Systemic administration of vitamins C and E attenuates nociception induced by chronic constriction injury of the sciatic nerve in rats

Efficacy assessment of novel methanimine derivatives in chronic constriction injury-induced neuropathic model: An in-vivo, ex-vivo and In-Silico approach

The multicomponent etiology, complex clinical implications, dose-based side effect and degree of pain mitigation associated with the current pharmacological therapy is incapable in complete resolution of chronic neuropathic pain patients which necessitates the perpetual requirement of novel medication therapy. Therefore, this study explored the ameliorative aptitude of two novel methanimine imitative like (E)-N-(4-nitrobenzylidene)-4‑chloro-2-iodobenzamine (KB 09) and (E)-N-(4-methylbenzylidene)-4‑chloro-2-iodobenzamine (KB 10) in chronic constriction injury (CCI) of sciatic nerve induced neuropathic pain in rat model. Standard behavioral tests like dynamic and static allodynia, cold, thermal and mechanical hyperalgesia along with rotarod activity were performed at various experimental days like 0, 3, 7, 14 and 21. Enzyme linked immunosorbent assay (ELISA) on spinal tissue and antioxidant assays on sciatic nerve were executed accompanied by molecular docking and simulation studies. Prolonged ligation of sciatic nerve expressively induced hyperalgesia as well as allodynia in rats. KB 09 and KB 10 substantially attenuated the CCI elicited hyperalgesia and allodynia. They significantly reduced the biomarkers of pain and inflammation like Interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α) in ELISA and while enhanced the GSH, SOD and CAT and diminished the MDA levels during antioxidant assays. KB 09 displayed -9.62 kcal/mol with TNF-α and -7.68 kcal/mol binding energy with IL-6 whereas KB 10 exhibited binding energy of -8.20 kcal/mol with IL-6 while -11.68 kcal/mol with TNF-α and hence both trial compounds ensured stable interaction with IL-6 and TNF-α during computational analysis. The results advocated that both methanimine derivatives might be novel candidates for attenuation of CCI-induced neuropathic pain prospects via anti-nociceptive, anti-inflammatory and antioxidant mechanisms.

Pitavastatin attenuates neuropathic pain induced by partial sciatic nerve in Wistar rats

OBJECTIVES

Pitavastatin is a competitive HMG-CoA reductase inhibitor for lowering of cholesterol level and low density lipoprotein cholesterol. This study was designed to evaluate the effect of pitavastatin in neuropathic pain induced by partial sciatic nerve ligation along with neuronal changes in Wister rats.

METHODS

Pitavastatin was started three days prior to the surgery and continued for 14 days The pain was determined by thermal hyperalgesia and cold allodynia. The biochemical changes were estimated at the end of the study. The levels of cytokines were measured using an ELISA test. Western blot analysis was used to detect levels of expression of JNK, p-JNK, ERK, p-ERK, p38MAPK, p-p38MAPK. The sciatic nerve was investigated histopathologically.

KEY FINDINGS

Pitavastatin significantly ameliorated nerve pain induced by PSNL and also attenuated the biochemical changes in a dose-dependent manner. The levels of inflammatory mediators were inhibited by pitavastatin. There was significant improvement in sciatic nerve fibres histology. The levels of p-38, p-ERK, and p-JNK and their associated phosphorylated proteins were reduced after treatment with pitavastatin.

CONCLUSION

The present study indicates that treatment with pitavastatin reversed the PSNL-induced neuropathy in Wister rats and may be an additional therapeutic strategy in the management of neuropathic pain.

Involvement of GABAergic, glutamatergic, opioidergic, and brain-derived neurotrophic factor systems in the trigeminal neuropathic pain process

Trigeminal neuropathic pain (TNP) is an intense pain condition characterized by hyperalgesia and allodynia; however, its neural mechanisms are not completely understood. Its management is complex, and studies that investigate its biochemical mechanisms are important for improving clinical approaches. This study aimed to evaluate the involvement of GABAergic, glutamatergic, and opioidergic systems and brain-derived neurotrophic factor (BDNF) levels in the TNP process in rats. TNP is induced by chronic constriction injury of the infraorbital nerve (CCI-ION). Nociceptive responses were evaluated using the facial von Frey test before and after the administration of GABAergic and opioidergic agonists and glutamatergic antagonists. The rats were divided into vehicle-treated control (C), sham-surgery (SS), and CCI-ION groups, and then subdivided into the vehicle (V)-treated SS-V and CCI-ION-V groups, SS-MK801 and CCI-ION-MK801, treated with the N-methyl-d-aspartate receptor selective antagonist MK801; SS-PB and CCI-ION-PB, treated with phenobarbital; SS-BZD and CCI-ION-BZD, treated with diazepam; SS-MOR and CCI-ION-MOR, treated with morphine. BDNF levels were evaluated in the cerebral cortex, brainstem, trigeminal ganglion, infraorbital branch of the trigeminal nerve, and serum. CCI-ION induced facial mechanical hyperalgesia. Phenobarbital and morphine reversed the hyperalgesia induced by CCI-ION, and the CCI-BZD group had an increased nociceptive threshold until 60 min. CCI-ION-GLU increased the nociceptive threshold at 60 min. Cerebral cortex and brainstem BDNF levels increased in the CCI-ION and SS groups. Only the CCI group presented high levels of BDNF in the trigeminal ganglion. Our data suggest the involvement of GABAergic, glutamatergic, and opioidergic systems and peripheral BDNF in the TNP process.

