Type 2/Th2-driven inflammation impairs olfactory sensory neurogenesis in mouse chronic rhinosinusitis model.

BACKGROUND: Chronic rhinosinusitis (CRS) with nasal polyps (CRSwNP) is a chronic inflammatory disease often accompanied by impairment of sense of smell. This symptom has been somewhat overlooked, and its relationship to inflammatory cytokines, tissue compression, neuronal loss, and neurogenesis is still unclear. METHODS: In order to elucidate potential mechanisms leading to CRS in humans, we have established a type 2/T helper type 2 cell (Th2)-mediated allergic CRS mouse model, based on house dust mite (HDM) and Staphylococcus aureus enterotoxin B (SEB) sensitization. The inflammatory status of the olfactory epithelium (OE) was assessed using histology, biochemistry, and transcriptomics. The sense of smell was evaluated by studying olfactory behavior and recording electro-olfactograms (EOGs). RESULTS: After 22 weeks, a typical type 2/Th2-mediated inflammatory profile was obtained, as demonstrated by increased interleukin (IL)-4, IL-5, and IL-13 in the OE. The number of mast cells and eosinophils was increased, and infiltration of these cells into the olfactory mucosa was also observed. In parallel, transcriptomic and histology analyses indicated a decreased number of immature olfactory neurons, possibly due to decreased renewal. However, the number of mature sensory neurons was not affected and neither the EOG nor olfactory behavior was impaired. CONCLUSION: Our mouse model of CRS displayed an allergic response to HDM + SEB administration, including the type 2/Th2 inflammatory profile characteristic of human eosinophilic CRSwNP. Although the sense of smell did not appear to be altered in these conditions, the data reveal the influence of chronic inflammation on olfactory neurogenesis, suggesting that factors unique to humans may be involved in CRSwNP-associated anosmia.

Establishment of a human nasal epithelium model of histamine-induced inflammation to assess the activity of fexofenadine as an inverse agonist and its link to clinical benefit.

Background: Fexofenadine (FEX) is an antihistamine that acts as an inverse agonist against histamine (HIS) receptor 1 (H1R), which mediates the allergic reaction. Inverse agonists may be more potent than neutral antagonists, as they bind the same receptor as the agonist (HIS) but stabilize the inactive form and induce an opposite pharmacological response, suppressing the basal activity of H1R and preventing HIS from binding. This study aims to establish and validate a model of HIS-induced inflammation based on fully reconstituted human nasal epithelial tissue to assess the activity of FEX as an inverse agonist in this model and explore its link to clinical benefit. Methods: The model was developed using nasal MucilAir™ (Epithelix) in vitro epithelium challenged by HIS. Two conditions were assessed in a side-by-side comparison: tissue was exposed to HIS + FEX with or without FEX pre-treatment (one-hour prior to HIS challenge). Tissue functionality, cytotoxicity, H1R gene expression, and inflammatory cytokines were assessed. Results: HIS at 100 µM induced significant 3.1-fold and 2.2-fold increases for inflammatory biomarkers interleukin (IL)-8 and IL-6, respectively (p < 0.0001), as well as rapid upregulation of H1R mRNA. Inflammatory biomarkers were inhibited by FEX and H1R expression was significantly reduced (p < 0.0001). FEX alone decreased H1R expression at all doses tested. With one-hour FEX pre-treatment, there was significantly higher downregulation of IL-8 (p < 0.05) and further downregulation of H1R expression and IL-6 versus without FEX pre-treatment; the effects of FEX were improved from 22% to 40%. Conclusion: A model of HIS-induced airway inflammation was established based on IL-8, IL-6 and H1R gene expression and was validated with FEX. FEX works as an inverse agonist, with a higher effect when used before+during versus only during the HIS challenge. Taking FEX before+during allergen exposure, or when symptoms first occur, may reduce basal activity and H1R gene expression, providing stronger protection against the worsening of symptoms upon allergen exposure.

The neurotensin receptor antagonist SR 142948A blocks the efflux of dopamine evoked in nucleus accumbens by neurotensin ejection into the ventral tegmental area.

The neuropeptide neurotensin (NT) exerts a wide range of central and peripheral effects. In particular, ejection of NT (10(-7) M, 65 nl) into the ventral tegmental area (VTA) in anaesthetised rats pre-treated with pargyline increases the dopamine (DA) efflux within the nucleus accumbens (NAcc) as measured by differential pulse amperometry (DPA) combined with carbon fibre electrodes. However, this effect is not blocked by systemic pre-treatment with the potent and selective non-peptide NT receptor antagonists SR 48692 and SR 142948A, at any dose studied. The present study was designed to determine the ability of these NT receptor antagonists to block the increase in DA efflux evoked within the NAcc when they are locally applied with the peptide into the VTA. The competitive N-methyl- D-aspartate (NMDA) receptor antagonist, 2-amino-5-phosphonopentanoic acid (AP-5), applied into the VTA 1 min before NMDA, blocked the effect of NMDA on DA efflux concentration and volume dependently, thus demonstrating the suitability of our experimental procedure for characterizing both an agonist and an antagonist specific for receptors present on mesencephalic dopaminergic neurons and involved in the regulation of DA efflux within the NAcc. Intra-VTA application of SR 142948A blocked the NT-evoked increase in DA efflux within the NAcc dose dependently whereas SR 48692, at the concentration used, was inactive. These results suggest that NT regulates mesencephalic dopaminergic activity through NT receptors sensitive to SR 142948A, but possibly not to SR 48692.

Specific involvement of neurotensin type 1 receptor in the neurotensin-mediated in vivo dopamine efflux using knock-out mice.

Abstract Neurotensin is a tridecapeptide neurotransmitter known to be involved in psychiatric disorders, various physiological processes and several different neurobiological mechanisms, including modulation of accumbal dopamine release. Two neurotensin extracellular binding sites, namely NT1- and NT2-receptor (NT1R and NT2R), have been cloned from the rat brain. These receptors are distinguishable by their different in vitro pharmacological properties but the available pharmacological tools have weak in vivo potency and specificity. The use of genetically engineered knock-out mice has provided a powerful alternative to the classical pharmacological approach to investigate their respective roles. In this study, using in vivo differential pulse amperometry, we show that, in wild-type mice, neurotensin application into the ventral tegmental area dose-dependently evokes dopamine efflux in the nucleus accumbens. This neurotensin-mediated efflux is dramatically decreased in mice lacking NT1R while it is unaffected in NT2R-deleted mice. This finding indicates that a large part of the dopamine efflux evoked by neurotensin in the nucleus accumbens of wild-type mice is mediated via NT1R present in the ventral tegmental area.