Antimycin A as a mitochondria damage agent induces an S phase arrest of the cell cycle in HeLa cells

Fam96a is essential for the host control of Toxoplasma gondii infection by fine-tuning macrophage polarization via an iron-dependent mechanism

BACKGROUND

Toxoplasmosis affects a quarter of the world's population. Toxoplasma gondii (T.gondii) is an intracellular parasitic protozoa. Macrophages are necessary for proliferation and spread of T.gondii by regulating immunity and metabolism. Family with sequence similarity 96A (Fam96a; formally named Ciao2a) is an evolutionarily conserved protein that is highly expressed in macrophages, but whether it play a role in control of T. gondii infection is unknown.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, we utilized myeloid cell-specific knockout mice to test its role in anti-T. gondii immunity. The results showed that myeloid cell-specific deletion of Fam96a led to exacerbate both acute and chronic toxoplasmosis after exposure to T. gondii. This was related to a defectively reprogrammed polarization in Fam96a-deficient macrophages inhibited the induction of immune effector molecules, including iNOS, by suppressing interferon/STAT1 signaling. Fam96a regulated macrophage polarization process was in part dependent on its ability to fine-tuning intracellular iron (Fe) homeostasis in response to inflammatory stimuli. In addition, Fam96a regulated the mitochondrial oxidative phosphorylation or related events that involved in control of T. gondii.

CONCLUSIONS/SIGNIFICANCE

All these findings suggest that Fam96a ablation in macrophages disrupts iron homeostasis and inhibits immune effector molecules, which may aggravate both acute and chronic toxoplasmosis. It highlights that Fam96a may autonomously act as a critical gatekeeper of T. gondii control in macrophages.

Aurora kinase A/AURKA functionally interacts with the mitochondrial ATP synthase to regulate energy metabolism and cell death

Cancer cells often hijack metabolic pathways to obtain the energy required to sustain their proliferation. Understanding the molecular mechanisms underlying cancer cell metabolism is key to fine-tune the metabolic preference of specific tumors, and potentially offer new therapeutic strategies. Here, we show that the pharmacological inhibition of mitochondrial Complex V delays the cell cycle by arresting breast cancer cell models in the G0/G1 phase. Under these conditions, the abundance of the multifunctional protein Aurora kinase A/AURKA is specifically lowered. We then demonstrate that AURKA functionally interacts with the mitochondrial Complex V core subunits ATP5F1A and ATP5F1B. Altering the AURKA/ATP5F1A/ATP5F1B nexus is sufficient to trigger G0/G1 arrest, and this is accompanied by decreased glycolysis and mitochondrial respiration rates. Last, we discover that the roles of the AURKA/ATP5F1A/ATP5F1B nexus depend on the specific metabolic propensity of triple-negative breast cancer cell lines, where they correlate with cell fate. On one hand, the nexus induces G0/G1 arrest in cells relying on oxidative phosphorylation as the main source of energy. On the other hand, it allows to bypass cell cycle arrest and it triggers cell death in cells with a glycolytic metabolism. Altogether, we provide evidence that AURKA and mitochondrial Complex V subunits cooperate to maintain cell metabolism in breast cancer cells. Our work paves the way to novel anti-cancer therapies targeting the AURKA/ATP5F1A/ATP5F1B nexus to lower cancer cell metabolism and proliferation.

Metallothionein 3 Inhibits 3T3-L1 Adipocyte Differentiation via Reduction of Reactive Oxygen Species

Metallothionein 3 (MT3), also known as a neuronal growth-inhibitory factor, is a member of the metallothionein family and is involved in a variety of biological functions, including protection against metal toxicity and reactive oxygen species (ROS). However, less is known about the role of MT3 in the differentiation of 3T3-L1 cells into adipocytes. In this study, we observed that MT3 levels were downregulated during 3T3-L1 adipocyte differentiation. Mt3 overexpression inhibited adipocyte differentiation and reduced the levels of the adipogenic transcription factors C/EBPα and PPARγ. Further analyses showed that MT3 also suppressed the transcriptional activity of PPARγ, and this effect was not mediated by a direct interaction between MT3 with PPARγ. In addition, Mt3 overexpression resulted in a decrease in ROS levels during early adipocyte differentiation, while treatment with antimycin A, which induces ROS generation, restored the ROS levels. Mt3 knockdown, on the other hand, elevated ROS levels, which were suppressed upon treatment with the antioxidant N-acetylcysteine. Our findings indicate a previously unknown role of MT3 in the differentiation of 3T3-L1 cells into adipocytes and provide a potential novel target that might facilitate obesity treatment.

