The role of glial-neuronal metabolic cooperation in modulating progression of multiple sclerosis and neuropathic pain

Increased levels of advanced oxidation protein products (AOPPs) were associated with nociceptive behavior and clinical scores in an experimental progressive autoimmune encephalomyelitis model (PMS-EAE)

Multiple sclerosis (MS) is a neurodegenerative disease that affects the central nervous system (CNS) generating neuropathic pain and anxiety. Primary progressive MS (PPMS) is the most disabling clinical form, and the patients present an intense neurodegenerative process. In this context, the advanced oxidation protein products (AOPPs) are oxidized compounds and their accumulation in plasma has been related to clinical disability in MS patients. However, the involvement of AOPPs in neuropathic pain- and anxiety-like symptoms was not previously evaluated. To assess this, female mice C57BL/6J were used to induce progressive experimental autoimmune encephalomyelitis (PMS-EAE). Clinical score, weight, strength of plantar pressure, rotarod test, mechanical allodynia, and cold hypersensitivity were evaluated before induction (baseline) and on days 7th , 10th , and 14th post-immunization. We assessed nest building, open field, and elevated plus-maze tests 13 days post-immunization. Animals were killed at 14 days post-immunization; then, AOPPs levels, NADPH oxidase, and myeloperoxidase (MPO) activity were measured in the prefrontal cortex, hippocampus, and spinal cord samples. The clinical score increased 14th post-immunization without changes in weight and mobility. Reduced paw strength, mechanical allodynia, and cold allodynia increased in the PMS-EAE animals. PMS-EAE mice showed spontaneous nociception and anxiety-like behavior. AOPPs concentration, NADPH oxidase, and MPO activity increase in CNS structures. Multivariate analyses indicated that the rise of AOPPs levels, NADPH oxidase, and MPO activity influenced the clinical score and cold allodynia. Thus, we indicated the association between non-stimuli painful perception, anxiety-like, and CNS oxidative damage in the PMS-EAE model.

Research trends and hotspots of neuropathic pain in neurodegenerative diseases: a bibliometric analysis

Background

Neuropathic pain is caused by a neurological injury or disease and can have a significant impact on people's daily lives. Studies have shown that neuropathic pain is commonly associated with neurodegenerative diseases. In recent years, there has been a lot of literature on the relationship between neuropathic pain and neurodegenerative diseases. However, bibliometrics is rarely used in analyzing the general aspects of studies on neuropathic pain in neurodegenerative diseases.

Methods

The bibliometric analysis software CiteSpace and VOSviewer were used to analyze the knowledge graph of 387 studies in the Science Citation Index Expanded of the Web of Science Core Collection Database.

Results

We obtained 2,036 documents through the search, leaving 387 documents after culling. 387 documents were used for the data analysis. The data analysis showed that 330 papers related to neuropathic pain in neurodegenerative diseases were published from 2007-2022, accounting for 85.27% of all published literature. In terms of contributions to the scientific study of neuropathic pain, the United States is in the top tier, with the highest number of publications, citations, and H-indexes.

Conclusion

The findings in our study may provide researchers with useful information about research trends, frontiers, and cooperative institutions. Multiple sclerosis, Parkinson's disease, and Alzheimer's disease are the three most studied neurodegenerative diseases. Among the pathological basis of neurodegenerative diseases, microglia-regulated neuroinflammation is a hot research topic. Deep brain stimulation and gamma knife radiosurgery are two popular treatments.

Very-long-chain fatty acids induce glial-derived sphingosine-1-phosphate synthesis, secretion, and neuroinflammation

VLCFAs (very-long-chain fatty acids) are the most abundant fatty acids in myelin. Hence, during demyelination or aging, glia are exposed to higher levels of VLCFA than normal. We report that glia convert these VLCFA into sphingosine-1-phosphate (S1P) via a glial-specific S1P pathway. Excess S1P causes neuroinflammation, NF-κB activation, and macrophage infiltration into the CNS. Suppressing the function of S1P in fly glia or neurons, or administration of Fingolimod, an S1P receptor antagonist, strongly attenuates the phenotypes caused by excess VLCFAs. In contrast, elevating the VLCFA levels in glia and immune cells exacerbates these phenotypes. Elevated VLCFA and S1P are also toxic in vertebrates based on a mouse model of multiple sclerosis (MS), experimental autoimmune encephalomyelitis (EAE). Indeed, reducing VLCFA with bezafibrate ameliorates the phenotypes. Moreover, simultaneous use of bezafibrate and fingolimod synergizes to improve EAE, suggesting that lowering VLCFA and S1P is a treatment avenue for MS.

