Early diabetes-induced biochemical changes in the retina: comparison of rat and mouse models.
OBJECTIVE
Recently, various transgenic and knock-out mouse models have become available for studying the pathogenesis of diabetic retinopathy. At the same time, diabetes-induced retinal changes in the wild-type mice remain poorly characterised. The present study compared retinal biochemical changes in rats and mice with similar (6-week) durations of streptozotocin-induced diabetes.


METHODS
The experiments were performed on Wistar rats and C57Bl6/J mice. Retinal glucose, sorbitol, fructose, lactate, pyruvate, glutamate, alpha-ketoglutarate and ammonia were measured spectrofluorometrically by enzymatic methods. Vascular endothelial growth factor (VEGF) protein was assessed by ELISA, and poly(ADP-ribosyl)ation by immunohistochemistry and western blot analysis. Free mitochondrial and cytosolic NAD(+)/NADH ratios were calculated from the glutamate and lactate dehydrogenase systems.


RESULTS
Retinal glucose concentrations were similarly increased in diabetic rats and mice, vs controls. Diabetic rats manifested approximately 26- and 5-fold accumulation of retinal sorbitol and fructose, respectively, whereas elevation of both metabolites in diabetic mice was quite modest. Correspondingly, diabetic rats had (1) increased retinal malondialdehyde plus 4-hydroxyalkenal concentrations, (2) reduced superoxide dismutase (SOD), glutathione peroxidase, glutathione reductase and glutathione transferase activities, (3) slightly increased poly(ADP-ribose) immunoreactivity and poly(ADP-ribosyl)ated protein abundance, and (4) VEGF protein overexpression. Diabetic mice lacked these changes. SOD activity was 21-fold higher in murine than in rat retinas (the difference increased to 54-fold under diabetic conditions), whereas other antioxidative enzyme activities were 3- to 10-fold lower. With the exception of catalase, the key antioxidant defence enzyme activities were increased, rather than reduced, in diabetic mice. Diabetic rats had decreased free mitochondrial and cytosolic NAD(+)/NADH ratios, consistent with retinal hypoxia, whereas both ratios remained in the normal range in diabetic mice.


CONCLUSIONS
Mice with short-term streptozotocin-induced diabetes lack many biochemical changes that are clearly manifest in the retina of streptozotocin-diabetic rats. This should be considered when selecting animal models for studying early retinal pathology associated with diabetes.
Obrosova
I G
IG
Pennington Biomedical Research Center, Louisiana State University System, 6400 Perkins Road, Baton Rouge, LA 70808, USA. obrosoig@pbrc.edu
Drel
V R
VR
Kumagai
A K
AK
Szábo
C
C
Pacher
P
P
Stevens
M J
MJ
D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D002374:Catalase / Q000378:metabolism; D003921:Diabetes Mellitus, Experimental / Q000097:blood / Q000503:physiopathology*; D003930:Diabetic Retinopathy / Q000503:physiopathology*; D004797:Enzyme-Linked Immunosorbent Assay; D019803:Glutathione Disulfide / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D051381:Rats; D017208:Rats, Wistar; D012016:Reference Values; D012160:Retina / Q000503:physiopathology*; D013045:Species Specificity; D042461:Vascular Endothelial Growth Factor A / Q000032:analysis
D001786:Blood Glucose; D042461:Vascular Endothelial Growth Factor A; D002374:Catalase; D019803:Glutathione Disulfide