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Austin C, Kumar P, Carter EA, Lee J, Smith TM, Hinde K, Arora M, Lay PA. Stress exposure histories revealed by biochemical changes along accentuated lines in teeth. CHEMOSPHERE 2023; 329:138673. [PMID: 37054846 PMCID: PMC10167648 DOI: 10.1016/j.chemosphere.2023.138673] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/06/2023] [Revised: 03/23/2023] [Accepted: 04/10/2023] [Indexed: 05/03/2023]
Abstract
The regular incremental secretion of enamel and dentine can be interrupted during periods of stress resulting in accentuated growth lines. These accentuated lines, visible under light microscopy, provide a chronology of an individual's stress exposure. Previously, we showed that small biochemical changes along accentuated growth lines detected by Raman spectroscopy, coincided with the timing of medical history events and disruptions of weight trajectory in teeth from captive macaques. Here, we translate those techniques to study biochemical changes related to illness and prolonged medical treatment during early infancy in humans. Chemometric analysis revealed biochemical changes related to known stress-induced changes in circulating phenylalanine as well as other biomolecules. Changes in phenylalanine are also known to affect biomineralization which is reflected in changes in the wavenumbers of hydroxyapatite phosphate bands associated with stress in the crystal lattice. Raman spectroscopy mapping of teeth is an objective, minimally-destructive technique that can aid in the reconstruction of an individual's stress response history and provide important information on the mixture of circulating biochemicals associated with medical conditions, as applied in epidemiological and clinical samples.
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Affiliation(s)
- Christine Austin
- Senator Frank R. Lautenberg Environmental Health Sciences Laboratory, Department of Environmental Medicine and Public Health, Icahn School of Medicine at Mount Sinai, New York, NY, 10029, USA.
| | - Piyush Kumar
- Senator Frank R. Lautenberg Environmental Health Sciences Laboratory, Department of Environmental Medicine and Public Health, Icahn School of Medicine at Mount Sinai, New York, NY, 10029, USA
| | - Elizabeth A Carter
- Sydney Analytical, The University of Sydney, Sydney, New South Wales, 2006, Australia; School of Chemistry, The University of Sydney, Sydney, New South Wales, 2006, Australia
| | - Joonsup Lee
- Sydney Analytical, The University of Sydney, Sydney, New South Wales, 2006, Australia; School of Chemistry, The University of Sydney, Sydney, New South Wales, 2006, Australia
| | - Tanya M Smith
- Australian Research Centre for Human Evolution, Griffith University, 170 Kessels Road, Nathan, Queensland, 4111, Australia; Griffith Centre for Social and Cultural Research, Parklands Drive, Southport, Queensland, 4222, Australia
| | - Katie Hinde
- School of Human Evolution and Social Change, Arizona State University, Tempe, AZ, 85281, USA; Center for Evolution and Medicine, Arizona State University, Tempe, AZ, 85281, USA
| | - Manish Arora
- Senator Frank R. Lautenberg Environmental Health Sciences Laboratory, Department of Environmental Medicine and Public Health, Icahn School of Medicine at Mount Sinai, New York, NY, 10029, USA
| | - Peter A Lay
- Sydney Analytical, The University of Sydney, Sydney, New South Wales, 2006, Australia; School of Chemistry, The University of Sydney, Sydney, New South Wales, 2006, Australia
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Gerbi L, Austin C, Pedretti NF, McRae N, Amarasiriwardena CJ, Mercado-García A, Torres-Olascoaga LA, Tellez-Rojo MM, Wright RO, Arora M, Elena C. Biomarkers of maternal lead exposure during pregnancy using micro-spatial child deciduous dentine measurements. ENVIRONMENT INTERNATIONAL 2022; 169:107529. [PMID: 36191488 PMCID: PMC9576006 DOI: 10.1016/j.envint.2022.107529] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/28/2022] [Revised: 08/22/2022] [Accepted: 09/16/2022] [Indexed: 06/16/2023]
Abstract
BACKGROUND Lead is a toxic chemical of public health concern, however limited biomarkers are able to reconstruct prior lead exposures in early-life when biospecimens are not collected and stored. Although child tooth dentine measurements accurately assess past child perinatal lead exposure, it has not been established if they reflect maternal exposure in pregnancy. AIM To assess the prenatal relationship between child tooth dentine and maternal blood lead measurements and to estimate maternal lead exposure during the 2nd and 3rd trimesters of pregnancy from weekly child dentine profiles. METHODS We measured early-life lead exposure in child tooth dentine and maternal blood from 419 child-mother dyads enrolled in the Programming Research in Obesity, Growth, Environment and Social Stress (PROGRESS) cohort. We employed the Super-Learner algorithm to determine the relationship of dentine lead data with maternal blood lead concentrations and to predict maternal lead from child dentine lead data in blinded analyses. We validated and quantified the bias of our results internally. RESULTS Mothers had moderate blood lead levels (trimesters: 2nd = 29.45 ug/L, 3rd = 31.78 ug/L). Trimester-averaged and weekly child dentine lead measurements were highly correlated with maternal blood levels in the corresponding trimesters. The predicted trimester-specific maternal lead levels were significantly correlated with actual measured blood values (trimesters: 2nd = 0.83; 3rd = 0.88). Biomarkers of maternal lead exposure discriminated women highly exposed to lead (>mean) with 85 % and 96 % specificity in the 2nd and 3rd trimesters, respectively, with 80 % sensitivity. DISCUSSION Weekly child dentine lead levels can serve as biomarkers of past child and maternal lead exposures during pregnancy.
