Cutting Edge: Hemokinin Has Substance P-Like Function and Expression in Inflammation

Neuronal Control of Skin Function: The Skin as a Neuroimmunoendocrine Organ

This review focuses on the role of the peripheral nervous system in cutaneous biology and disease. During the last few years, a modern concept of an interactive network between cutaneous nerves, the neuroendocrine axis, and the immune system has been established. We learned that neurocutaneous interactions influence a variety of physiological and pathophysiological functions, including cell growth, immunity, inflammation, pruritus, and wound healing. This interaction is mediated by primary afferent as well as autonomic nerves, which release neuromediators and activate specific receptors on many target cells in the skin. A dense network of sensory nerves releases neuropeptides, thereby modulating inflammation, cell growth, and the immune responses in the skin. Neurotrophic factors, in addition to regulating nerve growth, participate in many properties of skin function. The skin expresses a variety of neurohormone receptors coupled to heterotrimeric G proteins that are tightly involved in skin homeostasis and inflammation. This neurohormone-receptor interaction is modulated by endopeptidases, which are able to terminate neuropeptide-induced inflammatory or immune responses. Neuronal proteinase-activated receptors or transient receptor potential ion channels are recently described receptors that may have been important in regulating neurogenic inflammation, pain, and pruritus. Together, a close multidirectional interaction between neuromediators, high-affinity receptors, and regulatory proteases is critically involved to maintain tissue integrity and regulate inflammatory responses in the skin. A deeper understanding of cutaneous neuroimmunoendocrinology may help to develop new strategies for the treatment of several skin diseases.

Spinal Manipulative Therapy Reduces Inflammatory Cytokines but Not Substance P Production in Normal Subjects

OBJECTIVE

To examine the effect of a single spinal manipulation therapy (SMT) on the in vitro production of inflammatory cytokines, tumor necrosis factor alpha, and interleukin (IL) 1beta, in relation to the systemic (in vivo) levels of neurotransmitter substance P (SP).

METHODS

Sixty-four asymptomatic subjects were assigned to SMT, sham manipulation, or venipuncture control group. SMT subjects received a single adjustment in the thoracic spine. Blood and serum samples were obtained from subjects before and then at 20 minutes and 2 hours after intervention. Whole-blood cultures were activated with lipopolysaccharide (LPS) for 24 hours. Cytokine production in culture supernatants and serum SP levels were assessed by specific immunoassays.

RESULTS

Over the study period, a significant proportion (P </= .05) of sham and control subjects demonstrated progressive increases in the synthesis of tumor necrosis factor alpha and IL-1beta. Conversely, in a comparable proportion of cultures from SMT-derived subjects, the production of both cytokines decreased gradually. Normalization of the observed alterations to reflect the changes relative to self-baselines demonstrated that, within 2 hours after intervention, the production of both cytokines increased significantly (P < .001 to .05) in both controls. In contrast, a significant (P < .001 to .05) reduction of proinflammatory cytokine secretion was observed in cultures from SMT-receiving subjects. In all study groups, serum levels of SP remained unaltered within 2 hours after intervention.

CONCLUSIONS

SMT-treated subjects show a time-dependent attenuation of LPS-induced production of the inflammatory cytokines unrelated to systemic levels of SP. This suggests SMT-related down-regulation of inflammatory-type responses via a central yet unknown mechanism.

Quantification of hemokinin-1 peptide production and secretion from mouse B cells

Hemokinin-1 is a recent addition to the family of mammalian tachykinins and is thought to play an important role in B cell and T cell lymphopoiesis. The mRNA coding for this peptide was expressed in some B lymphocyte cell lines including 70Z/3.12, ABE-8.1/2, and RAW8.1 cells, suggesting the possibility that hemokinin-1 may function in an autocrine or paracrine manner in these cells. Therefore, we quantified secretion of this peptide from the 70Z/3.12 cell line expressing hemokinin-1 mRNA. Despite a sensitive radioimmunoassay, we were surprised to find that hemokinin-1 secretion from confluent cells was below the level of detection of this assay. Furthermore, cell lysates routinely demonstrated a low or undetectable immunoreactive peptide. Collectively these studies show a limited production of hemokinin-1 peptide by transformed B cells.

