The relationship of embryotoxicity to disposition of 2-methoxyethanol in mice

Effect of syringic acid on steroid and gonadotropic hormones, hematological indices, sperm characteristics and morphologies, and markers of tissue damage in methyl cellosolve-administered rats

Methyl cellosolve (MTC) is an established gonadotoxic and hematotoxic compound that is commonly and universally utilized in herbicide, liquid soap, stain, dye, paint, and brake fluid manufacturing industries as a solvent. Due to its wide range usage, this study therefore investigated the effect of syringic acid (SYAC) on hematological indices, sperm characteristics and morphologies, and markers of tissue damage in MTC administered male Wistar rats. Thirty (30) rats divided into six groups were used. Rats in group 1 served as control, those in group 2 were administered MTC for 30 consecutive days, those in groups 3, 4, and 5 were treated with 25, 50, and 75 mg/kg body weight of SYAC respectively also for 30 consecutive days immediately after each day MTC administrations, while rats in group 6 received 75 mg/kg body weight of SYAC only throughout. Compared with control, administrations of MTC resulted in a significant decrease in spermatozoa count, number of normal and live spermatozoa, Hb count, MCH, MCHC, serum TC, and LH, while number of abnormal spermatozoa, RBC and WBC counts, activities of serum AST, ALT, GGT, LDH, and ADH were significantly increased. Treatments with 25 mg/kg of SYAC significantly reduced the RBC and WBC counts, serum activities of AST, ALT, GGT, and increased TC concentration. Treatments with 50 mg/kg SYAC significantly lowered the number of abnormal spermatozoa, RBC count, activities of serum ALT, AST, LDH, ADH, and increased the number of normal spermatozoa, MCV, MCH, and MCHC, while 75 mg/kg of SYAC significantly decreased the serum activities of AST, ALT, GGT, LDH, ADH, and increased serum TC concentration. Findings from this study have revealed the hepatoprotective effect of SYAC at all doses investigated but did not confer spermatoprotection and hematoprotection against MTC-induced toxicities, and looking at the 3 doses investigated, 50 mg/kg of SYAC yielded the best effect.

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MTC significantly decreased live sperm, sperm count, MCH, MCHC, and Hb counts.

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MTC significantly increased number of abnormal sperm, RBC and WBC counts.

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MTC significantly increased serum activities of AST, ALT, GGT, LDH, and ADH.

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SYAC significantly decreased RBC and WBC counts, AST, ALT, GGT, LDH, and ADH.

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SYAC significantly increased number of normal sperm, MCV, MCH, and MCHC counts.

An Interlaboratory Evaluation of Five Pairs of Teratogens and Non-teratogens in Post-implantation Rat Embryo Culture

The usefulness of the post-implantation rat embryo culture method in screening xenobiotic compounds for developmental toxicity was validated in four laboratories with five pairs of compounds. This approach was chosen to provide information on the interlaboratory reproducibility of the results and to compare the effects of chemical analogues in embryo culture. By testing analogous compounds which are known to have different embryotoxic potencies in vivo, the discriminating power of the embryo culture method for the compound classes under study could be optimally assessed. The classes selected for testing were triazole antifungals, phthalic ester metabolites, substituted pyridines, sulphonamides and methylated xanthines. In summary, it was possible to distinguish between the compounds in three of the pairs, it was not possible to discriminate between the compounds of one pair, and it was possible to discriminate between the compounds of the other pair at two out of the four laboratories. The embryo culture results generally show a good correspondence with the embryotoxic properties of the compounds tested in vivo, although the embryo culture method appeared to be able to discriminate between only some of the pairs of chemical analogues. Some discrepancies may have arisen among the laboratories, because of methodological differences. These results suggest that the post-implantation rat embryo culture method may be a useful tool for screening xenobiotics within classes of compounds known to interfere with embryogenesis during the period of development represented in culture.

Methyl cellosolve-induced renal oxidative stress and time-dependent up-regulation of pro-inflammatory cytokines, apoptotic, and oncogenic markers in rats

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MC significantly increased and decrease the kidney levels of MDA and NO respectively after 14 and 21 days.

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MC administration resulted in the disorganization of the renal redox system.

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MC significantly increased the kidney levels of TNF-α and IL-6 after 7, 14 and 21 days, and IL-1β after 14 and 21 days.

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MC significantly increased kidney p53, Bax, and caspase-3 after 14 and 21 days, and decreased Bcl-2 after 14 and 21 days.

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MC significantly increased the kidney levels of c-Myc and K-Ras after 7, 14 and 21 days.

Methyl cellosolve (MC) is used in production of textile, paints, stains, inks, surface coatings, and anti-icing additive in hydraulic fluids and jet fuel. Consequently, the present study investigated its effect on renal cells, in a time-course study in male Wistar rats. Animals were orally administered 50 mg/kg body weight of MC for a period of 7, 14, and 21 days. Following 7 days of administration of MC, there was a significant increase in the levels of K-Ras, c-Myc, TNF-α, IL-6 and NO, while GSH level and SOD activity were significantly reduced compared with control. At the end of 14 days exposure, RKW, GSH, NO, and Bcl-2 levels were significantly decreased, while levels of K-Ras, c-Myc, p53, Bax, caspase-3, TNF-α, IL-1β, IL-6, MDA and GPx activity were significantly increased compared with control. After 21 days of MC administration, RKW, GSH, NO, IL-10 and Bcl-2 levels were significantly decreased, while levels of K-Ras, c-Myc, p53, Bax, caspase-3, TNF-α, IL-1β, IL-6, MDA and GST activity were significantly increased compared with control. Exposures to MC in any way should be strictly avoided as it could trigger renal damage through the disorganization of the antioxidant system, up-regulation of inflammatory, apoptotic, and oncogenic markers in rats.

Methoxyacetic acid inhibits histone deacetylase and impairs axial elongation morphogenesis of mouse gastruloids in a retinoic acid signaling-dependent manner

BACKGROUND

Teratogenic potential has been linked to various industrial compounds. Methoxyacetic acid (MAA) is a primary metabolite of the widely used organic solvent and plasticizer, methoxyethanol and dimethoxyethyl phthalate, respectively. Studies using model animals have shown that MAA acts as the proximate teratogen that causes various malformations in developing embryos. Nonetheless, the molecular mechanisms by which MAA exerts its teratogenic effects are not fully understood.

METHODS

Gastruloids of mouse P19C5 pluripotent stem cells, which recapitulate axial elongation morphogenesis of gastrulation-stage embryos, were explored as an in vitro model to investigate the teratogenic action of MAA. Morphometric parameters of gastruloids were measured to evaluate the morphogenetic effect, and transcript levels of various developmental regulator genes were examined to assess the impact on gene expression patterns. The effects of MAA on the level of retinoic acid (RA) signaling and histone deacetylase activity were also measured.

RESULTS

MAA reduced axial elongation of gastruloids at concentrations comparable to the teratogenic plasma level (5 mM) in vivo. MAA at 4 mM significantly altered the expression profiles of developmental regulator genes. In particular, it upregulated the RA signaling target genes. The concomitant suppression of RA signaling using a pharmacological agent alleviated the morphogenetic effect of MAA. MAA at 4 mM also significantly reduced the activity of purified histone deacetylase protein.

CONCLUSIONS

MAA impaired axial elongation morphogenesis in a RA signaling-dependent manner in mouse gastruloids, possibly through the inhibition of histone deacetylase.

Effects of ethylene glycol monomethyl ether and its metabolite, 2-methoxyacetic acid, on organogenesis stage mouse limbs in vitro

Exposure to ethylene glycol monomethyl ether (EGME), a glycol ether compound found in numerous industrial products, or to its active metabolite, 2-methoxyacetic acid (2-MAA), increases the incidence of developmental defects. Using an in vitro limb bud culture system, we tested the hypothesis that the effects of EGME on limb development are mediated by 2-MAA-induced alterations in acetylation programming. Murine gestation day 12 embryonic forelimbs were exposed to 3, 10, or 30 mM EGME or 2-MAA in culture for 6 days to examine effects on limb morphology; limbs were cultured for 1 to 24 hr to monitor effects on the acetylation of histones (H3K9 and H4K12), a nonhistone protein, p53 (p53K379), and markers for cell cycle arrest (p21) and apoptosis (cleaved caspase-3). EGME had little effect on limb morphology and no significant effects on the acetylation of histones or p53 or on biomarkers for cell cycle arrest or apoptosis. In contrast, 2-MAA exposure resulted in a significant concentration-dependent increase in limb abnormalities. 2-MAA induced the hyperacetylation of histones H3K9Ac and H4K12Ac at all concentrations tested (3, 10, and 30 mM). Exposure to 10 or 30 mM 2-MAA significantly increased acetylation of p53 at K379, p21 expression, and caspase-3 cleavage. Thus, 2-MAA, the proximate metabolite of EGME, disrupts limb development in vitro, modifies acetylation programming, and induces biomarkers of cell cycle arrest and apoptosis

Toxicity of ethylene glycol monomethyl ether: impact on testicular gene expression

Methoxyacetic acid (MAA), the active biological oxidation product of the industrial solvent ethylene glycol monomethyl ether (EGME), causes acute toxicity in several species including humans. MAA primarily affects tissues with rapidly dividing cells and high rates of energy metabolism, including testes, thymus and the fetus. Testicular toxicity, one of the most prominent consequences of EGME, and MAA, exposure, results from apoptosis of primary spermatocytes and is associated with changes in the expression of various genes and signalling pathways. This review of EGME metabolism and its organ-specific toxicities emphasizes genes and signalling pathways that are modulated by EGME exposure and their relevance to the molecular mechanisms underlying EGME and MAA toxicity. Of particular importance are the genes that code for oxidative stress response factors, protein kinases, and nuclear hormone receptors. Nuclear receptors and protein kinases regulate multiple cellular processes and are critical for signalling events required for spermatogenesis. De-regulation of their activity by EGME or MAA leads to inappropriate signalling in testicular cells. Oxidative stress in spermatocytes exposed to MAA triggers mitochondrial release of cytochrome C, activation of caspases and ultimately apoptosis. Detailed investigation of the molecular responses to MAA exposure may help elucidate the overall impact and extent of toxicity seen following EGME exposure. Finally, given the effects of EGME on multiple genes and signalling pathways in the testis, mixture studies combining EGME, or MAA, with other testicular toxicants may help identify toxicities that are aggravated by EGME exposure.

