Placental creatine metabolism in cases of placental insufficiency and reduced fetal growth

Creatine and pregnancy outcomes: a prospective cohort study of creatine metabolism in low-risk pregnant females

BACKGROUND

Physiological adaptations during pregnancy alter nutrient and energy metabolism. Creatine may be important for maintaining cellular energy homeostasis throughout pregnancy. However, the impact of pregnancy on endogenous and exogenous creatine availability has never been comprehensively explored.

OBJECTIVES

To undertake a prospective cohort study and determine the physiological ranges of creatine and associated metabolites throughout human pregnancy.

METHODS

Females with a singleton low-risk pregnancy were recruited at an Australian health service. Maternal blood and urine were collected at 5-time points from 10-36 weeks of gestation, and cord blood and placental samples were collected at birth. Creatine and associated amino acids and metabolites of creatine synthesis were analyzed. Dietary data were captured to determine effects of exogenous creatine intake. Associations between creatine metabolism and neonatal growth parameters were examined.

RESULTS

Two hundred and eighty-two females were included. Maternal plasma creatine remained stable throughout pregnancy [β: -0.003 μM; 95% confidence interval (CI): -0.07, 0.07; P = 0.94], though urinary creatine declined in late gestation (β: 0.38 μM/mmol/L creatinine (CRN); 95% CI: -0.47, -0.29; P < 0.0001). Plasma guanidinoacetate (GAA; the precursor to creatine during endogenous synthesis) fell from 10-29 weeks of gestation before rising until birth (β: -0.38 μM/mmol/L CRN; 95% CI: -0.47, -0.29; P < 0.0001). Urinary GAA followed an opposing pattern (β: 2.52 μM/mmol/L CRN; 95% CI: 1.47, 3.58, P < 0.001). Animal protein intake was positively correlated with maternal plasma creatine until ∼32 weeks of gestation (β: 0.07-0.18 μM; 95% CI: 0.006, 0.25; P ≤ 0.001). There were no links between creatine and neonatal growth, but increased urinary GAA in early pregnancy was associated with a slight reduction in head circumference at birth (β: -0.01 cm; 95% CI: -0.02, -0.004; P = 0.003).

CONCLUSIONS

Although maternal plasma creatine concentrations were highly conserved, creatine metabolism appears to adjust throughout pregnancy. An ability to maintain creatine concentrations through diet and shifts in endogenous synthesis may impact fetal growth. This trial was registered at [registry name] as ACTRN12618001558213.

The Umbilical Cord Creatine Flux and Time Course of Human Milk Creatine across Lactation

(1) Background: The aim of the present paper was to study fetal and infant creatine (Cr) supply to improve nutrition and neuroprotection in term and especially in preterm infants. The primary outcomes were the placental Cr flux at the end of pregnancy and the time course of human milk (HM) Cr. (2) Methods: The estimation of placental Cr flux was based on umbilical arterial and venous cord blood Cr in 10 term infants after elective caesarian section. HM Cr, creatinine (Crn), and macronutrients were measured longitudinally in 10 mothers across the first 6 months of breastfeeding. (3) Results: At the end of pregnancy, the mean fetal Cr flux was negative (-2.07 mmol/min). HM Cr was highest in colostrum, decreased significantly within the first 2 weeks of breastfeeding (p < 0.05), and did not change significantly thereafter. HM Cr was not correlated with HM Crn or macronutrient composition. (4) Conclusions: The present data suggest that fetal endogenous Cr synthesis covers the needs at the end of pregnancy. However, high colostrum Cr and HM Cr levels, independent of macronutrient composition, suggest that there may be a critical Cr demand immediately after birth that needs to be covered by enteral supply.