Probucol attenuates NF-κB/NLRP3 signalling and augments Nrf-2 mediated antioxidant defence in nerve injury induced neuropathic pain

Neuroinflammation is one of the most significant pathological drivers following nerve injury which along with immune cell activation, oxidative stress and other associated molecular mechanisms contribute to development of neuropathic pain characterized by hyperalgesia and allodynia. In the current study we have investigated the pharmacological effect of probucol (prb) using chronic constriction injury (CCI) of sciatic nerve induced neuropathic pain (NP) model in rats. CCI of sciatic nerve resulted in marked decrease in pain threshold along with perturbations in anti-oxidant defence, enhanced inflammatory mediators and abnormal foot posture. Administration of prb at the doses of 8 and 16 mg/kg, p.o. for 14 days significantly attenuated the behavioural, biochemical and functional deficits following CCI of sciatic nerve. To further explore the molecular mechanisms of prb, we assessed the post treatment levels of inflammatory and oxidative stress markers like NLRP3 inflammasome, NF-κB and associated proinflammatory molecules such as IL-1 β, TNF-α & IL-6 along with Nrf-2 and HO-1. Our findings demonstrated that CCI induced changes in levels of these markers were dose dependently reversed by administration of prb. Of note, at molecular level the elevated expression of transcription factors such as NF-κB which is crucial for Nlrp3 activation and diminished levels of Nrf-2 were manifested following CCI induction, these changes were markedly reversed with 14 days treatment of prb at both the doses. Our findings highlighted the dual pharmacological effect of prb, anti-inflammatory and anti-oxidant via modulation of NF-κB/NLRP3 signalling and Nrf-2 pathway in attenuation of CCI of sciatic nerve induced NP.

Spine adjusting instrument (Impulse®) attenuates nociception and modulates oxidative stress markers in the spinal cord and sciatic nerve of a rat model of neuropathic pain

OBJECTIVE

Oxidative stress plays an important role in neuropathic pain. Spinal manipulative therapy (SMT) can exert beneficial effects in pain outcomes in humans and animal models. SMT can also modulate oxidative stress markers in both humans and animals. We aimed to determine the effect of Impulse®-assisted SMT (ISMT) on nociception and oxidative stress biomarkers in the spinal cord and sciatic nerve of rats with neuropathic pain (NP).

METHODS

NP was induced by chronic constriction injury (CCI) of the sciatic nerve. Animals were randomly assigned to naive, sham (rats with sciatic nerve exposure but without ligatures) and CCI, with and without ISMT. ISMT was applied onto the skin area corresponding to the spinous process of L4-L5, 3 times/week, for 2 weeks. Mechanical threshold, latency to paw withdrawal to thermal stimulus and oxidative stress biomarkers in spinal cord and sciatic nerve were the main outcomes evaluated.

RESULTS

ISMT significantly increased mechanical threshold and withdrawal latency after CCI. In the spinal cord, ISMT prevented the increase of pro-oxidative superoxide anion generation and hydrogen peroxide levels. Lipid hydroperoxide levels both in the spinal cord and in the sciatic nerve were attenuated by ISMT. Total antioxidant capacity increased in the spinal cord and sciatic nerve of CCI rats with and without ISMT. CCI and ISMT did not significantly change the total thiol content of the spinal cord.

CONCLUSIONS

Our findings suggest reduced oxidative stress in the spinal cord and/or nerve may be an important mechanism underlying a therapeutic effect of SMT to manage NP non-pharmacologically.

The antioxidant N-(2-mercaptopropionyl)-glycine (tiopronin) attenuates expression of neuropathic allodynia and hyperalgesia

The current pharmacotherapy of neuropathic pain is inadequate as neuropathic pain involves varied clinical manifestations with multifactorial etiology, modulated by a cascade of physical and molecular events leading to different clinical presentations of pain. There is an accumulating evidence of the involvement of oxidative stress in neuropathy, and antioxidants have shown promise in mitigating neuropathic pain syndromes. To explore the evidence supporting this beneficial proclivity of antioxidants, this study investigated the antinociceptive effectiveness of N-(2-mercaptopropionyl)glycine or tiopronin, a well-recognized aminothiol antioxidant, in a refined chronic constriction injury (CCI) rat model of neuropathic pain. Tiopronin (10, 30, and 90 mg/kg, i.p.) and pregabalin (30 mg/kg, i.p.) were administered daily after CCI surgery. The neuropathic paradigms of mechanical/cold allodynia and mechanical/heat hyperalgesia were assessed on days 3, 7, 14, and 21 post-nerve ligation. At the end of study, malondialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT), and glutathione (GSH) levels were estimated in the sciatic nerve, dorsal root ganglion, and spinal cord for assessing the extent of oxidative stress. The expression of neuropathic nociception was attenuated by tiopronin which was observed as a significant attenuation of CCI-induced allodynia and hyperalgesia. Tiopronin reversed the neuronal oxidative stress by significantly reducing MDA, and increasing SOD, CAT, and GSH levels. Pregabalin also showed similar beneficial propensity on CCI-induced neuropathic aberrations. These findings suggest prospective neuropathic pain attenuating efficacy of tiopronin and further corroborated the notion that antioxidants are effective in mitigating the development and expression of neuropathic pain and underlying neuronal oxidative stress.

