Total Bile Acid Pool Size Research Articles

Cholesterol absorption in cirrhosis: The role of total and individual bile acid pool size

Dietary cholesterol absorption was studied in patients with either “mild” (n = 23) or “severe” (n = 12) liver cirrhosis in relation to both total and individual bile acid pool size. Cholesterol absorption was significantly reduced in both groups of patients, and it was inversely related (r = −0.68; p < 0.001) to the severity of the disease. Total, cholic acid, and deoxycholic acid pool sizes were significantly reduced in cirrhosis, and a correlation was found between cholesterol absorption and cholic acid pool size (r = 0.78; p < 0.001). In 5 patients, cholesterol absorption and bile acid pool size were estimated both before and after treatment with cholic acid (15 mg/kg/day) plus ampicillin (2 g/day). The treatment was followed by a mean threefold increase of cholic acid pool and by a sharp enhancement of cholesterol absorption in each patient. In conclusion, cholesterol absorption is often impaired in cirrhosis and is related to the severity of the disease. The correlation between cholic acid pool and cholesterol absorption and the constant increase of the absorption values after cholic acid pool expansion suggest that the size of cholic acid pool may be considered as an important factor in the regulation of cholesterol absorption.

Bile lipid alterations in taurine-depleted monkeys

Newborn cebus and cynomolgus monkeys, differing in their inherent taurine-glycine conjugation of bile acids, were fed taurine-free soy protein infant formula (Isomil) with or without added taurine (500 mg/kg dry diet). After 5 months, monkeys were anesthetized, their enterohepatic circulation interrupted, and their bile pool drained for 4.5 h. Bile acid conjugation, total bile acid pool size, biliary lipid composition, and theoretical maximal cholesterol solubility in bile were determined. Taurine depletion in cebus monkey, an obligate taurine conjugator (97%), did not reduce bile acid conjugation with taurine, or did it alter bile acid pool size, biliary lipid composition, or theoretical maximal cholesterol solubility in bile. Conversely, taurine depletion in cynomolgus, a species normally conjugating with some glycine (15 to 20%), significantly reduced conjugation of taurine with bile acids from 84 to 64%, essentially doubling that of glycine from 16 to 36%. Furthermore, theoretical maximal cholesterol solubility in cynomolgus bile improved significantly as a result of taurine depletion. This improvement was associated with increased percentage distribution of biliary phospholipid from 17 to 33%, in turn reflecting an increase in the taurochenodeoxycholate to taurocholate ratio from 0.7 to 2.9. Concomitant increase in biliary cholesterol concentration associated with increased glycine conjugation precluded any changes in the percent saturation of bile which remained constant at 130% for both dietary groups of cynomolgus. Taurochenodeoxycholate uniquely conserved taurine in the face of body taurine depletion. Taurine availability thus potentially has a substantial influence on bile acid characteristics and cholesterol solubility in a glycine conjugating primate.

Kinetics of the enterohepatic circulation during fasting: Biliary lipid secretion and gallbladder storage

In both experimental animals and humans, cholesterol saturation of bile increases by varying degrees during interruption of the enterohepatic circulation. Thus, dynamic aspects of the enterohepatic circulation during fasting—including gallbladder filling and emptying, and fasting outputs of biliary lipids—should be important considerations for the pathogenesis of gallstones. Therefore, for the present report, we developed and validated techniques of estimating storage capacity of the gallbladder and hepatic outputs of biliary lipids during fasting. These new methods require the use of bilirubin and [14C]cholic acid as “endogenous” and “exogenous” bile markers, respectively; with them, amounts of bile acids in the nocturnal gallbladder may be determined and related to total bile acid pool size. In studies on 6 cholecystectomized subjects, we showed that hourly outputs of bilirubin were constant throughout the day, so that in addition to monitoring gallbladder function, this marker may be used to calculate nocturnal outputs of biliary lipids. In 7 subjects with gallstones and radiologically functioning gallbladders, measurements of nocturnal storage of bile acids in the gallbladder preoperatively (bilirubin marker method) and intraoperatively ([14C]cholic acid method) gave comparable results. These studies were extended to include 14 control subjects without gallstones, 12 subjects with cholesterol gallstones, and 6 subjects with pigment stones. Mean pool size of bile acids in subjects with cholesterol stones was smaller (1818 ± SEM 278 mg) than that in controls (2624 ± 524 mg) or in those with pigment stones (2422 ± 481 mg); however, these differences were not statistically significant. Percentage of the total bile acid pool stored overnight in the gallbladder also was not different in the three groups, being 58 ± 7% for controls, 47 ± 6% for cholesterol, and 54 ± 8% for pigment stone subjects. Volumes of gallbladder contents (bile plus gallstones) were similar in the 2 groups with stones. While subjects with cholesterol cholelithiasis had the highest cholesterol saturation of bile, no inverse correlation could be found between either total bile acid pool or nocturnal gallbladder bile acid mass, and saturation indices of bile for the groups as a whole. During fasting, hepatic bile became increasingly saturated because of a relatively well-maintained secretion of cholesterol. The mean fasting output was 67 ± 3% of the mean 24-hr secretion compared to 51 ± 3% and 54 ± 4%, respectively, for bile acids and phospholipids. The nocturnal increase in biliary cholesterol:phospholipid molar ratio was variable from subject to subject, and the degree of this variability was crucial in determining the subsequent change in bile saturation.

