Suppression of Placental Metallothionein 1 and Zinc Transporter 1 mRNA Expressions Contributes to Fetal Heart Malformations Caused by Maternal Zinc Deficiency

Cardiovascular Diseases and Zinc

Zinc is structurally and functionally essential for more than 300 enzymes and 2000 transcription factors in human body. Intracellular labile zinc is the metabolically effective zinc and tiny changes in its concentrations significantly affect the intracellular signaling and enzymatic responses. Zinc is crucial for the embrionic and fetal development of heart. Therefore, it is shown to be related with a variety of congenital heart defects. It is involved in epithelial-to-mesenchymal transformation including endocardial cushion development, which is necessary for atrioventricular septation as well as the morphogenesis of heart valves. In atherosclerosis, monocyte endothelial adhesion, and diapedesis, activation and transformation into macrophages and forming foam cells by the ingestion of oxidized LDL are monocyte related steps which need zinc. Intracellular zinc increases intracellular calcium through a variety of pathways and furthermore, zinc itself can work as a second messenger as calcium. These demonstrate the significance of intracellular zinc in heart failure and arterial hypertension. However, extracellular zinc has an opposite effect by blocking calcium channels, explaining decreased serum zinc levels, contrary to the increased cardiomyocyte and erythrocyte zinc levels in hypertensive subjects. These and other data in the literature demonstrate that zinc has important roles in healthy and diseased cardiovascular system but zinc-cardiovascular system relationship is so complex that, it has not been explained in all means. In this article, we try to review some of the available knowledge about this complex relationship.

Exposure to essential and non-essential trace elements and risks of congenital heart defects: A narrative review

Congenital heart defects (CHDs) are congenital abnormalities involving the gross structures of the heart and large blood vessels. Environmental factors, genetic factors and their interactions may contribute to the pathogenesis of CHDs. Generally, trace elements can be classified into essential trace elements and non-essential trace elements. Essential trace elements such as copper (Cu), zinc (Zn), iron (Fe), selenium (Se), and manganese (Mn) play important roles in human biological functions such as metabolic function, oxidative stress regulation, and embryonic development. Non-essential trace elements such as cadmium (Cd), arsenic (As), lead (Pb), nickle (Ni), barium (Ba), chromium (Cr) and mercury (Hg) are harmful to health even at low concentrations. Recent studies have revealed the potential involvement of these trace elements in the pathogenesis of CHDs. In this review, we summarized current studies exploring exposure to essential and non-essential trace elements and risks of CHDs, in order to provide further insights for the pathogenesis and prevention of CHDs.

Characteristics of Zn Content and Localization, Cu-Zn SOD, and MT Levels in the Tissues of Marginally Zn-Deficient Mice

Zinc (Zn) is an important trace element in the human body, and Zn deficiency affects the Zn content of major tissues. Marginal Zn deficiency is more common than severe Zn deficiency in humans. The objective of the present study was to compare the content and distribution of Zn and the change in the copper (Cu)-Zn superoxide dismutase (SOD) and metallothionein (MT) levels of soft tissues. Mice were fed with 30 mg/kg (control) or 10 mg/kg (marginally Zn-deficient, MZD) Zn diet for 35 days. We observed that only the Zn contents of serum, bones, and muscles in the control group were higher than those in the MZD group. Autometallography (AMG) was used as a method for staining Zn ions, and the semi-quantitative result indicated that the AMG products of the liver, duodenum, heart, lung, testes, and epididymis in the control group were higher than those in the MZD group. Furthermore, the contents of MT and the activities of Cu-Zn SOD in the testes, brain, duodenum, and liver were higher in the control group than those in the MZD group. However, the AMG products and the activities of Cu-Zn SOD of the kidney in the MZD group were more/higher than those in the control group. These results indicated that a change in the total Zn content of soft tissues may be not obvious and insensitive, and thus, more attention should be given to the distribution and localization of Zn ions. The functional indicators, MT and Cu-Zn SOD, are suitable biomarkers for evaluating zinc nutritional status. The brain, testes, duodenum, and liver are susceptive organs to Zn deficiency.

