Methoxyacetic Acid Research Articles

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.

Exposure to ethylene glycol ethers and spermatogenic disorders in man: a case-control study.

A case-control study was conducted among first time patients at a clinic for reproductive disorders. The study group consisted of 1019 cases, defined as patients diagnosed infertile or subfertile on the basis of a spermiogram and 475 controls who were diagnosed as normally fertile by the same procedure. Possible exposure to ethylene glycol ethers was assessed by the presence of the urinary metabolites methoxyacetic acid (MAA) and ethoxyacetic acid (EAA) respectively for 2-methoxyethanol and 2-ethoxyethanol or their acetates. In total, EAA was detected in 39 cases and six controls, with a highly significant odds ratio of 3.11 (p = 0.004). On the other hand, MAA was only found in one case and two controls. The presence of EAA in urine proved to be strongly associated with exposure to preparations containing solvents, especially paint products, and with some groups of occupations, the most important of which were also directly or possibly connected with paint products. The absence of a significant correlation between the concentration of urinary EAA and the various measures of sperm quality could be explained by the expected latent period between exposure and observed effects. Other temporal aspects of the relation between exposure as judged from the presence of urinary EAA and diagnosis are also discussed.

Stage-specific expression of rat transition protein 2 mRNA and possible localization to the chromatoid body of step 7 spermatids by in situ hybridization using a nonradioactive riboprobe.

The present study has used methoxyacetic acid (MAA)-induced depletion of specific germ cell types in the rat and in situ hybridization with nonradioactive riboprobes to determine the stages of the spermatogenic cycle at which there is expression of the mRNA for the basic chromosomal protein transition protein 2 (TP2). On Northern blots, an abundant mRNA was detectable in samples from control adult rats, but the amount of message was markedly reduced when RNA was extracted from the testes of rats treated 14 and 21 days previously with methoxyacetic acid. These testes were depleted specifically of step 7-12 spermatids, suggesting that these cells contain TP2 mRNA. When tissue sections were subjected to in situ hybridization, the TP2 mRNA was localized at the cellular and subcellular levels. Messenger RNA for TP2 was first detectable in spermatids at step 7. In these spermatids, at high magnification, in addition to some positive reaction in the cytoplasm, intense staining was located to a perinuclear structure consistent with localization of mRNA within the chromatoid body. The amount of TP2 mRNA in the cytoplasm increased as remodelling of the early spermatid nucleus progressed and was highest in step 10 and 11 spermatids at stages X and XI. Thereafter, the mRNA decreased until it was undetectable in step 14 spermatids at stage XIV. The localization of TP2 mRNA to the chromatoid body of step 7 spermatids would be consistent with this organelle being a storage site for long-lived mRNAs utilized later in spermiogenesis.

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.

Urinary creatine profiles after administration of cell-specific testicular toxicants to the rat.

Cell-specific testicular toxicants have been used to examine the distribution of creatine within the rat testis, and to examine the potential use of creatinuria as a non-invasive indicator of testicular damage. Groups of rats were administered single doses of various toxicants: a germ cell toxicant (methoxyacetic acid, MAA), one of two Sertoli cell toxicants (di-n-pentyl phthalate, DPP or 1,3-dinitrobenzene, 1,3-DNB), or a Leydig cell toxicant (ethane-1,2-dimethane sulphonate, EDS). Urinary creatine and creatinine levels were monitored in 24 h periods over the following 48 h, after which time the testes were removed, weighed and, after processing, sections were examined by light microscopy. All four treatments resulted in reductions in relative testis weight (RTW) and produced morphological changes similar to those which have been previously reported. In addition, MAA, DPP and 1,3-DNB all caused significant elevations in urinary creatine excretion and the urinary creatine:creatinine ratio (Cr/Crn) within 24 h. EDS had no such effect. We conclude that creatine is associated with the cells of the seminiferous epithelium, and that elevated urinary excretion of creatine may serve as a non-invasive marker for damage to these cells in vivo.

Characterization of urinary metabolites from [1,2,methoxy-13C]-2-methoxyethanol in mice using 13C nuclear magnetic resonance spectroscopy.

