Effects of hyperketonemia on mouse embryonic and fetal glucose metabolism in vitro

The interplay between glucose and ketone bodies in neural stem cell metabolism

Glucose is the primary energy source for neural stem cells (NSCs), supporting their proliferation, differentiation, and quiescence. However, the high demand for glucose during brain development often exceeds its supply, leading to the utilization of alternative energy sources including ketone bodies. Ketone bodies, including β-hydroxybutyrate, are short-chain fatty acids produced through hepatic ketogenesis and play a crucial role in providing energy and the biosynthetic components for NSCs when required. The interplay between glucose and ketone metabolism influences NSC behavior and fate decisions, and disruptions in these metabolic pathways have been linked to neurodevelopmental, neuropsychiatric, and neurodegenerative disorders. Additionally, ketone bodies exert neuroprotective effects on NSCs and modulate cellular responses to oxidative stress, energy maintenance, deacetylation, and inflammation. As such, understanding the interdependence of glucose and ketone metabolism in NSCs is crucial to understanding their roles in NSC function and their implications for neurological conditions. This article reviews the mechanisms of glucose and ketone utilization in NSCs, their impact on NSC function, and the therapeutic potential of targeting these metabolic pathways in neurological disorders.

Effects of Lipoic Acid Supplementation on Activities of Cyclooxygenases and Levels of Prostaglandins E2 and F2α Metabolites, in the Offspring of Rats with Streptozotocin-Induced Diabetes

Background. Our aim was to evaluate the protective effect of lipoic acid (LA) on fetal outcome of diabetic mothers. Methods. Diabetes was induced in female rats using streptozotocin and rats were made pregnant. Pregnant control (group 1; n = 9; and group 2; n = 7) or pregnant diabetic (group 3; n = 10; and group 4; n = 8) rats were treated daily with either LA (groups 2 and 4) or vehicle (groups 1 and 3) between gestational days 0 and 15. On day 15 of gestation, the fetuses, placentas, and membranes were dissected, examined morphologically, and then homogenized, to measure cyclooxygenase (COX) activities and metabolisms of prostaglandin (PG) E₂ (PGEM) and PGF₂α (PGFM) levels. The level of total glutathione was measured in the maternal liver and plasma and in all fetuses. Results. Supplementation of diabetic rats with LA was found to significantly (p < 0.05) reduce resorption rates in diabetic rats and led to a significant (p < 0.05) increase in liver, plasma, and fetuses total glutathione from LA-TD rats as compared to those from V-TD. Decreased levels of PGEM and elevated levels of PGFM in the fetuses, placentas, and membranes were characteristic of experimental diabetic gestation associated with malformation. The levels of PGEM in malformed fetuses from LA-TD mothers was significantly (p < 0.05) higher than those in malformed fetuses from V-TD rats. Conclusions. LA treatment did not completely prevent the occurrence of malformations. Thus, other factors may be involved in the pathogenesis of the diabetes-induced congenital malformations.

Periconceptional care of women with diabetes mellitus

Pregestational diabetes is a common complication of pregnancy that can be associated with severe maternal and fetal morbidity. In addition, some women could have progression of diabetic complications secondary to pregnancy. Preconception care can significantly reduce pregnancy complications with a dramatic impact on the diabetic mother and her infant. For those women whose condition could be hastened by conception education, better understanding and an improved decision should be available to them and their families. Because unplanned pregnancy is common among diabetic women, they should be counseled early for the importance of preconception care in the progression of this disease.

