Effects of methionine supplement on methionine incorporation in rat embryos cultured in vitro

Effects of supplemental L-methionine on E-64 [trans-epoxysuccinyl-1-leucyl-amido (4-guanido) butane]-induced dysmorphology in rat embryos cultured in vitro

E-64 [trans-epoxysuccinyl-1-leucyl-amido (4-guanido) butane] is teratogenic, inducing a spec-trum of malformations in vivo and producing similar effects in vitro. Numerous studies support the concept that E-64-induced malformations result from embryonic nutritionaldeficiency, without affecting the maternal nutritional status. This has provided a useful model with which to investigate the nutritional requirements of the early embryo, as well as the role of various nutrients in the etiology of congenital defects. In the current investigation, we examined effects of L-methionine on E-64-induced embryotoxicity in vitro. For these experiments, we cultured rat embryos 9.5 days postconception (p.c.) for 48 hours with E-64 and/or L-methionine. We found that the addition of L-methionine to E-64-exposed cultures reduced optic abnormality and increased embryo protein. These results suggest that embryopathy largely results from a deficiency of L-methionine although E-64 limits the supply of all amino acids to the embryo. Furthermore, although endocytosis and degradation of proteins by the visceral yolk sac (VYS) supply most amino acids to the embryo, free amino acids may be compensatory when this source is reduced. These results support those of previous investigations that suggest L-methionine is a limiting nutrient for embryonic development.

Combination therapy with folic acid and methionine in the prevention of retinoic acid-induced cleft palate in mice

BACKGROUND

During formation of the secondary palate, clefting may result when critical developmental events are altered. The purpose of this study was to reduce the incidence of retinoic acid (RA)-induced cleft palate (CP) in mice by the co-administration of folic acid (FA), methionine (ME) or a combination of both.

METHODS

Four groups of time-pregnant Swiss Webster mice were injected intraperitoneally with 50 mg/kg RA on gestational day (GD) 10. Likewise, 4.0 mg/kg FA and 187 mg/kg ME were administered on GD 8-11. The experiment included a control group (RA plus H2O) and three experimental groups, (RA plus therapeutic doses of FA, ME, or FA + ME). Necropsies were carried out on GD 18 and pups were analyzed for teratogenic effects.

RESULTS

Litters that received no therapy exhibited 100% CP with individual pups showing 76% susceptibility. Each therapy administered separately reduced the frequency of CP to approximately 6%, and the combination of FA and ME completely prevented the occurrence of RA-induced cleft palate (0%). A second experiment was conducted in which therapy levels were decreased by 25%. Litters that did not receive therapy experienced 100% clefting and individual pups exhibited CP at 86%. These therapies administered separately did not alter significantly the frequency of cleft palate. The combined doses of FA and ME, however, lowered significantly the frequency of cleft palate to 46%. Decreases in limb and tail defects with FA + ME therapy were also observed in both experiments.

CONCLUSIONS

Although FA and ME, at appropriate levels, can reduce individually the frequency of RA-induced cleft palate and other defects in mice, the results from the present study suggest that there is an additive interaction between the two therapeutic agents that can reduce further the teratogenic impact of RA. Further studies are needed to assess the mechanism of action of concomitant doses of FA and ME in the reduction of drug-induced birth defects.

Effects of methionine on selenium embryotoxicity in cultured rat embryos

Effects of methionine, an essential amino acid, on the embryotoxicity of selenium (Se) were examined using the rat embryo culture. Rat embryos at day 9.5 of gestation were cultured for 48 h in the presence of sodium selenite at 10 and 20 microM or sodium selenate at 30 and 100 microM with or without the addition of 1 mM DL-methionine. Selenite at 20 microM or selenate at 100 microM alone increased the incidence of embryonic malformation and inhibited the embryonic growth. The addition of methionine increased the incidence of embryonic malformation at 10 microM of selenite but decreased the incidence of embryonic malformation at 100 microM of selenate. On the other hand, the addition of methionine partially restored the inhibited embryonic growth at 20 microM of selenite or at 100 microM of selenate. It was considered from these results that the methionine availability in the embryonic environment and the oxidation state of Se are critical in Se embryotoxicity.

Folic acid supplementation of pregnant mice suppresses heat-induced neural tube defects in the offspring

Neural tube defects (NTD) are a group of malformations that result from the failure of the neural tube to close early in embryonic development and among the most common congenital malformations in humans. It has been reported that a substantial proportion of NTD in humans can be prevented by folic acid (FA) supplementation prior to conception and during the first months of pregnancy, and myo-inositol (MI) was shown to reduce the incidence of NTD in curly tail mice which are not prevented by FA. Brief maternal hyperthermia (HT) early in pregnancy has been implicated in NTD both in humans and laboratory animals, and anterior NTD including exencephaly and anencephaly are induced frequently when pregnant mice are exposed to HT. We examined the effect of FA or MI supplementation of pregnant mice on the occurrence of heat-induced NTD in the offspring. When pregnant mice were treated with FA (3 mg/kg) daily from gestational day (GD) 0.5 through GD 9.5 and heated at GD 8.5, the prevalence of NTD in the fetuses (26.6%) was significantly lower than the corresponding figure in the HT alone group (38.6%; P < 0.05). However we failed to detect the preventive effect of MI (500 mg/kg). The results of this study suggest that prenatal FA supplementation decreases HT-induced NTD in mice and sufficient FA intake during early pregnancy may be recommended to avoid the birth of malformed children.