A new concept affecting restoration of inflammation-reactive astrocytes

Herkinorin ameliorates neuronal damage in a pentylenetetrazol-induced epilepsy rat model through altering microglial and astrocytic activation by inhibiting PARP1 and NF-κB

BACKGROUND

Altered astrocytic and microglial functions have been shown to mediate inflammation and oxidative stress in epilepsy. Herkinorin, a novel mu opioid receptor (MOR) agonist, has a neuroprotective role in ischemic brain injury. In this report, we sought to explore the effects and mechanism of herkinorin in the treatment of epilepsy and neuronal damage.

METHODS

SH-SY5Y cells were treated with pentylenetetrazol (PTZ) and herkinorin. The viability, reactive oxygen species (ROS) release, and apoptosis of the cells were detected. A rat epilepsy model was induced via PTZ injection, and herkinorin was used for pretreatment. Immunofluorescence staining and immunohistochemistry were used to observe neuronal damage and microglial and astrocyte activation in the hippocampal CA1/3 region. Western blotting was used to determine the expression profiles of PARP1 and NF-κB.

RESULTS

PTZ substantially facilitated SH-SY5Y cell apoptosis, induced oxidative stress and promoted NLRP3-ASC-Caspase-1 inflammasome activation. Herkinorin attenuated SH-SY5Y cell damage mediated by PTZ and suppressed PARP1 and NF-κB. The activation of PARP1 by lipopolysaccharide (LPS) aggravated SH-SY5Y cell injury, and herkinorin treatment reversed these LPS-mediated effects. In in vivo experiments, herkinorin hampered epileptic seizures in rats and weakened PTZ-induced neuronal damage in the hippocampus. Moreover, herkinorin reduced PTZ-induced neuroinflammation, resulting in "M1" to "M2" polarization of microglia and "A1" to "A2" polarization of astrocytes. Moreover, herkinorin inhibited the expression of PARP1 and NF-κB phosphorylation in the hippocampus.

CONCLUSION

Herkinorin ameliorates PTZ-induced neuroinflammation in epileptic rats by inhibiting PARP1 and NF-κB and regulating microglial and astrocytic activation.

Hepatic encephalopathy complications are diminished by piracetam via the interaction between mitochondrial function, oxidative stress, inflammatory response, and locomotor activity

Background

of the study: Hepatic encephalopathy (HE) is a complication in which brain ammonia (NH4+) levels reach critically high concentrations because of liver failure. HE could lead to a range of neurological complications from locomotor and behavioral disturbances to coma. Several tactics have been established for subsiding blood and brain NH4+. However, there is no precise intervention to mitigate the direct neurological complications of NH4+.

Purpose

It has been found that oxidative stress, mitochondrial damage, and neuro-inflammation play a fundamental role in NH4+ neurotoxicity. Piracetam is a drug used clinically in neurological complications such as stroke and head trauma. Piracetam could significantly diminish oxidative stress and improve brain mitochondrial function.

Research methods

In the current study, piracetam (100 and 500 mg/kg, oral) was used in a mice model of HE induced by thioacetamide (TA, 800 mg/kg, single dose, i.p).

Results

Significant disturbances in animals' locomotor activity, along with increased oxidative stress biomarkers, including reactive oxygen species formation, protein carbonylation, lipid peroxidation, depleted tissue glutathione, and decreased antioxidant capacity, were evident in the brain of TA-treated mice. Meanwhile, mitochondrial permeabilization, mitochondrial depolarization, suppression of dehydrogenases activity, and decreased ATP levels were found in the brain of the TA group. The level of pro-inflammatory cytokines was also significantly high in the brain of HE animals.

Conclusion

It was found that piracetam significantly enhanced mice's locomotor activity, blunted oxidative stress biomarkers, decreased inflammatory cytokines, and improved mitochondrial indices in hyperammonemic mice. These data suggest piracetam as a neuroprotective agent which could be repurposed for the management of HE.

Pharmacological Investigations in Glia Culture Model of Inflammation

Astrocytes and microglia are the main cell population besides neurons in the central nervous system (CNS). Astrocytes support the neuronal network via maintenance of transmitter and ion homeostasis. They are part of the tripartite synapse, composed of pre- and postsynaptic neurons and perisynaptic astrocytic processes as a functional unit. There is an increasing evidence that astroglia are involved in the pathophysiology of CNS disorders such as epilepsy, autoimmune CNS diseases or neuropsychiatric disorders, especially with regard to glia-mediated inflammation. In addition to astrocytes, investigations on microglial cells, the main immune cells of the CNS, offer a whole network approach leading to better understanding of non-neuronal cells and their pathological role in CNS diseases and treatment. An in vitro astrocyte-microglia co-culture model of inflammation was developed by Faustmann et al. (2003), which allows to study the endogenous inflammatory reaction and the cytokine expression under drugs in a differentiated manner. Commonly used antiepileptic drugs (e.g., levetiracetam, valproic acid, carbamazepine, phenytoin, and gabapentin), immunomodulatory drugs (e.g., dexamethasone and interferon-beta), hormones and psychotropic drugs (e.g., venlafaxine) were already investigated, contributing to better understanding mechanisms of actions of CNS drugs and their pro- or anti-inflammatory properties concerning glial cells. Furthermore, the effects of drugs on glial cell viability, proliferation and astrocytic network were demonstrated. The in vitro astrocyte-microglia co-culture model of inflammation proved to be suitable as unique in vitro model for pharmacological investigations on astrocytes and microglia with future potential (e.g., cancer drugs, antidementia drugs, and toxicologic studies).

