Antinociceptive interaction of (±)-CPP and propentofylline in monoarthritic rats

Microglia polarization in nociplastic pain: mechanisms and perspectives

Nociplastic pain is the third classification of pain as described by the International Association for the Study of Pain (IASP), in addition to the neuropathic and nociceptive pain classes. The main pathophysiological mechanism for developing nociplastic pain is central sensitization (CS) in which pain amplification and hypersensitivity occur. Fibromyalgia is the prototypical nociplastic pain disorder, characterized by allodynia and hyperalgesia. Much scientific data suggest that classical activation of microglia in the spinal cord mediates neuroinflammation which plays an essential role in developing CS. In this review article, we discuss the impact of microglia activation and M1/M2 polarization on developing neuroinflammation and nociplastic pain, besides the molecular mechanisms engaged in this process. In addition, we mention the impact of microglial modulators on M1/M2 microglial polarization that offers a novel therapeutic alternative for the management of nociplastic pain disorders. Illustrating the mechanisms underlying microglia activation in central sensitization and nociplastic pain. LPS lipopolysaccharide, TNF-α tumor necrosis factor-α, INF-γ Interferon gamma, ATP adenosine triphosphate, 49 P2Y12/13R purinergic P2Y 12/13 receptor, P2X4/7R purinergic P2X 4/7 receptor, SP Substance P, NK-1R Neurokinin 1 receptor, CCL2 CC motif ligand 2, CCR2 CC motif ligand 2 receptor, CSF-1 colony-stimulating factor 1, CSF-1R colony-stimulating factor 1 receptor, CX3CL1 CX3C motif ligand 1, CX3XR1 CX3C motif ligand 1 receptor, TLR toll-like receptor, MAPK mitogen-activated protein kinases, JNK jun N-terminal kinase, ERK extracellular signal-regulated kinase, iNOS Inducible nitric oxide synthase, IL-1β interleukin-1β, IL-6 interleukin-6, BDNF brain-derived neurotrophic factor, GABA γ-Aminobutyric acid, GABAR γ-Aminobutyric acid receptor, NMDAR N-methyl-D-aspartate receptor, AMPAR α-amino-3-hydroxy-5-methyl-4-isoxazolepropi-onic acid receptor, IL-4 interleukin-4, IL-13 interleukin-13, IL-10 interleukin-10, Arg-1 Arginase 1, FGF fibroblast growth factor, GDNF glial cell-derived neurotrophic factor, IGF-1 insulin-like growth factor-1, NGF nerve growth factor, CD Cluster of differentiation.

Inhibition of Connexin 43 and Phosphorylated NR2B in Spinal Astrocytes Attenuates Bone Cancer Pain in Mice

Bone cancer pain (BCP) is common in patients with advanced cancers when the tumors are metastasized to bone. The limited understanding of the complex pathogenesis of BCP leads to the poor effectiveness of clinical treatment. Previous studies have shown that astrocyte-specific connexin (Cx) 43, a forming protein of gap junction (GJ) and hemichannel, and N-methyl-D-aspartate receptors (NMDARs), especially the phosphorylated NMDAR 2B subunit (NR2B) phosphorylated NR2B (p-NR2B) subunit are involved in BCP. However, the relationship between Cx43 and p-NR2B in BCP remains unclear. In the present study, we investigated the expressions of Cx43, glial fibrillary acidic protein (GFAP, a marker of astrocytes), and p-NR2B in the spinal dorsal horn (SDH) in a mouse model of BCP established by intra-femural inoculation of Lewis lung carcinoma (LLC) cells via intrathecal (ith) injection of the GJ/hemichannel blocker carbenoxolone (CARB) and the NMDAR antagonist MK801, respectively. We found that the characters of BCP were mimicked by intra-femural inoculation of LLC cells in mice, and the expressions of Cx43, GFAP and p-NR2B in BCP mice were remarkably increased in a time-dependent manner from day 7 to day 21 after cell inoculation with a gradual aggravate in spontaneous pain and mechanical allodynia. Furthermore, Cx43 was predominantly expressed in the spinal astrocytes. Both CARB and MK801 inhibited the expressions of Cx43, GFAP and p-NR2B with attenuated pain hypersensitivity in BCP mice. In addition, Cx43 was co-localized with p-NR2B in the SDH, which further evidenced the presence of functional NR2B in the spinal astrocytes in BCP mice. Our findings demonstrate that inhibition of Cx43 and p-NR2B in spinal astrocytes could attenuate BCP in mice and Cx43 and p-NR2B in the astrocytes of the SDH may play an important role via their combination action in the development and maintenance of BCP in mice. These results may provide a potential therapeutic target in the prevention and/or treatment of BCP.

