Serotonin and opiate involvement in the antinociceptive effect of acetylsalicylic acid

Combination Drug Therapy for the Management of Chronic Neuropathic Pain

Chronic neuropathic pain (NP) is an increasingly prevalent disease and leading cause of disability which is challenging to treat. Several distinct classes of drugs are currently used for the treatment of chronic NP, but each drug targets only narrow components of the underlying pathophysiological mechanisms, bears limited efficacy, and comes with dose-limiting side effects. Multimodal therapies have been increasingly proposed as potential therapeutic approaches to target the multiple mechanisms underlying nociceptive transmission and modulation. However, while preclinical studies with combination therapies showed promise to improve efficacy over monotherapy, clinical trial data on their efficacy in specific populations are lacking and increased risk for adverse effects should be carefully considered. Drug-drug co-crystallization has emerged as an innovative pharmacological approach which can combine two or more different active pharmaceutical ingredients in a single crystal, optimizing pharmacokinetic and physicochemical characteristics of the native molecules, thus potentially capitalizing on the synergistic efficacy between classes of drugs while simplifying adherence and minimizing the risk of side effects by reducing the doses. In this work, we review the current pharmacological options for the treatment of chronic NP, focusing on combination therapies and their ongoing developing programs and highlighting the potential of co-crystals as novel approaches to chronic NP management.

Preemptive Analgesic and Antioxidative Effect of Curcumin for Experimental Migraine

OBJECTIVE

Our study aimed to investigate the analgesic and antioxidative stress effects of Curcumin (CC) in experimental migraine induced by Nitroglycerin (NTG) on rats, compared with Indomethacin (ID) and Propranolol (PP) treatments.

MATERIAL AND METHODS

Five groups of 10 rats treated i.p. were investigated: control group (healthy rats) injected with saline solution (0.9%), NTG-control group injected with NTG (1 mg/100 gbw, bw = body weight), and three groups with pretreatment applied 30 min previous to the formalin test (NTG + CC group: Curcumin (10 mg/100 gbw), NTG + PP group: Propranolol (100 μg/100 gbw), and NTG + ID group: Indomethacin (0.5 mg/100 gbw)). Formalin test was performed and number of flinches and shakes were counted. Several oxidative stress parameters were also assessed.

RESULTS

The smallest values of malondialdehyde (MDA), nitric oxide (NOx), and total oxidative status (TOS) were observed on NTG + CC with significant differences as compared with the control group (p < 0.0001). The group pretreated with Curcumin proved significantly smaller number of flinches and shakes compared with both NTG + PP and NTG + ID.

CONCLUSION

Our study demonstrates a superior activity of Curcumin not only versus control, but also versus Propranolol and Indomethacin.

Roles of serotonergic and adrenergic receptors in the antinociception of selective cyclooxygenase-2 inhibitor in the rat spinal cord

Background

The analgesic mechanisms of cyclooxygenase (COX)-2 inhibitors have been explained mainly on the basis of the inhibition of prostaglandin biosynthesis. However, several lines of evidence suggest that their analgesic effects are mediated through serotonergic or adrenergic transmissions. We investigated the roles of these neurotransmitters in the antinociception of a selective COX-2 inhibitor at the spinal level.

Methods

DUP-697, a selective COX-2 inhibitor, was delivered through an intrathecal catheter to male Sprague-Dawley rats to examine its effect on the flinching responses evoked by formalin injection into the hindpaw. Subsequently, the effects of intrathecal pretreatment with dihydroergocristine, prazosin, and yohimbine, which are serotonergic, α1 adrenergic and α2 adrenergic receptor antagonists, respectively, on the analgesia induced by DUP-697 were assessed.

Results

Intrathecal DUP-697 reduced the flinching response evoked by formalin injection during phase 1 and 2. But, intrathecal dihydroergocristine, prazosin, and yohimbine had little effect on the antinociception of intrathecal DUP-697 during both phases of the formalin test.

Conclusions

Intrathecal DUP-697, a selective COX-2 inhibitor, effectively relieved inflammatory pain in rats. Either the serotonergic or adrenergic transmissions might not be involved in the analgesic activity of COX-2 inhibitors at the spinal level.

