Pingping Shen

The cytotoxicity of cadmium based, aqueous phase -Synthesized, quantum dots and its modulation by surface coating

In this report, we evaluated the cytotoxicity of a series of quantum dots (QDs) directly synthesized in aqueous phase, i.e., thiols-stabilized CdTe, CdTe/CdS core-shell structured and CdTe/CdS/ZnS core-shell-shell structured QDs, with a variety of cell lines including K562 and HEK293T. We have demonstrated that the CdTe QDs are highly toxic for cells due to the release of cadmium ions. Epitaxial growth of a CdS layer reduces the cytotoxicity of QDs to a small extent. However, the presence of a ZnS outlayer greatly improves the biocompatibility of QDs, with no observed cytotoxicity even at very high concentration and long-time exposure in cells. Our systematic investigation clearly shows that the cytotoxicity of QDs can be modulated through elaborate surface coatings and that the CdTe/CdS/ZnS core-shell-shell structured QDs directly synthesized in aqueous phase are highly promising biological fluorescent probes for cellular imaging.

The cytotoxicity of CdTe quantum dots and the relative contributions from released cadmium ions and nanoparticle properties

A systematic study was carried out on the relationship between the cytotoxicity of quantum dots (QDs) and free cadmium ions using CdCl(2) solution with known amounts of Cd(2+) as the control. We found that the CdTe QDs were more cytotoxic than CdCl(2) solutions even when the intracellular Cd(2+) concentrations were identical in HEK293 cells treated with them, implying the cytotoxicity of CdTe QDs cannot attributed solely to the toxic effect of free Cd(2+). Moreover, we discovered that the cytotoxicity of QDs was based on the concentration of total QDs ingested by cells. Our data clearly showed that specific properties of nanoparticles have an obvious influence on their cytotoxicity.

Induction of Apoptosis in Mouse Liver by Microcystin-LR A Combined Transcriptomic, Proteomic, And Simulation Strategy

Microcystins (MCs) are a family of cyclic heptapeptide hepatotoxins produced by freshwater species of cyanobacteria that have been implicated in the development of liver cancer, necrosis, and even deadly intrahepatic bleeding. MC-LR, the most toxic MC variant, is also the most commonly encountered in a contaminated aquatic system. This study presents the first data in the toxicological research of MCs that combines the use of standard apoptotic assays with transcriptomics, proteomic technologies, and computer simulations. By using histochemistry, DNA fragmentation assays, and flow cytometry analysis, we determined that MC-LR causes rapid, dose-dependent apoptosis in mouse liver when BALB/c mice are treated with MC-LR for 24 h at doses of either 50, 60, or 70 μg/kg of body weight. We then used gene expression profiling to demonstrate differential expressions (>2-fold) of 61 apoptosis-related genes in cells treated with MC-LR. Further proteomic analysis identified a total of 383 proteins of which 35 proteins were up-regulated and 30 proteins were down-regulated more than 2.5-fold when compared with controls. Combining computer simulations with the transcriptomic and proteomic data, we found that low doses (50 μg/kg) of MC-LR lead to apoptosis primarily through the BID-BAX-BCL-2 pathway, whereas high doses of MC-LR (70 μg/kg) caused apoptosis via a reactive oxygen species pathway. These results indicated that MC-LR exposure can cause apoptosis in mouse liver and revealed two independent pathways playing a major regulatory role in MC-LR-induced apoptosis, thereby contributing to a better understanding of the hepatotoxicity and the tumor-promoting mechanisms of MCs.

