Methionine-enkephalin secreted by human colorectal cancer cells suppresses T lymphocytes

Opiorphin: an endogenous human peptide with intriguing application in diverse range of pathologies

Mammalian zinc ectopeptidases have significant functions in deactivating neurological and hormonal peptide signals on the cell surface. The identification of Opiorphin, a physiological inhibitor of zinc ectopeptidases that inactivate enkephalin, has revealed its strong analgesic effects in both chemical and mechanical pain models. Opiorphin achieves this by increasing the transmission of endogenous opioids, which are dependent on the body's own opioid system. The function of opiorphin is closely linked to the rat sialorphin peptide, which inhibits pain perception by enhancing the activity of naturally occurring enkephalinergic pathways that depend on μ- and δ-opioid receptors. Opiorphin is highly intriguing in terms of its physiological implications within the endogenous opioidergic pathways, particularly in its ability to regulate mood-related states and pain perception. Opiorphin can induce antidepressant-like effects by influencing the levels of naturally occurring enkephalin, which are released in response to specific physical and/or psychological stimuli. This effect is achieved through the modulation of delta-opioid receptor-dependent pathways. Furthermore, research has demonstrated that opiorphin's impact on the cardiovascular system is facilitated by the renin-angiotensin system (RAS), sympathetic ganglia, and adrenal medulla, rather than the opioid system. Hence, opiorphin shows great potential as a solitary candidate for the treatment of several illnesses such as neurodegeneration, pain, and mood disorders.

Interactions Between Endogenous Opioids and the Immune System

The endogenous opioid system, which consists of opioid receptors and their ligands, is widely expressed in the nervous system and also found in the immune system. As a part of the body's defense machinery, the immune system is heavily regulated by endogenous opioid peptides. Many types of immune cells, including macrophages, dendritic cells, neutrophils, and lymphocytes are influenced by endogenous opioids, which affect cell activation, differentiation, proliferation, apoptosis, phagocytosis, and cytokine production. Additionally, immune cells also synthesize and secrete endogenous opioid peptides and participate peripheral analgesia. This chapter is structured into two sections. Part one focuses on immunoregulatory functions of central endogenous opioids; and part two describes how opioid peptide-containing immune cells participate in local analgesia.

The Opioid Growth Factor in Growth Regulation and Immune Responses in Cancer

It has become apparent that endogenous opioids act not only as neurotransmitters and neuromodulators, but have multiple functions in the body. Activation of the opioid system by opiate drugs is associated with a risk of cancer development through direct stimulation of tumor cell proliferation and through immunosuppression. In contrast, the endogenous peptide opioid [Met5]-enkephalin, now commonly referred to as Opioid Growth Factor (OGF), negatively regulates cell proliferation in a wide number of cells during development, homeostasis, and neoplasia. This action is mediated through the opioid growth factor receptor, originally designated the zeta (ζ) opioid receptor. Further, contrary to the traditional notion of opiates as immunosuppressive, endogenous OGF has been shown to possess a number of positive immunomodulatory properties and may provide a beneficial effect in cancer by augmenting the activity of cells involved in both innate and acquired immunity. Taken together, the evidence supports consideration of opioid peptides such as OGF as new strategies for cancer therapy.

Methionine enkephalin inhibited cervical cancer migration as well as invasion and activated CD11b+ NCR1+ NKs of tumor microenvironment

This study was to study the role of methionine enkephalin (menk) in cell invasion and migration as well as NK cells activation of tumor microenvironment in cervical cancer. The results showed that menk inhibited cervical cancer migration and invasion. In addition, we found menk affected epithelial to mesenchymal transition (EMT) related indicators, with increasing E-cadherin level, decreasing N-cadherin and vimentin level. Through in vivo mouse model, we found that menk IFNγ and NKP46 expression was upregulated in tumor tissues by menk compared with controls, while LAG3 expression was inhibited by menk, besides, there was an upregulation of CD11b+ NCR1+ NKs of tumor microenvironment in cervical cancer. Therefore, we concluded that menk inhibited cancer migration and invasion via affecting EMT related indicators and activated CD11b+ NCR1+ NKs of tumor microenvironment in cervical cancer, laying a theoretical foundation for the further clinical treatment of menk.

