Isolation and characterization of a cholesterol crystallization promoter from human bile

BACKGROUND

Recent studies on the pathogenesis of cholesterol gallstone disease have focused on the potential importance of an imbalance between biliary proteins having either inhibitory or promoting activities on nucleation and/or growth of cholesterol crystals as the initial stage in stone formation. The current study describes the purification and partial characterization of a 42-kilodalton biliary glycoprotein that shows concentration-dependent cholesterol crystallization-promoting activity.

METHODS

Chromatographic methods were used for separation and purification. Characterization steps included electrophoresis, deglycosylation, amino acid and carbohydrate analysis, and activity analysis by crystal growth assay.

RESULTS

The 42-kilodalton purified glycoprotein is an extensively glycosylated (37%) monomer with an acidic isoelectric point (pl < 4.1) that is probably based on the sialic acid content of the carbohydrate moiety. Enzymatic N-deglycosylation removes the carbohydrate moiety and inactivates the promoting activity. Furthermore, enzymatic proteolysis results in both its complete structural degradation and functional inactivation. Although the glycoprotein was isolated from normal human gallbladder biles, its presence in gallstone-associated samples is clearly shown.

CONCLUSIONS

This report outlines biochemical features of a human biliary glycoprotein that may be of major pathophysiological significance in gallstone disease.

Hepatic excretion and metabolism of polyethylene glycols and mannitol in the cat

The biliary clearances of fluid phase markers like erythritol and mannitol have been used to estimate canalicular bile flow. Larger fluid phase marker molecules like polyethylene glycol (PEG) 900 are excreted more extensively into bile, and it has been suggested that the biliary clearance of these give a more accurate measure of canalicular water flux than those of erythritol and mannitol. In this study, the biliary excretion of PEG 900 was compared with that of mannitol during choleresis induced by either sodium taurocholate or secretin. The biliary excretion of PEG 900 exceeded that of mannitol by a factor of 94. The biliary clearance of these markers was not influenced by secretin-induced choleresis. Using ion-exchange chromatography and fast atom bombardment mass spectrometry (FABMS) it was demonstrated that 26% of the PEG molecules are excreted into bile after oxidation to carboxylic acids, whereas sulphate conjugation is negligible. The majority of the PEG molecules (74%) were secreted unchanged, which supports the hypothesis of a mainly passive movement of PEG with the water flux into bile. FABMS showed an enrichment of larger PEG molecules in bile, which supports a previous finding that among differently sized PEGs the 1074-Da molecules have the highest biliary excretion.

Location of enkephalinase and functional effects of [Leu5]enkephalin and inhibition of enkephalinase in the feline main pancreatic and bile duct sphincters

1. Morphological studies have demonstrated enkephalinergic nerve fibres in proximity to the sphincter of Oddi, and opiates are known to contract this sphincter. In this study, the flow resistances in the common bile duct and main pancreatic duct sphincters were studied simultaneously in anaesthetized cats using a perfusion technique. 2. Naloxone did not affect the activity of these sphincters under basal conditions, indicating that there is no basal enkephalinergic tone. 3. The response to [Leu5]enkephalin (0.015-15 micrograms/kg), morphine (1 mg/kg) and ketamine (10 mg/kg) was a naloxone-sensitive increased activity in the sphincters with a raised frequency of phasic contractions. The threshold dose for an effect of [Leu5]enkephalin on the sphincter of Oddi was 0.015 microgram/kg and a maximal response was observed at 0.75 microgram/kg. There were no differences in the response of the main pancreatic duct sphincter and the bile duct sphincter to the different drugs. 4. Immunoautoradiographic studies demonstrated enkephalinase in the sphincter++ of Oddi. 5. Acetorphan (3 mg/kg intravenously), which inhibits endogenous enkephalinase both in the peripheral and the central nervous system when administered parenterally, caused a naloxone-sensitive contraction, whereas thiorphan (3-20 mg/kg), an enkephalinase inhibitor that does not easily penetrate the blood-brain barrier, had no effect on the sphincter of Oddi. 6. These results show that endogenous and exogenous opiates influence the function of the feline sphincter of Oddi and that enkephalins may be involved in the physiological control of this sphincter, although not under basal conditions.

