Neurokinin-1 receptor blockade and murine lung tumorigenesis

Biological and Pharmacological Aspects of the NK1-Receptor

The neurokinin 1 receptor (NK-1R) is the main receptor for the tachykinin family of peptides. Substance P (SP) is the major mammalian ligand and the one with the highest affinity. SP is associated with multiple processes: hematopoiesis, wound healing, microvasculature permeability, neurogenic inflammation, leukocyte trafficking, and cell survival. It is also considered a mitogen, and it has been associated with tumorigenesis and metastasis. Tachykinins and their receptors are widely expressed in various human systems such as the nervous, cardiovascular, genitourinary, and immune system. Particularly, NK-1R is found in the nervous system and in peripheral tissues and are involved in cellular responses such as pain transmission, endocrine and paracrine secretion, vasodilation, and modulation of cell proliferation. It also acts as a neuromodulator contributing to brain homeostasis and to sensory neuronal transmission associated with depression, stress, anxiety, and emesis. NK-1R and SP are present in brain regions involved in the vomiting reflex (the nucleus tractus solitarius and the area postrema). This anatomical localization has led to the successful clinical development of antagonists against NK-1R in the treatment of chemotherapy-induced nausea and vomiting (CINV). The first of these antagonists, aprepitant (oral administration) and fosaprepitant (intravenous administration), are prescribed for high and moderate emesis.

Differential roles for Bim and Nur77 in thymocyte clonal deletion induced by ubiquitous self-antigen

Negative selection, primarily mediated through clonal deletion of self-reactive thymocytes, is critical for establishing self-tolerance and preventing autoimmunity. Recent studies suggest that the molecular mechanisms of negative selection differ depending on the thymic compartment and developmental stage at which thymocytes are deleted. Using the physiological HY(cd4) TCR transgenic model of negative selection against ubiquitous self-antigen, we previously found that one of the principal mediators implicated in clonal deletion, Bim, is required for caspase-3 activation but is ultimately dispensable for negative selection. On the basis of these data, we hypothesized that Nur77, another molecule thought to be a key mediator of clonal deletion, could be responsible for Bim-independent deletion. Despite comparable Nur77 induction in thymocytes during negative selection, Bim deficiency resulted in an accumulation of high-affinity-signaled thymocytes as well as impairment in caspase-mediated and caspase-independent cell death. Although these data suggested that Bim may be required for Nur77-mediated cell death, we found that transgenic Nur77 expression was sufficient to induce apoptosis independently of Bim. However, transgenic Nur77-induced apoptosis was significantly inhibited in the context of TCR signaling, suggesting that endogenous Nur77 could be similarly regulated during negative selection. Although Nur77 deficiency alone did not alter positive or negative selection, combined deficiency in Bim and Nur77 impaired clonal deletion efficiency and significantly increased positive selection efficiency. Collectively, these data shed light on the different roles for Bim and Nur77 during ubiquitous Ag-mediated clonal deletion and highlight potential differences from their reported roles in tissue-restricted Ag-mediated clonal deletion.

A peptide probe for the detection of neurokinin-1 receptor by disaggregation enhanced fluorescence and magnetic resonance signals

We report a novel peptide probe for the detection of neurokinin-1 receptor using disaggregation-caused signal enhancement. The probe was obtained via the aggregation of a modified substance P in a terpyridine-Fe (II) complex with Gd (III)-DOTA into well-defined nanostructures, which effectively weaken ligand fluorescence and slow the exchange rate of inner-sphere water molecules. This probe disaggregates upon binding to the neurokinin-1 receptor and activates the contrast agents to generate a fluorescent signal that positively enhances magnetic resonance imaging contrast and allows for the detection of overexpressed receptors on tumor cells and the identification of lung cancer using serum samples.

Tachykinins and their receptors: contributions to physiological control and the mechanisms of disease

The tachykinins, exemplified by substance P, are one of the most intensively studied neuropeptide families. They comprise a series of structurally related peptides that derive from alternate processing of three Tac genes and are expressed throughout the nervous and immune systems. Tachykinins interact with three neurokinin G protein-coupled receptors. The signaling, trafficking, and regulation of neurokinin receptors have also been topics of intense study. Tachykinins participate in important physiological processes in the nervous, immune, gastrointestinal, respiratory, urogenital, and dermal systems, including inflammation, nociception, smooth muscle contractility, epithelial secretion, and proliferation. They contribute to multiple diseases processes, including acute and chronic inflammation and pain, fibrosis, affective and addictive disorders, functional disorders of the intestine and urinary bladder, infection, and cancer. Neurokinin receptor antagonists are selective, potent, and show efficacy in models of disease. In clinical trials there is a singular success: neurokinin 1 receptor antagonists to treat nausea and vomiting. New information about the involvement of tachykinins in infection, fibrosis, and pruritus justifies further trials. A deeper understanding of disease mechanisms is required for the development of more predictive experimental models, and for the design and interpretation of clinical trials. Knowledge of neurokinin receptor structure, and the development of targeting strategies to disrupt disease-relevant subcellular signaling of neurokinin receptors, may refine the next generation of neurokinin receptor antagonists.

