Studies on the genotoxic effect of chromium oxide (Cr VI): Interaction with deoxyribonucleic acid in solution

The combined effects of bisphenol S and hexavalent chromium on alpha-glucosidase: Intermolecular interaction, structural and functional changes

The co-contamination of heavy metal ions and organic pollutants has posed a threat to human health. Herein, this study investigated the intermolecular interactions of bisphenol S (BPS) and hexavalent chromium (Cr(VI)) under both individual and coexisting conditions, with alpha-glucosidase (AG), a key enzyme in carbohydrate metabolism, and the corresponding effects on the structure and function of AG. Multiple spectroscopic and molecular docking methods were employed to conduct the investigation in vitro and in silico. The results indicated that both BPS and Cr(VI) quenched the fluorescence of AG via a combined static and dynamic quenching processes. At 310 K, the binding constants of AG with BPS in the AG-BPS and (AG-Cr(VI))-BPS systems were 1.84 × 104 and 2.03 × 104 L mol-1, and the binding constants of AG with Cr(VI) in the AG-Cr(VI) and (AG-BPS)-Cr(VI) systems were 6.14 × 103 and 4.35 × 103 L mol-1. Cr(VI) could significantly affect the binding site of BPS in AG, while BPS had a minimal impact on the binding site of Cr(VI) in AG. BPS and Cr(VI) caused varied structural alterations of AG, and the impact of their coexistence on the structure of AG was related to the order in which they were added. Both BPS and Cr(VI) had a concentration-related effect on AG activity. This study provides valuable insights into the molecular mechanisms underlying the combined toxic effects of BPS and Cr(VI) on AG, highlighting the potential health risks associated with their environmental co-exposure.

Interactions between chromium species and DNA in vitro and their potential role in the toxicity of hexavalent chromium

Epidemiological and animal studies have supported the carcinogenicity of hexavalent chromium [Cr(VI)]; however, molecular changes responsible for the induction of cancer by Cr(VI) are not entirely understood. Numerous mechanistic studies suggested the role of oxidative stress and genotoxicity in Cr(VI)-mediated carcinogenesis; however, specific types of DNA damage have not yet been conclusively attributed to specific chromium species or other reactive byproducts generated in biological systems exposed to Cr(VI). Due to the remarkably complex chemistry and biological effects of chromium species generated through the intracellular reduction of Cr(VI), their relevance for Cr(VI)-mediated carcinogenesis has not yet been fully elucidated and continues to be a subject of ongoing discussions in the field. In this report, we describe a complex world of chromium species and their reactivity with DNA and other biologically relevant molecules in vitro to inform a more complete understanding of Cr(VI)-mediated toxicity. In addition, we discuss previous results in the context of in vitro models and analytical methods to reconcile some conflicting findings on the biological role of chromium species.

The Cytotoxicity, DNA Fragmentation, and Decreasing Velocity Induced By Chromium(III) Oxide on Rainbow Trout Spermatozoa

The present study aimed to determine the cytotoxicity of chromium(III) oxide micro particles (Cr₂O₃-Ps) in rainbow trout (Oncorhynchus mykiss) spermatozoa. Firstly, Cr₂O₃-Ps were synthesized and structurally characterized the surface, morphological for particle size and thermal properties. In addition, its structural and elemental purity was determined using energy-dispersive X-ray (EDX) spectrum and elemental maps. Structural purity, thermal properties, and stability of Cr₂O₃-Ps were also examined in detail by performing thermal analysis techniques. The cytotoxicity of Cr₂O₃-Ps was measured by the observation of velocities, antioxidant activities, and DNA damages in rainbow trout spermatozoa after exposure during 3 h in vitro incubation. The straight line velocity (VSL), the curvilinear velocity (VCL), and the angular path velocity (VAP) of spermatozoa decreased after exposure to Cr₂O₃-Ps. While the superoxide dismutase (SOD) and the catalase (CAT) decreased, the lipid peroxidation increased in a dose-dependent manner. However, the total glutathione (tGSH) was not affected in this period. DNA damages were also determined in spermatozoa using Comet assay. According to DNA in tail (%) data, DNA damages have been detected with gradually increasing concentrations of Cr₂O₃-Ps. Furthermore, all of class types which are categorized as the intensity of DNA fragmentation has been observed between 50 and 500 µg/L concentrations of Cr₂O₃-Ps exposed to rainbow trout spermatozoa. At the end of this study, we determined that the effective concentrations (EC50) were 76.67 µg/L for VSL and 87.77 µg/L for VCL. Finally, these results about Cr₂O₃-Ps may say to be major risk concentrations over 70 µg/L for fish reproduction in aquatic environments.

