A comparison of hyperalgesia and neurogenic inflammation induced by melittin and capsaicin in humans

Impact of bee venom supplement on productive performance, health status and economics of weaned male rabbits: Considering breed and dosage factors

The objectives of the present study were to investigate the potential effects of purified bee venom (BV) on various aspects of growth, carcass, antioxidant, intestinal bacterial count and economic considerations in rabbits. A total of 240 male rabbits, comprising two distinct breeds (V-Line and New Zealand White [NZW]), 5 weeks old, with an average live body weight (BW) of 680 ± 20 g, were randomly divided into six groups, each containing 30 rabbits. Each group had five replicates, with six rabbits in each replicate. The allocation of animals to the groups followed a fully factorial design, incorporating two factors: breed (V-Line and NZW) and four levels of purified BV derived from Apis Mellifera. The control group (G1) received a basal diet without additives. The other three groups (G2, G3 and G4) received the basal diet with BV supplementation in their drinking water at 0.5, 1 and 2 mg/L respectively. The study results indicated that NZW rabbits significantly enhanced feed conversion ratio while maintaining consistent carcass attributes compared to the V-Line breed. Despite variations in growth parameters being less pronounced, the supplementation of BV at levels of 1-2 mg/L demonstrated significant improvements in various other parameters. Notably, the interaction between the BV supplement and the breed factor (p < 0.001) yielded notable distinctions in most production metrics, encompassing BW, weight gain, feed conversion, carcass attributes and blood parameters. Increasing levels of BV supplementation, particularly at 1 mg/L, led to substantial improvements in serum and tissue metabolites. Moreover, the levels of total bacterial count and Escherichia coli in the jejunum and colon were significantly diminished, while the population of Lactobacilli in the colon was augmented (p < 0.001) in rabbits from both breeds receiving BV supplementation (1-2 mg/L) compared to the control group. The results underscore the potential of the BV supplement to enhance final weights, bolster antioxidant status and mitigate the presence of pathogenic bacteria, thereby contributing to enhanced economic efficiency in rabbits. Further inquiries are warranted to comprehensively investigate BV supplementation's potential advantages and limitations across different breeds and dosage levels.

The current landscape of the antimicrobial peptide melittin and its therapeutic potential

Melittin, a main component of bee venom, is a cationic amphiphilic peptide with a linear α-helix structure. It has been reported that melittin can exert pharmacological effects, such as antitumor, antiviral and anti-inflammatory effects in vitro and in vivo. In particular, melittin may be beneficial for the treatment of diseases for which no specific clinical therapeutic agents exist. Melittin can effectively enhance the therapeutic properties of some first-line drugs. Elucidating the mechanism underlying melittin-mediated biological function can provide valuable insights for the application of melittin in disease intervention. However, in melittin, the positively charged amino acids enables it to directly punching holes in cell membranes. The hemolysis in red cells and the cytotoxicity triggered by melittin limit its applications. Melittin-based nanomodification, immuno-conjugation, structural regulation and gene technology strategies have been demonstrated to enhance the specificity, reduce the cytotoxicity and limit the off-target cytolysis of melittin, which suggests the potential of melittin to be used clinically. This article summarizes research progress on antiviral, antitumor and anti-inflammatory properties of melittin, and discusses the strategies of melittin-modification for its future potential clinical applications in preventing drug resistance, enhancing the selectivity to target cells and alleviating cytotoxic effects to normal cells.

Melittin: a possible regulator of cancer proliferation in preclinical cell culture and animal models

BACKGROUND

Melittin is a water-soluble cationic peptide derived from bee venom that has been thoroughly studied for the cure of different cancers. However, the unwanted interactions of melittin produce hemolytic and cytotoxic effects that hinder their therapeutic applications. To overcome the shortcomings, numerous research groups have adopted different approaches, including conjugation with tumor-targeting proteins, gene therapy, and encapsulation in nanoparticles, to reduce the non-specific cytotoxic effects and potentiate their anti-cancerous activity.

PURPOSE

This article aims to provide mechanistic insights into the chemopreventive activity of melittin and its nanoversion in combination with standard anti-cancer drugs for the treatment of cancer.

METHODS

We looked over the pertinent research on melittin's chemopreventive properties in online databases such as PubMed and Scopus.

CONCLUSION

In the present article, the anti-cancerous effects of melittin on different cancers have been discussed very nicely, as have their possible mechanisms of action to act against different tumors. Besides, it interacts with different signal molecules that regulate the diverse pathways of cancerous cells, such as cell cycle arrest, apoptosis, metastasis, angiogenesis, and inflammation. We also discussed the recent progress in the synergistic combination of melittin with standard anti-cancer drugs and a nano-formulated version of melittin for targeted delivery to improve its anticancer potential.

Bee Products for Poultry and Rabbits: Current Challenges and Perspectives

Poultry and rabbit production are important and rapidly growing agricultural subsectors, particularly in several developing countries. To ensure the sustainability of poultry and rabbit production, realistic poultry and rabbit farming practices must be improved. Apitherapy is a traditional alternative medicine that involves the prevention and treatment of some diseases with several bee products including propolis, royal jelly, pollen, and venom. More feeding investigations on the numerous benefits of bee products for poultry and rabbits are crucial to be addressed. Poultry and rabbit production has recently experienced numerous challenges, including climate change, disease spread, and antibiotic misuse. Improving animal welfare, health, and production is a top priority for all livestock farms, as is supplying consumers with safe and healthy products. Therefore, this review aims to collect and investigate recent relevant literature on the use of bee products, as feed additives, drinking water supplements, and injections, for poultry and rabbits to improve animal health and production. From the current findings, bee products can improve the growth and immunological performance of small-livestock animals, such as poultry and rabbits, by activating digestive enzymes, maintaining microbial balance, and promoting vitamin synthesis. Therefore, bee products could be a promising natural alternative to growth promoters, reproductive stimulants, and immunological enhancers in poultry and rabbit farms to provide safe and healthy products for humans.

You are what you eat-ecological niche and microhabitat influence venom activity and composition in aquatic bugs

True water bugs (Nepomorpha) are mostly predacious insects that live in aquatic habitats. They use their piercing-sucking mouthparts to inject venomous saliva that facilitates the capture and extra-oral digestion of prey animals, but their venom can also be deployed for defence. In Central Europe, nepomorph species representing different families coexist in the same habitat. However, their feeding ecology, including venom composition and deployment, has not been investigated in detail. We used an integrated proteotranscriptomic and bioactivity-based approach to test whether venom composition and activity differ between four water bug species sharing the same habitat but occupying different ecological niches. We found considerable species-dependent differences in the composition of digestive enzymes and venom components that probably evolved as adaptations to particular food sources, foraging strategies and/or microhabitats. The venom of Corixa punctata differed substantially from that of the three strictly predatory species (Ilyocoris cimicoides, Notonecta glauca and Nepa cinerea), and the abundance of herbivory-associated proteins confirms a mostly plant-based diet. Our findings reveal independent adaptations of the digestive and defensive enzyme repertoires accompanied by the evolution of distinct feeding strategies in aquatic bugs.

