Anti-Obesity and Anti-Diabetic Effects of Acacia Polyphenol in Obese Diabetic KKAy Mice Fed High-Fat Diet

Abstract

Acacia polyphenol (AP) extracted from the bark of the black wattle tree (Acacia meansii) is rich in unique catechin-like flavan-3-ols, such as robinetinidol and fisetinidol. The present study investigated the anti-obesity/anti-diabetic effects of AP using obese diabetic KKAy mice. KKAy mice received either normal diet, high-fat diet or high-fat diet with additional AP for 7 weeks. After the end of administration, body weight, plasma glucose and insulin were measured. Furthermore, mRNA and protein expression of obesity/diabetic suppression-related genes were measured in skeletal muscle, liver and white adipose tissue. As a result, compared to the high-fat diet group, increases in body weight, plasma glucose and insulin were significantly suppressed for AP groups. Furthermore, compared to the high-fat diet group, mRNA expression of energy expenditure-related genes (PPARα, PPARδ, CPT1, ACO and UCP3) was significantly higher for AP groups in skeletal muscle. Protein expressions of CPT1, ACO and UCP3 for AP groups were also significantly higher when compared to the high-fat diet group. Moreover, AP lowered the expression of fat acid synthesis-related genes (SREBP-1c, ACC and FAS) in the liver. AP also increased mRNA expression of adiponectin and decreased expression of TNF-α in white adipose tissue. In conclusion, the anti-obesity actions of AP are considered attributable to increased expression of energy expenditure-related genes in skeletal muscle, and decreased fatty acid synthesis and fat intake in the liver. These results suggest that AP is expected to be a useful plant extract for alleviating metabolic syndrome.

Figure 1

Histology of epididymal adipose tissue (a) and mean adipocyte surface area (b). KKAy mice were given a LF, a HF, HF containing 2.5% AP (HF/AP 2.5%) or HF containing 5.0% AP (HF/AP 5.0%) for 7 weeks. White adipose tissue around the testis was removed, fixed in 10% neutral-buffered formalin, paraffinized and stained using HE (a). Mean surface area for epididymal white adipocytes was measured using Image J software (b). Details of the diets are given in the “Materials and Methods” section. Data represent means ± SDs for seven sections per group. Tukey's test: **P < .01 versus LF; ^## P < .01 versus HF.

Figure 2

Representative histological sections of liver stained with HE (a) or oil red O (b). KKAy mice were given a LF, a HF, HF containing 2.5% AP (HF/AP 2.5%) or HF containing 5.0% AP (HF/AP 5.0%) for 7 weeks. The liver was removed, fixed in 10% neutral-buffered formalin, paraffinized and stained using HE (a). A cryostat was also used to prepare tissue sections for staining with oil red O (b). Details of the diets are given in the “Materials and Methods” section.

Figure 3

Effect of acacia polyphenol on mRNA expression in skeletal muscle. KKAy mice were given a LF, HF, HF containing 2.5% AP (HF/AP 2.5%) or HF containing 5.0% AP (HF/AP 5.0%) for 7 weeks. Skeletal muscle was removed, and mRNA expressions were measured using real-time RT-PCR, using β-actin as a housekeeping gene. All mRNA expressions are given as percentages compared to the LF group (100%). Details of the diets are given in the “Materials and Methods” section. Data represent means ± SDs for six mice per group. Tukey's test: *P < .05 versus LF; **P < .01 versus LF; ^# P < .05 versus HF; ^## P < .01 versus HF.

Figure 4

Effect of acacia polyphenol on protein expression of CPT1, ACO and UCP3 in skeletal muscle. KKAy mice were given a LF, a HF, HF containing 2.5% AP (HF/AP 2.5%) or HF containing 5.0% AP (HF/AP 5.0%) for 7 weeks. The skeletal muscle was removed, and protein expression was measured by western blotting, using β-actin as a housekeeping gene. All protein expressions are given as percentages compared to the LF group (100%). Details of the diets are given in the “Materials and Methods” section. Data represent means ± SDs for six mice per group. Tukey's test: **P < .01 versus LF; ^# P < .05 versus HF; ^## P < .01 versus HF.

Figure 5

Effect of acacia polyphenol on mRNA expression in the liver. KKAy mice were given a LF, a HF, HF containing 2.5% AP (HF/AP 2.5%) or HF containing 5.0% AP (HF/AP 5.0%) for 7 weeks. The liver was removed and mRNA expression was measured by real-time RT-PCR using β-actin as a housekeeping gene. All mRNA expressions are given as percentages compared to the LF group (100%). Details of the diets are given in the “Materials and Methods” section. Data represent means ± SDs for six mice per group. Tukey's test: *P < .05 versus LF; **P < .01 versus LF; ^# P < .05 versus HF; ^## P < .01 versus HF.

Figure 6

Effect of acacia polyphenol on mRNA expression in epididymal white adipose tissue. KKAy mice were given a LF, HF, HF containing 2.5% AP (HF/AP 2.5%) or HF containing 5.0% AP (HF/AP 5.0%) for 7 weeks. White adipose tissue around the testis was removed, and mRNA expression was measured by real-time RT-PCR, using β-actin as a housekeeping gene. All mRNA expressions are given as percentages compared to the LF group (100%). Details of diets are given in the “Materials and Methods” section. Data represent means ± SDs for six mice per group. Tukey's test: *P < .05 versus LF; **P < .01 versus LF; ^## P < .01 versus HF.

Figure 7

Hypothetical mechanisms of anti-obesity/diabetic actions of acacia polyphenol.