Anxiolytic effects of polydatin through the blockade of neuroinflammation in a chronic pain mouse model

Background

Chronic pain is frequently comorbid with anxiety disorder, thereby complicating its treatment. Polydatin, a component from the root of Polygonum cuspidatum, has shown neuroprotection in the central nervous system. However, its effects on pain and anxiety processing have been rarely investigated. In this study, mice were injected with complete Freund’s adjuvant (CFA) at the hindpaw to induce pain- and anxiety-like behaviors.

Results

Treatment with polydatin (25 mg/kg) alleviated the anxiety-like behaviors but not pain perception in these mice. Polydatin treatment reversed the upregulation of N-methyl-D-aspartic acid receptors and GluA1-containing α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid receptors in the amygdala of CFA-injected mice. Additionally, this treatment reduced the levels of proinflammatory cytokines, namely, tumor necrosis factor-alpha and interleukin-1β, in the amygdala. Furthermore, activated nuclear factor kappa-B signaling was blocked in the amygdala from CFA-injected mice. By using docking technology, we found potential structural binding between polydatin and IκB kinase beta.

Conclusion

This study indicates the anxiolytic effects of polydatin by suppressing inflammatory cytokines in the amygdala.

Corticomotor correlates of somatosensory reaction time and variability in individuals with post concussion symptoms

Persistent post concussion symptoms (PPCS) describe the condition when an individual experiences chronic symptoms, particularly fatigue, beyond the expected time of recovery. The aim of this study was to quantify the effect of fatigue and related ongoing symptoms on somatosensory and corticomotor pathways using reaction time (RT) testing, and single-pulse and paired-pulse transcranial magnetic stimulation (TMS). Eighty-three participants (nine female, mean age 37.9 ± 11.5 years) were divided into two groups (persistent symptoms versus asymptomatic) following self-report based upon previously published clinical symptom scores. All participants completed somatosensory and visuomotor RT testing, as well as corticomotor excitability and inhibition measurements via TMS. Participants in the persistent symptom group (n = 38) reported greater number of previous concussions (t = 2.81, p = 0.006) and significantly higher levels of fatigue and related symptoms in the asymptomatic group (n = 45; t = 11.32, p < 0.006). Somatosensory RT showed significant slowing and increased variability in the persistent symptoms group (p < 0.001), however no significant differences were observed between groups for visuomotor RTs. Transcranial magnetic stimulation revealed differences between groups for intracortical inhibition at all stimulus intensities and paired pulse measures. The results indicate that somatosensory and corticomotor systems reflect on-going fatigue. From a practical perspective, objective and simplistic measures such as somatosensory and corticomotor measures can be used in the assessment of PPCS and gauging the efficacy of post concussion rehabilitation programmes.

Anti-inflammatory effects induced by ultralow concentrations of bupivacaine in combination with ultralow concentrations of sildenafil (Viagra) and vitamin D3 on inflammatory reactive brain astrocytes

Network coupled cells, such as astrocytes, regulate their cellular homeostasis via Ca²⁺ signals spread between the cells through gap junctions. Intracellular Ca²⁺ release is controlled by different signaling pathways that can be stimulated by ATP, glutamate and serotonin (5-HT). Based on our findings, all these pathways are influenced by inflammatory agents and must be restored to fully recover the Ca²⁺ signaling network. An ultralow concentration of the local anesthetic agent bupivacaine reduced 5-HT-evoked intracellular Ca²⁺ release, and an ultralow concentration of the phosphodiesterase-5 inhibitor sildenafil in combination with vitamin D3 reduced ATP-evoked intracellular Ca²⁺ release. Combinations of these three substances downregulated 5-HT-, glutamate- and ATP-evoked intracellular Ca²⁺ release to a more normal Ca²⁺ signaling state. Furthermore, inflammatory Toll-like receptor 4 expression decreased with a combination of these three substances. Substance P receptor neurokinin (NK)-1 expression was reduced by ultralow concentrations of bupivacaine. Here, bupivacaine and sildenafil (at extremely low concentrations) combined with vitamin D3 have potential anti-inflammatory properties. According to the present study, drug combinations at the right concentrations, especially extremely low concentrations of bupivacaine and sildenafil, affect different cellular biochemical mechanisms and represent a potential solution for downregulating inflammatory parameters, thereby restoring cells or networks to normal physiological homeostasis.

Low-grade inflammation causes gap junction-coupled cell dysfunction throughout the body, which can lead to the spread of systemic inflammation

BACKGROUND AND AIMS

Gap junction-coupled cells form networks in different organs in the body. These networks can be affected by inflammatory stimuli and become dysregulated. Cell signaling is also changed through connexin-linked gap junctions. This alteration affects the surrounding cells and extracellular matrix in organs. These changes can cause the spread of inflammatory substances, thus affecting other network-linked cells in other organs in the body, which can give rise to systemic inflammation, which in turn can lead to pain that can turn into chronic.

METHODS

This is a review based on literature search and our own research data of inflammatory stimuli that can affect different organs and particularly gap-junction-coupled cells throughout the body.

CONCLUSIONS

A remaining question is which cell type or tissue is first affected by inflammatory stimuli. Can endotoxin exposure through the air, water and body start the process and are mast cells the first target cells that have the capacity to alter the physiological status of gap junction-coupled cells, thereby causing breakdown of different barrier systems?

IMPLICATIONS

Is it possible to address the right cellular and biochemical parameters and restore inflammatory systems to a normal physiological level by therapeutic strategies?

