acid 2-butoxyethyl ester standards were detected in the corresponding radioactive HPLC fractions. Fatty acid ethyl ester synthase (FAEES), purified from the rat liver microsomal fraction, was also found to catalyze the formation of 18:1 fatty acid 2-butoxyethyl ester. These studies demonstrate that BE is metabolized nonoxidatively via conjugation with long-chain fatty acids, and the formation of these esters appears to be catalyzed by the enzyme(s) involved in fatty acid conjugation of xenobiotic alcohols. However, the biological significance of BE conjugation with fatty acids remains to be investigated.

Acyltransferases↗

PubMed1996

Identification of residues 99, 220, and 221 of human cytochrome P450 2C19 as key determinants of omeprazole activity.

Human P450 2C19 is selective for 4'-hydroxylation of S-mephenytoin and 5-hydroxylation of omeprazole, while the structurally homologous P450 2C9 has low activity toward these substrates. To identify the critical amino acids that determine the specificity of human amino acids that determine the specificity of human P450 2C19, we constructed chimeras of p450 2C9 replacing various proposed substrate binding sites (SRS) with those of P450 2C19 and then replaced individual residues of P450 2C19 and then replaced individual residues of P450 2C9 by site-directed mutagenesis. The 339 NH2-terminal amino acid residues (SRS-1-SRS-4) and amino acids 160-383 (SRS-2-SRS-5) of P450 2C19 conferred omeprazole 5-hydroxylase activity to P450 2C9. In contract, the COOH terminus of P450 2C19 (residues 340-490 including SRS-5 and SRS-6), residues 228-339 (SRS-3 and SRS-4) and residues 292-383 (part of SRS-4 and SRS-5) conferred only modest increases in activity. A single mutation Ile99 --> His increased omeprazole 5-hydroxylase to approximately 51% of that of P450 2C19. A chimera spanning residues 160-227 of P450 2C19 also exhibited omeprazole 5-hydroxylase activity which was dramatically enhanced by the mutation Ile99 --> His. A combination of two mutations, Ile99 --> His and Ser200 --> Pro, converted P450 2C9 to an enzyme with a turnover number of omeprazole 5-hyrdroxylation, which resembled that of P450 /c19. Mutation of Pro221 --> Thr enhanced this activity. Residue 99 is within SRS-1, but amino acids 220 and 221 are in the F-G loop and outside any known SRS. Mutation of these three amino acids did not confer significant S-mephenytoin 4'-hydroxylase activity to P450 2C9, although chimeras containing SRS-1-SRS-4 and SRS-2-SRS-5 of P450 2C19 exhibited activity toward this substrate. Our results thus indicate that amino acids 99, 220, and 221 are key residues that determine the specificity of P450 2C19 for omeprazole.

Aryl Hydrocarbon Hydroxylases↗

PubMed1996

Comparative disposition of acrylonitrile and methacrylonitrile: quantitative whole-body autoradiographic studies in rats.

Following intravenous administration of an equimolar (0.216 mmol/kg) radioactive dose of acrylonitrile (2-[14C]VCN, 11.5 mg/kg) or methacrylonitrile (2-[14C]MeVCN, 14.5 mg/kg), the tissue distribution, covalent interaction, and elimination were compared (at 5 min to 48 hr) in male Fischer 344 rats using whole-body autoradiography (WBA). Autoradiographs obtained from freeze-dried or acid-extracted sections of animals treated with 2-[14C]VCN showed that radioactivity accumulated in the liver, lung, bone marrow, adipose tissues, kidney, gastrointestinal tract, and spleen. In animals treated with 2-[14C]MeVCN, the respiratory tissues contained high levels of 14C at an early period (5 min), while the gastrointestinal mucosa, adrenal cortex, liver, and kidney contained high levels of radioactivity at later periods (8, 24, and 48 hr). Quantitatively, lower uptake and irreversible interactions of 14C were observed in autoradiographs of rats treated with 2-[14C]MeVCN compared with those treated with 2-[14C]VCN. Rats given 2-[14C]VCN eliminated only 27% of administered radioactivity (exhaled air, urine, and feces), whereas rats treated with 2-[14C]MeVCN eliminated, by all routes, 65% of the total radioactive dose. Both WBA and elimination studies indicated that 2-[14C]VCN and/or its metabolites were rapidly distributed, extensively bound, and slowly eliminated from tissues. 2-[14C]MeVCN and/or its metabolites, however, were rapidly distributed and eliminated, mostly via the lung. The study indicated that the substitution of a methyl group on the alpha-carbon of the alpha-beta unsaturated aliphatic nitrile VCN, to form MeVCN, imparted qualitative and quantitative differences in the disposition of these two compounds.

