Investigation of the effect of telmisartan on experimentally induced peripheral nerve injury in rats

Losartan attenuates acetic acid enema-induced visceral hypersensitivity by inhibiting the ACE1/Ang II/AT1 receptor axis in enteric glial cells

Enteric glial cells (EGCs) play an important role in visceral hypersensitivity associated with irritable bowel syndrome (IBS). Losartan (Los) is known to reduce pain; however, its function in IBS is unclear. The present study aimed to investigate Los's therapeutic effect on visceral hypersensitivity in IBS rats. Thirty rats were randomly divided into control, acetic acid enema (AA), AA + Los low, medium and high dose groups in vivo. EGCs were treated with lipopolysaccharide (LPS) and Los in vitro. The molecular mechanisms were explored by assessing the expression of EGC activation markers, pain mediators, inflammatory factors and angiotensin-converting enzyme 1(ACE1)/angiotensin II (Ang II)/Ang II type 1 (AT1) receptor axis molecules in colon tissue and EGCs. The results showed that the rats in the AA group showed significantly higher visceral hypersensitivity than the control rats, which was alleviated by different doses of Los. The expression of GFAP, S100β, substance P (SP), calcitonin gene-related peptide (CGRP), transient receptor potential vanilloid 1 (TRPV1), tumor necrosis factor (TNF), interleukin-1β (IL-1β) and interleukin-6 (IL-6) was considerably increased in colonic tissues of AA group rats and LPS-treated EGCs compared with control rats and EGCs, and reduced by Los. In addition, Los reversed ACE1/Ang II/AT1 receptor axis upregulation in AA colon tissues and LPS-treated EGCs. These results show that Los inhibits ACE1/Ang II/AT1 receptor axis upregulation by suppressing EGC activation, resulting in reduced expression of pain mediators and inflammatory factors, thereby alleviating visceral hypersensitivity.

Renin-Angiotensin-System Inhibitors for the Prevention of Chemotherapy-Induced Peripheral Neuropathy: OncoToxSRA, a Preliminary Cohort Study

Chemotherapy-induced peripheral neuropathy (CIPN) is a frequent and dose-limiting adverse side effect of treatment. CIPN affects the oncological prognosis of patients, as well as their quality of life. To date, no specific pharmacological therapy has demonstrated effectiveness in preventing CIPN. Accumulating preclinical evidence suggests that renin-angiotensin system (RAS) inhibitors may have neuroprotective effects. One hundred and twenty patients were included in this observational study and were followed from the beginning of their neurotoxic chemotherapy schedule until their final assessment, at least one month after its cessation. The National Cancer Institute's common toxicity criteria 4.0 (NCI-CTC 4.0) were used to grade the severity of adverse events. Follow-ups also included electrochemical skin conductance and scales for pain, quality of life and disability. Among patients receiving a platinum-based regimen, the mean grade of sensory neuropathy (NCI-CTC 4.0) was significantly lower in the RAS inhibitor group after the end of their anticancer treatment schedule. Because of the observational design of the study, patients in the RAS inhibitor group cumulated comorbidities at risk of developing CIPN. Randomized controlled trials in platinum-based regimens would be worth conducting in the future to confirm the neuroprotective potential of RAS inhibitors during chemotherapy.

Neuroprotective Effect of Ramipril Is Mediated by AT2 in a Mouse MODEL of Paclitaxel-Induced Peripheral Neuropathy

Paclitaxel (PTX)-induced peripheral neuropathy (PIPN) induces numerous symptoms affecting patient quality of life, leading to decreased doses or even to cessation of anticancer therapy. Previous studies have reported that a widely used drug, ramipril, improves neuroprotection in several rodent models of peripheral neuropathy. The protective role of the angiotensin II type 2 receptor (AT2) in the central and peripheral nervous systems is well-established. Here, we evaluate the effects of ramipril in the prevention of PIPN and the involvement of AT2 in this effect. Paclitaxel was administered in wild type or AT2-deficient mice on alternate days for 8 days, at a cumulative dose of 8 mg/kg (2 mg/kg per injection). Ramipril, PD123319 (an AT2 antagonist), or a combination of both were administered one day before PTX administration, and daily for the next twenty days. PTX-administered mice developed mechanical allodynia and showed a loss of sensory nerve fibers. Ramipril prevented the functional and morphological alterations in PTX mice. The preventive effect of ramipril against tactile allodynia was completely absent in AT2-deficient mice and was counteracted by PD123319 administration in wild type mice. Our work highlights the potential of ramipril as a novel preventive treatment for PIPN, and points to the involvement of AT2 in the neuroprotective role of ramipril in PIPN.

