Schwann cell mitochondria as key regulators in the development and maintenance of peripheral nerve axons

Citric Acid: A Nexus Between Cellular Mechanisms and Biomaterial Innovations

Citrate-based biodegradable polymers have emerged as a distinctive biomaterial platform with tremendous potential for diverse medical applications. By harnessing their versatile chemistry, these polymers exhibit a wide range of material and bioactive properties, enabling them to regulate cell metabolism and stem cell differentiation through energy metabolism, metabonegenesis, angiogenesis, and immunomodulation. Moreover, the recent US Food and Drug Administration (FDA) clearance of the biodegradable poly(octamethylene citrate) (POC)/hydroxyapatite-based orthopedic fixation devices represents a translational research milestone for biomaterial science. POC joins a short list of biodegradable synthetic polymers that have ever been authorized by the FDA for use in humans. The clinical success of POC has sparked enthusiasm and accelerated the development of next-generation citrate-based biomaterials. This review presents a comprehensive, forward-thinking discussion on the pivotal role of citrate chemistry and metabolism in various tissue regeneration and on the development of functional citrate-based metabotissugenic biomaterials for regenerative engineering applications.

Platinum-based chemotherapy induces demyelination of Schwann cells in oral squamous cell carcinoma treatment

BACKGROUND

Cisplatin, carboplatin, and oxaliplatin are the only three platinum-based antineoplastic drugs that have been accepted worldwide for treating various cancers. Up to 83.6% of patients treated with platinum-based antineoplastic drugs will develop chemotherapy-induced peripheral neuropathy (CIPN), manifesting as sensory paresthesias, dysesthesias, and hypoesthesias that can cause significant adverse impact to daily activities.

AIM

To investigate how these three platinum-based drugs affect mitochondrial function and myelination state of Schwann cells and the signalling pathway involved.

METHOD

2 μM Cisplatin, 20 μM carboplatin, and 1 μM oxaliplatin were used to inhibit the growth of CAL-27 by 20% respectively. These drugs were then used to induce chemotherapy-induced peripheral neuropathy in Rat Schwann Cells (RSC96). The changes in cell metabolism and myelin formation in RSC96 were investigated.

RESULT

Cisplatin and carboplatin, but not oxaliplatin increased intracellular and mitochondrial reactive oxygen species in RSC96. Only Cisplatin and carboplatin decreased mitochondrial membrane potential (ΔΨm) and ATP production in RSC96. Both Cisplatin and carboplatin led to demyelination of RSC96, characterized by increased expression of p75NTR and decreased expression of myelin protein zero (MPZ).

CONCLUSION

Cisplatin and carboplatin, but not oxaliplatin, caused mitochondrial dysfunction and induced demyelination in RSC96 while showing similar toxicity to head and neck cancer cells. Oxaliplatin may be a potential chemotherapy drug to prevent CIPN in patients with head and neck cancer.

Ablation of Argonaute 2 in Schwann cells accelerates the progression of diabetic peripheral neuropathy

Schwann cells (SCs) form myelin and provide metabolic support for axons, and are essential for normal nerve function. Identification of key molecules specific to SCs and nerve fibers may provide new therapeutic targets for diabetic peripheral neuropathy (DPN). Argonaute2 (Ago2) is a key molecular player that mediates the activity of miRNA-guided mRNA cleavage and miRNA stability. Our study found that Ago2 knockout (Ago2-KO) in proteolipid protein (PLP) lineage SCs in mice resulted in a significant reduction of nerve conduction velocities and impairments of thermal and mechanical sensitivities. Histopathological data revealed that Ago2-KO significantly induced demyelination and neurodegeneration. When DPN was induced in both wild-type and Ago2-KO mice, Ago2-KO mice exhibited further decreased myelin thickness and exacerbated neurological outcomes compared with wild-type mice. Deep sequencing analysis of Ago2 immunoprecipitated complexes showed that deregulated miR-206 in Ago2-KO mice is highly related to mitochondrial function. In vitro data showed that knockdown of miR-200 induced mitochondrial dysfunction and apoptosis in SCs. Together, our data suggest that Ago2 in SCs is essential to maintain peripheral nerve function while ablation of Ago2 in SCs exacerbates SC dysfunction and neuronal degeneration in DPN. These findings provide new insight into the molecular mechanisms of DPN.

