Effects of the Oral Administration of K2Cr2O7 and Na2SeO3 on Ca, Mg, Mn, Fe, Cu, and Zn Contents in the Heart, Liver, Spleen, and Kidney of Chickens

A Comprehensive Review of Lab-Scale Studies on Removing Hexavalent Chromium from Aqueous Solutions by Using Unmodified and Modified Waste Biomass as Adsorbents

Anthropogenic activities and increasing human population has led to one of the major global problems of heavy metal contamination in ecosystems and to the generation of a huge amount of waste material biomass. Hexavalent chromium [Cr(VI)] is the major contaminant introduced by various industrial effluents and activities into the ecosystem. Cr(VI) is a known mutagen and carcinogen with numerous detrimental effects on the health of humans, plants, and animals, jeopardizing the balance of ecosystems. Therefore, the remediation of such a hazardous toxic metal pollutant from the environment is necessary. Various physical and chemical methods are available for the sequestration of toxic metals. However, adsorption is recognized as a more efficient technology for Cr(VI) remediation. Adsorption by utilizing waste material biomass as adsorbents is a sustainable approach in remediating hazardous pollutants, thus serving the dual purpose of remediating Cr(VI) and exploiting waste material biomass in an eco- friendly manner. Agricultural biomass, industrial residues, forest residues, and food waste are the primary waste material biomass that could be employed, with different strategies, for the efficient sequestration of toxic Cr(VI). This review focuses on the use of diverse waste biomass, such as industrial and agricultural by-products, for the effective remediation of Cr(VI) from aqueous solutions. The review also focuses on the operational conditions that improve Cr(VI) remediation, describes the efficacy of various biomass materials and modifications, and assesses the general sustainability of these approaches to reducing Cr(VI) pollution.

Toxicity mechanisms and remediation strategies for chromium exposure in the environment

Chromium (Cr) is the seventh most abundant chemical element in the Earth’s crust, and Cr(III) and Cr(VI) are common stable valence states of Cr. Several Cr-containing substances, such as FeOCr2O3 and stainless-steel products, exist in nature and in life. However, Cr(VI) is toxic to soil, microorganisms, and plants and poses a serious threat to human health through direct and indirect exposure. By collecting published journal literature, we found that Cr(VI) can cause acute and chronic toxicity in organisms and has carcinogenic effects, and the mechanisms causing these toxicity include endoplasmic reticulum stress, autophagy and apoptosis. However, the relationship between these mechanisms remains unclear. Many methods have been researched to purify chromium, but each of these methods has its own advantages and disadvantages. Therefore, this review summarizes the hazards of chromium and the mechanisms of chromium toxicity after entering cells and provides a number of methods for chromium contamination management, providing a direction for the next step in chromium toxicology and contamination decontamination research.

Platycodon grandiflorus Polysaccharides Alleviate Cr(VI)-Induced Apoptosis in DF-1 Cells via ROS-Drp1 Signal Pathway

Hexavalent chromium (Cr(VI)) is a widespread heavy metal that has been identified as a human carcinogen, and acute or chronic exposure to Cr(VI) can cause organ damage. Platycodon grandiflorus polysaccharide (PGPS) is a constituent extracted from the Chinese herb Platycodon grandiflorus, which has various pharmacological effects. Therefore, the author investigated the role of PGPSt in Cr(VI)-induced apoptosis in chicken embryo fibroblast cell lines (DF-1 cells). Firstly, this study infected DF-1 cells using Cr(VI) to set up a model for cytotoxicity and then added PGPSt. Then, the intracellular reactive oxygen species (ROS), mitochondrial membrane potential (MMP), and apoptosis rate were evaluated. The results showed that PGPSt could inhibit Cr(VI)-induced mitochondrial damage and increase the apoptosis rate. For further exploration of the mechanism of regulation of PGPSt, the ROS-Drp1 pathway was investigated. The antioxidant N-acetyl-L-cysteine (NAC) and mitochondrial division inhibitor 1(Mdivi-1) were added, respectively. The results showed that the NAC and Mdivi-1 restored abnormal mitochondrial fission and cell apoptosis. Thus, PGPSt can alleviate Cr(VI)-induced apoptosis of DF-1 cells through the ROS-Drp1 signaling pathway, which may suggest new research ideas for developing new drugs to alleviate Cr(VI) toxicity.

