Immunoradiometric assay for follistatin: serum immunoreactive follistatin levels in normal adults and pregnant women

Abstract

A sensitive and specific immunoradiometric assay for follistatin was developed using antifollistatin mouse monoclonal and rabbit polyclonal antibodies. The sensitivity of the assay was 0.5 micrograms/L, and cross-reactivities with recombinant human activin A and bovine inhibin were less than 0.1%. The intra- and interassay coefficients of variation were less than 10%, and the recovery rate was about 90% in human serum. The addition of activin A to the same sample resulted in a minimal influence on follistatin recovery, indicating that this assay system can measure the total level of activin-bound and unbound follistatin. Gel filtration analysis of human serum showed that the majority of immunoreactivity was eluted in a larger molecular size position than that of free follistatin, suggesting that the large part of follistatin is bound to other proteins, presumably activins, in serum. Using this assay, immunoreactive follistatin levels in various biological fluids and human sera were examined. The dose-response curves of porcine follicular and amniotic fluids were parallel to the standard curve, and porcine follicular fluid contained extremely high follistatin immunoreactivity (5.6 mg/L). The serum follistatin level in normal human volunteers was 13.3 +/- 4.7 micrograms/L (mean +/- SD; n = 60), with a tendency to increase gradually with age. On the other hand, the serum follistatin level was remarkably elevated in pregnant women (62.7 +/- 35.3 micrograms/L; n = 57), with a positive correlation with weeks of pregnancy. These data indicated that circulating immunoreactive follistatin is detectable in human serum, and the levels vary with physiological conditions such as aging and pregnancy.

Inhibition of myostatin with emphasis on follistatin as a therapy for muscle disease

“…Overall, measurements of follistatin during the menstrual cycle show few changes 15,18,29. However, a notable exception is during pregnancy, when follistatin concentrations rise toward term in parallel with activin 15,76,79. Follistatin is widely distributed throughout multiple organs, and the majority of follistatin found in the circulation is likely secreted from the walls of blood vessels.…”

Activin A and Follistatin as Biomarkers for Ectopic Pregnancy and Missed Abortion

“…The coordinated synthesis of FS with activin is the main regulator of the local bioactivity of activin, as binding of activin to FS is almost irreversible [5, 6]. Amongst activins, the role of serum activin A as a predictor of pregnancy failure has been the focus of heated debate amongst researchers suggesting that measurements of activin A can identify pregnant women at risk of developing missed abortion (MA) or EP, while others have failed to report such an association [2, 7–14].…”

“…Both factors are involved in the complex mechanisms allowing the establishment and the maintenance of pregnancy. Their serum concentrations rise throughout viable pregnancy [5, 6] and decline in a state of nonviable trophoblasts [17–20]. Furthermore, their serum concentrations are significantly lower in serial measurements in women who subsequently miscarried when compared with live births [11, 19–21].…”

Serum follistatin concentrations are increased in patients with septicaemia

“…FS and activin are detectable in serum (Demura et al, 1992(Demura et al, , 1993Sakai et al, 1992;Klein et al, 1993;Gilfillan & Robertson, 1994;Khoury et al, 1995;Knight et al, 1996;Tilbrook et al, 1996;McFarlane et al, 1996;Wakatsuki et al, 1996;Sakamoto et al, 1996) and FS concentrations in serum increase with age (Wakatsuki et al, 1996). Evidence that pharmacological concentrations of both polypeptides can affect pituitary hormone secretion in vivo, might suggest that the peptides could have endocrine functions (Inouye et al, 1991;Carroll et al, 1991;DePaolo et al, 1991: Stouffer et al, 1993Woodruff et al, 1993;Meriggiola et al, 1994;Tilbrook et al, 1996).…”

“…Evidence that pharmacological concentrations of both polypeptides can affect pituitary hormone secretion in vivo, might suggest that the peptides could have endocrine functions (Inouye et al, 1991;Carroll et al, 1991;DePaolo et al, 1991: Stouffer et al, 1993Woodruff et al, 1993;Meriggiola et al, 1994;Tilbrook et al, 1996). At present, however, the sources of FS and activin in serum are unknown, and a wealth of in vivo experiments show that the gonads are not the major source of circulating FS and activin (Sakai et al, 1992;Demura et al, 1993;Klein et al, 1993;Gilfillan & Robertson, 1994;Khoury et al, 1995;Tilbrook et al, 1996;McFarlane et al, 1996;Wakatsuki et al, 1996;Sakamoto et al, 1996;Phillips et al, 1996;Kettel et al, 1996). This makes endocrine gonadal-pituitary feedback of the polypeptides unlikely.…”