Acrylonitrile↗

PubMed1996

The role of the CYP2C9-Leu359 allelic variant in the tolbutamide polymorphism.

Tolbutamide undergoes hydroxylation in humans via a cytochrome P450-mediated pathway. The primary P450 isozyme responsible for this metabolism is thought to be CYP2C9. Population studies have indicated the existence of slow metabolizers of tolbutamide (approximately 1 in 500) suggesting a rare polymorphism associated with 2C9. Several allelic variants of 2C9 have been identified; however, the effect of these allelic variations on metabolism in vivo is not established. In the present study, the coding regions, intron-exon junctions, and upstream region of CYP2C9 were amplified by PCR and sequenced in two slow metabolizers. One individual was homozygous for Leu359/Leu359 and the other individual was heterozygous for Arg144/Cys144 and for Ile359/Leu359. No other genetic variations in 2C9 were detected in these individuals. PCR-RFLP tests showed that Arg144 Tyr358 Ile359 Gly417 is the principle CYP2C9 allele. Frequencies of the rarer Leu359 and Cys144 alleles were 0.06 and 0.08, respectively, in a Caucasian-American population and 0.005 and 0.01 respectively in African-Americans. The frequency of the Leu359 allele was 0.026 in Chinese-Taiwanese, but the Cys144 allele was not detected in this population. Studies in a recombinant yeast expression system showed that the Leu359 variant had the highest Km and the lowest Vmac for hydroxylation of tolbutamide of all the CYP2C9 allelic variants. This allelic variant also had the highest Km for the 7-hydroxylation of S-warfarin. The present data suggest that the incidence of the Leu359 allelic variant of CYP2C9 may account for the occurrence of poor metabolizers of tolbutamide.

Alleles↗

PubMed1996

Excretion and identification of methacrylonitrile metabolites in the bile of male F344 rats.

Methacrylonitrile (MAN) is structurally similar to the known carcinogen acrylonitrile (AN), has similar industrial uses, and is occasionally used as its replacement. In contrast to AN, minimal information is available on the toxicity, carcinogenicity, or metabolism of MAN. Earlier work in this laboratory demonstrated that, in rats, MAN is primarily eliminated in the expired air as unchanged MAN, acetone, and CO2. Two mercapturic acids were identified in the urine of rats and mice treated with MAN. In the present work, the common bile duct of anesthetized rats was cannulated. The animals received a single gavage dose of 58 mg/kg 2-[14C]MAN. Bile was collected before and after MAN administration. Bile flow and MAN-derived radioactivity were determined at each time point. MAN had a minimal effect on bile flow and 4 to 6% of the administered MAN dose was excreted in the bile within 6 hr after dosing. HPLC analysis of bile showed two major metabolites, which were identified as 1-(S-glutathionyl)-2-propanone and 1-(S-glutathionyl)-2-cyanopropane by using NMR spectra and chemical synthesis. The ratio of the two metabolites in MAN-treated rats was approximately 2:1. Pretreatment of rats with sodium phenobarbital caused minimal quantitative or qualitative changes in the biliary excretion of MAN metabolites. In contrast, pretreatment of rats with beta-diethylaminoethyl diphenylpropylacetate before MAN administration resulted in a significant decrease in the ratio of 1-(S-glutathionyl)-2-propanone to 1-(S-glutathionyl)-2-cyanopropane (1:2). These data, especially the identification of 1-(S-glutathionyl)-2-propanone, indirectly demonstrated that MAN is metabolized via an epoxide intermediate (1-cyano-1-methyloxirane). Modulation of MAN metabolism by the P450 modulators suggested that this metabolic pathway is catalyzed via the cytochrome P450 enzymes. This work also confirms that MAN undergoes direct reaction with reduced glutathione via a Michael addition. Because of earlier work demonstrated that AN undergoes similar metabolism, MAN might have a qualitative toxicity profile similar to that of acryonitrile.

