Beryllium: genotoxicity and carcinogenicity

Beryllium (Be) has physical-chemical properties, including low density and high tensile strength, which make it useful in the manufacture of products ranging from space shuttles to golf clubs. Despite its utility, a number of standard setting agencies have determined that beryllium is a carcinogen. Only a limited number of studies, however, have addressed the underlying mechanisms of the carcinogenicity and mutagenicity of beryllium. Importantly, mutation and chromosomal aberration assays have yielded somewhat contradictory results for beryllium compounds and whereas bacterial tests were largely negative, mammalian test systems showed evidence of beryllium-induced mutations, chromosomal aberrations, and cell transformation. Although inter-laboratory differences may play a role in the variability observed in genotoxicity assays, it is more likely that the different chemical forms of beryllium have a significant effect on mutagenicity and carcinogenicity. Because workers are predominantly exposed to airborne particles which are generated during the machining of beryllium metal, ceramics, or alloys, testing of the mechanisms of the mutagenic and carcinogenic activity of beryllium should be performed with relevant chemical forms of beryllium.     

Relative toxicities of particulate and soluble forms of beryllium to a rat liver parenchymal cell line in culture and possible mechanisms of uptake.

The relative toxicities of particulate beryllium phosphate, soluble beryllium sulphate and a beryllium sulphosalicylate complex to a rat liver parencymal derived cell line have been examined in culture. Due to the propensity of beryllium salts to form beryllium phosphate in solution the incubation medium used was free of inorganic phosphate. Cell death measured by the loss of cellular lactate dehydrogenase into the medium can be produced within 76 h from beryllium phosphate and beryllium sulphosalicylate or 48 h from beryllium sulphate provided the cells have, irrespective of the form of added beryllium, taken up a minimum of 2--5 nmol Be/10(6) cells. Whilst beryllium phosphate was readily taken up as a particle, beryllium complexed with excess sulphosalicylate was not so markedly accumulated by the cells except possibly by formation of small amounts of beryllium phosphate in the medium as a result of inorganic phosphate lost from the cells. The extent of beryllium uptake from beryllium sulphate quantitatively most resembled that observed for beryllium phosphate but was largely independent of beryllium phosphate formation in the medium and not accompanied by the uptake of the SO42- anion. However, the accumulation of beryllium derived from beryllium sulphate did appear to be associated with the production of a sedimentable from believed most probably to be colloidal beryllium hydroxide. The uptake of all forms of beryllium was temperature sensitive and metabolic inhibitor studies and treatment of the cells with trypsin or neuraminidase supported the view that the distinct behaviour of beryllium derived from beryllium sulphate may be related to the enhanced toxicity of this form both under the conditions used and when administered to experimental animals.     

Modulating the strength of tetrel bonding through beryllium bonding

Quantum chemical calculations were performed to investigate the stability of the ternary complexes BeH₂···XMH₃···NH₃ (X?=?F, Cl, and Br; M?=?C, Si, and Ge) and the corresponding binary complexes at the atomic level. Our results reveal that the stability of the XMH₃···BeH₂ complexes is mainly due to both a strong beryllium bond and a weak tetrel–hydride interaction, while the XMH₃···NH₃ complexes are stabilized by a tetrel bond. The beryllium bond with a halogen atom as the electron donor has many features in common with a beryllium bond with an O or N atom as the electron donor, although they do exhibit some different characteristics. The stability of the XMH₃···NH₃ complex is dominated by the electrostatic interaction, while the orbital interaction also makes an important contribution. Interestingly, as the identities of the X and M atoms are varied, the strength of the tetrel bond fluctuates in an irregular manner, which can explained by changes in electrostatic potentials and orbital interactions. In the ternary systems, both the beryllium bond and the tetrel bond are enhanced, which is mainly ascribed to increased electrostatic potentials on the corresponding atoms and charge transfer. In particular, when compared to the strengths of the tetrel and beryllium bonds in the binary systems, in the ternary systems the tetrel bond is enhanced to a greater degree than the beryllium bond.

