Phenobarbital-induced protection against toxicity of toluene and benzene in the rat

Screening of sleep assisting drug candidates with a Drosophila model

Lately, Drosophila has been favored as a model in sleep and circadian rhythm research due to its conserved mechanism and easily manageable operation. These studies have revealed the sophisticated parameters in whole-day sleep profiles of Drosophila, drawing connections between Drosophila sleep and human sleep. In this study, we tested several sleep deprivation protocols (mechanical shakes and light interruptions) on Drosophila and delineated their influences on Drosophila sleep. We applied a daytime light-deprivation protocol (DD) mimicking jet-lag to screen drugs that alleviate sleep deprivation. Characteristically, classical sleep-aid compounds exhibited different forms of influence: phenobarbital and pentobarbital modified total sleep time, while melatonin only shortened the latency to sleep. Such results construct the basis for further research on sleep benefits in other treatments in Drosophila. We screened seven herb extracts, and found very diverse results regarding their effect on sleep regulation. For instance, Panax notoginseng and Withania somnifera extracts displayed potent influence on total sleep time, while Melissa officinalis increased the number of sleep episodes. By comparing these treatments, we were able to rank drug potency in different aspects of sleep regulation. Notably, we also confirmed the presence of sleep difficulties in a Drosophila Alzheimer’s disease (AD) model with an overexpression of human Abeta, and recognized clear differences between the portfolios of drug screening effects in AD flies and in the control group. Overall, potential drug candidates and receipts for sleep problems can be identified separately for normal and AD Drosophila populations, outlining Drosophila’s potential in drug screening tests in other populations if combined with the use of other genetic disease tools.

4: Final Report on the Safety Assessment of Toluene

Toluene has a wide variety of noncosmetic applications. However, the cosmetic use is limited to nail products at concentrations up to 50%. Toluene was practically nontoxic when given orally to rats; acute oral LD50 values ranged from 2.6 g/kg to 7.5 g/kg. Results of animal studies indicated that undiluted Toluene is a skin irritant. No skin irritation or sensitization was observed in subjects treated with cosmetic products containing 31-33% Toluene. No phototoxic or photoallergic reactions were noted in subjects treated with 25% or 30% Toluene. The sole cosmetic use of Toluene is in products intended to be applied directly to the nail; therefore, human skin exposure to this ingredient will be minimal under conditions of cosmetic use. On the basis of the available data and the limited user skin exposure from cosmetic products containing Toluene, it is concluded that this ingredient is safe for cosmetic use at the present practices of use and concentration.

ATSDR evaluation of health effects of benzene and relevance to public health

As part of its mandate, the Agency for Toxic Substances and Disease Registry (ATSDR) prepares toxicological profiles on hazardous chemicals found at Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) National Priorities List (NPL) sites that have the greatest public health impact. These profiles comprehensively summarize toxicological and environmental information. This article constitutes the release of portions of the Toxicological Profile for Benzene. The primary purpose of this article is to provide public health officials, physicians, toxicologists, and other interested individuals and groups with an overall perspective on the toxicology of benzene. It contains descriptions and evaluations of toxicological studies and epidemiological investigations and provides conclusions, where possible, on the relevance of toxicity and toxicokinetic data to public health.

Toxicokinetics of organic solvents: a review of modifying factors

This article reviews, with an emphasis on human experimental data, factors known or suspected to cause changes in the toxicokinetics of organic solvents. Such changes in the toxicokinetic pattern alters the relation between external exposure and target dose and thus may explain some of the observed individual variability in susceptibility to toxic effects. Factors shown to modify the uptake, distribution, biotransformation, or excretion of solvent include physical activity (work load), body composition, age, sex, genetic polymorphism of the biotransformation, ethnicity, diet, smoking, drug treatment, and coexposure to ethanol and other solvents. A better understanding of modifying factors is needed for several reasons. First, it may help in identifying important potential confounders and eliminating negligible ones. Second, the risk assessment process may be improved if different sources of variability between external exposures and target doses can be quantitatively assessed. Third, biological exposure monitoring may be also improved for the same reason.

Identification of quinol thioethers in bone marrow of hydroquinone/phenol-treated rats and mice and their potential role in benzene-mediated hematotoxicity

Metabolism of benzene is required to produce the classical hematological disorders associated with its exposure. After coadministration of hydroquinone (0.9 mmol/kg, ip) and phenol (1.1 mmol/kg, ip) to male Sprague-Dawley rats and DBA/2 mice, 2-(glutathion-S-yl)hydroquinone was identified in the bone marrow of both species. 2,5-Bis(glutathion-S-yl)hydroquinone, 2,6-bis(glutathion-S-yl)hydroquinone, and 2,3,5-tris(glutathion-S-yl)hydroquinone were also observed in the bone marrow of rats but were detected only sporadically in mice. Both species produced 2-(cystein-S-ylglycinyl)hydroquinone, 2-(cystein-S-yl)hydroquinone, and 2-(N-acetylcystein-S-yl)hydroquinone, indicating the presence of a functional mercapturic acid pathway in bone marrow. The ability of bone marrow to acetylate 2-(cystein-S-yl)hydroquinone and deacetylate 2-(N-acetylcystein-S-yl)hydroquinone was confirmed in vitro. Total quinol thioether concentrations were higher in, and eliminated more slowly from, the bone marrow of mice. Intravenous injection of 100 micromol/kg 2-(glutathion-S-yl)hydroquinone to rats gave rise to substantially lower bone marrow C(max) and AUC values compared to values found following coadministration of hydroquinone/phenol, suggesting that the major fraction of the GSH conjugates present in bone marrow are formed in situ. Finally, the erythrotoxicity of several of these conjugates was determined in rats using the erythrocyte 59Fe incorporation assay. Administration of 2,3,5-tris(glutathion-S-yl)hydroquinone (17 micromol/kg, iv), 2,6-bis(glutathion-S-yl)hydroquinone (50 micromol/kg, iv), and benzene (11 mmol/kg, sc) significantly decreased 59Fe incorporation into reticulocytes to 45 +/- 6%, 28 +/- 3%, and 20 +/- 9% of control values, respectively. Although the doses of 2,3,5-tris(glutathion-S-yl)hydroquinone and 2,6-bis(glutathion-S-yl)hydroquinone represented only 0.2% and 0.4% of the dose of benzene, both conjugates reduced 59Fe incorporation to the same degree as benzene. 2-(Glutathion-S-yl)hydroquinone had no effect at the dose tested (200 micromol/kg, iv). In summary, these data suggest that hydroquinone-glutathione conjugates are erythrotoxic and may contribute to benzene-mediated hematotoxicity.

