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)     

Teratogenicity and embryotoxicity of titanocene dichloride in mice

The teratogenic and embryotoxic effects of the antitumor agent titanocene dichloride (TDC) were investigated after application of single doses of TDC (30 or 60 mg/kg) to pregnant mice on days 8, 10, 12, 14 or 16 of gestation. The fetuses were removed on day 18 by caesarian section and examined for external, internal and skeletal malformations as well as for toxic phenomena. The most striking result was the occurrence of cleft palate in numerous fetuses (10% of the fetuses, 30 mg/kg; 40-50%, 60 mg/kg) after TDC application on days 10 and 12. Besides the additional appearance of costal malformations in some fetuses, no other malformations were recognizable. On the other hand, the embryotoxic influence of TDC was significant and caused diminution of the number of live fetuses per litter, marked and dose-dependent reduction of mean fetal body weight after TDC application on day 8 through day 16 and distinct retardation of skeletal ossification.     

Dose-response relationship of cadmium embryotoxicity in cultured mouse embryos

Mouse embryos were exposed in vitro to 1.2 to 2.2 μM cadmium, and effects on embryotoxicity were examined after 39 h of culture. Teratogenic responses similar to in vivo were obtained at 1.2 to 2.2 μM with concomitant reduction in embryonic protein, while embryo deaths were increased from 13.8 to 93.3% at 2.0 to 2.2 μM. The response data of both teratogenicity and growth parameters, including embryonic protein, head lenght, crown-rump lenght, somite number, and protein and diameter of yolk sac, were acceptably fitted to a cadmium is a critical parameter in the manifestation of teratogenic potential, (b) as an estimation of interference in the growth of embryos, embryonic protein is one of the most sensitive endpoints while somite number is an insensitive criterion, and (c) a linear log-probit regression is applicable to the analyses of embryotoxicity data, including growth parameters in whole-embryo culture systems.     

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.     

Dose-response relationship of cadmium embryotoxicity in cultured mouse embryos

Mouse embryos were exposed in vitro to 1.2 to 2.2 microM cadmium, and effects on embryotoxicity were examined after 39 h of culture. Teratogenic responses similar to in vivo were obtained at 1.2 to 2.2 microM with concomitant reduction in embryonic protein, while embryo deaths were increased from 13.8 to 93.3% at 2.0 to 2.2 microM. The response data of both teratogenicity and growth parameters, including embryonic protein, head length, crown-rump length, somite number, and protein and diameter of yolk sac, were acceptably fitted to a linear log-probit regression. These results suggest that (a) In chronic exposure conditions, the concentration of cadmium is a critical parameter in the manifestation of teratogenic potential, (b) as an estimation of interference in the growth of embryos, embryonic protein is one of the most sensitive endpoints while somite number is an insensitive criterion, and (c) a linear log-probit regression is applicable to the analyses of embryotoxicity data, including growth parameters in whole-embryo culture systems.     

The oxidative disposition of potassium cyanide in mice

The role of oxidative metabolism in the disposition of potassium cyanide (KCN), was investigated in mice administered KCN, (4.6 mg/kg, s.c.) containing 4.5 microCi [14C]KCN. The expired pulmonary metabolites, [14C]hydrocyanic acid (HCN) and 14CO2, were collected and analyzed. Approximately 1% and 2% of the KCN dose was expired as [14C]HCN and 14CO2, respectively. Expiration of the pulmonary metabolites was decreased following pretreatment with sodium nitrite, sodium thiosulfate, oxygen, or a combination of cyanide antidotes. Treatment with hydrogen peroxide lowered the amount of [14C]HCN expired and did not alter the expiration of 14CO2. Treatment with 3-amino-1,2,4-triazole (catalase inhibitor), superoxide dismutase, or diethyldithiocarbamic acid (superoxide dismutase inhibitor) did not change the amount of [14C]HCN expired. However, superoxide dismutase significantly increased the amount of 14CO2 expired, whereas diethyldithiocarbamic acid decreased 14CO2 expiration. The results from these studies suggest that in vivo cyanide can be oxidized to CO2 and treatment with agents that alter the availability of endogenous superoxide and/or hydrogen peroxide can alter the rate of cyanide oxidation.     

