Abstract:
Perilla frutescens is a plant rich in phytochemicals, which are widely investigated for their biologicals activities in leaves, seeds and oil. During the oil extraction process from perilla seeds, there is a residue called perilla seed residue which still contains bioactive phytochemicals. Therefore, this research aimed to investigate effect of perilla seed residue crude extract (PCE) on the development of insulin resistance from high-fat diet (HFD) in obese rat and the anti-diabetic effect in rat induced by HFD with streptozotocin. Perilla seed residue was extracted with 80% ethanol ratio 1 to 10 to obtain the PCE yield about 8.6 %. The phenolic acid content was 78.02 ± 1.44 mg of GAE / g extract whereas the flavonoid content was 67.63±0.67 mg of CE / g extract. PCE had antioxidant capacity equal to 94.911±5.09 and 107.99±9.40 mg of Trolox equivalent per 1 g of extract by ABTS and FRAP assay, respectively, whereas equal to 110.34±16.19 mg of ascorbic acid equivalent per 1 gram of extract by DPPH assay. The concentration of phytochemicals in PCE including rosmarinic acid, luteolin and apigenin were 30.36±0.03, 9.48±0.02 and 3.14±0.004 mg/g of PCE, respectively. To induce obesity and insulin resistance, male Wistar rats were fed with HFD for 6 weeks. For developing the diabetic rat model, HFD-treated rats were separated for a single intraperitoneal injection by streptozotocin (STZ) at 35 mg/kg bw. Subsequently, low- and high concentrations PCE (100 mg/kg bw and 1,000 mg/kg bw, respectively) were administered orally for 4 weeks, alongside metformin (100 mg/kg bw) as a positive control. Food/water intake, bodyweight, and fasting blood glucose were recorded weekly. An oral glucose tolerance test (OGTT) was performed in the final week. Post-euthanasia, blood, adipose tissue, and pancreatic tissue were collected for further analysis. In HFD-treated rats, both low- and high concentrations of PCE prevent the increasing of weight gain with reducing fat accumulation in adipose tissue. PCE administration normalized blood glucose levels and insulin secretion in HFD-treated rats to levels comparable to those of the control group. A decrease in HOMA-IR scores was observed in PCE-treated rats, indicating retarded insulin resistance and glycemic control in HFD-fed rats. These beneficial effects are likely attributable to the ability of PCE to attenuate inflammation and oxidative stress while enhancing antioxidant capacity. Both low and high dose PCE diminished inflammation by reducing macrophage infiltration in adipose tissue, which is the primary site of insulin resistance development. Additionally, PCE suppressed the expression of inflammation-related genes in adipose tissue, including TNF-α, IL-6, IL-1β, iNOS, and COX-2 and reduced circulating proinflammatory cytokines, including TNF-α, IL-6, and IL-1β, by 44%, 50%, and 28%, respectively. In diabetic rats, PCE improved diabetic symptoms such as decrease water and food intake, and increase body weight. PCE, particularly at low concentrations (100 mg/kg bw), reduced blood glucose levels by 43% and enhanced insulin secretion by 206% in diabetic rats with compromised pancreatic β-cell function due to streptozotocin induction. PCE appeared to promote β-cell regeneration, as evidenced by a 240% and 215% increase in the number and size of the islets of Langerhans, respectively, which is associated with enhanced insulin secretion and improved glucose utilization. Additionally, PCE reduced pancreatic inflammation, as demonstrated by suppressed the expression of inflammation-related genes in pancreatic tissue, including TNF-α, IL-6, IL-1β, iNOS, and COX-2 and decreased systemic inflammation, oxidative stress while enhancing antioxidant capacity in the blood. PCE administration reduced circulating levels of the pro-inflammatory cytokines TNF-α, IL-6, and IL-1β by 36%, 50%, and 33%, respectively. Furthermore, PCE effectively lowered VLDL-C and triglyceride levels in the blood. In conclusion, PCE demonstrates potential to attenuate insulin resistance by reducing fat deposition and adipose tissue inflammation ; therefore, it is expected to prevent insulin resistance in HFD-treated rats. Additionally, PCE can alleviate diabetes by improving metabolic parameters associated with hyperglycemia via improved pancreatic β-cell function and dyslipidemia in experimental animals. Therefore, these experimental results support the utilization of perilla seed residue to develop a natural product against insulin resistance and diabetes, as well as its incorporation into other health products to enhance its value.