Background Tetrahydrobiopterin is a cofactor of endothelial NO synthase ( eNOS ), which is critical to embryonic heart development. We aimed to study the effects of sapropterin (Kuvan), an orally active synthetic form of tetrahydrobiopterin on eNOS uncoupling and congenital heart defects ( CHD s) induced by pregestational diabetes mellitus in mice. Methods and Results Adult female mice were induced to pregestational diabetes mellitus by streptozotocin and bred with normal male mice to produce offspring. Pregnant mice were treated with sapropterin or vehicle during gestation. CHD s were identified by histological analysis. Cell proliferation, eNOS dimerization, and reactive oxygen species production were assessed in the fetal heart. Pregestational diabetes mellitus results in a spectrum of CHD s in their offspring. Oral treatment with sapropterin in the diabetic dams significantly decreased the incidence of CHD s from 59% to 27%, and major abnormalities, such as atrioventricular septal defect and double‐outlet right ventricle, were absent in the sapropterin‐treated group. Lineage tracing reveals that pregestational diabetes mellitus results in decreased commitment of second heart field progenitors to the outflow tract, endocardial cushions, and ventricular myocardium of the fetal heart. Notably, decreased cell proliferation and cardiac transcription factor expression induced by maternal diabetes mellitus were normalized with sapropterin treatment. Furthermore, sapropterin administration in the diabetic dams increased eNOS dimerization and lowered reactive oxygen species levels in the fetal heart. Conclusions Sapropterin treatment in the diabetic mothers improves eNOS coupling, increases cell proliferation, and prevents the development of CHD s in the offspring. Thus, sapropterin may have therapeutic potential in preventing CHD s in pregestational diabetes mellitus.

Women with pre‐gestational diabetes have a higher risk of producing children with congenital heart defects (CHDs), caused predominantly by hyperglycemia‐induced oxidative stress. In this study, we evaluated if exercise during pregnancy could mitigate oxidative stress and reduce the incidence of CHDs in the offspring of diabetic mice. Female mice were treated with streptozotocin to induce pre‐gestational diabetes, then mated with healthy males to produce offspring. They were also given access to running wheels 1 week before mating and allowed to exercise voluntarily until E18.5. Heart morphology, gene expression, and oxidative stress were assessed in foetal hearts. Maternal voluntary exercise results in a significantly lower incidence of CHDs from 59.5% to 25%. Additionally, diabetes‐induced defects in coronary artery and capillary morphogenesis were also lower with exercise. Myocardial cell proliferation and epithelial‐mesenchymal transition at E12.5 was significantly lower with pre‐gestational diabetes which was mitigated with maternal exercise. Cardiac gene expression of Notch1 , Snail1 , Gata4 and Cyclin D1 was significantly higher in the embryos of diabetic mice that exercised compared to the non‐exercised group. Furthermore, maternal exercise produced lower reactive oxygen species (ROS) and oxidative stress in the foetal heart. In conclusion, maternal exercise mitigates ROS and oxidative damage in the foetal heart, and results in a lower incidence of CHDs in the offspring of pre‐gestational diabetes. Exercise may be an effective intervention to compliment clinical management and further minimize CHD risk in mothers with diabetes.

Congenital heart defects (CHDs) are the most prevalent and serious birth defect, occurring in 1% of all live births. Pregestational maternal diabetes is a known risk factor for the development of CHDs, elevating the risk in the child by more than four-fold. As the prevalence of diabetes rapidly rises among women of childbearing age, there is a need to investigate the mechanisms and potential preventative strategies for these defects. In experimental animal models of pregestational diabetes induced-CHDs, upwards of 50% of offspring display congenital malformations of the heart, including septal, valvular, and outflow tract defects. Specifically, the imbalance of nitric oxide (NO) and reactive oxygen species (ROS) signaling is a major driver of the development of CHDs in offspring of mice with pregestational diabetes. NO from endothelial nitric oxide synthase (eNOS) is crucial to cardiogenesis, regulating various cellular and molecular processes. In fact, deficiency in eNOS results in CHDs and coronary artery malformation. Embryonic hearts from diabetic dams exhibit eNOS uncoupling and oxidative stress. Maternal treatment with sapropterin, a cofactor of eNOS, and antioxidants such as N-acetylcysteine, vitamin E, and glutathione as well as maternal exercise have been shown to improve eNOS function, reduce oxidative stress, and lower the incidence CHDs in the offspring of mice with pregestational diabetes. This review summarizes recent data on pregestational diabetes-induced CHDs, and offers insights into the important roles of NO and ROS in embryonic heart development and pathogenesis of CHDs in maternal diabetes.

