Serum half-life and biological activity of mutants of human insulin-like growth factor I which do not bind to serum binding proteins.
We have characterized the biological properties of two mutants of human insulin-like growth factor I (IGF-I) which, as we have shown previously, have normal affinity for the type I IGF receptor, but drastically reduced affinity for the acid-stable components of human serum binding proteins. [Phe-1,Val1,Asn2,Gln3,His4,Ser8,His9,Glu12 ,Tyr15,Leu16]IGF I (B-chain mutant) and [Gln3,Ala4,Tyr15,Leu16]IGF I have 1000 and 500 times lower affinity than IGF-I for the native 150K binding protein in adult rat serum. Like IGF-I, these two peptides migrate as monomers during size exclusion chromatography on TSK 125. [125I]IGF-I, [125I]B-chain mutant, and [125I] [Gln3,Ala4,Tyr15,Leu16]IGF-I have in vivo serum half-lives of 100, 27.5, and 26.9 min, respectively, after iv injection. These data suggest that serum binding protein-bound peptide is cleared from the serum more slowly than free peptide. The tissue distributions of [125I]IGF-I and [125I]B-chain mutant are similar 10 min after dosing, with more than 80% of the tissue-sequestered intact radioactive peptides in the kidney. Despite decreased serum half-lives, the B-chain mutant and [Gln3,Ala4,Tyr15,Leu16]IGF-I are, respectively, 4 times and twice as active as IGF-I in stimulating the incorporation of [14C]glucose into glycogen in rat diaphragm in vivo. This effect of IGF-I is thought to be mediated by the type 1 IGF receptor in muscle, since the same doses of peptide that stimulated glycogen synthesis more than 30-fold did not stimulate the incorporation of [14C]glucose into total lipid in adipose tissue, an effect known to be mediated by the insulin receptor. These data support the hypothesis that serum- or tissue-derived binding proteins impair the ability of IGF-I to exert its effects through the type 1 IGF receptor in vivo.
Cascieri
M A
MA
Department of Biochemical Endocrinology, Merck, Sharp, and Dohme Research Laboratories, Rahway, New Jersey 07065.
Saperstein
R
R
Hayes
N S
NS
Green
B G
BG
Chicchi
G G
GG
Applebaum
J
J
Bayne
M L
ML
D000273:Adipose Tissue / Q000187:drug effects / Q000378:metabolism; D000818:Animals; D001798:Blood Proteins / Q000378:metabolism*; D002352:Carrier Proteins / Q000097:blood*; D006003:Glycogen / Q000096:biosynthesis; D006207:Half-Life; D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I / Q000235:genetics / Q000493:pharmacokinetics* / Q000494:pharmacology; D008055:Lipids / Q000096:biosynthesis; D008297:Male; D009132:Muscles / Q000187:drug effects / Q000378:metabolism; D009154:Mutation; D051381:Rats; D011919:Rats, Inbred Strains; D013002:Somatomedins / Q000493:pharmacokinetics*; D013329:Structure-Activity Relationship; D014018:Tissue Distribution
D001798:Blood Proteins; D002352:Carrier Proteins; D018969:Insulin-Like Growth Factor Binding Proteins; D008055:Lipids; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I; D006003:Glycogen