kb-141 and Hypercholesterolemia

Thyroid hormone (T3) and its receptor (TR) have the diverse effects on the lipid metabolism and hypothyroidism causes hypercholesterolaemia characterized by increased levels of low-density ripoproteins (LDL). There are multiple TR isoforms such as TRalpha1, TRbeta1 and TRbeta2, of which expressions are known to be tissue-specific. For example, TRbeta1 is the major TR in the liver while T3 action is mediated via TRalpha1 in the heart. The X-ray crystallography of the ligand-binding domain of TRs enabled the development of TRbeta isoform specific T3 analogues including GC1. Without tachycardia, GC1 selectively targets the TRbeta1 in the liver and decreases cholesterol levels with more potent efficacy than that of atorvastatin, a potent HMG-CoA reductase. However, the reduction of serum TSH by GC1 should be overcome in future. Current reports also describe the existence of the complex cross-talks in the lipid metabolism between TR and other nuclear hormone receptors including peroxisome proliferator -activated receptors (PPARs), liver X receptor alpha (LXRalpha) and farnesoid X receptors (FXRs). Understanding for the function of TRs and other nuclear factors may provide the new approach to the control of hypercholesterolaemia.

Topics: Animals; Cholesterol, LDL; Drug Design; Humans; Hypercholesterolemia; Hypothyroidism; Lipid Metabolism; Phenyl Ethers; Phenylacetates; Protein Isoforms; Receptors, Cytoplasmic and Nuclear; Receptors, Thyroid Hormone; Transcription Factors; Transcription, Genetic; Triiodothyronine

Few treatments for obesity exist and improvements for treatment of hyperlipidemia are still desirable. Thyroid hormone receptors (TRs) regulate body weight, adiposity, and cholesterol levels. However, thyroid hormones can have deleterious effects, particularly cardiac acceleration, that limits the use of hormones in the treatment of obesity. There is evidence that the TRbeta subtype mediates lowering of blood cholesterol levels and possibly elevation of metabolic rate, whereas TRalpha appears to control heart rate. In studies, described in this review article, we examined the effects of selective TRbeta activation on metabolic rate and heart rate in mice, rats and monkeys. T3 had a greater effect on increasing heart rate in wild type (WT) than in TRalpha-/- mice (ED15 values of 34 and 469 nmol/kg/day, respectively). T3 increased metabolic rate (MVO2) in both WT and TRalpha-/- mice, but the effect on TRalpha-/- mice was less pronounced compared to WT mice. Stimulation of MVO2 is mediated by both TRalpha and TRbeta, but with different profiles. In cholesterol-fed rats, KB-141, a selective TRbeta agonist, increased MVO2 with a 10-fold selectivity and lowered cholesterol with a 27-fold selectivity vs. tachycardia. In primates, KB-141 caused significant, cholesterol, Lp(a) and body weight reduction after 1 week of treatment with no effect on heart rate. These data suggest that selective TRbeta agonists may represent a novel class of drugs for the treatment of obesity, hypercholesterolemia and elevated Lp(a), which may make them useful therapeutics for patients with metabolic syndrome.

Topics: Animals; Cholesterol; Heart; Heart Rate; Humans; Hypercholesterolemia; Obesity; Phenyl Ethers; Phenylacetates; Structure-Activity Relationship; Thyroid Hormone Receptors beta; Tissue Distribution; Weight Loss

Phosphonic acid (PA) thyroid hormone receptor (TR) agonists were synthesized to exploit the poor distribution of PA-based drugs to extrahepatic tissues and thereby to improve the therapeutic index. Nine PAs showed excellent TR binding affinities (TRbeta(1), K(i) < 10 nM), and most of them demonstrated significant cholesterol lowering effects in a cholesterol-fed rat (CFR) model. Unlike the corresponding carboxylic acid analogue and T(3), PA 22c demonstrated liver-selective effects by inducing maximal mitochondrial glycerol-3-phosphate dehydrogenase activity in rat liver while having no effect in the heart. Because of the low oral bioavailability of PA 22c, a series of prodrugs was synthesized and screened for oral efficacy in the CFR assay. The liver-activated cyclic 1-(3-chlorophenyl)-1,3-propanyl prodrug (MB07811) showed potent lipid lowering activity in the CFR (ED(50) 0.4 mg/kg, po) and good oral bioavailability (40%, rat) and was selected for development for the treatment of hypercholesterolemia.

