Paclitaxel-induced painful neuropathy is associated with changes in mitochondrial bioenergetics, glycolysis, and an energy deficit in dorsal root ganglia neurons

Desloratadine ameliorates paclitaxel-induced peripheral neuropathy and hypersensitivity reactions in mice

Paclitaxel (PTX) serves as a primary chemotherapy agent against diverse solid tumors including breast cancer, lung cancer, head and neck cancer and ovarian cancer, having severe adverse effects including PTX-induced peripheral neuropathy (PIPN) and hypersensitivity reactions (HSR). A recommended anti-allergic agent diphenhydramine (DIP) has been used to alleviate PTX-induced HSR. Desloratadine (DLT) is a third generation of histamine H1 receptor antagonist, but also acted as a selective antagonist of 5HTR2A. In this study we investigated whether DLT ameliorated PIPN-like symptoms in mice and the underlying mechanisms. PIPN was induced in male mice by injection of PTX (4 mg/kg, i.p.) every other day for 4 times. The mice exhibited 50% reduction in mechanical threshold, paw thermal response latency and paw cold response latency compared with control mice. PIPN mice were treated with DLT (10, 20 mg/kg, i.p.) 30 min before each PTX administration in the phase of establishing PIPN mice model and then administered daily for 4 weeks after the model was established. We showed that DLT administration dose-dependently elevated the mechanical, thermal and cold pain thresholds in PIPN mice, whereas administration of DIP (10 mg/kg, i.p.) had no ameliorative effects on PIPN-like symptoms. We found that the expression of 5HTR2A was selectively elevated in the activated spinal astrocytes of PIPN mice. Spinal cord-specific 5HTR2A knockdown by intrathecal injection of AAV9-5Htr2a-shRNA significantly alleviated the mechanical hyperalgesia, thermal and cold hypersensitivity in PIPN mice, while administration of DLT (20 mg/kg) did not further ameliorate PIPN-like symptoms. We demonstrated that DLT administration alleviated dorsal root ganglion neuronal damage and suppressed sciatic nerve destruction, spinal neuron apoptosis and neuroinflammation in the spinal cord of PIPN mice. Furthermore, we revealed that DLT administration suppressed astrocytic neuroinflammation via the 5HTR2A/c-Fos/NLRP3 pathway and blocked astrocyte-neuron crosstalk by targeting 5HTR2A. We conclude that spinal 5HTR2A inhibition holds promise as a therapeutic approach for PIPN and we emphasize the potential of DLT as a dual-functional agent in ameliorating PTX-induced both PIPN and HSR in chemotherapy. In summary, we determined that spinal 5HTR2A was selectively activated in PIPN mice and DLT could ameliorate the PTX-induced both PIPN- and HSR-like pathologies in mice. DLT alleviated the damages of DRG neurons and sciatic nerves, while restrained spinal neuronal apoptosis and CGRP release in PIPN mice. The underlying mechanisms were intensively investigated by assay against the PIPN mice with 5HTR2A-specific knockdown in the spinal cord by injection of adeno-associated virus 9 (AAV9)-5Htr2a-shRNA. DLT inhibited astrocytic NLRP3 inflammasome activation-mediated spinal neuronal damage through 5HTR2A/c-FOS pathway. Our findings have supported that spinal 5HTR2A inhibition shows promise as a therapeutic strategy for PIPN and highlighted the potential advantage of DLT as a dual-functional agent in preventing against PTX-induced both PIPN and HSR effects in anticancer chemotherapy.

Macrophage: A key player in neuropathic pain

Research on the relationship between macrophages and neuropathic pain has flourished in the past two decades. It has long been believed that macrophages are strong immune effector cells that play well-established roles in tissue homeostasis and lesions, such as promoting the initiation and progression of tissue injury and improving wound healing and tissue remodeling in a variety of pathogenesis-related diseases. They are also heterogeneous and versatile cells that can switch phenotypically/functionally in response to the micro-environment signals. Apart from microglia (resident macrophages of both the spinal cord and brain), which are required for the neuropathic pain processing of the CNS, neuropathic pain signals in PNS are influenced by the interaction of tissue-resident macrophages and BM infiltrating macrophages with primary afferent neurons. And the current review looks at new evidence that suggests sexual dimorphism in neuropathic pain are caused by variations in the immune system, notably macrophages, rather than the neurological system.

Current understanding of the molecular mechanisms of chemotherapy-induced peripheral neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is the most common off-target adverse effects caused by various chemotherapeutic agents, such as cisplatin, oxaliplatin, paclitaxel, vincristine and bortezomib. CIPN is characterized by a substantial loss of primary afferent sensory axonal fibers leading to sensory disturbances in patients. An estimated of 19-85% of patients developed CIPN during the course of chemotherapy. The lack of preventive measures and limited treatment options often require a dose reduction or even early termination of life-saving chemotherapy, impacting treatment efficacy and patient survival. In this Review, we summarized the current understanding on the pathogenesis of CIPN. One prominent change induced by chemotherapeutic agents involves the disruption of neuronal cytoskeletal architecture and axonal transport dynamics largely influenced by the interference of microtubule stability in peripheral neurons. Due to an ineffective blood-nerve barrier in our peripheral nervous system, exposure to some chemotherapeutic agents causes mitochondrial swelling in peripheral nerves, which lead to the opening of mitochondrial permeability transition pore and cytochrome c release resulting in degeneration of primary afferent sensory fibers. The exacerbated nociceptive signaling and pain transmission in CIPN patients is often linked the increased neuronal excitability largely due to the elevated expression of various ion channels in the dorsal root ganglion neurons. Another important contributing factor of CIPN is the neuroinflammation caused by an increased infiltration of immune cells and production of inflammatory cytokines. In the central nervous system, chemotherapeutic agents also induce neuronal hyperexcitability in the spinal dorsal horn and anterior cingulate cortex leading to the development of central sensitization that causes CIPN. Emerging evidence suggests that the change in the composition and diversity of gut microbiota (dysbiosis) could have direct impact on the development and progression of CIPN. Collectively, all these aspects contribute to the pathogenesis of CIPN. Recent advances in RNA-sequencing offer solid platform for in silico drug screening which enable the identification of novel therapeutic agents or repurpose existing drugs to alleviate CIPN, holding immense promises for enhancing the quality of life for cancer patients who undergo chemotherapy and improve their overall treatment outcomes.

SIRT3 alleviates painful diabetic neuropathy by mediating the FoxO3a-PINK1-Parkin signaling pathway to activate mitophagy

INTRODUCTION

Painful diabetic neuropathy (PDN) is a common complication of diabetes. Previous studies have implicated that mitochondrial dysfunction plays a role in the development of PDN, but its pathogenesis and mechanism have not been fully investigated.

METHODS

In this study, we used high-fat diet/low-dose streptozotocin-induced rats as a model of type 2 diabetes mellitus. Behavioral testing, whole-cell patch-clamp recordings of dorsal root ganglion (DRG) neurons, and complex sensory nerve conduction velocity studies were used to assess peripheral neuropathy. Mitochondrial membrane potential (MMP), ATP, tissue reactive oxygen species, and transmission electron microscopy were used to evaluate the function and morphology of mitochondria in DRG. Real-time PCR, western blot, and immunofluorescence were performed to investigate the mechanism.

RESULTS

We found that damaged mitochondria were accumulated and mitophagy was inhibited in PDN rats. The expression of sirtuin 3 (SIRT3), which is an NAD+-dependent deacetylase in mitochondria, was inhibited. Overexpression of SIRT3 in DRG neurons by intrathecally administered LV-SIRT3 lentivirus ameliorated neurological and mitochondrial dysfunctions. This was evidenced by the reversal of allodynia and nociceptor hyperexcitability, as well as the restoration of MMP and ATP levels. Overexpression of SIRT3 restored the inhibited mitophagy by activating the FoxO3a-PINK1-Parkin signaling pathway. The effects of SIRT3 overexpression, including the reversal of allodynia and nociceptor hyperexcitability, the improvement of impaired mitochondria and mitophagy, and the restoration of PINK1 and Parkin expression, were counteracted when FoxO3a siRNA was intrathecally injected.

CONCLUSION

These results showed that SIRT3 overexpression ameliorates PDN via activation of FoxO3a-PINK1-Parkin-mediated mitophagy, suggesting that SIRT3 may become an encouraging therapeutic strategy for PDN.

Peripheral mu-opioid receptor activation by dermorphin [D-Arg2, Lys4] (1-4) amide alleviates behavioral and neurobiological aberrations in rat model of chemotherapy-induced neuropathic pain

Paclitaxel, a frequently utilized chemotherapeutic agent, often gives rise to severe and distressing sensory neuropathy in patients undergoing chemotherapy. Unfortunately, current therapeutics for chemotherapy-induced neuropathic pain (CINP) demonstrate limited effectiveness and are burdened with the potential for central side effects such as sedation, respiratory depression, cognitive impairment, and addiction, posing substantial clinical challenges. In light of these limitations, present study is designed to investigate the therapeutic potential of Dermorphin [D-Arg2, Lys4] (1-4) amide (DALDA), a preferential peripherally acting mu-opioid receptor agonist, in rat model of CINP. The primary objective was to assess the analgesic properties of DALDA and elucidate the underlying mechanisms governing its therapeutic activity. Our findings revealed that DALDA treatment significantly ameliorated paclitaxel-induced evoked and spontaneous ongoing pain in rats without causing drug addiction and other central side effects. Molecular analyses further unveiled that paclitaxel administration resulted in increased expression of TRP channels, NR2B, voltage-gated sodium channels (VGSCs) and neuroinflammatory markers in both the dorsal root ganglion (DRG) and the spinal cord (L4-L5 region) of rats. DALDA treatment significantly downregulated ion channels (TRPs, VGSCs) and NR2B expressions, concomitant with the inhibition of microglial activation, resulting in the suppression of oxido-nitrosative stress and neuroinflammatory cascade. Findings from the current study suggests that peripheral mu-opioid receptors may offer a potential target for the treatment of patients suffering from CINP, offering new avenues for improved pain relief while minimizing central side effects.

