Effects of 17beta-oestradiol and norethisterone acetate on sulfonation and sialylation of gonadotrophins in post-menopausal women

Abstract

Background: The number of terminal sialic acid and sulfonated N-acetylgalactosamine (SO(3)-GalNAc) on gonadotrophins in serum varies during the menstrual cycle and changes at menopause, suggesting that gonadal steroids modify their oligosaccharide synthesis. Our objective was to determine the effects of 17beta-oestradiol (E(2)) and a progestogen, norethisterone acetate (NETA), on the sulfonation and sialylation of gonadotrophins in post-menopausal women.

Methods: Serum samples were obtained from eight post-menopausal women treated with 20 mg E(2) implants every 6 months, from four women who in addition were treated daily with 5 mg NETA orally for a 2-week period, and from four women who got this NETA treatment during a 4-week period. Sera from 11 non-treated post-menopausal women served as a reference group. The gonadotrophin serum concentrations, the number of SO(3)-GalNAc and sialic acid residues per serum luteinizing hormone (LH) and follicle-stimulating hormone (FSH) molecule, and the distributions of molecules with 0-1-2-3-4 sulfonated residues were measured.

Results: The E(2)-treated post-menopausal women had considerably less (P < 0.001) sialic acid and slightly more (P < 0.01) SO(3)-GalNAc per serum LH and FSH molecule than the non-treated. Two weeks of NETA treatment increased the sulfonation of LH (P < 0.01) and FSH (P < 0.05) concomitantly with decreased (P < 0.05) sialylation of LH.

Conclusion: The primary effect of E(2) treatment was a decrease in sialylation and, due to competition for the same substrate, a secondary and consequentially minor increase in sulfonation of LH and FSH. The primary effect of the NETA therapy was an increase in the sulfonation of LH and FSH concomitantly with secondary and consequentially decreases in sialylation of LH.

Figure 1.

Relationship between LH concentration and changes in the number of sialic acid (open star) and sulfonated (filled circle) residues and negatively charged residues (filled square) on the oligosaccharides per LH molecule after 2 and 4 weeks of NETA therapy in two E₂-implant-treated post-menopausal women. The average numbers of sialic acid (SA^-) and sulfonated (SO₃^-) residues per serum LH molecule at the start of NETA treatment are given (w = weeks).

Figure 2.

Relationship between FSH concentration and changes in the number of sialic acid (open star) and sulfonated (filled circle) residues and negatively charged residues (filled square) on the oligosaccharides per FSH molecule after 2 and 4 weeks of NETA therapy in two E₂-implant-treated post-menopausal women. The average numbers of sialic acid (SA^-) and sulfonated (SO₃^-) residues per serum FSH molecule at the start of NETA treatment are given (w = weeks).

Figure 3.

Mean ± SEM of average number of sialic acid (lower panels) and sulfonated GalNAc (upper panels) residues per serum LH (left panels) and FSH (right panels) molecule in four groups of post-menopausal women. NETA was given to E₂-implant-treated women, and sera were taken at the start (E₂-implant) and after 2 (E₂+2wNETA) and 4 (E₂+4wNETA) weeks of treatment (non-treated = a reference group of non-treated post-menopausal women). Statistical comparison with preceding group. *P < 0.05; **P < 0.01; ***P < 0.001. Figures in parentheses indicate number of women in each group.

Figure 4.

Relationship between serum LH (upper panel) and FSH (lower panel) concentration and number of sialic acid (open star) and sulfonated GalNAc (filled circle) residues per molecule in four groups of post-menopausal women. NETA was given to E₂-implant-treated women, and sera were taken at the start (E₂-implant) and after 2 (E₂+2wNETA) and 4 (E₂+4wNETA) weeks of treatment (non-treated = a reference group of nine non-treated post-menopausal women). Significance of difference in number of residues/concentration is indicated. *P < 0.05; **P < 0.01; ***P < 0.001; ns = not significant. Figures in parentheses indicate number of women in each group.