Intrathecal [6]-Gingerol Administration Alleviates Peripherally induced Neuropathic Pain in Male Sprague-Dawley Rats

Ginger alleviates mechanical hypersensitivity and anxio-depressive behavior in rats with diabetic neuropathy through beneficial actions on gut microbiome composition, mitochondria, and neuroimmune cells of colon and spinal cord

The relationship among gut microbiota, mitochondrial dysfunction/neuroinflammation, and diabetic neuropathic pain (DNP) has received increased attention. Ginger has antidiabetic and analgesic effects because of its anti-inflammatory property. We examined the effects of gingerols-enriched ginger (GEG) supplementation on pain-associated behaviors, gut microbiome composition, and mitochondrial function and neuroinflammation of colon and spinal cord in DNP rats. Thirty-three male rats were randomly divided into 3 groups: control group, DNP group (high-fat diet plus single dose of streptozotocin at 35 mg/kg body weight, and GEG group (DNP+GEG at 0.75% in the diet for 8 weeks). Von Frey and open field tests were used to assess pain sensitivity and anxio-depressive behaviors, respectively. Colon and spinal cord were collected for gene expression analysis. 16S rRNA gene sequencing was done from cecal samples and microbiome data analysis was performed using QIIME 2. GEG supplementation mitigated mechanical hypersensitivity and anxio-depressive behavior in DNP animals. GEG supplementation suppressed the dynamin-related protein 1 protein expression (colon) and gene expression (spinal cord), astrocytic marker GFAP gene expression (colon and spinal cord), and tumor necrosis factor-α gene expression (colon, P < .05; spinal cord, P = .0974) in DNP rats. GEG supplementation increased microglia/macrophage marker CD11b gene expression in colon and spinal cord of DNP rats. GEG treatment increased abundance of Acinetobacter, Azospirillum, Colidextribacter, and Fournierella but decreased abundance of Muribaculum intestinale in cecal feces of rats. This study demonstrates that GEG supplementation decreased pain, anxio-depression, and neuroimmune cells, and improved the composition of gut microbiomes and mitochondrial function in rats with diabetic neuropathy.

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.

The Effect of Ginger and Its Sub-Components on Pain

Zingiber officinale Roscoe (ginger) has long been used as an herbal medicine to treat various diseases, and its main sub-components, [6]-gingerol and [6]-shogaol, were also reported to have anti-inflammatory, anti-oxidant, and anti-tumor effects. However, their effects on various types of pain and their underlying mechanisms of action have not been clearly analyzed and understood yet. Thus, in this review, by analyzing 16 studies that used Z. officinale, [6]-gingerol, and [6]-shogaol on mechanical, spontaneous and thermal pain, their effects and mechanisms of action have been analyzed. Pain was induced by either nerve injury or chemical injections in rodents. Nine studies analyzed the analgesic effect of Z. officinale, and four and three studies focused on [6]-gingerol and [6]-shogaol, respectively. Seven papers have demonstrated the underlying mechanism of action of their analgesic effects. Studies have focused on the spinal cord and one on the dorsal root ganglion (DRG) neurons. Involvement and change in the function of serotonergic receptors (5-HT_1A, _B, _D, and _5A), transient receptor potential vanilloid 1 (TRPV1), N-methyl-D-aspartate (NMDA) receptors, phosphorylated extracellular signal-regulated kinase 1/2 (pERK1/2), histone deacetylase 1 (HDAC1), voltage-gated sodium channel 1.8 (Na_v1.8), substance P (SP), and sciatic nerve’s morphology have been observed.