Melatonin Relieves Paclitaxel-Induced Neuropathic Pain by Regulating pNEK2-Dependent Epigenetic Pathways in DRG Neurons

The neurohormone melatonin (MLT) demonstrates promising potential in ameliorating neuropathic pain induced by paclitaxel (PTX) chemotherapy. However, little is known about its protective effect on dorsal root ganglion (DRG) neurons in neuropathic pain resulting from the chemotherapeutic drug PTX. Here, PTX-treated rats revealed that intrathecal administration of MLT dose-dependently elevated hind paw withdrawal thresholds and latency, indicating that MLT significantly reversed PTX-induced neuropathic pain. Mechanistically, the analgesic effects of MLT were found to be mediated via melatonin receptor 2 (MT2), as pretreatment with an MT2 receptor antagonist inhibited these effects. Moreover, intrathecal MLT injection reversed the pNEK2-dependent epigenetic program induced by PTX. All of the effects caused by MLT were blocked by pretreatment with an MT2 receptor-selective antagonist, 4P-PDOT. Remarkably, multiple MLT administered during PTX treatment (PTX+MLTs) exhibited not only rapid but also lasting reversal of allodynia/hyperalgesia compared to single-bolus MLT administered after PTX treatment (PTX+MLT). In addition, PTX+MLTs exhibited greater efficacy in reversing PTX-induced alterations in pRSK2, pNEK2, JMJD3, H3K27me3, and TRPV1 expression and interaction in DRG neurons than PTX+MLT. These results indicated that MLT administered during PTX treatment reduced the incidence and/or severity of neuropathy and had a better inhibitory effect on the pNEK2-dependent epigenetic program compared to MLT administered after PTX treatment. In conclusion, MLT/MT2 is a promising therapy for the treatment of pNEK2-dependent painful neuropathy resulting from PTX treatment. MLT administered during PTX chemotherapy may be more effective in the prevention or reduction of PTX-induced neuropathy and maintaining quality.

An up-to-date view of paclitaxel-induced peripheral neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN),referring to the damage to the peripheral nerves caused by exposure to a neurotoxic chemotherapeutic agent, is a common side effect amongst patients undergoing chemotherapy. Paclitaxel-induced peripheral neuropathy (PIPN) can lead to dose reduction or early cessation of chemotherapy, which is not conducive to patients'survival. Even after treatment is discontinued, PIPN symptoms carried a greater risk of worsening and plagued the patient's life, leading to long-term morbidity in survivors. Here, we summarize the research progress for clinical manifestations, risk factors, pathogenesis, prevention and treatment of PIPN, so as to embark on the path of preventing PIPN with prolongation of patient's life quality on a long-term basis.

Phosphate NIMA-Related Kinase 2-Dependent Epigenetic Pathways in Dorsal Root Ganglion Neurons Mediates Paclitaxel-Induced Neuropathic Pain

BACKGROUND

The microtubule-stabilizing drug paclitaxel (PTX) is an important chemotherapeutic agent for cancer treatment and causes peripheral neuropathy as a common side effect that substantially impacts the functional status and quality of life of patients. The mechanistic role for NIMA-related kinase 2 (NEK2) in the progression of PTX-induced neuropathic pain has not been established.

METHODS

Adult male Sprague-Dawley rats intraperitoneally received PTX to induce neuropathic pain. The protein expression levels in the dorsal root ganglion (DRG) of animals were measured by biochemical analyses. Nociceptive behaviors were evaluated by von Frey tests and hot plate tests.

RESULTS

PTX increased phosphorylation of the important microtubule dynamics regulator NEK2 in DRG neurons and induced profound neuropathic allodynia. PTX-activated phosphorylated NEK2 (pNEK2) increased jumonji domain-containing 3 (JMJD3) protein, a histone demethylase protein, to specifically catalyze the demethylation of the repressive histone mark H3 lysine 27 trimethylation (H3K27me3) at the Trpv1 gene, thereby enhancing transient receptor potential vanilloid subtype-1 (TRPV1) expression in DRG neurons. Moreover, the pNEK2-dependent PTX response program is regulated by enhancing p90 ribosomal S6 kinase 2 (RSK2) phosphorylation. Conversely, intrathecal injections of kaempferol (a selective RSK2 activation antagonist), NCL 00017509 (a selective NEK2 inhibitor), NEK2-targeted siRNA, GSK-J4 (a selective JMJD3 inhibitor), or capsazepine (an antagonist of TRPV1 receptor) into PTX-treated rats reversed neuropathic allodynia and restored silencing of the Trpv1 gene, suggesting the hierarchy and interaction among phosphorylated RSK2 (pRSK2), pNEK2, JMJD3, H3K27me3, and TRPV1 in the DRG neurons in PTX-induced neuropathic pain.

CONCLUSIONS

pRSK2/JMJD3/H3K27me3/TRPV1 signaling in the DRG neurons plays as a key regulator for PTX therapeutic approaches.

Intrathecal rapamycin attenuates the mechanical hyperalgesia of paclitaxel-induced peripheral neuropathy in mice

Paclitaxel is an extensively used chemotherapy antitumor drug and paclitaxel-induced peripheral neuropathy (PIPN) is one of the most common side effect. Rapamycin, originally used as an adjuvant drug for chemotherapy, has recently been found to possess potential neuroprotective activities. Our purposes of this study are to verify the effect of rapamycin on PIPN, which contributes to a new target for PIPN treatment. Mice were given paclitaxel or rapamycin with different injection methods. Paw withdrawal threshold was tested at different time points for mechanical sensitivity assessment. Administration of paclitaxel, both 2 mg/kg and 5 mg/kg, could induce mechanical hypersensitivity. 0.01 mg intrathecal injection of rapamycin showed the best effect on attenuate the mechanical hyperalgesia of PIPN. Intrathecal injection of only rapamycin would not induce the mechanical hyperalgesia while when rapamycin and paclitaxel were used together the mechanical hyperalgesia induced by paclitaxel could be attenuated. Paclitaxel could induce mechanical hyperalgesia in mice and rapamycin could attenuate such mechanical hyperalgesia of PIPN.

PGC1α: an emerging therapeutic target for chemotherapy-induced peripheral neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN)-mediated paresthesias are a common complication in cancer patients undergoing chemotherapy. There are currently no treatments available to prevent or reverse CIPN. Therefore, new therapeutic targets are urgently needed to develop more effective analgesics. However, the pathogenesis of CIPN remains unclear, and the prevention and treatment strategies of CIPN are still unresolved issues in medicine. More and more studies have demonstrated that mitochondrial dysfunction has become a major factor in promoting the development and maintenance of CIPN, and peroxisome proliferator-activated receptor gamma (PPARγ) coactivator 1α (PGC1α) plays a significant role in maintaining the mitochondrial function, protecting peripheral nerves, and alleviating CIPN. In this review, we highlight the core role of PGC1α in regulating oxidative stress and maintaining normal mitochondrial function and summarize recent advances in its therapeutic effects and mechanisms in CIPN and other forms of peripheral neuropathy. Emerging studies suggest that PGC1α activation may positively impact CIPN mitigation by modulating oxidative stress, mitochondrial dysfunction, and inflammation. Therefore, novel therapeutic strategies targeting PGC1α could be a potential therapeutic target in CIPN.

Khellin as a selective monoamine oxidase B inhibitor ameliorated paclitaxel-induced peripheral neuropathy in mice

BACKGROUND

Treatment of paclitaxel (PTX)-induced peripheral neuropathy (PIPN) is full of challenges because of the unclear pathogenesis of PIPN. Herbal folk medicine Khellin (Khe) is a natural compound extracted from Ammi visnaga for treatment of renal colics and muscle spasms.

PURPOSE

Here, we aimed to assess the potential of Khe in ameliorating PIPN-like pathology in mice and investigate the underlying mechanisms.

METHODS

PIPN model mice were conducted by injection of PTX based on the published approach. The capability of Khe in ameliorating the PTX-induced neurological dysfunctions was assayed by detection of nociceptive hypersensitivities including mechanical hyperalgesia, thermal hypersensitivity, and cold allodynia in mice. The underlying mechanisms were investigated by assays against the PIPN mice with MAOB-specific knockdown in spinal cord and dorsal root ganglion (DRG) tissues by injection of adeno-associated virus (AAV)-MAOB-shRNA.

RESULTS

We determined that MAOB not MAOA is highly overexpressed in the spinal cord and DRG tissues of PIPN mice and Khe as a selective MAOB inhibitor improved PIPN-like pathology in mice. Khe promoted neurite outgrowth, alleviated apoptosis, and improved mitochondrial dysfunction of DRG neurons by targeting MAOB. Moreover, Khe inhibited spinal astrocytes activation and suppressed neuroinflammation of spinal astrocytes via MAOB/NF-κB/NLRP3/ASC/Caspase1/IL-1β pathway.

CONCLUSION

Our work might be the first to report that MAOB not MAOA is selectively overexpressed in the spinal cord and DRG tissues of PIPN mice, and all findings have highly addressed the potency of selective MAOB inhibitor in the amelioration of PIPN-like pathology and highlighted the potential of Khe in treating PTX-induced side effects.

