Targeting TRPV4 Channels for Cancer Pain Relief.

Despite the unique and complex nature of cancer pain, the activation of different ion channels can be related to the initiation and maintenance of pain. The transient receptor potential vanilloid 4 (TRPV4) is a cation channel broadly expressed in sensory afferent neurons. This channel is activated by multiple stimuli to mediate pain perception associated with inflammatory and neuropathic pain. Here, we focused on summarizing the role of TRPV4 in cancer etiology and cancer-induced pain mechanisms. Many studies revealed that the administration of a TRPV4 antagonist and TRPV4 knockdown diminishes nociception in chemotherapy-induced peripheral neuropathy (CIPN). Although the evidence on TRPV4 channels' involvement in cancer pain is scarce, the expression of these receptors was reportedly enhanced in cancer-induced bone pain (CIBP), perineural, and orofacial cancer models following the inoculation of tumor cells to the bone marrow cavity, sciatic nerve, and tongue, respectively. Effective pain management is a continuous problem for patients diagnosed with cancer, and current guidelines fail to address a mechanism-based treatment. Therefore, examining new molecules with potential antinociceptive properties targeting TRPV4 modulation would be interesting. Identifying such agents could lead to the development of treatment strategies with improved pain-relieving effects and fewer adverse effects than the currently available analgesics.

Increased levels of advanced oxidation protein products (AOPPs) were associated with nociceptive behavior and clinical scores in an experimental progressive autoimmune encephalomyelitis model (PMS-EAE).

Multiple sclerosis (MS) is a neurodegenerative disease that affects the central nervous system (CNS) generating neuropathic pain and anxiety. Primary progressive MS (PPMS) is the most disabling clinical form, and the patients present an intense neurodegenerative process. In this context, the advanced oxidation protein products (AOPPs) are oxidized compounds and their accumulation in plasma has been related to clinical disability in MS patients. However, the involvement of AOPPs in neuropathic pain- and anxiety-like symptoms was not previously evaluated. To assess this, female mice C57BL/6J were used to induce progressive experimental autoimmune encephalomyelitis (PMS-EAE). Clinical score, weight, strength of plantar pressure, rotarod test, mechanical allodynia, and cold hypersensitivity were evaluated before induction (baseline) and on days 7th, 10th, and 14th post-immunization. We assessed nest building, open field, and elevated plus-maze tests 13 days post-immunization. Animals were killed at 14 days post-immunization; then, AOPPs levels, NADPH oxidase, and myeloperoxidase (MPO) activity were measured in the prefrontal cortex, hippocampus, and spinal cord samples. The clinical score increased 14th post-immunization without changes in weight and mobility. Reduced paw strength, mechanical allodynia, and cold allodynia increased in the PMS-EAE animals. PMS-EAE mice showed spontaneous nociception and anxiety-like behavior. AOPPs concentration, NADPH oxidase, and MPO activity increase in CNS structures. Multivariate analyses indicated that the rise of AOPPs levels, NADPH oxidase, and MPO activity influenced the clinical score and cold allodynia. Thus, we indicated the association between non-stimuli painful perception, anxiety-like, and CNS oxidative damage in the PMS-EAE model.

Alpha-lipoic acid reduces nociception by reducing oxidative stress and neuroinflammation in a model of complex regional pain syndrome type I in mice.

