Protective effects of FK506 against glutamate-induced neurotoxicity in retinal cell culture.
OBJECTIVE
To examine the effects of FK506 on glutamate neurotoxicity in cultured retinal neurons.


METHODS
Experiments were performed with primary retinal cultures obtained from 17- to 19-day-old rat fetuses. To assess the effects of FK506 and other drugs on glutamate neurotoxicity, cultures were treated with a drug beginning 10 minutes before application of glutamate and continuing during the subsequent 10 minutes of glutamate exposure. The treated cells were then incubated for 1 hour in a drug-free and glutamate-free medium. After a 1-hour incubation, cell viability was quantitatively measured by the trypan blue exclusion method.


RESULTS
Brief exposure to glutamate markedly decreased cell viability. FK506 protected against glutamate neurotoxicity in a dose-dependent manner. Rapamycin is a competitive inhibitor of FK506 that binds FK506 binding protein. Simultaneous application of rapamycin and FK506 negated the protective effects of FK506. Cyclosporin A, which binds and inhibits calcineurin, mimicked the protective effects of FK506. Treatment with FK506 did not affect the intracellular maximum Ca2+ concentration induced by glutamate application. Although FK506 exhibited protective action against Ca2+ ionophore-induced neurotoxicity, it had no effect on nitric oxide-induced neurotoxicity. Treatment with FK506 reduced the activity of nitric oxide synthase (NOS).


CONCLUSIONS
FK506 protected against glutamate neurotoxicity by inhibiting NOS activity in cultured retinal neurons.
Kikuchi
M
M
Department of Ophthalmology and Visual Sciences, Graduate School of Medicine, Kyoto University, Japan.
Kashii
S
S
Mandai
M
M
Yasuyoshi
H
H
Honda
Y
Y
Kaneda
K
K
Akaike
A
A
D000818:Animals; D065095:Calcineurin Inhibitors; D002118:Calcium / Q000378:metabolism; D018929:Cell Culture Techniques; D002470:Cell Survival / Q000187:drug effects; D016572:Cyclosporine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005333:Fetus; D018698:Glutamic Acid / Q000633:toxicity*; D009474:Neurons / Q000187:drug effects* / Q000201:enzymology; D009569:Nitric Oxide / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000378:metabolism; D011090:Polyenes / Q000494:pharmacology; D051381:Rats; D012160:Retina / Q000187:drug effects* / Q000201:enzymology; D020123:Sirolimus; D016559:Tacrolimus / Q000037:antagonists & inhibitors / Q000494:pharmacology*
D065095:Calcineurin Inhibitors; D011090:Polyenes; D009569:Nitric Oxide; D018698:Glutamic Acid; D016572:Cyclosporine; D019001:Nitric Oxide Synthase; D002118:Calcium; D020123:Sirolimus; D016559:Tacrolimus