DG, Sun L, Banjara B, Mosley-Kellum K, Dinh TC, Singh M. Cannabidiol-Loaded Extracellular Vesicles from Human Umbilical Cord Mesenchymal Stem Cells Alleviate Paclitaxel-Induced Peripheral Neuropathy

In cancer patients, chronic paclitaxel (PTX) treatment causes excruciating pain, limiting its use in cancer chemotherapy. The neuroprotective potential of synthetic cannabidiol (CBD) and CBD formulated in extracellular vesicles (CBD-EVs) isolated from human umbilical cord derived mesenchymal stem cells was investigated in C57BL/6J mice with PTX-induced neuropathic pain (PIPN). The particle size of EVs and CBD-EVs, surface roughness, nanomechanical properties, stability, and release studies were all investigated. To develop neuropathy in mice, PTX (8 mg/kg, i.p.) was administered every other day (four doses). In terms of decreasing mechanical and thermal hypersensitivity, CBD-EVs treatment was superior to EVs treatment or CBD treatment alone (p < 0.001). CBD and CBD-EVs significantly reduced mitochondrial dysfunction in dorsal root ganglions and spinal homogenates of PTX-treated animals by modulating the AMPK pathway (p < 0.001). Studies inhibiting the AMPK and 5HT1A receptors found that CBD did not influence the neurobehavioral or mitochondrial function of PIPN. Based on these results, we hypothesize that CBD and CBD-EVs mitigated PIPN by modulating AMPK and mitochondrial function.

Paclitaxel, but Not Cisplatin, Affects Satellite Glial Cells in Dorsal Root Ganglia of Rats with Chemotherapy-Induced Peripheral Neurotoxicity

Chemotherapy-induced peripheral neurotoxicity is one of the most common dose-limiting toxicities of several widely used anticancer drugs such as platinum derivatives (cisplatin) and taxanes (paclitaxel). Several molecular mechanisms related to the onset of neurotoxicity have already been proposed, most of them having the sensory neurons of the dorsal root ganglia (DRG) and the peripheral nerve fibers as principal targets. In this study we explore chemotherapy-induced peripheral neurotoxicity beyond the neuronocentric view, investigating the changes induced by paclitaxel (PTX) and cisplatin (CDDP) on satellite glial cells (SGC) in the DRG and their crosstalk. Rats were chronically treated with PTX (10 mg/Kg, 1qwx4) or CDDP (2 mg/Kg 2qwx4) or respective vehicles. Morpho-functional analyses were performed to verify the features of drug-induced peripheral neurotoxicity. Qualitative and quantitative immunohistochemistry, 3D immunofluorescence, immunoblotting, and transmission electron microscopy analyses were also performed to detect alterations in SGCs and their interconnections. We demonstrated that PTX, but not CDDP, produces a strong activation of SGCs in the DRG, by altering their interconnections and their physical contact with sensory neurons. SGCs may act as principal actors in PTX-induced peripheral neurotoxicity, paving the way for the identification of new druggable targets for the treatment and prevention of chemotherapy-induced peripheral neurotoxicity.

Soluble epoxide hydrolase inhibition alleviates chemotherapy induced neuropathic pain

Chemotherapy induced peripheral neuropathy (CIPN) is a particularly pernicious form of neuropathy and the associated pain is the primary dose-limiting factor of life-prolonging chemotherapy treatment. The prevalence of CIPN is high and can last long after treatment has been stopped. Currently, late in the COVID-19 pandemic, there are still increased psychological pressures on cancer patients as well as additional challenges in providing analgesia for them. These include the risks of nonsteroidal anti-inflammatory drug (NSAID) analgesics potentially masking early infection symptoms and the immunosuppression of steroidal and opiate based approaches. Even without these concerns, CIPN is often inadequately treated with few therapies that offer significant pain relief. The experiments we report use soluble epoxide hydrolase inhibitors (sEHI) which relieved this intractable pain in preclinical models. Doses of EC5026, an IND candidate intended to treat neuropathic pain, elicited dose dependent analgesic responses in multiple models including platinum-based, taxane, and vinca alkaloid-based CIPN pain in Sprague Dawley rats. At the same time as a class, the sEHI are known to result in fewer debilitating side effects of other analgesics, likely due to their novel mechanism of action. Overall, the observed dose-dependent analgesia in both male and female rats across multiple models of chemotherapy induced neuropathic pain holds promise as a useful tool when translated to the clinic.

Serum sodium ions and chloride ions associated with taxane-induced peripheral neuropathy in Chinese patients with early-stage breast cancer: A nation-wide multicenter study

BACKGROUND

Taxane-induced peripheral neuropathy (TIPN) is a debilitating adverse effect of cancer treatments with taxanes which may require a reduction or discontinuation chemotherapy and affect clinical and survival outcomes. A number of factors have contributed to the increasing prevalence of TIPN. Nonetheless, limited knowledge exists of potential prechemotherapy blood-based biochemical factors associated with TIPN development.

METHODS

We recruited breast cancer patients at seven cancer institutions in China. Participants aged 18 years or older with stage I to III breast cancer who scheduled to undergo primary neoadjuvant and adjuvant chemotherapy with taxanes were eligible. Eligible patients underwent patient-reported neuropathy assessments using the EORTC-CIPN20 questionnaire. Patients completed the questionnaire before commencing treatment and after every cycle. For every patient, we selected the highest TIPN toxicity score for analysis since the first cycle. The posttreatment TIPN severity was compared with blood-based biochemical factors within 30 days before commencing treatment. Independent samples t tests, Mann-Whitney U tests and linear regression were used to identify blood-based and clinical associations with TIPN development.

RESULTS

The study included 873 breast cancer participants who received paclitaxel, docetaxel or nanoparticle albumin-bound (nab)-paclitaxel. In the whole cohort, factors associated with higher TIPN toxicity scores were higher cumulative chemotherapy dose (β = 0.005; 95% CI, 0.004 to 0.006; P < .001), lower sodium ions (β = -0.24; 95% CI, -0.39 to -0.09; P = .002) and higher chloride ions (β = 0.30; 95% CI, 0.16 to 0.44; P < .001).

CONCLUSIONS

The findings suggest that breast cancer patients with a higher cumulative chemotherapy dose, lower pretreatment sodium ions, and higher pretreatment chloride ions receiving taxanes should receive closer monitoring to mitigate the development of short-term and long-term TIPN.

Paclitaxel Inhibits KCNQ Channels in Primary Sensory Neurons to Initiate the Development of Painful Peripheral Neuropathy

Cancer patients undergoing paclitaxel infusion usually experience peripheral nerve degeneration and serious neuropathic pain termed paclitaxel-induced peripheral neuropathy (PIPN). However, alterations in the dose or treatment schedule for paclitaxel do not eliminate PIPN, and no therapies are available for PIPN, despite numerous studies to uncover the mechanisms underlying the development/maintenance of this condition. Therefore, we aimed to uncover a novel mechanism underlying the pathogenesis of PIPN. Clinical studies suggest that acute over excitation of primary sensory neurons is linked to the pathogenesis of PIPN. We found that paclitaxel-induced acute hyperexcitability of primary sensory neurons results from the paclitaxel-induced inhibition of KCNQ potassium channels (mainly KCNQ2), found abundantly in sensory neurons and axons. We found that repeated application of XE-991, a specific KCNQ channel blocker, induced PIPN-like alterations in rats, including mechanical hypersensitivity and degeneration of peripheral nerves, as detected by both morphological and behavioral assays. In contrast, genetic deletion of KCNQ2 from peripheral sensory neurons in mice significantly attenuated the development of paclitaxel-induced peripheral sensory fiber degeneration and chronic pain. These findings may lead to a better understanding of the causes of PIPN and provide an impetus for developing new classes of KCNQ activators for its therapeutic treatment.

Neurophysiopathological Aspects of Paclitaxel-induced Peripheral Neuropathy

Chemotherapy is widely used as a primary treatment or adjuvant therapy for cancer. Anti-microtubule agents (such as paclitaxel and docetaxel) are used for treating many types of cancer, either alone or in combination. However, their use has negative consequences that restrict the treatment's ability to continue. The principal negative effect is the so-called chemotherapy-induced peripheral neuropathy (CIPN). CIPN is a complex ailment that depends on diversity in the mechanisms of action of the different chemotherapy drugs, which are not fully understood. In this paper, we review several neurophysiological and pathological characteristics, such as morphological changes, changes in ion channels, mitochondria and oxidative stress, cell death, changes in the immune response, and synaptic control, as well as the characteristics of neuropathic pain produced by paclitaxel.

TRPA1 modulation by Sigma-1 receptor prevents oxaliplatin-induced painful peripheral neuropathy

Chemotherapy-induced peripheral neuropathy is a frequent, disabling side effect of anticancer drugs. Oxaliplatin, a platinum compound used in the treatment of advanced colorectal cancer, often leads to a form of chemotherapy-induced peripheral neuropathy characterized by mechanical and cold hypersensitivity. Current therapies for chemotherapy-induced peripheral neuropathy are ineffective, often leading to the cessation of treatment. Transient receptor potential ankyrin 1 (TRPA1) is a polymodal, non-selective cation-permeable channel expressed in nociceptors, activated by physical stimuli and cellular stress products. TRPA1 has been linked to the establishment of chemotherapy-induced peripheral neuropathy and other painful neuropathic conditions. Sigma-1 receptor is an endoplasmic reticulum chaperone known to modulate the function of many ion channels and receptors. Sigma-1 receptor antagonist, a highly selective antagonist of Sigma-1 receptor, has shown effectiveness in a phase II clinical trial for oxaliplatin chemotherapy-induced peripheral neuropathy. However, the mechanisms involved in the beneficial effects of Sigma-1 receptor antagonist are little understood. We combined biochemical and biophysical (i.e. intermolecular Förster resonance energy transfer) techniques to demonstrate the interaction between Sigma-1 receptor and human TRPA1. Pharmacological antagonism of Sigma-1R impaired the formation of this molecular complex and the trafficking of functional TRPA1 to the plasma membrane. Using patch-clamp electrophysiological recordings we found that antagonists of Sigma-1 receptor, including Sigma-1 receptor antagonist, exert a marked inhibition on plasma membrane expression and function of human TRPA1 channels. In TRPA1-expressing mouse sensory neurons, Sigma-1 receptor antagonists reduced inward currents and the firing of actions potentials in response to TRPA1 agonists. Finally, in a mouse experimental model of oxaliplatin neuropathy, systemic treatment with a Sigma-1 receptor antagonists prevented the development of painful symptoms by a mechanism involving TRPA1. In summary, the modulation of TRPA1 channels by Sigma-1 receptor antagonists suggests a new strategy for the prevention and treatment of chemotherapy-induced peripheral neuropathy and could inform the development of novel therapeutics for neuropathic pain.