Acrylonitrile↗

PubMed1996

Species differences in the disposition and metabolism of nalidixic acid.

Nalidixic acid (NA) is an antimicrobial drug that has been used to treat urinary tract infections. A study of NA by the National Toxicology Program indicated that chronic administration in the diet at doses equivalent to 82 and 175 mg/kg/day for rats, and 175 and 475 mg/kg/day for mice resulted in neoplastic lesions in the preputial and clitoral glands of male and female Fischer 344 rats, respectively, but not in male and female B6C3F1 mice. Our study was designed to evaluate the metabolic basis of this species and tissue-dependent carcinogenicity. [14C]NA was administered by oral gavage as a suspension in corn oil at doses of 20, 200 or 500 mg/kg. Based on urinary excretion data, at least 35 to 46 and 57 to 79% of dose was absorbed from the gastrointestinal tracts of mice and rats, respectively. NA-derived radioactivity was excreted primarily in urine and feces. The urinary and fecal metabolite profiles were species dependent. At 72 hr after administration, in both genders of rats and mice, the highest concentrations of radioactivity were observed in the liver, and the lowest were in the brain and adipose tissue. The preputial and clitoral glands of male and female rats, respectively, contained consistently and substantially higher concentrations of radioactivity compared to all other tissues, with the exception of liver. In mice, the levels of radioactivity in these tissues were near or below quantifiable levels. The metabolism and disposition characteristics of NA were linear in male and female mice over a dose range of 20 to 500 mg/kg: in rats, they were dose dependent. Results of this study suggest that the species- and tissue-dependent differences in carcinogenicity of NA were associated with differences in metabolism and disposition between the two species.

Animals↗

PubMed1996

Human CYP2C19 is a major omeprazole 5-hydroxylase, as demonstrated with recombinant cytochrome P450 enzymes.

Omeprazole (OP) is a potent antiulcer drug that is metabolized by liver cytochrome P450 (P450) enzymes. However, the identities of the P450 isoforms responsible for its metabolism have been controversial. 5-Hydroxyomeprazole (5OH-OP) formation cosegregates with the polymorphism of (S)-mephenytoin 4'-hydroxylation in humans, which is now known to be mediated by CYP2C19. Previous in vitro studies have indicated that liver microsomal 50H-OP formation correlates with both (S)-mephenytoin 4'-hydroxylase and CYP3A content. Inhibitor and CYP2C antibody studies also suggested that both enzymes may be involved in the 5-hydroxylation of OP, whereas CYP3A appears to be the predominant enzyme involved in OP sulfone (OP-S) formation. The present studies assessed the contribution of various CYP2C and CYP3A4 enzymes to OP metabolism by using recombinant human enzymes. CYP2C19, CYP2C8, CYP2C18, and CYP2C9 formed a single metabolite with an HPLC retention time identical to that of 5OH-OP. The turnover number for CYP2C19 was 13.4 +/- 1.4 nmol/min/nmol of P450, whereas those for CYP2C8, CYP2C18, and CYP2C9 were 2.2 +/- 0.1, 1.5 +/- 0.1, and approximately equal to 0.5 nmol/min/nmol of P450, respectively. Recombinant human CYP3A4 formed 5OH-OP and OP-S with turnover numbers of 5.7 +/- 1.1 and 7.4 +/- 0.9 nmol/min/nmol of P450, respectively, and formed a minor unidentified metabolite. CYP2C19 had a substantially lower KM for 5OH-OP formation than did CYP3A4, CYP2C8, or CYP2C18. Antibody to CYP2C proteins inhibited approximately equal to 70% of OP 5-hydroxylation at low substrate concentrations, comparable to those that may be encountered at therapeutically relevant doses, whereas antibody to CYP3A4 inhibited approximately equal to 30% of the activity. At high substrate concentrations, the contributions of the two enzymes to OP hydroxylation were roughly comparable (40-50%). In contrast, OP-S formation was completely inhibited by antibody to CYP3A4 proteins. The present study provides the first direct confirmation, using human recombinant P450 enzymes and selective antibody inhibition, that CYP2C19 is a major high affinity OP 5-hydroxylase and CYP3A4 is a low affinity OP-hydroxylating enzyme. The current work also shows, for the first time, that other CYP2C enzymes (CYP2C8, CYP2C9, and CYP2C18) may contribute to OP hydroxylation at high substrate concentrations. In contrast, OP-S was formed principally by CYP3A4.

