Central release of nitric oxide mediates antinociception induced by aerobic exercise

Evaluation of the systemic and spinal antinociceptive effect of a new hybrid NSAID tetrahydropyran derivative

Pain is responsible for inducing physical and mental stress, interfering negatively in patients' quality of life. Classic analgesic drugs, such as opioids and non-steroidal anti-inflammatory drugs, are known for their wide range of adverse effects, making it important to develop new drugs. Thus, this study aimed to analyse the action of the hybrid compound cis- (±) -acetate of 4-chloro-6- (naphthalene-1-yl) -tetrahydro-2h-pyran -2-yl) methyl2- (2- [2,6-dichlorophenylamine] phenyl (LS19) under acute nociceptive conditions, and deepened the understanding of the responsible mechanisms. Male Swiss mice were evaluated in the acetic acid-induced abdominal writhing, formalin, tail flick, capsaicin- and glutamate-induced nociception, thermal stimulation in animals injected with capsaicin and rotarod tests besides the acute and subchronic toxicological evaluation. The compound showed effect on the acetic acid-induced abdominal writhing, formalin (both phases), tail flick, thermal stimulation in animals injected with capsaicin and capsaicin-induced nociception tests. In the study of the mechanism of action was observed reversion of the antihyperalgesic effect of the compound from the previous intraperitoneal and intrathecal administration of naloxone, nor-binaltorphimine, naltrindole, methylnaltrexone, 7-nitroindazole, L-NAME, ODQ, glibenclamide on the tail flick test. In the thermal stimulation in animals injected with capsaicin, the compound showed antinociceptive effect by oral and intraplantar routes, besides to reducing the levels of TNF-α, IL-1β and PGE2 in the paws previously administered with capsaicin. There were no signs of acute and subchronic intoxication with the compound. In summary, the compound LS19 presented spinal and local antihyperalgesic effect, demonstrating participation of the opioid/NO/cGMP/K+ ATP pathway and TRPV1 receptors and it demonstrated safety in its use in mice.

Analgesic Effect of Ziziphus abyssinica Involves Inhibition of Inflammatory Mediators and Modulation of KATP Channels, Opioidergic and Nitrergic Pathways

The diversity offered by natural products has timelessly positioned them as a good source for novel therapeutics for the management of diverse medical conditions, including pain. This study evaluated hydro-ethanolic root bark extract of Ziziphus abyssinica (ZAE) as well as β-amyrin and polpunonic acid isolated from the plant for analgesic property. The study also investigated the mechanism responsible for this action in the extract. The antinociceptive potential of ZAE (30, 100, and 300 mg/kg, p. o.) was assessed using the tail-immersion test (TIT), acetic acid-induced writhing test (AAT), and formalin test (FT). The extract’s effect on acute and chronic musculoskeletal pain was also assessed by administering carrageenan unilaterally into the rat gastrocnemius muscles and measuring pain at 12 h and 10 days for acute and chronic pain respectively. The involvement of pro-inflammatory mediators (prostaglandin E₂, bradykinin, TNF-α, and IL-1β) was assessed. The possible pathways mediating the observed analgesic effect of ZAE were further assessed using the antagonists: naloxone, glibenclamide, N^G-L-nitro-arginine methyl ester (L-NAME), atropine, nifedipine, and yohimbine in the FT. Also the analgesic effect of two triterpenoid compounds, β-amyrin and polpunonic acid, previously isolated from the plant was assessed using the TIT. The anti-nociceptive activity of ZAE was demonstrated in the TIT by the significant (p < 0.05) increase in tail withdrawal threshold in ZAE-treated mice. ZAE also markedly reduced writhing and paw licking responses in both AAT and FT and significantly (p < 0.05) attenuated both acute and chronic musculoskeletal pain. ZAE also significantly reversed hyperalgesia induced by intraplantar injection of PGE₂, bradykinin, TNF-α, and IL-1β. Furthermore, data revealed the involvement of opioidergic, ATP-sensitive K⁺ channels and NO-cGMP pathways in the analgesic effect of ZAE. Both β-amyrin and polpunonic acid exhibited analgesic activity in the tail suspension test. Our study demonstrates ZAE as an important source of new therapeutic agents for pain management.

