Vitamin C deficient reduces proliferation in a human periventricular tumor stem cell-derived glioblastoma model

Bioactive compounds from Actinidia arguta fruit as a new strategy to fight glioblastoma

In recent years, there has been a significant demand for natural products as a mean of disease prevention or as an alternative to conventional medications. The driving force for this change is the growing recognition of the abundant presence of valuable bioactive compounds in natural products. On recent years Actinia arguta fruit, also known as kiwiberry, has attracted a lot of attention from scientific community due to its richness in bioactive compounds, including phenolic compounds, organic acids, vitamins, carotenoids and fiber. These bioactive compounds contribute to the fruit's diverse outstanding biological activities such as antioxidant, anti-inflammatory, neuroprotective, immunomodulatory, and anti-cancer properties. Due to these properties, the fruit may have the potential to be used in the treatment/prevention of various types of cancer, including glioblastoma. Glioblastoma is the most aggressive form of brain cancer, displaying 90 % of recurrence rate within a span of 2 years. Despite the employment of an aggressive approach, the prognosis remains unfavorable, emphasizing the urgent requirement for the development of new effective treatments. The preclinical evidence suggests that kiwiberry has potential impact on glioblastoma by reducing the cancer self-renewal, modulating the signaling pathways involved in the regulation of the cell phenotype and metabolism, and influencing the consolidation of the tumor microenvironment. Even though, challenges such as the imprecise composition and concentration of bioactive compounds, and its low bioavailability after oral administration may be drawbacks to the development of kiwiberry-based treatments, being urgent to ensure the safety and efficacy of kiwiberry for the prevention and treatment of glioblastoma. This review aims to highlight the potential impact of A. arguta bioactive compounds on glioblastoma, providing novel insights into their applicability as complementary or alternative therapies.

Mitoepigenetics and gliomas: epigenetic alterations to mitochondrial DNA and nuclear DNA alter mtDNA expression and contribute to glioma pathogenicity

Epigenetic mechanisms allow cells to fine-tune gene expression in response to environmental stimuli. For decades, it has been known that mitochondria have genetic material. Still, only recently have studies shown that epigenetic factors regulate mitochondrial DNA (mtDNA) gene expression. Mitochondria regulate cellular proliferation, apoptosis, and energy metabolism, all critical areas of dysfunction in gliomas. Methylation of mtDNA, alterations in mtDNA packaging via mitochondrial transcription factor A (TFAM), and regulation of mtDNA transcription via the micro-RNAs (mir 23-b) and long noncoding RNAs [RNA mitochondrial RNA processing (RMRP)] have all been identified as contributing to glioma pathogenicity. Developing new interventions interfering with these pathways may improve glioma therapy.

Relevant Membrane Transport Proteins as Possible Gatekeepers for Effective Pharmacological Ascorbate Treatment in Cancer

Despite the increasing number of newly diagnosed malignancies worldwide, therapeutic options for some tumor diseases are unfortunately still limited. Interestingly, preclinical but also some clinical data suggest that the administration of pharmacological ascorbate seems to respond well, especially in some aggressively growing tumor entities. The membrane transport and channel proteins are highly relevant for the use of pharmacological ascorbate in cancer therapy and are involved in the transfer of active substances such as ascorbate, hydrogen peroxide, and iron that predominantly must enter malignant cells to induce antiproliferative effects and especially ferroptosis. In this review, the relevant conveying proteins from cellular surfaces are presented as an integral part of the efficacy of pharmacological ascorbate, considering the already known genetic and functional features in tumor tissues. Accordingly, candidates for diagnostic markers and therapeutic targets are mentioned.

Vitamin C Deficiency Reduces Neurogenesis and Proliferation in the SVZ and Lateral Ventricle Extensions of the Young Guinea Pig Brain

Although scurvy, the severe form of vitamin C deficiency, has been almost eradicated, the prevalence of subclinical vitamin C deficiency is much higher than previously estimated and its impact on human health might not be fully understood. Vitamin C is an essential molecule, especially in the central nervous system where it performs numerous, varied and critical functions, including modulation of neurogenesis and neuronal differentiation. Although it was originally considered to occur only in the embryonic brain, it is now widely accepted that neurogenesis also takes place in the adult brain. The subventricular zone (SVZ) is the neurogenic niche where the largest number of new neurons are born; however, the effect of vitamin C deficiency on neurogenesis in this key region of the adult brain is unknown. Therefore, through BrdU labeling, immunohistochemistry, confocal microscopy and transmission electron microscopy, we analyzed the proliferation and cellular composition of the SVZ and the lateral ventricle (LVE) of adult guinea pigs exposed to a vitamin-C-deficient diet for 14 and 21 days. We found that neuroblasts in the SVZ and LVE were progressively and significantly decreased as the days under vitamin C deficiency elapsed. The neuroblasts in the SVZ and LVE decreased by about 50% in animals with 21 days of deficiency; this was correlated with a reduction in BrdU positive cells in the SVZ and LVE. In addition, the reduction in neuroblasts was not restricted to a particular rostro–caudal area, but was observed throughout the LVE. We also found that vitamin C deficiency altered cellular morphology at the ultrastructural level, especially the cellular and nuclear morphology of ependymal cells of the LVE. Therefore, vitamin C is essential for the maintenance of the SVZ cell populations required for normal activity of the SVZ neurogenic niche in the adult guinea pig brain. Based on our results from the guinea pig brain, we postulate that vitamin C deficiency could also affect neurogenesis in the human brain.

