Cianflone K, Vu H, Zhang Z, Sniderman A D
McGill Unit for the Prevention of Cardiovascular Disease, Royal Victoria Hospital, Montreal, Canada.
Atherosclerosis. 1994 Jun;107(2):125-35. doi: 10.1016/0021-9150(94)90014-0.
This study examines the effects of extracellular albumin on hepatic apo B-100 metabolism. To do so, a transformed human liver cell line, HepG2, was used as a hepatocyte model and the concentration of albumin in the medium was varied between 0 and 5 g%. Apo B-100 and apo A1 concentrations in the medium were determined by specific enzyme-linked immunoassay (ELISA) and intracellular synthesis of cholesterol ester and triglyceride were determined by addition of appropriate radiolabels to the medium. The data demonstrate that the reduction of extracellular albumin concentration resulted in increased apo B-100 concentration in the medium. Apo A1 secretion, however, was unaffected. While the differences in apo B-100 concentration in the medium were statistically significant (33% +/- 7%, P < 0.0025, 0 g% albumin compared to 5 g% albumin in the medium), the absolute magnitude of the effect under these conditions was relatively modest. Nevertheless, the changes were consistent and evident over incubation periods as long as 8 days. Of interest, although triglyceride synthesis was unaffected, cholesterol ester synthesis changed such that as albumin concentration decreased, synthesis of cholesterol ester increased paralleling the changes in apo B-100 (170% +/- 9%, P < 0.005). These findings were extended by studying interventions which altered cholesterol ester synthesis. Addition of the compound 58-035 (5 micrograms/ml, a specific inhibitor of acylcholesterol acyltransferase activity) resulted in substantial inhibition of cholesterol ester synthesis (39% to 66%, P < 0.025 and P < 0.005, respectively) and apo B-100 concentrations in the medium which decreased by 20% to 28%, P < 0.025. Triglyceride synthesis, in contrast, increased significantly by 32% P < 0.025. Therefore, addition of 58-035 confirmed the previous findings of a parallel relation between cholesterol ester synthesis and apo B-100 concentration in the medium. Nonetheless, albumin still had an additional inhibitory effect on cholesterol ester and apo B-100 secretion. Of interest, when chylomicron remnants (25 micrograms/ml cholesterol), which cause apo B-100 secretion to increase by more than threefold, were added to the medium, albumin now had a more pronounced absolute effect on apo B-100 secretion with a 48% inhibition observed as albumin was increased from 0 to 5 g% in the medium (P < 0.0125). The effect of extracellular albumin on the low density lipoprotein (LDL) pathway was also examined. No differences in non-specific cell association component were detected.(ABSTRACT TRUNCATED AT 400 WORDS)
本研究探讨细胞外白蛋白对肝脏载脂蛋白B - 100代谢的影响。为此，使用一种转化的人肝细胞系HepG2作为肝细胞模型，并将培养基中白蛋白的浓度在0至5 g%之间变化。通过特异性酶联免疫吸附测定（ELISA）测定培养基中载脂蛋白B - 100和载脂蛋白A1的浓度，并通过向培养基中添加适当的放射性标记物来测定细胞内胆固醇酯和甘油三酯的合成。数据表明，细胞外白蛋白浓度的降低导致培养基中载脂蛋白B - 100浓度升高。然而，载脂蛋白A1的分泌未受影响。虽然培养基中载脂蛋白B - 100浓度的差异具有统计学意义（33%±7%，P < 0.0025，培养基中0 g%白蛋白与5 g%白蛋白相比），但在这些条件下该效应的绝对幅度相对较小。尽管如此，在长达8天的孵育期内，这些变化是一致且明显的。有趣的是，虽然甘油三酯合成未受影响，但胆固醇酯合成发生了变化，即随着白蛋白浓度降低，胆固醇酯合成增加，与载脂蛋白B - 100的变化平行（170%±9%，P < 0.005）。通过研究改变胆固醇酯合成的干预措施，这些发现得到了扩展。添加化合物58 - 035（5微克/毫升，酰基胆固醇酰基转移酶活性的特异性抑制剂）导致胆固醇酯合成大幅抑制（分别为39%至66%，P < 0.025和P < 0.005），培养基中载脂蛋白B - 100浓度降低20%至28%，P < 0.025。相比之下，甘油三酯合成显著增加32%，P < 0.025。因此，添加58 - 035证实了先前关于胆固醇酯合成与培养基中载脂蛋白B - 100浓度之间平行关系的发现。尽管如此，白蛋白对胆固醇酯和载脂蛋白B - 100的分泌仍有额外的抑制作用。有趣的是，当向培养基中添加乳糜微粒残粒（25微克/毫升胆固醇）时，其可使载脂蛋白B - 100分泌增加三倍以上，此时白蛋白对载脂蛋白B - 100分泌的绝对效应更为明显，当培养基中白蛋白从0增加到5 g%时，观察到有48%的抑制作用（P < 0.0125）。还研究了细胞外白蛋白对低密度脂蛋白（LDL）途径的影响。未检测到非特异性细胞结合成分的差异。（摘要截短于400字）