Aqueous leaf extract from Luehea divaricata Mart. Modulates oxidative stress markers in the spinal cord of rats with neuropathic pain

ETHNOPHARMACOLOGICAL RELEVANCE

Reactive oxygen species (ROS) play an important role in neuropathic pain (i.e., pain caused by lesion or disease of the somatosensory system). We showed previously that the aqueous extract prepared from Luehea divaricata leaves, a plant explored by native ethnic groups of Brazil to treat different pathologic conditions, exhibits good antioxidant activity and induces analgesia in rats with neuropathic pain (J Ethnopharmacol, 2020; 256:112761. doi: 10.1016/j.jep.2020.112761). The effect was comparable to that of gabapentin, a drug recommended as first-line treatment for neuropathic pain. However, increasing evidence has indicated the need to accurately determine the oxidative stress level of an individual before prescribing supplemental antioxidants.

AIM OF THE STUDY

This study assessed the effects of the oral administration of aqueous extract from leaves of L. divaricata on the sciatic functional index (SFI) and spinal-cord pro-oxidant and antioxidant markers of rats with neuropathic pain.

MATERIALS AND METHODS

Placement of four loose chromic thread ligatures around the sciatic nerve produced chronic constriction injury (CCI) of the sciatic nerve, a commonly employed animal model to study neuropathic pain. Aqueous extract from leaves of L. divaricata (100, 300, 500 and 1000 mg/kg), gabapentin (50 mg/kg) and aqueous extract (500 mg/kg) + gabapentin (30 mg/kg) were administrated per gavage daily for 10 or 35 days post-CCI. Antinociception was assessed using the von Frey test while SFI showed functional recovery post-nerve lesion throughout the experimental period. At days 10 and 35 post-surgery, the lumbosacral spinal cord and a segment of the injured sciatic nerve were dissected out and used to determine lipid hydroperoxide levels and total antioxidant capacity (TAC). The spinal cord was also used to determine superoxide anion generation (SAG), hydrogen peroxide (H₂O₂) levels and total thiol content.

RESULTS

As expected, the extract, gabapentin and extract + gabapentin induced antinociception in CCI rats. While no significant functional recovery was found at 10 days post-CCI, a significant recovery was found in SFI of extract-treated CCI rats at 21 and 35 days post-CCI. A significant functional recovery was found already at day 10 post-CCI in gabapentin and gabapentin + extract-treated CCI rats. The extract treatment prevented increases in lipid hydroperoxides levels and TAC in injured sciatic nerve, which were found in this tissue of vehicle-treated rats at 10 days post-CCI. Extract also prevented an increase in SAG, H₂O₂ and lipid hydroperoxides levels in the spinal cord, which were elevated in this tissue of vehicle-treated rats at 10 and 35 days post-CCI. Extract also prevented a decrease in total thiol content and an increase in TAC in the spinal cord of CCI rats in these same time periods.

CONCLUSIONS

Aqueous extract from L. divaricata leaves was demonstrated, for the first time, to improve SFI and modulate oxidative stress markers in injured sciatic nerve and spinal cord of CCI rats. Thus, the antinociceptive effect of the extract involves modulation of oxidative stress markers in injured sciatic nerve and spinal cord.

High-Dose Vitamin C in Advanced-Stage Cancer Patients

High-dose intravenously administered vitamin C (IVC) is widely used in cancer patients by complementary and alternative medicine practitioners. The most frequent indications for IVC therapy result from the belief in its effectiveness as a potent anti-cancer agent which additionally enhances chemosensitivity of cancer cells and reduces chemotherapy-related toxicities and fatigue intensity. In this narrative review, we decided to deal with this issue, trying to answer the question whether there is any scientific evidence supporting the rationale for application of high-dose IVC therapy in advanced-stage cancer patients. Although results obtained from preclinical studies demonstrated that millimolar ascorbate plasma concentrations achievable only after IVC administration were cytotoxic to fast-growing malignant cells and inhibited tumor growth as well as prolonged the survival of laboratory animals, such positive effects were not found in human studies with advanced-stage cancer patients. We also have not found the rationale for the use of IVC to increase the effectiveness of chemotherapy and to reduce the chemotherapy-induced toxicity in the above mentioned group. Nevertheless, in palliative care, high-dose IVC might be considered as a therapy improving the quality of life and reducing cancer-related symptoms, such as fatigue and bone pain. However, because of the absence of placebo-controlled randomized trials on IVC efficacy in advanced-stage cancer patients, the placebo effect cannot be excluded.