A teratoproteomics analysis: heat shock protein 70 is upregulated in mouse forelimb bud by methoxyacetic acid treatment

BACKGROUND

Methoxyacetic acid (MAA) causes fetal limb abnormalities when the substance is administrated on gestation day (GD) 11 in mice. Limb abnormalities are caused mainly by extensive cell death in the mesoderm of the limb plate. This investigation focused on identifying a protein that is linked with mouse limb teratogenicity.

METHODS

A single dose of MAA at 10 mmol/kg body weight was administered by gavage on GD 11; controls were administered vehicle only. Dams were killed by cervical dislocation 4 hr after treatment and forelimb buds were isolated from both the control and treated embryos. Proteins in forelimb buds GD 11 + 4 hr were precipitated out using 40-60% ammonium sulfate and were then analyzed by 2D SDS-PAGE. Excised protein spots were identified by mass spectrometry and amino acid internal sequence analysis. Identified protein was further confirmed by Western blotting.

RESULTS

Two-dimensional gel analysis indicated that 1 protein spot of 81.7 kDa/pI 7.3 was overexpressed, and the protein matched heat shock protein 70 (HSP70; accession no. P08109, SwissProt).

CONCLUSIONS

The results suggest that MAA, when administered to pregnant mice, upregulates HSP70 in the forelimb buds.

The mechanism of ethylene glycol ether reproductive and developmental toxicity and evidence for adverse effects in humans

Numerous experimental studies have established that only a few among the large family of ethylene glycol ethers (EGEs) elicit toxicity on reproduction in either gender. Notable are the monomethyl (EGME) and monoethyl (EGEE) ethers and their respective acetate esters whose production volumes have dramatically declined. Oxidation to the respective monoalkoxy acids is a prerequisite for toxicity. The most potent EGE reproductive toxicant is EGME (via 2-methoxyacetic acid; MAA), which elicits developmental phase-specific insults on either conceptus or on testes. Toxicity at either target site is markedly attenuated by simple physiological compounds such as acetate, formate, glycine, D-glucose and serine. Lack of solid EGME occupational exposure data and the need to improve the scientific foundations for animal data extrapolations, prompted the development of physiologically based pharmacokinetic (PBPK) models for pregnancy application. Interspecies (mouse-rat) and different exposure routes (including inhalation) were experimentally validated. Such PBPK models were then extrapolated to potential occupational exposures, using rather limited human MAA pharmacokinetic data. PBPK model predictions of human blood levels upon simulated inhalation exposure to the 5 ppm threshold limit value (TLV) for 8 h were approximately 60 microM were well below those causing adverse effects in pregnant mice or rats. This conclusion concurs with the lack of objective analytical chemistry data for EGME/MAA in occupational settings, regardless of the potential route of exposure. There are no exposure data that can be linked in a cause-and-effect association to adverse human reproductive outcomes.

Evaluation of the protective effectiveness of gloves from occupational exposure to 2-methoxyethanol using the biomarkers of 2-methoxyacetic acid levels in the urine and plasma

AIMS

To evaluate the protective effectiveness of gloves from occupational exposure to 2-methoxyethanol (2-ME); and to examine the association of 2-methoxyacetic acid (MAA) in urine and plasma collected simultaneously from low 2-ME exposure and high 2-ME exposure workers in a semiconductor copper laminate circuit board manufacturing plant.

METHODS

Eight hour time weighted breathing zone monitoring was performed to verify the 2-ME exposure classification between workers in regular and special operations. Urine and plasma samples were simultaneously collected from 74 exposed and 80 non-exposed workers. MAA concentrations in the urine (UMAA) and plasma (PMAA) were measured using previously published methods. Three types of gloves worn by workers (cotton, rubber, and no gloves) were recorded by direct observations in the workplace and validated by person-to-person interview. Protective effectiveness indices (PEI) were used to evaluate the glove effectiveness.

RESULTS

There was no detectable 2-ME/MAA in the air, or in urine and plasma samples in non-exposed workers. The average UMAA and PMAA in special operations were 72.63 mg/g Cr. and 29.72 mg/l, significantly higher than values in regular operations (5.44 mg/g Cr. and 2.58 mg/l, respectively). PMAA showed satisfactory correlation to UMAA in all participants from both regular and special operations. The rubber gloves provided significant reduction in 2-ME uptake, whereas cotton gloves provided little protection with fluctuating effectiveness, based on PEI estimates.

CONCLUSIONS

PMAA, similar to UMAA, could serve as a specific biomarker for 2-ME exposure. Wearing impermeable rubber gloves during high risk tasks can reduce major 2-ME exposure. Other improvements, including engineering control, should be provided to diminish worker exposure to 2-ME in occupational environments.

Follow up study of haematological effects in workers exposed to 2-methoxyethanol

AIMS

To examine the association between 2-methoxyethanol (2-ME) exposure and haematological effects, as well as the recovery from these haematological effects with continuous reduction in exposure to 2-ME.

METHODS

Twenty nine exposed and 90 non-exposed workers were recruited. Haematological parameters, eight hour full shift personal exposure to 2-ME, and urinary 2-methoxyacetic acid (MAA) were repeatedly measured in three consecutive surveys within six months.

RESULTS

Results of haematological examination in the first exposure survey showed that haemoglobin, packed cell volume, and red blood cell count in the male exposed workers were significantly lower than those in the comparison workers. The frequency of anaemia in the exposed group (42%) was significantly higher than that in the comparison group (3%). The haematological effects were significantly associated with the urinary MAA of exposed workers. The haematological effects had returned to normal in the first follow up survey 2.5 months later, when a reduction in 2-ME exposure was noted. Haematological results of the second follow up examination six months later remained normal. The mean airborne exposure of 2-ME in the three surveys dropped from 35.7 to 2.65, then to 0.55 ppm. The mean urinary MAA of exposed workers in the three surveys was reduced from 57.7 to 24.6, then to 13.5 mg/g creatinine (n = 29). The reduction in exposure through both inhalation and potential dermal contact with 2-ME might account for the haematological recovery.

CONCLUSION

2-ME is a haematological toxin which leads to anaemia in exposed workers. However, the toxic haematological effects of 2-ME persist for only a short period of time after cessation or reduction of exposure.

Developmental Toxicity Interactions of Methanol and Radiofrequency Radiation or 2-Methoxyethanol in Rats

This research was undertaken to determine potential interactions among chemical and physical agents. Radiofrequency (RF) radiation is used in numerous workplaces, and many workers are concurrently exposed to RF radiation and various chemicals. The developmental toxicity of RF radiation is associated with the degree and duration of hyperthermia induced by the exposure. Previous animal research indicates that hyperthermia induced by an elevation in ambient temperature can potentiate the toxicity and teratogenicity of some chemical agents. We previously demonstrated that combined exposure to RF radiation (10 MHz) and the industrial solvent, 2-methoxyethanol (2ME), enhanced teratogenicity in rats. Interactions were noted at even the lowest levels of 2ME tested, but only at hyperthermic levels of RF radiation. The purpose of the present research is to investigate if the interactive effects noted for RF radiation and 2ME are unique to these agents, or if similar interactions might be seen with other chemicals. Because methanol is widely used as a solvent as well as fuel additive, and, at high levels, is teratogenic in animals, we selected methanol as a chemical to address generalizability. Based on the literature and our pilot studies, 0, 2, or 3 g/kg methanol (twice, at 6-hour intervals) were administered on gestation day 9 or 13 to groups of 10 Sprague-Dawley rats. Dams treated on day 9 were given methanol and exposed to RF radiation sufficient to maintain colonic temperature at 41°C for 60 minutes (or sham). Those treated on day 13 were given methanol plus either 0 or 100 mg/kg 2ME. Because we observed that methanol produced hypothermia, some groups were given the initial dose of methanol concurrently with the RF or 2ME, and others were given the first dose of methanol 1.5 hours prior to RF or 2ME. Dams were sacrificed on gestation day 20, and the fetuses were examined for external malformations. The results indicate that RF radiation or methanol on day 9 increased the incidence of resorbed fetuses, but no interactive effects were observed. The resorptions were highest in groups given the experimental treatments 1.5 hours apart. The higher dose of methanol also reduced fetal weights. Administration of 2ME or methanol on day 13 increased the rate of malformations, and there was evidence of a positive interaction between 2ME and methanol. Fetal weights were reduced by 2ME and methanol alone, but no interaction was observed. Also, separation of the dosing with the teratogens did not affect the results. These results point out that interactions in developmental toxicology, such as those of RF radiation, 2ME, and methanol that we have studied, are complex, and such interactions cannot be fully understood or predicted without more research. It is important that combined exposure effects be considered when developing both physical agent and chemical agent exposure guidelines and intervention strategies.

