Although a cholesterol supersaturation of gallbladder bile has been identified as the underlying pathophysiologic defect, the molecular pathomechanism of gallstone formation in humans remains poorly understood. A deficiency of the apical sodium bile acid transporter (ASBT) and ileal lipid binding protein (ILBP) in the small intestine may result in bile acid loss into the colon and might promote gallstone formation by reducing the bile acid pool and increasing the amount of hydrophobic bile salts. To test this hypothesis, protein levels and mRNA expression of ASBT and ILBP were assessed in ileal mucosa biopsies of female gallstone carriers and controls. Neither ASBT nor ILBP levels differed significantly between gallstone carriers and controls. However, when study participants were subgrouped by body weight, ASBT and ILBP protein were 48% and 67% lower in normal weight gallstone carriers than in controls (P , 0.05); similar differences were found for mRNA expression levels. The loss of bile transporters in female normal weight gallstone carriers was coupled with a reduction of protein levels of hepatic nuclear factor 1A and farnesoid X receptor. In conclusion, in normal weight female gallstone carriers, the decreased expression of ileal bile acid transporters may form a molecular basis for gallstone formation.-Bergheim, I., S. Harsch, O. Mueller, S. Schimmel, P. Fritz, and E. F. Stange. Apical sodium bile acid transporter and ileal lipid binding protein in gallstone carriers. J. Lipid Res. 2006. 47: 42-50. Supplementary key words gallstone . intestine . nuclear receptor Despite decades of research, gallstone disease remains a significant health problem worldwide, particularly in the female adult population. In the United States and European countries, 10-20% of adults develop gallstones, mostly cholesterol-rich stones (1). Even though cholesterol supersaturation of gallbladder bile has been identified as the underlying pathophysiologic defect (2), the molecular pathogenesis of cholesterol gallstone formation remains poorly understood. Disorders contributing to the cholesterol supersaturation of bile could result from a) uncoupling of phospholipid and/or cholesterol secretion from bile acid secretion or b) augmentation of hepatic cholesterol synthesis or uptake. The source of the excess cholesterol is unclear, but it is probably derived from lipoprotein (3) rather than from synthesis (4). Furthermore, evidence is available that c) alterations of intestinal bile acid recycling (5), d) prolonged intestinal transit (5), e) altered bile salt synthesis, and f ) gallbladder motility defects are important in human gallstone formation and biliary pain (6). Accordingly, the pools of cholic and chenodeoxycholic acid have been found to be reduced in most normal weight gallstone patients, whereas that of deoxycholic acid is often increased (7). Cholic acid is almost completely 7-a-dehydroxylated to deoxycholic acid by anaerobic bacteria in the colon (8), and z30-40% of this deoxycholic acid is absorbed from the in...

Cholelithiasis is a multifactorial process, and several mechanisms have been postulated. A decreased expression of the ileal apical sodium-dependent bile acid transporter (ASBT) and of the cytosolic ileal lipid binding protein (ILBP) was recently described in female non-obese patients. The role of the recently identified organic solute transporters a and b (OSTa, OSTb) in gallstone pathogenesis remains unclear. Therefore, we performed analysis of OSTa-OSTb in gallstone patients according to body weight. Ileal mucosal biopsies were collected during routine colonoscopy from female gallstone carriers (n 5 19) and controls (n 5 34). OSTa-OSTb mRNA expression was measured using the LightCycler sequence detection system; protein was analyzed by immunohistochemistry and Western blot. The mRNA expression of OSTa-OSTb was significantly reduced (OSTa: 3.3-fold, P 5 0.006; OSTb: 2.6-fold, P 5 0.03) in normal-weight but not overweight gallstone carriers compared with controls. OSTa-OSTb protein levels also showed a reduction by 40-67%. The expression of OSTaOSTb correlated positively with ASBT (r 5 0.65, 0.58, respectively), ILBP (r 5 0.77, 0.67), and the farnesoid X receptor (r 5 0.58, 0.50). Fibroblast growth factor-19 showed a 2.8-fold reduction (P 5 0.06), and liver receptor homolog-1 showed a 2-fold reduction (P 5 0.04) in nonobese patients. In conclusion, an impaired function of all three ileal bile acid transporters may lead to low ileal bile acid reabsorption and an altered bile acid pool composition and therefore may contribute to the formation of gallstones in non-obese patients. Bile acids are powerful detergents and play a critical role in multiple biological processes. They are synthesized in the liver, stored in the gallbladder, and released postprandially into the small intestine, where they are crucial for the absorption of lipophilic nutrients (1). The reuptake of bile acids from the terminal ileum is an important step in bile acid homeostasis and a major factor determining bile acid pool size (2). The major mechanism for ileal bile acid uptake is the active transport by the apical sodiumdependent bile acid transporter (ASBT), located in the brush border (3, 4). The subsequent intracellular transport of bile acids is mediated by the cytosolic ileal lipid binding protein (ILBP), which shuttles bile acids to the basolateral membrane (5, 6). Responsible for secretion of bile acids into the portal circulation are the basolateral organic solute transporters a and b (OSTa, OSTb) (7).In a recent study, we showed that female gallstone carriers exhibit a decreased ileal expression of ASBT and ILBP and their most relevant transcription factors, farnesoid X receptor (FXR) and hepatic nuclear factor 1 a (HNF1a) (8). This decrease was observed on both the mRNA and protein levels and may explain bile lithogenicity by an intestinal bile acid loss. However, compatible with differences in cholesterol handling in lean and obese subjects (9), this effect was weight specific and observed only in normal-weight subjects...