Synthetic Secoisolariciresinol Diglucoside Attenuates Established Pain, Oxidative Stress and Neuroinflammation in a Rodent Model of Painful Radiculopathy

Painful cervical radiculopathy is characterized by chronic neuroinflammation that lowers endogenous antioxidant responses leading to the development of oxidative stress and pain after neural trauma. Therefore, antioxidants such as secoisolariciresinol diglucoside (SDG), that promote antioxidant signaling and reduce oxidative damage may also provide pain relief. This study investigated if repeated systemic administration of synthetic SDG after a painful root compression reduces the established pain, oxidative stress and spinal glial activation that are typically evident. SDG was administered on days 1-3 after compression and the extent of oxidative damage in the dorsal root ganglia (DRG) and spinal cord was measured at day 7 using the oxidative stress markers 8-hydroxguanosine (8-OHG) and nitrotyrosine. Spinal microglial and astrocytic activation were also separately evaluated at day 7 after compression. In addition to reducing pain, SDG treatment reduced both spinal 8-OHG and nitrotyrosine, as well as peripheral 8-OHG in the DRG. Moreover, SDG selectively reduced glial activation by decreasing the extent of astrocytic but not microglial activation. These findings suggest that synthetic SDG may attenuate existing radicular pain by suppressing the oxidative stress and astrocytic activation that develop after painful injury, possibly identifying it as a potent therapeutic for painful radiculopathies.

Neuroinflammation, oxidative stress and their interplay in neuropathic pain: Focus on specialized pro-resolving mediators and NADPH oxidase inhibitors as potential therapeutic strategies

Neuropathic pain (NP) is a chronic condition that results from a lesion or disease of the nervous system, greatly impacting patients' quality of life. Current pharmacotherapy options deliver inadequate and/or insufficient responses and thus a significant unmet clinical need remains for alternative treatments in NP. Neuroinflammation, oxidative stress and their reciprocal relationship are critically involved in NP pathophysiology. In this context, new pharmacological approaches, aiming at enhancing the resolution phase of inflammation and/or restoring redox balance by targeting specific reactive oxygen species (ROS) sources, are emerging as potential therapeutic strategies for NP, with improved efficacy and safety profiles. Several reports have demonstrated that administration of exogenous specialized pro-resolving mediators (SPMs) ameliorates NP pathophysiology. Likewise, deletion or inhibition of the ROS-generating enzyme NADPH oxidase (NOX), particularly its isoforms 2 and 4, results in beneficial effects in NP models. Notably, SPMs also modulate oxidative stress and NOX also regulates neuroinflammation. By targeting neuroinflammatory and oxidative pathways, both SPMs analogues and isoform-specific NOX inhibitors are promising therapeutic strategies for NP.

Aqueous extract from Luehea divaricata Mart. Leaves reduces nociception in rats with neuropathic pain

ETHNOPHARMACOLOGICAL RELEVANCE

Luehea divaricata, popularly known in Brazil as "açoita-cavalo", has been widely explored by different ethnic groups native to Brazil to treat different pathologic conditions, including inflammatory pain. However, no report could be found on the effect that extract of L. divaricata has on neuropathic pain. This is an important topic because convergent and divergent mechanisms underlie inflammatory vs. neuropathic pain indicate that there may not always be a clear mechanistic delineation between these two conditions.

AIM OF THE STUDY

The study aimed to determine antioxidant activity and macronutrient composition of aqueous extract from leaves of L. divaricata, and the effect of oral administration on nociception in rats with chronic constriction injury (CCI) of sciatic nerve-induced neuropathic pain, one of the most commonly employed animal models of neuropathic pain.

MATERIALS AND METHODS

The antioxidant activity of the extract was evaluated by total phenolic content and DPPH, ABTS^●+ and ORAC methods. Vitexin was determined by HPLC to show that the composition of the extract of the present study is similar to that used in previous studies with this genus. Total sugar and sucrose concentrations were assessed by the anthrone method, while glucose and triacilglycerides were determined using commercially available kits. Fructose concentration was calculated from values for total sugars, glucose and sucrose. Total protein was determined by Bradford assay. The effect on DNA strand breaking was investigated by inhibition of strand breaking of supercoiled DNA by hydroxyl radical. The antinociceptive effects of aqueous extract (100, 300, 500, and 1000 mg/kg, i.g.) were evaluated on thermal and mechanical thresholds for neuropathic pain induced by chronic constriction injury (CCI) of the sciatic nerve in rats. We also compared the antinociceptive effect of the extract (500 mg/kg, i.g.) with that induced by gabapentin (50 mg/kg, i.g.), a first-line clinical treatment for neuropathic pain. The effect of co-administration of extract (500 mg/kg, i.g.) and low-dose gabapentin (30 mg/kg, i.g.) was also assessed. In addition, the effect of the extract on body weight, and blood and hepatic parameters were investigated to reveal possible side effects of treatment.

