Contribution of Nrf2 Modulation to the Mechanism of Action of Analgesic and Anti-inflammatory Drugs in Pre-clinical and Clinical Stages

Despite the progress that has occurred in recent years in the development of therapies to treat painful and inflammatory diseases, there is still a need for effective and potent analgesics and anti-inflammatory drugs. It has long been known that several types of antioxidants also possess analgesic and anti-inflammatory properties, indicating a strong relationship between inflammation and oxidative stress. Understanding the underlying mechanisms of action of anti-inflammatory and analgesic drugs, as well as essential targets in disease physiopathology, is essential to the development of novel therapeutic strategies. The Nuclear factor-2 erythroid related factor-2 (Nrf2) is a transcription factor that regulates cellular redox status through endogenous antioxidant systems with simultaneous anti-inflammatory activity. This review summarizes the molecular mechanisms and pharmacological actions screened that link analgesic, anti-inflammatory, natural products, and other therapies to Nrf2 as a regulatory system based on emerging evidences from experimental disease models and new clinical trial data.

Phytic Acid Decreases Oxidative Stress and Intestinal Lesions Induced by Fumonisin B₁ and Deoxynivalenol in Intestinal Explants of Pigs

The purpose of the present study was to investigate the effects of phytic acid (IP6) on morphological and immunohistochemical parameters and oxidative stress response in intestinal explants of pigs exposed to fumonisin B₁ (FB₁) and/or deoxynivalenol (DON). The jejunal explants were exposed to the following treatments: vehicle, IP6 5 mM, DON 10 µM, FB₁ 70 µM, DON 10 µM + FB₁ 70 µM, DON 10 µM + IP6 5 mM, FB₁ 70 µM + IP6 5 mM, and DON 10 µM + FB₁ 70 µM + IP6 5 mM. The decrease in villus height and goblet cell density was more evident in DON and DON + FB₁ treatments. In addition, a significant increase in cell apoptosis and cell proliferation and a decrease in E-cadherin expression were observed in the same groups. DON and FB₁ exposure increased cyclooxygenase-2 expression and decreased the cellular antioxidant capacity. An increase in lipid peroxidation was observed in DON- and FB₁-treated groups. IP6 showed beneficial effects, such as a reduction in intestinal morphological changes, cell apoptosis, cell proliferation, and cyclooxygenase-2 expression, and an increase in E-cadherin expression when compared with DON, FB₁ alone, or DON and FB₁ in association. IP6 inhibited oxidative stress and increased the antioxidant capacity in the explants exposed to mycotoxins.

Contribution of Spinal Cord Oligodendrocytes to Neuroinflammatory Diseases and Pain

BACKGROUND

Neuroinflammatory diseases that affect spinal cord or associated spinal nerves represent challenging conditions for management in current medicine because of their complex pathology, poor prognosis, and high morbidity, which strikingly reduces the quality of life of patients. In this sense, a better understanding of the cellular and molecular mechanisms of spinal cord neuroinflammation might contribute to the development of novel therapies. Oligodendrocytes have unique and vital biological properties in central nervous system (CNS) homeostasis and physiology. A growing body of experimental evidence demonstrates that these glial cells are involved in the pathophysiological mechanisms underlying many chronic, neurodegenerative, and incapacitating CNS disorders. These cells also have important implications for the development and maintenance of neural plasticity and chronic pain states. On the other hand, evidence indicates that oligodendrocytes and their products may act in favor of CNS promoting beneficial effects orchestrating CNS tissue repair after injury.

OBJECTIVE

The present review aims to explore the multi-faceted actions of spinal cord oligodendrocyte progenitors cells (OPCs) and mature oligodendrocytes in CNS inflammation and pathology, addressing their roles in experimental and clinical settings. A major focus was given to spinal cord amyotrophic lateral sclerosis, multiple sclerosis (MS)/experimental autoimmune encephalomyelitis (EAE), traumatic injury and pain processing.

