Antihypertriglyceridemia activities of naturally fermented green tea, Heukcha, extract through modulation of lipid metabolism in rats fed a high-fructose diet

Abstract

Hypertriglyceridemia, a symptom of elevated triglyceride level in the blood, is a potent risk factor for cardiovascular and metabolic disorders. Among the numerous treatments to regulate circulating triglyceride levels, fibrates are widely used to treat hypertriglyceridemia, although they also have side effects such as hepatotoxicity and gallstone formation. In the present study, we aimed to investigate the blood triglyceride-lowering effects of a naturally fermented green tea extract (NFGT) and the underlying mechanisms on hypertriglyceridemia in vitro and in vivo models. NFGT suppressed the expression of lipogenic genes, while augmented expression of fatty acid oxidation-related genes in cultured cells, leading to the significant decrease of intracellular triglyceride content. NFGT treated group in fructose-induced hypertriglyceridemic rat model significantly decreased plasma and hepatic triglyceride, which was accompanied by an increase in excretion of fecal fat. Taken together, we propose that NFGT could be potentially a novel functional ingredient to prevent or treat hypertriglyceridemia.

Keywords: Hypertriglyceridemia; Lipid metabolism; Naturally fermented green tea; Pancreatic lipase.

Fig. 1

NFGT regulates the expression of genes involved in lipid metabolism in HepG2 cells. Human HepG2 hepatocytes were incubated with NFGT at various concentration for 72 h. Cell viability was assessed by MTT assay (A). The cells were exposed to fenofibrate (Feno; 10 μM) or naturally fermented green tea extract (NFGT; 10, 30, 100, and 300 μg/ml, respectively) for 24 h. After incubation, cells were washed with PBS twice and the relative mRNA level of lipogenic genes (B), and fatty acid oxidation-related genes (C) were determined using quantitative RT-PCR analysis. All assays were executed in triplicate and results were presented as mean ± S.E. of three separate experiments. *p < 0.05, **p < 0.01 vs. vehicle control (−)

Fig. 2

NFGT diminishes the fructose-induced TG accumulation in HepG2 cells. HepG2 cells were treated with fenofibrate (Feno; 10 μM) or naturally fermented green tea extract (NFGT; 10, 30, and 100 μg/ml, respectively) for 24 h. And then, cells were incubated with fructose (5.5 mM) for a further 72 h. Intracellular TG in hepatocytes was stained with fluorescent dye Nile red and photographed. Scale bar represents 100 µm (A). Relative TG accumulation was measured through a Tecan multiplate reader (B). The values represent the mean ± S.E. ^## p < 0.01 vs. the fructose-untreated normal control; *p < 0.05, **p < 0.01 vs. fructose-treated vehicle control

Fig. 3

NFGT inhibits pancreatic lipase activity. Lipase activity from porcine pancreas Type II is determined using a coupled enzyme reaction in the absence or presence of increasing concentrations (NFGT: 10, 30, 100, 300, and 1000 µg/ml, respectively) of naturally fermented green tea extract, which results in a colorimetric (570 nm) produce proportional to the enzymatic activity present. Each experiment was independently performed at least three times

Fig. 4

NFGT alleviates hypertriglyceridemia in the SD rats. The effect of NFGT (150 and 300 mg/kg) was examined on plasma TG levels in rats with Triton- (A) or fructose- (B) induced hypertriglyceridemia. The values represent the mean ± S.E. ^# p < 0.05 vs. the Triton- or fructose-untreated normal control; *p < 0.05, **p < 0.01 vs. Triton- or fructose-treated vehicle control

Fig. 5

NFGT ameliorates intrahepatic TG accumulation and lipogenesis in the SD rats. The effect of NFGT (150, and 300 mg/kg) was investigated on the levels of hepatic TG (A), the fecal lipid (B), and mRNA expression of lipid metabolism-related genes (C) in the fructose-induced hypertriglyceridemic rats. The values represent the mean ± S.E. ^# p < 0.05, ^## p < 0.01 vs. the fructose-untreated normal control; *p < 0.05, **p < 0.01 vs. fructose-treated vehicle control

Fig. 6

NFGT modulates lipid metabolism-related gene expression in cultured myocytes. Differentiated C2C12 myocytes were treated with fenofibrate (Feno; 10 μM) or naturally fermented green tea extract (NFGT; 10, 30, 100, and 300 μg/ml, respectively) for 24 h. Relative mRNA expression related to energy metabolism in myocytes was examined with qPCR and normalized by cyclophilin. All assays were executed in triplicate and results were presented as mean ± SE of three separate experiments. *p < 0.05, **p < 0.01 vs. vehicle control (−)