A mouse model for Glut-1 haploinsufficiency

Glut-1 deficiency syndrome (Glut-1 DS, OMIM #606777) is characterized by infantile seizures, developmental delay, acquired microcephaly and hypoglycorrhachia. It is caused by haploinsufficiency of the blood-brain barrier hexose carrier. Heterozygous mutations or hemizygosity of the GLUT-1 gene cause Glut-1 DS. We generated a heterozygous haploinsufficient mouse model by targeted disruption of the promoter and exon 1 regions of the mouse GLUT-1 gene. GLUT-1+/- mice have epileptiform discharges on electroencephalography (EEG), impaired motor activity, incoordination, hypoglycorrhachia, microencephaly, decreased brain glucose uptake as measured by positron emission tomography (PET) scan and decreased brain Glut-1 expression by western blot (66%). The GLUT-1+/- murine phenotype mimics the classical human presentation of Glut-1 DS. This GLUT-1+/- mouse model creates an opportunity to investigate Glut-1 function, to examine the pathophysiology of Glut-1 DS in vivo and to evaluate new treatment strategies.

Lipoic acid prevention of neural tube defects in offspring of rats with streptozocin-induced diabetes

OBJECTIVE

Increased oxidant stress has been suggested to play a role in the pathogenesis of disturbed embryogenesis in diabetic pregnancies. The present study was conducted to determine whether administration of lipoic acid, a naturally occurring antioxidant, would reduce the incidence of diabetic embryopathy in the streptozocin-induced diabetic rat model.

STUDY DESIGN

After conception, rats were randomly distributed to 5 groups. From day 1, rats were daily injected intraperitoneally with either lipoic acid, 30 mg/kg, or vehicle. At day 6, rats from groups 3, 4, and 5 were made diabetic by a single intraperitoneal injection of streptozocin. Group 4 rats were injected with lipoic acid from day 1 to day 6, after vehicle treatment until day 17. At day 17 of gestation, rats were killed. The fetuses were released from the yolk sacs and surrounding decidua and were examined for size, resorption rate, and neural tube defects.

RESULTS

Pregnant diabetic rats treated with vehicle lost weight during pregnancy (-3.2 +/- 1.9 g/d), as opposed to normal pregnancy-related weight gain (3.5 +/- 0.5 g/d). Treatment with lipoic acid protected against diabetes-induced weight loss, without a measurable effect on fed-state glucose concentrations. Daily treatment with lipoic acid (pregnancy days 1 to 17) was efficient in reducing the resorption rate from 24.0% +/- 9.5% in vehicle-treated diabetic rats to 10.2% +/- 4.8% in lipoic acid-treated diabetic rats (P <.05). The rate of neural tube defects in diabetic rats treated with lipoic acid throughout the pregnancy was reduced from 26.0% +/- 7.0% to 10.2% +/- 3.2% (P <.05). In rats treated only during pregnancy days 1 to 5 (before diabetes induction), lipoic acid failed to exert its protective effects against neural tube defects, which emphasizes the importance of the presence of lipoic acid during the organogenesis period. The atherosis of placental vasculature demonstrated in the vehicle-treated diabetic rats was absent from placentas obtained from lipoic acid-treated diabetic animals.

CONCLUSIONS

Our data demonstrate a protective effect of lipoic acid against diabetic embryopathy, fetal losses, and ultrastructural alteration of diabetic placentas.

Metabolic alteration in neural tissue of rat embryos exposed to beta-hydroxybutyrate during organogenesis

Hyperketonemia has been identified as an important factor in diabetic pregnancy affecting growth and development of the offspring. In order to assess the immediate metabolic alterations in embryos caused by excess ketone bodies, we studied rat embryonic neural tissue exposed to a high concentration of beta-hydroxybutyrate in vitro. Beta-hydroxybutyrate inhibited oxygen uptake of the neural tissue of day 9 and day 10 embryos by 12.8% and 1 1.2%, but did not affect that of day 11 and day 12 tissue. In contrast, glucose utilization of the neural tissue of day 9 and day 10 embryos was not altered. However, a 30% decrease in glucose utilization was observed in the neural tissue of day 11 and day 12 embryos exposed to beta-hydroxybutyrate. Thus, beta-hydroxybutyrate induced different metabolic alterations in the embryonic neural tissue during early and late organogenesis, which suggests different modes of teratogenic action of ketone bodies in different parts of gestation.

