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Journal of Steroid Biochemistry & Molecular Biology 111 (2008) 262–267 Contents lists available at ScienceDirect Journal of Steroid Biochemistry and Molecular Biology journal homepage: www.elsevier.com/locate/jsbmb Anti-obesity, anti-diabetic, and lipid lowering effects of the thyroid receptor  subtype selective agonist KB-141 Galina Bryzgalova a , Suad Effendic a , Akhtar Khan a , Stefan Rehnmark b , Peter Barbounis c , Jamie Boulet c , Gao Dong c , Rajni Singh c , Sue Shapses d , Johan Malm b , Paul Webb e , John D. Baxter e , Gary J. Grover c,f,∗ a Department of Molecular Medicine and Surgery, Karolinska Institute, Stockholm SE-171 76, Sweden Karo Bio AB, Novum, Huddinge SE-141 57, Sweden c Eurofins-Product Safety Laboratories, 2394 Highway 130, Dayton, NJ 08810, USA d Department of Nutritional Sciences, Rutgers, The State University of New Jersey, 96 Lipman Drive, New Brunswick, NJ 08901-8525, USA e Department of Medicine, University of California, San Francisco, CA 94143, USA f Department of Physiology and Biophysics, Robert Wood Johnson Medical School, Piscataway, NJ 08559, USA b a r t i c l e i n f o Article history: Received 14 February 2008 Received in revised form 16 May 2008 Accepted 16 June 2008 Keywords: Thyroid hormones Obesity KB-141 Cholesterol a b s t r a c t Selective thyroid hormone receptor subtype- (TR) 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 TR 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 0.5 mg/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 TR activation may be useful strategy to attenuate features of the metabolic syndrome. © 2008 Elsevier Ltd. All rights reserved. 1. Introduction The anti-obesity and lipid-lowering activity of thyroid hormones has long tantalized pharmacologists and physicians [1–5]. The increase in adiposity and cholesterol seen in hypothyroid patients can be reduced by well-managed replacement therapy [6]. Thyroid hormone induced increases in metabolic rate and fatty acid utilization [7–9] contribute to the anti-obesity actions of the hormones. Thyroid hormone analogs reduce serum cholesterol through effects on high-density lipoprotein (HDL) and low-density lipoprotein pathways [10,11]. Unfortunately, treatment of obesity ∗ Corresponding author at: Eurofins-PSL, 2394 Highway 130, Dayton, NJ 08810, USA. Tel.: +1 732 438 4100; fax: +1 732 355 3275. E-mail address: [email protected] (G.J. Grover). 0960-0760/$ – see front matter © 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.jsbmb.2008.06.010 and hyperlipidemia in euthyroid subjects with naturally occurring thyroid hormones, T3 and T4 , is not viable because of deleterious cardiac effects, including tachycardia, arrhythmias and heart failure (8,12), and excessive increases in metabolic rate (8,12). Indeed, the lack of selectivity of these agents resulted in failure of an illfated series of studies using dinitrophenol with or without thyroid hormones [1]. While selective thyroid hormone receptor (TR) agonists that modestly increase metabolic rate over a large dose range, with minimal effects on the heart, could potentially be used as antiobesity and/or lipid-lowering agents, selectivity has been hard to achieve because restricted structure–activity relationships around the diphenyl-ether scaffold allow limited chemical modifications [13]. Recent discoveries of novel means of separating TR activities has led to development of compounds, including KB-141, GC-1, and MB07811 with pharmacologically selective profiles different from G. Bryzgalova et al. / Journal of Steroid Biochemistry & Molecular Biology 111 (2008) 262–267 263 T3 [12–15]. These efforts have been facilitated by determinations of the three dimensional structures of the ligand binding domains of the ␣ and  isoforms of the thyroid hormone receptor (TR) [2,7,13]. One way to separate beneficial effects of thyroid hormone analogs from harmful is to tailor ligands to particular TR