Induction of a non-apoptotic mode of cell death associated with autophagic characteristics with steroidal maleic anhydrides and 7β-hydroxycholesterol on glioma cells

Dual perspective on autophagy in glioma: Detangling the dichotomous mechanisms of signaling pathways for therapeutic insights

Autophagy is a normal physiological process that aids the recycling of cellular nutrients, assisting the cells to cope with stressed conditions. However, autophagy's effect on cancer, including glioma, is uncertain and involves complicated molecular mechanisms. Several contradictory reports indicate that autophagy may promote or suppress glioma growth and progression. Autophagy inhibitors potentiate the efficacy of chemotherapy or radiation therapy in glioma. Numerous compounds stimulate autophagy to cause glioma cell death. Autophagy is also involved in the therapeutic resistance of glioma. This review article aims to detangle the complicated molecular mechanism of autophagy to provide a better perception of the two-sided role of autophagy in glioma and its therapeutic implications. The protein and epigenetic modulators of the cytoprotective and cytotoxic role of autophagy are described in this article. Moreover, several signaling pathways are associated with autophagy and its effects on glioma. We have reviewed the molecular pathways and highlighted the signaling axis involved in cytoprotective and cytotoxic autophagy. Additionally, this article discusses the role of autophagy in therapeutic resistance, including glioma stem cell maintenance and tumor microenvironment regulation. It also summarizes several investigations on the anti-glioma effects of autophagy modulators to understand the associated mechanisms and provide insights regarding its therapeutic implications.

Steroidal epoxides as anticancer agents in lung, prostate and breast cancers: The case of 1,2-epoxysteroids

Cancer continues to be a serious threat to human health worldwide. Lung, prostate and triple-negative breast cancers are amongst the most incident and deadliest cancers. Steroidal compounds are one of the most diversified therapeutic classes of compounds and they were proven to be efficient against several types of cancer. The epoxide function has been frequently associated with anticancer activity, particularly the 1,2-epoxide function. For this reason, three 1,2-epoxysteroid derivatives previously synthesised (EP1, EP2 and EP3) and one synthesised for the first time (oxysteride) were evaluated against H1299 (lung), PC3 (prostate) and HCC1806 (triple-negative breast) cancer cell lines. A human non-tumour cell line, MRC-5 (normal lung cell line) was also used. EP2 was the most active compound in all cell lines with IC50 values of 2.50, 3.67 and 1.95 µM, followed by EP3 with IC50 values of 12.65, 15.10 and 14.16 µM in H1299, PC3 and HCC1806 cells, respectively. Additional studies demonstrated that EP2 and EP3 induced cell death by apoptosis at lower doses and apoptosis/necrosis at higher doses, proving that their effects were dose-dependent. Both compounds also exerted their cytotoxicity by ROS production and by inducing double-strand breaks. Furthermore, EP2 and EP3 proved to be much less toxic against a normal lung cell line, MRC5, indicating that both compounds might be selective, and they also demonstrated suitable in silico ADME and toxicity parameters. Finally, none of the compounds induced haemoglobin release. Altogether, these results point out the extreme relevance of both compounds, especially EP2, in the potential treatment of these types of cancer.

Therapeutic Applications of Oxysterols and Derivatives in Age-Related Diseases, Infectious and Inflammatory Diseases, and Cancers

Oxysterols, resulting from the oxidation of cholesterol, are formed either by autoxidation, enzymatically, or by both processes. These molecules, which are provided in more or less important quantities depending on the type of diet, are also formed in the body and their presence is associated with a normal physiological activity. Their increase and decrease at the cellular level and in biological fluids can have significant consequences on health due or not to the interaction of some of these molecules with different types of receptors but also because oxysterols are involved in the regulation of RedOx balance, cytokinic and non-cytokinic inflammation, lipid metabolism, and induction of cell death. Currently, various pathologies such as age-related diseases, inflammatory and infectious diseases, and several cancers are associated with abnormal levels of oxysterols. Due to the important biological activities of oxysterols, their interaction with several receptors and their very likely implications in several diseases, this review focuses on these molecules and on oxysterol derivatives, which are often more efficient, in a therapeutic context. Currently, several oxysterol derivatives are developed and are attracting a lot of interest.

