Stability of frozen serum levels of insulin-like growth factor-I, insulin-like growth factor-II, insulin-like growth factor binding protein-3, transforming growth factor β, soluble fas, and superoxide dismutase activity for the JACC study

BACKGROUND: Subjects of the Japan Collaborate Cohort Study (JACC Study) gave peripheral blood samples collected between 1988 and 1990. We conducted to investigate whether levels of serum components measured after 9 years of frozen storage are stable or not. METHODS: To assess the degradation of frozen serum components in the JACC Study, we compared levels of various components (IGF-I, IGF-II, IGFBP-3, TGF-beta 1, sFas, and total SOD activity) between fresh and stored sera collected from other inhabitants. Serum levels of constituents were measured by immunoradiometric assay (IGF-I, IGF-II and IGFBP-3), quantitative enzyme immunoassay (TGF-beta 1), enzyme-linked immuno-adsorbent assay (sFas), and an improved nitrite method (SOD activity). RESULTS: The coefficients of variation for intra- and inter-assay precisions of the measurements were less than 9%. Levels of IGF-I, IGF-II, IGFBP-3, TGF-beta 1 and sFas in sera after storage for 9 years at 80 degrees C were similar to those of fresh sera newly collected from inhabitants. The distributions of serum IGF-I, IGF-II, IGFBIP-3, TGF-beta 1, sFas and SOD activity for specimens collected from different individuals tended to be similar to those of serum levels for frozen specimens collected from different individuals and stored for 9 years. CONCLUSIONS: There was no statistically significant difference in distribution of measured values of IGF-I, IGF-II, IGFBP-3, TGF-beta 1, and sFas between newly collected sera and frozen specimens stored for 9 years. Thus, measurements of these serum constituents of specimens stored for the JACC Study can be reliably used in nested case-control study.