Targeting inflammation as a treatment modality for neuropathic pain in spinal cord injury: a randomized clinical trial

Synergistic effects of tetramethylpyrazine and astragaloside IV on spinal cord injury via alteration of astrocyte A1/A2 polarization through the Sirt1-NF-κB pathway

OBJECTIVE

Reactive astrocytes are hallmarks of traumatic spinal cord injury (T-SCI) and are associated with neuropathic pain (NP). Mediating the functional phenotype of reactive astrocytes helps neural repair and ameliorates NP in T-SCI. Here, we aimed to explore the role of tetramethylpyrazine (TMPZ) and astragaloside IV (AGS-IV) in astrocyte polarization and the underlying molecular mechanism in T-SCI.

METHODS

Primary cultured astrocytes from mice were treated with LPS or conditioned medium from "M1" polarized microglia (M1-CM), followed by TMPZ and/or AGS-IV administration. The expression levels of "A1" astrocyte-specific markers (including C3, GBP2, Serping1, iNOS), "A2" astrocyte-specific markers (including S100a10 and PTX3), Sirt1 and NF-κB were detected via western blotting. TNF-α and IL-1β levels were detected via ELISA. RT-PCR was used to evaluate OIP5-AS1 and miR-34a expression. si-OIP5-AS1 or the Sirt1 inhibitor EX-527 was administered to astrocytes. A spinal cord injury (SCI) model was constructed in Sprague-Dawley (SD) rats. Alterations in astrocytic "A1/A2" polarization in the spinal cord tissues were evaluated.

RESULTS

LPS and M1-CM induced "A1" polarization of primary astrocytes. TMPZ and ASG IV could substantially reduce the expression of "A1"-related biomarkers but enhance "A2"-related biomarkers. OIP5-AS1 and Sirt1 levels were reduced in "A1"-polarized astrocytes, while miR-34a and p-NF-κB p65 were elevated. TMPZ and ASG IV enhanced OIP5-AS1 and Sirt1 levels and, in contrast, attenuated the changes in miR-34a and p-NF-κB p65 levels. Notably, the TMPZ and ASG IV combination had stronger effects on astrocyte polarization than the single treatment with TMPZ or ASG IV. OIP5-AS1 knockdown and Sirt1 inhibition both reversed the regulatory effects of TMPZ and ASG IV in astrocytic polarization. According to the in vivo experiments, the expression of "A1"-associated markers was enhanced in the spinal cords of SCI rats. The TMPZ and ASG IV combination reduced astrocytic "A1" polarization and enhanced astrocytic "A2" polarization. The expression of lncRNA OIP5-AS1 and Sirt1 was enhanced by TMPZ and ASG IV, while that of miR-34a and p-NF-κB p65 was inhibited.

CONCLUSION

The combination of TMPZ and ASG IV can ameliorate dysregulated astrocytic polarization induced by spinal cord injury by affecting the lncRNA OIP5-AS1-Sirt1-NF-κB pathway.

NMDA Receptors Regulate Oxidative Damage in Keratinocytes during Complex Regional Pain Syndrome in HaCaT Cells and Male Rats

Complex regional pain syndrome (CRPS), a type of primary chronic pain, occurs following trauma or systemic disease and typically affects the limbs. CRPS-induced pain responses result in vascular, cutaneous, and autonomic nerve alterations, seriously impacting the quality of life of affected individuals. We previously identified the involvement of keratinocyte N-methyl-d-asparagic acid (NMDA) receptor subunit 2 B (NR2B) in both peripheral and central sensitizations in CRPS, although the mechanisms whereby NR2B functions following activation remain unclear. Using an in vivo male rat model of chronic post-ischemia pain (CPIP) and an in vitro oxygen-glucose deprivation/reoxygenation (OGD/R) cell model, we discovered that oxidative injury occurs in rat keratinocytes and HaCaT cells, resulting in reduced cell viability, mitochondrial damage, oxidative damage of nucleotides, and increased apoptosis. In HaCaT cells, OGD/R induced increases in intracellular reactive oxygen species levels and disrupted the balance between oxidation and antioxidation by regulating a series of antioxidant genes. The activation of NMDA receptors via NMDA exacerbated these changes, whereas the inhibition of the NR2B subunit alleviated them. Co-administration of ifenprodil (an NR2B antagonist) and NMDA (an NMDA receptor agonist) during the reoxygenation stage did not result in any significant alterations. Furthermore, intraplantar injection of ifenprodil effectively reversed the altered gene expression that was observed in male CPIP rats, thereby revealing the potential mechanisms underlying the therapeutic effects of peripheral ifenprodil administration in CRPS. Collectively, our findings indicate that keratinocytes undergo oxidative injury in CRPS, with NMDA receptors playing regulatory roles.

The dual role of microglia in neuropathic pain after spinal cord injury: Detrimental and protective effects

Spinal cord injury (SCI) is a debilitating condition that is frequently accompanied by neuropathic pain, resulting in significant physical and psychological harm to a vast number of individuals globally. Despite the high prevalence of neuropathic pain following SCI, the precise underlying mechanism remains incompletely understood. Microglia are a type of innate immune cell that are present in the central nervous system (CNS). They have been observed to have a significant impact on neuropathic pain following SCI. This article presents a comprehensive overview of recent advances in understanding the role of microglia in the development of neuropathic pain following SCI. Specifically, the article delves into the detrimental and protective effects of microglia on neuropathic pain following SCI, as well as the mechanisms underlying their interconversion. Furthermore, the article provides a thorough overview of potential avenues for future research in this area.

Immune Status of Individuals with Traumatic Spinal Cord Injury: A Systematic Review and Meta-Analysis

Individuals with spinal cord injury (SCI) have higher infection rates compared to those without SCI. In this review, the immune status difference between individuals with and without traumatic SCI is investigated by examining their peripheral immune cells and markers. PubMed, Cochrane, EMBASE, and Ovid MEDLINE were searched without language or date restrictions. Studies reporting peripheral immune markers' concentration and changes in functional capabilities of immune cells that compared individuals with and without SCI were included. Studies with participants with active infection, immune disease, and central nervous system (CNS) immune markers were excluded. The review followed the PRISMA guidelines. Effect estimates were measured by Weighted Mean Difference (WMD) using a random-effects model. Study quality was assessed using the National Heart, Lung, and Blood Institute Quality Assessment Tool. Fifty-four studies (1813 with SCI and 1378 without SCI) contributed to the meta-analysis. Leukocytes (n = 23, WMD 0.78, 95% CI 0.17; 1.38, I2 83%), neutrophils (n = 11, WMD 0.76, 95% CI 0.09; 1.42, I2 89%), C-reactive protein (CRP) (n = 12, WMD 2.25, 95% CI 1.14; 3.56, I2 95%), and IL6 (n = 13, WMD 2.33, 95% CI 1.20; 3.49, I2 97%) were higher in individuals with SCI vs. without SCI. Clinical factors (phase of injury, completeness of injury, sympathetic innervation impairment, age, sex) and study-related factors (sample size, study design, and serum vs. plasma) partially explained heterogeneity. Immune cells exhibited lower functional capability in individuals with SCI vs. those without SCI. Most studies (75.6%) had a moderate risk of bias. The immune status of individuals with SCI differs from those without SCI and is clinically influenced by the phase of injury, completeness of injury, sympathetic innervation impairment, age, and sex. These results provide information that is vital for monitoring and management strategies to effectively improve the immune status of individuals with SCI.

Estrogen plays an important role by influencing the NLRP3 inflammasome

The nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3) inflammasome is an important part of the natural immune system that plays an important role in many diseases. Estrogen is a sex hormone that plays an important role in controlling reproduction and regulates many physiological and pathological processes. Recent studies have indicated that estrogen is associated with disease progression. Estrogen can ameliorate some diseases (e. g, sepsis, mood disturbances, cerebral ischemia, some hepatopathy, Parkinson's disease, amyotrophic lateral sclerosis, inflammatory bowel disease, spinal cord injury, multiple sclerosis, myocardial ischemia/reperfusion injury, osteoarthritis, and renal fibrosis) by inhibiting the NLRP3 inflammasome. Estrogen can also promote the development of diseases (e.g., ovarian endometriosis, dry eye disease, and systemic lupus erythematosus) by upregulating the NLRP3 inflammasome. In addition, estrogen has a dual effect on the development of cancers and asthma. However, the mechanism of these effects is not summarized. This article reviewed the progress in understanding the effects of estrogen on the NLRP3 inflammasome and its mechanisms in recent years to provide a theoretical basis for an in-depth study.