Urinary 2-methoxy acetic acid accumulation in response to 2-methoxy ethanol exposure

Urinary 2-methoxy acetic acid reportedly has a long half-life (77.1 hr) in humans. The authors studied urinary 2-methoxy acetic acid in a group of 18 workers exposed to 2-methoxy ethanol from Monday to Saturday following a 7-d cease in production. The weekly time-weighted average exposure concentration of 2-methoxy ethanol was 4.5 ppm. The urinary 2-methoxy acetic acid of exposed workers was increased significantly, from 18.5 microg/ml (10.6 mg/gm creatinine) on Monday (prior to work) to 48.4 microg/ml (46.5 mg/gm creatinine) on Friday (after work), to 51.2 microg/ml (45.6 mg/gm creatinine) on Saturday after work. These levels occurred, despite that fact that the daily mean time-weighted average 2-methoxy ethanol exposures were very consistent and were close to the current Taiwan Permissible Exposure Limit of 5 ppm. These urinary 2-methoxy acetic acid levels were much higher than levels that occur with inhalation only, and they demonstrate that skin absorption is a significant contributor to 2-methoxy ethanol exposure. The high background concentrations of 2-methoxy acetic acid in the preshift urine samples following a 7-d production halt confirm that there is a long half-life of 2-methoxy acetic acid in humans. The determination of urinary 2-methoxy acetic acid is recommended for exposure assessment of 2-methoxy ethanol.

Interactions of radiofrequency radiation-induced hyperthermia and 2-methoxyethanol teratogenicity in rats

Radiofrequency (RF) radiation is used in a variety of workplaces. In addition to RF radiation, many workers are concurrently exposed to numerous chemicals; exposed workers include those involved with the microelectronics industry, plastic sealers, and electrosurgical units. The developmental toxicity of RF radiation is associated with the degree and duration of hyperthermia induced by the exposure. Previous animal research indicates that hyperthermia induced by an elevation in ambient temperature can potentiate the toxicity and teratogenicity of some chemical agents. We previously demonstrated that combined exposure to RF radiation (10 MHz) and the industrial solvent, 2-methoxyethanol (2ME), produces enhanced teratogenicity in rats. The purpose of the present research is to determine the effects of varying the degree and duration of hyperthermia induced by RF radiation (sufficient to maintain colonic temperatures at control [38.5], 39.0, 40.0, or 41.0 degrees C for up to 6 h) and 2ME (100 mg/kg) administered on gestation day 13 of rats. Focusing on characterizing the dose-response pattern of interactions, this research seeks to determine the lowest interactive effect level. Day 20 fetuses were examined for external and skeletal malformations. The results are consistent with previous observations. Significant interactions were observed between 2ME and RF radiation sufficient to maintain colonic temperatures at 41 degrees C for 1 h, but no consistent interactions were seen at lower temperatures even with longer durations. These data indicate that combined exposure effects should be considered when developing both RF radiation and chemical exposure guidelines and intervention strategies.

Toxicity review of ethylene glycol monomethyl ether and its acetate ester

Ethylene glycol monomethyl ether (EGME) and its acetate ester (EGMEA) are highly flammable, colorless, moderately volatile liquids with very good solubility properties. They are used in paints, lacquers, stains, inks and surface coatings, silk-screen printing, photographic and photo lithographic processes, for example, in the semiconductor industry, textile and leather finishing, production of food-contact plastics, and as an antiicing additive in hydraulic fluids and jet fuel. EGME and EGMEA are efficiently absorbed by inhalation as well as via dermal penetration. Dermal absorption may contribute substantially to the total uptake following skin contact with liquids or vapours containing EGME or EGMEA. EGMEA is rapidly converted to EGME in the body and the two substances are equally toxic in animals. Therefore, the two substances should be considered as equally hazardous to man. Effects on peripheral blood, testes, and sperm have been reported at occupational exposure levels ranging between 0.4 and 10 ppm EGME in air, and with additional, possibly substantial, dermal exposure. Severe malformations and disturbed hematopoiesis have been linked with exposure to EGME and EGMEA at unknown, probably high, levels. Embryonic deaths in monkeys and impaired spermatogenesis in rabbits have been reported after daily oral doses of 12 and 25 mg per kg body weight, respectively. In several studies, increased frequency of spontaneous abortions, disturbed menstrual cycle, and subfertility have been demonstrated in women working in the semiconductor industry. The contribution of EGME in relation to other exposure factors in the semiconductor industry is unclear.

Development of a physiologically based pharmacokinetic model of 2-methoxyethanol and 2-methoxyacetic acid disposition in pregnant rats

An accurate description of developing embryos' exposure to a xenobiotic is a desirable component of mechanism-based risk assessments for humans exposed to potential developmental toxicants during pregnancy. 2-Methoxyethanol (2-ME), a solvent used in the manufacture of semiconductors, is embryotoxic and teratogenic in all species tested including nonhuman primates. 2-Methoxyacetic acid (2-MAA) is the primary metabolite of 2-ME and the proximate embryotoxic agent. The objective of the work described here was to adapt an existing physiologically based pharmacokinetic (PBPK) model for 2-ME and 2-MAA kinetics during midorganogenesis in mice to rats on gestation days (GD) 13 and 15. Blood and tissue data were analyzed using the extrapolated PBPK model that was modified to simulate 2-ME and 2-MAA kinetics in maternal plasma and total embryo tissues in pregnant rats. The original mouse model was simplified by combining the embryos and placenta with the richly perfused tissue compartment. The model includes a description of the growth of the developing embryo and changes in the physiology of the dam during pregnancy. Biotransformation pathways of 2-ME to either ethylene glycol (EG) or to 2-MAA were described as first-order processes based on the data collected from rats by Green et al., (Occup. Hyg. 2, 67-75, 1996). Tissue partition coefficients (PCs) for 2-ME and 2-MAA were determined for a variety of maternal tissues and the embryos. Model simulations closely reflected the biological measurement of 2-ME and 2-MAA concentrations in blood and embryo tissue following gavage or iv administration of 2-ME or 2-MAA. The PBPK model for rats as described here is well suited for extrapolation to pregnant women and for assessment of 2-MAA dosimetry under various conditions of possible human exposure to 2-ME.

Correlation between urinary 2-methoxy acetic acid and exposure of 2-methoxy ethanol

OBJECTIVES

To examine the correlation between airborne 2-methoxy ethanol (ME) exposures and the urinary 2-methoxy acetic acid (MAA) and to recommend a biological exposure index (BEI) for ME.

METHODS

8 Hour time weighted average (TWA) personal breathing zone samples and urine samples before and after the shift were collected from Monday to Saturday for 27 workers exposed to ME and on Friday for 30 control workers.

RESULTS

No correlation was found between airborne exposure to ME and urinary MAA for nine special operation workers due to the use of personal protective equipment. For 18 regular operation workers, a significant correlation (r = 0.702, p = 0.001) was found between urinary MAA (mg/g creatinine) on Friday at the end of the shift and the weekly mean exposures of ME in a 5 day working week. The proposed BEI, which corresponds to exposure for 5 days and 8 hours a day to 5 ppm, extrapolated from the regression equation is 40 mg MAA/g creatinine. A significant correlation was also found between the weekly increase of urinary MAA (Friday after the shift minus Monday before the shift) and the weekly mean exposures of ME (r = 0.741). The recommended value of the weekly increase of urinary MAA for 5 days repeated exposures of 5 ppm ME is 20 mg/g creatinine. No urinary MAA was detected in workers in the non-exposed control group.

CONCLUSIONS

The Friday urinary MAA after the shift or the weekly increase of urinary MAA is a specific and a good biomarker of weekly exposure to ME.

Improved method to measure urinary alkoxyacetic acids

OBJECTIVES

To simplify the current preparation of samples, and to improve the specificity and reliability of the conventional analytical methods to measure urinary alkoxyacetic acids.

METHODS

Samples containing alkoxyacetic acids including methoxy, ethoxy, and butoxyacetic acids (MAA, EAA, and BAA) were acidified with HCl and extracted with a mixed solvent of methylene chloride and isopropyl alcohol, then analysed by gas chromatography/mass spectrometry (GC/MS).

RESULTS

Optimal results were obtained when pH was 1.05-1.45, the ratio of methylene chloride and isopropyl alcohol was 2:1, and when extraction time was 10 minutes. Over the concentration range 0.3-200 micrograms/ml, MAA, EAA, and BAA could be determined with a pooled coefficient of variation (nine concentrations, six replicate samples) of 5.55%, 6.37%, and 6.41%, respectively. Urine samples were stable for at least 5 months and 3 freeze-thaw cycles at -20 degrees C. The limits of detection of MAA, EAA, and BAA were 0.055, 0.183, and 0.009 microgram/ml, respectively. The matrix effect of urine samples was negligible for MAA and EAA, but were marginally significant for BAA. The average recoveries of alkoxyacetic acids were 99%-101%. In urine samples MAA from 15 exposed workers showed a strong linear correlation (r = 0.999, slope = 1.01) between the new GC/MS method and Sakai's GC method.

