The ceramide-S1P pathway as a druggable target to alleviate peripheral neuropathic pain

The Effect of Spinal Cord Stimulation on Spinal Dorsal Horn Lipid Expression in Experimental Painful Diabetic Polyneuropathy: A Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry Imaging Study

OBJECTIVES

Diabetes-induced peripheral nerve fiber damage can cause painful diabetic polyneuropathy (PDPN), induced by central sensitization through proinflammatory processes in the spinal dorsal horn. Disturbances in spinal dorsal horn lipid metabolism play a major role in proinflammatory regulation. Conventional (Con)-spinal cord stimulation (SCS) is an alternative treatment for pain relief in PDPN, whereas differential target multiplexed (DTM)-SCS could be more effective than Con-SCS, specifically targeting the spinal inflammatory response. We hypothesize that Con- and DTM-SCS differentially affect lipid metabolism in the spinal cord of PDPN animals. To study pain relief mechanisms, we analyzed lipid expression in the spinal dorsal horn using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry imaging (MSI).

MATERIAL AND METHODS

Diabetes was induced through streptozotocin (STZ) injection in 28 rats, of which 12 developed PDPN. These and four nondiabetic animals (sham STZ) were implanted with a quadripolar lead and stimulated with Con-, DTM-, or Sham-SCS for 48 hours. Mechanical sensitivity was assessed using Von Frey filaments after 24 and 48 hours. After 48 hours of SCS, the spinal cord was collected, and lipids were analyzed using MALDI-TOF MSI.

RESULTS

STZ-induced hypersensitivity in the hind paws was reduced by Con- and DTM-SCS. PDPN induction decreased the expression of a glycosphingolipid in laminae 3 of the spinal dorsal horn. After 48 hours of Con- and DTM-SCS, expression levels of several lipids in the spinal dorsal horn decreased, including (HexCer 36:1;O, 40:1;O3), diacylglycerophosphocholines (PC 36:1, 38:6, 40:5), and diacylglycerophosphoserines (PS 36:4).

CONCLUSIONS

Both Con- and DTM-SCS provide pain relief and decrease spinal dorsal horn lipid expression of PDPN animals, highlighting the complex effects of SCS on the spinal cord physiology. STZ-induced PDPN has a limited effect on lipid expression in the spinal dorsal horn.

The TRPC5 receptor as pharmacological target for pain and metabolic disease

The transient receptor potential canonical (TRPC) channels are a group of highly homologous nonselective cation channels from the larger TRP channel family. They have the ability to form homo- and heteromers with varying degrees of calcium (Ca2+) permeability and signalling properties. TRPC5 is the one cold-sensitive among them and likewise facilitates the influx of extracellular Ca2+ into cells to modulate neuronal depolarization and integrate various intracellular signalling pathways. Recent research with cryo-electron microscopy revealed its structure, along with clear insight into downstream signalling and protein-protein interaction sites. Investigations using global and conditional deficient mice revealed the involvement of TRPC5 in metabolic diseases, energy balance, thermosensation and conditions such as osteoarthritis, rheumatoid arthritis, and inflammatory pain including opioid-induced hyperalgesia and hyperalgesia following tooth decay and pulpitis. This review provides an update on recent advances in our understanding of the role of TRPC5 with focus on metabolic diseases and pain.

S1P/S1PR1 signaling is involved in the development of nociceptive pain

Background

Pain is a complex perception involving unpleasant somatosensory and emotional experiences. However, the underlying mechanisms that mediate its different components remain unclear. Sphingosine-1-phosphate (S1P), a metabolite of sphingomyelin and a potent lipid mediator, initiates signaling via G protein-coupled receptors (S1PRs) on cell surfaces. It serves as a second messenger in cellular processes such as proliferation and apoptosis. Nevertheless, the neuropharmacology of sphingolipid signaling in pain conditions within the central nervous system remains largely unexplored and controversial.