Multiple Sclerosis and the Endogenous Opioid System

Multiple sclerosis (MS) is an autoimmune disease characterized by chronic inflammation, neuronal degeneration and demyelinating lesions within the central nervous system. The mechanisms that underlie the pathogenesis and progression of MS are not fully known and current therapies have limited efficacy. Preclinical investigations using the murine experimental autoimmune encephalomyelitis (EAE) model of MS, as well as clinical observations in patients with MS, provide converging lines of evidence implicating the endogenous opioid system in the pathogenesis of this disease. In recent years, it has become increasingly clear that endogenous opioid peptides, binding μ- (MOR), κ- (KOR) and δ-opioid receptors (DOR), function as immunomodulatory molecules within both the immune and nervous systems. The endogenous opioid system is also well known to play a role in the development of chronic pain and negative affect, both of which are common comorbidities in MS. As such, dysregulation of the opioid system may be a mechanism that contributes to the pathogenesis of MS and associated symptoms. Here, we review the evidence for a connection between the endogenous opioid system and MS. We further explore the mechanisms by which opioidergic signaling might contribute to the pathophysiology and symptomatology of MS.

Research progress of opioid growth factor in immune-related diseases and cancer diseases

Methionine enkephalin (MENK) has an important role in both neuroendocrine and immune systems. MENK was known as an opioid growth factor (OGF) for its growth regulatory characteristics. OGF interacts with the OGF receptor (OGFr) to inhibit DNA synthesis by upregulating p16 and/or p21, which delays the cell cycle transition from G0/G1 to S phase, and inhibits cell proliferation. In addition, OGF combines with OGFr in immune cells to exert its immunomodulatory activity and regulate immune function. OGF has been studied as an immunomodulator in a variety of autoimmune diseases, including multiple sclerosis, inflammatory bowel disease, diabetes and viral infections, and has been proven to relieve symptoms of certain diseases in animal and in vitro experiments. Also, OGF and OGFr have various anti-tumor molecular mechanisms. OGF can be used as the primary therapy alone or combined with other drugs to treat tumors. This article summarizes the research progress of OGF in immune-related diseases and cancer diseases.

Neuroimmune Regulation of Surgery-Associated Metastases

Surgery remains an essential therapeutic approach for most solid malignancies. Although for more than a century accumulating clinical and experimental data have indicated that surgical procedures themselves may promote the appearance and progression of recurrent and metastatic lesions, only in recent years has renewed interest been taken in the mechanism by which metastasizing of cancer occurs following operative procedures. It is well proven now that surgery constitutes a risk factor for the promotion of pre-existing, possibly dormant micrometastases and the acceleration of new metastases through several mechanisms, including the release of neuroendocrine and stress hormones and wound healing pathway-associated immunosuppression, neovascularization, and tissue remodeling. These postoperative consequences synergistically facilitate the establishment of new metastases and the development of pre-existing micrometastases. While only in recent years the role of the peripheral nervous system has been recognized as another contributor to cancer development and metastasis, little is known about the contribution of tumor-associated neuronal and neuroglial elements in the metastatic disease related to surgical trauma and wound healing. Specifically, although numerous clinical and experimental data suggest that biopsy- and surgery-induced wound healing can promote survival and metastatic spread of residual and dormant malignant cells, the involvement of the tumor-associated neuroglial cells in the formation of metastases following tissue injury has not been well understood. Understanding the clinical significance and underlying mechanisms of neuroimmune regulation of surgery-associated metastasis will not only advance the field of neuro–immuno–oncology and contribute to basic science and translational oncology research but will also produce a strong foundation for developing novel mechanism-based therapeutic approaches that may protect patients against the oncologically adverse effects of primary tumor biopsy and excision.