Analysis of microcystins in cyanobacteria blooms and surface water samples from Meiliang Bay, Taihu Lake, China

Taihu Lake is the third largest freshwater lake in China. In recent years, the water pollution of cyanobacteria blooms has become a severe problem in this area. Microcystins (MCs) are an important group of toxic compounds mainly produced by some cyanobacteria species and have both acute and chronic hepatotoxic effects on animals and humans. This paper presents the first data on the identification and detection of MCs in both natural occurring cyanobacteria blooms and surface water samples (0-0.5 m), collected from Meiliang Bay, Taihu Lake, China. A conventional method for extraction and isolation of MCs from cyanobacteria blooms was applied. High-performance liquid chromatography (HPLC) analysis showed that the main toxic component in the cyanobacteria materials was MC-LR. The monoclonal antibody (mAb) against MC-LR produced by hybridoma technique was employed for direct competitive ELISA to detect the concentrations of MCs in bloom and water samples collected in 2001. The results not only revealed the presence of MCs but also temporal variations of MCs levels of three sampling stations in Meiliang Bay in 1 year. It is obvious that the MC contents were relatively higher during warm months and related with the status of eutrophication. Our study indicates the threat associated with MCs in water body of Taihu Lake. To prevent the MCs potential hazard on public health in this area, some necessary measures of monitoring and control of growth of cyanobacteria are urgently needed.

Apoptosis induced by methylene-blue-mediated photodynamic therapy in melanomas and the involvement of mitochondrial dysfunction revealed by proteomics

Methylene blue (MB) is a widely studied agent currently under investigation for its properties relating to photodynamic therapy (PDT). Recent studies have demonstrated that MB exhibits profound phototoxicity affecting a variety of tumor cell lines. However, the mechanistic explanation for methylene‐blue‐mediated photodynamic therapy (MB‐PDT) in the context of melanoma therapy is still obscure. In the present study, B16F1 melanoma cells were treated by MB‐PDT under different conditions, and thereafter subjected to cell viability detection assays. MB‐PDT could induce intense apoptotic cell death through a series of steps beginning with the photochemical generation of reactive oxygen species that activate the caspase‐9/caspase‐3 apoptosis pathway. Blocking activation of caspase‐3 and induction of oxidative stress by caspase inhibitor and by glutathione, respectively, markedly reduced apoptotic cell death in vitro. Importantly, proteomics study defining altered protein expression in treated cells suggests the involvement of several mitochondrial proteins playing important roles in electron transfer chain, implying mitochondrial dysfunction during the treatment. Furthermore, a transplantable mouse melanoma model was utilized to estimate the effectiveness of MB‐PDT in vivo. The treated mice displayed decreased tumor size and prolonged survival days, which was associated with enhanced apoptotic cell death. These results, offering solid evidence of the induction of mitochondria‐related apoptosis in tumor cells, reveal new aspects of MB‐PDT having potential to be a palliative treatment of melanoma. (Cancer Sci 2008; 99: 2019–2027)

Effects of cyanobacteria bloom extract on some parameters of immune function in mice.

Microcystis aeruginosa is a common cyanobacterium in water blooms that appear world widely in eutrophic freshwaters, and its toxic blooms have caused many death and illness cases. This paper presents the first data on the immunotoxicity of a microcystin (MC) extract of cyanobacteria bloom collected from Taihu Lake, China to BALB/c mice. The cyanobacteria bloom extract (CBE) containing MCs was administered by i.p. injection for 14 days at three sublethal doses of 16, 32, 64 mg lyophilized algae cells/kg body weight. Exposure to CBE decreased body weights dose-dependently. Meanwhile, liver body weight ratios were markedly increased. The significant differences were also observed in spleen and thymus body ratios upon the elevation of treatment dose comparing to control. CBE was also found to reduce the phagocytosis evaluated using phagocytic index of peritoneal phagocyte; this suppression was not evident in percentage phagocytosis. Treatment of CBE produced the inhibition of lipopolysaccharide-induced lymphoproliferation and the dose-dependent decrease of the numbers of antibody-forming cells in mice that were immunized by using T-dependent antigen sheep red blood cells. However, CBE did not affect concanavalin A-induced T cell proliferation. Our results demonstrate that exposure to CBE resulted in immunosuppression in mice.

Involvement of JNK regulation in oxidative stress-mediated murine liver injury by microcystin-LR.