METHODS

This review analyses and discusses published original research articles regarding the role of OPCs/oligodendrocytes in spinal cord inflammation and pain processing.

RESULTS AND CONCLUSION

Findings from a number of clinical and experimental paradigms suggest spinal cord OPCs/oligodendrocytes are a potential therapeutic target for the control of neuroinflammation.

Naringenin Eye Drops Inhibit Corneal Neovascularization by Anti-Inflammatory and Antioxidant Mechanisms

Purpose

To investigate the effect of naringenin eye drops in corneal neovascularization induced by alkali (1 N NaOH) burn in mice.

Methods

Corneal neovascularization in the right eye of male Swiss mice was induced by alkali. Treatment with naringenin eye drops (0.08-80 μg; 8 μL of 0.01-10 g/L solution) or vehicle (saline) started 2 days before corneal neovascularization was induced and was performed twice a day. Mice were treated up until the time animals were euthanized and cornea tissue was collected for testing, which was 2, 4, and 6 hours after alkali stimulus for cytokine and antioxidant capacity measurements, and 3 and/or 7 days after alkali stimulus for the assessment of corneal epithelial thickness and neovascularization, neutrophil, and macrophage recruitment, and vascular endothelial growth factor (Vegf), platelet-derived growth factor (Pdgf), matrix metalloproteinase-14 (Mmp14), and pigment epithelium-derived factor (Pedf) mRNA expression.

Results

Naringenin eye drops inhibited alkali burn-induced neutrophil (myeloperoxidase activity and recruitment of Lysm-GFP+ cells) and macrophage (N-acetyl-β-D glucosaminidase activity) recruitment into the eye, decrease in epithelial thickness, and neovascularization in the cornea. Further, naringenin inhibited alkali-induced cytokine (IL-1β and IL-6) production, Vegf, Pdgf, and Mmp14 mRNA expression, and the reduction of ferric reducing antioxidant power and Azinobis-(3-Ethylbenzothiazoline 6-Sulfonic acid) radical scavenging capacity as well as increased the reduced glutathione and protein-bound sulfhydryl groups levels.

Conclusions

Collectively, these results indicate that naringenin eye drops are protective in alkali-induced corneal burn by inhibiting leukocyte recruitment, the proangiogenic factor expression, inflammatory cytokine production, and loss of antioxidant defenses.

Targeting IL-33/ST2 signaling: regulation of immune function and analgesia

INTRODUCTION

IL-33 signals through ST2 receptor and promotes inflammation by activating downstream pathways culminating in the production of pro-inflammatory mediators such as IL-1β, TNF-α, and IL-6 in an NF-κB-dependent manner. In fact, compelling evidence has demonstrated the importance of IL-33/ST2 in both innate and adaptive immune responses in diseases presenting pain as an important clinical symptom. Areas covered: IL-33 is a pleiotropic cytokine with varied immune functions. Dysregulation of this pathway has been described as a key step in varied immune responses. Further, IL-33 contributes to peripheral and spinal cord nociceptor neuron sensitization in innate and adaptive inflammatory immune responses as well as in neuropathic and cancer pain. In this sense, targeting IL-33/ST2 signaling is a promising therapeutic approach. Expert opinion: The modulation of IL-33/ST2 signaling represents a possible approach in regulating immune functions. In addition to immune function, strategies targeting IL-33/ST2 signaling pathway display a favorable preclinical analgesic profile in both acute and chronic models of pain. Therefore, IL-33-targeting therapies represent a potential target for the development of novel analgesic drugs given that IL-33 activates, for instance, neutrophils, mast cells, macrophages, astrocytes, and microglia that are important cells in the induction and maintenance of chronic pain states.

Capsaicin: Current Understanding of Its Mechanisms and Therapy of Pain and Other Pre-Clinical and Clinical Uses

In this review, we discuss the importance of capsaicin to the current understanding of neuronal modulation of pain and explore the mechanisms of capsaicin-induced pain. We will focus on the analgesic effects of capsaicin and its clinical applicability in treating pain. Furthermore, we will draw attention to the rationale for other clinical therapeutic uses and implications of capsaicin in diseases such as obesity, diabetes, cardiovascular conditions, cancer, airway diseases, itch, gastric, and urological disorders.

