Increase in PGE2 biosynthesis induces a Bax dependent apoptosis correlated to patients’ survival in glioblastoma multiforme

Lipidomics-driven drug discovery and delivery strategies in glioblastoma

With few viable treatment options, glioblastoma (GBM) is still one of the most aggressive and deadly types of brain cancer. Recent developments in lipidomics have demonstrated the potential of lipid metabolism as a therapeutic target in GBM. The thorough examination of lipids in biological systems, or lipidomics, is essential to comprehending the changed lipid profiles found in GBM, which are linked to the tumor's ability to grow, survive, and resist treatment. The use of lipidomics in drug delivery and discovery is examined in this study, focusing on how it may be used to find new biomarkers, create multi-target directed ligands, and improve drug delivery systems. We also cover the use of FDA-approved medications, clinical trials that use lipid-targeted medicines, and the integration of lipidomics with other omics technologies. This study emphasizes lipidomics as a possible tool in developing more effective treatment methods for GBM by exploring various lipid-centric techniques.

Emerging Lipid Targets in Glioblastoma

GBM accounts for most of the fatal brain cancer cases, making it one of the deadliest tumor types. GBM is characterized by severe progression and poor prognosis with a short survival upon conventional chemo- and radiotherapy. In order to improve therapeutic efficiency, considerable efforts have been made to target various features of GBM. One of the targetable features of GBM is the rewired lipid metabolism that contributes to the tumor's aggressive growth and penetration into the surrounding brain tissue. Lipid reprogramming allows GBM to acquire survival, proliferation, and invasion benefits as well as supportive modulation of the tumor microenvironment. Several attempts have been made to find novel therapeutic approaches by exploiting the lipid metabolic reprogramming in GBM. In recent studies, various components of de novo lipogenesis, fatty acid oxidation, lipid uptake, and prostaglandin synthesis have been considered promising targets in GBM. Emerging data also suggest a significant role hence therapeutic potential of the endocannabinoid metabolic pathway in GBM. Here we review the lipid-related GBM characteristics in detail and highlight specific targets with their potential therapeutic use in novel antitumor approaches.

Apoptosis Regulation in Osteoarthritis and the Influence of Lipid Interactions

Osteoarthritis (OA) is one of the most common chronic diseases in human and animal joints. The joints undergo several morphological and histological changes during the development of radiographically visible osteoarthritis. The most discussed changes include synovial inflammation, the massive destruction of articular cartilage and ongoing joint destruction accompanied by massive joint pain in the later stadium. Either the increased apoptosis of chondrocytes or the insufficient apoptosis of inflammatory macrophages and synovial fibroblasts are likely to underly this process. In this review, we discuss the current state of research on the pathogenesis of OA with special regard to the involvement of apoptosis.

The inducible prostaglandin E synthase (mPGES-1) in neuroinflammatory disorders

The cyclooxygenase (COX)/prostaglandin E2 (PGE2) signaling pathway has emerged as a critical target for anti-inflammatory therapeutic development in neurological diseases. However, medical use of COX inhibitors in the treatment of various neurological disorders has been limited due to well-documented cardiovascular and cerebrovascular complications. It has been widely proposed that modulation of downstream microsomal prostaglandin E synthase-1 (mPGES-1) enzyme may provide more specificity for inhibiting PGE2-elicited neuroinflammation. Heightened levels of mPGES-1 have been detected in a variety of brain diseases such as epilepsy, stroke, glioma, and neurodegenerative diseases. Subsequently, elevated levels of PGE2, the enzymatic product of mPGES-1, have been demonstrated to modulate a multitude of deleterious effects. In epilepsy, PGE2 participates in retrograde signaling to augment glutamate release at the synapse leading to neuronal death. The excitotoxic demise of neurons incites the activation of microglia, which can become overactive upon further stimulation by PGE2. A selective mPGES-1 inhibitor was able to reduce gliosis and the expression of proinflammatory cytokines in the hippocampus following status epilepticus. A similar mechanism has also been observed in stroke, where the overactivation of microglia by PGE2 upregulated the expression and secretion of proinflammatory cytokines. This intense activation of neuroinflammatory processes triggered the secondary injury commonly observed in stroke, and blockade of mPGES-1 reduced infarction size and edema, suppressed induction of proinflammatory cytokines, and improved post-stroke well-being and cognition. Furthermore, elevated levels of PGE2 have been shown to intensify the proliferation of glioma cells, mediate P-glycoprotein expression at the blood-brain barrier (BBB) and facilitate breakdown of the BBB. For these reasons, targeting mPGES-1, the central and inducible enzyme of the COX cascade, may provide a more specific therapeutic strategy for treating neuroinflammatory diseases.

DAXX-ATRX regulation of p53 chromatin binding and DNA damage response

DAXX and ATRX are tumor suppressor proteins that form a histone H3.3 chaperone complex and are frequently mutated in cancers with the alternative lengthening of telomeres (ALT). Here, we show that DAXX and ATRX knock-out (KO) U87-T cells that have acquired ALT-like features have defects in p53 chromatin binding and DNA damage response. RNA-seq analysis revealed that p53 pathway is among the most perturbed. ChIP-seq and ATAC-seq revealed a genome-wide reduction in p53 DNA-binding and corresponding loss of chromatin accessibility at many p53 response elements across the genome. Both DAXX and ATRX null cells showed a depletion of histone H3.3 and accumulation of γH2AX at many p53 sites, including subtelomeres. These findings indicate that loss of DAXX or ATRX can compromise p53 chromatin binding and p53 DNA damage response in ALT-like cells, providing a link between histone composition, chromatin accessibility and tumor suppressor function of p53.

Fatty acids and their lipid mediators in the induction of cellular apoptosis in cancer cells

The oxygenation of polyunsaturated fatty acids such as arachidonic and linoleic acid through enzymes like lipoxygenases (LOXs) are common and often leads to the production of various bioactive lipids that are important both in acute inflammation and its resolution and thus in disease progression. Amongst the several isoforms of LOX that are expressed in mammals, 15-lipoxygenase (15-LOX) has shown to be crucial in the context of inflammation. Moreover, being expressed in cells of the immune system, as well as in epithelial cells; the enzyme has been shown to crosstalk with a number of important signalling pathways. Mounting evidences from recent reports suggest that 15-LOX has anti-cancer activities which are dependent or independent of its metabolites, and is executed through several downstream pathways like cGMP, PPAR, p53, p21 and NAG-1. However, it is still unclear whether the up-regulation of 15-LOX is associated with cancer cell apoptosis. Monoamine oxidase A (MAO-A), on the other hand, is a mitochondrial flavoenzyme which is believed to be involved in the pathogenesis of atherosclerosis and inflammation and in many other neurological disorders. MAO-A has also been reported as a potential therapeutic target in different types of cancers like prostate cancer, lung cancer etc. In this review, we discussed about the role of fatty acids and their lipid mediators in cancer cell apoptosis. Here we particularly focused on the contribution of oxidative enzymes like 15-LOX and MAO-A in mediating apoptosis in lung cancer cell after fatty acid induction.

