THYROTROPIC ACTIVITY OF BASIC ISOELECTRIC FORMS OF HUMAN CHORIONIC-GONADOTROPIN EXTRACTED FROM HYDATIDIFORM MOLE TISSUES

hCG is known to have thyroid-stimulating activity and may cause hypert hyroidism in patients with trophoblastic diseases. hCG occurs in norma l and molar pregnancy with breaks or nicks in the alpha- or beta-subun it peptide linkage and with substantial heterogeneity in the compositi on and degree of branching within the oligosaccharide side-chains. The bioactivity of hCG is markedly influenced by these structural variati ons. We purified hCG from five hydatidiform moles, using chromatofocus ing separation after gel filtration. The hCG molecules were fractionat ed according to their isoelectric points, with a linear pH gradient fr om 3.2-6.1 and a final 1.0 mol/L NaCl step elution. The hCG immunoreac tivity of each fraction was measured by RIA, and the thyroid-stimulati ng activity of hCG was determined by means of the cAMP response in Chi nese hamster ovary cells expressing functional human TSH receptors (Ch inese hamster ovary-JP09 cells). The chromatofocusing profile showed t hat hCG from the moles was eluted in six or seven major peaks at pH 6. 1, 5.5, 5.3, 4.8, 3.8, and 3.2 and with 1.0 mol/L NaCl, whereas hCG ex tracted from serum of hydatidiform moles and standard hCG preparation CR-127 extracted from pregnancy urine showed only small peaks at pH gr eater than 5.3. Each fraction increased cAMP production significantly in Chinese hamster ovary-JP09 cells. The relative bioactivity/immunore activity, represented as the ratio of cAMP/hCG (picomoles per IU), was significantly higher in basic components (pI 6.1, 6.2 +/- 1.2; pI 5.5 , 4.4 +/- 2.7; pI 5.3, 5.8 +/- 0.3) than in hCG CR-127 (bioactivity/im munoreactivity, 0.42; P < 0.05). The difference in pI of each hCG isof orm was attributable to the extent of sialylation; basic hCG isoforms contained less sialic acid by immunological detection using lectins. T hese results indicate that isoforms of hCG with more thyrotropic activ ity were produced by trophoblastic tissues in patients with hydatidifo rm mole. We speculate that these isoforms of hCG may be responsible fo r the hyperthyroidism in some patients with hydatidiform moles.