Cytoprotective activities of representative nutrients from the Mediterranean diet and of Mediterranean oils against 7-ketocholesterol- and 7β-hydroxycholesterol-induced cytotoxicity: Application to age-related diseases and civilization diseases

7-ketocholesterol and 7β-hydroxycholesterol are two oxysterols mainly formed by the autoxidation of cholesterol. These two molecules are interconvertible via specific enzymes. These two oxysterols are often observed at increased amounts in biological fluids as well as tissues and organs affected during age-related diseases and in diseases of civilization such as cardiovascular, neurodegenerative, and ocular diseases as well as type 2 diabetes and metabolic syndrome. Noteworthy, 7-ketocholesterol and 7β-hydroxycholesterol induce oxidative stress and inflammation, which are frequently observed in patients with age-related and civilization diseases. For this reason, the involvement of these two oxysterols in the pathophysiology of these diseases is widely suspected. In addition, the toxicity of these oxysterols can lead to death by oxiapoptophagy characterized by oxidative stress, apoptosis induction and autophagy criteria. To prevent, or even treat, certain age-related or civilization diseases associated with increased levels of 7-ketocholesterol and 7β-hydroxycholesterol, the identification of molecules or mixtures of molecules attenuating or inhibiting the toxic effects of these oxysterols allows to consider new treatments. In this context, many nutrients present in significant amounts in the Mediterranean diet, especially tocopherols, fatty acids, and polyphenols, have shown cytoprotective activities as well as several Mediterranean oils (argan and olive oils, milk thistle seed oil, and pistacia lentiscus seed oil). Consequently, a nutraceutical approach, rich in nutrients present in the Mediterranean diet, could thus make it possible to counteract certain age-related and civilization diseases associated with increased levels of 7-ketocholesterol and 7β-hydroxycholesterol.

Can oxysterols work in anti-glioblastoma therapy? Model studies complemented with biological experiments

Despite the progress made in recent years in the field of oncology, the results of glioblastoma treatment remain unsatisfactory. In this paper, cholesterol derivatives - oxysterols - have been investigated in the context of their anti-cancer activity. First, the influence of three oxysterols (7-K, 7β-OH and 25-OH), differing in their chemical structure, on the properties of a model membrane imitating glioblastoma multiforme (GBM) cells was investigated. For this purpose, the Langmuir monolayer technique was applied. The obtained results clearly show that oxysterols modify the structure of the membrane by its stiffening, with the 7-K effect being the most pronounced. Next, the influence of 7-K on the nanomechanical properties of glioblastoma cells (U-251 line) was verified with AFM. It has been shown that 7-K has a dose-dependent cytotoxic effect on glioblastoma cells leading to the induction of apoptosis as confirmed by viability tests. Interestingly, significant changes in membrane structure, characteristic for phospholipidosis, has also been observed. Based on our results we believe that oxysterol-induced apoptosis and phospholipidosis are related and may share common signaling pathways. Dysregulation of lipids in phospholipidosis inhibit cell proliferation and may play key roles in the induction of apoptosis by oxysterols. Moreover, anticancer activity of these compounds may be related to the immobilization of cancer cells as a result of stiffening effect caused by oxysterols. Therefore, we believe that oxysterols are good candidates as new therapeutic molecules as an alternative to the aggressive treatment of GBM currently in use.

Different functions of vitamin E homologues in the various types of cell death induced by oxysterols

24(S)-Hydroxycholesterol (24S-OHC) and 25-hydroxycholesterol (25-OHC) are produced by cholesterol 24-hydroxylase and cholesterol 25-hydroxylase, respectively. The purpose of the present study was to determine the type of cell death induced by these oxysterols in neuronal cells, hepatic cells, and keratinocytes, and to elucidate the inhibitory effect of vitamin E homologues on various types of cell death. In human neuronal cells (SH-SY5Y cells), 24S-OHC and 25-OHC caused a cell death that was independent of caspase activation. We reported previously that the esterification of 24S-OHC by acyl-CoA:cholesterol acyltransferase 1 (ACAT1) and the resulting formation of a lipid droplet (LD)-like structure are responsible for the 24S-OHC-induced neuronal cell death. Here, we found that 25-OHC also induced ACAT1-mediated 25-OHC esterification and LD formation in neuronal cells. 25-OHC-induced cell death was inhibited by α-tocopherol (α-Toc) but not by α-tocotrienol (α-Toc3), as observed for 24S-OHC-induced cell death in SH-SY5Y cells. In human hepatic cells (HepG2 cells), these oxysterols caused a cell death that was caspase- and oxysterol-esterification-independent. This cell death was suppressed by both α-Toc and α-Toc3, suggesting the involvement of free-radical-mediated lipid peroxidation in the cell death induced by these oxysterols in hepatic cells. In human keratinocytes (HaCaT cells), these oxysterols caused a caspase-dependent but oxysterol-esterification-independent cell death that was inhibited by α-Toc but not by α-Toc3. These results suggest that α-Toc and α-Toc3 act as radical-scavenging antioxidants against oxysterol-induced cell death in the same way in hepatic cells, whereas their behavior is different in inhibition of cell death in neuronal cells and keratinocytes. Collectively, these results demonstrated that 24S-OHC and 25-OHC induced the same type of cell death in each of the cell types examined, and that α-Toc and α-Toc3 exerted different effects, depending on the type of cell death.