Topics: Animals; Cholesterol; Disease Models, Animal; Dose-Response Relationship, Drug; Drug Design; Drug Evaluation, Preclinical; Glycerolphosphate Dehydrogenase; Hypercholesterolemia; Ligands; Liver; Molecular Structure; Organophosphonates; Prodrugs; Rats; Rats, Sprague-Dawley; Receptors, Thyroid Hormone; Stereoisomerism; Structure-Activity Relationship

Selective thyroid hormone receptor subtype-beta (TRbeta) agonists have received attention as potential treatments for hypercholesterolemia and obesity, but have received less attention as treatments for diabetes, partly because this condition is not improved in thyroid hormone excess states. The TRbeta selective agonist KB-141 induces 5-10% increases in metabolic rate and lowering of plasma cholesterol levels without tachycardia in lean rats, unlike the major active thyroid hormone, T3. In the current study, we determined whether KB-141 promotes weight loss in obese animals and whether it exhibits anti-diabetogenic effects. Body weight, adiposity (DEXA), and lipid levels were examined following p.o. administration of KB-141 to obese Zucker fa/fa rats at 0.00547-0.547 mg/kg/day for 21 days, and in ob/ob mice at 0.5mg/kg/day KB-141 for 7 days. In rats, KB-141 reduced body weight by 6 and 8%, respectively, at 0.167 and 0.0547 mg/kg/day without tachycardia and adiposity was reduced at 0.167 mg/kg/day (5-6%). In ob/ob mice, KB-141 lowered serum cholesterol (35%), triacylglycerols (35%) and both serum and hepatic free fatty acids (18-20%) without tachycardia. Treatment of ob/ob mice with KB-141 (0.0547 or 0.328 mg/kg/day over 2 weeks) improved glucose tolerance and insulin sensitivity in a dose-dependent manner with no effect on heart rate. Thus, KB-141 elicits anti-obesity, lipid lowering and anti-diabetic effects without tachycardia suggesting that selective TRbeta activation may be useful strategy to attenuate features of the metabolic syndrome.

Topics: Animals; Anti-Obesity Agents; Body Weight; Diabetes Mellitus; Female; Humans; Hypercholesterolemia; Hypoglycemic Agents; Hypolipidemic Agents; Mice; Mice, Obese; Molecular Structure; Obesity; Phenyl Ethers; Phenylacetates; Rats; Rats, Zucker; Thyroid Hormone Receptors beta

Thyroid hormones [predominantly 3,5,3'-triiodo-L-thyronine (T3)] regulate cholesterol and lipoprotein metabolism, but cardiac effects restrict their use as hypolipidemic drugs. T3 binds to thyroid hormone receptors (TRs) alpha and beta. TRbeta is the predominant isoform in liver, whereas T3 effects on heart rate are mediated mostly by TRalpha. Drugs that target TRbeta or exhibit tissue-selective uptake may improve plasma lipid levels while sparing the heart. Here, we asked how the TRbeta- and liver uptake-selective agonist GC-1 influences cholesterol and triglyceride metabolism in euthyroid mice. GC-1 treatment reduced serum cholesterol levels by 25% and serum triglycerides by 75% in chow-fed mice and also attenuated diet-induced hypercholesterolemia. GC-1 reduced plasma high-density lipoprotein cholesterol levels; increased expression of the hepatic high-density lipoprotein receptor, SR-BI; stimulated activity of cholesterol 7alpha-hydroxylase; and increased fecal excretion of bile acids. Collectively, these results suggest that GC-1 stimulates important steps in reverse cholesterol transport. Use of TRbeta and uptake selective agonists such as GC-1 should be further explored as a strategy to improve lipid metabolism in dyslipoproteinemia.

Topics: Acetates; Analysis of Variance; Animals; Bile Acids and Salts; Cardiovascular Diseases; CD36 Antigens; Cholesterol; Cholesterol 7-alpha-Hydroxylase; Feces; Gene Expression Regulation; Hypercholesterolemia; Immunoblotting; Liver; Male; Mice; Mice, Inbred C57BL; Phenols; Phenyl Ethers; Phenylacetates; Receptors, Immunologic; Receptors, Scavenger; Reverse Transcriptase Polymerase Chain Reaction; Thyroid Hormone Receptors beta; Triglycerides; Triiodothyronine