Genetic variants of CYP4F12 gene are associated with glioma susceptibility

Glioma is a common and fatal primary malignant tumor of the central nervous system, and its prognosis is poor. To determine the susceptibility markers of gliomas in Chinese population we conducted a genome-wide association study (GWAS) of glioma in the Han Chinese population, with a total of 485 glioma cases and 485 controls. Genotyping was conducted using the Applied Biosystems Axiom Precision Medicine Diversity Array. Besides, we carried out imputation using IMPUTE 2.0 software, and the 1000 Genomes Phase 3 was used as the reference panel. The logistic regression model was used to analyze the association of each SNP with glioma risk, assuming an additive genetic model, which was implemented in PLINK version 1.9. Odds ratio (OR) and 95% confidence interval (CI) were estimated from logistic regression analysis with adjustment for age and gender. The results revealed that the SNP (rs688755) in the exon region of CYP4F12 at 19p13.12 reached genome-wide significance associated with gliomas (P = 2.35 × 10^-8 , OR = 3.55, 95% CI = 2.20-5.74). Our findings provide deeper insight into the genetic contribution to glioma in different populations.

Design, synthesis and biological evaluation of N-anthraniloyl tryptamine derivatives as pleiotropic molecules for the therapy of malignant glioma

COX-2 and STAT3 are two key culprits in the glioma microenvironment. Herein, to inhibit COX-2 and block STAT3 signaling, we disclosed 27 N-anthraniloyl tryptamine compounds based on the combination of melatonin derivatives and N-substituted anthranilic acid derivatives. Among them, NP16 showed the best antiproliferative activity and moderate COX-2 inhibition. Of note, NP16 decreased the level of p-JAK2 and p-STAT3, and blocked the nuclear translocation of STAT3 in GBM cell lines. Moreover, NP16 downregulated the MMP-9 expression of BV2 cells in a co-culture system of BV2 and C6 glioma cells, abrogated the proliferative/invasive/migratory abilities of GBM cells, induced apoptosis by ROS and the Bcl-2-regulated apoptotic pathway, and induced obvious G₂/M arrest in glioma cells in vitro. Furthermore, NP16 displayed favorable pharmacokinetic profiles covering long half-life (11.43 ± 0.43 h) and high blood-brain barrier permeability. Finally, NP16 effectively inhibited tumor growth, promoted the survival rate, increased the expression of E-cadherin and reduced overproduction of PGE₂, MMP-9, VEGF-A and the level of p-STAT3 in tumor tissue, and improved the anxiety-like behavior in C6 glioma model. All these evidences demonstrated N-anthraniloyl tryptamine derivatives as multifunctional anti-glioma agents with high potency could drain the swamp to beat glioma.

Intracellular prostaglandin E2 contributes to hypoxia-induced proximal tubular cell death

Proximal tubular cells (PTC) are particularly vulnerable to hypoxia-induced apoptosis, a relevant factor for kidney disease. We hypothesized here that PTC death under hypoxia is mediated by cyclo-oxygenase (COX-2)-dependent production of prostaglandin E₂ (PGE₂), which was confirmed in human proximal tubular HK-2 cells because hypoxia (1% O₂)-induced apoptosis (i) was prevented by a COX-2 inhibitor and by antagonists of prostaglandin (EP) receptors and (ii) was associated to an increase in intracellular PGE₂ (iPGE₂) due to hypoxia-inducible factor-1α-dependent transcriptional up-regulation of COX-2. Apoptosis was also prevented by inhibitors of the prostaglandin uptake transporter PGT, which indicated that iPGE₂ contributes to hypoxia-induced apoptosis (on the contrary, hypoxia/reoxygenation-induced PTC death was exclusively due to extracellular PGE₂). Thus, iPGE₂ is a new actor in the pathogenesis of hypoxia-induced tubular injury and PGT might be a new therapeutic target for the prevention of hypoxia-dependent lesions in renal diseases.

TOM20-mediated transfer of Bcl2 from ER to MAM and mitochondria upon induction of apoptosis

In this work, we have explored the subcellular localization of Bcl2, a major antiapoptotic protein. In U251 glioma cells, we found that Bcl2 is localized mainly in the ER and is translocated to MAM and mitochondria upon induction of apoptosis; this mitochondrial transfer was not restricted to the demonstrator cell line, even if cell-specific modulations exist. We found that the Bcl2/mitochondria interaction is controlled by TOM20, a protein that belongs to the protein import machinery of the mitochondrial outer membrane. The expression of a small domain of interaction of TOM20 with Bcl2 potentiates its anti-apoptotic properties, which suggests that the Bcl2–TOM20 interaction is proapoptotic. The role of MAM and TOM20 in Bcl2 apoptotic mitochondrial localization and function has been confirmed in a yeast model in which the ER–mitochondria encounter structure (ERMES) complex (required for MAM stability in yeast) has been disrupted. Bcl2–TOM20 interaction is thus an additional player in the control of apoptosis.

The role of exosome lipids in central nervous system diseases

Central nervous system (CNS) diseases are common diseases that threaten human health. The CNS is highly enriched in lipids, which play important roles in maintaining normal physiological functions of the nervous system. Moreover, many CNS diseases are closely associated with abnormal lipid metabolism. Exosomes are a subtype of extracellular vesicles (EVs) secreted from multivesicular bodies (MVBs) . Through novel forms of intercellular communication, exosomes secreted by brain cells can mediate inter-neuronal signaling and play important roles in the pathogenesis of CNS diseases. Lipids are essential components of exosomes, with cholesterol and sphingolipid as representative constituents of its bilayer membrane. In the CNS, lipids are closely related to the formation and function of exosomes. Their dysregulation causes abnormalities in exosomes, which may, in turn, lead to dysfunctions in inter-neuronal communication and promote diseases. Therefore, the role of lipids in the treatment of neurological diseases through exosomes has received increasing attention. The aim of this review is to discuss the relationship between lipids and exosomes and their roles in CNS diseases.

