Study on the antipyretic activity and potential mechanism of Indigo Naturalis on lipopolysaccharide-induced fever rat model

Abstract Background As a Traditional Chinese Medicine with an antipyretic effect, Indigo Naturalis (IN) has a long history of application in China. It is often used with other heat-clearing drugs to treat high fever in children, which is different from other heat-clearing medicines. But its antipyretic effect and mechanism have not been fully elucidated yet. And the heat-clearing development of IN lacks convincing current evidence. Methods This study aimed to uncover the antipyretic effect and mechanism of IN on infectious fever by rectal temperature, pyrogen cytokines and metabolomics. Materials and Methods Firstly, the antipyretic effect of IN on LPS-induced fever rats was evaluated by the changes in rat rectal temperature. Then, the content of PGE2 and cAMP in the hypothalamus and TNF-α, IL-1β and IL-6 in the serum were determined by ELISA. Finally, the plasma and urine samples of febrile rats were analyzed in combination with UHPLC-Q-TOF-MS to explore the antipyretic mechanism of IN. Results Compared with pyrexia model rats, the rectal temperature of rats treated with Indigo Naturalis was suppressed after 0.5 h (P <0.01). The enzyme-linked immunosorbent assay (ELISA) showed that the expression of tumor necrosis TNF-α (P <0.01) and IL-6 (P <0.05) were suppressed by IN. A total of 11 endogenous metabolites were identified from the plasma samples of the IN group, the model group and the control group. Furthermore,15 metabolites were identified in the urine samples. Pathway analysis showed that IN mainly regulated glycerophospholipid metabolism, glucuronide mutual conversion and tryptophan metabolism. Conclusion This study clarified the exact effect of IN on infectious fever. It mainly works by regulating pyrogenic cytokines and glycerophospholipid pathways. The present research provided a deeper understanding of the traditional heat-clearing effect of IN. It provided a reference for the further scientific research of IN and the selection of antipyretic drugs in clinical practice.