Isobolographic analysis of interaction between cyclooxygenase inhibitors and tramadol in acetic acid-induced writhing in mice

Indian Shot (Canna Indica L). Leaves Provide Valuable Insights into the Management of Inflammation and Other Associated Disorders Offering Health Benefits

Background

Throughout history, plants have played a crucial role in advancing medicinal treatments by providing a diverse range of compounds for the development of innovative therapies. Canna indica L. a tropical herb of the Cannaceae family, also known as Indian shot, has a rich history of traditional use in treating ailments like inflammation, malaria, dysentery, fever, dropsy, and diarrhea.

Objective

This comprehensive research invesigates the extract preparation of C. indica leaves using multidisciplinary analytical approaches for this extract in order to shed light on its therapeutic potentials.

Methods

The research, an international collaboration involving researchers from Bangladesh and China, utilized GC-MS/MS analysis to identify bioactive compounds across different C. indica extracts. Biological assays were conducted to assess antimicrobial activity using the disc diffusion method (in vitro), cytotoxicity through the brine shrimp lethality assay (in vitro), analgesic effects via the acetic acid-induced writhing test (in vivo), and antidiarrheal activity with the castor oil-induced diarrhea model (in vivo). Molecular docking studies were performed to determine binding affinities with Epidermal Growth Factor Receptor (EGFR), Dihydrofolate Reductase (DHFR), Delta Opioid Receptor (DOR), Tumor Necrosis Factor-alpha (TNF-α), and Cyclooxygenase-2 (COX-2) receptors.

Results

The GC-MS/MS analysis identified 35, 43, 27, and 20 compounds in dichloromethane, aqueous, petroleum ether, and ethyl acetate extracts, respectively. The aqueous (AQSF) and dichloromethane (DCMSF) extracts showed notable antimicrobial activity, particularly against gram-negative bacteria. Cytotoxicity tests indicated that ethyl acetate (EASF) and dichloromethane (DCMSF) fractions were potent. Analgesic activity was highest in DCMSF, and antidiarrheal effects were dose-dependent, with DCMSF showing the greatest efficacy. Molecular docking revealed strong affinities of Ergostane-3,5,6,12,25-pentol, 25-acetate, (3.beta.,5.alpha.,6.beta.,12.beta).- for EGFR and Norgestrel for COX-2.

Conclusion

This research provides valuable insights into the bioactivity evaluation of C. indica, bridging the gap between its chemical composition and diverse biological effects. The findings contribute to the growing body of knowledge in natural product-based drug discovery and underscore the significance of C. indica as a potential source of novel therapeutic agents to treat inflammation and other disease states.

Chemico-pharmacological evaluation of the methanolic leaf extract of Catharanthus ovalis: GC-MS/MS, in vivo, in vitro, and in silico approaches

Introduction: Natural plant-based medicines have gained popularity recently as a major source of inventive, risk-free, and more potent secondary bioactive compounds with medicinal potential. Catharanthus ovalis is a perennial shrub containing various indole alkaloids cultivated extensively for local medical purposes. Methods: This research is conducted to identify the phytocompounds present in the leaves of C. ovalis and its central and peripheral analgesic, thrombolytic, and membrane-stabilizing activities through tail immersion, acetic acid-induced writhing, human blood clot lysis, and erythrocyte lysis by heat and hypotonic solution methods, respectively. Results and discussion: A total of 39 compounds were identified using GC-MS/MS techniques, including hexadecanoic acid, methyl ester (56.749%), methyl stearate (29.782%), carvacrol and its TBDMS derivative (12.586%), and 9-octadecenoic acid, methyl ester, (E)-] (9.297%) presented in high quantity. The highest tail immersion latency was observed for the 600 mg/kg extract of C. ovalis crude extract. Both 400 and 600 mg/kg doses of C. ovalis crude extract exhibited prominent peripheral analgesic activity. The maximum thrombolytic effect was observed by DCM soluble fraction extract by inhibiting 54.87% of the clot. However, the aqueous-soluble fraction of this extract manifested an excellent membrane-stabilizing effect by showing 73.98% and 87.51% hemolysis against heat- and hypotonic-induced hemolysis, respectively. Some of the compounds were identified as active agents against different receptors related to these diseases, which supported the findings of in vitro and in vivo tests. Conclusion: Further investigation needs to be conducted to specify and identify the exact mechanism of action of these compounds.

Nalbuphine alleviates inflammation by down-regulating NF-κB in an acute inflammatory visceral pain rat model

Introduction

Nalbuphine can relieve patients’ inflammation response after surgery compared to other opioid drugs. However, its molecular mechanism has not been clear. Activation of NF-κB signaling pathway under oxidative stress and inflammation can maintain pain escalation.

Methods

We firstly investigated the effect of nalbuphine on writhing test and mechanical allodynia using a rat model of inflammatory visceral pain (acetic acid (AA) administrated). Cytokines (including tumor necrosis factor (TNF)-α, Interleukin (IL)-1β, IL-2, and IL-6 in plasma were tested with ELISA technology. Expression levels of TNF-α, IκBα and p-NF-κB p65 at the spinal cord (L3–5) were measured by western blot or RT-qPCR.

Results

We found that the paw withdrawal threshold (PWT) values of rats were reduced in the model group, while the numbers of writhing, levels of IL-1β, IL-2, IL-6, and TNF-α in plasma, and p-NF-κB protein and its gene expressions in the lumbar spinal cord were up-regulated. Subcutaneously injection of nalbuphine (10 μg/kg) or PDTC (NF-κB inhibitor) attenuated acetic acid-induced inflammatory pain, and this was associated with reversal of up-regulated IL-1β, IL-2, IL-6, and TNF-α in both plasma and spinal cord. Furthermore, acetic acid increased p-NF-κB and TNF-α protein levels in the white matter of the spinal cord, which was attenuated by nalbuphine. These results suggested that nalbuphine can significantly ameliorate inflammatory pain via modulating the expression of NF-κB p65 as well as inflammation factors level in the spinal cord.

Conclusion

In conclusion, nalbuphine inhibits inflammation through down-regulating NF-κB pathway at the spinal cord in a rat model of inflammatory visceral pain.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40360-022-00573-7.