Aspects of human uterine creatine metabolism during the menstrual cycle and at term pregnancy†

Creatine metabolism likely contributes to energy homeostasis in the human uterus, but whether this organ synthesizes creatine and whether creatine metabolism is adjusted throughout the menstrual cycle and with pregnancy are largely unknown. This study determined endometrial protein expression of creatine-synthesizing enzymes arginine:glycine amidinotransferase (AGAT) and guanidinoacetate methyltransferase (GAMT), creatine kinase (CKBB), and the creatine transporter (SLC6A8) throughout the menstrual cycle in fertile and primary infertile women. It also characterized creatine metabolism at term pregnancy, measuring aspects of creatine metabolism in myometrial and decidual tissue. In endometrial samples, AGAT, GAMT, SLC6A8, and CKBB were expressed in glandular and luminal epithelial cells. Except for SLC6A8, the other proteins were also located in stromal cells. Irrespective of fertility, AGAT, GAMT, and SLC6A8 high-intensity immunohistochemical staining was greatest in the early secretory phase of the menstrual cycle. During the proliferative phase, staining for SLC6A8 protein was greater (P = 0.01) in the primary infertile compared with the fertile group. Both layers of the term pregnant uterus contained creatine, phosphocreatine, guanidinoacetic acid, arginine, glycine, and methionine; detectable gene and protein expression of AGAT, GAMT, CKBB, and ubiquitous mitochondrial CK (uMt-CK); and gene expression of SLC6A8. The proteins AGAT, GAMT, CKBB, and SLC6A8 were uniformly distributed in the myometrium and localized to the decidual glands. In conclusion, endometrial tissue has the capacity to produce creatine and its capacity is highest around the time of fertilization and implantation. Both layers of the term pregnant uterus also contained all the enzymatic machinery and substrates of creatine metabolism.

Identifying placental metabolic biomarkers of preterm birth using nuclear magnetic resonance of intact tissue samples

INTRODUCTION

Our understanding of the etiology of preterm birth (PTB) is incomplete; however, recent evidence has found a strong association between placental dysfunction and PTB. Altered placental metabolism may precede placental dysfunction and therefore the study of placental metabolic profiles could identify early biomarkers of PTB. In this study, we evaluated the placental metabolome in PTB in intact tissue samples using nuclear magnetic resonance (NMR) and spectral editing.

METHODS

Placental tissue samples were collected from nine term pregnancies and nine preterm pregnancies (<37 weeks' gestation). 1H NMR experiments on unprocessed tissue samples were performed using a high field magnet (500 MHz spectrometer) and a comprehensive multiphase NMR probe. The relative concentrations of 23 metabolites were corrected for gestational age and compared between groups.

RESULTS

The relative concentration of valine, glutamate and creatine were significantly decreased while alanine, choline and glucose were elevated in placentas from PTB pregnancies compared to controls (p < 0.05). Multivariate analysis using principal component analysis showed the PTB and control groups were significantly separated (p < 0.0001) and pathway analysis identified perturbations in the glycine, serine and threonine metabolism, aminoacyl-tRNA biosynthesis and valine, leucine and isoleucine biosynthesis pathways.

CONCLUSION

PTB is associated with significant alterations in placental metabolism. This study helps improve our understanding of the etiology of PTB. It also highlights the potential for small molecule metabolites to serve as placental metabolic biomarkers to aid in the prediction and diagnosis of PTB. The results can be translated to clinical use via in utero magnetic resonance spectroscopy.

Placental, Foetal, and Maternal Serum Metabolomic Profiles in Pregnancy-Associated Cancer: Walker-256 Tumour Model in a Time-Course Analysis

Cancer during pregnancy presents a delicate coexistence, imposing ethical and professional challenges on both the patient and medical team. In this study, we aimed to explore in a pre-clinical model the impact of tumour evolution in serum, placental and foetal metabolomics profiles during pregnancy in a time-course manner. Pregnant Wistar rats were distributed into two experimental groups: Control (C) and Walker-256 tumour-bearing (W). The rats were euthanised on three different gestational periods: at 12 days post-conception (dpc), at 16 dpc, and at 19 dpc. Serum, placenta and foetal metabolomic profiles were performed by 1H-NMR spectra following the analyses using Chenomx NMR Analysis Software V8.3. The tumour evolution was exponential, affecting the placental metabolomic profile during all the pregnancy stages. The placental tissue in tumour-bearing dams developed at a lower speed, decreasing the foetus's weight. Associated with the serum metabolomic changes related to tumour growth, the placental metabolomic alterations impacted many metabolic pathways related to energy provision, protein synthesis and signalling, which directly harmed the foetus's development. The development of the foetus is clearly affected by the damage induced by the tumour evolution, which alters the metabolic profile of both the serum and the placenta, impairing early embryonic development.