Role of SIRT1 in sepsis-induced encephalopathy: Molecular targets for future therapies

Sepsis induces neuroinflammation, BBB disruption, cerebral hypoxia, neuronal mitochondrial dysfunction, and cell death causing sepsis-associated encephalopathy (SAE). These pathological consequences lead to short- and long-term neurobehavioural deficits. Till now there is no specific treatment that directly improves SAE and its associated behavioural impairments. In this review, we discuss the underlying mechanisms of sepsis-induced brain injury with a focus on the latest progress regarding neuroprotective effects of SIRT1 (silent mating type information regulation-2 homologue-1). SIRT1 is an NAD+ -dependent class III protein deacetylase. It is able to modulate multiple downstream signals (including NF-κB, HMGB, AMPK, PGC1α and FoxO), which are involved in the development of SAE by its deacetylation activity. There are multiple recent studies showing the neuroprotective effects of SIRT1 in neuroinflammation related diseases. The proposed neuroprotective action of SIRT1 is meant to bring a promising therapeutic strategy for managing SAE and ameliorating its related behavioural deficits.

Solasodine Containing Solanum torvum L. Fruit Extract Prevents Chronic Constriction Injury-Induced Neuropathic Pain in Rats: In Silico and In Vivo Evidence of TRPV1 Receptor and Cytokine Inhibition

This study aimed to assess the efficacy of ethanolic extract of Solanum torvum L. fruit (EESTF) containing solasodine in treating chronic constriction injury (CCI)-induced neuropathic pain in rats. Three-dimensional (3D) simulation studies of solasodine binding were conducted on the TRPV1 receptor, IL-6, and TNF-α structures. For in vivo justification, an assessment of behavioral, biochemical, and histological changes was designed after a CCI-induced neuropathic pain model in rats. On days 7, 14, and 21, CCI significantly increased mechanical, thermal, and cold allodynia while producing a functional deficit. IL-6, TNF-α, TBARS, and MPO levels also increased. SOD levels of catalase and reduced glutathione levels also decreased. Administration of pregabalin (30 mg/kg, oral), solasodine (25 mg/kg, oral), and EESTF (100 and 300 mg/kg, oral) significantly reduced CCI-induced behavioral and biochemical changes (P < 0.05). The protective nature of EESTF was also confirmed by histological analysis. Capsaicin, a TRPV1 receptor agonist, abolished the antinociceptive effects of EESTF when used previously. From the observations of the docking studies, solasodine acted as an antagonist at TRPV1, whereas the docking scores of solasodine against TNF-α and IL-6 were reported to be -11.2 and -6.04 kcal/mol, respectively. The attenuating effect of EESTF might be related to its antagonistic effects on TRPV1, suppression of cytokines, and anti-inflammatory and antioxidant properties.

Thermosensitive hydrogel-based GPR124 delivery strategy for rebuilding blood-spinal cord barrier

Spinal cord injury (SCI) causes blood-spinal cord barrier (BSCB) disruption, leading to secondary damage, such as hemorrhagic infiltration, inflammatory response, and neuronal cell death. It is of great significance to rebuild the BSCB at the early stage of SCI to alleviate the secondary injury for better prognosis. Yet, current research involved in the reconstruction of BSCB is insufficient. Accordingly, we provide a thermosensitive hydrogel-based G protein-coupled receptor 124 (GPR124) delivery strategy for rebuilding BSCB. Herein, we firstly found that the expression of GPR124 decreased post-SCI and demonstrated that treatment with recombinant GPR124 could partially alleviate the disruption of BSCB post-SCI by restoring tight junctions (TJs) and promoting migration and tube formation of endothelial cells. Interestingly, GPR124 could also boost the energy metabolism of endothelial cells. However, the absence of physicochemical stability restricted the wide usage of GPR124. Hence, we fabricated a thermosensitive heparin-poloxamer (HP) hydrogel that demonstrated sustained GPR124 production and maintained the bioactivity of GPR124 (HP@124) for rebuilding the BSCB and eventually enhancing functional motor recovery post-SCI. HP@124 hydrogel can encapsulate GPR124 at the lesion site by injection, providing prolonged release, preserving wounded tissues, and filling injured tissue cavities. Consequently, it induces synergistically efficient integrated regulation by blocking BSCB rupture, decreasing fibrotic scar formation, minimizing inflammatory response, boosting remyelination, and regenerating axons. Mechanistically, giving GPR124 activates energy metabolism via elevating the expression of phosphoenolpyruvate carboxykinase 2 (PCK2), and eventually restores the poor state of endothelial cells. This research demonstrated that early intervention by combining GPR124 with bioactive multifunctional hydrogel may have tremendous promise for restoring locomotor recovery in patients with central nervous system disorders, in addition to a translational approach for the medical therapy of SCI.

Sexually dimorphic extracellular vesicle responses after chronic spinal cord injury are associated with neuroinflammation and neurodegeneration in the aged brain

BACKGROUND

Medical advances have made it increasingly possible for spinal cord injury (SCI) survivors to survive decades after the insult. But how SCI affects aging changes and aging impacts the injury process have received limited attention. Extracellular vesicles (EVs) are recognized as critical mediators of neuroinflammation after CNS injury, including at a distance from the lesion site. We have previously shown that SCI in young male mice leads to robust changes in plasma EV count and microRNA (miR) content. Here, our goal was to investigate the impact of biological sex and aging on EVs and brain after SCI.

METHODS

Young adult age-matched male and female C57BL/6 mice were subjected to SCI. At 19 months post-injury, total plasma EVs were isolated by ultracentrifugation and characterized by nanoparticle tracking analysis (NTA). EVs miR cargo was examined using the Fireplex® assay. The transcriptional changes in the brain were assessed by a NanoString nCounter Neuropathology panel and validated by Western blot (WB) and flow cytometry (FC). A battery of behavioral tests was performed for assessment of neurological function.

RESULTS

Transcriptomic changes showed a high number of changes between sham and those with SCI. Sex-specific changes were found in transcription networks related to disease association, activated microglia, and vesicle trafficking. FC showed higher microglia and myeloid counts in the injured tissue of SCI/Female compared to their male counterparts, along with higher microglial production of ROS in both injured site and the brain. In the latter, increased levels of TNF and mitochondrial membrane potential were seen in microglia from SCI/Female. WB and NTA revealed that EV markers are elevated in the plasma of SCI/Male. Particle concentration in the cortex increased after injury, with SCI/Female showing higher counts than SCI/Male. EVs cargo analysis revealed changes in miR content related to injury and sex. Behavioral testing confirmed impairment of cognition and depression at chronic time points after SCI in both sexes, without significant differences between males and females.

CONCLUSIONS

Our study is the first to show sexually dimorphic changes in brain after very long-term SCI and supports a potential sex-dependent EV-mediated mechanism that contributes to SCI-induced brain changes.

A Systematic Review of the Interventions for Management of Pain in Patients After Spinal Cord Injury

Chronic pain is a very common problem in patients with spinal cord injury (SCI) as it affects 80% of these patients, which negatively affects their quality of life. Despite many advantages that exist in the management of any type of pain (neuropathic, nociceptive, mixed) in these patients, there is no cure, and the analgesic effect of some treatments is inadequate. This study aims to conduct an evidence-based systematic review regarding the various interventions used for the management of pain after SCI. The PubMed, Physiotherapy Evidence Database (PEDro), and Cochrane Library databases were searched from 1969 to 2023. The risk of bias was assessed using the PEDro scoring system. A total of 57 studies met the inclusion criteria and were included in this systematic review. Among the different interventions at present, 18 studies examined the role of oral medications, 11 studies examined the role of minimally invasive methods (injection and infusion), 16 studies investigated physiotherapy and alternative treatments, and 12 studies examined the role of repetitive transcranial magnetic stimulation (rTMS), transcranial direct current stimulation (tDCS), and cranial electrotherapy stimulation (CES) in the management of pain in patients after SCI. Gabapentin and pregabalin are very effective in managing chronic neuropathic pain after SCI, and pregabalin also seems to reduce anxiety and sleep disturbances in the patients. It is noteworthy that lamotrigine, valproate, and carbamazepine do not have an analgesic effect, but mirogabalin is a novel and promising drug. Antidepressants (selective serotonin reuptake inhibitors and serotonin and noradrenaline reuptake inhibitors) did not reduce the pain of the patients, although some studies showed an efficacy of amitriptyline especially in depressed patients and tramadol should be considered short-term with caution. Also, tDCS and rTMS reduced pain. Moreover, botulinum toxin type A, lidocaine, ketamine, and intrathecal baclofen significantly reduced pain intensity, although the sample of the studies was small. Physiotherapy and alternative treatments seem to relieve pain, and transcutaneous electrical nerve stimulation had the greatest reduction of pain intensity. In conclusion, several pharmaceutical and non-pharmaceutical methods exist, which can reduce pain in patients after SCI. The type of intervention can be considered by the physician depending on the patients' preference, age, medical history, type of pain, and associated symptoms. However, more studies with greater samples and with better methodological quality should be conducted.

