Diabetic retinopathy continues to be the leading cause of legal blindness among working-age individuals. The earliest histological features of diabetic retinopathy include neuroretinal damage, capillary basement membrane thickening, loss of pericytes and loss of endothelial cells. At advanced stages, neovascularization, the hallmark of proliferative diabetic retinopathy (PDR) occurs, and blindness can result from relentless abnormal fibrovascular proliferation with subsequent bleeding and retinal detachment. Macular oedema is another retinal complication of diabetes that is responsible for a major part of vision loss, particularly in type 2 diabetes. The breakdown of the blood retinal barrier and the consequent vascular leakage and thickening of retina are the main events involved in its pathogenesis. Although a tight control of both blood glucose levels and hypertension are essential to prevent or arrest progression of the disease, the recommended goals are difficult to achieve in many patients. Laser photocoagulation treatment soon after the onset of PDR significantly reduces the incidence of severe vision loss. However, the optimal timing for laser treatment is frequently passed and, in addition, it is not uniformly successful in halting visual decline. For all these reasons, new pharmacological treatments based on the understanding of the pathophysiological mechanisms of diabetic retinopathy have been developed in recent years. There is mounting evidence to suggest that angiogenic factors play a crucial role in PDR development, vascular endothelial growth factor (VEGF) being the most relevant. Other growth factors or cytokines such as insulin-like growth factor I (IGF-1), hepatocyte growth factor (HGF), basic fibroblast growth factor (b-FGF), platelet derived growth factor (PDGF), pro-inflammatory cytokines and angiopoetins, are also involved in the pathogenesis of PDR. However, the intraocular synthesis of angiogenic factors is counterbalanced by the synthesis of antiangiogenic factors. Therefore, the balance between the angiogenic and antiangiogenic factors rather than angiogenic factors themselves will be crucial in determining the progression of PDR. The main antiangiogenic factor is the pigment epithelium derived factor (PEDF) but the transforming growth factor beta (TGF-beta), thrombospondin (TSP) and somatostatin are also among the intraocullary synthesized antiangiogenic factors.

OBJECTIVE -To test the hypothesis that a reduction of somatostatin (SST) in the retina exists in patients without clinically detectable diabetic retinopathy and that it is associated with retinal neurodegeneration.RESEARCH DESIGN AND METHODS -Human diabetic postmortem eyes (n ϭ 10) without clinically detectable retinopathy were compared with eyes (n ϭ 10) from nondiabetic donors. SST mRNA (RT-PCR) and SST-28 immunoreactivity (confocal laser) were measured separately in neuroretina and retinal pigment epithelium (RPE). In addition, SST-28 (radioimmunoassay) was measured in the vitreous fluid. Glial fibrillar acidic protein (GFAP) was assessed by immunofluorescence and Western blot. Apoptotic cells were quantified using transferasemediated dUTP nick-end labeling.RESULTS -A higher expression of SST was detected in RPE than neuroretina in both groups. SST mRNA levels and SST-28 immunoreactivity were significantly lower in both RPE and the neuroretina from diabetic donors compared with nondiabetic donors. These results were in agreement with those obtained by measuring SST-28 in the vitreous fluid of the same donors. Increased GFAP and a higher degree of apoptosis were observed in diabetic retinas compared with nondiabetic retinas. These changes were most evident in patients with the higher deficit of SST.CONCLUSIONS -Underproduction of SST is an early event in the eyes of diabetic patients and is associated with glial activation and neural death. In addition, our results suggest that RPE is an important source of SST in the human eye. The possible role of the lower production of SST in the pathogenesis of diabetic retinopathy requires further investigation. Diabetes Care 30:2902-2908, 2007D iabetic retinopathy is the most common complication of diabetes and remains the leading cause of new blindness among working-age individuals in developed countries (1). Although diabetic retinopathy has been traditionally viewed as a disorder of retinal vasculature, retinal neurodegeneration may be a primary pathology that gives rise to microvascular changes (2,3). The degenerative changes in the neuroretina include increased apoptosis, glial cell reactivity, microglial activation, and altered glutamate metabolism. When occurring together, these changes may explain some of the functional deficits in vision appearing in diabetes before the onset of vascular abnormalities. In fact, abnormal electroretinograms have been found in patients with type 1 diabetes previous to the development of clinically detectable vascular retinal pathology (4), as well as in rats at short time intervals after the onset of experimental diabetes (5).Somatostatin (SST) is a widely distributed peptide, and its diverse biological functions include neurotransmission and antisecretory and antiproliferative activities (6). SST and its receptors are found in the neuroretina of various species, including humans, and growing evidence suggests that in the retina, SST acts both as a neuromodulator and antiangiogenic factor (7). SST production in the human retina ha...