Antinociceptive antibiotics-loaded into solid lipid nanoparticles of prolonged release: Measuring pharmacological efficiency and time span on chronic monoarthritis rats

Pain is a sensory experience of a complex physiological nature in which is not only involved the nervous system. Among its many features is the development of chronic pain that is more complicated to treat because of the central somatization processes involved, becoming inefficient treatments used in other forms of pain. Among them is the role of glial cells, whose participation is such that some authors have proposed to chronic pain as a gliopathy. Because of this, the drug target of possible treatments focuses on modulating nociceptive response affecting transduction into the central nervous system through affecting synapses in the dorsal horn of the spinal cord. Solid lipid nanoparticles enter the central nervous system, protecting the drug, and in addition to the advantage of having greater absorption surface, all factors that improve drug activity. This work is based on the development and characterization of lipid nanoparticles of solid phase incorporating two antibiotics, minocycline, and ciprofloxacin with antinociceptive properties and challenged them with a rat monoarthritis model using Sprague-Dawley adult male rats. The solid lipid nanoparticles were prepared to modify the lipid, and surfactant amounts to obtain the best encapsulation capacity of the antibiotics, size and z potential. By using the Randall-Selitto test, we measured its pharmacological efficiency as an anti-inflammatory and measuring the time span the antibiotics are active. The encapsulated antibiotics were at least 50% more efficient than the antibiotic alone, and that is possible to measure anti-inflammatory activity up to seven days after the antibiotic application. The former is important for example, in the veterinary field, since a single application of the antibiotic will be necessary for the complete treatment, avoiding excessive stress for the animals. We can conclude that antinociceptive antibiotics encapsulation is a very effective, environmentally safe and inexpensive method for improving the pharmacological efficiency and time span the antibiotics are acting. Since these antibiotics are both anti-microbial and antinociceptive, his use in the field of veterinary presents the advantage of being adequate in single doses, with the saving of time and stress to the animals under treatment.

Systemic administration of propentofylline, ibudilast, and (+)-naltrexone each reverses mechanical allodynia in a novel rat model of central neuropathic pain

Central neuropathic pain (CNP) is a debilitating consequence of central nervous system damage for which current treatments are ineffective. To explore mechanisms underlying CNP, we developed a rat model involving T13/L1 dorsal root avulsion. The resultant dorsal horn damage creates bilateral below-level (L4-L6) mechanical allodynia. This allodynia, termed spinal neuropathic avulsion pain, occurs in the absence of confounding paralysis. To characterize this model, we undertook a series of studies aimed at defining whether spinal neuropathic avulsion pain could be reversed by any of 3 putative glial activation inhibitors, each with distinct mechanisms of action. Indeed, the phosphodiesterase inhibitor propentofylline, the macrophage migration inhibitory factor inhibitor ibudilast, and the toll-like receptor 4 antagonist (+)-naltrexone each reversed below-level allodynia bilaterally. Strikingly, none of these impacted spinal neuropathic avulsion pain upon first administration but required 1 to 2 weeks of daily administration before pain reversal was obtained. Given reversal of CNP by each of these glial modulatory agents, these results suggest that glia contribute to the maintenance of such pain and enduring release of macrophage migration inhibitory factor and endogenous agonists of toll-like receptor 4 is important for sustaining CNP. The markedly delayed efficacy of all 3 glial modulatory drugs may prove instructive for interpretation of apparent drug failures after shorter dosing regimens.

PERSPECTIVE

CNP that develops after trauma is often described by patients as severe and intolerable. Unfortunately, current treatments are not effective. This work suggests that using pharmacologic treatments that target glial cells could be an effective clinical treatment for CNP.

Electrophysiological Study of the Antinociception Produced by the Coapplication of (±)-CPP and Propentofylline in Monoarthritic Rats

The NMDA receptor is central in the generation and maintenance of chronic pain. This receptor has several sites of modulation. One is the glutamate recognition site that can be blocked by (±)-3-(2-carboxypiperazin-yl)propyl-1-phosphoric acid or (±)-CPP. We investigated whether the effect of glial inhibition produced by propentophylline (PPF) can be enhanced when combined with (±)-CPP. We used Sprague-Dawley rats with experimental monoarthritis, administering intrathecally the ED₃₀ for both drugs (3.97 μg of (±)-CPP and 1.42 μg of PPF), since this combination produces an antinociceptive supra-additive effect when used in mechanical nociception (Randall-Selitto test). The combination of (±)-PPF and CPP produced an antinociceptive effect which was greater than that each drug alone as tested by both the C reflex and windup. We conclude that the antinociceptive effect of the combination of (±)-PPF and CPP possibly generates a supra additive interaction type in monoarthritic rats.