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Affiliation(s)
- Lucia Gerbi
- Department of Environmental Medicine and Public Health, Icahn School of Medicine at Mount Sinai, New York, NY, United States
| | - Christine Austin
- Department of Environmental Medicine and Public Health, Icahn School of Medicine at Mount Sinai, New York, NY, United States
| | - Nicolo Foppa Pedretti
- Department of Environmental Medicine and Public Health, Icahn School of Medicine at Mount Sinai, New York, NY, United States
| | - Nia McRae
- Department of Environmental Medicine and Public Health, Icahn School of Medicine at Mount Sinai, New York, NY, United States
| | - Chitra J Amarasiriwardena
- Department of Environmental Medicine and Public Health, Icahn School of Medicine at Mount Sinai, New York, NY, United States
| | | | | | - Martha M Tellez-Rojo
- National Institute of Perinatology (INPer), Mexico City, Mexico; National Institute of Public Health (INSP), Cuernavaca, Mexico
| | - Robert O Wright
- Department of Environmental Medicine and Public Health, Icahn School of Medicine at Mount Sinai, New York, NY, United States
| | - Manish Arora
- Department of Environmental Medicine and Public Health, Icahn School of Medicine at Mount Sinai, New York, NY, United States
| | - Colicino Elena
- Department of Environmental Medicine and Public Health, Icahn School of Medicine at Mount Sinai, New York, NY, United States.
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Němec I, Smrčka V, Pokorný J. The Effect of Sensory Innervation on the Inorganic Component of Bones and Teeth; Experimental Denervation - Review. Prague Med Rep 2019; 119:137-147. [PMID: 30779698 DOI: 10.14712/23362936.2019.1] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022] Open
Abstract
The effect of the nervous system on bone remodelling has been described by many studies. Sensory and autonomic nerves are present in the bone. Immunohistochemical analysis of the bone have indicated the presence of neuropeptides and neurotransmitters that act on bone cells through receptors. Besides carrying sensory information, sensory neurons produce various neuropeptides playing an important role in maintaining bone and tooth pulp homeostasis, and dentin formation. Bone tissue and teeth contain organic and inorganic components. Bone cells enable bone mineralization and ensure its formation and resorption. Studies focused on the effects of the nervous system on the bone are proceeded using various ways. Sensory denervation itself can be achieved using capsaicin causing chemical lesion to the nerve. Surgical ways of causing only sensory lesion to nerves are substantially limited because many peripheral nerves are mixed and contain a motor component as well. From this point of view, the experimental model with transection of inferior alveolar nerve is appropriate. This nerve provides sensory innervation of the bone and teeth of the mandible. The purpose of our paper is to provide an overview of the effects exerted by the nervous system on the inorganic component of the bone and teeth, and also to present an overview of the used experimental models. As we assume, the transection of inferior alveolar nerve could be reflected in changed contents and distribution of chemical elements in the bone and teeth of rat mandible. This issue has not been studied so far.
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Affiliation(s)
- Ivo Němec
- Department of Otorhinolaryngology and Maxillofacial Surgery, Third Faculty of Medicine, Charles University and Military University Hospital Prague, Prague, Czech Republic.
| | - Václav Smrčka
- Department of Plastic Surgery, First Faculty of Medicine, Charles University and Na Bulovce Hospital, Prague, Czech Republic.,Institute for History of Medicine and Foreign Languages, First Faculty of Medicine, Charles University, Prague, Czech Republic
| | - Jaroslav Pokorný
- Institute of Physiology, First Faculty of Medicine, Charles University, Prague, Czech Republic
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Horton MK, Hsu L, Claus Henn B, Margolis A, Austin C, Svensson K, Schnaas L, Gennings C, Hu H, Wright R, Rojo MMT, Arora M. Dentine biomarkers of prenatal and early childhood exposure to manganese, zinc and lead and childhood behavior. ENVIRONMENT INTERNATIONAL 2018; 121:148-158. [PMID: 30205321 PMCID: PMC6373872 DOI: 10.1016/j.envint.2018.08.045] [Citation(s) in RCA: 65] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/13/2018] [Revised: 08/20/2018] [Accepted: 08/20/2018] [Indexed: 05/04/2023]
Abstract
BACKGROUND Metal exposure alters neurodevelopmental outcomes; little is known about critical windows of susceptibility when exposure exerts the strongest effect. OBJECTIVE To examine associations between dentine biomarkers of manganese (Mn), zinc (Zn) and lead (Pb) and later childhood behaviors. METHODS Subjects enrolled in a longitudinal birth cohort study in Mexico City provided naturally shed deciduous teeth. We estimated weekly prenatal and postnatal dentine Mn, Zn and Pb concentrations in teeth using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and measured behavior at ages 8-11 years of age using the Behavior Assessment System for Children, 2nd edition (BASC-2). We used distributed lag models and lagged weighted quantile sum regression to identify the role of individual and combined dentine biomarkers of Mn, Zn and Pb on behavioral outcomes controlling for maternal education and gestational age. RESULTS Among the 133 subjects included in this study, prenatal and early postnatal dentine Mn appeared protective against childhood behavioral problems, specifically hyperactivity and attention. Postnatal dentine Mn was associated with increased reporting of internalizing problems, specifically anxiety. At 6 months, a 1-unit increase (unit = 1 SD of log concentration) in Mn was associated with a 0.18-unit (unit = 1 SD of BASC-2 score) increase in internalizing symptoms score and a 0.25-unit increase in anxiety. Postnatal Pb was associated with increasing anxiety symptoms; at 12 months, a 1-unit increase in Pb was associated with a 0.4 unit increase in anxiety symptoms. When examined as a metal mixture, we observed two potential windows of susceptibility to increased anxiety symptoms: the first window (0-8 months) appeared driven by Mn, the second window (8-12 months) was driven by the metal mixture and dominated by Pb. A 1-unit increase in the mixture index was associated with a 0.7-unit increase in SD of anxiety symptoms. CONCLUSIONS Childhood behaviors may demonstrate postnatal windows of susceptibility to individual and mixed metal concentrations measured in deciduous teeth. Prenatal dentine Mn may be protective, while excessive early postnatal Mn may increase risk for adverse behaviors. In combination, higher concentrations of Mn, Zn and Pb may have an adverse impact on behavior.
