Vitreous levels of placental growth factor correlate with activity of proliferative diabetic retinopathy and are not influenced by bevacizumab treatment

Abstract

PurposePlacental growth factor (PlGF) is a member of the VEGF family that plays an important role in experimental models of diabetic retinopathy and retinal neovascularization. We aimed to investigate whether vitreous levels of PlGF correlated with proliferative diabetic retinopathy (PDR) status, VEGF levels, and bevacizumab treatment. We also analysed PDR membranes to confirm the presence of the PlGF receptor, FLT1, in endothelial cells.MethodsThis was a case-control study: undiluted vitreous fluid samples were obtained from 28 active PDR patients without preoperative bevacizumab treatment, 21 active PDR patients with preoperative bevacizumab treatment, 18 inactive PDR patients, and 21 control patients. PlGF and VEGF levels in samples were determined by enzyme-linked immunosorbent assay. Immunohistochemistry for FLT1 was performed on human PDR membranes.ResultsCompared to control, vitreous PlGF levels were higher in both active PDR without bevacizumab (P<0.0001) and with bevacizumab (P<0.0001). There was no significant difference in PlGF between active PDR patients without and with bevacizumab (P=0.56). Compared to active PDR, PlGF levels were significantly reduced in inactive PDR (P=0.004). PlGF levels were highly correlated with VEGF levels in active PDR. VEGFR1 was expressed in endothelial cells in human PDR membranes.ConclusionThe strong correlation of PlGF levels with PDR disease status and expression of FLT1 in human PDR membranes suggest that PlGF has a pathogenic role in proliferative diabetic retinopathy. Therapeutic targeting of PlGF with agents like aflibercept may be beneficial.

Figure 1

PlGF levels in the vitreous among active PDR without (n=28) or with (n=21) bevacizumab treatment, inactive PDR (n=18) and no DR (n=21).

Figure 2

VEGF levels in the vitreous among active PDR without (n=25) or with (n=19) bevacizumab treatment, inactive PDR (n=16) and no DR (n=19).

Figure 3

Correlations between vitreous levels of VEGF and PlGF in active PDR without bevacizumab treatment by Spearman's correlation coefficient test, either with inclusion of all values (a) or with exclusion of the three highest values (b). r and P values are shown in the figure.

Figure 4

The expression of FLT1 in PDR membranes. (a, b) IHC staining of FLT1 in membranes from active PDR patients. FLT1 is expressed in endothelial cells lining the lumen of blood vessels (black arrows). (c, d) CD31 staining confirmed the distribution of microvascular endothelial cells in adjacent sections from PDR membranes that were used in (a) and (b). (e) H&E staining in adjacent sections from PDR membranes that were used in (a) and (b). The images were taken using × 20 objective.