Nitric Oxide Signaling in Neurodegeneration and Cell Death

Characterising lipoteichoic acid as an in vitro model of acute neuroinflammation

Toll-like receptor 2 (TLR2) is a primary sensor for pathogens, including those derived from gram-positive bacteria. It can also mediate the effects of endogenous inflammatory signals such as β-amyloid peptide (Aβ), thus promoting the microglial activation and subsequent neuronal dysfunction, characteristic of chronic neuroinflammatory conditions. More recently, a role for TLR2 has been proposed in the pathogenesis of disorders associated with acute inflammation, including anxiety and depression. The current study aims to characterise the acute effects of the TLR2 agonist lipoteichoic acid (LTA) on microglial activation and neuronal integrity, and to evaluate the influence of LTA exposure on sensitivity to the inflammation and neuronal dysfunction associated with Aβ. Using BV2 and N2a cells as an in vitro model, we highlight that acute exposure to LTA robustly promotes inflammatory cytokine and nitric oxide (NO) production in microglia but also in neurons, similar to that reported under longer-term and chronic inflammatory conditions. Moreover, we find that exposure to LTA can enhance sensitivity to subthreshold Aβ, promoting an 'M1'-like phenotype in microglia and provoking dysregulation of neuronal activity in acute hippocampal slices. Anti-inflammatory agents, including mimetics of brain-derived neurotrophic factor (BDNF), have proven effective at alleviating chronic neuroinflammatory complications. We further examined the effects of 7,8,3-trihydroxyflavone (7,8,3-THF), a small-molecule TrkB agonist, on LTA-induced microglial activation. We report that 7,8,3-THF can significantly ameliorate interleukin (IL)-6 and NO production in LTA-stimulated BV2 cells. Taken together, our findings offer support for exploration of TLR2 as a potential target for therapeutic intervention into acute neuroinflammatory conditions. Moreover we propose that exposure to gram-positive bacterial pathogens may promote sensitivity to the inflammatory changes characteristic of the aged brain.

Neuroprotective Effect of Bergamot Juice in 6-OHDA-Induced SH-SY5Y Cell Death, an In Vitro Model of Parkinson's Disease

Much evidence suggests that both oxidative stress and apoptosis play a key role in the pathogenesis of Parkinson’s disease (PD). The present study aims to evaluate the protective effect of bergamot juice (BJ) against 6-hydroxydopamine (6-OHDA)- or H₂O₂-induced cell death. Treatment of differentiated SH-SY5Y human neuroblastoma cells with 6-OHDA or H₂O₂ resulted in cell death that was significantly reduced by the pre-treatment with BJ. The protective effects of BJ seem to correlate with the reduction of intracellular reactive oxygen species and nitric oxide generation caused by 6-OHDA or H₂O₂. BJ also attenuated mitochondrial dysfunction, caspase-3 activation, imbalance of pro- and anti-apoptotic proteins, MAPKs activation and reduced NF-ĸB nuclear translocation evoked by neurotoxic agents. Additionally, BJ exhibited excellent antioxidant capability in cell-free assays. Collectively, our results suggest that BJ exerts neuroprotective effect through the interplay with specific cell targets and its antioxidant activity, making it worthy of consideration for the management of neurodegenerative diseases.

Cellular mechanisms underlying the rapid depolarization caused by oxygen and glucose deprivation in layer III pyramidal cells of the somatosensory cortex

Cortical pyramidal neurons show rapid and irreversible membrane depolarization in response to oxygen-glucose depolarization (OGD). In this study, we investigated cellular mechanisms responsible for rapid depolarization caused by OGD in layer III pyramidal neurons of the mouse somatosensory cortex. When OGD solution was perfused in the presence of Ca²⁺ chelator and inhibitors of ryanodine receptors (RyRs) and inositol 1,4,5-trisphosphate receptors (IP₃Rs) in the pipette solution or in the presence of inhibitors of NMDA receptors (NMDARs), voltage-gated Ca²⁺ channels (VGCCs), and canonical transient receptor potential (TRPC) channels in the perfusion solution, the latency of the rapid depolarization was significantly prolonged compared to the control. In addition, when OGD solution was perfused in the presence of scavengers of nitric oxide and reactive oxygen species in the perfusion solution or in the presence of calcineurin inhibitors in the pipette solution, the latency of the rapid depolarization was significantly prolonged compared to the control. These data indicate that OGD-induced intracellular Ca²⁺ increases mediated by Ca²⁺ influx through NMDARs, VGCCs and TRPC channels as well as by Ca²⁺ release from RyRs and IP₃Rs lead to mitochondrial impairment, which may facilitate the generation of the rapid depolarization via dysfunction of Na⁺-K⁺-ATPase due to decreased ATP production.