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Affiliation(s)
- Megan K Horton
- Department of Environmental Medicine and Public Health, Icahn School of Medicine at Mount Sinai, One Gustave Levy Place, Box 1057, New York, NY 10029, United States of America
| | - Leon Hsu
- Department of Environmental Medicine and Public Health, Icahn School of Medicine at Mount Sinai, One Gustave Levy Place, Box 1057, New York, NY 10029, United States of America
| | - Birgit Claus Henn
- Department of Environmental Health, Boston University School of Public Health, 715 Albany St., Boston, MA 02118, United States of America
| | - Amy Margolis
- Division of Child and Adolescent Psychiatry, Columbia University Medical Center, 1051 Riverside Drive New York, New York 10032, United States of America
| | - Christine Austin
- Department of Environmental Medicine and Public Health, Icahn School of Medicine at Mount Sinai, One Gustave Levy Place, Box 1057, New York, NY 10029, United States of America
| | - Katherine Svensson
- Department of Environmental Medicine and Public Health, Icahn School of Medicine at Mount Sinai, One Gustave Levy Place, Box 1057, New York, NY 10029, United States of America
| | - Lourdes Schnaas
- Division of Research in Community Interventions, Instituto Nacional de Perinatología, Montes Urales 800, Lomas Virreyes, Mexico City CP 11000, Mexico
| | - Chris Gennings
- Department of Environmental Medicine and Public Health, Icahn School of Medicine at Mount Sinai, One Gustave Levy Place, Box 1057, New York, NY 10029, United States of America
| | - Howard Hu
- Dalla Lana School of Public Health, University of Toronto, Health Sciences Building, 155 College Street, 6(th) floor, Toronto M5T 3M7, Canada
| | - Robert Wright
- Department of Environmental Medicine and Public Health, Icahn School of Medicine at Mount Sinai, One Gustave Levy Place, Box 1057, New York, NY 10029, United States of America
| | - Martha María Téllez Rojo
- Center for Nutrition and Health Research, National Institute of Public Health (Mexico), Universidad 655, Cuernavaca 62100, Mexico.
| | - Manish Arora
- Department of Environmental Medicine and Public Health, Icahn School of Medicine at Mount Sinai, One Gustave Levy Place, Box 1057, New York, NY 10029, United States of America
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Austin C, Richardson C, Smith D, Arora M. Tooth manganese as a biomarker of exposure and body burden in rats. ENVIRONMENTAL RESEARCH 2017; 155:373-379. [PMID: 28279842 PMCID: PMC5862712 DOI: 10.1016/j.envres.2017.03.004] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/03/2017] [Revised: 03/01/2017] [Accepted: 03/02/2017] [Indexed: 05/09/2023]
Abstract
BACKGROUND Neonates and children are particularly vulnerable to the toxic effects of excess manganese (Mn), but studies of Mn exposure during these developmental periods are hampered by a lack of validated biomarkers. Deciduous teeth may be used to assess Mn exposure during these developmental periods but require further validation to determine the relationship between tooth Mn, Mn in target tissues, and exposure. OBJECTIVES To determine the relationship of tooth Mn concentrations with: (i) exposure dose, (ii) the timing/duration of exposure, and (iii) with Mn concentrations in blood, brain and bone. METHODS Rats in different treatment groups were orally exposed to 0, 25 or 50µg/g/day Mn either from postnatal day (PND) 1 - 21 and culled at PND 24, from PND 1 - 21 and culled as adults (>PND 290), or from PND 1 - throughout life and culled at >290 PND. Mn was measured in second molars, femurs, brain and blood by ICP-MS. RESULTS Tooth Mn increased significantly with dose in rats exposed for 21 PND and culled at 24 PND (p<0.001). In rats culled at >290 PND, tooth Mn increased with exposure duration (p<0.001) and reflected exposure duration. A significant, positive association between tooth Mn and Mn levels in blood (Spearman's rho 0.69, p<0.01) brain (rho 0.59, p<0.05) and bone (rho 0.69, p<0.01) was observed in animals with lifelong exposure. Tooth Mn and Mn levels in bone were also significantly positively associated in animals exposed only early in life (rho 0.76, p<0.001). CONCLUSIONS Teeth are a sensitive biomarker of active and past Mn exposure and Mn burden in tissues. Unlike blood, teeth retain information on exposure history over the short and long-term.
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Affiliation(s)
- Christine Austin
- Department of Environmental Medicine and Public Health, Icahn School of Medicine at Mount Sinai, New York, NY, USA; Institute of Dental Research, Westmead Millennium Institute, Westmead Hospital, and Oral Pathology and Oral Medicine, Faculty of Dentistry, University of Sydney, Sydney, NSW, Australia
| | - Cardius Richardson
- Microbiology and Environmental Toxicology, University of California, Santa Cruz, CA, USA
| | - Donald Smith
- Microbiology and Environmental Toxicology, University of California, Santa Cruz, CA, USA.
| | - Manish Arora
- Department of Environmental Medicine and Public Health, Icahn School of Medicine at Mount Sinai, New York, NY, USA.