NSAIDs, Opioids, Cannabinoids and the Control of Pain by the Central Nervous System

Nonsteroidal anti-inflammatory drugs (NSAIDs) act upon peripheral tissues and upon the central nervous system to produce analgesia. A major central target of NSAIDs is the descending pain control system. The rostral structures of the descending pain control system send impulses towards the spinal cord and regulate the transmission of pain messages. Key structures of the descending pain control system are the periaqueductal gray matter (PAG) and the rostral ventromedial region of the medulla (RVM), both of which are critical targets for endogenous opioids and opiate pharmaceuticals. NSAIDs also act upon PAG and RVM to produce analgesia and, if repeatedly administered, induce tolerance to themselves and cross-tolerance to opioids. Experimental evidence shows that this is due to an interaction of NSAIDs with endogenous opioids along the descending pain control system. Analgesia by NSAIDs along the descending pain control system also requires an activation of the CB1 endocannabinoid receptor. Several experimental approaches suggest that opioids, NSAIDs and cannabinoids in PAG and RVM cooperate to decrease GABAergic inhibition and thus enhance the descending flow of impulses that inhibit pain.

Mechanisms of non-opioid analgesics beyond cyclooxygenase enzyme inhibition

Non-opioid analgesics including both selective and non-selective cyclooxygenase (COX) inhibitors and acetaminophen are the most widely used treatments for pain. Inhibition of COX is thought to be largely responsible for both the therapeutic and adverse effects of this class of drugs. Accumulating evidence over the past two decades has demonstrated effects of non-opioids beyond the inhibition of COX and prostaglandin synthesis that might also explain their therapeutic and adverse effects. These include their interaction with endocannabinoids, nitric oxide, monoaminergic, and cholinergic systems. Moreover, the recent development of microarray technology that allows the study of human gene expression suggests multiple pathways that may be related to the analgesic and anti-inflammatory effects of non-opioids. The present review will discuss the multiple actions of non-opioids and their interactions with these systems during inflammation and pain, suggesting that COX inhibition is an incomplete explanation for the actions of non-opioids and proposes the involvement of multiple selective targets for their analgesic, as well as, their adverse effects.

Increased activity of serotonin uptake in platelets in medication overuse headache following regular intake of analgesics and triptans

We investigated the effect of chronic administration of different pain medications on the activity of the serotonin transporter (SERT) in patients with medication overuse headache (MOH). We measured the kinetic of platelet 5-HT uptake (maximal velocity, V_max and the Michaelis–Menten constant, K_m) in patients with overuse of triptans (tMOH, n = 15) or analgesics (aMOH, n = 14) before and after drug withdrawal, as well as in headache-free healthy subjects (n = 15) and patients with episodic migraine (EM, n = 16). V_max was increased similarly in both, tMOH and aMOH compared to healthy subjects and patients with EM and normalized after withdrawal in parallel to the improvement of headache frequency. Average K_m was similar in all groups at baseline and not affected by the withdrawal. The data demonstrate a transient increase of SERT activity in patients with analgesic and triptan induced MOH but do not allow to differentiate whether the increase of serotonin uptake is caused by regular intake of analgesics or triptans or is a consequence of frequent headache attacks.

Chronic Subarachnoid Administration of 1-(4chlorobenzoyl)-5methoxy-2methyl-1H-indole-3 Acetic Acid (Indomethacin): An Evaluation of Its Neurotoxic Effects in an Animal Model

Neuraxial administration of nonsteroid antiinflammatory drugs has been suggested as an alternative in the management of intractable pain, but there is little evidence that the neurotoxic effects of indomethacin by this route of administration have been evaluated. In this study, we evaluated histological neurotoxicity of indomethacin after its subarachnoid administration in guinea pigs. The hypothesis tested was "Does subarachnoid administration of indomethacin produce damage in the spinal cord of guinea pigs?" Ten male guinea pigs were anesthetized, and a polyamide catheter connected to a subcutaneous osmotic micro-pump was implanted at the L2-3 level. Animals were randomly assigned in 2 groups of 5 animals each. Indomethacin or saline solution was administered by continuous infusion (0.5 microL/h) for 14 days. Neurotoxicity was determined by spinal cord histopathology. There was no evidence of toxicity in the histological examinations of either group. These data suggest that subarachnoid administration of indomethacin infusion, at these doses, did not produce lesions typical of neurotoxicity in the spinal cord. We have concluded that epidural administration of indomethacin may be considered an alternative for application in human pain management, although more studies to determine its safety are required.