Anti-Ulcer Agents↗

PubMed1995

Prostaglandin synthase 1 gene disruption in mice reduces arachidonic acid-induced inflammation and indomethacin-induced gastric ulceration.

Cyclooxygenases 1 and 2 (COX-1 and COX-2) are key enzymes in prostaglandin biosynthesis and the target enzymes for the widely used nonsteroidal anti-inflammatory drugs. To study the physiological roles of the individual isoforms, we have disrupted the mouse Ptgs1 gene encoding COX-1. Homozygous Ptgs1 mutant mice survive well, have no gastric pathology, and show less indomethacin-induced gastric ulceration than wild-type mice, even though their gastric prostaglandin E2 levels are about 1% of wild type. The homozygous mutant mice have reduced platelet aggregation and a decreased inflammatory response to arachidonic acid, but not to tetradecanoyl phorbol acetate. Ptgs1 homozygous mutant females mated to homozygous mutant males produce few live offspring. COX-1-deficient mice provide a useful model to distinguish the physiological roles of COX-1 and COX-2.

Animals↗

PubMed1995

Spermatocyte toxicity of 2-methoxyethanol (ME) in rats and guinea pigs: evidence for the induction of apoptosis.

2-Methoxyethanol (ME) produces testicular lesions characterized by pachytene spermatocyte degeneration in rats and guinea pigs which differ in onset, severity, and morphological characteristics. In the rat, degenerating spermatocytes appear necrotic at 24 hr, while in the guinea pig they appear apoptotic 96 hr after the start of three daily doses. To further examine if the spermatocyte degeneration in both species represented necrosis or apoptosis, the extent and nature of nuclear DNA fragmentation after ME exposure were assessed both visually using an in situ nucleotide 3' end-labeling (ISEL) procedure and by DNA gel electrophoresis. Testes from rats given a single oral dose of ME (200 mg/kg) showed the expected pachytene spermatocyte degeneration 24 hr after dosing, with the nuclear chromatin degradation typical of necrosis. In contrast, testes from guinea pigs given daily oral doses of ME (200 mg/kg) showed spermatocyte degeneration at only 96 hr after the start of dosing, with marked peripheral nuclear chromatin condensation characteristic of apoptosis. Coincident with the appearance of morphologic changes, degenerating spermatocytes in both species contained fragmented DNA as revealed by the ISEL procedure. The pattern of DNA fragmentation on agarose gels in both species consisted of ordered multiples or "ladders" of approximately 200 base pairs, a hallmark of apoptosis, with their appearance coincident with the time course of morphologic spermatocyte degeneration and ISEL staining. Preliminary data reveal the appearance of divalent metal cation-dependent endonuclease activity at pH 7.0 in ME-treated immature (24-day-old) rat testis that produces a similar pattern of DNA fragmentation and which appears to be distinct from activity associated with the spontaneous germ cell degeneration observed in testes of this age. In summary, in vivo ME exposure induces spermatocyte apoptosis in both the rat and guinea pig despite differing morphological classifications and time of onset of cell death. Future studies will focus on further characterization of the testicular endonuclease in the rat and the potential role of increased intracellular Ca2+ as a "triggering" stimulus in ME-induced spermatocyte apoptosis.

Animals↗

PubMed1995

Comparative disposition of 2,3-epoxy-1-propanol (glycidol) in rats following oral and intravenous administration.

