Histologic localization of indocyanine green dye in aging primate and human ocular tissues with clinical angiographic correlation

OBJECTIVE

This study aimed to histologically localize indocyanine green (ICG) dye in the geriatric primate and human eye and to correlate these findings with clinical ICG angiography.

DESIGN

The study design was a clinicopathologic correlation.

PARTICIPANTS

Six eyes of three geriatric monkeys (Maccaca mulatta) with macular drusen, 19 to 29 years of age, housed at the California Primate Research Center and an enucleated human eye from a 66-year-old patient with choroidal melanoma were examined.

INTERVENTION

All six monkey eyes and the human eye underwent clinical ICG angiography. Five monkey eyes were enucleated at varying intervals after intravenous ICG dye injection for histologic examination. One monkey eye was removed without prior ICG injection as an age-matched control. The human eye was enucleated after intravenous injection of ICG dye.

MAIN OUTCOME MEASURES

Infrared fluorescence microscopy of freeze-dried tissue sections was performed to detect ICG fluorescence. Histologic sections were stimulated with an 810-nm diode laser, and the fluorescence emitted was detected with a Hamamatsu infrared camera. The images were digitally recorded. The distribution of fluorescence on histologic examination was correlated with the fluorescence of the clinical ICG angiogram.

RESULTS

Infrared fluorescence microscopy of monkey sections localized fluorescence within retinal and choroidal vessels early after injection of ICG dye. The ICG fluorescence was seen in the extravascular choroidal stroma within 10 minutes after injection. The stromal fluorescence persisted in sections obtained 50 minutes after injection of ICG. The retinal pigment epithelium (RPE)-Bruch's membrane complex was brightly fluorescent in the middle- and late-stage histologic sections. Drusen deposits were brightly fluorescent at all timepoints examined. Similar findings were observed in freeze-dried tissue sections of the human eye. The fluorescence detected on histologic sections correlated closely with the fluorescence of the clinical ICG angiograms for the same interval.

CONCLUSIONS

The ICG dye does not remain solely within the choroidal intravascular space but extravasates into the choroidal stroma and accumulates within the RPE. Extravascular ICG binds to drusen material. These findings will enhance the interpretation of clinical ICG angiography.

Retinal degeneration in transgenic mice with photoreceptor-specific expression of a dominant-negative fibroblast growth factor receptor

Mutant cDNAs coding for dominant-negative forms of the fibroblast growth factor receptors 1 (FGFR-1) and 2 (FGFR-2) that lack tyrosine kinase activity were ligated to a 2.2 kb DNA fragment containing the bovine rhodopsin promoter and used to generate transgenic mice. Six independent lines were generated with the FGFR-1 construct, and five were generated with the FGFR-2 construct. Five of the six FGFR-1 mutant lines and all five FGFR-2 mutant lines showed transgene expression in the retina by reverse transcription-PCR. By both in situ hybridization and immunohistochemistry, mutant FGFRs were found to be expressed specifically in photoreceptors of transgene-positive FGFR-1 and FGFR-2 mice. Lines expressing the FGFR-2 mutant showed progressive photoreceptor degeneration; the retinas showed minimal or no abnormalities at 1 month, but by 2 months they showed focal areas of thinning of the outer nuclear layer and disruption of photoreceptors. By 2-4 months, areas of complete loss of photoreceptors were seen. These abnormalities were not seen in control littermates not expressing the transgene. Mice from two FGFR-1 mutant lines showed focal areas of thinning of the outer nuclear layer and numerous photoreceptors with fragmented chromatin, whereas the other FGFR-1 lines showed minimal or no abnormalities. These data indicate that perturbation of FGF signaling in photoreceptors is associated with progressive photoreceptor degeneration, suggesting that one or more of the FGFs may act as a survival factor for photoreceptor cells.

Comparison of techniques for transscleral diode photocoagulation in the rabbit

PURPOSE

To assess the optimum probe design and treatment parameters for transscleral diode laser retinopexy.

