Anti-inflammatory properties of the mu opioid receptor support its use in the treatment of colon inflammation

The role of transient receptor potential vanilloid 1 (TRPV1) receptors in dextran sulfate-induced colitis in mice

The aim of this study was to investigate the involvement of transient receptor potential vanilloid 1 (TRPV1) receptors in oral dextran sulfate sodium-induced (DSS) colitis using TRPV1 knockout mice and their wild-type C57BL/6 counterparts. DSS (2% or 5%) was administered orally ad libitum for 7 days; the controls received tap water. Animal weight, stool consistency, and blood content were scored every day to calculate the disease activity index (DAI). After sacrificing the mice on day 7, the colons were cut into three equal segments (proximal, intermediate, and distal) for histology, myeloperoxidase (MPO), and cytokine measurements. In the 2% DSS-treated group, the lack of TRPV1 receptors decreased the DAI. Each colon segment of wild-type animals showed more than two-fold increase of MPO activity and more severe histological changes compared to the knockouts. This difference was not observed in case of 5% DSS, when extremely severe inflammation occurred in both groups. IL-1beta production was not altered by the absence of TRPV1. In conclusion, activation of TRPV1 channels enhances the clinical symptoms, histopathological changes, and neutrophil accumulation induced by 2% DSS. Elucidating the modulator role of TRPV1 channels in inflammatory bowel diseases may contribute to the development of novel anti-inflammatory drugs for their therapy.

Hemorphins act as homeostatic agents in response to endotoxin-induced stress

The effect of synthetic LVV-hemorphin-7 and hemorphin-7 on hypothalamo-pituitary-adrenocortical axis activity in response to endotoxin-induced stress was studied. The intraperitoneal (ip) endotoxin (lipopolysaccaride, LPS) (0.5 mg/kg) administration in combination with hemorphin (1 mg/kg) induce significant decrease in plasma corticosterone and modest decrease in plasma levels of tumor necrosis factor-alpha (TNFalpha) in compare with elevated levels of both corticosterone and TNFalpha in plasma of rats received LPS administration alone. Increased activity of calcineurin in both plasma and brain of rats received ip administration of LPS, was recovered under LPS + hemorphin treatment. In two independent proteome analysis, using 2-dimensional fluorescence difference gel electrophoresis and the isotope coded protein label technology, peptidyl-prolyl cis-trans-isomerase A (cyclophilin A) was identified as regulated by hemorphins protein in mouse brain. A therapeutic potential of hemorphins and mechanisms of their homeostatic action in response to endotoxin-induced stress are discussed.

Peripheral mechanisms of pain and analgesia

This review summarizes recent findings on peripheral mechanisms underlying the generation and inhibition of pain. The focus is on events occurring in peripheral injured tissues that lead to the sensitization and excitation of primary afferent neurons, and on the modulation of such mechanisms. Primary afferent neurons are of particular interest from a therapeutic perspective because they are the initial generator of noxious impulses traveling towards relay stations in the spinal cord and the brain. Thus, if one finds ways to inhibit the sensitization and/or excitation of peripheral sensory neurons, subsequent central events such as wind-up, sensitization and plasticity may be prevented. Most importantly, if agents are found that selectively modulate primary afferent function and do not cross the blood-brain-barrier, centrally mediated untoward side effects of conventional analgesics (e.g. opioids, anticonvulsants) may be avoided. This article begins with the peripheral actions of opioids, turns to a discussion of the effects of adrenergic co-adjuvants, and then moves on to a discussion of pro-inflammatory mechanisms focusing on TRP channels and nerve growth factor, their signaling pathways and arising therapeutic perspectives.

