Endoplasmic Reticulum Stress Differently Modulates the Release of IL-6 and IL-8 Cytokines in Human Glial Cells.

Endoplasmic reticulum (ER) stress is a significant player in the pathophysiology of various neurodegenerative and neuropsychiatric disorders. Despite the established link between ER stress and inflammatory pathways, there remains a need for deeper exploration of the specific cellular mechanisms underlying ER stress-mediated neuroinflammation. This study aimed to investigate how the severity of ER stress (triggered by different concentrations of tunicamycin) can impact the release of proinflammatory cytokines IL-6 and IL-8 from astrocytes and microglia, comparing the effects with those induced by well-known immunostimulants-tumor necrosis factor alpha (TNF-α) or lipopolysaccharide (LPS). Mild ER stress has a distinct effect on the cytokine release compared to more intense stress levels, i.e., diminished IL-6 production was accompanied by an increase in IL-8 level, which was significantly more pronounced in astrocytes than in microglia. On the contrary, prolonged or more severe ER stress induced inflammation in glial cells, leading to a time- and concentration-dependent buildup of proinflammatory IL-6, but unlike inflammatory agents, an ER stress inducer diminished IL-8 secretions by glial cells. The differences could hold importance in identifying ER stress markers as potential drug targets for the treatment of neurodegenerative diseases or mood disorders, yet this requires confirmation in more complex animal studies.

PPARγ, NF-κB and the UPR pathway as new molecular targets in the anti-inflammatory actions of NSAIDs: Novel applications in cancers and central nervous system diseases?

Non-steroidal anti-inflammatory drugs (NSAIDs) such as aspirin, diclofenac, ibuprofen, or celecoxib have a well-established and unquestionable role in the human therapeutic arsenal, but still new perspectives are being discovered. This review presents new anti-inflammatory mechanisms of NSAIDs action, other than the classical one, i.e., the inhibition of cyclooxygenase (COX) isoforms leading to the prostanoids synthesis blockage. Literature data show that this group of drugs can activate anti-inflammatory peroxisome proliferator-activated receptor gamma (PPARγ), inhibit pro-inflammatory nuclear factor-κB (NF-κB) activation or modulate the components of the unfolded protein response (UPR) pathway. These alternative pathways induced by NSAIDs may not only enhance their basic anti-inflammatory mechanism of action but also promote other effects of the drugs such as anti-cancer. It was also proved that neuroinflammation, with the involvement of NF-κB, PPARγ and the components of the UPR pathway has an essential impact on the development of central nervous system (CNS) diseases. Thus, it seems possible that these new molecular targets may expand the use of NSAIDs, e.g., in the treatment of cancers and/or CNS disorders.

Ketamine - A New Antidepressant Drug with Anti-Inflammatory Properties.

Ketamine is a new, potent and rapid-acting antidepressant approved for therapy of treatment-resistant depression, which has a different mechanism of action than currently-available antidepressant therapies. It owes its uniquely potent antidepressant properties to a complex mechanism of action, which currently remains unclear. However, it is thought that it acts by modulating the functioning of the glutamatergic system, which plays an important role in the process of neuroplasticity associated with depression. However, preclinical and clinical studies have also found ketamine to reduce inflammation, either directly or indirectly (by activating neuroprotective branches of the kynurenine pathway), among patients exhibiting higher levels of inflammation. Inflammation and immune system activation are believed to play key roles in the development and course of depression. Therefore, the present work examines the role of the antidepressant effect of ketamine and its anti-inflammatory properties in the treatment of depression. SIGNIFICANCE STATEMENT: The present work examines the relationship between the antidepressant effect of ketamine and its anti-inflammatory properties, and the resulting benefits in treatment-resistant depression (TRD). The antidepressant mechanism of ketamine remains unclear, and there is an urgent need to develop new therapeutic strategies for treatment of depression, particularly TRD.

Antidepressant mechanisms of ketamine's action: NF-κB in the spotlight.

