Caffeine reverses antinociception by oxcarbazepine by inhibition of adenosine A1 receptors: Insights using knockout mice

Caffeine Impaired Acupuncture Analgesia in Inflammatory Pain by Blocking Adenosine A1 Receptor

Caffeine consumption inhibits acupuncture analgesic effects by blocking adenosine signaling. However, existing evidence remains controversial. Hence, this study aimed to examine the adenosine A1 receptor (A1R) role in moderate-dose caffeine-induced abolishing effect on acupuncture analgesia using A1R knockout mice (A1R-/-). We assessed the role of A1R in physiological sensory perception and its interaction with caffeine by measuring mechanical and thermal pain thresholds and administering A1R and adenosine 2A receptor antagonists in wild-type (WT) and A1R-/- mice. Formalin- and complete Freund's adjuvant (CFA)-induced inflammatory pain models were recruited to explore moderate-dose caffeine effect on pain perception and acupuncture analgesia in WT and A1R-/- mice. Moreover, a C-fiber reflex electromyogram in the biceps femoris was conducted to validate the role of A1R in the caffeine-induced blockade of acupuncture analgesia. We found that A1R was dispensable for physiological sensory perception and formalin- and CFA-induced hypersensitivity. However, genetic deletion of A1R impaired the antinociceptive effect of acupuncture in A1R-/- mice under physiological or inflammatory pain conditions. Acute moderate-dose caffeine administration induced mechanical and thermal hyperalgesia under physiological conditions but not in formalin- and CFA-induced inflammatory pain. Moreover, caffeine significantly inhibited electroacupuncture (EA) analgesia in physiological and inflammatory pain in WT mice, comparable to that of A1R antagonists. Conversely, A1R deletion impaired the EA analgesic effect and decreased the caffeine-induced inhibitory effect on EA analgesia in physiological conditions and inflammatory pain. Moderate-dose caffeine administration diminished the EA-induced antinociceptive effect by blocking A1R. Overall, our study suggested that caffeine consumption should be avoided during acupuncture treatment. PERSPECTIVE: Moderate-dose caffeine injection attenuated EA-induced antinociceptive effect in formalin- and CFA-induced inflammatory pain mice models by blocking A1R. This highlights the importance of monitoring caffeine intake during acupuncture treatment.

Anti-neuropathic effect of 7,3'-dihydroxyflavone in paclitaxel induced peripheral neuropathy in mice involving GABAA, KATP channel and adenosine receptors

Peripheral neuropathy induced by chemotherapeutic agents is the most common dose-limiting adverse effect observed in patients during and after treatment of malignancies. Many flavones have been reported to ameliorate neuropathy of different origin in experimental animals and their possible mode of action explored. The present study aims to investigate 7,3'-dihydroxyflavone for its anti-neuropathic effect against paclitaxel induced peripheral neuropathy in mice by employing behavioural tests such as mechanical allodynia, cold allodynia and thermal hyperalgesia. The possible involvement of GABA_A, K_ATP channels and adenosine receptors in the anti-neuropathic effect of 7,3'-dihydroxyflavone was also studied by employing suitable interacting drugs. Treatment with 7,3'-dihydroxyflavone (50, 100 or 200 mg/kg, s.c) significantly and dose-dependently reduced the paw withdrawal response score in both mechanical and cold allodynia and also increased the tail flick response time in thermal hyperalgesia due to paclitaxel-induced neuropathy. Pre-treatment with glibenclamide (10 mg/kg, i.p), caffeine (50 mg/kg, i.p) or bicuculline (2 mg/kg, i.p) significantly reversed the anti-neuropathic effect of 7,3'-dihydroxyflavone in behavioral tests. In conclusion, the present investigation identified 7,3'-dihydroxyflavone as a potential candidate with anti-neuropathic effect against paclitaxel induced peripheral neuropathy involving K_ATP channels, adenosine and GABA_A receptors.

Targeting Adenosine Receptors: A Potential Pharmacological Avenue for Acute and Chronic Pain

Adenosine is a purine nucleoside, responsible for the regulation of multiple physiological and pathological cellular and tissue functions by activation of four G protein-coupled receptors (GPCR), namely A₁, A_2A, A_2B, and A₃ adenosine receptors (ARs). In recent years, extensive progress has been made to elucidate the role of adenosine in pain regulation. Most of the antinociceptive effects of adenosine are dependent upon A₁AR activation located at peripheral, spinal, and supraspinal sites. The role of A_2AAR and A_2BAR is more controversial since their activation has both pro- and anti-nociceptive effects. A₃AR agonists are emerging as promising candidates for neuropathic pain. Although their therapeutic potential has been demonstrated in diverse preclinical studies, no AR ligands have so far reached the market. To date, novel pharmacological approaches such as adenosine regulating agents and allosteric modulators have been proposed to improve efficacy and limit side effects enhancing the effect of endogenous adenosine. This review aims to provide an overview of the therapeutic potential of ligands interacting with ARs and the adenosinergic system for the treatment of acute and chronic pain.