The sex-specific role of sensory neuron LKB1 on metabolic stress-induced mechanical hypersensitivity and mitochondrial respiration

Pain disorders induce metabolic stress in peripheral sensory neurons by reducing mitochondrial output, shifting cellular metabolism, and altering energy use. These processes implicate neuronal metabolism as an avenue for creating novel therapeutics. Liver kinase B1 (LKB1) mediates the cellular response to metabolic stress by inducing the AMPK pathway. The LKB1-AMPK pathway increases energy producing processes, including mitochondrial output. These processes inhibit pain by directly or indirectly restoring energetic balance within a cell. Although the LKB1-AMPK pathway has been linked to pain relief, it is not yet known which cell is responsible for this property, as well any direct ties to cellular metabolism. To elucidate this, we developed a genetic mouse model where LKB1 is selectively removed from Nav1.8-pain sensory neurons and metabolically stressed them by fasting for 24 hours. We found females, but not males, had neuron-specific, LKB1-dependent restoration of metabolic stress-induced mitochondrial metabolism. This was reflected in mechanical hypersensitivity, where the absence of LKB1 led to hypersensitivity in female, but not male, animals. This discrepancy suggests a sex- and cell-specific contribution to LKB1-depdendent fasting-induced mechanical hypersensitivity. While our data represent a potential role for LKB1 in anti-pain pathways in a metabolic-specific manner, more must be done to investigate these sex differences.

Proteome and Network Analysis Provides Novel Insights Into Developing and Established Chemotherapy-Induced Peripheral Neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is a debilitating side-effect of cancer therapies. So far, the development of CIPN cannot be prevented, neither can established CIPN be reverted, often leading to the cessation of necessary chemotherapy. Thus, there is an urgent need to explore the mechanistic basis of CIPN to facilitate its treatment. Here we used an integrated approach of quantitative proteome profiling and network analysis in a clinically relevant rat model of paclitaxel-induced peripheral neuropathy. We analysed lumbar rat DRG at two critical time points: (1) day 7, right after cessation of paclitaxel treatment, but prior to neuropathy development (pre-CIPN); (2) 4 weeks after paclitaxel initiation, when neuropathy has developed (peak-CIPN). In this way we identified a differential protein signature, which shows how changes in the proteome correlate with the development and maintenance of CIPN, respectively. Extensive biological pathway and network analysis reveals that, at pre-CIPN, regulated proteins are prominently implicated in mitochondrial (dys)function, immune signalling, neuronal damage/regeneration, and neuronal transcription. Orthogonal validation in an independent rat cohort confirmed the increase of β-catenin (CTNNB1) at pre-CIPN. More importantly, detailed analysis of protein networks associated with β-catenin highlights translationally relevant and potentially druggable targets. Overall, this study demonstrates the enormous value of combining animal behaviour with proteome and network analysis to provide unprecedented insights into the molecular basis of CIPN. In line with emerging approaches of network medicine our results highlight new avenues for developing improved therapeutic options aimed at preventing and treating CIPN.

Preclinical evidence for mitochondrial DNA as a potential blood biomarker for chemotherapy-induced peripheral neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is a serious dose-limiting side effect of several first-line chemotherapeutic agents including paclitaxel, oxaliplatin and bortezomib, for which no predictive marker is currently available. We have previously shown that mitochondrial dysfunction is associated with the development and maintenance of CIPN. The aim of this study was to evaluate the potential use of mitochondrial DNA (mtDNA) levels and complex I enzyme activity as blood biomarkers for CIPN. Real-time qPCR was used to measure mtDNA levels in whole blood collected from chemotherapy- and vehicle-treated rats at three key time-points of pain-like behaviour: prior to pain development, at the peak of mechanical hypersensitivity and at resolution of pain-like behaviour. Systemic oxaliplatin significantly increased mtDNA levels in whole blood prior to pain development. Furthermore, paclitaxel- and bortezomib-treated animals displayed significantly higher levels of mtDNA at the peak of mechanical hypersensitivity. Mitochondrial complex I activity in whole blood was assessed with an ELISA-based Complex I Enzyme Activity Dipstick Assay. Complex I activity was not altered by any of the three chemotherapeutic agents, either prior to or during pain-like behaviour. These data demonstrate that blood levels of mtDNA are altered after systemic administration of chemotherapy. Oxaliplatin, in particular, is associated with higher mtDNA levels before animals show any pain-like behaviour, thus suggesting a potential role for circulating mtDNA levels as non-invasive predictive biomarker for CIPN.

Macrophages transfer mitochondria to sensory neurons to resolve inflammatory pain

The current paradigm is that inflammatory pain passively resolves following the cessation of inflammation. Yet, in a substantial proportion of patients with inflammatory diseases, resolution of inflammation is not sufficient to resolve pain, resulting in chronic pain. Mechanistic insight into how inflammatory pain is resolved is lacking. Here, we show that macrophages actively control resolution of inflammatory pain remotely from the site of inflammation by transferring mitochondria to sensory neurons. During resolution of inflammatory pain in mice, M2-like macrophages infiltrate the dorsal root ganglia that contain the somata of sensory neurons, concurrent with the recovery of oxidative phosphorylation in sensory neurons. The resolution of pain and the transfer of mitochondria requires expression of CD200 receptor (CD200R) on macrophages and the non-canonical CD200R-ligand iSec1 on sensory neurons. Our data reveal a novel mechanism for active resolution of inflammatory pain.

Association of Genetic Variant at Chromosome 12q23.1 With Neuropathic Pain Susceptibility

IMPORTANCE

Neuropathic pain (NP) has important clinical and socioeconomic consequences for individuals and society. Increasing evidence indicates that genetic factors make a significant contribution to NP, but genome-wide association studies (GWASs) are scant in this field and could help to elucidate susceptibility to NP.

OBJECTIVE

To identify genetic variants associated with NP susceptibility.

DESIGN, SETTING, AND PARTICIPANTS

This genetic association study included a meta-analysis of GWASs of NP using 3 independent cohorts: ie, Genetics of Diabetes Audit and Research in Tayside Scotland (GoDARTS); Generation Scotland: Scottish Family Health Study (GS:SFHS); and the United Kingdom Biobank (UKBB). Data analysis was conducted from April 2018 to December 2019.

EXPOSURES

Individuals with NP (ie, case participants; those with pain of ≥3 months' duration and a Douleur Neuropathique en 4 Questions score ≥3) and individuals with no pain (ie, control participants) with or without diabetes from GoDARTS and GS:SFHS were identified using validated self-completed questionnaires. In the UKBB, self-reported prescribed medication and hospital records were used as a proxy to identify case participants (patients recorded as receiving specific anti-NP medicines) and control participants.

MAIN OUTCOMES AND MEASURES

GWAS was performed using linear mixed modeling. GWAS summary statistics were combined using fixed-effect meta-analysis. A total of 51 variants previously shown to be associated with NP were tested for replication.

RESULTS

This study included a total of 4512 case participants (2662 [58.9%] women; mean [SD] age, 61.7 [10.8] years) and 428 489 control participants (227 817 [53.2%] women; mean [SD] age, 62.3 [11.5] years) in the meta-analysis of 3 cohorts with European descent. The study found a genome-wide significant locus at chromosome 12q23.1, which mapped to SLC25A3 (rs369920026; odds ratio [OR] for having NP, 1.68; 95% CI, 1.40-2.02; P = 1.30 × 10-8), and a suggestive variant at 13q14.2 near CAB39L (rs7992766; OR, 1.09; 95% CI, 1.05-1.14; P = 1.22 × 10-7). These mitochondrial phosphate carriers and calcium binding genes are expressed in brain and dorsal root ganglia. Colocalization analyses using expression quantitative loci data found that the suggestive variant was associated with expression of CAB39L in the brain cerebellum (P = 1.01 × 10-14). None of the previously reported variants were replicated.

CONCLUSIONS AND RELEVANCE

To our knowledge, this was the largest meta-analyses of GWAS to date. It found novel genetic variants associated with NP susceptibility. These findings provide new insights into the genetic architecture of NP and important information for further studies.

Pathomechanisms of Paclitaxel-Induced Peripheral Neuropathy

Peripheral neuropathy is one of the most common side effects of chemotherapy, affecting up to 60% of all cancer patients receiving chemotherapy. Moreover, paclitaxel induces neuropathy in up to 97% of all gynecological and urological cancer patients. In cancer cells, paclitaxel induces cell death via microtubule stabilization interrupting cell mitosis. However, paclitaxel also affects cells of the central and peripheral nervous system. The main symptoms are pain and numbness in hands and feet due to paclitaxel accumulation in the dorsal root ganglia. This review describes in detail the pathomechanisms of paclitaxel in the peripheral nervous system. Symptoms occur due to a length-dependent axonal sensory neuropathy, where axons are symmetrically damaged and die back. Due to microtubule stabilization, axonal transport is disrupted, leading to ATP undersupply and oxidative stress. Moreover, mitochondria morphology is altered during paclitaxel treatment. A key player in pain sensation and axonal damage is the paclitaxel-induced inflammation in the spinal cord as well as the dorsal root ganglia. An increased expression of chemokines and cytokines such as IL-1β, IL-8, and TNF-α, but also CXCR4, RAGE, CXCL1, CXCL12, CX3CL1, and C3 promote glial activation and accumulation, and pain sensation. These findings are further elucidated in this review.

