Abstract
Purpose
Hard exudates (HEs) are one of the main factors affecting vision in patients with diabetic retinopathy (DR) and diabetic macular edema (DME). Anti-vascular endothelial growth factor (anti-VEGF) is the main therapy for DME, but its effect on Müller glia phagocytosis remains unclear. The aim of this study was to investigate the effects of conbercept on phagocytosis of HEs by Müller glia in DR and elucidate the underlying mechanism(s).
Methods
Twenty-one eyes from 17 patients diagnosed with DR or DME underwent optical coherence tomography (OCT) imaging at baseline and one week after each consecutive intravitreal conbercept injection (ICI), administered three times with an interval of over one month between each injection, to assess changes in HEs. The rat Müller cell line (rMC-l) was cultured under high glucose conditions to mimic a diabetic environment. Cells were treated with oxidized low-density lipoprotein (Ox-LDL) alone or in combination with conbercept. Cell viability was assessed using the Cell Counting Kit-8 (CCK-8). The phagocytosis of Ox-LDL by rMC-l cells with or without conbercept was examined via immunofluorescence, flow cytometry, and Western blot. Gene expressions of several scavenger receptors and transporters involved in lipid metabolism, including RAGE, LOX-1, TLR-4, CD36, SR-AII, and ABCG-1, were analyzed using quantitative real-time polymerase chain reaction (qRT-PCR).
Results
The area of the HEs exhibited minimal changes following the initial ICI, whereas a significant decrease in area was observed after three consecutive injections. The viability of rMC-l cells was obviously reduced at higher concentrations of conbercept (> 100 µg/mL). Under high glucose conditions, rMC-l cells phagocytosed Ox-LDL, particularly locolized around the nucleus, and conbercept further enhanced this phagocytosis. Ox-LDL treatment increased the expression of the receptors and transporters involved in phagocytosis and lipid metabolism, while conbercept treatment further enhanced their expressions, except for ABCG-1 which was decreased.
Conclusion
This study confirmed that Conbercept treatment can effectively reduce the area of HEs in DR and DME. This therapeutic effect may be attributed to the enhanced phagocytic capability of Müller glia towards HEs, which is mediated by the regulation of key lipid metabolism receptors and transport proteins. These findings provide novel mechanisms underlying the facilitation of HEs clearance in DR and DME by anti-VEGF therapy, thereby establishing a theoretical basis for future therapeutic strategies.