Intraduodenal conjugated bile salts exert negative feedback control on gall bladder emptying in the fasting state without affecting cholecystokinin release or antroduodenal motility

New Avenues in the Regulation of Gallbladder Motility-Implications for the Use of Glucagon-Like Peptide-Derived Drugs

CONTEXT

Several cases of cholelithiasis and cholecystitis have been reported in patients treated with glucagon-like peptide 1 (GLP-1) receptor agonists (GLP-1RAs) and GLP-2 receptor agonists (GLP-2RAs), respectively. Thus, the effects of GLP-1 and GLP-2 on gallbladder motility have been investigated. We have provided an overview of the mechanisms regulating gallbladder motility and highlight novel findings on the effects of bile acids and glucagon-like peptides on gallbladder motility.

EVIDENCE ACQUISITION

The articles included in the present review were identified using electronic literature searches. The search results were narrowed to data reporting the effects of bile acids and GLPs on gallbladder motility.

EVIDENCE SYNTHESIS

Bile acids negate the effect of postprandial cholecystokinin-mediated gallbladder contraction. Two bile acid receptors seem to be involved in this feedback mechanism, the transmembrane Takeda G protein-coupled receptor 5 (TGR5) and the nuclear farnesoid X receptor. Furthermore, activation of TGR5 in enteroendocrine L cells leads to release of GLP-1 and, possibly, GLP-2. Recent findings have pointed to the existence of a bile acid-TGR5-L cell-GLP-2 axis that serves to terminate meal-induced gallbladder contraction and thereby initiate gallbladder refilling. GLP-2 might play a dominant role in this axis by directly relaxing the gallbladder. Moreover, recent findings have suggested GLP-1RA treatment prolongs the refilling phase of the gallbladder.

CONCLUSIONS

GLP-2 receptor activation in rodents acutely increases the volume of the gallbladder, which might explain the risk of gallbladder diseases associated with GLP-2RA treatment observed in humans. GLP-1RA-induced prolongation of human gallbladder refilling may explain the gallbladder events observed in GLP-1RA clinical trials.

Phosphatidylcholine as a constituent in the colonic mucosal barrier--physiological and clinical relevance

Phosphatidylcholine (PC) is an important constituent of the gastrointestinal tract. PC molecules are not only important in intestinal cell membranes but also receiving increasing attention as protective agents in the gastrointestinal barrier. They are largely responsible for establishing the hydrophobic surface of the colon. Decreased phospholipids in colonic mucus could be linked to the pathogenesis of ulcerative colitis, a chronic inflammatory bowel disease. Clinical studies revealed that therapeutic addition of PC to the colonic mucus of these patients alleviated the inflammatory activity. This positive role is still elusive, however, we hypothesized that luminal PC has two possible functions: first, it is essential for surface hydrophobicity, and second, it is integrated into the plasma membrane of enterocytes and it modulates the signaling state of the mucosa. The membrane structure and lipid composition of cells is a regulatory component of the inflammatory signaling pathways. In this perspective, we will shortly summarize what is known about the localization and protective properties of PC in the colonic mucosa before turning to its evident medical importance. We will discuss how PC contributes to our understanding of the pathogenesis of ulcerative colitis and how reinforcing the luminal phospholipid monolayer can be used as a therapeutic concept in humans.

Micellar lipid composition profoundly affects LXR-dependent cholesterol transport across CaCo2 cells

Intraluminal phospholipids affect micellar solubilization and absorption of cholesterol. We here study cholesterol transport from taurocholate-phospholipid-cholesterol micelles to CaCo2 cells, and associated effects on ABC-A1 mediated cholesterol efflux. Micellar incorporation of egg-yolk-phosphatidylcholine markedly increased apical retention of the sterol with decreased expression of ABC-A1, an effect that is prevented by synthetic liver X receptor (LXR) or retinoid X receptor (RXR) agonists. On the other hand, incorporation of lyso-phosphatidylcholine (LysoPC) increased ABC-A1-HDL-dependent basolateral cholesterol efflux, an effect that is abated when LXR is silenced. Thus, the modulation of cholesterol metabolism via intraluminal phospholipids is related to the activity of the oxysterol nuclear receptor LXR.

Relationship between entero-hepatic bile acid circulation and interdigestive migrating myoelectrical activity in rats

AIM: To investigate the effects of entero-hepatic bile acid circulation on the inter-digestive migrating myoelectrical complex (MMC) in rats.

