Early stages of gallstone formation in guinea pig are associated with decreased biliary sensitivity to cholecystokinin

Cholecystokinin and gastrin receptors targeting in gastrointestinal cancer

Cholecystokinin and Gastrin are amongst the first gastrointestinal hormone discovered. In addition to classical actions (contraction of gallbladder, growth and secretion in the stomach and pancreas), these also act as growth stimulants for gastrointestinal malignancies and cell lines. Growth of these tumours is inhibited by antagonists of the cholecystokinin and gastrin receptors. These receptors provides most promising approach in clinical oncology and several specific radiolabelled ligands have been synthesized for specific tumour targeting and therapy of tumours overexpressing these receptors. Therefore, definition of the molecular structure of the receptor involved in the autocrine/paracrine loop may contribute to novel therapies for gastrointestinal cancer. Hence, this review tries to focus on the role and distribution of these hormones and their receptors in gastrointestinal cancer with a brief talk about the clinical trial using available agonist and antagonist in gastrointestinal cancers.

Cholecystokinin

PURPOSE OF REVIEW

The hormone cholecystokinin was discovered in 1928 because of its ability to induce gallbladder contraction. Since then, cholecystokinin has been shown to possess multiple functions in the gastrointestinal tract and brain. This review discusses several significant developments in cholecystokinin biology that show how it plays a role in gastrointestinal diseases, including control of appetite.

RECENT FINDINGS

Cholecystokinin was shown to induce satiety by interacting through CCK-1 receptors located in specialized regions of the hindbrain. Cholecystokinin also inhibits expression of orexigenic peptides in the hypothalamus and prevents stimulation of specialized neurons by ghrelin. In the pancreas, cholecystokinin increased the proliferation of insulin-producing beta cells and reduced insulin-induced hyperphagia. Elevated cholecystokinin levels decreased appetite and reduced intestinal inflammation caused by parasites and bacterial toxins.

SUMMARY

Understanding the mechanisms by which cholecystokinin regulates orexigenic pathways in the body may lead to strategies for controlling appetite-related disorders such as obesity and bulimia. The reduction of intestinal inflammation by dietary fats (by elevating cholecystokinin) suggests that the hormone plays an integrated role in regulating the ingestion and digestion of food that may be relevant to inflammatory diseases of the gastrointestinal tract.

Cholecystokinin (CCK) down regulates PGE2 and PGI2 release in inflamed Guinea pig gallbladder smooth muscle cell cultures

This study examines the hypothesis that cholecystitis down-regulates Guinea pig gallbladder (GPGB) smooth muscle cholecystokinin (CCK)-stimulated prostaglandin (PG) release. Guinea pig gallbladder from Control and 48 h bile duct ligated (BDL) animals were placed in cell culture and grown to confluence. The cultures underwent Western Blot analysis for smooth muscle cell content of COX-1, COX-2, Prostacyclin Synthase (PS), or were incubated with CCK at 10(-8)M or 10(-6)M with and without indomethacin for 1h and analyzed for release of 6-keto-PGF1alpha, PGE2 and TxB2 by EIA. BDL increased Guinea pig gallbladder cell culture basal PGE2 and PGI2 release which was in part due to increased COX-2 content. CCK incubation down-regulated BDL Guinea pig gallbladder cell culture release of 6-keto-PGF1alpha and PGE2 and down-regulated COX-2 content but did not alter the Control group. The decrease in CCK-mediated BDL cell Guinea pig gallbladder release may be an endogenous mechanism to limit physiologic derangements induced by increased endogenous gallbladder PG synthesis during early acute cholecystitis.

Gallbladder motor function, plasma cholecystokinin and cholecystokinin receptor of gallbladder in cholesterol stone patients

AIM: To study the interactive relationship of gallbladder motor function, plasma cholecystokinin (CCK) and cholecystokinin A receptor (CCK-R) of gallbladder in patients with cholesterol stone disease.