Enzymes induced by ethanol differently affect the pharmacokinetics of trichloroethylene and 1,1,1-trichloroethane

This study was undertaken to clarify the effect of enzymes induced by ethanol consumption on the pharmacokinetics of trichloroethylene (TRI, a highly metabolised substance) and 1,1,1-trichloroethane (1,1,1-TRI, a poorly metabolised substance). Rats maintained on a control liquid diet or a liquid diet containing ethanol (2 g/day/rat) for not less than three weeks were exposed to either TRI (50, 100, 500, and 1000 ppm) or 1,1,1-TRI (50, 100, and 500 ppm) by inhalation for six hours and the concentration of each compound in the blood and the urinary excretion of metabolites (trichloroethanol and trichloroacetic acid) were measured over several hours. Ethanol, which increased the in vitro metabolism of both compounds about fivefold, enhanced the in vivo metabolism of TRI only at high levels of exposure (marginally at 500 and considerably at 1000 ppm), whereas the metabolism of 1,1,1-TRI was enhanced at all concentrations tested. Moreover, there was a definite difference in the effect of induction of enzymes between the two solvents: the enhanced metabolism of TRI in vivo was shown by a decrease in the blood concentration of TRI as well as by an increase in the urinary excretion of its metabolites, whereas that of 1,1,1-TRI was shown by an increase in the urinary excretion of its metabolites alone. These results suggest that the induction of enzymes differentially affects the pharmacokinetics of TRI and 1,1,1-TRI in human occupational exposure: TRI metabolism may be increased only at concentrations much higher than the current occupational exposure limit (mostly 50 ppm), whereas 1,1,1-TRI metabolism may be increased at an exposure similar to occupational exposure.

Free radical induction in the brain and liver by products of toluene catabolism

Toluene and its metabolites have been studied with respect to their reactive oxygen species-enhancing potential in isolated systems and in vivo. The induction of reactive oxygen species (ROS) production was assayed using the probe 2',7'-dichlorodihydrofluorescin diacetate (DCFH-DA). Intraperitoneal injection of toluene, benzyl alcohol or benzaldehyde caused a significant elevation in the rate of ROS formation within hepatic mitochondrial fractions (P2). In the brain, only toluene induced ROS formation, while benzyl alcohol and benzaldehyde did not have any effect. Glutathione (GSH) levels were depressed in liver and brain regions from toluene-treated rats. However, no such depression was evident in brains treated with toluene metabolites. P2 fractions from phenobarbital-pretreated rats exhibited a heightened ROS response when challenged with toluene, in vitro. Pretreatment of rats in vivo with 4-methylpyrazole, an alcohol dehydrogenase inhibitor, or sodium cyanamide, an aldehyde dehydrogenase inhibitor, prior to exposure to toluene, caused a significant decrease and increase, respectively, in toluene-stimulated rates of ROS generation in the CNS and liver. Electron spin resonance spectroscopy, employing the spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO), was conducted. Incubation of the spin trap with P2 fractions and toluene or benzaldehyde elicited a spectrum corresponding to the hydroxyl radical. Incubation of benzaldehyde with aldehyde dehydrogenase produced a strong signal that was blocked completely by superoxide dismutase and inhibited partially by catalase, suggesting the presence of superoxide radicals and the involvement of the iron-catalyzed Haber-Weiss reaction leading to the production of hydroxyl radicals. Thus, ROS generation during toluene catabolism may occur at two steps: cytochrome P450 oxidation and aldehyde dehydrogenase oxidation. In addition, GSH may play an important role in protection against the induction of ROS generation in the CNS and liver following exposure to toluene.

Exposure to various benzene derivatives differently induces cytochromes P450 2B1 and P450 2E1 in rat liver

Benzene (B), toluene (T), ethylbenzene (EB), styrene (S) and xylene isomers (oX, mX, pX) are important environmental pollutants and B is a proved human carcinogen. Their inhalation by male Wistar rats (4 mg/l, 20 h/day, 4 days) caused cytochrome P450 (P450) induction. The degree of P450 2B1 induction increased and that of 2E1 decreased in the series B, T, EB, S, oX, mX and pX, as estimated by Western blots, while neither solvent was as effective for 2B1 induction as phenobarbital and B was more effective for 2E1 than ethanol. The levels of several other P450s decreased after exposure to these solvents, B being most effective. Exposure to these solvents increased in vitro hepatic microsomal oxidation of B and aniline (AN) (2E1 substrates) 3 to 6-fold, indicating induction of this P450. T oxidation was increased 2 to 4-fold and chlorobenzene (ClB) oxidation 3-fold. Sodium phenobarbital (PB, 80 mg/kg/day, 4 days, i.p.) did not increase ethylmorphine (EM) and benzphetamine (BZP) demethylation (2B1 substrates), neither of the B derivatives did so, and oX decreased it; however, pentoxyresorufin O-dealkylation was well related to the immunochemically detected 2B1 levels in control, PB and B microsomes. PB did not increase B, but increased T and ClB oxidation 2-4 and 3-fold, respectively, indicating possible 2B1 role in their oxidation. B oxidation after various inducers was related to immunochemical 2E1 levels, T and ClB oxidation to both 2B1 and 2E1 and AN oxidation to 2E1 and 1A2 levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Toluene-induced oxidative stress in several brain regions and other organs

The in vivo dose-response relationship between toluene and reactive oxygen species (ROS) formation in rat brain, liver, kidney, and lung, and the time-course of these effects has been characterized. The rate of oxygen radical formation was measured using the probe 2',7'-dichlorofluorescin diacetate. In vivo exposure to various doses of toluene (0.5, 1.0, and 1.5 g/kg ip) elicited a dose-dependent elevation of ROS generation within crude mitochondrial fractions obtained from rat lung and kidney, and within crude synaptosomal fractions from cerebellum. ROS formation in crude mitochondrial fractions from liver, and crude synaptosomal fractions from striatum and hippocampus, reached a maximum value at relatively low doses of toluene. Of the brain regions, the hippocampus had the highest induced levels of ROS. In vivo exposure to a single dose of toluene (1.5 g/kg ip), revealed that toluene-induced ROS reached a peak within 2 h, which correlated directly with measured toluene blood levels. This elevated oxidative activity was maintained throughout the next 24 h, even though blood values of toluene decreased to negligible amounts. These results demonstrate that exposure to toluene results in broad systemic elevation in the normal rate of oxygen radical generation, with such effects persisting in the tissues despite a rapid decline in toluene blood levels. Acute exposure to toluene may lead to extended ROS-related changes, and this may account for some of the clinical observations made in chronic toluene abusers.

