Research Progress on Chemical Constituents and Pharmacological Effects of Dihuang (Rehmanniae Radix)

Abstract To date, more than 300 compounds have been isolated and identified from Dihuang (Rehmanniae Radix). Analysis of the chemical composition distribution reveals significant differences among different processed products and plant parts. Xiandihuang (Radix Rehmanniae Recens) contains a greater variety of compounds, and the processing methods significantly impact the types and quantities of compounds, with most components decreasing as processing intensifies. Furthermore, although the leaves and root tubers of Dihuang (Rehmanniae Radix) share consistency in chemical constituent types—including iridoids, phenylethanoid glycosides, ionones, etc.—there are differences in the specific monomeric compounds and their content. They exhibit unique site specificity in the distribution of certain compound classes, such as nitrogen-containing compounds, sesquiterpenoids, and lignans. Iridoids, phenylethanoid glycosides, and polysaccharides are the primary material basis for the pharmacological efficacy of Dihuang (Rehmanniae Radix), demonstrating activities such as hypoglycemic, antiosteoporotic, antitumor, and anti-inflammatory effects. Future research directions may focus on the following aspects: First, directed breeding and gene editing. Based on superior varieties and leveraging their genetic advantages, key genes regulating the biosynthesis of active components like iridoids, ionones, phenylethanoids, and sesquiterpenoids can be precisely located. Targeted modification via gene editing can then be employed for variety improvement. Concurrently, high-density linkage maps constructed from the genetic differences among varieties can be used to analyze relevant quantitative trait loci, providing molecular genetic evidence for the directed breeding of superior rehmannia varieties. Second, pharmacological optimization research based on compositional specificity. Investigating the mechanism of action in specific diseases and the synergistic effects of multicomponents according to the compositional characteristics of different varieties can provide a basis for clinical “variety selection based on syndrome differentiation.”