Met-enkephalins in patients with inflammatory bowel diseases

Endogenous Opioids in Crohn's Disease

Caring for patients with Crohn's disease (CD) is a serious challenge in modern medicine. The increasing incidence of CD among adolescents and the severe course of the disease create the need for new methods of diagnosis and therapy. Endogenous opioids are a group of low molecular weight chemical compounds with analgesic and anti-inflammatory properties. Endorphins, enkephalins, and dynorphins may have potentially beneficial effects on the course of CD. Previous research data on this topic are inconsistent. Some authors have reported an increase in the concentration of leukocytes during the course of inflammatory bowel disease (IBD) while others have described a downward trend, explained by DPP-IV enzyme activity. Even fewer data are available on plasma endo-opioid level. There is also a lack of comprehensive studies that have assessed the endo-opioid system in patients with IBD. Therefore, the objective of this study was to measure the serum concentrations of human β-endorphin, human proenkephalin (A), and human big dynorphin in CD patients in the acute phase of the disease, during hospital treatment, and in the remission state. All determinations were performed using ELISA kits. The results of our study showed that the concentrations of all the tested endo-opioids, especially β-endorphin and proenkephalin (A), were reduced in adolescents with CD compared to those in the healthy control group, during the acute phase of the disease, and in the remission state. Modulation of the endogenous opioid system and the use of selective nonnarcotic agonists of opioid receptors seems to be promising goals in the future treatment of CD.

Acute Low Dose Naltrexone Increases β-Endorphin and Promotes Neuronal Recovery Following Hypoxia-Ischemic Stroke in Type-2 Diabetic Mice

Diabetic patients experience significant mortality and poor recovery following ischemic stroke. Our clinical and basic science studies demonstrate an overall immune suppression in the periphery of diabetic stroke patients, as well as within the central nervous system (CNS) of type-2 diabetic mice following hypoxia-ischemia (HI). Low doses of naltrexone (LDN) improved clinical outcomes in many autoimmune diseases by acting on opioid receptors to release β-endorphin which in turn balances inflammatory cytokines and modulates the opioid growth factor (OGF)-opioid growth factor receptor (OGFr) pathway. We hypothesized that in our model of diabetic mice, LDN treatment will induce the release of β-endorphin and improve CNS response by promoting neuronal recovery post HI. To test this hypothesis, we induced HI in 10 week old male db/db and db/ + mice, collected tissue at 24 and 72 h post HI, and measured OGF levels in plasma and brain tissue. The infarct size and number of OGF + neurons in the motor cortex, caudate and hippocampus (CA3) were measured. Following HI, db/db mice had significant increases in brain OGF expression, increased infarct size and neurological deficits, and loss of OGFr + neurons in several different brain regions. In the second experiment, we injected LDN (1 mg/kg) intraperitoneally into db/db and db/ + mice at 4, 24, and 48 h post HI, and collected brain tissue and blood at 72 h. Acute LDN treatment increased β-endorphin and OGF levels in plasma and promoted neuronal recovery in db/db mice compared to phosphate buffer saline (PBS)-treated diabetic mice suggesting a protective or regenerative effect of LDN.

Opioid growth factor receptor: Anatomical distribution and receptor colocalization in neurons of the adult mouse brain

The opioid growth factor (OGF) is an endogenous peptide that binds to the nuclear-associated receptor (OGFr), and plays a significant role in the proliferation of developing, renewing, and healing tissues. The receptor is widely expressed in a variety of organs, however its distribution in the brain remains unknown. In this study, we investigated the distribution of OGFr in different brain regions of male heterozygous (-/+ Lepr ^db/J), non -diabetic mice and determined the localization of the receptor in three major brain cell types, astrocytes, microglia, and neurons. Immunofluorescence imaging revealed that the highest number of OGFr was in hippocampal CA3 subregion followed by primary motor cortex, hippocampal CA2, thalamus, caudate and hypothalamus in a descending order. Double immunostaining revealed receptor colocalization with neurons and little or no colocalization in microglia and astrocytes. The highest percentage of OGFr positive neurons was identified in the CA3. Hippocampal CA3 neurons play an important role in memory processing, learning and behavior, and motor cortex neurons are important for muscle movement. However, the significance of the OGFr receptor in these brain regions and its relevance in diseased conditions are not known. Our findings provide a basis for understanding the cellular target and interaction of the OGF- OGFr pathway in neurodegenerative diseases such as Alzheimer's, Parkinson's, and stroke where hippocampus and cortex have an important role. This foundational data may also be useful in drug discovery to modulate OGFr by opioid receptor antagonist in various CNS diseases.