P2Y1 Purinergic Receptor Contributes to Remifentanil-Induced Cold Hyperalgesia via Transient Receptor Potential Melastatin 8-Dependent Regulation of N-methyl-d-aspartate Receptor Phosphorylation in Dorsal Root Ganglion

BACKGROUND

Remifentanil can induce postinfusion cold hyperalgesia. N-methyl-d-aspartate receptor (NMDAR) activation and upregulation of transient receptor potential melastatin 8 (TRPM8) membrane trafficking in dorsal root ganglion (DRG) are critical to cold hyperalgesia derived from neuropathic pain, and TRPM8 activation causes NMDAR-dependent cold response. Contribution of P2Y1 purinergic receptor (P2Y1R) activation in DRG to cold pain hypersensitivity and NMDAR activation induced by P2Y1R upregulation in neurons are also unraveled. This study explores whether P2Y1R contributes to remifentanil-induced cold hyperalgesia via TRPM8-dependent regulation of NMDAR phosphorylation in DRG.

METHODS

Rats with remifentanil-induced cold hyperalgesia were injected with TRPM8 antagonist or P2Y1R antagonist at 10 minutes before remifentanil infusion. Cold hyperalgesia (paw lift number and withdrawal duration on cold plate) was measured at -24, 2, 6, 24, and 48 hours following remifentanil infusion. After the last behavioral test, P2Y1R expression, TRPM8 expression and membrane trafficking, and NMDAR subunit (NR1 and NR2B) expression and phosphorylation in DRG were detected by western blot, and colocalization of P2Y1R with TRPM8 was determined by double-labeling immunofluorescence. Two-way repeated measures analysis of variance (ANOVA) or 2 × 2 factorial design ANOVA with repeated measures was used to analyze behavioral data of cold hyperalgesia. One-way ANOVA followed by Bonferroni post hoc comparisons was used to analyze the data in western blot and immunofluorescence.

RESULTS

Remifentanil infusion (1 μg·kg-1·min-1 for 60 minutes) induced cold hyperalgesia (hyperalgesia versus control, paw lift number and withdrawal duration on cold plate at 2-48 hours, P < .0001) with upregulated NR1 (hyperalgesia versus naive, 48 hours, mean ± standard deviation [SD], 114.00% ± 12.48% vs 41.75% ± 5.20%, P < .005) and NR2B subunits expression (104.13% ± 8.37% vs 24.63% ± 4.87%, P < .005), NR1 phosphorylation at Ser896 (91.88% ± 7.08% vs 52.00% ± 7.31%, P < .005) and NR2B phosphorylation at Tyr1472 (115.75% ± 8.68% vs 59.75% ± 7.78%, P < .005), TRPM8 expression (115.38% ± 9.27% vs 40.50% ± 4.07%, P < .005) and membrane trafficking (112.88% ± 5.62% vs 48.88% ± 6.49%, P < .005), and P2Y1R expression (128.25% ± 14.86% vs 45.13% ± 7.97%, P < .005) in DRG. Both TRPM8 and P2Y1R antagonists attenuated remifentanil-induced cold hyperalgesia and downregulated increased NR1 and NR2B expression and phosphorylation induced by remifentanil (remifentanil + RQ-00203078 versus remifentanil + saline, NR1 phosphorylation, 69.38% ± 3.66% vs 92.13% ± 4.85%; NR2B phosphorylation, 72.25% ± 6.43% vs 111.75% ± 11.00%, P < .0001). NMDAR activation abolished inhibition of TRPM8 and P2Y1R antagonists on remifentanil-induced cold hyperalgesia. P2Y1R antagonist inhibited remifentanil-evoked elevations in TRPM8 expression and membrane trafficking and P2Y1R-TRPM8 coexpression (remifentanil + 2'-deoxy-N6-methyl adenosine 3',5'-diphosphate [MRS2179] versus remifentanil + saline, coexpression, 8.33% ± 1.33% vs 22.19% ± 2.15%, P < .0001).

CONCLUSIONS

Attenuation of remifentanil-induced cold hyperalgesia by P2Y1R inhibition is attributed to downregulations in NMDAR expression and phosphorylation via diminishing TRPM8 expression and membrane trafficking in DRG.

Chemotherapy and peripheral neuropathy

Chemotherapy-induced peripheral neurotoxicity (CIPN) is a major dose-limiting side effect of many anti-cancer agents, including taxanes, platinums, vinca alkaloids, proteasome inhibitors, immunomodulatory drugs, and antibody-drug conjugates. The resultant symptoms often persist post treatment completion and continue to impact on long-term function and quality of life for cancer survivors. At present, dose reduction remains the only strategy to prevent severe neuropathy, often leading clinicians to the difficult decision of balancing maximal treatment exposure and minimal long-lasting side effects. This review examines the clinical presentations of CIPN with each class of neurotoxic treatment, describing signs, symptoms, and long-term outcomes. We provide an update on the proposed mechanisms of nerve damage and review current data on clinical and genetic risk factors contributing to CIPN development. We also examine recent areas of research in the treatment and prevention of CIPN, with specific focus on current clinical trials and consensus recommendations for CIPN management.

Redox-sensitive TRP channels: a promising pharmacological target in chemotherapy-induced peripheral neuropathy

INTRODUCTION

Chemotherapy-induced peripheral neuropathy (CIPN) and its related pain is a major side effect of certain chemotherapeutic agents used in cancer treatment. Available analgesics are mostly symptomatic, and on prolonged treatment, patients become refractive to them. Hence, the development of improved therapeutics that act on novel therapeutic targets is necessary. Potential targets include the redox-sensitive TRP channels [e.g. TRPA1, TRPC5, TRPC6, TRPM2, TRPM8, TRPV1, TRPV2, and TRPV4] which are activated under oxidative stress associated with CIPN.

AREAS COVERED

We have examined numerous neuropathy-inducing cancer chemotherapeutics and their pathophysiological mechanisms. Oxidative stress and its downstream targets, the redox-sensitive TRP channels, together with their potential pharmacological modulators, are discussed. Finally, we reflect upon the barriers to getting new therapeutic approaches into the clinic. The literature search was conducted in PubMed upto and including April 2021.

EXPERT OPINION

Redox-sensitive TRP channels are a promising target in CIPN. Pharmacological modulators of these channels have reduced pain in preclinical models and in clinical studies. Clinical scrutiny suggests that TRPA1, TRPM8, and TRPV1 are the most promising targets because of their pain-relieving potential. In addition to the analgesic effect, TRPV1 agonist-Capsaicin possesses a disease-modifying effect in CIPN through its restorative property in damaged sensory nerves.

Sensory Neurons, Neuroimmunity, and Pain Modulation by Sex Hormones

The inclusion of women in preclinical pain studies has become more commonplace in the last decade as the National Institutes of Health (NIH) released its "Sex as a Biological Variable" mandate. Presumably, basic researchers have not had a comprehensive understanding about neuroimmune interactions in half of the population and how hormones play a role in this. To date, we have learned that sex hormones contribute to sexual differentiation of the nervous system and sex differences in behavior throughout the lifespan; however, the cycling of sex hormones does not always explain these differences. Here, we highlight recent advances in our understanding of sex differences and how hormones and immune interactions influence sensory neuron activity to contribute to physiology and pain. Neuroimmune mechanisms may be mediated by different cell types in each sex, as the actions of immune cells are sexually dimorphic. Unfortunately, the majority of studies assessing neuronal contributions to immune function have been limited to males, so it is unclear if the mechanisms are similar in females. Finally, pathways that control cellular metabolism, like nuclear receptors, have been shown to play a regulatory role both in pain and inflammation. Overall, communication between the neuroimmune and endocrine systems modulate pain signaling in a sex-dependent manner, but more research is needed to reveal nuances of these mechanisms.

Corydalis saxicola Bunting total alkaloids attenuate paclitaxel-induced peripheral neuropathy through PKCε/p38 MAPK/TRPV1 signaling pathway

Background

Corydalis saxicola Bunting, affiliated with the Papaveraceae Juss., has been proven to work well in anti-inflammation, hemostasis, and analgesia. This study was designed to observe the effect and potential mechanism of Corydalis saxicola Bunting total alkaloids (CSBTA) on paclitaxel-induced peripheral neuropathy (PIPN).

Materials and methods

Rats were injected 2 mg/kg paclitaxel 4 times and administrated with 30 or 120 mg/kg CSBTA. Mechanical and thermal allodynia and hyperalgesia were tested. After 40 days, serum was collected to detect PGE2, TNF-α, and IL-1β by ELISA. The L4-L6 segment spinal cord, DRG, and plantar skin were harvested, and Western-blot or RT-qPCR analyzed protein and gene levels of pro-inflammatory cytokines, p38 MAPK, PKCε, and TRPV1. The PIPN cell model was established with paclitaxel (300 nM, 5 d) in primary DRG neurons. We examined the effect of CSBTA (25 μg/ml or 50 μg/ml) by measuring the mRNA levels in PGE2, TNF-α and CGRP, and the protein expression on the PKCε/p38 MAPK/TRPV1 signaling pathway in the PIPN cell model.

Results

The results showed that CSBTA effectively ameliorated allodynia and hyperalgesia, and regulated cytokines' contents (PGE2, TNF-α, and IL-1β) and neuropeptides (CGRP and SP) in different tissues in vivo. In addition, CSBTA significantly decreased cytokine gene levels of DRG neurons (PGE2, TNF-α, and CGRP) and the protein expressions of PKCε/p38 MAPK/TRPV1 signaling pathway in vivo and in vitro.

Conclusion

Therefore, CSBTA has a perspective therapeutic effect on the treatment of paclitaxel-induced peripheral neuropathy.