Cassia artemisiodes attenuates nociceptive and diabetes-induced neuropathic pain modalities apropos antioxidant and anti-inflammatory mechanisms

Cassia plants have a considerable position in conventional systems of medicine. The possible anti-nociceptive, anti-inflammatory, and anti-neuropathic properties of Cassia artemisiodes (CAD) extract were tested using the standard animal models. In this study, in vitro antioxidant, cyclooxygenase (COX-1 and 2), and 5-lipoxygenase (5-LOX) inhibitory assays were performed. The anti-inflammatory activity was evaluated using carrageenan, histamine, and serotonin-induced paw edema models. Antipyretic activity, thermally and chemically-induced nociception, and naloxone antagonistic activities were carried out. The CAD extract was tested for anti-neuropathic activity in the streptozotocin-induced diabetic neuropathy model. Suppressing the effect of CAD extract on the mRNA level of inducible nitric oxide synthase (iNOS), COX-2, and pro-inflammatory cytokines (TNF-α, IL-1β, IL-6) was determined by performing RT-PCR. The CAD extract inhibited COX-2 and 5-LOX enzymes, paw inflammation, and reduced nociceptive behaviors. The mRNA gene expression of iNOS, COX-2, and inflammatory cytokines was reduced significantly with increased DPPH scavenging activity. The extract significantly reduced the diabetes-induced neuropathic pain. In a nutshell, these results recommended that the CAD extract has anti-nociceptive and anti-neuropathic activities due to inhibition of inflammatory and oxidative signaling.

Antinociceptive activity of the ethanolic extract of Trixis angustifolia DC

The antinociceptive activity of the ethanolic extract of Trixis angustifolia DC. (EETx) was investigated using the acetic acid-induced writhing and the hot-plate tests in mice. In the acetic acid-induced writhing test, mice treated with EETx (50, 100 and 200 mg/kg, p.o.) exhibited reduced writhing (38%, 67%, and 74%, respectively). In the hot-plate test, the three doses administrated increased the nociceptive response time. The phytochemical analysis of EETx led to the isolation of three known compounds, hygric acid (1), 5,6-Dihydroxy-7,8,4'-trimethoxyflavone (2) and xanthomicrol (3). Compound 1 was identified for the first time in this species. These results demonstrate that T. angustifolia has potential central and peripheral antinociceptive effects and support the ethnomedicinal use of this plant.

Morphine Perinatal Exposure Induces Long-Lasting Negative Emotional States in Adult Offspring Rodents

Psychoactive substances during pregnancy and lactation is a key problem in contemporary society, causing social, economic, and health disturbance. In 2010, about 30 million people used opioid analgesics for non-therapeutic purposes, and the prevalence of opioids use during pregnancy ranged from 1% to 21%, representing a public health problem. This study aimed to evaluate the long-lasting neurobehavioral and nociceptive consequences in adult offspring rats and mice exposed to morphine during intrauterine/lactation periods. Pregnant rats and mice were exposed subcutaneously to morphine (10 mg/kg/day) during 42 consecutive days (from the first day of pregnancy until the last day of lactation). Offspring were weighed on post-natal days (PND) 1, 5, 10, 15, 20, 30, and 60, and behavioral tasks (experiment 1) or nociceptive responses (experiment 2) were assessed at 75 days of age (adult life). Morphine-exposed female rats displayed increased spontaneous locomotor activity. More importantly, both males and female rats perinatally exposed to morphine displayed anxiety- and depressive-like behaviors. Morphine-exposed mice presented alterations in the nociceptive responses on the writhing test. This study showed that sex difference plays a role in pain threshold and that deleterious effects of morphine during pre/perinatal periods are nonrepairable in adulthood, which highlights the long-lasting clinical consequences related to anxiety, depression, and nociceptive disorders in adulthood followed by intrauterine and lactation morphine exposure.

Infusion of aerial parts of Salvia chudaei Batt. & Trab. from Algeria: Chemical, toxicological and bioactivities characterization

ETHNOPHARMACOLOGICAL RELEVANCE

Salvia chudaei Batt. & Trab. from Algeria is traditionally used to relieve several dysfunctions, including inflammatory and pain-related situations.

AIM OF THE STUDY

This work aimed to confirm scientifically the referred properties. For that, the phenolic composition and antioxidant activity were evaluated as well as acute toxicity, anti-inflammatory and analgesic effects of different doses of the infusion of S. chudaei aerial parts.

MATERIALS AND METHODS

Infusion of aerial parts of S. chudaei was prepared and screened for phenolic composition by generalized methods TPC and TFC then by LC-DAD-ESI/MSn. DPPH and FRAP were used to evaluate antioxidant activity. Using mice, acute toxicity, anti-inflammatory by carrageenan-induced paw edema, and analgesic by acetic acid-induced writhing and formalin-induced pain activities were tested.

RESULTS

The infusion showed 2018 mg GAE/100g DW of phenolics and 1956 mg ECE/100g DW of flavonoids. Phenolic profile by LC-DAD-ESI/MSn revealed the presence of ten compounds: syringic acid hexoside derivative, kaempferol-O-diglucuronide, kaempferol-O-deoxyhexoside-hexoside, kaempferol-O-glucuronide, apigenin-O-diglucuronide, caffeic acid, 4-O-caffeoylquinic acid, eriodictyol-O-glucuronide, rosmarinic acid hexoside, and rosmarinic acid. This acid was the major compound representing 54% of the total content of the identified compounds and an absolute content of 18 mg/g of extract. Additionally, the infusion exhibited a good antioxidant activity (DPPH: 81 μmol TE/g DW, FRAP: 438 μmol FSE/g DW). By oral administration to mice, the infusion showed a significant (p<0.05) dose-dependent reduction of carrageenan-induced inflammation and inhibition of formalin-induced pain (late and early phase) and acetic acid-induced writhing compared with the control. On the other hand, infusion up to 8 g/kg b.w. showed no signs of toxicity or mortality.

CONCLUSION

This study reveals, for the first time, that the infusion of the aerial parts of S. chudaei is not toxic in a single dose and has remarkable antioxidant, anti-inflammatory, and analgesic activities, supporting the use of this species in folk medicine.

Anti-inflammatory and antinociceptive effects of Curcuma kwangsiensis and its bioactive terpenoids in vivo and in vitro

ETHNOPHARMACOLOGICAL RELEVANCE

"Curcumae Radix", the dried rhizomes of Curcuma kwangsiensis documented in Chinese pharmacopoeia, has been traditionally used for the treatment of inflammatory and pain diseases, such as jaundice and red urine, cleaning the heart-fire and depression, arthralgia, and dysmenorrhea. However, according to literature surveys, anti-inflammatory and antinociceptive studies of C. kwangsiensis have been seldom reported so far.

AIM OF THE STUDY

The current study focuses on the anti-inflammatory and antinociceptive effects of C. kwangsiensis and discovering the bioactive compounds for its traditional usages both in vivo and in vitro, which could provide scientific justification about its traditional use.

