Bioactive compounds for neuropathic pain: An update on preclinical studies and future perspectives

The Impact of Nutrition on Pain: A Narrative Review of Recent Literature

PURPOSE OF REVIEW

Pain is a complex phenomenon that affects millions of individuals worldwide and poses a significant burden on public health. While pain management typically focuses on pharmacological and physical interventions, emerging research suggests that nutrition plays a crucial role in pain modulation. This narrative review aims to explore the relationship between nutrition and pain, providing a comprehensive overview of recent literature. The review covers various dietary factors, including macronutrients, micronutrients, dietary patterns, and specific dietary interventions. Additionally, the potential mechanisms underlying the impact of nutrition on pain are discussed. The findings highlight the potential for dietary interventions to complement traditional pain management approaches and provide valuable insights for future research and clinical practice.

RECENT FINDINGS

Literature suggested the impact of healthy nutrition on improvement in pain and that certain types of food may increase and worsen different pain conditions. Nutrition plays an important role in modulating pain. It is important to counsel patients in pain on best diet for their pain condition to alleviate pain. Our article summarizes very well the issue of nutrition and pain and provides a guide to all practitioners caring for patients with chronic pain.

Treatment of neuropathic pain by traditional Chinese medicine: An updated review on their effect and putative mechanisms of action

Neuropathic pain (NP) is a common chronic pain with heterogeneous clinical features, and consequent lowering of quality of life. Currently, although conventional chemical drugs can effectively manage NP symptoms in the short term, their long-term efficacy is limited, and they come with significant side effects. In this regard, traditional Chinese medicine (TCM) provides a promising avenue for treating NP. Numerous pharmacological and clinical studies have substantiated the effectiveness of TCM with multiple targets and mechanisms. We aimed to outline the characteristics of TCM, including compound prescriptions, single Chinese herbs, active ingredients, and TCM physical therapy, for NP treatment and discussed their efficacy by analyzing the pathogenesis of NP. Various databases, such as PubMed, Web of Science, China National Knowledge Infrastructure, and Wanfang database, were searched. We focused on recent research progress in NP treatment by TCM. Finally, we proposed the future challenges and emerging trends in the treatment of NP. TCM demonstrates significant clinical efficacy in NP treatment, employing multi-mechanisms. Drawing from the theory of syndrome differentiation, four types of dialectical treatments for NP by compound TCM prescriptions were introduced: promoting blood circulation and removing blood stasis; promoting blood circulation and promote Qi flow; warming Yang and benefiting Qi; soothing the liver and regulating Qi. Meanwhile, 33 single Chinese herbs and 25 active ingredients were included. In addition, TCM physical therapy (e.g., acupuncture, massage, acupoint injection, and fumigation) also showed good efficacy in NP treatment. TCM, particularly through the use of compound prescriptions and acupuncture, holds bright prospects in treating NP owing to its diverse holistic effects. Nonetheless, the multi-targets of TCM may result in possible disadvantages to NP treatment, and the pharmacological mechanisms of TCM need further evaluation. Here, we provide an overview of NP treatment via TCM, based on the pathogenesis and the potential therapeutic mechanisms, thus providing a reference for further studies.

[6]-Shogaol and [6]-Gingerol active ingredients may improve neuropathic pain by suppressing cytokine levels in an experimental model

Background/aim

Neuropathic pain (NP) is a type of chronic pain usually caused by damage to the somatosensory system. Bioactive antioxidant compounds, such as curcumin and ginger, are widely preferred in the treatment of NP. However, the ingredient-based mechanism that underlies their pain-relieving activity remains unknown. The aim of this study was to investigate the therapeutic effects of trans-[6]-Shogaol and [6]-Gingerol active ingredients of the Zingiber officinale Roscoe extract on the spinal cord and cortex in the neuroinflammatory pathway in rats with experimental sciatic nerve injury.

Materials and methods

Forty-six volatile phenolic components were identified in ginger samples using gas chromatography-mass spectrometry analysis. Thirty 3-month-old male 250-300 g Wistar Albino rats were divided into three groups as (i) sham, (ii) chronic constriction injury (CCI), and (iii) CCI+ginger. NP was induced using the CCI model. A ginger extract treatment enriched with trans-[6]-shogaol and [6]-gingerol active ingredients was administered by gavage at 200 mg/kg/day for 7 days. On the 14th day of the experiment, locomotor activity was evaluated in open field and hyperalgesia in tail flick tests.