Multidrug resistance-associated transporter 2 regulates mucosal inflammation by facilitating the synthesis of hepoxilin A3

Neutrophil transmigration across mucosal surfaces contributes to dysfunction of epithelial barrier properties, a characteristic underlying many mucosal inflammatory diseases. Thus, insight into the directional movement of neutrophils across epithelial barriers will provide important information relating to the mechanisms of such inflammatory disorders. The eicosanoid hepoxilin A(3), an endogenous product of 12-lipoxygenase activity, is secreted from the apical surface of the epithelial barrier and establishes a chemotactic gradient to guide neutrophils from the submucosa across epithelia to the luminal site of an inflammatory stimulus, the final step in neutrophil recruitment. Currently, little is known regarding how hepoxilin A(3) is secreted from the intestinal epithelium during an inflammatory insult. In this study, we reveal that hepoxilin A(3) is a substrate for the apical efflux ATP-binding protein transporter multidrug resistance-associated protein 2 (MRP2). Moreover, using multiple in vitro and in vivo models, we show that induction of intestinal inflammation profoundly up-regulates apical expression of MRP2, and that interfering with hepoxilin A(3) synthesis and/or inhibition of MRP2 function results in a marked reduction in inflammation and severity of disease. Lastly, examination of inflamed intestinal epithelia in human biopsies revealed up-regulation of MRP2. Thus, blocking hepoxilin A(3) synthesis and/or inhibiting MRP2 may lead to the development of new therapeutic strategies for the treatment of epithelial-associated inflammatory conditions.

CEACAM1 and the regulation of mucosal inflammation

Inflammatory bowel disease (IBD) is characterized by unrestrained T-cell activation that results in the production of a variety of inflammatory cytokines and other mediators. Understanding the mechanisms of T-cell regulation is therefore of significant importance to IBD and other forms of dysregulated-mucosal inflammation. An area that is of significant interest are the cell autonomous mechanisms of T-cell regulation through proteins that have natural inhibitory functions when expressed on T lymphocytes. One such molecule is carcinoembryonic antigen cell adhesion molecule 1 (CEACAM1). CEACAM1 is primarily an activation-induced cell-surface molecule that functions as a co-inhibitory receptor. Homophilic ligation of CEACAM1 on T cells leads to a signaling mechanism, which results in inhibition of a broad range T-cell functions. CEACAM1 therefore represents a new potential therapeutic target in the treatment of IBD.

Insights from advances in research of chemically induced experimental models of human inflammatory bowel disease

Inflammatory bowel disease (IBD), the most important being Crohn's disease and ulcerative colitis, results from chronic dysregulation of the mucosal immune system in the gastrointestinal tract. Although the pathogenesis of IBD remains unclear, it is widely accepted that genetic, environmental, and immunological factors are involved. Recent studies suggest that intestinal epithelial defenses are important to prevent inflammation by protecting against microbial pathogens and oxidative stresses. To investigate the etiology of IBD, animal models of experimental colitis have been developed and are frequently used to evaluate new anti-inflammatory treatments for IBD. Several models of experimental colitis that demonstrate various pathophysiological aspects of the human disease have been described. In this manuscript, we review the characteristic features of IBD through a discussion of the various chemically induced experimental models of colitis (e.g., dextran sodium sulfate-, 2,4,6-trinitrobenzene sulfonic acid-, oxazolone-, acetic acid-, and indomethacin-induced models). We also summarize some regulatory and pathogenic factors demonstrated by these models that can, hopefully, be exploited to develop future therapeutic strategies against IBD.

micro-Opioid receptor activation prevents acute hepatic inflammation and cell death

BACKGROUND AND AIMS

The detrimental impact of opioid agonist on the clinical management of inflammatory diseases remains elusive. Given the anti-inflammatory properties of the mu-opioid receptor (MOR) agonists at the intestinal barrier, we hypothesised that MOR activation might also dampen acute hepatic inflammation and cell death-major determinants in the pathogenesis of liver diseases.

PATIENTS AND METHODS

The expression of MOR in liver biopsy specimens and peripheral blood mononuclear cells of untreated patients with chronic hepatitis C virus infection and controls, primary hepatocytes and cell lines was determined by quantitative PCR, immunoblotting and/or immunohistochemistry. The effects of peripheral MOR agonist (d-Ala2,NMe-Phe4,Gly5-ol (DAMGO)) and/or antagonist (naloxone methiodide) were explored in two models of acute hepatitis in mice. MOR-deficient mice were used to evaluate the essential regulatory role of MOR during carbon tetrachloride (CCl(4))-induced hepatitis. The role of DAMGO in cell death was investigated using terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling (TUNEL) analysis and quantification of lactate dehydrogenase release.