The Importance and Control of Low-Grade Inflammation Due to Damage of Cellular Barrier Systems That May Lead to Systemic Inflammation

Systemic low-grade inflammation can be initiated in vivo after traumatic injury or in chronic diseases such as neurodegenerative, metabolic, and autoimmune diseases. Inducers of inflammation trigger production of inflammatory mediators, which alter the functionality of tissues and organs and leads to harmful induction of different barrier systems in the body, where the blood-brain barrier, the blood-retinal barrier, blood-nerve barrier, blood-lymph barrier and the blood-cerebrospinal fluid barrier play major roles. The different barriers are unique but structured in a similar way. They are equipped with sophisticated junctional complexes where different connexins, protein subunits of gap junction channels and hemichannels, constitute important partners. The cells involved in the various barriers are coupled in networks, are excitable but do not express action potentials and may be targets for inflammation leading to changes in several biochemical cellular parameters. During any type of inflammation barrier break-down is observed where any form of injury can start with low-grade inflammation and may lead to systemic inflammation.

Neurophysiological abnormalities in individuals with persistent post-concussion symptoms

Concussion injury results in a rapid onset of transient neurological impairment that can resolve quickly, or sometimes evolve over time, but usually resolve within seven to 10 days. However, a small but noticeable cohort (~10%) of individuals continues to experience persistent lingering effects, particularly fatigue, recognized as post-concussion symptoms (PCS). This study explored neurophysiological mechanisms in people with persistent PCS. Studies involved using self-report post-concussion fatigue scale, transcranial magnetic stimulation (TMS) and somatosensory stimulation in those with diagnosed PCS (n = 20; 36.1 ± 14.0 yr., 4 female; mean time post-concussion 15.4 ± 7.6 months) to fully recovered individuals (n = 20; 33.8 ± 6.6 yr., 2 female; post-concussion 12.9 ± 6.6 months) and healthy controls (n = 20; 37.7 ± 8.0 yr., 3 female). PCS participants demonstrated a significantly higher self-report fatigue (score: PCS 20.2 [95% CI 17.4-22.9], Recovered 6.2 [3.1-9.3], Control 2.75 [0.6-4.8]). PCS participants showed a worsening of reaction time (F_2,57 = 4.214; p = 0.020) and increased reaction time variability (F_2,57 = 5.505; p = 0.007). Somatosensory differences were observed for amplitude discrimination (F_2,57 = 5.166; p = 0.009), temporal order judgment (F_2,57 = 4.606; p = 0.014) and duration discrimination (F_2,57 = 6.081; p = 0.004). Increased intracortical inhibition in TMS single pulse suprathreshold stimulation (110%: F_2,57 = 6.842; p = 0.002; 130%: F_2,57 = 4.900; p = 0.011; 150%: F_2,57 = 4.638; p = 0.014; 170%: F_2,57 = 9.845; p < 0.001) and paired pulse protocols was also seen (SICI: F_2,57 = 23.390; p < 0.001, and LICI: F_2,57 = 21.603; p < 0.001). Using non-invasive stimulation techniques, this novel study showed increased cortical inhibition and compromised central information processing, suggesting neural mechanisms underpinning ongoing fatigue, allowing for potential clinical rehabilitation strategies.

Anti-inflammatory effects induced by pharmaceutical substances on inflammatory active brain astrocytes-promising treatment of neuroinflammation

Background

Pharmaceutical treatment with probable anti-inflammatory substances that attack cells in various ways including receptors, ion channels, or transporter systems may slow down the progression of inflammatory conditions. Astrocytes and microglia are the most prominent target cells for inflammation in the central nervous system. Their responses upon inflammatory stimuli work through the NO/cyclic GMP/protein kinase G systems that can downregulate the ATP-induced Ca²⁺ signaling, as well as G protein activities which alter Na⁺ transporters including Na⁺/K⁺-ATPase pump activity, Toll-like receptor 4 (TLR4), glutamate-induced Ca²⁺ signaling, and release of pro-inflammatory cytokines. The rationale for this project was to investigate a combination of pharmaceutical substances influencing the NO and the G_i/G_s activations of inflammatory reactive cells in order to make the cells return into a more physiological state. The ATP-evoked Ca²⁺ signaling is important maybe due to increased ATP release and subsequent activation of purinergic receptors. A balance between intercellular Ca²⁺ signaling through gap junctions and extracellular signaling mediated by extracellular ATP may be important for physiological function.

Methods

Astrocytes in primary cultures were incubated with lipopolysaccharide in a physiological glucose concentration for 24 h to induce inflammatory reactivity. The probable anti-inflammatory substances sildenafil and 1α,25-Dihydroxyvitamin D3 together with endomorphin-1, naloxone, and levetiracetam, were used in the presence of high glucose concentration in the medium to restore the cells. Glutamate-, 5-HT-, and ATP-evoked intracellular Ca²⁺ release, Na⁺/K⁺-ATPase expression, expression of inflammatory receptors, and release of tumor necrosis factor alpha were measured.

Results

Sildenafil in ultralow concentration together with 1α,25-Dihydroxyvitamin D3 showed most prominent effects on the ATP-evoked intracellular Ca²⁺ release. The μ-opioid agonist endomorphin-1, the μ-opioid antagonist naloxone in ultralow concentration, and the antiepileptic agent levetiracetam downregulated the glutamate-evoked intracellular Ca²⁺ release and TLR4. The combination of the pharmaceutical substances in high glucose concentration downregulated the glutamate- and ATP-evoked Ca²⁺ signaling and the TLR4 expression and upregulated the Na⁺/K⁺-ATPase pump.

Conclusion

Pharmaceutical treatment with the combination of substances that have potential anti-inflammatory effects, which attack different biochemical mechanisms in the cells may exert decisive effects to downregulate neuroinflammation in the nervous system.

