The lack of transcriptionally active Nrf2 triggers colon dysfunction in female mice - The role of estrogens

BACKGROUND AND AIM

The proper functioning of the gastrointestinal system relies on an intricate crosstalk between a plethora of cell types and signaling pathways. Recently we identified that the lack of NRF2 transcriptional activity (NRF2 tKO) triggers significant colon microscopical alterations, still they do not affect the general functioning of mice. Therefore, in this study, we aimed to address the gender-dependent impact of NRF2 transcriptional deficiency on colon function, and relate them to an established model of inflammatory bowel disease (IBD).

METHODS

In the study we subjected 3- and 6-month old mice deficient in IL-10 and NRF2 transcriptional activity and wild-type counterparts to tests assessing colon functionality, and histological analyses. To address the role of estrogens, we attempted to rescue the phenotype by the delivery of 17β-estradiol through subcutaneous implants.

RESULTS

In females, NRF2 transcriptional abrogation, like IL-10 deficiency, triggers a functional and microscopic phenotype, that resembles IBD. The females are significantly more affected by the dysfunctional phenotype, and the functional impairmentdecreases with age. We found that NRF2 transcriptional activity influences 17β-estradiol level and the estrogen receptors expression and location. Exogenous delivery of 17β-estradiol normalized colon motility in the NRF2 tKO mice, which is related to enhanced ERβ signaling.

CONCLUSIONS

Summing up, in this study, we underline that NRF2 transcriptional deficiency or the lack of IL-10 results in pronounced GI functional decline in young females. Mechanistically, we show that the impaired distal colon motility is dependent on ERβ signaling. Targeting estrogen signaling seems a promising therapeutic strategy to counteract colonic dysfunction.

Peptidomimetics and Their Applications for Opioid Peptide Drug Discovery

Despite various advantages, opioid peptides have been limited in their therapeutic uses due to the main drawbacks in metabolic stability, blood-brain barrier permeability, and bioavailability. Therefore, extensive studies have focused on overcoming the problems and optimizing the therapeutic potential. Currently, numerous peptide-based drugs are being marketed thanks to new synthetic strategies for optimizing metabolism and alternative routes of administration. This tutorial review briefly introduces the history and role of natural opioid peptides and highlights the key findings on their structure-activity relationships for the opioid receptors. It discusses details on opioid peptidomimetics applied to develop therapeutic candidates for the treatment of pain from the pharmacological and structural points of view. The main focus is the current status of various mimetic tools and the successful applications summarized in tables and figures.

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.

The Involvement of the Endogenous Opioid System in the Gastrointestinal Aging in Mice and Humans

Nearly 20% of elderly patients suffer from constipation, but the age-related changes in the gastrointestinal (GI) tract remain insufficiently elucidated. In this study, the alterations within the endogenous opioid system (EOS) as a potential cause of constipation in the elderly were evaluated. The GI functions were assessed in vitro and in vivo and compared between 6-, 12- and 18-month old mice. Moreover, the effect of opioid receptor (MOP, DOP, KOP) agonists on the mouse GI tract functions and the EOS components expression in mouse tissues and colonic biopsies from patients with functional constipation were determined. In the oldest mice, the GI peristalsis was significantly impaired as compared to the younger groups. The tissue response to MOP and DOP, but not KOP, agonists weakened with age in vitro; for DOP, it was confirmed in vivo. In the mouse upper GI tract, Oprm1, Oprd1, Oprk1 expression decreased with age; in the colon, Oprm1 expression increased. There were no differences in the expression of these genes in the colonic biopsies from patients >50 years old as compared to the younger group. In conclusion, the age-related impairment of the GI peristalsis may result from reduced MOP and DOP response to the activation with opioid agonists or the alterations in the EOS expression.

Chiral secondary amino acids, their importance, and methods of analysis

Naturally occurring secondary amino acids, with proline as the main representative, contain an alpha-imino group in a cycle that is typically four-, five-, and six-membered. The unique ring structure exhibits exceptional properties-conformational rigidity, chemical stability, and specific roles in protein structure and folding. Many proline analogues have been used as valuable compounds for the study of metabolism of both prokaryotic and eukaryotic cells and for the synthesis of compounds with desired biological, pharmaceutical, or industrial properties. The D-forms of secondary amino acids play different roles in living organisms than the L-forms. They have different metabolic pathways, biological, physiological, and pharmacological effects, they can be indicators of changes and also serve as biomarkers of diseases. In the scientific literature, the number of articles examining D-amino acids in biological samples is increasing. The review summarises information on the occurrence and importance of D- and L-secondary amino acids-azetidic acid, proline, hydroxyprolines, pipecolic, nipecotic, hydroxypipecolic acids and related peptides containing these D-AAs, as well as the main analytical methods (mostly chromatographic) used for their enantiomeric determination in different matrices (biological samples, plants, food, water, and soil).

