Review article: serotonin receptors and transporters -- roles in normal and abnormal gastrointestinal motility

The role of pharmacogenetics in nonmalignant gastrointestinal diseases

Genetic variation influences the absorption and efflux of drugs in the intestine, the metabolism of drugs in the liver and the effects of these drugs on their target proteins. Indeed, variations in genes whose products have a role in the pathophysiology of nonmalignant gastrointestinal diseases, such as IBD, have been shown to affect the response of patients to therapy. This Review provides an overview of pharmacogenetics in the management of nonmalignant gastrointestinal diseases on the basis of data from clinical trials. Genetic variants that have the greatest effect on the management of patients with IBD involve the metabolism of thiopurines. Variation in drug metabolism by cytochrome P450 enzymes also requires attention so as to avoid drug interactions in patients receiving tricyclic antidepressants and PPIs. Few genotyping tests are currently used in the clinical management of patients with nonmalignant gastrointestinal diseases, owing to a lack of data from clinical trials showing their effectiveness in predicting nonresponse or adverse outcomes. However, pharmacogenetics could have a beneficial role in enabling pharmacotherapy for nonmalignant gastrointestinal diseases to be targeted to the individual patient.

Smoking cessation pharmacogenetics: analysis of varenicline and bupropion in placebo-controlled clinical trials

Despite effective therapies for smoking cessation, most smokers find quitting difficult and most successful quitters relapse. Considerable evidence supports a genetic risk for nicotine dependence; however, less is known about the pharmacogenetics of smoking cessation. In the first pharmacogenetic investigation of the efficacy of varenicline and bupropion, we examined whether genes important in the pharmacodynamics and pharmacokinetics of these drugs and nicotine predict medication efficacy and adverse events. Subjects participated in randomized, double-blind, placebo-controlled smoking cessation clinical trials, comparing varenicline, a nicotinic acetylcholine receptor (nAChR) partial agonist, with bupropion, a norepinephrine/dopamine reuptake inhibitor, and placebo. Primary analysis included 1175 smokers of European ancestry, and 785 single nucleotide polymorphisms from 24 genes, representing 254 linkage disequilibrium (LD) bins (genes included nAChR subunits, additional varenicline-specific genes, and genes involved in nicotine or bupropion metabolism). For varenicline, continuous abstinence (weeks 9-12) was associated with multiple nAChR subunit genes (including CHRNB2, CHRNA5, and CHRNA4) (OR=1.76; 95% CI: 1.23-2.52) (p<0.005); for bupropion, abstinence was associated with CYP2B6 (OR=1.78; 95% CI: 1.27-2.50) (p<0.001). Incidence of nausea was associated with several nAChR subunit genes (OR=0.50; 95% CI: 0.36-0.70) (p<0.0001) and time to relapse after quitting was associated with HTR3B (HR=1.97; 95% CI: 1.45-2.68) (p<0.0001). These data provide evidence for multiple genetic loci contributing to smoking cessation and therapeutic response. Different loci are associated with varenicline vs bupropion response, suggesting that additional research may identify clinically useful markers to guide treatment decisions.

Serotonin-immunoreactive neurons and mast cells in the mouse esophagus suggest involvement of serotonin in both motility control and neuroimmune interactions

BACKGROUND

Serotonin is a major transmitter in the gastrointestinal tract, but little is known about the serotonergic system in the esophagus.

METHODS

The aim of this study was to use multilabel immunofluorescence to characterize serotonin-positive nerve cell bodies and fibers and their relationship with other neuronal and non-neuronal elements in the mouse esophagus. Antibodies against serotonin, vesicular acetylcholine transporter (VAChT), choline acetyltransferase (ChAT), protein gene product 9.5 (PGP 9.5), and α-bungarotoxin (α-BT), were used.

KEY RESULTS

Serotonin-containing perikarya represented ∼10% of all PGP 9.5-positive myenteric neurons. Serotonin-positive varicose nerve fibers were found in the lamina muscularis mucosae and present on ∼13% of α-BT-labeled motor endplates in addition to VAChT-immunoreactive motor terminals. As ChAT-positive neurons of the compact formation of the nucleus ambiguus were negative for serotonin, serotonin-positive varicosities on motor endplates are presumed to be of enteric origin. On the other hand, cholinergic ambiguus neurons were densely supplied with serotonin-positive varicosities. The tela submucosa and tunica adventitia contained large numbers of serotonin-positive mast cells, a few of which were in close association with serotonin-positive nerve fibers.

CONCLUSIONS & INFERENCES

The mouse esophagus is endowed with a rich serotonin-positive intrinsic innervation, including enteric co-innervation of striated muscles. Serotonin may modulate vagal motor innervation of esophageal-striated muscles not only at the central level via projections of the raphe nuclei to the nucleus ambiguus but also at the peripheral level via enteric co-innervation. In addition, mast cells represent a non-neuronal source of serotonin, being involved in neuroimmune processes.

Bladder pain syndrome/interstitial cystitis in twin sisters

PURPOSE

We determined the genetic contribution of and associated factors for bladder pain syndrome using an identical twin model.

MATERIALS AND METHODS

Multiple questionnaires were administered to adult identical twin sister pairs. The O'Leary-Sant Interstitial Cystitis Symptom and Problem Index was administered to identify individuals at risk for bladder pain syndrome. Potential associated factors were modeled against the bladder pain syndrome score with the twin pair as a random effect of the factor on the bladder pain syndrome score. Variables that showed a significant relationship with the bladder pain syndrome score were entered into a multivariable model.

RESULTS

In this study 246 identical twin sister pairs (total 492) participated with a mean age (± SD) of 40.3 ± 17 years. Of these women 45 (9%) were identified as having a moderate or high risk of bladder pain syndrome (index score greater than 13). There were 5 twin sets (2%) in which both twins met the criteria. Correlation of bladder pain syndrome scores within twin pairs was estimated at 0.35, suggesting a genetic contribution to bladder pain syndrome. Multivariable analysis revealed that increasing age (estimate 0.46 [95% CI 0.2, 0.7]), irritable bowel syndrome (1.8 [0.6, 3.7]), physical abuse (2.5 [0.5, 4.1]), frequent headaches (1.6 [0.6, 2.8]), multiple drug allergies (1.5 [0.5, 2.7]) and number of self-reported urinary tract infections in the last year (8.2 [4.7, 10.9]) were significantly associated with bladder pain syndrome.

CONCLUSIONS

Bladder pain syndrome scores within twin pairs were moderately correlated, implying some genetic component. Increasing age, irritable bowel syndrome, frequent headaches, drug allergies, self-reported urinary tract infections and physical abuse were factors associated with higher bladder pain syndrome scores.

Modulation of human serotonin transporter expression by 5-HTTLPR in colon cells

Serotonin (5-HT) is a monoamine neurotransmitter and plays important roles in several of the human body's systems. Known as a primary target for psychoactive drug development, the 5-HT transporter (5-HTT, SERT) plays a critical role in the regulation of serotonergic function by reuptaking 5-HT. The allelic variation of 5-HTT expression is caused by functional gene promoter polymorphism with two principal variant alleles, 5-HTT gene-linked polymorphic region (5-HTTLPR). It has been demonstrated that 5-HTTLPR is associated with numerous neuropsychiatric disorders. The functional roles of 5-HTTLPR have been reported in human choriocarcinoma (JAR), lymphoblast and raphe cells. To date, the significance of 5-HTTLPR in gastrointestinal tract-derived cells has never been elucidated. Thus, the impact of 5-HTTLPR on 5-HTT transcription was studied in SW480 human colon carcinoma cells, which were shown to express 5-HTT. We found 42-bp fragment in long (L) allele as compared to short (S) allele, and this allelic difference resulted in 2-fold higher transcriptional efficiency of L allele (P < 0.05) as demonstrated using a functional reporter gene assay. Nevertheless, the transcriptional effect of estrogen and glucocorticoid on 5-HTT expression via 5-HTTLPR was not found in this cell line. Our study was the first to demonstrate the molecular role of this allelic variation in gastrointestinal tract cells.

