Peroxynitrites and impaired modulation of nitric oxide concentrations in embryos from diabetic rats during early organogenesis

Severity of prepregnancy diabetes on the fetal malformations and viability associated with early embryos in rats†

Preexisting/pregestational diabetes enhances the risk of birth defects. Several factors have been involved during the implantation process, such as cytokines (granulocyte-macrophage-colony-stimulating factor [GM-CSF]). The objective was to evaluate the effects of two levels of diabetes on the redox status of preimplantation embryos during the implantation process to comprehend how both are involved in embryo and fetal viability against maternal diabetes. Female Sprague-Dawley rats received streptozotocin at birth (mild diabetes [MD]) or at adulthood (severe diabetes [SD]) to obtain two experimental diabetes intensities. After confirming the diabetic status, the nondiabetic and diabetic groups were mated around day 110 of life. At gestational day (GD) 21, fetuses were assessed for viability and malformations and ovaries for embryo loss before implantation. Other pregnant nondiabetic and diabetic rats were sacrificed at GD2-4 for maternal and preimplantation embryo oxidative stress markers, maternal serum insulin, uterine fluid GM-CSF, and preimplantation embryo morphological analysis. MD and SD caused abnormal redox levels, lower GM-CSF and insulin levels during the preimplantation period, and embryonic loss before implantation. SD caused lower fetal viability and higher fetal malformation percentages at GD21. The SD dam-derived preimplantation embryos presented lower glutathione levels and higher thiobarbituric acid reactive substances concentration at GD3 and an increased frequency of abnormal preimplantation embryos at GD4. In conclusion, preexisting diabetes leads to complications in the implantation process. Furthermore, maternal oxidative stress and other metabolic changes alter the redox state and morphological structure of preimplantation embryos, contributing to damaged growth and development in late pregnancy.

Effects of diets high in animal or plant protein on oxidative stress in individuals with type 2 diabetes: A randomized clinical trial

High-protein diet is a promising strategy for diabetes treatment supporting body weight control, improving glycaemic status, cardiovascular risk factors and reducing liver fat. Here, we investigated effects of diets high in animal (AP) or plant (PP) protein on oxidative stress and antioxidant status in individuals with type 2 diabetes (T2DM). 37 obese individuals (age 64.3 ± 1.0 years) with T2DM were randomized to an isocaloric diet (30 energy(E)% protein, 30 E% fat and 40 E% carbohydrates) rich in AP or PP for 6 weeks. Markers of oxidative and nitrosative stress and antioxidant status in plasma and nitrate/nitrite levels in urine were assessed. Gene expression in subcutaneous adipose tissue (SAT) was analysed by RNA-Seq and real-time PCR. Both AP and PP diets similarly reduced plasma levels of malondialdehyde (PAP = 0.003, PPP = 1.6 × 10-4) and protein carbonyls (PAP = 1.2 × 10-4, PPP = 3.0 × 10-5) over 6 weeks. Nitrotyrosine (NT) increased upon both AP and PP diets (PAP = 0.005, PPP = 0.004). SAT expression of genes involved in nitric oxide (NO) and oxidative stress metabolism and urine NO metabolite (nitrate/nitrite) levels were not changed upon both diets. Plasma levels of carotenoids increased upon PP diet, whereas retinol, alpha- and gamma-tocopherol slightly decreased upon both diets. AP and PP diets similarly improve oxidative stress but increase nitrosative stress markers in individuals with T2DM. Mechanisms of the NT regulation upon high-protein diets need further investigation.

High sucrose low copper diet in pregnant diabetic rats induces transient oxidative stress, hypoxia, and apoptosis in the offspring's liver

BACKGROUND

Hyperglycemia-related oxidative stress and hypoxia are important mechanisms responsible for diabetes-induced embryopathy and other complications. High sucrose low copper diet (HSD), but not regular diet (RD), induces type 2 diabetes in the inbred Cohen diabetic sensitive (CDs) rats but not in the Sabra control rats. We recently demonstrated long-term changes of DNA methylation and gene expression in various groups of genes, including genes involved in oxidant-antioxidant activity in the liver of 2-4-week-old CDs offspring of diabetic dams. We now studied the postnatal effects of diabetes and/or HSD on several liver metabolic parameters in these offspring.

METHODS

we studied lipid peroxidation, activity of the antioxidants enzymes superoxide dismutase (SOD) and Catalase (CAT). By immunohistochemistry: protein oxidation by nitrotyrosine staining, hypoxia inducing factor1α (HIF1α), apoptosis [caspase 3, bcl-2-like protein (BAX)], proliferation [proliferating cell nuclear antigen (PCNA)] and NF-κB.

