Natural products evaluated in neuropathic pain models - a systematic review

Examination of the effects of vitexin and vitexin-loaded solid lipid nanoparticles on neuropathic pain and possible mechanisms of action

This research aims to investigate the possible antiallodynic and antihyperalgesic effects of pure vitexin and vitexin-loaded solid lipid nanoparticles (SLN) on neuropathic pain and the pathways mediating these effects. Chronic constriction nerve injury was induced in female rats, and the effects of vitexin at the doses of 5, 10, 20, 40 mg/kg were evaluated. Ketanserin, ondansetron, WAY-100635, yohimbine and bicuculin, which are antagonists of receptors on pain pathways. were used to examine the mechanisms of the effects of vitexin. Pure vitexin exhibited antiallodynic activity at all administered doses, whereas antihyperalgesic activity was not observed at 5 mg/kg vitexin dose. SLN formulation was prepared with 5 mg/kg vitexin, the lowest dose. Vitexin-loaded formulation significantly increased antiallodynic and antihyperalgesic effects. Ondansetron, WAY-100635, yohimbine, and bicuculine antagonized the antiallodynic and antihyperalgesic effects of vitexin. So, it was concluded that serotonin (5-hydroxtryptamine, 5-HT) receptor subtypes 5-HT3 and 5-HT1A, alpha-2 adrenergic, and γ-Aminobutyric acid type A (GABA-A) receptors are involved in the antiallodynic and antihyperalgesic activity of vitexin. In conclusion, vitexin and vitexin-loaded formulation have the potential for clinical use in neuropathic pain management, and different pain pathways contributed to this effect. And also, it is thought that vitexin-loaded SLN formulation is more effective than pure vitexin, which will provide an advantage in treatment.

Gooderoside A from Anoectochilus elatus attenuates acute and chronic pains by inhibiting NO/cGMP and IRAK4/IRAK1/TAK1 signaling pathways

ETHNOPHARMACOLOGICAL RELEVANCE

Anoectochilus elatus Lindl. was traditionally used for pain treatment and Gooderoside A (GA) was regarded as its principal constituent.

AIM OF THE STUDY

To investigate whether GA can be responsible for the antinociceptive activity of A. elatus and explore its underlying mechanism.

MATERIALS AND METHODS

Acetic acid-induced abdominal writhing and tail flick tests were employed to evaluate the antinociceptive activity of ethanolic extract of A. elatus (EEA) and GA. Formalin test was used to ascertain the antinociceptive pattern of GA. Entobarbital sodium induced sleep test was adopted to exclude its hypnotic effect, while open-field test was performed to rule out its motor impairment effect. Chronic constriction injury (CCI)-induced neuropathic pain in rats was developed to evaluate its efficacy on neuropathic pain, and BV-2 cells were used to explore the underlying mechanism.

RESULTS

EEA and GA, significantly inhibited chemical and thermal nociception. GA suppressed nociception in formalin test in both phase I and II, whereas methylene blue and L-NAME partially reversed its efficacy. GA located inner and slightly blocked sodium channel current, and did not show any hypnotic effect or motor impairment effect. Crucially, GA markedly attenuated chronic neuropathic pain in rats, inhibited the phosphorylation of IRAK4, IRAK1 and TAK1, and suppressed MAPKs pathway in BV-2 cells.

CONCLUSION

GA relieved acute and chronic pains in vivo. The mechanism of action involves the blocking of NO/cGMP and IRAK4/IRAK1/TAK1 pathways. These results suggested GA may be a promising candidate for antinociceptive drug development.

Oral treatment with Berberine reduces peripheral nociception: Possible interaction with different nociceptive pathways activated by different allogeneic substances

ETHNOPHARMACOLOGICAL RELEVANCE

Berberine was identified in extracts of Berberis ruscifolia Lam., a plant used in traditional medicine as an analgesic. Its presence may be involved in the reported pharmacological activity of this species. However, there is still a lack of scientific research concerning its analgesic activity in the peripheral nervous system.

AIM OF THE STUDY

To investigate Berb-induced antinociception in the formalin test and to evaluate several pathways related to its pharmacological antinociceptive effects in chemical models of nociception in mice.

MATERIALS AND METHODS

The antinociceptive activity of Berb was assessed by inducing the paw licking in mice with different allodynic agents. In the formalin test, the antiedematous and antithermal effect of Berb was evaluated simultaneously in the same experiment. Other nociceptive behavior produced by endogenous [prostaglandin E2 (PGE2), histamine (His), glutamate (Glu) or bradykinin (BK)] or exogenous [capsaicin (Caps) and cinnamaldehyde (Cin)] chemical stimuli, and activators as protein kinase A (PKA) and C (PKC), were also evaluated.The in vivo doses for p.o. were 3 and 30 mg/kg.

RESULTS

Berb, at 30 mg/kg p.o., showed a significant inhibition of the nociceptive action in formalin in both phases being stronger at the inflammatory phase (59 ± 9%) and more active than Asp (positive control) considering the doses evaluated. Moreover, Berb inhibited the edema (34 ± 10%), but not the temperature in the formalin test. Regarding the different nociceptive signaling pathways evaluated, the most relevant data were that the administration of p.o. of Berb, at 30 mg/kg, caused significant inhibition of nociception induced by endogenous [His (72 ± 11%), PGE2 (78 ± 4%), and BK (51 ± 7%)], exogenous [Cap (68 ± 4%) and Cinn (57 ± 5%)] compounds, and activators of the PKA [(FSK (86 ± 3%)] and PKC [(PMA(86 ± 6%)] signaling pathway. Berb did not inhibit the nociceptive effect produced by Glu.

CONCLUSION

The present study demonstrated, for the first time, the potential of Berb in several nociceptive tests, with the compound present in B. ruscifolia contributing to the analgesic effect reported for this species.

Exploring the Effectiveness of Ajwain Cream in Treating Taxane-induced Peripheral Neuropathy in Cancer Patients: A Pilot, Randomised and Double-blind Clinical Trial

Objectives

Chemotherapy-induced peripheral neuropathy is a common disorder among cancer patients receiving various chemotherapeutic protocols. The present study aimed to explore the feasibility of ajwain (Trachyspermum ammi [L.] Sprague) cream in treating peripheral neuropathy symptoms triggered by taxane chemotherapeutic agents.

Materials and Methods

This was a pilot, double-blind, and randomised clinical trial on patients with peripheral neuropathy attributable to chemotherapy with taxane drugs during 2021-2022 in Tehran. Patients received ajwain or placebo cream for four weeks and filled out the chemotherapy-induced peripheral neuropathy assessment tool (CIPNAT) at the start and end finale of the trial. Side effects were also noted.

Results

Thirty patients suffering from breast, lung, gastro-intestinal, or prostate cancer were allocated to each of the drug and placebo groups. The mean difference in CIPNAT score between the groups was 0.83, demonstrating the statistical ineffectiveness of the drug compared with the placebo (P = 0.372). The safety profile showed promising outcomes at the end of the trial.

Conclusion

Although the effectiveness of ajwain cream was unacceptable in treating chemotherapy-induced peripheral neuropathy symptoms, multicentre controlled trials with ample sample size are mandatory for an all-inclusive inference.

Pigment epithelium-derived factor enhances peripheral nerve regeneration through modulating oxidative stress and stem cells: An experimental study

Peripheral nerve injury is common and negatively affects an individual's quality of life. Drugs used for peripheral nerve regeneration should aim to eliminate symptoms such as neuropathic pain and have therapeutic effects. In recent studies, pigment epithelium-derived factor (PEDF) has been considered an essential therapeutic agent because of its potential neuroprotective properties. In this study, we aimed to investigate the efficacy of locally applied PEDF for peripheral nerve regeneration. Twenty-four Wistar albino male rats were used. The study groups included Injury (n = 12) and Injury+PEDF (n = 12). An injury model was created by applying 50 N pressure to the right sciatic nerves in groups, and 10 μg/kg local PEDF was injected into the Injury+PEDF group. After 28 days of recovery, functional tests and stereological, immunohistochemical, and biochemical analyses were performed. A significant difference was found between the Injury and Injury+PEDF groups in amplitude, whereas no difference was found in latency. The number of myelinated axons and the myelinated axon area increased significantly in the Injury+PEDF group, while no statistically significant difference was found in myelin sheath thickness. Superoxide dismutase, catalase, and glutathione peroxidase activities were increased by PEDF, whereas they were suppressed in mesenchymal stem cells. PEDF exerts functional, quantitative, and antioxidative effects on sciatic nerve injury during neuroregeneration. In addition, when oxidative stress parameters were examined, it was seen that PEDF reduced oxidative stress following sciatic nerve injury.