Effect of baclofen on liquid and solid gastric emptying in rats

CONTEXT

Gamma-aminobutyric acid (GABA) is a potent inhibitory neurotransmitter. There is evidence that GABA(B) receptors located in the dorsal complex and in afferent fibers of the vagus nerve participate in the control of gastrointestinal motility.

OBJECTIVE

To assess the intracerebroventricularly (ICV) and intravenously (IV) effect of baclofen, a GABA(B) receptor agonist, on liquid and solid gastric emptying in rats.

METHODS

Adult male Wistar rats weighing 250-300 g (n = 6-8 animals) were used. Gastric emptying of liquid test meals labeled with phenol red was evaluated by the determination of percent gastric retention (%GR) 10 and 15 min after orogastric administration of saline and 10% glucose meals, respectively. Baclofen was injected ICV (1 and 2 µg/animal) through a tube implanted into the lateral ventricle of the brain and was injected IV (1 and 2 mg/kg) into a tail vein. The gastric emptying of liquid was determined 10 or 30 min after ICV and IV baclofen administration, respectively. The gastric emptying of the solid meal was assessed by the determination of percent gastric retention 2 h after the beginning of the ingestion of the habitual ratio by the animal, consumed over a period of 30 min. Baclofen was administered ICV (1 and 2 µg/animal) or IV (1 and 2 mg/kg) immediately after the end of the ingestion of the solid meal. The control groups received vehicle (sterile saline solution) ICV or IV.

RESULTS

The group of animals receiving baclofen ICV (2 mg/animal) presented a significantly lower (P<0.05, Tukey test) %GR (mean ± SEM) of the saline (18.1 ± 2.5%) compared to control (33.2 ± 2.2%). In the group receiving the drug IV, the gastric retention of the same test meal did not differ from control. ICV and IV administration of baclofen had no effect on the gastric emptying of the 10% glucose solution compared to control. ICV administration of 1 or 2 mg baclofen/animal significantly increased the gastric retention of the solid test meal (57.9 ± 6.5% and 66.6 ± 6.3%, respectively) compared to control (35.1 ± 4.4%). The same phenomenon was observed only with the IV dose of 2 mg/kg (71.9 ± 2.6%) compared to control (52.7 ± 2.8%).

CONCLUSION

Baclofen administered: 1. ICV (2 µg/animal), but not IV, increased gastric emptying of a non-caloric isotonic liquid test meal (saline); 2. when administered ICV or IV, it had no effect of gastric emptying of a 10% glucose solution; 3) when administered ICV (1 and 2 mg/animal) and IV (2 mg/kg) it delayed the gastric emptying of the solid meal.

Serotonin receptor type 3 antagonists improve obesity-associated fatty liver disease in mice

Obesity is a major cause for nonalcoholic fatty liver disease (NAFLD). Previous studies suggested that alterations in intestinal motility and permeability contribute to the development of NAFLD. Serotonin and serotonin receptor type 3 (5-HT(3)R) are key factors in the regulation of intestinal motility and permeability. Therefore, we studied the effect of the 5-HT(3)R antagonists tropisetron and palonosetron on the development of NAFLD in leptin-deficient obese mice. Four-week-old ob/ob mice and lean controls were treated for 6 weeks orally with tropisetron or palonosetron at 0.2 mg/kg per day. We determined markers of liver damage and inflammation, portal endotoxin levels, and duodenal concentrations of serotonin, serotonin-reuptake transporter (SERT), occludin, and claudin-1. Tropisetron treatment significantly reduced liver fat content (-29%), liver inflammation (-56%), and liver cell necrosis (-59%) in ob/ob mice. The beneficial effects of tropisetron were accompanied by a decrease in plasma alanine aminotransferase and portal vein plasma endotoxin levels, an attenuation of enhanced MyD88 and tumor necrosis factor-α mRNA expression in the liver, and an increase of tight junction proteins in the duodenum. Tropisetron treatment also caused a reduction of elevated serotonin levels and an increase of SERT in the duodenum of ob/ob mice. Palonosetron had similar effects as tropisetron with regard to the reduction of liver fat and other parameters. Tropisetron and palonosetron are effective in attenuating NAFLD in a genetic mouse model of obesity. The effect involves the intestinal nervous system, resulting in a reduction of endotoxin influx into the liver and subsequently of liver inflammation and fat accumulation.

Neostigmine-induced contraction and nitric oxide-induced relaxation of isolated ileum from STZ diabetic guinea pigs

Both delayed gastrointestinal transit and autonomic neuropathy have been documented in patients with diabetes mellitus. The mechanism of neostigmine, an agent that mimics release of acetylcholine from autonomic neurons by prokinetic agents, to contract smooth muscle, despite dysfunctional enteric neural pathways, was determined using isolated ilea from STZ-treated and control guinea pigs. Both bethanechol- and neostigmine-induced contractions were stronger in diabetic ileum. Bethanechol-induced contractions of control but not diabetic ileum were increased by low dose scopolamine suggesting reduced activation of presynaptic muscarinic autoreceptors in diabetic ileum. The muscarinic receptor antagonist 4-DAMP strongly, but the nicotinic receptor antagonist hexamethonium only weakly, reduced neostigmine-induced contractions of control and diabetic ilea. The amount of acetylcholine, inferred from tissue choline content, was increased in diabetic ileum. Nicotinic neural and noncholinergic postjunctional smooth muscle receptors contributed more strongly to neostigmine-induced contractions in diabetic than control ileum. Relaxation of diabetic ileum by exogenous nitric oxide generated from sodium nitroprusside was comparable to control ileum, but smooth muscle relaxation by l-arginine using neuronal nitric oxide synthase to generate nitric oxide was weaker in diabetic ileum with evidence for a role for inducible nitric oxide synthase. Despite autonomic neuropathy, neostigmine strongly contracted ileum from diabetic animals but by a different mechanism including stronger activation of postjunctional muscarinic receptors, greater synaptic acetylcholine, stronger activation of noncholinergic excitatory pathways, and weaker activation of inhibitory pathways. A selective medication targeting a specific neural pathway may more effectively treat disordered gastrointestinal transit in patients with diabetes mellitus.

Role of serotonin in the pathogenesis of chronic constipation

Serotonin (5-hydroxytryptamine, 5-HT) is a monoamine neurotransmitter of profound importance in the enteric nervous system. About 95% of the serotonin in the body is found in the GI tract; 90% is in enterochromaffin cells (EC cells) and the remaining 10% in enteric neurons. It plays a key role in the initiation of peristaltic and secretory reflexes and in the modulation of visceral sensations. There are many reports of serotonin in functional bowel disorders, and most of them mainly focus on irritable bowel syndrome (IBS), but serotonin in constipation is rarely reported. Chronic constipation (CC) is a commonly encountered disease, especially in elderly patients. The role of 5-HT plays in CC has been emphasized, and its effects in physiology, pathology and treatment of CC are continuously being resolved. This article is a review of the progress in understanding the role of 5-HT in the pathogenesis and treatment of chronic constipation.

Prucalopride: the evidence for its use in the treatment of chronic constipation

Introduction:

Chronic constipation is a common condition that is difficult to treat. Existing options for the treatment of patients with different subgroups of constipation are limited. A new efficacious and safe drug is needed to limit the frequently observed adverse effects induced by laxatives, to improve general wellbeing and quality of life, and to provide an alternative for enemas or even resectional surgery in patients in whom stimulant laxatives cause disabling adverse effects or fail to increase bowel movement frequency.

Aims:

The purpose of this article is to assess the current evidence supporting the use of the selective and high affinity serotonin-4 (5-HT₄) receptor agonist prucalopride in the management of chronic constipation.