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

Among different types of chronic pain, neuropathic pain (NP), arising from damage to the nervous system, including peripheral fibers and central neurons, is notoriously difficult to treat and affects 7-10% of the general population. Currently available treatment options for NP are limited and opioid analgesics have severe side effects and can result in opioid use disorder. Recent studies have exhibited the role of dietary bioactive compounds in the mitigation of NP. Here, we assessed the effects of commonly consumed bioactive compounds (ginger, curcumin, omega-3 polyunsaturated fatty acids, epigallocatechin gallate, resveratrol, soy isoflavones, lycopene, and naringin) on NP and NP-related neuroinflammation. Cellular studies demonstrated that these bioactive compounds reduce inflammation via suppression of NF-κB and MAPK signaling pathways that regulate apoptosis/cell survival, antioxidant, and anti-inflammatory responses. Animal studies strongly suggest that these regularly consumed bioactive compounds have a pronounced anti-NP effect as shown by decreased mechanical allodynia, mechanical hyperalgesia, thermal hyperalgesia, and cold hyperalgesia. The proposed molecular mechanisms include (1) the enhancement of neuron survival, (2) the reduction of neuronal hyperexcitability by activation of antinociceptive cannabinoid 1 receptors and opioid receptors, (3) the suppression of sodium channel current, and (4) enhancing a potassium outward current in NP-affected animals, triggering a cascade of chemical changes within, and between neurons for pain relief. Human studies administered in this area have been limited. Future randomized controlled trials are warranted to confirm the findings of preclinical efficacies using bioactive compounds in patients with NP.

Dietary supplementation of gingerols- and shogaols-enriched ginger root extract attenuate pain-associated behaviors while modulating gut microbiota and metabolites in rats with spinal nerve ligation

Neuroinflammation is a central factor in neuropathic pain (NP). Ginger is a promising bioactive compound in NP management due to its anti-inflammatory property. Emerging evidence suggests that gut microbiome and gut-derived metabolites play a key role in NP. We evaluated the effects of two ginger root extracts rich in gingerols (GEG) and shogaols (SEG) on pain sensitivity, anxiety-like behaviors, circulating cell-free mitochondrial DNA (ccf-mtDNA), gut microbiome composition, and fecal metabolites in rats with NP. Sixteen male rats were divided into four groups: sham, spinal nerve ligation (SNL), SNL+0.75%GEG in diet, and SNL+0.75%SEG in diet groups for 30 days. Compared to SNL group, both SNL+GEG and SNL+SEG groups showed a significant reduction in pain- and anxiety-like behaviors, and ccf-mtDNA level. Relative to the SNL group, both SNL+GEG and SNL+SEG groups increased the relative abundance of Lactococcus, Sellimonas, Blautia, Erysipelatoclostridiaceae, and Anaerovoracaceae, but decreased that of Prevotellaceae UCG-001, Rikenellaceae RC9 gut group, Mucispirillum and Desulfovibrio, Desulfovibrio, Anaerofilum, Eubacterium siraeum group, RF39, UCG-005, Lachnospiraceae NK4A136 group, Acetatifactor, Eubacterium ruminantium group, Clostridia UCG-014, and an uncultured Anaerovoracaceae. GEG and SEG had differential effects on gut-derived metabolites. Compared to SNL group, SNL+GEG group had higher level of 1'-acetoxychavicol acetate, (4E)-1,7-Bis(4-hydroxyphenyl)-4-hepten-3-one, NP-000629, 7,8-Dimethoxy-3-(2-methyl-3-buten-2-yl)-2H-chromen-2-one, 3-{[4-(2-Pyrimidinyl)piperazino]carbonyl}-2-pyrazinecarboxylic acid, 920863, and (1R,3R,7R,13S)-13-Methyl-6-methylene-4,14,16-trioxatetracyclo[11.2.1.0∼1,10∼.0∼3,7∼]hexadec-9-en-5-one, while SNL+SEG group had higher level for (±)-5-[(tert-Butylamino)-2'-hydroxypropoxy]-1_2_3_4-tetrahydro-1-naphthol and dehydroepiandrosteronesulfate. In conclusion, ginger is a promising functional food in the management of NP, and further investigations are necessary to assess the role of ginger on gut-brain axis in pain management.