RESULTS

The key role of MOR in the prevention of acute hepatic inflammation and cell death in vivo and in vitro is reported. Whereas MOR gene expression increased transiently in the model of acute liver injury and TNFalpha-treated HepG2 cells, an impaired expression of MOR mRNA in human chronic hepatitis C samples was found. Furthermore, preventive administration of the selective MOR agonist DAMGO enhanced hepatoprotective-signalling pathways in vivo that were blocked by using naloxone methiodide. Consistently, genetic and pharmacological inhibition of MOR enhanced the severity associated with experimental hepatotoxin-induced hepatitis. Finally, treatment with DAMGO was shown to prevent cell death in vitro in HepG2 cells in a MOR-dependent manner and to prevent concanavalin A- and CCl(4)-induced cell death in vivo, providing a possible explanation for the anti-inflammatory role of MOR activation in the liver.

CONCLUSIONS

The results indicate that MOR agonists may prevent acute hepatitis and hold promising therapeutic use to maintain remission in both chronic inflammatory bowel and liver diseases.

Visceral pain perception is determined by the duration of colitis and associated neuropeptide expression in the mouse

BACKGROUND

Even though inflammation is a traditional tool for the induction of hyperalgesia in many tissues, recent observations suggest that not all inflammatory processes produce this change. Tolerance to colorectal distension (CRD) is reduced in patients with acute ulcerative colitis but is increased in patients with chronic inflammatory bowel disease. This suggests that the nature of the inflammatory infiltrate influences visceral perception.

AIM

To test this hypothesis by assessing responses to CRD in mice with mild, acute or chronic colitis.

METHODS

CRD responses were measured in mice with mild non-specific colitis, and dextran sodium sulphate (DSS)-induced acute and chronic colitis. Responses were compared with tissue infiltrate and damage, interleukin (IL)1beta and myeloperoxidase (MPO) activity and substance P, beta-endorphin and micro opioid receptor (MOR) expression.

RESULTS

Mild and acute colitis were associated with increased responsiveness to CRD. In contrast, CRD responses were not increased in mice with chronic colitis and this difference was not due to altered colonic wall compliance. MPO and IL1beta levels were greater in acute than in chronic colitis. Larger increases in tissue substance P were seen in acute than in chronic DSS, whereas CD4 T cells, beta-endorphin and MOR expression were evident only in chronic colitis. An inverse correlation was seen between substance P and MOR in these tissues.

CONCLUSIONS

Acute colitis increased responsiveness to CRD and is accompanied by an acute inflammatory infiltrate and increased tissue substance P. Chronic DSS is accompanied by an increase in beta-endorphin and MOR expression, and CD4 T cells, but no change in compliance or CRD responses. We conclude that acute inflammation generates hyperalgesia, whereas chronic inflammation involves infiltration by lymphocytes accompanied by MOR and beta-endorphin up regulation, and this provides an antinociceptive input that restores normal visceral perception.

Battle of animal models

This is a brief summary of the animal models session held during the 12th Annual Meeting of the Society on NeuroImmune Pharmacology, Santa Fe, NM, USA. This session provided important information for participants on availability and utility of animal models for the studies of HIV-1 central nervous system infection and drug abuse. It highlighted animal model relevance to human disease/condition, its utility for the studies of pathogenesis, potential importance for the development of therapeutics, and demonstrated limitations/pitfalls.

No evidence for an involvement of the p38 and JNK mitogen-activated protein in inflammatory bowel diseases

Involvement of mitogen-activated protein (MAPK) in inflammatory bowel disease (IBD) remains enigmatic. We sought to evaluate the expression and activity of p38 and JNK MAPK in IBD and 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced colitis; and the effects of a p38 inhibitor, SB203580, in TNBS colitis. P38 and JNK were quantified in colonic mucosa of 28 IBD patients and 19 controls and in 77 TNBS or control mice treated or not with SB203580. Colitis severity was assessed by survival, macroscopic and microscopic scoring, and molecular markers. Expression and activity of p38 and JNK were similar in IBD patients and controls and not modified by inflammation. In mice, p38 and JNK expression or activity did not increase following the induction of colitis. SB203580 decreased the p38 activity but displayed no clinical nor biological therapeutic effect. In conclusion, these results minimize the role of p38 and JNK in inflammatory colitis and the interest of p38 as a therapeutic target in IBD.