2-Methoxyethanol (2-ME) is an industrial solvent that induces developmental and testicular toxicity in laboratory animals. Oxidation of 2-ME to 2-methoxyacetic acid (2-MAA) is required for the generation of these adverse effects. The urinary metabolites of 2-ME were investigated to characterize the fate of 2-ME and 2-MAA. 13C NMR spectroscopy was used to detect and assign metabolites in the urine of pregnant CD-1 mice following administration of 250 mg/kg of [1,2,methoxy-13C]-2-ME. Two-dimensional NMR methods were used to correlate signals from the labeled carbons in each 2-ME metabolite and to determine the number of hydrogens attached to each carbon. Structures were assigned from the NMR data together with calculated values of shift for biochemically feasible metabolites and by comparison to standards. Pathways involved in forming metabolites assigned in this study include transformation of 2-ME via ethylene glycol, conjugation with glucuronide or sulfate, and oxidation to 2-MAA. Additional metabolites were assigned that can be formed from further conversion of 2-MAA to glycine and glucuronide conjugates, as well as metabolites derived from the incorporation of 2-methoxyacetyl CoA derivatives into intermediary metabolism. Elucidation of the further metabolism of 2-MAA may be important for understanding the mechanisms by which 2-ME induces adverse effects.

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 constantrate 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 constantrate 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 ( C max ) 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 ( C max 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, r 2 0.91–0.92). The correlation with C max was less favorable ( r 2 0.74–0.81) over the dose range studied. In a further experiment designed to investigate the importance of AUC vs C max 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 C max . This resulted in >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. Furthermore, there was excellent linear correlation between AUC levels of the alkoxyacid in the embryonic compartments and those in the maternal plasma, following all dosing regimes ( r 2 ≥ 0.98), indicating the latter to be a good predictor of teratogenic outcome under the exposure conditions that were examined. It is unknown whether this relationship will extend to lower dose ranges.

Comparative immunosuppression of various glycol ethers orally administered to Fischer 344 rats

Oral dosing of adult male F344 rats with the glycol ether 2-methoxyethanol (ME) or its principal metabolite 2-methoxyacetic acid (MAA) results in the suppression of the primary plaque-forming cell (PFC) response to trinitrophenyl-lipopolysaccharide (TNP-LPS). In the present study, the PFC response to TNP-LPS was used to evaluate the immunotoxic potential of ethylene glycol (EG) as well as the glycol ethers 2-methoxyethyl acetate (MEA), 2-(2-methoxyethoxy) ethanol, bis(2-methoxyethyl) ether, 2-ethoxyethanol and its principal metabolite 2-ethoxyacetic acid, 2-ethoxyethyl acetate, and 2-butoxyethanol relative to ME and MAA. Rats were immunized with TNP-LPS and then exposed 4 and 28 hr later to 50, 100, 200, or 400 mg/kg of glycol ether or EG. Three days following immunization, the PFC response to TNP-LPS was determined. In addition to ME and MAA, only MEA, which was as effective as ME, suppressed the PFC response to TNP-LPS. Concomitant administration of the alcohol dehydrogenase inhibitor 4-methylpyrazole with ME or MEA prevented suppression of the PFC response by these glycol ethers. These results indicate that of the chemicals tested only ME, MEA, and MAA are immunosuppressive, and that oxidative metabolism via alcohol dehydrogenase is necessary for ME- and MEA-suppression of the response to TNP-LPS.

Evaluation of the role of germ cells in regulating the route of secretion of immunoactive inhibin from the rat testis.

