Melittin selectively activates capsaicin-sensitive primary afferent fibers

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.

Perineural pretreatment of bee venom attenuated the development of allodynia in the spinal nerve ligation injured neuropathic pain model; an experimental study

Background

Diluted bee venom (BV) is known to have anti-nociceptive and anti-inflammatory effects. We therefore assessed whether perineural bee venom pretreatment could attenuate the development of neuropathic pain in the spinal nerve ligation injured animal model.

Methods

Neuropathic pain was surgically induced in 30 male Sprague Dawley rats by ligation of the L5 and L6 spinal nerves, with 10 rats each treated with saline and 0.05 and 0.1 mg BV. Behavioral testing for mechanical, cold, and thermal allodynia was conducted on postoperative days 3 to 29. Three rats in each group and 9 sham operated rats were sacrificed on day 9, and the expression of transient receptor potential vanilloid type 1 (TRPV1), ankyrin type 1 (TRPA1), and melastatin type 8 (TRPM8) receptors in the ipsilateral L5 dorsal root ganglion was analyzed.

Results

The perineural administration of BV to the spinal nerves attenuated the development of mechanical, thermal, and cold allodynia, and the BV pretreatment reduced the expression of TRPV1, TRPA1, TRPM8 and c − Fos in the ipsilateral dorsal root ganglion.

Conclusion

The current study demonstrates that the perineural pretreatment with diluted bee venom before the induction of spinal nerve ligation significantly suppresses the development of neuropathic pain. Furthermore, this bee venom induced suppression was strongly related with the involvement of transient receptor potential family members.

The inhibitory effect of somatostatin receptor activation on bee venom-evoked nociceptive behavior and pCREB expression in rats

The present study examined nociceptive behaviors and the expression of phosphorylated cAMP response element-binding protein (pCREB) in the dorsal horn of the lumbar spinal cord and the dorsal root ganglion (DRG) evoked by bee venom (BV). The effect of intraplantar preapplication of the somatostatin analog octreotide on nociceptive behaviors and pCREB expression was also examined. Subcutaneous injection of BV into the rat unilateral hindpaw pad induced significant spontaneous nociceptive behaviors, primary mechanical allodynia, primary thermal hyperalgesia, and mirror-thermal hyperalgesia, as well as an increase in pCREB expression in the lumbar spinal dorsal horn and DRG. Octreotide pretreatment significantly attenuated the BV-induced lifting/licking response and mechanical allodynia. Local injection of octreotide also significantly reduced pCREB expression in the lumbar spinal dorsal horn and DRG. Furthermore, pretreatment with cyclosomatostatin, a somatostatin receptor antagonist, reversed the octreotide-induced inhibition of the lifting/licking response, mechanical allodynia, and the expression of pCREB. These results suggest that BV can induce nociceptive responses and somatostatin receptors are involved in mediating the antinociception, which provides new evidence for peripheral analgesic action of somatostatin in an inflammatory pain state.

Activation of tetrodotoxin-resistant sodium channel NaV1.9 in rat primary sensory neurons contributes to melittin-induced pain behavior

Tetrodotoxin-resistant (TTX-R) sodium channels NaV1.8 and NaV1.9 in dorsal root ganglion (DRG) neurons play important roles in pathological pain. We recently reported that melittin, the major toxin of whole bee venom, induced action potential firings in DRG neurons even in the presence of a high concentration (500 nM) of TTX, indicating the contribution of TTX-R sodium channels. This hypothesis is fully investigated in the present study. After subcutaneous injection of melittin, NaV1.8 and NaV1.9 significantly upregulate mRNA and protein expressions, and related sodium currents also increase. Double immunohistochemical results show that NaV1.8-positive neurons are mainly medium- and small-sized, whereas NaV1.9-positive ones are only small-sized. Antisense oligodeoxynucleotides (AS ODNs) targeting NaV1.8 and NaV1.9 are used to evaluate functional significance of the increased expressions of TTX-R sodium channels. Behavioral tests demonstrate that AS ODN targeting NaV1.9, but not NaV1.8, reverses melittin-induced heat hypersensitivity. Neither NaV1.8 AS ODN nor NaV1.9 AS ODN affects melittin-induced mechanical hypersensitivity. These results provide previously unknown evidence that upregulation of NaV1.9, but not NaV1.8, in small-sized DRG neurons contributes to melittin-induced heat hypersensitivity. Furthermore, melittin-induced biological effect indicates a potential strategy to study properties of TTX-R sodium channels.

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.

Capsaicin prevents the hyperalgesia induced by peripheral group I mGluRs activation

Group 1 metabotropic glutamate receptors (mGluRs) are expressed in peripheral and central neural tissues and involved in peripheral and central sensitization in various pain models. However, there are limited reports that activation of peripheral group I mGluRs could evoke pain. Furthermore, any behavioral evidences could not be found out, showing what kind of afferent fibers are involved in peripheral mGluRs-mediated hyperalgesia. This study was undertaken to clarify whether peripherally injected group I mGluRs agonists could induce pain-related behaviors and capsaicin-sensitive afferent fibers might be involved in the hyperalgesia. To assess pain sensitivity, mechanical threshold for paw withdrawal response (PWT) was measured and number of spontaneous flinching behavior was counted. Intraplantar injection of group I mGluR agonist, (RS)-3,5-dihydroxyphenylglycine (DHPG) and mGluR5 agonist, (RS)-2-chloro-5-hydroxyphenyglycine (CHPG) immediately induced pain-like behaviors, such as decrease of PWT and increased number of flinchings. These agonists-induced pain-like behaviors were blocked by group I mGluRs antagonist, (RS)-1-aminoindan-1,5-dicarboxylic acid (AIDA) and mGluR5 antagonist, 2-methyl-6-(phenylethynyl) pyridine hydrochloride (MPEP). Perineural pretreatment of 1% capsaicin solution significantly reduced pain-related behaviors induced by DHPG and CHPG, proposing that capsaicin-sensitive primary afferent fibers could be responsible for the hyperalgesia induced by activation of peripheral group I mGluRs. This study presents the first behavioral evidence that peripheral group I mGluRs activation could induce spontaneous as well as mechanical hyperalgesia and capsaicin-sensitive afferent fiber could be implicated the group I mGluR mediated hyperalgesia.

