Abstract: Objective: To study the preventive effect of forsythin extract from Forsythia suspensa leaves on obesity induced by high-fat diet in rats. Methods: A total of 48 SD rats were divided into six groups of blank control, model control, low-, medium- and high-dose forsythin extract treatment (made in our laboratory, containing 13.3% forsythin) and forsythin standard (98% purity) treatment. The rats in the low-, medium- and high-dose forsythin extract groups were orally administered with forsythin extract at doses of 0.2, 0.4 and 1.2 g/(kg mb·d), containing 26.6, 53.2, and 159.6 mg/(kg mb·d) of forsythin, respectively. Forsythin standard was administered at a dose of 54.3 mg/(kg mb·d), similar to the middle-dose forsythin extract. The rats in the blank control group were provided with a basal diet whereas those in the other groups were given a high-fat diet. The administration lasted for 6 weeks. Then, food intake, body mass, obesity index (Lee’s index), fat index, and the serum levels of total cholesterol (TC), triglyceride (TG), low density lipoprotein cholesterol (LDL-C), high density lipoprotein cholesterol (HDL-C), total bile acid (TBA), leptin (LP) and free fatty acids (FFA) were measured and pathological sections of adipose tissue were examined. Results: The serum levels of TC, LDL-C, TBA, LP, and FFA in the model control group were significantly higher than those in the blank control group (P < 0.05). Pathological examination showed that compared with the blank control group, the number of fat cells in the model control group was reduced, and the adipocytes were full of fat and enlarged with significantly larger equivalent diameter, perimeter and area than those in the blank control group (P < 0.05), besides, fat mass and its coefficient, Lee’s index and body mass were significantly higher than those in the control group, indicating successful obesity induction in rats. In addition, compared with the model control group, the forsythin extract especially at the high dose lowered serum TC, LDL-C, LP and FFA in obese rats, and improved the pathological status of adipose tissue, reducing the number and size of adipocytes, but was ineffective at the low dose. The area of adipocytes in the low-dose forsythin extract group was reduced in contrast to the model control group (P < 0.05), the perimeter and area of adipocytes in the middle-dose group were both decreased (P < 0.05), and the equivalent diameter, perimeter and area in the high-dose group were all decreased. The forsythin extract especially at the high dose lowered the visceral fat mass and coefficient, Lee’s index, and body mass of obese rats, and the middle-dose forsythin extract was as effective as forsythin standard. Conclusion: The forsythin extract can prevent obesity induced by high-fat diet in rats through the forsythin contained in it.

Key words: Forsythia suspensa leaves; forsythin; high-fat diet; obese rats; obesity prevention