Loss Of Intraepidermal Nerve Fibers Research Articles

Netazepide, an Antagonist of Cholecystokinin Type 2 Receptor, Prevents Vincristine-Induced Sensory Neuropathy in Mice.

Among the vinca-alkaloid class, vincristine is a potent chemotherapeutic agent with significant neurotoxic effects and is employed to address a wide spectrum of cancer types. Recently, the therapeutic potential of the cholecystokinin type 2 receptor (CCK2R) as a target for vincristine-induced peripheral neuropathy (VIPN) was demonstrated. In this study, the impact of preventive CCK2R blockade using netazepide (Trio Medicines Ltd., London, UK) was investigated in a mouse model of vincristine-induced peripheral neuropathy. Netazepide is a highly selective CCK2R antagonist under development for the treatment of patients with gastric neuroendocrine tumors caused by hypergastrinemia secondary to chronic autoimmune atrophic gastritis. Vincristine-induced peripheral neuropathy was induced by intraperitoneal injections of vincristine at 100 µg/kg/d for 7 days (D0 to D7). Netazepide (2 mg/kg/d or 5 mg/kg/d, per os) was administered one day before vincristine treatment until D7. Vincristine induced a high tactile allodynia from D1 to D7. VIPN was characterized by dorsal root ganglion neuron (DRG) and intraepidermal nerve fiber (IENF) loss, and enlargement and loss of myelinated axons in the sciatic nerve. Netazepide completely prevented the painful symptoms and nerve injuries induced by vincristine. In conclusion, the fact that netazepide protected against vincristine-induced peripheral neuropathy in a mouse model strongly supports the assessment of its therapeutic potential in patients receiving such chemotherapy.

Endothelial Glycocalyx in the Peripheral Capillaries is Injured Under Oxaliplatin-Induced Neuropathy

Oxaliplatin, a platinum-based anticancer drug, is associated with peripheral neuropathy (oxaliplatin-induced peripheral neuropathy, OIPN), which can lead to worsening of quality of life and treatment interruption. The endothelial glycocalyx, a fragile carbohydrate-rich layer covering the luminal surface of endothelial cells, acts as an endothelial gatekeeper and has been suggested to protect nerves, astrocytes, and other cells from toxins and substances released from the capillary vessels. Mechanisms underlying OIPN and the role of the glycocalyx remain unclear. This study aimed to define changes in the three-dimensional ultrastructure of capillary endothelial glycocalyx near nerve fibers in the hind paws of mice with OIPN. The mouse model of OPIN revealed disruption of the endothelial glycocalyx in the peripheral nerve compartment, accompanied by vascular permeability, edema, and damage to the peripheral nerves. To investigate the potential treatment interventions, nafamostat mesilate, a glycocalyx protective agent was used in tumor-bearing male mice. Nafamostat mesilate suppressed mechanical allodynia associated with neuropathy. It also prevented intra-epidermal nerve fiber loss and improved vascular permeability in the peripheral paws. The disruption of endothelial glycocalyx in the capillaries that lie within peripheral nerve bundles is a novel finding in OPIN. Furthermore, these findings point toward the potential of a new treatment strategy targeting endothelial glycocalyx to prevent vascular injury as an effective treatment of neuropathy as well as of many other diseases. PerspectiveOIPN damages the endothelial glycocalyx in the peripheral capillaries, increasing vascular permeability. In order to prevent OIPN, this work offers a novel therapy approach that targets endothelial glycocalyx.

Lanatoside C inhibits herpes simplex virus 1 replication by regulating NRF2 distribution within cells

BackgroundIn the past decades, extensive research has been conducted to identify new drug targets for the treatment of Herpes simplex virus type 1 (HSV-1) infections. However, the emergence of drug-resistant HSV-1 strains remains a major challenge. This necessitates the identification of new drugs with novel mechanisms of action. Lanatoside C (LanC), a cardiac glycoside (CG) approved by the US Food and Drug Administration (FDA), has demonstrated anticancer and antiviral properties. Nevertheless, its potential as an agent against HSV-1 infections and the underlying mechanism of action are currently unknown. PurposeThis study aimed to investigate the antiviral activity of LanC against HSV-1 and elucidate its molecular mechanisms. MethodsThe in vitro antiviral activity of LanC was assessed by examining the levels of viral genes, proteins, and virus titers in HSV-1-infected ARPE-19 and Vero cells. Immunofluorescence (IF) analysis was performed to determine the intracellular distribution of NRF2. Additionally, an in vivo mouse model of HSV-1 infection was developed to evaluate the antiviral activity of LanC, using indicators such as intraepidermal nerve fibers (IENFs) loss and viral gene inhibition. ResultsOur findings demonstrate that LanC significantly inhibits HSV-1 replication both in vitro and in vivo. The antiviral effect of LanC is mediated by the perinuclear translocation of NRF2. ConclusionsLanC exhibits anti-HSV-1 effects in viral infections, which are associated with the intracellular translocation of NRF2. These findings suggest that LanC has the potential to serve as a novel NRF2 modulator in the treatment of viral diseases.

