Effects of lubiprostone on human uterine smooth muscle cells

The cannabinoid receptor CB1 affects the proliferation and apoptosis of adenomyotic human uterine smooth muscle cells of the junctional zone: a mechanism study

BACKGROUND

The denomyotic junctional zone (JZ) plays an important role in the pathogenesis of adenomyosis. Proliferating cell nuclear antigen (PCNA) is an important nuclear marker of cell proliferation. This study aimed to evaluate the effects of the cannabinoid receptor CB1 on proliferation and apoptosis in the JZ in women with and without adenomyosis.

METHODS

JZ smooth muscle cells (JZSMCs) of the adenomyosis and control groups were collected and cultivated. Immunohistochemistry and immunoblotting were used for protein localization and expression detection of CB1 and PCNA. Additionally, qRT-PCR was used to quantitatively analyse the mRNA expression of the two. AM251 and ACEA were used to regulate the function of CB1 receptors, and CCK-8 assay and flow cytometry assay were used to verify the proliferation and apoptosis of JZSMCs after regulation.

RESULTS

We demonstrated that in normal JZSMCs CB1 and PCNA messenger RNA (mRNA) and protein expression was significantly higher in the proliferative phase of the menstrual cycle than in the secretory phase. CB1 and PCNA expression in JZSMCs from women with ADS was significantly higher than that in control women and did not significantly differ across the menstrual cycle. CB1 receptor antagonist AM251 inhibited the proliferation of adenomyotic JZSMCs in a dose-dependent manner. The CB1 receptor agonist ACEA significantly promoted the proliferation of adenomyotic JZSMCs. The apoptosis rate of adenomyotic JZSMCs treated with AM251 was significantly higher than that of JZSMCs from the untreated control group. The apoptosis rate was significantly decreased in the ACEA group compared with that in the untreated control group. Furthermore, AM251 suppressed the phosphorylation of AKT and Erk1/2 in adenomyotic JZSMCs. The CB1 agonist ACEA significantly promoted the phosphorylation of AKT and Erk1/2.

CONCLUSIONS

Our results indicated that the levels of CB1 and PCNA were increased in patients with adenomyosis and that cyclic changes were lost. CB1 may affect uterine JZ proliferation and apoptosis in adenomyosis by enhancing AKT and MAPK/Erk signalling.

Identification of the fatty acid activation site on human ClC-2

Fatty acids (including lubiprostone and cobiprostone) are human ClC-2 (hClC-2) Cl^- channel activators. Molecular and cellular mechanisms underlying this activation were examined. Role of a four-amino acid PKA activation site, RGET₆₉₁, of hClC-2 was investigated using wild-type (WT) and mutant (AGET, RGEA, and AGAA) hClC-2 expressed in 293EBNA cells as well as involvement of PKA, intracellular cAMP concentration ([cAMP]_i), EP₂, or EP₄ receptor agonist activity. All fatty acids [lubiprostone, cobiprostone, eicosatetraynoic acid (ETYA), oleic acid, and elaidic acid] caused significant rightward shifts in concentration-dependent Cl^- current activation (increasing EC₅₀s) with mutant compared with WT hClC-2 channels, without changing time and voltage dependence, current-voltage rectification, or methadone inhibition of the channel. As with lubiprostone, cobiprostone activation of hClC-2 occurred with PKA inhibitor (myristoylated protein kinase inhibitor) present or when using double PKA activation site (RRAA₆₅₅/RGEA₆₉₁) mutant. Cobiprostone did not activate human CFTR. Fatty acids did not increase [cAMP]_i in hClC-2/293EBNA or T84 cells. Using T84 CFTR knockdown cells, cobiprostone increased hClC-2 Cl^- currents without increasing [cAMP]_i, while PGE₂ and forskolin-IBMX increased both. Fatty acids were not agonists of EP₂ or EP₄ receptors. L-161,982, a supposed EP₄-selective inhibitor, had no effect on lubiprostone-activated hClC-2 Cl^- currents but significantly decreased T84 cell barrier function measured by transepithelial resistance and fluorescent dextran transepithelial movement. The present findings show that RGET₆₉₁ of hClC-2 (possible binding site) plays an important functional role in fatty acid activation of hClC-2. PKA, [cAMP]_i, and EP₂ or EP₄ receptors are not involved. These studies provide the molecular basis for fatty acid regulation of hClC-2.