MATERIAL AND METHODS

The anti-inflammatory and antinociceptive assays of various layers (ME, EA, AQS) from C. kwangsiensis were achieved by carrageenan-induced paw edema and acetic acid-induced writhing animal models, respectively. The most bioactive part, EA layer was further phytochemically investigated by multiple step chromatography techniques. The structures of these isolates were unambiguously elucidated by means of extensive spectroscopic and chemical methods, and comparison with corresponding data of the reported literature. Four major sesquiterpenoids (4, 6, 14, and 15) were achieved for their anti-inflammatory and antinociceptive assays by the two aforementioned animal models in vivo. All the isolated compounds were evaluated for their anti-inflammatory effects via detecting inflammatory mediator releases (COX-2, IL-1β, and TNF-α) in RAW 264.7 macrophage cells induced by LPS.

RESULTS

The ME and EA layers significantly alleviated the paw edema caused by carrageenan and decreased the number of writhes induced by acetic acid at the dose of 200 and/or 100 mg/kg in comparison to the control group (p < 0.01/0.05), and the EA layer exhibited better activity than that of ME layer. Subsequent phytochemical investigation on EA layer of C. kwangsiensis exhibited that three new terpenoid compounds (1-3), identified as (12Z,14R)-7β-hydroxylabda-8(17),12-diene-14,15,16-triol (1), (12Z,14S)- 7β-hydroxlabda-8(17),12-diene-14,15,16-triol (2), and (4S)-hydroxy-(8)-methoxy-(5S)-(H)-guaia1(10),7(11)-dien-12,8-olide (3), together with twenty-two known analogs were isolated. Furthermore, four major sesquiterpenoids (4, 6, 14, and 15) significantly relieved the paw edema and number of writhes at 100 and/or 50 mg/kg (p < 0.05/0.01). Likewise, the majority of sesqui- and diterpenoids isolated could remarkably inhibited the secretion of inflammatory mediators (COX-2, IL-1β, and TNF-α) in LPS-stimulated RAW 264.7 macrophages cells at the concentration of 20 μg/mL, comparable to DXM used as the positive control. All the results suggested that EA layer from C. kwangsiensis possessed the anti-inflammatory and antinociceptive activities, and these sesqui- and diterpenoids could be the effective constituents responsible for relieving inflammation.

CONCLUSION

The present studies undoubtedly determined the anti-inflammatory and antinociceptive material basis of C. kwangsiensis, including the EA layer and its precise components, which presented equivalent or better anti-inflammatory effects than that of positive control (ASP/DXM) in vivo and in vitro. These results not only would account for scientific knowledge for traditional use of C. kwangsiensis, but also provide credible theoretical foundation for the further development of anti-inflammatory and antinociceptive agents.

Anti-Inflammatory, Antinociceptive, and Antioxidant Properties of Anacardic Acid in Experimental Models

Anacardic acid (AA), a compound extracted from cashew nut liquid, exhibits numerous pharmacological activities. The aim of the current investigation was to assess the anti-inflammatory, antinociceptive, and antioxidant activities of AA in mouse models. For this, Swiss albino mice were pretreated with AA (10, 25, 50 mg/kg, intraperitoneally, ip) 30 min prior to the administration of carrageenan, as well as 25 mg/kg of prostaglandin E2, dextran, histamine, and compound 48/80. The antinociceptive activity was evaluated by formalin, abdominal, and hot plate tests, using antagonist of opioid receptors (naloxene, 3 mg/kg, ip) to identify antinociceptive mechanisms. Results from this study revealed that AA at 25 mg/kg inhibits carrageenan-induced edema. In addition, AA at 25 mg/kg reduced edema and leukocyte and neutrophilic migration to the intraperitoneal cavity, diminished myeloperoxidase activity and malondialdehyde concentration, and increased the levels of reduced glutathione. In nociceptive tests, it also decreased licking, abdominal writhing, and latency to thermal stimulation, possibly via interaction with opioid receptors. Taken together, these results indicate that AA exhibits anti-inflammatory and antinociceptive actions and also reduces oxidative stress in acute experimental models, suggesting AA as a promising compound in the pharmaceutical arena.

Methanol Extract of Dicranopteris linearis Leaves Attenuate Pain via the Modulation of Opioid/NO-Mediated Pathway

Dicranopteris linearis leaf has been reported to exert antinociceptive activity. The present study elucidates the possible mechanisms of antinociception modulated by the methanol extract of D. linearis leaves (MEDL) using various mouse models. The extract (25, 150, and 300 mg/kg) was administered orally to mice for 30 min priot to subjection to the acetic acid-induced writhing-, hot plate- or formalin-test to establish the antinociceptive profile of MEDL. The most effective dose was then used in the elucidation of possible mechanisms of action stage. The extract was also subjected to the phytochemical analyses. The results confirmed that MEDL exerted significant (p < 0.05) antinociceptive activity in those pain models as well as the capsaicin-, glutamate-, bradykinin- and phorbol 12-myristate 13-acetate (PMA)-induced paw licking model. Pretreatment with naloxone (a non-selective opioid antagonist) significantly (p < 0.05) reversed MEDL effect on thermal nociception. Only l-arginine (a nitric oxide (NO) donor) but not N(ω)-nitro-l-arginine methyl ester (l-NAME; a NO inhibitor) or 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ; a specific soluble guanylyl cyclase inhibitor) significantly (p < 0.05) modified MEDL effect on the writhing test. Several polyphenolics and volatile antinociceptive compounds were detected in MEDL. In conclusion, MEDL exerted the opioid/NO-mediated antinociceptive activity, thus, justify D. linearis as a potential source for new analgesic agents development.

Long-Lasting Anti-Inflammatory and Antinociceptive Effects of Acute Ammonium Glycyrrhizinate Administration: Pharmacological, Biochemical, and Docking Studies

The object of the study was to estimate the long-lasting effects induced by ammonium glycyrrhizinate (AG) after a single administration in mice using animal models of pain and inflammation together with biochemical and docking studies. A single intraperitoneal injection of AG was able to produce anti-inflammatory effects in zymosan-induced paw edema and peritonitis. Moreover, in several animal models of pain, such as the writhing test, the formalin test, and hyperalgesia induced by zymosan, AG administered 24 h before the tests was able to induce a strong antinociceptive effect. Molecular docking studies revealed that AG possesses higher affinity for microsomal prostaglandin E synthase type-2 compared to type-1, whereas it seems to locate better in the binding pocket of cyclooxygenase (COX)-2 compared to COX-1. These results demonstrated that AG induced anti-inflammatory and antinociceptive effects until 24-48 h after a single administration thanks to its ability to bind the COX/mPGEs pathway. Taken together, all these findings highlight the potential use of AG for clinical treatment of pain and/or inflammatory-related diseases.

