Effect of human Angiostatin protein on human angiogenesis in vitro.

Angiostatin, a 38-kD fragment of plasminogen, inhibits angiogenesis in both animal tumor models and in vitro endothelial cell models. However, human Angiostatin has not been tested in vitro against an intact human tissue target to determine its ability to inhibit the initiation or subsequent promotion of the human angiogenic response. We hypothesized that high doses of human Angiostatin would inhibit the development of an angiogenic response in an intact human vessel target, and would suppress the subsequent growth of blood vessels following the initiation of an angiogenic response. To test these hypotheses, full-thickness human placental vein disks were cultured for 15 days in an in vitro fibrin-thrombin clot assay. This assay system had been used to evaluate the efficacy of a wide variety of compounds. Vessels were obtained from three placentas. Treatments included a control medium plus fetal bovine serum (FBS), heparin-steroid (300 micro g/ml heparin and 350 micro g/ml hydrocortisone; a treatment known to inhibit angiogenesis) and Angiostatin at doses from 1 x 10(-4) to 1 x 10(-9) M. In the control groups, 81% of vessels initiated an angiogenic response compared to 53% of the vessels treated with heparin-steroid. Angiostatin (10(-4)-10(-9) M) decreased the initiation of an angiogenic response, but this was not statistically significant. Of the disks that initiated an angiogenic response, the mean ( +/- standard error of the mean (SEM)) semi-quantitative visual angiogenic index (AI) of the control vessels was 9 +/- 1.7 on day 15. In comparison, the mean AI of heparin-steroid treated vessels was 3.7 +/- 0.4. Angiostatin at doses of 10(-4)-10(-9) M also failed to inhibit blood vessel growth after initiation of the angiogenic response. Based on these observations, we cannot demonstrate significant activity of human Angiostatin (10(-4)-10(-9) M) against the initiation or promotion of a human angiogenic response in this in vitro model of angiogenesis using an intact human vessel target.