Impact of intraamniotic inflammation on tryptophan metabolism in the placenta-fetal brain axis in rats

The placenta plays a crucial role beyond nutrient transfer, acting as a dynamic endocrine organ that significantly influences maternal physiology and fetal development. It responds rapidly to even slight changes in the in utero environment to promote fetal survival. Disruptions in placental function are increasingly recognized as key contributors to the origins of neurodevelopmental disorders. In this study, we employed advanced technology to induce intrauterine inflammation through ultrasound-guided administration of LPS into gestational sacs. We then evaluated its effects on the gene expression of enzymes involved in TRP metabolism and conducted a comprehensive LC/MS analysis of the metabolome in the placenta and fetal brain of Wistar rats. Our results show that intraamniotic injection of LPS induces a robust inflammatory response leading to significant alterations in TRP metabolism, including downregulation of tryptophan hydroxylase (TPH) in the placenta, resulting in a decrease in serotonin (5-HT) levels. Similarly, in the fetal brain, exposure to LPS led to reduced Tph expression and increased monoamine oxidase expression, suggesting a decrease in 5-HT synthesis and an increase in its degradation. Furthermore, an upregulation of the kynurenine pathway was observed in both the placenta and fetal brain. Moreover, we detected a shift toward neurotoxicity, evidenced by an imbalance between neuroprotective and neurotoxic metabolites, including decreased levels of kynurenic acid and upregulation of kynurenine monooxygenase in the fetal brain. In conclusion, our findings reveal significant alterations in TRP metabolism following intrauterine inflammation, potentially contributing to neurodevelopmental disorders.