Evidence review:

There are now convincing data from phase II and multicenter phase III randomized, double-blind, placebo-controlled trials that prucalopride treatment results in a clinically meaningful increase in the number of spontaneous complete bowel movements, a reduction of perceived severity of symptoms and improved disease-related quality of life in a significant proportion of patients. There is a rapid onset of the effect and the improvement is maintained for at least 12 weeks.

Prucalopride in a dose of up to 4 mg per day appeared generally well tolerated and devoid of serious cardiac events. Adverse events, most frequently headache and nausea, are usually mild or moderate and occur mainly during the first days of treatment. Prucalopride should be used with prudence and with careful assessment of the benefit-risk ratio until more clinical and electrophysiologic data become available, because relatively few patients have been exposed to the drug for long periods of time.

Place in therapy:

Prucalopride 1–2 mg once daily may be given to patients suffering from chronic constipation for whom laxatives do not provide adequate relief of their symptoms. Patients with severe constipation and slow transit, who frequently develop tolerance to stimulant laxatives, are also eligible for prucalopride treatment.

Serotonin receptor modulators in the treatment of irritable bowel syndrome

The aim of this article is to review the pathophysiology and clinical role of serotonin receptor modulators used in the treatment of irritable bowel syndrome. Serotonin is an important monoamine neurotransmitter that plays a key role in the initiation of peristaltic and secretory refl exes, and in modulation of visceral sensations. Several serotonin receptor subtypes have been characterized, of which 5HT3, 5HT4, and 5HT1b are the most important for GI function. 5HT4 agonists (eg, tegaserod) potentiate peristalsis initiated by 5HT1 receptor stimulation. 5HT4 agonists are therefore useful in constipation predominant form of IBS and in chronic constipation. 5HT3 antagonists (Alosetron and Cilansetron) prevent the activation of 5HT3 receptors on extrinsic afferent neurons and can decrease the visceral pain associated with IBS. These agents also retard small intestinal and colonic transit, and are therefore useful in diarrhea-predominant IBS. Tegaserod has been demonstrated in several randomized, placebo controlled trials to relieve global IBS symptoms as well as individual symptoms of abdominal discomfort, number of bowel movements and stool consistency. Several randomized, controlled trials have shown that alosetron relieves pain, improves bowel function, and provides global symptom improvement in women with diarrhea-predominant irritable bowel syndrome. However, ischemic colitis and severe complications of constipation have been major concerns leading to voluntary withdrawal of Alosetron from the market followed by remarketing with a comprehensive risk management program.

Gut feelings: the emerging biology of gut-brain communication

The concept that the gut and the brain are closely connected, and that this interaction plays an important part not only in gastrointestinal function but also in certain feeling states and in intuitive decision making, is deeply rooted in our language. Recent neurobiological insights into this gut-brain crosstalk have revealed a complex, bidirectional communication system that not only ensures the proper maintenance of gastrointestinal homeostasis and digestion but is likely to have multiple effects on affect, motivation and higher cognitive functions, including intuitive decision making. Moreover, disturbances of this system have been implicated in a wide range of disorders, including functional and inflammatory gastrointestinal disorders, obesity and eating disorders.

Intestinal glucose-induced calcium-calmodulin kinase signaling in the gut-brain axis in awake rats

BACKGROUND

Lumenal glucose initiates changes in gastrointestinal (GI) function, including inhibition of gastric emptying, stimulation of pancreatic exocrine and endocrine secretion, and intestinal fluid secretion. Glucose stimulates the release of GI hormones and 5-hydroxytryptamine (5-HT), and activates intrinsic and extrinsic neuronal pathways to initiate changes in GI function. The precise mechanisms involved in luminal glucose-sensing are not clear; studying gut endocrine cells is difficult due to their sparse and irregular localization within the epithelium.

METHODS

Here we show a technique to determine activation of gut epithelial cells and the gut-brain pathway in vivo in rats using immunohistochemical detection of the activated, phosphorylated, form of calcium-calmodulin kinase II (pCaMKII).

KEY RESULTS

Perfusion of the gut with glucose (60 mg) increased pCaMKII immunoreactivity in 5-HT-expressing enterochromaffin (EC) cells, cytokeratin-18 immunopositive brush cells, but not in enterocytes or cholecystokinin-expressing cells. Lumenal glucose increased pCaMKII in neurons in the myenteric plexus and nodose ganglion, nucleus of the solitary tract, dorsal motor nucleus of the vagus and the arcuate nucleus. pCaMKII expression in neurons, but not in EC cells, was significantly attenuated by pretreatment with the 5-HT(3) R antagonist ondansetron. Deoxynojirimycin, a selective agonist for the putative glucose sensor, sodium-glucose cotransporter-3 (SGLT-3), mimicked the effects of glucose with increased pCaMKII in ECs and neurons; galactose had no effect.

CONCLUSIONS & INFERENCES

The data suggest that native EC cells in situ respond to glucose, possibly via SGLT-3, to activate intrinsic and extrinsic neurons and thereby regulate GI function.

Do the Micronutrients Zinc and Magnesium Play a Role in Adult Depression?

Depression is a widespread disorder that affects more than 120 million people worldwide. The unsatisfactory clinical efficacy and adverse effects of antidepressant medication have prompted the search for novel treatments. Micronutrient deficiencies may play a role in the development of depression, and recent research studies have explored the use of micronutrient supplementation as an adjunct to the pharmacotherapy of this psychiatric illness. This article provides a review of the empirical evidence linking zinc and magnesium deficiency and depression, discusses possible mechanisms of action in the psychopathology and therapy of depression, and explores the nursing and registered dietitian implications of these findings.

5-hydroxytryptamine generates tonic inward currents on pacemaker activity of interstitial cells of cajal from mouse small intestine

In this study we determined whether or not 5-hydroxytryptamine (5-HT) has an effect on the pacemaker activities of interstitial cells of Cajal (ICC) from the mouse small intestine. The actions of 5-HT on pacemaker activities were investigated using a whole-cell patch-clamp technique, intracellular Ca(2+) ([Ca(2+)](i)) analysis, and RT-PCR in ICC. Exogenously-treated 5-HT showed tonic inward currents on pacemaker currents in ICC under the voltage-clamp mode in a dose-dependent manner. Based on RT-PCR results, we found the existence of 5-HT(2B, 3, 4, and 7) receptors in ICC. However, SDZ 205557 (a 5-HT(4) receptor antagonist), SB 269970 (a 5-HT7 receptor antagonist), 3-tropanylindole - 3 - carboxylate methiodide (3-TCM; a 5-HT(3) antagonist) blocked the 5-HT-induced action on pacemaker activity, but not SB 204741 (a 5-HT(2B) receptor antagonist). Based on [Ca(2+)](i) analysis, we found that 5-HT increased the intensity of [Ca(2+)](i). The treatment of PD 98059 or JNK II inhibitor blocked the 5-HT-induced action on pacemaker activity of ICC, but not SB 203580. In summary, these results suggest that 5-HT can modulate pacemaker activity through 5-HT(3, 4, and 7) receptors via [Ca(2+)](i) mobilization and regulation of mitogen-activated protein kinases.

