▎HCG Research

What is the research background of hCG?

hCG plays a crucial role in reproductive medicine, including maintaining early pregnancy and inducing ovulation in assisted reproductive technologies. Natural hCG is primarily extracted from pregnant women's urine, presenting limitations in supply and purity assurance. This fails to meet growing clinical demands, necessitating the development of synthetic hCG to provide a more stable and reliable drug source.

Advancements in genetic engineering technology have enabled the cloning and expression of the hCG gene, laying the technical foundation for synthetic hCG research. By introducing the hCG gene into host cells such as yeast or Chinese hamster ovary (CHO) cells, recombinant expression of hCG can be achieved. Synthetic hCG provides purer samples for structural and functional studies, facilitating deeper understanding of its mechanisms of action and enabling the development of more effective therapeutic approaches. Additionally, synthetic hCG can be used to prepare diagnostic reagents, enhancing the accuracy of pregnancy diagnosis and monitoring related conditions.

What is the mechanism of action for hCG?

Mechanism in maintaining pregnancy: hCG is primarily produced by differentiated syncytiotrophoblast cells and serves as a crucial embryonic signal essential for sustaining pregnancy. It activates multiple signaling cascades by binding to the luteinizing hormone/human chorionic gonadotropin receptor (LHCGR). Research by Nwabuobi C indicates that through direct or indirect interactions with the transforming growth factor beta receptor (TGFβR), it activates maternal signaling pathways such as Smad2, protein kinase C (PKC), and/or protein kinase A (PKA). In promoting uterine endothelial angiogenesis, hCG helps provide adequate nutrition and oxygen for embryonic development; In maintaining uterine myometrial quiescence, it creates a stable intrauterine environment conducive to embryo implantation and development; In promoting immune regulation at the maternal-fetal interface, hCG modulates the maternal immune system to prevent rejection of the embryo, ensuring successful pregnancy progression^[1].

Mechanism of action in improving endometrial receptivity: In vivo experiments using an embryo implantation dysfunction (EID) mouse model and human endometrial epithelial cells (EECs) revealed that hCG enhances endometrial receptivity in EID mice. hCG regulates the miR-126-3p/PIK3R2 axis by promoting miR-126-3p expression and inhibiting PIK3R2, while miR-126-3p targets PIK3R2. EEC proliferation was enhanced after hCG treatment but inhibited when miR-126-3p was downregulated. Both in vivo and in vitro experiments confirmed that hCG enhances endometrial receptivity and facilitates embryo implantation by activating the PI3K/Akt/eNOS pathway via the miR-126-3p/PIK3R2 axis^[2].

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Figure 1 hCG improved endometrial receptivity in EID mice^[2].

Impact of glycosylation on hormonal mechanisms: Studies on the glycosylated moiety of hCG indicate that removing different sugar residues from hCG derivatives differentially affects their binding capacity to rat Leydig cells and their ability to stimulate testosterone and cyclic AMP (cAMP) synthesis. With sequential removal of sialic acid, galactose, N-acetylglucosamine, and mannose residues, the effective hormone dose required to stimulate steroid production progressively increased, while the capacity to stimulate cAMP accumulation significantly decreased. Low-dose glycosidase-treated hormone derivatives exhibited additive effects when analyzed with hCG for their ability to stimulate testosterone synthesis. However, these derivatives were potent inhibitors of hCG-induced cAMP accumulation, suggesting that glycosylation removal minimally affects hormone-cell binding while diminishing the ability of bound hormones to activate adenylate cyclase. This further underscores the critical role of glycosylation in signal transduction within the hCG mechanism of action^[3].

What are the applications of hCG?

Early pregnancy diagnosis: Synthetic hCG is used to prepare detection reagents. In clinical practice, pregnancy is determined by measuring hCG levels in a woman's urine or blood. Approximately 6–7 days after fertilization, trophoblast cells begin secreting hCG. As gestation progresses, hCG levels in both blood and urine rise rapidly. Using synthetic hCG as a standard allows for the precise establishment of a standard curve for detection reagents, enabling accurate quantification of hCG content in samples. For example, common pregnancy test strips rely on immunochromatography technology, where antibodies prepared from synthetic hCG specifically bind to hCG in urine, with a color reaction indicating pregnancy status. Typically, after a missed period, women can use such methods for preliminary pregnancy assessment, providing a basis for subsequent prenatal care and management^[1].

Monitoring pregnancy-related conditions: During pregnancy, tracking dynamic changes in maternal hCG levels aids in diagnosing and monitoring various pregnancy-related disorders. For example, in ectopic pregnancies, where the fertilized egg implants outside the uterine cavity, the trophoblastic cells develop abnormally. This results in lower hCG secretion compared to normal intrauterine pregnancies and a prolonged doubling time. Continuous monitoring of blood hCG levels, combined with ultrasound examinations, facilitates early detection of ectopic pregnancies. This allows for timely intervention and treatment, preventing severe complications. Additionally, for trophoblastic diseases like hydatidiform mole, hCG levels typically show abnormal elevation. Post-treatment, continuous hCG monitoring can assess therapeutic efficacy and detect recurrence. Persistently elevated or rising hCG levels indicate potential residual disease or relapse, necessitating further investigation and intervention ^[1].

What are the experimental advances regarding hCG?

Contraceptive vaccines developed using the full β-subunit of hCG as the immunogen and a 37-amino acid peptide segment (C-terminus 109-145) as the immunogen have passed preclinical toxicity and safety trials and completed Phase I and Phase II clinical trials. In a comparative Phase I clinical trial involving 116 female volunteers who had undergone tubal ligation, three β-hCG-based vaccine formulations were tested. Results showed that all vaccinated women developed antibodies against hCG and tetanus, indicating these vaccines effectively stimulate the human immune response ^[4].

To achieve birth control and treat hormone-related diseases, researchers developed vaccines targeting hCG. Immunogens were prepared by linking synthetic peptides representing the natural primary structure of the hCG β-subunit to protein carriers. During development, researchers synthesized multiple peptides of varying lengths selected from the C-terminal region of the β subunit and tested their ability to induce antibodies capable of reacting with hCG and neutralizing its activity in vivo. Ultimately, a 37-amino acid peptide segment representing the C-terminal region of the β subunit was selected as the vaccine antigen. Diphtheria toxoid was chosen as the carrier, leading to the preparation of the first prototype vaccine. Following trials across multiple species, this vaccine successfully induced significant antibody levels against hCG, and a marked reduction in fertility was observed in immunized baboons. This provided new insights and potential approaches for human fertility control and related disease treatment ^[5].

Conclusion

As a key glycoprotein hormone, hCG plays a central regulatory role in the reproductive system: in females, it acts by binding to the luteinizing hormone/ chorionic gonadotropin receptor (LHCGR) to sustain early pregnancy (supporting luteal progesterone secretion and creating a stable uterine environment), promoting oocyte maturation and ovulation, and enhancing endometrial receptivity to facilitate embryo implantation. In males, it stimulates Leydig cells to synthesize and secrete testosterone, aiding reproductive organ development and spermatogenesis.

About The Author

The above-mentioned materials are all researched, edited and compiled by Peptisource.

Scientific Journal Author

Nwabuobi C is a researcher focusing on the field of human chorionic gonadotropin (hCG) studies. Their research mainly centers on analyzing the biological functions of hCG and exploring its connections with clinical applications. Nwabuobi C often adopts a combination of experimental methods such as molecular biology techniques and clinical sample analysis to conduct in-depth research, aiming to deepen the understanding of the physiological mechanisms of hCG and its practical value in clinical scenarios. Nwabuobi C is listed in the reference of citation [1].

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