Blood-retinal Barrier Permeability Research Articles

Diversité des œdèmes maculaires

Macular edema typically occurs as the final ocular manifestation of many intraocular or systemic diseases with fluid collection within the macular layers due to the breakdown of the blood-retinal barrier. This could be chemically mediated by VEGF, because increased VEGF has been shown to increase blood-retinal barrier permeability, or mechanically induced by vitreomacular traction causing hemodynamic or retinal pigment epithelium pump disturbances. This article reviews the different clinical entities of macular edema, focusing on their physiopathological concepts and on the current therapeutic strategies for their management.

Intravitreal Triamcinolone Acetonide Inhibits Breakdown of the Blood-Retinal Barrier Through Differential Regulation of VEGF-A and Its Receptors in Early Diabetic Rat Retinas

OBJECTIVETo elucidate the mechanism of the unique beneficial effect of intravitreal steroid therapy on diabetic macular edema, we investigated the effect of locally administered triamcinolone acetonide (TA) on the expression of vascular endothelial growth factor (VEGF)-A and its receptors in retinas of rats with streptozotocin (STZ)-induced diabetes. We then correlated the expression of these proteins with breakdown of the blood-retinal barrier (BRB).RESEARCH DESIGN AND METHODSThirty-two eyes of 16 diabetic and nondiabetic rats were divided into four groups. TA was injected into the vitreous of the right eye, and saline was injected into the left eye (control) 3.5 weeks after induction of diabetes. Retinas were harvested 48 h following treatment. mRNA and protein expression of VEGF-A, VEGF-A receptor 1 (fms-like tyrosine kinase [FLT]-1), and VEGF-A receptor 2 (fetal liver kinase [FLK]-1) were determined by real-time RT-PCR and immunohistochemistry. BRB permeability was quantitated by measuring extravasated endogenous albumin and retinal thickness.RESULTSDiabetes-induced retinal thickness and albumin extravasation were significantly reduced in TA-treated diabetic retinas to a level similar to that in sham-treated nondiabetic eyes. A close correlation between albumin leakage and increased expression of both Vegf-a and Flk-1 was noted in the diabetic retinas. TA downregulated the expression of Vegf-a and Flk-1 but upregulated the expression of Flt-1. TA did not alter the expression of these genes in nondiabetic retinas.CONCLUSIONSIntravitreal injection of TA stabilizes the BRB in association with regulation of Vegf-a, Flk-1, and Flt-1 expression in retinas in the early stages of diabetes.

Inducible Nitric Oxide Synthase Isoform Is a Key Mediator of Leukostasis and Blood-Retinal Barrier Breakdown in Diabetic Retinopathy

Nitric oxide (NO) is involved in leukostasis and blood-retinal barrier (BRB) breakdown in the early stages of diabetic retinopathy (DR), but it is unclear which NO synthase (NOS) isoforms are primarily involved. In this study, the authors aimed to clarify the involvement of constitutive (eNOS, nNOS) and inducible NOS (iNOS) isoforms and the mechanisms underlying NO-mediated leukostasis and BRB breakdown. Diabetes was induced with streptozotocin for 2 weeks. Mice were treated with a NOS inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME), which shows a preference for constitutive isoforms over iNOS. Vessel leakage was assessed with Evans blue. Leukostasis was quantified in flat-mounted retinas with confocal microscopy, in vivo with a scanning laser ophthalmoscope, and in vitro in a retinal endothelial cell line. ICAM-1, occludin, and ZO-1 levels were assessed by Western blot, flow cytometry, or immunohistochemistry. Nitrotyrosine content was assessed by immunohistochemistry. Diabetes increased leukostasis within retinal vessels and BRB permeability, which were reduced by L-NAME. Similar effects were observed in diabetic iNOS knockout mice. In diabetic mouse retinas, ICAM-1 protein levels increased, whereas the immunoreactivity of tight junction proteins, occludin and ZO-1 decreased, in correlation with increased protein levels of all NOS isoforms. Those effects were prevented by L-NAME and also in diabetic iNOS knockout mice. High glucose and nitrosative/oxidative stress also increased leukostasis caused by ICAM-1 upregulation. These results indicate that the iNOS isoform plays a predominant role in leukostasis and BRB breakdown. The mechanism involves ICAM-1 upregulation and tight junction protein downregulation.

