Immunostimulatory properties of heat-resistant RNA in a decoction of Glycyrrhizae Radix

Research on the bioactive components of herbal medicines have been conducted mainly on the secondary metabolites of herbal plants. Accordingly, limited information is available on primary metabolites (carbohydrates, amino acids, lipids, and nucleic acids) and their biological effects. Here, we focused on the heat-resistant RNA of a decoction of Glycyrrhizae Radix and showed its immunostimulatory effects. The RNA activated NF-κB/AP-1 and induced TNF-α production in murine macrophages. Further analysis revealed that the RNA was around 90 nucleotides long. RNA sequencing (RNA-Seq) by next generation sequencing (NGS) showed that approximately 30% of the NGS reads were mapped to the genome of Glycyrrhiza uralensis, which is plant material of Glycyrrhizae Radix. Further analysis of the other 70% of reads indicated that the RNA contained RNA sequences that could be mapped to various microorganisms. Together, these results propose nucleic acids as a new research field in the bioactive components of herbal medicines.