Reduction of Obesity and Insulin Resistance through Dual Targeting of VAT and BAT by a Novel Combination of Metabolic Cofactors

Abstract

Obesity is an epidemic disease worldwide, characterized by excessive fat accumulation associated with several metabolic perturbations, such as metabolic syndrome, insulin resistance, hypertension, and dyslipidemia. To improve this situation, a specific combination of metabolic cofactors (MC) (betaine, N-acetylcysteine, L-carnitine, and nicotinamide riboside) was assessed as a promising treatment in a high-fat diet (HFD) mouse model. Obese animals were distributed into two groups, orally treated with the vehicle (obese + vehicle) or with the combination of metabolic cofactors (obese + MC) for 4 weeks. Body and adipose depots weights; insulin and glucose tolerance tests; indirect calorimetry; and thermography assays were performed at the end of the intervention. Histological analysis of epidydimal white adipose tissue (EWAT) and brown adipose tissue (BAT) was carried out, and the expression of key genes involved in both fat depots was characterized by qPCR. We demonstrated that MC supplementation conferred a moderate reduction of obesity and adiposity, an improvement in serum glucose and lipid metabolic parameters, an important improvement in lipid oxidation, and a decrease in adipocyte hypertrophy. Moreover, MC-treated animals presented increased adipose gene expression in EWAT related to lipolysis and fatty acid oxidation. Furthermore, MC supplementation reduced glucose intolerance and insulin resistance, with an increased expression of the glucose transporter Glut4; and decreased fat accumulation in BAT, raising non-shivering thermogenesis. This treatment based on a specific combination of metabolic cofactors mitigates important pathophysiological characteristics of obesity, representing a promising clinical approach to this metabolic disease.

Keywords: adipose tissue; insulin resistance; metabolic cofactors; obesity; thermogenesis.

Figure 1

Obese mice supplemented with MC had reduced body weight and smaller visceral WAT depots with an improved biochemical profile. Effects of MC treatment on: (A) body weight gain; (B) RQ for 24 h; (C) fat oxidation. Weights of different adipose tissue depots: (D) inguinal (IWAT); (E) epididymal (EWAT); (F) mesenchymal (MWAT); (G) retroperitoneal (RWAT). (H) weight of VATs (EWAT + MWAT + RWAT). Serum biochemical parameters of: (I) triglycerides; (J) total cholesterol; (K) LDL-cholesterol; (L) HDL-cholesterol; and (M) LDL/HDL ratio. Data are mean ± SEM. * p < 0.05, ** p < 0.01, **** p < 0.0001.

Figure 2

MC supplementation promotes a reduction in the adipocyte size, increasing lipolysis and fatty acid oxidation. Effects of treatments on adipocyte hypertrophy (A) Representative micrographs of hematoxylin–eosin stained EWAT sections from obese + vehicle and obese + MC groups (bar = 100 µm); (B) adipocyte area; (C) adipocyte size distribution; and (D) EWAT mRNA expression of genes related to lipolysis (Hsl, Plin, Atgl and Mgl), de novo lipogenesis (Acc1 and Scd1), and fatty acid oxidation (Cpt1a and Acox1). Data are mean ± SEM. * p < 0.05, ** p < 0.01.

Figure 3

MC supplementation promotes improved glucose and insulin resistance by increasing the expression of Glut4 in EWAT. (A) Fasting glucose; (B) fasting insulin; (C) HOMA-IR; (D) glucose tolerance test (GTT) and area under the curve (AUC); (E) insulin tolerance test (ITT) and AUC; (F) EWAT mRNA expression of Glut1 and Glut4. Data are mean ± SEM. * p < 0.05, ** p < 0.01, *** p < 0.001, **** p < 0.0001.

Figure 4

MC supplementation increases BAT thermogenesis. Effects of treatments on: (A) brown adipose tissue (BAT) weight; (B) representative micrographs of hematoxylin–eosin-stained BAT sections (Bar = 100 µm); (C) lipid droplets, and (D) and quantification of the lipid droplet surface. (E) BAT mRNA expression of genes related to BAT function (Ucp1, Pgc1a, Prdm16, Dio2, and Fgf21); de novo lipogenesis (Fasn and Ppara); lipolysis (Hsl, Atgl and Mgl); fatty acid oxidation (Acox and Cpt1b); and glucose uptake (Glut1 and Glut4). (F,G) Representative thermographic images of the BAT skin area and quantification. Data are mean ± SEM. * p < 0.05, ** p < 0.01, *** p < 0.001, **** p < 0.0001.