Contributions of autophagic and apoptotic mechanisms to CrTX-induced death of K562 cells

PLA2-MjTX-II from Bothrops moojeni snake venom exhibits antimetastatic and antiangiogenic effects on human lung cancer cells

Phospholipases A2 (PLA2s) from snake venom possess antitumor and antiangiogenic properties. In this study, we evaluated the antimetastatic and antiangiogenic effects of MjTX-II, a Lys49 PLA2 isolated from Bothrops moojeni venom, on lung cancer and endothelial cells. Using in vitro and ex vivo approaches, we demonstrated that MjTX-II reduced cell proliferation and inhibited fundamental processes for lung cancer cells (A549) growth and metastasis, such as adhesion, migration, invasion, and actin cytoskeleton decrease, without significantly interfering with non-tumorigenic lung cells (BEAS-2B). Furthermore, MjTX-II caused cell cycle alterations, increased reactive oxygen species production, modulated the expression of pro- and antiangiogenic genes, and decreased vascular endothelial growth factor (VEGF) expression in HUVECs. Finally, MjTX-II inhibited ex vivo angiogenesis processes in an aortic ring model. Therefore, we conclude that MjTX-II exhibits antimetastatic and antiangiogenic effects in vitro and ex vivo and represents a molecule that hold promise as a pharmacological model for antitumor therapy.

Role of Bioactive Compounds in the Regulation of Mitochondrial Dysfunctions in Brain and Age-Related Neurodegenerative Diseases

Mitochondria are multifunctional organelles that participate in a wide range of metabolic processes, including energy production and biomolecule synthesis. The morphology and distribution of intracellular mitochondria change dynamically, reflecting a cell’s metabolic activity. Oxidative stress is defined as a mismatch between the body’s ability to neutralise and eliminate reactive oxygen and nitrogen species (ROS and RNS). A determination of mitochondria failure in increasing oxidative stress, as well as its implications in neurodegenerative illnesses and apoptosis, is a significant developmental process of focus in this review. The neuroprotective effects of bioactive compounds linked to neuronal regulation, as well as related neuronal development abnormalities, will be investigated. In conclusion, the study of secondary components and the use of mitochondrial features in the analysis of various neurodevelopmental diseases has enabled the development of a new class of mitochondrial-targeted pharmaceuticals capable of alleviating neurodegenerative disease states and enabling longevity and healthy ageing for the vast majority of people.

South American snake venoms with abundant neurotoxic components. Composition and toxicological properties. A literature review

In South America there are three snake genera with predominantly neurotoxic venoms: Crotalus, Micrurus and Hydrophis, which include nine species/subspecies, 97 species and a single marine species, respectively. Although accidents with neurotoxic venoms are less frequent than those with anticoagulant, cytotoxic or necrotic venoms (e.g. from Bothrops), they are of major public health importance. Venoms from genus Crotalus have been extensively studied, while data on the venoms from the other two genera are very limited, especially for Hydrophis. The venoms of North and South American Crotalus species show biochemical and physiopathological differences. The former species cause bothrops-like envenomation symptoms, while the latter mainly have neurotoxic and myotoxic effects, leading to respiratory paralysis and, occasionally, renal failure by myoglobinuria and death, often with no local lesions. Micrurus and Hydrophis also cause neurotoxic envenomations. Many studies have isolated, identified and characterized new enzymes and toxins, thus expanding the knowledge of snake venom composition. The present review summarizes the currently available information on neurotoxic venoms from South American snakes, with a focus on protein composition and toxicological properties. It also includes some comments concerning potential medical applications of elapid and crotalic toxins.

Novel Approaches of Dysregulating Lysosome Functions in Cancer Cells by Specific Drugs and Its Nanoformulations: A Smart Approach of Modern Therapeutics

The smart strategy of cancer cells to bypass the caspase-dependent apoptotic pathway has led to the discovery of novel anti-cancer approaches including the targeting of lysosomes. Recent discoveries observed that lysosomes perform far beyond just recycling of cellular waste, as these organelles are metabolically very active and mediate several signalling pathways to sense the cellular metabolic status. These organelles also play a significant role in mediating the immune system functions. Thus, direct or indirect lysosome-targeting with different drugs can be considered a novel therapeutic approach in different disease including cancer. Recently, some anticancer lysosomotropic drugs (eg, nortriptyline, siramesine, desipramine) and their nanoformulations have been engineered to specifically accumulate within these organelles. These drugs can enhance lysosome membrane permeabilization (LMP) or disrupt the activity of resident enzymes and protein complexes, like v-ATPase and mTORC1. Other anticancer drugs like doxorubicin, quinacrine, chloroquine and DQ661 have also been used which act through multi-target points. In addition, autophagy inhibitors, ferroptosis inducers and fluorescent probes have also been used as novel theranostic agents. Several lysosome-specific drug nanoformulations like mixed charge and peptide conjugated gold nanoparticles (AuNPs), Au-ZnO hybrid NPs, TPP-PEG-biotin NPs, octadecyl-rhodamine-B and cationic liposomes, etc. have been synthesized by diverse methods. These nanoformulations can target cathepsins, glucose-regulated protein 78, or other lysosome specific proteins in different cancers. The specific targeting of cancer cell lysosomes with drug nanoformulations is quite recent and faces tremendous challenges like toxicity concerns to normal tissues, which may be resolved in future research. The anticancer applications of these nanoformulations have led them up to various stages of clinical trials. Here in this review article, we present the recent updates about the lysosome ultrastructure, its cross-talk with other organelles, and the novel strategies of targeting this organelle in tumor cells as a recent innovative approach of cancer management.

The anti-cancer potential of crotoxin in estrogen receptor-positive breast cancer: Its effects and mechanism of action

Estrogen receptor-positive (ER⁺) breast cancer is the most diagnosed subtype of breast cancer. Currently, aromatase inhibitors (AIs) are used as first-line treatment option in this type of tumors, however they cause several side effects, which is why new therapeutic approaches are demanding. The South American rattlesnake Crotalus durissus terrificus produces a venom enriched in several bioactive substances, like phospholipases A₂ (PLA₂). One of those is crotoxin, a β-neurotoxin, that has already been reported for its anti-cancer properties in different cancers. Recently, its clinical interest has emerged and, in fact, a clinical trial in patients with advanced cancer is underway. Considering this, in this work, we studied the biological mechanisms behind the anti-cancer effects of crotoxin B (CTX) in an ER⁺ aromatase-overexpressing breast cancer cell line (MCF-7aro cells). Results revealed that CTX impairs MCF-7aro cells growth, through a cell cycle arrest at G₂/M phase, inhibition of ERK1/2 pathway and by apoptosis through activation of caspase-8. In addition, it can be considered a safe natural compound as did not affect non-cancerous cells and only showed anti-growth effects in breast cancer cells. Therefore, this study represents an important landmark to better understand the effects and mechanisms of action of crotoxin in ER⁺ breast cancer.