JI017 Attenuates Oxaliplatin-Induced Cold Allodynia via Spinal TRPV1 and Astrocytes Inhibition in Mice

Oxaliplatin, a well-known chemotherapeutic agent, can induce severe neuropathic pain, which can seriously decrease the quality of life of patients. JI017 is an herb mixture composed of Aconitum carmichaelii, Angelica gigas, and Zingiber officinale. Its anti-tumor effect has been reported; however, the efficacy of JI017 against oxaliplatin-induced allodynia has never been explored. Single oxaliplatin injection [6 mg/kg, intraperitoneal, (i.p.)] induced both cold and mechanical allodynia, and oral administration of JI017 (500 mg/kg) alleviated cold but not mechanical allodynia in mice. Real-time polymerase chain reaction (PCR) analysis demonstrated that the upregulation of mRNA of spinal transient receptor potential vanilloid 1 (TRPV1) and astrocytes following oxaliplatin injection was downregulated after JI017 treatment. Moreover, TRPV1 expression and the activation of astrocytes were intensely increased in the superficial area of the spinal dorsal horn after oxaliplatin treatment, whereas JI017 suppressed both. The administration of TRPV1 antagonist [capsazepine, intrathecal (i.t.), 10 μg] attenuated the activation of astrocytes in the dorsal horn, demonstrating that the functions of spinal TRPV1 and astrocytes are closely related in oxaliplatin-induced neuropathic pain. Altogether, these results suggest that JI017 may be a potent candidate for the management of oxaliplatin-induced neuropathy as it decreases pain, spinal TRPV1, and astrocyte activation.

Zingiber officinale Roscoe Rhizomes Attenuate Oxaliplatin-Induced Neuropathic Pain in Mice

Oxaliplatin is a platinum derivative chemotherapeutic drug widely used against cancers, but even a single treatment can induce a severe allodynia that requires treatment interruption and dose diminution. The rhizome of Zingiber officinale roscoe (Z. officinale, ginger), has been widely used in traditional medicine to treat various diseases causing pain; however, its effect against oxaliplatin-induced neuropathic pain has never been assessed. In mice, a single oxaliplatin (6 mg/kg, i.p.) treatment induced significant cold and mechanical allodynia. Cold and mechanical allodynia were assessed by acetone drop and von Frey filament tests, respectively. Water extracts of Z. officinale (100, 300, and 500 mg/kg, p.o.) significantly attenuated both cold and mechanical allodynia induced by oxaliplatin. Intrathecal pre-treatment with the antagonist 5-HT1A (NAN-190, i.t., 1 μg), but not with the antagonist 5-HT2A (ketanserin, i.t., 1 μg), significantly blocked the analgesic effect of Z. officinale against both cold and mechanical allodynia. However, 5-HT3 antagonist (MDL-72222, i.t., 15 μg) administration only blocked the anti-allodynic effect of Z. officinale against cold allodynia. Real-time PCR analysis demonstrated that Z. officinale significantly increased the mRNA expression of the spinal 5-HT1A receptor that was downregulated after oxaliplatin injection. These results suggest that Z. officinale may be a viable treatment option for oxaliplatin-induced neuropathic pain.

Use of medicinal plants for headache, and their potential implication in medication-overuse headache: Evidence from a population-based study in Nepal

Background

In Nepal, traditional treatment using medicinal plants is popular. Whereas medication-overuse headache is, by definition, caused by excessive use of acute headache medication, we hypothesized that medicinal plants, being pharmacologically active, were as likely a cause.

Methods

We used data from a cross-sectional, nationwide population-based study, which enquired into headache and use of medicinal plants and allopathic medications. We searched the literature for pharmacodynamic actions of the medicinal plants.

Results

Of 2100 participants, 1794 (85.4%) reported headache in the preceding year; 161 (7.7%) reported headache on ≥15 days/month, of whom 28 (17.4%) had used medicinal plants and 117 (72.7%) allopathic medication(s). Of 46 with probable medication-overuse headache, 87.0% (40/46) were using allopathic medication(s) and 13.0% (6/46) medicinal plants, a ratio of 6.7:1, higher than the overall ratio among those with headache of 4.9:1 (912/185). Of 60 plant species identified, 49 were pharmacodynamically active on the central nervous system, with various effects of likely relevance in medication-overuse headache causation.

Conclusions

MPs are potentially a cause of medication-overuse headache, and not to be seen as innocent in this regard. Numbers presumptively affected in Nepal are low but not negligible. This pioneering project provides a starting point for further research to provide needed guidance on use of medicinal plants for headache.

