Yingmei Zhang

Global DNA hypomethylation, rather than reactive oxygen species (ROS), a potential facilitator of cadmium-stimulated K562 cell proliferation

Cell proliferation plays a critical role in the process of cadmium (Cd) carcinogenesis. Although both induction of reactive oxygen species (ROS) and alteration of DNA methylation are involved in Cd-stimulated cell proliferation, the detailed mechanism of Cd-stimulated cell proliferation remains poorly understood. In this study, K562 cells pre-treated with N-acetylcysteine (NAC) or methionine (Meth) were exposed to Cd to investigate the potential contribution of ROS and global DNA methylation pathways in Cd-induced cell proliferation. The results showed that Cd-stimulated cell proliferation, increased ROS and DNA damage levels, and induced global DNA hypomethylation. The increases of ROS and DNA damage levels were attenuated by pre-treatment with NAC. Cd-stimulated cell proliferation did not appear to be suppressed through eliminating ROS by NAC. However, methionine was shown to prevent Cd-induced global DNA hypomethylation and Cd-stimulated cell proliferation. Our results suggest that global DNA hypomethylation, rather than ROS, is a potential facilitator of Cd-stimulated K562 cell proliferation.

Heavy metal concentrations in water, sediment, and tissues of two fish species (Triplohysa pappenheimi, Gobio hwanghensis) from the Lanzhou section of the Yellow River, China

In order to assess the condition of heavy metal pollution in the Yellow River, Lanzhou section, China, and to quantify heavy metal (copper, lead, zinc, and cadmium) contents in tissues (liver, kidney, gills, and muscles) of two fish species (Triplophysa pappenheimi and Gobio hwanghensis), levels of these four metals in the water body, sediment, and tissues of the two fish were measured using inductively coupled plasma-atomic emission spectrometry. The metal levels from this study were compared with the threshold values in the guidelines of water, sediment, and food given by the National Environmental Protection Agency of China, the National Oceanic and Atmospheric Administration of America, and the National Standards Management Department of China. We found the mean concentrations of Cu, Pb, Zn, and Cd in THE water body, sediment, and muscles of two fish species were far below the values in guidelines. We also found that the type of metals present and their concentrations varied in different tissues and species. The results suggested that (1) Cu, Pb, Zn, and Cd did not contaminate the aquatic ecosystem severely and did not threaten the safety of human consumption in the Yellow River, Lanzhou section, and (2) organs that are sensitive to accumulating heavy metals may be useful to develop bioindicators for monitoring metal contamination. Considering environmental variables, further study is necessary before deciding which fish species or tissue could be the ideal bioindicators for aquatic pollution.

Mediating effect of ROS on mtDNA damage and low ATP content induced by arsenic trioxide in mouse oocytes

Mitochondria provide most of the adenosine triphosphates (ATP) necessary for the maturation of oocytes. Various environmental toxicants would lead damage to mitochondrial DNA (mtDNA) and hence interfere with oocytes development. In the current study, the effect of arsenic trioxide (As2O3) on the common 3867 bp deletion and the copy number of mtDNA in mitochondria of mouse oocytes in vivo or in vitro, as well as the molecular pathway leading to the damage were investigated. PCR strategy was used to detect the damage of mtDNA. Reactive oxygen species (ROS) and ATP content in oocytes were checked to determine the influence of As2O3 on oxidative stress and activity of mitochondria. The results showed that As2O3 could obviously decrease the copy number of mtDNA and cause severe 3867 bp deletion in mitochondria together with elevated ROS level, while ATP content was decreased. Co-treatment with N-Acetyl-Cysteine (NAC) efficiently eliminated ROS induced by As2O3, lessened the mtDNA damage and enhanced ATP content in mouse oocytes both in vivo and in vitro. Taken together, the present study revealed that As2O3 could cause severe mtDNA damage and decrease ATP content by inducing excessive ROS, and this damage would then probably restrain the further development of mouse oocytes.

Cadmium induces mitophagy through ROS-mediated PINK1/Parkin pathway.

