Isodon excisus (Maxim.) Kudô
Identity
Botanical and Nomenclatural Classification
Isodon excisus (Maxim.) Kudô carries several accepted synonyms: Amethystanthus excisus (Maxim.), Rabdosia excisa (Maxim.), and Plectranthus excisus Maxim. Within the NCBI taxonomic framework, it is classified in the order Lamiales, family Lamiaceae, subfamily Nepetoideae, tribe Ocimeae, subtribe Isodoninae. The species was first published in Mem. Fac. Sci. Taihoku Imp. Univ. 2: 133 (1929); its native range is the Russian Far East to Korea, and it is a perennial that grows primarily in the temperate biome.
In Chinese, the plant is called 尾叶香茶菜 (wěi yè xiāng chá cài). Isodon excisus, known as Oh Ri Bang Pul in Korea, belongs to the genus Isodon and is distributed in Korea and Japan.
Geographic Distribution and Morphology
The species is native to northern China, the Russian Far East, Japan, and Korea, and is characterized by distinctive foliage and branched heads of small lilac flowers reaching up to 1 m in height. The leaves have a particularly interesting apex, sometimes deeply notched, but virtually always with a long, drawn-out, tail-like tip. Its native range spans the Amur, China North-Central, Khabarovsk, Korea, Manchuria, and Primorye regions, and it is a perennial plant that grows primarily in the temperate biome.
Common Forms and Preparations
Research studies have examined the aerial parts of the plant — stems, leaves, and flowers — as the primary source material. The methanol extract of the aerial parts of Isodon excisus has been the most frequently studied preparation in pharmacological contexts. Quantitative determination of diterpenoids has been conducted using reverse-phase high-performance liquid chromatography (RP-HPLC) from extracts of the aerial parts. The plant has also been processed as an aqueous extract (decoction) and as diethyl ether extract for specific bioassay-guided fractionation studies. More recently, gold nanoparticles have been biosynthesized using Isodon excisus (Maxim.) Kudô leaf tissue, with the formation of these nanoparticles confirmed using various analytical techniques. No commercially standardized dosage form or pharmacopoeial preparation has been formally established for I. excisus as a dietary supplement as of the available literature.
Traditional and Historical Use
Korean Folk Medicine
Isodon excisus, known as Oh Ri Bang Pul in Korea, is distributed in Korea and Japan. Extracts have been used in folk medicine in Korea for treating bruises, inflammation, and pain. The plant species belonging to the Lamiaceae family is widely found in Korea, where it has traditionally been used in folk medicine to treat gastrointestinal and detoxification issues.
Chinese Traditional Medicine
The aerial part of I. excisus is used in traditional Chinese medicine to treat various diseases. The genus Isodon (Lamiaceae) includes approximately 100 species of wild plants, of which 80 species and 25 varieties are found in China. About 30 species are used to treat esophageal cancer, rheumatism, and chronic pharyngitis in Chinese folk medicine.
Japanese and Russian Traditional Context
Kamebakaurin is an active constituent of both Rabdosia japonica and Rabdosia excisa (i.e., Isodon excisus), which are utilized in Chinese traditional medicine for improving symptoms in patients with allergies. The plant is documented across multiple East Asian and Russian Far Eastern herbalist traditions, though formal classical monograph records specific to this species are not yet compiled in a major pharmacopeia such as the Chinese Pharmacopoeia or WHO monograph series.
Broader Genus Context
A large number of diterpenoids from related Isodon species have been developed into anti-cancer drugs such as oridonin, eriocalyxin A, and rabdophyllin G. Extracts and effective fractions enriched in diterpenoids have been approved into the market as drugs, such as Dong-ling-cao tablets (Isodon rubescens), Xiao-yan-lidan tablets, and Weifuchun tablets. Isodon excisus, while related to these commercially developed species, has not yet given rise to approved pharmaceutical products as of available literature.
Key Constituents and Active Compounds
Diterpenoids — Primary Bioactive Class
Pharmacological studies of I. excisus have shown that diterpenoids are the main biologically active compounds of this plant, with demonstrated antitumor, antibacterial, anti-inflammatory, and antioxidant properties. Diterpenoids are the primary bioactive constituents of Isodon plants.
Bioactivity-guided isolation of the methanol extract yielded five new diterpenoids, excisusin A–E (compounds 1–5), along with seven known compounds: inflexarabdonin I, inflexarabdonin G, inflexin, inflexanin A, inflexanin B, inflexinol, and inflexarabdonin A.