Long-term disposition of phencyclidine in mice

The disposition of 3H-phencyclidine (PCP), as well as total metabolites, was studied in mice up to 21 days after either iv or po administration. Thirty minutes after either iv or po administration the highest concentrations of 3H-PCP were found in stomach. The next highest levels were in fat (iv), liver (po), and intestines (po) and the lowest levels were found in brain and plasma (iv and po). Twenty-four hours later, the levels of 3H-PCP in all tissues were less than 2% of the concentrations after 30 min. After 3 days, the only detectable levels were in fat, and were less than 1% of the 30-min levels. Trace quantities of 3H-PCP were detected in fat at 7, 14, and 21 days. The disposition of total metabolites differed from that of 3H-PCP in that total metabolite levels were highest in stomach, liver, and intestines 30 min after administration of 3H-PCP by both routes. After 24 hr the concentration of total metabolites in all tissues far exceeded that of 3H-PCP. The highest concentration of metabolites remained in liver, stomach, and intestines for 24 hr, but after 3 days the levels in stomach and intestines fell considerably. Metabolite levels were sustained in lung and liver up to 14 days and in lung up to 21 days. Mice were also treated with seven daily gavages of 3H-PCP to determine the extent of 3H-PCP and metabolite accumulation. 3H-PCP was found only in fat 7, 14, and 21 days after the last treatment, but these levels were quite low. Metabolite levels in lung and liver at all time points were 5-10 times greater than those following acute treatment. 3H-PCP does not appear to be sequestered to an appreciable extent in any tissue in mice, whereas metabolites do accumulate in lung and liver for long periods of time.     

The possible role of one-carbon moieties in 2-methoxyethanol and 2-methoxyacetic acid-induced developmental toxicity

The ethylene glycol ether, 2-methoxyethanol (2-ME), is rapidly (less than 1 hr) oxidized to 2-methoxyacetic acid (2-MAA). Both agents are selectively embryotoxic and equipotent in causing digit malformations when given to CD-1 mice on gestation Day 11. Previous observations have shown that simple physiological compounds such as formate, acetate, glycine, and glucose ameliorate the embryotoxicity of 2-ME. A common link for all of the attenuating agents may be oxidation pathways involving tetrahydrofolic acid (THF) as a catalyst for one-carbon transfer into purine and pyrimidine bases. In the present study serine at 16.5 mmol/kg, which reacts directly with THF, was as effective as formate in almost completely eliminating digit malformations resulting from treatment with 2-ME. Unlike formate, serine was equally effective against 2-MAA-induced dysmorphogenesis and the attenuating efficacy remained unchanged when serine administration was delayed for up to 8 hr after 2-ME or 2-MAA exposure. The protective effect of sarcosine, which is an intermediate in a pathway leading from choline to glycine and a structural analog of 2-MAA, was also determined. Both concomitant (43, 16.5, or 3.3 mmol/kg) and delayed (16.5 mmol/kg at 6 hr) sarcosine administration resulted in significantly less 2-ME-induced paw dysmorphogenesis. In addition, acetate administration was delayed for increasing intervals after 2-ME to determine the time at which attenuation would no longer occur, and acetate was effective for as long as 12 hr after 2-ME. These results support our hypothesis that 2-MAA, which has a long biological half-life, may interfere with the availability of one-carbon units for incorporation into purine and pyrimidine bases. Alterations in availability of these precursors might be expected to affect DNA and/or RNA synthesis and thereby influence normal cellular proliferation and differentiation in the developing embryo.     

