Few treatments for obesity exist and, whereas efficacious therapeutics for hyperlipidemia are available, further improvements are desirable. Thyroid hormone receptors (TRs) regulate both body weight and cholesterol levels. However, thyroid hormones also have deleterious effects, particularly on the heart. The TR␤ subtype is involved in cholesterol lowering and possibly elevating metabolic rate, whereas TR␣ appears to be more important for control of heart rate (HR). In the current studies, we examined the effect of TR␤ activation on metabolic rate and HR with either TR␣1 ؊͞؊ mice or the selective TR␤ agonist KB-141 in mice, rats, and monkeys. 3,5,3 -triiodi-L-thyronine (T3) had a greater effect on increasing HR in WT than in TR␣ ؊͞؊ mice (ED15 values of 34 and 469 nmol͞kg͞day, respectively). T 3 increased metabolic rate [whole body oxygen consumption (MV O 2 )] in both WT and TR␣ ؊͞؊ mice, but the effect in the TR␣ 1 ؊͞؊ mice at the highest dose was half that of the WT mice. Thus, stimulation of MV O 2 is likely due to both TR␣ and -␤. T3 had equivalent potency for cholesterol reduction in WT and TR␣ ؊͞؊ mice. KB-141 increased MVO 2 with selectivities of 16.5-and 11.2-fold vs. HR in WT and TR␣ 1 ؊͞؊ mice, respectively. KB-141 also increased MV O 2 with a 10-fold selectivity and lowered cholesterol with a 27-fold selectivity vs. HR in rats. In primates, KB-141 caused significant cholesterol, lipoprotein (a), and body-weight reduction (up to 7% after 1 wk) with no effect on HR. TR␤-selective agonists may constitute a previously uncharacterized class of drugs to treat obesity, hypercholesterolemia, and elevated lipoprotein (a).O besity and atherosclerosis are important medical problems with major impact on morbidity and mortality. Current treatments for obesity have shown limited efficacy and safety; therefore, there is a need for improved therapies (1). A major risk factor for atherosclerosis is low-density lipoprotein (LDL) cholesterol. Although there are excellent treatments for elevated LDL cholesterol, therapeutic goals are commonly not met. As targets for lowering of cholesterol become more aggressive, there is a need for more modalities to meet these goals. Lipoprotein (a) [Lp(a)] is an important risk factor, elevated in many patients with premature atherosclerosis, and few therapies lower Lp(a) (2).Thyroid hormones reduce body weight, LDL cholesterol, and Lp(a); thus, exploitation of these properties may be useful for therapy (3-6). Unfortunately, endogenous thyroid hormones are nonselective and produce undesirable side effects, particularly cardiac stimulation (7,8). Development of thyromimetics devoid of cardiac effects could have therapeutic potential as antiobesity and lipid-lowering agents.Thyroid hormone receptors (TRs) are divided into two primary subtypes (TR␣ and -␤), which are the products of two genes of the superfamily of nuclear hormone receptors (4, 7). TRs mediate distinct physiologic effects due to differences in tissue abundance or receptor-specific activity (9). Studies in patients with th...

The importance of glucokinase (GK; EC 2.7.1.12) in glucose homeostasis has been demonstrated by the association of GK mutations with diabetes mellitus in humans and by alterations in glucose metabolism in transgenic and gene knockout mice. Liver GK activity in humans and rodents is allosterically inhibited by GK regulatory protein (GKRP). To further understand the role of GKRP in GK regulation, the mouse GKRP gene was inactivated. With the knockout of the GKRP gene, there was a parallel loss of GK protein and activity in mutant mouse liver. The loss was primarily because of posttranscriptional regulation of GK, indicating a positive regulatory role for GKRP in maintaining GK levels and activity. As in rat hepatocytes, both GK and GKRP were localized in the nuclei of mouse hepatocytes cultured in low-glucose-containing medium. In the presence of fructose or high concentrations of glucose, conditions known to relieve GK inhibition by GKRP in vitro, only GK was translocated into the cytoplasm. In the GKRP-mutant hepatocytes, GK was not found in the nucleus under any tested conditions. We propose that GKRP functions as an anchor to sequester and inhibit GK in the hepatocyte nucleus, where it is protected from degradation. This ensures that glucose phosphorylation is minimal when the liver is in the fasting, glucose-producing phase. This also enables the hepatocytes to rapidly mobilize GK into the cytoplasm to phosphorylate and store or metabolize glucose after the ingestion of dietary glucose. In GKRP-mutant mice, the disruption of this regulation and the subsequent decrease in GK activity leads to altered glucose metabolism and impaired glycemic control. G lucokinase (GK; EC 2.7.1.12), the principal hexokinase in liver parenchymal cells and in pancreatic ␤ cells, is a critical component of the physiological glucose-sensing apparatus (1). In humans, GK heterozygous mutations lead to the autosomal, dominant, maturity-onset diabetes of the young (MODY) (2, 3) phenotype. In mice, changes in GK activity by gene knockout and by overexpression resulted in altered glucose homeostasis and demonstrated that modest changes in liver GK activity alone were sufficient to cause significant alterations in blood glucose levels (4-9). Liver GK activity has been reported to be lower in some obese humans with type 2 diabetes mellitus when compared with nondiabetic normal weight or obese individuals, suggesting a role for liver GK in glucose homeostasis in type 2 diabetes (10).In the liver, GK activity is allosterically inhibited by GK regulatory protein (GKRP) (11-13). This protein, found in the livers of all animal species where GK is present, shows no inhibitory effect on other known hexokinases (11-13). In rodents, GKRP inhibition of GK is relieved by high concentrations of glucose and by fructose 1-phosphate, and is potentiated by fructose 6-phosphate (11-13). Recent studies have demonstrated that both GK and GKRP are in the nucleus of rat hepatocytes cultured in a medium containing 5.5 mM glucose (14,15). When the growth medium w...

A novel, highly potent, orally active, nonsteroidal tissue selective androgen receptor (AR) modulator (BMS-564929) has been identified, and this compound has been advanced to clinical trials for the treatment of age-related functional decline. BMS-564929 is a subnanomolar AR agonist in vitro, is highly selective for the AR vs. other steroid hormone receptors, and exhibits no significant interactions with SHBG or aromatase. Dose response studies in castrated male rats show that BMS-564929 is substantially more potent than testosterone (T) in stimulating the growth of the levator ani muscle, and unlike T, highly selective for muscle vs. prostate. Key differences in the binding interactions of BMS-564929 with the AR relative to the native hormones were revealed through x-ray crystallography, including several unique contacts located in specific helices of the ligand binding domain important for coregulatory protein recruitment. Results from additional pharmacological studies effectively exclude alternative mechanistic contributions to the observed tissue selectivity of this unique, orally active androgen. Because concerns regarding the potential hyperstimulatory effects on prostate and an inconvenient route of administration are major drawbacks that limit the clinical use of T, the potent oral activity and tissue selectivity exhibited by BMS-564929 are expected to yield a clinical profile that provides the demonstrated beneficial effects of T in muscle and other tissues with a more favorable safety window.