Endocrine Abstracts

Introduction: Human chorionic gonadotropin (hCG) is a glycoprotein hormone composed by two subunits, an alpha subunit common to all gonadotropins and a specific beta subunit. hCG is produced by trophoblast cells as differently glycosylated isoforms with a wide range of molecular weight, from 30 to 50 KDa (‘regular’ hCG is 37 KDa). hCG is used in the treatment of infertility. The aim of this study is to analyse and compare the composition of different commercial hCG.

Design: Three hCG preparations from pregnancy urine (50 mIU Gonasi-IBSA, 50 mIU Pregnyl-Organon, 70 mIU Sigma C0434), one recombinant (5 ng r-hCG, Ovidrel-Serono) and an urinary hMG (75–300 mIU Meropur-Ferring) were compared by 12% SDS–PAGE and western blotting using a polyclonal antibody against hCG beta subunit (Dako A0231). Different conditions were used in processing all the preparations such as denaturing and reducing samples or preserving their ‘native’ conformation. The western blotting patterns were confirmed by ConA Affinity Chromatography.

Results: Despite no particular differences were observed under denaturing-reducing conditions, we found qualitatively and quantitatively peculiar patterns under ‘native’ conditions. In the urinary hCG preparations up to three isoforms were found with different molecular weights (32, 37 and 45 KDa; n=4). In contrast, in r-hCG four variants were found (one doublet at 31–32 KDa and a doublet more expressed at 44–45 KDa; n=4). All preparations, including hMG, seem to contain hyperglycosylated hCG (hCG-H) of about 45 KDa which was characterized against hCG-H purified from human choriocarcinoma cell line (JEG-3) culture medium as control. ConA Affinity Chromatography confirmed that all the isoforms detected were glycosylation variants of hCG.

Conclusions: The commercial hCG and hMG preparations consist of several isoforms which differ in molecular weight and grade of glycosylation. Surprisingly, r-hCG has a wider range of glycosylated variants than urinary hCG. The peculiar signal pattern observed by western blotting demonstrates the heterogeneity of hCG in commercial preparations.