The metabolism of higher chlorinated benzene isomers

Urinary metabolites of a novel quinoxaline non-nucleoside reverse transcriptase inhibitor in rabbit, mouse and human: identification of fluorine NIH shift metabolites using NMR and tandem MS

1. The urinary metabolites of (S)-2-ethyl-7-fluoro-3-oxo-3,4-dihydro-2H-quinoxaline-carboxylic acid isopropylester (GW420867X) have been investigated in samples obtained following oral administration to rabbit, mouse and human. GW420867X underwent extensive biotransformation to form hydroxylated metabolites and glucuronide conjugates on the aromatic ring, and on the ethyl and isopropyl side-chains in all species. In rabbit urine, a minor metabolite was detected and characterized as a cysteine adduct that was not observed in mouse or man. 2. The hydroxylated metabolites and corresponding glucuronide conjugates were isolated by semi-preparative HPLC and characterized using NMR, LC-NMR and LC-MS/MS. The relative proportions of fluorine-containing metabolites were determined in animal species by 19F-NMR signal integration. 3. The fluorine atom of the aromatic ring underwent NIH shift rearrangement in the metabolites isolated and characterized in rabbit, mouse and human urine. 4. The characterization of the NIH shift metabolites in urine enabled the detection and confirmation of the presence of these metabolites in human plasma.

Occurrence of the NIH shift upon the cytochrome P450-catalyzed in vivo and in vitro aromatic ring hydroxylation of fluorobenzenes

The in vivo cytochrome P450-catalyzed aromatic hydroxylation of a series of fluorobenzenes was investigated with special emphasis on the importance of the fluorine NIH shift. The results obtained demonstrate a minor role for the NIH shift in the metabolism of the fluorobenzenes to phenolic metabolites in control male Wistar rats. These in vivo results could indicate that (1) the NIH shift is an inherently minor process for fluorine substituents or (2) it is a potentially significant process but the presumed epoxide that leads to formation of the NIH-shifted metabolite is lost to an alternative metabolic pathway. In contrast to the in vivo data, in vitro experiments showed a significant amount of an NIH-shifted metabolite for 1,4-difluorobenzene. This result eliminates the explanation that the NIH shift is an inherently minor process for fluorine substituents. Results of additional experiments presented in this paper show that the reduced tendency of fluorine-substituted benzenes to undergo an NIH shift in vivo can-at least in part-be ascribed to the possible existence of alternative pathways for metabolism of the epoxide, such as, for example, GSH conjugation, being more efficient for fluorinated than chlorinated arene oxides.

Metabolism of sertindole: identification of the metabolites in the rat and dog, and species comparison of liver microsomal metabolism

1. The main exretion pathways of a novel antipsychotic drug, sertindole, in the rat and dog are faecal excretion via intestinal secretion and biliary excretion respectively. 2. Similar liver microsomal metabolic patterns were observed in the rat, monkey, and man, and Lu 30-131 (5-hydroxy-serindole) and Lu 30-148 (4-hydroxy-serindole) were the major metabolites, and Lu 25-073 (nor-sertindole) and Lu 28-092 (dehydro-sertindole) were minor ones. In the dog, however, Lu 31-096 (3'-fluoro-4'-hydroxy-sertindole) and Lu 30-148 (4-hydroxy-sertindole) were the major metabolites, and Lu 25-073 (nor-sertindole), Lu 28-092 (dehydro-sertindole), and Lu 30-131 (5-hydroxy-sertindole) were minor ones. These findings suggest that the metabolism of sertindole in man resembles those in the rat and monkey and is different from that in the dog. 3. Rat in vitro and in vivo liver metabolites, dog liver microsomal metabolites, and dog biliary metabolites were isolated and identified by liquid chromatography/mass spectrometry and/or 1H-nmr. 4. Two metabolites, Lu 31-096 (3'-fluoro-4'-hydroxy-sertindole) and Lu 31-154 (3'-fluoro-4'-hydroxy-dehydro-sertindole), were formed via the 'NIH shift' mechanism. 5. Sertindole is metabolized by hydroxylation at the 4- and 5-positions on the imidazolidinone ring, N-dealkylation, and an NIH shift at the fluorophenyl group. Further metabolism (dehydration, oxidation, hydroxylation, glucuronidation and sulphation) was also observed. 6. In the rat, oxidation at the imidazolidinone ring and N-dealkylation are the main metabolic reactions. On the other hand, in the dog, the NIH shift at the fluorophenyl group, followed by conjugation is the main metabolic pathway.