Results

In behavioural experiments, a significant decrease was observed in the CCI group compared to the sham group, while a significant increase was observed in the CCI+ginger group compared to the CCI group (p < 0.05). In the spinal cord and cortex tissues, there was a significant increase in the TNF-α, IL-1β, and IL-18 neuroinflammation results of the CCI group compared to the sham group, while there was a significant decrease in the CCI+ginger group compared to the CCI group.

Conclusion

In this study, ginger treatment was shown to have a therapeutic effect on neuroinflammation against sciatic nerve damage.

Turmeric Bioactive Compounds Alleviate Spinal Nerve Ligation-Induced Neuropathic Pain by Suppressing Glial Activation and Improving Mitochondrial Function in Spinal Cord and Amygdala

This study examined the effects of turmeric bioactive compounds, curcumin C3 complex® (CUR) and bisdemethoxycurcumin (BDMC), on mechanical hypersensitivity and the gene expression of markers for glial activation, mitochondrial function, and oxidative stress in the spinal cord and amygdala of rats with neuropathic pain (NP). Twenty-four animals were randomly assigned to four groups: sham, spinal nerve ligation (SNL, an NP model), SNL+100 mg CUR/kg BW p.o., and SNL+50 mg BDMC/kg BW p.o. for 4 weeks. Mechanical hypersensitivity was assessed by the von Frey test (VFT) weekly. The lumbosacral section of the spinal cord and the right amygdala (central nucleus) were collected to determine the mRNA expression of genes (IBA-1, CD11b, GFAP, MFN1, DRP1, FIS1, PGC1α, PINK, Complex I, TLR4, and SOD1) utilizing qRT-PCR. Increased mechanical hypersensitivity and increased gene expression of markers for microglial activation (IBA-1 in the amygdala and CD11b in the spinal cord), astrocyte activation (GFAP in the spinal cord), mitochondrial dysfunction (PGC1α in the amygdala), and oxidative stress (TLR4 in the spinal cord and amygdala) were found in untreated SNL rats. Oral administration of CUR and BDMC significantly decreased mechanical hypersensitivity. CUR decreased CD11b and GFAP gene expression in the spinal cord. BDMC decreased IBA-1 in the spinal cord and amygdala as well as CD11b and GFAP in the spinal cord. Both CUR and BDMC reduced PGC1α gene expression in the amygdala, PINK1 gene expression in the spinal cord, and TLR4 in the spinal cord and amygdala, while they increased Complex I and SOD1 gene expression in the spinal cord. CUR and BDMC administration decreased mechanical hypersensitivity in NP by mitigating glial activation, oxidative stress, and mitochondrial dysfunction.

Involvement of Oxidative Stress and Nutrition in the Anatomy of Orofacial Pain

Pain is a very important problem of our existence, and the attempt to understand it is one the oldest challenges in the history of medicine. In this review, we summarize what has been known about pain, its pathophysiology, and neuronal transmission. We focus on orofacial pain and its classification and features, knowing that is sometimes purely subjective and not well defined. We consider the physiology of orofacial pain, evaluating the findings on the main neurotransmitters; in particular, we describe the roles of glutamate as approximately 30-80% of total peripheric neurons associated with the trigeminal ganglia are glutamatergic. Moreover, we describe the important role of oxidative stress and its association with inflammation in the etiogenesis and modulation of pain in orofacial regions. We also explore the warning and protective function of orofacial pain and the possible action of antioxidant molecules, such as melatonin, and the potential influence of nutrition and diet on its pathophysiology. Hopefully, this will provide a solid background for future studies that would allow better treatment of noxious stimuli and for opening new avenues in the management of pain.

Honokiol-Rich Magnolia officinalis Bark Extract Attenuates Trauma-Induced Neuropathic Pain

Neuropathic pain (NP) affects about 8% of the general population. Current analgesic therapies have limited efficacy, making NP one of the most difficult to treat pain conditions. Evidence indicates that excessive oxidative stress can contribute to the onset of chronic NP and several natural antioxidant compounds have shown promising efficacy in NP models. Thus, this study aimed to investigate the pain-relieving activity of honokiol (HNK)-rich standardized extract of Magnolia officinalis Rehder & E. Wilson bark (MOE), well known for its antioxidant and anti-inflammatory properties, in the spared nerve injury (SNI) model. The molecular mechanisms and efficacy toward neuroinflammation were investigated in spinal cord samples from SNI mice and LPS-stimulated BV2 microglia cells. MOE and HNK showed antioxidant activity. MOE (30 mg/kg p.o.) produced an antiallodynic effect in SNI mice in the absence of locomotor impairment, reduced spinal p-p38, p-JNK1, iNOS, p-p65, IL-1ß, and Nrf2 overexpression, increased IL-10 and MBP levels and attenuated the Notch signaling pathway by reducing Jagged1 and NEXT. These effects were prevented by the CB1 antagonist AM251. HNK reduced the proinflammatory response of LPS-stimulated BV2 and reduced Jagged1 overexpression. MOE and HNK, by modulating oxidative and proinflammatory responses, might represent interesting candidates for NP management.