Mini-Review: Mitochondrial dysfunction and chemotherapy-induced neuropathic pain

Chemotherapy-induced peripheral neuropathy (CIPN) is a somatosensory axonopathy in cancer patients receiving any of a variety of widely-use antitumor agents. CIPN can lead to long-lasting neuropathic pain that limits the dose or length of otherwise life-saving cancer therapy. Accumulating evidence over the last two decades indicates that many chemotherapeutic agents cause mitochondrial injury in the peripheral sensory nerves by disrupting mitochondrial structure and bioenergetics, increasing nitro-oxidative stress and altering mitochondrial transport, fission, fusion and mitophagy. The accumulation of abnormal and dysfunctional mitochondria in sensory neurons are linked to axonal growth defects resulting in the loss of intraepidermal nerve fibers in the hands and feet, increased spontaneous discharge and the sensitization of peripheral sensory neurons that provoke and promote changes in the central nervous system that establish a chronic neuropathic pain state. This has led to the propose mitotoxicity theory of CIPN. Strategies that improve mitochondrial function have shown success in preventing and reversing CIPN in pre-clinical animal models and have begun to show some progress toward translation to the clinic. In this review, we will review the evidence for, the causes and effects of and current strategies to target mitochondrial dysfunction in CIPN.

Preparation and characterization of paclitaxel palmitate albumin nanoparticles with high loading efficacy: an in vitro and in vivo anti-tumor study in mouse models

BACKGROUND

Combination of the prodrug technique with an albumin nano drug-loaded system is a novel promising approach for cancer treatment. However, the long-lasting and far-reaching challenge for the treatment of cancers lies in how to construct the albumin nanometer drug delivery system with lead compounds and their derivatives.

METHODS

In this study, we reported the preparation of injectable albumin nanoparticles (NPs) with a high and quantitative drug loading system based on the Nab^TM technology of paclitaxel palmitate (PTX-PA).

RESULTS

Our experimental study on drug tissue distribution in vivo demonstrated that the paclitaxel palmitate albumin nanoparticles (Nab-PTX-PA) remained in the tumor for a longer time post-injection. Compared with saline and paclitaxel albumin nanoparticles (Abraxane^®), intravenous injection of Nab-PTX-PA not only reduced the toxicity of the drug in normal organs, and increased the body weight of the animals but maintained sustained release of paclitaxel (PTX) in the tumor, thereby displaying an excellent antitumor activity. Blood routine analysis showed that Nab-PTX-PA had fewer adverse effects or less toxicity to the normal organs, and it inhibited tumor cell proliferation more effectively as compared with commercial paclitaxel albumin nanoparticles.

CONCLUSIONS

This carrier strategy for small molecule drugs is based on naturally evolved interactions between long-chain fatty acids (LCFAs) and Human Serum Albumin (HSA), demonstrated here for PTX. Nab-PTX-PA shows higher antitumor efficacy in vivo in breast cancer models. On the whole, this novel injectable Nab-PTX-PA has great potential as an effective drug delivery system in the treatment of breast cancer.

Neuropathic pain: Spotlighting anatomy, experimental models, mechanisms, and therapeutic aspects

The International Association for the Study of Pain defines neuropathic pain as "pain arising as a direct consequence of a lesion or disease affecting the somatosensory system". The associated changes can be observed in the peripheral as well as the central nervous system. The available literature discusses a wide variety of causes as predisposing for the development and amplification of neuropathic pain. Further, key interactions within sensory pathways have been discovered, but no common molecular mechanism leading to neuropathic pain has been identified until now. In the first part of this review, the pain mediating lateral spinothalamic tract is described. Different in vivo models are presented that allow studying trauma-, chemotherapy-, virus-, and diabetes-induced neuropathic pain in rodents. We furthermore discuss approaches to assess neuropathic pain in these models. Second, the current knowledge about cellular and molecular mechanisms suggested to underlie the development of neuropathic pain is presented and discussed. A summary of established therapies that are already applied in the clinic and novel, promising approaches closes the paper. In conclusion, the established animal models are able to emulate the diversity of neuropathic pain observed in the clinics. However, the assessment of neuropathic pain in the presented in vivo models should be improved. The determination of common molecular markers with suitable in vitro models would simplify the assessment of neuropathic pain in vivo. This would furthermore provide insights into common molecular mechanisms of the disease and establish a basis to search for satisfying therapeutic approaches.

The role of PPARγ in chemotherapy-evoked pain

Although millions of people are diagnosed with cancer each year, survival has never been greater thanks to early diagnosis and treatments. Powerful chemotherapeutic agents are highly toxic to cancer cells, but because they typically do not target cancer cells selectively, they are often toxic to other cells and produce a variety of side effects. In particular, many common chemotherapies damage the peripheral nervous system and produce neuropathy that includes a progressive degeneration of peripheral nerve fibers. Chemotherapy-induced peripheral neuropathy (CIPN) can affect all nerve fibers, but sensory neuropathies are the most common, initially affecting the distal extremities. Symptoms include impaired tactile sensitivity, tingling, numbness, paraesthesia, dysesthesia, and pain. Since neuropathic pain is difficult to manage, and because degenerated nerve fibers may not grow back and regain normal function, considerable research has focused on understanding how chemotherapy causes painful CIPN so it can be prevented. Due to the fact that both therapeutic and side effects of chemotherapy are primarily associated with the accumulation of reactive oxygen species (ROS) and oxidative stress, this review focuses on the activation of endogenous antioxidant pathways, especially PPARγ, in order to prevent the development of CIPN and associated pain. The use of synthetic and natural PPARγ agonists to prevent CIPN is discussed.

Modeling chemotherapy induced neurotoxicity with human induced pluripotent stem cell (iPSC) -derived sensory neurons

Chemotherapy-induced peripheral neuropathy (CIPN) is a frequent, potentially irreversible adverse effect of cytotoxic chemotherapy often leading to a reduction or discontinuation of treatment which negatively impacts patients' prognosis. To date, however, neither predictive biomarkers nor preventive treatments for CIPN are available, which is partially due to a lack of suitable experimental models. We therefore aimed to evaluate whether sensory neurons derived from induced pluripotent stem cells (iPSC-DSN) can serve as human disease model system for CIPN. Treatment of iPSC-DSN for 24 h with the neurotoxic drugs paclitaxel, bortezomib, vincristine and cisplatin led to axonal blebbing and a dose dependent decline of cell viability in clinically relevant IC₅₀ ranges, which was not observed for the non-neurotoxic compounds doxorubicin and 5-fluorouracil. Paclitaxel treatment effects were less pronounced after 24 h but prominent when treatment was applied for 72 h. Global transcriptome analyses performed at 24 h, i.e. before paclitaxel-induced cell death occurred, revealed the differential expression of genes of neuronal injury, cellular stress response, and sterol pathways. We further evaluated if known neuroprotective strategies can be reproduced in iPSC-DSN and observed protective effects of lithium replicating findings from rodent dorsal root ganglia cells. Comparing sensory neurons derived from two different healthy donors, we found preliminary evidence that these cell lines react differentially to neurotoxic drugs as expected from the variable presentation of CIPN in patients. In conclusion, iPSC-DSN are a promising platform to study the pathogenesis of CIPN and to evaluate neuroprotective treatment strategies. In the future, the application of patient-specific iPSC-DSN could open new avenues for personalized medicine with individual risk prediction, choice of chemotherapeutic compounds and preventive treatments.

Effects of Curcumin and Its Different Formulations in Preclinical and Clinical Studies of Peripheral Neuropathic and Postoperative Pain: A Comprehensive Review

Lesion or disease of the somatosensory system leads to the development of neuropathic pain. Peripheral neuropathic pain encompasses damage or injury of the peripheral nervous system. On the other hand, 10–15% of individuals suffer from acute postoperative pain followed by persistent pain after undergoing surgeries. Antidepressants, anticonvulsants, baclofen, and clonidine are used to treat peripheral neuropathy, whereas opioids are used to treat postoperative pain. The negative effects associated with these drugs emphasize the search for alternative therapeutics with better efficacy and fewer side effects. Curcumin, a polyphenol isolated from the roots of Curcuma longa, possesses antibacterial, antioxidant, and anti-inflammatory properties. Furthermore, the low bioavailability and fast metabolism of curcumin have led to the advent of various curcumin formulations. The present review provides a comprehensive analysis on the effects of curcumin and its formulations in preclinical and clinical studies of neuropathic and postoperative pain. Based on the positive outcomes from both preclinical and clinical studies, curcumin holds the promise of mitigating or preventing neuropathic and postoperative pain conditions. However, more clinical studies with improved curcumin formulations are required to involve its use as adjuvant to neuropathic and postoperative drugs.

Neuroimmune Consequences of eIF4E Phosphorylation on Chemotherapy-Induced Peripheral Neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is a major dose-limiting side effect that occurs in up to 63% of patients and has no known effective treatment. A majority of studies do not effectively assess sex differences in the onset and persistence of CIPN. Here we investigated the onset of CIPN, a point of therapeutic intervention where we may limit, or even prevent the development of CIPN. We hypothesized that cap-dependent translation mechanisms are important in early CIPN development and the bi-directional crosstalk between immune cells and nociceptors plays a complementary role to CIPN establishment and sex differences observed. In this study, we used wild type and eIF4E-mutant mice of both sexes to investigate the role of cap-dependent translation and the contribution of immune cells and nociceptors in the periphery and glia in the spinal cord during paclitaxel-induced peripheral neuropathy. We found that systemically administered paclitaxel induces pain-like behaviors in both sexes, increases helper T-lymphocytes, downregulates cytotoxic T-lymphocytes, and increases mitochondrial dysfunction in dorsal root ganglia neurons; all of which is eIF4E-dependent in both sexes. We identified a robust paclitaxel-induced, eIF4E-dependent increase in spinal astrocyte immunoreactivity in males, but not females. Taken together, our data reveals that cap-dependent translation may be a key pathway that presents relevant therapeutic targets during the early phase of CIPN. By targeting the eIF4E complex, we may reduce or reverse the negative effects associated with chemotherapeutic treatments.