Healthy dietary indices and noncancer pain: a systematic review of cross-sectional and longitudinal studies

ABSTRACT

Pain is a global public health problem given its high prevalence and incidence, long duration, and social and economic impact. There is growing interest in nutrition as potential modifiable risk factor related to pain; however, the associations between healthy dietary patterns and pain have not yet been well established. Thus, we aimed to systematically review and synthesise current cross-sectional and longitudinal evidence on the relationship between a priori healthy dietary patterns and noncancer pain among adults aged ≥18 years. We identified relevant published cross-sectional and longitudinal studies by systematically searching several electronic databases from inception to September 2021. Risk of bias was assessed using the modified Newcastle-Ottawa scale for cohort studies. A total of 14 cross-sectional and 6 longitudinal studies were included in the review. These studies measured different dietary scores/indices, such as different measures of adherence to the Mediterranean diet and the dietary inflammatory index. Pain ascertainment methods and pain measurements used differed across studies. All 20 of the included studies had different study designs and statistical analysis. Of these studies, 10 reported an inverse association between adherence to a healthy dietary pattern and pain, 5 reported mixed results, and 5 reported no associations. Despite notable heterogeneity, 50% of included observational studies reported that adherence to a healthy diet, particularly the Mediterranean diet, is inversely associated with pain. Of note, the cross-sectional design of most studies precludes any causal interpretation. Moreover, limited and inconsistent evidence from longitudinal studies highlights the need for further studies.

Role of Integrative Health on Neuropathic Pain

PURPOSE OF REVIEW

Patients diagnosed with neuropathic pain experience continuous or intermittent spontaneous pain throughout their lives. Pharmacological treatments often provide limited relief; therefore, a multidisciplinary approach should be utilized to manage neuropathic pain. This review examines the current literature on integrative health modalities (anti-inflammatory diets, functional movement, acupuncture, meditation, and transcutaneous therapy) for treating patients with neuropathic pain.

RECENT FINDINGS

The use of an anti-inflammatory diet, functional movement, acupuncture, meditation, and transcutaneous therapy in treating neuropathic pain has been investigated in prior literature with positive outcomes. However, there remains a large void in evidence-based knowledge and clinical applicability for these interventions. Overall, integrative health offers a cost-efficient and harmless way of creating a multidisciplinary approach to managing neuropathic pain. There are many complementary approaches to treating neuropathic pain as part of an integrative medicine approach. Research is needed to explore other herbs and spices not yet reported in the peer-review literature. Additionally, follow-on research is needed to understand the clinical applicability of the proposed interventions as well as the dose and timing of the interventions to predict response and duration.

Pain-resolving immune mechanisms in neuropathic pain

Interactions between the immune and nervous systems are of central importance in neuropathic pain, a common and debilitating form of chronic pain caused by a lesion or disease affecting the somatosensory system. Our understanding of neuroimmune interactions in pain research has advanced considerably. Initially considered as passive bystanders, then as culprits in the pathogenesis of neuropathic pain, immune responses in the nervous system are now established to underpin not only the initiation and progression of pain but also its resolution. Indeed, immune cells and their mediators are well-established promoters of neuroinflammation at each level of the neural pain pathway that contributes to pain hypersensitivity. However, emerging evidence indicates that specific subtypes of immune cells (including antinociceptive macrophages, pain-resolving microglia and T regulatory cells) as well as immunoresolvent molecules and modulators of the gut microbiota-immune system axis can reduce the pain experience and contribute to the resolution of neuropathic pain. This Review provides an overview of the immune mechanisms responsible for the resolution of neuropathic pain, including those involved in innate, adaptive and meningeal immunity as well as interactions with the gut microbiome. Specialized pro-resolving mediators and therapeutic approaches that target these neuroimmune mechanisms are also discussed.

Exploring Novel Therapeutic Targets in the Common Pathogenic Factors in Migraine and Neuropathic Pain

Migraine and neuropathic pain (NP) are both painful, disabling, chronic conditions which exhibit some symptom similarities and are thus considered to share a common etiology. The calcitonin gene-related peptide (CGRP) has gained credit as a target for migraine management; nevertheless, the efficacy and the applicability of CGRP modifiers warrant the search for more effective therapeutic targets for pain management. This scoping review focuses on human studies of common pathogenic factors in migraine and NP, with reference to available preclinical evidence to explore potential novel therapeutic targets. CGRP inhibitors and monoclonal antibodies alleviate inflammation in the meninges; targeting transient receptor potential (TRP) ion channels may help prevent the release of nociceptive substances, and modifying the endocannabinoid system may open a path toward discovery of novel analgesics. There may exist a potential target in the tryptophan-kynurenine (KYN) metabolic system, which is closely linked to glutamate-induced hyperexcitability; alleviating neuroinflammation may complement a pain-relieving armamentarium, and modifying microglial excitation, which is observed in both conditions, may be a possible approach. Those are several potential analgesic targets which deserve to be explored in search of novel analgesics; however, much evidence remains missing. This review highlights the need for more studies on CGRP modifiers for subtypes, the discovery of TRP and endocannabinoid modulators, knowledge of the status of KYN metabolites, the consensus on cytokines and sampling, and biomarkers for microglial function, in search of innovative pain management methods for migraine and NP.

Resveratrol suppresses neuroinflammation to alleviate mechanical allodynia by inhibiting Janus kinase 2/signal transducer and activator of transcription 3 signaling pathway in a rat model of spinal cord injury

Background

Neuropathic pain (NP) is one of intractable complications of spinal cord injury (SCI) and lacks effective treatment. Resveratrol (Res) has been shown to possess potent anti-inflammatory and anti-nociceptive effects. In this study, we investigated the analgesic effect of Res and its underlying mechanism in a rat model of SCI.

Methods

The rat thoracic (T10) spinal cord contusion injury model was established, and mechanical thresholds were evaluated during an observation period of 21 days. Intrathecal administration with Res (300 μg/10 μl) was performed once a day for 7 days after the operation. On postoperative day 7, the expressions of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and interleukin-6 (IL-6) were determined by enzyme-linked immunosorbent assay (ELISA) and Real-time quantitative PCR (RT-qPCR), the expression of Janus kinase 2/signal transducer and activator of transcription 3 (JAK2/STAT3) signaling pathway was determined by western blot and RT-qPCR, and the co-labeled phospho-STAT3 (p-STAT3) with neuronal nuclear antigen (NeuN), glial fibrillary acidic protein (GFAP), and ionized calcium-binding adapter molecule 1 (Iba-1) were explored by double immunofluorescence staining in the lumbar spinal dorsal horns. The temporal changes of p-STAT3 were investigated by western blot on the 1st, 3rd, 7th, 14th, and 21st days after the operation.

Results

Intrathecal administration with Res for 7 successive days alleviated mechanical allodynia of rats during the observation period. Meanwhile, treatment with Res suppressed the production of pro-inflammatory factors TNF-α, IL-1β and IL-6, and inhibited the expressions of phospho-JAK2 and p-STAT3 in the lumbar spinal dorsal horns on postoperative day 7. Additionally, the protein expression of p-STAT3 was significantly increased on the 1st day following the operation and remained elevated during the next 21 days, immunofluorescence suggested that the up-regulated p-STAT3 was co-located with glial cells and neurons.

