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A Rapid Method for Analyzing Serum Pro-Insulin-Like Growth Factor-II in Patients with Non-Islet Cell Tumor Hypoglycemia

Department of Endocrinology, William Harvey Research Institute, Queen Mary University of London, London EC1M 6BQ, United Kingdom

Address all correspondence and requests for reprints to: Cecilia Camacho-Hübner, M.D., Department of Endocrinology, 51-53 Bartholomew Close, St. Bartholomew’s Hospital, London EC1A 7BE, United Kingdom. E-mail: c.camacho-hubner{at}qmul.ac.uk.

Abstract

Context: Non-islet cell tumor hypoglycemia (NICTH) results from the hypersecretion of pro-IGF-II by a large, usually mesenchymal tumor. Detection of pro-IGF-II in serum is a potential tumor marker in these patients.

Objective: The aim of this study was to validate a rapid and reliable method for determining serum pro-IGF-II.

Patients: Serum samples from 16 patients with NICTH were studied.

Main Outcome Measure: The main outcome measure was serum concentration of pro-IGF-II determined by immunoblot analysis of pro-IGF-II and mature IGF-II after 16.5% tricine-SDS-PAGE, which was compared with pro-IGF-II measured by standard RIA after size-exclusion acid chromatography.

Results: The analyses of patients’ sera by size-exclusion acid chromatography showed that 68 ± 19% of IGF-II were present in the pro-IGF-II form, whereas only 18 ± 4% corresponded to pro-IGF-II in controls. Scanning densitometry of immunoblots showed 67 ± 16% in the bands corresponding to pro-IGF-II in patients’ sera, compared with 27 ± 9% in controls. The detection sensitivity of tricine-SDS-PAGE method was the same as for size-exclusion chromatography, but the tricine-SDS-PAGE method is quicker and requires smaller amounts of serum.

Conclusion: Tricine-SDS-PAGE followed by IGF-II immunoblot analysis provides a rapid, reproducible, and sensitive method for the separation of serum pro-IGF-II from mature IGF-II and is a useful laboratory evaluation of patients with a clinical diagnosis of NICTH.

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