Capsaicin, a Phytochemical From Chili Pepper, Alleviates the Ultraviolet Irradiation-Induced Decline of Collagen in Dermal Fibroblast via Blocking the Generation of Reactive Oxygen Species

Capsaicin, a major ingredient in chili pepper, has broad pharmaceutical applications, including relieving pain, anti-inflammation, and treating psoriasis. In dermatological biology, capsaicin has been shown to prevent the ultraviolet (UV)-induced melanogenesis via TRPV1 receptor. To strengthen the roles of capsaicin in skin function, the damaged skin, triggered by exposure to UV, was reversed by capsaicin in both in vitro and in vivo models. In cultured dermal fibroblasts, the exposure to UV induced a decrease of collagen synthesis and increases expression of matrix metalloproteinases (MMPs), generation of reactive oxygen species (ROS), and phosphorylation of Erk and c-Jun, and these events subsequently led to skin damage. However, the UV-mediated damages could be reversed by pre-treatment with capsaicin in a dose-dependent manner. The effect of capsaicin in blocking the UV-mediated collagen synthesis was mediated by reducing generation of ROS in dermal fibroblasts, instead of the receptor for capsaicin. Hence, capsaicin has high potential value in applying as an agent for anti-skin aging in dermatology.

Melittin administration ameliorates motor function, prevents apoptotic cell death and protects Purkinje neurons in the rat model of cerebellar ataxia induced by 3-Acetylpyridine

Cerebellar ataxia (CA) is a condition in which cerebellar dysfunction leads to movement disorders such as dysmetria, asynergy and dysdiadochokinesia. This study investigates the therapeutic effects of Melittin (MEL) on 3-acetylpyridine-induced (3-AP) cerebellar ataxia (CA) rat model. Initially, CA rat models were generated by 3-AP administration followed by the intraperitoneal injection of MEL. Then, motor performance and electromyography (EMG) activity were assessed. Afterwards, the pro-inflammatory cytokines were analyzed in the cerebellar tissue. Moreover, the anti-apoptotic role of MEL in CA and its relationship with the protection of Purkinje cells were explored. The findings showed that the administration of MEL in a 3-AP model of ataxia improved motor coordination (P < 0.001) and neuro-muscular activity (p < 0.05), prevented the cerebellar volume loss (P < 0.01), reduced the level of inflammatory cytokines (p < 0.05) and thwarted the degeneration of Purkinje cells against 3-AP toxicity (P < 0.001). Overall, the findings imply that the MEL attenuates the 3-AP-induced inflammatory response. As such, it could be used as a treatment option for CA due to its anti-inflammatory effects.

A Review of Honeybee Venom Allergens and Allergenicity

Honeybee venom is a source of proteins with allergenic properties which can result in in various symptoms, ranging from local reactions through to systematic life-threatening anaphylaxis, or even death. According to the World Allergy Organization (WAO), honeybee venom allergy is one of the most common causes of anaphylaxis. Among the proteins present in honeybee venom, 12 protein fractions were registered by the World Health Organization’s Allergen Nomenclature Sub-Committee (WHO/IUIS) as allergenic. Most of them are highly immunogenic glycoproteins that cross-react with IgE and, as a consequence, may give false positive results in allergy diagnosis. Allergenic fractions are different in terms of molecular weight and biological activity. Eight of these allergenic fractions have also been identified in honey. This explains frequent adverse reactions after consuming honey in people allergic to venom and sheds new light on the causes of allergic symptoms in some individuals after honey consumption. At the same time, it also indicates the possibility of using honey as a natural source of allergen in specific immunotherapy.

Recent developments in animal venom peptide nanotherapeutics with improved selectivity for cancer cells

Animal venoms are a rich source of bioactive peptides that efficiently modulate key receptors and ion channels involved in cellular excitability to rapidly neutralize their prey or predators. As such, they have been a wellspring of highly useful pharmacological tools for decades. Besides targeting ion channels, some venom peptides exhibit strong cytotoxic activity and preferentially affect cancer over healthy cells. This is unlikely to be driven by an evolutionary impetus, and differences in tumor cells and the tumor microenvironment are probably behind the serendipitous selectivity shown by some venom peptides. However, strategies such as bioconjugation and nanotechnologies are showing potential to improve their selectivity and potency, thereby paving the way to efficiently harness new anticancer mechanisms offered by venom peptides. This review aims to highlight advances in nano- and chemotherapeutic tools and prospective anti-cancer drug leads derived from animal venom peptides.

Improving the reproductive, immunity and health status of rabbit does using honey bee venom

The aim of the present study was to investigate the long-term effect of using bee venom (BV) on the reproductive performance, immune, and health status of rabbit does and its effect on their litters. Sixty mature does, from Spanish V-line rabbit stock, were randomly assigned to four homogeneous groups with 15 does each. The 1^st , 2^nd and 3^rd groups were injected twice weekly under the neck skin with 0.1 ml solution contains 0.1, 0.2 and 0.3 mg BV/rabbit respectively. The 4^th group served as a control group. From the results, litter size at birth, litter weight and survival rate at weaning age as well as milk yield were significantly (p ≤ 0.05) increased in BV groups than in the control group. Serum estradiol 17-β (E2) was significantly (p ≤ 0.05) higher (15%) in the rabbit does treated with BV compared to the control group. The treated does with BV at any study doses showed a gradual and significant (p ≤ 0.05) decrease (12%) in serum progesterone levels (P4) compared to the control. They also showed a significant (p≤0.05) increase in conception (17%) and fertility rates (10%) compared to the control does. Treatment of rabbit does with BV caused a gradual and significant (p ≤ 0.05) reduction in both aspartate aminotransferase (AST) (16%) and alanine aminotransferase (ALT) (37%) liver enzyme activities. Additionally, results have shown that BV resulted in a gradual and significant (p ≤ 0.05) increase in total antioxidant capacity (TAC), antioxidative enzymes such as glutathione S-transferase (GST) and glutathione peroxidase (GPx), serum IgG, IgM and IgA levels with significant (p ≤ 0.05) decrease in malondialdehyde (MDA) and thiobarbituric acid reactive substances (TBARS) in BV groups compared to the control group. Results suggest that BV can be used in rabbit farming as an effective and safe alternative to artificial chemical drugs (sexual-stimulants) to improve certain reproductive traits, immune response and health.

A test-retest reliability study of assessing small cutaneous fibers by measuring current perception threshold with pin electrodes

Background

The quantitative measurement of current perception threshold (CPT) has been used as a method to assess the function of nerve fibers in neuropathy diseases. The aim of this study was to assess the test-retest reliability measuring CPT using the circular pin electrodes for assessing the function of cutaneous thin nerve fibers.

Methods

CPT measurement was repeated on two separate days with at least one-week interval in 55 volunteers. Superficial blood flow (SBF) and skin temperature (ST) were measured on the skin in an around area concentric to the circular pin electrodes after the process of finding CPTs. The coefficient of variation (CV) and intra-class correlation coefficient (ICC) were calculated. The correlation between each two of CPT, SBF increment and ST increment was analyzed.

Results

No significant differences were found for CPT, SBF and ST between two sessions. SBF was found to be significantly increased after the process of finding CPT. CPT values of males were found to be higher than females. SBF increment was found to be positively correlated with ST increment. The ICC values for CPT, SBF and ST were 0.595, 0.852 and 0.728, respectively. The CV values for CPT, SBF and ST were 25.53%, 12.59% and 1.94%, respectively.

Conclusions

The reliability of CPT measurement using circular pin electrodes is fair, and need consistence of measurements in longitudinal studies.