Antiepileptic drugs as analgesics/adjuvants in inflammatory pain: current preclinical evidence

Inflammatory pain is the most common type of pain that is treated clinically. The use of currently available treatments (classic analgesics - NSAIDs, paracetamol and opioids) is limited by insufficient efficacy and/or side effects/tolerance development. Antiepileptic drugs (AEDs) are widely used in neuropathic pain treatment, but there is substantial preclinical evidence on their efficacy against inflammatory pain, too. In this review we focus on gabapentinoids (gabapentin and pregabalin) and dibenzazepine AEDs (carbamazepine, oxcarbazepine, and recently introduced eslicarbazepine acetate) and their potential for relieving inflammatory pain. In models of somatic, visceral and trigeminal inflammatory pain, that have a translational value for inflammatory conditions in locomotor system, viscera and head/face, AEDs have demonstrated analgesic activity. This activity was mostly consistent, dependent on the dose and largely independent on the site of inflammation and method of its induction, nociceptive stimuli, species, specific drug used, its route of administration and dosing schedule. AEDs exerted comparable efficacy with classic analgesics. Effective doses of AEDs are lower than toxic doses in animals and, when expressed as equivalent human doses, they are largely overlapping with AEDs doses already used in humans for treating epilepsy/neuropathic pain. The main mechanism of antinociceptive/antihyperalgesic action of gabapentinoids in inflammatory pain models seems to be α₂δ-dependent suppression of voltage-gated calcium channels in primary sensory neurons that leads to reduced release of neurotransmitters in the spinal/medullar dorsal horn. The suppression of NMDA receptors via co-agonist binding site primarily at spinal sites, activation of various types of K⁺ channels at spinal and peripheral sites, and activation of noradrenergic and serotonergic descending pain modulatory pathways may also contribute. Inhibition of voltage-gated sodium channels along the pain pathway is probably the main mechanism of antinociceptive/antihyperalgesic effects of dibenzazepines. The recruitment of peripheral adrenergic and purinergic mechanisms and central GABAergic mechanisms may also contribute. When co-administered with classic/other alternative analgesics, AEDs exerted synergistic/additive interactions. Reviewed data could serve as a basis for clinical studies on the efficacy/safety of AEDs as analgesics/adjuvants in patients with inflammatory pain, and contribute to the improvement of the treatment of various inflammatory pain states.

Potent Anti-inflammatory and Analgesic Actions of the Chloroform Extract of Dendropanax morbifera Mediated by the Nrf2/HO-1 Pathway

Dendropanax morbifera LEVEILLE (DP) has been used in traditional Korean medicines to treat a variety of inflammatory diseases. Although the in vitro anti-inflammatory potential of this plant is understood, its in vivo efficacy and underlying molecular mechanism of anti-inflammatory effects are largely unknown. We elucidated the anti-inflammatory and analgesic activities and the underlying molecular mechanisms of DP using in vitro and in vivo models. Lipopolysaccharide (LPS)-stimulated murine macrophages were used to analyze the in vitro anti-inflammatory potential of DP extract and to elucidate the underlying mechanisms. In vivo animal models of phorbol 12-myristate 13-acetate (TPA)-induced ear edema and acetic acid-induced writhing response tests were used to analyze the in vivo anti-inflammatory effects and anti-nociceptive effects of DP extract, respectively. Methanolic extract of DP (DPME) significantly inhibited the release of nitric oxide (NO) and prostaglandin E2 (PGE2) in LPS-activated macrophages. Among the five sub-fractions, the chloroform fraction (DP-C) showed the most potent suppressive effects against pro-inflammatory mediators and cytokines in LPS-stimulated macrophages. These effects were attributed to inhibition of nuclear factor-κB (NF-κB) nuclear translocation and c-Jun N terminal kinase (JNK) 1/2 phosphorylation and to activation of NF-E2-related factor 2/heme oxygenase-1 (Nrf2/HO-1) signaling. DP-C exhibited strong protective in vivo effects in TPA-induced ear edema mouse model and acetic acid-induced writhing response test. Our data suggest that DP-C has potent anti-inflammatory and analgesic activities and may be a promising treatment against a variety of inflammatory diseases.

sec-Butylpropylacetamide (SPD), a new amide derivative of valproic acid for the treatment of neuropathic and inflammatory pain

Chronic pain is a multifactorial disease comprised of both inflammatory and neuropathic components that affect ∼20% of the world's population. sec-Butylpropylacetamide (SPD) is a novel amide analogue of valproic acid (VPA) previously shown to possess a broad spectrum of anticonvulsant activity. In this study, we defined the pharmacokinetic parameters of SPD in rat and mouse, and then evaluated its antinociceptive potential in neuropathic and acute inflammatory pain models. In the sciatic nerve ligation (SNL) model of neuropathic pain, SPD was equipotent to gabapentin and more potent than its parent compound VPA. SPD also showed either higher or equal potency to VPA in the formalin, carrageenan, and writhing tests of inflammatory pain. SPD showed no effects on compound action potential properties in a sciatic nerve preparation, suggesting that its mechanism of action is distinct from local anesthetics and membrane stabilizing drugs. SPD's activity in both neuropathic and inflammatory pain warrants its development as a potential broad-spectrum anti-nociceptive drug.

Evaluation of the analgesic effects of ammoxetine, a novel potent serotonin and norepinephrine reuptake inhibitor

AIM

The selective serotonin (5-HT) and norepinephrine (NE) reuptake inhibitors (SNRIs) are commonly used for the treatment of neuropathic pain and fibromyalgia. Ammoxetine ((±)-3-(benzo[d] [1,3]dioxol-4-yloxy)-N-methyl-3-(thiophen-2-yl)propan-1-amine) has been identified as a novel potent SNRI. In this study, we evaluated the acute analgesic properties of ammoxetine in different animal models of pain, and examined the involvement of monoamines in its analgesic actions.

METHODS

The analgesic effects of ammoxetine were assayed using models of acetic acid- and formalin-induced pain in mice, neuropathic pain induced by sciatic nerve injury (SNI), chronic constriction injury (CCI) and reserpine-induced fibromyalgia pain in rats. The contents of 5-HT and NE in brain regions of fibromyalgia rats were measured using HPLC-ECD. In all the experiments, duloxetine was used as a positive control drug.

RESULTS

Oral administration of ammoxetine (0.625-10 mg/kg) or duloxetine (2.5-40 mg/kg) dose-dependently decreased the number of acetic acid-induced writhing and formalin-induced first phase and second phase paw licking time in mice. Oral administration of ammoxetine (2.5-10 mg/kg) or duloxetine (10 mg/kg) alleviated mechanical allodynia in SNI and CCI rats and thermal hyperalgesia in CCI rats. The antiallodynic effect of ammoxetine in CCI rats was abolished by pretreatment with para-chlorophenylalanine methyl ester hydrochloride (PCPA, a 5-HT synthesis inhibitor) or α-methyl-para-tyrosine methylester (AMPT, a catecholamine synthesis inhibitor). Oral administration of ammoxetine (30 mg/kg) or duloxetine (50 mg/kg) significantly attenuated tactile allodynia in rats with reserpine-induced fibromyalgia. In the fibromyalgia rats, administration of ammoxetine (10, 30 mg/kg) or duloxetine (30, 50 mg/kg) dose-dependently increased the levels of 5-HT and NE, and decreased the metabolite ratio of 5-HT (5-HIAA/5-HT) in the spinal cord, hypothalamus, thalamus and prefrontal cortex.

