Intestinal inflammation-associated hypersensitivity is attenuated in a DSS model of colitis in Sigma-1 knockout C57BL/6 mice

Digging deeper into pain: an ethological behavior assay correlating well-being in mice with human pain experience

ABSTRACT

The pressing need for safer, more efficacious analgesics is felt worldwide. Preclinical tests in animal models of painful conditions represent one of the earliest checkpoints novel therapeutics must negotiate before consideration for human use. Traditionally, the pain status of laboratory animals has been inferred from evoked nociceptive assays that measure their responses to noxious stimuli. The disconnect between how pain is tested in laboratory animals and how it is experienced by humans may in part explain the shortcomings of current pain medications and highlights a need for refinement. Here, we survey human patients with chronic pain who assert that everyday aspects of life, such as cleaning and leaving the house, are affected by their ongoing level of pain. Accordingly, we test the impact of painful conditions on an ethological behavior of mice, digging. Stable digging behavior was observed over time in naive mice of both sexes. By contrast, deficits in digging were seen after acute knee inflammation. The analgesia conferred by meloxicam and gabapentin was compared in the monosodium iodoacetate knee osteoarthritis model, with meloxicam more effectively ameliorating digging deficits, in line with human patients finding meloxicam more effective. Finally, in a visceral pain model, the decrease in digging behavior correlated with the extent of disease. Ultimately, we make a case for adopting ethological assays, such as digging, in studies of pain in laboratory animals, which we believe to be more representative of the human experience of pain and thus valuable in assessing clinical potential of novel analgesics in animals.

Multimodal therapies and strategies for the treatment of interstitial cystitis/bladder pain syndrome in Taiwan

Interstitial cystitis/bladder pain syndrome (IC/BPS) is a chronic disease characterized by bladder pain, frequency, and nocturia. The most common pathologies include chronic inflammation and bladder urothelium dysfunction. According to the bladder condition with or without Hunner's lesions, IC/BPS can be divided into "IC" in patients with Hunner's lesion (HIC) and "BPS" in those without Hunner's lesion (NHIC). Previous studies have reported greater central sensitization and interorgan cross-talk in patients with NHIC. Multimodal treatments have been recommended in clinical guidelines under the biopsychosocial model. The bladder-gut-brain axis has also been speculated, and multimodal therapies are necessary. Unfortunately, currently, no treatment has been reported durable for IC/BPS. Patients with IC/BPS usually experience anxiety, depression, holistic physical responses, and even threats to social support systems. The lack of durable treatment outcomes might result from inadequate diagnostic accuracy and differentiation of clinical phenotypes based on the underlying pathophysiology. Precision assessment and treatment are essential for optimal therapy under definite IC/BPS phenotype. This article reviewed currently available literature and proposed a diagnosis and treatment algorithm. Based on bladder therapy combined with suitable physical and psychological therapies, a well-grounded multimodal therapy and treatment algorithm for IC/BPS following a diagnostic protocol are indispensable.

Evolving acidic microenvironments during colitis provide selective analgesic targets for a pH-sensitive opioid

ABSTRACT

Targeting the acidified inflammatory microenvironment with pH-sensitive opioids is a novel approach for managing visceral pain while mitigating side effects. The analgesic efficacy of pH-dependent opioids has not been studied during the evolution of inflammation, where fluctuating tissue pH and repeated therapeutic dosing could influence analgesia and side effects. Whether pH-dependent opioids can inhibit human nociceptors during extracellular acidification is unexplored. We studied the analgesic efficacy and side-effect profile of a pH-sensitive fentanyl analog, (±)- N -(3-fluoro-1-phenethylpiperidine-4-yl)- N -phenyl propionamide (NFEPP), during the evolution of colitis induced in mice with dextran sulphate sodium. Colitis was characterized by granulocyte infiltration, histological damage, and acidification of the mucosa and submucosa at sites of immune cell infiltration. Changes in nociception were determined by measuring visceromotor responses to noxious colorectal distension in conscious mice. Repeated doses of NFEPP inhibited nociception throughout the course of disease, with maximal efficacy at the peak of inflammation. Fentanyl was antinociceptive regardless of the stage of inflammation. Fentanyl inhibited gastrointestinal transit, blocked defaecation, and induced hypoxemia, whereas NFEPP had no such side effects. In proof-of-principle experiments, NFEPP inhibited mechanically provoked activation of human colonic nociceptors under acidic conditions mimicking the inflamed state. Thus, NFEPP provides analgesia throughout the evolution of colitis with maximal activity at peak inflammation. The actions of NFEPP are restricted to acidified layers of the colon, without common side effects in normal tissues. N -(3-fluoro-1-phenethylpiperidine-4-yl)- N -phenyl propionamide could provide safe and effective analgesia during acute colitis, such as flares of ulcerative colitis.

