The management of visceral pain is a major clinical problem in patients affected by gastrointestinal disorders. The poor knowledge about pain chronicization mechanisms prompted us to study the functional and morphological alterations of the gut and nervous system in the animal model of persistent visceral pain caused by 2,4-dinitrobenzenesulfonic acid (DNBS). This agent, injected intrarectally, induced a colonic inflammation peaking on day 3 and remitting progressively from day 7. In concomitance with bowel inflammation, the animals developed visceral hypersensitivity, which persisted after colitis remission for up to three months. On day 14, the administration of pain-relieving drugs (injected intraperitoneally and intrathecally) revealed a mixed nociceptive, inflammatory and neuropathic pain originating from both the peripheral and central nervous system. At this time point, the colonic histological analysis highlighted a partial restitution of the tunica mucosa, transmural collagen deposition, infiltration of mast cells and eosinophils, and upregulation of substance P (SP)-positive nerve fibers, which were surrounded by eosinophils and MHC-II-positive macrophages. A significant activation of microglia and astrocytes was observed in the dorsal and ventral horns of spinal cord. These results suggest that the persistence of visceral pain induced by colitis results from maladaptive plasticity of the enteric, peripheral and central nervous systems.

: The management of pain in patients affected by diabetic neuropathy still represents an unmet therapeutic need. Recent data highlighted the pain-relieving efficacy of glucosinolates deriving from Brassicaceae. The purpose of this study was to evaluate the anti-hyperalgesic efficacy of Eruca sativa defatted seed meal, along with its main glucosinolate, glucoerucin (GER), on diabetic neuropathic pain induced in mice by streptozotocin (STZ). The mechanism of action was also investigated. Hypersensitivity was assessed by paw pressure and cold plate tests after the acute administration of the compounds. Once bio-activated by myrosinase, both E. sativa defatted meal (1 g kg−1 p.o.) and GER (100 µmol kg−1 p.o., equimolar to meal content) showed a dose-dependent pain-relieving effect in STZ-diabetic mice, but the meal was more effective than the glucosinolate. The co-administration with H2S scavengers abolished the pain relief mediated by both E. sativa meal and GER. Their effect was also prevented by selectively blocking Kv7 potassium channels. Repeated treatments with E. sativa meal did not induce tolerance to the anti-hypersensitive effect. In conclusion, E. sativa meal can be suggested as a new nutraceutical tool for pain relief in patients with diabetic neuropathy.

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: To study new target-oriented molecules that are active against rheumatoid arthritis-dependent pain, new dual inhibitors incorporating both a carbonic anhydrase (CA)-binding moiety and a cyclooxygenase inhibitor (NSAID) were tested in a rat model of rheumatoid arthritis induced by CFA intra-articular (i.a.) injection. A comparison between a repeated per os treatment and a single i.a. injection was performed. CFA (50 µL) was injected in the tibiotarsal joint, and the effect of per os repeated treatment (1 mg kg−1) or single i.a injection (1 mg ml−1, 50 µL) with NSAIDs-CAIs hybrid molecules, named 4 and 5, was evaluated. The molecules 4 and 5, which were administered daily for 14 days, significantly prevented CFA-induced hypersensitivity to mechanical noxious (Paw pressure test) and non-noxious stimuli (von Frey test), the postural unbalance related to spontaneous pain (Incapacitance test) and motor alterations (Beam balance test). Moreover, to study a possible localized activity, 4 and 5 were formulated in liposomes (lipo 4 and lipo 5, both 1 mg ml-1) and directly administered by a single i.a. injection seven days after CFA injection. Lipo 5 decreased the mechanical hypersensitivity to noxious and non-noxious stimuli and improved motor coordination. Oral and i.a. treatments did not rescue the joint, as shown by the histological analysis. This new class of potent molecules, which is able to inhibit at the same time CA and cyclooxygenase, shows high activity in a preclinical condition of rheumatoid arthritis, strongly suggesting a novel attractive pharmacodynamic profile.

Pharmacological tools for chronic visceral pain management are still limited and inadequate. A 3 adenosine receptor (A 3 AR) agonists are effective in different models of persistent pain. Recently, their activity has been related to the block of N-type voltage-gated Ca 21 channels (Ca v 2.2) in dorsal root ganglia (DRG) neurons. The present work aimed to evaluate the efficacy of A 3 AR agonists in reducing postinflammatory visceral hypersensitivity in both male and female rats. Colitis was induced by the intracolonic instillation of 2,4dinitrobenzenesulfonic acid (DNBS; 30 mg in 0.25 mL 50% EtOH). Visceral hypersensitivity was assessed by measuring the visceromotor response and the abdominal withdrawal reflex to colorectal distension. The effects of A 3 AR agonists (MRS5980 and Cl-IB-MECA) were evaluated over time after DNBS injection and compared to that of the selective Ca v 2.2 blocker PD173212, and the clinically used drug linaclotide. A 3 AR agonists significantly reduced DNBS-evoked visceral pain both in the postinflammatory (14 and 21 days after DNBS injection) and persistence (28 and 35 days after DNBS) phases. Efficacy was comparable to effects induced by linaclotide. PD173212 fully reduced abdominal hypersensitivity to control values, highlighting the role of Ca v 2.2. The effects of MRS5980 and Cl-IB-MECA were completely abolished by the selective A 3 AR antagonist MRS1523. Furthermore, patch-clamp recordings showed that A 3 AR agonists inhibited Ca v 2.2 in dorsal root ganglia neurons isolated from either control or DNBS-treated rats. The effect on Ca 21 current was PD173212-sensitive and prevented by MRS1523. A 3 AR agonists are effective in relieving visceral hypersensitivity induced by DNBS, suggesting a potential therapeutic role against abdominal pain.