RESULTS

In the Sabra rats fed HSD only few, early and transitional changes were observed in lipid peroxidation, SOD and CAT activity. In the CDs fed HSD more significant changes in lipid and protein oxidation, HIF1α, apoptosis and proliferation were observed, persisting for longer.

CONCLUSIONS

The changes in the Sabra rats HSD were attributed to the pro-oxidant effects of the diet and those in the diabetic CDs to the HSD and maternal diabetes. In light of the DNA methylation changes in the liver of the CDs HSD, we presume that changes in gene expression are responsible for our findings, and that similar changes may lead to the metabolic syndrome at adulthood.

Effect of the antioxidant idebenone on maternal diabetes-induced embryo alterations during early organogenesis

RESEARCH QUESTION

Can maternal treatments with idebenone, a structural analogue of coenzyme Q10, prevent alterations on markers of proinflammatory-prooxidant processes, on the expression of genes involved in mitochondrial biogenesis and function, and on the apoptotic rate in embryos from mild diabetic rats?

DESIGN

A mild diabetic rat model was induced by neonatal-streptozotocin administration (90 mg/kg subcutaneously). Female diabetic rats and controls were mated with healthy males. From day 1 of pregnancy, control and diabetic rats were orally treated with idebenone (100 mg/kg daily). On day 10.5 of gestation, the embryos were explanted and prepared for immunohistochemical studies, for the evaluation of gene expression by reverse transcription polymerase chain reaction and for TdT (terminal deoxynucleotidyl transferase)-mediated dUDP nick-end-labelling assay analysis.

RESULTS

Embryos from mild diabetic rats showed increased levels of nitrated proteins, 4-hydroxynonenal and matrix metalloproteinase 9, which were prevented by idebenone administration. We also found a decreased embryonic expression of cytochrome c oxidase and reduced mRNA levels of peroxisome proliferator activated receptor-γ coactivator-1-α and nuclear respiratory factor-1, both of which were prevented by idebenone administration to the diabetic pregnant rats. Embryos from mild diabetic rats also showed an increased apoptotic rate, which was diminished by idebenone treatment.

CONCLUSION

Maternal idebenone treatment ameliorates altered parameters related to the prooxidant-proinflammatory environment found in embryos from mild diabetic rats, suggesting a putative treatment to prevent diabetes-induced embryo alterations.

Embryonic defence mechanisms against glucose-dependent oxidative stress require enhanced expression of Alx3 to prevent malformations during diabetic pregnancy

Oxidative stress constitutes a major cause for increased risk of congenital malformations associated to severe hyperglycaemia during pregnancy. Mutations in the gene encoding the transcription factor ALX3 cause congenital craniofacial and neural tube defects. Since oxidative stress and lack of ALX3 favour excessive embryonic apoptosis, we investigated whether ALX3-deficiency further increases the risk of embryonic damage during gestational hyperglycaemia in mice. We found that congenital malformations associated to ALX3-deficiency are enhanced in diabetic pregnancies. Increased expression of genes encoding oxidative stress-scavenging enzymes in embryos from diabetic mothers was blunted in the absence of ALX3, leading to increased oxidative stress. Levels of ALX3 increased in response to glucose, but ALX3 did not activate oxidative stress defence genes directly. Instead, ALX3 stimulated the transcription of Foxo1, a master regulator of oxidative stress-scavenging genes, by binding to a newly identified binding site located in the Foxo1 promoter. Our data identify ALX3 as an important component of the defence mechanisms against the occurrence of developmental malformations during diabetic gestations, stimulating the expression of oxidative stress-scavenging genes in a glucose-dependent manner via Foxo1 activation. Thus, ALX3 deficiency provides a novel molecular mechanism for developmental defects arising from maternal hyperglycaemia.

Maternal diabetes modulates offspring cell proliferation and apoptosis during odontogenesis via the TLR4/NF-κB signalling pathway

OBJECTIVES

Maternal gestational diabetes leads to an adverse in utero environment and increases the risk of malformations during embryo organogenesis. In the present study, we analysed the effects of maternal diabetes on tooth germ cell proliferation and apoptosis in offspring, and investigated their underlying mechanisms.