Metabonomic phenotyping reveals an embryotoxicity of deca-brominated diphenyl ether in mice

Recent studies have demonstrated that polybrominated diphenyl ethers (PBDEs), a group of industrial chemicals, could disrupt thyroid hormone homeostasis and exhibit neurotoxicity, reproductive toxicity, and embryotoxicity. However, clear evidence of embryotoxicity and neurotoxicity of many of these congeners, such as deca-BDE, one of the least bioactive congeners of PBDEs, is still lacking. In the present study, we investigated deca-BDE embryotoxicity by quantitative analysis of two essential thyroid hormones (T4 and T3) and a variety of small-molecule metabolites in the serum of deca-BDE-dosed pregnant mice. Four groups of pregnant C57 mice were administrated with deca-BDE in 20% fat emulsion at a dose of 150, 750, 1,500, or 2,500 mg/kg body weight via gastric intubation on gestation days (g.d.s) 7 to 9, while a control group was given 20% fat emulsion. Maternal mice were euthanized on g.d. 16 and examined for external malformations of the fetus. Maternal serum samples were collected and analyzed by the enzyme linked immunosorbent assay (ELISA) and gas chromatography-time-of-flight mass spectrometry (GC-TOF MS). Using multivariate statistical analysis, we observed a significantly altered metabolic profile associated with deca-BDE embryotoxicity in maternal serum. Our results also demonstrated that deca-BDE at a dose of 2?500 mg/kg body weight induced significant disruption of thyroid hormone metabolism, the TCA cycle, and lipid metabolism in maternal mice, which subsequently led to a significant inhibition of fetal growth and development. We concluded that deca-BDE-induced embryotoxicity closely correlated with global metabolic disruption that can be characterized by thyroid hormone deficiency, disrupted lipid metabolism, and a depleted level of cholesterol in maternal mice.     

超氧化物歧化酶在动物体内的药代动力学和体内过程

本文采用直接测定生物样品中超氧化物歧化酶(SOD)活性的极谱法,研究了家兔iv三种不同剂量和im高剂量SOD后的药代动力学以及小鼠ipSOD后的组织分布和尿粪排泄的特点.家兔iv和imSOD的血清SOD活性-时间数据符合线性二室开放模型,其t_(1/2β)分别为49.7,46.1,40.5和118.5 min,im生物利用度为72.0％。小鼠ip SOD后1～3 h,组织中的SOD活性以胆囊和胃为最高,然后依次为肌肉、肺、肝、脑和肾,而心脏和睾丸最低;由尿粪排泄的SOD活性甚少,24 h内的累积排泄量分别仅为给药剂量的1.48和0.45％。     

Reproductive toxicity of 2-methoxyethanol applied dermally to occluded and nonoccluded sites in male rats

12-Methoxyethanol (2-ME), also known as Methyl Cellosolve, was applied on the backs of Sprague-Dawley male rats at dose levels of 0, 625, 1250, or 2500 mg/kg/day on occluded (covered) sites, and 0, 1250, 2500, or 5000 mg/kg/day on nonoccluded (uncovered) sites for 7 consecutive days. Because deaths occurred at a dose level of 2500 mg/kg/day among rats with occluded test sites, dosing of this group was discontinued after 5 days. The number and morphology of caudal epididymal sperm, number of testicular spermatids, and weights of reproductive organs were determined on Weeks 4, 7, 10, and 15; fertility was assessed on Weeks--1, 4, 7, 10, and 14. The effects of treatment were dose-related and included a decline in epididymal sperm count and testicular spermatid count, a reduction in weights of testes and epididymides, an increase in the number of sperm with abnormal morphology, and a reduction in fertility in rats exposed to 2-ME. The above effects were seen with or without occlusion, but they were more severe and recovery proceeded at a slower rate when the skin sites were covered.     

The disposition of free and liposomally encapsulated antimalarial primaquine in mice

Plasma clearance, urinary excretion and tissue distribution of radiolabeled free (FPQ)_and liposome-entrapped Primaquine (LPQ) in mice were monitored for 2 hr following intravenous administration. FPQ is eliminated very rapidly from the plasma and excreted predominantly in the urine, probably largely in a metabolized form. In decreasing order of magnitude, pronounced accumulation of label occurs in the lives, kidneys, lungs and skeletal muscle. Less than 1 per cent of the total initial dose is recovered in other tissues. Partial erythrocytic sequestration results in drug levels higher and more persistent in blood cells than in the plasma. Compared to the free drug form, Primaquine entrapped within negatively charged liposomes of the cholesterol-rich multilamellar type exhibits a prolonged plasmatic half-life and, within the observation period, excretion is 8-fold reduced. Liver accumulation of label is doubled, acconting for close to 50% of the injected dose; splenic uptake is tripled, while accumulation in the lungs, kidneys, heart and brain is drasticaly reduced. These differences in pharmacodynamic behaviour may explain why liposomal entrapment leads to diminished acute Primaquine toxicity.     