Progression of Diabetic Macular Edema: Correlation with Blood–Retinal Barrier Permeability, Retinal Thickness, and Retinal Vessel Diameter

To study the progression of diabetic macular edema (DME) in relation to baseline retinal thickness, retinal vascular leakage, and retinal trunk vessel diameters. In this single-center study, 45 patients were enrolled with 62 eligible eyes defined as having DME of a grade less than clinically significant macular edema (CSME). From the start, the patients were included in a multicenter study exploring the effect of ruboxistaurin versus placebo for 3.4 years. Subsequently, the patients were followed up for a mean of 5.7 years by optical coherence tomography, fundus photography, and vitreous fluorometry. Baseline values in eyes that progressed to photocoagulation treatment were compared with values from eyes that did not reach this endpoint. In the 22 eyes of 18 patients in which CSME was diagnosed and treated, mean retinal vascular leakage at baseline was 5.6 (95% CI 4.2-7.6) nm/s, whereas eyes that did not progress to photocoagulation had a significantly lower mean leakage at baseline of 3.4 (95% CI 2.7-4.3) nm/s. No significant difference was found for measures of baseline retinal thickness or summarized retinal trunk vessel diameters. Eyes that progressed to photocoagulation treatment (mean delay to treatment, 3.6 years) had significantly higher foveal thicknesses than did nonprogressing eyes, from 18 months after study initiation. Progression to photocoagulation treatment for CSME was associated with higher retinal vascular leakage at baseline, whereas baseline retinal vessel diameters and retinal thickness were comparable in progressing and nonprogressing eyes. Baseline leakage was the strongest predictor of progression from non-CSME to photocoagulation for CSME.

Manganese-Enhanced MRI Studies of Alterations of Intraretinal Ion Demand in Models of Ocular Injury

To provide proof-of-concept that the extent of intraretinal manganese uptake after systemic MnCl(2) injection, detected with manganese-enhanced MRI (MEMRI), assesses alterations in intraretinal ion demand in models of ocular insult. In Sprague-Dawley rats, retinal ion demand and thickness were measured from MEMRI data collected before, 4 hours after, or 1, 3, and 7 days after intraperitoneal injection of MnCl(2). Choroidal contribution or blood-retinal barrier permeability surface area product (BRB PS') was determined using MRI after Gd-DTPA injection. Ocular injury was evaluated 24 hours after intravitreal injection of phosphate-buffered saline (PBS, vehicle) or PBS + ouabain, or after intraperitoneal injection of sodium iodate. Manganese retinal toxicity was assessed by comparing full-field, white-flash electroretinographic (ERG) data obtained before and after systemic MnCl(2) administration. Rat choroidal thickness was measured from cross-sections prepared from paraformaldehyde-perfused adult rats. Comparing pre- and post-Gd-DTPA images demonstrated minimal choroidal contribution to intraretinal analysis. Intraretinal signal intensity returned to baseline by 7 days after MnCl(2) injection. After ouabain injection, receptor and postreceptor uptake of manganese were subnormal (P < 0.05). After sodium iodate exposure, intraretinal manganese uptake was supernormal (P < 0.05) and did not increase with increasing BRB PS'. ERG data did not show any effect of MnCl(2) on photoreceptor a-wave and postreceptor b-wave relative to baseline at either observation time. MEMRI measurements of uptake of systemically administered and nontoxic doses of manganese appear to be a powerful approach for measuring alteration in intraretinal ion demand in models of ocular injury.

Short‐term effects of intravitreal triamcinolone on retinal vascular leakage and trunk vessel diameters in diabetic macular oedema