Importance of the Role of ω-3 and ω-6 Polyunsaturated Fatty Acids in the Progression of Brain Cancer

Brain cancer is one of the most malignant types of cancer in both children and adults. Brain cancer patients tend to have a poor prognosis and a high rate of mortality. Additionally, 20-40% of all other types of cancer can develop brain metastasis. Numerous pieces of evidence suggest that omega-3-polyunsaturated fatty acids (ω-PUFAs) could potentially be used in the prevention and therapy of several types of cancer. PUFAs and oxylipins are fundamental in preserving physiological events in the nervous system; it is, therefore, necessary to maintain a certain ratio of ω-3 to ω-6 for normal nervous system function. Alterations in PUFAs signaling are involved in the development of various pathologies of the nervous system, including cancer. It is well established that an omega-6-polyunsaturated fatty acid (ω-6 PUFA)-rich diet has a pro-tumoral effect, whereas the consumption of an ω-3 rich diet has an anti-tumoral effect. This review aims to offer a better understanding of brain cancer and PUFAs and to discuss the role and impact of PUFAs on the development of different types of brain cancer. Considering the difficulty of antitumor drugs in crossing the blood-brain barrier, the therapeutic role of ω-3/ω-6 PUFAs against brain cancer would be a good alternative to consider. We highlight our current understanding of the role of PUFAs and its metabolites (oxylipins) in different brain tumors, proliferation, apoptosis, invasion, angiogenesis, and immunosuppression by focusing on recent research in vitro and in vivo.

Prostaglandin E2 increases migration and proliferation of human glioblastoma cells by activating transient receptor potential melastatin 7 channels

Recent studies showed that both prostaglandin E2 (PGE2) and transient receptor potential melastatin 7 (TRPM7) play important roles in migration and proliferation of human glioblastoma cells. In this study, we tested the association between PGE2 and TRPM7. We found that PGE2 increased TRPM7 currents in HEK293 and human glioblastoma A172 cells. The PGE2 EP3 receptor antagonist L‐798106 abrogated the PGE2 stimulatory effect, while EP3 agonist 17‐phenyl trinor prostaglandin E2 (17‐pt‐PGE2) mimicked the effect of PEG2 on TRPM7. The TRPM7 phosphotransferase activity‐deficient mutation, K1646R had no effect on PGE2 induced increase of TRPM7 currents. Inhibition of protein kinase A (PKA) activity by Rp‐cAMP increased TRPM7 currents. TRPM7 PKA phosphorylation site mutation S1269A abolished the PGE2 effect on TRPM7 currents. PGE2 increased both mRNA and membrane protein expression of TRPM7 in A172 cells. Knockdown of TRPM7 by shRNA abrogated the PGE2 stimulated migration and proliferation of A172 cells. Blockage of TRPM7 with 2‐aminoethoxydiphenyl borate (2‐APB) or NS8593 had a similar effect as TRPM7‐shRNA. In conclusion, our results demonstrate that PGE2 activates TRPM7 via EP3/PKA signalling pathway, and that PGE2 enhances migration and proliferation of human glioblastoma cells by up‐regulation of the TRPM7 channel.

DP1 receptor signaling prevents the onset of intrinsic apoptosis in eosinophils and functions as a transcriptional modulator

Prostaglandin (PG) D₂ is the ligand for the G-protein coupled receptors DP1 (D-type prostanoid receptor 1) and DP2 (also known as chemoattractant receptor homologous molecule, expressed on Th2 cells; CRTH2). Both, DP1 and DP2 are expressed on the cellular surface of eosinophils; although it has become quite clear that PGD₂ induces eosinophil migration mainly via DP2 receptors, the role of DP1 in eosinophil responses has remained elusive. In this study, we addressed how DP1 receptor signaling complements the pro-inflammatory effects of DP2. We found that PGD₂ prolongs the survival of eosinophils via a DP1 receptor-mediated mechanism that inhibits the onset of the intrinsic apoptotic cascade. The DP1 agonist BW245c prevented the activation of effector caspases in eosinophils and protected mitochondrial membranes from depolarization which-as a consequence-sustained viability of eosinophils. DP1 activation in eosinophils enhanced the expression of the anti-apoptotic gene BCL-X_L , but also induced pro-inflammatory genes, such as VLA-4 and CCR3. In HEK293 cells that overexpress recombinant DP1 and/or DP2 receptors, activation of DP1, but not DP2, delayed cell death and stimulated proliferation, along with induction of serum response element (SRE), a regulator of anti-apoptotic, early-response genes. We conclude that DP1 receptors promote the survival via SRE induction and induction of pro-inflammatory genes. Therefore, targeting DP1 receptors, along with DP2, may contribute to anti-inflammatory therapy in eosinophilic diseases.

The Role of mPGES-1 in Inflammatory Brain Diseases

Prostaglandin E₂ (PGE₂) has been thought to be an important mediator of inflammation in peripheral tissues, but recent studies clearly show the involvement of PGE₂ in inflammatory brain diseases. In some animal models of brain disease, the genetic disruption and chemical inhibition of cyclooxygenase (COX)-2 resulted in the reduction of PGE₂ and amelioration of symptoms, and it had been thought that PGE₂ produced by COX-2 may be involved in the progression of injuries. However, COX-2 produces not only PGE₂, but also some other prostanoids, and thus the protective effects of COX-2 inhibition, as well as severe side effects, may be caused by the inhibition of prostanoids other than PGE₂. Therefore, to elucidate the role of PGE₂, studies of microsomal prostaglandin E synthase-1 (mPGES-1), an inducible terminal enzyme for PGE₂ synthesis, have recently been an active area of research. Studies from mPGES-1 deficient mice provide compelling evidence for its role in a variety of inflammatory brain diseases, such as ischemic stroke, Alzheimer's disease and epilepsy, and clues for developing new therapeutic treatments for brain diseases by targeting mPGES-1. Considering that COX inhibitors may non-selectively suppress the production of many types of prostanoids that are essential for normal physiological functioning of the brain and peripheral tissues, as well as induce gastro-intestinal, renal and cardiovascular complications, mPGES-1 inhibitors are expected to be injury-selective and have fewer side-effects when treating human brain diseases. Thus, this paper focuses on recent studies that have demonstrated the involvement of mPGES-1 in pathological brain diseases.