The metabolism of pentachlorobenzene by rat liver microsomes: the nature of the reactive intermediates formed

Metabolism of [14C]-pentachlorobenzene by liver microsomes from dexamethasone-induced rats results in the formation of pentachlorophenol and 2,3,4,6-tetrachlorophenol as major primary metabolites in a ratio of 4:1, with 2,3,4,5- and 2,3,5,6-tetrachlorophenols as minor metabolites. The unsubstituted carbon atom is thus the favourite site of oxidative attack, but the chlorine substituted positions still play a sizable role. As secondary metabolites both para- and ortho-tetrachlorohydroquinone are formed (1.4 and 0.9% of total metabolites respectively). During this cytochrome P450-dependent conversion of pentachlorobenzene, 5-15% of the total amount of metabolites becomes covalently bound to microsomal protein. Ascorbic acid inhibits this binding to a considerable extent, indicating that quinone metabolites play an important role in the binding. However, complete inhibition was never reached by ascorbic acid, nor by glutathione, suggesting that other reactive intermediates, presumably epoxides, are also responsible for covalent binding.

Metabolism of 1,2,3,4-, 1,2,3,5-, and 1,2,4,5-tetrachlorobenzene in the squirrel monkey

The metabolism of three tetrachlorobenzene isomers (TeCB) was investigated in the squirrel monkey. The animals were administered orally 6 single doses of 14C-labeled 1,2,3,4-, 1,2,4,5-, or 1,2,3,5-tetrachlorobenzene over a 3-wk period at levels ranging from 50 to 100 mg/kg body weight (b.w.) and kept in individual metabolism cages to collect urine and feces for radioassay. Approximately 38% (1,2,3,4-TeCB), 36% (1,2,3,5-TeCB), and 18% (1,2,4,5-TeCB) of the doses were excreted respectively in the feces 48 h postadministration. In monkeys dosed with 1,2,3,4-TeCB, unchanged compound accounted for 50% of the fecal radioactivity; its fecal metabolites were identified as 1,2,4,5-tetrachlorophenol (TeCP, 22%), N-acetyl-S-(2,3,4,5-tetrachlorophenyl) cysteine (18%), 2,3,4,5-tetrachlorophenyl sulfinic acid (3%), 2,3,4-trichlorophenyl methyl sulfide (0.6%), and 2,3,4,5-tetrachlorophenyl methyl sulfide (0.2%). As was the case with 1,2,3,4-TeCB, unchanged compound accounted for more than 50% of the fecal radioactivity found in the monkeys dosed with 1,2,3,5-TeCB. The fecal metabolites of 1,2,3,5-TeCB consisted of 2,3,4,5-TeCP (2%), 2,3,4,6-TeCP (14%), 2,3,5,6-TeCP (9%), and 2,3,5,6-tetrachlorophenyl sulfinic acid (15%). No metabolites were detected in the feces of monkeys dosed with 1,2,4,5-TeCB. While the fecal route represented the major route of excretion for 1,2,3,4-TeCB, the other two isomers were eliminated exclusively in the feces. The above data in the squirrel monkey are different from those obtained with the rat and the rabbit, and demonstrate the different metabolic pathways for the isomers.

Excretion, distribution and metabolism of 1,2,4-trichlorobenzene in rats

1,2,4-Trichlorobenzene (TCB) labeled with C-14 was given perorally to rats at a dosage of 50 mg/kg for excretion and distribution studies. About 66% and 17% of the oral dose was excreted in the urine and feces, respectively, within 7 days. Trapped radioactivity in the expired air amounted to 2.1% of the dose, but production of labeled carbon dioxide was negligible. Tissue residues were evenly distributed throughout the organs and tissues examined, except for the adipose tissue which consistently had a little higher concentration. The urinary, fecal and expiratory metabolites were identified. Free 2,4,5- and 2,3,5-trichlorophenol (TCP) and their conjugates were mainly detected in the urine. 5- or 6-Sulfhydryl, methylthio, methylsulfoxide and methylsulfone derivatives of TCB were also detected as minor metabolites. Dichlorobenzenes and unchanged TCB were confirmed in the expired air. Reductive dechlroination seems to be catalysed by intestinal microflora enzymes.