Toluene metabolism in isolated rat hepatocytes: effects of in vivo pretreatment with acetone and phenobarbital

Hepatocytes isolated from control, acetone- and phenobarbital-pretreated rats were used to study the metabolic conversion of toluene to benzyl alcohol, benzaldehyde, benzoic acid and hippuric acid at low (< 100 microM) and high (100-500 microM) toluene concentrations. The baseline formation rates of toluene metabolites (benzyl alcohol, benzoic acid and hippuric acid) were 2.9 +/- 1.7 and 10.0 +/- 2.3 nmol/mg cell protein/60 min at low and high toluene concentrations, respectively. In vivo pretreatment of rats with acetone and phenobarbital increased the formation of metabolites: at low toluene concentrations 3- and 5-fold, respectively; at high toluene concentrations no significant increase (acetone) and 8-fold increase (phenobarbital). Apparent inhibition by ethanol, 7 and 60 mM, was most prominent at low toluene concentrations: 63% and 69%, respectively, in control cells; 84% and 91% in acetone-pretreated cells, and 32% (not significant) and 51% in phenobarbital-pretreated cells. Ethanol also caused accumulation of benzyl alcohol. The apparent inhibition by isoniazid was similar to that of ethanol at low toluene concentrations. Control and acetone-pretreated cells were apparently resistant towards metyrapone; the decrease was 49% and 64% in phenobarbital-pretreated cells at low and high toluene concentrations, respectively. In these cells, the decrease in presence of combined ethanol and metyrapone was 95% (low toluene concentrations). 4-Methyl-pyrazole decreased metabolite formation extensively in all groups. Benzaldehyde was only found in the presence of an aldehyde dehydrogenase inhibitor. Increased ratio benzoic/hippuric acid was observed at high toluene concentrations. These results demonstrate that toluene oxidation may be studied by product formation in isolated hepatocytes. However, the influence of various enzymes in the overall metabolism could not be ascertained due to lack of inhibitor specificity.

Metabolism of trans,trans-muconaldehyde by aldehyde and alcohol dehydrogenases: identification of a novel metabolite

The metabolism of trans,trans-muconaldehyde (MA), a highly reactive alpha,beta-unsaturated dialdehyde, was examined in vitro using purified yeast alcohol and aldehyde dehydrogenases (ADH and ALDH, respectively). In the presence of NAD(+)-fortified ALDH, the mono-oxidation product (acid/aldehyde) was the primary metabolite formed with trace amounts of the dioxidation product (trans,trans-muconic acid). In NADH-fortified reactions with ADH, both the mono- and direduction products (hydroxy/aldehyde and dihydroxy, respectively) were readily detected. Oxidation and reduction products of MA were formed in incubates containing both dehydrogenases together with either NAD+ or NADH. Unexpectedly, an additional metabolite was detected, which was a major product in both NAD(+)- and NADH-fortified systems containing ALDH and ADH in combination and whose formation could be inhibited by pyrazole (an ADH inhibitor). ALDH-mediated oxidation of a synthetic standard of the hydroxy/aldehyde derivative of MA resulted in formation of this new metabolite, which was also a major product formed by rat hepatocytes incubated with MA. Using HPLC/photodiode array detection, the new metabolite was found to cochromatograph and have a uv spectrum identical to that of a synthetic standard of the hydroxy/acid derivative of MA. The metabolite was confirmed as the hydroxy/acid derivative of MA after preparative HPLC, TMS derivatization, and GC/MS analysis. The hydroxy/acid metabolite was not formed during ADH-mediated reduction of the mono-oxidation product of MA, suggesting that this metabolite was formed by yeast dehydrogenases via a primary reduction of MA and subsequent oxidation of the hydroxy/aldehyde to the hydroxy/acid. These data show that the hydroxy/acid derivative is a novel metabolite of MA, which arises from the interaction of both oxidative and reductive routes of metabolism.

The hearing loss associated with exposure to toluene is not caused by a metabolite

Exposure to toluene causes a marked hearing loss in rats, and this effect has been observed in some human solvent abusers. The issue of whether toluene or one of its metabolites is responsible for this effect has not been examined. To attempt to resolve this issue, we manipulated the metabolism, and thus the circulating levels, of toluene as follows. Two groups of rats were exposed to phenobarbital (PB) in their drinking water (0.1%) for seven days to induce detoxifying liver enzymes; two other groups had access to PB-free water. Then half of the rats exposed to PB or water were exposed to filtered air or a concentration of toluene expected to cause hearing loss. Levels of toluene in blood were markedly reduced by the PB and the excretion of hippuric acid was increased. All rats were tested for auditory sensitivity by brainstem auditory-evoked response (BAER) audiometry using a 16-kHz tone pip. The rats exposed to toluene alone showed a marked reduction in the integrated BAER waveform, indicative of the expected hearing deficit. None of the other treated rats showed any deviation from controls (i.e., water and air). These results provide strong evidence that toluene itself is responsible for the auditory dysfunction. Toluene also caused the rats to increase their fluid consumption and urine output; these effects were not altered by PB. Identification of toluene as the proximal ototoxicant should facilitate the search for the mechanism of this effect.

Hydroxylation of phenol to hydroquinone catalyzed by a human myeloperoxidase-superoxide complex: possible implications in benzene-induced myelotoxicity

Benzene, a known human myelotoxin and leukemogen is metabolized by liver cytochrome P-450 monooxygenase to phenol. Further hydroxylation of phenol by cytochrome P-450 monooxygenase results in the formation of mainly hydroquinone, which accumulates in the bone marrow. Bone marrow contains high levels of myeloperoxidase. Here we report that phenol hydroxylation to hydroquinone is also catalyzed by human myeloperoxidase in the presence of a superoxide anion radical generating system, hypoxanthine and xanthine oxidase. No hydroquinone formation was detected in the absence of myeloperoxidase. At low concentrations superoxide dismutase stimulated, but at high concentrations inhibited, the conversion of phenol to hydroquinone. The inhibitory effect at high superoxide dismutase concentrations indicates that the active hydroxylating species of myeloperoxidase is not derived from its interaction with hydrogen peroxide. Furthermore, catalase a hydrogen peroxide scavenger, was found to have no significant effect on hydroxylation of phenol to hydroquinone, supporting the lack of hydrogen peroxide involvement. Mannitol (a hydroxyl radical scavenger) was found to have no inhibitory effect, but histidine (a singlet oxygen scavenger) inhibited hydroquinone formation. Based on these results we postulate that a myeloperoxidase-superoxide complex spontaneously rearranges to generate singlet oxygen and that this singlet oxygen is responsible for phenol hydroxylation to hydroquinone. These results also suggest that myeloperoxidase dependent hydroquinone formation could play a role in the production and accumulation of hydroquinone in bone marrow, the target organ of benzene-induced myelotoxicity.