Pimaradienoic Acid Inhibits Carrageenan-Induced Inflammatory Leukocyte Recruitment and Edema in Mice: Inhibition of Oxidative Stress, Nitric Oxide and Cytokine Production

Pimaradienoic acid (PA; ent-pimara-8(14),15-dien-19-oic acid) is a pimarane diterpene found in plants such as Vigueira arenaria Baker (Asteraceae) in the Brazilian savannas. Although there is evidence on the analgesic and in vitro inhibition of inflammatory signaling pathways, and paw edema by PA, its anti-inflammatory effect deserves further investigation. Thus, the objective of present study was to investigate the anti-inflammatory effect of PA in carrageenan-induced peritoneal and paw inflammation in mice. Firstly, we assessed the effect of PA in carrageenan-induced leukocyte recruitment in the peritoneal cavity and paw edema and myeloperoxidase activity. Next, we investigated the mechanisms involved in the anti-inflammatory effect of PA. The effect of PA on carrageenan-induced oxidative stress in the paw skin and peritoneal cavity was assessed. We also tested the effect of PA on nitric oxide, superoxide anion, and inflammatory cytokine production in the peritoneal cavity. PA inhibited carrageenan-induced recruitment of total leukocytes and neutrophils to the peritoneal cavity in a dose-dependent manner. PA also inhibited carrageenan-induced paw edema and myeloperoxidase activity in the paw skin. The anti-inflammatory mechanism of PA depended on maintaining paw skin antioxidant activity as observed by the levels of reduced glutathione, ability to scavenge the ABTS cation and reduce iron as well as by the inhibition of superoxide anion and nitric oxide production in the peritoneal cavity. Furthermore, PA inhibited carrageenan-induced peritoneal production of inflammatory cytokines TNF-α and IL-1β. PA presents prominent anti-inflammatory effect in carrageenan-induced inflammation by reducing oxidative stress, nitric oxide, and cytokine production. Therefore, it seems to be a promising anti-inflammatory molecule that merits further investigation.

Vanillic Acid Inhibits Inflammatory Pain by Inhibiting Neutrophil Recruitment, Oxidative Stress, Cytokine Production, and NFκB Activation in Mice

Vanillic acid (1) is a flavoring agent found in edible plants and fruits. It is an oxidized form of vanillin. Phenolic compounds form a substantial part of plant foods used as antioxidants with beneficial biological activities. These compounds have received considerable attention because of their role in preventing human diseases. Especially, 1 presents antibacterial, antimicrobial, and chemopreventive effects. However, the mechanisms by which 1 exerts its anti-inflammatory effects in vivo are incompletely understood. Thus, the effect of 1 was evaluated in murine models of inflammatory pain. Treatment with 1 inhibited the overt pain-like behavior induced by acetic acid, phenyl-p-benzoquinone, the second phase of the formalin test, and complete Freund's adjuvant (CFA). Treatment with 1 also inhibited carrageenan- and CFA-induced mechanical hyperalgesia, paw edema, myeloperoxidase activity, and N-acetyl-β-D-glucosaminidase activity. The anti-inflammatory mechanisms of 1 involved the inhibition of oxidative stress, pro-inflammatory cytokine production, and NFκB activation in the carrageenan model. The present study demonstrated 1 presents analgesic and anti-inflammatory effects in a wide range of murine inflammation models, and its mechanisms of action involves antioxidant effects and NFκB-related inhibition of pro-inflammatory cytokine production.

