Genistein attenuates retinal inflammation associated with diabetes by targeting of microglial activation.
OBJECTIVE
Diabetic retinopathy (DR) is associated with microglial activation and increased levels of inflammatory cytokines. Genistein, a tyrosine kinase inhibitor, has been shown to possess anti-inflammatory potential that so far untested in animal models of diabetes. The aims of this study are to evaluate the efficacy of genistein for alleviation of diabetes-induced retinal inflammation and also to gain insight into the molecular mechanisms involved therein by analyzing the effect of genistein on concomitant microglia activation in the diabetic retina and in isolated cells.


METHODS
Streptozotocin (STZ)-induced diabetic Sprague Dawley rats were used. After diabetes was established for two weeks a single intravitreal injection of genistein or vehicle was performed. Forty-eight hours later, rats were killed, their retinal and vitreal samples were processed for Quantitative Real Time-PCR (qRT-PCR) and Enzyme-linked immunosorbent assay (ELISA) analyses, respectively. For the in vitro study, isolated microglial cells from retinas of newborn rats were used.


RESULTS
mRNA as well as protein levels for tumor necrosis factor α (TNF-α), a robust marker of inflammation, were increased in the retina early in the course of diabetes. Moreover, diabetes resulted in elevation of ionized calcium binding adaptor molecule-1 (Iba1) mRNA, known to be upregulated in activated microglia. These effects of diabetes in retina were all reduced by intervention treatment with genistein. Using an in vitro bioassay, we demonstrated the release of TNF-α from microglia activated by glycated albumin, a risk factor for diabetic disorders. This inflammatory signal involves the activation of tyrosine kinase and its subsequent events, ERK and P38 MAPKs. Genistein represses the release of TNF-α and significantly inhibits ERK and P38 phosphorylation in activated microglial cells by acting as a tyrosine kinase inhibitor.


CONCLUSIONS
These findings show genistein to be effective in dampening diabetes-induced retinal inflammation by interfering with inflammatory signaling (ERK and P38 MAPKs) that occurs in activated microglia. This beneficial effect of genistein may represent a new intervention therapy to modulate early pathological pathways long before the occurrence of vision loss among diabetics.
Department of Ophthalmology, Medical College of Georgia, Augusta, GA 30912, USA.
Ahmed S
AS
Ibrahim
Mamdouh M
MM
El-Shishtawy
Alejandro
A
Peña
Gregory I
GI
Liou
D000818:Animals; D000893:Anti-Inflammatory Agents / Q000008:administration & dosage / Q000494:pharmacology / Q000627:therapeutic use; D003921:Diabetes Mellitus, Experimental; D003930:Diabetic Retinopathy / Q000150:complications* / Q000188:drug therapy* / Q000473:pathology; D004789:Enzyme Activation / Q000187:drug effects; D048049:Extracellular Signal-Regulated MAP Kinases; D019833:Genistein / Q000008:administration & dosage / Q000494:pharmacology* / Q000627:therapeutic use*; D017127:Glycation End Products, Advanced; D007249:Inflammation / Q000150:complications / Q000188:drug therapy* / Q000473:pathology; D058449:Intravitreal Injections; D008297:Male; D017628:Microglia / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism / Q000473:pathology; D010766:Phosphorylation / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000008:administration & dosage / Q000494:pharmacology / Q000627:therapeutic use; D051381:Rats; D017207:Rats, Sprague-Dawley; D012160:Retina / Q000187:drug effects / Q000473:pathology*; D012709:Serum Albumin / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism; D000093423:Glycated Serum Albumin
D000893:Anti-Inflammatory Agents; D017127:Glycation End Products, Advanced; D047428:Protein Kinase Inhibitors; D012709:Serum Albumin; D014409:Tumor Necrosis Factor-alpha; D019833:Genistein; D048049:Extracellular Signal-Regulated MAP Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D000093423:Glycated Serum Albumin