Suppression of Ocular Vascular Inflammation through Peptide-Mediated Activation of Angiopoietin-Tie2 Signaling.

Persistent inflammation is a complication associated with many ocular diseases. Changes in ocular vessels can amplify disease responses and contribute to vision loss by influencing the delivery of leukocytes to the eye, vascular leakage, and perfusion. Here, we report the anti-inflammatory activity for AXT107, a non-RGD, 20-mer αvß3 and α5ß1 integrin-binding peptide that blocks vascular endothelial growth factor (VEGF)-signaling and activates tyrosine kinase with immunoglobulin and EGF-like domains 2 (Tie2) using the normally inhibitory ligand angiopoietin 2 (Ang2). Tumor necrosis factor α (TNFα), a central inflammation mediator, induces Ang2 release from endothelial cells to enhance its stimulation of inflammation and vascular leakage. AXT107 resolves TNFα-induced vascular inflammation in endothelial cells by converting the endogenously released Ang2 into an agonist of Tie2 signaling, thereby disrupting both the synergism between TNFα and Ang2 while also preventing inhibitor of nuclear factor-κB α (IκBα) degradation directly through Tie2 signaling. This recovery of IκBα prevents nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) nuclear localization, thereby blocking NF-κB-induced inflammatory responses, including the production of VCAM-1 and ICAM-1, leukostasis, and vascular leakage in cell and mouse models. AXT107 also decreased the levels of pro-inflammatory TNF receptor 1 (TNFR1) without affecting levels of the more protective TNFR2. These data suggest that AXT107 may provide multiple benefits in the treatment of retinal/choroidal and other vascular diseases by suppressing inflammation and promoting vascular stabilization.

Fenofibrate-Loaded Biodegradable Nanoparticles for the Treatment of Experimental Diabetic Retinopathy and Neovascular Age-Related Macular Degeneration.

Fenofibrate is a peroxisome proliferator-activated receptor α (PPARα) agonist and has been shown to have therapeutic effects on diabetic retinopathy (DR). However, the effects of fenofibrate through systemic administration are not as potent as desired due to inefficient drug delivery to the retina. The present study aimed to explore the sustained therapeutic effects of fenofibrate-loaded biodegradable nanoparticles (NP) on both DR and neovascular age-related macular degeneration (AMD). Fenofibrate was successfully encapsulated into poly(lactic- co-glycolic acid) (PLGA) NP (Feno-NP), and Feno-NP were optimized by varying polymer composition to achieve high drug loading and prolonged drug release. The Feno-NP made of PLGA 34 kDa demonstrated a drug content of 6% w/w and a sustained drug release up to 60 days in vitro. Feno-NP (PLGA 34 kDa) was selected for following in vivo studies, and one single intravitreal (IVT) injection of Feno-NP into rat eyes with a 30G fine needle maintained sustained fenofibric acid drug level in the eye for more than 60 days. The efficacy of Feno-NP in DR and neovascular AMD was investigated using streptozotocin (STZ)-induced diabetic rats, laser-induced choroidal neovascularization (CNV) rats, and very low-density lipoprotein receptor knockout ( Vldlr -/-) mice. Therapeutic effects of Feno-NP were evaluated by measuring electroretinogram (ERG), retinal vascular leakage, leukostasis, CNV size, and retinal levels of vascular endothelial growth factor (VEGF) and intracellular adhesion molecule-1 (ICAM-1). In diabetic rats, Feno-NP ameliorated retinal dysfunctions, reduced retinal vascular leakage, inhibited retinal leukostasis, and downregulated the overexpression of VEGF and ICAM-1 at 8 weeks after one IVT injection. In addition, Feno-NP reduced retinal vascular leakage and CNV formation in both CNV rats and Vldlr -/- mice. Moreover, no toxicity of Feno-NP or Blank-NP to retinal structure and function was detected. Feno-NP exhibited good physiochemical characteristics and controlled drug release profile, conferring prolonged beneficial effects on DR and neovascular AMD.

Curcumolide reduces diabetic retinal vascular leukostasis and leakage partly via inhibition of the p38MAPK/NF-κ B signaling.