Colocalization and regulated physical association of presynaptic serotonin transporters with A₃ adenosine receptors

Activation of A₃ adenosine receptors (A₃ARs) rapidly enhances the activity of antidepressant-sensitive serotonin (5-HT) transporters (SERTs) in vitro, ex vivo, and in vivo. A₃AR agonist stimulation of SERT activity is lost in A₃AR knockout mice. A₃AR-stimulated SERT activity is mediated by protein kinase G1 (PKGI)- and p38 mitogen-activated protein kinase (MAPK)-linked pathways that support, respectively, enhanced SERT surface expression and catalytic activation. The mechanisms by which A₃ARs target SERTs among other potential effectors is unknown. Here we present evidence that A₃ARs are coexpressed with SERT in midbrain serotonergic neurons and form a physical complex in A₃AR/hSERT cotransfected cells. Treatment of A₃AR/SERT-cotransfected Chinese hamster ovary cells with the A₃AR agonist N⁶-(3-iodobenzyl)-N-methyl-5'-carbamoyladenosine (1 μM, 10 min), conditions previously reported to increase SERT surface expression and 5-HT uptake activity, enhanced the abundance of A₃AR/SERT complexes in a PKGI-dependent manner. Cotransfection of SERT with L90V-A₃AR, a hyperfunctional coding variant identified in subjects with autism spectrum disorder, resulted in a prolonged recovery of receptor/transporter complexes after A₃AR activation. Because PKGI and nitric-oxide synthetase are required for A₃AR stimulation of SERT activity, and proteins PKGI and NOS both form complexes with SERT, our findings suggest a mechanism by which signaling pathways coordinating A₃AR signaling to SERT can be spatially restricted and regulated, as well as compromised by neuropsychiatric disorders.

Therapeutics of 5-HT3 receptor antagonists: current uses and future directions

The 5-Hydroxytryptamine3 (5-HT3) receptor is a member of the cys-loop family of ligand gated ion channels, of which the nicotinic acetylcholine receptor is the prototype. All other 5-HT receptors identified to date are metabotropic receptors. The 5-HT3 receptor is present in the central and peripheral nervous systems, as well as a number of non-nervous tissues. As an ion channel that is permeable to the cations, Na(+), K(+), and Ca(2+), the 5-HT3 receptor mediates fast depolarizing responses in pre- and post-synaptic neurons. As such, 5-HT3 receptor antagonists that are used clinically block afferent and efferent synaptic transmission. The most well established physiological roles of the 5-HT3 receptor are to coordinate emesis and regulate gastrointestinal motility. Currently marketed 5-HT3 receptor antagonists are indicated for the treatment of chemotherapy, radiation, and anesthesia-induced nausea and vomiting, as well as irritable bowel syndrome. Other therapeutic uses that have been explored include pain and drug addiction. The 5-HT3 receptor is one of a number of receptors that play a role in mediating nausea and vomiting, and as such, 5-HT3 receptor antagonists demonstrate the greatest anti-emetic efficacy when administered in combination with other drug classes.

Impaired uptake of serotonin by platelets from patients with irritable bowel syndrome correlates with duodenal immune activation

BACKGROUND & AIMS

Patients with irritable bowel syndrome with diarrhea (IBS-D) have increased mucosal serotonin (5-hydroxytryptamine [5-HT]) availability, possibly because immune activation reduces activity of the 5-HT transporter (SERT). We investigated the relationship between mucosal and platelet SERT and immune activation of the duodenal mucosa in patients with IBS-D.

METHODS

We quantified mucosal intraepithelial lymphocytes (IELs), mast cells, and enterochromaffin cells in blood samples, measured levels of SERT messenger RNA (mRNA) in mucosal samples, and assessed platelet uptake of 5-HT and platelet membrane binding of (3)H-paroxetine in samples from 29 healthy volunteers (HVs), 20 patients with IBS-D, and 20 untreated patients with celiac disease.

RESULTS

Patients with IBS-D or celiac disease had increased numbers of IELs and mast cells compared with HVs (both P < .001). Levels of SERT mRNA were reduced in the mucosa of patients with IBS-D or celiac disease and were inversely correlated with numbers of IELs (r = -0.72, P < .0001). Uptake of 5-HT by platelets from patients with IBS-D or celiac disease was reduced (mean, 17.1 ± 3.5 and 28.3 ± 4.1 nmol·min(-1)·mg(-1), respectively) compared with HVs (50.8 ± 8.0 nmol·min(-1)·mg(-1), P < .01 and P = .05, respectively). Binding of paroxetine to membranes of platelets from patients with IBS-D (median [interquartile range], 226 [92-405] fmol/mg protein) was significantly greater than that from HVs (109 [69-175] fmol/mg protein) and correlated inversely with platelet uptake of 5-HT (r = -0.62, P = .03). Tryptase release from incubated biopsy samples was significantly increased in patients with IBS-D (2.2 [0.42-3.5] vs 0.50 [0.25-0.86] ng·mL(-1)·mg(-1) for HVs; P = .03).

CONCLUSIONS

Platelet SERT is reduced in IBS-D and associated with reduced levels of SERT mRNA and duodenal immune activation.

Serotonin receptor diversity in the human colon: Expression of serotonin type 3 receptor subunits 5-HT3C, 5-HT3D, and 5-HT3E

Since the first description of 5-HT₃ receptors more than 50 years ago, there has been speculation about the molecular basis of their receptor heterogeneity. We have cloned the genes encoding novel 5-HT3 subunits 5-HT3C, 5-HT3D, and 5-HT3E and have shown that these subunits are able to form functional heteromeric receptors when coexpressed with the 5-HT3A subunit. However, whether these subunits are actually expressed in human tissue remained to be confirmed. In the current study, we performed immunocytochemistry to locate the 5-HT3A as well as the 5-HT3C, 5-HT3D, and 5-HT3E subunits within the human colon. Western blot analysis was used to confirm subunit expression, and RT-PCR was employed to detect transcripts encoding 5-HT₃ receptor subunits in microdissected tissue samples. This investigation revealed, for the first time, that 5-HT3C, 5-HT3D, and 5-HT3E subunits are coexpressed with 5-HT3A in cell bodies of myenteric neurons. Furthermore, 5-HT3A and 5-HT3D were found to be expressed in submucosal plexus of the human large intestine. These data provide a strong basis for future studies of the roles that specific 5-HT₃ receptor subtypes play in the function of the enteric and central nervous systems and the contribution that specific 5-HT₃ receptors make to the pathophysiology of gastrointestinal disorders such as irritable bowel syndrome and dyspepsia.

The role of experimental models in developing new treatments for irritable bowel syndrome

Irritable bowel syndrome (IBS) is characterized by chronic, recurrent abdominal pain and altered bowel habits and is currently defined by symptom criteria and the absence of detectable organic disease. The underlying pathophysiology remains incompletely understood. Despite considerable efforts by the scientific community and the pharmaceutical industry to develop novel pharmacological treatments aimed at chronic visceral pain, the traditional approach to identifying and evaluating novel drugs for this target have largely failed to translate into effective IBS treatments. However, several novel drugs aimed at normalizing bowel movements have produced clinical effects, not only on the primary target, but also on pain and discomfort. While some of the commonly used experimental animal models for the pain dimension of IBS have some face and construct validity, the predictive validity of most of the models is either unknown, or has been disappointing. A reverse translational approach is proposed, which is based on identification and characterization of brain endophenotypes in patients, followed by translation of these endophenotypes for pharmacological studies in rodent models.

Influence of acute tryptophan depletion on gastric sensorimotor function in humans

Peripheral serotonin (5-hydrodytryptamine; 5-HT) is involved in the regulation of gastrointestinal motility and sensation, whereas centrally it plays a role in mood regulation. A dysfunctional serotonergic system may provide a plausible link between functional dyspepsia symptoms and its high psychosocial comorbidity such as anxiety and depression. The aim of this study was to evaluate the effect of decreased 5-HT synthesis by acute tryptophan depletion (ATD) on gastric sensorimotor function and nutrient tolerance, anxiety scores, and gastrointestinal mucosal 5-HT concentrations in healthy volunteers. All subjects were studied under a control condition and during ATD. Gastric sensorimotor function and nutrient tolerance were assessed using a barostat (n = 16, mean age 28.8 ± 1.4 yr) and a satiety drinking test (n = 13, mean age 27.3 ± 1.4 yr). Anxiety during the barostat was evaluated using State-Trait Anxiety Inventory (STAI) questionnaire. 5-HT concentrations were measured in fundic and duodenal mucosal biopsies by means of ELISA and immunohistochemistry. ATD significantly decreased plasma tryptophan levels compared with control in every experiment. ATD did not affect gastric sensitivity and compliance but decreased the sensation of nausea during balloon distension (AUC: 17.4 ± 4.3 vs. 11.4 ± 3.4 mm·mmHg, P = 0.030). ATD enhanced the postprandial volume increase (ANOVA, P < 0.05), but this was not accompanied by augmented nutrient tolerance (848 ± 110 vs. 837 ± 99 ml, nonsignificant). ATD had no effect on STAI state anxiety scores. No evidence was found for an effect on the number of enterochromaffin cells, but ATD reduced 5-HT levels in the duodenal mucosa. ATD alters gastric postprandial motor function and distension-induced nausea. These findings confirm involvement of 5-HT in the control of gastric accommodation and sensitivity.