Skin innervation across amyotrophic lateral sclerosis clinical stages: new prognostic biomarkers.

Over recent decades, peripheral sensory abnormalities, including the evidence of cutaneous denervation, have been reported among the non-motor manifestations in amyotrophic lateral sclerosis (ALS). However, a correlation between cutaneous innervation and clinical features has not been found. The aims of this study were to assess sensory involvement by applying a morpho-functional approach to a large population of ALS patients stratified according to King's stages and correlate these findings with the severity and prognosis of the disease. We recruited 149 ALS patients and 41 healthy controls. Patients undertook clinical questionnaires for small fibre neuropathy symptoms (Small Fiber Neuropathy Symptoms Inventory Questionnaire) and underwent nerve conductions studies (NCS) and 3-mm punch skin biopsies from leg, thigh and fingertip. We assessed intraepidermal nerve fibre (IENF) and Meissner corpuscle (MC) density by applying an indirect immunofluorescence technique. Moreover, a subset of 65 ALS patients underwent a longitudinal study with repeat biopsies from the thigh at 6- and 12-month follow-ups. Serum NfL levels were measured in 40 patients. Sensory symptoms and sensory NCS abnormalities were present in 32.2% and 24% of patients, respectively, and increased across clinical stages. Analogously, we observed a progressive reduction in amplitude of the sensory and motor ulnar nerve potential from stage 1 to stage 4. Skin biopsy showed a significant loss of IENFs and MCs in ALS compared with healthy controls (all P < 0.001). Across the clinical stages, we found a progressive reduction in MCs (P = 0.004) and an increase in IENFs (all P < 0.027). The increase in IENFs was confirmed by the longitudinal study. Interestingly, the MC density inversely correlated with NfL level (r = -0.424, P = 0.012), and survival analysis revealed that low MC density, higher NfL levels and increasing IENF density over time were associated with a poorer prognosis (all P < 0.024). To summarize, in patients with ALS, peripheral sensory involvement worsens in parallel with motor disability. Furthermore, the correlation between skin innervation and disease activity may suggest the use of skin innervation as a putative prognostic biomarker.

Spinal Neuronal miR-124 Inhibits Microglial Activation and Contributes to Preventive Effect of Electroacupuncture on Chemotherapy-Induced Peripheral Neuropathy in Mice.

Chemotherapy-induced peripheral neuropathy (CIPN) is a persistent and irreversible side effect of antineoplastic agents. Patients with CIPN usually show chronic pain and sensory deficits with glove-and-stocking distribution. However, whether spinal neuronal microRNA (miR)-124 is involved in cisplatin-induced peripheral neuropathy remains to be studied. In this study, miR-124 was significantly reduced in the spinal dorsal horn in CIPN mice. Overexpression of neuronal miR-124 induced by injecting adeno-associated virus with neuron-specific promoter into the spinal cord of mice prevented the development of mechanical allodynia, sensory deficits, and the loss of intraepidermal nerve fibers induced by cisplatin. Meanwhile, cisplatin-induced M1 microglia activation and the release of proinflammatory cytokines were significantly inhibited by overexpression of neuronal miR-124. Furthermore, electroacupuncture (EA) treatment upregulated miR-124 expression in the spinal dorsal horn of CIPN mice. Interestingly, downregulation of spinal neuronal miR-124 significantly inhibited the regulatory effect of EA on CIPN and microglia activity as well as spinal neuroinflammation induced by cisplatin. These results demonstrate that spinal neuronal miR-124 is involved in the prevention and treatment of EA on cisplatin-induced peripheral neuropathy in mice. Our findings suggest that spinal neuronal miR-124 might be a potential target for EA effect, and we provide, to our knowledge, a new experimental basis for EA prevention of CIPN.