CONCLUSIONS

The simplified non-derivatisation pretreatment of samples coupled with GC/MS can provide a specific, sensitive, simple, safe, and reliable method for the biological monitoring of occupational exposure of ethylene glycol ethers.

Developmental toxicity interactions of salicylic acid and radiofrequency radiation or 2-methoxyethanol in rats

Radiofrequency (RF) radiation is used in a variety of workplaces where workers are concurrently exposed to chemicals. Combined exposure to RF radiation (10 MHz) and the industrial solvent, 2-methoxyethanol (2ME), produces enhanced teratogenicity in rats. The purpose of the present research was to determine if the synergistic effects noted for RF radiation and 2ME are generalizable to other chemicals. Since salicylic acid (SA) is widely used as an analgesic and is teratogenic in animals, SA was selected to address generalizability. Based on the literature and our pilot studies, 0, 250, or 350 mg/kg SA were administered by gavage on gestation Day 9 or 13 to rats. Concurrently rats given SA on Day 9 were exposed to RF radiation sufficient to maintain colonic temperature at 41 degrees C for 60 min (or sham). Those given SA on Day 13 were also given 0 or 100 mg/kg 2ME (gavage). Dams were sacrificed on gestation Day 20, and the fetuses were examined for external malformations. The data provide no evidence of synergistic interactions between RF radiation and salicylic acid (resorptions and malformations). Limited evidence of antagonism was observed between 2ME and salicylic acid (fetal weights). This investigation highlights the importance of additional research on interactions in developmental toxicology, and emphasizes the need to consider combined exposure effects when developing both physical agent and chemical agent exposure guidelines and intervention strategies.

The role of metabolism in 2-methoxyethanol-induced suppression of in vitro polyclonal antibody responses by rat and mouse lymphocytes

Previous studies from this laboratory have shown that the glycol ether 2-methoxyethanol (ME) produces immunosuppression in the rat but not in the mouse. To investigate possible mechanisms for this species difference in ME-induced immunotoxicity, the effects of ME and its metabolites, 2-methoxyacetic acid (MAA) and 2-methoxyacetaldehyde (MAAD), on in vitro polyclonal antibody responses by Fisher 344 rat and B6C3F1 mouse lymphocytes, were studied. MAAD and MAA suppressed IgM and IgG production by both mouse and rat lymphocytes at non-cytotoxic doses. However, ME had no effect on antibody production by either mouse or rat lymphocytes. Lower concentrations of MAA suppressed rat lymphocyte IgM and IgG production (at 0.5 and 1.0 mM MAA, respectively) compared with mouse lymphocytes (2.0 mM MAA). IgM and IgG production by both rat and mouse lymphocytes was suppressed at comparable concentrations of MAAD (0.3 mM MAAD). The role that metabolism of ME to its immunosuppressive forms plays in this in vitro suppression was demonstrated using hepatocyte-lymphocyte co-cultures. IgM production by both mouse and rat lymphocytes was suppressed at a lower concentration of ME following co-culture with mouse (12.5 mM ME) versus rat (25 and 50 mM ME) hepatocytes. These in vitro results indicate that rat lymphocytes are more sensitive to MAA than are mouse lymphocytes and that mouse hepatocytes have a greater capacity to metabolize ME to its immunosuppressive metabolites than do rat hepatocytes. In addition, MAAD is more immunotoxic than MAA, suggesting that this metabolite may be the proximate immunotoxicant. These observation may partially explain the species differences in ME-induced immunosuppression in vivo.

Serine-enhanced restoration of 2-methoxyethanol-induced dysmorphogenesis in the rat embryo and near-term fetus

Effects of serine on restorative growth were characterized by comparing embryo/fetal responses after maternal exposure to 2-methoxyethanol (ME) and ME + serine by gavage on gestation day (gd) 13, a day of heightened limb sensitivity. Paws (gd 20) and limb buds (gd 15) were examined after ME alone at 50, 100, and 250 mg/kg, and after ME (either 100 or 250 mg ME/kg) + serine (1734 mg serine/kg) administered within minutes (0 hr) to 24 hr after ME. Paw development was not altered after ME at 100 mg/kg, but was highly sensitive to 250 mg ME/kg with all fetuses and litters exhibiting defects (ectrodactyly, syndactyly, and short digit) in the preaxial region. In contrast, the limb bud displayed dose-related incidences of abnormalities after maternal treatment with the low and high levels of ME. The condensing (precartilaginous, pentadactyl pattern) and noncondensing (undifferentiated mesenchymal cells) regions exhibited changes in their size, number, and location. Serine administration after 250 mg ME/kg was effective in reducing the occurrence of paw dysmorphogenesis with its protection potency inversely related to its delay of administration (i.e., 0% paw defect incidence after 0-hr delay, 25% after 4-hr delay, 41-45% after 8- and 12-hr delays, and 76% after 24-hr delay). The occurrences of limb bud pattern disturbances produced by ME were also markedly decreased by serine cotreatment. Higher incidences of embryonic defects versus those of fetal defects demonstrate that restorative growth followed ME exposure. Serine attenuation of ME teratogenicity appears to emanate from enhanced restorative growth so that tissue damage, which otherwise would be expressed as a defect at parturition, is repaired and replaced to resume development of the limb toward its normal structure.

Multiple chemical exposures: synergism vs. individual exposure levels

Exposure to single chemicals is known to produce congenital malformations in both pregnant animals and humans exposed at sufficiently high intensity. However, real life involves multiple, simultaneous exposures. Using as a database the 43 multiple chemical exposure studies located by Nelson (Teratology 49:33-71; 1994) where synergism was reported, we explored the degree to which such concerns may be realistic from the viewpoint of the current standard developmental toxicity safety evaluation process. Focusing on the assessment of the lowest tested dose of a given agent participating in synergistic activity as compared to its threshold level for eliciting toxicity when administered alone, we found that while the availability of adequate data was limited, all cases, with the possible exception of one, demonstrated synergistic toxic expression only when at least one, and usually both, compounds were used at or above their individual threshold for toxicity. These findings suggest that in animals such phenomena of synergistic chemical interactions are likely to occur only when at least one and more likely both agents are administered at or above their individual threshold for toxicity. To the extent animal studies are predictive of human developmental hazards due to single chemical exposures, available data do not establish multiple chemical exposures as a major human developmental concern.

Effects of 2-methoxyethanol on mouse neurulation

The potent developmental toxicant, 2-methoxyethanol (2-ME), elicits exencephaly in near-term mouse fetuses following a single maternal treatment early on gestation day (gd) 8. Deleterious morphological consequences to the neurulating embryo shortly after exposure have not been reported. The present study was designed to fill this gap and to investigate the impact of 2-ME treatment on cell death patterns in the embryonic neural folds. Dams were injected subcutaneously with saline, 250 or 325 mg 2-ME/kg 2 hr prior to the beginning of gd 8. The effect of 2-ME on gross and microscopic neural development was examined in conceptuses on gd 9, 6 hr (9:6), 10:6, and 18:0. Compared to saline, 2-ME treatment increased the percentage of embryos with open neural tubes (ONTs) at all gestation days. Although few statistically significant differences (P < 0.05) existed among the ONT rates on the 3 observation days, an interesting biological response occurred. Both high and low 2-ME doses appeared to elicit the greatest incidence of neural tube patency on gd 9:6 (affecting approximately 27% of embryos). During the subsequent 24 hr, recovery occurred and many neural folds apparently closed. Consequently, the ONT incidences on gd 10:6 (approximately 11%) were quite similar to the gd 18 exencephaly rates elicited by both chemical treatments (approximately 15%). A dose response was not seen due to a substantial increase in resorption rates following the 325 mg/kg dose. Compared to the other treatment groups, the low 2-ME dose significantly inhibited embryonic growth as indicated by reduced crown-rump and head lengths and increased incidence of developmentally delayed brain maturation. To evaluate chemically induced changes in cell death, neurulating embryos were collected on gd 8:6 and either immersed in the vital dye, Nile blue sulfate (NBS), or processed for histopathology. In 2-ME-exposed embryos, excessive NBS uptake occurred in neural fold neuroepithelium at sites of nonclosure. Using histopathology, the extent of cell death in the cephalic neural folds was dependent on the 2-ME dose, and the neuroepithelium was more severely affected than the mesenchyme. These observations suggest 1) a trend toward repair and catch-up growth later in gestation which may ameliorate the overt early effects of 2-ME, and 2) an association between enhanced cell death and regions of the neural tube particularly vulnerable to nonclosure.

Effects of reactive oxygen species (ROS) modulators, TEMPOL and catalase, on methoxyacetaldehyde (MALD) -induced chromosome aberrations in Chinese hamster ovary (CHO)-AS52 cells

Methoxyacetaldehyde (MALD), a metabolite of 2-methoxyethanol, has been shown to be clastogenic and mutagenic in CHO-AS52 cells. PCR-based-deletion screening of MALD induced CHO-AS52 mutants indicates that MALD induces large deletion mutation. Since MALD has an aldehyde as its reactive functional group, it can react with aldehyde oxidase to produce superoxide. The generation of these reactive oxygen species (superoxide, hydrogen peroxide and hydroxyl radical) may be the mechanism for genotoxicity of MALD. In the present study, TEMPOL and catalase which are ROS modulators were used to study the effects on MALD-induced chromosome damage in CHO-AS52 cells. The results showed that neither TEMPOL nor catalase can protect cells from MALD-induced chromosome aberrations. Therefore, the generation of reactive oxygen species may not be the primary mechanism of action of MALD.