METHODS: Gallbladder motility was studied by ultrasonography in 33 patients with gallbladder stone and 10 health subjects as controls. Plasma CCK concentration was measured by radioimmunoassay in fasting status (CCK-f) and in 30 min after lipid test meal (CCK-30). Radioligand method was employed to analyze the amount and activity of CCK-R from 33 gallstone patients having cholecystectomy and 8 persons without gallstone died of severe trauma as controls.

RESULTS: The percentage of cholesterol in the gallstone composition was more than 70%. The cholesterol stone type was indicated for the patients with gallbladder stone in this study. Based on the criterion of gallbladder residual fraction of the control group, 33 gallstone patients were divided into two subgroups, contractor group (14 cases) and non-contractor group (19 cases). The concentration of CCK-30 was significantly higher in non-contractor group than that in both contractor group and control group (55.86±3.86 pmol/L vs 37.85±0.88 pmol/L and 37.95±0.74 pmol/L, P<0.01), but there was no difference between contractor group and control group. Meanwhile no significant difference of the concentration of CCK-f could be observed among three groups. The amount of CCK-R was lower in non-contractor group than those in both control group and contractor group (10.27±0.94 fmol/mg vs 24.59±2.39 fmol/mg and 22.66±0.55 fmol/mg, P<0.01). The activity of CCK-R shown as KD in non-contractor group decreased compared to that in control group and contractor group. Only was the activity of CCK-R lower in contractor group than that in control group. The ejection fraction correlated closely with the amount of CCK-R (r = 0.9683, P<0.01), and the concentration of CCK-30 correlated negatively with the amount of CCK-R closely (r = -0.9627, P<0.01).

CONCLUSION: The distinctive interactive relationship of gallbladder emptying, plasma CCK and CCK-R in gallbladder from this study suggested that the defect of CCK-R may be a key point leading to the impairment of gallbladder motor function and the pathogenesis of cholesterol gallstone formation may differ in two subgroups of gallstone patient, gallbladder non-contractor group or contractor group.

Smooth muscle function and dysfunction in gallbladder disease

The gallbladder epithelium and smooth muscle layer are exposed to concentrated biliary solutes, including cholesterol and potentially toxic hydrophobic bile salts, which are able to influence muscle contraction. Physiologically, gallbladder tone is regulated by spontaneous muscle activity, hormones, and neurotransmitters released into the muscle from intrinsic neurons and extrinsic sympathetic nerves. Methods to explore gallbladder smooth muscle function in vitro include cholecystokinin (CCK) receptor-binding studies and contractility studies. In human and animal models, studies have focused on cellular and molecular events in health and disease, and in vitro findings mirror in vivo events. The interplay between contraction and relaxation of the gallbladder muscularis leads in vivo to appropriate gallbladder emptying and refilling during fasting and postprandially. Defective smooth muscle contractility and/or relaxation are found in cholesterol stone-containing gallbladders, featuring a type of gallbladder leiomyopathy; defects of CCKA receptors and signal transduction may coexist with abnormal responses to oxidative stress and inflammatory mediators. Abnormal smooth musculature contractility, impaired gallbladder motility, and increased stasis are key factors in the pathogenesis of cholesterol gallstones.

Review article: in vitro studies of gall-bladder smooth muscle function. Relevance in cholesterol gallstone disease

The interplay between contraction and relaxation in the gall-bladder muscularis leads to appropriate gall-bladder emptying and refilling during fasting and in the postprandial state in vivo. Several studies in both human and animal models have focused on cellular and molecular events in the gall-bladder wall in health and disease in vitro. Principal methods to study gall-bladder smooth muscle function include receptor binding studies (at the level of plasmamembranes or histological sections), phase contrast microscopy (at the level of isolated smooth muscle cells), and tensiometry (at the level of smooth muscle strips or the whole gall-bladder). At a very early stage, cholesterol gallstone disease is characterized by exposure of the gall-bladder wall to excess of biliary cholesterol and the cytotoxic effect of the bile salt deoxycholate. On a long-term basis, a form of gall-bladder leiomyopathy develops with defects involving the mechanisms of signal transduction at the level of plasmamembranes. The end-stage result is pathological contraction and/or relaxation of smooth musculature, impaired gall-bladder motility and gall-bladder stasis, all key factors in the pathogenesis of biliary cholesterol crystallization and gallstones.