MATERIALS AND METHODS

A rat model of maternal diabetes was induced by intraperitoneal injection of streptozotocin and the pregnant rats were divided into three groups: controls, the diabetic group and diabetic group with insulin treatment. Offspring of the three groups were collected and cell proliferation and apoptosis in tooth germs were analysed. Primary dental papilla cells and dental epithelial stem cells were isolated and treated with high glucose in vitro, in an attempt to simulate maternal diabetes-induced hyperglycaemia in vivo.

RESULTS

Maternal diabetes significantly affected cell proliferation and apoptosis in offspring tooth germs. The TLR4/NF-ĸB signalling pathway was activated in the tooth germs of offspring of diabetic dams. High glucose treatment activated the TLR4/NF-ĸB signalling pathway in primary dental papilla cells and dental epithelial stem cells in vitro, resulting in suppression of cell proliferation and enhancement of apoptosis. TLR4 knockdown significantly reduced adverse effects induced by high glucose treatment.

CONCLUSIONS

Maternal gestational diabetes significantly impaired dental epithelial and mesenchymal cell proliferation and apoptosis in offspring, possibly by activation of the TLR4/NF-ĸB signalling pathway.

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.

Maternal diabetes impairs oxidative and inflammatory response in murine placenta

Placenta is the major exchange surface between mother and fetus and plays a pivotal role in fetal development. A better understanding of the mechanisms by which diabetes alters placental function may allow better management of diabetes pregnancies. In this study, we attempt to investigate the effect of diabetic milieu with and without malformation on placental function. In order to investigate the impact of diabetic pregnancy on oxidative stress, endothelial and vascular functions of placental tissue, we mated diabetic and non-diabetic female rats with normal male rats. At gestational day 17, we terminated pregnancy, assessed fetuses for malformations and isolated placenta for measurement of various parameters of placental function. Our results show that maternal diabetes induced a state of oxidative stress in placenta, which disrupts normal signaling, activating apoptosis, as well as perturbing endothelial and vascular placental functions. The coalescence of these insults on various levels of placental function could contribute to the pleiotropic nature of diabetes-induced placental stress.

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.

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.

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.

The role of oxidative stress in the pathophysiology of gestational diabetes mellitus

Normal human pregnancy is considered a state of enhanced oxidative stress. In pregnancy, it plays important roles in embryo development, implantation, placental development and function, fetal development, and labor. However, pathologic pregnancies, including gestational diabetes mellitus (GDM), are associated with a heightened level of oxidative stress, owing to both overproduction of free radicals and/or a defect in the antioxidant defenses. This has important implications on the mother, placental function, and fetal well-being. Animal models of diabetes have confirmed the important role of oxidative stress in the etiology of congenital malformations; the relative immaturity of the antioxidant system facilitates the exposure of embryos and fetuses to the damaging effects of oxidative stress. Of note, there are only a few clinical studies evaluating the potential beneficial effects of antioxidants in GDM. Thus, whether or not increased antioxidant intake can reduce the complications of GDM in both mother and fetus needs to be explored. This review provides an overview and updated data on our current understanding of the complications associated with oxidative changes in GDM.

Endoplasmic reticulum stress in maternal diabetes-induced cardiac malformations during critical cardiogenesis period

BACKGROUND

Cardiac abnormalities, including atrioventricular (AV) septal defects (AVSDs), are the most common birth defects in diabetic embryopathy. The AV septum is derived from the endocardial cushions, which undergo development and remodeling during septation. The impact of maternal diabetes on these processes needs to be identified. Maternal diabetes disturbs the function of the endoplasmic reticulum (ER). The role of ER stress in cardiac malformation remains to be delineated to gain information for developing therapy.

METHODS

Female mice were induced diabetic via intravenous injection of streptozotocin. Pregnant mice were made hyperglycemic at desired embryonic (E) days. AVSDs were examined histologically at E15.5. ER stress-associated factors were examined and quantified using immunohistochemical and immunoblot assays at E10.5. The role of ER stress in endocardial cell migration was investigated by treating endocardial cushion explants that were cultured in high glucose with an organic chaperone molecule, sodium 4-phenylbutyrate.

RESULTS

The rate of AVSDs in the embryos that were exposed to maternal hyperglycemia during the period of endocardial cushion development was significantly higher than that in those during endocardial cushion remodeling. ER stress was increased in the hearts. Amelioration of ER stress restored endocardial cell migration under hyperglycemic conditions.

CONCLUSIONS

The development, rather than remodeling, of the endocardial cushions is the cardiomorphogenic process that is susceptible to the insult of maternal hyperglycemia in the formation of AVSDs. Maternal diabetes increases ER stress in the developing heart. ER stress plays an essential role in mediating the effect of hyperglycemia on endocardial cell migration.