During normal sexual maturation of the male rat there is a progressive change in the route of secretion of inhibin by the Sertoli cell, from a predominantly basal route of secretion in prepuberty to a predominantly apical route of secretion in adulthood. This change may be monitored by comparing the levels of inhibin in testicular (TV), spermatic and peripheral (PV) venous blood and the levels in testicular interstitial fluid (IF). This study has assessed the role of germ cells in effecting this change by assessing (a) the effect of total germ cell depletion by X-irradiation of the males in utero, and (b) the effect of selective germ cell depletion in adulthood using the testicular toxicant, methoxyacetic acid (MAA). Female rats were X-irradiated on day 20 of gestation to produce male offspring whose testes were germ-cell deficient. Blood and IF samples were collected from groups of these offspring and age-matched controls at 35 and 100 days of age. In blood and IF samples, inhibin concentrations were significantly higher at 35 days of age than at 100 days. The absence of germ cells in X-irradiated animals did not affect the age-related fall in inhibin levels, nor the change in the predominant route of secretion of inhibin from the testis into blood. Testosterone was almost undetectable in 35-day-old controls, but was raised significantly by 100 days of age. In X-irradiated animals, testosterone levels were increased significantly at 35 days of age, and the levels in most samples were increased even more substantially by 100 days of age. However, PV levels of testosterone in 100-day-old X-irradiated animals were significantly lower than in controls. LH and FSH levels were raised in X-irradiated animals compared with their age-matched controls, but FSH levels in X-irradiated animals still fell with age, as in the controls. The role of specific germ cell types in regulating the route of secretion of inhibin from the normal adult testis was studied after depletion (80-100%) of pachytene and later spermatocytes by a single oral administration of MAA (650 mg/kg) to adult rats. At 3 days after MAA treatment, coincident with the loss of pachytene spermatocytes, plasma inhibin levels were increased significantly in blood and IF samples, and this was associated with a dramatic change in the route of secretion of inhibin from the testis, with increased secretion of this peptide via the base of the Sertoli cell into IF and TV blood.(ABSTRACT TRUNCATED AT 400 WORDS)

The role of specific germ cell types in modulation of the secretion of androgen-regulated proteins (ARPs) by stage VI–VIII seminiferous tubules from the adult rat

This study has assessed the role of specific germ cell types in modulating the secretion of seven previously identified androgen-regulated proteins (ARPs) as well as the increase in overall level of protein secretion by seminiferous tubules (ST) at stages VI–VIII of the spermatogenic cycle in the rat. Methoxyacetic acid (MAA) was administered at 650 mg/kg to induce 80–100% depletion of pachytene and later spermatocytes; ST at stages VI–VIII were then isolated at 4, 18 and 30 days after MAA treatment when pachytene spermatocytes (PS), round spermatids (RS) or elongate spermatids (ES), respectively, were depleted selectively. By comparison with ST isolated from controls or from rats 4 days after ethanedimethane sulphonate (EDS)-induced testosterone withdrawal, the overall level of incorporation of 35S-methionine into ST-secreted proteins was assessed after culture for 22 h at 32°C as well as the relative abundance of ARPs identified by two-dimensional sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). Depletion of PS caused a substantial decrease in abundance of ARP-6 (53–57 kDa; p I 5.7–5.8) and ARP-7 (56–59 kDa; p I 5.9–6.2) and minor and more variable decreases in ARP-3 (27–30 kDa; p I 7.4) and ARP-4 (38 kDa; p I 6.0–6.2); ARP-6 and ARP-7 are comparable in size to the A and B forms of P-Mod-S, a product of the peritubular cells. Depletion of RS resulted in the complete disappearance of ARP-2 (13–14.5 kDa; p I 7.3–7.6), a decrease in abundance of ARP-7 and variable decreases in ARP-1 (9̃.5 kDa; p I 6.9–7.4) and ARP-6; ARP-1 and -2 are thought to be Sertoli cell-secreted proteins. Depletion of ES had no effect on secretion of the ARPs. Depletion of PS, RS or ES resulted in significant ( P < 0.001) decreases of 26, 38 and 42% respectively in the overall level of incorporation of methionine into ST-secreted proteins, but this was significantly less than the decrease (55%) induced by EDS-induced testosterone withdrawal. These results show that the androgen-dependent changes in secretion of proteins, which occur specifically at stages VI–VIII of the normal spermatogenic cycle, are largely, if not completely, dependent on a normal germ cell complement, with each germ cell type regulating the secretion of proteins essential for its own development. These findings thus add to the growing evidence for the complex functional inter-dependence of all of the cell types in the testis, and probably explain why previous studies with isolated Sertoli cells have failed to identify the ARPs.

