Insulin-regulated serine and lipid metabolism drive peripheral neuropathy.

Diabetes represents a spectrum of disease in which metabolic dysfunction damages multiple organ systems including liver, kidneys and peripheral nerves1,2. Although the onset and progression of these co-morbidities are linked with insulin resistance, hyperglycaemia and dyslipidaemia3-7, aberrant non-essential amino acid (NEAA) metabolism also contributes to the pathogenesis of diabetes8-10. Serine and glycine are closely related NEAAs whose levels are consistently reduced in patients with metabolic syndrome10-14, but the mechanistic drivers and downstream consequences of this metabotype remain unclear. Low systemic serine and glycine are also emerging as a hallmark of macular and peripheral nerve disorders, correlating with impaired visual acuity and peripheral neuropathy15,16. Here we demonstrate that aberrant serine homeostasis drives serine and glycine deficiencies in diabetic mice, which can be diagnosed with a serine tolerance test that quantifies serine uptake and disposal. Mimicking these metabolic alterations in young mice by dietary serine or glycine restriction together with high fat intake markedly accelerates the onset of small fibre neuropathy while reducing adiposity. Normalization of serine by dietary supplementation and mitigation of dyslipidaemia with myriocin both alleviate neuropathy in diabetic mice, linking serine-associated peripheral neuropathy to sphingolipid metabolism. These findings identify systemic serine deficiency and dyslipidaemia as novel risk factors for peripheral neuropathy that may be exploited therapeutically.

Converging Effects of Chronic Pain and Binge Alcohol Consumption on Anterior Insular Cortex Neurons Projecting to the Dorsolateral Striatum in Male Mice.

Chronic pain and alcohol use disorder (AUD) are highly comorbid, and patients with chronic pain are more likely to meet the criteria for AUD. Evidence suggests that both conditions alter similar brain pathways, yet this relationship remains poorly understood. Prior work shows that the anterior insular cortex (AIC) is involved in both chronic pain and AUD. However, circuit-specific changes elicited by the combination of pain and alcohol use remain understudied. The goal of this work was to elucidate the converging effects of binge alcohol consumption and chronic pain on AIC neurons that send projections to the dorsolateral striatum (DLS). Here, we used the Drinking-in-the-Dark (DID) paradigm to model binge-like alcohol drinking in mice that underwent spared nerve injury (SNI), after which whole-cell patch-clamp electrophysiological recordings were performed in acute brain slices to measure intrinsic and synaptic properties of AIC→DLS neurons. In male, but not female, mice, we found that SNI mice with no prior alcohol exposure consumed less alcohol compared with sham mice. Electrophysiological analyses showed that AIC→DLS neurons from SNI-alcohol male mice displayed increased neuronal excitability and increased frequency of miniature excitatory postsynaptic currents. However, mice exposed to alcohol prior to SNI consumed similar amounts of alcohol compared with sham mice following SNI. Together, our data suggest that the interaction of chronic pain and alcohol drinking have a direct effect on both intrinsic excitability and synaptic transmission onto AIC→DLS neurons in mice, which may be critical in understanding how chronic pain alters motivated behaviors associated with alcohol.

Mu-Opioid Receptor (MOR) Dependence of Pain in Chemotherapy-Induced Peripheral Neuropathy.