Retinal inflammation in a hyperglycemic condition is believed to play a crucial role in the development of diabetic retinopathy, and targeting inflammatory mediators is a promising strategy for the control of diabetic retinopathy. Curcumolide, a novel sesquiterpenoid with a unique 5/6/5 tricyclic skeleton, was isolated from Curcuma wenyujin. In this study, we demonstrate that treatment with curcumolide alleviated retinal inflammatory activities both in vitro and in vivo in a STZ-induced diabetic rat model and in TNF-α-stimulated HUVECs. Curcumolide alleviated retinal vascular permeability and leukostasis and attenuated the overexpression of TNF-α and ICAM-1 in diabetic retinas. Moreover, curcumolide also inhibited inducible p38 MAPK and NF-κB activation and the subsequent induction of proinflammatory mediators. These data suggest potential treatment strategies against diabetic retinopathy, particularly in the early stages of the disease.

The effect of Shengpuhuang-tang on retinal inflammation in streptozotocin-induced diabetic rats by NF-κB pathway.

ETHNOPHARMACOLOGICAL RELEVANCE: Diabetic retinopathy (DR) is a terrible microvascular disorder causing blindness. Retinal inflammation is the early stage in DR, which is believed to play a crucial role in the development of it. Shengpuhuang-tang (ST), a traditional herbal formula, which has effective treatment of fundus bleeding disorder. ST exerts protective effects against DR in rats, but its underlying mechanism of this efficacy remains unknown. Thus, the objective of this study is to examine the mechanism and the efficacy of ST on retinal inflammation in streptozotocin-induced diabetic rats. MATERIALS AND METHODS: The administration of ST was initiated at 4 weeks after diabetes induction and continued for 12 weeks. Retinal vessel permeability was evaluated by using FITC-dextran and Evans blue. Retinal leukostasis was evaluated with FITC-coupled concanavalin A lectin (ConA). Moreover, western blotting was performed to detect TNF-α, ICAM-1 and the relative expression levels of IκBα, IKKß, and p65 in vivo. RESULTS: The results showed that the retinal inflammation in streptozotocin-induced diabetic rats was significantly decreased by ST. ST could decreased the expression levels of TNF-α, ICAM-1 and inhibited the expression of p-IKKß, p-p65 and IκBα. It could also inhibited the nuclear transfer of p65. CONCLUSIONS: In conclusion, these data suggested that ST may have potential treatment strategies against early stage of diabetic retinopathy through NF-κB pathway.

Phosphomannopentaose sulfate (PI-88) inhibits retinal leukostasis in diabetic rat.

Retinal leukostasis, mediated by intracellular adhesion molecule-1 (ICAM-1) and vascular endothelial growth factor (VEGF), has been implicated in the pathogenesis of early diabetic retinopathy. Phosphomannopentaose sulfate (PI-88) is a highly sulfonated oligosaccharide which inhibits heparanase activity and competes with heparan sulfate binding to growth factors. In this study, we evaluated whether PI-88 could inhibit retinal leukostasis in strepotzotocin(STZ)-induced diabetic rat and elucidated the possible mechanisms. Diabetes was induced in Sprague-Dawley rats by intraperitoneal injection (i.p.) of STZ. Three months after induction, diabetic rats were administered PI-88 (25 mg/kg body weight) or vehicle solution daily via i.p. for 14 consecutive days. Leukostasis was analyzed on retinal flatmounts by concanavalin A and CD45 immunofluorescence staining. Retinal function was analyzed by electroretinography (ERG). ICAM-1 and VEGF levels in retinas were studied by Western blot and enzyme-linked immunosorbent assay (ELISA) respectively. The systemic administration of PI-88, but not vehicle, significantly decreased the number of adherent leukocytes in retinas by 52.24% (P<0.001) and led to significant preservation (about 50%, P<0.001) of scotopic ERG a- and b-wave amplitudes in treated diabetic rats as compared to those of diabetic control rats. These changes were associated with downregulation of ICAM-1 (45%, P<0.001) and VEGF (26.83+/-2.01 versus 40.8+/-3.24 pg/mg, P<0.01) in retinas of PI-88 treated diabetic rats as compared to those of diabetic control rats. PI-88 significantly inhibited retinal leukostasis and reversed retinal dysfunction by a mechanism that may include decreased ICAM-1 and VEGF expression in diabetic rats. Our data suggests that PI-88 is a promising agent for the treatment of diabetic retinopathy.