Selenium regulates Nrf2 signaling to prevent hepatotoxicity induced by hexavalent chromium in broilers

Hexavalent chromium (Cr(Ⅵ)) is considered to be a common environmental pollutant, which widely exists in industrial effluents and wastes and then potentially noxious effects to the health of the poultry. Studies have reported that selenium (Se), which is one of the essential trace elements of the poultry and participates in the oxidative metabolism, can alleviate Cr(Ⅵ)-induced organ damage by inhibiting oxidative stress, but its specific molecular mechanism remains unclear. Herein, animal models of Cr(Ⅵ)- and Se-exposure were constructed using broilers to investigate the antagonistic mechanism of Se to Cr(Ⅵ)-induced hepatotoxicity. In this experiment, the four groups of broiler models were used as the research objects: control, Se, Se plus Cr, and Cr groups. Histopathology and ultrastructure liver changes were observed. Liver-somatic index, serum biochemistry, oxidative stress, Nrf2 pathway related factors, and autophagy-related genes were also determined. Overall, Se was found to ameliorate the disorganized structure, hepatic insufficiency, and oxidative damage caused by Cr(Ⅵ) exposure. Electron microscopy analysis further showed that the number of autophagosomes was obviously decreased after Se treatment compared to Cr group. Furthermore, gene and protein expression analyses illustrated that the levels of Nrf2, glutathione peroxidase 1 (GPx-1), NAD(P)H: quinone oxidoreductase 1 (NQO1), and mechanistic target of rapamycin (mTOR) in the Se&Cr group was upregulated, along with decreased expression of Beclin 1, ATG5 and LC3 compared to the Cr group. These suggest that Se can repair the oxidative lesion and autophagy induced by Cr(Ⅵ) exposure in broiler livers by upregulating the Nrf2 signaling pathway.

Cr(VI) promotes tight joint and oxidative damage by activating the Nrf2/ROS/Notch1 axis

This study aimed to investigate whether Cr(VI) induced tight joint and oxidative damage in the small intestine, as mediated by the nuclear factor erythroid 2-related factor 2 (Nrf2)/reactive oxygen species (ROS)/Notch1 axis crosstalk. Thirty-two ICR mice were obtained and subjected to Cr(VI) via intragastric administration daily for 5 days. Western blot (WB) analysis, enzyme-linked immunosorbent assay (ELISA), immunohistochemistry (IHC) staining, and immunofluorescence (IF) staining were applied to detect small intestinal damage, Nrf2, Notch1, and respective downstream targets in this research. Results showed that Cr(VI) led to the tight joint and oxidative damage in the small intestine of mice. Nrf2 was stimulated, and Notch1 (Notch intracellular domain, NICD1) was activated to translocate into the nucleus and activate an antioxidant action. These findings were validated by WB analysis and IF staining. ROS levels increased as the Cr(VI) concentration increased. The colocalization analysis of Nrf2 and NICD1 implied that a crosstalk between Nrf2 and Notch1 existed. Therefore, this study indicated that the Nrf2/ROS/Notch1 axis crosstalk could aggravate the tight joint and oxidative damage in the small intestine after Cr(VI) treatment.

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.

Protective Effect of Purple Tomato Anthocyanidin on Chromium(VI)-Induced Autophagy in LMH Cells by Inhibiting Endoplasmic Reticulum Stress

