Chromium (VI)-induced transformation is enhanced by Zn deficiency in BALB/c 3T3 cells

Zinc Deficiency Decreases Neurite Extension via CRMP2 Signal Pathway

Previous reports indicated that zinc deficiency could increase the risk of infectious diseases and developmental retardation in children. In experimental study, it has been reported that zinc deficiency during the embryonic period inhibited fetal growth, and disturbed neural differentiation and higher brain function later in adulthood. Although it has been suggested that zinc deficiency during development can have significant effects on neuronal differentiation and maturation, the molecular mechanisms of the effects of low zinc on neuronal differentiation during development have not been elucidated in detail. This study was performed to determine the effects of low zinc status on neurite outgrowth and collapsin response mediator protein 2 (CRMP2) signal pathway. Low zinc suppressed neurite outgrowth, and caused increase levels of phosphorylated CRMP2 (pCRMP2) relative to CRMP2, and decrease levels of phosphorylated glycogen synthase kinase 3β (pGSK3β) relative to GSK3β in human neuroblastoma cell line (SH-SY5Y) cells on days 1, 2, and 3 of neuronal differentiation induction. Neurite outgrowth inhibited by low zinc was restored by treatment with the GSK3β inhibitor CHIR99021. These results suggested that low zinc causes neurite outgrowth inhibition via phosphorylation of CRMP2 by GSK3β. In conclusion, this study is the first to demonstrate that CRMP signaling is involved in the suppression of neurite outgrowth by low zinc.

Bioreduction of toxicity influenced by bioactive molecules secreted under metal stress by Azotobacter chroococcum

Heavy metal pollution destruct soil microbial compositions and functions, plant's performance and subsequently human health. Culturable microbes among many metal abatement strategies are considered inexpensive, viable and environmentally safe. In this study, nitrogen fixing bacterial strain CAZ3 recovered from chilli rhizosphere tolerated 100, 1000 and 1200 µg mL^-1 of cadmium, chromium and nickel, respectively and was identified as Azotobacter chroococcum by 16S rDNA sequence analysis. Under metal stress, cellular morphology of A. chroococcum observed under SEM was found distorted and shrinkage of cells was noticed when grown with 50 µg mL^-1 of Cd (cell size 1.7 µm) and 100 of µg mL^-1 Ni (cell size 1.3 µm) compared to untreated control (cell size 1.8 µm). In the presence of 100 µg mL^-1 of Cr, cells became elongated and measured 1.9 µm in size. Location of metals inside the cells was revealed by EDX. A dose dependent growth arrest and consequently the death of A. chroococcum cells was revealed under CLSM. A. chroococcum CAZ3 secreted 320, 353 and 133 µg EPS mL^-1 when grown with 100 µg mL^-1 each of Cd, Cr and Ni, respectively. The EDX revealed the presence of 0.4, 0.07 and 0.24% of Cd, Cr and Ni, respectively within EPS extracted from metal treated cells. Moreover, a dark brown pigment (melanin) secreted by A. chroococcum cells under metal pressure displayed tremendous metal chelating activity. The EDX spectra of melanin extracted from metal treated cells of A. chroococcum CAZ3 displayed 0.53, 0.22 and 0.12% accumulation of Cd, Cr and Ni, respectively. The FT-IR spectra of EPS and melanin demonstrated stretching vibrations and variations in surface functional groups of bacterial cells. The C-H stretching of CH₃ in fatty acids and CH₂ groups, stretching of N-H bond of proteins and O-H bond of hydroxyl groups caused the shifting of peaks in the EPS spectra. Similar stretching vibrations were recorded in metal treated melanin which involved CHO, alkyl, carboxylate and alkene groups resulting in significant peak shifts. Nuclear magnetic resonance (NMR) spectrum of EPS extracted from A. chroococcum CAZ3 revealed apparent peak signals at 4.717, 9.497, 9.369 and 9.242 ppm. However, ¹H NMR peaks were poorly resolved due largely to the impurity/viscosity of the EPS. The entrapment of metals by EPS and melanin was confirmed by EDX. Also, the induction and excretion of variable amounts of metallothioneins (MTs) by A. chroococcum under metal pressure was interesting. Conclusively, the present findings establish- (i) cellular damage due to Cd, Cr and Ni and (ii) role of EPS, melanin and MTs in adsorption/complexation and concurrently the removal of heavy metals. Considering these, A. chroococcum can be promoted as a promising candidate for supplying N efficiently to plants and protecting plants from metal toxicity while growing under metal stressed environment.

Can zinc protect cells from the cytotoxic effects of cobalt ions and nanoparticles derived from metal-on-metal joint arthroplasties?

Objectives

Recently, high failure rates of metal-on-metal (MOM) hip implants have raised concerns of cobalt toxicity. Adverse reactions occur to cobalt nanoparticles (CoNPs) and cobalt ions (Co²⁺) during wear of MOM hip implants, but the toxic mechanism is not clear.

Methods

To evaluate the protective effect of zinc ions (Zn²⁺), Balb/3T3 mouse fibroblast cells were pretreated with 50 μM Zn²⁺ for four hours. The cells were then exposed to different concentrations of CoNPs and Co²⁺ for four hours, 24 hours and 48 hours. The cell viabilities, reactive oxygen species (ROS) levels, and inflammatory cytokines were measured.

