S-nitrosoglutathione inhibits inducible nitric oxide synthase upregulation by redox posttranslational modification in experimental diabetic retinopathy.
OBJECTIVE
Diabetic retinopathy (DR) is associated with nitrosative stress. The purpose of this study was to evaluate the beneficial effects of S-nitrosoglutathione (GSNO) eye drop treatment on an experimental model of DR.


METHODS
Diabetes (DM) was induced in spontaneously hypertensive rats (SHR). Treated animals received GSNO eye drop (900 nM or 10 μM) twice daily in both eyes for 20 days. The mechanisms of GSNO effects were evaluated in human RPE cell line (ARPE-19).


RESULTS
In animals with DM, GSNO decreased inducible nitric oxide synthase (iNOS) expression and prevented tyrosine nitration formation, ameliorating glial dysfunction measured with glial fibrillary acidic protein, resulting in improved retinal function. In contrast, in nondiabetic animals, GSNO induced oxidative/nitrosative stress in tissue resulting in impaired retinal function. Nitrosative stress was present markedly in the RPE layer accompanied by c-wave dysfunction. In vitro study showed that treatment with GSNO under high glucose condition counteracted nitrosative stress due to iNOS downregulation by S-glutathionylation, and not by prevention of decreased GSNO and reduced glutathione levels. This posttranslational modification probably was promoted by the release of oxidized glutathione through GSNO denitrosylation via GSNO-R. In contrast, in the normal glucose condition, GSNO treatment promoted nitrosative stress by NO formation.


CONCLUSIONS
In this study, a new therapeutic modality (GSNO eye drop) targeting nitrosative stress by redox posttranslational modification of iNOS was efficient against early damage in the retina due to experimental DR. The present work showed the potential clinical implications of balancing the S-nitrosoglutathione/glutathione system in treating DR.
Renal Pathophysiology Laboratory and Investigation on Diabetes Complications, School of Medical Sciences (FCM), University of Campinas (UNICAMP), Campinas, São Paulo, Brazil.
Mariana A B
MA
Rosales
Kamila C
KC
Silva
Diego A
DA
Duarte
Marcelo G
MG
de Oliveira
Gabriela F P
GF
de Souza
Rodrigo R
RR
Catharino
Mônica S
MS
Ferreira
Jose B
JB
Lopes de Faria
Jacqueline M
JM
Lopes de Faria
D000704:Analysis of Variance; D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D002460:Cell Line; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism*; D003930:Diabetic Retinopathy / Q000188:drug therapy / Q000378:metabolism; D004195:Disease Models, Animal; D004596:Electroretinography / Q000187:drug effects; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism; D005978:Glutathione / Q000378:metabolism; D006801:Humans; D020030:Nitric Oxide Donors / Q000494:pharmacology* / Q000627:therapeutic use; D052247:Nitric Oxide Synthase Type II / Q000378:metabolism*; D009883:Ophthalmic Solutions / Q000494:pharmacology; D051381:Rats; D017382:Reactive Oxygen Species / Q000378:metabolism; D012160:Retina / Q000187:drug effects / Q000378:metabolism; D026422:S-Nitrosoglutathione / Q000494:pharmacology* / Q000627:therapeutic use; D014443:Tyrosine / Q000031:analogs & derivatives / Q000378:metabolism; D015854:Up-Regulation
D015415:Biomarkers; D005904:Glial Fibrillary Acidic Protein; D020030:Nitric Oxide Donors; D009883:Ophthalmic Solutions; D017382:Reactive Oxygen Species; C002744:3-nitrotyrosine; D014443:Tyrosine; D026422:S-Nitrosoglutathione; D052247:Nitric Oxide Synthase Type II; D005978:Glutathione
S-glutathionylation; S-nitrosoglutathione; diabetic retinopathy; nitrosative stress; retinal pigment epithelium