Interplay between biochemical processes and network properties generates neuronal up and down states at the tripartite synapse

Neuronal up and down states have long been known to exist both in vitro and in vivo. A variety of functions and mechanisms have been proposed for their generation, but there has not been a clear connection between the functions and mechanisms. We explore the potential contribution of cellular-level biochemistry to the network-level mechanisms thought to underlie the generation of up and down states. We develop a neurochemical model of a single tripartite synapse, assumed to be within a network of similar tripartite synapses, to investigate possible function-mechanism links for the appearance of up and down states. We characterize the behavior of our model in different regions of parameter space and show that resource limitation at the tripartite synapse affects its ability to faithfully transmit input signals, leading to extinction-down states. Recovery of resources allows for "reignition" into up states. The tripartite synapse exhibits distinctive "regimes" of operation depending on whether ATP, neurotransmitter (glutamate), both, or neither, is limiting. Our model qualitatively matches the behavior of six disparate experimental systems, including both in vitro and in vivo models, without changing any model parameters except those related to the experimental conditions. We also explore the effects of varying different critical parameters within the model. Here we show that availability of energy, represented by ATP, and glutamate for neurotransmission at the cellular level are intimately related, and are capable of promoting state transitions at the network level as ignition and extinction phenomena. Our model is complementary to existing models of neuronal up and down states in that it focuses on cellular-level dynamics while still retaining essential network-level processes. Our model predicts the existence of a "final common pathway" of behavior at the tripartite synapse arising from scarcity of resources and may explain use dependence in the phenomenon of "local sleep." Ultimately, sleeplike behavior may be a fundamental property of networks of tripartite synapses.

Wuzi Yanzong Pill relieves CPZ-induced demyelination by improving the microenvironment in the brain

Ethnopharmacology relevance

Wuzi Yanzong Pill (WYP), a well-known prescription for invigorating the kidney and essence, which is widely used to treat infertility such as oligoasthenospermia. Studies have shown that WYP can be used to treat neurological diseases, but its therapeutic effects and mechanisms for multiple sclerosis (MS) remain unclear.

Aim of the study

Based on the establishment of Cuprizone (CPZ)-induced demyelination model, this study determined the effect of WYP on remyelination by detecting changes in the microenvironment of the central nervous system.

Materials and methods

C57BL/6 mice were divided into three groups. The CPZ group and CPZ + WYP group were fed with 0.2% CPZ feed, and the control group was fed normal feed, for 6 weeks. At the end of the second week, the CPZ + WYP group was gavaged with WYP solution (16 g/kg/d), and the other two groups were gavaged with normal saline twice a day with an interval of 12 h each time, for 4 weeks. Forced swimming and elevated plus maze were used to detect changes in anxiety and depression before and after treatment. Luxol fast blue staining and the expression of MBP were used to evaluate the demyelination of the brain. Western blot was used to detect the expression of microglia and their subtype markers Iba-1, Arg-1, iNOS, the expression of neurotrophic factors BDNF, GDNF, CNTF, and the expression of oligodendrocyte precursor cells NG2. ELISA detected the content of IL-6, IL-1β, IL-10, TGF-β, BDNF, GDNF, CNTF in the brain. The distribution of Iba-1 in the corpus callosum was observed by immunofluorescence.

Results

The results showed that on the basis of improving mood abnormalities and demyelination, WYP reduced the protein content of Iba-1 and iNOS, increased the protein content of Arg-1, and reduce accumulation of microglia in the corpus callosum. In addition, WYP reduced the secretion of IL-6 and IL-1β while promoting the secretion of IL-10 and TGF-β. After WYP intervention treatment, the levels of neurotrophic factors BDNF, GDNF, CNTF increased. Due to the improvement of inflammatory and nutritional environment in the CNS, promoting the proliferation of NG2 oligodendrocyte, increased the expression of MBP, and repairing myelin sheath.

