Role of TNF-α in the mechanisms responsible for preterm delivery induced by Stx2 in rats

BACKGROUND AND PURPOSE Infections with a strain of Escherichia coli producing Shiga toxins could be one of the causes of fetal morbidity and mortality in pregnant women. We have previously reported that Shiga toxin type 2 (Stx2) induces preterm delivery in pregnant rats. In this study, we evaluate the role of TNF-alpha, PGs and NO in the Stx2-induced preterm delivery. EXPERIMENTAL APPROACH Pregnant rats were treated with Stx2 (0.7 ng g(-1)) and killed at different times after treatment. Placenta and decidua were used to analyse NOS activity by the conversion of L-[C-14]arginine into L-[C-14]citrulline, levels of PGE(2) and PGF(2 alpha) assessed by radioimmunoassay, and cyclooxygenase (COX) proteins by Western blot. TNF-alpha level was analysed in serum by ELISA and by cytotoxicity in L929 cells. The inhibitor of inducible NOS, aminoguanidine, the COX-2 inhibitor, meloxicam, and the competitive inhibitor of TNF-alpha, etanercept, were used alone or combined to inhibit NO, PGs and TNF-alpha production respectively, to prevent Stx2-induced preterm delivery. KEY RESULTS Stx2 increased placental PGE(2) and decidual PGF(2 alpha) levels as well as COX-2 expression in both tissues. Aminoguanidine and meloxicam delayed the preterm delivery time but did not prevent it. Etanercept blocked the TNF-alpha increase after Stx2 treatment and reduced the preterm delivery by approximately 30%. The combined action of aminoguanidine and etanercept prevented Stx2-induced preterm delivery by roughly 70%. CONCLUSION AND IMPLICATIONS Our results demonstrate that the increased TNF-alpha and NO induced by Stx2 were the predominant factors responsible for preterm delivery in rats.