Increased susceptibility to diet-induced gallstones in liver fatty acid binding protein knockout mice

Abstract

Quantitative trait mapping identified a locus colocalizing with L-Fabp, encoding liver fatty acid binding protein, as a positional candidate for murine gallstone susceptibility. When fed a lithogenic diet (LD) for 2 weeks, LFabp 2/2 mice became hypercholesterolemic with increased hepatic VLDL cholesterol secretion. Seventy-five percent of L-Fabp 2/2 mice developed solid gallstones compared with 6% of wild-type mice with an increased gallstone score (3.29 versus 0.62, respectively; P , 0.01). Hepatic free cholesterol content, biliary cholesterol secretion, and the cholesterol saturation index of hepatic bile were increased in LD-fed L-Fabp 2/2 mice. Chow-fed L-Fabp 2/2 mice demonstrated increased fecal bile acid (BA) excretion accompanied by decreased ileal Asbt expression. By contrast, there was an increased BA pool and decreased fecal BA excretion in LD-fed L-Fabp 2/2 mice, associated with increased proximal intestinal Asbt mRNA expression, suggesting that intestinal BA absorption was enhanced in LD-fed L-Fabp 2/2 mice. The increase in biliary BA secretion and enterohepatic pool size in LD-fed L-Fabp 2/2 mice was accompanied by downregulation of Cyp7a1 mRNA and increased intestinal mRNA abundance of Fgf-15, Fxr, and Fabp6. These findings suggest that changes in hepatic cholesterol metabolism and biliary lipid secretion as well as changes in enterohepatic BA metabolism increase gallstone susceptibility in LD fed L-Fabp Gallstone disease is a major health problem in western society, and its attendant complications and comorbidities impose a substantial financial burden on the health care economy (1). Among the factors that predispose to cholesterol cholelithiasis, considerable attention has focused on environmental modifiers, such as obesity, because even in populations at increased genetic risk there appears to be a strong link between gallstone susceptibility and body habitus that may be further modified in a gender-specific manner (2). However, despite recent advances in the mechanisms that link hepatic insulin resistance and gallstone susceptibility (3), there remain many unanswered questions concerning the pathways by which alterations in hepatic lipid metabolism result in biliary cholesterol supersaturation, leading to cholesterol monohydrate crystal formation and eventually the emergence of gallstones (4).Our understanding of the genetic factors that predispose to gallstone formation has been advanced through study of inbred murine crosses in which susceptibility loci have been mapped using diet-induced gallstone formation as a quantitative trait. Using this approach, .23 quantitative trait loci have been mapped, allowing formal evaluation of potential candidate genes [reviewed in (2)]. Among these loci, Liver fatty acid binding protein (L-Fabp) emerged as a positional candidate from a quantitative trait loci near D6Mit123 on chromosome 6 (71.5 Mb, 30 centimorgans) (2, 5). L-Fabp is an abundant cytosolic lipid binding protein expressed in mammalian enterocytes and hepatocytes with a flexible lipid...

Disruption of the Murine Protein Kinase Cβ Gene Promotes Gallstone Formation and Alters Biliary Lipid and Hepatic Cholesterol Metabolism

“…Previous animal studies showed that some but by no means all murine models of obesity are associated with increased gallstone susceptibility. Indeed, prior studies in L-Fabp Ϫ/Ϫ mice have demonstrated protection against high fat diet-induced obesity in the setting of a strikingly increased susceptibility to lithogenic diet-induced gallstone formation (33). These paradoxical findings suggest that obesity itself is not a gallstone risk but rather that specific alterations in key pathophysiologic pathways leading to obesity may in turn augment susceptibility to both diseases (49).…”

“…Bile samples were stored at Ϫ80°C until analyzed. Biliary phospholipids and cholesterol were determined enzymatically using a phospholipids B kit and a cholesterol E kit from Wako Chemicals (32,33). Cholesterol saturation indices in hepatic bile were calculated using published parameters (34).…”

“…Cholesterol saturation indices in hepatic bile were calculated using published parameters (34). Total bile acid content and individual bile acid concentrations were measured via high performance liquid chromatography (32,33). In brief, 100 l of diluted hepatic bile (1:20 dilution prepared in methanol) was injected onto a Pursuit C18 reverse phase column (Varian, Lake Forest, CA) using a Rainin HPXL HPLC system (Varian).…”

“…Bile acid standards were purchased from Steraloids Inc. (Newport, RI) or from Calbiochem. The hydrophobic index of hepatic bile samples was calculated as described earlier (32,33).…”

“…A total of 10 mice/genotype were analyzed for gallstone formation, and a subset (6/genotype) was used to determine lipid secretion rates and bile acid species. C and D, CSIs and hydrophobicity indices were calculated as described earlier (32,33). Each value represents the mean Ϯ S.D.…”