Cholesterol and bile acid synthesis in Hep G2 cells. Metabolic effects of 26- and 7 α-hydroxycholesterol

Abstract

1. Using a human hepatoma (Hep G2) cell line that continually synthesizes 3 beta-hydroxy-5-cholenoic acid, lithocholic acid, chenodeoxycholic acid and cholic acid we have determined the metabolism and biological effects of 26-hydroxycholesterol and 7 alpha-hydroxycholesterol. 2. Addition of 26-hydroxycholesterol to the medium (6 microM) downregulated cholesterol and chenodeoxycholic acid synthesis. 3. The predominant metabolite of 26-hydroxycholesterol was 3 beta-hydroxy-5-cholenoic acid. 4. Cholesterol synthesis was not affected by the addition of 7 alpha-hydroxycholesterol (6 and 12 microM). The predominant metabolite of 7 alpha-hydroxycholesterol was chenodeoxycholic acid. 5. In Hep G2 cells 7 alpha-hydroxylation of 26-hydroxycholesterol is not well expressed.

Effects of CYP7A1 overexpression on cholesterol and bile acid homeostasis

“…A range of 0.01-2.2 M has previously been demonstrated in the serum of healthy humans (3). A concentration of 6-12 M of 7␣-hydroxycholesterol had not previously been shown to downregulate HMGR activity in HepG2 cells (23). In our studies, the addition of 7␣-hydroxycholesterol to medium to obtain a 1 M concentration had no effect on HMGR activity.…”

“…As reference, 7␣-hydroxycholesterol serum levels have been reported to be in the range of 0.01-2.2 M in healthy humans (3). In other studies, the addition of 6-12 M concentrations of 7␣-hydroxycholesterol have not been shown to downregulate HMG-R activity in HepG2 cells (23). 7␣-Hydroxycholesterol-induced cell toxicity was assessed as previously described (34).…”

Regulation of bile acid synthesis

“…reported to be a powerful inhibitor of cholesterol synthesis (19,20). Extensive recent review of reactions and steps involved in the bile acid biosynthesis pathways is available (13).…”

27‐Hydroxycholesterol modulation of low density lipoprotein metabolism in cultured human hepatic and extrahepatic cells

“…inactivating) oxysterol repressor(s) [43]. Since Hep G2 cells are able to synthesize bile acids [44,45], and since 27-OH-C is a physiological bile acid precursor [22&l], part of this exogenously administered oxysterol can be utilized for this me~boli~ pathway and therefore it may not be completely available for regulating LDL receptors. This difference between the two oxysterols is in favor of a role, if any, of 27-OH-C in the regulation of cholesterol metabolism in extra-hepatic tissues; it has been, in fact, recently proposed that 27-OH-C is an intacrine regulator of sterol metabolism in ovarian cells [26].…”