RESULTS

The extract showed high content of total phenol; good reducing capacity for DPPH, ABTS^●+ and ORAC assays; presence of vitexin; and a high capacity to inhibit strand breaking of supercoiled DNA. The predominant sugar was sucrose, followed by glucose and fructose. Total protein was greater than triacylglycerides, with the latter being present in a trace amount in the extract. The extract increased the thermal and mechanical thresholds, which was reduced by CCI. The antinociceptive effect was comparable to gabapentin and was also found after co-administration of extract and low-dose gabapentin. No significant change was found in body weight and blood and hepatic indicators after extract treatment.

CONCLUSIONS

Aqueous extract from L. divaricata leaves was as effective as gabapentin at attenuating CCI-induced neuropathic pain, indicating for first time the therapeutic potential of this species for this type of pain.

Effect of ethanolic extract of Solanum virginianum Linn. on neuropathic pain using chronic constriction injury rat model and molecular docking studies

The present research work was designed to examine the neuroprotective effect of ethanolic extract of Solanum virginianum Linn. (SV) in chronic construction injury (CCI) of sciatic nerve-induced neuropathic pain in rats. The extract was initially standardized by high-performance thin-layer chromatography using solasodine as a biomarker and was then subjected to assess the degree of mechanical allodynia, thermal allodynia, mechanical hyperalgesia, thermal hyperalgesia and biochemical evaluations. Administration of SV (100 and 200 mg/kg; p.o.) and pregabalin (10 mg/kg; p.o.) as a reference standard significantly debilitated hyperalgesia and allodynia and notably restored the altered antioxidant level and pro-inflammatory cytokine (IL-1β and TNF-α) expression in a dose-dependent manner. Further, to appraise the mechanistic approach of solasodine, docking simulation studies were done on the 3D structure of the voltage-gated N-type calcium channel (Cav 2.2), R-type calcium channel (Cav 2.3) and sodium channel (Nav 1.7), and the results revealed that solasodine properly positioned into Phe 19, Leu 32, Met 51 and Met 71 (FLMM pocket) of Cav 2.2 and Cav 2.3 and being a competitor of Ca²⁺/N-lobe it may inactivate these calcium channels but did not bind into the desired binding pocket of Nav 1.7. Thus, the study confirmed the role of solasodine as a major biomarker for the observed neuroprotective nature of Solanum virginianum.

Graviola Fruit Bar Added Acerola By-Product Extract Protects Against Inflammation and Nociception in Adult Zebrafish (Danio rerio)

Studies involving foods associated with pain reversal and anti-inflammatory effects using zebrafish are rarely reported in the literature. This study aimed to evaluate the effect of graviola (Annona muricata L.) fruit bar (GFB) and GFB added with acerola (Malpighia glabra L) seed extract (ASE) on acute nociception and abdominal inflammation in adult zebrafish (Danio rerio). Acute nociception was induced by formalin, capsaicin, cinnamaldehyde, acidic saline, glutamate (cutaneous models), and hypertonic saline (corneal model), and inflammation was induced by carrageenan. Both GFB and ASE exhibited antinociceptive effect modulated by the nitrergic system, guanylate cyclase, and transient receptor potential ankyrin 1 and acid-sensing ion channels. The antinociceptive effect of GFB also appears to be modulated by the opioid system and glutamatergic receptors (N-methyl-D-aspartate receptor). Only ASE presented corneal antinociceptive effect. Both samples showed anti-inflammatory effect, being more significant the effect of GFB. The addition of acerola by-product extract in GFB results in a product with greater biological potential.

Spinal Manipulation Therapy Improves Tactile Allodynia and Peripheral Nerve Functionality and Modulates Blood Oxidative Stress Markers in Rats Exposed to Knee-Joint Immobilization

OBJECTIVE

The purpose of our study was to evaluate the effect of manually assisted lumbar spinal manipulation therapy on tactile allodynia, peripheral nerve functional recovery, and oxidative markers in rats exposed to knee immobilization-inducing hypersensitivity.

METHODS

Tactile allodynia and sciatic, tibial, and peroneal functional indices were assessed before the knee joint immobilization, 24 hours after the knee cast removal, and 24 hours after 3 weeks of lumbar therapy with the Activator Adjusting Instrument, model 4 (AAI 4). Subsequently, the blood was collected from each rat, and oxidative markers such as lipid hydroperoxide levels; nitric oxide metabolites; and superoxide dismutase, catalase, and glutathione peroxidase activities were assessed.

RESULTS

The AAI 4 improved the immobilization-induced allodynia and recovered the peripheral nerve functional indices impaired after knee immobilization. Immobilized rats treated with AAI 4 therapy presented a lack of significant changes in lipid hydroperoxides and nitric oxide metabolites in the plasma contrasting with rats that were kept freely in their cages, with no therapy applied, which presented elevated lipid hydroperoxides levels. Also, the antioxidant catalase enzymatic activity decreased in the blood of rats immobilized and treated with AAI 4.