Nephroprotective Efficacy of Selenium and Zinc Against Potassium Dichromate-Induced Renal Toxicity in Pregnant Wistar Albino Rats

Hexavalent chromium (CrVI) compounds are potent toxicants commonly used in numerous industries. Thus, potential toxic effects and health hazards are of high relevance. Selenium (Se) and zinc (Zn) are known for their antioxidant and chemoprotective properties. However, little is known about their protective effects against CrVI-induced renal damage during pregnancy. In this context, the present study aimed to investigate the protective efficacy of these two essential elements against potassium dichromate-induced nephrotoxicity in pregnant Wistar Albino rats. Female rats were divided into control and four treated groups of six each receiving subcutaneously on the 3rd day of pregnancy, K₂Cr₂O₇ (10 mg/kg, s.c. single dose) alone, or in association with Se (0.3 mg/kg, s.c. single dose), ZnCl₂ (20 mg/kg, s.c. single dose) or both of them simultaneously. The nephrotoxic effects were monitored by the evaluation of plasma renal parameters, oxidative stress biomarkers, DNA damage, and renal Cr content. The obtained results showed that K₂Cr₂O₇ disturbed renal biochemical markers, induced oxidative stress and DNA fragmentation in kidney tissues, and altered renal histoarchitecture. The co-administration of Se and/or ZnCl₂ has exhibited pronounced chelative, antioxidant, and genoprotective effects against K₂Cr₂O₇-induced renal damage and attenuated partially the histopathological alterations. These results suggest that Se and Zn can be used as efficient nephroprotective agents against K₂Cr₂O₇-induced toxicity in pregnant Wistar Albino rats.

Protective effects of selenium and zinc against potassium dichromate-induced thyroid disruption, oxidative stress, and DNA damage in pregnant Wistar rats

Hexavalent chromium (CrVI) is an environmental pollutant and an endocrine-disrupting metal. Se and Zn are essential trace elements, known to play a crucial role in thyroid homeostasis. However, there is a lack of data reporting thyrotoxicity during gestation. In this study, we investigated the protective effects of selenium and zinc against potassium dichromate-induced thyrotoxicity in pregnant Wistar rats. Thirty pregnant Wistar rats were divided into control and four treated groups receiving subcutaneously (s.c) on the 3rd day of pregnancy, K2Cr2O7 (10 mg/kg, s.c) alone, or in association with Se (0.3 mg/kg, s.c), ZnCl2 (20 mg/kg, s.c), or both of them simultaneously. The hormonal profile, oxidative stress biomarkers, DNA damage, and histological modifications were evaluated. Our main findings showed that K2Cr2O7 promoted hypothyroidism, oxidative stress, genotoxicity, and histological alterations in the thyroid gland. The co-treatment with Se or ZnCl2 has mitigated K2Cr2O7-induced thyrotoxicity in pregnant Wistar rats by exhibiting antioxidant and genoprotective effects. However, the combined co-treatment of both of them was less thyroprotective, and therefore, further investigations on the synergetic interaction of Se and Zn against CrVI toxicity using different doses and exposure routes are required.

Antagonistic effects of nano-selenium on broilers hepatic injury induced by Cr(VI) poisoning in AMPK pathway