Effects of sodium selenite on methylmercury embryotoxicity and teratogenicity in mice.

Female IVCS mice were fed food containing methylmercury (MeHg) at 0, 15.9, or 31.9 nmol/g food and drinking water containing sodium selenite at 0, 11.4, or 22.8 nmol/ml for 30 days before gestation and thereafter up to Day 18 of gestation. Groups receiving MeHg had (1) affected estrus cycles, (2) decreased litter size accompanied by increased implantation sites, resorptions, dead embryos, and dead fetuses, (3) increased incidence of cleft palate, and (4) retarded fetal growth. Selenite was not teratogenic and even at the high dose, generally only retarded fetal growth. The low dose of selenite when combined with the high dose of MeHg, increased the incidence of resorptions and implantation sites. Embryolethality was decreased and the incidence of cleft palate was increased in the group receiving the high dose of selenite combined with the high dose of MeHg.     

Comparative studies on the embryotoxicity of 2-methyl-4-chlorophenoxyacetic acid, mecoprop and dichlorprop in NMRI mice

From the group of herbicidal phenoxy carbonic acids, 2-methyl-4-chlorophenoxyacetic acid (MCPA; 0-500 mg/kg), 2-(4-chloro-2-methyl-phenoxy) propionic acid (mecoprop/MCPP; 0-700 mg/kg) and 2-(2,4-dichlorophenoxy) propionic acid (dichlorprop/2,4-DP; 0-500 mg/kg) as well as the dextrorotatory compounds of MCPP (MCPPD; 0-500 mg/kg) and 2,4-DP (2,4-DPD; 0-500 mg/kg) were studied in NMRI mice after oral administration between days 6-15 of pregnancy. All five substances proved to be embryotoxic and teratogenic in varying intensity. MCPA proved to be most effective: it was embryotoxic from doses of 100 mg/kg and teratogenic from 200 mg/kg. The remaining compounds (MCPP, MCPPD, 2,4-DP, 2,4-DPD) were embryotoxic from doses of 300 mg/kg and caused malformations of the skeleton from 400 mg/kg. The embryocidal and teratogenic potencies of the dextrorotatory components of MCPA and 2,4-DP exceeded those of the corresponding racemates. Influences of MCPPD and 2,4-DPD upon postimplantative loses, frequency of cleft palates and wavy ribs appeared already at dosages being 100-200 mg/kg below those of the racemates given to the respective groups of experimental animals. Additional alterations of the skeleton were observed which did not occur following administration of the racemic mixtures: deformed centrums of thoracic vertebra and exencephaly.     

The disposition of the enantiomers of warfarin following chronic administration to rats: relationship to anticoagulant response

A model of chronic anticoagulation has been used to investigate the whole liver and subcellular disposition of the individual enantiomers of warfarin in the Wistar rat in relation to anticoagulant response. Consistent pharmacodynamic responses were achieved by dosing daily with R-warfarin (0.4, or 0.8 mg kg-1 day-1 i.p.) or S-warfarin (0.1 mg kg-1 day-1 i.p.). After the administration of increasing doses of R-warfarin, prothrombin times were dose-dependent (16.3 +/- 0.5 s, 0.1 mg kg-1 day-1; 21.6 +/- 1.7 s, 0.4 mg kg-1 day-1; 55.1 +/- 9.0 s, 0.8 mg kg-1 day-1; results all measured 24 h after the final dose). Increasing doses of R-warfarin also produced increases in plasma, whole liver, and cytosolic concentrations of warfarin. However, there were no significant differences between the microsomal concentrations of R-warfarin in the three groups. The dose of S-warfarin required to produce a consistent and significant increase in the prothrombin time was four-fold lower than the dose of R-warfarin required to cause a similar effect. Plasma concentrations of S-warfarin were not significantly different from those seen after 0.4 mg kg-1 day-1 R-warfarin. Whole liver and cytosolic concentrations of the S-enantiomer were lower than those observed after a dose of 0.4 mg kg-1 day-1 R-warfarin. However, consistent with microsomal concentrations following increasing doses of R-warfarin, there was no significant difference between microsomal concentrations of R(+)- and S(-)-warfarin.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of morphine on methotrexate disposition in mice