CONCLUSION

These results suggest that manually assisted lumbar spinal manipulation therapy modulates systemic oxidative stress, which possibly contributes to the analgesia and recovery of peripheral nerve functionality.

Role of receptor-interacting protein 1/receptor-interacting protein 3 in inflammation and necrosis following chronic constriction injury of the sciatic nerve

Nerve damage often leads to nervous system dysfunction and neuropathic pain. The serine-threonine kinases receptor-interacting protein 1 (RIP1) and 3 (RIP3) are associated with inflammation and cell necrosis. This study aimed to explore the role of RIP1 and RIP3 in sciatic nerve chronic constriction injury (CCI) in mice. On a total of thirty mice, sciatic nerve CCI was performed. The paw withdrawal threshold was measured using Von Frey filaments. The mRNA expression and protein levels of inflammatory factors RIP1 and RIP3 in the dorsal root ganglion (DRG), spinal cord (SC) and hippocampus (HIP) were also determined. We found that paw withdrawal threshold was significantly reduced from the second day after the operation, and the levels of tumour necrosis factor-α and interferon-γ in DRG, SC and HIP were significantly increased on the eighth and 14th days in CCI mice. Furthermore, the downstream signalling molecules of RIP1 and RIP3, GTPase dynamin-related protein-1, NLR family pyrin domain containing-3 (NLRP3) and nuclear factor κB-p65 were upregulated. Increased protein levels of programmed cell death protein 1, which indicate cell death of peripheral and central nervous tissue, were induced by CCI of the sciatic nerve. Overall, this study showed that RIP1 and RIP3 were highly expressed in DRG, SC and HIP of the sciatic nerve in CCI mice and may be involved in chronic neuroinflammation and neuronecrosis.

Caffeic acid phenethyl ester attenuates neuropathic pain by suppressing the p38/NF-κB signal pathway in microglia

Background

Management of neuropathic pain is still a clinical challenge. Evidence has accumulated indicating that propolis is effective in attenuating neuropathic pain; however, the mechanism is not fully understood. Our present study investigated the effects and the possible mechanism of caffeic acid phenethyl ester (CAPE), the main ingredient of propolis, in improving neuropathic pain via its inhibition on p38/NF-κB signal pathway in microglia.

Materials and methods

Chronic constriction injury (CCI) mice model and the microglial cell line BV-2 were used to investigate the effects and the mechanism of CAPE. Cell signaling was measured by real-time PCR, Western blotting and immunofluorescence assay.

Results

CAPE relieved neuropathic pain behaviors induced by CCI in mice. CAPE also inhibited CCI-induced activation of microglia. Furthermore, CAPE suppressed the phosphorylation of p38 mitogen-activated protein kinase, inhibited the translocation of NF-κB and decreased the expression of proinflammatory cytokines tumor necrosis factor-α, IL-1β and IL-6.

Conclusion

CAPE was found to be an effective and safe drug candidate for alleviating neuropathic pain by its powerful inhibition on the P38/NF-κB signal pathway.

The efficacy of microemulsion-based delivery to improve vitamin E properties: evaluation of the antinociceptive, antioxidant, antidepressant- and anxiolytic-like activities in mice

Objectives

A microemulsion-based delivery system was designed to improve vitamin E (VE) properties, and its antinociceptive, antioxidant, antidepressant- and anxiolytic-like activities in mice were evaluated.

Methods

Male Swiss mice received, by intragastric route, canola oil (20 ml/kg), blank microemulsion (B-ME) (20 ml/kg), VE free (VE-F) (200 mg/kg) or VE microemulsion (VE-ME) (200 mg/kg). In acute treatment, a single dose of treatments was administrated and 30 min after behavioural tests were performed. In the subchronic treatment, mice received such treatments, once a day, for 8 days. On the eighth day, behavioural tests were performed.

Key findings

In the subchronic treatment, VE-ME increased entries and spent time in the open arms in the elevated plus-maze test and decreased the immobility time in the tail suspension test, but no change was found after acute treatment. Acute and subchronic treatments with VE-ME increased response latency to thermal stimulus in the hot-plate test. VE-ME decreased the thiobarbituric acid reactive species levels in the acute and subchronic protocols. Additionally, in subchronic treatment, VE-ME increased renal catalase activity, but VE-F reduced its activity.

Conclusions

Vitamin E-microemulsions showed antioxidant, antinociceptive, antidepressant- and anxiolytic-like actions; thus, ME-based delivery improved pharmacological properties of VE.

Functional interaction between N-methyl-D-aspartate receptor and ascorbic acid during neuropathic pain induced by chronic constriction injury of the sciatic nerve

BACKGROUND

Neuropathic pain is a chronic pain condition, which is resistant to therapy. Ascorbate was released because of the activation of glutaminergic neurons. Due to the important role of N-methyl-D-aspartate (NMDA) receptors in the pathophysiology of neuropathic pain, this study investigated the analgesic efficacy of ascorbic acid (AA) in neuropathic pain condition and the role of NMDA receptors in this effect.