Stimulation of cardiomyogenesis of embryonic stem cells by nitric oxide downstream of AMP-activated protein kinase and mTOR signaling pathways

Nitric oxide (NO) is a key regulator of cardiomyogenesis of embryonic stem (ES) cells. However, signaling pathways involving the energy sensor AMP-activated protein kinase (AMPK) and/or mammalian target of rapamycin (mTOR) resulting in NO generation and stimulation of cardiomyogenesis are currently not known. Herein, the role of AMPK- versus mTOR-regulated signaling pathways and the impact of NO for cardiomyogenesis of mouse ES cells were investigated. Activation of AMPK by 5-amino-4-imidazolecarboxamide riboside (AICAr) or metformin as well as inactivation of AMPK by compound C (Comp C), siRNA ablation of AMPKα2, or exogenous ATP stimulated cardiomyogenesis of ES cells. Inhibition of AMPK by Comp C resulted in phosphorylation of mTOR and generation of NO. NO generation was likewise achieved when AMPK was either activated by AICAr or mTOR was inhibited by rapamycin, suggesting that NO generation occurred by two mutually active parallel signaling pathways, one being AMPK dependent and mTOR independent (AICAr pathway) and the other being AMPK independent and mTOR dependent (Comp C pathway). Consequently, cardiomyogenesis as well as NO generation was completely abrogated when ES cells were cultivated in the presence of rapamycin and Comp C, which inhibit both signaling pathways. The impact of NO for cardiomyogenesis of ES cells was corroborated in experiments showing that the effects of Comp C on cardiomyogenesis of ES cells were abolished by the NO synthase inhibitors NG-monomethyl-l-arginine and N (G)-nitro-l-arginine methyl ester. In summary, our data demonstrate that NO generation downstream of AMPK and mTOR is activated by distinct, interacting signaling pathways that initiate cardiomyogenesis of ES cells.

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.

Hyperglycemia and hypoxia are interrelated in their teratogenic mechanism: studies on cultured rat embryos

BACKGROUND

Hyperglycemia and hypoxia are well-known teratogens that may affect many animal species, including man. One of the main mechanisms of teratogenic action of both seems to be increased oxidative stress. The purpose of this study was to evaluate the hypothesis that in the developing embryo hyperglycemia also leads to hypoxia, both resulting in oxidative damage.

METHODS

The study was performed on 10.5-day-old rat embryos of the regular Sabra strain cultured for 28 hours in hyperglycemic or hypoxic conditions. Embryonic growth and rate of anomalies was assessed at the end of the culture period. The embryonic oxidative damage was investigated by studying the levels of Malondialdehyde (MDA) to determine the lipid peroxidation. The redox status was studied by measuring the activity of Catalase-like (CAT) and Super Oxide Dismutase (SOD) enzymes and the amount of Low Molecular Weight Antioxidants (LMWA). In addition, we studied by immunohistochemistry in the embryos and yolk sacs the amount of nitrotyrosine as an additional marker for the extent of oxidative stress. The amounts of the redox and hypoxia sensitive transcription factors HIF1alpha, NFkB, and IkB were also studied by immunohistochemistry.

RESULTS

Both hyperglycemia and hypoxia increased the rate of congenital anomalies mainly of the heart, neural tube, and brain. Embryonic growth and scoring were decreased only by hypoxia. Both hyperglycemia and hypoxia increased embryonic oxidative stress as evidenced by increased lipid peroxidation, increased nitrotyrosine and LMWA, but only minimal changes in CAT and SOD activity. Severe hyperglycemia also caused hypoxia, as evidenced by increased HIF1alpha. Thus, there seems to be an interrelation between hyperglycemia and hypoxia, both resulting in embryonic damage apparently by enhanced oxidative stress.

CONCLUSIONS

Both hyperglycemia and hypoxia seem to exert their embryotoxicity through a similar mechanism of increased oxidative stress in the embryo in a stage when its antioxidant capacity is still weak. Moreover, hyperglycemia also seems to induce hypoxia, intensifying diabetes-induced embryopathy.

Prevention of neural tube defects by loss of function of inducible nitric oxide synthase in fetuses of a mouse model of streptozotocin-induced diabetes

AIMS/HYPOTHESIS

Maternal diabetes during pregnancy increases the risk of congenital malformations such as neural tube defects (NTDs). Although the mechanism of this effect is uncertain, it is known that levels of nitric oxide synthase (NOS) and nitric oxide are elevated in embryos of a mouse model of diabetes. We postulated that overproduction of nitric oxide causes diabetes-induced congenital malformations and that inhibition of inducible NOS (iNOS) might prevent diabetic embryopathy.