N-Terminally Lipidated Sialorphin Analogs-Synthesis, Molecular Modeling, In Vitro Effect on Enkephalins Degradation by NEP and Treatment of Intestinal Inflammation in Mice

Pharmacotherapy for inflammatory bowel disease (IBD) is difficult, and some patients do not respond to currently available treatments. Therefore, the discovery of novel anti-IBD agents is imperative. Our aim was the synthesis of lipidated analogs of sialorphin and the in vitro characterization of their effect on the degradation of Met-enkephalin by neutral endopeptidase (NEP). We also investigated in vivo whether the most active inhibitor (peptide VIII) selected in the in vitro studies could be a potential candidate for the treatment of colitis. Peptides were synthesized by the solid-phase method. Molecular modeling technique was used to explain the effect of fatty acid chain length in sialorphin analogs on the ligand-enzyme interactions. The anti-inflammatory effect was evaluated in the dextran sulphate sodium (DSS)-induced model of colitis in mice. Peptide VIII containing stearic acid turned out to be in vitro the strongest inhibitor of NEP. We have also shown that the length of the chain of stearic acid fits the size of the grove of NEP. Peptides VII and VIII exhibited in vivo similar anti-inflammatory activity. Our results suggest that lipidation of sialorphin molecule is a promising direction in the search for NEP inhibitors that protect enkephalins.

Central administration of human opiorphin alleviates dextran sodium sulfate-induced colitis in mice through activation of the endogenous opioid system

The opioid system plays a crucial role in maintaining gastrointestinal homeostasis. Endogenous opioid peptide enkephalins have anti-inflammatory effect and participate in the treatment of inflammatory bowel diseases (IBDs). Here, we investigated the effect of natural enkephalinase inhibitor human opiorphin (HO) on dextran sodium sulfate (DSS)-induced colitis in mice. Our results showed that central administration of HO attenuated DSS-induced colitis, as indicated by the reduction of disease activity index (DAI) scores, macroscopic scores, histological scores, and the myeloperoxidase (MPO) activity. Moreover, HO alleviated DSS-induced inflammation by decreasing inflammatory cytokines TNF-α, IL-6, and IL-1β, and increasing anti-inflammatory cytokine IL-10 in both serum and colon tissues in DSS-treated mice. The potential anti-inflammatory effect of HO at a dose of 40 μg/kg was observed as evidenced by a decrease in nuclear factor κB (NF-κB) p65, toll-like receptor-4 (TLR-4), iNOS, and COX-2. HO also improved intestinal barrier function by enhancing the expression of tight junction proteins. Furthermore, HO treatment significantly inhibited activities of neutral endopeptidase (NEP) and aminopeptidase N (APN), elevated serum enkephalins concentrations, and increased expressions of mu and delta opioid receptors. In addition, pretreatment with opioid receptor antagonist naloxone hydrochloride (NH) compromised the protective effect of HO and aggravated colitis symptoms, as indicated by inhibited anti-inflammatory effects, disrupted intestinal barrier function, and decreased opioid receptor activity. In conclusion, these data indicate that HO protects against DSS-induced colitis by inhibiting TLR4/NF-κB pathway activation and improving intestinal barrier function through activation of the endogenous opioid system. Therefore, targeting the opioid system with peptidase inhibitors intervention would be a novel strategy in the therapy of IBD.

Inhibition of Serine Proteases as a Novel Therapeutic Strategy for Abdominal Pain in IBS

Serine proteases are heavily present in the gastrointestinal tract where they are essential in numerous physiological processes. An imbalance in the proteolytic activity is a central mechanism underlying abdominal pain in irritable bowel syndrome (IBS). Therefore, protease inhibitors are emerging as a promising therapeutic tool to manage abdominal pain in this functional gastrointestinal disorder. With this review, we provide an up-to-date overview of the implications of serine proteases in the development of abdominal pain in IBS, along with a critical assessment of the current developments and prospects of protease inhibitors as a therapeutic tool. In particular, we highlight the current knowledge gap concerning the identity of dysregulated serine proteases that are released by the rectal mucosa of IBS patients. Finally, we suggest a workflow with state-of-the-art techniques that will help address the knowledge gap, guiding future research towards the development of more effective and selective protease inhibitors to manage abdominal pain in IBS.