Kinetic studies on toluene metabolism in ethanol- and phenobarbital-induced rat liver microsomes in vitro

In vitro metabolism of toluene was investigated at substrate concentrations of 0.03-6.25 mM in liver microsomes from control and ethanol- and phenobarbital (PB)-treated rats. Three metabolites, benzylalcohol (BA), o- and p-cresol, were measured by high-performance liquid chromatograph. BA was the main metabolite of toluene, whereas o- and p-cresol contributed only 1.1-1.5% and 1.7-2.8% of total metabolites, respectively, in microsomes from control rats. Ethanol treatment showed little effect on the percentages of three metabolites, but PB increased the percentages of o- and p-cresol to as high as 5.5% and 8.0%, respectively, following the increase in toluene concentration. There were two different isozymes with different Km involved in the side-chain hydroxylation of toluene in microsomes from control and ethanol-treated rats. One had a low Km value (0.13-0.17 mM) and could be greatly induced with ethanol treatment. The other was a high Km isozyme (0.60-0.87 mM). PB-induced isozyme showed a similar Km value to that of the high Km isozyme existing in microsomes from control and ethanol-treated rats. Two isozymes were involved in the formation of p-cresol in microsomes of control rats: the low-Km type had a similar value (0.15 mM) to the low isozyme of BA formation, but the high Km isozyme had a larger value (2.04 mM) than the high isozyme of BA. Only one enzyme responsible for o-cresol formation was detected in microsomes of control rats, and had a similar Km (2.11 mM) to that of the high Km isozyme of p-cresol.(ABSTRACT TRUNCATED AT 250 WORDS)

Differences in the metabolism and disposition of inhaled [3H]benzene by F344/N rats and B6C3F1 mice

Benzene is a potent hematotoxin and has been shown to cause leukemia in man. Chronic toxicity studies indicate that B6C3F1 mice are more susceptible than F334/N rats to benzene toxicity. The purpose of the studies presented in this paper was to determine if there were metabolic differences between F344/N rats and B6C3F1 mice which might be responsible for this increased susceptibility. Metabolites of benzene in blood, liver, lung, and bone marrow were measured during and following a 6-hr 50 ppm exposure to benzene vapor. Hydroquinone glucuronide, hydroquinone, and muconic acid, which reflect pathways leading to potential toxic metabolites of benzene, were present in much greater concentrations in the mouse than in rat tissues. Phenylsulfate, a detoxified metabolite, and an unknown water-soluble metabolite were present in approximately equal concentrations in these two species. These results indicate that the proportion of benzene metabolized via pathways leading to the formation of potentially toxic metabolites as opposed to detoxification pathways was much higher in B6C3F1 mice than in F344 rats, which may explain the higher susceptibility of mice to benzene-induced hematotoxicity and carcinogenicity.

Health effects of the alkylbenzenes. I. Toluene

The alkylbenzenes, toluene being the most common example, represent a class of six-membered ring aromatic compounds that have a variety of alkyl groups attached. These chemicals are liquids with relatively low boiling points and are used primarily as solvents or as starting materials in the synthesis of other chemicals and drugs. They are also integral components of gasoline, distillate fuels and other petroleum products. These substituted aromatics are economically important in the chemical, petroleum, pharmaceutical, polymer, paint and dye industries. Alkylbenzenes such as toluene, xylene, ethylbenzene, styrene and cumene are toxicologically important since they are produced, used or disposed of in the largest quantities and therefore might pose significant and potential health risks to man and the environment. In general, the toxicity of alkylbenzenes has been found to be relatively low. Also, for the most part, human and environmental risks are low; however, there may be a few operations where the potential for high exposure could exist. These exposures are minimized by workplace controls or personal protective equipment. Furthermore, health risks for humans are minimized by guidelines for maximum allowable exposure concentrations which have been established for the workplace. This present paper reviews the toxicology and disposition of toluene in animals and humans.

Changes in the excretion of endogenous glycine conjugate as a possible artifact in toxicological experiments

Changes in the urinary excretion of hippuric acid (HIA) and phenaceturic acid (PUA) as well as their metabolic precursors, i.e. benzoic (BA) and phenylacetic acid (PAA), in rats housed in glass metabolic cages for 4 days were monitored using gas-liquid chromatography. The amount of HIA excreted was 128 +/- 63 mumol/kg for female and 79 +/- 43 mumol/kg for male rats in the first 24 h and decreased to 11 +/- 7 mumol/kg (p less than 0.01) for female and 3.2 +/- 2.4 mumol/kg (p less than 0.001) for male rats on the 2nd day. These values remained nearly at the same level until the end of the experiment. The amount of PUA decreased from 48 +/- 12 mumol/kg on the 1st day to 22 +/- 9 mumol/kg (p less than 0.05) on the 2nd day by male rats, whereas by the females the decrease from 30 +/- 9 mumol/kg to 21 +/- 8 mumol/kg was not significant. The decrease in the excretion of glycine conjugates was compensated by a parallel increase in the level of unconjugated BA and PAA.

Chemical of current interest--benzene

Benzene is one of the world's major commodity chemicals. It is derived from petroleum and coal and is used both as a solvent and as a starting material in chemical syntheses. The numerous industrial uses of benzene over the last century need not be recounted here, but the most recent addition to the list of uses of benzene is as a component in a mixture of aromatic compounds added to gasoline for the purpose of replacing lead compounds as anti-knock ingredients. The best known and longest recognized toxic effect of benzene is the depression of bone marrow function seen in occupationally exposed individuals. These people have been found to display anemia, leucopenia, and/or thrombocytopenia. When pancytopenia, i.e., the simultaneous depression of all three cell types, occurs and is accompanied by bone marrow necrosis, the syndrome is called aplastic anemia. In addition to observing this decrease in humans and relating it to benzene exposure, it has been possible to establish animal models which mimic the human disease. The result has been considerable scientific investigation into the mechanism of benzene toxicity. Although the association between benzene exposure and aplastic anemia has been recognized and accepted throughout most of this century, it is only recently that leukemia, particularly of the acute myelogenous type, has been related to benzene. The acceptance of benzene as an etiological agent in aplastic anemia in large measure derives from our ability to reproduce the disease in most animals treated with sufficiently high doses of benzene over the necessary time period. Unfortunately, despite extensive efforts in several laboratories, it has not been possible to establish a reproducible, reliable model for the study of benzene-induced leukemia. The recent demonstration that several animals exposed to benzene either by inhalation or in the drinking water during studies by Drs. B. Goldstein and C. Maltoni suggests that such a model may be forthcoming. Nevertheless, at this time it is not clear whether bone marrow damage of the type that leads to aplastic anemia is required for the development of leukemia. Most studies of benzene toxicity have involved dosing animals with benzene either by inhalation or by injection, using high doses to ensure a toxic response. Very few studies have concentrated on the oral route of administration and none have concentrated on administering benzene by mouth at the low doses occasionally detected in drinking water.(ABSTRACT TRUNCATED AT 400 WORDS)