The theoretical and empirical case for in vitro developmental toxicity screens, and potential applications

In vitro assays for the screening of developmental toxicity potential have been under development for approximately 15 years. During that period, we have learned that assays consisting of primary cultures of embryonic tissues or cells, intact embryos in culture, or free-living embryos are capable of distinguishing between mammalian developmental toxicants and nondevelopmental toxicants with an accuracy of > or = 80%. Despite this level of performance, there is still considerable reluctance among the scientific community to employ these assays for preliminary screening. In this paper, I review the theoretical basis for the predictiveness of these assays, outline the empirical data indicating their utility in screening toxicants, discuss the major limitations of in vitro assays and how they can be managed, and suggest applications for in vitro pre-screens. The embryo-derived assays should work because they continue to develop in vitro, and the underlying cellular and molecular processes driving this development are the same as those in the mammalian embryo in situ, and therefore, susceptible to the same insults. The assays do work, as specific mechanisms of developmental toxicity have been demonstrated in vitro, and because extensive validation studies have shown them to be highly concordant with traditional in vivo screens. The assays are inherently limited by the fact that they do not include all the levels of complexity of the maternal-embryonic unit; however, these limitations can be minimized by thoughtful assay selection, study design, and interpretation. Potential applications are suggested that complement but do not replace in vivo testing. Pre-screens will make product development more efficient and add to our knowledge about the developmental toxicity of previously untested compounds. In vivo screening would still be conducted on all classes of substances that are currently tested for developmental toxicity; however, fewer chemicals with high likelihood of being developmentally toxic, and therefore not appropriate for further commercial consideration, would be evaluated in these costly screens.

Induction of deletion mutations by methoxyacetaldehyde in Chinese hamster ovary (CHO)-AS52 cells

We have reported previously that methoxyacetaldehyde (MALD), a metabolite of 2-methoxyethanol, induces gpt gene mutations in Chinese hamster ovary (CHO)-AS52 cells but not hprt gene mutations in the standard CHO-K1-BH4 cells. In addition, MALD induces chromosome aberrations in both CHO cell lines. The data presented suggest that MALD induces deletion-type mutations. In this study, we analyzed MALD-induced CHO-AS52 mutants for deletion-type mutations using the nested-polymerase chain reaction (nested-PCR) assay. Spontaneous CHO-AS52 mutants are used as untreated control. Ethylnitrosourea (ENU)-induced CHO-AS52 mutants are used as negative control for multilocus deletions since ENU is a potent inducer of point mutations. The results show that the frequency of MALD-induced mutants containing total deletion of the gpt gene is 42.4% which is 2.3-fold higher than that from spontaneous mutants (18.6%). The frequency of ENU-induced deletion mutation is 3%. The data substantiate our hypothesis that MALD induces major deletion mutations.

Physiologically based pharmacokinetics of methoxyacetic acid: dose-effect considerations in C57BL/6 mice

Methoxyacetic acid (MAA), a weak acid with a pKa of 3.57, was used to test the broad hypothesis that distribution of weak acids in maternal and fetal tissues is determined principally by the pKa of the acid and the pH values of tissue and fluid compartments and to examine tissue dose-teratogenesis relationships, as well as administered dose-teratogenesis relationships. Five related experimental studies were conducted in pregnant C57BL/6CrIBR mice: a conventional dose-response study of developmental toxicity and transplacental pharmacokinetics in mice, a second dose-response study in which reproductive outcomes in litters from individual dams were related to individual pharmacokinetic behavior, a protein-binding experiment, an embryo tissue localization study, and determination of pH in maternal and embryonic compartments after exposure to MAA. MAA was administered intraperitoneally at 9:00 a.m. on day 10 of gestation, at doses ranging from 88 to 164 mg/kg. Localization within the forelimb bud of the embryo, an MAA target site, was determined by computerized image analysis of the distribution of radiolabeled MAA. The kinetic predictions of a physiologically based model incorporating tissue pH values and MAA pKa agreed well with observed concentrations at the lowest dose. However, at intermediate and higher doses, concentrations in both maternal and embryonic tissues were consistently underestimated. MAA was bound neither to maternal plasma proteins nor to embryonic proteins. Intermediate and higher doses of MAA caused dose-dependent transient depressions in tissue pH, but these were not of sufficient duration to bring predicted tissue concentrations into congruence with the concentrations observed. Distribution of MAA within the forelimb bud was broadly consistent with the pH hypothesis, but MAA concentration was not increased in the distal postaxial sector that is the site of the precursor cells of the missing digits. Internal exposure to MAA, defined as the area under the maternal plasma or embryo concentration curve (AUC), was not proportional to administered dose, but AUC-response relationships generated by the group and individual dose-response studies were comparable. While AUC may be a useful measure of effective MAA dose, it cannot be accurately predicted at teratogenic doses of this agent by the model as it is presently structured.

Role of formate in methanol-induced exencephaly in CD-1 mice

Mouse embryos develop exencephaly when dams are exposed by inhalation to high concentrations (> or = 10,000 ppm) of methanol on gestational day 8 (GD8; copulation plug = GD0). The present study examined the role of formate, an oxidative metabolite of methanol, in the development of methanol-induced exencephaly in CD-1 mice and cultured mouse embryos. The pharmacokinetics and developmental toxicity of sodium formate (750 mg/kg by gavage), a 6-hr methanol inhalation (10,000 or 15,000 ppm), or methanol gavage (1.5 g/kg) in pregnant CD-1 mice on GD8 were determined. Gross morphological evaluations for neural tube closure status in embryos or exencephaly in near-term fetuses were performed. Decidual swellings and maternal plasma were analyzed for methanol and formate. The mean (+/- S.E.M.) end-of-exposure plasma methanol concentration was 223 +/- 23 mM following the 6-hr, 15,000 ppm methanol inhalation. There were no changes in blood or decidual swelling formate concentrations under any of the methanol exposure conditions. Peak formate levels in plasma (1.05 +/- 0.2 mM; control 0.5 +/- 0.3 mM) and decidual swelling (2.0 +/- 0.2 mM; control 1.1 +/- 0.2 mM) from pregnant mice (GD8) given sodium formate (750 mg/kg, po) were similar to those observed following a 6-hr methanol inhalation of 15,000 ppm (plasma = 0.75 +/- 0.1 mM; decidual swelling = 2.2 +/- 0.3 mM) but did not result in exencephaly.(ABSTRACT TRUNCATED AT 250 WORDS)

Interactive developmental toxicity of radiofrequency radiation and 2-methoxyethanol in rats

Concurrent exposures to chemical and physical agents occur in the workplace; exposed workers include those involved with the microelectronics industry, plastic sealers, and electrosurgical units. Previous animal research indicates that hyperthermia induced by an elevation in ambient temperature can potentiate the toxicity and teratogenicity of some chemical agents. We previously demonstrated that combined exposure to radiofrequency (RF; 10 MHz) radiation, which also induces hyperthermia and is teratogenic to exposed animals, and the industrial solvent, 2-methoxyethanol (2ME), produces enhanced teratogenicity in rats. The present study replicates and extends the previous research investigating the enhanced teratogenicity of combined RF radiation and 2ME exposures. The interactive dose-related teratogenicity of RF radiation (sham exposure or maintaining colonic temperatures at 42.0 degrees C for 0, 10, 20, or 30 min) and 2ME (0, 75, 100, 125, or 150 mg/kg) was investigated by administering various combinations of RF radiation and 2ME to groups of rats on gestation days 9 or 13; gestation-day 20 fetuses were examined for external, skeletal, and visceral malformations. The results are consistent with and extend our previous research findings. Synergism was observed between RF radiation and 2ME for some treatment combinations, but not for others. The study also clarified which gestational periods, RF radiation exposure durations, and 2ME doses would be most informative in future interaction studies to determine the lowest interactive effect level. Day 9 exposures generally evidenced little effect by 2ME, either by itself or in combination with RF radiation. In contrast, day 13 exposures resulted in highly significant effects from 2ME and RF radiation. The structures showing strong evidence of effects from both 2ME and RF radiation after exposure on gestation day 13 were the forepaw digits, forepaw phalanges, hindpaw digits, hindpaw phalanges, hind limbs, metacarpals, and metatarsals. Statistical analyses did not show a global synergistic effect, but did show evidence for a synergistic effect at intermediate levels of the dose ranges. Future research will address potential interactions at lower doses.

Species and strain comparisons of immunosuppression by 2-methoxyethanol and 2-methoxyacetic acid

2-Methoxyethanol (ME) and its principal metabolite 2-methoxyacetic acid (MAA) have been shown in our laboratory to be immunosuppressive in male Fischer 344 rats. In this study several strains of 12-week-old female rats and mice were used to compare the immunosuppressive activity of equimolar concentrations of ME and MAA on the trinitrophenyl-lipopolysaccharide (TNP-LPS) antibody plaque-forming cell (PFC) response, which we previously demonstrated to be a sensitive end point. Female inbred Lewis, Fischer 344 and Wistar/Furth, and outbred Sprague-Dawley rats were dosed by gavage with either ME or MAA at dosages of 0.33 to 2.64 mmol/kg/day for 10 consecutive days. Female inbred C3H and C57BL/6J, hybrid B6C3F1, and outbred CD-1 mice were similarly dosed with equimolar dosages of 0.66 to 5.28 mmol/kg/day ME or MAA. All animals were immunized on day 9 of dosing and PFC responses evaluated 3 days later. Suppression of the PFC response was observed in all strains of rats at 2.64 mmol/kg/day ME or MAA. Lewis and Wistar/Furth rats were found to be the most sensitive strains with suppression at levels as low as 0.66 mmol/kg/day ME or MAA. While ME and MAA dosing resulted in suppression of the TNP PFC response in all the rat strains tested, such treatment did not suppress this PFC response in any of the mouse strains examined. These results indicate that under the conditions of this study rats, but not mice, are immunosuppressed by ME and MAA exposure, and that the susceptibility to immunosuppression differs among rat strains.