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Graphical Abstract A tetrel bond can be strengthened greatly by a beryllium bond

     

Effect of a beryllium complex on growth of Pseudomonas fluorescens (types R and S). I. Influence on the lag phase]

The toxicity of beryllium for Pseudomonas fluorescens is studied with the aid of an anionic complex of the element which is stable in peptone medium at pH 6 during the period of investigation. The toxic effect is characterized by an increase in the lag phase which is proportional to the square of the beryllium concentration. Further, a process of progressive adaptation is observed when the concentration of the beryllium complex is gradually increased.     

Immunogenetic factors in beryllium sensitization and chronic beryllium disease

Exposure to beryllium in the workplace can cause beryllium sensitization and chronic beryllium disease. Sensitization to beryllium can be detected in the laboratory using the beryllium lymphocyte proliferation test. It was shown that anti-HLA antibodies could block the beryllium-specific response in the beryllium lymphocyte proliferation test, thereby implicating HLA genes in chronic beryllium disease. A supratypic genetic marker, HLA-DPB1*E69, was found to be strongly associated with immunologic sensitization to beryllium and chronic beryllium disease in beryllium workers. However, there are 40 HLA-DPB1 gene variants that have E69 but that also have other DNA sequence variations. The purpose of the study was to evaluate the evidence for potential differential susceptibility that may be associated with the physical characteristics of HLA protein molecules for which different HLA-DPB1*E69 variants code; that is, do some HLA-DPB1*E69 variants convey higher risk of beryllium sensitization and chronic beryllium disease than others. To do this, two approaches were pursued: first, detailed analysis of the findings from the published literature was performed, and second, computational chemistry was used to seek clues concerning the physical properties of the HLA protein molecules for which these alleles code. Among the 40 HLA-DPB1 gene variants that code for E69, molecular epidemiological studies have suggested a risk hierarchy, where some variants appear to convey low to moderate risk of chronic beryllium disease (e.g., HLA-DPB1*0201, approximately 3-fold increased risk), some convey an intermediate risk (e.g., HLA-DPB1*1901, approximately 5-fold) and others convey high risk (e.g., HLA-DPB1*1701, >10-fold). Molecular modeling has been used to further investigate a potential mechanistic basis for these observations. We found a strong correlation between the hierarchical order of risk of chronic beryllium disease associated with specific alleles and the predicted surface electrostatic potential and charge of the corresponding isotypes. Therefore, when alleles were grouped by the relative negative charge on the molecules for which they code, the data suggest that those alleles associated with the most negatively charged proteins carry the greatest risk of beryllium sensitization and disease.     

Characteristics of beryllium bonds; a QTAIM study

The nature of beryllium bonds formed between BeX2 (X is H, F and Cl) and some Lewis bases have been investigated. The distribution of the Laplacian of electron density shows that there is a region of charge depletion around the Be atom, which, according to Laplacian complementary principal, can interact with a region of charge concentration of an atom in the base and form a beryllium bond. The molecular graphs of the investigated complexes indicate that beryllium in BeH2 and BeF2 can form “beryllium bonds” with O, N and P atoms but not with halogens. In addition, eight criteria based on QTAIM properties, including the values of electron density and its Laplacian at the BCP, penetration of beryllium and acceptor atom, charge, energy, volume and first atomic moment of beryllium atom, have been considered and compared with the corresponding ones in conventional hydrogen bonds. These bonds share many common features with very strong hydrogen bonds, however,some differences have also been observed.     

The search for Rydberg matter: Beryllium

Results are presented from theoretical investigations of condensed excited states of beryllium by the Hartree-Fock method with allowance for the width of the atomic levels. It is shown that, during the excitation of a beryllium atom in the X-ray energy range, the 2p states split, the one-electron energy levels are shifted by unequal amounts, the 2s and 2p states mix at excitation energies of 10 and 14 Ry, and the atom is stabilized at energies higher than 6.7 Ry. In the optical range of excitation energies, a condensed excited state of beryllium with a lifetime on the order of 0.1 fs is revealed.     