Peripheral and spinal mechanisms of antinociceptive action of lumiracoxib

The possible participation of the nitric oxide (NO)-cyclic GMP-K(+) channel pathway, serotonergic or opioidergic system on lumiracoxib-induced local or intrathecal antinociception was assessed in the formalin test. Local or intrathecal administration of lumiracoxib dose-dependently produced antinociception in the second phase of the test. Moreover, local or intrathecal pretreatment with N(G)-L-nitro-arginine methyl ester (L-NAME, NO synthesis inhibitor), 1H-(1,2,4)-oxadiazolo(4,2-a)quinoxalin-1-one (ODQ, guanylyl cyclase inhibitor), glibenclamide (ATP-sensitive K(+) channel blocker), charybdotoxin and apamin (large- and small-conductance Ca(2+)-activated-K(+) channel blockers, respectively) or margatoxin (voltage-dependent K(+) channel blocker), but not N(G)-D-nitro-arginine methyl ester (D-NAME) or vehicle, significantly prevented lumiracoxib-induced antinociception. The intrathecal injection of methiothepin (serotonin receptor antagonist) reduced lumiracoxib-induced intrathecal antinociception. Local peripheral or intrathecal naloxone did not modify either local or intrathecal lumiracoxib-induced antinociception. Results suggest that lumiracoxib activates the NO-cyclic GMP-K(+) channels to produce local and intrathecal antinociception. Data also suggest that lumiracoxib activates the intrathecal serotonergic system, but not opioid receptors either at peripheral or spinal sites.

Spinal serotonergic system is partially involved in antinociception induced by Trigonella foenum-graecum (TFG) leaf extract

It has been reported that Trigonella foenum-graecum (TFG) extract exerts analgesic, anti-inflammatory and anti-pyretic effects in different experimental models. The major objective of this paper was to investigate the site and mechanism of the analgesia induced by Trigonella foenum-graecum extract. We studied the analgesic effects of different doses of Trigonella foenum-graecum extract after i.p., i.t. and i.c.v. administration in formalin test, using male NMRI rats (200-250 g). Trigonella foenum-graecum extract showed analgesic effects in i.p. (1 g/kg) and i.t. (0.5, 1, and 2 mg/rat) (P < 0.05 in all groups) but not in i.c.v. (1 and 3 mg/rat) administrations. Based on the similarities between the effects of Trigonella foenum-graecum extract with those of nonsteroidal anti-inflammatory drugs (NSAIDs) and the role of 5-HT system in analgesic effects of NSAIDs, we tried to investigate the role of spinal 5-HT system in analgesic effects of Trigonella foenum-graecum extract. After lesioning of spinal 5-HT system by 5,7-dihydroxytryptamine (5,7-DHT), it was shown that the analgesic effect of Trigonella foenum-graecum extract (0.5 and 3 mg/rat) in the second phase of formalin test, was abolished completely and reduced relatively after using a low-dose (0.5 mg/rat) and a high-dose (3 mg/rat), respectively (P < 0.05). So, the antinociception partially remained (P < 0.05) after using the latter dose. Meanwhile, administration of naloxone (2mg/kg, i.p.) had no effect on the Trigonella foenum-graecum extract (1 g/kg, i.p.) analgesia. In conclusion, this study confirms the central action of Trigonella foenum-graecum extract and that spinal 5-HT system is partially involved in the analgesia induced by it in the second phase of formalin test and also indicates for co-existence of other analgesic mechanism(s).

