The Emerging Role of Quercetin in the Treatment of Chronic Pain

Synaptic plasticity and neuroprotection: The molecular impact of flavonoids on neurodegenerative disease progression

Flavonoids are a broad family of polyphenolic chemicals that are present in a wide variety of fruits, vegetables, and medicinal plants. Because of their neuroprotective qualities, flavonoids have attracted a lot of interest. The potential of flavonoids to control synaptic plasticity-a crucial process underlying memory, learning, and cognitive function-is becoming more and more clear. Dysregulation of synaptic plasticity is a feature of neurodegenerative diseases such as amyotrophic lateral sclerosis (0.4 %), Parkinson's (1-2 %), Alzheimer's (5-7 %), and Huntington's ((0.2 %)). This review discusses the molecular mechanisms via which flavonoids influence synaptic plasticity as well as their therapeutic potential in neurodegenerative diseases. Flavonoids modulate key signaling pathways such as MAPK/ERK and PI3K/Akt/mTOR to support neuroprotection, synaptic plasticity, and neuronal health, while also influencing neurotrophic factors (BDNF, NGF) and their receptors (TrkB, TrkA). They regulate neurotransmitter receptors like GABA, AMPA, and NMDA to balance excitatory and inhibitory transmission, and exert antioxidant effects via the Nrf2-ARE pathway and anti-inflammatory actions by inhibiting NF-κB signaling, highlighting their potential for treating neurodegenerative diseases. These varied reactions support the preservation of synapse function and neuronal integrity in the face of neurodegenerative insults. Flavonoids can reduce the symptoms of neurodegeneration, prevent synaptic loss, and enhance cognitive function, according to experimental studies. However, there are still obstacles to using these findings in clinical settings, such as limited bioavailability and the need for consistent dose. The focus of future research should be on improving flavonoid delivery systems and combining them with conventional medications.

Rutin: a pain-relieving flavonoid

Rutin (vitamin P or rutoside) is a citrus flavonoid glycoside that has shown beneficial health effects in different organs against various conditions including inflammation and pain. The majority of rutin therapeutic benefits are ascribed to its antioxidant and anti-inflammatory properties. This review article discusses studies that investigated pain-relieving activity of rutin and summarizes the reported mechanisms of action. Rutin pain-relieving effect has been studied in streptozotocin-induced diabetes, chronic constriction injury, and oxaliplatin-, formalin-, acetic acid- and glutamate-induced nociception in mice or rats. Based on the literature, rutin analgesic effects are induced through potentiation of antioxidant arsenal, reduction of inflammatory cytokines (e.g., Tumor necrosis factor alpha (TNF-α) and interleukin-1β) levels, suppression of cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) expressions and modulation of MAPK, NF-κB and Nrf-2/HO-1 signaling. Preclinical findings on rutin pain-relieving activity are promising, however, its safety profile needs to be more thoroughly investigated and clinical trials should be conducted to assess its analgesic effects in humans.

Peroxisome proliferator-activated receptor gamma: A promising therapeutic target for the treatment of chronic pain

Chronic pain represents an incapacitating medical condition that profoundly impacts the patients' quality of life. Managing chronic pain poses a significant challenge for healthcare professionals due to its multifaceted nature and the limited effectiveness of current treatment options. Therefore, novel therapeutic interventions are crucially required for the management of chronic pain. Peroxisome proliferator-activated receptor gamma (PPARγ), a nuclear receptor, exerts regulatory effects on physiological processes such as glucose and lipid metabolism. Emerging studies demonstrate that PPARγ is a critical regulator of the expression of various genes, including those of anti-inflammatory cytokines and antioxidant enzymes. Substantial evidence indicates decreased expression of PPARγ in the sciatic nerve, dorsal root ganglia, and spinal cord dorsal horn in animal models of chronic pain. Furthermore, natural or synthetic PPARγ agonists had inhibitory effects on nociceptive hypersensitivity in various animal models of chronic pain. This review summarizes and discusses preclinical evidence demonstrating the therapeutic potential of PPARγ agonists in chronic pain management. The available evidence indicates that PPARγ activation reduces chronic pain by inhibiting neuroinflammation and oxidative stress as well as modulation of opioidergic system. Overall, the use of PPARγ agonists is a promising therapeutic approach for treating chronic pain; however, further research regarding its detailed mechanisms is warranted.

The Effects and Mechanisms of Phytochemicals on Pain Management and Analgesic

Phytochemicals can be an essential treatment for chronic pain. This narrative review will summarize and critically analyze the evidence surrounding these substances in pain management. We will introduce phytochemicals, discuss their associated mechanisms, and comment on their viability for potential treatment. There have been decades of research on phytochemical therapies for pain management, but the authors limited the scope of the investigation to the last 25 years. This literature review will serve as a foundation for the pain practitioner to understand where these treatments fit in the paradigm for chronic pain treatment. Assess the integration of phytochemicals within pain management fully.

