High Gamma-Aminobutyric Acid (GABA) Oolong Tea Alleviates High-Fat Diet-Induced Metabolic Disorders in Mice

Abstract

Obesity and overweight are associated with an increasing risk of developing health conditions and chronic non-communicable diseases, including cardiovascular diseases, cancer, musculoskeletal problems, respiratory problems, and mental health, and its prevalence is rising. Diet is one of three primary lifestyle interventions. Many bioactive components in tea especially oolong tea, including flavonoids, gamma-aminobutyric acid (GABA), and caffeine were reported to show related effects in reducing the risk of obesity. However, the effects of GABA oolong tea extracts (OTEs) on high-fat diet (HFD)-induced obesity are still unclear. Therefore, this study aims to explore whether the intervention of GABA OTEs can prevent HFD-induced obesity and decipher its underlying mechanisms using male C57BL/6 J mice. The result indicated that GABA OTEs reduced leptin expression in epididymal adipose tissue and showed a protective effect on nonalcoholic fatty liver disease. It promoted thermogenesis-related protein of uncoupling protein-1 and peroxisome proliferator-activated receptor-gamma coactivator (PGC-1α), boosted lipid metabolism, and promoted fatty acid oxidation. It also reduced lipogenesis-related protein levels of sterol regulatory element binding protein, acetyl-CoA carboxylase, and fatty acid synthase and inhibited hepatic triglyceride (TG) levels. These data suggest that regular drinking of GABA oolong tea has the potential to reduce the risk of being overweight, preventing obesity development through thermogenesis, lipogenesis, and lipolysis.

Figure 1

Effects of OTE supplementation on HFD-fed C57BL/6 mice. (A) Photographs of representative mice from each group at the end of treatment, (B) growth curve of mice aged 5 weeks at start, (C) food intake, (D) water intake, (E) food efficiency ratio, and (F) fasting blood glucose level measured by a glucose meter. Data are expressed as the means ± SD (N = 8). Differences were analyzed by one-way ANOVA and Duncan’s multiple-range tests. The values with different letters (a–c) are significantly different (p < 0.05) between each group.

Figure 2

Effects of OTE supplementation on fat weight, size distribution, and histology of epididymal and inguinal adipocyte in HFD-fed C57BL/6 mice. Adipose tissues were removed and weighed immediately after being sacrificed. Epididymal and inguinal adipocyte was fixed, dehydrated, and embedded, and 3 μm fat sections were stained with H&E stain. (A) Representative photographs of each group, (B) epididymal fat weight, (C) scapular brown fat weight, (D) inguinal adipose tissue, (E) representative images of H&E staining of paraffin sections of epididymal adipocyte (magnification: 200×), (F) representative images of H&E staining of paraffin sections of inguinal adipocyte (magnification: 400×), (G) frequency of adipocyte sizes in epididymal adipocyte, and (H) frequency of adipocyte sizes in inguinal adipocyte. Data are expressed as the means ± SD (N = 8). Differences were analyzed by one-way ANOVA and Duncan’s multiple-range tests. The values with different letters (a–c) are significantly different (p < 0.05) between each group.

Figure 3

Effects of OTE supplementation on adiponectin and leptin level of epididymal adipose tissue and serum adiponectin, leptin, and serum L/A ratio in HFD-fed C57BL/6 mice. The serum was measured using a commercial kit. (A) Western blotting analysis of hormones, (B) adiponectin, (C) leptin, (D) serum adiponectin, (E) serum leptin, and (F) serum L/A ratio. Data are expressed as the means ± SD (N = 4–5 for western blot, and N = 8 for serum analysis). Differences were analyzed by one-way ANOVA and Duncan’s multiple-range tests. The values with different letters (a–b) are significantly different (p < 0.05) between each group.

Figure 4

Effects of OTE supplementation on the appearance of organ, weight, liver histology, and hepatic triglycerides level in HFD-fed C57BL/6 mice. The liver, kidney, and spleen were removed and weighed immediately after sacrificed and were fixed, dehydrated, and embedded, 5 μm liver sections were stained with H&E stain. (A) Representative photographs of each group, (B) weight of liver, (C) weight of kidney, (D) weight of spleen, (E). hepatic triglycerides level, and (F) representative images of H&E staining of paraffin sections of the liver (magnification: 200×). The central vein is abbreviated to CV. Data are expressed as the means ± SD (N = 8). Differences were analyzed by one-way ANOVA and Duncan’s multiple-range tests. The values with different letters (a–c) are significantly different (p < 0.05) between each group.

Figure 5

Effects of OTE supplementation on lipolysis-related proteins and lipogenesis-related proteins of epididymal adipose tissue in HFD-fed C57BL/6 mice. (A) Protein levels of epididymal adipose tissue on lipolysis-related pathways were analyzed by western blot. (B) ATGL and (C) p-HSL/HSL protein bands were quantified by Image J. (D) Protein levels of epididymal adipose tissue on lipogenesis-related pathways were analyzed by western blot. (E) p-AMPK/AMPK, (F) SREBP-1c, (G) ACC, and (H) FASN protein bands were quantified by Image J. Data are expressed as the means ± SD (N = 4–5). Differences were analyzed by one-way ANOVA and Duncan’s multiple-range tests. The values with different letters (a–b) are significantly different (p < 0.05) between each group.

Figure 6

Effect of OTE supplementation on lipolysis-related proteins of inguinal adipose tissue and thermogenesis-related proteins of scapular brown adipose tissue in HFD-fed C57BL/6 mice. Protein levels were analyzed by western blot protein bands and were quantified by Image J. (A) Protein levels of inguinal adipose tissue on the lipolysis-related pathway. (B) ATGL protein band, (C) p-HSL/HSL protein bands, (D) protein levels of scapular brown adipose tissue on thermogenesis-related pathway, (E) PGC-1α, protein band, (F) PPARγ protein band, and (G) UCP-1 protein bands. Data are expressed as the means ± SD (N = 4–5 for western blot). Differences were analyzed by one-way ANOVA and Duncan’s multiple-range tests. The values with different letters (a–b) are significantly different (p < 0.05) between each group.

Figure 7

Effect of OTE supplementation on lipogenesis-related proteins, fatty acid oxidation-related proteins, and lipogenesis-related mRNA of the liver in HFD-fed C57BL/6 mice. The protein levels were analyzed by western blot, protein bands were quantified by Image J and related to hepatic de novo lipogenesis, SREBP-1, ACC1, FASN, and PPARα relative mRNA expressions were evaluated by qPCR. (A) Protein levels of liver on lipogenesis-related pathway, (B) p-AMPK/AMPK protein bands, (C) SREBP-1c protein bands, (D) p-ACC/ACC protein bands, (E) FASN protein bands, (F) PPARα protein bands, and (G) hepatic de novo lipogenesis related mRNA (SREBP-1, ACC1, FASN, and PPARα mRNA expressions). Data are expressed as the means ± SD (N = 3–4). Differences were analyzed by one-way ANOVA and Duncan’s multiple-range tests. The values with different letters (a–c) are significantly different (p < 0.05) between each group.