We recently demonstrated that transient attenuation of Toll-like receptor 4 (TLR4) in dorsal root ganglion (DRG) neurons, can both prevent and reverse pain associated with chemotherapy-induced peripheral neuropathy (CIPN), a severe side effect of cancer chemotherapy, for which treatment options are limited. Given the reduced efficacy of opioid analgesics to treat neuropathic, compared with inflammatory pain, the cross talk between nociceptor TLR4 and mu-opioid receptors (MORs), and that MOR and TLR4 agonists induce hyperalgesic priming (priming), which also occurs in CIPN, we determined, using male rats, whether (1) antisense knockdown of nociceptor MOR attenuates CIPN, (2) and attenuates the priming associated with CIPN, and (3) CIPN also produces opioid-induced hyperalgesia (OIH). We found that intrathecal MOR antisense prevents and reverses hyperalgesia induced by oxaliplatin and paclitaxel, two common clinical chemotherapy agents. Oxaliplatin-induced priming was also markedly attenuated by MOR antisense. Additionally, intradermal morphine, at a dose that does not affect nociceptive threshold in controls, exacerbates mechanical hyperalgesia (OIH) in rats with CIPN, suggesting the presence of OIH. This OIH associated with CIPN is inhibited by interventions that reverse Type II priming [the combination of an inhibitor of Src and mitogen-activated protein kinase (MAPK)], an MOR antagonist, as well as a TLR4 antagonist. Our findings support a role of nociceptor MOR in oxaliplatin-induced pain and priming. We propose that priming and OIH are central to the symptom burden in CIPN, contributing to its chronicity and the limited efficacy of opioid analgesics to treat neuropathic pain.

Structural polymorphism of the nucleic acids in pentanucleotide repeats associated with the neurological disorder CANVAS.

Short tandem repeats are inherently unstable during DNA replication depending on repeat length, and the expansion of the repeat length in the human genome is responsible for repeat expansion disorders. Pentanucleotide AAGGG and ACAGG repeat expansions in intron 2 of the gene encoding replication factor C subunit 1 (RFC1) cause cerebellar ataxia, neuropathy, vestibular areflexia syndrome (CANVAS) and other phenotypes of late-onset cerebellar ataxia. Herein, we reveal the structural polymorphism of the RFC1 repeats associated with CANVAS in vitro. Single-stranded AAGGG repeat DNA formed a hybrid-type G-quadruplex, whereas its RNA formed a parallel-type G-quadruplex with three layers. The RNA of the ACAGG repeat formed hairpin structure comprising C-G and G-C base pairs with A:A and GA:AG mismatched repeats. Furthermore, both pathogenic repeat RNAs formed more rigid structures than those of the nonpathogenic repeat RNAs. These findings provide novel insights into the structural polymorphism of the RFC1 repeats, which may be closely related to the disease mechanism of CANVAS.

Gene therapy approaches for obesity-induced adipose neuropathy: Device-targeted AAV-mediated neurotrophic factor delivery to adipocytes in subcutaneous adipose.

Maintaining functional adipose innervation is critical for metabolic health. We found that subcutaneous white adipose tissue (scWAT) undergoes peripheral neuropathy (PN) with obesity, diabetes, and aging (reduced small-fiber innervation and nerve/synaptic/growth-cone/vesicle markers, altered nerve activity). Unlike with nerve injuries, peripheral nerves do not regenerate with PN, and therefore new therapies are needed for treatment of this condition affecting 20-30 million Americans. Here, we validated a gene therapy approach using an adipocyte-tropic adeno-associated virus (AAV; serotype Rec2) to deliver neurotrophic factors (brain-derived neurotrophic factor [BDNF] and nerve growth factor [NGF]) directly to scWAT to improve tissue-specific PN as a proof-of-concept approach. AAVRec2-BDNF intra-adipose delivery improved tissue innervation in obese/diabetic mice with PN, but after longer periods of dietary obesity there was reduced efficacy, revealing a key time window for therapies. AAVRec2-NGF also increased scWAT innervation in obese mice and was more effective than BDNF, likely because Rec2 targeted adipocytes, the tissue's endogenous NGF source. AAVRec2-NGF also worked well even after 25 weeks of dietary obesity, unlike BDNF, which likely needs a vector that targets its physiological cellular source (stromal vascular fraction cells). Given the differing effects of AAVs carrying NGF versus BDNF, a combined therapy may be ideal for PN.

Pathogenic TNF-α drives peripheral nerve inflammation in an Aire-deficient model of autoimmunity.

