Increased Zn/Glutathione Levels and Higher Superoxide Dismutase-1 Activity as Biomarkers of Oxidative Stress in Women with Long-Term Dental Amalgam Fillings: Correlation between Mercury/Aluminium Levels (in Hair) and Antioxidant Systems in Plasma

RESEARCH ARTICLE Increased Zn/Glutathione Levels and Higher Superoxide Dismutase-1 Activity as Biomarkers of Oxidative Stress in Women with Long-Term Dental Amalgam Fillings: Correlation between Mercury/Aluminium Levels (in Hair) and Antioxidant Systems in Plasma María Eugenia Cabaña-Muñoz1,2*, José María Parmigiani-Izquierdo1, Luis Alberto BravoGonzález2, Hee-Moon Kyung3, José Joaquín Merino4* OPEN ACCESS Citation: Cabaña-Muñoz ME, Parmigiani-Izquierdo JM, Bravo-González LA, Kyung H-M, Merino JJ (2015) Increased Zn/Glutathione Levels and Higher Superoxide Dismutase-1 Activity as Biomarkers of Oxidative Stress in Women with Long-Term Dental Amalgam Fillings: Correlation between Mercury/ Aluminium Levels (in Hair) and Antioxidant Systems in Plasma. PLoS ONE 10(6): e0126339. doi:10.1371/ journal.pone.0126339 Academic Editor: Gianfranco Pintus, University of Sassari, ITALY 1 Centro CIROM, Centro de Implantología y Rehabilitación Oral Multidisciplinaria, Murcia, Spain, 2 Facultad de Medicina, Universidad de Murcia, UMU, Unidad Docente de Ortodoncia, Murcia, Spain, 3 Department of Orthodontics, Dental School, Kyungpook Nacional University, Daegu, Korea, 4 IUIN, Instituto de Investigación Neuroquímica, Universidad Complutense de Madrid, (U.C.M), Madrid, Spain * (JJM); (MEC) Abstract Background The induction of oxidative stress by Hg can affect antioxidant enzymes. However, epidemiological studies have failed to establish clear association between dental fillings presence and health problems. Received: October 1, 2014 Accepted: April 1, 2015 Objectives Published: June 15, 2015 To determine whether heavy metals (in hair), antioxidant enzymes (SOD-1) and glutathione levels could be affected by the chronic presence of heavy metals in women who had dental amalgam fillings. Copyright: © 2015 Cabaña-Muñoz et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are included within the paper. Funding: This study has been supported by own findings from Maria Eugenia Cabaña (CIROM Clinic (Murcia, Spain; personnal money). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Materials and Methods 55 hair samples (42 females with amalgam fillings and 13 female control subjects) were obtained. All subjects (mean age 44 years) who had dental amalgam filling for more than 10 years (average 15 years). Certain metals were quantified by ICP-MS (Mass Spectrophotometry) in hair (μg/g: Al, Hg, Ba, Ag, Sb, As, Be, Bi, Cd, Pb, Pt, Tl, Th, U, Ni, Sn, Ti) and SOD-1 and Glutathione (reduced form) levels in plasma. Data were compared with controls without amalgams, and analyzed to identify any significant relation between metals and the total number of amalgam fillings, comparing those with four or less (n = 27) with those with PLOS ONE | DOI:10.1371/journal.pone.0126339 June 15, 2015 1 / 11 Higher SOD-1 Activity in Female Long-Term Carriers of Dental Amalgams Competing Interests: The authors declare that there are no conflicts of interest. All authors do not have competing interests and financial disclosures that declare from CIROM or other affiliations. There is no employment, consultancy, patents, or products in development that could interfere with the publication of this manuscript in PLOS ONE. The authors confirm that this does not affect PLOS ONE policies on sharing data and materials, as detailed online in our guide for authors. This does not alter the authors' adherence to PLOS ONE policies on sharing data and materials. more than four (n = 15). As no significant differences were detected, the two groups were pooled (Amlgam; n = 42). Findings Hg, Ag, Al and Ba were higher in the amalgam group but without significant differences for most of the heavy metals analyzed. Increased SOD-1 activity and glutathione levels (reduced form) were observed in the amalgam group. Aluminum (Al) correlated with glutathione levels while Hg levels correlated with SOD-1. The observed Al/glutathione and Hg/ SOD-1 correlation could be adaptive responses against the chronic presence of mercury. Conclusions Hg, Ag, Al and Ba levels increased in women who had dental amalgam fillings for long periods. Al correlated with glutathione, and Hg with SOD-1. SOD-1 may be a possible biomarker for assessing chronic Hg toxicity. Introduction Richardson et al. (2011) estimate that over 180 million Americans carry a total of more than one billion restored teeth (based on 2001–2004 population statistics) [1]. Mercury toxicity varies between different types of mercury and its organic forms are much more toxic than inorganic forms [2,3]. Although dental amalgam fillings seem to be safe, they are nevertheless a significant chronic contributor to mercury body burden [4,5,6]. Heavy metals and oligoelements can be detected in human urine, plasma or hair samples by inductively coupled plasmamass spectrometry (ICP-MS) [7]. However, many epidemiological studies have failed to establish clear association between amalgam fillings presence and health problem [2]. The induction of oxidative stress by Hg is caused in part by the interaction between Hg and antioxidant enzymes [8]. One way that cells remove ROS is by producing proteins such as glutathione and metallothionein that bind to ROS and form more hydrophilic compounds that are easily excreted through Glutathione S-transferases [9]. Copper and zinc-containing superoxide dismutase, (Cu/Zn- cytoplasmic enzyme (SOD-1) metabolizes superoxide radicals to molecular oxygen and hydrogen peroxide, providing defense against oxygen toxicity [9,10,11]. For this reason, there is a need to establish whether the Hg from dental amalgam fillings can increase heavy metal release and affect glutathione or SOD-1 activity as compensatory mechanism in patients (women). Objectives The present study set out to quantify a plethora of heavy metals levels (μg/g: Al, Hg, Ba, Ag, Sb, As, Be, Bi, Cd, Pb, Pt, Tl, Th, U, Ni, Sn, Ti) in the hair of woman who had dental amalgam fillings for at least 10 years (average 15 years), comparing the data obtained with women control subjects without amalgams. Data were analyzed to find out if the presence of these heavy metal levels was dependent of the total number of dental fillings. For this purpose, subjects (women) were divided into two groups: those with four or fewer dental amalgam fillings (<4; n = 27) and those with more than four in their mouth (>4; n = 15); pooled:dental Amalgam filling group, n = 42 (Amalgam). PLOS ONE | DOI:10.1371/journal.pone.0126339 June 15, 2015 2 / 11 Higher SOD-1 Activity in Female Long-Term Carriers of Dental Amalgams Reduced glutathione levels and SOD-activity were also analyzed as possible compensatory mechanisms in t (...truncated)