Moving Pieces in a Cellular Puzzle: A Cryptic Peptide from the Scorpion Toxin Ts14 Activates AKT and ERK Signaling and Decreases Cardiac Myocyte Contractility via Dephosphorylation of Phospholamban

Cryptic peptides (cryptides) are biologically active peptides formed after proteolysis of native precursors present in animal venoms, for example. Proteolysis is an overlooked post-translational modification that increases venom complexity. The tripeptide KPP (Lys-Pro-Pro) is a peptide encrypted in the C-terminus of Ts14-a 25-mer peptide from the venom of the Tityus serrulatus scorpion that has a positive impact on the cardiovascular system, inducing vasodilation and reducing arterial blood pressure of hypertensive rats among other beneficial effects. A previous study reported that KPP and its native peptide Ts14 act via activation of the bradykinin receptor B2 (B2R). However, the cellular events underlying the activation of B2R by KPP are unknown. To study the cell signaling triggered by the Ts14 cryptide KPP, we incubated cardiac myocytes isolated from C57BL/6 mice with KPP (10^-7 mol·L^-1) for 0, 5, or 30 min and explored the proteome and phosphoproteome. Our results showed that KPP regulated cardiomyocyte proteins associated with, but not limited to, apoptosis, muscle contraction, protein turnover, and the respiratory chain. We also reported that KPP led to AKT phosphorylation, activating AKT and its downstream target nitric oxide synthase. We also observed that KPP led to dephosphorylation of phospholamban (PLN) at its activation sites (S16 and T17), leading to reduced contractility of treated cardiomyocytes. Some cellular targets reported here for KPP (e.g., AKT, PLN, and ERK) have already been reported to protect the cardiac tissue from hypoxia-induced injury. Hence, this study suggests potential beneficial effects of this scorpion cryptide that needs to be further investigated, for example, as a drug lead for cardiac infarction.

Effect of bee venom on reproductive performance and immune response of male rabbits

The current study aimed to investigate the effects of injecting bucks with different doses of bee venom (BV) on reproductive performance and immune response during the summer season. Forty-eight male V-line rabbits were randomly distributed among four homogeneous groups (12 bucks each). Three groups were injected BV under the neck skin with 0.1 (G1), 0.2 (G2) and 0.3 (G3) mg/rabbit twice weekly over 20 wks of treatment period. The 4^th group (G0) was not injected BV and served as a control group. Buck groups that were treated with BV showed significantly (p≤0.05) shorter reaction time (increased libido) compared to the control, and this effect was BV dose-dependent manner. Viable sperm and concentration, total sperm output, live sperm, and fertility percentage were significantly (p≤0.05) higher in BV groups than in the control group. Additionally, testosterone concentration, and some other blood biochemical constituents (total protein, albumin, and glucose) were significantly (p≤0.05) higher in BV groups than those in the control group. The BV doses resulted in a significant (p≤0.05) increase of antioxidant indices (TAC, GST, and GSH) compared to the control group. Furthermore, the Immunoglobulin A (IgA) and immunoglobulin M (IgM) were significantly (p≤0.05) higher in BV groupscompared to the control group. From these results, we concluded that BV had significant positive impacts on some semen quality traits, sexual behavior, blood biochemical parameters, blood antioxidant content, lipid peroxidation biomarkers, and immune response in V-line bucks.

Synergistic Effects of Melittin and Plasma Treatment: A Promising Approach for Cancer Therapy

Melittin (MEL), a small peptide component of bee venom, has been reported to exhibit anti-cancer effects in vitro and in vivo. However, its clinical applicability is disputed because of its non-specific cytotoxicity and haemolytic activity in high treatment doses. Plasma-treated phosphate buffered saline solution (PT-PBS), a solution rich in reactive oxygen and nitrogen species (RONS) can disrupt the cell membrane integrity and induce cancer cell death through oxidative stress-mediated pathways. Thus, PT-PBS could be used in combination with MEL to facilitate its access into cancer cells and to reduce the required therapeutic dose. The aim of our study is to determine the reduction of the effective dose of MEL required to eliminate cancer cells by its combination with PT-PBS. For this purpose, we have optimised the MEL threshold concentration and tested the combined treatment of MEL and PT-PBS on A375 melanoma and MCF7 breast cancer cells, using in vitro, in ovo and in silico approaches. We investigated the cytotoxic effect of MEL and PT-PBS alone and in combination to reveal their synergistic cytological effects. To support the in vitro and in ovo experiments, we showed by computer simulations that plasma-induced oxidation of the phospholipid bilayer leads to a decrease of the free energy barrier for translocation of MEL in comparison with the non-oxidized bilayer, which also suggests a synergistic effect of MEL with plasma induced oxidation. Overall, our findings suggest that MEL in combination with PT-PBS can be a promising combinational therapy to circumvent the non-specific toxicity of MEL, which may help for clinical applicability in the future.

A novel melittin nano-liposome exerted excellent anti-hepatocellular carcinoma efficacy with better biological safety

Melittin is the main effective component of bee venom and has extensive biological functions; however, serious side effects have restricted its clinical application. Preclinical and clinical studies showed that the main adverse events were allergic reaction and pain at the administration site. To decrease the toxicity, we prepared melittin nano-liposomes by encapsulating melittin with poloxamer 188 and explored the inhibitory activities on liver cancer together with biological safety. Here, we showed that melittin nano-liposomes significantly inhibited the survival of hepatocellular carcinoma (HCC) cells in vitro and prominently suppressed the growth of subcutaneous and orthotopic HCC transplantation tumors in vivo. It was important that it induced less inflammation and allergy in mice compared with melittin. Overall, melittin nano-liposomes would have a better application in HCC therapy due to its significant anti-tumor activity and better biological safety.

Test-Retest Reliability of 10 Hz Conditioning Electrical Stimulation Inducing Long-Term Potentiation (LTP)-Like Pain Amplification in Humans

Background

10 Hz conditioning electrical stimulation (CES) has been shown to induce long-term potentiation (LTP)-like pain amplification similar to traditional 100 Hz CES in healthy humans. The aim of this study was to assess the test-retest reliability and to estimate sample sizes required for future crossover and parallel study designs.

Methods

The 10 Hz paradigm (500 rectangular pulses lasting 50 s) was repeated on two separate days with one week interval in twenty volunteers. Perceptual intensities to single electrical stimulation (SES) at the conditioned skin site and to mechanical stimuli (pinprick and light stroking) in immediate vicinity to the conditioned skin site were recorded. Superficial blood flow (SBF) was assessed as indicator of neurogenic inflammation. All outcome measures were assessed with 10 min interval three times before and six times after the CES. The coefficient of variation and intra-class correlation coefficient were calculated within session and between sessions. Sample sizes were estimated for future crossover (Ncr) and parallel (Np) drug testing studies expected to detect a 30% decrease for the individual outcome measure following 10 Hz CES.

Results

Perceptual intensity ratings to light stroking (Ncr = 2, Np = 33) and pinprick stimulation (491 mN) (Ncr = 6, Np = 54) increased after CES and showed better reliability in crossover than parallel design. The SBF increased after CES, and then declined until reaching a plateau 20 minutes postCES. SBF showed acceptable reliability both in crossover and parallel designs (Ncr = 3, Np = 13). Pain ratings to SES were reliable, but with large estimated sample sizes (Ncr = 634, Np = 11310) due to the minor pain amplification.

Conclusions

The reliability of 10 Hz CES was acceptable in inducing LTP-like effects in the assessments of superficial blood flow, heterotopic mechanical hyperalgesia, and dysesthesia in terms of sample sizes for future crossover study designs.