subtypes [2]. There are two primary ligand binding TR subtypes (␣, ) that are products of distinct genes [7]. Both are ubiquitously expressed [7,15]. However, a major action of the predominant ligand regulated form of TR␣, TR␣1 , is on heart rate [7,14–17], whereas the predominant form of TR, TR1 , display preferential effects on cholesterol lowering through the liver [8,15–17]. Accordingly, the TR selective agonist KB-141 and a similar TR selective compound (GC-1) that also displays tissue and liver selective uptake reduce cholesterol at doses that do not affect heart [8,17,18]. Both compounds exhibit 10–30-fold dose windows in which 5–10% increases in metabolic rate and 80% reductions in cholesterol are seen without tachycardia in lean rats [8,17–19]. Villicev et al. [20] showed larger increases in metabolic rate with GC-1 in lean Wistar rats (>50–70%) after 6 weeks of treatment and found that this effect was accompanied by loss of body weight with no increases in food consumption, unlike T3 . Significant weight reduction was also seen for KB-141 and GC-1 in lean primates [8], and Erion et al. [14] reported that KB-141 reduced body weight in a mouse model of diet induced obesity (DIO mice). However, it has not been reported whether KB141 or GC-1 can promote weight loss in other models of obesity and whether this occurs via loss of adiposity or lean body mass. Thus, in current studies, we addressed whether we could show a reduction of weight via loss of adiposity in Zucker fatty rats without promoting cardiac acceleration. We also addressed whether KB-141 can promote weight loss in an animal model of obesity that more closely mimics the metabolic syndrome, namely ob/ob mice that are obese and have diabetes resembling type 2 diabetes in man. Effects of TR selective ligands on glucose homeostasis have not been investigated in detail. Since obesity and hyperlipidemia are prevalent in the metabolic syndrome and are regulated by the TR selective ligands, the question arises as to whether TR selective compounds could affect glucose homeostasis. Hyperthyroid patients can experience a worsening of diabetes [21]; thus it is not obvious that selective activation of TR signaling pathways would have any beneficial effect. Thus, in the current study, we determined effects of KB-141 (Fig. 1) on glucose homeostasis in the diabetic ob/ob mouse. used, as all of our previous work used females and we tend to observe less variability in weight change with females. To assess effects on cholesterol as an indication of TR effects, these animals were put on a high cholesterol diet (1.5% cholesterol + 0.5% cholic acid) ad lib for 2 weeks prior to drug administration and the amount consumed daily at the end of this period was maintained throughout the remainder of the study. Diet restriction was used because a previous study using GC-1 showed differences in food consumption and we wanted to remove this as a variable [20]. In all groups, animals completely consumed their food throughout the drug treatment period. KB-141 or vehicle was given p.o. once daily for 3 weeks by oral gavage. Vehicle was 10% m-pyrol, 5% ethanol, 5% cremaphor and 80% water. Rats were divided into the following groups with n = 10 per group: vehicle, 0.00547 mg/kg/day KB-141, 0.0547 mg/kg/day KB-141, or 0.547 mg/kg/day KB-141. Doses were chosen based on molar doses previously used for metabolic rate determination (0.00547 mg/kg = 15.4 nmol/kg; 0.0547 = 154 nmol/kg; 0.547 = 1540 nmol/kg) [8]. Body weights and food consumption were measured daily. Two hours after the last dose, rats were anesthetized with 30 mg/kg pentobarbital i.p. and HR was determined for 5 min using a lead II ECG. Blood was withdrawn for measurement of serum cholesterol (Cholesterol kit, Roche Diagnostics), serum chemistries, and liver function tests (alanine aminotransferase; ALT, aspartate aminotransferase; AST, Idexx, MA, USA). To determine the effect of KB-141 on body composition (adiposity) and TSH, Zucker