Hematotoxic Effects Research Articles

A Correlative Study on Red Blood Cell Parameters and Urine Trans, Trans-Muconic Acid in Subjects with Occupational Benzene Exposure

Benzene is of particular concern because of recent research indicating that benzene exposure can result in toxicity. The hematotoxic effect of benzene is mentioned. However, there is little knowledge about the correlation between the biomarker of benzene exposure and changes in red blood cell parameters. Here, the correlation between the urine trans, trans-muconic acid (ttMA) level and red blood cell parameters were studied in 30 Thai subjects at risk. The regression analysis shows no significant correlation between urine ttMA and any studied red cell parameters (Hb, MCV or MCH). Based on our hematologic data, we proposed that only investigation for the urine ttMA might be not sufficient in detection of alteration in red blood cell parameters in the exposed population. Combinations between biomarker and hematological test are recommended.

Biological properties of low molecular mass peptide dendrimers

A series of new, low molecular mass, lysine-based peptide dendrimers with varying distribution of cationic and aromatic groups in the structure were synthesized. They expressed antimicrobial activity against Gram-positive ( Staphylococcus aureus) and Gram-negative ( Escherichia coli) bacteria as well as against fungal pathogens ( Candida albicans). Their cytotoxic, haematotoxic, and genotoxic effects were studied. It appears that degree of branching and steric distribution and types of hydrophobic (aromatic) groups and cationic centres are important components of dendrimeric structure and influence both antimicrobial potency and toxicity. Such 3D structure of our dendrimers mimics that of the natural antimicrobial peptides and can be achieved by application of dendrimer chemistry.

Benzene metabolites block gap junction intercellular communication: Role in hematotoxicity and leukemia?

A metabolite of benzene, trans, trans-muconaldehyde (MUC) was found to be a strong inhibitor of gap junction intercellular communication (GJIC) with potency similar to that of chlordane. Hydroquinone and the MUC metabolite OH–M–CHO were also strong inhibitors of GJIC. The other MUC metabolites tested, CHO–M–COOH and OH–M–COOH had weak effects on GJIC, while COOH–M–COOH had no effect. Benzene showed no effect on GJIC. The relative potency of the metabolites on GJIC is similar to what is observed with regard to hematotoxic effects. The effect of MUC on GJIC took place in parallel with a strong cellular loss of connexin 43. Substances found to inhibit connexin 43 dependent GJIC have been shown to disrupt normal hematopoietic development. The finding that benzene metabolites interfere with gap junction functionality, and especially the loss of connexin 43 induced by MUC, should be considered concerning the mechanism of benzene-induced hematotoxicity.

Metabolites of benzene are potent inhibitors of gap-junction intercellular communication

Chronic exposure to benzene has been shown to lead to bone marrow depression and the development of leukemia. The mechanism underlying the carcinogenicity of benzene is unknown, although a number of genetic changes including chromosomal aberrations have been associated with benzene toxicity. Metabolism of benzene is required for the induced toxicological effects. We have investigated the effect of trans,trans-muconaldehyde (MUC), hydroquinone (HQ), and four MUC metabolites on gap-junction intercellular communication (GJIC). Inhibition of GJIC has been considered a possible predictor of tumor promoters and non-genotoxic carcinogens, and shown to result in perturbation of hematopoiesis. MUC was found to be a strong inhibitor of GJIC (EC50=12 micromol L(-1)) in rat liver epithelial cells IAR20, with potency similar to that of chlordane (EC50=7 micromol L(-1)). HQ inhibited GJIC with an EC50 of 25 micromolmol L(-1), and the metabolite OH/CHO with an EC50 of 58 micromol L(-1). The other MUC metabolites tested, CHO/COOH and OH/COOH were weak inhibitors of GJIC whereas COOH/COOH had no effect. Benzene itself had no effect on GJIC when tested in concentrations up to 20 micromol L(-1). The relative potency observed for the metabolites on GJIC is similar to their hematotoxic effects. The effect of MUC on GJIC was observed to take place concordant with a dramatic loss of connexin 43 (Cx43) from the cells as visualized by Western blotting. Substances with the ability to inhibit Cx43-dependent GJIC have previously been observed to interfere with normal hematopoietic development. The ability of benzene metabolites to interfere with gap-junction functionality, and especially the dramatic loss of Cx43 induced by MUC, should therefore be considered as a possible mechanism for benzene-induced hematotoxicity and development of leukemia.