Possible ethnic difference in toluene metabolism: a comparative study among Chinese, Turkish and Japanese solvent workers

Toluene metabolism was studied in 192 Chinese workers in comparison with that in 130 Japanese and 17 Turks. Time-weighted average concentrations of toluene in the breathing zone of workers were measured utilizing passive dosimeters, and hippuric acid (HA) and omicron-cresol (omicron C) concentrations in shift-end spot urine samples by high-performance liquid chromatography (HPLC) and gas chromatography (GC), respectively. Under similar exposure conditions, male Japanese excreted almost twice as much HA as male Chinese, although such difference was less marked between female Chinese and Japanese. In contrast, the excretion of oC did not differ between the two ethnic groups. The ratio of oC over HA was highest among Turkish workers followed by Chinese, and lowest among Japanese. Possible roles of differences in toxicogenetics as well as in life patterns were discussed.

Correlation between the induction of micronuclei in bone marrow by benzene exposure and the excretion of metabolites in urine of CD-1 mice

Male and female CD-1 mice received single oral doses of benzene (220, 440, and 880 mg/kg) and were pretreated with modifiers of the mixed-function oxidase enzyme activities. Urinary metabolites (MT) (0-24 and 24-48 hr) were quantified by high-performance liquid chromatography. The micronucleus test was performed at 30 h. The following pretreatments were used to correlate micronucleus formation and the excreted benzene MT: 3-Methylcholanthrene and beta-naphthoflavone led to a marked increase in micronuclei (MN) and MT, whereas phenobarbital caused a slight increase, and SKF-525A had no effect. MN and MT were decreased when benzene was administered by the ip route or toluene was given simultaneously. Females had a lower number of MN and excreted more unconjugated phenol than did males. Muconic acid, hydroquinone, and phenol glucuronide and MN correlated well. They were dependent on both the dose and route of administration of benzene, being most inducible by P-448 inducers, in males more than females. The administration of hydroquinone induced MN, but phenol or catechol (200, 250, and 150 mg/kg, po, respectively) did not, and none of these compounds yielded trans, trans-muconic acid, a benzene MT in urine. This study establishes that benzene myeloclastogenicity is a function of its metabolism and that quantification of urinary metabolites could provide reliable correlates of this effect in vivo.

A comparative study of the effects of benzene, toluene, and xylenes on their in vitro metabolism and drug-metabolizing enzymes in rat liver

Male Sprague-Dawley rats were injected ip with benzene, toluene, or a mixture of xylene isomers at 20 mmol hydrocarbon/kg daily for 3 days. The effects of administration of these hydrocarbons upon their own in vitro metabolism, as well as upon cytochrome P-450, NADPH-cytochrome c reductase, aminopyrine N-demethylase, aniline hydroxylase, glutathione, glutathione S-transferase, and UDPglucuronyltransferase in liver were studied. Each hydrocarbon studied increased its own in vitro metabolism. Benzene had no effect on the metabolism of toluene or xylenes. Toluene and xylenes increased the metabolism of benzene, toluene, and xylenes. Cytochrome P-450 was elevated by toluene and xylenes, but was not affected by benzene. NADPH-cytochrome c reductase was induced by all three hydrocarbons. Aminopyrine N-demethylase and aniline hydroxylase were induced by toluene and xylenes and were not affected by benzene. Glutathione was elevated by benzene, decreased by xylenes, and not affected by toluene. Glutathione S-transferase was induced differentially by these hydrocarbons toward various substrates: toward 1-chloro-2,4-dinitrobenzene by benzene and toluene, toward 1,2-dichloro-4-nitrobenzene by benzene and xylenes, and no effect toward 1,2-epoxy-3-(p-nitrophenoxy)propane by any hydrocarbons. UDPglucuronyltransferase was induced by benzene and toluene when o-aminophenol and phenol were used as the substrate. Xylenes had no effect. Benzene was more effective at inducing conjugation enzymes. Xylenes were more effective at inducing cytochrome P-450 dependent enzymes. Toluene was equipotent at inducing both types of enzymes. The results indicate that the addition of methyl groups to the aromatic ring affects the inductive pattern of these monocyclic aromatic hydrocarbons.

Effects of ethanol and phenobarbital administration on the metabolism and toxicity of benzene

Effects of ethanol- and phenobarbital(PB)-treatment on the metabolism of benzene in vitro and in vivo, and on the benzene-induced hemotoxicity, were investigated. Ethanol consumption markedly enhanced in vitro metabolism of both benzene and phenol in rat liver, whereas PB-treatment, which enhanced the metabolism of phenol to some degree (about one-third of ethanol-induced enhancement), did not affect the metabolism of benzene. In a single exposure experiment with rats, ethanol increased benzene metabolism in vivo as evidenced by accelerated disappearance of benzene from the blood as well as by elevated urinary excretion of phenol, whereas PB produced little or no significant influence on the metabolism. In a 3-week exposure experiment, ethanol administration accelerated benzene disappearance from the blood in agreement with the single exposure experiment, but it tended to decrease urinary phenol excretion with repetition of exposure, probably due to concomitant stimulation of subsequent phenol metabolism by ethanol. Again, PB-treatment produced only a negligible effect on the metabolism of benzene. Ethanol consumption aggravated benzene-induced hemopoietic disorder as evidenced by a marked decrease in the peripheral white blood cell number. PB produced a protective effect on the toxicity. It is concluded that ethanol potentiates benzene toxicity by accelerating (1) hydroxylation of benzene, a rate-limiting step of benzene metabolism and (2) transformation of phenol into highly toxic metabolites.