BackgroundCholelithiasis is a multifactorial process and several mechanisms of gallstone formation have been postulated. As one of these mechanisms, a decreased expression of the ileal apical sodium-dependent bile acid transporter gene SLC10A2 in gallstone carriers was described previously. In this study the SLC10A2 gene was investigated to identify novel genetic variants and their association with gallstone formation.Methodology/Principal FindingsStudy subjects were selected with the presence or absence of gallstones confirmed by ultrasound and medical history. Genomic DNA was obtained from blood leukocytes. Sequence analysis was performed of all six exonic and flanking regions as well as of 2,400 base pairs of the SLC10A2 promoter in a cohort of gallstone carriers and control subjects from Stuttgart, Germany. Genotype frequencies of newly identified genetic variants (n = 6) and known single nucleotide polymorphisms (n = 24) were established using MALDI-TOF mass spectrometry. Six new genetic variants were found within the SLC10A2 gene. Although none of the variants was linked to gallstone disease in the Stuttgart cohort overall, the minor allele of SNP rs9514089 was more prevalent in male non-obese gallstone carriers (p = 0.06680, OR = 11.00). In a separate population from Aachen, Germany, the occurrence of rs9514089 was two-fold higher in gallstone patients (22%) than in corresponding controls (11%) (p = 0.00995, OR = 2.19). In the pooled Aachen/Stuttgart cohort rs9514089 was highly significantly linked to cholelithiasis (p = 0.00767, OR = 2.04). A more frequent occurrence was observed for male gallstone carriers (22%) compared to controls (9%) (p = 0.01017, OR = 2.99), for the total normal weight group (p = 0.00754, OR = 2.90), and for male non-obese gallstone patients (p = 0.01410, OR = 6.85). Moreover, for the minor allele of rs9514089 an association with low plasma cholesterol levels was found especially in gallstone carriers (p = 0.05).Conclusions/SignificanceWe have identified SLC10A2 as a novel susceptibility gene for cholelithiasis in humans. Comprehensive statistical analysis provides strong evidence that rs9514089 is a genetic determinant especially in male non-obese gallstone carriers. The minor allele of rs9514089 is related to differences in plasma cholesterol levels among the subjects.

BackgroundGallstone disease is associated with p.D19H of ABCG8 as well as alterations of cholesterol and bile acid metabolism. However, molecular mechanisms have not been fully elucidated. It is important to understand the link between the sterol transporters ABCG5/8 and NPC1L1 and intestinal cholesterol absorption as well as de novo synthesis in gallstone patients stratified according to 19H risk allele. Moreover, the functional importance of the 19H variant on intestinal ABCG8 feature remains to be clarified.MethodsMeasurements of serum surrogate markers of cholesterol absorption (plant sterols: sitosterol, campesterol) and synthesis (cholesterol precursor: lathosterol) were carried out by gas chromatography/mass spectrometry (GC/MS). For expression studies, total RNA was isolated from 168 ileal biopsies of study participants with (34) and without gallstone disease (134). Messenger RNA was measured by LightCycler real-time PCR. Genomic DNA was obtained from blood leukocytes. Genotype frequencies of p.D19H were established using MALDI-TOF mass spectrometry.ResultsCompared to controls, cholesterol absorption but not synthesis in gallstone carriers was diminished by about 21% based on low serum sitosterol (P = 0.0269) and campesterol (P = 0.0231) to cholesterol ratios. D19H was found to be significantly associated with gallstones (odds ratio [OR] = 2.9, P = 0.0220, 95% confidence interval [CI]:1.22-6.89), particularly in the overweight cohort (OR = 3.2, P = 0.0430, 95% CI:1.07-9.26). Cholesterol absorption was about 24% lower in individuals carrying p.D19H compared to wild type (Psitosterol = 0.0080, Pcampesterol = 0.0206). Moreover, irrespective of phenotype, carriers of p.D19H displayed a significant lower absorption than carriers of the major allele. The most pronounced effect on cholesterol absorption ratio was observed for serum campesterol levels (wild type controls to mutated controls 28%, P = 0.0347 and wild type controls to gallstone carriers with 19H allele 37%, P = 0.0030). Notably, ABCG5/8 and NPC1L1 expression was similar in gallstone carriers and controls regardless of p.D19H presence.ConclusionsBoth gallstone disease and p.D19H of ABCG8 are associated with diminished cholesterol absorption. However, p.D19H is not responsible for the differences in small intestinal sterol transporter expression.