Humoral mechanisms and clinical aspects of biliary tract motility

This review is intended to summarize current information on neurohumoral regulation of the gallbladder and sphincter of Oddi motility under both physiological and pathological circumstances with emphasis on Hungarian contributions to today's knowledge. The mechanism of action of neurohumoral agents that interact on these segments of the biliary tract, and the explored details of the stimulation-contraction/relaxation coupling process of these substances, will be discussed. A modified classification of biliary tract motility disorders with new diagnostic and therapeutic approaches will also be provided. This information will aid understanding of the pathogenesis of motor disorders of the gallbladder and sphincter of Oddi, and will indicate possibilities for pharmacological exploitation in the treatment of diseases resulting from biliary tract motility abnormalities.

Gallbladder emptying in vivo, bile composition, and nucleation of cholesterol crystals in patients with cholesterol gallstones

BACKGROUND/AIMS

Impaired postprandial gallbladder emptying may provide time for progressive bile concentration with formation of instable cholesterol-rich vesicles and fast nucleation of cholesterol crystals. The aim of this study was to assess postprandial gallbladder emptying, bile composition, and nucleation of cholesterol crystals in the same patient.

METHODS

In 30 patients with cholesterol gallstones, postprandial gallbladder emptying was measured ultrasonographically. In each patient, gallbladder bile composition (obtained at cholecystectomy) and nucleation of cholesterol crystals was determined. Patients were divided in 22 strong contractors (> 50% postprandial gallbladder emptying) and 8 weak contractors.

RESULTS

In weak contractors, bile salt and phospholipid concentrations were much higher than in strong contractors (234.6 +/- 24.7 vs. 130.3 +/- 10.8 mmol/L [P < 0.001] and 44.5 +/- 3.5 vs. 30.2 +/- 3.1 mmol/L [P < 0.05], respectively). Cholesterol concentrations were comparable in strong and weak contractors. Consequently, total lipid concentration was significantly higher (15.5 +/- 1.4 and 9.2 +/- 0.7 g/dL; P < 0.001) and cholesterol saturation index significantly lower (0.90 +/- 0.08 and 1.61 +/- 0.17; P < 0.001) in weak contractors. Nucleation time, percentage of cholesterol in vesicles, bile salt species, and molecular species of phosphatidylcholine were not significantly different.

CONCLUSION

Differences in bile composition can be linked to different patterns of postprandial gallbladder emptying and may point to two different pathways of gallstone formation.

Cholesterol gallstone formation in man and potential treatments of the gallbladder motility defect

Cholelithiasis affects 10-15% of the adult population in Western society, and about 75% of gallstones are of cholesterol type. Hepatic hypersecretion of cholesterol with the formation of instable cholesterol-rich vesicles in bile, an imbalance between nucleation-inhibiting and nucleation-promoting proteins with further aggregation of cholesterol crystals in a gallbladder with a motility defect (stasis), all play a role in the pathogenesis of cholesterol gallstones. Experimental animal models suggest that gallstone formation can be prevented by improving gallbladder emptying. Thus, a better understanding of the causes underlying the impaired gallbladder motor function in patients with gallstones might lead to the selection of therapeutic approaches for those individuals who are at increased risk for the formation or recurrence of gallstones. The present article focuses on current concepts and theories on the pathogenesis of cholesterol gallstones with emphasis on the gallbladder motility defect. Several treatment strategies for the correction of gallbladder hypomotility are also discussed.

Physiology and pathophysiology of gallbladder motility

Most significant gallbladder disease is associated with gallbladder stasis. Gallbladder motility is controlled by a complex interplay of hormonal and neural factors. Experimental and clinical studies have demonstrated impaired motility in gallstone disease, and experimental evidence indicates that motility disturbances precede gallstone formation. The ability to measure gallbladder motility clinically has also resulted in better diagnosis and treatment for patients with chronic acalculous cholecystitis.