METHODS

Mice were rendered hyperglycaemic by intraperitoneal injection of streptozotocin. The incidence of congenital malformations including NTDs was evaluated on gestational day 18.5. We assessed the involvement of iNOS in diabetes-induced malformation by administering ONO-1714, a specific inhibitor of iNOS, to pregnant mice with streptozotocin-induced diabetic mice and by screening mice with iNOS deficiency due to genetic knockout (iNos(-/-)).

RESULTS

ONO-1714 markedly reduced the incidence of congenital anomalies, including NTDs, in fetuses of a mouse model of diabetes. It also prevented apoptosis in the head region of fetuses, indicating that iNOS is involved in diabetes-related congenital malformations. Indeed, no NTDs were observed in fetuses of diabetic iNos(-/-) mice and the incidence of other malformations was also markedly reduced.

CONCLUSIONS/INTERPRETATION

We conclude that increased iNOS activity during organogenesis plays a crucial role in the pathogenesis of diabetes-induced malformations and suggest that inhibitors of iNOS might help prevent malformations, especially NTDs, in diabetic pregnancy.

Uterine artery function in a mouse model of pregnancy complicated by diabetes

It has been demonstrated previously that endothelium-dependent vasodilatation is impaired in myometrial arteries from women with gestational diabetes, which may play a role in mediating complications observed in diabetic pregnancies. It is not known which aspects of endothelium-dependent vasodilatation are impaired, thus a mouse model of pregnancy complicated by streptozotocin-induced diabetes was established to investigate underlying mechanisms. Uterine arteries from term-pregnant, diabetic and control C57Bl6/J mice were assessed using acetylcholine (ACh; 10(-10)-10(-5)M) in the presence or absence of a nitric oxide (NO) synthase inhibitor (L-NNA; 10(-5)M), a cyclooxygenase (COX) inhibitor (indomethacin; 10(-5)M) or the two in combination. Sensitivity to ACh was comparable between diabetic and control mice. However, the contribution of endothelium-dependent vasodilators was significantly altered. L-NNA significantly inhibited the relaxation of arteries from diabetic compared to control mice (65+/-11% vs 18+/-6%; p<.05). L-NNA and indomethacin significantly inhibited the relaxation of arteries from diabetic mice compared to control (87+/-5% vs 33+/-14%; p<0.05). These data indicate that endothelium-dependent relaxation of the uterine artery of control, pregnant mice was largely mediated by the non-NO/non-COX component. Surprisingly, arteries from diabetic mice were primarily dependent on NO, which may affect compensatory capacity as the disease progresses.

Leptin in embryos from control and diabetic rats during organogenesis: a modulator of nitric oxide production and lipid homeostasis

BACKGROUND

Leptin is involved in many metabolic and reproductive events and its levels are altered by the diabetic pathology. In this study, leptin concentrations and leptin effects on both nitric oxide (NO) and lipid concentrations were investigated in embryos from control and diabetic rats.

METHODS

Diabetes was induced by neonatal streptozotocin administration (90 mg/kg). Embryos from control and diabetic rats were obtained on days 10.5 and 13.5 of gestation, corresponding to early organogenesis and post-placentation periods respectively. Leptin was analysed by enzyme immunoanalysis and immunohistochemistry. Nitrates and nitrites were assessed as an index of NO production. Lipid concentrations were analysed by thin layer chromatography.

RESULTS

Leptin concentrations were decreased in embryos obtained from diabetic rats on days 10.5 and 13.5 of gestation when compared to controls. NO concentrations, elevated in diabetic embryopathy, were diminished in the presence of leptin in the embryos obtained from control and diabetic animals both during early organogenesis and after placentation. Leptin additions reduced phospholipid, cholesterol and cholesteryl ester concentrations in embryos obtained from diabetic rats during early organogenesis, although no leptin effects on lipid concentrations were observed in control embryos at this developmental stage. In embryos obtained on day 13.5 of gestation leptin additions reduced cholesteryl ester concentrations in controls, and diminished cholesteryl ester, triglycerides and phospholipids in embryos from diabetic rats.

CONCLUSIONS

We demonstrated that leptin plays a role in the regulation of NO concentrations and lipid homeostasis during embryo organogenesis and that the diabetic environment causes a reduction of leptin concentrations in rat embryos.