Oral contraceptives raise the cholesterol saturation of bile by increasing biliary cholesterol secretion

To discover the mechanism by which oral contraceptives increase the level of cholesterol saturation of human bile, we measured biliary lipid secretion rates, gallbladder and hepatic bile lipid composition, bile acid pool size, bile acid composition, and plasma lipoprotein levels in five healthy women during routine oral contraceptive treatment and again during normal menstrual cycles on no medication. The molar percent cholesterol in both gallbladder and hepatic bile was higher in every subject while taking oral contraceptives ( p < .02). Oral contraceptive usage was accompanied by a significant enhancement of biliary cholesterol secretion (65 versus 46 mg/hr, p < .01), but there was no significant change in bile acid or phospholipid secretion, total bile acid pool size, or bile acid composition. These findings indicate that oral contraceptive usage increases biliary cholesterol secretion, thereby raising the level of cholesterol saturation of bile and predisposing to cholesterol precipitation and gallstone formation.

The effect of polyunsaturated fats on bile acid metabolism and cholelithiasis in squirrel monkeys

Squirrel monkeys (Saimiri sciureus) were fed diets containing safflower oil, butter, or coconut oil and 1 mg cholesterol/cal for 15--17 mo to examine the effect of type of fat on cholelithiasis and bile acid metabolism. Controls were fed low cholesterol diets containing an isocaloric mixture of the three fats. Cholic acid fractional catabolic rate, pool size, chenodeoxycholic acid pool size, and total bile acid pool size and excretion rate were estimated using a modification of Lindstedt's isotopic turnover procedure. The animals fed the safflower oil diet had the highest incidence of cholelithiasis (9/10) when compared to those fed butter (3/7) and coconut oil (1/7). Animals consuming the low cholesterol control diet did not develop gallstones. The butter- and coconut oil-fed groups had significantly (p less than 0.05) expanded bile acid pools when compared to controls, and the butter-fed group had a significantly increased (p less than 0.05) cholic acid fractional catabolic rate. The safflower oil group had the smallest mean bile acid pool and the highest mean lithogenic index of the cholesterol-fed groups. It was concluded that the safflower oil-fed animals had a higher incidence of cholelithiasis than the butter group because, unlike the latter group, they did not compensate for a high cholesterol intake by stimulating bile acid synthesis. The animals consuming coconut oil apparently did not absorb cholesterol to the extent of the other groups and as a result their bile did not become saturated with cholesterol.

Sex differences in the size of bile acid pools

In view of the excess prevalence of gallstones among women and the association of gallstones with diminished bile acid pool size, we measured bile acid pools in 27 male and 25 female healthy human volunteers. The average bile acid pool in the women was significantly smaller than in the men (2.25 ± .12 g versus 2.88 ± .16 g; p = 0.003). Chenodeoxycholic acid pool size, computed from bile acid composition data available in 43 of these subjects, was also smaller in women than men (0.94 ± 0.06 versus 1.22 ± 0.07 g; p = 0.004). Age, race, and body size bore no statistically significant relationship to bile acid pool size. Biliary cholesterol saturation was positively correlated with weight and obesity and showed a significant inverse correlation with chenodeoxycholic acid pool size, but not with total bile acid pool size. These findings suggest a possible mechanism for the higher prevalence of gallstones among women.

