Mitochondrial Membrane Disruption Research Articles

Ellagic acid protects against arsenic toxicity in isolated rat mitochondria possibly through the maintaining of complex II.

Chronic arsenic exposure has been linked to many health problems including diabetes and cancer. In the present study, we assessed the protective effect of ellagic acid (EA) against toxicity induced by arsenic in isolated rat liver mitochondria. Reactive oxygen species (ROS) and mitochondrial membrane potential decline were assayed using dichlorofluorescein diacetate and rhodamine 123, respectively, and dehydrogenase activity obtained by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide conversion assay. Arsenic increased ROS levels and mitochondrial dysfunction, which led to a reduction in mitochondrial total dehydrogenase activity. Mitochondria pretreated with EA exposed to arsenic at various concentrations led to a reversal of ROS production and mitochondrial damage. Our results showed that mitochondria were significantly affected when exposed to arsenic, which resulted in excessive ROS production and mitochondrial membrane disruption. Pretreatment with EA, reduced ROS amounts, mitochondrial damage, and restored total dehydrogenase activity specifically associated with mitochondrial complex II. EA protective characteristics may be accomplished particularly throughout the mitochondrial maintenance either directly by its antioxidant property or indirectly through its maintaining of complex II. These findings also suggest a potential role for EA in treating or preventing mitochondria associated disorders.

Selective mechanism of action of dietary peptides from common bean on HCT116 human colorectal cancer cells through loss of mitochondrial membrane potential and DNA damage

The inhibitory effect of pure peptides from common bean on human colorectal cancer cells, their ability to enhance oxaliplatin effects, and mechanisms of action were evaluated. Peptides GLTSK, LSGNK, GEGSGA, MTEEY, and MPACGSS were tested for cytotoxic effects on HCT116 and CCD-33Co human normal colon cells; no peptide was toxic to normal cells. GLTSK (IC50 = 134.6 µM) and GEGSGA (IC50 = 156.7 µM) exerted anti-proliferative effects on HCT116 cells; LSGNK, MTEEY, and MPACGSS were less potent. GLTSK (γ = 0.64) and GEGSGA (γ = 0.78) interacted synergistically with oxaliplatin inhibiting HCT116 cells. GLTSK caused loss of mitochondrial potential (Δψm) (15.8%) and increased intracellular ROS (12.1-fold) suggesting mitochondrial membrane disruption. GEGSGA caused arrest in G1 phase (63.6% of cell population) and promoted cleavage of PARP (183.7%) suggesting DNA damage. GEGSGA and oxaliplatin caused activation and nuclear translocation of p53. Thus, peptides from common beans selectively induced apoptosis through loss of Δψm and DNA damage on human colorectal cancer cells.

Dermoscopy and Reflectance Confocal Microscopy for Monitoring the Treatment of Actinic Keratosis with Ingenol Mebutate Gel: Report of Two Cases.

IntroductionA relatively novel application for dermoscopy and reflectance confocal microscopy (RCM) is their use in the monitoring of topical treatment response for non-melanoma skin cancer. Actinic keratosis (AK) is the early phase of a multistep biologic continuum leading to invasive squamous cell carcinoma. A number of topical therapies are now available for the treatment of AK but their disadvantages include long treatment duration and prolonged local reactions. Ingenol mebutate is a newer therapy for AK which is only applied for 2 or 3 days.Case ReportDermoscopy and RCM findings in two patients with AK treated with ingenol mebutate confirm that it induces rapid lesion necrosis and specific neutrophil-mediated, antibody-dependent cellular cytotoxicity. Necrosis occurs via mitochondrial membrane disruption, with subsequent eradication of residual tumor cells via transient inflammation. Local skin reactions to ingenol mebutate should be considered part of the drug’s mechanism of action rather than an adverse effect.ConclusionIngenol mebutate is a valuable therapy for the treatment of AK. This case report adds further evidence to the usefulness of dermoscopy and RCM in the assessment and monitoring of treatment outcome.Electronic supplementary materialThe online version of this article (doi:10.1007/s13555-016-0094-9) contains supplementary material, which is available to authorized users.