Mu opioid receptor expression is increased in inflammatory bowel diseases: implications for homeostatic intestinal inflammation

BACKGROUND AND AIMS

Recent studies with mu opioid receptor (MOR) deficient mice support a physiological anti-inflammatory effect of MOR at the colon interface. To better understand the potential pharmacological effect of certain opiates in inflammatory bowel diseases (IBD), we (1) evaluated the regulation in vivo and in vitro of human MOR expression by inflammation; and (2) tested the potential anti-inflammatory function of a specific opiate (DALDA) in inflamed and resting human mucosa.

PATIENTS AND METHODS

Expression of MOR mRNA and protein was evaluated in healthy and inflamed small bowel and colonic tissues, isolated peripheral blood mononuclear cells and purified monocytes, and CD4+ and CD8+ T cells from healthy donors and IBD patients. The effect of cytokines and nuclear factor kappaB (NFkappaB) activation on MOR expression in lymphocyte T and monocytic human cell lines was assessed. Finally, DALDA induced anti-inflammatory effect was investigated in mucosal explants from controls and IBD patients.

RESULTS

MOR was expressed in ileal and colonic enteric neurones as well as in immunocytes such as myeloid cells and CD4+ and CD8+ T cells. Overexpressed in active IBD mucosa, MOR was significantly enhanced by cytokines and repressed by NFkappaB inhibitor in myeloid and lymphocytic cell lines. Furthermore, ex vivo DALDA treatment dampened tumour necrosis factor alpha mRNA expression in the colon of active IBD patients.

CONCLUSIONS

Given the increased expression of MOR and the ex vivo beneficial effect of DALDA in active IBD, natural and/or synthetic opioid agonists could help to prevent overt pathological intestinal inflammation.

The putative role of endogenous and exogenous opiates in inflammatory bowel disease

The mu opioid receptor (MOR) is upregulated in inflammatory bowel disease, prompting consideration of the development of selective MOR agonists for the treatment of inflammatory bowel disease

Hepatitis C virus infection down-regulates the expression of peroxisome proliferator-activated receptor alpha and carnitine palmitoyl acyl-CoA transferase 1A

AIM

To elucidate the role of the peroxisome proliferator-activated receptor alpha (PPARalpha) and its target gene carnitine palmitoyl acyl-CoA transferase 1A (CPT1A) in the pathogenesis of hepatitis C virus (HCV) infection.

METHODS

Liver samples were collected from the patients with chronic HCV infection and controls. HepG2 cells were transfected with vector pEF352neo carrying. Two independent clones (clone N3 and N4) stably expressing HCV core protein were analyzed. Total RNA was extracted from cells and liver tissues. PPARalpha and CPT1A mRNAs were quantified by real-time polymerase chain reaction (PCR) using SYBR Green Master. Total extracted proteins were separated by polyacrylamide gel electrophoresis, and electroblotted. Membranes were incubated with the anti-PPARalpha antibody, then with a swine anti-rabbit IgG conjugated to horseradish peroxidase for PPARalpha. Protein bands were revealed by an enhanced chemiluminescence reaction for PPARalpha. For immunohistochemical staining of PPARalpha, sections were incubated with the primary goat polyclonal antibody directed against PPARalpha at room temperature.

RESULTS

Real-time PCR indicated that the PPARalpha level and expression level of CPT1A gene in hepatitis C patients lowered significantly as compared with the controls (1.8+/-2.8 vs 13+/-3.4, P = 0.0002; 1.1+/-1.5 vs 7.4+/-1, P = 0.004). Western blot results showed that the level of PPARalpha protein in the livers of hepatitis C patients was lower than that in controls (2.3+/-0.3 vs 3.6+/-0.2, P = 0.009). The immunohistochemical staining results in chronic hepatitis C patients indicated a decrease in PPARalpha staining in hepatocytes compared with those in the control livers. The in vitro studies found that in the N3 and N4 colon stably expressing HCV core protein, the PPARalpha mRNA levels were significantly lower than that in the controls.

CONCLUSION

The impaired intrahepatic PPARalpha expression is associated with the pathogenic mechanism in hepatic injury during chronic HCV infection. HCV infection reduced the expression of PPARalpha and CPT1A at the level of not only mRNAs but also proteins. PPARalpha plays an important role in the pathogenesis of chronic HCV infection, but the impaired function of this nuclear receptor in HCV infection needs further studies.