Chemotherapeutic Agent-Induced Vulvodynia, an Experimental Model

Vulvodynia is a chronic clinical condition associated with vulvar pain that can impair the sexual, social, and psychological life of women. There is a need for more research to develop novel strategies and therapies for the treatment of vulvodynia. Vulvodynia in experimental animal models induced via infections, allergens, and diabetes are tedious and with lessor induction rate. The objective of the study was to explore the possibility of inducing vulvodynia using a chemotherapeutic agent in a rodent model. Paclitaxel is commonly used in treating breast and ovarian cancer, whose dose-limiting side effect is peripheral neuropathy. Studies have shown that peripheral neuropathy is one of the etiologies for vulvodynia. Following paclitaxel administration (2 mg/kg i.p.), the intensity of vulvar hypersensitivity was assessed using a series of von Frey filaments (0.008 to 1 g) to ensure the induction of vulvodynia. Vulvodynia was induced from day 2 and was well sustained for 11 days. Furthermore, the induced vulvodynia was validated by investigating the potentiation of a flinch response threshold, upon topical application and systemic administration of gabapentin, a commonly used medication for treating neuropathic pain. The results demonstrate that vulvodynia was induced due to administration of paclitaxel. The fact that chemotherapeutic agent-induced vulvodynia was responsive to topical and parenterally administered gabapentin provides validity to the model. The study establishes a new, relatively simple and reliable animal model for screening drug molecules for vulvar hypersensitivity.

Using QSAR Models to Predict Mitochondrial Targeting by Small-Molecule Xenobiotics Within Living Cells

Prediction of mitochondrial targeting, or prediction of exclusion from mitochondria, of small-molecule xenobiotics (biocides, drugs, probes, toxins) can be achieved using an algorithm derived from QSAR modeling. Application of the algorithm requires knowing the chemical structures of all ionic species of the xenobiotic compound in question, and for certain numerical structure parameters (AI, CBN, log P, pK _a, and Z) to be obtained for all such species. Procedures for specification of the chemical structures; estimation of the structure parameters; and application of the algorithm are described in an explicit protocol.

Paclitaxel antitumor effect improvement in lung cancer and prevention of the painful neuropathy using large pegylated cationic liposomes

Paclitaxel (PTX), a drug widely used in lung cancer, has serious limitations including the development of peripheral neurotoxicity, which may lead to treatment discontinuation and therapy failure. The transport of PTX in large cationic liposomes could avoid this undesirable effect, improving the patient's prognosis. PTX was encapsulated in cationic liposomes with two different sizes, MLV (180-200 nm) and SUV (80-100 nm). In both cases, excellent biocompatibility and improved internalization and antitumor effect of PTX were observed in human and mice lung cancer cells in culture, multicellular spheroids and cancer stem cells (CSCs). In addition, both MLV and SUV with a polyethylene glycol (PEG) shell, induced a greater tumor volume reduction than PTX (56.4 % and 57.1 % vs. 36.7 %, respectively) in mice. Interestingly, MLV-PEG-PTX did not induce either mechanical or heat hypersensitivity whereas SUV-PEG-PTX produced a similar response to free PTX. Analysis of PTX distribution showed a very low concentration of the drug in the dorsal root ganglia (DRG) with MLV-PEG-PTX, but not with SUV-PEG-PTX or free PTX. These results support the hypothesis that PTX induces peripheral neuropathy by penetrating the endothelial fenestrations of the DRG (80-100 nm, measured in mice). In conclusion, our larger liposomes (MLV-PEG-PTX) not only showed biocompatibility, antitumor activity against CSCs, and in vitro and in vivo antitumor effect that improved PTX free activity, but also protected from PTX-induced painful peripheral neuropathy. These advantages could be used as a new strategy of lung cancer chemotherapy to increase the PTX activity and reduce its side effects.

Human Induced Pluripotent Stem Cell Derived Sensory Neurons are Sensitive to the Neurotoxic Effects of Paclitaxel

Chemotherapy‐induced peripheral neuropathy (CIPN) is a dose‐limiting adverse event associated with treatment with paclitaxel and other chemotherapeutic agents. The prevention and treatment of CIPN are limited by a lack of understanding of the molecular mechanisms underlying this toxicity. In the current study, a human induced pluripotent stem cell–derived sensory neuron (iPSC‐SN) model was developed for the study of chemotherapy‐induced neurotoxicity. The iPSC‐SNs express proteins characteristic of nociceptor, mechanoreceptor, and proprioceptor sensory neurons and show Ca²⁺ influx in response to capsaicin, α,β‐meATP, and glutamate. The iPSC‐SNs are relatively resistant to the cytotoxic effects of paclitaxel, with half‐maximal inhibitory concentration (IC₅₀) values of 38.1 µM (95% confidence interval (CI) 22.9–70.9 µM) for 48‐hour exposure and 9.3 µM (95% CI 5.7–16.5 µM) for 72‐hour treatment. Paclitaxel causes dose‐dependent and time‐dependent changes in neurite network complexity detected by βIII‐tubulin staining and high content imaging. The IC₅₀ for paclitaxel reduction of neurite area was 1.4 µM (95% CI 0.3–16.9 µM) for 48‐hour exposure and 0.6 µM (95% CI 0.09–9.9 µM) for 72‐hour exposure. Decreased mitochondrial membrane potential, slower movement of mitochondria down the neurites, and changes in glutamate‐induced neuronal excitability were also observed with paclitaxel exposure. The iPSC‐SNs were also sensitive to docetaxel, vincristine, and bortezomib. Collectively, these data support the use of iPSC‐SNs for detailed mechanistic investigations of genes and pathways implicated in chemotherapy‐induced neurotoxicity and the identification of novel therapeutic approaches for its prevention and treatment.

Herbal Decoction Divya-Peedantak-Kwath Alleviates Allodynia and Hyperalgesia in Mice Model of Chemotherapy-Induced Peripheral Neuropathy via Modulation in Cytokine Response

The widely used cancer treatment, chemotherapy, causes severe long-term neuropathic pain in 30–40% cases, the condition clinically known as chemotherapy-induced peripheral neuropathy (CIPN). Approved conventional analgesics are sometimes ineffective, while others like opioids have undesirable side effects like addiction, seizures, and respiratory malfunctioning. Tricyclic antidepressants and anticonvulsants, although exhibit anti-allodynic effects in neuropathy, also have unpleasant side effects. Thus, alternative medicines are being explored for CIPN treatment. Despite scattered reports on different extracts from different plants having potential anti-allodynic effects against CIPN, no established medicine or formulation of herbal origin exists. In this study, efficacy of an herbal decoction, formulated based on ancient medicinal principles and protocols for treating neuropathic pain, Divya-Peedantak-Kwath (DPK), has been evaluated in a paclitaxel (PTX)-induced peripheral neuropathic mouse model. We observed that DPK has prominent anti-allodynic and anti-hyperalgesic effects and acts as a nociceptive modulator for CIPN. With exhibited antioxidative effects, DPK restored the redox potential of the sciatic nerves to the normal. On histopathological evaluation, DPK prevented the PTX-induced lesions in the sciatic nerve, in a dose-dependent manner. It also prevented inflammation by modulating the levels of pro-inflammatory cytokines involved in CIPN pathogenesis. Our observations evinced that DPK can alleviate CIPN by attenuating oxidative stress and concomitant neuroinflammation through immune modulation.

The biology and engineered modeling strategies of cancer-nerve crosstalk

A recent finding critical to cancer aggravation is the interaction between cancer cells and nerves. There exist two main modes of cancer-nerve interaction: perineural invasion (PNI) and tumor innervation. PNI occurs when cancer cells infiltrate the adjacent nerves, and its relative opposite, tumor innervation, occurs when axons extend into tumor bodies. Like most cancer studies, these crosstalk interactions have mostly been observed in patient samples and animal models at this point, making it difficult to understand the mechanisms in a controlled manner. As such, in recent years in vitro studies have emerged that have helped identify various microenvironmental factors responsible for cancer-nerve crosstalk, including but not limited to neurotrophic factors, neurotransmitters, chemokines, cancer-derived exosomes, and Schwann cells. The versatility of in vitro systems warrants continuous development to increase physiological relevance to study PNI and tumor innervation, for example by utilizing biomimetic three-dimensional (3D) culture systems. Despite the wealth of 3D in vitro cancer models, comparatively there exists a lack of 3D in vitro models of nerve, PNI, and tumor innervation. Native-like 3D in vitro models of cancer-nerve interactions may further help develop therapeutic strategies to curb nerve-mediated cancer aggravation. As such, we provide an overview of the key players of cancer-nerve crosstalk and current in vitro models of the crosstalk, as well as cancer and nerve models. We also discuss a few future directions in cancer-nerve crosstalk research.

Mitochondrial bioenergetics, glial reactivity, and pain-related behavior can be restored by dichloroacetate treatment in rodent pain models

Glial reactivity in the dorsal horn of the spinal cord is a hallmark in most chronic pain conditions. Neuroinflammation-associated reactive glia, in particular astrocytes, have been shown to exhibit reduced mitochondrial respiratory function. Here, we studied the mitochondrial function at the lumbar spinal cord tissue from complete Freund's adjuvant-induced inflammatory pain rat and chronic constriction injury mouse models by high-resolution respirometry. A significant decrease in mitochondrial bioenergetic parameters at the injury-related spinal cord level coincided with highest astrocytosis. Oral administration of dichloroacetate (DCA) significantly increased mitochondrial respiratory function by inhibiting pyruvate dehydrogenase kinase and decreased glial fibrillary acidic protein and Iba-1 immunoreactivity in spinal cord. Importantly, DCA treatment significantly reduced the ipsilateral pain-related behavior without affecting contralateral sensitivity in both pain models. Our results indicate that mitochondrial metabolic modulation with DCA may offer an alternative therapeutic strategy to alleviate chronic and persistent inflammatory pain.