Abstract Context and objective: Recent reports have highlighted the relationship between cadmium (Cd) and autophagy, however, whether Cd can activate mitophagy remains enigmatic. This study aims to investigate the effects of Cd on mitophagy and its potential mechanism. Methods: Mice were intraperitoneally injected with Cd for 3 d. Mitochondrial membrane potential (MMP), mitophagosomes, LC3-II/LC3-I ratio, PINK1 level and mitochondrial mass were evaluated to indicate the effects of Cd on mitophagy. To elucidate the mechanism, reactive oxygen species (ROS) scavenger N-acetyl-l-cysteine (NAC) or acetyl-l-carnitine (ALC) as well as the mitophagy inhibitor cyclosporine A (CsA) were introduced to verify the role of ROS in mitophagy. Results and conclusions: The results showed that Cd significantly induced MMP collapse and typical mitophagosomes formation, increased LC3-II/LC3-I ratio and PINK1 level, and decreased mitochondrial mass, revealing that Cd could induce mitophagy. However, NAC or ALC pretreatment markedly decreased Cd-induced ROS and simultaneously rescued MMP and mitochondrial mass, suggesting ROS played a crucial role in regulating mitophagy. NAC or ALC also dramatically lessened PINK1 level and mitochondrial accumulation of Parkin, indicating that ROS were related to PINK1/Parkin pathway. Notably, CsA compromised Cd-induced mitophagy, PINK1 accumulation and Parkin translocation while failed to block ROS increase, suggesting ROS functioned as an upstream signal for PINK1/Parkin pathway. Taken together, the results indicated that Cd induced ROS-mediated mitophagy through PINK1/Parkin pathway in kidneys of mice. The present study proposes a new perspective to evaluate the nephrotoxicity and its molecular mechanism under Cd exposure in vivo.

EGCG inhibits Cd2+-induced apoptosis through scavenging ROS rather than chelating Cd2+ in HL-7702 cells

Abstract Context and objective: Epigallocatechin-3-gallat (EGCG), the major catechin in green tea, shows a potential protective effect against heavy metal toxicity to humans. Apoptosis is one of the key events in cadmium (Cd2+)-induced cytotoxicity. Nevertheless, the study of EGCG on Cd2+-induced apoptosis is rarely reported. The objective of this study was to clarify the effect and detailed mechanism of EGCG on Cd2+-induced apoptosis. Methods: Normal human liver cells (HL-7702) were treated with Cd2+ for 21 h, and then co-treated with EGCG for 3 h. Cell viability, apoptosis, intracellular reactive oxygen species (ROS), malondialdehyde (MDA), mitochondrial membrane potential (MMP) and caspase-3 activity were detected. On the other hand, the chelation of Cd2+ with EGCG was tested by UV-Vis spectroscopy analysis and Nuclear Magnetic Resonance (1H NMR) spectroscopy under neutral condition (pH 7.2). Results and conclusion: Cd2+ significantly decreased the cell viability and induced apoptosis in HL-7702 cells. Conversely, EGCG co-treatment resulted in significant inhibition of Cd2+-induced reduction of cell viability and apoptosis, implying a rescue effect of EGCG against Cd2+ poisoning. The protective effect most likely arises from scavenging ROS and maintaining redox homeostasis, as the generation of intracellular ROS and MDA is significantly reduced by EGCG, which further prevents MMP collapse and suppresses caspase-3 activity. However, no evidence is observed for the chelation of EGCG with Cd2+ under neutral condition. Therefore, a clear conclusion from this work can be made that EGCG could inhibit Cd2+-induced apoptosis by acting as a ROS scavenger rather than a metal chelating agent.

ROS act as an upstream signal to mediate cadmium-induced mitophagy in mouse brain

As a well known generator of reactive oxygen species (ROS), cadmium (Cd) is found to be an effective inducer of mitophagy in mouse kidney and liver cells. Here, we aim to elucidate whether Cd can also initiate mitophagy in mouse brain and what role ROS play in this process. Our results showed that Cd caused overproduction of ROS. Meanwhile, Cd induced mitophagy, as indicated by the collapse of mitochondrial membrane potential (MMP), formation of mitophagosomes, increases of PINK1 level and LC3-II/LC3-I ratio and decrease of mitochondrial mass. Scavenging of ROS by N-acetyl-L-cysteine (NAC) or acetyl-L-carnitine (ALC) rescued MMP and mitochondrial mass, and squelched PINK1 level, mitochondrial accumulation of Parkin and LC3-II/LC3-I ratio, suggesting that ROS were associated with Cd-induced mitophagy. Cyclosporine A (CsA), an inhibitor of mitophagy, blocked Cd-induced mitophagy and PINK1/Parkin pathway but failed to suppress ROS increase, revealing that ROS are the causes rather than the results of Cd-induced mitophagy. In conclusion, this study suggested that ROS functioned on the upstream of PINK1/Parkin pathway to mediate Cd-induced mitophagy.

2,4-Dichlorophenol induces apoptosis in primary hepatocytes of grass carp (Ctenopharyngodon idella) through mitochondrial pathway

2,4-Dichlorophenol (2,4-DCP), a major type of chlorophenols, has been widely used to produce some herbicides and pharmaceuticals, yet due to its incomplete degradation and bioaccumulation characteristics, it is toxic to aquatic organisms. Apoptosis is one of the most severe outcomes of cell poisoning and injury. So far, the potential molecular mechanism of 2,4-DCP-induced apoptosis has not been reported. This study showed that 2,4-DCP significantly induced apoptosis in primary hepatocytes of grass carp (Ctenopharyngodon idella). 2,4-DCP exposure upregulated mRNA of caspase-3, reduced the mitochondrial membrane potential (Δψm), increased intracellular reactive oxygen species (ROS) and the Bax/Bcl-2 ratio, while protection of mitochondria with acetyl-l-carnitine hydrochloride (ALC) rescued 2,4-DCP-induced apoptosis, restored the Δψm and reduced the Bax/Bcl-2 ratio. Taken together, this is the first study that has identified that 2,4-DCP exposure induced apoptosis through the mitochondria-dependent pathway in primary hepatocytes of grass carp.