From the aerial part of I. excisus plants growing in the Russian Far East, six diterpenoids have been isolated: rabdokunmin C (1), excisanin A (2), kamebakaurin (3), weisiensin C (4), wikstroemioidin T (5), and excisanin E (6). The dominant diterpenoid in the aerial part of I. excisus is kamebakaurin, present at (0.72 ± 0.07)%, while wikstroemioidin T and weisiensin C occur at (0.011 ± 0.002)% and (0.010 ± 0.002)%, respectively. Excisanin A is present in trace amounts in I. excisus.
A novel 14,20-epoxy-ent-kaurene diterpenoid, excisanin H (1), and three new ent-kaurene diterpenoids (2–4) were isolated from aerial parts of Rabdosia excisa (I. excisus), along with eight known ent-kaurene diterpenoids.
A new pyrrolidinone diterpenoid, excisusin F, was isolated from the aerial parts of Isodon excisus (Lamiaceae), together with four known compounds; structures were determined mainly by NMR (1D and 2D) and mass spectrometry.
A new diterpenoid glucoside, isodonin C, was isolated from the aerial parts of Rabdosia excisa, along with three known diterpenoids: excisanin B, kamebakaurin, and kamebanin.
Triterpenoids and Phenolic Compounds
The diethyl ether extract of Isodon excisus var. coreanus exhibited significant inhibitory activity in an aromatase assay. Bioactivity-guided fractionation led to the isolation of three active compounds: inflexin (ent-1α-hydroxy-3β,6a-diacetoxykaur-16-en-11,15-dione), ursolic acid, and ursolic acid 3-O-acetate.
From the aqueous fraction of a methanol extract of the aerial part of Isodon excisus var. coreanus, compounds including a chlorogenic acid-related caffeic acid ester (compound I), a ferulic acid glucoside (compound II), an ent-kauranoid glucoside (compound III), and a triterpenoid glucoside (compound IV) were isolated and identified. Two new compounds, isodonin A and isodonin B, were named from this investigation.
Overall Chemical Diversity of the Genus
Over the last decade, great efforts have been made to conduct phytochemistry research on the genus Isodon, leading to the isolation and identification of a number of diterpenoids. These newly reported diterpenoids with diverse structures have led to new findings on their biological functions and chemical synthesis research; one major review covers more than 600 new diterpenoids, including their structures, classifications, biogenetic pathways, bioactivities, and chemical synthesis.
Mechanisms of Action
NF-κB Inhibition
The methanol extract of the aerial parts of Isodon excisus was found to have significant inhibitory effects on the activation of NF-κB in murine macrophage RAW264.7 cells. The development of specific inhibitors that can block NF-κB activation is an approach for the treatment of cancer, autoimmune, and inflammatory diseases. Several diterpenoids from the genus, including oridonin, ponicidin, and related compounds, were found to be potent inhibitors of NF-κB transcription activity and the expression of its downstream targets, cyclooxygenase-2 (COX-2) and inducible nitric-oxide synthase (iNOS). All of the diterpenoids directly interfere with the DNA-binding activity of NF-κB to its response DNA sequence.
Sol-gel biochip and surface plasmon resonance analysis showed that inflexinol, isolated from I. excisus, binds to the p50 subunit of NF-κB. These results suggest that inflexinol inhibits colon cancer cell growth via induction of apoptotic cell death through inactivation of NF-κB by a direct modification of a cysteine residue in the p50 subunit.
Nitric Oxide Suppression
Excisusin F and inflexarabdonin E (isolated from I. excisus) showed potent inhibitory effects on LPS-induced nitric oxide production in RAW264.7 cells, with IC50 values of 10.4 and 3.8 μM, respectively. Related kaurane diterpenoid compounds showed comparable inhibitory effects on LPS-induced production of NO and PGE2, and activation of NF-κB without affecting cell viability. These results suggest that kaurane diterpenes exert their inhibitory effects on the production of NO and PGE2 through the suppression of NF-κB activation, which may be partially responsible for the anti-inflammatory activities of the genus Isodon.
