Dietary vitamin and lipid therapy rescues aberrant signaling and apoptosis and prevents hyperglycemia-induced diabetic embryopathy in rats

Aberrant lipid accumulation in the mouse visceral yolk sac resulting from maternal diabetes and obesity

Maternal diabetes and obesity in pregnancy are well-known risk factors for structural birth defects, including neural tube defects and congenital heart defects. Progeny from affected pregnancies are also predisposed to developing cardiometabolic disease in later life. Based upon in vitro embryo cultures of rat embryos, it was postulated that nutrient uptake by the yolk sac is deficient in diabetic pregnancies. In contrast, using two independent mouse models of maternal diabetes, and a high-fat diet-feeding model of maternal obesity, we observed excessive lipid accumulation at 8.5 days in the yolk sac. The numbers as well as sizes of intracellular lipid droplets were increased in yolk sacs of embryos from diabetic and obese pregnancies. Maternal metabolic disease did not affect expression of lipid transporter proteins, including ApoA1, ApoB and SR-B1, consistent with our earlier report that expression of glucose and fatty acid transporter genes was also unchanged in diabetic pregnancy-derived yolk sacs. Colocalization of lipid droplets with lysosomes was significantly reduced in the yolk sacs from diabetic and obese pregnancies compared to yolk sacs from normal pregnancies. We therefore conclude that processing of lipids is defective in pregnancies affected by maternal metabolic disease, which may lead to reduced availability of lipids to the developing embryo. The possible implications of insufficient supply of lipids -and potentially of other nutrients-to the embryos experiencing adverse pregnancy conditions are discussed.

Nutrient Transporter Gene Expression in the Early Conceptus-Implications From Two Mouse Models of Diabetic Pregnancy

Maternal diabetes in early pregnancy increases the risk for birth defects in the offspring, particularly heart, and neural tube defects. While elevated glucose levels are characteristic for diabetic pregnancies, these are also accompanied by hyperlipidemia, indicating altered nutrient availability. We therefore investigated whether changes in the expression of nutrient transporters at the conception site or in the early post-implantation embryo could account for increased birth defect incidence at later developmental stages. Focusing on glucose and fatty acid transporters, we measured their expression by RT-PCR in the spontaneously diabetic non-obese mouse strain NOD, and in pregnant FVB/N mouse strain dams with Streptozotocin-induced diabetes. Sites of expression in the deciduum, extra-embryonic, and embryonic tissues were determined by RNAscope in situ hybridization. While maternal diabetes had no apparent effects on levels or cellular profiles of expression, we detected striking cell-type specificity of particular nutrient transporters. For examples, Slc2a2/Glut2 expression was restricted to the endodermal cells of the visceral yolk sac, while Slc2a1/Glut1 expression was limited to the mesodermal compartment; Slc27a4/Fatp4 and Slc27a3/Fatp3 also exhibited reciprocally exclusive expression in the endodermal and mesodermal compartments of the yolk sac, respectively. These findings not only highlight the significance of nutrient transporters in the intrauterine environment, but also raise important implications for the etiology of birth defects in diabetic pregnancies, and for strategies aimed at reducing birth defects risk by nutrient supplementation.

Deficiency of the oxidative stress-responsive kinase p70S6K1 restores autophagy and ameliorates neural tube defects in diabetic embryopathy

BACKGROUND

Autophagy is highly active in neuroepithelial cells of the developing neuroepithelium, and impairment of autophagy leads to neural tube defects. In this study, we have found that maternal diabetes suppresses autophagy that leads to neural tube defects and consequent cellular imbalance in the endoplasmic reticulum where critical events occur, leading to the induction of diabetic embryopathy. Because the mammalian target of rapamycin pathway suppresses autophagy, we hypothesized that 70 kDa ribosomal protein S6 kinase 1 (p70S6K1), a major downstream effector of mammalian target of rapamycin, mediates the inhibitory effect of maternal diabetes on autophagy in the developing neuroepithelium.

OBJECTIVE

We investigated whether p70S6K1 mediates the inhibitory effect of maternal diabetes on autophagy during neurulation. We also examined whether p70S6K1 deficiency restores autophagy and therefore relieves endoplasmic reticulum stress and inhibits maternal diabetes-induced apoptosis, which leads to reduction in neural tube defect incidence in diabetic embryopathy.

STUDY DESIGN

Female p70S6K1 heterogeneous knockout (p70S6K1+/-) mice were bred with male p70S6K1 heterogeneous knockout (p70S6K1+/-) mice to generate wild-type (WT), p70S6K1+/- and p70S6K1 knockout (p70S6K1-/-) embryos. Embryos at embryonic day 8.5 were harvested for the assessment of indices of autophagy, endoplasmic reticulum stress, and apoptosis. Neural tube defect incidence in embryos was determined at embryonic day 10.5. For in vitro studies, small interfering RNA knockdown of p70S6K1 in C17.2 mouse neural stem cells was used to determine the effect of p70S6K1 deficiency on autophagy impairment and endoplasmic reticulum stress under high glucose conditions.

RESULTS

Knockout of the Rps6kb1 gene, which encodes for p70S6K1, ameliorated maternal diabetes-induced NTDs and restored autophagosome formation in neuroepithelial cells suppressed by maternal diabetes. Maternal diabetes-suppressed conversion of LC3-I (microtubule-associated protein 1A/1B-light chain 3) to LC3-II, an index of autophagic activity, in neurulation stage embryos was abrogated in the absence of p70S6K1. p70S6K1 knockdown in neural stem cells also restored autophagosome formation and the conversion of LC3-I to LC3-II. The activation of the major unfolded protein response, indicated by phosphorylation of inositol-requiring enzyme 1 alpha, and protein kinase R-like endoplasmic reticulum kinase, and eukaryotic translation initiation factor 2α, and the increase of the endoplasmic reticulum stress marker, C/EBP homologous protein, were induced by maternal diabetes in vivo and high glucose in vitro. Unfolded protein response and endoplasmic reticulum stress induced by maternal diabetes or high glucose were reduced by Rps6kb1 deletion or p70S6K1 knockdown, respectively. Rps6kb1 knockout blocked maternal diabetes-induced caspase cleavage and neuroepithelial cell apoptosis. The superoxide dismutase mimetic Tempol abolished high glucose-induced p70S6K1 activation.

CONCLUSION

The study revealed the critical involvement of p70S6K1 in the pathogenesis of diabetic embryopathy.

Severe Uncontrolled Maternal Hyperglycemia Induces Microsomia and Neurodevelopment Delay Accompanied by Apoptosis, Cellular Survival, and Neuroinflammatory Deregulation in Rat Offspring Hippocampus

Maternal diabetes constitutes an unfavorable intrauterine environment for offspring development. Although it is known that diabetes can cause brain alterations and increased risk for neurologic disorders, the relationship between neuroimmune activation, brain changes, and neurodevelopment deficits in the offspring remains unclear. In order to elucidate the short- and long-term biological basis of the developmental outcomes caused by the severe uncontrolled maternal hyperglycemia, we studied apoptosis, neurogenesis, and neuroinflammation pathways in the hippocampus of neonates and young rats born to diabetic dams. Diabetes was induced on gestational day 5 by an injection of streptozotocin. Evaluations of milestones, body growth, and inhibitory avoidance were performed to monitor the offspring development and behavior. Hippocampal modifications were studied through cellular survival by BrdU in the dentate gyrus, expression of apoptosis-regulatory proteins (procaspase 3, caspase 3, and Bcl-2), BDNF, and neuroinflammatory modulation by interleukins, MHC-I, MHC-II, Iba-1, and GFAP proteins. Severe maternal diabetes caused microsomia and neurodevelopmental delay in pups and decrease of Bcl-2, procaspase 3, and caspase 3 in the hippocampus. Moreover, in a later stage of development, it was found an increase of TNF-α and a decrease of procaspase 3, caspase 3, MHC-I, IL-1β, and BDNF in the hippocampus, as well as impairment in cellular survival in the dentate gyrus. This study showed significant short- and long-term commitments on the development, apoptosis, cell survival, and neuroinflammation in the offspring hippocampus induced by severe uncontrolled maternal hyperglycemia. The data reinforce the need for treatment of maternal hyperglycemic states during pregnancy and breast-feeding.