Ramipril Alleviates Oxaliplatin-Induced Acute Pain Syndrome in Mice

Oxaliplatin is a key drug for colorectal cancer that causes OXP-induced peripheral neuropathy, a dose-limiting effect characterized by cold and tactile hyperesthesia. The relationship between the sensory nervous system and modulation of the renin-angiotensin system has been described, focusing on pain and neurodegeneration in several animal models. We assessed the effect of the RAS modulator, ramipril, an angiotensin converting-enzyme inhibitor in a mouse model of OXP-induced acute pain syndrome. OXP was administered in Swiss mice at a cumulative dose of 15 mg/kg (3 x 5 mg/kg/3 days, i.p.). RAM was administered i.p. every day from 24 h before the first OXP injection until the end of the experiments. We evaluated OIAS development and treatment effects by sensorimotor tests, intraepidermal nerve fiber and dorsal root ganglia-neuron immunohistochemical analyses, and sciatic nerve ultrastructural analysis. OXP-treated mice showed tactile allodynia and cold hypersensitivity, without motor impairment and evidence of nerve degeneration. RAM prevented cold sensitivity and improved recovery of normal tactile sensitivity in OXP-treated mice. Our finding that RAM alleviates OXP-induced pain is a step towards evaluating its therapeutic potential in patients receiving OXP treatment.

Angiotensin receptors and neuropathic pain

Growing evidence implicates the renin-angiotensin system (RAS) in multiple facets of neuropathic pain (NP). This narrative review focuses primarily on the major bioactive RAS peptide, Angiotensin II (Ang II), and its receptors, namely type 1 (AT1R) and type 2 (AT2R). Both receptors are involved in the development of NP and represent potential therapeutic targets. We first discuss the potential role of Ang II receptors in modulation of NP in the central nervous system. Ang II receptor expression is widespread in circuits associated with the perception and modulation of pain, but more studies are required to fully characterize receptor distribution, downstream signaling, and therapeutic potential of targeting the central nervous system RAS in NP. We then describe the peripheral neuronal and nonneuronal distribution of the RAS, and its contribution to NP. Other RAS modulators (such as Ang (1-7)) are briefly reviewed as well. AT1R antagonists are analgesic across different pain models, including NP. Several studies show neuronal protection and outgrowth downstream of AT2R activation, which may lead to the use of AT2R agonists in NP. However, blockade of AT2R results in analgesia. Furthermore, expression of the RAS in the immune system and a growing appreciation of neuroimmune crosstalk in NP add another layer of complexity and therapeutic potential of targeting this pathway. A growing number of human studies also hint at the analgesic potential of targeting Ang II signaling. Altogether, Ang II receptor signaling represents a promising, far-reaching, and novel strategy to treat NP.

In vivo identification of small molecules mediating Gpr126/Adgrg6 signaling during Schwann cell development

Gpr126/Adgrg6, an adhesion family G protein-coupled receptor (aGPCR), is required for the development of myelinating Schwann cells in the peripheral nervous system. Myelin supports and insulates vertebrate axons to permit rapid signal propagation throughout the nervous system. In mammals and zebrafish, mutations in Gpr126 arrest Schwann cells at early developmental stages. We exploited the optical and pharmacological tractability of larval zebrafish to uncover drugs that mediate myelination by activating Gpr126 or functioning in parallel. Using a fluorescent marker of mature myelinating glia (Tg[mbp:EGFP-CAAX]), we screened hypomorphic gpr126 mutant larvae for restoration of myelin basic protein (mbp) expression along peripheral nerves following small molecule treatment. Our screens identified five compounds sufficient to promote mbp expression in gpr126 hypomorphs. Using an allelic series of gpr126 mutants, we parsed the ability of small molecules to restore mbp, suggesting differences in drug efficacy dependent on Schwann cell developmental state. Finally, we identify apomorphine hydrochloride as a direct small molecule activator of Gpr126 using combined in vivo/in vitro assays and show that aporphine class compounds promote Schwann cell development in vivo. Our results demonstrate the utility of in vivo screening for aGPCR modulators and identify small molecules that interact with the gpr126-mediated myelination program.

