Treatment with neurokinin-1 receptor antagonist reduces severity of inflammatory bowel disease induced by Cryptosporidium parvum

Cellular metabolism of substance P produces neurokinin-1 receptor peptide agonists with diminished cyclic AMP signaling

Substance P (SP) is released from sensory nerves in the arteries and heart. It activates neurokinin-1 receptors (NK1Rs) causing vasodilation, immune modulation, and adverse cardiac remodeling. The hypothesis was tested: SP and SP metabolites activate different second messenger signaling pathways. Macrophages, endothelial cells, and fibroblasts metabolized SP to N- and C-terminal metabolites to varying extents. SP 5-11 was the most abundant metabolite followed by SP 1-4, SP 7-11, SP 6-11, SP 3-11, and SP 8-11. In NK1R-expressing human embryonic kidney 293 (HEK293) cells, SP and some C-terminal SP metabolites stimulate the NK1R, promoting the dissociation of several Gα proteins, including Gαs and Gαq from their βγ subunits. SP increases intracellular calcium concentrations ([Ca]i) and cyclic 3',5'-adenosine monophosphate (cAMP) accumulation with similar -log EC50 values of 8.5 ± 0.3 and 7.8 ± 0.1 M, respectively. N-terminal metabolism of SP by up to five amino acids and C-terminal deamidation of SP produce peptides that retain activity to increase [Ca]i but not to increase cAMP. C-terminal metabolism results in the loss of both activities. Thus, [Ca]i and cAMP signaling are differentially affected by SP metabolism. To assess the role of N-terminal metabolism, SP and SP 6-11 were compared with cAMP-mediated activities in NK1R-expressing 3T3 fibroblasts. SP inhibits nuclear factor κB (NF-κB) activity, cell proliferation, and wound healing and stimulates collagen production. SP 6-11 had little or no activity. Cyclooxygenase-2 (COX-2) expression is increased by SP but not by SP 6-11. Thus, metabolism may select the cellular response to SP by inhibiting or redirecting the second messenger signaling pathway activated by the NK1R.NEW & NOTEWORTHY Endothelial cells, macrophages, and fibroblasts metabolize substance P (SP) to N- and C-terminal metabolites with SP 5-11 as the most abundant metabolite. SP activates neurokinin-1 receptors to increase intracellular calcium and cyclic AMP. In contrast, SP metabolites of N-terminal metabolism and C-terminal deamidation retain the ability to increase calcium but lose the ability to increase cyclic AMP. These new insights indicate that the metabolism of SP directs cellular functions by regulating specific signaling pathways.

Neuropeptide substance P and the immune response

Substance P is a peptide mainly secreted by neurons and is involved in many biological processes, including nociception and inflammation. Animal models have provided insights into the biology of this peptide and offered compelling evidence for the importance of substance P in cell-to-cell communication by either paracrine or endocrine signaling. Substance P mediates interactions between neurons and immune cells, with nerve-derived substance P modulating immune cell proliferation rates and cytokine production. Intriguingly, some immune cells have also been found to secrete substance P, which hints at an integral role of substance P in the immune response. These communications play important functional roles in immunity including mobilization, proliferation and modulation of the activity of immune cells. This review summarizes current knowledge of substance P and its receptors, as well as its physiological and pathological roles. We focus on recent developments in the immunobiology of substance P and discuss the clinical implications of its ability to modulate the immune response.

Neuropeptide analysis of oral mucosa in diabetic rats

OBJECTIVE

Increasing evidence indicates that different neuropeptide-containing nerve elements are involved in the immune system and influence the inflammation of the gastrointestinal tract. The aim of this study was to investigate the morphological localization and distribution of the different immunoreactive (IR) nerve fibers and immunocompetent cells in the oral mucosa (e.g. tongue, gingiva) and compare the results with data received from streptozotocin (STZ)-induced diabetic rats.

MATERIALS AND METHODS

The different nerve elements and immunocytes were detected by ABC immunohistochemistry.

RESULTS

The IR nerve fibers were found in the tunica propria of oral mucosa with different densities. These IR nerve fibers were mainly located beneath the epithelial lining, around the blood vessels and glands, and some of them were also located in the taste buds. After 2 weeks of STZ treatment the total number of IR nerve fibers, especially the SP and neuropeptide Y (NPY) IR ones, was significantly increased (p < 0.05), as was also the number of immunocytes (lymphocytes, plasma cells, mast cells). Some of these cells also showed immunoreactivity for substance P (SP) and NPY. In several cases the SP IR nerve fibers were found in close proximity to the immunocytes. Electron microscopic investigation also revealed the close association between the IR nerve fibers and immunocompetent cells where the gap was 1 µm or even less.

CONCLUSIONS

The close anatomical associations suggest communication between nerve fibers and immune cells which can be crucial for maintaining mucosal homeostasis and for ensuring an appropriate response to injury.