This study aimed to investigate the role of purple tomato anthocyanin (PTA) in autophagy induced by chromium(VI) in a chicken hepatocellular carcinoma cell line (LMH cells). LMH cells were exposed to Cr(VI), PTA, and Cr(VI) + PTA. The changes in endoplasmic reticulum (ER) stress, autophagy, related proteins, and COX-2 were detected. Results showed that the cell viability was reduced after Cr(VI) treatment, and the decrease was also restrained by 3-MA or PTA. Levels of ER stress-related proteins (GRP78/Bip and PERK) and COX-2 increased after Cr(VI) treatment, which resulted in an increase in autophagy-related proteins (Beclin1 and LC3-II), inhibition of autophagy pathway protein mTOR, and degradation of autophagy-related protein p62, leading to excessive autophagy and cell damage. Meanwhile, the changes of these indicators induced by Cr(VI) were alleviated by PTA. In conclusion, our study suggested that Cr(VI) can induce excessive autophagy in LMH cells, while PTA can ameliorate Cr(VI)-induced autophagy by inhibiting ER stress.

Effects of Cr(VI)-induced calcium-sensing receptor activation on DF-1 cell pyroptosis

This study aims to investigate the effects of Cr(VI)-induced calcium-sensing receptor (CaSR) activation on DF-1 cell pyroptosis. Previous studies show that Cr(VI) could accumulate in the body of chickens and change Ca levels. Hence, a Ca-related pathway may be an important mechanism participating in some pathological processes. Pyroptosis level, which is meditated by CaSR, increases under Cr(VI) accumulation. In the present study, pyroptosis was determined by flow cytometry to detect SYTOX blue and caspase-1 staining followed by morphological observation. Interleukin (IL)-1β and IL-18 levels were detected by ELISA, while CaSR protein and [Ca²⁺]_i contents were detected by Western blot and fluorescence microplate spectrophotometry, respectively. The results showed that Cr(VI) causes DF-1 cell pyroptosis in a time- and dose-dependent manner and that this effect is caspase-1 dependent. Further experiments indicated that pyroptosis could be induced by Cr(VI) and is accompanied by up-regulated [Ca²⁺]_i content. CaSR inhibition led to decreases in pyroptosis level. Some mechanisms may be involved in Cr(VI)-triggered CaSR activation and enhance DF-1 cell pyroptosis. Taken together, the results of this study support future investigations on Cr(VI)-induced pyroptosis in DF-1 cells.

Study on the mechanism underlying Al-induced hepatotoxicity based on the identification of the Al-binding proteins in liver

Aluminum (Al) is the most abundant metal element in the earth's crust, and is implicated in the pathogenesis of liver lesions. However, the mechanisms underlying Al³⁺-induced hepatotoxicity are still largely elusive. Based on analysis with native gel electrophoresis, Al³⁺ plus 8-hydroxyquinoline staining and LC-MS/MS, the proteins with high Al³⁺ affinity were identified to be carbamoyl-phosphate synthase, adenosylhomocysteinase, heat shock protein 90-alpha, carbonic anhydrase 3, serum albumin and calreticulin. These proteins are involved in physiological processes such as the urea cycle, redox reactions, apoptosis and so on. Then we established an Al³⁺-treated rat model for biochemical tests, morphology observation and Ca²⁺ homeostasis analysis, in order to evaluate the extent of oxidative damage, hepatic histopathology and specific indicators of Al³⁺-related proteins in liver. Our findings indicated the high-affinity interactions with Al³⁺ perturbed the normal function of the above proteins, which could account for the mechanism underlying Al³⁺-induced hepatotoxicity.

Effect of selenium nanoparticles against abnormal fatty acid metabolism induced by hexavalent chromium in chicken's liver

The effect of selenium on excessive fatty acid-induced apoptosis and abnormal amino acid metabolism in the liver is well known, because it is an important site in the fatty acid metabolism pathway. However, the protective role of nano-elemental selenium (nano-Se) supplementation against hexavalent chromium (K₂Cr₂O₇)-induced abnormal fatty acid metabolism has not been evaluated yet. Therefore, we conducted chicken experiments with different nano-Se supplementation doses to investigate the role of nano-Se against Cr(VI)-induced adverse effects. For this purpose, a total of 120 1-day-old chicks were randomly divided into control group, Cr(VI)-exposed group, protection group, treatment group, prevention group, and nano-Se control group. The results of RT-qPCR showed that the nano-Se supplementation notably downregulated (P < 0.01) the messenger RNA (mRNA) expression levels of fatty acid synthase (FASN), whereas nano-Se supplementation significantly upregulated (P < 0.01) the mRNA expression level of acyl-coenzyme A oxidase 1 (ACOX1) in chicken's liver at day 35 of the experiment. Similar results were further verified by western blot analysis. Moreover, nano-Se supplementation significantly enhanced and reduced the antibody expression levels of ACOX1 and FASN in immunohistochemical analysis, respectively. Thus, finally, it was concluded that nano-Se can alleviate K₂Cr₂O₇-induced abnormal fatty acid metabolism in chicken's liver.