METHODS

For this purpose, adult male rats were randomly allocated to experimental groups (n=8 in each group). Neuropathic pain was induced by chronic constriction injury (CCI) of the sciatic nerve. During the second week after CCI, animals received a single injection of 1, 3, 5, or 10 mg/kg of AA intraperitoneally and pain threshold was determined 15 and 60 min later. The antinociceptive effect of chronic administration was also evaluated by intraperitoneal injection (IP) of 3 mg/kg AA for 3 weeks. To determine the role of NMDA receptors, separate groups of animals 30 min after single injection of AA (1 mg/kg) animals received i.p. injection of ketamine (5 mg/kg), MK-801 (0.01 mg/kg), or glutamate (1000 nmol) and were tested 20 min afterwards. Data analyzed by ANOVA and Newman-Keuls tests and p<0.05 were considered as significant.

RESULTS

IP of 3, 5 and 10 mg/kg increased the pain threshold during the second week after CCI (p<0.05, F=3 in tactile allodynia and p<0.01, F=3.2 in thermal and mechanical hyperalgeisa). Chronic administration of AA also produced antinociceptive effect. Ascorbic acid (1 mg/kg, i.p.) inhibited MK-801 and ketamine-induced antinociception response significantly (p<0.001, F=2). It also prevented the analgesic effect of glutamate administration (p<0.001, F=2).

CONCLUSIONS

The results indicated that AA produced a dose-dependent antinociceptive effect that seems to mediate through its interaction with NMDA receptors.

Effects of Methanol Fraction from Leaves of Schinus terebinthifolius Raddi on Nociception and Spinal-Cord Oxidative Biomarkers in Rats with Neuropathic Pain

We determined the antioxidant potential of fractions obtained from leaves of Schinus terebinthifolius, a medicinal plant known in Brazil as aroeira, to select the fraction with the best yield and antioxidant performance. These qualities were found in the methanol fraction (MeF), which was administered intraperitoneally (20 mg/kg/day) for 3 and 10 days to rats with chronic constriction injury (CCI) of the sciatic nerve, a model of neuropathic pain. The MeF increased the mechanical and thermal thresholds that had been lowered by CCI. In parallel, the lumbosacral spinal cord showed an increase in superoxide dismutase but a decrease in glutathione peroxidase and glutathione-S-transferase activities in saline- and MeF-treated CCI rats. Catalase activity decreased only in saline-treated CCI rats for 10 days. Total thiols decreased in saline- and MeF-treated CCI rats. Ascorbic acid increased in these rats at day 3 but only in saline-treated CCI rats at day 10. No change was found in hydrogen peroxide and lipid hydroperoxide. Open-field and elevated plus-maze tests and blood parameters of liver function did not change. Thus, the MeF from leaves of S. terebinthifolius has an antinociceptive action with no toxic effects, and it affects oxidant biomarkers in the spinal cord of rats with CCI.

Treatment with ascorbic acid and α-tocopherol modulates oxidative-stress markers in the spinal cord of rats with neuropathic pain

Vitamin E (vit. E) and vitamin C (vit. C) are antioxidants that inhibit nociception. The effect of these vitamins on oxidative-stress markers in the spinal cord of rats with chronic constriction injury (CCI) of the sciatic nerve is unknown. This study investigated the effect of intraperitoneal administration of vit. E (15 mg·kg-1·day-1) and vit. C (30 mg·kg-1·day-1), given alone or in combination, on spinal cord oxidative-stress markers in CCI rats. Adult male Wistar rats weighing 200-250 g were divided equally into the following groups: Naive (rats did not undergo surgical manipulation); Sham (rats in which all surgical procedures involved in CCI were used except the ligature), and CCI (rats in which four ligatures were tied loosely around the right common sciatic nerve), which received injections of vitamins or vehicle (saline containing 1% Tween 80) for 3 or 10 days (n=6/each group). The vitamins prevented the reduction in total thiol content and the increase in superoxide-anion generation that were found in vehicle-treated CCI rats. While nitric-oxide metabolites increased in vehicle-treated CCI rats 3 days after surgery, these metabolites did not show significant changes in vitamin-treated CCI rats. In all rats, total antioxidant capacity and hydrogen-peroxide levels did not change significantly. Lipid hydroperoxides increased 25% only in vehicle-treated CCI rats. These changes may contribute to vit. C- and vit. E-induced antinociception, because scavenging reactive oxygen species seems to help normalize the spinal cord oxidative status altered by pain.

