A study of the ability of tissue plasminogen activator to diffuse into the subretinal space after intravitreal injection in rabbits.
OBJECTIVE
Intravitreal injections of tissue plasminogen activator have been used to lyse fibrin from blood in the subretinal space, despite the lack of proof that tissue plasminogen activator can diffuse across the retina. We tested whether tissue plasminogen activator injected into the vitreous could penetrate the neural retina and enter the subretinal space.


METHODS
We injected a mixture of 50 microg of tissue plasminogen activator (70 kD) labeled with fluorescein isothiocyanate and rhodamine B isothiocyanate-labeled dextran, which has a lower molecular weight (20 kD), into the midvitreous cavity of one eye in each of 18 rabbits. The eyes were enucleated after 3, 6, and 24 hours, and cryosections were examined with epifluorescent microscopy to determine the distribution of the labeled molecules. We also evaluated tissue plasminogen activator pharmacokinetics in one eye each of 18 rabbits in which a subretinal clot was induced by injecting autologous blood (50 microL) into the subretinal space through the sclera. Fluorescein isothiocyanate-labeled tissue plasminogen activator was injected into the vitreous 2 days after induction of the subretinal clot.


RESULTS
Fluorescein isothiocyanate-labeled tissue plasminogen activator was present at the vitreal surface of the retina in a linear array in all 36 eyes studied, whereas the rhodamine B isothiocyanate-labeled dextran had diffused throughout the neural retina in the same sections. No fluorescein isothiocyanate signal was observed in the neural retina or in the subretinal clot. Vitreous hemorrhage caused by retinal perforation was observed in all eyes with intraretinal hemorrhage in which fluorescein isothiocyanate fluorescence was seen in the neural retina and inside the clot.


CONCLUSIONS
Intravitreal tissue plasminogen activator did not diffuse through the intact neural retina to reach a subretinal clot. This study demonstrates no scientific rationale for the intravitreal tissue plasminogen activator treatment of submacular hemorrhage without vitreous hemorrhage presumably caused by an overlying retinal break.
Kamei
M
M
Cole Eye Institute and Division of Ophthalmology, The Cleveland Clinic Foundation, Ohio 44195, USA.
Misono
K
K
Lewis
H
H
D000818:Animals; D004058:Diffusion; D004195:Disease Models, Animal; D005343:Fibrinolytic Agents / Q000493:pharmacokinetics*; D016650:Fluorescein-5-isothiocyanate / Q000493:pharmacokinetics; D005456:Fluorescent Dyes / Q000493:pharmacokinetics; D007267:Injections; D008856:Microscopy, Fluorescence; D010960:Plasminogen Activators / Q000493:pharmacokinetics*; D011817:Rabbits; D011994:Recombinant Proteins / Q000493:pharmacokinetics; D012160:Retina / Q000378:metabolism* / Q000473:pathology; D012166:Retinal Hemorrhage / Q000378:metabolism* / Q000473:pathology; D012171:Retinal Vessels / Q000293:injuries; D012235:Rhodamines / Q000493:pharmacokinetics; D012421:Rupture; D010959:Tissue Plasminogen Activator / Q000493:pharmacokinetics*; D014822:Vitreous Body / Q000378:metabolism* / Q000473:pathology; D014823:Vitreous Hemorrhage / Q000209:etiology
D005343:Fibrinolytic Agents; D005456:Fluorescent Dyes; D011994:Recombinant Proteins; D012235:Rhodamines; C027755:rhodamine isothiocyanate; D010960:Plasminogen Activators; D010959:Tissue Plasminogen Activator; D016650:Fluorescein-5-isothiocyanate