CONCLUSION

Ammoxetine effectively alleviates inflammatory, continuous, neuropathic and fibromyalgia-related pain in animal models, which can be attributed to enhanced neurotransmission of 5-HT and NE in the descending inhibitory systems.

Antinociceptive effects of dehydrocorydaline in mouse models of inflammatory pain involve the opioid receptor and inflammatory cytokines

Dehydrocorydaline (DHC) is an alkaloidal component isolated from Rhizoma corydalis. Previous studies have shown that DHC has anti-inflammatory and anti-tumor effects and that it can protect the cardiovascular system. However, there are few studies of the antinociceptive effects of DHC in vivo. This study explored the antinociceptive effects and possible mechanisms of DHC in mice using two inflammatory pain models: the acetic acid-induced writhing test and the formalin paw test. The intraperitoneal administration of DHC (3.6, 6 or 10 mg/kg) showed a dose-dependent antinociceptive effect in the acetic acid-induced writhing test and significantly attenuated the formalin-induced pain responses in mice. The antinociceptive effects of DHC were not associated with changes in the locomotor activity or motor responses of animals, and no obvious acute or chronic toxic effects were observed in the mice. Furthermore, the use of naloxone confirmed the involvement of the opioid receptor in the central antinociceptive effects of DHC. DHC reduced formalin-induced paw edema, which indicated that DHC may produce an anti-inflammatory effect in the periphery. In the formalin test, DHC decreased the expression of caspase 6 (CASP6), TNF-α, IL-1β and IL-6 proteins in the spinal cord. These findings confirm that DHC has antinociceptive effects in mice.

Preclinical Assessment of Inflammatory Pain

While acute inflammation is a natural physiological response to tissue injury or infection, chronic inflammation is maladaptive and engenders a considerable amount of adverse pain. The chemical mediators responsible for tissue inflammation act on nociceptive nerve endings to lower neuronal excitation threshold and sensitize afferent firing rate leading to the development of allodynia and hyperalgesia, respectively. Animal models have aided in our understanding of the pathophysiological mechanisms responsible for the generation of chronic inflammatory pain and allowed us to identify and validate numerous analgesic drug candidates. Here we review some of the commonly used models of skin, joint, and gut inflammatory pain along with their relative benefits and limitations. In addition, we describe and discuss several behavioral and electrophysiological approaches used to assess the inflammatory pain in these preclinical models. Despite significant advances having been made in this area, a gap still exists between fundamental research and the implementation of these findings into a clinical setting. As such we need to characterize inherent pathophysiological pathways and develop new endpoints in these animal models to improve their predictive value of human inflammatory diseases in order to design safer and more effective analgesics.

Ellagic acid enhances the antinociceptive action of carbamazepine in the acetic acid writhing test with mice

CONTEXT

Ellagic acid (EA) produced antinociceptive and anti-inflammatory effects through the central and peripheral sites of action.

OBJECTIVE

The objective of the current study was to examine the functional interaction between ellagic acid and carbamazepine (CBZ) on pain.

MATERIALS AND METHODS

Fourteen groups of mice (8-10 each) were used in this study. Pain was induced by intraperitoneal acetic acid in mice (writhing test) and the functional interaction was analyzed using the isobolographic method. EA at doses 0.3, 1, 3, and 10 mg/kg and carbamazepine at doses 3, 10, 20, and 30 mg/kg, alone and also in combination (1/2, 1/4, and 1/8 of the drug's ED50) were intraperitoneally administered 30 min before acetic acid (0.6% v/v). Then, the abdominal writhes were counted during a 25-min period.

RESULTS

EA (0.3-10 mg/kg, i.p.) and CBZ (3-30 mg/kg, i.p.) inhibited the writhing response evoked by acetic acid. Fifty percent effective dose (ED50) values against this tonic pain were 1.02 mg/kg and 6.40 mg/kg for EA and CBZ, respectively. The antinociception induced by EA showed higher potency than that of carbamazepine. Co-administration of increasing fractional increments of ED50 values of EA and CBZ produced additive interaction against writhing responses, as revealed by isobolographic analysis.

DISCUSSION AND CONCLUSION

These results suggest that a combination of carbamazepine and ellagic acid may be a new strategy for the management of neuropathic pain such as what occurs in trigeminal neuralgia, since the use of carbamazepine is often limited by its adverse effects and by reduction of its analgesic effect through microsomal enzyme induction.

Analgesic effect of Chinese herbal formula Hua-Jian-Ba-Du ointment on visceral pain in mice induced by acetic acid

INTRODUCTION

Visceral pain is one of the most important pains caused by cancer or other diseases, and most of the medications may lead to tolerance, addiction, and toxic side effects. Hua-Jian-Ba-Du Ointment (HJBDO), which is a commonly used conjugate based on traditional Chinese medicine theory, has been effective against visceral pain. Here, we verify the efficacy and underlying mechanism of HJBDO in an acetic-acid induced visceral pain model.

METHODS

Mice were subjected to acetic acid with or without HJBDO. Hua-Jian-Ba-Du Ointment at low (7.5 mL/kg•d), moderate (15 mL/kg•d), and high (30 mL/kg•d) dosages was applied on the abdomen, 3 times per day for 3 days. The acetic acid writhing test was used to evaluate antinociception. Interleukin-2 (IL-2) in serum, tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and prostaglandin E2 (PGE2) in peritoneal fluid were detected by ELISA. 5-hydroxytryptamine (5-HT), norepinephrine (NE), dopamine (DA), and β-endorphin (β-EP) were examined by high performance liquid chromatography and radioimmunoassay, respectively. N-methyl-D-aspartic acid receptor (NMDAR1) and c-fos expressions in both rostral ventromedial medulla (RVM) and spinal dorsal horn were determined by western blot.

RESULTS

Hua-Jian-Ba-Du Ointment at 3 dosage levels produced dose-dependent antinociception and shortened the latent time. Hua-Jian-Ba-Du Ointment at high or moderate dosage inhibited the release of TNF-α, IL-6, and PGE2, as well as increased the release of IL-2. Hua-Jian-Ba-Du Ointment could also increase NE and 5-HT contents and decrease the NE content. No effect of HJBDO at 3 dosages on the DA system was detected. Furthermore, HJBDO could suppress the expressions of NMDAR and c-fos in both RVM and spinal dorsal horn.

