Synergistic effect of cholecystokinin octapeptide and angiotensin II in reversal of morphine induced analgesia in rats

Shedding Light on the Pharmacological Interactions between μ-Opioid Analgesics and Angiotensin Receptor Modulators: A New Option for Treating Chronic Pain

The current protocols for neuropathic pain management include µ-opioid receptor (MOR) analgesics alongside other drugs; however, there is debate on the effectiveness of opioids. Nevertheless, dose escalation is required to maintain their analgesia, which, in turn, contributes to a further increase in opioid side effects. Finding novel approaches to effectively control chronic pain, particularly neuropathic pain, is a great challenge clinically. Literature data related to pain transmission reveal that angiotensin and its receptors (the AT1R, AT2R, and MAS receptors) could affect the nociception both in the periphery and CNS. The MOR and angiotensin receptors or drugs interacting with these receptors have been independently investigated in relation to analgesia. However, the interaction between the MOR and angiotensin receptors has not been excessively studied in chronic pain, particularly neuropathy. This review aims to shed light on existing literature information in relation to the analgesic action of AT1R and AT2R or MASR ligands in neuropathic pain conditions. Finally, based on literature data, we can hypothesize that combining MOR agonists with AT1R or AT2R antagonists might improve analgesia.

Analgesia for Sheep in Commercial Production: Where to Next?

Simple Summary

Increasing societal and customer pressure to provide animals with ‘a life worth living’ continues to apply pressure on industry to alleviate pain associated with husbandry practices, injury and illness. Although a number of analgesic solutions are now available for sheep, providing some amelioration of the acute pain responses, this review has highlighted a number of potential areas for further research.

Abstract

Increasing societal and customer pressure to provide animals with ‘a life worth living’ continues to apply pressure on livestock production industries to alleviate pain associated with husbandry practices, injury and illness. Over the past 15–20 years, there has been considerable research effort to understand and develop mitigation strategies for painful husbandry procedures in sheep, leading to the successful launch of analgesic approaches specific to sheep in a number of countries. However, even with multi-modal approaches to analgesia, using both local anaesthetic and non-steroidal anti-inflammatory drugs (NSAID), pain is not obliterated, and the challenge of pain mitigation and phasing out of painful husbandry practices remains. It is timely to review and reflect on progress to date in order to strategically focus on the most important challenges, and the avenues which offer the greatest potential to be incorporated into industry practice in a process of continuous improvement. A structured, systematic literature search was carried out, incorporating peer-reviewed scientific literature in the period 2000–2019. An enormous volume of research is underway, testament to the fact that we have not solved the pain and analgesia challenge for any species, including our own. This review has highlighted a number of potential areas for further research.

Effect of captopril, an angiotensin-converting enzyme inhibitor, on morphine analgesia and tolerance in rats, and elucidating the inflammation and endoplasmic reticulum stress pathway in this effect

The purpose of current study was to examine the possible involvement of captopril, an angiotensin-converting enzyme inhibitor, on nociception, morphine analgesia and morphine tolerance development involving inflammation and ER-stress pathways in rats. In this study, thirty-six male Wistar rats were used. Animals were divided into six groups: Saline, 50 mg/kg captopril, 5 mg/kg morphine, morphine + captopril, morphine tolerance and morphine tolerance + captopril. The resulting analgesic effect was measured with hot plate and tail flick analgesia tests. The dorsal root ganglions (DRG) tissues were collected for inflammation parameters, endoplasmic reticulum (ER) stress and apoptosis proteins by using ELISA. Captopril showed anti-nociceptive effect when given alone (p < 0.05 to p < 0.01). In addition, captopril increased the analgesic effect of morphine (p < 0.05 to p < 0.001) and also decreased the tolerance to morphine at a significant level (p < 0.05 to p < 0.001). However, it decreased inflammation and ER-stress when applied with single-dose morphine and tolerance induction (p < 0.001). Moreover, captopril decreased apoptosis proteins after tolerance development (p < 0.001). In conclusion, captopril has antinociceptive properties, increasing analgesic effect of morphine, and preventing tolerance development. These effects may occur by suppressing inflammation and ER-stress pathways.