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de Figueiredo FAT, Ramos J, Kawakita ERH, Bilal AS, de Sousa FB, Swaim WD, Issa JPM, Gerlach RF. Lead line in rodents: an old sign of lead intoxication turned into a new method for environmental surveillance. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2016; 23:21475-21484. [PMID: 27510160 DOI: 10.1007/s11356-016-7336-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/14/2016] [Accepted: 07/27/2016] [Indexed: 06/06/2023]
Abstract
The "lead line" was described by Henry Burton in 1840. Rodents are used as sentinels to monitor environmental pollution, but their teeth have not been used to determine lead. To determine whether lead deposits can be observed in the teeth of lead-exposed animals, since the gingival deposits known as "lead line" would likely have a correlate in the calcified tissue to which the gums are opposed during life. Male Wistar rats were exposed to lead in the drinking water (30 mg/L) since birth until 60 days-old. Molars and the incisors of each hemimandible were analyzed by scanning electron microscopy (SEM) on regular and backscattered electrons (BSE) mode. Elements were determined using electron dispersive spectroscopy (EDS). Clean cervical margins were observed on control teeth, as opposed to the findings of extensive deposits on lead-exposed animals, even in hemimandibles that had been exhumed after being buried for 90 days. BSE/EDS indicated that those deposits were an exogenous material compatible with lead sulfite. Presence of calcium, phosphorus, magnesium, carbon, lead, and oxygen is presented. Lead-exposed animals presented marked root resorption. The lead deposits characterized here for the first time show that the "lead line" seen in gums has a calcified tissue counterpart, that is detectable post-mortem even in animals exposed to a low dose of lead. This is likely a good method to detect undue lead exposure and will likely have wide application for pollution surveillance using sentinels.
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Affiliation(s)
- Fellipe Augusto Tocchini de Figueiredo
- Department of Morphology, Physiology, and Basic Pathology, School of Dentistry of Ribeirao Preto (FORP), University of Sao Paulo (USP), Avenida do Cafe S/N, Monte Alegre, Ribeirao Preto, Sao Paulo, CEP 14040-904, Brazil.
| | - Junia Ramos
- Department of Morphology, Physiology, and Basic Pathology, School of Dentistry of Ribeirao Preto (FORP), University of Sao Paulo (USP), Avenida do Cafe S/N, Monte Alegre, Ribeirao Preto, Sao Paulo, CEP 14040-904, Brazil
| | - Erika R Hashimoto Kawakita
- Department of Morphology, Physiology, and Basic Pathology, School of Dentistry of Ribeirao Preto (FORP), University of Sao Paulo (USP), Avenida do Cafe S/N, Monte Alegre, Ribeirao Preto, Sao Paulo, CEP 14040-904, Brazil
| | - Alina S Bilal
- Department of Morphology, Physiology, and Basic Pathology, School of Dentistry of Ribeirao Preto (FORP), University of Sao Paulo (USP), Avenida do Cafe S/N, Monte Alegre, Ribeirao Preto, Sao Paulo, CEP 14040-904, Brazil
| | - Frederico B de Sousa
- Department of Morphology, Science Health Center, Federal University of Paraiba (UFPB), Joao Pessoa, Paraiba, Brazil
| | - William D Swaim
- National Institute for Dental and Craniofacial Research (NIDCR), National Institutes of Health (NIH), Bethesda, MD, USA
| | - Joao P Mardegan Issa
- Department of Morphology, Physiology, and Basic Pathology, School of Dentistry of Ribeirao Preto (FORP), University of Sao Paulo (USP), Avenida do Cafe S/N, Monte Alegre, Ribeirao Preto, Sao Paulo, CEP 14040-904, Brazil
| | - Raquel F Gerlach
- Department of Morphology, Physiology, and Basic Pathology, School of Dentistry of Ribeirao Preto (FORP), University of Sao Paulo (USP), Avenida do Cafe S/N, Monte Alegre, Ribeirao Preto, Sao Paulo, CEP 14040-904, Brazil
- Graduate Program in Pharmacology and Toxicology, Faculty of Medicine of Ribeirao Preto (FMRP), University of Sao Paulo (USP), Avenida Bandeirantes 3400, Ribeirao Preto, Sao Paulo, CEP: 14049-900, Brazil
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Wang Y, Specht A, Liu Y, Finney L, Maxey E, Vogt S, Zheng W, Weisskopf M, Nie LH. Microdistribution of lead in human teeth using microbeam synchrotron radiation X-ray fluorescence (μ-SRXRF). X-RAY SPECTROMETRY : XRS 2016; 46:19-26. [PMID: 32863464 PMCID: PMC7451221 DOI: 10.1002/xrs.2720] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Lead (Pb) exposure is known to be associated with adverse effects on human health, especially during the prenatal period and early childhood. The Pb content in teeth has been suggested as a useful biomarker for the evaluation of cumulative Pb exposure. This study was designed to employ the microbeam synchrotron radiation X-ray fluorescence technique to determine the microdistribution of Pb within the tooth to evaluate the reliability of the technique and the effectiveness of tooth Pb as a biomarker of Pb exposure. The results showed that in the incisor sample, Pb primarily deposited in secondary dentine region close to the pulp and secondarily at enamel exterior. In addition, Pb colocalised with Zn, indicating a positive correlation between Pb and Zn. By contrast,in the two molar samples, Pb accumulated principally in the pulp, and secondarily in the enamel. At the same time, Pb in these two molar samples colocalised with Ca instead of Zn as was observed in the incisor sample. Several batches of line scans further confirmed the conclusions. The feasibility of using microbeam synchrotron radiation X-ray fluorescence to determine the microdistribution of Pb in teeth and of using the tooth Pb, especially in dentine, as a biomarker was discussed.
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Affiliation(s)
- Yufei Wang
- School of Health Sciences, Purdue University, West Lafayette, IN, 47907, USA
| | - Aaron Specht
- School of Health Sciences, Purdue University, West Lafayette, IN, 47907, USA
| | - Yingzi Liu
- School of Health Sciences, Purdue University, West Lafayette, IN, 47907, USA
| | - Lydia Finney
- Advanced Photon Source, Argonne National Laboratory, Lemont, IL, 60439, USA
| | - Evan Maxey
- Advanced Photon Source, Argonne National Laboratory, Lemont, IL, 60439, USA
| | - Stefan Vogt
- Advanced Photon Source, Argonne National Laboratory, Lemont, IL, 60439, USA
| | - Wei Zheng
- School of Health Sciences, Purdue University, West Lafayette, IN, 47907, USA
| | - Marc Weisskopf
- Departments of Environmental Health and Epidemiology, Harvard T.H. Chan School of Public Health, Boston, MA, 02215, USA
| | - Linda H Nie
- School of Health Sciences, Purdue University, West Lafayette, IN, 47907, USA
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Abstract
PURPOSE OF REVIEW The exposome concept proposes a comprehensive assessment of environmental exposures from the prenatal period onwards. However, determining exposure timing, especially over the prenatal period, is a major challenge in environmental epidemiologic studies. RECENT FINDINGS For decades, teeth have been used to estimate long-term cumulative exposure to metals. Recently developed high-dimensional analytical methods, which combine sophisticated histological and chemical analysis to precisely sample tooth layers that correspond to specific life stages, have the potential to reconstruct the exposome in the second and third trimesters of prenatal development and during early childhood. SUMMARY A retrospective temporal exposomic approach that precisely measures exposure intensity 'and timing' during prenatal and early childhood development would substantially aid epidemiologic investigations, particularly case-control studies of rare health outcomes.