CONCLUSION

Our results exhibited the analgesic effect of HJBDO on visceral pain in mice, and this effect might be mediated by the regulation of inflammation and neurotransmitters.

Analgesic, anti-inflammatory, and chondroprotective activities of Cryptolepis buchanani extract: in vitro and in vivo studies

Cryptolepis buchanani Roem. & Schult. is widely used in folk medicine in Southeast Asia for treating muscle tension and arthritis. This study aimed to investigate an analgesic activity of the methanol extract of C. buchanani (CBE) in acetic acid-induced writhing response in mice, and to examine its anti-inflammatory activity in ethyl phenylpropiolate- (EPP-) induced ear edema and carrageenan-induced paw edema in rats. Its effects on cartilage degradation induced by interleukin-1β (IL-1β) in porcine cartilage explant culture were also determined. This study demonstrated that CBE significantly reduced acetic acid-induced writhing response. It also inhibited edema formation in both EPP-induced ear edema and carrageenan-induced paw edema models. In cartilage explant culture, CBE significantly reduced the sulfated glycosaminoglycan and hyaluronan released into culture media while it reserved the uronic acid and collagen within the cartilage tissues. It also suppressed the matrix metalloproteinase-2 activity with no effect on cell viability. In conclusion, CBE shows analgesic, anti-inflammatory, and chondroprotective effects in this preliminary study. Therefore, CBE may be useful as an alternative treatment for osteoarthritis.

Isobolographic analysis of the opioid-opioid interactions in a tonic and a phasic mouse model of induced nociceptive pain

Background

Opioids have been used for the management of pain and coadministration of two opioids may induce synergism. In a model of tonic pain, the acetic acid writhing test and in a phasic model, the hot plate, the antinociceptive interaction between fentanyl, methadone, morphine, and tramadol was evaluated.

Results

The potency of opioids in the writhing test compared to the hot plate assay was from 2.5 (fentanyl) to 15.5 (morphine) times, respectively. The ED₅₀ was used in a fixed ratio for each of the six pairs of opioid combinations, which, resulted in a synergistic antinociception except for methadone/tramadol and fentanyl/tramadol which were additive, in the hot plate. The opioid antagonists naltrexone, naltrindole and nor-binaltorphimine, suggests that the synergism of morphine combinations are due to the activation of MOR subtypes with partially contribution of DOR and KOR, however fentanyl and methadone combinations are partially due to the activation of MOR and DOR subtypes and KOR lack of participation. The antinociceptive effects of tramadol combinations, are partially due to the activation of MOR, DOR and KOR opioid subtypes.

Conclusion

These results suggets that effectiveness and magnitude of the interactions between opioids are dependent on pain stimulus intensity.

Antinociceptive, anti-inflammatory and antipyretic activities of the leaf methanol extract of Ruta graveolens L. (Rutaceae) in mice and rats

BACKGROUND

Ruta graveolens has been used to treat toothache, earache, rheumatism and fever with little scientific evidence corroborating these uses.

MATERIALS AND METHODS

The leaf methanol extract of Ruta graveolens was evaluated for antinociceptive activity using the acetic acid writhing and hot-plate tests in mice, also anti-inflammatory and antipyretic activities using the carrageenan-induced oedema and E. coli-induced pyrexia tests in rats, respectively.

RESULTS

R. graveolens (100 mg/kg, i.p.), significantly reduced the number of acetic acid-induced writhes by 54 %. R. graveolens (400 mg/kg, i.p.), significantly delayed the reaction time in mice to thermal stimulation 15, 30, 45, and 60 min after treatment. Combined treatment of the lowest and sub-effective doses of the leaf methanol extract (25 mg/kg, i.p.), and indomethacin (10 mg/kg, i.p.) significantly reduced the number of acetic acid-induced writhes in mice. The leaf methanol extract of R. graveolens (50 - 400 mg/kg, i.p.), significantly reduced carrageenan-induced oedema over the 4 h period of testing. Combined treatment of the lowest doses of R. graveolens (25 mg/kg, i.p.) and indomethacin (2 mg/kg, i.p.) produced a significant reduction in carrageenan-induced oedema over the 4 h period of testing. R. graveolens (100 -400 mg/kg, i.p.) significantly reduced E. coli-induced pyrexia over the 5 h period of testing. Given together, the lowest dose of R. graveolens (25 mg/kg, i.p.) and pentoxifylline (10 mg/kg, i.p.) produced a significant reduction in pyrexia induced by E. coli (50 µg/kg, i.m.) over the 5 h period of measurement. The LD50 value obtained for R. graveolens was greater than 4000mg/kg (p.o), suggesting that the plant species may be safe in or nontoxic to mice.

CONCLUSION

The data obtained indicate that R. graveolens has antinociceptive, anti-inflammatory and antipyretic activities, justifying the use of the plant species by traditional medicine practitioners in the management and treatment of pain, inflammation and fever.

Antinociceptive synergy between diclofenac and morphine after local injection into the inflamed site

BACKGROUND

Combinations of non-steroidal anti-inflammatory drugs with opioids are frequently used to reduce opioid doses required in the clinical management of acute pain. The present study was designed to evaluate the possible antinociceptive interaction between morphine and diclofenac at peripheral level in male rats.

METHODS

Drugs were chosen based on their efficacy in the treatment of this kind of pain and as representative drugs of their respective analgesic groups. For the formalin test, 50 μ of 1% formalin solution was injected subcutaneously into the right hind paw. The interaction between morphine and diclofenac was evaluated by using isobolographic analysis and interaction index. Drug interaction was examined by administering fixed-ratio combinations of morphine-diclofenac (1 : 1 and 3 : 1) of their respective ED30 fractions.

RESULTS

Diclofenac and morphine reduced flinching behavior in a dose-dependent manner during phase 2 but not phase 1 of the formalin test. Isobolographic analysis showed a synergistic interaction for the combination of morphine and diclofenac after local peripheral administration.

CONCLUSIONS

Data suggest that the combination of morphine with diclofenac at the site of injury is synergistic and could be useful in the treatment of wounds, bruises, rheumatisms and other painful peripheral conditions associated with an inflammatory process.

