Differential antinociceptive effects of sendide, a NK1-receptor antagonist, and morphine in the capsaicin test

A focused review on CB2 receptor-selective pharmacological properties and therapeutic potential of β-caryophyllene, a dietary cannabinoid

The endocannabinoid system (ECS), a conserved physiological system emerged as a novel pharmacological target for its significant role and potential therapeutic benefits ranging from neurological diseases to cancer. Among both, CB1 and CB2R types, CB2R have received attention for its pharmacological effects as antioxidant, anti-inflammatory, immunomodulatory and antiapoptotic that can be achieved without causing psychotropic adverse effects through CB1R. The ligands activate CB2R are of endogenous, synthetic and plant origin. In recent years, β-caryophyllene (BCP), a natural bicyclic sesquiterpene in cannabis as well as non-cannabis plants, has received attention due to its selective agonist property on CB2R. BCP has been well studied in a variety of pathological conditions mediating CB2R selective agonist property. The focus of the present manuscript is to represent the CB2R selective agonist mediated pharmacological mechanisms and therapeutic potential of BCP. The present narrative review summarizes insights into the CB2R-selective pharmacological properties and therapeutic potential of BCP such as cardioprotective, hepatoprotective, neuroprotective, nephroprotective, gastroprotective, chemopreventive, antioxidant, anti-inflammatory, and immunomodulator. The available evidences suggest that BCP, can be an important candidate of plant origin endowed with CB2R selective properties that may provide a pharmacological rationale for its pharmacotherapeutic application and pharmaceutical development like a drug. Additionally, given the wide availability in edible plants and dietary use, with safety, and no toxicity, BCP can be promoted as a nutraceutical and functional food for general health and well-being. Further, studies are needed to explore pharmacological and pharmaceutical opportunities for therapeutic and preventive applications of use of BCP in human diseases.

The Bisphosphonates Clodronate and Etidronate Exert Analgesic Effects by Acting on Glutamate- and/or ATP-Related Pain Transmission Pathways

Bisphosphonates (BPs) are typical anti-bone-resorptive drugs, with nitrogen-containing BPs (N-BPs) being stronger than non-nitrogen-containing BPs (non-N-BPs). However, N-BPs have inflammatory/necrotic effects, while the non-N-BPs clodronate and etidronate lack such side effects. Pharmacological studies have suggested that clodronate and etidronate can (i) prevent the side effects of N-BPs in mice via inhibition of the phosphate transporter families SLC20 and/or SLC34, through which N-BPs enter soft-tissue cells, and (ii) also inhibit the phosphate transporter family SLC17. Vesicular transporters for the pain transmitters glutamate and ATP belong to the SLC17 family. Here, we examined the hypothesis that clodronate and etidronate may enter neurons through SLC20/34, then inhibit SLC17-mediated transport of glutamate and/or ATP, resulting in their decrease, and thereby produce analgesic effects. We analyzed in mice the effects of various agents [namely, intrathecally injected clodronate, etidronate, phosphonoformic acid (PFA; an inhibitor of SLC20/34), and agonists of glutamate and ATP receptors] on the nociceptive responses to intraplantar injection of capsaicin. Clodronate and etidronate produced analgesic effects, and these effects were abolished by PFA. The analgesic effects were reduced by N-methyl-D-aspartate (agonist of the NMDA receptor, a glutamate receptor) and α,β-methylene ATP (agonist of the P2X-receptor, an ATP receptor). SLC20A1, SLC20A2, and SLC34A1 were detected within the mouse lumbar spinal cord. Although we need direct evidence, these results support the above hypothesis. Clodronate and etidronate may be representatives of a new type of analgesic drug. Such drugs, with both anti-bone-resorptive and unique analgesic effects without the adverse effects associated with N-BPs, might be useful for osteoporosis.

