Age-related changes in serum insulin-like growth factor-binding proteins in women.
Plasma insulin-like growth factor-I (IGF-I) concentrations are reported to decline with advancing age. Five IGF-binding proteins (IGF-BPs) have recently been characterized in human serum, although their biological role beyond circulatory transport of IGF-I is unknown. We studied plasma IGF-I (by RIA) and serum IGF-BPs (by Western ligand blotting) in healthy elderly (n = 21) and healthy young (n = 22) women to determine if aging alters IGF-I and its high affinity BPs. Plasma IGF-I was significantly lower in the elderly than in the young group (0.78 +/- 0.08 vs. 1.22 +/- 0.11 U/ml; P less than 0.005). The number and size of IGF-BPs did not differ between age groups, but the IGF-BP binding ratios (binding of one BP fraction/binding of all fractions) for the BP-53 acid-stable complex (41.5K and 38.5K BPs), the 30K IGF-BP, and the 24K IGF-BP were all lower in the elderly than in the young group (P less than 0.01 for each fraction, elderly vs. young). In contrast, the 34K IGF-BP binding ratio was significantly greater in the elderly than in the young (0.30 +/- 0.03 vs. 0.12 +/- 0.01; P less than 0.001) and correlated closely with advancing age (r = 0.64; P less than 0.01). The changes in IGF-BPs found in the elderly are quite similar to alterations in serum IGF-BPs previously reported in GH deficiency. Since several IGF-BPs in vitro have been shown to modulate the mitogenic activity of IGF-I, the serum IGF-BP changes noted above may be important for the growth and maintenance of connective tissue, muscle, and bone during the aging process.
Donahue
L R
LR
Department of Nutrition, University of Maine, Orono 04473.
Hunter
S J
SJ
Sherblom
A P
AP
Rosen
C
C
D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000097:blood*; D015153:Blotting, Western; D002352:Carrier Proteins / Q000097:blood*; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D006801:Humans; D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I / Q000032:analysis; D011863:Radioimmunoassay
D002352:Carrier Proteins; D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I