The increased activity of a transcription factor inhibits autophagy in diabetic embryopathy

BACKGROUND

Maternal diabetes induces neural tube defects and stimulates the activity of the forkhead box O3 (Fox)O3a in the embryonic neuroepithelium. We previously demonstrated that deleting the FOXO3a gene ameliorates maternal diabetes-induced neural tube defects. Macroautophagy (hereafter referred to as "autophagy") is essential for neurulation. Rescuing autophagy suppressed by maternal diabetes in the developing neuroepithelium inhibits neural tube defect formation in diabetic pregnancy. This evidence suggests a possible link between FoxO3a and impaired autophagy in diabetic embryopathy.

OBJECTIVE

We aimed to determine whether maternal diabetes suppresses autophagy through FoxO3a, and if the transcriptional activity of FoxO3a is required for the induction of diabetic embryopathy.

STUDY DESIGN

We used a well-established type 1 diabetic embryopathy mouse model, in which diabetes was induced by streptozotocin, for our in vivo studies. To determine if FoxO3a mediates the inhibitory effect of maternal diabetes on autophagy in the developing neuroepithelium, we induced diabetic embryopathy in FOXO3a gene knockout mice and FoxO3a dominant negative transgenic mice. Embryos were harvested at embryonic day 8.5 to determine FoxO3a and autophagy activity and at embryonic day 10.5 for the presence of neural tube defects. We also examined the expression of autophagy-related genes. C17.2 neural stem cells were used for in vitro examination of the potential effects of FoxO3a on autophagy.

RESULTS

Deletion of the FOXO3a gene restored the autophagy markers, lipidation of microtubule-associated protein 1A/1B-light chain 3I to light chain 3II, in neurulation stage embryos. Maternal diabetes decreased light chain 3I-positive puncta number in the neuroepithelium, which was restored by deleting FoxO3a. Maternal diabetes also decreased the expression of positive regulators of autophagy (Unc-51 like autophagy activating kinase 1, Coiled-coil myosin-like BCL2-interacting protein, and autophagy-related gene 5) and the negative regulator of autophagy, p62. FOXO3a gene deletion abrogated the dysregulation of autophagy genes. In vitro data showed that the constitutively active form of FoxO3a mimicked high glucose in repressing autophagy. In cells cultured under high-glucose conditions, overexpression of the dominant negative FoxO3a mutant blocked autophagy impairment. Dominant negative FoxO3a overexpression in the developing neuroepithelium restored autophagy and significantly reduced maternal diabetes-induced apoptosis and neural tube defects.

CONCLUSION

Our study revealed that diabetes-induced FoxO3a activation inhibited autophagy in the embryonic neuroepithelium. We also observed that FoxO3a transcriptional activity mediated the teratogenic effect of maternal diabetes because dominant negative FoxO3a prevents maternal diabetes-induced autophagy impairment and neural tube defect formation. Our findings suggest that autophagy activators could be therapeutically effective in treating maternal diabetes-induced neural tube defects.

Deficient Vitamin E Uptake During Development Impairs Neural Tube Closure in Mice Lacking Lipoprotein Receptor SR-BI

SR-BI is the main receptor for high density lipoproteins (HDL) and mediates the bidirectional transport of lipids, such as cholesterol and vitamin E, between these particles and cells. During early development, SR-BI is expressed in extraembryonic tissue, specifically in trophoblast giant cells in the parietal yolk sac. We previously showed that approximately 50% of SR-BI^-/- embryos fail to close the anterior neural tube and develop exencephaly, a perinatal lethal condition. Here, we evaluated the role of SR-BI in embryonic vitamin E uptake during murine neural tube closure. Our results showed that SR-BI^-/- embryos had a very low vitamin E content in comparison to SR-BI^+/+ embryos. Whereas SR-BI^-/- embryos with closed neural tubes (nSR-BI^-/-) had high levels of reactive oxygen species (ROS), intermediate ROS levels between SR-BI^+/+ and nSR-BI^-/- embryos were detected in SR-BI^-/- with NTD (NTD SR-BI^-/-). Reduced expression of Pax3, Alx1 and Alx3 genes was found in NTD SR-BI^-/- embryos. Maternal α-tocopherol dietary supplementation prevented NTD almost completely (from 54% to 2%, p < 0.001) in SR-BI^-/- embryos and normalized ROS and gene expression levels. In sum, our results suggest the involvement of SR-BI in the maternal provision of embryonic vitamin E to the mouse embryo during neural tube closure.

α-Tocopherol and Hippocampal Neural Plasticity in Physiological and Pathological Conditions

Neuroplasticity is an "umbrella term" referring to the complex, multifaceted physiological processes that mediate the ongoing structural and functional modifications occurring, at various time- and size-scales, in the ever-changing immature and adult brain, and that represent the basis for fundamental neurocognitive behavioral functions; in addition, maladaptive neuroplasticity plays a role in the pathophysiology of neuropsychiatric dysfunctions. Experiential cues and several endogenous and exogenous factors can regulate neuroplasticity; among these, vitamin E, and in particular α-tocopherol (α-T), the isoform with highest bioactivity, exerts potent effects on many plasticity-related events in both the physiological and pathological brain. In this review, the role of vitamin E/α-T in regulating diverse aspects of neuroplasticity is analyzed and discussed, focusing on the hippocampus, a brain structure that remains highly plastic throughout the lifespan and is involved in cognitive functions. Vitamin E-mediated influences on hippocampal synaptic plasticity and related cognitive behavior, on post-natal development and adult hippocampal neurogenesis, as well as on cellular and molecular disruptions in kainate-induced temporal seizures are described. Besides underscoring the relevance of its antioxidant properties, non-antioxidant functions of vitamin E/α-T, mainly involving regulation of cell signaling molecules and their target proteins, have been highlighted to help interpret the possible mechanisms underlying the effects on neuroplasticity.

Reevaluation of Antioxidative Strategies for Birth Defect Prevention in Diabetic Pregnancies

Diabetes mellitus in early pregnancy is the most severe maternal disease that is counted for 10% of newborn infants with structural defects. With the rapid increases in the number of diabetic women in childbearing age, the birth defect rate is projected to elevate dramatically. Thus, prevention of embryonic malformations becomes an urgent task. Animal studies have revealed an involvement of oxidative stress in diabetic embryopathy and treatment with antioxidants can reduce embryonic abnormalities. However, the failure of clinical trials using free radical-scavenging antioxidants to alleviate oxidative stress-related diseases prompts researchers to reevaluate the strategy in birth defect prevention. Hyperglycemia also disturbs other intracellular homeostasis, generating aberrant conditions. Perturbed folding of newly synthesized proteins causes accumulation of unfolded and misfolded proteins in the lumen of the endoplasmic reticulum (ER). The ER under the stress activates signaling cascades, known as unfolded protein response, to suppress cell mitosis and/or trigger apoptosis. ER stress can be ameliorated by chemical chaperones, which promote protein folding. Hyperglycemia also stimulates the expression of nitric oxide (NO) synthase 2 (NOS2) to produce high levels of NO and reactive nitrogen species and augment protein nitrosylation and nitration, resulting in nitrosative stress. Inhibition of NOS2 using inhibitors has been demonstrated to reduce embryonic malformations in diabetic animals. Therefore, targeting ER and nitrosative stress conditions using specific agents to prevent birth defects in diabetic pregnancies warrant further investigations. Simultaneously targeting multiple stress conditions using combined agents is a potentially effective and feasible approach.

Identification of novel cell survival regulation in diabetic embryopathy via phospholipidomic profiling

Diabetes mellitus in early pregnancy causes birth defects by disturbing metabolic homeostasis and increasing programmed cell death in the embryo. Over-activation of phospholipase Cβ3 and γ1 suggests disturbed phospholipid metabolism, which is an important in regulation of cell signaling and activity. Metabolomic examinations reveal significant changes in the profile of phospholipid metabolism. Among the metabolites, levels of phosphatidylinositol bisphosphate (PIP2) are increased. PIP2 effector PTEN (phosphatase and tensin homolog deleted on chromosome 10) is activated. Activation of protein kinase Bα (PKBα, or AKT1) and mTOR (mechanistic target of rapamycin) is decreased. Inhibition of PLCs and PTEN suppresses over-generation of reactive oxygen species and inhibition of PLCs prevents fragmentation of mitochondria in neural stem cells cultured in high glucose. These observations suggest that maternal hyperglycemia disrupts phospholipid metabolism, leading to perturbation of mitochondrial dynamics and redox homeostasis and suppression of the PKB-mTOR cell survival signaling in the embryos.