Genetic and Pharmacological Blockade of Sigma-1 Receptors Attenuates Inflammation-Associated Hypersensitivity during Acute Colitis in CD1 Mice

Sigma-1 receptors (σ1Rs) are implicated in nociception, including pain sensitization, and inflammation. We assessed the role of σ1Rs on acute colitis-associated hypersensitivity using both genetic (constitutive knockout) and pharmacological blockade of the receptor. Colitis was induced in CD1 wild-type (WT) and σ1R KO mice (exposure to dextran sodium sulfate, 3%). A von Frey test was used to assess referred mechanosensitivity (abdominal and plantar withdrawal responses). The effects of the selective σ1R antagonists BD1063 and E-52862 were also assessed in WT animals. The expression of immune and sensory-related markers (RT-qPCR, Western blot) was assessed in the colon and lumbosacral spinal cord. The genetic ablation or pharmacological blockade of σ1Rs attenuated acute colonic inflammation in a similar manner. Mechanosensitivity was similar in WT and σ1R KO mice before colitis. In WT mice, but not in σ1R KO, colitis was associated with the development of referred mechanical hypersensitivity, manifested as a reduction in the withdrawal thresholds to mechanical probing (paw and abdominal wall). In WT mice, BD1063 and E-52862 blocked colitis-associated hypersensitivity. A genotype- and treatment-related differential regulation of sensory-related markers was detected locally (colon) and within the spinal cord. σ1Rs are involved in the development of acute intestinal inflammation and its associated referred mechanical hypersensitivity. The selective modulation of sensory-related pathways within the colon and spinal cord might be part of the underlying mechanisms. These observations support the pharmacological use of σ1R antagonists for the treatment of intestinal inflammation-induced hypersensitivity.

Long-lasting visceral hypersensitivity in a model of DSS-induced colitis in rats

BACKGROUND

Persistent visceral hypersensitivity is a key component of functional and inflammatory gastrointestinal diseases. Current animal models fail to fully reproduce the characteristics of visceral pain in humans, particularly as it relates to persistent hypersensitivity. This work explores the validity of DSS-induced colitis in rats as a model to mimic chronic intestinal hypersensitivity.

METHODS

Exposure to DSS (5% for 7 days) was used to induce colitis in rats. Thereafter, changes in viscerosensitivity (visceromotor responses to colorectal distension-CRD), the presence of somatic referred pain (mechanosensitivity of the hind paws, von Frey test) and the expression (qRT-PCR) of sensory-related markers (colon, lumbosacral DRGs, and lumbosacral spinal cord) were assessed at different times during the 35 days period after colitis induction.

RESULTS

Following colitis, a sustained increase in visceromotor responses to CRD were observed, indicative of the presence of visceral hypersensitivity. Responses in animals without colitis remained stable over time. In colitic animals, somatic referred hypersensitivity was also detected. DSS-induced colitis was associated to a differential expression of sensory-related markers (with both pro- and anti-nociceptive action) in the colon, lumbosacral DRGs and lumbosacral spinal cord; indicating the presence of peripheral and central sensitization.

CONCLUSIONS AND INFERENCES

DSS-induced colitis in rats is associated to the generation of a long-lasting state of visceral (colonic) hypersensitivity, despite clinical colitis resolution. This model reproduces the changes in intestinal sensitivity characteristics of inflammatory and functional gastrointestinal disorders in humans and can be used in the characterization of new pharmacological treatments against visceral pain.

Sigma-1 receptor: A potential target for the development of antidepressants

Though a great many of studies on the development of antidepressants for the therapy of major depression disorder (MDD) and the development of antidepressants have been carried out, there still lacks an efficient approach in clinical practice. The involvement of Sigma-1 receptor in the pathological process of MDD has been verified. In this review, recent research focusing on the role of Sigma-1 receptor in the etiology of MDD were summarized. Preclinical studies and clinical trials have found that stress induce the variation of Sigma-1 receptor in the blood, brain and heart. Dysfunction and absence of Sigma-1 receptor result in depressive-like behaviors in rodent animals. Agonists of Sigma-1 receptor show not only antidepressant-like activities but also therapeutical effects in complications of depression. The mechanisms underlying antidepressant-like effects of Sigma-1 receptor may include suppressing neuroinflammation, regulating neurotransmitters, ameliorating brain-derived neurotrophic factor and N-Methyl-D-Aspartate receptor, and alleviating the endoplasmic reticulum stress and mitochondria damage during stress. Therefore, Sigma-1 receptor represents a potential target for antidepressants development.