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Andra SS, Austin C, Arora M. Tooth matrix analysis for biomonitoring of organic chemical exposure: Current status, challenges, and opportunities. ENVIRONMENTAL RESEARCH 2015; 142:387-406. [PMID: 26219084 PMCID: PMC4609267 DOI: 10.1016/j.envres.2015.06.032] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/18/2015] [Revised: 06/21/2015] [Accepted: 06/25/2015] [Indexed: 05/18/2023]
Abstract
Epidemiological evidence supports associations between prenatal exposure to environmental organic chemicals and childhood health impairments. Unlike the common choice of biological matrices such as urine and blood that can be limited by short half-lives for some chemicals, teeth provide a stable repository for chemicals with half-life in the order of decades. Given the potential of the tooth bio-matrix to study long-term exposures to environmental organic chemicals in human biomonitoring programs, it is important to be aware of possible pitfalls and potential opportunities to improve on the current analytical method for tooth organics analysis. We critically review previous results of studies of this topic. The major drawbacks and challenges in currently practiced concepts and analytical methods in utilizing tooth bio-matrix are (i) no consideration of external (from outer surface) or internal contamination (from micro-odontoblast processes), (ii) the misleading assumption that whole ground teeth represent prenatal exposures (latest formed dentine is lipid rich and therefore would absorb and accumulate more organic chemicals), (iii) reverse causality in exposure assessment due to whole ground teeth, and (iv) teeth are a precious bio-matrix and grinding them raises ethical concerns about appropriate use of a very limited resource in exposure biology and epidemiology studies. These can be overcome by addressing the important limitations and possible improvements with the analytical approach associated at each of the following steps: (i) tooth sample preparation to retain exposure timing, (ii) organics extraction and pre-concentration to detect ultra-trace levels of analytes, (iii) chromatography separation, (iv) mass spectrometric detection to detect multi-class organics simultaneously, and (v) method validation, especially to exclude chance findings. To highlight the proposed improvements we present findings from a pilot study that utilizes tooth matrix biomarkers to obtain trimester-specific exposure information for a range of organic chemicals.
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Affiliation(s)
- Syam S Andra
- Exposure Biology, Lautenberg Environmental Health Sciences Laboratory, Department of Preventive Medicine, Icahn School of Medicine at Mount Sinai, New York, NY, USA.
| | - Christine Austin
- Exposure Biology, Lautenberg Environmental Health Sciences Laboratory, Department of Preventive Medicine, Icahn School of Medicine at Mount Sinai, New York, NY, USA; Faculty of Dentistry, University of Sydney, Sydney, NSW, Australia
| | - Manish Arora
- Exposure Biology, Lautenberg Environmental Health Sciences Laboratory, Department of Preventive Medicine, Icahn School of Medicine at Mount Sinai, New York, NY, USA; Faculty of Dentistry, University of Sydney, Sydney, NSW, Australia.
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Abstract
PURPOSE OF REVIEW Accurate prenatal exposure assessment is one of the major challenges in environmental epidemiologic studies. Variations in placental transport make maternal biospecimens unreliable for many chemicals and fetal specimens collected at birth do not provide information on exposure timing over the prenatal period. RECENT FINDINGS The skeletal compartment is an important chemical repository, making calcified tissues important for measuring exposure. For decades teeth have been used to estimate long-term cumulative exposure to metals and some organic chemicals. Recently developed methodologies that combine sophisticated histological and chemical analysis to precisely sample tooth layers that correspond to specific life stages have the potential to reconstruct exposure in the second and third trimesters of prenatal development and during early childhood. SUMMARY Such a retrospective biomarker that precisely measures exposure intensity and timing during prenatal development would substantially aid epidemiologic investigations, particularly case-control studies of rare health outcomes.
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Costa de Almeida GR, de Sousa Guerra C, de Angelo Souza Leite G, Antonio RC, Barbosa F, Tanus-Santos JE, Gerlach RF. Lead contents in the surface enamel of primary and permanent teeth, whole blood, serum, and saliva of 6- to 8-year-old children. THE SCIENCE OF THE TOTAL ENVIRONMENT 2011; 409:1799-1805. [PMID: 21353293 DOI: 10.1016/j.scitotenv.2011.01.004] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/08/2010] [Revised: 12/20/2010] [Accepted: 01/05/2011] [Indexed: 05/30/2023]
Abstract
This study aimed to evaluate associations of Pb-enamel values determined in two successive enamel microbiopsies taken from a primary and a permanent tooth, and to assess how Pb-enamel correlates with Pb-blood and Pb-serum as well as whole (Pb-whole-saliva), submandibular/sublingual (Pb-sub-saliva) and parotid saliva (Pb-parotid-saliva). The study population included 444 children aged 6 to 8years attending 4 government schools in the district of Campos Eliseos, in Ribeirao Preto, Sao Paulo State, Brazil. Whole blood, serum, parotid, submandibular/sublingual ("sub-saliva"), and whole saliva were collected in trace element-free tubes. Two successive microbiopsies were taken from the surface of a primary and a permanent tooth of each child. Lead concentrations were determined by inductively coupled plasma mass spectrometry (ICP-MS). There was a significant correlation between primary and permanent teeth in terms of Pb-enamel, for both the first and the second microbiopsies. When the median Pb-enamel values were compared between the two genders using only the highest 10th percentile Pb-enamel, there was a significant difference between girls and boys for both primary (474.2 vs 910.0μg/g, respectively; p=0.02) and permanent teeth (739.5 vs 1325μg/g, respectively; p=0.04). There were no significant correlations between Pb-enamel and Pb-blood or between Pb-enamel and lead in the 3 different salivas. However, there was a statistically significant correlation between Pb-enamel and Pb-serum when only the highest 10th percentile Pb-enamel was analyzed (r=0.57 and p=0.0002 for primary teeth; r=0.56 and p<0.0001, for permanent teeth). In conclusion, our findings have demonstrated a significant correlation between Pb-enamel found in primary and permanent teeth, as well as a significant correlation between Pb-serum and lead in primary and permanent tooth enamel. Boys presented higher Pb-enamel than girls. Our study also suggests that Pb-enamel has no correlation with Pb-blood or with lead in the 3 different salivas.
