Helenalin Facilitates Reactive Oxygen Species-Mediated Apoptosis and Cell Cycle Arrest by Targeting Thioredoxin Reductase-1 in Human Prostate Cancer Cells.

BACKGROUND Helenalin is a pseudoguaianolide natural product with anti-cancer activities. This study investigated the underlying mechanism of the anti-prostate cancer effects of helenalin in vitro. MATERIAL AND METHODS CCK-8 assay was performed to detect the optimal concentrations of helenalin in DU145 and PC-3 cells. After exposure to helenalin and/or reactive oxygen species (ROS) inhibitor, ROS production was assessed by DCFH-DA staining. Thioredoxin reductase-1 (TrxR1) expression was detected by RT-qPCR and western blot. Moreover, apoptosis and cell cycle were evaluated by flow cytometry. Following TrxR1 knockdown or overexpression, TrxR1 expression, ROS generation, apoptosis, cell cycle, migration, and invasion were examined in cells co-treated with helenalin. RESULTS Helenalin distinctly repressed the viability of prostate cancer cells in a concentration-dependent manner. We chose 8 µM and 4 µM as the optimal concentrations of helenalin for DU145 and PC-3 cells, respectively. Helenalin treatment markedly triggered ROS production and lowered TrxR1 expression, which was ameliorated by ROS inhibitor. Exposure to helenalin facilitated apoptosis as well as G0/G1 cell cycle arrest, which was reversed by ROS inhibitor. Helenalin relieved the inhibitory effect of TrxR1 on ROS production. Furthermore, helenalin ameliorated the decrease in apoptosis rate and the shortening of G0/G1 phase as well as the increase in migration and invasion induced by TrxR1 overexpression. CONCLUSIONS Our findings revealed that helenalin accelerated ROS-mediated apoptosis and cell cycle arrest via targeting TrxR1 in human prostate cancer cells.

Honokiol Alleviates Oxidative Stress-Induced Neurotoxicity via Activation of Nrf2.

Honokiol (Hon), a polyphenol and main active ingredient from the bark of Magnolia officinalis, has been documented as having multiple pharmacological functions, including neuroprotection. However, the mechanisms underlying its neuroprotective effects are not well-defined. In this study, we reported that Hon attenuates the H2O2- or 6-hydroxydopamine (6-OHDA)-induced apoptosis of PC12 cells by increasing the glutathione level and upregulating a multitude of cytoprotective proteins, including heme oxygenase 1, NAD(P)H:quinone oxidoreductase 1, thioredoxin 1, and thioredoxin reductase 1. Further studies reveal that Hon promotes transcription factor Nrf2 nuclear translocation and activation. Moreover, the cytoprotection of Hon was antagonized by silence of Nrf2 expression, highlighting the fact that Nrf2 is critically engaged in the cellular functions of Hon. Taken together, our study identified that Hon is an effective agonist of Nrf2 in the neuronal system and displays potent neuroprotection against oxidative stress-mediated PC12 cell damage. These findings indicate that Hon is promising for further development as a therapeutic drug against oxidative stress-related neurodegenerative disorders.

Transforming growth factor-beta1 regulates the fate of cultured spinal cord-derived neural progenitor cells.

OBJECTIVES: We have evaluated the physiological roles of transforming growth factor-beta1 (TGF-beta1) on differentiation, migration, proliferation and anti-apoptosis characteristics of cultured spinal cord-derived neural progenitor cells. METHODS: We have used neural progenitor cells that had been isolated and cultured from mouse spinal cord tissue, and we also assessed the relevant reaction mechanisms using an activin-like kinase (ALK)-specific inhibitory system including an inhibitory RNA, and found that it involved potential signalling molecules such as phosphatidylinositol-3-OH kinase (PI3K)/Akt and mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK1/2). RESULTS AND CONCLUSIONS: Transforming growth factor-beta1-mediated cell population growth was activated after treatment and was also effectively blocked by an ALK41517-synthetic inhibitor (4-(5-benzo(1,3) dioxol-5-yl-4-pyridine-2-yl-1H-imidazole-2-yl) benzamide (SB431542) and ALK siRNA, thereby indicating the involvement of SMAD2 in the TGF-beta1-mediated growth and migration of these neural progenitors cells (NPC). In the present study, TGF-beta1 actively induced NPC migration in vitro. Furthermore, TGF-beta1 demonstrated extreme anti-apoptotic behaviour against hydrogen peroxide-mediated apoptotic cell death. At low dosages, TGF-beta1 enhanced (by approximately 76%) cell survival against hydrogen peroxide treatment via inactivation of caspase-3 and -9. TGF-beta1-treated NPCs down-regulated Bax expression and cytochrome c release; in addition, the cells showed up-regulated Bcl-2 and thioredoxin reductase 1. They also had increased p38, Akt and ERK1/2 phosphorylation, showing the involvement of both the PI3K/Akt and MAPK/ERK1/2 pathways in the neuroprotective effects of TGF-beta1. Interestingly, these effects operate on specific subtypes of cells, including neurones, neural progenitor cells and astrocytes in cultured spinal cord tissue-derived cells. Lesion sites of spinal cord-overexpressing TGF-beta1-mediated prevention of cell death, cell growth and migration enhancement activity have been introduced as a possible new basis for therapeutic strategy in treatment of neurodegenerative disorders, including spinal cord injuries.

Effect of mercury(II) on Nrf2, thioredoxin reductase-1 and thioredoxin-1 in human monocytes.

OBJECTIVES: Human blood levels of mercury are commonly 10nM, but may transiently reach 50-75nM after dental amalgam placement or removal. Controversy persists about the use of mercury because the effects of these 'trace' levels of mercury are not clear. Concentrations of mercury > or =5000nM unequivocally alter redox balance in blood cells including monocytes. In the current study, we tested a hypothesis that concentrations of mercury <100nM altered levels and activities of key proteins that maintain monocytic redox balance. METHODS: Human THP1 monocytes were exposed to 10-75nM of Hg(II) for 6-72h, with or without activation by lipopolysaccharide (LPS). The redox management proteins Nrf2 and thioredoxin-1 (Trx1) were separated by electrophoresis, then quantified by immunoblotting. The activity of the seleno-enzyme thioredoxin reductase (TrxR1), important in maintaining Trx1 redox balance, was measured by cell-free and cell-dependent assays. RESULTS: Concentrations of Hg(II) between 10-75nM increased Nrf2 levels (3.5-4.5 fold) and decreased Trx1 levels (2-3 fold), but these changes persisted <24h. Hg(II) potently inhibited (at concentrations of 5-50nM) TrxR1 activity in both cell-free and intracellular assays. Furthermore, Hg(II) transiently amplified LPS-induced Nrf2 levels by 2-3 fold and limited LPS-induced decreases in Trx1. All effects of Hg(II) were mitigated by pre-adding N-acetyl-cysteine (NAC) or sodium selenide (Na2SeO3), supplements of cellular thiols and selenols, respectively. SIGNIFICANCE: Our results suggest that nanomolar concentrations of Hg(II) transiently alter cellular redox balance in monocytes that trigger changes in Nrf2 and Trx1 levels. These changes indicate that monocytes have a capacity to adapt to trace concentrations of Hg(II) that are introduced into the bloodstream after dental amalgam procedures or fish consumption. The ability of monocytes to adapt suggests that low levels of mercury exposure from dental amalgam may not overtly compromise monocyte function.