Biochemical Markers of Insulin-Like Growth Factor-I Misuse in Athletes: The Response of Serum IGF-I, Procollagen Type III Amino-Terminal Propeptide, and the GH-2000 Score to the Administration of rhIGF-I/rhIGF Binding Protein-3 Complex

Abstract

The GH-2000 and GH-2004 research groups developed a method for detecting GH misuse in athletes based on the measurement of serum IGF-I and procollagen type III amino-terminal propeptide (P-III-NP). There are reports that IGF-I is also misused by athletes, but currently there is no internationally recognized test designed to detect recombinant human IGF-I misuse. The objective of the study was to examine the response of serum IGF-I, P-III-NP, and the GH-2000 score to recombinant human (rh) IGF-I/rhIGF binding protein-3 (IGFBP-3) administration in recreational athletes. This was a randomized, double-blind, placebo-controlled rhIGF-I/rhIGFBP-3 administration study at Southampton General Hospital (Southampton, United Kingdom). Fifty-six recreational athletes (26 women, 30 men) participated in the study. Participants were randomized to treatment with low-dose (30 mg/d) or high-dose (60 mg/d) rhIGF-I/rhIGFBP-3 complex or placebo for 28 days. Blood was collected throughout the drug administration and washout periods. Serum IGF-I and P-III-NP were measured using commercial immunoassays and GH-2000 scores were calculated. IGF-I, P-III-NP, and the GH-2000 score rose in response to both low- and high-dose rhIGF-I/rhIGFBP-3 administration. The relative maximum response of IGF-I (approximately 4-fold increase in women and men) was greater than that of P-III-NP (40%-50% increase in women, 35%-50% increase in men). The GH-2000 formulae, which incorporate IGF-I and P-III-NP results, detected up to 61% of women and 80% of men in the rhIGF-I/rhIGFBP-3 groups but, using IGF-I concentrations alone, the sensitivity increased to 94% in both women and men during the administration period. The rise in P-III-NP after rhIGF-I/rhIGFBP-3 administration is small compared with that after rhGH administration. Although rhIGF-I/rhIGFBP-3 administration can be detected using the GH-2000 score method, a test based on serum IGF-I alone provides better sensitivity.