Expression, distribution and function of kinin B1 receptor in the rat diabetic retina.

BACKGROUND AND PURPOSE: The kinin B1 receptor contributes to vascular inflammation and blood-retinal barrier breakdown in diabetic retinopathy (DR). We investigated the changes in expression, cellular localization and vascular inflammatory effect of B1 receptors in retina of streptozotocin diabetic rats. EXPERIMENTAL APPROACH: The distribution of B1 receptors on retinal cell types was investigated by immunocytochemistry. Effects of B1 receptor agonist, R-838, and antagonist, R-954, on retinal leukocyte adhesion, gene expression of kinin and VEGF systems, B1 receptor immunoreactivity, microgliosis and capillary leakage were measured. Effect of B1 receptor siRNA on gene expression was also assessed. KEY RESULTS: mRNA levels of the kinin and VEGF systems were significantly enhanced at 2 weeks in streptozotocin (STZ)-retina compared to control-retina and were further increased at 6 weeks. B1 receptor mRNA levels remained increased at 6 months. B1 receptor immunolabelling was detected in vascular layers of the retina, on glial and ganglion cells. Intravitreal R-838 amplified B1 and B2 receptor gene expression, B1 receptor levels (immunodetection), leukostasis and vascular permeability at 2 weeks in STZ-retina. Topical application (eye drops) of R-954 reversed these increases in B1 receptors, leukostasis and vascular permeability. Intravitreal B1 receptor siRNA inhibited gene expression of kinin and VEGF systems in STZ-retina. Microgliosis was unaffected by R-838 or R-954 in STZ-retina. CONCLUSION AND IMPLICATIONS: Our results support the detrimental role of B1 receptors on endothelial and glial cells in acute and advanced phases of DR. Topical application of the B1 receptor antagonist R-954 seems a feasible therapeutic approach for the treatment of DR.

Characterization of retinal leukostasis and hemodynamics in insulin resistance and diabetes: role of oxidants and protein kinase-C activation.

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

Herbal cardiotonic pills prevent gut ischemia/reperfusion-induced hepatic microvascular dysfunction in rats fed ethanol chronically.

AIM: Cardiotonic Pill (CP), an oral herbal medicine that includes Danshen (Salviae Miltiorrhizae), Panax notoginseny and Dyroblanops aromatica gaertn, has been clinically used for vascular diseases such as occlusive vasculitis, coronary diseases, atherosclerosis, and cerebral infarction. The main component, Salviae Miltiorrhizae, has been reported to prevent cerebral and intestinal reperfusion injury. However, little is known about the effect of CP on hepatic microcirculation. Thus, this study aimed to determine whether CP could affect hepatic microvascular dysfunction elicited by gut ischemia/reperfusion (I/R) in rats fed ethanol chronically. METHODS: Male Wistar rats were pair-fed with a liquid diet containing ethanol or isocaloric control diet for 6 wk. After laparotomy, one lobe of the liver was examined through an inverted intravital microscope. The rats were exposed to 30 min of gut ischemia followed by 60 min of reperfusion. Rhodamine-6G-labeled leukocytes in the sinusoids were observed 90 min after the onset of superior mesenteric artery occlusion. Plasma tumor necrosis factor (TNF)-alpha and endotoxin levels were measured 1 h after the onset of reperfusion. Plasma alanine aminotransferase (ALT) activities were measured 6 h after the onset of reperfusion. In another set of experiments, CP (0.8 g/kg, intragastrically) was administered 1 and 24 h before the onset of ischemia. RESULTS: In control rats, gut I/R elicited increases in the number of stationary leukocytes, and plasma TNF-alpha and endotoxin levels and plasma ALT activities. These changes were mitigated by pretreatment with CP. In ethanol-fed rats, the gut I/R-induced increases in the number of stationary leukocytes, plasma endotoxin levels and ALT activities were enhanced. Pretreatment with CP attenuated the enhancement of gut I/R-induced responses by chronic ethanol consumption. CONCLUSION: These results suggest that CP prevents the gut I/R-induced hepatic microvascular dysfunction and hepatocellular injury. A reduction of inflammatory responses such as TNF-alpha production via reduction of blood endotoxin levels appears to be involved in the mechanisms. Chronic ethanol consumption enhances gut I/R-induced hepatic microvascular and hepatocellular injury. CP also attenuates an enhancement of gut I/R-induced responses by chronic ethanol consumption via the reduction of blood endotoxin levels.

