Cellular Senescence: Pathogenic Mechanisms in Lung Fibrosis.

Pulmonary fibrosis is a chronic and fatal lung disease that significantly impacts the aging population globally. To date, anti-fibrotic, immunosuppressive, and other adjunct therapy demonstrate limited efficacies. Advancing our understanding of the pathogenic mechanisms of lung fibrosis will provide a future path for the cure. Cellular senescence has gained substantial interest in recent decades due to the increased incidence of fibroproliferative lung diseases in the older age group. Furthermore, the pathologic state of cellular senescence that includes maladaptive tissue repair, decreased regeneration, and chronic inflammation resembles key features of progressive lung fibrosis. This review describes regulatory pathways of cellular senescence and discusses the current knowledge on the senescence of critical cellular players of lung fibrosis, including epithelial cells (alveolar type 2 cells, basal cells, etc.), fibroblasts, and immune cells, their phenotypic changes, and the cellular and molecular mechanisms by which these cells contribute to the pathogenesis of pulmonary fibrosis. A few challenges in the field include establishing appropriate in vivo experimental models and identifying senescence-targeted signaling molecules and specific therapies to target senescent cells, known collectively as "senolytic" or "senotherapeutic" agents.

Analgesic activity and mechanism of action of a Beta vulgaris dye enriched in betalains in inflammatory models in mice.

Evidence demonstrates the pronounced anti-inflammatory activity of a beetroot (Beta vulgaris) dye enriched in betalains obtained using precipitation with ethanol. Herein, we expand upon our previous observations and demonstrate the analgesic and antioxidant effect of betalains. Betalains [10-1000 mg/kg; intraperitoneal route (i.p.)] diminished acetic acid- and PBQ-induced abdominal contortions, and the overt pain-like behaviour induced by complete Freund`s adjuvant (CFA) and formalin (intraplantar; i.pl.) injection. Moreover, betalains (100 mg/kg) administered by various routes [i.p. or subcutaneous (s.c.)] or as a post-treatment reduced carrageenin- or CFA-induced hyperalgesia. Mechanistically, betalains mitigated carrageenin-induced tumour necrosis factor-alpha (TNF-α), interleukin (IL)-1ß, superoxide anion levels, and lipid peroxidation. Betalains also stopped the depletion of reduced glutathione (GSH) levels and ferric reducing ability produced by carrageenin, as well as upregulated Nrf2 and Ho1 transcript expression in the plantar tissue of mice. Furthermore, betalains showed hydroxyl radical, 2,2'-azino-di-(3-ethylbenzthiazoline-6-sulphonic acid) radical (ABTS+), and 2,2-diphenyl-1-picryl-hydrazyl radical (DPPH•) scavenging ability and iron-chelating activity (bathophenantroline assay), and inhibited iron-independent and iron-dependent lipid peroxidation (LPO) in vitro. Finally, betalains-treated bone marrow-derived macrophages exhibited lower levels of cytokines (TNF-α and IL-1ß), and superoxide anion levels and nuclear factor kappa B (NF-κB) activation following lipopolysaccharide (LPS) stimulation. Therefore, this betalain-rich dye extracted using a novel precipitation approach presents prominent analgesic effect in varied models of pain by mechanisms targeting cytokines and oxidative stress.

Quercetin Enhances Ligand-induced Apoptosis in Senescent Idiopathic Pulmonary Fibrosis Fibroblasts and Reduces Lung Fibrosis In Vivo.

Although cellular senescence may be a protective mechanism in modulating proliferative capacity, fibroblast senescence is now recognized as a key pathogenic mechanism in idiopathic pulmonary fibrosis (IPF). In aged mice, abundance and persistence of apoptosis-resistant senescent fibroblasts play a central role in nonresolving lung fibrosis after bleomycin challenge. Therefore, we investigated whether quercetin can restore the susceptibility of senescent IPF fibroblasts to proapoptotic stimuli and mitigate bleomycin-induced pulmonary fibrosis in aged mice. Unlike senescent normal lung fibroblasts, IPF lung fibroblasts from patients with stable and rapidly progressing disease were highly resistant to Fas ligand (FasL)-induced and TNF-related apoptosis-inducing ligand (TRAIL)-induced apoptosis. Senescent IPF fibroblasts exhibited decreased expression of FasL and TRAIL receptors and caveolin-1, as well as increased AKT activation, compared with senescent normal lung fibroblasts. Although quercetin alone was not proapoptotic, it abolished the resistance to FasL- or TRAIL-induced apoptosis in IPF fibroblasts. Mechanistically, quercetin upregulated FasL receptor and caveolin-1 expression and modulated AKT activation. In vivo quercetin reversed bleomycin-induced pulmonary fibrosis and attenuated lethality, weight loss, and the expression of pulmonary senescence markers p21 and p19-ARF and senescence-associated secretory phenotype in aged mice. Collectively, these data indicate that quercetin reverses the resistance to death ligand-induced apoptosis by promoting FasL receptor and caveolin-1 expression and inhibiting AKT activation, thus mitigating the progression of established pulmonary fibrosis in aged mice. Therefore, quercetin may be a viable therapeutic option for IPF and other age-related diseases that progress with the accumulation of senescent fibroblasts.

