Protective effects of peptide FK18 against neuro-excitotoxicity in SH-SY5Y cells

Growth factors and their peptide mimetics for treatment of traumatic brain injury

Traumatic brain injury (TBI) is a leading cause of disability in adults, caused by a physical insult damaging the brain. Growth factor-based therapies have the potential to reduce the effects of secondary injury and improve outcomes by providing neuroprotection against glutamate excitotoxicity, oxidative damage, hypoxia, and ischemia, as well as promoting neurite outgrowth and the formation of new blood vessels. Despite promising evidence in preclinical studies, few neurotrophic factors have been tested in clinical trials for TBI. Translation to the clinic is not trivial and is limited by the short in vivo half-life of the protein, the inability to cross the blood-brain barrier and human delivery systems. Synthetic peptide mimetics have the potential to be used in place of recombinant growth factors, activating the same downstream signalling pathways, with a decrease in size and more favourable pharmacokinetic properties. In this review, we will discuss growth factors with the potential to modulate damage caused by secondary injury mechanisms following a traumatic brain injury that have been trialled in other indications including spinal cord injury, stroke and neurodegenerative diseases. Peptide mimetics of nerve growth factor (NGF), hepatocyte growth factor (HGF), glial cell line-derived growth factor (GDNF), brain-derived neurotrophic factor (BDNF), platelet-derived growth factor (PDGF) and fibroblast growth factor (FGF) will be highlighted, most of which have not yet been tested in preclinical or clinical models of TBI.

Extracellular Adenosine Triphosphate Binding to P2Y1 Receptors Prevents Glutamate-Induced Excitotoxicity: Involvement of Erk1/2 Signaling Pathway to Suppress Autophagy

Glutamate-induced neuroexcitotoxicity could be related to the pathophysiology of some neurodegenerative diseases including Parkinson’s disease and Alzheimer’s disease. Extracellular ATP exerts a wide variety of functions, such as attenuating Aβ-mediated toxicity, inhibiting N-Methyl-D-Aspartate (NMDA) receptor subunit combinations, and aggravating ischemic brain injury. However, the effect of extracellular ATP on glutamate-induced neuroexcitotoxicity remains largely unknown. Herein, we showed that extracellular ATP prevented the glutamate-induced excitotoxicity via binding to its P2Y1 receptors. We found that excessive glutamate triggered cellular reactive oxygen species (ROS) overproduction and mitochondrial membrane potential damage, which were significantly attenuated by extracellular ATP. Besides, glutamate activated autophagy, as illustrated by the increased protein level of autophagic marker LC3II and decreased level of p62, and glutamate-induced neuroexcitotoxicity could be completely abolished by autophagy inhibitor chloroquine. In addition, we revealed that extracellular ATP activated Erk1/2 signaling to suppress autophagy and to exert its neuroprotective effects, which was further reduced by autophagy agonist rapamycin and the selective Erk1/2 inhibitor PD0325901. Taken together, our findings suggest that extracellular ATP binding to P2Y1 receptors protected against glutamate-induced excitotoxicity via Erk1/2-mediated autophagy inhibition, implying the potential of ATP for the treatment of neurodegenerative disorders.

Protective Effect of Patchouli Alcohol Against SH-SY5Y Cell Injury Induced by Aβ25-35 via the Reduction of Oxidative Stress and Apoptosis

Patchouli alcohol (PA) has multiple pharmacological activities, but its protective effect against SH-SY5Y cell injury induced by Aβ25-35 has not been reported. It has been recorded that phosphatidylinositol 3-hydroxykinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR) pathway plays an important role in neuroprotection. The purpose of this study was to investigate the protective effect of PA against SH-SY5Y cell injury induced by Aβ25-35 and its underlying mechanism. The results showed that compared with that in the Aβ25-35-induced injury group, the survival rate of SH-SY5Y cells increased ( P < .01) in the different PA-treated groups and the lactic dehydrogenase activity decreased significantly ( P < .01) in the 10, 20, and 40 μg/mL PA groups; compared with those in the Aβ25-35-induced injury group, the malonyldialdehyde contents in SH-SY5Y cells decreased ( P < .05 or P < .01), while the superoxide dismutase, glutathione peroxidase, and catalase activities increased significantly ( P < .05 or P < .01) in the different PA-treated groups; compared with those in the Aβ25-35-induced injury group, the apoptosis rates, and the mRNA and protein levels of Caspase-3 and Bax in SH-SY5Y cells decreased ( P < .05 or P < .01), while the mRNA and protein levels of Bcl-2, and phosphorylated Akt (p-Akt) and phosphorylated mTOR protein levels increased significantly ( P < .05 or P < .01) in the different PA-treated groups. The above results indicate that PA can inhibit the oxidative stress and apoptosis of SH-SY5Y cells induced by Aβ25-35 by regulating the PI3K/Akt/mTOR pathway, to protect the SH-SY5Y cells from the injury induced by Aβ25-35.

Peptides Derived from Growth Factors to Treat Alzheimer's Disease

Alzheimer's disease (AD) is a devastating neurodegenerative disease characterized by progressive neuron losses in memory-related brain structures. The classical features of AD are a dysregulation of the cholinergic system, the accumulation of amyloid plaques, and neurofibrillary tangles. Unfortunately, current treatments are unable to cure or even delay the progression of the disease. Therefore, new therapeutic strategies have emerged, such as the exogenous administration of neurotrophic factors (e.g., NGF and BDNF) that are deficient or dysregulated in AD. However, their low capacity to cross the blood-brain barrier and their exorbitant cost currently limit their use. To overcome these limitations, short peptides mimicking the binding receptor sites of these growth factors have been developed. Such peptides can target selective signaling pathways involved in neuron survival, differentiation, and/or maintenance. This review focuses on growth factors and their derived peptides as potential treatment for AD. It describes (1) the physiological functions of growth factors in the brain, their neuronal signaling pathways, and alteration in AD; (2) the strategies to develop peptides derived from growth factor and their capacity to mimic the role of native proteins; and (3) new advancements and potential in using these molecules as therapeutic treatments for AD, as well as their limitations.