Synthesis, Pharmacological Evaluation, and Molecular Modeling of Lappaconitine-1,5-Benzodiazepine Hybrids

Diterpenoid alkaloids, originating from the amination of natural tetracyclic diterpenes, have long interested scientists due to their medicinal uses and infamous toxicity which has limited the clinical application of the native compound. Alkaloid lappaconitine extracted from various Aconitum and Delphinium species has displayed extensive bioactivities and active ongoing research to reduce its adverse effects. A convenient route to construct hybrid molecules containing diterpenoid alkaloid lappaconitine and 3H-1,5-benzodiazepine fragments was proposed. The key stage involved the formation of 5'-alkynone-lappaconitines in situ by acyl Sonogashira coupling of 5'-ethynyllappaconitine, followed by cyclocondensation with o-phenylenediamine. New hybrid compounds showed low toxicity and outstanding analgesic activity in experimental pain models, which depended on the nature of the substituent in the benzodiazepine nucleus. An analogous dependence was also shown for the antiarrhythmic activity in the epinephrine arrhythmia test in vivo. Studies on the isolated atrium have shown that the mechanism of action of the new compounds is included the blockade of beta-adrenergic receptors and potassium channels. Molecular docking analysis was conducted to determine the binding potential of target molecules with the voltage-gated sodium channel NaV1.5. All obtained results provide a basis for future rational modifications of lappaconitine, reducing side effects, while retaining its therapeutic effects.

Neuroprotective mechanism of Ajugarin-I against Vincristine-Induced neuropathic pain via regulation of Nrf2/NF-κB and Bcl2 signalling

Vincristine (VCR) is a well-known chemotherapeutic agent that frequently triggers neuropathic pain. Ajugarin-I (Aju-I) isolated from Ajuga bracteosa exerts antioxidant, anti-inflammatory, and neuroprotective properties. The present study was designed to investigate the ameliorative potential of Aju-I against VCR-induced neuropathic pain and explored the underlying mechanism involved. The neuroprotective potential of Aju-I was first confirmed against hydrogen peroxide (H₂O₂)-induced cytotoxicity and oxidative stress in PC12 cells. For neuropathic pain induction, vincristine was given intraperitoneally (i.p.) into adult male albino mice (BALB/c) of the same age (8-12 weeks old) for 10 days (days 1-10). Aju-I (1 and 5 mg/kg) doses were administered from day 11 to 21 intraperitoneally (i.p.) after the neuropathic induction. Initially, behavioral tests such as thermal hyperalgesia, mechanical allodynia, and cold allodynia were performed to investigate the antinociceptive potential of Ajugarin-I (1 and 5 mg/kg, b.w). The nuclear factor-erythroid factor 2-related factor 2(Nrf2), nuclear factor-κB (NF-κB), BCL2-associated × protein (Bax), and B-cell-lymphoma-2 (Bcl-2) signaling proteins were determined by immunohistochemistry and western blot. Additionally, inflammatory cytokines, antioxidant, and oxidative stress parameters were also measured in the spinal cord and sciatic nerve. The behavioral results demonstrated that Aju-I (5 mg/kg) markedly alleviated VCR-induced neuropathic pain behaviors including hyperalgesia and allodynia. It reversed the histological alterations caused by VCR in the sciatic nerve, spinal cord, and brain. It significantly alleviated oxidative stress and inflammation by regulating the immunoreactivity of Nrf2/NF-κB signaling. It suppressed apoptosis by regulating the immunoreactivity of Bcl-2/Bax and Caspase-3. The flow cytometry and comet analysis also confirmed its anti-apoptotic potential. It considerably improved the antioxidant status and mitigated VCR-induced inflammatory cytokines. High-performance liquid chromatography (HPLC) analysis indicated that Aju-I crosses the blood-brain barrier (BBB) and penetrated the brain tissue. These findings suggest that Aju-I treatment inhibited vincristine-induced neuropathy via regulation of Nrf2/NF-κB and Bcl2 signaling.

Sea urchin (Diadema savignyi) extract as a novel protective agent against cisplatin induced neurotoxicity in rats

Neurotoxicity is a severe side effect of platinum compounds used for cancer chemotherapy such as Cisplatin. This neurotoxicity leads to severe cognitive and nervous dysfunction, therefore, limiting the dose of Cisplatin and compromising the treatment protocol.The present study investigates the neuroprotective effect of Sea Urchins which is a marine animal known for its rich bioactive compounds. Male Sprague Dawley rats received Cisplatin (2 mg/kg body weight) for 4 weeks, two times per week, followed by Sea Urchin extracts (50 and 100 mg/kg body weight) twice weekly for 4 weeks.Results show that rats treated with Urchin's extracts showed a significant improvement in the thermal (heat and cold) sensitivity compared to untreated rats. Liver enzymes Alanine Aminotransferase (ALT) and Aspartate Aminotransferase (AST) and Urea levels were also significantly decreased back to normal following treatment with sea urchin extracts. Brain tissue oxidative stress marker Nitric oxide (NO) and lipid peroxidation marker Malondialdehyde (MDA) increased significantly in the cisplatin-treated rats while the reduced glutathione levels (GSH) and catalase activity (CAT) showed a significant decrease. Treatment with sea Urchin extracts reversed these changes.Histological and immunohistochemical examination of the cerebral cortex reveled degenerative changes such as karyopyknosis and shrunken necrotic ghost like neurons in the cisplatin treated groups. There was also strong positive Glial fibrillary acidic protein (GFAP) reactivity and a negative B-cell leukemia/lymphoma 2 protein (Bcl2) reaction in most apparent neurons, indicating strong apoptotic changes. Treatment with Urchin extracts reversed these changes. Quantification of cerebral cortex neurons also revealed the strong effect of the extracts. Cisplatin treated groups showed 3708 cells/ mm3 compared to 8091 cells/mm³ in the normal rats. Extract treatment increased the neuronal numbers to almost normal levels. Quantification of the Immuno-histochemical expression of GFAP showed an increase by 10-folds after cisplatin administration. A remarkable decline from the cisplatin group was seen in the extract treated groups.In Conclusion, Sea Urchins extracts possess a strong neuroprotective activity and could provide a novel therapeutic method to prevent Cisplatin-induced neurotoxicity.

Topical Traditional Chinese Medicines for Cancer Pain: A Systematic Review and Meta-analysis of Randomized Controlled Trials

BACKGROUND AND OBJECTIVES

Safe and effective management of cancer-related pain is a worldwide challenge. In the search for treatment options, natural products used in Chinese herbal medicines (CHMs) have received attention in clinical studies for their effects on cancer-related pain. The objective of this systematic review is to evaluate the clinical evidence for topically applied CHMs as adjunctive treatments for cancer pain management.

METHODS

Nine biomedical databases and 4 clinical trial registries were searched for randomized-controlled trials (RCTs) that reported measures of pain and/or quality of life. Risk of bias was assessed using the Cochrane tool. Meta-analysis employed mean difference (MD) with 95% confidence intervals (random effects).

RESULTS

Twenty (20) RCTs (1636 participants) met the inclusion criteria. Meta-analyses were grouped based on the comparisons and outcome measures. For pain intensity, there was a greater reduction in the topical CHM group versus placebo (MD -0.72 [-1.04, -0.40]), no difference when compared to tramadol (MD -0.15 [-0.38, 0.08]), and a greater reduction when topical CHMs were combined with conventional analgesic medications (MD -0.67 [-0.93, -0.40]). Analgesic onset time was reduced in the CHM group compared to tramadol (MD -26.02 [-27.57, -24.47] minutes), and for CHMs combined with conventional medications (MD -19.17 [-21.83, -16.52] minutes). When CHMs were combined with analgesic medications, improvements were found for duration of analgesia (MD 1.65 [0.78, 2.51] hours), analgesic maintenance dose (MD -31.72 [-50.43, -13.01] milligrams/day), and quality of life.

CONCLUSION

Addition of topical CHMs to conventional analgesic medications was associated with improved outcomes for pain intensity, some other pain-related outcomes, and measures of quality of life. Limitations included methodological issues in some studies and considerable heterogeneity in some pooled results.

Euphorbia tirucalli latex loaded polymer nanoparticles: Synthesis, characterization, in vitro release and in vivo antinociceptive action

The encapsulation of drugs in micro and nanocarriers has helped to resolve mechanisms of cellular resistance and decrease drug side effects as well. In this study, poly(D,L-lactide-co-glycolide) (PLGA) was used to encapsulate the Euphol active substance-containing latex from Euphorbia tirucalli (E-latex). The nanoparticles (NP) were prepared using the solvent evaporation method and the physical and chemical properties were evaluated using spectrophotometric techniques. FTIR was used to prove the formation of the ester bond between the E-latex and PLGA-NP. The UV-Vis spectroscopic technique was used to show that more than 75% of the latex was encapsulated; the same technique was used to determine the release profile of the compound at different pH values, as well as determining the speed with which the process occurs through kinetic models, and it was observed that the best adjustments occurred for the Korsmeyer-Peppas model and the Higuchi model. The DLS technique was used to determine the diameter of the particles produced as well as their zeta potential (ZP). The sizes of the particles varied from 497 to 764 nm, and it was observed that the increase in E-latex concentration causes a reduction in the diameter of the NP and an increase in the ZP (-1.44 to -22.7 mV), due to more functional groups from latex film being adsorbed to the NPs surfaces. The thermogravimetric experiments exhibit the glass transition temperatures (Tg) that is appropriate for the use of formulated NPs as a stable drug delivery device before use. The in vivo activity of E-NPs (30 and 100 mg/Kg/p.o.) was tested against carrageenan-induced mechanical hypernociception. The data demonstrated a significantly antinociceptive effect for E-NPs, suggesting that E-latex nanoencapsulation preserved its desired properties.

