Potential benefits of Rehmanniae Radix after ancient rice‐steaming process in promotion of antioxidant activity in rats' health

Rice steam processed product of Rehmanniae Radix (RSRR), one of the processed products of Rehmanniae Radix (RR), is popular as an herbal medicine and food. However, the health‐promoting effects and mechanisms of RSRR are still unclear. In this study, 10‐week‐old Sprague–Dawley female rats were treated with different processed products of RR. No organ coefficient differences were observed between RSRR and the control group, indicating that RSRR did not cause damage to the rats. Compared with other RR products, superoxide dismutase, glutathione, and catalase levels were significantly higher and malondialdehyde levels were significantly lower in the RSRR group, indicating that RSRR exerted a better antioxidant effect. Gene expression analysis showed that hemoglobin genes (Hba‐a1, Hba‐a2, Hbb‐bs, Hbb, Hbq1b, Hbb‐b1, and LOC103694857) may be potential biomarkers to evaluate the antioxidant effect of RSRR. Antioxidation‐related signaling pathways in GO annotation, including cellular oxidant detoxification, hydrogen peroxide metabolic process, hemoglobin complex, and oxygen binding signaling pathways were significantly enriched, indicating these pathways may represent the antioxidant mechanism of RSRR. To explore the main active compounds primarily responsible for the antioxidant activity of RSRR, UPLC‐Q‐TOF‐MS was used and six components (catalpol, rehmannioside A, rehmannioside D, melittoside, ajugol, and verbascoside) were identified in rat serum. Catalpol and rehmannioside A were predicted to be the major active components by network pharmacology. These results suggested that RSRR exhibits antioxidant activity and has health‐promoting properties. This study provides a scientific basis for the antioxidant mechanism and clinical use of RSRR.