Ethylene glycol potentiated didecyldimethylammonium chloride toxicity in human bronchial epithelial cells

Didecyldimethylammonium chloride (DDAC) is an antimicrobial agent used as a preservative in household products. DDAC is toxic in human lung cells and in mouse lung. Aerosol products that contain DDAC often include ethylene glycol (EG) as a solvent; no safety information is available for respiratory toxicity of this combination (DDAC and EG). Human bronchial epithelial cells (BEAS-2B) were exposed (24 h) to DDAC and EG, separately or together. DDAC showed concentration-dependent cytotoxicity. EG did not affect cell viability. Compared to DDAC alone, EG and DDAC together enhanced mitochondrial damage and cell membrane disruption. Increased reactive oxygen species and decreased glutathione levels were seen in cells treated with the combination. Intracellular DDAC concentrations were elevated in the presence of EG. EG potentiated DDAC toxicity in lung cells by inducing oxidative stress through enhanced cellular uptake of DDAC. The use of these chemicals together in spray-type products should be carefully considered.

Defining the Role of Arylsulfatase B (N‐Acetylgalactosamine 4‐Sulfatase) in Cellular Metabolism

Arylsulfatase B (ARSB; N‐acetylgalactosamine 4‐sulfatase) is the lysosomal and membrane enzyme that removes 4‐sulfate groups from the non‐reducing end of chondroitin 4‐sulfate and dermatan sulfate, and thereby regulates their degradation. Studies have demonstrated decline in ARSB in patients with cystic fibrosis and in malignant human mammary, prostate, and colonic epithelial tissues. Several molecules, including Interleukin‐8, high molecular weight kininogen, BMP4, and galectin‐3, bind preferentially to more or less sulfated C4S, affecting cell‐cell and cell‐extracellular matrix interactions. Previously, we reported that hypoxia reduced ARSB activity and that decline in ARSB replicated the effects of hypoxia on the expression of 84 genes in a hypoxia gene array. Both hypoxia and silencing ARSB decreased the ratios of reduced glutathione to GSSG and of cellular sulfhydryls to sulfides. Recent experiments in ARSB‐deficient mice and human epithelial cells following ARSB silencing have shown: increased serum lactate, increased 2,3‐DPG, increased extracellular acidfication, reduced oxygen consumption rate, reduced mitochondrial membrane potential, disruption of inner and outer mitochondrial membranes by electron microscopy, and increased NADPH to NADP and NADH to NAD ratios. These findings suggest profound effects of decline in ARSB on cellular metabolism and oxidation‐reduction reactions. Sulfate reduction is utilized in protists, plants, and algae for energy production. Impairment of sulfate reduction due to unavailability of sulfate due to ARSB deficiency may help to explain the occurrence of aerobic glycolysis in human cells.

Silibinin prevents dopaminergic neuronal loss in a mouse model of Parkinson's disease via mitochondrial stabilization.

Parkinson's disease (PD) is a progressive neurodegenerative disease characterized by the selective loss of dopaminergic neurons in the nigrostriatal pathway. The lipophile 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) can cross the blood-brain barrier and is subsequently metabolized into toxic1-methyl-4-phenylpyridine (MPP(+) ), which causes mitochondrial dysfunction and the selective cell death of dopaminergic neurons. The present article reports the neuroprotective effects of silibinin in a murine MPTP model of PD. The flavonoid silibinin is the major active constituent of silymarin, an extract of milk thistle seeds, and is known to have hepatoprotective, anticancer, antioxidative, and neuroprotective effects. In the present study, silibinin effectively attenuated motor deficit and dopaminergic neuronal loss caused by MPTP. Furthermore, in vitro study confirmed that silibinin protects primary cultured neurons against MPP(+) -induced cell death and mitochondrial membrane disruption. The findings of the present study indicate that silibinin has neuroprotective effects in MPTP-induced models of PD rather than antioxidative or anti-inflammatory effects and that the neuroprotection afforded might be mediated by the stabilization of mitochondrial membrane potential. Furthermore, these findings suggest that silibinin protects mitochondria in MPTP-induced PD models and that it offers a starting point for the development of treatments that ameliorate the symptoms of PD.