The timing point of exercise intervention regulates neuropathic pain-related molecules in the ipsilateral dorsal root ganglion neurons after sciatic nerve injury

The purpose of this study was to determine whether the timing of tread-mill exercise application can control expression levels of neuropathic pain- and regeneration-related proteins in the ipsilateral lumbar 4 (L4) to 6 (L6) dorsal root ganglion cells (DRG) after sciatic nerve injury (SNI). The experimental rats were randomly divided into five groups: the normal control, SNI+sedentary (IS), exercise+SNI (EI), SNI+exercise (IE), exercise+SNI+exercise (EIE) groups. The rats in exercise groups per-formed treadmill exercise at a speed of 8 m/min for 30 min once a day during 14 days before and/or after SNI. For investigating the expression of specific neuropathic pain and regeneration-related proteins in DRG, we prepared L4 to L6 DRG in the ipsilateral side. In the quantitative analysis, growth associated protein 43 (GAP-43) and brain-derived neurotrophic factor levels were further increased in the ipsilateral DRG at all treadmill exercise groups than those in IS group. In the histological findings, GAP-43 was qualitatively increased IE and EIE groups than IS group at DRG. Wnt3a and β-catenin were dramatically downregulated in EIE and IE groups than IS groups. In addition, nuclear factor kappa-light-chain-enhancer of activated B cells and tumor necrosis factor-α were significantly decreased in IE and EIE groups than IS group in the ipsilateral DRG. Our findings suggested novel information that regular low-intensity exercise before and/or after SNI might be a therapeutic and preventive approaches for relieving neuropathic pain and improving axonal elongation after peripheral nerve injury.

Rosmarinic Acid Reduces Microglia Senescence: A Novel Therapeutic Approach for the Management of Neuropathic Pain Symptoms

The worldwide incidence of neuropathic pain is around 7–8% and is associated with significant and disabling comorbidities (sleep disturbances, depression, anxiety). It is now known that cellular ageing of microglia contributes to neurodegenerative diseases, mood disorders, and, even if with less evidence, chronic pain. The aim of this work was to investigate in vitro and in vivo the senolytic activity of rosmarinic acid (RA) to be exploited for the management of NP symptoms. BV2 cells were stimulated with LPS 500 ng/mL for 24 h. Treatment with RA 1 µM improved cell viability and reduced IL-1ß release leading to an attenuation of neuroinflammation. We then moved on to test the efficacy of RA in reducing microglial senescence. In our model, BV2 cells were stimulated with LPS 500 ng/mL every 72 h for 4 h/day, over a period of 10 days. RA 1 µM reduced the expression of the β-galactosidase enzyme, reduced the release of senescence-associated secretory phenotype (SASP) factors, increased cell viability, and reduced the presence of nuclear foci of senescence (SAHF), well-known cellular senescence markers. In the Spared Nerve Injury (SNI) model, 28 days from surgery, repeated oral administration of RA 5 mg/kg reduced hyperalgesia and NP-associated symptoms, such as anxiety and depression. A reduction of senescence markers was detected on both hippocampal and spinal samples of SNI-treated mice. This study represents a starting point for investigating the role of microglial senescence as a possible pharmacological target in controlling symptoms related to the more advanced stages of peripheral neuropathy.

Local effects of natural alkylamides from Acmella oleracea and synthetic isobutylalkyl amide on neuropathic and postoperative pain models in mice

Neuropathic and postoperative pain are clinical conditions that impair the patient's quality of life. The current pharmacotherapy of both painful states is ineffective and accompanied by several side effects. In order to develop new therapeutics targets, the secondary metabolites of plants have been extensively studied. Acmella oleracea ("jambu") is a native plant from the Amazon region and rich in alkylamides, bioactive compounds responsible for inducing anesthetic and chemesthetic sensations. We previously demonstrated that the intraplantar administration of an hexanic fraction (HF) rich in alkylamides from jambu and the synthetic isobutylalkyl amide (IBA) at 0.1 μg/20 μL can promote antinociceptive and anti-inflammatory effects. Thus, this study aimed to evaluate the local effect of HF and IBA (0.1 μg/20 μL) on neuropathic (partial sciatic nerve ligation, PSNL) and postoperative pain (plantar incision surgery, PIS) models in mice. Seven days after the PSNL, the mechanical (von Frey test) and cold (acetone-evoked evaporative cooling) allodynia, and digital gait parameters were analyzed. The intraplantar HF and IBA treatments attenuated the mechanical and cold allodynia as well as the static (max. Contact and print area) and dynamic (stand duration) parameters of digital gait analyses. On the day after PIS, the mechanical allodynia, heat hyperalgesia (hot plate, 52 ± 0.1°C), and spontaneous nociception scores were evaluated. Topical treatment with HF reduced the mechanical allodynia, heat hyperalgesia, and spontaneous nociception scores. In contrast, IBA treatment only partially reduced the mechanical allodynia. In summary, the local treatment with HF was effective on both neuropathic and postoperative pain, as opposed to IBA, which only had an effect on neuropathic pain.

Carvone and its pharmacological activities: A systematic review

Natural products from plants have gained prominence in the search for therapeutic alternatives. Monoterpenes, such as carvone, are suggested as candidates for the treatment of several diseases. Therefore, the objective of this study is to review the pharmacological activities of carvone in experimental models in vitro and in vivo. For this, the searches were carried out in May 2020 (upgraded in July 2021) in the databases of PubMed, Web of Science and Scopus and gathered studies on the pharmacological activities of carvone. Two independent reviewers performed the selection of articles using the Rayyan application, extracted the relevant data and assessed the methodological quality of the selected studies using Syrcle's risk of bias tool. Ninety-one articles were selected that described 10 pharmacological activities of carvone, such as antimicrobial, antispasmodic, anti-inflammatory, antioxidant, antinociceptive, anticonvulsant, among others. The evaluation of the methodological quality presented an uncertain risk of bias for most studies. In light of that, carvone stands out as a viable and promising alternative in the treatment of several pathological conditions. However, carrying out studies to evaluate possible mechanisms of action and the safety of this monoterpene is recommended.

Limonene, a citrus monoterpene, non-complexed and complexed with hydroxypropyl-β-cyclodextrin attenuates acute and chronic orofacial nociception in rodents: Evidence for involvement of the PKA and PKC pathway

BACKGROUND

Chronic orofacial pain is a serious public health problem with a prevalence of 7-11% in the population. This disorder has different etiologies and characteristics that make pharmacological treatment difficult. Natural products have been shown to be a promising source of treatments for the management of chronic pain, as an example the terpenes.

PURPOSE

The aim of this study was to evaluate the anti-nociceptive and anti-inflammatory effects of one of these terpenes, d-limonene (LIM - a common monoterpene found in citrus fruits) alone and complexed with hydroxypropyl-β-cyclodextrin (LIM/HPβCD) in preclinical animal models.

METHODS

Orofacial pain was induced by the administration of hypertonic saline on the corneal surface, the injection of formalin into the temporomandibular joint (TMJ), or chronic constriction injury of the infraorbital nerve (CCI-IoN). The study used male Wistar rats and Swiss mice treated with LIM (50 mg/kg), LIM/HPβCD (50 mg/kg), vehicle (control), gabapentin or morphine, and eyes wiping (induced by hypertonic saline), face rubbing (formalin-induced in TMJ) or mechanical hyperalgesia (provoked by CCI-IoN) were assessed. Additionally, ELISA was used to measure TNF-α, and western blot analysis to assess levels of PKAcα, NFκB, p38MAPK and phosphorylated PKC substrates. Serum levels of aspartate aminotransferase (AST) and alanine transferase (ALT) were also evaluated.

RESULTS

LIM and LIM/HPβCD significantly reduced (p < 0.001) corneal nociception and formalin-induced TMJ nociception. In addition, both substances attenuated (p < 0.001) mechanical hyperalgesia in the CCI-IoN model. The antinociceptive effect induced by LIM and HPβCD/LIM was associated with decreased TNF-α levels, downregulation of the NFκB and p38MAPK signalling pathways and reduced PKC substrate phosphorylation and PKA immunocontent. Moreover, the results demonstrated that complexation with HPβCD was able to decrease the therapeutic dose of LIM.

CONCLUSION

LIM was found to be a promising molecule for the treatment of orofacial pain due to its capacity to modulate some important mediators essential to the establishment of pain, and HPβCD can be a key tool to improve the profile of LIM.

