Transcriptional and physiological responses of HepG2 cells exposed to diethyl maleate: time course analysis

A systematic analysis of Nrf2 pathway activation dynamics during repeated xenobiotic exposure

Oxidative stress leads to the activation of the Nuclear factor-erythroid-2-related factor 2 (Nrf2) pathway. While most studies have focused on the activation of the Nrf2 pathway after single chemical treatment, little is known about the dynamic regulation of the Nrf2 pathway in the context of repeated exposure scenarios. Here we employed single cell live imaging to quantitatively monitor the dynamics of the Nrf2 pathway during repeated exposure, making advantage of two HepG2 fluorescent protein reporter cell lines, expressing GFP tagged Nrf2 or sulfiredoxin 1 (Srxn1), a direct downstream target of Nrf2. High throughput live confocal imaging was used to measure the temporal dynamics of these two components of the Nrf2 pathway after repeated exposure to an extensive concentration range of diethyl maleate (DEM) and tert-butylhydroquinone (tBHQ). Single treatment with DEM or tBHQ induced Nrf2 and Srxn1 over time in a concentration-dependent manner. The Nrf2 response to a second treatment was lower than the response to the first exposure with the same concentration, indicating that the response is adaptive. Moreover, a limited fraction of individual cells committed themselves into the Nrf2 response during the second treatment. Despite the suppression of the Nrf2 pathway, the second treatment resulted in a three-fold higher Srxn1-GFP response compared to the first treatment, with all cells participating in the response. While after the first treatment Srxn1-GFP response was linearly related to Nrf2-GFP nuclear translocation, such a linear relationship was less clear for the second exposure. siRNA-mediated knockdown demonstrated that the second response is dependent on the activity of Nrf2. Several other, clinically relevant, compounds (i.e., sulphorophane, nitrofurantoin and CDDO-Me) also enhanced the induction of Srxn1-GFP upon two consecutive repeated exposure. Together the data indicate that adaptation towards pro-oxidants lowers the Nrf2 activation capacity, but simultaneously primes cells for the enhancement of an antioxidant response which depends on factors other than just Nrf2. These data provide further insight in the overall dynamics of stress pathway activation after repeated exposure and underscore the complexity of responses that may govern repeated dose toxicity.

The effect of insecticide synergist treatment on genome-wide gene expression in a polyphagous pest

Synergists can counteract metabolic insecticide resistance by inhibiting detoxification enzymes or transporters. They are used in commercial formulations of insecticides, but are also frequently used in the elucidation of resistance mechanisms. However, the effect of synergists on genome-wide transcription in arthropods is poorly understood. In this study we used Illumina RNA-sequencing to investigate genome-wide transcriptional responses in an acaricide resistant strain of the spider mite Tetranychus urticae upon exposure to synergists such as S,S,S-tributyl phosphorotrithioate (DEF), diethyl maleate (DEM), piperonyl butoxide (PBO) and cyclosporin A (CsA). Exposure to PBO and DEF resulted in a broad transcriptional response and about one third of the differentially expressed genes (DEGs), including cytochrome P450 monooxygenases and UDP-glycosyltransferases, was shared between both treatments, suggesting common transcriptional regulation. Moreover, both DEF and PBO induced genes that are strongly implicated in acaricide resistance in the respective strain. In contrast, CsA treatment mainly resulted in downregulation of Major Facilitator Superfamily (MFS) genes, while DEGs of the DEM treatment were not significantly enriched for any GO-terms.

On–off–on fluorescence sensing of glutathione in food samples based on a graphitic carbon nitride (g-C3N4)–Cu2+ strategy

A novel fluorescence sensor based on a g-C₃N₄ nanosheet–Cu²⁺ system has been developed for rapid, sensitive and selective sensing of glutathione (GSH) in food samples.

Detection of glutathione in vitro and in cells by the controlled self-assembly of nanorings

Taking advantage of a reduction-controlled biocompatible condensation reaction and self-assembly, we have developed a new method for the determination of glutathione (GSH) concentration in vitro and in HepG2 human liver cancer cells. Upon reduction by GSH under physiological conditions (pH 7.4 in buffer), the small molecule CBT-Cys(SEt) condenses and self-assembles into nanorings, increasing the UV absorbance at 380 nm (with significant linear correlation in the 0-87 μM GSH range and a limit of detection of 1 μM). This method is also selective to GSH rather than cysteine in biological samples. Through the use of added internal standards, we successfully determined the concentration of GSH in HepG2 cells to be 14.96 μM (2.99 fmol/cell). To better understand the mechanism of nanoring self-assembly, the condensation product of CBT-Cys(SEt) formed using different concentrations of GSH and different reaction times were characterized by transmission electron microscopy (TEM).

High molecular weight isoforms of growth hormone in cells of the immune system

A substantial body of research exists to support the idea that cells of the immune system produce growth hormone (GH). However, the structure and mechanism of action of lymphocyte-derived GH continues to remain largely unknown. Here we present the results of Western analysis of whole cell extracts showing that different molecular weight isoforms of GH of approximately 100, 65, and 48 kDa can be detected in primary mouse cells of the immune system and in the mouse EL4 cell line. The identity of the 65 and 48 kDa isoforms of GH were confirmed by mass spectrometry. The various isoforms were detected in both enriched T and B spleen cell populations. The large molecular weight isoform appears to reside primarily in the cytoplasm, whereas the lower molecular weight 65 and 48 kDa isoforms were detected primarily in the nucleus. These results also suggest that GH isoforms are induced by oxidative stress. In EL4 cells overexpressing GH, the expression of luciferase controlled by a promoter containing the antioxidant response element is increased almost threefold above control. The data suggest that the induction of isoforms of the GH molecule in cells of the immune system may be an important mechanism of adaptation and/or protection of lymphoid cells under conditions of oxidative stress.

