The analgesic effects and mechanisms of orally administered eugenol

Dynamics of eugenol included in β-cyclodextrin by nuclear magnetic resonance and molecular simulations

Eugenol-β-cyclodextrin complex has been widely used because of the enhanced stability and conservation of the properties of eugenol. Applications in food and health sciences have been shown previously, which makes this complex an excellent model to understand and develop methodologies for the analysis and prediction of physical properties. In this work, the dynamics of eugenol incorporated into β-cyclodextrin are presented, using NMR relaxation rates, and the predictive capabilities of molecular dynamics simulations are discussed. Results show a hindered rotation of eugenol around the principal inertial axes when located inside β-cyclodextrin. Moreover, a translational movement of the whole complex is demonstrated.

Eugenol and lidocaine inhibit voltage-gated Na+ channels from dorsal root ganglion neurons with different mechanisms

Eugenol (EUG) is a bioactive monoterpenoid used as an analgesic, preservative, and flavoring agent. Our new data show EUG as a voltage-gated Na+ channel (VGSC) inhibitor, comparable but not identical to lidocaine (LID). EUG inhibits both total and only TTX-R voltage-activated Na+ currents (INa) recorded from VGSCs naturally expressed on dorsal root ganglion sensory neurons in rats. Inhibition is quick, fully reversible, and dose-dependent. Our biophysical and pharmacological analyses showed that EUG and LID inhibit VGSCs with different mechanisms. EUG inhibits VGSCs with a dose-response relationship characterized by a Hill coefficient of 2, while this parameter for the inhibition by LID is 1. Furthermore, in a different way from LID, EUG modified the voltage dependence of both the VGSC activation and inactivation processes and the recovery from fast inactivated states and the entry to slow inactivated states. In addition, we suggest that EUG, but not LID, interacts with VGSC pre-open-closed states, according to our data.

An intra-oral flavor detection task in freely moving mice

Flavor plays a critical role in the pleasure of food. Flavor research has mainly focused on human subjects and revealed that many brain regions are involved in flavor perception. However, animal models for elucidating the mechanisms of neural circuits are lacking. Herein, we demonstrate the use of a novel behavioral task in which mice are capable of flavor detection. When the olfactory pathways of the mice were blocked, they could not perform the task. However, behavioral accuracy was not affected when the gustatory pathway was blocked by benzocaine. These results indicate that the mice performed this detection task mainly based on the olfaction. We conclude that this novel task can contribute to research on the neural mechanisms of flavor perception.

The Application of Handheld Near-Infrared Spectroscopy and Raman Spectroscopic Imaging for the Identification and Quality Control of Food Products

The following investigations describe the potential of handheld NIR spectroscopy and Raman imaging measurements for the identification and authentication of food products. On the one hand, during the last decade, handheld NIR spectroscopy has made the greatest progress among vibrational spectroscopic methods in terms of miniaturization and price/performance ratio, and on the other hand, the Raman spectroscopic imaging method can achieve the best lateral resolution when examining the heterogeneous composition of samples. The utilization of both methods is further enhanced via the combination with chemometric evaluation methods with respect to the detection, identification, and discrimination of illegal counterfeiting of food products. To demonstrate the solution to practical problems with these two spectroscopic techniques, the results of our recent investigations obtained for various industrial processes and customer-relevant product examples have been discussed in this article. Specifically, the monitoring of food extraction processes (e.g., ethanol extraction of clove and water extraction of wolfberry) and the identification of food quality (e.g., differentiation of cocoa nibs and cocoa beans) via handheld NIR spectroscopy, and the detection and quantification of adulterations in powdered dairy products via Raman imaging were outlined in some detail. Although the present work only demonstrates exemplary product and process examples, the applications provide a balanced overview of materials with different physical properties and manufacturing processes in order to be able to derive modified applications for other products or production processes.

Eugenol: In Vitro and In Ovo Assessment to Explore Cytotoxic Effects on Osteosarcoma and Oropharyngeal Cancer Cells

Cancer is a significant health problem worldwide; consequently, new therapeutic alternatives are being investigated, including those found in the vegetable kingdom. Eugenol (Eug) has attracted attention for its therapeutic properties, especially in stomatology. The purpose of this study was to investigate the cytotoxicity of Eug, in vitro, on osteosarcoma (SAOS-2) and oropharyngeal squamous cancer (Detroit-562) cells, as well as its potential irritant effect in ovo at the level of the chorioallantoic membrane (CAM). The data obtained following a 72 h Eug treatment highlighted the reduction in cell viability up to 41% in SAOS-2 cells and up to 37% in Detroit-562 cells, respectively. The apoptotic-like effect of Eug was indicated by the changes in cell morphology and nuclear aspect; the increase in caspase-3/7, -8 and -9 activity; the elevated expression of Bax and Bad genes; and the increase in luminescence signal (indicating phosphatidylserine externalization) that preceded the increase in fluorescence signal (indicating the compromise of membrane integrity). Regarding the vascular effects, slight signs of coagulation and vascular lysis were observed, with an irritation score of 1.69 for Eug 1 mM. Based on these results, the efficiency of Eug in cancer treatment is yet to be clarified.