Postnatal development of the serotonin signaling system in the mucosa of the guinea pig ileum

BACKGROUND

Serotonin is an important neurohumoral molecule in the gut but its signaling system is not fully developed in the neonatal gastrointestinal (GI) tract. This study aimed to evaluate the postnatal maturation of serotonin signaling in the small intestine.

METHODS

In vitro amperometry for real-time measurement of serotonin at the mucosal surface, immunoblot, immunohistochemistry and high-performance liquid chromatography (HPLC) were used to examine serotonin handling in ileal segments from guinea pigs of different ages.

KEY RESULTS

Extracellular serotonin levels significantly declined over the first three postnatal weeks, after which the levels increased and reached their maximum at 9 weeks postnatally. Serotonin levels were insensitive to the inhibition of the serotonin transporter (SERT) until the animals reached 3 weeks old. Measurement of serotonin and its metabolite 5-hydroxyindole acetic acid (5-HIAA) in the mucosa revealed that the serotonin turnover was significantly lower in neonates. Immunoblot and immunohistochemistry showed that SERT expression was extremely low in the neonatal period. Serotonin staining in cross-section showed that enterochromaffin (EC) cells were preferentially localized in the crypt region in neonates and the number of EC cells was significantly higher in 9-week-old animals.

CONCLUSIONS & INFERENCES

SERT expression is low in the neonatal intestine and serotonin signaling matures postnatally. Extracellular serotonin levels decrease during the first three neonatal weeks as SERT expression increases. Extracellular serotonin levels increase after 3 weeks (weaning) possibly due to an increase in EC cell numbers. Postnatal maturation of serotonin signaling coincides with dietary changes in the developing guinea pig.

The neurochemistry of human aggression

Various data from scientific research studies conducted over the past three decades suggest that central neurotransmitters play a key role in the modulation of aggression in all mammalian species, including humans. Specific neurotransmitter systems involved in mammalian aggression include serotonin, dopamine, norepinephrine, GABA, and neuropeptides such as vasopressin and oxytocin. Neurotransmitters not only help to execute basic behavioral components but also serve to modulate these preexisting behavioral states by amplifying or reducing their effects. This chapter reviews the currently available data to present a contemporary view of how central neurotransmitters influence the vulnerability for aggressive behavior and/or initiation of aggressive behavior in social situations. Data reviewed in this chapter include emoiric information from neurochemical, pharmaco-challenge, molecular genetic and neuroimaging studies.

Treatment of Nausea and Vomiting During Chemotherapy

Nausea and vomiting are two of the most troubling side effects patients experience during chemotherapy. While newly available treatments have improved our ability to manage nausea and vomiting, anticipatory and delayed nausea and vomiting are still a major problem for patients receiving chemotherapy. Many cancer patients will delay or refuse future chemotherapy treatments and contemplate stopping chemotherapy altogether because of their fear of experiencing further nausea and vomiting. The purpose of this article is to provide an overview of the patho-psychophysiology of chemotherapy-induced nausea and vomiting and the recommended guidelines for treatment.

Anesthetic Routines: The Anesthesiologist's Role in GI Recovery and Postoperative Ileus

All patients undergoing bowel resection experience postoperative ileus, a transient cessation of bowel motility that prevents effective transit of intestinal contents or tolerance of oral intake, to varying degrees. An anesthesiologist plays a critical role, not only in the initiation of surgical anesthesia, but also with the selection and transition to effective postoperative analgesia regimens. Attempts to reduce the duration of postoperative ileus have prompted the study of various preoperative, perioperative, and postoperative regimens to facilitate gastrointestinal recovery. These include modifiable variables such as epidural anesthesia and analgesia, opioid-sparing anesthesia and analgesia, fluid restriction, colloid versus crystalloid combinations, prokinetic drugs, and use of the new peripherally acting mu-opioid receptor (PAM-OR) antagonists. Review and appropriate adaptation of these multiple modifiable interventions by anesthesiologists and their surgical colleagues will facilitate implementation of a best-practice management routine for bowel resection procedures that will benefit the patient and the healthcare system.

Effects of a 5-HT(3) antagonist, ondansetron, on fasting and postprandial small bowel water content assessed by magnetic resonance imaging

BACKGROUND

5-HT(3) antagonists have been shown to be effective in relieving the symptoms of irritable bowel syndrome with diarrhoea (IBS-D). Using a recently validated magnetic resonance imaging (MRI) method, we have demonstrated reduced fasting small bowel water content (SBWC) in IBS-D associated with accelerated small bowel transit. We hypothesized that slowing of transit with ondansetron would lead to an increase in SBWC by inhibiting fasting motility.

AIM

To assess the effects of ondansetron compared with placebo in healthy volunteers on SBWC and motility in two different groups of subjects, one studied using MRI and another using manometry.

METHODS

Healthy volunteers were given either a placebo or ondansetron on the day prior to and on the study day. Sixteen volunteers underwent baseline fasting and postprandial MRI scans for 270 min. In a second study, a separate group of n = 18 volunteers were intubated and overnight migrating motor complex (MMC) recorded. Baseline MRI scans were carried out after the tube was removed.

RESULTS

Fasting SBWC was markedly increased by ondansetron (P < 0.0007). Ondansetron reduced the overall antroduodenal Motility Index (P < 0.04). The subjects who were intubated had significantly lower fasting SBWC (P < 0.0002) compared with the group of subjects who were not intubated.

CONCLUSIONS

The 5-HT(3) receptor antagonism increased fasting small bowel water. This was associated with reduced fasting antroduodenal Motility Index which may explain the clinical benefit of such drugs.

5-HT(3) receptors: role in disease and target of drugs

Serotonin type 3 (5-HT(3)) receptors are pentameric ion channels belonging to the superfamily of Cys-loop receptors. Receptor activation either leads to fast excitatory responses or modulation of neurotransmitter release depending on their neuronal localisation. 5-HT(3) receptors are known to be expressed in the central nervous system in regions involved in the vomiting reflex, processing of pain, the reward system, cognition and anxiety control. In the periphery they are present on a variety of neurons and immune cells. 5-HT(3) receptors are known to be involved in emesis, pain disorders, drug addiction, psychiatric and GI disorders. Progress in molecular genetics gives direction to personalised medical strategies for treating complex diseases such as psychiatric and functional GI disorders and unravelling individual drug responses in pharmacogenetic approaches. Here we discuss the molecular basis of 5-HT(3) receptor diversity at the DNA and protein level, of which our knowledge has greatly extended in the last decade. We also evaluate their role in health and disease and describe specific case-control studies addressing the involvement of polymorphisms of 5-HT3 subunit genes in complex disorders and responses to drugs. Furthermore, we focus on the actual state of the pharmacological knowledge concerning not only classical 5-HT(3) antagonists--the setrons--but also compounds of various substance classes targeting 5-HT(3) receptors such as anaesthetics, opioids, cannabinoids, steroids, antidepressants and antipsychotics as well as natural compounds derived from plants. This shall point to alternative treatment options modulating the 5-HT(3) receptor system and open new possibilities for drug development in the future.