Electrophysiologic Patterns of Symptomatic Vincristine-Induced Peripheral Neuropathy in Children with Acute Lymphocytic Leukemia

Acute lymphocytic leukemia is one of the most common cancers in children. Multi-drug chemotherapy is used for treatment, and the representative drug is vincristine. Although various side effects may occur due to vincristine, the association with peripheral neuropathy is high compared to that of other drugs. This study focused on children under the age of 18 years of age with ALL who received chemotherapy containing vincristine. We retrospectively analyzed the results of a nerve conduction study and a cumulative dose of vincristine in 30 children diagnosed with peripheral neuropathy. The average cumulative dose until diagnosis of vincristine-induced peripheral neuropathy was 14.99 ± 1.21 mg/m², and motor nerves were predominantly involved. Additionally, a marked decrease in average amplitude was also observed in motor nerves. In addition, when the relationship between the incidence of peripheral neuropathy and the cumulative dose was analyzed through the survival curve, about 50% of children developed peripheral neuropathy at a dose of 15.5 ± 1.77 mg/m². Based on the electrophysiological characteristics of pediatric vincristine-induced peripheral neuropathy, as well as the relationship between the incidence rate and the cumulative dose, it is possible to observe more closely the vincristine-induced peripheral neuropathy occurrence in children with ALL at an appropriate time.

Inhibiting apoptosis of Schwann cell under the high-glucose condition: A promising approach to treat diabetic peripheral neuropathy using Chinese herbal medicine

Diabetic peripheral neuropathy (DPN) is a common complication of diabetes. Glycemic control and lifestyle alterations cannot prevent the development of DPN; therefore, investigating effective treatments for DPN is crucial. Schwann cells (SCs) maintain the physiological function of peripheral nerves and promote the repair and regeneration of injured nerves. Inhibiting the apoptosis of SCs through various pathological pathways in a high-glucose environment plays an important role in developing DPN. Therefore, inhibiting the apoptosis of SCs can be a novel treatment strategy for DPN. Previous studies have indicated the potential of Chinese herbal medicine (CHM) in treating DPN. In this study, we have reviewed the effects of CHM (both monomers and extracts) on the apoptosis of SCs by interfering with the production of advanced glycation end products, oxidative stress, and endoplasmic reticulum stress pathological pathways. This review will demonstrate the potentialities of CHM in inhibiting apoptosis in SCs, providing new insights and perspectives for treating DPN.

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.

Application of Hybrid Electrically Conductive Hydrogels Promotes Peripheral Nerve Regeneration

Peripheral nerve injury (PNI) occurs frequently, and the prognosis is unsatisfactory. As the gold standard of treatment, autologous nerve grafting has several disadvantages, such as lack of donors and complications. The use of functional biomaterials to simulate the natural microenvironment of the nervous system and the combination of different biomaterials are considered to be encouraging alternative methods for effective tissue regeneration and functional restoration of injured nerves. Considering the inherent presence of an electric field in the nervous system, electrically conductive biomaterials have been used to promote nerve regeneration. Due to their singular physical properties, hydrogels can provide a three-dimensional hydrated network that can be integrated into diverse sizes and shapes and stimulate the natural functions of nerve tissue. Therefore, conductive hydrogels have become the most effective biological material to simulate human nervous tissue's biological and electrical characteristics. The principal merits of conductive hydrogels include their physical properties and their electrical peculiarities sufficient to effectively transmit electrical signals to cells. This review summarizes the recent applications of conductive hydrogels to enhance peripheral nerve regeneration.

