ABSTRACT
A potent lipid-lowering thyromimetic (CGS 26214) devoid of cardiac and thermogenic activity was identified based on its ability to preferentially access and bind the nuclear fraction of hepatocytes over that of myocytes in culture. The difference in access achieved with CGS 26214 was at least 100-fold better for hepatocytes than for myocytes. This in vitro hepatoselectivity resulted in a compound with unprecedented in vivo lipid-lowering potency with a minimal effective dose of 1 microgram/kg in rats and dogs (approximately 25x that of L-T3). At the same time, CGS 26214 was free of any cardiovascular effects up to the highest dose tested of 25 mg/kg and 100 micrograms/kg in rats and dogs, respectively.
Subject(s)
Body Temperature/drug effects , Cardiovascular System/drug effects , Glyoxylates/pharmacology , Hypolipidemic Agents/pharmacology , Animals , Animals, Newborn , Anticholesteremic Agents/metabolism , Anticholesteremic Agents/pharmacology , Binding, Competitive , Carcinoma, Hepatocellular/pathology , Cardiac Output/drug effects , Cell Nucleus/drug effects , Cell Nucleus/metabolism , Cholesterol/blood , Dogs , Drug Evaluation, Preclinical , Glyoxylates/metabolism , Heart/drug effects , Hypercholesterolemia/blood , Hypolipidemic Agents/metabolism , Liver/drug effects , Liver Neoplasms/pathology , Male , Myocardial Contraction/drug effects , Organ Specificity , Oxygen Consumption/drug effects , Rats , Rats, Sprague-Dawley , Receptors, LDL/metabolism , Safety , Thyroid Hormones/pharmacology , Triglycerides/blood , Triiodothyronine/metabolism , Tumor Cells, CulturedABSTRACT
DiI-LDL (3,3'-dioctadecylindocarbocyanine-low density lipoprotein) has been extensively used in morphological and microscopic studies of receptor-mediated metabolism of LDL in many cell lines. To date the use of this fluorescent probe in a quantitative assay of LDL receptor activity has not been widely used in studies with multiple samples due to the lack of a practical method for quantitatively recovering cell-associated DiI. Therefore, detection by 125I-labeled LDL has remained the method of choice for assaying LDL receptor activity rapidly and reliably. In this paper, we describe a rapid, simple, and nonradioactive assay of LDL receptor activity using DiI-LDL. The increased sensitivity of this method was achieved by modifications to the labeling procedure of LDL and to the extraction of DiI from cells for subsequent fluorescence determination. These modifications did not affect the affinity of DiI-LDL toward HepG2 cells, and the assay was easily adapted to a rapid screen for LDL receptor modulators in this cell model.
Subject(s)
Carbocyanines , Fluorescent Dyes , Lipoproteins, LDL/metabolism , Receptors, LDL/metabolism , Binding, Competitive , Carcinoma, Hepatocellular , Humans , Hydroxycholesterols/pharmacology , Iodine Radioisotopes , Liver Neoplasms , Lovastatin/pharmacology , Tumor Cells, CulturedABSTRACT
This study was designed to determine whether the conjugation product of L-T3 with cholic acid would result in a liver-targeted compound (CGH 509A) with hypocholesterolemic (HC) activity significantly dissociable from cardiovascular (CV) and thyroxine-suppressing (TS) effects normally observed with thyroid hormone. Evaluation of HC activity in lipemic rats showed that CGH 509A was 6 times less potent than L-T3 with ED25 values estimated at 150 and 25 nmol/kg, respectively. CV function measured as changes in atrial rate, atrial tension and heart weight was determined in euthyroid rats. CGH 509A was at least 64 times less cardio-stimulant than L-T3 with minimum effective doses estimated at 2350 and 37 nmol/kg, respectively. TS activity was assessed in euthyroid rats as the potency of any compound to reduce plasma T4 levels. CGH 509A was 50 times less potent than-L-T3 with ED50 values estimated at 900 and 18 nmol/kg, respectively. From these results, it is clear that, while L-T3 was equally potent on HC, CV and TS activities, the HC potency of CGH 509A was at least 15 and 6 times greater than its CV and TS potencies, respectively.
