Effect of drugs modulating serotonergic system on the analgesic action of paracetamol in mice

Effect of Ethanol Extract of Soursop (Annona muricata L.) Stem Bark on Rat Liver Function

<b>Background and Objective:</b> Paracetamol does not cause toxic effects if given in therapeutic doses, namely below 4 g per day. Use of paracetamol at a dose of more than 4 g per day can result in hepatotoxicity. This study aims to compare the hepatoprotector potency of the ethanol extract of soursop stem bark (<i>A. muricata</i>) against the enzyme activity of SGOT and SGPT in rats induced by toxic doses of paracetamol. <b>Materials and Methods:</b> A Completely Randomized Design (CRD) comprised of 6 treatment groups and 3 replications. Total 27 white male rats were induced hepatotoxicity with 1350 mg of paracetamol on the 7th day, except for normal control (K0) which was given aquadest. The tested animals received akuades as the negative control (K-) 11.34 mg kg¹ b.wt., of Hepa-Q as the positive control (K+), ethanol extract stem bark <i>Annona muricata</i> at a dose of 150 mg kg¹ BB (P1), 300 mg kg¹ BB (P2) and 600 mg kg¹ BB (P3). <b>Results:</b> There was a significant difference (p<0.05) in the levels of SGOT and SGPT after giving ethanol extract of soursop (<i>A. muricata</i>) stem bark. The best treatment for reducing SGOT and SGPT levels in rats induced by paracetamol was the administration of ethanol extract of <i>A. muricata</i> stem bark at a dose of 600 mg kg¹ BB. <b>Conclusion:</b> Based on the results of the study, it was concluded that all ethanol extract of <i>Annona muricata</i> L. stem bark (EEAMSB) doses had the potential to reduce the levels of AST and ALT in paracetamol-induced rats.

Systematic Review of Systemic and Neuraxial Effects of Acetaminophen in Preclinical Models of Nociceptive Processing

Acetaminophen (APAP) in humans has robust effects with a high therapeutic index in altering postoperative and inflammatory pain states in clinical and experimental pain paradigms with no known abuse potential. This review considers the literature reflecting the preclinical actions of acetaminophen in a variety of pain models. Significant observations arising from this review are as follows: 1) acetaminophen has little effect upon acute nociceptive thresholds; 2) acetaminophen robustly reduces facilitated states as generated by mechanical and thermal hyperalgesic end points in mouse and rat models of carrageenan and complete Freund’s adjuvant evoked inflammation; 3) an antihyperalgesic effect is observed in models of facilitated processing with minimal inflammation (eg, phase II intraplantar formalin); and 4) potent anti-hyperpathic effects on the thermal hyperalgesia, mechanical and cold allodynia, allodynic thresholds in rat and mouse models of polyneuropathy and mononeuropathies and bone cancer pain. These results reflect a surprisingly robust drug effect upon a variety of facilitated states that clearly translate into a wide range of efficacy in preclinical models and to important end points in human therapy. The specific systems upon which acetaminophen may act based on targeted delivery suggest both a spinal and a supraspinal action. Review of current targets for this molecule excludes a role of cyclooxygenase inhibitor but includes effects that may be mediated through metabolites acting on the TRPV1 channel, or by effect upon cannabinoid and serotonin signaling. These findings suggest that the mode of action of acetaminophen, a drug with a long therapeutic history of utilization, has surprisingly robust effects on a variety of pain states in clinical patients and in preclinical models with a good therapeutic index, but in spite of its extensive use, its mechanisms of action are yet poorly understood.

Nanotechnology for Pain Management: Current and Future Therapeutic Interventions

Pain is one of the most common medical conditions and affects more Americans than diabetes, heart disease, and cancer combined. Current pain treatments mainly rely on opioid analgesics and remain unsatisfactory. The life-threatening side effects and addictive properties of opioids demand new therapeutic approaches. Nanomedicine may be able to address these challenges as it allows for sensitive and targeted treatments without some of the burdens associated with current clinical pain therapies. This review discusses the physiology of pain, the current landscape of pain treatment, novel targets for pain treatment, and recent and ongoing efforts to effectively treat pain using nanotechnology-based approaches. We highl ight advances in nanoparticle-based drug delivery to reduce side effects, gene therapy to tackle the source of pain, and nanomaterials-based scavenging to proactively mediate pain signaling.

Paracetamol (acetaminophen): A familiar drug with an unexplained mechanism of action

