Endogenous opioids are involved in morphine and dipyrone analgesic potentiation in the tail flick test in rats

Inherent Dangers of Using Non-US Food and Drug Administration-Approved Substances of Abuse

Use of US Food and Drug Administration-approved substances of abuse has innate risks due to pharmacologic and pharmacokinetic properties of the medications, but the risk when using nonapproved drug products is much greater. Unbeknownst to the user, the dose of active ingredients in substances of abuse can vary substantially between different products because of manufacturing practices or improper storage. Even naturally occurring substances of abuse can have extensive dosage variability because of effects of the growing season and conditions, or differences in harvesting, storage, or manufacture of the finished products. Many illicit substances are adulterated, to make up for intentional underdosing or to enhance the effect of the intended active ingredient. These adulterants can be dangerous and produce direct cardiovascular, neurologic, hematologic, or dermatologic reactions or obscure adverse effects. Finally, an illicit substance can be contaminated or substituted for another one during its manufacture, leading to differences in adverse events, adverse event severity, or the drug interaction profile. Substances can be contaminated with microbes that induce infections or heavy metals that can damage organs or cause cancer. This milieu of undisclosed substances can also induce drug interactions. For reasons that are discussed, individuals who use substances of abuse are at increased risk of morbidity or mortality if they develop coronavirus disease 2019. Health professionals who treat patients with acute, urgent events associated with substances of abuse, or those treating the chronic manifestations of addiction, need to appreciate the complex and variable composition of substances of abuse and their potential health effects.

Design, Synthesis, and Biological Evaluation of the Third Generation 17-Cyclopropylmethyl-3,14β-dihydroxy-4,5α-epoxy-6β-[(4'-pyridyl)carboxamido]morphinan (NAP) Derivatives as μ/κ Opioid Receptor Dual Selective Ligands

μ opioid receptor (MOR) agonists have been widely applied for treating moderate to severe pain. However, numerous adverse effects have been associated with their application, including opioid-induced constipation (OIC), respiratory depression, and addiction. On the basis of previous work in our laboratory, NAP, a 6β- N-4'-pyridyl substituted naltrexamine derivative, was identified as a peripheral MOR antagonist that may be used to treat OIC. To further explore its structure-activity relationship, a new series of NAP derivatives were designed, synthesized, and biologically evaluated. Among these derivatives, NFP and NYP significantly antagonized the antinociception effect of morphine. Whereas NAP acted mainly peripherally, its derivatives NFP and NYP actually can act centrally. Furthermore, NFP produced significantly lesser withdrawal symptoms than naloxone at similar doses. These results suggest that NFP has the potential to be a lead compound to treat opioid abuse and addiction.

Antinociceptive tolerance to NSAIDs in the anterior cingulate cortex is mediated via endogenous opioid mechanism

BACKGROUND

In the past decade several studies have reported that in some brain areas, particularly, in the midbrain periaqueductal gray matter, rostral ventro-medial medulla, central nucleus of amygdala, nucleus raphe magnus, and dorsal hippocampus, microinjections of non-steroidal anti-inflammatory drugs (NSAIDs) induce antinociception with distinct development of tolerance. Given this evidence, in this study we investigated the development of tolerance to the analgesic effects of NSAIDs diclofenac, ketorolac and xefocam microinjected into the rostral part of anterior cingulate cortex (ACC) in rats.

METHODS

Male Wistar experimental and control (saline) rats were implanted with a guide cannula in the ACC and tested for antinociception following microinjection of NSAIDs into the ACC in the tail-flick (TF) and hot plate (HP) tests. Repeated measures of analysis of variance with post-hoc Tukey-Kramer multiple comparison tests were used for statistical evaluations.

RESULTS

Treatment with each NSAID significantly enhanced the TF and HP latencies on the first day, followed by a progressive decrease in the analgesic effect over a 4-day period, i.e., developed tolerance. Pretreatment with an opioid antagonist naloxone completely prevented the analgesic effects of the three NSAIDs in both behavioral assays.