Mechanisms involved in the antinociceptive effects of orally administered oleanolic acid in the mouse

The antinociceptive effects of oleanolic acid were examined in ICR mice. Oleanolic acid administered orally (1, 5 and 10 mg/kg) showed an antinociceptive effect in a dose-dependent manner as measured in the acetic acid-induced writhing test. In the time- course study, duration of antinociceptive action of oleanolic acid maintained at least for 60 min. In addition, the cumulative nociceptive response time for intraplantar formalin injection (2nd phase), intrathecal injection of substance P (0.7 μg) or glutamate (20 μg) was diminished by oleanolic acid. Intraperitoneal (i.p.) pretreatment with naloxone (opioid receptor antagonist) or methysergide (5-HT serotonergic receptor antagonist) attenuated antinociceptive effect induced by oleanolic acid in the writhing test. However, yohimbine (adrenergic receptor antagonist) did not affect antinociception induced by oleanolic acid. The results indicate that oleanolic acid shows an antinociceptive property in various pain models such as writhing, formalin, substance P and glutamate pain tests. Furthermore, this antinociceptive effect of oleanolic acid may be mediated by opioidergic and serotonergic receptors, but not adrenergic receptors.

Relative potency of pregabalin, gabapentin, and morphine in a mouse model of visceral pain

PURPOSE

Pregabalin is probably more effective than prototype gabapentin in different kinds of pain treatments. This study was performed to compare the potency of gabapentin, pregabalin, and morphine in a well-established model of visceral pain.

METHODS

The number of abdominal contractions was counted for 30 min in adult male mice that received different doses of pregabalin, gabapentin, morphine, or placebo intraperitoneally 30 min before receiving 0.6% acetic acid 10 mL·kg(-1).The antinociceptive effect of each drug dose was determined as a percentage of the reduction in the number of acetic acid-induced writhes. The effective doses, for 20%, 50%, and 80% response (ED(20), ED(50), and ED(80), respectively), of each drug were calculated using least squares linear regression analysis, and then dose-response curves were compared.

RESULTS

Pregabalin, gabapentin, and morphine produced a linear dose-dependent antinociceptive effect (coefficient of determination [r(2)] > 0.9). No difference was observed between slopes of dose-response curves. The ED(50) estimates (95% confidence interval) for pregabalin, gabapentin, and morphine were 17.1 (12.9 to 22.1) mg·kg(-1), 87.1 (45.8 to 129.8) mg·kg(-1), and 0.2 (0.1 to 0.3) mg·kg(-1), respectively.

CONCLUSION

In this animal model of visceral pain, all three drugs exhibited parallel dose-response curves. Pregabalin had five times the potency of gabapentin and 1/85(th) the potency of morphine. Similar potency ratios may apply in clinical practice. Despite some limitations of animal studies, this model could be useful for comparing new analgesics in visceral pain treatment.

Antioxidant, antinociceptive, and anti-inflammatory effects of carotenoids extracted from dried pepper (Capsicum annuum L.)

Carotenoids extracted from dried peppers were evaluated for their antioxidant, analgesic, and anti-inflammatory activities. Peppers had a substantial carotenoid content: guajillo 3406 ± 4 μg/g, pasilla 2933 ± 1 μg/g, and ancho 1437 ± 6 μg/g of sample in dry weight basis. A complex mixture of carotenoids was discovered in each pepper extract. The TLC analysis revealed the presence of chlorophylls in the pigment extract from pasilla and ancho peppers. Guajillo pepper carotenoid extracts exhibited good antioxidant activity and had the best scavenging capacity for the DPPH(+) cation (24.2%). They also exhibited significant peripheral analgesic activity at 5, 20, and 80 mg/kg and induced central analgesia at 80 mg/kg. The results suggest that the carotenoids in dried guajillo peppers have significant analgesic and anti-inflammatory benefits and could be useful for pain and inflammation relief.

Hop extract produces antinociception by acting on opioid system in mice

In the present study, the antinociceptive profiles of hop extract were characterized in ICR mice. Hop extract administered orally (from 25 to 100 mg/kg) showed an antinociceptive effect in a dose-dependent manner as measured in the acetic acid-induced writhing test. Antinociceptive action of hop extract was maintained at least for 60 min. Moreover, cumulative response time of nociceptive behaviors induced with intraplantar formalin injection was reduced by hop extract treatment during the 2nd phases. Furthermore, the cumulative nociceptive response time for intrathecal injection of substance P (0.7 µg) or glutamate (20 µg) was diminished by hop extract. Intraperitoneal pretreatment with naloxone (an opioid receptor antagonist) attenuated antinociceptive effect induced by hop extract in the writhing test. However, methysergide (a 5-HT serotonergic receptor antagonist) or yohimbine (an α₂-adrenergic receptor antagonist) did not affect antinociception induced by hop extract in the writhing test. Our results suggest that hop extract shows an antinociceptive property in various pain models. Furthermore, the antinociceptive effect of hop extract may be mediated by opioidergic receptors, but not serotonergic and α₂-adrenergic receptors.

Phytochemical investigation and in vitro antinociceptive activity of Clerodendrum indicum leaves

The crude ethanolic extracts of Clerodendrum indicum Linn. leaves were investigated for possible antinociceptive activity using acetic acid induced writhing model in mice. Phytochemical analysis was also carried out according to the standard procedures to identify the presence of different phytoconstituents in the ethanolic extract of the plant leaves. The study results showed 38.91 and 55.24% inhibition of writhings in the tested mice when ethanolic extract of Clerodendrum indicum Linn. leaves at doses of 250 and 500 mg kg(-1) body weight was given intraperitoneally, respectively. The study results were also compared with antinociceptive activity of the standard drug, Diclofenac sodium (68.37% inhibition) used at 25 mg kg(-1) body weight. At the above doses, the crude ethanolic extract of the plant showed significant antinociceptive activity in dose dependent fashion in acetic acid-induced writhing model in mice. The inhibition of writhings was calculated in respective to control group and it was found that p-values (<0.0001) obtained in all cases were extremely statistically significant. However, the phytochemical analysis showed the presence of alkaloid, steroid, saponin, tannin, reducing sugar and gum. The results suggest that crude ethanolic extracts of Clerodendrum indicum leaves possess significant antinociceptive properties justifying its folkloric use as analgesics and further research is necessary to isolate the principle phytochemical constituent(s) responsible for this activity.

Antinociceptive and Anti-Inflammatory Activities of Leaf Methanol Extract of Cotyledon orbiculata L. (Crassulaceae)

Leaf methanol extract of C. orbiculata L. was investigated for antinociceptive and anti-inflammatory activities using acetic acid writhing and hot-plate tests and carrageenan-induced oedema test in mice and rats, respectively. C. orbiculata (100–400 mg/kg, i.p.) significantly inhibited acetic acid-induced writhing and significantly delayed the reaction time of mice to the hot-plate-induced thermal stimulation. Paracetamol (300 mg/kg, i.p.) significantly inhibited the acetic acid-induced writhing in mice. Morphine (10 mg/kg, i.p.) significantly delayed the reaction time of mice to the thermal stimulation produced with hot plate. Leaf methanol extract of C. orbiculata (50–400 mg/kg, i.p.) significantly attenuated the carrageenan-induced rat paw oedema. Indomethacin (10 mg/kg, p.o.) also significantly attenuated the carrageenan-induced rat paw oedema. The LD₅₀ value obtained for the plant species was greater than 4000 mg/kg (p.o.). The data obtained indicate that C. orbiculata has antinociceptive and anti-inflammatory activities, justifying the folklore use of the plant species by traditional medicine practitioners in the treatment of painful and inflammatory conditions. The relatively high LD₅₀ obtained shows that C. orbiculata may be safe in or nontoxic to mice.

