Reduction-oxidation (redox) state regulation of matrix metalloproteinase activity in human fetal membranes

Objective: The mechanisms underlying membrane rupture at term and preterm are obscure. Collagenolytic activity of matrix metalloproteinases in amniochorionic membranes increases during spontaneous term and preterm labor associated with intra-amniotic infection. We sought to test the hypothesis that reduction-oxidation homeostasis, which is altered in inflammatory states, directly regulates amniochorionic matrix metalloproteinases. Study Design: Membranes were collected from 7 patients undergoing elective cesarean delivery at term, rinsed thoroughly, and immediately incubated in phosphate-buffered sodium chloride solution at 37°C for 24 hours. Matrix metalloproteinase activity in the culture medium was assayed by substrate-gel electrophoresis and normalized against the dry weight of the tissue incubated. Superoxide anions were generated in the presence of membranes by a xanthine (2 mmol/L) and xanthine oxidase (20 mU/mL) mixture and monitored by reduction of ferri–cytochrome c to ferro–cytochrome c. Incubations were performed in the presence of xanthine alone, a xanthine–xanthine oxidase mixture, superoxide dismutase (500 U/mL), a xanthine–xanthine oxidase–superoxide dismutase mixture, nitro-l -arginine (a nitric oxide synthase inhibitor, 1 mmol/L), xanthine–xanthine oxidase–nitro-l -arginine, S-nitroso-N -acetylpenicillamine (a nitric oxide donor, 10 mmol/L), xanthine–xanthine oxidase–S-nitroso-N -acetylpenicillamine, N -acetylcysteine (a thiol-containing antioxidant, 0.1, 1, or 10 mmol/L), lipopolysaccharide (100 ng/mL), or lipopolysaccharide–N -acetylcysteine. Intracellular generation of superoxide anions was monitored by the reduction of nitroblue tetrazolium to formazan. Results: Basal matrix metalloproteinase 9 and matrix metalloproteinase 2 levels were detected in all samples. Superoxide anions significantly increased matrix metalloproteinase 9 activity but did not increase matrix metalloproteinase 2 activity, which effect was reversed by the addition of superoxide dismutase. N -acetylcysteine reduced basal activity of both matrix metalloproteinase 9 and matrix metalloproteinase 2 to 20%. Importantly, N -acetylcysteine completely inhibited intracellular formazan formation in cultured membranes both in the absence and in the presence of lipopolysaccharide. Neither nitric oxide synthase inhibition nor the nitric oxide donor S-nitroso-N -acetylpenicillamine had any effect on fetal membrane matrix metalloproteinase activity. Conclusion: Matrix metalloproteinase activity in human fetal membranes is reduction-oxidation (redox)–regulated. Matrix metalloproteinase 9 activity in human fetal membranes is directly increased by superoxide anion, a byproduct of macrophages and neutrophils. Neither nitric oxide donors nor nitric oxide synthase inhibitors significantly affect matrix metalloproteinase activity in human fetal membranes. The glutathione precursor N -acetylcysteine dramatically inhibits amniochorionic matrix metalloproteinase activity in addition to inhibiting intrinsic superoxide generation within the tissue. Thus thiol-reducing agents, such as N -acetylcysteine, may be beneficial in preventing preterm premature rupture of the membranes. (Am J Obstet Gynecol 2000;182:458-64.)