Deciduous teeth as a tool to record early life exposure of zinc nutrition

Abstract

Background: Zinc (Zn) is an abundant micronutrient and has essential roles in human growth and development. Zn deposition in human teeth has been reported and related to environmental exposures, such as pollution, disease, and dietary intake. The deciduous tooth lifespan is from the prenatal until childhood period, thus, it may record Zn exposure in children over this critical time frame. With the age-related incremental features of dentine and the development of micro-sampling techniques, Zn deposition may be analysed at different time points using Laser Ablation (LA)-ICP-MS in combination with dental histology. Zn is obtained from the diet and the distribution throughout the body and within cells is regulated by saturable, carrier-mediated transport proteins, known as ZnTs and ZIPs. The precise mechanism by which Zn is transported from the circulatory system of the pulp to the tooth hard tissue, however, remains unclear. The objective of this study therefore, was to analyse the Zn/Ca ratio in dentine of deciduous teeth in individuals consuming different levels of Zn during the pregnancy and infancy period, and elucidate the expression of Zn transporter in pulp tissue at the mRNA level in relation to dietary zinc intake. Aims: to explore the use of the deciduous tooth dentine to record Zn exposure during pregnancy through to the infancy period, and to analyse the level of Zn transporter expression at the mRNA level in human dental pulp related to dietary intake of Zn. Methods: Children, who attended Child Dental Clinic at Educational Dental Hospital of Universitas Indonesia for deciduous teeth extraction, paired with their mother were recruited for this study. Dentine from extracted deciduous teeth was prepared for elemental analysis (Zn, Ca and Sr) at different age points using LA-ICP-MS and dental histology. Sr distribution was used as a reference element since it has been studied widely in relation with dietary changes. The pulp from the same teeth was removed and prepared for RNA isolation. Food frequency questionnaires were developed to gather information on daily Zn intake of the mother during pregnancy and children during infancy. RNA from dental pulp of the human deciduous teeth were isolated and Zn transporter expression at the RNA level measured using RT-qPCR. In addition, human odontoblast cells were used as an in vitro model to analyse Zn transporter expression at mRNA level in response to high- and low-Zn exposure, using RT-qPCR. Results: This study showed Zn distribution within dentine of deciduous teeth reflected Zn exposure during pregnancy and infancy period, as well as different feeding regimes during the first six month of life. There were differential patterns of Zn transporter ii expression in human pulp RNA and in the human odontoblast cell line, levels of Zn transporter expression were altered in response to extracellular levels of Zn exposure. Conclusion: For the first time, we have shown a differential level of Zn distribution within dentine of deciduous teeth in relation to dietary Zn intake during pregnancy and the infancy period. The expression of Zn transporters in dental pulp indicates homeostatic control of Zn uptake into dental tissue, which may be regulated by dietary Zn intake.