Genotoxic Activities of Aniline and its Metabolites and Their Relationship to the Carcinogenicity of Aniline in the Spleen of Rats

Aniline (in the form of its hydrochloride) has been shown to induce a rather rare spectrum of tumors in the spleen of Fischer 344 rats. The dose levels necessary for this carcinogenic activity were in a range where also massive effects on the blood and non-neoplastic splenotoxicity as a consequence of methemoglobinemia were to be observed. This review aimed at clarifying if aniline itself or one of its metabolites has a genotoxic potential which would explain the occurrence of the spleen tumors in rats as a result of a primary genetic activity. The database for aniline and its metabolites is extremely heterogeneous. With validated assays it ranges from a few limited Ames tests (o- and m-hydroxyacetanilide, phenylhydroxylamine, nitrosobenzene) to a broad range of studies covering all genetic endpoints partly with several studies of the same or different test systems (aniline, p-aminophenol, p-hydroxyacetanilide). This makes a direct comparison rather difficult. In addition, a varying number of results with as yet not validated systems are available for aniline and its metabolites. Most results, especially those with validated and well performed/documented studies, did not indicate a potential of aniline to induce gene mutations. In five different mouse lymphoma tests, where colony sizing was performed only in one test, aniline was positive. If this indicates a peculiar feature of a point mutagenic potential or does represent a part of the clastogenic activity for which there is evidence in vitro as well as in vivo remains to be investigated. There is little evidence for a DNA damaging potential of aniline. The clastogenic activity in vivo is confined to dose levels, which are close to lethality essentially due to hematotoxic effects. The quantitatively most important metabolites for experimental animals as well as for humans (p-aminophenol, p-hydroxyacetanilide) seem to have a potential for inducing chromosomal damage in vitro and, at relatively high dose levels, also in vivo. This could be the explanation for the clastogenic effects that have been observed after high doses/concentrations with aniline. They do not induce gene mutations and there is little evidence for a DNA damaging potential. None of these metabolites revealed a splenotoxic potential comparable to that of aniline in studies with repeated or long-term administration to rats. The genotoxicity database on those metabolites with a demonstrated and marked splenotoxic potential, i.e. phenylhydroxylamine, nitrosobenzene, is unfortunately very limited and does not allow to exclude with certainty primary genotoxic events in the development of spleen tumors. But quite a number of considerations by analogy from other investigations support the conclusion that the effects in the spleen do not develop on a primary genotoxic basis. The weight of evidences suggests that the carcinogenic effects in the spleen of rats are the endstage of a chronic high-dose damage of the blood leading to a massive overload of the spleen with iron, which causes chronic oxidative stress. This conclusion, based essentially on pathomorphological observations, and analogy considerations thereof by previous authors, is herewith reconfirmed under consideration of the more recently reported studies on the genotoxicity of aniline and its metabolites, on biochemical measurements indicating oxidative stress, and on the metabolism of aniline. It is concluded that there is no relationship between the damage to the chromosomes at high, toxic doses of aniline and its major metabolites p-aminophenol/p-hydroxyacetanilide and the aniline-induced spleen tumors in the rat.

Decrease in brain serotonin level and short term memory loss in mice: a preliminary study

Most of the information on the effects of benzene center around its hematotoxic and genotoxic effects. However, its effect on central neurotransmitters is inconclusive in terms of cognitive behavior of the host. The present results showed for the first time that chronic exposure to benzene, in drinking water, significantly inhibited serotonin (5-hydroxytryptamine (5-HT)) level in serotonergic neuron rich regions of the murine brain. This was paralleled with loss of short term memory, as evidenced by passive avoidance test, of the benzene treated animals.

