Farrants A K, Nilsson A, Pedersen J I
Institute for Nutrition Research, School of Medicine, University of Oslo, Norway.
J Lipid Res. 1993 Dec;34(12):2041-50.
We have examined the ability of HepG2 human hepatoblastoma cells and 7800 C1 Morris rat hepatoma cells to convert 3 alpha, 7 alpha, 12 alpha-trihydroxy-5 beta-cholestanoic acid (THCA) and 3 alpha, 7 alpha-dihydroxy-5 beta-cholestanoic acid (DHCA) to cholic acid and chenodeoxycholic acid, respectively. Cell extracts from both these cell lines could neither form cholic acid from THCA nor from the activated form, THCA-CoA. This suggests that both cell lines are defective in two enzyme activities involved in the pathway, the microsomal THCA-CoA ligase and the peroxisomal THCA-CoA oxidase. Furthermore, we show that the subsequent enzymes are active in the conversion to bile acids, because the product of the THCA-CoA oxidase, 3 alpha, 7 alpha, 12 alpha-trihydroxy-5 beta-cholest-24-enoyl-coenzyme A (delta 24-THCA-CoA) or delta 24-THCA in the presence of THCA-CoA ligase, are converted to cholic acid by both cell lines. HepG2 cells were able to slowly form chenodeoxycholic acid and cholic acid from 5 beta-cholestane-3 alpha, 7 alpha-diol and 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha-triol, respectively, in 24- and 96-h incubations. The rate of cholic acid formation was lower than the rate for chenodeoxycholic acid and there was a clear accumulation of THCA. 7800 C1 Morris cells had no ability to form cholic acid or chenodeoxycholic acid after 96 h incubation. We conclude that these two cell lines have defects in two enzyme activities involved in the peroxisomal oxidation in bile acid formation, the microsomal THCA-CoA ligase and the peroxisomal THCA-CoA oxidase.
我们研究了HepG2人肝癌细胞和7800 C1莫里斯大鼠肝癌细胞分别将3α,7α,12α-三羟基-5β-胆甾烷酸（THCA）和3α,7α-二羟基-5β-胆甾烷酸（DHCA）转化为胆酸和鹅去氧胆酸的能力。这两种细胞系的细胞提取物既不能从THCA也不能从其活化形式THCA-CoA形成胆酸。这表明这两种细胞系在该途径中涉及的两种酶活性方面存在缺陷，即微粒体THCA-CoA连接酶和过氧化物酶体THCA-CoA氧化酶。此外，我们表明后续的酶在转化为胆汁酸的过程中是有活性的，因为在存在THCA-CoA连接酶的情况下，THCA-CoA氧化酶的产物3α,7α,12α-三羟基-5β-胆甾-24-烯酰辅酶A（δ24-THCA-CoA）或δ24-THCA可被这两种细胞系转化为胆酸。在24小时和96小时的孵育中，HepG2细胞能够分别从5β-胆甾烷-3α,7α-二醇和5β-胆甾烷-3α,7α,12α-三醇缓慢形成鹅去氧胆酸和胆酸。胆酸的形成速率低于鹅去氧胆酸的形成速率，并且THCA有明显的积累。7800 C1莫里斯细胞在孵育96小时后没有形成胆酸或鹅去氧胆酸的能力。我们得出结论，这两种细胞系在胆汁酸形成的过氧化物酶体氧化过程中涉及的两种酶活性方面存在缺陷，即微粒体THCA-CoA连接酶和过氧化物酶体THCA-CoA氧化酶。