DNA-PKcs modulates progenitor cell proliferation and fibroblast senescence in idiopathic pulmonary fibrosis.

BACKGROUND: Recent studies have highlighted the contribution of senescent mesenchymal and epithelial cells in Idiopathic Pulmonary Fibrosis (IPF), but little is known regarding the molecular mechanisms that regulate the accumulation of senescent cells in this disease. Therefore, we addressed the hypothesis that the loss of DNA repair mechanisms mediated by DNA protein kinase catalytic subunit (DNA-PKcs) in IPF, promoted the accumulation of mesenchymal progenitors and progeny, and the expression of senescent markers by these cell types. METHODS: Surgical lung biopsy samples and lung fibroblasts were obtained from patients exhibiting slowly, rapidly or unknown progressing IPF and lung samples lacking any evidence of fibrotic disease (i.e. normal; NL). The expression of DNA-Pkcs in lung tissue was assessed by quantitative immunohistochemical analysis. Chronic inhibition of DNA-PKcs kinase activity was mimicked using a highly specific small molecule inhibitor, Nu7441. Proteins involved in DNA repair (stage-specific embryonic antigen (SSEA)-4+ cells) were determined by quantitative Ingenuity Pathway Analysis of transcriptomic datasets (GSE103488). Lastly, the loss of DNA-PKc was modeled in a humanized model of pulmonary fibrosis in NSG SCID mice genetically deficient in PRKDC (the transcript for DNA-PKcs) and treated with Nu7441. RESULTS: DNA-PKcs expression was significantly reduced in IPF lung tissues. Chronic inhibition of DNA-PKcs by Nu7441 promoted the proliferation of SSEA4+ mesenchymal progenitor cells and a significant increase in the expression of senescence-associated markers in cultured lung fibroblasts. Importantly, mesenchymal progenitor cells and their fibroblast progeny derived from IPF patients showed a loss of transcripts encoding for DNA damage response and DNA repair components. Further, there was a significant reduction in transcripts encoding for PRKDC (the transcript for DNA-PKcs) in SSEA4+ mesenchymal progenitor cells from IPF patients compared with normal lung donors. In SCID mice lacking DNA-PKcs activity receiving IPF lung explant cells, treatment with Nu7441 promoted the expansion of progenitor cells, which was observed as a mass of SSEA4+ CgA+ expressing cells. CONCLUSIONS: Together, our results show that the loss of DNA-PKcs promotes the expansion of SSEA4+ mesenchymal progenitors, and the senescence of their mesenchymal progeny.

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.

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-ß-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-1ß, 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.

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-1ß, 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.

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-ß-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-1ß, 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.

Standard of care drugs do not modulate activity of senescent primary human lung fibroblasts.

Cellular senescence is crucial in the progression of idiopathic pulmonary fibrosis (IPF), but it is not evident whether the standard-of-care (SOC) drugs, nintedanib and pirfenidone, have senolytic properties. To address this question, we performed colorimetric and fluorimetric assays, qRT-PCR, and western blotting to evaluate the effect of SOC drugs and D + Q on senescent normal and IPF lung fibroblasts. In this study, we found that SOC drugs did not provoke apoptosis in the absence of death ligand in normal or IPF senescent lung fibroblasts. Nintedanib increased caspase-3 activity in the presence of Fas Ligand in normal but not in IPF senescent fibroblasts. Conversely, nintedanib enhanced B cell lymphoma 2 expression in senescent IPF lung fibroblasts. Moreover, in senescent IPF cells, pirfenidone induced mixed lineage kinase domain-like pseudokinase phosphorylation, provoking necroptosis. Furthermore, pirfenidone increased transcript levels of FN1 and COL1A1 in senescent IPF fibroblasts. Lastly, D + Q augmented growth differentiation factor 15 (GDF15) transcript and protein levels in both normal and IPF senescent fibroblasts. Taken together, these results establish that SOC drugs failed to trigger apoptosis in senescent primary human lung fibroblasts, possibly due to enhanced Bcl-2 levels by nintedanib and the activation of the necroptosis pathway by pirfenidone. Together, these data revealed the inefficacy of SOC drugs to target senescent cells in IPF.

Dendritic cells in COVID-19 immunopathogenesis: insights for a possible role in determining disease outcome.