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.

Activation of ERK1/2 in the primary injury site is required to maintain melittin-enhanced wind-up of rat spinal wide-dynamic-range neurons

Peripheral modulation of wind-up enhancement induced by peripheral tissue injury is investigated in rat spinal wide-dynamic-range (WDR) neurons. After subcutaneous (s.c.) injection of melittin, a pain-related peptidergic component separated from bee venom, the responsiveness of spinal cord WDR neuron to repeated suprathreshold (1.5T, the intensity threshold) electrical stimuli is enhanced. Comparing with the less effects on early response (0-100 ms), melittin significantly increases late response (100 ms to the next stimulus artifact) and after-discharge (starting from 2s after the last stimulus artifact) with 189% and 546%, respectively. Peripheral administration of a specific MEK inhibitor, 1,4-diamino-2,3-dicyano-1,4-bis-[o-aminophenylmercapto] butadiene (U0126, 1 microg) gradually suppresses, but not completely blocks melittin-enhanced wind-up to the similar level of baseline. The inhibitions of U0126 are mainly on late response and after-discharge with 49% and 65%, respectively. Peripheral administration of three doses of U0126 (0.1, 1, 10 microg) has no effects on melittin-induced local paw edema regardless of either pre- or post-treatment of the drug. We conclude that peripheral ERKs pathway in the primary injury site is required to maintain melittin-enhanced wind-up of rat spinal cord wide-dynamic-range neurons.

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.

Extracellular signal-regulated kinases mediate melittin-induced hypersensitivity of spinal neurons to chemical and thermal but not mechanical stimuli

Subcutaneous melittin injection causes central plasticity at the spinal level in wide-dynamic-range (WDR) neurons, which are hypersensitive to various nociceptive stimuli. Previous behavioral studies demonstrated that the mitogen-activated protein kinases (MAPKs) extracellular signal-regulated kinase 1/2(ERK1/2), p38 MAPK, and c-Jun N-terminal kinase are involved in both peripheral and spinal processing of melittin-induced nociception and hypersensitivity. Yet the functional roles of the three MAPKs vary among different stimulus modalities, and must be further studied at the cellular level in vivo. In this report, extracellular single unit recordings were performed to investigate whether activation of ERK1/2 in the primary injury site of melittin is essential to the establishment of a spinally sensitized state. Localized peripheral administration of a single dose of the MEK inhibitor U0126 (1 μg/10 μl) significantly suppressed neuronal hyper-responsiveness to thermal stimulus and chemical (melittin)-induced tonic firing of WDR neurons after full establishment of a spinally sensitized state. However, U0126 failed to affect mechanical hypersensitivity to both noxious and non-noxious stimuli. Melittin-induced enhancement of thermal hypersensitivity was also greatly inhibited by a single dose of capsazepine, a thermal nociceptor (TRPV1) blocker. These results suggest that activation of the ERK signaling pathway in the periphery is likely necessary for maintenance of a spinally sensitized state; activation of ERK1/2 in the primary injury site may regulate TRPV1, leading to dorsal horn hypersensitivity to thermal and chemical stimuli. ERK signaling pathways are not likely to be associated with melittin-induced dorsal horn hypersensitivity to mechanical stimuli.

Substantial role of locus coeruleus-noradrenergic activation and capsaicin-insensitive primary afferent fibers in bee venom's anti-inflammatory effect

Several lines of evidence indicate significant interactions between the immune and nervous systems. Our recent study reveals that 'bee venom (BV) induced anti-inflammatory effect' (BVAI) was produced by sympathetic preganglionic neuronal activation and subsequent adrenomedullary catecholamine release in a zymosan-induced inflammation model. However, the specific peripheral input and the supraspinal neuronal systems that are involved in this BVAI remain to be defined. Here we show that subcutaneous BV injection into left hind limb significantly reduces zymosan-induced leukocyte migration and that this effect is completely inhibited by denervation of the left sciatic nerve. This BVAI was not affected by the destruction of capsaicin-sensitive primary afferent fibers using either neonatal capsaicin or resiniferatoxin (RTX) pretreatment. BV injection into the left hind limb significantly increased Fos expression in the contralateral locus coeruleus (LC) in non-inflamed mice. In zymosan-inflamed mice, BV injection produced a further increase in LC Fos expression as compared with non-inflamed mice. This BV-induced Fos increase in the LC was not affected by RTX pretreatment. Pharmacological blockage of central noradrenergic activity by either central chemical sympathectomy (i.c.v. 6-hydroxydopamine) or alpha2 adrenoceptor antagonism (i.c.v. idazoxan) completely blocked BVAI. Taken together, these results suggest that BVAI is mediated by peripheral activation of capsaicin-insensitive primary afferent fibers and subsequent central noradrenergic activation including the LC.

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.

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.