Effect of coadministration of caffeine and either adenosine agonists or cyclic nucleotides on ketorolac analgesia

Caffeine and rheumatoid arthritis: A complicated relationship

The current ideal goal of rheumatoid arthritis (RA) management is to resolve joint and systemic inflammation by using pharmacological interventions, assuming this will correspondingly lead to overall well-being. Nonetheless, it has emerged that a substantial number of RA patients do not reach optimal disease control. Thus suggesting the holistic management of subjective symptoms might be overlooked. This poses significant medical challenges; hence the proposal of incorporating lifestyle interventions as part of a multidimensional approach. Among these aspects, both patients and physicians perceive the important role of nutrition. This review shall examine how caffeine, one of the most studied bioactive components of the most widely consumed beverages, may potentially interfere with RA management. In particular, the mechanism by which caffeine affects RA pathogenesis, as a trigger for RA onset or flare, including its influence on rheumatic drug metabolism and the most common RA comorbidities and constitutional symptoms are outlined, highlighting important knowledge gaps and unmet research needs.

Characterization of the trigeminovascular actions of several adenosine A2A receptor antagonists in an in vivo rat model of migraine

BACKGROUND

Migraine is considered a neurovascular disorder, but its pathophysiological mechanisms are not yet fully understood. Adenosine has been shown to increase in plasma during migraine attacks and to induce vasodilation in several blood vessels; however, it remains unknown whether adenosine can interact with the trigeminovascular system. Moreover, caffeine, a non-selective adenosine receptor antagonist, is included in many over the counter anti-headache/migraine treatments.

METHODS

This study used the rat closed cranial window method to investigate in vivo the effects of the adenosine A_2A receptor antagonists with varying selectivity over A₁ receptors; JNJ-39928122, JNJ-40529749, JNJ-41942914, JNJ-40064440 or JNJ-41501798 (0.3-10 mg/kg) on the vasodilation of the middle meningeal artery produced by either CGS21680 (an adenosine A_2A receptor agonist) or endogenous CGRP (released by periarterial electrical stimulation).

RESULTS

Regarding the dural meningeal vasodilation produced neurogenically or pharmacologically, all JNJ antagonists: (i) did not affect neurogenic vasodilation but (ii) blocked the vasodilation produced by CGS21680, with a blocking potency directly related to their additional affinity for the adenosine A₁ receptor.

CONCLUSIONS

These results suggest that vascular adenosine A_2A (and, to a certain extent, also A₁) receptors mediate the CGS21680-induced meningeal vasodilation. These receptors do not appear to modulate prejunctionally the sensory release of CGRP. Prevention of meningeal arterial dilation might be predictive for anti-migraine drugs, and since none of these JNJ antagonists modified per se blood pressure, selective A_2A receptor antagonism may offer a novel approach to antimigraine therapy which remains to be investigated in clinical trials.

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.

Methylxanthines and pain

Caffeine, an antagonist of adenosine A(1), A(2A) and A(2B) receptors, is known as an adjuvant analgesic in combination with non-steroidal anti-inflammatory drugs (NSAIDs) and acetaminophen in humans. In preclinical studies, caffeine produces intrinsic antinociceptive effects in several rodent models, and augments the actions of NSAIDs and acetaminophen. Antagonism of adenosine A(2A) and A(2B) receptors, as well as inhibition of cyclooxygenase activity at some sites, may explain intrinsic antinociceptive and adjuvant actions. When combined with morphine, caffeine can augment, inhibit or have no effect depending on the dose, route of administration, nociceptive test and species; inhibition reflects spinal inhibition of adenosine A(1) receptors, while augmentation may reflect the intrinsic effects noted above. Low doses of caffeine given systemically inhibit antinociception by several analgesics (acetaminophen, amitriptyline, oxcarbazepine, cizolirtine), probably reflecting block of a component of action involving adenosine A(1) receptors. Clinical studies have demonstrated adjuvant analgesia, as well as some intrinsic analgesia, in the treatment of headache conditions, but not in the treatment of postoperative pain. Caffeine clearly exhibits complex effects on pain transmission; knowledge of such effects is important for understanding adjuvant analgesia as well as considering situations in which dietary caffeine intake may have an impact on analgesic regimens.

