Quantification of the GH/IGF-axis components: lessons from human studies

Area of Science:

• Endocrinology
• Biochemical Assays
• Molecular Biology

Background:

• Traditional bioassays for IGF-I were abandoned due to laboriousness and lack of specificity.
• Immunoassays, while providing extensive data, overlook IGF-binding proteins (IGFBPs) and IGF-II interactions.
• Understanding the bioactivity of circulating hormones like IGF-I and GH is crucial for physiological and pathophysiological insights.

Purpose of the Study:

• To reintroduce and validate a cell-based bioassay for measuring IGF-I bioactivity.
• To develop a method for determining free Growth Hormone (GH) levels in serum.
• To investigate the interaction between GH and GH-binding protein (GHBP).

Main Methods:

• Established a cell-based kinase receptor activation (KIRA) assay using cells transfected with the human IGF-I receptor (IGF-IR).
• The KIRA assay measures IGF-IR phosphorylation as a specific output signal.
• Developed an ultrafiltration assay to isolate free GH in undiluted serum under in vivo-like conditions.

Main Results:

• The KIRA bioassay provides novel information on the IGF system by integrating various components into a single signal: IGF-IR activation.
• The bioassay's performance is comparable to traditional IGF-I immunoassays.
• The ultrafiltration assay allows for the determination of free GH and its interaction with GHBP.

Conclusions:

• The re-established bioassay offers a more comprehensive assessment of IGF-I bioactivity than immunoassays.
• The developed free GH assay enhances understanding of GH pharmacokinetics and bioactivity.
• These bioassays provide valuable tools for studying the complex IGF and GH systems.