Immune cells infiltrate the peripheral nervous system (PNS) after injury and with autoimmunity, but their net effect is divergent. After injury, immune cells are reparative, while in inflammatory neuropathies (e.g., Guillain Barré Syndrome and chronic inflammatory demyelinating polyneuropathy), immune cells are proinflammatory and promote autoimmune demyelination. An understanding of immune cell phenotypes that distinguish these conditions may, therefore, reveal new therapeutic targets for switching immune cells from an inflammatory role to a reparative state. In an autoimmune regulator (Aire)-deficient mouse model of inflammatory neuropathy, we used single-cell RNA sequencing of sciatic nerves to discover a transcriptionally heterogeneous cellular landscape, including multiple myeloid, innate lymphoid, and lymphoid cell types. Analysis of cell-cell ligand-receptor interactions uncovered a macrophage-mediated tumor necrosis factor-α (TNF-α) signaling axis that is induced by interferon-γ and required for initiation of autoimmune demyelination. Developmental trajectory visualization suggested that TNF-α signaling is associated with metabolic reprogramming of macrophages and polarization of macrophages from a reparative state in injury to a pathogenic, inflammatory state in autoimmunity. Autocrine TNF-α signaling induced macrophage expression of multiple genes (Clec4e, Marcksl1, Cxcl1, and Cxcl10) important in immune cell activation and recruitment. Genetic and antibody-based blockade of TNF-α/TNF-α signaling ameliorated clinical neuropathy, peripheral nerve infiltration, and demyelination, which provides preclinical evidence that the TNF-α axis may be effectively targeted to resolve inflammatory neuropathies.

Quantitative proteomics unveils known and previously unrecognized alterations in neuropathic nerves.

Charcot-Marie-Tooth disease type 1E (CMT1E) is an inherited autosomal dominant peripheral neuropathy caused by mutations in the peripheral myelin protein 22 (PMP22) gene. The identical leucine-to-proline (L16P) amino acid substitution in PMP22 is carried by the Trembler J (TrJ) mouse and is found in CMT1E patients presenting with early-onset disease. Peripheral nerves of patients diagnosed with CMT1E display a complex and varied histopathology, including Schwann cell hyperproliferation, abnormally thin myelin, axonal degeneration, and subaxonal morphological changes. Here, we have taken an unbiased data-independent analysis (DIA) mass spectrometry (MS) approach to quantify proteins from nerves of 3-week-old, age and genetic strain-matched wild-type (Wt) and heterozygous TrJ mice. Nerve proteins were dissolved in lysis buffer and digested into peptide fragments, and protein groups were quantified by liquid chromatography-mass spectrometry (LC-MS). A linear model determined statistically significant differences between the study groups, and proteins with an adjusted p-value of less than 0.05 were deemed significant. This untargeted proteomics approach identified 3759 quality-controlled protein groups, of which 884 demonstrated differential expression between the two genotypes. Gene ontology (GO) terms related to myelin and myelin maintenance confirm published data while revealing a previously undetected prominent decrease in peripheral myelin protein 2. The dataset corroborates the described pathophysiology of TrJ nerves, including elevated activity in the proteasome-lysosomal pathways, alterations in protein trafficking, and an increase in three macrophage-associated proteins. Previously unrecognized perturbations in RNA processing pathways and GO terms were also discovered. Proteomic abnormalities that overlap with other human neurological disorders besides CMT include Lafora Disease and Amyotrophic Lateral Sclerosis. Overall, this study confirms and extends current knowledge on the cellular pathophysiology in TrJ neuropathic nerves and provides novel insights for future examinations. Recognition of shared pathomechanisms across discrete neurological disorders offers opportunities for innovative disease-modifying therapeutics that could be effective for distinct neuropathies.

Chronic Administration of Cannabinoid Agonists ACEA, AM1241, and CP55,940 Induce Sex-Specific Differences in Tolerance and Sex Hormone Changes in a Chemotherapy-Induced Peripheral Neuropathy.