Crosstalk between Opioid and Anti-Opioid Systems: An Overview and Its Possible Therapeutic Significance

Opioid peptides and receptors are broadly expressed throughout peripheral and central nervous systems and have been the subject of intense long-term investigations. Such studies indicate that some endogenous neuropeptides, called anti-opioids, participate in a homeostatic system that tends to reduce the effects of endogenous and exogenous opioids. Anti-opioid properties have been attributed to various peptides, including melanocyte inhibiting factor (MIF)-related peptides, cholecystokinin (CCK), nociceptin/orphanin FQ (N/OFQ), and neuropeptide FF (NPFF). These peptides counteract some of the acute effects of opioids, and therefore, they are involved in the development of opioid tolerance and addiction. In this work, the anti-opioid profile of endogenous peptides was described, mainly taking into account their inhibitory influence on opioid-induced effects. However, the anti-opioid peptides demonstrated complex properties and could show opioid-like as well as anti-opioid effects. The aim of this review is to detail the phenomenon of crosstalk taking place between opioid and anti-opioid systems at the in vivo pharmacological level and to propose a cellular and molecular basis for these interactions. A better knowledge of these mechanisms has potential therapeutic interest for the control of opioid functions, notably for alleviating pain and/or for the treatment of opioid abuse.

Role of angiotensin modulation in primary headaches

The renin-angiotensin system (RAS) is a major regulatory system controlling many different homeostatic mechanisms both within the brain and in the periphery. While it is primarily associated with blood pressure and salt/water regulation, increasing evidence points to the involvement of the RAS in both headache disorders specifically and pain regulation in general. Several publications have indicated that drugs blocking various elements of the renin-angiotensin system lead to a reduction in migraine. Additionally, interventions on different angiotensin peptides or their receptors have been shown to both reduce and increase pain in animal models. As such, modulation of the renin-angiotensin system is a promising approach to the treatment of headaches and other pain conditions.

Interplay between RAS and opioids: opening the Pandora of complexities

Angiotensin and endogenous opioids are important bioactive neuropeptides, which are widely distributed in the brain and peripheral regions to produce diverse biological and neurobiological activities. An endogenous opioid system includes proopiomelanocortin-derived enkephalin, dynorphin and endorphin that act on their specific receptors such as delta (δ), kappa (κ) and mu (μ) receptors. Research evidence demonstrates significant positive as well as negative interactions between renin angiotensin system (RAS) and endogenous opioids in the brain and periphery. The diverse actions of Ang II are possibly mediated indirectly through endogenous opioids, while opioids are also shown to activate RAS components suggesting the up-regulation of each system in concern with each other. On the contrary, there are reports suggesting a negative correlation between RAS and opioid system. Research evidence also supports the notion that Ang II acts as anti-opioid peptide to decrease the actions of opioids. Moreover, opioids-induced decline in angiotensin release and functioning has also been reported. Co-administration of ACE inhibitors with opioids exhibits significant interactions possibly due to decreased metabolism of opioids leading to potentiation of their actions. The present review describes the complexities of positive and negative interactions between RAS and opioids along with possible mechanisms responsible for these interactions.

Reactive oxygen species and autophagy associated apoptosis and limitation of clonogenic survival induced by zoledronic acid in salivary adenoid cystic carcinoma cell line SACC-83

Salivary adenoid cystic carcinoma is an epithelial tumor in the head and neck region. Despite its slow growth, patients with salivary adenoid cystic carcinoma exhibit poor long term survival because of a high rate of distant metastasis. Lung and bone are common distant metastasis sites. Zoledronic acid, a third generation bisphosphonate, has been used for tumor-induced osteolysis due to bone metastasis and has direct antitumor activity in several human neoplasms. Here, we observed that zoledronic acid inhibited salivary adenoid cystic carcinoma cell line SACC-83 xenograft tumor growth in nude mice. In vitro, zoledronic acid induced apoptosis and reduced clonogenic survival in SACC-83. Flow cytometry and western blotting indicated that the cell cycle was arrested at G0/G1. Zoledronic acid treatment upregulated reactive oxygen species as well as the autophagy marker protein LC-3B. Reactive oxygen species scavenger N-acetylcysteine and autophagy antagonist 3-methyladenine decreased zoledronic acid-induced apoptosis and increased clonogenic survival. Silencing of the autophagy related gene Beclin-1 also decreased zoledronic acid-induced apoptosis and inhibition of clonogenic formation. In addition, isobolographic analysis revealed synergistic effects on apoptosis when zoledronic acid and paclitaxel/cisplatin were combined. Taken together, our results suggest that zoledronic acid induced apoptosis and reduced clonogenic survival via upregulation of reactive oxygen species and autophagy in the SACC-83 cell line. Thus, zoledronic acid should be considered a promising drug for the treatment of salivary adenoid cystic carcinoma.