Endogenous opioid analgesia in peripheral tissues and the clinical implications for pain control

Opioid receptors are widely expressed in the central and peripheral nervous system as well as in numerous nonneuronal tissues. Both animal models and human clinical data support the involvement of peripheral opioid receptors in analgesia, particularly in inflammation where both opioid receptor expression and efficacy are increased. Immune cells have been shown to contain numerous opioid peptides such as beta-endorphin (END), met-enkephalin (ENK), and dynorphin-A (DYN), although the predominant opioid peptide involved in immune-cell mediated antinociception is thought to be END. These opioid-containing immune cells migrate to inflamed tissues during a complex process of recruitment by chemokines, adhesion, and extravasation. In these tissues, opioid peptide is released from the immune cells upon stimulation with corticotrophin-releasing factor (CRF), noradrenaline, and interleukin 1beta (IL-1beta), and the immune cells return to the local lymph node depleted of peptide. Consistent with this model, systemic immunosuppression may lead to impaired endogenous analgesia as competent immune cells are essential to achieve release of endogenous opioid peptides within inflamed tissue. A further level of complexity is added by the observation that exogenous opioids may impair immune cell function, although there is some evidence to suggest that endogenous opioid peptides do not share this immunosuppressive effect. Improving our understanding of endogenous opioid mechanisms will provide valuable insight towards the development of novel treatments for pain with improved side effect profiles.

The involvement of nitric oxide in the enhanced expression of mu-opioid receptors during intestinal inflammation in mice

Intestinal inflammation enhances the potency of mu-opioid receptor (MOR) agonists inhibiting gastrointestinal transit and increases the expression of MOR in mice intestine. The precise mechanisms implicated in the increased expression of MOR during intestinal inflammation are not known. The aim of the study is to evaluate if nitric oxide released during intestinal inflammation could modulate MOR gene expression and affect gastrointestinal transit. Intestinal inflammation was induced by the intragastric administration of croton oil. In CD-1 mice, with and without inflammation, we evaluated the anti-transit effects of morphine in animals treated with NOS inhibitors (L-NAME and L-NIL) and the intestinal levels of iNOS enzyme mRNA. The anti-transit effects of morphine and the expression of MOR mRNA in the gut of wild-type (WT) and iNOS-/- mice were also assessed. Gastrointestinal transit was measured with charcoal meal and mRNA levels determined by real-time PCR. In CD-1 mice, inflammation induced a 10-fold increase (P<0.0001) in iNOS mRNA levels in the gut. The absence of iNOS gene and treatment of CD-1 mice with L-NAME or L-NIL abolished the increased antitransit effects of morphine observed during inflammation. Moreover, although the basal levels of MOR mRNA were similar in WT and iNOS animals (-/-), intestinal inflammation only increased the MOR expression in the gut of WT (P<0.01) but not in iNOS-/- mice. The results suggest that nitric oxide derived from the increased expression of iNOS is implicated in the enhanced effects of morphine and in the upregulation of MOR gene transcription observed during intestinal inflammation.

Vasoactive intestinal peptide impairs leucocyte migration but fails to modify experimental murine colitis

Inflammatory bowel diseases are chronic inflammatory disorders of the gastrointestinal tract. Vasoactive intestinal peptide (VIP) is a neuropeptide with known anti-inflammatory activity. We have demonstrated previously that administration of VIP inhibits leucocyte migration in a murine model of delayed-type hypersensitivity, and anti-inflammatory efficacy is supported by other studies. The aim of this study was to investigate the VIP effects in a murine model of intestinal inflammation. Colitis was induced in BALB/c mice by a 2.5 mg enema of 2,4,6-trinitrobenzenesulphonic acid (TNBS) and the mice were killed on day 7. Mice were administered either a 3-day (therapeutic) or 7-day (prophylactic) constant infusion of VIP by subcutaneously implanted mini-osmotic pumps, or intraperitoneal (i.p.) injection of VIP on alternate days over 7 days. Clinical disease scores, weight changes, histopathology of colon tissues, plasma VIP levels, cytokine levels and chemotaxis of peripheral blood mononuclear cells were evaluated. After administration of TNBS, mice quickly developed severe colitis accompanied by dramatic body weight loss (20% by day 6) and high mortality (30%). Prophylactic treatment using high-dose VIP abrogated leucocyte chemotaxis; however, it failed to ameliorate the weight loss and mortality. Moreover, VIP delivered either by constant infusion or i.p. failed to modify the clinical, histological or cytokine markers of disease. Our studies show that, despite an ability to inhibit chemokine-induced chemotaxis of mononuclear cells, VIP was unable to modulate TNBS-induced colitis. This contrasts with the efficacy of VIP in models of mild inflammatory disease and suggests that VIP is unlikely to provide a useful model for novel anti-IBD therapy.

