Cytoprotective and Neurotrophic Effects of Octadecaneuropeptide (ODN) in in vitro and in vivo Models of Neurodegenerative Diseases.

Octadecaneuropeptide (ODN) and its precursor diazepam-binding inhibitor (DBI) are peptides belonging to the family of endozepines. Endozepines are exclusively produced by astroglial cells in the central nervous system of mammals, and their release is regulated by stress signals and neuroactive compounds. There is now compelling evidence that the gliopeptide ODN protects cultured neurons and astrocytes from apoptotic cell death induced by various neurotoxic agents. In vivo, ODN causes a very strong neuroprotective action against neuronal degeneration in a mouse model of Parkinson's disease. The neuroprotective activity of ODN is based on its capacity to reduce inflammation, apoptosis, and oxidative stress. The protective effects of ODN are mediated through its metabotropic receptor. This receptor activates a transduction cascade of second messengers to stimulate protein kinase A (PKA), protein kinase C (PKC), and mitogen-activated protein kinase (MAPK)-extracellular signal-regulated kinase (ERK) signaling pathways, which in turn inhibits the expression of proapoptotic factor Bax and the mitochondrial apoptotic pathway. In N2a cells, ODN also promotes survival and stimulates neurite outgrowth. During the ODN-induced neuronal differentiation process, numerous mitochondria and peroxisomes are identified in the neurites and an increase in the amount of cholesterol and fatty acids is observed. The antiapoptotic and neurotrophic properties of ODN, including its antioxidant, antiapoptotic, and pro-differentiating effects, suggest that this gliopeptide and some of its selective and stable derivatives may have therapeutic value for the treatment of some neurodegenerative diseases.

Neuroprotection with the Endozepine Octadecaneuropeptide, ODN.

The term endozepines designates a family of astroglia-secreted proteins including the diazepambinding inhibitor (DBI) and its processing products, which have been originally isolated and characterized as endogenous ligands of benzodiazepine receptors. It is now clearly established that the octadecaneuropeptide ODN (DBI33-50), acting through the central-type benzodiazepine receptor or a metabotropic receptor, exerts important functions such as proconflict behavior, induction of anxiety, inhibition of pentobarbital-provoked sleep, decrease of water consumption and reduction of food intake. To mediate its effects, ODN regulates both glial cell and neuronal activities by acting on neurosteroid biosynthesis and/or neuropeptide expression. In addition, ODN stimulates astrocyte proliferation and protects both neurons and astrocytes from oxidative stress-induced cell death. The antiapoptotic effect of ODN on neural cells is mediated through activation of the ODN metabotropic receptor positively coupled to PKA, PKC and MAPK/ERK transduction pathways, which ultimately reduces the pro-apoptotic gene Bax and stimulates Bcl-2 expressions, and inhibits intracellular reactive oxygen species accumulation. The imbalance in favor of Bcl2 promotes mitochondria functions and blocks in turn caspases activation while at the same time, ODN also activates the endogenous antioxidant system i.e. glutathione biosynthesis, and expression and activities of antioxidant enzymes. In cultured astrocytes, DBI expression is up-regulated during moderate oxidative stress, and authentic ODN production is increased, suggesting that ODN may act as a paracrine factor protecting neighboring neurons. Taken together, the remarkable effect of ODN on the apoptotic cascade suggests that innovative ODN derivatives could potentially be useful for treatment of cerebral injuries involving oxidative stress and neurodegeneration.

Neuroprotective effects of the gliopeptide ODN in an in vivo model of Parkinson's disease.

Parkinson's disease (PD) is a neurodegenerative disorder characterized by a progressive loss of dopamine (DA) neurons through apoptotic, inflammatory and oxidative stress mechanisms. The octadecaneuropeptide (ODN) is a diazepam-binding inhibitor (DBI)-derived peptide, expressed by astrocytes, which protects neurons against oxidative cell damages and apoptosis in an in vitro model of PD. The present study reveals that a single intracerebroventricular injection of 10 ng ODN 1 h after the last administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) prevented the degeneration of DA neurons induced by the toxin in the substantia nigra pars compacta of mice, 7 days after treatment. ODN-mediated neuroprotection was associated with a reduction of the number of glial fibrillary acidic protein-positive reactive astrocytes and a strong inhibition of the expression of pro-inflammatory genes such as interleukins 1ß and 6, and tumor necrosis factor-α. Moreover, ODN blocked the inhibition of the anti-apoptotic gene Bcl-2, and the stimulation of the pro-apoptotic genes Bax and caspase-3, induced by MPTP in the substantia nigra pars compacta. ODN also decreased or even in some cases abolished MPTP-induced oxidative damages, overproduction of reactive oxygen species and accumulation of lipid oxidation products in DA neurons. Furthermore, DBI knockout mice appeared to be more vulnerable than wild-type animals to MPTP neurotoxicity. Taken together, these results show that the gliopeptide ODN exerts a potent neuroprotective effect against MPTP-induced degeneration of nigrostriatal DA neurons in mice, through mechanisms involving downregulation of neuroinflammatory, oxidative and apoptotic processes. ODN may, thus, reduce neuronal damages in PD and other cerebral injuries involving oxidative neurodegeneration.

Endogenous Expression of ODN-Related Peptides in Astrocytes Contributes to Cell Protection Against Oxidative Stress: Astrocyte-Neuron Crosstalk Relevance for Neuronal Survival.

