Functional link between adenosine and insulin: a hypothesis for fetoplacental vascular endothelial dysfunction in gestational diabetes

Gestational Diabetes-Placental Expression of Human Equilibrative Nucleoside Transporter 1 (hENT1): Is Delayed Villous Maturation an Adaptive Pattern?

Gestational diabetes mellitus (GDM) is a metabolic disease that can affect placental villous maturation and villous vascularity. The main effects of GDM on placental growth are a delay of villous maturation (DVM) and decreased formation of vasculo-syncytial membranes (VSM). Human equilibrative nucleoside transporter-1 (hENT1) is an adenosine transporter expressed in the human umbilical vein endothelial cells (HUVEC) and human placental microvascular endothelium cells (hPMEC). Its role is crucial in maintaining physiological fetal adenosine levels during pregnancy, and its reduction has been described in GDM. Twenty-four placentas from pregnancies with a confirmed diagnosis of GDMd and twenty-four matched non-GDM placentas (controls) were retrospectively analyzed to investigate the immunohistochemical expression of hENT1 in HUVEC and hPMEC. The study included the quantitative evaluation of VSM/mm² in placental tissue and the immunohistochemical quantitative evaluation of Ki-67, PHH3, and p57 in villous trophoblast. hENT1 expression was higher in all the vascular districts of the control cases compared to the GDMd placentas (p < 0.0001). The VSM/mm² were lower in the GDMd cases, while the Ki-67, PHH3, and p57 were higher when compared to the control cases. To our knowledge, this is the first report of hENT1 expression in the human placentas of GDM patients. The absence/low expression of hENT1 in all the GDMd patients may indicate a potential role in microvascular adaptative mechanisms. The trophoblasts' proliferative/antiapoptotic pattern (high Ki-67, high PHH3, and high p57 count) may explain the statistically significant lower number of VSM/mm² found in the GDMd cases.

Comparison of Diagnostic Values of Maternal Arginine Concentration for Different Pregnancy Complications: A Systematic Review and Meta-Analysis

Abnormal arginine metabolism contributes to the development of intrauterine growth restriction (IUGR), preeclampsia (PE), and gestational diabetes mellitus (GDM), which increase the health burden of mothers and induce adverse birth outcomes. However, associations between maternal arginine concentration and different pregnancy complications have not been systematically compared. The PubMed, ScienceDirect, and Web of Science databases were searched for peer-reviewed publications to evaluate the diagnostic value of plasma arginine concentration in complicated pregnancies. Standardized mean difference (SMD) of the arginine concentration was pooled by a random effects model. The results show that increased maternal arginine concentrations were observed in IUGR (SMD: 0.48; 95% CI: 0.20, 0.76; I² = 47.0%) and GDM (SMD: 0.46; 95% CI: 0.11, 0.81; I² = 82.3%) cases but not in PE patients (SMD: 0.21; 95% CI: −0.04, 0.47; I² = 80.3%) compared with the normal cohorts. Subgroup analyses indicated that the non-fasting circulating arginine concentration in third trimester was increased significantly in GDM and severe IUGR pregnancies, but the change mode was dependent on ethnicity. Additionally, only severe PE persons were accompanied by higher plasma arginine concentrations. These findings suggest that maternal arginine concentration is an important reference for assessing the development of pregnancy complications.

Metabolomic Biomarkers in Gestational Diabetes Mellitus: A Review of the Evidence

Gestational diabetes mellitus (GDM) is the fastest growing type of diabetes, affecting between 2 to 38% of pregnancies worldwide, varying considerably depending on diagnostic criteria used and sample population studied. Adverse obstetric outcomes include an increased risk of macrosomia, and higher rates of stillbirth, instrumental delivery, and birth trauma. Metabolomics, which is a platform used to analyse and characterise a large number of metabolites, is increasingly used to explore the pathophysiology of cardiometabolic conditions such as GDM. This review aims to summarise metabolomics studies in GDM (from inception to January 2021) in order to highlight prospective biomarkers for diagnosis, and to better understand the dysfunctional metabolic pathways underlying the condition. We found that the most commonly deranged pathways in GDM include amino acids (glutathione, alanine, valine, and serine), carbohydrates (2-hydroxybutyrate and 1,5-anhydroglucitol), and lipids (phosphatidylcholines and lysophosphatidylcholines). We also highlight the possibility of using certain metabolites as predictive markers for developing GDM, with the use of highly stratified modelling techniques. Limitations for metabolomic research are evaluated, and future directions for the field are suggested to aid in the integration of these findings into clinical practice.