Role of the tachykinin NK1 receptor in a murine model of cigarette smoke-induced pulmonary inflammation

Background

The tachykinins, substance P and neurokinin A, present in sensory nerves and inflammatory cells such as macrophages and dendritic cells, are considered as pro-inflammatory agents. Inflammation of the airways and lung parenchyma plays a major role in the pathogenesis of chronic obstructive pulmonary disease (COPD) and increased tachykinin levels are recovered from the airways of COPD patients. The aim of our study was to clarify the involvement of the tachykinin NK₁ receptor, the preferential receptor for substance P, in cigarette smoke (CS)-induced pulmonary inflammation and emphysema in a mouse model of COPD.

Methods

Tachykinin NK₁ receptor knockout (NK₁-R^-/-) mice and their wild type controls (all in a mixed 129/sv-C57BL/6 background) were subjected to sub acute (4 weeks) or chronic (24 weeks) exposure to air or CS. 24 hours after the last exposure, pulmonary inflammation and development of emphysema were evaluated.

Results

Sub acute and chronic exposure to CS resulted in a substantial accumulation of inflammatory cells in the airways of both WT and NK₁-R^-/- mice. However, the CS-induced increase in macrophages and dendritic cells was significantly impaired in NK₁-R^-/- mice, compared to WT controls, and correlated with an attenuated release of MIP-3α/CCL20 and TGF-β1. Chronic exposure to CS resulted in development of pulmonary emphysema in WT mice. NK₁-R^-/- mice showed already enlarged airspaces upon air-exposure. Upon CS-exposure, the NK₁-R^-/- mice did not develop additional destruction of the lung parenchyma. Moreover, an impaired production of MMP-12 by alveolar macrophages upon CS-exposure was observed in these KO mice. In a pharmacological validation experiment using the NK₁ receptor antagonist RP 67580, we confirmed the protective effect of absence of the NK₁ receptor on CS-induced pulmonary inflammation.

Conclusion

These data suggest that the tachykinin NK₁ receptor is involved in the accumulation of macrophages and dendritic cells in the airways upon CS-exposure and in the development of smoking-induced emphysema. As both inflammation of the airways and parenchymal destruction are important characteristics of COPD, these findings may have implications in the future treatment of this devastating disease.

Activation of neurokinin-1 receptors during ozone inhalation contributes to epithelial injury and repair

We investigated the importance of neurokinin (NK)-1 receptors in epithelial injury and repair and neutrophil function. Conscious Wistar rats were exposed to 1 ppm ozone or filtered air for 8 hours, followed by an 8-hour postexposure period. Before exposure, we administered either the NK-1 receptor antagonist, SR140333, or saline as a control. Ethidium homodimer was instilled into lungs as a marker of necrotic airway epithelial cells. After fixation, whole mounts of airway dissected lung lobes were immunostained for 5-bromo-2'-deoxyuridine, a marker of epithelial proliferation. Both ethidium homodimer and 5-bromo-2'-deoxyuridine-positive epithelial cells were quantified in specific airway generations. Rats treated with the NK-1 receptor antagonist had significantly reduced epithelial injury and epithelial proliferation compared with control rats. Sections of terminal bronchioles showed no significant difference in the number of neutrophils in airways between groups. In addition, staining ozone-exposed lung sections for active caspase 3 showed no apoptotic cells, but ethidium-positive cells colocalized with the orphan nuclear receptor, Nur77, a marker of nonapoptotic, programmed cell death mediated by the NK-1 receptor. An immortalized human airway epithelial cell line, human bronchial epithelial-1, showed no significant difference in the number of oxidant stress-positive cells during exposure to hydrogen peroxide and a range of SR140333 doses, demonstrating no antioxidant effect of the receptor antagonist. We conclude that activation of the NK-1 receptor during acute ozone inhalation contributes to epithelial injury and subsequent epithelial proliferation, a critical component of repair, but does not influence neutrophil emigration into airways.