Antinociceptive activity of a synthetic curcuminoid analogue, 2,6-bis-(4-hydroxy-3-methoxybenzylidene)cyclohexanone, on nociception-induced models in mice

This study investigated the potential antinociceptive efficacy of a novel synthetic curcuminoid analogue, 2,6-bis-(4-hydroxy-3-methoxybenzylidene)cyclohexanone (BHMC), using chemical- and thermal-induced nociception test models in mice. BHMC (0.03, 0.1, 0.3 and 1.0 mg/kg) administered via intraperitoneal route (i.p.) produced significant dose-related inhibition in the acetic acid-induced abdominal constriction test in mice with an ID(50) of 0.15 (0.13-0.18) mg/kg. It was also demonstrated that BHMC produced significant inhibition in both neurogenic (first phase) and inflammatory phases (second phase) of the formalin-induced paw licking test with an ID(50) of 0.35 (0.27-0.46) mg/kg and 0.07 (0.06-0.08) mg/kg, respectively. Similarly, BHMC also exerted significant increase in the response latency period in the hot-plate test. Moreover, the antinociceptive effect of the BHMC in the formalin-induced paw licking test and the hot-plate test was antagonized by pre-treatment with the non-selective opioid receptor antagonist, naloxone. Together, these results indicate that the compound acts both centrally and peripherally. In addition, administration of BHMC exhibited significant inhibition of the neurogenic nociception induced by intraplantar injections of glutamate and capsaicin with ID(50) of 0.66 (0.41-1.07) mg/kg and 0.42 (0.38-0.51) mg/kg, respectively. Finally, it was also shown that BHMC-induced antinociception was devoid of toxic effects and its antinociceptive effect was associated with neither muscle relaxant nor sedative action. In conclusion, BHMC at all doses investigated did not cause any toxic and sedative effects and produced pronounced central and peripheral antinociceptive activities. The central antinociceptive activity of BHMC was possibly mediated through activation of the opioid system as well as inhibition of the glutamatergic system and TRPV1 receptors, while the peripheral antinociceptive activity was perhaps mediated through inhibition of various inflammatory mediators.

Inhibition of ERK phosphorylation by substance P N-terminal fragment decreases capsaicin-induced nociceptive response

Previous research has demonstrated that substance P N-terminal fragments produced by the action of several different enzymes in the spinal cord could reduce nociception when injected intrathecally (i.t.) into mice. The present study examined the possible involvement of spinal extracellular signal-regulated protein kinase (ERK), a mitogen-activated protein kinase (MAPK), in i.t. substance P (1-7)-induced antinociception as assayed by the capsaicin test. The i.t. injection of substance P (1-7) (20-80 nmol) into mice resulted in a dose-dependent attenuation of paw-licking/biting behavior induced by intraplantar injection of capsaicin, which was reversed by co-injection of [D-Pro(2), D-Phe(7)]substance P (1-7), a D-isomer and antagonist of substance P (1-7). In Western blot analysis, intraplantar injection of capsaicin (400 and 1600 ng/paw) produced an increase of ERK phosphorylation in the dorsal spinal cord, whereas expression of p38 and c-Jun N-terminal kinase (JNK) phosphorylation was unchanged by capsaicin treatment. In parallel to the behavioral results, i.t. substance P (1-7) inhibited capsaicin-induced ERK phosphorylation, which was reversed by [D-Pro(2), D-Phe(7)]substance P (1-7), a substance P (1-7) antagonist. Both nociceptive behavioral response and spinal ERK activation induced by intraplantar capsaicin were reduced by U0126, an upstream inhibitor of ERK phosphorylation. Taken together, these findings suggest that the activation of ERK, but not p38 and JNK MAPKs in the spinal cord, contributes to intraplantar capsaicin-induced nociception, and that blocking ERK activation via substance P (1-7) binding sites may provide significant antinociception at the spinal cord level.

