Geissoschizine methyl ether can be simultaneously measured with rhynchophylline and hirsutine in Yokukansan extract

Yokukansan (YKS) is a Kampo prescription used to treat neurosis, insomnia, and behavioral and psychological symptoms of dementia (BPSD). Previous studies have reported that geissoschizine methyl ether (GM), an indole alkaloid from Uncaria species, is the principal active constituent of YKS in the treatment of BPSD. Within YKS, GM originates from Uncaria Hook (UH), a component of natural drugs. Rhynchophylline (RIN) and hirsutine (HIR) are specified as quantitative marker constituents of YKS in the Japanese Pharmacopoeia 18th Revision (JP18) to determine the total alkaloid content. Given the recent focus on the pharmacological activity of GM, this study examined an HPLC method for detecting GM, RIN, and HIR in YKS extracts. RIN, HIR, and GM were detected as well-resolved peaks in the YKS extract under JP18 assay conditions. Comparison with the Uncaria Hook-depleted YKS extract showed no apparent matrix interference at the retention times of these alkaloids. In addition, this method was applied to most of the tested C18 columns, meeting the JP18 specifications. These findings indicate that the Japanese Pharmacopoeia assay framework can be extended to enable concurrent measurement of GM, RIN, and HIR in YKS extracts, thereby providing additional alkaloid information without requiring a separate GM-specific assay.