What comes after macrolides and other motilin stimulants?

The influence of herbal medicine on serum motilin and its effect on human and animal model: a systematic review

Introduction: Motilin (MLN) is a gastrointestinal (GI) hormone produced in the upper small intestine. Its most well understood function is to participate in Phase III of the migrating myoelectric complex component of GI motility. Changes in MLN availability are associated with GI diseases such as gastroesophageal reflux disease and functional dyspepsia. Furthermore, herbal medicines have been used for several years to treat various GI disorders. We systematically reviewed clinical and animal studies on how herbal medicine affects the modulation of MLN and subsequently brings the therapeutic effects mainly focused on GI function. Methods: We searched the PubMed, Embase, Cochrane, and Web of Science databases to collect all articles published until 30 July 2023, that reported the measurement of plasma MLN levels in human randomized controlled trials and in vivo herbal medicine studies. The collected characteristics of the articles included the name and ingredients of the herbal medicine, physiological and symptomatic changes after administering the herbal medicine, changes in plasma MLN levels, key findings, and mechanisms of action. The frequency patterns (FPs) of botanical drug use and their correlations were investigated using an FP growth algorithm. Results: Nine clinical studies with 1,308 participants and 20 animal studies were included in the final analyses. Herbal medicines in clinical studies have shown therapeutic effects in association with increased levels of MLN, including GI motility regulation and symptom improvement. Herbal medicines have also shown anti-stress, anti-tumor, and anti-inflammatory effects in vivo. Various biochemical markers may correlate with MLN levels. Markers may have a positive correlation with plasma MLN levels included ghrelin, acetylcholine, and secretin, whereas a negative correlation included triglycerides and prostaglandin E2. Markers, such as gastrin and somatostatin, did not show any correlation with plasma MLN levels. Based on the FP growth algorithm, Glycyrrhiza uralensis and Paeonia japonica were the most frequently used species. Conclusion: Herbal medicine may have therapeutic effects mainly on GI symptoms with involvement of MLN regulation and may be considered as an alternative option for the treatment of GI diseases. Further studies with more solid evidence are needed to confirm the efficacy and mechanisms of action of herbal medicines. Systematic Review Registration: https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=443244, identifier CRD42023443244.

The Role of GI Peptides in Functional Dyspepsia and Gastroparesis: A Systematic Review

Functional dyspepsia (FD) and gastroparesis (GP) are common disorders of the upper gastrointestinal tract. The pathophysiology of these conditions is likely to be heterogenous, and factors such as altered motility, sensitivity and response to nutrition have been identified as putative underlying mechanisms. Motility, sensitivity as well as responses to nutrition can be influenced or mediated by peptide hormones and serotonin released from the gastrointestinal mucosa. This review summarizes the role of GI peptides in functional dyspepsia and gastroparesis. In most studies, the levels of somatostatin, ghrelin, and motilin did not differ between healthy volunteers and FD or GP patients, but higher symptom burden was often correlated with higher peptide levels. Ghrelin and motilin receptor agonists showed promising results in improvement of the gastric emptying, but the link with improvement of symptoms is less predictable. Serotonin agonists have a potential to improve symptoms in both FD and idiopathic gastroparesis. Drugs acting on the GLP-1 and on the PYY receptors deserve further investigation. There is a need for systematic large scale studies.

Prokinetics in the Management of Functional Gastrointestinal Disorders

PURPOSE OF REVIEW

The goal of this review is to review the current status of prokinetics and to place it in historical context. Impaired motility and thus propulsion have long been thought to play important roles in the pathogenesis of a number of gastrointestinal disorders including gastroesophageal reflux disease (GERD), gastroparesis, chronic idiopathic pseudo-obstruction, and constipation. Historically, disordered motility was also thought to contribute to a number of functional gastrointestinal disorders such as functional dyspepsia (FD) and irritable bowel syndrome (IBS).