CONCLUSIONS

These findings support the concept that the development of tolerance to the antinociceptive effects of NSAIDs is mediated via an endogenous opioid system possibly involving descending pain modulatory systems.

Antinociceptive tolerance to NSAIDs in the agranular insular cortex is mediated by opioid mechanism

Several lines of investigations have shown that in some brain areas, in particular, in the midbrain periaqueductal gray matter, rostral ventromedial medulla, central nucleus of amygdala, nucleus raphe magnus, and dorsal hippocampus, microinjections of nonsteroidal anti-inflammatory drugs (NSAIDs) induce antinociception with distinct development of tolerance. The agranular insular cortex (AIC) is a small region of the cerebral cortex located on the lateral area of the rat’s cerebral hemisphere that is involved in the perception and response to pain. In the present study, we investigated the development of tolerance to the analgesic effects of NSAIDs diclofenac, ketorolac, and xefocam microinjected into the AIC in rats. Male Wistar rats receiving NSAIDs into the AIC were tested for antinociception by tail-flick and hot plate tests. Treatment with each NSAID significantly enhanced the tail-flick and hot plate latencies on the first day, followed by a progressive decrease in the analgesic effect over a 4-day period, ie, they developed tolerance. Pretreatment with an opioid antagonist naloxone completely prevented, and posttreatment naloxone abolished, the analgesic effects of the three NSAIDs in both behavioral assays. These findings support the notion that the development of tolerance to the antinociceptive effects of NSAIDs is mediated via an endogenous opioid system possibly involving descending pain modulatory systems.

Antinociceptive tolerance to NSAIDs in the rat formalin test is mediated by the opioid mechanism

BACKGROUND

In the past decade it has been shown that tolerance develops to the antinociceptive effect of repeated systemic administration of commonly used non-steroidal anti-inflammatory drugs (NSAIDs) in acute pain models using rats. This is similar to the tolerance observed with opioid-induced analgesia. In the present study, we investigated the development of tolerance to the analgesic effects of NSAIDs diclofenac, ketorolac and xefocam in a chronic inflammatory pain model, the formalin test.

METHODS

Male Wistar rats receiving intraplantar formalin were tested for antinociception following intraperitoneal injection of NSAIDs in thermal paw withdrawal (Hargreaves) test and mechanical paw withdrawal (von Frey) test. Repeated measures analysis of variance with post-hoc Tukey-Kramer multiple comparison tests were used for statistical evaluations.

RESULTS

Treatment with each NSAID significantly elevated the thermal paw withdrawal latency and mechanical paw withdrawal threshold on the first day, followed by a progressive decrease in the analgesic effect over a 4-day period, i.e., tolerance developed. With daily intraplantar injections of formalin, there was a trend toward reduced antinociceptive effects of diclofenac and ketorolac while xefocam exhibited a significant reduction (tolerance). It is noteworthy that the NSAID tolerant groups of rats still exhibited a strong hyperalgesia during phase I formalin following administration of each NSAID, an effect not observed in non-tolerant rats. Pretreatment with naloxone completely prevented the analgesic effects of these three NSAIDs in both behavioral assays.

CONCLUSIONS

The present findings support the notion that the development of tolerance to the antinociceptive effects of NSAIDs in an inflammatory pain model is mediated via an endogenous opioid system possibly involving descending pain modulatory systems.

Metamizole (dipyrone) effects on sevoflurane requirements and postoperative hyperalgesia in rats

