Polychromatic angiography for the assessment of VEGF-induced BRB dysfunction in the rabbit retina.

PURPOSE: To determine the utility of polychromatic angiography (PCA) in the assessment of VEGF-induced blood retinal barrier (BRB) dysfunction in rabbits. METHODS: Twenty-six eyes of 24 Dutch Belted rabbits were injected intravitreally with 1.25 µg (group A, n = 5), 10 µg (group C, n = 7), or 4 µg (group B, n = 6; group D, n = 4; and group E, n = 4) of VEGF on day 0. Groups D and E were also injected intravitreally with 1.25 µg and 12.5 µg bevacizumab, respectively, on day 2. On days 0, 2, 4, 7, 11, and 14, PCA was performed using a contrast agent mixture composed of fluorescein sodium, indocyanine green, PCM102, and PCM107 and imaged with a modified fundus camera. PCA scores were based on detected leaking fluorophores. RESULTS: On day 7, there was a statistically significant difference between PCA scores of group A (0.6 ± 0.89) and both groups B (2.67 ± 1.37, P = 0.0154) and C (3.33 ± 0.52, P = 0.00085). There was also a statistically significant difference between groups B and E (PCA score 0.75 ± 0.96, P = 0.032) on day 7. On day 11, there was statistically significant difference between group C (1.80 ± 1.1) and both groups A (0, P = 0.021) and B (0.33 ± 0.52, P = 0.037). CONCLUSIONS: A differential response to both increasing VEGF dose and administration of bevacizumab could be discerned using the PCA. PCA allowed stratification of VEGF-induced BRB dysfunction and inhibitory effects of bevacizumab therapy in the rabbit retina.

In vivo assessment of the permeability of the blood-brain barrier and blood-retinal barrier to fluorescent indoline derivatives in zebrafish.

BACKGROUND: Successful delivery of compounds to the brain and retina is a challenge in the development of therapeutic drugs and imaging agents. This challenge arises because internalization of compounds into the brain and retina is restricted by the blood-brain barrier (BBB) and blood-retinal barrier (BRB), respectively. Simple and reliable in vivo assays are necessary to identify compounds that can easily cross the BBB and BRB. METHODS: We developed six fluorescent indoline derivatives (IDs) and examined their ability to cross the BBB and BRB in zebrafish by in vivo fluorescence imaging. These fluorescent IDs were administered to live zebrafish by immersing the zebrafish larvae at 7-8 days post fertilization in medium containing the ID, or by intracardiac injection. We also examined the effect of multidrug resistance proteins (MRPs) on the permeability of the BBB and BRB to the ID using MK571, a selective inhibitor of MRPs. RESULTS: The permeability of these barriers to fluorescent IDs administered by simple immersion was comparable to when administered by intracardiac injection. Thus, this finding supports the validity of drug administration by simple immersion for the assessment of BBB and BRB permeability to fluorescent IDs. Using this zebrafish model, we demonstrated that the length of the methylene chain in these fluorescent IDs significantly affected their ability to cross the BBB and BRB via MRPs. CONCLUSIONS: We demonstrated that in vivo assessment of the permeability of the BBB and BRB to fluorescent IDs could be simply and reliably performed using zebrafish. The structure of fluorescent IDs can be flexibly modified and, thus, the permeability of the BBB and BRB to a large number of IDs can be assessed using this zebrafish-based assay. The large amount of data acquired might be useful for in silico analysis to elucidate the precise mechanisms underlying the interactions between chemical structure and the efflux transporters at the BBB and BRB. In turn, understanding these mechanisms may lead to the efficient design of compounds targeting the brain and retina.

Size-selective and in vitro assessment of inner blood retina barrier permeability.

Assessment of tight junction integrity in vitro is fundamental when studying molecular processes that may be implicated in barrier dysfunction. At the blood brain and inner blood retina barrier (BBB and iBRB, respectively) adjacent endothelial cells lining the microvasculature have been shown to have very low rates of fluid phase transcytosis and high electrical resistances, due in part to the expression of tight junction proteins at the apical periphery of these cells. While these high electrical resistances are difficult to achieve in vitro, owing to complex interactions of endothelial cells in vivo with astrocytes and pericytes, it is possible to make an assessment of paracellular permeability when cells are analysed on a number of different fronts. In this regard, we will outline here a method for determining trans-endothelial electrical resistance, tracer molecule diffusion, and tight junction protein localization in primary cultures of bovine retinal microvascular endothelial cells. This system allows for the screening of a wide range of pro- and anti-angiogenic molecules in an in vitro model of the iBRB and can accurately assess the role individual tight junction proteins play in maintaining tight junction integrity in response to various cell stimuli.