Research on the Effects of Levetiracetam in Spinal Cord Injury Model in Rats: An Experimental Study

Purpose: Despite advances in spinal biomechanic research, surgical techniques, and rehabilitation processes, no significant improvement has been identified in the treatment of spinal cord injury (SCI) and neurological recovery. Aim of the Study: This study was designed to investigate the potential therapeutic effects of methylprednisolone and levetiracetam on SCI. Materials and Methods: In this study, 42 male Wistar Albino rats, each weighing 300-350 g, were separated into three main groups: control group, acute and subacute stage groups. With the exception of the control group, a T7-8 dorsal laminectomy was performed on the spinal column of the rats. A temporary vascular aneurysm clip was then applied to the spinal cord for 1 min to create SCI and methylprednisolone or levetiracetam was administered intraperitoneally to all except the control and SHAM control groups. The damaged spinal cord was removed for histopathological and biochemical examinations. Results: Both pharmacological agents were determined to have improved the histopathological architecture in damaged neural tissues during the acute period of SCI, but could not sustain this activity in the subacute period. Neither pharmacological agent affected the biochemical data in the acute nor subacute stages. Conclusions: Both pharmacological agents showed histopathological healing effects in injured tissues during the acute phase of SCI in this rat model but these effects could not be sustained in the subacute period. No effect on biochemical data was seen in either the acute or subacute period. There is a need for further advanced studies to determine the effects of levetiracetam on the healing processes in SCI.

Inhibitive Effects of FGF2/FGFR1 Pathway on Astrocyte-Mediated Inflammation in vivo and in vitro After Infrasound Exposure

Infrasound, a kind of ambient noise, can cause severe disorders to various human organs, specially to central nervous system (CNS). Our previous studies have shown that infrasound-induced CNS injury was closely related with astrocytes activation and astrocytes-mediated neuroinflammation, but the underlying molecular mechanisms are still largely unclear. FGF2/FGFR1 (Fibroblast growth factor 2/Fibroblast growth factor receptor 1) pathway was reported to play an important role in anti-inflammation in CNS disorders. To further study the possible roles of FGF2/FGFR1 pathway in infrasound-induced CNS injury, here we exposed Sprague-Dawley rats or cultured astrocytes to 16 Hz, 150 dB infrasound, and explored the effects of FGF2 on infrasound-induced astrocytes activation and neuroinflammation. Western blotting, immunofluorescence and liquid chip method were used in this experiment. Our results showed that after 3- or 7-day exposure (2 h/day) of rats as well as 2 h exposure of cultured astrocytes to 16 Hz, 150 dB infrasound, astrocyte-expressed FGFR1 was downregulated in vivo and in vitro. FGF2 pretreatment not only inhibited infrasound-induced astrocyte activation in rat hippocampal CA1 region, but also reduced the levels of pro-inflammatory cytokines, such as TNF-α, IL-1β, IL-18, IL-6, and IFN-γ in vitro and in vivo. However, FGF2 significantly upregulated the expression of FGFR1. Furthermore, we showed that FGF2 could attenuate IκBα phosphorylation, NF-κB p65 translocation, pro-inflammatory cytokines levels, and neuronal loss in the CA1 region induced by infrasound. On the contrary, PD173074, a special antagonist of FGFR1, could reverse the effects above in vitro and in vivo. Taken together, our findings showed that FGF2/FGFR1 pathway may exert inhibitive effects on astrocyte-mediated neuroinflammation in vitro and in vivo after infrasound exposure.

Biochemical alterations in inflammatory reactive chondrocytes: evidence for intercellular network communication

Chondrocytes are effectively involved in the pathophysiological processes of inflammation in joints. They form cellular processes in the superficial layer of the articular cartilage and form gap junction coupled syncytium to facilitate cell-to-cell communication. However, very little is known about their physiological cellular identity and communication. The aim with the present work is to evaluate the physiological behavior after stimulation with the inflammatory inducers interleukin-1β and lipopolysaccharide. The cytoskeleton integrity and intracellular Ca²⁺ release were assessed as indicators of inflammatory state. Cytoskeleton integrity was analyzed through cartilage oligomeric matrix protein and actin labeling with an Alexa 488-conjugated phalloidin probe. Ca²⁺ responses were assessed through the Ca²⁺ sensitive fluorophore Fura-2/AM. Western blot analyses of several inflammatory markers were performed. The results show reorganization of the actin filaments. Glutamate, 5-hydoxytryptamine, and ATP evoked intracellular Ca²⁺ release changed from single peaks to oscillations after inflammatory induction in the chondrocytes. The expression of toll-like receptor 4, the glutamate transporters GLAST and GLT-1, and the matrix metalloproteinase-13 increased. This work demonstrates that chondrocytes are a key part in conditions that lead to inflammation in the cartilage. The inflammatory inducers modulate the cytoskeleton, the Ca²⁺ signaling, and several inflammatory parameters. In conclusion, our data show that the cellular responses to inflammatory insults from healthy and inflammatory chondrocytes resemble those previously observed in astrocyte and cardiac fibroblasts networks.