Ruthenium(II)-Dithiocarbazates as Anticancer Agents: Synthesis, Solution Behavior, and Mitochondria-Targeted Apoptotic Cell Death

The reaction of the Ru(PPh₃ )₃ Cl₂ with HL^1-3 -OH (-OH stands for the oxime hydroxyl group; HL¹ -OH=diacetylmonoxime-S-benzyldithiocarbazonate; HL² -OH=diacetylmonoxime-S-(4-methyl)benzyldithiocarbazonate; and HL³ -OH=diacetylmonoxime-S-(4-chloro)benzyl-dithiocarbazonate) gives three new ruthenium complexes [Ru^II (L^1-3 -H)(PPh₃ )₂ Cl] (1-3) (-H stands for imine hydrogen) coordinated with dithiocarbazate imine as the final products. All ruthenium(II) complexes (1-3) have been characterized by elemental (CHNS) analyses, IR, UV-vis, NMR (¹ H, ¹³ C, and ³¹ P) spectroscopy, HR-ESI-MS spectrometry and also, the structure of 1-2 was further confirmed by single crystal X-ray crystallography. The solution/aqueous stability, hydrophobicity, DNA interactions, and cell viability studies of 1-3 against HeLa, HT-29, and NIH-3T3 cell lines were performed. Cell viability results suggested 3 being the most cytotoxic of the series with IC₅₀ 6.9±0.2 μM against HeLa cells. Further, an apoptotic mechanism of cell death was confirmed by cell cycle analysis and Annexin V-FITC/PI double staining techniques. In this regard, the live cell confocal microscopy results revealed that compounds primarily target the mitochondria against HeLa, and HT-29 cell lines. Moreover, these ruthenium complexes elevate the ROS level by inducing mitochondria targeting apoptotic cell death.

Characterization of mitochondrial respiratory complexes involved in the regulation of myoblast differentiation

During myoblast differentiation, mitochondria undergo numerous changes that are necessary for the progression of the myogenic program. Notably, we previously showed that alteration in mitochondrial activity was able to control the expression of keys regulator of cell cycle withdrawal and terminal differentiation. Here, we assessed whether inhibition of one of the respiratory complexes was a key factor in the regulation of myogenic differentiation in C2C12 cells, and was associated with alteration in reactive oxygen species (ROS) production. C2C12 cells were treated from proliferation to differentiation with specific inhibitors of mitochondrial complexes at a concentration that were inhibiting respiration but not altering cell morphology. Proliferation was significantly repressed with inhibition of complexes I, II, and III, or mitochondrial protein synthesis (using Chloramphenicol treatment), while complex IV inhibition did not alter myoblast proliferation compared to control cells. Moreover, inhibition of complexes I and II altered cell cycle regulators, with p21 protein expression upregulated since proliferation and p27 protein expression reduced at differentiation. Myotubes formation and myogenin expression were blunted with complexes I and II inhibitors while MyoD protein expression was maintained, suggesting an alteration in its transcriptional activity. Finally, a decrease in overall ROS production was observed with continuous inhibition of mitochondrial complexes I-IV. In summary, our data provide evidence that complexes I and II may be the primary regulators of C2C12 myogenic differentiation. This occurs through specific regulation of myogenic rather than cell cycle regulators expression and ROS production at mitochondrial rather than cell level.

Antimycin A shows selective antiproliferation to oral cancer cells by oxidative stress-mediated apoptosis and DNA damage

The antibiotic antimycin A (AMA) is commonly used as an inhibitor for the electron transport chain but its application in anticancer studies is rare. Recently, the repurposing use of AMA in antiproliferation of several cancer cell types has been reported. However, it is rarely investigated in oral cancer cells. The purpose of this study is to investigate the selective antiproliferation ability of AMA treatment on oral cancer cells. Cell viability, flow cytometry, and western blotting were applied to explore its possible anticancer mechanism in terms of both concentration- and exposure time-effects. AMA shows the higher antiproliferation to two oral cancer CAL 27 and Ca9-22 cell lines than normal oral HGF-1 cell lines. Moreover, AMA induces the production of higher reactive oxygen species (ROS) levels and pan-caspase activation in oral cancer CAL 27 and Ca9-22 cells than in normal oral HGF-1 cells, providing the possible mechanism for its selective antiproliferation effect of AMA. In addition to ROS, AMA induces mitochondrial superoxide (MitoSOX) generation and depletes mitochondrial membrane potential (MitoMP). This further supports the AMA-induced oxidative stress changes in oral cancer CAL 27 and Ca9-22 cells. AMA also shows high expressions of annexin V in CAL 27 and Ca9-22 cells and cleaved forms of poly (ADP-ribose) polymerase (PARP), caspase 9, and caspase 3 in CAL 27 cells, supporting the apoptosis-inducing ability of AMA. Furthermore, AMA induces DNA damage (γH2AX and 8-oxo-2'-deoxyguanosine [8-oxodG]) in CAL 27 and Ca9-22 cells. Notably, the AMA-induced selective antiproliferation, oxidative stress, and DNA damage were partly prevented from N-acetylcysteine (NAC) pretreatments. Taken together, AMA selectively kills oral cancer cells in an oxidative stress-dependent mechanism involving apoptosis and DNA damage.