A computational model of human granulopoiesis to simulate the hematotoxic effects of multicycle polychemotherapy

AbstractModerate intensification of conventional multicycle chemotherapy has recently been shown to improve treatment results in malignant lymphomas and might prove to be beneficial also in other malignancies. However, the feasibility of such regimens is mainly limited by their granulopoietic toxicity. To identify and quantify the basic cell kinetic mechanisms of damage and stimulation caused by cytotoxic drugs and recombinant human granulocyte colony-stimulating factor (rhG-CSF), respectively, we developed a mathematical model of human granulopoiesis that allows simulation of leukocyte concentration profiles under 10 different multicycle polychemotherapy regimens with varying drug composition, dosage, and scheduling, including rhG-CSF assistance. Clinical data on leukocyte profiles were obtained from large numbers of patients treated within several multicenter trials. Simulation studies show that the leukocyte profiles of all regimens can be appropriately fitted using one single set of assumptions and parameters for the cell kinetic effects of cytotoxic drugs and rhG-CSF. Furthermore, the model can be used to explain the interindividual heterogeneity of hematotoxicity by a differential chemosensitivity, which might be useful in drug scheduling for specific risk groups. It is demonstrated that the model can be used to design and to select new drug schedules for subsequent clinical trial testing.

S20.1: A biomathematical model of human granulopoiesis to simulate the hematotoxic effects of polychemotherapy

S20.1: A biomathematical model of human granulopoiesis to simulate the hematotoxic effects of polychemotherapy

Biomonitoring of aromatic amines VI: determination of hemoglobin adducts after feeding aniline hydrochloride in the diet of rats for 4 weeks.

The assessment of the carcinogenic properties of aniline is still controversial. Aniline has, if at all, genotoxic properties but is also acutely toxic and it has been proposed that the hematotoxic effects are responsible for the formation of hemangiosarcomas and fibrosarcomas in the spleen of male rats. As part of a bigger project in which the pathology of male Fischer F344 rats was studied after feeding 10, 30, or 100 mg/kg body weight aniline hydrochloride for 1 and 4 weeks in the diet, the aniline-hemoglobin (Hb) adducts were determined as a biochemical effect marker during those periods. An improved method for the work-up procedure and the adduct analysis was developed for this purpose. The Hb adduct levels increased proportionately with dose after 1 week, which indicates that metabolic activation was not saturated. After 4 weeks of feeding, the adduct levels increased less than proportionately, which suggests that a saturation process is involved. Since it is unlikely that metabolic activation was saturated, the results could be explained by a more rapid clearance of stressed erythrocytes at the carcinogenic dose level. The latter interpretation is supported by other observations which indicate that erythrocytes are damaged dose dependently. A no-observed-effect level (NOEL) has not been reached but could be close to the low dose of 10 mg/kg body weight per day. The Hb adduct formation at the low dose, however, indicates that this should not be considered a no-effect level (NEL). The results support the conclusion that hemolytic anemia is an essential prerequisite for aniline toxicity and tumor development, but they do not fully explain the tissue specificity.

Rapid suppression of hematopoiesis by standard or pegylated interferon-α

Background & Aims: Treatment of chronic hepatitis C with interferon (IFN)-α often has hematotoxic effects. We evaluated the effects of acute vs. chronic and standard vs. pegylated IFN-α on hematopoiesis. Methods: We studied hematopoiesis in 46 patients with chronic hepatitis C receiving single high-dose IN-Fα2b followed by daily dose standard or weekly pegylated IFN before combination antiviral therapy. Results: Single high-dose therapy resulted in a significant drop in hemoglobin (HB), leukocytes, and platelet count. Although platelets, stimulated by a significant increase in thrombopoietin (TPO), and leukocytes recovered quickly, HB remained below baseline for 7 days. Daily standard or weekly pegylated IFN-α leads to a more pronounced drop in all 3 lineages with concomitant increases in TPO and erythropoietin (EPO). No difference was observed between standard and pegylated IFN, except for HB, which fell more during pegylated IFN therapy. Consecutive combination antiviral therapy aggravated the anemia but not the drop in leukocytes or thrombocytes. Conclusions: The drop in all 3 hematopoietic lineages through IFN-α treatment, high-dose standard, standard daily dose, or pegylated, is caused by a combination of bone marrow inhibition and probably some other rapid acting mechanisms. Hematopoietic growth factors are increased as a consequence but cannot overcome the bone marrow suppression.GASTROENTEROLOGY 2002;123:141-151

