Francesco De Logu

TRPA1 mediates trigeminal neuropathic pain in mice downstream of monocytes/macrophages and oxidative stress

Despite intense investigation, the mechanisms of the different forms of trigeminal neuropathic pain remain substantially unidentified. The transient receptor potential ankyrin 1 channel (encoded by TRPA1) has been reported to contribute to allodynia or hyperalgesia in some neuropathic pain models, including those produced by sciatic nerve constriction. However, the role of TRPA1 and the processes that cause trigeminal pain-like behaviours from nerve insult are poorly understood. The role of TRPA1, monocytes and macrophages, and oxidative stress in pain-like behaviour evoked by the constriction of the infraorbital nerve in mice were explored. C57BL/6 and wild-type (Trpa1(+/+)) mice that underwent constriction of the infraorbital nerve exhibited prolonged (20 days) non-evoked nociceptive behaviour and mechanical, cold and chemical hypersensitivity in comparison to sham-operated mice (P < 0.05-P < 0.001). Both genetic deletion of Trpa1 (Trpa1(-/-)) and pharmacological blockade (HC-030031 and A-967079) abrogated pain-like behaviours (both P < 0.001), which were abated by the antioxidant, α-lipoic acid, and the nicotinamide adenine dinucleotide phosphate oxidase inhibitor, apocynin (both P < 0.001). Nociception and hypersensitivity evoked by constriction of the infraorbital nerve was associated with intra- and perineural monocytic and macrophagic invasion and increased levels of oxidative stress by-products (hydrogen peroxide and 4-hydroxynonenal). Attenuation of monocyte/macrophage increase by systemic treatment with an antibody against the monocyte chemoattractant chemokine (C-C motif) ligand 2 (CCL2) or the macrophage-depleting agent, clodronate (both P < 0.05), was associated with reduced hydrogen peroxide and 4-hydroxynonenal perineural levels and pain-like behaviours (all P < 0.01), which were abated by perineural administration of HC-030031, α-lipoic acid or the anti-CCL2 antibody (all P < 0.001). The present findings propose that, in the constriction of the infraorbital nerve model of trigeminal neuropathic pain, pain-like behaviours are entirely mediated by the TRPA1 channel, targeted by increased oxidative stress by-products released from monocytes and macrophages clumping at the site of nerve injury.

The TRPA1 channel mediates the analgesic action of dipyrone and pyrazolone derivatives

Although still used by hundreds of millions of people worldwide, the mechanism of the analgesic action of the pyrazolone derivatives (PDs), dipyrone, propyphenazone and antipyrine remains unknown. The transient receptor potential ankyrin 1 (TRPA1) channel, expressed by nociceptors, is emerging as a major pain transduction pathway. We hypothesized that PDs target the TRPA1 channel and by this mechanism produce their analgesic effect.

Steroidal and non-steroidal third-generation aromatase inhibitors induce pain-like symptoms via TRPA1.

Use of aromatase inhibitors (AIs), exemestane, letrozole and anastrozole, for breast cancer therapy is associated with severe pain symptoms, the underlying mechanism of which is unknown. The electrophilic nature of AIs suggests that they may target the transient receptor potential ankyrin 1 (TRPA1) channel, a major pathway in pain transmission and neurogenic inflammation. AIs evoke TRPA1-mediated calcium response and current in rodent nociceptors and human cells expressing the recombinant channel. In mice, AIs produce acute nociception, which is exaggerated by pre-exposure to proalgesic stimuli, and, by releasing sensory neuropeptides, neurogenic inflammation in peripheral tissues. AIs also evoke mechanical allodynia and decreased grip strength, which do not undergo desensitization on prolonged AI administration. These effects are markedly attenuated by TRPA1 pharmacological blockade or in TRPA1-deficient mice. TRPA1 is a major mediator of the proinflammatory/proalgesic actions of AIs, thus suggesting TRPA1 antagonists for the treatment of pain symptoms associated with AI use.

TRP functions in the broncho-pulmonary system

The current understanding of the role of transient receptor potential (TRP) channels in the airways and lung was initially based on the localization of a series of such channels in a subset of sensory nerve fibers of the respiratory tract. Soon after, TRP channel expression and function have been identified in respiratory nonneuronal cells. In these two locations, TRPs regulate physiological processes aimed at integrating different stimuli to maintain homeostasis and to react to harmful agents and tissue injury by building up inflammatory responses and repair processes. There is no doubt that TRPs localized in the sensory network contribute to airway neurogenic inflammation, and emerging evidence underlines the role of nonneuronal TRPs in orchestrating inflammation and repair in the respiratory tract. However, recent basic and clinical studies have offered clues regarding the contribution of neuronal and nonneuronal TRPs in the mechanism of asthma, chronic obstructive pulmonary disease, idiopathic pulmonary fibrosis, cough, and other respiratory diseases.