Cyclic derivative of morphiceptin Dmt-cyclo-(D-Lys-Phe-D-Pro-Asp)-NH2(P-317), a mixed agonist of MOP and KOP opioid receptors, exerts anti-inflammatory and anti-tumor activity in colitis and colitis-associated colorectal cancer in mice

Endogenous opioid system is involved in the maintenance of the intestinal homeostasis. Recently, we proved that stimulation of opioid receptors using P-317, a cyclic morphiceptin analog, resulted in the alleviation of acute colitis in mice. The aim of the current study was to assess the effect of P-317 during colitis and colitis-associated colorectal cancer in mice. Colitis was induced by addition of dextran sodium sulfate (DSS) into drinking water. Colitis-associated colorectal cancer was induced by a single intraperitoneal injection of azoxymethane (AOM) and subsequent addition of DSS into drinking water (week 2, 5, 8). During macroscopic damage evaluation the samples were collected and used for biochemical (MPO activity assay), molecular (qPCR and western blot) and histological studies. In experimental colitis, P-317 induced an anti-inflammatory response as indicated by macroscopic and microscopic scores. In the colitis-associated colorectal cancer model, a significant difference in colorectal tumor development was observed between vehicle- and P-317-treated mice. P-317 decreased the total number of colonic tumors and inhibited MPO activity. Hematoxylin and eosin staining confirmed anti-tumor activity of P-317. The expression of TNF-α was decreased in P-317-treated mice as compared to the vehicle-treated group. P-317 decreased proliferation as well as β-catenin expression in tumors. P-317, a mixed MOP and KOP receptor agonist, induced an anti-inflammatory response in experimental colitis and decreased tumor development in colitis-associated colorectal cancer in mice.

Cyclic derivatives of morphiceptin possess anti-transit effect in the gastrointestinal tract and alleviate abdominal pain in mice

BACKGROUND

Irritable bowel syndrome (IBS) is a chronic condition with recurring gastrointestinal (GI) symptoms: altered motility and abdominal pain. As endogenous opioid system participates in pain perception and in the control of GI peristalsis, opioids have been proposed as a promising therapy in IBS. In a previous study, we observed that morphiceptin derivative, P-317 (Dmt-cyclo-(D-Lys-Phe-D-Pro-Asp)-NH₂), presents promising features to be applied in IBS. In this project, we tested whether modifications in cyclic morphiceptin-based structure: fluorination (compound 1) or peptide bond reduction (compound 2) improve pharmacological effect.

METHODS

We evaluated tested derivatives in the mouse GI system under physiological (GI transit) and pathophysiological (castor oil diarrhea, stress-induced hypermotility, visceral pain) conditions.

RESULTS

Both compounds prolonged GI transit. Compound 1 and P-317 inhibited upper GI transit and motility of the colon; compound 2 remained inactive. Compound 1 and P-317 inhibited hypermotility in stressed mice and delayed the acute diarrhea in comparison to control. Only P-317 exerted antinociceptive effect. None of tested derivatives, similar to P-317, affected locomotor activity.

CONCLUSIONS

Compound 1 is equally effective as P-317 in the mouse GI tract. The peptide bond reduction decreased the activity of compound 2. Fluorination appears to be an efficient way to increase the effects of morphiceptin analogs in the GI tract.