Methods

Chronic nociceptive pain models were induced in vivo by intraplantar injection of 20 μL complete Freund's adjuvant (CFA) into the left hind paws. We assessed S1P and S1PR1 expression in the spinal cords of CFA model mice. Functional antagonists of S1PR1 or S1PR1-specific siRNA were administered daily following CFA model establishment. Paw withdrawal response frequency (PWF) and paw withdrawal latency (PWL) were measured to evaluate mechanical allodynia and thermal hyperalgesia, respectively. RT-PCR assessed interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α levels. Western blotting and immunofluorescence were used to analyze glial fibrillary acidic protein (GFAP), ionized calcium-binding adapter molecule (Iba1), STAT3, ERK, and p38 MAPK protein expression.

Results

In the chronic nociceptive pain model induced by CFA, S1P and S1PR1 expression levels were significantly elevated, leading to activation of spinal cord glial cells. S1PR1 activation also promoted MMP2-mediated cleavage of mature IL-1β. Additionally, S1PR1 activation upregulated phosphorylation of STAT3, ERK, and p38 MAPK in glial cells, profoundly impacting downstream signaling pathways and contributing to chronic nociceptive pain.

Conclusion

The S1P/S1PR1 axis plays a pivotal role in the cellular and molecular mechanisms underlying nociceptive pain. This signaling pathway modulates glial cell activation and the expression of pain-related genes (STAT3, ERK, p38 MAPK) and inflammatory factors in the spinal dorsal horn. These findings underscore the potential of targeting the S1P system for developing novel analgesic therapies.

Effect of age on metabolomic changes in a model of paclitaxel-induced peripheral neurotoxicity

BACKGROUND AND AIMS

Chemotherapy-induced peripheral neurotoxicity (CIPN) is one of the most common dose-limiting side effects of paclitaxel (PTX) treatment. Many age-related changes have been hypothesized to underlie susceptibility to damage or impaired regeneration/repair after nerve injury. The results of these studies, however, are inconclusive and other potential biomarkers of nerve impairment need to be investigated.

METHODS

Twenty-four young (2 months) and 24 adult (9 months) Wistar male rats were randomized to either PTX treatment (10 mg/kg i.v. once/week for 4 weeks) or vehicle administration. Neurophysiological and behavioral tests were performed at baseline, after 4 weeks of treatment and 2-week follow-up. Skin biopsies and nerve specimens collected from sacrificed animals were examined for intraepidermal nerve fiber (IENF) density assessment and nerve morphology/morphometry. Blood and liver samples were collected for targeted metabolomics analysis.

RESULTS

At the end of treatment, the neurophysiological studies revealed a reduction in sensory nerve action potential amplitude (p < .05) in the caudal nerve of young PTX-animals, and in both the digital and caudal nerve of adult PTX-animals (p < .05). A significant decrease in the mechanical threshold was observed only in young PTX-animals (p < .001), but not in adult PTX-ones. Nevertheless, both young and adult PTX-rats had reduced IENF density (p < .0001), which persisted at the end of follow-up period. Targeted metabolomics analysis showed significant differences in the plasma metabolite profiles between PTX-animals developing peripheral neuropathy and age-matched controls, with triglycerides, diglycerides, acylcarnitines, carnosine, long chain ceramides, sphingolipids, and bile acids playing a major role in the response to PTX administration.

INTERPRETATION

Our study identifies for the first time multiple related metabolic axes involved in PTX-induced peripheral neurotoxicity, and suggests age-related differences in CIPN manifestations and in the metabolic profile.