The peptide Phα1β, from spider venom, acts as a TRPA1 channel antagonist with antinociceptive effects in mice.

Peptides from venomous animals have long been important for understanding pain mechanisms and for the discovery of pain treatments. Here, we hypothesized that Phα1β, a peptide from the venom of the armed spider Phoneutria nigriventer, produces analgesia by blocking the TRPA1 channel.

Phα1β acts as a TRPA1 antagonist with antinociceptive effects in mice

Peptides from venomous animals have long been important for understanding pain mechanisms and for the discovery of pain treatments. Here, we hypothesized that Phα1β, a peptide from the venom of the armed spider Phoneutria nigriventer, produces analgesia by blocking the TRPA1 channel.

Immunomodulating property of MAPK inhibitors: From translational knowledge to clinical implementation

Treatment of metastatic melanoma was radically changed by the introduction of inhibitors of BRAF, an oncogene mutated in 40–50% of patients. Another area of advancement was the use of immunotherapy, and specifically, immune checkpoint inhibitors. There is compelling evidence that oncogenic BRAF, in addition to driving melanoma proliferation, differentiation and survival, induces T-cell suppression directly through the secretion of inhibitory cytokines or through membrane expression of co-inhibitory molecules such as the PD-1 ligands PD-L1 or PD-L2. Furthermore, the presence of oncogenic BRAF leads to an immune suppressive phenotype characterized by the presence of inhibitory immune cells such as regulatory T cells, myeloid-derived suppressor cells, or tumor-associated macrophages, which can in turn inhibit the function of tumor-infiltrating T cells. Growing evidence suggests that, in addition to their established molecular mechanism of action, the therapeutic efficacy of BRAF inhibitors and MEK inhibitors relies on additional factors that affect the tumor–host interactions, including the enhancement of melanoma antigen expression and the increase in immune response against tumor cells. Focus of the present review is to summarize the off target mechanisms of response to BRAF inhibitors and MEK inhibitors and the synergy between targeted therapy and immunotherapy as the biological source to open a window of strategic opportunities for the design of new exciting clinical trials.

The anti‐migraine component of butterbur extracts, isopetasin, desensitizes peptidergic nociceptors by acting on TRPA1 cation channel

The mechanism of the anti‐migraine action of extracts of butterbur [Petasites hybridus (L.) Gaertn.] is unknown. Here, we investigated the ability of isopetasin, a major constituent of these extracts, to specifically target TRPA1 channel and to affect functional responses relevant to migraine.

Schwann cell TRPA1 mediates neuroinflammation that sustains macrophage-dependent neuropathic pain in mice

It is known that transient receptor potential ankyrin 1 (TRPA1) channels, expressed by nociceptors, contribute to neuropathic pain. Here we show that TRPA1 is also expressed in Schwann cells. We found that in mice with partial sciatic nerve ligation, TRPA1 silencing in nociceptors attenuated mechanical allodynia, without affecting macrophage infiltration and oxidative stress, whereas TRPA1 silencing in Schwann cells reduced both allodynia and neuroinflammation. Activation of Schwann cell TRPA1 evoked NADPH oxidase 1 (NOX1)-dependent H2O2 release, and silencing or blocking Schwann cell NOX1 attenuated nerve injury-induced macrophage infiltration, oxidative stress and allodynia. Furthermore, the NOX2-dependent oxidative burst, produced by macrophages recruited to the perineural space activated the TRPA1–NOX1 pathway in Schwann cells, but not TRPA1 in nociceptors. Schwann cell TRPA1 generates a spatially constrained gradient of oxidative stress, which maintains macrophage infiltration to the injured nerve, and sends paracrine signals to activate TRPA1 of ensheathed nociceptors to sustain mechanical allodynia.Following peripheral nerve injury, influx of immune cells to the site may contribute to the development of chronic pain. Here the authors show that TRPA1 is expressed on Schwann cells and contributes to immune cell influx in a mouse model of neuropathic pain.

The antimigraine butterbur ingredient, isopetasin, desensitises peptidergic nociceptors via the transient receptor potential ankyrin 1 channel

The mechanism of the anti‐migraine action of extracts of butterbur [Petasites hybridus (L.) Gaertn.] is unknown. Here, we investigated the ability of isopetasin, a major constituent of these extracts, to specifically target TRPA1 channel and to affect functional responses relevant to migraine.