Conclusion

Our results indicated that WYP promoted the proliferation and development of oligodendrocytes by improving the CNS microenvironment, effectively alleviating demyelination.

Metabolomics detects clinically silent neuroinflammatory lesions earlier than neurofilament-light chain in a focal multiple sclerosis animal model

Background

Despite widespread searches, there are currently no validated biofluid markers for the detection of subclinical neuroinflammation in multiple sclerosis (MS). The dynamic nature of human metabolism in response to changes in homeostasis, as measured by metabolomics, may allow early identification of clinically silent neuroinflammation. Using the delayed-type hypersensitivity (DTH) MS rat model, we investigated the serum and cerebrospinal fluid (CSF) metabolomics profiles and neurofilament-light chain (NfL) levels, as a putative marker of neuroaxonal damage, arising from focal, clinically silent neuroinflammatory brain lesions and their discriminatory abilities to distinguish DTH animals from controls.

Methods

¹H nuclear magnetic resonance (NMR) spectroscopy metabolomics and NfL measurements were performed on serum and CSF at days 12, 28 and 60 after DTH lesion initiation. Supervised multivariate analyses were used to determine metabolomics differences between DTH animals and controls. Immunohistochemistry was used to assess the extent of neuroinflammation and tissue damage.

Results

Serum and CSF metabolomics perturbations were detectable in DTH animals (vs. controls) at all time points, with the greatest change occurring at the earliest time point (day 12) when the neuroinflammatory response was most intense (mean predictive accuracy [SD]—serum: 80.6 [10.7]%, p < 0.0001; CSF: 69.3 [13.5]%, p < 0.0001). The top discriminatory metabolites at day 12 (serum: allantoin, cytidine; CSF: glutamine, glucose) were all reduced in DTH animals compared to controls, and correlated with histological markers of neuroinflammation, particularly astrogliosis (Pearson coefficient, r—allantoin: r = − 0.562, p = 0.004; glutamine: r = − 0.528, p = 0.008). Serum and CSF NfL levels did not distinguish DTH animals from controls at day 12, rather, significant differences were observed at day 28 (mean [SEM]—serum: 38.5 [4.8] vs. 17.4 [2.6] pg/mL, p = 0.002; CSF: 1312.0 [379.1] vs. 475.8 [74.7] pg/mL, p = 0.027). Neither serum nor CSF NfL levels correlated with markers of neuroinflammation; serum NfL did, however, correlate strongly with axonal loss (r = 0.641, p = 0.001), but CSF NfL did not (p = 0.137).

Conclusions

While NfL levels were elevated later in the pathogenesis of the DTH lesion, serum and CSF metabolomics were able to detect early, clinically silent neuroinflammation and are likely to present sensitive biomarkers for the assessment of subclinical disease activity in patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02614-8.

Thinking outside the box: non-canonical targets in multiple sclerosis

Multiple sclerosis (MS) is an immune-mediated disease of the central nervous system that causes demyelination, axonal degeneration and astrogliosis, resulting in progressive neurological disability. Fuelled by an evolving understanding of MS immunopathogenesis, the range of available immunotherapies for clinical use has expanded over the past two decades. However, MS remains an incurable disease and even targeted immunotherapies often fail to control insidious disease progression, indicating the need for new and exceptional therapeutic options beyond the established immunological landscape. In this Review, we highlight such non-canonical targets in preclinical MS research with a focus on five highly promising areas: oligodendrocytes; the blood-brain barrier; metabolites and cellular metabolism; the coagulation system; and tolerance induction. Recent findings in these areas may guide the field towards novel targets for future therapeutic approaches in MS.

Differences in Neuropathic Pain and Radiological Features Between AQP4-ON, MOG-ON, and IDON

Purpose

The purpose of this study was to investigate pain and radiological features of different types of first-episode demyelinating optic neuritis (ON).