Glycidol (2,3-epoxy-1-propanol), an industrial chemical, has been shown to be a reproductive toxicant in short-term studies and a carcinogen in rats and mice in oncogenicity studies. The reproductive toxicity of glycidol was believed to result from its conversion to alpha-chlorohydrin by the action of HCl in the stomach. The comparative disposition of glycidol was investigated in rats following oral (po) or intravenous (iv) administration at doses of 37.5 and 75 mg/kg. These were the doses used in the National Toxicology Program (NTP) oncogenicity study with glycidol. Approximately 87-92% of the dose was absorbed from the gastrointestinal tract of the rat. [14C]Glycidol equivalents were eliminated in urine (40-48% of dose in 72 h), feces (5-12%), and exhaled as CO2 (26-32%). At both doses, 9-12% and 7-8% (estimated) of the dose remained in tissues at 24 and 72 h following dosing, respectively. In general, the concentrations of glycidol equivalents in tissues were proportional to the dose. The highest concentrations of radioactivity were observed in blood cells, thyroid, liver, kidney, and spleen, and the lowest in adipose tissue, skeletal muscle, and plasma. The pattern of distribution of radioactivity in tissues was similar for both the iv and po routes. The total recovery of radioactivity ranged from 87 to 91% of dose. Urinary radioactivity was resolved by high-performance liquid chromatography (HPLC) analysis into 15 metabolites. There were one major (14-21% of the dose) and four lesser metabolites (each representing 2-8%); the others were minor, each representing 1% or less of the dose. In general, the urinary metabolic profile was similar following either iv or po administration at the two doses studied. Previous studies by other investigators suggested that alpha-chlorohydrin, which was presumably formed from glycidol by the HCl in the stomach, was metabolized and excreted in urine as beta-chlorolactic acid. The results of the present study show that very little, if any, urinary radioactivity coeluted with authentic beta-chlorolactic acid following either iv or po administration. Therefore, it is concluded that the conversion of glycidol to alpha-chlorohydrin is quantitatively insignificant. However, it may be significant with regard to glycidol reproductive toxicity. Also, the NTP oncogenicity study with glycidol was carried out within the dose range in which its disposition characteristics were linear.

1-Propanol↗

PubMed1994

Determination of 1-methoxy-2-propanol and its metabolite 1,2-propanediol in rat and mouse plasma by gas chromatography.

A method utilizing capillary GC and flame ionization detection was developed for the simultaneous determination of 1-methoxy-2-propanol (propylene glycol monomethyl ether; PGME) and its metabolite 1,2-propanediol (propylene glycol; PG) in rat and mouse plasma. The calibration graphs for rat and mouse plasma were linear with correlation coefficients at > 0.997 over the range 2-700 micrograms/ml. The limit of quantification was ca. 2 micrograms/ml (2 ng on-column) for both compounds in plasma of each species. The ranges of the precision and accuracy for PGME were 2.8-8.8% and 3.2-13%, respectively, and for PG were 11-26% and 10-25%, respectively. The recovery of PGME from rat and mouse plasma was ca. 73% and for PG it was ca. 65 and 31% from rat and mouse plasma, respectively. The method was used to study the oral absorption and metabolism of PGME in mice. PGME was readily absorbed and metabolized to PG following oral gavage administration at 90 mg/kg. The maximum concentrations of PGME and PG in plasma were attained at 20 and 30 min following dosing, respectively.

Animals↗

PubMed1994

Evidence that CYP2C19 is the major (S)-mephenytoin 4'-hydroxylase in humans.

The present study assesses the role of members of the human CYP2C subfamily in the 4'-hydroxylation of (S)-mephenytoin. When recombinant CYP2C proteins were expressed using a yeast cDNA expression system, 2C19 stereospecifically 4'-hydroxylated (S)-mephenytoin with a turnover number at least 10 times higher than that of human liver microsomes. 2C9 (both Ile359 and Leu359 alleles) and 2C18 (Thr385 and Met385 alleles) metabolized this substrate at a rate 100-fold lower than 2C19, and metabolism by these 2C proteins was not stereospecific for the S-enantiomer. 2C8 exhibited very little mephenytoin 4'-hydroxylase activity. In contrast, the Ile359 allele of 2C9 had a high turnover number for the hydroxylation of tolbutamide, while the Leu359 allele was less active toward this substrate. Immunoblot analysis of 16 human liver donor samples indicated that (S)-mephenytoin 4'-hydroxylase activity correlated with the hepatic CYP2C19 content, but it did not correlate with the hepatic content of CYP2C9. Moreover, direct sequencing of the polymerase chain reaction (PCR) products of 2C9 mRNA from six of these human livers through areas of known allelic variations indicated that the identity of the allele of 2C9 (Cys144 vs Arg, Tyr358 vs Cys, Ile359 vs Leu, or Gly417 vs Asp) did not appear to influence (S)-mephenytoin 4'-hydroxylase activity in these samples. These data indicate that 2C19 is the principal determinant of (S)-mephenytoin 4'-hydroxylase activity in human liver.

Aryl Hydrocarbon Hydroxylases↗

PubMed1994

Comparison of the testicular effects of 2-methoxyethanol (ME) in rats and guinea pigs.