In vitro toxicity of ET-743 and aplidine, two marine-derived antineoplastics, on human bone marrow haematopoietic progenitors: comparison with the clinical results

Ecteinascidine-743 (ET-743) and aplidine are two marine-derived antineoplastics currently in phase II development. With the aim of evaluating whether in vitro haematopoietic studies can predict the toxicity of these two drugs in patients, human bone marrow (BM) samples were incubated with these drugs under conditions which mimicked the administration exposures used in the clinics. As it was observed in different cancer cell lines, ET-743 was more toxic on an equimolar basis in human hematopoietic progenitors (inhibitory concentration reducing the viability to 50% after 24 h exposures; IC5024h: 10–50 nM) compared with doxorubicin (IC5024h values: 280–460 nM), used as a control anticancer drug. In contrast to the high haematotoxic effects observed for ET-743, similar IC values were obtained for aplidine (IC5024h: 150–530 nM) compared with doxorubicin. For both ET-743 and aplidine, the megakaryocytic progenitor was the most sensitive, compared with the other haematopoietic progenitors (IC50 values were 3- to 5-fold lower in the CFU-Megs compared with the CFU-GMs). The observation that the Cmax observed in patients treated with the aplidine maximum tolerated dose (MTD) (7.1 nM) was 21–75 fold lower than the IC5024h value observed for the different haematopoietic progenitors is highly consistent with the lack of haematotoxicity observed in patients treated with this drug. In the case of ET-743, differences between the Cmax value corresponding to the MTD (2.6 nM) and the in vitro IC50 values corresponding to the different progenitors were much lower (4–19-fold), also consistent with the haematotoxicity that was observed in patients treated at recommended doses (RDs) and MTDs. Although CFU-Megs were more sensitive than CFU-GM progenitors to ET-743 in vitro, clinical data showed that neutropenic events were more frequent than thrombocytopenic episodes. Aiming to further improve the predictive value of in vitro IC values corresponding to the different haematopoietic progenitors, additional refinement parameters derived from pharmacokinetic and animal studies are proposed.

Use of in vitro assays to assess hematotoxic effects of environmental compounds.

The number of chemicals being introduced into the environment increases and many of these substances may pose a health risk to exposed individuals. Many environmental toxicants with a potential toxicity to the hematopoietic system have been identified by animal experiments. Owing to the risks of severe chronic hematopoietic disorders, it is important to screen chemicals for their hematotoxicity. The aim of this work was to identify, through the use of in vitro techniques, targets for hematotoxic effects. Our study focused on myeloid and erythroid hematopoietic progenitors and stromal stem cells as possible targets. The in vitro assays showed that various hematotoxic compounds exert different effects on these cell populations. In vitro exposure of murine bone marrow cells to various inorganic (cadmium, lead) and organic (benzene metabolites, lindane. benzo-[a]-pyrene (BaP), PCB (polychlorinated biphenyl) congeners) environmental chemicals indicated that hematopoietic or stromal bone marrow cells were targets for most of the chemicals. Stromal cells were more affected by lead, cadmium, and BaP compared to myeloid cells. Benzene and phenol gave no response, but the metabolites catechol and hydroquinone were equally toxic to the stromal and the myeloid progenitor cells. Among the PCBs tested, PCB126 was most toxic. Human progenitor cells derived from cord blood were exposed in vitro to catechol, hydroquinone, lead nitrate, and PCBs. Human hematopoietic cells were sensitive to the tested compounds. Human erythroid progenitors are more susceptible to lead exposure than are myeloid progenitors. Based on the in vitro tests, humans are more sensitive to lead, catechol, and PCB126 than are mice. In contrast to the murine data, humans responded with individual differences to lead and PCB126.

The potential role of topoisomerase II inhibition in hydroquinone-induced alterations in the maturation of mouse myeloblasts.