Pharmacological evaluation underlying the antinociceptive activity of two new hybrids NSAIDs tetrahydropyran derivatives

The development of analgesic drugs is still a necessity due to the inefficiency of the current treatments for some pathological conditions and also due to the adverse effects produced by these drugs. The aim of this study was to deepen the pharmacological study of two new hybrids NSAIDs tetrahydropyran derivatives, regarding their antinociceptive effects on acute pain in mice. Male swiss mice were evaluated in the acetic acid-induced abdominal writhing, formalin, tail-flick, open-field, glutamate- and capsaicin-induced paw licking tests, and in vitro Cox inhibition assay, besides the acute toxicological evaluation. The compounds had an effect on the acetic acid-induced abdominal writhing, formalin (both phases), and tail-flick tests. In the study of the mechanism of action was observed reversion of the antinociceptive effect of the compounds from the previous administration of naloxone, L-NAME (L-nitro-arginine methyl ester), ODQ (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one), glibenclamide, and nor-binaltorphimine, by the intrathecal and intraperitoneal routes. The prior administration of MK-801 suggests that the modulation of NMDA receptor contributes to the antinociceptive effect of compounds. In summary, hybrid compounds presented central antinociceptive effect, demonstrating participation of the NO-cGMP-K⁺ ATP pathway, κ-opioid, and NMDA receptors. In addition, the compounds showed inhibition of cyclo-oxygenase enzymes and adverse effects were not observed with dose 300 times greater than the dose used experimentally.

Exercise-induced hypoalgesia is present in people with Parkinson's disease: Two observational cross-sectional studies

BACKGROUND

Exercise is prescribed for people with Parkinson's disease to address motor and non-motor impairments, including pain. Exercise-induced hypoalgesia (i.e., an immediate reduction in pain sensitivity following exercise) is reported in the general population; however, the immediate response of pain sensitivity to exercise in people with Parkinson's disease is unknown. The purpose of this study was to investigate if exercise-induced hypoalgesia is present following isometric and aerobic exercise in people with Parkinson's disease, and if so, if it varies with the dose of aerobic exercise.

METHODS

Thirty people with idiopathic Parkinson's disease and pain-free age-matched controls completed two observational studies evaluating the response to: (a) right arm isometric exercise; and (b) treadmill walking at low and moderate intensities. Pressure pain thresholds were measured over biceps brachii and quadriceps muscles immediately before and after exercise, with increased thresholds after exercise indicating exercise-induced hypoalgesia.

RESULTS

Pressure pain thresholds increased in the Parkinson's disease group at all tested sites following all exercise bouts (e.g., isometric exercise, right bicep 29%; aerobic exercise, quadriceps, moderate intensity 8.9%, low intensity 7.1% (p ≤ 0.008)), with no effect of aerobic exercise dose (p = 0.159). Similar results were found in the control group.

CONCLUSIONS

Overall, people with Parkinson's disease experienced an exercise-induced hypoalgesia response similar to that of the control group, the extent of which did not vary between mild and moderate doses of aerobic exercise. Further research is warranted to investigate potential longer term benefits from exercise in the management of pain in this population.

SIGNIFICANCE

Isometric and aerobic exercise reduces pain sensitivity in people with Parkinson's disease. As exercise is important for people with Parkinson's disease, these results provide assurance that people with Parkinson's disease and pain can exercise without an immediate increase in pain sensitivity. The reduction in pain sensitivity with both modes and with low and moderate intensities of aerobic exercise suggests that people with Parkinson's disease can safely choose the mode and intensity of exercise that best suits their needs.

Antinociceptive activity of petroleum ether fraction obtained from methanolic extract of Clinacanthus nutans leaves involves the activation of opioid receptors and NO-mediated/cGMP-independent pathway

BACKGROUND

Methanol extract (MECN) of Clinacanthus nutans Lindau leaves (family Acanthaceae) demonstrated peripherally and centrally mediated antinociceptive activity via the modulation of opioid/NO-mediated, but cGMP-independent pathway. In the present study, MECN was sequentially partitioned to obtain petroleum ether extract of C. nutans (PECN), which was subjected to antinociceptive study with aims of establishing its antinociceptive potential and determining the role of opioid receptors and L-arginine/nitric oxide/cyclic-guanosine monophosphate (L-arg/NO/cGMP) pathway in the observed antinociceptive activity.

METHODS

The antinociceptive potential of orally administered PECN (100, 250, 500 mg/kg) was studied using the abdominal constriction-, hot plate- and formalin-induced paw licking-test in mice (n = 6). The effect of PECN on locomotor activity was also evaluated using the rota rod assay. The role of opioid receptors was determined by pre-challenging 500 mg/kg PECN (p.o.) with antagonist of opioid receptor subtypes, namely β-funaltrexamine (β-FNA; 10 mg/kg; a μ-opioid antagonist), naltrindole (NALT; 1 mg/kg; a δ-opioid antagonist) or nor-binaltorphimine (nor-BNI; 1 mg/kg; a κ-opioid antagonist) followed by subjection to the abdominal constriction test. In addition, the role of L-arg/NO/cGMP pathway was determined by prechallenging 500 mg/kg PECN (p.o.) with L-arg (20 mg/kg; a NO precursor), 1H-[1, 2, 4] oxadiazolo [4,3-a]quinoxalin-1-one (ODQ; 2 mg/kg; a specific soluble guanylyl cyclase inhibitor), or the combinations thereof (L-arg + ODQ) for 5 mins before subjection to the abdominal constriction test. PECN was also subjected to phytoconstituents analyses.