Effects of inhibitors on luminal opening of Ca2+ binding sites in an E2P-like complex of sarcoplasmic reticulum Ca22+-ATPase with Be22+-fluoride

We document here the intrinsic fluorescence and 45Ca2+ binding properties of putative "E2P-related" complexes of Ca2+-free ATPase with fluoride, formed in the presence of magnesium, aluminum, or beryllium. Intrinsic fluorescence measurements suggest that in the absence of inhibitors, the ATPase complex with beryllium fluoride (but not those with magnesium or aluminum fluoride) does constitute an appropriate analog of the "ADP-insensitive" phosphorylated form of Ca2+-ATPase, the so-called "E2P" state. 45Ca2+ binding measurements, performed in the presence of 100 mm KCl, 5 mm Mg2+, and 20% Me2SO at pH 8, demonstrate that this ATPase complex with beryllium fluoride (but again not those with magnesium or aluminum fluoride) has its Ca2+ binding sites accessible for rapid, low affinity (submillimolar) binding of Ca2+ from the luminal side of SR. In addition, we specifically demonstrate that in this E2P-like form of ATPase, the presence of thapsigargin, 2,5-di-tert-butyl-1,4-dihydroxybenzene, or cyclopiazonic acid prevents 45Ca2+ binding (i.e. presumably prevents opening of the 45Ca2+ binding sites on the SR luminal side). Since crystals of E2P-related forms of ATPase have up to now been described in the presence of thapsigargin only, these results suggest that crystallizing an inhibitor-free E2P-like form of ATPase (like its complex with beryllium fluoride) would be highly desirable, to unambiguously confirm previous predictions about the exit pathway from the ATPase transmembrane Ca2+ binding sites to the SR luminal medium.     

Hygienic and toxicological aspects of occupational and environmental exposure to beryllium

As the production of missile, nuclear devices and electronics grew and modern industrial technologies emerged the risk of the occupational exposure to beryllium has become increasingly common and widespread. The environmental burden of beryllium is also on the increase, not only as a result of emissions from plants producing and processing beryllium, or its alloys and compounds, but also from burning coal of higher beryllium content in some localities. This article discusses primarily the hygienic and toxicologic aspects of beryllium and its threat to human health. The following topics are included in this review: occurrence, production and uses of beryllium; its metabolism and experimental toxicology; clinical toxicology and pathogenesis of berylliosis; hygienic and epidemiologic aspects of berylliosis; berylliosis treatment and prevention. Berylliosis is here characterized as a disease combining clinical manifestations of pneumosclerosis, allergy to beryllium and, in its granulomatous form, autoimmune reactions. Importantly, the available technical means and measures can ensure that the both occupational and environmental exposure to beryllium can be kept below the established MAC values. If occasionally impossible, special preventive measures should be adopted. It is essential that all persons with allergy be prophylactically excluded from work at risk of exposure to beryllium.     

Mutagenicity, carcinogenicity and teratogenicity of beryllium

The carcinogenicity of a number of beryllium compounds has been confirmed in experiments on laboratory animals and this metal has to be treated as a possible carcinogenic threat to man. These carcinogenic properties are associated with mutagenic activity as shown by the results of short-term tests performed in vitro with beryllium chloride and beryllium sulfate. These soluble beryllium compounds can produce some infidelity of in vitro synthesis, forward gene mutations in microorganisms and in mammalian cells. They are also able to induce cell transformation. In addition to the positive results obtained in several short-term assays beryllium compounds have been found to bind to nucleoproteins, to inhibit certain enzymes needed for DNA synthesis, to bind nucleic acids to cell membranes and to inhibit microtubule polymerization. The teratogenicity of beryllium salts is relatively unknown and needs additional investigation.     

