The Additive Antinociceptive Effect of Resveratrol and Ketorolac in the Formalin Test in Mice.

Pain represents one of the leading causes of suffering and disability worldwide. Currently available drugs cannot treat all types of pain and may have adverse effects. Hence, the use of pharmacological combinations is an alternative treatment strategy. Therefore, this study aimed to evaluate the combination of resveratrol and ketorolac through isobolographic analysis. CD1 mice were used to study the antinociceptive effect of this combination using the formalin test and the study was divided into two phases. In the first phase, four individual doses of each drug were evaluated, totaling eight testing groups. From these data, the median effective doses (ED50) of each drug were calculated. In the second phase, four testing groups were used to evaluate the combination of sub-doses of both drugs and obtain the experimental ED50. To evaluate gastric damage, five groups were employed, including indomethacin, vehicle, resveratrol, ketorolac, and combined resveratrol and ketorolac groups. Stomach samples from the mice were taken after 5 h of treatment, and the area of the ulcers was determined. Resveratrol plus ketorolac elicited a reduction in nociceptive behavior during both phases of the formalin test, and isobologram analysis revealed that the theoretical and experimental ED50 values of resveratrol and ketorolac did not differ significantly, implying an additive interaction between the drugs. Additionally, the drug combination did not generate gastric ulcers, thus enhancing the desired effects without increasing the adverse effects. Consequently, these findings substantiate the efficacy of the resveratrol and ketorolac combination in the formalin test, thereby highlighting its potential as a viable alternative for alleviating pain.

Optogenetic and Chemogenic Control of Pain Signaling: Molecular Markers.

Pain is a complex experience that involves physical, emotional, and cognitive aspects. This review focuses specifically on the physiological processes underlying pain perception, with a particular emphasis on the various types of sensory neurons involved in transmitting pain signals to the central nervous system. Recent advances in techniques like optogenetics and chemogenetics have allowed researchers to selectively activate or inactivate specific neuronal circuits, offering a promising avenue for developing more effective pain management strategies. The article delves into the molecular targets of different types of sensory fibers such as channels, for example, TRPV1 in C-peptidergic fiber, TRPA1 in C-non-peptidergic receptors expressed differentially as MOR and DOR, and transcription factors, and their colocalization with the vesicular transporter of glutamate, which enable researchers to identify specific subtypes of neurons within the pain pathway and allows for selective transfection and expression of opsins to modulate their activity.

N-palmitoylethanolamide synergizes the antinociception of morphine and gabapentin in the formalin test in mice.

OBJECTIVE: The antinociceptive pharmacological interaction between N-palmitoylethanolamide (PEA) and morphine (MOR), as well as gabapentin (GBP), was investigated to obtain synergistic antinociception at doses where side effects were minimal. In addition, the possible antinociceptive mechanism of PEA + MOR or PEA + GBP combinations was explored. METHODS: Individual dose-response curves (DRCs) of PEA, MOR and GBP were evaluated in female mice in which intraplantar nociception was induced with 2% formalin. Isobolographic method was used to detect the pharmacological interaction in the combination of PEA + MOR or PEA + GBP. KEY FINDINGS: The ED50 was calculated from the DRC; the order of potency was MOR > PEA > GBP. The isobolographic analysis was obtained at a 1:1 ratio to determine the pharmacological interaction. The experimental values of flinching (PEA + MOR, Zexp = 2.72 ± 0.2 µg/paw and PEA + GBP Zexp = 2.77 ± 0.19 µg/paw) were significantly lower than those calculated theoretically (PEA + MOR Zadd = 7.78 ± 1.07 and PEA + GBP Zadd = 24.05 ± 1.91 µg/paw), resulting in synergistic antinociception. Pretreatment with GW6471 and naloxone demonstrated that peroxisome proliferator-activated receptor alpha (PPARα) and opioid receptors are involved in both interactions. CONCLUSIONS: These results suggest that MOR and GBP synergistically enhance PEA-induced antinociception through PPARα and opioid receptor mechanisms. Furthermore, the results suggest that combinations containing PEA with MOR or GBP could be of interest in aiding the treatment of inflammatory pain.