SUMOylation Modulates Reactive Oxygen Species (ROS) Levels and Acts as a Protective Mechanism in the Type 2 Model of Diabetic Peripheral Neuropathy.

Diabetic peripheral neuropathy (DPN) is the prevalent type of peripheral neuropathy; it primarily impacts extremity nerves. Its multifaceted nature makes the molecular mechanisms of diabetic neuropathy intricate and incompletely elucidated. Several types of post-translational modifications (PTMs) have been implicated in the development and progression of DPN, including phosphorylation, glycation, acetylation and SUMOylation. SUMOylation involves the covalent attachment of small ubiquitin-like modifier (SUMO) proteins to target proteins, and it plays a role in various cellular processes, including protein localization, stability, and function. While the specific relationship between high blood glucose and SUMOylation is not extensively studied, recent evidence implies its involvement in the development of DPN in type 1 diabetes. In this study, we investigated the impact of SUMOylation on the onset and progression of DPN in a type 2 diabetes model using genetically modified mutant mice lacking SUMOylation, specifically in peripheral sensory neurons (SNS-Ubc9-/-). Behavioural measurement for evoked pain, morphological analyses of nerve fibre loss in the epidermis, measurement of reactive oxygen species (ROS) levels, and antioxidant molecules were analysed over several months in SUMOylation-deficient and control mice. Our longitudinal analysis at 30 weeks post-high-fat diet revealed that SNS-Ubc9-/- mice exhibited earlier and more pronounced thermal and mechanical sensation loss and accelerated intraepidermal nerve fibre loss compared to control mice. Mechanistically, these changes are associated with increased levels of ROS both in sensory neuronal soma and in peripheral axonal nerve endings in SNS-Ubc9-/- mice. In addition, we observed compromised detoxifying potential, impaired respiratory chain complexes, and reduced levels of protective lipids in sensory neurons upon deletion of SUMOylation in diabetic mice. Importantly, we also identified mitochondrial malate dehydrogenase (MDH2) as a SUMOylation target, the activity of which is negatively regulated by SUMOylation. Our results indicate that SUMOylation is an essential neuroprotective mechanism in sensory neurons in type 2 diabetes, the deletion of which causes oxidative stress and an impaired respiratory chain, resulting in energy depletion and subsequent damage to sensory neurons.

Complement Receptor C3aR1 Contributes to Paclitaxel-Induced Peripheral Neuropathic Pain in Mice and Rats.

Cancer chemotherapy-induced neuropathic pain is a devastating pain syndrome without effective therapies. We previously reported that rats deficient in complement C3, the central component of complement activation cascade, showed a reduced degree of paclitaxel-induced mechanical allodynia (PIMA), suggesting that complement is integrally involved in the pathogenesis of this model. However, the underlying mechanism was unclear. Complement activation leads to the production of C3a, which mediates inflammation through its receptor C3aR1. In this article, we report that the administration of paclitaxel induced a significantly higher expression level of C3aR1 on dorsal root ganglion (DRG) macrophages and expansion of these macrophages in DRGs in wild-type (WT) compared with in C3aR1 knockout (KO) mice. We also found that paclitaxel induced less severe PIMA, along with a reduced DRG expression of transient receptor potential channels of the vanilloid subtype 4 (TRPV4), an essential mediator for PIMA, in C3aR1 KO than in WT mice. Treating WT mice or rats with a C3aR1 antagonist markedly attenuated PIMA in association with downregulated DRG TRPV4 expression, reduced DRG macrophages expansion, suppressed DRG neuron hyperexcitability, and alleviated peripheral intraepidermal nerve fiber loss. Administration of C3aR1 antagonist to TRPV4 KO mice further protected them from PIMA. These results suggest that complement regulates PIMA development through C3aR1 to upregulate TRPV4 on DRG neurons and promote DRG macrophage expansion. Targeting C3aR1 could be a novel therapeutic approach to alleviate this debilitating pain syndrome.

Broad-spectrum neuroprotection exerted by DDD-028 in a mouse model of chemotherapy-induced neuropathy.

