Bacterial Endotoxin Increases Type II Phospholipase A2 Immunoreactive Content and Phospholipase A2 Enzymatic Activity in Human Choriodecidua1

Abstract

The aim of this study was to establish the effect of bacterial endotoxin lipopolysaccharide (LPS) on type II phospholipase A2 (PLA2) content and in vitro net PLA2 enzymatic activity in human choriodecidua. More particularly, the objective was to ascertain whether an increase in type II PLA2 tissue content and PLA2 enzymatic activity is associated with the previously documented stimulatory effect of LPS on prostaglandin E2 (PGE2) release from choriodecidua. Choriodecidua explants were incubated in RPMI 1640 (control) or RPMI 1640 containing LPS (0.1 ng/ml to 10 micrograms/ml) for up to 24 h. Under the incubation conditions utilized, LPS (1 μg/ml) stimulated the release of PGE2 3-fold (p < 0.001, n = 4 tissues), in a time-dependent manner (p < 0.005). Tissue immunoreactive (ir)-type II PLA2 content and PLA2 enzymatic activity were determined by monoclonal antibody sandwich ELISA and radiolabeled enzyme assay procedures, respectively. The tissue content of type II PLA2 immunoreactivity in choriodecidua obtained from women (n = 7) at term but not in labor averaged 155 ± 24 ng/ml DNA. PLA2 enzymatic activity average 29.8 ± 5.1 pmol phosphatidylethanolamine (PE)/mg DNA/h. LPS at a concentration of 1 μg/ml increased immunoreactive type II PLA2 tissue content by 180% of the control value (p < 0.05, n = 7) within 1 h of exposure and remained significantly elevated for 18 h when compared to controls (174% of control, p < 0.01, n = 7). This increase in type 11 PLA2 tissue content was associated with a significant increase in PLA enzymatic activity at both 1 h and 18 h of incubation (140% of control, p < 0.02, n = 7 and 180% of control, p < 0.01, n = 7, respectively). These data establish type II PLA2 as a locus of action of LPS in human choriodecidua and support an etiological role for LPS in the increased phospholipid metabolism and eicosanoid formation that occur in human gestational tissues at the time of bacterial infection-associated preterm labor.