Horopito - Forest Herbs Research Scientific Summary
Horopito – The Ancient Herb
Horopito (Pseudowintera colorata) only grows in New Zealand. This ancient shrub is a member of the primitive Winteraceae family, common to the Southern Pacific. It has features of the earliest evolved flowering plants, and appears in the fossil record over 65 million years ago. It is a very slow growing plant that lacks the specialist water conducting tubes found in nearly all other flowering plants. It grows well only in damp areas, especially under temperate rainforest (1). The red colouration on the leaves may give protection against harsh ultraviolet radiation (2) and the pungent taste is a deterrent to insects and animals (3).
Horopito has a long history of medicinal use by New Zealand’s indigenous Maori population. The leaves were bruised, steeped in water and used for paipai (a skin disease) and venereal diseases. The leaves were chewed for toothache (4). It was also used for skin diseases like ringworm. A decoction of the leaves was often used to allay inward pain and is honoured with the name ‘Maori painkiller.’ (5)
In 1982 Professor J.R.L. Walker and his team at New Zealand’s University of Canterbury isolated a sesquiterpene dialdehyde called polygodial in the leaves of Horopito.
In vivo laboratory testing demonstrated that an extract from Horopito had strong anti-fungal activity against the yeast a (6). The activity of polygodial from the extract was compared with that of Amphotericin B (a proprietary pharmaceutical product used to treat systemic mycoses) and found to be stronger and faster acting. The polygodial extract from Horopito gave larger zones of inhibition against C. albicans and was effective from day one whereas the inhibitory effect of Amphotericin B against C. albicans required three to four days incubation to become effective (7).
Terpenes are a large class of chemical compounds found in natural products. Many of them have important biological properties. (8) Kolorex Horopito leaves contain at least 21 terpenes (of which the sesquiterpene polygodial is dominant) and at least four flavonoids (9).
Horopito grows wild through much of New Zealand’s elevated and high rainfall regions but varies in appearance and growth habit. In 1998 Forest Herbs Research Ltd commissioned research to compare all the major population groups. Leaf samples were extracted and assayed for polygodial content and their effectiveness against C. albicans. Antifungal activity testing (using the zone of inhibition test) against C. albicans showed a five-fold difference between the most active and least active subspecies (10). Kolorex Horopito is derived from only the most active plants.
Recent research by P. colorata experts in New Zealand has provided further evidence that polygodial is present in higher concentrations in red leaves (11). The interiors of red margined leaves were also found to be richer in polygodial than those of green leaves. The colour of dried Kolorex Horopito leaves is distinctively red/purple when compared with many populations in the wild.
Antifungal and Antibacterial Activity
In 1998 Professor Kubo’s team at Berkeley University used in vitro macrobroth dilution testing to demonstrate that polygodial had strong antifungal activity against the yeast like fungi C. albicans, C. utilis, C. krusei, Cryptococcus neoformans, S. cerevisiae and also filamentous fungi including T. mentagrophytes, T. ruburum and Penicillium marneffei. They found polygodial’s antifungal activity was strongly increased under acidic conditions while variation in incubation temperature and inoculum size had little effect. Unlike Amphotericin B, polygodial did not show any haemolytic activity (rupture of red blood cells) and its mode of action was concluded to be different from that of existing antifungal drugs (12).
In the area of food preservation polygodial exhibits synergistic fungicidal properties. Sorbic acid is considered one of the least harmful preservatives in use but high concentrations are necessary for fungicidal activity. The fungicidal activity of sorbic acid against S. cerevisiae was enhanced 64-fold and that of benzoic acid 400-fold when these common preservatives were combined with half the minimum fungicidal concentration of polygodial (13). EDTA is another food preservative upon which polygodial exerts a synergistic effect, presumably by facilitating its transport into yeast cells (14). Zygosaccharomyces baillii is a spoilage yeast that can survive in acid media with ethanol such as wine, however polygodial controls it at very low concentrations (15). Research in this area highlights the potential of Kolorex Horopito extracts to be used as natural preservatives.
In addition to its antifungal activities, polygodial has moderate antibacterial activity against both gram positive bacteria (including Bacillus subtilis and Staphylococcus aureus) and gram negative bacteria (including Escherichia coli and Salmonella choleraesuis) with minimum bactericidal concentrations ranging from 100-400ug/ml (16).