Evidence for a central mechanism of action of S-(+)-ketoprofen

It has been observed that some non-steroidal anti-inflammatory drugs (NSAIDs) may act through several mechanisms, in addition to central inhibition of prostaglandin synthesis. These other mechanisms include the L-arginine-nitric oxide (L-arginine-NO) pathway, as well as endogenous opiate and serotonergic mechanisms. Some of these mechanisms can explain the efficacy of NSAIDs in chronic pain conditions such as rheumatoid arthritis. The present study was designed to elucidate the involvement of the above pathways/mechanisms in the antinociceptive effect of S-(+)-ketoprofen at supraspinal and spinal levels. S-(+)-ketoprofen induced dose-dependent antinociception in the pain-induced functional impairment model in the rat. The antinociceptive effect of S-(+)-ketoprofen was not altered by i.t. or intracerebroventricula (i.c.v.) pre-treatment with L-arginine (29.6 microg/site) and L-nitro-arginine-monomethylester (L-NAME) (21.1 microg/site) and neither was the effect of S-(+)-ketoprofen modified by the opiate antagonist, naloxone (1 mg/kg, s.c.). In marked contrast, both i.c.v. administration of the 5-hydroxytryptamine (5-HT)(1)/5-HT(2)/5-HT(7) receptor antagonist, methiothepin (1.5 microg/site), and i.t. administration of the 5-HT(3)/5-HT(4) receptor antagonist, tropisetron (0.9 microg/site), significantly inhibited the S-(+)-ketoprofen-induced antinociceptive effect. These data suggest that the antinociceptive response to S-(+)-ketoprofen involves serotoninergic mechanisms via both supraspinal 5-HT(1)/5-HT(2)/5-HT(7) receptors and 5-HT(3) receptors located at spinal level. A role of the L-arginine-NO and opiate systems in S-(+)-ketoprofen-induced antinociception in the pain-induced functional impairment model in the rat model seems unlikely.

Chronic daily headache: a scientist's perspective

Certain features of chronic daily headache, namely, increased headache frequency, expansion of headache area, and cutaneous allodynia, may imply sensitization of central nociceptive neurons in the trigeminal pathway. Repetitive activation of the trigeminal nerve can lead to a biologic and functional change in trigeminal nucleus caudalis neurons, characterized by a decrease in nociceptive threshold and receptive field expansion. Suppression of the endogenous pain control system can facilitate the process of central sensitization. Evidence of such suppression in patients with chronic daily headache includes decreased platelet serotonin, up-regulation of 5-HT2A receptors, increased platelet nitric oxide production, and increased levels of substance P and nerve growth factor in the cerebrospinal fluid. Results from a number of animal experiments have indicated that chronic analgesic exposure leads to changes in serotonin content and density of 5-HT2A receptors in the central nervous system. This plasticity of the serotonin-dependent pain control system may accelerate the process of sensitization; a biologic outcome that is expressed clinically by the development of chronic daily headache associated with analgesic overuse.

Nitroglycerin-induced activation of monoaminergic transmission in the rat

When administered to migraine patients, nitroglycerin induces a spontaneous-like migraine attack, with a latency of several hours. Nitroglycerin acts directly and/or indirectly on the central nervous system, through the release of nitric oxide (NO). Systemic administration of the drug to the rat causes neuronal activation in selected subcortical areas, particularly in monoaminergic nuclei of the brainstem. In this study, we sought to investigate whether this activation correlates with changes in monoaminergic neurotransmission. For this purpose, we evaluated the tissue levels of catecholamines and serotonin in the hypothalamus, mesencephalon, pons and medulla of rats treated with systemic nitroglycerin or vehicle, at different time points (1, 2 and 4 h). We also evaluated the peripheral sympathetic response to the drug by measuring the concentrations of plasma catecholamines. Nitroglycerin caused an early (1 h) increase in cerebral (pons) and plasma levels of norepinephrine, followed by a delayed (4 h) decrease in medullary and pontine levels of serotonin. The initial noradrenergic activation may reflect the autonomic response to the rapid cardiovascular effects of the drug, while the delayed response may result from the interaction of nitroglycerin-released NO and 5-HT in central areas devoted to the modulation of nociception. These data might therefore help to clarify the mechanisms underlying the delayed migraine attack observed in migraine sufferers after systemic administration of nitroglycerin.

Pathophysiology of chronic daily headache

Despite no clear explanation of the mechanism underlying chronic daily headache, sensitization of central nociceptive neurons is one possibility. Either prolonged activation of peripheral nociceptors or any factors that can alter the endogenous pain control system can trigger this process. A decrease in platelet serotonin has been observed in patients with chronic tension-type headache as well as migraine patients with medication-induced headache. It was also shown that chronic analgesic exposure led to changes in the serotonin content and the density of the 5-HT(2A) receptor in the cerebral cortex. The plasticity of the serotonin-dependent pain control system may facilitate the process of sensitization and results in the development of chronic daily headache.

Are there predictive factors for long-term outcome after withdrawal in drug-induced chronic daily headache?

OBJECTIVES

To investigate prognostic factors for long-term outcome of patients after inpatient withdrawal because of drug-induced chronic daily headache.