Neurotoxicity of chemotherapeutics involves peculiar alterations in the structure and function, including abnormal nerve signal transmission, of both the peripheral and central nervous system. The lack of effective pharmacological approaches to prevent chemotherapy-induced neurotoxicity necessitates the identification of innovative therapies. Recent evidence suggests that repeated treatment with the pentacyclic pyridoindole derivative DDD-028 can exert both pain-relieving and glial modulatory effects in mice with paclitaxel-induced neuropathy. This work is aimed at assessing whether DDD-028 is a disease-modifying agent by protecting the peripheral nervous tissues from chemotherapy-induced damage. Neuropathy was induced in animals by paclitaxel injection (2.0 mg kg -1 i.p). DDD-028 (10 mg kg -1 ) and the reference drug, pregabalin (30 mg kg -1 ), were administered per os daily starting concomitantly with the first injection of paclitaxel and continuing 10 days after the end of paclitaxel treatment. The behavioural tests confirmed the antihyperalgesic efficacy of DDD-028 on paclitaxel-induced neuropathic pain. Furthermore, the electrophysiological analysis revealed the capacity of DDD-028 to restore near-normal sensory nerve conduction in paclitaxel-treated animals. Histopathology evidence indicated that DDD-028 was able to counteract effectively paclitaxel-induced peripheral neurotoxicity by protecting against the loss of intraepidermal nerve fibers, restoring physiological levels of neurofilament in nerve tissue and plasma, and preventing morphological alterations occurring in the sciatic nerves and dorsal root ganglia. Overall, DDD-028 is more effective than pregabalin in preventing chemotherapy-induced neurotoxicity. Thus, based on its potent antihyperalgesic and neuroprotective efficacy, DDD-028 seems to be a viable prophylactic medication to limit the development of neuropathies consequent to chemotherapy.

Autonomic Small-Fiber Pathology in Patients With Fibromyalgia

In this clinical and skin biopsy study, we aimed to investigate whether fibromyalgia-associated small-fiber pathology (SFP), consisting of an intraepidermal nerve fiber loss, implies damage of dermal autonomic nerve fibers and how this damage is associated with autonomic symptoms that patients with fibromyalgia syndrome experience. Using skin biopsy, we investigated intraepidermal nerve fiber density, piloerector muscle, and sweat gland nerve fiber density (SGNFD) in 138 participants, that is, 58 patients with fibromyalgia syndrome, 48 healthy subjects, and 32 patients with small-fiber neuropathy. In patients with fibromyalgia-associated SFP, we also investigated how the different skin biopsy variables correlated with autonomic symptoms, as assessed with the Composite Autonomic Symptom Score 31 questionnaire. We found that in patients with fibromyalgia-associated SFP, the piloerector muscle and SGNFD were lower than that in healthy subjects. However, the autonomic small-fiber damage had no correlation with autonomic symptoms severity. In patients with SFP, the intraepidermal, piloerector muscle, and SGNFD were higher than that in patients with small-fiber neuropathy. Our clinical and skin biopsy study shows that patients with fibromyalgia have a reduction of dermal autonomic small fibers paralleling the intraepidermal nerve fiber loss, thus indicating that SFP also implies autonomic small nerve fiber damage. However, the autonomic small-fiber damage we found had no correlation with the severity of autonomic symptoms, and thus its clinical impact is still undetermined. PerspectiveIn patients with fibromyalgia, SFP also affects autonomic fibers. These novel data provide additional insights into the pathophysiology of fibromyalgia syndrome, highlighting the complex role of small-fiber damage in the clinical picture of fibromyalgia.

Schwann Cell-Derived Exosomes Ameliorate Paclitaxel-Induced Peripheral Neuropathy Through the miR-21-Mediated PTEN Signaling Pathway.

Paclitaxel-induced peripheral neuropathy (PIPN) is a neurological disorder resulting from paclitaxel (PTX) treatment for cancer patients. There are currently no drugs available that can definitively prevent or treat PIPN. Exosomes are cell-secreted nanoscale vesicles that mediate communication between neurons and glial cells. We found that Schwann cell-derived exosomes (SC-EXOs) robustly improved PIPN both in vitro and in vivo. In vivo studies showed that SC-EXOs were able to alleviate PTX-induced mechanical nociceptive sensitization in rats. Pathomorphological analysis showed that SC-EXOs ameliorated PTX-induced plantar intraepidermal nerve fiber loss and dorsal root ganglion (DRG) injury. Additionally, the results of in vitro studies showed that SC-EXOs had significant protective effects on the DRG cells damaged by PTX, and did not affect the antitumor effect of PTX against Hela cells. Further, mechanism research revealed that SC-EXOs promoted axonal regeneration and protected damaged neurons by upregulating miR-21 to repress the phosphatase and tensin homolog (PTEN) pathway, which could improve PIPN. Taken together, these findings suggest that SC-EXOs ameliorate PTX-induced peripheral neuropathy via the miR-21-mediated PTEN signaling pathway, which provides a novel strategy for the treatment of PIPN.