The pathogenesis of diabetes-associated congenital malformations

Congenital malformations convey a major financial and social burden to society. Epidemiologic, clinical, and animal studies indicate that these malformations occur in early pregnancy, are influenced by an aberrant metabolic fuel milieu, and seem to result from a combination of more than one factor acting synchronously. Unfortunately, during the critical period of organogenesis, the pregnancy is hardly recognizable, making evaluation and study of relevant maternal embryonic parameters extremely difficult. Additionally, there are obvious limitations to human study for technical and ethical reasons. Animal experimentation, however, has demonstrated that these malformations can be produced in many vertebrates and are similar to those seen in humans. The mechanism for induction of dysmorphogenesis in experimental diabetic pregnancy has been shown to include generation of free oxygen radicals and are associated with alterations in the embryonic levels of arachidonic acid, prostaglandins, and myo-inositol. Most of the earlier experimental studies focused on defects at the level of the embryo excluding the extraembryonic membranes. Current investigations provide evidence that the yolk sac has an integral role in diabetic embryopathy. The experimental use of several different compounds, such as arachidonic acid, myo-inositol, and antioxidants, offers significant promise for the future in possibly serving as a pharmacologic prophylaxis against diabetic embryopathy.

The infant of the diabetic mother

The history of the medical success in treatment of the pregnant diabetic woman and her infant in the twentieth century illustrates how the combined efforts of dedicated clinicians and researchers have resulted in dramatic improvements in outcome for this patient group. This article discusses fetal growth, metabolic complications of the infant of the diabetic mother, risk of respiratory distress syndrome, hypertrophic cardiomyopathy, and congenital anomalies.

Diamide-induced alterations of intracellular thiol status and the regulation of glucose metabolism in the developing rat conceptus in vitro

Direct oxidation of embryonic reduced glutathione (GSH) by a thiol oxidant, diamide, has been demonstrated to result in increased glutathione disulfide (GSSG) and protein-glutathione mixed disulfide (protein-S-SG) formation, which is accompanied by embryotoxicity and reductions in amniotic fluid volume. The altered functions of critical proteins or enzymes caused by the formation of protein-S-SG perturb cellular metabolism and may be involved in the embryotoxicity produced by GSH oxidation. The present study investigates changes in the metabolism of glucose through glycolysis and the pentose phosphate shunt pathways (PPP) and their related enzymes under the oxidative conditions produced by diamide exposure in organogenesis-stage rat conceptus (gestational day 10) in vitro. The metabolism of glucose via the PPP, measured as amounts of CO2 production from D-[1-14C]-glucose, was significantly increased in the conceptus exposed to 100-500 microM diamide to levels 2.5-3-fold those of controls. It was found that these substantial increases in the PPP activity did not correlate well with a moderate activation of glucose 6-phosphate dehydrogenase (G6PD) activity, the key enzyme in the PPP pathway. Changes in glycolysis due to diamide treatment were also determined by measurements of lactate production from D-[U-14C]-glucose. Production of lactate by the conceptus exposed to 250-500 microM diamide for 60 min was reduced (to approximately 54% of control values) concomitantly with a significant inhibition of the glycolytic enzymes, glyceraldehyde 3-phosphate dehydrogenase (GPD) and phosphofructokinase (PFK), indicating an overall decrease in glycolysis. Diamide was found to produce a differential effect on the enzymatic activities determined in this study, with greater degrees of inhibition seen in the tissue supernatants from the visceral yolk sac (VYS) compared to those from the embryo. Activities of GPD and PFK were decreased to approximately 22% and 43% control values, respectively, when determined in the supernatants from the VYS of the conceptus exposed to 500 microM diamide for 60 min. In addition, more than 90% of the GPD activity in the VYS, but not the embryo, was rapidly inhibited by the thiol alkylating agent N-ethylmaleimide (NEM, 100 microM) within 15 min of the exposure. In contrast to diamide and NEM, no alterations in lactate production were seen in the conceptus treated with the GSH depletor L-buthionine-S,R-sulfoximine (1 mM) for 5 hr in the culture media. Further experiments demonstrated that the activity of the GPD, inhibited by a 30-min incubation with 500 microM diamide, can be reversed after removal of diamide and that this effect was potentiated by subsequent treatment with dithiothreitol (30 mM), a thiol reducing agent. These results indicated the involvement of thiol/disulfide status in regulation of the metabolism of glucose in the developing conceptus and support the hypothesis that GSH oxidation and protein-S-SG formation could be a critical event associated with mechanisms of embryotoxicity elicited by oxidative stress. It was suggested in this study that, under these experimental conditions, embryotoxicity induced by diamide is primarily mediated via altered VYS functions, including disrupted energy production (glycolysis).