Chrysin-Loaded Microemulsion: Formulation Design, Evaluation and Antihyperalgesic Activity in Mice

Chrysin is a bioactive flavonoid found in pollens, passion flowers, honey, royal jelly, and propolis, which is commonly used as an ingredient in natural food supplements and is primarily responsible for their pharmacological properties. A transparent chrysin-loaded microemulsion (CS-ME) prepared through a ternary phase diagram was evaluated for use as an antihyperalgesic formulation. It was formulated with 40% Labrasol® (surfactant), 5% isopropyl myristate (oil phase) and 55% water (aqueous phase) and classified as an oil-in-water (O/W) microsized system (74.4 ± 15.8 nm). Its negative Zeta potential (−16.1 ± 1.9 mV) was confirmed by polarized light microscopy and dynamic light scattering analysis. In vitro studies in Franz-type static diffusion cells showed that chrysin release from CS-ME followed zero-order kinetics. Oral administration of CS-ME in mice resulted in a statistically significantly reduction (p < 0.05) in carrageenan-induced mechanical hyperalgesia compared to the control group. Treatment with CS-ME also showed anti-inflammatory activity by significantly decreasing the TNF-α level (p < 0.01) and increasing that of IL-10 (p < 0.05) compared to the control group. These results suggest that the proposed microsystem is a promising vector for the release of chrysin, being able to improve its capacity to modulate inflammatory and nociceptive responses.

Norditerpenoid alkaloids from Aconitum and Delphinium: structural relevance in medicine, toxicology, and metabolism

Covering: 77 A.D. up to 2020Norditerpenoid alkaloids (NDA), typically N-ethylpiperidine containing C19 or C18 natural product diterpenes, are hexacycles with several contiguous often oxygenated stereocentres. As a function of their structural complexity, they display important pharmacological activities. The processed plants are used as important folk drugs and four NDAs have now been clinically approved. Many metabolism studies on Aconitum alkaloids have been reported as the understanding of their biotransformation in living systems and in cell-free systems is important for the development of these alkaloids as drugs. This Highlight sets out the missing links in NDA biosynthesis, their biological applications, SAR, toxicity, metabolism, and analytical studies.

Effect of herbal extracts on peripheral nerve regeneration after microsurgery of the sciatic nerve in rats

Background

Recent experimental studies using herbal extracts have shown the possibility of peripheral nerve regeneration. This study aimed to investigate the effects of herbal extracts on peripheral nerve regeneration in a rat sciatic nerve injury model.

Methods

A total of 53 rats were randomly assigned to a control group or one of four experimental groups. In all rats, the sciatic nerve was completely severed and microscopic epineural end-to-end neurorrhaphy was performed. Normal saline (2 mL) was topically applied to the site of nerve repair in the control group, whereas four different herbal extracts – 2 mL each of Astragalus mongholicus Bunge, Coptis japonica (Thunb.) Makino, Aconitum carmichaelii Debeaux, or Paeonia lactiflora Pall. – were topically applied to the site of nerve repair in each experimental group. Nerve conduction studies were performed at an average of 11.9 weeks after the operation, and conduction velocity and proximal and distal amplitudes were measured. Biopsies were performed at an average of 13.2 weeks after the initial neurorrhaphy. The quality of nerve anastomosis and perineural adhesion to the surrounding soft tissues was macroscopically evaluated. The neuroma size at the site of the neurorrhaphy was microscopically measured, whereas the size of the scar tissue was evaluated relative to the diameter of the repaired nerve.

Results

The nerve conduction study results showed the highest nerve conduction velocity in the experimental group that used the Coptis japonica (Thunb.) Makino extract and the highest proximal and distal amplitudes in the experimental group that used the Aconitum carmichaelii Debeaux extract. Macroscopic evaluations after the second operation showed that grade 2 perineural adhesion was found in 70.8% of rats. The mean neuroma size in the Coptis japonica (Thunb.) Makino, Aconitum carmichaelii Debeaux, and Paeonia lactiflora Pall. groups showed statistically significant decreases relative to the control group. The mean scar tissue formation index in the Paeonia lactiflora Pall. group showed a statistically significant decrease relative to the control group.

Conclusions

The peripheral nerve regeneration effect of the herbal extracts was confirmed through decreased neuroma and scar tissue formation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12906-021-03335-w.

Effects of Curcumin and Its Different Formulations in Preclinical and Clinical Studies of Peripheral Neuropathic and Postoperative Pain: A Comprehensive Review

Lesion or disease of the somatosensory system leads to the development of neuropathic pain. Peripheral neuropathic pain encompasses damage or injury of the peripheral nervous system. On the other hand, 10–15% of individuals suffer from acute postoperative pain followed by persistent pain after undergoing surgeries. Antidepressants, anticonvulsants, baclofen, and clonidine are used to treat peripheral neuropathy, whereas opioids are used to treat postoperative pain. The negative effects associated with these drugs emphasize the search for alternative therapeutics with better efficacy and fewer side effects. Curcumin, a polyphenol isolated from the roots of Curcuma longa, possesses antibacterial, antioxidant, and anti-inflammatory properties. Furthermore, the low bioavailability and fast metabolism of curcumin have led to the advent of various curcumin formulations. The present review provides a comprehensive analysis on the effects of curcumin and its formulations in preclinical and clinical studies of neuropathic and postoperative pain. Based on the positive outcomes from both preclinical and clinical studies, curcumin holds the promise of mitigating or preventing neuropathic and postoperative pain conditions. However, more clinical studies with improved curcumin formulations are required to involve its use as adjuvant to neuropathic and postoperative drugs.

Efficacy of Essential Oils in Pain: A Systematic Review and Meta-Analysis of Preclinical Evidence

Background: The demand for essential oils (EOs) has been steadily growing over the years. This is mirrored by a substantial increase in research concerned with EOs also in the field of inflammatory and neuropathic pain. The purpose of this present systematic review and meta-analysis is to investigate the preclinical evidence in favor of the working hypothesis of the analgesic properties of EOs, elucidating whether there is a consistent rational basis for translation into clinical settings.

Methods: A literature search has been conducted on databases relevant for medical scientific literature, i.e., PubMed/MEDLINE, Scopus, and Web of Science from database inception until November 2, 2020, following the PRISMA (Preferred Reporting Items for Systematic reviews and Meta-Analyses) criteria for systematic reviews and meta-analyses.

Results: The search was conducted in order to answer the following PICOS (participants/population, interventions, comparisons, outcomes, and study design) question: are EOs efficacious in reducing acute nociceptive pain and/or neuropathic pain in mice experimental models? The search retrieved 2,491 records, leaving 954 studies to screen after the removal of duplicates. The title and abstract of all 954 studies were screened, which left 127 records to evaluate in full text. Of these, 30 articles were eligible for inclusion.

Conclusion: Most studies (27) assessed the analgesic properties of EOs on acute nociceptive pain models, e.g. the acetic acid writhings test, the formalin test, and the hot plate test. Unfortunately, efficacy in neuropathic pain models, which are a more suitable model for human conditions of chronic pain, had fewer results (only three studies). Moreover, some methodologies raised concerns in terms of the risk of bias. Therefore, EOs with proven efficacy in both types of pain were corroborated by methodologically consistent studies, like the EO of bergamot, which should be studied in clinical trials to enhance the translational impact of preclinical modeling on clinical pain research.

HPLC-DAD-UV analysis, anti-inflammatory and anti-neuropathic effects of methanolic extract of Sideritis bilgeriana (lamiaceae) by NF-κB, TNF-α, IL-1β and IL-6 involvement

Medicinal plants remain an invaluable source for therapeutics of diseases that affect humanity. Sideritis bilgeriana (Lamiaceae) is medicinal plant used in Turkey folk medicine to reduce inflammation and pain, but few studies scientific corroborates its medicinal use so creating a gap between popular use and scientific evidence. Thus, we aimed to evaluate the pharmacological effects of the methanolic extract of S. bilgeriana (MESB) in rodents nociception models and also performed its phytochemical analysis. Firstly, a screening was carried out that enabled the identification of the presence of phenolic compounds and flavonoids. In view of this, a chromatographic method by HPLC-DAD-UV was developed that made it possible to identify chlorogenic acid and its quantification in MESB. MESB-treated mice (MESB 50, 100 and 200 mg/kg, p.o.) reduced mechanical hyperalgesia and myeloperoxidase activity (p < 0.01), and also showed a reduced pain behavior in capsaicin test. In the carrageenan-induced pleurisy test, MESB (100 mg/kg p.o.) significantly reduced the leukocyte (polymorphonuclear) count in the pleural cavity and equally decreased the TNF-α and IL-1β levels (p < 0.001). In the PSNL model, mechanical hyperalgesia was reduced on the first evaluation day and during the 7 days of evaluation compared to the vehicle group (p < 0.001). Thermal hyperalgesia was also reduced 1 h after treatment compared to the vehicle group (p < 0.001) and reversed the loss of force initially displayed by the animals, thus inferring an analgesic effect in the muscle strength test. Analysis of the marrow of these animals showed a decrease in the level of pro-inflammatory cytokine IL-6 (p < 0.001) and factor NF-κB, in relation to the control group (p < 0.05). Moreover, the MESB treatment produced no noticeable side effects, no disturb in motor performance and no signs of gastric or hepatic injury. Together, the results suggests that MESB could be useful to management of inflammation and neuropathic pain mainly by the management of pro-inflammatory mediators (NF-κB, TNF-α, IL-1β and IL-6), so reinforcing its use in popular medicine and corroborating the need for further chemical and pharmacological studies for the species.

