The effect of palm oil-derived tocotrienol-rich fraction in preserving normal retinal vascular diameter in streptozotocin-induced diabetic rats

Purpose Angiogenesis in diabetic retinopathy (DR) is associated with increased retinal expression of angiopoietin-2 (Ang-2) and protein kinase C (PKC). Tocotrienol-rich fraction (TRF) has been shown to reduce the expression vascular endothelial growth factor (VEGF) in several experimental models. However, its effect against other angiogenic markers such as Ang-2 and PKC in rat model of diabetes remains unknown. Therefore, we investigated the effect of TRF on the retinal vascular changes and Ang-2 and PKC expressions in rats with streptozotocin (STZ)-induced DR. Methods Sprague–Dawley rats were divided into normal control rats (N) which received vehicle, and diabetic rats which either received vehicle (DV) or 100 mg/kg of TRF (DT). Diabetes was induced with intraperitoneal injection of STZ (60 mg/kg body weight). Treatments were given orally, once daily, for 12 weeks after confirmation of hyperglycaemia. Fundus photographs were captured at baseline, 6- and 12-week post-STZ injection and average diameter of retinal veins and arteries were measured. At 12-week post-STZ injection, rats were euthanised, and retinae were collected for measurement of Ang-2 and PKC gene and protein expressions. Results Retinal venous and arterial diameters were significantly greater in DV compared to DT at week 12 post-STZ injection ( p < 0.001 and < 0.05, respectively). The vessel diameter measurements in DT were comparable to N and this effect of TRF was associated with significantly lower Ang-2 and PKC gene and protein expressions compared to DV. Conclusion Oral TRF reduces the expression of retinal angiogenic markers and preserves the retinal vascular diameter of rats with STZ-induced DR.