Butein, a potential drug for the treatment of bone cancer pain through bioinformatic and network pharmacology

Bone cancer pain is a difficult-to-treat pathologic condition that impairs the patient's quality of life. The effective therapy options for BCP are restricted due to the unknown pathophysiology. Transcriptome data were obtained from the Gene Expression Omnibus database and differentially expressed gene extraction was performed. DEGs integrated with pathological targets found 68 genes in the study. Butein was discovered as a possible medication for BCP after the 68 genes were submitted to the Connectivity Map 2.0 database for drug prediction. Moreover, butein has good drug-likeness properties. To collect the butein targets, we used the CTD, SEA, TargetNet, and Super-PRED databases. Furthermore, Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses revealed butein's pharmacological effects, indicating that butein may aid in treating BCP by altering the hypoxia-inducible factor, NF-kappa B, angiogenesis, and sphingolipid signaling pathways. Moreover, the pathological targets integrated with drug targets were obtained as the shared gene set A, which was analyzed by ClueGO and MCODE. Biological process analysis and MCODE algorithm further analyzed that BCP related targets were mainly involved in signal transduction process and ion channel-related pathways. Next, we integrated targets related to network topology parameters and targets of core pathways, identified PTGS2, EGFR, JUN, ESR1, TRPV1, AKT1 and VEGFA as butein regulated hub genes by molecular docking, which play a critical role in its analgesic effect. This study lays the scientific groundwork for elucidating the mechanism underlying butein's success in the treatment of BCP.

ATP-releasing SWELL1 channel in spinal microglia contributes to neuropathic pain

Following peripheral nerve injury, extracellular adenosine 5'-triphosphate (ATP)-mediated purinergic signaling is crucial for spinal cord microglia activation and neuropathic pain. However, the mechanisms of ATP release remain poorly understood. Here, we show that volume-regulated anion channel (VRAC) is an ATP-releasing channel and is activated by inflammatory mediator sphingosine-1-phosphate (S1P) in microglia. Mice with microglia-specific deletion of Swell1 (also known as Lrrc8a), a VRAC essential subunit, had reduced peripheral nerve injury-induced increase in extracellular ATP in spinal cord. The mutant mice also exhibited decreased spinal microgliosis, dorsal horn neuronal hyperactivity, and both evoked and spontaneous neuropathic pain-like behaviors. We further performed high-throughput screens and identified an FDA-approved drug dicumarol as a novel and potent VRAC inhibitor. Intrathecal administration of dicumarol alleviated nerve injury-induced mechanical allodynia in mice. Our findings suggest that ATP-releasing VRAC in microglia is a key spinal cord determinant of neuropathic pain and a potential therapeutic target for this debilitating disease.

ATP-releasing SWELL1 channel in spinal microglia contributes to neuropathic pain

Following peripheral nerve injury, extracellular ATP-mediated purinergic signaling is crucial for spinal cord microglia activation and neuropathic pain. However, the mechanisms of ATP release remain poorly understood. Here, we show that volume-regulated anion channel (VRAC) is an ATP-releasing channel and is activated by inflammatory mediator sphingosine-1-phosphate (S1P) in microglia. Mice with microglia-specific deletion of Swell1 (also known as Lrrc8a), a VRAC essential subunit, had reduced peripheral nerve injury-induced increase in extracellular ATP in spinal cord. The mutant mice also exhibited decreased spinal microgliosis, dorsal horn neuronal hyperactivity, and both evoked and spontaneous neuropathic pain-like behaviors. We further performed high-throughput screens and identified an FDA-approved drug dicumarol as a novel and potent VRAC inhibitor. Intrathecal administration of dicumarol alleviated nerve injury-induced mechanical allodynia in mice. Our findings suggest that ATP-releasing VRAC in microglia is a key spinal cord determinant of neuropathic pain and a potential therapeutic target for this debilitating disease.

Lipid and metabolic alteration involvement in physiotherapy for chronic nonspecific low back pain

BACKGROUND

Chronic nonspecific low back pain (cNLBP) is a common health problem worldwide, affecting 65-80% of the population and greatly affecting people's quality of life and productivity. It also causes huge economic losses. Manual therapy (MT) and therapeutic exercise (TE) are effective treatment options for cNLBP physiotherapy-based treatment. However, the underlying mechanisms that promote cNLBP amelioration by MT or TE are incompletely understood.