Intraplantar injection of bergamot essential oil induces peripheral antinociception mediated by opioid mechanism

This study investigated the effect of bergamot essential oil (BEO) containing linalool and linalyl acetate as major volatile components in the capsaicin test. The intraplantar injection of capsaicin (1.6 μg) produced a short-lived licking/biting response toward the injected paw. The nociceptive behavioral response evoked by capsaicin was inhibited dose-dependently by intraplantar injection of BEO. Both linalool and linalyl acetate, injected into the hindpaw, showed a significant reduction of nociceptive response, which was much more potent than BEO. Intraperitoneal (i.p.) and intraplantar pretreatment with naloxone hydrochloride, an opioid receptor antagonist, significantly reversed BEO- and linalool-induced antinociception. Pretreatment with naloxone methiodide, a peripherally acting μ-opioid receptor preferring antagonist, resulted in a significant antagonizing effect on antinociception induced by BEO and linalool. Antinociception induced by i.p. or intrathecal morphine was enhanced by the combined injection of BEO or linalool. The enhanced effect of combination of BEO or linalool with morphine was antagonized by pretreatment with naloxone hydrochloride. Our results provide evidence for the involvement of peripheral opioids, in the antinociception induced by BEO and linalool. Combined administration of BEO or linalool acting at the peripheral site, and morphine may be a promising approach in the treatment of clinical pain.

Intraplantar injection of bergamot essential oil into the mouse hindpaw: effects on capsaicin-induced nociceptive behaviors

Despite the increasing use of aromatherapy oils, there have not been many studies exploring the biological activities of bergamot (Citrus bergamia, Risso) essential oil (BEO). Recently, we have investigated the effects of BEO injected into the plantar surface of the hindpaw in the capsaicin test in mice. The intraplantar injection of capsaicin produced an intense and short-lived licking/biting response toward the injected hindpaw. The capsaicin-induced nociceptive response was reduced significantly by intraplantar injection of BEO. The essential oils of Clary Sage (Salvia sclarea), Thyme ct. linalool (linalool chemotype of Thymus vulgaris), Lavender Reydovan (Lavandula hybrida reydovan), and True Lavender (Lavandula angustifolia), had similar antinociceptive effects on the capsaicin-induced nociceptive response, while Orange Sweet (Citrus sinensis) essential oil was without effect. In contrast to a small number of pharmacological studies of BEO, there is ample evidence regarding isolated components of BEO which are also found in other essential oils. The most abundant compounds found in the volatile fraction are the monoterpene hydrocarbons, such as limonene, gamma-terpinene, beta-pinene, and oxygenated derivatives, linalool and linalyl acetate. Of these monoterpenes, the pharmacological activities of linalool have been examined. Following intraperitoneal (i.p.) administration in mice, linalool produces antinociceptive and antihyperalgesic effects in different animal models in addition to anti-inflammatory properties. Linalool also possesses anticonvulsant activity in experimental models of epilepsy. We address the importance of linalool or linalyl acetate in BEO-or the other essential oil-induced antinociception.

Mechanisms of Nociception Evoked by Intrathecal High-dose Morphine

Morphine is recommended by WHO as the analgesic of choice for effective treatment of moderate to severe cancer pain . Indeed spinally administered morphine at small doses injected intrathecally (i.t.) or intracerebroventricularly into animals produces a profound antinociception at both spinal and supraspinal sites. Conversely, high doses of spinally administered morphine elicit a series of scratching, biting and licking in mice, and vocalization and agitation in rats, indicative of a spontaneous nociceptive behavioural response. Hyperalgesia and allodynia are also induced by such morphine treatment in humans as well as animals. These behaviours are not an opioid receptor-mediated event. This article will review the potential mechanisms of spinally mediated nociceptive behaviour evoked by i.t. morphine at high concentrations. We will discuss a possible presynaptic release of nociceptive neurotransmitters/neuromodulators (e.g., substance P, glutamate and dynorphin) in the primary afferent fibers following i.t. high-dose morphine. There must be an intimate interaction of i.t. high-dose morphine with tachykinin neurokinin 1 (NK1) receptors and multiple sites on the N-methyl-D-aspartate (NMDA) receptor complex in the dorsal spinal cord. Since the effect of NMDA receptor activation and the associated Ca2+ influx results in production of nitric oxide (NO) by activation of NO synthase, it seems that spinal NO also plays an important role in nociception evoked by i.t. high-dose morphine. Morphine-3-glucuronide, one of the major metabolites of morphine, has been found to evoke nociceptive behaviour similar to that of i.t. high-dose morphine. It is plausible that morphine-3-glucuronide may be responsible for nociception seen after i.t. high-dose morphine treatment. The demonstration of neural mechanism underlying morphine-induced nociception provides a pharmacological basis for improved pain management with morphine at high doses.

