Cohen L H, van Vliet A, Roodenburg L, Jansen L M, Griffioen M
Gaubius Laboratory IVVO-TNO, Leiden, The Netherlands.
Biochem Pharmacol. 1993 Jun 9;45(11):2203-8. doi: 10.1016/0006-2952(93)90190-8.
The possible difference between lovastatin (mevinolin, MK-803), simvastatin (MK-733) and pravastatin (CS-514), all chemically-related competitive inhibitors of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase, were tested in the human hepatoma cell line Hep G2, which is often used as a model for the human hepatocyte. After an 18-hr incubation of the cells with the drugs, pravastatin (IC50 = 1900 nM) was less potent than simvastatin and lovastatin (IC50 = 34 and 24 nM, respectively) in inhibiting the sterol synthesis. As a consequence of this inhibition, the HMG-CoA reductase mRNA levels and squalene synthase activity, both negatively-regulated by sterols, were increased equally by simvastatin and lovastatin, whereas the induction by pravastatin was much less. In contrast, there were fewer differences between the compounds in inhibiting HMG-CoA reductase activity, when assayed directly in Hep G2 cell homogenates (IC50 values = 18, 61 and 95 nM for simvastatin, lovastatin and pravastatin, respectively). Moreover, in experiments with human hepatocytes in primary culture the IC50 values for inhibition of the cholesterol synthesis by simvastatin and pravastatin were of the same order of magnitude (23 and 105 nM, respectively). The results are therefore explained as follows: the three drugs act in the same way within the Hep G2 cell in terms of inhibiting HMG-CoA reductase and their subsequent effect on the feedback regulation of the cholesterol synthesis, i.e. increasing squalene synthase and HMG-CoA reductase mRNA. However, pravastatin seems to be less able to enter the cells compared with simvastatin and lovastatin, possibly because of the higher hydrophobicity of the latter compounds. The observation with human hepatocytes suggests that in Hep G2 cells a specific hepatic transporter is missing. On one hand the human hepatoma cell line Hep G2 has proved to be a good model for the study of the feedback regulation of enzymes of the cholesterol biosynthetic pathway such as HMG-CoA reductase and squalene synthase, but, on the other hand seems to be less suitable as a model for the study of specific uptake of drugs, e.g. the vastatins, in human hepatocytes.
洛伐他汀（美维诺林，MK - 803）、辛伐他汀（MK - 733）和普伐他汀（CS - 514）均为3 - 羟基 - 3 - 甲基戊二酰辅酶A（HMG - CoA）还原酶的化学相关竞争性抑制剂，在常被用作人肝细胞模型的人肝癌细胞系Hep G2中对它们之间可能存在的差异进行了测试。在用药物对细胞进行18小时孵育后，普伐他汀（IC50 = 1900 nM）在抑制固醇合成方面的效力低于辛伐他汀和洛伐他汀（IC50分别为34和24 nM）。由于这种抑制作用，受固醇负调控的HMG - CoA还原酶mRNA水平和角鲨烯合酶活性，在辛伐他汀和洛伐他汀作用下均有同等程度的升高，而普伐他汀的诱导作用则小得多。相比之下，当在Hep G2细胞匀浆中直接检测时，这几种化合物在抑制HMG - CoA还原酶活性方面的差异较小（辛伐他汀、洛伐他汀和普伐他汀的IC50值分别为18、61和95 nM）。此外，在原代培养的人肝细胞实验中，辛伐他汀和普伐他汀抑制胆固醇合成的IC50值处于同一数量级（分别为23和105 nM）。因此，结果可解释如下：这三种药物在Hep G2细胞内抑制HMG - CoA还原酶及其随后对胆固醇合成反馈调节的作用方式相同，即增加角鲨烯合酶和HMG - CoA还原酶mRNA。然而，与辛伐他汀和洛伐他汀相比，普伐他汀进入细胞的能力似乎较弱，这可能是因为后两种化合物的疏水性更高。对人肝细胞的观察表明，在Hep G2细胞中缺少一种特定的肝脏转运蛋白。一方面，人肝癌细胞系Hep G2已被证明是研究胆固醇生物合成途径中酶（如HMG - CoA还原酶和角鲨烯合酶）反馈调节的良好模型，但另一方面，它似乎不太适合作为研究药物（如他汀类药物）在人肝细胞中特异性摄取的模型。
