Caffeine inhibits antinociception by acetaminophen in the formalin test by inhibiting spinal adenosine A1 receptors

doi:10.1016/j.ejphar.2011.10.036

European Journal of Pharmacology

Volume 674, Issues 2–3, 15 January 2012, Pages 248-254

https://doi.org/10.1016/j.ejphar.2011.10.036 Get rights and content

Abstract

The present study examined effects of caffeine on antinociception by acetaminophen in the formalin test in mice. It demonstrates that caffeine 10 mg/kg inhibits antinociception produced by acetaminophen 300 mg/kg i.p. against phase 2 flinches. Chronic administration of caffeine in the drinking water (0.1, 0.3 g/l) for 8 days also inhibits the action of acetaminophen. The selective adenosine A₁ receptor antagonist DPCPX 1 mg/kg i.p. mimics the action of caffeine, but the selective adenosine A_2A receptor antagonist SCH58261 3 mg/kg i.p. does not. While acetaminophen produced the same effect in mice that were +/+, +/− and −/− for adenosine A₁ receptors, inhibition of antinociception by caffeine was seen only in +/+ and +/− mice. A higher dose of caffeine, 40 mg/kg, produced an intrinsic antinociception against formalin-evoked flinches, an effect also seen when caffeine was administered intrathecally. SCH58261 30 nmol, but not DPCPX 10 nmol, also produced antinociception when administered intrathecally indicating involvement of adenosine A_2A receptors in spinal antinociception. Caffeine reversal of acetaminophen results from actions in the spinal cord, as intrathecal DPCPX 10 nmol inhibited antinociception by systemic acetaminophen; this was also observed in +/+ but not in −/− adenosine A₁ receptor mice. We propose that spinal adenosine A₁ receptors contribute to the action of acetaminophen secondarily to involvement of descending serotonin pathways and release of adenosine within the spinal cord. Inhibition of acetaminophen antinociception by doses of caffeine relevant to dietary human intake levels suggests a more detailed consideration of acetaminophen–caffeine interactions in humans is warranted.

Introduction

Acetaminophen is a widely used over-the-counter analgesic, as well as a prescription analgesic, and is consumed by millions of people daily. Despite sharing several pharmacological properties with cyclooxygenase inhibitors, it exhibits additive analgesic effects with such agents in clinical studies (Ong et al., 2010), and this suggests a distinct mechanism of action. Recent preclinical studies indicate that antinociception by acetaminophen involves serotonergic, cannabinoid and vanilloid mechanisms (Bertolini et al., 2006, Mallet et al., 2008, Mallet et al., 2010). 5-HT mechanisms are now also implicated in the action of acetaminophen in humans (Bandschapp et al., 2011, Pickering et al., 2006).

Caffeine, which is widely consumed in the diet, is also added as a drug to acetaminophen formulations as an adjuvant analgesic. The analgesic adjuvant properties of caffeine were recognized in the mid-1980s (Laska et al., 1984) and have been confirmed more recently (Anneken et al., 2010, Palmer et al., 2010). In preclinical studies, caffeine augmented antinociception by acetaminophen at some doses when effects of a wide range of doses of caffeine (10–100 mg/kg) were determined (Granados-Soto et al., 1993, Siegers, 1973), supporting such adjuvant actions. Caffeine exhibits intrinsic antinociceptive actions in several preclinical models, attributed to block of adenosine A_2A and/or A_2B receptors (reviewed in Sawynok, 2011a), and such actions may contribute to adjuvant analgesic actions of caffeine. There are also reports that modest doses of caffeine (10 mg/kg) inhibit antinociception by acetaminophen (Godfrey et al., 2006), including in studies that observed augmentation of antinociception with higher doses of caffeine (Granados-Soto et al., 1993, commented on in Granados-Soto and Casteneda-Hernández, 1999, Siegers, 1973). These lower doses of caffeine also inhibit antinociception by several other analgesic agents, an action attributed to block of adenosine A₁ receptors (Sawynok, 2011b). Caffeine has a similar affinity for binding to and inhibiting adenosine A₁ and A_2A receptors, and these actions are considered to be the most relevant to the pharmacology of caffeine at usual dietary intake levels (Fredholm et al., 1999).

In the present study, we examined effects of caffeine, given both acutely and chronically using doses and regimens considered relevant to human intake levels, on antinociception by acetaminophen (see Discussion). We used the formalin test as a model of pain that involves ongoing activation of sensory afferents and recruitment of ascending and descending circuitry involved in pain signalling and modulation, as this model may be more relevant to chronic pain states than threshold tests in which the stimulus is phasic. Furthermore, we used adenosine A₁ receptor gene deletion mice and selective adenosine A₁ and A_2A receptor antagonists (DPCPX or 8-cyclopentyl-1,3-dipropylxanthine, and SCH58261 or 5-amino-7-(2-phenylethyl)-2-(2-furyl)pyrazolo [4,3-e]-1,2,4-triazolol[1,5-c]pyrimidine, respectively) (Bruns et al., 1987, Zocchi et al., 1996) to determine the specific adenosine receptors involved in caffeine actions. Finally, caffeine and selective A₁ and A_2A receptor antagonists were given spinally by acute lumbar puncture along with systemic administration of acetaminophen in order to determine whether interactions involving adenosine receptors occurred within the spinal cord.