Multimodal Probes: Superresolution and Transmission Electron Microscopy Imaging of Mitochondria, and Oxygen Mapping of Cells, Using Small-Molecule Ir(III) Luminescent Complexes

We describe an Ir(III)-based small-molecule, multimodal probe for use in both light and electron microscopy. The direct correlation of data between light- and electron-microscopy-based imaging to investigate cellular processes at the ultrastructure level is a current challenge, requiring both dyes that must be brightly emissive for luminescence imaging and scatter electrons to give contrast for electron microscopy, at a single working concentration suitable for both methods. Here we describe the use of Ir(III) complexes as probes that provide excellent image contrast and quality for both luminescence and electron microscopy imaging, at the same working concentration. Significant contrast enhancement of cellular mitochondria was observed in transmission electron microscopy imaging, with and without the use of typical contrast agents. The specificity for cellular mitochondria was also confirmed with MitoTracker using confocal and 3D-structured illumination microscopy. These phosphorescent dyes are part of a very exclusive group of transition-metal complexes that enable imaging beyond the diffraction limit. Triplet excited-state phosphorescence was also utilized to probe the O₂ concentration at the mitochondria in vitro, using lifetime mapping techniques.

Pulse frequency dependency of photobiomodulation on the bioenergetic functions of human dental pulp stem cells

Photobiomodulation (PBM) therapy contributes to pain relief, wound healing, and tissue regeneration. The pulsed wave (PW) mode has been reported to be more effective than the continuous wave (CW) mode when applying PBM to many biological systems. However, the reason for the higher effectiveness of PW-PBM is poorly understood. Herein, we suggest using delayed luminescence (DL) as a reporter of mitochondrial activity after PBM treatment. DL originates mainly from mitochondrial electron transport chain systems, which produce reactive oxygen species (ROS) and adenosine triphosphate (ATP). The decay time of DL depends on the pulse frequencies of applied light, which correlate with the biological responses of human dental pulp stem cells (hDPSCs). Using a low-power light whose wavelength is 810 nm and energy density is 38 mJ/cm², we find that a 300-Hz pulse frequency prolonged the DL pattern and enhanced alkaline phosphatase activity. In addition, we analyze mitochondrial morphological changes and their volume density and find evidence supporting mitochondrial physiological changes from PBM treatment. Our data suggest a new methodology for determining the effectiveness of PBM and the specific pulse frequency dependency of PBM in the differentiation of hDPSCs.

Marine Streptomyces sp. derived antimycin analogues suppress HeLa cells via depletion HPV E6/E7 mediated by ROS-dependent ubiquitin-proteasome system

Four new antimycin alkaloids (1–4) and six related known analogs (5–10) were isolated from the culture of a marine derived Streptomyces sp. THS-55, and their structures were elucidated by extensive spectroscopic analysis. All of the compounds exhibited potent cytotoxicity in vitro against HPV-transformed HeLa cell line. Among them, compounds 6–7 were derived as natural products for the first time, and compound 5 (NADA) showed the highest potency. NADA inhibited the proliferation, arrested cell cycle distribution, and triggered apoptosis in HeLa cancer cells. Our molecular mechanic studies revealed NADA degraded the levels of E6/E7 oncoproteins through ROS-mediated ubiquitin-dependent proteasome system activation. This is the first report that demonstrates antimycin alkaloids analogue induces the degradation of high-risk HPV E6/E7 oncoproteins and finally induces apoptosis in cervical cancer cells. The present work suggested that these analogues could serve as lead compounds for the development of HPV-infected cervical cancer therapeutic agents, as well as research tools for the study of E6/E7 functions.

β-Cell deletion of Nr4a1 and Nr4a3 nuclear receptors impedes mitochondrial respiration and insulin secretion

β-Cell insulin secretion is dependent on proper mitochondrial function. Various studies have clearly shown that the Nr4a family of orphan nuclear receptors is essential for fuel utilization and mitochondrial function in liver, muscle, and adipose. Previously, we have demonstrated that overexpression of Nr4a1 or Nr4a3 is sufficient to induce proliferation of pancreatic β-cells. In this study, we examined whether Nr4a expression impacts pancreatic β-cell mitochondrial function. Here, we show that β-cell mitochondrial respiration is dependent on the nuclear receptors Nr4a1 and Nr4a3. Mitochondrial respiration in permeabilized cells was significantly decreased in β-cells lacking Nr4a1 or Nr4a3. Furthermore, respiration rates of intact cells deficient for Nr4a1 or Nr4a3 in the presence of 16 mM glucose resulted in decreased glucose mediated oxygen consumption. Consistent with this reduction in respiration, a significant decrease in glucose-stimulated insulin secretion rates is observed with deletion of Nr4a1 or Nr4a3. Interestingly, the changes in respiration and insulin secretion occur without a reduction in mitochondrial content, suggesting decreased mitochondrial function. We establish that knockdown of Nr4a1 and Nr4a3 results in decreased expression of the mitochondrial dehydrogenase subunits Idh3g and Sdhb. We demonstrate that loss of Nr4a1 and Nr4a3 impedes production of ATP and ultimately inhibits glucose-stimulated insulin secretion. These data demonstrate for the first time that the orphan nuclear receptors Nr4a1 and Nr4a3 are critical for β-cell mitochondrial function and insulin secretion.

