Modulation of host immunity by sensory neurons.

Recent studies have uncovered a new role for sensory neurons in influencing mammalian host immunity, challenging conventional notions of the nervous and immune systems as separate entities. In this review we delve into this groundbreaking paradigm of neuroimmunology and discuss recent scientific evidence for the impact of sensory neurons on host responses against a wide range of pathogens and diseases, encompassing microbial infections and cancers. These valuable insights enhance our understanding of the interactions between the nervous and immune systems, and also pave the way for developing candidate innovative therapeutic interventions in immune-mediated diseases highlighting the importance of this interdisciplinary research field.

Kaurenoic Acid Reduces Ongoing Chronic Constriction Injury-Induced Neuropathic Pain: Nitric Oxide Silencing of Dorsal Root Ganglia Neurons.

Kaurenoic acid (KA) is a diterpene extracted from Sphagneticola trilobata (L.) Pruski. KA presents analgesic properties. However, the analgesic activity and mechanisms of action of KA in neuropathic pain have not been investigated so far; thus, we addressed these points in the present study. A mouse model of neuropathic pain was induced by chronic constriction injury (CCI) of the sciatic nerve. Acute (at the 7th-day post-CCI surgery) and prolonged (from 7-14th days post-CCI surgery) KA post-treatment inhibited CCI-induced mechanical hyperalgesia at all evaluated time points, as per the electronic version of von Frey filaments. The underlying mechanism of KA was dependent on activating the NO/cGMP/PKG/ATP-sensitive potassium channel signaling pathway since L-NAME, ODQ, KT5823, and glibenclamide abolished KA analgesia. KA reduced the activation of primary afferent sensory neurons, as observed by a reduction in CCI-triggered colocalization of pNF-κB and NeuN in DRG neurons. KA treatment also increased the expression of neuronal nitric oxide synthase (nNOS) at the protein level as well as the intracellular levels of NO in DRG neurons. Therefore, our results provide evidence that KA inhibits CCI neuropathic pain by activating a neuronal analgesic mechanism that depends on nNOS production of NO to silence the nociceptive signaling that generates analgesia.

Chikungunya Virus and Its Envelope Protein E2 Induce Hyperalgesia in Mice: Inhibition by Anti-E2 Monoclonal Antibodies and by Targeting TRPV1.

Chikungunya virus is an arthropod-borne infectious agent that causes Chikungunya fever disease. About 90% of the infected patients experience intense polyarthralgia, affecting mainly the extremities but also the large joints such as the knees. Chronic disease symptoms persist for months, even after clearance of the virus from the blood. Envelope proteins stimulate the immune response against the Chikungunya virus, becoming an important therapeutic target. We inactivated the Chikungunya virus (iCHIKV) and produced recombinant E2 (rE2) protein and three different types of anti-rE2 monoclonal antibodies. Using these tools, we observed that iCHIKV and rE2 protein induced mechanical hyperalgesia (electronic aesthesiometer test) and thermal hyperalgesia (Hargreaves test) in mice. These behavioral results were accompanied by the activation of dorsal root ganglia (DRG) neurons in mice, as observed by calcium influx. Treatment with three different types of anti-rE2 monoclonal antibodies and absence or blockade (AMG-9810 treatment) of transient receptor potential vanilloid 1 (TRPV1) channel diminished mechanical and thermal hyperalgesia in mice. iCHIKV and rE2 activated TRPV1+ mouse DRG neurons in vitro, demonstrating their ability to activate nociceptor sensory neurons directly. Therefore, our mouse data demonstrate that targeting E2 CHIKV protein with monoclonal antibodies and inhibiting TRPV1 channels are reasonable strategies to control CHIKV pain.

Hesperidin Methyl Chalcone Reduces the Arthritis Caused by TiO2 in Mice: Targeting Inflammation, Oxidative Stress, Cytokine Production, and Nociceptor Sensory Neuron Activation.