The Nrf2 Activator Vinylsulfone Reduces High Glucose-Induced Neural Tube Defects by Suppressing Cellular Stress and Apoptosis

The nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway is one of the primary pathways responsible for the cellular defense system against oxidative stress. Oxidative stress-induced apoptosis is a causal event in diabetic embryopathy. Thus, the Nrf2 pathway may play an important role in the induction of diabetic embryopathy. In the present study, we investigated the potentially protective effect of the Nrf2 activator, vinylsulfone, on high glucose-induced cellular stress, apoptosis, and neural tube defects (NTDs). Embryonic day 8.5 (E8.5) whole mouse embryos were cultured in normal (5 mmol/L) or high (16.7 mmol/L) glucose conditions, with or without vinylsulfone. At a concentration of 10 μmol/L, vinylsulfone had an inhibitory effect on high glucose-induced NTD formation, but it was not significant. At a concentration of 20 μmol/L, vinylsulfone significantly reduced high glucose-induced NTDs. In addition, 20 μmol/L vinylsulfone abrogated the high glucose-induced oxidative stress markers lipid hydroperoxide (LPO), 4-hydroxynonenal (4-HNE), and nitrotyrosine-modified proteins. The high glucose-induced endoplasmic reticulum (ER) stress biomarkers were also suppressed by 20 μmol/L vinylsulfone through the inhibition of phosphorylated protein kinase RNA-like ER kinase (PERK), inositol requiring protein 1α (IRE1a), eukaryotic initiation factor 2α (eIF2a), upregulated C/EBP-homologous protein (CHOP), binding immunoglobulin protein (BiP), and x-box binding protein 1 (XBP1) messenger RNA splicing. Furthermore, 20 μmol/L vinylsulfone abolished caspase 3 and caspase 8 cleavage, markers of apoptosis, in embryos cultured under high glucose conditions. The Nrf2 activator, vinylsulfone, is protective against high glucose-induced cellular stress, caspase activation, and subsequent NTD formation. Our data suggest that vinylsulfone supplementation is a potential therapy for diabetes-associated neurodevelopmental defects.

Advances in revealing the molecular targets downstream of oxidative stress-induced proapoptotic kinase signaling in diabetic embryopathy

Preexisting maternal diabetes is a high-risk factor of diabetic embryopathy, such as neural tube defects and congenital heart defects. Maternal diabetes significantly increases the production of reactive oxygen species, resulting in oxidative stress and diabetic embryopathy. Multiple cellular and metabolic factors contribute to these processes. Forkhead box O (FoxO)-3a has been demonstrated as a key transcription factor in the signaling transduction pathways responsible for maternal diabetes-induced birth defects. Apoptosis signal-regulating kinase 1 (ASK1) activated by oxidative stress stimulates nuclear translocation of FoxO3a, resulting in the overexpression of tumor necrosis factor receptor 1-associated death domain protein, which, in turn, leads to caspase-8 activation and apoptosis. Maternal diabetes-activated c-Jun N-terminal kinase (JNK)-1/2, downstream effectors of ASK1, can be blocked by superoxide dismutase-1 overexpression, suggesting that oxidative stress is responsible for JNK1/2 signaling activation. Deletion of JNK1/2 significantly suppressed the activity of FoxO3a. These observations indicate that maternal diabetes-induced oxidative stress stimulates the activation of ASK1, JNK1/2, FoxO3a, tumor necrosis factor receptor 1-associated death domain protein, caspase-8 cleavage, and finally, apoptosis and diabetic embryopathy.

Oxidative stress is responsible for maternal diabetes-impaired transforming growth factor beta signaling in the developing mouse heart

OBJECTIVE

Oxidative stress plays a causal role in diabetic embryopathy. Maternal diabetes induces heart defects and impaired transforming growth factor beta (TGFβ) signaling, which is essential for cardiogenesis. We hypothesize that mitigating oxidative stress through superoxide dismutase 1 (SOD1) overexpression in transgenic (Tg) mice reverses maternal hyperglycemia-impaired TGFβ signaling and its downstream effectors.

STUDY DESIGN

Day 12.5 embryonic hearts from wild-type (WT) and SOD1 overexpressing embryos of nondiabetic (ND) and diabetic mellitus (DM) dams were used for the detection of oxidative stress markers: 4-hydroxynonenal (4-HNE) and malondlaldehyde (MDA), and TGFβ1, 2, and 3, phosphor (p)-TGFβ receptor II (TβRII), p-phosphorylated mothers against decapentaplegic (Smad)2, and p-Smad3. The expression of 3 TGFβ-responsive genes was also assessed. Day 11.5 embryonic hearts were explanted and cultured ex vivo, with or without treatments of a SOD1 mimetic (Tempol; Enzo Life Science, Farmingdale, NY) or a TGFβ recombinant protein for the detection of TGFβ signaling intermediates.

RESULTS

Levels of 4-HNE and MDA were significantly increased by maternal diabetes, and SOD1 overexpression blocked the increase of these 2 oxidative stress markers. Maternal diabetes suppresses the TGFβ signaling pathway by down-regulating TGFβ1 and TGFβ3 expression. Consequently, phosphorylation of TβRII, Smad2, and Smad3, downstream effectors of TGFβ, and expression of 3 TGFβ-responsive genes were reduced by maternal diabetes, and these reductions were prevented by SOD1 overexpression. Treatment with Tempol or TGFβ recombinant protein restored high-glucose-suppressed TGFβ signaling intermediates and responsive gene expression.

CONCLUSION

Oxidative stress mediates the inhibitory effect of hyperglycemia in the developing heart. Antioxidants, TGFβ recombinant proteins, or TGFβ agonists may have potential therapeutic values in the prevention of heart defects in diabetic pregnancies.

Decoding the oxidative stress hypothesis in diabetic embryopathy through proapoptotic kinase signaling

Maternal diabetes-induced birth defects occur in 6-10% of babies born to mothers with pregestational diabetes, representing a significant maternal-fetal health problem. Currently, these congenital malformations represent a significant maternal-fetal medicine issue, but are likely to create an even greater public health threat as 3 million women of reproductive age (19-44 years) have diabetes in the United States alone, and this number is expected to double by 2030. Neural tube defects (NTDs) and congenital heart defects are the most common types of birth defects associated with maternal diabetes. Animal studies have revealed that embryos under hyperglycemic conditions exhibit high levels of oxidative stress resulting from enhanced production of reactive oxygen species and impaired antioxidant capability. Oxidative stress activates a set of proapoptotic kinase signaling intermediates leading to abnormal cell death in the embryonic neural tube, which causes NTD formation. Work in animal models also has revealed that maternal diabetes triggers a series of signaling intermediates: protein kinase C (PKC) isoforms, PKCα, βII and δ; apoptosis signal-regulating kinase 1; c-Jun-N-terminal kinase (JNK)1/2; caspase; and apoptosis. Specifically, maternal diabetes in rodent models activates the proapoptotic unfolded protein response and endoplasmic reticulum (ER) stress. A reciprocal causation between JNK1/2 activation and ER stress exists in diabetic embryopathy. Molecular studies further demonstrate that deletion of the genes for Prkc, Ask1, Jnk1, or Jnk2 abolishes maternal diabetes-induced neural progenitor apoptosis and ameliorates NTD formation. Similar preventive effects are also observed when apoptosis signal-regulating kinase 1, JNK1/2, or ER stress is inhibited. Cell membrane stabilizers and antioxidant supplements are also effective in prevention of diabetes-induced birth defects. Mechanistic studies have revealed important insights into our understanding the cause of diabetic embryopathy and have provided a basis for future interventions against birth defects or other pregnancy complications associated with maternal diabetes. The knowledge of a molecular pathway map identified in animal studies has created unique opportunities to identify molecular targets for therapeutic intervention.

Effect of maternal diabetes on the embryo, fetus, and children: congenital anomalies, genetic and epigenetic changes and developmental outcomes

INTRODUCTION

Pregestational and gestational diabetes mellitus (PGDM; GDM) are significant health concerns because they are associated with an increased rate of malformations and maternal health complications.

METHODS

We reviewed the data that help us to understand the effects of diabetes in pregnancy.