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Affiliation(s)
- Glauce Regina Costa de Almeida
- Department of Morphology, Estomatology and Physiology, Dental School of Ribeirao Preto, University of Sao Paulo - FORP/USP, Av. do Café, S/N, Monte Alegre, CEP 14040-904, Ribeirao Preto-SP, Brazil
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12
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Arora M, Hare D, Austin C, Smith DR, Doble P. Spatial distribution of manganese in enamel and coronal dentine of human primary teeth. THE SCIENCE OF THE TOTAL ENVIRONMENT 2011; 409:1315-9. [PMID: 21211818 DOI: 10.1016/j.scitotenv.2010.12.018] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/13/2010] [Revised: 12/04/2010] [Accepted: 12/06/2010] [Indexed: 05/06/2023]
Abstract
Emerging evidence indicates that excessive exposure to manganese (Mn) during the prenatal period and early childhood may result in neurodevelopmental deficits. However, accurate exposure biomarkers are not well established, limiting our understanding of exposure-response relationships over these susceptible periods of development. Naturally shed deciduous teeth are potentially a useful biomarker of environmental exposure to Mn. However, the uptake and distribution of Mn in human teeth has not been studied in detail. Mn distribution was measured at high resolution (~20 μm) in eight human primary teeth using laser ablation-inductively coupled plasma-mass spectrometry. A bio-imaging methodology was applied to construct detailed elemental maps of three incisors, and bone meal (NIST SRM 1486) was used to validate the analyses. The distribution of Mn in enamel and coronal dentine showed a distinct and reproducible pattern. In enamel, the ⁵⁵Mn:⁴³Ca ratio was highest at the outer edge of enamel (range=0.57 to 4.74) for approximately 20-40 μm but was substantially lower in deeper layers (range=0.005 to 0.013). The highest levels of Mn were observed in dentine immediately adjacent the pulpal margin (⁵⁵Mn:⁴³Ca range=2.27 to 6.95). Importantly, a clearly demarcated high Mn zone was observed in dentine at the incisal end of the teeth. Using confocal laser scanning microscopy to visualize the neonatal line, this region was identified as being in the prenatally formed dentine. The high-resolution map of the spatial distribution of Mn in human primary teeth highlighted specific reproducible patterns of Mn distribution in enamel and coronal dentine.
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Affiliation(s)
- Manish Arora
- Institute of Dental Research, Westmead Centre for Oral Health, Westmead Hospital, Westmead, Australia.
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Molina G, Costa de Almeida G, de Souza Guerra C, Cury J, de Almeida A, Barroso R, Gerlach R. Lead Deposition in Bovine Enamel during a pH-Cycling Regimen Simulating the Caries Process. Caries Res 2011; 45:469-74. [DOI: 10.1159/000330602] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2010] [Accepted: 06/27/2011] [Indexed: 11/19/2022] Open
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Sawan RMM, Leite GAS, Saraiva MCP, Barbosa F, Tanus-Santos JE, Gerlach RF. Fluoride increases lead concentrations in whole blood and in calcified tissues from lead-exposed rats. Toxicology 2010; 271:21-6. [PMID: 20188782 DOI: 10.1016/j.tox.2010.02.002] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2009] [Revised: 02/01/2010] [Accepted: 02/02/2010] [Indexed: 10/19/2022]
Abstract
Higher blood lead (BPb) levels have been reported in children living in communities that receive fluoride-treated water. Here, we examined whether fluoride co-administered with lead increases BPb and lead concentrations in calcified tissues in Wistar rats exposed to this metal from the beginning of gestation. We exposed female rats and their offspring to control water (Control Group), 100mg/L of fluoride (F Group), 30mg/L of lead (Pb Group), or 100mg/L of fluoride and 30mg/L of lead (F+Pb Group) from 1 week prior to mating until offspring was 81 days old. Blood and calcified tissues (enamel, dentine, and bone) were harvested at day 81 for lead and fluoride analyses. Higher BPb concentrations were found in the F+Pb Group compared with the Pb Group (76.7+/-11.0microg/dL vs. 22.6+/-8.5microg/dL, respectively; p<0.001). Two- to threefold higher lead concentrations were found in the calcified tissues in the F+Pb Group compared with the Pb Group (all p<0.001). Fluoride concentrations were similar in the F and in the F+Pb Groups. These findings show that fluoride consistently increases BPb and calcified tissues Pb concentrations in animals exposed to low levels of lead and suggest that a biological effect not yet recognized may underlie the epidemiological association between increased BPb lead levels in children living in water-fluoridated communities.