Corneal confocal microscopy demonstrates sensory nerve loss in children with autism spectrum disorder.

Autism spectrum disorder (ASD) is a developmental disorder characterized by difficulty in communication and interaction with others. Postmortem studies have shown cerebral neuronal loss and neuroimaging studies show neuronal loss in the amygdala, cerebellum and inter-hemispheric regions of the brain. Recent studies have shown altered tactile discrimination and allodynia on the face, mouth, hands and feet and intraepidermal nerve fiber loss in the legs of subjects with ASD. Fifteen children with ASD (age: 12.00 ± 3.55 years) and twenty age-matched healthy controls (age: 12.83 ± 1.91 years) underwent corneal confocal microscopy (CCM) and quantification of corneal nerve fiber morphology. Corneal nerve fibre density (fibers/mm2) (28.61 ± 5.74 vs. 40.42 ± 8.95, p = 0.000), corneal nerve fibre length (mm/mm2) (16.61 ± 3.26 vs. 21.44 ± 4.44, p = 0.001), corneal nerve branch density (branches/mm2) (43.68 ± 22.71 vs. 62.39 ± 21.58, p = 0.018) and corneal nerve fibre tortuosity (0.037 ± 0.023 vs. 0.074 ± 0.017, p = 0.000) were significantly lower and inferior whorl length (mm/mm2) (21.06 ± 6.12 vs. 23.43 ± 3.95, p = 0.255) was comparable in children with ASD compared to controls. CCM identifies central corneal nerve fiber loss in children with ASD. These findings, urge the need for larger longitudinal studies to determine the utility of CCM as an imaging biomarker for neuronal loss in different subtypes of ASD and in relation to disease progression.

Meteorin Alleviates Paclitaxel-Induced Peripheral Neuropathic Pain in Mice

Chemotherapy-induced peripheral neuropathy is a challenging condition to treat, and arises due to severe, dose-limiting toxicity of chemotherapeutic drugs such as paclitaxel. This often results in debilitating sensory and motor deficits that are not effectively prevented or alleviated by existing therapeutic interventions. Recent studies have demonstrated the therapeutic effects of Meteorin, a neurotrophic factor, in reversing neuropathic pain in rodent models of peripheral nerve injury induced by physical trauma. Here, we sought to investigate the potential antinociceptive effects of recombinant mouse Meteorin (rmMeteorin) using a paclitaxel-induced peripheral neuropathy model in male and female mice. Paclitaxel treatment (4 × 4 mg/kg, i.p.) induced hind paw mechanical hypersensitivity by day 8 after treatment. Thereafter, in a reversal dosing paradigm, five repeated injections of rmMeteorin (.5 and 1.8 mg/kg s.c. respectively) administered over 9 days produced a significant and long-lasting attenuation of mechanical hypersensitivity in both sexes. Additionally, administration of rmMeteorin ( .5 and 1.8 mg/kg), initiated before and during paclitaxel treatment (prevention dosing paradigm), reduced the establishment of hind paw mechanical hypersensitivity. Repeated systemic administration of rmMeteorin in both dosing paradigms decreased histochemical signs of satellite glial cell reactivity as measured by glutamine synthetase and connexin 43 protein expression in the dorsal root ganglion. Additionally, in the prevention administration paradigm rmMeteorin had a protective effect against paclitaxel-induced loss of intraepidermal nerve fibers. Our findings indicate that rmMeteorin has a robust and sustained antinociceptive effect in the paclitaxel-induced peripheral neuropathy model and the development of recombinant human Meteorin could be a novel and effective therapeutic for chemotherapy-induced peripheral neuropathy treatment. PerspectiveChemotherapy neuropathy is a major clinical problem that decreases quality of life for cancer patients and survivors. Our experiments demonstrate that Meteorin treatment alleviates pain-related behaviors, and signs of neurotoxicity in a mouse model of paclitaxel neuropathy.

Early Diagnosis in Cerebellar Ataxia, Neuropathy, Vestibular Areflexia Syndrome (CANVAS) by Focusing on Major Clinical Clues: Beyond Ataxia and Vestibular Impairment.