word count: 248Main text word count: 4,612Figures: 9; Tables: 1 Supplementary Table: 1; Supplementary Figure: 1References: 50All rights reserved. No reuse allowed without permission.(which was not peer-reviewed) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity.The copyright holder for this preprint . http://dx.doi.org/10.1101/304006 doi: bioRxiv preprint first posted online Apr. 18, 2018; 2 ABSTRACT Aims: Tetrahydrobiopterin (BH4) is a co-factor of endothelial nitric oxide synthase (eNOS), which is critical to embryonic heart development. We aimed to study the effects of sapropterin (Kuvan®), an orally active synthetic form of BH4 on eNOS uncoupling and congenital heart defects (CHDs) induced by pregestational diabetes in mice.Methods: Adult female mice were induced to pregestational diabetes by streptozotocin and bred with normal males to produce offspring. Pregnant mice were treated with sapropterin or vehicle during gestation. CHDs were identified by histological analysis. Cell proliferation, eNOS dimerization and reactive oxygen species (ROS) production were assessed in the fetal heart. Results:Pregestational diabetes results in a spectrum of CHDs in their offspring. Oral treatment with sapropterin in the diabetic dams significantly decreased the incidence of CHDs from 59% to 27% and major abnormalities, such as atrioventricular septal defect and double outlet right ventricle were absent in the sapropterin treated group. Lineage tracing reveals that pregestational diabetes results in decreased commitment of second heart field progenitors to the outflow tract, endocardial cushions, and ventricular myocardium of the fetal heart. Notably, decreased cell proliferation and cardiac transcription factor expression induced by maternal diabetes were normalized with sapropterin treatment. Furthermore, sapropterin administration in the diabetic dams increased eNOS dimerization and lowered ROS levels in the fetal heart.Conclusions: Sapropterin treatment in the diabetic mothers improves eNOS coupling, increases cell proliferation and prevents the development of CHDs in the offspring. Thus, sapropterin may have therapeutic potential in preventing CHDs in pregestational diabetes.

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Maternal cigarette smoking is a risk factor for congenital heart defects (CHDs). Nicotine replacement therapies are often offered to pregnant women following failed attempts of smoking cessation. However, the impact of nicotine on embryonic heart development is not well understood. In the present study, the effects of maternal nicotine exposure (MNE) during pregnancy on foetal heart morphogenesis were studied. Adult female mice were treated with nicotine using subcutaneous osmotic pumps at 0.75 or 1.5 mg/kg/day and subsequently bred with male mice. Our results show that MNE dose‐dependently increased CHDs in foetal mice. CHDs included atrial and ventricular septal defects, double outlet right ventricle, unguarded tricuspid orifice, hypoplastic left ventricle, thickened aortic and pulmonary valves, and ventricular hypertrophy. MNE also significantly reduced coronary artery size and vessel abundance in foetal hearts. Moreover, MNE resulted in higher levels of oxidative stress and altered the expression of key cardiogenic regulators in the developing heart. Nicotine exposure reduced epicardial‐to‐mesenchymal transition in foetal hearts. In conclusion, MNE induces CHDs and coronary artery malformation in mice. These findings provide insight into the adverse outcomes of foetuses by MNE during pregnancy.