RESULTS

Diabetic embryopathy can affect any developing organ system, but cardiovascular and neural tube defects are among the most frequent anomalies. Other complications include preeclampsia, preterm delivery, fetal growth abnormalities, and perinatal mortality. Neurodevelopmental studies on offspring of mothers with diabetes demonstrated increased rate of Gross and Fine motor abnormalities, of Attention Deficit Hyperactivity Disorder, learning difficulties, and possibly also Autism Spectrum Disorder. The mechanisms underlying the effects of maternal hyperglycemia on the developing fetus may involve increased oxidative stress, hypoxia, apoptosis, and epigenetic changes. Evidence for epigenetic changes are the following: not all progeny are affected and not to the same extent; maternal diet may influence pregnancy outcomes; and maternal diabetes alters embryonic transcriptional profiles and increases the variation between transcriptomic profiles as a result of altered gene regulation. Research in animal models has revealed that maternal hyperglycemia is a teratogen, and has helped uncover potential therapeutic targets which, when blocked, can mitigate or ameliorate the negative effects of diabetes on the developing fetus.

CONCLUSIONS

Tight metabolic control, surveillance, and labor management remain the cornerstone of care for pregnant women with diabetes, but advances in the field indicate that new treatments to protect the mother and baby are not far from becoming clinical realities.

Streptozotocin-induced diabetes models: pathophysiological mechanisms and fetal outcomes

Glucose homeostasis is controlled by endocrine pancreatic cells, and any pancreatic disturbance can result in diabetes. Because 8% to 12% of diabetic pregnant women present with malformed fetuses, there is great interest in understanding the etiology, pathophysiological mechanisms, and treatment of gestational diabetes. Hyperglycemia enhances the production of reactive oxygen species, leading to oxidative stress, which is involved in diabetic teratogenesis. It has also been suggested that maternal diabetes alters embryonic gene expression, which might cause malformations. Due to ethical issues involving human studies that sometimes have invasive aspects and the multiplicity of uncontrolled variables that can alter the uterine environment during clinical studies, it is necessary to use animal models to better understand diabetic pathophysiology. This review aimed to gather information about pathophysiological mechanisms and fetal outcomes in streptozotocin-induced diabetic rats. To understand the pathophysiological mechanisms and factors involved in diabetes, the use of pancreatic regeneration studies is increasing in an attempt to understand the behavior of pancreatic beta cells. In addition, these studies suggest a new preventive concept as a treatment basis for diabetes, introducing therapeutic efforts to minimize or prevent diabetes-induced oxidative stress, DNA damage, and teratogenesis.

Superoxide dismutase 1 overexpression in mice abolishes maternal diabetes-induced endoplasmic reticulum stress in diabetic embryopathy

OBJECTIVE

Both oxidative stress and endoplasmic reticulum stress (ER stress) are causal events in diabetic embryopathy. We tested whether oxidative stress causes ER stress.

STUDY DESIGN

Wild-type (WT) and superoxide dismutase 1 (SOD1)-overexpressing day 8.75 embryos from nondiabetic WT control with SOD1 transgenic male and diabetic WT female with SOD1 transgenic male were analyzed for ER stress markers: C/EBP-homologous protein (CHOP), calnexin, eukaryotic initiation factor 2α (eIF2α), protein kinase ribonucleic acid (RNA)-like ER kinase (PERK), binding immunoglobulin protein, protein disulfide isomerase family A member 3, kinases inositol-requiring protein-1α (IRE1α), and the X-box binding protein (XBP1) messenger RNA (mRNA) splicing.

RESULTS

Maternal diabetes significantly increased the levels of CHOP, calnexin, phosphorylated (p)-eIF2α, p-PERK, and p-IRE1α; triggered XBP1 mRNA splicing; and enhanced ER chaperone gene expression in WT embryos. SOD1 overexpression blocked these diabetes-induced ER stress markers.

CONCLUSION

Mitigating oxidative stress via SOD1 overexpression blocks maternal diabetes-induced ER stress in vivo.

Maternal hyperglycemia activates an ASK1-FoxO3a-caspase 8 pathway that leads to embryonic neural tube defects

Neural tube defects result from failure to completely close neural tubes during development. Maternal diabetes is a substantial risk factor for neural tube defects, and available evidence suggests that the mechanism that links hyperglycemia to neural tube defects involves oxidative stress and apoptosis. We demonstrated that maternal hyperglycemia correlated with activation of the apoptosis signal-regulating kinase 1 (ASK1) in the developing neural tube, and Ask1 gene deletion was associated with reduced neuroepithelial cell apoptosis and development of neural tube defects. ASK1 activation stimulated the activity of the transcription factor FoxO3a, which increased the abundance of the apoptosis-promoting adaptor protein TRADD, leading to activation of caspase 8. Hyperglycemia-induced apoptosis and the development of neural tube defects were reduced with genetic ablation of either FoxO3a or Casp8 or inhibition of ASK1 by thioredoxin. Examination of human neural tissues affected by neural tube defects revealed increased activation or abundance of ASK1, FoxO3a, TRADD, and caspase 8. Thus, activation of an ASK1-FoxO3a-TRADD-caspase 8 pathway participates in the development of neural tube defects, which could be prevented by inhibiting intermediates in this cascade.

New concepts in diabetic embryopathy

Diabetes mellitus is responsible for nearly 10% of fetal anomalies in diabetic pregnancies. Although aggressive perinatal care and glycemic control are available in developed countries, the birth defect rate in diabetic pregnancies remains higher than that in the general population. Major cellular activities (ie, proliferation and apoptosis) and intracellular metabolic conditions (ie, nitrosative, oxidative, and endoplasmic reticulum stress) have been shown to be associated with diabetic embryopathy using animal models. Translating advances made in animal studies into clinical applications in humans requires collaborative efforts across the basic research, preclinical, and clinical communities.

Oxidative stress-induced JNK1/2 activation triggers proapoptotic signaling and apoptosis that leads to diabetic embryopathy

Oxidative stress and apoptosis are implicated in the pathogenesis of diabetic embryopathy. The proapoptotic c-Jun NH(2)-terminal kinases (JNK)1/2 activation is associated with diabetic embryopathy. We sought to determine whether 1) hyperglycemia-induced oxidative stress is responsible for the activation of JNK1/2 signaling, 2) JNK1 contributes to the teratogenicity of hyperglycemia, and 3) both JNK1 and JNK2 activation cause activation of downstream transcription factors, caspase activation, and apoptosis, resulting in neural tube defects (NTDs). Wild-type (WT) embryos from nondiabetic WT dams and WT, superoxide dismutase (SOD)1-overexpressing, jnk1(+/-), jnk1(-/-), and jnk2(-/-) embryos exposed to maternal hyperglycemia were used to assess JNK1/2 activation, NTDs, activation of transcription factors downstream of JNK1/2, caspase cascade, and apoptosis. SOD1 overexpression abolished diabetes-induced activation of JNK1/2 and their downstream effectors: phosphorylation of c-Jun, activating transcription factor 2, and E twenty-six-like transcription factor 1 and dephosphorylation of forkhead box class O3a. jnk1(-/-) embryos had significantly lower incidences of NTDs than those of WT or jnk1(+/-) embryos. Either jnk1 or jnk2 gene deletion blocked diabetes-induced activation of JNK1/2 signaling, caspases 3 and 8, and apoptosis in Sox1(+) neural progenitors of the developing neural tube. Our results show that JNK1 and JNK2 are equally involved in diabetic embryopathy and that the oxidative stress-JNK1/2-caspase pathway mediates the proapoptotic signals and the teratogenicity of maternal diabetes.

Down regulation of the proliferation and apoptotic pathways in the embryonic brain of diabetic rats

Compelling evidence shows that the offspring subjected to uncontrolled hyperlycemia during gestation display behavioral, neurochemical, and cellular abnormalities during adulthood. However, the molecular mechanisms underlying these defects remain elusive. Previous studies have shown an increased rate of apoptosis and a decreased index of neuronal proliferation associated with diabetic embryopathy. The aim of the present study was to determine whether impairments in apoptotic related proteins also occur in the developing central nervous system from non-malformed embryos exposed to uncontrolled gestational hyperglycemia. Pregnant rats injected with either streptozotocin or vehicle were killed on gestational day 19. Offspring brains were quickly removed to evaluate protein expression by Western blotting. Embryonic brains from diabetic rats exhibited a decrease in the cell survival p-Akt expression (52.83 ± 24.35%) and in the pro-apoptotic protein Bax (56.16 ± 6.47%). Moreover, the anti-apoptotic protein Bcl-2 showed a non-significant increase while there were no changes in Procaspase 3 or cleaved Caspase 3 proteins. The cytoskeleton proteins NF-200 and GFAP were also examined. Neither NF-200 nor GFAP showed differences in embryonic brains from diabetic rats compared to controls. Altogether, these results indicate that both proliferation and apoptotic pathways are decreased in the brain from the developing offspring of diabetic rats. Since selective neuronal apoptosis, as well as selective cell proliferation, are specifically involved in brain organogenesis, it is possible that simultaneous impairments during the perinatal period contribute to the long lasting alterations observed in the adult brain.

