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Early-life Co-exposure to fluoride and lead modifies the tissue distribution of essential and toxic trace elements.
| Journal of Trace Elements in Medicine and Biology | Macedo-Ribeiro N, Tostes-Figueiredo J, de Oliveira ML, Stenico RS, Leite IG, Gomes EB, Braga S, Campos MLAM, da Veiga MAMS, Barbosa F Jr, Gerlach RF. | 95:127871.
Brazil Brain Chemical Co-Exposures Kidney Lead Liver Animal Study

Abstract

Highlights

  • Co-exposure to fluoride significantly enhances lead accumulation in the brain and kidney.
  • Fluoride and lead exposures altered the distribution of essential and toxic trace elements in soft tissues.
  • Lead alone increased levels of Al, As, Ba, Cu, Mn, and Zn in various organs.
  • Fluoride modified the toxicokinetics of lead and bone-seeking elements like Sr and Ba.
  • This is the first study to demonstrate fluoride-mediated modulation of the metallome in developing rats.

Exposure to toxic metals such as lead (Pb) during early development is known to induce long-lasting physiological and neurological effects. However, little is known about how co-exposure to fluoride (F)—a common environmental and dietary element—modulates Pb toxicokinetics and the homeostasis of other trace elements in soft and mineralized tissues. This study aimed to evaluate the effects of early-life exposure to Pb (30 µg/L) and/or F (50 µg/L) on the distribution of nine trace elements (Al, As, Ba, Cd, Cu, Mn, Pb, Sr, and Zn) in soft organs (brain, heart, kidney, liver) and bone of Wistar rats. Animals were exposed via drinking water from gestation until postnatal day 30. Elemental concentrations were measured by inductively coupled plasma mass spectrometry (ICP-MS), and group differences were considered statistically significant at p < 0.0013 (Bonferroni-corrected). Co-exposure to Pb and F resulted in a 2-fold increase in Pb concentrations in the brain and a 40-fold increase in the kidney. Fluoride exposure alone increased Mn in the liver, while Pb exposure alone led to elevated levels of Al, As, Ba, and Pb in the heart; As in the brain and kidney; Mn and Zn in the liver; and Cu in the kidney. Notably, co-exposure modified the distribution of several elements beyond Pb, including reductions in Cd and As in soft tissues and altered deposition of bone-seeking elements like Sr and Ba. To our knowledge, this is the first study demonstrating that fluoride can alter lead distribution and significantly affect the soft-tissue metallomic profile during early development. These findings highlight the importance of considering metal-metal interactions in environmental toxicology and suggest that fluoride may act as a modifier of metal toxicity. Further studies are warranted to investigate the functional consequences of these alterations and their implications for organ development and health outcomes in exposed populations.

Introduction

The toxic effects of environmental contaminants are notably more severe during early development, with gestational and early postnatal exposure to metals being associated with long-term impacts on organ function and disease susceptibility [1], [2], [3]. Studies in animal models have also demonstrated that low-dose exposure to metals like lead (Pb) during gestation can result in persistent alterations in metabolism and behavior [4], [5], [6]. Lead remains a metal of high concern, currently ranked second in toxicity among environmental metals by the Agency for Toxic Substances and Disease Registry (ATSDR) [7], and is frequently detected in fine particulate matter (PM2.5), soil, water across urban and rural settings [8], plumbing, traditional medicines, and occupational environments [9]. While the impact of Pb on blood and bone compartments has been extensively studied [10], its distribution in soft tissues, particularly under co-exposure scenarios with other elements such as fluoride (F), remains poorly characterized.

Fluoride, traditionally recognized for its benefits in caries prevention, has recently drawn the attention of the scientific community due to its potential neurotoxic properties [11], [12], [13]. Fluoride has a high affinity for calcium (Ca2+) and phosphate (PO43-), and it changes the equilibrium of the hydroxyapatite precipitation reaction, forming fluorapatite, as already shown by McCann [14] at concentrations ranging from 1 ppm to 2.5% of sodium fluoride (NaF) [14]. Fluoride influences apatite solubility, which underlies its protective effect against dental caries [15], [16]. Since apatite also incorporates trace elements from the surrounding medium, F exposure may alter their incorporation. However, only a few studies have evaluated fluoride’s impact on the elemental composition of calcified tissues under controlled regimens [17], [18], [19], [20].