Effects of disulfiram on the oxidation of benzaldehyde and acetaldehyde in rat liver

The in vitro oxidation of benzaldehyde and acetaldehyde was studied in liver samples from disulfiram-treated and control rats. With 25 microM substrate, both cytosol and mitochondria appeared to make a nearly equal contribution to the oxidation of benzaldehyde, whereas ca. 90% of acetaldehyde oxidation occurred in mitochondria. When the Km values for benzaldehyde with aldehyde dehydrogenase (ALDH) were determined, two Km values (3 and 120 microM) were obtained with mitochondria, but only a single Km value (25 microM) was obtained with the cytosolic fraction. The relatively high Km (2.9 mM) found with microsomes makes it unlikely that microsomes are important in the oxidation of benzaldehyde. In intact mitochondria, with 200 microM acetaldehyde or benzaldehyde the matrix space enzyme accounted for 77 and 62%, respectively, of the total ALDH activity. When the activity was determined in a mixture containing both substrates, the activity was found not to be additive, indicating that both substrates are oxidized by the same matrix space enzyme. With subcellular fractions, from livers of disulfiram-treated and control rats, a greater degree of inhibition of ALDH was obtained when acetaldehyde was a substrate compared to that with benzaldehyde in cytosol and mitochondria. Microsomal ALDH was not inhibited by disulfiram. In liver slices from rats given disulfiram, a statistically significant inhibition was found when either 25 or 250 microM acetaldehyde was used (46 and 33%). With benzaldehyde, a significant inhibition (24%) was observed only with the lower substrate concentration. Finding that both mitochondrial fractions and slices were less inhibited at the higher substrate concentration implies that the high Km enzyme is not inhibited. It can be concluded that, in rat, disulfiram inhibiting liver ALDH not only affects oxidation of acetaldehyde, but also that of benzaldehyde.

Coexposure to toluene and p-xylene in man: central nervous functions

Sixteen men were studied in an exposure chamber to assess the effect of four hours' exposure to toluene (3.25 mmol/m3), xylene (2.84 mmol/m3), a mixture of toluene and xylene (2.20 + 0.94 mmol/m3), and a control condition. With the aid of microcomputers, subjects performed tests of simple reaction time, short term memory, and choice reaction time immediately after entering the chamber, after two, and after four hours' exposure. The results indicate that the performance on the tests was unaffected by exposure. In the light of this result the risk of an acute effect on central nervous functions after exposure for four hours at concentrations that do not exceed the Swedish threshold limit values was considered to be minimal.

Enhanced metabolism of volatile hydrocarbons in rat liver following food deprivation, restricted carbohydrate intake, and administration of ethanol, phenobarbital, polychlorinated biphenyl and 3-methylcholanthrene: a comparative study

The effects of food deprivation, carbohydrate restriction and ethanol consumption on the metabolism of eight volatile hydrocarbons (benzene, toluene, styrene, chloroform, carbon tetrachloride, 1,2-dichloroethane, 1,1-dichloroethylene and trichloroethylene) in rats were compared with the effects of enzyme induction by phenobarbital (PB), polychlorinated biphenyl (PCB) and 3-methylcholanthrene (MC) on the metabolism of these compounds. Although causing a marked increase both in microsomal protein and cytochrome p-450 contents, PB (80 mg/kg per day for three days) and PCB (a single dose of 500 mg/kg) induced only a limited range of enzyme activity: PB increased the metabolism of toluene, styrene, chloroform, carbon tetrachloride and trichloroethylene, and PCB only increased those of toluene, styrene and trichloroethylene. MC (20 mg/kg per day for three days) had no effect on the metabolism of any of the hydrocarbons studied. In contrast, food deprivation, carbohydrate restriction and three-week ingestion of ethanol (2.0 g/day), each enhanced the metabolism of all the hydrocarbons with little or no increase in microsomal protein and cytochrome P-450 contents. PB, PCB and MC treatments enhanced the activity of enzymes involved in conjugation reactions, UDP-glucuronyltransferase and glutathione S-transferase, whereas the dietary manipulation and ethanol consumption produced no significant effect on these enzymes. It is concluded that ethanol consumption. lowered carbohydrate intake and food deprivation affect the metabolism and toxicity of volatile hydrocarbons differently from PB, PCB or MC.

Benzene myeloclastogenicity: a function of its metabolism

Using the micronucleus test we have found no significant difference between germ-free and conventional (non-germ-free) male CD-1 mice gavaged twice with 440 or 880 mg benzene/kg. Hence, the higher myeloclastogenicity observed previously with the p.o. (4-6 times) than with the i.p. route of benzene administration was ruled out as being due to the involvement of gut flora in benzene biotransformation. Pretreatment of males with 3-methylcholanthrene or beta-naphthoflavone, inducers of P-448 monooxygenase, but not phenobarbital, an inducer of P-450, significantly enhanced the myeloclastogenic effect of a single oral dose of benzene (440 mg/kg). Single oral doses of phenol, catechol, or hydroquinone (250, 150, and 200 mg/kg, respectively) failed to reproduce the potent myeloclastogenic effect of benzene. In fact, only hydroquinone was mildly clastogenic. The relation between benzene's myeloclastogenicity and metabolism is discussed.

The effects of ethanol on the kinetics of toluene in man

Eleven men were exposed in an exposure chamber to toluene vapor (3.2 mmol/m3, 4.5 hr) with and without a simultaneous po intake of ethanol (15 mmol/kg body wt). The ethanol was administered 70 to 85 min after the onset of the toluene exposure to achieve maximum concentrations of toluene and ethanol in blood at the same time. During the exposure period the solvent concentrations in inspired and expired air as well as the pulmonary ventilation were determined. The solvent concentrations in blood were measured during and for 3 hr after the exposure period. No effect of ethanol on the pulmonary ventilation could be seen during the exposure period. Ethanol decreased the total uptake as well as the relative uptake of toluene. The maximum toluene concentration in the blood increased from 7.4 to 12.5 mumol/liter in the presence of ethanol and apparent clearance of toluene decreased significantly. Toluene exerted no effect on the uptake and elimination of ethanol in blood. The results indicate an influence of a moderate dose of ethanol on the kinetics of toluene. The distribution and/or elimination of toluene from the blood was inhibited resulting in increased tissue exposure.

Increased o- and p-cresol/hippuric acid ratios in the urine of four strains of rat exposed to toluene at thousands-ppm levels

Rats (Fisher, Wistar, Donryu and Sprague-Dawley strains) were exposed to 5 approximately 3500 ppm toluene for 8 h, and urine samples were analyzed for hippuric acid and cresols. While hippuric acid increased in proportion to the exposure concentration, a sharp increase in o-cresol excretion was observed at high toluene concentrations so that the o-cresol/hippuric acid ratio was elevated after 500 approximately 3500 ppm exposures. Changes in the p-cresol: hippuric acid ratio were less marked. There were strain differences in toluene metabolism. Fisher rats were highest and Sprague-Dawley rats lowest in o-cresol excretion and in the o-cresol: hippuric acid ratio, whereas Wistar rats excreted p-cresol most abundantly.

