Diurnal variation of metabolites in three individual participants

The circadian system influences virtually all biological functions. Understanding the impact of circadian variation on metabolism may provide insight into mechanisms of circadian-associated disorders and guide the implementation of chrono-therapy. Previous research has reported circadian variation in 7–20% of metabolites in human blood. In this study, untargeted metabolomics profiles were measured using blood of two healthy men and one healthy woman, collected every 2 h for up to 48 h under carefully controlled conditions. The pattern of variation of each metabolite over time was examined on each participant separately, using both one- and two-order harmonic models. A total of 100 of 663 metabolites, representing all metabolite categories, showed diurnal rhythmic concentrations that exceeded the Bonferroni threshold (P −5). Overall, peak times of many metabolites were clustered during the afternoon-midnight, including the majority of amino acids, all peptides, all lysolipids and all phospholipids, whereas the majority of steroids peaked in the morning. We observed substantial inter-individual variation for both peak times and amplitudes in these three subjects. In conclusion, at least 15% of blood metabolites, representing a broad group of biological pathways, exhibit diurnal variation in three participants. The average peak times of most of these metabolites are clustered in morning or afternoon-midnight. Further work is needed to validate and extend this work in more individuals.昼夜节律系统（circadian system）几乎影响所有生物学功能。探究昼夜节律波动对代谢的影响，或可揭示节律相关疾病的发病机制，并为时辰疗法（chrono-therapy）的实施提供指导。既往研究已证实，人类血液中7%~20%的代谢物存在昼夜节律波动。本研究采集两名健康男性与一名健康女性的血液样本，在严格受控的实验条件下每2小时采样一次，最长采样时长达48小时，并对样本进行非靶向代谢组学（untargeted metabolomics）分析以获取代谢物谱。本研究针对每名受试者，分别采用一阶与二阶谐波模型，解析每种代谢物随时间的波动模式。663种涵盖全部代谢物类别的代谢物中，共有100种的浓度呈现昼夜节律性波动，且其显著性超过邦费罗尼校正阈值（Bonferroni threshold，P −5）。总体而言，多数代谢物的浓度峰值集中于午后至午夜时段，包括绝大多数氨基酸、全部肽类、所有溶血磷脂（lysolipids）与磷脂（phospholipids）；而多数类固醇类物质的浓度峰值则出现在清晨。本研究观察到，三名受试者的代谢物峰值时间与波动幅度均存在显著的个体间差异。综上，在本次研究的三名受试者中，至少15%的血液代谢物（涵盖广泛的生物学通路）呈现昼夜节律波动；其中多数代谢物的平均峰值时间集中于清晨或午后至午夜时段。未来仍需开展更多研究，在更大规模的受试者群体中验证并拓展本研究的结论。