RECENT FINDINGS

As we learn more of the pathophysiology of FD, IBS, GERD, constipation, and gastroparesis, the limitations of a therapeutic strategy based on the stimulation of motility (i.e., the use of a prokinetic) have become apparent and the disappointments of the past explained. The development of prokinetic drugs has also been hampered by the non-selective nature of many of the agents studied to date which resulted in some unexpected side effects. There is still an unmet need for an effective and safe prokinetic, but drug development in this area must be mindful of the challenges of the area and the need for selectivity for a given target receptor.

Prokinetics in the Management of Functional Gastrointestinal Disorders

A variety of common and some not common gastrointestinal syndromes are thought to be based on impaired gut motility. For some, the role of motility is well defined, for others and the functional gastrointestinal disorders, in particular, the role of hypo- or dysmotility remains unclear. Over the years pharmacological and physiological laboratories have developed drugs which stimulate gut motility; many have been evaluated in motility and functional disorders with what can best be described as mixed results. Lack of receptor specificity and resultant expected and unexpected adverse events have led to the demise of some of these agents. Newer, more selective agents offer promise but the heterogeneity of the clinical disorders they target continues to pose a formidable challenge to drug development in this area.

Motilin: towards a new understanding of the gastrointestinal neuropharmacology and therapeutic use of motilin receptor agonists

The gastrointestinal hormone motilin has been known about for >40 years, but after identification of its receptor and subsequent development of new tools and methods, a reappraisal of its actions is required. Firstly, it is important to note that motilin and ghrelin receptors are members of the same family (similar genomic organization, gastrointestinal distribution and abilities to stimulate gastrointestinal motility), yet each fails to recognize the ligand of the other; and whereas ghrelin and ghrelin receptors are widespread outside the gastrointestinal tract, motilin and its receptors are largely restricted to the gastrointestinal tract. Secondly, although some studies suggest motilin has activity in rodents, most do not, and receptor pseudogenes exist in rodents. Thirdly, motilin preferentially operates by facilitating enteric cholinergic activity rather than directly contracting the muscle, despite the relatively high expression of receptor immunoreactivity in muscle. This activity is ligand-dependent, with short-lasting actions of motilin contrasting with longer-lasting actions of the non-selective and selective motilin receptor agonists erythromycin and GSK962040. Finally, the use of erythromycin (also an antibiotic drug) to treat patients requiring acceleration of gastric emptying has led to concerns over safety and potential exacerbation of antibiotic resistance. Replacement motilin receptor agonists derived from erythromycin (motilides) have been unsuccessful. New, non-motilide, small molecule receptor agonists, designed to minimize self-desensitization, are now entering clinical trials for treating patients undergoing enteral feeding or with diabetic gastroparesis. Thus, for the translational pharmacologist, the study of motilin illustrates the need to avoid overreliance on artificial systems, on structural information and on animal studies.

LINKED ARTICLES

This article is part of a themed section on Neuropeptides. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2013.170.issue-7.

The migrating motor complex: control mechanisms and its role in health and disease

The migrating motor complex (MMC) is a cyclic, recurring motility pattern that occurs in the stomach and small bowel during fasting; it is interrupted by feeding. The MMC is present in the gastrointestinal tract of many species, including humans. The complex can be subdivided into four phases, of which phase III is the most active, with a burst of contractions originating from the antrum or duodenum and migrating distally. Control of the MMC is complex. Phase III of the MMC with an antral origin can be induced in humans through intravenous administration of motilin, erythromycin or ghrelin, whereas administration of serotonin or somatostatin induces phase III activity with duodenal origin. The role of the vagus nerve in control of the MMC seems to be restricted to the stomach, as vagotomy abolishes the motor activity in the stomach, but leaves the periodic activity in the small bowel intact. The physiological role of the MMC is incompletely understood, but its absence has been associated with gastroparesis, intestinal pseudo-obstruction and small intestinal bacterial overgrowth. Measuring the motility of the gastrointestinal tract can be important for the diagnosis of gastrointestinal disorders. In this Review we summarize current knowledge of the MMC, especially its role in health and disease.