SARS-CoV-2 is the causative agent of the COVID-19 pandemic. This novel coronavirus emerged in China, quickly spreading to more than 200 countries worldwide. Although most patients are only mildly ill or even asymptomatic, some develop severe pneumonia and become critically ill. One of the biggest unanswered questions is why some develop severe disease, whilst others do not. Insight on the interaction between SARS-CoV-2 and the immune system and the contribution of dysfunctional immune responses to disease progression will be instrumental to the understanding of COVID-19 pathogenesis, risk factors for worst outcome, and rational design of effective therapies and vaccines. In this review we have gathered the knowledge available thus far on the epidemiology of SARS-COV-2 infection, focusing on the susceptibility of older individuals, SARS-CoV-2-host cell interaction during infection and the immune response directed at SARS-CoV-2. Dendritic cells act as crucial messengers linking innate and adaptative immunity against viral infections. Thus, this review also brings a focused discussion on the role of dendritic cells and their immune functions during SARS-CoV-2 infection and how immune evasion strategies of SARS-CoV-2 and advancing age mediate dendritic cell dysfunctions that contribute to COVID-19 pathogenesis and increased susceptibility to worst outcomes. This review brings to light the hypothesis that concomitant occurrence of dendritic cell dysfunction/cytopathic effects induced by SARS-CoV-2 and/or aging may influence disease outcome in the elderly. Lastly, a detailed discussion on the effects and mechanisms of action of drugs currently being tested for COVID-19 on the function of dendritic cells is also provided.

Ovarian toxicity by fusariotoxins in pigs: Does it imply in oxidative stress?

Mycotoxins are natural contaminants of food and feed occurring worldwide. Deoxynivalenol (DON) and fumonisin B1 (FB1) are the most frequent fusariotoxins and induce immune and intestinal toxicity in humans and animals. Recently, an association between mycotoxins exposure and impaired fertility has been suggested. However, the effects of these mycotoxins on the reproductive system are not well established. This study aimed to evaluate the effects of FB1 and DON, in combination or alone, on the ovarian morphology and oxidative responses using porcine explants. Seventy-two explants were obtained from six pigs and submitted to the following treatments: control (MEM medium), DON (10 µM), FB1 (100 µM FB1), and DON + FB1 (10 µM + 100 µM). Histological and immunohistochemical assays were performed to evaluate ovarian changes, cell proliferation, and apoptosis. Oxidative stress response was evaluated through lipid peroxidation and antioxidant capacity response assays. The exposure to mycotoxins induced significant histological changes in the ovaries, which were characterized by a decrease in viable follicles and increase in degenerated follicles. A significant decrease in granulosa cell proliferation was observed in explants exposed to all mycotoxins. In addition the multi-contaminated treatment was responsible for an increase in the cell apoptosis index of growing follicles. On the other hand, the FB1 and multi-contaminated treatments induced a significant decrease in lipid peroxidation accompanied by an increase in antioxidant responses. Altogether, our results indicate a reproductive toxicity induced by fusariotoxins. Moreover, mycotoxins, alone or in combination, modulate oxidative stress response, interfering with the production of free radicals and affecting the reproductive capacity of pigs.

Antibody-mediated depletion of CCR10+EphA3+ cells ameliorates fibrosis in IPF.

Idiopathic pulmonary fibrosis (IPF) is characterized by aberrant repair that diminishes lung function via mechanisms that remain poorly understood. CC chemokine receptor (CCR10) and its ligand CCL28 were both elevated in IPF compared with normal donors. CCR10 was highly expressed by various cells from IPF lungs, most notably stage-specific embryonic antigen-4-positive mesenchymal progenitor cells (MPCs). In vitro, CCL28 promoted the proliferation of CCR10+ MPCs while CRISPR/Cas9-mediated targeting of CCR10 resulted in the death of MPCs. Following the intravenous injection of various cells from IPF lungs into immunodeficient (NOD/SCID-γ, NSG) mice, human CCR10+ cells initiated and maintained fibrosis in NSG mice. Eph receptor A3 (EphA3) was among the highest expressed receptor tyrosine kinases detected on IPF CCR10+ cells. Ifabotuzumab-targeted killing of EphA3+ cells significantly reduced the numbers of CCR10+ cells and ameliorated pulmonary fibrosis in humanized NSG mice. Thus, human CCR10+ cells promote pulmonary fibrosis, and EphA3 mAb-directed elimination of these cells inhibits lung fibrosis.

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.

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 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.

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-1ß, 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.

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-ß-D glucosaminidase activity) recruitment into the eye, decrease in epithelial thickness, and neovascularization in the cornea. Further, naringenin inhibited alkali-induced cytokine (IL-1ß 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.