Pharmacological, Pharmacokinetic, and Pharmacogenomic Aspects of Functional Gastrointestinal Disorders

This article reviews medications commonly used for the treatment of patients with functional gastrointestinal disorders. Specifically, we review the animal models that have been validated for the study of drug effects on sensation and motility; the preclinical pharmacology, pharmacokinetics, and toxicology usually required for introduction of new drugs; the biomarkers that are validated for studies of sensation and motility endpoints with experimental medications in humans; the pharmacogenomics applied to these medications and their relevance to the FGIDs; and the pharmacology of agents that are applied or have potential for the treatment of FGIDs, including psychopharmacologic drugs.

Advancing treatment options for chronic idiopathic constipation

INTRODUCTION

Chronic constipation is a global problem affecting all ages and associated with considerable morbidity and significant financial burden for society. Though formerly defined on the basis of a single symptom, infrequent defecation; constipation is now viewed as a syndrome encompassing several complaints such as difficulty with defecation, a sense of incomplete evacuation, hard stools, abdominal discomfort and bloating.

AREAS COVERED

The expanded concept of constipation has inevitably led to a significant change in outcomes in clinical trials, as well as in patient expectations from new therapeutic interventions. The past decades have also witnessed a proliferation in therapeutic targets for new agents. Foremost among these have been novel prokinetics, a new category, prosecretory agents and innovative approaches such as inhibitors of bile salt transport. In contrast, relatively few effective therapies exist for the management of those anorectal and pelvic floor problems that result in difficult defecation.

EXPERT OPINION

Though constipation is a common and often troublesome disorder, many of those affected can resolve their symptoms with relatively simple measures. For those with more resistant symptoms a number of novel, effective and safe options now exist. Those with defecatory difficulty (anismus, pelvic floor dysfunction) continue to represent a significant management challenge.

ClC-2 regulation of intestinal barrier function: Translation of basic science to therapeutic target

The ClC-2 chloride channel is a member of the voltage-gated chloride channel family. ClC-2 is involved in various physiological processes, including fluid transport and secretion, regulation of cell volume and pH, maintaining the membrane potential of the cell, cell-to-cell communication, and tissue homeostasis. Recently, our laboratory has accumulated evidence indicating a critical role of ClC-2 in the regulation of intestinal barrier function by altering inter-epithelial tight junction composition. This review will detail the role of ClC-2 in intestinal barrier function during intestinal disorders, including experimental ischemia/reperfusion injury and dextran sodium sulfate (DSS)-induced inflammatory bowel disease. Details of pharmacological manipulation of ClC-2 via prostone agonists will also be provided in an effort to show the potential therapeutic relevance of ClC-2 regulation, particularly during intestinal barrier disruption.

Effects of combined progesterone and 17β-estradiol treatment on the transcriptome of cultured human myometrial smooth muscle cells

A transcriptomic analysis of cultured human uterine smooth muscle cells (hUtSMCs) was performed to examine gene expression profiles in smooth muscle in an environment containing the two major steroid hormones that regulate the human myometrium in physiological states associated with estrous, pregnancy, labor, and pathophysiological states such as leiomyoma and endometrial cancer. hUtSMCs were treated with progesterone (P4) and 17β-estradiol (E2) individually and in combination, in the presence and absence of RU486 (mifepristone). Transcription of many genes was modulated in the presence of P4 or E2 alone, but almost six times more genes were transcriptionally modulated in the presence of the P4/E2 hormone combination. In total 796 annotated genes were significantly differentially expressed in the presence of both P4 and E2 relative to their expression in untreated cells. Functional withdrawal of P4 by addition of RU486 effectively reversed almost all transcriptional changes caused by P4/E2 treatment. Gene ontology analysis of differentially expressed genes revealed a strong association between P4/E2 treatment and downregulated expression of genes involved in cell communication, signal transduction, channel activity, inflammatory response, and differentiation. Upregulated processes included cell survival, gene transcription, steroid hormone biosynthesis, muscle development, insulin receptor signaling, and cell growth.