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.

Current overview of opioids in progression of inflammatory bowel disease; pharmacological and clinical considerations

Inflammatory bowel diseases (IBD) belong to a subgroup of persistent, long-term, progressive, and relapsing inflammatory conditions. IBD may spontaneously develop in the colon, resulting in tumor lesions in inflamed regions of the intestine, such as invasive carcinoma. The benefit of opioids for IBD treatment is still questionable, thereby we investigated databases to provide an overview in this context. This review demonstrates the controversial role of opioids in IBD therapy, their physiological and pharmacological functions in attenuating the IBD symptoms, and in improving inflammatory, oxidative stress, and the quality of life factors in IBD subjects. Data were extracted from clinical, in vitro, and in vivo studies in English, between 1995 and 2019, from PubMed, Google Scholar, Scopus, and Cochrane library. Based on recent reports, there are promising opportunities to target the opioid system and control the IBD symptoms. This study suggests a novel approach for future treatment of functional and inflammatory disorders such as IBD.

Neutral endopeptidase (NEP) inhibitors - thiorphan, sialorphin, and its derivatives exert anti-proliferative activity towards colorectal cancer cells in vitro

Neutral endopeptidase (NEP) is an enzyme implicated in development of different tumors, e.g. colorectal cancer (CRC). In this study, the anti-cancer effects of NEP inhibitors, thiorphan (synthetic compound) and sialorphin (naturally occurring pentapeptide) on CRC cells were investigated. Moreover, we synthesized some derivatives of sialorphin (alanine scan analogues: AHNPR, QANPR, QHAPR, QHNAR; N-acetylated sialorphin; C-amidated sialorphin, and C-amidated alanine scan analogues) to examine the biological activity of these inhibitors on CRC cells. The cytotoxic activity of the NEP inhibitors against CRC cell lines (SW620 and LS180) and normal human fibroblasts (HSF) was evaluated. Additionally, the influence of NEP inhibitors on proliferation, cell cycle progression, induction of apoptosis, and the level of phosphorylation of MAP kinases and mTORC1 signaling pathway proteins in CRC cells were examined. The NEP inhibitors were non-cytotoxic to HSF cells; however, most of them slightly decreased the viability and inhibited proliferation of CRC cells. The N-acetylation or C-amidation of sialorphin or its alanine scan analogues resulted in decreased or abolished anti-proliferative activity of the NEP inhibitors towards the CRC cells. Additionally, thiorphan and sialorphin enhanced the anti-proliferative activity of other CRC-cell growth inhibitors (atrial natriuretic peptide-ANP and melphalan-MEL). The mechanisms involved in the anti-proliferative effects of the tested inhibitors were mediated via NEP and associated with induction of cell cycle arrest in the G0/G1 phase, increased activity of ERK1/2, and a reduced level of phosphorylation of mTOR (Ser2448), 4E-BP1, and p70S6K. However, the NEP inhibitors did not induce apoptosis in the CRC cells. These results have indicated that thiorphan and sialorphin or its derivatives AHNPR, QANPR, QHAPR, and QHNAR have the potential to be used as agents in treatment of patients with CRC.

Involvement of central opioid receptors in protective effects of methadone on experimental colitis in rats

PURPOSE

There are several lines of evidence on the protective roles of opioids in gastrointestinal inflammatory conditions. This study aims to distinguish the central and peripheral roles of methadone, a non-selective opioid receptor agonist, in an acute model of ulcerative colitis in male rats.