Daikenchuto attenuates visceral pain and suppresses eosinophil infiltration in inflammatory bowel disease in murine models

BACKGROUND AND AIM

Daikenchuto (DKT), a traditional Japanese formula, comprises four herbal medicines and is used for abdominal pain. Inflammatory bowel disease (IBD) includes ulcerative colitis (UC) and Crohn's disease (CD) and is characterized by colonic inflammation and chronic abdominal pain. The present study aimed to investigate whether DKT suppresses colonic hypersensitivity and inflammation associated with IBD in animal models.

METHODS

Sprague-Dawley rats were administered 4% sodium dextran sulfate (DSS) or trinitrobenzene sulfate (TNBS) in the colon to establish UC or CD models, respectively. DKT and 5-aminosalicylic acid (5-ASA) were administered orally once a day from Days 3 to 7 after induction of colitis. On Day 7, visceral pain and inflammation were evaluated by measuring the visceromotor response (VMR) to colorectal distention (CRD) and inflammatory indicators, including histological score, length of leukocyte infiltration, MPO activity, and eosinophil count.

RESULTS

DSS and TNBS increased VMR to CRD and the inflammation indicators. DKT, but not 5-ASA, suppressed the VMR to CRD in DSS- and TNBS-treated rats. DKT and 5-ASA decreased the eosinophil count in both IBD models. In DSS-treated rats, 5-ASA, but not DKT, suppressed the MPO activity. In TNBS-treated rats, neither 5-ASA nor DKT suppressed MPO activity.

CONCLUSION

These results suggest that DKT is beneficial for abdominal pain associated with IBD. The anti-inflammatory effect of DKT on IBD may involve inhibition of eosinophils. The mechanism of anti-inflammatory effect of DKT partially differs from that of 5-ASA. Coapplication of DKT and conventional medicine may produce a positive synergy effect for IBD treatment.

Eugenol and Other Vanilloids Hamper Caenorhabditis elegans Response to Noxious Heat

Eugenol, a known vanilloid, was frequently used in dentistry as a local analgesic in addition, antibacterial and neuroprotective effects were also reported. Eugenol, capsaicin and many vanilloids are interacting with the transient receptor potential vanilloid 1 (TRPV1) in mammals and the TRPV1 is activated by noxious heat. The pharmacological manipulation of the TRPV1 has been shown to have therapeutic value. Caenorhabditis elegans (C. elegans) express TRPV orthologs (e.g. OCR-2, OSM-9) and it is a commonly used animal model system to study nociception as it displays a well-defined and reproducible nocifensive behavior. After exposure to vanilloid solutions, C. elegans wild type (N2) and mutants were placed on petri dishes divided in quadrants for heat stimulation. Thermal avoidance index was used to phenotype each tested C. elegans experimental groups. The results showed that eugenol, vanillin and zingerone can hamper nocifensive response of C. elegans to noxious heat (32-35 °C) following a sustained exposition. Also, the effect was reversed 6 h post exposition. Furthermore, eugenol and vanillin did not target specifically the OCR-2 or OSM-9 but zingerone did specifically target the OCR-2 similarly to capsaicin. Further structural and physicochemical analyses were performed. Key parameters for quantitative structure-property relationships (QSPR), quantitative structure-activity relationships (QSAR) and frontier orbital analyses suggest similarities and dissimilarities amongst the tested vanilloids and capsaicin in accordance with the relative anti-nociceptive effects observed.

Capsaicin and Its Analogues Impede Nocifensive Response of Caenorhabditis elegans to Noxious Heat

Capsaicin is the most abundant pungent molecule identified in red chili peppers, and it is widely used for food flavoring, in pepper spray for self-defense devices and recently in ointments for the relief of neuropathic pain. Capsaicin and several other related vanilloid compounds are secondary plant metabolites. Capsaicin is a selective agonist of the transient receptor potential channel, vanilloid subfamily member 1 (TRPV1). After exposition to vanilloid solution, Caenorhabditis elegans wild type (N2) and mutants were placed on petri dishes divided in quadrants for heat stimulation. Thermal avoidance index was used to phenotype each tested C. elegans experimental groups. The data revealed for the first-time that capsaicin can impede nocifensive response of C. elegans to noxious heat (32-35 °C) following a sustained exposition. The effect was reversed 6 h post capsaicin exposition. Additionally, we identified the capsaicin target, the C. elegans transient receptor potential channel OCR-2 and not OSM-9. Further experiments also undoubtedly revealed anti-nociceptive effect for capsaicin analogues, including olvanil, gingerol, shogaol and curcumin.