The influence of simple aromatics on benzene clastogenicity

The micronucleus test was performed in male ICR Swiss mice following modification of benzene metabolism by co-administration of aniline, pyridine or naphthalene, or by prior injection of alpha-naphthoflavone. HPLC profiles of urinary metabolites were compared to the effects of these compounds on clastogenicity. Pyridine inhibited both benzene clastogenicity and its metabolism. Aniline and naphthalene increased the clastogenicity and slightly altered the metabolism of benzene. alpha-Naphthoflavone inhibited benzene clastogenicity and metabolism only at high doses. Since 3-methylcholanthrene and phenobarbital both increase the metabolism of benzene but only 3-methylcholanthrene increases benzene clastogenicity, specific P450 isozymes may be responsible for different biological effects of benzene, and alterations in these effects might be caused by a shift from one isozyme to another.

Involvement of iron and free radicals in benzene toxicity

The 59Fe distribution after a single i.v. injection of 59Fe citrate in rats exposed to benzene was studied in circulating erythrocytes and organs up to period of 1 hr to 14 days. The iron content was significantly higher in bone marrow and liver compared to a control group of animals. A few cells with hemosiderin granules were observed in the benzene-administered group. Benzene increased lipid peroxidation in the liver and bone marrow and iron accelerated it further. Superoxide dismutase activities measured in terms of epinephrine auto-oxidation, an indirect measure of superoxide anion generation was enhanced in the benzene-treated groups. The data suggest the involvement of oxygen activation in benzene toxicity.

Modifications in the myeloclastogenic effect of benzene in mice with toluene, phenobarbital, 3-methylcholanthrene, Aroclor 1254 and SKF-525A

Benzene was studied in its target organ of effect, the bone marrow, with the micronucleus test and metaphase analysis. Male and female CD-1 mice were treated with 2 doses of benzene (440 mg/kg) or toluene (860 or 1720 mg/kg) or both 24 h apart, and sacrificed 30 h (or 54 h) after the first dose. Benzene-treated animals were pretreated with phenobarbital (PB), 3-methylcholanthrene (3-MCA), SKF-525A, or Aroclor 1254. Toluene showed no clastogenic activity and reduced the clastogenic effect of benzene when the mixture was given. None of the pretreatments protected against the clastogenic effect of benzene. 3-MCA pretreatment greatly promoted benzene myeloclastogenicity. Females were consistently more resistant to benzene than males. Dose-response curves in benzene-treated mice were much steeper with 3-MCA induction than without. Chromosomal damage was higher with p.o. than i.p. benzene administration.

Effects of pretreatment with toluene, phenobarbital and 3-methylcholantrene on the in vivo metabolism of toluene and on the excretion of hippuric acid in the rat

The limit of the capacity of male adult Sprague-Dawley rats to metabolize toluene and excrete it as hippuric acid was reached at a dose of 10 mmol toluene/kg. At this dose of benzoic acid or hippuric acid, the excretion of hippuric acid was 1.5-fold and 4-fold, respectively, greater than that following this dose of toluene. When toluene was given after phenobarbital pretreatment the excretion rate of hippuric acid increased 3-4-fold, but 3-methylcholanthrene pretreatment had no effect. Consecutive toluene exposures increased hippuric acid excretion on the third day by about 2-fold. It seems that the side-chain oxidation is the rate-limiting step in toluene metabolism of uninduced rats, and toluene accelerates its own metabolism by inducing cytochrome P-450 dependent microsomal monooxygenases.

[Problems in the biological monitoring of benzene exposure]

The biological monitoring of workers exposed to benzene containing mixtures by phenol analysis in urine is complicated by the facts that varying amounts of phenolic compounds are also produced by other precursors than benzene and that coexposure with other chemicals can cause interactions in metabolism and elimination rates. In order to overcome these difficulties it is proposed a) to abandon the colorimetric methods and to use only gas chromatography as a standard and reference method, b) as an overall monitoring concept always to determine phenol pre-exposure values as well as the cresol and creatinine concentrations in urine, and to combine biological monitoring whenever possible with personal air sampling.

Effects of xylene exposure on the metabolism of antipyrine in vitro and in vivo in the rat

Exposure of male rats to different concentrations of xylene for 3 days induced, in a dose-dependent way, the in vitro liver microsomal metabolism of antipyrine. The degree of induction was statistically significant at an exposure level of 250 ppm and maximal (2.5-fold increase) at 2000 ppm. This increase was of the same magnitude as after phenobarbital treatment. Female rats had a lower basal antipyrine metabolism than males, but exhibited a greater relative increase in antipyrine metabolism following xylene exposure. Cytochrome P-450 isozymes, purified from xylene- and phenobarbital-treated animals, were efficient catalysts of antipyrine metabolism, with turnover numbers of 33.3 and 21.1, respectively. A reduction in the half-life of antipyrine to 39% of preexposure values occurred after exposure of male rats to 1000 ppm of xylene for 3 days. Exposure to lower xylene levels did not produce significant alterations in antipyrine elimination half-life. In vitro, xylene was shown to be a non-competitive metabolic inhibitor of antipyrine. Experiments in vivo indicated that inhibition is not important at relatively low xylene exposure levels. It is concluded that induction of hepatic monooxygenases by xylene can be demonstrated, with antipyrine as a test drug, both in vitro and in vivo.

Dose dependent induction of rat liver microsomal cytochrome P-450 and microsomal enzymatic activities after inhalation of toluene and dichloromethane

Sprague-Dawley rats were exposed, by inhalation, to toluene and dichloromethane (500, 1,500 or 3,000 p.p.m.) and to benzene (1,500 p.p.m.) for three days. Toluene and benzene increased the concentration of liver microsomal cytochrome P-450. A dose dependent increase in the in vitro liver microsomal formation of several metabolites of biphenyl and benzo(a)pyrene was observed for both dichloromethane and toluene. At the highest dose-level the increase in the vitro formation of benzo(a)pyrene-7,8-dihydrodiol was more than three-fold for both dichloromethane and toluene whereas the formation of benzo(a)pyrene-4,5-dihydrodiol increased more than five-fold following exposure to toluene but less than two-fold after exposure to dichloromethane. Our results suggest that dichloromethane and toluene can modify the metabolism and thereby the toxicity of other environmental contaminants.

