Temporal metabolomics state in pregnant rat: Analysis of amniotic fluid, placenta, and maternal plasma at embryonic and fetal time points

INTRODUCTION

During pregnancy, the dynamic metabolic demands for fetal growth require a continuous supply of essential metabolites. Understanding maternal metabolome changes during gestation is crucial for predicting disease risks in neonates.

METHODS

The study aimed to characterize the placental and amniotic fluid (AF) metabolomes during gestation in rats at gestational days GD-13 and 19 reflecting the end of the embryonic and fetal periods, respectively, and the maternal plasma, using metabolomics (LC-MS) and chemometrics. The objective was to highlight, through univariate and multivariate analyses, the complementarity of the data obtained from these different biological matrices.

RESULTS

The biological matrix had more impact on the metabolome composition than the gestational stage. The placental and AF metabolomes showed specific metabolome evolving over the two gestational stages. Analyzing the three targeted metabolomes revealed evolving pathways in arginine and proline metabolism/glutathione metabolism and phenylalanine metabolism; purine metabolism; and carbohydrate metabolism. Significantly, lipid metabolism in the placenta exhibited substantial changes with higher levels of certain phosphatidylethanolamine and sphingomyelins at GD19 while some cholesteryl esters and some glycosphingolipids levels being in higher levels at GD13.

DISCUSSION

These data highlight the metabolic gradients (mainly in placenta, also in AF, but only a few in plasma) observed through embryonic patterning and organ development during mid-to late gestation.

Maternal Rat Metabolomics: Amniotic Fluid and Placental Metabolic Profiling Workflows

Studying the metabolome of specific gestational compartments is of growing interest in the context of fetus developmental disorders. However, the metabolomes of the placenta and amniotic fluid (AF) are poorly characterized. Therefore, we present the validation of a fingerprinting methodology. Using pregnant rats, we performed exhaustive and robust extractions of metabolites in the AF and lipids and more polar metabolites in the placenta. For the AF, we compared the extraction capabilities of methanol (MeOH), acetonitrile (ACN), and a mixture of both. For the placenta, we compared (i) the extraction capabilities of dichloromethane, methyl t-butyl ether (MTBE), and butanol, along with (ii) the impact of lyophilization of the placental tissue. Analyses were performed on a C18 and hydrophilic interaction liquid chromatography combined with high-resolution mass spectrometry. The efficiency and the robustness of the extractions were compared based on the number of the features or metabolites (for untargeted or targeted approach, respectively), their mean total intensity, and their coefficient of variation (% CV). The extraction capabilities of MeOH and ACN on the AF metabolome were equivalent. Lyophilization also had no significant impact and usefulness on the placental tissue metabolome profiling. Considering the placental lipidome, MTBE extraction was more informative because it allowed extraction of a slightly higher number of lipids, in higher concentration. This proof-of-concept study assessing the metabolomics and lipidomics of the AF and the placenta revealed changes in both metabolisms, at two different stages of rat gestation, and allowed a detailed prenatal metabolic fingerprinting.

OR10-1 Regulation of Glucocorticoid Metabolism: A Novel Function for Thyroid Hormones?

Glucocorticoid hormone metabolism and action are regulated by the 11-beta hydroxysteroid dehydrogenase (11βHSD) isozymes: the 11βHSD2, mostly expressed in the distal nephron, converts cortisol [F] into cortisone [E] in humans or corticosterone [B] into 11-dehydrocorticosterone [A] in rodents (11-dehydro derivatives being inactive compounds), and the 11βHSD1, ubiquitously expressed but abundant in the liver, catalyzes the opposite reaction. Under pathophysiological conditions of severe hypothyroidism, altered glucocorticoid metabolism has been observed, with decreased [F] to [E] conversion^1,2. However, direct functional relationship between these two hormonal pathways has never been demonstrated to date. Using bioinformatics analyses, we identified five thyroid hormone response elements in the promoter region of the murine hsd11b2 gene. Therefore, we aimed at investigating whether thyroid hormones (T3) directly regulate expression and/or activity of the 11βHSD2 enzyme. We used three complementary models: human and mouse translational studies and molecular analyses in HEK293T cells and in fully differentiated KC3AC1 cortical collecting duct cells. Children and adults in hypo- or hyperthyroidism status were first compared either to age- and sex-matched euthyroid controls, or to themselves after reaching a euthyroid status. The urinary [E]/[F] ratio measured by LC-MS/MS method, was used as an index of renal 11βHSD2 activity. Interestingly, a 60% decrease in the [E]/[F] ratio was observed in hypothyroid patients, corroborating our hypothesis (p<0.05). Next, a mouse model of hyperthyroidism, generated by administrating T3 in drinking water, led to a significant 10% increase in renal 11βHSD2 mRNA and protein levels compared to wild type mice (n=10, p<0.05). Furthermore, we demonstrated in HEK293T cells that T3 transactivates the mouse hsd11b2 promoter cloned upstream the luciferase reporter gene via the Thyroid Receptor α1(TRα1). Finally, we showed that T3 exposure induces a 50% increase in 11βHSD2 mRNA levels in KC3AC1 cells, in a dose-dependent and time-dependent manner (as early as 6 h) (p<0.01). This induction was abrogated by Actinomycin D or DRB, two inhibitors of transcription, underlining a transcriptional regulatory mechanism. In addition, 11βHSD2 enzymatic activity, quantified by the [F] to [E] conversion ratio measured by LC-MS/MS in cell supernatants, increased significantly by 20% (p<0.05) after 24 h exposure to 100 nM T3. ChIP experiments further demonstrated a T3-dependent specific recruitment of the TRα1 onto the hsd11b2 promoter region. Altogether, our findings constitute the first demonstration that thyroid hormones directly regulate expression and activity of the renal 11βHSD2 enzyme, thereby controlling glucocorticoid metabolism and action. References: (1) Boonen et al, NEJM, 2013; (2) Warner et al, J Endocrinol, 2010.