mTOR Inhibition Mitigates Molecular and Biochemical Alterations of Vigabatrin-Induced Visual Field Toxicity in Mice.
Gamma-vinyl-γ-aminobutyric acid (GABA) (vigabatrin) is an antiepileptic drug and irreversible GABA transaminase inhibitor associated with visual field impairment, which limits its clinical utility. We sought to relate altered visual evoked potentials associated with vigabatrin intake to transcriptional changes in the mechanistic target of rapamycin (mTOR) pathway and GABA receptors to expose further mechanisms of vigabatrin-induced visual field loss.



Vigabatrin was administered to mice via an osmotic pump for two weeks to increase GABA levels. Visual evoked potentials were examined, eye samples were collected, and gene expression was measured by quantitative reverse transcription-polymerase chain reaction. Similarly, human retinal pigment epithelial cells (ARPE19) were exposed to vigabatrin and treated with mTOR inhibitors for mTOR pathway analysis and to assess alterations in organelle accumulation by microscopy.



Dysregulated expression of transcripts in the mTOR pathway, GABAA/Breceptors, metabotropic glutamate (Glu) receptors 1/6, and GABA/glutamate transporters in the eye were found in association with visual evoked potential changes during vigabatrin administration. Rrag genes were upregulated in both mouse eye and ARPE19 cells. Immunoblot of whole eye revealed greater than three fold upregulation of a 200 kDa band when immunoblotted for ras-related guanosine triphosphate binding D. Microscopy of ARPE19 cells revealed selective reversal of vigabatrin-induced organelle accumulation by autophagy-inducing drugs, notably Torin 2. Changes in the mTOR pathway gene expression, including Rrag genes, were corrected by Torin 2 in ARPE19 cells.



Our studies, indicating GABA-associated augmentation of RRAG and mTOR signaling, support further preclinical evaluation of mTOR inhibitors as a therapeutic strategy to potentially mitigate vigabatrin-induced ocular toxicity.
Division of Experimental and Systems Pharmacology, College of Pharmacy, Washington State University, Spokane, Washington.
Kara R
KR
Vogel
Division of Experimental and Systems Pharmacology, College of Pharmacy, Washington State University, Spokane, Washington.
Garrett R
GR
Ainslie
Elson S. Floyd College of Medicine, Washington State University, Spokane, Washington.
Michelle A
MA
Schmidt
Elson S. Floyd College of Medicine, Washington State University, Spokane, Washington.
Jonathan P
JP
Wisor
Division of Experimental and Systems Pharmacology, College of Pharmacy, Washington State University, Spokane, Washington. Electronic address: mike.gibson@wsu.edu.
K Michael
KM
Gibson
D000818:Animals; D002460:Cell Line; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005074:Evoked Potentials, Visual / Q000187:drug effects / Q000502:physiology; D005123:Eye / Q000187:drug effects / Q000473:pathology / Q000503:physiopathology; D006801:Humans; D008810:Mice, Inbred C57BL; D020559:Monomeric GTP-Binding Proteins / Q000378:metabolism; D020011:Protective Agents / Q000494:pharmacology*; D018079:Receptors, GABA / Q000378:metabolism; D055213:Retinal Pigment Epithelium / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D020888:Vigabatrin / Q000633:toxicity*; D014794:Visual Fields / Q000187:drug effects* / Q000502:physiology
D004791:Enzyme Inhibitors; D020011:Protective Agents; D018079:Receptors, GABA; C546842:MTOR protein, human; C546843:mTOR protein, mouse; D058570:TOR Serine-Threonine Kinases; D020559:Monomeric GTP-Binding Proteins; D020888:Vigabatrin
ARPE19 cells; GABA; epilepsy; gene expression; mTOR; vigabatrin; visual evoked potentials; visual field loss