Unlike non-steroidal anti-inflammatory drugs (NSAIDs), metamizole has poor anti-inflammatory effects; and is suitable for models where analgesia, but not anti-inflammatory effects, is desirable. Like opioids, these drugs produce perioperative analgesia while reducing anaesthetic requirements, but it remains unclear whether they may develop tolerance or hyperalgesia, and thus decrease in analgesic efficacy. The aim was to determine whether tolerance or hyperalgesia to metamizole occurred in rats, and whether the sevoflurane minimum alveolar concentration (MAC) was affected. In a randomized, prospective, controlled study, male Wistar rats ( n = 8 per group) were administered metamizole (300 mg/kg, day 4). Previously, the following treatments were provided: daily metamizole for four days (0-3), morphine (10 mg/kg; positive control, day 0 only) or saline (negative control). The main outcome measures were mechanical (MNT) and warm thermal (WNT) nociceptive quantitative sensory thresholds. The baseline sevoflurane MAC and the reduction produced by the treatments were also determined. The mean (SD) baseline MAC [2.4(0.2)%vol] was decreased by morphine and metamizole by 45(11)% and 33(7)% ( P = 0.000, both), respectively. Baseline MNT [35.4(4.5) g] and WNT [13.2(2.4) s] were decreased by morphine and metamizole: MNT reduction of 22(6)% ( P = 0.000) and 22(7)% ( P = 0.001), respectively and WNT reduction of 34(14)% ( P = 0.000) and 24(13)% ( P = 0.001). The baseline MAC on day 4 was neither modified by treatments nor the MAC reduction produced by metamizole (days 0 and 4; P > 0.05). In conclusion, repeated metamizole administration may produce hyperalgesia, although it may not modify its anaesthetic sparing effect. The clinical relevance of this effect in painful research models requiring prolonged analgesic therapy warrants further investigation.

Alkynylation of heterocyclic compounds using hypervalent iodine reagent

The alkynylation of various nitrogen- and/or sulphur-containing heterocyclic compounds using hypervalent iodine TMS-EBX by utilization of tertiary amines under mild conditions is described. The developed metal-free methodology furnishes the corresponding alkynylated heterocycles bearing quaternary carbon in high yields.

Injectable liposomal formulations of opiorphin as a new therapeutic strategy in pain management

BACKGROUND

Conventional and PEGylated liposomes were developed, aimed at improving the pain-killing effect of opiorphin.

METHODS

The antinociceptive action of the formulations was investigated on rats (tail-flick test), and compared with that of opiorphin and morphine aqueous solutions (all at 5 mg/kg).

RESULTS

Opiorphin loading in conventional liposomes enabled a 28% AUC increase with respect to free peptide. PEGylated liposomes provided AUC values 80, 60 and 40% higher than free peptide, morphine and opiorphin-loaded conventional liposomes, respectively. Moreover, opiorphin entrapment in PEGylated liposomes increased analgesic effect duration by more than 50%. These results were attributed to the greater effectiveness of PEGylated liposomes in protecting the drug and prolonging its circulation time.

CONCLUSION

Opiorphin-loaded PEGylated-liposomes can represent a valid alternative to morphine in pain management.

Tolerance effects of non-steroidal anti-inflammatory drugs microinjected into central amygdala, periaqueductal grey, and nucleus raphe: Possible cellular mechanism

Pain is a sensation related to potential or actual damage in some tissue of the body. The mainstay of medical pain therapy remains drugs that have been around for decades, like non-steroidal anti-inflammatory drugs (NSAIDs), or opiates. However, adverse effects of opiates, particularly tolerance, limit their clinical use. Several lines of investigations have shown that systemic (intraperitoneal) administration of NSAIDs induces antinociception with some effects of tolerance. In this review, we report that repeated microinjection of NSAIDs analgin, clodifen, ketorolac and xefocam into the central nucleus of amygdala, the midbrain periaqueductal grey matter and nucleus raphe magnus in the following 4 days result in progressively less antinociception compared to the saline control testing in the tail-flick reflex and hot plate latency tests. Hence, tolerance develops to these drugs and cross-tolerance to morphine in male rats. These findings strongly support the suggestion of endogenous opioid involvement in NSAIDs antinociception and tolerance in the descending pain-control system. Moreover, the periaqueductal grey-rostral ventro-medial part of medulla circuit should be viewed as a pain-modulation system. These data are important for human medicine. In particular, cross-tolerance between non-opioid and opioid analgesics should be important in the clinical setting.