The uptake and subsequent loss of beryllium by rat liver parenchymal and non-parenchymal cells after the intravenous administration of particulate and soluble forms

A cell isolation technique has been used to study the uptake and subsequent loss of beryllium (Be) by rat liver after intravenous administration of non-lethal doses of either particulate beryllium phosphate or the more hepatotoxic soluble BeSO₄. It has been shown that beryllium phosphate is removed from the blood predominantly by the non-parenchymal (sinusoidal) cells of the liver and to a lesser extent more slowly by the parenchymal cells. After 24 h when the parenchymal cells have reached maximal Be content there has been a 50% loss of Be from the non-parenchymal cells and a similar loss from whole liver which is reflected in an increased level of Be in the blood. The Be count of non-parenchymal cells subsequently decreases much more slowly in a manner similar to that of the parenchymal cells, both being only halved during the following week. Within 24–48 h some redistribution of Be to the spleen occurs and it is suggested that this in part may be the result of Kupffer cell death. In splenectomized animals a high proportion of this redistributed Be appears to be retaken up by the liver mainly by the parenchymal cell population. After administration of BeSO₄, which is known to form beryllium phosphate in plasma, a greater proportion of the Be is taken up slowly by the parenchymal cells and no redistribution of Be to the spleen is observed. It is suggested that this behaviour is related primarily to the smaller size and nature of the beryllium phosphate particles formed in plasma under these conditions. The rate of loss of Be from both the parenchymal and non-parenchymal cells is similar to that measured in beryllium phosphate treated animals. It has been estimated that liver cell death is produced when the cell content exceeds 2–3 nmol Be/10⁶ cells although parenchymal cells appear to be more sensitive to Be derived from BeSO₄ than preformed beryllium phosphate.     

Nitric acid dissolution of large mixed cellulose ester filters for beryllium determination

Defense program use of beryllium has resulted in the need for a wide variety of sampling methods to assess the potential for airborne beryllium particulates. One technique employed in field sampling uses large (8 × 10 in.) mixed cellulose ester (MCE) filters in high volume air samplers. Standard methods for the acid digestion and analysis of the large MCE filters cannot be utilized as the increase in filter mass leads to an uncontrolled exothermic reaction (open flames). As this compromises data quality and presents a significant safety hazard, we propose here an alternative method for digesting these large filters to ensure a solution compatible with ICP-AES (inductively coupled plasma-atomic emission spectroscopy) analysis. The method is a modification of well accepted hot plate digestion methods, which avoids the use of the most hazardous acids such as perchloric or hydrofluoric. While only beryllium was investigated, it is likely that other metals on filters could be digested by this method. Filter media were spiked with a variety of beryllium sources to test the digestion, including beryllium solution spikes, beryllium metal, beryllium oxide and beryllium in soil. Recovery of beryllium metal (103%), beryllium in soil (96%) and beryllium solution spikes (93%) were excellent.     

Uptake, distribution and binding of beryllium to organelles of the rat liver cell

1. Male rats were injected intravenously with amounts ranging from 0.08 to 111.0mumoles of [(7)Be]beryllium sulphate/kg. body wt. The distribution in the rat and the subcellular distribution of beryllium in the liver were determined. 2. Within the entire dose range a higher specific activity of beryllium was present in a mitochondrial fraction containing the lysosomes. Purification of this fraction confirmed that beryllium is taken up by lysosomes. 3. With doses approaching the LD(50), beryllium was also found in increasing amounts to be present in the liver cell nuclei. Beryllium also showed affinity towards isolated cell nuclei in vitro. Evidence is presented that they have one class of binding sites for beryllium. Mitochondria have less affinity for beryllium. 4. No evidence could be obtained of an affinity of beryllium for DNA or RNA by fractionation of nuclei and dialysis experiments. 5. The presence of beryllium in liver cell nuclei may be relevant to the effects of beryllium on nuclear structure and function.     

