Experimental study and mathematical modeling of toxic metals combined action as a scientific foundation for occupational and environmental health risk assessment. A summary of results obtained by the Ekaterinburg research team (Russia)

Modeling mixtures interactions in environmental toxicology

In the environment, organisms are exposed to mixtures of different toxicants, which may interact in ways that are difficult to predict when only considering each component individually. Adapting and expanding tools from pharmacology, the toxicology field uses analytical, graphical, and computational methods to identify and quantify interactions in multi-component mixtures. The two general frameworks are concentration addition, where components have similar modes of action and their effects sum together, or independent action, where components have dissimilar modes of action and do not interact. Other interaction behaviors include synergism and antagonism, where the combined effects are more or less than the additive sum of individual effects. This review covers foundational theory, methods, an in-depth survey of original research from the past 20 years, current trends, and future directions. As humans and ecosystems are exposed to increasingly complex mixtures of environmental contaminants, analyzing mixtures interactions will continue to become a more critical aspect of toxicological research.

Comparative and Combined In Vitro Vasotoxicity of Nanoparticles Containing Lead and Cadmium

In vitro toxicological experiments were performed on an endothelial cell line exposed to different doses of spherical nanoparticles of cadmium and/or of lead sulfides with mean diameter 37 ± 5 nm and 24 ± 4 nm, respectively. Toxic effects were estimated by Luminescent Cell Viability Assay, endothelin-1 concentration and cell size determination. Some dose-response relationships were typically monotonic (well approximated with hyperbolic function) while others were bi- or even 3-phasic and could be described within the expanded hormesis paradigm. The combined toxicity type variated depending on the effect it was assessed by.

Effects of the occupational exposure on health status among petroleum station workers, Khartoum State, Sudan

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Mean blood lead level for exposed group of non-smokers was 0.58 mg/l.

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Mean blood lead level for exposed group of smokers was 1.49 mg/l.

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Mean value of lead in urine of smokers were 1.59 mg/L & 1.16 mg/L in both groups.

Objective

The hazards of petroleum station activities are greatly emphasized due to their negative impact on workers’ health and safety concerns. This study aims to assess the effect of occupational exposure among the workers in various petroleum station at the Khartoum State, Sudan.

Methods

An analytical and experimental study design is followed where 60 participants were selected through purposive sampling technique. The participants were recruited from the petroleum workstation and were considered as the lead exposed group whereas the participants who lived faraway from the petroleum station and had no exposure to lead were considered as un-exposed group. To avoid the effects of smoking on lead concentration we further divided these groups into smokers and non-smokers. IBM, SPSS was used for the statistical analysis of the collected data.

Results

The results show that there is no significant difference in white blood cells (WBCs) count between exposed and unexposed lead group. We also did not find significant difference in Red blood cells (RBCs) count. Participant from both groups had normal range of haemoglobin (Hb). However, haematocrit (Hct) levels were elevated in both of these groups. We also tested the platelet count in these groups and found that platelet count was slightly lower in lead exposed group as compared to the unexposed group but average count was found within the normal range. Finally, the lead concentration in serum and urine was detected of the participants. Results reveal that the serum lead concentration of non-smokers (0.58 mg/l) in the exposed group was higher than in non-smokers of unexposed group (0.49 mg/l). The lead concentration in serum of smokers in exposed group was also high (1.49 mg/l) than the lead concentration detected in serum of smokers in unexposed group (1.14 mg/l). Urine lead levels of exposed group was also high than the unexposed group in smokers and non-smokers. Mean value of lead in urine among non-smokers of the exposed and unexposed group were 0.76 mg/L and 0.19 mg/L respectively. In the case of smokers, 1.59 mg/L and 1.16 mg/L were the mean value of lead in urine for both exposed and unexposed groups respectively.

Conclusion

From the given results it can be concluded that health safety measures for workers must be implemented to maintain good health status of workers at petroleum stations.

