Neutrophils Are Associated With Capillary Closure in Spontaneously Diabetic Monkey Retinas

Abstract

Type 2 diabetes develops spontaneously in obese aging rhesus monkeys (Macaca mulatta). This study investigates the association between polymorphonuclear leukocytes and development of retinopathy. Blood pressure and plasma glucose levels were determined in 15 diabetic and 6 nondiabetic monkeys. The plasma levels of total cholesterol, LDL cholesterol, HDL cholesterol, and triglycerides were determined just before the start of the animal's final decline and elective necropsy. Retinas were incubated for ADPase (labels viable retinal blood vessels) and nonspecific esterase (labels neutrophils) activities. Polymorphonuclear leukocytes were counted per millimeter squared of retina. After the retina was flat-embedded in glycol methacrylate, tissue sections were taken through areas of interest and observed microscopically. Elevated numbers of intravascular polymorphonuclear leukocytes were present adjacent to areas with retinal capillary nonperfusion. There were significantly more polymorphonuclear leukocytes per millimeter squared in diabetic retinas (6.91 ؎ 5.01) compared with normal retinas (1.45 ؎ 1.62, P ‫؍‬ 0.018). Severity of hypertension in diabetes was also significantly associated with greater numbers of polymorphonuclear leukocytes (P ‫؍‬ 0.02). There was a significant positive exponential correlation between the number of polymorphonuclear leukocytes per millimeter squared and the level of total cholesterol (R ‫؍‬ 0.907), LDL cholesterol (R ‫؍‬ 0.875), the total cholesterol-to-HDL cholesterol ratio (R ‫؍‬ 0.86), and total triglycerides (R ‫؍‬ 0.888). This study demonstrates that severity of diabetes and the development of retinopathy are associated with increased numbers of polymorphonuclear leukocytes in the retina of diabetic monkeys. Hypertension, high plasma levels of LDL cholesterol and triglycerides, and low plasma levels of HDL cholesterol also are associated with increased polymorphonuclear leukocytes in retina. Diabetes 54:1534 -1542, 2005 A n early event in diabetic retinopathy is retinal capillary nonperfusion. Recent evidence suggests that leukocytes may initiate vaso-occlusion in diabetic retinal microvasculature (1). Miyamoto et al. (2) and Ogura (3) used acridine orange labeling and a scanning laser ophthalmoscope to observe leukocytes in diabetic rats. The number of leukocytes trapped in the retinal microcirculation was significantly elevated in streptozotocin-induced diabetic rats (2.5-fold) and Otsuka Long-Evans Tokushima Fatty (OLETF) rats (2-fold) in the early stages of diabetes compared with nondiabetic rats. They hypothesized that accumulation of leukocytes in diabetic retinas during the preretinopathy stage could cause microvascular occlusions and dysfunction, in turn causing retinopathy. Barouch et al. (4) later demonstrated that the increase in leukocyte accumulation or leukostasis was dependent on the adhesion molecule responsible for modulating firm adherence of leukocytes to endothelial cells, intracellular adhesion molecule-1 (ICAM-1), which is elevated in human diabetic retina (...

Angiogenic Factors and Cytokines in Diabetic Retinopathy

“…However, though well established in rodent models of DR, there is no direct clinical evidence that leukostasis is occurring in DR patients. Evidence for leukostasis leading to retinal capillary nonperfusion in the retinas of obese aging rhesis monkeys was obtained by Kim and co-workers [140]. Although the analysis was not blinded and included "selected regions of interest" rather than randomly-selected regions, these authors found increased numbers of esterase staining granulocytes in retinal capillaries of diabetic versus control monkeys.…”

S-glutathionylation: relevance in diabetes and potential role as a biomarker

“…Other proinflammatory effects related to Grx1 S-glutathionylation have been reported. Neutrophils play a key role in inflammation processes, such as those related to diabetic nephropathy (Galkina and Ley, 2006), adipose tissue inflammation and diabetic retinopathy (Kim et al, 2005). Neutrophils from diabetic patients have decreased phagocytic activity, impaired bacterial killing and significantly more superoxide generation compared to control neutrophils.…”

Membrane tubulovesicular extensions (cytonemes)

“…The firm adhesion of neutrophils to the endothelium is responsible for capillary closure and the development of diabetic angiopathies. 94,95 In the circulation, shear stress and a network of mediators, such as prostanoids and nitric oxide (NO) prevent firm leukocyte adhesion to the endothelium. 96 Both endothelial cells and neutrophils express constitutively active NO synthase isoforms, such as eNOS in endothelial cells and nNOS (neuronal) and iNOS (inducible) in neutrophils, for the production of NO.…”