Anti-Inflammatory and Anti-Migratory Activities of Isoquinoline-1-Carboxamide Derivatives in LPS-Treated BV2 Microglial Cells via Inhibition of MAPKs/NF-κB Pathway

Eleven novel isoquinoline-1-carboxamides (HSR1101~1111) were synthesized and evaluated for their effects on lipopolysaccharide (LPS)-induced production of pro-inflammatory mediators and cell migration in BV2 microglial cells. Three compounds (HSR1101~1103) exhibited the most potent suppression of LPS-induced pro-inflammatory mediators, including interleukin (IL)-6, tumor necrosis factor-alpha, and nitric oxide (NO), without significant cytotoxicity. Among them, only N-(2-hydroxyphenyl) isoquinoline-1-carboxamide (HSR1101) was found to reverse LPS-suppressed anti-inflammatory cytokine IL-10, so it was selected for further characterization. HSR1101 attenuated LPS-induced expression of inducible NO synthase and cyclooxygenase-2. Particularly, HSR1101 abated LPS-induced nuclear translocation of NF-κB through inhibition of IκB phosphorylation. Furthermore, HSR1101 inhibited LPS-induced cell migration and phosphorylation of mitogen-activated protein kinases (MAPKs) including extracellular signal-regulated kinase 1/2, c-Jun N-terminal kinase, and p38 MAPK. The specific MAPK inhibitors, U0126, SP600125, and SB203580, suppressed LPS-stimulated pro-inflammatory mediators, cell migration, and NF-κB nuclear translocation, indicating that MAPKs may be the upstream kinase of NF-κB signaling. Collectively, these results demonstrate that HSR1101 is a potent and promising compound suppressing LPS-induced inflammation and cell migration in BV2 microglial cells, and that inhibition of the MAPKs/NF-κB pathway mediates its anti-inflammatory and anti-migratory effects. Based on our findings, HSR1101 may have beneficial impacts on various neurodegenerative disorders associated with neuroinflammation and microglial activation.

Modulation of AMPA Receptors by Nitric Oxide in Nerve Cells

Nitric oxide (NO) is a gaseous molecule with a large number of functions in living tissue. In the brain, NO participates in numerous intracellular mechanisms, including synaptic plasticity and cell homeostasis. NO elicits synaptic changes both through various multi-chain cascades and through direct nitrosylation of targeted proteins. Along with the N-methyl-d-aspartate (NMDA) glutamate receptors, one of the key components in synaptic functioning are α-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptors—the main target for long-term modifications of synaptic effectivity. AMPA receptors have been shown to participate in most of the functions important for neuronal activity, including memory formation. Interactions of NO and AMPA receptors were observed in important phenomena, such as glutamatergic excitotoxicity in retinal cells, synaptic plasticity, and neuropathologies. This review focuses on existing findings that concern pathways by which NO interacts with AMPA receptors, influences properties of different subunits of AMPA receptors, and regulates the receptors’ surface expression.

Chicoric acid improves neuron survival against inflammation by promoting mitochondrial function and energy metabolism

Chicoric acid (CA), a major nutraceutical component of a typical Mediterranean vegetable, chicory, possesses excellent antioxidant and anti-inflammatory bioactivities. This work aimed to elucidate the effects of CA on neuron survival against inflammation and the underlying molecular mechanisms. Results demonstrated that CA promoted SH-SY5Y cells' autophagic vesicle formation, up-regulated autophagic elongation phase related gene expressions, and inhibited apoptosis stimulated by microglial conditioned culture medium (MCM). In addition, CA significantly improved mitochondrial function and regulated redox homeostasis related signaling pathways such as MAPKs and PI3K/AKT. MCM with CA notably increased the expressions of PGC-1α, SIRT1 and enhanced the phosphorylation of AMPK, promoting energy metabolism. On the other hand, the underlying mechanisms of the intervention of CA in MCM-induced cell apoptosis were partly due to its direct protective effect on SH-SY5Y cells and inhibition of microglial inflammatory factor release. This establishes a theoretical foundation for neuro-nutrition intervention studies of natural functional food components, and provides new clues for developing health foods containing CA.

