New drug targets for the treatment of gout arthritis: what's new?

INTRODUCTION: Gout arthritis (GA) is an intermittent inflammatory disease affecting approximately 10% of the worldwide population. Symptomatic phases (acute flares) are timely spaced by asymptomatic periods. During an acute attack, redness, joint swelling, limited movement, and excruciating pain are common symptoms. However, the current available therapies are not fully effective in reducing symptoms and offer numerous side effects. Therefore, unveiling new drug targets and effector molecules are required in developing novel GA therapeutics. AREAS COVERED: This review discusses the pathophysiological mechanisms of GA and explores potential pharmacological targets to ameliorate disease outcome. In addition, we listed promising pre-clinical studies demonstrating effector molecules with therapeutical potential. Among those, we emphasized the importance of natural products, including traditional Chinese medicine formulas and their multitarget mechanisms of action. EXPERT OPINION: In our search, we observed that there is a massive gap between pre-clinical and clinical knowledge. Only a minority (4.4%) of clinical trials aimed to intervene by applying natural products or current hot targets described herein. In this sense, we envisage four possibilities for GA therapeutics, which include the repurposing of existing therapies, ALX/FPR2 agonism for improvement in disease outcome, the use of multitarget drugs (e.g. natural products), and targeting the neuroinflammatory component of GA.

Pimenta pseudocaryophyllus (Gomes) Landrum extract inhibits inflammatory pain in mice: targeting neutrophil recruitment, oxidative stress, and cytokine production.

Pimenta pseudocaryophyllus (Gomes) Landrum is a Brazilian native plant. The mechanisms by which it promotes analgesia are unknown. We demonstrated the analgesic effect of P. pseudocaryophyllus dried extract (3 mg/kg; i.p.) in the following models of inflammatory pain (maximal inhibition): phenyl-p-benzoquinone (89%), formalin (72% - 1st phase and 96% - 2nd phase for flinches, and 50% - 1st phase and 71% - 2nd phase for licking behavior), complete Freund's adjuvant (95% - flinches and 33% - licking behavior), and carrageenin (56% - mechanical and 85% - thermal hyperalgesia) without motor impairment. Its analgesic effect depends on inhibiting neutrophil recruitment (95% - histopathology, 83% - myeloperoxidase activity, and 80% - LysM-eGFP mice), oxidative stress (86% - GSH and 98% - superoxide anion), and cytokine production (35% - IL-33, 80% - TNF-α, and 95% - IL-1ß). The present study advances in understanding the analgesic mechanisms of P. pseudocaryophyllus.

Sphagneticola trilobata (L.) Pruski-derived kaurenoic acid prevents ovalbumin-induced asthma in mice: Effect on Th2 cytokines, STAT6/GATA-3 signaling, NFκB/Nrf2 redox sensitive pathways, and regulatory T cell phenotype markers.

ETHNOPHARMACOLOGICAL RELEVANCE: Sphagneticola trilobata (L.) Pruski is used in traditional medicine in Brazil for inflammatory diseases treatment including asthma. The diterpene kaurenoic acid (KA) is one of its active compounds, but whether KA activity could explain the traditional use of S. trilobata in asthma is unknown. AIM: Investigate KA effect and mechanisms in asthma. METHODS: Experimental asthma was induced by ovalbumin immunization and challenge in male Swiss mice. KA (0.1-10 mg/kg, gavage) was administered 1 h before the ovalbumin challenge. Total leukocytes, eosinophil, and mast cell were counted in bronchoalveolar lavage fluid (BALF), and lung histopathology was performed. Lung mRNA expression of Th2 and regulatory T cells markers, and BALF type 2 cytokine production were quantitated. NFκB activation and oxidative stress-related components in pulmonary tissue were measured. RESULTS: KA inhibited the migration of total leukocytes and eosinophils to BALF, reduced lung histopathology (inflammatory cells and mast cells), mRNA expression of IL-33/ST2, STAT6/GATA-3 and NFκB activation in the lung, and reduced IL-33, IL-4, IL-5 production in the BALF. KA also reduced the mRNA expression of iNOS and gp91phox, and superoxide anion production accompanied by the induction of Nrf2, HO-1 and NQO1 mRNA expression, thus, exerting an antioxidant effect. Finally, KA induced nTreg-like and Tr1-like, but not Th3-like markers of suppressive T cell phenotypes in the lung tissue. CONCLUSION: KA prevents antigen-induced asthma by down-regulating Th2 and NFκB/cytokine-related pathways, and up-regulating Nrf2 and regulatory T cells' markers. Thus, explaining the ethnopharmacological use of S. trilobata for the treatment of lung inflammatory diseases.