Developmental phase alters dosimetry-teratogenicity relationship for 2-methoxyethanol in CD-1 mice

The industrial solvent 2-methoxyethanol (2-ME) elicits phase-specific terata in mice through its primary metabolite and proximate toxicant, 2-methoxyacetic acid (2-MAA). Recent pharmacokinetic studies indicate that the incidence and severity of digit malformations induced in CD-1 mice by 2-ME exposure on gestation day (gd) 11 (copulation plug = gd 0) correlate better with the total 2-MAA exposure over time (= area under the curve; AUC) than with its peak concentrations (Cmax) in maternal plasma, embryo and extraembryonic fluid. In this study, the phase specificity of exencephaly induction by 2-ME was investigated to ascertain whether the 2-ME/2-MAA dosimetry-teratogenicity relationship remains consistent throughout organogenesis. Following a single intravenous (iv) bolus dose of 250 mg 2-ME/kg given to pregnant mice, exposure on gd 8 was decidedly the gestation day that best balanced low embryo lethality and high malformation incidence as recorded in near-term fetuses. Concentrations of 2-MAA were measured during distribution and elimination in maternal plasma and conceptuses following iv bolus doses of 175, 250, and 325 mg 2-ME/kg, as well as during and after termination of subcutaneous (sc) constant-rate infusion (4, 6, and 8 hr; 8 microliters/hr) of 277, 392, and 606 mg 2-ME/kg total doses. For all administration regimens, exencephaly incidence rates were determined in fetuses on gd 18. Similar plasma 2-MAA Cmax values (approximately 5 mmol/l) and fetal malformation frequencies (approximately 12%) were induced by sc infusion of 392 mg 2-ME/kg or a bolus dose of 250 mg 2-ME/kg. However, the AUC produced by infusion was significantly larger than that following the iv bolus dose (38 vs. 26 mmol.hr/l, respectively). In both maternal plasma and conceptuses, the correlation coefficients between Cmax and exencephaly rates, as well as developmental toxicity, were higher than they were for AUC and those end points. This outcome suggests that dosimetry-teratogenicity determinants may be quite specific for a distinct developmental phase during which a particular organ differentiates and a specific chemical acts upon the embryo.

Cytogenetic effects of 2-methoxyethanol and its metabolite, methoxyacetaldehyde, in mammalian cells in vitro

Glycol ethers such as 2-methoxyethanol (2-ME) are reproductive toxins. The genotoxicity of 2-ME, especially its metabolites: methoxyacetaldehyde (MALD) and methoxyacetic acid (MAA), is not adequately investigated yet. We have shown previously that MALD induced mutation in the bacterial gpt gene which is inserted in an autosome of CHO-AS52 cell line but not in the hprt gene on the X chromosome of CHO-K1-BH4 cell line. These data suggest that MALD induces major deletion-type mutation. If this prediction is correct we would expect to observe that MALD is an efficient inducer of chromosome aberrations in both CHO cell lines. We have conducted a cytogenetic study using both CHO cell lines and human lymphocytes to investigate this phenomenon. Our results show that human lymphocytes treated with 10-30 mM MALD for 1 h or 0.05-0.5 mM MALD for 24 h induced significant dose-dependent increase of sister-chromatid exchanges (SCE) (p < 0.05). It also induced significant dose-dependent increase (p < 0.05) of chromosome aberrations in human lymphocytes (10-40 mM treated for 1 h, or 0.05-2.5 mM for 24 h) and in both CHO cell lines (1.25-20 mM for 3 h). Treatment of these cells with the parent compound, 2-ME did not induce chromosome aberrations nor SCE unless very high doses of the chemical were used. In conclusion, these results indicate that MALD is clastogenic to different cell types therefore it is potentially carcinogenic. The genotoxic effects of 2-ME in humans will be dependent upon the metabolic capability of individuals to bioactivate 2-ME to MALD.

Comparative metabolism of bis(2-methoxyethyl) ether by rat and human hepatic microsomes: formation of 2-methoxyethanol

Rat hepatic microsomes catalysed the NADPH-dependent cleavage of the central ether linkage of bis(2-methoxyethyl) ether (diglyme) yielding 2-methoxyethanol (2ME). Microsomes isolated from phenobarbital- or ethanol-pretreated rats exhibited an increased capacity to cleave diglyme to 2ME. This ethanol-induced increase in 2ME formation was not observed if incubations contained the cytochrome P450IIE1 inhibitor isoniazid. Pretreatment of rats with diglyme significantly increased microsomal P-450 levels, P-450-associated enzyme activities and the conversion of diglyme to 2ME. Following the diglyme pretreatment, an almost 30-fold increase in pentoxyresorufin dealkylase activity (P450IIB1/2) was evident in rat hepatic microsomes. Human hepatic microsomes also catalysed the NADPH-dependent cleavage of diglyme to 2ME. The formation of 2ME from diglyme correlated with the aniline hydroxylase activity (P450IIE1) levels measured in human hepatic microsomes. Studies using microsomes isolated from a cell line transfected with specific human P-450 cDNAs indicate that human CYP2E1 catalyses the conversion of diglyme to 2ME. These results suggest that the central ether linkage of diglyme is cleaved by rat and human P-450 and the specific involvement of hepatic P450IIE1 in this process is implicated.

Evaluation of the clastogenic effects of 2-methoxyethanol in mice

2-Methoxyethanol (ethylene glycol monomethyl ether; EGME) is present in many industrial and consumer products, therefore, many individuals in the population are exposed to EGME. Although the toxicity of this compound is well documented its genotoxicity has not been adequately investigated using updated cytogenetic procedures. We have conducted studies to determine the clastogenic effects of EGME and its metabolite, methoxyacetaldehyde (MALD), in bone-marrow cells of B6C3F1 mice after their acute and subchronic exposure to the chemicals by the oral route. In addition, the effects after acute intravenous treatment with EGME were investigated. Mice treated with cyclophosphamide (CP) under similar experimental conditions were used as positive controls. Mice treated acutely with EGME or MALD were also implanted with bromodeoxyuridine tablets to label cells so that only cells at their first post-treatment mitoses were selected for chromosome analyses. Our data show that none of the concentrations of EGME (35-2500 mg/kg body weight) nor MALD (20-1000 mg/kg) caused any induction of chromosome aberrations even though cytotoxic doses were used. On the other hand, CP caused significant increases in chromosome damage. The data suggest that EGME and MALD are either non-clastogenic in vivo or that our mice are able to detoxify the two chemicals. In order to clarify these possibilities, pharmacokinetic and metabolic studies need to be conducted.

Mouse placenta: hemodynamics in the main maternal vessel and histopathologic changes induced by 2-methoxyethanol and 2-methoxyacetic acid following maternal dosing

The two main maternal vessels that are a major, if not the entire, source of maternal blood for the mouse placenta are unique in possessing intraluminal valvular projections. The morphologic configuration of these projections suggests their potential to converge, diverge, and rotate blood currents flowing under systolic pressure. The intravascular occurrence of circular fibrin bodies composed of concentric fibrin strands coagulated from the plasma and almost no blood cellular elements in these strands lends credence to this concept. Histopathologic changes in the extraembryonic and embryonic tissues induced by an intraperitoneal injection of 250 or 500 mg/kg of 2-methoxyethanol, or its metabolite, 2-methoxyacetic acid, via oral gavage were determined 48 hr after dosing CD-1 mice on day 11 of pregnancy. Both compounds caused 1) marked congestion and dilatation, associated with or without fibrinous occlusions, of the main maternal vessel of the placenta, 2) serosanguinous exudation and maternal hemorrhages from the placental periphery, 3) necrosis and desquamation involving the mesometrial surface or peripheral edge of the placenta, 4) translabyrinthine embryonic hemorrhage into the maternal circulation, and 5) embryonic hemorrhages into the exocoelomic, amniotic, and pericardial cavities. These lesions signify a disordered maternal circulation in the placenta suggestive of potentially serious pathologic effects. These lesions may play a role in the resorption, reduction in fetal body weight, and syndactyly or oligodactyly attributed to 2-methoxyethanol and 2-methoxyacetic acid.

Determination of urinary alkoxyacetic acids by a rapid and simple method for biological monitoring of workers exposed to glycol ethers and their acetates

In control subjects and workers exposed to glycol ethers and their acetates, we determined the urinary metabolites (three alkoxyacetic acids) by a simple and rapid method. Levels of urinary metabolites were significantly higher in the solvent workers than in the nonexposed subjects. The exposure levels measured by personal monitoring of breathing zone air were far below the threshold limit value. The present results indicate that determination of urinary alkoxyacetic acids by the practical method used here is useful for evaluating excessive exposure to solvents.