In Vivo and In Silico Study of the Antinociceptive and Toxicological Effect of the Extracts of Petiveria alliacea L. Leaves.

Petiveria alliacea L. is an herb used in traditional medicine in Mexico and its roots have been studied to treat pain. However, until now, the antinociceptive properties of the leaves have not been investigated, being the main section used empirically for the treatment of diseases. For this reason, this study aimed to evaluate the antinociceptive and toxoicological activity of various extracts (aqueous, hexanic, and methanolic) from P. alliacea L. leaves in NIH mice and to perform an in silico analysis of the phytochemical compounds. Firstly, the antinociceptive effect was analyzed using the formalin model and the different doses of each of the extracts that were administered orally to obtain the dose-response curves. In addition, acute toxicity was determined by the up and down method and serum biochemical analysis. Later, the phytochemical study of extracts was carried out by thin layer chromatography (TLC) and visible light spectroscopy, and the volatile chemical components were analyzed by gas chromatography-mass spectrometry (GC/MS). Moreover, the most abundant compounds identified in the phytochemical study were analyzed in silico to predict their biological activity (PASSonline) and toxicology (OSIRIS Property Explorer). As a result, it was known that all extracts at doses from 10 to 316 mg/kg significantly reduced the pain response in both phases of the formalin model, with values of 50-60% for the inflammatory response. The toxicological studies (DL50) exhibited that all extracts did not cause any mortality up to the 2000 mg/kg dose level. This was corroborated by the values in the normal range of the biochemical parameters in the serum. Finally, the phytochemical screening of the presence of phenolic structures (coumarins, flavonoids) and terpenes (saponins and terpenes) was verified, and the highest content was of a lipid nature, 1.65 ± 0.54 meq diosgenin/mL in the methanolic extract. A total of 54 components were identified, 11 were the most abundant, and only four (Eicosane, Methyl oleate, 4-bis(1-phenylethyl) phenol, and Ethyl linolenate) of them showed a probability towards active antinociceptive activity in silico greater than 0.5. These results showed that the P. alliacea L. leaf extract possesses molecules with antinociceptive activity.

Differential Antinociceptive Efficacy of Peel Extracts and Lyophilized Juices of Three Varieties of Mexican Pomegranate (Punica granatum L.) in the Formalin Test.

Pharmacological treatment of pain often causes undesirable effects, so it is necessary to look for natural, safe, and effective alternatives to alleviate painful behavior. In this context, it is known that different parts of pomegranate have been widely consumed and used as preventive and therapeutic agents since ancient times. For example, it has been shown to have an antinociceptive effect, however, there are many varieties. Each part has been found to display unique and attractive pharmacological activities. The content of the active phytochemicals in pomegranate depends on the cultivar, geographical region, the maturity, and the processing method. In this context, the effects of various pomegranate varieties and other parts of the pomegranate (e.g., peel and juice) on pain behavior have not been examined. The aim was to evaluate and compare the antinociceptive effect of ethanolic extracts (PEx) and lyophilized juices (Lj) of three varieties of pomegranate in the formalin test. In addition, computer-aided analysis was performed for determining biological effects and toxicity. Peels were extracted with ethanol and evaporated by rotary evaporation, and juices were filtered and lyophilized. Wistar rats (N = 48) were randomly distributed into 8 groups (n = 6) (Vehicle, Acetylsalicylic Acid, PEx1, PEx2, PEx3, Lj1, Lj2, and Lj3). The formalin test (2%) was carried out, which consists of administering formalin in paw and counting the paw flinches for 1 h, with prior administration of treatments. All samples have an antinociceptive effect (phase 1: 2.8-10%; phase 2: 23.2-45.2%). PEx2 and Lj2 had the greatest antinociceptive effect (57.8-58.9%), and bioactive compounds such as tannins and flavonoids showed promising pharmacodynamic properties that may be involved in the antinociceptive effect, and can be considered as a natural alternative for the treatment of nociceptive and inflammatory pain.

