Purpose: Bactericidal/permeability-increasing protein (BPI), an antibacterial and lipopolysaccharide-neutralizing protein, also has an antiangiogenic effect. To evaluate the therapeutic role of BPI in ischemic retinopathies, the antiangiogenic activity of a human recombinant 21-kDa modified N-terminal fragment of BPI (rBPI(21)), which has the biological properties of the holoprotein, and a peptidomimetic (XMP.Z) derived from BPI were examined.
Methods: The effects of rBPI(21) and XMP.Z on VEGF-induced growth of bovine retinal microvascular endothelial cells (BRECs) and on serum-induced growth of bovine retinal pericytes (BRPs) and retinal pigment epithelial cells (BRPECs) were evaluated by determining total DNA content. The neonatal mouse model of retinopathy of prematurity (ROP) was used to study the effect of XMP.Z in vivo. Intraperitoneal injections of the peptidomimetic (10 mg/kg) were administered every 24 hours for 5 days (postnatal [P]12-P17) during induction of neovascularization. Retinal neovascularization was evaluated using flatmounts of fluorescein-dextran-perfused retinas and quantitated by counting retinal cell nuclei anterior to the internal limiting membrane. RESULTS. VEGF (25 ng/mL) increased the total DNA per well of BRECs by 120% +/- 50% (P < 0.001), which was inhibited by addition of rBPI(21) or XMP.Z, with decreases of 77% +/- 15% (P < 0.05) and 107% +/- 19% (P < 0.01) at maximum effective doses of 75 and 15 microg/mL rBPI(21) and XMP.Z, respectively. In contrast, rBPI(21) at 75 microg/mL enhanced the total DNA per well of BRP 53% +/- 14% (P < 0.001) in the presence of 5% fetal bovine serum (FBS), whereas XMP.Z enhanced BRP growth by 27% +/- 7% (P < 0.001) at 5 microg/mL. In the presence of 10% FBS, rBPI(21) and XMP.Z increased BRP growth by 91% +/- 35% (P < 0.001) and 43% +/- 18% (P < 0.01), respectively. In the oxygen-induced ROP neonatal mouse model, retinal neovascularization was decreased by 40% +/- 16% (n = 5, P < 0.01) when animals were treated with XMP.Z.
Conclusions: Two BPI-derived compounds, rBPI(21) and XMP.Z, significantly suppressed VEGF-induced BREC growth in vitro, while conversely enhancing the growth of BRPs, even above that induced by 20% FBS. When tested in animals, XMP.Z also suppressed ischemia-induced retinal neovascularization in mice. These data suggest that BPI-derived compounds may have unique therapeutic potential for proliferative retinal diseases such as diabetic retinopathy, if physiological levels can be achieved in clinical settings.