To assess retinal vascular permeability and vessel diameter changes after intravitreal triamcinolone acetonide (IVTA) injection in eyes with persistent foveal thickening after photocoagulation for diabetic macular oedema (DMO). We calculated the blood-retinal barrier permeability as measured by vitreous fluorophotometry, artery and venous vessel diameter at the temporal vascular arcades as measured on digital fundus photos, and retinal thickness as measured by optical coherence tomography. Seven patients with type 2 diabetes and DMO were examined immediately before and 1 week after IVTA 2 mg. The study was designed as an open-label interventional case series using the fellow eyes as untreated controls. One week after IVTA, we observed that, compared with baseline values, blood-retinal barrier permeability had decreased to 27.2 +/- 3.6% (p < 0.0001), retinal artery diameter had decreased to 94.9 +/- 0.02% (p = 0.05), retinal vein diameter had decreased to 89.2 +/- 0.03% (p = 0.02) and foveal thickness had decreased to 68.7 +/- 6.9% (p = 0.004). Visual acuity (VA) improved by 7.4 +/- 2.2 letters (p = 0.01). No significant change was observed in control eyes except that mean VA deteriorated by 2.6 +/- 0.9 letters (p = 0.03). Changes in permeability were closely correlated to changes in retinal thickness (R = 0.84) and venoule diameter (R = 0.93) in treated eyes. Intravitreal injection of triamcinolone acetonide in eyes with DMO is followed by a marked reduction in retinal vascular leakage and a concomitant reduction in retinal vessel calibre.

Effect of calcium dobesilate on progression of early diabetic retinopathy: a randomised double-blind study

The study was carried out to confirm the effect of calcium dobesilate (CaD) compared to placebo (PLA) on the blood-retinal barrier (BRB) permeability in early diabetic retinopathy (DR). Adults with type II diabetes and early diabetic retinopathy (below level 47 of ETDRS grading and PVPR between 20 and 50x10(-6)/ min, plasma-free fluorescein) were included in this double-blind placebo-controlled study. Treatment was 2 g daily for 24 months. The primary parameter, posterior vitreous penetration ratio (PVPR), was measured every 6 months by fluorophotometry. Secondary parameters were fundus photography, fluorescein angiography and safety assessments. Metabolic control was performed every 3 months. A total of 194 patients started the treatment (98 CaD, 96 PLA) and 137 completed the 24-month study (69 CaD, 68 PLA). Both treatment groups were comparable at baseline, with ETDRS level 10 in about 59% of patients. Mean PVPR change from baseline after 24 months was significantly (P=0.002) lower in the CaD group [-3.87 (SD 12.03)] than in the PLA group [+2.03 (SD 12.86)], corresponding to a 13.2% decrease in the CaD group and a 7.3% increase in the PLA group. PVPR evolution was also analysed by HbA1c classes (<7%, between 7 and 9%, > or =9%) and results confirmed the superiority of CaD independently of the diabetes control level. A highly significant difference [CaD: -3.38 (SD 13.44) versus PLA: +3.50 (SD 13.70)] was also obtained in a subgroup of patients without anti-hypertensive and/or lipid-lowering agents (P=0.002 at 24 months). A further analysis of the secondary parameters showed significant changes in favour of CaD in the evolution from baseline to the last visit of haemorrhages (P=0.029), DR level (P=0.0006) and microaneurysms (P=0.013). Regarding safety, only 2.5% (n=5 patients/ events) of all adverse events reported were assessed as possibly or probably related to the test drug, while all serious adverse events were reported as unlikely. There was no statistical difference between groups. Calcium dobesilate 2 g daily for 2 years shows a significantly better activity than placebo on prevention of BRB disruption, independently of diabetes control. Tolerance was very good.

Deletion of Smooth Muscle α-Actin Alters Blood–Retina Barrier Permeability and Retinal Function

Vascular smooth muscle (SM) cells and pericytes are essential for normal vascular development. SM alpha-actin null mice were used to determine whether vascular SM and pericyte contractile functions, and not merely their presence, are necessary for vascular development, normal blood-retina barrier (BRB) permeability, and retinal function. Age-matched SM alpha-actin null and wild-type mice were analyzed. Retinal structure, vascular pattern, and SM cell and pericyte distribution were analyzed histologically. Retinal vascular permeability (RVP) was measured with the Evans blue dye method. Electroretinography (ERG) was performed to evaluate retinal function. Deletion of SM alpha-actin did not result in any alterations in retinal morphology, vascular pattern, or SM cell and pericyte ensheathing of vessels in SM alpha-actin null mice. A significant increase in RVP was observed in SM alpha-actin null mice at both postnatal day (P)50 and P75 (P<0.05 and P<0.001, respectively). ERG analysis demonstrated a significant reduction in both rod and cone function in SM alpha-actin null mice at P22, P45, and P75 (P<0.01 at all ages). These results demonstrate that SM alpha-actin in SM cells and pericytes is not necessary for the formation of a normal retinal vascular pattern; however, SM alpha-actin is necessary for SM cells and pericytes to interact with endothelial cells to form a fully functional BRB. These results are important in understanding the role of contractile gene expression in the maintenance and function of the BRB and may provide a model for studying pathologic conditions, such as diabetes, that alter the function of this barrier.