CANVAS, a rare disorder responsible for late-onset ataxia of autosomal recessive inheritance, can be misdiagnosed. We investigated a series of eight patients with sensory neuropathy and/or an unexplained cough, who appeared to suffer from CANVAS, and we emphasized the clinical clues for early diagnosis. Investigations included clinical and routine laboratory analyses, skin biopsy, nerve biopsy and molecular genetics. The eight patients had clinical and/or laboratory evidence of sensory neuronopathy. All but one had neuropathic pain that had started in an asymmetric fashion in two patients. A chronic cough was a prominent feature in our eight patients and had started years before neuropathic symptoms in all but one. The course of the disease was slow, and ataxia remained mild in all. Five patients were initially thought to have immune-mediated sensory neuronopathy and received immunotherapy. Skin biopsies showed a near complete and non-length-dependent loss of intraepidermal nerve fibers. Moreover, nerve biopsy findings suggested a prominent involvement of small myelinated and unmyelinated fibers. The burden of CANVAS extends far beyond cerebellar ataxia and vestibular manifestations. Indeed, our study shows that a chronic cough and neuropathic pain may represent a major source of impairment in these patients and should not be overlooked to allow an early diagnosis and prevent unnecessary immunotherapy.

SEPT9 Upregulation in Satellite Glial Cells Associated with Diabetic Polyneuropathy in a Type 2 Diabetes-like Rat Model.

Despite the worldwide prevalence and severe complications of type 2 diabetes mellitus (T2DM), the pathophysiological mechanisms underlying the development of diabetic polyneuropathy (DPN) are poorly understood. Beyond strict control of glucose levels, clinical trials for reversing DPN have largely failed. Therefore, understanding the pathophysiological and molecular mechanisms underlying DPN is crucial. Accordingly, this study explored biochemical and neuropathological deficits in a rat model of T2DM induced through high-fat diet (HFD) feeding along with two low-dose streptozotocin (STZ) injections; the deficits were explored through serum lipid, neurobehavioral, neurophysiology, neuropathology, and immunohistochemistry examinations. Our HFD/STZ protocol induced (1) mechanical hyperalgesia and depression-like behaviors, (2) loss of intraepidermal nerve fibers (IENFs) and reduced axonal diameters in sural nerves, and (3) decreased compound muscle action potential. In addition to hyperglycemia, which was correlated with the degree of mechanical hyperalgesia and loss of IENFs, we observed that hypertriglyceridemia was the most dominant deficit in the lipid profiles of the diabetic rats. In particular, SEPT9, the fourth component of the cytoskeleton, increased in the satellite glial cells (SGCs) of the dorsal root ganglia (DRG) in the T2DM-like rats. The number of SEPT9(+) SGCs/DRG was correlated with serum glucose levels and mechanical thresholds. Our findings indicate the putative molecular mechanism underlying DPN, which presumably involves the interaction of SGCs and DRG neurons; nevertheless, further functional research is warranted to clarify the role of SEPT9 in DPN.

Small Fiber Neuropathy with Inadequate Response to Medical Therapy: Diagnosis and Treatment of Small Fiber Neuropathy

Small-fiber neuropathies are a heterogeneous group of disorders affecting thinly myelinated Aδ and unmyelinated C fibers. Patients generally present with neuropathic pain, while dysesthesia, allodynia, pain, burning sensations, and cold sensations are frequently present in a length-dependent pattern. Additional autonomic features of the gastrointestinal, urinary, or cardiovascular systems are frequently observed. Deep-tendon reflexes and nerve conduction tests yield normal results. Skin biopsy is useful for the diagnosis, and can demonstrate the loss of intraepidermal nerve fibers in small-fiber neuropathy and has a diagnostic sensitivity of 80%. Although many causes of small-fiber neuropathy have been reported, the cause remains unknown in 30-50% of the cases. Treatment is directed at the underlying etiology and is supported with symptomatic treatment.

NAD+ Precursors Repair Mitochondrial Function in Diabetes and Prevent Experimental Diabetic Neuropathy.