Arthroplasty is an orthopedic surgical procedure that replaces a dysfunctional joint by an orthopedic prosthesis, thereby restoring joint function. Upon the use of the joint prosthesis, a wearing process begins, which releases components such as titanium dioxide (TiO2) that trigger an immune response in the periprosthetic tissue, leading to arthritis, arthroplasty failure, and the need for revision. Flavonoids belong to a class of natural polyphenolic compounds that possess antioxidant and anti-inflammatory activities. Hesperidin methyl chalcone's (HMC) analgesic, anti-inflammatory, and antioxidant effects have been investigated in some models, but its activity against the arthritis caused by prosthesis-wearing molecules, such as TiO2, has not been investigated. Mice were treated with HMC (100 mg/kg, intraperitoneally (i.p.)) 24 h after intra-articular injection of 3 mg/joint of TiO2, which was used to induce chronic arthritis. HMC inhibited mechanical hyperalgesia, thermal hyperalgesia, joint edema, leukocyte recruitment, and oxidative stress in the knee joint (alterations in gp91phox, GSH, superoxide anion, and lipid peroxidation) and in recruited leukocytes (total reactive oxygen species and GSH); reduced patellar proteoglycan degradation; and decreased pro-inflammatory cytokine production. HMC also reduced the activation of nociceptor-sensory TRPV1+ and TRPA1+ neurons. These effects occurred without renal, hepatic, or gastric damage. Thus, HMC reduces arthritis triggered by TiO2, a component released upon wearing of prosthesis.

Ehrlich Tumor Induces TRPV1-Dependent Evoked and Non-Evoked Pain-like Behavior in Mice.

We standardized a model by injecting Ehrlich tumor cells into the paw to evaluate cancer pain mechanisms and pharmacological treatments. Opioid treatment, but not cyclooxygenase inhibitor or tricyclic antidepressant treatments reduces Ehrlich tumor pain. To best use this model for drug screening it is essential to understand its pathophysiological mechanisms. Herein, we investigated the contribution of the transient receptor potential cation channel subfamily V member 1 (TRPV1) in the Ehrlich tumor-induced pain model. Dorsal root ganglia (DRG) neurons from the Ehrlich tumor mice presented higher activity (calcium levels using fluo-4 fluorescent probe) and an increased response to capsaicin (TRPV1 agonist) than the saline-injected animals (p < 0.05). We also observed diminished mechanical (electronic von Frey) and thermal (hot plate) hyperalgesia, paw flinching, and normalization of weight distribution imbalance in TRPV1 deficient mice (p < 0.05). On the other hand, TRPV1 deficiency did not alter paw volume or weight, indicating no significant alteration in tumor growth. Intrathecal injection of AMG9810 (TRPV1 antagonist) reduced ongoing Ehrlich tumor-triggered mechanical and thermal hyperalgesia (p < 0.05). Therefore, the contribution of TRPV1 to Ehrlich tumor pain behavior was revealed by genetic and pharmacological approaches, thus, supporting the use of this model to investigate TRPV1-targeting therapies for the treatment of cancer pain.

Resolvin D5 (RvD5) Reduces Renal Damage Caused by LPS Endotoxemia in Female Mice.

In self-revolving gram-negative Escherichia coli infection, Resolvin D5 (RvD5) was found to enhance bacteria phagocytosis and reduce the production of inflammatory mediators, contributing to the resolution of infection. LPS (lipopolysaccharide) is a gram-negative bacterial structure product which activates the immune system and, at high doses, leads to endotoxemia. To our knowledge, the effect of RvD5 against LPS endotoxemia has not been investigated to date. Female Swiss mice received an i.p. treatment with RvD5 (0.1, 1 or 10 ng/animal). After 1 h, they were stimulated with LPS (10 mg/kg, i.v.), and samples were collected after additional 6 h. The resulting data demonstrated that RvD5 protected the kidneys (urea and creatinine serum levels) from tissue injury. These effects were related to an improvement in histopathological parameters and a reduction of enzymatic markers of leukocyte infiltration, pro-inflammatory cytokine (IL-1ß, TNF-α, and IL-6) production, and oxidative stress. Antioxidant markers were also increased by RvD5, but IL-10 (an anti-inflammatory cytokine) levels were unaltered. We also observed that RvD5 reduced the infiltration of CD45+ hematopoietic cells into the kidneys, reduced the activation of NFκB and promoted the Nrf2 pathway by reducing Keap-1 levels. Our data indicate that RvD5 may be a therapeutic possibility to reduce kidney lesions in LPS endotoxemia.