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 ∼5% of the radioactivity administered as a single teratogenic oral dose (3.3 mmol/kg on Gestation Day [gd] 11) as 14CO 2. 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 (∼50%), and the glycine conjugate of 2-MAA (∼25%). Short-term (4 hr) whole embryo culture on gd 11 with 3 m m 2-MAA and a tracer dose of [1- 14C]2-MAA, [2- 14C]2-MAA, or [ methoxy- 14C]2-MAA showed that 14CO 2 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 14CO 2, while embryos apparently did not. The production of labeled CO 2 from [2- 14C]2-ME suggests that 2-methoxyacetyl∼CoA (the precursor for amino acid conjugation with glycine) entered into the tricarboxylic acid (TCA) cycle. This interpretation is supported by the inhibition of 14CO 2 evolution elicited by fluoroacetate (0.1 or 1.0 m m) and sodium acetate (5 m m). It is not yet clear whether entry of 2-methoxyacetyl∼CoA as a “false substrate” in the TCA cycle is of significance for the embryotoxic effects of 2-ME/2MAA.

Evaluation of the immunotoxicity of orally administered 2-methoxyacetic acid in Fischer 344 rats

We previously demonstrated that the glycol ether 2-methoxyethanol (ME) is immunotoxic in the rat. In this study, the immunotoxicity of 2-methoxyacetic acid (MAA), the principal metabolite of ME, was evaluated in adult male Fischer 344 rats. Rats were dosed by gavage with MAA on 10 consecutive days at dosages ranging from 50 to 200 mg/kg/day. Thymic involution, in the absence of body weight loss, was observed at 100 and 200 mg/kg/day MAA. Lymphoproliferative responses to the mitogens concanavalin A, phytohemagglutinin, and pokeweed mitogen were also reduced at these dosages. The in vitro generated cytotoxic T lymphocyte response was reduced at 200 mg/kg/day MAA. The mixed lymphocyte reaction and natural killer cell activity were unaffected by exposure to MAA. Enumeration of splenic lymphocyte populations revealed a reduction in the percentage of W3 25 -positive cells at 100 and 150 mg/kg/day and an increase in the percentage of OX39-positive cells at 200 mg/kg/day; however, no changes in the absolute number of either of these subsets were observed. The plaque forming cell (PFC) response to trinitrophenyl-lipopolysaccharide (TNP-LPS) was suppressed at 50–200 mg/kg/day MAA, while the PFC response to sheep red blood cells (SRBC) was elevated at 50 mg/kg/day. Immunization of rats with TNP-LPS or SRBC followed by oral exposure to MAA at 4 and 28 hr postimmunization resulted in the suppression of the PFC response to TNP-LPS and SRBC at dosages of 100 and 200 mg/kg and 200 and 400 mg/kg, respectively. Equal suppression of the PFC response to TNP-LPS was achieved at equimolar concentrations of ME and MAA. The effects of MAA on the immune system of the rat presented here are very similar to results reported from this lab for ME-induced immune alterations. These results, along with results of experiments in which ME-induced suppression of the PFC response to TNP-LPS was reversed by 4-methylpyrazole, an inhibitor of the oxidation of ME to MAA by alcohol dehydrogenase, indicate that MAA is the proximate immunotoxicant following exposure to the glycol ether 2-methoxyethanol.