Embryonic growth impaired by maternal hypoglycemia during early organogenesis in normal and diabetic rats

The effect of maternal hypoglycemia on early organogenesis was studied in normal and diabetic rats. Female Wistar rats were made diabetic by an intravenous injection of streptozotocin (45 mg/kg) 2-3 weeks before conception. On day 9.5 or 10.5 of embryo development, both control and diabetic dams received saline or Actrapid human insulin (400 mU/rat) intraperitoneally after 19-h starvation. The fasting plasma glucose levels in diabetic dams decreased from approximately 23 to 8 mM. Hypoglycemia as low as 3.5 mM was maintained for 60 min in insulin-treated mother rats. Pregnancy was terminated on day 11.6 of embryo development. A significant growth retardation was found in diabetic embryos as compared with normal embryos. Maternal hypoglycemia lowered the DNA content in normal but not diabetic embryos, while the teratogenic effect of maternal hypoglycemia was not pronounced in either normal or diabetic embryos. These data may suggest that maternal hypoglycemia in vivo in early pregnancy influences the embryogenesis but not teratogenesis of rat embryos.

Biochemical basis for D,L,-beta-hydroxybutyrate-induced teratogenesis

Previous investigations have demonstrated that a potential mechanism for D,L,-beta-hydroxybutyrate (BOHB)-induced teratogenesis in neurulating mouse embryos (5-6 somite stage) after 24 hours of exposure in vitro is mediated by an inhibition of the pentose phosphate pathway (PPP) (Hunter, et al. '87). Employing conceptuses of an earlier stage (2-3 somite stage), the biochemistry of BOHB-induced abnormalities was examined further by exposing embryos to 32 mM BOHB for 24 hour and comparing results with controls with respect to the rate of metabolism via the PPP, de novo pyrimidine biosynthesis (PB), and BOHB utilization. Moreover, the capability of these BOHB-exposed embryos to recover from such an insult was also assessed by transferring them to fresh control medium and allowing them to grow for an additional 36 hours. Both controls and BOHB-exposed embryos showed a progressive increase in rate of BOHB utilization between days 9 and 11.5 of gestation in vitro. Exposure to ketone body produced a 100% rate of neural tube defects and a 25.2% decrease in total embryonic protein content. In contrast to results obtained at the 5-6 somite stage, no inhibition of the PPP in whole conceptuses, embryos, or visceral yolk sacs was observed in the group exposed to BOHB at the 2-3 somite stage. Furthermore, a 7.5 mM D-ribose supplement, an intermediate in the PPP, was unable to rescue the younger embryos from BOHB-induced abnormalities and growth retardation. On the other hand, BOHB produced a 34.3% decrease in pyrimidine biosynthesis in the 2-3 somite embryos, but not in the visceral yolk sac. In addition, embryos recovered biochemically after being transferred to control medium, demonstrating a 25.5% overshoot in pyrimidine biosynthesis. Therefore, the mechanism of BOHB-induced teratogenesis appears to differ depending on the stage of embryonic development at the time of initial exposure.