Ischemia-Reperfusion Injury of Sciatic Nerve in Rats: Protective Role of Combination of Vitamin C with E and Tissue Plasminogen Activator

An ischemia/reperfusion injury of rat's sciatic nerve was experimentally developed. In this model, we measured the in vivo production of superoxide radical, as a marker of oxidative stress and the occludin expression as an indicator of blood-nerve barrier function and we examined potential protective innervations against these abnormalities. Right sciatic nerves of the animals underwent 3 h of ischemia followed by 7 days of reperfusion and were divided into three groups: ischemic, pretreated with vitamin C in conjunction with vitamin E and treated with tissue plasminogen activator. Compared to measurements from left sciatic nerves used as sham, the ischemic group showed significantly increased superoxide radical and reduced expression of occludin in western blot and immunohistochemistry. No such differences were detected between sham and nerves in the vitamin or tissue plasminogen activator groups. It is suggested that the experimental ischemia/reperfusion model was suitable for studying the relationship between oxidative state and blood-nerve barrier. The reversion of abnormalities by the applied neuroprotective agents might prove to be a clinically important finding in view of the implication of vascular supply derangement in various neuropathies in humans.

Nuclear factor kappa B regulated monocyte chemoattractant protein-1/chemokine CC motif receptor-2 expressing in spinal cord contributes to the maintenance of cancer-induced bone pain in rats

BACKGROUND

Chemokine, monocyte chemoattractant protein-1 (MCP-1), is a potential factor to cause cancer-induced bone pain (CIBP). NF-κB signaling is very important in mediating the expression of chemokines and may have a role in CIBP. However, the mechanism is still unclear. This study investigates the role of NF-κB in CIBP by regulating MCP-1/chemokine CC motif receptor-2 (CCR2) signaling pathway.

METHODS

A rat CIBP model was established by injecting Walker-256 cells into the tibia medullary cavity. Nine days later, animals were intrathecally administrated with MCP-1 neutralizing antibody, CCR2 antagonist (RS504393), or NF-кB inhibitor (BAY11-7081). Mechanical paw withdrawal threshold was used to assess pain behavior and sciatic functional index, and radiographic images were adopted to evaluate the damage of nerve and bone. The spinal cords were harvested for Western blot and quantitative reverse transcription polymerase chain reaction. The distribution of MCP-1, CCR2, and NF-кB was detected by double immunofluorescent staining.

RESULTS

CIBP caused remarkable bone destruction, injury of sciatic and femoral nerve, and persistent (>15 days) mechanical allodynia in rats. Tumor cell inoculation upregulate MCP-1 and NF-кB in activated neurons as well as CCR2 in neurons and microglia of the spinal cord. MCP-1 antibody, RS504393, and BAY11-7081 partially reversed CIBP-induced mechanical allodynia, and CIBP regulated the expression levels of pro-inflammatory cytokines, tumor necrosis factor-α and interferon-γ, and anti-inflammatory cytokine, interleukin 4, and BAY11-7081 lowered CIBP-induced MCP-1 and CCR2 expressions in a dose-dependent manner.

CONCLUSION

In conclusion, NF-кB signaling pathway regulates the expressions of MCP-1/CCR2-induced inflammatory factors in the spinal cord of CIBP rats.

Effects of N-acetylcysteine on spinal cord oxidative stress biomarkers in rats with neuropathic pain

N-acetylcysteine (NAC) inhibits nociceptive transmission. This effect has been associated partly with its antioxidant properties. However, the effect of NAC on the levels of lipid hydroperoxides (a pro-oxidant marker), content of ascorbic acid (a key antioxidant molecule of nervous tissue) and total antioxidant capacity (TAC) is unknown. Thus, our study assessed these parameters in the lumbosacral spinal cord of rats with chronic constriction injury (CCI) of the sciatic nerve, one of the most commonly employed animal models of neuropathic pain. Thirty-six male Wistar rats weighing 200–300 g were equally divided into the following groups: Naive (rats did not undergo surgical manipulation); Sham (rats in which all surgical procedures involved in CCI were used except the ligature), and CCI (rats in which four ligatures were tied loosely around the right common sciatic nerve). All rats received intraperitoneal injections of NAC (150 mg·kg⁻¹·day⁻¹) or saline for 1, 3, or 7 days. Rats were killed 1, 3, and 7 days after surgery. NAC treatment prevented the CCI-induced increase in lipid hydroperoxide levels only at day 1, although the amount was higher than that found in naive rats. NAC treatment also prevented the CCI-induced increase in ascorbic acid content, which occurred at days 1, 3, and 7. No significant change was found in TAC with NAC treatment. The changes observed here may be related to the antinociceptive effect of NAC because modulation of oxidative-stress parameters seemed to help normalize the spinal cord oxidative status altered by pain.

Nutritional and Nanotechnological Modulators of Microglia

Microglia are the essential responders to alimentary, pharmacological, and nanotechnological immunomodulators. These neural cells play multiple roles as surveyors, sculptors, and guardians of essential parts of complex neural circuitries. Microglia can play dual roles in the central nervous system; they can be deleterious and/or protective. The immunomodulatory effects of alimentary components, gut microbiota, and nanotechnological products have been investigated in microglia at the single-cell level and in vivo using intravital imaging approaches, and different biochemical assays. This review highlights some of the emerging questions and topics from studies involving alimentation, microbiota, nanotechnological products, and associated problems in this area of research. Some of the advantages and limitations of in vitro and in vivo models used to study the neuromodulatory effects of these factors, as well as the merits and pitfalls of intravital imaging modalities employed are presented.