Acute gout attacks produce severe joint pain and inflammation associated with monosodium urate (MSU) crystals leading to oxidative stress production. The transient potential receptor ankyrin 1 (TRPA1) is expressed by a subpopulation of peptidergic nociceptors and, via its activation by endogenous reactive oxygen species, including hydrogen peroxide (H2O2), contributes to pain and neurogenic inflammation. The aim of this study was to investigate the role of TRPA1 in hyperalgesia and inflammation in a model of acute gout attack in rodents. Inflammatory parameters and mechanical hyperalgesia were measured in male Wistar rats and in wild-type (Trpa1(+/+)) or TRPA1-deficient (Trpa1(-/-)) male mice. Animals received intra-articular (ia, ankle) injection of MSU. The role of TRPA1 was assessed by receptor antagonism, gene deletion or expression, sensory fiber defunctionalization, and calcitonin gene-related peptide (CGRP) release. We found that nociceptor defunctionalization, TRPA1 antagonist treatment (via ia or oral administration), and Trpa1 gene ablation abated hyperalgesia and inflammatory responses (edema, H2O2 generation, interleukin-1β release, and neutrophil infiltration) induced by ia MSU injection. In addition, we showed that MSU evoked generation of H2O2 in synovial tissue, which stimulated TRPA1 producing CGRP release and plasma protein extravasation. The MSU-elicited responses were also reduced by the H2O2-detoxifying enzyme catalase and the reducing agent dithiothreitol. TRPA1 activation by MSU challenge-generated H2O2 mediates the entire inflammatory response in an acute gout attack rodent model, thus strengthening the role of the TRPA1 receptor and H2O2 production as potential targets for treatment of acute gout attacks.
Objective. Gout is a common cause of inflammatory arthritis and is provoked by the accumulation of monosodium urate (MSU) crystals. However, the underlying mechanisms of the pain associated with acute attacks of gout are poorly understood. The aim of this study was to evaluate the role of transient receptor potential ankyrin 1 (TRPA-1) and TRPA-1 stimulants, such as H 2 O 2 , in a rodent model of MSU-induced inflammation.Methods. MSU or H 2 O 2 was injected into the hind paws of rodents or applied in cultured sensory neurons, and the intracellular calcium response was measured in vitro. Inflammatory or nociceptive responses in vivo were evaluated using pharmacologic, genetic, or biochemical tools and methods.Results. TRPA-1 antagonism, TRPA-1 gene deletion, or pretreatment of peptidergic TRP-expressing primary sensory neurons with capsaicin markedly decreased MSU-induced nociception and edema. In addition to these neurogenic effects, MSU increased H 2 O 2 levels in the injected tissue, an effect that was abolished by the H 2 O 2 -detoxifying enzyme catalase. H 2 O 2 , but not MSU, directly stimulated sensory neurons through the activation of TRPA-1. The nociceptive responses evoked by MSU or H 2 O 2 injection were attenuated by the reducing agent dithiothreitol. In addition, MSU injection increased the expression of TRPA-1 and TRP vanilloid channel 1 (TRPV-1) and also enhanced cellular infiltration and interleukin-1 levels, and these effects were blocked by TRPA-1 antagonism.Conclusion. Our results suggest that MSU injection increases tissue H 2 O 2 , thereby stimulating TRPA-1 on sensory nerve endings to produce inflammation and nociception. TRPV-1, by a previously unknown mechanism, also contributes to these responses.Gout is the most common cause of painful inflammatory arthritis among men and postmenopausal women. Mainly because of an aging population and lifestyle changes, the incidence and prevalence of gout are steadily increasing (1,2). Poorly controlled gout leads to a limitation of activities and a significant decrease in health-related quality of life (3). Signs and symptoms of gout are caused by soft tissue deposits of monosodium urate (MSU) crystals, which trigger episodes of intense articular and periarticular inflammation and excruciating pain (1,4). However, the underlying mechanism of the inflammatory process in gout that results in sensory symptoms and pain is poorly understood. Accordingly,
Spermine and spermidine are natural polyamines that are produced mainly via decarboxylation of l-ornithine and the sequential transfer of aminopropyl groups from S-adenosylmethionine to putrescine by spermidine synthase and spermine synthase. Spermine and spermidine interact with intracellular and extracellular acidic residues of different nature, including nucleic acids, phospholipids, acidic proteins, carboxyl- and sulfate-containing polysaccharides. Therefore, multiple actions have been suggested for these polycations, including modulation of the activity of ionic channels, protein synthesis, protein kinases, and cell proliferation/death, within others. In this review we summarize these neurochemical/neurophysiological/morphological findings, particularly those that have been implicated in the improving and deleterious effects of spermine and spermidine on learning and memory of naïve animals in shock-motivated and nonshock-motivated tasks, from a historical perspective. The interaction with the opioid system, the facilitation and disruption of morphine-induced reward and the effect of polyamines and putative polyamine antagonists on animal models of cognitive diseases, such as Alzheimer's, Huntington, acute neuroinflammation and brain trauma are also reviewed and discussed. The increased production of polyamines in Alzheimer's disease and the biphasic nature of the effects of polyamines on memory and on the NMDA receptor are also considered. In light of the current literature on polyamines, which include the description of an inborn error of the metabolism characterized by mild-to moderate mental retardation and polyamine metabolism alterations in suicide completers, we can anticipate that polyamine targets may be important for the development of novel strategies and approaches for understanding the etiopathogenesis of important central disorders and their pharmacological treatment.
The transient receptor potential vanilloid 1 (TRPV1) receptor is relevant to the perception of noxious information and has been studied as a therapeutic target for the development of new analgesics. The goal of this study was to perform in vivo and in vitro screens to identify novel, efficacious, and safe TRPV1 antagonists isolated from leaves of the medicinal plant Vernonia tweedieana Baker. All of the fractions and the hydroalcoholic extract produced antinociception in mice during the capsaicin test, but the dichloromethane fraction also had antioedematogenic effect. Among the compounds isolated from the dichloromethane fraction, only ␣-spinasterol reduced the nociception and edema induced by capsaicin injection. Moreover, ␣-spinasterol demonstrated good oral absorption and high penetration into the brain and spinal cord of mice. ␣-Spinasterol was able to displace [ 3 H]resiniferatoxin binding and diminish calcium influx mediated by capsaicin. Oral administration of the dichloromethane fraction and ␣-spinasterol also produced antinociceptive effect in the noxious heat-induced nociception test; however, they did not change the mechanical threshold of naive mice. The treatment with ␣-spinasterol did not produce antinociceptive effect in mice systemically pretreated with resiniferatoxin. In addition, ␣-spinasterol and the dichloromethane fraction reduced the edema, mechanical, and heat hyperalgesia elicited by complete Freund's adjuvant paw injection. The dichloromethane fraction and ␣-spinasterol did not affect body temperature or locomotor activity. In conclusion, ␣-spinasterol is a novel efficacious and safe antagonist of the TRPV1 receptor with antinociceptive effect.
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