Differential effects of intraplantar capsazepine and ruthenium red on capsaicin-induced desensitization in mice

Intraplantar injection of capsaicin (1.6 microg/paw) into the mouse hindpaw produced an acute paw-licking/biting response. This study was designed (1) to investigate the antinociceptive effects of intraplantar administration of capsazepine, a competitive vanilloid receptor antagonist, and ruthenium red, a noncompetitive antagonist, in the nociceptive licking/biting response induced by intraplantar injection of capsaicin, and (2) to determine whether these compounds were able to prevent capsaicin-induced desensitization in mice. Both capsazepine and ruthenium red produced a dose-dependent reduction in the capsaicin-induced nociceptive response. In licking/biting response to intraplantar capsaicin, ruthenium red was more potent than capsazepine in producing antinociceptive activity as assayed by the capsaicin test. The first injection of capsaicin induced a profound desensitization to the second and third injections of capsaicin at the interval of 15 or 30 min. The capsaicin-induced desensitization was prevented dose-dependently by antinociceptive doses of capsazepine, whereas ruthenium red in doses exhibiting antinociceptive activity was without effect on capsaicin-induced desensitization. The present results suggest that both capsazepine and ruthenium red can produce a local peripheral antinociceptive action, which may be mediated by inhibiting the membrane ion channel activated by capsaicin. In addition, these data suggest that capsazepine may act in the mechanism clearly different from ruthenium red in the capsaicin-induced nociceptive desensitization.

Antiemetic effects of sendide, a peptide tachykinin NK1 receptor antagonist, in the ferret

The antiemetic activity of sendide, a new peptide tachykinin NK1 receptor antagonist, against cisplatin-induced emesis was investigated using ferrets. The frequency of cisplatin (10 mg/kg, i.p.)-induced retching (104.6 +/- 14.3/6 h) and vomiting (19.0 +/- 3.0/6 h) was significantly reduced by pretreatment with sendide (3.0 mg/kg, s.c.) (14.0 +/- 8.1/6 h and 1.8 +/- 1.2/6 h, respectively). Intravenous bolus injection of substance P (1-10 microg/kg) or 5-hydroxytryptamine (5-HT) (10-50 microg/kg) produced a dose-dependent increase in the abdominal afferent vagus nerve activity. The change from pre-injection level in the afferent nerve activity induced by substance P (1 microg/kg, i.v.) (453.7 +/- 51.5%) was significantly reduced by pretreatment with either sendide (100 microg/kg, i.v.) (276.1 +/- 50.1%, P < 0.05) or granisetron, a 5-HT3 receptor antagonist (1 mg/kg, i.v.) (146.3 +/- 14.0%, P < 0.01). The amount of 5-HT released into the solution during a 1-h exposure to 2-methyl-5-HT (10(-6) M), a 5-HT3 receptor agonist, was significantly increased (317.9 +/- 46.7%, P < 0.05) compared with that of the control tissues (160.4 +/- 8.1%). The 2-methyl-5-HT-induced 5-HT release was significantly inhibited by administration of sendide (10(-6) M) (174.0 +/- 21.6%, P < 0.05) or granisetron (10(-6) M) (186.6 +/- 27.3%, P < 0.05). Since sendide does not penetrate the central nervous system, these results suggest that the antiemetic effects of sendide are due to the inhibition of NK1 and 5-HT3 receptors on the emetic peripheral detector sites.