Copper deficiency in pregnancy: effect on maternal and fetal polyol metabolites

The present study was undertaken to determine whether the mortality of the fetus and the neonate of copper-deficient rats consuming fructose during pregnancy is associated with an aberration in carbohydrate metabolism. A total of 84 Sprague-Dawley rats were fed a copper-deficient or a copper-adequate diet containing fructose or starch for 19 or 21 days after conception. The consumption of a fructose-based diet during pregnancy resulted in higher concentrations of maternal blood fructose, sorbitol, triglyceride, and uric acid when compared with a starch diet. The placenta contained more than 10-fold the concentration of glucose and more than double the concentrations of fructose, triglycerides, and sorbitol when fructose was the dietary carbohydrate compared with starch. The livers of fetuses belonging to the fructose dietary group exhibited high concentrations of glucose and sorbitol. In addition, fetal blood contained higher concentrations of glucose, fructose, sorbitol, and triglycerides than the corresponding values from the starch dietary group. The consumption of a copper-deficient diet containing fructose during pregnancy resulted in massive subcutaneous hemorrhages of the fetus. In contrast, this pathology was rare in other dietary groups. The combination of copper deficiency with fructose feeding resulted in more than double the concentration of sorbitol in fetal liver, and higher concentrations of insulin and dopamine of fetal blood compared with the consumption of a copper-deficient diet containing starch.(ABSTRACT TRUNCATED AT 250 WORDS)

Morphological and physiological effects of beta-hydroxybutyrate on rat embryos grown in vitro at different stages

Diabetic women are more likely to give birth to infants with congenital malformations than are nondiabetic women. Rodent embryos have been used as a model for the study of abnormal fetal development associated with maternal diabetes, and some of the metabolic factors which are altered in diabetes, such as raised glucose and ketones, have been shown to cause abnormal development of rodent embryos in vitro. The present work explores further the teratogenicity of beta-hydroxybutyrate to rat embryos. To determine the sensitivities of rat embryos at different stages of their development, rat embryos at 9.5 days of gestation have been cultured in vitro for 24 or 48 h, with or without 4 x 10(-2) M beta-hydroxybutyrate for all or part of the culture period. The embryos have been examined by scanning electron microscopy, and a detailed morphometric analysis of one tissue, the neuroepithelium, has been undertaken. The results confirm that beta-hydroxybutyrate causes abnormal development of rat embryos. The results of experiments in which embryos were exposed to beta-hydroxybutyrate for only part of a 48 h culture show that embryos exposed to beta-hydroxybutyrate for a complete 48 h culture are more severely affected than embryos exposed to beta-hydroxybutyrate for only part of the culture and that embryos are more vulnerable to beta-hydroxybutyrate during the first half of a 48 h culture (equivalent to 9.5 to 10.5 days of gestation) than during the second half of a 48 h culture (10.5 to 11.5 days of gestation). The results of experiments in which embryos were cultured with beta-hydroxybutyrate from 9.5 days of gestation for 24 h (equivalent to 9.5 to 10.5 days of gestation) showed that some effects of beta-hydroxybutyrate are already apparent after 24 hours in culture. Many of the abnormalities produced by beta-hydroxybutyrate can be classified as embryonic retardations rather than malformations--that is, embryos show features characteristic of normal, but younger, embryos. Embryos exposed to beta-hydroxybutyrate for the complete 48 h culture period consume less glucose and produce less lactate than control embryos on a per embryo basis, but not on a per microgram protein basis, suggesting that the reduced metabolism is an effect of beta-hydroxybutyrate-induced developmental delay rather than a cause of it.(ABSTRACT TRUNCATED AT 400 WORDS)

Fuel-mediated teratogenesis: biochemical effects of hypoglycemia during neurulation in mouse embryos in vitro

