Vision loss in diabetic retinopathy (DR) is ascribed primarily to retinal vascular abnormalities—including hyperpermeability, hypoperfusion, and neoangiogenesis—that eventually lead to anatomical and functional alterations in retinal neurons and glial cells. Recent advances in retinal imaging systems using optical coherence tomography technologies and pharmacological treatments using anti-vascular endothelial growth factor drugs and corticosteroids have revolutionized the clinical management of DR. However, the cellular and molecular mechanisms underlying the pathophysiology of DR are not fully determined, largely because hyperglycemic animal models only reproduce limited aspects of subclinical and early DR. Conversely, non-diabetic mouse models that represent the hallmark vascular disorders in DR, such as pericyte deficiency and retinal ischemia, have provided clues toward an understanding of the sequential events that are responsible for vision-impairing conditions. In this review, we summarize the clinical manifestations and treatment modalities of DR, discuss current and emerging concepts with regard to the pathophysiology of DR, and introduce perspectives on the development of new drugs, emphasizing the breakdown of the blood-retina barrier and retinal neovascularization.
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For the past several decades, tremendous efforts have been made to decrease the complications of diabetes, including diabetic retinopathy. New diagnostic modalities like ultrawide field fundus fluorescein angiography and spectral domain optical coherence tomography has allowed more accurate diagnosis of early diabetic retinopathy and diabetic macular edema. Antivascular endothelial growth factors are now extensively used to treat diabetic retinopathy and macular edema with promising results. There remains uncertainty over the long term effects and the socioeconomic costs of these agents.
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Targeting Netrin-1 and -4 as a Novel Diagnostic Parameter and Treatment Option for Diabetic Retinopathy
To accelerate the healing of diabetic wounds, various kinds of growth factors have been employed. It is the short half-life of administered growth factors in hostile wound beds that have limited wide-spread clinical usage. To overcome this limitation, growth factor gene therapy could be an attractive alternative rather than direct application of factors onto the wound beds. We administered two growth factor DNAs, epidermal growth factor (EGF) and vascular endothelial growth factor (VEGF) into a cutaneous wound on diabetic mice. We compared the different characteristics of the healing wounds.
Streptozotocin was injected intraperitoneally to induce diabetes into C57BL/6J mice. The ultrasound micro-bubble destruction method with SonoVue as a bubbling agent was used for non-viral gene delivery of EGF828 and VEGF165 DNAs. Each gene was modified for increasing efficacy as FRM-EGF828 or minicircle VEGF165. The degree of neoangiogenesis was assessed using qualitative laser Doppler flowmetry. We compared wound size and histological findings of the skin wounds in each group.
In both groups, accelerated wound closure was observed in the mice receiving gene therapy compared with non treated diabetic control mice. Blood flow detected by laser doppler flowmetry was better in the VEGF group than in the EGF group. Wound healing rates and histological findings were more accelerated in the EGF gene therapy group than the VEGF group, but were not statistically significant.
Both non-viral EGF and VEGF gene therapy administrations could improve the speed and quality of skin wound healing. However, the detailed histological characteristics of the healing wounds were different.
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While there is an evidence that the anti-inflammatory properties of spironolactone can attenuate proteinuria in type 2 diabetes, its effects on vascular endothelial growth factor (VEGF) expression in diabetic nephropathy have not been clearly defined. In this study, we examined the effects of spironolactone, losartan, and a combination of these two drugs on albuminuria, renal VEGF expression, and inflammatory and oxidative stress markers in a type 2 diabetic rat model.
Thirty-three Otsuka-Long-Evans-Tokushima-Fatty (OLETF) rats were divided into four groups and treated with different medication regimens from weeks 25 to 50; OLETF diabetic controls (
At week 50, the albumin-to-creatinine ratio was significantly decreased in the losartan and combination groups compared to the control OLETF group. No decrease was detected in the spironolactone group. There was a significant reduction in renal VEGF, transforming growth factor (TGF)-β, and type IV collagen mRNA levels in the spironolactone- and combination regimen-treated groups. Twenty-four hour urine monocyte chemotactic protein-1 levels were comparable in all four groups but did show a decreasing trend in the losartan and combination regimen groups. Twenty-four hour urine malondialdehyde levels were significantly decreased in the spironolactone- and combination regimen-treated groups.
These results suggest that losartan alone and a combined regimen of spironolactone and losartan could ameliorate albuninuria by reducing renal VEGF expression. Also, simultaneous treatment with spironolactone and losartan may have protective effects against diabetic nephropathy by decreasing TGF-β and type IV collagen expression and by reducing oxidative stress in a type 2 diabetic rat model.
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Diabetic vascular complications are among the leading causes of morbidity and mortality in diabetic patients. In the past, many studies have focused on the mechanisms of hyperglycemia-induced chronic vascular complications via the formation of toxic metabolites such as oxidative stress, advanced glycosylated end products, persistent activation of protein kinase C, and increased sorbitol concentrations. However, vascular complications result from imbalances caused by increases in systemic toxic metabolites, such as those that occur under conditions of hyperglycemia and dyslipidemia, and by reductions in endogenous protective factors such as insulin, vascular endothelial growth factor, and platelet derived growth factor. This review outlines some of the evidence supporting the importance of enhancing endogenous regenerative factors.
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