Ginger extract and its compound, 6-shogaol, attenuates painful diabetic neuropathy in mice via reducing TRPV1 and NMDAR2B expressions in the spinal cord

ETHNOPHARMACOLOGICAL RELEVANCE

In silico data revealed that the active compound of ginger (Zingiber officinale Roscoe), 6-shogaol, has strong affinity toward transient receptor potential vanilloid-1 (TRPV-1). TRPV-1 is expressed in nervous tissue and pancreatic β-cells. Prolonged induction of TRPV-1 is related to the expression of N-methyl-D-aspartate receptor subunit 2B (NMDAR2B). However, there are no data on TRPV-1 and NMDAR2B expressions in nervous tissue after 6-shogaol or ginger extract treatment nor pancreatic islet morphology and insulin expression in mice model of painful diabetic neuropathy (PDN).

AIM OF THE STUDY

This study aimed to investigate the mechanism of action of ginger extract and its compound, 6-shogaol, on pancreatic islets as well as on expressions of TRPV-1 and NMDAR2B in the spinal cord of streptozotocin (STZ)-induced mice model of PDN.

MATERIALS AND METHODS

Sixty-four 5-6 weeks old male-Balb/C mice were induced with 110 mg/kgBW STZ i.p., while eight mice were used as control group. Mice with blood glucose level ≥200 mg/d, that suffered hyperalgesia and allodynia were classified as PDN mice. Hot plate and von Frey filament tests were performed once a week until termination. At day 28 after considered as PDN, ginger extracts, 6-shogaol or gabapentin as control treatment were given once daily for 21 days until day 49, except for the diabetic control group. Upon termination, mice' pancreas were fixed, processed as paraffin sections and stained with hematoxylin eosin. Total volume of pancreatic islets was estimated using Cavalieri methods. Immunohistochemistry on pancreatic sections were performed to observe insulin expression. mRNA was extracted from lumbar segments of the spinal cord, followed by cDNA preparation and quantitative Real-Time Polymerase Chain Reaction (qRT-PCR) to measure the expressions of TRPV1 and NMDAR2B. The mean differences between groups were analyzed using one-way analysis of variance (ANOVA) with p < 0.05 considered statistically significant.

RESULTS

Ginger extracts and 6-shogaol alleviated hyperalgesia and allodynia. The groups that received ginger extract 400 mg/kgBW or 6-shogaol 15 mg/kgBW had significantly lower TRPV1 and NMDAR2B expressions in the spinal cord compared to the diabetic control group (p < 0.001; p < 0.05). However, no differences in volume of pancreatic islets (p > 0.05) nor insulin expression were observed in all PDN groups.

CONCLUSION

Ginger extracts and its compound, 6-shogaol, reduced pain symptoms in PDN via its effect on decreasing TRPV1 and NMDAR2B expressions in the spinal cord, with very limited effect on pancreatic islets.

Structural biology of thermoTRPV channels

Essential for physiology, transient receptor potential (TRP) channels constitute a large and diverse family of cation channels functioning as cellular sensors responding to a vast array of physical and chemical stimuli. Detailed understanding of the inner workings of TRP channels has been hampered by a lack of atomic structures, though structural biology of TRP channels has been an enthusiastic endeavor since their molecular identification two decades ago. These multi-domain integral membrane proteins, exhibiting complex polymodal gating behavior, have been a challenge for traditional X-ray crystallography, which requires formation of well-ordered protein crystals. X-ray structures remain limited to a few TRP channel proteins to date. Fortunately, recent breakthroughs in single-particle cryo-electron microscopy (cryo-EM) have enabled rapid growth of the number of TRP channel structures, providing tremendous insights into channel gating and regulation mechanisms and serving as foundations for further mechanistic investigations. This brief review focuses on recent exciting developments in structural biology of a subset of TRP channels, the calcium-permeable, non-selective and thermosensitive vanilloid subfamily of TRP channels (TRPV1-4), and the permeation and gating mechanisms revealed by structures.

