Phosphorus 31 magnetic resonance spectroscopy of perifused human placental villi under varying oxygen concentrations

Glycolysis: A fork in the path of normal and pathological pregnancy

Glucose metabolism is vital to the survival of living organisms. Since the discovery of the Warburg effect in the 1920s, glycolysis has become a major research area in the field of metabolism. Glycolysis has been extensively studied in the field of cancer and is considered as a promising therapeutic target. However, research on the role of glycolysis in pregnancy is limited. Recent evidence suggests that blastocysts, trophoblasts, decidua, and tumors all acquire metabolic energy at specific stages in a highly similar manner. Glycolysis, carefully controlled throughout pregnancy, maintains a dynamic and coordinated state, so as to maintain the homeostasis of the maternal-fetal interface and ensure normal gestation. In the present review, we investigate metabolic remodeling and the selective propensity of the embryo and placenta for glycolysis. We then address dysregulated glycolysis that occurs in the cellular interactive network at the maternal-fetal interface in miscarriage, preeclampsia, fetal growth restriction, and gestational diabetes mellitus. We provide new insights into the field of maternal-fetal medicine from a metabolic perspective, thus revealing the mystery of human pregnancy.

Assessment of prenatal cerebral and cardiac metabolic changes in a rabbit model of fetal growth restriction based on 13C-labelled substrate infusions and ex vivo multinuclear HRMAS

BACKGROUND

We have used a previously reported rabbit model of fetal growth restriction (FGR), reproducing perinatal neurodevelopmental and cardiovascular impairments, to investigate the main relative changes in cerebral and cardiac metabolism of term FGR fetuses during nutrient infusion.

METHODS

FGR was induced in 9 pregnant New Zealand rabbits at 25 days of gestation: one horn used as FGR, by partial ligation of uteroplacental vessels, and the contralateral as control (appropriate for gestation age, AGA). At 30 days of gestation, fasted mothers under anesthesia were infused i.v. with 1-13C-glucose (4 mothers), 2-13C-acetate (3 mothers), or not infused (2 mothers). Fetal brain and heart samples were quickly harvested and frozen down. Brain cortex and heart apex regions from 30 fetuses were studied ex vivo by HRMAS at 4°C, acquiring multinuclear 1D and 2D spectra. The data were processed, quantified by peak deconvolution or integration, and normalized to sample weight.

RESULTS

Most of the total 13C-labeling reaching the fetal brains/hearts (80-90%) was incorporated to alanine and lactate (cytosol), and to the glutamine-glutamate pool (mitochondria). Acetate-derived lactate (Lac C2C3) had a slower turnover in FGR brains (~ -20%). In FGR hearts, mitochondrial turnover of acetate-derived glutamine (Gln C4) was slower (-23%) and there was a stronger accumulation of phospholipid breakdown products (glycerophosphoethanolamine and glycerophosphocholine, +50%), resembling the profile of non-infused control hearts.

CONCLUSIONS

Our results indicate specific functional changes in cerebral and cardiac metabolism of FGR fetuses under nutrient infusion, suggesting glial impairment and restricted mitochondrial metabolism concomitant with slower cell membrane turnover in cardiomyocytes, respectively. These prenatal metabolic changes underlie neurodevelopmental and cardiovascular problems observed in this FGR model and in clinical patients, paving the way for future studies aimed at evaluating metabolic function postnatally and in response to stress and/or treatment.

In vivo ³¹P-MR spectroscopy in normal pregnancy, early and late preeclampsia: a study of placental metabolism

INTRODUCTION

Preeclampsia affects about 3% of pregnancies and the placenta is believed to play a major role in its pathophysiology. Lately, the role of the placenta has been hypothesised to be more pronounced in preeclampsia of early (<34 weeks) rather than late (≥ 34 weeks) onset. (31)P Magnetic Resonance Spectroscopy (MRS) enables non-invasive, in vivo studies of placental metabolism. Our aim was to study placental energy and membrane metabolism in women with normal pregnancies and those with early and late onset preeclampsia.

METHODS

The study population included fourteen women with preeclampsia (five with early onset and nine with late onset preeclampsia) and sixteen women with normal pregnancy (seven with early and nine with late pregnancy). All women underwent a (31)P-MRS examination of the placenta.

RESULTS

The phosphodiester (PDE) spectral intensity fraction of the total (31)P signal and the phosphodiester/phosphomonoester (PDE/PME) spectral intensity ratio was higher in early onset preeclampsia than in early normal pregnancy (p = 0.03 and p = 0.02). In normal pregnancy the PDE spectral intensity fraction and the PDE/PME spectral intensity ratio increased with increasing gestational age (p = 0.006 and p = 0.001).

DISCUSSION

Since PDE and PME are related to cell membrane degradation and formation, respectively, our findings indicate increased cell degradation and maybe also decreased cell proliferation in early onset preeclampsia compared to early normal pregnancy, and with increasing gestational age in normal pregnancy.