Desensitization of transient receptor potential vanilloid type-1 (TRPV1) channel as promising therapy of irritable bowel syndrome: characterization of the action of palvanil in the mouse gastrointestinal tract

TRPV1 are involved in the control of the gastrointestinal (GI) functions and pain sensation. Their activation induces pain but it is followed by desensitization, which in turn causes analgesia. The studies from the last two decades indicate that TRPV1 are involved in visceral hypersensitivity in the GI tract and pathogenesis of irritable bowel syndrome (IBS). Therefore, the aim of this study is to assess the action of fast desensitizing agonist of TRPV1, palvanil (N-palmitoyl-vanillamine), in the murine GI tract and on nociception to evaluate its potential application in the therapy of IBS. The effect of palvanil on smooth muscle contractility was evaluated using organ baths. The impact of palvanil on intestinal secretion was assessed in Ussing chambers. In vivo, the action of palvanil (0.1–1 mg/kg) was assessed in whole GI transit, fecal pellet output, and colonic bead expulsion tests. The antinociceptive potency of palvanil was tested in the mustard oil-induced pain test. Palvanil inhibited colonic contractions (evoked by electrical field stimulation, EFS) and decreased the ion transport in the colon stimulated with forskolin. It did not affect secretion in experiments with veratridine. In vivo, palvanil prolonged whole GI transit at all doses tested. At the lower dose tested, it accelerated colonic motility during first 60 min following injection. By contrast, at the dose of 1 mg/kg, colonic motility was inhibited. Palvanil induced antinociceptive action at all tested doses in mustard oil-induced pain test. TRPV1 fast-desensitizing compounds, i.e., palvanil, may be promising agents in the therapy of IBS since it modulates intestinal motility and reduces visceral pain.

Enkephalinase inhibitors, potential therapeutics for the future treatment of diarrhea predominant functional gastrointestinal disorders

The endogenous opioid system (EOS) is considered being a crucial element involved in the pathophysiology of irritable bowel syndrome (IBS) as it regulates gastrointestinal (GI) homeostasis through modulation of motility and water and ion secretion/absorption. Along with opioid receptors (ORs), the following components of EOS can be distinguished: 1. endogenous opioid peptides (EOPs), namely enkephalins, endorphins, endomorphins and dynorphins, and 2. peptidases, which regulate the metabolism (synthesis and degradation) of EOPs. Enkephalins, which are δ-opioid receptors agonists, induce significant effects in the GI tract as they act as potent pro-absorptive neurotransmitters. The action of enkephalins and other EOPs is limited, since EOPs are easily and rapidly inactivated by a natural metalloendopeptidase (enkephalinase/neprilysin) and aminopeptidase N. Studies show that the activity of EOPs can be enhanced by inhibition of these enzymes. In this review, we discuss the antidiarrheal and antinociceptive potential of enkephalinase inhibitors. Furthermore, our review is to answer the question whether enkephalinase inhibitors may be helpful in the future treatment of diarrhea predominant functional GI disorders.

Toward an effective peripheral visceral analgesic: responding to the national opioid crisis

This minireiew summarizes recent new developments in visceral analgesics. This promising field is important, as a new approach to address abdominal pain with peripheral visceral analgesics is considered a key approach to addressing the current opioid crisis. Some of the novel compounds address peripheral pain mechanisms through modulation of opioid receptors via biased ligands, nociceptin/orphanin FQ opioid peptide (NOP) receptor, or dual action on NOP and μ-opioid receptor, buprenorphine and morphiceptin analogs. Other compounds target nonopioid mechanisms, including cannabinoid (CB2), N-methyl-d-aspartate, calcitonin gene-related peptide, estrogen, and adenosine A_2B receptors and transient receptor potential (TRP) channels (TRPV1, TRPV4, and TRPM8). Although current evidence is based predominantly on animal models of visceral pain, early human studies also support the evidence from the basic and animal research. This augurs well for the development of nonaddictive, visceral analgesics for treatment of chronic abdominal pain, an unmet clinical need.

Advancements in drug development for diarrhea-predominant irritable bowel syndrome

INTRODUCTION

Diarrhea-predominant irritable bowel syndrome (IBS-D) is a common disorder characterized by a complex pathophysiology hampering optimal targeted drug development. Recent advances in our understanding of key underlying mechanisms prompted novel therapeutics including novel pharmacological approaches.

AREAS COVERED

This review summarizes the latest advancements in the pipeline of IBS-D drugs focusing on new pharmacological targets, efficacy and safety of medicinal products considering the recent harmonization of regulatory requirements by the FDA and the EMA.

EXPERT OPINION

The new 5-HT₃ receptor antagonist ramosetron appears a promising therapeutic approach devoid of significant adverse events, although it is presently unavailable in Western countries, most likely because of the precautionary approach taken by regulatory agencies with this drug class. New pharmacological concepts on full agonists/antagonists, mixed-receptor activity and novel drug targets may streamline the present drug pipeline along with the adherence on new regulatory guidelines on outcome measures. Eluxadoline can be taken as an example of this paradigm shift. It has now been granted marketing authorization for IBS-D on both sides of the Atlantic, but it is still considered as a second-line agent by the NICE. There is still much work to be done to fully cover clinical needs of patients with IBS-D.