The diterpene from Sphagneticola trilobata (L.) Pruski, kaurenoic acid, reduces lipopolysaccharide-induced peritonitis and pain in mice.

ETHNOPHARMACOLOGICAL RELEVANCE: Sphagneticola trilobata (L.) Pruski is a plant species belonging to the Asteraceae family. Kaurenoid acid (KA) is a diterpene metabolite and one of the active ingredients of Sphagneticola trilobata (L.) Pruski. Extracts containing KA are used in traditional medicine to treat pain, inflammation, and infection. AIM: The goal of the present study was to investigate the in vivo effects of KA (1-10 mg/kg, per oral gavage) upon LPS inoculation in mice by intraperitoneal (i.p.) or intraplantar (i.pl.; subcutaneous plantar injection) routes at the dose of 200 ng (200 µL or 25 µL, respectively). METHODS: In LPS paw inflammation, mechanical and thermal hyperalgesia MPO activity and oxidative imbalance (TBARS, GSH, ABTS and FRAP assays) were evaluated. In LPS peritonitis we evaluated leukocyte migration, cytokine production, oxidative stress, and NF-κB activation. RESULTS: KA inhibited LPS-induced mechanical and thermal hyperalgesia, MPO activity and modulated redox status in the mice paw. Pre- and post-treatment with KA inhibited migration of neutrophils and monocytes in LPS peritonitis. KA inhibited the pro-inflammatory/hyperalgesic cytokine (e.g., TNF-α, IL-1ß and IL-33) production while enhanced anti-inflammatory/analgesic cytokine IL-10 in peritoneal cavity. In agreement with the effect of KA over pro-inflammatory cytokines it inhibited oxidative stress (total ROS, superoxide production and superoxide positive cells) and NF-κB activation during peritonitis. CONCLUSION: KA efficiently dampens LPS-induced peritonitis and hyperalgesia in vivo, suggesting it as a suitable candidate to control excessive inflammation and pain during gram-negative bacterial infections and bringing mechanistic explanation to the ethnopharmacological application of Sphagneticola trilobata (L.) Pruski in inflammation and infection.

The specialised pro-resolving lipid mediator maresin 1 reduces inflammatory pain with a long-lasting analgesic effect.

BACKGROUND AND PURPOSE: Maresin 1 (MaR1) is a specialised pro-resolving lipid mediator with anti-inflammatory and analgesic activities. In this study, we addressed the modulation of peripheral and spinal cord cells by MaR1 in the context of inflammatory pain. EXPERIMENTAL APPROACH: Mice were treated with MaR1 before intraplantar injection of carrageenan or complete Freund's adjuvant (CFA). Mechanical hyperalgesia was assessed using the electronic von Frey and thermal hyperalgesia using a hot plate. Spinal cytokine production and NF-κB activation were determined by ELISA and astrocytes and microglia activation by RT-qPCR and immunofluorescence. CGRP release by dorsal root ganglia (DRG) neurons was determined by EIA. Neutrophil and macrophage recruitment were determined by immunofluorescence, flow cytometry, and colorimetric methods. Trpv1 and Nav1.8 expression and calcium imaging of DRG neurons were determined by RT-qPCR and Fluo-4AM respectively. KEY RESULTS: MaR1 reduced carrageenan- and CFA-induced mechanical and thermal hyperalgesia and neutrophil and macrophage recruitment proximal to CGRP+ fibres in the paw skin. Moreover, MaR1 reduced NF-κB activation, IL-1ß and TNF-α production, and spinal cord glial cells activation. In the DRG, MaR1 reduced CFA-induced Nav1.8 and Trpv1 mRNA expression and calcium influx and capsaicin-induced release of CGRP by DRG neurons. CONCLUSIONS AND IMPLICATIONS: MaR1 reduced DRG neurons activation and CGRP release explaining, at least in part, its analgesic and anti-inflammatory effects. The enduring analgesic and anti-inflammatory effects and also post-treatment activity of MaR1 suggest that specialised pro-resolving lipid mediators have potential as a new class of drugs for the treatment of inflammatory pain.

The citrus flavanone naringenin attenuates zymosan-induced mouse joint inflammation: induction of Nrf2 expression in recruited CD45+ hematopoietic cells.