Opposing roles of PGD2 in GBM

BACKGROUND

The World Health Organization classifies glioblastoma (GBM) as a grade IV astrocytoma. Despite the advances in chemotherapy, surgery, and radiation treatments that improve a patient's length of survival, the overall trajectory of the disease remains unchanged. GBM cells produce significant levels of various types of bioactive lipids. Prostaglandin D₂ (PGD₂) influences both pro- and anti-tumorigenic activities in the cell; however, its role in GBM is unclear. Therefore, this study aimed to identify the impact of PGD₂ on GBM cell activities in vitro.

METHODS

First we looked to identify the presence of the PGD₂ synthesis pathway through RT-PCR, immunohistochemistry, and HPLC-MS/MS in three GBM cell lines. Then, to observe PGD₂'s effects on cell count and apoptosis/mitosis (Hoechst 33342 stain), and migration (Transwell Assay), the cells were treated in vitro with physiological (<1μM) and/or supraphysiological (>1μM) concentrations of PGD₂ over 72h. HPLC-MS/MS was used to identify the lipid composition of patients with either Grade II/III gliomas or GBM.

RESULTS

We identified the presence of endogenous PGD₂ with its corresponding enzymes and receptors. Exogenous PGD₂ both increased cell count (<1μM) and decreased cell count (10μM) in a concentration-dependent manner. There were no significant effects on apoptosis. A significant decrease in mitotic activity was seen only in U251MG, and a significant increase was seen in migration with 5μM PGD₂ treatments. A very significant increase of PGD₂ was seen from Grade II/III gliomas to GBM.

CONCLUSIONS

Our study demonstrates that prostaglandin D₂ possesses a dynamic, concentration-dependent effect in GBM cell activities. The increase of PGD₂ production in GBM patients suggests a pro-tumorigenic role of PGD₂ in glioma growth and invasion. Therefore, prostaglandin signaling in GBM requires further investigation to identify new targets for more effective therapies.

Cell biology-metabolic crosstalk in glioma

The renewed interest in cancer metabolism in recent years has been fuelled by the identification of the involvement of key oncogenes and tumour suppressor genes in the control of metabolic pathways. Many of these alterations lead to dramatic changes in bioenergetics, biosynthesis and redox balance within tumour cells. The complex relationship between tumour cell metabolism and the tumour microenvironment has turned this field of biochemistry and cell biology into a challenging and exciting area for study. In the case of gliomas the involvement of altered metabolic pathways including glycolysis, oxidative phosphorylation and glutaminolysis are pointing the way to new possibilities for treatment. The tumour-promoting effects of inflammation are an emerging hallmark of cancer and the role of the eicosanoids in gliomas is an area of active research to elucidate the importance of individual eicosanoids in glioma cell proliferation, migration and immune escape. In this review, the different aspects of metabolic reprogramming which occur in gliomas are highlighted and their relationship to glioma cell biology and the wider tumour microenvironment is described.

Prostaglandin E2 Signaling: Alternative Target for Glioblastoma?

Elevated cyclooxygenase-2 (COX-2) and the associated inflammation within the brain contribute to glioblastoma development. However, medical use of COX inhibitors in glioblastoma treatment has been limited due to their well-documented vascular toxicity and inconsistent outcomes from recent human studies. Prostaglandin E2 (PGE2) has emerged as a principal mediator for COX-2 cascade-driven gliomagenesis. Are PGE2 terminal synthases and receptors feasible therapeutic targets for glioblastoma?

Cyclooxygenase-2 in glioblastoma multiforme

Glioblastoma multiforme (GBM) represents the most prevalent brain primary tumor, yet there is a lack of effective treatment. With current therapies, fewer than 5% of patients with GBM survive more than 5 years after diagnosis. Mounting evidence from epidemiological studies reveals that the regular use of nonsteroidal anti-inflammatory drugs (NSAIDs) is correlated with reduced incidence of GBM, suggesting that cyclooxygenase-2 (COX-2) and its major product within the brain, prostaglandin E2 (PGE₂), are involved in the development and progression of GBM. Here, we highlight our current understanding of COX-2 in GBM proliferation, apoptosis, invasion, angiogenesis, and immunosuppression by focusing on recent in vitro and in vivo experimental data. We also discuss the feasibility of COX-2 as a therapeutic target for GBM in light of the latest human studies.

Prostaglandin E2 promotes proliferation of skeletal muscle myoblasts via EP4 receptor activation

We recently demonstrated that conditioned media (CM) from osteocytes enhances myogenic differentiation of myoblasts, suggesting that signaling from bone may be important for skeletal muscle myogenesis. The effect of CM was closely mimicked by prostaglandin E₂ (PGE₂), a bioactive lipid mediator in various physiological or pathological conditions. PGE₂ is secreted at high levels by osteocytes and such secretion is further enhanced under loading conditions. Although four types of receptors, EP1 to EP4, mediate PGE₂ signaling, it is unknown whether these receptors play a role in myogenesis. Therefore, in this study, the expression of EPs in mouse primary myoblasts was characterized, followed by examination of their roles in myoblast proliferation by treating myoblasts with PGE₂ or specific agonists. All four PGE₂ receptor mRNAs were detectable by quantitative real-time PCR (qPCR), but only PGE₂ and EP4 agonist CAY 10598 significantly enhance myoblast proliferation. EP1/EP3 agonist 17-phenyl trinor PGE₂ (17-PT PGE₂) and EP2 agonist butaprost did not have any significant effects. Moreover, treatment with EP4 antagonist L161,982 dose-dependently inhibited myoblast proliferation. These results were confirmed by cell cycle analysis and the gene expression of cell cycle regulators. Concomitant with the inhibition of myoblast proliferation, treatment with L161,982 significantly increased intracellular reactive oxygen species (ROS) levels. Cotreatment with antioxidant N-acetyl cysteine (NAC) or sodium ascorbate (SA) successfully reversed the inhibition of myoblast proliferation and ROS overproduction caused by L161,982. Therefore, PGE₂ signaling via the EP4 receptor regulates myogenesis by promoting myoblast proliferation and blocking this receptor results in increased ROS production in myoblasts.

