Eun H. Park

Lovastatin alters biliary lipid composition and dissolves gallstones: A long-term study in prairie dogs

Lovastatin, an inhibitor of the rate-limiting enzyme in cholesterol biosynthesis, is widely used to treat hypercholesterolemia. We investigated the long-term effects of lovastatin alone and in combination with ursodeoxycholic acid on biliary lipid composition and gallstone dissolution. Forty-two prairie dogs were fed 1.2% cholesterol diet for 5 weeks, and cholecystectomy was performed on 6 animals to confirm gallstones. The remaining animals were maintained on a 0.4% cholesterol diet and were randomized to receive placebo, lovastatin (3.3 mg/g diet), ursodeoxycholic acid (10 mg/g), or combination of both drugs. After 10 weeks, animals underwent cholecystectomy. Dissolution response to therapy was determined, and serum and biliary lipids were measured. All treatment groups had significant reductions in serum cholesterol. Lovastatin treatment reduced both hepatic and gallbladder bile cholesterol, altered bile acid composition, and induced a 79% total response compared to placebo. Although ursodeoxycholic treatment induced a 44% response, long-term combination treatment elevated both gallbladder bile cholesterol and calcium and failed to produce an augmented response. These data suggest that lovastatin therapy alone may promote gallstone dissolution in humans.

Functional Characterization of Na(+)/(H+) Exchangers in Primary Cultures of Prairie Dog Gallbladder

Gallbladder Na+ absorption is linked to gallstone formation in prairie dogs. We previously reported Na+/H+ exchanger (NHE1-3) expression in native gallbladder tissues. Here we report the functional characterization of NHE1, NHE2 and NHE3 in primary cultures of prairie dog gallbladder epithelial cells (GBECs). Immunohistochemical studies showed that GBECs grown to confluency are homogeneous epithelial cells of gastrointestinal origin. Electron microscopic analysis of GBECs demonstrated that the cells form polarized monolayers characterized by tight junctions and apical microvilli. GBECs grown on Snapwells exhibited polarity and developed transepithelial short-circuit current, Isc, (11.6 ± 0.5 µA · cm−2), potential differences, Vt (2.1 ± 0.2 mV), and resistance, Rt (169 ± 12 Ω · cm2). NHE activity in GBECs assessed by measuring dimethylamiloride-inhibitable 22Na+ uptake under a H+ gradient was the same whether grown on permeable Snapwells or plastic wells. The basal rate of 22Na+ uptake was 21.4 ± 1.3 nmol · mg prot−1 · min−1, of which 9.5 ± 0.7 (~45%) was mediated through apically-restricted NHE. Selective inhibition with HOE-694 revealed that NHE1, NHE2 and NHE3 accounted for ~6%, ~66% and ~28% of GBECs’ total NHE activity, respectively. GBECs exhibited saturable NHE kinetics (Vmax 9.2 ± 0.3 nmol · mg prot−1 · min−1; Km 11.4 ± 1.4 mM Na+). Expression of NHE1, NHE2 and NHE3 mRNAs was confirmed by RT-PCR analysis. These results demonstrate that the primary cultures of GBECs exhibit Na+ transport characteristics similar to native gallbladder tissues, suggesting that these cells can be used as a tool for studying the mechanisms of gallbladder ion transport both under physiologic conditions and during gallstone formation.

Gallbladder Na+/H+ exchange activity is up‐regulated prior to cholesterol crystal formation

Background  Gallbladder Na+ and H2O absorption are increased prior to gallstone formation and may promote cholesterol nucleation. Na+/H+ exchange (NHE) isoforms NHE2 and NHE3 are involved in gallbladder Na+ transport in prairie dogs. We examined whether increased gallbladder Na+ absorption observed during early gallstone formation is the result of NHE up‐regulation.