Hypoglycemia has been reported to induce congenital malformations and growth retardation in rodent embryos during the period of neural tube closure in vitro. However, the biochemical alterations responsible for the production of the dysmorphogenic effects have not been evaluated. Therefore, the rates of glucose metabolism by glycolysis, citric acid cycle, oxidative pentose phosphate pathway (PPP), and anabolic utilization were evaluated in mouse embryos and extraembryonic membranes using the whole embryo culture technique. Altered glucose metabolism by glycolysis and oxidative PPP, as well as altered anabolic synthesis, were produced by exposure to hypoglycemia. In embryos exposed to mild hypoglycemia (80 mg/dl) altered metabolism by the PPP and an associated effect on nucleic acid synthesis were in part responsible for the dysmorphogenic effects of this treatment. In contrast, severe hypoglycemia (40 mg/dl) appeared to have an immediate effect on glycolytic metabolism in addition to effects on the PPP and nucleic acid synthesis. Therefore, a multifactorial biochemical mechanism contributes to the induction of malformations by severe hypoglycemia in mouse embryos in vitro. Furthermore, the differential effects of moderate vs. severe hypoglycemia on glycolytic metabolism, and possibly energy production, may account for the differences in the severity of these treatments on embryonic growth and the incidence of malformations.

Effects of human diabetic serum on the in vitro development of mouse preimplantation embryos

The effects of sera from different types of human diabetes (type I with and without ketoacidosis; type II treated with insulin or Daonil or untreated) on the in vitro development of early preimplantation mouse embryos were studied. In controls, 20% of blastocysts failed to develop successfully when grown for 72 h in RPMI medium supplemented with 10% fetal bovine serum and 50% nondiabetic human serum. In experiments using 50% diabetic serum, the highest embryotoxic effect was found in type-I diabetes with and without ketoacidosis: The percents of undeveloped embryos were 66 and 58, respectively. In type-II diabetes, embryotoxic effects were found among all studied types: The percent of undeveloped blastocysts varied from 36% in insulin-treated type-II diabetes to 44% in untreated type-II diabetes. A high correlation was found between the number of undeveloped embryos and the blood concentrations of metabolic diabetic factors: glucose (r = .53-.64 in type-I diabetes), B-HOB (r = .7-.77 in type-II diabetes untreated or treated with Daonil), acetoacetate (r = .66 in insulin-treated type-II diabetes), and HbA1c (r = .89 in insulin-treated type-II diabetes or .99 in Daonil-treated type-II diabetes). A concentration of 80% serum was embryo-toxic when obtained from nondiabetic or from diabetic human. The possible role of diabetic metabolic factors in causing increased risk of spontaneous abortions and infertility among diabetic women is discussed.

Embryonic catch-up growth after exposure to the ketone body D,L,-beta-hydroxybutyrate in vitro

The capability of rodent embryos to recover in growth and development subsequent to exposure to an insult was investigated employing whole embryo culture. Early somite stage mouse embryos were exposed to 32 mM D,L,-beta-hydroxybutyrate (D,L,-beta OHB) for 24 hr (Period I), and were then transferred and maintained in control medium for an additional 36 hr maximum (Period II). Growth of this recovery group (Group B) was monitored at various time points of Period II and the results were compared with an unexposed control group (Group A) and another continuously-exposed reference group (Group C). At the end of Period I, 100% of D,L,-beta OHB-exposed embryos exhibited neural tube closure defects and were growth retarded. At 36 hr of Period II, cranial and caudal neural tube defects of Group B embryos were reduced to 3-7% and 0%, respectively. These embryos also demonstrated an excess in growth velocity during recovery so that at the end of Period II, total protein content was comparable to control values. In contrast, Group C embryos remained growth retarded and showed a significant increase in cranial and caudal neural tube defects (20 and 75%, respectively). Thus, neurulating mouse embryos were capable of catch-up growth following an embryotoxic exposure to D,L,-beta OHB. The progression of development of total protein values and morphological features such as elimination of neural tube defects was intimately related to the amount of time allowed for recovery. Moreover, an elevation of growth rate over normality, which is characteristic of catch-up growth, was observed.

