The impact of food contaminants on the bioavailability of trace metals

Bioaccessibility of Cd and its Correlation with Divalent Mineral Nutrients in Locally Grown Rice from Two Provinces in China

Rice and rice products are the main sources of Cd contamination in humans. The total and bioaccessible concentrations of Cd and three divalent nutrients, Mn, Cu, and Zn, in locally grown rice grains from Hunan and Guangdong Provinces in China were investigated. An in vitro physiologically based extraction test method was introduced to evaluate the bioaccessibility of the target metals in the rice grains. The mean concentrations of Cd in the rice grains were 0.245 mg/kg and 0.235 mg/kg from Hunan and Guangdong Provinces, respectively. Large variations were observed in the Cd concentrations, indicating a heterogeneous distribution of Cd contamination throughout the study areas. The bioaccessibility of Cd, Mn, and Zn in the gastrointestinal fractions was significantly lower than that in the gastric fractions. In contrast, the bioaccessibility of Cu at the intestinal phase was detected in the rice grains from both provinces. The correlation analysis showed significant relationships between total Cd concentrations and bioaccessible Cd fractions, indicating that higher total Cd in rice grains always resulted in higher bioaccessible Cd. Consistent correlations in the rice grains were observed between Zn and Mn. However, a lack of correlation was found between Cd and Zn in the current study. Risk assessment according to bioaccessible Cd would significantly reduce the exposure risk to Cd from rice consumption.

Association of Urinary and Blood Concentrations of Heavy Metals with Measures of Bone Mineral Density Loss: a Data Mining Approach with the Results from the National Health and Nutrition Examination Survey

Osteoporosis and its consequence of fragility fracture represent a major public health problem. Human exposure to heavy metals has received considerable attention over the last decades. However, little is known about the influence of co-exposure to multiple heavy metals on bone density. The present study aimed to examine the association between exposure to metals and bone mineral density (BMD) loss. Blood and urine concentrations of 20 chemical elements were selected from 3 cycles (2005-2010) NHANES (National Health and Nutrition Examination Survey), in which we included white women over 50 years of age and previously selected for BMD testing (N = 1892). The bone loss group was defined as participants having T-score < - 1.0, and the normal group was defined as participants having T-score ≥ - 1.0. We developed classification models based on support vector machines capable of determining which factors could best predict BMD loss. The model which included the five-best features-selected from the random forest were age, body mass index, urinary concentration of arsenic (As), cadmium (Cd), and tungsten (W), which have achieved high scores for accuracy (92.18%), sensitivity (90.50%), and specificity (93.35%). These data demonstrate the importance of these factors and metals to the classification since they alone were capable of generating a classification model with a high prediction of accuracy without requiring the other variables. In summary, our findings provide insight into the important, yet overlooked impact that arsenic, cadmium, and tungsten have on overall bone health.

Manganese in the Diet: Bioaccessibility, Adequate Intake, and Neurotoxicological Effects

Manganese (Mn) is an essential element that participates in several biological processes. Mn serves as a cofactor for several enzymes, such as glutamine synthetase and oxidoreductases, that have an important role in the defense of the organisms against oxidative stress. The diet is the main source of Mn intake for humans, and adequate daily intake levels for this metal change with age. Moreover, in higher amounts, Mn may be toxic, mainly to the brain. Here, we provide an overview of Mn occurrence in food, addressing its bioaccessibility and discussing the dietary standard and recommended intake of Mn consumption. In addition, we review some mechanisms underlying Mn-induced neurotoxicity.

In vitro oral bioaccessibility investigation and human health risk assessment of heavy metals in wheat grains grown near the mines in North China

There is limited research on the effects of gut microbiota on bioaccessibility of heavy metals in wheat grains. In this study, bioaccessibility of heavy metals (Cu, Cd, Pb, and Zn) in wheat was determined to elucidate transfer characteristics in the soil-grain-human systems near two large-scale mining areas in Shandong Province, North China using the physiologically-based extraction test (PBET) in combination with a simulator of human intestinal microbial ecosystems (SHIME). The results showed the bioconcentration factors (BCFs) of Cu, Cd, Pb, and Zn were 0.123-0.327, 0.188-0.478, 0.019-0.099, and 0.262-0.825, respectively. Significant and positive correlations were observed between heavy metals in soils and wheat grains. In the simulated colon phase, bioaccessibility of Cd and Zn significantly decreased to 7.81% and 8.81%, respectively, being 53% and 64% of that in the simulated small intestinal phase. However, bioaccessibility of Pb showed an obvious escalating trend, being 2.4 times higher than that of intestinal incubation. Based on the estimated daily intakes and contribution, the relative high contribution of Cu to the benchmark dose in both phases, Cu metabolism by human gut microbiota should be considered in human health risk assessment regarding wheat consumption.