rats (425–450 g) were cholesterol-fed as described above for 2 weeks before treatment for 21 days with vehicle (n = 10) or 0.164 mg/kg/day KB-141 (470 nmol/kg; n = 10) and diet restriction as described above. This dose was chosen to be clinically relevant with 1–2% body weight loss per week. Body weights and food consumption were monitored daily and at the end of the study, the rats were anesthetized and HR determined as described above. A blood sample was withdrawn for measurement of rat serum TSH (Idexx, rat TSH ELISA) and blood chemistries (Idexx, MA, USA). The carcasses were frozen in a normal reclining position and body composition was measured with a densitometer (DEXA), the Prodigy Advanced system (GE-LUNAR Corp.) with small animal software [22]. From this, changes in percent adiposity were determined. We were unable to find a dose of T3 that reduced body weight without inducing florid thyrotoxicosis leading to mortality. The heart rates in these animals are always very high and the animals are most likely more susceptible to heart failure than lean animals [8]. 2. Methods 2.2. Effect of KB-141 on hyperlipidemia in ob/ob mice 2.1. Effects of KB-141 on Zucker fa/fa rats: effect on body weight and adiposity The studies in this section were approved by the EurofinsProduct Safety Laboratories Institutional Animal Care and Use Committee. Zucker fa/fa (fatty, nondiabetic) female rats had fasting glucose levels of 95 ± 8 mg/dL, were relatively healthy and were 425–450 g (Harlan, Indianapolis, IN, USA). Female rats were Fig. 1. Chemical structures of T3 (3,5,3 -triiodo-l-thyronine) and KB-141. The studies in this section were approved by the KaroBio Institutional Animal Care and Use Committee. Female ob/ob mice (37–43 g, Harlan) were obtained from the animal colony at the Karolinska Institute and were fed standard rodent chow diet (Lactamin AB, Kimstad, Sweden) ad lib and had free access to water. They were cholesterol-fed for 2 weeks by incorporating 1.5% cholesterol and 0.5% cholic acid into their regular chow. They were then given 0.547 mg/kg KB-141 via oral gavage daily for 7 days and maintained on the high cholesterol diet ad lib for the duration of the study. Body weights and food consumption were measured daily. After 7 days, blood was collected from the vena cava by a syringe and livers were removed. Serum and livers were analyzed for cholesterol, triacyglycerols, and NEFA using Roche Diagnostics kits. An additional group (n = 6) was run at the highest dose (0.547 mg/kg/day) and tested for heart rate changes as described above. Seven days of treatment was chosen so that significant lipid-lowering can be observed. We chose to use ob/ob mice because this species is more sensitive to lipidlowering effects of thyromimetics than Zucker rats. The lower limit 264 G. Bryzgalova et al. / Journal of Steroid Biochemistry & Molecular Biology 111 (2008) 262–267 Table 1 Absolute body weight data for the beginning of the study (pre-drug, 2 weeks post-cholesterol feeding) and at day 21 of KB-141 treatment (last day of study) for body weight, heart rate and serum cholesterol for KB-141 or vehicle treated Zucker rats Vehicle KB-141 (0.00547 mg/kg/day) KB-141 (0.0547 mg/kg/day) KB-141 (0.547 mg/kg/day) Body weight (g) Pre-drug Post-drug 523 ± 6 572 ± 9 527 ± 7 540 ± 11 524 ± 8 543 ± 9 528 ± 7 527 ± 7* Heart rate (BPM) Serum cholesterol (mg/dL) 340 ± 5 256 ± 10 330 ± 5 267 ± 11 327 ± 20 240 ± 10 355 ± 8 218 ± 11* Mean ± S.E.M. * Significantly different from vehicle group value (p < 0.05). N = 10 per group. of quantitation (LLQ) for cholesterol was 0.2 g/mL and the LLQ for triglycerides was 0.1 nmol. The measurements were repeatable and the standard errors low as will be seen in Section 3. 