Biomedical applications of snake venom: from basic science to autoimmunity and rheumatology

Snake venoms have components with diverse biological actions that are extensively studied to identify elements that may be useful in biomedical sciences. In the field of autoimmunity and rheumatology, various findings useful for the study of diseases and potential drug development have been reported. The study of disintegrins, proteins that block the action of integrins, has been useful for the development of antiplatelet agents and principles for the development of immunosuppressants and antineoplastics. Several proteins in snake venoms act on the coagulation cascade, activating factors that have allowed the development of tests for the study of coagulation, including Russell's viper venom time, which is useful in the diagnosis of antiphospholipid syndrome. Neurotoxins with either pre- or postsynaptic effects have been used to study neurogenic synapses and neuromuscular plaques and the development of analgesics, muscle relaxants and drugs for neurodegenerative diseases. Various components act by inhibiting cells and proteins of the immune system, which will allow the development of anti-inflammatory and immunosuppressive drugs. This review summarizes the usefulness of the components of snake venoms in the fields of autoimmunity and rheumatology, which can serve as a basis for diverse translational research.

EGCG exerts its protective effect by mitigating the release of lysosomal enzymes in aged rat liver on exposure to high cholesterol diet

The aim is to test the hypothesis whether the cholesterol loaded lysosomes are capable of mediating lysosomal membrane permeabilization (LMP) during aging and to study the efficacy of epigallocatechin-3-gallate (EGCG) in preserving the lysosomal membrane stability. Aged rats were fed with high cholesterol diet (HCD) and treated with EGCG orally. Serum and tissue lipid status, cholesterol levels in lysosomal fraction, activities of lysosomal enzymes in lysosomal, and cytosolic fractions were measured. Transmission electron microscopic studies (TEM), oil red "O" (ORO) staining, and immunohistochemical analysis of oxidized low density lipoprotein (OxLDL) were carried out. Significant increase in serum, tissue lipid profile, and lysosomal cholesterol levels were observed in aged HCD-fed rats with a concomitant decrease in high density lipoprotein (HDL) levels. We also observed a significant increase in lipid accumulation in hepatocytes of aged HCD-fed rats by TEM, ORO, and immunohistochemical staining. Upon treatment with EGCG to aged HCD-fed animals, we found augmented levels of HDL with a concomitant decrease in lysosomal cholesterol levels and other lipoproteins. TEM studies and immunohistochemistry of OxLDL also showed a marked reduction in lipid deposition of hepatocytes. Thus, EGCG has preserved the lysosomal membrane stability in HCD stressed aged rats. SIGNIFICANCE OF THE STUDY: The research article is focused mainly on the effect of EGCG and its capability on mitigating the release of lysosomal enzymes in aged animals fed with HCD. The study signifies the cellular function of the organelle lysosome following administration of aged rats with HCD, which would make the readers to understand the action of EGCG and the interrelationship of both cholesterol and activity of lysosomes when cholesterol is loaded.

Autophagy Induced by Oxygen-Glucose Deprivation Mediates the Injury to the Neurovascular Unit

BACKGROUND Autophagy is characterized by the degradation of cellular components in autophagosomes. It plays a significant role in cerebral ischemic injury and has a complex functional connection with apoptosis. The neurovascular unit (NVU) is a structural and functional unit of the nervous system presented as a therapeutic target of stroke. This study aimed to investigate the effect of autophagy induced by ischemic damage on NVUs. MATERIAL AND METHODS SH-SY5Y cells, C6 cells, and rat brain microvascular endothelial cells were cultured with oxygen-glucose deprivation (OGD) exposure for different time durations, and 3-methyladenine (3-MA) was added as an autophagy inhibitor. In all 3 cell lines, lactate dehydrogenase (LDH) release was measured. Furthermore, apoptosis was detected using Annexin V-fluorescein isothiocyanate/propidium iodide labeling and immunofluorescence staining. Autophagosomes were observed through AO/MDC (acridine orange/monodansycadaverine) double staining. LC3-II expression levels were evaluated by western blot analysis. RESULTS In the OGD groups of 3 cell lines, LDH leakage, and apoptotic rates were obviously increased. Remarkable increase in LC3-II expression was found in the OGD groups of SH-SY5Y cells and C6 cells. However, 3-MA decreased the LC3-II expression to varying degrees. CONCLUSIONS OGD could induce the over-activation of autophagy and augment the apoptotic activity in neurons and glial cells of NVUs.

L-amino acid oxidase from Bothrops atrox snake venom triggers autophagy, apoptosis and necrosis in normal human keratinocytes

Snake venom L-amino acid oxidases (LAAOs) are flavoproteins, which perform diverse biological activities in the victim such as edema, myotoxicity and cytotoxicity, contributing to the development of clinical symptoms of envenomation. LAAO cytotoxicity has been described, but the temporal cascade of events leading to cell death has not been explored so far. This study evaluates the involvement of LAAO in dermonecrosis in mice and its cytotoxic effects in normal human keratinocytes, the major cell type in the epidermis, a tissue that undergoes extensive necrosis at the snakebite site. Pharmacological inhibition by the antioxidant NAC (N-acetyl cysteine) prevented B. atrox venom-induced necrosis. Consistent with the potential role of oxidative stress in wounding, treatment with purified LAAO decreased keratinocyte viability with an Effective Concentration (EC₅₀) of 5.1 μg/mL. Cytotoxicity caused by LAAO was mediated by H₂O₂ and treated cells underwent autophagy, followed by apoptosis and necrosis. LAAO induced morphological alterations that precede cell death. Our results show the chronological events leading to cell death and the temporal resolution from autophagy, apoptosis and necrosis as distinct mechanisms triggered by LAAO. Fluorescently-labelled LAAO was efficiently and rapidly internalized by keratinocytes, suggesting that catalysis of intracellular substrates may contribute to LAAO toxicity. A better understanding of LAAO cytotoxicity and its mechanism of action will help to identify potential therapeutic strategies to ameliorate localized snake envenomation symptoms.

Lysosomal cell death mechanisms in aging

Lysosomes are degradative organelles essential for cell homeostasis that regulate a variety of processes, from calcium signaling and nutrient responses to autophagic degradation of intracellular components. Lysosomal cell death is mediated by the lethal effects of cathepsins, which are released into the cytoplasm following lysosomal damage. This process of lysosomal membrane permeabilization and cathepsin release is observed in several physiopathological conditions and plays a role in tissue remodeling, the immune response to intracellular pathogens and neurodegenerative diseases. Many evidences indicate that aging strongly influences lysosomal activity by altering the physical and chemical properties of these organelles, rendering them more sensitive to stress. In this review we focus on how aging alters lysosomal function and increases cell sensitivity to lysosomal membrane permeabilization and lysosomal cell death, both in physiological conditions and age-related pathologies.

