Tryptophan catabolism and the intrauterine renin-angiotensin system in pregnancy

Indoleamine 2,3-dioxygenase (IDO) and tryptophan 2,3-dioxygenase (TDO) are key enzymes for tryptophan (Trp) degradation in the placenta, that is crucial for immune tolerance during pregnancy. Intrauterine renin-angiotensin system is also involved in the progression of a healthy pregnancy. Angiotensin (Ang) (1-7) inhibits the pro-inflammatory actions of Ang II, maintaining the integrity of fetal membranes. Since the correlation between Trp catabolism and intrauterine Ang (1-7) has never been investigated, we aimed to assess the co-expression of IDO, TDO and Ang (1-7) in the placenta. We also studied plasma levels of Trp and its catabolite kinurenine (kyn), and their correlation with placental IDO and TDO expression.