Sigma-1 receptor antagonist (BD-1063) potentiates the antinociceptive effect of quercetin in neuropathic pain induced by chronic constriction injury.

Neuropathic pain is characterized by the presence of hyperalgesia and allodynia. Pharmacological treatments include the use of antiepileptics such as pregabalin or gabapentin, as well as antidepressants; however, given the role of the sigma-1 receptor in the generation and maintenance of pain, it has been suggested that sigma-1 receptor antagonists may be effective. There are also other alternatives that have been explored, such as the use of flavonoids such as quercetin. Due to the relevance of drug combinations in therapeutics, the objective of this work was to evaluate the effect of the combination of BD-1063 with quercetin in a chronic sciatic nerve constriction model using the "Surface of Synergistic Interaction" analysis method. The combination had preferable additive or synergistic effects, with BD-1063 (17.8 mg/kg) + QUER (5.6 mg/kg) showing the best antinociceptive effects. The required doses were also lower than those used individually to obtain the same level of effect. Our results provide the first evidence that the combination of a sigma-1 receptor antagonist and the flavonoid quercetin may be useful in the treatment of nociceptive behaviors associated with neuropathic pain, suggesting a new therapeutic alternative for this type of pain.

Haloperidol potentiates antinociceptive effects of morphine and disrupt opioid tolerance.

Haloperidol is an antipsychotic agent recently described as an antinociceptive drug able to mediate the antagonism of sigma-1 receptors while morphine is an opioid used in the treatment of neuropathic pain. The objectives of this work were to determine the type of interaction generated by the combination of morphine and haloperidol in neuropathic pain induced by chronic constriction injury and to evaluate morphine tolerance and side effects. The antiallodynic and anti-hyperalgesic effects of morphine (0.01-3.16 mg/kg, s.c.) and haloperidol (0.0178-0.1778 mg/kg, s.c.) were determined after single-doses, in monotherapy and combined, using the acetone and von Frey tests, respectively. Evaluations were performed until 10-days postsurgery. Data were processed using "Surface of Synergic Interaction analysis". The rotarod test was used to evaluate motor coordination, and the constipation test was performed using 5% charcoal. The effects of haloperidol and BD-1063, sigma-1 receptor antagonists, naloxone and PRE-084 (sigma-1 agonist) were determined using the morphine-tolerance model. Morphine (0.0316 mg/kg)+haloperidol (0.0178 mg/kg) was determined to be the optimal combination. Morphine-tolerance was observed on day 5 after 11 administrations, although in animals that received the combination, tolerance was delayed until day 8. PRE-084 and naloxone administered on day 5 in animals treated with the combination resulted in a blockade of its antiallodynic effects. Adverse effects of constipation or motor incoordination were not shown in animals treated with morphine + haloperidol. In conclusion, haloperidol enhances the antinociceptive effects of morphine without significant adverse effects, as it is able to disrupt or delay the morphine-tolerance in neuropathic pain.

Synergistic interaction between haloperidol and gabapentin in a model of neuropathic nociception in rat.

Preclinical studies have reported that sigma-1 receptor antagonists may have efficacy in neuropathic pain states. The sigma-1 receptor is a unique ligand-operated chaperone present in crucial areas for pain control, in both the peripheral and central nervous system. This study assesses the synergistic antihyperalgesic and antiallodynic effect of haloperidol, a sigma-1 antagonist, combined with gabapentin in rats with peripheral neuropathy. Wistar rats male were subjected to chronic constriction injury (CCI) of the sciatic nerve. The effects of systemic administration of gabapentin and the sigma-1 receptor antagonist, haloperidol, were examined at 11 days post-CCI surgery. An analysis of Surface of Synergistic Interaction was used to determine whether the combination's effects were synergistic. Twelve combinations showed various degrees of interaction in the antihyperalgesic and antiallodynic effects. In hyperalgesia, three combinations showed additive effects, four combinations showed supra-additive effects, and three combinations produced an effect limited by the maximum effect. In allodynia, five combinations showed additive effects, two combinations showed supra-additive effects, and five combinations produced antihyperalgesic effects limited by the maximum effect. These findings indicate that the administration of some specific combination of gabapentin and haloperidol can synergistically reduce nerve injury-induced allodynia and hyperalgesia. This suggests that the haloperidol-gabapentin combination can improve the antiallodynic and antihyperalgesic effects in a neuropathic pain model.