SOD1 suppresses maternal hyperglycemia-increased iNOS expression and consequent nitrosative stress in diabetic embryopathy

OBJECTIVE

Hyperglycemia induces oxidative stress and increases inducible nitric oxide synthase (iNOS) expression. We hypothesized that oxidative stress is responsible for hyperglycemia-induced iNOS expression.

STUDY DESIGN

iNOS-luciferase activities, nitrosylated protein, and lipid peroxidation markers 4-hydroxynonenal and malondialdehyde were determined in parietal yolk sac-2 cells exposed to 5 mmol/L glucose or high glucose (25 mmol/L) with or without copper zinc superoxide dismutase 1 (SOD1) treatment. Levels of iNOS protein and messenger RNA, nitrosylated protein, and cleaved caspase-3 and -8 were assessed in wild-type embryos and SOD1-overexpressing embryos from nondiabetic and diabetic dams.

RESULTS

SOD1 treatment diminished high glucose-induced oxidative stress, as evidenced by 4-hydroxynonenal and malondialdehyde reductions, and it blocked high glucose-increased iNOS expression, iNOS-luciferase activities, and nitrosylated protein. In vivo SOD1 overexpression suppressed hyperglycemia-increased iNOS expression and nitrosylated protein, and it blocked caspase-3 and -8 cleavage.

CONCLUSION

We conclude that oxidative stress induces iNOS expression, nitrosative stress, and apoptosis in diabetic embryopathy.

Resveratrol prevents impairment in activation of retinoic acid receptors and MAP kinases in the embryos of a rodent model of diabetic embryopathy

Diabetes induces impairments in gene expression during embryonic development that leads to premature and improper tissue specialization. Retinoic acid receptors (RARs and retinoid X receptor [RXRs]) and mitogen-activated protein kinases (MAPKs) play crucial roles during embryonic development, and their suppression or activation has been shown as a determinant of the fate of embryonic organogenesis. We studied the activation of RARs and MAPKs in embryonic day 12 (E12) in embryos of rats under normal, diabetic, and diabetic treated with resveratrol ([RSV]; 100 mg/kg body weight) conditions. We found downregulation of RARs and RXRs expressions as well as their DNA-binding activities in the embryos exhibiting developmental delays due to diabetes. Furthermore, the phosphorylation of extracellular signal-regulated kinase (ERK) 1/2 was decreased and phosphorylation of c-Jun N-terminal kinase (JNK) 1/2 and p38 was increased. Interestingly, embryos of diabetic rats treated with RSV showed normalized patterns of RARs, RXRs, neuronal markers, and ERK, JNK and p38 phosphorylation.

Reduction in embryonic malformations and alleviation of endoplasmic reticulum stress by nitric oxide synthase inhibition in diabetic embryopathy

Maternal diabetes-induced neural tube defects (NTDs) are associated with increased programmed cell death (apoptosis) in the neuroepithelium, which is related to intracellular nitrosative stress. To alleviate nitrosative stress, diabetic pregnant mice were fed via gavage an inhibitor of nitric oxide (NO) synthase (NOS) 2, L-N6-(1-iminoethyl)-lysine (L-NIL; 80 mg/kg), once a day from embryonic (E) day 7.5 to 9.5 during early stages of neurulation. The treatment significantly reduced NTD rate in the embryos, compared with that in vehicle (normal saline)-treated diabetic group. In addition to alleviation of nitrosative stress, endoplasmic reticulum (ER) stress was also ameliorated, assessed by quantification of associated factors. Apoptosis was reduced, indicated by caspase 8 activation. These results show that nitrosative stress is important in diabetes-induced NTDs via exacerbating ER stress, leading to increased apoptosis. Oral treatment with NOS-2 inhibitor alleviates nitrosative and ER stress, decreases apoptosis, and reduces NTDs in the embryos, providing information for further interventional studies to reduce diabetes-associated birth defects.

Diabetes-induced birth defects: what do we know? What can we do?

Birth defects are the leading cause of infant mortality in the United States, which has one of the highest infant mortality rates in the developed world. Many of these birth defects can be attributed to pre-existing, or pregestational, diabetes in pregnancy, which significantly increases a mother's risk of having a child with a major birth defect. Strict preconceptional and early pregnancy glucose control, supplementation with multivitamins and fatty acids, and lower glycemic dietary management have been shown to reduce the incidence of birth defects in experimental and epidemiologic studies. However, because more than half of pregnancies are unplanned, these methods are not generalizable across the population. Thus, better interventions are urgently needed. Based on what we know about the molecular pathophysiology of diabetic embryopathy, our laboratory and others are developing interventions against to key molecular targets in this multifactorial disease process.

Diabetic embryopathy

Diabetic embryopathy reflects a scientific enigma--how does a seemingly rich intrauterine environment manage to disturb the development of the embryo? Which compounds in that environment may be teratogenic--and how shall we find them? How can we investigate a putative dose-response nature of the teratogen, i.e., how can we monitor the effects of varied severity of the diabetic state (which can be varied in a number of metabolic ways) on the embryonic development? Here, the whole embryo culture (WEC) technique provides an excellent tool for such studies. WEC is thus currently used to investigate the effect of graded levels of diabetes (e.g., hyperglycemia, hyperketonemia, increased branched chain amino acid (BCAA) levels), and putative antiteratogenic agents (antioxidants, folic acid, arachidonic acid, inositol), as well as the effect of different embryonic genotypes on diabetes-induced (mal)development. WEC is the only method, which is able to couple specific embryonic maldevelopment to precise changes in substrate levels or the (epi)genotype of the embryo. Using this method, we have been able to demonstrate that a diabetic environment--culture of embryos in serum from diabetic animals or in serum with increased levels of glucose, β-hydroxybutyrate or α-ketoisocaproic acid (KIC)--causes increased embryonic maldevelopment, and that this dysmorphogenesis is blocked by the addition of ROS scavenging agents to the culture medium. Genetically, others and we have demonstrated that Pax-3 downregulation predisposes for diabetes-induced dysmorphogenesis.

Folic acid and safflower oil supplementation interacts and protects embryos from maternal diabetes-induced damage

Maternal diabetes increases the risk of embryo malformations. Folic acid and safflower oil supplementations have been shown to reduce embryo malformations in experimental models of diabetes. In this study we here tested whether folic acid and safflower oil supplementations interact to prevent embryo malformations in diabetic rats, and analyzed whether they act through the regulation of matrix metalloproteinases (MMPs), their endogenous inhibitors (TIMPs), and nitric oxide (NO) and reactive oxygen species production. Diabetes was induced by streptozotocin administration prior to mating. From Day 0.5 of pregnancy, rats did or did not receive folic acid (15 mg/kg) and/or a 6% safflower oil-supplemented diet. Embryos and decidua were explanted on Day 10.5 of gestation for further analysis of embryo resorptions and malformations, MMP-2 and MMP-9 activities, TIMP-1 and TIMP-2 levels, NO production and lipid peroxidation. Maternal diabetes induced resorptions and malformations that were prevented by folic acid and safflower oil supplementation. MMP-2 and MMP-9 activities were increased in embryos and decidua from diabetic rats and decreased with safflower oil and folic acid supplementations. In diabetic animals, the embryonic and decidual TIMPs were increased mainly with safflower oil supplementation in decidua and with folic acid in embryos. NO overproduction was decreased in decidua from diabetic rats treated with folic acid alone and in combination with safflower oil. These treatments also prevented increases in embryonic and decidual lipid peroxidation. In conclusion, folic acid and safflower oil supplementations interact and protect the embryos from diabetes-induced damage through several pathways related to a decrease in pro-inflammatory mediators.