Synergic effect of 3'-azido-3'-deoxythymidine and arsenic trioxide in suppressing hepatoma cells.

The aim of this study was to investigate the synergic antitumor effects of arsenic trioxide (As2O3) and 3′-azido-3′-deoxythymidine (AZT) on hepatoma cells and explore the possible molecular basis of these effects. These results showed that AZT enhanced the inhibitory effect of As2O3 on HepG2 and SMMC-7721 cell growth. The IC50 of As2O3 in combination with AZT was lower than that of As2O3 alone. A concentration-dependent synergic effect of As2O3 and AZT (CI <1) was observed in all the tested combinations of these compounds. These results also showed that the combination of As2O3 and AZT dramatically and significantly increased the number of apoptotic cells in HepG2 and SMMC-7721 cells. Studies in vivo showed that the combination of As2O3 and AZT was statistically superior to either As2O3 or AZT alone in the treatment of tumor-bearing mice. As2O3 (1 mg/kg) containing AZT (50 mg/kg) inhibits proliferation of implanted hepatoma 22 by 56.35%. These results suggest that treating hepatoma with a combinination of As2O3 and AZT offers the advantages of reduced toxic side effects and improved therapeutic efficacy. To understand the mechanism through which As2O3 and AZT suppress tumors, we studied the effects of these compounds, both separately, and in combination, on telomerase and caspase-3 activity. The results showed that the growth inhibitory and apoptotic effects of As2O3 and AZT on human hepatoma cells could be related to the inhibition of telomerase and the activation of caspase 3.

Assessment of the bioavailability, bioaccessibility and transfer of heavy metals in the soil-grain-human systems near a mining and smelting area in NW China

Elucidating the transfer behaviour of heavy metals from soils to grains and ultimately to humans is of great significance for both human health risk assessment and pollution control. In this study, the bioavailability of heavy metals (Cd, Cu, Pb, Zn, Cr and Ni) in farmland soils and bioaccessibility in grains (spring wheat, maize and rice) were determined to elaborate transfer dynamics in the soil-grain-human systems near a mining and smelting area in the Dongdagou watershed, Baiyin district, Gansu province, NW China. The results showed that Cd, Cu, Pb and Zn concentrations in soils were elevated compared to background levels, while Cr and Ni concentrations were relatively low throughout the region. High levels of bioavailable soil Cd were found using both EDTA and CH3COOH extraction methods. Mean concentrations of Cd, Pb and Zn in spring wheat grains and the Cd and Cr concentrations in maize grains exceeded the relevant maximum levels for pollutants according to the Chinese national standards for food safety. Except for Ni (41.90%) and Pb (31.39%), heavy metal bioaccessibility was relatively low in grains, ranging from 10.80% (Cd) to 17.18% (Zn). CH3COOH-extracted Cd, Pb and Ni, EDTA-extracted Zn, and total Cu in soils were the best indices for evaluation of uptake in grains (R2=0.54-0.91, p<0.001). Internal exposure doses of Cd and Ni in humans from spring wheat grain consumption was predicted by the linear correlations between bioaccessible and total metal concentrations (R2=0.61 and 0.67; p<0.001). The results from this study provide sufficient data and theoretical support for the use of these methods for local pollution prevention and control.

Design, synthesis and biological evaluation of novel sesquiterpene mustards as potential anticancer agents

Several novel series of sesquiterpene mustards (SMs) bearing nitrogen mustard and glutathione (GSH)-reactive α-methylene-γ-butyrolactone groups were successfully prepared for the first time and showed excellent antiproliferative activities in vitro. Among them, compounds 2e and 2g displayed the highest antiproliferative properties with IC50 values ranging from 2.5 to 8.7 μM. The selectivity of these two compounds was evaluated by SRB method against human cancer and normal hepatic cells (HepG2 and L02). The induction of apoptosis and effects on the cell cycle distribution with compounds 2e and 2g were investigated by Hoechst 33,258 staining and flow cytometry, which exhibited that they could induce selective cell apoptosis and cell cycle arrest in HepG2 and L02 cells. In addition, further investigation showed that compounds 2e and 2g could obviously inhibit the proliferation of HepG2 cells by inducing significant DNA cross-linking and depleting GSH in cell media. The good cytotoxicity and selectivity of compounds 2e and 2g pointed them as promising leads for anticancer drug design.