Methods

Eighty-three patients presenting with first-episode aquaporin-4 (AQP4) antibody-associated ON (AQP4-ON; n = 28), myelin oligodendrocyte glycoprotein (MOG) antibody-associated ON (MOG-ON; n = 26) and idiopathic demyelinating optic neuritis (IDON, n = 29) were included in this retrospective case-control study. We assessed optic nerve lesions on magnetic resonance imaging (MRI), acute pain associated with onset of optic neuritis and clinical characteristics of those ON patients with different serum autoantibody status.

Results

24 AQP4-ON patients (85.75%), 23 MOG-ON patients (88.5%) and 24 IDON patients (82.8%) suffered from ON-associated pain. MOG-ON had mostly retro-orbital pain; AQP4-ON and IDON had mostly neuropathic pain. In addition, pain was more severe in AQP4ON patients than in other ON patients. In MRI, bilateral involvement was more common in AQP4-ON than IDON (26.9 and 3.7%); radiological optic nerve head swelling was more common in MOG-ON than in AQP4-ON and IDON (68.0 vs. 23.1 vs. 25.9%). MRI lesion in peri-optic nerve sheath was more common in AQP4-ON (53.8 vs. 16.0 vs. 3.7%). In 70 patients with ON-associated pain, gadolinium enhancement of orbital optic nerve was most common in MOG-ON patients (82.4 vs. 55.0 vs. 33.3%, P = 0.018), and enhancement of optic chiasma was most common in AQP4-ON patients (40.0 vs. 5.9 vs. 6.7%, P = 0.015). Perineural and orbital enhancement was observed only in patients with MOG-ON (P < 0.001). The length of enhancement was longer in AQP4-ON patients than in MOG-ON and IDON patients.

Conclusion

Pain is a common symptom in patients with all types of demyelinating ON. AQP4-ON is frequently associated with severe ON-associated pain and longitudinally extensive optic nerve inflammatory lesions. Intra-orbital and peri-optic inflammation were more frequently observed in patients with MOG-ON, which was closely related to optic disc swelling and retro-orbital pain provoked by eye movements.

Neuropathic Pain in Multiple Sclerosis and Its Animal Models: Focus on Mechanisms, Knowledge Gaps and Future Directions

Multiple sclerosis (MS) is a multifaceted, complex and chronic neurological disease that leads to motor, sensory and cognitive deficits. MS symptoms are unpredictable and exceedingly variable. Pain is a frequent symptom of MS and manifests as nociceptive or neuropathic pain, even at early disease stages. Neuropathic pain is one of the most debilitating symptoms that reduces quality of life and interferes with daily activities, particularly because conventional pharmacotherapies do not adequately alleviate neuropathic pain. Despite advances, the mechanisms underlying neuropathic pain in MS remain elusive. The majority of the studies investigating the pathophysiology of MS-associated neuropathic pain have been performed in animal models that replicate some of the clinical and neuropathological features of MS. Experimental autoimmune encephalomyelitis (EAE) is one of the best-characterized and most commonly used animal models of MS. As in the case of individuals with MS, rodents affected by EAE manifest increased sensitivity to pain which can be assessed by well-established assays. Investigations on EAE provided valuable insights into the pathophysiology of neuropathic pain. Nevertheless, additional investigations are warranted to better understand the events that lead to the onset and maintenance of neuropathic pain in order to identify targets that can facilitate the development of more effective therapeutic interventions. The goal of the present review is to provide an overview of several mechanisms implicated in neuropathic pain in EAE by summarizing published reports. We discuss current knowledge gaps and future research directions, especially based on information obtained by use of other animal models of neuropathic pain such as nerve injury.

