Increases in leukostasis/monocyte adhesion to the capillary endothelium (leukostasis) and decreases in retinal blood flow may be causally associated and are implicated in the pathogenesis of diabetic retinopathy. In this study, we demonstrate that increases in leukostasis are observed in insulin-resistant states without diabetes, whereas decreases in retinal blood flow require diabetes and hyperglycemia. Microimpaction studies using beads mimicking retinal capillary obstruction by leukocytes did not affect retinal blood flow. In diabetic rats, treatment with the antioxidant ␣-lipoic acid normalized the amount of leukostasis but not retinal blood flow. In contrast, treatment with D-␣-tocopherol and protein kinase-C ␤-isoform inhibition (LY333531) prevented the increases in leukostasis and decreases in retinal blood flow in diabetic rats. Serum hydroxyperoxide, a marker of oxidative stress, was increased in diabetic rats, but normalized by treatment with antioxidants ␣-lipoic acid and D-␣-tocopherol and, surprisingly, PKC ␤-isoform inhibition. These findings suggest that leukostasis is associated with endothelial dysfunction, insulin resistance, and oxidative stress but is not related to retinal blood flow and is not sufficient to cause diabetic-like retinopathy. Moreover, treatment with PKC ␤ inhibition is effective to normalize diabetes or hyperglycemia-induced PKC ␤-isoform activation and oxidative stress. Diabetes 52:829 -837, 2003

Aims/hypothesis. The renin angiotensin system is emerging as a potential therapeutic target for diabetic retinopathy. This study examines the effects of angiotensin-converting-enzyme inhibition by captopril and angiotensin AT 1 receptor antagonism using candesartan-cilexetil on retinal blood flow and acetylcholinestimulated vasodilatation in normotensive diabetic rats. Methods. Non-diabetic or streptozotocin-induced diabetic rats were treated for 2 weeks with captopril (100 mg/kg/day) or candesartan cilexetil (2 mg/kg/day). Retinal haemodynamics were measured using video fluorescein angiography. Effects of exogenous acetylcholine on retinal haemodynamics were examined following intravitreal injection. Total retinal diacylglycerol was labelled using diacylglycerol kinase, separated by thin-layer chromatography, and quantified using autoradiography. Results. Diabetic rats had prolonged retinal mean circulation time and decreased retinal blood flow compared with non-diabetic rats. Treatment of diabetic rats with either captopril or candesartan blocked the development of these blood flow abnormalities. Intraviteral injection of acetylcholine (10 −5 mol/l) in non-diabetic rats increased retinal blood flow by 53.9±22.0% relative to baseline whereas this response to acetylcholine was blunted in diabetic rats (4.4±19.6%, p<0.001). Candesartan treatment of diabetic rats restored the acetylcholine-stimulated retinal blood flow response to 60.0±18.7% compared with a 56.2+20.1% response in candesartan-treated non-diabetic rats. Total retinal diacylglycerol levels were increased in diabetic rats (3.75±0.98 nmol/mg, p<0.05) compared with non-diabetic rats (2.13±0.25 nmol/mg) and candesartan-treatment of diabetic rats normalized diacylglycerol levels (2.10±0.25 nmol/mg, p<0.05). Conclusion/interpretation. This report provides evidence that angiotensin-converting enzyme inhibition and AT 1 receptor antagonism ameliorates retinal haemodynamic dysfunctions in normotensive diabetic rats. [Diabetologia (2004) 47:113-123]

OBJECTIVE—To evaluate corneal advanced glycation end product (AGE) fluorescence in patients with diabetes and in healthy control subjects. RESEARCH DESIGN AND METHODS—Corneal autofluorescence was measured in 26 eyes of 26 patients with type 2 diabetes (mean age 57.0 years; mean disease duration 12.2 years; mean HbA1c 7.1%) and 13 eyes of 13 healthy age-matched control subjects (mean age 57.9 years). The patients with type 2 diabetes were divided into the following groups: patients without diabetic retinopathy (DR), patients without proliferative diabetic retinopathy (PDR), and patients with PDR. Corneal autofluorescence was measured by fluorophotometry with the wavelength that is characteristic of AGE fluorescence (excitation and emission 360–370 nm and 430–450 nm, respectively). We defined peak corneal autofluorescence levels as corneal AGE fluorescence values. We compared the corneal AGE fluorescence values in the four groups. RESULTS—In the PDR group (11.9 ± 3.9 arbitrary units [mean ± SD]), the corneal AGE fluorescence values were significantly higher compared with the control subjects (6.9 ± 1.3 arbitrary units), the patients without DR (7.4 ± 2.1 arbitrary units), and the patients without PDR (6.9 ± 2.2 arbitrary units) (P &lt; 0.05). CONCLUSIONS—We found that corneal AGEs may increase in patients with diabetes and PDR compared with control subjects, patients without DR, and patients without PDR. In the patients with PDR, increased corneal AGEs may play a role in diabetic keratopathy.