Impact of Oxysterols on Cell Death, Proliferation, and Differentiation Induction: Current Status

Oxysterols are oxidized derivatives of cholesterol produced by enzymatic activity or non-enzymatic pathways (auto-oxidation). The oxidation processes lead to the synthesis of about 60 different oxysterols. Several oxysterols have physiological, pathophysiological, and pharmacological activities. The effects of oxysterols on cell death processes, especially apoptosis, autophagy, necrosis, and oxiapoptophagy, as well as their action on cell proliferation, are reviewed here. These effects, also observed in several cancer cell lines, could potentially be useful in cancer treatment. The effects of oxysterols on cell differentiation are also described. Among them, the properties of stimulating the osteogenic differentiation of mesenchymal stem cells while inhibiting adipogenic differentiation may be useful in regenerative medicine.

Attenuation of 7-ketocholesterol- and 7β-hydroxycholesterol-induced oxiapoptophagy by nutrients, synthetic molecules and oils: Potential for the prevention of age-related diseases

Age-related diseases for which there are no effective treatments include cardiovascular diseases; neurodegenerative diseases such as Alzheimer's disease; eye disorders such as cataract and age-related macular degeneration; and, more recently, Severe Acute Respiratory Syndrome (SARS-CoV-2). These diseases are associated with plasma and/or tissue increases in cholesterol derivatives mainly formed by auto-oxidation: 7-ketocholesterol, also known as 7-oxo-cholesterol, and 7β-hydroxycholesterol. The formation of these oxysterols can be considered as a consequence of mitochondrial and peroxisomal dysfunction, leading to increased in oxidative stress, which is accentuated with age. 7-ketocholesterol and 7β-hydroxycholesterol cause a specific form of cytotoxic activity defined as oxiapoptophagy, including oxidative stress and induction of death by apoptosis associated with autophagic criteria. Oxiaptophagy is associated with organelle dysfunction and in particular with mitochondrial and peroxisomal alterations involved in the induction of cell death and in the rupture of redox balance. As the criteria characterizing 7-ketocholesterol- and 7β-hydroxycholesterol-induced cytotoxicity are often simultaneously observed in major age-related diseases (cardiovascular diseases, age-related macular degeneration, Alzheimer's disease) the involvement of these oxysterols in the pathophysiology of the latter seems increasingly likely. It is therefore important to better understand the signalling pathways associated with the toxicity of 7-ketocholesterol and 7β-hydroxycholesterol in order to identify pharmacological targets, nutrients and synthetic molecules attenuating or inhibiting the cytotoxic activities of these oxysterols. Numerous natural cytoprotective compounds have been identified: vitamins, fatty acids, polyphenols, terpenes, vegetal pigments, antioxidants, mixtures of compounds (oils, plant extracts) and bacterial enzymes. However, few synthetic molecules are able to prevent 7-ketocholesterol- and/or 7β-hydroxycholesterol-induced cytotoxicity: dimethyl fumarate, monomethyl fumarate, the tyrosine kinase inhibitor AG126, memantine, simvastatine, Trolox, dimethylsufoxide, mangafodipir and mitochondrial permeability transition pore (MPTP) inhibitors. The effectiveness of these compounds, several of which are already in use in humans, makes it possible to consider using them for the treatment of certain age-related diseases associated with increased plasma and/or tissue levels of 7-ketocholesterol and/or 7β-hydroxycholesterol.

Hydromethanolic root and aerial part extracts from Echium arenarium Guss suppress proliferation and induce apoptosis of multiple myeloma cells through mitochondrial pathway