Chemotherapy-induced peripheral neuropathy (CIPN) is a common side effect of chemotherapy treatment, routinely manifesting as increased pain sensitivity (allodynia) in distal extremities. Despite its prevalence, effective treatment options are limited. Cannabinoids are increasingly being evaluated for their ability to treat chronic pain conditions, including CIPN. While previous studies have revealed sex differences in cannabinoid-mediated antinociception in acute and chronic pain models, there is a paucity of studies addressing potential sex differences in the response of CIPN to cannabinoid treatment. Therefore, we evaluated the long-term antiallodynic efficacy of cannabinoid receptor type 1 (CB1)-selective, cannabinoid receptor type 2 (CB2)-selective, and CB1/CB2 mixed agonists in the cisplatin CIPN model, using both male and female mice. CB1 selective agonism was observed to have sex differences in the development of tolerance to antiallodynic effects, with females developing tolerance more rapidly than males, while the antiallodynic effects of selective CB2 agonism lacked tolerance development. Compound-specific changes to the female estrous cycle and female plasma estradiol levels were noted, with CB1 selective agonism decreasing plasma estradiol while CB2 selective agonism increased plasma estradiol. Chronic administration of a mixed CB1/CB2 agonist resulted in increased mRNA expression of proinflammatory cytokines and endocannabinoid regulatory enzymes in female spinal cord tissue. Ovarian tissue was noted to have proinflammatory cytokine mRNA expression following administration of a CB2 acting compound while selective CB1 agonism resulted in decreased proinflammatory cytokines and endocannabinoid regulatory enzymes in testes. These results support the need for further investigation into the role of sex and sex hormones signaling in pain and cannabinoid-mediated antinociceptive effects. SIGNIFICANCE STATEMENT: CIPN is a common side effect of chemotherapy. We have found that both CB1 and CB2 receptor agonism produce antinociceptive effects in a cisplatin CIPN model. We observed that tolerance to CB1-mediated antinociception developed faster in females and did not develop for CB2-mediated antinociception. Additionally, we found contrasting roles for CB1/CB2 receptors in the regulation of plasma estradiol in females, with CB1 agonism attenuating estradiol and CB2 agonism enhancing estradiol. These findings support the exploration of cannabinoid agonists for CIPN.

Dorsal root ganglion inflammation by oxaliplatin toxicity: DPEP1 as possible target for peripheral neuropathy prevention.

BACKGROUND: Peripheral neuropathy (PN) constitutes a dose-limiting side effect of oxaliplatin chemotherapy that often compromises the efficacy of antineoplastic treatments. Sensory neurons damage in dorsal root ganglia (DRG) are the cellular substrate of PN complex molecular origin. Dehydropeptidase-1 (DPEP1) inhibitors have shown to avoid platin-induced nephrotoxicity without compromising its anticancer efficiency. The objective of this study was to describe DPEP1 expression in rat DRG in health and in early stages of oxaliplatin toxicity. To this end, we produced and characterized anti-DPEP1 polyclonal antibodies and used them to define the expression, and cellular and subcellular localization of DPEP1 by immunohistochemical confocal microscopy studies in healthy controls and short term (six days) oxaliplatin treated rats. RESULTS: DPEP1 is expressed mostly in neurons and in glia, and to a lesser extent in endothelial cells. Rats undergoing oxaliplatin treatment developed allodynia. TNF-𝛼 expression in DRG revealed a pattern of focal and at different intensity levels of neural cell inflammatory damage, accompanied by slight variations in DPEP1 expression in endothelial cells and in nuclei of neurons. CONCLUSIONS: DPEP1 is expressed in neurons, glia and endothelial cells of DRG. Oxaliplatin caused allodynia in rats and increased TNF-α expression in DRG neurons. The expression of DPEP1 in neurons and other cells of DRG suggest this protein as a novel strategic molecular target in the prevention of oxaliplatin-induced acute neurotoxicity.

Nicotinamide riboside activates SIRT3 to prevent paclitaxel-induced peripheral neuropathy.