Superior Cervical Ganglionectomy Induces Changes in Growth Factor Expression in the Rat Retina

To determine whether sympathetic nerves regulate expression of known angiogenic growth factors. Surgical sympathectomy (SNX) was used to remove sympathetic innervation to the eye. Real-time PCR was used to measure steady state mRNA expression of VEGF, VEGFR-2, angiopoietin-1, and Tie2. Western blot analysis was performed to assess protein expression. Blood-retinal barrier (BRB) permeability surface area product (PS) was measured using enhanced MRI on a separate group of control and SNX rats. mRNA of both VEGF and VEGFR-2 decreased significantly at 6 weeks after SNX. VEGF protein expression also decreased significantly. VEGFR-2 protein was unchanged. Both angiopoietin-1 and Tie2 mRNA expression increased significantly after SNX. Immunoblot analysis showed that angiopoietin-1 protein expression coincided with its mRNA expression. Tie2 protein expression was unaffected. Sympathetic denervation did not significantly increase BRB PS. Surgical SNX results in a reduction in VEGF gene and protein expression, while increasing protein expression of Ang-1. These findings suggest that sympathetic nerves regulate the expression of angiogenic growth factors in rat retina.

Effect of Ruboxistaurin on Blood–Retinal Barrier Permeability in Relation to Severity of Leakage in Diabetic Macular Edema

The purpose of the study was to investigate the effect of orally administered ruboxistaurin (RBX, LY333531), a selective protein kinase C beta inhibitor, on the permeability of the blood-retinal barrier in patients with diabetic macular edema. Forty-one patients with diabetic macular edema were randomly assigned to an 18-month randomized, placebo-controlled, double-masked trial including four study arms (4, 16, or 32 mg/d RBX, or placebo). The RBX group comprised 30 patients (42 eyes) and the placebo group 11 patients (13 eyes). Retinal vascular leakage was assessed using vitreous fluorometry at baseline and after 3, 12, and 18 months. Statistical analysis of the effect of treatment accounted for repeated measurements and tested potential interaction with baseline permeability, HbA(1c), and arterial blood pressure. Statistical analysis and modeling demonstrated a significant interaction between RBX treatment at any dosage and baseline permeability (P = 0.032, mixed models). A threefold or higher increase in retinal vascular leakage at baseline was associated with a significant reduction (30%) in retinal vascular leakage after RBX treatment compared with placebo. Visual acuity was normal at baseline and remained unchanged throughout the study. RBX treatment was associated with a reduction of retinal vascular leakage in eyes that had diabetic macular edema and markedly elevated leakage at baseline. These data suggest that clinical benefit from RBX treatment may be most prominent in patients with severe macular edema at baseline, and trials investigating this therapy may benefit from stratification according to baseline leakage.

Statins Ameliorate Endothelial Barrier Permeability Changes in the Cerebral Tissue of Streptozotocin-Induced Diabetic Rats

Statins may have favorable effects on endothelial barrier function. The effect of rosuvastatin and simvastatin therapy (10 mg/kg) for 5 weeks on blood-brain barrier (BBB), blood-retinal barrier (BRB), and cardiac muscle permeability of streptozotocin-induced diabetic rats was studied. The size-selective permeability of different vascular beds to a group of fluorescein isothiocyanate dextrans of varying molecular weights was measured. The volume of distribution of 250-, 70-, and 40-kDa dextrans in the cerebral tissue of diabetic rats were significantly increased. The volume of distribution of these dextrans in cerebral tissue was normalized by both statins. Diabetes did not significantly alter the BRB, but both statins decreased the volume of distribution of 70- and 40-kDa dextrans in the retina. The volume of distribution of 40 kDa in cardiac muscle was increased in diabetes, and this change was prevented with statin treatment. Treatment with rosuvastatin and mevalonate (150 mg/kg in drinking water for 5 weeks) did not alter the volume of distribution measurements. We concluded that 1) diabetes in rats is associated with significant changes in the BBB permeability; 2) statin treatment improves the endothelial barrier function in cerebral tissue, retina, and cardiac muscle; and 3) this statin effect could not be attributed to HMGCoA reductase inhibition.