Isolation, characterization and screening of the in vitro cytotoxic activity of a novel L-amino acid oxidase (LAAOcdt) from Crotalus durissus terrificus venom on human cancer cell lines

An L-amino acid oxidase (LAAOcdt) from Crotalus durissus terrificus venom was purified to homogeneity in a two-step procedure using molecular exclusion on Sephadex G-75, followed by Phenyl Sepharose FF chromatography. The molecular mass of the purified enzyme was 113 kDa, as determined by SDS-PAGE under reducing conditions. LAAOcdt showed amino acid homology to other L-amino acid oxidases isolated from different snake venoms. The comparative analysis of the internal peptide sequences of the NNPGILEYPVKPSEEGK fragments by LC-MS/MS spectrometry revealed 100% identity with C. durissus cumanensis LAAO. The purified protein catalyzed the oxidative deamination of L-amino acids, and the most specific substrates were L-Tyr and L-Phe. The enzyme presented optimum activity at pH 7.4 and at 44 °C. LAAOcdt also showed hemolytic activity (0.6-20 μg/μL) and induced both the formation plasma clots (5-100 μg/μL) and platelet aggregation (2.5 × 10(-3), 5.0 × 10(-3) and 10 × 10(-3) μg/mL), as well as bactericidal activity (2.5-10 μg/μL) against Staphylococcus aureus. Moreover, LAAOcdt exhibited cytotoxicity in distinct cancer cell lines, which presented a heterogeneous response profile. The mean IC50 value was 10.5 μg/mL. Glioma and pancreatic carcinoma cells were the most sensitive cell lines; they showed mean IC50 values of 7.2 μg/mL and 7.4 μg/mL, respectively. The exposure of the drug-sensitive cells to LAAOcdt for 24 h upregulated activated p-H2AX and efficiently decreased P42/P44 (ERK) activation in glioma cells (HCB151), which suggested an anti-proliferative effect. In addition, increased p21 expression was observed in SiHa cells, which showed a resistant phenotype. On the other hand, the flow cytometry and immunoblotting analyses showed that the enzyme did not induce cancer cell apoptosis. These results suggest that another cell death mechanism might contribute to the LAAOcdt-induced cytotoxicity. Taken together, this work may help to elucidate the function and structure of LAAOcdt by providing the basis for further investigations on its efficacy in cancer treatment.

Elaborating the role of natural products-induced autophagy in cancer treatment: achievements and artifacts in the state of the art

Autophagy is a homeostatic process that is highly conserved across different types of mammalian cells. Autophagy is able to relieve tumor cell from nutrient and oxidative stress during the rapid expansion of cancer. Excessive and sustained autophagy may lead to cell death and tumor shrinkage. It was shown in literature that many anticancer natural compounds and extracts could initiate autophagy in tumor cells. As summarized in this review, the tumor suppressive action of natural products-induced autophagy may lead to cell senescence, provoke apoptosis-independent cell death, and complement apoptotic cell death by robust or target-specific mechanisms. In some cases, natural products-induced autophagy could protect tumor cells from apoptotic death. Technical variations in detecting autophagy affect data quality, and study focus should be made on elaborating the role of autophagy in deciding cell fate. In vivo study monitoring of autophagy in cancer treatment is expected to be the future direction. The clinical-relevant action of autophagy-inducing natural products should be highlighted in future study. As natural products are an important resource in discovery of lead compound of anticancer drug, study on the role of autophagy in tumor suppressive effect of natural products continues to be necessary and emerging.

Hibiscus sabdariffa leaf polyphenolic extract induces human melanoma cell death, apoptosis, and autophagy

Melanoma is the least common but most fatal form of skin cancer. Previous studies have indicated that an aqueous extract of Hibiscus sabdariffa leaves possess hypoglycemic, hypolipidemic, and antioxidant effects. In this study, we want to investigate the anticancer activity of Hibiscus leaf polyphenolic (HLP) extract in melanoma cells. First, HLP was exhibited to be rich in epicatechin gallate (ECG) and other polyphenols. Apoptotic and autophagic activities of HLP and ECG were further evaluated by DAPI stain, cell-cycle analysis, and acidic vascular organelle (AVO) stain. Our results revealed that both HLP and ECG induced the caspases cleavages, Bcl-2 family proteins regulation, and Fas/FasL activation in A375 cells. In addition, we also revealed that the cells presented AVO-positive after HLP treatments. HLP could increase the expressions of autophagy-related proteins autophagy-related gene 5 (ATG5), Beclin1, and light chain 3-II (LC3-II), and induce autophagic cell death in A375 cells. These data indicated that the anticancer effect of HLP, partly contributed by ECG, in A375 cells. HLP potentially could be developed as an antimelanoma agent.

Crotoxin induces apoptosis and autophagy in human lung carcinoma cells in vitro via activation of the p38MAPK signaling pathway

AIM

Crotoxin (CrTX) is the primary toxin in South American rattlesnake (Crotalus durissus terrificus) venom, and exhibits antitumor and other pharmacological actions in vivo and in vitro. Here, we investigated the molecular mechanisms of the antitumor action of CrTX in human lung carcinoma cells in vitro.

METHODS

Human lung squamous carcinoma SK-MES-1 cells were tested. The cytotoxicity of CrTX was evaluated in both MTT and colony formation assays. Cell cycle was investigated with flow cytometry. Cell apoptosis was studied with Hoechst 33258 and Annexin V-FITC staining. The levels of relevant proteins were analyzed using Western blot assays.

RESULTS

CrTX (25, 50, 100 μmol/L) inhibited the growth and colony formation of SK-MES-1 cells in dose- and time-dependent manners. CrTX increased the proportion of S phase cells and dose-dependently induced cell apoptosis, accompanied by down-regulating the expression of proliferating cell nuclear antigen (PCNA), and increasing the level of cleaved caspase-3. Furthermore, CrTX dose-dependently increased the expression of autophagy-related proteins LC3-II and beclin 1, and decreased the level of p62 in the cells. Moreover, CrTX (50 μmol/L) significantly increased p38MAPK phosphorylation in the cells. Pretreatment of the cells with SB203580, a specific inhibitor of p38MAPK, blocked the inhibition of CrTX on cell proliferation, as well as CrTX-induced apoptosis and cleaved caspase-3 expression.

CONCLUSION

The p38MAPK signaling pathway mediates CrTX-induced apoptosis and autophagy of human lung carcinoma SK-MES-1 cells in vitro.

AMP-activated protein kinase is involved in induction of protective autophagy in astrocytes exposed to oxygen-glucose deprivation

AMP-activated kinase (AMPK) acts as the intracellular ATP depletion sensor, which detects and limits increases in the AMP/ATP ratio. AMPK may be significantly activated under stress conditions that deplete cellular ATP levels such as ischemia/hypoxia or glucose deprivation. Recent studies strongly suggest that AMPK participates in autophagy regulation, but it is not known whether AMPK activated by ischemia regulates autophagy in astrocytes and the consequence of autophagy activation in ischemic astrocytes are unclear. We have investigated the contribution of AMPK to autophagy activation in rat primary astrocyte cultures subjected to ischemia-simulating conditions (combined oxygen glucose deprivation, OGD) and its potential effects on astrocyte damage induced by OGD (1-12 h). The evidence supports the conclusion that AMPK activation at early stages of OGD is involved in induction of protective autophagy in astrocytes. Inhibition of AMPK, either by siAMPKα1 or by compound C, significantly attenuated the expression of autophagy-related proteins and decrease of astrocyte viability following OGD. The findings provide additional data about the role of AMPK in ischemic astrocytes and downstream responses that may be involved in OGD-induced protective autophagy.