An electroceutical approach enhances myelination via upregulation of lipid biosynthesis in the dorsal root ganglion

As the myelin sheath is crucial for neuronal saltatory conduction, loss of myelin in the peripheral nervous system (PNS) leads to demyelinating neuropathies causing muscular atrophy, numbness, foot deformities and paralysis. Unfortunately, few interventions are available for such neuropathies, because previous pharmaceuticals have shown severe side effects and failed in clinical trials. Therefore, exploring new strategies to enhance PNS myelination is critical to provide solution for such intractable diseases. This study aimed to investigate the effectiveness of electrical stimulation (ES) to enhance myelination in the mouse dorsal root ganglion (DRG) - an ex vivo model of the PNS. Mouse embryonic DRGs were extracted at E13 and seeded onto Matrigel-coated surfaces. After sufficient growth and differentiation, screening was carried out by applying ES in the 1-100 Hz range at the beginning of the myelination process. DRG myelination was evaluated via immunostaining at the intermediate (19 DIV) and mature (30 DIV) stages. Further biochemical analyses were carried out by utilizing RNA sequencing, qPCR and biochemical assays at both intermediate and mature myelination stages. Imaging of DRG myelin lipids was carried out via time-of-flight secondary ion mass spectrometry (ToF-SIMS). With screening ES conditions, optimal condition was identified at 20 Hz, which enhanced the percentage of myelinated neurons and average myelin length not only at intermediate (129% and 61%) but also at mature (72% and 17%) myelination stages. Further biochemical analyses elucidated that ES promoted lipid biosynthesis in the DRG. ToF-SIMS imaging showed higher abundance of the structural lipids, cholesterol and sphingomyelin, in the myelin membrane. Therefore, promotion of lipid biosynthesis and higher abundance of myelin lipids led to ES-mediated myelination enhancement. Given that myelin lipid deficiency is culpable for most demyelinating PNS neuropathies, the results might pave a new way to treat such diseases via electroceuticals.

Quality Control Mechanisms of Mitochondria: Another Important Target for Treatment of Peripheral Neuropathy

Mitochondria provide energy for various cellular activities and are involved in the regulating of several physiological and pathological processes. Mitochondria constitute a dynamic network regulated by numerous quality control mechanisms; for example, division is necessary for mitochondria to develop, and fusion dilutes toxins produced by the mitochondria. Mitophagy removes damaged mitochondria. The etiologies of peripheral neuropathy include congenital and acquired diseases, and the pathogenesis varies; however, oxidative stress caused by mitochondrial damage is the accepted pathogenesis of peripheral neuropathy. Regulation and control of mitochondrial quality might point the way toward potential treatments for peripheral neuropathy. This article will review mitochondrial quality control mechanisms, their involvement in peripheral nerve diseases, and their potential therapeutic role.

Activation of mTORC1 and c-Jun by Prohibitin1 loss in Schwann cells may link mitochondrial dysfunction to demyelination

Schwann cell (SC) mitochondria are quickly emerging as an important regulator of myelin maintenance in the peripheral nervous system (PNS). However, the mechanisms underlying demyelination in the context of mitochondrial dysfunction in the PNS are incompletely understood. We recently showed that conditional ablation of the mitochondrial protein Prohibitin 1 (PHB1) in SCs causes a severe and fast progressing demyelinating peripheral neuropathy in mice, but the mechanism that causes failure of myelin maintenance remained unknown. Here, we report that mTORC1 and c-Jun are continuously activated in the absence of Phb1, likely as part of the SC response to mitochondrial damage. Moreover, we demonstrate that these pathways are involved in the demyelination process, and that inhibition of mTORC1 using rapamycin partially rescues the demyelinating pathology. Therefore, we propose that mTORC1 and c-Jun may play a critical role as executioners of demyelination in the context of perturbations to SC mitochondria.