Effects of ortho-eugenol on anxiety, working memory and oxidative stress in mice

Ortho-eugenol is a synthetic derivative from eugenol, the major compound of clove essential oil, which has demonstrated antidepressant and antinociceptive effects in pioneering studies. Additionally, its effects appear to be dependent on the noradrenergic and dopaminergic systems. Depression and anxiety disorders are known to share a great overlap in their pathophysiology, and many drugs are effective in the treatment of both diseases. Furthermore, high levels of anxiety are related to working memory deficits and increased oxidative stress. Thus, in this study we investigated the effects of acute treatment of ortho-eugenol, at 50, 75 and 100 mg/kg, on anxiety, working memory and oxidative stress in male Swiss mice. Our results show that the 100 mg/kg dose increased the number of head-dips and reduced the latency in the hole-board test. The 50 mg/kg dose reduced malondialdehyde levels in the prefrontal cortex and the number of Y-maze entries compared to the MK-801-induced hyperlocomotion group. All doses reduced nitrite levels in the hippocampus. It was also possible to assess a statistical correlation between the reduction of oxidative stress and hyperlocomotion after the administration of ortho-eugenol. However, acute treatment was not able to prevent working memory deficits. Therefore, the present study shows that ortho-eugenol has an anxiolytic and antioxidant effect, and was able to prevent substance-induced hyperlocomotion. Our results contribute to the elucidation of the pharmacological profile of ortho-eugenol, as well as to direct further studies that seek to investigate its possible clinical applications.

Inhibition of acid sensing ion channels by eugenol in rat trigeminal ganglion neurons

Eugenol is widely used as an analgesic in the dental treatment. The underlying mechanisms may involve its modulation of various ion channels. Acid-sensing ion channels (ASICs) are pH sensors and expressed in trigeminal ganglion (TG) neurons. In the present study, we found that eugenol concentration-dependently inhibited ASIC currents in TG neurons with an IC₅₀ of 98.8 ± 7.4 μM. Eugenol decreased the maximum response to acidic pH and did not alter pH_0.5 in the concentration-response curve of acidic pH, suggesting a noncompetitive inhibition of ASICs by eugenol. G-proteins were not involved in eugenol-induced inhibition, since pre-application of eugenol also decreased ASIC currents in the presence of the G-protein blocker GDP-β-S. In addition, eugenol also partly inhibited ASIC3 currents in Chinese hamster ovary cells transfected with ASIC3. In conclusion, eugenol partly inhibited ASIC currents in TG neurons in a concentration-dependent, non-competitive and G-protein independent manner. These results suggested that the ASICs could be a molecular target for eugenol in TG neurons, which contributed to its analgesic effect.

Molecular Mechanisms of Action of Eugenol in Cancer: Recent Trends and Advancement

BACKGROUND

Cancer is, at present, among the leading causes of morbidity globally. Despite advances in treatment regimens for cancer, patients suffer from poor prognoses. In this context, the availability of vast natural resources seems to alleviate the shortcomings of cancer chemotherapy. The last decade has seen a breakthrough in the investigations related to the anticancer potential of dietary phytoconstituents. Interestingly, a handsome number of bioactive principles, ranging from phenolic acids, phenylpropanoids, flavonoids, stilbenes, and terpenoids to organosulphur compounds have been screened for their anticancer properties. Among the phenylpropanoids currently under clinical studies for anticancer activity, eugenol is a promising candidate. Eugenol is effective against cancers like breast, cervical, lung, prostate, melanomas, leukemias, osteosarcomas, gliomas, etc., as evident from preclinical investigations.

OBJECTIVE

The review aims to focus on cellular and molecular mechanisms of eugenol for cancer prevention and therapy.

METHODS

Based on predetermined criteria, various scholarly repositories, including PubMed, Scopus, and Science Direct were analyzed for anticancer activities of eugenol.

RESULTS

Different biochemical investigations reveal eugenol inducing cytotoxicity, inhibiting phases of the cell cycles, programmed cell death, and auto-phagocytosis in studied cancer lines; thus, portraying eugenol as a promising anticancer molecule. A survey of current literature has unveiled the molecular mechanisms intervened by eugenol in exercising its anticancer role.

CONCLUSION

Based on the critical analysis of the literature, eugenol exhibits vivid signaling pathways to combat cancers of different origins. The reports also depict the advancement of novel nano-drug delivery approaches upgrading the therapeutic profile of eugenol. Therefore, eugenol nanoformulations may have enormous potential for both the treatment and prevention of cancer.

