Hyperglycemia potentiates the effect of ionic calcium in photoreceptor ellipsoid zone disruption in diabetic retinopathy

External Limiting Membrane, Photoreceptor Ellipsoid Zone Disruption, and Retinal Pigment Epithelium Alterations in Diabetic Retinopathy

Objective Diabetic retinopathy (DR), a microvascular complication of diabetes, is a leading cause of preventable blindness. Spectral domain optical coherence tomography (SD-OCT) provides cross-sectional and topographical imaging of the retina. SD-OCT resolves outer retinal layers into three hyperreflective bands—external limiting membrane (ELM), ellipsoid zone (EZ), and retinal pigment epithelium (RPE). In this article, we have studied the role of these outer retinal layers in structural and molecular changes taking place in DR.

Materials and Methods Articles with clinical features, pathogenesis, diagnosis, and treatment of DR were thoroughly studied. Articles were searched on PubMed, MEDLINE, and Cochrane Library from 2000 to 2020. Studies focusing on the role of ELM, EZ, and RPE in pathogenesis of DR based on SD-OCT were included.

Results The long-standing hyperglycemia leads to protein glycosylation resulting in formation of advanced glycation end products (AGEs). AGEs have an impact through their effect on retinal microvasculature, vascular endothelial growth factor (VEGF), intercellular adhesion molecule-1, nitrosative and oxidative stress, and vitamin D and calcium metabolism. All these factors have been linked with disruption of outer retinal layers. AGEs lead to vascular endothelial dysfunction and release of proangiogenic factors by increasing the expression of VEGF in retinal pericytes and RPE cells. This leads to leakage and fluid accumulation resulting in diabetic macular edema (DME). In DME, there is sequential disruption of ELM and EZ and decrease in visual acuity (VA). The RPE alterations have been reported to be associated with the severity of DR and decrease in VA. Anti-VEGF therapy, most common treatment of DME, leads to restoration of barrier effect of ELM, it was found to be restored first followed by EZ restoration. Newer anti-AGEs agents and their receptor blockers are being developed which have a positive effect on maintaining the health of RPE.

Conclusion A complex molecular association exists between the structural changes in ELM, EZ, and RPE in DR. SD-OCT is an indispensable tool to study these changes as integrity of these outer layers of retina is essential for maintaining visual function of retina in DR.

Elevated advanced glycation end products are associated with subfoveal ellipsoid zone disruption in diabetic macular edema

Purpose:

Advanced glycation end products (AGEs), due to increased production and a slow turnover rate, serve as mediators of “metabolic memory” even after the resolution of hyperglycemia. A prospective study was undertaken to evaluate the association of AGEs with subfoveal ellipsoid zone (EZ) disruption in diabetic macular edema (DME).

Methods:

A tertiary-care-center-based cross-sectional study included 40 consecutive cases with DME and 20 healthy controls in the age group of 40–65 years. All the study subjects underwent spectral-domain optical coherence tomography (SD-OCT) for cross-sectional imaging of the retina. The EZ was defined as a hyperreflective band below the external limiting membrane. The disruption of EZ was graded as intact EZ and disrupted EZ. Serum AGEs were assessed by assay of N^ε-carboxymethyl-lysine (N^ε-CML) using the standard protocol. Data were analyzed statistically.

Results:

Subfoveal EZ disruption was noted in 80% (32/40) of the cases of DME. In the cases without EZ disruption, visual acuity (LogMAR VA) was 0.60 ± 0.52, whereas in cases with EZ disruption, LogMAR VA was 0.96 ± 0.56 (P < 0.001). In the cases without EZ disruption, N^ε-CML was 94.31 ± 57 ng/mL, whereas in cases with EZ disruption N^ε-CML was 120.64 ± 71.98 ng/mL (P < 0.001).

Conclusion:

In DME, increased levels of AGEs are significantly associated with EZ disruption on SD-OCT.

Normal parathyroid hormone and non-proliferative diabetic retinopathy in patients with type 2 diabetes

AIMS/INTRODUCTION

To investigate the associations between parathyroid hormone (PTH) and non-proliferative diabetic retinopathy (NPDR) in patients with type 2 diabetes mellitus.

MATERIALS AND METHODS

Data were collected from 2,322 patients with type 2 diabetes mellitus in hospital between 2017 and 2019. The odds ratio (OR) and the corresponding 95% confidence interval related to the quartiles of PTH were obtained by logistic regression analysis after adjusting the potential confounding variation.

