Remodeling of the Carbohydrate Chains of hCG by Use of Sialyltransferases: Effects on the Biological Activity

Human chorionic gonadotropin (hCG) is a glycoprotein hormone which contains both N- and O-linked carbohydrate chains. It consists of two subunits, a and 8. The a-subunit contains two N-linked carbohydrate chains: a mono-antenna and a non-fucosylated bi-antenna. The $-subunit contains both (two) N and (four) O-linked carbohydrate structures. Both of the N-linked carbohydrate chainsare biantennary, one of which is fucosylated

SIALYLTRANSFERASES; THEIR SPECIFICITY AND THEIR USE IN CARBOHYDRATE REMODELLING.

In order to apply sialyltransferases in the remodelling of the carbohydrate chains on biologically active glycoproteins, it is a prerequisite to know the fine specificity of these enzymes. In this report the specificity of several sialyltransferses involved in the sialylation of O- and N-linked oligosaccharide chains is reviewed. Also novel results on the branch specificity of a3- and a6-sialyltransferase are reported. The potential application of these enzymes in carbohydrate remodelling was studied using human chorionic gonadotropin (hCG) as a model glycoprotein. Differently sialylated preparations of this hormone were obtained and tested for their stimulatory effect on steroidogenesis in Leydig cells in vitro. Asialo-hCcG appeared to be only 45% as effective as native hCG. a3-Resialylation of the O-linked chains on the ß-subunit of this hormone did not restore the biological activity to a higher level. By contrast, 55% a6- resialylation of the N-linked chains yielded a preparation which was almost as active as native hCG. Interestingly, further sialylation by the a6-sialyltransferase resulted in a decrease of the bio-activity to levels lower than obtained with asialo-hcG. It is concluded that the lectin-carbohydrate binding, which is part of the process that triggers the biological respons of the target cell can be mimicked by N-linked chains carrying a6-linked sialic acid. However, too high a density of such residues interferes with this interaction

Treatment with the gonadotrophin-releasing hormone antagonist ganirelix in women undergoing ovarian stimulation with recombinant follicle stimulating hormone is effective, safe and convenient: Results of a controlled, randomized, multicentre trial

A multicentre, open-label, randomized study of the gonadotrophin-releasing hormone (GnRH) antagonist ganirelix (Orgalutran®/Antagon(TM)) was performed in women undergoing ovarian stimulation with recombinant FSH (rFSH:Puregon®). The study was designed as a non-inferiority study using a long protocol of buserelin (intranasal) and rFSH as a reference treatment. A total of 730 subjects was randomized in a treatment ratio of 2:1 (ganirelix:buserelin) using an interactive voice response system which stratified for age, type of infertility and planned fertilization procedure [IVF or intracytoplasmic sperm injection (ICSI)]. The median duration of GnRH analogue treatment was 5 days in the ganirelix group and 26 days in the buserelin group, whereas the median total rFSH dose was 1500 IU and 1800 IU respectively. In addition, in the ganirelix group the mean duration of stimulation was 1 day shorter. During ganirelix treatment the incidence of LH rises (LH ≥10 IU/l) was 2.8% versus 1.3% during rFSH stimulation in the buserelin group. On the day of triggering ovulation by human chorionic gonadotrophin (HCG), the mean number of follicles ≥11 mm diameter was 10.7 and 11.8, and the median serum oestradiol concentrations were 1190 pg/ml and 1700 pg/ml in the ganirelix and buserelin groups respectively. The mean number of oocytes per retrieval was 9.1 and 10.4 respectively, whereas the mean number of good quality embryos was 3.3 and 3.5 respectively. The fertilization rate was equal in both groups (62.1%), and the same mean number of embryos (2.2) was replaced. The mean implantation rates were 15.7% and 21.8%, and the ongoing pregnancy rates per attempt were 20.3% and 25.7% in the ganirelix and buserelin groups respectively. Evaluation of all safety data indicated that the ganirelix regimen was safe and well tolerated. The overall incidence of ovarian hyperstimulation syndrome was 2.4% in the ganirelix group and 5.9% in the reference group. The results of this study support a safe, short and convenient treatment regimen of ganirelix, resulting in a good clinical outcome for patients undergoing ovarian stimulation for IVF or ICSI.SCOPUS: ar.jinfo:eu-repo/semantics/publishe