Adjuvant treatment with ursodeoxycholic acid reduces acute rejection after liver transplantation

Acute rejection, occurring with a reported frequency of 50-70%, is still a dominating problem after liver transplantation. Medication with ursodeoxycholic acid (UDCA) has beneficial effects in different cholestatic conditions and has also been shown to reduce HLA class I antigen expression on hepatocytes in patients with PBC. Since August 1989 we have consecutively treated all patients with primary graft function with UDCA (n = 41). Patients transplanted in the first half of 1989 served as a control group (n = 8). All patients in this study were given sequential quadruple drug immunosuppression. The treatment group were given oral UDCA 10 mg/kg per day. During the first postoperative month, 17% of the UDCA-treated patients had an episode of acute rejection compared with 75% of the control patients (P < 0.01). Liver biochemistry tests 1 month postoperatively were significantly better in patients treated with UDCA. The results suggest that adjuvant treatment with UDCA reduces acute liver graft rejection.

Effect of short-term indomethacin treatment on the clinical course of acute obstructive cholecystitis

In acute obstructive cholecystitis the increased intraluminal pressure in the gallbladder is reduced by nonsteroid anti-inflammatory drugs which effectively relieve biliary pain. To investigate if such drugs influence the clinical course, a double-blind study was performed in which indomethacin (suppositories 75 mg b.d.) was tested against placebo in 34 patients with acute obstructive cholecystitis. During the 3-day treatment period both the indomethacin and the placebo group improved significantly as regards pyrexia, pain, abdominal tenderness and leukocytosis. The indomethacin group showed significantly greater improvement than the placebo group in temperature, pain and white blood cell count on day 1, and significantly greater reduction of abdominal tenderness on day 2. The serum bilirubin fell significantly during the 3-day period in the indomethacin, but not the placebo group. The hospital stay in cases without early surgery was significantly shorter in the indomethacin group (5.4 vs. 8.5 days). Because of its favourable effect on the clinical course of acute cholecystitis, rectally administered indomethacin is useful for patients awaiting operation or scheduled for later elective surgery.

Adrenergic influence on bile secretion--an experimental study in the cat

The influence on bile secretion of electrical stimulation of the splanchnic nerves and arterial infusion of adrenergic agonists was studied in anaesthetized cats. The bile salt secretion was supported by a continuous intravenous infusion of sodium glycocholate. Electrical stimulation of the splanchnic nerves reduced the volume outflow of bile from 0.71 to 0.44 ml h-1 kg-1 body wt and raised the bile acid concentration in bile, while the bile salt secretion rate was not affected. This response was reduced but not blocked by pretreatment with phentolamine, an alpha-adrenergic blocker, at a dose that prevented the blood pressure response. Infusion of noradrenaline, a mainly alpha-adrenergic agonist, into the hepatic artery mimicked the response. Infusion of isoprenaline, a beta-adrenergic agonist, also reduced the volume outflow of bile from the liver. The biliary clearances of mannitol and polyethylene glycol 900, both of which are suggested to reflect canalicular events, were reduced by stimulation of the splanchnic nerves and infusion of noradrenaline. It is concluded that stimulation of the alpha-adrenergic receptors reduces the bile acid-independent bile secretion. This reduction in bile flow induced by stimulation of the splanchnic nerves and infusion of noradrenaline is elicited mainly at the canalicular level.

Biliary excretion of different sized polyethylene glycols in the cat

Polyethylene glycol (PEG) 900 is excreted more extensively into bile than mannitol and erythritol. In this study, the biliary recovery of intravenously injected marker molecules was analysed in anaesthetised cats with ligated renal pedicles. It was demonstrated that among polyethylene glycols sized 292-1250 Da, the species sized 1074 Da was maximally excreted in the bile. After 5 h, about 12% of the injected amount of this molecular species was recovered in bile. Both larger and smaller polyethylene glycol molecules had a lower biliary excretion. The distribution of different sized PEGs in the range 766-1250 Da in serum was fairly constant and cannot explain the recovery profile in bile. 14C-Labelled mannitol was recovered in bile to the extent of 0.7% of the amount given i.v. after 5 h, a figure that corresponds to that obtained for polyethylene glycol with a size of 370 Da. Bile/plasma ratios during steady state conditions of labelled PEG 450, PEG 900, PEG 2500 and PEG 4000 were 10, 36, 3 and 4, respectively. The results may be tentatively explained by restricted passage of the larger PEG molecules into the canaliculi, and leakage of the smaller molecules from bile back to plasma.

