Bile Acids and Gallstones: Epidemiology, Pathogenesis, Diagnosis, and Management


Gallbladder stones

CBD stones

Cholesterol stone (%)



Bilirubin stone
Black pigment stone (%)



Brown pigment stone (%)



Others (%)



6.3 Cholesterol Gallstone Pathogenesis

Cholesterol gallstone formation is processed by two major steps: (1) metabolic abnormalities, genetics and defects of lipid metabolism, and (2) physical-chemical events, bile cholesterol supersaturation, cholesterol crystal nucleation, and crystal growth to macroscopic stones (Table 6.2). The gallbladder and intestines play a role in these processes.

Table 6.2
Cholesterol gallstone pathogenesis

Genetics and defects of lipid metabolism

Bile cholesterol supersaturation

Cholesterol crystal nucleation

Crystal growth to macroscopic stones

(Clinical symptoms)

6.3.1 Metabolic Abnormalities

Cholesterol gallstone formation is based primarily upon the defect of cholesterol homeostasis mainly in the hepatobiliary system [513]. Cholesterol is an insoluble molecule that is eliminated from the liver into bile through ATP-binding cassette transporter (ABC) G5/G8, and, similarly, biliary secretion of phospholipids and bile acids is mediated by ABCB4 (MDR3) and ABCB11 (BSEP), respectively (Fig. 6.1). Bile cholesterol is predominantly originated from high-density lipoprotein (HDL) fraction, and the hepatic uptake of HDL cholesterol is mediated through scavenger receptor class B type 1 (SRB1), a receptor for HDL [1422]. Under physiological circumstances, cholesterol in bile is a solubilized bile salt micelle, which is physicochemically stabilized. Once metabolic defects occur, bile becomes metastable due to cholesterol supersaturation to promote cholesterol crystallization, the so-called nucleation, an initial step for cholesterol gallstone formation.


Fig. 6.1
Formation of bile supersaturated with cholesterol (Reused with permission from Ref. [87]). Bile cholesterol is predominantly originated from HDL and secreted through ABCG5/ABCG8. Excess cholesterol leads to bile supersaturation, with a relatively high ratio to phospholipids and bile acid

Bile acids are capable for solubilizing bile cholesterol by forming micelles, and such a cholesterol solubility is based upon a relative composition of cholesterol to bile acid and phospholipids. Especially, the bile acid composition in an enterohepatic circulation pool is a crucial factor to dictate potential to solubilize cholesterol. In this regard, deoxycholate, a secondary bile acid, is increased in enterohepatic circulation pool in cholesterol gallstone disease [23]. Since deoxycholate suppresses hepatic de novo synthesis of primary bile salt, biliary cholesterol secretion relatively increases to enhance bile cholesterol saturation [24]. Intestinal hypomotility induces prolonged intestinal transit times to prolong exposure time of primary bile salt, cholate, to gut microbiota to produce deoxycholate, and, therefore, this eventually attributes gallstone formation [25, 26].

6.3.2 Cholesterol Crystal Nucleation and Growth to Macroscopic Gallstones

The cholesterol crystal nucleation process is accelerated by mucins produced and secreted by the gallbladder wall, and such a gallbladder function is mediated through arachidonate-prostanoid pathway (Fig. 6.2). The gallbladder epithelium absorbs lipids from bile in a different manner for cholesterol, phospholipid, and bile salts to reduce bile cholesterol saturation, and its impairment leads to formation of metastable bile [27, 28]. Thus, gallbladder dysfunction in motility plays a role in cholesterol gallstone formation process [28, 29], and contractility defects associated with cholesterol gallstones are attributable to excess membrane accumulation in gallbladder smooth muscle cells of bile cholesterol [3032]. Further, increases in mucin synthesis and secretion of the gallbladder, mediated by arachidonate-prostanoid pathway, accelerate cholesterol crystallization and growth, and eventually macroscopic gallstones form in the gallbladder cavity.