Associations of Arginine with Gestational Diabetes Mellitus in a Follow-Up Study

In the reported study we applied the targeted metabolomic profiling employing high pressure liquid chromatography coupled with triple quadrupole tandem mass spectrometry (HPLC–MS/MS) to understand the pathophysiology of gestational diabetes mellitus (GDM), early identification of women who are at risk of developing GDM, and the differences in recovery postpartum between these women and normoglycemic women. We profiled the peripheral blood from patients during the second trimester of pregnancy and three months, and one year postpartum. In the GDM group Arg, Gln, His, Met, Phe and Ser were downregulated with statistical significance in comparison to normoglycemic (NGT) women. From the analysis of the association of all amino acid profiles of GDM and NGT women, several statistical models predicting diabetic status were formulated and compared with the literature, with the arginine-based model as the most promising of the screened ones (area under the curve (AUC) = 0.749). Our research results have shed light on the critical role of arginine in the development of GDM and may help in precisely distinguishing between GDM and NGT and earlier detection of GDM but also in predicting women with the increased type 2 diabetes mellitus (T2DM) risk.

Smoking and Endothelial Dysfunction

Cigarette smoking is one of the most important health concerns worldwide. Even though the rate of smoking is declining in developed countries, it is still experiencing growth in developing regions. Many studies have examined the relationship between smoking, as an established risk factor, and cardiovascular diseases. We provide an updated review of the underlying mechanisms of smokinginduced cardiovascular diseases, with a focus on the relationship between smoking and oxidative stress, particularly from the perspective of endothelial cell dysfunction. We review smoking-induced oxidative stress as a trigger for a generalized vascular inflammation associated with cytokine release, adhesion of inflammatory cells and, ultimately, disruption of endothelial integrity as a protective barrier layer. We also briefly discuss the harms related to the vaping of electronic cigarettes, which many erroneously consider as a safe alternative to smoking. We conclude that even though e-cigarette could be a helpful device during the transition period of cigarette quitting, it is by no means a safe substitute.

Adenosine kinase and cardiovascular fetal programming in gestational diabetes mellitus

Gestational diabetes mellitus (GDM) is a detrimental condition for human pregnancy associated with endothelial dysfunction and endothelial inflammation in the fetoplacental vasculature and leads to increased cardio-metabolic risk in the offspring. In the fetoplacental vasculature, GDM is associated with altered adenosine metabolism. Adenosine is an important vasoactive molecule and is an intermediary and final product of transmethylation reactions in the cell. Adenosine kinase is the major regulator of adenosine levels. Disruption of this enzyme is associated with alterations in methylation-dependent gene expression regulation mechanisms, which are associated with the fetal programming phenomenon. Here we propose that cellular and molecular alterations associated with GDM can dysregulate adenosine kinase leading to fetal programming in the fetoplacental vasculature. This can contribute to the cardio-metabolic long-term consequences observed in offspring after exposure to GDM.

Pro-angiogenic Role of Insulin: From Physiology to Pathology

The underlying molecular mechanisms involve in the regulation of the angiogenic process by insulin are not well understood. In this review article, we aim to describe the role of insulin and insulin receptor activation on the control of angiogenesis and how these mechanisms can be deregulated in human diseases. Functional expression of insulin receptors and their signaling pathways has been described on endothelial cells and pericytes, both of the main cells involved in vessel formation and maturation. Consequently, insulin has been shown to regulate endothelial cell migration, proliferation, and in vitro tubular structure formation through binding to its receptors and activation of intracellular phosphorylation cascades. Furthermore, insulin-mediated pro-angiogenic state is potentiated by generation of vascular growth factors, such as the vascular endothelial growth factor, produced by endothelial cells. Additionally, diseases such as insulin resistance, obesity, diabetes, and cancer may be associated with the deregulation of insulin-mediated angiogenesis. Despite this knowledge, the underlying molecular mechanisms need to be elucidated in order to provide new insights into the role of insulin on angiogenesis.

Is a low level of free thyroxine in the maternal circulation associated with altered endothelial function in gestational diabetes?