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Affiliation(s)
- Rosangela M M Sawan
- School of Dentistry of Ribeirao Preto, University of Sao Paulo (FORP/USP), Av do Café s/n, 14040-904, Ribeirão Preto, SP, Brazil
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de Souza Guerra C, Fernanda Gerlach R, Graciele Villela Pinto N, Coutinho Cardoso S, Moreira S, Pereira de Almeida A, Teixeira Alves Peixoto I, Henrique Meloni C, Lemos Mota C, Fernando de Oliveira L, Braz D, Cely Barroso R. X-ray fluorescence with synchrotron radiation to elemental analysis of lead and calcium content of primary teeth. Appl Radiat Isot 2010; 68:71-5. [DOI: 10.1016/j.apradiso.2009.08.005] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2009] [Revised: 08/05/2009] [Accepted: 08/07/2009] [Indexed: 10/20/2022]
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Costa de Almeida GR, Molina GF, Meschiari CA, Barbosa de Sousa F, Gerlach RF. Analysis of enamel microbiopsies in shed primary teeth by Scanning Electron Microscopy (SEM) and Polarizing Microscopy (PM). THE SCIENCE OF THE TOTAL ENVIRONMENT 2009; 407:5169-5175. [PMID: 19540564 DOI: 10.1016/j.scitotenv.2009.04.044] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/12/2009] [Revised: 04/23/2009] [Accepted: 04/24/2009] [Indexed: 05/27/2023]
Abstract
The aims of this study were 1) to verify how close to the theoretically presumed areas are the areas of enamel microbiopsies carried out in vivo or in exfoliated teeth; 2) to test whether the etching solution penetrates beyond the tape borders; 3) to test whether the etching solution demineralizes the enamel in depth. 24 shed upper primary central incisors were randomly divided into two groups: the Rehydrated Teeth Group and the Dry Teeth Group. An enamel microbiopsy was performed, and the enamel microbiopsies were then analyzed by Scanning Electron Microscopy (SEM) and Polarizing Microscopy (PM). Quantitative birefringence measurements were performed. The "true" etched area was determined by measuring the etched enamel using the NIH Image analysis program. Enamel birefringence was compared using the paired t test. There was a statistically significant difference when the etched areas in the Rehydrated teeth were compared with those of the Dry teeth (p=0.04). The etched areas varied from -11.6% to 73.5% of the presumed area in the Rehydrated teeth, and from 6.6% to 61.3% in the Dry teeth. The mean percentage of variation in each group could be used as a correction factor for the etched area. Analysis of PM pictures shows no evidence of in-depth enamel demineralization by the etching solution. No statistically significant differences in enamel birefringence were observed between values underneath and outside the microbiopsy area in the same tooth, showing that no mineral loss occurred below the enamel superficial layer. Our data showed no evidence of in-depth enamel demineralization by the etching solution used in the enamel microbiopsy proposed for primary enamel. This study also showed a variation in the measured diameter of the enamel microbiopsy in nineteen teeth out of twenty four, indicating that in most cases the etching solution penetrated beyond the tape borders.
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Affiliation(s)
- Glauce Regina Costa de Almeida
- Department of Morphology, Stomatology and Physiology, Dental School of Ribeirão Preto, University of São Paulo - FORP/USP, Av. do Café, S/N, Monte Alegre, CEP 14040-904, Ribeirão Preto, SP, Brazil.
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de Almeida GRC, de Souza Guerra C, Tanus-Santos JE, Barbosa F, Gerlach RF. A plateau detected in lead accumulation in subsurface deciduous enamel from individuals exposed to lead may be useful to identify children and regions exposed to higher levels of lead. ENVIRONMENTAL RESEARCH 2008; 107:264-270. [PMID: 18304525 DOI: 10.1016/j.envres.2008.01.002] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/19/2007] [Revised: 11/08/2007] [Accepted: 01/02/2008] [Indexed: 05/26/2023]
Abstract
In a previous study, we showed 4 times more lead in surface deciduous enamel (1.9-5.9 microm) of a notoriously contaminated area (Bauru, São Paulo State, Brazil) in comparison to samples from a region with no lead contamination described (Ribeirão Preto, São Paulo State, Brazil). The samples from the more superficial enamel (1.9-3.18 microm) showed higher amounts of lead and the highest variability, while in the subsurface enamel (3.18-5.9 microm) a plateau in lead content was detected in children living in the contaminated environment (around 600 microg/g). Here we expand our previous study, and use only samples obtained from subsurface enamel (Ribeirão Preto, n=186; Bauru, n=20). We tried to distinguish regions with more children with lead above the threshold of 600 microg/g of lead in enamel. We tested whether differences in the percentage of children with ''high" lead (600 microg/g) could be observed among the different Kindergartens studied in Ribeirão Preto. We also tested whether these results were different from the ones provided by conventional comparison of the data. Ribeirão Preto showed almost 4 times less lead than Bauru (p<0.0001), and a statistically significant difference was found only in Ribeirão Preto between Kindergarten 2 and 5 (p<0.01). Twelve percent of the children from Ribeirão Preto had "high" lead, while 55% of the children from Bauru did so. However, when we looked at the percentages of children with "high" lead in each Kindergarten, and compared them, a whole new picture emerged, in which we could see children with "high" lead concentrated mainly in 3 Kindergartens from Ribeirão Preto, with Kindergarten 5 with 33% of the children with "high" lead, being statistically different from all Kindergartens, except 4 and 6. The threshold of 600 microg/g of lead in subsurface enamel was tentatively settled here after the plateau seen in exposed children, and enabled us to identify locations with more children exposed to a higher amount of lead.
