Tetramethylpyrazine nitrone protects retinal ganglion cells against N-methyl-d-aspartate-induced excitotoxicity.
Adding a free radical-scavenging nitrone moiety on tetramethylpyrazine, we have previously synthesized a chemical named 2-[[(1,1-dimethylethyl)oxidoimino]-methyl]-3,5,6-trimethylpyrazine (tetramethylpyrazine nitrone, or TBN) and proved its neuroprotective effect but with limited understanding of its mechanism. Here we ask if TBN protects retinal ganglion cells (RGCs) against excitotoxicity induced by NMDA and explore the underlying mechanism. NMDA was intravitreally injected to induce RGC injury in rats, followed by daily intraperitoneal administrations of TBN. Measurements of TBN concentration at different times after intraperitoneal administration showed that more than 200 μM TBN reached the aqueous humor quickly. Then RGCs' survival was evaluated by quantifying Brn3-positive cells, and retinal functions were examined by electroretinogram and visual behaviors. TBN significantly increased the survival of RGCs after NMDA insult, recovered the amplitude of photopic negative responses to flash, and restored the visual behavior. Furthermore, TBN inhibited the apoptotic process, as indicated by the elevated ratios of cleaved caspase-3/caspase-3 and of Bax/Bcl-2, and decreased the level of reactive oxygen species. Moreover, TBN reduced RGC's calcium overload induced by NMDA or by KCl. Whole-cell patch recording from RGCs further showed that TBN slightly but significantly inhibited L-type calcium channels, but had little effect on T-type calcium channel or NMDA-, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid(AMPA)-induced current. Thus our data indicate that TBN alleviates NMDA-elicited injury of rat RGCs both morphologically and functionally, possibly by inhibiting the L-type calcium channel thus reducing Ca2+overload and by directly scavenging free radicals. Therefore, TBN may be a novel candidate for treating excitotoxicity-related visual disorders such as glaucoma.
GHM Institute of CNS Regeneration, Jinan University, Guangzhou, China.
Xiaopeng
X
Luo
GHM Institute of CNS Regeneration, Jinan University, Guangzhou, China.
Yankun
Y
Yu
GHM Institute of CNS Regeneration, Jinan University, Guangzhou, China.
Zongqin
Z
Xiang
Institute of New Drug Research and Guangzhou Key Laboratory of Innovative Chemical Drug Research in Cardio-cerebrovascular Diseases, Jinan University, Guangzhou, China.
Huisu
H
Wu
GHM Institute of CNS Regeneration, Jinan University, Guangzhou, China.
Seeram
S
Ramakrishna
Institute of New Drug Research and Guangzhou Key Laboratory of Innovative Chemical Drug Research in Cardio-cerebrovascular Diseases, Jinan University, Guangzhou, China.
Yuqiang
Y
Wang
GHM Institute of CNS Regeneration, Jinan University, Guangzhou, China.|Co-Innovation Center of Neuroregeneration, Nantong University, Jiangsu, China.|Joint International Research Laboratory of CNS Regeneration, Ministry of Education of PRC, Guangzhou, China.
Kwok-Fai
KF
So
Institute of New Drug Research and Guangzhou Key Laboratory of Innovative Chemical Drug Research in Cardio-cerebrovascular Diseases, Jinan University, Guangzhou, China.
Zaijun
Z
Zhang
GHM Institute of CNS Regeneration, Jinan University, Guangzhou, China.|Co-Innovation Center of Neuroregeneration, Nantong University, Jiangsu, China.|Joint International Research Laboratory of CNS Regeneration, Ministry of Education of PRC, Guangzhou, China.
Ying
Y
Xu
D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D001522:Behavior, Animal / Q000187:drug effects; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D004596:Electroretinography; D018690:Excitatory Amino Acid Agonists / Q000633:toxicity*; D005260:Female; D007267:Injections; D016202:N-Methylaspartate / Q000037:antagonists & inhibitors* / Q000633:toxicity*; D018696:Neuroprotective Agents / Q000494:pharmacology*; D010775:Photic Stimulation; D011719:Pyrazines / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D017382:Reactive Oxygen Species / Q000378:metabolism; D012165:Retinal Ganglion Cells / Q000187:drug effects*; D014785:Vision, Ocular / Q000187:drug effects; D014822:Vitreous Body
C560643:2-(((1,1-dimethylethyl)oxidoimino)methyl)-3,5,6-trimethylpyrazine; D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D018690:Excitatory Amino Acid Agonists; D018696:Neuroprotective Agents; D011719:Pyrazines; D017382:Reactive Oxygen Species; D016202:N-Methylaspartate

NMDA
; L-type calcium channel; excitotoxicity; free radical; retinal ganglion cells