Safety and Efficacy of Medicinal Plants Used to Manufacture Herbal Products with Regulatory Approval in Uganda: A Cross-Sectional Study

Introduction

The Uganda National Drug Authority requires phytochemical screening, freedom from microbial contamination, and evidence of safety and efficacy of the constituent plants to register herbal products. Since Uganda has no pharmacopeia, safety, efficacy, and plant processing information are not readily available. We documented the plant materials used to manufacture products in Uganda and established evidence of their safety and efficacy and availability of monographs.

Methods

The NDA register of herbal products was reviewed, and a product list was extracted. The herbal products were purchased from local pharmacies, and their labels were studied to identify plant ingredients and drug use. Literature was reviewed to document evidence of the safety and efficacy of the plant materials concerning manufacturer's claims. Also, the WHO and available African Pharmacopeia were searched to establish the availability of the plant monographs.

Results

Of the 84 NDA-registered local products, only 18 were obtained from the market; 82% were indicated for respiratory tract disorders. Thirty-three plant materials were listed with Eucalyptus globulus Labill, being the commonest. Several in vitro and in vivo studies demonstrate efficacy, thus supporting the use of the selected plant species for empirical treatment as stated on the product label. While most plants were safe, some species such as Albizia coriaria Oliv. had dose-dependent toxicities that cannot be predicted in combinations. The WHO, African Pharmacopoeia, and West African Herbal Pharmacopoeia had only 16 plant monographs of the 33 plants of interest. Nevertheless, Aloe vera (L.) Burm.f., Azadirachta indica A.Juss., Zingiber officinale Roscoe, and Allium sativum L. monographs were published by all three pharmacopoeias.

Conclusions

Preclinical evidence of safety and efficacy exists in the literature for most of the plants used to manufacture registered herbal products in Uganda. More specific bioassays and clinical trials are required for the products to provide conclusive evidence of safety and toxicity. Monographs are urgently needed for the Ugandan plants.

Synergistic Herb-Herb Interaction of the Antinociceptive and Anti-Inflammatory Effects of Syzygium aromaticum and Rosmarinus officinalis Combination

The use of alternative medicine to treat pain has been increased, and the combination of several medicinal plants for its relief is a common practice in traditional medicine. The present study is aimed at determining whether a combination of Syzygium aromaticum (S. aromaticum) and Rosmarinus officinalis L. (R. officinalis) potentiates their antinociceptive and anti-inflammatory effects. These effects were explored using the formalin and carrageenan assays in rats, respectively. Animals received local pretreatment with S. aromaticum oil or R. officinalis ethanolic extract (0.1-100 μg/paw) alone or combined in a 1 : 1 rate. Concentration-response curves were built to compare pharmacological responses after an individual administration of S. aromaticum, R. officinalis, or their combination. The pharmacological interaction was investigated by an isobolographic study using the EC₅₀ of each component in a fixed 1 : 1 ratio. S. aromaticum and R. officinalis administered alone showed significant and concentration-dependent antinociceptive and anti-inflammatory effects, but R. officinalis was more potent than S. aromaticum in both the antinociceptive and anti-inflammatory effects (EC₅₀ = 7.96 ± 0.6 μg/paw vs. EC₅₀ = 41.6 ± 1.7 μg/paw; EC₅₀ = 1.97 ± 0.3 μg/paw vs. EC₅₀ = 26.9 ± 2.5 μg/paw, respectively). The isobolographic analysis of the combination of these species in a 1 : 1 ratio showed a synergistic interaction between S. aromaticum and R. officinalis since Z _mix (experimental value) was lower than Z _add (theoretical value) for both the antinociceptive effect (Z _mix = 0.45 ± 0.1 < Z _add = 24.8 ± 1.3) and the anti-inflammatory effect (Z _mix = 5.2 ± 0.6 < Z _add = 14.4 ± 2.2), suggesting a potentiation for both pharmacological effects. These results prove evidence of the efficacy of mixture herb-herb used in folk medicine for pain therapy. It also emphasizes the requirement of pharmacological studies to explore the efficacy and safety of herb interactions.

Impact of eugenol on in vivo model of 6-hydroxydopamine-induced oxidative stress

Oxidative stress is involved in many pathological disturbs, such as neurodegenerative disorders. Eugenol (Eug) is a phenolic compound with antioxidant and neuroprotective activities. Then, this study was conducted to investigate the potential neuroprotective effects of Eug on oxidative stress model induced by 6-hydroxydopamine (6-OHDA) in rats. First, the in vivo oxidative stress model was performed by intrastriatal injection (int.) of 6-OHDA (21 µg), followed by the treatment of Eug (0.1, 1, and 10 mg/kg/7 d) per os (p.o.). On the 7 d, behavioral tests were performed. On the 8 d, all the animals were euthanasied and their cerebral areas were excised for neurochemical and transcriptional analyses. The results showed that the treatment with Eug promoted neuroprotective effects on in vivo through reducing of oxidative stress and modulation of genes related to antioxidant activity. Furthermore, animals treated with Eug demonstrated returning of behavioral performance and body weight gain to normal conditions. Thus, this study reports the neuroprotective effects of Eug against oxidative stress induced by 6-OHDA in rats.