Leukostasis Retinopathy: A New Clinical Manifestation of Chronic Myeloid Leukemia With Severe Hyperleukocytosis.

The authors report a new clinical manifestation of chronic myeloid leukemia. A 41-year-old man presented with significant visual loss, leading to a diagnosis of chronic myeloid leukemia. His white blood count exceeded that of any previously reported case of the disease with documented retinal findings (562,000/mm(3)), and clinical evaluation revealed the blockage of temporal retinal vessels by white blood cells. Hematologic findings resolved within 1 month of chemotherapy with dasatinib, and further treatment with intravitreal anti-VEGF agents resulted in the complete resolution of fundus findings. The authors propose that leukostasis retinopathy be recognized as a clinical manifestation of this life-threatening disease.

FT011, a Novel Cardiorenal Protective Drug, Reduces Inflammation, Gliosis and Vascular Injury in Rats with Diabetic Retinopathy.

Diabetic retinopathy features inflammation as well as injury to glial cells and the microvasculature, which are influenced by hypertension and overactivity of the renin-angiotensin system. FT011 is an anti-inflammatory and anti-fibrotic agent that has been reported to attenuate organ damage in diabetic rats with cardiomyopathy and nephropathy. However, the potential therapeutic utility of FT011 for diabetic retinopathy has not been evaluated. We hypothesized that FT011 would attenuate retinopathy in diabetic Ren-2 rats, which exhibit hypertension due to an overactive extra-renal renin-angiotensin system. Diabetic rats were studied for 8 and 32 weeks and received intravitreal injections of FT011 (50 µM) or vehicle (0.9% NaCl). Comparisons were to age-matched controls. In the 8-week study, retinal inflammation was examined by quantitating vascular leukocyte adherence, microglial/macrophage density and the expression of inflammatory mediators. Macroglial Müller cells, which exhibit a pro-inflammatory and pro-angiogenic phenotype in diabetes, were evaluated in the 8-week study as well as in culture following exposure to hyperglycaemia and FT011 (10, 30, 100 µM) for 72 hours. In the 32-week study, severe retinal vasculopathy was examined by quantitating acellular capillaries and extracellular matrix proteins. In diabetic rats, FT011 reduced retinal leukostasis, microglial density and mRNA levels of intercellular adhesion molecule-1 (ICAM-1). In Müller cells, FT011 reduced diabetes-induced gliosis and vascular endothelial growth factor (VEGF) immunolabeling and the hyperglycaemic-induced increase in ICAM-1, monocyte chemoattractant protein-1, CCL20, cytokine-induced neutrophil chemoattractant-1, VEGF and IL-6. Late intervention with FT011 reduced acellular capillaries and the elevated mRNA levels of collagen IV and fibronectin in diabetic rats. In conclusion, the protective effects of FT011 in cardiorenal disease extend to key elements of diabetic retinopathy and highlight its potential as a treatment approach.

Management of life-threatening pulmonary leukostasis with single agent imatinib mesylate during CML myeloid blast crisis.

Pulmonary leukostasis is a rare but serious and often fatal complication of chronic myeloid leukemia (CML) in blast crisis and acute myeloid leukemia. Treatment options are limited for these patients. Imatinib mesylate (STI-571, Gleevec, Novartis) is a potent and selective inhibitor of the BCR-abl tyrosine kinase, the molecular abnormality that causes CML. The case of a 74-year-old man with a history of CML who presented in myeloid blast crisis with pulmonary leukostasis characterized by increasing dyspnea, hypoxemia, fever, and impending respiratory failure is reported. The patient was treated with single agent imatinib mesylate (IM) with rapid decrease in his white blood cell count (WBC) and marked improvement in his respiratory status. No electrolyte abnormalities consistent with tumor lysis syndrome were observed. IM may be an effective single agent therapy for pulmonary leukostasis in patients with CML blast crisis who are at the risk for tumor lysis.

Silybin reduces obliterated retinal capillaries in experimental diabetic retinopathy in rats.

