Characterization of the cold and hot natures of raw and processed Rehmanniae Radix by integrated metabolomics and network pharmacology

The processing of Chinese materia medica (CMM) is one of the characteristics and advantages of traditional Chinese medicine (TCM). Occasionally, the processing of CMM might reverse the cold/hot nature of CMM. For example, the nature of raw Rehmanniae Radix (RR) is cool, while the processed Rehmanniae Radix (PR) by steaming is hot. Because the cold/hot nature of CMM is defined by the body's response to CMMs, a metabolomics approach, allowing the monitoring of the fluctuation of endogenous metabolites related to an exogenous stimulus, might be an ideal tool to uncover the cold/hot nature of different forms of Rehmanniae Radix. An integrated strategy combining metabolomics and network pharmacology was applied to illuminate the different natures of raw and processed Rehmanniae Radix . Mice were orally administered RR and PR once daily for ten days. The entire metabolic changes in the plasma of mice were profiled by ultra-high performance liquid chromatography/quadrupole time-of-flight mass spectrometry (UHPLC/Q-TOF MS). Furthermore, network pharmacology analysis was performed to identify the underlying targets related to iridoids that significantly changed during the processing. The metabolomics analysis results demonstrated a clear separation of the metabolic phenotypes among the control, RR and two PR groups in both the positive and negative modes. Nine lysophosphatidylcholines (LysoPCs), LysoPC (16:0), LysoPC (18:2), LysoPC (18:1), LysoPC (22:6), LysoPC (20:2), LysoPC (18:0), LysoPC (16:1), LysoPC (20:4) and LysoPC (20:5), that decreased in the RR-treated group, but increased in the PR-treated group, were identified to be potential biomarkers related to the natures of RR and PR. The network pharmacology results indicated that four iridoids in Rehmanniae Radix, 8-epiloganic acid, 6- O - p -coumaroyl ajugol, 6- O - p -hydroxybenzoyl ajugol and ajugol, might play important roles in the different natures of raw and processed Rehmanniae Radix. There might be a strong connection between the cold/hot nature of different forms of Rehmanniae Radix and LysoPC metabolism. This study offers new insight into the cold/hot nature of Rehmanniae Radix.