Phytotoxicity, cytotoxicity and chemical composition of Spondias mombin Linn. Stem bark

Background

Spondias mombin Linn. is a tropical climate plant with wide applications in ethnomedicinal practice. This study evaluates the phytotoxicity, cytotoxicity and chemical composition of the plant’s stem bark.

Methods

Dried stem bark sample of Spondias mombin Linn. was subjected to exhaustive extraction and partitioned into sub-fractions (hexane-ethylacetate, ethylacetate, ethylacetate-methanol and methanol) by graded polarity technique. The phytotoxicity and cytotoxicity indices of the crude hydro-ethanol extract and fractions were evaluated using Lemna minor and brine shrimp lethality assays, respectively, while chemical composition of the oily hexane:ethylacetate fraction was determined by gas chromatography-mass spectroscopy (GC-MS) technique.

Results

Phytotoxicity was dose-dependent which ranged from low (crude plant extract), moderate (hexane-ethylacetate and methanol fractions), high (ethylaacetate-methanol fraction) to significant toxicity (ethylacetate fraction) at the highest dose. However, for brine shrimp lethality assay only hexane-ethylacetate (LD50: 284.02 μg/mL) and ethylacetate (LD50: 210.24 μg/mL) fractions were cytotoxic at the highest dose. The GC-MS profile of the oily hexane:ethylacetate fraction identified sixty-eight compounds comprising hydrocarbons, fatty acids, alcohols, steroids, nitrogen and fluoride-containing compounds, terpenes and esters.

Conclusion

This study concludes that fractions of Spondias mombin Lin. could be potentially toxic. While its phytotoxic potential can be useful in the agrochemical industry for the production of natural herbicides, its cytotoxic property can be cautiously harnessed for ethnomedicinal purposes.

Antinociceptive effects of intrathecal cimifugin treatment: a preliminary rat study based on formalin test

Background

Cimifugin is one of the components of the root of Saposhnikovia divaricata. The extract derived from S. divaricata is traditionally used as an analgesic. This study was conducted to evaluate the analgesic effect of intrathecal cimifugin in the formalin test.

Methods

Male Sprague–Dawley rats (n = 20) were randomized into four groups for intrathecal administration of 70% dimethylsulfoxide and various doses of cimifugin (100 μg, 300 μg, and 1,000 μg). The typical flinch response after the injection of 5% formalin into the hind paw was assessed in two distinct phases: phase 1 until 10 min, and phase 2 from 10 min to 60 min. ED₅₀ values were calculated via linear regression.

Results

Intrathecal cimifugin significantly reduced the flinch response in both phases of the formalin test. Significant antinociceptive effects of cimifugin were found with the dose of 300 μg in phase 1 and the dose of 100 μg in phase 2. The ED₅₀ value (95% confidence intervals) of intrathecal cimifugin was 696.1 (360.8–1,342.8) μg during phase 1 and 1,242.8 (42.0–48,292.5) μg during phase 2.

Conclusions

Intrathecal cimifugin has an antinociceptive effect against formalin-induced pain. Cimifugin has an anti-inflammatory effect at low concentrations, and non-inflammatory analgesic effect at higher concentrations.

The role of spinally located dopamine D2 receptors in the regulation of the blood glucose level in mice

BACKGROUND

The possible role of dopamine D₂ receptors located in the spinal cord in the regulation of the blood glucose level have not been investigated before.

METHODS

In the present study, the effect of D₂ receptor agonist and antagonist administered intrathecal (it) injection on the blood glucose level were examined in the Institute of Cancer Research (ICR) mice.

RESULTS

We found that it injection with carmoxirole (D₂ receptor agonist) caused an elevation of the blood glucose level in a dose-dependent manner. Carmoxirole-induced increase of the blood glucose was significantly attenuated by L-741,626 (D₂ receptor antagonist). Previously, we indicated that intrathecal (it) treatment with 0.1 μg/5 μl pertussis toxin (PTX, a G_i/G_o inhibitor) produces a hypoglycemic effect in ICR in a long-term manner. In the present study, it pretreatment with PTX for 6 days almost abolished the hyperglycemic effect induced by carmoxirole. The plasma insulin level was elevated by carmoxirole, and L-741,626 or PTX pretreatment reduced carmoxirole-induced increment of the insulin level. In addition, the plasma corticosterone level was increased by carmoxirole but it pretreatment with L-741,626 or PTX did not affect carmoxirole-induced increment of the corticosterone level.

CONCLUSION

Our results suggest that D₂ receptors located in the spinal cord play an important role in the elevation of the blood glucose level. Spinally located inhibitory G-proteins appear to be involved in hyperglycemic effect induced by carmoxirole.