Regulation of Pain Genes-Capsaicin vs Resiniferatoxin: Reassessment of Transcriptomic Data

Emerging evidence has shown a strong association between neuropathic pain and chronic diseases. In recent years, the treatment of neuropathic pain has attracted more attention. Natural products, such as capsaicin and resiniferatoxin, have been well utilized to treat this disease. In this study, we aim to compare the regulatory effects of capsaicin and resiniferatoxin on pain-related genes as well as on genes with no direct association with pain. Public transcriptomic and microarray data on gene expression in the dorsal root ganglia and genes associated with TRPV1 (+) neurons were obtained from the GEO database and then analyzed. Differentially expressed genes were selected for further functional analysis, including pathway enrichment, protein-protein interaction, and regulatory network analysis. Pain-associated genes were extracted with the reference of two pain gene databases and the effects of these two natural drugs on the pain-associated genes were measured. The results of our research indicate that as compared to capsaicin, resiniferatoxin (RTX) regulates more non pain-associated genes and has a negative impact on beneficial genes (off-targets) which are supposed to alleviate nociception and hypersensitivity by themselves. So, based on this study, we may conclude that capsaicin may be less potent when compared to RTX, but it will elicit considerably less adverse effects too. Thereby confirming that capsaicin could be used for the efficient alleviation of neuropathic pain with possibly fewer side effects.

Effects of alkaloids on peripheral neuropathic pain: a review

Neuropathic pain is a debilitating pathological pain condition with a great therapeutic challenge in clinical practice. Currently used analgesics produce deleterious side effects. Therefore, it is necessary to investigate alternative medicines for neuropathic pain. Chinese herbal medicines have been widely used in treating intractable pain. Compelling evidence revealed that the bioactive alkaloids of Chinese herbal medicines stand out in developing novel drugs for neuropathic pain due to multiple targets and satisfactory efficacy. In this review, we summarize the recent progress in the research of analgesic effects of 20 alkaloids components for peripheral neuropathic pain and highlight the potential underlying molecular mechanisms. We also point out the opportunities and challenges of the current studies and shed light on further in-depth pharmacological and toxicological studies of these bioactive alkaloids. In conclusion, the alkaloids hold broad prospects and have the potentials to be novel drugs for treating neuropathic pain. This review provides a theoretical basis for further applying some alkaloids in clinical trials and developing new drugs of neuropathic pain.

In silico analysis of polyphenols and flavonoids for design of human Nav1.7 inhibitors

Neuropathic pain is commonly associated with lesion or disease of the somatosensory system and often reflected as indicator of impaired life. Although the central nervous system is main regulator of pain but for initiation and maintenance of the neuropathic pain is regulated by peripheral nervous system. Sodium channels particularly Nav1.7, Nav1.8, Nav 1.9 are key stake holders in the peripheral neuropathy, activation of these sodium channels might lead to genesis and propagation. Flavonoids and polyphenols showed promising effects in neuropathic pain. Here we are reporting In silico analysis of some selected flavonoids and polyphenols on sodium activated voltage channel 1.7 to explore the structural fragments required for binding. Results indicated Baicalin, Butrin, Dihydromonospermoside, Icariin, Isocoreopsin and Isosaponarin are showing promising docking score with sodium activated voltage channel 1.7 than other compounds. Structural modification of these promising leads keeping pharamcophoric requirement intact may yield potent Nav1.7 inhibitors for peripheral pain management.Communicated by Ramaswamy H. Sarma.

Repeated administration of a flavonoid-based formulated extract from citrus peels significantly reduces peripheral inflammation-induced pain in the rat

Depression-related disorders are the first cause of disability worldwide according to the World Health Organization, and there is limited availability of effective antidepressant medications without side effects. Similarly, pain management is a public health concern particularly due to the increase in use of opioid medications, which have a significant side effect profile. Flavonoids can modulate numerous physiological functions including emotional and anti-nociceptive processes. Gold lotion (GL) is a natural product based on the extract of six citrus peels rich in flavonoids (0.45 mg/ml) with numerous reported biological activities. In the present study, we investigated the effect of repeated administration of GL in a battery of behavioral tests, including the open field test (OFT), forced swim test (FST), and von Frey test (vFT), in rats. While the OFT measured anxiolytic-related effects, the FST evaluated depression-related behavior. The vFT evaluated mechanical allodynia in two rat models of peripheral inflammation induced by carrageenan or complete Freund's adjuvant (CFA) administration. Treatment with GL reduced mechanical allodynia after either carrageenan or CFA administration. On the other hand, repeated GL administration did not modulate any behavior evaluated by OFT or FST. Consumption of GL inhibits behavioral signs of inflammatory pain. Therefore, GL may be a valuable analgesic product to be used for inflammatory pain.

Exploring the Promise of Flavonoids to Combat Neuropathic Pain: From Molecular Mechanisms to Therapeutic Implications

Neuropathic pain (NP) is the result of irregular processing in the central or peripheral nervous system, which is generally caused by neuronal injury. The management of NP represents a great challenge owing to its heterogeneous profile and the significant undesirable side effects of the frequently prescribed psychoactive agents, including benzodiazepines (BDZ). Currently, several established drugs including antidepressants, anticonvulsants, topical lidocaine, and opioids are used to treat NP, but they exert a wide range of adverse effects. To reduce the burden of adverse effects, we need to investigate alternative therapeutics for the management of NP. Flavonoids are the most common secondary metabolites of plants used in folkloric medicine as tranquilizers, and have been claimed to have a selective affinity to the BDZ binding site. Several studies in animal models have reported that flavonoids can reduce NP. In this paper, we emphasize the potentiality of flavonoids for the management of NP.

Stephalagine, an aporphine alkaloid from Annona crassiflora fruit peel, induces antinociceptive effects by TRPA1 and TRPV1 channels modulation in mice

Pain relief represents a critical unresolved medical need. Consequently, the search for new analgesic agents is intensively studied. Annona crassiflora, a native species of the Brazilian Savanna, represents a potential source for painful treatment. This study aimed to investigate the antinociceptive potential of A. crassiflora fruit peel, focusing on its major alkaloid, stephalagine, in animal models of pain evoked by the activation of transient receptor potential ankyrin 1 (TRPA1) and vanilloid 1 (TRPV1) channels. Male C57BL/6/J mice were submitted to formalin-, cinnamaldehyde-, and capsaicin-induced nociception tests to assess nociceptive behavior, and to the open-field and rotarod tests for motor performance analyses. Moreover, the stephalagine's effect was tested on capsaicin- and cinnamaldehyde-induced Ca²⁺ influx in spinal cord synaptosomes. In silico assessments of the absorption, distribution, metabolism and central nervous system permeability of stephalagine were carried out. The ethanol extract and alkaloidal fraction reduced the nociception induced by formalin. When administered by oral route (1 mg/kg), stephalagine reduced the spontaneous nociception and paw edema induced by TRPV1 agonist, capsaicin, and by TRPA1 agonists, cinnamaldehyde- and formalin, without altering the animals' locomotor activity. The prediction of in silico pharmacokinetic properties of stephalagine suggests its capacity to cross the blood-brain barrier. Furthermore, this alkaloid reduces the capsaicin- and cinnamaldehyde-mediated Ca²⁺ influx, indicating a possible modulation of TRPV1 and TRPA1 channels, respectively. Together, our results support the antinociceptive and anti-edematogenic effects of the A. crassiflora fruit peel and suggest that these effects are triggered, at least in part, by TRPV1 and TRPA1 modulation by stephalagine.