Fig. 6.2
Events for cholesterol gallstone formation process in the gallbladder (Reused with permission from Ref. [87]). Cholesterol crystal nucleation and growth are promoted by mucin hypersecretion mediated through arachidonate-prostanoid pathway

Studies in model and native bile have suggested the presence of two distinct mechanisms for cholesterol crystallization [33]. In bile with relatively high phosphatidylcholine contents, aggregation and fusion of cholesterol-rich vesicles result in the formation of multilamellar vesicles, which give rise to cholesterol monohydrate crystals [34, 35] as summarized in Fig. 6.3. At lower phosphatidylcholine contents, vesicles may become unstable and spawn anhydrous cholesterol crystals. This occurs similarly with increasing of cholesterol in composition. Such a microscopic event of cholesterol crystal nucleation in in vitro study using the supersaturated model bile solution is shown in Fig. 6.4. Cholesterol crystal nucleation is dictated in a balance of nucleation-effecter substances of promoters and inhibitors and protein and non-protein components [36]. Meanwhile, concanavalin A-binding fraction has been reported to promote cholesterol crystallization in bile [37] and, thereafter, demonstrated to contain pronase-resistant glycoprotein component of the low-density protein-lipid complex, the carcinoembryonic antigen-related adhesion molecule 1 [38]. Taken together, crystallization-effecting potentials of biliary components are based upon imbalance among anti- and pro-nucleating factors.


Fig. 6.3
Bile lipid particulate species and cholesterol crystallization (Reused with permission from Ref. [11])


Fig. 6.4
Cholesterol crystallization in cholesterol-supersaturated bile

6.3.3 Role of Genetics

Human susceptibility to cholesterol gallstones is partially under genetic control. Genetic studies led to significant progress in the characterization of Lith genes that control cholesterol gallstone formation in mice [39]. Only specific strains of mice form gallstones by feeding with a lithogenic diet, and a “gallstone map” has been compiled to the relationships between genetic loci, such as Lith genes, which control the regulation of nucleating factor expression [40]. Recent progress in genetics provides the susceptibility of heredity contribution to gallstone formation for apolipoproteins E and B and cholesterol 7alpha-hydroxylase genes [4146]. Further, based upon understanding of the role of ABCG5 and ABCG8 in digestive systems, liver and intestine, the association of polymorphism of ABCG8 with gallstone diseases has been published [4758]. The most studied loci are D19H, T400K, and Y54C, and a meta-analysis of the association between each locus and gallstone disease shows the strong association of D19H polymorphism with gallstone disease. T400K and Y54C polymorphism are less associated [56]. Taken together, the role of disease genetics is still to be elucidated.

6.4 Pigment Gallstone Pathogenesis

Pigment stones are divided into two major types, black pigment stone and brown pigment stone. Black pigment stones consist dominantly of calcium bilirubinate, produced increasingly under hemolysis. Black pigment gallstones are composed mostly of polymerized shape of calcium bilirubinate and formed in noninfectious gallbladder. In contrast, brown pigment stones are formed, following biliary infection of anaerobic bacteria [59]. In principle, the risk factor is biliary secretion of excess bilirubin conjugates, resulting from hemolysis, ineffective erythropoiesis, or induced enterohepatic cycling of unconjugated bilirubin in association with gallbladder hypomotility caused by diabetes mellitus, total parenteral nutrition, and truncal vagotomy [6063].

Black pigment stones consist of calcium phosphate and/or carbonate, whereas brown pigment stones are composed of amorphous calcium salts of long-chain saturated fatty acids. In addition, cholesterol is present in both types, with a higher proportion for brown pigment stones [64], especially intrahepatic stones [7]. Also, a mixed mucin glycoprotein matrix secreted by biliary epithelial cells promotes both types of pigment gallstones on the basis of biliary hypersecretion of bilirubin conjugates and endogenous biliary β-glucuronidase hydrolysis of bilirubin conjugates in gallbladder bile to precipitate as insoluble calcium salts. Further, reactive oxygen species, secreted by gallbladder mucosa when inflamed, promote precipitation of calcium bilirubinate polymers, and, therefore, its suppression is to be of therapeutic benefit in pigment gallstone treatment.

