Oleic acid modulates the partitioning of cholesterol from micellar bile salt solution

The effects of monounsaturated fatty acid (oleic acid) on cholesterol monomer activity and on the rate of cholesterol influx were studied in vitro. A polyethylene disc method was employed to determine cholesterol monomer activity in constant sodium taurocholate-cholesterol micellar solution containing different oleic acid concentration levels at pH 5.5, 6.5 and 7.2. In addition, the effect of oleic acid on the rates of cholesterol influx was determined using an everted rat jejunal sac technique. At pH 5.5, increased oleic acid concentration from 5 to 10 mM resulted in significant decreased apparent cholesterol monomer activity (3.8 +/- 0.21 nmol/disc vs 1.0 +/- 0.08, P less than 0.001). At pH 6.5, apparent cholesterol monomer activity was 2.3 +/- 0.19 nmol/disc at 5 mM and 0.5 +/- 0.09 at 16 mM oleic acid level (P less than 0.001). Apparent monomer activity of cholesterol in micellar solutions at pH 7.2 used for the influx study at 5 and 15 mM oleic acid concentration level was 1.8 +/- 0.14 and 0.7 +/- 0.08 nmol/disc, respectively (P less than 0.001). Thus there was a significant decrease in cholesterol monomer activity by the addition of oleic acid at each pH. The rate of cholesterol influx across the brush border membrane of the rat jejunum at 5 and 15 mM oleic acid concentration level was 3.2 +/- 0.31 and 1.5 +/- 0.21 nmol/100 mg dry weight tissues/min, respectively (P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)