Effect of intravitreal ranibizumab on fibrovascular membranes in patients with proliferative diabetic retinopathy

AIM: To assess the effects of intravitreal ranibizumab(IVR) on angiogenesis and glial activity of the fibrovascular membrane(FVM) in patients with proliferative diabetic retinopathy(PDR). METHODS: Forty-two eyes from 42 patients with PDR requiring vitrectomy were included and divided into two groups: control group(n=16) did not receive IVR, while IVR group(n=26) underwent IVR 5 d before vitrectomy. FVM specimens were collected by the same surgeon during the interventions. Histopathological morphology was examined by hematoxylin-eosin(H-E) staining and cell densities in the FVM was assessed. Microvessels were outlined by immunohistochemical staining of CD31 and microvessel density(MVD) assessed as an index of FVM angiogenesis. Dual-color immunofluorescence staining, and confocal microscopy was used to detect co-localization and relative expression levels of glial fibrillary acidic protein(GFAP) and α-smooth muscle actin(α-SMA) as markers of glialmesenchymal transition(GMT). The GMT index(GI;ratio of relative GFAP/α-SMA expression) was used to semi-quantify the degree of GMT or glial activity of FVMs. RESULTS: H-E staining showed similar vascularization in both groups, with microvessels and scattered stromal cells in the matrix. Infiltrated cell densities did not differ significantly between the two groups(P>0.05). The MVD of the IVR group(130.62±15.46/mm~2) was significantly lower than that of the controls(142.25±19.16/mm~2, P<0.05). In both groups, all sections were strongly immunostained for GFAP and α-SMA. The Pearson’s correlation coefficients(PCC) of intensity of automated pixel count of two markers indicated GFAP and α-SMA co-stained well and GMT participated in the remolding of FVMs in PDR. The mean relative GFAP expression in the IVR group was significantly lower, whereas that of α-SMA was significantly higher than in controls(P<0.05). GI in the IVR group(1.10±0.10) was significantly lower than in the controls(1.21±0.12, P<0.05). CONCLUSION: IVR can reduce angiogenesis, glial activity of FVM and promote glial-fibrotic transformation by reducing MVD and promoting GMT but does not decrease the cell density in patients with PDR.