Silybin has been previously reported to possess anti-inflammatory properties, raising the possibility that it may reduce vascular damage in diabetic retinopathy. Present study was designed to investigate this potential effect of silybin and its underlying mechanisms in experimental diabetic retinopathy. Diabetes was induced with streptozotocin (STZ) plus high-fat diet in Sprague-Dawley rats, and silybin was administrated for 22 weeks after the induction of diabetes. Histochemical and immunofluorescence techniques were used to assess the obliterated retinal capillaries, leukostasis, and level of retinal intercellular adhesion molecule-1 (ICAM-1). Western blot was performed to quantitate the expression of retinal ICAM-1. Results showed that silybin treatment significantly prevented the development of obliterated retinal capillaries in diabetes, compared with vehicle treatment. In addition, leukostasis and level of the retinal ICAM-1 were found to decrease considerably in silybin-treated diabetic groups. In conclusion, these results indicate that silybin reduces obliterated retinal capillaries in experimental diabetes, and the recovered retinal vascular leukostasis and level of ICAM-1 at least partly contributes to the preventive effect of silybin.

Respiratory events at the earliest phase of acute myeloid leukemia.

Acute myeloid leukemia (AML) can result in acute respiratory failure (ARF) during the first days, requiring intensive care unit (ICU) admission in half the cases. We describe three leukemia-specific syndromes responsible for ARF: leukostasis, pulmonary leukemic infiltration (PLI) and acute lysis pneumopathy (ALP). We retrospectively analyzed clinical and laboratory data from 114 patients admitted to a medical ICU within 10 days after a diagnosis of AML. Respiratory events (REs) occurred in 95 patients and were leukemia-specific in 58 patients (61%). Day-28 mortality was 34.5% in patients with leukemia-specific REs (leukostasis, 41%; PLI, 23%; and ALP, 31%) and 48.6% in patients with other REs. By multivariate analysis, independent risk factors for death were age > 50 (odds ratio, 13; 95% confidence interval, 3-51), Eastern Cooperative Oncology Group (ECOG) status ≥ 2 (5.4; 1.8-17) and need for invasive mechanical ventilation (19; 5-75). Dexamethasone therapy was protective (0.26; 0.09-0.8), suggesting a role as a preventive treatment in patients with AML-related non-infectious pulmonary involvement.

Effects of p38 MAPK inhibition on early stages of diabetic retinopathy and sensory nerve function.

Purpose. p38 mitogen-activated protein kinase (MAPK) is known to play a regulatory role in inflammatory processes in disease. Inflammation has been linked also to the development of diabetic retinopathy in rodents. This study was conducted to evaluate the effect of a p38 MAPK inhibitor on the development of early stages of diabetic retinopathy in rats. Methods. Streptozotocin-diabetic rats were assigned to two groups-treated with the p38 MAPK inhibitor PHA666859 (Pfizer, New York, NY) and untreated-and compared with age-matched nondiabetic control animals. Results. At 2 months of diabetes, insulin-deficient diabetic control rats exhibited significant increases in retinal superoxide, nitric oxide (NO), cyclooxygenase (COX)-2, and leukostasis within retinal microvessels. All these abnormalities were significantly inhibited by the p38 MAPK inhibitor (25 mg/kgBW/d). At 10 months of diabetes, significant increases in the number of degenerate (acellular) capillaries and pericyte ghosts were measured in control diabetic rats versus those in nondiabetic control animals, and pharmacologic inhibition of p38 MAPK significantly inhibited all these abnormalities (all P < 0.05). This therapy also had beneficial effects outside the eye in diabetes, as evidenced by the inhibition of a diabetes-induced hypersensitivity of peripheral nerves to light touch (tactile allodynia). Conclusions. p38 MAPK plays an important role in diabetes-induced inflammation in the retina, and inhibition of p38 MAPK offers a novel therapeutic approach to inhibiting the development of early stages of diabetic retinopathy and other complications of diabetes.

Targeting leukostasis for the treatment of early diabetic retinopathy.

