Heterogeneous hCG and hMG commercial preparations result in different intracellular signalling but induce a similar long-term progesterone response in vitro

Abstract

Study question: Are four urinary hCG/menotropin (hMG) and one recombinant preparation characterized by different molecular features and do they mediate specific intracellular signaling and steroidogenesis?

Summary answer: hCG and hMG preparations have heterogeneous compositions and mediate preparation-specific cell signaling and early steroidogenesis, although similar progesterone plateau levels are achieved in 24 h-treated human primary granulosa cells in vitro.

What is known already: hCG is the pregnancy hormone marketed as a drug for ARTs to induce final oocyte maturation and ovulation, and to support FSH action. Several hCG formulations are commercially available, differing in source, purification methods and biochemical composition.

Study design, size, duration: Commercial hCG preparations for ART or research purposes were compared in vitro.

Participants/materials, setting, methods: The different preparations were quantified by immunoassay with calibration against the hCG standard (Fifth IS; NIBSC 07/364). Immunoreactivity patterns, isoelectric points and oligosaccharide contents of hCGs were evaluated using reducing and non-reducing Western blotting, capillary isoelectric-focusing immunoassay and lectin-ELISA, respectively. Functional studies were performed in order to evaluate intracellular and total cAMP, progesterone production and β-arrestin 2 recruitment by ELISA and BRET, in both human primary granulosa lutein cells (hGLC) and luteinizing hormone (LH)/hCG receptor (LHCGR)-transfected HEK293 cells, stimulated by increasing hormone concentrations. Statistical analysis was performed using two-way ANOVA and Bonferroni post-test or Mann-Whitney's U-test as appropriate.

Main results and the role of chance: Heterogeneous profiles were found among preparations, revealing specific molecular weight patterns (20-75 KDa range), isoelectric points (4.0-9.0 pI range) and lectin binding (P < 0.05; n = 7-10). These drug-specific compositions were linked to different potencies on cAMP production (EC50 1.0-400.0 ng/ml range) and β-arrestin 2 recruitment (EC50 0.03-2.0 μg/ml) in hGLC and transfected HEK293 cells (P < 0.05; n = 3-5). In hGLC, these differences were reflected by preparation-specific 8-h progesterone production although similar plateau levels of progesterone were acheived by 24-h treatment (P ≥ 0.05; n = 3).

Large scale data: N/A.

Limitations, reasons for caution: The biological activity of commercial hCG/hMG preparations is provided in International Units (IU) by in-vivo bioassay and calibration against an International Standard, although it is an unsuitable unit of measure for in-vitro studies. The re-calibration against recombinant hCG,quantified in grams, is based on the assumption that all of the isoforms and glycosylation variants have similar immunoreactivity.

Wider implications of the findings: hCG/hMG preparation-specific cell responses in vitro may be proposed to ART patients affected by peculiar ovarian response, such as that caused by polycystic ovary syndrome. Otherwise, all the preparations available for ART may provide a similar clinical outcome in healthy women.

Study funding and competing interest(s): This study was supported by a grant of the Italian Ministry of Education, University and Research (PRIN 2015XCR88M). The authors have no conflict of interest.

Keywords: FSHFSH; LHLH; gonadotropin; hCGhCG; hMGhMG.