Copper Complexing Capacity and Trace Metal Content in Common and Balsamic Vinegars: Impact of Organic Matter

Complex formation is among the mechanisms affecting metal bioaccessibility. Hence, the quantification of organic metal complexation in food items is of interest. Organic ligands in solutions of environmental and/or food origin function as buffering agents against small changes in dissolved metal concentrations, being able to maintain free metal ion concentrations below the toxicity threshold. Organic matter in vinegars consists of bioactive compounds, such as polyphenols, Maillard reaction endproducts, etc., capable of complexing metal ions. Furthermore, transition metal ions are considered as micronutrients essential for living organisms exerting a crucial role in metabolic processes. In this study, differential pulse anodic stripping voltammetry (DPASV), a sensitive electrochemical technique considered to be a powerful tool for the study of metal speciation, was applied for the first time in vinegar samples. The concentrations of Cu complexing ligands (L_T) in 43 vinegars retailed in Greece varied between 0.05 and 52 μM, with the highest median concentration determined in balsamic vinegars (14 μM), compared to that of common vinegars (0.86 μM). In 21% of the vinegar samples examined, L_T values were exceeded by the corresponding total Cu concentrations, indicating the presence of free Cu ion and/or bound within labile inorganic/organic complexes. Red grape balsamic vinegars exhibited the highest density of Cu ligands per mass unit of organic matter compared to other foodstuffs such as herbal infusions, coffee brews, and beers. Among the 16 metals determined in vinegars, Pb is of particular importance from a toxicological point of view, whereas further investigation is required regarding potential Rb biomagnification.

Fluorescent Porous Silica Microspheres for Highly and Selectively Detecting Hg2+ and Pb2+ Ions and Imaging in Living Cells

In this work, SiO₂ microspheres were first prepared by a conventional Stöber method and then etched by NaOH solution to obtain porous ones. By tuning the degree of etching, specific surface area of SiO₂ microspheres could be controlled. Then, small fluorescent molecules are synthesized and incorporated onto the surface and/or pores of the SiO₂ via layer-by-layer reaction to obtain fluorescent microspheres, namely, SiO₂-NH₂-BODIPY (SiNBB), SiO₂-NH₂-BODIPY-indole-benzothiazole (SiNBIT), and SiO₂-NH₂-BODIPY-indole-benzoxazole (SiNBIO). The as-prepared microspheres SiNBB exhibit highly sensitive and selective recognition ability for Hg²⁺ and Pb²⁺. When SiNBB encounters Hg²⁺ and Pb²⁺, the fluorescence intensity of SiNBB is increased up to fivefold. SiNBIT and SiNBIO are solely sensitive to Hg²⁺, and both have a single high sensitivity to recognize Hg²⁺. The adsorption efficiency of Hg²⁺ by the three fluorescent microspheres SiNBB, SiNBIT, and SiNBIO reached 2.91, 0.99, and 0.98 g/g of microspheres, respectively. Experimental results of A549 cells and zebrafish indicate that the fluorescent microspheres are permeable to cell membranes and organisms. The distribution of Hg²⁺ in the brain of zebrafish was obtained by the fluorescence confocal imaging technique, and Hg²⁺ was successfully detected in A549 cells and zebrafish.

Investigation of bioaccessibility of Cu, Fe, Mn, and Zn in market vegetables in the colon using PBET combined with SHIME

The in vitro bioaccessibility of trace metals associated with oral ingestion of market vegetables (lettuce, pak choi, cole, and leaf lettuce) of Beijing, China was studied. The physiologically based extraction test (PBET) combined with the Simulator of Human Intestinal Microbial Ecosystem (SHIME) was applied to simulate stomach, small intestine, and colon of human. In the gastro-intestinal phases, the bioaccessibility of Cu, Fe, Mn, and Zn varied within 5.7–75.5%, 17.3–50.4%, 13.3–49.1%, and 19.9–63.7%, respectively. There was no significant difference in the metal bioaccessibility between the gastric and small intestinal phases, except for higher Cu bioaccessibility in the small intestine. Besides, the bioaccessibility of the four trace metals in the colon phase was first ever reported. A significant decline in Cu bioaccessibility (1.8–63.7%) and slight increases in the bioaccessibility of Fe (16.7–56.4%), Mn (21.2–71.6%), and Zn (15.7–69.7%) were revealed, which could mainly be attributed to the effect of colon microbiota. In addition, the estimated daily intakes (EDIs) of Cu, Fe, Mn, and Zn were worked out to be 0.7, 8.8, 2.7, and 4.5 μg kg⁻¹ body weight d⁻¹, based on which the potential influences of these trace metals in vegetables on the health of the local consumers was demonstrated.

