Apoptotic gene expression in neuropathic pain

Pain initiated or caused by a primary lesion or dysfunction in the nervous system is defined as neuropathic pain. It results from direct injury to nerves in the peripheral or central nervous system and is associated with several clinical symptoms. Neuropathic pain treatment is extremely difficult, as it is a very complex disease, involving several molecular pathways. Excitatory or inhibitory pathways controlling neuropathic pain development show altered gene expression, caused by peripheral nerve injury.
This study used several experimental pain models to demonstrate the occurrence of programmed cell death in the centers controlling pain induction and maintenance, such as spinal cord and pre-frontal cortex. We combined behavioural, molecular and morphological approaches to assess the involvement of bcl-2 gene family and caspases in neuropathic pain. Chronic constriction injury (CCI) and spared nerve injury (SNI) of rodent sciatic nerve induced the appearance of pain-like behaviours, such as hyperalgesia and allodynia. An early (2-3 days post-CCI) apoptosis appeared in the spinal cord neurons as the pro-apoptotic bax gene increased (320±19%). The incidence of apoptosis appeared to be limited to the first few days following nerve injury. Subsequently, increased expression of anti-apoptotic bcl-2 family genes may inhibit further neuron loss. SNI triggered apoptotic pathway and caspases activation in pre-frontal cortex 7, 14, and 21 days post-injury. Among the time-points analyzed, RT-PCR analysis showed increased expression of the bax/bcl-2 ratio (40±2%), bid (16±2%), caspase-1 (84±3%), caspase-8 (53±6%), caspase-9 (25±6%), caspase-12 (58±2%), TNF (32±2%) genes in the cortex by 7 days post-injury. Western blot analysis showed increased active Caspase-3 protein levels in the cortex at 3, 7, 14, and 21 post-surgery. This study shows that apoptotic genes could be an useful pharmacological target in neuropathic pain controlling.
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Editorial: Glial cells, maladaptive plasticity, and neurodegeneration: Mechanisms, targeted therapies, and future directions

Understanding the biological complexity of the central nervous system (CNS) is a frontier in neuroscience. Morphological organization of the CNS represents the basis for its functional properties underlying higher brain functions; therefore, efforts are needed to boost the comprehension of the organization of the CNS, from the ultrastructural to the functional-networks level.To date, two highly integrated and interconnected cellular networks substantiate the anatomofunctional organization of CNS: neurons and non-neuronal cells, namely glial cells. Glial cells, including astrocytes, oligodendrocytes, and microglia, actively participate in many complex functions within the CNS (immunity surveillance and inflammatory response, metabolic and synaptic homeostasis, modulation of blood-brain barrier?BBB) (Volterra and Meldolesi, 2005). Moreover, interaction with the elements of the extracellular matrix (ECM), an active player for long-term plasticity and circuit maintenance, adds another level of complexity to the modern model of the synapse structure (tetrapartite synapse) (Song and Dityatev, 2018). Therefore, if on one hand glial cells allow adaptive synaptic plasticity of CNS in several physiological conditions modulating synaptic transmission, homeostasis, and neural pathways signaling, then on the other, when activated, they boost inflammatory response and perturb neuroglial interactions, synaptic circuitry, and plasticity. This new condition, called maladaptive synaptic plasticity, may represent an early stage of neuroinflammatory processes in neurodegenerative disorders (Papa et al., 2014). Recently, it has been hypothesized that the morpho-functional heterogeneity of astrocytes in different brain regions might explain the regional diversity of astrocytic response to an external injury and the selectivity of neuronal degeneration (Cragnolini et al., 2018, 2020). Therefore, the comprehension of these mechanisms is relevant for the development of targeted therapies for clinical management of neurodegenerative disorders. Only through unraveling the complex interactions between the different cell types at the synapse, we will truly understand synaptic plasticity, higher brain functions, and how perturbations of these interactions contribute to brain diseases with dramatic clinical impact.Fil: Korai, Sohaib Ali. Università degli Studi della Campania "Luigi Vanvitelli"; ItaliaFil: Sepe, Giovanna. Università degli Studi della Campania "Luigi Vanvitelli"; ItaliaFil: Luongo, Livio. Università degli Studi della Campania "Luigi Vanvitelli"; ItaliaFil: Cragnolini, Andrea Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones Biológicas y Tecnológicas. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Instituto de Investigaciones Biológicas y Tecnológicas; ArgentinaFil: Cirillo, Giovanni. Università degli Studi della Campania "Luigi Vanvitelli"; Itali