Harpagophytum procumbens Extract Ameliorates Allodynia and Modulates Oxidative and Antioxidant Stress Pathways in a Rat Model of Spinal Cord Injury

Spinal cord injury (SCI) is a deliberating disorder with impairments in locomotor deficits and incapacitating sensory abnormalities. Harpagophytum procumbens (Hp) is a botanical widely used for treating inflammation and pain related to various inflammatory and musculoskeletal conditions. Using a modified rodent contusion model of SCI, we explored the effects of this botanical on locomotor function and responses to mechanical stimuli, and examined possible neurochemical changes associated with SCI-induced allodynia. Following spinal cord contusion at T10 level, Hp (300 mg/kg, p.o.) or vehicle (water) was administered daily starting 24 h post-surgery, and behavioral measurements made every-other day until sacrifice (Day 21). Hp treatment markedly ameliorated the contusion-induced decrease in locomotor function and increased sensitivity to mechanical stimuli. Determination of Iba1 expression in spinal cord tissues indicated microglial infiltration starting 3 days post-injury. SCI results in increased levels of 4-hydroxynonenal, an oxidative stress product and proalgesic, which was diminished at 7 days by treatment with Hp. SCI also enhanced antioxidant heme oxygenase-1 (HO-1) expression. Concurrent studies of cultured murine BV-2 microglial cells revealed that Hp suppressed oxidative/nitrosative stress and inflammatory responses, including production of nitric oxide and reactive oxygen species, phosphorylation of cytosolic phospholipases A₂, and upregulation of the antioxidative stress pathway involving the nuclear factor erythroid 2-related factor 2 and HO-1. These results support the use of Hp for management of allodynia by providing resilience against the neuroinflammation and pain associated with SCI and other neuropathological conditions.

Protective effects of a polyphenol-enriched fraction of the fruit peel of Annona crassiflora Mart. on acute and persistent inflammatory pain

Different parts of Annona crassiflora Mart., a native species from Brazilian savanna, were traditionally used for the treatment of a wide variety of ailments including arthritis. Thus, this study aimed to investigate the possible antinociceptive and anti-inflammatory properties of a polyphenol-enriched fraction of the fruit peel of A. crassiflora, named here as EtOAc, in mice. Pro-inflammatory cytokines and nitric oxide (NO) production were evaluated in LPS-activated macrophages. Then, EtOAc fraction was administered by oral route in male C57BL/6/J mice, and the animals were submitted to glutamate-induced nociception and complete Freund's adjuvant (CFA)-induced monoarthritis tests to assess nociception (mechanical, spontaneous and cold pain) and inflammation (edema and neutrophil infiltration), and to the open-field and rotarod tests for motor performance analysis. EtOAc fraction inhibited the production of IL-6 and NO in the LPS-induced macrophages, and reduced spontaneous nociception induced by glutamate, without altering the animals' locomotor activity. In addition, the polyphenol-enriched fraction was able to revert the early and late hyperalgesia induced by CFA, as well as edema at the acute phase. Reduction of myeloperoxidase activity and inflammatory cell infiltration was observed in the paw tissue of mice injected with CFA and treated with EtOAc fraction. Together, our results support the antinociceptive and anti-inflammatory effects of the polyphenol-enriched fraction of A. crassiflora fruit peel and suggest that these effects are triggered, at least in part, by suppressing pro-inflammatory cytokines and neutrophils infiltration.

Eplingiella fruticosa (Lamiaceae) essential oil complexed with β-cyclodextrin improves its anti-hyperalgesic effect in a chronic widespread non-inflammatory muscle pain animal model

Eplingiella fruticosa (Lamiaceae), formally known as Hyptis fruticosa, is an important aromatic medicinal herb used in folk medicine in northeastern Brazil. We aimed to evaluate the anti-hyperalgesic effect of essential oil obtained from E. fruticosa (HypEO) complexed with βCD (HypEO-βCD) in a chronic widespread non-inflammatory muscle pain animal model (a mice fibromyalgia-like model, FM). The HypEO was extracted by hydro distillation and its chemical composition was determined by GC-MS/FID. Moreover, Fos protein expression in the spinal cord was assessed by immunofluorescence. (E)-caryophyllene, bicyclogermacrene, 1,8-cineole, α-pinene, β-pinene and 21 other compounds were identified in the HypEO. The treatment with HypEO-βCD produced a longer-lasting anti-hyperalgesic effect compared to HypEO, without alterations in motor coordination or myorelaxant effects. Moreover, HypEO and HypEO-βCD produced a significant anti-hyperalgesic effect over 7 consecutive treatment days. Immunofluorescence assay demonstrated a decrease in Fos protein expression in the spinal cord (p < 0.001). We demonstrated that the anti-hyperalgesic effect produced by HypEO was improved after complexation with β-CD and this seems to be related to the central pain-inhibitory pathway, suggesting the possible use of E. fruticosa for chronic pain management.

Involvement of the PKA pathway and inhibition of voltage gated Ca2+ channels in antihyperalgesic activity of Lippia grata/β-cyclodextrin

Neuropathic pain (NP) is a difficult condition to treat because of the modest efficacy of available drugs. New treatments are required. In the study we aimed to investigate the effects of the essential oil from Lippia grata alone or complexed in β-cyclodextrin (LG or LG-βCD) on persistent inflammatory and neuropathic pain in a mouse model. We also investigated Ca²⁺ currents in rat dorsal root ganglion (DRG) neurons. Male Swiss mice were treated with LG or LG/β-CD (24 mg/kg, i.g.) and their effect was evaluated using an acute inflammatory pleurisy model and nociception triggered by intraplantar injection of an agonist of the TRPs channels. We also tested their effect in chronic pain models: injection of Freund's Complete Adjuvant and partial sciatic nerve ligation (PSNL). In the pleurisy model, LG reduced the number of leukocytes and the levels of TNF-α and IL-1β. It also inhibited cinnamaldehyde and menthol-induced nociceptive behavior. The pain threshold in mechanical and thermal hyperalgesia was increased and paw edema was decreased in models of inflammatory and neuropathic pain. PSNL increased inflammatory protein contents and LG and LG-βCD restored the protein contents of TNF-α, NF-κB, and PKA, but not IL-1β and IL-10. LG inhibited voltage gated Ca²⁺ channels from DRG neurons. Our results suggested that LG or LG-βCD produce anti-hyperalgesic effect in chronic pain models through reductions in TNF-α levels and PKA, and inhibited voltage-gated calcium channels and may be innovative therapeutic agents for the management of NP.

Antinociceptive and antioxidant effects of extract enriched with active indole alkaloids from leaves of Tabernaemontana catharinensis A. DC

ETHNOPHARMACOLOGICAL RELEVANCE

Ethnopharmacological knowledge is important for the identification of active compounds from natural products. Pain may have different aetiologies with complex mechanisms. Tabernaemontana catharinensis A. DC. is well known for indole alkaloids, being used empirically in folk medicine, with antimicrobial and anti-inflammatory as well as antiofidic actions among others.

AIM OF THE STUDY

This work aims to evaluate the antinociceptive and antioxidant effect in mice of the alkaloids extract from leaves of Tabernaemontana catharinensis A. DC. (AITc).

MATERIALS AND METHODS

The AITc was produced by ultrasound and acid-base extraction, and the chemical composition was evaluated by high resolution mass spectrometry. Male mice (Mus musculus), Swiss, were used for in vivo tests. The AITc was administrated at doses of 1.0, 5.0, and 10.0 mg/kg in acetic acid model, formalin, tail-immersion, hot plate, and open field tests, and compared to saline, morphine, or diazepam controls, depending on the test. The toxicological, biochemical, haemogram and antioxidant effect were evaluated in mouse organs such as liver, brain, kidneys, spleen and stomach.

RESULTS

In total, 10 compounds were identified in the AITc, being from the indole alkaloids from the ibogan and corynanthean classes. The extract in doses ranging from 5.0 to 10.0 mg/kg showed an antinociceptive effect for acetic acid, inhibiting by 47.7% and 61.6%. In the same line, reductions of 47.1% (first phase) and 43.6% (second phase) were observed for the 5.0 mg/kg dose in the formalin test. However, tail-immersion and hot plate tests did not show considerable modifications in the latency period, while in the open field test there was an inhibition of only 5.1%. It was observed no differences in NO levels and total antioxidant status of the mice in any of the studie tissues.

CONCLUSIONS

The results justify the use of this plant in traditional medicine. in vivo tests indicate that these compounds possess central and peripheral mechanisms of action. This is study that reports the nociceptive action of these alkaloids, also including toxicity tests, which are intended to guarantee the safety of use of extracts of this plant.

Comparison of sildenafil, fluoxetine and its co-administration against chronic constriction injury induced neuropathic pain in rats: An influential additive effect

Current drug treatment available for neuropathic pain (NP) provides meager and partial pain relief due to incomplete efficacy and dose-dependent adverse effect. Hence, combination therapy can provide prolongation in analgesic effect with milder side effects. The present investigation aimed at observing the effects of sildenafil (SD) on Fluoxetine (FLX) in attenuation of chronic constriction injury (CCI) induced NP in rats. CCI was achieved in rats by placing four loose ligations around the sciatic nerve and rats were received respective treatments on SD and FLX till 14 days further behaviors parameters like heat hyperalgesia and allodynia, pin prick and acetone drop test were executed in order to access thermal, mechanical and cold allodynia, respectively, on a predetermined time interval. On the 21st day the animals were sacrificed for determination of total protein, myeloperoxidase activity in the adjoining muscular tissues while glutathione and TNF-α in the sciatic nerve. Co-administration of SD + FLX + CCI gave the pronounced effect that was superior over individual responses of SD and FLX in all behavioral as well as biochemical parameters. It was observed that attenuation in the altered behavioral pattern of CCI induced rats was modified prominently from 3rd day only in a group of rats treated with SD + FLX + CCI. The whole study was finally supported by histopathological results. Finally, it was concluded that SD produces an additive effect when given with FLX in attenuation of NP may be due to elevation in the level of intracellular concentrations of cyclic guanosine monophosphate which further causes downregulation of calcium channel.