Maternal dietary loads of α-tocopherol differentially influence fear conditioning and spatial learning in adult offspring

α-Tocopherol, the main component of vitamin E, is well known to be a radical scavenger, so an increased intake of vitamin E is recommended in complicated pregnancy, to prevent possible fetus damage by free radical. In a previous work, we found that maternal α-tocopherol supplementation affects PKC-mediated cellular signaling and hippocampal synaptic plasticity in developing brain; the latter effect persists in adulthood. Here, adult rats maternally exposed to supranutritional doses of α-tocopherol were evaluated for Contextual Fear Conditioning and spatial learning in Morris Water Maze, two different hippocampus-dependent learning tasks. Moreover, anxiety, spontaneous activity, and explorative drive were also evaluated as factors potentially affecting learning performance. Treated rats showed a different behavior with respect to controls: performance in Contextual Fear Conditioning was improved, while spatial learning tested in Morris Water Maze, was impaired. The improvement of fear response was not ascribable to differences in anxiety level and/or spontaneous activity; thus it appears to be a specific effect of α-tocopherol overloading during brain development. On the contrary, the impaired performance in Morris Water Maze exhibited by treated rats can be in part explained by their enhanced explorative drive. Although extrapolation from rats to humans is difficult, a caveat in assuming supranutritional doses of vitamin E in pregnancy arises from this study.

SOD1 overexpression in vivo blocks hyperglycemia-induced specific PKC isoforms: substrate activation and consequent lipid peroxidation in diabetic embryopathy

OBJECTIVE

Oxidative stress plays a causative role in diabetic embryopathy. We tested whether mitigating oxidative stress, using superoxide dismutase 1 (SOD1) transgenic (Tg) mice, would block hyperglycemia-induced specific protein kinase C (PKC) isoform activation and its downstream cascade.

STUDY DESIGN

Day 8.5 embryos from nondiabetic wild-type control (NC), diabetic mellitus wild-type (DM), and diabetic SOD1-Tg mice (DM-SOD1-Tg) were used for detection of phosphorylated (p-) PKCα/βII and p-PKCδ, and levels of 2 prominent PKC substrates, phosphorylated myristoylated alanine-rich protein kinase C substrate (MARCKS) and receptor for activated C kinase 1 (RACK1), and lipid peroxidation markers, 4-hydroxynonenal (4-HNE) and malondialdehyde (MDA).

RESULTS

Levels of p-PKCα/βII, p-PKCδ, p-MARCKS, 4-HNE, and MDA were significantly elevated in the DM group compared with those in the NC group and the DM-SOD1-Tg group. The NC and DM-SOD1-Tg groups had comparable levels of these protein and lipid peroxidation markers. RACK1 levels did not differ among the 3 groups.

CONCLUSION

Mitigating oxidative stress by SOD1 overexpression blocks maternal hyperglycemia-induced activation of specific PKC isoforms and downstream cascades.

Evolutionary interactions between diabetes and development

Because of the complications of diabetes affecting the mothers and their fetus/newborns are less known, this review examined the epidemiologic and mechanistic issues involved in the developmental programming of diabetic mothers. This overview showed that sperm, egg, zygote or blastocyst derived from diabetic parents may develop into offspring with high risk of any type of diabetes, even if placed in a normal uterus, producing developmental delay, embryopathy, geno- and cyto-toxicity, teratogenic changes, free radicals and apoptosis. These early insults may then lead to an increased rate of miscarriage and congenital anomalies depending on free radicals signaling and cell-death pathways involved by the diabetogenic agents. Furthermore, sperm, egg, zygote or blastocyst from normal parents will have an increased risk of diabetes if placed in a diabetic uterus. Interestingly, diabetes has deleterious effect on male/female reproductive functions and on the development of the blastocysts/embryos. Indeed, this review hypothesized that the long-term effects of diabetes during the pregnancy (gestational diabetes) may influence, generally, on the health of the embryos, newborns (perinatal life) and adulthood. However, there are obvious species differences between pregnant women and animal models. Thus, maintaining normoglycaemia during pregnancy may play an important role in a healthy life for the newborns.

Genetic and environmental influence on diabetic rat embryopathy

We assessed genetic and environmental influence on fetal outcome in diabetic rat pregnancy. Crossing normal (N) and manifestly diabetic (MD) Wistar Furth (W) and Sprague-Dawley (L) females with W or L males yielded four different fetal genotypes (WW, LL, WL, and LW) in N or MD rat pregnancies for studies. We also evaluated fetal outcome in litters with enhanced or diminished severity of maternal MD state, denoted MD(+)WL and MD(-)LW. The MDWW litters had less malformations and resorptions (0 and 19%) than the MDLL litters (17 and 30%). The MDWL litters (0 and 8%) were less maldeveloped than the MDLW litters (9 and 22%), whereas the MD(+)WL (3 and 23%) and MD(-)LW (1 and 17%) litters showed increased and decreased dysmorphogenesis (compared with MDWL and MDLW litters). The pregnant MDW rats had lower serum levels of glucose, fructosamine, and branched-chain amino acids than the pregnant MDL rats, whereas the pregnant MD(+)W and MD(-)L rats had levels comparable with those of the MDL and MDW rats, respectively. The 8-iso-PGF2α levels of the malformed MDLW offspring were increased compared with the nonmalformed MDLW offspring. Diabetes decreased fetal heart Ret and increased Bmp-4 gene expression in the MDLW offspring and caused decreased GDNF and Shh expression in the malformed fetal mandible of the MDLW offspring. We conclude that the fetal genome controls the embryonic dysmorphogenesis in diabetic pregnancy by instigating a threshold level for the teratological insult and that the maternal genome controls the teratogenic insult by (dys)regulating the maternal metabolism.

The role of Raf-1 kinase in diabetic retinopathy

Many metabolic pathways, including oxidative stress, PKC and the polyol pathway have been implicated in the development of diabetic retinopathy, but despite extensive research, its pathogenesis remains unclear. Recent studies have shown the role of a low-molecular-weight GTP-binding protein (H-Ras)-mediated signaling pathway in its development. The key effector protein of Ras function is a threonine/serine kinase-Raf kinase, and this kinase is involved in a variety of functions, including the cell cycle and proliferation and apoptosis. In animal models of diabetic retinopathy, Raf kinase is activated in the retina and its microvasculature. Activated Raf kinase is associated with increased apoptosis of retinal capillary cells, the process that precedes the development of retinal histopathology, and inhibition of Raf kinase ameliorates apoptosis. In clinical settings, inhibitors of Raf kinase have shown promising results in cancer treatment, and Raf kinase antisense oligonucleotides, iCo 007, is now in Phase II trial for macular edema, a chronic ocular disease associated with retinal neovascularization. Further elucidating the role of Raf kinase in diabetic retinopathy, and advances in the generation of antisense therapy for chronic diseases, should help test Raf antisense oligonucleotides for the treatment of this blinding complication that diabetic patients fear the most.

Resveratrol prevents embryonic oxidative stress and apoptosis associated with diabetic embryopathy and improves glucose and lipid profile of diabetic dam

SCOPE

Diabetic embryopathy, a consequence of diabetic pregnancy, is associated with increase in embryonic oxidative stress and apoptosis, which lead to severe embryonic damage at early stage of organogenesis.

METHODS AND RESULTS

This study investigated if resveratrol, found in red grapes and blue-berries, may prevent diabetes-induced oxidative stress and apoptosis in embryos and have beneficial effects in diabetic dams. A rodent model of diabetic embryopathy was used. Diabetes was associated with lowered reduced glutathione levels (26.98%), increased total thiol (100.47%) and lipid peroxidation (124.73%) in embryos, and increased blood sugar (384.03%), cholesterol (98.39%) and triglyceride (1025.35%) in diabetic dams. Increased apoptosis (272.20%) was also observed in the embryos of diabetic dams. Administration of resveratrol (100 mg/kg body weight (b.w.)) during pregnancy prevented both oxidative stress and apoptosis in embryos. Resveratrol reduced embryonic maldevelopment by improving embryo weight (41.23%), crown rump length (16.50%) and somite number (11.22%). It further improved the glucose (33.32%) and lipid (cholesterol 41.74%, triglyceride 60.64%) profile of the diabetic dams, which also represents the protective role of resveratrol in diabetes.

CONCLUSION

Resveratrol was found to prevent embryonic oxidative stress and apoptosis. It also improved glucose and lipid profile of diabetic dams, indicating the beneficial effects in diabetic pregnancy.