Contribution of nociceptin/orphanin FQ receptors to the anti-nociceptive and hypothermic effects of dipyrone

BACKGROUND

Dipyrone is one of the most commonly used non-opioid analgesic and antipyretic drug. Its anti-nociceptive and hypothermic effects have long been suspected to be centrally mediated. The involvement of the most recently discovered opioid peptide, nociceptin/orphanin FQ (N/OFQ), and its receptor (NOP) in pain transmission is controversial. It appears to be pro-nociceptive when administered supra-spinally, but exerts anti-nociceptive effects when injected spinally or systemically.

OBJECTIVE

Investigation of the role of the N/OFQ system in paracetamol-induced anti-nociception and hypothermia led us to determine its role in the anti-nociceptive and hypothermic effects of dipyrone. Material and Methods Hot-plate and tail-flick tests were used to assess nociception, and a rectal thermometer was used to measure rectal temperature in mice.

RESULTS

Mice injected with dipyrone (150, 300, 600 mg/kg, i.p.) displayed dose-related anti-nociception and hypothermia. The NOP receptor antagonist JTC-801 (3 mg/kg, i.p.), at a dose that exerted no effect when used alone, alleviated dipyrone-induced anti-nociception but did not reverse dipyrone-induced hypothermia.

CONCLUSION

We conclude that NOP receptors participate in the anti-nociceptive, but not in the hypothermic, effects of dipyrone.

Is Hippocampus Susceptible to Antinociceptive Tolerance to NSAIDs Like the Periaqueductal Grey?

Emotional distress is the most undesirable feature of painful experience. Numerous studies have demonstrated the important role of the limbic system in the affective-motivational component of pain. The purpose of this paper was to examine whether microinjection of nonsteroidal anti-inflammatory drugs (NSAIDs), Clodifen, Ketorolac, and Xefocam, into the dorsal hippocampus (DH) leads to the development of antinociceptive tolerance in male rats. We found that microinjection of these NSAIDs into the DH induces antinociception as revealed by a latency increase in the tail-flick (TF) and hot plate (HP) tests compared to controls treated with saline into the DH. Subsequent tests on consecutive three days, however, showed that the antinociceptive effect of NSAIDs progressively decreased, suggesting tolerance developed to this effect of NSAIDs. Both pretreatment and posttreatment with the opioid antagonist naloxone into the DH significantly reduced the antinociceptive effect of NSAIDs in both pain models. Our data indicate that microinjection of NSAIDs into the DH induces antinociception which is mediated via the opioid system and exhibits tolerance.

Antinociceptive tolerance to NSAIDs microinjected into dorsal hippocampus

Background

Pain is characterized as a complex experience, dependent not only on the regulation of nociceptive sensory systems, but also on the activation of mechanisms that control emotional processes in limbic brain areas such as the amygdala and the hippocampus. Several lines of investigations have shown that in some brain areas, particularly the midbrain periaqueductal gray matter, rostral ventro-medial medulla, central nucleus of amygdala and nucleus raphe magnus, microinjections of non-steroidal anti-inflammatory drugs (NSAIDs) induce antinociception with distinct development of tolerance. The present study was designed to examine whether microinjection of NSAIDs, clodifen, ketorolac and xefocam into the dorsal hippocampus (DH) leads to the development of antinociceptive tolerance in male rats.

Methods

The experiments were carried out on experimental and control (with saline) white male rats. Animals were implanted with a guide cannula in the DH and tested for antinociception following microinjection of NSAIDs into the DH in the tail-flick (TF) and hot plate (HP) tests. Repeated measures of analysis of variance with post-hoc Tukey-Kramer multiple comparison tests were used for statistical evaluations.

Results

We found that microinjection of these NSAIDs into the DH induces antinociception as revealed by a latency increase in the TF and HP tests compared to controls treated with saline into the DH. Subsequent tests on days 2 and 3, however, showed that the antinociceptive effect of NSAIDs progressively decreased, suggesting tolerance developed to this effect of NSAIDs. Both pretreatment and post-treatment with the opioid antagonist naloxone into the DH significantly reduced the antinociceptive effect of NSAIDs in both pain models.

Conclusions

Our results indicate that microinjection of NSAIDs into the DH induces antinociception which is mediated via the opioid system and exhibits tolerance.