Inflammatory activation of human cardiac fibroblasts leads to altered calcium signaling, decreased connexin 43 expression and increased glutamate secretion

Cardiac fibroblasts, which are abundant in heart tissue, are involved not only in extracellular matrix homeostasis and repair, but also in cardiac remodeling after a myocardial infarction that, in turn, can lead to loss of cardiac function and heart failure. Ca²⁺ signaling is functionally important in many cell types, but the roles of fibroblast signaling and inflammation in the pathogenesis of heart disease are unclear. Here, we tested the hypothesis that inflammatory activation affects cardiac fibroblasts, both in terms of Ca²⁺ signaling and their capacity for intercellular communication through the gap junction channel protein connexin 43 (Cx43). We examined Ca²⁺ responses induced by known modulators of cardiac function such as glutamate, ATP and 5-hydroxytryptamine (5-HT) in human cardiac fibroblasts, under normal and inflammatory conditions. We showed that activation of human cardiac fibroblasts by lipopolysaccharide (LPS) for 24 h altered Ca²⁺ signaling, increased TLR4 and decreased Cx43 expression. In the fibroblasts, LPS treatment increased glutamate-evoked and decreased 5-HT-evoked Ca²⁺ signals. LPS activation also induced increased secretion of glutamate and proinflammatory cytokines from these cells. In summary, we propose that inflammatory stimuli can affect intracellular Ca²⁺ release, Cx43 expression, glutamate release and cytokine secretion in human cardiac fibroblasts. Inflammatory conditions may, therefore, impair intercellular network communication between fibroblasts and cardiomyocytes potentially contributing to cardiac dysfunction.

Effects of interleukin-1ß on cortical spreading depolarization and cerebral vasculature

During brain damage and ischemia, the cytokine interleukin-1ß is rapidly upregulated due to activation of inflammasomes. We studied whether interleukin-1ß influences cortical spreading depolarization, and whether lipopolysaccharide, often used for microglial stimulation, influences cortical spreading depolarizations. In anaesthetized rats, cortical spreading depolarizations were elicited by microinjection of KCl. Interleukin-1ß, the IL-1 receptor 1 antagonist, the GABAA receptor blocker bicuculline, and lipopolysaccharide were administered either alone or combined (interleukin-1ß + IL-1 receptor 1 antagonist; interleukin-1ß + bicuculline; lipopolysaccharide + IL-1 receptor 1 antagonist) into a local cortical treatment area. Using microelectrodes, cortical spreading depolarizations were recorded in a non-treatment and in the treatment area. Plasma extravasation in cortical grey matter was assessed with Evans blue. Local application of interleukin-1ß reduced cortical spreading depolarization amplitudes in the treatment area, but not at a high dose. This reduction was prevented by IL-1 receptor 1 antagonist and by bicuculline. However, interleukin-1ß induced pronounced plasma extravasation independently on cortical spreading depolarizations. Application of lipopolysaccharide reduced cortical spreading depolarization amplitudes but prolonged their duration; EEG activity was still present. These effects were also blocked by IL-1 receptor 1 antagonist. Interleukin-1ß evokes changes of neuronal activity and of vascular functions. Thus, although the reduction of cortical spreading depolarization amplitudes at lower doses of interleukin-1ß may reduce deleterious effects of cortical spreading depolarizations, the sum of interleukin-1ß effects on excitability and on the vasculature rather promote brain damaging mechanisms.

Sildenafil (Viagra(®)) prevents and restores LPS-induced inflammation in astrocytes

Astrocytes are effectively involved in the pathophysiological processes in the central nervous system (CNS) and may contribute to or protect against development of inflammatory and degenerative diseases. Sildenafil is a potent and selective phosphodiesterase-5 (PDE-5) inhibitor, which induces cyclic GMP accumulation. However, the mechanisms of actions on glial cells are not clear. The aim of the present work is to evaluate the role of sildenafil in lipopolysaccharide (LPS)-stimulated astrocytes. The cytoskeleton integrity and Ca(2+) waves were assessed as indicators of inflammatory state. Two main groups were done: (A) one prevention and (B) one restoration. Each of these groups: A1: control; A2: LPS for 24h; A3: sildenafil 1 or 10μM for 4h and then sildenafil 1 or 10μM+LPS for 24h. B1: control; B2: LPS for 24h; B3: LPS for 24h and then LPS+sildenafil 1 or 10μM for 24h. Cytoskeleton integrity was analyzed through GFAP immunolabeling and actin labeling with an Alexa 488-conjugated phalloidin probe. Calcium responses were assessed through a Ca(2+)-sensitive fluorophore Fura-2/AM. The results show that both preventive and restorative treatments with sildenafil (in both concentrations) reduced the Ca(2+) responses in intensity and induced a more organized actin fiber pattern, compared to LPS treated cells. This work demonstrated for the first time that astrocytes are a key part of the sildenafil protective effects in the CNS.

Autophagy resolves early retinal inflammation in Igf1-deficient mice

Insulin-like growth factor-1 (IGF-1) is a growth factor with differentiating, anti-apoptotic and metabolic functions in the periphery, and anti-inflammatory properties in the nervous system. Mice that have mutations in the Igf1 gene, rendering the gene product inactive (Igf1^−/−), present with age-related visual loss accompanied by structural alterations in the first synapses of the retinal pathway. Recent advances have revealed a crucial role of autophagy in immunity and inflammation. Keeping in mind this close relationship, we aimed to decipher these processes in the context of the defects that occur during ageing in the retina of Igf1^−/− mice. Tnfa and Il1b mRNAs, and phosphorylation of JNK and p38 MAPK were elevated in the retinas of 6- and 12-month old Igf1^−/− mice compared to those in age-matched Igf1^+/+ controls. In 6-month-old Igf1^−/− retinas, increased mRNA levels of the autophagy mediators Becn1, Atg9, Atg5 and Atg4, decreased p62 (also known as SQSTM1) protein expression together with an increased LC3-II:LC3-I ratio reflected active autophagic flux. However, in retinas from 12-month-old Igf1^−/− mice, Nlrp3 mRNA, processing of the IL1β pro-form and immunostaining of active caspase-1 were elevated compared to those in age-matched Igf1^+/+ controls, suggesting activation of the inflammasome. This effect concurred with accumulation of autophagosomes and decreased autophagic flux in the retina. Microglia localization and status of activation in the retinas of 12-month-old Igf1^+/+ and Igf1^−/− mice, analyzed by immunostaining of Cd11b and Iba-1, showed a specific distribution pattern in the outer plexiform layer (OPL), inner plexiform layer (IPL) and inner nuclear layer (INL), and revealed an increased number of activated microglia cells in the retina of 12-month-old blind Igf1^−/− mice. Moreover, reactive gliosis was exclusively detected in the retinas from 12-month-old blind Igf1^−/− mice. In conclusion, this study provides new evidence in a mouse model of IGF-1 deficiency that autophagy is an adaptive response that might confer protection against persistent inflammation in the retina during ageing.