Moving towards supraspinal TRPV1 receptors for chronic pain relief

Transient receptor potential vanilloid type 1 (TRPV1) receptor is a non selective ligand-gated cation channel activated by capsaicin, heat, protons and endogenous lipids termed endovanilloids. As well as peripheral primary afferent neurons and dorsal root ganglia, TRPV1 receptor is also expressed in spinal and supraspinal structures such as those belonging to the endogenous antinociceptive descending pathway which is a circuitry of the supraspinal central nervous system whose task is to counteract pain. It includes periaqueductal grey (PAG) and rostral ventromedial medulla (RVM) whose activation leads to analgesia. Such an effect is associated with a glutamate increase and the activation of OFF and inhibition of ON cell population in the rostral ventromedial medulla (RVM). Activation of the antinociceptive descending pathway via TPRV1 receptor stimulation in the PAG may be a novel strategy for producing analgesia in chronic pain. This review will summarize the more recent insights into the role of TRPV1 receptor within the antinociceptive descending pathway and its possible exploitation as a target for new pain-killer agents in chronic pain conditions, with particular emphasis on the most untreatable pain state: neuropathic pain

Long-Lasting Effects of Human Mesenchymal Stem Cell Systemic Administration on Pain-Like Behaviors, Cellular, and Biomolecular Modifications in Neuropathic Mice

Background: Neuropathic pain (NP) is an incurable disease caused by a primary lesion in the nervous system. NP is a progressive nervous system disease that results from poorly defined neurophysiological and neurochemical changes. Its treatment is very difficult. Current available therapeutic drugs have a generalized nature, sometime acting only on the temporal pain properties rather than targeting the several mechanisms underlying the generation and propagation of pain. Methods: Using biomolecular and immunohistochemical methods, we investigated the effect of the systemic injection of human mesenchymal stem cells (hMSCs) on NP relief. We used the spared nerve injury (SNI) model of NP in the mouse. hMSCs were injected into the tail vein of the mouse. Stem cell injection was performed 4 days after sciatic nerve surgery. Neuropathic mice were monitored every 10 days starting from day 11 until 90 days after surgery. Results: hMSCs were able to reduce pain-like behaviors, such as mechanical allodynia and thermal hyperalgesia, once injected into the tail vein. An anti-nociceptive effect was detectable from day 11 post surgery (7 days post cell injection). hMSCs were mainly able to home in the spinal cord and pre-frontal cortex of neuropathic mice. Injected hMSCs reduced the protein levels of the mouse pro-inflammatory interleukin IL-1β and IL-17 and increased protein levels of the mouse anti-inflammatory interleukin IL-10, and the marker of alternatively activated macrophages CD106 in the spinal cord of SNI mice. Conclusion: As a potential mechanism of action of hMSCs in reducing pain, we suggest that they could exert their beneficial action through a restorative mechanism involving: (i) a cell-to-cell contact activation mechanism, through which spinal cord homed hMSCs are responsible for switching pro-inflammatory macrophages to anti-inflammatory macrophages; (ii) secretion of a broad spectrum of molecules to communicate with other cell types. This study could provide novel findings in MSC pre-clinical biology and their therapeutic potential in regenerative medicine

Bitter Taste Receptors and Endocrine Disruptors: Cellular and Molecular Insights from an In Vitro Model of Human Granulosa Cells

Endocrine disrupting chemicals (EDCs) are compounds that interfere with the synthesis, transport and binding action of hormones responsible for reproduction and homeostasis. Some EDCs compounds are activators of Taste bitter Receptors, a subclass of taste receptors expressed in many extraoral locations, including sperm and follicular somatic cells. This makes TAS2Rs attractive molecules to study and investigate to shed light on the effect of EDCs on female reproduction and fertility. This study aims to assess the effect of selected EDCs [namely Biochanin A (BCA), caffeine, Daidzein, Genistein and Isoflavone] on hGL5, an immortalized cell line exhibiting characteristics coherent with primary follicular granulosa cells. After demonstrating that this model expresses all the TAS2Rs (TAS2R3, TAS2R4, TAS2R14, TAS2R19, TAS2R43) specifically expressed by the primary human granulosa cells, we demonstrated that BCA and caffeine significantly affect mitochondrial footprint and intracellular lipid content, indicating their contribution in steroidogenesis. Our results showed that bitter taste receptors may be involved in steroidogenesis, thus suggesting an appealing mechanism by which these compounds affect the female reproductive system

5'-C-ethyl-tetrazolyl-N 6-substituted adenosine and 2-chloro-adenosine derivatives as highly potent dual acting A1 adenosine receptor agonists and A3 adenosine receptor antagonists

A series of N(6)-substituted-5'-C-(2-ethyl-2H-tetrazol-5-yl)-adenosine and 2-chloro-adenosine derivatives was synthesized as novel, highly potent dual acting hA1AR agonists and hA3AR antagonists, potentially useful in the treatment of glaucoma and other diseases. The best affinity and selectivity profiles were achieved by N(6)-substitution with a 2-fluoro-4-chloro-phenyl- or a methyl- group. Through an in silico receptor-driven approach, the molecular bases of the hA1- and hA3AR recognition and activation of this series of 5'-C-ethyl-tetrazolyl derivatives were explained