New insights into molecular pathways in colorectal cancer: Adiponectin, interleukin-6 and opioid signaling

Colorectal cancer (CRC) is one of the most common cause of death among neoplasms around the world. The environmental factors, like diet and obesity, are crucial in CRC pathogenesis by creating cancer-favorable microenvironment and hormonal changes. Adiponectin, the adipose tissue-specific hormone, is generally considered to negatively correlate with CRC development. The interleukin 6 (IL-6) is one of the most important pro-inflammatory cytokine connected with CRC, which is strongly inflammation-associated. The opioids are variable group substantially correlated with cancers - the endogenous opioids affect immune system and cell cycle including proliferation and cell death whereas exogenous opioids are leading clinically used analgesics in terminal cancer patients. In this review we discuss the involvement of adiponectin, IL-6 and opioids in CRC pathogenesis, their link with obesity, possible cross-talk and potential novel therapeutic approach in CRC treatment.

The paradoxical role of methionine enkephalin in tumor responses

Methionine enkephalin (MENK) is an opioid peptide composed of five amino acids with multiple biological activities. Since its discovery, MENK has become prominent in neuroregulation and immunoregulation. Tumors have increasingly been a spotlight because of their terrible trends and refractory characteristic. The therapeutic potential of MENK was investigated on a large scale, and there are numerous evidences that MENK exerts anti-tumor effects via two mechanisms. The first mechanism explains the enhanced anti-tumor immune effects of MENK. The second mechanism shows that MENK directly inhibits tumor cell proliferation. However, numerous reports have clarified the pro-tumor role of MENK by inhibiting T and B cell proliferation, promoting tumor cell growth by binding to opioid receptors, leading to desensitization of lymphocytes, and inducing tolerance. It is particularly intriguing that dual reactions are triggered when MENK combines with its opioid receptors; thus, anti-tumor response of the whole body is influenced. This review will expound the dual roles of MENK in tumor responses based on immune cells, cytokines, and tumor cells to provide better suggestions for its application in tumor treatment.

The novel mechanism of anticancer effect on gastric cancer through inducing G0/G1 cell cycle arrest and caspase-dependent apoptosis in vitro and in vivo by methionine enkephalin

Background

Gastric cancer (GC) is the second cause of cancer-related deaths. Methionine enkephalin (MENK), an endogenous opioid peptide, has immunological and antitumor activity.

Purpose

The aim of this work was to investigate whether MENK could exhibit activity against human GC in vitro and in vivo.

Materials and methods

Human GC cells were treated with MENK. Cell viability, colony formation, cell morphology, cell cycle, and apoptosis were assessed. The effects of MENK on gene expression of OGFr, Bax, BCL-2, caspase-3, PARP, Ki67, cyclin D1, c-myc, survivin were quantifed by qRT-PCR. Western blot was used to analyze the effects of MENK on protein expression of OGFr, Bax, BCL-2, caspase-3, PARP. The anti-tumor activity of MENK in gastic carcinoma was also investigated with animal experiments.

Results

The results indicate that MENK could significantly inhibit the growth of human GC cells SGC7901 and HGC27 in a concentration- and time-dependent manner, decrease the number of cell colonies, and arrest cell cycle in the G0/G1 phase by causing a decrease in Ki67, cyclin D1, and c-myc mRNA. Furthermore, MENK could induce tumor cell apoptosis associated with the upregulation of Bax, a corresponding downregulation of BCL-2 and survivin, and activation of caspase-3 and PARP. Moreover, MENK upregulated the expression of opioid receptors (OGFr) in SGC7901 and HGC27 cells. The interaction between MENK and OGFr in SGC7901 and HGC27 cells appears to be essential for the antitumor activity of MENK.

Conclusion

We conclude that MENK may be a potential drug for the treatment of GC.

Human Antimicrobial Peptides in Bodily Fluids: Current Knowledge and Therapeutic Perspectives in the Postantibiotic Era

Antimicrobial peptides (AMPs) are an integral part of the innate immune defense mechanism of many organisms. Due to the alarming increase of resistance to antimicrobial therapeutics, a growing interest in alternative antimicrobial agents has led to the exploitation of AMPs, both synthetic and isolated from natural sources. Thus, many peptide-based drugs have been the focus of increasing attention by many researchers not only in identifying novel AMPs, but in defining mechanisms of antimicrobial peptide activity as well. Herein, we review the available strategies for the identification of AMPs in human body fluids and their mechanism(s) of action. In addition, an overview of the distribution of AMPs across different human body fluids is provided, as well as its relation with microorganisms and infectious conditions.