Antimycin A induces death of the human pulmonary fibroblast cells via ROS increase and GSH depletion

Antimycin A (AMA) inhibits the growth of various cells via stimulating oxidative stress-mediated death. However, little is known about the anti-growth effect of AMA on normal primary lung cells. Here, we investigated the effects of AMA on cell growth inhibition and death in human pulmonary fibroblast (HPF) cells in relation to reactive oxygen species (ROS) and glutathione (GSH) levels. AMA inhibited the growth of HPF cells with an IC50 of ~150 µM at 24 h. AMA induced a G1 phase arrest of the cell cycle and it also triggered apoptosis accompanied by the loss of mitochondrial membrane potential (MMP; ∆Ψm). AMA increased ROS levels including O2᛫- in HPF cells from the early time point of 25 min. It induced GSH depletion in HPF cells in a dose-dependent manner. Z-VAD (a pan-caspase inhibitor) did not significantly prevent cell death and MMP (∆Ψm) loss induced by AMA. N-acetylcysteine (NAC; an antioxidant) attenuated cell growth inhibition, death and MMP (∆Ψm) loss in AMA-treated HPF cells and NAC generally decreased the ROS level in these cells as well. Vitamin C enhanced cell growth inhibition, death, GSH depletion and O2᛫- levels in 100 µM AMA-treated HPF cells whereas this agent strongly attenuated these effects in 200 µM AMA-treated cells. In conclusion, AMA inhibited the growth of HPF cells via apoptosis as well as a G1 phase arrest of the cell cycle. AMA-induced HPF cell death was related to increased ROS levels and GSH depletion.

Desacetyluvaricin induces S phase arrest in SW480 colorectal cancer cells through superoxide overproduction

Annonaceous acetogenins (ACGs) are a group of fatty acid-derivatives with potent anticancer effects. In the present study, we found desacetyluvaricin (Dau) exhibited notable in vitro antiproliferative effect on SW480 human colorectal carcinoma cells with IC50 value of 14 nM. The studies on the underlying mechanisms revealed that Dau inhibited the cancer cell growth through induction of S phase cell cycle arrest from 11.3% (control) to 33.2% (160 nM Dau), which was evidenced by the decreased protein expression of cyclin A Overproduction of superoxide, intracellular DNA damage, and inhibition of MEK/ERK signaling pathway, were also found involved in cells exposed to Dau. Moreover, pre-treatment of the cells with ascorbic acid significantly prevented the Dau-induced overproduction of superoxide, DNA damage and cell cycle arrest. Taken together, our results suggest that Dau induces S phase arrest in cancer cells by firstly superoxide overproduction and subsequently the involvement of various signaling pathways.

DNA damage and S phase arrest induced by Ochratoxin A in human embryonic kidney cells (HEK 293)

Ochratoxin A (OTA) is a ubiquitous mycotoxin with potential nephrotoxic, hepatotoxic and immunotoxic effects. The mechanisms underlying the nephrotoxicity of OTA remain obscure. To investigate DNA damage and the changes of the cell cycle distribution induced by OTA, human embryonic kidney cells (HEK 293 cells) were incubated with various concentrations of OTA for 24h in vitro. The results indicated that OTA treatment led to the production of reactive oxygen species (ROS) and to a decrease of the mitochondrial membrane potential (ΔΨm). OTA-induced DNA damage in HEK 293 cells was evidenced by DNA comet tails formation and increased expression of γ-H2AX. In addition, OTA could induce cell cycle arrest at the S phase in HEK 293 cells. The expression of key cell cycle regulatory factors that were critical to the S phase, including cyclin A2, cyclin E1, and CDK2, were further detected. The expression of cyclin A2, cyclin E1, and CDK2 were significantly decreased by OTA treatment at both the mRNA and protein levels. The apoptosis of HEK 293 cells after OTA treatment was observed using Hoechst 33342 staining. The results confirmed that OTA did induce apoptosis in HEK 293 cells. In conclusion, our results provided new insights into the molecular mechanisms by which OTA might promote nephrotoxicity.

Paeoniflorin isolated from Paeonia lactiflora attenuates osteoblast cytotoxicity induced by antimycin A

The protective effects of paeoniflorin isolated from Paeonia lactiflora against pharmacological inhibition of the respiratory chain were studied using osteoblastic MC3T3-E1 cells. Here we show that paeoniflorin decreases cell death induced by antimycin A, an inhibitor of mitochondrial complex III. Paeoniflorin restored antimycin A-induced inactivation of phosphoinositide 3-kinase (PI3K) and thioredoxin reductase, suggesting that PI3K and thioredoxin reductase may be involved in paeoniflorin-induced cytoprotective responses. We also examined the effect of paeoniflorin on mitochondrial dysfunction and oxidative stress induced by antimycin A. Paeoniflorin inhibited mitochondrial membrane potential dissipation, ATP loss, inactivation of complexes I and IV, cytochrome c release, and cardiolipin oxidation induced by antimycin A. In addition, paeoniflorin prevented antimycin A-induced ROS release and nitrotyrosine increase. These results imply that paeoniflorin protects osteoblasts from antimycin A-induced cell death via improved mitochondrial function.

