A rapid method for analysing serum pro-insulin-like growth factor-II (pro-IGF-II) in patients with non-islet cell tumour hypoglycaemia (NICTH)
F Miraki-Moud, JP Monson, GM Besser, AB Grossman & C Camacho-Hübner
NICTH is a well-recognised syndrome associated with overproduction of pro-IGF-II, usually secreted by large mesenchymal tumours. The determination of pro-IGF-II is currently laborious and cumbersome. The aim of the present study was to therefore establish a quick method for determining serum pro-IGF-II. Serum samples from 13 patients with NICTH were obtained after informed consent and these samples were studied and compared to sex- and age-matched controls. Serum concentrations of pro-IGF-II were measured by RIA after size-exclusion acid chromatography and compared to the analyses of pro-IGF-II and IGF-II by immunoblot analysis. Serum samples were loaded onto the 16.5 percent tricine-sodium dodecyl sulphate polyacrylamide gel electrophoresis (tricine SDS-PAGE), transferred to the nitrocellulose membranes and probed with an IGF-II antibody. Results showed that serum IGF-I and IGFBP-3 levels were significantly reduced in NICTH compared to controls (P less than 0.001 and P less than 0.05, respectively). In contrast, serum IGFBP-2 levels were markedly elevated in these patients compared to controls (P less than 0.0001). Total IGF-II levels were within the normal range and the values were no different from controls but the distribution of IGF-II forms differed between patients and controls. Size-exclusion acid chromatography showed that 74 plus/minus 15 percent of IGF-II was present in the pro-IGF-II form, whereas only 18 plus/minus 4 percent corresponded to pro-IGF-II in controls. Scanning densitometry of immunoblots showed 74 plus/minus 6 percent in the band corresponding to pro-IGF-II compared to 27 plus/minus 9 percent in controls. The detection sensitivity of tricine SDS-PAGE method was the same as for size-exclusion chromatography, but this method is rapid and requires smaller amounts of serum. In conclusion, tricine SDS-PAGE analysis provides a useful, reproducible and sensitive method for the separation of the pro-IGF-II from mature IGF-II, and can be useful in the diagnosis of NICTH.