Conclusion

Our current results indicated that intrathecal administration with Res effectively alleviated mechanical allodynia after SCI in rats, and its analgesic mechanism might be to suppress neuroinflammation by partly inhibiting JAK2/STAT3 signaling pathway.

Research progress on the mechanism of chronic neuropathic pain

Chronic neuropathic pain (CNP) refers to pain that lasts for more than three months due to a disease or an injury to the somatosensory nervous system. The incidence of CNP has been increasing in the world, causing it to become a global concern and patients often experience spontaneous pain, hyperalgesia, abnormal pain or even abnormal sensation as some of its main symptoms. In addition to serious pain and poor physical health, CNP also negatively affects patients' mental health, thus impacting the overall quality of their lives. The pathogenesis of CNP is not clear, but some studies have proved that central sensitization, peripheral sensitization, neuroinflammation, dysfunction in descending nociceptive modulatory systems, oxidative stress reaction, activation of glial cells and psychological factors play an important role in the occurrence and development of CNP. In this context, this article summarizes the current research progress on the mechanism of CNP to provide a basis for further research in preventing and treating the disease.

Nutrition Education to Reduce Metabolic Dysfunction for Spinal Cord Injury: A Module-Based Nutrition Education Guide for Healthcare Providers and Consumers

Spinal cord injury (SCI) results in a high prevalence of neurogenic obesity and metabolic dysfunction. The increased risk for neurogenic obesity and metabolic dysfunction is mainly due to the loss of energy balance because of significantly reduced energy expenditure following SCI. Consequently, excessive energy intake (positive energy balance) leads to adipose tissue accumulation at a rapid rate, resulting in neurogenic obesity, systemic inflammation, and metabolic dysfunction. The purpose of this article is to review the existing literature on nutrition, dietary intake, and nutrition education in persons with SCI as it relates to metabolic dysfunction. The review will highlight the poor dietary intakes of persons with SCI according to authoritative guidelines and the need for nutrition education for health care professionals and consumers. Nutrition education topics are presented in a module-based format with supporting literature. The authors emphasize the role of a diet consisting of low-energy, nutrient-dense, anti-inflammatory foods consistent with the Dietary Guidelines for Americans' MyPlate to effectively achieve energy balance and reduce the risk for neurogenic obesity and metabolic dysfunction in individuals with SCI.

Systemic inflammation after spinal cord injury: A review of biological evidence, related health risks, and potential therapies

Individuals with chronic traumatic spinal cord injury (SCI) develop progressive multi-system health problems that result in clinical illness and disability. Systemic inflammation is associated with many of the common medical complications and acquired diseases that accompany chronic SCI, suggesting that it contributes to a number of comorbid pathological conditions. However, many of the mechanisms that promote persistent systemic inflammation and its consequences remain ill-defined. This review describes the significant biological factors that contribute to systemic inflammation, major organ systems affected, health risks, and the potential treatment strategies. We aim to highlight the need for a better understanding of inflammatory processes, and to establish appropriate strategies to address inflammation in SCI.

Pharmacological and non-pharmacological therapeutic interventions for the treatment of spinal cord injury-induced pain

Spinal cord injury (SCI) is a complex neurophysiological disorder, which can result in many long-term complications including changes in mobility, bowel and bladder function, cardiovascular function, and metabolism. In addition, most individuals with SCI experience some form of chronic pain, with one-third of these individuals rating their pain as severe and unrelenting. SCI-induced chronic pain is considered to be "high impact" and broadly affects a number of outcome measures, including daily activity, physical and cognitive function, mood, sleep, and overall quality of life. The majority of SCI pain patients suffer from pain that emanates from regions located below the level of injury. This pain is often rated as the most severe and the underlying mechanisms involve injury-induced plasticity along the entire neuraxis and within the peripheral nervous system. Unfortunately, current therapies for SCI-induced chronic pain lack universal efficacy. Pharmacological treatments, such as opioids, anticonvulsants, and antidepressants, have been shown to have limited success in promoting pain relief. In addition, these treatments are accompanied by many adverse events and safety issues that compound existing functional deficits in the spinally injured, such as gastrointestinal motility and respiration. Non-pharmacological treatments are safer alternatives that can be specifically tailored to the individual and used in tandem with pharmacological therapies if needed. This review describes existing non-pharmacological therapies that have been used to treat SCI-induced pain in both preclinical models and clinical populations. These include physical (i.e., exercise, acupuncture, and hyper- or hypothermia treatments), psychological (i.e., meditation and cognitive behavioral therapy), and dietary interventions (i.e., ketogenic and anti-inflammatory diet). Findings on the effectiveness of these interventions in reducing SCI-induced pain and improving quality of life are discussed. Overall, although studies suggest non-pharmacological treatments could be beneficial in reducing SCI-induced chronic pain, further research is needed. Additionally, because chronic pain, including SCI pain, is complex and has both emotional and physiological components, treatment should be multidisciplinary in nature and ideally tailored specifically to the patient.

Emerging Evidence for Intrathecal Management of Neuropathic Pain Following Spinal Cord Injury

A high prevalence of patients with spinal cord injury (SCI) suffer from chronic neuropathic pain. Unfortunately, the precise pathophysiological mechanisms underlying this phenomenon have yet to be clearly elucidated and targeted treatments are largely lacking. As an unfortunate consequence, neuropathic pain in the population with SCI is refractory to standard of care treatments and represents a significant contributor to morbidity and suffering. In recent years, advances from SCI-specific animal studies and translational models have furthered our understanding of the neuronal excitability, glial dysregulation, and chronic inflammation processes that facilitate neuropathic pain. These developments have served advantageously to facilitate exploration into the use of neuromodulation as a treatment modality. The use of intrathecal drug delivery (IDD), with novel pharmacotherapies, to treat chronic neuropathic pain has gained particular attention in both pre-clinical and clinical contexts. In this evidence-based narrative review, we provide a comprehensive exploration into the emerging evidence for the pathogenesis of neuropathic pain following SCI, the evidence basis for IDD as a therapeutic strategy, and novel pharmacologics across impactful animal and clinical studies.

Resveratrol Inhibition of the WNT/β-Catenin Pathway following Discogenic Low Back Pain

Low back pain (LBP) management is an important clinical issue. Inadequate LBP control has consequences on the mental and physical health of patients. Thus, acquiring new information on LBP mechanism would increase the available therapeutic tools. Resveratrol is a natural compound with many beneficial effects. In this study, we investigated the role of resveratrol on behavioral changes, inflammation and oxidative stress induced by LBP. Ten microliters of Complete Freund’s adjuvant (CFA) was injected in the lumbar intervertebral disk of Sprague Dawley rats to induce degeneration, and resveratrol was administered daily. Behavioral analyses were performed on day zero, three, five and seven, and the animals were sacrificed to evaluate the molecular pathways involved. Resveratrol administration alleviated hyperalgesia, motor disfunction and allodynia. Resveratrol administration significantly reduced the loss of notochordal cells and degenerative changes in the intervertebral disk. From the molecular point of view, resveratrol reduced the 5th/6th lumbar (L5–6) spinal activation of the WNT pathway, reducing the expression of WNT3a and cysteine-rich domain frizzled (FZ)8 and the accumulation of cytosolic and nuclear β-catenin. Moreover, resveratrol reduced the levels of TNF-α and IL-18 that are target genes strictly downstream of the WNT/β-catenin pathway. It also showed important anti-inflammatory activities by reducing the activation of the NFkB pathway, the expression of iNOS and COX-2, and the levels of PGE2 in the lumbar spinal cord. Moreover, resveratrol reduced the oxidative stress associated with inflammation and pain, as shown by the observed reduced lipid peroxidation and increased GSH, SOD, and CAT activities. Therefore, resveratrol administration controlled the WNT/β-catenin pathway and the related inflammatory and oxidative alterations, thus alleviating the behavioral changes induced by LBP.