A porcine model for acute distal aortic occlusion

Periarterial and intramural nerves and lymphatics as well as the vascular endothelium may influence pathophysiologic responses to acute arterial occlusion. For study of such pathophysiologic patterns, experimental models resembling the clinical situation are therefore preferable. In this porcine study acute distal aortic occlusion was mimicked by use of a balloon catheter introduced via a vascular graft anastomosed to the lateral aortic wall. Peripheral circulatory disturbance was assessed by measurements of femoral vein blood flow, skin blood flow in the hind foot and oxygen tension in the calf muscle, which verified the degree of ischemia. During the 4-hour ischemic period, repeated arterial and venous blood gas analyses showed increasing acidosis in effluent venous blood from the hind limbs, which after reperfusion slowly normalized. As highly reproducible conditions are achievable with the present experimental model, it can be used for studies of pathophysiologic responses to acute distal aortic occlusion.

Functional and morphological relationships between the feline main pancreatic and bile duct sphincters

To analyze the relationships between the bile duct and main pancreatic duct sphincters, the resistance to flow through these sphincters was studied simultaneously with perfusion techniques in anesthetized cats. Basal flow resistance was higher in the pancreatic sphincter than in the bile duct sphincter. The pressure in one duct system was not affected by the flow in the other. The muscular activities in the sphincters were usually well coordinated. Distention of the upper biliary tract or the pancreatic duct system reduced the flow resistance in both sphincters. Cholecystokinin-8 (0.01 micrograms), duodenal distention, and sublingual glyceryl trinitrate (0.4 mg) also relaxed both sphincters, whereas secretin in a dose that induced pancreatic secretion had no consistent effect. Morphine increased flow resistance in both systems. These functional studies indicate that the 2 sphincters share smooth muscle fibers at the level where the flow resistances arise, and there are thus no grounds for separate control of the sphincters. There was no evidence of a functionally common sphincter ampulla. The conclusions drawn from the manometric results were supported by morphological findings in this study.

Hepatobiliary compensation for the loss of gallbladder function after cholecystectomy. An experimental study in the cat

The side effects of the removal of a functioning gallbladder are surprisingly few, and it has been suggested, but never demonstrated, that the hepatobiliary tract then adjusts to compensate for the loss of gallbladder function. In this study the effects of cholecystectomy on bile acid kinetics, bile flow, and biliary clearance of mannitol were studied in cats 6-8 weeks after cholecystectomy. An enhanced recycling rate of a diminished bile acid pool was found. The bile flow was reduced and the bile acid concentration in hepatic bile was increased, but fasting bile acid secretion rate was not changed. Both when the bile acid secretion rate was reduced by drainage via an acute bile fistula and when it was enhanced by intravenous infusion of glycocholic acid, there was a lower bile acid-independent flow in the cholecystectomy group. This reduced bile flow after cholecystectomy was not explained by the higher proportion of deoxycholic acid present in the bile of the cholecystectomized animals. Biliary clearance of mannitol, which is supposed to reflect the canalicular inflow, was not reduced, indicating that the reduction in bile flow is explained by a reduced fluid secretion or an enhanced fluid reabsorption in the bile ductules and ducts after cholecystectomy. In this manner the bile ducts compensate for the loss of the absorptive function of the gallbladder after cholecystectomy.

Naloxone-reversible inhibition of gall-bladder mucosal fluid secretion in experimental cholecystitis in the cat by acetorphan, an enkephalinase inhibitor