Echium arenarium Guss is a Mediterranean plant traditionally used in healing skin wound and it was reported exhibiting potent antioxidant, antibacterial, and antiparasitic activities. However, antitumoral activities of this plant have not yet been explored. Here we investigated for the first time, root (EARE) and aerial part (EAAPE) extracts of E. arenarium Guss to examine cytotoxicity and apoptosis activation pathway on U266 human multiple myeloma (MM) cell line. We demonstrated that EARE and EAAPE decreased U266 cell viability in a dose dependent manner. Based on 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, EARE was significantly two times more efficient (IC50 value 41 μg/ml) than EAAPE (IC50 value 82 μg/ml) considering 48 h of treatment. Furthermore, after 24 h of exposure to 100 μg/ml of EARE or EAAPE, cell cycle showed remarkable increase in sub-G1 population and a decrease of U266 cells proportion in G1 phase. In addition, EARE increased cell percentage in S phase. Moreover, analysis revealed that EAAPE or EARE induced apoptosis of U266 cells after 24 h of treatment. Interestingly, depolarization of mitochondrial membrane potential and activation of caspase 3/7 were demonstrated in treated U266 cells. Phytochemical analysis of E. arenarium extracts showed that EARE exhibited the highest content of total phenolic content. Interestingly, six phenolic compounds were identified. Myricitrin was the major compound in EARE, followed by luteolin 7-O-glucoside, resorcinol, polydatin, Trans-hydroxycinnamic acid, and hyperoside. These findings proved that an intrinsic mitochondria-mediated apoptosis pathway probably mediated the apoptotic effects of E. arenarium Guss extracts on U266 cells, and this will suggest several action plans to treat MM.

Apoptosis inducing properties of 3-biotinylate-6-benzimidazole B-nor-cholesterol analogues

In this work, a series of Biotin-substituted B-nor-cholesteryl benzimidazole compounds were synthesized. The antiproliferativeactivities of these compounds were evaluated in vitro using a series of human cancer cell lines, including HeLa (cervical cancer), SKOV3 (ovarian cancer), T-47D (thymus gland cancer), MCF-7 (human breast cancer) and HEK293T (normal renal epithelial) cells. These compounds displayed distinct antiproliferative activities against the currently tested cancer cells. The apoptotic properties induced by compound 6d were further investigated. Our results showed that compound 6d could induce the apoptosis of SKOV3 cells, blocking the cell growth in S-phase. Western blotting analyses revealed that compound 6d can induce cell apoptosis via the mitochondria-dependent pathway.

ROS-Triggered Autophagy Is Involved in PFOS-Induced Apoptosis of Human Embryo Liver L-02 Cells

The liver is the primary target organ for perfluorooctane sulphonate (PFOS), a recently discovered persistent organic pollutant. However, the mechanisms mediating hepatotoxicity remain unclear. Herein, we explored the relationship between reactive oxygen species (ROS) and autophagy and apoptosis induced by PFOS in L-02 cells, which are incubated with different concentrations of PFOS (0, 50, 100, 150, 200, or 250 μmol/L) for 24 or 48 hrs at 37°C. The results indicated that PFOS exposure decreased cell activities, enhanced ROS levels in a concentration-dependent manner, decreased mitochondrial membrane potential (MMP), and induced autophagy and apoptosis. Compared with the control, 200 μmol/L PFOS increased ROS levels; enhanced the expression of Bax, cleaved-caspase-3, and LC3-II; induced autophagy; decreased MMP; and lowered Bcl-2, p62, and Bcl-2/Bax ratio. The antioxidant N-acetyl cysteine (NAC) protected MMP against PFOS-induced changes and diminished apoptosis and autophagy. Compared with 200 μmol/L PFOS treatment, NAC pretreatment reversed the increase in ROS, Bax, and cleaved-caspase-3 protein caused by PFOS, lowered the apoptosis rate increased by PFOS, and increased the levels of MMP and Bcl-2/Bax ratio decreased by PFOS. The autophagy inhibitor 3-methyladenine and chloroquine decreased apoptosis and cleaved-caspase-3 protein level and increased the Bcl-2/Bax ratio. In summary, our results suggest that ROS-triggered autophagy is involved in PFOS-induced apoptosis in L-02 cells.

New 3β-hydroxysteroid-indolamine conjugates: Design, synthesis and inhibition of C6 glioma cell proliferation

Four novel indole steroids based on dehydroepiandrosterone (IS-1), estrone (IS-2) and pregnenolone (IS-3) were obtained and studied for their ability to inhibit C6 glioma proliferation. A reduction in cell proliferation by 52 ± 13% was observed for IS-1 at 10 μM, whereas IS-3 and abiraterone acetate at 10 μM caused a 36 ± 8% decrease. Surprisingly, the cellular effects reported for abiraterone, namely, cytochrome P450 CYP17A1 inhibition and endoplasmic reticulum stress were not detected for IS-1. However, both abiraterone and IS-1 significantly increased glutathione levels. Docking studies predicted good affinity of IS-1 to liver X receptors and regulatory protein Keap1, which are proposed to be involved in the compounds' antiproliferative activity.