Bile Salt Kinetics in Cystic Fibrosis: Influence of Pancreatic Enzyme Replacement

Bile acid kinetics was investigated by stable isotope dilution technique in 6 children (ages 3/sup 1///sub 2/ months to 4/sup 1///sub 2/ years) with previously untreated cystic fibrosis. All of the patients had clinical and laboratory evidence of malabsorption, normal intestinal mucosal function, as judged by glucose absorption, intestinal histology, disaccharidase levels, and normally functioning gallbladders. The children were maintained on a constant diet throughout the study period; fat intake averaged 4.2 g per kg per day. Before administration of pancreatic enzyme replacement, fat excretion equalled 50 +- 4% (mean +- SE) of intake and was reduced to 20 +- 1.0% of intake after therapy. Total bile acid pool size nearly doubled during enzyme replacement from 379 +- 32 ..mu..moles per kg to 620 +- 36 ..mu..moles per kg with secondary bile acids comprising 57% of the total pool before therapy and 40% after therapy. The data indicate that both primary and secondary bile acids are conserved within the enterohepatic circulation during enzyme therapy, and that the mechanism for the regulation of hepatic bile acid synthesis is intact in cystic fibrosis. However, the demonstration that large amounts of bile acid continue to be excreted during therapy suggests that interruption ofmore » the enterohepatic circulation continues and that deficiencies of the intraluminal phase may persist during enzyme therapy in this disease.« less

Effect of Phenobarbital on Biliary Lipid Metabolism in Normal Man

The efficacy of phenobarbital in altering biliary lipid composition in normal man was investigated by determining parameters of biliary lipid metabolism in 8 human subjects without biliary tract disease before and after oral phenobarbital administration at a dose of approximately 3 mg per kg per day for 25 to 54 days. In 8 subjects studied, phenobarbital did not produce any statistically significant changes in the following parameters: bile lipid composition, cholesterol saturation index, total bile acid pool size, daily fractional turnover rate of cholic acid, hepatic secretion rates of cholesterol, bile acids, or phospholipids, and the fraction of the total bile acid pool represented by individual bile acids. Therefore, phenobarbital is not an effective agent, at least when used alone, in inducing changes in bile lipid composition during a short term of administration in normal man. This would indicate that phenobarbital would not be a useful modality in the prevention of the development of cholesterol gallstones, but its prophylactic value in subjects with bile of higher lithogenicity cannot be predicted from these studies.

Effects of contraceptive steroids and pregnancy on bile composition and kinetics in the baboon

The effects of subcutaneous implants of ethinyl estradiol (EE) and norethindrone (NE) alone and in combination and pregnancy on bile composition and kinetics were studied in the baboon. Treatment with EE significantly (p less than .01) reduced biliary cholesterol; the addition of NE enhanced this effect. NE alone however produced a slight increase in biliary cholesterol. During the third trimester of pregnancy both biliary cholesterol and the lithogenic index were significantly (p less than .05) decreased. The chenodeoxycholic acid pool (CAP) size was significantly (p less than .05) decreased by EE and further decreased by EE plus NA (p less than .01). NET alone resulted in an increase in CAP size. CAP size was also reduced by pregnancy though the reduction was not significant (p less than .05) until the third trimester. EE plus NE significantly (p less than .05) increased deoxycholic acid pool (DAP) size though NE along could not sustain this increase. DAP size in pregnancy decreased during the third trimester. No net change in total bile acid pool size was observed during any of the periods of EE or EE plus NE though there was a significant (p less than .05) net decrease in total bile salt pool size during the third trimester of pregnancy. The relevance of the findings to the formation of gallstones in the human female is discussed.