Viol LC, Maia AFDS, Santos EG, da Silva ÍEP, Mendes TADO, da Silva AM, Dias RS, da Silva CC, Polêto MD, Teixeira RR, de Paula SO. Discovery of novel West Nile Virus protease inhibitor based on isobenzonafuranone and triazolic derivatives of eugenol and indan-1,3-dione scaffolds

The West Nile Virus (WNV) NS2B-NS3 protease is an attractive target for the development of therapeutics against this arboviral pathogen. In the present investigation, the screening of a small library of fifty-eight synthetic compounds against the NS2-NB3 protease of WNV is described. The following groups of compounds were evaluated: 3-(2-aryl-2-oxoethyl)isobenzofuran-1(3H)-ones; eugenol derivatives bearing 1,2,3-triazolic functionalities; and indan-1,3-diones with 1,2,3-triazolic functionalities. The most promising of these was a eugenol derivative, namely 4-(3-(4-allyl-2-methoxyphenoxy)-propyl)-1-(2-bromobenzyl)-1H-1,2,3-triazole (35), which inhibited the protease with IC50 of 6.86 μmol L-1. Enzyme kinetic assays showed that this derivative of eugenol presents competitive inhibition behaviour. Molecular docking calculations predicted a recognition pattern involving the residues His51 and Ser135, which are members of the catalytic triad of the WNV NS2B-NS3 protease.

Effects of Eugenol on Pain Response to the Formalin Test and Plasma Antioxidant Activity in High Fructose Drinking Water in Male Rats

Background:

Increased consumption of fructose in recent years has increased the risk of developing metabolic syndrome. In this syndrome, induction of oxidative stress, cellular dysfunction, and decrease of antioxidant capacity can change response to pain. Therefore, this study aims to investigate the antinociceptive and antioxidant effects of eugenol on metabolic syndrome induced by a fructose-rich diet in rats.

Methods:

The rats were randomly assigned to five groups, to be under experiment for eight weeks. The first, control group, the second fructose 10% plus tween 0.5% (Fr + veh), the third fructose 10% (Fr), and the fourth fructose 10% plus a single dose of eugenol 100 mg/kg (Fr + EoS). However, the fifth obtained fructose 10% plus a continuous dose of eugenol 20 mg/kg/day (Fr + EoC) for the last 10 days of the experiment. After formalin test, blood samples were taken from the animals’ hearts followed by analysis for biochemical factors.

Results:

This study shows that fructose administration does not change any pain response and there are not any changes in pain response between Fr group and control group. However, treatment with single and continuous dose of eugenol in Fr + EoS and Fr + EoC groups significantly decreases response to pain in the first and second phase of formalin test in comparison with Fr group (P<0.05). Continuous does of eugenol improved serum malondialdehyde and total antioxidant capacity levels in Fr + Eoc group in comparison with Fr group.

Conclusions:

In the present work, new findings suggest the beneficial effects of eugenol in pain relief, improved serum glucose, insulin levels, and improved antioxidant activity in metabolic syndrome.

Antinociceptive action of Achillea biebersteinii methanolic flower extract is mediated by interaction with cholinergic receptor in mouse pain models

Achillea biebersteinii is a perennial aromatic herb that grows in the Mediterranean area. The leaves of this plant are used in foods as bittering and appetizing agents. In folk medicine, it is used for the treatment of stomachache and abdominal pain. In this study, the analgesic effect of A. biebersteinii methanolic flower extract was tested in three pain models, namely: writhing, tail-flick and paw-licking (formalin) tests. A. biebersteinii extract inhibited abdominal cramps produced by acetic acid. The effect of A. biebersteinii was better than that of 70 mg/kg indomethacin. In tail flick, A. biebersteinii extract increased latency at 30 min and was as effective as 100 mg/kg diclofenac sodium. In formalin test, A. biebersteinii extracts decreased paw-licking and flinching response in early and late phases. Atropine blocked the action of A. biebersteinii extract (300 mg/kg) in the late phase of formalin test as well as in writhing and tail-flick tests. GC-MS analysis revealed that ascaridole and iso-ascaridole were the main constituents of A. biebersteinii flower extract. In conclusion, this study shows for the first time that the antinociceptive effect of A. biebersteinii is mediated by the cholinergic receptor.

Eugenol enhances proliferation and migration of mouse bone marrow-derived mesenchymal stem cells in vitro

Mesenchymal stem cells (MSCs) have received considerable attention in regenerative medicine during the past decade. Eugenol is a natural and versatile vegetable molecule, which has a wide variety of therapeutic effects. Although different biological and pharmaceutical functions of Eugenol are well known, its effect on MSCs has not been studied yet. Therefore, this study was focused on investigating the effect of Eugenol on the proliferation and migration of bone marrow (BM)-derived MSCs in vitro. To do so, BM-MSCs were isolated from 4 to 8 weeks old NMRI mice. Cytotoxicity of Eugenol on MSCs was evaluated by MTT assay at 24, 48 and 72 h after treatment. In addition, its effect was assessed on the proliferation and migration of MSCs using wound healing assay in vitro and quantitative gene expression analysis for Oct4, Sox2, Cyclin-D1, Rex1, Tex10, Cxcr4, Vla4 and c-Met. Results showed that Eugenol reduced the number of MSCs in a dose- and time-dependent manner. The median inhibition concentration of Eugenol on MSCs was 400 μg/ml at 24 and 48 h and 200 μg/ml at 72 h after treatment. Moreover, about 90% viability of MSCs was detected at concentrations ≤12.5 μg/ml. The wound healing assay and gene expression analysis demonstrated that Eugenol promoted the migratory potential of MSCs through up-regulation of c-Met. Moreover, Eugenol has enhanced the proliferation of MSCs via over-expression of Sox2, Rex1 and Tex10. In conclusion, this study revealed that Eugenol enhances the proliferation and migration of MSCs, and thus this will be beneficial to the field of regenerative medicine.

