Early effects of colectomy and endorectal pullthrough operation on biliary lipid composition

Inhibiting intestinal NPC1L1 activity prevents diet-induced increase in biliary cholesterol in Golden Syrian hamsters

Niemann-Pick C1-like 1 (NPC1L1) facilitates the uptake of sterols into the enterocyte and is the target of the novel cholesterol absorption inhibitor, ezetimibe. These studies used the Golden Syrian hamster as a model to delineate the changes in the relative mRNA expression of NPC1L1 and other proteins that regulate sterol homeostasis in the enterocyte during and following cessation of ezetimibe treatment and also to address the clinically important question of whether the marked inhibition of cholesterol absorption alters biliary lipid composition. In hamsters fed a low-cholesterol, low-fat basal diet, the abundance of mRNA for NPC1L1 in the small intestine far exceeded that in other regions of the gastrointestinal tract, liver, and gallbladder. In the first study, female hamsters were fed the basal diet containing ezetimibe at doses up to 2.0 mg.day(-1).kg body wt(-1). At this dose, cholesterol absorption fell by 82%, fecal neutral sterol excretion increased by 5.3-fold, and hepatic and intestinal cholesterol synthesis increased more than twofold, but there were no significant changes in either fecal bile acid excretion or biliary lipid composition. The ezetimibe-induced changes in intestinal cholesterol handling were reversed when treatment was withdrawn. In a second study, male hamsters were given a diet enriched in cholesterol and safflower oil without or with ezetimibe. The lipid-rich diet raised the absolute and relative cholesterol levels in bile more than fourfold. This increase was largely prevented by ezetimibe. These data are consistent with the recent finding that ezetimibe treatment significantly reduced biliary cholesterol saturation in patients with gallstones.

Oxysterols from human bile induce apoptosis of canine gallbladder epithelial cells in monolayer culture

Oxysterols have been detected in various mammalian organs and blood. Biliary epithelium is exposed to high concentrations of cholesterol, and we have identified three keto-oxysterols (cholest-4-en-3-one, cholesta-4,6-dien-3-one, cholesta-3,5-dien-7-one) in human bile and gallstones. Because the effects of oxysterols on biliary physiology are not well defined, we investigated their biological effects on dog gallbladder epithelial cells. Enriched medium (culture medium containing taurocholate and lecithin and cholesterol +/- various oxysterols) was applied to confluent monolayers of dog gallbladder epithelial cells in culture. Cytotoxicity and apoptosis were studied by morphological analysis and flow cytometry. Oxysterols in the mitochondrial fraction were identified by gas chromatography/mass spectrometry, whereas release of cytochrome c from mitochondria was assayed by spectrophotometry and Western blot analysis. Compared with cells treated with culture medium or with enriched medium containing cholesterol, oxysterol-treated cells showed significantly increased apoptosis (P < 0.05). Exogenously applied oxysterols were recovered from the mitochondrial fraction. Cytochrome c release from mitochondria was increased significantly by cholest-4-en-3-one, cholesta-4,6-dien-3-one, and 5beta-cholestan-3-one (all P < 0.05). Thus oxysterols recovered from human bile and gallstones induce apoptosis of biliary epithelium via a mitochondrial-dependent pathway and may play a role in the pathogenesis of chronic inflammation and carcinogenesis in the gallbladder.

Early and long-term effects of colectomy and endorectal pullthrough on bile acid profile

OBJECTIVE

Although total colectomy with mucosal proctectomy and endorectal pullthrough affects two sites critical to the enterohepatic circulation of bile acids, little information is available regarding the manner in which normal digestive physiology is altered by these procedures. This study defines the early and long-term effects of colectomy and endorectal pullthrough on bile acid profile and the long-term effects on biliary lipid metabolism.

SUMMARY BACKGROUND DATA

Specific changes in bile acid absorption have been reported in patients after ileal resection. Recent studies from our laboratory indicate that in the early postoperative period, colectomy with endorectal pullthrough causes a significant decrease in gallbladder bile concentrations of total bile acids, cholesterol, phospholipids, and calcium. The observation by several authors that the pouch undergoes morphologic and perhaps functional adaptation suggest that these changes may be transient and perhaps reversible.

METHODS

These studies were done in an awake, unanesthetized canine model that allows periodic sampling of gallbladder bile without creation of an external biliary fistula and its associated sequelae. Animals were ultimately randomly assigned to either laparotomy and gallbladder cannulation (N = 6), or gallbladder cannulation with total colectomy and ileorectal anastomosis (N = 7), or biliary cannulation, colectomy, mucosal proctectomy and endorectal pullthrough with ileal reservoir (N = 5).

RESULTS

Six weeks after operation, colectomy and ileorectal anastomosis were associated with a significant alteration in the relative composition of bile acids in gallbladder bile. These early changes were manifested by a significant (p < 0.05) increase in taurocholic acid and a concomitant decrease in taurodeoxycholic acid. These changes became even more pronounced in the ileorectal anastomosis group 12 weeks after colectomy and ileorectostomy. Although similar changes in the relative concentrations of individual bile acids occurred in the 6-week endorectal animals, bile acid profile was restored to normal by 12 weeks.

CONCLUSIONS

Colectomy with ileorectal anastomosis leads to early and significant changes in bile acid profile, which persist and become even more pronounced with time. In contrast, the construction of an ileal reservoir after colectomy facilitates restoration of a normal bile acid profile. We propose that these alterations in bile acid metabolism result from adaptation of the ileal reservoir as its mucosa assumes functional characteristics of normal colon.