Caffeine accelerates absorption and enhances the analgesic effect of acetaminophen

The aim of this study was to determine the analgesic effect of acetaminophen compared to a combination of both caffeine and acetaminophen or caffeine alone using tonic and phasic pain stimulation. Twenty-four subjects were treated orally with 1000 mg acetaminophen, 130 mg caffeine, and a combination of both in a 4-way crossover, double-blind, placebo-controlled study. Pharmacokinetics and analgesic effects were assessed by means of an experimental pain model based on pain-related cortical potentials after phasic stimulation of the nasal mucosa with CO(2) and based on pain ratings after tonic stimulation with dry air. Analgesic effects of acetaminophen and acetaminophen plus caffeine but not caffeine alone caused a significant reduction of pain-related cortical potentials beginning 30 minutes after medication. The combination demonstrated an enhanced effect throughout the observation time up to 3 hours. Caffeine accelerated acetaminophen absorption, indicated by enhanced early AUCs. Significant analgesic effects of the combination on tonic pain ratings were found throughout the observation time as compared to acetaminophen and placebo. In this study, caffeine enhanced and prolonged the analgesic activity of acetaminophen.

Possible activation of the NO-cyclic GMP-protein kinase G-K+ channels pathway by gabapentin on the formalin test

The effect of modulators of the nitric oxide-cyclic GMP-protein kinase G-K+ channels pathway on the local peripheral antinociceptive action induced by gabapentin was assessed in the rat 1% formalin test. Local peripheral administration of gabapentin produced a dose-dependent antinociception in the second phase of the test. Gabapentin-induced antinociception was due to a local action as its administration in the contralateral paw was ineffective. Local peripheral pretreatment of the paws with NG-L-nitro-arginine methyl ester (L-NAME, a nitric oxide synthesis inhibitor), 1H-(1,2,4)-oxadiazolo(4,2-a)quinoxalin-1-one (ODQ, a soluble guanylyl cyclase inhibitor) and KT-5823 (a protein kinase G inhibitor) dose-dependently reduced gabapentin-induced antinociception. Likewise, glibenclamide or tolbutamide (ATP-sensitive K+ channel inhibitors), 4-aminopyridine or tetraethylammonium (non-selective inward rectifier K+ channel inhibitors) or charybdotoxin (large-conductance Ca2+-activated-K+ channel blocker), but not apamin (small-conductance Ca2+-activated-K+ channel blocker) or naloxone (opioid receptor antagonist), reduced the antinociception induced by gabapentin. Our data suggest that gabapentin could activate the nitric oxide-cyclic GMP-protein kinase G-K+ channels pathway in order to produce its peripheral antinociceptive effect in the rat 1% formalin test.

A benefit-risk assessment of caffeine as an analgesic adjuvant

Caffeine has been an additive in analgesics for many years. However, the analgesic adjuvant effects of caffeine have not been seriously investigated since a pooled analysis conducted in 1984 showed that caffeine reduces the amount of paracetamol (acetaminophen) necessary for the same effect by approximately 40%. In vitro and in vivo pharmacological research has provided some evidence that caffeine can have anti-nociceptive actions through blockade of adenosine receptors, inhibition of cyclo-oxygenase-2 enzyme synthesis, or by changes in emotion state. Nevertheless, these actions are only considered in some cases. It is suggested that the actual doses of analgesics and caffeine used can influence the analgesic adjuvant effects of caffeine, and doses that are either too low or too high lead to no analgesic enhancement. Clinical trials suggest that caffeine in doses of more than 65 mg may be useful for enhancement of analgesia. However, except for in headache pain, the benefits are equivocal. While adding caffeine to analgesics increases the number of patients who become free from headache [rate ratio = 1.36, 95% confidence interval (CI) 1.17 to 1.58], it also leads to more patients with nervousness and dizziness (relative risk = 1.60, 95% CI 1.26 to 2.03). It is suggested that long-term use or overuse of analgesic medications is associated with rebound headache. However, there is no robust evidence that headache after use or withdrawal of caffeine-containing analgesics is more frequent than after other analgesics. Case-control studies have shown that caffeine-containing analgesics are associated with analgesic nephropathy (odds ratio = 4.9, 95% CI 2.3 to 10.3). However, no specific contribution of caffeine to analgesic nephropathy can be identified from these studies. Whether caffeine produces nephrotoxicity on its own, or increases nephrotoxicity due to analgesics, is yet to be established.