Prosecretory effect of loperamide in ileal and colonic mucosae of mice displaying high or low swim stress-induced analgesia associated with high and low endogenous opioid system activity

BACKGROUND

Irritable bowel syndrome (IBS) is characterized by abdominal pain, bloating, and changes in bowel habit. The aim of this study was to characterize the effect of loperamide hydrochloride (LOP) and naloxone hydrochloride (NLX), an opioid agonist and antagonist, respectively, on electrolyte equilibrium in ileal and colonic mucosae and to estimate the possible influence of divergent activity of the endogenous opioid system (EOS) on IBS therapy.

METHODS

Two mouse lines bidirectionally selected for high (HA) and low (LA) swim stress-induced analgesia associated with high and low EOS activity were used in this study. To assess the effect of LOP and NLX on HA/LA lines in vivo, we used the castor oil-induced diarrhea model. Changes in electrolyte equilibrium were determined on the basis of short-circuit current (ΔI_sc ) in isolated mouse ileum and colon exposed to LOP and NLX and stimulated by forskolin (FSK), veratridine (VER), and bethanechol (BET).

KEY RESULTS

In vivo, we found that LOP significantly prolonged time to appearance of diarrhea in HA and LA lines. In vitro, LOP and NLX increased ΔI_sc in FSK- and VER-stimulated colonic tissue, respectively, in HA line. In the ileum, LOP increased ΔI_sc in FSK- and VER-stimulated tissue and decreased ΔI_sc in BET-stimulated tissues in HA line.

CONCLUSIONS & INFERENCES

Individual differences in EOS activity may play a crucial role in the response to the IBS-D therapy, thus some patients may be at an increased risk of side effects such as constipation or diarrhea.

G protein-coupled estrogen receptor and estrogen receptor ligands regulate colonic motility and visceral pain

BACKGROUND

Diarrhea-predominant irritable bowel syndrome (IBS-D) is a functional gastrointestinal (GI) disorder, which occurs more frequently in women than men. The aim of our study was to determine the role of activation of classical estrogen receptors (ER) and novel membrane receptor, G protein-coupled estrogen receptor (GPER) in human and mouse tissue and to assess the possible cross talk between these receptors in the GI tract.

METHODS

Immunohistochemistry was used to determine the expression of GPER in human and mouse intestines. The effect of G-1, a GPER selective agonist, and estradiol, a non-selective ER agonist, on muscle contractility was characterized in isolated preparations of the human and mouse colon. To characterize the effect of G-1 and estradiol in vivo, colonic bead expulsion test was performed. G-1 and estradiol activity on the visceral pain signaling was assessed in the mustard oil-induced abdominal pain model.

KEY RESULTS

GPER is expressed in the human colon and in the mouse colon and ileum. G-1 and estradiol inhibited muscle contractility in vitro in human and mouse colon. G-1 or estradiol administered intravenously at the dose of 20 mg/kg significantly prolonged the time to bead expulsion in females. Moreover, G-1 prolonged the time to bead expulsion and inhibited GI hypermotility in both genders. The injection of G-1 or estradiol resulted in a significant reduction in the number of pain-induced behaviors in mice.

CONCLUSIONS AND INFERENCES

GPER and ER receptors are involved in the regulation of GI motility and visceral pain. Both may thus constitute an important pharmacological target in the IBS-D therapy.

Methyl-orvinol-Dual activity opioid receptor ligand inhibits gastrointestinal transit and alleviates abdominal pain in the mouse models mimicking diarrhea-predominant irritable bowel syndrome

BACKGROUND

Diarrhea-predominant irritable bowel syndrome (IBS-D) is a functional disorder of the gastrointestinal (GI) tract. The major IBS-D symptoms include diarrhea, abdominal pain and discomfort. High density of opioid receptors (ORs) in the GI tract and their participation in the maintenance of GI homeostasis make ORs ligands an attractive option for developing new anti-IBS-D treatments. The aim of this study was to characterize the effect of methyl-orvinol on the GI motility and secretion and in mouse models mimicking symptoms of IBS-D.

