Effects of intrathecal and intracerebroventricular administration of luteolin in a rat neuropathic pain model

From Plant to Chemistry: Sources of Active Opioid Antinociceptive Principles for Medicinal Chemistry and Drug Design

Pain continues to be an enormous global health challenge, with millions of new untreated or inadequately treated patients reported annually. With respect to current clinical applications, opioids remain the mainstay for the treatment of pain, although they are often associated with serious side effects. To optimize their tolerability profiles, medicinal chemistry continues to study novel ligands and innovative approaches. Among them, natural products are known to be a rich source of lead compounds for drug discovery, and they hold potential for pain management. Traditional medicine has had a long history in clinical practice due to the fact that nature provides a rich source of active principles. For instance, opium had been used for pain management until the 19th century when its individual components, such as morphine, were purified and identified. In this review article, we conducted a literature survey aimed at identifying natural products interacting either directly with opioid receptors or indirectly through other mechanisms controlling opioid receptor signaling, whose structures could be interesting from a drug design perspective.

Potential anxiolytic and antidepressant-like effects of luteolin in a chronic constriction injury rat model of neuropathic pain: Role of oxidative stress, neurotrophins, and inflammatory factors

This study aimed to examine the effects of luteolin (LUT) on chronic neuropathic pain (NP)-induced mood disorders (i.e., anxiety and depression) by regulating oxidative stress, neurotrophic factors (NFs), and neuroinflammation. Chronic constrictive injury (CCI) was used to induce NP in the animals. Animals in the treatment groups received LUT in three doses of 10, 25, and 50 mg/kg for 21 days. The severity of pain and mood disorders were examined. Finally, animals were sacrificed, and their brain tissue was used for molecular and histopathological studies. CCI led to cold allodynia and thermal hyperalgesia. Mood alterations were proven in the CCI group, according to the behavioral tests. Levels of glial cell-derived neurotrophic factor (GDNF), brain-derived neurotrophic factor (BDNF), B-cell lymphoma-2 (Bcl2), superoxide dismutase (SOD), catalase (CAT), and nuclear factor erythroid-2-related factor 2 (Nrf2) were reduced in the hippocampus (HPC) and prefrontal cortex (PFC). Furthermore, the levels of MDA, Bcl-2-associated X protein (Bax), and inflammatory markers, including nuclear factor kappa B (NF-κB), NLR family pyrin domain containing 3 (NLRP3), interleukin-1β (IL-1β), IL-18, IL-6, and tumor necrosis factor-α (TNF-α) significantly increased in the HPC and PFC following CCI induction. LUT treatment reversed the behavioral alterations via regulation of oxidative stress, neurotrophines, and inflammatory mediators in the HPC and PFC. Findings confirmed the potency of LUT in the improvement of chronic pain-induced anxiety- and depressive-like symptoms, probably through antioxidant, anti-inflammatory, and neuroprotective properties in the HPC and PFC.

Stem cell therapy combined with luteolin alleviates experimental neuropathy

Neuropathic pain is a chronic condition that causes long-term burning sensations. Despite significant efforts, current treatments for neuropathic pain are ineffective in curing the condition, which means new therapeutic options must be developed. One such option is the use of stem cell therapy in combination with anti-inflammatory herbal components, which has shown promise in treating neuropathic pain. The study aimed to investigate the effects of bone marrow mesenchymal stem cells (BM-MSCs) with luteolin on sensory deficits and pathological changes in a neuropathic model. The results showed that luteolin, either alone or in combination with BM-MSCs, effectively reduced sensory deficits related to mechanical and thermal hypersensitivity. In addition, luteolin alone and combined with BM-MSCs reduced oxidative stress in neuropathic rats and inhibited cellular responses, particularly reactive astrocytes. The study concluded that combining luteolin and BM-MSCs may offer an effective therapeutic strategy for patients with neuropathic pain, although further research is needed.

Optimized Chitosan-Based Nanoemulsion Improves Luteolin Release

Luteolin (LUT) is a flavonoid found in several edible and medicinal plants. It is recognized for its biological activities such as antioxidant, anti-inflammatory, neuroprotective, and antitumor effects. However, the limited water solubility of LUT leads to poor absorption after oral administration. Nanoencapsulation may improve the solubility of LUT. Nanoemulsions (NE) were selected for the encapsulation of LUT due to their biodegradability, stability, and ability to control drug release. In this work, chitosan (Ch)-based NE was developed to encapsulate luteolin (NECh-LUT). A 2³ factorial design was built to obtain a formulation with optimized amounts of oil, water, and surfactants. NECh-LUT showed a mean diameter of 67.5 nm, polydispersity index 0.174, zeta potential of +12.8 mV, and encapsulation efficiency of 85.49%. Transmission electron microscopy revealed spherical shape and rheological analysis verified the Newtonian behavior of NECh-LUT. SAXS technique confirmed the bimodal characteristic of NECh-LUT, while stability analysis confirmed NECh-LUT stability when stored at room temperature for up to 30 days. Finally, in vitro release studies showed LUT controlled release up to 72 h, indicating the promising potential of NECh-LUT to be used as novel therapeutic option to treat several disorders.

Nutraceuticals: A Promising Approach Towards Diabetic Neuropathy

BACKGROUND

Various nutraceuticals from different sources have various beneficial actions and have been reported for many years. The important findings from the research conducted using various nutraceuticals exhibiting significant physiological and pharmacological activities have been summarized.