Ketamine recently approved for therapy of treatment-resistant depression shows a complex and not fully understood mechanism of action. Apart from its classical glutamatergic N-methyl-D-aspartate receptor antagonistic action, it is thought that anti-inflammatory properties of the drug are of clinical relevance due to the contribution of activated inflammatory mediators to the pathophysiology of depression and non-responsiveness of a group of patients to current antidepressant therapies. In a search of the mechanism underlying anti-inflammatory effects of ketamine, the nuclear factor kappa B transcription factor (NF-κB) has been proposed as a target for ketamine. The NF-κB forms precisely regulated protein signaling cascades enabling a rapid response to cellular stimuli. In the central nervous systems, NF-κB signaling appears to have pleiotropic but double-edged functions: on the one hand it participates in the regulation of processes that are crucial in the treatment of depression, such as neuroplasticity, neurogenesis or neuronal survival, on the other - in the activation of neuroinflammation and cell death. Ketamine has been found to reduce inflammation mediated by NF-κB, leading to decreased level of pro-inflammatory cytokines and other inflammatory or stress mediators. Therefore, this review presents recent data on the significance of the NF-κB cascade in the mechanism of ketamine's action and its future perspectives in designing new strategies for the treatment of depression.

Gut Microbiota Metabolites Differentially Release Gliotransmitters from the Cultured Human Astrocytes: A Preliminary Report.

Butyrate and indole-3-propionic acid represent the CNS-available gut microbiota metabolites exhibiting potentially beneficial effects on human brain function and being tested as antidepressants. Astrocytes represent one of the putative targets for the gut metabolites; however, the mechanism of action of butyrate and indole-3-propionic acid is not well understood. In order to test this mechanism, a human astrocyte cell-line culture was treated with the compounds or without them, and the supernatants were collected for the analysis of ATP and glutamate gliotransmitter release with the use of luminescent and fluorescent methods, respectively. A 10-min incubation of astrocytes with 1-5 mM butyrate increased the ATP gliotransmitter release by 78% (95%CI: 45-119%), p < 0.001. The effect was found to be mediated by the cytosolic Ca2+ mobilization. Both 10-min and 24-h treatments with indole-3-propionic acid produced no significant effects on the release of gliotransmitters. The results for glutamate release were inconclusive due to a specific glutamate release pattern discovered in the tested model. This preliminary report of butyrate-induced ATP gliotransmitter release appears to provide a novel mechanistic explanation for the beneficial effect of this gut microbiota metabolite on brain function; however, the results require further evaluation in more composed models.

Diclofenac Diminished the Unfolded Protein Response (UPR) Induced by Tunicamycin in Human Endothelial Cells.

Diclofenac belongs to the class of nonsteroidal anti-inflammatory drugs (NSAIDs), which are amongst the most frequently prescribed drugs to treat fever, pain and inflammation. Despite the presence of NSAIDs on the pharmaceutical market for several decades, epidemiological studies have shown new clinical applications of NSAIDs, and new mechanisms of their action were discovered. The unfolded protein response (UPR) activated under endoplasmic reticulum (ER) stress is involved in the pathophysiology of many diseases and may become a drug target, therefore, the study evaluated the effects of diclofenac on the tunicamycin-induced UPR pathways in endothelial cells. RT PCR analysis showed that diclofenac significantly inhibited activation of ER stress-responsive genes, i.e., CHOP/DITT3, GRP78/HSPA5 and DNAJB9. Additionally, the drug diminished the significant upregulation and release of the GRP78 protein, as evaluated using the ELISA assay, which was likely to be involved in the mechanism of the UPR activation resulting in apoptosis induction in endothelial cells. These results suggest the value of diclofenac as a factor capable of restoring the ER homeostasis in endothelial cells by diminishing the UPR.

The Importance of Endoplasmic Reticulum Stress as a Novel Antidepressant Drug Target and Its Potential Impact on CNS Disorders.

Many central nervous system (CNS) diseases, including major depressive disorder (MDD), are underpinned by the unfolded protein response (UPR) activated under endoplasmic reticulum (ER) stress. New, more efficient, therapeutic options for MDD are needed to avoid adverse effects and drug resistance. Therefore, the aim of the work was to determine whether UPR signalling pathway activation in astrocytes may serve as a novel target for antidepressant drugs. Among the tested antidepressants (escitalopram, amitriptyline, S-ketamine and R-ketamine), only S-ketamine, and to a lesser extent R-ketamine, induced the expression of most ER stress-responsive genes in astrocytes. Furthermore, cell viability and apoptosis measuring assays showed that (R-)S-ketamine did not affect cell survival under ER stress. Under normal conditions, S-ketamine played the key role in increasing the release of brain-derived neurotrophic factor (BDNF), indicating that the drug has a complex mechanism of action in astrocytes, which may contribute to its therapeutic effects. Our findings are the first to shed light on the relationship between old astrocyte specifically induced substance (OASIS) stabilized by ER stress and (R-)S-ketamine; however, the possible involvement of OASIS in the mechanism of therapeutic ketamine action requires further study.