Cr (chromium, with common valence states of III and VI) is one of the common broiler feed additives. Liver injury and metabolic disorders could be caused by Cr_(VI) (hexavalent chromium) poisoning in broilers. Oxidative damage and metabolic disorders of organisms caused by heavy metals could be antagonized by nano-Se (nano-selenium). Nano-Se was chosen to study the antagonism of Cr_(VI) poisoning in broilers. AMPK (Adenosine 5^,-monophosphate-activated protein kinase) is known as a "cell energy regulator" and plays a key regulatory role in carbohydrate and lipid metabolism. AMPK pathway and ACACA/CPT1A two genes were selected to study the prevention and treatment of nano-Se on Cr_(VI) poisoning in broilers and its molecular mechanism. For this purpose, 180 1-day-old AA (Arbor Acres) broilers were selected and randomly divided into 6 groups (n = 30) for further testing. After feeding as planned for 35 days, the livers of such broilers were taken for further examination including histopathological examination, differential gene expression analysis, and further validation on both mRNA and protein levels using related techniques like RT-qPCR, western blot, and immunohistochemistry (IHC). The histopathological examination suggested that the liver cells of the Cr_(VI) poisoning group were more severely injured than the nano-Se addition group. RT-qPCR results showed that the relative expression of ACACA gene in the Cr_(VI) poisoning group was significantly increased (P < 0.05), while the CPT1A gene's expression was significantly decreased (P < 0.01). Those results were reversed in the nano-Se addition group. Western blot results were consistent with RT-qPCR and both suggested antagonism of nano-Se on Cr_(VI). Through morphological and histopathological observation, as well as the measurement of the mRNA and protein expression levels of ACACA and CPT1A genes in AMPK pathway, it was confirmed that nano-Se has certain preventive and protective effects on Cr_(VI) poisoning in broiler chickens. Furthermore, the adverse effects of Cr_(VI) on carbohydrate and lipid metabolism in broilers can be antagonized by nano-Se through AMPK pathway. A new method and experimental basis were provided to the future study of Cr_(VI) poisoning in broilers.

Study on influencing factors and mechanism of removal of Cr(VI) from soil suspended liquid by bentonite-supported nanoscale zero-valent iron

In order to clarify the mechanism and effect of bentonite-supported nanoscale zero-valent iron (nZVI@Bent) on Cr(VI) removal in soil suspended liquid, nZVI@Bent was prepared by liquid-phase reduction method in this research. A number of factors, including the mass ratio of Fe²⁺ to bentonite during preparation of nZVI@Bent, nZVI@Bent dosage, soil suspended liquid pH value and reaction temperature were assessed to determine their impact on the reduction of Cr(VI) in soil suspended liquid. The nZVI@Bent was characterized by scanning electron microscope (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) to analyze the mechanism of removal of Cr(VI) from the soil. The results showed that the temperature of soil suspended liquid had a significant effect on the removal efficiency. Calculated by the Arrhenius formula, nZVI@Bent removes Cr(VI) from the soil suspended liquid as an endothermic reaction with a reaction activation energy of 47.02 kJ/mol, showed that the reaction occurred easily. The removal of mechanism Cr(VI) from the soil by nZVI@Bent included adsorption and reduction, moreover, the reduction process can be divided into direct reduction and indirect reduction. According to XPS spectrogram analysis, the content of Cr(III) in the reaction product was 2.1 times of Cr(VI), indicated that the reduction effect was greater than the adsorption effect in the process of Cr(VI) removal. The experiment proved that nZVI@Bent can effectively remove Cr(VI) from soil suspension, and can provide technical support for repairing Cr(VI)-polluted paddy fields.

The evaluation of Cr-curcumin-DNA complexation by experimental and theoretical approaches

Chromium(III) chloride mediates DNA-DNA cross-linking. Some chromium complexes promote programmed cell death in specific ligand environment through binding to DNA. One strategy that can be supposed for reduction of Cr³⁺ binding affinity to DNA is using curcumin as a chelator. In the current study, the [Cr(Curcumin)(EtOH)₂](NO₃)₂ (CCC) was synthesized and characterized by UV/Vis, FT-IR, CHN and spectrophotometric titration techniques. The mole ratio plot revealed a 1:1 complex between Cr³⁺ and curcumin in solution. Binding interaction of this complex with calf thymus-DNA (CT-DNA) was investigated using UV/Vis, circular dichroism (CD), FT-IR and cyclic voltammetry. The intrinsic binding constants of CCC with DNA, measured by UV/Vis and cyclic voltammetry, were 1.60 × 10⁵ and 1.13 × 10⁵, respectively. The thermodynamic studies showed that the reaction is enthalpy and entropy favoured. CD analysis revealed that only Λ-CCC interacts with DNA and Δ-CCC form has no tendency towards DNA. Based on FT-IR studies, it was understood that CCC interacts with DNA via minor groove binding. The docking simulation was carried out for finding the binding mode of CCC to DNA, too. All of data demonstrated that the curcumin significantly reduced the affinity of Cr³⁺ to the DNA and the form of Δ-CCC has no interaction with DNA.