METHODS

An extensive investigation of literature was done using several worldwide electronic scientific databases like PUBMED, SCOPUS, Science Direct, Google Scholar, etc. The entire manuscript is available in the English language that is used for our various compounds of interest. These databases were thoroughly reviewed and summarized.

RESULTS

Nutraceuticals obtained from various sources play a vital role in the management of peripheral neuropathy associated with diabetes. Treatment with nutraceuticals has been beneficial as an alternative in preventing the progression. In particular, in vitro and in vivo studies have revealed that a variety of nutraceuticals have significant antioxidant and anti-inflammatory properties that may inhibit the early diabetes-driven molecular mechanisms that induce DPN.

CONCLUSION

Nutraceuticals obtained from different sources like a plant, an animal, and marine have been properly utilized for the safety of health. In our opinion, this review could be of great interest to clinicians, as it offers a complementary perspective on the management of DPN. Trials with a well-defined patient and symptom selection have shown robust pharmacological design as pivotal points to let these promising compounds become better accepted by the medical community.

Luteolin: A promising natural agent in management of pain in chronic conditions

Pain due to chronic conditions is a frequent and insufficiently addressed problem. Current drug options for pain management (either in cases of chronic inflammatory conditions or neuropathy) do not adequately treat pain. Moreover, they are associated with important adverse events in long term use. Luteolin is a flavonoid widely present in the plant kingdom and its sources have been assembled in a comprehensive list of this paper. Luteolin has shown in several research studies a range of pharmacological properties; anti-inflammatory, antioxidant, neuroprotective, and analgesic. In this article, we summarize the effects and potential benefits from introducing luteolin as an adjuvant agent in established protocols for pain management. We review the most indicative in vivo and in vitro evidence of how luteolin can target the molecular pathways involved in pathogenesis of chronic inflammatory and neuropathic pain. The data reviewed strongly support luteolin's promising benefits in pain management and raise the need for further clinical trials that can establish its role in clinical practice.

Bioflavonoid exerts analgesic and anti-inflammatory effects via transient receptor potential 1 channel in a rat model

BACKGROUND

Pain is an uncomfortable sensation in the body. Kaempferol is a flavonoid with antinociceptive effects. Transient receptor potential (TRP) channels have been characterized in the sensory system.

OBJECTIVE

This study evaluated the central antinociceptive effect of Kaempferol and possible mechanisms of action of transient receptor potential cation channel subfamily V member 1 (TRPV1).

METHODS

Capsaicin as a TRPV agonist (5 μg/μL, intracerebroventricular [ICV]) and capsazepine as its antagonist (10 μg/μL, icv) were used to test the analgesic effect of kaempferol (1.5 mg, ICV). Morphine (10 μg, ICV) was used as a positive control. The other groups were treated with a combination of kaempferol and capsaicin, kaempferol and capsazepine, and capsaicin and capsazepine. The cannula was implanted in the cerebroventricular area. The tail-flick, acetic acid, and formalin tests were used to assess analgesic activity. For evaluation of antiinflammatory effect, the formalin-induced rat paw edema was used.

RESULTS

Kaempferol significantly decreased pain in the acute pain models, including the tail-flick and the first phase of the formalin test. In the late phase of the formalin test, as a valid model of nociception, capsazepine inhibited the antinociceptive effect of kaempferol.

CONCLUSIONS

Kaempferol has an analgesic effect in the acute pain model and can affect inflammatory pain. Also, the TRPV1 channel plays a role in the antinociceptive activity of kaempferol.

Antinociceptive effect of Mansoa alliacea polar extracts involves opioid receptors and nitric oxide in experimental nociception in mice

To evaluate the antinociceptive effect and the possible mechanism of action of two polar extracts of Mansoa alliacea, a medicinal plant used in Perú, Brazil, and Mexico to treat rheumatic pain, we used the formalin and hot-plate tests in mice. We found that ethanolic (MA-EtOH) and aqueous (MA-AQ) extracts of M. alliacea induced antinociceptive effects in both nociceptive tests. The antinociceptive efficacy of the highest dosage (300 mg/kg) of both extracts were also compared by using intraperitoneal and oral administration in the formalin test. Results showed that intraperitoneal injection of the two extracts produced better antinociceptive effects than that obtained by their oral administration. The mechanism of action involved in their antinociceptive activity was determined in the formalin test. Results showed that the presence of A784168 (TRPV1 antagonist) did not alter the antinociceptive effect induced by any of the M. alliacea extracts, whereas naltrexone (opioid antagonist) partially prevented the antinociceptive effect only of MA-EtOH in both phases of the formalin test. Furthermore, the effects of the extracts were diminished by L-NAME (inhibitor of nitric oxide synthase), but not by ODQ (inhibitor of the soluble guanylyl cyclase) or glibenclamide (blocker of K⁺_ATP channels) in the neurogenic phase. However, the effect of MA-AQ was diminished by all the inhibitors in the inflammatory phase. These results support the use of M. alliacea as a potential natural product with efficacy for pain relief depending on the form of preparation and the route of administration by involving opioid receptors and the production of nitric oxide.