2.3. Effect of KB-141 on diabetes in ob/ob mice The studies in this section were approved by the Karolinska Institute Animal Care and Use Committee. Female ob/ob mice (42–46 g) were given KB-141 (0.0547 mg/kg or 0.328 mg/kg; 924 nmol/kg) dissolved in 99% carboxymethylcellulose (0.25%)/1% ethanol via oral gavage, once daily for 14 days. The doses were based on the molar doses reported previously for KB-141 [8]. Vehicletreated animals received an equal volume of solvent. Body weight and food intake were measured every second day in mice treated with KB-141 at 0.328 mg/kg/day dose, but only the pre-test and final body weights were measured for the lower dose. After 14 days of vehicle or KB-141 treatment (n = 8 per group), an intraperitoneal glucose tolerance test (IPGTT) was performed in overnight fasted mice. Blood glucose was measured at the basal state (0 min) and at 10, 30, 60 and 120 min after a glucose load (2 g/kg, i.p.). Blood glucose concentrations were measured using a MediSence glucose analyzer (Abbott Scandinavia AB, Solna, Sweden) as blood was collected from the tail vein. Two days later an intraperitoneal insulin tolerance test (IPITT) was performed in the same animals. For this purpose, blood glucose concentrations were measured at the basal state, and mice were injected with insulin (0.25 U/kg, i.p.). Blood glucose concentrations were measured 10 min after insulin injection (0 min), followed by administration of glucose (1 g/kg, ip). Blood glucose concentrations were measured at 15, 30, 60, 90 and 120 min after the glucose load as described above. The area under the curve (AUC) for the glucose excursion was calculated from the SigmaPlot 2001 for Windows Version 7.101 (SPSS Inc.). A group of ob/ob mice was tested at the 0.328 mg/kg dose (n = 6) for the same duration of the study for determination of the effect of KB-141 on heart rate. Heart rate was determined using lead II ECG as described above. 2.4. Statistics For comparisons of two groups, Student’s t-test was used with p < 0.05 being considered significant. With more than two groups or variables were compared, analysis of variance was used with a Newman–Keuls post hoc test with p < 0.05 being considered significant. KB-141 reduced body weight gain relative to the vehicle treated group (Table 1). Weight loss, expressed as percent change from their pre-treatment values, achieved statistical significance for the 0.547 (9.4%) and 0.0547 (5.7%) mg/kg/day doses of KB-141. Serum cholesterol was reduced in a dose-dependent manner. This effect was smaller than previously seen in lean cholesterol-fed rats (8); cholesterol reduction (14.8%) was statistically significant only at the highest dose (0.547 mg/kg/day) of KB-141. No changes in BUN, liver enzymes, creatinine, or electrolytes were seen for any group (data not shown). No changes in liver enzymes, electrolytes, pH, or creatinine levels suggested normal liver and renal function in these animals. We addressed whether KB-141 induced weight loss seen is due to loss of adiposity in another group of Zucker rats treated with 0.164 mg/kg/day KB-141 for 21 days. As shown above, this dose gives significant weight reduction in the clinically relevant range of 1–2% per week (Table 2). Pre-treatment weights were similar for vehicle and drug groups (data not shown). Significant reduction of weight (6.7%) was observed for KB-141 compared to vehicletreated animals. Percent adiposity was also significantly reduced by 5.4% confirming that the decrease in weight gain arises primarily from loss of adipose tissue rather than lean body mass (no loss of lean body mass was detected). No effect on HR was observed. Serum cholesterol was not significantly reduced in this study, but TR receptors were activated as shown by TSH suppression. Blood chemistries for this group of animals were normal suggesting a lack of toxicity and confirming the lack of muscle wasting (BUN, creatine phosphokinase) in these animals as seen with the DEXA. Plasma ALT and AST levels were normal suggesting a lack of liver toxicity and creatinine levels were normal suggesting normal kidney function (data not shown). 