PROCEDURES

Fifty-five patients (36 females) were re-examined by means of a standardized interview after inpatient withdrawal. The mean observation period was 9.28 +/- 2.85 years (mean +/- SD; median 8.58; range 5.00-13.50).

RESULTS

Five years after withdrawal, one-third of the patients (34.6%) had an overall favourable outcome, one-third (32.7%) had no recurrent drug overuse and reported a clear-cut improvement of headache, and one-third (32.7%) developed recurrent drug overuse. Most relapses occurred within 2 years, and a small percentage within 5 years. No predictors for long-term outcome after inpatient withdrawal were found.

CONCLUSIONS

All patients with drug-induced chronic daily headache should be considered as good candidates for inpatient withdrawal, and no patient should be excluded from that therapy.

[Aspirin, pain and inflammation]

SUBJECT

Acetylsalicylic acid (ASA) is among the most commonly analgesic, antipyretic and anti-inflammatory used drugs. The anti-inflammatory effects of ASA are mediated by the inhibition of cyclooxygenase enzymes with the subsequent decrease of prostaglandin synthesis.

NEW DATA

However, since this discovery of Vane in 1971, much of other mechanisms of anti-inflammatory action, without relation with cyclooxygenases, have been proposed. ASA has peripheric analgesic properties by reducing prostaglandin biosynthesis. But there is evidence that the analgesic effects could be mediated by central mechanisms with changes in the monoaminergic and opioid systems. ASA is essentially used in moderate pains with an inflammatory component (rheumatological disorders, headaches, dental and postoperative pains).

PERSPECTIVES

The clinical use of ASA at anti-inflammatory dose is less frequent because the other non steroidal anti-inflammatory drugs are as effective as ASA, but they are associated with less side effects. Nevertheless, the synergism of ASA and morphine association and the possible involvement of the central serotonergic and opiatergic systems in the antinociceptive activity of ASA could confer a greater role of ASA in pain management.

Acetylsalicylic acid potentiates the antinociceptive effect of morphine in the rat: involvement of the central serotonergic system

Acetylsalicylic acid and morphine are the most widely distributed and most frequently used drugs in the relief of pain, but their analgesic activity has adverse side-effects. Mixtures containing these two drugs are frequently used to relieve mild to moderate pain despite the paucity of relevant experimental evidence so far published. We set out to study the possible antinociceptive effect of a combination of subactive doses of the two drugs in rats. A combination of low doses of acetylsalicylic acid (50 mg/kg i.p.) and morphine (3 mg/kg s.c.) was administered and the pain threshold was evaluated in the hot-plate and formalin tests, and 5-HT2 receptor binding capacity, 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) levels were measured in the cortex and pontine areas of the brain. The combination of acetylsalicylic acid and morphine had an analgesic effect in both tests that was associated with an increase in 5-HT levels and a decrease in 5-HT2 receptors in the cortex. These effects were either completely abolished or partially prevented by i.p. pretreatment with naloxone (1 mg/kg i.p.). Our results demonstrate that subactive doses of acetylsalicylic acid and morphine can exert analgesic and biochemical effects when given in combination in the rat and suggest an involvement of serotonergic and opiatergic systems.

Pineal opioid receptors and analgesic action of melatonin

Physicians have noted since antiquity that their patients complained of less pain and required fewer analgesics at night times. In most species, including the humans, the circulating levels of melatonin, a substance with analgesic and hypnotic properties, exhibit a pronounced circadian rhythm with serum levels being high at night and very low during day times. Moreover, melatonin exhibits maximal analgesic effects at night, pinealectomy abolishes the analgesic effects of melatonin, and mu opioid receptor antagonists disrupt the day-night rhythm of nociception. It is believed that melatonin, with its sedative and analgesic effects, is capable of providing a pain free sleep so that the body may recuperate and restore itself to function again at its peak capacity. Moreover, in conditions when pain is associated with extensive tissue injury, melatonin's ability to scavenge free radicals and abort oxidative stress is yet another beneficial effect to be realized. Since melatonin may behave as a mixed opioid receptor agonist-antagonist, it is doubtful that a physician simply could potentiate the analgesic efficacy of narcotics such as morphine by coadministering melatonin. Therefore, future research may synthesize highly efficacious melatonin analogues capable of providing maximum analgesia and hopefully being devoid of addiction liability now associated with currently available narcotics.