Hepatic gene expression profile in persimmon peel extract administrated GK rat

Persimmon (Diospyros kaki L. f.) is a most popular fruit in Asian countries but its peels are totally wasted despite of containing a plenty of antioxidants such as carotenoids and polyphenols. We prepared a fat-soluble extract from a persimmon peel (PP) fraction and fed type 2 diabetic Goto-Kakizaki (GK) rats with a PP extract-containing AIN-93G diet (PP diet) for 12 weeks. Compared with the control AIN-93G diet, the feeding of the PP diet reduced the plasma glutamic-pyruvate transaminase activity significantly, with accumulation of β-cryptoxanthin in the liver. A DNA microarray analysis revealed that the PP diet altered the hepatic gene expression profiles. In particular, insulin signaling pathway-related genes were significantly enriched in differentially expressed gene sets. Moreover, Western blotting analysis actually showed the promotion of IRβ tyrosine phosphorylation. All these data suggest that the PP extract administration to the GK rats improves their insulin resistance. Male GK rats (90–107 g), aged 5 weeks, were purchased from Japan SLC Co. (Hamamatsu, Japan). The rats were maintained in a room at 22 ± 1°C under a 12-h light-dark cycle (lights on at 0800) and administered a commercial diet (AIN-93G, Research Diets, Inc., New Brunswick, NJ, USA) for a week. The rats were allowed free access to diet and water. After one week, they were divided into two groups with similar average body weights. The control group rats (n = 4) were fed on the commercial diet, and the PP group rats (n = 4) on the same diet containing the PP extract. After the 12-week-feeding the liver was excised and analyzed the effect of PP extract administration on hepatic gene expression.

柿（Diospyros kaki L. f.）是亚洲地区极具人气的果品，但其果皮虽富含类胡萝卜素、多酚等多种抗氧化物质，却常被完全废弃。本研究从柿皮（PP）组分中制备脂溶性提取物，为2型糖尿病Goto-Kakizaki（GK）大鼠饲喂添加该提取物的AIN-93G合成饲料（PP饲料），持续干预12周。与饲喂基础AIN-93G合成饲料的对照组相比，PP饲料饲喂可显著降低大鼠血浆谷丙转氨酶（glutamic-pyruvate transaminase）活性，并使肝脏中β-隐黄质（β-cryptoxanthin）发生蓄积。基因芯片（DNA microarray）分析结果显示，PP饲料可改变大鼠肝脏基因表达谱；其中，胰岛素信号通路相关基因在差异表达基因集中显著富集。此外，蛋白质免疫印迹（Western blotting）分析进一步证实，PP饲料可促进胰岛素受体β（IRβ）的酪氨酸磷酸化。上述所有实验数据均表明，向GK大鼠灌胃柿皮提取物可改善其胰岛素抵抗。本研究购入5周龄、体重90~107 g的雄性GK大鼠，购自日本SLC公司（Hamamatsu, 日本）。大鼠饲养于温度22±1℃、12小时明暗循环（光照时段为08:00）的环境中，先饲喂商用AIN-93G合成饲料（Research Diets, Inc., 美国新泽西州新不伦瑞克市）适应1周，期间自由采食与饮水。1周后，按平均体重匹配原则将大鼠分为两组，每组4只：对照组大鼠饲喂基础AIN-93G合成饲料，PP组大鼠饲喂添加了柿皮提取物的同款饲料。12周饲喂周期结束后，处死大鼠并摘取肝脏，分析柿皮提取物灌胃对大鼠肝脏基因表达的影响。