Antinociceptive, antiedematous, and antiallodynic activity of 1H-pyrrolo[3,4-c]pyridine-1,3(2H)-dione derivatives in experimental models of pain

The aim of the presented study was to examine the potential antinociceptive, antiedematous (anti-inflammatory), and antiallodynic activities of two 1H-pyrrolo[3,4-c]pyridine-1,3(2H)-dione derivatives (DSZ 1 and DSZ 3) in various experimental models of pain. For this purpose, the hot plate test, the capsaicin test, the formalin test, the carrageenan model, and oxaliplatin-induced allodynia tests were performed. In the hot plate test, only DSZ 1 in the highest dose (20 mg/kg) was active but its effects appear to be due to sedatation rather than antinociceptiveness. In capsaicin-induced neurogenic pain model, both compounds displayed a significant antinociceptive activity. In the formalin test, DSZ 1 and DSZ 3 (5-20 mg/kg) revealed antinociceptive activity in both phases but it was more pronounced in the second phase of the test. In this test, pretreatment with caffeine, DPCPX reversed the antinociceptive effect of DSZ 3. On the other hand, pretreatment with L-NAME diminished the antinociceptive effect of DSZ 1. Pretreatment with naloxone did not affect antinociceptive activity of both compounds. Similar to ketoprofen, DSZ 1 and DSZ 3 showed antiedematous (antiinflammatory) and antihyperalgesic activity, and similar to lidocaine local anesthetic activity. Furthermore, both compounds (5 and 10 mg/kg) reduced tactile allodynia in acute and chronic phases of neuropathic pain. In the in vitro studies, DSZ 1 and DSZ 3 reduced the COX-2 level in LPS-activated RAW 264.7 cells, which suggests their anti-inflammatory activity. In conclusion, both DSZ 1 and DSZ 3 displayed broad spectrum of activity in several pain models, including neurogenic, tonic, inflammatory, and chemotherapy-induced peripheral neuropathic pain.

Far infrared-emitting ceramics decrease Freund's adjuvant-induced inflammatory hyperalgesia in mice through cytokine modulation and activation of peripheral inhibitory neuroreceptors

OBJECTIVE

The present study aimed to evaluate the analgesic and anti-inflammatory effects of far infrared-emitting ceramics (cFIRs) in a model of persistent inflammatory hyperalgesia and to elucidate the possible mechanisms of these effects.

METHODS

Mice were injected with complete Freund's adjuvant (CFA) and treated with cFIRs via placement on a pad impregnated with cFIRs on the bottom of the housing unit for different periods of time. Mice underwent mechanical hyperalgesia and edema assessments, and tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and IL-10 levels were measured. Twenty-four hours after CFA injection and 30 min before cFIR treatment, mice were pretreated with a nonselective adenosinergic antagonist, caffeine, the selective adenosine receptor A₁ antagonist, 1,3-dipropyl-8-cyclopentylxanthine (DPCPX), the selective cannabinoid receptor type 1 antagonist, AM281, the selective cannabinoid receptor type 2 antagonist, AM630, or the nonselective opioid receptor antagonist, naloxone, and mechanical hyperalgesia was assessed.

RESULTS

cFIRs statistically (P < 0.05) decreased CFA-induced mechanical hyperalgesia ((82.86 ± 5.21)% in control group vs (56.67 ± 9.54)% in cFIR group) and edema ((1699.0 ± 77.8) μm in control group vs (988.7 ± 107.6) μm in cFIR group). cFIRs statistically (P < 0.05) reduced TNF-α ((0.478 ± 0.072) pg/mg of protein in control group vs (0.273 ± 0.055) pg/mg of protein in cFIR group) and IL-1β ((95.81 ± 3.95) pg/mg of protein in control group vs (80.61 ± 4.71) pg/mg of protein in cFIR group) levels and statistically (P < 0.05) increased IL-10 ((18.32 ± 0.78) pg/mg of protein in control group vs (25.89 ± 1.23) pg/mg of protein in cFIR group) levels in post-CFA-injected paws. Peripheral pre-administration of inhibitory neuroreceptor antagonists (caffeine, DPCPX, AM281, AM630 and naloxone) prevented the analgesic effects of cFIRs (P < 0.05).