Welding fumes composition and their effects on blood heavy metals in albino rats

Toxic substances produced during welding include heavy metals, carbon monoxide, carbon dioxide, and nitrogen oxides. The study aims to evaluate the heavy metals concentration in welding fumes and the blood of the animals exposed to welding fumes. The fumes were collected from a welding site by a skilled welder and part of it was subjected to metals analysis. A total of 130 rats were divided into 13 groups. 12 groups were given doses calculated to correspond to real-life workers exposure regimes and 1 group served as control. The dosages were administered intratracheally after anesthetization weekly for 12 weeks. The animals were sacrificed and whole blood samples were collected for atomic absorption spectrophotometry. The metals in fumes analyzed were decreasing in order of Fe > K > Pb > Co > Cd > Ca > Ni > Mn > Zn > Cr > Al > Cu > Mg. Changes were observed in the behaviour of the test animals compared to the control indicating probable toxicity. The values of Pb, Cr, Fe, Mn, and Ni in the exposed animal's blood were higher than the control and increased relatively across the treatment groups. However, the values of Al and Zn were not significantly different from the control. These indicate that exposure to welding fumes having contained a significant amount of heavy metals has caused noticeable toxicity symptoms with simultaneous elevation in blood metal levels. Monitoring and regulation of these activities should be enforced by relevant authorities in Kano and Nigeria in general.

Some data on the comparative and combined toxic activity of nanoparticles containing lead and cadmium with special attention to their vasotoxicity

Moderate subchronic intoxication was induced in rats by repeated intraperitoneal injections of PbO (49.6 ± 16.0 nm) and/or CdO (57.0 ± 13.0 nm) nanoparticles (NP) three times a week during 6 weeks. In particular, there was a reduction in arterial blood pressure and in blood concentrations of a number of factors controlling vasoconstriction and vasodilation, particularly of endothelin 1 (ET-1). This toxic effect was attenuated with a bioprotective complex administered in the background. The study confirmed as well that the combined binary action typology varies depending on which effect it is estimated by.

Some outcomes and a hypothetical mechanism of combined lead and benzo(a)pyrene intoxication, and its alleviation with a complex of bioprotectors

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Rats were injected repeatedly intraperitoneally with lead acetate and/or benzo(а)pyrene solutions in various dose ratios.

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Under combined exposure the organism load with benzo(а)pyrene was increased while that with its metabolites reduced.

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The genotoxic effect of the combined exposure was higher than that of benzo(a)pyrene alone.

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This effect was inhibited by a complex of antitoxic bioprotectors.

Rats were exposed 3 times a week during 6 weeks to repeated intraperitoneal injections of lead acetate solution in water (Pb) and/or benzo(а)pyrene solution in petrolatum oil (B(а)P) in various dose ratios. Towards the end of the period, the animals developed a moderate subchronic intoxication having some features characteristic of lead effects. The type of combined toxicity estimated with the help of isoboles constructed by the Response Surface Methodology was found to be varied depending on a particular effect, its level, and dose ratio. However, Pb and B(a)P in combination often displayed an additive or even superadditive action. In the group exposed to this combination compared with the group of rats exposed to B(a)P alone, its concentration in the organism was increased while the concentration of some B(a)P oxidative metabolism products was reduced. Such inhibition of B(a)P biotransformation, assumingly associated with impaired heme and, thus, cytochrome P450 synthesis induced by lead intoxication, can serve as an explanation for certain enhancement of the genotoxic effect of B(a)P. This effect was not present in the same combined intoxication if a complex of antitoxic bioprotectors was being administered in the background.