Antinociceptive effects of minor cannabinoids, terpenes and flavonoids in Cannabis

Cannabis has been used for centuries for its medicinal properties. Given the dangerous and unpleasant side effects of existing analgesics, the chemical constituents of Cannabis have garnered significant interest for their antinociceptive, anti-inflammatory and neuroprotective effects. To date, Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD) remain the two most widely studied constituents of Cannabis in animals. These studies have led to formulations of THC and CBD for human use; however, chronic pain patients also use different strains of Cannabis (sativa, indica and ruderalis) to alleviate their pain. These strains contain major cannabinoids, such as THC and CBD, but they also contain a wide variety of cannabinoid and noncannabinoid constituents. Although the analgesic effects of Cannabis are attributed to major cannabinoids, evidence indicates other constituents such as minor cannabinoids, terpenes and flavonoids also produce antinociception against animal models of acute, inflammatory, neuropathic, muscle and orofacial pain. In some cases, these constituents produce antinociception that is equivalent or greater compared to that produced by traditional analgesics. Thus, a better understanding of the extent to which these constituents produce antinociception alone in animals is necessary. The purposes of this review are to (1) introduce the different minor cannabinoids, terpenes, and flavonoids found in Cannabis and (2) discuss evidence of their antinociceptive properties in animals.

Phenolics as GABAA Receptor Ligands: An Updated Review

Natural products can act as potential GABA modulators, avoiding the undesirable effects of traditional pharmacology used for the inhibition of the central nervous system such as benzodiazepines (BZD). Phenolics, especially flavonoids and phlorotannins, have been considered as modulators of the BZD-site of GABA_A receptors (GABA_ARs), with sedative, anxiolytic or anticonvulsant effects. However, the wide chemical structural variability of flavonoids shows their potential action at more than one additional binding site on GABA_ARs, which may act either negatively, positively, by neutralizing GABA_ARs, or directly as allosteric agonists. Therefore, the aim of the present review is to compile and discuss an update of the role of phenolics, namely as pharmacological targets involving dysfunctions of the GABA system, analyzing both their different compounds and their mechanism as GABAergic modulators. We focus this review on articles written in English since the year 2010 until the present. Of course, although more research would be necessary to fully establish the type specificity of phenolics and their pharmacological activity, the evidence supports their potential as GABA_AR modulators, thereby favoring their inclusion in the development of new therapeutic targets based on natural products. Specifically, the data compiled in this review allows for the directing of future research towards ortho-dihydroxy diterpene galdosol, the flavonoids isoliquiritigenin (chalcone), rhusflavone and agathisflavone (biflavonoids), as well as the phlorotannins, dieckol and triphlorethol A. Clinically, flavonoids are the most interesting phenolics due to their potential as anticonvulsant and anxiolytic drugs, and phlorotannins are also of interest as sedative agents.

Luteolin relieves lung cancer-induced bone pain by inhibiting NLRP3 inflammasomes and glial activation in the spinal dorsal horn in mice

BACKGROUND

Bone cancer pain (BCP) is one of the most severe complications in cancer patients. However, the pharmacological therapeutic approaches are limited. Luteolin, a major component of flavones, is widely distributed in plants and plays a critical role in the antinociceptive effects, but whether luteolin could alleviate cancer pain and its underlying mechanisms are not known.

HYPOTHESIS/PURPOSE

This study investigated the molecular mechanisms by which luteolin reduced BCP.

METHODS

Behavioral, pharmacological, immunohistochemical, and biochemical approaches were used to investigate the effect of luteolin on BCP.

RESULTS

Luteolin treatment ameliorated Lewis lung cancer (LLC)-induced bone pain in mice in a dose-dependent manner. Luteolin treatment could inhibit the activation of neurons, glial cells, and NOD-like receptor protein 3 (NLRP3) inflammasomes in the dorsal spinal cord in the BCP mouse model. Furthermore, phosphorylated p-38 mitogen-activated protein kinase (MAPK) in the spinal dorsal horn (SDH) was suppressed by luteolin treatment that could influence the analgesic and glial inhibition effects of luteolin.

CONCLUSION

Our results demonstrated that luteolin inhibited neuroinflammation by obstructing glial cell and NLRP3 inflammasome activation via modulating p38 MAPK activity in SDH, ultimately improving LLC-induced BCP.

Effects of intrathecal and intracerebroventricular microinjection of kaempferol on pain: possible mechanisms of action

Background and purpose:

Kaempferol (KM), a flavonoid, has an anti-inflammatory and anticancer effect and prevents many metabolic diseases. Nonetheless, very few studies have been done on the antinociceptive effects of KM. This research aimed at assessing the involvement of opioids, gamma-aminobutyric acid (GABA) receptors, and inflammatory mediators in the antinociceptive effects of KM in male Wistar rats.

Experimental approach:

The intracerebroventricular and/or intrathecal administration of the compounds was done for examining their central impacts on the thermal and chemical pain by the tail-flick and formalin paw tests. For assessing the role of opioid and GABA receptors in the possible antinociceptive effects of KM, several antagonists were used. Also, a rotarod test was carried out for assessing motor performance.

Findings/Results:

The intracerebroventricular and/or intrathecal microinjections of KM (40 μg/rat) had partially antinociceptive effects in the tail-flick test in rats (P < 0.05). In the formalin paw model, the intrathecal microinjection of KM had antinociceptive effects in phase 1 (20 and 40 μg/rat; P < 0.05 and P < 0.01, respectively) and phase 2 (20 and 40 μg/rat; P < 0.01 and P < 0.001, respectively). Using naloxonazine and/or bicuculline approved the involvement of opioid and GABA receptors in the central antinociceptive effects of KM, respectively. Moreover, KM reduced the expression levels of caspase 6, interleukin-1β, tumor necrosis factor-α, and interleukin-6. The antinociceptive effects of KM were not linked to variations in the locomotor activity.

