Distinct molecular events suggest different pathways for preterm labor and premature rupture of membranes

Role of tumor necrosis factor-alpha in the premature rupture of membranes and preterm labor pathways

OBJECTIVE

To further delineate the differences between the preterm labor and premature rupture of the membrane pathways, we investigated the role of the inflammatory cytokines as activators of matrix metalloproteinases 2 and 9 in human fetal membranes.

STUDY DESIGN

Normal amniochorionic membrane that is maintained in an organ explant system was stimulated with interleukin-1beta, tumor necrosis factor-alpha, or interleukin-6. The expression and activity of matrix metalloproteinases 2 and 9 in amniochorion was documented with reverse transcriptase-polymerase chain reaction and specific substrate activity assays. The matrix metalloproteinase inhibitor, tissue inhibitor of metalloproteinase-1, concentration was measured by enzyme-linked immunosorbent assay.

RESULTS

Interleukin-1beta, tumor necrosis factor-alpha, and interleukin-6 induced the expression of matrix metalloproteinase-9 messenger RNA, whereas matrix metalloproteinase-2 expression was constitutive in control and cytokine-stimulated tissues. Matrix metalloproteinase-2 activity did not change after cytokine stimulation. Active matrix metalloproteinase-9 was significantly higher in tumor necrosis factor-stimulated tissues, which conversely were not changed after interleukin-1 or interleukin-6 stimulation. Tissue inhibitor of metalloproteinase-1 levels were decreased after interleukin-1 and tumor necrosis factor stimulation but changed after interleukin-6 stimulation.

CONCLUSION

Only tumor necrosis factor-alpha increases matrix metalloproteinase-9 activity in amniochorion.

Neutrophil elastase and secretory leukocyte protease inhibitor in prelabor rupture of membranes, parturition and intra-amniotic infection

OBJECTIVE

Neutrophil elastase (NE), a multifunctional serine protease stored in azurophilic granules of mature neutrophils, is capable of intracellular degradation of proteins during phagocytosis and extracellular degradation of connective tissue during an inflammatory process. Secretory leukocyte protease inhibitor (SLPI) is a natural NE inhibitor present in amniotic fluid, fetal membranes and cervical mucus. An imbalance between NE and SLPI has been implicated as a mechanism of abnormal tissue destruction in chronic inflammatory diseases. The purpose of this study was to determine if parturition, premature rupture of the membranes (PROM) and microbial invasion of the amniotic cavity are associated with changes in amniotic fluid concentrations of NE and SLPI.

STUDY DESIGN

Amniotic fluid was retrieved by amniocentesis from 380 patients in the following groups: (1) preterm labor and intact membranes without microbial invasion of the amniotic cavity who delivered at term (n = 13) or prematurely (n = 26), and preterm labor with microbial invasion of the amniotic cavity (n = 9); (2) preterm PROM with (n = 34) and without (n = 51) microbial invasion of the amniotic cavity; and (3) term gestation without microbial invasion of the amniotic cavity with intact membranes not in labor (n = 63), in labor (n = 158), and with rupture of membranes not in labor (n = 26). Microbial invasion of the amniotic cavity was determined by a positive amniotic fluid culture for micro-organisms including aerobic, anaerobic and Mycoplasma species. NE and SLPI amniotic fluid levels were determined by highly specific and sensitive immunoassays.

RESULTS

Preterm PROM was associated with a significant increase in the amniotic fluid concentration of NE. Microbial invasion of the amniotic cavity was associated with a significant increase in the amniotic fluid concentration of NE in women with preterm labor and intact membranes, as well as in women with preterm PROM. Term and preterm parturition was associated with a significant increase in the amniotic fluid concentration of NE. In the absence of microbial invasion of the amniotic cavity, preterm and term PROM were associated with a significant reduction in the amniotic fluid concentration of SLPI.

CONCLUSION

Preterm PROM, microbial invasion of the amniotic cavity, and parturition at term and preterm are associated with a significant increase in the amniotic fluid concentration of NE. PROM is associated with a reduced amniotic fluid concentration of SLPI.

TNF-alpha promotes caspase activation and apoptosis in human fetal membranes

PURPOSE

Increased amniotic fluid tumor necrosis factor (TNF) is a marker of infection when associated with preterm labor and preterm premature rupture of the amniochorionic membranes (PROM). We have noted increased apoptosis in membranes derived from women with PROM. This study examines the role of TNF in promoting fetal membrane apoptosis.

METHODS

Amniochorion (n = 8), collected at the time of elective repeat cesarean section prior to labor from normal term gestation, were placed in an organ explant system. After 48 h in culture, the membranes were stimulated with recombinant TNF-alpha (20 ng/mL) for 24 h. Tissue frozen after stimulation was subjected to RT-PCR to study the expression of TNF-induced caspase genes. ELISA assayed the levels of proapoptotic p53 in tissues and cell death related nuclear matrix protein (NMP) in tissue culture supernatants. The activity of caspases in tissue homogenates was measured using substrates specific for caspase 2, 3, 6, 8, and 9. Results were analyzed by using the Wilcoxon nonparametric test for paired samples. A p < 0.05 was considered significant.

RESULTS

RT-PCR showed induction of caspases 2, 8, and 9 (caspase cascade initiators) in human fetal membranes after TNF stimulation. Caspases 3 and 6 (effector caspases) expression was constitutive in both TNF stimulated- and control membranes. Caspases, 2, 3, 8, and 9 activity was significantly higher in TNF-stimulated tissues compared with control, whereas, no significant change in caspase 6 activity was noticed. TNF-stimulated tissues released increased levels of NMP (24.03 U/mL) compared with control (13.5U/mL) (p = 0.03). TNF also increased p53 levels in the tissues (0.05 ng/mL) compared with control cultures (0.03 ng/mL; p = 0.02).

CONCLUSIONS

TNF increases proapoptotic p53 levels and caspase activities in fetal membranes. Increased NMP reflects cell death.