Creatine metabolism at the uterine-placental interface throughout gestation in sheep†

The placenta requires high levels of adenosine triphosphate to maintain a metabolically active state throughout gestation. The creatine-creatine kinase-phosphocreatine system is known to buffer adenosine triphosphate levels; however, the role(s) creatine-creatine kinase-phosphocreatine system plays in uterine and placental metabolism throughout gestation is poorly understood. In this study, Suffolk ewes were ovariohysterectomized on Days 30, 50, 70, 90, 110 and 125 of gestation (n = 3-5 ewes/per day, except n = 2 on Day 50) and uterine and placental tissues subjected to analyses to measure metabolites, mRNAs, and proteins related to the creatine-creatine kinase-phosphocreatine system. Day of gestation affected concentrations and total amounts of guanidinoacetate and creatine in maternal plasma, amniotic fluid and allantoic fluid (P < 0.05). Expression of mRNAs for arginine:glycine amidinotransferase, guanidinoacetate methyltransferase, creatine kinase B, and solute carrier 16A12 in endometria and for arginine:glycine amidinotransferase and creatine kinase B in placentomes changed significantly across days of gestation (P < 0.05). The arginine:glycine amidinotransferase protein was more abundant in uterine luminal epithelium on Days 90 and 125 compared to Days 30 and 50 (P < 0.01). The chorionic epithelium of placentomes expressed guanidinoacetate methyltransferase and solute carrier 6A13 throughout gestation. Creatine transporter (solute carrier 6A8) was expressed by the uterine luminal epithelium and trophectoderm of placentomes throughout gestation. Creatine kinase (creatine kinase B and CKMT1) proteins were localized primarily to the uterine luminal epithelium and to the placental chorionic epithelium of placentomes throughout gestation. Collectively, these results demonstrate cell-specific and temporal regulation of components of the creatine-creatine kinase-phosphocreatine system that likely influence energy homeostasis for fetal-placental development.

Reprogramming alternative macrophage polarization by GATM-mediated endogenous creatine synthesis: A potential target for HDM-induced asthma treatment

Cellular energy metabolism plays a crucial role in the regulation of macrophage polarization and in the execution of immune functions. A recent study showed that Slc6a8-mediated creatine uptake from exogenous supplementation modulates macrophage polarization, yet little is known about the role of the de novo creatine de novobiosynthesis pathway in macrophage polarization. Here, we observed that glycine amidinotransferase (GATM), the rate-limiting enzyme for creatine synthesis, was upregulated in alternative (M2) polarized macrophages, and was dependent on the transcriptional factor STAT6, whereas GATM expression was suppressed in the classical polarized (M1) macrophage. Next, we revealed that exogenous creatine supplementation enhanced IL-4-induced M2 polarization, confirming recent work. Furthermore, we revealed that genetic ablation of GATM did not affect expression of M1 marker genes (Nos2, IL1b, IL12b) or the production of nitric oxide in both peritoneal macrophages (PMs) and bone marrow-derived macrophages (BMDMs). By contrast, expression levels of M2 markers (Arg1, Mrc1, Ccl17 and Retnla) were lower following GATM deletion. Moreover, we found that deletion of GATM in resident alveolar macrophages (AMs) significantly blocked M2 polarization but with no obvious effect on the number of cells in knockout mice. Lastly, an upregulation of GATM was found in lung tissue and bronchoalveolar lavage fluid macrophages from HDM-induced asthmatic mice. Our study uncovers a previously uncharacterized role for the de novo creatine biosynthesis enzyme GATM in M2 macrophage polarization, which may be involved in the pathogenesis of related inflammatory diseases such as an T helper 2 (Th2)-associated allergic asthma.