Synthesis of thyroid hormones, thyroxine (T₄) and tri-iodothyronine (T₃), in the human fetus starts from 17 to 19th weeks of gestation. Despite the majority of normal pregnant women reaching adequate levels of circulating thyroid hormones, in some cases, women with normal pregnancies have low level of free T₄ during first trimester of pregnancy, suggesting that T₄ action may be compromised in those women and their fetuses. In addition, pathological low levels of thyroid hormones are detected in isolated maternal hypothyroxemia (IMH) and clinical hypothyroidism. Nevertheless, human placenta regulates T₃/T₄ concentration in the fetal circulation by modulating the expression and activity of both thyroid hormone transporters (THT) and deiodinases. Then, placenta can control the availability of T₃/T₄ in the feto-placental circulation, and therefore may generate an adaptive response in cases where the mother courses with low levels of T₄. In addition, T₃/T₄ might control vascular response in the placenta, in particularly endothelial cells may induce the synthesis and release of vasodilators such as nitric oxide (NO) or vasoconstrictors such as endothelin-1 mediated by these hormones. On the other hand, low levels of T₄ have been associated with increase in gestational diabetes (GD) markers. Since GD is associated with impaired placental vascular function characterized by increased NO synthesis in placental arteries and veins, as well as elevated placental angiogenesis, it is unknown whether reduced T₄ level at the maternal circulation could result in an altered placental endothelial function during GD. In this review, we analyze available information regarding thyroid hormones and endothelial dysfunction in GD; and propose that low maternal levels of T₄ observed in GD may be compensated by increased placental availability of T₃/T₄ via elevation in the activity of THT and/or reduction in deiodinases in the feto-placental circulation.

Role of equilibrative adenosine transporters and adenosine receptors as modulators of the human placental endothelium in gestational diabetes mellitus

Gestational diabetes mellitus (GDM) is a diseases that alters human placenta macro and microvascular reactivity as a result of endothelial dysfunction. The human placenta is a highly vascularized organ which lacks innervation, so blood flux is governed by locally released vasoactive molecules, including the endogenous nucleoside adenosine and the free radical nitric oxide (NO). Altered adenosine metabolism and uptake by the endothelium leads to increased NO synthesis which then turns-off the expression of genes coding for a family of nucleoside membrane transporters belonging to equilibrative nucleoside transporters, particularly isoforms 1 (hENT1) and 2 (hENT2). This mechanism leads to increased extracellular adenosine and, as a consequence, activation of adenosine receptors to further sustain a tonic activation of NO synthesis. This is a phenomenon that seems operative in the placental macro and microvascular endothelium in GDM. We here summarize the findings available in the literature regarding these mechanisms in the human feto-placental circulation. This phenomenon is altered in the feto-placental vasculature, which could be crucial for understanding GDM deleterious effects in fetal growth and development.

Purinergic signalling and diabetes

The pancreas is an organ with a central role in nutrient breakdown, nutrient sensing and release of hormones regulating whole body nutrient homeostasis. In diabetes mellitus, the balance is broken-cells can be starving in the midst of plenty. There are indications that the incidence of diabetes type 1 and 2, and possibly pancreatogenic diabetes, is rising globally. Events leading to insulin secretion and action are complex, but there is emerging evidence that intracellular nucleotides and nucleotides are not only important as intracellular energy molecules but also as extracellular signalling molecules in purinergic signalling cascades. This signalling takes place at the level of the pancreas, where the close apposition of various cells-endocrine, exocrine, stromal and immune cells-contributes to the integrated function. Following an introduction to diabetes, the pancreas and purinergic signalling, we will focus on the role of purinergic signalling and its changes associated with diabetes in the pancreas and selected tissues/organ systems affected by hyperglycaemia and other stress molecules of diabetes. Since this is the first review of this kind, a comprehensive historical angle is taken, and common and divergent roles of receptors for nucleotides and nucleosides in different organ systems will be given. This integrated picture will aid our understanding of the challenges of the potential and currently used drugs targeted to specific organ/cells or disorders associated with diabetes.

Maternal and fetal adropin levels in gestational diabetes mellitus

AIM

To evaluate maternal and cord blood serum adropin concentrations in pregnant women with gestational diabetes mellitus (GDM).

STUDY DESIGN

Twenty pregnant women with GDM and 20 gestational age-matched healthy pregnant women participated in the study. Maternal serum and cord blood adropin levels were assessed using an enzyme immunosorbent assay, at the time of birth. The relation of maternal serum and cord blood adropin levels with metabolic parameters were also assessed.

RESULTS

The mean maternal and cord serum adropin in the GDM group were significantly lower than those of the control women (P=0.01 and P<0.001, respectively). Maternal serum adropin levels did not correlate with either fetal serum adropin levels or maternal metabolic values.

CONCLUSION

The data suggest that low adropin levels may contribute to the underlying pathogenesis of GDM.