Metabolites of 1,2,3,4-tetrachlorobenzene in monkey urine

[14C(U)]-Labeled 1,2,3,4-tetrachlorobenzene was administered orally to squirrel monkeys. Urine was collected from these animals, pooled and analyzed for metabolites by thin-layer chromatography, high-performance liquid chromatography, and gas chromatography-mass spectroscopy. N-Acetyl-s-(2,3,4,5-tetrachlorophenyl) cysteine was shown to be the major metabolite and accounted for 85% of the radioactivity found in urine. A minor metabolite was identified as 2,3,4,5-tetrachlorophenol. This study demonstrates for the first time that an N-acetyl cysteine conjugate has been isolated and identified as metabolite of a chlorinated benzene. This pattern of chlorobenzene metabolism is significantly different from the one obtained with the rat and rabbit, where tetrachlorophenols constitute the major metabolites.

Effects of age and obesity on the metabolism of lindane by black a/a, yellow Avy/a, and pseudoagouti Avy/a phenotypes of (YS x VY) F1 hybrid mice

Lindane (gamma-hexachlorocyclohexane) has been shown to produce hepatomas in some strains of mice but not in others. Genetic factors and/or altered metabolism may play a role in the susceptibility to lindane-induced hepatomas. This study reports the effect of age and obesity on the comparative metabolism and disposition of lindane in obese yellow Avy/a and in lean pseudoagouti Avy/a and black a/a phenotypes of (YS x VY) F1 hybrid female mice at 8, 17, 30, 56, and 86 wk of age. At 24 h prior to sacrifice the mice were dosed p.o. with 18 mg lindane (containing 55 microCi [U-14C]lindane/kg). Aging altered the biotransformation of lindane such that while the excretion of lindane and its metabolites declined, the proportion of conjugated and polar metabolites increased. Tissue storage was elevated in older animals. In the yellow Avy/a mice, which are known to have a predisposition to the formation of hepatomas, there was accelerated and prolonged growth, reduced metabolite excretion, a greater proportion of conjugated metabolites, and higher dechlorinase activity compared to that of their pseudoagouti Avy/a and black a/a siblings.

Toxicity and QSAR of chlorophenols on Lebistes reticulatus

The 24-h toxicity of 20 substituted chlorophenols upon Lebistes reticulatus has been determined. The biological results have been tentatively connected with several of the following six parameters: logarithm of the octanol-water partition coefficient (log P); index of molecular connectivity (1 chi v); molecular refraction (RM); perimeter of the efficient section of the molecule (sigma D); constants of HAMMET (sigma); and melting point (F). A correlation is achieved using sigma D and sigma D2 with a correlation coefficient of 0.943.

Metabolism of 1,2,3,4-, 1,2,3,5-, and 1,2,4,5-tetrachlorobenzene in the rat

Adult male rats were given orally single doses of 14C-labeled 1,2,3,4-, 1,2,3,5-, or 1,2,4,5-tetrachlorobenzene (TCB) at 10 mg/kg body weight, and were housed in individual metabolism cages to collect urine and feces for radioassay. For 1,2,3,4- and 1,2,3,5-TCB, approximately 46-51% of the doses were excreted in urine and feces within 48 h after administration. During the same period only 8% of the administered 1,2,4,5-tetrachlorobenzene was excreted. Analysis of urine indicted that the tetrachlorobenzenes were biotransformed to a number of polar compounds. The metabolites for each of the three TCBs in decreasing order of quantities were as follows: 1,2,3,4-TCB, to 2,3,4,5- and 2,3,4,6-tetrachlorophenol and a trace of tetrachlorothiophenol and 2,3,4-trichlorophenol; 1,2,3,5-TCB, to 2,3,4,6-tetrachlorophenol, isomeric hydroxythrichlorothiophenols, and a trichlorophenol; 1,2,4,5-TCB, to 2,3,5,6-tetrachlorophenol, tetrachloroquinol, and a trichlorophenol.