Novel Drug Targets and Emerging Pharmacotherapies in Neuropathic Pain

Neuropathic pain is a debilitating condition characterized by abnormal signaling within the nervous system, resulting in persistent and often intense sensations of pain. It can arise from various causes, including traumatic nerve injury, neuropathy, and certain diseases. We present an overview of current and emerging pharmacotherapies for neuropathic pain, focusing on novel drug targets and potential therapeutic agents. Current pharmacotherapies, including tricyclic antidepressants, gabapentinoids, and serotonin norepinephrine re-uptake inhibitors, are discussed, as are emerging treatments, such as ambroxol, cannabidiol, and N-acetyl-L-cysteine. Additionally, the article highlights the need for further research in this field to identify new targets and develop more effective and targeted therapies for neuropathic pain management.

Flavonoids bridging the gut and the brain: intestinal metabolic fate, and direct or indirect effects of natural supporters against neuroinflammation and neurodegeneration

In recent years, experimental evidence suggested a possible role of the gut microbiota in the onset and development of several neurodegenerative disorders, such as AD and PD, MS and pain. Flavonoids, including anthocyanins, EGCG, the flavonol quercetin, and isoflavones, are plant polyphenolic secondary metabolites that have shown therapeutic potential for the treatment of various pathological conditions, including neurodegenerative diseases. This is due to their antioxidant and anti-inflammatory properties, despite their low bioavailability which often limits their use in clinical practice. In more recent years it has been demonstrated that flavonoids are metabolized by specific bacterial strains in the gut to produce their active metabolites. On the other way round, both naturally-occurring flavonoids and their metabolites promote or limit the proliferation of specific bacterial strains, thus profoundly affecting the composition of the gut microbiota which in turn modifies its ability to further metabolize flavonoids. Thus, understanding the best way of acting on this virtuous circle is of utmost importance to develop innovative approaches to many brain disorders. In this review, we summarize some of the most recent advances in preclinical and clinical research on the neuroinflammatory and neuroprotective effects of flavonoids on AD, PD, MS and pain, with a specific focus on their mechanisms of action including possible interactions with the gut microbiota, to emphasize the potential exploitation of dietary flavonoids as adjuvants in the treatment of these pathological conditions.

Gingerol-Enriched Ginger Supplementation Mitigates Neuropathic Pain via Mitigating Intestinal Permeability and Neuroinflammation: Gut-Brain Connection

Objectives: Emerging evidence suggests an important role of the gut-brain axis in the development of neuropathic pain (NP). We investigated the effects of gingerol-enriched ginger (GEG) on pain behaviors, as well as mRNA expressions of inflammation via tight junction proteins in GI tissues (colon) and brain tissues (amygdala, both left and right) in animals with NP.

Methods: Seventeen male rats were randomly divided into three groups: Sham, spinal nerve ligation (SNL, pain model), and SNL+0.375% GEG (wt/wt in diet) for 4 weeks. Mechanosensitivity was assessed by von Frey filament tests and hindpaw compression tests. Emotional responsiveness was measured from evoked audible and ultrasonic vocalizations. Ongoing spontaneous pain was measured in rodent grimace tests. Intestinal permeability was assessed by the lactulose/D-mannitol ratio in urine. The mRNA expression levels of neuroinflammation (NF-κB, TNF-α) in the colon and amygdala (right and left) were determined by qRT-PCR. Data was analyzed statistically.

Results: Compared to the sham group, the SNL group had significantly greater mechanosensitivity (von Frey and compression tests), emotional responsiveness (audible and ultrasonic vocalizations to innocuous and noxious mechanical stimuli), and spontaneous pain (rodent grimace tests). GEG supplementation significantly reduced mechanosensitivity, emotional responses, and spontaneous pain measures in SNL rats. GEG supplementation also tended to decrease SNL-induced intestinal permeability markers. The SNL group had increased mRNA expression of NF-κB and TNF-α in the right amygdala and colon; GEG supplementation mitigated these changes in SNL-treated rats.

Conclusion: This study suggests GEG supplementation palliated a variety of pain spectrum behaviors in a preclinical NP animal model. GEG also decreased SNL-induced intestinal permeability and neuroinflammation, which may explain the behavioral effects of GEG.