Presence of immunoreactive salusin-α in human serum and urine

Salusins, identified from a full-length enriched human cDNA library by bioinformatics analyses, show mitogenic, neuromodulatory and hemodynamic activities in rats. They are expressed in a wide variety of human tissues, but their precise structures and levels in human body fluids remain unknown. We developed a radioimmunoassay suitable for the detection of immunoreactive human salusin-alpha and characterized the molecular forms and concentrations of salusin-a in human serum and urine. The assay allowed for measurement of immunoreactive salusin-a concentrations as low as 1 fmol/tube after extraction of serum with an octyl-silica column, and the concentration required for 50% inhibition of binding was 40 fmol/tube. Cross-reactivities with salusin-beta and other bioactive peptides were negligible. Salusin-alpha-like immunoreactivity in normal human serum and urine ranged from 11.0 to 40.4 pmol/l (mean +/- S.D., 23.3 +/- 8.1 pmol/l, n = 31) and from 18.6 to 367.3 pmol/l (mean +/- S.D., 156.8 +/- 95.8 pmol/l), respectively. Reverse-phase high performance liquid chromatography coupled with radioimmunoassay detection revealed a major immunoreactive component that coeluted with authentic salusin-a. These data indicate the presence of salusin-a in human serum and urine, thereby verifying the initially predicted processing sites for salusin-a in humans. (c) 2006 Elsevier Inc. All rights reserved.