MARCH5-mediated quality control on acetylated Mfn1 facilitates mitochondrial homeostasis and cell survival

Mitochondrial dynamics and quality control have a central role in the maintenance of cellular integrity. Mitochondrial ubiquitin ligase membrane-associated RING-CH (MARCH5) regulates mitochondrial dynamics. Here, we show that mitochondrial adaptation to stress is driven by MARCH5-dependent quality control on acetylated Mfn1. Under mitochondrial stress conditions, levels of Mfn1 were elevated twofold and depletion of Mfn1 sensitized these cells to apoptotic death. Interestingly, overexpression of Mfn1 also promoted cell death in these cells, indicating that a fine tuning of Mfn1 levels is necessary for cell survival. MARCH5 binds Mfn1 and the MARCH5-dependent Mfn1 ubiquitylation was significantly elevated under mitochondrial stress conditions along with an increase in acetylated Mfn1. The acetylation-deficient K491R mutant of Mfn1 showed weak interaction with MARCH5 as well as reduced ubiquitylation. Neither was observed in the acetylation mimetic K491Q mutant. In addition, MARCH5-knockout mouse embryonic fibroblast and MARCH5(H43W)-expressing HeLa cells lacking ubiquitin ligase activity experienced rapid cell death upon mitochondrial stress. Taken together, a fine balance of Mfn1 levels is maintained by MARCH5-mediated quality control on acetylated Mfn1, which is crucial for cell survival under mitochondria stress conditions.

Anti-apoptotic effect of caspase inhibitors on H₂O₂-treated HeLa cells through early suppression of its oxidative stress

Oxidative stress-induced cytotoxicity in cervical cancer cells may be of toxicological interest. In the present study, the effects of exogenous H2O2 on cell growth and death in HeLa cervical cancer cells were investigated, and the anti-apoptotic effects of various caspase (pan-caspase, caspase-3, -8 or -9) inhibitors on H2O2-treated HeLa cells were also evaluated with regard to reactive oxygen species (ROS) and glutathione (GSH) levels. Based on MTT assays, H2O2 inhibited the growth of HeLa cells with an IC50 value of ~75 µM at 24 h. H2O2 increased the number of dead cells and Annexin V-FITC-positive cells in the HeLa cells, which was accompanied by the activation of caspase-3 and the loss of mitochondrial membrane potential (MMP; ΔΨm). However, relatively higher doses of H2O2 induced necrosis in HeLa cells. Caspase inhibitors significantly prevented H2O2-induced HeLa cell death. H2O2 increased ROS including O2•- at 24 h and increased the activity of catalase in HeLa cells. H2O2 also increased the ROS level at 1 h, and several caspase inhibitors attenuated the increased level at 1 h but not at 6, 12 and 24 h. H2O2 decreased the GSH level in HeLa cells at 1 h, and several caspase inhibitors attenuated the decreased level of GSH at this time. H2O2 induced GSH depletion at 24 h. In conclusion, H2O2 inhibited the growth of HeLa cells via apoptosis and/or necrosis, which was accompanied by intracellular increases in ROS levels and GSH depletion. Caspase inhibitors are suggested to suppress H2O2-induced oxidative stress to rescue HeLa cells at the early time point of 1 h.

Oxidative stress promotes D-GalN/LPS-induced acute hepatotoxicity by increasing glycogen synthase kinase 3β activity

Objective

Our previous studies have demonstrated that glycogen synthase kinase 3β (GSK3β) activity is increased in the progression of acute liver failure (ALF), which aggravates liver injury, while its regulatory mechanism remains elusive. This study is designated to address whether oxidative stress activates GSK3β to promote ALF.

Methods

In a murine model induced by d-galactosamine (d-GalN) (700 mg/kg) and LPS (10 μg/kg), N-acetylcysteine (300 mg/kg) or SB216763 (25 mg/kg) was used to inhibit oxidative stress or GSK3β activity, respectively. Serum alanine aminotransferase and aspartate aminotransferase levels were assessed. The parameters of oxidative stress were evaluated in liver tissue. Whether GSK3β inhibition protects hepatocytes from oxidative stress-induced cell apoptosis was investigated in vitro. Moreover, the activity of GSK3β was measured in the liver of chronic hepatitis B (CHB) patients and ALF patients.