Involvement of peripheral cyclooxygenase-1 and cyclooxygenase-2 in inflammatory pain

Pain-induced functional impairment in the rat (PIFIR) is a model of inflammatory and arthritic pain similar to that of clinical gout. Nociception is induced by the intra-articular injection of uric acid into the right hind limb, inducing its dysfunction. Animals then receive analgesic drugs and the recovery of functionality over time is assessed as an expression of antinociception. We have examined the role of peripheral prostaglandins synthesized by cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2) in inflammatory pain using the PIFIR model. Rofecoxib (a selective COX-2 inhibitor) and SC-560 (a selective COX-1 inhibitor) both produced dose-dependent effects. When the inhibitors were administered before uric acid, they showed similar potency, but the antinociceptive efficacy of SC-560 was lower than rofecoxib; the best antinociceptive effects were obtained with the dose of 100 microg/articulation of each inhibitor (pre-treatment). In post-treatment (inhibitors administered after the uric acid), rofecoxib showed the least antinociceptive effect and SC-560 was more potent than rofecoxib. The inhibition of both COX-1 and COX-2 produced a more profound analgesic effect than the inhibition of either COX-1 or COX-2 alone. The present data support the idea that both COX isoforms contribute to the development and maintenance of local inflammatory nociception. Thus, it could be expected that inhibition of both COX-1 and COX-2 is required for non-steroidal anti-inflammatory drugs (NSAID)-induced antinociception in the rat. These findings suggest that the therapeutic effects of NSAIDs may involve, at least in part, inhibition of COX-1 and COX-2.

Sildenafil increases diclofenac antinociception in the formalin test

The antinociceptive activity of an inhibitor of phosphodiesterase 5, alone or combined with diclofenac, was assessed in the formalin test. Local administration of diclofenac produced a significant antinociception in both phases of the formalin test in female Wistar rats. In contrast, 1-[4-ethoxy-3-(6,7-dihydro-1-methyl-7-oxo-3-propyl-1H-pyrazolo [3,4-d]pyrimidin-5-yl)phenylsulfonyl]-4-methyl piperazine (sildenafil, an inhibitor of phosphodiesterase 5) produced significant antinociception, only during the second phase of the formalin test. Non-effective doses of sildenafil (25-100 microg/paw) significantly increased the antinociceptive effect of an inactive dose of diclofenac (25 microg) in both phases of the test. The antinociception produced by the drugs alone or the combination was due to a local action, as its administration in the contralateral paw was ineffective. Since sildenafil is a potent and selective inhibitor of phosphodiesterase 5, our results suggest that this drug produced its antinociceptive activity, and increased that of diclofenac, probably through the inhibition of cyclic GMP degradation.

Effect of caffeine on antinociceptive action of ketoprofen in rats

BACKGROUND

To assess a possible synergistic antinociceptive interaction, the antinociceptive effects of ketoprofen (KET), and caffeine (CAF) administered either separately or in combinations were determined in a model of arthritic pain.

METHODS

Antinociceptive activity was assayed using "ellipsis pain-induced functional impairment in the rat" (PIFIR model). The antinociceptive efficacies were evaluated using several dose-response curves and time courses. The antinociceptive effects from the combination that produced the greater effect were compared with the maximal antinociceptive effect of either morphine, acetylsalicylic acid (ASA), or KET alone. The animals were administered with 0.05 mL intra-articular (i.a.) of uric acid to induce nociception. Groups of six rats received orally either ASA, morphine (MOR), KET, CAF, or a combination KET + CAF (24 combinations).

RESULTS

ASA (ED(50) 465.2 +/- 1.5 mg/kg), MOR (ED(50) 71.0 +/- 1.6 mg/kg), and KET (ED(50) 7.2 +/- 1.4 mg/kg) alone induced dose-dependent antinociception, whereas CAF alone showed no activity at the assayed doses. Nine combinations showed various degrees of potentiation (p <0.01), while the remainder exhibited the antinociceptive effect of KET only. Combinations of 17.8 mg/kg CAF with either 1.0, 1.8, 3.2, 5.6, or 10.0 mg/kg KET yielded the highest antinociceptive potentiations. For example, antinociceptive effect was 125.6 +/- 21.4 area units (au) with KET (3.2 mg/kg) alone, but the combination with CAF (17.8 mg/kg) showed 309.5 +/- 10.3 au. The median effective dose (ED(50)) of KET alone was 7.2 +/- 1.4 mg/kg, whereas the ED(50) of KET + CAF 17.8 mg/kg was 0.4 +/- 0.6 mg/kg: KET in the presence of CAF was approximately 18 times more potent than the analgesic drug without CAF.

CONCLUSIONS

These results showed that CAF was able to potentiate the analgesia of KET, but only at selected dose combinations: CAF in the doses of 10.0 and 17.8 mg/kg was able to potentiate the analgesic effect of KET, the most efficacious drug combination being CAF 17.8 mg/kg + KET 3.2 mg/kg. The combination of analgesic drugs and CAF can produce better antinociceptive effects than the analgesic drug alone. This knowledge will permit the selection of the therapeutically most effective combination ratio of drugs, employing lower doses of each drug.

