The influence of intraocular pressure on the transscleral diffusion of high-molecular-weight compounds.

PURPOSE: To evaluate the effects of intraocular pressure on the permeability of the human sclera to high-molecular-weight compounds. METHODS: Human transscleral permeability to FITC-albumin (70 kDa) and 70-kDa and 150-kDa FITC-dextran was determined at transscleral pressures from 0 to 60 mm Hg. For each compound at each pressure, six to eight experiments were performed. Scleral sections were mounted in a two-compartment perfusion chamber. Temperature was maintained at 37 degrees C. Fractions of choroidal perfusate were collected, and fluorescence was measured with a spectrofluorometer. From these data, scleral permeability K(trans) (in centimeters per second) was calculated. RESULTS: Permeability to FITC-albumin was decreased by approximately one half when pressure was elevated from 0 to 30 mm Hg (P < 0.05). No significant differences in permeability to 70-kDa FITC-dextran were observed at pressures from 0 to 60 mm Hg. Permeability to 150-kDa FITC-dextran decreased by a little more than one half when transscleral pressure was raised from 0 to 15 mm Hg and was approximately 10 times lower at 60 mm Hg than at 0 mm Hg (P < 0.01). CONCLUSIONS: Human sclera was permeable to compounds with a molecular weight of up to 150 kDa at transscleral pressures ranging from 0 to 60 mm Hg. Transscleral diffusion was relatively unaffected by the pressure gradient, although for 150-kDa FITC-dextran at 60 mm Hg a 10-fold decrease was observed compared with that at 0 mm Hg. These experiments suggest that high-molecular-weight compounds (e.g., immunoglobulins and oligonucleotides) could be effectively delivered transsclerally to the intraocular tissues under circumstances of physiological or elevated intraocular pressure.

In vitro sustained human transscleral drug delivery of fluorescein-labeled dexamethasone and methotrexate with fibrin sealant.

PURPOSE: To study the use of fibrin sealant as a drug delivery system for the sustained transscleral delivery of dexamethasone and methotrexate. METHODS: Scleral sections excised from moist-chamber-stored human globes were mounted in a perfusion chamber. Dexamethasone-fluorescein or methotrexate-fluorescein in either fibrin sealant or balanced salt solution (BSS) was applied to the episcleral surface. BSS was perfused to the choroidal side, fluorescence was measured in perfusate fractions, and an apparent scleral permeability P(A) was calculated for each solute-vehicle combination. RESULTS: P(A) for both compounds was significantly lower with fibrin sealant delivery compared to delivery in BSS (p < 0.001). However, the fibrin sealant vehicle provided a more sustained release of both drugs through 24 hr. CONCLUSIONS: Incorporating dexamethasone and methotrexate into a fibrin sealant provided a more gradual drug delivery and a more uniform delivery compared to dissolving these drugs in BSS. Fibrin sealant could be useful for transscleral delivery for posterior segment disease.

Subconjunctival carboplatin in fibrin sealant in the treatment of transgenic murine retinoblastoma.

PURPOSE: To evaluate the efficacy of subconjunctival carboplatin in fibrin sealant in the treatment of transgenic murine retinoblastoma. DESIGN: Experimental study using LHbeta-Tag transgenic mice in a randomized controlled trial. PARTICIPANTS AND CONTROLS: Thirty-three 10-week-old LHbeta-Tag transgenic mice: 22 carboplatin-treated animals and 11 control animals. METHODS: Three groups of 11 mice were treated with a single, 30 microl injection of fibrin sealant in the subconjunctival space of 1 eye; the opposite eye was left untreated as an internal control. Group 1 (low-dose group) received 37.5 mg/ml calculated concentration of carboplatin in fibrin sealant (0.66 mg measured total dose). Group 2 (high-dose group) received 75 mg/ml calculated concentration of carboplatin in fibrin sealant (1.23 mg measured total dose). Group 3 (control group) received fibrin sealant only. Mice were killed on day 22 after treatment. Eyes were serially sectioned, and retinal tumor burden was quantified by histopathologic analysis. For statistical analysis of treatment effects, eyes were divided into 6 groups: low-dose group, sealant-treated eyes; low-dose group, untreated eyes; high-dose group, sealant-treated eyes; high-dose group, untreated eyes; control group, sealant-treated eyes; and control group, untreated eyes. MAIN OUTCOME MEASURES: Main outcome measure was mean tumor burden per level per eye in each experimental group. RESULTS: The best therapeutic results were obtained in eyes treated with low-dose carboplatin in fibrin sealant, where no histopathologic evidence of toxicity was observed, and 6 of 11 eyes had zero tumor burden. Tumor burden in the remaining 5 eyes in this group was minimal (4 eyes) or moderate (1 eye) compared with mean control values. Mean tumor burden in this group was significantly smaller than mean tumor burden in untreated eyes from the same mice (P<0.004), sealant-treated eyes in the control group (P<0.004), and untreated eyes in the control group (P<0.002). Although a similar reduction in mean tumor burden was observed in eyes treated with high-dose carboplatin in fibrin sealant, 5 of 10 eyes analyzed in this group also demonstrated histopathologic evidence of severe toxicity. CONCLUSIONS: Subconjunctival carboplatin in fibrin sealant is effective in the treatment of transgenic murine retinoblastoma. A single injection of low-dose carboplatin in fibrin sealant was sufficient to induce complete or near-complete intraocular tumor regression in 10 of 11 eyes (91%), with no associated histologic evidence of toxicity. These results suggest that subconjunctival carboplatin in fibrin sealant provides sustained release and could have clinical use in the treatment of intraocular retinoblastoma.