Maternal hepatic effects of 1,2,4,5-tetrachlorobenzene in the rat

1,2,4,5-Tetrachlorobenzene (TCB) is an industrial intermediate used in the production of 2,4,5-trichlorophenoxyacetic acid. This herbicide contains trace quantities of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Because of possible maternal hepatic or reproductive effects of this uncharged, low-molecular weight, lipophilic chlorinated benzene 0, 30, 100, 300, and 1000 mg/kg/day of TCB was orally administered to rats on Days 9, 10, 11, 12, and 13 of gestation and the animals were sacrificed on Day 14 of pregnancy. No maternal deaths were recorded and body weight gain was significantly decreased only in the 1000 mg/kg/day group. Maternal liver weight, liver to body weight ratio, and hepatic microsomal protein content were unaffected by TCB treatment. Although Day 14 NADPH-cytochrome c reductase activity was not affected, the maternal hepatic microsomal cytochrome P-450 content was significantly increased by administration of 1000 mg/kg/day of TCB. Microsomal N-demethylation of aminopyrine was slightly increased from 2.4 to 3.4 and 3.5 nmole/mg protein/min at doses of 300 and 1000 mg/kg TCB. However, maternal hepatic microsomal ethoxyresorufin O-deethylase activity was greatly increased from 14 to 30, 40, 50, and 49 pmole/mg protein/min in pregnant rats administered 0, 30, 100, 300, and 1000 mg/kg/day TCB. The microsomal rates of p-nitrophenol and phenolphthalein glucuronidation in vitro were not increased by TCB administration. The maternal hepatic microsomal enzyme induction observed after TCB administration to pregnant rats suggests the presence both cytochrome P-450 and P-448 inducers in the sample of 1,2,4,5-tetrachlorobenzene used.

Differential induction of hepatic drug metabolizing enzymes in Japanese quail by 1,2,4-trichlorobenzene

The effects of single oral administration of 1,2,4-trichlorobenzene (TCB), 200, 400, 800 or 1600 mg/kg, and of daily oral administration of TCB, 400 mg/kg, for 3 consecutive days, on components of the microsomal monooxygenase system, glutathione, and the activities of cytosolic glutathione S-transferase and microsomal epoxide hydrolase in Japanese quail liver were studied. Cytochromes P-450 and b5 contents of liver microsomes and the activities of 7-ethoxyresorufin deethylase (7-ERD) and glutathione S-transferase were significantly increased 1 day after administration of single doses of TCB. Liver GSH and 7-ethoxycoumarin deethylase (7-ECD) activity were unchanged. Microsomal epoxide hydrolase activity was significantly decreased at TCB doses above 400 mg/kg. Increases in cytochromes and activities of 7-ERD and glutathione S-transferase were also seen following the 3-day administration of TCB, 400 mg/kg. In addition, liver GSH and the activity of NADPH-cytochrome c reductase were significantly increased whereas 7-ECD was significantly decreased by the 3-day treatment. These findings indicate that in Japanese quail, TCB is an inducer of 7-ERD and glutathione S-transferase but not of 7-ECD and epoxide hydrolase.

Maternal hepatic and embryonic effects of 1,2,4-trichlorobenzene in the rat

The possible maternal hepatic and reproductive effects of 1,2,4-trichlorobenzene (TCB) were assessed in rats given 0, 36, 120, 360, and 1200 mg/kg/day of TCB on Days 9-13 of gestation. The animals were sacrificed on Day 14 of pregnancy. Maternal deaths (2/9 rats, 6/6 rats) were recorded in the 360 and 1200 mg/kg/day treatment groups and body weight gain was significantly decreased in the 360 mg/kg/day TCB group. Maternal liver weight, liver/body weight ratio, and hepatic microsomal protein content were unaffected by TCB treatment. Although Day 14 NADPH-cytochrome c reductase activity was affected only at 360 mg/kg/day TCB, the maternal hepatic microsomal cytochrome P-450 content was significantly increased by administration of both 120 and 360 mg/kg/day of TCB. Hepatic microsomal aminopyrine N-demethylase, ethoxyresorufin O-deethylase, and UDP-glucuronyl transferase activity towards p-nitrophenol were also increased at 120 and 360 mg/kg TCB. Glutathione S-transferase activity to 1-chloro-2,4-dinitrobenzene and 1,2 dichloro-4-nitrobenzene were both increased by pretreatment with TCB. Although pretreatment with 360 mg/kg/day TCB did not increase resorptions, embryolethality, or teratogenicity, embryonic development was significantly retarded by all four growth criteria used (head length, crown-rump length, somite number, and protein content).