Osteosarcoma cells in early and late stages as cancer in vitro progression model for assessing the responsiveness of cells to silver nanoparticles.

Understanding of biology of osteosarcoma malignant progression is indispensable for enhancement of conventional chemotherapy by the use of silver nanoparticles (AgNPs). We presented an in vitro model of cancer progression closely resembling processes occurring in vivo in terms of protein profile. A comparison of cytotoxic and genotoxic potential of AgNPs in Saos-2 cells in early stages of cancerous progression (early passages) with the cells in advanced stages (late passages) demonstrated significantly reduced responsiveness of the late passage cells to nanoparticles toxicity. It was also confirmed by proteome analysis as we identified considerably higher number of differentially expressed proteins in Saos-2 cells in early passages compared to the late passage cells. Our studies showed that the ability of AgNPs as potential drug carriers to deliver a medication and/or to evoke toxic effects might be significantly diminished in advanced stages of cancer progression.

Interaction of Cationic Carbosilane Dendrimers and Their siRNA Complexes with MCF-7 Cells.

The application of siRNA in gene therapy is mainly limited because of the problems with its transport into cells. Utilization of cationic dendrimers as siRNA carriers seems to be a promising solution in overcoming these issues, due to their positive charge and ability to penetrate cell membranes. The following two types of carbosilane dendrimers were examined: CBD-1 and CBD-2. Dendrimers were complexed with pro-apoptotic siRNA (Mcl-1 and Bcl-2) and the complexes were characterized by measuring their zeta potential, circular dichroism and fluorescence of ethidium bromide associated with dendrimers. CBD-2/siRNA complexes were also examined by agarose gel electrophoresis. Both dendrimers form complexes with siRNA. Moreover, the cellular uptake and influence on the cell viability of the dendrimers and dendriplexes were evaluated using microscopic methods and XTT assay on MCF-7 cells. Microscopy showed that both dendrimers can transport siRNA into cells; however, a cytotoxicity assay showed differences in the toxicity of these dendrimers.

Dysfunction of endothelial cells exposed to nanomaterials assessed by atomic force spectroscopy.

The study of the impact of nanomaterials on endothelial cell elasticity with the atomic force spectroscopy (AFS) can be a significant model for assessing nanomaterials toxic effects in vitro. The mechanical properties of cells exposed to nanostructures can provide information not only about cellular nano and micro-structure, but also about cell physiology. The toxicity of nanostructures is an important issue which must be carefully considered when the optimal nanomaterial is defined. There are no universal properties characterizing such a nanomaterial, i.e. depending on the intended use, the requirements can be diverse. For example, for biomedical use a nanomaterial should not negatively affect the cells or should cause the expected therapeutic or diagnostic effects in justified cases. The present study was devoted to the effects of silver nanoparticles (SNPs), multi-walled carbon nanotubes (MWCNTs) and poly(amidoamine) (PAMAM) dendrimers of 4th generation on functioning of endothelial cells. Immortalized endothelial cells were exposed for 24 h to the tested nanomaterials used in concentrations reducing cellular viability to the levels of 90 % and 75 %. The innovative nature of our work is the comparison of cell elasticity performed with various AFS probes, which enabled detection of local and global elasticity alteration caused by the nanostructures. The obtained results demonstrated changes in elasticity of endothelial cell induced by the nanostructures, which were closely correlated with the level of cellular viability, forming of actin stress fibres and elevated levels of reactive oxygen species. Trend of changes in local and global elasticity of cells exposed to nanostructures was similar, but the magnitude of the response was dependent on the selected probe. SNPs and MWCNTs evoked cells stiffening, which was correlated with changes in production levels of reactive oxygen species (ROS) and the cytoskeletal alteration. Softening of cells exposed to PAMAM dendrimers correlated with increased number of apoptotic cells and ROS production levels. Based on the obtained results we conclude, that the structure and the type of nanostructure (nanoparticle) is essential for their localization inside the cells and for the toxic effect on the endothelial cells.

Comprehensive Biological Evaluation of Biomaterials Used in Spinal and Orthopedic Surgery.