Functional and molecular effects of mercury compounds on the human OCTN1 cation transporter: C50 and C136 are the targets for potent inhibition

The effect of mercury compounds has been tested on the organic cation transporter, hOCTN1. MeHg(+), Hg(2+), or Cd(2+) caused strong inhibition of transport. 1,4-Dithioerythritol (DTE), cysteine (Cys), and N-acetyl-l-cysteine reversed (NAC) the inhibition at different extents. 2-Aminoethyl methanethiosulfonate hydrobromide (MTSEA), a prototype SH reagent, exerted inhibition of transport similar to that observed for the mercurial agents. To investigate the mechanism of action of mercurials, mutants of hOCTN1 in which each of the Cys residues was substituted by Ala have been constructed, over-expressed in Escherichia coli, and purified. Tetraethylammonium chloride (TEA) uptake mediated by each mutant in proteoliposomes was comparable to that of wild type (WT). IC50 values of the WT and mutants for the mercury compounds were derived from dose-response analyses. The mutants C50A and C136A showed significant increase of IC50 indicating that the 2 Cys residues were involved in the interaction with the mercury compounds and inhibition of the transporter. The double mutant C50A/C136A was constructed; the lack of inhibition confirmed that the 2 Cys residues are the targets of mercury compounds. MTSEA showed similar behavior with respect to the mercurial reagents with the difference that increased IC50 was observed also in the C81A mutant. Similar results were obtained when transport was measured as acetylcholine uptake. Ethyl mercury (Thimerosal) inhibited hOCTN1 as well. C50A, C50A/C136A and, at very lower extent, C136A showed increased IC50 indicating that C50 was the major target of this mercury compound. The homology model of hOCTN1 was built using as template PiPT and validated by the experimental data on mutant proteins.

A generalized physiologically-based toxicokinetic modeling system for chemical mixtures containing metals

Background

Humans are routinely and concurrently exposed to multiple toxic chemicals, including various metals and organics, often at levels that can cause adverse and potentially synergistic effects. However, toxicokinetic modeling studies of exposures to these chemicals are typically performed on a single chemical basis. Furthermore, the attributes of available models for individual chemicals are commonly estimated specifically for the compound studied. As a result, the available models usually have parameters and even structures that are not consistent or compatible across the range of chemicals of concern. This fact precludes the systematic consideration of synergistic effects, and may also lead to inconsistencies in calculations of co-occurring exposures and corresponding risks. There is a need, therefore, for a consistent modeling framework that would allow the systematic study of cumulative risks from complex mixtures of contaminants.

Methods

A Generalized Toxicokinetic Modeling system for Mixtures (GTMM) was developed and evaluated with case studies. The GTMM is physiologically-based and uses a consistent, chemical-independent physiological description for integrating widely varying toxicokinetic models. It is modular and can be directly "mapped" to individual toxicokinetic models, while maintaining physiological consistency across different chemicals. Interaction effects of complex mixtures can be directly incorporated into the GTMM.

Conclusions

The application of GTMM to different individual metals and metal compounds showed that it explains available observational data as well as replicates the results from models that have been optimized for individual chemicals. The GTMM also made it feasible to model toxicokinetics of complex, interacting mixtures of multiple metals and nonmetals in humans, based on available literature information. The GTMM provides a central component in the development of a "source-to-dose-to-effect" framework for modeling population health risks from environmental contaminants. As new data become available on interactions of multiple chemicals, the GTMM can be iteratively parameterized to improve mechanistic understanding of human health risks from exposures to complex mixtures of chemicals.

Biosafety of flavonoids in rats: effects on copper and zinc homeostasis and interaction with low-level pesticide exposure

Two 30-day experiments (36 male Sprague-Dawley rats each) were conducted to determine effect of administering flavonoid mixture (FM) with concomitant exposure to a pesticide mixture (PM) or FM at varied levels on changes in concentrations of zinc and copper in tissues. In experiment 1, PM = chlorpyrifos, endosulfan, and thiram at 25% LD(50) was dissolved in soybean (SB) oil and gavage-fed 0.1 mL 5 days/week; FM in SB oil was mixed in AIN-93M diet at 1.0 and 5.0 mM/kg diet and fed ad libitum. The groups were Control (CON), PM, FM1, FM5, PM+FM1, and PM+FM5. In experiment 2, FM in 1% polyethylene glycol was gavage-fed (0.5 mL/5 days/week), at increasing levels(mg/kg body weight); the groups were CON, FM5, FM25, FM50, FM100, and FM200. In experiment 1, PM plus FM increased tissue Cu as compared to the CON by: plasma, 16-37%; liver, 9-20%; kidney, 13-41%; small intestinal mucosa (IM), 41%; and small intestines (SI), 77%. In experiment 2, FM fed at higher levels decreased tissue Cu by: plasma, 22-36%; liver, 23%; kidney, 24-44%; IM, 17-26%; and SI, 58% and 77%, as compared to respective CON. Kidney zinc increased at higher concentrations of FM by 14-34%. These results indicate that flavonoids can modify copper homeostasis depending on whether they are fed in the diet or by gavage.