Importance of genetic predisposition and maternal environment for the occurrence of congenital malformations in offspring of diabetic rats

Previous experimental studies have implicated a genetic component in the induction of malformations in the offspring of diabetic rats. We have compared the outcome of diabetic pregnancy in two outbred (sub)strains of Sprague-Dawley rats (with low incidence [H] and high incidence [U] of skeletal malformations in the offspring) and hybrids between them. The fetuses of diabetic H mothers had no skeletal malformations and the lowest frequency of resorptions (8-9%), regardless of embryo type (H/H or H/U). When the diabetic mother was U or from the hybrid strain (H/U) and the offspring were of the mixed H/U type, we found increased resorption (16-21%) and skeletal malformation (3-5%) rates. If instead the embryos contained a major U genome [either U/U or U/(H/U)], further increased resorptions (23-30%) and skeletal malformations (17-19%) resulted. The H/H and U/U embryonic susceptibility to defined teratogens (3-6 mg/ml D-glucose, 4-8 mM B-hydroxy-butyrate) were compared in whole embryo culture and found to be similar, suggesting that the malformations occurring in vivo may have a different etiology than those found in vitro. In the rat model studied, diabetes in the mother appears to cause a disturbance of early stages of embryogenesis in genetically predisposed embryos. This early disturbance results in skeletal malformations and seems to require inducing factor(s) in addition to increased levels of D-glucose and B-hydroxybutyrate. The findings are in concert with the notion of a mixed genetic-environmental etiology of malformations in (diabetic) pregnancy.

Development of rat embryos cultured in serum prepared from rats with streptozotocin-induced diabetes

The effects of 40, 50, and 60 mg/kg streptozotocin (SZ) on the body weights and the glucose concentration and the osmolarity of the serum of adult rats were determined. Serum prepared from these SZ-dosed rats was used in embryo culture experiments to investigate effects of diabetic serum on rat embryos during organogenesis. The diabetic serum resulting from each of the tested doses of SZ was teratogenic to 9.5-day rat explants (embryos and their membranes), causing a range of dysmorphic lesions including craniofacial defects, heart defects, and abnormalities of the branchial arches and the otic capsules. Explants cultured in serum prepared from rats dosed with 60 mg/kg SZ also showed abnormal morphology of both the visceral yolk sac and the embryonic blood cells in the yolk sac capillaries. The development of explants repeatedly transferred between control and diabetic serum indicated that the severity of the dysmorphic effect was dependent on the duration of exposure to diabetic serum. The alternation of sera did not in itself appear to be damaging to the embryos. Explants cultured in control serum, control serum with its glucose concentration increased to that of the diabetic serum, or diabetic serum all took up the same amount of glucose from their culture medium; 30% of the embryos from the diabetic serum were abnormal compared to only 4% from the control serum and the control serum plus glucose.

Metabolism of D- and DL-beta-hydroxybutyrate by mouse embryos in vitro

Rates of 14CO2 production by mouse conceptuses in vitro from D- and DL-[3-14C]-beta-hydroxybutyrate (beta OHB) were determined during the period of organogenesis (days 9 through 12 of gestation) in the presence of 4 to 32 mmol/L DL-beta OHB. During this time period the rates 14CO2 production from D-beta OHB metabolism are concentration-dependent, increase on each day of gestation, and the site of metabolism appears to shift from the visceral yolk sac placenta to the embryo proper. In contrast to fetal and neonatal tissues, the rates of 14CO2 production from DL-beta OHB oxidation is significantly greater than from D-beta OHB suggesting that the utilization of the L-isomer may be equal to or greater than that of the D-form.