METHODS

Seventeen recruited subjects were randomly divided into an MT group and a TE group. Subjects in the MT group performed muscular relaxation, myofascial release, and mobilization for 20 min during each treatment session. The treatment lasted for a total of six sessions, once every two days. Subjects in the TE group completed motor control and core stability exercises for 30 min during each treatment session. The motor control exercise included stretching of the trunk and extremity muscles through trunk and hip rotation and flexion training. Stabilization exercises consisted of the (1) bridge exercise, (2) single-leg-lift bridge exercise, (3) side bridge exercise, (4) two-point bird-dog position with an elevated contralateral leg and arm, (5) bear crawl exercise, and (6) dead bug exercise. The treatment lasted for a total of six sessions, with one session every two days. Serum samples were collected from subjects before and after physiotherapy-based treatment for lipidomic and metabolomic measurements.

RESULTS

Through lipidomic analysis, we found that the phosphatidylcholine/phosphatidylethanolamine (PC/PE) ratio decreased and the sphingomyelin/ceramide (SM/Cer) ratio increased in cNLBP patients after MT or TE treatment. In addition, eight metabolites enriched in pyrimidine and purine differed significantly in cNLBP patients who received MT treatment. A total of nine metabolites enriched in pyrimidine, tyrosine, and galactose pathways differed significantly in cNLBP patients after TE treatment during metabolomics analysis.

CONCLUSION

Our study was the first to elucidate the alterations in the lipidomics and metabolomics of cNLBP physiotherapy-based treatment and can expand our knowledge of cNLBP physiotherapy-based treatment.

The FKBP51 Inhibitor SAFit2 Restores the Pain-Relieving C16 Dihydroceramide after Nerve Injury

Neuropathic pain is a pathological pain state with a broad symptom scope that affects patients after nerve injuries, but it can also arise after infections or exposure to toxic substances. Current treatment possibilities are still limited because of the low efficacy and severe adverse effects of available therapeutics, highlighting an emerging need for novel analgesics and for a detailed understanding of the pathophysiological alterations in the onset and maintenance of neuropathic pain. Here, we show that the novel and highly specific FKBP51 inhibitor SAFit2 restores lipid signaling and metabolism in nervous tissue after nerve injury. More specifically, we identify that SAFit2 restores the levels of the C16 dihydroceramide, which significantly reduces the sensitization of the pain-mediating TRPV1 channel and subsequently the secretion of the pro-inflammatory neuropeptide CGRP in primary sensory neurons. Furthermore, we show that the C16 dihydroceramide is capable of reducing acute thermal hypersensitivity in a capsaicin mouse model. In conclusion, we report for the first time the C16 dihydroceramide as a novel and crucial lipid mediator in the context of neuropathic pain as it has analgesic properties, contributing to the pain-relieving properties of SAFit2.

Combination of paeoniflorin and liquiritin alleviates neuropathic pain by lipid metabolism and calcium signaling coordination

Neuropathic pain (NP) affects 7%–10% of the general population and is still hard to cure. Here, we validated the therapeutic effect and demonstrated the mechanism of paeoniflorin and liquiritin combination (PL) on NP from the perspective of integrated lipidomics and transcriptomics for the first time. SwissTargetPrediction indicated that PL mainly targets lipid metabolism. Notably, lipidomics revealed that imbalanced lipid levels in the NP model could be reprogrammed to normal levels by PL treatment. RNA-sequencing showed that PL treatment could also rebalance the lipid metabolism in an indirect manner. Pathway analysis highly enriched the calcium signaling pathway among the most significant categories. Altogether, these findings suggested that PL can not only balance the lipid metabolism in direct and indirect manners but also reverse the dysfunctional activation of the calcium signaling pathway, thereby alleviating NP. This helps to better understand the mechanisms of NP and provides a new important potential therapeutic option for NP.