New challenges in the study of the mammalian tachykinins

There is an expanding repertoire of mammalian tachykinins produced by a variety of tachykinin genes, gene splicing events and peptide processing. Novel tachykinin-binding molecules/receptors are proposed, but only, three tachykinin receptors are identified with certainty. The question remains - do more tachykinin receptors exist or is there just the need to reappraise our understanding of the known receptors? The tachykinin NK1 receptor, the preferred receptor for both substance P and the peripheral SP-like endokinins, exists in several tissue-specific conformations and isoforms and may provide some clues. This review addresses recent advances in this exciting field and raises challenging new concepts.

Hemokinin-1 has Substance P-like function in U-251 MG astrocytoma cells: A pharmacological and functional study

Substance P (SP) triggers responses in astrocytoma cells, which are considered important for proliferation and neuroimmunomodulatory activity. In this study, we compared the effects of SP with those of the novel tachykinin Hemokinin-1 (HK-1) in the human astrocytoma cell line U-251 MG. We show that U-251 MG cells express high levels of Neurokinin-1 (NK-1) receptors. The binding affinities of 125I-SP and 125I-mHK-1 to these receptors were in a similar, subnanomolar range. HK-1 and SP stimulated Ca2+ mobilization and induced increased cytokine mRNA expression. A specific NK-1 receptor antagonist blocked the observed effects. We conclude that there are no qualitative differences in SP and HK-1-evoked responses, suggesting that both peptides act through NK-1 receptors in U-251 MG cells. Moreover, we show TAC4 mRNA expression in gliomas, indicating a possible involvement of HK-1 in glioma biology.

IL-12 induction of mRNA encoding substance P in murine macrophages from the spleen and sites of inflammation

Substance P (SP), a neuropeptide, interacts with the neurokinin 1 receptor (NK-1R) on immune cells to help control IFN-gamma production. In murine schistosomiasis mansoni, schistosome worms produce ova that incite focal Th2-type granulomatous inflammation within the liver and intestines. Normal gut is characterized by a controlled state of inflammation. IL-10 knockout mice develop chronic Th1-type colitis spontaneously. Both schistosome granulomas and gut mucosa display an SP immune regulatory circuit. However, the origin and regulation of SP production at these sites of inflammation are poorly understood. Macrophages are a potential source of SP. We therefore studied macrophages (F4/80(+)) from these models of inflammation. SP mRNA (preprotachykinin A (PPT A)) was detected within the schistosome granuloma, spleen, and lamina propria macrophages. Compared with those from wild-type mice, granuloma macrophages from STAT6(-/-) mice had 10-fold higher PPT A mRNA expression, whereas in STAT4(-/-) animals, PPT A mRNA expression was nearly abolished. IL-12 signals via STAT4 to induce Th1-type inflammation. It was demonstrated that IL-12, but not IL-18, induces SP mRNA expression in resting splenic macrophages from Schistosoma-infected mice and in wild-type lamina propria mononuclear cells. Thus, macrophages are a source for SP at these sites of chronic inflammation, and IL-12 and STAT4 are regulators of macrophage SP mRNA expression.

Targeting tachykinins for the treatment of obstructive airways disease

The tachykinin family of peptides are distributed throughout the nervous system and are thought to play a critical role in inflammation and immunomodulation. Tachykinins have been implicated in the pathogenesis of many diseases and disease processes including inflammatory pain, emesis, depression, Parkinson's disease and inflammatory bowel syndrome. In the airways of animals, substance P and neurokinin A are released from a subset of airway sensory nerves, and evoke vasodilatation, bronchoconstriction, mucus secretion, leukocyte recruitment, airways hyperreactivity and cough. These observations have led to suggestions that tachykinins may also be viable targets for the treatment of obstructive airways disease. Clinical trials in humans assessing the utility of tachykinin receptor antagonists such as nepadutant and saredutant for the treatment of asthma are limited, and the results for the most part have been inconclusive. Several new tachykinin receptor antagonists have been recently designed to target multiple tachykinin receptor subtypes and to readily penetrate into the central nervous system. Future clinical trials with these compounds should help to shed some light on the role of tachykinins in obstructive airways disease.