suppressive drugs and used in most transplantation centers to prevent organ rejection. It is a cyclic polypeptide, consisting of 11 amino acids and has a molecular weight of 1,202 The aim of this study was to elucidate the possible d. It is insoluble in water but soluble in many organic solcauses of elevated low-density lipoprotein (LDL)-cholesvents, and it is thus a lipophilic drug. Cyclosporine selectively terol levels in transplanted patients treated with the iminhibits the interleukin-2-driven proliferation of activated T munosuppressant drug, cyclosporine. HepG2 cells, from lymphocytes with a subsequent suppression of proliferation a well-differentiated cell-line of hepatoma cells, were and generation of cytotoxic T lymphocytes, while sparing cultured and used as a model for in vitro hepatocytic T-suppressor-cell subpopulations. Patients, who are liver LDL uptake. Different concentrations of cyclosporine, transplant recipients and use this drug to prevent organ rewhich were within the range of concentrations found in jection are, however, prone to be afflicted by cardiovascular humans treated with cyclosporine, were added to tissue disease due to the development of atherosclerosis and atherculture medium together with 125 I-LDL. The results oma formation, a result of cyclosporine-caused elevation of showed that cyclosporine reduced LDL uptake and degblood low-density lipoprotein (LDL)-cholesterol levels. [1][2][3][4][5] radation in HepG2 cells by about 25%. The cells were
The mechanism whereby cyclosporine causes high LDLalso pretreated with cyclosporine for 1 to 24 hours and cholesterol levels to occur has not yet been clarified. Due to then incubated with new medium containing labeled its hydrophobic property, cyclosporine binds to lipoproteins LDL for 2 hours at 4ЊC in an LDL-binding assay. The and in plasma is bound to high-density lipoproteins (33%data showed that cyclosporine reduced the subsequent 46%), to low-density lipoproteins (28%-35%), and to very-low-LDL binding. Cyclosporine has no toxic effects on HepG2 density lipoproteins (VLDL) (6%-19%) 6,7 ; therefore, lipoprocells, as shown by unchanged growth capacity of the teins act as carriers for cyclosporine.
cells. By means of a 50-fold excess of unlabeled LDL,
Lipoproteins, according to their densities, are categorized a monoclonal anti-LDL receptor antibody, and dextran into chylomicrons, chylomicron remnants, VLDL, intermedisulfate, we also evaluated if this inhibition of LDL bindate-density lipoproteins, LDL, and high-density lipoproteins. ing occurred through the LDL receptor-mediated path-VLDL and LDL are the major cholesterol carriers in the way, through non-LDL receptor-mediated pathways, or blood. VLDL is secreted from the intestine and the liver. 8 through both. The results show that cyclosporine re-Liver-derived VLDL is converted to LDL, and this conversion duces LDL binding and uptake by mainly inhibiting the is primarily mediated by the enzyme lipoprotein lipase. 8 In LDL receptor-mediated pathway. We also studied the humans, approximately one half of the VLDL particles are effect of the LDL-cyclosporine complex on the binding converted to LDL. The liver is also responsible for about two of labelled LDL. The presence of cyclosporine in the LDL thirds of the catabolism of LDL. 9 The uptake of LDL occurs particle does not influence the binding behaviour of LDL mainly through LDL receptors, even though non-LDL recepto its receptor. We also found that cyclosporine reduces tor-mediated pathways play a role in liver catabolism of LDL. 9 Also, a recent study showed that cyclosporine reduces the expression of the LDL receptor messenger RNA apolipoprotein B secretion 10 and thus VLDL secretion in (mRNA) by about 40%. Thus, the interpretation of this HepG2. This means that the cause of elevation of LDL-cholesstudy is that cyclosporine can cause an increase in LDLterol level in cyclosporine-treated patients is probably not cholesterol in the plasma of transplantation patients by due to an increase of secretion of VLDL but to other mechareducing the catabolism of LDL in the liver by inhibiting nisms, such as an interference with LDL catabolism. The mainly the LDL receptor-mediated catabolism through human hepatoma cell line HepG2 is a well-defined humanan effect on LDL receptor synthesis. (HEPATOLOGY derived cell line. The cells are highly differentiated and have 1996;24:613-619.) maintained secretory functions, such as lipoprotein secretion, and they also have functional LDL receptors. 11,12 The aim of this study was to investigate whether cyclosporine reduces LDL catabolism in the liver. To study this, HepG2 cells were Abbreviations: LDL, low-density lipoprotein; VLDL, very-low-density lipoprotein; EDTA, used as an in vitro model. ethylenediaminetetraacetic acid; PBS, phosphate-buffered saline; BSA, bovine serum albumin; mRNA, messenger RNA; DMSO, dimethyl sulfoxide.