Bone growth and metabolism are regulated by several trace elements, including Ca, iron (Fe), zinc (Zn), copper (Cu), phosphorus (P), and magnesium (Mg), whose imbalance may contribute to bone disorders such as osteoporosis [21], [22]. These elements influence bone health not only through incorporation into the matrix, but also by modulating cellular processes via enzyme interactions [23]. Approximately 30–40% of human proteins interact with metal ions [24], [25], and nearly half of all enzymes require metal cofactors to function [26]. Organs with high metabolic demand, especially the brain, are particularly sensitive to trace element imbalances [27], [28]. Toxic metals and semi-metals, such as Pb, cadmium (Cd), and arsenic (As), may disrupt the homeostasis of essential elements by interfering with proteins such as metallothioneins and metal-dependent ATPases [29], [30], impairing physiological processes such as redox balance and gene expression [31], [32], [33]. Nevertheless, the extent to which F alters the metal distribution or accumulation patterns remains largely unexplored.

This study aimed to evaluate the distribution of nine trace elements (aluminum (Al), As, barium (Ba), Cd, Cu, manganese (Mn), Pb, strontium (Sr), and Zn) in bone, plasma, and soft tissues (brain, heart, kidney, and liver) of 30-day-old rats exposed since gestation to either Pb, F, or both. We hypothesized that F co-exposure would influence Pb toxicokinetics and potentially modulate the distribution of other trace elements in soft tissues. The rationale behind this hypothesis is the fact that F is used to precipitate fluorapatite, a mineral composed mainly of phosphate and calcium, in which some other metals can also precipitate due to their chemical similarities with Ca, and have been described as “bone-seeking agents” [34], [35]. In this study, we studied some “bone-seeking” and other potentially toxic elements, along with essential elements.

Section snippets

Materials

High-purity de-ionized water (resistivity 18.2 M? cm-1), Millipore RiOs-DI™, USA, was used throughout this work for rinsing glassware and preparing the samples. Nitric acid (HNO3) (Qhemis, Brazil) used for digestion purposes was previously purified in a quartz sub-boiling system (Kürner Analysentechnik) before use. Multi-element solutions (10 mg/L) were obtained from PerkinElmer (Shelton, CT, USA). Triton® X-100 and TMAH 25% (w/v) were purchased from Sigma–Aldrich (St. Louis, USA). All plastic

Results

Table 1 shows the concentrations of Ba, Cd, Pb, and Sr found in the different tissues. Table 2 shows the concentrations of Al, As, Cu, Mn, and Zn in the same tissues of the 30-day-old animals. While the elements shown in Table 1 have been described as “bone-seeking elements” [34], [35], the elements shown in Table 2 have not been described as such. The selection of these other chemical elements was based on the description of their presence in bone and soft tissues, and our intention to include

Discussion

To our knowledge, this is the first study to report the metallomic profile of young animals exposed to either low doses of Pb, moderate doses of F, or co-exposed to both (Pb+F group). The results are consistent with previous studies on Pb distribution in calcified tissues, demonstrating increased Pb accumulation in these tissues in the presence of F in young Wistar rats [19]. However, so far, no study has demonstrated an increase in kidney Pb levels due to moderate F exposure, nor a doubling of

Conclusion

Gestational and early postnatal exposure to lead, fluoride, or their combination profoundly altered the distribution of essential and toxic elements across multiple tissues, with the kidney and bone showing the most pronounced disruptions. Co-exposure increased Pb concentrations by over 40-fold in the kidney and 10-fold in the bone, while also reducing bone levels of essential metals such as Zn, Cu, and Mn. These findings suggest a synergistic interaction between Pb and F that compromises trace

CRediT authorship contribution statement

Rafael Soares Stenico: Writing – review & editing, Methodology, Investigation. Eliude Barbosa Gomes: Writing – review & editing, Methodology, Investigation. Isaque Guerreiro Leite: Writing – review & editing, Methodology, Investigation. Maria Lucia Arruda Moura Campos: Writing – review & editing, Validation, Methodology, Investigation. Samya Braga: Writing – review & editing, Methodology, Investigation. Fernando Barbosa Jr: Writing – review & editing, Validation, Methodology, Investigation.

Funding

The authors acknowledge the financial support provided by the following Brazilian funding agencies: The Sao Paulo Research Foundation (FAPESP, grant nº 2022/00626-6; grant nº 2022/00629-5; grant nº 2025/15660-3; grant nº 2025/12654-2), Coordination for the Improvement of Higher Education (CAPES), and National Council for Scientific and Technological Development (CNPq).

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

References (100)

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