The influence of citalopram on interdigestive gastrointestinal motility in man

BACKGROUND

Administration of 5-hydroxytryptamine (5HT) and selective 5HT receptor ligands modifies interdigestive motility in animals and in man.

AIM

To study the effect of citalopram, a selective 5-HT reuptake inhibitor, on interdigestive motility in man.

METHODS

In 20 healthy subjects, antroduodenojejunal motor activity was studied manometrically. Basal interdigestive motor activity was recorded until the passage of two activity fronts. Ten minutes after the second activity front, placebo or 20 mg of citalopram was administered intravenously in a double-blind randomized fashion. Recording continued until the passage of two more activity fronts had occurred.

RESULTS

Administration of citalopram induced a premature small intestinal phase 3 after 35 +/- 6.4 min, compared to 120 +/- 17 min after placebo P < 0.01. Citalopram shortened MMC cycle length at the expense of phase 1 and phase 2 and significantly increased the motility index during phase 2 in the antrum and the small intestine.

CONCLUSIONS

In the interdigestive state in man, intravenous administration of the selective 5-HT reuptake inhibitor citalopram induces a premature intestinal phase 3 and suppresses gastric activity fronts. Phase 2 motility is stimulated both in the stomach and in the small bowel after citalopram. These data suggest that 5HT is involved in the control of interdigestive motility.

Acute tryptophan depletion increases experimental nausea but also induces hunger in healthy female subjects

BACKGROUND

Acute tryptophan depletion (ATD) is an experimental model to reduce central serotonin levels.

METHODS

Thirty-eight healthy female subjects were randomly assigned to two groups (ATD and control) in a randomized, double-blinded parallel-group design. Following a standardized and balanced amino acid diet (including 1.21 g tryptophan) on the first day, they received either a protein drink without tryptophan (but substituted by other amino acids) (ATD condition) or the balanced protein drink with tryptophan (control condition) 24 h later. Four hours after its consumption, they were exposed to a standard rotation procedure. Symptom ratings (SR), ratings of hunger and mood scores were taken prior to rotation, at each break, and 15 and 30 min thereafter, together with saliva cortisol samples.

KEY RESULTS

Five subjects could not tolerate the entire rotation procedure and were excluded from analysis. For the remaining n = 33, SR and hunger ratings were higher during ATD than during control conditions, but mood was unaffected. Cortisol levels rose significantly with rotation but were unaffected by ATD. High baseline cortisol levels were associated with lower SR during rotation. The protective effects of morning cortisol were pronounced during the menstrual and follicular phase of the cycle and not present during ovulation and the luteal phase.

CONCLUSIONS & INFERENCES

Acute tryptophan depletion is associated with increased symptoms of nausea in healthy female subjects when exposed to body rotation. Acute tryptophan depletion also increases hunger rating. These opposite effects may indicate independent actions of the serotonin on central and peripheral functions.

New-generation 5-HT4 receptor agonists: potential for treatment of gastrointestinal motility disorders

IMPORTANCE OF THE FIELD

Gastrointestinal (GI) dysmotility is an important mechanism in functional GI disorders (FGIDs) including constipation, irritable bowel syndrome, functional dyspepsia, and gastroparesis. 5-hydroxytryptamine(4) (5-HT(4)) receptors are targets for the treatment of GI motility disorders. However, older 5-HT(4) receptor agonists had limited clinical success because they were associated with changes in the function of the cardiac HERG potassium channel.

AREAS COVERED IN THIS REVIEW

We conducted a PubMed search using the following key words alone or in combination: 5-HT(4), safety, toxicity, pharmacokinetics, pharmacodynamics, clinical trial, cardiac, hERG, arrhythmia, potassium current, elderly, prucalopride, ATI-7505, and velusetrag (TD-5108), to review mechanisms of action, clinical efficacy, safety and tolerability of three new-generation 5-HT(4) receptor agonists.

WHAT THE READER WILL GAIN

Prucalopride, ATI-7505, and velusetrag (TD-5108) are highly selective, high-affinity 5-HT(4) receptor agonists that are devoid of action on other receptors within their therapeutic range. Their efficacy has been demonstrated in pharmacodynamic studies which demonstrate acceleration of colonic transit and, to a variable degree, in clinical trials that significantly relieve chronic constipation. Currently available evidence shows that the new 5-HT(4) receptor agonists have safe cardiac profiles.

TAKE HOME MESSAGE

New-generation 5-HT(4) receptor agonists and future drugs targeting organ-specific splice variants are promising approaches to treat GI dysmotility, particularly colonic diseases.

The role of 5-HT3 and 5-HT4 receptors in the adaptive mechanism of colonic transit following the parasympathetic denervation in rats

BACKGROUND

Clinical studies show that disturbed colonic motility induced by extrinsic nerves damage is restored over time. We studied whether 5-HT3 and 5HT4 receptors are involved in mediating the adaptive mechanisms following parasympathetic denervation.

METHODS

Parasympathetic denervation of the entire colon was achieved by bilateral pelvic nerve transection and truncal vagotomy in rats. Colonic transit was measured by calculating the geometric center (GC) of 51Cr distribution. Expression of 5-HT3 and 5HT4 receptor mRNA was determined by real time RT-PCR.

RESULTS

Parasympathetic denervation caused a significant delay in colonic transit (GC=4.36) at postoperative day (POD) 1, compared with sham operation (GC=6.31). Delayed transit was gradually restored by POD 7 (GC=5.99) after the denervation. Restored colonic transit was antagonized by the administration of 5-HT3 and 5HT4 receptors antagonists at POD 7. 5-HT3 and 5HT4 receptors mRNA expression were significantly increased in the mucosal/submucosal layer at POD 3 or POD 7, whereas no significant difference was observed in the longitudinal muscle layers adherent with the myenteric plexus (LMMP).

CONCLUSIONS

It is suggested that up-regulation of 5-HT3 and 5-HT4 receptors expression in the mucosal/submucosal layer is involved to restore the delayed transit after the parasympathetic denervation in rats.

The role of 5-HT3 and 5-HT4 receptors in the adaptive mechanism of colonic transit following the parasympathetic denervation in rats

BACKGROUND

Clinical studies show that disturbed colonic motility induced by extrinsic nerves damage is restored over time. We studied whether 5-HT3 and 5HT4 receptors are involved in mediating the adaptive mechanisms following parasympathetic denervation.

METHODS

Parasympathetic denervation of the entire colon was achieved by bilateral pelvic nerve transection and truncal vagotomy in rats. Colonic transit was measured by calculating the geometric center (GC) of 51Cr distribution. Expression of 5-HT3 and 5HT4 receptor mRNA was determined by real time RT-PCR.

RESULTS

Parasympathetic denervation caused a significant delay in colonic transit (GC=4.36) at postoperative day (POD) 1, compared with sham operation (GC=6.31). Delayed transit was gradually restored by POD 7 (GC=5.99) after the denervation. Restored colonic transit was antagonized by the administration of 5-HT3 and 5HT4 receptors antagonists at POD 7. 5-HT3 and 5HT4 receptors mRNA expression were significantly increased in the mucosal/submucosal layer at POD 3 or POD 7, whereas no significant difference was observed in the longitudinal muscle layers adherent with the myenteric plexus (LMMP).

CONCLUSIONS

It is suggested that up-regulation of 5-HT3 and 5-HT4 receptors expression in the mucosal/submucosal layer is involved to restore the delayed transit after the parasympathetic denervation in rats.