Mode of Action
Using S. cerevisiae as a model, polygodial was found to act as a potent antifungal. It uses various processes but polygodial’s primary antifungal action is as a nonionic surfactant. It damages the permeability barrier of yeast cells. (17) Disruption of the cell membrane surface induces cell leakage in the human neuroblastoma cells (18). It is also likely that polygodial permeates by passive diffusion across the plasma membrane, and once inside the cells may react with a variety of intracellular compounds (19).
The structural features that are responsible for the biological activity of polygodial and similar drimane compounds have been the subject of much research. Originally the activity was thought to be due to the aldehyde groups especially the one at C8 (17). The latest contribution to this debate gives evidence that the double bond in the drimane skeleton (between C7 and C8) is a necessary structural feature. The molecular electrostatic potential was also found to be a feature. This work also confirmed the minimum fungicidal concentrations of many naturally occurring and semi-synthetic drimanes similar to polygodial. Polygodial showed the best minimum fungicidal concentration of all the compounds tested (20).
Toxicology and Mutagenicity
Toxicological assessment of Kolorex Horopito indicates that this formula is not toxic following acute exposure up to the level of 2 grams per kg bodyweight. At this dosage satisfactory body weight gains were maintained and macroscopic examination of the abdominal and thoracic cavities revealed no abnormalities (21).
In contrast to compounds of a similar structure with strong biological activity, polygodial has been shown to be nonmutagenic (Ames and V79/HGPRT assay), and exhibit the least cytotoxicity (21).
Plants containing polygodial have been traditionally used as foods or medicines in Japan (22), South America and Africa. There is no documented historical evidence of toxicity of Horopito by either oral ingestion or topical application.
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9 Larsen, L. A. (2001). Literature Survey of the Constituents of Pseudowintera colorata. NZ Institute for Crop and Food Research (FHR on File).
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11 Cooney, L. J., van Klink, J. W., Hughes, N. M., Perry, N. B., Schaefer, H. M., Menzies, I. J., & Gould, K. S. (2012). Red Leaf Margins Indicate Increased Polygodial Content and Function as Visual Signals to Reduce Herbivory in Pseudowintera colorata. New Phytologist, 194: 488–497. doi: 10.1111/j.1469-8137.2012.04063.x
12 Lee, S. H., Lee, J. R., Lunde, C. S., & Kubo, I. (1999). In Vitro Antifungal Susceptibilities of Candida albicans and other Fungal Pathogens to Polygodial, a Sesquiterpene Dialdehyde, Planta Medica, 65, 205-208.
13 Kubo, I., & Lee, S. H. (1998). Potentiation of Antifungal Activity of Sorbic Acid. J. Agric. Food Chem., 46, 4052-4055.
14 Kubo, I., Lee, S. H., & Ha, T. J. (2005). Effect of EDTA Alone and in Combination with Polygodial on the Growth of Saccharomyces cerevisiae, J. Agric. Food Chem., 53(5), 1818-1822.
15 Fujita, K., & Kubo, I. (2005). Naturally Occurring Antifungal Agents Against Zygosaccharomyces bailii and Their Synergism, J. Agric. Food Chem., 53, 5187-5191.
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18 Forsby, A., Walum, E., & Sterner, O. (1992). The Effect of Six Sesquiterpenoid Unsaturated Dialdehydes on Cell Membrane Permeability in Human Neuroblastoma SH-SY5Y cells. Chemico-Biological Interactions, 84 (1), 85-95.
19 Kubo, I., Fujita, K., & Lee, S. H. (2001). Antifungal Mechanism of Polygodial. Journal of Agricultural and Food Chemistry, 49(3),1607-1611.
20 Derita, M., Montenegro, I., Garibotto, F., Enriz, R. D., Fritis, M. C., & Zacchino, S. A. (2013). Structural Requirements for the Antifungal Activities of Natural Drimane Sesquiterpenes and Analogues, Supported by Conformational and Electronic Studies. Molecules, 18(2), 2029–2051. doi:10.3390/molecules18022029.
21 Winkelman, E. (2008). Toxicological Assessment of Horopito (Pseudowintera colorata). GlaxoSmithKline Memorandum.
22 Jansen, B.J. & de Groot, A. (2004). Occurrence, Biological Activity and Synthesis of Drimane Sesquiterpenoids. Natural Product Reports, 21(4), 449-477.