Inhibition of Neuronal Nitric Oxide Synthase by Ethyl Pyruvate in Schwann Cells Protects Against Peripheral Nerve Degeneration

Glycolytic System in Axons Supplement Decreased ATP Levels after Axotomy of the Peripheral Nerve

Wallerian degeneration (WD) occurs in the early stages of numerous neurologic disorders, and clarifying WD pathology is crucial for the advancement of neurologic therapies. ATP is acknowledged as one of the key pathologic substances in WD. The ATP-related pathologic pathways that regulate WD have been defined. The elevation of ATP levels in axon contributes to delay WD and protects axons. However, ATP is necessary for the active processes to proceed WD, given that WD is stringently managed by auto-destruction programs. But little is known about the bioenergetics during WD. In this study, we made sciatic nerve transection models for GO-ATeam2 knock-in rats and mice. We presented the spatiotemporal ATP distribution in the injured axons with in vivo ATP imaging systems, and investigated the metabolic source of ATP in the distal nerve stump. A gradual decrease in ATP levels was observed before the progression of WD. In addition, the glycolytic system and monocarboxylate transporters (MCTs) were activated in Schwann cells following axotomy. Interestingly, in axons, we found the activation of glycolytic system and the inactivation of the tricarboxylic acid (TCA) cycle. Glycolytic inhibitors, 2-deoxyglucose (2-DG) and MCT inhibitors, a-cyano-4-hydroxycinnamic acid (4-CIN) decreased ATP and enhanced WD progression, whereas mitochondrial pyruvate carrier (MPC) inhibitors (MSDC-0160) did not change. Finally, ethyl pyruvate (EP) increased ATP levels and delayed WD. Together, our findings suggest that glycolytic system, both in Schwann cells and axons, is the main source of maintaining ATP levels in the distal nerve stump.

The contribution of an imbalanced redox signalling to neurological and neurodegenerative conditions

Nitric oxide and other redox active molecules such as oxygen free radicals provide essential signalling in diverse neuronal functions, but their excess production and insufficient scavenging induces cytotoxic redox stress which is associated with numerous neurodegenerative and neurological conditions. A further component of redox signalling is mediated by a homeostatic regulation of divalent metal ions, the imbalance of which contributes to neuronal dysfunction. Additional antioxidant molecules such as glutathione and enzymes such as super oxide dismutase are involved in maintaining a physiological redox status within neurons. When cellular processes are perturbed and generation of free radicals overwhelms the antioxidants capacity of the neurons, a resulting redox damage leads to neuronal dysfunction and cell death. Cellular sources for production of redox-active molecules may include NADPH oxidases, mitochondria, cytochrome P450 and nitric oxide (NO)-generating enzymes, such as endothelial, neuronal and inducible NO synthases. Several neurodegenerative and developmental neurological conditions are associated with an imbalanced redox state as a result of neuroinflammatory processes leading to nitrosative and oxidative stress. Ongoing research aims at understanding the causes and consequences of such imbalanced redox homeostasis and its role in neuronal dysfunction.

Free radical biology in neurological manifestations: mechanisms to therapeutics interventions

Recent advancements and growing attention about free radicals (ROS) and redox signaling enable the scientific fraternity to consider their involvement in the pathophysiology of inflammatory diseases, metabolic disorders, and neurological defects. Free radicals increase the concentration of reactive oxygen and nitrogen species in the biological system through different endogenous sources and thus increased the overall oxidative stress. An increase in oxidative stress causes cell death through different signaling mechanisms such as mitochondrial impairment, cell-cycle arrest, DNA damage response, inflammation, negative regulation of protein, and lipid peroxidation. Thus, an appropriate balance between free radicals and antioxidants becomes crucial to maintain physiological function. Since the 1brain requires high oxygen for its functioning, it is highly vulnerable to free radical generation and enhanced ROS in the brain adversely affects axonal regeneration and synaptic plasticity, which results in neuronal cell death. In addition, increased ROS in the brain alters various signaling pathways such as apoptosis, autophagy, inflammation and microglial activation, DNA damage response, and cell-cycle arrest, leading to memory and learning defects. Mounting evidence suggests the potential involvement of micro-RNAs, circular-RNAs, natural and dietary compounds, synthetic inhibitors, and heat-shock proteins as therapeutic agents to combat neurological diseases. Herein, we explain the mechanism of free radical generation and its role in mitochondrial, protein, and lipid peroxidation biology. Further, we discuss the negative role of free radicals in synaptic plasticity and axonal regeneration through the modulation of various signaling molecules and also in the involvement of free radicals in various neurological diseases and their potential therapeutic approaches. The primary cause of free radical generation is drug overdosing, industrial air pollution, toxic heavy metals, ionizing radiation, smoking, alcohol, pesticides, and ultraviolet radiation. Excessive generation of free radicals inside the cell R1Q1 increases reactive oxygen and nitrogen species, which causes oxidative damage. An increase in oxidative damage alters different cellular pathways and processes such as mitochondrial impairment, DNA damage response, cell cycle arrest, and inflammatory response, leading to pathogenesis and progression of neurodegenerative disease other neurological defects.

