Functional IGFBP-3: A new diagnostic measure?
By Markus Langkamp, QC mgr. Mediagnost, PhD: 10.06.08 in Endocrinology
Insulin-like growth factor (IGF) – I is a mitogenic and antiapoptotic petide. Its bioavailability is strictly regulated by specific binding proteins (IGFBP).
The most abundant IGFBP in the circulation is IGFBP-3 which forms together with the acid-labile subunit and IGF-I a ternary complex – a kind of IGF-I storage, the degradation of this complex is reduced and therewith the shelf-life of bound IGF increased.
IGF-I is set free of this complex by proteolytic cleavage of the binding protein and the acid-labile subunit.
Beside matrix metalloproteases also plasmin and prostate-specific antigen are able to cleave IGFBP-3.
Thus, biological availability of IGF-I is regulated by the proteolytic activity in human serum.
It is known that in several physiological and pathological circumstances the amount of fragmented IGFBP-3 is increased e.g. in pregnancy, acromegaly, acute renal failure and diabetes.
A direct correlation of the amount of fragmented IGFBP-3 and growth hormone deficiency or idiopathic short stature has not been shown until today.
The question whether fragmented or intact IGFBP-3 is of diagnostic value is still not finally answered.
Mostly, western ligand blots were used to assess the amount of fragmented IGFBP-3. This technology is very time consuming and a quantification is only possible by densitometry.
A newly available immunoassay allows the fast and easy measurement of intact, IGF-I binding IGFBP-3 in human serum.
This could allow more clinical studies on the relevance of fragmentation of IGFBP-3 as diagnostic means.