Mitochondrial membrane disruption by aggregation products of ALS-causing superoxide dismutase-1 mutants

More than 140 mutations in the SOD1 gene cause aggregation of the affected protein in familial forms of amyotrophic lateral sclerosis (fALS) which is a fatal progressive neurodegenerative disorder selectively affecting motor neurons. The causes of motor neuron death in ALS are poorly understood in general, but for fALS, aberrant oligomerization of SOD1 mutant proteins has been strongly concerned. Increasing evidences indicate that the interaction of amyloid aggregates with membranes is critical in the onset and progression of amyloid diseases. In spite of gathering reports describing mechanisms of membrane permeabilization by aggregates in model membranes, studies focused at characterizing the events occurring in biological membranes are exceptional. To gain insight into possible mechanisms of cytotoxicity at the membrane level, we describe interaction of the fibrillation products of the wild type (WT) and two mutants (E100K, D125H) of SOD1 obtained under destabilizing conditions with mitochondrial membranes. Release of mitochondrial enzymes, malate dehydrogenase (MDH) and adenylate kinase (AK), upon exposure to SOD1 aggregates demonstrates that these aggregates could affect membrane integrity. This effect correlates with the surface hydrophobicity of oligomers and their tendency toward amyloid formation, with the most toxic oligomers having high hydrophobicity and increased amount of amyloid formation.

Nanodelivery of Parthenolide Using Functionalized Nanographene Enhances its Anticancer Activity.

Advances in anticancer chemotherapy have been hindered by the lack of biocompatibility of new prospective drugs. One significant challenge concerns water insolubility, which compromises the bioavailability of the drugs leading to increased dosage and higher systemic toxicity. To overcome these problems, nanodelivery has been established as a promising approach for increasing the efficacy and lowering the required dosage of chemotherapeutics. The naturally derived compound, parthenolide (PTL), is known for its anti-inflammatory and anticancer activity, but its poor water solubility limits its clinical value. In the present study, we have used carboxyl-functionalized nanographene (fGn) delivery to overcome the extreme hydrophobicity of this drug. A water-soluble PTL analog, dimethylamino parthenolide (DMAPT), was also examined for comparison with the anticancer efficacy of our PTL-fGn complex. Delivery by fGn was found to increase the anticancer/apoptotic effects of PTL (but not DMAPT) when delivered to the human pancreatic cancer cell line, Panc-1. The IC50 value for PTL decreased from 39 µM to 9.5 µM when delivered as a mixture with fGn. The IC50 of DMAPT did not decrease when delivered as DMAPT-fGn and was significantly higher than that for PTL-fGn. There were significant increases in ROS formation and in mitochondrial membrane disruption in Panc-1 cells after PTL-fGn treatment as compared to PTL treatment, alone. Increases in toxicity were also seen with apoptosis detection assays using flow cytometry, ethidium bromide/acridine orange/DAPI staining, and TUNEL. Thus, fGn delivery was successfully used to overcome the poor water solubility of PTL, providing a strategy for improving the effectiveness of this anticancer agent.

Mitochondria: a pathogenic paradigm in hypertensive renal disease.

Mitochondria were first described in 1840 as bioblasts, elementary organisms responsible for vital cellular functions, but were subsequently named mitochondria, from the Greek names mitos (thread) and chondros (granule), which describes their appearance during spermatogenesis.1 Their discovery generated substantial interest given their structure resembling bacteria, which led in subsequent years to important scientific discoveries positioning mitochondria as the energy powerhouse of the cell. The unique architecture of mitochondria, consisting of 2 membranes (outer and inner) and compartments (intermembrane space and matrix), is crucial for their vital functions. Mitochondria serve not only as primary sources of cellular energy, but also modulate several cellular processes, including oxidative phosphorylation, calcium homeostasis, thermogenesis, oxygen sensing, proliferation, and apoptosis.2 Therefore, mitochondrial injury and dysfunction might be implicated in the pathogenesis of several diseases. Hypertension accounts for nearly 30% of patients reaching end-stage renal disease.3 Renal injury secondary to hypertension or to ischemia associated with renovascular hypertension (distal to renal artery stenosis) may have significant and detrimental effect on health outcomes. Studies have highlighted several deleterious pathways, including inflammation, oxidative stress, and fibrosis that are activated in the hypertensive kidney, eliciting functional decline.4,5 However, the precise molecular mechanisms responsible for renal injury have not been fully elucidated. Over the past few years, increasing evidence has established the experimental foundations linking mitochondrial alterations to hypertensive renal injury (Table). Mitochondriopathies, abnormalities of energy metabolism secondary to sporadic or inherited mutations in nuclear or mitochondrial DNA (mtDNA) genes, may contribute to the development and progression of hypertension and its complications. In addition, several studies have reported mitochondrial damage and dysfunction consequent to hypertensive renal disease. View this table: Table. Evidence of Renal Mitochondrial Damage in Models of Hypertension and Antihypertensive Treatment Importantly, hypertensive-induced renal injury is characterized by activation of several deleterious pathways, including oxidative stress, renin–angiotensin–aldosterone …

Silencing of JMJD2B induces cell apoptosis via mitochondria-mediated and death receptor-mediated pathway activation in colorectal cancer.