Biological acceptance is one of the most important aspects of a biomaterial and forms the basis for its clinical use. The aim of this study was a comprehensive biological evaluation (cytotoxicity test, bacterial colonization test, blood platelets adhesion test and transcriptome and proteome analysis of Saos-2 cells after contact with surface of the biomaterial) of biomaterials used in spinal and orthopedic surgery, namely, Ti6Al4V ELI (Extra Low Interstitials), its modified version obtained as a result of melting by electron beam technology (Ti6Al4V ELI-EBT), polyether ether ketone (PEEK) and polished medical steel American Iron and Steel Institute (AISI) 316L (the reference material). Biological tests were carried out using the osteoblasts-like cells (Saos-2, ATCC HTB-85) and bacteria Escherichia coli (DH5α). Results showed lack of cytotoxicity of all materials and the surfaces of both Ti6Al4V ELI and PEEK exhibit a significantly higher resistance to colonization with E. coli cells, while the more porous surface of the same titanium alloy produced by electron beam technology (EBT) is more susceptible to microbial colonization than the control surface of polished medical steel. None of the tested materials showed high toxicity in relation to E. coli cells. Susceptibility to platelet adhesion was very high for polished medical steel AISI 316L, whilst much lower for the other biomaterials and can be ranked from the lowest to the highest as follows: PEEK < Ti6Al4V ELI < Ti6Al4V ELI-EBT. The number of expressed genes in Saos-2 cells exposed to contact with the examined biomaterials reached 9463 genes in total (ranging from 8455 genes expressed in cells exposed to ELI to 9160 genes in cells exposed to PEEK). Whereas the number of differentially expressed proteins detected on two-dimensional electrophoresis gels in Saos-2 cells after contact with the examined biomaterials was 141 for PEEK, 223 for Ti6Al4V ELI and 133 for Ti6Al4V ELI-EBT. Finally, 14 proteins with altered expression were identified by mass spectrometry. In conclusion, none of the tested biomaterials showed unsatisfactory levels of cytotoxicity. The gene and protein expression analysis, that represents a completely new approach towards characterization of these biomaterials, showed that the polymer PEEK causes much more intense changes in gene and protein expression and thus influences cell metabolism.

Endothelial cell aging detection by means of atomic force spectroscopy.

Endothelial cell aging is related to changes not only in cell phenotype, such as luminal changes, intimal and medial thickening, and increased vascular stiffness, but encompasses different cell responses to various substances including drugs or nanomaterials. In the present work, time- and dose-dependent elasticity changes evoked by silver nanoparticles in endothelial cells in early (below 15) passages were analyzed. Silver nanoparticle concentrations of 3, 3.6, and 16 µg/mL were selected for elasticity measurements for long incubation (24 hours) and of 1 and 3 µg/mL for monitoring dynamic elasticity changes of 1-, 3-, and 6-hour incubations. Surprisingly, a significant reduction in the cells elasticity modulus at lower number of passages exposed to silver nanoparticles used at 3 µg/mL for 24 hours was demonstrated. These results are in contrast to those obtained for endothelial cells in late (33-43) passages that may result from cellular aging in response to nanosilver. Furthermore, for short incubation times (1 and 3 hours), SNP-induced significant increase in the cell elasticity modulus was detected. In current work, we also attempted to answer the question whether the changes in cell elasticity were induced by the silver nanoparticles stabilized with polyvinyl pyrrolidone or by stabilizer itself. Elasticity measurements were supplemented by observations made with transmission electron microscopy and scanning electron microscopy, which confirmed the presence of silver nanoparticles inside the cells and on the cell membrane. Additionally, activation of reactive oxygen species was detected for cells exposed to SNPs for 1 and 3 hours, which was accompanied by increased cell elasticity modulus suggesting a possible mechanism of observed phenomenon.

Designing laser-modified surface structures on titanium alloy custom medical implants using a hybrid manufacturing technology.

The hybrid technology combines an efficient material-removal process and implant surface treatment by the laser reducing time of manufacture process compared to currently used machining technologies. It also permits precise structuring of the implant material surface. Six structures of the Ti6Al4V ELI surface were designed and studied how the structure topography prepared with the hybrid technology affected the Escherichia coli adhesion to the surface and viability, as well as the growth, adhesion, and viability of human osteogenic Saos-2 cells cultured on the investigated surfaces. Results have confirmed that the microtopography of medical titanium alloy plays a beneficial role in bacterial adhesion and viability (number of bacteria found on reference surface: [5.9 ± 0.44] × 106 CFU/ml, sample no. 3: [8.8 ± 0.93] × 104 CFU/ml, and sample no. 5: [1.2 ± 0.23] × 107 CFU/ml; CFU - Colony Forming Unit). All tested structured surfaces enabled good cell attachment and proliferation of Saos-2 cells (viability of Saos-2 cells [% of control] for reference surface: 81.93%; sample no. 3: 75% and sample no. 5: 100%). Transcriptome analysis of genes commonly expressed in the process of osseointegration demonstrated that the use of hybrid technology allows designing structures that enhance osseointegration but it should be coupled with other methods of preventing bacterial growth, or with a different strategy to limit microbial colonization with the satisfactory osseointegration potential.

