Exendin-4 Protects Human Retinal Pigment Epithelial Cells from H2O2-Induced Oxidative Damage via Activation of NRF2 Signaling.

AIMS: Oxidative damage plays a vital role in the pathogenesis of age-related macular degeneration (AMD). Exendin-4 (EX4), a glucagon-like peptide-1 receptor agonist, possesses several pharmacological functions, such as anti-inflammatory and antioxidative properties. However, the effects and mechanism of EX4 on oxidative stress in retinal pigment epithelial (RPE) cells induced by hydrogen peroxide (H2O2) remain unclear. The present study aimed to investigate the protective mechanism of EX4 on human RPE cells subjected to oxidative stress. METHODS: Human RPE ARPE-19 cells were treated with H2O2 to induce oxidative damage. Cell viability was determined by Cell Counting Kit-8 and lactate dehydrogenase assay. Levels of intracellular reactive oxygen species (ROS), malonyldialdehyde (MDA), superoxide dismutase (SOD), and glutathione peroxidase (GSH) were measured using commercial kits. The expression of nuclear factor erythroid 2-related factor-2 (NRF2), heme oxygenase-1 (HO-1), and NAD(P)H:quinone oxidoreductase-1 (NQO-1) was measured using reverse transcription quantitative polymerase chain reaction assay and western blot, respectively. RESULTS: H2O2 significantly induced oxidative stress to reduce viability of RPE cells and increased intracellular ROS generation. EX4 significantly ameliorated H2O2-induced oxidative damage by reducing intracellular ROS generation, decreasing MDA concentration, and increasing antioxidant enzymes activities (SOD and GSH). In addition, EX4 markedly increased expression of NRF2, HO-1, and NQO-1 and significantly improved protein expression of NRF2 and HO-1 in H2O2-treated ARPE-19 cells, caused by increased nuclear NRF2 protein expression. NRF2 knockdown by targeted siRNA alleviated EX4-mediated HO-1 expression and significantly nullified EX4-mediated RPE cell protection against H2O2. CONCLUSIONS: EX4 attenuated oxidative damage induced by H2O2 in ARPE-19 cells through the activation of the NRF2 signaling pathway. The findings suggested that EX4 may be a potential therapeutic agent for the treatment of AMD.

Changes in metabolic markers in insulin-producing ß-cells during hypoxia-induced cell death as studied by NMR metabolomics.

This study was designed to investigate changes in the metabolites in the intracellular fluid of the pancreatic ß-cell line INS-1 to identify potential early and late biomarkers for predicting hypoxia-induced cell death. INS-1 cells were incubated under normoxic conditions (95% air, 5% CO2) or hypoxic conditions (1% O2, 5% CO2, 95% N2) for 2, 4, 6, 12, or 24 h. The biological changes indicating the process of cell death were analyzed using the MTT assay, flow cytometry, Western blotting, and immunostaining. Changes in the metabolic profiles from cell lysates were identified using ¹H nuclear magnetic resonance (¹H NMR) spectroscopy, and the spectra were analyzed by the multivariate model Orthogonal Projections to Latent Structure-Discriminant Analysis. Cell viability decreased approximately 40% after 12-24 h of hypoxia, coincident with a high level of cleaved caspase-3. A high level of HIF-1α was detected in the 12-24 h hypoxic conditions. The metabolite profiles were altered according to the degree of exposure to hypoxia. A spectral analysis showed significant differences in creatine-containing compounds at the early stage (2-6 h) and taurine-containing compounds at the late stage (12-24 h), with the detection of HIF-1α and cleaved caspase-3 in cells exposed to hypoxia compared to normoxia. Glycerophosphocholine decreased during the early stage hypoxia. The change in taurine- and creatine-containing compounds and choline species could be involved in the ß-cell death process as inhibitors or activators of cell death. Our results imply that assessment by ¹H NMR spectroscopy would be a useful tool to predict the cell death process and to identify molecules regulating hypoxia-induced cell death mechanisms.

Investigation of discriminant metabolites in tamoxifen-resistant and choline kinase-alpha-downregulated breast cancer cells using 1H-nuclear magnetic resonance spectroscopy.