Melittin, the Major Pain-Producing Substance of Bee Venom

Melittin is a basic 26-amino-acid polypeptide that constitutes 40-60% of dry honeybee (Apis mellifera) venom. Although much is known about its strong surface activity on lipid membranes, less is known about its pain-producing effects in the nervous system. In this review, we provide lines of accumulating evidence to support the hypothesis that melittin is the major pain-producing substance of bee venom. At the psychophysical and behavioral levels, subcutaneous injection of melittin causes tonic pain sensation and pain-related behaviors in both humans and animals. At the cellular level, melittin activates primary nociceptor cells through direct and indirect effects. On one hand, melittin can selectively open thermal nociceptor transient receptor potential vanilloid receptor channels via phospholipase A2-lipoxygenase/cyclooxygenase metabolites, leading to depolarization of primary nociceptor cells. On the other hand, algogens and inflammatory/pro-inflammatory mediators released from the tissue matrix by melittin's pore-forming effects can activate primary nociceptor cells through both ligand-gated receptor channels and the G-protein-coupled receptor-mediated opening of transient receptor potential canonical channels. Moreover, subcutaneous melittin up-regulates Nav1.8 and Nav1.9 subunits, resulting in the enhancement of tetrodotoxin-resistant Na(+) currents and the generation of long-term action potential firing. These nociceptive responses in the periphery finally activate and sensitize the spinal dorsal horn pain-signaling neurons, resulting in spontaneous nociceptive paw flinches and pain hypersensitivity to thermal and mechanical stimuli. Taken together, it is concluded that melittin is the major pain-producing substance of bee venom, by which peripheral persistent pain and hyperalgesia (or allodynia), primary nociceptive neuronal sensitization, and CNS synaptic plasticity (or metaplasticity) can be readily induced and the molecular and cellular mechanisms underlying naturally-occurring venomous biotoxins can be experimentally unraveled.

Effect of melittin on mice stomach

Melittin, the main bee venom component, has many positive biological effects and a relatively low toxicity in various cell types. However, there is no evidence of the effect of melittin on gastrointestinal cells. In the present study, we investigated the histological and immuonohistochemical effects of melittin on mice stomach. Adult male mice (Albino Swiss) were randomly divided into two groups (7 mice for each group): control group and melittin only treated group (10 and 40 μg/kg). These mice were sacrificed, then samples from the stomach were collected and prepared for histopathological studies by using alcian blue stain and immuonohistochemical studies by using smooth muscle actin (SMA) antibody. Treatment with melittin alone do not cause any harmful effect on the stomach tissue where the microscopic examination of Alcian blue stained section showed the normal distribution of the mucous secreting cells of the stomach tissues. On other hand, no changes were observed on smooth muscle cells. This study demonstrated the safety of using melittin on gastrointestinal tissues if used in definite dose and for suitable duration, which offers an opportunity for its use as a treatment for many diseases of the gastrointestinal tract.

Unravelling the mystery of capsaicin: a tool to understand and treat pain

A large number of pharmacological studies have used capsaicin as a tool to activate many physiological systems, with an emphasis on pain research but also including functions such as the cardiovascular system, the respiratory system, and the urinary tract. Understanding the actions of capsaicin led to the discovery its receptor, transient receptor potential (TRP) vanilloid subfamily member 1 (TRPV1), part of the superfamily of TRP receptors, sensing external events. This receptor is found on key fine sensory afferents, and so the use of capsaicin to selectively activate pain afferents has been exploited in animal studies, human psychophysics, and imaging studies. Its effects depend on the dose and route of administration and may include sensitization, desensitization, withdrawal of afferent nerve terminals, or even overt death of afferent fibers. The ability of capsaicin to generate central hypersensitivity has been valuable in understanding the consequences and mechanisms behind enhanced central processing of pain. In addition, capsaicin has been used as a therapeutic agent when applied topically, and antagonists of the TRPV1 receptor have been developed. Overall, the numerous uses for capsaicin are clear; hence, the rationale of this review is to bring together and discuss the different types of studies that exploit these actions to shed light upon capsaicin working both as a tool to understand pain but also as a treatment for chronic pain. This review will discuss the various actions of capsaicin and how it lends itself to these different purposes.

miR-203 regulates nociceptive sensitization after incision by controlling phospholipase A2 activating protein expression

BACKGROUND

After incision keratinocytes in the epidermis become activated to produce a range of pain-related mediators. microRNA 203 (miR-203) is known to be involved in keratinocyte growth, differentiation, and skin inflammation. We hypothesized that one or more of these mediators might be under the control of miR-203.

METHODS

The expression of miR-203 and its target gene, phospholipase A2 activating protein (PLAA), were examined after hind paw incision in mice. We investigated the local effect of intraplantar PLAA peptide injection in normal mice and the effects of a selective secretory phospholipase A2 inhibitor (HK064) on PLAA or incision-induced mechanical allodynia. Last, we investigated the role of substance P signaling in regulating miR-203 and PLAA expression in vitro and in vivo.

RESULTS

Levels of miR-203 were strongly down-regulated in keratinocytes after incision. Informatics-based approaches identified PLAA as a likely candidate for regulation by miR-203. PLAA caused mechanical allodynia and conditioned place aversion but not thermal sensitization. HK064 reduced mechanical allodynia after incision and after intraplantar injection of PLAA. Using preprotachykinin gene knockout mice or with neurokinin-1 selective antagonist LY303870 treatment, we observed that substance P-mediated signaling was also required for miR-203 and PLAA regulation after incision. Finally, using the rat epidermal keratinocyte cell line, we observed that a miR-203 mimic molecule could block the substance P-induced increase in PLAA expression observed under control conditions.

CONCLUSIONS

miR-203 may regulate expression of the novel nociceptive mediator PLAA after incision. Furthermore, the regulation of miR-203 and PLAA levels is reliant upon intact substance P signaling.

Involvement of peripheral NMDA receptor in melittin-induced thermographic flare

Intradermal injection of an active compound of European honeybee toxin, melittin, into the forearm in humans produces temporary pain and evokes sustained increase of local skin temperature. This increase of skin temperature is suppressed by the pretreatment of a voltage gated sodium channel blocker, lidocaine, suggesting that neurogenic inflammation is involved in the skin temperature increase after the melittin treatment. In this study, we tested a hypothesis that the melittin-induced skin temperature increase is augmented by an N-methyl-D-aspartate (NMDA) glutamate receptor that is present on the peripheral terminals of cutaneous primary afferents. Skin temperature was examined after the local application of incremental doses of melittin by a computer-assisted-thermography in pentobarbital-anesthetized rats. Local subcutaneous glutamate was collected through a microdialysis probe and glutamate levels were measured by a high pressure liquid chromatography with electrochemical detection method. Intraplantar injection of melittin resulted in the increase of subcutaneous glutamate levels and the increase of local skin temperature, which was partially attenuated by co-injection of an NMDA receptor antagonist, MK-801. In addition, intraplantar injection of NMDA itself increased the local skin temperature. Our data suggest that melittin-induced increase of skin temperature is enhanced through the activation of peripheral NMDA receptors by locally released glutamate. We suggest that topical administration of NMDA receptor antagonists could be an effective treatment of neuro-inflammatory pain.

Alterations of GSH and MDA levels and their association with bee venom-induced DNA damage in human peripheral blood leukocytes

Bee venom (BV) has toxic effects in a variety of cell systems and oxidative stress has been proposed as a possible mechanism of its toxicity. This study investigated the in vitro effect of BV on glutathione (GSH) and malondialdehyde (MDA) levels, and their association with BV-induced DNA strand breaks and oxidative DNA damage in human peripheral blood leukocytes (HPBLs). Blood samples were treated with BV at concentrations ranging from 0.1 to 10 μg/ml over different lengths of time, and DNA damage in HPBLs was monitored with the alkaline and formamidopyrimidine glycoslyase (FPG)-modified comet assays, while GSH and MDA levels were determined in whole blood. Results showed a significant increase in overall DNA damage and FPG-sensitive sites in DNA of HPBLs exposed to BV compared with HPBLs from controls. An increase in DNA damage (assessed with both comet assays) was significantly associated with changes in MDA and GSH levels. When pretreated with N-acetyl-L-cysteine, a source of cysteine for the synthesis of the endogenous antioxidant GSH, a significant reduction of the DNA damaging effects of BV in HPBLs was noted. This suggests that oxidative stress is at least partly responsible for the DNA damaging effects of BV.