Microcystin-LR (MC-LR) produced by cyanobacteria in diverse water systems is a potent specific hepatotoxin and has been documented to induce various liver diseases via oxidative stress. However, the underlying mechanisms are largely unknown. In the current study, we investigated the molecular events involved in the oxidative liver injury by MC-LR. Our results demonstrated that MC-LR induced liver injury in mice through a series of steps that began with the production of reactive oxygen species (ROS), which stimulated the sustained activation of JNK and its downstream targets, AP-1 and Bid. Furthermore, the mitochondrial proteomic analysis indicated that JNK activation affected some crucial enzymes of energy metabolism, led to mitochondria dysfunction, which contributed to hepatocyte apoptosis and oxidative liver injury by MC-LR. Our results reveal significant insights into the mechanisms of liver injury induced by microcystins, and serve as a framework for deciphering the role of JNK in oxidative stress-associated liver diseases.

Estrogen Represses Hepatocellular Carcinoma (HCC) Growth via Inhibiting Alternative Activation of Tumor-associated Macrophages (TAMs)

Background: Hepatocarcinoma cancer (HCC) occurs more often in men than in women, and little is known about its underlying molecular mechanisms. Results: We identify that 17β-estradiol (E2) could suppress tumor growth via regulating the polarization of macrophages. Conclusion: Estrogen functions as a suppressor for macrophage alternative activation. Significance: These studies introduce a novel mechanism for suppressing male-predominant HCC. Hepatocarcinoma cancer (HCC), one of the most malignant cancers, occurs significantly more often in men than in women; however, little is known about its underlying molecular mechanisms. Here we identified that 17β-estradiol (E2) could suppress tumor growth via regulating the polarization of macrophages. We showed that E2 re-administration reduced tumor growth in orthotopic and ectopic mice HCC models. E2 functioned as a suppressor for macrophage alternative activation and tumor progression by keeping estrogen receptor β (ERβ) away from interacting with ATP5J (also known as ATPase-coupling factor 6), a part of ATPase, thus inhibiting the JAK1-STAT6 signaling pathway. These studies introduce a novel mechanism for suppressing male-predominant HCC.

Two independent positive feedbacks and bistability in the Bcl-2 apoptotic switch.

Background The complex interplay between B-cell lymphoma 2 (Bcl-2) family proteins constitutes a crucial checkpoint in apoptosis. Its detailed molecular mechanism remains controversial. Our former modeling studies have selected the ‘Direct Activation Model’ as a better explanation for experimental observations. In this paper, we continue to extend this model by adding interactions according to updating experimental findings. Methodology/Principal Findings Through mathematical simulation we found bistability, a kind of switch, can arise from a positive (double negative) feedback in the Bcl-2 interaction network established by anti-apoptotic group of Bcl-2 family proteins. Moreover, Bax/Bak auto-activation as an independent positive feedback can enforce the bistability, and make it more robust to parameter variations. By ensemble stochastic modeling, we also elucidated how intrinsic noise can change ultrasensitive switches into gradual responses. Our modeling result agrees well with recent experimental data where bimodal Bax activation distributions in cell population were found. Conclusions/Significance Along with the growing experimental evidences, our studies successfully elucidate the switch mechanism embedded in the Bcl-2 interaction network and provide insights into pharmacological manipulation of Bcl-2 apoptotic switch as further cancer therapies.

Robustness analysis identifies the plausible model of the Bcl-2 apoptotic switch.

In this paper two competing models of the B‐cell lymphoma 2 (Bcl‐2) apoptotic switch were contrasted by mathematical modeling and robustness analysis. Since switch‐like behaviors are required for models that attempt to explain the all‐or‐none decisions of apoptosis, ultrasensitivity was employed as a criterion for comparison. Our results successfully exhibit that the direct activation model operates more reliably to achieve a robust switch in cellular conditions. Moreover, by investigating the robustness of other important features of the Bcl‐2 apoptotic switch (including low Bax basal activation, inhibitory role of anti‐apoptotic proteins and insensitivity to small perturbations) the direct activation model was further supported. In all, we identified the direct activation model as a more plausible explanation for the Bcl‐2 apoptotic switch.