Metabolites linked to changes in choline kinase-α (CK-α) expression and drug resistance, which contribute to survival and autophagy mechanisms, are attractive targets for breast cancer therapies. We previously reported that autophagy played a causative role in driving tamoxifen (TAM) resistance of breast cancer cells (BCCs) and was also promoted by CK-α knockdown, resulting in the survival of TAM-resistant BCCs. There is no comparative study yet about the metabolites resulting from BCCs with TAM-resistance and CK-α knockdown. Therefore, the aim of this study was to explore the discriminant metabolic biomarkers responsible for TAM resistance as well as CK-α expression, which might be linked with autophagy through a protective role. A total of 33 intracellular metabolites, including a range of amino acids, energy metabolism-related molecules and others from cell extracts of the parental cells (MCF-7), TAM-resistant cells (MCF-7/TAM) and CK-α knockdown cells (MCF-7/shCK-α, MCF-7/TAM/shCK-α) were analyzed by proton nuclear magnetic resonance spectroscopy (1H-NMRS). Principal component analysis (PCA) and partial least square discriminant analysis (PLS-DA) revealed the existence of differences in the intracellular metabolites to separate the 4 groups: MCF-7 cells, MCF-7/TAM cells, MCF-7-shCK-α cells, and MCF-7/TAM/shCK-α cells. The metabolites with VIP>1 contributed most to the differentiation of the cell groups, and they included fumarate, UA (unknown A), lactate, myo-inositol, glycine, phosphocholine, UE (unknown E), glutamine, formate, and AXP (AMP/ADP/ATP). Our results suggest that these altered metabolites would be promising metabolic biomarkers for a targeted therapeutic strategy in BCCs that exhibit TAM-resistance and aberrant CK-α expression, which triggers a survival and drug resistance mechanism.

Downregulation of Choline Kinase-Alpha Enhances Autophagy in Tamoxifen-Resistant Breast Cancer Cells.

Choline kinase-α (Chk-α) and autophagy have gained much attention, as they relate to the drug-resistance of breast cancer. Here, we explored the potential connection between Chk-α and autophagy in the mechanisms driving to tamoxifen (TAM) resistance, in estrogen receptor positive (ER+) breast cancer cells (BCCs). Human BCC lines (MCF-7 and TAM-resistant MCF-7 (MCF-7/TAM) cells) were used. Chk-α expression and activity was suppressed by the transduction of shRNA (shChk-α) with lentivirus and treatment with CK37, a Chk-α inhibitor. MCF-7/TAM cells had higher Chk-α expression and phosphocholine levels than MCF-7 cells. A specific downregulation of Chk-α by the transduction of shChk-α exhibited a significant decrease in phosphocholine levels in MCF-7 and MCF-7/TAM cells. The autophagy-related protein, cleaved microtubule-associated protein light chain 3 (LC3) and autophagosome-like structures were significantly increased in shChk-α-transduced or CK37-treated MCF-7 and MCF-7/TAM cells. The downregulation of Chk-α attenuated the phosphorylation of AKT, ERK1/2, and mTOR in both MCF-7 and MCF-7/TAM cells. In MCF-7 cells, the downregulation of Chk-α resulted in an induction of autophagy, a decreased proliferation ability and an activation of caspase-3. In MCF-7/TAM cells, despite a significant decrease in proliferation ability and an increase in the percentage of cells in the G0/G1 phase of the cell cycle, the downregulation of Chk-α did not induced caspase-dependent cell death and further enhanced autophagy and G0/G1 phase arrest. An autophagy inhibitor, methyladenine (3-MA) induced death and attenuated the level of elevated LC3 in MCF-7/TAM cells. Elucidating the interplay between choline metabolism and autophagy will provide unique opportunities to identify new therapeutic targets and develop novel treatment strategies that preferentially target TAM-resistance.

MRI of breast tumor initiating cells using the extra domain-B of fibronectin targeting nanoparticles.

The identification of breast tumor initiating cells (BTICs) is important for the diagnosis and therapy of breast cancers. This study was undertaken to evaluate whether the extra domain-B of fibronectin (EDB-FN) could be used as a new biomarker for BTICs and whether EDB-FN targeting superparamagnetic iron oxide nanoparticles (SPIONs) could be used as a magnetic resonance imaging (MRI) contrast agent for BTIC imaging in vitro and in vivo. BTICs (NDY-1) exhibited high EDB-FN expression, whereas non-BTICs (MCF-7, BT-474, SUM-225, MDA-MB-231) did not exhibit EDB-FN expression. Furthermore, Cy3.3-labeled EDB-FN specific peptides (APTEDB) showed preferential binding to the targeted NDY-1 cells. To construct an EDB-FN targeted imaging probe, APTEDB was covalently attached to a thermally cross-linked SPION (TCL-SPION) to yield APTEDB-TCL-SPION. In the in vitro MRI of cell phantoms, selective binding of APTEDB-TCL-SPION to NDY-1 cells was evident, but little binding was observed in MCF-7 cells. After the intravenous injection of APTEDB-TCL-SPION into the NDY-1 mouse tumor xenograft model, a significant decrease in the signal within the tumor was observed in the T2*-weighted images; however, there was only a marginal change in the signal of non-targeting SPIONs such as APTscramble-TCL-SPION or TCL-SPION. Taken together, we report for the first time that EDB-FN was abundantly expressed in BTICs and may therefore be useful as a new biomarker for identifying BTICs. Our study also suggests that APTEDB-TCL-SPION could be used as an MRI contrast agent for BTIC imaging.