Hypericum perforatum Reduces Paracetamol-Induced Hepatotoxicity and Lethality in Mice by Modulating Inflammation and Oxidative Stress

Hypericum perforatum is a medicinal plant with anti-inflammatory and antioxidant properties, which is commercially available for therapeutic use in Brazil. Herein the effect of H. perforatum extract on paracetamol (acetaminophen)-induced hepatotoxicity, lethality, inflammation, and oxidative stress in male swiss mice were investigated. HPLC analysis demonstrated the presence of rutin, quercetin, hypericin, pseudohypericin, and hyperforin in H. perforatum extract. Paracetamol (0.15-3.0 g/kg, p.o.) induced dose-dependent mortality. The sub-maximal lethal dose of paracetamol (1.5 g/kg, p.o.) was chosen for the experiments in the study. H. perforatum (30-300 mg/kg, i.p.) dose-dependently reduced paracetamol-induced lethality. Paracetamol-induced increase in plasma aspartate aminotransferase (AST) and alanine aminotransferase (ALT) concentrations, and hepatic myeloperoxidase activity, IL-1β, TNF-α, and IFN-γ concentrations as well as decreased reduced glutathione (GSH) concentrations and capacity to reduce 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonate radical cation; ABTS˙(+) ) were inhibited by H. perforatum (300 mg/kg, i.p.) treatment. Therefore, H. perforatum protects mice against paracetamol-induced lethality and liver damage. This effect seems to be related to the reduction of paracetamol-induced cytokine production, neutrophil recruitment, and oxidative stress.

The superoxide anion donor, potassium superoxide, induces pain and inflammation in mice through production of reactive oxygen species and cyclooxygenase-2

It is currently accepted that superoxide anion (O₂^•−) is an important mediator in pain and inflammation. The role of superoxide anion in pain and inflammation has been mainly determined indirectly by modulating its production and inactivation. Direct evidence using potassium superoxide (KO₂), a superoxide anion donor, demonstrated that it induced thermal hyperalgesia, as assessed by the Hargreaves method. However, it remains to be determined whether KO₂ is capable of inducing other inflammatory and nociceptive responses attributed to superoxide anion. Therefore, in the present study, we investigated the nociceptive and inflammatory effects of KO₂. The KO₂-induced inflammatory responses evaluated in mice were: mechanical hyperalgesia (electronic version of von Frey filaments), thermal hyperalgesia (hot plate), edema (caliper rule), myeloperoxidase activity (colorimetric assay), overt pain-like behaviors (flinches, time spent licking and writhing score), leukocyte recruitment, oxidative stress, and cyclooxygenase-2 mRNA expression (quantitative PCR). Administration of KO₂ induced mechanical hyperalgesia, thermal hyperalgesia, paw edema, leukocyte recruitment, the writhing response, paw flinching, and paw licking in a dose-dependent manner. KO₂ also induced time-dependent cyclooxygenase-2 mRNA expression in the paw skin. The nociceptive, inflammatory, and oxidative stress components of KO₂-induced responses were responsive to morphine (analgesic opioid), quercetin (antioxidant flavonoid), and/or celecoxib (anti-inflammatory cyclooxygenase-2 inhibitor) treatment. In conclusion, the well-established superoxide anion donor KO₂ is a valuable tool for studying the mechanisms and pharmacological susceptibilities of superoxide anion-triggered nociceptive and inflammatory responses ranging from mechanical and thermal hyperalgesia to overt pain-like behaviors, edema, and leukocyte recruitment.

Pimaradienoic acid inhibits inflammatory pain: inhibition of NF-κB activation and cytokine production and activation of the NO-cyclic GMP-protein kinase G-ATP-sensitive potassium channel signaling pathway