Complex regional pain syndrome type I (CRPS-I) is a disabling pain condition without adequate treatment. Chronic post-ischemia pain injury (CPIP) is a model of CRPS-I that causes allodynia, spontaneous pain, inflammation, vascular injury, and oxidative stress formation. Antioxidants, such as alpha lipoic acid (ALA), have shown a therapeutic potential for CRPS-I pain control. Thus, we aim to evaluate if ALA repeated treatment modulates neuroinflammation in a model of CRPS-I in mice. We used male C57BL/6 mice to induce the CPIP model (O-ring torniquet for 2 h in the hindlimb). For the treatment with ALA or vehicle (Veh) mice were randomly separated in four groups and received 100 mg/kg orally once daily for 15 days (CPIP-ALA, CPIP-Veh, Control-ALA, and Control-Veh). We evaluated different behavioral tests including von Frey (mechanical stimulus), acetone (cold thermal stimulus), rotarod, open field, hind paw edema determination, and nest-building (spontaneous pain behavior). Also, hydrogen peroxide (H2O2) levels, NADPH oxidase and superoxide dismutase (SOD) activity in the sciatic nerve and spinal cord, and Iba1, Nrf2, and Gfap in spinal cord were evaluated at 16 days after CPIP or sham induction. Repeated ALA treatment reduced CPIP-induced mechanical and cold allodynia and restored nest-building capacity without causing locomotor or body weight alteration. ALA treatment reduced SOD and NADPH oxidase activity, and H2O2 production in the spinal cord and sciatic nerve. CPIP-induced neuroinflammation in the spinal cord was associated with astrocyte activation and elevated Nfr2, which were reduced by ALA. ALA repeated treatment prevents nociception by reducing oxidative stress and neuroinflammation in a model of CRPS-I in mice.

Characterization of Depression- and Anxiety-Like Behaviours in a Mouse Model of Relapsing-Remitting Multiple Sclerosis.

Relapsing-remitting multiple sclerosis (RRMS) is an autoimmune neurological disease and is the most common subtype of MS. In addition, it is associated with the development of depression and anxiety. To date, depressive- and anxiety-like behaviours were only studied using models of progressive MS, which causes severe motor alterations. Thus, we sought to standardise the depressive and anxiety-like behaviours in an RRMS model induced by experimental autoimmune encephalomyelitis (RR-EAE) in mice. The RR-EAE model was induced in C57BL/6 female mice using myelin oligodendrocyte glycoprotein (MOG35-55) antigen and Quillaja saponin (Quil A) as an adjuvant. The immunisation of RR-EAE did not induce locomotor alteration but caused relapsing-remitting induction of clinical scores in mice until 35 post-immunization (p.i.). Also, increased levels of tumour necrosis factor alpha (TNF-α), astrocyte marker (GFAP), and microglial markers (IBA-1) were detected in the prefrontal cortex at 35 p.i. of RR-EAE. In the open field test, RR-EAE mice showed decreased time spent at the centre and sniffing behaviour (at days 21 and 34 p.i.). Also, on day 35 p.i. the RR-EAE group spent less time in the open arms and had decreased open-arm entries compared to control mice in the elevated plus maze (EPM) test, confirming the anxiety-like behaviour. At day 36° p.i. in the tail suspension test, mice showed depression-like behaviour with decreased latency time and increased immobility time. Thus, the RR-EAE model mimics the neuroinflammatory and behavioural features of the RRMS, including depression- and anxiety-like symptoms.

Prevalence of depression and anxiety in the different clinical forms of multiple sclerosis and associations with disability: A systematic review and meta-analysis.

Multiple sclerosis (MS) is a chronic neurodegenerative and autoimmune disease. Motor, sensory and cognitive deficits in MS are commonly accompanied by psychiatric disorders. Depression and anxiety affect the quality of life of MS patients, and the treatment is still not well-established. Prevalence rates in MS patients for depression and anxiety vary widely between studies. However, the prevalence of these psychiatric disorders in the subgroups of MS patients and their association with a disability has not been studied yet. Therefore, this systematic review and meta-analysis proposes to estimate the prevalence of depression and anxiety in MS and to perform subgroup analyses (study type, Extended Disability Status Scale/EDSS, duration of MS, region, type of MS) on observational studies. The protocol was registered in PROSPERO (4202125033). A computerized search on PubMed, EMBASE and Scopus for studies on depression and anxiety in MS was performed from 2015 to 2021, and 12 articles were included. Most of the studies in the meta-analysis had a low risk of bias. The prevalence of depression was 27.01% (MS), 15.78% (relapsing-remitting multiple sclerosis/RRMS), and 19.13% (progressive multiple sclerosis/PMS). For anxiety the prevalence was 35.19% (MS), 21.40% (RRMS), and 24.07% (PMS). The prevalence of depression/anxiety for patients with EDSS <3 was 26.69/45.56% and for EDSS >3 was 22.96/26.70%. Using HADS-A (8) the prevalence was 38.5% and for depression was 22.4%. Then, our study brought together current data regarding psychiatric disorders in MS patients, which are comorbidities that affect the quality of life of these patients.