Reprogramming alternative macrophage polarization by GATM-mediated endogenous creatine synthesis: A potential target for HDM-induced asthma treatment

Cellular energy metabolism plays a crucial role in the regulation of macrophage polarization and in the execution of immune functions. A recent study showed that Slc6a8-mediated creatine uptake from exogenous supplementation modulates macrophage polarization, yet little is known about the role of the de novo creatine de novobiosynthesis pathway in macrophage polarization. Here, we observed that glycine amidinotransferase (GATM), the rate-limiting enzyme for creatine synthesis, was upregulated in alternative (M2) polarized macrophages, and was dependent on the transcriptional factor STAT6, whereas GATM expression was suppressed in the classical polarized (M1) macrophage. Next, we revealed that exogenous creatine supplementation enhanced IL-4-induced M2 polarization, confirming recent work. Furthermore, we revealed that genetic ablation of GATM did not affect expression of M1 marker genes (Nos2, IL1b, IL12b) or the production of nitric oxide in both peritoneal macrophages (PMs) and bone marrow-derived macrophages (BMDMs). By contrast, expression levels of M2 markers (Arg1, Mrc1, Ccl17 and Retnla) were lower following GATM deletion. Moreover, we found that deletion of GATM in resident alveolar macrophages (AMs) significantly blocked M2 polarization but with no obvious effect on the number of cells in knockout mice. Lastly, an upregulation of GATM was found in lung tissue and bronchoalveolar lavage fluid macrophages from HDM-induced asthmatic mice. Our study uncovers a previously uncharacterized role for the de novo creatine biosynthesis enzyme GATM in M2 macrophage polarization, which may be involved in the pathogenesis of related inflammatory diseases such as an T helper 2 (Th2)-associated allergic asthma.

A remarkable rodent: Regeneration and reproduction in spiny mice (Acomys)

Although certain organisms are chosen and employed to better understand a specific problem in biology (so-called model organisms), sometimes an animal model reveals its' biomedical importance by happenstance. In many ways, the advent of spiny mice (Acomys) as an emerging model to study regeneration and menstruation stands as a case study in scientific pseudoserendipity (Diaz de Chumaceiro, 1995). As we recount in this chapter, the discovery of these phenotypes, while not entirely accidental, was nonetheless unexpected. In addition to recounting how we uncovered these unusual mammalian traits, we outline recent work by our groups and others that has begun to outline the cellular and genetic mechanisms underlying bonafide mammalian tissue regeneration and a human-like mode of reproduction in spiny mice.

The Effects of In Utero Fetal Hypoxia and Creatine Treatment on Mitochondrial Function in the Late Gestation Fetal Sheep Brain

Near-term acute hypoxia in utero can result in significant fetal brain injury, with some brain regions more vulnerable than others. As mitochondrial dysfunction is an underlying feature of the injury cascade following hypoxia, this study is aimed at characterizing mitochondrial function at a region-specific level in the near-term fetal brain after a period of acute hypoxia. We hypothesized that regional differences in mitochondrial function would be evident, and that prophylactic creatine treatment would mitigate mitochondrial dysfunction following hypoxia; thereby reducing fetal brain injury. Pregnant Border-Leicester/Merino ewes with singleton fetuses were surgically instrumented at 118 days of gestation (dGa; term is ~145 dGA). A continuous infusion of either creatine (n = 15; 6 mg/kg/h) or isovolumetric saline (n = 16; 1.5 ml/kg/h) was administered to the fetuses from 121 dGa. After 10 days of infusion, a subset of fetuses (8 saline-, 7 creatine-treated) were subjected to 10 minutes of umbilical cord occlusion (UCO) to induce a mild global fetal hypoxia. At 72 hours after UCO, the fetal brain was collected for high-resolution mitochondrial respirometry and molecular and histological analyses. The results show that the transient UCO-induced acute hypoxia impaired mitochondrial function in the hippocampus and the periventricular white matter and increased the incidence of cell death in the hippocampus. Creatine treatment did not rectify the changes in mitochondrial respiration associated with hypoxia, but there was a negative relationship between cell death and creatine content following treatment. Irrespective of UCO, creatine increased the proportion of cytochrome c bound to the inner mitochondrial membrane, upregulated the mRNA expression of the antiapoptotic gene Bcl2, and of PCG1-α, a driver of mitogenesis, in the hippocampus. We conclude that creatine treatment prior to brief, acute hypoxia does not fundamentally modify mitochondrial respiratory function, but may improve mitochondrial structural integrity and potentially increase mitogenesis and activity of antiapoptotic pathways.