To investigate the molecular mechanism of colorectal cancer (CRC) cell apoptosis induced by the Jumonji domain containing 2B (JMJD2B) silencing. Both HCT116 and LoVo CRC cell lines were used for analyses. Cell apoptosis after JMJD2B silencing was determined by flow cytometry. JC-1 fluorescence probe was applied to measure the mitochondrial outer membrane permeabilization by flow cytometry and fluorescence microscopy. Immunofluorescence was used to detect cytochrome C translocation from mitochondria to cytosol after JMJD2B silencing. The efficacy of JMJD2B silencing on the protein levels of Bcl-2 family, caspase proteins, CCAAT/enhancer binding protein homologous protein (CHOP) and glucose-regulated protein 78 (GRP78) were detected by Western blot. JMJD2B silencing induced CRC cell apoptosis via a decrease of the anti-apoptotic gene Bcl-2 family expression, leading to the translocation of Bak and Bax proteins and the promotion of mitochondrial membrane disruption, resulting in the release of cytochrome C from mitochondria and subsequent caspase-9 and caspase-3 cleavage. It also increased the amount of cleaved caspase-8 involved in the death receptor-related apoptotic pathway. Bcl-2 homology 3 interacting-domain death agonist (Bid), a specific caspase-8 substrate involved in the Fas signaling pathway, subsequently induced cleavage via caspase-8 activation. However, levels of CHOP and GRP78 remained unchanged after JMJD2B silencing. JMJD2B silencing induced CRC cell apoptosis via both mitochondria-related and death receptor-related pathways. The cleavage of Bid activated by caspase-8 might serve as a crosstalk mediator between these two pathways in CRC.

Cytotoxicity mechanism of non-viral carriers polyethylenimine and poly-l-lysine using real time high-content cellular assay

Cationic polymers polyethylenimine (PEI) and poly-l-lysine (PLL) used as non-viral gene/drug delivery vehicles, showed high cytotoxicity but their molecular mechanisms of toxicity have been inadequately understood. Therefore, we tried to investigate the toxicity pathway triggered by these polymers through a high-content cellular imaging technique. The results revealed that PEI induced apoptosis via an intrinsic pathway, whereas PLL showed cytotoxicity through both intrinsic and extrinsic caspase cascade. Both PEI and PLL provide different apoptotic activities on HepG2 cells depending on their molecular weight. The degree of apoptosis of PEI also depends on its structure. The branched PEI showed higher cytotoxicity than linear PEI. This observation was verified through Annexin V-FITC/PI assay and real-time high-content monitoring of cytosolic calcium, mitochondrial membrane disruption, and caspase-3 activation methods. The study therefore provides important implications on the molecular mechanisms of PEI and PLL induced cytotoxicity.

SIRT1 Positively Regulates Autophagy and Mitochondria Function in Embryonic Stem Cells Under Oxidative Stress

SIRT1, an NAD-dependent deacetylase, plays a role in regulation of autophagy. SIRT1 increases mitochondrial function and reduces oxidative stress, and has been linked to age-related reactive oxygen species (ROS) generation, which is highly dependent on mitochondrial metabolism. H2O2 induces oxidative stress and autophagic cell death through interference with Beclin 1 and the mTOR signaling pathways. We evaluated connections between SIRT1 activity and induction of autophagy in murine (m) and human (h) embryonic stem cells (ESCs) upon ROS challenge. Exogenous H2 O2 (1 mM) induced apoptosis and autophagy in wild-type (WT) and Sirt1-/- mESCs. High concentrations of H2O2 (1 mM) induced more apoptosis in Sirt1-/-, than in WT mESCs. However, addition of 3-methyladenine, a widely used autophagy inhibitor, in combination with H2O2 induced more cell death in WT than in Sirt1-/- mESCs. Decreased induction of autophagy in Sirt1-/- mESCs was demonstrated by decreased conversion of LC3-I to LC3-II, lowered expression of Beclin-1, and decreased LC3 punctae and LysoTracker staining. H2O2 induced autophagy with loss of mitochondrial membrane potential and disruption of mitochondrial dynamics in Sirt1-/- mESCs. Increased phosphorylation of P70/85-S6 kinase and ribosomal S6 was noted in Sirt1-/- mESCs, suggesting that SIRT1 regulates the mTOR pathway. Consistent with effects in mESCs, inhibition of SIRT1 using Lentivirus-mediated SIRT1 shRNA in hESCs demonstrated that knockdown of SIRT1 decreased H2O2-induced autophagy. This suggests a role for SIRT1 in regulating autophagy and mitochondria function in ESCs upon oxidative stress, effects mediated at least in part by the class III PI3K/Beclin 1 and mTOR pathways.