Summary:Igf1-deficient mice show chronic inflammation in the retina, and we reveal that controlling inflammation through autophagy in young mice could prevent loss of retinal function.

Ultralow Dose of Naloxone as an Adjuvant to Intrathecal Morphine Infusion Improves Perceived Quality of Sleep but Fails to Alter Persistent Pain: A Randomized, Double-blind, Controlled Study

Supplemental Digital Content is available in the text.

Introduction:

This randomized, cross-over, double-blind, controlled study of continuous intrathecal morphine administration in patients with severe, long-term pain addresses whether the supplementation of low doses of naloxone in this setting is associated with beneficial clinical effects.

Methods:

All of the study subjects (n=11) provided informed consent and were recruited from a subset of patients who were already undergoing long-term treatment with continuous intrathecal morphine because of difficult-to-treat pain. The patients were (in a randomized order) also given intrathecal naloxone (40 ng/24 h or 400 ng/24 h). As control, the patients’ ordinary dose of morphine without any additions was used. The pain (Numeric Rating Scale, NRS) during activity, perceived quality of sleep, level of activity, and quality of life as well as the levels of several proinflammatory and anti-inflammatory cytokines in the blood were assessed. The prestudy pain (NRS during activity) in the study group ranged from 3 to 10.

Results:

A total of 64% of the subjects reported improved quality of sleep during treatment with naloxone at a dose of 40 ng per 24 hours as compared with 9% with sham treatment (P=0.024). Although not statistically significant, pain was reduced by 2 NRS steps or more during supplemental treatment with naloxone in 36% of subjects when using the 40 ng per 24 hours dose and in 18% of the subjects when using naloxone 400 ng per 24 hours dose. The corresponding percentage among patients receiving unaltered treatment was 27%.

Conclusions:

To conclude, the addition of an ultralow dose of intrathecal naloxone (40 ng/24 h) to intrathecal morphine infusion in patients with severe, persistent pain improved perceived quality of sleep. We were not able to show any statistically significant effects of naloxone on pain relief, level of activity, or quality of life.

Therapeutic innovation: Inflammatory-reactive astrocytes as targets of inflammation

This study aimed to test pharmaceutical compounds targeting astrocytes showing inflammatory dysregulation. The primary rat brain cultures were treated with different batches of serum with or without microglia added to make the cells inflammatory-reactive. Lipopolysaccharide (LPS) and tryptase were used as inflammatory inducers. Expression levels of Toll-like receptor 4 (TLR4), Na⁺/K⁺-ATPase, and matrix metalloprotease-13 (MMP-13), as well as actin filament organization, pro-inflammatory cytokines, and intracellular Ca²⁺ release, were evaluated. LPS combined with tryptase upregulated TLR4 expression, whereas Na⁺/K⁺-ATPase expression was downregulated, ATP-evoked Ca²⁺ transients were increased, actin filaments were reorganized and ring structures instead of stress fibers were observed. Other aims of the study were to prevent astrocytes from becoming inflammatory-reactive and to restore inflammatory dysregulated cellular changes. A combination of the μ-opioid antagonist (-)-naloxone in ultra-low concentrations, the non-addictive μ-opioid agonist (-)-linalool, and the anti-epileptic agent levetiracetam was examined. The results indicated that this drug cocktail prevented the LPS- and tryptase-induced inflammatory dysregulation. The drug cocktail could also restore the LPS- and tryptase-treated cells back to a normal physiological level in terms of the analyzed parameters.

Opioid-induced hyperalgesia: Cellular and molecular mechanisms

Opioids produce strong analgesia but their use is limited by a paradoxical hypersensitivity named opioid-induced hyperalgesia (OIH) that may be associated to analgesic tolerance. In the last decades, a significant number of preclinical studies have investigated the factors that modulate OIH development as well as the cellular and molecular mechanisms underlying OIH. Several factors have been shown to influence OIH including the genetic background and sex differences of experimental animals as well as the opioid regimen. Mu opioid receptor (MOR) variants and interactions of MOR with different proteins were shown important. Furthermore, at the cellular level, both neurons and glia play a major role in OIH development. Several neuronal processes contribute to OIH, like activation of neuroexcitatory mechanisms, long-term potentiation (LTP) and descending pain facilitation. Increased nociception is also mediated by neuroinflammation induced by the activation of microglia and astrocytes. Neurons and glial cells exert synergistic effects, which contribute to OIH. The molecular actors identified include the Toll-like receptor 4 and the anti-opioid systems as well as some other excitatory molecules, receptors, channels, chemokines, pro-inflammatory cytokines or lipids. This review summarizes the intracellular and intercellular pathways involved in OIH and highlights some mechanisms that may be challenged to limit OIH in the future.