Antiallodynic effect induced by [6]-gingerol in neuropathic rats is mediated by activation of the serotoninergic system and the nitric oxide-cyclic guanosine monophosphate-adenosine triphosphate-sensitive K+ channel pathway

The present study evaluated the possible antiallodynic effect induced by [6]-gingerol in rats with L5-L6 spinal nerve ligation (SNL). Moreover, we determined the possible mechanism underlying the antiallodynic effect induced by [6]-gingerol in neuropathic rats. The animals underwent L5-L6 SNL for the purpose of developing tactile allodynia. Tactile allodynia was measured with von Frey filaments. Intrathecal administration of [6]-gingerol reversed SNL-induced tactile allodynia. The [6]-gingerol-induced antiallodynic effect was prevented by the intrathecal administration of methiothepin (30 μg per rat; nonselective 5-hydroxytryptamine [5-HT] antagonist), WAY-100635 (6 μg per rat; selective 5-HT_1A receptor antagonist), SB-224289 (5 μg per rat; selective 5-HT_1B receptor antagonist), BRL-15572 (4 μg per rat; selective 5-HT_1D receptor antagonist), and SB-659551 (6 μg per rat; selective 5-HT_5A receptor antagonist), but naloxone (50 μg per rat; nonselective opioid receptor antagonist) did not prevent the [6]-gingerol-induced antiallodynic effect. Moreover, intrathecal administration of Nω-nitro-l-arginine methyl ester (100 μg per rat; nonselective nitric oxide [NO] synthase inhibitor), 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (10 μg per rat; inhibitor of guanylate cyclase), and glibenclamide (50 μg per rat; channel blocker of adenosine triphosphate [ATP]-sensitive K⁺ channels) prevented the [6]-gingerol-induced antiallodynic effect. These data suggest that the antiallodynic effect induced by [6]-gingerol is mediated by the serotoninergic system involving the activation of 5-HT_1A/1B/1D/5A receptors, as well as the NO-cyclic guanosine monophosphate-ATP-sensitive K⁺ channel pathway but not by the opioidergic system.

Ginger rhizome enhances the anti-inflammatory and anti-nociceptive effects of paracetamol in an experimental mouse model of fibromyalgia

BACKGROUND

The dried rhizome of ginger has been widely used for more than 2500 years in folk medicine for the treatment of various diseases that involve inflammation or are caused by oxidative stress.

AIMS

This study was designed to compare the anti-nociceptive and anti-inflammatory effect of dried powdered ginger rhizome (GR) and paracetamol (APAP) on an experimental mouse model of fibromyalgia syndrome (FMS) induced by intermittent cold stress (ICS).

METHODS

Forty-eight female C57BL/6 J mice were used for the experiments. The animals were allocated in six groups (n = 8). Each group received one of the following treatments for 8 weeks: healthy control, ICS group, ICS + APAP (40 mg/Kg/day), ICS + GR (0.5%); ICS + GR (1%), and ICS + GR (0.5%) + APAP (40 mg/Kg/day). After treatment, symptoms of FMS were induced by intermittent cold stress (ICS).

RESULTS AND CONCLUSIONS

GR consumption improved mechanical and thermal allodynia and mechanical hyperalgesia and improved behavioural changes related to cognitive disturbances, anxiety, and depression. In addition, GR also significantly decreased the inflammatory response of proinflammatory mediators such as NO, PGE2, TXB2, and IL-1β in LPS-stimulated macrophages. The effects of APAP were significantly enhanced by co-administration with GR. These findings provide evidence that the daily consumption of GR enhances the anti-nociceptive effect of APAP in mice, improves other cognitive disturbances associated with chronic pain, and reduces the inflammatory state generated in an experimental FMS model.