6.5 Clinical Managements

Gallstones cause certain typical symptoms: abdominal or back pain, fever, nausea and/or vomiting, and jaundice. Colic pain at the right upper quadrant is less frequent, and considerable cases remain asymptomatic. The typical history is to be as follows: a hypochondrial pain at the right side starts following oily meal, radiating to the right scapula or shoulder, and thereafter reaches a peak level within several hour. Usually gallstone-associated pain is improved by stone moving back to original position or passing through physiological strictures, but most patients find recurrent pain within 10 years after the first attack [65]. According to the Japanese Society of Gastroenterology Practice Guidelines for gallstone diseases 2009, asymptomatic gallstone patients are not recommended to undergo therapeutics, but recommended to a conservative follow-up (Fig. 6.5) [66]. Nevertheless, cases with gallbladder wall thickness or nonfunctioning, or hard condition for image assessment, can be subjected to prophylactic cholecystectomy. Patients with increased risk for gallbladder cancer, with large stones of diameter of >3 cm, and with chronic cholecystitis such as “porcelain gallbladder” are recommended to prophylactic cholecystectomy [67, 68].


Fig. 6.5
Flowchart of therapeutic managements [66]

Symptomatic gallstone patients need treatment, and laparoscopic cholecystectomy is to be a standard modality. The US National Institutes of Health consensus conference concluded that laparoscopic cholecystectomy is safe and cost-effective compared with open cholecystectomy [69]. For cases not indicated to surgery, optional treatments are oral dissolution for cholesterol gallstones; the indication is to be floating, radiolucent, diameter of <15 mm, CT score <60 HU, and functioning gallbladder [7074]. A representative case is successfully treated by a combination of ursodeoxycholic acid (400 mg per day) and chenodeoxycholic acid (200 mg per day) that is shown in Fig. 6.6. UDCA monotherapy is also effective in mixed-type cholesterol gallstone dissolution as shown in Fig. 6.7. The underlying mechanism(s) of such an action of bile acids is understood as the enhancement of micelle formation by CDCA and liquid formation to dissolve cholesterol by UDCA (Fig. 6.8) [75, 76]. Extracorporeal shock wave lithotripsy (ESWL) can be considered for cholesterol gallstone, solitary, radiolucent, diameter of <20 mm, CT score <50 HU, and functioning gallbladder. Of the nonsurgical treatment, gallstone recurrence after treatment together with cost-benefit analysis is the weakness with less priority compared to laparoscopic cholecystectomy [77]. Bile acid adjuvant therapy is recommended for this technique in order to shorten a treatment period. On the other hand, cases complicated with acute cholecystitis are managed according to severity, periods after onset, and physical status; laparoscopic cholecystectomy with or without biliary drainage such as percutaneous transhepatic gallbladder drainage (PTGBD), percutaneous transhepatic gallbladder aspiration (PTGBA), endoscopic nasal gallbladder drainage (ENGBD) [7886].


Fig. 6.6
Bile acid treatment of floating cholesterol gallstones (UDCA + CDCA combination therapy)


Fig. 6.7
Bile acid treatment of mixed-type cholesterol gallstones (UDCA monotherapy)


Fig. 6.8
Mechanism(s) of action of UDCA: liquid crystal formation by UDCA leads to cholesterol gallstone dissolution

6.6 Future Direction

Recent investigations provide evidences to understand underlying mechanism(s) of gallstone formation process in the aspects of physiology, physical chemistry, molecular biology, and genetics of biliary lipid metabolism, supplying ideas of future strategies for prevention and/or nonsurgical therapeutics, instead for cholecystectomy. Based upon epidemiological studies that reveal an increased overall mortality of gallstone patients in association with diabetes and cardiovascular diseases, but not cancers, this field should be shifted to handling metabolic disorders for lipids, bile acids, and other nutrients.


This work was supported in part by the Health and Labour Sciences Research Grant for intrahepatic gallstones awarded to S.T.

Conflict of Interest Statement

None declared.



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Sep 30, 2017 | Posted by in GASTROENTEROLOGY | Comments Off on Bile Acids and Gallstones: Epidemiology, Pathogenesis, Diagnosis, and Management
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