Antinociceptive and antineuropathic effects of Trifolium resupinatum L. on formalin-induced nociception and cervical spinal cord hemi-contusion: Underlying Mechanisms

ETHNOPHARMACOLOGICAL RELEVANCE

Trifolium resupinatum L. (Fabaceae), known as Persian clover, ethnomedicinally used in Persian folk medicine to treat peritoneal inflammation, rheumatism, and back pain.

AIM OF THE STUDY

To investigate the antineuropathic and antinociceptive activities of Trifolium resupinatum leaves essential oil (TREO) in male Wistar rats, as well as to explore the potential mechanisms of action.

MATERIALS AND METHODS

The antinociceptive activity of TREO and its main constituents, quercetin (Qc) was assessed using the formalin-induced paw licking test. Moreover, the potential mechanisms of antinociception were evaluated through various competitive and non-competitive antagonisms. Additionally, the antineuropathic potential was investigated using the cervical spinal cord hemi-contusion (CCS) model, and the role of phosphorylated Stat-3 was analyzed using Western blotting.

RESULTS

TREO exerted significant antinociceptive activity (P < 0.01) in both phases of the formalin-induced test; however, its effects were more pronounced in the second phase. Modulators of the NO-cGMP-K+ channel pathway significantly reversed the antinociceptive activity of TREO (P < 0.05). Additionally, antagonists of TRPV1 and TRPV2, as well as CB1 and GABAA receptors, significantly reversed the antinociceptive effects of TREO (P < 0.05). In another study, both TREO and Qc significantly attenuated hyperalgesia and mechanical allodynia (P < 0.01) when evaluated using the CCS-induced nociception model. Notably, TREO also reduced the expression levels of interleukin-1 beta, interleukin-2, and tumor necrosis factor alpha in CCS-induced rats (P < 0.05).

CONCLUSION

TREO and Qc exhibit both antinociceptive and anti-neuropathic activities. The antinociceptive effects are partially mediated through the NO-cGMP-K+ channel pathways, along with the activation of TRPV, GABA, and cannabinoid receptors. Furthermore, the anti-neuropathic activity of TREO may be partially regulated through the inhibition of cytokines.

The Unripe Carob Extract (Ceratonia siliqua L.) as a Potential Therapeutic Strategy to Fight Oxaliplatin-Induced Neuropathy

BACKGROUND

Oxaliplatin-induced neuropathy (OIN) is a severe painful condition that strongly affects the patient's quality of life and cannot be counteracted by the available drugs or adjuvants. Thus, several efforts are devoted to discovering substances that can revert or reduce OIN, including natural compounds. The carob tree, Ceratonia siliqua L., possesses several beneficial properties. However, its antalgic properties have not been substantially investigated and only a few investigations have been conducted on the unripe carob (up-CS) pods. Thus, the aims of this study were to evaluate for the first time the unripe variety of Apulian carob, chemically characterized and profiled as antioxidant potential of polyphenolic compounds as well as to investigate the ability of up-CS to reduce the neurotoxicity in a mouse model of oxaliplatin-induced neuropathic pain.

METHODS

By UHPLC-HRMS/MS analyses, 50 phenolic compounds, belonging mainly to n-galloylated glucoses and flavonoids were detected.

RESULTS

In a mouse model of oxaliplatin-induced neurotoxicity (2.4 mg/kg, 10 injections over two weeks), acute per os treatment with up-CS provoked a dose-dependent pain-relieving effect that completely counteracted oxaliplatin hypersensitivity at the dose of 200 mg/kg. Repeated oral administration of up-CS (100 mg/kg), concomitantly with oxaliplatin injection, exerted a protective effect against the development of thermal and mechanical allodynia. In addition, up-CS exerted a neuroprotective role against oxaliplatin-induced astrocytes activation in the spinal cord measured as GFAP-fluorescence intensity.

CONCLUSIONS

Overall, our study contributes to the knowledge on up-CS properties by highlighting its protective activity in the painful condition related to the administration of oxaliplatin.