Zinc

Since the discovery of manifest Zn deficiency in 1961, the increasing number of studies demonstrated the association between altered Zn status and multiple diseases. In this chapter, we provide a review of the most recent advances on the role of Zn in health and disease (2010-20), with a special focus on the role of Zn in neurodegenerative and neurodevelopmental disorders, diabetes and obesity, male and female reproduction, as well as COVID-19. In parallel with the revealed tight association between ASD risk and severity and Zn status, the particular mechanisms linking Zn2+ and ASD pathogenesis like modulation of synaptic plasticity through ProSAP/Shank scaffold, neurotransmitter metabolism, and gut microbiota, have been elucidated. The increasing body of data indicate the potential involvement of Zn2+ metabolism in neurodegeneration. Systemic Zn levels in Alzheimer's and Parkinson's disease were found to be reduced, whereas its sequestration in brain may result in modulation of amyloid β and α-synuclein processing with subsequent toxic effects. Zn2+ was shown to possess adipotropic effects through the role of zinc transporters, zinc finger proteins, and Zn-α2-glycoprotein in adipose tissue physiology, underlying its particular role in pathogenesis of obesity and diabetes mellitus type 2. Recent findings also contribute to further understanding of the role of Zn2+ in spermatogenesis and sperm functioning, as well as oocyte development and fertilization. Finally, Zn2+ was shown to be the potential adjuvant therapy in management of novel coronavirus infection (COVID-19), underlining the perspectives of zinc in management of old and new threats.

Role of zinc in female reproduction

Zinc is a critical component in a number of conserved processes that regulate female germ cell growth, fertility, and pregnancy. During follicle development, a sufficient intracellular concentration of zinc in the oocyte maintains meiotic arrest at prophase I until the germ cell is ready to undergo maturation. An adequate supply of zinc is necessary for the oocyte to form a fertilization-competent egg as dietary zinc deficiency or chelation of zinc disrupts maturation and reduces the oocyte quality. Following sperm fusion to the egg to initiate the acrosomal reaction, a quick release of zinc, known as the zinc spark, induces egg activation in addition to facilitating zona pellucida hardening and reducing sperm motility to prevent polyspermy. Symmetric division, proliferation, and differentiation of the preimplantation embryo rely on zinc availability, both during the oocyte development and post-fertilization. Further, the fetal contribution to the placenta, fetal limb growth, and neural tube development are hindered in females challenged with zinc deficiency during pregnancy. In this review, we discuss the role of zinc in germ cell development, fertilization, and pregnancy with a focus on recent studies in mammalian females. We further detail the fundamental zinc-mediated reproductive processes that have only been explored in non-mammalian species and speculate on the role of zinc in similar mechanisms of female mammals. The evidence collected over the last decade highlights the necessity of zinc for normal fertility and healthy pregnancy outcomes, which suggests zinc supplementation should be considered for reproductive age women at risk of zinc deficiency.

An assessment of serum-dependent impacts on intracellular accumulation and genomic response of per- and polyfluoroalkyl substances in a placental trophoblast model

Per- and polyfluoroalkyl substances (PFAS), a class of environmental contaminants, have been detected in human placenta and cord blood. The mechanisms driving PFAS-induced effects on the placenta and adverse pregnancy outcomes are not well understood. This study investigated the impact of perfluorooctanesulfonic acid (PFOS), perfluorooctanoic acid (PFOA), and a replacement PFAS known as hexafluoropropylene oxide dimer acid (HFPO-DA, tradename GenX) on placental trophoblasts in vitro. Several key factors were addressed. First, PFAS levels in cell culture reagents at baseline were quantified. Second, the role of supplemental media serum in intracellular accumulation of PFAS in a human trophoblast (JEG3) cell line was established. Finally, the impact of PFAS on the expression of 96 genes involved in proper placental function in JEG3 cells was evaluated. The results revealed that serum-free media (SFM) contained no detectable PFAS. In contrast, fetal bovine serum-supplemented media (SSM) contained PFNA, PFUdA, PFTrDA, and 6:2 FTS, but these PFAS were not detected internally in cells. Intracellular accumulation following 24 hr treatments was significantly higher when cultured in SFM compared to SSM for PFOS and PFOA, but not HFPO-DA. Treatment with PFAS was associated with gene expression changes (n = 32) in pathways vital to placental function, including viability, syncytialization, inflammation, transport, and invasion/mesenchymal transition. Among the most robust PFAS-associated changes were those observed in the known apoptosis-related genes, BAD and BAX. These results suggest a complex relationship between PFAS, in vitro culture conditions, and altered expression of key genes necessary for proper placentation.