Paclitaxel (PTX) is a microtubule stabilizer that disrupts the normal cycle of microtubule depolymerization and repolymerization, leading to cell cycle arrest and cancer cell death. It is commonly used as a first-line chemotherapeutics for various malignancies, such as breast cancer, non-small cell lung cancer, and ovarian cancer. However, PTX chemotherapy is associated with common and serious side effects, including chemotherapy-induced peripheral neuropathy (CIPN). As cancer treatment advances and survival rates increase, the impact of CIPN on patients' quality of life has become more significant. To date, there is no effective treatment strategy for CIPN. Surtuin3 (SIRT3) is a nicotinamide adenine dinucleotide (NAD+) dependent protein deacetylase located on mitochondria. It transfers the acetyl group of the lysine side chain of acetylated substrate proteins to NAD+, producing deacetylated proteins to regulate mitochondrial energy metabolic processes. SIRT3 has been found to play an important role in various diseases, including aging, neurodegenerative diseases, cancer, heart disease, metabolic diseases, etc. However, the role of SIRT3 in CIPN is still unknown. This study found for the first time that activating SIRT3 helps to improve paclitaxel-induced CIPN. Nicotinamide riboside (NR) can protect dorsal root ganglion (DRG) mitochondria against oxidative damage caused by paclitaxel through activating SIRT3-MnSOD2 and SIRT3-Nrf2 pathway. Moreover, NR can enhance the anticancer activity of paclitaxel. Together, our research provides new strategy and candidate drug for the treatment of CIPN.

Chemical sensors detect and resolve proteome aggregation in peripheral neuropathy cell model induced by chemotherapeutic agents.

As a consequence of somatosensory nervous system injury or disease, neuropathic pain is commonly associated with chemotherapies, known as chemotherapy-induced peripheral neuropathy (CIPN). However, the mechanisms underlying CIPN-induced proteome aggregation in neuronal cells remain elusive due to limited detection tools. Herein, we present series sensors for fluorescence imaging (AggStain) and proteomics analysis (AggLink) to visualize and capture aggregated proteome in CIPN neuronal cell model. The environment-sensitive AggStain imaging sensor selectively binds and detects protein aggregation with 12.3 fold fluorescence enhancement. Further, the covalent AggLink proteomic sensor captures cellular aggregated proteins and profiles their composition via LC-MS/MS analysis. This integrative sensor platform reveals the presence of proteome aggregation in CIPN cell model and highlights its potential for broader applications in assessing proteome stability under various cellular stress conditions.

Dihydromyricetin reverses capecitabine-induced peripheral myelin dysfunction through modulation of oxidative stress.

Previous clinical reports have shown that capecitabine, an oral prodrug of 5-fluorouracil (5-Fu), can induce peripheral neuropathy, resulting in numbness, paresthesia and hypoesthesia. However, the mechanism through which capecitabine causes peripheral nerve injury remains unclear. Here, we demonstrate that systemic administration of capecitabine leads to myelin abnormalities in the peripheral nerves of mice, which are possibly attributed to the death of Schwann cells, the myelinating cells in the peripheral nervous system. Furthermore, our results show that 5-Fu induces significant oxidative stress in Schwann cells by inhibiting the expression of the anti-oxidative protein DJ-1, leading to a decrease in Schwann cell markers. We found that the anti-oxidant dihydromyricetin (DMY) reverses 5-Fu-induced Schwann cell death and oxidative stress and alleviates capecitabine-induced myelin abnormalities. Taken together, our data indicate that capecitabine induces peripheral myelin dysfunction by regulating DJ-1-mediated oxidative stress in Schwann cells and reveal DMY as a potential therapeutic strategy for capecitabine-induced peripheral neuropathy.

Metabolomics analysis reveals characteristic metabolites in different levels of oxaliplatin-induced neurotoxicity.

Oxaliplatin (L-OHP), a third-generation platinum-based anti-tumor drug, finds widespread application in the first-line treatment of metastatic colorectal cancer. Despite its efficacy, the drug's usage is curtailed by a litany of side effects, with L-OHP-induced peripheral neuropathy (OIPN) being the most debilitating. This condition can be classified into varying degrees of severity. Employing serum metabolomics, a high-sensitivity, high-throughput technique, holds promise as a method to identify biomarkers for clinical assessment and monitoring of OIPN patients across different severity levels. In our study, we analyzed serum metabolites in patients with different OIPN levels using ultra-performance liquid chromatography-high resolution mass spectrometry. By employing statistical analyses and pathway enrichment studies, we aimed to identify potential biomarkers and metabolic pathways. Our findings characterized the serum metabolic profiles of patients with varying OIPN levels. Notably, pathway analysis revealed a significant correlation with lipid metabolism, amino acid metabolism, and energy metabolism. Multivariate statistical analysis and receiver operator characteristic curve evaluation pointed to anhalamine and glycochenodeoxycholic acid as potential biomarkers for OIPN C and A, which suggest that serum metabolomics may serve as a potent tool for exploring the metabolic status of patients suffering from diverse diseases and for discovering novel biomarkers.