Prohibitin 1 is essential to preserve mitochondria and myelin integrity in Schwann cells

In peripheral nerves, Schwann cells form myelin and provide trophic support to axons. We previously showed that the mitochondrial protein prohibitin 2 can localize to the axon-Schwann-cell interface and is required for developmental myelination. Whether the homologous protein prohibitin 1 has a similar role, and whether prohibitins also play important roles in Schwann cell mitochondria is unknown. Here, we show that deletion of prohibitin 1 in Schwann cells minimally perturbs development, but later triggers a severe demyelinating peripheral neuropathy. Moreover, mitochondria are heavily affected by ablation of prohibitin 1 and demyelination occurs preferentially in cells with apparent mitochondrial loss. Furthermore, in response to mitochondrial damage, Schwann cells trigger the integrated stress response, but, contrary to what was previously suggested, this response is not detrimental in this context. These results identify a role for prohibitin 1 in myelin integrity and advance our understanding about the Schwann cell response to mitochondrial damage.

Mitochondrial Bioenergetic, Photobiomodulation and Trigeminal Branches Nerve Damage, What's the Connection? A Review

Background: Injury of the trigeminal nerve in oral and maxillofacial surgery can occur. Schwann cell mitochondria are regulators in the development, maintenance and regeneration of peripheral nerve axons. Evidence shows that after the nerve injury, mitochondrial bioenergetic dysfunction occurs and is associated with pain, neuropathy and nerve regeneration deficit. A challenge for research is to individuate new therapies able to normalise mitochondrial and energetic metabolism to aid nerve recovery after damage. Photobiomodulation therapy can be an interesting candidate, because it is a technique involving cell manipulation through the photonic energy of a non-ionising light source (visible and NIR light), which produces a nonthermal therapeutic effect on the stressed tissue. Methods: The review was based on the following questions: (1) Can photo-biomodulation by red and NIR light affect mitochondrial bioenergetics? (2) Can photobiomodulation support damage to the trigeminal nerve branches? (preclinical and clinical studies), and, if yes, (3) What is the best photobiomodulatory therapy for the recovery of the trigeminal nerve branches? The papers were searched using the PubMed, Scopus and Cochrane databases. This review followed the ARRIVE-2.0, PRISMA and Cochrane RoB-2 guidelines. Results and conclusions: The reliability of photobiomodulatory event strongly bases on biological and physical-chemical evidence. Its principal player is the mitochondrion, whether its cytochromes are directly involved as a photoacceptor or indirectly through a vibrational and energetic variation of bound water: water as the photoacceptor. The 808-nm and 100 J/cm² (0.07 W; 2.5 W/cm²; pulsed 50 Hz; 27 J per point; 80 s) on rats and 800-nm and 0.2 W/cm² (0.2 W; 12 J/cm²; 12 J per point; 60 s, CW) on humans resulted as trustworthy therapies, which could be supported by extensive studies.

Early disruption of nerve mitochondrial and myelin lipid homeostasis in obesity-induced diabetes

Diabetic neuropathy is a major complication of diabetes. Current treatment options alleviate pain but do not stop the progression of the disease. At present, there are no approved disease-modifying therapies. Thus, developing more effective therapies remains a major unmet medical need. Seeking to better understand the molecular mechanisms driving peripheral neuropathy, as well as other neurological complications associated with diabetes, we performed spatiotemporal lipidomics, biochemical, ultrastructural, and physiological studies on PNS and CNS tissue from multiple diabetic preclinical models. We unraveled potentially novel molecular fingerprints underlying nerve damage in obesity-induced diabetes, including an early loss of nerve mitochondrial (cardiolipin) and myelin signature (galactosylceramide, sulfatide, and plasmalogen phosphatidylethanolamine) lipids that preceded mitochondrial, myelin, and axonal structural/functional defects; started in the PNS; and progressed to the CNS at advanced diabetic stages. Mechanistically, we provided substantial evidence indicating that these nerve mitochondrial/myelin lipid abnormalities are (surprisingly) not driven by hyperglycemia, dysinsulinemia, or insulin resistance, but rather associate with obesity/hyperlipidemia. Importantly, our findings have major clinical implications as they open the door to novel lipid-based biomarkers to diagnose and distinguish different subtypes of diabetic neuropathy (obese vs. nonobese diabetics), as well as to lipid-lowering therapeutic strategies for treatment of obesity/diabetes-associated neurological complications and for glycemic control.

