The role of lutein-rich purple sweet potato leaf extract on the amelioration of diabetic retinopathy in streptozotocin-induced Sprague–Dawley rats

**Background:** Diabetic retinopathy (DR) is a common complication of diabetes mellitus, characterized by microvascular changes, retinal lesions, and vision impairment. Current treatments such as anti-VEGF therapy, laser photocoagulation, and vitrectomy have significant side effects. Natural extracts, particularly those rich in antioxidants like lutein, are being explored as alternative therapies. Purple sweet potato leaves (PSPL) are rich in lutein, a potent antioxidant with anti-diabetic and anti-inflammatory properties. This study aimed to evaluate the effect of PSPL extract on DR in streptozotocin (STZ)-induced male Sprague–Dawley rats.

**Methods:** Fresh PSPL were extracted with 80% ethanol, and the crude extract was mixed with maltodextrin and dried. Male SD rats (150–200 g) were divided into two groups: one fed a standard diet (n=10) and the other a high-fat diet (HFD, n=40). HFD-fed rats were injected intraperitoneally with a single dose of 60 mg/kg STZ to induce diabetes. Diabetes was confirmed on day 7 (FBG ≥11.1 mmol/L). Rats were then divided into five groups (n=8 per group): normal control (NS) given normal saline, diabetic control (DNS) given normal saline, diabetic rats given 25 mg/kg gliclazide (D25G), diabetic rats given 200 mg/kg PSPL extract (DT 200), and diabetic rats given 400 mg/kg PSPL extract (DT 400). Treatments were administered orally for 12 weeks. Body weight, calorie intake, and water intake were recorded weekly. At week 12, OGTT was performed, and FBG was measured at weeks 5, 10, and 12. Serum and retinal insulin, IL-17A, and antioxidant markers (FRAP, GSH, TAC) were measured using ELISA kits. Retinal thickness, blood vessel thickness, and outer nuclear layer (ONL) thickness were measured. Lenticular clarity was assessed under a binocular microscope. Histopathological analysis of the retina and pancreas was performed, and morphometry of islets of Langerhans was conducted.

**Key Results:** The DT 400 group showed a significant reduction in FBG at week 12 (13.27 ± 0.92 mmol/L) compared to DNS (19.25 ± 2.13 mmol/L, p<0.05). OGTT AUC was significantly lower in DT 200 and DT 400 compared to DNS (p<0.05). Serum and retinal insulin levels were significantly higher in DT 200, DT 400, and D25G compared to DNS (p<0.05). IL-17A levels in serum and retina were significantly lower in all treated groups compared to DNS (p<0.05). Antioxidant markers (FRAP, GSH, TAC) were significantly higher in serum and retina of treated groups compared to DNS (p<0.05). Retinal blood vessel thickness was significantly lower in DT 200, DT 400, and D25G compared to DNS (p<0.05). Overall retinal thickness and ONL thickness were significantly greater in treated groups compared to DNS (p<0.05). Lenticular clarity was improved in DT 200, DT 400, and D25G, with reduced cataract severity. Histopathology showed that DT 200, DT 400, and D25G preserved normal retinal and pancreatic architecture, while DNS showed degeneration and atrophy. Morphometry revealed that the area of islets of Langerhans and number of β-cells were significantly higher in treated groups compared to DNS (p<0.05).

**Clinical Implications:** This study demonstrates that lutein-rich PSPL extract, particularly at 400 mg/kg, effectively ameliorates DR pathology in STZ-induced diabetic rats by reducing hyperglycemia, restoring insulin levels, reducing inflammation (IL-17A), enhancing antioxidant defenses, and preserving retinal and pancreatic structure. These findings suggest that PSPL extract may serve as a natural, safe, and cost-effective adjunctive therapy for DR. However, human clinical trials are needed to confirm efficacy and safety in patients with diabetic retinopathy.