Haloperidol Decreases Hyperalgesia and Allodynia Induced by Chronic Constriction Injury.

Neuropathic pain has proven to be a difficult condition to treat, so investigational therapy has been sought that may prove useful, such as the use of sigma-1 antagonists. Haloperidol (HAL) is a compound that shows a high affinity with these receptors, acting as an antagonist. Therefore, the objective of this study was to demonstrate its effect in an experimental model of neuropathic pain and corroborate its antagonistic action of the sigma-1 receptors under these conditions. BD-1063 was used as a sigma-1 antagonist control, and gabapentin (Gbp) was used as a positive control. The antihyperalgesic and anti-allodynic effects of the drugs were determined after single-dose trials. In every case, the effects increased in a dose-dependent manner. HAL had the same efficacy as both BD-1063 and Gbp. In the analysis of pharmacological potency, in which the ED50 were compared, HAL was the most potent drug of all. The effect of HAL on chronic constriction injury (CCI) rats was reversed by the sigma-1 agonist (PRE-084). HAL reversed the hyperalgesic and allodynic effects of PRE-084 in naïve rats. The dopamine antagonist, (-)-sulpiride, showed no effect in CCl rats. These results suggest that HAL presents an antinociceptive effect via sigma-1 receptor antagonism at the spinal level in the CCl model.

N-(2-morpholin-4-yl-ethyl)-2-(1naphthyloxy)acetamide inhibits the chronic constriction injury-generated hyperalgesia via the antagonism of sigma-1 receptors.

The most used therapeutic treatment to relieve neuropathic pain is that of neuromodulators such as anti-epileptics or anti-depressants; however, there are alternatives that may be potentially useful. The sigma-1 receptor is a therapeutic target that has shown favorable results at preclinical levels. The aim of this study was to evaluate the anti-hyperalgesic effect of N-(2-morpholin-4-yl-ethyl)-2-(1-naphthyloxy) acetamide (NMIN) in a chronic constriction injury model (CCI) and compare it both a sigma-1 antagonist (BD-1063) and also Gabapentin, as well as determine its possible role as an antagonist of sigma-1 receptors. The anti-hyperalgesic effects of Gabapentin (10.0, 17.8, 31.6, 56.2 and 100mg/kg, s.c.), BD-1063 (5.6, 10.0, 17.8, 31.6 and 56.2mg/kg, s.c.) and NMIN (31.6, 10.0, 316mg/kg and 562mg/kg, s.c.) were determined after single-doses, using the von Frey test in the CCI model. NMIN had the same efficacy as BD-1063, but both show less efficacy than Gabapentin. In an analysis of pharmacological potency, the ED50 were compared with it being found that BD-1063 is the most potent drug, followed by Gabapentin and NMIN. The anti-hyperalgesic effect of NMIN on CCI rats was reversed by (+)-pentazocine (s.c. route) and by PRE-084 (i.t. route), both sigma-1 agonists. Furthermore, NMIN reversed the hyperalgesic effect of PRE-084 in naïve rats. These results suggest that NMIN has an anti-hyperalgesic effect on the CCI model, and that one of its mechanisms of action is as a sigma-1 antagonist, being a significant role the blocking of these receptors at the spinal level.

Nociceptive Alteration by High Sucrose Diet in Hypoestrogenic Wistar Rats.