Current management of functional dyspepsia: impact of Rome III subdivision

Functional dyspepsia (FD) is a highly prevalent disease characterized by symptoms originating from the gastroduodenal region in the absence of underlying organic disease. The Rome III consensus made a distinction between meal-induced and meal-unrelated symptoms and proposed subdivision of FD into postprandial distress syndrome and epigastric pain syndrome. The applicability of this subdivision and the impact on management are areas of active research. So far, empirical approaches are still employed for the treatment of FD, although various therapeutic modalities for FD have been explored; acid-suppressive, prokinetic, and fundic relaxant drugs, antidepressants and psychological therapies. FD remains a challenge and presents unmet clinical needs.

The roles of motilin and ghrelin in gastrointestinal motility

In structure, ghrelin resembles motilin. The two peptides are considered to be members of the motilin-ghrelin peptide family. Motilin is considered to be an endocrine regulator of the interdigestive migrating contractions, the fasted motor pattern in the gastrointestinal (GI) tract. It has been reported that ghrelin stimulates GI motility. The gastrokinetic capacity of ghrelin has been well documented in the rodent. However, there have been few positive reports of the gastrokinetic capacity of ghrelin in dogs. Some reports with human subjects have shown that an i.v. ghrelin injection accelerated gastric emptying of a meal and improved meal-related symptoms. These results suggest that ghrelin has potential as a prokinetic. However, it seems unlikely that plasma ghrelin would play a physiological role in these digestive physiological events and stimulate gastric emptying, as these outcomes would appear to be in contradiction with the suppression of the endogenous release of ghrelin after eating. The physiological roles of ghrelin need to be clarified.

Diabetic gastroparesis: diagnosis and management

Gastric emptying is frequently abnormal in patients with long-standing type 1 and type 2 diabetes mellitus. Symptoms commonly associated with disordered gastric emptying include nausea, vomiting, bloating and epigastric pain, while patients are also at risk of malnutrition, weight loss, impaired drug absorption, disordered glycaemic control and poor quality of life. Although often attributed to the presence of irreversible autonomic neuropathy, acute hyperglycaemia represents a potentially reversible cause of gastric dysfunction in diabetes. Scintigraphy represents the gold standard for measuring gastric emptying. The management of diabetic gastroparesis is less than optimal, partly because the pathogenesis has not been clearly defined. Treatment approaches include dietary modification and optimization of glycaemia, and the use of prokinetic drugs, while novel therapies such as gastric electrical stimulation are the subject of ongoing investigation.

Risk of aspiration in patients on enteral nutrition: frequency, relevance, relation to pneumonia, risk factors, and strategies for risk reduction

Upper digestive feeding intolerance, as evidenced by high gastric residual volume and vomiting, is the most common complication among hospitalized patients receiving enteral nutrition. These patients are at high risk of developing aspiration pneumonia, which in turn is associated with prolonged hospital stay and increased mortality. Most episodes of aspiration are small in volume and do not lead to pneumonia. The likelihood of pneumonia increases with multiple aspirations. Pneumonia is also more common in critically ill patients who have bacterial colonization of the oropharynx. Gastric residual volume is commonly used as a means to assess aspiration risk during tube feeding. However, recent studies have demonstrated that this measurement has limited sensitivity. The approach to minimizing the frequency of aspiration during tube feeding involves assessment of the patient's degree of risk and initiation of appropriate measures directed at risk reduction.

Determinants of symptom pattern in idiopathic severely delayed gastric emptying: gastric emptying rate or proximal stomach dysfunction?

BACKGROUND

Idiopathic gastroparesis is a syndrome characterised by severely delayed gastric emptying of solids without an obvious underlying organic cause. Although delayed gastric emptying is traditionally considered the mechanism underlying the symptoms in these patients, poor correlations with symptom severity have been reported.

AIMS

To investigate proximal stomach function and to study the correlation of delayed gastric emptying and proximal stomach dysfunction with symptom pattern and severity in idiopathic gastroparesis.

METHODS

58 consecutive patients (19 men, mean (standard deviation) age 41 (2) years) with severely delayed solid gastric emptying (gastric half-emptying time (t(1/2))>109 min) without an organic cause were recruited. They filled out a symptom-severity questionnaire and underwent a gastric barostat study for assessment of gastric sensitivity and accommodation. Correlation of these mechanisms with symptom pattern and overall symptom severity (sum of individual symptoms) was analysed.