Results

CoNPs and Co²⁺ can induce the increase of ROS and inflammatory cytokines, such as tumour necrosis factor α (TNF-α), interleukin-1β (IL-1β) and interleukin-6 (IL-6). However, Zn pretreatment can significantly prevent cytotoxicity induced by CoNPs and Co²⁺, decrease ROS production, and decrease levels of inflammatory cytokines in Balb/3T3 mouse fibroblast cells.

Conclusion

These results suggest that Zn pretreatment can provide protection against inflammation and cytotoxicity induced by CoNPs and Co²⁺ in Balb/3T3 cells.

Cite this article: Y. Liu, H. Zhu, H. Hong, W. Wang, F. Liu. Can zinc protect cells from the cytotoxic effects of cobalt ions and nanoparticles derived from metal-on-metal joint arthroplasties? Bone Joint Res 2017;6:649–655. DOI: 10.1302/2046-3758.612.BJR-2016-0137.R2.

Metal-mediated Epigenetic Regulation of Gene Expression

Epigenetics is the study of heritable changes in gene expression that occur without alterations in the DNA sequence. Several studies have shown that environmental chemicals can alter epigenetic modifications, including histone modifications and DNA methylation. Environmental chemicals may show toxic effects via epigenetic mechanism-regulated changes in gene expression. Previously, we reported that zinc treatment rapidly decreased Lys(4)-trimethylated and Lys(9)-acetylated histone H3 in the metallothionein (MT) promoter, and also decreased total histone H3. The chromatin structure in the MT promoter may be locally disrupted by zinc-induced nucleosome removal. We also showed that chromium (VI) inhibited MT gene transcription by modifying the transcription potential of the co-activator p300. MT is a small cysteine-rich protein that is active in zinc homeostasis, cadmium detoxification, and protection against reactive oxygen species. Epigenetic changes might influence the cytoprotective function of the MT gene. In this review, I briefly summarize the results of previous studies and discuss the mechanisms and toxicological significance of metal-mediated epigenetic modifications.

Adverse effects of parental zinc deficiency on metal homeostasis and embryonic development in a zebrafish model

The high prevalence of zinc deficiency is a global public health concern, and suboptimal maternal zinc consumption has been associated with adverse effects ranging from impaired glucose tolerance to low birthweights. The mechanisms that contribute to altered development and poor health in zinc deficient offspring are not completely understood. To address this gap, we utilized the Danio rerio model and investigated the impact of dietary zinc deficiency on adults and their developing progeny. Zinc deficient adult fish were significantly smaller in size, and had decreases in learning and fitness. We hypothesized that parental zinc deficiency would have an impact on their offspring's mineral homeostasis and embryonic development. Results from mineral analysis showed that parental zinc deficiency caused their progeny to be zinc deficient. Furthermore, parental dietary zinc deficiency had adverse consequences for their offspring including a significant increase in mortality and decreased physical activity. Zinc deficient embryos had altered expression of genes that regulate metal homeostasis including several zinc transporters (ZnT8, ZnT9) and the metal-regulatory transcription factor 1 (MTF-1). Zinc deficiency was also associated with decreased expression of genes related to diabetes and pancreatic development in the embryo (Insa, Pax4, Pdx1). Decreased expression of DNA methyltransferases (Dnmt4, Dnmt6) was also found in zinc deficient offspring, which suggests that zinc deficiency in parents may cause altered epigenetic profiles for their progeny. These data should inform future studies regarding zinc deficiency and pregnancy and suggest that supplementation of zinc deficient mothers prior to pregnancy may be beneficial.

Rationale for the Successful Management of EDTA Chelation Therapy in Human Burden by Toxic Metals

Exposure to environmental and occupational toxicants is responsible for adverse effects on human health. Chelation therapy is the only procedure able to remove toxic metals from human organs and tissue, aiming to treat damage related to acute and/or chronic intoxication. The present review focuses on the most recent evidence of the successful use of the chelating agent ethylenediaminetetraacetic acid (EDTA). Assessment of toxic-metal presence in humans, as well as the rationale of EDTA therapy in cardiovascular and neurodegenerative diseases, is reported.

Toxicology of organic-inorganic hybrid molecules: bio-organometallics and its toxicology

Bio-organometallics is a research strategy of biology that uses organic-inorganic hybrid molecules. The molecules are expected to exhibit useful bioactivities based on the unique structure formed by interaction between the organic structure and intramolecular metal(s). However, studies on both biology and toxicology of organic-inorganic hybrid molecules have been incompletely performed. There can be two types of toxicological studies of bio-organometallics; one is evaluation of organic-inorganic hybrid molecules and the other is analysis of biological systems from the viewpoint of toxicology using organic-inorganic hybrid molecules. Our recent studies indicate that cytotoxicity of hybrid molecules containing a metal that is nontoxic in inorganic forms can be more toxic than that of hybrid molecules containing a metal that is toxic in inorganic forms when the structure of the ligand is the same. Additionally, it was revealed that organic-inorganic hybrid molecules are useful for analysis of biological systems important for understanding the toxicity of chemical compounds including heavy metals.