Intravitreal injection of triptolide attenuates subretinal fibrosis in laser-induced murine model

BackgroundChoroidal neovascularization (CNV) is a common cause of irreversible blindness in elderly patients in developed countries, and subretinal fibrosis is an advanced stage of CNV. Currently, there is no effective clinical treatment for subretinal fibrosis.PurposeTo investigate whether intravitreal injection of triptolide (TP) could attenuate subretinal fibrosis and determine its underlying mechanisms.MethodsCNV was induced by laser photocoagulation in C57BL/6J mice. Immediately after laser photocoagulation, 1 μl of free TP (10 μg), TP-nanolip-PEG (TP-loaded PEGylated nanoliposomes containing 10 μg TP), or the same volume of phosphate-buffered saline (PBS) was intravitreally administered to each respective group. Areas and ratios of subretinal fibrosis were calculated seven days after laser injury. Additionally, expression levels of M2 macrophage-related markers, molecules of the transforming growth factor (TGF)-β1/Smad signaling pathway, and markers for epithelial-mesenchymal transition (EMT) and endothelial-to-mesenchymal transition (EndoMT) were detected both in vitro and in vivo.ResultsThe areas of subretinal fibrosis were significantly reduced in both the free TP (10993.87 ± 2416.90 μm²) and TP-nanolip-PEG (7695.32 ± 2121.91 μm²) groups when compared with the PBS group (15971.97 ± 3203.10 μm²) (p < 0.05, n = 6). The ratio of subretinal fibrosis in the free TP monomer (20.8 ± 4.2%) and TP-nanolip-PEG (12.5 ± 4.0%) groups was lower than that in the PBS control group (41.7 ± 5.3%) (p < 0.01, n = 6). Moreover, both TP and TP-nanolip-PEG suppressed the polarization of M2 macrophages and downregulated gene expressions of TGF-β1, Smad 2, Smad 3, α-SMA, and collagen I (p < 0.05), but upregulated the gene expression of E-cadherin (p < 0.05), thus reversing TGF-β1 induced EMT/EndoMT and attenuating subretinal fibrosis.ConclusionsTP could attenuate subretinal fibrosis by suppressing the polarization of M2 macrophages and TGF-β1 induced EMT/EndoMT. TP-nanolip-PEG enhanced the inhibitory effects of TP on subretinal fibrosis, suggesting its therapeutic potential for CNV-related subretinal fibrosis.