Radiation-induced PGE2 sustains human glioma cells growth and survival through EGF signaling

Glioblastoma Multiforme (GBM) is the most common brain cancer in adults. Radiotherapy (RT) is the most effective post-operative treatment for the patients even though GBM is one of the most radio-resistant tumors. Dead or dying cells within the tumor are thought to promote resistance to treatment through mechanisms that are very poorly understood. We have evaluated the role of Prostaglandin E2 (PGE₂), a versatile bioactive lipid, in GBM radio-resistance. We used an in vitro approach using 3D primary cultures derived from representative GBM patients. We show that irradiated glioma cells produced and released PGE₂ in important quantities independently of the induction of cell death. We demonstrate that the addition of PGE₂ enhances cell survival and proliferation though its ability to trans-activate the Epithelial Growth Factor receptor (EGFR) and to activate β-catenin. Indeed, PGE₂ can substitute for EGF to promote primary cultures survival and growth in vitro and the effect is likely to occur though the Prostaglandin E2 receptor EP2.

Intracellular EP2 prostanoid receptor promotes cancer-related phenotypes in PC3 cells

Prostaglandin E2 (PGE2) and hypoxia-inducible factor-1α (HIF-1α) affect many mechanisms that have been involved in the pathogenesis of prostate cancer (PC). HIF-1α, which is up-regulated by PGE2 in LNCaP cells and PC3 cells, has been shown to contribute to metastasis and chemo-resistance of castrate-resistant PC (a lethal form of PC) and to promote in PC cells migration, invasion, angiogenesis and chemoresistance. The selective blockade of PGE2-EP2 signaling pathway in PC3 cells results in inhibition of cancer cell proliferation and invasion. PGE2 affects many mechanisms that have been shown to play a role in carcinogenesis such as proliferation, apoptosis, migration, invasion and angiogenesis. Recently, we have found in PC3 cells that most of these PGE2-induced cancer-related features are due to intracellular PGE2 (iPGE2). Here, we aimed to study in PC3 cells the role of iPGE2-intracellular EP2 (iEP2)-HIF-1α signaling in several events linked to PC progression using an experimental approach involving pharmacological inhibition of the prostaglandin uptake transporter and EGFR and pharmacological and genetic modulation of EP2 receptor and HIF-1α. We found that iPGE2 increases HIF-1α expression through iEP2-dependent EGFR transactivation and that inhibition of any of the axis iEP2-EGFR-HIF-1α in cells treated with PGE2 or EP2 agonist results in prevention of the increase in PC3 cell proliferation, adhesion, migration, invasion and angiogenesis in vitro. Of note, PGE2 induced EP2 antagonist-sensitive DNA synthesis in nuclei isolated from PC3 cells, which indicates that they have functional EP2 receptors. These results suggest that PGE2-EP2 dependent intracrine mechanisms involving EGFR and HIF-1α play a role in PC.

Targeting microsomal prostaglandin E2synthase-1 (mPGES-1): the development of inhibitors as an alternative to non-steroidal anti-inflammatory drugs (NSAIDs)

AA cascade and several key residues in the 3D structure of mPGES-1.

Vaccine therapies for patients with glioblastoma

Glioblastoma (GBM) is a high-grade glial tumor with an extremely aggressive clinical course and a median overall survival of only 14.6 months following maximum surgical resection and adjuvant chemoradiotherapy. A central feature of this disease is local and systemic immunosuppression, and defects in patient immune systems are closely associated with tumor progression. Immunotherapy has emerged as an important adjuvant in the therapeutic armamentarium of clinicians caring for patients with GBM. The fundamental aim of immunotherapy is to augment the host antitumor immune response. Active immunotherapy utilizes vaccines to stimulate adaptive immunity against tumor-associated antigens. A vast array of vaccine strategies have advanced from preclinical study to active clinical trials in patients with recurrent or newly diagnosed GBM, including those that employ peptides, heat shock proteins, autologous tumor cells, and dendritic cells. In this review, the rationale for glioma immunotherapy is outlined, and the prevailing forms of vaccine therapy are described.

Bioactive lipids and the control of Bax pro-apoptotic activity

Lipids are key regulators of cell physiology through the control of many aspects of cellular life and survival. In particular, lipids have been implicated at different levels and through many different mechanisms in the cell death program called apoptosis. Here, we discuss the action of lipids in the regulation of the activation and the integration of Bax into the mitochondrial outer membrane, a key pro-apoptotic member of the BCL-2 family. We describe how, during apoptosis, lipids can act simultaneously or in parallel as receptors or ligands for Bax to stimulate or inhibit its pro-death activity.

Prostaglandin E2 induces apoptosis in cultured rat microglia

Prostaglandin E2 (PGE2) plays a critical role in the modulation of microglial function including migration and phagocytosis through EP2, which increases intracellular cyclic adenosine monophosphate (AMP) concentration. In the present study, we found that PGE2 reduces cell viability in microglia. PGE2 decreased 3-(4,5-dimethylthiazol-2-thiazolyl)-2,5-diphenyltetrazolium bromide (MTT) reduction and increased lactate dehydrogenase release, deoxyribonucleic acid fragmentation, and poly(ADP-ribose) polymerase cleavage after 24h incubation, suggesting that PGE2 induces apoptosis in these cells. An EP2 agonist, butaprost, and an EP4 agonist, PGE1 alcohol, also induced apoptosis, while an EP1 agonist, 17-phenyl trinor PGE2, or an EP3 agonist, sulprostone, at 10(-6)M did not. On the other hand, EP1-EP4 antagonists, SC-51322, AH6809, L-798106, or GW627368X, up to 10(-5)M did not affect the decrease in MTT reduction by PGE2. Intracellular cyclic AMP accumulation was induced by butaprost, but not 17-phenyl trinor PGE2, sulprostone, or PGE1 alcohol at 10(-6)M. Additionally, we previously reported that PGE2-induced intracellular cyclic AMP accumulation was reversed by AH6809. Besides EP receptors, one of other targets was thought to be prostaglandin transporter, but its inhibitors, bromocresol green or U-46619 up to 10(-5)M did not affect the decrease in MTT reduction by PGE2. These results suggest that PGE2 induces apoptosis in microglia independent of intracellular cyclic AMP concentration, and there are different mechanisms between PGE2-induced apoptosis and the modulation of microglial function.

