Gonadotropin Glycoforms Circulating in Women Using Progestins of the Levonorgestrel Family for Contraception

Abstract

Context

The progestins of the levonorgestrel family are 13-ethylgonane progestins, commonly used for contraception in women. One contraceptive effect of these progestins is inhibition of ovulation, which may be a result of changes in gonadotropin glycosylation patterns. Gonadotropin glycoforms differ in number of glycans and bioactivity: more bioactive low-N-glycosylated glycoforms, diglycosylated luteinizing hormone (LHdi) and triglycosylated follicle-stimulating hormone (FSHtri), and less bioactive fully N-glycosylated glycoforms, LHtri and FSHtetra.

Objective

Characterize the glycosylation patterns on the circulating gonadotropin glycoforms in women using 13-ethylgonane progestins for contraception.

Design, Subjects, Main Outcome Measures

Serum samples, collected from 92 healthy women using 13-ethylgonane progestins for contraception, were included. Forty women used progestin-only continuously and 52 used progestins combined with ethinylestradiol (EE) for 3 weeks followed by a hormone-free week. Concentration, sulfonation, and sialylation of each glycoform were determined and compared with follicular phase values of normal menstrual cycles.

Results

The progestin-only group had significantly increased serum levels, decreased sulfonation, and increased sialylation of LHdi. The LHdi/FSHtri ratio was increased. The progestin+EE group had significantly decreased gonadotropin glycoform concentrations and decreased sialylation of FSHtri. The progestin+EE effect on sialylation of FSHtri occurred later during the treatment cycle in contrast to the effect on FSHtri concentration.

Conclusions

The 2 different progestin treatments induced different effects on the glycan synthesis and concentrations of more bioactive low-glycosylated gonadotropins. Progestin-only treatment increased sialylation and decreased sulfonation of LHdi molecules, contributing to sustained higher levels of bioactive LHdi molecules. Progestin+EE treatment decreased sialylation of FSHtri, contributing to a shorter half-life and decreased levels of bioactive FSHtri.