The Critical Role of Nutrition Care to Improve Pain Management: A Global Call to Action for Physical Therapist Practice

Physical therapists have unique education in the comprehensive biopsychosocial assessment and treatment of chronic pain and its mechanisms. Recently, physical therapists have raised awareness regarding the impact of nutrition on promoting health and managing noncommunicable diseases. Robust evidence supports the implementation of nutrition in physical therapist education and practice. Of particular interest for the physical therapist are investigations that use dietary interventions for the treatment of chronic pain. Yet physical therapists have received little guidance regarding their role in nutrition care for pain management and may pass on opportunities to counsel their patients on the connection between nutrition and pain. Therefore, a clinical paradigm shift and unified voice within the profession is called on to encourage physical therapists to develop tailored multimodal lifestyle interventions that include nutrition care for the management of chronic pain. This Perspective describes evidence supporting the implementation of nutrition care in physical therapist practice, supports the role of nutritional pain management for physical therapists, and encourages the use of nutrition care for primary, secondary, tertiary, prevention, health promotion, and wellness related to chronic pain. To achieve these aims, this Perspective offers suggestions for how physical therapists can (1) enhance clinical decision making; (2) expand professional, jurisdictional, and personal scope of practice; (3) evolve entry-level education; and (4) stimulate new investigations in nutrition care and pain science research. In doing so, physical therapists can assert their role throughout the pain management continuum, champion innovative research initiatives, and enhance public health by reducing the impact of chronic pain.

IMPACT

The nutrition care process for pain management is defined as the basic duty to provide adequate and appropriate nutrition education and counseling to people living with pain. Including the nutrition care process as part of a multimodal approach to pain management provides an opportunity for physical therapists to assert their role throughout the pain management continuum. This includes championing innovative research initiatives and enhancing public health by reducing the impact of chronic pain for over 50 million Americans.

The CanPain SCI clinical practice guidelines for rehabilitation management of neuropathic pain after spinal cord injury: 2021 update

STUDY DESIGN

Clinical practice guidelines.

OBJECTIVES

The objective was to update the 2016 version of the Canadian clinical practice guidelines for the management of neuropathic pain in people with spinal cord injury (SCI).

SETTING

The guidelines are relevant for inpatient, outpatient and community SCI rehabilitation settings in Canada.

METHODS

The guidelines were updated in accordance with the Appraisal of Guidelines for Research and Evaluation II tool. A Steering Committee and Working Group reviewed the relevant evidence on neuropathic pain management (encompassing screening and diagnosis, treatment and models of care) after SCI. The quality of evidence was scored using Grading of Recommendations Assessment, Development and Evaluation (GRADE). A consensus process was followed to achieve agreement on recommendations and clinical considerations.

RESULTS

The working group identified and reviewed 46 additional relevant articles published since the last version of the guidelines. The panel agreed on 3 new screening and diagnosis recommendations and 8 new treatment recommendations. Two key changes to these treatment recommendations included the introduction of general treatment principles and a new treatment recommendation classification system. No new recommendations to model of care were made.

CONCLUSIONS

The CanPainSCI recommendations for the management of neuropathic pain after SCI should be used to inform practice.

The Impact of Sub-maximal Exercise on Neuropathic Pain, Inflammation, and Affect Among Adults With Spinal Cord Injury: A Pilot Study

Introduction: Persons with spinal cord injury (SCI) often report high levels of neuropathic pain (NP) and poor well-being, which may result from increased inflammation. This study examined the impact of sub-maximal aerobic exercise on NP, inflammation and psychological affect among adults with SCI. Methods: Eight active adults with tetraplegia (n-4, AIS A-C) and paraplegia (n = 4, AIS A-C) performed 30-min of arm-crank aerobic exercise and reported their ratings of perceived exertion (RPE) each minute. Measures of NP, affect, and inflammatory cytokines (IL-6, IL-10, IL-1ra, TNF-α) were taken pre-(T₀), immediately post-(T₁), and 90-min post-exercise (T₂). Results: NP decreased between T₀ and T₁ for tetraplegics (-60%, d = 0.47; CI = -0.32, 2.02) and paraplegics (-16%, d = 0.15; CI = -0.30, 0.90). Correlations between change in cytokines and change in NP were medium-to large for tetraplegics (rs ranged from -0.820 to 0.965) and paraplegics (rs ranged from -0.598 to 0.833). However, the pattern of correlations between change in cytokines and affect was inconsistent between groups. Lower baseline levels of IL-1ra predicted greater decreases in NP immediately post-exercise (r = 0.83, p = 0.01). Conclusion: Sub-maximal exercise can positively impact NP for some persons with SCI. Further experimental research should identify the optimal exercise intensity to reduce NP for persons with SCI, in addition to understanding biomarkers which may predict changes in NP. Clinical Trial Registration: www.ClinicalTrials.gov, identifier NCT03955523.

Peripheral Immune Dysfunction: A Problem of Central Importance after Spinal Cord Injury

Simple Summary

Spinal cord injury can result in an increased vulnerability to infections, but until recently the biological mechanisms behind this observation were not well defined. Immunosuppression and concurrent sustained peripheral inflammation after spinal cord injury have been observed in preclinical and clinical studies, now termed spinal cord injury-induced immune depression syndrome. Recent research indicates a key instigator of this immune dysfunction is altered sympathetic input to lymphoid organs, such as the spleen, resulting in a wide array of secondary effects that can, in turn, exacerbate immune pathology. In this review, we discuss what we know about immune dysfunction after spinal cord injury, why it occurs, and how we might treat it.

Abstract

Individuals with spinal cord injuries (SCI) exhibit increased susceptibility to infection, with pneumonia consistently ranking as a leading cause of death. Despite this statistic, chronic inflammation and concurrent immune suppression have only recently begun to be explored mechanistically. Investigators have now identified numerous changes that occur in the peripheral immune system post-SCI, including splenic atrophy, reduced circulating lymphocytes, and impaired lymphocyte function. These effects stem from maladaptive changes in the spinal cord after injury, including plasticity within the spinal sympathetic reflex circuit that results in exaggerated sympathetic output in response to peripheral stimulation below injury level. Such pathological activity is particularly evident after a severe high-level injury above thoracic spinal cord segment 6, greatly increasing the risk of the development of sympathetic hyperreflexia and subsequent disrupted regulation of lymphoid organs. Encouragingly, studies have presented evidence for promising therapies, such as modulation of neuroimmune activity, to improve regulation of peripheral immune function. In this review, we summarize recent publications examining (1) how various immune functions and populations are affected, (2) mechanisms behind SCI-induced immune dysfunction, and (3) potential interventions to improve SCI individuals’ immunological function to strengthen resistance to potentially deadly infections.

High leukotriene B4 serum levels increase risk of painful diabetic neuropathy among type 2 diabetes mellitus patients

Background

Painful diabetic neuropathy is one of the most common complications of type 2 diabetes mellitus, with approximately 30–50% of people will experience diabetic neuropathy. Chronic hyperglycemia will cause an inflammatory process that will trigger an immune response included leukotrienes. Leukotriene B4 is associated with hemoglobin glycation levels. This study aimed to determine high serum leukotriene B4 levels and other factors as a risk factor for painful diabetic neuropathy in type 2 diabetes mellitus patient.

Results

Forty-two subjects with 22 cases (median age 56.5 ± 4.9 years) and 20 controls (median age 56.5 ± 5.2 years) group were collected. In bivariate analysis, significant factor for high risk PDN was high leukotriene B4 serum level (OR 5.10; 95% CI 1.34–19.4, p 0.014). Meanwhile, insignificant factors were anti-diabetic drugs (OR 2.139; 0.62–7.37; p = 0.226), and duration of diabetes mellitus (OR 2.282; 0.56–9.25; p = 0.315). Independent risk factor was serum leukotriene B4 levels (OR 5.10; 95% CI 1.336–19.470; p = 0.017).

Conclusions

In this study, high leukotriene B4 serum levels increase the risk of painful diabetic neuropathy among type 2 diabetes mellitus. The leukotriene B4 may consider as a potential biomarker for early detection in high risk for PDN and early treatment.

The Potential Role of Inflammation in Modulating Endogenous Hippocampal Neurogenesis After Spinal Cord Injury

Currently there are approximately 291,000 people suffering from a spinal cord injury (SCI) in the United States. SCI is associated with traumatic changes in mobility and neuralgia, as well as many other long-term chronic health complications, including metabolic disorders, diabetes mellitus, non-alcoholic steatohepatitis, osteoporosis, and elevated inflammatory markers. Due to medical advances, patients with SCI survive much longer than previously. This increase in life expectancy exposes them to novel neurological complications such as memory loss, cognitive decline, depression, and Alzheimer's disease. In fact, these usually age-associated disorders are more prevalent in people living with SCI. A common factor of these disorders is the reduction in hippocampal neurogenesis. Inflammation, which is elevated after SCI, plays a major role in modulating hippocampal neurogenesis. While there is no clear consensus on the mechanism of the decline in hippocampal neurogenesis and cognition after SCI, we will examine in this review how SCI-induced inflammation could modulate hippocampal neurogenesis and provoke age-associated neurological disorders. Thereafter, we will discuss possible therapeutic options which may mitigate the influence of SCI associated complications on hippocampal neurogenesis.