Force-velocity characteristics of isolated myocardium preparations from rats exposed to subchronic intoxication with lead and cadmium acting separately or in combination

This investigation continues our study of the effects of Pb-Cd poisoning on the heart, extending the enquiry from isometric to auxotonic contractions, thereby examining the effect on the ability of myocardial tissues to perform mechanical work. Different shifts were revealed in myocardial force-velocity relations following subchronic exposure of rats to lead acetate and cadmium chloride acting separately, in combination, or in combination with a bioprotective complex (BPC). The experiments were conducted on isolated preparations of trabecules and papillary muscles of the right ventricle in physiological loading conditions and on isolated heart muscle contractile proteins examined by the in vitro motility assay. The results of the latter correlate with the shifts in the ratio of cardiac myosin isoforms. The amount of work performed by the myocardium was calculated on the basis of the tension-shortening loop area and was found to be similar in the preparations from all experimental groups. This fact presumably reflects adaptive capacity of the myocardial function even when contractility is damaged due to the metallic intoxication of a moderate severity. Some characteristics of rat myocardium altered by the impact of lead-cadmium intoxication became fully or partly normalized if intoxication developed against background administration of a bioprotective complex (BPC). Together with previously reported results obtained in the isometric mode of contractility, all these results strengthen the scientific foundations of risk assessment and risk management projects in the occupational and environmental conditions characterized by human exposure to lead and/or cadmium.

An overview of experiments with lead-containing nanoparticles performed by the Ekaterinburg nanotoxicological research team

Over the past few years, the Ekaterinburg (Russia) interdisciplinary nanotoxicological research team has carried out a series of investigations using different in vivo and in vitro experimental models in order to elucidate the cytotoxicity and organ-systemic and organism-level toxicity of lead-containing nanoparticles (NP) acting separately or in combinations with some other metallic NPs. The authors claim that their many-sided experience in this field is unique and that some of their important results have been obtained for the first time. This paper is an overview of the team's previous publications in different journals. It is suggested to be used as a compact scientific base for assessing health risks associated not only with the production and usage of engineered lead-containing NPs but also with their inevitable by-production as toxic air pollutants in the metallurgy of lead, copper or their alloys and in soldering operations.

Some Peculiarities in the Dose Dependence of Separate and Combined In Vitro Cardiotoxicity Effects Induced by CdS and PbS Nanoparticles With Special Attention to Hormesis Manifestations

Spherical nanoparticles (NPs) of cadmium and lead sulfides (diameter 37 ± 5 and 24 ± 4 nm, respectively) have been found to be cytotoxic for HL-1 cardiomyocytes as evidenced by decrease in adenosine triphosphate-dependent luminescence. Cadmium sulfide (CdS)-NPs were discovered to produce a much greater cytotoxic impact than lead sulphide (PbS)-NP. Given the same dose range, CdS-NP reduced the number of calcium spikes. A similar effect was observed for small doses of PbS-NP. In addition to cell hypertrophy under the impact of certain doses of CdS-NP and PbS-NP, doses causing cardiomyocyte size reduction were identified. For these 3 outcomes, we obtained both monotonic "dose-response" functions (well approximated by the hyperbolic function) and different variants of non-monotonic ones for which we found adequate mathematical expressions by modifying certain models of hormesis available in the literature. Data analysis using a response surface linear model with a cross-term provided new support to the previously established postulate that a diversity of types of joint action characteristic of one and the same pair of damaging agents is one of the important assertions of the general theory of combined toxicity.

Changes in rat myocardium contractility under subchronic intoxication with lead and cadmium salts administered alone or in combination

Subchronic intoxications induced in male rats by repeated intraperitoneal injections of lead acetate and cadmium chloride, administered either alone or in combination, are shown to affect the biochemical, cytological and morphometric parameters of blood, liver, heart and kidneys. The single twitch parameters of myocardial trabecular and papillary muscle preparations were measured in the isometric regime to identify changes in the heterometric (length-force) and chronoinotropic (frequency-force) contractility regulation systems. Differences in the responses of these systems in trabecules and papillary muscles to the above intoxications are shown. A number of myocardium mechanical characteristics changing in rats under the effect of a combined lead-cadmium intoxication and increased proportion of α-myosin heavy chains were observed to normalize fully or partially if such intoxication was induced against background administration of a proposed bioprotective complex. Based on the experimental results and literature data, some assumptions are suggested concerning the mechanisms of the cardiotoxic effects produced by lead and cadmium.