Prevention by Dietary Polyphenols (Resveratrol, Quercetin, Apigenin) Against 7-Ketocholesterol-Induced Oxiapoptophagy in Neuronal N2a Cells: Potential Interest for the Treatment of Neurodegenerative and Age-Related Diseases

The Mediterranean diet is associated with health benefits due to bioactive compounds such as polyphenols. The biological activities of three polyphenols (quercetin (QCT), resveratrol (RSV), apigenin (API)) were evaluated in mouse neuronal N2a cells in the presence of 7-ketocholesterol (7KC), a major cholesterol oxidation product increased in patients with age-related diseases, including neurodegenerative disorders. In N2a cells, 7KC (50 µM; 48 h) induces cytotoxic effects characterized by an induction of cell death. When associated with RSV, QCT and API (3.125; 6.25 µM), 7KC-induced toxicity was reduced. The ability of QCT, RSV and API to prevent 7KC-induced oxidative stress was characterized by a decrease in reactive oxygen species (ROS) production in whole cells and at the mitochondrial level; by an attenuation of the increase in the level and activity of catalase; by attenuating the decrease in the expression, level and activity of glutathione peroxidase 1 (GPx1); by normalizing the expression, level and activity of superoxide dismutases 1 and 2 (SOD1, SOD2); and by reducing the decrease in the expression of nuclear erythroid 2-like factor 2 (Nrf2) which regulates antioxidant genes. QCT, RSV and API also prevented mitochondrial dysfunction in 7KC-treated cells by counteracting the loss of mitochondrial membrane potential (ΨΔm) and attenuating the decreased gene expression and/or protein level of AMP-activated protein kinase α (AMPKα), sirtuin 1 (SIRT1) and peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) implicated in mitochondrial biogenesis. At the peroxisomal level, QCT, RSV and API prevented the impact of 7KC by counteracting the decrease in ATP binding cassette subfamily D member (ABCD)3 (a peroxisomal mass marker) at the protein and mRNA levels, as well as the decreased expresssion of genes associated with peroxisomal biogenesis (Pex13, Pex14) and peroxisomal β-oxidation (Abcd1, Acox1, Mfp2, Thiolase A). The 7KC-induced decrease in ABCD1 and multifunctional enzyme type 2 (MFP2), two proteins involved in peroxisomal β-oxidation, was also attenuated by RSV, QCT and API. 7KC-induced cell death, which has characteristics of apoptosis (cells with fragmented and/or condensed nuclei; cleaved caspase-3; Poly(ADP-ribose) polymerase (PARP) fragmentation) and autophagy (cells with monodansyl cadaverine positive vacuoles; activation of microtubule associated protein 1 light chain 3–I (LC3-I) to LC3-II, was also strongly attenuated by RSV, QCT and API. Thus, in N2a cells, 7KC induces a mode of cell death by oxiapoptophagy, including criteria of OXIdative stress, APOPTOsis and autoPHAGY, associated with mitochondrial and peroxisomal dysfunction, which is counteracted by RSV, QCT, and API reinforcing the interest for these polyphenols in prevention of diseases associated with increased 7KC levels.

7-Ketocholesterol- and 7β-Hydroxycholesterol-Induced Peroxisomal Disorders in Glial, Microglial and Neuronal Cells: Potential Role in Neurodegeneration : 7-ketocholesterol and 7β-hydroxycholesterol-Induced Peroxisomal Disorders and Neurodegeneration

Peroxisomopathies are qualitative or quantitative deficiencies in peroxisomes which lead to increases in the level of very-long-chain fatty acids (VLCFA) and can be associated with more or less pronounced dysfunction of central nervous system cells: glial and microglial cells. Currently, in frequent neurodegenerative diseases, Alzheimer's disease (AD) and multiple sclerosis (MS), peroxisomal dysfunction is also suspected due to an increase in VLCFA, which can be associated with a decrease of plasmalogens, in these patients. Moreover, in patients suffering from peroxisomopathies, such as X-linked adrenoleukodystrophy (X-ALD), AD, or MS, the increase in oxidative stress observed leads to the formation of cytotoxic oxysterols: 7-ketocholesterol (7KC) and 7β-hydroxycholesterol (7β-OHC). These observations led to the demonstration that 7KC and 7β-OHC alter the biogenesis and activity of peroxisomes in glial and microglial cells. In X-ALD, AD, and MS, it is suggested that 7KC and 7β-OHC affecting the peroxisome, and which also induce mitochondrial dysfunctions, oxidative stress, and inflammation, could promote neurodegeneration. Consequently, the study of oxisome in peroxisomopathies, AD and MS, could help to better understand the pathophysiology of these diseases to identify therapeutic targets for effective treatments.