Rapamycin induces of protective autophagy in vascular endothelial cells exposed to oxygen-glucose deprivation

The protective potential of rapamycin has been reported in a few experimental models of brain ischemia, both in vivo and in vitro. Although the precise cellular processes underlying the neuroprotective effects of rapamycin in experimental models of stroke remain unknown, the current experimental data suggest that the mechanism of action of the drug may result from the mTOR-mediated autophagy induction. However, it is unclear whether the activation of autophagy acts as a pro-death or pro-survival factor in vascular endothelial cells in ischemic brain damage. It seems to be very important, since stroke affects not only neurons and astrocytes but also microvessels. In the present study, we used human umbilical vein endothelial cells (HUVEC) subjected to ischemia-simulating conditions (combined oxygen and glucose deprivation, OGD) for 6h to determine potential effect of rapamycin-induced autophagy on HUVEC damage. The drug at concentrations of 100 and 1000nM increased the expression of Beclin 1 and LC3-II together with a significant increase in the p62 degradation in ischemic HUVEC. Treatment with rapamycin in OGD significantly increased the cell viability, indicating that the drug exerts cytoprotective effect. The inhibition of Beclin 1 by siRNAs significantly attenuated the expression of autophagy-related proteins and reduced HUVEC viability following OGD and rapamycin treatment. Our findings demonstrated that toxicity of simulated ischemia conditions were enhanced in HUVEC when autophagy was blocked, and that rapamycin effectively prevented OGD-evoked damage by induction of protective autophagy via inhibition of the mTOR pathway.

Antinociceptive activity of crotoxin in the central nervous system: a functional Magnetic Resonance Imaging study

Crotoxin, the main neurotoxic component of the venom of South American rattlesnake (Crotalus durissus terrificus), is reported to have potent antinociceptive activity. Several authors have shown mainly in behavioral pain models that crotoxin induces antinociceptive effects, supposed to be mediated by actions on the central nervous system. The antinociceptive effects of crotoxin (45 μg/kg ip) in rats were verified in this study by increased response latencies in a Hargreaves test and tail flick test. In addition, it was demonstrated that crotoxin does not lead to motor impairments during a rotarod test and open field test. The main objective, carried out by blood oxygen level dependent functional Magnetic Resonance Imaging (BOLD fMRI) in anesthetized rats, was to determine which specific brain structures are involved in these antinociceptive effects. Moreover, potential antihyperalgesic effects were investigated by inducing a local hyperalgesia on the left hind paw. Therefore, antinociceptive effects (right paw) and antihyperalgesic effects (left paw) of crotoxin were able to be differentiated. As a result, crotoxin exhibited dominant antihyperalgesic but also antinociceptive effects during pain stimulation. Reductions of BOLD signal already occurred in brain input structures but were most prominent in primary and secondary somatosensory cortices. In conclusion, BOLD fMRI in anesthetized rats proved to be a helpful tool in toxinology, particularly in unraveled mechanisms of modulating nociception in the central nervous system by (potential) analgesics like crotoxin.

Propofol prevents cerebral ischemia-triggered autophagy activation and cell death in the rat hippocampus through the NF-κB/p53 signaling pathway

Propofol (2,6-diisopropylphenol) has been shown to attenuate neuronal injury under a number of experimental conditions; however, the mechanisms involved in its neuroprotective effects remain unclear. We therefore investigated whether inhibition of p53 induction by propofol contributes to the neuroprotection of cerebral ischemic cell death through both autophagic and apoptotic mechanisms. A transient global cerebral ischemia-reperfusion (I/R) model was produced with a 10-min, 2-vessel occlusion. The change in target genes including damage-regulated autophagy modulator (DRAM), microtubule-associated protein 1 light chain 3 (LC3), Beclin 1, cathepsin D, cathepsin B, p53-upregulated modulator of apoptosis (PUMA), Bax and Bcl-2 upon p53 inhibition was assessed with the co-administration of the intravenous anesthetic propofol and 3-methyladenine (3-MA), Pifithrin-alpha (PFT-α) or SN50. The I/R-induced increases of protein levels of p53 and LC3-II were significantly inhibited by treatment with propofol, 3-MA or PFT-α. The I/R-induced increases of protein levels of DRAM, Beclin 1, active cathepsin D and cathepsin B were significantly inhibited by treatment with propofol, PFT-α or SN50. The negative effects of the I/R-induced up-regulation of PUMA and Bax and the down-regulation of Bcl-2 in the rat hippocampus were all blocked by treatment with propofol, PFT-α or SN50. Our results suggest that cerebral I/R can induce nuclear factor-kappa B-dependent expression of p53. The autophagic and apoptotic mechanisms participate in programed cell death by regulating the p53-mediated pathway. Our results are the first to show that propofol, at clinically relevant concentrations, attenuated cell death through both autophagic and apoptotic mechanisms in the rat hippocampus after a cerebral I/R insult.

Growth inhibitory effects and molecular mechanisms of crotoxin treatment in esophageal Eca-109 cells and transplanted tumors in nude mice

AIM

To investigate the antitumor actions of the Crotalus durissus neurotoxin (crotoxin) on human esophageal carcinoma (Eca-109) cells in vitro and transplanted esophageal Eca-109 tumors in nude mice.

METHODS

The growth-inhibitory effect was analyzed in Eca-109 cells using MTT assay. Cell morphology changes in nuclei were observed using Hoechst 33342 staining, while apoptosis and cell cycle distribution were examined by flow cytometry. RT-PCR was used to measure the Bcl-2, p15, and caspase-3 p17 gene expression levels. A tumor transplantation model was established by inoculation of Eca-109 cells were into female Balb/c nude mice. Crotoxin (25, 50, and 100 mg/kg) was subcutaneously injected into the transplanted tumors every 2 d for a total of 10 injections. Tumor size and weight were measured. Bcl-2, p15, and caspase-3 p17 protein expression in transplanted tumors was analyzed using Western blotting.

RESULTS

Crotoxin (25, 50, and 100 μg/mL) inhibited the growth of Eca-109 cells in a dose-dependent manner with inhibition rates of 22.9%, 35.8%, and 57.2%, respectively. Hoechst 33342 staining revealed apoptotic cells with pyknotic nuclear chromatin after crotoxin treatment. In Eca-109 cells, crotoxin induced apoptosis and G1 block, significantly upregulated the expression of p15 and caspase-3 p17 genes and downregulated the expression of Bcl-2 gene. Furthermore, crotoxin inhibited the growth of Eca-109 tumors in nude mice in a dose-dependent manner. Western blotting showed that crotoxin increased p15 and caspase-3 p17 protein levels and reduced Bcl-2 protein level in tumor specimens.

CONCLUSION

Crotoxin inhibits the growth of Eca-109 cells in vitro via apoptosis induction and G1 block. Local administration of crotoxin inhibits the growth of subcutaneously transplanted Eca-109 cells in nude mice, possibly via increasing p15 and caspase-3 p17 protein expression and reducing Bcl-2 protein expression.