Modulation of High-Fat Diet-Induced Brain Oxidative Stress by Ferulate-Rich Germinated Brown Rice Ethyl Acetate Extract

The oxidative stress resulting from the production of reactive oxygen species plays a vital role in inflammatory processes and is associated with neurodegenerative changes. In view of the ability of germinated brown rice (GBR) to improve learning and memory, this present study aimed to investigate the mechanistic basis of GBR’s neuroprotection in a high-fat diet (HFD)-induced oxidative changes in adult Sprague–Dawley rats. Ferulate-rich GBR ethyl acetate extract (GBR-EA; 100 mg/kg and 200 mg/kg body weight) was supplemented orally for the last 3 months of 6 months HFD feeding during the study. GBR-EA supplementation was found to improve lipid profile and serum antioxidant status, when compared to the HFD group. Elevated mRNA expressions of SOD1, SOD2, SOD3, Catalase, and GPX were demonstrated in the frontal cortex and hippocampus of GBR-EA treated animals. The pro-inflammatory changes induced by HFD in the hippocampus were attenuated by GBR-EA through the downregulation of CRP and TNF- α and upregulation of PPAR-γ. GBR also reduced the hippocampal mRNA expression and enzyme level of acetylcholinesterase. In conclusion, this study proposed the possible transcriptomic regulation of antioxidant and inflammation in neurodegenerative processes resulting from high cholesterol consumption, with an emphasis on GBR’s potential to ameliorate such changes.

Emerging evidence for compromised axonal bioenergetics and axoglial metabolic coupling as drivers of neurodegeneration

Impaired bioenergetic capacity of the nervous system is thought to contribute to the pathogenesis of many neurodegenerative diseases (NDD). Since neuronal synapses are believed to be the major energy consumers in the nervous system, synaptic derangements resulting from energy deficits have been suggested to play a central role for the development of many of these disorders. However, long axons constitute the largest compartment of the neuronal network, require large amounts of energy, are metabolically and structurally highly vulnerable, and undergo early injurious stresses in many NDD. These stresses likely impose additional energy demands for continuous adaptations and repair processes, and may eventually overwhelm axonal maintenance mechanisms. Indeed, pathological axon degeneration (pAxD) is now recognized as an etiological focus in a wide array of NDD associated with bioenergetic abnormalities. In this paper I first discuss the recognition that a simple experimental model for pAxD is regulated by an auto-destruction program that exhausts distressed axons energetically. Provision of the energy substrate pyruvate robustly counteracts this axonal breakdown. Importantly, energy decline in axons is not only a consequence but also an initiator of this program. This opens the intriguing possibility that axon dysfunction and pAxD can be suppressed by preemptively energizing distressed axons. Second, I focus on the emerging concept that axons communicate energetically with their flanking glia. This axoglial metabolic coupling can help offset the axonal energy decline that activates the pAxD program but also jeopardize axon integrity as a result of perturbed glial metabolism. Third, I present compelling evidence that abnormal axonal energetics and compromised axoglial metabolic coupling accompany the activation of the pAxD auto-destruction pathway in models of glaucoma, a widespread neurodegenerative condition with pathogenic overlap to other common NDD. In conclusion, I propose a novel conceptual framework suggesting that therapeutic interventions focused on bioenergetic support of the nervous system should also address axons and their metabolic interactions with glia.

Inhibition of nitric oxide production enhances the activity of facial nerve tubulin polymerization and the ability of tau to promote microtubule assembly after neurorrhaphy

We previously reported that inhibition of nitric oxide (NO) production promotes rat reconnected facial nerve regeneration. However, the underlying mechanism is obscure. Microtubule assembly is known to be essential to axon regeneration; nevertheless, tubulins and microtubule-associated proteins (MAPs) have been demonstrated as targets for NO and peroxynitrite. Thus, we hypothesized that NO and/or peroxynitrite may affect facial nerve regeneration via influencing on microtubule assembly. First, tubulins and tau (a MAP) were extracted from facial nerves of normal rats, treated with NO donor or peroxynitrite, and processed for microtubule assembly assay. We found that peroxynitrite, DEA NONOate, and Angeli's salt reduced the tubulin polymerization activity to a greater extent than GSNO, SIN-1, and SNAP. Additionally, SIN-1, peroxynitrite, and Angeli's salt impaired the ability of tau to promote microtubule assembly. Next, nitrosative stress biomarkers 3-nitrotyrosine (3-NT) and S-nitrosylated cysteine (SNO-Cys) were immunolabeled in facial nerves. Both biomarkers were highly upregulated in proximal and distal stumps of reconnected facial nerves at 3 days and 1 week after neurorrhaphy. Notably, the expression of 3-NT was greatly reduced at 2 weeks, whereas that of SNO-Cys was maintained. Conversely, inhibition of NO production with L-NAME prevented the upregulation of SNO-Cys. Further, we used tubulins and tau extracted from facial nerves of sham-operated, nerve suture + vehicle treatment, and nerve suture + L-NAME treatment rats to perform microtubule assembly assay. We found that L-NAME treatment enhanced polymerization activity of tubulins and ability of tau to promote microtubule assembly. It is noteworthy that α-tubulin plays a more important role than β-tubulin since the activity of microtubule assembly using α-tubulin extracted from L-NAME-treated rats was greatly elevated, whereas that using β-tubulin extracted from L-NAME-treated rats was not. Overall, our findings support that inhibition of NO production reduces nitrosative stress, and may thus facilitate microtubule assembly and facial nerve regeneration.