Comparative toxicity of 1,2,3,4-, 1,2,4,5-, and 1,2,3,5-tetrachlorobenzene in the rat: results of acute and subacute studies

Groups of 10 male and 10 female rats were dosed orally with 1,2,3,4-, 1,2,4,5-, or 1,2,3,5-tetrachlorobenzene (TCB) at levels that ranged from 200 to 4000 mg/kg, and were observed clinically for 14 d. LD50 values for 1,2,3,4-, 1,2,4,5-, and 1,2,3,5-TCB were found to be 1470, 3105, and 2297 mg/kg, respectively, in male rats. In females, the LD50 values were found to be 1167 and 1727 mg/kg for 1,2,3,4- and 1,2,3,5-TCB, respectively. Clinical signs of toxicity included depression, flaccid muscle tone, prostration, piloerection, loose stool, hypothermia, dacryorrhea, coma, and death. In a subacute study, groups of 10 males and 10 females were fed diets containing 0, 0.5, 5.0, 50, or 500 ppm 1,2,3,4-, 1,2,4,5-, or 1,2,3,5-TCB for 28 d. No deaths or clinical signs of toxicity were observed, and neither growth rate nor food consumption was affected. At 500 ppm, 1,2,4,5- but not 1,2,3,4- or 1,2,3,5-TCB caused a significant increase in the liver weight and serum cholesterol of male and female rats. Hepatic microsomal aniline hydroxylase and ethoxyresorufin deethylase were induced by 500 ppm 1,2,4,5-TCB. Hepatic microsomal aminopyrine demethylase activity was increased by the administration of this compound at 50 ppm and higher in males and at 500 ppm in the females. Rats fed 1,2,3,4- and 1,2,3,5-TCB at 500 ppm also showed a significant increase in aminopyrine demethylase activity. Moderate to severe histological changes were found in the liver, thyroid, kidney, and lungs of rats fed 500 ppm 1,2,4,5-TCB. Histological changes in the tissues produced by the administration of the 1,2,3,4- and 1,2,3,5-isomer were mild even at the highest dose levels. Tissue residue data showed that 1,2,4,5-TCB accumulated at much higher levels than the other two isomers. The results suggest that the position of chlorine substitution can affect the tissue accumulation and toxicity of chlorinated benzenes in rats.

Maternal hepatic and embryonic effects of 1,2,3,4-tetrachlorobenzene in the rat

To assess possible maternal hepatic and reproductive effects of this uncharged, low molecular weight, lipophilic chlorinated benzene 0, 100, 300 and 1000 mg/kg/day of 1,2,3,4-tetrachlorobenzene (TCB) was orally administered to pregnant rats on days 9-13 of gestation and the animals were killed on day 14 of pregnancy. Phenobarbital and beta-naphthoflavone were administered to other pregnant rats as positive hepatic controls. Maternal mortality (7/19 rats) was increased and body weight gain was greatly decreased in the 1000 mg/kg/day TCB group. Liver to body weight ratio and hepatic microsomal protein content were unaffected by any TCB treatment. On day 14 maternal NADPH-cytochrome c reductase activity was increased at 1000 mg/kg/day, while the maternal hepatic microsomal cytochrome P-450 content was significantly induced by both 300 and 1000 mg/kg/day of TCB. Microsomal N-demethylation of aminopyrine was increased from 2.6 to 4.0 and 4.5 nmol/mg protein/min at doses of 300 and 1000 mg/kg TCB, respectively. However, maternal hepatic microsomal ethoxyresorufin O-deethylase activity was not consistently increased by TCB. Hepatic glutathione S-transferase activity towards 1,2-dichloro-4-nitrobenzene was increased only by the 1000 mg/kg/day TCB treatment. The rate of microsomal p-nitrophenol and phenolphthalein glucuronidation was increased by TCB administration. Embryonic growth was adversely affected by TCB treatment. Yolk sac diameter, embryonic crown-rump length, and head length were all decreased by treatment with 300 mg/kg/day TCB. This TCB treatment did not significantly elevate the number of dead or abnormal embryos.