Rapamycin induces differentiation of glioma stem/progenitor cells by activating autophagy

Glioma stem/progenitor cells (GSPCs) are considered to be responsible for the initiation, propagation, and recurrence of gliomas. The factors determining their differentiation remain poorly defined. Accumulating evidences indicate that alterations in autophagy may influence cell fate during mammalian development and differentiation. Here, we investigated the role of autophagy in GSPC differentiation. SU-2 cells were treated with rapamycin, 3-methyladenine (3-MA) plus rapamycin, E64d plus rapamycin, or untreated as control. SU-2 cell xenografts in nude mice were treated with rapamycin or 3-MA plus rapamycin, or untreated as control. Western blotting and immunocytochemistry showed up-regulation of microtubule-associated protein light chain-3 (LC3)–II in rapamycin-treated cells. The neurosphere formation rate and the number of cells in each neurosphere were significantly lower in the rapamycin treatment group than in other groups. Real-time PCR and immunocytochemistry showed down-regulation of stem/progenitor cell markers and up-regulation of differentiation markers in rapamycin-treated cells. Transmission electron microscopy revealed autophagy activation in rapamycin-treated tumor cells in mice. Immunohistochemistry revealed decreased Nestin-positive cells and increased GFAP-positive cells in rapamycin-treated tumor sections. These results indicate that rapamycin induces differentiation of GSPCs by activating autophagy.

Interactions of PLA2-s from Vipera lebetina, Vipera berus berus and Naja naja oxiana venom with platelets, bacterial and cancer cells

Secretory phospholipasesA₂ (sPLA₂s) form a large family of structurally related enzymes widespread in nature. Herein, we studied the inhibitory effects of sPLA₂s from Vipera lebetina (VLPLA₂), Vipera berus berus (VBBPLA₂), and Naja naja oxiana (NNOPLA₂) venoms on (i) human platelets, (ii) four different bacterial strains (gram-negative Escherichia coli and Vibrio fischeri; gram-positive Staphylococcus aureus and Bacillus subtilis) and (iii) five types of cancer cells (PC-3, LNCaP, MCF-7, K-562 and B16-F10) in vitro. sPLA₂s inhibited collagen-induced platelet aggregation: VBBPLA₂ IC₅₀ = 0.054, VLPLA₂ IC₅₀ = 0.072, NNOPLA₂ IC₅₀ = 0.814 μM. p-Bromophenacylbromide-inhibited sPLA₂ had no inhibitory action on platelets. 36.17 μM VBBPLA₂ completely inhibited the growth of gram-positive Bacillus subtilis whereas no growth inhibition was observed towards gram-negative Escherichia coli. The inhibitory action of sPLA₂s (~0.7 μM and ~7 μM) towards cancer cells depended on both venom and cell type. VBBPLA₂ (7.2 μM) inhibited significantly the viability of K-562 cells and the cell death appeared apoptotic. The sPLA₂s exhibited no inhibitory effect towards LNCaP cells and some effect (8%–20%) towards other cells. Thus, already sub-μM concentrations of sPLA₂s inhibited collagen-induced platelet aggregation and from the current suite of studied svPLA₂s and test cells, VBBPLA₂ was the most growth inhibitory towards Bacillus subtilis and K-562 cells.

Excessive autophagy contributes to neuron death in cerebral ischemia

AIMS

To determine the extent to which autophagy contributes to neuronal death in cerebral hypoxia and ischemia.

METHODS

We performed immunocytochemistry, western blot, cell viability assay, and electron microscopy to analyze autophagy activities in vitro and in vivo.

RESULTS

In both primary cortical neurons and SH-SY5Y cells exposed to oxygen and glucose deprivation (OGD)for 6 h and reperfusion (RP) for 24, 48, and 72 h, respectively, an increase of autophagy was observed as determined by the increased ratio of LC3-II to LC3-I and Beclin-1 (BECN1) expression. Using Fluoro-Jade C and monodansylcadaverine double-staining, and electron microscopy we found the increment in autophagy after OGD/RP was accompanied by increased autophagic cell death, and this increased cell death was inhibited by the specific autophagy inhibitor, 3-methyladenine. The presence of large autolysosomes and numerous autophagosomes in cortical neurons were confirmed by electron microscopy. Autophagy activities were increased dramatically in the ischemic brains 3-7 days postinjury from a rat model of neonatal cerebral hypoxia/ischemia as shown by increased punctate LC3 staining and BECN1 expression.

CONCLUSION

Excessive activation of autophagy contributes to neuronal death in cerebral ischemia.

Propofol prevents autophagic cell death following oxygen and glucose deprivation in PC12 cells and cerebral ischemia-reperfusion injury in rats

Background

Propofol exerts protective effects on neuronal cells, in part through the inhibition of programmed cell death. Autophagic cell death is a type of programmed cell death that plays elusive roles in controlling neuronal damage and metabolic homeostasis. We therefore studied whether propofol could attenuate the formation of autophagosomes, and if so, whether the inhibition of autophagic cell death mediates the neuroprotective effects observed with propofol.

Methodology/Principal Findings

The cell model was established by depriving the cells of oxygen and glucose (OGD) for 6 hours, and the rat model of ischemia was introduced by a transient two-vessel occlusion for 10 minutes. Transmission electron microscopy (TEM) revealed that the formation of autophagosomes and autolysosomes in both neuronal PC12 cells and pyramidal rat hippocampal neurons after respective OGD and ischemia/reperfusion (I/R) insults. A western blot analysis revealed that the autophagy-related proteins, such as microtubule-associated protein 1 light chain 3 (LC3-II), Beclin-1 and class III PI3K, were also increased accordingly, but cytoprotective Bcl-2 protein was decreased. The negative effects of OGD and I/R, including the formation of autophagosomes and autolysosomes, the increase in LC3-II, Beclin-1 and class III PI3K expression and the decline in Bcl-2 production were all inhibited by propofol and specific inhibitors of autophagy, such as 3-methyladenine (3-MA), LY294002 and Bafilomycin A1 (Baf),. Furthermore, in vitro OGD cultures and in vivo I/R rats showed an increase in cell survival following the administration of propofol, as assessed by an MTT assay or histochemical analyses.

Conclusions/Significance

Our data suggest that propofol can markedly attenuate autophagic processes via the decreased expression of autophagy-related proteins in vitro and in vivo. This inhibition improves cell survival, which provides a novel explanation for the pleiotropic effects of propofol that benefit the nervous system.