Conclusion and implications:

It can be concluded that KM has remarkable antinociceptive effects at a spinal level, which is associated with the presence of the inflammatory state. These impacts were undetectable following injections in the lateral ventricle. The possible mechanisms of KM antinociception are possibly linked to various modulatory pathways, including opioid and GABA receptors.

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.

In Vitro and In Vivo Effects of Flavonoids on Peripheral Neuropathic Pain

Neuropathic pain is a common symptom and is associated with an impaired quality of life. It is caused by the lesion or disease of the somatosensory system. Neuropathic pain syndromes can be subdivided into two categories: central and peripheral neuropathic pain. The present review highlights the peripheral neuropathic models, including spared nerve injury, spinal nerve ligation, partial sciatic nerve injury, diabetes-induced neuropathy, chemotherapy-induced neuropathy, chronic constriction injury, and related conditions. The drugs which are currently used to attenuate peripheral neuropathy, such as antidepressants, anticonvulsants, baclofen, and clonidine, are associated with adverse side effects. These negative side effects necessitate the investigation of alternative therapeutics for treating neuropathic pain conditions. Flavonoids have been reported to alleviate neuropathic pain in murine models. The present review elucidates that several flavonoids attenuate different peripheral neuropathic pain conditions at behavioral, electrophysiological, biochemical and molecular biological levels in different murine models. Therefore, the flavonoids hold future promise and can be effectively used in treating or mitigating peripheral neuropathic conditions. Thus, future studies should focus on the structure-activity relationships among different categories of flavonoids and develop therapeutic products that enhance their antineuropathic effects.

Intrathecally administered perampanel alleviates neuropathic and inflammatory pain in rats

Chronic pain conditions such as neuropathic pain and persistent inflammatory pain are difficult to manage. Alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors modulate nociceptive processing at the spinal dorsal horn. Previous studies have shown that intrathecal AMPA receptor antagonists exert antinociception in various pain states. Perampanel is a selective, noncompetitive inhibitor of the AMPA receptor and used clinically as an antiepileptic drug. Little is known about antinociceptive action of perampanel in the spinal cord. Here, we explored whether intrathecal perampanel attenuates neuropathic and inflammatory pain. A chronic constriction injury (CCI) to the sciatic nerve was induced in male Sprague-Dawley rats. We evaluated the effects of intrathecal perampanel (10, 30, or 100 μg) on mechanical and cold hyperalgesia using the electronic von Frey and cold plate tests, respectively. Normal rats were assessed in terms of inflammatory nociception using the formalin test, and motor function employing the rotarod test. In the CCI rats, spinally applied perampanel inhibited mechanical and cold hyperalgesia dose-dependently. In normal rats, perampanel remarkably suppressed the early- and late-phase responses in the formalin test, and it weakly affected motor performance for a short period at the highest dose. These results suggest that perampanel exerts antinociceptive actions on neuropathic and persistent inflammatory pain in the spinal cord. Perampanel may be safe and beneficial remedy for patients with such pain conditions. In addition, AMPA receptor can be a promising target for treatment of chronic pain.

Fructus Viticis methanolic extract attenuates trigeminal hyperalgesia in migraine by regulating injury signal transmission

Migraine, characterized by hyperalgesia of the trigeminovascular system, is a severe condition that leads to severe reductions in the quality of life. Upon external stimulation, the levels of various neurotransmitters, including aspartic acid (Asp), glutamic acid (Glu), γ-amino butyric acid (GABA), norepinephrine (NE) and 5-hydroxytryptamine (5-HT), are significantly altered; this directly or indirectly promotes trigeminal hypersensitivity. Fructus Viticis is a Traditional Chinese Medicine with analgesic properties to provide efficient relief of migraine. In the present study, the underlying mechanisms of the analgesic effect of Fructus Viticis methanolic extract were assessed in rats with nitroglycerin-induced migraine. The plasma levels of the neurotransmitters calcitonin gene-related peptide (CGRP) and substance P (SP), as well as the amount of c-fos immunoreactive cells (c-fos IR cells) in the brain, were detected. The analgesic effect was obvious, as Fructus Viticis methanolic extract ameliorated migraine-like behaviours in nitroglycerin-induced rats. The levels of 5-HT, GABA and NE in the brain of migraine model rats was lower compared with that of control rats, whereas opposite observations were made in the contents of excitatory amino acids. Pre-treatment with Fructus Viticis methanolic extract elevated the levels of 5-HT, GABA and NE, and also lowered the levels of excitatory amino acids, including Glu and Asp. In addition, treatment with Fructus Viticis methanolic extract lowered the plasma levels of CGRP and SP and decreased the c-fos IR cells in the brainstem. The present study provided a further scientific basis for the anti-migraine effects of Fructus Viticis.