Simultaneous transcriptome and proteome analysis of EA.hy926 cells under stress conditions induced by nanomaterials.

Today, the extensive and constantly growing number of applications in the field of nanotechnology poses a lot of questions about the potential toxicity of nanomaterials (NMs) toward cells of different origins. In our work we employed the tools of molecular biology to evaluate changes that occur in human endothelial cells at the transcriptomic and proteomic level, following 24 h of exposure to three different classes of NMs. Using microarray technology, we demonstrated that 24 h of exposure to silver nanoparticles (SNPs), multiwalled carbon nanotubes (MWCNTs) and polyamidoamine dendrimers (PAMAMs) leads to changes in 299, 1271, and 431 genes, respectively, influencing specific molecular pathways. The 2D-DIGE and mass spectrometry analysis revealed that differentially expressed proteins were involved in numerous cellular processes, for example, cytoskeletal reorganization, cell growth and proliferation, or response to stress. Both, transcriptome and proteome alterations indicate reorganization of mechanism regulating cell functioning. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1024-1034, 2019.

Human brain endothelial barrier cells are distinctly less vulnerable to silver nanoparticles toxicity than human blood vessel cells: A cell-specific mechanism of the brain barrier?

The blood-brain barrier (BBB) constitutes a distinctive and tightly regulated interface between the brain and the peripheral circulation. The objective of studies was to compare responses of human endothelial cells representing the model of blood vessels - EA.hy926 and HUVEC cells and the model of the brain endothelial barrier - HBEC5i cells to silver nanoparticles (SNPs). A contact of SNPs with endothelial cells resulted in a formation of SNP agglomerates. Consequently, the SNPs uptake by endothelial cells affected cell viability and membrane integrity however observed responses were different. Brain endothelial barrier HBEC5i cells were much less vulnerable to SNPs toxicity comparing to EA.hy926 and HUVEC cells. It can be ascribed to the presence of specialized cellular components of the brain barrier, protecting HBEC5i cells against toxic SNPs. Fundamental understanding of SNPs inducing the BBB dysfunction may initiate engineering novel SNPs which are safe for the BBB and thereby safe for the brain.

Orexins protect neuronal cell cultures against hypoxic stress: an involvement of Akt signaling.

Orexins A and B are peptides produced mainly by hypothalamic neurons that project to numerous brain structures. We have previously demonstrated that rat cortical neurons express both types of orexin receptors, and their activation by orexins initiates different intracellular signals. The present study aimed to determine the effect of orexins on the Akt kinase activation in the rat neuronal cultures and the significance of that response in neurons subjected to hypoxic stress. We report the first evidence that orexins A and B stimulated Akt in cortical neurons in a concentration- and time-dependent manner. Orexin B more potently than orexin A increased Akt phosphorylation, but the maximal effect of both peptides on the kinase activation was very similar. Next, cultured cortical neurons were challenged with cobalt chloride, an inducer of reactive oxygen species and hypoxia-mediated signaling pathways. Under conditions of chemical hypoxia, orexins potently increased neuronal viability and protected cortical neurons against oxidative stress. Our results also indicate that Akt kinase plays an important role in the pro-survival effects of orexins in neurons, which implies a possible mechanism of the orexin-induced neuroprotection.

Orexins/hypocretins stimulate accumulation of inositol phosphate in primary cultures of rat cortical neurons.

BACKGROUND: Orexins A and B (also named hypocretins 1 and 2) are hypothalamic peptides with pleiotropic activity. They signal through two G protein-coupled receptors: OX1R and OX2R. We have previously demonstrated that both types of orexin receptors are expressed in cultured rat cortical neurons, and stimulation of the predominant OX2R inhibits cyclic AMP synthesis. In the present work, we examined effects of orexins on inositol phosphate (IP) accumulation in rat cortical neurons. METHODS: Experiments were performed on primary neuronal cell cultures prepared from Wistar rat embryos on day 17 of gestation. Following 1 h incubation with orexins, IP levels were measured using the ELISA IP-One assay kit. RESULTS: Orexins A and B increased, in a concentration-dependent manner, IP accumulation in primary neuronal cell cultures from rat cerebral cortex. Both peptides acted with a similar potency. The calculated EC50 values were 6.0 nM and 10.4 nM for orexin A and orexin B, respectively. CONCLUSION: The results indicate that in cultured rat cortical neurons orexin receptors are also coupled to inositol phosphates signaling pathway.