Autophagy regulates endoplasmic reticulum stress in ischemic preconditioning

Recent studies have suggested that autophagy plays a prosurvival role in ischemic preconditioning (IPC). This study was taken to assess the linkage between autophagy and endoplasmic reticulum (ER) stress during the process of IPC. The effects of IPC on ER stress and neuronal injury were determined by exposure of primary cultured murine cortical neurons to 30 min of OGD 24 h prior to a subsequent lethal OGD. The effects of IPC on ER stress and ischemic brain damage were evaluated in rats by a brief ischemic insult followed by permanent focal ischemia (PFI) 24 h later using the suture occlusion technique. The results showed that both IPC and lethal OGD increased the LC3-II expression and decreased p62 protein levels, but the extent of autophagy activation was varied. IPC treatment ameliorated OGD-induced cell damage in cultured cortical neurons, whereas 3-MA (5-20 mM) and bafilomycin A 1 (75-150 nM) suppressed the neuroprotection induced by IPC. 3-MA, at the dose blocking autophagy, significantly inhibited IPC-induced HSP70, HSP60 and GRP78 upregulation; meanwhile, it also aggregated the ER stress and increased activated caspase-12, caspase-3 and CHOP protein levels both in vitro and in vivo models. The ER stress inhibitor Sal (75 pmol) recovered IPC-induced neuroprotection in the presence of 3-MA. Rapamycin 50-200 nM in vitro and 35 pmol in vivo 24 h before the onset of lethal ischemia reduced ER stress and ischemia-induced neuronal damage. These results demonstrated that pre-activation of autophagy by ischemic preconditioning can boost endogenous defense mechanisms to upregulate molecular chaperones, and hence reduce excessive ER stress during fatal ischemia.

The microtubule depolymerizing agent naphthazarin induces both apoptosis and autophagy in A549 lung cancer cells

Naphthazarin (DHNQ, 5,8-dihydroxy-l,4-naphthoquinone) is a naturally available 1,4-naphthoquinone derivatives. In this study, we focused on elucidating the cytotoxic mechanism of naphthazarin in A549 non-small cell lung carcinoma cells. Naphthazarin reduced the A549 cell viability considerably with an IC(50) of 16.4 ± 1.6 μM. Naphthazarin induced cell death in a dose- and time-dependent manner by activating apoptosis and autophagy pathways. Specifically, we found naphthazarin inhibited the PI3K/Akt cell survival signalling pathway, measured by p53 and caspase-3 activation, and PARP cleavage. It also resulted in an increase in the ratio of Bax/Bcl2 protein levels, indicating activation of the mitochondrial apoptotic pathway. Similarly naphthazarin triggered LC3II expression and induced autophagic flux in A549 cells. We demonstrated further that naphthazarin is a microtubule inhibitor in cell-free system and in A549 cells. Naphthazarin treatment depolymerized interphase microtubules and disorganised spindle microtubules and the majority of cells arrested at the G(2)/M transition. Together, these data suggest that naphthazarin, a microtubule depolymerizer which activates dual cell death machineries, could be a potential novel chemotherapeutic agent.

Anti-tumor activity of CrTX in human lung adenocarcinoma cell line A549

AIM

To assess the cytotoxic effect of crotoxin (CrTX), a potent neurotoxin extracted from the venom of the pit viper Crotalus durissus terrificus, in human lung adenocarcinoma A549 cells and investigated the underlying mechanisms.

METHODS

A549 cells were treated with gradient concentrations of CrTX, and the cell cycle and apoptosis were analyzed using a flow cytometric assay. The changes of cellular effectors p53, caspase-3 and cleaved caspase-3, total P38MAPK and pP38MAPK were investigated using Western blot assays. A549 xenograft model was used to examine the inhibition of CrTX on tumor growth in vivo.

RESULTS

Treatment of A549 cells with CrTX (25-200 μg/mL) for 48 h significantly inhibited the cell growth in a dose-dependent manner (IC(50)=78 μg/mL). Treatment with CrTX (25 μg/mL) for 24 h caused G1 arrest and induced cell apoptosis. CrTX (25 μg/mL) significantly increased the expression of wt p53, cleaved caspase-3 and phospho-P38MAPK. Pretreatment with the specific P38MAPK inhibitor SB203580 (5 μmol/L) significantly reduced CrTX-induced apoptosis and cleaved caspase-3 level, but G(1) arrest remained unchanged and highly expressed p53 sustained. Intraperitoneal injection of CrTX (10 μg/kg, twice a week for 4 weeks) significantly inhibited A549 tumor xenograft growth, and decreased MVD and VEGF levels.

CONCLUSION

CrTX produced significant anti-tumor effects by inducing cell apoptosis probably due to activation of P38MAPK and caspase-3, and by cell cycle arrest mediated by increased wt p53 expression. In addition, CrTX displayed anti-angiogenic effects in vivo.

TEM observation of ultrasound-induced mitophagy in nasopharyngeal carcinoma cells in the presence of curcumin

The present study was designed to observe the initiation of mitophagy in tumor cells after ultrasound treatment in the presence of curcumin under transmission electron microscopy. Nasopharyngeal carcinoma CNE2 cells were incubated with 10 μM curcumin and then exposed to ultrasound for 8 sec at an intensity of 0.46 W/cm(2). Severely swollen mitochondria, disrupted mitochondria and mitophagy were noted in the CNE2 cells after ultrasound treatment in the presence of curcumin. Our findings demonstrated that ultrasound treatment in the presence of curcumin significantly initiated mitophagy in CNE2 cells, which suggests that mitophagy serves as an important event in the process of cell death of nasopharyngeal carcinoma cells.

Kill one bird with two stones: potential efficacy of BCR-ABL and autophagy inhibition in CML

The introduction of imatinib in the treatment of chronic myeloid leukemia (CML) represents the most successful example of targeted therapy in human cancer. However, leukemic stem cells are insensitive to tyrosine kinase inhibitors (TKIs) and contribute to the persistence of disease by representing a reservoir of selfrenewing cells that replenish the disease after drug discontinuation. This finding has refocused the interest of scientists toward drug combinations, ie, treating with TKIs and simultaneously targeting alternative survival mechanisms. One candidate target mechanism is autophagy, a cellular recycling process that acts as a cytoprotective shield in CML cells in response to TKI-induced stress and in other cancer cells surviving in an inhospitable microenvironment. On that basis, inhibition of autophagy has now become an exciting option for combination treatment in cancer, and clinical trials have been initiated in solid and hemopoietic tumors such as CML, chronic lymphocytic leukemia, and multiple myeloma. This review describes the biology of CML and elucidates how the molecular driver BCR-ABL led to the development of TKIs. We then discuss the molecular regulation of autophagy and the potential for autophagy inhibition as the next step in our attempt to tackle the problem of CML persistence to offer a curative option.

Effects of the Crotalus durissus terrificus snake venom on hepatic metabolism and oxidative stress

Snake venoms present different action mechanisms because of their complex composition, represented mainly by toxins and enzymes. This work aimed to investigate the effects of the Crotalus durissus terrificus(Cdt) venom in the liver. Wistar rats were inoculated intraperitoneally with saline (control) or Cdt venom. After 3, 4, or 6 h, the following parameters were analyzed: (a) hepatic function, (b) oxidative stress parameters, and (c) the metabolism of alanine in the isolated perfused liver. Plasma activities of alanine aminotransferase and aspartate aminotransferase and hepatic glutathione S-transferase and catalase presented significant elevation in rats inoculated with 300 μg ⋅ kg(-1) Cdt venom. Liver lipoperoxidation was enormously increased by venom doses of 100, 200, and 300 μg ⋅kg(-1) , whereas glutathione S-transferase was not changed. Perfused livers from rats inoculated with 1500 μg ⋅kg(-1) venom showed increased production of lactate, pyruvate, and ammonia when alanine was the metabolic substrate. These results demonstrate that the Cdt venom can produce several changes in hepatocytes. The causes of the changes are possibly related to the disequilibrium in the redox homeostasis but also to specific needs of the poisoned organism, for example, an increased supply of lactate and pyruvate in response to an increased activity of the Cori cycle.

