Pyroglutamic acid promotes survival of retinal ganglion cells after optic nerve injury.
OBJECTIVE
To determine whether pyroglutamic acid (PGA) enhances the survival of retinal ganglion cells (RGCs) after optic nerve (ON) transection in vivo and RGCs in culture.


METHODS
The RGCs of rats were retrogradely labeled by Fluorogold (FG)-soaked sponges placed on both superior colliculi. Seven days later, the ON was transected, and PGA was immediately injected into the vitreous. Seven or fourteen days later, the number of FG-labeled RGCs was counted on flat-mounted retinas to obtain the mean densities of FG-labeled RGCs. To determine whether the survival effect of PGA was related to excitatory amino acid transporter (EAAT), L-trans-pyrrolidine-2,4 dicarboxylate (PDC), a nonselective glutamate transport inhibitor, was injected into vitreous with the PGA. In primary retinal cultures, RGCs were identified as cells that were immunopositive to beta III tubulin three days after beginning the culture with and without PDC.


RESULTS
The mean density of FG-labeled RGCs was reduced from 2249 +/- 210 to 920 +/- 202 cells/mm(2) (p < 0.001) on day 7 after the ON transection. The mean density RGCs was significantly higher at 1213 +/- 159 cells/mm(2) after 0.5% PGA injection immediately after the ON transaction than eyes injected with the vehicle at 1007 +/- 122 cells/mm(2) (p = 0.035). One percent PGA was the most effective concentration for survival-promoting effects on RGCs, and the mean density of the RGCs was 1464 +/- 102/mm(2) (p < 0.001). Fourteen days after 1% PGA, the mean density of FG-labeled RGCs was significantly higher than that with vehicle (204 +/- 23/mm(2) versus 145 +/- 17 cells/mm(2); p < 0.01). Simultaneous application of 1% PGA and PDC blocked the survival effects of PGA on day 7 after ON transection. The presence of PGA increased the number of beta III tubulin-positive cells.


CONCLUSIONS
PGA promotes the survival of axotomized RGCs in adult mammalian retinas possibly mediated by the EAATs.
Oono
Shinichirou
S
Department of Ophthalmology, Hyogo College of Medicine, Hyogo, Japan.
Kurimoto
Takuji
T
Nakazawa
Toru
T
Miyoshi
Tomomitsu
T
Okamoto
Norio
N
Kashimoto
Ryosuke
R
Tagami
Yuichi
Y
Ito
Yoshimasa
Y
Mimura
Osamu
O
D000818:Animals; D019771:Axotomy; D002452:Cell Count; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D003998:Dicarboxylic Acids / Q000494:pharmacology; D050491:Glutamate Plasma Membrane Transport Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D007267:Injections; D008297:Male; D014179:Neurotransmitter Uptake Inhibitors / Q000494:pharmacology; D009900:Optic Nerve / Q000601:surgery; D011759:Pyrrolidines / Q000494:pharmacology; D011761:Pyrrolidonecarboxylic Acid / Q000008:administration & dosage / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D012165:Retinal Ganglion Cells / Q000166:cytology* / Q000378:metabolism; D013266:Stilbamidines; D014404:Tubulin / Q000378:metabolism; D014822:Vitreous Body
C049774:2-hydroxy-4,4'-diamidinostilbene, methanesulfonate salt; D003998:Dicarboxylic Acids; D050491:Glutamate Plasma Membrane Transport Proteins; D014179:Neurotransmitter Uptake Inhibitors; D011759:Pyrrolidines; D013266:Stilbamidines; C488416:Tubb3 protein, rat; D014404:Tubulin; C083486:pyrrolidine-2,4-dicarboxylic acid; D011761:Pyrrolidonecarboxylic Acid