Intestinal antiinflammatory effect of 5-aminosalicylic acid is dependent on peroxisome proliferator-activated receptor-gamma

5-aminosalicylic acid (5-ASA) is an antiinflammatory drug widely used in the treatment of inflammatory bowel diseases. It is known to inhibit the production of cytokines and inflammatory mediators, but the mechanism underlying the intestinal effects of 5-ASA remains unknown. Based on the common activities of peroxisome proliferator–activated receptor-γ (PPAR-γ) ligands and 5-ASA, we hypothesized that this nuclear receptor mediates 5-ASA therapeutic action. To test this possibility, colitis was induced in heterozygous PPAR-γ^+/− mice and their wild-type littermates, which were then treated with 5-ASA. 5-ASA treatment had a beneficial effect on colitis only in wild-type and not in heterozygous mice. In epithelial cells, 5-ASA increased PPAR-γ expression, promoted its translocation from the cytoplasm to the nucleus, and induced a modification of its conformation permitting the recruitment of coactivators and the activation of a peroxisome-proliferator response element–driven gene. Validation of these results was obtained with organ cultures of human colonic biopsies. These data identify PPAR-γ as a target of 5-ASA underlying antiinflammatory effects in the colon.

Yersinia pseudotuberculosis anti-inflammatory components reduce trinitrobenzene sulfonic acid-induced colitis in the mouse

Rectal instillation of trinitrobenzene sulfonic acid (TNBS) induces acute colitis in the mouse. We tested the efficacy of Yersinia pseudotuberculosis anti-inflammatory components in preventing TNBS-triggered colitis. Animals were orally inoculated with virulence-attenuated Yersinia cells (a phoP mutant) prior to TNBS administration. Under these experimental conditions, colonic lesions and tumor necrosis factor alpha mRNA levels were significantly reduced.

The endogenous cannabinoid system protects against colonic inflammation

Excessive inflammatory responses can emerge as a potential danger for organisms' health. Physiological balance between pro- and anti-inflammatory processes constitutes an important feature of responses against harmful events. Here, we show that cannabinoid receptors type 1 (CB1) mediate intrinsic protective signals that counteract proinflammatory responses. Both intrarectal infusion of 2,4-dinitrobenzene sulfonic acid (DNBS) and oral administration of dextrane sulfate sodium induced stronger inflammation in CB1-deficient mice (CB1(-/-)) than in wild-type littermates (CB1(+/+)). Treatment of wild-type mice with the specific CB1 antagonist N-(piperidino-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-pyrazole-3-carboxamide (SR141716A) mimicked the phenotype of CB1(-/-) mice, showing an acute requirement of CB1 receptors for protection from inflammation. Consistently, treatment with the cannabinoid receptor agonist R(-)-7-hydroxy-Delta(6)-tetra-hydrocannabinol-dimethylheptyl (HU210) or genetic ablation of the endocannabinoid-degrading enzyme fatty acid amide hydrolase (FAAH) resulted in protection against DNBS-induced colitis. Electrophysiological recordings from circular smooth muscle cells, performed 8 hours after DNBS treatment, revealed spontaneous oscillatory action potentials in CB1(-/-) but not in CB1(+/+) colons, indicating an early CB1-mediated control of inflammation-induced irritation of smooth muscle cells. DNBS treatment increased the percentage of myenteric neurons expressing CB1 receptors, suggesting an enhancement of cannabinoid signaling during colitis. Our results indicate that the endogenous cannabinoid system represents a promising therapeutic target for the treatment of intestinal disease conditions characterized by excessive inflammatory responses.