Recombinant human thyroid-stimulating hormone: initial bioactivity assessment using human fetal thyroid cells.

We have assessed the bioactivity of newly available recombinant human TSH (rec-hTSH) using human fetal thyroid cells, with the longer term aim of assessing its use for clinical applications. Rec-hTSH caused a consistent and dose-related increase in thyroid monolayer cell cAMP release and human thyroglobulin (hTg) secretion, confirming its bioactivity. Repetitive studies (n = 5) allowed us to derive an estimated biopotency for the rec-hTSH preparation examined of 5.6 IU/mg compared to 10 IU/mg for commercially available bovine TSH for human use. The rec-hTSH had a bioimmune ratio of 0.55, similar to that of purified pituitary hTSH standards, Furthermore, rec-hTSH induced thyroid epithelial cell growth, as evidenced by a decrease in thyroid cell doubling time from 54 +/- 2.1 to 31 +/- 1.7 h (P less than 0.005). Hence, rec-hTSH is a potent glycoprotein hormone preparation when measured in a homologous human thyroid cell culture system. Rec-hTSH could serve as a future definitive International Standard and has the potential for a useful diagnostic and therapeutic reagent.