Results

In vivo, N-acetylcysteine ameliorated the d-GalN/LPS-induced hepatotoxicity and reduced GSK3β activity; GSK3β inhibition increased hepatic superoxide dismutase activity and the glutathione content, decreased malondialdehyde production in the liver tissues; while GSK3β inhibition suppressed the JNK activation in the liver and decreased cytochrome c release from mitochondria. In vitro, GSK3β inhibition lessened hepatocytes apoptosis induced by H₂O₂ or Antimycin A, as demonstrated by decreased LDH activity, and reduced cleavage of caspase-3 expression. Furthermore, GSK3β activity in the CHB patients was increased in the phase of ALF.

Conclusions

Results indicate that GSK3β activation contributes to liver injury by participating in oxidative stress response in ALF and is, therefore, a potential therapeutic target for ALF.

Inhibition of mitochondrial complex III blocks neuronal differentiation and maintains embryonic stem cell pluripotency

The mitochondrion is emerging as a key organelle in stem cell biology, acting as a regulator of stem cell pluripotency and differentiation. In this study we sought to understand the effect of mitochondrial complex III inhibition during neuronal differentiation of mouse embryonic stem cells. When exposed to antimycin A, a specific complex III inhibitor, embryonic stem cells failed to differentiate into dopaminergic neurons, maintaining high Oct4 levels even when subjected to a specific differentiation protocol. Mitochondrial inhibition affected distinct populations of cells present in culture, inducing cell loss in differentiated cells, but not inducing apoptosis in mouse embryonic stem cells. A reduction in overall proliferation rate was observed, corresponding to a slight arrest in S phase. Moreover, antimycin A treatment induced a consistent increase in HIF-1α protein levels. The present work demonstrates that mitochondrial metabolism is critical for neuronal differentiation and emphasizes that modulation of mitochondrial functions through pharmacological approaches can be useful in the context of controlling stem cell maintenance/differentiation.

Simvastatin enhances human osteoblast proliferation involved in mitochondrial energy generation

Simvastatin has been shown to stimulate osteogenic cell differentiation. Our previous study showed osteoblasts on trabecular surface are increased by simvastatin treatment in animal study. However, whether simvastatin stimulates osteoblast proliferation and by what molecular mechanism have not been adequately investigated. Because the mitochondrial function is crucial for cell survival and proliferation, we hypothesize that simvastatin may promote human osteoblast (hOBs) proliferation and it may be related to mitochondrial function. Our results showed that simvastatin significantly enhanced proliferation and increased both mRNA and protein levels of cyclin D2, Bcl-2 and the ratio of Bcl-2 to Bax (Bcl-2/Bax). Furthermore, simvastatin increased mitochondrial activity and ATP content of hOBs. Most importantly, treatment with ATP synthase blocker, oligomycin, significantly decreased both simvastatin-stimulated ATP content and cell proliferation, and completely reversed the simvastatin-induced up-regulation of cyclin D2 and Bcl-2 expression in hOBs. On the other hand, rotenone, the complex I blocker, also partially blocked simvastatin-stimulated ATP content and cell proliferation, but the blocker did not suppress the effect of simvastatin on cyclin D2 and Bcl-2 expression. These results indicate that the up-regulation of cyclin D2 and Bcl-2/Bax by simvastatin depends on the intact function of ATP synthase in the mitochondria of hOBs. It suggests that simvastatin may promote hOB proliferation, at least partly, via up-regulating mitochondrial function and subsequently cyclin D2 and Bcl-2/Bax expression. The findings provide new information for the basic medical science in bone physiology and for new therapy strategy of simvastatin on bone formation in future.

In vitro reactive oxygen species production by mitochondria from the rabbitfish Siganus fuscessens livers and the effects of Irgarol-1051

In this study, the mitochondria from the livers of Siganus fuscessens were exposed to the Irgarol-1051with or without respiratory chain inhibitors using succinate or malate as the substrate, and the effects on mitochondrial ROS production were tested. The mitochondrial ROS production was significantly enhanced by antimycin A with an increase of more than three folds but not by rotenone and NaN3, and this may suggest complex III is the major ROS-producing site. Irgarol-1051 treatments gave a somewhat contradictory result: this chemical can inhibit the mitochondrial ROS production but the inhibition decreased with the increase of doses. These contradictory data about Irgarol-1051 may be explained by the balance between the effects of inhibition through the opening of small-size pores and stimulation through blocking electron transfer, but the mechanism laid behind needs more evidence to support. As Irgarol-1051 was continuously used in antifouling and its bio-concentration factor is up to 160 in fish, the toxic effect of Irgarol-1051 on aquatic animals should be paid more attention to.

