Recombinant IGF-I (human)

According to the regulations of the World Anti-Doping Agency (WADA), growth promoting peptides such as the insulin-like growth factor-I (IGF-I) and its synthetic analogues belong to the class of prohibited compounds. While several assays to quantify endogenous IGF-I have been established, the potential misuse of synthetic analogues such as LongR3-IGF-I, R3-IGF-I and Des1-3-IGF-I remains a challenge and superior pharmacokinetic properties have been described for these analogues. Within the present study, it was demonstrated that the target peptides can be successfully detected in plasma samples by means of magnetic beads-based immunoaffinity purification and subsequent nanoscale liquid chromatographic separation with high resolution mass spectrometric detection. Noteworthy, the usage of a specific antibody for LongR3-IGF-I enables the determination in low ng/mL levels despite the presence of an enormous excess of endogenous human IGF-I. In addition, different metabolism studies (in-vitro and in-vivo) were performed using sophisticated strategies such as incubation with skin tissue microsomes, degradation in biological fluids (for all analogues), and administration to rats (for LongR3-IGF-I). Herewith, several C-and N-terminally truncated metabolites were identified and their relevancy was additionally confirmed by in-vivo experiments with rodents. Especially for LongR3-IGF-I, a metabolite ((Des1-11)-LongR3-IGF-I) was identified that prolonged the detectability in-vivo by a factor of approximately 2. The method was validated for qualitative interpretation considering the parameters specificity, identification capability, recovery (26-60%), limit of detection (0.5ng/mL), imprecision (<25%), linearity, stability, and matrix effects. A stable isotope labelled (15N)-IGF-I was used as internal standard to control all sample preparation steps.

Peptide analysis in doping controls by means of nano-UPLC coupled high resolution/high mass accuracy mass spectrometry provides the state-of-the-art technique in modern sports drug testing. The present study describes a recent application of this technique for the qualitative determination of different urinary insulin-like growth factor (IGF) related peptides. After simultaneous isolation by solid phase extraction and magnetic particle-based immunoaffinity purification, target analytes (IGF-1, IGF-2, Des1-3-IGF-1, R(3)-IGF-1 and longR(3)-IGF-1) were separated by nano-liquid chromatography prior to mass spectrometric detection. Endogenously produced IGF-1 and IGF-2, as well as the degradation product Des1-3-IGF-1, were frequently detected in urine samples from healthy volunteers in a concentration range of 20-400 pg mL(-1). The impact of IGF binding proteins (IGFBPs), being also present in urine, was potentially estimated by an additional ultrafiltration step in the sample preparation procedure. The synthetic analogue longR(3)-IGF-1, which is assumed to be subject to misuse by cheating athletes, was also analysed and detected in fortified urine samples. Besides the intact molecule, an N-terminally truncated degradation product Des1-10-longR(3)-IGF-1 was identified as the more stable target for doping controls using urine samples. The method was validated for qualitative purposes considering the parameters specificity, limit of detection (20-50 pg mL(-1)), recovery (10-35%), precision (<20%), linearity, robustness and stability.

Although the effect of insulin-like growth factors (IGFs) in fetal adrenocortical cells has been investigated extensively, the role of the IGF system in the adult human adrenal gland remains unclear. In the present study we investigated the effect of recombinant human IGF-I and IGF-II on cortisol, dehydroepiandrosterone sulfate (DHEA-S) and cAMP synthesis in adult human adrenocortical cells in primary culture. Both IGFs stimulate basal as well as adrenocorticotropin (ACTH)-induced steroid secretion in a time- and dose-dependent fashion. While both IGFs (6.5 nM) induced only a moderate 2-fold increase in basal cortisol output after 48 h, the effect on basal DHEA-S secretion was significantly stronger, with a 2.7- and 3.7-fold stimulation by IGF-I and IGF-II respectively. Similarly, IGF-II enhanced ACTH-induced cortisol and DHEA-S secretion more potently than IGF-I. In dose-response experiments, the maximum stimulation of ACTH-induced DHEA-S secretion was induced by 1.6 nM IGF-I (2-fold increase) or IGF-II (2.9-fold increase), while the maximum response of cortisol secretion was elicited only at 13 nM IGF-I (2-fold increase) or IGF-II (2.5-fold increase). This resulted in a significant shift of the DHEA-S dose-response curves to the left, indicating a relative selective stimulation of androgen biosynthesis by physiologically low concentrations (0.4-3.2 nM) of IGF-II, and less potently by IGF-I. At all doses tested, the steroidogenic effect of IGF-II was significantly stronger than the effect of IGF-I. Although both IGF receptors are present in adult human adrenocortical cells, the steroidogenic effect of IGF-II is mediated through the IGF-I receptor, since [Arg54,55]IGF-II, which only binds to the IGF-I receptor, was equipotent with native IGF-II, whereas [Leu27]IGF-II, which preferentially binds to the type II IGF receptor, did not show any effect. In addition, [des1-3]IGF-I, which exhibits only minimal binding to IGFBPs, was significantly more potent than native IGF-I in stimulating adrenal steroid biosynthesis, and elicited almost the same maximum stimulatory effect as IGF-II and [des1-6]IGF-II. By Western ligand blotting of conditioned medium it was shown that adult human adrenocortical cells secrete various IGF-binding proteins (IGFBPs), which are induced differentially by treatment with ACTH. In conclusion, these results demonstrate that: (1)IGF-II stimulates basal as well as ACTH-induced DHEA-S and cortisol secretion from adult human adrenocortical cells more potently than IGF-I; (2) both IGFs predominantly stimulate androgen biosynthesis; (3) the steroidogenic effect of IGF-I and IGF-II is mediated through interaction with the IGF-I receptor; (4) the different steroidogenic potency of IGF-I and IGF-II might be explained by interaction of these ligands with locally produced IGFBPs. These data indicate that the IGF system plays an important role in the regulation of the differentiated function of adult human adrenocortical cells.