Antinociceptive Effect of Single Components Isolated from Agrimonia pilosa Ledeb. Extract

Agrimonia pilosa Ledeb. produces an antinociceptive effect in ICR mice in both chemically induced and thermal pain models. In the present study, we examined the antinociceptive effects of single components isolated from Agrimonia pilosa Ledeb. (AP) extract in ICR mice. Three active compounds isolated from AP, including rutin, luteolin-7-O-glucuronide, and apigenin-7-O-glucuronide, were isolated and identified by comparing EI-MS, 1H-, 13C-NMR, and UV. We studied the antinociceptive effects of three single components administered orally at doses of 10 and 20 mg/kg in monosodium urate (MSU)-treated pain model as measured by von Frey test. Among these compounds, apigenin-7-O-glucuronide was more effective in the production of antinociceptive effects. We further characterized the antinociceptive effects and possible mechanisms of apigenin-7-O-glucuronide in writhing and formalin tests. Oral administration of Apigenin-7-O-glucuronide caused a reduction in the number of writhing and effectively reduced the pain behavior observed during the second phase of the formalin test in a dose-dependent manner. In addition, the pretreatment of yohimbine instead of naloxone or methysergide attenuated apigenin-7-O-glucuronide-induced antinociception in the writhing test. Moreover, apigenin-7-O-glucuronide caused reduction in the expression of p-P38, p-CREB, and p-mTOR induced by formalin injection. Our results indicate that apigenin-7-O-glucuronide shows an antinociceptive effect in various pain models. In addition, spinal α2-adrenergic receptors appear to be involved in the production of antinociception induced by apigenin-7-O-glucuronide. Furthermore, the antinociceptive effect of apigenin-7-O-glucuronide appears to be mediated by reduction in the expression of p-P38, p-CREB and p-mTOR levels in the spinal cord.

Neuroimmune Responses Mediate Depression-Related Behaviors following Acute Colitis

Many patients with visceral inflammation develop pain and psychiatric comorbidities such as major depressive disorder, worsening the quality of life and increasing the risk of suicide. Here we show that neuroimmune activation in mice with dextran sodium sulfate-induced colitis is accompanied by the development of pain and depressive behaviors. Importantly, treatment with the flavonoid luteolin prevented both neuroimmune responses and behavioral abnormalities, suggesting a new potential therapeutic approach for patients with inflammatory bowel diseases.

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Acute colitis triggers long-term events related to depression

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Leukocytes infiltrate into brain vasculature

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Luteolin abolishes leukocyte infiltration and visceral hypersensitivity

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Luteolin abolishes depression-related behaviors

Inhibition of MicroRNA-195 Alleviates Neuropathic Pain by Targeting Patched1 and Inhibiting SHH Signaling Pathway Activation

Trigeminal neuralgia (TN) is a type of chronic neuropathic pain that is caused by peripheral nerve lesions that result from various conditions, including the compression of vessels, tumors and viral infections. MicroRNAs (miRs) are increasingly recognized as potential regulators of neuropathic pain. Previous evidence has demonstrated that miR-195 is involved in neuropathic pain, but the mechanism remains unclear. To investigate the pathophysiological role of miR-195 and Shh signaling in TN, persistent facial pain was induced by infraorbital nerve chronic constriction injury (CCI-IoN), and facial pain responses were evaluated by Von Frey hairs. qPCR and Western blotting were used to determine the relative expression of miR-195 and Patched1, the major receptor of the Sonic Hedgehog (Shh) signaling pathway, in the caudal brain stem at distinct time points after CCI-IoN. Here, we found that the expression of miR-195 was increased in a rat model of CCI-IoN. In contrast, the expression of Patched1 decreased significantly. Luciferase assays confirmed the binding of miR-195 to Patched1. In addition, the overexpression of miR-195 by an intracerebroventricular (i.c.v) administration of LV-miR-195 aggravated facial pain development, and this was reversed by upregulating the expression of Patched1. These results suggest that miR-195 is involved in the development of TN by targeting Patched1 in the Shh signaling pathway, thus regulating extracellular glutamate.

Mansoa alliacea extract presents antinociceptive effect in a chronic inflammatory pain model in mice through opioid mechanisms

In some chronic disorders, as in arthritis, the inflammatory pain persists beyond the inflammation control becoming pathological. Its treatment shows limited efficacy and adverse effects which compromises patients' quality of life. Mansoa alliacea, known as 'cipo alho', is popularly used as analgesic and others species of this genus show anti-inflammatory actions. We investigated the anti-inflammatory and antinociceptive potential of M. alliacea extract in an inflammatory pain model which presents inflammatory characteristics similar to those caused by arthritis, through of the intraplantar injection of complete Freund's adjuvant (CFA) in mice. The extract chromatographic analysis revealed the presence of ρ-coumaric, ferulic and chlorogenic acids, luteolin, and apigenin. The treatment with M. alliacea prevented and reversed the CFA-induced mechanical allodynia with maximum inhibition (I_max) of 100% and 90 ± 10%, respectively. The co-administration of M. alliacea extract plus morphine enhanced the anti-allodynic effect with I_max of 100%. The M. alliacea extract also reverted the CFA-induced thermal hyperalgesia with I_max of 3.6 times greater compared to the vehicle and reduced the thermal threshold under physiological conditions. However, M. alliacea extract did not reduce the CFA-induced edema and myeloperoxidase activity. Additionally, non-selective and δ-selective opioid receptor antagonists, but not κ-opioid, prevented extract anti-allodynic effect with I_max of 98 ± 2% and 93 ± 2%, respectively. Moreover, M. alliacea extract did not induce adverse effects commonly caused by opioids and other analgesic drugs, at least in the tested pharmacological doses after the acute treatment. M. alliacea extract presents antinociceptive activity in an inflammatory pain model, which presents inflammatory characteristics similar to those arthritis-induced, without causing adverse effects in tested pharmacological doses. These effects seem to be mediated mainly via δ-opioid receptors.