The effects of a high-fat/high-carbohydrate meal on leukocyte populations in adults with chronic spinal cord injury

STUDY DESIGN

Secondary analysis of aggregated case series data.

OBJECTIVES

To examine the effects of a high-fat/high-carbohydrate meal on leukocyte populations in adults with a chronic SCI.

SETTING

University-based laboratories in British Columbia, Canada.

METHODS

Ten individuals (M = 9) with a traumatic SCI (>1-year post-injury; M = 15.5 years; n = 2 sensory complete, n = 7 motor complete) participated in this study. Participants arrived fasted (≥12 h) prior to both the control (quiet sitting, no food/drink) and experimental meal conditions (high-fat/high-carb meal: 880 kcal, 52 g fat, 73 g carbohydrates, 29 g protein). Blood samples were taken in the fasted state and at 120-min post-meal/baseline in both conditions. Immune cell counts were assessed using multi-color flow cytometry.

RESULTS

A significant time × condition interaction effect was seen in CD3+, CD4+, and CD8+ T cells as well as CD56+ and CD3+/CD56+ natural killer (NK) cells (p < 0.05). CD14+/CD16+ monocytes and CD19+ B cells approached a significant time × condition interaction (p < 0.07). A main effect of time was observed in CD19+ B cells (p < 0.05). Cell counts for T-lymphocytes and NK cells followed the general trend of an increase in the control condition from baseline to 120-min with no change observed following the experimental meal condition.

CONCLUSIONS

Following the HFHC meal, immune cells did not show the same general increase observed following the control condition. Future research is needed to determine if there are any potential consequences of these immune cell responses in immunosuppressed populations and if other factors (e.g., diurnal variation) might influence immune cell response.

Can FDA-Approved Immunomodulatory Drugs be Repurposed/Repositioned to Alleviate Chronic Pain?

Pain is among the most widespread chronic health condition confronting society today and our inability to manage chronic pain contributes to the opioid abuse epidemic in America. The immune system is known to contribute to acute and chronic pain, but only limited therapeutic treatments such as non-steroid anti-inflammatory drugs have resulted from this knowledge. The last decade has shed light on neuro-immune interactions mediating the development, maintenance, and resolution of chronic pain. Here, we do not aim to perform a comprehensive review of all immune mechanisms involved in chronic pain, but to briefly review the contribution of the main cytokines and immune cells (macrophages, microglia, mast cells and T cells) to chronic pain. Given the urgent need to address the Pain crisis, we provocatively propose to repurpose/reposition FDA-approved immunomodulatory drugs for their potential to alleviate chronic pain. Repositioning or repurposing offers an attractive way to accelerate the arrival of new analgesics.

[Carbon Monoxide and Pain Regulation: A Review]

Carbon monoxide (CO) is an endogenous gasotransmitter produced by the degradation of heme in the presence of heme oxygenase (HO) in mammals. It has been demonstrated that CO participates in a variety of physiological activities and pathological processes, and is closely related to cell protection and homeostasis maintenance in organ tissues. It has been shown by a growing number of studies that CO may play a regulatory and interventional role in the process of the occurrence and development of pain through a variety of mechanisms of action. However, its mechanism of action is still not fully understood and the uncontrollable factors concerning CO administration also placed considerable limitation to its application. This paper reviews the potential targets and pathways of CO in pain regulation and discusses the challenges and opportunities in the clinical application of CO in order to provide suggestions for further exploration and development of CO analgesics.

Interrelationship of Neurogenic Obesity and Chronic Neuropathic Pain in Persons With Spinal Cord Injury

The prevalence of obesity and of neuropathic pain are both estimated at above 50% in the population of people with chronic spinal cord injury (SCI). These secondary consequences of SCI have significant negative impact on physical functioning, activities of daily living, and quality of life. Investigations of relationships between weight or body composition and chronic neuropathic pain in people with SCI are lacking, but investigations in non-SCI cohorts suggest an association between obesity and the presence and severity of neuropathic pain conditions. In the present article, we present a review of the literature linking obesity and neuropathic pain and summarize findings suggesting that metabolic syndrome and chronic, systemic inflammation due to excess adiposity increase the risk for neuropathic pain after an SCI.

A bioactive injectable self-healing anti-inflammatory hydrogel with ultralong extracellular vesicles release synergistically enhances motor functional recovery of spinal cord injury

The repair and motor functional recovery after spinal cord injury (SCI) remains a worldwide challenge. The inflammatory microenvironment is one of main obstacles on inhibiting the recovery of SCI. Using mesenchymal stem cells (MSCs) derived extracellular vesicles to replace MSCs transplantation and mimic cell paracrine secretions provides a potential strategy for microenvironment regulation. However, the effective preservation and controlled release of extracellular vesicles in the injured spinal cord tissue are still not satisfied. Herein, we fabricated an injectable adhesive anti-inflammatory F127-polycitrate-polyethyleneimine hydrogel (FE) with sustainable and long term extracellular vesicle release (FE@EVs) for improving motor functional recovery after SCI. The orthotopic injection of FE@EVs hydrogel could encapsulate extracellular vesicles on the injured spinal cord, thereby synergistically induce efficient integrated regulation through suppressing fibrotic scar formation, reducing inflammatory reaction, promoting remyelination and axonal regeneration. This study showed that combining extracellular vesicles into bioactive multifunctional hydrogel should have great potential in achieving satisfactory locomotor recovery of central nervous system diseases.

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The novel FE hydrogel was designed for encapsulating the extracellular vesicles (FE@EVs).

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FE hydrogel exert the capabilities of temperature-responsive, injectable, adhesive and biocompatible.

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FE hydrogel with sustainable and long-term extracellular vesicle release for improving motor functional recovery after SCI.

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FE@EVs plays a vital role in pathological process of spinal cord injury in rats.

PPARα Agonist WY-14643 Relieves Neuropathic Pain through SIRT1-Mediated Deacetylation of NF-κB

Inflammation caused by neuropathy contributes to the development of neuropathic pain (NP), but the exact mechanism still needs to be understood. Peroxisome proliferator-activated receptor α (PPARα), an important inflammation regulator, might participate in the inflammation in NP. To explore the role of PPARα in NP, the effects of PPARα agonist WY-14643 on chronic constriction injury (CCI) rats were evaluated. The results showed that WY-14643 stimulation could decrease inflammation and relieve neuropathic pain, which was relative with the activation of PPARα. In addition, we also found that the SIRT1/NF-κB pathway was involved in the WY-14643-induced anti-inflammation in NP, and activation of PPARα increased SIRT1 expression, thus reducing the proinflammatory function of NF-κB. These data suggested that WY-14643 might serve as an inflammation mediator, which may be a potential therapy option for NP.

A conductive dual-network hydrogel composed of oxidized dextran and hyaluronic-hydrazide as BDNF delivery systems for potential spinal cord injury repair

Spinal cord injury (SCI) often causes neuronal death and axonal degeneration. In this study, we report a new strategy for preparing injectable and conductive polysaccharides-based hydrogels that could sustainably deliver brain-derived neurotrophic factor (BDNF) for SCI repair. We used poly(lactic-co-glycolic acid) (PLGA) as a carrier to encapsulate BDNF. The resulting microspheres were then modified with tannic acid (TA). The polysaccharides-based hydrogel composed of oxidized dextran (Dex) and hyaluronic acid-hydrazide (HA) was mixed with TA-modified microspheres to form the ultimate BDNF@TA-PLGA/Dex-HA hydrogel. Our results showed that the hydrogel had properties similar to natural spinal cords. Specifically, the hydrogel had soft mechanical properties and high electrical conductivity. The cross-sectional morphology of the hydrogel exhibited a continuous and porous structure. The swelling and degradation behaviors of the Dex-HA hydrogel in vitro indicated the incorporation of TA into hydrogel matrix could improve the stability of the hydrogel matrix as well as extend the release time of BDNF from the matrix. Furthermore, results from immunostaining and real-time PCR demonstrated that BDNF@TA-PLGA/Dex-HA hydrogel could promote the differentiation of neural stem cells (NSCs) into neurons and inhibit astrocyte differentiation in vitro. These results show the great potential of this hydrogel as a biomimetic material in SCI regeneration.