Glycol ethers produce both hemato- and testicular toxicity in animals, which is dependent on both the alkyl chain length and animal species used. Ethylene glycol monobutyl ether (2-butoxyethanol, BE) causes hemolytic anemia in rats but not in guinea pigs, and red blood cells from both guinea pigs and humans are minimally affected in vitro by the active metabolite 2-butoxyacetic acid. This demonstrates the importance of animal species selection for assessing human risk to BE exposure. 2-Methoxyethanol (ME) produces testicular lesions in rats characterized primarily by the degeneration of spermatocytes undergoing meiotic division with minimal or no hemolytic changes. Because of the differential hemolytic response to BE between rats and guinea pigs, the present study addressed whether the testicular response to ME was similarly dichotomous. Adult rats or guinea pigs were given a single dose of either 200 or 300 mg ME/kg by gavage, and testicular and hemolytic changes were assessed 24 hr after treatment. Testis histology in rats showed dose-dependent degeneration of dividing spermatocytes in stage XIV tubules as expected, with only minimal hemolytic changes, also as expected. In contrast, no testicular or hemolytic effects were observed in guinea pigs 24 hr after either single ME dose. In a subsequent study, a single dose or multiple (3 daily) doses of 200 mg ME/kg were given, and animals were examined at 4 days after the start of treatment. Testes from rats given both single and multiple ME doses showed, as expected, tubules depleted of spermatocytes and early spermatids. In guinea pigs, spermatocyte degeneration was observed in stage III/IV tubules for both dosing schemes, but was much less severe and widespread and differed from rats in morphological characteristics, specifically in the appearance of nuclear chromatin degeneration. In the rat, degenerating spermatocytes showed uniformly condensed and dispersed chromatin, while in the guinea pig they showed marked chromatin condensation at the nuclear periphery. No hemolytic changes were observed in either species or dosing scheme. In summary, although ME-associated testicular lesions were observed in both species, they differed significantly in onset, characteristics, and severity. Both the nature of the differential testicular response to ME and a comparison to the in vitro human testicular response to the active metabolite 2-methoxyacetic acid are subjects of future study.

Animals↗

PubMed1994

Physiologically based pharmacokinetics of 2-butoxyethanol and its major metabolite, 2-butoxyacetic acid, in rats and humans.

A physiologically based pharmacokinetic model was developed to describe the disposition of 2-butoxyethanol (CAS 111-76-2) and its major metabolite, 2-butoxyacetic acid, in rats and humans. A previous human inhalation model by Johanson (Toxicol. Lett. 34, 23 (1986)) was expanded to include additional routes of exposure, physiological descriptions for rats, competing pathways for metabolism of 2-butoxyethanol, and measured partition coefficients for 2-butoxyethanol and 2-butoxyacetic acid. Simulations were compared to data gathered from rats following either intravenous infusion or oral or inhalation exposure and from humans following either inhalation or dermal exposure to 2-butoxyethanol. It was necessary to add equations for both protein binding of 2-butoxyacetic acid in blood and saturable elimination of 2-butoxyacetic acid by the kidneys to consistently describe the data. While the model predicted that rats metabolize 2-butoxyethanol and eliminate the acid metabolite faster per kilogram body weight than humans, the balance of these two processes in addition to physiological differences between species resulted in higher predicted peak blood concentrations as well as total areas under the blood concentration time curves for 2-butoxyacetic acid for rats versus humans. These species differences in kinetics coupled with the fact that human blood is significantly less susceptible than rat blood to the hemolytic effects of 2-butoxyacetic acid indicate that there is considerably less risk for hemolysis in humans as a result of exposure to 2-butoxyethanol than would have been predicted solely from standard toxicity studies with rats.

Administration, Cutaneous↗

PubMed1994

Comparative metabolism and disposition of acrylonitrile and methacrylonitrile in rats.