METHODS

Ulcerative colitis was induced by intrarectal administration of acetic acid 4%. Methadone was injected subcutaneously (s.c.), 5 and 10 mg/kg, and intracerebroventricular (i.c.v.), 50 and 300 ng/rat. Opioid antagonists were employed. Methylnaltrexone (MNTX; 5 mg/kg, i.p.), a peripherally acting opioid receptor antagonist, and naltrexone (NTX; 5 mg/kg, i.p. and 10 ng/rat, i.c.v.), a peripherally and centrally acting opioid receptor antagonist were injected before methadone (10 mg/kg, s.c. and or 300 ng/rat, i.c.v.) administration. NTX (5 mg/kg, i.p. and 10 ng/rat, i.c.v.) were administered 30 min prior to administration of methadone (10 mg/kg, s.c. and 300 ng/rat, i.c.v.), respectively. MNTX (5 mg/kg, i.p.) was injected 30 min prior to methadone (10 mg/kg, s.c.). Seventy-two hours following colitis induction, macroscopic and microscopic mucosal lesions, and the colonic levels of tumor necrosis factor-alpha (TNF-α) and interleukin-1β (IL-1β) were determined.

RESULTS

Methadone (300 ng/rat, i.c.v.) and Methadone (5 and 10 mg/kg, s.c.) improved the macroscopic and microscopic scores through opioid receptors. Also, a significant reduction in TNF-α and IL-1β was observed. Peripherally and centrally injected NTX significantly reversed methadone 10 mg/kg s.c. anti-inflammatory effects while MNTX could not completely reverse this effect. Moreover, centrally administered methadone (300 ng/rat) showed the anti-inflammatory effect which was reversed by central administration of NTX (10 ng/rat).

CONCLUSIONS

The opioid receptors mainly the central opioid receptors may mediate the protective actions of methadone on the experimental model of inflammatory bowel disease in rat.

Alanine scan of sialorphin and its hybrids with opiorphin: synthesis, molecular modelling and effect on enkephalins degradation

Enkephalins are involved in a number of physiological processes. However, these peptides are quickly degraded by peptidases, e.g. the neutral endopeptidase (NEP). Inhibition of the enzymatic degradation of enkephalins is one of the possible approaches to prolong their activity. Selective inhibitor of NEP, sialorphin, is the attractive lead compound for enkephalins degradation studies. In this work, an alanine scan of sialorphin and a series of its hybrids with opiorphin, synthesised by the solid phase method, were performed. The effect of the peptides on degradation of Met-enkephalin by NEP in vitro was investigated. Molecular modelling technique was used to identify residues responsible for protein–ligand interactions. We showed that substitution of amino acids Gln¹, Pro⁴ and Arg⁵ of sialorphin for Ala significantly reduced the half-life of Met-enkephalin in the presence of NEP. [Ala³]sialorphin displayed a higher inhibitory potency against NEP than sialorphin. Substitution of His² for Ala led to a compound which was as active as lead compound. Sialorphin has a structure which hardly tolerates substitution in its sequence at positions 1, 4 and 5. The conversion of His² for alanine in sialorphin is tolerated very well. The higher inhibitory potency of [Ala³]sialorphin than sialorphin against NEP is caused by removal of the hydrophilic residue (Asn) and a better fit of the peptide to the enzyme-binding pocket. The role of side chains of sialorphin in degradation of enkephalin by NEP has been explored. This study also provides an important SAR information essential for further drug design.

T-lymphocyte-derived enkephalins reduce Th1/Th17 colitis and associated pain in mice

BACKGROUND

Endogenous opioids, including enkephalins, are fundamental regulators of pain. In inflammatory conditions, the local release of opioids by leukocytes at the inflammatory site inhibits nociceptor firing, thereby inducing analgesia. Accordingly, in chronic intestinal T_h1/T_h17-associated inflammation, enkephalins released by colitogenic CD4⁺ T lymphocytes relieve inflammation-induced visceral pain. The present study aims to investigate whether mucosal T-cell-derived enkephalins also exhibit a potent anti-inflammatory activity as described for exogenous opioid drugs in T_h1/T_h17-associated colitis.

METHODS

The anti-inflammatory effects of endogenous opioids were investigated in both T_h1/T_h17-associated (transfer of CD4⁺CD45RB^high T lymphocytes) and T_h2-associated (oxazolone) colitis models in mice. Inflammation-induced colonic damage and CD4⁺ T cell subsets were compared in mice treated or not treated with naloxone methiodide, a peripheral antagonist of opioid receptors. The anti-inflammatory activity of T-cell-derived enkephalins was further estimated by comparison of colitis severity in immunodeficient mice into which naïve CD4⁺CD45RB^high T lymphocytes originating from wild-type or enkephalin-knockout mice had been transferred.