Magnetic labeling of pancreatic ß-cells modulates the glucose- and insulin-induced phosphorylation of ERK1/2 and AKT.

This study was undertaken to investigate the effect of a magnetic resonance imaging (MRI) contrast agent, superparamagnetic iron oxide nanoparticle (SPIO), on signal transduction by glucose and insulin in pancreatic ß-cells. INS-1 cells were labeled in culture medium containing clinically approved SPIO for 24 h. Labeled and unlabeled cells were stimulated with glucose (25 mM) or insulin (0.1-1 µM) for 12 h. The phosphorylation of extracellular signal-regulated kinase1/2 (ERK1/2) and protein kinase B (AKT) and intracellular insulin protein levels were assessed by Western blotting. After labeling with increasing amounts of SPIO, cytotoxicity was not observed, yet the intracellular iron concentration increased in a dose-dependent manner. SPIO labeling (200 µg Fe ml(-1)) induced a significant increase in ERK1/2 and AKT phosphorylation (labeled vs unlabeled, p < 0.05), but significantly reduced the glucose-stimulated phosphorylation of ERK1/2 and AKT and insulin-stimulated phosphorylation of AKT (labeled vs unlabeled, p < 0.05). The level of intracellular insulin protein was found to be lower in labeled cells than unlabeled cells (labeled vs unlabeled, p < 0.05). This study demonstrates that SPIO labeling alters some fundamental functional variables, at least in INS-1 cells, through modulation of the glucose- or insulin-induced activation of ERK1/2 and AKT, which leads to insulin biosynthesis.

Comparison of Two Ultrasmall Superparamagnetic Iron Oxides on Cytotoxicity and MR Imaging of Tumors.

PURPOSE: This study was performed to compare the cytotoxicity and magnetic resonance (MR) contrast in diverse cultured cells and xenograft tumors models of two ultra-small superparamagnetic iron oxides (USPIOs), thermally cross-linked superparamagnetic iron oxide nanoparticles (TCL-SPION) and monocrystalline iron oxide nanoparticles (MION-47). MATERIALS AND METHODS: Transmission electron microscopy (TEM) images and R(2) relaxivity values of the TCL-SPION and MION-47 were obtained and the cell viability and cell growth velocity of treated and untreated human fibroblasts and human umbilical vein endothelial cells (HUVEC) were evaluated. The effect of TCL-SPION and MION-47 on the secretion of interlukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α), the production of nitric oxides and the mitochondrial membrane potentials in murine macrophage cells (RAW264.7) was compared. Human hepatocellular carcinoma cells (HepG2, 5x10(5)) were subcutaneously injected into nude mice (BALB/c) and in vivo MR imaging of tumors before and after injection with TCL-SPION or MION-47 (12.5 mg Fe/kg) was performed on a 1.5 Tesla MRI scanner. RESULTS: On TEM images, the average core diameter of TCL-SPION was 9 nm whereas that of MION-47 was 5 nm. TCL- SPION (345.0 ± 6.2 mM(-1)sec(-1)) had higher relaxivity (R(2)) than MION-47 (130.7 ± 1.1 mM(-1)sec(-1)). Significant changes in cell viability and growth were not found in human fibroblasts and HUVEC exposed to TCL-SPION and MION-47. However, IL-6 and TNF-α secretions increased dose-dependently and significantly in the macrophages treated with MION-47 or TCL-SPION. TCL-SPION had a lower stimulatory effect on IL-6 secretions than did MION-47 (P <0.05) and nitric oxides were produced in the macrophages by MION-47 but not TCL-SPION. A change in the mitochondrial membrane potential of the macrophages was observed 24 hours after the exposure, and MION-47 induced more collapses of the mitochondrial membrane potential than did TCL-SPION. In the in vivo MR imaging, 33.0 ± 1.3% and 7.5 ± 0.4% signal intensity decrease on T(2)*-weighted images was observed in the tumors injected with TCL-SPION and MION-47, respectively. CONCLUSION: Due to the modified surface properties and larger core size of its iron oxide nanoparticles, TCL-SPION achieves lower cytotoxicity and better tumor MR contrast than MION-47. Our study suggests that TCL-SPION may be used as a new platform for tumor imaging and therapy monitoring.