Saponins of Tribulus terrestris attenuated neuropathic pain induced with vincristine through central and peripheral mechanism

The study comprises exploring the effects of saponins from Tribulus terrestris (TT) in attenuating the neuropathic pain caused by vincristine (100 μg/ml i.p.) for 10 days (in two 5 day cycles with 2 days pause). Mechanical hyperalgesia and allodynia were assessed by Randall-Sellitto and electronic von Frey tests, respectively. Chemical- induced nociception was assessed by formalin test. Neurophysiological effect of the extract was evaluated by recording sciatic functional index (SFI) on the test days (7, 10, 14, and 21) and sciatic nerve conduction velocity test (SNCV) on the last day. Inflammatory mediators (TNF-α, IL-1β, and IL-6) in both sciatic nerve and brain and brain neurotransmitters, glutamate and aspartate, were measured to support the behavioral response. The saponins of TT-treated group were found to be effective in the behavioral experiments, implying its activity both centrally and peripherally in attenuating pain. The inflammatory mediators in both sciatic nerve and brain (TNF-α, IL-1β, and IL-6) were found to be attenuated with TT saponin treatment in comparison to vincristine-treated group, indicating its anti-inflammatory property. The excitatory neurotransmitters, L-glutamic acid and L-aspartic acid, were also found to be attenuated with TT saponins, implying restoration of neuronal damage and synaptic activity caused by high amount of glutamate due to excess TNF-α in brain and reversing the nociceptive threshold lowered due to aspartate. Thus, TT(S) is peripherally and centrally active in lowering the inflammatory mediators, reversing the neuronal damage and increasing the nociceptive threshold caused due to peripheral neuropathy.

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.

Antinociceptive Activity of Methanolic Extract of Clinacanthus nutans Leaves: Possible Mechanisms of Action Involved

Methanolic extract of Clinacanthus nutans Lindau leaves (MECN) has been proven to possess antinociceptive activity that works via the opioid and NO-dependent/cGMP-independent pathways. In the present study, we aimed to further determine the possible mechanisms of antinociception of MECN using various nociceptive assays. The antinociceptive activity of MECN was (i) tested against capsaicin-, glutamate-, phorbol 12-myristate 13-acetate-, bradykinin-induced nociception model; (ii) prechallenged against selective antagonist of opioid receptor subtypes (β-funaltrexamine, naltrindole, and nor-binaltorphimine); (iii) prechallenged against antagonist of nonopioid systems, namely, α₂-noradrenergic (yohimbine), β-adrenergic (pindolol), adenosinergic (caffeine), dopaminergic (haloperidol), and cholinergic (atropine) receptors; (iv) prechallenged with inhibitors of various potassium channels (glibenclamide, apamin, charybdotoxin, and tetraethylammonium chloride). The results demonstrated that the orally administered MECN (100, 250, and 500 mg/kg) significantly (p < 0.05) reversed the nociceptive effect of all models in a dose-dependent manner. Moreover, the antinociceptive activity of 500 mg/kg MECN was significantly (p < 0.05) inhibited by (i) antagonists of μ-, δ-, and κ-opioid receptors; (ii) antagonists of α₂-noradrenergic, β-adrenergic, adenosinergic, dopaminergic, and cholinergic receptors; and (iii) blockers of different K⁺ channels (voltage-activated-, Ca²⁺-activated, and ATP-sensitive-K⁺ channels, resp.). In conclusion, MECN-induced antinociception involves modulation of protein kinase C-, bradykinin-, TRVP1 receptors-, and glutamatergic-signaling pathways; opioidergic, α₂-noradrenergic, β-adrenergic, adenosinergic, dopaminergic, and cholinergic receptors; and nonopioidergic receptors as well as the opening of various K⁺ channels. The antinociceptive activity could be associated with the presence of several flavonoid-based bioactive compounds and their synergistic action with nonvolatile bioactive compounds.

Phytochemical profile and mechanisms involved in the anti-nociception caused by the hydroethanolic extract obtained from Tocoyena formosa (Cham. & Schltdl.) K. Schum (Jenipapo-bravo) leaves in mice

Tocoyena formosa, a small ornamental tree growing in the dry regions of central Brazil, is commonly known as 'genipapo do bravo'. This is a medicinal plant traditionally used as an analgesic for rheumatic pain, lower back pain and myalgia, however its use is carried out without scientific evidence, which thus justifies the development of studies to investigate and prove its therapeutic potential. Therefore, the objective of this study was to evaluate the phytochemical profile of Tocoyena formosa (Cham. & Schlecht.) K. Schum (TFLHE) and the mechanisms involved in its anti-nociceptive effect. The TFLHE revealed the presence of gallic acid, catechin, chlorogenic acid, caffeic acid, ellagic acid, rutin, quercetin and luteolin. The TFLHE at doses of 200 and 400mg/kg significantly decreased acetic acid-induced abdominal contortions, the reaction time for the formalin test in both phases and increased the paw withdrawal time in the hot plate thermal stimulus test. The 200mg/kg dose also significantly inhibited the plantar mechanical hyperalgesia intensity induced by formalin within 24h.

TREATMENT

with the TFLHE did not cause significant changes in motor performance and coordination in the Rota Rod test. The investigation on the possible mechanism of antinociceptive action of TFLHE indicates the involvement of opioid, glutamatergic, nitric oxide/cGMP and vanilloid systems. It is concluded that the TFLHE has an antinociceptive effect promoted by the aforementioned mechanisms.

