Up-regulation of low density lipoprotein receptor by a novel isobenzofranone derivative, MD-700

Stimulatory effects of a novel isobenzofranone, MD-700, on low density lipo protein (LDL) receptor activity were investigated in vitro and In vivo. MD- 700 at 0.03 mu g/ml elevated the expression of LDL receptor in HepG2 cells within 4 h. Corresponding to this. uptake of fluorescent labeled-LDL (3,3'- dioctadecylindocarbocyanine-LDL) by the cells increased linearly in time- a nd dose-dependent manner by MD-700 for up to 12 h. In the experiment using HepG2 cells transiently transfected with promoter-luciferase gene construct s, MD-700 increased luciferase activity in a dose-dependent manner from 0.0 3 to 0.1 mu g/ml. In contrast, luciferase activity was not stimulated by MD -700 in construct with a deleted sterol regulatory element (SRE)-1, suggest ing importance of SRE-1 in stimulation of the LDL receptor gene promoter by MD-700. Binding experiments on liver membranes from MD-700-treated hamster s showed about a 60% increase in I-125-labeled LDL binding. A Scatchard plo t revealed that MD-700 increased the maximal binding without affecting bind ing affinity. In contrast to findings with an inhibitor of 3-hydroxy-3-meth ylglutaryl coenzyme A reductase. pravastatin, MD-700 had no effect on the s terol synthesis in hamster liver homogenates. These results suggest that MD -700 stimulates the expression of LDL receptor, presumably in a manner inde pendent of change in sterol metabolism, and thereby promotes LDL clearance. Hypocholesterolemic actions of MD-700 in hamsters were then examined. MD-7 00 lowered serum cholesterol levels in hamsters fed normal chow or a high-f at diet. Fractionation of serum lipoproteins demonstrated that MD-700 selec tively decreased LDL and very low density lipoprotein cholesterol. Dose-dep endent decrease in serum cholesterol was also seen in hypercholesterolemic rats. Thus, the hypocholesterolemic action of MD-700 may be attributed to u p-regulation of the LDL receptor, based on stimulation of the transcription of the LDL receptor gene. Although pravastatin stimulates LDL uptake and l owers serum cholesterol in a manner similar to that seen with MD-700, the m echanism responsible for hypocholesterolemic action appears to differ. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.