Metabolism of rabbit angiostatin glycoforms I and II in rabbits: angiostatin-I leaves the intravascular space faster and appears to have greater anti-angiogenic activity than angiostatin-II.
Plasminogen (PLG) exists in the circulation as two glycoforms, I and II. Angiostatin (AST) is a polypeptide that has been cleaved from the kringle region of PLG and has strong anti-angiogenic properties. AST-I and AST-II, which consisted only of kringles 1 through 3, were prepared by the action of urokinase on purified rabbit PLG-I and PLG-II, respectively, in the presence of N-acetyl cysteine, followed by affinity chromatography on lysine-Sepharose. Purified AST-I and AST-II were tested for functional activity with a chick chorioallantoic membrane (CAM) model; when similar amounts were applied to a 6-day CAM, AST-I was substantially more effective than AST-II in decreasing vascular supply to the CAM over a 72-hour period; this activity correlated with a loss of capillaries, probably through apoptosis of endothelial cells. Radiolabeled AST-I and AST-II (iodine 125 and iodine 131) were co-injected intravenously into healthy rabbits to determine their clearances from plasma measured over 3 days. Over a dose range of 0.08 to 2.7 microg/kg, the fractional catabolic rate within the intravascular space (j(3)) indicated that AST-I was cleared 3-fold to 4-fold more rapidly than AST-II (P < .001). The catabolic half-life of AST-I (2.01 +/- 0.19 days) was significantly less than that of AST-II (2.62 +/- 0.20 days). The faster clearance of AST-I from the intravascular space was matched by its more rapid passage than AST-II to the extravascular space of various organs over 60 minutes in vivo. This property of AST-I as compared with AST-II may partially explain its greater anti-angiogenic potential. From the plasma concentrations of PLG-I and PLG-II and their relative behaviors toward rabbit VX-2 lung tumors in vivo, we predict that substantially greater quantities of AST-II than AST-I may be released into the extravascular space of tumors.
Hatton
M W
MW
Department of Pathology and Molecular Medicine, McMaster University Health Sciences Centre, and the Hamilton Regional Cancer Centre, Ontario, Canada.
Day
S
S
Southward
S M
SM
Dereske
M
M
Ross
B
B
Seidlitz
E
E
Singh
G
G
Richardson
M
M
D043168:Angiostatins; D000818:Animals; D002196:Capillaries / Q000378:metabolism; D002642:Chick Embryo; D004730:Endothelium, Vascular / Q000378:metabolism; D007457:Iodine Radioisotopes; D007536:Isomerism; D018919:Neovascularization, Physiologic / Q000187:drug effects*; D010446:Peptide Fragments / Q000737:chemistry / Q000302:isolation & purification / Q000493:pharmacokinetics*; D010958:Plasminogen / Q000737:chemistry / Q000302:isolation & purification / Q000493:pharmacokinetics*; D011817:Rabbits; D013045:Species Specificity; D013640:Tarsal Joints / Q000378:metabolism
D007457:Iodine Radioisotopes; D010446:Peptide Fragments; D043168:Angiostatins; D010958:Plasminogen