Axon degeneration in diabetic peripheral neuropathy (DPN) is associated with impaired NAD+ metabolism. We tested whether the administration of NAD+ precursors, nicotinamide mononucleotide (NMN) or nicotinamide riboside (NR), prevents DPN in models of Type 1 and Type 2 diabetes. NMN was administered to streptozotocin (STZ)-induced diabetic rats and STZ-induced diabetic mice by intraperitoneal injection at 50 or 100 mg/kg on alternate days for 2 months. mice The were fed with a high fat diet (HFD) for 2 months with or without added NR at 150 or 300 mg/kg for 2 months. The administration of NMN to STZ-induced diabetic rats or mice or dietary addition of NR to HFD-fed mice improved sensory function, normalized sciatic and tail nerve conduction velocities, and prevented loss of intraepidermal nerve fibers in skin samples from the hind-paw. In adult dorsal root ganglion (DRG) neurons isolated from HFD-fed mice, there was a decrease in NAD+ levels and mitochondrial maximum reserve capacity. These impairments were normalized in isolated DRG neurons from NR-treated mice. The results indicate that the correction of NAD+ depletion in DRG may be sufficient to prevent DPN but does not significantly affect glucose tolerance, insulin levels, or insulin resistance.

The Cannabidiol Analog PECS-101 Prevents Chemotherapy-Induced Neuropathic Pain via PPARγ Receptors

Chemotherapy-induced peripheral neuropathy (CIPN) is the main dose-limiting adverse effect of chemotherapy drugs such as paclitaxel (PTX). PTX causes marked molecular and cellular damage, mainly in the peripheral nervous system, including sensory neurons in the dorsal root ganglia (DRG). Several studies have shown the therapeutic potential of cannabinoids, including cannabidiol (CBD), the major non-psychotomimetic compound found in the Cannabis plant, to treat peripheral neuropathies. Here, we investigated the efficacy of PECS-101 (former HUF-101), a CBD fluorinated analog, on PTX-induced neuropathic pain in mice. PECS-101, administered after the end of treatment with PTX, did not reverse mechanical allodynia. However, PECS-101 (1 mg/kg) administered along with PTX treatment caused a long-lasting relief of the mechanical and cold allodynia. These effects were blocked by a PPARγ, but not CB1 and CB2 receptor antagonists. Notably, the effects of PECS-101 on the relief of PTX-induced mechanical and cold allodynia were not found in macrophage-specific PPARγ-deficient mice. PECS-101 also decreased PTX-induced increase in Tnf, Il6, and Aif1 (Iba-1) gene expression in the DRGs and the loss of intra-epidermal nerve fibers. PECS-101 did not alter motor coordination, produce tolerance, or show abuse potential. In addition, PECS-101 did not interfere with the chemotherapeutic effects of PTX. Thus, PECS-101, a new fluorinated CBD analog, could represent a novel therapeutic alternative to prevent mechanical and cold allodynia induced by PTX potentially through the activation of PPARγ in macrophages.

Spinal Neuronal GRK2 Contributes to Preventive Effect by Electroacupuncture on Cisplatin-Induced Peripheral Neuropathy in Mice.

BACKGROUND:The main symptoms of chemotherapy-induced peripheral neuropathy (CIPN) include pain and numbness. Neuronal G protein–coupled receptor kinase 2 (GRK2) plays an important role in various pain models. Cisplatin treatment can induce the activation of proinflammatory microglia in spinal cord. The purpose of this study was to investigate the role of spinal neuronal GRK2 in cisplatin-induced CIPN and in the prevention of CIPN by electroacupuncture (EA).METHODS:The pain and sensory deficit behaviors of mice were examined by von Frey test and adhesive removal test. The expression of neuronal GRK2 in the spinal cord is regulated by intraspinal injection of adeno-associated virus (AAV) containing neuron-specific promoters. The protein levels of GRK2, triggering receptor expressed on myeloid cells 2 (TREM2), and DNAX-activating protein of 12 kDa (DAP12) in spinal dorsal horn were detected by Western blot, the density of intraepidermal nerve fibers (IENFs) was detected by immunofluorescence, and microglia activation were evaluated by real-time polymerase chain reaction (PCR).RESULTS:In this study, cisplatin treatment led to the decrease of GRK2 expression in the dorsal horn of spinal cord. Overexpression of neuronal GRK2 in spinal cord by intraspinal injection of an AAV vector expressing GRK2 with human synapsin (hSyn) promotor significantly inhibited the loss of IENFs and alleviated the mechanical pain and sensory deficits induced by cisplatin. Real-time PCR analysis showed that the overexpression of neuronal GRK2 significantly inhibited the messenger RNA (mRNA) upregulation of proinflammatory cytokine interleukin (IL)-1β, IL-6, inducible nitric oxide synthase (iNOS), and M1 microglia marker cluster of differentiation (CD)16 induced by cisplatin. Furthermore, the TREM2 and DAP12, which has been demonstrated to play a role in microglia activation and in the development of CIPN, were also downregulated by overexpression of neuronal GRK2 in this study. Interestingly, preventive treatment with EA completely mimics the effect of overexpression of neuronal GRK2 in the spinal cord in this mouse model of cisplatin-induced CIPN. EA increased GRK2 level in spinal dorsal horn after cisplatin treatment. Intraspinal injection of AAV vector specifically downregulated neuronal GRK2, completely reversed the regulatory effect of EA on CIPN and microglia activation. All these indicated that the neuronal GRK2 mediated microglial activation contributed to the process of CIPN.CONCLUSIONS:Neuronal GRK2 in the spinal cord contributed to the preventive effect of EA on CIPN. The neuronal GRK2 may be a potential target for CIPN intervention.

