Steroid binding properties of the 2nd WHO International Standard for sex hormone-binding globulin

Background: Stocks of 95/560, the 1st International Standard for sex hormone-binding globulin (SHBG), are running out, and 08/266 has been prepared as a replacement. We compared the steroid binding capacities of 95/560 and 08/266. Methods: 95/560 and 08/266 stored at -20 degrees C, and accelerated thermal degradation samples of 08/266 were subjected to gelfiltration. Binding of the SHBG-containing fractions to a dihydrotestosterone derivative was then investigated using a surface plasmon resonance biosensor. The SHBG content of the gelfiltration fractions was determined with an immunoassay. Steroid binding capacity of each standard was then calculated as the mean of the ratio of biosensor binding/SHBG concentration. Affinity constants for the SHBG steroid interaction were calculated. Results: Maximum achievable biomolecular interactions were lower for 95/560 than for the 08/266 preparations. 95/560 exhibited steroid binding capacity only half as high as any of the novel standards, as well as a lower affinity constant for the SHBG steroid interaction. No significant differences could be observed between the samples of 08/266 stored at different temperatures. Conclusions: The steroid binding capacity of 08/266 is two times higher than that of 95/560. Steroid binding of lyophilized 08/266 is preserved at storage temperatures of up to 45 degrees C for at least 6 months.