Intestine-Targeted DGAT1 Inhibition Improves Obesity and Insulin Resistance without Skin Aberrations in Mice

<div><p>Objective</p><p>Diacylglycerol O-acyltransferase 1 (DGAT1) catalyzes the final committed step in triglyceride biosynthesis. DGAT1 null mice are known to be resistant to diet-induced obesity, and more insulin sensitive relative to the wild-type; however, the mice exhibit abnormalities in the skin. This work determined whether the intestine-targeted DGAT1 inhibitor could improve obesity and insulin resistance without skin aberrations in mice.</p><p>Design and Methods</p><p>We synthesized 2 DGAT1 inhibitors: Compound A, described in the patent application from the Japan Tobacco, and Compound B (A-922500), reported by Abbott Laboratories. Both compounds were evaluated for inhibitory activities against DGAT1 enzymes and effects on the skin in mice <i>in vivo.</i> Compound B was further investigated for effects on obesity and insulin resistance in diet-induced-obese (DIO) mice.</p><p>Results</p><p>The 2 compounds comparably inhibited the DGAT1 enzyme activity and the cellular triglyceride synthesis <i>in vitro</i>, while they showed different distribution patterns in mice <i>in vivo</i>. Compound A, which distributed systemically, caused skin aberrations, while Compound B, which preferentially distributed to the intestine, improved obesity and insulin resistance without skin aberrations in DIO mice.</p><p>Conclusions</p><p>Our results suggest that the intestine is the key tissue in which DGAT1 plays a role in promoting obesity and insulin resistance.</p></div

Plasma and tissue concentrations after single oral dosing of Compound A and Compound B.

<p>Plasma, skin, and intestine samples were collected from the mice orally administered 30 mg/kg Compound A (A) or B (B). Data are expressed as means ± SD of 3 animals.</p

Effects of Compound A and Compound B on the triglyceride synthesis.

<p>The effects of Compound A and Compound B on the triglyceride synthesis in HT-29 human colon cells (A) and in HepG2 human liver cells (B). Data are expressed as means + SEM of 3 assays. *<i>P</i><0.05 and **<i>P</i><0.01. Statistical analyses between the vehicle (Veh) group and compound-treated groups were performed by the Dunnett’s multiple comparison test.</p

Summary of the effects of Compound A and Compound B.

a<p>The 50% inhibitory concentration (IC₅₀) for each compound in the enzymes expressed in insect microsomes.</p><p>Summary of the effects of Compound A and Compound B.</p

Effects of Compound B on the plasma triglyceride (A, B) and glucagon-like peptide-1 (C) levels.

<p>The changes in plasma triglyceride (A) and AUCtriglyceride (−5−180 min) of plasma triglyceride (B), and the plasma GLP-1 levels 2 h following corn oil administration (C) are indicated. The plasma GLP-1 levels of the mice given corn oil are higher than the control mice (Cont). Data are expressed as means + SEM of 6–8 animals. *<i>P</i><0.05 and **<i>P</i><0.01. Statistical analyses between the vehicle (Veh)-treated group and Compound B-treated groups were performed by the Dunnett’s multiple comparison test. ##<i>P</i><0.01. Statistical analyses between the vehicle-treated group and the control group were performed by the t-test.</p

Microphotographs of the skin from the diet-induced-obese (DIO) mice.

<p>Microphotographs of the skin from the diet-induced-obese (DIO) mice treated with vehicle (10% Pluronic F-68 for Compound A, 1% Tween 80 for Compound B), 30 mg/kg Compound A once daily (A), or 30 mg/kg Compound B twice daily (B) for 4 weeks. The sebaceous gland is surrounded with a circle. The mice administered Compound A showed moderate skin aberrations derived from atrophy of the sebaceous gland. There were no injurious or inflammatory changes, and the skin aberrations recovered 2 weeks after the Compound A withdrawal. There were no skin aberrations in the mice administered Compound B. The sebaceous gland sizes are plotted (C). Data are expressed as means + SEM (N = 4). **<i>P</i><0.01. Statistical analyses between the vehicle-treated group and Compound-treated groups were performed by the Dunnett’s multiple comparison test.</p

Effects of Compound B in diet-induced-obese (DIO) mice.

<p>Mice were orally treated with 1% Tween 80 (vehicle; Veh) or 30 mg/kg Compound B twice daily for 4 weeks. The time-course of body weight changes (A) and the body weight gain at 4 weeks of Compound B treatment (B) are indicated respectively. The body weight of the mice fed a high-fat diet is significantly higher than the control mice (Cont) fed a standard rodent chow during the 4-week treatment period. The plasma glucose level (C), plasma insulin concentration (D), mesenteric adipose tissue weight (E), epididymal adipose tissue weight (F), liver weight (G), content of hepatic triglyceride (H), and the content of hepatic total-cholesterol (I) at 4 weeks of Compound B treatment are indicated respectively. Data are expressed as means ± SEM of 9–10 animals. *<i>P</i><0.05 and **<i>P</i><0.01. Statistical analyses between the vehicle-treated group and Compound B-treated groups were performed by the Dunnett’s multiple comparison test. ##<i>P</i><0.01. Statistical analyses between the vehicle-treated group and the control group were performed by the t-test.</p

Chemical structures of Compound A (A) and Compound B (B).

<p>Chemical structures of Compound A (A) and Compound B (B).</p