Effects of diethylene glycol monomethyl ether on pregnancy and postnatal development in rats

The effects of oral treatment of Wistar rats with diethylene glycol monomethyl ether (diEGME) were examined. In a preliminary dose-finding study with non-pregnant rats, diEGME treatment at doses up to 4,000 mg/kg/day on 11 consecutive days decreased relative weights of thymus and pituitary gland, white and red blood cell counts, hemoglobin concentrations and hematocrit levels. In pregnant rats, treatment at doses of > 3,000 mg/kg/day (over gestation days 7-17) caused total resorption of all litters. In teratology and postnatal studies, pregnant rats were treated with diEGME at doses of 0, 200, 600, and 1,800 mg/kg/day from day 7 through 17 of gestation. At 200 mg/kg, there were no adverse effects on either dams, fetuses, or neonates. At 600 mg/kg, dams were not affected, but fetal body weights were decreased, and fetal thymus and ossification were adversely affected. At 1,800 mg/kg, maternal thymus weights and food consumption were decreased, and visceral malformations of the cardiovascular system were seen in 28.0% of the fetuses. Only 6.3% of the pups delivered by dams treated with 1,800 mg/kg of diEGME survived for 4 days after birth. Thus, diEGME was teratogenic in Wistar rats, but the spectrum differed from that in Sprague-Dawley rats. In addition to teratogenicity, diEGME had significant adverse effects on postnatal development. The most sensitive organ to diEGME was the thymus in both dams and fetuses.

Mutagenicity and cytotoxicity of 2-methoxyethanol and its metabolites in Chinese hamster cells (the CHO/HPRT and AS52/GPT assays)

2-Methoxyethanol (ethylene glycol monomethyl ether) (EGME), is one of the most commonly used solvents for industrial and consumer products. Although the solvent has been shown to be a reproductive toxin the genotoxic activities of EGME especially its metabolites, have not been adequately investigated. The mutagenicity and cytotoxicity of EGME and its major metabolites, methoxyacetaldehyde (MALD) and methoxyacetic acid (MAA) in Chinese hamster ovary (CHO) cells were therefore examined by us. We have determined the mutagenicity of these compounds at the hypoxanthine-guanine phosphoribosyltransferase (hprt) locus in CHO-K1-BH4 cells (CHO/HPRT assay) and the xanthine-guanine phosphoribosyl transferase (gpt) locus in CHO AS52 cells (AS52/GPT assay). The results show that these chemicals are not mutagenic to the hprt locus in CHO-K1-BH4 cells either with or without rat liver S9 mix as the metabolic activating system. With AS52 cells, only MALD is mutagenic in the absence of S9. It induced a dose-dependent mutagenic response. A dose-dependent cytotoxicity was induced by all compounds in both cell lines. MALD is the most and EGME is the least cytotoxic compounds. Our study shows that a metabolite of EGME, MALD, is highly cytotoxic and likely induces deletion-type mutations in AS52 cells. The genotoxic effect of EGME is, therefore, dependent upon its metabolism and its detection is dependent upon the assays used.

Differences between rats and mice in the immunosuppressive activity of 2-methoxyethanol and 2-methoxyacetic acid

Previous studies from this laboratory have demonstrated that 2-methoxyethanol (ME) and its principal metabolite 2-methoxyacetic acid (MAA) are immunosuppressive in young adult male Fischer 344 rats. In the present study, the immunosuppressive potential of ME and MAA was evaluated in young adult female Fischer 344 rats and C57BL/6J mice. Rats and mice were dosed by gavage with either ME or MAA in water, at dosages ranging from 50-400 mg/kg/day, for 10 consecutive days. Rats and mice were examined for alterations in body, spleen and thymus weights and mitogen-induced proliferation of splenic lymphocytes in vitro; separate groups were employed for the antibody plaque-forming cell (PFC) response to trinitrophenyl-lipopolysaccharide (TNP-LPS). Rats dosed at 100-400 mg/kg/day ME and rats dosed at 50-400 mg/kg/day MAA had decreased thymus weights in the absence of decreased body or spleen weights. Lymphoproliferative (LP) responses to concanavalin A (Con A), phytohemagglutinin (PHA), pokeweed mitogen (PWM) and Salmonella typhimurium mitogen (STM) were all reduced in rats treated with all dosages of ME. Rats treated with MAA displayed similar reductions in these LP responses except that the responses to PWM and STM in rats dosed at 50 mg/kg/day were not reduced. In contrast to the effects of ME and MAA on these end points in the rat, no thymic involution or suppression of LP responses were observed in mice dosed at 50-400 mg/kg/day. The PFC response to TNP-LPS was suppressed in rats dosed with either ME or MAA at dosages of 100-400 mg/kg/day. ME and MAA, however, failed to suppress the PFC response in mice immunized with TNP-LPS. These results indicate that unlike Fischer 344 rats, C57BL/6J mice are insensitive to the immunosuppressive effects of ME and MAA at the dosages employed in this study. Whether the different sensitivities of these two rodent species to ME- and MAA-induced immunosuppression are due to immunologic, pharmacokinetic or metabolic differences within each species remains to be determined.

2-Methoxyacetic acid dosimetry-teratogenicity relationships in CD-1 mice exposed to 2-methoxyethanol

The teratogen 2-methoxyethanol (2-ME), an industrial solvent, was administered to pregnant CD-1 mice either as a single subcutaneous (sc) bolus dose (100-250 mg/kg) or via constant-rate infusion from sc implanted osmotic minipumps (34.7 or 69.4 mg/kg/hr for up to 12 hr) on gestation Day 11, when embryonic paw development is maximally sensitive to perturbation by this agent. The sc entry route most closely reflects likely human exposures via dermal penetration, while bolus and constant-rate infusion administrations were contrasted to mimic potential occupational exposure scenarios. The pharmacokinetic profiles of 2-methoxyacetic acid (2-MAA), the proximate toxic metabolite of 2-ME, were quantitated, generating peak concentration (Cmax) and total 2-MAA exposure values (24-hr area under the concentration-time curve; AUC) in the maternal plasma, extraembryonic fluid, and embryo. The total 2-ME dose (mg/kg) required to achieve similar 2-MAA levels (Cmax or AUC) in these compartments was 2- to 3-fold higher by constant-rate infusion than by bolus injection; therefore, no simple association existed between 2-MAA levels and the total 2-ME dose, when the dose rate was not considered. Similarly, there was no good correlation between the combined total 2-ME doses and the fetal malformation rate, although clear dose-response patterns for paw malformations were observed in litters and fetuses for each individual dosing regimen. However, the combined 2-MAA pharmacokinetic data from each of the dosing regimens demonstrated that during the phase of maximum susceptibility of paw morphogenesis to disruption by 2-MAA (from gd 11 to gd 11.5), a strong linear correlation existed between fetal malformation incidence and 2-MAA AUC levels in either maternal plasma or embryonic compartments (linear correlation coefficient, r2 0.91-0.92). The correlation with Cmax was less favorable (r2 0.74-0.81) over the dose range studied. In a further experiment designed to investigate the importance of AUC vs Cmax regarding 2-ME teratogenicity, infusion of 2-ME (34.7 mg/kg/hr for 8 hr) beginning 2.5 hr after bolus loading (175 mg/kg) provided an increased 24-hr 2-MAA AUC without increased Cmax. This resulted in greater than 70% of the fetuses having various digit malformations (micro-, syn-, ectro-, and polydactyly), compared to only 32-35% of fetuses with mostly stunted digits when either dose was applied singularly. These data support total 2-MAA exposure (AUC levels), rather than peak 2-MAA concentrations, as the principle determinant of teratogenesis following exposure to 2-ME.(ABSTRACT TRUNCATED AT 400 WORDS)

2-Methoxyethanol metabolism in pregnant CD-1 mice and embryos

Upon oxidation to 2-methoxyacetic acid (2-MAA), 2-methoxyethanol (2-ME) causes malformations in all animal species that have been examined. Commonly, 2-MAA is thought to be the proximate toxicant. However, our previous studies with [1,2-14C]2-ME and the present data obtained with [1-14C]2-MAA, [2-14C]2-ME and [methoxy-14C]2-ME revealed that metabolism beyond 2-MAA occurs. Regardless of the 14C position, dams exhaled approximately 5% of the radioactivity administered as a single teratogenic oral dose (3.3 mmol/kg on Gestation Day [gd] 11) as 14CO2. With all isotopic variants urine contained 70-80% of the dose within 24 hr after administration and 13-18% in the next 24 hr. Three labeled products were resolved using HPLC: an unidentified Peak A (12-18% of dose), 2-MAA (approximately 50%), and the glycine conjugate of 2-MAA (approximately 25%). Short-term (4 hr) whole embryo culture on gd 11 with 3 mM 2-MAA and a tracer dose of [1-14C]2-MAA, [2-14C]2-MAA, or [methoxy-14C]2-MAA showed that 14CO2 evolved from the former two substrates, while there was none detectable from the latter. The data indicate that dams metabolized [methoxy-14]2-MAA to 14CO2, while embryos apparently did not. The production of labeled CO2 from [2-14C]2-ME suggests that 2-methoxyacetyl approximately CoA (the precursor for amino acid conjugation with glycine) entered into the tricarboxylic acid (TCA) cycle. This interpretation is supported by the inhibition of 14CO2 evolution elicited by fluoroacetate (0.1 or 1.0 mM) and sodium acetate (5 mM). It is not yet clear whether entry of 2-methoxyacetyl approximately CoA as a "false substrate" in the TCA cycle is of significance for the embryotoxic effects of 2-ME/2MAA.