Analgesic-Like Activity of Essential Oil Constituents: An Update

The constituents of essential oils are widely found in foods and aromatic plants giving characteristic odor and flavor. However, pharmacological studies evidence its therapeutic potential for the treatment of several diseases and promising use as compounds with analgesic-like action. Considering that pain affects a significant part of the world population and the need for the development of new analgesics, this review reports on the current studies of essential oils’ chemical constituents with analgesic-like activity, including a description of their mechanisms of action and chemical aspects.

Effects of topical and systemic administration of Eugenia caryophyllata buds essential oil on corneal anesthesia and analgesia

Clinical studies suggest that essential oil of Eugenia caryophyllata (Clove) buds (EOEC) is efficacious in the treatment of dental pain. In the present study, we investigated the analgesic and local anesthetic effects of EOEC and its possible mechanisms of action in acute corneal pain in rats. EOEC was extracted by hydro-distillation in a Clevenger type apparatus from clove buds. The acute corneal pain was induced by applying a drop (40 µl) of 5 M NaCl solution on the corneal surface, and the numbers of eye wipes were counted during the first 30 s. The mechanical sensation of the cornea was evaluated by calibrated Von Frey filaments. Systemic administration of EOEC (100 and 200 mg/kg, SC) and morphine (2.5 and 5 mg/kg, IP) produced a significant antinociceptive effect in acute corneal pain. Pretreatment with naloxone or atropine prevented the EOEC-induced analgesia. However, L-arginine and methylene blue did not change the suppressive effect of EOEC on corneal pain response. Topical application of EOEC, eugenol and lidocaine significantly decreased corneal sensitivity. Combination treatments of eugenol (25 µg) with lidocaine (0.5%) and EOEC (50 µg) with lidocaine (0.5%) also significantly suppressed corneal sensitivity. Systemic administration of EOEC produced analgesia in the acute corneal pain through mechanisms that involved both opioidergic and cholinergic systems. In addition, topical instillation of EOEC, eugenol, and lidocaine produced local anesthesia in the rat cornea. Sub-anesthetic doses of EOEC or eugenol produced a significant local anesthetic effect when concurrently used with the sub-anesthetic dose of lidocaine.

Ortho-eugenol exhibits anti-nociceptive and anti-inflammatory activities

Ortho-eugenol is a much used phenylpropanoid whose ability to reduce pain and inflammation has never been studied. Researching ortho-eugenol's antinociceptive and anti-inflammatory activity, and its possible mechanisms of action is therefore of interest. The administration of vehicle, ortho-eugenol (50, 75 and 100mg/kg i.p.), morphine (6mg/kg, i.p.) or dexamethasone (2mg/kg, s.c.) occurred 30min before the completion of pharmacological tests. Pretreatment with ortho-eugenol did not change motor coordination test results, but reduced the number of writhes and licking times in the writhing test and glutamate test, respectively. The reaction time from thermal stimulus was significantly increased in the hot plate test after administration of ortho-eugenol. Treatment with yohimbine reversed the antinociceptive effect of ortho-eugenol, suggesting involvement of the adrenergic system. In anti-inflammatory tests, ortho-eugenol inhibited acetic acid induced vascular permeability and leukocyte migration, reducing TNF-α and IL-1β by virtue of its suppression of NF-κB and p38 phosphorylated forms in the peritonitis test. From these results, ortho-eugenol antinociceptive effects mediated by the adrenergic system and anti-inflammatory activity through regulation of proinflammatory cytokines and phosphorylation of NF-kB and p38 become evident for the first time.

Analgesic Potential of Essential Oils

Pain is an unpleasant sensation associated with a wide range of injuries and diseases, and affects approximately 20% of adults in the world. The discovery of new and more effective drugs that can relieve pain is an important research goal in both the pharmaceutical industry and academia. This review describes studies involving antinociceptive activity of essential oils from 31 plant species. Botanical aspects of aromatic plants, mechanisms of action in pain models and chemical composition profiles of the essential oils are discussed. The data obtained in these studies demonstrate the analgesic potential of this group of natural products for therapeutic purposes.