The Protective Effect of Apamin on LPS/Fat-Induced Atherosclerotic Mice

Apamin, a peptide component of bee venom (BV), has anti-inflammatory properties. However, the molecular mechanisms by which apamin prevents atherosclerosis are not fully understood. We examined the effect of apamin on atherosclerotic mice. Atherosclerotic mice received intraperitoneal (ip) injections of lipopolysaccharide (LPS, 2 mg/kg) to induce atherosclerotic change and were fed an atherogenic diet for 12 weeks. Apamin (0.05 mg/kg) was administered by ip injection. LPS-induced THP-1-derived macrophage inflammation treated with apamin reduced expression of tumor necrosis factor (TNF)-α, vascular cell adhesion molecule (VCAM)-1, and intracellular cell adhesion molecule (ICAM)-1, as well as the nuclear factor kappa B (NF-κB) signaling pathway. Apamin decreased the formation of atherosclerotic lesions as assessed by hematoxylin and elastic staining. Treatment with apamin reduced lipids, Ca(2+) levels, and TNF-α in the serum from atherosclerotic mice. Further, apamin significantly attenuated expression of VCAM-1, ICAM-1, TGF-β1, and fibronectin in the descending aorta from atherosclerotic mice. These results indicate that apamin plays an important role in monocyte/macrophage inflammatory processing and may be of potential value for preventing atherosclerosis.

Secondary heat hyperalgesia induced by melittin in humans

Melittin, which is a principal protein of honeybee venom, can induce mechanical hyperalgesia in humans. The characteristics of the melittin induced mechanical hyperalgesia are quantitatively and qualitatively different from those evoked by capsaicin. The aim of the present study was to investigate in detail secondary heat hyperalgesia induced by melittin in humans. In six healthy volunteers, 10 microg of melittin was injected intradermally on the volar forearm, and VAS score to radiant heat stimuli (focused light from a xenon lamp) was assessed around the injection site 5, 30, and 60 min after injection. For normalization purposes, a pain rating index was calculated as the individual heat evoked VAS scores obtained after melittin divided by the individual baseline VAS scores. A two-way ANOVA revealed a significant increase of the pain rating index over time (F=3.6; P=0.03). The pain rating index at 60 min was significantly larger than at 5 min (P=0.04) and at 30 min (P=0.03). These results demonstrated slowly developing secondary heat hyperalgesia after injection of melittin. A possible contribution of peripheral inflammatory responses to the manifestation of secondary heat hyperalgesia is suggested, which in reality render the distinction between the primary and secondary area of heat hyperalgesia unnecessary.

Effects of SKF-96365, a TRPC inhibitor, on melittin-induced inward current and intracellular Ca2+ rise in primary sensory cells

OBJECTIVE

Melittin (MEL) is a major component of bee venom and can produce both persistent spontaneous nociception and pain hypersensitivity when injected subcutaneously in the periphery. The present study aimed to examine the roles of transient receptor potential canonical (TRPC) channels in mediation of MEL-induced activation of primary nociceptive cells.

METHODS

Whole-cell patch-clamp and laser scanning confocal calcium detection were used to evaluate the effects of SKF-96365, a TRPC inhibitor, applied on the acutely isolated dorsal root ganglion (DRG) cells of rat, on MEL-induced increase in intracellular calcium concentration ([Ca(2+)](i)) and inward current.

RESULTS

Under voltage-clamp mode, 43.9% (40/91) DRG cells were evoked to give rise to the inward current by 2 μmol/L MEL, which could be significantly suppressed by 3 doses of SKF-96365 (1, 5 and 10 μmol/L) in a dose-dependent manner. Of the other 210 cells, 67.6% responded to MEL with an intracellular Ca(2+) rise, as revealed by confocal calcium imaging. Of these MEL-sensitive cells, 46.5% (66/142) were suppressed by the highest dose of SKF-96365.

CONCLUSION

MEL-induced activation of small to medium-sized DRG cells can be suppressed by SKF-96365, suggesting the involvement of TRPC channels in the mediation of MEL-induced activation of primary nociceptive cells.

Melittin activates TRPV1 receptors in primary nociceptive sensory neurons via the phospholipase A2 cascade pathways

Previous studies demonstrated that melittin, the main peptide in bee venom, could cause persistent spontaneous pain, primary heat and mechanical hyperalgesia, and enhance the excitability of spinal nociceptive neurons. However, the underlying mechanism of melittin-induced cutaneous hypersensitivity is unknown. Effects of melittin applied topically to acutely dissociated rat dorsal root ganglion neurons were studied using whole-cell patch clamp and calcium imaging techniques. Melittin induced intracellular calcium increases in 60% of small (<25 μm) and medium (<40 μm) diameter sensory neurons. In current clamp, topical application of melittin evoked long-lasting firing in 55% of small and medium-sized neurons tested. In voltage clamp, melittin evoked inward currents in sensory neurons in a concentration-dependent manner. Repeated application of melittin caused increased amplitude of the inward currents. Most melittin-sensitive neurons were capsaicin-sensitive, and 65% were isolectin B4 positive. Capsazepine, the TRPV1 receptor inhibitor, completely abolished the melittin-induced inward currents and intracellular calcium transients. Inhibitions of signaling pathways showed that phospholipase A(2), but not phospholipase C, was involved in producing the melittin-induced inward currents. Inhibitors of cyclooxygenases (COX) and lipoxygenases (LOX), two key components of the arachidonic acid metabolism pathway, each partially suppressed the inward current evoked by melittin. Inhibitors of protein kinase A (PKA), but not of PKC, also abolished the melittin-induced inward currents. These results indicate that melittin can directly excite small and medium-sized sensory neurons at least in part by activating TRPV1 receptors via PLA2-COXs/LOXs cascade pathways.

The nociceptive and anti-nociceptive effects of bee venom injection and therapy: a double-edged sword

Bee venom injection as a therapy, like many other complementary and alternative medicine approaches, has been used for thousands of years to attempt to alleviate a range of diseases including arthritis. More recently, additional theraupeutic goals have been added to the list of diseases making this a critical time to evaluate the evidence for the beneficial and adverse effects of bee venom injection. Although reports of pain reduction (analgesic and antinociceptive) and anti-inflammatory effects of bee venom injection are accumulating in the literature, it is common knowledge that bee venom stings are painful and produce inflammation. In addition, a significant number of studies have been performed in the past decade highlighting that injection of bee venom and components of bee venom produce significant signs of pain or nociception, inflammation and many effects at multiple levels of immediate, acute and prolonged pain processes. This report reviews the extensive new data regarding the deleterious effects of bee venom injection in people and animals, our current understanding of the responsible underlying mechanisms and critical venom components, and provides a critical evaluation of reports of the beneficial effects of bee venom injection in people and animals and the proposed underlying mechanisms. Although further studies are required to make firm conclusions, therapeutic bee venom injection may be beneficial for some patients, but may also be harmful. This report highlights key patterns of results, critical shortcomings, and essential areas requiring further study.

Secondary heat hyperalgesia detected by radiant heat stimuli in humans: Evaluation of stimulus intensity and duration

Diverging observations on secondary hyperalgesia to heat stimuli have been reported in the literature. No studies have investigated the importance of heat stimulus intensity and duration for the assessment of secondary heat hyperalgesia. The present study was designed to investigate systematically (1) if pain sensitivity to radiant heat stimuli (focused Xenon light) is altered in the area of secondary punctuate hyperalgesia induced by intradermal injection of capsaicin and (2) if heat stimulus duration and intensity had an influence on the ability to detect secondary heat hyperalgesia. Pain ratings to radiant heat stimuli from a focused xenon lamp were assessed within the area of secondary punctuate hyperalgesia in fifteen volunteers before and after intradermal injection of capsaicin. The stimulus conditions were systematically varied between three intensity levels (0.8, 1.0 and 1.2 x heat pain threshold (PT)) and four duration steps (200, 350, 500 and 750 ms). The present study shows that long duration (350-750 ms) and low intensity (0.8 and 1.0 x PT) radiant heat stimuli were adequate to detect secondary heat hyperalgesia.