Apoptotic Pathways
Investigation of the whole plant of Isodon excisus resulted in the isolation of two new apoptosis inhibitors. These compounds inhibited etoposide-induced apoptosis in U937 cells with IC50 values of 10.2 and 52.4 μg/mL, respectively. The genus Isodon (also called Rabdosia) is a rich source of diterpenoids, especially the highly oxidized kaurane diterpenes. Kaurane diterpenoid compounds have a number of biological properties such as the induction of apoptosis and cytotoxicity against cancer cells, as well as anti-inflammatory effects through inactivation of NF-κB.
FcεRI Signaling (Allergy/Mast Cell Pathway)
Kamebakaurin — the dominant diterpenoid in I. excisus — is an active constituent of both Rabdosia japonica and Rabdosia excisa, which are utilized in Chinese traditional medicine for improving symptoms in patients with allergies. A 2024 study published in International Archives of Allergy and Immunology examined kamebakaurin's effects on antigen-induced mast cell activation via inhibition of the FcεRI signaling pathway. Kaurane diterpenes have been identified from numerous medicinal plants used for treatment of inflammation and cancer; kamebakaurin and other kaurane diterpenes have been shown to selectively inhibit activation of the transcription factor NF-κB, a central mediator of apoptosis and immune responses.
Aromatase Inhibition
The diethyl ether extract of I. excisus var. coreanus exhibited significant inhibitory activity in an aromatase assay. Bioactivity-guided fractionation identified inflexin, ursolic acid, and ursolic acid 3-O-acetate as the active aromatase-inhibitory compounds. For the cellular physiology of sex steroid-sensitive cells, the androgen/estrogen ratio may be more important than the action of either hormone alone. This ratio is controlled in vertebrates by aromatase; its inhibition is crucial for the treatment of estrogen-dependent diseases such as breast cancer and gynecomastia in males.
Scientific Evidence by Area of Use
Anti-inflammatory Activity
Evidence level: Preclinical only (in vitro and limited in vivo).
As part of an ongoing search for plant-derived NF-κB inhibitors, the methanol extract of the aerial parts of Isodon excisus was found to have significant inhibitory effects on NF-κB activation in murine macrophage RAW264.7 cells. Bioactivity-guided isolation yielded five new diterpenoids (excisusins A–E) along with seven known compounds, all evaluated for inhibitory effects on LPS-induced NF-κB activation and nitric oxide production. This work, published in the Journal of Natural Products (2007) by researchers at Chungbuk National University, Korea, represents cell-based (in vitro) evidence only. No human clinical trial data on anti-inflammatory endpoints for I. excisus have been published in the reviewed literature.
A new pyrrolidinone diterpenoid, excisusin F, was isolated from the aerial parts of I. excisus. Excisusin F and inflexarabdonin E showed potent inhibitory effects on LPS-induced nitric oxide production in RAW264.7 cells, with IC50 values of 10.4 and 3.8 μM, respectively. A separate study investigated inflexin's effects on microglial NF-κB activation, consistent with a broader anti-neuroinflammatory potential for compounds from this species.
Anticancer and Cytotoxic Activity
Evidence level: Preclinical only (in vitro cell lines; one in vivo murine model); no human data.
A novel 14,20-epoxy-ent-kaurene diterpenoid, excisanin H, and three new ent-kaurene diterpenoids were isolated from aerial parts of Rabdosia excisa (I. excisus). The absolute configuration of excisanin H was determined, and these ent-kaurene diterpenoids all showed significant cytotoxic activity against P388 murine leukemia cells.
Researchers isolated and characterized several kaurane diterpenoids from I. excisus, finding that inflexinol has strong NF-κB inhibitory effects on LPS-treated macrophage RAW264.7 cells and astrocytes. Sol-gel biochip and surface plasmon resonance analysis showed that inflexinol binds to the p50 subunit of NF-κB, suggesting that inflexinol inhibits colon cancer cell growth via induction of apoptotic cell death through direct modification of a cysteine residue in the p50 subunit. This study, published in Molecular Cancer Therapeutics (2009) by the American Association for Cancer Research, used colon cancer cell lines (in vitro) and represents mechanistic cell-culture data only.
Investigation of the whole plant of Isodon excisus resulted in the isolation of two new apoptosis inhibitors (designated as compounds 1 and 2). Compounds 1 and 2 inhibited etoposide-induced apoptosis in U937 cells with IC50 values of 10.2 and 52.4 μg/mL, respectively. This work (published in Journal of Natural Products, 2001) identified I. excisus constituents as potential anti-apoptotic agents in U937 human leukemic cells under specific chemotherapeutic contexts, again limited to cell-line experiments.