Astroglial cells are important actors in the defense of brain against oxidative stress injuries. Glial cells synthesize and release the octadecaneuropeptide ODN, a diazepam-binding inhibitor (DBI)-related peptide, which acts through its metabotropic receptor to protect neurons and astrocytes from oxidative stress-induced apoptosis. The purpose of the present study is to examine the contribution of the endogenous ODN in the protection of astrocytes and neurons from moderate oxidative stress. The administration of H2O2 (50 µM, 6 h) induced a moderate oxidative stress in cultured astrocytes, i.e., an increase in reactive oxygen species, malondialdehyde, and carbonyl group levels, but it had no effect on astrocyte death. Mass spectrometry and QPCR analysis revealed that 50 µM H2O2 increased ODN release and DBI mRNA levels. The inhibition of ODN release or pharmacological blockage of the effects of ODN revealed that in these conditions, 50 µM H2O2 induced the death of astrocytes. The transfection of astrocytes with DBI siRNA increased the vulnerability of cells to moderate stress. Finally, the addition of 1 nM ODN to culture media reversed cell death observed in DBI-deficient astrocytes. The treatment of neurons with media from 50 µM H2O2-stressed astrocytes significantly reduced the neuronal death induced by H2O2; this effect is greatly attenuated by the administration of an ODN metabotropic receptor antagonist. Overall, these results indicate that astrocytes produce authentic ODN, notably in a moderate oxidative stress situation, and this glio- and neuro-protective agent may form part of the brain defense mechanisms against oxidative stress injury.

Hemoglobin-Improved Protection in Cultured Cerebral Cortical Astroglial Cells: Inhibition of Oxidative Stress and Caspase Activation.

Oxidative stress plays a major role in triggering astroglial cell death in diverse neuropathological conditions such as ischemia and neurodegenerative diseases. Numerous studies indicate that hemoglobin (Hb) is expressed in both resting and reactive glia cells, but nothing is known regarding a possible role of Hb on astroglial cell survival. Thus, the purpose of the present study was to investigate the potential glioprotective effect of Hb on hydrogen peroxide (H2O2)-induced oxidative stress and apoptosis in cultured rat astrocytes. Our study demonstrates that administration of graded concentrations of Hb (10-12 to 10-6 M) to H2O2-treated astrocytes reduces cell death in a concentration-dependent manner. H2O2 treatment induces the accumulation of reactive oxygen species (ROS) and nitric oxide (NO), a drop of the mitochondrial membrane potential, and a stimulation of caspase-3/7 activity. Exposure of H2O2-treated cells to Hb was accompanied by marked attenuations of ROS and NO surproductions, mitochondrial membrane potential reduction, and caspase-3/7 activity increase. The protective action of Hb was blocked by the protein kinase A (PKA) inhibitor H89, the protein kinase C (PKC) inhibitor chelerythrine, and the mitogen-activated protein (MAP)-kinase kinase (MEK) inhibitor U0126. Taken together, these data demonstrate for the first time that Hb is a glioprotective factor that protects astrocytes from apoptosis induced by oxidative stress and suggest that Hb may confer neuroprotection in neurodegenerative diseases. The anti-apoptotic activity of Hb on astrocytes is mediated through the PKA, PKC, and MAPK transduction pathways and can be accounted for by inhibition of oxidative stress-induced mitochondrial dysfunctions and caspase activation.

Neuroglobin protects astroglial cells from hydrogen peroxide-induced oxidative stress and apoptotic cell death.

Oxidative stress, resulting from accumulation of reactive oxygen species, plays a critical role in astroglial cell death occurring in diverse neuropathological conditions. Numerous studies indicate that neuroglobin (Ngb) promotes neuron survival, but nothing is known regarding the action of Ngb in astroglial cell survival. Thus, the purpose of this study was to investigate the potential glioprotective effect of Ngb on hydrogen peroxide (H2 O2 )-induced oxidative stress and apoptosis in cultured mouse astrocytes. Incubation of cells with subnanomolar concentrations of Ngb (10-14 -10-10  M) was found to prevent both H2 O2 -evoked reduction in surviving cells number and accumulation of reactive oxygen species in a concentration-dependent manner. Furthermore, Ngb treatment abolishes H2 O2 -induced increase in mitochondrial oxygen consumption rates. Concomitantly, Ngb treatment rescues H2 O2 -associated reduced expression of endogenous antioxidant enzymes (superoxide dismutases and catalase) and prevents the stimulation of the expression of pro-inflammatory genes (inducible nitric oxide synthase, cyclooxygenase-2, and interleukin (IL) IL-6 and IL-33). Moreover, Ngb blocks the stimulation of Bax (pro-apoptotic) and the inhibition of Bcl-2 (anti-apoptotic) gene expression induced by H2 O2 , which in turn abolishes caspase 3 activation. The protective effect of Ngb upon H2 O2 induced activation of caspase 3 activity and cell death can be accounted for by activation of protein kinase A and mitogen-activated protein kinase transduction cascade. Finally, we demonstrate that Ngb increases Akt phosphorylation and prevents H2 O2 -provoked inhibition of ERK and Akt phosphorylation. Taken together, these data demonstrate for the first time that Ngb is a glioprotective agent that prevents H2 O2 -induced oxidative stress and apoptotic astroglial cell death. Protection of astrocytes from oxidative insult may thus contribute to the neuroprotective effect of Ngb.