Effects of lubiprostone on pacemaker activity of interstitial cells of cajal from the mouse colon

Lubiprostone is a chloride (Cl^-) channel activator derived from prostaglandin E₁ and used for managing constipation. In addition, lubiprostone affects the activity of gastrointestinal smooth muscles. Interstitial cells of Cajal (ICCs) are pacemaker cells that generate slow-wave activity in smooth muscles. We studied the effects of lubiprostone on the pacemaker potentials of colonic ICCs. We used the whole-cell patch-clamp technique to determine the pacemaker activity in cultured colonic ICCs obtained from mice. Lubiprostone hyperpolarized the membrane and inhibited the generation of pacemaker potentials. Prostanoid EP₁, EP₂, EP₃, and EP₄ antagonists (SC-19220, PF-04418948, 6-methoxypyridine-2-boronc acid N-phenyldiethanolamine ester, and GW627368, respectively) did not block the response to lubiprostone. _L-NG-nitroarginine methyl ester (_L-NAME, an inhibitor of nitric oxide synthase) and 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ, an inhibitor of guanylate cyclase) did not block the response to lubiprostone. In addition, tetraethylammonium (TEA, a voltage-dependent potassium [K⁺] channel blocker) and apamin (a calcium [Ca²⁺]-dependent K⁺ channel blocker) did not block the response to lubiprostone. However, glibenclamide (an ATP-sensitive K⁺ channel blocker) blocked the response to lubiprostone. Similar to lubiprostone, pinacidil (an opener of ATP-sensitive K⁺ channel) hyperpolarized the membrane and inhibited the generation of pacemaker potentials, and these effects were inhibited by glibenclamide. These results suggest that lubiprostone can modulate the pacemaker potentials of colonic ICCs via activation of ATP-sensitive K⁺ channel through a prostanoid EP receptor-independent mechanism.

Transcriptomic effects of estradiol treatment on cultured human uterine smooth muscle cells

Contractility of the myometrial smooth muscle cells during the estrous cycle and pregnancy is modulated by estrogen but the temporal expression of estrogen (relative to progesterone) and the type of contraction involved are distinctly different in pregnancy and estrous. This in vitro cell culture study investigated the global gene expression profile of human uterine smooth muscle cells (hUtSMCs) following 17β-estradiol (E2) treatment. In response to E2 treatment 540 genes, many of which have not been previously described as estrogen responsive, were identified as significantly differentially expressed. These genes are involved in biological processes that include muscle contraction, cell migration and adhesion, apoptosis and phosphorylation. Evidence from this study suggests that 17β-estradiol may have effects that are contrary to an overall contraction phenotype. The hUtSMC in vitro culture system is a useful model to investigate steroid effects on smooth muscle cells and may provide additional clues as to how smooth muscle cells behave in vivo.

Lubiprostone for chronic constipation in adults

Lubiprostone (Amitiza-Sucampo Pharma Europe), a chloride-channel activator is licensed for the treatment of chronic idiopathic constipation in adults. It received a marketing authorisation in the UK in September 2012. In this article, we consider the evidence for lubiprostone in the management of constipation and how the treatment fits with current management strategies for constipation.

Emerging treatments for chronic constipation

INTRODUCTION

Chronic constipation (CC) is a common problem worldwide and, for some sufferers, a cause of considerable morbidity. Recent definitions of CC have moved from the former emphasis on stool frequency alone to a broader concept that strives to encompass the various symptoms that may bother afflicted individuals. Accordingly, new therapies attempt to not only increase frequency of defecation but also to address such symptoms as satisfaction with bowel action, straining, bloating, and distension.

AREAS COVERED

To provide context the relative merits and problems related to conventional laxative-based approaches to constipation are first reviewed and then more recent novel pharmacological approaches to the management of constipation assessed. The focus is on two classes of compounds, selective prokinetics and prosecretory agents, and studies on their efficacy and safety in chronic idiopathic constipation were retrieved and evaluated.

EXPERT OPINION

While undoubtedly effective, high-quality evidence to support laxatives, the traditional remedies for constipation, is remarkably scarce due, in large part, to the absence, until very recently, of high-quality randomized controlled clinical trials. The selective prokinetic agent prucalopride and the prosecretory agents lubiprostone and linaclotide have shown efficacy and been associated with a good safety record in large well-conducted clinical studies. Other novel approaches, such as the inhibition of ileal bile salt absorption, offer particular promise.