Section snippets

Animals

All experiments were approved by the University Committee on Laboratory Animals and complied with the Canadian Council of Animal Care Guidelines for the ethical use of animals. Male C57Bl6 mice (Charles River Laboratory, Quebec, Canada) weighing 20–25 g, or both sexes of adenosine A₁ receptor +/+, +/− and −/− knock-out mice, generated on a C57Bl6 background, raised in-house and between 20 and 30 g, were used. Genotypes of the knock-out colony mice were verified by DNA extraction from tail-clips

Effects of acute and chronic caffeine administration on antinociception by acetaminophen in the formalin test

Acetaminophen 300 mg/kg, given i.p. as a 20 min pretreatment, reduced cumulative phase 2 flinching behaviours produced by 2% formalin in mice by ~ 60% (Fig. 1A, B). A dose of 100 mg/kg acetaminophen was ineffective in reducing such behaviours. Caffeine 10 mg/kg, also given i.p. 20 min before formalin, had no intrinsic effect on phase 2 flinching behaviours produced by 2% formalin (Fig. 1C, D) but significantly reduced the antinociceptive action of acetaminophen (Fig. 1C, E). When caffeine was given

Involvement of adenosine in antinociception by acetaminophen

The mechanism of antinociceptive action of acetaminophen is incompletely understood, but it is now known to involve serotonergic, cannabinoid and vanilloid mechanisms (Bertolini et al., 2006, Mallet et al., 2008, Mallet et al., 2010). The present study demonstrates that caffeine, which blocks adenosine A₁ and A_2A receptors with a comparable affinity (Fredholm et al., 1999), inhibits antinociception by acetaminophen, and implicates spinal adenosine A₁ receptors in the mechanism by which

Conclusions

The present study clearly reveals an involvement of spinal adenosine A₁ receptors in antinociception by acetaminophen, and proposes that this may be secondary to activation of descending serotonergic pathways and subsequent release of adenosine within the spinal cord. Cannabinoid systems have recently been implicated in antinociception by acetaminophen. Given that A₁ adenosine and CB₁ cannabinoid receptors exhibit interactions, and that chronic dosing of caffeine, at modest dosing levels

Acknowledgements

This work was supported by the Canadian Institutes of Health Research. We are grateful to Bertil Fredholm (Karolinska Institute, Stockholm, Sweden) who supplied the initial adenosine A₁ receptor gene deletion mice, and whose laboratory performed genotyping analysis on colony bred mice.

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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.
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Endogenous adenosine systems have largely been implicated in drug actions by the demonstration that caffeine (non-selective A1R and A2AR antagonist) (see Section The issue of caffeine), in doses up to 7.5–10 mg/kg, inhibits antinociception, and when this occurs, it is generally also seen with a selective A1R antagonist (DPCPX most commonly used). Thus, caffeine and/or DPCPX, given systemically, inhibit antinociception by systemic amitriptyline (Esser and Sawynok, 2000; Ulugol et al., 2002; Sawynok et al., 2008), carbamazepine and oxcarbazepine (Tomić et al., 2004; Sawynok et al., 2010), venlafaxine (Yaba et al., 2006, but see Abed et al., 2015), acetaminophen (Godfrey et al., 2006; Sawynok and Reid, 2012), allopurinol (Schmidt et al., 2009; Essawy and Elbaz, 2013), tramadol (Sawynok et al., 2013), levetiracetam (Tomić et al., 2015), sumatriptan (Tomić et al., 2015), and gabapentin (Martins et al., 2015b), all of which are currently used clinically. Caffeine and/or DPCPX also inhibit the action of: (1) experimental agents such as cizoliritine (Aubel et al., 2007), inosine (Nascimento et al., 2010), guanosine (Schmidt et al., 2010), and selenide compounds (Savegnago et al., 2008; Luchese et al., 2010; Marcondes Sari et al., 2014), as well as (2) agents considered to be supplements or herbal remedies such as linalool (Peana et al., 2006), fructose 1,6-bisphosphate (Valério et al., 2009), paeoniflorin (main active ingredient in root of Paeonia lactiflora Pall) (Zhang et al., 2009), Artemia scopara extract (Habib and Waheed, 2013), Daniella oliveri extract (Boyce et al., 2013; theophylline was used instead of caffeine), norisoboldine from Radix Linderae (Gao et al., 2014), and Muntingia calabura extract (Zakaria et al., 2014).
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Neuropharmacology and AnalgesiaCaffeine inhibits antinociception by acetaminophen in the formalin test by inhibiting spinal adenosine A1 receptors

Abstract

Introduction

Section snippets

Animals

Effects of acute and chronic caffeine administration on antinociception by acetaminophen in the formalin test

Involvement of adenosine in antinociception by acetaminophen

Conclusions

Acknowledgements

Pain

Eur. J. Pharmacol.

J. Am. Diet. Assoc.

Eur. J. Pharmacol.

J. Pharmacol. Toxicol.

Pain

Eur. J. Pharmacol.

Neuroscience

Pain

Eur. J. Pharmacol.

Pain

Neurosci. Lett.

Neurosci. Lett.

Brain Res.

Brain Res.

Pain

Antinociceptive effects of novel A2B adenosine receptor antagonists

J. Pharmacol. Exp. Ther.

Efficacy of fixed combinations of acetylsalicylic acid, acetaminophen and caffeine in the treatment of idiopathic headache: a review

Eur. J. Neurol.

Paracetamol: new vistas of an old drug

CNS Drug Rev.

Orally administered paracetamol does not act locally in the formalin test. Evidence for a supraspinal, serotonin-dependent antinociceptive mechanism

Anesthesiol.

Neuropharmacology and Analgesia
Caffeine inhibits antinociception by acetaminophen in the formalin test by inhibiting spinal adenosine A₁ receptors

Antinociceptive effects of novel A_2B adenosine receptor antagonists