Opuntia humifusa partitioned extracts inhibit the growth of U87MG human glioblastoma cells

Opuntia humifusa, a member of the Cactaceae family widely distributed in the southern regions of the Korean peninsula, has potential bioactive functions and medicinal benefits. In the present study, we investigated the effect of hexane, ethyl acetate extracts and water partitioned fraction of O. humifusa on proliferation, G1 arrest and apoptosis in U87MG human glioblastoma cells. Glioblastoma cellular proliferation was evaluated using the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay, and the effects of O. humifusa partitioned extracts on cell cycle and apoptosis were analyzed by flow cytometry. Our results revealed that when U87MG cells were treated with hexane extracts and water partitioned fraction of O. humifusa, the number of viable cells decreased in a concentration-dependent manner. In addition, water partitioned fractions of O. humifusa induced G1 arrest and non-apoptotic cell death as well as significant increases in ROS production in U87MG cells. In conclusion, water partitioned fractions of O. humifusa induce G1 arrest and inhibit U87MG human glioblastoma cell proliferation.

Novel interaction of selenium-binding protein with glyceraldehyde-3-phosphate dehydrogenase and fructose-bisphosphate aldolase of Arabidopsis thaliana

The metabolic role and regulation of selenium, particularly in plants, is poorly understood. One of the proteins probably involved in the metabolic regulation of this element is the selenium-binding protein (SBP) with homologues present across prokaryotic and eukaryotic species. The high degree of conservation of SBP in different organisms suggests that this protein may play a role in fundamental biological processes. In order to gain insight into the biochemical function of SBP in plants we used the yeast two-hybrid system to identify proteins that potentially interact with an Arabidopsis thaliana (L.) Heynh. homologue. Among the putative binding partners of SBP, a NADP-dependent glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and a fructose-bisphosphate aldolase (FBA) were found as reliable positive candidates. The interaction of these proteins with SBP was confirmed by in vitro binding assays. Previous findings in Escherichia coli, demonstrated the direct binding of selenium to both GAPDH and aldolase. Therefore our results reveal the interaction, at least in pairs, of three proteins that are possibly linked to selenium and suggest the existence of a protein network consisting of at least SBP, GAPDH and FBA, triggered by or regulating selenium metabolism in plant cells.

Complementary roles for toxicologic pathology and mathematics in toxicogenomics, with special reference to data interpretation and oscillatory dynamics

Toxicogenomics is an emerging multidisciplinary science that will profoundly impact the practice of toxicology. New generations of biologists, using evolving toxicogenomics tools, will generate massive data sets in need of interpretation. Mathematical tools are necessary to cluster and otherwise find meaningful structure in such data. The linking of this structure to gene functions and disease processes, and finally the generation of useful data interpretation remains a significant challenge. The training and background of pathologists make them ideally suited to contribute to the field of toxicogenomics, from experimental design to data interpretation. Toxicologic pathology, a discipline based on pattern recognition, requires familiarity with the dynamics of disease processes and interactions between organs, tissues, and cell populations. Optimal involvement of toxicologic pathologists in toxicogenomics requires that they communicate effectively with the many other scientists critical for the effective application of this complex discipline to societal problems. As noted by Petricoin III et al (Nature Genetics 32, 474-479, 2002), cooperation among regulators, sponsors and experts will be essential for realizing the potential of microarrays for public health. Following a brief introduction to the role of mathematics in toxicogenomics, "data interpretation" from the perspective of a pathologist is briefly discussed. Based on oscillatory behavior in the liver, the importance of an understanding of mathematics is addressed, and an approach to learning mathematics "later in life" is provided. An understanding of pathology by mathematicians involved in toxicogenomics is equally critical, as both mathematics and pathology are essential for transforming toxicogenomics data sets into useful knowledge.

Reactive oxygen species-independent G1 arrest induced by evening primrose extract in Ehrlich ascites tumor cells

We previously demonstrated that evening primrose extract (EPE) induced apoptosis in Ehrlich ascites tumor cells (EATC), and this effect was specific on tumor cells. Furthermore, our results demonstrated that EPE exposure elicited a rapid increase in the activity of superoxide dismutase and intracellular peroxides levels. These changes caused translocation of Bax to mitochondria and a subsequent release of mitochondrial cytochrome c. However, no activation of caspase-3 was observed in EPE-treated EATC. On the other hand, apoptosis-inducing factor (AIF) was translocated from mitochondria to nuclei. The EPE-induced translocation of AIF was suppressed with the addition of catalase, suggesting that the rapid intracellular peroxide levels after addition of EPE triggers off induction of apoptosis, which is AIF-mediated and caspase-independent. In this study, we have shown that EPE elicited a dose-dependent accumulation of cells in the G1 phase and inhibited DNA synthesis. Our results also demonstrated that cell cycle arrest and inhibition of proliferation in EATC by EPE are associated with decreased Rb phosphorylation. Furthermore, inhibitions of Rb phosphorylation and DNA synthesis by EPE were not suppressed with the addition of catalase. The present study suggests that intracellular peroxides, which trigger off induction of apoptosis, are not the trigger of EPE-induced G1 arrest in cell cycle.