Inhibition of in vitro fertilization of mouse gametes by sulfated sialic acid polymers

The effect of sialic acid (N-acetyl neuraminic acid), sialic acid dimer, si alic acid polymers (colominic acid) and sulfated colominic acid on the acti vity of hyaluronidase, on the dispersion of cumulus cells by mouse sperm an d on ill vitro mouse fertilization (sperm penetration of zona pellucida) we re evaluated. Bovine testicular hyaluronidase activity was significantly in hibited by colominic acid and sulfated colominic acid, but not by sialic ac id and its dimer, The dispersion of cumulus cells from eggs by mouse sperm was also inhibited by colominic acid and sulfated colominic acid. In vitro fertilization of mouse gametes was inhibited by sulfated colominic acid. Th e IC50 value of sulfated colominic acid-induced inhibition of fertilization was 0.3 mg/ml (ca. 0.9 mM), The value changed from 0.9 mM for cumulus-surr ounded egg to 1.5 mar for cumulus free-egg, On the other hand, colominic ac id showed Little or no inhibitory effect on mouse in vitro fertilization at 0.5 mg/ml (ca. 1.5 mM). This antifertility activity by sulfated colominic acid did not appear to be due to an effect on sperm motility or on the oocy tes, These results suggest that (1) the cumulus cells surrounding the eggs were dispersed by sperm hyaluronidase, (2) hyaluronidase was inhibited by c olominic acid and by sulfated colominic acid, (3) sulfated colominic acid i nhibits sperm penetration of zona pellucida by the inhibition of hyaluronid ase and/or some enzymes required for mouse gametes fertilization.