Dietary Interventions Are Beneficial for Patients with Chronic Pain: A Systematic Review with Meta-Analysis

Background

The standard Western diet is high in processed hyperpalatable foods that displace nutrient-dense whole foods, leading to inflammation and oxidative stress. There is limited research on how these adverse metabolic drivers may be associated with maladaptive neuroplasticity seen in chronic pain and whether this could be attenuated by a targeted nutritional approach. The aim of this study was to review the evidence for whole-food dietary interventions in chronic pain management.

Method

A structured search of eight databases was performed up to December 2019. Two independent reviewers screened studies and evaluated risk of bias by using the National Institutes of Health assessment tool for controlled or pre–post studies and the Joanna Briggs checklist for case reports. A meta-analysis was performed in Review Manager.

Results

Forty-three studies reporting on 48 chronic pain groups receiving a whole-food dietary intervention were identified. These included elimination protocols (n = 11), vegetarian/vegan diets (n = 11), single-food changes (n = 11), calorie/macronutrient restriction (n = 8), an omega-3 focus (n = 5), and Mediterranean diets (n = 2). A visual analog scale was the most commonly reported pain outcome measure, with 17 groups reporting a clinically objective improvement (a two-point or 33% reduction on the visual analog scale). Twenty-seven studies reported significant improvement on secondary metabolic measures. Twenty-five groups were included in a meta-analysis that showed a significant finding for the effect of diet on pain reduction when grouped by diet type or chronic pain type.

Conclusion

There is an overall positive effect of whole-food diets on pain, with no single diet standing out in effectiveness. This suggests that commonalities among approaches (e.g., diet quality, nutrient density, weight loss) may all be involved in modulating pain physiology. Further research linking how diet can modulate physiology related to pain (such as inflammation, oxidative stress, and nervous system excitability) is required.

Dietary Interventions for Treatment of Chronic Pain: Oxidative Stress and Inflammation

Chronic pain is highly prevalent in the United States, impacting 28.4% of the adult population, or 69.6 million people, as of 2016. Chronic pain is often associated with anxiety, depression, and restrictions in mobility and daily activities, substantially reducing quality of life. Analgesics, especially opioids, are one of the primary pharmaceutical treatment methods for chronic pain. However, prescription opioid misuse and abuse has become increasingly prevalent and concerning, prompting the need for research into alternative treatment methods which avoid the side effects of traditional treatments. Chronic pain is, in part, thought to be the result of oxidative stress and inflammation, and clinical research has indicated links between these conditions and diet. Thus, dietary interventions are a particularly promising therapeutic treatment for chronic pain, with numerous studies suggesting that diet has a noticeable effect on pain as far down as the cellular level. In this review article, data from a number of clinical trials assessing the effect of three diets—antioxidant-rich, low-carbohydrate, and Mediterranean—on oxidative stress and inflammation is compiled and discussed in the context of chronic pain. Clinical data suggests that low-carbohydrate diets and Mediterranean diets both are especially promising dietary interventions.

Cannabinoids and an anti-inflammatory diet for the treatment of neuropathic pain after spinal cord injury (The CATNP Study): study protocol for a randomized controlled trial

STUDY DESIGN

Multicenter, randomized, double-blind, placebo controlled, clinical trial.

OBJECTIVE

The objective of this paper is to evaluate the effectiveness of cannabinoids and an anti-inflammatory diet, alone and in combination, for the management of neuropathic pain (NP) after spinal cord injury (SCI).

SETTING

Two Canadian SCI rehabilitation centers.

METHODS

A sample of 144 individuals with SCI will receive either an anti-inflammatory diet, cannabinoids or a placebo for 6 weeks. Following this, a combined effect of these treatments will be evaluated for a further 6 weeks. The primary outcome measure will be the change in NP as assessed by the numeric rating scale (NRS). Secondary outcomes will include changes in inflammation, mood, sleep, spasticity, cost-effectiveness, and function.

CONCLUSION

This study will assess the efficacy of an anti-inflammatory diet and cannabinoids (individually and in combination) for the treatment of NP following SCI. Results may reveal a cost-effective, side-effect free intervention strategy which could be utilized for the long-term management of NP following SCI.

Nutritional intervention in chronic pain: an innovative way of targeting central nervous system sensitization?

INTRODUCTION

Few treatment programs for chronic pain nowadays take a dietary pattern or adipose status into account.

AREAS COVERED

An important role of neuroinflammation in chronic pain is now well established, at least in part due to increased central nervous system glial activation. Based on preclinical studies, it is postulated that the interaction between nutrition and central sensitization is mediated via bidirectional gut-brain interactions. This model of diet-induced neuroinflammation and consequent central sensitization generates a rationale for developing innovative treatments for patients with chronic pain. Methods: An umbrella approach to cover the authors' expert opinion within an evidence-based viewpoint.

EXPERT OPINION

A low-saturated fat and low-added sugar dietary pattern potentially decreases oxidative stress, preventing Toll-like receptor activation and subsequent glial activation. A low-saturated fat and low-added sugar diet might also prevent afferent vagal nerve fibers sensing the pro-inflammatory mediators that come along with a high-(saturated) fat or energy-dense dietary pattern, thereby preventing them to signal peripheral inflammatory status to the brain. In addition, the gut microbiota produces polyamines, which hold the capacity to excite N-methyl-D-aspartate receptors, an essential component of the central nervous system sensitization. Hence, a diet reducing polyamine production by the gut microbiota requires exploration as a therapeutic target for cancer-related and non-cancer chronic pain.

Dementia, Depression, and Associated Brain Inflammatory Mechanisms after Spinal Cord Injury

Evaluation of the chronic effects of spinal cord injury (SCI) has long focused on sensorimotor deficits, neuropathic pain, bladder/bowel dysfunction, loss of sexual function, and emotional distress. Although not well appreciated clinically, SCI can cause cognitive impairment including deficits in learning and memory, executive function, attention, and processing speed; it also commonly leads to depression. Recent large-scale longitudinal population-based studies indicate that patients with isolated SCI (without concurrent brain injury) are at a high risk of dementia associated with substantial cognitive impairments. Yet, little basic research has addressed potential mechanisms for cognitive impairment and depression after injury. In addition to contributing to disability in their own right, these changes can adversely affect rehabilitation and recovery and reduce quality of life. Here, we review clinical and experimental work on the complex and varied responses in the brain following SCI. We also discuss potential mechanisms responsible for these less well-examined, important SCI consequences. In addition, we outline the existing and developing therapeutic options aimed at reducing SCI-induced brain neuroinflammation and post-injury cognitive and emotional impairments.

Novel Neuropathic Pain Mechanisms Associated With Allergic Inflammation

Allergic diseases are associated with central and peripheral nervous system diseases such as autism spectrum disorders and eosinophilic granulomatosis with polyangiitis, which frequently causes mononeuritis multiplex. Thus, it is possible that patients with an atopic constitution might develop multifocal inflammation in central and peripheral nervous system tissues. In a previous study in Japan, we reported a rare form of myelitis with persistent neuropathic pain (NeP) in patients with allergic disorders. However, the underlying mechanism of allergic inflammation-related NeP remains to be elucidated. First, we analyzed the effect of allergic inflammation on the nociceptive system in the spinal cord. Mice with atopy showed microglial and astroglial activation in the spinal cord and tactile allodynia. In a microarray analysis of isolated microglia from the spinal cord, endothelin receptor type B (EDNRB) was the most upregulated cell surface receptor in mice with atopy. Immunohistochemical analysis demonstrated EDNRB expression was upregulated in microglia and astroglia. The EDNRB antagonist BQ788 abolished glial activation and allodynia. These findings indicated that allergic inflammation induced widespread glial activation through the EDNRB pathway and NeP. Second, we investigated whether autoantibody-mediated pathogenesis underlies allergic inflammation-related NeP. We detected specific autoantibodies to small dorsal root ganglion (DRG) neurons and their nerve terminals in the dorsal horns of NeP patients with allergic disorders. An analysis of IgG subclasses revealed a predominance of IgG2. These autoantibodies were mostly colocalized with isolectin B4- and P2X3-positive unmyelinated C-fiber type small DRG neurons. By contrast, immunostaining for S100β, a myelinated DRG neuron marker, showed no colocalization with patient IgG. Immunoprecipitation and liquid chromatography-tandem mass spectrometry identified plexin D1 as a target autoantigen. Patients with anti-plexin D1 antibodies often present with burning pain and thermal hyperalgesia. Immunotherapies, including plasma exchange, are effective for NeP management. Therefore, anti-plexin D1 antibodies may be pathogenic for immune-mediated NeP, especially under allergic inflammation conditions. Thus, allergic inflammation may induce NeP through glial inflammation in the spinal cord and the anti-plexin D1 antibody-mediated impairment of small DRG neurons.