The physiological effects of creatine supplementation in fetal sheep before, during and after umbilical cord occlusion and global hypoxia

The aim of this study was to investigate the effects of direct creatine infusion on fetal systemic metabolic and cardiovascular responses to mild acute in utero hypoxia. Pregnant ewes (n=28) were surgically instrumented at 118 days gestation (dGa). A constant intravenous infusion of creatine (6 mg.kg^-1.h^-1) or isovolumetric saline (1.5 ml.h^-1) began at 121 dGa. After 10 days, fetuses were subjected to 10-minute umbilical cord occlusion (UCO) to induce mild global hypoxia (saline-UCO, n=8; creatine-UCO, n=7) or sham UCO (saline-control, n=6; creatine-control, n=7). Cardiovascular, arterial blood gases and metabolites, and plasma creatine were monitored prior to, during, and then for 72 hours following the UCO. Total creatine content in discrete fetal brain regions was also measured. Fetal creatine infusion increased plasma concentrations 5-fold but had no significant effects on any measurement pre-UCO. Creatine did not alter fetal physiology during the UCO or in the early recovery stage, up to 24 hours after UCO. During the late recovery stage, 24-72 hours after UCO, there was a significant reduction in the arterial oxygen pressure and saturation in creatine fetuses (P_{UCO x TREATMENT} = 0.02 and0.04, respectively). At 72 hours after UCO, significant creatine loading was detected in cortical grey matter, hippocampus, thalamus and striatum (P_TREATMENT = 0.01-0.001). In the striatum, the UCO itself increased total creatine content (P_UCO = 0.019). Overall, fetal creatine supplementation may alter oxygen flux following an acute hypoxic insult. Increasing total creatine content in the striatum may also be a fetal adaptation to acute oxygen deprivation.

Creatine Metabolism in Female Reproduction, Pregnancy and Newborn Health

Creatine metabolism is an important component of cellular energy homeostasis. Via the creatine kinase circuit, creatine derived from our diet or synthesized endogenously provides spatial and temporal maintenance of intracellular adenosine triphosphate (ATP) production; this is particularly important for cells with high or fluctuating energy demands. The use of this circuit by tissues within the female reproductive system, as well as the placenta and the developing fetus during pregnancy is apparent throughout the literature, with some studies linking perturbations in creatine metabolism to reduced fertility and poor pregnancy outcomes. Maternal dietary creatine supplementation during pregnancy as a safeguard against hypoxia-induced perinatal injury, particularly that of the brain, has also been widely studied in pre-clinical in vitro and small animal models. However, there is still no consensus on whether creatine is essential for successful reproduction. This review consolidates the available literature on creatine metabolism in female reproduction, pregnancy and the early neonatal period. Creatine metabolism is discussed in relation to cellular bioenergetics and de novo synthesis, as well as the potential to use dietary creatine in a reproductive setting. We highlight the apparent knowledge gaps and the research “road forward” to understand, and then utilize, creatine to improve reproductive health and perinatal outcomes.

NLRP3 Inflammasome and Its Critical Role in Gynecological Disorders and Obstetrical Complications

Inflammasomes, intracellular, multimeric protein complexes, are assembled when damage signals stimulate nucleotide-binding oligomerization domain receptors (NLRs). Several inflammasomes have been reported, including the NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3), NLRP1, NLRP7, ice protease-activating factor (IPAF), absent in melanoma 2 (AIM2) and NLR family CARD domain-containing protein 4 (NLRC4). Among these inflammasomes, the NLRP3 inflammasome is the most well-studied in terms of structure and function. Unlike other inflammasomes that can only be activated by a finite number of pathogenic microorganisms, the NLRP3 inflammasome can be activated by the imbalance of the internal environment and a large number of metabolites. The biochemical function of NLRP3 inflammasome is to activate cysteine-requiring aspartate proteinase-1 (caspase-1), which converts pro-IL-1β and pro-IL-18 into their active forms, namely, IL-1β and IL-18, which are then released into the extracellular space. The well-established, classic role of NLRP3 inflammasome has been implicated in many disorders. In this review, we discuss the current understanding of NLRP3 inflammasome and its critical role in gynecological disorders and obstetrical complications.