Polyphenols: From Classification to Therapeutic Potential and Bioavailability

Though ubiquitous in nature, polyphenols gained scientific prominence only after the pioneering work of researchers like E. Fischer and K. Freudenberg, who demonstrated their potential beyond traditional applications, such as in the leather industry. Today, these bioactive compounds are recognized for their diverse therapeutic roles, including their use as adjuvants in cancer treatment, cancer prevention, and their anti-inflammatory and antioxidant properties. Additionally, polyphenols have demonstrated benefits in managing obesity, cardiovascular diseases, and neuromodulation. Their synthesis is influenced by environmental and genetic factors, with their concentrations varying based on the intensity of these variables, as well as the stage of ripening. This review provides a comprehensive overview of polyphenols, covering their classification, chemical structures, and bioavailability. The mechanisms influencing bioavailability, bioaccessibility, and bioactivity are explored in detail, alongside an introduction to their bioactive effects and associated metabolic pathways. Specific examples, such as the bioavailability of polyphenols in coffee and various types of onions, are analyzed. Despite their promising biological activities, a significant limitation of polyphenols lies in their inherently low oral bioavailability. However, their systemic circulation and the bioactive by-products formed during digestion present exciting opportunities for further research and application.

Trifluoro-Icaritin Ameliorates Neuroinflammation Against Complete Freund's Adjuvant-Induced Microglial Activation by Improving CB2 Receptor-Mediated IL-10/β-endorphin Signaling in the Spinal Cord of Rats

The underlying pathogenesis of chronic inflammatory pain is greatly complex, but the relevant therapies are still unavailable. Development of effective candidates for chronic inflammatory pain is highly urgent. We previously identified that trifluoro-icaritin (ICTF) exhibited a significant therapeutic activity against complete Freund's adjuvant (CFA)-induced chronic inflammatory pain, however, the precise mechanisms remain elusive. Here, the paw withdrawal threshold (PWT), paw withdrawal latency (PWL), and CatWalk gait analysis were used to determine the pain-related behaviors. The expression and co-localization of pain-related signaling molecules were detected by Western blot and immunofluorescence staining. Our results demonstrated that ICTF (3.0 mg/kg, i.p.) effectively attenuated mechanical allodynia, thermal hyperalgesia and improved motor dysfunction induced by CFA, and the molecular docking displayed that CB2 receptor may be the therapeutic target of ICTF. Furthermore, ICTF not only up-regulated the levels of CB2 receptor, IL-10, β-endorphin and CD206, but also reduced the expression of P2Y12 receptor, NLRP3, ASC, Caspase-1, IL-1β, CD11b, and iNOS in the spinal cord of CFA rats. Additionally, the immunofluorescence staining from the spinal cord showed that ICTF significantly increased the co-expression between the microglial marker Iba-1 and CB2 receptor, IL-10, β-endorphin, respectively, but markedly decreased the co-localization between Iba-1 and P2Y12 receptor. Conversely, intrathecal administration of CB2 receptor antagonist AM630 dramatically reversed the inhibitory effects of ICTF on CFA-induced chronic inflammatory pain, leading to a promotion of pain hypersensitivity, abnormal gait parameters, microglial activation, and up-regulation of P2Y12 receptor and NLRP3 inflammasome, as well as the inhibition of CB2 receptor and IL-10/β-endorphin cascade. Taken together, these findings highlighted that ICTF alleviated CFA-induced neuroinflammation by enhancing CB2 receptor-mediated IL-10/β-endorphin signaling and suppressing microglial activation in the spinal cord, and uncovered that CB2 receptor may be exploited as a novel and promising target for ICTF treatment of chronic inflammatory pain.

Association between dietary intake of flavonoids and chronic low back pain: a cross-sectional study

Aim

The purpose of this study was to explore the association between flavonoids intake and chronic low back pain (CLBP).

Methods

This cross-sectional study analyzed data from the National Health and Nutrition Examination Survey. Dietary flavonoids intake was assessed using a two-day recall questionnaire on dietary intake. CLBP was defined based of self-reported question. Weighted univariate and multivariate logistic regression models were performed to evaluate the relationship between flavonoids intake and CLBP. Additionally, subgroup analyses were conducted based on age, sedentary behavior time, arthritis, depression, and sleep disorder.

Results

A total of 3,136 adults were included, and 460 participants developed CLBP. After adjusting confounders, compared with the lowest total flavonoids intake tertile (reference group), flavonoids intake with highest tertile (>170 mg) was associated with reduced odds of CLBP [odds ratio (OR) =0.74, 95% confidence interval (CI): 0.57-0.95]. This relationship of flavonoids intake with CLBP remained statistically significant among participants aged ≥45 years (OR = 0.52, 95%CI: 0.35-0.76), with sedentary behavior time of >3 h (OR = 0.60, 95%CI: 0.41-0.86), with arthritis (OR = 0.51, 95%CI: 0.29-0.90), depression (OR = 0.48, 95%CI: 0.24-0.98), and sleep disorder (OR = 0.27, 95%CI: 0.12-0.60).