RESULTS

Peripheral opioid receptor blockade increases the severity of T_h1/T_h17-induced colitis and attenuates T_h2 oxazolone colitis. The opposite effects of naloxone methiodide treatment in these two models of intestinal inflammation are dependent on the potency of endogenous opioids to promote a T_h2-type immune response. Accordingly, the transfer of enkephalin-deficient CD4⁺CD45RB^high T lymphocytes into immunodeficient mice exacerbates inflammation-induced colonic injury.

CONCLUSIONS

Endogenous opioids, including T-cell-derived enkephalins, promote a T_h2-type immune response, which, depending on the context, may either attenuate (T_h1/T_h17-associated) or aggravate (T_h2-associated) intestinal inflammation.

Stress activates pronociceptive endogenous opioid signalling in DRG neurons during chronic colitis

AIMS AND BACKGROUND

Psychological stress accompanies chronic inflammatory diseases such as IBD, and stress hormones can exacerbate pain signalling. In contrast, the endogenous opioid system has an important analgesic action during chronic inflammation. This study examined the interaction of these pathways.

METHODS

Mouse nociceptive dorsal root ganglia (DRG) neurons were incubated with supernatants from segments of inflamed colon collected from patients with chronic UC and mice with dextran sodium sulfate (cDSS)-induced chronic colitis. Stress effects were studied by adding stress hormones (epinephrine and corticosterone) to dissociated neurons or by exposing cDSS mice to water avoidance stress. Changes in excitability of colonic DRG nociceptors were measured using patch clamp and Ca²⁺ imaging techniques.

RESULTS

Supernatants from patients with chronic UC and from colons of mice with chronic colitis caused a naloxone-sensitive inhibition of neuronal excitability and capsaicin-evoked Ca²⁺ responses. Stress hormones decreased signalling induced by human and mouse supernatants. This effect resulted from stress hormones signalling directly to DRG neurons and indirectly through signalling to the immune system, leading to decreased opioid levels and increased acute inflammation. The net effect of stress was a change endogenous opioid signalling in DRG neurons from an inhibitory to an excitatory effect. This switch was associated with a change in G protein-coupled receptor excitatory signalling to a pathway sensitive to inhibitors of protein kinase A-protein, phospholipase C-protein and G protein βϒ subunits.

CONCLUSIONS

Stress hormones block the inhibitory actions of endogenous opioids and can change the effect of opioid signalling in DRG neurons to excitation. Targeting these pathways may prevent heavy opioid use in IBD.

Anti-inflammatory effect of novel analogs of natural enkephalinase inhibitors in a mouse model of experimental colitis

Aim: The pharmacotherapy of inflammatory bowel disease is difficult and currently available treatments bring mostly poor and unsatisfactory results. Results: The purpose of this work was the synthesis of opiorphin, sialorphin, spinorphin and a series of their analogs and the in vitro characterization of their effect on degradation of enkephalin by neutral endopeptidase and aminopeptidase N. Consequently, we investigated in vivo the anti-inflammatory effect of the most active inhibitors selected in the in vitro studies (Pal-KKQRFSR & Pal-KKQHNPR). Putative inhibitor – enzyme (neutral endopeptidase or aminopeptidase N) complexes are also presented and their binding interfaces are identified. Conclusion: Our results suggest that Pal-KKQHNPR has the potential to become a valuable template for anti-inflammatory therapeutics for the treatment of GI tract inflammation.

Intestinal inflammation and pain management

Intestinal inflammation results in the production of inflammatory pain-inducing mediators that may directly activate colon sensory neurons. Endogenous opioids produced by mucosal effector CD4(+) T lymphocytes identified as colitogenic may paradoxically counterbalance the local pro-algesic effect of inflammatory mediators by acting on opioid receptors expressed on sensory nerve endings. The review will focus on the endogenous immune-mediated regulation of visceral inflammatory pain, current pain treatments in inflammatory bowel diseases and prospectives on new opioid therapeutic opportunities to alleviate pain but avoiding common centrally-mediated side effects.