Beryllium uptake and related biological effects studied in THP-1 differentiated macrophages

Investigation of cellular uptake of metal compounds is important in understanding metal-related toxicity and diseases. Inhalation of beryllium aerosols can cause chronic beryllium disease, a progressive, granulomatous fibrosis of the lung. Studies in laboratory animals and cultured animal cells indicate that alveolar macrophages take up beryllium compounds and participate in a hypersensitivity immune response to a beryllium-containing antigen. In the present work, human monocyte cell line THP-1 was induced with phorbol myristate acetate to differentiate into a macrophage. This cell with characteristics of human alveolar macrophages was employed to study cellular beryllium uptake and related biological effects. Morphological changes, phagocytosis of fluorescent latex beads, and cell surface CD14 expression were used to verify the successful differentiation of THP-1 monocytes into macrophages. An improved mass spectrometry method for quantitative analysis of intracellular beryllium as opposed to the traditional radioisotopic approach was developed using ICP-MS. The influence of the solubility of beryllium compounds, exposure duration, and beryllium concentration on the incorporation of beryllium was studied. Our data indicated that the uptake of particulate BeO was much more significant than that of soluble BeSO(4), suggesting the major cellular uptake pathway is phagocytosis. Nevertheless, subsequent DAPI nuclear staining and PARP cleavage study indicated that beryllium uptake had a negligible effect on the apoptosis of THP-1 macrophages compared to the unstimulated macrophage control. Meanwhile, no substantial variation of tumour necrosis factor-alpha production was observed for THP-1 macrophages upon beryllium exposure. These data imply alveolar macrophages could have some level of tolerance to beryllium and this may explain why most Be-exposed individuals remain healthy throughout life.     

Theoretical study of penta- and heteropentadienyl beryllium complexes coordinated to hydrogen molecules

A series of penta- and heteropentadienyl [CH₂CHCHCHXBe]⁺, (X?=?CH₂, O, NH, S) complexes has been theoretically studied. All calculated complexes show beryllium atoms with two, three, and five coordination numbers. The density functional theory (DFT) was used to determine the electron and structural behavior of those beryllium complexes. The nature of the ligands plays an important role in the form of binding to the beryllium atom. Beryllium structures 1–4 are able to coordinate only one hydrogen molecule. A molecular orbital analysis for all complexes was performed in order to know more about the nature of their bonding scheme.     

The induction of chromosome damage in CHO cells by beryllium and radiation given alone and in combination

Studies were conducted to determine the effects of BeSO4 or X rays, alone and in combination, on cell cycle kinetics, cell killing, and the production of chromosome aberrations in Chinese hamster ovary (CHO) cells. The concentration of BeSO4 required to kill 50% of CHO cells exposed to BeSO4 for 20 h was determined to be 1.1 mM with 95% confidence intervals of 0.72 to 1.8 mM. During the last 2 h of the 20-h beryllium treatment (0.2 and 1.0 mM), cells were exposed to 0.0, 1.0, or 2.0 Gy of X rays. Exposure to either BeSO4 or X rays produced a change in cell cycle kinetics which resulted in an accumulation of cells in the G2/M stage of the cell cycle. However, combined exposure to both agents resulted in a block similar to that observed following exposure to X rays only. The background level of chromosome damage was 0.05 +/- 0.015 aberrations/cell in the CHO cells. Seven hours after the end of exposure to 0.2 and 1.0 mM beryllium, 0.03 +/- 0.003 and 0.09 +/- 0.02 aberrations/cell, respectively, were observed. The data for chromosome aberrations following X-ray exposure were fitted to a linear model with a coefficient of 0.14 +/- 0.01 aberrations/cell/Gy. When beryllium was combined with the X-ray exposure the interactive response was predicted by a multiplicative model and was significantly higher (P less than 0.05) than predicted by an additive model. The influence of time after radiation exposure on the interaction between beryllium and X rays was also determined. No interaction between beryllium and X-ray exposure in the induction of chromosome-type aberrations (P greater than 0.05) was detected. The frequency of chromatid-type exchanges and total aberrations was significantly higher (P less than 0.05) in the radiation plus beryllium-exposed cells when compared to cells exposed to X rays only, at both 9 and 12 h after X-ray exposure. These data suggest that the multiplicative interaction may be limited to cells in the S and G2 stages of the cell cycle.     