p53 induction contributes to excitotoxic neuronal death in rat striatum through apoptotic and autophagic mechanisms

The present study sought to investigate mechanisms by which p53 induction contributes to excitotoxic neuronal injury. Rats were intrastriatally administered the N-methyl-D-aspartate (NMDA) receptor agonist quinolinic acid (QA), the changes in the expression of p53 and its target genes involved in apoptosis and autophagy, including p53-upregulated modulator of apoptosis (PUMA), Bax, Bcl-2, damage-regulated autophagy modulator (DRAM) and other autophagic proteins including microtubule-associated protein 1 light chain 3 (LC3) and beclin 1 were assessed. The contribution of p53-mediated autophagy activation to apoptotic death of striatal neurons was assessed with co-administration of the nuclear factor-kappaB (NF-kappaB) inhibitor SN50, the p53 inhibitor Pifithrin-alpha (PFT-alpha) or the autophagy inhibitor 3-methyladenine (3-MA). The increased formation of autophagosomes and secondary lysosomes were observed with transmission electron microscope after excitotoxin exposure. QA induced increases in the expression of p53, PUMA, Bax and a decrease in Bcl-2. These changes were significantly attenuated by pre-treatment with SN50, PFT-alpha or 3-MA. SN50, PFT-alpha or 3-MA also reversed QA-induced upregulation of DRAM, the ratio of LC3-II/LC3-I and beclin 1 protein levels in the striatum. QA-induced internucleosomal DNA fragmentation and loss of striatal neurons were robustly inhibited by SN50, PFT-alpha or 3-MA. These results suggest that overstimulation of NMDA receptors can induce NF-kappaB-dependent expression of p53. p53 participates in excitotoxic neuronal death probably through both apoptotic and autophagic mechanisms.

Notexin upregulates Fas and FasL protein expression of human neuroblastoma SK-N-SH cells through p38 MAPK/ATF-2 and JNK/c-Jun pathways

Notechis scutatus scutatus notexin induced an increase in Fas and FasL protein expression of human neuroblastoma SK-N-SH cells in a dose- and time-dependent manner. Moreover, notexin treatment upregulated transcription of Fas/FasL mRNA. Downregulation of FADD blocked notexin-induced procaspase-8 degradation and cleavage of Bid and rescued viability of notexin-treated cells. Upon exposure to notexin, activation of JNK and p38 MAPK was observed in SK-N-SH cells. Notexin-induced upregulation of Fas and FasL was suppressed by SB202190 (p38 MAPK inhibitor) and S600125 (JNK inhibitor). Downregulation of p38alpha MAPK and JNK1 by siRNA proved that upregulation of Fas/FasL was related to p38alpha MAPK and JNK1 activation. Notexin treatment evoked p38alpha MAPK-mediated ATF-2 phosphorylation and JNK1-mediated c-Jun phosphorylation. Knockdown of c-Jun and ATF-2 by siRNA or overexpression of dominant-negative c-Jun and ATF-2 revealed that both c-Jun and ATF-2 were crucial for Fas/FasL upregulation. Taken together, our data indicate that notexin-induced upregulation of Fas and FasL is triggered by p38 MAPK/ATF-2 and JNK/c-Jun signaling pathways in SK-N-SH cells.

Molecular mechanisms of excitotoxicity and their relevance to pathogenesis of neurodegenerative diseases

A pivotal role for excitotoxicity in neurodegenerative diseases is gaining increasingly more acceptance, but the underlying mechanisms through which it participates in neurodegeneration still need further investigation. Excessive activation of glutamate receptors by excitatory amino acids leads to a number of deleterious consequences, including impairment of calcium buffering, generation of free radicals, activation of the mitochondrial permeability transition and secondary excitotoxicity. Recent studies implicate excitotoxicity in a variety of neuropathological conditions, suggesting that neurodegenerative diseases with distinct genetic etiologies may share excitotoxicity as a common pathogenic pathway. Thus, understanding the pathways involved in excitotoxicity is of critical importance for the future clinical treatment of many neurodegenerative diseases. This review discusses the current understanding of excitotoxic mechanisms and how they are involved in the pathogenesis of neurodegenerative diseases.

Inhibition of autophagy by 3-MA enhances the effect of 5-FU-induced apoptosis in colon cancer cells

BACKGROUND

5-fluorouracil-(5-FU)-based adjuvant chemotherapy is widely used for the treatment of colorectal cancer. However, 5-FU resistance in the course of treatment has become more common. Therefore, new therapeutic strategies and/or new adjuvant drugs still need to be explored.

METHODS

Two colon-cancer-derived cell lines, colon26 and HT29, were used to investigate the effect of 5-FU, 3-methyladenine (3-MA, an autophagy inhibitor), or their combination on apoptotic cell death and autophagy. MTT assay, Hochest plus propidium iodide (PI) staining, and DNA fragmentation assay were used to observe apoptosis. Meanwhile, monodansylcadaverine (MDC) was used to detect autophagy. Finally, immunoblotting assay was used to explore the molecular change that occurred.

RESULTS

We observed the apoptosis induced by 5-FU in colon cancer cells. Meanwhile, autophagy was also stimulated. The combination treatment of 3-MA and 5-FU significantly increased the apoptotic cell death. By isolating the subcellular fractions of mitochondria and cytosol, we observed that the release of cytochrome c was increased in combination-treated cells. Cytochrome c resulted in the activation of caspase-3, thus activating PARP. Moreover, the anti-apoptotic protein, Bcl-xL, was significantly downregulated by 3-MA.

CONCLUSIONS

Our results suggest that 5-FU-induced apoptosis in colon cancer cells can be enhanced by the inhibitor of autophagy, 3-MA. Autophagy might play a role as a self-defense mechanism in 5-FU-treated colon cancer cells, and its inhibition could be a promising strategy for the adjuvant chemotherapy of colon cancer.

Lysosomal membrane permeabilization in cell death

Mitochondrial outer membrane permeabilization (MOMP) constitutes one of the major checkpoint(s) of apoptotic and necrotic cell death. Recently, the permeabilization of yet another organelle, the lysosome, has been shown to initiate a cell death pathway, in specific circumstances. Lysosomal membrane permeabilization (LMP) causes the release of cathepsins and other hydrolases from the lysosomal lumen to the cytosol. LMP is induced by a plethora of distinct stimuli including reactive oxygen species, lysosomotropic compounds with detergent activity, as well as some endogenous cell death effectors such as Bax. LMP is a potentially lethal event because the ectopic presence of lysosomal proteases in the cytosol causes digestion of vital proteins and the activation of additional hydrolases including caspases. This latter process is usually mediated indirectly, through a cascade in which LMP causes the proteolytic activation of Bid (which is cleaved by the two lysosomal cathepsins B and D), which then induces MOMP, resulting in cytochrome c release and apoptosome-dependent caspase activation. However, massive LMP often results in cell death without caspase activation; this cell death may adopt a subapoptotic or necrotic appearance. The regulation of LMP is perturbed in cancer cells, suggesting that specific strategies for LMP induction might lead to novel therapeutic avenues.