Interaction of chromium(III) or chromium(VI) with catalase and its effect on the structure and function of catalase: An in vitro study

Heavy metal chromium (Cr) poses a severe health risk to humans via food chain contamination. In this study, the interactions of either trivalent chromium (Cr(III)) or hexavalent chromium (Cr(VI)) with catalase (CAT) were investigated via multi-spectroscopic studies and computational simulations. The fluorescence analysis showed that Cr(III) and Cr(VI) quenched the fluorescence of CAT through a dynamic and a static quenching mechanism, respectively. The binding constant of Cr(VI) with CAT was 3.44×10⁴lmol^-1 at 298K. Other detailed binding characterizations of the Cr(VI)-CAT complex were also obtained using spectra analysis and molecular docking. Synchronous fluorescence, UV-vis and circular dichroism (CD) spectral studies showed that either Cr(III) or Cr(VI) induced conformational changes of CAT, but the degree of influence was different. The response of CAT activity to Cr(III) or Cr(VI) was found to be variable depending on their valence states and concentrations.

The impact of humic acid on chromium phytoextraction by aquatic macrophyte Lemna minor

Studies assessing chromium phytoextration from natural waters rarely consider potential implications of chromium speciation in the presence of ubiquitous humic substances. Therefore, the present study investigated the influence of environmentally relevant concentration of humic acid (TOC = 10 mg L(-1)) on chromium speciation (Cr = 0.15 mg L(-1)) and consequently on phytoextraction by aquatic macrophyte duckweed Lemna minor. In absence of humic acid, only hexavalent chromium was present in water samples and easily taken up by L. minor. Chromium uptake resulted in a significant reduction of growth rate by 22% and decrease of chlorophyll a and chlorophyll b contents by 48% and 43%, respectively. On the other hand, presence of humic acid significantly reduced chromium bioavailability (57% Cr uptake decrease) and consequently it did not cause any measurable effect to duckweed. Such effect was related to abiotic reduction of hexavalent chromium species to trivalent. Hence, findings of our study suggest that presence of humic acid and chromium speciation cannot be neglected during phytoextraction studies.

Modulation of hexavalent chromium-induced genotoxic damage in peripheral blood of mice by epigallocatechin-3-gallate (EGCG) and its relationship to the apoptotic activity

This study was conducted to investigate the relationship between modulation of genotoxic damage and apoptotic activity in Hsd:ICR male mice treated with (-)-epigallocatechin-3-gallate (EGCG) and hexavalent chromium [Cr(VI)]. Four groups of 5 mice each were treated with (i) control vehicle only, (ii) EGCG (10 mg/kg) by gavage, (iii) Cr(VI) (20 mg/kg of CrO3) intraperitoneally (ip), and (iv) EGCG in addition to CrO3 (EGCG-CrO3). Genotoxic damage was evaluated by examining presence of micronucleated polychromatic erythrocytes (MN-PCE) obtained from peripheral blood of the caudal vein at 0, 24, 48, and 72 h after treatment. Induction of apoptosis and cell viability were assessed by differential acridine orange/ethidium bromide (AO/EB) staining. EGCG treatment produced no significant changes in frequency of MN-PCE. However, CrO3 treatment significantly increased number of MN-PCE at 24 and 48 h post injection. Treatment with EGCG prior to CrO3 injection decreased number of MN-PCE compared to CrO3 alone. The MN-PCE reduction was greater than when EGCG was administered ip. The frequency of early apoptotic cells was elevated at 48 h following EGCG, CrO3, or EGCG-CrO3 exposure, with highest levels observed in the combined treatment group, while the frequencies of late apoptotic cells and necrotic cells were increased only in EGCG-CrO3 exposure. Our findings support the view that EGCG is protective against genotoxic damage induced by Cr(VI) and that apoptosis may contribute to elimination of DNA-damaged cells (MN-PCE) when EGCG was administered prior to CrO3. Further, it was found that the route of administration of EGCG plays an important role in protection against CrO3-induced genotoxic damage.

Genotoxicity of tri- and hexavalent chromium compounds in vivo and their modes of action on DNA damage in vitro

Chromium occurs mostly in tri- and hexavalent states in the environment. Hexavalent chromium [Cr(VI)] compounds are extensively used in diverse industries, and trivalent chromium [Cr(III)] salts are used as micronutrients and dietary supplements. In the present work, we report that they both induce genetic mutations in yeast cells. They both also cause DNA damage in both yeast and Jurkat cells and the effect of Cr(III) is greater than that of Cr(VI). We further show that Cr(III) and Cr(VI) cause DNA damage through different mechanisms. Cr(VI) intercalates DNA and Cr(III) interferes base pair stacking. Based on our results, we conclude that Cr(III) can directly cause genotoxicity in vivo.