Eugenol inhibits the GABAA current in trigeminal ganglion neurons

Eugenol has sedative, antioxidant, anti-inflammatory, and analgesic effects, but also serves as an irritant through the regulation of a different set of ion channels. Activation of gamma aminobutyric acid (GABA) receptors on sensory neurons leads to the stabilization of neuronal excitability but contributes to formalin-induced inflammatory pain. In this study, we examined the effect of eugenol on the GABA-induced current in rat trigeminal ganglia (TG) neurons and in human embryonic kidney (HEK) 293 cells expressing the GABAA receptor α1β2γ2 subtype using the whole-cell patch clamp technique. RT-PCR and Western blot analysis were used to confirm the expression of GABAA receptor γ2 subunit mRNA and protein in the TG and hippocampus. Eugenol decreased the amplitude ratio of the GABA-induced current to 27.5 ± 3.2% (p < 0.05) in TG neurons, which recovered after a 3-min washout. In HEK 293 cells expressing the α1β2γ2 subtype, eugenol inhibited GABA-induced currents in a dose-dependent manner. Application of eugenol also decreased the GABA response in the presence of a G-protein blocker. Eugenol pretreatment with different concentrations of GABA resulted in similar inhibition of the GABA-induced current in a non-competitive manner. In conclusion, eugenol inhibits the GABA-induced current in TG neurons and HEK 293 cells expressing the GABAA receptor in a reversible, dose-dependent, and non-competitive manner, but not via the G-protein pathway. We suggest that the GABAA receptor could be a molecular target for eugenol in the modulation of nociceptive information.

Eugenol-rich Fraction of Syzygium aromaticum (Clove) Reverses Biochemical and Histopathological Changes in Liver Cirrhosis and Inhibits Hepatic Cell Proliferation

Background:

Dried flower bud of Syzygium aromaticum (clove) is rich in eugenol, an antioxidant and antiinflammatory compound that can protect liver against injury. Clove, besides eugenol, also contains other pharmacologically active phytochemicals such as β-sitosterol and ascorbic acid. This study reports the effect of eugenol-rich fraction (ERF) of clove on liver cirrhosis induced by thioacetamide.

Methods:

Cirrhosis of the liver, which predisposes to hepatocellular carcinoma, was induced by administering thioacetamide (0.03%) in drinking water for 16 weeks. Cirrhotic animals were divided into two groups; the treated group was administered ERF for 9 weeks, one week after discontinuation of thioacetamide, while the other group received normal saline for a similar duration of time.

Results:

The treatment with ERF, as determined by histopathology and through a battery of biochemical markers of hepatic injury, oxidative stress and drug metabolizing enzymes, significantly ameliorated the signs of liver cirrhosis. It lowered the elevated levels of alkaline phosphatase, γ-glutamyl transferase and other biochemical changes in liver cirrhosis. Histopathology of the liver corroborated the effect of ERF with biochemical findings. ERF treatment further inhibited cell proliferation, as demonstrated by reduced [³H]-thymidine uptake.

Conclusions:

Data provide evidence supporting the protective action of ERF on liver cirrhosis. The study assumes significance because cirrhosis predisposes the liver to cancer, which is characterized by abnormal cell proliferation. ERF in this study is reported to inhibit hepatic cell proliferation and at the same time decrease oxidative stress, which might be the mechanism of protection against liver cirrhosis.

Composition of Essential Oil from Aerial and Underground Parts of Geum rivale and G. urbanum Growing in Poland

A study of the composition of essential oils from aerial and underground parts of Geum rivale L. and Geum urbanum L. growing in Poland led to the identification of 130 compounds. The main compound of the essential oil from underground parts of G. urbanum was eugenol (69.2%), whereas cis-myrtanal (53.3%) was the major constituent of the essential oil from roots of G. rivale. The essential oils from aerial parts of the plants contained large amounts of aliphatic compounds with ( Z)-3-hexenol (38.4%) being the dominant constituent of the essential oil from aerial parts of G. urbanum and 1-octen-3-ol (33.9%) from G. rivale.

Medicinal formulations of a Kanda tribal healer--a tribe on the verge of disappearance in Bangladesh