3.2. Lipid-lowering studies in ob/ob mice In ob/ob mice, KB-141 reduced serum levels of total cholesterol (36%), triacylglyerols (28%), NEFA (18%) (Table 3), and liver triacylglycerols (30%), but not hepatic cholesterol levels. KB-141 also caused a significant decrease in weight but did not affect heart rate at this dose. The body weights of the two groups were similar before treatment (36.1 ± 0.5 and 35.9 ± 0.4 g for vehicle and Table 2 Effect of 0.164 mg/kg KB-141 or vehicle on Zucker fa/fa (nondiabetic) rats treated for 21 days on heart rate, serum TSH (thyroid stimulating hormone), body weight and percent adiposity as measured by DEXA Vehicle KB-141 (0.164 mg/kg/day) 3. Results 62.1 507 2.4 397 ± ± ± ± 1.1 3 0.7 2 58.7 478 0.6 398 ± ± ± ± 1.1* 7* 0.2* 5 Percent change from vehicle −5.4 −6.8 −75 0 3.1. Effects of KB-141 on body weights and adiposity in Zucker obese rats Percent adiposity Body weight (g) TSH (ng/mL) Heart rate (beats/min) Body weights were similar for all groups at the beginning of the study. The vehicle treated animals gained weight over time and Mean ± S.E.M. * Significantly different from vehicle group value (p < 0.05). n = 10 per group. G. Bryzgalova et al. / Journal of Steroid Biochemistry & Molecular Biology 111 (2008) 262–267 265 Table 3 Effect of 7 days treatment with vehicle or 0.547 mg/kg KB-141 on serum and liver cholesterol, serum and liver triacylgycerols, and serum non-esterified fatty acids (NEFA) in cholesterol-fed ob/ob mice Serum cholesterol (mg/dL) Vehicle 506 ± 12 0.547 mg/kg KB-141 336 ± 14* Serum triacylglyerols (mg/dL) Liver cholesterol (mg/g tissue) Liver triacylglycerols (mg/g tissue) Serum NEFA (mM) 447 ± 5 323 ± 14* 113 ± 3 119 ± 4 42 ± 9 25 ± 7* 5.1 ± 0.2 4.2 ± 0.2* Mean ± S.E.M. * Significantly different from vehicle group value (p < 0.05). n = 8 per group. drug, respectively), but KB-141 significantly reduced body weight by approximately 9% (38.6 ± 0.4 and 35.3 ± 0.6 g for vehicle and KB141, respectively). Food consumption was the same in all animals. No overt signs of toxicity were noted and blood chemistries were normal so the animals did not appear to be losing weight due to toxicity. ning and the end of the study for the 0.054 mg/kg dose: 44 ± 0.5 and 45.1 ± 0.4 g pre-study weights for vehicle and B-141, respectively, and post-treatment and 47.7 ± 1.0 and 43.1 ± 0.4 g for vehicle and KB-141, respectively, showing approximately 8% weight loss for KB-141 versus vehicle. Food intake was similar in KB-141 and vehicle-treated mice and KB-141 did not cause any change in heart rate. 3.3. Anti-diabetic effects of KB-141 4. Discussion We determined effects of a 2-week KB-141 treatment on glucose tolerance and insulin sensitivity in ob/ob mice. Assessed by IPGTT, the 0.0547 and 0.328 mg/kg/day doses of KB-141 led to significant decreases in fasting blood glucose levels (Fig. 2). Similar effects were also observed following glucose challenge with a significantly (p < 0.05) reduced AUC (by 33 and 47%, respectively) compared to vehicle-treated animals. Therefore, KB-141 improves glucose tolerance in ob/ob mice. After insulin and glucose challenge (IPITT study), done 2 days after the IPGTT test, KB-141 significantly lowered basal (0 time), peak (15 min) and decline (30–120 min) blood glucose concentrations (Fig. 3). AUCs for the 0.328 and 0.0547 mg/kg/day doses of KB-141 were significantly (p < 0.05) lower (67 and 54%, respectively) compared to vehicle-treated animals. Hence, insulin sensitivity was also improved in the KB-141-treated mice. Weight reduction, not the primary end point of this study, was significant in the KB-141 treated animals. With 0.054 and 0.328 mg/kg/day groups KB-141 reduced body weight by 8% (only pre-and post-study weights taken for low dose) and 18% (Fig. 4) compared to vehicle-treated mice at the end of study. For the low dose group body weights were only measured at the begin- Fig. 2. IPGTT in ob/ob mice treated with KB-141141 at dose of 0.054 mg/kg/day (open circle), 0.328 mg/kg (black triangle) or vehicle-treated group (black circle) for 