Cures from nature
In modern medicine, a natural chemical is mostly the starting point for the development of synthetic pharmaceuticals. However, some natural chemicals are too complex for this to be economic. One example is the breast cancer drug taxol, which is prepared from plantation-grown yew trees in the United States.
Mānuka (Leptospermum scoparium) is one of the most widespread of the woody plants in New Zealand, growing from Cape Rēinga down to Stewart Island, and from coastal swamps up to the subalpine zones. Māori used it in medicines, such as infusions for stomach complaints.
Antibiotic effect: leptospermone
In the 1990s a group of Māori from the East Cape of the North Island, working with scientist Noel Porter, found that extracts from the leaves of local mānuka shrubs had an antibiotic effect. This is due to a high level of the active ingredient, a natural chemical called leptospermone. It acts against the methicillin-resistant bacterium Staphylococcus aureus – the original ‘super bug’ that is a serious problem in hospitals.
Mānuka is sometimes called tea tree, but New Zealand mānuka oil is distinct, both chemically and in its antibiotic properties, from Australian tea tree oil.
The good oil
Mānuka oil, and creams containing it, are sold as a treatment for skin infections. The leaves are harvested sustainably from natural stands of mānuka, but the development of plantations is under way. To extract the oil, steam is passed through the cut foliage, condensed, and then separated, leaving the essential oil.
Most mānuka does not yield essential oils with the antibiotic properties of East Cape mānuka oil. The related kānuka (Kunzea ericoides) is often confused with mānuka, but it gives a very different essential oil, with no leptospermone and much weaker antibiotic properties.
Mānuka honey is made by bees that collect nectar from mānuka flowers. In some areas the honey has antibiotic properties, but this does not appear to be the effect of the chemical leptospermone, as in the leaf oil. Researchers at Waikato University and Industrial Research Ltd (a Crown Research Institute), have tried to identify the active chemicals in mānuka honey, in order to optimise production and quality. In 2007 researchers at the Technical University of Dresden, Germany, identified the active chemical as the compound methyl glyoxal. Later that year the United States Food and Drug Administration approved the marketing and selling of a wound dressing impregnated with mānuka honey.
Poisons as medicines
Plant poisons have potential as medicines if used at the right dose – for example digitalis (which regulates and strengthens the heartbeat, and is poisonous in overdose) is obtained from foxgloves.
Prostratin from Pimelea
In New Zealand, pinatoro or Strathmore weed (Pimelea prostrata) has poisoned animals, and was the original source of the toxin known as prostratin. The same compound has since been isolated from a Samoan plant used in traditional medicine, and found to have activity against human immunodeficiency virus (HIV). New Zealand Pimelea could be another source of prostratin if this compound is developed as a treatment.
Horopito’s antifungal effect
A search for new medicines from New Zealand native plants at the University of Canterbury led to the discovery that an extract of leaves of horopito (Pseudowintera colorata) was active against the yeast Candida albicans, which causes the fungal disease thrush. The natural product that causes the burning, pungent taste of horopito is polygodial, the active antifungal ingredient. A Nelson company is growing this species and selling herbal medicines containing powdered leaves and leaf extracts.