METHODS

Transscleral diode photocoagulation was performed on the eyes of Dutch-belted rabbits using three different transscleral probes: a straight, 400-microns diameter probe; a prism-tipped 400-microns diameter probe; and a prism-tipped 900-microns diameter probe.

RESULTS

Transscleral diode photocoagulation with all three probe types was an effective method of ablating the retina and creating chorioretinal adhesions. Both the burn diameter and the mean radiant output energy requirement increased as the burn duration and probe aperture diameter was increased. Explosive retinal holes were encountered in 12% of the burns created with the straight probe. The use of the prism-tipped probes significantly reduced the incidence of retinal holes to < 4% (P < 0.005). Histopathologically, all burns were grade III in intensity with severe choroidal injury. In many of the burns, there was histopathologic evidence of thermal injury to the inner sclera. The frequency of these inner scleral changes was reduced with a long burn duration (5 seconds).

CONCLUSION

This study confirms that diode transscleral photocoagulation is a feasible method of thermal retinopexy. The use of the prism-tipped probes and long duration burns resulted in the fewest adverse reactions.

Low glutathione reductase and peroxidase activity in age-related macular degeneration

Age-related macular degeneration (ARMD) may result from events initiated by reactive oxygen species. Blood samples from 18 patients with ARMD and 18 similarly aged controls were analysed for activities of important antioxidants. Blood glutathione reductase activity was lower in patients with ARMD compared with controls (p = 0.035). The activities of glutathione peroxidase (p = 0.18) and erythrocyte superoxide dismutase (p = 0.29) were similar between the two groups by a Student's two sample t test. Logistic regression was used to determine which enzyme activities were associated with ARMD after adjusting for possible confounding variables: smoking history, age, multivitamin use, and cardiovascular disease. Glutathione reductase activity (p = 0.05) and glutathione peroxidase activity (p = 0.065) were significantly associated with ARMD by this analysis. The relation of glutathione reductase and glutathione peroxidase activity to ARMD merits further study.

Serum is chemotactic for retinal-derived glial cells

Retinal glial cells participate in nearly all proliferative retinopathies. Little is known about factors that can stimulate these cells to migrate from the retina and proliferate. We cultured retinal glial cells from immature rats and observed the migratory and proliferative responses to serum (0% to 10%) and two of its components, platelet-derived growth factor (PDGF) (0 to 30 ng/mL) and fibronectin (0 to 20 mg/L). We found that 1% serum causes a fivefold increase in migration of the retinal glia and a 170% increase in proliferation over baseline. Fibronectin caused a threefold increase in migration at 30 mg/L, and PDGF caused a fourfold increase at 20 ng/mL, but only PDGF caused an increase in proliferation (300% at 10 ng/mL).

Resolution and activity of adenylate cyclase components in a zwitterionic cholate derivative [3-[(3-cholamidopropyl) dimethylammonio]-1-propanesulfonate]

Bovine brain adenylate cyclase was solubilized with 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS), sodium cholate, sodium deoxycholate, or these detergents plus (NH4)2SO4. The specific activity of the extract obtained with 13 mM CHAPS alone was several times those of the other detergent extracts with or without (NH4)2SO4. After solubilization with 13 mM CHAPS, gel filtration completely separated the catalytic unit (C) from the guanine nucleotide binding protein (G/F). C activity when assayed with 5 mM Mn2+ was 5 times that assayed with 10 mM Mg2+ and was unresponsive to GPP(NH)P. C activity was increased approximately 150% by GPP(NH)P in the presence of G/F extracted from human erythrocyte ghosts and approximately 100% by Ca2+ plus calmodulin in assays with Mg2+. On gel filtration and/or density gradient centrifugation, the physical properties of C from brain or AC- cells and G/F from bovine or pig erythrocytes in CHAPs were similar to those observed in other detergents. It appears that the use of CHAPS for solubilization of adenylate cyclase and separation of C and G/F may well prove advantageous in studies of the molecular interactions between the protein subunits and activators of the enzyme as well as for the initial purification of C.