The mechanism by which exposure to the industrial solvent benzene (BZ) can result in aplastic anemia or leukemia (see Snyder and Kalf, 1994 for review) has been under intensive investigation. Topoisomerase (topo) II inhibitors are used clinically as cancer chemotherapeutic agents and can also lead to secondary AML (see Felix, 1998; Leone et al., 1999 for review). Hydroquinone (HQ), a hematotoxic metabolite of BZ, has been shown to inhibit purified human topo II (Hutt and Kalf, 1996; Frantz et al., 1996). It has therefore been suggested that some of the hematotoxic effects of BZ may be mediated by the ability of some of its metabolites to inhibit topo II activity (Whysner, 2000). In the studies presented here a normal, IL-3 dependent mouse myeloblast cell line (32D.3 (G)) was used to determine whether the hematotoxic effects of BZ may result from inhibition of topo II by HQ. The 32D.3 (G) myeloblasts undergo differentiation and maturation to neutrophils upon treatment with the physiological inducer, granulocyte colony-stimulating factor (G-CSF) (Metcalf, 1985; Valtieri et al., 1987). In this system HQ treatment inhibits apoptosis, induces differentiation of myeloblasts to the myelocyte stage, and blocks maturation to the neutrophil (Hazel et al., 1995), a series of events similar to those observed in AML, which is characterized by clonal expansion of immature granulocytes (Lowenberg and Delwel, 1991). There is evidence linking topo II activity to differentiation and maturation in the HL-60, human leukemia cell line. In this system 3-nitrobenzothiazolo[3,2-a]quinolinium, an inhibitor of topo II activity, has been shown to induce incomplete myeloid differentiation (Baez and Sepulveda, 1992).

Hematologic reference ranges in a population of patients with schizophrenia.

The potential hematotoxic effects of antipsychotic drugs are well known and may limit the use of some effective therapies. Although some previous studies have suggested that patients with schizophrenia may have altered "normal" values, only limited data were available. It is now believed that biological values do not usually follow a normal distribution; therefore, reference ranges are frequently used when interpreting laboratory tests in clinical practice and in research. However, it may be important to use disease-specific hematologic reference ranges when evaluating laboratory test results for patients with schizophrenia. In this study, data taken from patients with schizophrenia prior to treatment in previous phase II and phase III pharmaceutical studies were analyzed to produce reference ranges for a variety of hematologic parameters. An increased variability was shown in the reference ranges for all white blood cell indices between patients with schizophrenia and the population without schizophrenia. Certain reference values also showed heterogeneity for gender, age, and racial descent. This study suggests that abnormal hematologic findings in patients with schizophrenia should be assessed in the context of a valid reference range. This information will be of value to psychiatrists, laboratory scientists, and other physicians who encounter hematologic problems in patients with schizophrenia, as well as in the assessment of the adverse effects of new therapeutic agents.

Comparative toxicity of known and putative metabolites of 1,3-butadiene in human CD34 + bone marrow cells

Species-specific susceptibility to the hematotoxic effects of 1,3-butadiene (BD) is well known. Previous studies have revealed that murine bone marrow is uniquely susceptible to toxicity following exposure to the parent compound in vivo or exposure of bone marrow cells to the monoepoxide metabolite, 3,4-epoxybutane, in vitro. Studies described herein compare the relative ability of putative and known BD metabolites to produce concentration dependent suppression of colony formation and cytotoxicity in human CD34 + bone marrow cells. Compounds evaluated included 3,4-epoxybutane, d, l-butane-bis-oxide, meso-butane-bis-oxide and (2S,3R)-3-epoxybutane-1,2-diol. In contrast to results previously observed in mice, only the bis-oxides produced significant suppression of colony formation at potentially relevant concentrations (10 −8 to 10 −3 M). No enantiospecific differences were observed between the meso- and d, l-bis-oxides and no significant lineage-specific differences in susceptibility to inhibition of clonogenic response were observed among early multi-potential myeloid and erythroid hematopoietic progenitor cells. The relative potencies of the bis-oxides were found to be comparable to that of the prototype hematotoxic compound, hydroquinone. These results confirm previous studies that reveal marked species-specific differences in the susceptibility of bone marrow cells to 3,4-epoxybutane. Moreover, these results suggest that the bis-oxides of BD are capable of suppressing the clonogenic function of human hematopoietic progenitor cells, if, in fact, they are produced in human bone marrow in significant concentration. Further interpretation of these findings requires a better understanding of the metabolism of BD in humans.

Hematotoxicity of the chinese herbal medicine Tripterygium wilfordii hook f in CD34-positive human bone marrow cells.