Integrins protect sensory neurons in models of paclitaxel-induced peripheral sensory neuropathy.

Chemotherapy-induced peripheral neuropathy (CIPN) is a major side effect from cancer treatment with no known method for prevention or cure in clinics. CIPN often affects unmyelinated nociceptive sensory terminals. Despite the high prevalence, molecular and cellular mechanisms that lead to CIPN are still poorly understood. Here, we used a genetically tractable Drosophila model and primary sensory neurons isolated from adult mouse to examine the mechanisms underlying CIPN and identify protective pathways. We found that chronic treatment of Drosophila larvae with paclitaxel caused degeneration and altered the branching pattern of nociceptive neurons, and reduced thermal nociceptive responses. We further found that nociceptive neuron-specific overexpression of integrins, which are known to support neuronal maintenance in several systems, conferred protection from paclitaxel-induced cellular and behavioral phenotypes. Live imaging and superresolution approaches provide evidence that paclitaxel treatment causes cellular changes that are consistent with alterations in endosome-mediated trafficking of integrins. Paclitaxel-induced changes in recycling endosomes precede morphological degeneration of nociceptive neuron arbors, which could be prevented by integrin overexpression. We used primary dorsal root ganglia (DRG) neuron cultures to test conservation of integrin-mediated protection. We show that transduction of a human integrin ß-subunit 1 also prevented degeneration following paclitaxel treatment. Furthermore, endogenous levels of surface integrins were decreased in paclitaxel-treated mouse DRG neurons, suggesting that paclitaxel disrupts recycling in vertebrate sensory neurons. Altogether, our study supports conserved mechanisms of paclitaxel-induced perturbation of integrin trafficking and a therapeutic potential of restoring neuronal interactions with the extracellular environment to antagonize paclitaxel-induced toxicity in sensory neurons.

Ion mobility-mass spectrometry reveals the role of peripheral myelin protein dimers in peripheral neuropathy.

Peripheral myelin protein (PMP22) is an integral membrane protein that traffics inefficiently even in wild-type (WT) form, with only 20% of the WT protein reaching its final plasma membrane destination in myelinating Schwann cells. Misfolding of PMP22 has been identified as a key factor in multiple peripheral neuropathies, including Charcot-Marie-Tooth disease and Dejerine-Sottas syndrome. While biophysical analyses of disease-associated PMP22 mutants show altered protein stabilities, leading to reduced surface trafficking and loss of PMP22 function, it remains unclear how destabilization of PMP22 mutations causes mistrafficking. Here, native ion mobility-mass spectrometry (IM-MS) is used to compare the gas phase stabilities and abundances for an array of mutant PM22 complexes. We find key differences in the PMP22 mutant stabilities and propensities to form homodimeric complexes. Of particular note, we observe that severely destabilized forms of PMP22 exhibit a higher propensity to dimerize than WT PMP22. Furthermore, we employ lipid raft-mimicking SCOR bicelles to study PMP22 mutants, and find that the differences in dimer abundances are amplified in this medium when compared to micelle-based data, with disease mutants exhibiting up to 4 times more dimer than WT when liberated from SCOR bicelles. We combine our findings with previous cellular data to propose that the formation of PMP22 dimers from destabilized monomers is a key element of PMP22 mistrafficking.

Ion Channel and Transporter Involvement in Chemotherapy-Induced Peripheral Neurotoxicity.