The Kanda tribe is one of the lesser known small tribes of Bangladesh with an estimated population of about 1700 people (according to them), and on the verge of extinction as a separate entity. To some extent, they have assimilated with the surrounding mainstream Bengali-speaking population, but they still maintain their cultural practices including traditional medicinal practices, for which they have their own tribal healers. Nothing at all has been documented thus far about their traditional medicinal practices and formulations, which are on the verge of disappearance. The Kanda tribe can be found only in scattered tea gardens of Sreemangal in Sylhet district of Bangladesh; dispersion of the tribe into small separated communities is also contributing to the fast losing of traditional medicinal practices. The objective of the present study was to conduct an ethnomedicinal survey among the traditional healers of the Kanda tribe (in fact, only one such healer was found after extensive searches). Information was collected from the healer with the help of a semi-structured questionnaire and the guided field-walk method. A total of 24 formulations were obtained from the healer containing 34 plants including two plants, which could not be identified. Besides medicinal plants, the Kanda healer also used the body hairs of the Asiatic black bear (Ursus thibetanus) and bats (Pteropus giganteus giganteus) in one of his formulation for treatment of fever with shivering. The ailments treated by the Kanda healer were fairly common ailments like cuts and wounds, skin diseases, helminthiasis, fever, respiratory problems (coughs, asthma), gastrointestinal disorders (stomach pain, constipation, diarrhea), burning sensations during urination, various types of pain (headache, body ache, toothache, ear ache), conjunctivitis, poisonous snake, insect or reptile bites, jaundice, and bone fractures. A number of important drugs in allopathic medicine like quinine, artemisinin, and morphine (to name only a few) have been discovered from observing indigenous medicinal practices. From that view point, the formulations used by the Kanda healer merit scientific studies for their potential in the discovery of cheap and effective new drugs. Scientific validation of the medicinal formulations of the Kanda healer can also be effective for treatment of ailments among this tribe, which does not have or does not want to have any contact with modern medicine.

Endogenous opiates and behavior: 2011

This paper is the thirty-fourth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2011 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 (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration (Section 16); and immunological responses (Section 17).

Ameliorative Effects of Scopoletin from Crossostephium chinensis against Inflammation Pain and Its Mechanisms in Mice

Scopoletin exists in nature as an anti-oxidant, hepatoprotective, and anti-inflammatory activities reagent. In this study, we have investigated the analgesic effects of the scopoletin using the models of acetic acid-induced writhing response and the formalin test, the anti-inflammatory effects of scopoletin using model of λ-carrageenan (Carr)-induced paw edema. The treatment of ICR mice with scopoletin inhibited the numbers of writhing response and the formalin-induced pain in the late phase. This study demonstrated that the administration of scopoletin resulted in the reduction of Carr-induced mice edema, and it increased the activities of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) after Carr injection. We also demonstrated scopoletin significantly attenuated the malondialdehyde (MDA) level in the edema paw after Carr injection. Scopoletin decreased the NO, tumor necrosis factor (TNF-α) and prostaglandin E2 (PGE₂) levels on serum after Carr injection. Scopoletin decreased Carr-induced inducible NO synthase (iNOS) and cyclooxygenase-2 (COX-2) expressions in the edema paw. These anti-inflammatory mechanisms of scopoletin might be related to the decrease in the level of MDA via increasing the activities of SOD, CAT, and GPx in the edema paw. Also, scopoletin could affect the production of NO, TNF-α, and PGE₂, and therefore affect the anti-inflammatory effects.

Eugenol--from the remote Maluku Islands to the international market place: a review of a remarkable and versatile molecule

Eugenol is a major volatile constituent of clove essential oil obtained through hydrodistillation of mainly Eugenia caryophyllata (=Syzygium aromaticum) buds and leaves. It is a remarkably versatile molecule incorporated as a functional ingredient in numerous products and has found application in the pharmaceutical, agricultural, fragrance, flavour, cosmetic and various other industries. Its vast range of pharmacological activities has been well-researched and includes antimicrobial, anti-inflammatory, analgesic, anti-oxidant and anticancer activities, amongst others. In addition, it is widely used in agricultural applications to protect foods from micro-organisms during storage, which might have an effect on human health, and as a pesticide and fumigant. As a functional ingredient, it is included in many dental preparations and it has also been shown to enhance skin permeation of various drugs. Eugenol is considered safe as a food additive but due to the wide range of different applications, extensive use and availability of clove oil, it is pertinent to discuss the general toxicity with special reference to contact dermatitis. This review summarises the pharmacological, agricultural and other applications of eugenol with specific emphasis on mechanism of action as well as toxicity data.

Stimulus selection for intranasal sensory isolation: eugenol is an irritant

Both the olfactory and the trigeminal systems are able to respond to intranasal presentations of chemical vapor. Accordingly, when the nose detects a volatile chemical, it is often unclear whether we smell it, feel it, or both. The distinction may often be unimportant in our everyday perception of fragrances or aromas, but it can matter in experiments that purport to isolate olfactory processes or study the interaction between olfaction and chemesthesis. Researchers turn to a small pool of compounds that are believed to be "pure olfactory" stimuli with little or no trigeminal impact. The current report reexamines one such commonly used compound, namely eugenol, a flavor and fragrance ingredient that has anesthetic properties under some conditions. Using a standard method involving many trials during an experimental session (Experiment 1), subjects were unable to reliably lateralize eugenol, consistent with claims that this compound is detected primarily through olfaction. However, with more limited exposure (Experiments 2 and 3), subjects were able to lateralize eugenol. We speculate that anesthetic properties of eugenol could blunt its trigeminal impact in some paradigms. Regardless, the current experiments suggest that eugenol can in fact stimulate the trigeminal nerve but in a complex concentration-dependent manner. Implications and strategies for selection of model odorants are discussed.