CONCLUSION

These data provide additional support for the use of cFIRs in the treatment of painful inflammatory conditions and contribute to our understanding of the neurobiological mechanisms of the therapeutic effects of cFIRs.

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.

Influences of smoking and caffeine consumption on trigeminal pain processing

Background

Many human and animal studies have shown the influence of nicotine and caffeine on pain perception and processing. This study aims to investigate whether smoking or caffeine consumption influences trigeminal pain processing.

Methods

Sixty healthy subjects were investigated using simultaneous recordings of the nociceptive blink reflex (nBR) and pain related evoked potentials (PREP) following nociceptive electrical stimulation on both sides of the forehead (V1). Thirty subjects were investigated before and after smoking a cigarette, as well as before and after taking a tablet of 400 mg caffeine.

Results

After smoking PREP showed decreased N2 and P2 latencies indicating central facilitation at supraspinal (thalamic or cortical) level. PREP amplitudes were not changed. NBR showed a decreased area under the curve (AUC) indicating central inhibition at brainstem level. After caffeine intake no significant changes were observed comparing nBR and PREP results before consumption.

Conclusions

Smoking influences trigeminal pain processing on supraspinal and brainstem level. In the investigated setting, caffeine consumption does not significantly alter trigeminal pain processing. This observation might help in the further understanding of the pathophysiology of pain disorders that are associated with excessive smoking habits such as cluster headache. Previous smoking has to be taken into account when performing electrophysiological studies to avoid bias of study results.

Caffeine as an adjuvant therapy to opioids in cancer pain: a randomized, double-blind, placebo-controlled trial

CONTEXT

Opioid therapy often shows insufficient efficacy and substantial adverse events in patients with advanced cancer.

OBJECTIVES

To assess the efficacy of caffeine infusion as an adjuvant analgesic to opioid therapy in patients with advanced cancer.

METHODS

A double-blind, randomized, placebo-controlled trial was conducted in the palliative care wards of two teaching hospitals in South Korea. A total of 20 of 41 participants were assigned to the caffeine group and 21 to the placebo group. The participants received caffeine (200mg) or normal saline intravenously once a day for two days. The primary outcome was pain, which was measured using a 10-point rating scale. Other outcomes included drowsiness, confusion, nausea, sleep disturbance, fatigue, and sadness.

RESULTS

Three participants (two in the caffeine group and one in the placebo group) dropped out after the first intervention because of insomnia; thus, 38 participants completed the trial. Pain score was significantly lower in the caffeine group than in the placebo group after the second trial (P=0.038). The mean reduction in pain intensity in the caffeine group was 0.833 (95% confidence interval [CI] 0.601-1.066), whereas that in the placebo group was 0.350 (95% CI 0.168-0.532). Considering an improvement higher than 30% from baseline as the threshold value, drowsiness improved significantly in the caffeine group after the first trial (P=0.041). Adverse event rate did not differ between the two groups.

CONCLUSION

Caffeine infusion significantly reduced pain and drowsiness, but the reduction did not reach clinical significance in patients with advanced cancer undergoing opioid therapy. Further investigations are warranted.

Caffeine at Moderate Doses Can Inhibit Acupuncture-Induced Analgesia in a Mouse Model of Postoperative Pain

BACKGROUND

The use of acupuncture in the treatment of pain conditions has been extensively investigated. However, the influence of dietary ingredients on acupuncture-induced analgesia (AA) remains unexplored. Recently, the role of adenosine receptors in AA has been shown, and caffeine, one of the world's most commonly consumed dietary ingredients, is an antagonist of these receptors. In this study, the postincisional pain model was used to investigate caffeine's influence on AA.

METHOD

Mice submitted to plantar incision surgery were treated with acupuncture needling after administration of acute or chronic caffeine. Acupuncture needling was performed using two different types of stimuli, manual acupuncture and electroacupuncture bilaterally in the acupoint SP6.

RESULTS

We found that acute preadministration of caffeine (10 mg/kg, i.p.) completely reversed AA in both types of acupuncture. In the chronic preadministration, we used two doses that mimicked the average daily caffeine consumption in Western countries and China. Interestingly, the Western dose of caffeine (70 mg/kg/day) administered during 8 days in the drinking water reversed AA and the Chinese dose (4 mg/kg/day) administered during the same period did not.