Increased capsaicin receptor TRPV1 in the peritoneum of women with chronic pelvic pain

OBJECTIVE

To investigate the expression of capsaicin receptor [transient receptor potential vanilloid type-1 (TRPV1)] in the peritoneum of women with chronic pelvic pain (CPP).

METHODS

A case-control study was conducted on 25 women with CPP and 10 controls. Samples of the rectouterine excavation (2 cm) were obtained by laparoscopy, fixed in 4% formaldehyde, and underwent immunohistochemistry analysis using rabbit anti-TRPV1 (1:400) polyclonal antibodies and anti-protein gene product 9.5 (PGP 9.5) (1:2000) as a neuronal marker. Ten sequential images of high magnification fields (x40) were captured from each slide and the area identified with the antibody was calculated with Kontron V2.0 software.

RESULTS

Immunoreactivity to TRPV1 was sparsely detected in the nervous tissue and epithelium of endometriotic lesions. The percent area of immunoreactivity for TRPV1 [expressed as median (range)] was greater in specimens from women with CPP, 1.02% (0.54 to 2.93), than from women without the disease, 0.14% (0.07 to 1.12) (P<0.0001). This greater expression was not secondary to an increase in neuronal fibers because there was also a significant difference in the percent area TRPV1:PGP 9.5 ratio between women with CPP, 1.18 (0.26 to 4.63), and controls, 0.15 (0.06 to 0.95) (P=0.0003).

DISCUSSION

TRPV1 may play an important role in the maintenance and perpetuation of symptoms in women with CPP. In view of the immunoreactivity detected for TRPV1, the endometriotic lesion may have the ability to interfere with nociception or with the inflammatory peritoneal environment in women with CPP. Further studies are needed to elucidate the participation of TRPV1 in CPP and its association with endometriosis.

Radioprotective Effects of Honeybee Venom (Apis mellifera) Against 915-MHz Microwave Radiation–Induced DNA Damage in Wistar Rat Lymphocytes: In Vitro Study

The aim of this study is to investigate the radioprotective effect of bee venom against DNA damage induced by 915-MHz microwave radiation (specific absorption rate of 0.6 W/kg) in Wistar rats. Whole blood lymphocytes of Wistar rats are treated with 1 μg/mL bee venom 4 hours prior to and immediately before irradiation. Standard and formamidopyrimidine-DNA glycosylase (Fpg)–modified comet assays are used to assess basal and oxidative DNA damage produced by reactive oxygen species. Bee venom shows a decrease in DNA damage compared with irradiated samples. Parameters of Fpg-modified comet assay are statistically different from controls, making this assay more sensitive and suggesting that oxidative stress is a possible mechanism of DNA damage induction. Bee venom is demonstrated to have a radioprotective effect against basal and oxidative DNA damage. Furthermore, bee venom is not genotoxic and does not produce oxidative damage in the low concentrations used in this study.

Spinal Metabotropic Glutamate Receptors (mGluRs) are Involved in the Melittin-induced Nociception in Rats

Intraplantar injection of melittin has been known to induce sustained decrease of mechanical threshold and increase of spontaneous flinchings. The present study was undertaken to investigate how the melittin-induced nociceptive responses were modulated by changes of metabotropic glutamate receptor (mGluR) activity. Changes in paw withdrawal threshold (PWT), number of flinchings and paw thickness were measured at a given time point after injection of melittin (10 microg/paw) into the mid-plantar area of rat hindpaw. To observe the effects of mGluRs on the melittin-induced nociceptions, group I mGluR (AIDA, 100 microg and 200 microg), mGluR(1) (LY367385, 50 microg and 100 microg) and mGluR(5) (MPEP, 200 microg and 300 microg) antagonists, group II (APDC, 100 microg and 200 microg) and III (L-SOP, 100 microg and 200 microg) agonists were intrathecally administered 20 min before melittin injection. Intraplantar injection of melittin induced a sustained decrease of mechanical threshold, spontaneous flinchings and edema. The effects of melittin to reduce mechanical threshold and to induce spontaneous flinchings were significantly suppressed following intrathecal pre-administration of group I mGluR, mGluR(1) and mGluR(5) antagonists, group II and III mGluR agonists. Group I mGluR antagonists and group II and III mGluR agonists had no significant effect on melittin-induced edema. These experimental findings indicate that multiple spinal mGluRs are involved in the modulation of melittin-induced nociceptive responses.

Genotoxic potential of bee venom (Apis Mellifera) on human peripheral blood lymphocytes in vitro using single cell gel electrophoresis assay

Bee venom (BV) has been known to have therapeutic applications in traditional medicine to treat variety of diseases. It is also known that bee venom possesses anti-inflammatory and anticancer effects and that it can inhibit proliferation and induces apoptosis in cancer cells, but there is lack of information regarding genotoxicity of whole bee venom on normal human cells. In the present study, peripheral blood human lymphocytes from healthy donor were exposed in vitro to different concentration (5, 10, 25, 50 and 100 micro g/mL) of whole bee venom at different time periods (1, 6 and 24 hours). The single cell gel electrophoresis (SCGE) assay was used to evaluate the genotoxicity towards human cells. Results showed statistically significant increase in DNA damage caused in BV treated human lymphocytes compared to corresponding control cells for the tail length and tail moment. These results show that the extent of DNA damage, determined by the use of single cell gel electrophoresis is time and dose dependent. Based on the results it is clear that whole bee venom induces DNA damage and has genotoxic potential on human peripheral blood lymphocytes in vitro.

Roles of peripheral P2X and P2Y receptors in the development of melittin-induced nociception and hypersensitivity

A recent report from our laboratory shows that subcutaneous (s.c.) injection of melittin could induce persistent spontaneous nociception (PSN) and primary thermal or mechanical hyperalgesia. However, the exact peripheral mechanisms underlying melittin-induced multiple pain-related behaviors remain unclear. In this study, behavioral tests combined with pharmacological manipulations were used to explore potential roles of local P2X and P2Y receptors in melittin-induced inflammatory pain and hyperalgesia. Post-treatment of the primary injury site with s.c. injection of A-317491 (a potent P2X(3)/P2X(2/3) receptor antagonist) and Reactive Blue 2 (a potent P2Y receptor antagonist) could significantly suppress the development of melittin-evoked PSN and hypersensitivity (thermal and mechanical). Our control experiments demonstrated that local administration of either antagonist into the contralateral hindpaw produced no significant effect on any kind of pain-associated behaviors. Taken together, these data indicate that activation of P2X and P2Y receptors might be essential to the maintenance of melittin-induced primary thermal and mechanical hyperalgesia as well as on-going pain.

