Hyperhomocysteinemia from trimethylation of hepatic phosphatidylethanolamine during cholesterol cholelithogenesis in inbred mice.

UNLABELLED: Because hyperhomocysteinemia can occur in cholesterol gallstone disease, we hypothesized that this may result from trimethylation of phosphatidylethanolamine (PE), which partakes in biliary phosphatidylcholine (PC) hypersecretion during cholesterol cholelithogenesis. We fed murine strains C57L/J, C57BL/6J, SWR/J, AKR/J, PE N-methyltransferase (PEMT) knockout (KO), PEMT heterozygous (HET), and wildtype (WT) mice a cholesterol/cholic acid lithogenic diet (LD) for up to 56 days and documented biliary lipid phase transitions and secretion rates. We quantified plasma total homocysteine (tHcy), folate, and vitamin B12 in plasma and liver, as well as biliary tHcy and cysteine secretion rates. Rate-limiting enzyme activities of PC synthesis, PEMT and cytidine triphosphate: phosphocholine cytidylyltransferase (PCT), S-adenosylmethionine (SAM), and S-adenosylhomocysteine (SAH) were measured in liver homogenates. Other potential sources of plasma tHcy, glycine N-methyltransferase (GNMT) and guanidinoacetate N-methyltransferase (GAMT), were assayed by gene expression. Plasma tHcy and PEMT activities became elevated during cholelithogenesis in gallstone-susceptible C57L, C57BL/6, and SWR mice but not in the gallstone-resistant AKR mice. Persisting in C57L mice, which exhibit the greatest Lith gene burden, these increases were accompanied by elevated hepatic SAM/SAH ratios and augmented biliary tHcy secretion rates. Counter-regulation included remethylation of Hcy to methionine concurrent with decreased folate and vitamin B12 levels and Hcy transsulfuration to cysteine. Concomitantly, methylenetetrahydrofolate reductase (Mthfr), betaine-homocysteine methyltransferase (Bhmt), and cystathionine-ß-synthase (Cbs) were up-regulated, but Gnmt and Gamt genes were down-regulated. PEMT KO and HET mice displayed biliary lipid secretion rates and high gallstone prevalence rates similar to WT mice without any elevation in plasma tHcy levels. CONCLUSION: This work implicates up-regulation of PC synthesis by the PEMT pathway as a source of elevated plasma and bile tHcy during cholesterol cholelithogenesis.

High rate of complicated idiopathic gallstone disease in pediatric patients of a North American tertiary care center.

AIM: To assess spectrum and etiology of gallstones and biliary sludge in the pediatric population of a North American tertiary care centre. METHODS: Retrospective review of abdominal ultrasounds recorded at Saint Justine Hospital over a period of 24 mo (8/2003 to 8/2005) in patients < 19 years of age. Patients < 2 years of age were analyzed separately. RESULTS: The presence of gallstones was noted in 127 patients. In 107 it was a new diagnosis, in 48/105 (45.7%) patients > 2 years of age idiopathic gallstone disease was found. These 48 patients represent 2.1% of the population who required ultrasound for abdominal pain. Complicated gallstone disease occurred in 28/48 with idiopathic disease, mainly adolescent girls. Patients with hemolytic disorders, cystic fibrosis, oncologic diseases or kidney transplantation and gallstones were asymptomatic and stones were detected during routine abdominal ultrasound. Twenty two patients < 2 years of age not consulting for abdominal pain had gallstone disease of diverse etiology. Biliary sludge was seen in 84 patients, 78.5% on total parenteral nutrition. In 4 patients, sludge progressed to gallstones. CONCLUSION: Idiopathic gallstone disease and its rate of complication are more frequent in our cohort than expected from previous studies. Adolescent girls with abdominal pain and idiopathic gallstones require special attention for complicated disease course.

Abnormal hepatobiliary and circulating lipid metabolism in the Long-Evans Cinnamon rat model of Wilson's disease.