Dynamic contrast enhanced MRI in patients with diabetic macular edema: initial results

To assess the ability of dynamic contrast enhanced magnetic resonance imaging (DCE-MRI) to detect blood retinal barrier (BRB) damage in patients with diabetic macular edema (DME). DCE-MRI with 0.1 mmol Gd-DTPA was used to measure BRB permeability in 10 healthy and visually normal subjects and eight patients with DME, including five patients with non-clinically significant (NCS) DME and three patients with clinically significant (CS) DME. For each subject, the enhancement of the MRI signal intensity in the pre-macular vitreous was measured as a function of time following contrast injection. A linear regression analysis was performed on each subject and the slopes of the contrast enhancement functions were compared. The DCE-MRI procedure was well tolerated by all 18 subjects. However, in four subjects, excessive eye movements resulted in spurious results. Consequently, 78% (14/18) of the subjects provided usable data. The mean slope of the control group was not significantly ( p>0.05) different from zero (i.e. signal intensity in the pre-macular vitreous space was constant as a function of time post-contrast injection). For the diabetic patients, the average slope of the contrast enhancement function was significantly greater than in the control group ( p<0.01). Furthermore, for both diabetic sub-groups, the average slopes were greater ( p<0.05) than that for the control group but not significantly ( p>0.05) different from each other. This ‘proof of concept’ study demonstrated that DCE-MRI detects passive leakage through the BRB in diabetic patients with either NCS or CS macular edema. In future studies, DCE-MRI may be useful for early quantitative evaluation of drug treatment effects in patients with DME.

Dynamic contrast-enhanced MRI measurements of passive permeability through blood retinal barrier in diabetic rats.

To test the hypothesis that dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) provides a useful in vivo measure of passive blood retinal barrier permeability surface area product (BRB PS) in experimental diabetic retinopathy. BRB PS (cm(3)/min) was measured using DCE-MRI and Gd-DTPA (MW 590 Da) in urethane-anesthetized control rats, sodium iodate-treated rats, rats receiving intravitreally injected human serum albumin (HSA) or vascular endothelial growth factor/vascular permeability factor (VEGF/VPF), or in rats that were diabetic for 2, 4, 6, or 8 months. Sodium iodate-treated rats exhibited an eightfold increase (P < 0.05) in BRB PS compared to that in control animals. Furthermore, in iodate-treated rats, the average vitreous signal enhancement was linearly dependent on Gd-DTPA dose (r = 0.91, P < 0.0001). Six hours postinjection, VEGF/VPF-treated rats exhibited a threefold increase in BRB PS (P < 0.05) compared to eyes injected with HSA. In 2-, 4-, and 6-month diabetic rats, BRB PS was not significantly different (P > 0.05) from control BRB PS values. After 8 months of diabetes, a twofold increase (P < 0.05) in PS over control PS values was found. DCE-MRI demonstrated that the BRB becomes leaky immediately before death, possibly causing an artificial increase in retinal permeability in methods that require enucleation or retinal isolation to assess permeability. DCE-MRI provides a sensitive, noninvasive, and linear assay that accurately measures, without potential artifacts associated with death and enucleation, passive BRB PS in experimental diabetes. DCE-MRI BRB PS measurements are expected to provide a useful surrogate marker of drug treatment efficacy.

Fluorophotometric Evaluation of Blood-Retinal Barrier Permeability in Patients with Essential Hypertension

Aim: The fluorophotometric evaluation of the blood-retinal barrier (BRB) integrity in patients with essential hypertension (EH) without signs of BRB damage. Material and Methods: 55 subjects participated in the study: 36 patients with EH and 19 normotensive healthy volunteers; 22 men and 33 women. The protocol included ophthalmic examination, fluorescein angiography, fluorophotometry, laboratory tests (total cholesterol, LDL and HDL cholesterol, triglycerides, fibrinogen, serum creatinine concentration, fasting glucose concentration, oral glucose test), urinary cotinine concentration measurement and cotinine-creatinine ratio (CCR) calculation. Results: BRB permeability (P_BRB) in patients with EH was significantly higher than in the control group (2.24 ± 0.68 vs. 1.64 ± 0.64 nm/s; p = 0.003). In hypertensive patients with CCR >50 ng/mg, the P_BRB was significantly higher than the P_BRB in healthy volunteers not exposed to smoke (2.32 vs. 1.68 nm/s; p < 0.05). Conclusions: The P_BRB in patients with EH is significantly higher than that in the normotensive control group, which shows the damaging effect of EH on the BRB.

