Characterization of Retinal Leukostasis and Hemodynamics in Insulin Resistance and Diabetes

Abstract

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 α-lipoic acid normalized the amount of leukostasis but not retinal blood flow. In contrast, treatment with d-α-tocopherol and protein kinase-C β-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 α-lipoic acid and d-α-tocopherol and, surprisingly, PKC β-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 β inhibition is effective to normalize diabetes or hyperglycemia-induced PKC β-isoform activation and oxidative stress.