Effects of metabolic factors in the diabetic state on the in vitro development of preimplantation mouse embryos

The effects of insulin, glucagon, beta-hydroxybutyrate, and acetoacetate on the in vitro development of preimplantation mouse embryos were studied. In controls, 24% of blastocysts failed to develop successfully when grown for 72 h in Eagle's medium supplemented with 10% fetal calf serum. Insulin at concentrations of 1.0 and 2.0 IU/ml of culture medium interfered with development in 62-63% of the blastocysts. Preimplantation embryos showed a threshold pattern in their reaction to glucagon: its addition in concentrations of 0.0015 mM (5 micrograms/ml) did not significantly inhibit blastocyst development, while concentrations of 0.003 mM (10 micrograms/ml) inhibited 70% of blastocysts. The embryotoxic effects of ketone bodies were manifested only in relatively high doses. beta-hydroxybutyrate was embryotoxic at concentrations greater than 5 mg/ml, and its effects were dose dependent: 48 mM (6 mg/ml) inhibited 45% of blastocysts, while 80 mM (10 mg/ml) arrested 87% of embryos from further development. Acetoacetate at concentrations of 0.1 mM (10 micrograms/ml) inhibited the development of 50% of the blastocysts, and its effects were not dose dependent: concentrations of 1 mM (100 micrograms/ml) inhibited development in 63% of the embryos. The combination of the diabetic metabolic factors in relatively low concentrations was highly embryotoxic, especially when accompanied by hyperglycemia.

Effects of hyperglycemia and ketone bodies on the in vitro development of early somite rate embryos

The teratogenic effects of diabetes are attributed to the influence of hyperglycemia and hyperketonemia as well as to other metabolic factors. We studied the effects of ketone bodies and glucose on the development of early somite rat embryos (day 10 1/2 of gestation) cultured in vitro. D-glucose was added to normal rat serum in concentrations of 2, 5, and 10 mg/ml. Ketone bodies (acetoacetate and beta-hydroxybutyrate, B-HOB) were individually added to normal or to hyperglycemic sera (total glucose concentrations of 3 mg/ml) in the following concentrations: acetoacetate--5, 10, 20, and 40 micrograms/ml; B-HOB--2, 5, and 8 mg/ml. The higher concentrations of each of the substances induced growth retardation and abnormalities. The growth-retarding and teratogenic effects of a combination of the substances, glucose and B-HOB, glucose and acetoacetate, on the development of 10 1/2 day embryos were greater than when each substance was added separately, even at relatively low doses. The greatest teratogenic effects were observed when low concentrations of all three substances were added simultaneously to the culture medium. These results may have direct relevance to human diabetes since diabetes is characterized by a simultaneous elevation of serum levels of all these substances.

Maternal factors in developmental toxicity

The maternal organism provides the developing embryo with its physical environment, nutrients, and a mechanism for eliminating metabolic wastes. Since the physiological state of the pregnant female affects her ability to provide those requirements for the developing embryo, it is not surprising that there are maternal factors that can affect the wellbeing of the embryo. Extremes of maternal age in both humans and animals have been implicated in growth retardation, as well as autosomal trisomies. The influence of maternal size on fetal size is more pronounced among larger species with longer gestation periods such as humans and domestic animals. A clear relationship between the parity of the mother and potential developmental toxicity in humans has not been established due to the confounding influences of maternal age. Among laboratory rodents, however, it appears that offspring of multiparous animals are at increased risk of developmental toxicity. A variety of infectious agents, particularly viruses, have either been demonstrated or implicated as causes of developmental toxicity. In addition, hyperthermia is a possible confounding factor inherent with maternal infection. Although under experimental conditions hyperthermia is teratogenic in laboratory animals, a causative role for transient hyperthermia, which occurs during febrile states concomitant with infections, cannot be clearly established. Chronic maternal vascular disease states including essential hypertension, heart disease, or diabetes mellitus are likely to contribute to uteroplacental insufficiency and developmental toxicity. Poor maternal nutrition among humans contributes to growth retardation, but not to malformations. The production of "abnormal" maternal antibodies, such as are present in Rh incompatibility, can cause fetal wastage. An important maternal factor in humans is uteroplacental insufficiency, which can occur in normal states like twinning, as well as in abnormal conditions including reduced placental size, chronic maternal hypoxia, or uterine ischemia. Although all these maternal factors can contribute to developmental toxicity, they do not necessarily occur as isolated events. Some developmental toxicants exert deleterious effects within both the embryo and the maternal system.