RESULTS

PECN significantly (p < 0.05) inhibited nociceptive effect in all models in a dose-dependent manner. The highest dose of PECN (500 mg/kg) also did not significantly (p > 0.05) affect the locomotor activity of treated mice. The antinociceptive activity of PECN was significantly (p < 0.05) inhibited by all antagonists of μ-, δ-, and κ-opioid receptors. In addition, the antinociceptive activity of PECN was significantly (p < 0.05) reversed by L-arg, but insignificantly (p > 0.05) affected by ODQ. HPLC analysis revealed the presence of at least cinnamic acid in PECN.

CONCLUSION

PECN exerted antinocicpetive activity at peripheral and central levels possibly via the activation of non-selective opioid receptors and modulation of the NO-mediated/cGMP-independent pathway partly via the synergistic action of phenolic compounds.

Impact of physical exercise in cancer survivors during and after antineoplastic treatments

Cancer patients experience symptoms and adverse effects of treatments that may last even after the end of treatments. Exercise is a safe, non-pharmacological and cost-effective therapy that can provide several health benefits in cancer patient and survivors, reducing cancer symptoms and cancer treatment side effects. The purpose of this review is to describe how the physical exercise is capable to reduce cancer symptoms and cancer treatment side effects. We realized a pragmatic classification of symptoms, dividing them into physical, psychological and psycho-physical aspects. For each symptom we discuss causes, therapies, we analyse the effects of physical exercise and we summarize the most effective type of exercise to reduce the symptoms. This review also points out what are the difficulties that patients and survivors face during the practice of physical activity and provides some solutions to overcome these barriers. Related to each specific cancer, it emerges that type, frequency and intensity of physical exercise could be prescribed and supervised as a therapeutic program, like it occurs for the type, dose and duration of a drug treatment.

Possible mechanisms involved in the anti-nociceptive effects of hydro-ethanolic leaf extract of Ziziphus abyssinica

CONTEXT

Various parts of Ziziphus abyssinica Hochst ex. A. Rich (Rhamnaceae) have been used in Ghanaian and African traditional medicine as an analgesic. However, there are little scientific data to support the anti-nociceptive effects of the hydro-ethanolic leaf extract of Ziziphus abyssinica (EthE) as well as the possible mechanisms involved in its anti-nociceptive effects.

PURPOSE

To predict possible nociceptive pathways involved in the anti-nociceptive effects of EthE.

MATERIALS AND METHODS

The effect of EthE (30, 100 and 300 mg/kg) on intraplantar injection of pain mediators such as interleukin-1β, tumour necrosis factor-α, prostaglandin E₂ and bradykinin was evaluated in male Sprague Dawley rats using Randall-Selitto test for 5 h. The effect of specific antagonists to the opioidergic, adenosinergic, ATP-sensitive K⁺ channels, nitric oxide, serotonergic, muscarinic, adrenergic and voltage-gated calcium channel on the anti-nociceptive effect of EthE (100 mg/kg) was evaluated using the formalin test in male imprinting control region (ICR) mice for 1 h.

RESULTS

Pretreatment of the rats with EthE significantly reversed the hypernociception induced by intraplantar injection of TNF-α (F_4,120 = 10.86, p < 0.0001), IL-1β (F_4,120 = 14.71, p < 0.0001), bradykinin (F_4,80 = 12.52, p < 0.0001) and prostaglandin E₂ (F_5,144 = 6.165, p = 0.0001). The anti-nociceptive effect exhibited by EthE in the formalin test was reversed by systemic administration of N^G-l-nitro-arginine methyl ester, naloxone, theophylline and glibenclamide.

CONCLUSIONS

EthE inhibits hypernociception induced by TNF-α, IL-1β, bradykinin and prostaglandin E₂. EthE exhibited anti-nociceptive effects possibly mediated through opioidergic, adenosinergic, ATP-sensitive potassium channels and nitric oxide cyclic GMP pathways.