The peripheral nervous system can encounter alterations due to exposure to some of the most commonly used anticancer drugs (platinum drugs, taxanes, vinca alkaloids, proteasome inhibitors, thalidomide), the so-called chemotherapy-induced peripheral neurotoxicity (CIPN). CIPN can be long-lasting or even permanent, and it is detrimental for the quality of life of cancer survivors, being associated with persistent disturbances such as sensory loss and neuropathic pain at limb extremities due to a mostly sensory axonal polyneuropathy/neuronopathy. In the state of the art, there is no efficacious preventive/curative treatment for this condition. Among the reasons for this unmet clinical and scientific need, there is an uncomplete knowledge of the pathogenetic mechanisms. Ion channels and transporters are pivotal elements in both the central and peripheral nervous system, and there is a growing body of literature suggesting that they might play a role in CIPN development. In this review, we first describe the biophysical properties of these targets and then report existing data for the involvement of ion channels and transporters in CIPN, thus paving the way for new approaches/druggable targets to cure and/or prevent CIPN.

Manganese- and Platinum-Driven Oxidative and Nitrosative Stress in Oxaliplatin-Associated CIPN with Special Reference to Ca4Mn(DPDP)5, MnDPDP and DPDP.

Platinum-containing chemotherapeutic drugs are efficacious in many forms of cancer but are dose-restricted by serious side effects, of which peripheral neuropathy induced by oxidative-nitrosative-stress-mediated chain reactions is most disturbing. Recently, hope has been raised regarding the catalytic antioxidants mangafodipir (MnDPDP) and calmangafodipir [Ca4Mn(DPDP)5; PledOx®], which by mimicking mitochondrial manganese superoxide dismutase (MnSOD) may be expected to overcome oxaliplatin-associated chemotherapy-induced peripheral neuropathy (CIPN). Unfortunately, two recent phase III studies (POLAR A and M trials) applying Ca4Mn(DPDP)5 in colorectal cancer (CRC) patients receiving multiple cycles of FOLFOX6 (5-FU + oxaliplatin) failed to demonstrate efficacy. Instead of an anticipated 50% reduction in the incidence of CIPN in patients co-treated with Ca4Mn(DPDP)5, a statistically significant increase of about 50% was seen. The current article deals with confusing differences between early and positive findings with MnDPDP in comparison to the recent findings with Ca4Mn(DPDP)5. The POLAR failure may also reveal important mechanisms behind oxaliplatin-associated CIPN itself. Thus, exacerbated neurotoxicity in patients receiving Ca4Mn(DPDP)5 may be explained by redox interactions between Pt2+ and Mn2+ and subtle oxidative-nitrosative chain reactions. In peripheral sensory nerves, Pt2+ presumably leads to oxidation of the Mn2+ from Ca4Mn(DPDP)5 as well as from Mn2+ in MnSOD and other endogenous sources. Thereafter, Mn3+ may be oxidized by peroxynitrite (ONOO-) into Mn4+, which drives site-specific nitration of tyrosine (Tyr) 34 in the MnSOD enzyme. Conformational changes of MnSOD then lead to the closure of the superoxide (O2•-) access channel. A similar metal-driven nitration of Tyr74 in cytochrome c will cause an irreversible disruption of electron transport. Altogether, these events may uncover important steps in the mechanism behind Pt2+-associated CIPN. There is little doubt that the efficacy of MnDPDP and its therapeutic improved counterpart Ca4Mn(DPDP)5 mainly depends on their MnSOD-mimetic activity when it comes to their potential use as rescue medicines during, e.g., acute myocardial infarction. However, pharmacokinetic considerations suggest that the efficacy of MnDPDP on Pt2+-associated neurotoxicity depends on another action of this drug. Electron paramagnetic resonance (EPR) studies have demonstrated that Pt2+ outcompetes Mn2+ and endogenous Zn2+ in binding to fodipir (DPDP), hence suggesting that the previously reported protective efficacy of MnDPDP against CIPN is a result of chelation and elimination of Pt2+ by DPDP, which in turn suggests that Mn2+ is unnecessary for efficacy when it comes to oxaliplatin-associated CIPN.

Single-cell RNA-seq uncovers novel metabolic functions of Schwann cells beyond myelination.