Lubiprostone for the treatment of adult women with irritable bowel syndrome with constipation

Irritable bowel syndrome with constipation (IBS-C) affects approximately 5% of the population in western countries. The majority of those afflicted are women. Symptoms are often detrimental to the individual's quality of life and incur high healthcare costs to society. There is no evidence to support changes in lifestyle, laxatives or over the counter supplements. Tegaserod appeared to have promising results but was promptly removed from the market due to adverse cardiovascular events. In 2008, lubiprostone (Amitiza) was approved by the US Food and Drug Administration (FDA) for the treatment of women with IBS-C. It is thought to selectively activate type 2 chloride channels in the apical membrane of the intestinal epithelial cells leading to chloride secretion. As result, sodium and water are passively secreted generating peristalsis and laxation, without stimulating gastrointestinal smooth muscle. Several trials with predominantly female patients have shown it to be effective in the treatment of IBS-C. Overall lubiprostone was safe, well tolerated and associated with mostly benign side effects. Nausea and diarrhea were the most commonly reported. Though there are no head to head comparisons with other pharmacological agents, it is our opinion that lubiprostone should be tried as a first line pharmacotherapy for women with IBS-C at a dose of 8 μg BID. Thus far, lubiprostone offers a welcome approach to our narrow therapeutic armamentarium. Further understanding of its mechanism of action may provide additional insight into the pathophysiology of IBS-C.

Lubiprostone for the treatment of adults with constipation and irritable bowel syndrome

Chronic constipation and IBS-C are two of the most common functional bowel disorders encountered by primary care providers and gastroenterologists, affecting up to 27% of the population in Western countries [1-4]. The treatment of these disorders is often empiric and most current therapies are indicated for episodic constipation. Over time, most patients become refractory to one or more laxatives. Lubiprostone (Amitiza) has been approved by the US Food and Drug Administration (FDA) for the treatment of chronic-idiopathic constipation [6]. It is an oral bicyclic fatty acid that selectively activates type 2 chloride channels in the apical membrane of the intestinal epithelial cells, hence stimulating chloride secretion, along with passive secretion of sodium and water, inducing peristalsis and laxation, without stimulating gastrointestinal smooth muscle. Several trials have shown it to be effective in the treatment of chronic idiopathic constipation, and recently also IBS-C. It has little systemic absorption and almost free of any serious adverse effects, however, occasionally can cause nausea. Based on the available evidence, it is reasonable to conclude that lubiprostone should be added to the short list of evidence-based pharmacotherapies for chronic constipation and IBS-C. Given the overlap between chronic constipation and IBS-C, clinicians can consider two strategies when deciding on the initial dose of lubiprostone. Based on current product labeling, it is recommended that 8 μg bid be started in patients with IBS-C whereas 24 μg bid be used in those with chronic constipation. Thus far, lubiprostone offers a novel approach to our therapeutic armamentarium, however, there is a need for more drugs with different mechanisms of action, in order to treat constipation that is often multifunctional.

Lubiprostone activates Cl- secretion via cAMP signaling and increases membrane CFTR in the human colon carcinoma cell line, T84

BACKGROUND

Lubiprostone, used clinically (b.i.d.) to treat constipation, has been reported to increase transepithelial Cl(-) transport in T84 cells by activating ClC-2 channels.

AIM

To identify the underlying signaling pathway, we explored the effects of short-term and overnight lubiprostone treatment on second messenger signaling and Cl(-) transport.

METHODS

Cl(-) transport was assessed either as I(sc) across T84 monolayers grown on Transwells and mounted in Ussing chambers or by the iodide efflux assay. [cAMP](i) was measured by enzyme immunoassay, and [Ca(2+)](i) by Fluo-3 fluorescence. Quantitation of apical cell surface CFTR protein levels was assessed by Western blotting and biotinylation with the EZ-Link Sulfo-NHS-LC-LC-Biotin. ClC-2 mRNA level was studied by RT-PCR.