Occlusion of blood flow attenuates exercise-induced hypoalgesia in the occluded limb of healthy adults

Animal studies have demonstrated an important role of peripheral mechanisms as contributors to exercise-induced hypoalgesia (EIH). Whether these same mechanisms contribute to EIH in humans is not known. In the current study, pain thresholds were assessed in healthy volunteers ( n = 36) before and after 5 min of high-intensity leg cycling exercise and an equivalent period of quiet rest. Pressure pain thresholds (PPTs) were assessed over the rectus femoris muscle of one leg and first dorsal interosseous muscles (FDIs) of both arms. Blood flow to one arm was occluded by a cuff throughout the 5-min period of exercise (or rest) and postexercise (or rest) assessments. Ratings of pain intensity and pain unpleasantness during occlusion were also measured. Pain ratings during occlusion increased over time (range, 1.5 to 3.5/10, all d > 0.63, P < 0.001) similarly in the rest and exercise conditions ( d < 0.35, P > 0.4). PPTs at all sites were unchanged following rest (range, −1.3% to +0.9%, all d < 0.05, P > 0.51). Consistent with EIH, exercise significantly increased PPT at the leg (+29%, d = 0.69, P < 0.001) and the nonoccluded (+23%, d = 0.56, P < 0.001) and occluded (+8%, d = 0.19, P = 0.003) unexercised arms. However, the increase in the occluded arm was significantly smaller ( d = −1.03, P < 0.001). These findings show that blocking blood flow to a limb during exercise attenuates EIH, suggesting that peripheral factors contribute to EIH in healthy adults.

NEW & NOTEWORTHY This is the first demonstration in humans that a factor carried by the circulation and acting at the periphery is important for exercise-induced hypoalgesia. Further understanding of this mechanism may provide new insight to pain relief with exercise as well as potential interactions between analgesic medications and exercise.

Exploring the Mechanisms of Exercise-Induced Hypoalgesia Using Somatosensory and Laser Evoked Potentials

Exercise-induced hypoalgesia is well described, but the underlying mechanisms are unclear. The aim of this study was to examine the effect of exercise on somatosensory evoked potentials, laser evoked potentials, pressure pain thresholds and heat pain thresholds. These were recorded before and after 3-min of isometric elbow flexion exercise at 40% of the participant's maximal voluntary force, or an equivalent period of rest. Exercise-induced hypoalgesia was confirmed in two experiments (Experiment 1–SEPs; Experiment 2–LEPs) by increased pressure pain thresholds at biceps brachii (24.3 and 20.6% increase in Experiment 1 and 2, respectively; both d > 0.84 and p < 0.001) and first dorsal interosseous (18.8 and 21.5% increase in Experiment 1 and 2, respectively; both d > 0.57 and p < 0.001). In contrast, heat pain thresholds were not significantly different after exercise (forearm: 10.8% increase, d = 0.35, p = 0.10; hand: 3.6% increase, d = 0.06, p = 0.74). Contrasting effects of exercise on the amplitude of laser evoked potentials (14.6% decrease, d = −0.42, p = 0.004) and somatosensory evoked potentials (10.9% increase, d = −0.02, p = 1) were also observed, while an equivalent period of rest showed similar habituation (laser evoked potential: 7.3% decrease, d = −0.25, p = 0.14; somatosensory evoked potential: 20.7% decrease, d = −0.32, p = 0.006). The differential response of pressure pain thresholds and heat pain thresholds to exercise is consistent with relative insensitivity of thermal nociception to the acute hypoalgesic effects of exercise. Conflicting effects of exercise on somatosensory evoked potentials and laser evoked potentials were observed. This may reflect non-nociceptive contributions to the somatosensory evoked potential, but could also indicate that peripheral nociceptors contribute to exercise-induced hypoalgesia.

Emerging Relationships between Exercise, Sensory Nerves, and Neuropathic Pain

The utilization of physical activity as a therapeutic tool is rapidly growing in the medical community and the role exercise may offer in the alleviation of painful disease states is an emerging research area. The development of neuropathic pain is a complex mechanism, which clinicians and researchers are continually working to better understand. The limited therapies available for alleviation of these pain states are still focused on pain abatement and as opposed to treating underlying mechanisms. The continued research into exercise and pain may address these underlying mechanisms, but the mechanisms which exercise acts through are still poorly understood. The objective of this review is to provide an overview of how the peripheral nervous system responds to exercise, the relationship of inflammation and exercise, and experimental and clinical use of exercise to treat pain. Although pain is associated with many conditions, this review highlights pain associated with diabetes as well as experimental studies on nerve damages-associated pain. Because of the global effects of exercise across multiple organ systems, exercise intervention can address multiple problems across the entire nervous system through a single intervention. This is a double-edged sword however, as the global interactions of exercise also require in depth investigations to include and identify the many changes that can occur after physical activity. A continued investment into research is necessary to advance the adoption of physical activity as a beneficial remedy for neuropathic pain. The following highlights our current understanding of how exercise alters pain, the varied pain models used to explore exercise intervention, and the molecular pathways leading to the physiological and pathological changes following exercise intervention.