1. Morphine has been shown to slow the renal excretion of other drugs. The present study in mice evaluated the effects of morphine on the disposition of methotrexate (MTX), an antimetabolite eliminated by the kidneys. 2. Mice were injected with morphine (20 mg/kg) or saline s.c. After 30 min, 20-80 mg/kg MTX was injected i.v. Blood and urine samples were assayed for MTX by HPLC. 3. Morphine reduced plasma clearance (CL) of MTX from 0.147 +/- 0.015 to 0.061 +/- 0.009 mL/min per g bodyweight (P < 0.01). The area under the plasma concentration-time curve (AUC(0- infinity )) was raised by morphine from 151 +/- 18 to 369 +/- 36 micro g.mL per min (P < 0.01). Without morphine administration, 22-27% of an MTX dose was excreted into the urine in 30 min. The corresponding fractions excreted into the urine after morphine were reduced to 15-18% (P < 0.01). 4. Plasma levels of MTX administered intravenously to mice are elevated by the concomitant administration of morphine, which reduces renal elimination of MTX.     

Tissue and cellular disposition of paraquat in mice

Male C57B1/6J mice were injected intravenously with [methyl-¹⁴C]paraquat dichloride and frozen at 1, 3, 9, and 24 hr for whole-body autoradiography or with [methyl-³H]paraquat dichloride and the lungs were removed at 3, 24, and 48 hr for cellular autoradiography. The methods do not allow thawing or exposure of the tissues to solvents; this prevents translocation or removal of radioactivity. The whole-body autoradiographs revealed localization of radioactivity at all time intervals in melanin, lung, choroid plexus, muscle, and excretory pathways such as proximal tubules of kidney, urine, liver, gallbladder, and intestinal contents. The radioactivity in lung was much higher in certain discrete, unidentified areas at all time intervals except at 1 hr. The concentration was high in myocardium at 1 and 3 hr. Cellular resolution autoradiography revealed that the radioactivity within the lung was confined almost entirely to cells having the distribution of alveolar type II cells at the three time intervals studied. The radioactivity in these cells was easily washed away indicating that an active transport process was probably involved instead of binding to a cellular constituent. The localization suggested that choline might be antidotal to paraquat toxicity. However, there was not a significant increase in survival of mice given 100 mg/kg choline chloride simultaneously to or following treatment with 50 mg/kg paraquat chloride.     

The embryotoxicity of adriamycin in rat embryos in vitro

Adriamycin (ADR) is a widely used and highly valued antineoplastic agent but chronic treatment is limited by cardiotoxicity. To investigate its embryotoxic potential, cultured rat embryos were exposed to ADR at concentrations ranging from 0.4 to 1.2 μm. Within this range, ADR elicited decreases in growth parameters (somite numbers, embryonic length, and protein and DNA content), malformations involving the prosencephalic region, and embryolethality at the higher concentrations. Embryotoxicity was significantly increased (p < 0.05) when cultures included cofactors for cytochrome P-450-dependent biotransformation and a hepatic microsomal preparation (S-9) prepared from animals pretreated with 3-methylcholanthrene or a mixture of polychlorinated biphenyls (Aroclor 1254). When S-9 from control animals or from rats pretreated with phenobarbital was used, significant increases in ADR-elicited embryotoxicity were not observed. Substitution of NADH for NADPH as a cofactor reduced the incidence of malformations from 100 to 60% at ADR concentrations of 0.5 μm. Increasing O₂ concentrations partially counteracted the embryotoxic effects of ADR. Several other agents [including various antioxidants, compounds bearing free sulfhydryl groups, coenzyme Q₁₀, and superoxide dismutase (with or without catalase)] that prevent or reduce the cardiotoxicity of ADR without impairing its antineoplastic properties, failed to modify the embryotoxicity significantly. This suggested that the embryopathic and antineoplastic properties of ADR may share a common mechanism which is distinct from that responsible for cardiotoxicity.