Spatiotemporal lipidomics, biochemical, ultrastructural, and physiological characterization of peripheral and central nervous system tissue from multiple diabetic pre-clinical models.

Frequency-dependent changes in mitochondrial number and generation of reactive oxygen species in a rat model of vibration-induced injury

Regular use of vibrating hand tools results in cold-induced vasoconstriction, finger blanching, and a reduction in tactile sensitivity and manual dexterity. Depending upon the length and frequency, vibration induces regeneration, or dysfunction and apoptosis, inflammation and an increase in reactive oxygen species (ROS) levels. These changes may be associated with mitochondria, this study examined the effects of vibration on total and functional mitochondria number. Male rats were exposed to restraint or tail vibration at 62.5, 125, or 250 Hz. The frequency-dependent effects of vibration on mitochondrial number and generation of oxidative stress were examined. After 10 days of exposure at 125 Hz, ventral tail arteries (VTA) were constricted and there was an increase in mitochondrial number and intensity of ROS staining. In the skin, the influence of vibration on arterioles displayed a similar but insignificant response in VTA. There was also a reduction in the number of small nerves with exposure to vibration at 250 Hz, and a reduction in mitochondrial number in nerves in restrained and all vibrated conditions. There was a significant rise in the size of the sensory receptors with vibration at 125 Hz, and an elevation in ROS levels. Based upon these results, mitochondria number and activity are affected by vibration, especially at frequencies at or near resonance. The influence of vibration on the vascular system may either be adaptive or maladaptive. However, the effects on cutaneous nerves might be a precursor to loss of innervation and sensory function noted in workers exposed to vibration.

Glial mitochondrial function and dysfunction in health and neurodegeneration

Mitochondria play essential metabolic roles in neural cells. Mitochondrial dysfunction has profound effects on the brain. In primary mitochondrial diseases, mutations that impair specific oxidative phosphorylation (OXPHOS) proteins or OXPHOS assembly factors lead to isolated biochemical defects and a heterogeneous group of clinical phenotypes, including mitochondrial encephalopathies. A broader defect of OXPHOS function, due to mutations in proteins involved in mitochondrial DNA maintenance, mitochondrial biogenesis, or mitochondrial tRNAs can also underlie severe mitochondrial encephalopathies. While primary mitochondrial dysfunction causes rare genetic forms of neurological disorders, secondary mitochondrial dysfunction is involved in the pathophysiology of some of the most common neurodegenerative disorders, including Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis. Many studies have investigated mitochondrial function and dysfunction in bulk central nervous system (CNS) tissue. However, the interpretation of these studies has been often complicated by the extreme cellular heterogeneity of the CNS, which includes many different types of neurons and glial cells. Because neurons are especially dependent on OXPHOS for ATP generation, mitochondrial dysfunction is thought to be directly involved in cell autonomous neuronal demise. Despite being metabolically more flexible than neurons, glial mitochondria also play an essential role in the function of the CNS, and have adapted specific metabolic and mitochondrial features to support their diversity of functions. This review analyzes our current understanding and the gaps in knowledge of mitochondrial properties of glia and how they affect neuronal functions, in health and disease.

FGF10 Enhances Peripheral Nerve Regeneration via the Preactivation of the PI3K/Akt Signaling-Mediated Antioxidant Response

The process of axonal regeneration after peripheral nerve injury (PNI) is slow and mostly incomplete. Previous studies have investigated the neuroprotective effects of fibroblast growth factor 10 (FGF10) against spinal cord injury and cerebral ischemia brain injury. However, the role of FGF10 in peripheral nerve regeneration remains unknown. In this study, we aimed to investigate the underlying therapeutic effects of FGF10 on nerve regeneration and functional recovery after PNI and to explore the associated mechanism. Our results showed that FGF10 administration promoted axonal regeneration and functional recovery after nerve damage. Moreover, exogenous FGF10 treatment also prevented SCs from excessive oxidative stress-induced apoptosis, which was probably related to the activation of phosphatidylinositol-3 kinase/protein kinase B (PI3K/Akt) signaling. The inhibition of the PI3K/Akt pathway by the specific inhibitor LY294002 partially reversed the therapeutic effects of FGF10 both in vivo and in vitro. Thus, from our perspective, FGF10 may be a promising therapeutic drug for repairing sciatic nerve damage through countering excessive oxidative stress-induced SC apoptosis.