Neuroprotective Strategies for Neurological Disorders by Natural Products: An update

Nature has bestowed mankind with surplus resources (natural products) on land and water. Natural products have a significant role in the prevention of disease and boosting of health in humans and animals. These natural products have been experimentally documented to possess various biological properties such as antioxidant, anti-inflammatory and anti-apoptotic activities. In vitro and in vivo studies have further established the usefulness of natural products in various preclinical models of neurodegenerative disorders. Natural products include phytoconstituents, like polyphenolic antioxidants, found in herbs, fruits, nuts, vegetables and also in marine and freshwater flora. These phytoconstituents may potentially suppress neurodegeneration and improve memory as well as cognitive functions of the brain. Also, they are known to play a pivotal role in the prevention and cure of different neurodegenerative diseases, such as Alzheimer's disease, epilepsy, Parkinson's disease and other neuronal disorders. The large-scale neuro-pharmacological activities of natural products have been documented due to the result of either the inhibition of inflammatory processes, or the up-regulation of various cell survival proteins or a combination of both. Due to the scarcity of human studies on neuroprotective effects of natural products, this review focuses on the various established activities of natural products in in vitro and in vivo preclinical models, and their potential neuro-therapeutic applications using the available knowledge in the literature.

D-limonene exhibits superior antihyperalgesic effects in a β-cyclodextrin-complexed form in chronic musculoskeletal pain reducing Fos protein expression on spinal cord in mice

Chronic musculoskeletal pain is one of the main symptoms found in Fibromyalgia with unclear etiology and limited pharmacological treatment. The aim of this study was to complex LIM in β-cyclodextrin (LIM-βCD) and then evaluate its antihyperalgesic effect in an animal model of chronic musculoskeletal pain. Differential scanning calorimetry and scanning electron microscopy was used for the characterization of the inclusion complex. Male Swiss mice were used for experimental procedures where mechanical hyperalgesia, thermal hyperalgesia, muscular strength, Fos immunofluorescence was studied after induction of hyperalgesia. Mechanism of action was also investigated through tail flick test and capsaicin-induced nociception. Endothermic events and morphological changes showed that the slurry complex method was the best method for the complexation. After induction of hyperalgesia, the oral administration of LIM-βCD (50mg/kg) significantly increased the paw withdrawal threshold compared to uncomplexed limonene. Fos immunofluorescence showed that both compounds significantly decreased the number of Fos-positive cells in the dorsal horn. In nociceptive tests, FLU was able to reverse the antinociceptive effect of LIM-βCD. After intraplantar administration of capsaicin, LIM was able to significantly decrease time to lick. LIM-βCD has antihyperalgesic action superior to its uncomplexed form, with possible action in the dorsal horn of the spinal cord. These results suggest the possible applicability of LIM, uncomplexed or complexed with βCD, in conditions such as FM and neuropathic pain, for which there are currently only limited pharmacological options.

Oral treatment with essential oil of Hyptis spicigera Lam. (Lamiaceae) reduces acute pain and inflammation in mice: Potential interactions with transient receptor potential (TRP) ion channels

ETHNOPHARMACOLOGICAL RELEVANCE

The genus Hyptis comprehends almost 400 species widespread in tropical and temperate regions of America. The use of Hyptis spicigera Lam. (Lamiaceae) is reported in traditional medicine due to its gastroprotective, anti-inflammatory and analgesic properties.

AIM OF THE STUDY

The rationale of this study was to investigate the potential use of the essential oil of H. spicigera (EOHs) as analgesic.

MATERIAL AND METHODS

The antinociceptive effect of EOHs was verified analyzing acute nocifensive behavior of mice induced by chemical noxious stimuli [i.e., formalin and transient receptor potential (TRP) channels agonists]. We also verified the effects of EOHs on locomotor activity and motor performance in mice. Finally, we investigate the involvement of central afferent C-fibers with EOHs analgesic effect.

RESULTS

EOHs presented antinociceptive effect at 300 and 1000mg/kg on formalin-induced pain behavior model, presenting 50% and 72% of inhibition during the first phase (ED₅₀ =292mg/kg), and 85% and 100% during de second phase (ED₅₀ =205mg/kg), respectively. Temperature of the hind paw was reduced by EOHs treatment in a dose-dependent manner; oedema was diminished only by EOHs 1000mg/kg. EOHs does not impaired locomotor activity or motor performance. For mice injected with capsaicin, a TRPV1 activator, EOHs (1000mg/kg, ED₅₀ =660mg/kg) showed decreased (63%) nociceptive behavior. When injected with cinnamaldehyde (TRPA1 activator), mice treated with EOHs showed 23%, 43% and 66% inhibition on nociceptive behavior (100, 300 and 1000mg/kg, respectively; ED₅₀ 402mg/kg). When mice were injected with menthol (TRPM8 activator), EOHs showed 29%, 59% and 98% inhibition of nociceptive behavior (100, 300 and 1000mg/kg, respectively; with ED₅₀ =198mg/kg. Finally, when desensitized mice were injected with menthol, EOHs (300mg/kg) does not show antinociceptive effect.

CONCLUSIONS

This study demonstrated the efficacy of EOHs on experimental models of nociception. We have found the involvement of TRP channels V1, A1 and M8 with EOHs activity, which was remarkably potent and efficient in inhibiting pain evoked by menthol, a TRPM8 channel activator. TRPM8 channels from TRPV1+ C-fibers, but not TRPM8+ C-fibers nor TRPM8+ Aδ mechanosensory fibers, mediate EOHs analgesic effects.

Pro-inflammatory cytokines involvement in the hesperidin antihyperalgesic effects at peripheral and central levels in a neuropathic pain model

Emerging evidence proposes a link between immune changes and pain, which is consistent with the inflammation theory and the increased incidence of neurodegenerative diseases. Flavonoids have long been used because of their anti-inflammatory potential activity and they are considered a promising alternative to alleviate neuropathic pain. The aim of this study was to investigate the antihyperalgesic effect of hesperidin and the presence of pro-inflammatory cytokines evaluated at peripheral and central levels in the chronic constriction injury as model of neuropathic pain in rats. Mechanical and thermal hyperalgesia were assessed in the aesthesiometer and plantar tests, respectively, as related to the presence of cytokines concentrations (TNF-α, IL-1β and IL-6) in sciatic nerve and segments of the spinal cord after 15 days chronic constriction injury model in rats receiving vehicle or hesperidin. Antihyperalgesic response of hesperidin (100 mg/kg) was associated to the presence of cytokines mainly at several sections of the spinal cord suggesting not only peripheral but also its involvement in central sensitization in the experimental neuropathic pain.

Nanoemulsion Thermoreversible Pluronic F127-Based Hydrogel Containing Hyptis pectinata (Lamiaceae) Leaf Essential Oil Produced a Lasting Anti-hyperalgesic Effect in Chronic Noninflammatory Widespread Pain in Mice

We evaluated if a nanostructured thermoreversible Pluronic F127-based hydrogel incorporated with Hyptis pectinata leaf essential oil (NE-EOH) produces a long-lasting anti-hyperalgesic effect on chronic muscle pain in an animal model. We induced chronic muscle pain by injecting the gastrocnemius with saline injections. Paw and muscle withdrawal thresholds and motor performance were evaluated after treatment and compared with morphine, diazepam, or vehicle. Naloxone and methysergide administration tested the involvement of opioid and serotonin receptors, respectively. Sites of action in the central nervous system for the NE-EOH were examined by measuring substance P (SP) levels in the spinal cord and Fos protein in the brainstem. NE-EOH increased paw and muscle withdrawal thresholds when compared with vehicle but had no effect on motor function. This analgesic effect was reversed by both naloxone and methysergide. NE-EOH decreased elevated substance P levels and reduced Fos-labeled neurons in the spinal cord and increased the number of Fos-labeled neurons in the periaqueductal gray (PAG), nucleus raphe magnus (NRM), and locus coeruleus (LC). NE-EOH was shown to produce a lasting anti-hyperalgesic effect. It uses opioid and serotonin receptors, activates brainstem inhibitory pathways, and reduces the release of excitatory neurotransmitters in the spinal cord and is a substance with potential to be used in the treatment of noninflammatory pain conditions. Graphical Abstract.