Orexin A suppresses the growth of rat C6 glioma cells via a caspase-dependent mechanism.

Orexin A and orexin B (also known as hypocretins) are closely related peptides synthesized by hypothalamic neurons. They orchestrate diverse central and peripheral processes by stimulation of two G-protein coupled receptors, OX(1)R and OX(2)R. Recent studies have demonstrated the ability of orexins to promote a robust apoptosis in different cancer cells in culture and a potent growth reduction of human colon tumors in mice xenografts. Here we report effects of orexins on survival of rat C6 glioma cells, an experimental model for studies on glioblastoma multiforme (GBM). Quantitative real-time PCR demonstrated the expression of both types of orexin receptors in C6 cells. Orexin A and orexin B did not affect rat C6 glioma cell proliferation as assessed by [(3)H]thymidine incorporation assay. Incubation of the cells with orexin A (0.001-1 µM) resulted in a marked decrease of cell viability. The observed effect was caspase-dependent, as it was blocked by Z-VAD-fmk, a pan caspase inhibitor. In addition to that, a parallel increase in caspase-3 activity was observed. It is suggested that stimulation of orexin receptors induces death of rat C6 glioma cells through activation of caspase pathway.

Orexins/hypocretins acting at Gi protein-coupled OX 2 receptors inhibit cyclic AMP synthesis in the primary neuronal cultures.

Orexins A and B are newly discovered neuropeptides with pleiotropic activity. They signal through two G protein-coupled receptors: OX(1) and OX(2). In this study, we examined the expression of orexin receptors and effects of the receptors' activation on cyclic AMP formation in the primary neuronal cell cultures from rat cerebral cortex. Both types of orexin receptors were expressed in rat cortical neurons; the level of OX(2)R was markedly higher compared to OX(1)R. Orexin A (an agonist of OX(1)R and OX(2)R) and [Ala(11)-D-Leu(15)]orexin B (a selective agonist of OX(2)R) did not affect basal cyclic AMP formation in the primary neuronal cell cultures. Both peptides (0.001-1 µM) inhibited, in a concentration-dependent manner and IC(50) values in low nanomolar range, the increase in the nucleotide production evoked by forskolin (1 µM; a direct activator of adenylyl cyclase), pituitary adenylate cyclase-activating polypeptide (PACAP27; 0.1 µM), and vasoactive intestinal peptide (VIP; 3 µM). Effects of orexin A on forskolin-, PACAP27-, and VIP-stimulated cyclic AMP synthesis were blocked by TCS OX2 29 (a selective antagonist of OX(2)R), and unaffected by SB 408124 (a selective antagonist of OX(1)R). Pretreatment of neuronal cell cultures with pertussis toxin (PTX) abolished the inhibitory action of orexin A on forskolin- and PACAP-stimulated cyclic AMP accumulation. It is suggested that in cultured rat cortical neurons orexins, acting at OX(2) receptors coupled to PTX-sensitive G(i) protein, inhibit cyclic AMP synthesis.

Orexins promote survival of rat cortical neurons.

Orexin A and B (hypocretin-1 and -2) are hypothalamic peptides that exert their biological functions by stimulation of two specific, membrane-bound receptors, OX(1)R and OX(2)R. Recently, we have demonstrated the expression of both types of orexin receptors in rat cortical neurons, with the OX(2)R level being markedly higher compared to OX(1)R. In the present study we investigated the receptor-mediated effects of orexin A, an agonist of OX(1)R and OX(2) R, orexin B and [Ala(11)-D-Leu(15)]orexin B, preferential agonists of OX(2)R, on survival of cultured neurons derived from rat cerebral cortex. The three tested peptides markedly increased neuronal viability in a concentration-dependent manner. The pro-survival properties of orexins were associated with an attenuation of caspase-3 activity. Comparable potency of orexin A, orexin B and [Ala(11)-D-Leu(15)]orexin B suggests a predominant role of OX(2)R in the studied phenomenon. Our findings provide new insights into the role of orexins in CNS as potential neuroprotective factors.