Interleukin-1β influences functional regeneration following nerve injury in mice through nuclear factor-κB signaling pathway

This study focuses on investigating the role of interleukin-1β (IL-1β) in functional regeneration following nerve injury in mice. A microarray-based mRNA profiling study was used to analyze the expression level of IL-1β in peripheral nerve regeneration. Quantitative real-time polymerase chain reaction and Western blot were applied to assess the IL-1β expressions of C57BL/6J-crush and C57BL/6J-crush+IL-1β mice at different post-injury time-points after the standard sciatic nerve crush injury. The outcomes of nerve regeneration were evaluated by behavioral tests. IL-1β was found to be up-regulated in peripheral nerve regeneration and significantly raised on the 3rd day and returned to normal levels on the 14th day after nerve injury. Compared with C57BL/6J-crush+IL-1β mice, the nerve regeneration of C57BL/6J-crush mice was worse after nerve crush injury. IL-1β increased mechanical sensitivity and stimulated amplitude. IL-1β could benefit the recovery of sciatic nerve crush injury by facilitating nerve regeneration.

Candesartan prevents resiniferatoxin-induced sensory small-fiber neuropathy in mice by promoting angiotensin II-mediated AT2 receptor stimulation

Sensory defects associated with small-fiber neuropathy (SFN) can lead to profound disabilities. The relationship between the sensory nervous system and modulation of the renin-angiotensin system (RAS) has been described and focused on pain and neurodegeneration in several animal models. We have recently developed an experimental model of functional sensory neuropathy showing thermal hypoalgesia and neuropeptide depletion without nerve fiber degeneration. Here, we aimed to determine whether the modulation of angiotensin II (Ang II) activity could prevent sensory neuropathy induced by RTX. Control and RTX mice received ramipril, an Ang II converting enzyme (ACE) inhibitor, (0.5 mg/kg/day) or candesartan, an Ang II type 1 receptor (AT1R) blocker (0.5 mg/kg/day), one day before vehicle or RTX administration, and each day for the next seven days. Ramipril did not have a beneficial effect in RTX mice, whereas candesartan prevented thermal hypoalgesia and reduced neuropeptide depletion in intraepidermal nerve fibers and dorsal root ganglion neurons. The preventive effect of candesartan was not observed in mice deficient for the Ang II type 2 receptor (AT2R) and was counteracted in wild type mice by EMA200, an AT2R antagonist (3 mg/kg/day). Thus, candesartan may promote AT2R activation by blocking AT1R and increasing Ang II production and enhance its mechanisms of neuroprotection in our RTX model. Our finding that candesartan prevents nociception deficits and neuropeptide depletion encourages the evaluation of its therapeutic potential in patients presenting SFN, particularly those who experience chemotherapy-induced SFN.

Ganglioside promotes the bridging of sciatic nerve defects in cryopreserved peripheral nerve allografts

Previous studies have shown that exogenous gangliosides promote nervous system regeneration and synapse formation. In this study, 10 mm sciatic nerve segments from New Zealand rabbits were thawed from cryopreservation and were used for the repair of left sciatic nerve defects through allograft bridging. Three days later, 1 mL ganglioside solution (1 g/L) was subcutaneously injected into the right hind leg of rabbits. Compared with non-injected rats, muscle wet weight ratio was increased at 2-12 weeks after modeling. The quantity of myelinated fibers in regenerated sciatic nerve, myelin thickness and fiber diameter were elevated at 4-12 weeks after modeling. Sciatic nerve potential amplitude and conduction velocity were raised at 8 and 12 weeks, while conduction latencies were decreased at 12 weeks. Experimental findings indicate that ganglioside can promote the regeneration of sciatic nerve defects after repair with cryopreserved peripheral nerve allografts.