Opioid System Modulates the Immune Function: A Review

Opioid receptors and their ligands produce powerful analgesia that is effective in perioperative period and chronic pain managements accompanied with various side effects including respiratory depression, constipation and addiction etc. Opioids can also interfere with the immune system, not only participating in the function of the immune cells, but also modulating innate and acquired immune responses. The traditional notion of opioids is immunosuppressive. Recent studies indicate that the role of opioid receptors on immune function is complicated, working through various different mechanisms. Different opioids or opioids administrations show various effects on the immune system: immunosuppressive, immunostimulatory, or dual effect. It is important to elucidate the relationship between opioids and immune function, since immune system plays critical role in various physiological and pathophysiological processes, including the inflammation, tumor growth and metastasis, drug abuse, and so on. This review article tends to have an overview of the recent work and perspectives on opioids and the immune function.

Opioids, Neutral Endopeptidase, its Inhibitors and Cancer: Is There a Relationship among them?

The role of endogenous animal opioids in the biology of cancer is widely recognized but poorly understood. This is, among others, because of the short half-life of these peptides, which are quickly inactivated by endopeptidases, e.g., neutral endopeptidase (NEP, CD10). It has been established that NEP is engaged in the modulation of the tumor microenvironment, among others that of colon cancer, by exerting influence on cell growth factors, the extracellular matrix and other biologically active substances. Although there are some discrepancies among the findings on the role of both opioids and NEP in cancer development, authors agree that their role seems to depend on the origin, stage and grade of tumor, and even on the method of examination. Moreover, recently, natural inhibitors of NEP, such as sialorphin, opiorphin and spinorphin have been detected. Their analgesic activity has been established. It is interesting to ask whether there is a relationship among opioid peptides, tumor-associated NEP and its inhibitors.

Comparison and analysis of the animal models used to study the effect of morphine on tumour growth and metastasis

The effect of opioids on tumour growth and metastasis has been debated for many years, with recent emphasis on the possibility that they might influence the rate of disease-free survival after tumour resection when used in the perioperative pain management of cancer surgery patients. The literature presents conflicting and inconclusive in vitro and in vivo data about the potential effect of opioids, especially morphine, on tumour growth and metastasis. To inform clinical practice, appropriate animal models are needed to test whether opioids alter the course of tumour growth and metastasis. Here, we review the literature on animal-based studies testing the effect of morphine on cancer so far, and analyse differences between the models used that may explain the discrepancies in published results. Such analysis should elucidate the role of opioids in cancer and help define ideal pre-clinical models to provide definitive answers.

LINKED ARTICLES

This article is part of a themed section on Opioids: New Pathways to Functional Selectivity. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2015.172.issue-2.

Enriched protein screening of human bone marrow mesenchymal stromal cell secretions reveals MFAP5 and PENK as novel IL-10 modulators

The secreted proteins from a cell constitute a natural biologic library that can offer significant insight into human health and disease. Discovering new secreted proteins from cells is bounded by the limitations of traditional separation and detection tools to physically fractionate and analyze samples. Here, we present a new method to systematically identify bioactive cell-secreted proteins that circumvent traditional proteomic methods by first enriching for protein candidates by differential gene expression profiling. The bone marrow stromal cell secretome was analyzed using enriched gene expression datasets in combination with potency assay testing. Four proteins expressed by stromal cells with previously unknown anti-inflammatory properties were identified, two of which provided a significant survival benefit to mice challenged with lethal endotoxic shock. Greater than 85% of secreted factors were recaptured that were otherwise undetected by proteomic methods, and remarkable hit rates of 18% in vitro and 9% in vivo were achieved.

Role of macrophage polarization in tumor angiogenesis and vessel normalization: implications for new anticancer therapies

Angiogenesis, the formation of new capillary blood vessels from preexisting vasculature, is one of the hallmarks of cancer that is pivotal for tumor growth and metastasis. Tumor vessels are known to be abnormal, with typically aberrant, leaky and disordered vessels. Thus, the combination of angiogenesis inhibition and vessel normalization is a potential strategy for anticancer therapy. The solid tumor is composed of not only cancer cells, but also the nonmalignant resident stromal cells, such as bone-marrow-derived cells (BMDCs) and cancer-associated fibroblasts (CAFs). Tumor-associated macrophages (TAMs) are the most abundant cell components of BMDCs, which play a significant role in promoting tumor progression. Accumulating evidences from both patient biopsies and experimental animal models have shown that TAMs function in tumor angiogenesis and vessel abnormalization in a density- and phenotype-dependent manner. This chapter will discuss the evidence for the factors and signaling pathways that are involved in macrophage recruitment and polarization in the tumor microenvironment, and it summarizes the role and underlying molecular mechanisms of macrophage polarization in tumor angiogenesis and vessel normalization. In addition, an overview of the potential of targeting TAM polarization for anticancer therapy will be provided.