Macular alterations after small-incision cataract surgery

Purpose: To characterize macular edema that occurs after uneventful cataract surgery. Setting: Centre of Ophthalmology, University Hospital, Institute of Biomedical Research on Light and Image, Faculty of Medicine, University of Coimbra, Coimbra, Portugal. Methods: Thirty-two eyes of 32 patients had uneventful phacoemulsification with implantation of a foldable intraocular lens. Postoperatively, patients were examined at 3, 6, 12, and 30 weeks. The examinations included retinal leakage analysis (Zeiss CSLO), optical coherence tomography (Humphrey Instruments), and retinal thickness analysis (Talia Technology, Ltd.). Results were compared with those in a control group comprising healthy subjects. Results: Increases in retinal thickness (ie, over the mean ± 2 SD in the control group) reached a maximum at 6 weeks in 13 of 32 eyes (41%), after which recovery was progressive. At 30 weeks, all eyes had good visual acuity, but 7 eyes (22%) still had macular edema. The edema was located primarily in the central macular region. Leaking sites involving the vascular areas of the macula, which indicated areas of abnormal blood–retinal barrier permeability, were a frequent finding. The number of sites remained relatively stable during the first 12 weeks (88%) and decreased to 68% at 30 weeks, indicating a trend toward recovery. Conclusion: Macular edema after cataract surgery occurred primarily in the central region of the macula and was associated with the presence of leaking sites, which were located predominantly in the vascular regions of the central macula.

Transendothelial electrical resistance of bovine retinal capillary endothelial cells is influenced by cell growth patterns: an ultrastructural study.

The purpose of this study was to describe the ultrastructural features of an in vitro capillary endothelial cell model of blood-retinal barrier permeability and to relate morphological features with transendothelial electrical resistance. The electrical resistance of endothelial cell monocultures on small and large pore size polycarbonate Transwell filters was measured and compared with cocultures of endothelial cells and Müller cells. There was a wide variation in electrical resistance measurements with many preparations not achieving a functional barrier. The ultrastructural features associated with barrier function in vitro were studied by comparing cultures that exhibited a 'tight' or 'leaky' barrier when measured immediately prior to processing for electron microscopy. Preparations with low transendothelial electrical resistance were associated with irregular cell growth when studied morphologically. It was concluded that parallel light and electron microscopic studies are important for validation of in vitro models of vascular endothelial permeability.

Effects of Latanoprost on Blood-Retinal Barrier Permeability in Rabbits

Purpose: To investigate the effect of latanoprost (LP) on the inward and outward permeability (P_in and P_out) of the blood-retinal barrier (BRB). Methods: Four New Zealand white rabbits received topical LP (0.005%) once daily for 3 weeks in one eye and phosphate-buffered saline (PBS) in the fellow eye (topical group). Five New Zealand white rabbits were injected intravitreously with LP (0.1 ml, 0.005%) in one eye and PBS (0.1 ml) in the fellow eye (injection group). In the injection group, vitreous fluorophotometry (VFP) to estimate the P_in and differential vitreous fluorophotometry (DVF) to estimate the P_out were performed 60 min after LP was injected. After the baseline measurements, VFP and DVF were performed 60 and 180 min after intravenous injection of sodium fluorescein, respectively. Fluorescein (F) and fluorescein monoglucuronide (FG) concentrations were obtained by DVF, and the F/FG ratio was calculated as an index of the P_out. Results: In the topical group, there were no significant differences in the P_in or F/FG ratio between the LP- and the PBS-treated eyes. In the injection group, the P_in in the LP-treated eyes was significantly higher than in PBS-treated eyes (p < 0.05). There was no significant difference in the F/FG ratio between the two groups. Conclusion: Although we cannot exclude the effect of differences in species, the physiologic effect of LP, which increased the P_in, was seen in experimental studies. Because antiglaucoma drugs are generally used over an extended period, further clinical studies of the effect of LP on the BRB should be performed in patients who have BRB breakdown, such as in uveitis, and in patients who are pseudophakic and aphakic.

