The Nociceptive and Inflammatory Responses Induced by the Ehrlich Solid Tumor Are Changed in Mice Healed of Plasmodium berghei Strain ANKA Infection after Chloroquine Treatment

Comorbidities that involve infectious and noninfectious diseases, such as malaria and cancer, have been described. Cancer and malaria induce changes in the nociceptive and inflammatory responses through similar pathophysiological mechanisms. However, it is unclear whether malaria and antimalarial treatment can change the inflammatory and nociceptive responses induced by solid cancer. Therefore, the present study experimentally evaluated the effect of infection by Plasmodium berghei strain ANKA and chloroquine treatment on the nociceptive and inflammatory responses induced by the solid Ehrlich tumor in male BALB/c mice. On the 1st experimental day, mice were infected with Plasmodium berghei and injected with tumor cells in the left hind paw. From the 7th to the 9th experimental day, mice were treated daily with chloroquine. The parasitemia was evaluated on the 7th and 10th days after infection. On the 11th experimental day, mice were evaluated on the von Frey filament test, the hot plate test, and the paw volume test. At the end of the experimental tests on the 11th day, the peripheral blood of all mice was collected for dosing of IL-1β and TNF-α. The blood parasitemia significantly increased from the 7th to the 10th day. The chloroquine treatment significantly decreased the parasitemia on the 10th day. The presence of the tumor did not significantly change the parasitemia on the 7th and 10th days in mice treated and nontreated with chloroquine. On the 11th day, the mechanical and thermal nociceptive responses significantly increased in mice with tumors. The treatment with antimalarial significantly reduced the mechanical nociceptive response induced by tumors. The hyperalgesia induced by tumors did not change with malaria. The mechanical and thermal hyperalgesia induced by the tumor was significantly reduced in mice treated and healed from malaria. On the 11th day, the volume of the paw injected by the tumor was significantly increased. The mice treated with chloroquine, infected with malaria, or healed of malaria showed reduced paw edema induced by the tumor. Mice with tumors did not show a change in IL-β and TNF-α serum levels. Mice with tumors showed a significant increase in serum levels of IL-1β but not TNF-α when treated with chloroquine, infected with malaria, or healed of malaria. In conclusion, the results show that malaria infection and chloroquine treatment can influence, in synergic form, the nociceptive and inflammatory responses induced by the solid tumor. Moreover, the mechanical antinociception, the thermal hyperalgesia, and the antiedema effect observed in mice treated with chloroquine and healed from malaria can be related to the increase in the serum level of IL-1β.

Naringenin Inhibits Superoxide Anion-Induced Inflammatory Pain: Role of Oxidative Stress, Cytokines, Nrf-2 and the NO-cGMP-PKG-KATP Channel Signaling Pathway

In the present study, the effect and mechanism of action of the flavonoid naringenin were evaluated in superoxide anion donor (KO₂)-induced inflammatory pain in mice. Naringenin reduced KO₂-induced overt-pain like behavior, mechanical hyperalgesia, and thermal hyperalgesia. The analgesic effect of naringenin depended on the activation of the NO−cGMP−PKG−ATP-sensitive potassium channel (K_ATP) signaling pathway. Naringenin also reduced KO₂-induced neutrophil recruitment (myeloperoxidase activity), tissue oxidative stress, and cytokine production. Furthermore, naringenin downregulated KO₂-induced mRNA expression of gp91phox, cyclooxygenase (COX)-2, and preproendothelin-1. Besides, naringenin upregulated KO₂-reduced nuclear factor (erythroid-derived 2)-like 2 (Nrf2) mRNA expression coupled with enhanced heme oxygenase (HO-1) mRNA expression. In conclusion, the present study demonstrates that the use of naringenin represents a potential therapeutic approach reducing superoxide anion-driven inflammatory pain. The antinociceptive, anti-inflammatory and antioxidant effects are mediated via activation of the NO−cGMP−PKG−K_ATP channel signaling involving the induction of Nrf2/HO-1 pathway.

Jararhagin-induced mechanical hyperalgesia depends on TNF-α, IL-1β and NFκB in mice

Jararhagin is a hemorrhagic metalloprotease from Bothrops jararaca snake venom. The hyperalgesic mechanisms of jararhagin were investigated focusing on the role of proinflammatory cytokines (TNF-α and IL-1β) and the transcription factor NFκB. Intraplantar administration of jararhagin (1, 10, 100 and 1000 ng/paw) induced mechanical hyperalgesia, and increased TNF-α levels at 1, 3 and 5 h, and IL-1β levels at 0.5, 1 and 3 h after its injection in the paw tissue. Pre-treatment with morphine (2, 6, 12 μg/paw) inhibited jararhagin-induced mechanical hyperagesia. The systemic or local pre-treatment with etanercept (10 mg/kg and 100 μg/paw) and IL-1ra (30 mg/kg and 100 pg/paw) inhibited jararhagin-induced mechanical hyperalgesia. Co-administration of jararhagin (0.1 ng/paw) and TNF-α (0.1 pg/paw) or jararhagin (0.1 ng/paw) and IL-1β (1 pg/paw) enhanced the mechanical hyperalgesia. The systemic or local pre-treatment with PDTC (NFκB inhibitor; 100 mg/kg and 100 μg/paw) inhibited jararhagin-induced mechanical hyperalgesia as well as PDTC decreased the jararhagin-induced production of TNF-α and IL-1β. Thus, these data demonstrate the involvement of pro-inflammatory cytokines TNF-α and IL-1β and nuclear transcription factor NFκB in jararhagin-induced mechanical hyperalgesia indicating that targeting these mechanisms might contribute to reduce the pain induced by B. jararaca snake venom.

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.

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.