Effects of lead on anatomy, ultrastructure and concentration of nutrients in plants Oxycaryum cubense (Poep. & Kunth) Palla: a species with phytoremediator potential in contaminated watersheds

Lead (Pb) has been highlighted as a major pollutant of both terrestrial and aquatic ecosystems, causing negative impacts to these environments. The concentration of Pb in plants has increased in recent decades, mainly due to anthropogenic activities. This study has as a hypothesis that the species Oxycaryum cubense (Poep. & Kunth) Palla, abundant in aquatic environments, has the potential to be used a phytoremediator. The plants were grown in a hydroponic system with Pb in increasing concentrations (0, 4, 8, 16 and 32 mg l(-1)) for 15 days. Inductively coupled mass spectrometer (ICP OES) was used to determine the concentration of mineral nutrients and lead. Optical and transmission electron microscopy were used for the analysis of cellular damage induced by lead in roots and leaves. Ultrastructural alterations were observed as disorganization of thylakoids in the chloroplast and disruption of mitochondrial membranes in cells of leaf tissues of plants subjected to increasing Pb concentrations. There was accumulation of Pb, especially in the root system, affecting the absorption and translocation of some mineral nutrients analysed. In roots, there was reduction in the thickness of the epidermis in plants treated with Pb. This species was shown to be tolerant to the Pb concentrations evaluated, compartmentalizing and accumulating Pb mainly in roots. Due to these results, it may be considered a species with phytoremediation capacity for Pb, with potential rizofiltration of this metallic element in contaminated watersheds.

The Role of Oxidative Stress in Metals Toxicity; Mitochondrial Dysfunction as a Key Player

Metals can cause oxidative stress by increasing the formation of reactive oxygen species (ROS), which make antioxidants incapable of defiance against growing amounts of free radicals. Metal toxicity is related to their oxidative state and reactivity with other compounds. However, several reports about metals have been published in the recent years. Mitochondria, as a site of cellular oxygen consumption and energy production, can be a target for metals toxicity. Dysfunction of Mitochondrial oxidative phosphorylation led to the production of some metals toxicities metals through alteration in the activities of I, II, III, IV and V complexes and disruption of mitochondrial membrane. Reductions of adenosine triphosphate (ATP) synthesis or induction of its hydrolysis can impair the cellular energy production. In the present review study, the researchers have criticized reviews and some evidence about the oxidative stress as a mechanism of toxicity of metals. The metals disrupt cellular and antioxidant defense, reactive oxygen species (ROS) generation, and promote oxidative damage. The oxidative injuries induced by metals can be restored by use of antioxidants such as chelators, vitamin E and C, herbal medicine, and through increasing the antioxidants level. However, to elucidate many aspect of mechanism toxicity of metals, further studies are yet to be carried out.

ROS-mediated JNK/p38-MAPK activation regulates Bax translocation in Sorafenib-induced apoptosis of EBV-transformed B cells

Sorafenib (SRF) is a multi-kinase inhibitor that has been shown to have antitumor activity against several types of cancers, but the effect of SRF on EBV-transformed B cells is unknown. We report that SRF can induce the apoptosis of EBV-transformed B cells through JNK/p38-MAPK activation. SRF triggered the generation of reactive oxygen species (ROS), translocation of Bax into the mitochondria, disruption of mitochondrial membrane potential, activation of caspase-9, caspase-3 and PARP, and subsequent apoptosis. Moreover, we found that SRF exposure activated the phosphorylation of JNK and p38-MAPK and suppressed the phosphorylation of PI3K-p85 and Akt. N-acetyl-l-cysteine (NAC) inhibited the activation of JNK and p38-MAPK. SP600125 and SB203580 blocked apoptosis and mitochondrial membrane disruption but did not affect ROS production after SRF treatment. These findings provide novel insights into the molecular mechanisms driving SRF-mediated cell death and suggest that SRF could be a potential therapeutic drug for the treatment of EBV-related malignant diseases.

