Effects of rhIGF-I administration on bone turnover during short-term fasting.
Insulin-like growth factor-I (IGF-I) is a nutritionally dependent bone trophic hormone which stimulates osteoblast function and collagen synthesis in vivo and in vitro. We hypothesized that in the fasting state, IGF-I levels would decline significantly and would establish a model in which we could investigate the effects of IGF-I administration on bone turnover. We therefore studied 14 normal women ages 19-33 (mean, 24 +/- 4 [SD] years) during a complete 10-d fast. After 4 d of fasting, subjects were randomized to receive rhIGF-I or placebo subcutaneously twice a day for 6 d. Bone turnover was assessed using specific markers of formation (osteocalcin and type I procollagen carboxyl-terminal propeptide [PICP]) and resorption (pyridinoline, deoxypyridinoline, type I collagen crosslinked N-telopeptide [N-telopeptide] and hydroxyproline). Serum levels of PICP and osteocalcin decreased from 143 +/- 52 to 60 +/- 28 ng/ml (P = 0.001) and from 7.6 +/- 5.4 to 4.2 +/- 3.1 ng/ml (P = 0.001) respectively with 4 d of fasting. Urinary excretion of pyridinoline and deoxypyridinoline decreased from 96 +/- 63 to 47 +/- 38 nmol/mmol creatinine (P < 0.05) and from 28 +/- 17 to 14 +/- 11 nmol/mmol creatinine (P < 0.05) respectively. Mean IGF-I levels decreased from 310 +/- 81 to 186 +/- 78 ng/ml (P = 0.001). In the second part of the experimental protocol, serum osteocalcin and PICP levels increased 5- and 3-fold, respectively with rhIGF-I administration and were significantly elevated compared with the placebo group at the end of treatment (20.9 +/- 17.3 vs. 5.9 +/- 6.4 ng/ml for osteocalcin [P < 0.05] and 188 +/- 45 vs. 110 +/- 37 ng/ml for PICP [P < 0.05]). In contrast, all four markers of bone resorption, including urinary pyridinoline, deoxypyridinoline, N-telopeptide and hydroxyproline were unchanged with rhIGF-I administration. This report is the first to demonstrate that bone turnover falls rapidly with acute caloric deprivation in normal women. RhIGF-I administration uncouples bone formation in this setting by significantly increasing bone formation, but not resorption. These data suggest a novel use of rhIGF-I to selectively stimulate bone formation in states of undernutrition and low bone turnover.
Grinspoon
S K
SK
Neuroendocrine Unit, Massachusetts General Hospital, Boston 02114, USA.
Baum
H B
HB
Peterson
S
S
Klibanski
A
A
D000328:Adult; D016723:Bone Remodeling / Q000187:drug effects*; D002118:Calcium / Q000378:metabolism; D002352:Carrier Proteins / Q000097:blood; D005215:Fasting / Q000378:metabolism*; D005260:Female; D006801:Humans; D007279:Injections, Subcutaneous; D018969:Insulin-Like Growth Factor Binding Proteins; D007334:Insulin-Like Growth Factor I / Q000008:administration & dosage / Q000494:pharmacology*; D007668:Kidney / Q000378:metabolism; D010006:Osteoblasts / Q000187:drug effects* / Q000378:metabolism; D015675:Osteocalcin / Q000378:metabolism; D010281:Parathyroid Hormone / Q000378:metabolism; D010758:Phosphorus / Q000378:metabolism; D011994:Recombinant Proteins / Q000008:administration & dosage / Q000494:pharmacology; D016037:Single-Blind Method; D014807:Vitamin D / Q000378:metabolism
D002352:Carrier Proteins; D018969:Insulin-Like Growth Factor Binding Proteins; D010281:Parathyroid Hormone; D011994:Recombinant Proteins; D015675:Osteocalcin; D014807:Vitamin D; D010758:Phosphorus; D007334:Insulin-Like Growth Factor I; D002118:Calcium