Inhibition of dual leucine zipper kinase prevents chemotherapy-induced peripheral neuropathy and cognitive impairments.

Chemotherapy-induced peripheral neuropathy (CIPN) and chemotherapy-induced cognitive impairments (CICI) are common, often severe neurotoxic side effects of cancer treatment that greatly reduce quality of life of cancer patients and survivors. Currently, there are no Food and Drug Administration-approved agents for the prevention or curative treatment of CIPN or CICI. The dual leucine zipper kinase (DLK) is a key mediator of axonal degeneration that is localized to axons and coordinates the neuronal response to injury. We developed a novel brain-penetrant DLK inhibitor, IACS'8287, which demonstrates potent and highly selective inhibition of DLK in vitro and in vivo. Coadministration of IACS'8287 with the platinum derivative cisplatin prevents mechanical allodynia, loss of intraepidermal nerve fibers in the hind paws, cognitive deficits, and impairments in brain connectivity in mice, all without interfering with the antitumor activity of cisplatin. The protective effects of IACS'8287 are associated with preservation of mitochondrial function in dorsal root ganglion neurons and in brain synaptosomes. In addition, RNA sequencing analysis of dorsal root ganglia reveals modulation of genes involved in neuronal activity and markers for immune cell infiltration by DLK inhibition. These data indicate that CIPN and CICI require DLK signaling in mice, and DLK inhibitors could become an attractive treatment in the clinic when coadministered with cisplatin, and potentially other chemotherapeutic agents, to prevent neurotoxicities as a result of cancer treatment.

Protection against oxaliplatin-induced mechanical and thermal hypersensitivity in Sarm1−/− mice

Chemotherapy-induced peripheral neuropathy (CIPN) is a common dose-limiting side effect of cancer treatment, often associated with degeneration of sensory axons or their terminal regions. Presence of the slow Wallerian degeneration protein (WLDS), or genetic deletion of sterile alpha and TIR motif containing protein 1 (SARM1), which strongly protect axons from degeneration after injury or axonal transport block, alleviate pain in several CIPN models. However, oxaliplatin can cause an acute pain response, suggesting a different mechanism of pain generation. Here, we tested whether the presence of WLDS or absence of SARM1 protects against acute oxaliplatin-induced pain in mice after a single oxaliplatin injection. In BL/6 and WldS mice, oxaliplatin induced significant mechanical and cold hypersensitivities which were absent in Sarm1−/− mice. Despite the presence of hypersensitivity there was no significant loss of intraepidermal nerve fibers (IENFs) in the footpads of any mice after oxaliplatin treatment, suggesting that early stages of pain hypersensitivity could be independent of axon degeneration. To identify other changes that could underlie the pain response, RNA sequencing was carried out in DRGs from treated and control mice of each genotype. Sarm1−/− mice had fewer gene expression changes than either BL/6 or WldS mice. This is consistent with the pain measurements in demonstrating that Sarm1−/− DRGs remain relatively unchanged after oxaliplatin treatment, unlike those in BL/6 and WldS mice. Changes in levels of four transcripts – Alas2, Hba-a1, Hba-a2, and Tfrc – correlated with oxaliplatin-induced pain, or absence thereof, across the three genotypes. Our findings suggest that targeting SARM1 could be a viable therapeutic approach to prevent oxaliplatin-induced acute neuropathic pain.