Diabetic retinopathy, a vascular and inflammatory disease: Therapeutic implications

Diabetic retinopathy (DR) is the most common microvascular complication of diabetes and the leading cause of visual impairment in the working-age population in the Western world. Diabetic macular oedema (DME) is one of the major complications of DR. Therapy with intravitreal injections of anti-vascular endothelial growth factor (anti-VEGF) drugs has become the gold standard treatment for DR and its complications. However, these drugs have no effect on the pathogenesis of DR and must be administered frequently via invasive intravitreal injections over many years. Thus, there is a pressing need to develop new therapeutic strategies to improve the treatment of this devastating disease. Indeed, an increasing volume of data supports the role of the inflammatory process in the pathogenesis of DR itself and its complications, including both increased retinal vascular permeability and neovascularization. Inflammation may also contribute to retinal neurodegeneration. Evidence that low-grade inflammation plays a critical role in the pathogenesis of DME has opened up new pathways and targets for the development of improved treatments. Anti-inflammatory compounds such as intravitreal glucocorticoids, topical non-steroidal anti-inflammatory drugs (NSAIDs), antioxidants, inflammatory molecule inhibitors, renin-angiotensin system (RAS) blockers and natural anti-inflammatory therapies may all be considered to reduce the rate of administration of antineovascularization agents in the treatment of DR. This report describes the current state of knowledge of the potential role of anti-inflammatory drugs in controlling the onset and evolution of DR and DME.

Trace elements and diabetes: Assessment of levels in tears and serum

Tear film is critical for the well-being and homeostasis of the ocular surface. Although the composition of the tear film is well known, the composition of metallic elements have yet to be analysed. Despite trace elements metabolism has been reported to play a role in the pathogenesis of diabetes mellitus, a metabolic disease that affects several aspects of homeostasis, little is known in the literature regarding concentration and possible variation of metallic elements in tear film. We studied the concentrations of several essential and non-essential metallic elements in the tear fluid and serum of patients with type II diabetes mellitus and a group of non-diabetic controls. Serum and tear fluid were collected from 97 patients: 47 type II diabetic patients and 50 non-diabetic controls. Regarding tear film, there were statistically significant differences in Zinc, Chrome, Cobalt, Manganese, Barium, and Lead between groups; the values of all metallic elements were found to be statistically significant higher in patients with mellitus type II diabetes. Regarding serum values there was a statistically significant difference in Chrome, Cobalt, and Selenium values; the concentrations of Chrome and Cobalt were higher in the control group, while Selenium concentration was higher in diabetic patients. In patients with type II diabetes, metal elements with higher concentrations in tears compared to serum were: Lead, Barium, Manganese, Cobalt, and Chrome. In the control group, the metal elements with the highest concentration in tear film compared to serum were Chrome, Manganese, Barium, and Lead. In this study, we attempted to evaluate the possible effect of a disease, such as diabetes, on the metabolism of metallic elements. Although our evidence was very interesting, it is probably limited in its accuracy due to the fact that individuals in the control group harboured ocular pathologies. This work lays the foundation for future studies.

Diabetic Retinopathy: Vascular and Inflammatory Disease

Diabetic retinopathy (DR) is the leading cause of visual impairment in the working-age population of the Western world. The pathogenesis of DR is complex and several vascular, inflammatory, and neuronal mechanisms are involved. Inflammation mediates structural and molecular alterations associated with DR. However, the molecular mechanisms underlying the inflammatory pathways associated with DR are not completely characterized. Previous studies indicate that tissue hypoxia and dysregulation of immune responses associated with diabetes mellitus can induce increased expression of numerous vitreous mediators responsible for DR development. Thus, analysis of vitreous humor obtained from diabetic patients has made it possible to identify some of the mediators (cytokines, chemokines, and other factors) responsible for DR pathogenesis. Further studies are needed to better understand the relationship between inflammation and DR. Herein the main vitreous-related factors triggering the occurrence of retinal complication in diabetes are highlighted.

Effect of intravitreal bevacizumab on serum, aqueous, and vitreous humor levels of erythropoietin in patients with proliferative diabetic retinopathy

AIM

The aim of this study was to evaluate concentrations of erythropoietin (EPO) and vascular endothelial growth factor (VEGF) in serum, aqueous and vitreous humour of diabetic patients with proliferative retinopathy (PDR) and to verify their possible modifications induced by intravitreal injection of bevacizumab (IVB).