METHODS: Thirty-two rats were divided into four groups. Three pairs of bipolar silver electrodes were chronically implanted in the antrum, duodenum and jejunum. Three groups of them were ligated around the upper part of common bile duct (CBD). The experiments were performed in conscious and fasting state. The gastrointestinal myoelectrical activity was recorded. Ursodeoxycholic acid (UDCA) and saline were then perfused into stomachs of two groups with CBD obstruction and the effects of them on the MMC were observed.

RESULTS: A typical pattern of MMC was observed in normal fasting rats. MMC of antral and duodenal origin disappeared temporarily in earlier stage of CBD obstruction. While MMC of jejunum origin appeared. increased MMC cycle duration was seen after 4 d in rats with CBD obstruction. The MMC after CBD obstruction was characterized by an increased duration of phase II-like activity and decreased duration of phase I & III activity. Perfusion into stomachs with UDCA resulted in a shorter MMC cycle duration and a longer duration of phase III of duodenal origin compared to the normal group.

CONCLUSION: Entero-hepatic bile acid circulation initiates inter-digestive MMC of duodenal origin.

Effect of intraduodenal administration of ursodeoxycholic acid on interdigestive interaction between gallbladder motility, pancreatic secretion and endocrine activity

BACKGROUND

Gastroduodenal motorfunction, gallbladder motility, and pancreatic secretion are closely related during the interdigestive state. The extent to which application of ursodeoxycholic acid (UDC) influences this process is only partly understood.

AIM

As UDC is widely used for the therapy of gallbladder stones and of cholestatic liver disease, we wanted to define the immediate effect of UDC on interdigestive gallbladder and antroduodenal motility, biliary-pancreatic secretion and hormone release in man.

METHODS

Interdigestive gastrointestinal function in 10 healthy males (26-35 years) was studied twice after 12-hour fasting on 2 different days. Antroduodenal motility was continuously recorded manometrically over a complete interdigestive migrating motor complex (MMC) cycle. Gallbladder volume was evaluated sonographically in 5- to 7-min intervals during the MMC cycle. Pancreatic and biliary secretion was determined by a standard duodenal perfusion technique measuring chymotrypsin, amylase, lipase and bile salts in duodenal aspirates every 15 min. Plasma levels of pancreatic polypeptide (PP) and motilin were determined by radioimmunoassay in 15-min intervals. On 2 separate days, 7-10 days apart, each subject received intraduodenally either 10 mg/kg UDC (pH 8) or placebo 30 min after the first recorded duodenal MMC cycle phase III.

RESULTS

With placebo, the fasting gallbladder volume decreased slightly from phase I (32 +/- 8 ml) to the end of phase II (24 +/- 13 ml), but increased significantly from 31 +/- 14 ml (phase I) to 46 +/- 11 ml (phase III) after intraduodenal UDC application (p < 0.01). Pancreatic secretion was significantly reduced after UDC application at the end of phase II (secretion of chymotrypsin 10 +/- 3 U/min vs. 5 +/- 2 U/min, p < 0.01). Serum levels of PP were also reduced by UDC during the entire MMC cycle. This reached statistical significance at the end of phase II (84 +/- 8 pg/ml vs. 57 +/- 14 pg/ml; p < 0.05) and during phase III (86 +/- 19 pg/ml vs. 64 +/- 22 pg/ml; p < 0.05), while motilin slightly increased during the MMC cycle after UDC application. UDC instillation did not affect antroduodenal motility.

CONCLUSION

UDC exerts significant inhibitory effects on interdigestive gallbladder contractility, pancreatic secretion, and PP release. Whether these inhibitory effects are mediated by cholinergic pathways or other mechanisms requires further investigation.

Effects of motilin and ursodeoxycholic acid on gastrointestinal myoelectric activity of different origins in fasted rats

AIM: To investigate gastrointestinal migrating myoelectric complex (MMC) and the effects of porcine motilin and ursodeoxycholic acid (UDCA) on MMC of gastrointestinal tract of different origins in fasted rats.

METHODS: Three bipolar silver electrodes were chronically implanted on the antrum, duodenum and jejunum. Seven days later 24 experimental rats were divided into 2 groups. One group was injected with porcine motilin via sublingual vein at a dose of 20 μg/kg, the other group was perfused into stomach with UDCA. The gastrointestinal myoelectric activity was recorded 1 h before and 2 h after the test substance infusions into the rats.

RESULTS: In all fasted rats a typical pattern of MMC was observed. Among the totally 68 activity fronts recorded in fasted rats under control, 67% started in duodenum, and 33% in antrum. MMC cycle duration and duration of phase III of antral origin were longer than those of duodenal origin. Administration of 20 μg/kg porcine motilin induced a premature antral phase III of antral origin. But perfusion into stomach with UDCA resulted in shorter MMC cycle duration, longer duration of phase III of duodenal origin, which were followed with shorter cycle duration and duration of antral phase III.