Ethyl Pyruvate as a Potential Defense Intervention against Cytokine Storm in COVID-19?

COVID-19 is a deadly pandemic and has resulted in a huge loss of money and life in the past few months. It is well known that the SARS-CoV-2 gene mutates relatively slowly as compared to other viruses but still may create hurdles in developing vaccines. Therefore, there is a need to develop alternative routes for its management and treatment of COVID-19. Based on the severity of viral infection in COVID-19 patients, critically ill patients (∼5%, with old age, and comorbidities) are at high risk of morbidities. The reason for this severity in such patients is attributed to "misleading cytokine storm", which produces ARDS and results in the deaths of critically ill patients. In this connection, ethyl pyruvate (EP) controls these cytokines/chemokines, is an anti-inflammatory agent, and possesses a protective effect on the lungs, brain, heart, and mitochondria against various injuries. Considering these facts, we propose that the site-selective EP formulations (especially aerosols) could be the ultimate adjuvant therapy for the regulation of misleading cytokine storm in severely affected COVID-19 patients and could reduce the mortalities.

Ethyl pyruvate improves white matter remodeling in rats after traumatic brain injury

Background

Severe traumatic brain injury (TBI) results in long‐term neurological deficits associated with white matter injury (WMI). Ethyl pyruvate (EP) is a simple derivative of the endogenous energy substrate pyruvate with neuroprotective properties, but its role in recovery from WMI has not been explored.

Aims

This study examines the effect of EP treatment on rats following TBI using behavioral tests and white matter histological analysis up to 28 days post‐injury.

Materials and Methods

Anaesthetised adult rats were subjected to TBI by controlled cortical impact. After surgery, EP or Ringers solution (RS) was administrated intraperitoneally at 15 min after TBI and again at 12, 24, 36, 48, and 60 h after TBI. Sensorimotor deficits were evaluated up to day 21 after TBI by four independent tests. Immunofluorescence and transmission electron microscopy (TEM) were performed to assess white matter injury. Microglia activation and related inflammatory molecules were examined up to day 14 after TBI by immunohistochemistry or real‐time PCR.

Results

Here, we demonstrate that EP improves sensorimotor function following TBI as well as improves white matter outcomes up to 28 d after TBI, as shown by reduced myelin loss. Furthermore, EP administration during the acute phase of TBI recovery shifted microglia polarization toward the anti‐inflammatoryM2 phenotype, modulating the release of inflammatory‐related factors.

Conclusion

EP treatment may protect TBI‐induced WMI via modulating microglia polarization toward M2.

HMGB1 promoted P-glycoprotein at the blood-brain barrier in MCAO rats via TLR4/NF-κB signaling pathway

P-glycoprotein (P-gp) is located on the luminal surface of brain vascular endothelium and its status may determine the delivery of the agents into the brain tissues. Previous study showed that upregulation of P-gp at the blood-brain barrier (BBB) after ischemic stroke were mediated by nuclear factor-B (NF-kB) and tumour necrosis factor-α (TNF-α). Based on middle cerebral artery occlusion (MCAO) rats and oxygen-glucose deprivation (OGD) in co-culture of rat brain microvessel endothelial cells (rBMECs) and astrocytes system, the present data indicated that potentiated P-gp expression and activity in brain microvessels or rBMECs were associated with the increase in high-mobility group box 1 (HMGB1), Toll-like receptor 4 (TLR4) and activation of NF-kB and that HMGB1 can release from nucleus to the cytoplasm in activated astrocytes, then into the medium. Moreover, changes in TLR4, TIR domain-containing adaptor protein (TIRAP), NF-kB and P-gp in rBMECs were attenuated by addition of 1 mM ethyl pyruvate (EP), 10 μM TAK-242 and 10 μM pyrrolidine dithiocarbamate (PDTC), respectively. These results demonstrated that HMGB1 promoted P-gp at the BBB after cerebral ischemia via TLR4/NF-κB signaling pathway.