HPLC-DAD analysis, antinociceptive and anti-inflammatory properties of the ethanolic extract of Hyptis umbrosa in mice

Hyptis umbrosa (syn. Mesosphaerum sidifolium) (Lamiaceae Family) has been used to treat several conditions such as gastrointestinal disorders, skin infections, nasal congestion, fever and cramps. The objective of this study was to evaluate the chemical composition, analgesic and anti-inflammatory profiles of ethanol extract from leaves of Hyptis umbrosa (EEB). HPLC-DAD was used to determine the fingerprint chromatogram of the extract. Male Swiss mice were orally pretreated with EEB (100, 200 or 400 mg/kg; 60 min before initiating algesic stimulation) and antinociceptive activity was assessed using the acetic acid-induced writhing model, formalin test and hyperalgesia induced by glutamate or capsaicin. Also, peritonitis was induced by the intrathoracic injection of carrageenan to quantify the total number of leukocytes. The presence of phenolic compounds in the extract was confirmed using HPLC-DAD. The treatment with EEB, at all doses, produced a significant analgesic effect against acetic acid-induced antinociceptive activity. In the formalin test, only the 400-mg/kg-dose of EEB had a significant effect in the first phase. However, all doses tested were able to reverse nociception in the second phase. The effect of all doses of EEB also showed a significant antinociceptive effect in the glutamate and capsaicin tests and inhibited the carrageenan-induced leukocyte migration to the peritoneal cavity. The present study suggests that the EEB possesses peripheral analgesic action and showed potential in reducing the spreading of the inflammatory processes. Also, it seems to be related with vanilloid and glutamate receptors.

Phytochemical screening and analgesic profile of the lyophilized aqueous extract obtained from Chrysobalanus icaco leaves in experimental protocols

CONTEXT

Chrysobalanus icaco L. (Chrysobalanaceae) has been used for the treatment of abdominal pain and cramps.

OBJECTIVE

Assess the chemical and pharmacological profile of the lyophilized aqueous extract from C. icaco leaves (AEC).

MATERIALS AND METHODS

Chromatographic methods were used to assess compounds from AEC. Mice were treated with vehicle (control group) or AEC (100, 200 or 400 mg/kg, p.o.) (group with 7-8 mice) and the analgesic profile was assessed employing the acetic acid-induced writhing, formalin, hot plate tests and hyperalgesia induced by carrageenan (CG) or tumour necrosis factor-alpha. The animal motor performance was assessed using rota-rod and grip strength tests.

RESULTS

The chromatographic profile of AEC demonstrated the presence of terpenoid compounds. The acute pretreatment with AEC, at all doses, produced a significant (p < 0.01) inhibition of painful bahaviour (11.4 ± 3.6; 10.3 ± 2.8; 11.3 ± 2.2) when compared to the control group (24.7 ± 4.7) in acetic acid-induced writhing test. In the formalin test, AEC were effective in the second phase (p < 0.01) (57.2 ± 10.3; 56.3 ± 9.2; 54.7 ± 8.9) when compared to control group (121.9 ± 18.5). No response was observed in the hot plate test. The higher dose of AEC produced a significant (p < 0.01 or p < 0.05) inhibitory effect on the mechanical hyperalgesia test. AEC did not affect the motor performance of the mice.

DISCUSSION

The terpenoids from AEC are known for its analgesic and anti-inflammatory properties. So, these results corroborate the experiments using the AEC in inflammatory pain protocols.

CONCLUSION

Our results suggest that AEC act against inflammatory pain.

Food-Derived Natural Compounds for Pain Relief in Neuropathic Pain

Neuropathic pain, defined as pain caused by a lesion or disease of the somatosensory nervous system, is characterized by dysesthesia, hyperalgesia, and allodynia. The number of patients with this type of pain has increased rapidly in recent years. Yet, available neuropathic pain medicines have undesired side effects, such as tolerance and physical dependence, and do not fully alleviate the pain. The mechanisms of neuropathic pain are still not fully understood. Injury causes inflammation and immune responses and changed expression and activity of receptors and ion channels in peripheral nerve terminals. Additionally, neuroinflammation is a known factor in the development and maintenance of neuropathic pain. During neuropathic pain development, the C-C motif chemokine receptor 2 (CCR2) acts as an important signaling mediator. Traditional plant treatments have been used throughout the world for treating diseases. We and others have identified food-derived compounds that alleviate neuropathic pain. Here, we review the natural compounds for neuropathic pain relief, their mechanisms of action, and the potential benefits of natural compounds with antagonistic effects on GPCRs, especially those containing CCR2, for neuropathic pain treatment.

Neuroprotective Effect of Matrine in Mouse Model of Vincristine-Induced Neuropathic Pain

Chemotherapy drugs such as vincristine (VCR) can cause neuropathic pain, and there is still lack of ideal strategy to treat it. The current study was designed to investigate effect of matrine (MT) on VCR-induced neuropathic pain in animal model. VCR (75 μg/kg, i.p. for 10 consecutive days) was administered to induce painful neuropathy model in mice. MT (15, 30 and 60 mg/kg, i.p.) and pregabalin (10 mg/kg, i.p.) were administered for 11 consecutive days. Various tests were performed to assess the degree of pain at different days (1, 6, 11, 16, and 21). Von Frey hair, hot plate, cold-plate and paw pressure tests were conducted to assess the degree of mechanical allodynia, thermal hyperalgesia, cold allodynia and mechanical hyperalgesia in the hind paw respectively. The electrophysiological and histopathological changes were also analyzed. Furthermore, tissue malondialdehyde (MDA), total antioxidant capacity (T-AOC),superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), total calcium (TCA), myeloperoxidase (MPO), tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), interleukin-10 (IL-10) were measured to investigate possible involvement of MT in inflammation and oxidative stress. Administration of MT attenuated the VCR-induced behavioral alterations as well as electrophysiological and histopathological changes in a dose dependent manner. Further, MT also attenuated the VCR-induced oxidative stress (MDA, T-AOC, GSH-Px, SOD and TCA) and inflammation (MPO, TNF-α, IL-6 and IL-10). Taken together, MT ameliorated VCR-induced painful neuropathy, which might be attributed to neuroprotective effects by subsequent reduction in oxidative stress and anti-inflammatory actions.

Inclusion of terpenes in cyclodextrins: Preparation, characterization and pharmacological approaches

Terpenes constitute the largest class of natural products and are important resources for the pharmaceutical, food and cosmetics industries. However, due to their low water solubility and poor bioavailability there has been a search for compounds that could improve their physicochemical properties. Cyclodextrins (natural and derived) have been proposed for this role and have been complexed with different types of terpenes. This complexation has been demonstrated by using analytical techniques for characterizing complexes such as DSC, NMR, XRD, FTIR, and TGA. The formation of inclusion complexes has been able to improve drug characteristics such as bioavailability, solubility and stability; and to enhance biological activity and efficacy. This review shows strong experimental evidence that cyclodextrins improve the pharmacological properties of terpenes, and therefore need to be recognized as being possible targets for clinical use.

Chrysophyllum cainito leaves are effective against pre-clinical chronic pain models: Analysis of crude extract, fraction and isolated compounds in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Chrysophyllum cainito L. (Sapotaceae), commonly known as caimito or star apple, is a neotropical tree valued for its ornamental quality and edible fruits. Besides its culinary use, the leaves are also popularly used to treat diabetes mellitus and several inflammatory diseases.

AIM OF THIS STUDY

This study aimed to complement previous data obtained about the anti-hypersensitivity effects of the crude methanol extract (CME), CHCl3 fraction and isolated compounds obtained from C. cainito.

MATERIALS AND METHODS

The CME, CHCl3 fraction and two isolated triterpenes identified as 3β-Lup-20(29)-en-3-yl acetate (1) and Lup-20(29)-en-3β-O-hexanoate (2) were evaluated regarding their effects using clinical pain models, such as post-operative, inflammatory and neuropathic pain. Acute inflammatory pain models induced by PGE2, epinephrine, LPS and CFA were also used to improve the knowledge about the mechanism of action.

RESULTS

The animals treated with the CME and submitted to PGE2, epinephrine, LPS or CFA had the mechanical hypersensitivity significantly reduced. When repeatedly administered, the CME enhanced the mechanical withdrawal threshold of mice submitted to post-operative pain model, CFA-induced chronic inflammatory pain and two different models of neuropathic pain. In turn, the CHCl3 fraction presented anti-hypersensitivity effect against epinephrine- or LPS-induced hypersensitivity, with a more prominent activity in both the neuropathic pain models. The compound 1 seems to present the same profile of the CHCl3, whereas compound 2 exhibited activity similar to the CME.

CONCLUSIONS

This data suggests that the CME effect involves interference in the production, release or action of some chemical mediators, such as PGE2, sympathetic amines, cytokines, etc. Part of these effects was observed with the CHCl3 fraction, emphasizing the prominent inhibition of neuropathic pain. The results also demonstrated that part of the CME effects are due to the presence of the triterpenes 1 and 2, but it is important to mention that we cannot discard the effects of countless other compounds presented in the crude extract, acting in a synergic way.