Changes in nutrient intake and inflammation following an anti-inflammatory diet in spinal cord injury

Objective: The objective of the current study was to describe the observed changes in nutrient intakes following a 3-month anti-inflammatory diet, and to explore potential relationships between the change in nutrients and the change in various inflammatory mediators.Design: A secondary analysis of a prior randomized controlled clinical trial.Setting: Individuals with SCI within the Niagara region.Participants: Twenty individuals with various levels and severities of SCI.Intervention: Three-month anti-inflammatory diet.Outcome Measures: The change in nutrient intake and corresponding changes to various inflammatory mediators.Results: The treatment group demonstrated a significant reduction in fat intake (P = 0.02), a significant increase in protein intake (P = 0.02), and no change in carbohydrates (P = 0.23) or energy intake (P = 0.10). The treatment group showed a significant increase in some nutrients with established anti-inflammatory properties including vitamins A, C, and E, and omega-3 fatty acids (P < 0.01). Significant reductions in proinflammatory nutrients were observed including trans fatty acids (P = 0.05), caffeine (P < 0.01), and sodium (P = 0.02). The treatment group also showed significant reductions in the proinflammatory mediators interferon-y (P = 0.01), interleukin-1β (P < 0.01), and interleukin-6 (P < 0.05). Further, several proinflammatory mediators were negatively correlated with anti-inflammatory nutrients, including vitamin A, carotenoids, omega-3 fatty acids, and zinc.Conclusion: This study provides evidence that dietary alterations are effective at reducing chronic inflammation in individuals with SCI and provides a preliminary assessment of the related nutrient changes.

An injectable heparin-Laponite hydrogel bridge FGF4 for spinal cord injury by stabilizing microtubule and improving mitochondrial function

Rationale: Spinal cord injury (SCI) remains a critical clinical challenge. The controlled release of FGF4, a novel neuroprotective factor, from a versatile Laponite hydrogel to the injured site was a promising strategy to promote axon regeneration and motor functional recovery after SCI.

Methods: Characterization of Laponite, Laponite/Heparin (Lap/Hep) and Laponite/Heparin loaded with FGF4 (Lap/Hep@FGF4) hydrogels were measured by rheometer. Multiple comprehensive evaluations were used to detect motor functional recovery and the axonal rehabilitation after Lap/Hep@FGF4 treatment in vivo (SCI rat model). Moreover, microtubule dynamic and energy transportation, which regulated axonal regeneration was evaluated by Lap/Hep@FGF4 gel in vitro (primary neuron).

Results: FGF4 released from Lap/Hep gel locally achieves strong protection and regeneration after SCI. The Lap/Hep@FGF4 group revealed remarkable motor functional recovery and axonal regrowth after SCI through suppressing inflammatory reaction, increasing remyelination and reducing glial/fibrotic scars. Furthermore, the underlying mechanism of axonal rehabilitation were demonstrated via enhancing microtubule stability and regulating mitochondrial localization after Lap/Hep@FGF4 treatment.

Conclusion: This promising sustained release system provides a synergistic effective approach to enhance recovery after SCI underlying a novel mechanism of axonal rehabilitation, and shows a translational prospect for the clinical treatment of SCI.

Recent advances in nanotherapeutic strategies for spinal cord injury repair

Spinal cord injury (SCI) is a devastating and complicated condition with no cure available. The initial mechanical trauma is followed by a secondary injury characterized by inflammatory cell infiltration and inhibitory glial scar formation. Due to the limitations posed by the blood-spinal cord barrier, systemic delivery of therapeutics is challenging. Recent development of various nanoscale strategies provides exciting and promising new means of treating SCI by crossing the blood-spinal cord barrier and delivering therapeutics. As such, we discuss different nanomaterial fabrication methods and provide an overview of recent studies where nanomaterials were developed to modulate inflammatory signals, target inhibitory factors in the lesion, and promote axonal regeneration after SCI. We also review emerging areas of research such as optogenetics, immunotherapy and CRISPR-mediated genome editing where nanomaterials can provide synergistic effects in developing novel SCI therapy regimens, as well as current efforts and barriers to clinical translation of nanomaterials.

Maintenance of diet participation in individuals with spinal cord injury: effect on mood and neuropathic pain

Study design

One-year follow-up of a randomized clinical trial.

Objectives

Examine voluntary dietary compliance 1 year following the cessation of the intervention and the persistence of accrued benefits related to neuropathic pain and mood.

Setting

Outpatient rehabilitation program within the Niagara region.

Methods

Five individuals (4 female, 1 male; age 50.6 ± 11.8 years) with chronic SCI (C5-L3; ISNCSCI: A-D; 7-40 years post injury) who had previously completed a 3-month anti-inflammatory diet were reassessed after 1 year for measures related to dietary compliance, CES-D scores of depression, and NPQ scores of neuropathic pain.

Results

There was a significant reduction in diet compliance at the 1-year follow-up in comparison to the end of the dietary intervention at 3 months (92.6% versus 43.0%, p < 0.01). CES-D scores showed a trend toward an increase from 3 months to follow-up (8.0 versus 21.4, p = .10) whereby follow-up CES-D scores were no longer statistically different from baseline (p = 0.74). Sensory NPQ scores showed no significant change from 3 months to follow-up (25.2 versus 29.1, p = 0.42) and remained significantly lower than baseline (p = 0.02). Affective NPQ scores were significantly increased from 3 months to follow-up (27.7 versus 40.1, p = 0.05). Sensitivity NPQ scores showed no significant change from 3 month to follow-up (28.2 versus 33.5, p = 0.34), but returned to a score that was statistically similar to baseline (p = 0.15).

Conclusions

These results emphasize the importance of continued compliance to a diet with anti-inflammatory properties for the purposes of maintaining benefits related to mood and neuropathic pain in individuals with SCI.

Sponsorship

This study was supported by the Ontario Neurotrauma Foundation.

A systematic review and meta-analysis of nutrition interventions for chronic noncancer pain

BACKGROUND

This systematic review aimed to evaluate the impact of nutrition interventions on participant reported pain severity and intensity in populations with chronic pain.

METHODS

Eight databases were systematically searched for studies that included adult populations with a chronic pain condition, a nutrition intervention and a measure of pain. Where possible, data were pooled using meta-analysis. Seventy-one studies were included, with 23 being eligible for meta-analysis.

RESULTS

Studies were categorised into four groups: (i) altered overall diet with 12 of 16 studies finding a significant reduction in participant reported pain; (ii) altered specific nutrients with two of five studies reporting a significant reduction in participant reported pain; (iii) supplement-based interventions with 11 of 46 studies showing a significant reduction in pain; and (iv) fasting therapy with one of four studies reporting a significant reduction in pain. The meta-analysis found that, overall, nutrition interventions had a significant effect on pain reduction with studies testing an altered overall diet or just one nutrient having the greatest effect.

CONCLUSIONS

This review highlights the importance and effectiveness of nutrition interventions for people who experience chronic pain.

Barriers and facilitators to adhering to an anti-inflammatory diet for individuals with spinal cord injuries

The purpose of this study was to explore the barriers and facilitators of an anti-inflammatory diet in people with spinal cord injury. Six participants (age range of 23-68 years, three women and three men) who had previously completed an anti-inflammatory diet study were interviewed. Facilitators identified were family support, autonomy over meal choice, peer support, health benefits gained, and implementation of adherence strategies. The main barriers discussed were lack of motivation after study period ended, social events, diet expenses, and lack of knowledge about the diet. Several health benefits including reductions in pain, edema, and improvements in cognition and mobility were reported.