The role of nitric oxide on matrix metalloproteinase 2 (MMP2) and MMP9 in placenta and fetus from diabetic rats

Matrix metalloproteinases (MMPs) play an important role in tissue remodeling that accompanies the rapid growth, differentiation, and structural changes of the placenta and several fetal organs. In the present study, we investigated whether the diabetic maternal environment may alter the regulatory homeostasis exerted by nitric oxide (NO) on MMPs activity in the feto-placental unit from rats at midgestation. We found that NADPH-diaphorase activity, which reflects the distribution and activity of NO synthases (NOS), was increased in both placenta and fetuses from diabetic rats when compared with controls. In addition, while a NO donor enhanced MMP2 and MMP9 activities, a NOS inhibitor reduced these activities in the maternal side of the placenta from control rats. This regulatory effect of NO was only observed on MMP9 in the diabetic group. On the other hand, the NO donor did not modify MMP2 and MMP9 activities, while the NOS inhibitor reduced MMP9 activity in the fetal side of both control and diabetic placentas. In the fetuses, MMP2 was enhanced by the NO donor and reduced by the NO inhibitor in both fetuses from control and diabetic rats. Overall, this study demonstrates that NO is able to modulate the activation of MMPs in the feto-placental unit, and provides supportive evidence that increased NOS activity leads to NO overproduction in the feto-placental unit from diabetic rats, an alteration closely related to the observed MMPs dysregulation that may have profound implications in the formation and function of the placenta and the fetal organs.

Role of nitric oxide in chick embryonic organogenesis and dysmorphogenesis

BACKGROUND

Nitric oxide (NO), produced by the nitric oxide synthase family of enzymes, mediates multiple signaling functions, and when unchecked, NO causes pathological damage. Exposure of embryos to a variety of teratogens, including carbon monoxide (CO), has been shown to increase reactive intermediates, such as NO, and recent work showed that either the excess or absence of NO caused morphological defects. While endogenous NO is known to regulate many adult tissues, its role during embryonic organogenesis and/or in mediating responses to teratogen exposure has not been explored.

METHODS

We have examined here the presence of NO during normal chick embryonic organogenesis, and investigated the teratogenicity of NO through the application of sodium nitroprusside (SNP), which mimics NO overproduction, and NG-monomethyl-L-arginine (L-NMMA), which inhibits endogenous NOS activity.

RESULTS

Topical treatment with SNP or L-NMMA for 18 h resulted in morphological defects, specifically in the neural tube and somites, which corresponded to sites of altered apoptosis. The location of NO was histochemically correlated with the observed morphological defects. Coadministration of SNP or L-NMMA with CO showed functional coregulation and interaction between NO and CO in chick embryonic development.

CONCLUSIONS

Our results showed that regulation of NO is essential for normal axial development, that sites of altered NO expression correlate to those of altered apoptosis and dysmorphogenesis, and that CO coadministration resulted in a rectification of normal NO expression. Collectively, these results suggest that alteration in endogenous NO/CO signaling is responsible, at least in part, for the observed NO-induced teratogenesis.

PPARδ and its activator PGI2 are reduced in diabetic embryopathy: involvement of PPARδ activation in lipid metabolic and signalling pathways in rat embryo early organogenesis

Maternal diabetes significantly increases the risk of congenital malformations, and the mechanisms involved are not yet clarified. This study was designed to address peroxisome proliferator-activated receptor delta (PPARdelta) involvement in diabetic embryopathy. We investigated the concentrations of PPARdelta and its endogenous agonist prostaglandin (PG)I(2), as well as the effect of PPARdelta activation on lipid metabolism and PGE(2) concentrations in embryos from control and streptozotocin-induced diabetic rats during early organogenesis. Embryos from diabetic rats showed decreased concentrations of PPARdelta and its endogenous agonist PGI(2) when compared with controls. In embryos from control rats, the addition of the PPARdelta activators (cPGI(2) and PGA(1)) increased embryonic phospholipid levels and de novo phospholipid synthesis studied using (14)C-acetate as a tracer. PGE(2) formed from arachidonate released from phospholipid stores was also up-regulated by PPARdelta activators. In embryos from diabetic rats, reduced phospholipid synthesis and PGE(2) content were observed, and clearly up-regulated by cPGI(2) additions to values similar to those found in control embryos. These data suggest that PPARdelta may play an important role in lipid metabolic and signalling pathways during embryo organogenesis, developmental pathways that are altered in embryos from diabetic rats, possibly as a result of a reduction in levels of PPARdelta and its endogenous activator PGI(2).