Microscopic colitis and Medication Use

BACKGROUND: The incidence of microscopic colitis (MC) is increasing, but its etiology remains unknown. Case reports and limited controlled data suggest that commonly prescribed drugs may be triggers. The aim of this study was to evaluate the prevalence of selected medication use [Proton pump inhibitors (PPIs), HMG-CoA reductase inhibitors (statins), and Selective serotonin reuptake inhibitors (SSRIs)] in patients with MC compared to 'random controls' and 'diarrhea controls.' METHODS: All patients were selected from primary care practices of a university health system during 2002 to 2007. Patients with biopsy proven lymphocytic or collagenous colitis were identified as cases. Diarrhea controls consisted of a 10:1 random sample of patients with chronic diarrhea and normal colon biopsies. Ten random controls were matched to each case on sex and index date (date of biopsy proven diagnosis). Drugs prescribed within the year prior to the index date were collected from the electronic medical record system. RESULTS: 26 cases (median age 68.9 yrs), 259 random, and 259 diarrhea controls were identified. The adjusted ORs for PPI, SSRI, and statin prescription within 12 months of diagnosis of MC between cases and diarrhea controls were 0.28 (0.07-1.07), 0.87 (0.28-2.64), 1.12 (0.34-3.71) respectively. Use of PPI and statins was less common in MC patients than in random controls (p<0.05 for both comparisons). CONCLUSIONS: While prior data suggest that PPIs, statins, and SSRIs may be etiologically related to MC, our study found no increased association with these drugs.

Melatonin inhibits serotonin transporter activity in intestinal epithelial cells

Gastrointestinal serotonin (5-HT) and melatonin are two closely related neuromodulators which are synthesised in the enterochromaffin cells of the intestinal epithelium and which have been shown to be involved in the physiopathology of the gastrointestinal tract. The effects of 5-HT depend on 5-HT availability which is, in part, modulated by the serotonin transporter (SERT). This transporter provides an efficient 5-HT uptake after release and is expressed in the membrane of the enterocytes. Although the origin and effects of 5-HT and melatonin are similar, the interrelationship between them in the gastrointestinal tract is unknown. The main aim of this study was to determine whether melatonin affects SERT activity and expression, and, if so, to elucidate the mechanisms involved. Caco-2 cell line was used to carry out the study as these cells have been shown to endogenously express SERT. The results showed that melatonin inhibits SERT activity by affecting both V(max) and kt kinetic constants although SERT synthesis or intracellular trafficking did not appear to be affected. The melatonin effect seemed to be independent of melatonin receptors MT(1) and MT(2) and protein kinase C and cAMP intracellular pathways. Our results suggest that the inhibition of SERT might be due to a catalytic effect of melatonin on the allosteric citalopram-sensitive site in SERT. This study shows, for the first time, that melatonin modulates SERT activity, thus demonstrating the feedback system between melatonin and the serotoninergic system in the gastrointestinal tract.

Efficacy of celiac branch preservation in Roux-en-y reconstruction after laparoscopy-assisted distal gastrectomy

BACKGROUND

The present study investigated the efficacy of preserving the celiac branch of the vagus nerve after laparoscopy-assisted distal gastrectomy (LADG) with Roux-en-Y (R-Y) reconstruction.

METHODS

Between January 2004 and September 2008, a total of 159 consecutive patients who underwent LADG for gastric carcinoma were classified into groups according to preservation of the celiac branch of the vagus nerve-preservation group (P-LADG; n = 70) and the resection group (R-LADG; n = 89). The parameters analyzed included patient and tumor characteristics, operative details, postoperative outcomes, and nutritional state. The endoscopic findings of the gastric remnant and lower esophagus were evaluated at 12 months postoperatively.

RESULTS

In regard to postoperative complications, no significant differences were found between groups. With R-LADG, 14 patients suffered from dumping syndrome (15.7%), compared with only 2 patients with P-LADG (2.9%; P = .007). The amount of meal consumption compared with the preoperative value and the rate of weight reduction at 12 months postoperatively did not differ significantly between groups. Endoscopic findings showed significantly more residue with P-LADG (34.3%) than with R-LADG (16.9%; P = .011).

CONCLUSION

The celiac branch is useful in regulating gastrointestinal motility by maintaining postoperative physiologic function. Celiac branch preservation seems to represent a feasible and beneficial method for LADG.

The Impact of COMT-inhibition on Gastrointestinal Levodopa Absorption in Patients with Parkinson's Disease

The drug Levodopa (LD) is an efficient compound for the treatment of patients with Parkinson's disease (PD). Its short half life generates plasma behaviour of LD with peaks and troughs. Therefore, following the LD transport into the brain and the conversion to dopamine, an alternating stimulation of nigrostriatal postsynaptic dopamine receptors takes place. In the long term these fluctuations of dopamine concentrations supports onset of motor complications (MC) in PD patients. General opinion is that loss of central compensatory mechanisms of dopamine metabolism is responsible for the development of MC. However, in the periphery, LD troughs are preponderantly associated with the MC wearing off, which is the reappearance of motor symptoms with decreasing drug effect. Addition of the catechol-O-methyltransferase (COMT) inhibitor Entacapone (EN) to LD/carbidopa (CD) improved wearing off, since EN prolongs LD half life and avoids troughs. Plasma LD peaks are mostly related to the clinical manifestation of the MC dyskinesia, which appear as involuntary movements. One time addition of EN to a LD/CD formulation showed no increase of peripheral maximum LD concentration. But repeat combination of EN to each LD/CD intake elevated plasma LD bioavailability and peaks. Therefore switch from a LD/CD–-to a LD/CD/EN regime may also ask for reduction of LD/CD dosing or delay of the next LD/CD intake, to avoid onset of the most common peak dose dyskinesia. In conclusion, pharmacokinetic studies on peripheral LD metabolism and mode of intake underline their importance as peripheral components for MC manifestations in PD patients.

Serotonin reuptake transporter (SERT) plays a critical role in the onset of fructose-induced hepatic steatosis in mice

Elevated dietary fructose intake, altered intestinal motility, and barrier function may be involved in the development of nonalcoholic fatty liver disease (NAFLD). Because intestinal motility and permeability are also regulated through the bioavailability of serotonin (5-HT), we assessed markers of hepatic injury in serotonin reuptake transporter knockout (SERT(-/-)) and wild-type mice chronically exposed to different monosaccharide solutions (30% glucose or fructose solution) or water for 8 wk. The significant increase in hepatic triglyceride, TNF-alpha, and 4-hydroxynonenal adduct as well as portal endotoxin levels found in fructose-fed mice was associated with a significant decrease of SERT and the tight-junction occludin in the duodenum. Similar effects were not found in mice fed glucose. In contrast, in SERT(-/-) mice fed glucose, portal endotoxin levels, concentration of occludin, and indices of hepatic damage were similar to those found in wild-type and SERT(-/-) mice fed fructose. In fructose-fed mice treated with a 5-HT3 receptor antagonist, hepatic steatosis was significantly attenuated. Our data suggest that a loss of intestinal SERT is a critical factor in fructose-induced impairment of intestinal barrier function and subsequently the development of steatosis.

Role of MRP4 (ABCC4) in platelet adenine nucleotide-storage: evidence from patients with delta-storage pool deficiencies

We previously showed that the MRP4 (ABCC4) transporter is expressed in human platelet delta-granules and may be involved in ADP transport. We now demonstrate by immunoblotting and immunofluorescence microscopy that platelet MRP4 is absent in two patients with a platelet delta-storage pool deficiency (delta-SPD)-like phenotype with reduced platelet adenine nucleotide (AN) but normal serotonin levels, whereas their other membrane marker proteins of platelet granules were normally expressed and localized. In these patients, MRP4 was present in lymphocytes, and the coding region of their MRP4/ABCC4 gene did not show any mutation that explained the lack of expression. In platelets with "classic" delta-SPD (low AN and serotonin levels), MRP4 was quantitatively (immunoblot) normal, but, like other delta-granules membrane marker proteins (eg, LAMP2), was mostly displaced from delta-granules to patches at the plasma membrane, suggesting that platelets with classic delta-SPD have an abnormality that impairs the assembly of normal delta-granules. Thus, defective expression of platelet MRP4 is associated with selective defect in AN storage. The genetic basis of the new delta-SPD phenotype remains to be elucidated.