Metabonomic analysis of the hepatic injury suffer from hexavalent chromium poisoning in broilers

Chromium is used in daily life and has a wide range of functions. It plays an important role in protein synthesis and carbohydrate and lipid metabolism. Chromium is found in trivalent Cr(III) and hexavalent Cr(VI) form; Cr(III) is relatively stable and intimately participates with many phenomena of metabolisms. Whereas, Cr(VI) is toxic, which results in growth inhibition and leading to changes in components of antioxidant systems as well as secondary metabolites. However, the molecular mechanism that is involved in Cr (VI)-induced hepatotoxicity is still unclear. For this purpose, 40 chickens were randomly assigned into two groups: the normal group (feeding the basic diet and clear water), the chromium group (16%LD₅₀, 74.24 mg/kg/day K₂Cr₂O₇ ). The samples were subjected to pathological examination and UHPLC-QE-MS non-target metabolomics method for metabolomics analysis of broiler liver using principal component analysis (PCA) and partial least squares discriminant analysis (OPLS-DA). The central venous cells of the broiler liver in the chromium poisoning group showed turbidity and flaky necrosis, nuclear condensation, nuclear rupture, and even nuclear dissolution. The differential metabolite analysis between the chromium poisoning and the control group showed that 32 differential metabolites were upregulated and 15 were downregulated in positive ion mode. Whereas,17 differential metabolites were downregulated, and 35 were downregulated in negative ion mode (P ≤ 0.05). The potential marker substances are oleic acidamide, farnesylacetone, betaine, taurine, choline, and galactinol. Additionally, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways showed that the lipid metabolism, carbohydrate metabolism, nucleotide metabolism, amino acid metabolism, energy metabolism, membrane transport, digestive system, and nervous system were the most important metabolic pathways in the liver. This study provides a theoretical basis for the future understanding of the pathogenesis of chromium poisoning and a new insight of the subsequent molecular mechanism of chromium hepatotoxicity.

The regulatory role of COX-2 in the interaction between Cr(VI)-induced endoplasmic reticulum stress and autophagy in DF-1 cells

Hexavalent chromium (Cr(VI)) is a common environmental pollutant. Exposure of Cr(VI) can lead to cell autophagy, but the preventive measures for diminishing Cr(VI)-induced autophagy need further study. COX-2 can be induced by several heavy metals and can lead to endoplasmic reticulum (ER) stress and autophagy; thus, COX-2, ER stress, and autophagy may be related. This study mainly investigated the role of COX-2 in the eIF2α-ATF4 pathway, which is a major pathway in cell autophagy. In this study, Cr(VI) was used as a xenobiotic to determine changes in the parameters of ER stress, autophagy, and COX-2 levels. At the same time, a clear contrast was obtained by assigning positive and negative controls of ER stress and autophagy. The results showed that during Cr(VI) invasion, the parameters of ER stress and autophagy (such as BiP, PERK, p62, LC3-II, and mTOR) were enhanced, similarly to the positive control of ER stress and/or the autophagy controls. Such enhancement is a protective mechanism for cell survival. Additionally, the COX-2 levels increased. Moreover, when COX-2 was inhibited, the PERK level remained high, whereas the LC3-II level decreased. This finding suggests that COX-2 specifically affects the interaction between ER stress and autophagy. Notably, this study reveals that Cr(VI) can induce ER stress and autophagy in DF-1 cells and that COX-2 plays an essential role in the interaction between ER stress and autophagy.