Effects of microinjection of angiotensin II and captopril to VTA on morphine self-administration in rats

The dopaminergic mesolimbic system is considered to be crucial in rewarding actions of opiates. Recent studies have suggested probable interaction between the renin-angiotensin and mesolimbic dopaminergic systems. The present study was undertaken to investigate the effects of Ang II and captopril injection into VTA on morphine self-administration. Male Wistar rats were initially trained to receive small pellets of food by pressing the active lever in self-administration apparatus. The animals were divided into 4 groups (saline, morphine, captopril and Ang II) and were placed in self-administration apparatus and allowed to self-administer morphine (0.5 mg per infusion all test groups) or saline (saline group) during consecutive days, for 2 h/sessions. Captopril (30 mug) and Ang II (0.25 nmol) were injected into the VTA in the corresponding groups before each session. The numbers of active and passive levers pressed in each group have been recorded. The number of active lever pressing of morphine group was significantly higher than saline group (p < 0.001). In Ang II group, the number of active lever pressing was significantly lower than morphine group (p < 0.01). This study suggests the probable interaction between Ang II and opioid system in the VTA.

Microinjection of angiotensin II in the caudal ventrolateral medulla induces hyperalgesia

Nociceptive transmission from the spinal cord is controlled by supraspinal pain modulating systems that include the caudal ventrolateral medulla (CVLM). The neuropeptide angiotensin II (Ang II) has multiple effects in the CNS and at the medulla oblongata. Here we evaluated the expression of angiotensin type 1 (AT(1)) receptors in spinally-projecting CVLM neurons, and tested the effect of direct application of exogenous Ang II in the CVLM on nociceptive behaviors. Although AT(1)-immunoreactive neurons occurred in the CVLM, only 3% of AT(1)-positive neurons were found to project to the dorsal horn, using double-immunodetection of the retrograde tracer cholera toxin subunit B. In behavioral studies, administration of Ang II (100 pmol) in the CVLM gave rise to hyperalgesia in both the tail-flick and formalin tests. This hyperalgesia was significantly attenuated by local administration of the AT(1) antagonist losartan. The present study demonstrates that Ang II can act on AT(1) receptors in the CVLM to modulate nociception. The effect on spinal nociceptive processing is likely indirect, since few AT(1)-expressing CVLM neurons were found to project to the spinal cord. The renin-angiotensin system may also play a role in other supraspinal areas implicated in pain modulation.