Preclinical Research Obesity is a risk factor associated with alterations in pain perception. The aim of this study was to analyse a time-course of nociceptive responses (plantar test) in hypoestrogenic rats after the induction of obesity. Animals (hypoestrogenic and naïve) received either a hypercaloric or regular diet for 24 weeks. Thermal nociception and body weight were measured during this period. At the 4th and 17th weeks after treatment, oral glucose tolerance, blood insulin levels, abdominal fat weight, and uric acid levels were measured. The hypoestrogenic rats on a high sucrose diet had higher body weight and abdominal fat weight than control rats. A biphasic response was observed in the ovariectomized group fed with sucrose with thermal latency being decreased in the fourth week. During weeks 12-18, thermal latency increased compared to that of the hypoestrogenic control. There were no differences in basal blood glucose levels at the 4th and 17th weeks; however, oral glucose tolerance, insulin, and uric acid levels were altered. This indicated that increased body weight and fat as well as alteration sin glucose tolerance, hyperinsulinemia and hyperuricemia, may be associated with the biphasic nociceptive response. Drug Dev Res 77 : 258-266, 2016. © 2016 Wiley Periodicals, Inc.

Ketoprofen and antinociception in hypo-oestrogenic Wistar rats fed on a high sucrose diet.

Non-steroidal anti-inflammatory drugs such as ketoprofen are the most commonly used analgesics for the treatment of pain. However, no studies have evaluated the analgesic response to ketoprofen in conditions of obesity. The aim of this study was to analyse the time course of nociceptive pain in Wistar rats with and without hypo-oestrogenism on a high sucrose diet and to compare the antinociceptive response using ketoprofen. Hypo-oestrogenic and naïve rats received a hyper caloric diet (30% sucrose) or water ad libitum for 17 weeks, the thermal nociception ("plantar test" method) and body weight were tested during this period. A biphasic response was observed: thermal latency decreased in the 4th week (hyperalgesia), while from 12th to 17th week, thermal latency increased (hypoalgesia) in hypo-oestrogenic rats fed with high sucrose diet compared with the hypo-oestrogenic control group. At 4th and 17th weeks, different doses of ketoprofen (1.8-100mg/kg p.o.), were evaluated in all groups. The administration of ketoprofen at 4th and 17th weeks showed dose-dependent effects in the all groups; however, a greater pharmacological efficacy was observed in the 4th week in the hypo-oestrogenic animals that received sucrose. Nevertheless, in all the groups significantly diminish the antinociceptive effects in the 17th week. Our data showed that nociception was altered in the hypo-oestrogenic animals that were fed sucrose (hyperalgesia and hypoalgesia). Ketoprofen showed a dose-dependent antinociceptive effect at both time points. However, hypo-oestrogenism plus high-sucrose diet modifies the antinociceptive effect of ketoprofen.

Antinociceptive Effect of Racemic Flurbiprofen and Caffeine Co-Administration in an Arthritic Gout-Type Pain in Rats.

Preclinical Research Drug combinations are routinely used in the treatment of pain. In drug associations, adjuvants such as caffeine, are employed with different non-steroidal anti-inflammatories drugs (NSAIDs), however, at present does not exist studies showing the effect of the combination of racemic flurbiprofen (rac-Flur) in association with caffeine. The objective of this work was to evaluate the combination of rac-Flur + caffeine oral in arthritic gout-type pain in rats. The antinociceptive effects of the rac-Flur alone and in combination with caffeine were analyzed on a pain-induced functional impairment model in rat. rac-Flur induced a dose-dependent antinociceptive effect and caffeine did not present any effect. The combination of rac-Flur and caffeine achieve a higher percentage of antinociceptive effect compared with the individual administration of rac-Flur. The dose-response curve (DRCs) shows that the combination of rac-Flur (31.6 mg/kg) + caffeine (17.8 mg/kg) exhibited the maximal antinociceptive efficacy (294.0 ± 21.2 area units), while rac-Flur alone (31.6 mg/kg) showed 207.2 ± 35.2 au, thus indicating an increase in efficacy (potentiation). Furthermore, the DRCs of the combinations presented a displacement to the left, indicating a change in the potency. Caffeine is able to increase the effect of rac-Flur in the arthritic gout-type pain in rats. Drug Dev Res 77 : 192-198, 2016. © 2016 Wiley Periodicals, Inc.

The Antinociceptive Effects of Tramadol and/or Gabapentin on Rat Neuropathic Pain Induced by a Chronic Constriction Injury.