Seven novel analogues of 1-phenylethanolamine carboxamide derivatives, related to carboxamides isolated from Isodon excisus, were synthesized and evaluated for cytotoxic and apoptosis-induction properties against murine B16 melanoma and leukemia L1210 cell lines. Compounds containing no substitution at the 4′-position or containing a 4′-amino group were investigated, with amino-containing compounds being slightly more active than their unsubstituted congeners.
To date, approximately 1,000 diterpenoids from the Isodon genus have been shown to exhibit significant cytotoxicity, and many diterpenoids with anticancer activities, such as oridonin, eriocalyxin A, and rabdophyllin G, have been developed into new drugs. Despite these promising findings across the genus, I. excisus specifically has not advanced to clinical trials for any oncological indication.
Aromatase Inhibition and Hormone-Related Activity
Evidence level: In vitro biochemical assay only; no human data.
The diethyl ether extract of Isodon excisus var. coreanus exhibited significant inhibitory activity in an aromatase assay. Bioactivity-guided fractionation of the extract led to the isolation of three active compounds: inflexin, ursolic acid, and ursolic acid 3-O-acetate. This result, published in Archives of Pharmacal Research (2000), was obtained using an in vitro aromatase inhibition assay. No clinical data exist for this application.
Anti-allergic / Mast Cell Modulation
Evidence level: Preclinical (in vitro cell-based); no human data.
A 2024 paper by Asai et al. in International Archives of Allergy and Immunology examined kamebakaurin's suppression of antigen-induced mast cell activation by inhibition of the FcεRI signaling pathway. Kamebakaurin is an active constituent of both Rabdosia japonica and Rabdosia excisa, which are utilized in Chinese traditional medicine for improving symptoms in patients with allergies. The study is mechanistic and cell-based; human clinical data are absent.
Skin / Dermatological Applications
Evidence level: Exploratory in vitro (human keratinocyte cell culture); no clinical data.
In an exploratory study published in the Arabian Journal of Chemistry (2023), Isodon excisus — a plant species widely found in Korea — which has traditionally been used in folk medicine to treat gastrointestinal and detoxification issues, was found to have leaves that contain various biogenic phytomolecules. Gold nanoparticles were biosynthesized using leaf tissue from Isodon excisus (Maxim.) Kudô. Transmission electron microscopy revealed that the nanoparticles had sizes ranging from 10 to 100 nm and exhibited polygonal, triangular, and hexagonal shapes. At a concentration of 50 μg/mL, these nanoparticles did not exhibit any cytotoxic effects on HaCaT (human keratinocyte) cells. The study investigated the potential of these nanoparticles for treating inflammatory skin disorders. This remains exploratory work with no clinical translation.
Phytochemical Studies on Aqueous Fractions
Studies on the aerial part of Isodon excisus var. coreanus (Labiatae) led to the isolation of novel compounds from the aqueous fraction of a methanol extract, including a chlorogenic-acid related caffeic acid ester, a novel ferulic acid glucoside (isodonin A), and a novel ent-kaurene glucoside (isodonin B), among others. These phytochemical findings, published in Archives of Pharmacal Research, lay groundwork for future bioactivity assessment.
Body Systems and Health Areas of Association
- Immune system / inflammation: Extracts have been used in folk medicine in Korea for treating bruises, inflammation, and pain. Laboratory studies demonstrate multiple mechanisms of innate immune modulation, primarily through NF-κB and iNOS inhibition.
- Gastrointestinal system: I. excisus has traditionally been used in folk medicine to treat gastrointestinal and detoxification issues.
- Oncology (experimental): Isolated diterpenoids show preclinical cytotoxicity against multiple cancer cell lines including leukemia (P388, U937, K562 analogs), colon cancer, and others. Due to their complex, fast-changing carbon skeleton and multiple pharmacological activities, diterpenoids as anti-cancer drug candidates have gained attention.
- Endocrine system (experimental): Aromatase inhibitory constituents have been identified, suggesting potential relevance to estrogen-dependent conditions, though this is not yet clinically evaluated.
- Allergy/immunology: Kamebakaurin, the dominant diterpenoid, has demonstrated mast cell-inhibiting effects via FcεRI signaling in vitro.
- Skin (exploratory): Leaf-derived biosynthesized nanoparticles have been explored for anti-inflammatory effects in human keratinocytes in preliminary cell-culture studies.