CONCLUSION: In fasted rats, MMC could originate from antrum and duodenum respectively. The characteristics of MMC of different origins may contribute to the large variations within subjects. The mechanisms of different origins of phase III may be different. Porcine motilin and UDCA could affect MMC of different origins of the gastrointestinal tract in fasted state, respectively.

Compounded Versus Proprietary Sincalide for Evaluation of Gallbladder Ejection Fraction

OBJECTIVE

To report a comparison of compounded and proprietary sincalide in the evaluation of gallbladder ejection fraction during hepatobiliary scintigraphy.

CASE SUMMARIES

Two patients were referred to nuclear medicine with symptoms consistent with hepatobiliary dysfunction. Both underwent hepatobiliary scintigraphy to evaluate anatomic and physiologic tract patency of the hepatobiliary system. Compounded sincalide, an adjuvant pharmaceutical used to evaluate gallbladder ejection fraction, was infused during hepatobiliary scintigraphy, and gallbladder ejection fractions were 11% and 24%, respectively. Hepatobiliary scintigraphy was repeated on both patients 72 hours later with proprietary sincalide used as the adjuvant pharmaceutical. The gallbladder ejection fractions were 32% and 72%, respectively.

DISCUSSION

The use of sincalide to evaluate gallbladder ejection fraction in hepatobiliary scintigraphy is widely accepted in the surgical and nuclear medicine community. In late 2001, the sole manufacturer of sincalide announced indefinite unavailability of the product. Following the announcement, several compounding pharmacies began selling extemporaneously compounded sincalide as a replacement. Use of the compounded product has assumed therapeutic equivalence.

CONCLUSION

Significant differences in gallbladder ejection fraction between compounded sincalide and sincalide in our patients are likely due to the intrinsic variability in response to sincalide. Clinicians should be aware of this variability, as well as the potential effect of concomitant medications.

Sphingomyelin protects against apoptosis and hyperproliferation induced by deoxycholate: potential implications for colon cancer

High fecal deoxycholate levels may promote colonic cancer. Phospholipids protect against bile salt-induced cytotoxicity. We therefore aimed to examine whether the dietary phospholipid sphingomyelin could decrease hyperproliferation induced by deoxycholate. In CaCo2 cells, hyperproliferation (by bromodeoxyuridine assay), phosphorylation state of cellular proteins, and apoptosis with concomitant caspase-3 activity were evaluated after incubation with 50-500 microM deoxycholate, with or without sphingomyelin. At 2 and 4 hr of incubation, deoxycholate induced dose-dependent apoptosis, with concomitant caspase-3 activation. At 16 hr, apoptosis had decreased markedly, but there was dose-dependent hyperproliferation (with changed phosphorylation status of cellular proteins) at this time point. Sphingomyelin dose-dependently reduced deoxycholate-induced apoptosis and hyperproliferation. In conclusion, sphingomyelin reduces deoxycholate-induced hyperproliferation and apoptosis. These findings may have implications for colonic cancer prevention by dietary modification.

Effects of ileal bile salts on fasting small intestinal and gallbladder motility

In the fasting state, gallbladder emptying is related to phase III of the intestinal migrating motor complex. The effects of ileal infusion of mixed taurocholate-phospholipid micelles on fasting small intestinal motility (by a 17-channel catheter with side holes located in duodenum, jejunum and ileum) and gallbladder motility (by ultrasound) were investigated in eight healthy volunteers. After bile salt depletion by cholestyramine, 0.9% NaCl or mixed micelles were infused in the ileum during phase II of the migrating motor complex. Time to onset of subsequent phase III was significantly shorter after infusion of mixed micelles compared with 0.9% NaCl (32 +/- 5 min vs. 60 +/- 5 min, P = 0.01). Distal to the infusion port, numbers of pressure waves and their amplitudes were significantly lower during bile salt infusion compared with 15 min before infusion (11 +/- 6 per 15 min vs. 21 +/- 8 per 15 min, and 2.4 +/- 0.6 kPa vs. 2.8 +/- 0.5 kPa, respectively). Micellar infusions increased fasting gallbladder volumes to 170 +/- 5% of starting volumes (P < 0.0001). In conclusion, ileal infusion of mixed micelles influences the timing of phase III of the intestinal migrating motor complex, inhibits ileal motility and increases fasting gallbladder volumes. These findings may have important consequences for enterohepatic circulation of bile salts.