Animal models in diabetes and pregnancy

The worldwide increase in the incidence of diabetes, the increase in type 2 diabetes in women at reproductive ages, and the cross-generation of the intrauterine programming of type 2 diabetes are the bases for the growing interest in the use of experimental diabetic models in order to gain insight into the mechanisms of induction of developmental alterations in maternal diabetes. In this scenario, experimental models that present the most common features of diabetes in pregnancy are highly required. Several important aspects of human diabetic pregnancies such as the increased rates of spontaneous abortions, malformations, fetoplacental impairments, and offspring diseases in later life can be approached by using the appropriate animal models. The purpose of this review is to give a practical and critical guide into the most frequently used experimental models in diabetes and pregnancy, discuss their advantages and limitations, and describe the aspects of diabetes and pregnancy for which these models are thought to be adequate. This review provides a comprehensive view and an extensive analysis of the different models and phenotypes addressed in diabetic animals throughout pregnancy. The review includes an analysis of the surgical, chemical-induced, and genetic experimental models of diabetes and an evaluation of their use to analyze early pregnancy defects, induction of congenital malformations, placental and fetal alterations, and the intrauterine programming of metabolic diseases in the offspring's later life.

Maternal diet modulates the risk for neural tube defects in a mouse model of diabetic pregnancy

Pregnancies complicated by maternal diabetes have long been known to carry a higher risk for congenital malformations, such as neural tube defects. Using the FVB inbred mouse strain and the Streptozotocin-induced diabetes model, we tested whether the incidence of neural tube defects in diabetic pregnancies can be modulated by maternal diet. In a comparison of two commercial mouse diets, which are considered nutritionally replete, we found that maternal consumption of the unfavorable diet was associated with a more than 3-fold higher rate of neural tube defects. Our results demonstrate that maternal diet can act as a modifier of the risk for abnormal development in high-risk pregnancies, and provide support for the possibility that neural tube defects in human diabetic pregnancies might be preventable by optimized maternal nutrition.

Transgenic mice overproducing human thioredoxin-1, an antioxidative and anti-apoptotic protein, prevents diabetic embryopathy

AIMS/HYPOTHESIS

Experimental studies have suggested that apoptosis is involved in diabetic embryopathy through oxidative stress. However, the precise mechanism of diabetic embryopathy is not yet clear. Thioredoxin (TRX) is a small, ubiquitous, multifunctional protein, which has recently been shown to protect cells from oxidative stress and apoptosis. Using transgenic mice that overproduce human TRX-1 (TRX-Tg mice), we examined whether oxidative stress is involved in fetal dysmorphogenesis in diabetic pregnancies.

METHODS

Non-diabetic and streptozotocin-induced diabetic (DM) female mice were mated with male TRX-Tg mice. Pregnant mice were killed either at day 10 or day 17 of gestation, and viable fetuses and their placentas were recovered, weighed and assessed for gross and histological morphology, biochemical markers and gene expression.

RESULTS

In both wild-type (WT) and transgenic (Tg) groups, fetal and placental weights in the diabetic group were significantly decreased compared with the non-diabetic group. The incidence of malformation was higher in the diabetic group, and was significantly decreased in the TRX-Tg group (DM-WT vs DM-Tg; 28.6% vs 10.4%). Oxidative stress markers such as thiobarbituric acid reactive substances and 8-hydroxy-2'-deoxyguanosine were increased in DM-WT group fetuses but were decreased in fetuses from the DM-Tg group. Furthermore, immunohistochemically assayed apoptosis and cleaved caspase-3 production in embryonic neuroepithelial cells was significantly increased in the DM-WT group, and was significantly decreased in the DM-Tg group.

CONCLUSIONS/INTERPRETATION

These results indicate that oxidative stress is involved in diabetic embryopathy, and that the antioxidative protein TRX at least partially prevents diabetic embryopathy via suppression of apoptosis.

Hyperglycemia induces inducible nitric oxide synthase gene expression and consequent nitrosative stress via c-Jun N-terminal kinase activation

OBJECTIVE

Maternal diabetes has an adverse impact on embryonic development. We tested the hypothesis that hyperglycemia-induced c-Jun N-terminal kinases (JNK) 1/2 activation mediates inducible nitric oxide synthase (iNOS) induction.

STUDY DESIGN

Levels of iNOS messenger ribonucleic acid (mRNA) and nitrosylated protein were determined in cultured C57BL/6J conceptuses exposed to hyperglycemia (300 mg/dL glucose) and C57BL/6J embryos exposed to streptozotocin-induced diabetes. The iNOS-luciferase activity and endogenous reactive nitrogen species were determined in transfected PYS-2 (mouse teratocarcinoma) cells exposed to hyperglycemia (450 mg/dL glucose).

RESULTS

Hyperglycemia increased iNOS mRNA, and SP600125, a potent JNK1/2 inhibitor, abolished this effect. Hyperglycemia increased iNOS-luciferase activities, and SP600125 blocked this effect. Diabetes increased iNOS mRNA and jnk2 gene deletion abrogated this effect. Correlated with iNOS gene induction, both hyperglycemia in vitro and diabetes in vivo enhanced the production of reactive nitrogen species and increased protein nitrosylation. The jnk2 gene deletion blocked diabetes-induced protein nitrosylation.

CONCLUSION

JNK1/2 activation mediates hyperglycemia-induced iNOS gene expression and consequent nitrosative stress in diabetic embryopathy.

Epigallocatechin-3-gallate ameliorates hyperglycemia-induced embryonic vasculopathy and malformation by inhibition of Foxo3a activation

OBJECTIVE

Maternal hyperglycemia increases the risk of congenital malformations. Epigallocatechin-3-gallate (EGCG), a natural antioxidant purified from green tea, inhibits oxidative stress signaling. We propose that EGCG prevents hyperglycemia-induced malformation via inhibition of oxidative stress signaling. The objective of this study is to examine the effect of EGCG on hyperglycemia-induced adverse effects during embryonic development.

STUDY DESIGN

Day-9 rat conceptuses were cultured under euglycemic (150 mg/dL glucose) and hyperglycemic (300 mg/dL glucose) conditions in the presence or absence of 1 or 10 micromol/L of EGCG.

RESULTS

Both 1 and 10 micromol/L of EGCG significantly ameliorated hyperglycemia-induced embryonic vasculopathy and malformations. Hyperglycemia inactivated protein kinase B (Akt) by reducing phosphorylated Akt levels. EGCG reversed the inhibitory effect of hyperglycemia on Akt activation. EGCG also prevented hyperglycemia-reduced phosphorylated Forkhead transcription factor 3a levels.

CONCLUSION

EGCG prevented hyperglycemia-induced embryopathy through inhibition of Forkhead transcription factor 3a activation. This may have been mediated via the activation of Akt. These findings offer the potential for a possible pharmacological prophylaxis for hyperglycemia-induced embryonic malformations.

Cardioprotective effect of vitamin E: rescues of diabetes-induced cardiac malfunction, oxidative stress, and apoptosis in rat

AIM

This study was designed to assess the effect of vitamin E on cardiac autonomic neuropathy, cardiomyocyte apoptosis, and the status of oxidative stress in the heart under hyperglycemic conditions, in vivo.

METHODS

Wistar male rats (n=16) were made hyperglycemic by streptozotocin at 6 months of age. Normal Wistar rats (n=8) of the same age were used as the control group. Diabetic rats were divided into two groups, nontreated and those treated with vitamin E (300 mg/day). Stable hyperglycemic status was proved by levels of blood sugar and HbA(1c). Lipid peroxidation, protein oxidation, and cellular antioxidant defense were measured by 8-isoprotane, protein carbonyl content, and superoxide dismutase (SOD) activity, respectively.

RESULTS

Cardiac complications such as autonomic neuropathy as prolonged QT interval along with significant increases in level of 8-isoprotane, protein carbonyl content, and SOD activity were observed after 6 weeks. Structural abnormality was also observed as severe induction of apoptosis in cardiomyocytes.

CONCLUSION

Significant decline in apoptosis, lipid peroxidation, protein oxidation, and QT interval resulted from vitamin E administration, which strongly implies that this radical scavenger may promote a convalescing effect on diabetic cardiomyopathy through the attenuation of oxidative stress and abrogation of apoptotic signals, which was verified by restoring normal QT interval.

