Study on amniotic fluid metabolism in the second trimester of Trisomy 21

Non-Invasive Prenatal Screening for Down Syndrome: A Review of Mass-Spectrometry-Based Approaches

Down Syndrome or Trisomy 21 (T21) is a complex genetic disease characterized by the presence of an extra chromosome 21, which leads to multiple clinical features and manifestations that severely affect the patient's quality of life. Various methods of prenatal screening have been developed over time, allowing informed decision-making. However, a common drawback of the current methods for detecting T21 is their invasive nature. Over the past years, mass-spectrometry-based omics technologies have become a key tool for discovering biomarkers for the prenatal screening of T21, particularly focusing on proteins, peptide sequences, or metabolites in samples, like amniotic fluid, umbilical cord blood, and others. Recently, there has been a noticeable shift towards using less invasive biological sample types (e.g., maternal serum, plasma, and urine) reflecting a growing interest in non-invasive methods for prenatal screening. These advances aim to improve the sensitivity and accuracy for T21 detection while reducing the risks associated with more invasive procedures. The first section of this paper offers an in-depth review of studies utilizing mass-spectrometry-based omics for the prenatal screening of T21. This part provides an overview of the methodologies employed and their key findings. Instead, the subsequent section offers a comprehensive examination of the differentially expressed proteins (DEPs) and metabolites (DEMs) reported in the literature in T21 prenatal screening. Additionally, pathway analysis is carried out to explore the biological pathways that these molecules are involved in and how they relate to the clinical features of the syndrome. These findings aim to guide future research in the field and foster the development of more advanced, less invasive prenatal screening techniques for T21.

Screening and Predictive Biomarkers for Down Syndrome Through Amniotic Fluid Metabolomics

BACKGROUND

Down syndrome (DS) is a congenital disorder caused by the presence of an extra copy of all or part of chromosome 21. It is characterized by significant intellectual disability, distinct facial features, and growth and developmental challenges. The utilization of metabolomics to analyze specific metabolic markers in maternal amniotic fluid may provide innovative tools and screening methods for investigating the early pathophysiology of trisomy 21 at the functional level.

METHODS

Amniotic fluid samples were obtained via amniocentesis from 57 pregnancies with DS and 55 control pregnancies between 173/7 and 240/7 weeks of gestation. The targeted metabolomics focused on 34 organic acids, 17 amino acids, and 5 acylcarnitine metabolites. The untargeted metabolomics analysis concentrated on lipid profiles and included 602 metabolites that met quality control standards. Principal Component Analysis, Orthogonal Partial Least Squares Discriminant Analysis (OPLS-DA), and false discovery rate (FDR) adjustments were applied. MetaboAnalystR 5.0 was used to perform the metabolic pathway analysis on the identified differential metabolites.

RESULTS

Fifty differential metabolites, including L-glutamine, eight organic acids, and 41 lipids, were significantly altered in DS based on three criteria: VIP > 1 in the OPLS-DA model, FDR-adjusted p-value < 0.05, and |log2FC| > log2(1.5) from a volcano plot of all detected metabolites. An analysis of 212 differential metabolites, selected from both targeted and untargeted approaches (VIP > 1 in the OPLS-DA model and FDR-adjusted p-value < 0.05), revealed significant changes in nine metabolic pathways. Fourteen key metabolites were identified to establish a screening model for DS, achieving an area under the curve of 1.00.

CONCLUSIONS

Our results underscore the potential of metabolomics approaches in identifying concise and reliable biomarker combinations that demonstrate promising screening performance in DS.

Metabolic pathways for glucose and fructose: I synthesis and metabolism of fructose by ovine conceptuses†

Fructose, the most abundant hexose sugar in fetal fluids and the blood of sheep and other ungulates and cetaceans, is synthesized from glucose via the polyol pathway in trophectoderm and chorion. However, the cell-specific and temporal expression of enzymes for the synthesis and metabolism of fructose in sheep conceptuses (embryo and placental membranes) and placentomes has not been characterized. This study characterized key enzymes involved in fructose synthesis and metabolism by ovine conceptuses throughout pregnancy. Day 17 conceptuses expressed mRNAs for the polyol pathway (SORD and AKR1B1) and glucose and fructose metabolism (HK1, HK2, G6PD, OGT, and FBP), but not those required for gluconeogenesis (G6Pase or PCK). Ovine placentomes also expressed mRNAs for SORD, AKR1B1, HK1, and OGT. Fructose can be metabolized via the ketohexokinase (KHK) pathway, and isoforms, KHK-A and KHK-C, were expressed in ovine conceptuses from Day 16 of pregnancy and placentomes during pregnancy in a cell-specific manner. The KHK-A protein was more abundant in the trophectoderm and cotyledons of placentomes, while KHK-C protein was more abundant in the endoderm of Day 16 conceptuses and the chorionic epithelium in placentomes. Expression of KHK mRNAs in placentomes was greatest at Day 30 of pregnancy (P < 0.05), but not different among days later in gestation. These results provide novel insights into the synthesis and metabolism of fructose via the uninhibited KHK pathway in ovine conceptuses to generate ATP via the tricarboxylic cycle, as well as substrates for the pentose cycle, hexosamine biosynthesis pathway, and one-carbon metabolism required for conceptus development throughout pregnancy.

Study on amniotic fluid metabolism in the second trimester of Trisomy 21

BACKGROUND

Trisomy 21 is a common aneuploid condition in humans and accounts for approximately one quarter of all aneuploid live births. To date, early diagnosis of Trisomy 21 remains a challenging task. Metabolomics may prove an innovative tool to study the early pathophysiology of Trisomy 21 at a functional level.

METHODS

Ultra-performance liquid chromatography coupled with mass spectrometer (UPLC-MS) was used for untargeted metabolomic analysis of amniotic fluid samples from women having normal and trisomy 21 fetuses.

RESULTS

Many significantly changed metabolites were identified between amniotic fluid samples from Trisomy 21 pregnancies and normal euploid pregnancies, such as generally lower levels of several steroid hormones and their derivatives, higher levels of glutathione catabolites coupled with lower levels of gamma-glutamyl amino acids, and increased levels of phospholipid catabolites, sugars, and dicarboxylic acids. The identification of a human milk oligosaccharide in amniotic fluid may worth further investigation, since confirmation of this observation may have significant implications for regulation of fetal development.

CONCLUSIONS

The metabolisms in amniotic fluid from Trisomy 21 and normal pregnancies are quite different, and some of the significantly changed metabolites may be considered as candidates of early diagnostic biomarkers for Trisomy 21.