Induction on differentiation and modulation of bone marrow progenitor of dendritic cell by methionine enkephalin (MENK)

Methionine enkephalin (MENK), the endogenous neuropeptide, is known to exert direct effects on the neuroendocrine and the immune systems and participates in regulation of various functions of cells related to both the innate and adaptive immune systems. Dendritic cells (DCs) play important role in initiating and regulating T cell responses. The aim of this work is to investigate the effects of MENK on differentiation, maturation, and function of DCs derived from murine bone marrow progenitors (BM-derived DCs). Our result showed that MENK could induce BM-derived DCs to polarize predominantly to mDC subtype, rather than pDC both in vivo and in vitro, and this was in favor of Th1 response. BM-derived DCs, after treatment with MENK, up-regulated the expressions of MHC class II and key costimulatory molecules. Result by RT-PCR showed MENK could increase expressions of delta and kappa receptors on BM-derived DCs. Also MENK promoted BM-derived DCs to secret higher levels of proinflammatory cytokines of IL-12p70, TNF-α. Furthermore, differentiated BM-derived DCs treated with MENK displayed higher activity to induce allogeneic T cell proliferation and MENK also inhibited tumor growth in vivo and induced apoptosis of tumor cells in vitro. Thus, it is concluded that MENK could be an effective inducer of BM-derived DCs and might be a new therapeutic agent for cancer, as well as other immune handicapped disease. Also we may consider MENK as a potential adjuvant in vaccine preparation.

Comparison of stimulating effect on subpopulations of lymphocytes in human peripheral blood by methionine enkephalin with IL-2 and IFN-γ

The aim of this study was to investigate the effects of mechanisms of methionine enkephalin (MENK) on lymphocytes in human peripheral blood. We detected CD4+T cells, CD8+T cells, CD4+CD25+ regulatory T cells (Treg), dendritic cells (DCs), natural killer cells (NK), NKT cells and γδT cells before and after treatment with 10 (-12) M MENK, in cell culture by FCM and RT-PCR. Our findings show that MENK stimulating expansion of lymphocyte subpopulationns by inhibiting CD4+CD25+ regulatory T cells (Treg), which is unique discovery of our study. We may use MENK as a drug to treat cancer patients, whose immune systems are damaged by chemotherapy or radiotherapy.

Extending pharmacological spectrum of opioids beyond analgesia: multifunctional aspects in different pathophysiological states

Opioids are well known to exert potent central analgesic actions. In recent years, the numerous studies have unfolded the critical role of opioids in the pathophysiology of various diseases as well as in biological phenomenon of therapeutic interest. The endogenous ligands of opioid receptors are derived from three independent genes and their appropriate processing yields the major representative opioid peptides beta-endorphin, met-enkephalin, leu-enkephalin and dynorphin, respectively. These peptides and their derivatives exhibit different affinity and selectivity for the mu-, delta- and kappa-receptors located on the central and the peripheral neurons, neuroendocrine, immune, and mucosal cells and on many other organ systems. The present review article highlights the role of these peptides in central nervous system disorders such as depression, anxiety, epilepsy, and stress; gastrointestinal disorders such as diarrhea, postoperative ileus, ulceration, and irritable bowel syndrome; immune system and related inflammatory disorders such as osteoarthritis and rheumatoid arthritis; and others including respiratory, alcoholism and obesity/binge eating. Furthermore, the key role of opioids in different forms of pre- and post-conditioning including ischemic and pharmacological along with in remote preconditioning has also been described.

Endogenous opiates and behavior: 2009

This paper is the 32nd consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2009 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).