Long-Evans Cinnamon (LEC) rats exhibit a genetic defect in Atp7b gene, which is homologous to the human Wilson's disease gene, resulting in an inability to mobilize copper from the liver. This study was undertaken to gain insight into the relationship between liver copper accumulation and plasma lipid profile, circulating lipoprotein composition, hepatic sterol metabolism and biliary lipid secretion rates in 12-week-old LEC rats compared to control Long-Evans rats. Concomitant with hepatic copper deposition, LEC rats displayed increased content of triglycerides (TGs), free cholesterol (FC) and cholesteryl ester (CE) in the liver. Hepatic concentrations of malondialdehyde (MDA), an index of lipid peroxidation were also significantly elevated in LEC rats (50%). This steatosis was associated with aberrant microsomal apolipoprotein (apo) B-100 and microsomal triglyceride transfer protein (MTP) content, hypotriglyceridemia, hypocholesterolemia and abnormalities in both circulating lipoprotein composition and size. Atypical hepatobiliary sterol metabolism was established by the assessment of the activity of key intracellular enzymes for cholesterol homeostasis, which demonstrated, with respect to controls, a 40% reduction in 3-hydroxy-3-methylglutaryl coenzyme A reductase, a 30% reduction in cholesterol 7alpha-hydroxylase, and a 54% reduction in acyl CoA:cholesterol acyltransferase. During a 6-h biliary drainage, a decline in the bile acid output was recorded and might be linked to the low protein expression of the bile salt export pump (BSEP or ABCB11). Our data emphasize the crucial role of copper balance in hepatic sterol homeostasis and lipoprotein metabolism in LEC rats. Additional studies are needed to delineate the mechanisms of these disorders.

Dietary lecithin protects against cholestatic liver disease in cholic acid-fed Abcb4- deficient mice.

Mutations in multidrug resistance 3 gene (MDR3 or ABCB4) underlie progressive familial intrahepatic cholestasis type 3 (PFIC3), a severe pediatric liver disease progressing to cirrhosis. Abcb4-/- mice exhibit slowly developing hepatic lesions that can be accelerated by feeding a cholic acid (CA)-supplemented diet. We investigated the beneficial effects of a soybean lecithin (L)-supplemented diet in this model of liver disease. Abcb4-/- mice and wild-type (WT) controls were divided in four groups by the diet they were fed: control (C) diet, L-supplemented diet, CA-supplemented diet, and L- and CA-supplemented (L+CA) diet. After 2 wk on these regimens, liver enzymes and bilirubin were measured in serum with bile flow, total bile acids, and cholesterol (CHOL) and phospholipid (PL) concentrations in bile. Ductular hyperplasia, portal fibroblastic cell proliferation, myofibroblast activation, and hepatic fibrosis were quantified on liver sections. Abcb4-/- mice fed the C diet exhibited mild liver damage. CA produced very high elevations of serum liver enzymes and bilirubin with significant bile duct proliferation, peribiliary fibroblast activation, and fibrosis. The L-supplemented diet dramatically mitigated the hepatic damage in CA-supplemented diet animals. We conclude that L is protective against liver disease in Abcb4-/- mice and suggest that it could offer potential benefit in PFIC3.

Gangliogenesis in the enteric nervous system: roles of the polysialylation of the neural cell adhesion molecule and its regulation by bone morphogenetic protein-4.