Tolerance to Non-Opioid Analgesics is Opioid Sensitive in the Nucleus Raphe Magnus

Repeated injection of opioid analgesics can lead to a progressive loss of effect. This phenomenon is known as tolerance. Several lines of investigations have shown that systemic, intraperitoneal administration or the microinjection of non-opioid analgesics, non-steroidal anti-inflammatory drugs (NSAIDs) into the midbrain periaqueductal gray matter induces antinociception with some effects of tolerance. Our recent study has revealed that microinjection of three drugs analgin, ketorolac, and xefocam into the central nucleus of amygdala produce tolerance to them and cross-tolerance to morphine. Here we report that repeated administrations of these NSAIDs into the nucleus raphe magnus (NRM) in the following 4 days result in progressively less antinociception compare to the saline control, i.e., tolerance develops to these drugs in male rats. Special control experiments showed that post-treatment with the μ-opioid antagonist naloxone into the NRM significantly decreased antinociceptive effects of NSAIDs on the first day of testing in the tail-flick (TF) reflex and hot plate (HP) latency tests. On the second day, naloxone generally had trend effects in both TF and HP tests and impeded the development of tolerance to the antinociceptive effect of non-opioid analgesics. These findings strongly support the suggestion of endogenous opioid involvement in NSAIDs antinociception and tolerance in the descending pain-control system. Moreover, repeated injections of NSAIDs progressively lead to tolerance to them, cross-tolerance to morphine, and the risk of a withdrawal syndrome. Therefore, these results are important for human medicine too.

Flurbiprofen axetil enhances analgesic effect of fentanyl associated with increase in β-endorphin levels

PURPOSE

To examine the analgesic effect of preoperative administration of flurbiprofen axetil and that of postoperative administration of a combination of flurbiprofen axetil and fentanyl, as well as perioperative plasma β-endorphin (β-EP) levels in patients undergoing esophagectomy.

METHODS

Forty-five patients were randomly divided into three groups: group A: 100 mg flurbiprofen axetil preoperative, 10 μg/kg fentanyl + 10 ml placebo postoperative; group B: 100 mg flurbiprofen axetil preoperative, 10 μg/kg fentanyl + 100 mg flurbiprofen axetil postoperative; group C: 10 ml placebo preoperative, 10 μg/kg fentanyl + 10 ml placebo postoperative. Postoperative analgesia was achieved by intravenous infusion containing flurbiprofen axetil and/or fentanyl at 2.0 ml/h (total volume, 100 ml) using infusion pumps. The β-EP was measured at preanesthesia (T(1)), the end of surgery (T(2)), 24 h (T(3)), and 48 h (T(4)) after surgery. Visual analog scale scores (VAS) at T3, T4 (at rest), and rescue analgesic tramadol requirement was recorded.

RESULTS

The VAS of group B was significantly lower than group A and C (P < 0.01) at T(3) and T(4). The β-EP levels at T(2)-T(4) in group A did not differ significantly from those at T(1) (P > 0.05); however, the β-EP levels in group B at T(3)-T(4) increased significantly (P < 0.05), while those in group C increased at T(2) and decreased at T(4) (P < 0.05). The β-EP levels in group B at T(3) and T(4) were the highest as compared to its levels in groups A and C (P < 0.01). Tramadol consumption in group B was significantly lower than in groups A and C (P < 0.01).

CONCLUSION

These results show that flurbiprofen axetil enhances the analgesic effect of fentanyl associated with increase in β-EP levels.

Diaqua-bis[2,5-dichloro-N-(1,5-dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4-yl)benzene-sulfonamidato-κN]zinc(II)

In the title compound, [Zn(C(17)H(14)Cl(2)N(3)O(3)S)(2)(H(2)O)(2)], the Zn(II) ion has a tetra-hedral coordination formed by the two N atoms of the sulfonamide groups and the two water mol-ecules. Two inter- and two intra-molecular O-H⋯O hydrogen bonds are observed in the crystal structure.

Endogenous opiates and behavior: 2006

This paper is the 29th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning 30 years of research. It summarizes papers published during 2006 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurological disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).