Irritable bowel syndrome: methods, mechanisms, and pathophysiology. Neural and neuro-immune mechanisms of visceral hypersensitivity in irritable bowel syndrome

Irritable bowel syndrome (IBS) is characterized as functional because a pathobiological cause is not readily apparent. Considerable evidence, however, documents that sensitizing proinflammatory and lipotoxic lipids, mast cells and their products, tryptases, enteroendocrine cells, and mononuclear phagocytes and their receptors are increased in tissues of IBS patients with colorectal hypersensitivity. It is also clear from recordings in animals of the colorectal afferent innervation that afferents exhibit long-term changes in models of persistent colorectal hypersensitivity. Such changes in afferent excitability and responses to mechanical stimuli are consistent with relief of discomfort and pain in IBS patients, including relief of referred abdominal hypersensitivity, upon intra-rectal instillation of local anesthetic. In the aggregate, these experimental outcomes establish the importance of afferent drive in IBS, consistent with a larger literature with respect to other chronic conditions in which pain is a principal complaint (e.g., neuropathic pain, painful bladder syndrome, fibromyalgia). Accordingly, colorectal afferents and the environment in which these receptive endings reside constitute the focus of this review. That environment includes understudied and incompletely understood contributions from immune-competent cells resident in and recruited into the colorectum. We close this review by highlighting deficiencies in existing knowledge and identifying several areas for further investigation, resolution of which we anticipate would significantly advance our understanding of neural and neuro-immune contributions to IBS pain and hypersensitivity.

Neuroimmune interaction in inflammatory diseases

The inflammatory response is modulated through interactions among the nervous, endocrine, and immune systems. Intercommunication between immune cells and the autonomic nervous system is a growing area of interest. Spatial and temporal information about inflammatory processes is relayed to the central nervous system (CNS) where neuroimmune modulation serves to control the extent and intensity of the inflammation. Over the past few decades, research has revealed various routes by which the nervous system and the immune system communicate. The CNS regulates the immune system via hormonal and neuronal pathways, including the sympathetic and parasympathetic nerves. The immune system signals the CNS through cytokines that act both centrally and peripherally. This review aims to introduce the concept of neuroimmune interaction and discuss its potential clinical application, in an attempt to broaden the awareness of this rapidly evolving area and open up new avenues that may aid in the treatment of inflammatory diseases.

Changes of the different neuropeptide-containing nerve fibers and immunocells in the diabetic rat's alimentary tract

Peripheral neuropathy is a common complication of diabetes mellitus, where neuropeptides and immunocells might play important roles in the pathogenesis of the disease. In this article we have quantified the different neuropeptide-containing nerve fibers and immunocells in the streptozotocin-induced diabetic rat's alimentary tract (tongue, duodenum, colon) using immunohistochemical and immunocytochemical methods. The immunoreactive (IR) nerve fibers were found in all layers of the alimentary tract and their distribution pattern was similar in both control and diabetic groups. Mast cell-nerve fiber contacts were rarely found in the controls. However, after 4 weeks duration of diabetes the number of IR nerve fibers and the immunocompetent cells increased significantly (P < 0.05), and the number of mast cell-nerve fiber contacts was even more significantly increased (P < 0.001). The distance between nerve fibers and immunocells was about 1 mum or even less. Some of the mast cells were degranulated in the vicinity of nerve fibers. No immunocompetent cells were IR for any antisera in the control. However, after the streptozotocin treatment, a large number of the immunocompetent cells showed immunoreactivity for SP and NPY. Counting all immunocompetent cells in whole sections showed that 12.3% of them were IR for SP and 25.4% were IR for NPY. Increased number of SP-containing nerve fibers and immunocells in diabetes mellitus might be the reason for painful neuropathy and might amplify the inflammatory reaction in an axon reflex manner; the released histamine and leukotrienes, cytokines, and chemokines might cause inflammations and lesions of the mucosa.

Neurokinin NK1 and NK3 receptors as targets for drugs to treat gastrointestinal motility disorders and pain

NK1 and NK3 receptors do not appear to play significant roles in normal GI functions, but both may be involved in defensive or pathological processes. NK1 receptor antagonists are antiemetic, operating via vagal sensory and motor systems, so there is a need to study their effects on other gastro-vagal functions thought to play roles in functional bowel disorders. Interactions between NK1 receptors and enteric nonadrenergic, noncholinergic motorneurones suggest a need to explore the role of this receptor in disrupted colonic motility. NK1 receptor antagonism does not exert consistent analgesic activity in humans, but similar studies have not been carried out against pain of GI origin, where NK1 receptors may have additional influences on mucosal inflammatory or "irritant" processes. NK3 receptors mediate certain disruptions of intestinal motility. The activity may be driven by tachykinins released from intrinsic primary afferent neurones (IPANs), which induce slow EPSP activity in connecting IPANs and hence, a degree of hypersensitivity within the enteric nervous system. The same process is also proposed to increase C-fibre sensitivity, either indirectly or directly. Thus, NK3 receptor antagonists inhibit intestinal nociception via a "peripheral" mechanism that may be intestine-specific. Studies with talnetant and other selective NK3 receptor antagonists are, therefore, revealing an exciting and novel pathway by which pathological changes in intestinal motility and nociception can be induced, suggesting a role for NK3 receptor antagonism in irritable bowel syndrome.