Sensitivity Evaluation of Two Human Breast Cancer Cell Lines to Tamoxifen through Apoptosis Induction

Tamoxifen citrate (TAM) has been used to treat breast cancer in women for many years. The com-parative effects of TAM in inducing apoptosis were evaluated in estrogen receptor-positive (ER- positive MCF-7) and estrogen receptor-negative (ER-negative MDA-MB-231) human breast cancer cell lines in vitro in order to determine if these two cell lines differ in their sensitivity to TAM. Mi-tochondrial membrane permeability potential disruption was assessed in both cell lines by a lip-ophilic cationic dye (DePsipher assay, Trevigen, Inc.) utilizing fluorescence microscopy. Using this specific fluorochrome, we were able to associate mitochondrial membrane disruption to early, mid-, and late apoptotic cells. TAM induced cell death via apoptosis in both ER-positive and ER- negative cells, however, apoptosis induction was more pronounced in ER-positive MCF-7 compared to ER-negative MDA-MB-231 breast cancer cells. These findings may have some therapeutic use in the treatment of estrogen dependent and estrogen independent breast cancer.

Contribution of membrane progesterone receptor α to the induction of progesterone-mediated apoptosis associated with mitochondrial membrane disruption and caspase cascade activation in Jurkat cell lines

In the present study, we investigated the effects of progesterone (Pg) on the growth of A3 and its caspase-8-deficient mutant cell line, I9.2, both of which are subclones of a T-cell-derived leukemic Jurkat cell line that lacks the classic cytoplasmic/nuclear Pg receptor. Pg inhibited the cell growth of both cell lines in a dose- and time-dependent manner to a similar extent, regardless of the status of caspase-8 expression. The activation of caspase-9 and -3 was observed in both cell lines following treatment with 50 µM Pg for 24 h. In addition, the activation of caspase-8 was observed in A3 cells. The addition of the pan-caspase inhibitor Boc-D-FMK, significantly suppressed Pg-triggered cytocidal effects in both types of cells. Moreover, exposure to 50 µM Pg for 48 and 72 h resulted in lactate dehydrogenase leakage characteristic of the disruption of cellular membrane integrity. The function of membrane progesterone receptor α coupled directly with the Gi protein was revealed based on the restoration of Pg-triggered loss of mitochondrial membrane potential in the presence of pertussis toxin, an inhibitor specific for Gi protein. These results suggest that growth suppression accompanied with induction of apoptosis by Pg in both Jurkat clone cells was mediated through mitochondrial membrane disruption followed by the activation of the caspase cascade, as a result of the activation of non-genomic effects. The results of the present study provide novel insight into Pg actions toward its use for clinical application in patients with lymphocytic T cell leukemia.

6-C-Methyl Flavonoids Isolated from Pinus densata Inhibit the Proliferation and Promote the Apoptosis of the HL-60 Human Promyelocytic Leukaemia Cell Line

Three structurally related 6-C-methyl flavonoids isolated from Pinus densata, including 5,4'-dihydroxy-3,7,8-trimethoxy-6-C-methylflavone (PD1), 5,7,4'-trihydroxy-3,8-dimethoxy-6-C-methylflavone (PD2), and 5,7,4'-trihydroxy-3-methoxy-6-C-methylflavone (PD3), were tested for their ability to inhibit the proliferation and promote the apoptosis of the HL-60 human leukaemia cell line. Cytotoxicity assays in the HL-60 human cancer cell line demonstrated that 5,4'-dihydroxy-3,7,8-trimethoxy-6-C-methylflavone exhibited the most potent cytotoxicity of the three structurally related 6-C-methyl flavonoids. 5,4'-Dihydroxy-3,7,8-trimethoxy-6-C-methylflavone inhibited the proliferation of HL-60 cells in a dose-dependent manner with an IC₅₀ of 7.91 µM (48 h treatment). Furthermore, 5,4'-dihydroxy-3,7,8-trimethoxy-6-C-methylflavone-induced apoptosis was associated with mitochondrial membrane disruption and cytochome c release. Flow cytometry analyses revealed an increase in the hypodiploid population in 5,4'-dihydroxy-3,7,8-trimethoxy-6-C-methylflavone-treated HL-60 cells. Treatment with a concentration of 5,4'-dihydroxy-3,7,8-trimethoxy-6-C-methylflavone that induced apoptosis activated caspase-3 but did not activate caspase-1. A caspase-3 inhibitor (Ac-DEVD-CHO), but not a caspase-1 inhibitor (Ac-YVAD-CHO), reversed the cytotoxic effects of 5,4'-dihydroxy-3,7,8-trimethoxy-6-C-methylflavone in HL-60 cells. These data demonstrated that 5,4'-dihydroxy-3,7,8-trimethoxy-6-C-methylflavone effectively induced the apoptosis of HL-60 cells and exhibited significant anticancer activity via the mitochondrial caspase-3-dependent apoptosis pathway.