Basal Plasma Levels of Copeptin are Elevated in Inactive Inflammatory Bowel Disease after Bowel Resection

Evidence of interactions between the enteric nervous system, neuropeptides, and the immune system is growing. The aim of this study was to examine basal plasma levels of a variety of peptide precursors in patients with inflammatory bowel disease (IBD). In two middle-aged cohorts, Malmö Preventive Medicine (n = 5,415) and Malmö Diet and Cost Study (n = 6,103), individuals with the diagnosis of IBD were identified. Medical records were scrutinized. Three controls were matched for each patient. Copeptin, midregional fragments of adrenomedullin, pro-atrial natriuretic peptide, and proenkephalin A, as well as N-terminal protachykinin A and proneurotensin were analyzed in the plasma. Sixty-two IBD patients were identified. The only difference between patients and controls was higher copeptin levels in the patients compared with controls (P = 0.006), with higher copeptin levels in resected than unresected patients (P = 0.020). There was no difference in any precursor levels between Crohn’s disease and ulcerative colitis, between different distributions of disease lesions, or between different treatments.

Activation of μ opioid receptors modulates inflammation in acute experimental colitis

BACKGROUND

μ opioid receptors (μORs) are expressed by neurons and inflammatory cells, and mediate immune response. We tested whether activation of peripheral μORs ameliorates the acute and delayed phase of colitis.

METHODS

C57BL/6J mice were treated with 3% dextran sodium sulfate (DSS) in water, 5 days with or without the peripherally acting μOR agonist, [D-Ala2, N-Me-Phe4, Gly5-ol]-Enkephalin (DAMGO) or with DAMGO+μOR antagonist at day 2-5, then euthanized. Other mice received DSS followed by water for 4 weeks, or DSS with DAMGO starting at day 2 of DSS for 2 or 3 weeks followed by water, then euthanized at 4 weeks. Disease activity index (DAI), histological damage, and myeloperoxidase assay (MPO), as index of neutrophil infiltration, were evaluated. Cytokines and μOR mRNAs were measured with RT-PCR, and nuclear factor-kB (NF-kB), the antiapoptotic factor Bcl-xL, and caspase 3 and 7 with Western blot.

KEY RESULTS

DSS induced acute colitis with elevated DAI, tissue damage, apoptosis and increased MPO, cytokines, μOR mRNA, and NF-kB. DAMGO significantly reduced DAI, inflammatory indexes, cytokines, caspases, and NF-kB, and upregulated Bcl-xL, effects prevented by μOR antagonist. In DSS mice plus 4 weeks of water, DAI, NF-kB, and μOR were normal, whereas MPO, histological damage, and cytokines were still elevated; DAMGO did not reduce inflammation, and did not upregulate Bcl-xL.

CONCLUSIONS & INFERENCES

μOR activation ameliorated the acute but not the delayed phase of DSS colitis by reducing cytokines, likely through activation of the antiapoptotic factor, Bcl-xL, and suppression of NF-kB, a potentiator of inflammation.

Endogenous regulation of inflammatory pain by T-cell-derived opioids: when friend turns to foe

Painful sensation is a hallmark of microbe-induced inflammation. This inflammatory pain is downregulated a few days after infection by opioids locally released by effector T lymphocytes generated in response to microbe-derived antigens. This review focuses on the endogenous regulation of inflammatory pain associated with adaptive T-cell response and puts in perspective the clinical consequences of the opioid-mediated analgesic activity of colitogenic T lymphocytes in inflammatory bowel disease.

Anti-inflammatory and antinociceptive action of the dimeric enkephalin peptide biphalin in the mouse model of colitis: new potential treatment of abdominal pain associated with inflammatory bowel diseases