Subchronic inhalation toxicity of 1,3,5-trichlorobenzene

Male and female rats were exposed to 0, 10, 100 or 1000 mg/m3 of 1,3,5-trichlorobenzene vapors for 6 hours daily, 5 days a week, for up to 13 weeks. After 4 and 13 weeks of exposure, animals were sacrificed and examined for changes in blood, clinical chemistry, internal organs, and tissues resulting from the 1,3,5-trichlorobenzene treatment. No treatment-related effects on the blood and clinical chemistry were evident. The only effects that were considered treatment-related were a squamous metaplasia and hyperplasia in the respiratory epithelium in the nasal passages of high-dose rats and the increased incidence of dried red material on the faces of these rats during exposures compared with other groups.

Chlorinated phenols: occurrence, toxicity, metabolism, and environmental impact

Pentachlorophenol and the lower chlorinated phenols, tetra- and trichlorophenols, have gained an increasing use as fungicides, herbicides, insecticides, and precursors in the synthesis of other pesticides since the early 1930s. World-wide production totals about 200,000 tons. Production and use of chlorinated phenols have caused industrial hygiene problems but, otherwise, have not been recognized to create more than limited environmental problems. The introduction of modern analytical techniques, however, has revealed the ubiquitous occurrence of chlorophenols in the environment, and the discovery of chlorinated dimers, such as dibenzo-p-dioxins and dibenzofurans, as impurities in commercial chlorophenol formulations, has made a reevaluation of the chlorinated phenols necessary. The present article reviews recent studies on the toxicity and metabolism in mammals and aquatic organisms and the degradation of the chlorophenols under various conditions in the environment. Finally, the hazards of burning of chlorophenol wastes are discussed, as well as health considerations with regard to humans and the environment.

Various pharmacokinetic parameters in relation to enzyme-inducing abilities of 1,2,4-trichlorobenzene and 1,2,4-tribromobenzene

1,2,4-Trichlorobenzene (TCB) and 1,2,4-tribromobenzene (TBB) were administered for 7 d to rats at a dose of 1 mmol/kg.d. The animals were sacrificed at various times to observe the decline in enzyme induction. Carbon 14-labeled TCB and TBB were administered and the disposition of the radioactivity was determined. The influence of starvation and phenobarbital on the inductive effects of TCB and TBB was observed. p-Nitroanisole demethylation and EPN (O-ethyl O-p-nitrophenyl phenylphosphonothionate) detoxification increases declined with time but were still elevated 16 d after the last dose of TBB. Cytochorme P-450 and NADPH-cytochrome c reductase were alsoinduced. Tissue analysis showed greater retention of TBB than of TCB, with highest levels in the fats. More TCB than TBB was excreted in the urine, and fecal excretion was only 5-10% of the dose. The highest enzyme levels were found after 4 d of starvation following the 7 d of treatment and 6 d of recovery. Starvation resulted in increased plasma, fat, and liver concentrations and increased urinary excretion of 14C after TBB dosing. Phenobarbital treatment decreased the levels of induction by the halogenated benzenes. The results demonstrate that, on an equimolar basis, TBB leads to higher levels of induction that are maintained for longer periods than does TCB. Treatments, such as starvation and phenobarbital, that after storage in fat of these materials change the decline with time of the level of induction.

Effect of trichlorophenols on xenobiotic metabolism in the rat

Unlike halogenated benzenes, trichlorophenols did not induce xenobiotic metabolism in the rat. 2,3,5-, 2,3,6-, 2,4,5-, and 2,4,6-Trichlorophenol at doses as high as 400 mg/kg p.o. daily for 14 days did not alter EPN detoxification. Only 2,4,5-trichlorophenol at the highest dose decreased microsomal NADPH-cytochrome c reductase activity and cytochrome P-450 content. In vitro, all 4 isomers inhibited EPN detoxification and the demethylation of p-nitroanisole. UDP-glucuronyltransferase was not altered in vivo and was only slightly inhibited in vitro by 2,3,5- and 2,4,5-trichlorophenol. The compounds were not hepatotoxic as assessed by measurement of hepatic glucose-6-phosphatase and serum sorbitol dehydrogenase.