Aliphatic nitriles are a class of chemicals used in high volumes in the production of plastics and elastomers, in organic synthesis, and in production of a number of food packaging containers. Toxicity and metabolism of acrylonitrile (AN) are well characterized. On the other hand, minimal information is available on the toxicity or fate of structurally related, methacrylonitrile (MAN). In an attempt to predict the toxicity of MAN, the present studies were designed to compare the disposition of both nitriles in rats. After gavage administration of equimolar doses (0.87 mmol/kg) of 2-14C-MAN or 2-14C-AN to male F344 rats, both chemicals were well absorbed from the GI tract and distributed to all major tissues. However, major differences in the disposition of the two nitriles were observed. While approximately 39% of the administered MAN dose was eliminated as CO2 in 24 h after dosing, only 11% of an equimolar dose of AN was eliminated as such. In addition, 31% of the MAN dose was exhaled as organic volatiles in 24 h compared to less than 2% of an equivalent AN dose. MAN and acetone were identified by HPLC analysis of expired organic volatiles from MAN-treated rats. HPLC analysis showed that AN is the only organic volatile exhaled by AN-treated rats. Urinary excretion of MAN was 22% compared to 67% of an equivalent dose of AN. The major urinary metabolite from AN results from direct conjugation with GSH, whereas the major urinary metabolite from MAN results from conjugation of the epoxide with GSH.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetone↗

PubMed1994

Investigation of methacrylonitrile metabolism and the metabolic basis for the differences in its toxicity in rats and mice.

Methacrylonitrile (MAN) is an industrial chemical used to manufacture plastics and elastomers. The reported p.o. LD50 of MAN is 200 to 230 mg/kg in rats and 17 mg/kg in mice. Present investigations were undertaken to further characterize MAN metabolism and to study the metabolic basis for the species differences in its toxicity. Male F344 rats and B6C3F1 mice received a single gavage dose of 11.5 or 1.15 mg of [14C]MAN/kg and were placed in glass metabolism cages. Elimination of MAN in rats occurred primarily in expired air as unchanged MAN, acetone and CO2. Three major urinary metabolites of MAN were identified as N-acetyl-S-(2-cyanopropyl)-L-cysteine, N-acetyl-S-(2-hydroxypropyl)-L-cysteine and a deoxyuridine isomer. Quantitatively, rats and mice excreted ca. 7 and 49% of the high MAN dose in urine as N-acetyl-S-(2-hydroxypropyl)-L-cysteine, respectively. In addition, rats eliminated significantly more MAN-derived CO2 and deoxyuridine than mice. MAN elimination was almost complete within 24 hr after dosing and the tissue concentrations of MAN-derived radioactivity were, with the exception of the urinary bladder, consistently higher in rats than in mice. In conclusion, a quantitative difference between rats and mice in forming the epoxide intermediate, higher efficiency of mice to conjugate this intermediate with glutathione and greater capacity of rats to degrade it to acetone and CO2 are thought to contribute to the higher sensitivity of mice to MAN acute toxicity.

Animals↗

PubMed1993

Single dose blood toxicokinetics of methacrylonitrile in the F344 rat.

Methacrylonitrile (MAN) is a widely used industrial chemical. Minimal information is available on its effects or toxicokinetics; therefore, current investigations were undertaken as part of an overall effort to characterize MAN toxicity in laboratory animals. Groups of male F344 rats were administered MAN intravenously (29, 58, or 116 mg/kg) or perorally (58 mg/kg). Blood samples were collected at various time points after dosing and serum MAN concentrations were measured. Concentration versus time profiles were characterized by two phases and a two-compartment model was selected to fit the data. Toxicokinetic parameters were determined using Simusolv. The 39-min terminal half-life shows that 99% of an i.v. dose is eliminated in less than 5 hr, suggesting that the potential for MAN bioaccumulation is minimal. The volume of distribution at steady-state (747 ml/kg) indicates little distribution of MAN into tissues. Clearance is higher at 29 mg/kg than at the two other doses, suggesting that MAN elimination is saturable at doses above 29 mg/kg. MAN disposition is route-dependent. Approximately 36% of the i.v. dose was exhaled as unchanged MAN, while only 18% was eliminated via this route following po administration. MAN disposition data also suggest that a significant first-pass metabolism may occur because a higher percentage of metabolites was produced following oral vs i.v. administration. Perorally, 39% of the dose was exhaled as CO2 and 22% was excreted into the urine as metabolites over the 24-hr dosing interval. In comparison, following i.v. delivery, 26% of the dose was exhaled as CO2 and 16% was excreted into the urine as metabolites. About equal amounts of acetone were excreted following administration by either route. This information may prove useful in designing long-term toxicity studies for MAN by the National Toxicology Program and in interpreting the results of such studies.

Acetone↗