Dosage Forms and Dosages Reported in Studies
No standardized human dosage for Isodon excisus has been established in any pharmacopeia or regulatory monograph, and no clinical dosing trials have been reported. The following dosages appear only in preclinical research contexts:
- Apoptosis inhibition (in vitro): Two compounds isolated from I. excisus inhibited etoposide-induced apoptosis in U937 cells with IC50 values of 10.2 and 52.4 μg/mL, respectively.
- NF-κB and NO inhibition (in vitro): Excisusin F and inflexarabdonin E inhibited LPS-induced nitric oxide production in RAW264.7 cells with IC50 values of 10.4 and 3.8 μM, respectively.
- Skin cell safety threshold (in vitro): In human keratinocyte (HaCaT) studies, high doses above 50 μg/mL were found to be toxic; further studies were performed using non-toxic doses of 25 and 50 μg/mL.
- Dominant diterpenoid content in plant material: The dominant diterpenoid kamebakaurin was quantified by RP-HPLC at (0.72 ± 0.07)% of the dry aerial parts of I. excisus.
Safety Considerations and Interactions
No formal toxicological dossier, human safety trial, or regulatory safety assessment specific to Isodon excisus has been published in the peer-reviewed literature reviewed here. The following observations derive from available preclinical data:
In Vitro Cytotoxicity Threshold
In human keratinocyte (HaCaT) cell assays, doses of IE-AuNPs (nanoparticles derived from I. excisus) and plant extract above 50 μg/mL were found to be toxic. Non-toxic doses were determined to be 25 and 50 μg/mL. This data applies to an in vitro model and cannot be directly extrapolated to human oral or topical use.
Apoptosis Modulation: Dual-Edged Activity
Two compounds isolated from the whole plant inhibited etoposide-induced apoptosis in U937 cells with IC50 values of 10.2 and 52.4 μg/mL, respectively. This anti-apoptotic activity at certain concentrations is noteworthy, as it implies that some constituents may, in specific cell contexts, oppose rather than support programmed cell death — an important consideration when evaluating the plant in oncological contexts. Other constituents (inflexinol, excisanins) exhibit pro-apoptotic cytotoxic effects. The net biological consequence of I. excisus extracts on apoptosis is thus compound- and concentration-dependent based on current evidence.
Aromatase Inhibition and Potential Endocrine Effects
The diethyl ether extract of I. excisus var. coreanus exhibited significant aromatase inhibitory activity, with inflexin, ursolic acid, and ursolic acid 3-O-acetate identified as the active compounds. Given that aromatase inhibitors have well-characterized endocrine effects (including impacts on estrogen biosynthesis), this finding warrants caution particularly for populations sensitive to estrogenic changes, though no human data are available.
NF-κB Modulation — Immunological Implications
Diterpenoids from the Isodon genus are potent inhibitors of NF-κB transcription activity and the expression of its downstream targets, COX-2 and iNOS. All tested diterpenoids directly interfere with the DNA-binding activity of NF-κB to its response DNA sequence. Broad NF-κB inhibition has implications for immune suppression and inflammatory resolution that may interact with existing immunomodulatory medications, though this has not been evaluated in humans.
Absence of Formal Safety Data
The available scientific literature on Isodon excisus is confined to phytochemical characterization and in vitro bioactivity assays. No documented human clinical trials, formal toxicological studies, reproductive toxicity assessments, drug interaction data, or adverse event reports for I. excisus preparations were identified in the peer-reviewed sources reviewed. The safety profile of this plant in humans remains essentially uncharacterized in the scientific literature.
Summary of Evidence Strength
The scientific investigation of Isodon excisus is currently at an early, predominantly phytochemical and in vitro stage. The plant's diterpenoid-rich chemistry — particularly its ent-kaurane framework (kamebakaurin, inflexinol, excisusins A–H, inflexarabdonins, excisanins) — places it among the pharmacologically interesting members of the Isodon genus. Great efforts have been made to conduct phytochemistry research on the genus Isodon, which have led to the isolation and identification of numerous diterpenoids. These newly reported diterpenoids with diverse structures have led to new findings on their biological functions. However, as of the available peer-reviewed literature, no human clinical trials exist for Isodon excisus specifically, and its bioactive constituents have been investigated primarily in cell cultures and a limited number of murine models. Extrapolation from in vitro IC50 values to human efficacy or safety is not scientifically justified based on current data.
References
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