Leukocyte-endothelial interaction plays an important role in the early phase of the development of diabetic retinopathy. It has been studied extensively linking inflammatory processes to its development conducted to date in rats and mice, and have focused on insulin-deficient models. The molecular and functional changes that are characteristics of inflammation have been detected in retinas from diabetic animals and humans with involvement of multiple pathways that results in the final sequelae of increased permeability of the blood retinal barrier and finally ischemia that drives angiogenesis. Increased expression of Intracellular adhesion molecules heralds the onset of changes that results in attraction of leucocytes such as neutrophils. The consequent release of cytokines and growth factors such as vascular endothelial growth factor (VEGF), tumor necrosis factor-alpha, and interleukin 1-Beta results in increased permeability and retinal edema. Other indirect mediators involved include pathways such as the protein kinase C (PKC), renin-angiotensin system, enzymes such as the poly ADP-ribose polymerase, 3-hydroxy-3-methylglutaryl-coenzyme A reductase, nitric oxide synthetase and finally advanced glycation products. Therapy for early diabetic retinopathy may inhibit one or more of these pathways using drugs that can be given systemically, with local ocular applications having a more direct effect as in other eye diseases.

Anti-inflammatory and antioxidant effects of SERPINA3K in the retina.

PURPOSE: Previous studies by the authors have shown that retinal levels of SERPINA3K, a serine proteinase inhibitor, are decreased in an animal model with diabetic retinopathy (DR). The purpose of this study was to investigate the function of SERPINA3K and its role in DR. METHODS: For the oxygen-induced retinopathy (OIR) model, newborn rats were exposed to 75% O(2) from postnatal day (P) 7 to P12. Cultured retinal cells were treated with CoCl(2) or 2% O(2) to induce hypoxia. CM-H2DCFDA was used to determine the intracellular reactive oxygen species (ROS) level. Inflammatory factors were measured using Western blot analysis or ELISA. RESULTS: Intravitreal injection of SERPINA3K significantly reduced retinal vascular leakage and leukostasis in the OIR model. SERPINA3K also prevented the hypoxia-induced decrease of occludin, a tight junction protein, in the OIR rat retina and in cultured retinal capillary endothelial cells and retinal pigment epithelial cells. Further, SERPINA3K blocked the overexpression of proinflammatory factors, such as VEGF, TNF-alpha, and ICAM-1, in the retina of the OIR model and in cultured retinal cells exposed to hypoxia. VEGF was downregulated by SERPINA3K at the transcriptional level. Knockdown of SERPINA3K by siRNA resulted in the overexpression of VEGF and TNF-alpha in cultured retinal cells. Moreover, SERPINA3K significantly decreased ROS generation and upregulated the expression and activity of manganese superoxide dismutase and glutathione levels, suggesting antioxidant activity. CONCLUSIONS: SERPINA3K is an endogenous anti-inflammatory factor, and its anti-inflammatory effects may be mediated through antioxidant activity. Decreased retinal levels of SERPINA3K may contribute to retinal inflammation in DR.

Effect of topical nipradilol on retinal microvascular leukocyte adhesion in diabetic rats.

BACKGROUND: Retinal leukostasis plays an important role in the pathogenesis of diabetic retinopathy. OBJECTIVES: We studied the effects of nipradilol, a topical antiglaucoma alphabeta-blocker and nitric oxide donor, on the retinal vascular leukocyte adhesion of rats with diabetes. METHODS: Diabetes was induced in seven Brown-Norway rats by one intravenous injection (65 mg/kg) of streptozotocin and confirmed by blood glucose levels >350 mg/dl 48 h after the injection. Nipradilol solution was instilled in the right eye and nipradilol-free base solution in the left eye for 3 weeks, after which the retinal microcirculation was evaluated by acridine orange leukocyte digital fluorography using laser scanning ophthalmoscopy. Leukocytes trapped in the retina were counted around the optic disc in a 5-disc-diameter area and compared between the right and the left eye. RESULTS: The mean retinal leukostasis count in the nipradilol-treated eyes (19 +/- 15 cells) was significantly lower than in the untreated eyes (49 +/- 19 cells; p < 0.0008). The diameter of the retinal artery in the eyes treated with nipradilol significantly increased (111 +/- 13.5%) compared with untreated eyes (p < 0.03). CONCLUSIONS: Topical nipradilol significantly reduced retinal leukostasis in the retinal microcirculation in diabetic rats and may be a prophylactic agent for early diabetic retinopathy through its nitric oxide donor effects on the microcirculation.