Theofanis Vavilis

Researching glutamate – induced cytotoxicity in different cell lines: a comparative/collective analysis/study

Although glutamate is one of the most important excitatory neurotransmitters of the central nervous system, its excessive extracellular concentration leads to uncontrolled continuous depolarization of neurons, a toxic process called, excitotoxicity. In excitotoxicity glutamate triggers the rise of intracellular Ca2+ levels, followed by up regulation of nNOS, dysfunction of mitochondria, ROS production, ER stress, and release of lysosomal enzymes. Excessive calcium concentration is the key mediator of glutamate toxicity through over activation of ionotropic and metabotropic receptors. In addition, glutamate accumulation can also inhibit cystine (CySS) uptake by reversing the action of the CySS/glutamate antiporter. Reversal of the antiporter action reinforces the aforementioned events by depleting neurons of cysteine and eventually glutathione’s reducing potential. Various cell lines have been employed in the pursuit to understand the mechanism(s) by which excitotoxicity affects the cells leading them ultimately to their demise. In some cell lines glutamate toxicity is exerted mainly through over activation of NMDA, AMPA, or kainate receptors whereas in other cell lines lacking such receptors, the toxicity is due to glutamate induced oxidative stress. However, in the greatest majority of the cell lines ionotropic glutamate receptors are present, co-existing to CySS/glutamate antiporters and metabotropic glutamate receptors, supporting the assumption that excitotoxicity effect in these cells is accumulative. Different cell lines differ in their responses when exposed to glutamate. In this review article the responses of PC12, SH-SY5Y, HT-22, NT-2, OLCs, C6, primary rat cortical neurons, RGC-5, and SCN2.2 cell systems are systematically collected and analyzed.

Oxygen–Glucose Deprivation (OGD) Modulates the Unfolded Protein Response (UPR) and Inflicts Autophagy in a PC12 Hypoxia Cell Line Model

Hypoxia is the lack of sufficient oxygenation of tissue, imposing severe stress upon cells. It is a major feature of many pathological conditions such as stroke, traumatic brain injury, cerebral hemorrhage, perinatal asphyxia and can lead to cell death due to energy depletion and increased free radical generation. The present study investigates the effect of hypoxia on the unfolded protein response of the cell (UPR), utilizing a 16-h oxygen–glucose deprivation protocol (OGD) in a PC12 cell line model. Expression of glucose-regulated protein 78 (GRP78) and glucose-regulated protein 94 (GRP94), key players of the UPR, was studied along with the expression of glucose-regulated protein 75 (GRP75), heat shock cognate 70 (HSC70), and glyceraldehyde 3-phosphate dehydrogenase, all with respect to the cell death mechanism(s). Cells subjected to OGD displayed upregulation of GRP78 and GRP94 and concurrent downregulation of GRP75. These findings were accompanied with minimal apoptotic cell death and induction of autophagy. The above observation warrants further investigation to elucidate whether autophagy acts as a pro-survival mechanism that upon severe and prolonged hypoxia acts as a concerted cell response leading to cell death. In our OGD model, hypoxia modulates UPR and induces autophagy.

Low dose administration of glutamate triggers a non-apoptotic, autophagic response in PC12 cells

Background/Aims: Increasing amounts of the neurotransmitter glutamate are associated with excitotoxicity, a phenomenon related both to homeostatic processes and neurodegenerative diseases such as multiple sclerosis. Methods: PC12 cells (rat pheochromocytoma) were treated with various concentrations of the non-essential amino acid glutamate for 0.5-24 hours. The effect of glutamate on cell morphology was monitored with electron microscopy and haematoxylin-eosin staining. Cell survival was calculated with the MTT assay. Expression analysis of chaperones associated with the observed phenotype was performed using either Western Blotting at the protein level or qRT-PCR at the mRNA level. Results: Administration of glutamate in PC12 cells in doses as low as 10 μM causes an up-regulation of GRP78, GRP94 and HSC70 protein levels, while their mRNA levels show the opposite kinetics. At the same time, GAPDH and GRP75 show reduced protein levels, irrespective of their transcriptional rate. On a cellular level, low concentrations of glutamate induce an autophagy-mediated pro-survival phenotype, which is further supported by induction of the autophagic marker LC3. Conclusion: The findings in the present study underline a discrete effect of glutamate on neuronal cell fate depending on its concentration. It was also shown that a low dose of glutamate orchestrates a unique expression signature of various chaperones and induces cell autophagy, which acts in a neuroprotective fashion.

Calpain-Dependent Death in C6 Rat Glioma Cells, Exhibiting a Synergistic Effect with Temozolomide

Abstract Crocus sativus L., a dietary herb, has been used for various diseases including cancer. This is an in vitro study investigating the antineoplastic effect of the extract of the plant against C6 glioma rat cell line. The mechanism of cellular death and the synergistic effect of the extract with the alkylating agent temozolomide (TMZ) were investigated. Cellular viability was examined in various concentrations of the extract alone or in combination with TMZ. Apoptosis was determined with flow cytometry and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) and autophagy by western blotting of the light chain 3 (LC3)-II. Cellular viability was reduced after exposure to the extract with half maximal inhibition concentration at 3 mg/ml. Flow cytometry and TUNEL assay suggested that the extract does not induce apoptosis. Moreover, their combination increased the ratio dead/apoptotic cells 10-fold (P < 0.001). LC3-II protein levels reduced after Crocus extract while this effect was reversed when the calpain inhibitor MDL28170 was added, suggesting a calpain-dependent death possibly through autophagy. We concluded that the extract of Crocus increases dead cell number after 48 h of exposure. Our results suggest that the cell undergoes calpain-dependent programmed cell death while co-exposure to Crocus extract and TMZ enhances the antineoplastic effect of the latter.

Comorbid presentation of syringomyelia and Guillain-Barre syndrome, attributed to mycoplasma, in a 6-year-old female patient

Syringomyelia is the development of a fluid-filled cavity or syrinx within the spinal cord that can cause loss of sensation and muscle spasticity. Guillain-Barre syndrome (GBS) is a postinfection autoimmune disease, classified as an acute polyneuropathy. This report describes the emergency admission of a 6-year-old girl presenting with sudden pallor and pain in both lower limbs. The patient’s reflexes were normal, as were the results of her sonography, radiography and biochemical tests; however, spinal MRI revealed extensive compartmentalised syringomyelia extending from C2 to T3. A sensory and motor nerve conduction study revealed a demyelinating type motor polyneuropathy which, along with positive Mycoplasma pneumoniae test, was suggestive of GBS. Intravenous immunoglobulin infusion showed excellent results. In conclusion, we report a rare paediatric case of syringomyelia coexisting with GBS. It is important to bear in mind the possibility of other coexisting diseases even if MRI reveals definitive characteristics of another condition.