In vitro fertilization and embryo transfer alter human placental function through trophoblasts in early pregnancy

The mechanism underlying the potential risk associated with in vitro fertilization and embryo transfer (IVF‑ET) has been previously investigated but remains to be fully elucidated. As the placenta is a critical organ that sustains and protects the fetus, this is an important area of research. The aim of the present study was to determine the difference in trophoblast cell function in the first trimester between naturally conceived pregnancies and pregnancies achieved via IVF‑ET therapy. A total of 20 placental villi in first trimester samples were obtained through fetal bud aspiration from patients undergoing IVF‑ET due to oviductal factors between January 2016 and August 2018. In addition, a further 20 placental villi were obtained from those who naturally conceived and had normal pregnancies but were undergoing artificial abortion; these patients were recruited as the controls. Reverse transcription‑quantitative (RT‑q)PCR and semi‑quantitative immunohistochemical methods were used to detect the mRNA and protein expression of α‑fetoprotein (AFP), vascular endothelial growth factor (VEGF), transferrin (TF), tubulin β1 class VI (TUBB1), metallothionein 1G (MT1G), BCL2, glial cells missing transcription factor 1 (GCM1), epidermal growth factor (EGF) receptor (EGFR), PTEN and leukocyte associated immunoglobulin like receptor 2 (LAIR2) in villi from both groups. Differentially expressed genes were analyzed using Search Tool for the Retrieval of Interacting Genes, and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis was conducted. The RT‑qPCR data revealed that the mRNA expression levels of AFP, VEGF and TF were significantly higher in the IVF‑ET group than in the control group (P<0.05), and those of TUBB1, MT1G, BCL2, GCM1, EGFR, PTEN and LAIR2 were significantly lower (P<0.05). These gene products were expressed in the placental villus tissues, either in the cytoplasm, or in the membrane of syncytiotrophoblast and cytotrophoblast cells. The immunohistochemistry results were in line with those observed using RT‑qPCR. KEGG pathway analysis indicated that the trophoblast cell function of the IVF‑ET group in the first trimester was different from naturally conceived pregnancies with regard to proliferation, invasion, apoptosis and vascular development. The IVF‑ET process may trigger adaptive placental responses, and these compensatory mechanisms could be a risk for certain diseases later in life.

The Application of Curve Fitting on the Voltammograms of Various Isoforms of Metallothioneins-Metal Complexes

The translation of metallothioneins (MTs) is one of the defense strategies by which organisms protect themselves from metal-induced toxicity. MTs belong to a family of proteins comprising MT-1, MT-2, MT-3, and MT-4 classes, with multiple isoforms within each class. The main aim of this study was to determine the behavior of MT in dependence on various externally modelled environments, using electrochemistry. In our study, the mass distribution of MTs was characterized using MALDI-TOF. After that, adsorptive transfer stripping technique with differential pulse voltammetry was selected for optimization of electrochemical detection of MTs with regard to accumulation time and pH effects. Our results show that utilization of 0.5 M NaCl, pH 6.4, as the supporting electrolyte provides a highly complicated fingerprint, showing a number of non-resolved voltammograms. Hence, we further resolved the voltammograms exhibiting the broad and overlapping signals using curve fitting. The separated signals were assigned to the electrochemical responses of several MT complexes with zinc(II), cadmium(II), and copper(II), respectively. Our results show that electrochemistry could serve as a great tool for metalloproteomic applications to determine the ratio of metal ion bonds within the target protein structure, however, it provides highly complicated signals, which require further resolution using a proper statistical method, such as curve fitting.

Influence of intracellular zinc on cultures of rat cardiac neural crest cells

BACKGROUND

Developmental zinc (Zn) deficiency increases the incidence of heart anomalies in rat fetuses, in regions and structures derived from the outflow tract. Given that the development of the outflow tract requires the presence of cardiac neural crest cells (cNCC), we speculated that Zn deficiency selectively kills cNCC and could lead to heart malformations.

METHODS

Cardiac NCC were isolated from E10.5 rat embryos and cultured in control media (CTRL), media containing 3 μM of the cell permeable metal chelator N, N, N', N'-tetrakis (2-pyridylmethyl) ethylene diamine (TPEN), or in TPEN-treated media supplemented with 3 μM Zn (TPEN + Zn). Cardiac NCC were collected after 6, 8, and 24 h of treatment to assess cell viability, proliferation, and apoptosis.

RESULTS

The addition of TPEN to the culture media reduced free intracellular Zn pools and cell viability as assessed by low ATP production, compared to cells grown in control or Zn-supplemented media. There was an accumulation of reactive oxygen species, a release of mitochondrial cytochrome c into the cytoplasm, and an increased cellular expression of active caspase-3 in TPEN-treated cNCC compared to cNCC cultured in CTRL or TPEN + Zn media.

CONCLUSION

Zn deficiency can result in oxidative stress in cNCC, and subsequent decreases in their population and metabolic activity. These data support the concept that Zn deficiency associated developmental heart defects may arise in part as a consequence of altered cNCC metabolism.