Pimaradienoic acid (1) is a pimarane diterpene (ent-pimara-8(14),15-dien-19-oic acid) extracted at high amounts from various plants including Vigueira arenaria Baker. Compound 1 inhibited carrageenan-induced paw edema and acetic acid-induced abdominal writhing, which are its only known anti-inflammatory activities. Therefore, it is important to further investigate the analgesic effects of 1. Oral administration of 1 (1, 3, and 10 mg/kg) inhibited the acetic acid-induced writhing. This was also observed at 10 mg/kg via sc and ip routes. Both phases of the formalin- and complete Freund's adjuvant (CFA)-induced paw flinch and time spent licking the paw were inhibited by 1. Compound 1 inhibited carrageenan-, CFA-, and PGE2-induced mechanical hyperalgesia. Treatment with 1 inhibited carrageenan-induced production of TNF-α, IL-1β, IL-33, and IL-10 and nuclear factor κB activation. Pharmacological inhibitors also demonstrated that the analgesic effects of 1 depend on activation of the NO-cyclic GMP-protein kinase G-ATP-sensitive potassium channel signaling pathway. Compound 1 did not alter plasma levels of AST, ALT, or myeloperoxidase activity in the stomach. These results demonstrate that 1 causes analgesic effects associated with the inhibition of NF-κB activation, reduction of cytokine production, and activation of the NO-cyclic GMP-protein kinase G-ATP-sensitive potassium channel signaling pathway.

5-lipoxygenase deficiency reduces acetaminophen-induced hepatotoxicity and lethality

5-Lipoxygenase (5-LO) converts arachidonic acid into leukotrienes (LTs) and is involved in inflammation. At present, the participation of 5-LO in acetaminophen (APAP)-induced hepatotoxicity and liver damage has not been addressed. 5-LO deficient (5-LO⁻/⁻) mice and background wild type mice were challenged with APAP (0.3-6 g/kg) or saline. The lethality, liver damage, neutrophil and macrophage recruitment, LTB₄, cytokine production, and oxidative stress were assessed. APAP induced a dose-dependent mortality, and the dose of 3 g/kg was selected for next experiments. APAP induced LTB4 production in the liver, the primary target organ in APAP toxicity. Histopathological analysis revealed that 5-LO⁻/⁻ mice presented reduced APAP-induced liver necrosis and inflammation compared with WT mice. APAP-induced lethality, increase of plasma levels of aspartate aminotransferase and alanine aminotransferase, liver cytokine (IL-1β, TNF-α , IFN- γ, and IL-10), superoxide anion, and thiobarbituric acid reactive substances production, myeloperoxidase and N-acetyl-β-D-glucosaminidase activity, Nrf2 and gp91(phox) mRNA expression, and decrease of reduced glutathione and antioxidant capacity measured by 2,2'-azinobis(3-ethylbenzothiazoline 6-sulfonate) assay were prevented in 5-LO⁻/⁻ mice compared to WT mice. Therefore, 5-LO deficiency resulted in reduced mortality due to reduced liver inflammatory and oxidative damage, suggesting 5-LO is a promising target to reduce APAP-induced lethality and liver inflammatory/oxidative damage.

An interleukin-33/ST2 signaling deficiency reduces overt pain-like behaviors in mice

Interleukin (IL)-33, the most recent member of the IL family of cytokines, signals through the ST2 receptor. IL-33/ST2 signaling mediates antigen challenge-induced mechanical hyperalgesia in the joints and cutaneous tissues of immunized mice. The present study asked whether IL-33/ST2 signaling is relevant to overt pain-like behaviors in mice. Acetic acid and phenyl-p-benzoquinone induced significant writhing responses in wild-type (WT) mice; this overt nociceptive behavior was reduced in ST2-deficient mice. In an antigen-challenge model, ST2-deficient immunized mice had reduced induced flinch and licking overt pain-like behaviors. In the formalin test, ST2-deficient mice also presented reduced flinch and licking responses, compared with WT mice. Naive WT and ST2-deficient mice presented similar responses in the rota-rod, hot plate, and electronic von Frey tests, indicating no impairment of motor function or alteration in basal nociceptive responses. The results demonstrate that IL-33/ST2 signaling is important in the development of overt pain-like behaviors.