Antinociceptive and antidepressant-like effects of the crude extract of Vitex megapotamica in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Vitex megapotamica (Spreng) Moldenke has been used in South American folk medicine to treat inflammatory diseases. However, the effects of V. megapotamica on animal models of nociception and depression have not been evaluated.

AIM OF THE STUDY

This study investigated whether the crude leaf extract of V. megapotamica exhibits antinociceptive and antidepressant-like effects in a Freund's adjuvant-induced chronic inflammation and depression model.

MATERIALS AND METHODS

Chronic inflammation was induced in rats by the intraplantar administration of complete Freund's adjuvant (CFA; 100μl). The effect of oral crude extract of V. megapotamica (VmE; 3-30mg/kg, p.o.) on nociception (thermal hyperalgesia, mechanical allodynia and arthritis score), inflammation (edema, myeloperoxidase activity), immobility (forced swimming test), locomotor activity (open field), gastrointestinal transit, hyperalgesia and naloxone-precipitated morphine withdrawal syndrome was evaluated. Naloxone (0.4mg/kg, i.p.) was used to investigate the involvement of opioid system in the currently described effects of VmE.

RESULTS

Crude extract caused antinociceptive/antidepressant-like effects in the CFA-induced chronic inflammation model, which was prevented by naloxone. The VmE extract (10mg/kg, p.o.) did not alter the locomotor activity, gastrointestinal function and inflammatory parameters and did not cause hyperalgesia.

CONCLUSION

V. megapotamica induces opioid-dependent antinociception and antidepressant-like effect, without anti-inflammatory activity. The results support the use of VmE as analgesic and antidepressant.

Antihyperalgesic Effect of Hesperidin Improves with Diosmin in Experimental Neuropathic Pain

Neuropathic pain is caused by a primary lesion, dysfunction, or transitory perturbation in the peripheral or central nervous system. In this study, we investigated the hesperidin antihyperalgesic effects alone or combined with diosmin in a model of neuropathic pain to corroborate a possible synergistic antinociceptive activity. Mechanical and thermal hyperalgesia were assessed in the aesthesiometer and plantar tests, respectively, after chronic constriction injury (CCI) model in rats receiving hesperidin (HS, 5 doses from 10 to 1000 mg/kg) alone or combined with diosmin (DS, 10 and 100 mg/kg) in comparison to gabapentin (31.6 mg/kg). UHPLC-MS analysis of cerebral samples was used to recognize the central concentrations of these flavonoids. Participation of different receptors was also investigated in the presence of haloperidol, bicuculline, and naloxone antagonists. Acute hesperidin administration significantly decreased mechanical and thermal hyperalgesia in CCI rats. Antihyperalgesic response of hesperidin, improved by a combination with diosmin (DS10/HS100) in both stimuli, was blockaded by haloperidol, bicuculline, and naloxone, but not WAY100635, antagonists. Both flavonoids were detected in brain samples. In conclusion, hesperidin alone and combined with diosmin produces antihyperalgesic response in the CCI model in rats. Antihyperalgesic effect of DS10/HS100 combination involves central activity partially modulated by D₂, GABA_A, and opioids, but not by 5-HT_1A, receptors.

Luteolin inhibits GABAA receptors in HEK cells and brain slices

Modulation of the A type γ-aminobutyric acid receptors (GABA_AR) is one of the major drug targets for neurological and psychological diseases. The natural flavonoid compound luteolin (2-(3,4-Dihydroxyphenyl)- 5,7-dihydroxy-4-chromenone) has been reported to have antidepressant, antinociceptive, and anxiolytic-like effects, which possibly involve the mechanisms of modulating GABA signaling. However, as yet detailed studies of the pharmacological effects of luteolin are still lacking, we investigated the effects of luteolin on recombinant and endogenous GABA_AR-mediated current responses by electrophysiological approaches. Our results showed that luteolin inhibited GABA-mediated currents and slowed the activation kinetics of recombinant α1β2, α1β2γ2, α5β2, and α5β2γ2 receptors with different degrees of potency and efficacy. The modulatory effect of luteolin was likely dependent on the subunit composition of the receptor complex: the αβ receptors were more sensitive than the αβγ receptors. In hippocampal pyramidal neurons, luteolin significantly reduced the amplitude and slowed the rise time of miniature inhibitory postsynaptic currents (mIPSCs). However, GABA_AR-mediated tonic currents were not significantly influenced by luteolin. These data suggested that luteolin has negative modulatory effects on both recombinant and endogenous GABA_ARs and inhibits phasic rather than tonic inhibition in hippocampus.