Scutellaria baicalensis Extracts and Flavonoids Protect Rat L6 Cells from Antimycin A-Induced Mitochondrial Dysfunction

Antimycin A (AMA) damages mitochondria by inhibiting mitochondrial electron transport and can produce reactive oxygen species (ROS). ROS formation, aging, and reduction of mitochondrial biogenesis contribute to mitochondrial dysfunction. The present study sought to investigate extracts of Scutellaria baicalensis and its flavonoids (baicalin, baicalein, and wogonin), whether they could protect mitochondria against oxidative damage. The viability of L6 cells treated with AMA increased in the presence of flavonoids and extracts of S. baicalensis. ATP production decreased in the AMA treated group, but increased by 50% in cells treated with flavonoids (except wogonin) and extracts of S. baicalensis compared to AMA-treated group. AMA treatment caused a significant reduction (depolarized) in mitochondrial membrane potential (MMP), whereas flavonoid treatment induced a significant increase in MMP. Mitochondrial superoxide levels increased in AMA treated cells, whereas its levels decreased when cells were treated with flavonoids or extracts of S. baicalensis. L6 cells treated with flavonoids and extracts of S. baicalensis increased their levels of protein expression compared with AMA-treated cells, especially water extracts performed the highest levels of protein expression. These results suggest that the S. baicalensis extracts and flavonoids protect against AMA-induced mitochondrial dysfunction by increasing ATP production, upregulating MMP, and enhancing mitochondrial function.

The anti-proliferative effects of a palm oil-derived product and its mode of actions in human malignant melanoma MeWo cells

Melanoma incidence and mortality have risen dramatically in recent years. No effective treatment for metastatic melanoma exists; hence currently, an intense effort for new drug evaluation is being carried out. In this study, we investigated the effects of a palm oil-derived nanopolymer called Bio-12 against human malignant melanoma. The nanopolymers of Bio-12 are lipid esters derived from a range of fatty acids of palm oil. Our study aims to identify the anti-proliferative properties of Bio-12 against human malignant melanoma cell line (MeWo) and to elucidate the mode of actions whereby Bio-12 brings about cell death. Bio-12 significantly inhibited the growth of MeWo cells in a concentration- and time- dependent manner with a median inhibitory concentration (IC₅₀) value of 1/25 dilution after 72 h but was ineffective on human normal skin fibroblasts (CCD-1059sk). We further investigated the mode of actions of Bio-12 on MeWo cells. Cell cycle flow cytometry demonstrated that MeWo cells treated with increasing concentrations of Bio-12 resulted in S-phase arrest, accompanied by the detection of sub-G1 content, indicative of apoptotic cell death. Induction of apoptosis was further confirmed via caspase (substrate) cleavage assay which showed induction of early apoptosis in MeWo cells. In addition, DNA strand breaks which are terminal event in apoptosis were evident through increase of TUNEL positive cells and formation of a characteristic DNA ladder on agarose gel electrophoresis. Moreover, treatment of MeWo cells with Bio-12 induced significant increase in lactate dehydrogenase (LDH) activity. These results show that Bio-12 possesses the ability to suppress proliferation of human malignant melanoma MeWo cells and this suppression is at least partly attributed to the initiation of the S-phase arrest, apoptosis and necrosis, suggesting that it is indeed worth for further investigations.

Anti-proliferative and apoptotic effects of the novel taspine derivative tas41 in the Caco-2 cell line

Taspine was screened and isolated for the first time from Radix et Rhizoma Leonticis. Tas41 is a novel taspine derivative. We investigated the effects of tas41 on proliferation of the Caco-2 cell line using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), a fluorescence-activated cell sorter (FACS), enzyme-linked immunosorbent assay (ELISA), reverse transcription-polymerase chain reaction (RT-PCR) and western blotting (WB). Changes in the cell cycle, apoptosis, activation of caspase-3, caspase-8 and caspase-9, and expressions of vascular endothelial growth factor (VEGF) and epidermal growth factor (EGF) were investigated after Caco-2 cells were treated with tas41. At the same time, expressions of apoptosis protein bcl-2 and bax were determined. Tas41 was found to induce apoptosis in a concentration-dependent manner as confirmed by DNA fragmentation analysis, TUNEL assay and flow cytometry. Protein and mRNA expressions of EGF, VEGF, CDK2, bcl-2 and bax were evaluated by ELISA, WB and RT-PCR. Tas41 had a better anti-proliferative effect than taspine on Caco-2 cells. A DNA ladder and apoptosis was observed, and the increased apoptotic activity by tas41 was accompanied by a decrease in the expression of VEGF protein and mRNA. The activities of caspase-3, caspase-8 and caspase-9 were significantly increased in cells treated with tas41 compared with those in the control group. In addition, protein and mRNA expressions of bcl-2 were decreased, and protein and mRNA expressions of bax were increased. These findings demonstrate that tas41 can inhibit the proliferation of, and induce apoptosis in, Caco-2 cells by activating caspase-3, caspase-8 and caspase-9, downregulating the expressions of VEGF, upregulating the ratio of bax/bcl-2.

Antioxidants protect keratinocytes against M. ulcerans mycolactone cytotoxicity

BACKGROUND

Mycobacterium ulcerans is the causative agent of necrotizing skin ulcerations in distinctive geographical areas. M. ulcerans produces a macrolide toxin, mycolactone, which has been identified as an important virulence factor in ulcer formation. Mycolactone is cytotoxic to fibroblasts and adipocytes in vitro and has modulating activity on immune cell functions. The effect of mycolactone on keratinocytes has not been reported previously and the mechanism of mycolactone toxicity is presently unknown. Many other macrolide substances have cytotoxic and immunosuppressive activities and mediate some of their effects via production of reactive oxygen species (ROS). We have studied the effect of mycolactone in vitro on human keratinocytes--key cells in wound healing--and tested the hypothesis that the cytotoxic effect of mycolactone is mediated by ROS.