Background In Canada, as is found globally, women of reproductive age are a growing demographic of persons living with HIV. Combination antiretroviral therapy (cART) treatment enables women living with HIV (WLWH) to become pregnant without perinatal transmission, and they are increasingly planning to become pregnant. Since 2014, Canadian guidelines no longer recommend routine elective cesarean birth (CB) for women who are virally suppressed and receiving cART. It is unknown whether their obstetric care has changed since this update. Our objective was to describe trends in cesarean births among WLWH in Ontario, Canada, over a 12‐year period. Methods Our research is co‐led and codesigned with WLWH. We conducted a retrospective population‐level cohort study using linked health administrative databases at ICES (formally, the Institute for Clinical and Evaluative Sciences). Participants were all women who gave birth in Ontario, between 2006/07 and 2017/18. We assessed their intrapartum characteristics and used multivariable regression to determine an association between HIV status and CB, controlling for sociodemographic and clinical variables. Results Since 2014, the overall proportion of CB among WLWH remained stable and was higher than among women without HIV (39.9% vs 29.0%, P < 0.001). In addition, the proportion of primary CB decreased between 2006 and 2010 and between 2014 and 2018 (28.5%‐19.3%), whereas the proportion of repeat CB increased (13.1%‐20.5%, P = 0.013). Conclusions Because of decreasing HIV‐related indications for CB, more practitioners may be following the guidelines for first‐time mothers. Currently, no guidelines exist for care of WLWH with a previous CB, and opportunities for vaginal birth may be missed in this population.

Congenital heart defects (CHDs) account for 1–5% of live births and are the leading cause of death in the first year life. Pregestational diabetes increases the risk for CHDs over five fold. We have recently shown that pregestational diabetes in mice induces CHDs in 58% of offspring. Exposure of the embryo to a hyperglycemic environment leads to oxidative stress. Reactive oxygen species (ROS) production results in oxidation of proteins vital for heart development, such as endothelial nitric oxide synthase (eNOS). Activity of eNOS is down‐regulated in diabetes as it becomes uncoupled, and its cofactors are oxidized, leading to decreased nitric oxide production and increased superoxide formation.Tetrahydrobiopterin (BH4) is a principal co‐factor required for eNOS dimer stabilization, and is an endogenous antioxidant. In states of oxidative stress, BH4 is itself oxidized leading to eNOS uncoupling. Treatment with BH4 has been shown to recouple eNOS and improve vascular endothelial function in diabetes. The aim of this study was to investigate the effects of BH4 on fetal heart development in mice with pregestational diabetes.Pregestational diabetes was induced by administering streptozotocin (STZ, 75 mg/kg, IP for 3 days) to adult female C57BL/6 mice. BH4 (Kuvan 10 mg/kg/day) was orally administered to the pregnant females via dissolution in peanut butter. Diabetic pregnant mice without BH4 treatment served as controls. Embryos were collected at E18.5 for histological analysis of cardiac morphology and coronary artery formation. Our data show that pregestational diabetes resulted in a spectrum of CHDs including atrial septal defect (ASD), ventricular septal defects (VSD), atrioventricular septal defect (AVSD), and double outlet right ventricle (DORV). Maternal diabetes also resulted in coronary artery malformations, including decreased left and right main coronary artery diameter, artery abundance, and smooth muscle content. Notably, BH4 treatment significantly decreased the incidence of CHDs from 59.4 to 26.7% and abrogated major CHDs such as VSD, AVSD and DORV. BH4 treatment also rescued coronary artery malformations.Furthermore, lineage tracing was performed with a global double fluorescent Mef2C‐Cre;mT/mG mouse, where anterior second heart field (SHF) progenitors are labeled with GFP. Fate mapping revealed significantly reduced numbers of GFP+ SHF progenitors contributing to the outflow tract cushions at E9.5, endocardial cushions at E12.5 and ventricular walls at E12.5, indicating defects in proliferation, migration and myocardialization induced by maternal diabetes. Finally, western blot analysis revealed low eNOS dimer to monomer ratio in the STZ‐induced diabetic E12.5 ventricles; this was reversed by BH4 treatment. These results suggest that eNOS uncoupling may be responsible for decreased SHF progenitor cell recruitment, thereby causing the CHDs observed.In conclusion, eNOS uncoupling contributes to the development of CHDs induced by pregestational diabetes in mice. BH4 treatment recouples eNOS and prevents CHDs, implicating it as a therapeutic target for the potential prevention of CHDs caused by pregestational diabetes in patients.Support or Funding InformationThis study was supported by an operating grant from the Canadian Institutes of Health Research (CIHR) to Q.F. (grant #MOP‐119600)