Conclusion

Higher flavonoids intake was found to be negatively associated with the likelihood of CLBP. For the general adult population, consuming foods rich in flavonoids may be linked to a reduced risk of CLBP.

Mahuang Fuzi Xixin decoction: A potent analgesic for neuropathic pain targeting the NMDAR2B/CaMKIIα/ERK/CREB pathway

Neuropathic pain (NeP) is a condition charactesized by nervous system injury or dysfunction that affects a significant portion of the population. Current treatments are ineffective, highlighting the need for novel therapeutic approaches. Mahuang Fuzi Xixin decoction (MFXD) has shown promise for treating pain conditions in clinical practice; however, its potential against NeP and the underlying mechanisms remain unclear. This study identified 35 compounds in MFXD using ultra-high performance liquid chromatography coupled with high-resolution mass spectrometry (UHPLC-HRMS). The analgesic effects of MFXD on chronic constriction injury (CCI) rats were evaluated through the detection of mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL). The analgesic effects of MFXD in rats with chronic constriction injury (CCI) were evaluated by measuring the mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL). Low-dose MFXD (L-MFXD) group (4.8 g/kg) and high-dose MFXD (H-MFXD) group (9.6 g/kg) exhibited significantly higher MWT and TWL values than the CCI group on days 11 and 15 post-CCI surgery, substantiating the remarkable analgesic efficacy of MFXD. Network pharmacology analysis identified 58 key targets enriched in pathways such as long-term potentiation (LTP) and glutamatergic synapse. The MCODE algorithm further identified core targets with significant enrichment in LTP. Molecular docking revealed that mesaconitine, rosmarinic acid, and delgrandine from MFXD exhibited high binding affinity with NMDAR2B (-11 kcal/mol), CaMKIIα (-14.3 kcal/mol), and ERK (-10.8 kcal/mol). Western blot and immunofluorescence confirmed that H-MFXD significantly suppressed the phosphorylation levels of NMDAR2B, CaMKIIα, ERK, and CREB in the spinal cord tissue of CCI rats. In conclusion, this study demonstrates that MFXD possesses potent analgesic effects on NeP by suppressing the NMDAR2B/CaMKIIα/ERK/CREB signalling pathway. This study unlocks a path toward potentially revolutionising NeP treatment with MFXD, encouraging further research and clinical development.

Assessment of oral toxicity of Moringa oleifera Lam aqueous extract and its effect on gout induced in a murine model

Background and Aim

Although widely employed in traditional remedies globally, the safety and efficacy of Moringa oleifera remain inadequately documented through scientific research. This study evaluated the oral toxicity of M. oleifera leaf aqueous extract (MoAE) and its impact on gout-induced rats.

Materials and Methods

2000 mg/kg was given in a single dose during the acute oral toxicity test, while 100 mg/kg, 250 mg/kg, and 500 mg/kg were given daily for 28 days in the repeated dose toxicity test. 100 mg/kg, 250 mg/kg, and 500 mg/kg MoAE doses were administered during the assessment of its impact on gout caused by monosodium urate. In the hyperuricemia model induced by oxonic acid, serum uric acid levels were assessed and pain response was measured through acetic acid-induced writhing.

Results

In acute oral and 28-day repeated dose tests, no indications of toxicity were detected, while MoAE alleviated ankle joint swelling and reduced serum uric acid concentrations in arthritic rats, causing a significant reduction in acetic acid-induced contortions.

Conclusion

No acute oral toxicity or toxicity in 28-day repeated doses was found for MoAE, while it exhibited antiarthritic, antihyperuricemic, and pain-relieving effects in the murine model.

Toxicity Evaluation of a Non-Pain Pharmacopuncture Extract Using a Bacterial Reverse Mutation Test

Objectives

The objective of this study was to assess the genotoxicity of a no-pain pharmacopuncture (NPP) extract developed in 2022 using a bacterial reverse mutation assay, aiming to further substantiate the safety profile of NPP.

Methods

The genotoxicity evaluation involved a bacterial reverse mutation assay to assess the mutagenic potential of NPP extracts with and without metabolic activation. Histidine-requiring Salmonella typhimurium strains (TA98, TA100, TA1535, and TA1537) and tryptophan-requiring Escherichia coli strains (WP2uvrA) were used in the assay.

Results

The NPP extract did not induce a revertant colony count exceeding two times that of the negative control at any dose level in any of the tested strains, both with and without metabolic activation. Additionally, no growth inhibition or precipitation was observed in the presence of NPP.