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Affiliation(s)
- Glauce Regina Costa de Almeida
- Department of Morphology, Stomatology and Physiology, Dental School of Ribeirão Preto, University of São Paulo-FORP/USP, Av. do Café, S/N, Monte Alegre, CEP 14040-904, Ribeirão Preto, SP, Brazil
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Youravong N, Teanpaisan R, Norén JG, Robertson A, Dietz W, Odelius H, Dahlén G. Chemical composition of enamel and dentine in primary teeth in children from Thailand exposed to lead. THE SCIENCE OF THE TOTAL ENVIRONMENT 2008; 389:253-8. [PMID: 17910978 DOI: 10.1016/j.scitotenv.2007.08.053] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/28/2007] [Revised: 08/30/2007] [Accepted: 08/31/2007] [Indexed: 05/17/2023]
Abstract
Enamel and dentine in teeth of children with high blood levels of lead were analyzed by means of secondary ion mass spectrometry (SIMS) and X-ray micro-analyses (XRMA) and compare with teeth from children with low blood levels of lead. The SIMS analysis revealed detectable levels of Pb in dentine close to the pulp. The XRMA analyses could not detect any lead. There were no differences found in lead level in enamel of high lead level exposed teeth from low level exposed. The results confirm that children with high blood levels of lead have an uptake of lead in dentine close to the pulp.
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Affiliation(s)
- Nattaporn Youravong
- Department of Preventive Dentistry, Faculty of Dentistry, Prince of Songkla University, Songkhla, Thailand
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Costa de Almeida GR, Pereira Saraiva MDC, Barbosa F, Krug FJ, Cury JA, Rosário de Sousa MDL, Rabelo Buzalaf MA, Gerlach RF. Lead contents in the surface enamel of deciduous teeth sampled in vivo from children in uncontaminated and in lead-contaminated areas. ENVIRONMENTAL RESEARCH 2007; 104:337-45. [PMID: 17512519 DOI: 10.1016/j.envres.2007.03.007] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/01/2006] [Revised: 03/15/2007] [Accepted: 03/22/2007] [Indexed: 05/15/2023]
Abstract
This study aimed to: (1) measure lead contents in the surface enamel of two populations consisting of 4-6-year-old children, one from an apparently uncontaminated area (Ribeirão Preto, São Paulo State, SP, Brazil, n=247) and the other from an area notoriously contaminated with lead (Bauru, São Paulo State, Brazil, n=26); (2) compare biopsy depths between the two populations; (3) correlate biopsy depth with lead content; (4) stratify samples according to biopsy depth to compare lead contents in samples from similar biopsy depths. A surface enamel acid-etch microbiopsy was performed in vivo on a single upper deciduous incisor for each sample. Lead was measured by graphite furnace atomic absorption spectrometry (GFAAS) while phosphorus was measured colorimetrically to establish biopsy depth. Samples from both populations were classified into categories of similar biopsy depths based on biopsy depth quartiles. Median lead contents were statistically different between the Ribeirão Preto population (206 microg/g, range: 5-1399 microg/g) and the Bauru population (786 microg/g, range: 320-4711 microg/g) (p<0.001); however, biopsy depth did not differ between the Ribeirão Preto (3.9 microm, Standard Deviation, SD=0.9) and Bauru (3.8 microm, SD=0.9) populations (p=0.7940). Pearson's correlation coefficient for biopsy depths versus log10 lead values was -0.29 for Ribeirão Preto and -0.18 for Bauru. Lead contents were statistically different between the two populations for all quartiles of biopsy depth. These findings suggest that lead accumulated in the surface enamel of deciduous teeth is linked to the environment in which people reside, indicating that this tissue should be further explored as an accessible biomarker of lead exposure.
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Affiliation(s)
- Glauce Regina Costa de Almeida
- Department of Morphology, Estomatology and Physiology, Dental School of Ribeirão Preto, University of São Paulo-FORP/USP, Av. do Café, S/N, Monte Alegre, CEP 14040-904, Ribeirão Preto-SP, Brazil
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Arora M, Kennedy BJ, Ryan CG, Boadle RA, Walker DM, Harland CL, Lai B, Cai Z, Vogt S, Zoellner H, Chan SWY. The application of synchrotron radiation induced X-ray emission in the measurement of zinc and lead in Wistar rat ameloblasts. Arch Oral Biol 2007; 52:938-44. [PMID: 17521603 DOI: 10.1016/j.archoralbio.2007.04.003] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2007] [Revised: 04/04/2007] [Accepted: 04/06/2007] [Indexed: 12/31/2022]
Abstract
The development of analytical techniques for the measurement of trace elements in cellular compartments of developing teeth remains an important methodological issue in dental research. Recent advances in third generation synchrotron facilities have provided high brilliance X-ray sources that can be effectively used to study trace element distributions in small spatial regions with low detection limits. The present study describes for the first time the application of synchrotron radiation induced X-ray emission (SRIXE) in measuring the distribution of zinc and lead in the ameloblasts of developing Wistar rat teeth. Wistar rats were fed a standard rat diet, containing the normal dietary requirements of zinc, ad libitum and exposed to 100 ppm of lead in drinking water. Resin embedded sections of first mandibular molars were analysed using a 13.3 keV incident monochromatic X-ray beam focussed to a 0.2 microm spot. Characteristic X-rays arising from the entire thickness of the sample were measured using an energy dispersive detector for quantitative analysis of elemental concentrations. The results showed that intranuclear concentrations of zinc were greater than levels in the cytoplasm. Furthermore, nuclear and cytoplasmic concentrations of zinc in the maturation stage (742+/-27 and 424+/-25 ppm, respectively) were significantly higher than the zinc levels observed in the nucleus and cytoplasm of presecretory stage ameloblasts (132+/-10 and 109+/-10 ppm, respectively) (p<0.05). A clear lead signal above the background was not detected in the ameloblasts and lead concentrations could only be reliably measured in the developing enamel. Overall, SRIXE was an effective method of studying the spatial distribution of zinc in the cells of developing teeth and offered a unique combination of sub-micron spatial resolution and parts-per-million detection limits (0.8-1 and 0.6-1 ppm for zinc and lead, respectively).
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Affiliation(s)
- Manish Arora
- Cellular and Molecular Pathology Research Unit, Department of Oral Pathology, Faculty of Dentistry, University of Sydney, Westmead Centre for Oral Health, Westmead Hospital, Westmead, NSW 2145, Australia.
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