Degradation of Methyl β-D-Ribopyranoside and Methyl β-D-Xylopyranoside by Oxygen in Aqueous Sodium Hydroxide Solution

Abstract Methyl β-D-ribopyranoside (1) and methyl β-D-xylopyranoside (2) were degraded by oxygen (0.682 MPa partial pressure) in 1.25 M sodium hydroxide at 120°C. The degradations of 1 and 2 were similar to the previously reported degradations of 1,5-anhydroribitol (3) and 1,5-anhydroxylitol (4), respectively.4 Both hydrogen peroxide and stable organic peroxides were detected in the reactions of 1 and 2. The riboside 1 degraded faster than the xyloside 2. This difference in reactivity is proposed to be a function of the relative acidity of the glycosides. Ionization of hydroxyl groups is postulated to be favored in 1, thus facilitating the initiation of the free radical degradation. The degradations of both 1 and 2 exhibited complex kinetics indicating autoinhibited reactions. In spite of the differences in reactivity, glycosidic bond cleavage occurred in approximately 60% of the degradations for both 1 and 2. C-1 radicals, resulting from abstraction of the anomeric hydrogen atom, are proposed to cause the observed autoinhibition via termination reactions with α-hydroxyhydroperoxyl radicals. However, decomposition of the glycosides via C-1 radicals is not believed to constitute a major degradation pathway since the reactivities of 1 and 2 were essentially the same as the analogous 1,5-anhydroalditols, i.e. 3 and 4, respectively. The major acidic degradation products of 1 and 2 were identical, but were formed in different relative ratios. The major acidic products were methoxyacetic acid, lactic acid, glycolic acid, glyceric acid, a methyl 3-C-carboxyfuranoside, and two isomeric 2-C-carboxyfuranosides.

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 μCi 2-[ methoxy- 14C]ethanol) given to CD-1 mice on Gestation Day 11. l-Serine reduced the incidence of malformed fetuses from ≥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 14CO 2 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 ≤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.

Immunotoxicity of 2-methoxyethanol following oral administration in Fischer 344 rats

The immunotoxicity of the glycol ether 2-methoxyethanol (ME) was evaluated in adult Fischer 344 rats using a variety of in vitro and in vivo immune function assays. In the first phase of this study, male rats were dosed by oral gavage with ME in water, at dosages ranging from 50 to 200 mg/kg/day, for 10 consecutive days. Decreases in thymus weights were observed at dosages of 50–200 mg/kg/day in the absence of decreased body weights. Lymphoproliferative (LP) responses to concanavalin A and phytohemagglutinin were reduced at 50–200 mg/kg/day while pokeweed mitogen and Salmonella typhimurium mitogen responses were reduced at 200 mg/kg/day. No alterations were observed in natural killer cell activity, mixed lymphocyte reaction, or cytotoxic T lymphocyte responses. The frequency of W3 25 -positive splenocytes was reduced in rats dosed at 200 mg/kg/day. Interleukin-2 production was reduced in splenocytes from rats exposed to all dosages of ME. The plaque-forming cell (PFC) response to sheep red blood cells was enhanced in rats dosed at 50 mg/kg/day. However, the PFC response to trinitrophenyl-lipopolysaccharide (TNP-LPS) was suppressed at all dosages. Similary, the PFC response to TNP-LPS was suppressed in adult female rats dosed with ME. A reduction in the expulsion of adult worms was observed in rats dosed at 200 mg/kg/day that were infected with Trichinella spiralis. A number of male reproductive parameters were also evaluated in rats dosed with ME over 10 days. A significant reduction in testicular weight was observed in rats dosed at 200 mg/kg/day. In the second phase of this study, the PFC response to TNP-LPS was employed to assess the role that metabolism of ME to 2-methoxyacetic acid (MAA) plays in the immunotoxicity of this glycol ether. Ten-day oral dosing with MAA resulted in the inhibition of the PFC response to TNP-LPS at dosages of 50–200 mg/kg/day. Concomitant exposure of rats to ME and the alcohol dehydrogenase inhibitor 4-methylpyrazole blocked ME-induced suppression of this PFC response. Attempts to ameliorate ME-induced suppression of the PFC response with serine, which has been shown to reverse ME-induced developmental and reproductive toxicity, were unsuccessful. These results suggest that the immune system may be more sensitive than the reproductive system to the toxic effects of ME. Furthermore, it appears that MAA is the proximate toxicant for ME-induced alterations in the immune system, as has been demonstrated for ME-induced reproductive and developmental toxicity.