Properties, composition, and structure of stearic acid-stearate monolayers on alkaline earth solutions

Interactions between alkaline earth ions and the carboxylate ligand in a stearic acid surface film have been investigated by IR spectrophotometry and surface chemical procedures. The frequency and shape of the carboxylate absorption band and the effect of hydration and pH on band characteristics suggest that beryllium, magnesium, and calcium ions form calcium-type complexes with the stearate ligand while strontium and barium ions form both calcium-type complexes and more ionic barium-type complexes, which have lower carboxylate band maxima. Since IR band frequencies in anhydrous calcium-type complexes are directly proportional to the charge/(crystal radius) ratio, it is apparent that covalency decreases in the order: Be > Mg > Ca > Sr > Ba. The decreasing order of stability constants estimated from spectrophotometric titration data, Be > Ca > Mg > Sr > Ba, demonstrates that calcium behaves anomalously. This anomalous behavior is also apparent in the high solid-to-liquid phase transition temperature and small surface area of the calcium-carboxylate film compared to films composed of complexes with the other ions. A geometric factor related to the ionic radius and the radius of the carboxylate binding site formed by a calcium stearate lattice is proposed to explain the unique properties of calcium-carboxylate surface films. Although the beryllium complex has the highest carboxylate band frequency and stability constant, it gives an atypical "expanded" surface film. A hydrogen bonded lattice formed with a soluble beryllium monohydrate is suggested as an explanation for this film property.     

Modulating weak intramolecular interactions through the formation of beryllium bonds: complexes between squaric acid and BeH2

The electronic structure of the two most stable isomers of squaric acid and their complexes with BeH₂ were investigated at the B3LYP/6-311?+?G(3df,2p)// B3LYP/6-31?+?G(d,p) level of theory. Squaric acid forms rather strong beryllium bonds with BeH₂, with binding energies of the order of 60 kJ?mol^?1. The preferential sites for BeH₂ attachment are the carbonyl oxygen atoms, but the global minima of the potential energy surfaces of both EZ and ZZ isomers are extra-stabilized through the formation of a BeH···HO dihydrogen bond. More importantly, analysis of the electron density of these complexes shows the existence of significant cooperative effects between the beryllium bond and the dihydrogen bond, with both becoming significantly reinforced. The charge transfer involved in the formation of the beryllium bond induces a significant electron density redistribution within the squaric acid subunit, affecting not only the carbonyl group interacting with the BeH₂ moiety but significantly increasing the electron delocalization within the four membered ring. Accordingly the intrinsic properties of squaric acid become perturbed, as reflected in its ability to self-associate.

Thermodynamic and Transport Properties of Beryllium Vapor in the Supercritical Fluid State

The thermal and caloric equations of state, composition, and conductivity of a supercritical beryllium vapor are calculated using the earlier proposed “3+” chemical model, which incorporates atoms, electrons, ions, and electron jellium with allowance for interatomic and intercharge interactions. The introduction of an electron jellium makes it possible to describe the pressure-induced ionization and explain the increase in the conductivity of beryllium vapor under compression. The cohesive bond of atoms caused by the electron jellium compensates for interactions when calculating the composition and reduces the effect of intercharge interactions on the equation of state. The parameters of the beryllium critical point and the applicability domain of the model are discussed.     

Beryllium in the environment: Whether fatal for plant growth?

Beryllium could be a threatening heavy metal pollutant in the agro-ecosystem that may severely affect the performance of crops. Beryllium is used in various industries to make nuclear weapons and reactors, aircraft and space vehicle structures, instruments, and X-ray machines, and its entry into the environment is alarming for the productivity and sustainability of the ecosystem. In this review, we present a contemporary synthesis of the existing data regarding the toxic effects of beryllium on toxicity on biochemical and physiological processes in plants. Moreover, uptake, translocation, and assimilation of beryllium and its interaction with some essential mineral elements are also discussed. Although limited data are available regarding biochemical responses of plants to beryllium toxicity, we tried to clarify some basic physiological and biochemical steps that can be hampered by beryllium in plants. We linked our hypothetical concepts with previous evidence and provide a comprehensive summary of all possible remediation strategies that can be used for plants. Overall, we hope this review will be beneficial due to its practical implications and research directions.