CONCLUSIONS

These results indicate that the use of caffeine can inhibit the analgesic effect of different forms of acupuncture. In addition, our findings suggest that doses of caffeine relevant to dietary human intake levels could be a confounding factor in the context of acupuncture research.

Ankle joint mobilization affects postoperative pain through peripheral and central adenosine A1 receptors

BACKGROUND

Physical therapists frequently use joint mobilization therapy techniques to treat people with musculoskeletal dysfunction and pain. Several studies suggest that endogenous adenosine may act in an analgesic fashion in various pain states.

OBJECTIVE

The purpose of this study was to investigate the contribution of the adenosinergic system on the antihyperalgesic effect of ankle joint mobilization (AJM).

DESIGN

This was a experimental study.

METHODS

To test the hypothesis that the adrenosinergic system is involved in the antihyperalgesic effect of AJM, mice (25-35 g) submitted to plantar incision surgery were used as a model of acute postoperative pain. The mice were subjected to AJM for 9 minutes. Withdrawal frequency to mechanical stimuli was assessed 24 hours after plantar incision surgery and 30 minutes after AJM, adenosine, clonidine, or morphine treatments. The adenosinergic system was assessed by systemic (intraperitoneal), central (intrathecal), and peripheral (intraplantar) administration of caffeine. The participation of the A1 receptor was investigated using a selective adenosine A1 receptor subtype antagonist. In addition, previous data on the involvement of the serotonergic and noradrenergic systems in the antihyperalgesic effect of AJM were confirmed.

RESULTS

Ankle joint mobilization decreased mechanical hyperalgesia, and this effect was reversed by pretreatment of the animals with caffeine given by intraperitoneal, intraplantar, and intrathecal routes. In addition, intraplanar and intrathecal administrations of 1,3-dipropyl-8-cyclopentylxanthine (DPCPX, a selective adenosine A1 subtype receptor antagonist) or systemic administration of yohimbine or ρ-chlorophenylalanine methyl ester hydrochloride (PCPA) blocked the antihyperalgesia induced by AJM.

LIMITATIONS

The results are limited to animal models and cannot be generalized to acute pain in humans.

CONCLUSIONS

This study demonstrated the involvement of the adenosinergic system in the antihyperalgesic effect of AJM in a rodent model of pain and provides a possible mechanism basis for AJM-induced relief of acute pain.

Spinal serotonin 5-HT7 and adenosine A1 receptors, as well as peripheral adenosine A1 receptors, are involved in antinociception by systemically administered amitriptyline

The present study explored a link between spinal 5-HT(7) and adenosine A(1) receptors in antinociception by systemic amitriptyline in normal and adenosine A(1) receptor knock-out mice using the 2% formalin test. In normal mice, antinociception by systemic amitriptyline 3mg/kg was blocked by intrathecal administration of the selective adenosine A(1) receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) 10 nmol. Blockade was also seen in adenosine A(1) receptor +/+ mice, but not in -/- mice lacking these receptors. In both normal and adenosine A(1) receptor +/+ mice, the selective 5-HT(7) receptor antagonist (2R)-1-[(3-hydroxyphenyl)sulfonyl]-2-[2-(4-methyl-1-piperidinyl)ethyl]pyrrolidine hydrochloride (SB269970) 3 μg blocked antinociception by systemic amitriptyline, but it did not prevent antinociception in adenosine A(1) receptor -/- mice. In normal mice, flinching was unaltered when the selective 5-HT(7) receptor agonist (2S)-(+)-5-(1,3,5-trimethylpyrazol-4-yl)-2-(dimethylamino)tetralin (AS-19) 20 μg was administered alone, but increased when co-administered intrathecally with DPCPX 10 nmol or SB269970 3 μg. Intrathecal AS-19 decreased flinching in adenosine A(1) receptor +/+ mice compared to -/- mice. Systemic amitriptyline appears to reduce nociception by activating spinal adenosine A(1) receptors secondarily to 5-HT(7) receptors. Spinal actions constitute only one aspect of antinociception by amitriptyline, as intraplantar DPCPX 10 nmol blocked antinociception by systemic amitriptyline in normal and adenosine A(1) receptor +/+, but not -/- mice. Adenosine A(1) receptor interactions are worthy of attention, as chronic oral caffeine (0.1, 0.3g/L, doses considered relevant to human intake levels) blocked antinociception by systemic amitriptyline in normal mice. In conclusion, adenosine A(1) receptors contribute to antinociception by systemic amitriptyline in both spinal and peripheral compartments.