Identification and characterization of metalloproteinase inhibitor activity in human ovarian follicular fluid

Metalloproteinase inhibitors regulate collagenase activity in the extracellular matrix. To assess the role of metalloproteinase inhibitors in the ovulatory process, inhibitor activity was examined in human follicular fluid collected 2-4 h before ovulation. The relationship between inhibitor activity and steroid content was determined, and the inhibitors were partially purified and characterized. Inhibitory activity in follicular fluid (n = 25) correlated with both follicular estradiol (P < 0.001) and progesterone (P < 0.02) concentrations per follicle. Chromatographic separation of the follicular fluid on Sepharose 6B isolated two peaks of inhibitory activity. The inhibitor from the small mol wt (M(r)) peak shared many of the properties of tissue inhibitors of metalloproteinase. It was stable in response to heat (60 C) and methylamine (200 mM), and was destroyed by reduction and alkylation, a procedure reported to destroy previously characterized inhibitors. Partial purification by affinity and ion exchange chromatography demonstrated the inhibitor to be a glycoprotein with an approximate M(r) of 28-29K. The large M(r) inhibitor had an approximate size of 700K and exhibited many of the characteristics of α₂-macroglobulin, a serum-derived metalloproteinase inhibitor. It was sensitive to heat, methylamine, and reduction and alkylation. Thus, follicular fluid contains metalloproteinase inhibitor activity that is steroid related and may be hormonally regulated. Ovarian metalloproteinase inhibitors may act to regulate connective tissue remodeling during follicular rupture.