14 days. Blood glucose concentrations were measured before and after glucose load (2 g/kg, i.p.) at indicated time points. Data are presented as mean ± S.E.M., n = 8, *** p < 0.001. In current studies, we addressed whether KB-141 could influence obesity, cholesterol and diabetes in animal models that better reflect the metabolic syndrome in humans than those used in the past. We used Zucker fa/fa rats which, unlike lean rats that we used in our earlier studies [8], exhibit a predictable progression of obesity to examine effects on adiposity and cholesterol. We also used ob/ob mice, which exhibit obesity and impaired glucose tolerance, to determine effects on diabetes, cholesterol, NEFA and weight gain. To examine effects on plasma cholesterol levels, both species were cholesterol-fed to increase plasma LDL-cholesterol levels relative to the predominance of HDL-cholesterol prior to the cholesterolfeeding [8]. For Zucker rats, we chose a 3-week treatment period because this is sufficient to obtain metabolic rate changes that should affect body composition [8], and we restricted diet to control for altered food intake [19]. Relative to vehicle treated animals, 0.00547 and 0.0547 mg/kg/day doses of KB-141 modestly reduced body weight and 0.164 and 0.547 mg/kg/day doses yielded significant weight reductions. Using a 0.164 mg/kg/day dose of KB-141 to produce significant weight reductions in the clinically relevant range of 1–2% per week, we found that the reduction in adiposity matched the loss of body weight, and that there was no reduction in lean body Fig. 3. IPITT in ob/ob mice treated with KB-141 at dose of 0.054 mg/kg/day (open circle), 0.328 mg/kg/day (black triangle) or vehicle-treated group (black circle) for 14 days. Animals were injected first with insulin (25 U/kg, i.p.) and 10 min later with glucose (1.0 g/kg, i.p.). Blood glucose levels were measured at basal conditions and at different time points after glucose load. Data are presented as mean ± S.E.M., n = 8, *** p < 0.001. 266 G. Bryzgalova et al. / Journal of Steroid Biochemistry & Molecular Biology 111 (2008) 262–267 Fig. 4. Body weight in ob/ob mice treated with KB-141 at dose of 0.328 mg/kg/day (open circle) or vehicle-treated animals (black circle) for 14 days. Data are presented as mean ± S.E.M., n = 8, * p < 0.05, ** p < 0.001 and *** p < 0.001. mass. This was confirmed by the lack of significant findings in the blood chemistry data where BUN, creatine phosphokinase, creatinine, electrolytes and liver function tests were normal, indicative of little muscle wasting or other toxicity. This weight loss is similar to findings previously noted in lean rats and primates [8] and in DIO mice [14]. In lean primates in a stable growth phase, we previously showed that KB-141 caused dose-dependent weight reduction that was not associated with loss of lean body mass or overt toxicity [8]. Thus, KB-141 exhibits anti-obesity effects in relevant animal models. Important was the lack of tachycardia seen over a large dose range for KB-141. We only observed modest effects of KB-141 on serum cholesterol in the Zucker rat model (14.8%); this effect was obtained at a high dose that resulted in 7.9% decrease in body weight relative to control. The fact that these effects are weaker than obtained in other studies, for example, with GC-1, may be related to the fact that KB141 exhibits less preferential accumulation in liver than GC-1 [18]. Accordingly, reduction of cholesterol was associated with lowering of plasma TSH levels (75%; Table 2), presumably via actions on the hypothalamic pituitary axis. However, the studies could also imply that peripheral effects of the TR selective agonists are optimal for promotion of weight loss. We could not obtain direct comparisons of KB-141 with T3 in Zucker rats. While we did perform studies to assess effects of T3 on body weight, we could not find a dose at which weight reduction was observed in the absence of florid thyrotoxicosis