Effects of fasting on bile acid metabolism and biliary lipid composition in man

The effects of a four to six day fast on gallbladder bile lipid composition, bile acid pool size, bile acid composition, and cholic acid metabolism have been determined in normal human subjects. Total bile acid pool size and cholic acid pool size were measured before and after fasting by a one-sample technique previously validated in our laboratory. The rate of synthesis of cholic acid and its fractional turnover rate before fasting were measured using standard techniques. Estimates of fasting cholic acid synthesis rate and fractional turnover rate were calculated as daily averages from the change in cholic acid pool size, in combination with the change in cholic acid specific activity, during the fasting period. Since these estimates are approximate, a maximum value for cholic acid synthesis rate during fasting was also determined by assuming that the entire change in cholic acid specific activity during the fasting period occurred instantaneously. The molar percent of cholesterol in gallbladder bile was reduced in eight of nine subjects after a four to six day fast (p less than .01; mean reduction 30.5%). The molar percents of bile acid and phospholipid were not significantly altered by fasting. The cholesterol saturation index, calculated on the basis of these data, was reduced by an average of 31.0% after a four to six day fast (p less than .02). The average daily cholic acid synthesis rate and the fractional turnover rate were reduced in all six subjects on whom isotope kinetic studies were carried out. The mean decrease in synthesis rate was 68.5% (p less than .05; range 55.2-79.8%) while the mean decrease in fractional turnover rate was 64.4% (p less than .05; range 30.2-100%). Reduction in synthesis rate was confirmed by the determination of maximum fasting synthesis of cholic acid, which averaged 61.1% lower than synthesis in the fed period. Fasting had no consistent effect on total bile acid pool size, cholic acid pool size, or bile acid species composition.

Effect of Decreased Gallbladder Stimulation on Enterohepatic Cycling and Kinetics of Bile Acids

The effect of diet on the rate of enterohepatic recycling and bile acid kinetics was studied in groups of human subjects by reducing dietary protein and fat. The effect on enterohepatic cycling was assessed indirectly in control subjects, in patients with cholesterol cholelithiasis, and in patients with cholecystectomy by comparing output of breath 14-CO2 after the administration of a trace of cholyl [1-14-C]glycine during two periods: a control period when three meals containing protein and fat were eaten daily and a diet period, when protein and fat were excluded from the diet. Breath 14-CO2 output was not altered by diet in the patients with cholecystectomy. In the healthy subjects and in the patients with cholesterol cholelithiasis breath 14-CO2 output fell by approximately 50%, indicating that decreased endogenous cholecystokinin-pancreozymin stimulation had reduced but not eliminated enterohepatic recycling. Bile acid kinetics after administration of [2,4-3-H]cholic acid and [24-14-C]chenodeoxycholic acid were measured in 6 healthy subjects during a control period, when they ate a diet containing three daily meals containing fat and protein, and again not less than 4 months later during the 4th week of a diet during which they ate only one meal containing fat and protein every other day. tthe pool size of cholic and chenodeoxycholic acid rose significantly during the diet as did the total bile acid pool size. The daily fractional turnover rate of both primary bile acids fell significantly during the diet, but their synthesis rate was not significantly changed. It is concluded that (1) significant enterohepatic circulation of bile acids occurs even in the absence of dietary stimuli for gallbladder contraction; and (2) diet may significantly affect bile acid pool size and fractional turnover, while bile acid synthesis remains essentially unchanged.

Biliary lipid output during three meals and an overnight fast. II. Effect of chenodeoxycholic acid treatment in gallstone subjects.

Oral treatment with chenodeoxycholic acid causes dissolution of cholesterol gallstones in man. In order to determine the mechanism of this effect, we have measured 24-hour biliary lipid output, lipid composition of fasting gallbladder bile, and bile acid pool sizes before and during such treatment in six patients with radiolucent gallstones in functioning gallbladders. In all six patients, the degree of cholesterol saturation of fasting-state gallbladder bile was decreased during treatment to a level below the thermodynamic solubility line. This effect was due to a decrease in biliary cholesterol output, associated with conversion of more than 90% of the total bile acid pool to chenodeoxycholic acid. It could not be attributed to an increase in total bile acid pool size nor to an increase in biliary bile acid or phospholipid output.

Increased Bacterial Degradation of Bile Acids in Cholecystectomized Patients

Bile acid metabolism was studied in 10 patients previously cholecystectomized for cholesterol cholelithiasis, in 12 healthy subjects, and in 13 patients with cholesterol cholelithiasis (disease control subjects). The rate of bacterial deconjugation and 7-dehydroxylation was measured by using [2, 4-3H ]cholyl- [1-14C]glycine; measurements of synthesis and pool size were made simultaneously. Total bile acid pool size and biliary bile acid composition were determined by gas-liquid chromatography. Compared with healthy subjects, patients with cholecystectomy showed significantly increased deconjugation and dehydroxylation of the labeled cholylglycine. However, the pool of cholylglycine was considerably smaller, so that the absolute rate of deconjugation was similar. The pool of deoxycholylglycine was twice as large as that in the healthy control and the disease control subjects. In addition, ketohydroxy bile acids (resulting from bacterial dehydrogenation) composed 7 to 15% of the bile acid pool. The 7-keto and 12-keto derivatives of cholic acid were identified by mass spectrometry. The total bile acid pool in cholecystectomized patients did not differ from that in healthy control subjects but was larger than that in the disease control subjects. The size of the total bile acid pool in cholecystectomized patients correlated highly with the size of the pool of secondary bile acids, suggesting that its apparent return to a normal size in these patients after cholecystectomy could be explained in part by the increased input of secondary bile acids from the intestine.