Conclusion

Based on the findings, it can be concluded that the NPP extract exhibited no mutagenic potential in the in vitro genotoxicity tests conducted.

Molecular docking of quercetin: a promising approach for the development of new anti-inflammatory and analgesic drugs

The aim of this study is to investigate the antinociceptive, anti-inflammatory and antipyretic effects of quercetin. Additionally, molecular docking studies were conducted to evaluate potential interactions between quercetin and various molecular targets. Animal models were used to conduct a comprehensive pharmacological investigation of quercetin. Evaluation of analgesic activity revealed a reduction in the number of abdominal cramps during the twisting test and inhibition of pain during the second phase of the formaldehyde test. Additionally, evaluation of its anti-inflammatory activity showed a reduction in ear oedema. However, it is important to note that quercetin administration has not been shown to significantly reduce yeast-induced hyperthermia. The docking study revealed the high inhibitory potential of quercetin against the COX-2 receptor.

Orientin Reduces the Effects of Repeated Procedural Neonatal Pain in Adulthood: Network Pharmacology Analysis, Molecular Docking Analysis, and Experimental Validation

Background

Premature infants often undergo painful procedures and consequently experience repeated procedural neonatal pain. This can elicit hyperalgesia and cognitive impairment in adulthood. Treatments for neonatal pain are limited. Orientin is a flavonoid C-glycoside that has repeatedly been shown to have pharmacological effects in the past decades. The aim of this study was to systematically explore the effect of orientin on repeated procedural neonatal pain using network pharmacology, molecular docking analysis, and experimental validation.

Methods

Several compound-protein databases and disease-protein databases were employed to identify proteins that were both predicted targets of orientin and involved in neonatal pain. A protein-protein interaction (PPI) network was constructed, and Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses were performed to explore the potential mechanism of action. Molecular docking analysis was employed to calculate the binding energy and visualize the interactions between orientin and potential target proteins. Finally, a mouse model of repeated procedural neonatal pain was established and orientin was administered for 6 days. The mechanical and thermal pain thresholds were assessed in neonates and adult mice. A Morris water maze was employed to investigate cognitive impairment in adult mice.

Results

A total of 286 proteins that were both predicted targets of orientin and involved in neonatal pain were identified. The hub proteins were SRC, HSP90AA1, MAPK1, RHOA, EGFR, AKT1, PTPN11, ESR1, RXRA, and HRAS. GO analysis indicated that the primary biological process (BP), molecular function (MF), and cellular component (CC) were protein phosphorylation, protein kinase activity, and vesicle lumen, respectively. KEGG analysis revealed that the mitogen-activated protein kinase (MAPK) signaling pathway may be the key to the mechanism of action. Molecular docking analysis showed the high binding affinities of orientin for MAPK1, MAPK8, and MAPK14. In mice, orientin inhibited the hyperalgesia in the pain threshold tests in neonates and adult mice and cognitive impairment in adult mice. Immunofluorescence showed that phosphorylated MAPK1 (p-ERK) protein levels in the hippocampus and spinal dorsal horn were downregulated by orientin.

Conclusion

The findings suggested that orientin alleviates neonatal pain, and the MAPK signaling pathway is involved.

Reversal of Peripheral Neuropathic Pain by the Small-Molecule Natural Product Narirutin via Block of Nav1.7 Voltage-Gated Sodium Channel

Neuropathic pain is a refractory chronic disease affecting millions of people worldwide. Given that present painkillers have poor efficacy or severe side effects, developing novel analgesics is badly needed. The multiplex structure of active ingredients isolated from natural products provides a new source for phytochemical compound synthesis. Here, we identified a natural product, Narirutin, a flavonoid compound isolated from the Citrus unshiu, showing antinociceptive effects in rodent models of neuropathic pain. Using calcium imaging, whole-cell electrophysiology, western blotting, and immunofluorescence, we uncovered a molecular target for Narirutin's antinociceptive actions. We found that Narirutin (i) inhibits Veratridine-triggered nociceptor activities in L4-L6 rat dorsal root ganglion (DRG) neurons, (ii) blocks voltage-gated sodium (Na_V) channels subtype 1.7 in both small-diameter DRG nociceptive neurons and human embryonic kidney (HEK) 293 cell line, (iii) does not affect tetrodotoxin-resistant (TTX-R) Na_V channels, and (iv) blunts the upregulation of Na_v1.7 in calcitonin gene-related peptide (CGRP)-labeled DRG sensory neurons after spared nerve injury (SNI) surgery. Identifying Na_v1.7 as a molecular target of Narirutin may further clarify the analgesic mechanism of natural flavonoid compounds and provide an optimal idea to produce novel selective and efficient analgesic drugs.