A selective, high affinity 5-HT 2B receptor antagonist inhibits visceral hypersensitivity in rats

BACKGROUND

RS-127445 is a selective, high affinity 5-HT(2B)receptor antagonist. We investigated whether 5-HT(2B)receptor antagonists can reduce colonic visceral hypersensitivity caused by restraint stress or by proximal colonic inflammation.

METHODS

Visceral hypersensitivity was induced in rats by either restraint stress or injection of 2, 4, 6-trinitrobenzene sulfonic acid (TNBS) into the proximal colon. Restraint stress produced a significant increase in numbers of abdominal contractions evoked by colorectal distension (CRD), measured as a quantitative index of visceral nociception in rats. Seven days after TNBS injection, the pain threshold to CRD at the non-inflamed distal colon, that was determined as the minimum pressure required to evoke abdominal cramp, was significantly decreased. The effect of RS-127445 on visceral hypersensitivity was assessed in either naïve or TNBS-treated rats.

KEY RESULTS

Oral administration of a selective, high affinity 5-HT(2B)receptor antagonist, RS-127445, significantly inhibited visceral hypersensitivity provoked by restraint stress (35 to 74% inhibition at 1 to 10 mg kg(-1)). Oral RS-127445 produced a significant suppression of TNBS-induced visceral hypersensitivity (15 to 62% inhibition at 3 to 30 mg kg(-1)), although it was without significant effect on the visceral nociceptive threshold of naïve rats. RS-127445 (1 to 30 mg kg(-1), p.o.) also dose-dependently reduced the restraint stress-induced defecation in naïve and TNBS-treated rats.

CONCLUSIONS & INFERENCES

These results suggest that 5-HT(2B)receptors are involved in signaling from the colon in rats in which there is visceral hypersensitivity and that a selective 5-HT(2B)receptor antagonist could have therapeutic potential for the treatment of gut disorders characterized by visceral hypersensitivity.

Electrochemical measurements of serotonin (5-HT) release from the guinea pig mucosa using continuous amperometry with a boron-doped diamond microelectrode

Irritable bowel syndrome (IBS) is a common gastrointestinal (GI) disorder characterized by chronic abdominal discomfort, including pain, bloating and changes in bowel habits. The exact cause of IBS is not entirely understood. Recent studies have shown that IBS may be associated with altered serotonin (5-hydroxytryptamine, 5-HT) levels within the GI tract. About 90% of 5-HT in the human body is produced and stored in enterochromaffin (EC) cells that reside in the mucosal layer of the intestine. Measurements of serotonin availability locally in the mucosa can provide insight on the functionality of these cells and potentially the pathophysiology of the disease. In this study, we used continuous amperometry with a diamond microelectrode to record serotonin levels in vitro in the ileum mucosa as an oxidation current. The boron-doped diamond (BDD) microelectrode is quite practical for these measurements because if its low background signal, low sensitivity to solution pH changes, and excellent resistance to fouling by adsorbed serotonin oxidation reaction products. In fact, the measurements are only possible because of the unique properties of diamond. We present electrochemical data that demonstrate the diamond microelectrode's utility for assessment of enterochromaffin cell function. Confirmation that the oxidation current was associated with indogenous serotonin release came from pharmacological studies. We are hopeful that these types of in vitro electrochemical measurements will lead to a better understanding of the pathophysiology of IBS.

The effect of tegaserod on symptoms and quality of life in korean women with irritable bowel syndrome with constipation

INTRODUCTION

Tegaserod has been used for treatment of irritable bowel syndrome (IBS) but there is no data regarding its effect on Korean patients. The aim of this study was to evaluate the effect of tegaserod on symptoms and quality of life (QOL) in Korean female IBS patients with constipation and to evaluate the usefulness of the IBS-QOL in clinical study.

METHODS

A prospective, open labeled, multicenter study was performed. Female patients fulfilling Rome II criteria for IBS received 6 mg of tegaserod twice a day for 4 weeks. The efficacy on IBS symptoms and QOL was assessed using 7-point scaled symptom questionnaire and IBS-QOL questionnaire, respectively.

RESULTS

A total of 81 female patients (range 18-73 years of age) were enrolled in this study. Tegaserod therapy significantly reduced the overall symptom scores after 4 weeks (p <0.01). The improved symptoms included abdominal discomfort or pain, hard or lumpy stool, straining during a bowel movement, feeling of incomplete bowel movement, and abdominal fullness or bloating. The IBS-QOL of responders to tegaserod treatment was also significantly improved after 4 weeks (p <0.01). Furthermore, improvement of symptom scores significantly correlated with improvement of the IBS-QOL scores (r = -0.60, p <0.001).

CONCLUSIONS

Tegaserod 6 mg given twice daily improved the QOL as well as the bowel symptoms in Korean female IBS patients with constipation. The IBS-QOL can be used as a reliable end-point in clinical study.

The effect of mosapride citrate on constipation in patients with diabetes

OBJECTIVE

Constipation is one of the most common gastrointestinal complications suspected to degrade the quality of life in diabetic patients. Mosapride citrate is a novel selective 5-HT4 receptor agonist, which enhances gastric emptying and motility in the upper gastrointestinal tract facilitating acetylcholine release from the enteric cholinergic neurons. Since the receptors of 5-HT4 have been recently found in the lower intestine including the rectum in humans, we tested if mosapride improves constipation in diabetic patients.

PATIENTS AND METHODS

Diabetic patients with constipation were treated with mosapride citrate (15 mg/day, n=20) or domperidone (30 mg/day, n=12) as controls for 8 weeks. Bowel frequency was monitored and gastrointestinal symptoms were evaluated by Gastrointestinal Symptoms Rating Scale (GSRS).

RESULTS

Administration of mosapride resulted in increased bowel frequency after 4 and 8 weeks of administration, while no change was seen in the control group. Mosapride increased bowel frequency in even patients with diabetic polyneuropathy. Mosapride improved reflux and constipation evaluated by GSRS. As previously reported, glycemic control also improved by mosapride in these patients.

CONCLUSIONS

Administration of mosapride increased bowel frequency and ameliorated symptoms of reflux and constipation possibly stimulating the lower intestine. Given that mosapride has those beneficial aspects, it may be a useful prokinetic agent in treating diabetic patients with constipation.

The effect of tegaserod on symptoms and quality of life in korean women with irritable bowel syndrome with constipation

INTRODUCTION

Tegaserod has been used for treatment of irritable bowel syndrome (IBS) but there is no data regarding its effect on Korean patients. The aim of this study was to evaluate the effect of tegaserod on symptoms and quality of life (QOL) in Korean female IBS patients with constipation and to evaluate the usefulness of the IBS-QOL in clinical study.

METHODS

A prospective, open labeled, multicenter study was performed. Female patients fulfilling Rome II criteria for IBS received 6 mg of tegaserod twice a day for 4 weeks. The efficacy on IBS symptoms and QOL was assessed using 7-point scaled symptom questionnaire and IBS-QOL questionnaire, respectively.

RESULTS

A total of 81 female patients (range 18-73 years of age) were enrolled in this study. Tegaserod therapy significantly reduced the overall symptom scores after 4 weeks (p <0.01). The improved symptoms included abdominal discomfort or pain, hard or lumpy stool, straining during a bowel movement, feeling of incomplete bowel movement, and abdominal fullness or bloating. The IBS-QOL of responders to tegaserod treatment was also significantly improved after 4 weeks (p <0.01). Furthermore, improvement of symptom scores significantly correlated with improvement of the IBS-QOL scores (r = -0.60, p <0.001).

CONCLUSIONS

Tegaserod 6 mg given twice daily improved the QOL as well as the bowel symptoms in Korean female IBS patients with constipation. The IBS-QOL can be used as a reliable end-point in clinical study.