Laboratory of Molecular Pharmacognosy, Division of Pharmaceutical Sciences, Kanazawa University.
School of Pharmacy, Henan University of Chinese Medicine.
Biol Pharm Bull. 2022;45(7):955-961. doi: 10.1248/bpb.b21-01095.
Rehmannia glutinosa is an important medicinal plant in Asia, and its roots are used as an ingredient in herbal medicine. However, the roots exhibit different medicinal effects depending on the processing conditions. Since the catalpol content differs greatly during the process, the catalpol content is an essential index for quality evaluation. R. glutinosa roots have various weights, diameters, and lengths, and there are differences between individuals and within an individual immediately after harvest. We found that, catalpol content in the roots tended to increase as root diameter increased. Furthermore, it has been reported that catalpol content decreased with drying, and our results also supported this phenomenon. To clarify the reason for the decrease in catalpol content, we investigated the effect of β-glucosidase in R. glutinosa cells. An in situ assay for β-glucosidase activity revealed that the activity in the tissue inside the cambium disappeared one month after drying under natural conditions, and the activity in the tissue outside the cambium completely disappeared after two months. Because catalpol content remained almost unchanged even after drying for two months, it was clarified that β-glucosidase activity had minimal involvement in the decrease in catalpol content in R. glutinosa roots. Based on the above results, we proposed that slicing the roots and rapidly removing water by natural drying is best to obtain dry root with little loss of catalpol content.
地黄是亚洲重要的药用植物，其根部被用作草药的成分。然而，根的药用效果因加工条件而异。由于在加工过程中梓醇的含量差异很大，因此梓醇的含量是质量评价的重要指标。地黄的根具有不同的重量、直径和长度，并且在个体之间和个体收获后立即存在差异。我们发现，根的直径越大，梓醇的含量越高。此外，已有报道称梓醇含量随干燥而降低，我们的结果也支持了这一现象。为了阐明梓醇含量降低的原因，我们研究了地黄细胞中β-葡萄糖苷酶的作用。β-葡萄糖苷酶活性的原位测定表明，在自然条件下干燥一个月后，形成层内组织的活性消失，两个月后形成层外组织的活性完全消失。由于即使干燥两个月后梓醇含量几乎没有变化，因此可以清楚地表明，β-葡萄糖苷酶活性在地黄根中梓醇含量降低方面的作用很小。基于上述结果，我们提出将根切成薄片并通过自然干燥迅速去除水分是获得梓醇含量损失最小的干根的最佳方法。