The Effect of Arginine Intake on Colorectal Cancer: a Systematic Review of Literatures

Colorectal cancer (CRC) is one of the major reasons of mortality in the worldwide. There is clear evidence that some amino acids such as arginine can improve CRC and its complications. Hence, in this systematic review we evaluated the association between arginine intake and CRC improvement. We searched the PubMed, Scopus, ISI Web of Science, Cochrane library, and Google Scholar databases by using proper keywords to find the relevant literatures, published to March 2019. Nine human studies of 523 screened articles were included in present systematic review. The majority of studies have found a positive association between consumption of arginine and CRC improvement. Increased inducible nitric oxide (NO) synthase expression and subsequently increasing the NO concentration in the tumor and/or serum, after arginine intake may be responsible for these protective effects. Also, arginine consumption may reduce cell proliferation in CRC and it can enhance immune function after remove the tumor. Although the benefits of arginine consumption in CRC patients were reported in previous trials, the finding need replication in well-designed studies before final conclusion.

Formyl-methionyl-leucyl-phenylalanine Induces Apoptosis in Murine Neurons: Evidence for NO-Dependent Caspase-9 Activation

Formyl-methionyl-leucyl-phenylalanine (fMLP) may be present in the brain in the course of some infectious diseases of the central nervous system (CNS), although little is known about its role. This investigation was performed to study the effect of fMLP on neuron apoptosis. Our results showed that fMLP treatment of primary cultures of neurons was able to induce morphological features of apoptosis in cell cultures, as well as activation of the intrinsic apoptotic pathway, through the upregulation of caspase-9 and caspase-3. This effect contextually occurred to the pro-apoptotic protein Bax activation and cytochrome c release. The in vitro fMLP treatment was also able to induce, in a dose-dependent manner, the increase of inducible nitric oxide synthase (iNOS) expression accompanied by an up-regulation of nitric oxide (NO) release. When neuron cultures were pre-treated with 1400 W, a selective iNOS inhibitor, all of the apoptotic features were significantly reversed. Overall, these results demonstrated that fMLP treatment of neurons leads to intrinsic apoptosis activation, through iNOS expression regulation, suggesting a role for fMLP in CNS neurodegenerative processes.

Development of nNOS-positive preganglionic sympathetic neurons in the rat thoracic spinal cord

To gain a better understanding of the neuroplasticity of sympathetic neurons during postnatal ontogenesis, the distribution of neuronal nitric oxide synthase (nNOS) immunoreactivity was studied in sympathetic preganglionic neurons (SPN) in the spinal cord (Th2 segment) of female Wistar rats at different ages (newborn, 10-, 20-, 30-day-old; 2-, 6-month-old; 3-year-old). In all age groups, the majority of nNOS-immunoreactive (IR) neurons was observed in the nucleus intermediolateralis thoracolumbalis pars principalis. In the first month, the proportion of nNOS-IR neurons decreased significantly from 92 ± 3.4% in newborn to 55 ± 4.6% in 1-month-old, while the number of choline acetyltransferase (ChAT)-IR neurons increased from 74 ± 4.2% to 99 ± 0.3% respectively. Decreasing nNOS expression in the first 10 days of life was also confirmed by western blot analysis. Some nNOS-IR SPN also colocalized calbindin (CB) and cocaine and amphetamine-regulated transcript (CART). The percentage of NOS(+)/CB(-) SPN increased from 23 ± 3.6% in 10-day-old to 36 ± 4.2% in 2-month-old rats. Meanwhile, the proportion of NOS(+)/CART(-) neurons decreased from 82 ± 4.7% in newborn to 53 ± 6.1% in 1-month-old rats. The information provided here will also serve as a basis for future studies investigating the mechanisms of autonomic neuron development.

Garlic and Gaseous Mediators

Garlic (Allium sativum) and allied plant species are rich sources of sulfur compounds. Major roles for garlic and its sulfur constituents include the regulation of vascular homeostasis and the control of metabolic systems linked to nutrient metabolism. Recent studies have indicated that some of these sulfur compounds, such as diallyl trisulfide (DATS), alter the levels of gaseous signalling molecules including nitric oxide (NO), hydrogen sulfide (H₂S), and perhaps carbon monoxide (CO) in mammalian tissues. These gases are important in cellular processes associated with the cardiovascular system, inflammation, and neurological functions. Importantly, these studies build on the known biological effects of garlic and associated sulfur constituents. This review highlights our current understanding of the health benefits attributed to edible plants like garlic.