Isodon japonicus

The classical bitter principle of the Japanese drug, from which the herb takes its pharmaceutical name. Its intense bitterness is the basis of the traditional stomachic use, and like the other kauranoids it carries a reactive exocyclic enone.

The most heavily studied Isodon diterpenoid, better known as the marker of Isodon rubescens. It inhibits mast cell degranulation and induces apoptosis in tumour cells; its alpha-methylene cyclopentanone reacts with protein and glutathione thiols, which is the accepted basis of both its activity and its cytotoxicity.

Co-occurs with enmein and oridonin and contributes to the bitterness and cytotoxic profile of the herb. Its content, like the others, was shown to depend on drying temperature and on whether the material had been milled.

Inhibits platelet activation and thrombus formation preferentially through the collagen receptor GPVI pathway, and shows antitumour and anti-inflammatory activity in cell and rodent models. This is the constituent behind most published pharmacology attributed to the species, and it belongs to the variety rather than to Isodon japonicus in the strict sense.

Suppressed non-small-cell lung cancer cell proliferation and migration and sensitised the cells to cisplatin by binding SRC and inactivating PI3K/AKT signalling, confirmed in xenograft mice. Preclinical only.

The dominant water-soluble phenolics of the herb, alongside danshensu, caffeic acid and shimobashiric acid C. They are antioxidant and mildly antiplatelet, and they are the constituents that most distinguish the aerial part from the root.

Flavonoid fraction of the herb. Rutin and pedalitin were among the compounds that separate stem-and-leaf material from root material in chemometric analysis, so their presence is a useful check on which plant part has been supplied.

The Japanese name Hikiokoshi, meaning to raise someone up, comes from the legend that the priest Kobo Daishi revived a collapsed traveller by having him chew the plant, and the alternative name Enmeiso, life-prolonging herb, comes from the same story. The recorded use is narrow and consistent: a bitter stomachic for indigestion, poor appetite and abdominal pain. This is a legend attached to a name, not a textual prescription, and it should be read that way.

Japanese pharmacognosy sources record that when imported Gentiana lutea became unavailable, Enmeiso cultivated at a temple on Shodoshima was used in its place as a bitter stomachic, and that this is how the herb came into general use across Japan. The substitution is on bitterness, not on constituent class: gentian bitters are secoiridoids, these are ent-kaurane diterpenoids.

No entry for this species in the classical Chinese ben cao canon could be verified. Chinese use is regional and folk, concentrated in Henan, Jiangsu, Hubei, Gansu and Sichuan where the plant grows, and reaches the literature only through 20th-century compendia. The absence of a classical entry is itself worth recording: this is not a drug with a long documented Chinese prescribing tradition.