Sildenafil produces antinociception and increases morphine antinociception in the formalin test

The antinociceptive activity of an inhibitor of phosphodiesterase 5 alone or combined with morphine was assessed in the formalin test. Local administration of 1-[4-ethoxy-3-(6, 7-dihydro-1-methyl-7-oxo-3-propyl-1H-pyrazolo [3, 4-d]pyrimidin-5-yl)phenylsulfonyl]-4-methyl piperazine (sildenafil, inhibitor of phosphodiesterase 5) produced a dose-dependent antinociceptive effect in the second phase of the formalin test in female Wistar rats. In contrast, morphine produced antinociception in both phases. Sildenafil significantly increased the morphine-induced antinociception. The antinociception produced by the drugs alone or combined was due to a local action, as its administration in the contralateral paw was ineffective. Pretreatment of the paws with N(G)-L-nitro-arginine methyl ester (L-NAME, nitric oxide (NO) synthesis inhibitor), 1H-[1,2, 4]-oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, guanylyl cyclase inhibitor) or naloxone blocked the effect of the combination. Results suggest that opioid receptors, NO and cyclic GMP are relevant in the combination-induced antinociception. In conclusion, sildenafil produced antinociception and increased that produced by morphine, probably through the inhibition of cyclic GMP degradation.

Evidence for the participation of the nitric oxide-cyclic GMP pathway in the antinociceptive action of meloxicam in the formalin test

The involvement of the nitric oxide-cyclic GMP pathway in the antinociceptive action of the cyclooxygenase-2 preferential inhibitor meloxicam was assessed in the rat formalin test. Rats received local pretreatment with saline or meloxicam and then 50 microl of dilute formalin (1%). Local administration of meloxicam produced a dose-dependent antinociception in the second phase of the formalin test. The antinociception produced by meloxicam was due to a local action as its administration in the contralateral paw was ineffective. Local pretreatment of the paws with saline or N(G)-D-nitro-arginine methyl ester (D-NAME) did not affect the antinociception produced by meloxicam. However, N(G)-L-nitro-arginine methyl ester (L-NAME, a NO synthesis inhibitor) or 1H-(1,2,4)-oxadiazolo(4,2-a)quinoxalin-1-one (ODQ, a soluble guanylyl cyclase inhibitor) blocked in a dose-dependent way the effect of meloxicam. It is concluded that the peripheral antinociceptive effect of meloxicam involves a local NO-cyclic GMP pathway.

A review of the pharmacokinetic and pharmacodynamic factors in the potentiation of the antinociceptive effect of nonsteroidal anti-inflammatory drugs by caffeine

Caffeine is an effective analgesic adjuvant because it increases the antinociceptive effect of NSAIDs while reducing the probability of side effects. The mechanism by which caffeine increases the antinociceptive action of NSAIDs does not appear to include a pharmacokinetic interaction. The potentiation appears to be due to a pharmacokinetic mechanism including actions at the central and the peripheral levels. Because caffeine shifts the effect-compartment concentration-effect relation of NSAIDs to the left and this relationship is sigmoidal, there is no potentiation if the NSAID concentrations are too high or too low with respect to EC(50). The best potentiation can be observed if the NSAID doses used yield effect-compartment concentrations in the vicinity of EC(50). Therefore further investigation of the PK/PD relations of caffeine-NSAID combinations for different pain states and intensities is needed to optimize the therapeutic use of these mixtures.

Evidence for the participation of the nitric oxide-cyclic GMP pathway in the antinociceptive effect of nimesulide

The involvement of the nitric oxide-cyclic GMP pathway in the peripheral antinociception induced by the COX-2 preferential inhibitor nimesulide was assessed by using the formalin test in the rat. Intraplantar administration of nimesulide in the formalin-injured paw produced a significant antinociceptive effect that was due to a local action, because nimesulide administration in the contralateral paw was ineffective. Local pretreatment of the paws with saline or N(G)-D-nitro-arginine methyl ester (D-NAME, the inactive isomer of L-NAME) did not affect the antinociception produced by nimesulide. However, local administration of L-NAME (a nitric oxide synthesis inhibitor) or 1H-(1,2,4)-oxadiazolo(4, 2-a)quinoxalin-1-one (ODQ, a soluble guanylyl cyclase inhibitor) blocked the effect of nimesulide. Moreover, the antinociceptive effect of local nimesulide was potentiated by the coadministration of 3-morpholino-sydnonimine-HCl (SIN-1, a nitric oxide donor). It is concluded that nimesulide produces antinociception by a peripheral mechanism of action requiring activation of the nitric oxide-cyclic GMP pathway at the local level.