Effect of phenobarbital pretreatment on benzene biotransformation in the rat. II. 9,000 g supernatant and isolated perfused liver versus living rat

Factors responsible for different quantitative effect of phenobarbital (PB) pretreatment (sodium phenobarbital, 50 mg kg-1 day-1 for 3 days) on benzene metabolism to phenol in vivo and in vitro were studied in male Wistar rats. A more than 4-fold increase of benzene metabolism was observed wih 9,000 g supernatant of liver homogenate, 2.8- to 4-fold increase with isolated perfused liver; phenol formation in vivo after oral benzene was increased by PB 2-fold, but only shortly following benzene administration and the enhancement rapidly diminished to 1.15-fold increase in the total excreted phenol. Benzene concentrations i 9,000 g supernatant incubations were 2 mM, those with isolated perfused livers were up to 4 mM, but those in blood in vivo were below 0.3 mM; the effect of PB induction in vivo disappeared along with decreasing benzene and increasing phenol blood concentrations which surpassed benzene 2-3 h after oral benzene administration. The effect of benzene concentration on the manifestation of PB induction is also supported by almost a 2-fold increased phenol formation in PB rats over controls in vivo after repeated administration of benzene. The elimination of radioactive metabolites of orally administered benzene-14C, 3 mmoles kg-1, in urine was markedly inhibited by intraperitoneal administration of phenol (1.2 mmol kg-1), but not by pyrocatechol, resorcinol or hydroquinol (0.6 mmole kg-1, respectively) suggesting that phenol might inhibit benzene metabolism in vivo especially when its concentration exceeds that of benzene.

Modulation of benzene-induced lymphocytopenia in the rat by 2,4,5,2',4',5'-hexachlorobiphenyl and 3,4,3',4'-tetrachlorobiphenyl

Repeated administration of benzene (440 mg/kg/day, s.c.) to 6-week-old male Fischer-344 rats resulted in a progressive decline in the number of circulating lymphocytes. Pretreatment of these animals with 2,4,5,2',4',5'-hexachlorobiphenyl (HCB) or 3,4,3',4'-tetrachlorobiphenyl (TCB) protected against benzene toxicity for as long as 7 days, but not after 10 days of repeated dosing. Representative phase I (mixed-function oxidase) and phase II (conjugating) enzyme activities were measured to determine whether the altered susceptibility to benzene toxicity in TCB- and HCB-pretreated rats could be correlated with changes in the profile of hepatic oxidative and detoxification pathways. Measurement of 7-ethoxycoumarin O-deethylase and benzphetamine N-demethylase activities indicated that the loss of protection by HCB or TCB against benzene toxicity after 7 days was not associated with changes in the activities of hepatic mixed-function oxidases inducible by 3-methylcholanthrene or phenobarbital. The time course for the stimulation by TCB and return to control values, of UDP-glucuronosyl transferase activity, a potential route for the elimination of benzene metabolites, mirrored the time course for the protection against toxicity. Epoxide hydratase activity was induced 2- to 3-fold by HCB. Although stimulation of this pathway could result in a decreased concentration of phenol, this activity did not decline with the loss of protection. Hepatic 10 000 X g supernatant fractions, prepared from livers of rats given TCB, were incubated with a non-saturating concentration of [14C] benzene (equivalent to 19 nmol/mg wet wt. tissue). Under these conditions the metabolism of benzene was depressed (40% of control) 2 days after pretreatment; after 14 days, the metabolism of benzene returned to control values. This pattern correlated temporarily with the protection against lymphocytopenia. The data indicate that the protection against benzene toxicity in rats pretreated with HCB or TCB is not necessarily related to the capacity of these compounds to induce phase I activities. In rats pretreated with TCB, the data suggest that decreasing the concentration of primary benzene metabolites, either by inhibiting the hepatic metabolism of benzene or increasing hepatic conjugation activity is an important factor modulating toxicity.

Different role of biotransformation in the elimination of some important pharmaceuticals and industrial xenobiotics

Unlike lipophilic pharmaceuticals, many lipophilic industrial xenobiotics may be excreted unchanged due to their volatility. Consequently, enzyme induction of inhibition may thus affect only the rate of metabolism of the lipophilic drugs, whereas in case of volatile xenobiotics it is both the rate and the extent (metabolized portion) of their biotransformation which are influenced by these processes. The influence of these metabolic changes on the rate of elimination is more pronounced in lipophilic pharmaceuticals than in volatile xenobiotics whose alternative elimination via lungs compensates for the metabolic rate differences.

Partial hepatectomy reduces both metabolism and toxicity of benzene

Removal of 70--80% of the liver reduced both the metabolism and the toxicity of benzene in rats. Metabolism was evaluated by measuring the levels of urinary metabolites in both sham-operated and partially hepatectomized rats given 2200 mg/kg [3H]benzene sc. Toxicity was evaluated by measuring the incorporation of 59Fe into circulating erythrocytes according to the method of Lee et al. The observation that partial hepatectomy decreases benzene metabolism and protects against benzene toxicity indicates that the liver may play a primary role in the development of benzene-induced bone marrow toxicity. The fact that benzene administration also reduces the ability of the liver to regenerate after partial hepatectomy suggests that the regenerating liver may serve as a model system in lieu of the bone marrow for studying the mechanism by which benzene inhibits cell proliferation.

Distribution of Fe59 in benzene and iomex treated rats

The distribution of Fe59 in plasma and blood at various time intervals has been studied in control, benzene and iomex administered, and anemic rats. A significant difference between control and benzene, and iomex treated animals was observed in the rate of reappearance of Fe59 in blood circulation. The accumulation of Fe59 in various organs was noted at the end of 48 h. A significant increase in the radio-iron content was observed in bone marrow, spleen and liver of benzene and iomex treated rats as compared to those of control rats.

Effects of subacute toluene inhalation on its metabolism and disposition in rat

Exposure of adult male rats to 300 ppm of toluene for 1 to 15 weeks 6 h daily caused accumulation of the solvent in brain and in perirenal fat. The body solvent content tended to decrease during extended exposure which might be explained by the enhanced activity of drug-metabolizing enzymes in liver. Our findings also indicate that metabolic and functional adaptation takes place in longer exposures to low levels of toluene vapour.

Histochemical and histoenzymatic changes in mouse liver in subacute benzene intoxication

The investigations were performed on mice. They were divided into a control group and 4 experimental groups. The experimental animals were administered intraperitoneally benzene 6 X every 24 h. The animals were decapitated 30 min. 4, 12 and 24 h after the last benzene administration. During the experiment, dyeing for neutral lipids and glycogen was carried out, and the activity of NADH2-r.t., SDH, G-6-Pase, ATP-ase and ACP was estimated. A decrease of glycogen content in liver cells, deviations in the amount of neutral lipids, reversible decrease of mitochondrial enzymes activity, and intensification of the processes of intracellular catabolism were found.