Preclinical Research The current work evaluates the interaction between two commonly used drugs, tramadol (Tra) and gabapentin (Gbp). Dose-response curves (DRC) and isobolographic analysis were used to confirm their synergistic antihyperalgesic and anti-allodynic responses in a rat neuropathic pain model involving chronic constriction injury of the sciatic nerve and in von Frey and acetone tests. Tra and Gbp produced dose-dependent antihyperalgesic and anti-allodynic effects. Dose-response studies of combinations of Tra and Gbp in combination showed the DRC was leftward-shifted compared to the DRCs for each compound alone. One combination demonstrated both antihyperalgesic and anti-allodynic effects greater than those observed after individual administration. The remaining combinations demonstrated an additive effect. The Tra+Gbp combination demonstrated a potentiative effect with smaller doses of Tra. Additionally, it was determined lethal dose 50 (LD50 ) of Tra alone and tramadol + Gbp 10 using mice to 48 h post administration. The DRC (death) were similar for Tra alone and in Tra in combination, despite the improved effectiveness of Tra in the presence of GBP, 10 mg/kg. A combination of these drugs could be effective in neuropathic pain therapy because they can produce potentiative (at a low dose) or additive effects. Drug Dev Res 77 : 217-226, 2016. © 2016 Wiley Periodicals, Inc.

Antinociceptive Interactions Between Meloxicam and Gabapentin in Neuropathic Pain Depend on the Ratio used in Combination in Rats.

Preclinical Research Neuropathic pain is particularly difficult to treat because of its diverse etiologies and underlying pathophysiological mechanisms. Drug combinations have been proposed to effectively treat some neuropathies. In the present study the interaction of five combinations of meloxicam and gabapentin, were studied to assess the possible synergistic antinociceptive response in neuropathic pain using the von Frey and acetone tests in rat models. Coadministration of meloxicam and gabapentin increased the antihyperalgesic or antiallodynic effects as compared with the compounds administered alone. The area under the curve (AUC) of the antihyperalgesic effects produced by the combination of the two drugs was generally similar to the theoretical sum of effects produced by each drug alone. However, the AUC of the antiallodynic effect produced by one combination (meloxicam 1.0 mg/kg + gabapentin 10 mg/kg) was greater than the theoretical sum of the effects produced by each drug alone. The type of final interaction on the drug combinations can be additive or cause potentiation of antinociceptive effects and depends on the proportion of each compound used in dosing. Drug Dev Res 77 : 134-142, 2016. © 2016 Wiley Periodicals, Inc.

Antinociceptive effects of a new sigma-1 receptor antagonist (N-(2-morpholin-4-yl-ethyl)-2-(1-naphthyloxy)acetamide) in two types of nociception.

Pain has become an active clinical challenge due its etiological heterogeneity, symptoms and mechanisms of action. In the search for new pharmacological therapeutic alternatives, sigma receptors have been proposed as drug targets. This family consists of sigma-1 and sigma-2 receptors. The sigma-1 system is involved in nociception through its chaperone activity. Additionally, it has been shown that agonist to these receptors promote related sensitisation and pain hypersensitisation, suggesting the possible use of antagonists for sigma-1 receptors as an alternative therapy. The aim of this study was to evaluate the antinociceptive effect of a new sigma-1 receptor antagonist N-(2-morpholin-4-yl-ethyl)-2-(1-naphthyloxy)acetamida (NMIN) in two types of pain (arthritic and neuropathic) and to compare its efficacy and potency with reference drugs. The antinociceptive effects of NMIN were quantitatively evaluated using the pain-induced functional impairment model in the rat and the acetone test in a rat model of neuropathic pain. NMIN (sigma-1 receptor affinity of 324nM) did not show any antinociceptive activity in the arthritic pain model but showed a dose-dependent anti-allodynic effect in neuropathic pain. NMIN showed a similar efficacy compared to the effects obtained with morphine and the sigma-1 antagonist BD-1063. However, these reference drugs showed increased potency compared with NMIN. Our results suggest that sigma-1 receptors may play an important direct role in neuropathic pain but not in arthritic pain, supporting the hypothesis that NMIN may be useful for the treatment of neuropathic pain.