Roles of peripheral mitogen-activated protein kinases in melittin-induced nociception and hyperalgesia

Recently, we have reported that melittin, a major toxic peptide of the whole bee venom, plays a central role in production of local inflammation, nociception and hyperalgesia following the experimental honeybee's sting. However, the exact peripheral mechanisms underlying melittin-induced multiple pain-related behaviors are still less characterized. In the present study, we sought to investigate the potential roles of peripheral mitogen-activated protein kinases (MAPKs) in melittin-induced nociception and hyperalgesia by pre- and post-administration of three MAPK inhibitors, namely U0126 (1 mug, 10 mug) for extracellular signal-regulated kinase (ERK), SP600125 (10 mug, 100 mug) for c-Jun N-terminal kinase (JNK) and SB239063 (10 mug, 100 mug) for p38 MAPK, into the local inflamed area of one hind paw of rats. Both pre- and post-treatment with three drugs significantly suppressed the occurrence and maintenance of melittin-evoked persistent spontaneous nociception (PSN) and primary heat hyperalgesia, with little antinociceptive effect on mechanical hyperalgesia. In vehicle-treated group, ipsilateral injection of melittin produced no impact on thermal and mechanical sensitivity of the other hind paw, suggesting no occurrence of contralateral heat and mechanical hyperalgesia in the melittin test. In addition, local administration of each inhibitor into the contralateral hind paw exerted no significant influence on either PSN or heat/mechanical hyperalgesia tested in the primary injured hind paw, excluding the systemically pharmacological effects of the three drugs. Furthermore, local administration of the three compounds in naïve animals, respectively, did not change the basal pain sensitivity to either thermal or mechanical stimuli, suggesting lack of peripherally functional roles of the three MAPK subfamily members in normal pain sensitivity under the physiological state. Taken together, we conclude that activation of peripheral MAPKs, including ERK, JNK and p38, might contribute to the induction and maintenance of persistent ongoing pain and primary heat hyperalgesia in the melittin test. However, they are not likely to be involved in the processing of melittin-induced primary mechanical hyperalgesia, implicating a mechanistic separation between mechanical and thermal hyperalgesia in the periphery.

Cytotoxicity of honeybee (Apis mellifera) venom in normal human lymphocytes and HL-60 cells

Whole bee venom (BV) is used to treat inflammatory diseases in Korean traditional medicine. Various studies have demonstrated anti-inflammatory and anticancer effects of BV. The toxicity of individual components of BV has been widely studied, although few studies have reported on the toxicity of BV. We sought to evaluate the cytotoxicity of BV in normal human lymphocytes and HL-60 cells. When cells were treated with BV at concentrations of 1 or 5 microg/ml, BV induced cell death in a time-dependent manner until 24 h, but these cytotoxic effects ended thereafter. When cells were treated with BV at a concentration of 10 microg/ml, however, viability decreased until 72 h, which may have been due to the half-life of BV. Whole BV also inhibited proliferation in these cells. BV induced DNA fragmentation and micronuclei in HL-60 cells and DNA fragmentation in human lymphocytes. Phosphate and tensin homolog (PTEN) up-regulation in HL-60 cells may induce S-phase cell cycle arrest. Forkhead transcription factor (FKHR and FKHRL1) up-regulation in human lymphocytes by whole BV treatment may be involved in the repair of damaged DNA and reduce genotoxicity. Based on these results, whole BV may exert cytotoxicity in these two cells in a different fashion.

Region- or state-related differences in expression and activation of extracellular signal-regulated kinases (ERKs) in naïve and pain-experiencing rats

BACKGROUND

Extracellular signal-regulated kinase (ERK), one member of the mitogen-activated protein kinase (MAPK) family, has been suggested to regulate a diverse array of cellular functions, including cell growth, differentiation, survival, as well as neuronal plasticity. Recent evidence indicates a role for ERKs in nociceptive processing in both dorsal root ganglion and spinal cord. However, little literature has been reported to examine the differential distribution and activation of ERK isoforms, ERK1 and ERK2, at different levels of pain-related pathways under both normal and pain states. In the present study, quantitative blot immunolabeling technique was used to determine the spatial and temporal expression of ERK1 and ERK2, as well as their activated forms, in the spinal cord, primary somatosensory cortex (SI area of cortex), and hippocampus under normal, transient pain and persistent pain states.

RESULTS

In naïve rats, we detected regional differences in total expression of ERK1 and ERK2 across different areas. In the spinal cord, ERK1 was expressed more abundantly than ERK2, while in the SI area of cortex and hippocampus, there was a larger amount of ERK2 than ERK1. Moreover, phosphorylated ERK2 (pERK2), not phosphorylated ERK1 (pERK1), was normally expressed with a high level in the SI area and hippocampus, but both pERK1 and pERK2 were barely detectable in normal spinal cord. Intraplantar saline or bee venom injection, mimicking transient or persistent pain respectively, can equally initiate an intense and long-lasting activation of ERKs in all three areas examined. However, isoform-dependent differences existed among these areas, that is, pERK2 exhibited stronger response than pERK1 in the spinal cord, whereas ERK1 was more remarkably activated than ERK2 in the S1 area and hippocampus.

CONCLUSION

Taken these results together, we conclude that: (1) under normal state, while ERK immunoreactivity is broadly distributed in the rat central nervous system in general, the relative abundance of ERK1 and ERK2 differs greatly among specific regions; (2) under pain state, either ERK1 or ERK2 can be effectively phosphorylated with a long-term duration by both transient and persistent pain, but their response patterns differ from each other across distinct regions; (3) The long-lasting ERKs activation induced by bee venom injection is highly correlated with our previous behavioral, electrophysiological, morphological and pharmacological observations, lending further support to the functional importance of ERKs-mediated signaling pathways in the processing of negative consequences of pain associated with sensory, emotional and cognitive dimensions.

Pivotal involvement of neurogenic mechanism in subcutaneous bee venom-induced inflammation and allodynia in unanesthetized conscious rats

The bee venom (BV) model is a valid inflammatory pain model in animals and has been extended to human studies using its principle protein, mellitin. After subcutaneous (s.c.) injection of BV, long-lasting spontaneous nociception followed by thermal hyperalgesia, static allodynia, and local inflammatory response (edema) can be observed in rats. We hypothesize that (1) neurogenic components may contribute to the BV-induced inflammatory response and (2) static and dynamic mechanical allodynia may exist simultaneously in the BV model. Using different approaches including sciatic nerve transection (SCT), L4-L6 dorsal rhizotomy (DRT) and local treatment of the sciatic nerve with capsaicin, we found that SCT, DRT, and local capsaicin onto the sciatic nerve produced a significant inhibition of the BV-induced increase in volume of the injected paw, with a stronger effect of the SCT and the local capsaicin treatments than that of the DRT treatment. Static and dynamic mechanical allodynia in the BV test was assessed by measuring the paw withdrawal mechanical threshold and the paw withdrawal latency before and after the BV injection, respectively. Local capsaicin onto the sciatic nerve produced a significant inhibition of the BV-induced decrease in the paw withdrawal mechanical threshold, but not the paw withdrawal latency, of the injected paw. These findings suggest that neurogenic components, via dorsal root reflex and axon reflex mechanisms, are probably involved in the maintenance and the development of the BV-induced inflammation. In addition, the capsaicin-sensitive primary afferents may play differential roles in the development of the BV-induced static and dynamic mechanical allodynia.