RESULTS

At two different cut-off levels for gastric emptying (upper limit of normal t(1/2) up to 1.5 and 2 times), no significant change in symptom pattern occurred. 25 (43%) patients had impaired accommodation, and this was associated with higher prevalence of early satiety (p<0.005) and weight loss (p = 0.009). 17 (29%) patients had hypersensitivity to gastric distension, and this was associated with higher prevalences of epigastric pain (p = 0.005), early satiety (p = 0.04) and weight loss (p<0.005). Overall symptom severity was not correlated with gastric emptying or accommodation, but only with sensitivity to gastric distension (R = -0.3898, p = 0.003) and body weight (R = -0.4233, p = 0.001).

CONCLUSIONS

In patients with idiopathic gastroparesis, the symptom pattern is determined by proximal stomach dysfunction rather than by the severity of delayed emptying.

Erythromycin for prokinesis: imprudent prescribing?

Problems with antibiotic resistant bacteria are increasing in the hospital and particularly in the intensive care unit. Methicillin-resistant Staphylococcus aureus, Acinetobacter baumanii and extended spectrum beta-lactamase producing Gram-negative bacilli constitute a therapeutic and infection control challenge. Early enteral feeding improves survival in patients in the intensive care unit. Prokinetic agents are routinely used in patients with inappropriate gastrointestinal motility. The use of erythromycin at sub-therapeutic doses as a prokinetic agent is a cause of concern for the following reasons: it can increase the emergence and spread of antibiotic resistance and the likelihood of Clostridium difficile disease. The use of an antibiotic as a prokinetic agent does not constitute prudent antimicrobial prescribing and should be avoided. Alternative agents, whenever possible, should be used.

Pathogenesis and therapy for idiopathic dyspepsia

Functional dyspepsia (FD) is one of the most common gastrointestinal disorders. This review summarizes recent progress in our understanding of the pathogenesis and therapy for FD. Although distinction among FD, irritable bowel syndrome, and reflux disease is difficult in population-based studies, separate entities can be recognized in patients who seek medical attention. The pathogenesis of FD remains unclear, but recent studies have demonstrated a role for acute gastrointestinal infection in triggering FD and in genetic polymorphisms of G-proteins in predisposing to FD. The role of abnormalities in gastric motor function, visceral hypersensitivity, and psychosocial factors in the pathophysiology of dyspeptic symptoms has been the topic of multiple studies. Treatment options for FD remain limited. Recent studies have focused on acid-suppressive drugs and on novel prokinetics. Progress in our understanding of the pathogenesis and pathophysiology of FD may lead to new or improved treatment modalities. Areas of major advances are the role of infection and genetic predisposition and studies on the role of abnormalities in gastric motility and sensitivity.

Influence of erythromycin on gastric emptying and meal related symptoms in functional dyspepsia with delayed gastric emptying

BACKGROUND AND AIMS

Although delayed gastric emptying is considered a major pathophysiological mechanism in functional dyspepsia, the efficacy of prokinetic drugs has not been established. Recent studies using macrolide prokinetics were negative but receptor desensitisation may have played a role. The aim of the present study was to evaluate the influence on meal induced symptoms of acutely administered erythromycin in patients with gastroparesis.

METHODS

In 20 patients with functional dyspepsia, gastric emptying was studied twice using the (14)C octanoic acid and (13)C glycin breath test to establish the reproducibility of the test. Breath samples were taken before the meal and at 15 minute intervals for a period of 240 minutes postprandially. At each breath sampling, the patient was asked to grade the intensity (0-3) of six dyspeptic symptoms. Twenty four patients (three men, mean age 43.5 (3) years) with dyspeptic symptoms and delayed gastric emptying were studied twice after pretreatment with saline or erythromycin intravenously.