T2, a chloroform/methanol extract of the herb Tripterygium wilfordii Hook f, has been used in China for the treatment of autoimmune and inflammatory diseases for many years. Recent experimental evidence has confirmed that T2 has potent anti-inflammatory and immunosuppressive activity, and a United States Food and Drug Administration-approved clinical trial is currently exploring the efficacy of T2 in the treatment of rheumatoid arthritis. Despite the potential therapeutic benefits of T2, there is ample documentation that T2 is toxic, targeting, among other things, the hematopoietic system, and its use has resulted in cases of leukopenia, thrombocytopenia, and aplastic anemia. This investigation was undertaken to characterize the in vitro effects of T2 on primary human CD34-positive (CD34+) bone marrow cells. Our results demonstrate that T2 has a potent inhibitory effect on the clonogenic response of human bone marrow cells to exogenously added hematopoietic growth factors. The inhibition of colony formation by T2 is not the result of direct cytotoxicity or increased apoptosis and indicates a functional suppression of hematopoiesis. Additional experiments demonstrate that T2 also alters transcriptional regulation in bone marrow cells by inhibiting nuclear factor-kappaB. This transcription factor is found in CD34+ bone marrow cells and has been recently shown to be a requirement for colony formation. These results demonstrate that therapeutic concentrations of T2 exert a significant hematotoxic effect by inhibiting growth factor response in CD34+ bone marrow cells and suggest that inhibition of nuclear factor-kappaB may play a role in the blood dyscrasias encountered with the use of this drug.

Aluminum toxicity. Hematological effects

Sequential effects of intoxication with aluminum hydroxide (Al) (80 mg/Kg body weight, i.p., three times a week), were studied on rats from weaning and up to 28 weeks. The study was carried out on hematological and iron metabolism-related parameters on peripheral blood, at the end of the 1st, 2nd, 3rd, 4th, 5th and 6th months of exposure. As it was described that hematotoxic effects of Al are mainly seen together with high levels of uremia, renal function was measured at the same periods. The animals treated developed a microcytosis and was accompanied by a decrease in mean corpuscular hemoglobin (MCH). Significantly lower red blood cell counts (RBC million/μl) were found in rats treated during the 1st month. These values matched those obtained for control rats during the 2nd month. From the 3rd month onwards, a significant increase was observed as compared to control groups, and the following values were obtained by the 6th month: (T) 10.0±0.3 versus (C) 8.7±0.2 (million/μl). Both MCH and mean corpuscular volume (MCV) were found to be significantly lower in groups treated from the 2nd month. At the end of the 6th month the following values were found: MCH (T) 13.3±0.1 versus (C) 16.9±0.3 (pg); MCV (T) 42.1±0.7 versus (C) 51.8±0.9 (fl). Al was found responsible for lower serum iron concentration levels and in the percentage of transferrin saturation. Thus, although microcytic anemia constitutes an evidence of chronic aluminum exposure, prolonged exposure could lead to a recovery of hematocrit and hemoglobin concentration values with an increase in red cell number. Nevertheless, both microcytosis and the decrease of MCH would persist. These modifications took place without changes being observed in the renal function during the observation period.

Metallothionein-Null Mice Are Highly Susceptible to the Hematotoxic and Immunotoxic Effects of Chronic CdCl2 Exposure

Cadmium (Cd) is an environmental pollutant. Chronic exposure of humans to Cd results in various maladies, including anemia and altered immune function. Metallothionein (MT) has been proposed to play an important role in Cd detoxication. Thus, we hypothesized that intracellular MT protects against Cd-induced hematotoxicity and immunotoxicity. Control and MT-I/II knockout (MT-null) mice were given s.c. injections of CdCl2 over a wide range of doses, 6 times/week for up to 10 weeks. Cd-induced anemia was evident after 5 weeks of exposure and progressed with time. MT-null mice were about 10 times more susceptible to Cd-induced anemia, as evidenced by decreased erythrocytes (25%), hemoglobin concentration (30%), and hematocrit (35%) after 10 weeks of Cd injections. Cd produced dose- and time-dependent increases in neutrophils (7×), along with a marked elevation of serum IL-1β (6×) and TNF-α (20×) levels. MT-null mice were more susceptible than controls to Cd-induced alterations in peripheral leukocytes and cytokine levels. Chronic exposure to Cd also produced dose- and time-dependent splenomegaly (5×), with loss of lymphoid structure, inflammation, hyperplasia, appearance of giant cells, and fibrosis. Thymus weights were decreased by Cd in a dose-dependent manner (60%). MT-null mice were also approximately 10 times more susceptible than controls to these lesions. In conclusion, the present study demonstrates that repeated injections of Cd produces hematotoxic and immunotoxic effects, and intracellular MT protects against these chronic Cd-induced effects.