Exosomes as new vesicular lipid transporters involved in cell-cell communication and various pathophysiologies

Exosomes are nanovesicles that have emerged as a new intercellular communication system between an intracellular compartment of a donor cell towards the periphery or an internal compartment of a recipient cell. The bioactivity of exosomes resides not only in their protein and RNA contents but also in their lipidic molecules. Exosomes display original lipids organized in a bilayer membrane and along with the lipid carriers such as fatty acid binding proteins that they contain, exosomes transport bioactive lipids. Exosomes can vectorize lipids such as eicosanoids, fatty acids, and cholesterol, and their lipid composition can be modified by in-vitro manipulation. They also contain lipid related enzymes so that they can constitute an autonomous unit of production of various bioactive lipids. Exosomes can circulate between proximal or distal cells and their fate can be regulated in part by lipidic molecules. Compared to their parental cells, exosomes are enriched in cholesterol and sphingomyelin and their accumulation in cells might modulate recipient cell homeostasis. Exosome release from cells appears to be a general biological process. They have been reported in all biological fluids from which they can be recovered and can be monitors of specific pathophysiological situations. Thus, the lipid content of circulating exosomes could be useful biomarkers of lipid related diseases. Since the first lipid analysis of exosomes ten years ago detailed knowledge of exosomal lipids has accumulated. The role of lipids in exosome fate and bioactivity and how they constitute an additional lipid transport system are considered in this review.

Emerging concepts on the role of exosomes in lipid metabolic diseases

Dysregulation of lipid metabolism involves cellular communication mediated by cell contacts or exchange of bioactive lipids bound to soluble carriers or to lipoproteins. An increasing field is that of cellular communication mediated by nanovesicles called exosomes. Those vesicles are released from an internal compartment of viable cells, circulate in all biological fluids and can transfer material from cell-to-cells. Involvement of exosome trafficking in the transcellular metabolism of eicosanoids and cholesterol-related diseases including cancer is developed hereafter.

NADPH oxidase NOX5-S and nuclear factor κB1 mediate acid-induced microsomal prostaglandin E synthase-1 expression in Barrett's esophageal adenocarcinoma cells

The mechanisms of progression from Barrett's esophagus (BE) to esophageal adenocarcinoma (EA) are not known. Cycloxygenase-2 (COX-2)-derived prostaglandin E₂ (PGE₂) has been shown to be important in esophageal tumorigenesis. We have shown that COX-2 mediates acid-induced PGE₂ production. The prostaglandin E synthase (PGES) responsible for acid-induced PGE2 production in BE, however, is not known. We found that microsomal PGES1 (mPGES1), mPGES2, and cytosolic PGES (cPGES) were present in FLO EA cells. Pulsed acid treatment significantly increased mPGES1 mRNA and protein levels but had little or no effect on mPGES2 or cPGES mRNA. Knockdown of mPGES1 by mPGES1 small interfering RNA (siRNA) blocked acid-induced increase in PGE2 production and thymidine incorporation. Knockdown of NADPH oxidase, NOX5-S, a variant lacking calcium-binding domains, by NOX5 siRNA significantly inhibited acid-induced increase in mPGES1 expression, thymidine incorporation, and PGE2 production. Overexpression of NOX5-S significantly increased the luciferase activity in FLO cells transfected with a nuclear factor κB (NF-κB) in vivo activation reporter plasmid pNF-κB-Luc. Knockdown of NF-κB1 p50 by p50 siRNA significantly decreased acid-induced increase in mPGES1 expression, thymidine incorporation, and PGE₂ production. Two novel NF-κB binding elements, GGAGTCTCCC and CGGGACACCC, were identified in the mPGES1 gene promoter. We conclude that mPGES1 mediates acid-induced increase in PGE₂ production and cell proliferation. Acid-induced mPGES1 expression depends on activation of NOX5-S and NF-κB1 p50. Microsomal PGES1 may be a potential target to prevent or treat EA.

E series prostaglandins alter the proliferative, apoptotic and migratory properties of T98G human glioma cells in vitro

Background

In many types of cancer, prostaglandin E₂ (PGE₂) is associated with tumour related processes including proliferation, migration, angiogenesis and apoptosis. However in gliomas the role of this prostanoid is poorly understood. Here, we report on the proliferative, migratory, and apoptotic effects of PGE₁, PGE₂ and Ibuprofen (IBP) observed in the T98G human glioma cell line in vitro.

Methods

T98G human glioma cells were treated with IBP, PGE₁ or PGE₂ at varying concentrations for 24–72 hours. Cell proliferation, mitotic index and apoptotic index were determined for each treatment. Caspase-9 and caspase-3 activity was measured using fluorescent probes in live cells (FITC-LEHD-FMK and FITC-DEVD-FMK respectively). The migratory capacity of the cells was quantified using a scratch migration assay and a transwell migration assay.

Results

A significant decrease was seen in cell number (54%) in the presence of 50 μM IBP. Mitotic index and bromodeoxyuridine (BrdU) incorporation were also decreased 57% and 65%, respectively, by IBP. The apoptotic index was increased (167%) and the in situ activity of caspase-9 and caspase-3 was evident in IBP treated cells. The inhibition of COX activity by IBP also caused a significant inhibition of cell migration in the monolayer scratch assay (74%) and the transwell migration assay (36%).

In contrast, the presence of exogenous PGE₁ or PGE₂ caused significant increases in cell number (37% PGE₁ and 45% PGE₂). When mitotic index was measured no change was found for either PG treatment. However, the BrdU incorporation rate was significantly increased by PGE₁ (62%) and to a greater extent by PGE₂ (100%). The apoptotic index was unchanged by exogenous PGs. The addition of exogenous PGs caused an increase in cell migration in the monolayer scratch assay (43% PGE₁ and 44% PGE₂) and the transwell migration assay (28% PGE₁ and 68% PGE₂).

Conclusions

The present study demonstrated that treatments which alter PGE₁ and PGE₂ metabolism influence the proliferative and apoptotic indices of T98G glioma cells. The migratory capacity of the cells was also significantly affected by the change in prostaglandin metabolism. Modifying PG metabolism remains an interesting target for future studies in gliomas.

