Hamsters predisposed to sucrose-induced cholesterol gallstones (LPN strain) are more resistant to excess dietary cholesterol than hamsters that are not sensitive to cholelithiasis induction.

We compared the effects of cholesterol feeding in male hamsters from two strains with different propensities to sucrose-induced cholelithiasis; Laboratoire de Physiologie de la Nutrition (LPN) hamsters are predisposed to developing biliary cholesterol gallstones, whereas Janvier (JAN) hamsters are not. When fed a basal control diet, LPN hamsters had a lower cholesterolemia (-21%, P = 0.01) than JAN hamsters, and a higher activity of 3-hydroxy-3-methyl glutaryl coenzyme A reductase in liver (+148%, P = 0.018) and intestine (+281%, P < 0.0001). After feeding the same diet enriched with 0.3% cholesterol for 5 wk, cholesterolemia increased more dramatically in JAN hamsters (+235%, P < 0.001) than in LPN hamsters (+108%, P < 0.001), as did the liver concentration of cholesterol, which reached 152.30 +/- 13.00 and 44.41 +/- 9.06 micromol/g, respectively. Only JAN hamsters displayed hepatomegaly, with an increased cholesterol saturation index of the gallbladder bile (+100%, P < 0.01), due to the cholesterol challenge. In liver, cholesterol feeding reduced cholesterol 7alpha-hydroxylase activity and mRNA level, and stimulated sterol 27-hydroxylase and oxysterol 7alpha-hydroxylase activities. Hepatic levels of LDL receptor decreased by approximately 60% in both strains, whereas HDL receptor scavenger class B type 1 (SR-BI) levels were unaffected by dietary cholesterol. The greater resistance of LPN hamsters to the hypercholesterolemic diet can be explained by a lower capacity to store cholesterol in the liver and greater efficiency in reducing the activity of 3-hydroxy-3-methyl glutaryl coenzyme A reductase in response to cholesterol feeding [from 11263 to 261 pmol/(min x organ) in LPN hamsters and from 4530 to 694 pmol/(min x organ) in JAN hamsters]. These results highlight the usefulness of this two-strain model, which offers some analogy with the inverse association between the predisposition to cholelithiasis and the risk of atherosclerosis in humans.

Assay of microsomal oxysterol 7alpha-hydroxylase activity in the hamster liver by a sensitive method: in vitro modulation by oxysterols.

A method of assaying hepatic cytochrome P-450, oxysterol 7alpha-hydroxylase (CYP7B), was developed by combining the use of 25-[26,27-(3)H]hydroxycholesterol as a substrate and hydroxypropyl-beta-cyclodextrin as a substrate vehicle. When these assay conditions were tested, an undesirable transformation was observed of the reaction product, 7alpha,25-dihydroxycholesterol, into 3-oxo-7alpha,25-dihydroxy-4-cholesten by the activity of 3beta-hydroxy-Delta(5)-C(27) steroid oxydoreductase, a microsomal NAD(+) and NADP(+) dependent enzyme of bile acid metabolism. A great improvement was reached by using a continuous NADPH generating system which constantly re-transforms NADP(+) into NADPH, thus inhibiting this activity. This improved CYP7B assay, comparable to our previously described assay for cholesterol 7alpha-hydroxylase (CYP7A), allowed a 3-fold increase of the apparent enzyme activity. The possibility to simultaneously measure CYP7A and CYP7B activities on the same microsomal preparation was investigated. A marked decrease (-33%) in the CYP7B activity was noticed, while that of CYP7A remained unchanged. The CYP7B activity was observed to be inhibited by cholesterol (-30%) and also by the oxysterols 7alpha-hydroxycholesterol (-21%), 7beta-hydroxycholesterol (-25%) and epicoprostanol (-20%), and by cyclosporin A (-26%). It can be concluded that this sensible and easy to perform CYP7B assay allows to observe, at least in vitro, a modulation of the enzyme activity by oxysterols.