Peroxynitrite supports a metabolic reprogramming in merlin-deficient Schwann cells and promotes cell survival

Neurofibromatosis type 2 (NF2) is an autosomal-dominant disorder characterized by the development of bilateral vestibular schwannomas. The NF2 gene encodes the tumor suppressor merlin, and loss of merlin activity promotes tumorigenesis and causes NF2. Cellular redox signaling has been implicated in different stages of tumor development. Among reactive nitrogen species, peroxynitrite is the most powerful oxidant produced by cells. We recently showed that peroxynitrite-mediated tyrosine nitration down-regulates mitochondrial metabolism in tumor cells. However, whether peroxynitrite supports a metabolic shift that could be exploited for therapeutic development is unknown. Here, we show that vestibular schwannomas from NF2 patients and human, merlin-deficient (MD) Schwann cells have high levels of endogenous tyrosine nitration, indicating production of peroxynitrite. Furthermore, scavenging or inhibiting peroxynitrite formation significantly and selectively decreased survival of human and mouse MD-Schwann cells. Using multiple complementary methods, we also found that merlin deficiency leads to a reprogramming of energy metabolism characterized by a peroxynitrite-dependent decrease of oxidative phosphorylation and increased glycolysis and glutaminolysis. In MD-Schwann cells, scavenging of peroxynitrite increased mitochondrial oxygen consumption and membrane potential, mediated by the up-regulation of the levels and activity of mitochondrial complex IV. This increase in mitochondrial activity correlated with a decrease in the glycolytic rate and glutamine dependence. This is the first demonstration of a peroxynitrite-dependent reprogramming of energy metabolism in tumor cells. Oxidized proteins constitute a novel target for therapeutic development not only for the treatment of NF2 schwannomas but also other tumors in which peroxynitrite plays a regulatory role.

Mitochondrial contributions to neuronal development and function

Mitochondria are critical to tissues and organs characterized by high-energy demands, such as the nervous system. They provide essential energy and metabolites, and maintain Ca2+ balance, which is imperative for proper neuronal function and development. Emerging findings further underline the role of mitochondria in neurons. Technical advances in the last decades made it possible to investigate key mechanisms in neuronal development and the contribution of mitochondria therein. In this article, we discuss the latest findings relevant to the involvement of mitochondria in neuronal development, placing emphasis on mitochondrial metabolism and dynamics. In addition, we survey the role of mitochondrial energy metabolism and Ca2+ homeostasis in proper neuronal function, and the involvement of mitochondria in axon myelination.

Protective Effect of Baicalein on Oxidative Stress-induced DNA Damage and Apoptosis in RT4-D6P2T Schwann Cells

Background: Due to its high antioxidant activity, baicalein, a kind of flavonoid present in Radical Scutellariae, has various pharmacological effects. However, the protective effect against oxidative stress in Schwann cells, which plays an important role in peripheral neuropathy, has not yet been studied. In this study, the effects of baicalein on hydrogen peroxide (H₂O₂)-induced DNA damage and apoptosis in RT4-D6P2T Schwann cells were evaluated. Methods: Cell viability assay was performed using MTT assay and colony formation assay. Apoptosis was assessed by flow cytometry analysis and DNA fragmentation assay. The effects on DNA damage and ATP content were analyzed by comet method and luminometer. In addition, changes in protein expression were observed by Western blotting. Results: Our results show that baicalein significantly inhibits H₂O₂-induced cytotoxicity through blocking reactive oxygen species (ROS) generation. We also demonstrate that baicalein is to block H₂O₂-induced DNA damage as evidenced by inhibition of DNA tail formation and γH2AX phosphorylation. Moreover, baicalein significantly attenuated H₂O₂-induced apoptosis and mitochondrial dysfunction, and restored inhibition of ATP production. The suppression of apoptosis by baicalein in H₂O₂-stimulated cells was associated with reduction of increased Bax/Bcl-2 ratio, activation of caspase-9 and -3, and degradation of poly (ADP-ribose) polymerase. Conclusions: These results demonstrate that baicalein eliminates H₂O₂-induced apoptosis through conservation of mitochondrial function by the removal of ROS. Therefore, it is suggested that baicalein protects Schwann cells from oxidative stress, and may be beneficial for the prevention and treatment of peripheral neuropathy induced by oxidative stress.