leading to significant mortality. These observations could point to the utility of the TR selectivity of KB-141 in promoting weight loss. Unfortunately, we did not have the ability to measure metabolic rate in these studies and the precise contributions of this parameter to the loss of adiposity are not established. However, we suggest that it is likely that weight loss is related to enhanced metabolic rate; in previous studies, KB-141-induced weight loss was correlated with increases in metabolic rate [8] and the amount of food consumed was similar in all groups. KB-141 exhibited several potentially useful effects in ob/ob mice. We observed reductions in serum levels of total cholesterol (36%), triacylglycerides (28%) and NEFA (18%), and in hepatic levels of triglycerides (30%) but not hepatic cholesterol. These data are consistent with previously published data showing that thyromimetics increase fatty acid utilization [7,9,23–25] and the fact that we observe these effects in the absence of TR␣1 dependent effects on heart rate suggests that this could be a TR mediated phenomenon. Interestingly, thyromimetics are known to increase metabolic rate, in part, by increasing fatty acid cycling causing dissipation of energy [7,9,23–25] and our data raise the possibility that this effect contributes to loss of adiposity seen with KB-141. The observed decrease in hepatic triacylglycerols could also have relevance for prevention/treatment of both diabetes and hepatic steatosis, both of which are related to hepatic triacylglycerol content. Confirming reports of others [14] we also found that KB-141 promoted weight reduction that was independent of food intake even though the animals were treated for 2 weeks and were ad lib fed. Whereas some effects of the TR ligands, such as those on obesity and hepatic triaclyglycerol levels, might be expected to have a indirect beneficial effect on diabetes [13,26–28], previous experience has not suggested that thyroid hormone administration or hyperthyroidism amelioriates this condition [21]. Thus, of great interest was that KB-141 increased insulin-sensitivity and improved glucose tolerance as assessed by the IPGTT and insulin sensitivity as assessed by the IPITT in the ob/ob mice. Of note is that Erion et al. previously reported that KB-141 and the liver and TR selective agonist MB07811 reduced blood glucose levels in DIO mice and that MB07811 also reduced blood glucose in lean Sprague–Dalwey rats [14]. These investigators did not measure insulin sensitivity and did not draw attention to the fact that TR ligands might be used as anti-diabetic agents. Of further importance in the current study is that the effects of KB-141 on diabetes were observed in a few days, prior to fat loss, indicating that anti-diabetic actions are independent of obesity lowering activities. Thus, the data are supportive of the concept that TR selective ligands might be potent agents to treat diabetes and should receive further investigation in this respect. In conclusion, the TR selective ligand KB-141 elicits several effects that deserve further exploration. It elicits reductions in body weight and adiposity in obese Zucker rats and reductions in body weight in ob/ob mice that are similar to those observed previously by others using another TR agonist in DIO mice [14] and in lean rodents and primates [8]. KB-141 also elicits anti-diabetic actions that may be related to weight loss, but effects on glucose uptake may also be critical. These effects were seen despite a lack of effect on heart rate. These actions deserve further study as potential uses for treatment of metabolic syndrome in man. Disclosure GG, JB, GD, RS, PB, JD, SS, PW have nothing to declare; JM, SR are employees of KaroBio AB; JB has equity ownership in KaroBio and has taken consulting fees from KaroBio AB; GB, SE, AK received a grant from KaroBio to perform the diabetes study. References [1] S. 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