The neural crest-derived cells that colonize the fetal bowel become patterned into two ganglionated plexuses. The hypothesis that bone morphogenetic proteins (BMPs) promote ganglionation by regulating neural cell adhesion molecule (NCAM) polysialylation was tested. Transcripts encoding the sialyltransferases, ST8Sia IV (PST) and ST8Sia II (STX), which polysialylate NCAM, were detectable in fetal rat gut by E12 but were downregulated postnatally. PSA-NCAM-immunoreactive neuron numbers, but not those of NCAM, were developmentally regulated similarly. Circular smooth muscle was transiently (E16-20) PSA-NCAM-immunoreactive when it is traversed by migrating precursors of submucosal neurons. Neurons developing in vitro from crest-derived cells immunoselected at E12 with antibodies to p75(NTR) expressed NCAM and PSA-NCAM. BMP-4 promoted neuronal NCAM polysialylation and clustering. N-butanoylmannosamine, which blocks NCAM polysialylation, but not N-propanoylmannosamine, which does not, interfered with BMP-4-induced neuronal clustering. Observations suggest that BMP signaling enhances NCAM polysialylation, which allows precursors to migrate and form ganglionic aggregates during the remodeling of the developing ENS.

Identification of cholelithogenic enterohepatic helicobacter species and their role in murine cholesterol gallstone formation.

BACKGROUND & AIMS: Helicobacter spp are common inhabitants of the hepatobiliary and gastrointestinal tracts of humans and animals and cause a variety of well-described diseases. Recent epidemiologic results suggest a possible association between enterohepatic Helicobacter spp and cholesterol cholelithiasis, chronic cholecystitis, and gallbladder cancer. To test this, we prospectively investigated the effects of Helicobacter spp infection in cholesterol gallstone pathogenesis in the highly susceptible C57L/J mouse model. METHODS: Helicobacter spp-free adult male C57L mice were infected with several different enterohepatic Helicobacter spp or left uninfected and fed either a lithogenic diet or standard mouse chow for 8 and 18 weeks. At the conclusion of the study, bile was examined microscopically and diagnostic culture and polymerase chain reaction were performed. RESULTS: Mice infected with Helicobacter bilis or coinfected with Helicobacter hepaticus and Helicobacter rodentium and fed a lithogenic diet developed cholesterol gallstones at 80% prevalence by 8 weeks compared with approximately 10% in uninfected controls. Monoinfections with H hepaticus , Helicobacter cinaedi , and H rodentium gave a cholesterol gallstone prevalence of 40%, 30%, and 20%, respectively; the latter 2 groups did not differ significantly from uninfected animals. Neither infected nor uninfected mice fed a chow diet developed cholesterol gallstones. CONCLUSIONS: These findings, along with prior epidemiologic studies, suggest that Helicobacter spp play a major role in the pathophysiology of cholesterol gallstone formation in mice and perhaps humans.

Combined effects of EFA deficiency and tumor necrosis factor-alpha on circulating lipoproteins in rats.

Both tumor necrosis factor-alpha (TNF-alpha) and EFA deficiency (EFAD) have been established as causes of marked perturbations in lipid and lipoprotein metabolism. Excessive levels of circulating TNF-alpha can coexist with EFAD in various clinical disorders such as cystic fibrosis and type I diabetes. The present study therefore aimed to investigate their combined effects on lipid profile and lipoprotein composition by administering TNF-alpha to EFAD rats. Lipoprotein lipase (LPL), the rate-limiting enzyme in TG catabolism, was also measured in epididymal adipose tissue. EFAD, after a 4-wk period, induced significant increases in plasma TG (80%, P < 0.001), total cholesterol (TC, 27%, P < 0.025), and HDL-cholesterol (HDL-C, 62%). Two hours after the administration of TNF-alpha, a further rise in TG (43%, P < 0.05) was noted in controls, but not EFAD animals. TC and HDL-C were unaffected by TNF-alpha treatment. In addition, TNF-alpha modified lipoprotein-lipid composition. VLDL and HDL2 derived from EFAD rats were depleted in apolipoprotein (apo) E and apo A-II, and enriched in apo A-I 2 h after TNF-alpha administration. Finally, TNF-alpha decreased adipose tissue LPL activity in both control and EFAD animals. The TNF-alpha-induced inhibition was more marked in EFAD rats. The present results demonstrated that TNF-alpha can amplify or antagonize the effects of EFAD on lipid profile, lipoprotein composition, and LPL activity. These data also suggest that the host's nutritional status is a determining factor for the modulating effect of TNF-alpha on lipid metabolism.