GRP78-targeting subtilase cytotoxin sensitizes cancer cells to photodynamic therapy

Glucose-regulated protein 78 (GRP78) is an endoplasmic reticulum (ER)-resident chaperone and a major regulator of the unfolded protein response (UPR). Accumulating evidence indicate that GRP78 is overexpressed in many cancer cell lines, and contributes to the invasion and metastasis in many human tumors. Besides, GRP78 upregulation is detected in response to different ER stress-inducing anticancer therapies, including photodynamic therapy (PDT). This study demonstrates that GRP78 mRNA and protein levels are elevated in response to PDT in various cancer cell lines. Stable overexpression of GRP78 confers resistance to PDT substantiating its cytoprotective role. Moreover, GRP78-targeting subtilase cytotoxin catalytic subunit fused with epidermal growth factor (EGF-SubA) sensitizes various cancer cells to Photofrin-mediated PDT. The combination treatment is cytotoxic to apoptosis-competent SW-900 lung cancer cells, as well as to Bax-deficient and apoptosis-resistant DU-145 prostate cancer cells. In these cells, PDT and EGF-SubA cytotoxin induce protein kinase R-like ER kinase and inositol-requiring enzyme 1 branches of UPR and also increase the level of C/EBP (CCAAT/enhancer-binding protein) homologous protein, an ER stress-associated apoptosis-promoting transcription factor. Although some apoptotic events such as disruption of mitochondrial membrane and caspase activation are detected after PDT, there is no phosphatidylserine plasma membrane externalization or DNA fragmentation, suggesting that in DU-145 cells the late apoptotic events are missing. Moreover, in SW-900 cells, EGF-SubA cytotoxin potentiates PDT-mediated cell death but attenuates PDT-induced apoptosis. In addition, the cell death cannot be reversed by caspase inhibitor z-VAD, confirming that apoptosis is not a major cell death mode triggered by the combination therapy. Moreover, no typical features of necrotic or autophagic cell death are recognized. Instead, an extensive cellular vacuolation of ER origin is observed. Altogether, these findings indicate that PDT and GRP78-targeting cytotoxin treatment can efficiently kill cancer cells independent on their apoptotic competence and triggers an atypical, non-apoptotic cell death.

α-Synuclein Oligomers with Broken Helical Conformation Form Lipoprotein Nanoparticles

α-Synuclein (αS) is a membrane-binding protein with sequence similarity to apolipoproteins and other lipid-carrying proteins, which are capable of forming lipid-containing nanoparticles, sometimes referred to as "discs." Previously, it has been unclear whether αS also possesses this property. Using cryo-electron microscopy and light scattering, we found that αS can remodel phosphatidylglycerol vesicles into nanoparticles whose shape (ellipsoidal) and dimensions (in the 7-10-nm range) resemble those formed by apolipoproteins. The molar ratio of αS to lipid in nanoparticles is ∼1:20, and αS is oligomeric (including trimers and tetramers). Similar nanoparticles form when αS is added to vesicles of mitochondrial lipids. This observation suggests a mechanism for the previously reported disruption of mitochondrial membranes by αS. Circular dichroism and four-pulse double electron electron resonance experiments revealed that in nanoparticles αS assumes a broken helical conformation distinct from the extended helical conformation adopted when αS is bound to intact vesicles or membrane tubules. We also observed αS-dependent tubule and nanoparticle formation in the presence of oleic acid, implying that αS can interact with fatty acids and lipids in a similar manner. αS-related nanoparticles might play a role in lipid and fatty acid transport functions previously attributed to this protein.