TRPA1 involvement in depression- and anxiety-like behaviors in a progressive multiple sclerosis model in mice.

Progressive multiple sclerosis (PMS) is a neurological disease associated with the development of depression and anxiety, but treatments available are unsatisfactory. The transient receptor potential ankyrin 1 (TRPA1) is a cationic channel activated by reactive compounds, and the blockage of this receptor can reduce depression- and anxiety-like behaviors in naive mice. Thus, we investigated the role of TRPA1 in depression- and anxiety-like behaviors in a PMS model in mice. PMS model was induced in C57BL/6 female mice by the experimental autoimmune encephalomyelitis (EAE). Nine days after the PMS-EAE induction, behavioral tests (tail suspension and elevated plus maze tests) were performed to verify the effects of sertraline (positive control), selective TRPA1 antagonist (A-967,079), and antioxidants (α-lipoic acid and apocynin). The prefrontal cortex and hippocampus were collected to evaluate biochemical and inflammatory markers. PMS-EAE induction did not cause locomotor changes but triggered depression- and anxiety-like behaviors, which were reversed by sertraline, A-967,079, α-lipoic acid, or apocynin treatments. The neuroinflammatory markers (AIF1, GFAP, IL-1ß, IL-17, and TNF-α) were increased in mice's hippocampus. Moreover, this model did not alter TRPA1 RNA expression levels in the hippocampus but decrease TRPA1 levels in the prefrontal cortex. Moreover, PMS-EAE induced an increase in NADPH oxidase and superoxide dismutase activities and TRPA1 endogenous agonist levels (hydrogen peroxide and 4-hydroxynonenal). TRPA1 plays a fundamental role in depression- and anxiety-like behaviors in a PMS-EAE model; thus, it could be a possible pharmacological target for treating these symptoms in PMS.

Characterisation of nociception and inflammation observed in a traumatic muscle injury model in rats.

Muscle pain is the most prevalent type of pain in the world, but treatment remains ineffective. Thus, it is relevant to develop trustable animal models to understand the involved pain mechanisms. Therefore, this study characterised the nociception and inflammation in a traumatic muscle injury model in rats. A single blunt trauma impact on the right gastrocnemius muscle of male Wistar rats (250-350 g) was used as model for muscle pain. Animals were divided into four groups (sham/no treatment; sham/diclofenac 1%; injury/no treatment; injury/diclofenac 1%) and the topical treatment with a cream containing 1% monosodium diclofenac (applied at 2, 6, 12, 24, and 46 h after muscle injury; 200 mg/muscle) was used as an anti-inflammatory control. Nociception (mechanical and cold allodynia, or nociceptive score) and locomotor activity were evaluated at 26 and 48 h after injury. Also, inflammatory and oxidative parameters were evaluated in gastrocnemius muscle and the creatine kinase (CK) activity and lactate/glicose levels in rat's serum and plasma, respectively. Muscle injury caused mechanical and cold allodynia, and increased nociceptive scores, without inducing locomotor impairment. This model also increased the inflammatory cells infiltration (seen by myeloperoxidase and N-acetyl-ß-D-glucosaminidase activities and histological procedure), nitric oxide, interleukin (IL)-1ß, IL-6, and dichlorofluorescein fluorescence in muscle samples; and CK activity and lactate/glicose ratio. The treatment with 1% monosodium diclofenac reduced inflammatory cells infiltration, dichlorofluorescein fluorescence and lactate/glicose levels. Thus, we characterised the traumatic muscle injury as a reproducible model of muscle pain, which makes it possible to evaluate promising antinociceptive and anti-inflammatory therapies.

Hydroalcoholic extract of leaf of Arachis hypogaea L. (Fabaceae) did not induce toxic effects in the repeated-dose toxicity study in rats.