Soluble Epoxide Hydrolase Regulation of Lipid Mediators Limits Pain

The role of lipids in pain signaling is well established and built on decades of knowledge about the pain and inflammation produced by prostaglandin and leukotriene metabolites of cyclooxygenase and lipoxygenase metabolism, respectively. The analgesic properties of other lipid metabolites are more recently coming to light. Lipid metabolites have been observed to act directly at ion channels and G protein-coupled receptors on nociceptive neurons as well as act indirectly at cellular membranes. Cytochrome P450 metabolism of specifically long-chain fatty acids forms epoxide metabolites, the epoxy-fatty acids (EpFA). The biological role of these metabolites has been found to mediate analgesia in several types of pain pathology. EpFA act through a variety of direct and indirect mechanisms to limit pain and inflammation including nuclear receptor agonism, limiting endoplasmic reticulum stress and blocking mitochondrial dysfunction. Small molecule inhibitors of the soluble epoxide hydrolase can stabilize the EpFA in vivo, and this approach has demonstrated relief in preclinical modeled pain pathology. Moreover, the ability to block neuroinflammation extends the potential benefit of targeting soluble epoxide hydrolase to maintain EpFA for neuroprotection in neurodegenerative disease.

Taxane-induced neurotoxicity: Pathophysiology and therapeutic perspectives

Taxane-derived drugs are antineoplastic agents used for the treatment of highly common malignancies. Paclitaxel and docetaxel are the most commonly used taxanes; however, other drugs and formulations have been used, such as cabazitaxel and nab-paclitaxel. Taxane treatment is associated with neurotoxicity, a well-known and relevant side effect, very prevalent amongst patients undergoing chemotherapy. Painful peripheral neuropathy is the most dose-limiting side effect of taxanes, affecting up to 97% of paclitaxel-treated patients. Central neurotoxicity is an emerging side effect of taxanes and it is characterized by cognitive impairment and encephalopathy. Besides impairing compliance to chemotherapy treatment, taxane-induced neurotoxicity (TIN) can adversely affect the patient's life quality on a long-term basis. Despite the clinical relevance, not many reviews have comprehensively addressed taxane-induced neurotoxicity when they are used therapeutically. This article provides an up-to-date review on the pathophysiology of TIN and the novel potential therapies to prevent or treat this side effect.

Signaling pathways and gene co-expression modules associated with cytoskeleton and axon morphology in breast cancer survivors with chronic paclitaxel-induced peripheral neuropathy

Background

The major dose-limiting toxicity of paclitaxel, one of the most commonly used drugs to treat breast cancer, is peripheral neuropathy (paclitaxel-induced peripheral neuropathy). Paclitaxel-induced peripheral neuropathy, which persists into survivorship, has a negative impact on patient’s mood, functional status, and quality of life. Currently, no interventions are available to treat paclitaxel-induced peripheral neuropathy. A critical barrier to the development of efficacious interventions is the lack of understanding of the mechanisms that underlie paclitaxel-induced peripheral neuropathy. While data from preclinical studies suggest that disrupting cytoskeleton- and axon morphology-related processes are a potential mechanism for paclitaxel-induced peripheral neuropathy, clinical evidence is limited. The purpose of this study in breast cancer survivors was to evaluate whether differential gene expression and co-expression patterns in these pathways are associated with paclitaxel-induced peripheral neuropathy.

Methods

Signaling pathways and gene co-expression modules associated with cytoskeleton and axon morphology were identified between survivors who received paclitaxel and did (n = 25) or did not (n = 25) develop paclitaxel-induced peripheral neuropathy.

Results

Pathway impact analysis identified four significantly perturbed cytoskeleton- and axon morphology-related signaling pathways. Weighted gene co-expression network analysis identified three co-expression modules. One module was associated with paclitaxel-induced peripheral neuropathy group membership. Functional analysis found that this module was associated with four signaling pathways and two ontology annotations related to cytoskeleton and axon morphology.

Conclusions

This study, which is the first to apply systems biology approaches using circulating whole blood RNA-seq data in a sample of breast cancer survivors with and without chronic paclitaxel-induced peripheral neuropathy, provides molecular evidence that cytoskeleton- and axon morphology-related mechanisms identified in preclinical models of various types of neuropathic pain including chemotherapy-induced peripheral neuropathy are found in breast cancer survivors and suggests pathways and a module of genes for validation and as potential therapeutic targets.

Bortezomib and metformin opposingly regulate the expression of hypoxia-inducible factor alpha and the consequent development of chemotherapy-induced painful peripheral neuropathy

Chemotherapy-induced painful peripheral neuropathy is a significant clinical problem that is associated with widely used chemotherapeutics. Unfortunately, the molecular mechanisms by which chemotherapy-induced painful peripheral neuropathy develops have remained elusive. The proteasome inhibitor, bortezomib, has been shown to induce aerobic glycolysis in sensory neurons. This altered metabolic phenotype leads to the extrusion of metabolites which sensitize primary afferents and cause pain. Hypoxia-inducible factor alpha is a transcription factor that is known to reprogram cellular metabolism. Furthermore, hypoxia-inducible factor 1 alpha protein is constantly synthesized and undergoes proteasomal degradation in normal conditions. However, metabolic stress or hypoxia stabilizes the expression of hypoxia-inducible factor 1 alpha leading to the transcription of genes that reprogram cellular metabolism. This study demonstrates that treatment of mice with bortezomib stabilizes the expression of hypoxia-inducible factor 1 alpha. Moreover, knockdown of hypoxia-inducible factor 1 alpha, inhibition of hypoxia-inducible factor 1 alpha binding to its response element, or limiting its translation by using metformin prevent the development of bortezomib-induced neuropathic pain. Strikingly, the blockade of hypoxia-inducible factor 1 alpha expression does not attenuate mechanical allodynia in mice with existing bortezomib-induced neuropathic pain. These results establish the stabilization of hypoxia-inducible factor 1 alpha expression as the molecular mechanism by which bortezomib initiates chemotherapy-induced painful peripheral neuropathy. Crucially, these findings reveal that the initiation and maintenance of bortezomib-induced neuropathic pain are regulated by distinct mechanisms.

Recent advances in understanding chemotherapy-induced peripheral neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is a common cause of pain and poor quality of life for those undergoing treatment for cancer and those surviving cancer. Many advances have been made in the pre-clinical science; despite this, these findings have not been translated into novel preventative measures and treatments for CIPN. This review aims to give an update on the pre-clinical science, preventative measures, assessment and treatment of CIPN.

Association of small-fiber polyneuropathy with three previously unassociated rare missense SCN9A variants

Background: Small fiber polyneuropathy (SFN) involves ectopic firing and degeneration of small-diameter, somatic/autonomic peripheral axons. Causes include diabetes, inflammation and rare pathogenic mutations, including in SCN9-11 genes that encode small fiber sodium channels.

Aims: The aim of this study is to associate a new phenotype—immunotherapy-responsive SFN—with rare amino acid–substituting SCN9A variants and present potential explanations.

Methods: A retrospective chart review of two Caucasians with skin biopsy confirmed SFN and rare SCN9A single nucleotide polymorphisms not previously reported in neuropathy.

Results: A 47-year-old with 4 years of disabling widespread neuropathic pain and exertional intolerance had nerve- and skin biopsy–confirmed SFN, with blood tests revealing only high-titer antinuclear antibodies and low complement C4 consistent with B cell dysimmunity. Six years of intravenous immunoglobulin (IVIg) therapy markedly improved sensory and autonomic symptoms and normalized his neurite density. After whole exome sequencing revealed a potentially pathogenic SCN9A-A3734G variant, sodium channel blockers were tried. Herpes zoster left a 32-year-old with disabling exertional intolerance (“chronic fatigue syndrome”), postural syncope and tachycardia, arm and leg paresthesias, reduced sweating, and distal hairloss. Screening revealed antinuclear and potassium channel autoantibodies, so prednisone and then IVIg were prescribed with great benefit. During 4 years of immunotherapy, his symptoms and function improved, and all abnormal biomarkers (autonomic testing and skin biopsies) normalized. Whole exome sequencing then revealed two nearby compound heterozygous SCN9A variants that were computer-predicted to be deleterious.

Conclusions: These cases newly associate three novel amino acid–substituting SCN9A variants with immunotherapy-responsive neuropathy. Only larger studies can determine whether these are contributory or coincidental, but they associate new variants with moderate or high likelihood of pathogenicity with a new highly related phenotype.

Endoplasmic reticulum-mitochondria interplay in chronic pain: The calcium connection

Chronic pain is a debilitating condition that affects roughly a third to a half of the world's population. Despite its substantial effect on society, treatment for chronic pain is modest, at best, notwithstanding its side effects. Hence, novel therapeutics are direly needed. Emerging evidence suggests that calcium plays an integral role in mediating neuronal plasticity that underlies sensitization observed in chronic pain states. The endoplasmic reticulum and the mitochondria are the largest calcium repositories in a cell. Here, we review how stressors, like accumulation of misfolded proteins and oxidative stress, influence endoplasmic reticulum and mitochondria function and contribute to chronic pain. We further examine the shuttling of calcium across the mitochondrial-associated membrane as a mechanism of cross-talk between the endoplasmic reticulum and the mitochondria. In addition, we discuss how endoplasmic reticulum stress, mitochondrial impairment, and calcium dyshomeostasis are implicated in various models of neuropathic pain. We propose a novel framework of endoplasmic reticulum-mitochondria signaling in mediating pain hypersensitivity. These observations require further investigation in order to develop novel therapies for chronic pain.