1. Enkephalin immunoreactive nerve fibres have been demonstrated in the gall bladder of various mammals including man. In various tissues, enkephalins are partly degraded by a membrane metallo-endopeptidase, enkephalinase (EC 3.4.24.11). 2. Using 3H-labelled [D-Ala2,Leu5]enkephalin as a substrate, enkephalinase activity, immunoprecipitated by a monoclonal antibody directed against the rabbit kidney enzyme, was demonstrated in the feline gall bladder. Using the same antibody in 125I-labelled form, the peptidase was immunolocalized by autoradiography, mainly in the epithelium. 3. In experimental cholecystitis, elicited by implantation of human gall-stones into the cat gall bladder, the continuous fluid secretion into the lumen was inhibited by exogenous enkephalins. 4. Acetorphan, an enkephalinase inhibitor, was found to block fluid secretion by the inflamed gall bladder via a naloxone-sensitive mechanism, but not to affect fluid transport in the normal gall bladder. The drug also transiently contracted the gall bladder and increased bile outflow from the liver. 5. It is suggested that acetorphan, by reducing the degradation of endogenous enkephalins in the inflamed gall bladder, decreases fluid secretion by the epithelium and that enkephalinase inhibitors may find clinical applications in acute cholecystitis.

Hypercholeresis after release of protracted extrahepatic cholestasis. Case report

A case of hypercholeresis following release of protracted extrahepatic obstruction causing dehydration and metabolic acidosis is described. Possible background mechanisms for post-cholestasis hypercholeresis are briefly discussed.

Vasoactive intestinal peptide in the normal and inflamed feline gallbladder

Intravenous infusion of vasoactive intestinal peptide (VIP) causes gallbladder mucosal fluid secretion by an action on epithelial cell receptors in the cat. Gallbladder fluid secretion is observed also in experimental cholecystitis and this secretion is abolished when the intramural gallbladder nerves are blocked. In the present study, immunoreactive VIP was detected in the gallbladder contents (29 +/- 5 (S.E.M.) pM) in the obstructed lumen of the gallbladder in cats with experimental cholecystitis and gallbladder mucosal fluid secretion, but not in the normal feline gallbladder. During luminal perfusion of the gallbladder in vivo, the calculated secretion of VIP into the gallbladder lumen in animals with experimental cholecystitis was significantly higher (0.31 +/- 0.08 (S.E.M.), pmol/h) than in controls (0.11 +/- 0.02 (S.E.M.), pmol/h) while plasma levels of VIP were similar. Recovery of exogenously administered VIP was similar in normal and inflamed gallbladders. The present results support the hypothesis that intramural VIP-releasing nerve fibers may be activated in cholecystitis.

Prostaglandin precursor fatty acids in serum and bile as influenced by oophorectomy, contraceptive steroids and pregnancy. An experimental study in the cat

Variations in the occurrence of prostaglandin precursor fatty acids might be of importance for the pathogenesis of gallstones. Pregnancy and use of contraceptive steroids increase the risk of gallstones. The present study reports the relative fatty acid composition in serum and biliary phospholipids studied by gas-liquid chromatography in four groups of female cats, which were on a standard diet: 1) oophorectomized animals, 2) animals on contraceptive steroids, 3) pregnant animals and 4) control animals. It was consistently found that the portions of palmitic and linoleic acid were higher and stearic and arachidonic acid were lower in biliary than in serum lecithin. In biliary lysolecithin, sphingomyelin and cephaline there were only small portions of linoleic and negligible amounts of arachidonic acid. Oophorectomy, contraceptive steroids or pregnancy did not induce any gross changes in the fatty acid pattern of lecithin in serum or bile. In animals treated with contraceptive steroids a reduced portion of linoleic acid was seen in the bile lecithin, and in pregnant animals there was a reduction of omega 3 and omega 6 fatty acids in biliary lecithin.

Flow resistance in the feline choledocho-duodenal sphincter as studied by constant-pressure and constant-perfusion techniques

During interdigestive periods, there is a resistance to flow in the biliary tract exerted by the sphincter of Oddi, resulting in a pressure gradient between the common bile duct and the duodenum. In this experimental study, this flow resistance was studied with both a constant-flow and a constant-perfusion technique in fasted, anaesthetized cats. The flow resistance exerted by the sphincter is higher when it is perfused by a constant flow compared to when the common bile duct pressure is kept constant and the flow varies in response to its muscular activity. It was demonstrated with each method that the flow resistance in the choledocho-duodenal junction is reduced in response to distension of the biliary tree and gallbladder and also by distension of the duodenum. Cholecystokinin was shown to reduce the flow resistance in the choledocho-duodenal junction as estimated with either method.