Chick embryo neural retinal cell culture as a screen for developmental toxicity

An in vitro screen for developmental toxic potential of chemicals using primary cultures of chick embryo neural retina cells in described. The neural retinas of incubation Day 6.5 White Leghorn chick embryos are dissociated into single cells, which are subsequently maintained in a rotating suspension culture. Under normal circumstances, neural retina cells form spheroidal aggregates of a consistent size over the first 24 hr of culture, an event which is dependent on competent cell-cell interactions. Over the remaining 7-day period of culture, cells continue to divide and grow, and differentiation takes place. Each of these developmentally important events—aggregation, growth, and differentiation—is objectively and quantitatively measured as aggregate size and number, aggregate protein content, and glutamine synthetase (a marker of differentiation) activity, respectively. The effects on each developmental endpoint of 22 chemicals, 14 of which have been demonstrated to be developmentally toxic in one or more mammalian species in vivo, and 8 of which are not developmentally toxic, were evaluated. Chemicals were tested up to a concentration of 40 m m, or until marked cytolethality was observed. Of the known developmental toxicants, all but one, 2-methoxyethanol, affected one or more endpoints in the assay. The teratogenic metabolite of 2-methoxyethanol, 2-methoxyacetic acid, was active in the assay. None of the 8 nondevelopmental toxicants had any effect up to c concentration of 40 m m, or at biologically achievable concentrations (e.g., in vivo systemic concentrations at the LD50). Thus, the assay is 95% concordant with in vivo results for this set of chemicals. Quantitative comparisons were made (1) between developmentally toxic ip dosages in rats or mice in vivo and effective concentrations in the chick retina cell culture, and (2) between effective concentrations in chick retina cell culture and rodent whole embryo culture. In the first instance, 71% of the comparisons, and in the second instance, 89% of the comparisons, were within the same order of magnitude (and usually within a factor of two), indicating that the chick retina cell culture is also concordant with developmental toxic potency. Last, it was observed that test agents differentially affect developmental endpoints. Because the assay's endpoints are measured separately and objectively, it may be possible to use the assay to evaluate the effects of test agents on cellular development. The effects of tested chemicals on chick neural retina cells was consistent with reported effects of those chemicals. For example, chemicals which interfere with intercellular communication affected aggregation (e.g., all-trans retinoic acid, TPA), heavy metals (CdCl 2, HgCl 2) diminished growth, and chemicals which affect gene expression inhibited differentiation (e.g., bromodeoxyuridine, actinomycin D). Thus, the chick embryo retina assay appears to be capable of recapitulating in vivo developmental toxicity, and also may be useful in providing information about the mode of action of a developmental toxicant at the cellular level.

Evaluation of changes in the secretion of immunoactive inhibin by adult rat seminiferous tubules in vitro as an indicator of early toxicant action on spermatogenesis

