title: Elimination of radiolabelled recombinant human insulin-like growth factor binding protein-3 from the circulation, and its distribution amongst organs and tissues in adult male rats.
abstract: Most insulin-like growth factor-I (IGF-I) in blood is found in complex with IGF binding protein-3 (IGFBP-3). An additional association of IGFBP-3 with an acid-labile subunit is thought to severely limit its ability to cross the vascular endothelium. However, it is not clear whether IGFBP-3 which is not complexed to acid-labile subunit can gain access to tissues and contribute to the transcapillary transport of IGF-I. We have investigated the concentration time profile of 125I-labelled recombinant, non-glycosylated human IGFBP-3 in the rat circulation, its appearance within various organs, urine, and in peritoneal lavage fluid. Radiolabelled IGFBP-3 was administered as a single infusion over 1 min into the catheterized jugular vein of male Wistar rats. Blood was sampled from the femoral artery, and urine by cannulation of the bladder for up to 3 h. The peritoneal cavity was cannulated to allow for the collection of lavage fluid. In a separate series of animals various organs were collected up to 3 h following administration of 125I-labelled IGFBP-3, and the content of radiolabel estimated by gamma spectrometry. Radiolabelled IGFBP-3 was rapidly cleared from the circulation initially (half-life 25 min), however from 70 min life to 3 h the levels of radiolabel remained constant. Neutral gel filtration on Sephadex G200 revealed that 1 h following administration the majority of the [125I]IGFBP-3 existed within a complex of 100-120 kDa, likely to represent an association with the acid-labile subunit. Radioactivity was detected in urine within 30 min of IGFBP-3 administration, was maximally present at 60 min, but declined thereafter. A proportion of the radiolabel in urine represented degraded protein fragments of IGFBP-3, although only 8% of the administered radiolabel was excreted within urine over 3 h. Within 10 min of entry into blood 125I-labelled IGFBP-3 was found within peritoneal lavage fluid. Most of the radiolabel was accumulated within the kidneys, liver, stomach and intestine up to 3 h after administration. However, while the hepatic and renal content were maximal after 30 min, stomach content continued to rise over 1 h, and stabilized at 15% of administered dose for up to 3 h. The results suggest that when not in complex with the acid-labile subunit, IGFBP-3 can rapidly cross capillary endothelia from blood to extravascular compartments. While kidney and liver are likely sites of excretion and degradation, a substantial proportion of IGFBP-3 is also accumulated by gastrointestinal tissues.(ABSTRACT TRUNCATED AT 400 WORDS)
authors.affiliation: MRC Group in Fetal and Neonatal Health and Development, Lawson Research Institute, St. Joseph's Health Centre, London, Canada.
authors.forename: E
authors.initials: E
authors.lastname: Arany
authors.forename: P
authors.initials: P
authors.lastname: Zabel
authors.forename: D
authors.initials: D
authors.lastname: Freeman
authors.forename: D J
authors.initials: DJ
authors.lastname: Hill
mesh_terms: D000818:Animals; D002352:Carrier Proteins / Q000097:blood* / Q000302:isolation & purification / Q000493:pharmacokinetics*; D002850:Chromatography, Gel; D004591:Electrophoresis, Polyacrylamide Gel; D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D007457:Iodine Radioisotopes; D008297:Male; D008657:Metabolic Clearance Rate; D009928:Organ Specificity; D011865:Radioisotope Dilution Technique; D051381:Rats; D017208:Rats, Wistar; D011994:Recombinant Proteins / Q000097:blood / Q000302:isolation & purification / Q000493:pharmacokinetics*; D013997:Time Factors; D014018:Tissue Distribution
chemical_list: D002352:Carrier Proteins; D018969:Insulin-Like Growth Factor Binding Proteins; D007457:Iodine Radioisotopes; D011994:Recombinant Proteins; D007334:Insulin-Like Growth Factor I