Neural mechanism underlying acupuncture analgesia

Acupuncture has been accepted to effectively treat chronic pain by inserting needles into the specific "acupuncture points" (acupoints) on the patient's body. During the last decades, our understanding of how the brain processes acupuncture analgesia has undergone considerable development. Acupuncture analgesia is manifested only when the intricate feeling (soreness, numbness, heaviness and distension) of acupuncture in patients occurs following acupuncture manipulation. Manual acupuncture (MA) is the insertion of an acupuncture needle into acupoint followed by the twisting of the needle up and down by hand. In MA, all types of afferent fibers (Abeta, Adelta and C) are activated. In electrical acupuncture (EA), a stimulating current via the inserted needle is delivered to acupoints. Electrical current intense enough to excite Abeta- and part of Adelta-fibers can induce an analgesic effect. Acupuncture signals ascend mainly through the spinal ventrolateral funiculus to the brain. Many brain nuclei composing a complicated network are involved in processing acupuncture analgesia, including the nucleus raphe magnus (NRM), periaqueductal grey (PAG), locus coeruleus, arcuate nucleus (Arc), preoptic area, nucleus submedius, habenular nucleus, accumbens nucleus, caudate nucleus, septal area, amygdale, etc. Acupuncture analgesia is essentially a manifestation of integrative processes at different levels in the CNS between afferent impulses from pain regions and impulses from acupoints. In the last decade, profound studies on neural mechanisms underlying acupuncture analgesia predominately focus on cellular and molecular substrate and functional brain imaging and have developed rapidly. Diverse signal molecules contribute to mediating acupuncture analgesia, such as opioid peptides (mu-, delta- and kappa-receptors), glutamate (NMDA and AMPA/KA receptors), 5-hydroxytryptamine, and cholecystokinin octapeptide. Among these, the opioid peptides and their receptors in Arc-PAG-NRM-spinal dorsal horn pathway play a pivotal role in mediating acupuncture analgesia. The release of opioid peptides evoked by electroacupuncture is frequency-dependent. EA at 2 and 100Hz produces release of enkephalin and dynorphin in the spinal cord, respectively. CCK-8 antagonizes acupuncture analgesia. The individual differences of acupuncture analgesia are associated with inherited genetic factors and the density of CCK receptors. The brain regions associated with acupuncture analgesia identified in animal experiments were confirmed and further explored in the human brain by means of functional imaging. EA analgesia is likely associated with its counter-regulation to spinal glial activation. PTX-sesntive Gi/o protein- and MAP kinase-mediated signal pathways as well as the downstream events NF-kappaB, c-fos and c-jun play important roles in EA analgesia.

Decreased spinal cord opioid receptor mRNA expression and antinociception in a Theiler's murine encephalomyelitis virus model of multiple sclerosis

Multiple sclerosis patients typically experience increased pain that is relatively insensitive to opiate treatment. The mechanistic basis for this increased nociception is currently poorly understood. In the present study, we utilized the Theiler's murine encephalomyelitis virus (TMEV) model of MS to examine possible changes in spinal cord opioid receptor mRNA over the course of disease progression. TMEV infection led to significantly decreased mu, delta and kappa opioid receptor mRNA expression as analyzed by quantitative real-time PCR in both male and female mice at days 90, 150 and 180 post-infection (PI). Since opioid receptor mRNA expression decreased in TMEV mice, we examined whether opiate analgesia is also altered. TMEV infected female mice had significantly decreased opiate analgesia in thermal nociceptive tests beginning at day 90 PI, while TMEV-infected male mice did not display significantly decreased opiate analgesia until day 120 PI. The novel finding that opioid receptor expression is significantly decreased in the spinal cord of TMEV mice could explain the increased nociception and loss of opiate analgesia observed in both TMEV mice and multiple sclerosis patients.

Angiotensin converting enzyme inhibitor captopril modifies conditioned place preference induced by morphine and morphine withdrawal signs in rats

Angiotensin II and angiotensin converting enzyme (ACE) inhibitors have analgesic, anticonvulsant and antidepressive effects and in some cases they can antagonize morphine. In the present study effects of angiotensin II and ACE inhibitor captopril administered intracerobroventricularily (icv) on conditioned place preference induced by morphine as well as on morphine withdrawal signs has been evaluated in rats. Icv canullas were implanted in anesthetized male rats. Rats were allowed to recover from the surgery and conditioned place preference was induced by morphine, and the time spent in morphine compartment was compared in saline, morphine, captopril and Ang II groups. Morphine withdrawal signs were compared in three other groups of rats: morphine alone, captopril+morphine and Ang II+morphine 4 days after morphine injections (three times in each day) with naloxone injection on 4th day. Results with rats conditioned place preference induced by morphine showed that icv captopril decreased significantly the time in morphine compartment (P<0.01) while Ang II had no effect. In morphine dependent rats captopril decreased some withdrawal signs after naloxone precipitation (P<0.05 and P<0.01). Ang II administration augmented some of withdrawal signs than in the morphine group (P<0.01 and P<0.001). In conclusion captopril reduced conditioned place preference induced by morphine and some withdrawal signs in morphine dependent rats.