METHODOLOGY/PRINCIPAL FINDINGS

The effect of mycolactone on primary skin keratinocyte growth and cell numbers was investigated in serum free growth medium in the presence of different antioxidants. A concentration and time dependent reduction in keratinocyte cell numbers was observed after exposure to mycolactone. Several different antioxidants inhibited this effect partly. The ROS inhibiting substance deferoxamine, which acts via chelation of Fe(2+), completely prevented mycolactone mediated cytotoxicity.

CONCLUSIONS/SIGNIFICANCE

This study demonstrates that mycolactone mediated cytotoxicity can be inhibited by deferoxamine, suggesting a role of iron and ROS in mycolactone induced cytotoxicity of keratinocytes. The data provide a basis for the understanding of Buruli ulcer pathology and the development of improved therapies for this disease.

Cucurbitacin B induces apoptosis and S phase cell cycle arrest in BEL-7402 human hepatocellular carcinoma cells and is effective via oral administration

Cucurbitacin B is an anti-cancer drug candidate and its efficacy has been demonstrated in hepatocellular carcinoma (HCC). To explore its mechanism against HCC, BEL-7402 cells were treated with cucurbitacin B in vitro. Treatment with cucurbitacin B induced S phase arrest and apoptosis. The growth inhibition effect was associated with cyclin D1 and cdc-2 down regulations. Western blotting analysis of cell signaling molecules indicated that cucurbitacin B inhibited c-Raf activation without affecting STAT3 phosphorylation. Moreover, in vivo study demonstrated that cucurbitacin B is effective against BEL-7402 xenograft when administrated orally.

Induction of apoptosis and cell cycle arrest in human HCC MHCC97H cells with Chrysanthemum indicum extract

AIM: To investigate the effects of Chrysanthemum indicum extract (CIE) on inhibition of proliferation and on apoptosis, and the underlying mechanisms, in a human hepatocellular carcinoma (HCC) MHCC97H cell line.

METHODS: Viable rat hepatocytes and human endothelial ECV304 cells were examined by trypan blue exclusion and MTT assay, respectively, as normal controls. The proliferation of MHCC97H cells was determined by MTT assay. The cellular morphology of MHCC97H cells was observed by phase contrast microscopy. Flow cytometry was performed to analyze cell apoptosis with annexin V/propidium iodide (PI), mitochondrial membrane potential with rhodamine 123 and cell cycle with PI in MHCC97H cells. Apoptotic proteins such as cytochrome C, caspase-9, caspase-3 and cell cycle proteins, including P21 and CDK4, were measured by Western blotting.

RESULTS: CIE inhibited proliferation of MHCC97H cells in a time- and dose-dependent manner without cytotoxicity in rat hepatocytes and human endothelial cells. CIE induced apoptosis of MHCC97H cells in a concentration-dependent manner, as determined by flow cytometry. The apoptosis was accompanied by a decrease in mitochondrial membrane potential, release of cytochrome C and activation of caspase-9 and caspase-3. CIE arrested the cell cycle in the S phase by increasing P21 and decreasing CDK4 protein expression.

CONCLUSION: CIE exerted a significant apoptotic effect through a mitochondrial pathway and arrested the cell cycle by regulation of cell cycle-related proteins in MHCC97H cells without an effect on normal cells. The cancer-specific selectivity shown in this study suggests that the plant extract could be a promising novel treatment for human cancer.

Astaxanthin protects mitochondrial redox state and functional integrity against oxidative stress

Mitochondria combine the production of energy with an efficient chain of reduction-oxidation (redox) reactions but also with the unavoidable production of reactive oxygen species. Oxidative stress leading to mitochondrial dysfunction is a critical factor in many diseases, such as cancer and neurodegenerative and lifestyle-related diseases. Effective antioxidants thus offer great therapeutic and preventive promise. Investigating the efficacy of antioxidants, we found that a carotenoid, astaxanthin (AX), decreased physiologically occurring oxidative stress and protected cultured cells against strong oxidative stress induced with a respiratory inhibitor. Moreover, AX improved maintenance of a high mitochondrial membrane potential and stimulated respiration. Investigating how AX stimulates and interacts with mitochondria, a redox-sensitive fluorescent protein (roGFP1) was stably expressed in the cytosol and mitochondrial matrix to measure the redox state in the respective compartments. AX at nanomolar concentrations was effective in maintaining mitochondria in a reduced state. Additionally, AX improved the ability of mitochondria to remain in a reduced state under oxidative challenge. Taken together, these results suggest that AX is effective in improving mitochondrial function through retaining mitochondria in the reduced state.