Fluorescein transport through the blood-aqueous and blood-retinal barriers in diabetic macular edema

Purpose. To investigate the integrity of the blood-aqueous barrier (BAB) and the blood-retinal barrier (BRB) in diabetic patients with clinically significant macular edema (CSME). Methods. The rate constant (Kd(F)) of the BAB and the permeability of the blood-retinal barrier for non-protein bound fluorescein were determined simultaneously by fluorometry. Results were analysed pairwise in diabetic patients (n = 25) with CSME in one eye and without CSME in the other eye. Results. Kd(F) for the eyes with CSME was significantly increased compared to eyes without CSME (444 · 10 -6 min -1 and 387 · 10 -6 min -1 respectively, p = 0.01). The passive permeability of the BRB was also significantly increased in CSME (5.7 nm/sec and 3.5 nm/sec respectively, p = 0.009, n = 19). Conclusions. Both the rate constant of the BAB and the BRB permeability were significantly increased in CSME indicating that eye-specific factors are common for both barriers in diabetic patients with CSME.

Inhibitory effects of bucillamine on increased blood-retinal barrier permeability in streptozotocin-induced diabetic rats

Purpose. To investigate the effect of bucillamine for prevention of increasing blood-retinal barrier (BRB) permeability in streptozotocin (STZ)-induced diabetic rats. Methods. The groups included control and STZ-induced diabetic rats treated with or without bucillamine. Six months after intervention, the concentrations of reduced and oxidative glutathione (GSH and GSSG) in the retina were measured biochemically. In addition, vitreous fluorescein, which leaks from the vessels after intravenous injection of fluorescein sodium, was measured to evaluate BRB permeability. To evaluate the scavenging ability against the reactive oxygen species (ROS) in vitro, the second-order rate constant for the reaction of bucillamine with ROS was estimated from the kinetics based on the rate constant for the reaction of ROS. Results. The BRB permeability was significantly higher (p = 0.01) in diabetic rats not treated with bucillamine, and bucillamine inhibited the BRB permeability. The GSH concentration and the GSH/GSSG ratio in the retinas decreased in diabetic rats not treated with bucillamine; bucillamine inhibited the decrease of the GSH concentrations. The ROS scavenging activity of bucillamine was similar with that of GSH. Conclusions. In diabetic retinas, oxidative stress might increase, which may be one of the causes of BRB breakdown. The antioxidant effects of bucillamine might take part in inhibition of increased permeability of the BRB in diabetes.

Effect of acetazolamide on outward permeability of blood-retina barrier using differential vitreous flyorophotometry

Purpose. To measure fluorescein (F) and fluorescein monoglucuronide (FG) concentrations in the vitreous and evaluate the effect of acetazolamide (AZM) on the outward permeability of the blood-retina barrier (BRB) using differential vitreous fluorophotometry (DVF). Methods. DVF was performed 180 minutes after intravenous injection of AZM (5 mg/kg) and 50 mg of sodium fluorescein in six rabbits (AZM group). DVF also was performed in six rabbits injected intravenously with only 50 mg of sodium fluorescein (control group). The F/FG ratio was calculated based on the concentrations of F and FG obtained by DVF. DVF also was performed 180 minutes after 50 mg of intravenous injection of sodium fluorescein in five rabbits given probenecid (150 mg/kg) intraperitoneally (probenecid group). Results. The average F/FG ratio was 0.36 ± 0.17 (range, 0.22–0.66) in the AZM group, which was significantly smaller than the control value of 0.74 ± 0.22 (range, 0.50–1.60). The average F/FG ratio at 180 minutes after injection was 1.51 ± 0.46 (range, 0.94–2.00) in the probenecid group, which was significant higher (p < 0.05) than that of the AZM or control group. Conclusions. This study showed that the F/FG ratio might be a good indicator of the estimated outward permeability of the BRB using DVF and that AZM may accelerate the outward active transport function of the BRB.