RESULTS

Lubiprostone and the cAMP stimulator, forskolin, caused comparable and maximal increases of I(sc) in T84 cells. The I(sc) effects of lubiprostone and forskolin were each suppressed if the tissue had previously been treated with the other agent. These responses were unaltered even if the monolayers were treated with lubiprostone overnight. Lubiprostone-induced increases in iodide efflux were ~80% of those obtained with forskolin. Lubiprostone increased [cAMP](i). H89, bumetanide, or CFTR(inh)-172 greatly attenuated lubiprostone-stimulated Cl(-) secretion, whereas the ClC-2 inhibitor CdCl(2) did not. Compared to controls, FSK-treatment increased membrane-associated CFTR by 1.9 fold, and lubiprostone caused a 2.6-fold increase in apical membrane CFTR as seen by immunoblotting following cell surface biotinylation.

CONCLUSIONS

Lubiprostone activates Cl(-) secretion in T84 cells via cAMP, protein kinase A, and by increasing apical membrane CFTR protein.

Lubiprostone: evaluation of the newest medication for the treatment of adult women with constipation-predominant irritable bowel syndrome

Irritable bowel syndrome (IBS) is a chronic disorder that affects primarily female patients and is thought also to afflict approximately 7%-10% of the population of the Western World. Although bowel habits may change over the course of years, patients with IBS are characterized according to their predominant bowel habit, constipation (IBS-C), diarrhea (IBS-D), or mixed type (IBS-M), and treatments are focused toward the predominant symptom. Current treatments for IBS-C have included fiber, antispasmodics, osmotic and stimulant laxatives, and the now severely limited 5-HT(4) agonist tegaserod. No one agent has been universally successful in the treatment of this bothersome syndrome and the search for new agents continues. Lubiprostone (Amitiza(®)), a novel compound, is a member of a new class of agents called prostones and was approved for the treatment of chronic idiopathic constipation in 2006 at a dose of 24 μg twice daily and then in 2008 for the treatment of IBS-C in women only at a dose of 8 μg twice daily. Its purported mechanism is as a type 2 chloride channel activator, but recent evidence suggests that it may also work at the cystic fibrosis transport receptor. This article will compare the newly proposed mechanism of action of this compound to the purported mechanism and review the structure, pharmacology, safety, efficacy, and tolerability of this new therapeutic option. Clinical trial data leading to the approval of this agent for the treatment of IBS-C and the gender-based understanding of IBS, as well as this agent's place among existing and emerging therapies, will be examined.

Lubiprostone ameliorates the cystic fibrosis mouse intestinal phenotype

Background

Cystic fibrosis (CF) is caused by mutations in the CFTR gene that impair the function of CFTR, a cAMP-regulated anion channel. In the small intestine loss of CFTR function creates a dehydrated, acidic luminal environment which is believed to cause an accumulation of mucus, a phenotype characteristic of CF. CF mice have small intestinal bacterial overgrowth, an altered innate immune response, and impaired intestinal transit. We investigated whether lubiprostone, which can activate the CLC2 Cl^- channel, would improve the intestinal phenotype in CF mice.

Methods

Cftr^tm1UNC (CF) and wildtype (WT) littermate mice on the C57BL/6J background were used. Lubiprostone (10 μg/kg-day) was administered by gavage for two weeks. Mucus accumulation was estimated from crypt lumen widths in periodic acid-Schiff base, Alcian blue stained sections. Luminal bacterial load was measured by qPCR for the bacterial 16S gene. Gastric emptying and small intestinal transit in fasted mice were assessed using gavaged rhodamine dextran. Gene expression was evaluated by Affymetrix Mouse430 2.0 microarray and qRT-PCR.

Results

Crypt width in control CF mice was 700% that of WT mice (P < 0.001). Lubiprostone did not affect WT crypt width but, unexpectedly, increased CF crypt width 22% (P = 0.001). Lubiprostone increased bacterial load in WT mice to 490% of WT control levels (P = 0.008). Conversely, lubiprostone decreased bacterial overgrowth in CF mice by 60% (P = 0.005). Lubiprostone increased gastric emptying at 20 min postgavage in both WT (P < 0.001) and CF mice (P < 0.001). Lubiprostone enhanced small intestinal transit in WT mice (P = 0.024) but not in CF mice (P = 0.377). Among other innate immune markers, expression of mast cell genes was elevated 4-to 40-fold in the CF intestine as compared to WT, and lubiprostone treatment of CF mice decreased expression to WT control levels.

Conclusions

These results indicate that lubiprostone has some benefits for the CF intestinal phenotype, especially on bacterial overgrowth and the innate immune response. The unexpected observation of increased mucus accumulation in the crypts of lubiprostone-treated CF mice suggests the possibility that lubiprostone increases mucus secretion.