Phosphatidylcholine-enriched diet prevents gallstone formation in mice susceptible to cholelithiasis.

Cholesterol gallstones affect approximately 10-15% of the adult population in North America. Phosphatidylcholine (PC) is considered to be the main cholesterol solubilizer in bile. This study examined the effect of a PC-enriched diet on gallstone incidence in mice susceptible to cholelithiasis. The result obtained showed that the feeding of a lithogenic (LG) diet for 4 weeks or 8 weeks resulted in cholesterol gallstone incidences of 47% and 89%, respectively. These gallstone incidences were either reduced or prevented when the LG diet was enriched with 2% or 6% PC, respectively. The cholesterol saturation index (CSI) was reduced only in mice fed with LG + 6% PC diet as compared with mice fed the LG diet alone. However, in all groups, the CSI was significantly higher than in mice fed Purina chow diet. The biliary anionic polypeptide fraction (APF) was significantly increased in mice fed the LG + 2% PC diet and was reduced in those fed with LG + 6% PC diet. In conclusion, prevention or delay of gallstone formation was not due to a consistent effect on biliary lipid composition, suggesting a direct effect of PC on cholesterol solubilization and/or the effect of an additional nonlipid biliary component such as APF.

Effects of dietary soybean lecithin on plasma lipid transport and hepatic cholesterol metabolism in rats.

Dietary lecithin can stimulate bile formation and biliary lipid secretion, particularly cholesterol output in bile. Studies also suggested that the lecithin-rich diet might modify hepatic cholesterol homeostasis and lipoprotein metabolism. Therefore, we examined hepatic activities of 3-hydroxy-3 methylglutaryl coenzyme A reductase "HMG -CoA reductase", cholesterol 7 alpha-hydroxylase and acyl-CoA: cholesterol acyltransferase "ACAT" as well as plasma lipids and lipoprotein composition in rats fed diets enriched with 20% of soybean lecithin during 14 days. We also evaluated the content of hepatic canalicular membrane proteins involved in lipid transport to the bile (all P-glycoproteins as detected by the C 219 antibody and the sister of P-glycoprotein "spgp" or bile acid export pump) by Western blotting. As predicted, lecithin diet modified hepatic cholesterol homeostasis. The activity of hepatic HMG-CoA reductase and cholesterol 7 alpha-hydroxylase was enhanced by 30 and 12% respectively, while microsomal ACAT activity showed a dramatic decrease of 75%. As previously reported from ACAT inhibition, the plasma level and size of very low-density lipoprotein (VLDL) were significantly decreased and bile acid pool size and biliary lipid output were significantly increased. The canalicular membrane content of lipid transporters was not significantly affected by dietary lecithin. The current data on inhibition of ACAT activity and related metabolic effects by lecithin mimic the previously reported effects following drug-induced inhibition of ACAT activity, suggesting potential beneficial effects of dietary lecithin supplementation in vascular disease.

Lith genes control mucin accumulation, cholesterol crystallization, and gallstone formation in A/J and AKR/J inbred mice.