Palmitoylethanolamide reduces granuloma-induced hyperalgesia by modulation of mast cell activation in rats

The aim of this study was to obtain evidences of a possible analgesic role for palmitoylethanolamide (PEA) in chronic granulomatous inflammation sustained by mast cell (MC) activation in rats at 96 hours. PEA (200-400-800 μg/mL), locally administered at time 0, reduced in a concentration-dependent manner the expression and release of NGF in comparison with saline-treated controls. PEA prevented nerve formation and sprouting, as shown by histological analysis, reduced mechanical allodynia, evaluated by Von Frey filaments, and inhibited dorsal root ganglia activation. These results were supported by the evidence that MCs in granuloma were mainly degranulated and closely localized near nerve fibres and PEA significantly reduced MC degranulation and nerves fibre formation. These findings are the first evidence that PEA, by the modulation of MC activation, controls pain perception in an animal model of chronic inflammation, suggesting its potential use for the treatment of all those painful conditions in which MC activation is an initial key step

EP1 receptor within the ventrolateral periaqueductal grey controls thermonociception and rostral ventromedial medulla cell activity in healthy and neuropathic rat

The aim of this study was to investigate the expression of prostaglandin EP1 receptor within the ventrolateral periaqueductal grey (VL PAG). The role of VL PAG EP1 receptor in controlling thermonociception and rostral ventromedial medulla (RVM) activity in healthy and neuropathic rats was also examined. EP1 receptor was indeed found to be expressed within the VL PAG and co-localized with vesicular GABA transporter. Intra-VL PAG microinjection of ONO-DI-004, a selective EP1 receptor agonist, dose-dependently reduced tail flick latency as well as respectively increasing and decreasing the spontaneous activity of ON and OFF cells. Furthermore, it increased the ON cell burst and OFF cell pause. Intra-VL PAG prostaglandin E2 (PGE2) behaved similarly to ONO-DI-004. The effects of ONO-DI-004 and PGE2 were antagonized by intra-VL PAG L335677, a selective EP1 receptor antagonist. L335677 dose-dependently increased the tail flick latency and ongoing activity of the OFF cells, while reducing the ongoing ON cell activity. It also decreased the ON cell burst and OFF cell pause. In neuropathic rats using spare nerve injury (SNI) of the sciatic nerve model, EP1 receptor expression decreased in the VL PAG. However, ONO-DI-004 and L335677 were able to alter pain responses and ON and OFF cell activity, as they did in healthy animals. Collectively, these data show that within the VL PAG, EP1 receptor has a facilitatory effect on the nociceptive response and consistently affects RVM neuron activity. Thus, the blockade of EP1 receptor in the VL PAG leads to antinociception in neuropathic pain conditions, despite its down-regulation. The expression of EP1 receptor on GABAergic neurons is consistent with an EP1 receptor blockade-induced disinhibition of the antinociceptive descending pathway at VL PAG level

Altered gut microbiota and endocannabinoid system tone in vitamin D deficiency-mediated chronic pain

Abstract Recent evidence points to the gut microbiota as a regulator of brain and behavior, although it remains to be determined if gut bacteria play a role in chronic pain. The endocannabinoid system is implicated in inflammation and chronic pain processing at both the gut and central nervous system (CNS) levels. In the present study, we used low Vitamin D dietary intake in mice and evaluated possible changes in gut microbiota, pain processing and endocannabinoid system signaling. Vitamin D deficiency induced a lower microbial diversity characterized by an increase in Firmicutes and a decrease in Verrucomicrobia and Bacteroidetes. Concurrently, vitamin D deficient mice showed tactile allodynia associated with neuronal hyperexcitability and alterations of endocannabinoid system members (endogenous mediators and their receptors) at the spinal cord level. Changes in endocannabinoid (anandamide and 2-arachidonoylglycerol) levels were also observed in the duodenum and colon. Remarkably, the anti-inflammatory anandamide congener, palmitoylethanolamide, counteracted both the pain behaviour and spinal biochemical changes in vitamin D deficient mice, whilst increasing the levels of Akkermansia, Eubacterium and Enterobacteriaceae, as compared with vehicle-treated mice. Finally, induction of spared nerve injury in normal or vitamin D deficient mice was not accompanied by changes in gut microbiota composition. Our data suggest the existence of a link between Vitamin D deficiency – with related changes in gut bacterial composition – and altered nociception, possibly via molecular mechanisms involving the endocannabinoid and related mediator signaling systems