Intrathecal administration of p-hydroxymercuribenzoate or phosphoramidon/bestatin-combined induces antinociceptive effects through different opioid mechanisms

The antinociceptive effect of intrathecally (i.t.) administered protease inhibitors was tested against capsaicin (800 ng) injected into the dorsal surface of a hindpaw. Both p-hydroxymercuribenzoate (2-8 nmol), a cysteine protease inhibitor, and phosphoramidon (1-4 nmol), an endopeptidase 24.11 inhibitor in the presence of bestatin (0.25 nmol) an aminopeptidase inhibitor, administered i.t. 60 min prior to the injection of capsaicin produced a dose-dependent reduction of the capsaicin-induced paw licking and biting response. p-Hydroxymercuribenzoate (4 nmol)-induced antinociception was significantly antagonized by nor-binaltorphimine, a selective kappa-opioid receptor antagonist, but not by naltrindole, a selective delta-opioid receptor antagonist. On the other hand, phosphoramidon (4 nmol) /bestatin-induced antinociception was significantly antagonized by naltrindole, but not by nor-binaltorphimine. The results indicate that the antinociceptive effect of p-hydroxymercuribenzoate may be due to the inhibition of a cysteine protease degrading endogenous dynorphins whereas phosphoramidon in the presence of bestatin blocks the degradation of enkephalins.

Effect of spinal nitric oxide inhibition on capsaicin-induced nociceptive response

Pretreatment with the nitric oxide synthase (NOS) inhibitor L-NG-nitro arginine methyl ester (L-NAME), injected intraperitoneally (i.p.) or intrathecally (i.t.), produced a significant antinociception in the mouse assessed by the capsaicin-induced paw licking procedure. Varying the administration time of an effective dose of L-NAME (160nmol, i.t.) resulted in a significant decrease of the brief nociceptive behavioral response induced by capsaicin, even when L-NAME was given 2 hr before capsaicin. L-NAME, injected i.p. or i.t., produced a dose-related reduction in paw licking in the second phase of the formalin (2.0%) response without affecting the first phase. L-Arginine (600 mg/kg, i.p.) but not D-arginine (600 mg/kg, i.p.) reversed the antinociceptive effect of L-NAME in the capsaicin test. Antinociceptive effect of L-NAME, injected i.p. or i.t., was more potent in the second phase response of formalin-induced paw licking than in capsaicin-induced nociceptive response. The inhibitory action of L-NAME was reversed by L-arginine but not D-arginine in the second phase response. L-Arginine alone was without affecting capsaicin- and formalin-induced nociceptive responses. These results suggest that spinal nitric oxide (NO) may be involved in the mechanisms of capsaicin-induced brief nociceptive stimuli, but not in the first, acute phase of the formalin-induced response in mice.

The neurokinin-1 receptor antagonist, sendide, exhibits antinociceptive activity in the formalin test

Sendide is a selective and extremely potent antagonist of neurokinin-1 (NK1) receptors in the mouse spinal cord. The antinociceptive activities of sendide, an antagonist of NK1 receptors, and its analogue, [D-Trp7]sendide have been examined after intrathecal (i.t.) administrations in the mouse paw formalin test. Intrathecal administration of sendide (in pmol) reduced both the early and late phases of the formalin-induced licking response. [D-Trp7]sendide also produced a significant antinociceptive response with less potent activity than sendide. Even highest doses (4000 pmol sendide and 8000 pmol [D-Trp7]sendide) examined, there was no motor paralysis of the hindlimbs. Intrathecal morphine inhibited both the early and late phases of the formalin-induced licking response in a dose-dependent manner. The results indicate that the antinociceptive effects of sendide and [D-Trp7]sendide may be mediated at NK1 receptors in the formalin-induced nociception.