Activation of the Nrf2/HO-1 signaling pathway contributes to the protective effects of baicalein against oxidative stress-induced DNA damage and apoptosis in HEI193 Schwann cells

Baicalein, a flavonoid extracted from the roots of Scutellaria baicalensis Georgi., has various pharmacological effects due to its high antioxidant activity. However, no study has yet been conducted on the protective efficacy of baicalein against oxidative stress in Schwann cells. In this study, we evaluated the protective effect of baicalein on DNA damage and apoptosis induced by hydrogen peroxide (H₂O₂) in HEI193 Schwann cells. For this purpose, HEI193 cells exposed to H₂O₂ in the presence or absence of baicalein were applied to cell viability assay, immunoblotting, Nrf2-specific small interfering RNA (siRNA) transfection, comet assay, and flow cytometry analyses. Our results showed that baicalein effectively inhibited H₂O₂-induced cytotoxicity and DNA damage associated with the inhibition of reactive oxygen species (ROS) accumulation. Baicalein also weakened H₂O₂-induced mitochondrial dysfunction, increased the Bax/Bcl-2 ratio, activated caspase-9 and -3, and degraded poly(ADP-ribose) polymerase. In addition, baicalein increased not only the expression but also the phosphorylation of nuclear factor-erythroid 2 related factor 2 (Nrf2) and promoted the expression of heme oxygenase-1 (HO-1), a critical target enzyme of Nrf2, although the expression of kelch-like ECH-associated protein-1 was decreased. However, the inhibition of Nrf2 expression by transfection with Nrf2-siRNA transfection abolished the expression of HO-1 and antioxidant potential of baicalein. These results demonstrate that baicalein attenuated H₂O₂-induced apoptosis through the conservation of mitochondrial function while eliminating ROS in HEI193 Schwann cells, and the antioxidant efficacy of baicalein implies at least a Nrf2/HO-1 signaling pathway-dependent mechanism. Therefore, it is suggested that baicalein may have a beneficial effect on the prevention and treatment of peripheral neuropathy induced by oxidative stress.

The leptin receptor mutation of the obese Zucker rat causes sciatic nerve demyelination with a centripetal pattern defect

Young male Zucker rats with a leptin receptor mutation are obese, have a non-insulin-dependent diabetes mellitus (NIDDM), and other endocrinopathies. Tibial branches of the sciatic nerve reveal a progressive demyelination that progresses out of the Schwann cells (SCs) where electron-contrast deposits are accumulated while the minor lines or intermembranous SC contacts display exaggerated spacings. Cajal bands contain diversely contrasted vesicles adjacent to the abaxonal myelin layer with blemishes; they appear dispatched centripetally out of many narrow electron densities, regularly spaced around the myelin annulus. These anomalies widen and yield into sectors across the stacked myelin layers. Throughout the worse degradations, the adaxonal membrane remains along the axonal neuroplasm. This peripheral neuropathy with irresponsive leptin cannot modulate hypothalamic-pituitary-adrenal axis and SC neurosteroids, thus exacerbates NIDDM condition. Additionally, the ultrastructure of the progressive myelin alterations may have unraveled a peculiar, centripetal mode of trafficking maintenance of the peripheral nervous system myelin, while some adhesive glycoproteins remain between myelin layers, somewhat hindering the axon mutilation. Heading title: Peripheral neuropathy and myelin.