Recent development in antihyperalgesic effect of phytochemicals: anti-inflammatory and neuro-modulatory actions

INTRODUCTION

Pain is an unpleasant sensation triggered by noxious stimulation. It is one of the most prevalent conditions, limiting productivity and diminishing quality of life. Non steroidal anti inflammatory drugs (NSAIDs) are widely used as pain relievers in present day practice as pain is mostly initiated due to inflammation. However, due to potentially serious side effects, long term use of these antihyperalgesic drugs raises concern. Therefore there is a demand to search novel medicines with least side effects. Herbal products have been used for centuries to reduce pain and inflammation, and phytochemicals are known to cause fewer side effects. However, identification of active phytochemicals of herbal medicines and clear understanding of the molecular mechanism of their action is needed for clinical acceptance.

MATERIALS AND METHODS

In this review, we have briefly discussed the cellular and molecular changes during hyperalgesia via inflammatory mediators and neuro-modulatory action involved therein. The review includes 54 recently reported phytochemicals with antihyperalgesic action, as per the literature available with PubMed, Google Scholar and Scopus.

CONCLUSION

Compounds of high interest as potential antihyperalgesic agents are: curcumin, resveratrol, capsaicin, quercetin, eugenol, naringenin and epigallocatechin gallate (EGCG). Current knowledge about molecular targets of pain and their regulation by these phytochemicals is elaborated and the scope of further research is discussed.

[6]-Gingerol, from Zingiber officinale, potentiates GLP-1 mediated glucose-stimulated insulin secretion pathway in pancreatic β-cells and increases RAB8/RAB10-regulated membrane presentation of GLUT4 transporters in skeletal muscle to improve hyperglycemia in Leprdb/db type 2 diabetic mice

BACKGROUND

[6]-Gingerol, a major component of Zingiber officinale, was previously reported to ameliorate hyperglycemia in type 2 diabetic mice. Endocrine signaling is involved in insulin secretion and is perturbed in db/db Type-2 diabetic mice. [6]-Gingerol was reported to restore the disrupted endocrine signaling in rodents. In this current study on Leprdb/db diabetic mice, we investigated the involvement of endocrine pathway in the insulin secretagogue activity of [6]-Gingerol and the mechanism(s) through which [6]-Gingerol ameliorates hyperglycemia.

METHODS

Leprdb/db type 2 diabetic mice were orally administered a daily dose of [6]-Gingerol (200 mg/kg) for 28 days. We measured the plasma levels of different endocrine hormones in fasting and fed conditions. GLP-1 levels were modulated using pharmacological approaches, and cAMP/PKA pathway for insulin secretion was assessed by qRT-PCR and ELISA in isolated pancreatic islets. Total skeletal muscle and its membrane fractions were used to measure glycogen synthase 1 level and Glut4 expression and protein levels.

RESULTS

4-weeks treatment of [6]-Gingerol dramatically increased glucose-stimulated insulin secretion and improved glucose tolerance. Plasma GLP-1 was found to be significantly elevated in the treated mice. Pharmacological intervention of GLP-1 levels regulated the effect of [6]-Gingerol on insulin secretion. Mechanistically, [6]-Gingerol treatment upregulated and activated cAMP, PKA, and CREB in the pancreatic islets, which are critical components of GLP-1-mediated insulin secretion pathway. [6]-Gingerol upregulated both Rab27a GTPase and its effector protein Slp4-a expression in isolated islets, which regulates the exocytosis of insulin-containing dense-core granules. [6]-Gingerol treatment improved skeletal glycogen storage by increased glycogen synthase 1 activity. Additionally, GLUT4 transporters were highly abundant in the membrane of the skeletal myocytes, which could be explained by the increased expression of Rab8 and Rab10 GTPases that are responsible for GLUT4 vesicle fusion to the membrane.

CONCLUSIONS

Collectively, our study reports that GLP-1 mediates the insulinotropic activity of [6]-Gingerol, and [6]-Gingerol treatment facilitates glucose disposal in skeletal muscles through increased activity of glycogen synthase 1 and enhanced cell surface presentation of GLUT4 transporters.