Can we prevent diabetic birth defects with micronutrients?

Congenital malformations are more common in infants of diabetic women than in children of non-diabetic women. The mechanisms behind diabetes-induced congenital anomalies are not known. Disturbed micronutrient metabolism, in concert with oxidative stress, has been suggested as a cause of diabetes-induced malformations by several studies. In experimental work, administration of inositol, arachidonic acid and several antioxidative compounds, as well as folic acid, to the embryo, has proven to attenuate the teratogenic effects of a diabetic environment. Future therapeutic efforts may include supplementation with antioxidants or micronutrients, such as folic acid, to the pregnant diabetic woman, although exact compounds and doses need to be determined.

Maternal diabetes alters transcriptional programs in the developing embryo

Background

Maternal diabetes is a well-known risk factor for birth defects, such as heart defects and neural tube defects. The causative molecular mechanisms in the developing embryo are currently unknown, and the pathogenesis of developmental abnormalities during diabetic pregnancy is not well understood. We hypothesized that the developmental defects are due to alterations in critical developmental pathways, possibly as a result of altered gene expression. We here report results from gene expression profiling of exposed embryos from a mouse diabetes model.

Results

In comparison to normal embryos at mid-gestation, we find significantly altered gene expression levels in diabetes-exposed embryos. Independent validation of altered expression was obtained by quantitative Real Time Polymerase Chain Reaction. Sequence motifs in the promoters of diabetes-affected genes suggest potential binding of transcription factors that are involved in responses to oxidative stress and/or to hypoxia, two conditions known to be associated with diabetic pregnancies. Functional annotation shows that a sixth of the de-regulated genes have known developmental phenotypes in mouse mutants. Over 30% of the genes we have identified encode transcription factors and chromatin modifying proteins or components of signaling pathways that impinge on transcription.

Conclusion

Exposure to maternal diabetes during pregnancy alters transcriptional profiles in the developing embryo. The enrichment, within the set of de-regulated genes, of those encoding transcriptional regulatory molecules provides support for the hypothesis that maternal diabetes affects specific developmental programs.

Caspase-8: a key role in the pathogenesis of diabetic embryopathy

Maternal diabetes causes neural tube defects in embryos, which are associated with increased apoptosis in the neuroepithelium. Many factors, including effector caspases, have been shown to be involved in the events. However, the key regulators have not been identified and the underlying mechanisms remain to be addressed. Caspase-8, an initiator caspase, has been shown to be altered in diabetic embryopathy, suggesting a role as an upstream apoptotic regulator. Using mouse embryos as a model system, this study demonstrates that caspase-8 is required for the production of hyperglycemia-associated embryonic malformations. Caspase-8 was shown to be expressed in the developing neural tube. Its activity, as evidenced by enhanced cleavage, was increased by hyperglycemia. These changes were associated with increased formation of the active cleavage of Bid. Inhibition of caspase-8 activity in high glucose-challenged embryos reduced the rate of embryonic malformation and this was associated with decreased apoptosis in the neuroepithelium of the neural tube. Inhibition of caspase-8 activity also reduced hyperglycemia-induced Bid activation and caspase-9 cleavage. These data suggest that caspase-8 may control diabetic embryopathy-associated apoptosis via regulation of the Bid-stimulated mitochondrion/caspase-9 pathway.

Congenital anomalies in diabetic pregnancy

Congenital malformations are more common in infants of diabetic women than in children of non-diabetic women. The etiology, pathogenesis and prevention of the diabetes-induced malformations have spurred considerable clinical and basic research efforts. The ultimate aim of these studies has been to obtain an understanding of the teratogenic process, which may enable precise preventive therapeutic measures in diabetic pregnancies. The results of the clinical and basic studies support the view of an early gestational induction of the malformations in diabetic pregnancy by a teratogenic process of multifactorial etiology. There may be possible targets for new therapeutic efforts revealed by the research work. Thus, future additions to the therapeutic efforts may include supplementation with antioxidants and/or folic acid, although more research is needed to delineate the dosages and compounds to be used. As the research into genetic predisposition for the teratogenic induction of malformations by maternal diabetes starts to reveal new genes and gene products involved in the etiology of the malformations, a set of new targets for intervention may arise.

Decreased cardiac glutathione peroxidase levels and enhanced mandibular apoptosis in malformed embryos of diabetic rats

OBJECTIVE

To characterize normal and malformed embryos within the same litters from control and diabetic rats for expression of genes related to metabolism of reactive oxygen species (ROS) or glucose as well as developmental genes.

RESEARCH DESIGN AND METHODS

Embryos from nondiabetic and streptozotocin-induced diabetic rats were collected on gestational day 11 and evaluated for gene expression (PCR) and distribution of activated caspase-3 and glutathione peroxidase (Gpx)-1 by immunohistochemistry.

RESULTS

Maternal diabetes (MD group) caused growth retardation and an increased malformation rate in the embryos of MD group rats compared with those of controls (N group). We found decreased gene expression of Gpx-1 and increased expression of vascular endothelial growth factor-A (Vegf-A) in malformed embryos of diabetic rats (MDm group) compared with nonmalformed littermates (MDn group). Alterations of messenger RNA levels of other genes were similar in MDm and MDn embryos. Thus, expression of copper zinc superoxide dismutase (CuZnSOD), manganese superoxide dismutase (MnSOD), and sonic hedgehog homolog (Shh) were decreased, and bone morphogenetic protein-4 (Bmp-4) was increased, in the MD embryos compared with the N embryos. In MDm embryos, we detected increased activated caspase-3 immunostaining in the first visceral arch and cardiac area and decreased Gpx-1 immunostaining in the cardiac tissue; both findings differed from the caspase/Gpx-1 immunostaining of the MDn and N embryos.

CONCLUSIONS

Maternal diabetes causes growth retardation, congenital malformations, and decreased general antioxidative gene expression in the embryo. In particular, enhanced apoptosis of the first visceral arch and heart, together with decreased cardiac Gpx-1 levels, may compromise the mandible and heart and thus cause an increased risk of developing congenital malformation.

Demonstration of the essential role of protein kinase C isoforms in hyperglycemia-induced embryonic malformations

To address the role of PKC isoforms in hyperglycemia-induced apoptosis and malformations in the embryos of diabetic pregnancies, expression of PKCalpha, beta1, beta 2, gamma, delta, epsilon, and zeta was examined in the neural tube of rat embryos and showed to overlap with the regions of increased apoptosis. Levels of activated (phosphorylated) PKCalpha , beta2, and delta were increased in the embryos of diabetic dams whereas those of PKCepsilon and zeta were decreased when compared with those in control groups. Cytosolic phospholipase A(2) (cPLA(2)) was also activated. Blocking the activity of PKCalpha , beta2, and delta using isoform-specific inhibitors in embryos cultured in hyperglycemia (40 mM) reduced malformation rates when compared with those in untreated hyperglycemic and euglycemic (8.3 mM) groups. These observations demonstrate that PKCalpha, beta2, and delta play an essential role in diabetic embryopathy. Activation of cPLA(2) was also decreased, suggesting that PKCs mediate the hyperglycemic effects through the cPLA(2)-phospholipid peroxidation pathway.

Glycine decreases developmental damage induced by hyperglycaemia in mouse embryos

Hyperglycaemia induces neural tube defects and growth retardation in cultured mouse and rat embryos. In this study the possibility that glycine could prevent hyperglycaemia-induced embryopathy was researched. Early somite mouse embryos were cultured in normal medium, hyperglycaemic medium (50 mmol L(-1) glucose), or with glycine (1 mmol L(-1)) supplementation of normal and hyperglycaemic rat serum for 48 h. The embryo growth and differentiation were determined to estimate developmental and congenital malformations as well as lipid peroxidation levels. Adding glycine to the control culture medium did not affect embryonic development. Whereas the amino acid protected against telencephalon dysmorphogenesis, the decreased DNA content and number of somites, and the morphological score affectation induced by the hyperglycaemic medium, it had no preventive effect on the retarded differentiation of the otic system. Moreover, it prevented the high hyperglycaemia-induced lipoperoxidation levels of embryonic tissues. Embryos were partially protected from the hyperglycaemia-induced teratogenesis due to the antioxidative effect of glycine. As no other mechanisms related to the antiglycation or other protective effects of glycine were examined, the mechanism whereby it acted as an antiteratogenic agent needs further study.