Inhibition of cyclooxygenase-2 enhances immunotherapy against experimental brain tumors

Glioblastoma multiforme is the most common and aggressive malignant brain tumor in humans, and the prognosis is very poor despite conventional therapy. Immunotherapy represents a novel treatment approach, but the effect is often weakened by release of immune-suppressive molecules such as prostaglandins. In the current study, we investigated the effect of immunotherapy with irradiated interferon-γ (IFN-γ)-secreting tumor cells and administration of the selective cyclooxygenase-2 (COX-2) inhibitor parecoxib as treatment of established rat brain tumors. COX-2 inhibition and immunotherapy significantly enhanced the long-term cure rate (81% survival) compared with immunotherapy alone (19% survival), and there was a significant increase in plasma IFN-γ levels in animals treated with the combined therapy, suggesting a systemic T helper 1 immune response. COX-2 inhibition alone, however, did neither induce cure nor prolonged survival. The tumor cells were identified as the major source of COX-2 both in vivo and in vitro, and unmodified tumor cells produced prostaglandin E(2) in vitro, while the IFN-γ expressing tumor cells secreted significantly lower levels. In conclusion, we show that immunotherapy of experimental brain tumors is greatly potentiated when combined with COX-2 inhibition. Based on our results, the clinically available drug parecoxib may be added to immunotherapy against human brain tumors. Furthermore, the discovery that IFN-γ plasma levels can be used to determine the ongoing in vivo immune response has translational potential.

Microsomal Prostaglandin E2 Synthase-1

The prostanoids and leukotrienes (LTs) formed from arachidonic acid (AA) via the cyclooxygenase (COX)-1/2 and 5-lipoxygenase (5-LO) pathway, respectively, mediate inflammatory responses, chronic tissue remodelling, cancer, asthma and autoimmune disorders, but also possess homeostatic functions in the gastrointestinal tract, uterus, brain, kidney, vasculature and host defence. Based on the manifold functions of these eicosanoids, the clinical use of non-steroidal anti-inflammatory drugs (NSAIDs), a class of drugs that block formation of all prostanoids, is hampered by severe side-effects including gastrointestinal injury, renal irritations and cardiovascular risks. Therefore, anti-inflammatory agents interfering with eicosanoid biosynthesis require a well-balanced pharmacological profile to minimize these on-target side-effects. Current anti-inflammatory research aims at identifying compounds that can suppress the massive formation of pro-inflammatory prostaglandin (PG)E2 without affecting homeostatic PGE2 and PGI2 synthesis. The inducible microsomal prostaglandin E2 synthase-1 (mPGES-1) is one promising target enzyme. We will give an overview about the structure, regulation and function of mPGES-1 and then present novel inhibitors of mPGES-1 that may possess a promising pharmacological profile.

Increase in intracellular PGE2 induces apoptosis in Bax-expressing colon cancer cell

BACKGROUND

NSAIDs exhibit protective properties towards some cancers, especially colon cancer. Yet, it is not clear how they play their protective role. PGE2 is generally shown as the only target of the NSAIDs anticancerous activity. However, PGE2 known targets become more and more manifold, considering both the molecular pathways involved and the target cells in the tumour. The role of PGE2 in tumour progression thus appears complex and multipurpose.

METHODS

To gain understanding into the role of PGE2 in colon cancer, we focused on the activity of PGE2 in apoptosis in colon cancer cell lines.

RESULTS

We observed that an increase in intracellular PGE2 induced an apoptotic cell death, which was dependent on the expression of the proapoptotic protein Bax. This increase was induced by increasing PGE2 intracellular concentration, either by PGE2 microinjection or by the pharmacological inhibition of PGE2 exportation and enzymatic degradation.

CONCLUSIONS

We present here a new sight onto PGE2 in colon cancer cells opening the way to a new prospective therapeutic strategy in cancer, alternative to NSAIDs.

Molecular alterations in glioblastoma: potential targets for immunotherapy

Glioblastoma is the most common and deadly brain tumor, possibly arising from genetic and epigenetic alterations in normal astroglial cells. Multiple cytogenetic, chromosomal, and genetic alterations have been identified in glioblastoma, with distinct expression of antigens (Ags) and biomarkers that may alter therapeutic potential of this aggressive cancer. Current therapy consists of surgical resection, followed by radiation therapy and chemotherapy. In spite of these treatments, the prognosis for glioblastoma patients is poor. Although recent studies have focused on the development of novel immunotherapeutics against glioblastoma, little is known about glioblastoma-specific immune responses. A better understanding of the molecular interactions among glioblastoma tumors, host immune cells, and the tumor microenvironment may give rise to novel integrated approaches for the simultaneous control of tumor escape pathways and the activation of antitumor immune responses. This review provides a detailed overview concerning genetic alterations in glioblastoma, their effects on Ag and biomarker expression, and the future design of chemoimmunotherapeutics against glioblastoma.

Prostaglandins antagonistically control Bax activation during apoptosis

The Bax protein (Bcl-2-associated X protein) is pivotal for the apoptotic process. Bax, which resides in an inactive form in the cytosol of healthy cells, is activated during the early stages of apoptosis and becomes associated with mitochondria through poorly understood mechanisms. In this study, we show that a family of bioactive lipids, namely prostaglandins, regulates Bax-dependent apoptosis. The prostaglandin E(2) (PGE(2)) or its derivative PGA(2) binds to Bax, induces its change of conformation, and thereby triggers apoptosis. A cysteine present in the loop between the two transmembrane α-helices of Bax, Cys126 is critical for its activation. PGD(2) inhibits PGE(2) binding to Bax and PGE(2)-induced apoptosis, as well as cell death induced by staurosporine and UV-B in various cell lines. This result is consistent with the fact that apoptosis is accompanied during these treatments by an increase in PGE(2). This process is distinct, yet cooperative, from that involving the BH3-only protein Bid. Our results establish that the PGE(2)/PGD(2) balance is involved in a new early mechanism of control in the activation of Bax during apoptosis.

Microsomal prostaglandin E synthase-1 and 5-lipoxygenase: potential drug targets in cancer

There is strong evidence for a role of prostaglandin (PG)E(2) in cancer cell proliferation and tumour development. In PGE(2) biosynthesis, cyclooxygenases (COX-1/2) convert arachidonic acid to PGH(2), which can be isomerized to PGE(2) by PGE synthases, including microsomal PGE synthase-1 (MPGES-1). Data describing genetic deletions of MPGES-1 are reviewed. The results suggest that MPGES-1 is an alternative therapeutic target for cancer cells and tumours that express this enzyme. Several compounds that target COX-2 or MPGES-1 also inhibit 5-lipoxygenase. This may be advantageous for treatment of some forms of cancer.

