Figure 1. VEGF inhibits radiation-induced apoptosis via repression of ASMase activation.

(A) ASMase activity following 10 Gy is inhibited by VEGF pre-treatment. Irradiated BAEC samples were collected at the indicated times and ASMase activity measured by quantifying conversion of [¹⁴C]sphingomyelin to the product [¹⁴C]phosphocholine. Data (mean±s.d.) represent duplicate determinations from 2 experiments. (B) Radiation-induced ceramide generation is inhibited by VEGF pre-incubation. VEGF (1 ng/ml) was added 15 min before irradiation. Ceramide was quantified at the indicated times by the diacylglycerol kinase assay. Data (mean±s.d.) represent triplicate determinations from 2 experiments. (C, D) VEGF pre-treatment inhibits radiation-induced apoptosis. C₁₆-ceramide (C₁₆, 1 µM) was added 30 min prior to irradiation. Samples were fixed in 10% paraformaldehyde prior to bis-benzimide staining. For apoptosis quantification, data (mean±s.d) represent duplicate determinations of at least 400 bis-benzimide stained nuclei counted from 2 experiments. Caspase 3 activity was measured by quantitation of the luminescence of cleaved DEVD-AMC substrate. Data (mean±s.d.) represent duplicate points from 3 experiments.