RESULTS

Meal related symptom severity scores were reproducible. Treatment with erythromycin significantly enhanced solid and liquid gastric emptying (t(1/2) 146 (27) v 72 (7) minutes, respectively (p<0.01), and 87 (6) v 63 (5) minutes (p<0.001)). Only the severity of bloating was significantly improved by erythromycin (23 (3.9) v 14.5 (2.7); p<0.01); all other symptoms and the cumulative meal related symptom score were not altered by erythromycin.

CONCLUSIONS

In a setting where desensitisation played no role, erythromycin enhanced gastric emptying was not associated with a beneficial effect on meal related symptom severity.

Effects of a nonpeptide motilin receptor antagonist on proximal gastric motor function

AIM

To assess the effects of the motilin receptor antagonist RWJ-68023 on basal and motilin-stimulated proximal gastric volume.

METHODS

Eighteen healthy male volunteers received RWJ-68023 in two different doses or placebo for 135 min. After 45 min, subjects received a motilin infusion for 90 min. Proximal gastric volume was measured with a barostat at constant pressure and during isobaric distensions. Abdominal symptoms were scored using visual analogue scales. Motilin and RWJ-68023 concentrations were assessed by radioimmunoassay and liquid chromatography-mass spectrometry, respectively.

RESULTS

Both dosages of RWJ-68023 were safe and well tolerated. The most common adverse events were of gastrointestinal origin. RWJ-68023 did not affect basal proximal gastric volume, but the high-dose RWJ-68023 reduced the contractile effect of motilin on the stomach. This antagonizing effect of RWJ-68023 was only significant (P = 0.014) during the distension procedure.

CONCLUSIONS

The RWJ-68023 doses used in this study were selected to accomplish plasma concentrations that would block the motilin effect entirely. However, the antagonizing effect of RWJ-68023 was partial and only present when the tonic condition of the stomach was modulated by motilin.

Progress with novel pharmacological strategies for gastro-oesophageal reflux disease

Gastro-oesophageal reflux disease (GORD) is a chronic disorder characterised by an increased exposure of the oesophagus to intragastric contents. Currently, GORD symptoms are maintained under control with antisecretory agents, mainly gastric proton pump inhibitors (PPIs). Although impaired oesophageal motility may partly underlie the pathophysiology of GORD, the use of prokinetic agents has been found to be unsatisfactory. To date, novel pharmacological approaches for GORD are mainly related to the control of transient lower oesophageal sphincter (LOS) relaxations (TLOSRs). The majority of patients with GORD have reflux episodes during TLOSRs, which are evoked by gastric distension, mainly occurring after ingestion of a meal. Patients with reflux disease with normal peristalsis and without or with mild erosive disease could potentially benefit from anti-TLOSR therapy. This therapy might also be of value to treat some severe forms of esophagitis in combination with PPIs. GABA-B-receptor agonists are the most promising class of agents identified so far for TLOSR control. The GABA-B-receptor agonist, baclofen, is the most effective compound in inhibiting TLOSRs in humans. Since baclofen has several CNS adverse effects, novel orally available GABA-B agonists are needed for effective and well tolerated treatment of GORD. Endogenous or exogenous cholecystokinin (CCK) causes a reduction in LOS pressure, an increase in TLOSR frequency and a reduction in gastric emptying. In healthy volunteers and patients with GORD, loxiglumide, a selective CCK1-receptor antagonist, was found to reduce the rate of TLOSRs, although its effect on postprandial acid reflux may be modest. Orally effective CCK antagonists are not marketed to date. The anticholinergic agent atropine, given to healthy volunteers and patients with GORD, markedly reduced the rate of TLOSRs. Because of severe gastrointestinal (and other) adverse effects of anticholinergics, including worsening of supine acid clearance and constipation, it is unlikely that this class of drugs will have a future as anti-TLOSR agents on a routine basis. In spite of their effectiveness in reducing TLOSR rate, untoward adverse effects, such as addiction and severe constipation, currently limit the use of morphine and other opioid mu-receptor agonists. The same applies to nitric oxide synthase inhibitors, which are associated with marked gastrointestinal, cardiovascular, urinary and respiratory adverse effects. Animal studies provide promising evidence for the use of cannabinoid receptor 1 agonists, by showing potent inhibition of TLOSRs in the dog, thus opening a new route for clinical investigation in humans. A better understanding of TLOSR pathophysiology is a necessary step for the further development of novel drugs effective for anti-reflux therapy.