Effects of bee venom peptidergic components on rat pain-related behaviors and inflammation

To identify the active components of honeybee venom in production of inflammation and pain-related behaviors, five major peptidergic subfractions were separated, purified and identified from the whole honeybee venom. Among them, four active peptidergic components were characterized as apamin, mast-cell degranulating peptide (MCDP), phospholipase A(2) (PLA(2))-related peptide and melittin, respectively. All five subfractions were effective in production of local inflammatory responses (paw edema) in rats although the efficacies were different. Among the five identified subfractions, only MCDP, PLA(2)-related peptide and melittin were able to produce ongoing pain-related behaviors shown as paw flinches, while only apamin and melittin were potent to produce both thermal and mechanical hypersensitivity. As shown in our previous report, melittin was the most potent polypeptide in production of local inflammation as well as ongoing pain and hypersensitivity. To further explore the peripheral mechanisms underlying melittin-induced nociception and hypersensitivity, a single dose of capsazepine, a blocker of thermal nociceptor transient receptor potential vanilloid receptor 1, was treated s.c. prior to or after melittin administration. The results showed that both pre- and post-treatment of capsazepine could significantly prevent and suppress the melittin-induced ongoing nociceptive responses and thermal hypersensitivity, but were without influencing mechanical hypersensitivity. The present results suggest that the naturally occurring peptidergic substances of the whole honeybee venom have various pharmacological potencies to produce local inflammation, nociception and pain hypersensitivity in mammals, and among the five identified reverse-phase high pressure liquid chromatography subfractions (four polypeptides), melittin, a polypeptide occupying over 50% of the whole honeybee venom, plays a central role in production of local inflammation, nociception and hyperalgesia or allodynia following the experimental honeybee's sting. Peripheral transient receptor potential vanilloid receptor 1 is likely to be involved in melittin-produced ongoing pain and heat hyperalgesia, but not mechanical hyperalgesia, in rats.

Unilateral subcutaneous bee venom but not formalin injection causes contralateral hypersensitized wind-up and after-discharge of the spinal withdrawal reflex in anesthetized spinal rats

This study aimed to investigate the effect of tonic nociception on spinal withdrawal reflexes including (1) long lasting spontaneous responses elicited by subcutaneous (s.c.) administration of formalin (2.5%, 50 microl) and bee venom (BV, 0.2 mg/50 microl) into the hind paw and (2) corresponding ipsilateral (primary) and contralateral (secondary) hypersensitivity to noxious pinch and repetitive supra-threshold (1.5 x T) electrical stimuli at different frequencies (3 Hz: wind-up; 20 Hz: after-discharge) in anesthetized spinal rats. Spinal withdrawal reflexes were studied by simultaneously assessing single motor units (SMUs) electromyographic (EMG) activities from the bilateral medial gastrocnemius (MG) muscles. Subcutaneous formalin-induced persistent spontaneous SMU EMG responses were in typical biphasic manner with an apparent silent period (about 13-18 min), but in contrast, BV elicited monophasic long lasting (about 1 h) SMU EMG responses without any resting state. The mechanically and electrically evoked responsiveness of SMUs were enhanced significantly by ipsilateral BV injection, whereas enhanced electrically, but not mechanically, evoked responses (including wind-up and after-discharge) were found at the non-injection site of the contralateral hind paw. However, s.c. administration of formalin was only able to establish ipsilateral hypersensitivity of the SMUs to repeated electrical, not mechanical, stimulation. Neither mechanically nor electrically evoked contralateral hypersensitivity of the SMUs was found during the ipsilateral formalin-induced nociception. For pharmacological intervention, intrathecal administration of the non-N-methyl-d-aspartate (non-NMDA) receptor antagonist CNQX (40 nmol/10 microl), but not the non-competitive NMDA receptor antagonist MK-801 (40 nmol/10 microl), significantly depressed BV-induced contralateral hypersensitivity of the SMUs to repeated 3 Hz (wind-up) and 20 Hz (after-discharge) frequencies of electrical stimulation. Using the extracellular SMU recording technique, we found that s.c. administration of formalin and BV shows a significant difference in long lasting spontaneous firing of SMUs. This is consistent with previous observations in animal behavioral studies. Additionally, contralateral electrically evoked hypersensitivity of the SMUs was found only following BV injection, not in the formalin test. The maintenance and development of BV-induced contralateral hypersensitivity of the spinal withdrawal reflex to noxious electrical stimulation indeed depend on different central pharmacological receptors. The spinal non-NMDA, but not the NMDA, receptors may play important role in BV-induced contralateral central hyperexcitability and sensitization.

Mobilisation of specific T cells from lymph nodes in contact sensitivity requires substance P

Capsaicin-mediated depletion of neuropeptides in the skin was previously shown to abolish a dinitrocholorobenzene (DNCB)-induced contact sensitivity (CS) response. To understand the basis for this disruption, we explored whether nerve fibres innervating the draining lymph node (LN) could be involved. As expected, removal of the draining LN after DNCB sensitisation abolished the CS response. Furthermore, the CS response could be abolished by destroying the nerve fibres in the draining LN and could be restored by providing the LN with the neuropeptide substance P. The size of the CS response restored by substance P was dose dependent. The response was also inhibited by exposing the lymph node to a neurokinin-1 receptor antagonist which blocks binding of substance P. The results suggest that an afferent signal from the skin via the sympathetic arm of the central nervous system evokes an efferent signal to the LN which combines to regulate the CS response. The efferent signal may serve to control or release from the LN primed effector lymphocytes into the circulation.

Vasomotor response to cold stimulation in human capsaicin-induced hyperalgesic area

Cooling the skin induces sympathetically driven vasoconstriction, with some vasoparalytic dilatation at the lowest temperatures. Neurogenic inflammation, on the other hand, entails vasodilatation. In this study we investigated the balance between vasoconstriction and vasodilatation in an area of experimentally induced secondary hyperalgesia (2 degrees HA), in response to low-temperature stimulations. Fourteen healthy volunteers were exposed to three 30-s long cold stimuli (20, 10, and 0 degrees C) applied, at three adjacent sites, before (baseline) and 8 min after intradermal injection of 50 microg capsaicin to the volar forearm. The cold stimuli were applied distally to the injection site within the 2 degrees HA. Blood flux (BF) and skin temperatures were measured at four different regions (proximally, and distally to the capsaicin injection and at the 0, 10, and 20 degrees C thermode sites) all within the 2 degrees HA. The vascular measurements were conducted five times. Results showed a marked increase in BF after baseline cold stimulation (P<0.001) at the 0 degrees C compared with the three other sites. In addition, vasodilatory effect (elevated BF) was found following the capsaicin injection compared with baseline for all regions (P<0.001): the non-cooled area was dilated by 450+/-5.1%; The vasoconstrictive effect for the 10 and 20 degrees C did not overcome the capsaicin vasodilatation, but did reduce it, with dilatation of 364+/-7.0% and 329+/-7.3%, respectively. For 0 degrees C, a dilatation of 407+/-6.5% was seen. It is concluded that in this experimental model, and potentially in the equivalent clinical syndromes, vasodilatation induced by the inflammation is only slightly reduced by cold stimulation such that it is still dominant, despite some cold-induced vasoconstriction.

Activation of spinal extracellular signaling-regulated kinases by intraplantar melittin injection

Intraplantar injection of melittin, a major toxic peptide of whole bee venom, has been proved to cause alteration in both behavioral and spinal neuronal responses in rats. To see whether extracellular signaling-regulated kinases (ERK) in the spinal cord dorsal horn are activated and involved in induction and maintenance of persistent ongoing nociception, pain hypersensitivity and inflammation, three doses of U0126 (1,4-diamino-2,3-dicyano-1, 4-bis-[o-aminophenylmercapto]butadiene), a widely used specific MAP kinase kinase (MEK) inhibitor, were administered through chronic intrathecal catheterization prior to or after intraplantar injection of melittin. We found that: (1) the induction of melittin-induced persistent spontaneous nociception (PSN), mechanical and heat hypersensitivity could be suppressed by U0126 in a dose-related manner; (2) specific inhibition of ERK pathway suppressed the maintenance of melittin-induced PSN and heat hypersensitivity, while established mechanical hypersensitivity could not be reversed; and (3) intrathecal administration of U0126 had no effects on peripheral inflammation induced by melittin. This result suggests that spinal ERK pathway might be a common factor involved in inducing and maintaining pathophysiological processes of ongoing pain and heat hyperalgesia, while the role of ERK pathway in generation of the mechanical hypersensitivity is not consistent and remains to be further clarified.