Effect of Coffee Lipids (Cafestol and Kahweol) on Regulation of Cholesterol Metabolism in HepG2 Cells

Abstract

Abstract We studied the effect of the coffee diterpene alcohols, cafestol and kahweol, on cholesterol metabolism in HepG2 cells. Uptake of 125 I-tyramine cellobiose–labeled LDL was decreased by 15% to 20% ( P <.05) after 18 hours of preincubation with cafestol (20 μg/mL), whereas 25-hydroxycholesterol reduced uptake by 55% to 65% ( P <.05). Degradation of LDL in the presence of cafestol was decreased by 20% to 30% ( P <.05) under the same conditions. The effect of cafestol (20 μg/mL) on uptake and degradation of LDL was greatest (35% to 40%, P <.05) after 6 and 10 hours of preincubation, respectively. Furthermore, the effect of cafestol was also dependent on its concentration, and a significant decrease in the LDL uptake (19%) was observed at 10 μg/mL ( P <.05). Specific binding of LDL was reduced by 17% ( P <.05) and 60% ( P <.05) after preincubation with cafestol (20 μg/mL) and 25-hydroxycholesterol (5 μg/mL) for 6 hours, respectively, compared with control cells. Analysis of LDL binding showed that cafestol reduced the number of binding sites for LDL on the cell surface (capacity) by 35% ( P <.05). In contrast, no significant effect on the level of mRNA for the LDL receptor was observed after incubation with cafestol, whereas 25-hydroxycholesterol reduced the mRNA level for the LDL receptor by 40% to 50% ( P <.05). A fusion gene construct consisting of a synthetic sterol regulatory element-1 (SRE-1) promoter for the human LDL receptor coupled to the reporter gene for chloramphenicol acetyltransferase (CAT) was transfected into HepG2 cells. No change was observed in CAT activity in SRE-1–transfected cells after incubation with cafestol, whereas 25-hydroxycholesterol reduced CAT activity by 30% to 40% ( P <.05). Incorporation of [ 14 C]acetate into unesterified cholesterol and 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase activity were unaffected in cells incubated with cafestol as well as the cafestol-kahweol mixture compared with control cells. Moreover, cafestol and the cafestol-kahweol mixture did not promote increased incorporation of radiolabeled [ 14 C]oleic acid into cholesteryl esters after short-term incubation compared with control cells. On the other hand, 25-hydroxycholesterol caused a 70% to 90% reduction of cholesterol synthesis ( P <.05) and HMG-CoA reductase activity ( P <.05), decreased HMG-CoA reductase mRNA level by 70% to 80% ( P <.05), and promoted a twofold increase in cholesterol esterification ( P <.05). Finally, no effect of the coffee diterpenes on bile acid formation was observed. These results suggest that cafestol (and kahweol) may reduce the activity of hepatic LDL receptors and thereby cause extracellular accumulation of LDL.