Further verification of some postulates of the combined toxicity theory: New animal experimental data on separate and joint adverse effects of lead and cadmium

Outbred male rats were repeatedly injected intraperitoneally two-level sub-lethal doses of lead acetate and/or cadmium chloride solutions 3 times a week during 6 weeks. The animals developed explicit, even if moderate, subchronic intoxication characterized by a large number of indices, both common to both metals (including increased DNA fragmentation coefficient) and lead-specific. Special attention was paid to hemodynamic and electrocardiographic effects. The combined action of lead and cadmium was modeled with the help of the Response Surface Methodology to obtain additional support for the previously substantiated postulates of combined toxicity's typological ambiguity. This is dependent on which particular effect comes under consideration, on its level, and on the acting dose ratio. For one and the same toxic combination, the type of combined toxic action can vary from synergistic to contra-directional. In particular, the actions of lead and cadmium on blood pressure were found to be opposite in direction. Furthermore, it is shown once again that the systemic toxic effects of a metal combination, its in vivo genotoxicity included, can be more or less attenuated by background administration of a theoretically justified composition of biologically active agents.

More data on in vitro assessment of comparative and combined toxicity of metal oxide nanoparticles

Isolated and combined damaging effects of PbO and CuO nanoparticles were estimated on an established line of human fibroblasts by a decrease in: (a) the cellular dehydrogenase activity (MTT Assay), (b) the ATP content (Luminescent Cell Viability Assay), (c) the cellular proliferation, viability, spreading, and attachment to substrate evaluated integrally by continuous impedance-based measurement of the Normalized Cell Index. Using all these indices, we demonstrate an explicit dependence of cell damage on the concentrations of both metal oxide nanoparticle (MeO-NP) species. This dependence is adequately approximated with a hyperbolic function. At equal exposure levels, PbO-NP and CuO-NP demonstrate quantitatively similar cytotoxicities. The same was observed previously for some non-specific in vivo toxicity measures. The combined in vitro cytotoxicity has also been described mathematically using the Response Surface Methodology and found to be represented by various types, thus corroborating, in this respect also, the findings of a previous animal experiment with the same MeO-NPs.

Consequent stages of developing a multi-compartmental mechanistic model for chronically inhaled nanoparticles pulmonary retention

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A mechanistic model of inhaled particle pulmonary retention is adjusted to describe that of nanoparticles (NP).

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Its stucture and parameters were verified based on experiments with NPs of Fe₂O₃, SiO₂ and NiO.

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Unlike modeling mineral dusts retention, for nano-aerosols it proved necessary to describe NP solubilization .

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Under chronic inhalation exposure, a damage to clearance mechanisms makes adjust the model.

The paper retraces the development of a mechanistic multicompartmental system model describing particle retention in lungs under chronic inhalation exposures. This model was first developed and experimentally tested for various conditions of exposure to polydisperse dusts of SiO₂ or TiO₂. Later on it was successfully used as a basis for analyzing patterns in the retention of nanoparticles having different chemical compositions (Fe₂O₃, SiO₂, NiO). This is the first publication presenting the outcomes of modeling lung retention of nickel oxide nano-aerosols under chronic inhalation exposure.

The most significant adaptation of the above-mentioned model to the conditions of exposure to metal-oxide nanoparticles is associated with the need to describe mathematically not only the physiological mechanisms of their elimination but also their solubilization “in vivo” bearing in mind that the relative contribution of the latter may be different for nanoparticles of different nature and predominant in some cases.

Using nickel oxide as an example, it is suggested as well that damage to the physiological pulmonary clearance mechanisms by particularly toxic nanoparticles may result in lung toxicokinetics becoming nonlinear.