A method for culturing isolated seminiferous tubules (ST) from adult rats for 1–3 days has been developed and optimized rigorously on the basis of the secretion of immunoactive inhibin under basal conditions and after maximal stimulation with rat FSH or dibutyryl cyclic AMP. The effect on these cultures of three known testicular toxicants was assessed. Of these, two are though to act on the Sertoli cell, meta-dinitrobenzene (mDNB) and nitrobenzene (NB), while the third, methoxy acetic acid (MAA), is thought to act on pachytene spermatocytes. In addition, the effect of a possible testicular toxicant, 3-mononitrotoluene (3-MNT), was investigated. These data were compared with those obtained using cultures of immature rat Sertoli cells (SC) or SC + germ cells and with data on the effect of equivalent doses of the compounds on the secretion of immunoactive inhibin in vivo. In studies designed to optimize conditions for the secretion of immunoactive inhibin by ST in culture, significant effects were found of the type of culture medium used, the duration of culture, the total and individual length of tubules used, etc. All subsequent studies with toxicants utilized optimal conditions. Addition of either mDNB or NB to ST cultures at 10 −5 or 10 −3 m, or MAA at 10 −4 m, stimulated basal secretion of immunoactive inhibin by two- to fourfold on Days 1, 2, or 3 of culture while FSH or dibutyryl cyclic AMP-stimulated secretion of immunoactive inhibin was either unaffected or was enhanced to a small extent. At the same doses, mDNB or NB also enhanced secretion of immunoactive inhibin by SC cultures, although these effects were more variable and of smaller magnitude than the effects on ST cultures. In contrast, addition of up to 10 −3 m MAA to cocultures of SC + germ cells had no effect on the secretion of immunoactive inhibin. Exposure of rats in vivo to levels of mDNB, NB, or MAA similar to those which stimulated secretion of immunoactive inhibin in vitro resulted in a two- to fourfold increase in the levels of immunoactive inhibin in testicular interstitial fluid (IF) at 1 and 3 days post-treatment, and this was associated with early impairment of spermatogenesis (as judged by testis weight). In contrast to these effects, addition of 3-MNT to ST or SC cultures had no effect except at 10 −3 m, when the secretion of immunoactive inhibin was increased marginally. Treatment of rats with an equivalent dose of 3-MNT in vivo resulted in death, but exposure to the highest nonlethal dose (1 g/kg) had no significant effect either on spermatogenesis or on the levels of immunoactive inhibin in testicular IF. In view of these findings, it is concluded that modulation of the secretion of immunoactive inhibin by isolated ST from adult rats has considerable potential as an in vitro screening method for investigating potential adverse effects of chemicals on spermatogenesis, and thus merits more detailed evaluation. Moreover, because of the agreement between in vitro and in vivo findings, measurement of the levels of immunoactive inhibin levels in vivo in testicular IF (or blood) may also be useful in the detection of early adverse effects of chemicals on spermatogenesis.

Bis(2-methoxyethyl) ether: Metabolism and embryonic disposition of a developmental toxicant in the pregnant CD-1 mouse

An embryotoxic oral dose of bis(2-methoxyethyl) ether (DGDME), 3.73 mmol/kg body wt (500 mg/kg), administered on the 11th day of gestation to pregnant CD-1 mice was metabolized predominantly by O-demethylation to 2-(2-methoxyethoxy)ethanol with subsequent oxidation to (2-methoxyethoxy)acetic acid. Urinary excretion of this metabolite over 48 hr amounted to 63 ± 2% of the dose. A smaller percentage of the administered dose was metabolized at the central ether linkage to produce 2-methoxyethanol, which was further metabolized by alcohol dehydrogenase to methoxyacetic acid. Urinary excretion of methoxyacetic acid, a potent developmental toxicant, amounted to 28 ± 1% of the administered dose by 48 hr and was the second most prominent urinary metabolite. Unchanged DGDME and methoxyacetic acid were detected in the embryonic tissues from these animals, and embryos harvested after the initial 6-hr period showed detectable amounts of only methoxyacetic acid. The average amount of methoxyacetic acid per embryo was calculated to be 1.5 ± 1.0 μmol (5.9 mmol/kg body wt) at the 6-hr termination time. This finding suggests that the reported teratogenic effects of DGDME are due to methoxyacetic acid formed, either in the fetus or by hepatic metabolism in the dam with subsequent distribution to the embryonic tissue. These results suggest that such developmental toxicity may occur with structurally similar aprotic ethylene glycol ethers in which metabolic O-dearylation would yield 2-methoxyethanol.

Evidence for the control of testicular interstitial fluid volume in the rat by specific germ cell types