Increased creatine demand during pregnancy in Arginine: Glycine Amidino-Transferase deficiency: a case report

Background

Creatine (Cr), an amino acid derivative, is one of the most important sources of energy acting as both a spatial and temporal energy buffer through its phosphorylated analogue phosphocreatine (PCr) and creatine kinase (CK). Maternal Cr biosynthesis and metabolism seem to play an important role in pregnancy, as shown in preclinical and in healthy human pregnancy studies. Patients with Arginine:Glycine Amidino-Transferase deficiency (AGAT-d), due to the deficit of the first enzyme involved in Cr synthesis, are at a disadvantage due to their failure to synthesize Cr and their dependence on external intake, in contrast to normal subjects, where changes in Cr biosynthesis supply their needs.

We report the outcomes of a pregnancy in an AGAT-d woman, and the challenge we faced in managing her treatment with oral Cr to ensure optimal conditions for her fetus.

Case presentation

A 22-year-old AGAT-d woman referred to our Institute for the management of her first conception at 11 weeks of fetal gestational age. Sonographic monitoring at 20 w GA indicated a reduction of fetal growth, in particular of the head circumference that was below the 3^rd centile. Biochemical monitoring of Cr in biological fluids of the mother revealed a decline of the Cr concentrations, in particular in the urine sample, requiring prompt correction of the Cr dose. At 35 weeks of gestation the patient delivered a male infant, heterozygous for GATM mutation, with normal brain Cr levels; at one year the baby achieved typical developmental milestones.

Conclusions

This rare pregnancy demonstrates that Cr levels in the blood and urine of the mother with AGAT-d decreased since the first months of gestation. The increase of the Cr daily dose administered to the mother seems to have produced beneficial effects also on the fetus.

The Effects of Early-Onset Pre-Eclampsia on Placental Creatine Metabolism in the Third Trimester

Creatine is a metabolite important for cellular energy homeostasis as it provides spatio-temporal adenosine triphosphate (ATP) buffering for cells with fluctuating energy demands. Here, we examined whether placental creatine metabolism was altered in cases of early-onset pre-eclampsia (PE), a condition known to cause placental metabolic dysfunction. We studied third trimester human placentae collected between 27–40 weeks’ gestation from women with early-onset PE (n = 20) and gestation-matched normotensive control pregnancies (n = 20). Placental total creatine and creatine precursor guanidinoacetate (GAA) content were measured. mRNA expression of the creatine synthesizing enzymes arginine:glycine aminotransferase (GATM) and guanidinoacetate methyltransferase (GAMT), the creatine transporter (SLC6A8), and the creatine kinases (mitochondrial CKMT1A & cytosolic BBCK) was assessed. Placental protein levels of arginine:glycine aminotransferase (AGAT), GAMT, CKMT1A and BBCK were also determined. Key findings; total creatine content of PE placentae was 38% higher than controls (p < 0.01). mRNA expression of GATM (p < 0.001), GAMT (p < 0.001), SLC6A8 (p = 0.021) and BBCK (p < 0.001) was also elevated in PE placentae. No differences in GAA content, nor protein levels of AGAT, GAMT, BBCK or CKMT1A were observed between cohorts. Advancing gestation and birth weight were associated with a down-regulation in placental GATM mRNA expression, and a reduction in GAA content, in control placentae. These relationships were absent in PE cases. Our results suggest PE placentae may have an ongoing reliance on the creatine kinase circuit for maintenance of cellular energetics with increased total creatine content and transcriptional changes to creatine synthesizing enzymes and the creatine transporter. Understanding the functional consequences of these changes warrants further investigation.