Gingerol activates noxious cold ion channel TRPA1 in gastrointestinal tract

TRPA1 channels are non-selective cation channels that could be activated by plant-derived pungent products, including gingerol, a main active constituent of ginger. Ginger could improve the digestive function; however whether ginger improves the digestive function through activating TRPA1 receptor in gastrointestinal tract has not been investigated. In the present study, gingerol was used to stimulate cell lines (RIN14B or STC-1) while depletion of extracellular calcium. TRPA1 inhibitor (rethenium red) and TRPA1 gene silencing via TRPA1-specific siRNA were also used for mechanistic studies. The intracellular calcium and secretion of serotonin or cholecystokinin were measured by fura-2/AM and ELISA. Stimulation of those cells with gingerol increased intracellular calcium levels and the serotonin or cholecystokinin secretion. The gingerol-induced intracellular calcium increase and secretion (serotonin or cholecystokinin) release were completely blocked by ruthenium red, EGTA, and TRPA1-specific siRNA. In summary, our results suggested that gingerol derived from ginger might improve the digestive function through secretion releasing from endocrine cells of the gut by inducing TRPA1-mediated calcium influx.

Gingerols and shogaols: Important nutraceutical principles from ginger

Gingerols are the major pungent compounds present in the rhizomes of ginger (Zingiber officinale Roscoe) and are renowned for their contribution to human health and nutrition. Medicinal properties of ginger, including the alleviation of nausea, arthritis and pain, have been associated with the gingerols. Gingerol analogues are thermally labile and easily undergo dehydration reactions to form the corresponding shogaols, which impart the characteristic pungent taste to dried ginger. Both gingerols and shogaols exhibit a host of biological activities, ranging from anticancer, anti-oxidant, antimicrobial, anti-inflammatory and anti-allergic to various central nervous system activities. Shogaols are important biomarkers used for the quality control of many ginger-containing products, due to their diverse biological activities. In this review, a large body of available knowledge on the biosynthesis, chemical synthesis and pharmacological activities, as well as on the structure-activity relationships of various gingerols and shogaols, have been collated, coherently summarised and discussed. The manuscript highlights convincing evidence indicating that these phenolic compounds could serve as important lead molecules for the development of therapeutic agents to treat various life-threatening human diseases, particularly cancer. Inclusion of ginger or ginger extracts in nutraceutical formulations could provide valuable protection against diabetes, cardiac and hepatic disorders.

TRPs and pain

Pain usually occurs as a result of tissue damage and has a role in healing and protection. However, in certain conditions it has no functional purpose and can become chronic and debilitating. A demand for more effective treatments to deal with this highly prevalent problem requires a better understanding of the underlying mechanisms. TRP channels are associated with numerous sensory functions across a wide range of species. Investigation into the expression patterns, electrophysiological properties and the effects of channel deletion in transgenic animal models have produced a great deal of evidence linking these channels to transduction of noxious stimuli as well as signalling within the pain system.

Targeted liquid chromatography quadrupole ion trap mass spectrometry analysis of tachykinin related peptides reveals significant expression differences in a rat model of neuropathic pain

Animal models are widely used to perform basic scientific research in pain. The rodent chronic constriction injury (CCI) model is widely used to study neuropathic pain. Animals were tested prior and after CCI surgery using behavioral tests (von Frey filaments and Hargreaves test) to evaluate pain. The brain and the lumbar enlargement of the spinal cord were collected from neuropathic and normal animals. Tachykinin related peptides were analyzed by high performance liquid chromatography quadrupole ion trap mass spectrometry. Our results reveal that the β-tachykinin₅₈₋₇₁, SP and SP₃₋₁₁ up-regulation are closely related to pain behavior. The spinal β-tachykinin₅₈₋₇₁, SP and SP₃₋₁₁ concentrations were significantly up-regulated in neuropathic animals compared with normal animals (p<0.001; p<0.001 and p<0.05, respectively). In contrast, the spinal SP5₅₋₁₁ concentration in neuropathic animals revealed a significant down-regulation compared with normal animals (p<0.05). The brain β-tachykinin₅₈₋₇₁ and SP concentrations were significantly up-regulated (p<0.05 and p<0.001, respectively). Interestingly, no significant concentration differences were observed in the spinal cord and brain for NKA, β-tachykinin₅₈₋₇₁, SP₁₋₇ and SP₆₋₁₁ (p>0.05). The β-tachykinin₅₈₋₇₁, SP and C-terminal SP metabolites could potentially serve as biomarkers in early drug discovery.