- Title
- Examining the role of essential micronutrient molybdenum in placental physiology and gestational health
- Creator
- Foteva, Vladimira
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2025
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- The placenta is a transient foetal organ that acts as the interface between maternal and foetal circulation, mediating nutrient exchange, waste excretion, hormone production and protection against xenobiotic threats. During the metabolically demanding process of pregnancy, increased levels of reactive oxygen species (ROS) can overwhelm the antioxidant reserve of the placenta, resulting in oxidative stress causing DNA damage, lipid peroxidation, cell apoptosis, and loss of tissue integrity. Reduction in placental function can prove catastrophic to the developing conceptus, with placental-mediated disorders of pregnancy, such as foetal growth restriction and stillbirth, increasing the risk of morbidity and mortality in the perinatal period, and contributing to long-term adverse maternal and foetal health outcomes. Developing cost-effective and minimally invasive strategies to support antioxidant function, and therefore placental and foetal health, are of paramount importance. Inadequate maternal nutrition is implicated in the development of placental dysfunction and subsequent gestational pathologies. Essential elements, termed micronutrients, are sourced from the diet in trace quantities, and are integral for the function of endogenous antioxidant enzymes, and promoting homeostatic function in placental tissue. An extensive body of work including in vitro, in vivo, and retrospective human studies, has linked micronutrients such as zinc, selenium and iron to placental health and positive gestational outcomes. The essential micronutrient molybdenum, however, remains understudied in this context. A transition metal with versatile chemical properties, molybdenum, in its bioactive configuration as the molybdate ion, forms the active site of several essential proteins. The molybdenum-containing enzymes are xanthine oxidase, aldehyde oxidase, sulfite oxidase, and the mitochondrial amidoxime reducing components 1 and 2, which are responsible for metabolising diverse substrates including xanthine, purines, and aldehydes. Deficiency of molybdate is lethal, but molybdenum-containing enzymes are also implicated in oxidative stress-induced pathologies due to generating reactive oxygen species in the process of their metabolic activity. This thesis therefore aims to investigate the multi-faceted physiological effects of molybdenum in the placenta and its role in gestational complications. Chapter 1 assesses the current breadth of knowledge relating molybdenum intake and metabolism to placental and gestational health. Concentrations of molybdenum in maternal circulation and placental tissue has been associated, both positively and negatively, with gestational diabetes mellitus, neural tube defects, and foetal growth due to molybdenum’s dual capacity as an anti- and pro-oxidant. We identified that within the literature there is a focus on molybdenum overexposure, and a lack of foundational in vitro studies assessing the effects of molybdenum at physiological levels in placental development. Furthermore, there is limited research on the relationship between molybdenum content and gestational pathologies with an oxidative stress component, such as foetal growth restriction. The second chapter of this thesis therefore investigated molybdenum content in placental tissue from healthy, foetal growth restricted, post-date and stillbirth pregnancies. Utilsing Synchrotron-based x-ray fluorescence microscopy this chapter provided spatial and quantitative data of 15 elements, spanning micronutrients, macronutrients and pollutants. Striking differences in element distribution and concentration were noted between pathological groups, but notably, molybdenum was the only element to significantly decrease in all pathologies in comparison to healthy term placental tissue. This study therefore provided both proof-of-concept for the use of synchrotron technology in analysis of placental tissue, and led to the hypothesis that molybdenum has a complex but vital role in the placental antioxidant response and cell survival. Consequently, Chapter 3 investigated the response of an immortalised first-trimester placental trophoblast cell line, HTR-8 SV/neo, to molybdenum supplementation at physiological levels, in the form of commonly found molybdate salts ammonium and sodium molybdate. This work aimed to elucidate the effects of molybdate supplementation on gene expression, protein levels and enzymatic activity of molybdenum containing enzymes, the cellular antioxidant response, angiogenesis and proliferation pathways, and bioenergetics. Significant differences in cellular response were found between ammonium molybdate and sodium molybdate, leading to the conclusion that the presence of ammonium was confounding in cell culture and limited molybdate acquisition by the cell, reflected in decreased viability and cell growth at high dosages, and decreased antioxidant gene expression at low physiological levels. Sodium molybdate was well tolerated by the cell, even at high supraphysiological concentration. Sodium molybdate also modulated expression of not only molybdenum containing enzymes, but angiogenic pathways, however, effects on antioxidant activity were minor in normal cell conditions. Molybdenum was found in the literature to have both antioxidant and pro-oxidant effects. Considering the differences in cellular response based on the salt used in Chapter 3, sodium molybdate was further utilised in vitro in Chapter 4, to investigate the effects of molybdenum in an oxidatively stressed cell model. The HTR-8 cell line was exposed to known oxidative stress-inducer hydrogen peroxide and concurrently exposed to sodium molybdate supplementation. Sodium molybdate significantly increased cell viability, and the enzymatic activity of antioxidant catalase, supporting our hypothesis that molybdenum has cytoprotective roles in placental physiology. Supplementation did not affect expression at the gene level, and was not dose-dependent, suggesting a narrow window of efficacy in placental cells. Gene expression of ROS-generating molybdoenzyme xanthine oxidase was upregulated in the presence of hydrogen peroxide alone, and supplementation with sodium molybdate further increased its activity, indicating that both pro-oxidant and antioxidant mechanistic pathways are activated in the presence of molybdenum. To investigate whether the developed in vitro cell model is reflective of placental mechanisms in vivo, gene expression of molybdenum containing enzymes and molybdenum metabolising proteins was analysed in healthy and foetal growth restricted (FGR) placentae. Reflective of our previous results, no significant differences were observed at the gene level with the exception of one molybdenum containing enzyme. This further indicates that molybdenum exerts its antioxidant effects at the enzymatic activity level, and possibly as a direct scavenger of ROS itself. Increases in xanthine oxidase gene expression following oxidative stress in vitro were not reflected in vivo, with no significant differences observed between healthy and FGR placentae. This may be due to differences in cell populations analysed in vitro (EVTs) and in vivo (villous trophoblasts), but further research is required. Overall, the findings presented in this thesis establish the multi-factorial effects of molybdenum within placental trophoblast cells, highlighting molybdenum’s association with gestational pathologies in vivo, and identifying possible mechanisms of antioxidant function and cytoprotection in vitro. These studies aimed to present molybdenum not just as a pollutant or toxic heavy metal but investigate its physiological functions and effects in the most important organ for gestational health. The understanding gained from this study provides a foundation for further research into molybdenum supplementation as a potential therapeutic or preventative strategy for reducing incidence of gestational complications.
- Subject
- molybdenum; placenta; molybdoenzymes; micronutrients; oxidative stress
- Identifier
- http://hdl.handle.net/1959.13/1520020
- Identifier
- uon:57435
- Rights
- Copyright 2025 Vladimira Foteva
- Language
- eng
- Full Text
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