Monoclonal Antibodies for Chronic Pain Treatment: Present and Future.

Chronic pain remains a major problem worldwide, despite the availability of various non-pharmacological and pharmacological treatment options. Therefore, new analgesics with novel mechanisms of action are needed. Monoclonal antibodies (mAbs) are directed against specific, targeted molecules involved in pain signaling and processing pathways that look to be very effective and promising as a novel therapy in pain management. Thus, there are mAbs against tumor necrosis factor (TNF), nerve growth factor (NGF), calcitonin gene-related peptide (CGRP), or interleukin-6 (IL-6), among others, which are already recommended in the treatment of chronic pain conditions such as osteoarthritis, chronic lower back pain, migraine, or rheumatoid arthritis that are under preclinical research. This narrative review summarizes the preclinical and clinical evidence supporting the use of these agents in the treatment of chronic pain.

New cannabinoid receptor antagonists as pharmacological tool.

Synthesis and pharmacological evaluation of a new series of cannabinoid receptor antagonists of indazole ether derivatives have been performed. Pharmacological evaluation includes radioligand binding assays with [3H]-CP55940 for CB1 and CB2 receptors and functional activity for cannabinoid receptors on isolated tissue. In addition, functional activity of the two synthetic cannabinoids antagonists 18 (PGN36) and 17 (PGN38) were carried out in the osteoblastic cell line MC3T3-E1 that is able to express CB2R upon osteogenic conditions. Both antagonists abolished the increase in collagen type I gene expression by the well-known inducer of bone activity, the HU308 agonist. The results of pharmacological tests have revealed that four of these derivatives behave as CB2R cannabinoid antagonists. In particular, the compounds 17 (PGN38) and 18 (PGN36) highlight as promising candidates as pharmacological tools.

Characterization of the nociceptive effect of carrageenan: Masseter versus gastrocnemius.

INTRODUCTION: To better understand the pathophysiology of chronic muscle pain, there are multiple animal models that mimic different acute/chronic pain conditions, such as carrageenan injection. Our previous studies demonstrated differences between muscles of different innervation in acute pain. In this study we characterized the effect of carrageenan in 2 muscles: masseter (trigeminal innervation) and gastrocnemius (spinal innervation). METHODS: Carrageenan (3%, 6%, and 9%) was injected into the masseter and gastrocnemius of rats. Mechanical, heat, and chemical nociceptive thresholds were measured for 14 days. RESULTS: Carrageenan did not induce mechanical allodynia or thermal hypersensitivity in either muscle. Instead, it induced a short-lasting mechanical hyperalgesia, greater in the masseter than in the gastrocnemius. CONCLUSION: Carrageenan injected into the masseter and gastrocnemius induces a short-lasting hyperalgesia. These results could indicate a higher susceptibility of orofacial muscles to this type of insult and, consequently, a difference between trigeminal and spinal innervation. Muscle Nerve 56: 804-813, 2017.

Promising biomedical subcutaneous delivery system in opioid disaccustom process: In vitro/in vivo evaluation of naloxone microparticles on antagonist effect of morphine.

The addiction induced by the misuse of opioids, is not only a public health emergency but also a social and economic welfare. The main therapy is based on opioid antagonists. Oral and injectable naltrexone administration is the most widely used, presenting some inconveniences: poor patient adherence to the oral daily dosing schedule, cases of hepatitis and clinically significant liver dysfunction. This study proposes the in vitro e in vivo evaluation of anti-opioid properties of naloxone loaded-poly(lactic-co-glycolic) acid microparticles (NX-MP). In previous studies, NX-MP showed in vitro sustained naloxone release for one week at least. Our results demonstrate the in vitro efficacy of the NX-MP antagonizing for 7 days the morphine effect in SH-SY5Y cells and myenteric plexus-longitudinal muscle preparations isolated from guinea-pig ileum. The in vivo evaluation of the NX-MP was carried out in mice testing the antagonism of the antinociceptive effect of morphine. Results showed that subcutaneous administration of NX-MP blocked the morphine effect. The results of this work suggest that the subcutaneous administration of NX-MP enhances naloxone therapeutic efficacy as non-addictive medication and could be a promising alternative to naltrexone. Furthermore, the dose of NX-MP can be adapted to the patient necessities. It would be an interesting advantage to treat opioid-addiction.