BACKGROUND: Naringenin is a biologically active analgesic, anti-inflammatory, and antioxidant flavonoid. Naringenin targets in inflammation-induced articular pain remain poorly explored. METHODS: The present study investigated the cellular and molecular mechanisms involved in the analgesic/anti-inflammatory effects of naringenin in zymosan-induced arthritis. Mice were pre-treated orally with naringenin (16.7-150 mg/kg), followed by intra-articular injection of zymosan. Articular mechanical hyperalgesia and oedema, leucocyte recruitment to synovial cavity, histopathology, expression/production of pro- and anti-inflammatory mediators and NFκB activation, inflammasome component expression, and oxidative stress were evaluated. RESULTS: Naringenin inhibited articular pain and oedema in a dose-dependent manner. The dose of 50 mg/kg inhibited leucocyte recruitment, histopathological alterations, NFκB activation, and NFκB-dependent pro-inflammatory cytokines (TNF-α, IL-1ß, and IL-33), and preproET-1 mRNA expression, but increased anti-inflammatory IL-10. Naringenin also inhibited inflammasome upregulation (reduced Nlrp3, ASC, caspase-1, and pro-IL-1ß mRNA expression) and oxidative stress (reduced gp91phox mRNA expression and superoxide anion production, increased GSH levels, induced Nrf2 protein in CD45+ hematopoietic recruited cells, and induced Nrf2 and HO-1 mRNA expression). CONCLUSIONS: Naringenin presents analgesic and anti-inflammatory effects in zymosan-induced arthritis by targeting its main physiopathological mechanisms. These data highlight this flavonoid as an interesting therapeutic compound to treat joint inflammation, deserving additional pre-clinical and clinical studies.

15d-PGJ2-loaded nanocapsules ameliorate experimental gout arthritis by reducing pain and inflammation in a PPAR-gamma-sensitive manner in mice.

Gout arthritis (GA) is a painful inflammatory disease in response to monosodium urate (MSU) crystals in the joints. 15deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2) is a natural activator of PPAR-γ with analgesic, anti-inflammatory, and pro-resolution properties. Thus, we aimed to evaluate the effect and mechanisms of action of 15d-PGJ2 nanocapsules (NC) in the model of GA in mice, since a reduction of 33-fold in the dose of 15d-PGJ2 has been reported. Mice were treated with 15d-PGJ2-loaded NC, inert NC, free 15d-PGJ2 (without NC), or 15d-PGJ2-loaded NC+ GW9662, a PPAR-γ inhibitor. We show that 15d-PGJ2-loaded NC provided analgesic effect in a dose that the free 15d-PGJ2 failed to inhibiting pain and inflammation. Hence, 15d-PGJ2-loaded NC reduced MSU-induced IL-1ß, TNF-α, IL-6, IL-17, and IL-33 release and oxidative stress. Also, 15d-PGJ2-loaded NC decreased the maturation of IL-1ß in LPS-primed BMDM triggered by MSU. Further, 15d-PGJ2-loaded NC decreased the expression of the components of the inflammasome Nlrp3, Asc, and Pro-caspase-1, as consequence of inhibiting NF-κB activation. All effects were PPAR-γ-sensitive. Therefore, we demonstrated that 15d-PGJ2-loaded NC present analgesic and anti-inflammatory properties in a PPAR-γ-dependent manner inhibiting IL-1ß release and NF-κB activation in GA. Concluding, 15d-PGJ2-loaded NC ameliorates MSU-induced GA in a PPAR-γ-sensitive manner.

The citrus flavonone naringenin reduces lipopolysaccharide-induced inflammatory pain and leukocyte recruitment by inhibiting NF-κB activation.

Lipopolysaccharide (LPS) is the major structural component of Gram-negative bacteria cell wall and a highly pro-inflammatory toxin. Naringenin is found in Citrus fruits and exhibits antioxidant and anti-inflammatory properties through inhibition of NF-κB activation but its effects in LPS-induced inflammatory pain and leukocyte recruitment were not investigated yet. We investigated the effects of naringenin in mechanical hyperalgesia, thermal hyperalgesia and leukocyte recruitment induced by intraplantar injection of LPS in mice. We found that naringenin reduced hyperalgesia to mechanical and thermal stimuli, myeloperoxidase (MPO, a neutrophil and macrophage marker) and N-acetyl-ß-D-glucosaminidase (NAG, a macrophage marker) activities, oxidative stress and cytokine (TNF-α, IL-1ß, IL-6, and IL-12) production in the paw skin. In the peritoneal cavity, naringenin reduced neutrophil and mononuclear cell recruitment, and abrogated MPO and NAG activity, cytokine and superoxide anion production, and lipid peroxidation. In vitro, pre-treatment with naringenin inhibited superoxide anion and cytokine (TNF-α, IL-1ß, IL-6, and IL-12) production by LPS-stimulated RAW 264.7 macrophages. Finally, we demonstrated that naringenin inhibited NF-κB activation in vitro and in vivo. Therefore, naringenin is a promising compound to treat LPS-induced inflammatory pain and leukocyte recruitment.

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.