Peripheral participation of cholecystokinin in the morphine-induced peripheral antinociceptive effect in non-diabetic and diabetic rats

The effects of cholecystokinin (CCK-8) and the CCK receptor antagonist proglumide, on antinociception induced by local peripheral (subcutaneous) injected morphine in non-diabetic (ND) and streptozotocin-induced diabetic (D) rats, were examined by means of the formalin test. Morphine induced dose-dependent antinociception both in ND and D rats. However, in D rats, antinociceptive morphine potency was about twofold less than in ND rats. Pre-treatment with CCK-8 abolished the antinociceptive effect of morphine in a dose-dependent manner in both groups of rats. Additionally, proglumide enhanced the antinociceptive effect induced by all doses of morphine tested. Both CCK-8 and proglumide had no effect on flinching behaviour when given alone to ND rats. Unlike ND rats, in D rats proglumide produced dose-dependent antinociception and CCK-8 enhanced formalin-evoked flinches, as observed during the second phase of the test. In conclusion, our data show a decrease in peripheral antinociceptive potency of morphine when diabetes was present. Additionally, peripheral CCK plays an antagonic role to the peripheral antinociceptive effect of morphine, additional to the well known CCK/morphine interaction at spinal and supraspinal level.

The effects of sarmesin, an Angiotensin II analogue on seizure susceptibility, memory retention and nociception

The present research studies the effects of sarmesin [Sar(1)Tyr(OMe)(4)] Angiotensin II (ANG II), an analogue of ANG II, on the seizure susceptibility, memory activity and nociception. It was found that this octapeptide, administered i.c.v., dose-dependently decreased the seizure intensity (pentylenetetrazol (PTZ) generalized seizure model and PTZ kindling) and augmented PTZ seizure threshold in mice. Sarmesin impaired the memory upon re-testing of rats 24 h later in the passive avoidance test. It decreased the pain threshold in a paw pressure nociceptive assay in rats. ANG II exerted pronociceptive effect as well. Taken together, these results reveal sarmesin as a behaviorally active peptide in the studied experimental animal models.

Interaction of angiotensin II and adenosine A1 and A2A receptor ligands on the writhing test in mice

The effects of adenosine A1 and A2A receptor agonists and antagonists administered intraperitoneally (i.p.) and their interaction with angiotensin II (Ang II) administered intracerebroventricularly (i.c.v.) were studied in mice using the acetic acid-induced abdominal constriction test. Ang II (0.1 microg/mouse) induced antinociception in this model. The adenosine A1 receptor agonist N6-cyclopentyladenosine (CPA; 0.05, 0.25 and 0.5 mg/kg) also showed a well-developed antinociceptive effect. Ang II (0.1 microg/mouse) administered 5 min before CPA (0.25 mg/kg) decreased the number of writhes, i.e., it enhanced the antinociceptive effect of CPA. Losartan, an AT1 receptor antagonist (25 microg/mouse i.c.v.), enhanced the antinociceptive effect of CPA, while the AT2 receptor antagonist 1-[-4-(dimethylamino)-3-methylphenylmethyl]-5-diphenylacetyl)-4,5,6,7-tetrahydro 1H-4-imidazol [4,5c]pyridine-6 carboxylic acid, ditrifluoroacetate, dihydrate (PD 123319; 10 microg/mouse) had less effect. 8-Cyclopentyl-1,3-dipropylxanthine (DPCPX; 0.1 mg/kg), an adenosine A1 receptor antagonist, exhibited a pronociceptive effect and did not change the antinociceptive effect of Ang II. The adenosine A2A receptor agonist PD-125944 (DPMA; 0.1, 0.5 and 1 mg/kg) showed pronounced antinociceptive effect. Ang II (0.1 microg/mouse) did not significantly influence the antinociceptive effect of DPMA (0.1 mg/kg). The A2A receptor antagonist 3,7-dimethyl-1-propargilxanthine (DMPX; 0.1 mg/kg) had no effect on the number of writhes and did not influence the effect of Ang II. These data indicate that the antinociceptive effect of Ang II interacts with that produced by adenosine A1 receptor agonist.