Glial dysfunction and persistent neuropathic postsurgical pain

BACKGROUND

Acute pain in response to injury is an important mechanism that serves to protect living beings from harm. However, persistent pain remaining long after the injury has healed serves no useful purpose and is a disabling condition. Persistent postsurgical pain, which is pain that lasts more than 3 months after surgery, affects 10-50% of patients undergoing elective surgery. Many of these patients are affected by neuropathic pain which is characterised as a pain caused by lesion or disease in the somatosensory nervous system. When established, this type of pain is difficult to treat and new approaches for prevention and treatment are needed. A possible contributing mechanism for the transition from acute physiological pain to persistent pain involves low-grade inflammation in the central nervous system (CNS), glial dysfunction and subsequently an imbalance in the neuron-glial interaction that causes enhanced and prolonged pain transmission.

AIM

This topical review aims to highlight the contribution that inflammatory activated glial cell dysfunction may have for the development of persistent pain.

METHOD

Relevant literature was searched for in PubMed.

RESULTS

Immediately after an injury to a nerve ending in the periphery such as in surgery, the inflammatory cascade is activated and immunocompetent cells migrate to the site of injury. Macrophages infiltrate the injured nerve and cause an inflammatory reaction in the nerve cell. This reaction leads to microglia activation in the central nervous system and the release of pro-inflammatory cytokines that activate and alter astrocyte function. Once the astrocytes and microglia have become activated, they participate in the development, spread, and potentiation of low-grade neuroinflammation. The inflammatory activated glial cells exhibit cellular changes, and their communication to each other and to neurons is altered. This renders neurons more excitable and pain transmission is enhanced and prolonged. Astrocyte dysfunction can be experimentally restored using the combined actions of a μ-opioid receptor agonist, a μ-opioid receptor antagonist, and an anti-epileptic agent. To find these agents we searched the literature for substances with possible anti-inflammatory properties that are usually used for other purposes in medicine. Inflammatory induced glial cell dysfunction is restorable in vitro by a combination of endomorphine-1, ultralow doses of naloxone and levetiracetam. Restoring inflammatory-activated glial cells, thereby restoring astrocyte-neuron interaction has the potential to affect pain transmission in neurons.

CONCLUSION

Surgery causes inflammation at the site of injury. Peripheral nerve injury can cause low-grade inflammation in the CNS known as neuroinflammation. Low-grade neuroinflammation can cause an imbalance in the glial-neuron interaction and communication. This renders neurons more excitable and pain transmission is enhanced and prolonged. Astrocytic dysfunction can be restored in vitro by a combination of endomorphin-1, ultralow doses of naloxone and levetiracetam. This restoration is essential for the interaction between astrocytes and neurons and hence also for modulation of synaptic pain transmission.

IMPLICATIONS

Larger studies in clinical settings are needed before these findings can be applied in a clinical context. Potentially, by targeting inflammatory activated glial cells and not only neurons, a new arena for development of pharmacological agents for persistent pain is opened.

Cardiotonic Steroids as Modulators of Neuroinflammation

Cardiotonic steroids (CTS) are a class of specific ligands of the Na(+), K(+)- ATPase (NKA). NKA is a P-type ATPase that is ubiquitously expressed and although well known to be responsible for the maintenance of the cell electrochemical gradient through active transport, NKA can also act as a signal transducer in the presence of CTS. Inflammation, in addition to importantly driving organism defense and survival mechanisms, can also modulate NKA activity and memory formation, as well as being relevant to many chronic illnesses, neurodegenerative diseases, and mood disorders. The aim of the current review is to highlight the recent advances as to the role of CTS and NKA in inflammatory process, with a particular focus in the central nervous system.

Endothelial proliferation modulates neuron-glia survival and differentiation in ischemic stress

Background

Recent studies have shown that endothelial proliferation and angiogenic response are characteristic of degenerative events, such that the magnitude of endothelial activation is reflective of the progression of neurodegeneration.

Purpose

This study sets out to, compare, the degenerative changes seen in the parietal cortex (PC) and periventricular zone (PVZ) after cyanide toxicity or vascular occlusion.

Methods

Global vascular occlusion (VO) and cyanide toxicity (CN) were induced in separate sets of male adult wistar rats for 10 days (treatment phase). Subsequently, the treatment was discontinued for another 10 days (withdrawal phase) (CN-I and VO-I). A separate group of control was maintained for 10 days and received normal saline for this duration. The animals were euthanized at day 10 (treatment and control) and day 20 (withdrawal) after which the tissue was processed for antigen retrieval immunohistochemistry to demonstrate; H&E (general histology) CD31/PECAM 1(endothelial proliferation), CD45 (monocyte/phagocyte), GFAP (glia), NSE (neuron), Ki-67 (cell proliferation) and NF (neurofilament). Total cell count, immunopositive cell counts, arterial wall thickness and lumen width were determined and plotted using ANOVA with significance set at P<0.05*.

Results

We observed an increase in endothelial proliferation (↑CD31), glia activation and a decrease in neuron count in vascular occlusion and cyanide toxicity after the treatment phase (degeneration). The neuron count increased (↑NSE) after withdrawal of cyanide treatment and vascular occlusion and was accompanied by a corresponding decrease in endothelial and glia activation (↓CD31/GFAP). Degenerative changes were more prominent in cyanide toxicity when compared with vascular occlusion. The increase in CD45 expression coupled with a reduced CD31/GFAP after the withdrawal phase was evident of vascular remodeling and neurosurvival.

Conclusion

We conclude that neuronal degeneration in cyanide toxicity or vascular occlusion is dependent on an increase in endothelial proliferation (↑CD31), glia activation (↑GFAP) and a decrease in monocyte expression (↓CD45); representing a pro-inflammatory response. Furthermore, cyanide toxicity induced more prominent degenerative changes when compared with the vascular occlusion due to a higher CD31/GFAP expression. Subsequent withdrawal of the ischemia facilitated a reduction in GFAP/CD31 with a corresponding increase in monocytes (↑CD45) for vascular remodeling and neurosurvival. The VO-I showed a significant increase in vascular remodelling than the CN-I due to a more significant increase in monocytic expression (CD45) after the withdrawal of the occlusion. Generally, we found that degeneration was prominent in the parietal cortex and less in the periventricular zone for both forms of ischemia.