Following on from our recent evidence that Sertoli cells may regulate testicular interstitial fluid (IF) volume, this study has assessed whether depletion of specific germ cell types in vivo is associated with changes in recovered IF volume. Germ cell depletion was induced by either a single oral administration of 650 mg methoxyacetic acid (MAA)/kg or exposure of the testes to local heating (43 degrees C for 30 min). Treatment with MAA induced depletion or loss of most pachytene and later spermatocytes at 1-3 days and, because of maturation depletion, this resulted in the specific depletion of later germ cell types at 7-35 days. Testicular IF volume was unchanged at 1-7 days after MAA treatment but was increased significantly (P less than 0.01) at 14 days and was nearly doubled (P less than 0.001) at 21 days, before returning to control levels at 28-42 days. Serum LH (and FSH) levels were generally higher in MAA-treated rats, especially at 21 and 28 days, but there was no obvious correlation between LH levels and IF volume changes. Similarly, there was no relationship between IF volume changes and testicular weight or IF levels of testosterone. The increase in IF volume at 14-21 days after MAA treatment coincided with specific depletion of the later elongate spermatids (steps 14-19) and, when these cells reappeared in the testis, IF volume normalized. This possible causal association was studied further in rats exposed to local testicular heating which, within 3 days, caused major depletion of pachytene spermatocytes and early (step 1-8) spermatids.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of Changes in the Secretion of Immunoactive Inhibin by Adult Rat Seminiferous Tubules in Vitro as an Indicator of Early Toxicant Action on Spermatogenesis

Evaluation of Changes in the Secretion of Immunoactive Inhibin by Adult Rat Seminiferous Tubules in Vitro as an Indicator of Early Toxicant Action on Spermatogenesis. Allenby, G., Foster, P. M. D., and Sharpe, R. M. (1991). Fundam. Appl. Toxicol16, 710–724. A method for culturing isolated seminiferous tubules (ST) from adult rats for 1–3 days has been developed and optimized rigorously on the basis of the secretion of immunoactive inhibin under basal conditions and after maximal stimulation with rat FSH or dibutyryl cyclic AMP. The effect on these cultures of three known testicular toxicants was assessed. Of these, two are thought to act on the Sertoli cell, meta-dinitrobenzene (mDNB) and nitrobenzene (NB), while the third, methoxy acetic acid (MAA), is thought to act on pachytene spermatocytes. In addition, the effect of a possible testicular toxicant, 3-mononitrotoluene (3-MNT), was investigated. These data were compared with those obtained using cultures of immature rat Sertoli cells (SC) or SC + germ cells and with data on the effect of equivalent doses of the compounds on the secretion of immunoactive inhibin in vivo. In studies designed to optimize conditions for the secretion of immunoactive inhibin by ST in culture, significant effects were found of the type of culture medium used, the duration of culture, the total and individual length of tubules used, etc. All subsequent studies with toxicants utilized optimal conditions. Addition of either mDNB or NB to ST cultures at 10−5 or 10−3 m, or MAA at 10−4 m, stimulated basal secretion of immunoactive inhibin by two- to fourfold on Days 1, 2, or 3 of culture while FSH or dibutyryl cyclic AMP-stimulated secretion of immunoactive inhibin was either unaffected or was enhanced to a small extent. At the same doses, mDNB or NB also enhanced secretion of immunoactive inhibin by SC cultures, although these effects were more variable and of smaller magnitude than the effects on ST cultures. In contrast, addition of up to 10−3 m MAA to cocultures of SC + germ cells had no effect on the secretion of immunoactive inhibin. Exposure of rats in vivo to levels of mDNB, NB, or MAA similar to those which stimulated secretion of immunoactive inhibin in vitro resulted in a two-to fourfold increase in the levels of immunoactive inhibin in testicular interstitial fluid (IF) at 1 and 3 days post-treatment, and this was associated with early impairment of spermatogenesis (as judged by testis weight). In contrast to these effects, addition of 3-MNT to ST or SC cultures had no effect except at 10−3 m, when the secretion of immunoactive inhibin was increased marginally. Treatment of rats with an equivalent dose of 3-MNT in vivo resulted in death, but exposure to the highest nonlethal dose (1 g/kg) had no significant effect either on spermatogenesis or on the levels of immunoactive inhibin in testicular IF. In view of these findings, it is concluded that modulation of the secretion of immunoactive inhibin by isolated ST from adult rats has considerable potential as an in vitro screening method for investigating potential adverse effects of chemicals on spermatogenesis, and thus merits more detailed evaluation. Moreover, because of the agreement between in vitro and in vivo findings, measurement of the levels of immunoactive inhibin levels in vivo in testicular IF (or blood) may also be useful in the detection of early adverse effects of chemicals on spermatogenesis.