Using Various Nonlinear Response Surfaces for Mathematical Description of the Type of Combined Toxicity

The article considers the problem of characterizing the type of combined action produced by a mixture of toxic substances with the help of nonlinear response functions. Most attention is given to second-order models: the linear model with a cross-term and the quadratic model. General propositions are formulated based on the data on combined toxicity patterns previously obtained by the Ekaterinburg nanotoxicology team in animal experiments and analyzed with the help of the linear model with a cross-term. It is shown now that the quadratic model features these general characteristics in full measure, but interpretation of combined toxicity types based on isobolograms obtained by the quadratic model is more difficult. This suggests that where both models ensure a comparable quality of combined toxicity type identification, it would be enough to use the linear model with a cross-term.

Combined Subchronic Toxicity of Aluminum (III), Titanium (IV) and Silicon (IV) Oxide Nanoparticles and Its Alleviation with a Complex of Bioprotectors

Stable suspensions of metal/metalloid oxide nanoparticles (MeO-NPs) obtained by laser ablation of 99.99% pure elemental aluminum, titanium or silicon under a layer of deionized water were used separately, or in three binary combinations, or in a ternary combination to induce subchronic intoxications in rats. To this end, the MeO-NPs were repeatedly injected intraperitoneally (i.p.) 18 times during 6 weeks before measuring a large number of functional, biochemical, morphological and cytological indices for the organism’s status. In many respects, the Al₂O₃-NP was found to be the most toxic species alone and the most dangerous component of the combinations studied. Mathematical modeling with the help of the Response Surface Methodology showed that, as well as in the case of any other binary toxic combinations previously investigated by us, the organism’s response to a simultaneous exposure to any two of the MeO-NP species under study was characterized by a complex interaction between all possible types of combined toxicity (additivity, subadditivity or superadditivity of unidirectional action and different variants of opposite effects) depending on which outcome this type was estimated for and on effect and dose levels. With any third MeO-NP species acting in the background, the type of combined toxicity displayed by the other two remained virtually the same or changed significantly, becoming either more or less unfavorable. Various harmful effects produced by the (Al₂O₃-NP + TiO₂-NP + SiO₂-NP)-combination, including its genotoxicity, were substantially attenuated by giving the rats per os during the entire exposure period a complex of innocuous bioactive substances expected to increase the organism’s antitoxic resistance.

The most important inferences from the Ekaterinburg nanotoxicology team's animal experiments assessing adverse health effects of metallic and metal oxide nanoparticles

During 2009-2017 we have studied nanoparticles of elemental silver or gold and of iron, copper, nickel, manganese, lead, zinc, aluminium and titanium oxides (Me-NPs) using, in most cases, a single low-dose intratracheal instillation 24 h before the bronchoalveolar lavage to obtain a fluid for cytological and biochemical assessment and, in all cases, repeated intraperitoneal injections in non-lethal doses to induce subchronic intoxications assessed by a lot of toxicodynamic and toxicokinetic features. We have also studied the same effects for a number of relevant combinations of these Me-NPs and have revealed some important patterns of their combined toxicity. Besides, we have carried out long-term inhalation experiments with Fe2O3, NiO and amorphous SiO2 nano-aerosols. We have demonstrated that Me-NPs are much more noxious as compared with their fine micrometric counterparts although the physiological mechanisms of their elimination from the lungs proved to be highly active. Even if water-insoluble, Me-NPs are significantly solubilized in some biological milieus in vitro and in vivo, which may explain some important peculiarities of their toxicity. At the same time, the in situ cytotoxicity, organ-systemic toxicity and in vivo genotoxicity of Me-NPs strongly depends on specific mechanisms characteristic of a particular metal. For some of the Me-NPs studied, we have proposed standards of presumably safe concentrations in workplace air. Along with this, we have proved that the adverse effects of Me-NPs could be significantly alleviated by background or preliminary administration of adequately composed combinations of some bioprotectors.