Astrocyte roles in traumatic brain injury

Astrocytes sense changes in neural activity and extracellular space composition. In response, they exert homeostatic mechanisms critical for maintaining neural circuit function, such as buffering neurotransmitters, modulating extracellular osmolarity and calibrating neurovascular coupling. In addition to upholding normal brain activities, astrocytes respond to diverse forms of brain injury with heterogeneous and progressive changes of gene expression, morphology, proliferative capacity and function that are collectively referred to as reactive astrogliosis. Traumatic brain injury (TBI) sets in motion complex events in which noxious mechanical forces cause tissue damage and disrupt central nervous system (CNS) homeostasis, which in turn trigger diverse multi-cellular responses that evolve over time and can lead either to neural repair or secondary cellular injury. In response to TBI, astrocytes in different cellular microenvironments tune their reactivity to varying degrees of axonal injury, vascular disruption, ischemia and inflammation. Here we review different forms of TBI-induced astrocyte reactivity and the functional consequences of these responses for TBI pathobiology. Evidence regarding astrocyte contribution to post-traumatic tissue repair and synaptic remodeling is examined, and the potential for targeting specific aspects of astrogliosis to ameliorate TBI sequelae is considered.

Endogenous opiates and behavior: 2013

This paper is the thirty-sixth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2013 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, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.

Increased levels of sphingosine-1-phosphate in cerebrospinal fluid of patients diagnosed with tick-borne encephalitis

Background

Tick-borne encephalitis (TBE) is a serious acute central nervous system infection that can result in death or long-term neurological dysfunctions. We hypothesize that changes in sphingosine-1-phosphate (S1P) concentration occur during TBE development.

Methods

S1P and interleukin-6 (IL-6) concentrations in blood plasma and cerebrospinal fluid (CSF) were measured using HPLC and ELISA, respectively. The effects of S1P on cytoskeletal structure and IL-6 production were assessed using rat astrocyte primary cultures with and without addition of plasma gelsolin and the S1P receptor antagonist fingolimod phosphate (FTY720P).

Results

We report that acute inflammation due to TBE virus infection is associated with elevated levels of S1P and IL-6 in the CSF of infected patients. This elevated concentration is observed even at the earliest neurologic stage of disease, and may be controlled by glucocorticosteroid anti-inflammatory treatment, administered to patients unresponsive to antipyretic drugs and who suffer from a fever above 39°C. In vitro, treatment of confluent rat astrocyte monolayers with a high concentration of S1P (5 μM) results in cytoskeletal actin remodeling that can be prevented by the addition of recombinant plasma gelsolin, FTY720P, or their combination. Additionally, gelsolin and FTY720P significantly decreased S1P-induced release of IL-6.

Conclusions

TBE is associated with increased concentration of S1P and IL-6 in CSF, and this increase might promote development of inflammation. The consequences of increased extracellular S1P can be modulated by gelsolin and FTY720P. Therefore, blocking the inflammatory response at sites of infection by agents modulating S1P pathways might aid in developing new strategies for TBE treatment.

Actin filament reorganization in astrocyte networks is a key functional step in neuroinflammation resulting in persistent pain: novel findings on network restoration

In recent years, the importance of glial cell activation in the generation and maintenance of long-term pain has been investigated. One novel mechanism underlying long-lasting pain is injury-induced inflammation in the periphery, followed by microglial activation in the dorsal horn of the spinal cord, which results in local neuroinflammation. An increase in neuronal excitability may follow, with intense signaling along the pain tracts to the thalamus and the parietal cortex along with other cortical regions for the identification and recognition of the injury. If the local neuroinflammation develops into a pathological state, then the astrocytes become activated. Previous studies in which lipopolysaccharide (LPS) was used to induce inflammation have shown that in a dysfunctional astrocyte network, the actin cytoskeleton is reorganized from the normally occurring F-actin stress fibers into the more diffusible, disorganized, ring-form globular G-actin. In addition, Ca(2+) signaling systems are altered, Na(+)- and glutamate transporters are downregulated, and pro-inflammatory cytokines, particularly IL-1β, are released in dysfunctional astrocyte networks. In a series of experiments, we have demonstrated that these LPS-induced changes in astrocyte function can be restored by stimulation of Gi/o and inhibition of Gs with a combination of a μ-receptor agonist and ultralow concentrations of a μ-receptor antagonist and by inhibition of cytokine release, particularly IL-1β, by the antiepileptic drug levetiracetam. These findings could be of clinical significance and indicate a novel treatment for long-term pain.

The use of low-dose naltrexone (LDN) as a novel anti-inflammatory treatment for chronic pain

Low-dose naltrexone (LDN) has been demonstrated to reduce symptom severity in conditions such as fibromyalgia, Crohn's disease, multiple sclerosis, and complex regional pain syndrome. We review the evidence that LDN may operate as a novel anti-inflammatory agent in the central nervous system, via action on microglial cells. These effects may be unique to low dosages of naltrexone and appear to be entirely independent from naltrexone's better-known activity on opioid receptors. As a daily oral therapy, LDN is inexpensive and well-tolerated. Despite initial promise of efficacy, the use of LDN for chronic disorders is still highly experimental. Published trials have low sample sizes, and few replications have been performed. We cover the typical usage of LDN in clinical trials, caveats to using the medication, and recommendations for future research and clinical work. LDN may represent one of the first glial cell modulators to be used for the management of chronic pain disorders.