Review article: new receptor targets for medical therapy in irritable bowel syndrome

BACKGROUND

Despite setbacks to the approval of new medications for the treatment of irritable bowel syndrome, interim guidelines on endpoints for irritable bowel syndrome (IBS) trials have enhanced interest as new targets for medical therapy are proposed based on novel mechanisms or chemical entities.

AIMS

To review the approved lubiprostone, two targets that are not meeting expectations (tachykinins and corticotrophin-releasing hormone), the efficacy and safety of new 5-HT(4) agonists, intestinal secretagogues (chloride channel activators, and guanylate cyclase-C agonists), bile acid modulation, anti-inflammatory agents and visceral analgesics.

METHODS

Review of selected articles based on PubMed search and clinically relevant information on mechanism of action, safety, pharmacodynamics and efficacy.

RESULTS

The spectrum of peripheral targets of medical therapy addresses chiefly the bowel dysfunction of IBS and these effects are associated with pain relief. The pivotal mechanisms responsible for the abdominal pain or visceral sensation in IBS are unknown. The new 5-HT(4) agonists are more specific than older agents and show cardiovascular safety to date. Secretory agents have high specificity, low bioavailability and high efficacy. The potential risks of agents 'borrowed' from other indications (such as hyperlipidaemia, inflammatory bowel disease or somatic pain) deserve further study.

CONCLUSIONS

There is reason for optimism in medical treatment of IBS with a spectrum of agents to treat bowel dysfunction. However, visceral analgesic treatments are still suboptimal.

Lubiprostone: chronic constipation and irritable bowel syndrome with constipation

Lubiprostone is a bicyclic fatty acid metabolite analogue of prostaglandin E1. The FDA has approved lubiprostone for the treatment of chronic constipation in men and women and the treatment of women with irritable bowel syndrome with constipation (IBS-C). Lubiprostone specifically activates type-2-chloride channels on the apical membrane of epithelial cells. Lubiprostone acts locally within the intestinal tract, is rapidly metabolized and has very low systemic bioavailability. Animal studies have demonstrated that lubiprostone increases gastrointestinal fluid secretion in a dose-dependent manner. Clinical studies performed in men and women with chronic constipation using 24 microg of lubiprostone twice-daily demonstrated objective improvement in stool frequency and consistency, as well as symptoms of straining and incomplete evacuation. A multi-center study of patients with IBS-C found that 8 microg of lubiprostone twice-daily improved both global and individual symptoms of irritable bowel syndrome. Lubiprostone is generally well tolerated and serious adverse events are rare. The most common reported side effects are nausea, headache and diarrhea. This monograph provides a brief overview on chloride channel function in the gastrointestinal tract, describes the structure, function, and pharmacokinetics of lubiprostone, and discusses the safety and efficacy of this new medication for the treatment of chronic constipation and IBS-C.

Lubiprostone: Clinical applications beyond constipation

In comparison to polyethylene glycol, lubiprostone offers other advantages and is increasingly being used as an adjunctive agent in diagnostic as well as management strategies not only in gastroenterology, but in other fields. For instance, lubiprostone exerts beneficial effects in cystic fibrosis tissues. It augmernts the chloride secretion in these cells by activating non-cystic fibrosis transmembrane regulator (CFTR) secretion of chloride by afflicted respiratory epithelia. Lubiprostone also seems to improve visualization of the gastrointestinal tract during procedures such as colonoscopy. This is especially true if the lubiprostone is administered prior to bowel cleansing with agents such as polyethylene glycol electrolyte (PEG-E). Lubiprostone also enhances and stimulates contraction in colonic as well as gastric muscles and may thus further contribute as a prokinetic agent. Besides these effects, lubiprostone also causes hyperpolarization in other tissues such as uterine muscle cells. This may prove to be of significant clinical benefit in the management of uterine pathologies in the near future.