Peripheral mechanisms involved in Tityus bahiensis venom-induced pain.

Scorpionism is a public health burden in Brazil. Tityus bahiensis is responsible for most accidents in the Southeastern region of Brazil. Here, the hyperalgesic mechanisms of Tityus bahiensis venom were investigated, focusing on the role of pro-inflammatory cytokines (tumor necrosis factor alpha [TNF-α] and interleukin 1 beta [IL-1ß]) and activation of the transcription factor NFκB. Intraplantar (i.pl.) administration of Tityus bahiensis venom (0.2, 0.6, 1.2 and 2.4 µg/20 µL i.pl.) induced mechanical hyperalgesia and thermal hyperalgesia. The 2.4 µg dose of Tityus bahiensis venom induced overt pain-like behavior and increased myeloperoxidase (MPO) and N-acetyl-beta-D-glucosaminidase (NAG) activities, TNF-α and IL-1ß levels in the paw tissue. Systemic pre-treatment with etanercept (soluble TNF-α receptor; 10 mg/kg), IL-1ra (IL-1 receptor antagonist; 30 mg/kg) and pyrrolidine dithiocarbamate (PDTC, nuclear factor kappa B [NFκB] inhibitor; 100 mg/kg) inhibited Tityus bahiensis venom-induced mechanical and thermal hyperalgesia, MPO and NAG activity and overt pain-like behavior. These data demonstrate the involvement of TNF-α and IL-1ß signaling as well as NFκB activation in Tityus bahiensis venom-induced mechanical and thermal hyperalgesia, overt pain-like behavior, and MPO activity and NAG activity, indicating thus, that targeting these mechanisms might contribute to reducing the pain in this scorpionism.

Hesperidin methyl chalcone interacts with NFκB Ser276 and inhibits zymosan-induced joint pain and inflammation, and RAW 264.7 macrophage activation.

Arthritis can be defined as a painful musculoskeletal disorder that affects the joints. Hesperidin methyl chalcone (HMC) is a flavonoid with analgesic, anti-inflammatory, and antioxidant effects. However, its effects on a specific cell type and in the zymosan-induced inflammation are unknown. We aimed at evaluating the effects of HMC in a zymosan-induced arthritis model. A dose-response curve of HMC (10, 30, or 100 mg/kg) was performed to determine the most effective analgesic dose after intra-articular zymosan stimuli. Knee joint oedema was determined using a calliper. Leukocyte recruitment was performed by cell counting on knee joint wash as well as histopathological analysis. Oxidative stress was measured by colorimetric assays (GSH, FRAP, ABTS and NBT) and RT-qPCR (gp91phox and HO-1 mRNA expression) performed. In vitro, oxidative stress was assessed by DCFDA assay using RAW 264.7 macrophages. Cytokine production was evaluated in vivo and in vitro by ELISA. In vitro NF-κB activation was analysed by immunofluorescence. We observed HMC reduced mechanical hypersensitivity and knee joint oedema, leukocyte recruitment, and pro-inflammatory cytokine levels. We also observed a reduction in zymosan-induced oxidative stress as per increase in total antioxidant capacity and reduction in gp91phox and increase in HO-1 mRNA expression. Accordingly, total ROS production and macrophage NFκB activation were diminished. HMC interaction with NFκB p65 at Ser276 was revealed using molecular docking analysis. Thus, data presented in this work suggest the usefulness of HMC as an analgesic and anti-inflammatory in a zymosan-induced arthritis model, possibly by targeting NFκB activation in macrophages.