Endogenous opiates and behavior: 2014

This paper is the thirty-seventh consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2014 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (endogenous opioids and receptors), and the roles of these opioid peptides and receptors in pain and analgesia (pain and analgesia); stress and social status (human studies); tolerance and dependence (opioid mediation of other analgesic responses); learning and memory (stress and social status); eating and drinking (stress-induced analgesia); alcohol and drugs of abuse (emotional responses in opioid-mediated behaviors); sexual activity and hormones, pregnancy, development and endocrinology (opioid involvement in stress response regulation); mental illness and mood (tolerance and dependence); seizures and neurologic disorders (learning and memory); electrical-related activity and neurophysiology (opiates and conditioned place preferences (CPP)); general activity and locomotion (eating and drinking); gastrointestinal, renal and hepatic functions (alcohol and drugs of abuse); cardiovascular responses (opiates and ethanol); respiration and thermoregulation (opiates and THC); and immunological responses (opiates and stimulants). This paper is the thirty-seventh consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2014 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (endogenous opioids and receptors), and the roles of these opioid peptides and receptors in pain and analgesia (pain and analgesia); stress and social status (human studies); tolerance and dependence (opioid mediation of other analgesic responses); learning and memory (stress and social status); eating and drinking (stress-induced analgesia); alcohol and drugs of abuse (emotional responses in opioid-mediated behaviors); sexual activity and hormones, pregnancy, development and endocrinology (opioid involvement in stress response regulation); mental illness and mood (tolerance and dependence); seizures and neurologic disorders (learning and memory); electrical-related activity and neurophysiology (opiates and conditioned place preferences (CPP)); general activity and locomotion (eating and drinking); gastrointestinal, renal and hepatic functions (alcohol and drugs of abuse); cardiovascular responses (opiates and ethanol); respiration and thermoregulation (opiates and THC); and immunological responses (opiates and stimulants).

Time-Dependent Metabolism of Luteolin by Human UDP-Glucuronosyltransferases and Its Intestinal First-Pass Glucuronidation in Mice

Luteolin is a well-known flavonoid with various pharmacological properties but has low bioavailability due to glucuronidation. This study investigated the time-course of luteolin glucuronidation by 12 human UDP-glucuronosyltransferases (UGTs) and its intestinal first-pass metabolism in mice. Six metabolites, including two novel abundant diglucuronides [3',7-O-diglucuronide (diG) and 4',7-diG] and four known ones, were identified. UGT1A6 and UGT1A9 generated almost only monoglucuronides (G's). The production of 3',7-diG followed a sequential time-dependent process along with decrease of 3'-G mainly by UGT1A1, indicating that 3',7-diG was produced from 3'-G. Metabolism in mice intestine differed from that in humans. Probenecid, a nonspecific UGT inhibitor, did not affect absorption but significantly inhibited production of 7-, 4'-, and 3'-G, and enhanced the formation of another novel metabolite, 5-G, in mice. In conclusion, diglucuronide formation is time-dependent and isoform-specific. UGT1A1 preferentially generates diG, whereas UGT1A6 and UGT1A9 share a preference for G production.

Flavonoid nutraceuticals and ionotropic receptors for the inhibitory neurotransmitter GABA

Flavonoids that are found in nutraceuticals have many and varied effects on the activation of ionotropic receptors for GABA, the major inhibitory neurotransmitter in our brains. They can act as positive or negative modulators enhancing or reducing the effect of GABA. They can act as allosteric agonists. They can act to modulate the action of other modulators. There is considerable evidence that these flavonoids are able to enter the brain to influence brain function. They may have a range of effects including relief of anxiety, improvement in cognition, acting as neuroprotectants and as sedatives. All of these effects are sought after in nutraceuticals. A number of studies have likened flavonoids to the widely prescribed benzodiazepines as 'a new family of benzodiazepine receptor ligands'. They are much more than that with many flavonoid actions on ionotropic GABA receptors being insensitive to the classic benzodiazepine antagonist flumazenil and thus independent of the classic benzodiazepine actions. It is time to consider flavonoids in their own right as important modulators of these vital receptors in brain function. Flavonoids are rarely consumed as a single flavonoid except as dietary supplements. The effects of mixtures of flavonoids and other modulators on GABAA receptors need to be more thoroughly investigated.

Antinociceptive effect of intracerebroventricular administration of glycine transporter-2 inhibitor ALX1393 in rat models of inflammatory and neuropathic pain

Glycinergic transmission has an important role in regulating nociception in the spinal cord. The glycine transporter-2 (GlyT2) is localized at presynaptic terminals of glycinergic neurons and eliminates glycine from the synaptic cleft to terminate glycinergic transmission. Systemic and intrathecal administration of GlyT2 inhibitors alleviate various types of pain. Although the GlyT2s and glycine receptors are widely distributed in the central nervous system, little is known about the role of glycinergic transmission in pain perception at supraspinal regions. The present study examined the antinociceptive effect of intracerebroventricular (i.c.v.) administration of the selective GlyT2 inhibitor ALX1393 on inflammatory and neuropathic pain in experimental models. For i.c.v. administration, a guide cannula was implanted into the right lateral ventricle of male Sprague-Dawley rats. Normal rats were used to assess inflammatory nociception using the formalin test and motor function using the rotarod test. Chronic constriction injury (CCI) to the sciatic nerve was induced in the rats. The CCI rats were then used to assess mechanical, cold, and thermal hyperalgesia using the electronic von Frey test, cold plate test, and the plantar test, respectively. ALX1393 (25, 50, and 100 μg) was administered i.c.v. to examine its effects on supraspinal antinociception. Supraspinal ALX1393 in normal rats suppressed the late-phase response in the formalin test but did not affect motor performance. In the CCI rats, ALX1393 inhibited mechanical and cold hyperalgesia in a dose-dependent manner. The antihyperalgesic effects of ALX1393 (100 μg) were reversed completely by i.c.v. pretreatment with a glycine receptor antagonist strychnine (10 μg). These results suggest that GlyT2 contributes to nociceptive transmission at supraspinal level and that the selective GlyT2 inhibitor is a promising candidate for the treatment of inflammatory and neuropathic pain without causing motor dysfunction.