METHODS

This prospective observational study was performed on patients who underwent vitrectomy for proliferative diabetic retinopathy and macular hole or pucker. The study sample consisted of 33 patients with proliferative diabetic retinopathy and 20 non-diabetic patients with macular hole or pucker. EPO and VEGF levels in serum, aqueous and vitreous humour were measured in both groups. In diabetic patients measures were performed before and after IVB.

RESULTS

EPO and VEGF levels in aqueous and vitreous humour were markedly increased in diabetic patients with PDR as compared with those recorded in the control group (P<0.001); contrarily, EPO serum levels were similar in both groups (p=not significant). IVB did not affect EPO levels (aqueous 39.1 ± 29.2 vs. 38.6 ± 26.1; vitreous 179.3 ± 88.3 vs. 131.6 ± 67.8; serum 9.2 ± 5.8 vs. 6.9 ± 3.7 mUI/mL); conversely, VEGF concentration significantly decreased 15 days after IVB in serum and ocular fluids (aqueous 141.6 ± 12.3 vs. 81.4 ± 5.4; vitreous 180.4 ± 45.8 vs. 95.8 ± 23.6; serum 113.9 ± 52.8 vs. 73.2 ± 65.6 mUI/mL).

CONCLUSION

These findings demonstrate that the production of VEGF and EPO is regulated by different mechanisms. Intraocular levels of EPO in diabetic patients were significantly higher than those recorded in serum, suggesting a local production. In addition, bevacizumab does not influence intraocular levels of EPO.

Serum and intraocular concentrations of erythropoietin and vascular endothelial growth factor in patients with type 2 diabetes and proliferative retinopathy

AIM

This study compared systemic and intraocular concentrations of erythropoietin (EPO) and vascular endothelial growth factor (VEGF) in patients with type 2 diabetes (T2D) and proliferative diabetic retinopathy (PDR) with levels in patients without diabetes, and looked for possible correlations between the concentrations found and other variables analyzed.

METHODS

Concentrations of EPO and VEGF were measured in the aqueous and vitreous humours and serum of patients undergoing vitrectomy for PDR (33 patients) or for macular holes or puckers (20 control patients). EPO was assayed by radioimmunoassay, with a lower limit of detection (LOD) of 1.0 mIU/mL. VEGF was assayed using enzyme-linked immunosorbent assay (ELISA), with a lower LOD of 10.0 pg/mL.

RESULTS

EPO concentrations in serum did not differ significantly between the two groups, whereas EPO in vitreous and aqueous were higher in diabetic than in non-diabetic patients. VEGF in serum was lower in diabetic patients than in non-diabetics; conversely, VEGF concentrations in vitreous were significantly higher in diabetic patients. A direct correlation was found between vitreous and aqueous EPO concentrations, and between vitreous EPO and blood glucose concentrations. A significant, negative correlation between vitreous EPO concentration and age was also recorded.

CONCLUSION

High EPO concentrations in the vitreous of patients with PDR and its correlation with blood glucose suggest that EPO could play a role in the pathogenesis of PDR. All possible factors affecting serum and ocular concentrations of EPO and VEGF should be determined to identify compounds able to prevent and control this serious microvascular complication of diabetes.

Defining reference values of trace elements in the tear film: diagnostic methods and possible applications

The study has been performed on tears of apparently healthy subjects who live and work in urban and rural areas, respectively. After the collection the following elements were investigated: chromium (Cr); arsenic (As); copper (Cu); zinc (Zn); selenium (Se); rubidium (Rb); barium (Ba); lead (Pb) and cobalt (Co). Significantly higher values of As were found in subjects living and working in rural areas as compared to those found in urban area residents (0.290 vs. 0.025; p<0.001). Conversely, Ba and Pb were significantly lower in rural area residents (1.10 vs. 2.50, p=0.027 and 1.70 vs. 1.10, p=0.057, respectively). Our data show that trace elements analysis in tears is possible; further studies could define if it could be a reliable biomarker in persons exposed to high concentration of trace elements due to working or environmental reasons.