Arachis hypogaea L. (peanut) leaf is traditionally used for the treatment of insomnia in Asia. However, studies describing the safety and toxicity profile for this plant preparation are limited. Thus, the goal of this study was to investigate the toxicity of peanut leaf hydroalcoholic extract (PLHE) repeated treatment. The extract was administered orally (100, 300 or 1000 mg/kg) in male and female Wistar rats for 28 days (OECD guideline 407). PLHE treatment did not cause mortality or weight variation in the animals. Also, there was no alteration on locomotor activity (open field test), motor coordination (rotarod test), or anxiety behaviour (elevated plus-maze test). Male rats had a reduction in relative liver weight (100 mg/kg) and an increase in total kidney weight (1000 mg/kg), but there was no change in biochemical and haematological parameters after PLHE treatment. Free extracellular double-stranded DNA (dsDNA) levels was also evaluated, but PLHE treatment did not increase this parameter in rat organs. Also, the dose of 1000 mg/kg of PLHE significantly increased the total thiols in the liver of females compared with the control animals. Thus, PLHE did not induce toxicity after repeated exposure for 28 days in rats.

TRPA1 activation mediates nociception behaviors in a mouse model of relapsing-remitting experimental autoimmune encephalomyelitis.

Central neuropathic pain is the main symptom caused by spinal cord lesion in relapsing-remitting multiple sclerosis (RRMS), but its management is still not effective. The transient receptor potential ankyrin 1 (TRPA1) is a pain detecting ion channel involved in neuropathic pain development. Thus, the aim of our study was to evaluate the role of TRPA1 in central neuropathic nociception induced by relapsing-remitting experimental autoimmune encephalomyelitis (RR-EAE) mouse model. In this model, we observed the development of similar clinical conditions of RRMS in C57BL/6 female mice through RR-EAE using MOG35-55 antigen and Quil A adjuvant. At the thirty-fifth day post-induction, C57BL/6 female mice demonstrated alteration in the RR-EAE score without motor impairment, mechanical and cold allodynia. Also, significative changes in demyelinating (Mog and olig-1) and neuroinflammatory (Iba1, Gfap and Tnfa) markers were observed, but this model did not alter Trpa1 RNA expression levels in the spinal cord. The hydrogen peroxide and 4-hydroxynonenal levels (TRPA1 agonists) were increased in RR-EAE induced mice, as well as the NADPH oxidase activity. The intragastric treatment of RR-EAE induced mice with TRPA1 antagonists (HC-030031 and A-967079) and antioxidant (α-lipoic acid and apocynin) caused an antiallodynic effect. Moreover, the intrathecal administration of TRPA1 antisense oligonucleotide, HC-030031, α-lipoic acid, and apocynin transiently attenuated mechanical and cold allodynia. Thus, TRPA1 plays a key role in the induction of neuropathic pain in this model of RR-EAE and can be a possible target for investigating the development of pain in RRMS patients.

Characterization of Cancer-Induced Nociception in a Murine Model of Breast Carcinoma.

Severe and poorly treated pain often accompanies breast cancer. Thus, novel mechanisms involved in breast cancer-induced pain should be investigated. Then, it is necessary to characterize animal models that are reliable with the symptoms and progression of the disease as observed in humans. Explaining cancer-induced nociception in a murine model of breast carcinoma was the aim of this study. 4T1 (104) lineage cells were inoculated in the right fourth mammary fat pad of female BALB/c mice; after this, mechanical and cold allodynia, or mouse grimace scale (MGS) were observed for 30 days. To determine the presence of bone metastasis, we performed the metastatic clonogenic test and measure calcium serum levels. At 20 days after tumor induction, the antinociceptive effect of analgesics used to relieve pain in cancer patients (acetaminophen, naproxen, codeine or morphine) or a cannabinoid agonist (WIN 55,212-2) was tested. Mice inoculated with 4T1 cells developed mechanical and cold allodynia and increased MGS. Bone metastasis was confirmed using the clonogenic assay, and hypercalcemia was observed 20 days after cells inoculation. All analgesic drugs reduced the mechanical and cold allodynia, while the MGS was decreased only by the administration of naproxen, codeine, or morphine. Also, WIN 55,212-2 improved all nociceptive measures. This pain model could be a reliable form to observe the mechanisms of breast cancer-induced pain or to observe the efficacy of novel analgesic compounds.