Comparative Analyses of Transcriptional Profiles in Mouse Organs Using a Pneumonic Plague Model after Infection with Wild-Type Yersinia pestis CO92 and Its Braun Lipoprotein Mutant

We employed Murine GeneChips to delineate the global transcriptional profiles of the livers, lungs, and spleens in a mouse pneumonic plague infection model with wild-type (WT) Y. pestis CO92 and its Braun lipoprotein (Δlpp) mutant with reduced virulence. These organs showed differential transcriptional responses to infection with WT Y. pestis, but the overall host functional processes affected were similar across all three tissues. Gene expression alterations were found in inflammation, cytokine signaling, and apoptotic cell death-associated genes. Comparison of WT and Δlpp mutant-infected mice indicated significant overlap in lipopolysaccharide- (LPS-) associated gene expression, but the absence of Lpp perturbed host cell signaling at critical regulatory junctions resulting in altered immune response and possibly host cell apoptosis. We generated a putative signaling pathway including major inflammatory components that could account for the synergistic action of LPS and Lpp and provided the mechanistic basis of attenuation caused by deletion of the lpp gene from Y. pestis in a mouse model of pneumonic plague.

Bax activation by the BH3-only protein Puma promotes cell dependence on antiapoptotic Bcl-2 family members

It is still unclear whether the BH3-only protein Puma (p53 up-regulated modulator of apoptosis) can prime cells to death and render antiapoptotic BH3-binding Bcl-2 homologues necessary for survival through its ability to directly interact with proapoptotic Bax and activate it. In this study, we provide further evidence, using cell-free assays, that the BH3 domain of Puma binds Bax at an activation site that comprises the first helix of Bax. We also show that, in yeast, Puma interacts with Bax and triggers its killing activity when Bcl-2 homologues are absent but not when Bcl-xL is expressed. Finally, endogenous Puma is involved in the apoptotic response of human colorectal cancer cells to the Bcl-2/Bcl-xL inhibitor ABT-737, even in conditions where the expression of Mcl-1 is down-regulated. Thus, Puma is competent to trigger Bax activity by itself, thereby promoting cellular dependence on prosurvival Bcl-2 family members.

Prostaglandin E2 synthases in neurologic homeostasis and disease

Prostaglandin E(2) synthases (PGES) currently comprise a group of three structurally and biologically distinct molecules. These enzymes are part of an important and complex paracrine signaling system involved in a wide range of biological processes. This review focuses on the normal physiological and pathological roles of these enzymes in the nervous system. Specific topics include the role of PGES(s) in fever and sickness behavior, inflammatory pain, and neural disease. Although the field is in its early stages, ongoing development of selective PGES inhibitors for possible use in people creates a significant need for more fully understanding the biological roles of these important enzymes.

Flow cytometry and in vitro analysis of human glioma-associated macrophages. Laboratory investigation

OBJECT

To date, glioma immunotherapy has been focused mostly on stimulating antitumor peripheral lymphocyte responses; however, some data suggest that microglia and/or macrophages (not lymphocytes) are the predominant inflammatory cells infiltrating gliomas. To study this hypothesis further, the authors analyzed inflammatory cell infiltrates in fresh human malignant glioma specimens and primary cultures.

METHODS

Single-cell suspensions from fresh operative malignant glioma specimens, obtained by stereotactic localization, were analyzed for CD11b and CD45 by using flow cytometry. A comparison was made with peripheral blood mononuclear cells. In a subset of patients, a more detailed flow cytometry analysis of Class I and II major histocompatibility complex, B7-1, B7-2, CD11c, and CD14 expression was performed. Macrophage-like cells in primary glioma cultures were similarly assessed.

RESULTS

Operative samples were obtained from 9 newly diagnosed malignant gliomas. The mean percent of CD45(+)/CD11b(-) cells (lymphocytes) was 2.48% (range 0.65-5.50%); CD45(dim)/CD11b(+) cells (microglia), 1.65% (range 0.37-3.92%); and CD45(bright)/CD11b+ (monocytes/macrophages), 6.25% (range 1.56-15.3%). More detailed fluorescence-activated cell sorting suggested that macrophage-like cells expressed Class I and II major histocompatibility complex, B7-2, and CD11c but not CD14 or B7-1. Primary human glioma cultures contained significant numbers of macrophage-like (CD45(bright)/CD11b(+)) cells, but these cells were lost with successive passages. These cells maintained the immunomarker profiles of macrophage-like cells from fresh specimens only if they were cultured in serum-free media.

CONCLUSIONS

The CD45(+)/CD11b(+) cells are the predominant inflammatory cell infiltrating human gliomas. Of this type, the CD45(bright)/CD11b(+) cells, a phenotype compatible with circulating macrophages in rodent models, and not microglia, are the most common. Their immunomarker profile is compatible with an immature antigen-presenting cell. They are present in primary glioma cultures but are lost in successive passages. Their role is enigmatic, and they may prove an important target for future glioma immunotherapy studies.

R(+)-methanandamide-induced apoptosis of human cervical carcinoma cells involves a cyclooxygenase-2-dependent pathway

PURPOSE

Cannabinoids have received renewed interest due to their antitumorigenic effects. Using human cervical carcinoma cells (HeLa), this study investigates the role of cyclooxygenase-2 (COX-2) in apoptosis elicited by the endocannabinoid analog R(+)-methanandamide (MA).

METHODS

COX-2 expression was assessed by RT-PCR and Western blotting. PGE2/PGD2 levels in cell culture supernatants and DNA fragmentation were measured by ELISA.

RESULTS

MA led to an induction of COX-2 expression, PGD2 and PGE2 synthesis. Cells were significantly less sensitive to MA-induced apoptosis when COX-2 was suppressed by siRNA or the selective COX-2 inhibitor NS-398. COX-2 expression and apoptosis by MA was also prevented by the ceramide synthase inhibitor fumonisin B1, but not by antagonists to cannabinoid receptors and TRPV1. In line with the established role of peroxisome proliferator-activated receptor gamma (PPARgamma) in the proapoptotic action of PGs of the D and J series, inhibition of MA-induced apoptosis was also achieved by siRNA targeting lipocalin-type PGD synthase (L-PGDS) or PPARgamma. A role of COX-2 and PPARgamma in MA-induced apoptosis was confirmed in another human cervical cancer cell line (C33A) and in human lung carcinoma cells (A549).

CONCLUSION

This study demonstrates COX-2 induction and synthesis of L-PGDS-derived, PPARgamma-activating PGs as a possible mechanism of apoptosis by MA.