SGK1.1 isoform is involved in nociceptive modulation, offering a protective effect against noxious cold stimulus in a sexually dimorphic manner.

The serum and glucocorticoid-regulated kinase 1 (SGK1) is a widely expressed protein in the Central Nervous System (CNS), involved in regulating the activity of a wide variety of ion channels and transporters and physiological functions, such as neuronal excitability. SGK1.1 is a neuronal splice isoform of SGK1, expressed exclusively in the CNS, distributed in brain and cerebellum, that decreases neuronal excitability via up-regulation of M-current, linked to Kv7.2/3 potassium channels. Strategies to maintain increased SGK1.1 activity could be helpful in decreasing neuronal hyperexcitability, as occurs in neuropathic pain. Transgenic mice overexpressing SGK1.1 (B6.Tg.sgk1) offer a particularly relevant opportunity to assess the physiological involvement of this protein in nociception. Behavior and physiological nociception were evaluated in male and female B6.Tg.sgk1 and wild-type mice (B6.WT), characterizing nociceptive thresholds to different nociceptive stimuli (thermal, chemical and mechanical), as well as the electrophysiological properties of cutaneous sensory Aδ-fibres isolated from the saphenous nerve. The acute antinociceptive effect of morphine was also evaluated. Compared with B6.WT animals, male and female B6.Tg.sgk1 mice showed increased spontaneous locomotor activity. Regarding nociception, there were no differences between transgenic and wild-type mice in heat, chemical and mechanical thresholds, but interestingly, male B6.Tg.sgk1 mice were less sensitive to cold stimulus; B6.Tg.sgk1 animals showed lower sensitivity to morphine. Electrophysiological properties of cutaneous primary afferent fibres were maintained. This is the first demonstration that the SGK1.1 isoform is involved in nociceptive modulation, offering a protective effect against noxious cold stimulus in a sexually dimorphic manner. B6.Tg.sgk1 mice offer a particularly relevant opportunity to further analyze the involvement of this protein in nociception, and studies in models of chronic, neuropathic pain are warranted.

Involvement of central and peripheral cannabinoid receptors on antinociceptive effect of tetrahydrocannabinol in muscle pain.

Cannabinoid (CB) receptors have emerged as an attractive therapeutic target for pain management in recent years and the interest in the use of cannabinoids is gradually increasing, particularly in patients where conventional treatments fail. Muscle pain is a major clinical problem and new pharmacological approaches are being studied. Recently, we have demonstrated that cannabinoid synthetic agonists are useful to reduce muscular pain in two animal models, where the local administration is effective. Now, we want to know if tetrahydrocannabinol (THC), a cannabinoid natural derivative with therapeutic use in humans, is also effective in reducing acute muscle pain. The antinociceptive effect of THC by systemic (i.p.) and local (i.m.) administration was tested in two animal models of acute muscle pain, rat masseter and gastrocnemius, induced by hypertonic saline (HS) injection. The drugs used were the non-selective agonist THC and two selective cannabinoid antagonists, AM251 (CB1) and AM630 (CB2). THC, i.p. and i.m. administered, reduced the nociceptive behaviours induced by HS in both muscular pain models. The antinociceptive effect induced by the systemic administration of THC was mediated by CB1 receptors in the masseter muscle whereas in gastrocnemius both CB1 and CB2 receptors participated. When THC was administered locally, only CB2 receptors were involved in the antinociceptive effect in both muscles. This study suggests that THC could be a future pharmacological option in the treatment of muscle pain. The local administration of THC could be an interesting option to treat this type of pain avoiding the central adverse effects.