CONCLUSIONS

Our findings could be explained by increased apoptosis due to ischaemia in early onset preeclampsia and also increased apoptosis with increasing gestational age in normal pregnancy.

Hypoxia and Lactate Production in Trophoblast Cells

The etiology of preeclampsia is unknown but is thought to be related to hypoxia in the placenta. We previously reported that the enzyme lactate dehydrogenase (LDH) has increased activity and gene expression in placentas from preeclamptic pregnancies [Tsoi SCM, Zheng J, Xu F, Kay HH. Differential expression of lactate dehydrogenase isozymes (LDH) in human placenta with high expression of LDH-A(4) isozyme in the endothelial cells of pre-eclampsia villi. Placenta 2001;22:317-22]. LDH is responsible for pyruvate conversion to lactate through glycolysis. In this study, we further investigated the role of hypoxia in primary trophoblast cells and a cultured cell line, JEG3 cells, to obtain a better understanding of how it affects the activities of lactate dehydrogenase, lactate production and regulatory genes, as a possible model for preeclampsia. Primary trophoblast cells and JEG3 cells were cultured under 1% oxygen. At 6, 12 and 24h, cells were analyzed for LDHA and LDHB isozyme activities, mRNA and protein expression compared to standard culture conditions. Lactate was measured from cell medium. The hypoxia inducible transcription factor (HIF-1alpha) protein expression was confirmed by western blot. Two lactate transporters (MCT1 and MCT4) mRNA and protein expression were also studied under hypoxia. Finally, lactate was measured in plasma obtained from patients with severe preeclampsia. Under hypoxic conditions, LDHA mRNA is increased in primary trophoblast cells and JEG3 cells. The HIF-1alpha protein expression is higher in hypoxia-treated JEG3 cells than control. LDHA isozyme activity and its protein expression are increased most significantly at 24h of culture under hypoxia. However, LDHB protein is unchanged while its mRNA is decreased. Lactate secretion from JEG3 cells under hypoxia is increased, as is the lactate levels in the plasma from preeclampsia patients. Of the two lactate transporters studied, MCT4 mRNA and protein level are increased under hypoxia. Our findings support the role of hypoxia in inducing HIF-1alpha activity in trophoblasts and increasing LDH transcription as well as its activity. Higher levels of lactate are produced and secreted which may contribute to the higher lactate levels in plasma of preeclamptic patients. These mechanisms may be important in the pathophysiology of preeclampsia.

Metabolite concentrations in human term placentae and their changes due to delayed collection after delivery

The present study was designed to quantify the major cellular metabolites in human placentae and their changes due to the confounding effect of time and subsequent hypoxia during sample collection using magnetic resonance spectroscopy ((1)H-and (31)P-MRS). The absolute placental concentrations of lactate, glucose, major amino acids and cellular volume/osmo-regulators, glutathione, high-energy phosphates, fatty acids, phospholipids, triglycerols, and cholesterol are reported. There were no spatial differences in metabolism or protein expression throughout the placenta. The most significant temporal changes, due to the collection time (from 1 to 25 min after delivery), were increased concentrations of lactate (r=0.996, statistically significant P< 0.01 after 11 min) and decreased concentration of glucose and ATP (r=-0.963 and -0.97, respectively, P< 0.01 after 11 min). The placental samples from the later collection groups (16-24 min) had also significantly lower level of NAD(+) (r=-0.95, P< 0.01). Only the latest collection group (21-24 min) had increased lipid peroxidation and changes in lipid metabolites (P< 0.01). We conclude that the optimal window for collecting placental tissue without incurring metabolic artifacts due to hypoxic conditions is within 9 min of placental delivery.

Energy charge monitoring via magnetic resonance spectroscopy 31P in the perfused human placenta: effects of cadmium, dinitrophenol and iodoacetate

Phosphorus 31 nuclear magnetic resonance spectroscopy as a non-invasive technique was applied to monitor the metabolic activity of the human placenta during perfusion in vitro. During control perfusions (n = 3) there was an initial increase in adenosine triphosphate (ATP) and a fall in inorganic phosphate (Pi). Thereafter, however, the level of both ATP and Pi remained constant throughout the perfusion period (11 h). Additional biochemical parameters such as glucose consumption, lactate production and the release of hormones, human chorionic gonadotrophin (hGC). measured in the perfusate samples, were also used to assess the viability of the placental tissue. As with ATP, all these biochemical parameters under the control conditions showed a stable rate of metabolic activity throughout the length of the experiments. In additional experiments, the effect of the metabolic inhibitor dinitrophenol (n = 2) and dinitrophenol (DNP) together with iodoacetic acid (IOA, n = 2) were studied. DNP (0.1 mM) alone showed a slight decrease of all parameters. In contrast, the addition of IOA (0.1 mM) with DNP (0.1 mM) not only blocked the production of ATP but also produced a substantial impact on placental metabolic activity. The effect of a toxic dose of cadmium (20 nmol/ml) was studied also (n = 3). This dose of cadmium demonstrated no effect on phosphorus metabolism. However, the rate of glucose consumption and the release of hCG were significantly reduced.