Protection against 2-methoxyethanol-induced teratogenesis by serine enantiomers: studies of potential alteration of 2-methoxyethanol pharmacokinetics

Several simple physiological compounds attenuate the teratogenic effects of 2-methoxyethanol (2-ME) when coadministered with 2-ME to mice. The mechanism of this protective action, however, has not been elucidated. Alteration of the kinetics of 2-ME and its oxidation product 2-methoxyacetic acid (2-MAA), the putative ultimate toxicant, was considered. D-Serine, the most efficacious attenuator, and L-serine (both 16.5 mmol/kg po) were examined for their abilities to mitigate 2-ME teratogenicity and to alter the disposition of an oral or sc bolus dose of 2-ME (3.3 mmol/kg containing 6 microCi 2-[methoxy-14C]ethanol) given to CD-1 mice on Gestation Day 11. L-Serine reduced the incidence of malformed fetuses from greater than or equal to 72% to 26-28%, while only 18 and 9% of fetuses were affected after coadministration of D-serine with sc and po 2-ME, respectively. Changes in the metabolism of orally administered 2-[14C]ME were specific to each enantiomer. D-Serine reduced the amount of 2-methoxy-N-acetylglycine eliminated in the urine to 70-75% of values observed with 2-ME alone, and concurrently increased the amount of urinary 2-MAA. L-Serine induced an initially higher rate of 14CO2 exhalation. Both enantiomers delayed gastrointestinal absorption of 2-ME, and significantly reduced 2-MAA levels in maternal plasma during the first hour after dosing. This resulted in a nonsignificant decrease (10-17%) in total embryonic exposure to 2-MAA. However, when 2-ME was injected sc, maternal plasma 2-ME/2-MAA pharmacokinetics were not affected by serine. In addition, dosing with 2.3 and 1.3 mmol 2-ME/kg sc alone showed that the embryo 2-MAA exposure levels which cause malformations in less than or equal to 35% fetuses were considerably lower than those measured following serine plus 3.3 mmol 2-ME/kg (po or sc). These data infer that serine does not protect against 2-ME-induced teratogenicity by altering 2-ME pharmacokinetics and reducing 2-MAA levels in the embryo.

Evaluation of 2-methoxyacetic acid toxicity on mouse germ cells by flow cytometry

Flow cytometric (FCM) DNA content measurements were carried out on testicular monocellular suspensions obtained from mice exposed per os to a single dose of 50, 100, 300, 600, and 900 mg/kg body weight (b.w.) of 2-methoxyacetic acid (MAA) in order to investigate its cytotoxic action on germ cells. The effects of MAA were evaluated 2, 7, 14, 28, and 45 d after treatment in terms of altered cell type ratios in FCM fluorescence distribution histograms. Testis weight and histological tissue sections were also analyzed. MAA induced marked changes in the relative percentages of tetraploid and haploid cells, indicating the occurrence of cytotoxic damage on primary spermatocytes. Multiparameter FCM analysis showed that, besides its action on nucleic acid synthesis, MAA can also affect the cellular energy metabolism reflected in an altered mitochondrial mass distribution on round spermatids surviving the MAA treatment. This study demonstrates that rapid and unique FCM procedures can be usefully applied in reproductive toxicology.

Marked increase in the teratogenicity of the combined administration of the industrial solvent 2-methoxyethanol and radiofrequency radiation in rats

Limited published animal research reports synergistic teratogenic effects following combined hyperthermia (induced by elevated ambient temperature) and administration of chemical teratogens. Radiofrequency (RF) radiation is widely used in occupational environments. Since RF radiation also elevates the body temperature of, and is teratogenic to, exposed animals, concurrent RF radiation and chemical agent administration may enhance teratogenicity. The present exploratory study, consisting of preliminary dose-finding studies and the primary study, was designed to investigate whether concurrent exposure of rats to RF radiation and the industrial solvent 2-methoxyethanol (2ME) can enhance the developmental toxicity of either agent acting alone. Preliminary dose-finding studies using small numbers of rats investigated the ability of various RF radiation conditions and doses of 2ME to produce external malformations (primarily of the paws) when administered on gestation day 13. Based on these preliminary studies, RF radiation exposure [sufficient to elevate rectal temperature to 42.0 degrees C (4 degrees C above normal for rats) for 30 min] and 2ME administration (150 mg/kg) were selected for the primary study. In the primary study, groups of 18 to 27 pregnant rats were administered RF radiation exposure and distilled water gavage, 2ME gavage and sham RF exposure, RF radiation exposure and 2ME gavage concurrently, or sham RF exposure and distilled water gavage. Pregnant rats were sacrificed on gestation day 20, and the offspring were examined for external malformations. Combined exposures enhanced the adverse effects produced by either experimental agent alone (no malformations were detected in the double sham group). Mean fetal malformations/litter increased from 14% after 2ME and sham RF (15/26 litters affected, with an average of 2 fetuses/litter malformed) and 30% after RF radiation and water gavage (10/18 litters affected, with an average of 4 fetuses/litter malformed), to 76% after the combined treatment (18/18 litters affected, with an average of 12 fetuses/litter malformed). In addition to a significant increase in the frequency of malformations, the severity of malformations also was enhanced by the combination treatment (on a relative severity ranking scale, the 2ME severity score was less than 1, the RF score was 3, and the combination score was 6). This study provided evidence of synergism between RF radiation and 2ME administration, but additional research will be required to characterize the extent of synergism between these two agents. Potential interactive effects between chemical and physical agents need to be investigated to determine the extent to which such interactions should impact occupational exposure standards.

The chemotherapeutic potential of glycol alkyl ethers: structure-activity studies of nine compounds in a Fischer-rat leukemia transplant model

Structure-activity studies with nine glycol alkyl ethers were conducted with a cellular leukemia transplant model in male Fischer rats. This in vivo assay measures the effects of chemical treatment on neoplastic progression in transplant recipients. Chemicals were given ad libitum in the drinking water simultaneously with the transplants and continued throughout the study. In all, 20 million leukemic cells were injected s.c. into syngeneic rats, which after 60 days resulted in a 10-fold increase in relative spleen weights, a 100-fold increase in white blood cell counts, and a 50% reduction in red blood cell (RBC) indices and platelet counts. At this interval, ethylene glycol monomethyl ether (2-ME) given at a dose of 2.5 mg/ml in the drinking water completely eliminated all clinical, morphological, and histopathological evidence of leukemia, whereas the same dose of ethylene glycol monoethyl ether (2-EE) reduced these responses by about 50%. Seven of the glycol ethers were ineffective as anti-leukemic agents, including ethylene glycol, the monopropyl, monobutyl, and monophenyl ethylene glycol ethers, diethylene glycol, and the monomethyl and monoethyl diethylene glycol ethers. 2-ME more than doubled the latency period of leukemia expression and extended survival for at least 210 days. A minimal effective dose for a 50% reduction in the leukemic responses was 0.25 mg/ml 2-ME in the drinking water (15 mg/kg body weight), whereas a 10-fold higher dose of 2-EE was required for equivalent antileukemic activity. In addition, the in vitro exposure of a leukemic spleen mononuclear cell culture to 2-ME caused a dose- and time-dependent reduction in the number of leukemia cells after a single exposure to 1-100 microM concentrations, whereas the 2-ME metabolite, 2-methoxyacetic acid, was only half as effective. The two glycol alkyl ethers with demonstrable anti-leukemic activity, 2-ME and 2-EE, also exhibited a favorable efficacy-to-toxicity ratio and should be considered for further development as chemotherapeutic agents.

Disposition of three glycol ethers administered in drinking water to male F344/N rats

The glycol ethers 2-methoxyethanol (ME), 2-ethoxyethanol (EE), and 2-butoxyethanol (BE) are widely used solvents in industrial and consumer applications. The reproductive, teratogenic, and hematotoxic effects of the glycol ethers are due to the alkoxyacetic acid metabolites of these compounds. The effect of alkyl group length on disposition of these three glycol ethers was studied in male F344/N rats allowed access for 24 hr to 2-butoxy[U-14C]ethanol, 2-ethoxy[U-14C]ethanol, or 2-methoxy[U-14C]ethanol in drinking water at three doses (180 to 2590 ppm), resulting in absorbed doses ranging from 100 to 1450 mumols/kg body wt. Elimination of radioactivity was monitored for 72 hr. The majority of the 14C was excreted in urine or exhaled as CO2. Less than 5% of the dose was exhaled as unmetabolized glycol ether. Distinct differences in the metabolism of the glycol ethers as a function of alkyl chain length were noted. For BE 50-60% of the dose was eliminated in the urine as butoxyacetic acid and 8-10% as CO2; for EE 25-40% was eliminated as ethoxyacetic acid and 20% as CO2; for ME 34% was eliminated as methoxyacetic acid and 10-30% as CO2. Ethylene glycol, a previously unreported metabolite of these glycol ethers, was excreted in urine, representing approximately 10, 18, and 21% of the dose for BE, EE, and ME, respectively. Thus, for longer alkyl chain lengths, a smaller fraction of the administered glycol ether was metabolized to ethylene glycol and CO2. Formation of ethylene glycol suggests that dealkylation of the glycol ethers occurs prior to oxidation to alkoxyacetic acid and, as such, represents an alternate pathway in the metabolism of these compounds that does not involve formation of the toxic acid metabolite.