Mitochondrial dysfunction induced by pancreatic and crotalic (Crotalus durissus terrificus) phospholipases A2 on rabbit proximal tubules suspensions

In the present study we show that phospholipases A2 isolated from porcine pancreas (PP-PLA2) and Crotalus durissus terrificus snake venom (SV-PLA2) induced dose-dependent increases of LDH release from rabbit proximal tubules in suspension. Both porcine and crotalic PLA(2)s induced increases in non-esterified fatty acid (NEFA) levels (microg of NEFA/mg of tubule protein). It was observed that the NEFA levels in the pellets were higher than in the supernatant for both PLA2, and were dose-dependent for the crotalic PLA2 group. Furthermore, snake venom PLA2 induced a decrease in mitochondrial membrane potential (DeltaPsi(m)) assessed by both JC-1 uptake and safranin O uptake. Porcine PLA2 produced no effects on JC-1 uptake with the highest concentrations and an unexpected increase in the group treated with the lowest concentration. In contrast, the safranin O method revealed decreases of energization with both phospholipases, so it had higher sensitivity to the presence of the increased NEFA levels. Addition of delipidated bovine serum albumin (dBSA) completely reversed the effects induced by phospholipases on DeltaPsi(m) measured with safranin O. Incubation with pancreatic and crotalic phospholipases A2 produced no changes on cell ATP levels. We conclude that the treatment of proximal tubule suspensions with porcine or crotalic phospholipases disturbed membrane integrity as well as mitochondrial function. Specific early NEFA-mediated mitochondrial effects of the phospholipases used in the present study are indicated by the benefit provided by dBSA.

Autophagy and tumor suppression: recent advances in understanding the link between autophagic cell death pathways and tumor development

Autophagy is a process by which the cell recycles its components through self-consumption of cellular organelles and bulk cytoplasm. In times of stress, it serves to generate much needed nutrients. When overactivated, however, the orderly destruction of organelles can lead to cell death. At times, autophagic cell death is used as an alternative to apoptosis to eliminate unwanted, damaged, or transformed cells. Consistent with this, tumorigenesis is associated with a downregulation in autophagy, and genes that mediate the execution of the process have been shown to be tumor suppressors. At the same time, basal autophagy has been harnessed by some tumor cells as a survival mechanism to protect against ischemia and signals that induce apoptosis. Thus, the relationship between autophagy and tumor development is complex. Here, we discuss the basic machinery of mammalian autophagy and its regulators, with specific emphasis on those genes that have been linked to cancer. Research supporting the divergent nature of autophagy in both tumor suppression and tumor progression is presented. We conclude with a survey of recent approaches to treating cancer with strategies that modulate autophagy.

Dynamic effects of autophagy on arsenic trioxide-induced death of human leukemia cell line HL60 cells

AIM

To evaluate the contribution of an autophagic mechanism to the As2O3- induced death of human acute myeloid leukaemia cell line HL60 cells.

METHODS

The growth inhibition of HL60 cells induced by As2O3 was assessed with 3-(4,5- dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide colorimetric assay. The activation of autophagy was determined with monodansylcadaverine labeling and transmission electron microscope. The role of autophagy in the As2O3-induced death of HL60 cells was assessed using autophagic and lysosomal inhibitors. Immunofluorescence, flow cytometry, and Western blot analysis were used to study the apoptotic and autophagic mechanisms.

RESULTS

After treatment with As2O3, the proliferation of HL60 cells was significantly inhibited and the formation of autophagosomes increased. The blockade of autophagy maturation with the autophagy-specific inhibitor 3-methyladenine (3-MA) or the lysosome-neutralizing agent NH4Cl 1 h before As2O3 potentiated the As2O3-induced death of HL60 cells. In contrast, 3-MA attenuated As2O3-induced death when administered 30 min after As2O3. 3-MA and NH4Cl also inhibited As2O3-induced upregulation of microtubule-associated protein 1 light chain 3, the protein required for autophagy in mammalian cells. Following As2O3, lysosomes were activated as indicated by increased levels of cathepsins B and L. The apoptotic response of HL60 cells to As2O3 was suggested by the collapse of mitochondrial membrane potential, release of cytochrome c from mitochondria, and the activation of caspase-3. Pretreatment with 3-MA prior to As2O3 amplified these apoptotic signals, while posttreatment with 3-MA 30 min after As2O3 attenuated the apoptotic pathways.

CONCLUSION

Autophagy plays complex roles in the As2O3-induced death of HL60 cells; it inhibits As2O3-induced apoptosis in the initiation stage, but amplifies the As2O3-mediated apoptotic program if it is persistently activated.

Autophagy is involved in cytotoxic effects of crotoxin in human breast cancer cell line MCF-7 cells

AIM

To investigate the role of crotoxin (CrTX)-induced autophagy in the death of MCF-7 cells, a caspase-3-deficient, human breast cancer cell line.

METHODS

Cultured MCF-7 cells were treated with various doses of CrTX, a phospholipase A2 (PLA2) isolated from the venom of the South American rattlesnake, Crotalus durissus terrificus. The cytotoxicity of CrTX in the presence and absence of caspase inhibitors was measured with methyl thiazolyl tetrazolium (MTT) and lactate dehydrogenase (LDH) leakage assays. The activation of autophagy was determined with transmission electron microscope and monodansylcadaverin (MDC) labeling. The upregulation of lysosomal enzymes, the release of cytochrome c (cyto-c), and the nuclear translocation of the apoptosis inducing factor (AIF) were examined by immunoblotting and immunofluorescence.

RESULTS

CrTX inhibited the viability of MCF-7 cells in a dose- and time-dependent manner. CrTX-activated autophagy was revealed by punctuate MDC labeling, and an increase in the formation of autophagosomes as well as apoptosis, as evidenced by nuclear condensation and fragmentation. The activation of cathepsin B, D, and L, in addition to the release of cytochrome c and the relocation of AIF into nuclei, were observed after CrTX treatment. Autophagy inhibitors 3-methyladenine (3-MA), NH4Cl, and the pan-caspase inhibitor, Z-Val-Ala-Asp-fluoromethylketone (Z-Vad-fmk), attenuated CrTX-induced cell death.

CONCLUSION

An autophagic mechanism contributes to the apoptosis of MCF-7 cells induced by CrTX.

Death pathways associated with photodynamic therapy

When the mitochondria and/or the endoplasmic reticulum were targeted by photodynamic therapy, photodamage to the anti-apoptotic protein Bcl-2 was observed. This led to an apoptotic outcome if that death pathway was available. Lysosomal photodamage ultimately resulted in activation of the pro-apoptotic protein Bid, also leading to apoptosis. Photodamage to the plasma membrane was associated with migration of sensitizers to the cytosol and procaspase photodamage, with apoptosis impaired. Where apoptosis was unavailable because of lack of necessary components of the program, an autophagic outcome has been observed. It is also clear that autophagy can occur along with apoptosis as a PDT response, and may play a role in immunologic responses to photodamaged tumor cells.