Lubiprostone stimulates secretion from tracheal submucosal glands of sheep, pigs, and humans

Lubiprostone, a putative ClC-2 chloride channel opener, has been investigated for its effects on airway epithelia (tracheas). Lubiprostone is shown to increase submucosal gland secretion in pigs, sheep, and humans and to increase short-circuit current (SCC) in the surface epithelium of pigs and sheep. Use of appropriate blocking agents and ion-substitution experiments shows anion secretion is the driving force for fluid formation in both glands and surface epithelium. From SCC concentration-response relations, it is shown that for apical lubiprostone K(d) = 10.5 nM with a Hill slope of 1.08, suggesting a single type of binding site and, from the speed of the response, close to the apical surface, confirmed the rapid blockade by Cd ions. Responses to lubiprostone were reversible and repeatable, responses being significantly larger with ventral compared with dorsal epithelium. Submucosal gland secretion rates following basolateral lubiprostone were, respectively, 0.2, 0.5, and 0.8 nl gl(-1) min(-1) in humans, sheep, and pigs. These rates dwarf any contribution surface secretion adds to the accumulation of surface liquid under the influence of lubiprostone. Lubiprostone stimulated gland secretion in two out of four human cystic fibrosis (CF) tissues and in two of three disease controls, chronic obstructive pulmonary disease and idiopathic pulmonary fibrosis (COPD/IPF), but in neither type of tissue was the increase significant. Lubiprostone was able to increase gland secretion rates in normal human tissue in the continuing presence of a high forskolin concentration. Lubiprostone had no spasmogenic activity on trachealis muscle, making it a potential agent for increasing airway secretion that may have therapeutic utility.

Effect of a chloride channel activator, lubiprostone, on colonic sensory and motor functions in healthy subjects

Lubiprostone, a bicyclic fatty acid chloride channel activator, is efficacious in treatment of chronic constipation and constipation-predominant irritable bowel syndrome. The study aim was to compare effects of lubiprostone and placebo on colonic sensory and motor functions in humans. In double-blind, randomized fashion, 60 healthy adults received three oral doses of placebo or 24 microg lubiprostone per day in a parallel-group, placebo-controlled trial. A barostat-manometry tube was placed in the left colon by flexible sigmoidoscopy and fluoroscopy. We measured treatment effects on colonic sensation and motility with validated methods, with the following end points: colonic compliance, fasting and postprandial tone and motility indexes, pain thresholds, and sensory ratings to distensions. Among participants receiving lubiprostone or placebo, 26 of 30 and 28 of 30, respectively, completed the study. There were no overall effects of lubiprostone on compliance, fasting tone, motility indexes, or sensation. However, there was a treatment-by-sex interaction effect for compliance (P = 0.02), with lubiprostone inducing decreased fasting compliance in women (P = 0.06) and an overall decreased colonic tone contraction after a standard meal relative to fasting tone (P = 0.014), with greater effect in women (P < 0.01). Numerical differences of first sensation and pain thresholds (P = 0.11 in women) in the two groups were not significant. We concluded that oral lubiprostone 24 microg does not increase colonic motor function. The findings of decreased colonic compliance and decreased postprandial colonic tone in women suggest that motor effects are unlikely to cause accelerated colonic transit with lubiprostone, although they may facilitate laxation. Effects of lubiprostone on sensitivity deserve further study.

Lubiprostone for constipation and irritable bowel syndrome with constipation

Chronic constipation and irritable bowel syndrome are heterogeneous disorders characterized by altered bowel habits, abdominal discomfort and/or difficult defecation. These conditions have a significant impact on patients' quality of life, as well as on the US economy, both in terms of healthcare costs and lost productivity. Treatment typically begins with lifestyle changes, increased fiber intake and osmotic and stimulant laxative intake. However, treatments for constipation vary in terms of their efficacy and safety. Furthermore, surveys of physicians and patients have revealed a strong desire for improved therapeutic options. Lubiprostone is a synthetic bicyclic fatty acid that is gut selective and stimulates type 2 chloride channels, resulting in increased chloride, sodium and water secretion into the lumen. The increased fluid secretion causes luminal distension, secondary peristalsis and laxation. Randomized Phase III trials have shown that lubiprostone is efficacious in the treatment of chronic idiopathic constipation and irritable bowel syndrome with constipation. The US FDA has approved lubiprostone at a dose of 24 microg twice daily for the treatment of chronic idiopathic constipation in adults, and at a dose of 8 microg twice daily for irritable bowel syndrome with constipation in adult women. Nausea, diarrhea and headaches are the most commonly reported side effects. In long-term studies, lubiprostone appears to be safe.