Retinal function after subconjunctival injection of carboplatin in fibrin sealant.

PURPOSE: To evaluate retinal function in a rabbit model after subconjunctival delivery of carboplatin in balanced saline solution (BSS) or fibrin sealant to determine possible retinal toxicity. METHODS: One group of rabbits (n = 5) received a unilateral subconjunctival injection of 12.2 +/- 1.0 mg/mL of carboplatin (Paraplatin) in BSS. Another group of rabbits (n = 5) received 25.1 +/- 7.7 mg/mL of carboplatin in fibrin sealant (Hemaseel APR). Rabbits injected with fibrin sealant only (n = 2) and BSS only (n = 2) were used as control groups. Electroretinographic recordings consisted of a series of intensities presented under dark- and light-adapted conditions. Electroretinograms were recorded before the injection (baseline) and 2 days, 1, 2, and 3 weeks after the injection. After 3 weeks, all rabbit eyes were obtained for histopathologic examination. RESULTS: Transient reductions in the dark-adapted b-wave amplitudes were noted 2 days after treatment for eyes injected with carboplatin compared with the vehicle-only treatment groups. Other treatment groups and postinjection time points showed no significant changes from baseline. Retinal structure and thickness were normal 3 weeks after treatment for all treatment groups. CONCLUSION: Subconjunctival delivery of carboplatin in fibrin sealant or BSS does not have a toxic effect on retinal function or structure in a non-tumor-bearing rabbit model at the doses used in this study at 3 weeks' follow-up.

Transscleral permeability and intraocular concentrations of cisplatin from a collagen matrix.

This study determined the in vitro permeability of cisplatin through isolated human sclera as delivered by a collagen matrix vehicle. Short-term and long-term intraocular levels of cisplatin were also measured in the rabbit eye after a subconjunctival injection. Cisplatin in either a collagen matrix vehicle or a control balanced salt solution (BSS) vehicle was applied to human sclera mounted in a specially designed in vitro perfusion chamber. The amount of cisplatin that diffused across the sclera was measured in hourly samples for 24 h using atomic absorption spectrometry. In vivo studies were also performed in Dutch Belted rabbits given subconjunctival injections of cisplatin in collagen matrix or in BSS. Eyes were enucleated at 1.5 h and 2 weeks after injection, frozen, and dissected to determine the intraocular cisplatin concentrations. Cisplatin had a peak in vitro scleral permeability constant of 8.3+/-1.2 x 10(-6) and 20.1+/-1.8 x 10(-6) cm/s, delivered in collagen matrix and in BSS, respectively (mean+/-S.D.). At the end of the in vitro experiments, 35.9+/-4.6% of the cisplatin remained in the collagen matrix, while 0.8+/-0.2% remained in the BSS vehicle. Subconjunctival injection of cisplatin in the collagen matrix vehicle achieved 3.3+/-0.1 microg/ml in the vitreous humor at 1.5 h and 0.1+/-0.1 microg/ml at 2 weeks. This vehicle also achieved a cisplatin concentration of 73.5+/-23.9 microg/mg in the choroid and retina at 1.5 h and 3.2+/-1.3 microg/mg at 2 weeks. Compared to BSS, the collagen matrix vehicle provided a more controlled release of cisplatin, and after subconjunctival injection into rabbits, attained higher drug levels in several ocular tissues.

Transscleral diffusion of carboplatin: an in vitro and in vivo study.

OBJECTIVES: To compare the in vitro scleral permeability of carboplatin using either a fibrin sealant or a balanced salt solution (BSS) vehicle and to measure in vivo ocular tissue levels following subconjunctival injection of carboplatin in fibrin sealant or BSS. METHODS: The permeability of carboplatin in fibrin sealant or BSS through human eye bank sclera was tested using an in vitro perfusion apparatus. Levels of carboplatin permeating the sclera were measured every hour for 24 hours using atomic absorption spectrometry. In vivo studies were performed in Dutch Belted rabbits injected subconjunctivally with carboplatin in either fibrin sealant or BSS; eyes were enucleated at 1(1/2) hours, 48 hours, and 2 weeks after injection, and levels of carboplatin were measured in various tissues. RESULTS: In vitro carboplatin in fibrin sealant had a peak permeability constant of 13.7 +/- 2.3 x 10(-6) cm/s; carboplatin in BSS, 27.0 +/- 1.7 x 10(-6) cm/s. After 24 hours, 33.2% +/- 1.8% of the carboplatin was retained in the fibrin sealant, while 5.5% +/- 1.0% was retained in the BSS. In vivo subconjunctival injection of carboplatin in fibrin sealant vehicle achieved 11.83 +/- 5.16 microg/mL in the vitreous at 1(1/2) hours and 0.03 +/- 0.06 microg/mL in the vitreous at 2 weeks. The fibrin sealant also attained 396.59 +/- 177.84 microg/mg in the choroid and retina at 1(1/2) hours and 3.38 +/- 1.97 microg/mg in the choroid and retina at 2 weeks. (Data are given as mean +/- SEM.) CONCLUSION: Fibrin sealant provided a more controlled and localized release of carboplatin and delivered carboplatin to the ocular tissues for up to 2 weeks. CLINICAL RELEVANCE: This study reports the use of fibrin sealant as a subconjunctival delivery vehicle for carboplatin, and quantifies ocular drug levels achieved in an animal model.