Brain Energy Deficit as a Source of Oxidative Stress in Migraine: A Molecular Basis for Migraine Susceptibility

People with migraine are prone to a brain energy deficit between attacks, through increased energy demand (hyperexcitable brain) or decreased supply (mitochondrial impairment). However, it is uncertain how this precipitates an acute attack. Here, the central role of oxidative stress is adduced. Specifically, neurons' antioxidant defenses rest ultimately on internally generated NADPH (reduced nicotinamide adenine dinucleotide phosphate), whose levels are tightly coupled to energy production. Mitochondrial NADPH is produced primarily by enzymes involved in energy generation, including isocitrate dehydrogenase of the Krebs (tricarboxylic acid) cycle; and an enzyme, nicotinamide nucleotide transhydrogenase (NNT), that depends on the Krebs cycle and oxidative phosphorylation to function, and that works in reverse, consuming antioxidants, when energy generation fails. In migraine aura, cortical spreading depression (CSD) causes an initial severe drop in level of NADH (reduced nicotinamide adenine dinucleotide), causing NNT to impair antioxidant defense. This is followed by functional hypoxia and a rebound in NADH, in which the electron transport chain overproduces oxidants. In migraine without aura, a similar biphasic fluctuation in NADH very likely generates oxidants in cortical regions farthest from capillaries and penetrating arterioles. Thus, the perturbations in brain energy demand and/or production seen in migraine are likely sufficient to cause oxidative stress, triggering an attack through oxidant-sensing nociceptive ion channels. Implications are discussed for the development of new classes of migraine preventives, for the current use of C57BL/6J mice (which lack NNT) in preclinical studies of migraine, for how a microembolism initiates CSD, and for how CSD can trigger a migraine.

Glial cell activation and altered metabolic profile in the spinal-trigeminal axis in a rat model of multiple sclerosis associated with the development of trigeminal sensitization

Trigeminal neuralgia is often an early symptom of multiple sclerosis (MS), and it generally does not correlate with the severity of the disease. Thus, whether it is triggered simply by demyelination in specific central nervous system areas is currently questioned. Our aims were to monitor the development of spontaneous trigeminal pain in an animal model of MS, and to analyze: i) glial cells, namely astrocytes and microglia in the central nervous system and satellite glial cells in the trigeminal ganglion, and ii) metabolic changes in the trigeminal system. The subcutaneous injection of recombinant MOG_1-125 protein fragment to Dark Agouti male rats led to the development of relapsing-remitting EAE, with a first peak after 13 days, a remission stage from day 16 and a second peak from day 21. Interestingly, orofacial allodynia developed from day 1 post injection, i.e. well before the onset of EAE, and worsened over time, irrespective of the disease phase. Activation of glial cells both in the trigeminal ganglia and in the brainstem, with no signs of demyelination in the latter tissue, was observed along with metabolic alterations in the trigeminal ganglion. Our data show, for the first time, the spontaneous development of trigeminal sensitization before the onset of relapsing-remitting EAE in rats. Additionally, pain is maintained elevated during all stages of the disease, suggesting the existence of parallel mechanisms controlling motor symptoms and orofacial pain, likely involving glial cell activation and metabolic alterations which can contribute to trigger the sensitization of sensory neurons.

Luteoloside Exerts Analgesic Effect in a Complete Freund's Adjuvant-Induced Inflammatory Model via Inhibiting Interleukin-1β Expression and Macrophage/Microglia Activation

Background

Flavonoid monomers are proved to have an anti-inflammatory effect and may also be promising for chronic pain treatment. In the present study, the analgesic effect and the relevant mechanisms of luteoloside, one of the flavonoid monomers, were investigated.

Methods

The analgesic effect of luteoloside was first evaluated in complete Freud’s adjuvant induced inflammatory model by von Frey test and Hargreaves test in both male and female mice. The interleukin-1β levels in plantar tissue, serum, dorsal root ganglion, and the dorsal horn of the spinal cord were determined by enzyme-linked immunosorbent assay or immunofluorescence. The activation of macrophage/microglia was tested by Iba-1 staining.

Results

Our data showed that luteoloside exhibited both acute and chronic analgesic phenotypes. Every single dose of luteoloside solution reached the peak transient analgesic effect 2 h after administration and lasted less than 6 h. About 14 consecutive days administration (one dose per day) later, luteoloside showed a sustained analgesic effect which lasted more than 24 h. Celecoxib 20 mg/kg combined with luteoloside 40 mg/kg achieved a similar analgesic effect as celecoxib 40 mg/kg alone. Luteoloside inhibited interleukin-1β expression in plantar tissue, dorsal root ganglion, the dorsal horn of spinal cord, and serum, after 14 days of continuous administration. Furthermore, our results also showed that the activation of macrophage/microglia in dorsal root ganglions were significantly inhibited 2 h after each single dose in daily luteoloside administration and recovered to a higher level 6 h later. These findings might be involved in the mechanisms of the acute analgesic effect of luteoloside.