METHODS

In vitro, the effects of methyl-orvinol on electrical field stimulated smooth muscle contractility and epithelial ion transport were characterized in the mouse colon. In vivo, the following tests were used to determine methyl-orvinol effect on mouse GI motility: colonic bead expulsion, whole GI transit and fecal pellet output. An antinociceptive action of methyl-orvinol was assessed in the mouse model of visceral pain induced by mustard oil.

RESULTS

Methyl-orvinol (10^-10 to 10^-6M) inhibited colonic smooth muscle contractions in a concentration-dependent manner. This effect was reversed by naloxone (non-selective opioid antagonist) and β-funaltrexamine (selective MOP antagonist). Experiments with a selective KOP receptor agonist, U50488 revealed that methyl-orvinol is a KOP receptor antagonist in the GI tract. Methyl-orvinol enhanced epithelial ion transport. In vivo, methyl-orvinol inhibited colonic bead expulsion and prolonged GI transit. Methyl-orvinol improved hypermotility and reduced abdominal pain in the mouse models mimicking IBS-D symptoms.

CONCLUSION

Methyl-orvinol could become a promising drug candidate in chronic therapy of functional GI diseases such as IBS-D.

Berberine Improves Intestinal Motility and Visceral Pain in the Mouse Models Mimicking Diarrhea-Predominant Irritable Bowel Syndrome (IBS-D) Symptoms in an Opioid-Receptor Dependent Manner

BACKGROUND AND AIMS

Berberine and its derivatives display potent analgesic, anti-inflammatory and anticancer activity. Here we aimed at characterizing the mechanism of action of berberine in the gastrointestinal (GI) tract and cortical neurons using animal models and in vitro tests.

METHODS

The effect of berberine was characterized in murine models mimicking diarrhea-predominant irritable bowel syndrome (IBS-D) symptoms. Then the opioid antagonists were used to identify the receptors involved. Furthermore, the effect of berberineon opioid receptors expression was established in the mouse intestine and rat fetal cortical neurons.

RESULTS

In mouse models, berberine prolonged GI transit and time to diarrhea in a dose-dependent manner, and significantly reduced visceral pain. In physiological conditions the effects of berberine were mediated by mu- (MOR) and delta- (DOR) opioid receptors; hypermotility, excessive secretion and nociception were reversed by berberine through MOR and DOR-dependent action. We also found that berberine increased the expression of MOR and DOR in the mouse bowel and rat fetal cortical neurons.

CONCLUSION

Berberine significantly improved IBS-D symptoms in animal models, possibly through mu- and delta- opioid receptors. Berberine may become a new drug candidate for the successful treatment of IBS-D in clinical conditions.

Calea zacatechichi dichloromethane extract exhibits antidiarrheal and antinociceptive effects in mouse models mimicking irritable bowel syndrome

Calea zacatechichi Schltdl. (Asteraceae alt. Compositae) is a Mexican plant commonly used in folk medicine to treat respiratory and gastrointestinal (GI) disorders. The objective of this study is to characterize the effect of C. zacatechichi extracts in mouse models mimicking the symptoms of irritable bowel syndrome (IBS). Powdered C. zacatechichi herb (leaves, stems, and flowers) was extracted with methanol. Methanolic extract was filtered and evaporated giving methanolic fraction. The residue was extracted with dichloromethane (DCM). Methanolic and DCM (200 mg/kg, per os) extracts were screened for their effect on GI motility in several in vitro tests, and the antidiarrheal and antinociceptive effects were assessed using mouse models. The influence of the DCM extract on motoric parameters and exploratory behaviors was also assessed. Finally, the composition of C. zacatechichi DCM extract was qualitatively analyzed using liquid chromatography-mass spectrometry (LC-MS) method. C. zacatechichi DCM extract significantly inhibited the contractility of mouse colon in vitro (IC₅₀ = 17 ± 2 μg/ml). Administration of the DCM extract in vivo (200 mg/kg, per os) significantly prolonged the time of whole GI transit (46 ± 1 vs. 117 ± 27 min for control and DCM-treated animals, respectively; P = 0.0023), inhibited hypermotility, and reduced pain in mouse models mimicking functional GI disorders. Our findings suggest that constituents of the C. zacatechichi DCM extract exhibit antidiarrheal and analgesic activity. The extract may thus become an attractive material for isolation of compounds that may be used as a supplementary treatment for pain and diarrhea associated with IBS in the future.