Biphalin, a mixed MOP/DOP agonist, displays a potent antinociceptive activity in numerous animal models of pain. The aim of the study was to characterize the anti-inflammatory and antinociceptive action of biphalin in the mouse models of colitis. The anti-inflammatory effect of biphalin (5mg/kg, twice daily, i.c. and i.p.) was characterized in a semi-chronic mouse model of colitis, induced by i.c. injection of trinitrobenzenesulfonic acid (TNBS). The antinociceptive action of biphalin (5mg/kg, i.p. and i.c.) in inflamed mice was assessed in mustard oil-induced model of visceral pain and in the hot plate test. In the semi-chronic mouse model of colitis, biphalin i.c. (5mg/kg), but not i.p. improved colitis macroscopic score (2.88±0.19 and 4.99±0.80 units for biphalin and vehicle treated animals, respectively). Biphalin injected i.p. and i.c. (5mg/kg) displayed a potent antinociceptive action in the mustard oil-induced pain test. In the hot plate test, biphalin (5mg/kg, i.p.) produced a potent antinociceptive activity in inflamed mice, suggesting central site of action. Our data suggest that biphalin may become a novel opioid-based analgesic agent in IBD therapy and warrant further investigation of its pharmacological profile.

Anti-inflammatory action of a novel orally available peptide 317 in mouse models of inflammatory bowel diseases

BACKGROUND

The endogenous opioid system constitutes an attractive target in the treatment of GI disorders, including inflammatory bowel diseases (IBD). The aim of our study was to characterize the anti-inflammatory and antinociceptive effect of P-317, a novel cyclic analog of opioid peptide morphiceptin, in animal models of IBD.

METHODS

The anti-inflammatory effect of P-317 after intraperitoneal (ip) and oral (po) administration was assessed in two mouse models of IBD - Crohn's disease, induced by intracolonic instillation of trinitrobenzenesulfonic acid (TNBS) and ulcerative colitis, induced by addition of dextran sodium sulfate (DSS) into drinking water. The antinociceptive action of P-317 was characterized in mice with acute colitis using mustard oil-induced pain test. Real time RT PCR was used to assess semiquantitatively the expression of IL-1β and TNF-α mRNA in mouse colonic samples. To translate our results to clinical conditions, MOP and KOP mRNA were quantified in human colonic biopsies from IBD patients.

RESULTS

P-317 (0.1mg/kg, ip and 1mg/kg, po) alleviated colonic inflammation in TNBS- and DSS-treated mice in the opioid receptor-dependent manner. The anti-inflammatory effect of P-317 was associated with the decrease in mRNA expression of proinflammatory cytokines. The antinociceptive effect of P-317 was observed after ip and po administration in mice with acute colitis.

CONCLUSION

Our results show a potent anti-inflammatory and antinociceptive effect of P-317 in mouse models of colitis upon activation of opioid receptors. The unique bioavailability of P-317 after oral administration suggests that it is a promising drug candidate for future treatment of IBD.

Physiology, signaling, and pharmacology of opioid receptors and their ligands in the gastrointestinal tract: current concepts and future perspectives

Opioid receptors are widely distributed in the human body and are crucially involved in numerous physiological processes. These include pain signaling in the central and the peripheral nervous system, reproduction, growth, respiration, and immunological response. Opioid receptors additionally play a major role in the gastrointestinal (GI) tract in physiological and pathophysiological conditions. This review discusses the physiology and pharmacology of the opioid system in the GI tract. We additionally focus on GI disorders and malfunctions, where pathophysiology involves the endogenous opioid system, such as opioid-induced bowel dysfunction, opioid-induced constipation or abdominal pain. Based on recent reports in the field of pharmacology and medicinal chemistry, we will also discuss the opportunities of targeting the opioid system, suggesting future treatment options for functional disorders and inflammatory states of the GI tract.

Alteration of neuromuscular transmissions in the hamster colon following the resolution of TNBS-induced colitis

The aim of this study was to determine whether trinitrobenzene sulfonic acid-induced colitis leads to alterations in enteric neuronal transmission in hamsters. We assessed the mechanical responses induced by the application of electrical field stimulation (EFS) in isolated segments of the distal colon. The EFS-induced relaxation and contraction were blocked by a nitric oxide synthase inhibitor and by the combination of antagonists for tachykinin NK1 and NK2 receptors and muscarinic acetylcholine receptors, respectively. The mechanical responses to EFS were attenuated in the inflamed colon at 7 days and were recovered by 30 days after inflammation treatment. In addition, we found that purinergic and opioidergic excitatory neural components are expressed following the resolution of colitis. These results suggest that colonic inflammation causes indiscriminate damage to enteric neurons but that neuronal components are restored and that new excitatory neural components, compensating for the contractile responses in smooth muscle after colitis, are expressed.