Lipidomic Profiling Identifies Serum Lipids Associated with Persistent Multisite Musculoskeletal Pain

Lipid mediators have been suggested to have a role in pain sensitivity and response; however, longitudinal data on lipid metabolites and persistent multisite musculoskeletal pain (MSMP) are lacking. This study was to identify lipid metabolic markers for persistent MSMP. Lipidomic profiling of 807 lipid species was performed on serum samples of 536 participants from a cohort study. MSMP was measured by a questionnaire and defined as painful sites ≥4. Persistent MSMP was defined as having MSMP at every visit. Logistic regression was used with adjustment for potential confounders. The Benjamini–Hochberg method was used to control for multiple testing. A total of 530 samples with 807 lipid metabolites passed quality control. Mean age at baseline was 61.54 ± 6.57 years and 50% were females. In total, 112 (21%) of the participants had persistent MSMP. Persistent MSMP was significantly associated with lower levels of monohexosylceramide (HexCer)(d18:1/22:0 and d18:1/24:0), acylcarnitine (AC)(26:0) and lysophosphatidylcholine (LPC)(18:1 [sn1], 18:2 [sn1], 18:2 [sn2], and 15-MHDA[sn1] [104_sn1]) after controlling for multiple testing. After adjustment for age, sex, body mass index, comorbidities, and physical activity, HexCer(d18:1/22:0 and d18:1/24:0) and LPC(15-MHDA [sn1] [104_sn1]) were significantly associated with persistent MSMP [Odds Ratio (OR) ranging from 0.25–0.36]. Two lipid classes—HexCer and LPC—were negatively associated with persistent MSMP after adjustment for covariates (OR = 0.22 and 0.27, respectively). This study identified three novel lipid signatures of persistent MSMP, suggesting that lipid metabolism is involved in the pathogenesis of persistent pain.

Emerging Roles of Ceramide in Cardiovascular Diseases

Ceramide is a core molecule of sphingolipid metabolism that causes selective insulin resistance and dyslipidemia. Research on its involvement in cardiovascular diseases has grown rapidly. In resting cells, ceramide levels are extremely low, while they rapidly accumulate upon encountering external stimuli. Recently, the regulation of ceramide levels under pathological conditions, including myocardial infarction, hypertension, and atherosclerosis, has drawn great attention. Increased ceramide levels are strongly associated with adverse cardiovascular risks and events while inhibiting the synthesis of ceramide or accelerating its degradation improves a variety of cardiovascular diseases. In this article, we summarize the role of ceramide in cardiovascular disease, investigate the possible application of ceramide as a new diagnostic biomarker and a therapeutic target for cardiovascular disorders, and highlight the remaining problems.

Multifarious Targets and Recent Developments in the Therapeutics for the Management of Bone Cancer Pain

Bone cancer pain (BCP) is a distinct pain state showing characteristics of both neuropathic and inflammatory pain. On average, almost 46% of cancer patients exhibit BCP with numbers flaring up to as high as 76% for terminally ill patients. Patients suffering from BCP experience a compromised quality of life, and the unavailability of effective therapeutics makes this a more devastating condition. In every individual cancer patient, the pain is driven by different mechanisms at different sites. The mechanisms behind the manifestation of BCP are very complex and poorly understood, which creates a substantial barrier to drug development. Nevertheless, some of the key mechanisms involved have been identified and are being explored further to develop targeted molecules. Developing a multitarget approach might be beneficial in this case as the underlying mechanism is not fixed and usually a number of these pathways are simultaneously dysregulated. In this review, we have discussed the role of recently identified novel modulators and mechanisms involved in the development of BCP. They include ion channels and receptors involved in sensing alteration of temperature and acidic microenvironment, immune system activation, sodium channels, endothelins, protease-activated receptors, neurotrophins, motor proteins mediated trafficking of glutamate receptor, and some bone-specific mechanisms. Apart from this, we have also discussed some of the novel approaches under preclinical and clinical development for the treatment of bone cancer pain.