CYCLOSPORINE INHIBITS CATABOLISM OF LOW-DENSITY LIPOPROTEINS IN HEPG2CELLS BY ABOUT 25-PERCENT

The aim of this study was to elucidate the possible causes of elevated low-density lipoprotein (LDL)-cholesterol levels in transplanted pati ents treated with the immunosuppressant drug, cyclosporine. HepG2 cell s, from a well-differentiated cell-line of hepatoma cells, were cultur ed and used as a model for in vitro hepatocytic LDL uptake, Different concentrations of cyclosporine, which were within the range of concent rations found in humans treated with cyclosporine, were added to tissu e culture medium together with I-125-LDL. The results showed that cycl osporine reduced LDL uptake and degradation in HepG2 cells by about 25 %, The cells were also pretreated with cyclosporine for 1 to 24 hours and then incubated with new medium containing labeled LDL for 2 hours at 4 degrees C in an LDL-binding assay. The data showed that cyclospor ine reduced the subsequent LDL binding. Cyclosporine has no toxic effe cts on HepG2 cells, as shown by unchanged growth capacity of the cells , By means of a 50-fold excess of unlabeled LDL, a monoclonal anti-LDL receptor antibody, and dextran sulfate, we also evaluated if this inh ibition of LDL binding occurred through the LDL receptor-mediated path way, through non-LDL receptor-mediated pathways, or through both, The results show that cyclosporine reduces LDL binding and uptake by mainl y inhibiting the LDL receptor-mediated pathway, We also studied the ef fect of the LDL-cyclosporine complex on the binding of labelled LDL, T he presence of cyclosporine in the LDL particle does not influence the binding behaviour of LDL to its receptor, We also found that cyclospo rine reduces the expression of the LDL receptor messenger RNA (mRNA) b y about 40%. Thus, the interpretation of this study is that cyclospori ne can cause an increase in LDL-cholesterol in the plasma of transplan tation patients by reducing the catabolism of LDL in the liver by inhi biting mainly the LDL receptor-mediated catabolism through an effect o n LDL receptor synthesis.