The analgesic effects and mechanisms of orally administered eugenol

In the present study, the antinociceptive profiles of eugenol were examined in ICR mice. Eugenol administered orally (from 1 to 10 mg/kg) showed an antinociceptive effect in a dose-dependent manner as measured in the acetic acid-induced writhing test. Duration of antinociceptive action of eugenol maintained at least for 30 min. Moreover, the cumulative response time of nociceptive behaviors induced by an intraplantar formalin injection was reduced by eugenol treatment during the 2(nd) phases. Furthermore, the cumulative nociceptive response time for intrathecal injection of substance P (0.7 μg) or glutamate (20 μg) was diminished by eugenol. Intraperitoneal pretreatment with yohimbine (α2-adrenergic receptor antagonist) or naloxone (opioid receptor antagonist) attenuated antinociceptive effect induced by eugenol in the writhing test. However, methysergide (5-HT serotonergic receptor antagonist) did not affect antinociception induced by eugenol in the writhing test. Our results suggest that eugenol shows an antinociceptive property in various pain models. Furthermore, this antinociceptive effect of eugenol may be mediated by α2-adrenergic and opioidergic receptors, but not serotonergic receptor.

Antihypernociceptive synergy between ibuprofen, paracetamol and codeine in rats

We investigated the effects of intraperitoneal injections of a combination of two cyclo-oxygenase inhibitors, ibuprofen and paracetamol, with a weak opiate, codeine, on nociception in Sprague Dawley rats. Administration of paracetamol (11, 44, and 88 mg/kg), ibuprofen (8.75, 35, and 140 mg/kg) or codeine (0.44, 1.75, and 3.5mg/kg) alone caused a dose-dependent inhibition of reperfusion hypernociception. Administration of a combination of 0.44 mg/kg codeine+8.75 mg/kg ibuprofen+11 mg/kg paracetamol, drug doses that did not significantly reduce reperfusion hypernociception when administered individually or in pairs, abolished reperfusion hypernociception, such that the antihypernociceptive efficacy of the combination was approximately 2.5-fold greater than that of the sum of the antihypernociceptive efficacy of the individual drugs. Coordinated motor function, tested using a rotarod, was not impaired at the doses we used. Thus, we have demonstrated that codeine, paracetamol and ibuprofen act synergistically to induce antihypernociception in rats at doses which do not affect motor function.

Antinociceptive profiles and mechanisms of orally administered vanillin in the mice

In the present study, the antinociceptive profiles of vanillin were examined in ICR mice. Vanillin administered orally (from 1 to 10 mg/kg) showed an antinociceptive effect in a dose-dependent manner as measured in the acetic acid-induced writhing test. Duration of antinociceptive action of vanillin maintained at least for 30 min. But, the cumulative response time of nociceptive behaviors induced by a subcutaneous (s.c.) formalin injection, intrathecal (i.t.) substance P (0.7 microg) or glutamate (20 microg) injection was not affected by vanillin. Intraperitoneal (i.p.) pretreatment with yohimbine (alpha2-adrenergic receptor antagonist) or naloxone (opioid receptor antagonist) attenuated antinociceptive effect induced by vanillin in the writhing test. However, phentolamine (alpha1-adrenergic receptor antagonist) or methysergide (5-HT serotonergic receptor antagonist) did not affect antinociception induced by vanillin in the writhing test. Our results suggest that vanillin exerts a selective antinociceptive property in the acetic acid-induced visceral inflammatory pain model. Furthermore, this antinociceptive effect of vanillin may be mediated by alpha2-adrenergic and opioid receptors, but not alpha1-adrenergic and serotonergic receptors.

Synergistic interactions between paracetamol and oxcarbazepine in somatic and visceral pain models in rodents

BACKGROUND

Combination therapy is a valid approach in pain treatment, in which a reduction of doses could reduce side effects and still achieve optimal analgesia. We examined the effects of coadministered paracetamol, a widely used non-opioid analgesic, and oxcarbazepine, a relatively novel anticonvulsant with analgesic properties, in a rat model of paw inflammatory hyperalgesia and in a mice model of visceral pain and determined the type of interaction between components.

METHODS

The effects of paracetamol, oxcarbazepine, and their combinations were examined in carrageenan-induced (0.1 mL, 1%) paw inflammatory hyperalgesia in rats and in an acetic acid-induced (10 mg/kg, 0.75%) writhing test in mice. In both models, drugs were coadministered in fixed-dose fractions of the 50% effective dose (ED(50)), and type of interaction was determined by isobolographic analysis.

RESULTS

Paracetamol (50-200 mg/kg peroral), oxcarbazepine (40-160 mg/kg peroral), and their combination (1/8, 1/4, 1/3, and 1/2 of a single drug ED(50)) produced a significant, dose-dependent antihyperalgesia in carrageenan-injected rats. In the writhing test in mice, paracetamol (60-180 mg/kg peroral), oxcarbazepine (20-80 mg/kg peroral), and their combination (1/16, 1/8, 1/4, and 1/2 of a single drug ED(50)) significantly and dose dependently reduced the number of writhes. In both models, isobolographic analysis revealed a significant synergistic interaction between paracetamol and oxcarbazepine, with a >4-fold reduction of doses of both drugs in combination, compared with single drugs ED(50).

CONCLUSIONS

The synergistic interaction between paracetamol and oxcarbazepine provides new information about combination pain treatment and should be explored further in patients, especially with somatic and/or visceral pain.

Synthesis and investigations of double-pharmacophore ligands for treatment of chronic and neuropathic pain

Acids 9a-f as possible bivalent ligands designed as a structural combination of opioid mu-agonist (Fentanyl) and NSAID (Indomethacin) activities and produced compounds which were tested as analgesics. The obtained series of compounds exhibits low affinity and activity both at opioid receptors and as cyclooxygenase (COX) inhibitors. One explanation of the weak opioid activity could be stereochemical peculiarities of these bivalent compounds which differ significantly from the fentanyl skeleton. The absence of significant COX inhibitory properties could be explained by the required substitution of an acyl fragment in the indomethacin structure for 4-piperidyl.