RESULTS

The patients were stratified into quartiles (Q1-Q4) based on the PTH levels, with the cut-off limits of ≤23.74, 23.74-29.47, 29.47-37.30 and >37.30 pg/mL in men, and ≤24.47, 24.47-31.22, 31.22-39.49 and >39.49 pg/mL in women. The first quartile (Q1) represents the lowest quartile and the fourth quartile (Q4) is the highest. According to the quartiles (Q1-Q4), the prevalence rate of NPDR in patients showed a significantly decreasing trend (37.9%, 36.3%, 34.0% vs 24.0% in men; 43.2%, 40.5%, 31.1% vs 26.2% in women, both P < 0.05). Independent of age, diabetes duration and other metabolic factors, multivariate logistic regression showed that participants in Q4 had a lower OR of NPDR than those in Q1 (OR 0.443, 95% confidence interval 0.300-0.654, P < 0.001 for men; OR 0.428, 95% confidence interval 0.283-0.646, P < 0.001 for women).

CONCLUSIONS

Low serum PTH levels were significantly associated with complications of NPDR in inpatients. Its causality remains to be further studied.

A Higher Serum Calcium Level is an Independent Risk Factor for Vision-Threatening Diabetic Retinopathy in Patients with Type 2 Diabetes: Cross-Sectional and Longitudinal Analyses

OBJECTIVE

An elevated serum calcium level is associated with a higher risk of type 2 diabetes (T2D), but its role in microvascular complications remains unclear. This study was conducted to investigate the association between serum calcium levels and vision-threatening diabetic retinopathy (VTDR).

METHODS

This study employed a cross-sectional and longitudinal design. The cross-sectional part included all patients treated for T2D at Shanghai General Hospital between 2007 and 2016, while the longitudinal part involved an overlapping cohort of diabetic patients without VTDR who were followed from their admission until December 2019. Multivariable logistic and Cox proportional hazard regression analyses were performed, respectively. VTDR was defined as severe nonproliferative diabetic retinopathy, proliferative diabetic retinopathy, or clinically significant macular edema.

RESULTS

A total of 3269 patients were included in the cross-sectional analysis, and 649 patients were included in the longitudinal analysis. In the cross-sectional analysis, higher corrected serum calcium (odds ratio: 1.31 per 0.1 mmol/L, 95% confidence interval: 1.16-1.49), younger age, longer diabetes duration, albuminuria, impaired renal function, and lower serum magnesium were independently associated with VTDR. In the longitudinal analysis, 95 subjects developed VTDR during follow-up (9.7 years, interquartile range: 7.4-10.9 years). Higher corrected serum calcium (hazard ratio: 1.38 per 0.1 mmol/L, 95% confidence interval: 1.10-1.72), younger age, longer diabetes duration, sub-VTDR, albuminuria, lower serum magnesium, and higher glycated hemoglobin were identified as independent risk factors for VTDR.

CONCLUSIONS

A higher serum calcium level may be an independent risk factor for VTDR in patients with T2D.

Chemerin/CMKLR1 Axis Promotes the Progression of Proliferative Diabetic Retinopathy

BACKGROUND

Diabetic retinopathy (DR) is a prevalent microvascular complication of diabetes, and the levels of chemerin were associated with the severity of DR. However, there is no research on chemerin in the development of proliferative diabetic retinopathy (PDR). Therefore, our study aimed to explore the relationship between chemerin and PDR.

METHODS

The levels of chemerin/chemokine-like receptor (CMKLR1), proinflammatory cytokines, and vascular endothelial growth factor (VEGF) in 90 cases of PDR and nonproliferative diabetic retinopathy (NPDR) patients and in high glucose (HG) stimulated human retinal pigment epithelium cells (ARPE-19) were evaluated by ELISA. Moreover, chemerin was added into HG-induced ARPE-19 cells to assess its effect on proinflammatory cytokines and VEGF.

RESULTS

The levels of chemerin/CMKLR1 were higher in PDR patients than NPDR ones, and chemerin was positively correlated with CMKLR1 in PDR patients. Compared to NPDR, the secretions of proinflammatory cytokines and VEGF were increased in PDR patients and positively correlated with chemerin/CMKLR1. Additionally, chemerin activated CMKLR1 and aggravated HG-induced cell injury, inflammatory responses, and VEGF expressions in ARPE-19 cells.

CONCLUSION

Our study demonstrated that chemerin/CMKLR1 axis aggravated the progression of PDR, which suggested that inhibition of chemerin might serve as a new therapeutic approach to treat PDR.