Glioblastoma Invasiveness and Collagen Secretion Are Enhanced by Vitamin C

Aims: Glioblastoma (GB) is one of the most aggressive brain tumors. These tumors modify their metabolism, increasing the expression of glucose transporters, GLUTs, which incorporate glucose and the oxidized form of vitamin C, dehydroascorbic acid (DHA). We hypothesized that GB cells preferentially take up DHA, which is intracellularly reduced and compartmentalized into the endoplasmic reticulum (ER), promoting collagen biosynthesis and an aggressive phenotype. Results: Our results showed that GB cells take up DHA using GLUT1, while GLUT3 and sodium-dependent vitamin C transporter 2 (SVCT2) are preferably intracellular. Using a baculoviral system and reticulum-enriched extracts, we determined that SVCT2 is mainly located in the ER and corresponds to a short isoform. Ascorbic acid (AA) was compartmentalized, stimulating collagen IV secretion and increasing in vitro and in situ cell migration. Finally, orthotopic xenografts induced in immunocompetent guinea pigs showed that vitamin C deficiency retained collagen, reduced blood vessel invasion, and affected glomeruloid vasculature formation, all pathological conditions associated with malignancy. Innovation and Conclusion: We propose a functional role for vitamin C in GB development and progression. Vitamin C is incorporated into the ER of GB cells, where it favors the synthesis of collagen, thus impacting tumor development. Collagen secreted by tumor cells favors the formation of the glomeruloid vasculature and enhances perivascular invasion. Antioxid. Redox Signal. 37, 538-559.

Pharmacological targets for the induction of ferroptosis: Focus on Neuroblastoma and Glioblastoma

Neuroblastomas are the main extracranial tumors that affect children, while glioblastomas are the most lethal brain tumors, with a median survival time of less than 12 months, and the prognosis of these tumors is poor due to multidrug resistance. Thus, the development of new therapies for the treatment of these types of tumors is urgently needed. In this context, a new type of cell death with strong antitumor potential, called ferroptosis, has recently been described. Ferroptosis is molecularly, morphologically and biochemically different from the other types of cell death described to date because it continues in the absence of classical effectors of apoptosis and does not require the necroptotic machinery. In contrast, ferroptosis has been defined as an iron-dependent form of cell death that is inhibited by glutathione peroxidase 4 (GPX4) activity. Interestingly, ferroptosis can be induced pharmacologically, with potential antitumor activity in vivo and eventual application prospects in translational medicine. Here, we summarize the main pathways of pharmacological ferroptosis induction in tumor cells known to date, along with the limitations of, perspectives on and possible applications of this in the treatment of these tumors.

Iron Transporters and Ferroptosis in Malignant Brain Tumors

Malignant brain tumors represent approximately 1.5% of all malignant tumors. The survival rate among patients is relatively low and the mortality rate of pediatric brain tumors ranks first among all childhood malignant tumors. At present malignant brain tumors remain incurable. Although some tumors can be treated with surgery and chemotherapy, new treatment strategies are urgent owing to the poor clinical prognosis. Iron is an essential trace element in many biological processes of the human body. Iron transporters play a crucial role in iron absorption and transport. Ferroptosis, an iron-dependent form of nonapoptotic cell death, is characterized by the accumulation of lipid peroxidation products and lethal reactive oxygen species (ROS) derived from iron metabolism. Recently, compelling evidence has shown that inducing ferroptosis of tumor cells is a potential therapeutic strategy. In this review, we will briefly describe the significant regulatory factors of ferroptosis, iron, its absorption and transport under physiological conditions, especially the function of iron transporters. Then we will summarize the relevant mechanisms of ferroptosis and its role in malignant brain tumors, wherein the role of transporters is not to be ignored. Finally, we will introduce the current research progress in the treatment of malignant brain tumors by inducing ferroptosis in order to explain the current biological principles of potential treatment targets and treatment strategies for malignant brain tumors.

SVCT2 Overexpression and Ascorbic Acid Uptake Increase Cortical Neuron Differentiation, Which Is Dependent on Vitamin C Recycling between Neurons and Astrocytes

During brain development, sodium–vitamin C transporter (SVCT2) has been detected primarily in radial glial cells in situ, with low-to-absent expression in cerebral cortex neuroblasts. However, strong SVCT2 expression is observed during the first postnatal days, resulting in increased intracellular concentration of vitamin C. Hippocampal neurons isolated from SVCT2 knockout mice showed shorter neurites and low clustering of glutamate receptors. Other studies have shown that vitamin C-deprived guinea pigs have reduced spatial memory, suggesting that ascorbic acid (AA) and SVCT2 have important roles in postnatal neuronal differentiation and neurite formation. In this study, SVCT2 lentiviral overexpression induced branching and increased synaptic proteins expression in primary cultures of cortical neurons. Analysis in neuroblastoma 2a (Neuro2a) and human subventricular tumor C3 (HSVT-C3) cells showed similar branching results. SVCT2 was mainly observed in the cell membrane and endoplasmic reticulum; however, it was not detected in the mitochondria. Cellular branching in neuronal cells and in a previously standardized neurosphere assay is dependent on the recycling of vitamin C or reduction in dehydroascorbic acid (DHA, produced by neurons) by glial cells. The effect of WZB117, a selective glucose/DHA transporter 1 (GLUT1) inhibitor expressed in glial cells, was also studied. By inhibiting GLUT1 glial cells, a loss of branching is observed in vitro, which is reproduced in the cerebral cortex in situ. We concluded that vitamin C recycling between neurons and astrocyte-like cells is fundamental to maintain neuronal differentiation in vitro and in vivo. The recycling activity begins at the cerebral postnatal cortex when neurons increase SVCT2 expression and concomitantly, GLUT1 is expressed in glial cells.