Gallstones: pathophysiology and dissolution.

Gallstones are composed predominantly of cholesterol, a water-insoluble lipid normally present in bile. Bile acids and lecithin in an aqueous medium aggregate to form mixed micelles, within which cholesterol can be solubilized. Most patients with gallstones have a deficiency of bile acids characterized by a decrease in the ratio of bile acids and lecithin to cholesterol in bile and a decrease in the total bile acid pool size. Ingestion of chenodeoxycholic acid corrects these abnormalities, and initial observations have demonstrated gallstone dissolution.

Effect of cholestyramine on bile acid metabolism in normal man.

The effect of cholestyramine administration on the enterohepatic circulation of bile acids was studied in eight normal volunteers. In six subjects the metabolism of sodium taurocholate-(14)C was determined after its intravenous injection before and during the 6th wk of cholestyramine administration, 16 g/day. In two subjects, the metabolism of cholic acid-(14)C was observed before and during the 2nd wk of cholestyramine, 16 g/day. Bile acid sequestration resulted in a more rapid disappearance of the injected primary bile acid and its metabolic products. The composition of fasting bile acids was promptly altered by cholestyramine to predominantly glycine-conjugated trihydroxy bile acid. In four subjects, unconjugated bile acid-(14)C was administered during cholestyramine administration; the relative proportion of glycine-conjugated bile acid-(14)C before enterohepatic circulation was similar to the relative proportion of unlabeled glycine-conjugated bile acid present in duodenal contents after an overnight fast, indicating that a hepatic mechanism was responsible for the elevated ratios of glycine- to taurine-conjugated bile acid (G: T ratios) observed. The relative proportions of both dihydroxy bile acids, chenodeoxycholic and deoxycholic, were significantly reduced. Steatorrhea did not occur, and the total bile acid pool size determined after an overnight fast was unaltered by cholestyramine. These findings suggest that in normal man bile acid sequestered from the enterohepatic circulation by cholestyramine is replaced by an increase in hepatic synthesis primarily via the pathway leading to production of glycocholic acid.

Relationship of Bile Acid Pool Size to the Formation of Lithogenic Bile in Female Indians of the Southwest

Bile acid kinetics and pool size were determined in 18 female American Indians of the Southwest. Eleven patients had a lithogenic bile and 7 patients had a normal bile. Eight of the patients with a lithogenic bile had cholesterol gallstones which were confirmed both at surgery and by analysis of the gallstones; the remaining 3 patients in this group had no radiological evidence of gallstones. The group of 7 patients with a normal bile had no evidence of gallstones by oral cholecystogram. The patients were administered orally 14C-cholic and 14C-chenodeoxycholic acids. The primary and total bile acid pools were found to be significantly smaller in patients with a lithogenic bile than in patients with a normal bile (1.1 g versus 1.6 g). The 3 patients with a lithogenic bile and no gallstones also had greatly diminished bile acid pools (under 1 g). The primary bile acids of patients with a lithogenic bile turned over at a faster rate than in patients with a normal bile. There was no significant difference in the daily production of the primary bile acids between the two groups. The production of primary bile acids in the female Indian averaged 350 mg per day. The data suggest that the diminished bile acid pool in the female Indians with a lithogenic bile resulted from an inability of the liver to synthesize adequate amounts of bile acids to compensate for bile acid excretion. Biliary lipid excretion was estimated from the total bile acid pool size and biliary lipid composition. Although there was a slight decrease in phospholipid and a slight increase in cholesterol excretion in the patients with a lithogenic bile, these differences were not significant. However, these alterations in biliary lipid excretion were of sufficient magnitude when coupled with the reduction in the bile acid pool to tip the bile out of the micellar zone. Based on the findings of this and earlier reports, it is suggested that a diminished bile acid pool could be responsible for the development of a bile supersaturated with cholesterol and subsequent cholesterol gallstone formation.