Prokinetic agents in critical care

Prokinetic agents are commonly used in intensive care, mainly to aid in early enteral feeding. The present commentary reviews some of the recently published papers and highlights the lack of a sizable evidence base, as well as the possible importance of euglycaemia in this important clinical area.

New developments in the treatment of functional dyspepsia

Functional dyspepsia is a clinical syndrome defined by chronic or recurrent pain or discomfort in the upper abdomen of unknown origin. Although generally accepted, investigators differently interpret this definition and clinical trials are often biased by inhomogeneous inclusion criteria. The poorly defined multifactorial pathogenesis of dyspeptic symptoms has hampered efforts to develop effective treatments. A general agreement exists on the irrelevant role played by Helicobacter pylori in the pathophysiology of functional dyspepsia. Gastric acid secretion is within normal limits in patients with functional dyspepsia but acid related symptoms may arise in a subgroup of them. Proton pump inhibitors appear to be effective in this subset of patients with dyspepsia. Non-painful dyspeptic symptoms are suggestive of underlying gastrointestinal motor disorders and such abnormalities can be demonstrated in a substantial proportion of patients. Postprandial fullness and vomiting have been associated with delayed gastric emptying of solids, and early satiety and weight loss to postcibal impaired accommodation of the gastric fundus. Prokinetics have been shown to exert beneficial effects, at least in some patients with dyspepsia. In contrast, drugs enhancing gastric fundus relaxation have been reported to improve symptoms, although conflicting results have also been published. An overdistended antrum may also generate symptoms, but its potential pathogenetic role and the effects of drugs on this abnormality have never been investigated formally. Visceral hypersensitivity plays a role in some dyspeptic patients and this abnormality is also a potential target for treatment. Both chemo- and mechanoreceptors can trigger hyperalgesic responses. Psychosocial abnormalities have been consistently found in functional digestive syndromes, including dyspepsia. Although useful in patients with irritable bowel syndromes (IBS), antidepressants have been only marginally explored in functional dyspepsia. Among the new potentially useful agents for the treatment of functional dyspepsia, serotonin 5-HT(4) receptor agonists have been shown to exert a prokinetic effect. Unlike motilides, 5-HT(4) receptor agonists do not appear to increase the gastric fundus tone and this may contribute to improve symptoms. 5-HT(3) receptor antagonists have been investigated mainly in the IBS and the few studies performed in functional dyspepsia have provided conflicting results. Also, kappa-opioid receptor agonists might be useful for functional digestive syndromes because of their antinociceptive effects, but available results in functional dyspepsia are scanty and inconclusive. Other receptors that represent potential clinical targets for antagonists include purinoceptors (i. e., P2X2/3 receptors), NMDA receptors (NR2B subtype), protease-activated receptor-2, the vanilloid receptor-1, tachykinin receptors (NK(1)/NK(2)) and cholecystokinin (CCK)(1) receptors.

Causes and treatment of functional dyspepsia

Functional dyspepsia is a clinical syndrome defined by upper abdominal symptoms without identifiable cause by conventional diagnostic means. Recent studies have established that functional dyspepsia is a heterogeneous disorder in which different pathophysiologic disturbances underlie different symptom profiles. Delayed gastric emptying is associated with postprandial fullness, nausea, and vomiting; impaired accommodation is associated with early satiety and weight loss; and hypersensitivity to gastric distention is associated with epigastric pain, belching, and weight loss. The pathogenesis of functional dyspepsia is unknown but may be postinfectious in a subgroup of patients. The role of psychological disturbances and of duodenal hypersensitivity requires further study. Treatment of the underlying pathophysiologic abnormality seems logical, but options for pharmacotherapy are limited to acid suppression, prokinetic drugs, and antidepressants. Psychotherapy can be considered for refractory patients. Several novel drug therapies are under evaluation.