Sex-dependent induction of alcohol dehydrogenase activity in rats

The glycolethers 2-methoxyethanol (2-ME), 2-ethoxyethanol (2-EE), and 2-butoxyethanol are widely used organic solvents with teratogenic, spermatotoxic, and hematotoxic effects due to the respective alkoxyacetic acid metabolites formed via alcohol dehydrogenase (ADH). ADH displays sexually dimorphic activities in adult rats, and is probably at least in part under the control of testosterone. The aim of this study was to investigate whether induction of ADH is also sex-dependent. Ethanol, 2-ME, and 2-EE were tested as inducers of hepatic and gastric ADH in female, male, and castrated male rats. The activity of hepatic ADH was higher in female than in male rats, while the activity of gastric ADH was higher in male than in female rats. The activities of ADH increased with increasing chain length of the glycolethers and alcohols. Castration of male rats led to a female pattern of ADH activity, i.e. increased activity of hepatic ADH and decreased activity of gastric ADH. Ethanol had no inducing effect on hepatic ADH in either male or female rats. 2-ME and 2-EE caused an increase in the activity of hepatic ADH in male and castrated male rats only. The present data demonstrate a different expression of ADH isoenzymes in male and female rats, and a sex-dependent induction of ADH isoenzymes. The different possible regulatory mechanisms for the different ADH isoenzymes require further investigation.

INFLUENCE OF GENDER AND ACETONE PRETREATMENT ON BENZENE METABOLISM IN MICE EXPOSED BY NOSE-ONLY INHALATION

Benzene (BZ) requires oxidative metabolism catalyzed by cytochrome P-450 2E1 (CYP 2E1) to exert its hematotoxic and genotoxic effects. We previously reported that male mice have a two-fold higher maximum rate of BZ oxidation compared with female mice; this correlates with the greater sensitivity of males to the genotoxic effects of BZ as measured by micronuclei induction and sister chromatid exchanges. The aim of this study was to quantitate levels of BZ metabolites in urine and tissues, and to determine whether the higher maximum rate of BZ oxidation in male mice would be reflected in higher levels of hydroxylated BZ metabolites in tissues and water-soluble metabolites in urine. Male and female B6C3F mice were exposed to 100 or 600 ppm 14C-BZ by nose-only inhalation 1 for 6 h. An additional group of male mice was pretreated with 1% acetone in drinking water for 8 d prior to exposure to 600 ppm BZ; this group was used to evaluate the effect of induction of CYP 2E1 on urine and tissue levels of BZ and its hydroxylated metabolites. BZ, phenol (PHE), and hydroquinone (HQ) were quantified in blood, liver, and bone marrow during exposure and postexposure, and water-soluble metabolites were analyzed in urine in the 48 h after exposure. Male mice exhibited a higher flux of BZ metabolism through the HQ pathway compared with females after exposure to either 100 ppm BZ (32.0 +/- 2.03 vs. 19.8 +/- 2.7% ) or 600 ppm BZ (14.7 +/- 1.42 vs. 7.94 +/- 0.76% ). Acetone pretreatment to induce CYP 2E1 resulted in a significant increase in both the percent and mass of urinary HQ glucuronide and muconic acid in male mice exposed to 600 ppm BZ. This increase was paralleled by three- to fourfold higher steady-state concentrations of PHE and HQ in blood and bone marrow of acetone-pretreated mice compared with untreated mice. These results indicate that the higher maximum rate of BZ metabolism in male mice is paralleled by a greater proportion of the total flux of BZ through the pathway for HQ formation, suggesting that the metabolites formed along this pathway may be responsible for the genotoxicity observed following BZ exposure.