We recently identified 2 Lith genes that determine cholesterol gallstone formation in C57L/J inbred mice, which show a gallstone prevalence of approximately 80% on feeding 1.0% cholesterol and 0.5% cholic acid. The aim of this study was to explore if the same Lith loci contribute to the variation in gallstone susceptibility in a new experimental cross. After 12 weeks of feeding the lithogenic diet to inbred mice of strains A/J and AKR/J as well as their F(1) progeny, we used microscopy of bile to assess mucin accumulation, crystallization pathways, and stone formation. Backcross progeny (n = 225) were phenotyped and genotyped selectively for microsatellite markers spanning the genome. Quantitative trait loci (QTL) affecting gallstone phenotypes were identified by linkage analysis. Both inbred strains showed accumulation of mucin gel and cholesterol supersaturation. However, only strain AKR developed gallstones (prevalence of 20%), whereas strain A showed a stable liquid crystalline state and no stones. QTL analysis identified a gallstone locus on chromosome 17 (Lith3). A second gene locus on chromosome 15 that controls mucin accumulation harbors the mucin gene Glycam1, which was shown to be expressed in gallbladder epithelia by immunohistochemistry. Gallstone and mucin loci colocalized with potential QTLs affecting the formation of cholesterol crystals. In conclusion, QTL analysis identified specific gene loci determining mucin accumulation, cholesterol crystallization, and gallstone formation. Characterization of the pathophysiologic roles of Lith3 and the new biliary mucin gene Glycam1 might provide insights into primary defects of human cholelithiasis and lead to new therapeutic strategies for prestone intervention.

Cholesterol gallstone formation in overweight mice establishes that obesity per se is not linked directly to cholelithiasis risk.

The relationship between obesity and cholesterol cholelithiasis is not well understood at physiologic or genetic levels. To clarify whether obesity per se leads to increased prevalence of cholelithiasis, we examined cholesterol gallstone susceptibility in three polygenic (KK/H1J, NON/LtJ, NOD/LtJ) and five monogenic [carboxypeptidase E (Cpe (fat)), agouti yellow (A(y)), tubby (tub), leptin (Lep(ob)), leptin receptor (Lepr (db))] murine models of obesity during ingestion of a lithogenic diet containing dairy fat, cholesterol, and cholic acid. At 8 weeks on the diet, one strain of polygenic obese mice was resistant whereas the others revealed low or intermediate prevalence rates of cholelithiasis. Monogenic obese mice showed distinct patterns with either high or low gallstone prevalence rates depending upon the mutation. Dysfunction of the leptin axis, as evidenced by the Lep(ob) and the Lepr (db) mutations, markedly reduced gallstone formation in a genetically susceptible background strain, indicating that in mice with this genetic background, physiologic leptin homeostasis is a requisite for cholesterol cholelithogenesis. In contrast, the Cpe (fat) mutation enhanced the prevalence of cholelithiasis markedly when compared with the background strain. Since CPE converts many prohormones to hormones, a deficiency of biologically active cholecystokinin is a likely contributor to enhanced susceptibility to cholelithiasis through compromising gallbladder contractility and small intestinal motility. Because some murine models of obesity increased, whereas others decreased cholesterol gallstone susceptibility, we establish that cholesterol cholelithiasis in mice is not simply a secondary consequence of obesity per se. Rather, specific genes and distinct pathophysiological pathways are responsible for the shared susceptibility to both of these common diseases.

Interacting QTLs for cholesterol gallstones and gallbladder mucin in AKR and SWR strains of mice.

We employed quantitative trait locus (QTL) mapping in a backcross between gallstone-susceptible SWR/J and gallstone-resistant AKR/J inbred mice to identify additional susceptibility loci for cholesterol gallstone formation. After 12 wk of feeding the mice a lithogenic diet, we phenotyped 330 backcross progeny for gallstones, gallbladder mucin accumulation, liver weight, and body weight. Marker-based regression analysis revealed significant single QTLs associated with gallstone formation on chromosome 9 and the liver weight/body weight ratio on chromosomes 5 and X. A search for gene pairs detected significant gene-gene interactions for mucin accumulation between loci on chromosomes 5 and 11 and suggestive gene-gene interactions linked to gallstone formation between the QTL on chromosome 9 and loci on chromosomes 6 and 15. These findings uncover new QTLs for cholesterol gallstones, reveal independent loci for mucin accumulation, and demonstrate the importance of considering gene-gene interactions in cholesterol cholelithiasis. According to standard nomenclature, the gallstone QTL on chromosome 9 is named Lith5.