Paracetamol (acetaminophen) is undoubtedly one of the most widely used drugs worldwide. As an over-the-counter medication, paracetamol is the standard and first-line treatment for fever and acute pain and is believed to remain so for many years to come. Despite being in clinical use for over a century, the precise mechanism of action of this familiar drug remains a mystery. The oldest and most prevailing theory on the mechanism of analgesic and antipyretic actions of paracetamol relates to the inhibition of CNS cyclooxygenase (COX) enzyme activities, with conflicting views on the COX isoenzyme/variant targeted by paracetamol and on the nature of the molecular interactions with these enzymes. Paracetamol has been proposed to selectively inhibit COX-2 by working as a reducing agent, despite the fact that in vitro screens demonstrate low potency on the inhibition of COX-1 and COX-2. In vivo data from COX-1 transgenic mice suggest that paracetamol works through inhibition of a COX-1 variant enzyme to mediate its analgesic and particularly thermoregulatory actions (antipyresis and hypothermia). A separate line of research provides evidence on potentiation of the descending inhibitory serotonergic pathway to mediate the analgesic action of paracetamol, but with no evidence of binding to serotonergic molecules. AM404 as a metabolite for paracetamol has been proposed to activate the endocannabinoid and the transient receptor potential vanilloid-1 (TRPV1) systems. The current review gives an update and in some cases challenges the different theories on the pharmacology of paracetamol and raises questions on some of the inadequately explored actions of paracetamol. List of Abbreviations: AM404, N-(4-hydroxyphenyl)-arachidonamide; CB1R, Cannabinoid receptor-1; Cmax, Maximum concentration; CNS, Central nervous system; COX, Cyclooxygenase; CSF, Cerebrospinal fluid; ED50, 50% of maximal effective dose; FAAH, Fatty acid amidohydrolase; IC50, 50% of the maximal inhibitor concentration; LPS, Lipopolysaccharide; NSAIDs, Non-steroidal anti-inflammatory drugs; PGE2, Prostaglandin E2; TRPV1, Transient receptor potential vanilloid-1.

The Contribution of Serotonergic Receptors and Nitric Oxide Systems in the Analgesic Effect of Acetaminophen: An Overview of the Last Decade

Acetaminophen is a widely used analgesic and antipyretic agent. It is also available in over the counter formulations, which has increased its wide use. There have been many studies to date that have aimed to evaluate the mechanism of the analgesic action of acetaminophen. Additional to the inhibition of the cyclooxygenase pathway in the central nervous system, the involvement of opioidergic, cannabinoidergic, dopaminergic, cholinergic, and nitrergic systems as well as the contribution of descending pain inhibitory systems like the bulbospinal serotonergic pathway has been proposed as possible mechanisms of the analgesic action of acetaminophen. In this review, we aimed to collect the data from studies revealing the contribution of the central serotonergic system and the role of central nervous system-located serotonergic receptor subtypes in the analgesic effect of acetaminophen. While doing this, we mainly focused on the research that has been performed in the last ten years and tried to link the previous data with the lately added results. In addition to serotonergic system involvement, we also reviewed the role of nitric oxide in the analgesic action of acetaminophen, especially with the new findings reported over the last decade.

Dose related effects of buspirone on pain, learning / memory and food intake

The present study concerned extending the therapeutic use of buspirone for treating pain and improving cognition. Effects of single and repeated administration of buspirone were therefore monitored on pain threshold in the hot plate test and on spatial memory in the water maze test in rats. Effects on cumulative food intake were also monitored. The drug was administered intraperitoneally in doses of 0.1, 0.3, 1.0 and 2.0 mg/kg. We found that single and repeated administration of buspirone in doses of 0.1 mg/kg decreased pain threshold in the hot plate test, while doses of 1.0 and 2.0 mg/kg increased it. Effects of single and repeated administration were not different. A dose of 0.3 mg/kg had no effect. Food intake increased following single as well as repeated administration of 0.1 mg/kg buspirone; higher doses had no effect. Low doses (0.1 and 0.3 mg/kg) improved acquisition and retention of memory in the water maze test, while memory extinction was reduced. Higher doses had either no effect (1.0 mg/kg) or impaired (2.0 mg/kg) performance in this test. The results suggest potential therapeutic use of selected doses of buspirone as an analgesic and nootropic drug.

Central dopaminergic system plays a role in the analgesic action of paracetamol: Preclinical evidence

Objective:

Even after 100 years of discovery, the exact mechanisms for the analgesic action of paracetamol are under scanner. It was recently proposed that paracetamol may act through different mechanisms, especially altering the serotoninergic system. The main objective of this preclinical study was to verify the role of drugs modulating dopaminergic system (l-dopa, bromocriptine, olanzapine) on the analgesic effect of paracetamol.

Materials and Methods:

Thirty adult male albino mice were divided into five groups: distilled water (0.5 ml/25 g), paracetamol (200 mg/kg), levodopa (10 mg/kg) + paracetamol, bromocriptine (5 mg/kg) + paracetamol (200 mg/kg), and olanzapine (2 mg/kg) + paracetamol (200 mg/kg). All drugs were administered orally for 14 days. Eddy's hot plate and tail immersion tests were used to determine analgesic activity. Tests were conducted 1 h after the drug administration on the 14^th day. After that, animals were sacrificed and brains were dissected out, to measure the levels of dopamine. Statistical comparisons among the groups were performed by one-way analysis of variance followed by Tukey-Kramer test.

Results:

Coadministration of l-dopa and bromocriptine with paracetamol increased the antinociceptive activity of paracetamol significantly, whereas coadministration of olanzapine with paracetamol decreased the analgesic activity of paracetamol in the Eddy's hot plate and tail immersion tests considerably. There was a significant increase (P < 0.001) in the levels of dopamine in the brains of mice, which received levodopa, bromocriptine, and paracetamol. However, it was opposite in the brains of animals which received olanzapine.

Conclusion:

The results suggest that analgesic action of paracetamol is influenced by dopaminergic system.