Insulin-increased L-arginine transport requires A(2A) adenosine receptors activation in human umbilical vein endothelium

Adenosine causes vasodilation of human placenta vasculature by increasing the transport of arginine via cationic amino acid transporters 1 (hCAT-1). This process involves the activation of A_2A adenosine receptors (A_2AAR) in human umbilical vein endothelial cells (HUVECs). Insulin increases hCAT-1 activity and expression in HUVECs, and A_2AAR stimulation increases insulin sensitivity in subjects with insulin resistance. However, whether A_2AAR plays a role in insulin-mediated increase in L-arginine transport in HUVECs is unknown. To determine this, we first assayed the kinetics of saturable L-arginine transport (1 minute, 37°C) in the absence or presence of nitrobenzylthioinosine (NBTI, 10 µmol/L, adenosine transport inhibitor) and/or adenosine receptors agonist/antagonists. We also determined hCAT-1 protein and mRNA expression levels (Western blots and quantitative PCR), and SLC7A1 (for hCAT-1) reporter promoter activity. Insulin and NBTI increased the extracellular adenosine concentration, the maximal velocity for L-arginine transport without altering the apparent K_m for L-arginine transport, hCAT-1 protein and mRNA expression levels, and SLC7A1 transcriptional activity. An A2AAR antagonist ZM-241385 blocked these effects. ZM241385 inhibited SLC7A1 reporter transcriptional activity to the same extent in cells transfected with pGL3-hCAT-1⁻¹⁶⁰⁶ or pGL3-hCAT-1⁻⁶⁵⁰ constructs in the presence of NBTI + insulin. However, SLC7A1 reporter activity was increased by NBTI only in cells transfected with pGL3-hCAT-1⁻¹⁶⁰⁶, and the ZM-241385 sensitive fraction of the NBTI response was similar in the absence or in the presence of insulin. Thus, insulin modulation of hCAT-1 expression and activity requires functional A_2AAR in HUVECs, a mechanism that may be applicable to diseases associated with fetal insulin resistance, such as gestational diabetes.

Gestational diabetes reduces adenosine transport in human placental microvascular endothelium, an effect reversed by insulin

Gestational diabetes mellitus (GDM) courses with increased fetal plasma adenosine concentration and reduced adenosine transport in placental macrovascular endothelium. Since insulin modulates human equilibrative nucleoside transporters (hENTs) expression/activity, we hypothesize that GDM will alter hENT2-mediated transport in human placental microvascular endothelium (hPMEC), and that insulin will restore GDM to a normal phenotype involving insulin receptors A (IR-A) and B (IR-B). GDM effect on hENTs expression and transport activity, and IR-A/IR-B expression and associated cell signalling cascades (p42/44 mitogen-activated protein kinases (p42/44^mapk) and Akt) role in hPMEC primary cultures was assayed. GDM associates with elevated umbilical whole and vein, but not arteries blood adenosine, and reduced hENTs adenosine transport and expression. IR-A/IR-B mRNA expression and p42/44^mapk/Akt ratios (‘metabolic phenotype’) were lower in GDM. Insulin reversed GDM-reduced hENT2 expression/activity, IR-A/IR-B mRNA expression and p42/44^mapk/Akt ratios to normal pregnancies (‘mitogenic phenotype’). It is suggested that insulin effects required IR-A and IR-B expression leading to differential modulation of signalling pathways restoring GDM-metabolic to a normal-mitogenic like phenotype. Insulin could be acting as protecting factor for placental microvascular endothelial dysfunction in GDM.

Fetoplacental vascular endothelial dysfunction as an early phenomenon in the programming of human adult diseases in subjects born from gestational diabetes mellitus or obesity in pregnancy

Gestational diabetes mellitus (GDM) and obesity in pregnancy (OP) are pathological conditions associated with placenta vascular dysfunction coursing with metabolic changes at the fetoplacental microvascular and macrovascular endothelium. These alterations are seen as abnormal expression and activity of the cationic amino acid transporters and endothelial nitric oxide synthase isoform, that is, the "endothelial L-arginine/nitric oxide signalling pathway." Several studies suggest that the endogenous nucleoside adenosine along with insulin, and potentially arginases, are factors involved in GDM-, but much less information regards their role in OP-associated placental vascular alterations. There is convincing evidence that GDM and OP prone placental endothelium to an "altered metabolic state" leading to fetal programming evidenced at birth, a phenomenon associated with future development of chronic diseases. In this paper it is suggested that this pathological state could be considered as a metabolic marker that could predict occurrence of diseases in adulthood, such as cardiovascular disease, obesity, diabetes mellitus (including gestational diabetes), and metabolic syndrome.