Aims/hypothesis The aim of this study was to compare the protein profile of vitreous fluid from diabetic patients with proliferative diabetic retinopathy (PDR) with that from nondiabetic patients with idiopathic macular holes (MH). The mRNA of proteins differentially produced was also assessed in the retinas from diabetic and non-diabetic donors. Materials and methods Vitreous humour from type 1 diabetic patients with PDR (n=8) and from non-diabetic patients with MH (n=10) closely matched in terms of age were studied. The comparative proteomic analysis was performed using fluorescence-based difference gel electrophoresis (DIGE). Differentially produced proteins (abundance ratio >1.4, p<0.05) were identified by mass spectrometry. Expressions of mRNA were measured by real-time RT-PCR in retinas from ten human eyes obtained at post-mortem (five eyes from diabetic subjects and five eyes from non-diabetic subjects). Results Eight proteins were highly produced in PDR patients in comparison with non-diabetic subjects: zinc-α 2 -glycoprotein (ZAG), apolipoprotein (apo) A1, apoH, fibrinogen A, and the complement factors C3, C4b, C9 and factor B). We found three proteins that were underproduced in PDR subjects: pigment epithelial derived factor (PEDF), interstitial retinol-binding protein (IRBP) and inter-α-trypsin inhibitor heavy chain (ITIH2). There was no overlap in the vitreous levels of the above-mentioned proteins between PDR patients and non-diabetic control subjects. The differential production of ZAG, C3, factor B, PEDF and IRBP was further confirmed by western blot, and was in agreement with mRNA levels detected in the retina. Conclusions/interpretation Proteomic analysis by DIGE, which permits an accurate quantitative comparison, was useful in identifying new potential candidates involved in the pathogenesis of PDR.

The pro-inflammatory cytokines IL-8 and MCP-1 are increased in the vitreous fluid of PDR patients without an increase in the anti-inflammatory cytokine IL-10. In addition, both IL-8 and MCP-1 intra-vitreous levels correlated with PDR activity, thus suggesting that these cytokines may be pathogenically important in PDR.

The role of the induction of oxidative stress as the mechanism of action of many antitumor drugs is acquiring an increasing interest. In such cases, the antitumor therapy success may be conditioned by the antioxidants present in our own body, which can be synthesized de novo (endogenous) or incorporated through the diet and nutritional supplements (exogenous). In this paper, we have reviewed different aspects of antioxidants, including their classification, natural sources, importance in diet, consumption of nutritional supplements, and the impact of antioxidants on health. Moreover, we have focused especially on the study of the interaction between antioxidants and antitumor therapy, considering both radiotherapy and chemotherapy. In this regard, we found that the convenience of administration of antioxidants during cancer treatment still remains a very controversial issue. In general terms, antioxidants could promote or suppress the effectiveness of antitumor treatment and even protect healthy tissues against damage induced by oxidative stress. The effects may depend on many factors discussed in the paper. These factors should be taken into consideration in order to achieve precise nutritional recommendations for patients. The evidence at the moment suggests that the supplementation or restriction of exogenous antioxidants during cancer treatment, as appropriate, could contribute to improving its efficiency.