Diabetic retinopathy is one of the microvascular complications in diabetes. The hallmark of early diabetic retinopathy is the loss of pericytes (Cogan et al. 1961). These changes lead to decreased capillary tonicity, increased retinal blood flow, formation of microaneurysms and uncontrolled proliferation of endothelial cells. Both the Diabetes Control and Complications Trial (DCCT) and United Kingdom Prospective Diabetes Study (UKPDS) have shown that hyperglycaemia is a major factor in the onset and progression of microvascular complications in diabetic patients (DCCT Research Group, 1993; UKPDS Group, 1998). The aim of this study is to evaluate the therapeutic potential of Gynura procumbens to prevent diabetic retinopathy. G. procumbens, a vigorous climbing herb belonging to the family Compositae, is found in various parts of Southeast Asia. The G. procumbens leaf is edible and has been reported to have antihyperglycaemic activity (Zhang & Tan, 2000). The methanol extract of G. procumbens leaf was evaluated for protection of cultured bovine retinal pericytes (BRP) against D-glucose-induced toxicity.

Subconfluence BRP (from eyes obtained from an abattoir) were incubated in 5 mM or 25 mM D-glucose, with or without the extract for 4 days. The protective effect of the extract on D-glucose-induced toxicity was determined by using Trypan Blue staining. Further, intracellular glucose concentrations were measured using the Amplex Red kit (Molecular Probes) and expression of GLUT1 protein determined by immunoblotting.

Incubation of BRP in 25 mM D-glucose for 4 days reduced the number of viable cells to 75 ± 2 % (mean ± S.E.M., n = 12) compared to the BRP in 5 mM D-glucose. The addition of non-toxic concentrations (2-10 µg ml^-1) of methanol leaf extract of G. procumbens significantly reversed the adverse effects of elevated D-glucose. Chronic exposure of the BRP to high glucose led to an increased accumulation of intracellular glucose (282 ± 52 vs. 98 ± 16 nmol (mg protein)^-1 in 5 mM glucose, means ± S.E.M., n = 3, Student’s unpaired t test, P < 0.01) and downregulation of GLUT1 protein (20 % vs. 5 mM glucose). These effects were partially reversed by G. procumbens at a dose of 10 µg ml^-1.

In conclusion, G. procumbens may be of therapeutic potential for the treatment of diabetic retinopathy.

This work was funded by the Malaysian Government and IRPA Project No.09-04-01-0030.