Schwann cells (SCs) support peripheral nerves under homeostatic conditions, independent of myelination, and contribute to damage in prediabetic peripheral neuropathy (PN). Here, we used single-cell RNA sequencing to characterize the transcriptional profiles and intercellular communication of SCs in the nerve microenvironment using the high-fat diet-fed mouse, which mimics human prediabetes and neuropathy. We identified four major SC clusters, myelinating, nonmyelinating, immature, and repair in healthy and neuropathic nerves, in addition to a distinct cluster of nerve macrophages. Myelinating SCs acquired a unique transcriptional profile, beyond myelination, in response to metabolic stress. Mapping SC intercellular communication identified a shift in communication, centered on immune response and trophic support pathways, which primarily impacted nonmyelinating SCs. Validation analyses revealed that neuropathic SCs become pro-inflammatory and insulin resistant under prediabetic conditions. Overall, our study offers a unique resource for interrogating SC function, communication, and signaling in nerve pathophysiology to help inform SC-specific therapies.

Target formation in muscle fibres indicates reinnervation - A proteomic study in muscle samples from peripheral neuropathies.

AIMS: Target skeletal muscle fibres - defined by different concentric areas in oxidative enzyme staining - can occur in patients with neurogenic muscular atrophy. Here, we used our established hypothesis-free proteomic approach with the aim of deciphering the protein composition of targets. We also searched for potential novel interactions between target proteins. METHODS: Targets and control areas were laser microdissected from skeletal muscle sections of 20 patients with neurogenic muscular atrophy. Samples were analysed by a highly sensitive mass spectrometry approach, enabling relative protein quantification. The results were validated by immunofluorescence studies. Protein interactions were investigated by yeast two-hybrid assays, coimmunoprecipitation experiments and bimolecular fluorescence complementation. RESULTS: More than 1000 proteins were identified. Among these, 55 proteins were significantly over-represented and 40 proteins were significantly under-represented in targets compared to intraindividual control samples. The majority of over-represented proteins were associated with the myofibrillar Z-disc and actin dynamics, followed by myosin and myosin-associated proteins, proteins involved in protein biosynthesis and chaperones. Under-represented proteins were mainly mitochondrial proteins. Functional studies revealed that the LIM domain of the over-represented protein LIMCH1 interacts with isoform A of Xin actin-binding repeat-containing protein 1 (XinA). CONCLUSIONS: In particular, proteins involved in myofibrillogenesis are over-represented in target structures, which indicate an ongoing process of sarcomere assembly and/or remodelling within this specific area of the muscle fibres. We speculate that target structures are the result of reinnervation processes in which filamin C-associated myofibrillogenesis is tightly regulated by the BAG3-associated protein quality system.

Inhibitors of the Mechanistic Target of Rapamycin Can Ameliorate Bortezomib-Induced Peripheral Neuropathy.

Bortezomib, an anticancer drug for multiple myeloma and mantle cell lymphoma, causes severe adverse events and leads to peripheral neuropathy. The associated neuropathy limits the use of bortezomib and could lead to discontinuation of the treatment; therefore, effective intervention is crucial. In the present study, we statistically searched for a drug that could alleviate bortezomib-induced peripheral neuropathy using adverse event self-reports. We observed that specific inhibitors of the mechanistic target of rapamycin (mTOR) lowered the incidence of bortezomib-induced peripheral neuropathy. These findings were experimentally validated in mice, which exhibited long-lasting mechanical hypersensitivity after repeated bortezomib treatment. This effect was inhibited for hours after a systemic injection with rapamycin or everolimus in a dose-dependent manner. Bortezomib-induced allodynia was accompanied by the activation of spinal astrocytes, and intrathecal injection of mTOR inhibitors or an inhibitor of ribosomal protein S6 kinase 1, a downstream target of mTOR, exhibited considerable analgesic effects in a dose-dependent manner. These results suggest that mTOR inhibitors, which are readily available to patients prescribed bortezomib, are one of the most effective therapeutics for bortezomib-induced peripheral neuropathy.