Conclusion

Luteoloside presents an analgesic effect via anti-inflammatory and other mechanisms such as inhibiting the activation of macrophage/microglia.

Ifenprodil Reduced Expression of Activated Microglia, BDNF and DREAM Proteins in the Spinal Cord Following Formalin Injection During the Early Stage of Painful Diabetic Neuropathy in Rats

The pharmacological inhibition of glial activation is one of the new approaches for combating neuropathic pain in which the role of glia in the modulation of neuropathic pain has attracted significant interest and attention. Neuron-glial crosstalk is achieved with N-methyl-D-aspartate-2B receptor (NMDAR-2B) activation. This study aims to determine the effect of ifenprodil, a potent noncompetitive NMDAR-2B antagonist, on activated microglia, brain-derived neurotrophic factors (BDNF) and downstream regulatory element antagonist modulator (DREAM) protein expression in the spinal cord of streptozotocin-induced painful diabetic neuropathy (PDN) rats following formalin injection. In this experimentation, 48 Sprague-Dawley male rats were randomly selected and divided into four groups: (n = 12): control, PDN, and ifenprodil-treated PDN rats at 0.5 μg or 1.0 μg for 7 days. Type I diabetes mellitus was then induced by injecting streptozotocin (60 mg/kg, i.p.) into the rats which were then over a 2-week period allowed to progress into the early phase of PDN. Ifenprodil was administered in PDN rats while saline was administered intrathecally in the control group. A formalin test was conducted during the fourth week to induce inflammatory nerve injury, in which the rats were sacrificed at 72 h post-formalin injection. The lumbar enlargement region (L4-L5) of the spinal cord was dissected for immunohistochemistry and western blot analyses. The results demonstrated a significant increase in formalin-induced flinching and licking behavior with an increased spinal expression of activated microglia, BDNF and DREAM proteins. It was also shown that the ifenprodil-treated rats following both doses reduced the extent of their flinching and duration of licking in PDN in a dose-dependent manner. As such, ifenprodil successfully demonstrated inhibition against microglia activation and suppressed the expression of BDNF and DREAM proteins in the spinal cord of PDN rats. In conclusion, ifenprodil may alleviate PDN by suppressing spinal microglia activation, BDNF and DREAM proteins.

Klotho Pathways, Myelination Disorders, Neurodegenerative Diseases, and Epigenetic Drugs

In this review we outline a rationale for identifying neuroprotectants aimed at inducing endogenous Klotho activity and expression, which is epigenetic action, by definition. Such an approach should promote remyelination and/or stimulate myelin repair by acting on mitochondrial function, thereby heralding a life-saving path forward for patients suffering from neuroinflammatory diseases. Disorders of myelin in the nervous system damage the transmission of signals, resulting in loss of vision, motion, sensation, and other functions depending on the affected nerves, currently with no effective treatment. Klotho genes and their single-pass transmembrane Klotho proteins are powerful governors of the threads of life and death, true to the origin of their name, Fates, in Greek mythology. Among its many important functions, Klotho is an obligatory co-receptor that binds, activates, and/or potentiates critical fibroblast growth factor activity. Since the discovery of Klotho a little over two decades ago, it has become ever more apparent that when Klotho pathways go awry, oxidative stress and mitochondrial dysfunction take over, and age-related chronic disorders are likely to follow. The physiological consequences can be wide ranging, potentially wreaking havoc on the brain, eye, kidney, muscle, and more. Central nervous system disorders, neurodegenerative in nature, and especially those affecting the myelin sheath, represent worthy targets for advancing therapies that act upon Klotho pathways. Current drugs for these diseases, even therapeutics that are disease modifying rather than treating only the symptoms, leave much room for improvement. It is thus no wonder that this topic has caught the attention of biomedical researchers around the world.