Revealing the role of leucine in improving the social avoidance behavior of depression through a combination of untargeted and targeted metabolomics.

Leucine is a common nutritional supplement, and recently, research concerned with the improvement role of leucine in neuropsychiatric disorders has been increasingly emphasized. However, it is unclear what role leucine plays in depression. In this study, the chronic social defeat stress (CSDS) model was used to simulate depression associated with social avoidance in humans. CSDS mice display a depressive state and social avoidance behavior. Untargeted serum metabolomics and pathway analysis indicated that abnormal amino acid metabolism may be the key to abnormal behavior in CSDS mice. Among these metabolites, leucine shows a specific and significant positive correlation with social interaction rate. Targeted metabolomics determine the decreased level of leucine and related metabolites in the serum and hippocampus of CSDS mice. Moreover, immunohistochemical results also indicate an increasing expression of IDO1 in hippocampal tissues in CSDS mice, and neurons may be damaged. Subsequently, leucine was administered to investigate its influence on CSDS mice, and the results revealed that leucine had a good effect on depressive states and social avoidance behaviors. Taken together, we aim to identify the important role of leucine as a functional food supplement to improve depression and social avoidance behavior through the above findings.