Vitexin inhibits inflammatory pain in mice by targeting TRPV1, oxidative stress, and cytokines

The flavonoid vitexin (1) is a flavone C-glycoside (apigenin-8-C-β-D-glucopyranoside) present in several medicinal and other plants. Plant extracts containing 1 are reported to possess antinociceptive, anti-inflammatory, and antioxidant activities. However, the only evidence that 1 exhibits antinociceptive activity was demonstrated in the acetic acid-induced writhing model. Therefore, the analgesic effects and mechanisms of 1 were evaluated. In the present investigation, intraperitoneal treatment with 1 dose-dependently inhibited acetic acid-induced writhing. Furthermore, treatment with 1 also inhibited pain-like behavior induced by phenyl-p-benzoquinone, complete Freund's adjuvant (CFA), capsaicin (an agonist of transient receptor potential vanilloid 1, TRPV1), and both phases of the formalin test. It was also observed that inhibition of carrageenan-, capsaicin-, and chronic CFA-induced mechanical and thermal hyperalgesia occurred. Regarding the antinociceptive mechanisms of 1, it prevented the decrease of reduced glutathione levels, ferric-reducing ability potential, and free-radical scavenger ability, inhibited the production of hyperalgesic cytokines such as TNF-α, IL-1β, IL-6, and IL-33, and up-regulated the levels of the anti-hyperalgesic cytokine IL-10. These results demonstrate that 1 exhibits an analgesic effect in a variety of inflammatory pain models by targeting TRPV1 and oxidative stress and by modulating cytokine production.

Analgesic activity of piracetam: effect on cytokine production and oxidative stress

Piracetam is a prototype of nootropic drugs used to improve cognitive impairment. However, recent studies suggest that piracetam can have analgesic and anti-inflammatory effects. Inflammatory pain is the result of a process that depends on neutrophil migration, cytokines and prostanoids release and oxidative stress. We analyze whether piracetam has anti-nociceptive effects and its mechanisms. Per oral pretreatment with piracetam reduced in a dose-dependent manner the overt pain-like behavior induced by acetic acid, phenyl-p-benzoquinone, formalin and complete Freund's adjuvant. Piracetam also diminished carrageenin-induced mechanical and thermal hyperalgesia, myeloperoxidase activity, and TNF-α-induced mechanical hyperalgesia. Piracetam presented analgesic effects as post-treatment and local paw treatment. The analgesic mechanisms of piracetam were related to inhibition of carrageenin- and TNF-α-induced production of IL-1β as well as prevention of carrageenin-induced decrease of reduced glutathione, ferric reducing ability and free radical scavenging ability in the paw. These results demonstrate that piracetam presents analgesic activity upon a variety of inflammatory stimuli by a mechanism dependent on inhibition of cytokine production and oxidative stress. Considering its safety and clinical use for cognitive function, it is possible that piracetam represents a novel perspective of analgesic.

Inflammatory biomarkers and oxidative stress measurements in patients with systemic lupus erythematosus with or without metabolic syndrome

The aims of the present study were to report the frequency of metabolic syndrome in systemic lupus erythematosus (SLE); to verify differences in inflammatory biomarkers and oxidative stress in SLE patients with or without metabolic syndrome; and to assess which metabolic syndrome components are associated with oxidative stress and disease activity. The study included 58 SLE patients and 105 controls. SLE patients were divided in two groups, with and without metabolic syndrome. 41.4% patients met the criteria for metabolic syndrome compared with 10.5% controls. Patients with SLE and metabolic syndrome had significantly raised serum uric acid, C-reactive protein (CRP), lipid hydroperoxides, and protein oxidation when compared with patients with SLE without metabolic syndrome. Lipid hydroperoxides were correlated with CRP, whereas protein oxidation was associated with waist circumference and uric acid. There was a positive association between serum C3 and C4 and glucose and between C3 and CRP. SLE disease activity index (SLEDAI) scores were positively correlated with body mass index (BMI) and waist circumference (WC). In conclusion, SLE patients have a high prevalence of metabolic syndrome and this syndrome directly contributes to increase inflammatory status and oxidative stress. Inflammatory processes, being overweight/obese, and uric acid may favor oxidative stress increases in patients with SLE and metabolic syndrome. C3 and C4 may have a positive acute-phase protein behavior in patients with SLE.